biomass downdraft gasifier

Acknovvledgments
PERTYQP

Since it is impossible for one or two authors to realistically comprehend a subject from all viewpoints, we have
solicited input
GOVERNMENT
from leading workers in the field. Early versions were sent to a number of investigators, and each was invited to comment on and
supplement our effort. We thereíore express our heartíelt thanks to the following reviewers for greatly enhancing the quality of the
final product:

Handbook of Biomạss
Downdraft Gasi/ier

Dr. Thomas Milne, Solar Energy Research Institute
Dr. Thomas McGowan, Georgia Institute of Technology
Mr. Matthevv Mendis, World Bank
Mr. Bill Nostrand, New England Gasiíication Associates

Engine Systems

Dr. Bjorn Kjellstrom, The Beijer Institute, Sweden
Dr. Hubert Stassen, Twente University, The Netherlands
Prof. Ibarra Cruz, University of Manila, The Philippines

We take final responsibility for the contents and omissions, and extend our apologies to those vvorkers whose work we may have
SERI/SP-271omitted.
-3022
ENERGY RESEARCH INS
unknowingly
DE880011

35 March
1988 ưc
Category:

TECHNICAL
LIBRARY

Organization and Use

A gasiíier converts solid fuel to gaseous
fuel.
A gasiíier system includes the gasiíication reactor itself, along with the auxiliary
OCĩ
7 1988
OOtKNt
COIORADO
equipment necessary to handle
the solids,
gases, and804QI
effluents going into or coming from the gasiíier. The íigure below shows the
major components of a gasifier system and the chapters in which they are discussed.

This handbook has been prepared by the Solar Energy Research Institute under the U.S.
Department of Energy Solar Technical Iníormation Program. It is intended as a guỉde to the
design, testing, operation, and manufacture of small-scale [less than 200 kw (270 hp)]
gasiíiers. A great deal of the information will be useíul for all levels of biomass gasification.
The handbook is meant to be a practical guide to gasiỉier systems, and a minimum amount of
space is devoted to questions of more theoretical interest.
We apologize in advance for mixing English and Scientiíique Internationale (SI) units.
VVhenever possible, we have used SI units, with the corresponding English units fol- lowing

in parentheses. Unfortunately, many of the íigures use English units, and it would have been
too difficult to convert all of these figures to both units. We have sup- plied a conversion
chart in the Appendix to make these conversions easier for the reader.
.Whole system. Ch. 9, 10

Mr. Bill Nostrand, One of our very helpíul reviewers, died in May 1985. Bỉll was num- ber
one in the ranks of those who became interested in gasiíỉcation because of its poten- tial for
supplying clean, renewable energy. We all will miss him. The improvement of gasiíication
systems will be noticeably slowed by his death.Notice
This
wasthis
prepared
as the
an account
of work of
sponsored
by who
an agency
of thegasifier
United systems
States government.
We report
dedicate
book to
Bill Nostrands
this world
will bring
to
Neither the United States govern- ment nor any agency thereoí, nor any of their employees, makes any
the level ofexpress

safety, cleanliness,
reliabilityany
required
realize or
their
full potential.
warranties,
or implied, and
or assumes
legal to
liability
responsibility for the accuracy,
completeness, or useíulness of any iníormation, apparatus, product, or process disclosed, or represents
that
its use
would not iníiinge privately owned rights. Reíerence herein to any speciíìc commercial
Thanks,
Bill.
product, process, or Service by trade name, trademark, manuíacturer, or otherwise does not necessarily
constitute
or and
imply
T. B. Reed
A. its
Dasendorsement, recommendation, or íavoring by the United States govern- ment or
any agency thereoí. The views and opinions of authors expressed herein do not necessarily State or
Golden,
Colorado
reílect
those

of the United States government or any agency thereof.
Printed in the United States of America Available from:
Superintendent of Documents U.S. Government Printing Office VVashington, DC 20402
National Technical Information Service U.S. Department of Commerce 5285 Port Royal Road Springfield,
VA 22161
Price: Microfiche A01 Printed Copy AO 7
A Product
the for pricing all publications. The code is determined by the number of pages in the
Codes
areofused
publication.
Information
pertaining
to theEnergy
pricing codes can be found
in the current issue of the following
Solar Technical
Intormation
Program Solar
A Division of Midwest Research Institute
publications
vvhich are generally available in most libraries: Energy
Research Abstracts (ERA);
Research Institute
for theand Technical Abstract
Government
Reports
Announcements
Scienti/ic
1617 Cole Boulévard,

Golden,
Colorado 80401-3393and Index (GRA and I);Operated
Reports (STAR)\ and publica- tion NTIS-PR-360 available from NTIS
at the aboveofaddress.
U.S. Department
Energy


11.9
Spark-Ignition
Engine Conversion ................................................................................................................................................... 107 51
7.1 Gas
Testing
......................................................................................................................................................................
regarded
as
on
y
emporary
mod
ca
ons
wara me
Table
1-1.
Summary
of the
Annual
Potential
”Deve

descr
p on
gas
er fTechnology
rucoron
and
1000 seventies.
wr
ers
and
workers
nons
heof
econs
d Un
una
e 51y
W
h in
hIntroduction..................................................................................................................................................................................................
s11.8.1
n m nd FEMA
con
rac ed
wEnergy
h Ha for
LaFon
ne 2.3manua
Future
opment

Dofrect
Engine
System
.........................................................................................................................................................
107
use
designs,
songs
continuous
ofthe
U.S.
Office
Assess7.2
research
group nThe
producer
gas (IGT1984)
In add
on
ar
c es
oftoday’s
n eresprocess
and
he
proceed
of
en
span
cond

ons
However
a
few
car
makers
wen
so
far
as
o
of
Existing
Sources
of
Biomass
in
the
United
States
opera
mass
ve
on
b
(LaFon
b
ograph
a
ne

es
1987)
of
und
The
fferen
gas
a
f
ed
er
ma
has
er
passed
a
can
of
he
B
omass
Energy
Founda
on
o
bu
d
a
pro
o

ype
Pred
c
ng
he
needs
and
d
rec
on
of
deve
opmen
n
11.8.2
Gas
Mixers
...............................................................................................................................................................
107
development
effort
and
lively
open
exchange
should
ment
(OTA)
recently
has

issued
a
report
calling
for
8.9
Disposal
of
Captured
Contaminants.......................................................................................................................................................92
4
3
nd
ec
and
D
ec
Gas
ca
on
P
ocesses
25a
13.4
Economics
............................................................................................................................................................................................
125
exce
en
gas

ca
on
work
s
proceed
ng
n
Canada
many
years
of
research
The
E
ec
r
c
Power
Research
Chap
er
2
7.3 er
and
......................................................................................................................
51
mod
yGas-Quality
he cou
bodydMeasurements

work
for wgas
fread
er ns
aRequirements
a ab
one par
Soon
con
use
he
reader
or
g
ve
an
mpress
on
of
a
eve
of
he
es
and
he
manua
s
now
n

he
process
of
be
ng
our
modern
wor
d
s
very
dangerous
because
we
don’
gas
ha
be
made
h
y
ava
s
enable
us
to incorporate
latter-day
and
national Braz
capability

for pp
emergency
of
Europe
he Ph
nes New implementation
Zea and and 108
o her
Ins
e 11.8.3
(EPRI)
hasPower
comm
ss
wo
schemical
udab
es eon
8.8.1
Char-Ầsh............................................................................................................................................................................92
413.3.1
nd
ec Time
Py
oLag
c......................................................................................................................................................
Gasava
ca
on
25

Costs
..........................................................................................................................................................................
af7.4
er ouDescription
he
ow-cos
gaso
neoned
became
agahe
n ...............................................................................................................
unders
and
ha cond
does ons
no w
ex s change
for gasandcawha
on 125
We
know
how
uFEMA
ure
our
pub
shed
byng
and
wrwar

e 3a 1“cra
sman
of Producer
Gas
andQuads/Yea
Itsclean,
Contaminants
51
10®
Dry
chemical
engineering
techniques
to
build
congasiíiers
(OTA
1984].
par s of
he
wor dD pr
mar y a he un vers y eve 109
use
of producer
gas
(M
er
1983
Schroeder
1985)

11.8.4
Engine
Startup
.........................................................................................................................................................
8.8.2
Tar
H
Current
Deve opments
Future
rect
413.3.2
3 2 wen
D
ec......................................................................................................................................................................................92
Gas
ca
on
Calculating
Energy
Costs
........................................................................................................................................
125
and mos
users
back
o burn
ngstory
gaso
ne rbecause

Tons/Year
hope and
h sw
manua
w ons
he reader
o pu
h25s
response
be S nce
hehe
f rsp OPEC
embargo
n 1973
7.3.1
ThenGas
Analysis
..................................................................................................................................................
51
venient,
and nreliable
systems.
A
recent
vrorkshop
on
Governmen
eres
gas
f

ca
on
has
ended
o
focus
Crop
residues
278.0
4.15
11.8.5
Ignition
Timing
........................................................................................................................................................
110
of 4s4conven
ence
P nc
8.8.3
p es o Ope
Condensate........................................................................................................................................................................92
a on o D
ec.......................................................................................................................................................
Gas e s
ma have
er a osc
n o perspec
27
we
a edPotential

be ve
ween a concern w h energy 126
sup13.3.3
Equipment
Cost
low-energy
gasification
tabulates
research and 1.2 Biomass
Energy
7.3.2e sys
Particulates26.5
.........................................................................................................................................................................
51
on
arge-sca
ems
Animal
manures
0.33
11.8.6
SparkPlugs
................................................................................................................................................................
110
p
es
and
bus
ness
as

norma
There
ore
we
can’
4
4
1
n
oduc
on
27
13.3.4
Conversion
Efficiency
and
Fuel
Consumption
...................................................................................................
127
development
needs...........................................................................................................................................................
(Easterling
1985). ...............................................................................................................................................
Biomass
is ch
a renewable
fuelare
that ke
supplies

2%
towe
3%
of
7.3.3
Tars
......................................................................................................................................................................................
55
9.1 Unused
Gasitìer
93
mill
24.1
0.41
11.10
Two-Cycle
Engine
Conversion
110can
pred
c
wh
d
rec
on
we
y
o
go
bu

1
3
2
Đooks
B
omass Systems
ca
on
s
perce
ved
by
he
ore
gn
a
d
3 gas
4
4
2
Ope
a
on
o
he
ưpd
a
Gas
e

27
13.3.5
The
Cost
of
Operating
Labor
.................................................................................................................................
127
1
3
6
Producer
Gas
R&D
Fund
ng
residues
The
accelerated
use
of
gasiíication
technologies
ulU.S.
energy
needs
and
an
even

larger
percentage
residues
83.2
1.41
7.5
Sampling
...........................................................................................................................................................................................
55in93
a easwass a he
poss
b eofopresearch
ons andandaccommerc
ors ha 111
affec
11.11
Diesel
Engine
Conversion
.......................................................................................................................................................
agenc
esThe
of
he deve
oped
coun
r es
(sucha asGas
he eU S
9.2Gas

Complete
Gasiíier
................................................................................................................................................................
2.2Logging
Current
Deve
Act
vSystem
There
grea
dea
aOTA
za413.3.6
4 3 opment
Ope
atheir
on
ot es
he
Downd
28
Maintenance
Costs
...................................................................................................................................................
127
timately
depends
upon
ability
to

compete
with
some
other
countries
(OTA
1980;
DOE
1982).
U
S
AID
has
had
a
s
rong
n
eres
n
producergas
echMunicipal
solid
130.0
1.63
he
cho
ce
7.4.1
Sample

Ports
....................................................................................................................................................................
55
Agency
for
In erna
ona
Deve
opmen
[U
Swas
AID])
as....................................................................................................................
a
thermal
process
isbuses
combustion,
which
yields
only
heat.
11.10.1
Diesel
Operation
with
Producer
Gas
111
on

d
rec
ed
oward
coa
and
b
omass
gas
ca
on
berucks
cars
and
n
Europe
and
probab
y
more
1.1H
Role
of
Gasitỉcation
in
Điomass
Conversion
Af
er
he

OPEC
o
embargo
of
1973
here
renewed
9.3
Storing,
Feeding,
and
Sealing
Solids
......................................................................................................................................................
2.1
stor
ca
Deve
opment
wastes
íossil
fuels,
4torests
4Beneíits
which
4
in
Facturn
o s Con
depends

o ng
on
S unknown
ab y 6.51
o Gas
factors
e Ope ano
onogy because
2893
projects
that
biomass
could
supply
from
7%
to
20%
(6oữers
a
means
for
reduc
ng
he
deStanding
384.0
13.5
Cost
........................................................................................................................................................................................

128
ma
or po11.10.2
en
a orms
energy
source
forEngines
many..........................................................................................................................................
parud
s of
he
Pyrolysis
uses
heat
tode
break
down
biomass
and
yields
7.4.2
Isokinetic
Sampling
........................................................................................................................................................
56
ween
1850
and
1950

Hovvever
cheap
and
p
en
u
gas
In
norma
mes
deve
opmen
s
dr
ven
by
economic
han
a
m
on
wor
dw
(Eg
off
1943)
However
hese
Starting
Diesel

112
n
eres
n
a
of
a
erna
ve
energy
nc
ng
gas
4
5
Cha
coa
Gas
ca
on
about
resources,
and
At
9.2.1
Characteristics
of
..................................................................................................................................................
93
17 quads*)

(OTA
1980)
sources
as28
pendency
ofannually
deve optars,
ng na
ons
onfrom
mpor
ed fuesuch
s 128
and
Totals
925.8
14.44
handbook
explains
how
biomass
be
converted
13.4.1
Value
ofPower
Produced
........................................................................................................................................
2 1 1This
Ear

y wor
Deve
opment
of
Gas
cat
on
deve
op
ngfrom
deconomics,
The
Be
er
Inspolitical
uSolids
ecan
ofconditions.
Sweden
has
charcoal,
wood-oils,
and
gases.
and
o
preven
ed
he
commerc

a
deve
opmen
of
he
considerations,
and
some
of
he
econom
c
ac
ors
mpress
ve
numbers
nc
uded
on
y
s
x
wood-fue
ed
7.6
Physical
Gas-Composition
Testing
.......................................................................................................................................................

57
coa
and
b
omass
Mos
of
he
ear
y
work
11.10.3
Throttling
at
Partial
Load
.......................................................................................................................................
113
aproduced
present
(1988),
gasiíication
and
other
alternative
energy
those
shown
in
Table

1-1
(Reed
1981),
if
it
can
be
made
4
6
Summa
y
29
has
suppor
ed
a
number
of
pro
ec
s
around
he
wor
d
9.2.2
Storage
...............................................................................................................................................................................
to

a
gas
in
a
downdraft
gasifier
and
gives
details
for
Does
not
nc
ude
unused
bark
from
wood
pu
p
m
s
organ
zed 13.4.2
wo
nheerna
ona
con
erences
hese

donor
Cogeneration
Possibilities
129
echno
excep
n gas
of
emergency
The
s
n- cAuenc
use
of
on
are
ed
n reader
Chap
ers93
veh
esogy
ninng
he
Un Round
ed
Smes
a ab
esca
and

wo
n sCanada
where
Gasiíìcation
processes
convert
biomass
into
combussuppor
bytesting,
ed .............................................................................................................................................................................
S a es
and for
ore
gn n United
energy
Raw
Gas
57
Gas
caed7.5.1
onare
was
dUn
scovered
ndependen
y......................................................................................................................................
bo
h
processes

being
developed
slowly
in
the
available
a
convenient
form
and
if
conversion
equip11.12
Increasing
Power
from
Producer-Gas-Fueled
Engines
......................................................................................................
113
The
Producer
Gas
e
of
S
ockho
m
Sweden
designing,

operating,
and
manuíacturing
9.2.3
Feeding
Solids
...................................................................................................................................................................
94
Source:
Reed
agenc
es
and
pub
shed
hree
vo
umes
of
recen
s
ud
es
re
erred
espec
a
y
o
a

number
of
exce
en
h
s
or
ca
13
In
n
es
of
emergency,
our
pr
or
es
change
ow-cos
gaso
ne
con
nued
o
be
ava
ab
e
hroughou

tible
gases
that
ideally
contain
all
the
energy
original13.6
Financing
.............................................................................................................................................................................................
129
es
abt er
shmen
s of
ocused
on Gas
arge-sca
coa
-fed
gas
ers
5 1 France
Gas
Des
gns
and
and
n 1798

and
by e1850
he
echno
1981
p
39Eng
States
because
relatively
supplíes
ofpower
mentovers
is accessible.
potential
world
7.5.2
Cleaned
......................................................................................................................................................................
an
gh organThe
za on
supporofedbiomass
by varforous
n-30
11.11.1
Mechanisms
ofPower
Loss
.....................................................................................................................................

11361
gasiíiers
and
gasiíìer
systems,
primarily
for
shaft
of
gas
ca
on
re evan
o Solid
heplentiíul
prob
ems
ofura
deve
oplownga
9.2.4
Sealing
Flows
.........................................................................................................................................................
books
Modern
Gas
Prođucers
(Rambush
1923)

dras
ca
yMany
and
qu
oc(Bioenergy
desfferen
opmen
sgas
occur
he
war
ar
were
wr
enpromo
on
fncaormaon94
ly
present
in
the
biomass.
In deve
practice,
gasiíĩcation
can
ha
were
n

ended
o
produce
syn
he
c
na
gas
as
ogy
had
been
deve
oped
o
he
po
n
ha
was
pos13.5.1
Government
Subsidies
in
the
Form
of
Tax
Incentives
......................................................................................

129
cost
gaseous
and
liquid
íossil
fuels.
However,
political
use
is
equally
great
1985).
erna
ona
deve
opmen
agenc
es
o
e
5 2rChemical
n11.11.2
oduc
30
generation
7.7
upe toGas
200

Composition
kw.
ItBreathing
is......................................................................................................................................................................
intended
to help convert
61
Engine
113
coun
es
(K
son
rom
1983
1985)
gSma
ves
accoun
of exper
ences
w inhrap
updra
and
coa
dur
ng an
ha
me
(see

Chap
er
1)on
Some
pho
of
Fans,
Blowers,
Ejectors,
............................................................................................................................................
convert
60%
to were
90%
ofgas
theoped
energy
biomass
into
fue
was
epractical
eres
nform
b....................................................................................................................................................
omass
or
bof
omass
B

s13.5.2
afrom
renewab
enenergy
wa..............................................................................................................................................
hfield
many
pos
sgasiíication
bomass
e9.4oThere
gh
much
London
wart
hCompressors
manu
ac
ured
gas
orgas
ers
deve
very
dand
yographs
dur
he95
changes
could

rapidly
and and
dramatically
alter
this
on
exchange
on
ca
othe
beng
ween
Financial
Institutions
129
aofEfficiency
into
en7.6.1
Gas
Samples
for
Chemical
Analysis
.............................................................................................................................
61
11.11.3
and
Power
Loss
....................................................................................................................................

114
5
3
Bas
c
Gas
e
Types
30
gas
ers
Generator
Gas
(Gengas
1950)
and
s
segas
ers
ed
o
veh
c
es
of
ha
era
are
shown
n

F
g
energy
in
the
gas.
Gasiiĩcation
processes
can
be
either
gas
ca
on
(PNL
1986]
excep
for
groups
concerned
9.3.1
Importance
of
Gas-Moving
System
Design
.................................................................................................................
ve
ea
ures

The
b
omass
eeds
ock
s
of
en
a
ow-cos
“gineered
own
gas”
from
coa
(S
nger
1958
Kaupp
1984a)
emergency
of
Wor
d
War
II
and
us
as
rap

d
y
d
sap15
Sou
h
Afr
ca
s
un
que
y
s
ua
ed
re
a
ve
o
producer
situation, design.
as witnessed
duringthe
the handbook
OPEC oil crises
deve
op ng
coun
r es I has sponsored wo ma or n-95
Although

íocuses on
*1
quad
=
10
Btu
7.6.2
Methods
of
Analysis
.........................................................................................................................................................
62
que
Wood
Gas
Generatorỷor
Vehicìes
(Nyga
ds
2-1
Mos
gas
ers
were
s
mp
y
“be
ed
on”

and
direct
(using
airqu
ord oxỵgen
through129
ex11.11.4
Blowers
.......................................................................................................................................
114
w h513.7
uses
nbecause
ess
deve
oped
coun
rA
es an
(NAS
Other
Considerations
.........................................................................................................................................................................
byproduc
of
agr
cusoon
ure
or
sandvonly

cu
ure
sechn
n -ash
Manu
ured
gas
he
cow ca
o1983
hey
peared
when
fue(K
s were
ava 1983
ab heat
e 1985)
Transpora
on31
4ac
Cha
coa
Gas
e sas
gas
research
s .......................................
hcrossed
gh

y Superchargers
deve
oped
9.3.2
Fans
ĩ...........................................................................................................................................
95
erna ona
con
erences
etos generate
rom
downdraft
gasiíication
the
method
suitable
for
1979)
g ve
he prreader
a comp
eUeS coverage
of
aof
othermic:
reactions)
or yindirect
(transíerring
heat

to
the
7.6.3
Water
Vapor
Analysis
......................................................................................................................................................
65
K
e
s
rom
1981
1983
1985)
and
pr
va
e
nd
v
duá
s
su
fur
11.11.5
con
en
and
Other

Methods
does
no
for
ncrease
Increasing
he
Producer
eve
of
Gas
Power
.........................................................................................
115
Un
ed
S
a
es
and
by
1920
mos
Amer
can
owns
and
s
a
very

h
gh
or
and
he
Depar
men
and
produces
much
of
s
fue
by
gas
ca
on
However
Blowers
.
96
small-scale
power
it.......................................................................................................................................................................
also
extensive detail
5 5 Cha9.3.3
coa ve systems,
sus
B omass

Fue gives
s
31
A
e eve
ofgas
fund
ng
($2
onbe
oburned
$5
m66
aspec
s of
downdraf
ers
dur
ng
d WarII
Gas
reactor
from
they outside).
The
gas
can
to(Skov
Reterences
1974

...............................................................................................................................................
her
1982
TIPI1986)
131
carbon
dhas
oxEngine
de
nLife
ahe
mosphere
he
subsequen
con
7.8
Analysis
supp
ed
of
gas
Test
Data
opopu
................................................................................................................................................................................
form
cook
and
Demodera
ense

curren
has
a fprogram
omWor
d ssem
na
e 115
nforaesso
aMo
na
vehe
ares
onden
ofsand
20
onngwhose
11.13
and
Engine
Wear
.................................................................................................................................................
biomass
fuels,
gas
testing
and
cleanup
in9.3.4
Ejectors
..............................................................................................................................................................................

96
on
yr)
has
been
ma
n
a
ned
s
nce
1975
by
DOE
Producers
and
Bỉast
Furnaces
(Gumz
1950)
ooks
5
6
The
C
ossd
a
Gas
e
32

produce
industrial
or
residential
heat,
to
run
engines
for
greenhouse
effec
(prov
ded
consump
on
does
no
gh ngma
hrough
heMass
oca
“gasworks
”coun
ma on 011 sma
gas ers n case of na ona
needs
ch
hose
of
ess

deve
oped
rBalances
esbwill
A ma
or
7.7.1
Balances
and
Energy
............................................................................................................................
66
strumentation,
11.12.1
and
safety
Engine
considerations
LifehaExpectancy
that
.............................................................................................................................................
be
of
115
Recen
y
here
has
been
ncreased

n
eres
n
omass
as
9.3.5
Turbochargers
and
Superchargers
.................................................................................................................................
97
“advanced
concep
” for
gasand
cak on
and
pyro
s wood
proaemergency
he her- However
modynam
cs
neor
coanoys
and
mechanical
or electrical
power,
toofmake

synthetic
Appendix
....................................................................................................................................................................
139
exceed
annua
produc
on)
Ca
be n ............................................................................................................................................
aken
o1985
eneconom
c cs
reasons
work
on32
wor
d7 con
erence
nSticking
mber
u e mus
za
on
May
5to
The
Upd
aữwho

Gas
e
use
all
those
work
with
gasiíiers
at
whatever
7.7.2
Flow
Rate
Characterization
67
a
renewab
e
energy
source
In
he
as
few
years
a
11.12.2
Intake
Valves
...............................................................................................................................................

116
cesses
Mos
of
he
work
s
a
med
a
arge
ndus
r
a
gas
caon
The
ar
c
e
by
Sch
ãpfer
and
Tob
er
In
1930
f rs
na

ura
gas
p on
peh.............................................................................................................................................................
nerenewab
was buecabason
os
fuels.
9.5
and
Product-Gas
Burners
sure
haFlares
bheomass
use
asons
fue
sbo
awood
gas f ers for veh c es s n progress n he Un ed S a es97
nc7.9
uded
weekong
sess
on
scale.
number
of
nd

s oand
have
bu o gas
verse ons
of
5 8 Particle-Size
The
mbev dua
Downd
a groups
Gas
erom
32
Measurement
.......................................................................................................................................................................
67
11.12.3
Oil
Thickening
and
Contamination
116
processes
and
sbiomass
suppor
abora
orwell
es
“Theore

ca
Prac ed
ca nmpor
Sgovernmen
ud es
ofalready
Opera
of
ranspor
na
Denver
he
ds......................................................................................................................
9.4.1
Flares
..................................................................................................................................................................................
97
(Lowderm
kura
1975gas
Reed
1978) 1985)
Today
many coun
r of
es
Durone
ng sense,
he
a eand

197ŨS,
we
ed ismore
han 40%
of
and
charcoa
manu
ac
ure
(NTRI
In
gasiíication
aon
sma combustion
downdraf
gas
ersParticle-Size
and
have
opera
edvery
hem
as
The
of
biomass
in
wood
stoves

and
in7.8.1
5
7
1
Typical
n
oduc
on
Distributions
...............................................................................................................................
67
32
ndus
r
a
fữms
and
un
vers
es
Progress
n
hese
Mo
orcars
on
Wood
Gas
”

(Sch
ãpfer
1937)
s
he
bes
Texas
As
p
pe
nes
cr
sscrossed
he
coun
ry
ow11.12.4
Tar/Oil
Accumulations
...........................................................................................................................................
116
(such as Ch
na Korea
Braz
and Sou h Afr ca) have
our
o
We
reserved
rauch

of
our
qu
d
fue
for
proven
technology.
Approximately
one
million
9.4.2
Burners
...............................................................................................................................................................................
98
demons
ra
undhas
sDesc
AcAnalysis
gasgas
f er-powered
dustrial
The
European
boilers
increased
Commun
dramatically
y....................................................................................................................................................

(EEC)
in
shown
sgasiíiers
repor
he
mee
ngs
ofcaDOE’s
Therprac
ca and
schere
enedwas
ữca dno
scuss
on
of sma
gas
ers
o
cos
na re
ura
sp
aced
manufac
ured
and
he
7.8.2

5 on
7gas
2 aEconom
pfew
on oof
....................................................................................................................................................................
hehe
Downd
mbe
67
33
ac ve
òres
onSieve
programs
ha
are
he aphas
ng
osome
n-Gas e programs
11.12.5
Engine
Corrosion
ranspor
and
governmen
o
deve
116

op
downdraft
were
used
to
operate
cars,
trucks,
veh
c Instrumentation
esand
from
effor
are
shown
n F gnen
and
areas,
acrease
grea
dea
íorest,
of hn sMicroscopic
eres
agricultural,
ba omass
and
energy
paper
a2-2

orms
areGas e mochem
ca
Convers
rac ors in(PNL
1986)
as99
appear
dur
ha
per
od
despread
soon
was
orgo
“Town
10.1once-w
and
..................................................................................................................................
he
wor
dryn cControl
ores
area
W ..............................................................................................................................................
h wastes
con
nued
gas

n nghe
Unelectric
edon
S aCon
es
(However
Sweden-Vo
vo
7.8.3
5 7 o3 a ndus
Supe
Ve
Size
oc
Analysis
y Hea
Load
and
S z ngers
35
boats,
trains,
and
generators
Europe
during
11.12.6
Engine
Warranty
.....................................................................................................................................................

11767
oday
one
can
ob
a
n
shop
p
ans
for
cons
ruc
ng
being
and
has
used
been
extensively
very
ac
ve
for
n
fuels
gas
f
by
ca

some
on
dur
Industries.
ng
he
as
we
as
a
o
her
mee
ngs
DOE
recen
y
sponsored
a
gas”
con
nued
o
be
used
n
Eng
and
un
he

197ŨS,
d 11.14
gence
he
prospec
s
for
mak
ng
b
omass
ru
y
manu
ac
ured
and
s
ored
10
000
un
s
for
emergency
Exhaust
Emissions
........................................................................................................................................................................
117
World

War
II
(Egloff
1943),
and
the
history
of
this
ex7.8.4
5
7
4
Aerodynamic
Tu
ndovvn
Ra
Size
o
Analysis
.............................................................................................................................................
67
36
10.2
The
Need
for
Instrumentation
and
Control............................................................................................................................................99

A
more
genera
survey
of
b
omass
herma
convers
on
gas
ersp an
(Nunn
khoven
1984
Mo
her
1982
Skov
However,
frenewab
ve fhe
years
(CEC
1980
1982
biomass
Br fo
dgwa
use

still
waits
for
oenerthe
mee
o exam
ne in
he Chapter
po en a 2.and
prob ems
ow
bu
s were
d ysman
ed
ow er
ng1984
he
d Bscovery
e more
wOther
sextensive
ead
mprove
use ) ng
perience
is
outlined
However,
theofwar’s

11.15
Devices
for
Producer-Gas
Power
Generation
................................................................................................................
117
was
pub
shed
dur
ng
1979-80
n
he
SERI
hree7.8.5
5
7
5
Graphic
D
sadvan
Analysis
ages
o
of
he
Size

mbe
Distribution
Des
gn
..........................................................................................................................
69
1974)
Un
or
una
e
y
no
body
of
n
orma
on
s
ava
10.3hGasiíier
Instruments
99
application
gy Nor
1985)
The
ofo EEC
improved
has ocused

conversion
methods,
h ghsuch
aspec
ass
energy
gas this
ca on
(Eas er ng
1985] bu
s curren as
y36
of
Sea
Today
a ..................................................................................................................................................................................
few pon
an he
s are
s ech
opera
ng
end
saw
emergency
measure
abandoned,
vo
ume
Survey

of
Biomass
Gasiỷication
(Reed
In
he
pr
va
e
sec
or
of
he
Un
ed
S
a
es
dur
ng
he
as
11.14.1
Gas
Turbines
................................................................................................................................................................
117
ab
e
o

he
p
e
her
he
a
er-day
hobby
s
s
or
he
r
5
8
The
7.8.6
S
a
ed
Physical
Downd
Size
a
Gas
Analysis
e
......................................................................................................................................................
70
38

gasiíication,
of
gas h rd
ca10.2.1
on
that
(such
match
as oxygen
biomass
gas
energy
ca.....................................................................................................................................................
on)
to processes
bu has
ocus
ng
on
d
rec
quefac
on
of
wood
The
s
a
us
of

Pressure
Measurement
99
n
he
wor
d
1.3 Gu
de to Gas
t catved
on Ln terature
inexpensive
gasoline
became
available
(Reed
1985b).
1981)
Thhere
s governmen
workbeen
subsequen
y and
was
pub
shed
10 years
has
a correspond
ng deve

deve
opmen
s8work
nvo
fu
-.................................................................................................................................................................
me
research
oExamples
evaofua se
11.14.2
Fuel
Cells
117
currently
acoun
so erpar
unded
requiring
n
liquid
sma
and
-sca
gaseous
e
gas
ers
fuels.
as

par
5
1
n
oduc
on
38
many
of
he
research
opmen
10.2.2
Gas Flow Measurement
...........................................................................................................................................
8.1 Gas
Cleaning
and
Conditioning
71
commerc
a gas
y of biomass
as forPrincipìes
of disrupted
Biomass
of b omass
ers
heat
applicaỉions

a 100
he
Development
gasiíication
was
in
cr such
caved11.14.3
ac5processes
ors
such
as
f ero.....................................................................................................................................
opera
on
gas
qua
y
perce
respons
bes
include
y gas
“assoc
lime,
a ed”
and
deve
brick
opExternal-Combustion

Devices
.................................................................................................................................
11838
82
Desc
poward
on glass,
he Sứa
ed
Downd
a Gas epro ec s and commerc a gas ers pro ec s was sum1 3 1of
B b10.2.3
ograph
Solid
Flow
Measurement
.........................................................................................................................................
103
Gasification
(Reed
1981)
The
work
Producer
Gas:
sca
e
found
n
umber

and
paper
m
s
There
has
been
1946
as
the
war
ended
and
inexpensive
(150/gal)
gas-c
eanup
sys
ems
eng neand
opera
on
and eng
ne Carré
wear
Introduction
.................................................................................................................................................................................................
71
manuíacture;
ng8.2coun

r5es
power
(Beenackers
generation;
van
and
transportation.
Swaa
1982
mar
zed
n
Surveỵof
Biomass
GasiỊication
(Reed
8 of
3 books
Unansvve
ons Abou
a ed Downd
The12.1
number
ar c esed Ques
and repor
s on
bheS
omass
Another
Fuel

for
MotorThe
1983)
n er-a esGas
n epower
genera
onTransport
a magnitude
a sma (NAS
sca
n103
he40
10.2.4
Temperature
Measurements
......................................................................................................................................
gasoline
became
available.
of edamage
........................................................................................................................................................................
Safe
1985
Br
dgwa
er
1984
NTRI
1985
Manurung

and
1981)
2 1 2Biomass,
Veh
c
e
Gas
t
ers
like
coal,
is
a
solid
fuel
and
thus
is
inherent8.3
The
Power
Theory
of
Gas
Cleanup
.........................................................................................................................................................
72
In
eres
n

sma
-sca
e
gas
ers
s
s
rong
among
orgas 10.4
ca Controls
on
y exceeds
1985b)
w h e
5 8eas
4 ................................................................................................................................................................................................
Mode ng10he000
S a (Reed
ed Downd
a Gas
42
con
exce
en atechnology
hed
s or
ve asbuy
vveback
as

Un aednsSan
a es
s mu
bycaa perspecrac
inflicted
on
gasifier
by ve
thispower
disruption
can
103
Beenackers
1985)
ty
and
Environmental
..........................................................................................................
119
less
convenient
tome
use
the
or liquid
gan
ons
ha
w of
hthan

essConsiderations
deve
coun
rOne
es fuels
such
many
mpor
an
sdea
ud
es
conduc
edgaseous
beoped
ore
1950
can
Sly
ar
abou
he
Wor
d
War
I
sma
gas
ers
EPRI

(Schroeder
1985)
has
eva
ua
ed
he
po
en
a
of
a
pro
ec
on
of
Corn
ng
deve
opmen
s
A
monumen
a
ra
es
n
some
s
a

es
under
he
Pub
c
U
es
8.4
Gas
Cleanup
Goals
...................................................................................................................................................................................
74
be
seen
by
the
fact
that
it
is
difficult
for
even
the
“ad5za
9ng
Ta
C
ack

ng
Gas
Ẽe
s
10.3.1
Fuel-Level
Controls An
..................................................................................................................................................
10342
to
which
we
become
of
as12.2
he
Wor
dhave
Bank
hecharcoa
Uaccustomed.
S when
Agency
for
Inoeeds
erna
ona
eas
ydeve
become

d...........................................................................................................................................................................................
scouraged
ngoverfview
ndocks
he
Introduction
119
oped
around
andCharacteristics
bryomass
gas
forPo
mak
e ec
c198ŨS
y The
Fores
Serv
cetests
of
work
Gas
Engine
Regu ers
aSmalỉ-Scale
ory
cyngAc
(PURPA)
d rto

scussed
nSystems,
Chap
er42
vanced”
technology
of
therProduce
achieve
on
1 3 4were
Commerc
a
ntormat
on
8.3.1
Gas
Contamìnant
..................................................................................................................................
74
5
9
1
n
oduc
on
Pressure
Controls
103
various

processes
now
inysuse
or
evaluation
for
Deve
opmen
and
he
equ
vansunder
en .......................................................................................................................................................
organ
zawork
ons
n
ear
erToxic
works
For
una
e
much
of
h
s
ear
y
has

o 12.3
opera
e10.3.2
veh
c
es
boa
ra
and
sma
e
ec
r
c
he
USDA
ho
ds
annua
mee
ngs
a
wh
ch
gas
f
ers
are
s
ava

ab
e
n
he
Un
ed
S
a
es
and
Germany
(Kaupp
13
what
was
routine
operation
in
the
1940s.
The
design,
Hazards
......................................................................................................................................................................................
119
8.3.2
Dirty
Gas
7443
5coun

9 2 rofesTypical
Combus
on
o Ta.............................................................................................................................................................
son ...............................................................................................................................................
Ano
her
source
gas
f er
nforma
s energy
prov
ded
by
converting
biomass
to
more
conventional
forms
10.3.3
Temperature
104
European
The
Producer
Gas
Round
ab

e and
(of
been
co
ec
ed some
of
has
been
summar
genera
ors
(Rambush
1923)
BeControls
ween
he
wozed
wor
d
dresearch,
(FPRS
1983)
1984a)
Inand
addmanuíacturing
onof odeve
o her
cons for
dera

onsdecade
h s ers
work
teams
of that
have
12.2.1
Carbon
Monoxide
.......................................................................................................................................................
119
A scussed
very ac
ve
area
opmen
sma
gas
s
10.5
Computer
Data
Logging
and
Control
..............................................................................................................................................
104
8.3.3
Gas
Cleanup

Goals
............................................................................................................................................................
7445
compan
es
deve
op
ng
commerc
a
gas
er
sys
ems
such
as
gas
5
9
or
3
liquid
The
fuels
ma
Ta
is
shown
C
ack

ng
in
Fig.
1-1
(Reed
he
Be
er
Ins
u
e
n
S
ockho
m)
has
pub
shed
a
some of
beenwas
repr pursued
n ed Wemos
offery here
an overwars
deve has
opmen
by ama
eur
con

a ns ane n-dep
rea
men the
of past
he use
of that
oressmall
and
all
disbanded.
We hhave
from
only
o
genera
power
n
developing
countries,
12.2.2
Creosote
........................................................................................................................................................................
121
Repor
s
on
governmen
programs
are
ma

n
a
ned
by
he
These
groups
wr Cleanup
eshows
adver
ngsunlight
brochures
as
1978).
The
is
to
of
books
on
on
drawn
oge
8.3.4
Design
.....................................................................................................................................................
7446
4body
Ca
agas

y how
csca
Ta
CTarget
ack
ng
vnumber
ew
of
of
know
edge
nand
order
he
p her
he
en
husEngine
as
sh5 s9figure
because
gaso
ne
was
re converted
aasoveof
y en
nagr
cu have

ura
res
dues resources
ữaction
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knowledge
thatTechn
has been
published,
wh ch
ben
omass
and
canno
eason whereas
y(OSTI)
afford
11.1biomass
Adaptation
and
Operation
.....................................................................................................................
10546
Off
ce
of
c
and
ca
In

orma
hey
wr
e
sc
en
c
ar
c
es
and
s
some
mes
through
either
traditional
activities
(e.g.,
5
10
Summa
y
echn
ca
exper
se
from
around
he

wor
d
In
add
on
12.4
Fire
Hazards
..........................................................................................................................................................................................
122
reader
oca
e
requ
red
ma
er
a
In
genera
he
more
expens
ve and s mpoferParticles
o use .........................................................................................................................................................................
han b omass In 1939 he
8.5 Classification
the
large
experience

incro
sbulk
They
doíirsthand
noea have
an
ec
d soperation
r che
bu 74
on
where
hey
can of
be
ob
ned
n ee have
herr campub
or
F qu
na dyfue
severa
pr
va
groups
shed
or
drecen
ffs11.2

cu
separa
e..........................................................................................................................................................................................
ac
ua ab
from
proranspor
ec ed inper
agriculture
and
or
new
novative
h12.5
group
has
ed
severa
erences
ono ormance
producer
Introduction
105
works
arehos
s sílviculture)
ava
e ocon
German
boockade

ha
ed
a.......................................................................................................................................................................
Europe
design
has
been
lost
and
íorgotten.
Environmental
Hazards
123
gr
d
so
power
sys
ems
of
10
o
1000
kw
are
very
8.6
Particle
Movement
and

Capture
Mechanisms
.......................................................................................................................................
74
6 1 techniques
Gas
t
er
Fabr
cat
on
and
Manutacture
pr
n
ed
cop
es
They
are
some
mes
d
ff
cu
o
ob
a
n48
repub

shed
gas
f
er
p
ans
or
gas
er
books
and
The
r
pub
ca
ons
shou
d
be
read
cr
ca
y
bu
usua
y
(e.g.,
as
energy
plantations,

coppicing,
and
gas 11.3
for
ess
oped
coun
rhees
e papers
s...................................................................................................................................................
M
ary
use
of ec
gaso
ne
rece
ved
op
prrom
or 1981
yhave
and1983
he
Gas
for
Transportation
105
Two
maProducer

or deve
co
ons
of
o(K
der
been
a er
rac heve
Thus
he1986
scay eofof
operas1974
onexhaus
has
aned
mpor
an
Gasiíication
was
rediscovered
in
an
era
of
fuel
a
or
g
na

supp
repor
s
Cop
es
pamph
e
s
(TIPI
Skov
Mo
her
1982
con
a
n
mpor
an
(
f
op
m
s
c)
n
orma
on
algaeculture)
now
being

developed.
1985)
Collectors
............................................................................................................................................................................................
7548
6 an
2 Dry
npopu
oduc
cmade
v8.7
a on
ons
had The
o U
fend
for ona
hemse
ves for
13.1
....................................................................................................................................................
Decision
Making
he
pas
decade
S Na
Academy
of
n uence

on
s Nygards
deve
n and
shortages
andwha
higher
prices,
there
gasiíỉer
11.4nProducer
Gas
for Electric
Povver
and Irrigation
...........................................................................................................................
105
of
hese
repor
s are
aoil
so oped
ava1979)
ab
eh sncase
GPO are
depos
ory
Nunn

khoven
1984
Biomass
resources
fall
into
two
categories:
wet
or
wetranspor
fue
s
Approx
ma
e
y
one
m
on
gas
ers
8.6.1
Gravity
Settling
Chambers
..............................................................................................................................................
7548
Sc
ences

pub
shed
a
b
b
ography
of
s
ex
ens
ve
6
3
Ma
e
a
s
o
Consữuc
on
gas from
charcoa
has been deve oped comengine
under
20 brar
countries
for
1 3 5Producer
Producer
..........................................................................................................................................................................

Gas
Research
124
There
are
awayeas
wo than
suchmay
es—one
Fbrar
na yesprojects
new
deve
opmen
s innmore
gas
ers
ex end
he
r
11.5
Gasifier
Types
Suitable
for
Shaft-Power
Generation
....................................................................................................................
105
table

biomass
(molasses,
starches,
and
manures)
and
dry
were
used
on opera
epapers
veh
cnes
es
wor
dw
de
dur
ngAnother
hewhere
war
co
ec
on
of
ear
y
n
Producer
Gas:

8.6.2
Cyclone
Separators
..........................................................................................................................................................
7548
merc
a
y
he
Ph
pp
(K
e
s
rom
1983)
producing
process
heat
and
electrical
and
mechanical
pub
c
and
one
un
vers
y—

n
each
State.
6
4
Me
hods
o
Cons
uc
on
use
o
o
her
new
areas
One
of
our
au
hors
(Das)
has
1
3
3
Gas
t
cat

on
Proceed
ngs
13.2 Introduction
...........................................................................................................................................................................................
124
biomass
Much
research
(woody
o and
aProducer
r deve
gasagricultural
ca
onEngine
s be
materials
ng
conduc
eds
years
subsequen
opmen
of
wood
producer
Fuel
for
Motor

(NAS
1983)
The
11.6The
Sizing
thenGas
to the
...........................................................................................................................................
105
more
han
1000
un
sTransport
have
opera
ed
Producer
gasand
8.6.3
Baghouse
Filter
80
power
(Kjellstrom
1983,
deve oped
a fsma
gas
f er1985).

su abIneyits
fors rebirth,
frepor
r ng ed
ahowever,
oundry
Curren
gas
ca
on
work
genera
a
con-49
residues).
aUn
var
ous
Biological
un
vers
es
processes
around
he
require
wor
d
wet
However

biomass
and
s
6
5
S
z
ng
and
Lay
ng
ou
he
P
pes
gas
un
s
s
a
es
amen
o
human
ngenu
y
n
he
face
13.3

Logistics
Assessment
..........................................................................................................................................................................
124
vers
y
of
Ca
orn
a
a
Dav
s
acqu
red
an
ex
ens
ve
genera
ed
for
ndus
r
a
hea
by
more
han
30

arge
un
s
the
existing
technology
has
uncovered
major
problems
8
6
4
E
ec
os
a
c
Co
e
P
ec
p
a
o
s
83
11.7
Engine
Selection

..................................................................................................................................................................................
106
The
o
her
au
hor
(Reed)
s
deve
op
ng
sma
ba
chype
ferences and hen appears n he pub shed proceedoperate
dco
ffadvers
cu
at
oor
near
hroom
s work
temperature.
fs prepar
occurr
These
ngprocese cher
ses,

unof
Ex
accoun
ss make
fasna
ng 1 3 7in
on
ofrace
papers
wh
e1984)
ng
State
oỷthe
6ec
6 ng
ns
sended
and
Con
oApplication
opera
nyumen
Braz
(Makray
13.2.1
Gasifier
..................................................................................................................................................
124
connection

with
effluent
and
gasapp
cleanup
and
the
fuel
Federa
Emergency
Management
gas
ers
for
cook
ng
and
gh
ng
caons
n
h
rd49
8
8
We
Sc
ubbe
s
84

11.6.1
Large-Vehicle
Engines
—
Truck
Engines
up
to
50
kw
.......................................................................................
106
ngs The U S Depar men of Energy (DOE) (PNL
shown
unded
on
on
the
a sma
lower
left
e side
The
of hEngine
Fig.
of
1-1,
and
include
hs

read
ng or
and
nform
hesca
reader
of work
bo
he Goss
promSystems
se and
Artỷor
Smaìì
Gas
Producer
supply,
which
were
less
important
during
the
emergency
Agency
(FEMA)
Gas
er
Work
6
5

1
Tempe
a
u
e
13.2.2
Equipment
Selection
Factors
...................................................................................................................................
124
wor d coun
1982
Eas reresng 1985) he U S Depar men 106
of49
8gas
7of
1ehe
P vers
ncSou
p ce
es
oof gas
We
Sc
ubbe
84
Fd
g ff
2 2 cu

Veh cs ees
sto
a eUn
OPEC
NAS
1983
íermentation
s(Kaupp
uden
a11.6.2
produce
yEngines
alcohols
Ca
orn
and
aaresadigestion
sn deto
Small
............................................................................................................................................................
us
ng
producer
(Eg
off
1941
1984a)
Mos
of
hese

papers
aDav
so 1943
he
of
World
War
II.
Today,
these
problems
must
be
solved
67 5a2 2NAS
Pon
essu
eEquSupply
13.2.3
Feedstock
.......................................................................................................................................................
124
Agr cu
ure (USDA)
Fores sProduc
s Research
produce
serves
methane.
menKaupp

because
has
spanned
aand
decade
Gengas
1950
1983
1984a)
The
downdraf
gas erishe
reached
hasghes
op8 11.6.3
Sc
ubbe
pmen
8649
Natural-Gas
Engines
.................................................................................................................................................
106
possessspec
on
of A
aKaupp
GATE
n Germanỵ
a so

if biomass
gasiíìcation
to reemerge
a fueldeve
source.
6
5
3
Gas
M
x
u
e
Soc
e
y
(FPRS
13.2.4
Regulations
..................................................................................................................................................................
124
and
nc
udes
bo
h
exper
men
a
and

heore
ca
s
ud
es
men
dur ng itheisemergency
Worad few
War years
II FEMA
has
Thermal
are he
onbeg
f8 11.6.4
e7nn
processes
íunction
Aad very
best
using
on
biomass
from
3angSERI
yWar
EquIIrecen
pmen
8849
A

ofAux
Wor
here pub
was
acagrea
dea
Diesel
Engines
...........................................................................................................................................................
Apparentlv,
going to oftake
for 106
the
1983
he
U
S
Env
ronmen
a
Pro
ec
on
Agency
(Goss
1979)
Twen
e
Un
vers

y
n
he
Ne
her
ands
has
6
5
4
Au
oma
c
Con
o
s
aken
n
eres
n
sma
-sca
e
gas
f
ers
because
hey
13.2.5
Labor

Needs
................................................................................................................................................................
124
Cogeneration
........................................................................................................................................................................................
íeedstocks
Indn11.8
aeres
State
with
Report
than
on
Biomass
are
of
n o/Art
a less
forms
of a50%
emamoisture
ve fue content
sGasiỷication
(Eg offand
1941
technology of the 198ŨS to be effectively applied to106
the49
(EPA)
and
he

Ins
u
e
of
Gas
Techno
ogy
(IGT)
had
a
arge
program
n
gas
ca
on
for
many
years
cou
d
unc
on
dur
ng
a
per
od
of
breakdown

n
our
oain
shown
(Par khon
1985)
the
right
con
side
aFinal
ns
ofmore
Fig.
1-1.
han
The
abs .................................................................................................................................
racwere
s of
Logistics
1943)
By13.2.6
1943
90%
of
he veh
cConsiderations
es1200
nsimplest

Sweden
accomplishments of the 1940s. Space-age advan- ces124

Chapter 1

Introduction and Guide to the Literature
and Research

(Groeneve
dgas
1980a
bonBy
Aarsen
1985
1985)
ar c es on
ca
as he
weend
asofanBuekens
assessmen
ofThes
powered
gas
ersenergy
he
warReed
here1978)
were
Fig. 1-1.by

(Source:
Un
yBiomass
of an
F000
or
da
aenGa paths
e has
apower
very ac
v abvers
y and
exce
snesv
of more
more
han
700
wood-gas
genera
orshan
ng ve

have y had
con anuom
ngc an eres
n o var
forms
of

supp
due
ackareoravailable
her ous
dfor
srup
on of
raaterials
and ocontrol
systems
gas
ca
on
and
have
sponsored
con
erences
dea
ng
conven ona fue s
F
e gas pub
ers be
w g h2-1
h s Veh
f e dc These
ca ore
ons1950
con a(Source

n many NAS 1983)
Contents
Contents vii
V

Handbook
oof
B omass
Downdra
Gas
er Eng
ne
Sys
ems
H
ory Curren
s era
andure
Fu ure
rec ons 73 5
n sroduc
on and Deve
Gu deopmen
o he L
andDResearch
2Handbook
Handbook
Downdraft
Engine
Systems

864Handbook
o o
B
omass
Downd
a Gas Gas
eGasitier
Eng
Sysne
ems
BBiomass
omass
Downdra
erne
Eng
Sys
ems
1
vi
viii
v Handbook
Handbook
Handbookof
oofBiomass
BBiomass
omass Downdraft
Downd
Downdraft
a Gasitier
Gas

Gasiíier
e Engine
Eng
Engine
ne Systems
Sys
Systems
ems Introduction and Guide to the Literature and Research


Table
3-7.Standards
Ultimate Analysis Data
for Selected Pyrolysis
Chars
(Dryweight
Basis,- VVeight
Percent)
MCW
=depending
(wet
dry completeness
weight)/wet
weight.
(3-1)
Table
3-1.
ASTM
for Proximate
Table

3-8.
Sultur ContentMethods
of Biomass
Fuels
biomass,
on the
ofcan
char
gasiíication.
sents
the
maximum
amount
of
energy
that
bePercent)
ob- tained
Table
3-6.
Ultimate
Analysis
Data
for
Selected
Solid
Fuels
and
Biomass
Materials

(Dry
Basis,
Weight
The
ash
content
of
biomass
is
typically
much
less
than
that
such
as
that
showninFig.
3-4
(Reed
1978b).
They
make
3.4.1
Densifying
Biomass
Fuels
3-4.Analysis
Approximate
Moisture

Material
H
N
3.2.2sThereĩore,
Physical
0
Tests
As
Referen
c
Higher
Heating
andTable
Ultimate
of
Wood
Feedstocks
it
is
important
to
provide
for
adequate
removal
%
Sulíur,
Reterenc
Sometimes,
moisture

content
is
reported
on
a
dryweight
from
combusting
the
fuel
and
is
a
necessary
value
forof
h
ce
of
coals,
but
some
forms
have
a
high
ash
content,
as
shown

in
excellent
gasifier
fuels
and
allow
the
fuel
to
be
stored
at
much
Contents
Typical
Fuels
Biomass
fuels
usuallyofhave
bulkBiomass
densities Test
from oneehalf to
Value
(kJ/g)
One
ofMCD,
the material.
most
important
physical characteristics

of biomass
Method
No.
this
bulky
Dry
Weight
basis,
where
calculating
the
efficiency
of
gasiíỉcatioii.
The
high
heating
Table
3-3. This
cancoal
lead as
to shown
ash melting
(known
“slagging”),
densities.
Densiíication
typically
con- sumes
only 1%

Material
Has presenting
N a
As
Referen
shigher
obulk density.
Higher
Heating
one-tenth
thatFuel
of
inc Table
3-11,
(Btu/lb)
Basis
Biomass
Retere
fuel is the
The
bulk density
is the weight
of
0.1
0.1
Moisture
Content
Fir
bark
char

49.9
4.0
24.5
21.
19.2
8,260
(1)some
h
ce
Because
charcoal
often
has
a in
high
value,
gasiũers
are
value
measured
in
this
test,
since
liquid
water
is
Proximate
Analysis
which

can
cause
severe
problems
ingasification.
some
gasiíiers.
A
to
2%(HHV)
of
theisweight
energy
contained
the
biomass;
for
MCD
=
(wet
dry
weight]/dry
weight.
(3-2)
Alfalfa
seed
straw
0.3
(1)
nce

Value
(kJ/g)
drawback
for
shipping,
storage,
and
Biomass
4
biomass
packed
loosely
in
a
Container
divided
by
(wt
%
Wet
(wt
%
2.6
0.1
6,100
sometimes
operated
to
produce
up

to
10%
charcoal
by
Rice
hull
char
36.0
0.4
11.7
49.
14.2
(1)
produced;
however,
the
low
heating
value
(LHV)
is
more
Standard
ASTM
method
is
available
for
measuring
the

residues,
drying
may
also
require
additional
energy,
but
(Btu/lb)
Moisture
E871
Almond
shells
<0.02
(1)1.2
fuels also
come
in coal
a wide
range
of sizes,
many
are
the volume
occupied.
Clearly,
is not
an toexact
number,
Dry

Basis)
Basis)
Values
given
in one
form
can
beit converted
the (1)
other
as
Pittsburgh
seam
75.5
5.0
3.1
4.9
10.
13,650
224.
0.8
Grass
straw
char
51.0
3.7ofas which
0.5
19.7
19.3
(1)

augering
charcoal
at the
end
of
theand
comrelevant
toout
thethe
amount
of31.67
energy
thisbiomass.
can
be
slagging
temperature
for ash (Table
3-1). (such
drying
simultaneously
increases
theproduced,
fuel8,300
value
ofílaming
the
Volatile
matter
E872

Barley
straw
0.14
(1)
not
suitable
for
fixed-bed
gasiíication
sawdust,
3
depending
on
the
exact
packing
of relationships:
the particles.
shown
in
Fig.
3-2
according
to
the
3
2.2
Woody
biomass,
40-60

67-150
(1)
Animal
waste
char^
34.5
1.9
0.9
7.9
48.
12.6
5,450
(1)
West
Kentucky
No.
11
74.4
5.1 by (2)
1.5
3.8
bustion
zone
(Pỵrenco).
7.3
This
31.23
13,460
the requirement
(2) for

for
calculated
from
thepublications
HHV value
shown
Table
4-1.Society
Ash
D1102
in detail7.9
in the
ofreduces
the in
American
The
Coffee
higher
hulls
heating
value
of straw,
the0.2
fuel
is husks).
determined
reacting
sander
dust,
shredder

fines,
and
3.1Utah
Introduction
green
8íeeding
coal
0.8 (1.3)
0.2
8,020
2
6.0
0.6
Municipal
solid
vvaste
54.9
1.1
1.8
41.
18.6
Some
biomass
forms,
with
ashto
or
dirt
contents,
are

coal
77.9
1.5
9.9
32.87
14,170
(1)
MCD
=4.1
MCW/(1
- high
MCW),
and
(3-3)
oxygen
(air)
and
increases
gas
quality
more
than
The
fuel
shape
and
characteristics
determine
vvhether
Woody

biomass,
15
17
(1)
Testing
Materials
(ASTM),
shown
in
Table
3-1.
The
Corn
cobs
0.001-0.007
The
heat
of
combustion
is
determined
by
the
composition
of
Ultimate
Analysis
the
fuel with
oxygen

inina abomb
calorimeter
and measuring
the
char
2because
3 16.9
Biomass
fuels
occur
multitude
of in
physical
The
1.2
(high
temperature)
VVyoming
Elkol
coal
71.5
5.3 forms.
4.2
29.49
12,710
difficult
densiíy
they
cause elemental
excessive

wear
of the
dried
6.80.9
MJ/Nm
, to
but
alsoinincreases
tar
content.
However,
no(2)
current
However,
biomass
residues
can
be
used
fixed-bed
gasiíiers
Straws
150.15
17
(1)
it
will
be
íeasible
to

simply
use
gravity
feedingconsiderable
techniques,
equipment
necessary
forcanperíorming
analysis
is
Com
íodder
(1,2)
the
biomass
and
fact
be
calculated
with
heat
released
to
a
known
quantity
of
water.
The
heat

released
MCW
=
MCD/(1
+
MCD).
(3-4)
E777
0.2
0.2
often-heard
manufacturer’s
claim
that
a 17
particular
gasifier
ccobs,
Redwood
charcoal
75.6
3.3lets or
18.4
2.3
12,40
(3)
Lignite
64.0
4.2
0.9

1.3
19.2
10.
24.85
10,712
(2)
die.
Also,
densiíìcation
is 28.8
an stirring
additional
expense,
so its
Stalks,
hulls
(1)
commercially
successful
small-scale
charcoal
production
in
if
they stalks
are
first
densiíied to 15
suitably
sízed

pelcubes
or
whether
assistance,
such
as
and
shaking,
will
be
Corn
0.05
(1)
shown
in
Table
3-2.
The
proximate
analỵsis
accuracy
from
during
this
procedure
repreHto“any
E777ment,
0afuels
4fortheof
0.2

0.0Moisture
(790°
1020°F)
Charcoal
80.3
3.1
11.3
3.4
31.02
13,370
(1)
can
gasiíy
biomass
fuel”
is a naive
and
(1)
Bagasse
70
230statecontents
typical
biomass
in
justification
will
depend
on
a comparison
of

theare shown
gasifiers
isThe
known
to
authors.
using
commercially
available
equipment
required.
angle
repose
for
particular
fuel
type
Oat
straw
0.23
(2)
E870
0gin
0.1
0.8
21.0
0.2 0.0
0.2
Douglas
fircan

52.3
40.5
9,050
(1)
Redwood
charcoal
78.8unique
3.5 (2)
13.2
4.1by
30.4
13,100
(3) and
each form
be expected 35
to0.26-0.31
have
problems
until
Municipal
reíuse
55 6.3
Table
3-4.
effect
of filling
moisture
content
on
heat

recovery
Cotton
trash
is generally
measured
a large
tube
with
the
fuel,dards
Charcoal
isThe
manuíactured
all
over
the
world,
and
stanN
E778 (1)
o9,500
= Oxygen
0.0
0.0
1.2
22.0
(860°
to
1725°F)
Doublas

fir
bark
56.2
5.9
36.7
(1)
proven
otherwise.
This
physical
disparity
accounts
in
(1)
part
Peat
90
900
and
combustion
efficiency
is
shown
in
Table
3-5.
Recoverable
Flax straw,
<0.01
(1)0.2

then liftingthe
thequality
tube and
thefor
fuel
to form
a pile.
The
determine
andallowing
suitability
uses
(Emrich
E775
H
=various
Hydrogen
s íeedlot
0.0
0.2
Pine
bark
52.3
38.8
2.9angle
8,780
(1)
Oak
charcoal
67.7 available

2.4 today.
14.4
14.9
24.7
10,660
(3)
110.4
125.8
Air
dry
(2)0.4
for the
large
number of gasiíier
designs
The
pelleted
heat
drops
dramatically
with20.4
increased
moisture
since
the
heat
Furfural
residue
(4)
angle

of
repose
is
the
from
the
horizontal
to
the
sides
of
H
=
Hydrogi
c
=
cárbon
c
=
cárbon
1985).
Recenttests
atthe
Colorado
School
of
Mines
have
3-11.
Bulk

of
Varỉous
0.1 Density
0.1
2.2water20.0
(820°
to
1185°F)
vvaste
VVestern
Gross
hemlock
Heating
50.4 WarTable
E711
41.4 Fuels
8,620recovered(1)
gasiíiers
used
vvidely Value
during 0.02
World
II5.8
used
specially
of
vaporization
of the
is not
normally

during
Olive
(1)
10,00
(1)
Milespits
1982
the
pile.
The
basic
feed
characteristic
is
more
easily
judged
tested
char
pellet
strength
at
various
stages
of
gasiiỉcation
0.1
0.0
0.2
21.0

2.1
0.1
3
3
Redwood
53.5
5.9 such(1)
40.3
9,040
(1)
Oak
charcoal
(1060°F)
64.6 Howevẽr,
0.4
15.5
17.4-1).
23.0 kg/m
9,910 Reterence
(3)
Fuel
Grading
Bulk
Density
prepared
1x2x2 cm
hardwood0.04
blocks.
blocks
(2)

Reed 1981
Peach
pits
from
the
angle
steepest
anglePercent)
(measured
0combustion
Idugout
“ (see Table
(Hubis
1983).
s 8000
3 of repose,
0.0
0.0
0.6
Table
3-3.
Proximate
Analysis
Data forof
Selected
Solid Fuels
and
Biomass
Materials
(Dry the

Basis,
VVeight
Beech
51.6
6.3
41.5
20.3
8,760
(1)
Contains
3.7%
chlorine
lumped
withaoxygen
0.1
could
represent
only
tiny
fraction
the
biomass
Peanut
husks
(4)
Sawdust
from the
horizontal)
177
by the sides

a pile
(1)
of fuel
Since
biomass
varies
in
its20.1
properties
fromofday
to (1)
day
and
0.0
0.0
6000
Hickory
49.7 loose
6.5 gasiíiers
43.1
0.7íormed
8,670
Peat
materials
(Finnish)
available
for 0.05-0.2
gasification.
Some
(5)

1
3.3.3
Biomass
Ash
Content
and
Effects
Pober, K. w.
and 3-2.
Bauer,Elemental
H. F. 1977. “The
Nature of Pyrolytic
Oil
from
Municipal
Solid
VVaste
.'
Fuels
from
Waste.
Anderson,
L.
L.
and
Tillman,
when
material
is
removed

from
the
bottom
of
the
pile.
Ễrom
load
to
load,
it
is
common
to
report
analyses
on
a
Table
Analyzer
Equipment
6.0
0.0Fixed
Sawdust
briquets
100
75
mm
55519.9 Ash
(1)D.dryA.,

Maple
50.6
0.3mm long
41.7
1.4(FC)
8,580 Reterence
(1)
Carbon
Peat,
currently
design
evolutions
thatonwill(6)
enable
X I 4000
Editors.general
Neware
York:undergoing
Academic Press,
pp.1.5-2.0
73-86.
Angles
approaching
or
exceeding
90°
are
a
good
indication

of
Table
3-5.
Effect
of
Moisture
Content
basis,
and
sometimes
on
a
moistureand
ashfree
(MAF)
diameter
0.0
0.0
0.6
Peat
dust
350-440
(2)
Poplar
51.6
6.3
41.5
20.7
8,920
(1)

Instrument
Oxida
Detectio
Fuels
with
content
require
much
attention
go aohigh
Rice
hulls
0.16
(1)
them
to w.
use
wider
range
ofCapability
fuels;
nevertheless,
fuel
a
(2)
Sanner,
s., a
Ortuglio,
c.,
VValters,

J. G.,
and Wolfson,
D.n
E.3 1970.
C 65
o nXv0.0
ebasis.
r“2000
s
i0o
n
Mash
u 350-620
rtoì ibridge
cip
aortoltunnel
a
n din greater
Coals
the
tendency
off the
fuel
theother
gasiíier.
It
is
then
a
simple

matter
calculate
speciỉic
Heat
Recovery
and
Combustion
Efficiency
nt
briquets
45
X
60
mm
<
100
(2)
Rice
hulls
38.5
5.7
0.5
39.8
15.
15.3
6,610
(1)
tor grate
gPas
disengagement,

and
positive
char-ash
Rice
straw
I nstraw
dErba
us
i a loxygen
R e t u0.10
s39.2
edetermining
i n thand
o5.1
Ucut
s e(1)
f&
u l M a 0.1
t econditions
i a l 35.8
sdesign,
b y this
r180-400
o l15.8
y s i s . U.S.
Bureau
of Mines;
Aug; RI
properties
aret rvery

important
in
satisíactory
Carlo
C,H,N,0
FID
5y
0.6
from
value.
Rice
19.2
6,540
(1)
(2)
33.9
55.8
10.3
Pittsburgh
seam
coal
(1)
7428. shells
removal.
The
slagging
behavior
of
various
crop

residues
and
Walnut
0.03-0.09
(1)
1104
Combusti
TC
operating
conditions.
Therefore,
these
multifeedstock
Moisture
(wt
Recoverabl
0.0
0.0
1.0
Charcoal
(10%
moisture)
beech
210-230
(3)
Sawdust
47.2
6.5
45.4
20.45

8,814
(3)
3.3
Other
Fuel
Parameters
(3)
Boley, c.pellets
c.
and
Landers,
w.
s.
1969.
E
n
t
r
a
i
n
m
e
n
t
D
r
y
i
n

g
a
n
d
C
a
r
b
o
n
ừ
a
t
i
o
n
o
f
W
o
o
d
44.4
51.4
4.2
(1)
on
Wyoming
Elkol
coal

oxygen
FID
&
The
ultimate
analysis
gives
the
chemical
composition
and
the
(2)
Chemical
Data
C,H,N,0,S
Wheat
straw
0.17
wood is shown in Table 3-10.
%)
e
gasiíiers
will
be
able
to
use
only
a

limited
range
of
biomass
Char
particle
size,£fm
W a chipped
s t e . VVashington, D.C.:0.08
U.S.
Bureau ofbirch
Mines;
Report
of 0.3
Investigations
7282.
0.2
6.0of
180-2003
Paper
43.4
5.8
44.3
17.57
7,572
(4)
TC
43.0
Lignite
Efficiency

46.6
10.4
(1)
The
tests
and
analyses
just
mentioned
are
in
widespread
use
b
higher
heating
value
the
fuels.
The
chemical
analysis
Systems
and
Wood,
(1)
Source:
Reed
1981
Heat

with controlled
specifications, and
anyonesoftwood
in-6.0
stalling blocks
such
0.1a
0.1
0.6
150-170
(3)
Redvvood
wastewood
53.4
39.9
21.26
(5)sulíur,
Oven
Woods
because lists
they the
werecarbon,
developed
for use oxygen,
in9,163
other nitrogen,
Industries.
(CDS1200)
íunctional
(%)

(1.7)
usually
hydrogen,
Wood,
general
0.00 Dry
0.00
(Btu/lb)
7097
82.5
gasiíier
should
have
tests run 0.02
on
the fuel softwood
to5.7
be used
beíore
0.2
0.0
slabs
130-150
(3)
Alabama
oak
49.5
41.3
3.3
19

18
8,266
(5)
Table
3-9.
Nitrogen
Content
of
Biomass
Fuels
Fig.
3-3.
Char-ash
content
and
carbon
content
versus
groups
char
particle
size
for
a
stratitied
bed
gasiíier
(Source:
Das
1985)

0.1
However,
many
more
needontoa0.2
be
developed
speciíically
Wood,
pine
bark
(4)
and
ash content
the tests
dry fuel
weight
percentage
basis.
VVestern
hemlock
84.8
15.0of
(2)
deciding
upon
a4.54
purchase.
The
ability

to
speciíy
fuel
woodwaste
gas
is because
of
charcoal’s
low
volatile
content.
At
the
HevvlettMnC>2
C,H,N
FID
&
and
in downdraft
gasiíiers
this
process7,380
stops at char- ash.
4.76
7036
mixed
60%
81.8
hard/40%
soft

170-190
(3)
Anímal
waste
42.7
5.5
2.4
0.3
31.3
17.8
17.1
(1)
(4)
86.2
0.1
Wood,
green
fir8.33
0.06
for
gasification
processes.
This
section
addresses
the effects
Douglas
13.7
(2)
Ultimate

analyses
for a number
of
biomass
andReterenc
other
solid
Biomass
Fuels
Packard
added
TC
%the
Nitrogen
parameters
isfir
very
important,
and
we
discuss
them
ín1.2
this
beginning
ofsolid
World
War II, most
gasiíiers
used

charcoal.
6.0
12.0
Wood
hardvvood
330
(3)
9.09
6975
81
1
Municipal
waste
47.6
0.3
32.9
19.83
8,546
(6)
Charcoal
durability
depends
on
resistance
of
the
charcoal
e
1.0
(4)

Wood,
kiln
dried
of
other
fuel
parameters
on
biomass
gasiíication,
illustrating
White
fir
84.4
13.1
0.5
(2)
HP-185
fuels
are
given
in
Table
3-6
and
for
various
chars
in
Table

3Dry
Weìght
chapter.
Fortunately,
a wide variety
of tests
are available
However,
13.0 Elmer
charcoal11.54
manuíacture
wastes
6912
approximately
softwood
80.4
50%forof
250
(3)
(4)
to
powdering
(duííing)
during
transport
or char
gasiíication.
Perkin
oxygen
C,H,N,0,S

TC
Wood,
airdried
0.08
Table
3-10.
Slagging
Behavior
of
Crop
Residues
and
Wood
12.8
0.2
(1)
Tillman,
D. A. 1978.
Wood
as
an
Energy
Resource.
New
York:
Ponderosa
pine
87.0
(2)
the

need
for
more
speciíic
testing
procedures.
The
basic
fuel
7.
Basis
4 energy
16.6
14.29
6853
79.7
Academic
Press.
biomass
and
charcoal
gasiíiers
can be
mixed
useíul50/50
tobiomass
those
290 maintain
(3)
the

of biomass
and
usuallythat
requires
hardwood
Barleythe
straw
0.59
240
Ideally,
charcoal
should
size
until the(1)
carbon
Redwood
16.1
0.4itsareand
(2)
parameters
important
gasiíier
design
Slagging
Fuels
%
Non-Slagging
Fuels
%
(2) starting

Bituminous
Coal
Research,
1974.
Gas
Generator
Research
and Development,
Phase
Process
Equipment
720.
(1)
G
as
iint igasiíication.
c adetector
tion
P rend
o6791
ị eofAsh
cWorld
tloose
UDegreeot
l83.5
tInc.
im
amost
t eSlagging
Stravv

Note
in Table
3-6
thatin80
biomass
isII. typically
very low in —
both
16.67
78.9
interested
as
a
material.
By
the
War
II,
FID—Flame
ionization
TC—
reaches
the21.0
end of the reduc- 0.16-0.56
tion2.0
zone. In practice,(1)
a(2)
wide
Ash
Com

cobs
Cedar
77.0
Development.
OCR-2ũ-F;
PB-235530/3GI.
00
—
C
h
e
m
i
c
a
l
A
n
a
l
y
s
i
s
L
o
g
,
Agricultural
particle

size
and
shape
320
23.0
18.75
6730
78.3
bales
nitrogen and
sulfuralfalfa
content seed
relative
to íossil fuels. However,
Thermal
conductivity
Source:instead
Reed
gasiíiers
used wood
of charcoal (Gengas 1950).
6.0
Barley
straw
mix
10.3
Severe
Cubed
straw
Com

todder
0.94
range
of
char
areGasitication.”
produced
zone,
Oven
Dry
Barks
Dept.,
Caliíornia,
Davís,
1979.
Green
can
contain
upY.,
to
water
by 1974.
weight,
so
itsXof Low
(3)
Wen,
c.awood
Y.,
Baìlie,

R.University
c., Lin, c.of
and50%
0’Brien,
w.
s.
“Production
Btu
Gas 7%
Involving
Coalparticles
Pyrolysis298
and
Ainmuch
dthe
v areduction
n c e(1)
svalues.
8Engineering
(4)
22.22
Alfalfa
seed
straw
cube
30
X
30
50
mm,

28.5
6604
76.8
1981
selected
biomass
íeedstocks
may
have
higher
particle
size
distribution
Today,
large
number
of
gasiíiers
built
in
the
Philippines
use
10.2
4.8
(2)
Partridge,
J.
R.,
“Manitoba

Crops
as
an
Energy
Source,”
Sixth
Annual
Cotton
gin
trash
1.34-2.09
(1)
Bean
straw
Severe
Almond
Shell
and
these
can
cause
a
plugging
problem
if
they
are
not
i
n

C
h
e
m
i
s
t
r
y
S
e
r
i
e
s
.
Vol.
131.
VVashington,
D.C.: American
Chemical
Society.
properties
vary
widely
with
moisture
content.
The
chemical

moisture
VVestern
hemlock
74.3
24.0
1.7
(2)
7
(4)are
Barley
Xsas
30
X
50 mm,
7%
33.3
25.00
The
and
nitrogen
selected
fuels
Bovverman,
F.straw
R. 1969.
Introductory
Chapter
to6482
P6.4
rother

i Manitoba,
ncube
ccountries
i p30
l e75.4
awell
n
rremoved.
a csulíur
tstalks
i cStirring
e sand
oand
f 300
I contents
n c i n1.28
eofr2.2
a t i and
o nbiomass
. Corey,
R. 1.5
c.,
editor.
charcoal,
and
charcoal
is used
in Winnipeg,
some
Conterence,

Biomass
Energy
Institute,
Canada,
Oct.
13,d Pchar
durability
íixed-carbon
content
Corn
(1)
Com
Moderate
Corn
cobs
augering
out
char
ash
are effective
New
York:stalks
John
Wiley
and
Sons. (expressed
composition
of
biomass
on

a
drỵ,
ash-free
basis)
moisture
Douglas
3
fir
70.6
27.2
(2)
Bean
straw
cube
30
X
30
X
50
mm,
7%
440
42.8
30.00
6178
71
8
(4)
1977. 1983; Kjellstrom 1983). It seems wise and probable
shown

inC
Tables
and
(Foley
Olive
3.2
Flax
Cotton
(5)
c. gin
c. andtrash
Landers, w. s. 1969. E n t r17.6
a i ncoals
m%
eof(bituminous,
nmoisture
t68.2
DSevere
r yandi n g ash
a níusion
dstraw,
a24.0
rpelleted
b3-8
opits
n
i304
z3-9.
a tthis
i 1.1

o nplugging
o f Wproblem
o o d (1)
techniques
for
preventing
(Rogers
temperature
2.6
moisture
isBoley,
6W
more
constant
of the various
White
73.4
(2)
(4)
(3)
Payne,
F.fir
A., e tthan
a that
i , D.C.:
"Gasitication-Combustion
Corncobs
Corn
cobs
11

50.0
33.33
5868
that
any
a
s
long-term
t
e
.
VVashington,
development
U.S.
of
Bureau
biomass
of
Mines;
gasiíication
Report
of
Investigations
will
7282.
17.2
Peach
pits
0.66
0.9

Cubed
cotton
stalks
Severe
Oatcontent
straw
(2)
is
relatively
simple
and
can be
períormed
with
aEngíneers
drying
oven,
1985;
Kaupp
1984b). Figure3-3
shows
the char ashcontent
Analysis
oflignite)
Exhaust,”
Society
of 3-1.
Agricultural
Summer
060.0

Ponderosa
pine
73.4
25.9
0.7
(2)
anthracite,
asAmerican
shown
in
Fig.
Furthermore,
more
(4)as
Corn
stalks
37.50
5252
cube
30
61.1
X
30
X
50
mm
391
ash
(6)
Sanner,

w.
s.,
Ortuglio,
c.,
Walters,
J.
G.,
and
Wolfson,
D.
E.
1970.
C
o
n
v
e
r
s
i
o
n
o
f
M
u
n
i
c
i

p
a
l
a
n
d
ul-0laboratory
timately
use
biomass
again,
rather
than charcoal.
10.4
Olive
pits
0.36
(1)
pellets
Severe
Prune
pits
0.5
Meeting,
San
Antonio,
TX, Paper
#80-3025,1980.
aRDF
íurnace,

and
a
balance.
The
ultũnate
a
function
of
particle
size
and
the
relation
betvveen
carbon
0.8
Redvvood
71.3
27.9
(2)
(4)
than
80%
of
the
biomass
is
volatile.
Coal
is

typically
only
Cotton
gin
trash
23%
moisture
343
66.6
40.00
4639
53.9
I n d u c.,
s “Current
t r hulls
i a lDevelopments
R e f u sandeProblems
into
U s eGasitication,”
í uSevere
l M a t emoisture
r i a l spits
b y P y rShell
o l y s(cracked)
i s . U.S. Bureau of Mines; (1)
Aug;
RI
content
VValnut
(4) Bailie, R. rice

in Biomasstechniques.
1.1
Pelleted
14.9
Peach
1.74
analỵsis
involves
more
advanced
chemical
As
charcoal
is the
converted
to gas
in 4019
ais gasiíier,
the coke,
ash
content
0.2
77428.
conversion 13
and 1
char size
for a stratified-bed
gasiíier. The
Cedar
86.7

(2)fuel
(4)
Peach
71.4
pits
41.67
11%
moisture
46.7
474
20%
volatile;
remaining
80%
unreactive
which
Sixth
Annual
Meeting,
Biomass
Energy
Institute,
Winnipeg,
Manitoba,
6.0
0.2
Peat asvalue.
0.5-3.0
Source:
Safflower

Reed
1981
straw
Douglas
Fir
wood
blocks
heating
(4)
Both
analyses
períormed
laboratories
rises.
3more
We
use
the
term
char-ash
to10%
describe
theMinor
end
Mill
Woodwaste
Samples
starts
biomass
(1-in.

birch
dowels)
on the farright(3)
of Fig.
Olive
pits
moisture
567
isFrom
diftobe
gasiíy
generally
Canada,
Oct.íicult
13,
1977.
Bliss,
c.can
and
Black, than
D. charcoal.
o.in commercial
1977. Biomass
Silvicultural
Prune
pits
0.32
(1)
1/4"
pelleted

walnut
5.8
Moderate
Municipal
tree
prunings
3.0
(4)
for
$25
to
$100.
product
from
char
gasiíìcation;
although
the
char-ash
is
still
(5)
Ekman,
E.
and
Asplund,
D.,
A
R
e

v
i
e
v
ự
o
f
3-3.
Ash
is
0.5%
and
carbon
conversion
is
zero,
of
course.
Prune
pits
8%
moisture
514
has
very
low
sulíur
and
ash
content

compared
to
coal.
Biomass
Farms,
Vol.
5,
Conversion
(3)
-4
mesh
redwood
shavings
76.2
23.5
0.3
3.3.1
Particle
Size
and
Shape
Shell
mix
Rice
hulls,
pelleted
0.57
(1)
Hogged
wood

VVheat
straw
and
corn
7.4
Severe
0.3
ehulls
a ranalysis
c
h Costs.
oupf to P
etheaash.
tVA:
G
a30
svariety
iXỉvolatile
i30
cERDA
a
black,
its e
may
contain
50%
incoming
-.100ílaming
Processes
and

McLean,
Mitre
Corporation;
Rice
After
pyrolysis679
half of the
carbon has been converted
(4)
(3)
-4R
mesh
Alabama
oakchips
74.7
21.9
3.3
The
proximate
determines
moisture
(M),
However,
unlike
coal,
biomass
comes
in cube
a The
wide

ofX- 50 mm
manuíacturing
residue
stalks
ạ 5 size
0.1
Safflower
stravv
0.62
(1)
Whole
log
wood
chips
t
i
o
n
i
n
F
i
n
l
a
n
ơ
.
Technical
Research

Centre
of
The
and
shape
of
the
fuel
particles
are
important
Contract
No.
EX-76-C-01
-2081.
determine
the
thickness
of
the
gasiíication
zone,
the
pressure
3.3.2
Charcoal
and
Char
Properties
cube

30
X
30
mm
(4)for
Safflower
straw
203 is 0.260-0.4
oxygen/air/steam
in (A),
updraít
gasiíiers
contacts
the
char-ash
the resulting charcoal
only slightly smaller (1)
than
its
matter
(VM),
ash
and
(by
dífference)
fixed
carbon
Municipal
physical
forms,

Retuse
making
itand
necessary
Major
tovalue
tailor
the
shapes
ofat X 50yet
Theoretical
values
based
on a Research
maximum
heating
of 8600
Btu/lb,
an initial
Rnland,
Fuel
and
Lubricant
Laboratory,
Espoo,
Finland.
Walnut
shells
determining
the

difficulty
of
moving
and
delivering
the
fuel,
drop
through
the
bed,
and
the
minimum
and
maximum
hearth
(4)
Source:
Kaupp
1984a
VValnut
shells
cracked
336
Components
the
grate
and
burns

out
carbon,
leaving
a
white
ash.
The
Carbon
original
size
is
(25%
the
name
35%
shrinkage).
applied
to
a
The
chemical
char
then
element
undergoes
that
wood
temperature
of
62°F,

a the
flue
gas G
temperature
ofrtests.
450°F,
an
initial
air
(6)
Rambush,
N.
E.,
M
o
d
e
r
n
a
s
P
o
d
u
c
e
r
s
,

content
(C)
of
a
fuel,
using
Standard
ASTM
Moisture
is
the
gasiíier,
fuel-drying
equipment,
feed
systems,
and
ashNational
average
waste
(4)
65.9
Wood,
general
9.1behavior559
25.0
(1.4)
as
well inas
the

of with
the 0.009-2.0
fuel
once
it is pure
in the
gasiíier.
8fore,
mm
pellets
load
forYork:
satisfactory
operation.
A uniíorm
particle
size
helps
(4)as
temperature
ofVan
62°F
andin
50%
excess air.
New
Nostrand,
1923.
principal
problem

updraft
gasiíiers
isatto110°c.
avoid
ash
slagging
occurs
gasiíication
dozens
reac- oftions
phỵsical
forms,
hot
pyrolysis
both
combustion
(such
analyzed
by
the
weight
loss
observed
The
volatile
removal
equipment
to
each
form.

Therethe
resulting
12.2
(4)
Nevvspaper
(9.4%
of
average
86.3
1.5
Coal
Fuels
Good
fuel
hopper
design
calls
for
a
cone
angle
that
is
double
(7)
Jenkins,
B., problems.
D
o
w

n
d
r
a
f
t
G
a
s
i
ỉ
i
c
a
t
i
o
n
overcome
some
Improving
the
grate
design,
as
well
(4)
Wood,
blocks
17%

moisture
256
Source:
Reed
1981
(melting),
since
it
will
plug
the
grate.
In
downdraft
gasifiers,
diamond
products,and
which
graphite)
consume
andthe
impure
carbon
(such
on both
as coke,
the surface
char-(4)
coal,
and

vvaste)
matter
driven
iní savery
crucibleo by
slow81.7
heating
tor
gasiíier
Paper
bòxes
(23.4%)
12.9
5.4
Cchar-ash
hischips
adesign
r areacts
cmust
toff
ewith
rbe
tclosed
i2 cfuel-specific.
scan
flong
Mtoa give
j oby
Anthracite
<1.5

(4)
UJ dugout
•“
the
angle
ofthe
repose.
With
an
angle
of repose
over
45°,
(4)
10%
moisture
167
as
added
agitation
or
stirring,
go
a
way
the
C0
and
H
0,

and
is
not
contacted
2
and
in
the
soot).
interior
Charcoal
of
particle.
reíers
As
to
interior
the
10%
carbon
to
is
30%
consumed
solid
and
the
sample
is
weighed

again.
The
high
heating
Magazine
paper
(6.8%)
(4)
69.2
7.3
23.4
C
a
l
i
í
o
r
n
i
a
B
i
o
m
a
s
s
D
e

r
i
v
e
d
'03
most
of
this
variation
is
due
to
the
variability
of
MAF
3.3.4950°c,
Biomass
Moisture
Content
and
Etìects
0.5-1.9
German
andnot
English
(4)
anthracite
the

may
flow
even pyrolysis.
in a straight
cỵlinder
and
will
Coal
(1)
830-900
trouble-free
operation
andnottocompletely
broaden
the
range
of
oxygen
solthe
is normally
consumed
in
carbon
the
í fuel
char
product
shrinks,
causing
biomass

and
Its
the
particle
tion
loses
can
Ffuel
uencountered
e
sgasiíier
,carbon
Ph.D.
Thesis,
of Agricul-yield
tural
Engineering,
1.1
rates
within
anDepartment
actual
gasiíier
a higher
(4)
Brown
paper
(5.6%)
89.1
9.8

content;
and
if from
reduced
to a íractures,
MAF
basis,
thecomposivariation
is(1)
much
bituminous
coal
The
moisture
content
greatlv
affects
both
the
operation
of
bituminous
770-930
require
either
an
inverted
cone
or
some

agitation
(Perry
20shapes
HHV
=
suitable
[34.1
c
for
+
132.2
gasification.
H
+
6.8
s
3.2fuel
Biomass
Fuel
Analysis
University ofgasiíier.
Calitornia,The
Davis,result
1980. is black char-ash with 70% to
a downdraft
vary
mechanical
from
50%
strength,

carbon
causing
to
more
crumbling.
than
80%
carThe
bon,
small
depending
íragments
volatile
content
and
a
lower
fixed
carbon
content
than
the
Pyrolysis
Chars
less.
American
coal
(4)
Source:
Kaupp

Coke
hard
380-530
(1) we
the gasifier
and
the
of
thekj/g
product
gas. These
issues
1973).
Smooth
hopper
are0.5-2
always
desirable.
- 1984a
1.53
A - quality
12.0 (O+N)]
(3-5)
80%
carbon.
This
carbon
gives
a good
tance

to
on
are
the
swept
temperature
away
by
gaswalls
conditions
velocity.
Returnof pvrolysis
ing to(see
Fig.Table
3-3,
slow
rate
used in
in
the following
ASTM
measurement,
but resischar30.0
yield
from
67.7and
2.3
u and
(4)
$ 3(2)

Redvvood
(790°
to
1020°F)
Brovvn
coal
0.5-2
soft
360-470
(1)
are
addressed
the
sections.
3.2.1
Proximate
and
Ultimate
Analysis
At
the
same
time,
itcfuels
is
important
to realize
excessive
that
there

is is
very
little
additional
activity.
Itconisthat
cỉear
that
larger
slagging.
However,
with
a+high
ash
tent
can cause
7).
see
Also,
a plateau
since
after
it ạcontains
pyrolysis
most
and
of
that
the original
theand

char
ash
ashfrom
remains
the
HHV
=
[146.6
+
568.8
H
29.4
s
6.6
A
lignites
the
gasiíĩer
expected
to
be
proportional
to
char
yield
from
Gasifiers
írequently
suffer
from

bridging
channeling
of
23.9
72.0
4.1
(2)
05
Redwood
(800°
to
1725°F)
Brown
coal
air
dry
lumps
650-670
íto(1)
of
Biomass
-C
_Fuels
£1the
(1) Gasiíication
Proịect
uttimate
Chemical
Two
types

of
analyses,
proximate
andused.
ultìmate,
agitation
results
in(O+N)]
excess
carbon
vvhich
in (3-6)
tum
- _and 3%
particles
carry
more
unreacted
carbon
with
them
than
do 3.4Beneficiation
slagging
the
area
of the
tuyeres,
ifcarryover,
they are

biomass,
between
2%
charcoal
typicalall
ly
waycontains
down
from
under
2%
1000
|im
10%
(1
<
3.3.5
Biomass
Heating
Value
25.8
59.3
14.9
(2)
the
ASTM
-in
test.
51.5
X

10 2 Btu/lb
the
fuel. The
size and
size
distributíon
oftothe
fuel
O
ơ
Oak
(820°
to
1135°F)
w
cc
=
( and corn
V
Vì
Analysis
Log,
Agricultural
Engineering
Department,
University
CLsize,
'o_
(1)

Rambush,
N. for
E., Modern
Gas
Producers,
New
York: Van Chunky
k
c
are
useful
deíiningthe
physical,
chemical,
and
fuel
reduces
the
efficiency
of
the
gasifier.
In
addition,
carbon
fuels
(such
as
mill
ends,

chips,
cobs),
ì
smaller
particles.
Thereíore,
the
conversion
efficiency
will
ơ)
mineral
mm)
particle
matter
(Emrich
indicat1985).
ing
that
this
size
particle
has
not
Oak
(1060°F)
27.1
55.6
(2)
Thus

inbe
combustion
andfor
updraít
gasiíiers
fuel
pas- and
ses
Nostrand,
1923.
. o
Itwhere
can
seen
in A,
Table
3-6
that
there
iswtthe
a%
wide
range
of
of Calitornia,
®Davis,
-o 1979.
2 17.3
« anộEnergy Source,”
The

proximate
analyses
selected
biomass
íeedstocks
>
5.?
£
c,
H, if
s,
o,oxygen/fuel
and
N biomass
are
the
ofminímum.
carbon,
ư
(2) have
Partridge,
R., “Manitoba
Crops as
Sixth
Anproperties
of
athe
particular
feedstock.
These of Peat

s
carryover
reduces
ratio,
since
the
carbon
vvhich
at J.char
least
oneFinland,
dimension
than(0.5
aCentre
few
be
maximized
of
large
char
is A
kept
toResearch
acol?larger
engaged
much
gasiíication.
Below
500 Research
|im

mm)
(2) values
Ekman,
E. removal
and
Asplund,
D.,
A
Review
0f
Gasitìcation
in
Technical
■ in
o
through
the
stages
heating
for
various
biomass
forms.
larger
lection
0
c
c
>
$

other
solids
are
shovvn
in
Table
3-3.
Note
that
more
than
70%
(1) analyses
Bituminous
Coal
Research,
Inc.
1974.
Gas Generator
Charcoal
Research
manuíacture
andIDevelopment,
dates
Phase to
II.nce,
Process
prehistoric
and Equipment
times

Deveíopment.
and
is
a
wellnua
Contere
Biomass
Energy
hydrogen,
sulíur,
ash,
oxygen,
and
nitrogen
in
the
fuel.
The
p
k
c
coS!
^
were
initially
developed
for
coal
and
are

widely
of
Finland,
Fuel
and
Lubricant
Research
Laboratory,
Espoo,
Finland.
requires
more
oxygen
than
the
biomass
for
gasiíication.
This
millimeters,
can
be
used
in
fixed-bed
gasiíiers
without
íurther
g a second plateau, indicating
The

balancevalues
betvveen
conversion
efficiency
ash
removal
we see
the end
of Oct.
char
«o
<
m0)
of
heating
has
recently
been
published
showing
OCR-2Ũ-F;
PB-235530/3GI.
Vi/innipeg,
Manitoba,
Canada,
13,
of
most
biomass
material

is—>
volatile
under
conditions
ofa From
Biomass
—>
Charcoal
Char-Ash
—>the
Ash
—>
Slag
established
industry
today
withmay
standards
-C
forseparaits
uses.
calculated
value
agrees
with
the
measured
value
with
an

c
ư
c
õ Institute,
Generator
Gas,
The
Svvedish
Experìence
1939-1945,
Solarthey
Energy
Research
Institute,
co, SERI/SP
$various
òũtion
available
from
commercial
laboratories.
They
are
in(3)
turn
reduces
the
oxygen
available

for
ílaming
pyrolysis
and
size
reduction,
though
require
from
will
be
fuel-specific.
5
o
p
gasiíication,
and
1977.
u
.)
u
33-140,
1979.
variatĩon
of
5-25
kj/g
(2000-10,000
Btu/lb)
for

various
ũ
(3)
Ekman,
E.
and
Asplund,
D.,
A
f
ì
e
v
i
e
w
o
f
the
test.
The
proximate
analysis
generally
includes
moisture
Charcoal
is
simpler
to

gasiíy,
and
it
is
easier
to
clean
up
the
(2)
Hovvlett,
K.
and
Gamache,
A.
1977.
Forest
and
Mill
Residues
as
Potential
Sources
of
Biomass.
Vol.
VI.
absolute
error
of

2.1%
for a residue
large is
number
biomass
described
increases
the
tar
íormation.
finesRand
Bulky
fuels,
The
finalforms
weight
of
the
char-ash
usuallyof2%
to 10%
(4) Jenkins,
B.rate
M., of
Downdraft
Gasiíication
Characteristics
of
Calitornia
Residue-Derived

sdirt.
eMaịor
ause
r cMTR
h 7347.
o fsuch Paselogs,
a
t branches,
G a s and
i í í straw,
cabiomass
(Domalski
However,
(b)
Final Report.
VA;
The Mitre
Corporation/Metrek
Division; ERDAContract
No.
Ee
(49-18)
2081;
content
measured
onMcLean,
aDepartment
wet 1986].
basis,
MCW,

where
gas
for
engine
than
biomass
materials
(Reed
1981).
Fuels,
Ph.D.
Thesis,
of
Engineering,
University
of
Calitornia,
Davis,
1980.
require
possibly
densiíication
ofSource:
the biomass
weight, depending on the char- ash removal
t i o chipping
n i n or
F i chopping
n l a n d and
, Technical

Research
Centre of
(3) Boley,Kaupp
c.
c.1984a
and Landers, w. s. 1969, Entrainment Drying and Carbonization of Wood VVaste. VVashington,
Finland,
Fuel
and Lubricant
Research Laboratory, Espoo, Finland.
beíore
use
in
most
gasiíiers.
rateD.C.:
andBureau
the char
durability.
However,
the
char-ash
residue
has
of Mines; Report of Investigations 7282.
Fig.
basis-dry
basis moisture
(Source:
1980,

Fig.
Fig. 3-2.
3-1. Wet
Elemental
(ultimate)
analysiscorìtent
of (a) comparison
coals and wood
andMcGowan
(b) biomass
fuels
(4)
Rambush,
E., M
od
ern
s Psion
r oofdBiomass
u c eEnergy
rs,
a(4) very
low density and so may occupy up to 20% of the
1-1)
(Sources:
Skov N.
1974,
35.
(©1974.
Used G
withapermisKlass, D. L. and Ghosh, s. 1973. “Fuel from Organic Wastes." Chemical Technology,

p.p.689.
New York:
1923.
Foundation,
Inc.)Van
and Nostrand,
Kaupp 1984a,
Fig. 96)
volume
of the
Source: Reed
1981original

Chapter 3

Gasitier Fuels

a

a

a

b

10
14 Handbook
Handbook of
of Biomass
Biomass Downdraft

Downdraft Gasitier
Gasitier Engine
Engine Systems
Systems
12
16 Handbook
Handbook of
of Biomass
Biomass Downdraft
Downdraft Gasitier
Gasitier Engine
Engine Systems
Systems

Gasiíier
Fuels
15
GasiíierFuels
Fuels17
9
Gasitier
Gasitier
Fuels
11
Gasitier
Fuels
13


where Mp is the fuel moisture %. We see

then in Fig. 3-5(b) that bone đry biomass corresponds to
47% total moisture input. The chemical moisture in bone dry
biomass provides more moisture than is needed for peak
heating value, and all fuel moisture reduces gas heating value.
Biomass can contain more than 50% moisture (wet basis)
when it is cut; it is generally desirable to dry biomass
containing more than 25% moisture (wet basis) before
gasiíication. Drying often can be ac- complished using waste
heat or solar energy. If the temperature of the drying air is too
high, the outer sur- faces of the chunk will become dry and
begin to pỵrolyze beíore the heat can reach the center. For
effi- cient drying, hot air, which if cooled to 60°-80°C would
be moisture saturated, is preíerred. The moisture slows
íeedstock drying (as well as slowing surface pyrolysis).

Thus more air is required, improving the
drying process [Thompson 1981). During operation of a
gasiíier and engine combination, 1-in. wood chips can be
dried from 50% to 5% moisture content, with drying capacity
Fig.spare,
3-4. Pelleting
process
(Source: Reedresidence
1978b)
to
using
a 20-minute
time with the hot engine
exhaust, tempered with 90% recycle of dryer gases.

Commercial dryers
are available
in many forms and sizes, and
0.6[2(1)
+ 16] (100%)
it is beyond the scope of this handbook to recommend such
12 +commercial-scale
0.2(1) + 0.6[2(1) operations.
+ 16]
equipment for
A simple batch
dryer for drying small quan- tities in shown in Fig. 3-6 and a
= 47%
(3-8)
commercial dryer is shown in Fig. 3-7.
and the total moisture input M T is

Fuel Moisture
+ Chemical Moisture
3.5 Biomass
Fuel Emissions

TheMy
sulíur content ofWet
biomass
fuels is usually very low
Fuel Weight
compared with íossil fuels, as can be seen from Tables
(100
- are corrosive, they make a

6 and 3-8. Since sulíur
oxides
= Mc +
MF
major contribution to engine
100 wear. The absence of sulíur in
Mc)
biomass fuels could allow a longer life for an engine
(3-9)
47producer
+ 0.53 Mp
operating=on
gas rather than on Petroleum fuels,
provided that the producer gas is free of other contaminants.
The nitrogen content of biomass fuels depends on the species
of biomass used, as well as the harvest time, as shown in
Table 3-9. Wood, dried stalks, hulls, and cobs have a very low
nitrogen content, while leaves, seeds, and bark have a higher
nitrogen content. Depending on the temperature of
gasiíication and combustion, this may signiíicantly lower the
nitrogen oxide emissions

final fuel cost versus other altematives (such as dif- íerent
fuels or other types of gasiíiers).

3.4.2

Drying Biomass Fuels

The moisture content of the biomass fuel affects the quality of

the gas that will be produced. Water requires about 2300 kj/kg
(1000 Btu/lb) to vaporize and 1500 kj/kg to raise to 700°c
during pyrolysis/gasifica- tion. Thereíore, this energy must be
subtracted from the heat budget of the gasiíer. Although it is
Dryer
physically pos- sible to gasiíy moderately high-moisture fuels
exit
in some gasiíiers, fuel moisture reduces the quality of the gas
tempera
Insulation
as shown in Fig. 3-5. It also reduces the throughput of the
ture
gasiíier and increases tar production. On the other hand,
sensor
charcoal gasification is just the opposite; inade- quate
(Te)
moisture input reduces the quality of char gas. Figure 3-5(b)
combines char gasiíication and wood gasiíication data to
illustrate the impact of total water inputs on gas quality. Total
water input includes fuel moisture, chemically bound water,
150
and air blast humidity
(i.e., all mass inputs in the ratio H 2 0).
Wet
140
We see in Fig.
3-5(b) that starting with dry gasiỉication, gas
biomass
130
heating value increases with increased moisture input up to a

12
peak betvveen 30% and 40% total moisture input. The gas
0
heating value then declines with additional moisture input.

Wet gas
discharge

\

Biomass can be considered as a source of water and charcoal
using the generic formula for biomass
CHị 4 O 0 e = CHq

2 (0.6 H20)

(3-7)

Fuel dryness is indicated by
so the chemical moisture M c in bone dry biomass is
dryer exit temperature (T E)

Chemical Moisture Fuel Weight

Wet gas
recycle

o—■
-

À\
ị SN

3 Sources
11
□
Heywood
_A
0 Schlảpfer
1937
-

f

Handbook of Biomass Downdraft Gasitier Engine Systems

B

1

(b)

18

Ể\
1\
"\

co
CD

Q > 10
QHBiomass
moisture
vvet basis% ~
Charcoal
moistureHeat
input
Flue
% wet biomass
1.ỉ
20 30
50. 10
gas or engine
1.1L1.
20

Fig. 3-6. Small batch dryer (Source: Das 1985)

Blower flow
rate QB

exhaust

40

2

60

c

Ồ
40
1,
0

Tota l mo isl ur e input a s pe rc enta ge of ma ss input inc l uding c hemic a ll y boun d wa t e r

FLOWRATE
QH

Fig. 3-5. (a) Effect of fuel moisture and oxygen on gas heating value (Source: Overend
1982, Fig. 5B)
(b) Effect of total moisture input on gas heating value

Gasitier Fuels 19


(up
The
tocharcoal
one
ratio
mile)yield
inC0/C0
pipelines.
(or
isof also
H
called
0)

is
gas,
a
A
quantitative
picture
pyrolysis
is isobtained
2 /H 2synthesis
The more
from
a2 It
biomass
íeedstock
highlỵ

(ị)
about 3-3).
0.25
all
of curve
thetochar
converted
to gas,coandfrom
the
andofTable
The
ofis Fig.
4-3 temperature
represents

pure
their
cooling
effect
helps
the
gas
Fuel
Although
ílaming
pyrolysis
iskeep
athe
new
concept
in explaining
and
the
process
ishopper
largely
self-regulating.
air
isAsused,
the
eííìciency
ofenergy
stoves;
inthe
Europe

LHV
isIfused.
a result,
íraction
ofin
in
wood
converted
to gas
reaches
pyrolysis
an
ìnert
gas
(such
as
nitrogen
or
argon).
Ifa
rising
above
this
temperature.
Below
800°c,
the
reactions
sequent
combustion

of
the
gas,
so
that
it
is
difficult
to
biomass
gasiíication,
partial
oxidatỉon
of small
and
large
greatly
enhance
obtained
each
unitpyrolysis
volume
of
resulting
gas
is stoves
diluted
with
atmospheric
nitrogen

to a
complished
withthe
air,energy
themore
gas
is also from
diluted
with
about
50%
Gasitication
processes
for
Biomass
combustion
is
complex
than
either
or
European
wood
are
typically
quoted
aschar
10
%vvithin
maximum.

With
oxỵgen,
some
the
ismore
not
pyrolysis
occurs
inless
air,about
the
curve
drops
more
steeply
of
30%
methanol,
of
the
biomass
ammonia,
is
methane,
burned
to
and
provide
gasoline.
the

The
energy
oxygen
for
(TGA).
In
this
technique,
a
small
piece
of
biomass
is
become
sluggish
and
very
little
product
íorms.
We
have
systems.
Hovvever,
the
final
emissions
depend
speciíimake

a
general
statement
producer
gas
3of
particles.
Industrial
charcoal
manuíacture
uses
very
slow
hydrocarbon
to coconverting
and
H 2 issolid
a (150Standard
industrial
biomass.
producer
gas molecules
value
of 5800-7700
kJ/Nm
200
Btu/scf).
nitrogen fromsince
the air.
fuels

toburned
gasification
the rest.
biomass
must
firstand
pyrolyze,
then of
be
efficientthan
comparable
wood
converted;
with
more oxygen,
some stoves.)
ofchar
the gasiíication
gas
and
the
regionírom
250°-400°Cbecausethe
char
and isproducts
must
gasiíication
either
the
purchased

or
exact
amount
making
suspended
onof
a balance
pan
inThe
aproduced
fumace,
the
temperature
modeled
the
reactions
ofU.S.
downdraft
using
cally
on be
the
properties
of the
gasiíier
and
the
subemissions.
heating
rates

to
achieve
charcoal
yields
of on-site,
more
than
30% ofit
process.
Texaco
has
used
an
oxygen
gasiíier
to
oxidize
When
oxygen
is
used
for
gasification,
a
medium-energy
gas
gaseous
fuels:
o
=

Oxygen
If
the creased
volatile
materials
area condensed,
they
produce
tars
partially
combusted
(gasiíied)
beíòredepends
itrate.
is fully
combusted.
the
temperature
risesalso.
very
rapidly
as temperatures
shown
inburns,
Fig.
4-4(a).
are
oxidized
As
the

char
it
economically
excess
prudent
required
only
larger
installations.
onexample
the
It efficiency
has
been
is
with
time
at
known
An
of
the
known
kinetic
values
and
that
the
measured
thein-principal

initialoxygen
dry
weight
ofofin
the
biomass.
The
intermediate
3find
The
advantages
direct
gasification
are
that
the
hydrocarbons
to co kJ/Nm
and H 2 , (300
as in Btu/scf)
the following
reaction(Reed
for a
process
containing
11,500
is obtained
and
oils
known

commonly
as
creosote.
4.2.4
Chemistry
of
Biomass
Gasitication
Thus,
it
is
desirable
to
operate
as
close
to
an
equivalence
ratio
However,
the
overall
global
reaction
of
biomass
combustion
eventually
reaches

the
ash
line
between
400°
and
500°c.
reported
of
the
process.
that
pipeline
It
can
distribution
be
imof
proved
low-energy
in
practice
gas
is
with
also
residual
change
by
a small

sample
offrom
flax
in charoil:
gasiíication correspond to those observed in
heating weight
rates
used
in experienced
proximate
analysis
usually
produce
B the
one-stage
process
is collect
very
simple,
the
direct
heat
transíer
typical
1982).
Medium-energy gas can be distributed economically
L = Lignin
These
materials
inbythepreheating

chimneys
of
airtight
wood
Aof
0.25
as(Reed
possible.
can be heated
represented
by of
The
change
in1983a;
composition
produced
by
air
or
oxygen
economically
insulation,
bypractical
drying,
for
or40°c/min
distances
to rapid
one
the

reactants.
if
the
air
A
shives
atbiomass
a rate
shown
in mile
Fig.
4-3.
One
gasiíier
Reedof1984).
Wedryrefer
toofthe
process
charcoal
yields
of
15%
to
20%.
Theisup
very
heating
rates
In
Fig.

4-3,
more
than
80%
the
total
mass
the
sample
G0
the
gases
to
the
is
very
efficient,
for
short distances
^Friction
seo'
stoves,
thegasiíication
piping
ofis gasiíiers,
and
the
valves
of
engines.

Most
6-carbon
anhydrosugars,
and
lỉgnin
isIdeally
an
irregular
polymer
of
20
C
H
+
5
0
10
CO
+
11
H
(4-5)
10an
22
2in
2one
gasiíication
is
shown
Fig.

4-l(b).
would
like
to
íascinating
for
question
is
in
compressed,
gasification
rather
is
how
than
the
compressing
reacting
sees
that
moisture
released
first,
at
100°c,
followed
by
the
observed
in

actual
bed
of
char
as
adiabatic
(no
heat
input]
4.1 used
Introduction
encountered
when
small
biomass
particles
are
gasiíied
and
CH 1 4O 0CE
g +=
1.05
O
is
volatilized
below
500°c,
leaving
an
additional

10%
z + (3.95 N\2 ]
17In to
How
is
it
possible
to
operate
exactly
at
this
ratio
of
0.25?
a
Cellulose
Ị
o
Biomass
of
the
companies
advertising
and
selling
updrait
gasiíiers
at
a

phenỵl
propane
units.
In
biomass,
these
three
polymers
form
14
add
the
smallest
amount
of
oxỵgen
possible
to
carry
the
the
products
larger
“know”
volume
how
of
producer
much
oxygen

gas
(McGovvan
to
use
(see
1984).
below).
volatile
materials
at
250°-450°C;
these
temperatures
are
char
gasiíìcation.
combusted
realize
charcoal
ỵields
of
less
than
15%
of
the
->
C0
+
0.7

H
0
+
(3.95
N
)
(4-1)
2
2
20%
of
the
original
mass
of
carbon
for
conversion
to
gas.
It
2
\
Gasifiers
are
relatively
simple
devices.
The
mechanics

of
The
resulting
gas,
called
synthesis
gas,
can
be
used
to
fixed
bed
gasiíier,
operation
at
lower
values
of
(|)
would
CH
/
4
• Peat1979).
1979
conference
no longer produce
them
(Reed

an
interpenetrating
system,
or block copolymer,
that4-l(b),
varies ina
\ biomass;
solid
composition
to the
composition
o in is
Fig.
important
in understanding
pyrolysis,
gasiíication,
and
initial
dry
weight
of
the
larger
is
now
recognized
matter
composed
of

their
operation,
such
asaverage
íeeding
and
gas
also
are
manuíacture
methanol,
hydrogen,
or
ammonia.
There
some
cause
charcoal
be that
produced
(as
shown
for low
(Ị)
in
4Coal
■
Char
4.2.5There
are

Thermodynamics
many
types
direct
of Gasitication
gasiíiers,
each
with
itsbiomass.
special
A.
The
CO
andco
H
inthe
thevolatile
hot
char
zone
can
react
below
where
CH
is conveyed
anof
íormula
forcleanup,
typical

2toíormed
a is
4O 0 0
composition
across
the
cell
walĩ.
Nevertheless,
inisFig.
large
If
the
gas
to
be
over
a
distance
in
a
pipeline,
mixture
of
and
H
,
according
to
the

íormula
combustion.
According produce
to the íigure,
a íraction
of char and
ash
2
size
íeedstocks
15%
to
25% charcoal.
monomers
(as
well
as
other
fragments)
of
the
cellulose,
simple.
The
successíul
operation
of
gasifiers,
however,
is

not
interest
in
the
Texaco
to
gasiíy
biomass
4(c)), to
andform
it using
would
up in constant
thesystem
unless
it isof
augered
virtues
deíects.
will
be discussed
inshown
Chapter
5.though
900°c
methane
according
toreactor
theBreeching
reaction:

(Actualand
composition
forofspeciíĩc
biomass
isenergy.
inchemical
Tables
sãmples,
there
is a build
relativelv
atomic
ratio
CHỊ
Thermodynamics
isThey
bookkeeping
of
burned
in No
anyneat
form
ortothe
used
as system
aAlremains
the
end.
Ifthe
airexist

isengine,
allowed
enter
the
after
hemicellulose,
and
lignin
polymer
thatsealỉ
make
up consumes
biomass
so
simple.
rules
because
thermodynamics
of
(Stevenson
1982].
During
updraữ
or
downdraft
gasiíication,
10%
to
20%
of

the
C2H
,h
or
shaken
out.
Operation
at
values
of
(Ị)
above
0.25
4i^Liquid
20 in
CHỊ
O
6
+
0.2
ũ
->
CO
+
0.7
H
(4-2)
4
0
2

2
3-3,
3-4,
3-6,
and
3-7).
The
nitrogen
is
shown
parentheses
thermodynamics
cannot
always
predict
what
will
happen
for
a
4 OQ g. (The ratios will vary slightly with species. Coal is
feedstock,
the
condensing
tars
will
plug
pipes
sometimes
in

pyrolỵsis,
the
carbon
(char)
will
burn,
leaving
the
ash
as
the
+ 3also
H2 —>
CH 4 + H2that
0 up rapidly.
(Evans
Ittheis
recognized
to 65% Hence,
of(4-9)
the
gasiíier
operation
areas
well
understood.
Yet,
nontrivial
biomass
will

remain
charcoal
after
pyrolysis
istake
complete.
charcoal1984).
and CO
because
it
isminutes.
an
inert
portion
of out
air
and
does
not
part
ina
ínot
fuels
about
CH 0 9temperature
O 0 ! but variesgoes
moreup
widely in composiparticular
process,
itIn

can
rulecases,
many
things
that
cannot
only
aproduct.
few
these
ittemperature,
isproduces
necessary
tosupply,
use
final
Each
form
of
biomass
slightly
dif4.4.4typically
Factors
Controlling
stability
ofto
Gasiíier
biomass
dry
vveight

can
be
converted
this
vvater-soluble
Uníortunately,
there
is
more
energy
contained
in
the
CO
and
thermodynamic
principles
dictate
the
air
In
an
updraít
gasifier,
air
entering
at
the
grate
initially

burns
maintaining
the
bed
at
a
constant
level
automatically
ensures
the reaction.
combustion
ofconverting
biomass
vvouldbe
/ of
Biomass
tion.)
The reĩationship
between unless
solid, liquid,
and gaseous
happen.
It For
was oxygen
mentioned
above
that
Eq.itthe
(4-2)

is
This
reaction
proceeds
catalyst
mode
of gasiíication
that
succeeds
tarsash.
to
íerent
char,
volatile
material,
“wood
oil,”
which
potentially
may form
the is
basis
of new
Operation
H 2 correct
than
is oxygen
contained
in slowly
the biomass,

sothere
that
thisa reaction
and
other
ingheat
variables
theinreactors
weand
build.
It
this
charquantities
tooperatliberate
and
C0of
to that
theofreaction:
2 according
the
input.
\o.5
omitted.
/
^
Coals
Ắ
fuels
is
easily

seen
in
Fìg.
4-l(a)
where
the
relative
atomic
thermodynamically
impossible
in
the
absence
added
heat
gas.
This
can
be
accomplished
either
by
cracking
(secondary
present;
however,
it
is
quite
exothermic

and
can
supply
heat
if
Knowledge
of
these
quantities,
as
well
as
Iniet
heođ
(counterflow
processes
for
wood
liqueíaction
(Roy
1983;
Scott
1983;
would
require
the
transíer
of
energy
from

some
external
is a tribute to thecpersistence
of experimentalists
that so much
+
0
C0
+
heat
(4-6)
o
2 ->
2 k}/g
concentrations
of
carbon,
hvdrogen,
and
oxygen
are
plotted
and
that
Eq.
(4-3)
actually
governs
the
reaction.

How
is
this
Ẩị
Chars
Solid
Gasiíer
operating
temperature
is
a
function
of
the
amount
of
This
combustion
only)
produces
20.9
(8990
Btu/lb)
when
ửie
pyrolysis)
or
by
partial
oxidation

in
Aaming
pyrolysis.
suitably
catalyzed.
the
temperature dependencies
of
the
reaction
and
Gaseo
Diebold
source, which
vvould
greatly
complicate the process.
progress
has been
made
in the
ofCombustion
so little
under4.4 Principles
of Operation
offace
Direct
9 4.3 for
Indirect
and

Direct
Gasitication
íuols
a variety
fuels.
Here
it is seen
thatThe
the temperature
solid íuels,
determined?
oxygen
fed
toof the
gasiữer
(Fig.
4-4(a)).
temperature
of the losses,
combustion
products
is low
enough
forany
all
us the
associated
weight
are
useíul

in understanding
gasiíier
Almost
immediately,
or
even
simultaneouslỵ,
the
C0
X
Products
2 and
1984)
.
Uníortunately,
these
oils
are
corrosive
and
highly
>
standing.
Nevertheless,
it
has
been
experience
in
related

Concurrent
with
thecharcoal,
emergence
of
biomass
asleft
an
important
Gasitiers
■*"fue
Spírol
tlights No.l
biomass,
coal
and
lie
in
the
lower
segment
of
In
practice,
some
excess
oxygen
must
then
be

added
for
Processes
response,
however,
changes
abruptly
at
an
equivalence
ratio
the
liquid
to
be
water,
and
this
is
the
value
that
would
be
operation
and
design.
\
H 2 0 the
present

react
with
the
char
to
produce
the
oxygenated,
so
that
íurther
Processing
will
be
required
to
fields
(such
as the
oil,gasiíier
gas, and
coal
combustion)
that
once
At
highin
temperature
where
gasiíication

takes
place
4
energy
source,
it and
wasgaseous
natural
that
coal
gasiíication
ls
the
diagram;
liquid
hydrocarbon
fuels
lie
the
gasiíication
(carrying
the
reaction
to
(ER)
approximately
0.25.
This
change
point,

or in
knee,
measured
in and
a work
bomb
calorimeter
and
reported as
ring
fuel
gases
co
H
to qualitatively
the
1
4.4.1The
Introduction
make of
a Indirect
high-grade
liquid
fuel
(Diebold
1986).
However,
mechanisms
results
shown

atriding
in2 according
Fig.
are 4-3
understood,
are
theonly
engineer
similar
is to
able
those
to
(typically
700°-1000°C),
there
arefollowing
areactions:
few
stable
interpretations
would
be of
carried
over
tosome
explain
biomass
4.3.1upper
(Pyrolitic)

Gasiíication
Q
left
section;
CO and
H
are
joined
bỵ
the
bisector
of H
the
point
o
in
Fig.
4-l(b)),
producing
C0 2 and
2 600°
20
occurs
for
temperatures
to
800°c
(900-1100
K),
the high heat of combustion or HHV as shown in Tables 3-6

.
they have been
burned
successíully
in on
in-biomass
dustrial gasiíication
boilers and
obtained
develop cleaner,
in a proximate
analysis
most biomass
Fortunately,
but
are
much
not
combinations
ofmore
principal
ofmake
biomass—
cthe
+ efficient
C0
-) 2processes.
Cof
oelements
(4-7)

Since
volatile
organic
molecules
up
gasiíication.
Even
today,
mostProducts
articles
triangle;
and
the
combustion
ofvapor
fuels,isproduces
C0unstable
according
to
It
is
now
recognized
that
wood-oil
2 and H
2 0,
at
depending
on

oxygen
source.
Gasiíier
pyrolysis
oils
and 4-1. In most practical2 combus- tion devices, the water
turbines
with (4-7)
only and
minor
modiíications
required
for the
identical
of
the knowledge
because
acheating
quired
in the
these
areoxygen.
higher
íields can
and
besamples
applied
are
to
carbon,

hydrogen,
These
are
approximately
80%
ofand
products
from
biomass
use
only
Eqs.
(4-8)
toand
ex- cracks
plain
biomass
gasiíication
Trunmon
ond^rates
lie
on
a
vertical
line
on
the
right.
temperatures
above

600°c
rapidly
at
700°
to
and
tars
that
are
stable
for
periods
of
1
second
or
more
at
escapes
to
the
atmosphere
as
a
gas,
and
the
heat
of
C

+
H
0-»C0-+H
(4-8)
2
2
4.4.3pyrolysis
of
the
burners
(Bowen
1982).
roìl2Downdraft
smaller
enhance
in
our
TGA
(seethrust
Chapter
3and
gasííication
processes.
c,
co, Operation
C0
, CH
,ofthe
0.L
The

relative
CH 14O
+ 0.41978;
ũ2 0.7Jasas
CO +
0.3 C0 2Eq.
+ 0.6
H 2 +applies
0.1 H 20to(4-3)
2understanding
4, H
0 . 6 Eq.
(Diebold
1985b),
principal
task
biomass
and
(4-4),
even
though
(4-4)
the
VH42Gasitier
VIninSIthis
s/
\ (but
Drive
800°cignore
to form

hydrocarbon
gases
as gasiíiers
methane, operate
ethane,
temperatures
below
600°c.
Since (such
updraít
vaporization of theQssembly
water is notkrecovered.
case,
the
Downdraft
gasiíiers
have
been
very
ossembly
Thermal
conversion
processes
for
biomass
are
indicated10%
by
concentration
of

these
species
that
wĩll
be
reached
Fuelhopper
The
first
reaction
is
called
the
Boudouard
reaction,
and
the
CO
COo
not
coal)
gasification
is
to
convert
this
condensible
volatile
80%
biomass

volatiles.
Biomass
pyrolysis
produces
only
In
chapter,
weLHV,
present
a summary
of the of
underlying
and
ethylene),
Hof
co,
and (temperatures
C0
In addition,
obtains
a 1%
below
an aER
0.25
lessone
than
600°C),
lowthis
heating
value,

2 , percent
successíul
for
operating
engines
the amount
low
tar
Typically
of 2 .methane
íormed
as
well.
0.5
the
arrowscharof few
Fig.
4-l(b).
Here
itcharcoal
is seenare
that
the
conversion
at
equilibrium
can
begases.
predicted
from

thebecause
pressure,
the
second
ispermanent
called
the
water-gas
reaction.
They
have
been
matter
to
A
secondary
task
is
to
convert
the
to
20%
coal,
and
the
is
very
reactive.
processes

that
occur
biomass
gasiíication.
We will
to
5% yield
of
a tar
composed
of from
polynuclear
and
considerable
quantities
of tars gas
are
emitted
witharomatics
theshown
product
20.4content.
kj/g(a)
(8770Most
Btu/lb),
be the
maximum
could
be
of would

theduring
work
reported
inheat
thisthat
book
was
(b)
Typical
properties
of chemical
producer
biomass
in
processes
move
the
tion ofare
biomass
to
of
each extensively
element,
and
the
equilibrium
constant
determined
studied
for

the
last
100
years in
connection
with
resulting
charcoal
also
to
gas.
Thereíore,
this cannot
be found
the composiprimary
explanation
for1979;
the
attempt
to
keep
the
explanation
simple
because
each
phenols
similar
to
those

in
coal
tar
(Antal
gas.
generated.
The
difference
between
LHV
and
HHV
is
small
for
períormed
on
downdraft
systems,
and
they
will
be
the
Table
4-2.
liquid
orgaseous
solid
fuel(b) regions,

either
bybiomass
biological or thermal
from
the
thermodynamic
properties
and
subcoal
biomass
gasiíication,
since
thetemperature,
principal
product
of
conversion
ofroll
biomass
to gas.
Fig 4-1.and
(a) Phase
shovving the
relative
proportìons
of
carbon, hydrogen,
and ject
oxygen
liquid,Trunmon

and
íueìs
Chemical
changes
during
íundamental
process
is basically
simple.
Chapter
gives
1984;
Diebold
dryversion
wood
butdiagram
increases
rapidly
moisture
content
of task
thea in solid,Diebold
The
most
important
types
of
fixed-bed
gasiíiers
for5mine

this
principal
gasifier
discussed
inthen
thewith
balance
of
book.
con an
processes
Reed
1981)
means.
In someof cases
(such as
the
to
energy
balance.
It is
possible
tothis
deterthe
coal
pyrolysis
is(Source:
coke
(carbon).
The

rate
of
the
reaction
has
In theassembly
gasifier
Fig. 4-5(b),
air oxygen/air
is injected gasiíication),
at the inter- face
more
extensive
description
of HHV
the operation
of
speciíic
1985).
wood.
(In
the United
States
the
isgasifiers
normally
for
are
thestudied
updraít

and
downdraft
of used
Fig.
Table
4-2.
Typical
Properties
of
In
the
downdraft
gasifier
of Fig.
contacts
the
are
spontaneous;
in
other
cases
(such
as
steam
species
that would
form
at equilibrium
as disappearance
a air

íunction
of 4-5.
been
by measuring
the
rate 4-5(b),
of
of 4.6 processes
between
the incoming biomass and the char. If too much char
Summary
gasiíiers.
arebeavailable
from
the literature
for
those
rating the Detailswill
3
These
discussed
in greater
detail
Chapter
Producer
from must
Biomass
pyrolyzing
beíore
it to

contacts
theHchar
and
ports
gasiíication)
considerable
energy
be expended
to of
cause
amount
of biomass
oxygen
added
the
system.
The
results
of
carbon,gasiíiers
coal,
or charcoal
while
passing
C0in
over
the
Pyrolytic
gasiíication
isaGas

accomplished
when
a portion
the
is
produced,
thetask
air of
consumes
excess
char
rather
than
2 0 or
2supIn
summary,
the
gasiíierthe
is threeíold:
interested
in aintroduction
more thorough
explanation
(Reed
1982; Kaupp
5,
but
a
brief
here

will
facilitate
understanding
of
acalculations
flame
similar
to
the
flame
that
is
generated
by
the
match
in
the
change.
of
this
type
are
shown
in
Figs.
4-4
and
3-5.
solid

(Nandi
1985;
Edrich
1985]”
fuel
or
char
is
burned
in
an
external
vessel
with
air,
and
the
biomass;
if
the
char
is
consumed
too
fast,
more
biomass
is
Table
4-1.

Properties
of Typical Biomass
Ridmg ring
0.00 biomass
0.20 0.40
0.60 volatile
0.80 matter,
1.00 1.20
1984a;
ReedThermal
1985b)7
the
íundamental
principles
involved.
• to pyrolyze
to produce
gas, and
Fig.
4-2.
As
in
the
case
of
the
match,
the
heat
from

the
resulting
heat
is
used
to
supply
the
energy
necessary
to
consumed.
Thus,
the
Imbert
gasifier
is
self
regulating.
At
Intel
seol—
Equivalence
Both of
these reactions
requireRatio
heattemperature
(i.e., they are enEquivalence Ratio
The
adiabatic

reaction
of
carbon
buming
volatiles
maintains
the
pyrolysis.
When
this
pyrolỵze
the
biomass.
The
principal
advantage
of
this
SERI
we
have
built
the
oxygen
gasiíier
shown
in
Fig.
5-12.
(b)

Combustion
Feed
chute
terms
“updraít
gasiíier”
and
“downdraft
gasiíỉer”
may
4.2 The
Biomass
Thermal
Conversion
dothermic
anddetermined
therefore
cool
the gas
(a) with airreactions)
biomass
or oxygen,
in this
manner,
is
• to convert the volatile matter to the permanent
gases,
CO,
Gas is
Gas

phenomenon
occurs
vvithin
a gasiíier,
supply
process
is this
thatwith
a amedium-energy
gas
We
operate
fixed flow of oxygen
andproduced
add Dry
biomass
seem
mechanical
descriptions
of limited
gas reacts.
flowair
patterns.
about like
25°c
every
of temperature
C0the
These
2 that that

shown
in trivial
Fig. for
4-4(a).
This1%
is
the
would
be
Processes
H
,
and
CH
2
4
Compound
Symbol
(vol.%)
(vól.%)
in
the
gasiũer
is
rapidly
consumed,
so
that
the
flame

gets
without
using
oxygen.
The
higher
energy
íaster
or the
slower
to tomaintain
In
practice,
however,
updraít
gasiíiers
can900°c,
tolerate
reactions
very
rapidly
atbiomass
temperatures
to
convert
carbon
co and H 2a. fixed bed level. In the
reached
if occur
biomass

came
to equilibrium
with
theover
speciíied
richer
as
pyrolysis
proceeds.
At the
end some
of ửie advantages
pyrolysis zone,
content
may be
required
for
pipelineofdelivery.
BuckRogers
gasifier
ofCO
Fig.long-distance
5-11, 21.0
a fraction
air is
moisture
feeds
and
thus
have

for
Typical
dry
biomass
tormula:
22.1
4.2.1high
Introduction
Carbon
and
amount
ofash-free
air
orof oxygen.
is no
These tasks are accomplished by partial
oxidation or pyrolysis
the
gases consist
mostly
about
of
(moistureand
[MAF]
basis)inCHiaequal
4(There
O
0 parts
The
disadvantage

that
a signiíicant
fraction
of tar10.2
maythe
be
introduced
throughis the
rotating
nozzles
and maintains
monoxide
producing
gas
for
combustion
burner.
However,
Carbon
COo
9.7
guarantee that processes
equilibrium
will
be reached
insome
any or
given
Thermal
for

biomass
involve
alla
in
various types
of gasiíiers.
6 2 , Hconversion
C0
co, and
H 25%
.c We
call
this
flame
in
dioxide
2 0,
produced,
and
indirect
heat
or
mass
transfer
is
required,
zone
at
that
level

(Walawender
1985).
4.2.2
Biomass
Pyrolysis
Hydrogen
H2
14.5
15.2
updraft
gasiíiers
produce
to
20%
volatile
tar-oils
and
H0
gasiíier,
but downdraft
gasifiers approach equilibrium
quite
of the following
processes:
—by
limited
supply
“flaming
pyrolysis,”
distinguishing

it
Composition
52.2
4.3 41.7
which
complicates
apparatus
and(lysis)
the
Pyrolytic
so
are -air
unsuitable
for operation of thus
engines.
Downdraft
VVater
(v) is thethebreaking
H2O
4.8process.
Pyrolysis
down
of avalues
material
closely
see
below.)
Some
gasiíiers
operate

at
lower
of
(vveight
%)
from
open
wood
ílames
with
unlimited
access
to
air
(Reed
1.6
Composition
(mole
33.3
46.7
20.0
gasiíication
will
notbe
discussed
because
it is1.7
only
Methane
ch

Pyrolysis:
Biomass
+ Heat
—>
oil, gas
4
gasiíiers
produce
typically
less
thanCharcoal,
1% tar-oils
and so are
heat
(pyro).
It is
theby
first
stepíurthor
in the
combustion
or
(Ị)
on
purpose
augering
charcoal
out
of
the

char
%) widely
1983a).
Flaming
pyrolysis
produces
most
ofreasons
the combustible
Nitrogen
n
48.4
50.8
The
oxygen
used
a
process
determines
practical
in oíbiomass.
large installations
and is not
as well-developed
as
2
3 in
used
for
engine

operation.
The
for
this
gasiíication
Whenbiomass
is
heated
in
the
absence
High Heating
Value
20.9
kJ/g
(8990
Gasifícation:
Biomass
+downdraft
Limited
oxygen
— > Fuel gas
zone in order to produce charcoal—a valuable bỵproduct—
gases
generated
during
gasiíication
and
the
products

and
temperature
of
the
reaction.
The
direct
gasiíication
with
oxygen
or
air.
Gas
High
Heating
difference are given bẽlow.
Btu/lb)
of
air
to about
350°c
(pyrolysis),
formsatcharand
to yield
the higher
gas heating
valueitshown
low (|)coal
in
Value:

Low Heating
Value
20.4
(8770
3
simultaneously
consumes
99%
of thekJ/g
is oxygen
the principal
oxygen
consumed
isBiomass
typically
astars.
the It
equivalence
Combustion:
+plotted
Stoichiometric*
Generator
gas
(wet
5506
kJ/Nm
(135.4
(chemical
Symbol:
C),

gases
(CO,
C0
,
H
,
H
0,
CH
), and
tar
2
2
2
4
4.3.2
Gasitication
Fig.
4-4[d].
Such
operation
is
not
a
true
gasiíication
but
might
Btu/lb)
bDirect

4.4.2mechanism
Operation
of
the
Updratt
Gasiíier
3
gas
downdraft
gasiíiers.
basis) (with gas
Btu/scf)
ratio,
(ị)for
- the
oxygen
relative
tìiat measured
requiredin for
Generator
(dry
5800
kJ/Nm
(142.5
The high heating
value
(HHV)combustion
is used
theinvalue
that

isto
usually
the
—>generation
Hot
products
vapors
an approximate
atomic
makeup
CH 1 2 Obed
0 5 ).
be
called
“gas/charification.”
In
entrained
or of
fluidized
b
Pyrolysis
and
gasification processes
are endothermic,
so heat
basis)
Btu/scf)
The
isobtained
shown

schematically
Fig.vvater
4-5(a).
laboratory
and gasiíier
would
during
combustion
ifinliquid
was
complete
combustion.
(Complete
of
biomass
with
If
theupdraft
íormula
for be
biomass
oil
is oxidation
taken
as approximately
Air
Ratio
Required
for
Gasitication:

The
tar
vapors
are
gases
at
the
temperature
of
pyrolysis
but
operation,
the
ratio
of
biomass
to
oxygen
can
be
varied
must be supplied in order for the processes to occur. In fact,
allowed
to enters
condense
outa as
a an
liquid.
The
lowFigs.

heating
value
(LHV)
isthe
obtained
Biomass
air
seal
(lock
hopper)
at
top
Fig.
3-7. Direct-heat
rotarythrough
ơryer
(Source:
Perry
1973,
20-35,
20-36)
oxygen
requires
vveight
ratio
of
1.476
[mass
of
Thermal

processes
have
high
throughputs
and
can,
CHỊ
partial
combustion
of
these
vapors
can
be
2.38
kg
wood/kg
air
2 OQ
5 , then typically
condense
to
form
a
smoke
composed
of
fine
tar
droplets

as
when water is produced as a vapor. The high heating value of typical biomass
independently.
In thistocase
<|) must be
set, typically
íixing
the
heat
required
accomplish
pyrolysis
and bỵ
raise
the
and
travels downward
into
aany
rising
streamofform.
of
hot (Biological
gas.
In low
the
oxygen/mass
ofoperate
biomass];
air,

aratio
6.36.)
A
very
infuelsprinciple,
on with
biomass
Fig.
(Ib/lb)
4-5.
Schematic diagram of (a) updratt and (b) downdraft gasiíier showing reactions
represented
approximately
by
the
they
cool.
will be decreased
in proportion
to
thereaction:
water and ash content, according to
Air Ratioflow
Required
for
Gas
Combustion:
oxidant
and
varying

fuel1.6-2.2
flow
maintain
a constant
products
tozone
600°c
isReed
about
kj/g
(700-800
Btu/lb],
pyrolysis
section,
the
gas
to the
tar-oil,
occurríng
in each
(Source:
1981, Figs.
8-6,to8-7)
or
oxỵgen
is hot
indicative
of pỵrolysis,
shown
at

left
processes
onlyuse
operate
on pyrolyzes
some
of the
thebiomass
components
of
thezero
relation:
CH^ 2 O 0 5 + 0.6 0 2
1.1
5 kg
wood/kg
temperature.
representing
6%
to
10%
of
the
heat
of
combustion
of
the and
dry
Aỉỉ

the
processes
involved
in
pyrolysis,
gas
iỉication,
charcoal,
and asome
gases.
theisreduction
the charcoal
of
the
ofC0
about
0.25
typical
ofzone
the gasiíication
biomass,
the
cellulose.)
LHV(Net)
= In
HHV(MAF)/(1
+ M + A)
-> figure;
0.5usually
CO +(Ị)

0.5
(4-4)
2 + 0.4 H 2 + 0.2 H 2 0
air
(Ib/lb)
biomass
(Reed
1984).
This
heat
is
supplied
directly
by
combustion
can
be
seen
in
the
Aaming
match
of
Fig.
4-2.
The
thus
reacts
with
to make

co
Hat
2 and
2 0 traction
2.
region
whereformed
M at
is the
theíraction
middle;
of
moisture
andrising
combustion
(wetC0
basis),
Ais
isHindicated
the
of
byash,
a ộand
and
> 1MAF
4.5 flame
Charcoal
Gasitication
Cellulose
isthe

a 2reduction
linear
polymer
of
anhydroglucose
units;
partially
combusting
the
volatile
tars
in
downdraft
gasiíiers;
desígnates
the
moistureand
ash-free
basis.
The
air/biomass
ratio
required
for
provides
heat
for
pyrolysis,
and
the

resulting
gases
and
(The
exact
0
-to-vapor-ratio
will
depend
These
values
are
based
on
ashand
moisture-free
biomass
with
the
Finally,
below
zone
incoming
air
burns
the
absorbed
in
the
endothermic

reduction
and
pyrolysis
reactions
the right.
hemicellulose
a(Ib/lb).
mixture composition
of polymers
5- andgasiíier
total combustion
6.27 kg/kg
The
manuỉacture
ofluminous
charcoal
forfrom
use
a sensible
synthetic
fuel
dates
composition
given
in Table
4-1.comes
The wet-gas
composition
is the
most

important
in
updraft
gasifiers,
it
the
heat
of
the
vapors
burn
in the
ílame
in as
a process
called
ũaming
on
the isexact
vapor
and
charcoal
to isproduce
C0 2 ofand
heat
above.
property
of
the gas
for mass

and and
energy
balances,
butthe
dry-gas composition
The
composition
of
the
gas
produced
is
shown
in
Fig.
4back
at
least
10,000
years
is
closely
associated
with
the
The
LHV
can
be
related

to
the
HHV
and
an
analysis
of
the
combustion
gases resulting
from
charcoal
gasiíication.
This
combustion
combustion.
After
the
flame
passes
a
given
point,
the
char
conditions.) Downdraft
gasiíiers
usuallỵ
produce
(Desrosiers

1982;
Reed
1985b).
Notevapors
that that
the
Depending
upon
the pyrolysis
conditions
in
amoìsture.
gasiíier,
one
can
is usually reporìed
of the dittìculty
ìn measuring
heating
Products
as:
4(b).
amount
of oil/tar,
energy
remaining
in
development
ofbecause
our

civilization.
Today,
charcoal
isThe
used
as
then
dilutes
thecontinue
product
gas(some
with matches
C0
and
may
may
not
to the
burn
are
are
less The
thanto 1%
theheat
reason
behind
combustion
C0
is exothermic,
and the

produced
in the
2 condensible
value ofor
the a
gas
is usually
calculated
from
gas composition,
using 2a value
of
generate
wide
range
of
vapors
(wood
oil
and
wood
tar)
in
Equivalence
Ratio
Equivalence
Ratio
HHV
=
LHV

+
F
h
m
w to gas is shown in Fig.
the
char
and
converted
from
solid
the
prime
of
heat
for
cooking
in
less
developed
3 source
3
H
0,
the
products
2
chemically
treated
to

prevent
the
charcoal
from
smoulderíng).
almost
exclusive
use
of
downdraft
gasiíiers
as
an
energy
13,400
kJ/Nm
(330
Btu/scf)
for
H
and
co,
and
41,900
kJ/Nm
(1030
Btu/scf)
for
gas
here

is
the
hot
gas.
If
the
pyrolysis
products
are
to
be
burned
where
Fm
is
the
vveight
traction
of
moisture
4-4(c).
The
low
heating
value
of
the
gas
is
shown

in
Fig.
4countries
also isisused
for the reduction
of many ores
in
methàne. theandmatch
(c)
When
extinguished,
remaining
wood
source
for operating
engines.
produced
in íigures
the
combustion200
gases, and hw is the heat of
immediately
heatforindowndraft
a boiler
for the
drying
400
These are
typicalfor
values

air or
gasitiers,
but they(close-coupled
can vary between
4(d).
Fromofthese
it isBtu/lb).
seen that at
an equivalence ratio
smelting
processes.
vaporization
water,
2283
J/g
(980
continues
to
undergo
residual
pyrolysis,
generating
a
visible
3
(°C)
Fig. 4-4. (a) Abiabatic reaction temperature for biomass otatomiccomposition CHi. 4O0.6Temperature
reacting operation),
with oxygen
andair,

plottedagainst
the equivalence
ratio, (ị),onthe
ratio ables
of oxygen
togas
that
4880
and
7320
kJ/Nm
Btu/scf),
depending
varisuch
as
then
the(120-180
presence
of condensible
vapors
in the
smoke
composed
ofvolume
the
condensed
tar
Source:for
Modiíied
data in

1981.gas composition for reactiorỉ with air (c) Energy in solid
required
completefrom
combustion
(b)Reed
Equilibrium
and gas
(d)loss,
Energy
per
ofgas (Source:
1981,
Figs. S-2 at-the
S-5)
gasitier
heat
biomass
moisture
content,Reed
anddroplets.
char removal
grate.
is
of
little
importance.
In
Fig. 4-3. Thermogravimetric
analysis
of a typical

biomass sample
heated
in the absence of air (Source:
Reed 1981,
Fig. 5-2)
Source:
Moditied
from data in Reed 1981.
*“stoichiometric,”
that quantity
required
for a complete
chemical
reaction
fact,
theCombustion
condensible
tars
represent
a high-energy
and
of combustion
with of
oxygen.
If the
combustion fuel
is ac4.2.3
Biomass
since
measure

it canon
beof
used
the
as of
a íeedstock
producer
gas
forfrom
the
quality.
chemiApproximately
cal
synthesis
through
thermogravimetric
analysis
from
gasiíier
systems
relative
to those
íossil
fuel
dependent
the
rate
heating
and
size of

the
biomass

Chapter 4

Principles of Gasitication

a

a

2

b

Fig. 4-2. Pyrolysis, gasitication, and combustion in the (laming match

24 Handbook of Biomass Downdraft Gasiíier
28
Gasitier Engine Systems
26
20
22Handbook
HandbookofofBiomass
BiomassDowndraft
DowndraftGasitier
GasitierEngine
EngineSystems
Systems

Principles
of Gasitication
Gasiíication
25
Principles
of
27
29
Principles
of Gasiíication
23
Principles of Gasitication 21


OJ

ring
was
qualitative
inSizes
nature,
the authors
haveleading
had
concalled the “Imbert”
gasiíier
(after
its entreprenurial
in-(Gengas
ventor,

units.
This
term
enables
one to compare
the períormance
of
hearth
with
unpyrolyzed
biomass,
to
5-4.
of
Zone
for
Different
Fuel
manuíacture
wastes
half of
theTable
energy
inPrediction
the
5.3Charcoal
Gasitiers
power
vehicles,
areTable

largely
self-purging.)
Yet,
it pyrolỵsis,
iswood
desirable
to Length
build.
ItUsually,
is zone
desirable
to contains
gasiíy
more
than
95%
ofa the
biomass,
wood
less
than
1% ash.
However,
tvvice
the
mass
of
oxygen
required
forData

biomass
and
Intions.
both
commercialization
ofas
5-1.
Maximum
Reported
and
Hearth
Load
of
Various
Gasifiers
T
o
Table
5-3.
siderable
experience
in tar
running
this The
interesting
techỊacques
Imbert)
although
itSizing
was

produced
by Superticial
dozens
of Velocity
a summary,
wide
variety
ofunderstanding
gasifiers
on
a and
commonbasis.
Thesize
maximum
momentarilỵ
high
rates
of
production.
fuel
also
is
1950).
On
the
other
hand,
Australia
worked
almost

gasify
ashigh
muchchar
of theconversion
charb as possible
before
its packing
the
charcoal
isdowndraft
consumed,
ìt eventually
collapses
to form
a
leaving
Updraít
only
5%
charcoal
char-ash.
gasiíiers
were
íirst
to be
Parameters
SmallChips
InchChips
SavvdustCubesPeat
hence

increases
the
overall
stratiíied
gasifier
have
made the
remarkable
c
d the
e for
—Gas
9
+this
Air/Oxygen
companies
undercharcoal
otherBiomass
names
during
World
War
II.
speciíic
hearth
loads
for
a
number
of

gasiíìers
are
shown
in
nological
antique.
Type
D
Vs
Reterence
very
important
proper
operation.
Crossdraữ
gasifiers
have
exclusively
with
during
period
because
of
that
Bh
Hearth
Load
Engine
Maximum
Povver

increases
the
pressure
drop.
Minimal
char-ash
removal
can
be
powdered
char-ash
that
may
represent
2%
to
10%
of
the
developed
for
vehicle
operation.
They
are
suitable
onlỵ
for
CẼ
oxygen/biomass

ratio.
up to 10%
ofDiameter
the gasifiers
biomass iswere
removed
progress
in only
a few
years
of
but
adata
great
deal
Superticial
Velíastest
Approximately
one Ifmillion
of these
mass
Table
5-1.
The
table
was
calculated
from
available
Peilets

the
time
and
thework,
smallest
thermal
massofon
of
-using
with
cõuntry’s
largeautomatically
íorest
acreage and
small
number
of vehicles.
The
ability
toresponse
remove
variable
amounts
of
char
a shows
moving
accomplished
byoxygen/fuel
pressure-sensing

total
biomass,
in as
turn
contain10%
to with
50%
ash.
Ash
low-tar
fuels
such
charcoal
anding
coke.
Figure
5-4
an
5.7.2
Description
of
the
Downdraft
(Imbert)
as
char-ashReíractory
atCylinder
the
grate,
the

ratio decreases;
effort
still
is
in
progress.
It
is
not
clear
whether
this
design
Number
Cylind
Gasolin
3
2
Proximate
Analysis:
(Dry
Basis)
produced
during
Worldthen
War
II, at
a Genẹrato
cost
of

about
$1000
U.S.
gasiíĩers
that
have
been
thoroughly
tested
and
lists
the
any
gas
producers
because
there
is
a
minimum
inventory
of
m
ft
m/s
ft/s
m
/cm
-h
MBtu/í^-h

grate
adds
a
second
design
issue
to
the
stratiíied
downdraft
Gasitier
Inputs
switches
that
activate
the
removal
mechanism
only
when
^Drying
contents
depend
on theconvenchar
content
the
updraít
charcoal
gasiíier
that was

usedofinImbert
thewood
earlv and
part the
of
oftheeach.
Dimensi
eroftoZone
rrealize that
Gas
eand
Gasitier
inNevertheless,
turn.
temperatures
of ílaming
combustion
decrease,
theis simplicity
charcoal
gasification
has
will
displace
and
Zone
.803
.90
.65
(1983)

It
important
the cost
of .90ultimately
maximum
superíĩcial
and
heating load
reported.
Note
hot
charcoal.
In one velocity
design,
a tional
downdraft
gasiíĩer
could
be
0begins to
§
gasiíier.
Char
consumes
more
than
Cylinde
ons,
vólum
pressure

Needed
Operati
degree
of
agitation.
The
greater
the
degree
of
char
reduction,
World
War II.
Air enters the
updraft
gasiíier
from below
the
Imbert
l-A
0.15
0.5
2.50
8.2
0.90
4.76
(Gengas
1950)
the

resultingmany
gas has
both
a higher
energy
content
and a charcoal
higher
attracted
investigators,
and
more
thanprimarily
2000
Char
.10
.35
producing
such
a unit
today
woulđ
depend
on the .10other
that in gasiíiers.
European
literature,
hearth
load startup
is

reported
in gas
Reíerring
to .188
5-1 andscheme
5-2,
the
upper
cylindrical
part
of
Cast-iron
operated
in
aFigs.
crossdraít
during
in order
to
rs
mm
e,
at
2300
on,
the
smaller
the
resulting
andthethe

higher
ash, asa
grate
and flows
upwardparticles
through.01
bed
to the
produce
4
110x
136
5.17
50
80
tarsystems
content.
This
added
control
of
the
oxygen/biomass
ratio
have
been
manufactured
in
the
Philippines.

A
large
l-A
0.30
1.0
0.63
2.1
0.23
1.19
(Gengas
1950)
Ash
.01
.009
.05
constriction
degree to which it could
be mass
produced
since
none
of
the
volume
units;
in
the
United
States,
it

is
reported
in
energy
the
inner
chamber
is
simply
a
magazine
for
the
wood
chips
or
Distillation
minimize
the
startup
time
(Kaupp
1984a).
5.1has
Introduction
° o(Kadyszewski
oFw
Biomass
( 0.955.8.4
in Fig.

3-3.the
The
downdraft
gasifier
startup
combustible
gas
(Kaupp
1984a).
High
at
theand
air
Modeling
stratỉíied
Water
not
.20 shown
.027
.05 temperatures
.25
number
are well-defined.
not
6cbeen
110
X136
7.75
75ring1.01986).130
Biomass

l-Aworking
0.30
3.1
0.34
(Graham
1983)
Zone
components
arecurrently
inherently
expensive.
units. biomass
other
fuel. During1.81
operation,
this
chamber
is
tuel o °BF o
D are
CHi 4
O0 6=0.402designs of gasifiers
Many
different
have
been
built
and
response
time

is
intermediate
between
the
fast
crossdraỀ
inlet
can
easily
cause
slagging
or
destruction
of
the
grate,
and
Downdraft
Gasiíier
Corp.
Fuel
Properties:
8 issue 110x
136
10.34
100
180
l-A
0.61
0.24

0.8
0.09
0.45
(Graham
1983)
° stratified
o o2.0
íilled
every
few
hours
as
required.
The
tố
5.6
The
Updraft
Gasitier
Adescribed
third
in
the
design
of
the
downdraft
gasiíier
In
Gertemtor

Gas
(Gengas
1950)
a
maximum
hearth
load
3
in can
the beextensive
literature
on this
(see
and steam
the
slow
gasiíier.
often
some
or updraít
C0
is
added
to the inlet
air to
moderate
Air
gasifiers
operated
either p

by íorcing
airsubject
through
the .40Agasifier
Density
g/cm
.40
5.5isSERI
The
Crossdratt
Gasitier
ò 0.28
mathematical
model
has2opened
been
developed
atthe
SERI
to 1.10
predict
3for
Air/ox
S-A
0.15
0.5
0.9
0.10
0.53
1982)

spring-loaded
cover
is
to1.00
charge(Reed
gasiíier,
and
The
updraft
gasiíier
has
been
the
principal
gasiíier
the
prevention
of1950;
bridging
and
channeling.
High-grade
(B[ lmax
) value
for
an Imbert-style
gasiíier
is about
0.9used
/hNote:

At(pressurized)
a heavy
load, 170
mm
cross
section
should
be
instead
3 of 150 mm
especially
Gengas
Skov
1974;
Foley
1983;
Kjellstrom
the
grate
temperature.
Charcoal
updraft
gasiíiers
fuel
or
by
drawing
the
airused
through

the fuel .20the
oNm are
Bulk
Density
g/cm
.15
.50
.45
The
Imbert
gasiíier
requires
a
low-moisture
(<20%
moisture)
behavior
and
dimensions
of
the
stratiíìed
downdraft
2 for 150
3 0.90
The
crossdraỉt
gasiíier
shown
in

Fig.
5-5
is
the
simplest
and
S-0
0.15
0.5
0.24
0.8
0.09
(Reed
1982)
then
it
is
closed
during
gasiíier
0
cross
section.
Q
coal
years,
and
there
are
dozens

in
operation
around
biomass
fuels
such
as
wood
blocks
or
pellets
will
flow
down
cm
.
In
other
words,
0.9
m
of
gas
is
produced
for
each
square
1983,1985;
Kaupp

1984a;
NAS1983).
Much
of
this
material
Reduction
characterized
by
comparatively
long
starting
times
and
poor
(suction).
In practice, gasiíiersFlaming
that fuel
engines generally use .50gasiíier
Void0.2
Fraction
Fv
.63
.50
.59
and
uniformly
blocky
fuel
in permits

order
allow
easy
gravity
(Reed0.05
1983a,
1984,
1985a).
Thetothe
model
is gasiíiers
based
upon
o (Walawender
ccollected
lightest
gasifier.
Air
enters
at
high
velocity
through
a single
operation.
The
spring
cover
to pop
open

Buck
Rogers
S-A
0.61
2.0
0.13
0.4
0.25
Source:
Adapted
from Gengas
1950,
32.
the
world.
In
fact,
World
War
II-type
Lurgi
now
through
the
gasiíier
under
the
iníluence
gravity.
However,

centimeter
of
cross-sectional
area
at mass
the
constriction.
This
Zone
has
been
by
A.Table
Kaupp
ofof the
University
of 1.00 feeding
Length
cm
2.00
5.00
1.00
Pyrolysis,
FP
response
because
of of
the
large
thermal

of the
hearth
and
the
suction
of the
engine
to
move
air through
the
gasiíier
and
Slide
Valve
<
through
the
constricted
hearth.
Twigs,
sticks,
and
0.45
CO
+
0.35
predicting
the
length

both
the
ílaining
pyrolysis
and
char
1985)
nozzle,
induces
substantial
circulation,
and
flows
across
the
to
relieve
pressure
in
the
case
of
a
gas
explosion,
thus
produce
a
large
share

of
the
gasoline
used
in
South
Aírica
by
Cũ (Chem
S-A
0.61
2.0
0.23
0.7
0.08
0.43
1985)
other
fuels
(such
as
stringy
chips,
sawdust,
and
rice
hulls)
can
corresponds
to

a
superíicial
gas
velocity
V
of
2.5
m/s
(8.2
s
California
at
Davis.
(Copies
of
these
papers
are
also
at
SERI
Width
cm
1.00
2.00
3.00
.30
fuel
zone.
cleanup

train,
and
these
are
called
“suction
gasifiers.”
We
will
cq 4 of
0.45
H2 char.
+ Hearth
Bỉomass
bark
shreds
must
bethefollowed
completely
removed.
The reduction
reaction
zones
from
properties
ofFischer-Tropsch
the biomass
fuels
andin
bed

fuel
and
This
produces
very
high
temperatures
in
functioning
as
a
safety
valve.
oxygen
gasification
by
catalytic
Zone
form
a
bridge,
preventing
continuous
flow
and
giving
rise
to
Silo
ft/s)

calculated
at
NTP*
from
the
throat
diameter
and
ignoring
Syn-Gas,
Inc.
S-A
0.76
2.5
1.71
5.6
0.62
3.26
(Graboski
Height
cm
.20
.50
3.00
.30
and
the H
German
Appropriate
Technology

Exchange only
[GATE]
in
describe
only
suction gasifiers
here; however,
minor
0.25
0 volume
Lock Hopper
area
at themanufacture
hearth
and
thegasoline.
protruding
nozzles
present
the
gasifier
throughput.
The zone
lengths
predicted
foron
a Average
very
and
results

inisproduction
low-tar
Charcoal
relatively
simple
and
car- hazards
ried
1985)
Dístilíạtiọri
zòne
conversion
of
the
very
highsmall
temperatures.
Obviously,
it0.76
desirable
toofuse
these
the presence
ofofgas
fuel.
This
to ais there
speciíic
About
one-third

thetoisway
upcorresponds
from
the bottom,
is a gas
set
Equivalent
cm
4.41
1.56
4.41
.51
s-o
Eschborn,
West
Germany.)
Anyone
interested
2.5
ina build
design
1.07
3.5
0.39
4.07
(Graboski
modiíications
are
required
to

at
which
the
passage
of
the
fuel
can
be
restricted,
thus
various
sizes
of
biomass
fuels
are
given
in
Table
5-4,
and
aon
low
(usually
5000
ppm),
is
still
high

enough
to
require
c
■
3
3
gas,
permitting
rapid
adjustment
to
engine
load
changes.
The
in
most
countries.
However,
it
requires
tight
Controls
Diameter
1985)
widely
available
biomass
residues.

Bridging
can
be
prevented
Volume
V
cm
.20
production
rate
2.00
of
9000
m
of
gas
45.00
per
square
meter
of
.07
crossof
radially
directed
air
nozzles
that
permit
air

to
be
drawn
into
Iron-plate
hearth
modiíication
and
improvement
would
be
well-advised
to
The
geometry
of
the
updraít
gasiíier
is
shown
in
Figs.
pressurized
(See
Chapter
8,
Data
in this table
are basedgasiíĩers.

on reports
on well-tested
gasitiers,
rather
manutacturers’
claims, etc.
causing
bridging
and channeling
followed
high tar
output,
2 thethan
diagram
of
the
gasiíier,
dimensioned
for2 dry
wood
chips,
isin
extensive
scrubbing
and
disposal
procedures.
fuel
and
ash

serve as
forthe
wallscm
of
gasifier,
manuíacturing
conditions
to toproduce
a bycharcoal
low
0.06
cshaking,
Area
Athemantle
12.00
78.00
1.38
bybecome
stirring,
orinsulation
agitating
bed
and,
since
the
sectional
area
per
hour down
(29,500

scf/ft
-h).
IfTypically,
the gas
has
a
the
chips
as
they
move
be
gasiíied.
there
acquainted
thisofmaterial
before
repeating
tried
5(a),
5-3,
and
5-4.
During
operation,
biomass
h
2 is fed into the
which
deals

with thewith
topics
blowers,
fans,
eịectors,
and 2.80shown
co
2pyrolỵsis
as
unpvrolyzed
biomass
falls
into
the
reaction
zone.
The
in
Fig.
5-13.
The
predicted
and
char
bed
H
0
lGasitierConditions:
is the
(nozzle

and
throat)
gasitier
ofall
ww
II. the
s
is the
stratified
Downdraft
Gasiíier.
Asignities
operation
on air,for
o onuse
oxygen.
3
0.64
COImbert
X 0.30
C0
0.54
Hconstricted
permitting
construction
for
parts
except
the
2mild-steel

2
volatile
content
that
is
suitable
in
charcoal
gasifiers.
Groeneveld
has
studied
the
recycle
of
gases
at
nozzle
temperatures
in the gasiíier
are
relatively
low,
it
is
(tỵpical)
energy
content
of
6.1

MJ/Nm
(150
Btu/scf),
this
are
an
odd
number
of
nozzles
so
that
the
hot
gases
from
One
and
tested techniques.
However,
many
of
the
documented
top
while
air
and
steam
are

fed
through
a
grate,
vvhich
often
compressors).
Ash
Zone
D
XFor
0.16
H zles
0 type
temperatures
and
chemical
composition
/ .15opposite
measured
/ (S),
inthe
the
char
2diameter
Fig.5-9.
nozzleFor
gasenểrgy
producer
(Soưrce:

Groeneveld
nozand
which
may
require
alloys
oror.15
Diameter
Imbert
gasitìers
(I), the
is measured
g ofatreíractory
the
mthroat
(upper
value)
at the
air
entryDowndraft
level
.15
value).
Stratitied
Downdraft
.15
V
and
developed
improved

understanding
the
tarCentral
combustion
possible
togrates,
use
adiameter
stainless
Steel
results
in (lower
acenter
specific
ofGasitiers
54.8 1980a)
-h (4.4
nozzle
do
not
impinge
on
design
variations
are
minor.
is
covered
with
ash. The

gratethe
israte
at the
base
ofGJ/m
thenozzle.
gasiíier,
2
Inside
insulation
by
ashes
isA
constant
at
all
levels.
q
bed
are
shown
in
Fig.
5-14.
The
interested
reader
is
reíerred
2

HeatTransíer
w/cm
2.00
2.00
2.00
2.00
some
cooling.
Air-cooled
or(Source:
water-cooled
nozzles
are
often
large
number
of
descriptive
articles
on
gasiíiers
ap- 5.4Charcoal
Fig.
5-3.
Diagram
of updraít
gasitication
Skov
1974
9. ©

1974.to
Useơ
with
versus
Fuels
and
improved
mixing
methods
shovvn
ininFig.
Fig.
5-9
permit
ithe1pyrolysis
stirring
arm
such
as the
one
shown
the
Buck
Rogers
MBtu/ft
-h].
The
diameter
of tothe
zone

at
the ofair
The
nozzles
areBiomass
attached
a distribution
and
the
air the
and
steam
react
with to
charcoal
from
The
superticial
velocity
is calculated
asInc.)
the volume of gas (taken at room temperature) to
through
area
vvithout
regard there
presence
of fuel. Itthe
has
units the

the papers
for
further
details,
which
are
beyond
scope
permission
Biomass
Energy
Foundation,
We
believe
that
íuture
improvements
to gasifiers
based
Feed
M
kg/h
10 passing
10
10
10
Cast-iron
v-hearth,
easily
required.

The
high
temperatures
reached
require
a below-ash
peared
during
World
War
II,will
but
scaleup
(Groeneveld
1980a,b).
Uníòrtunately,
there
is no
no
50 be.Rẹduction
^one
Ị______
30
40
500
1000
1500
gasiíier
ofofRate
Fig.

5-11.
nozzles
is
typically
about
twice
that
at
the
throat,
and
Table
510
20
maniíold
that
in
turn
is
attached
to
the
outer
surface
of
the
High-grade
charcoal
is
an

attractive
fuel
for
gasiíiers
vol/area-time
= length/time
= velocity.
biomass
to
produce
very
hot
C0
and
H
0.
In
turn,
the
C0
2
2
2 and
2
removable
this handbook.
Specitic
Feed
Rale(Kaupp
m

kg/m
h would
566orofcause
566
566
566
on
a to
better
of for
thehave
basic
processes,throughput
combined
The
fuel
hearth
prevent
load,understanding
Bh,drawings
slagging
is aoperation
practical
measure
1984a).
of
gasitier
gas
volume
(SI units)

throughput
(English
units).
detailed
been
located
overall
theory
of
Imbert
gasiíiers
that
1energy
shows
the
hearth
load
on
this
basis
also.
This
puts
the
hearth
inner
can.
This
maniíold
is

connected
through
the
outer
can
producer
gas
from
charcoal,
which
contains
very
little
H
0
react
endothermicallv
with
the
char
to
form
co
and
H
2
2
■ĩ- *.- . '
-.V
^

Composition
(%)
N 2 Downdraft
Free)
Awith
íourth
issue
to
begasiíier
addressed
the
design
of
stratiíied
5.8.2tar
of the
the
Stratỉfied
Gasitier
(5%-20%)
improved
(Desrosiers
measurements
1982)Fortunately,
makes
of in
gasifier
them
behavior
impractical

and
forbetter
high
Temperature
(K)
from
that
period.
formulas
permit
sizing
the
for
fuels
other
than
hardwood
load
forDescription
the
Imbert
type
gasiíier
on a gas
comparable
basis
to
the
to
aand

large
air-entry
port.
One
air
nozzle
isGas
in
line
condensate,
is through
simplest
clean.
Charcoal
according
to
Eqs. Gasitiers
(4-6]
(4-8).
The to
temperatures
at
the
The
crossdraít
gasiíier
is
generally
considered
suitable

only
5.9Tar-Cracking
Gasiíier
Parameters
downdraft
gasiíiers
is
bed
stabilization.
When
Grate
the
gasifier
Insulation
regulation
volatile
fuels
of goomctry
where
fuel
properties.
a clean
gas
Work
is required.
isfuel
under
various
for
determining

critical
dimensions
given
in air
a at
number
of
blocks.
The
and
flow
ofare
andway
are
quite
stratiíied
downdraft
gasiíier.
Knowledge
ofsteam
maximum
The
stratiíìed
downdraft
gasifier
with
this
port,
allowing
the

operator
to
ignite
gasifiers
were
overadding
much
of
Europe
during
thehearth
later
grate
must
berestricted
limited
by
either
or
recycled
for low-tar
fuels.centers
Some
success
has
been
observed
Pyrolysis
Zone:
operates

atreíerences
stable
steady
State,
the
Aaming
throughput
andof
at a
low
loads become
disproportionately high.
observed
an
optimum
relationship
between
the
hearthofwith
and
private
and
public
totempts
increase
our
understanding
the
the
older

(Gengas
1950;
Schlăpfer
1937).
complex,
making
any
atto
model
the
gasifier
very
Fluidized
beds
are
íavored
by
many
designers
for
loadcharcoal
permits
one
toII
calculate
thethe
size
of and
hearth
consists

cylindrical
vessel
with
aneeded
hearth
on
the
bed
through
this nozzle.
years
of
World
War
because
charcoal
exhaust
gas
to
prevent
damage
to
grate
slagging
from
unpyrolyzed
biomass,
but
the
nozzle-to-grate

spacing
is
5.9.1
Introduction
Reaction
Time
tp
s[40
43 A low speciíic73hearth load may 656
93 for
Oxygen
pỵrolysis
zone
advances
into
the
biomass
at is
theprovided
same
rate
also
cause
tara íormation
nozzle
areas.
For
instance,
maximum
power

was
obtained
gasiíication
process.
Consequently,
gasiíier
difficult
tasks
indeed.
(More
iníormation
in that
later
gasiíiers
producing
more
than
40
GJ(th)/h*
MBtu(th)/h]
various
engine
or
burner
sizes.
Dimensions
for
variety
of
the

bottom
as
shown
in
Figs.
5-10
to
5-12.
During
operation
highoperatìon,
temperatures
generated
when
carbon
reacts
withuse
the
critical
fuels
doreaction
notnozzles.
feedmakes
into
the
During
the
incoming
air
burns

and
pyrolyzes
some
Renewed
interest
inaUnscreened
biomass
gasiíication
has
maniíested
itselí
Fuel
Velocity
Vfthat
cm/s
.105
.031
cost
of
gas
cleanup
system
needed
for
engine
the
char130-mm
is(Das
consumed,
resulting

in of
a five
stationary
zone
at
problems.
A the
high
turndown
ratio
is
less
portant
for.035
elecừic
Ễrom
hearths
that
had
12-mm
Any
design
is1986).
in
State
This
ita.079The
discussions.)
and
for

gasiíiers
using
smaller
particle
(a) flux.
íeedstock
sizes.
In
(c)imImbert-type
gasiíiers
are
shown
in
Tables
5-2
and
5-3.
of
the
stratiíied
downdraft
gasiíier,
air
and
biomass
pass
Fig.
5-1.
Diagram
of

downdraft
gasitication
(Source:
Skov
1974,
Fig.
14.©
1974.
Used
with
(b)
air.
gasiíier
íreely
are
prone
toHowever,
bridging
and
channeling,
and
the3.38generally
of the wood,
most
theoftars
and
oils, Fu
andoperate
some
of full

the
in
the
fact
that
agasiíier
number
of
in-or1950,
dividuals
and
groups
have
Pyrolysis
Length
'phearth
cm
7.64
20.33
3.26
Fig.
5-6. V-hearth
Imbert
Gengas
Fig. -74)
Oxygen
Iniector
exceeds
the ofcost
the

gasiíier.
rthermore,
avariation
fixed
level
in
the
gasiíier.
this
zone
can
move
up
generators
and
irrigation
pumps
that
at
oforganize
either
the
nozzle
ring
from
these
difficult
tobed,
a (Source:
“handbook

of
gasiíier
design”
without
permission
of Biomass
Energy Foundation,
Irỉc.)
fluidized
air
rises
through
a grate
at high
enough
velocity
uniformly
downward
through
four constantly
zones,
hence
thesuch
name
Some
efforts
to
scale
the
Imbert

gasiíier
to larger
sizes
have
maximum
hearth
load
is
limited
by
many
ỉactors,
as
collapse
of
bridges
fills
the
ChárZÓne:
charcoal
that
fills
the
gasifier
below
the
nozzles.
Most
of
the

built
modern
versions
of
the
Imbert
gasiíier.
Plans
and
The
ascending,
hot,
reducing
gases
pyrolyze
the
incoming
even
if
tar
impurities
are
removed
in
íilters
and
scrubbers
(see
indimensions
very

dry
fuels,
consuming
the
fuel
reservoir
and
emerging
capacity.
a power
reduction.
Table
5-2
showsa
having
it outcaused
of date
beíore
the ink
is dry.
toReaction
levitate
the
particles
above
the
grate,
thusare
íòrming
“stratiỉied.”

The
open
top
ensures
uniíòrm
access
of
air the
or
realized
afor
increase
in
tar
(Goss
1979;
tc production
100
100
theandmechanical
integritỵ
the
char
bed
structure
within
mass
ofcomposition
biomass
is Reeơ

converted
to100
gas
within
thisto
Aaming
manuals
constructing
some
ofshowing
these
designs
available
Fig.
5-10. top
Schematic
ofTime
stratiíied
downdraft
gasiỉier
(a)
chemical
reaction,
ịb)heat
temperature
protiles,
(c)
Source:
p.
226)

results
inof
adisastrous
marked
cooling
of no
the
gas,
as
sensible-gas
is 100
biomass
and
cool
down
inof1984,
the
process.
Usually,
5%
20%
5-2.
Imbert
Nozzle
and
Hearth
Diameters
Chapter
8),
they

still
must
undergo
the
difficult
task
ofof
atsuccessíul
the
the
gasifier.
Since
more
fuel
iss Table
available,
the
nozzle
sizes
for
woodíueled
Imbert
gas
producers
“fluidized
bed.”
Above
bed
itself
the

vessel
increases
in
oxygen
todegree
the
ílaming
pyrolysis
zone,
as
opposed
to 80%
the
Char
Zone
lc
cm
3.10
3.50
Graham
1983).
However,
researchers
have
met
with
more
In
summary,
the

Imbert
design
survived
the
test
To
avoid
this
problem,
wethe
will
íĩrst
describe
the
construction
gasiíier,
ofone
agitation,
thehasfor
time
available
for
combustion
zone
since
contains
more
than
from
groups

(Mother
1982;
Skov
1974;
Nunnikhoven
converted
into
chemical
energy.
This
removes
most
ofA
the7.90
the
tars
and
oilsA
are
produced
atand
temperatures
too
low
disposal.
ofgasiíìer
the major
areas
future
gasifier

will
operate
inthis
“top-stabilized”
mode,
but
there
is
dr/dh gasiíier
dh
d
h
H
R
dm
AmThereíòre,
X 10.50
hbiomass
and
theseveral
vvider
for
nozzles
used
incausing
successful
Imbert
r variation
Range

of
Gas
diameter,
lowering
the
gas
velocity
and
particles
to
Imbert
gasiíier.
The
uppermost
layer
is
composed
ofMaximum
success
when
the
fuel
size
has
been
increased
with
the
of
time

and
mass
production.
It
is
relatively
inexpensive,
and
operation
of
a
number
of
historical
gasifiers
described
in
conversion.
High
velocities
can
disturb
the
char
and
fuel
volatile
matter
(Reed
1983a).

1984;
Rissler
1984).
Some
of
these
gasiíiers
have
been
Spring
satety
lid
100
dh
charcoal
and
improves
the
quality
of
the
gas.
Eventually,
the
signiíicant
cracking
and
are
carried
out

in
the
gas
stream
development will be the design
aand
substantial
heat loss
through
the open
top.
This results
in mm
Noles:
Calculations
based
on
the
mm
mm
mm
mm
mm
No
dh
Gaslast
Wood
SGB mm
gasiíiers.
(SGB

units
were
used
forsecond
2-cycle
pulsating
Output
max.
min.
recirculate
within
the
bed
itself.
The
recirculation
results
in
must
pass
beíore
it
reaches
the
grate.
This
zone
has
the
Air

reacts
with
pyrolyzing
biomass
in
the
zone,
and
unreacted
biomass
fuel
through
which
air
enters.
In
the
gasifier
size.
Billets
that
were
8have
cm
increate
diameter
15.still
cm
uses
materials

of remaining
construction,
isdries
easybecome
to fabricate,
and
the
literature
to
aid
in
understanding
various
bed, simple
causing
instability.
If char
fragments
dislodged
Fiam
Ah
attached
to
and
trucks
that
succeeded
in and
traversing
charcoal

is cars
“dissolved”
by
these
gases
and disintegrates
to
following
equations
and
(Desrosiers
1982).
The
heat
the
incoming
wet
lower
conversion
efficiency
and
could
a tradeoffs
fire
hazard.
Consumpt
The
gasiỉier
is
in

many
ways
self-adjusting.
If
there
is
3
3
flow
engines.)
Air
seal.
/h
Nm
/hchannels.
highofheat
and
mass
transfer
between
particle
andthat
gasparticular,
stream.
disadvantage
thatbiomass
char
and
ash
from

the
char
gasiíication
zoneIt
most
the
volatile
oil
islarge
burned
to
supply
heat
for
this
second
layer,
reacts
vvith
air
ine
Aaming
long
have
operated
well
in
Imbert-style
gasifiers
used

can
operated
by
motorists
with
a Nm
minimum
of training.
under
development.
must
remember
choice
and beairborne,
may
plug
the
bed
or
form
assumptions:
Time
of
pyrolysis:
tp
the
country
on
several
occasions.

In
n
smaller
chunks
andwood
aThe
finereader
powder
that
either
is swept
out
with=
biomass,
so charcoal
thatthey
almost
none
the
energy
lost
aspyrolysis.
(The
SERI
and
SGI
gasiíiers
operate
regularly
in the

this
topinsufficient
at
the
airofnozzles,
more
wood
issensible
burned
I is
also
must
pass
through
it
to
reach
the
grate.
However,
as
we
pyrolysis
as
explained
in
Chapter
4.
We
have

called
this
The
third
layer,
which
is
made
up
of
char
from
the
second
for
heating
applications
(Makray
1984).
(hp
+
F
h
)
p
V/A
q
Fuel
velocity:
Vf

=
supplies
low-tar
gas
from
highlv
volatile
fuels
with
a
high
A
larger
hearth
diameter
requires
either
a
higher
nozzle
of
Suspended
gasiíier
is
dictated
particle
both
by
gasiíiers
the

fuels
move
that
will
a
suspension
be
used
and
of
Thereíore,
a
little
agitation
can
effectively
increase
the
Mother
Earth
News
and
its
subsidiary,
Experímental
the
gases
to
the
cyclone

separator
or
falls
through
the
grate.
heat
in
the
gas.
stabilized
mode
with
oxygen
but
have
closed
reíractory
tops
and
pyrolyzed
to
make
more
charcoal.
If
too
much
char
forms

Fig. 5-8. High temperature zone oi a downdraft gas producer with wall tuyeres (Source:
mentioned
before,
it
provides
a gases.
“buffer”Inert
or reservoừ
of
process
“Aaming
pyrolysis,”
and
distinguish
itgasifiers
from
layer,
reduces
pyrolysis
char, which
m/Dgp
(1-Fv)
turndown
ratio.
velocity
or
some
other
means
penetrate

the
deeper
fuel
bed.
kg/h
the
biomass
use
toparticles
which
the
through
gas
will
a tohot
be
put.
íurnace,
We
will
causing
then
pyrolysis,
describe
maximum
specificthe
hearth
load.then
Vehicỉe
News,

have
períormed
extensive
tests
onmay
2
Tarspressure-íeeding
that
have
combustion
at must
the
nozzle
crack
Kaupp
1984a,
Fig.
55) escaped
and
apparatus.)
Fuel
be
added
at
a
during
high-load
conditions,
the char
level

rises
above
The
updraỉt
gasiíìer
throughput
is limited
to
about
10
GJ/h-m
Flaming
pyrolysis
zone
length:
Ip
=
charcoal
that
is
available
to
accommodate
changes
in
the
268/605.8“ílaming
60
268
150

80
256
100
5
7.5
7.8
4.5
1.33
4
combustion,”
which
occurs
in
the
absence
of
constitutes
the
íourth
layer,
normallv
is
too
cool
to
cause
30
14
This
leads

to
a
higher
pressure
drop
for
larger
hearths,
placing
some
The
combustion,
gasifiers
Stratitied
and
currently
reduction
Downdraft
under
to
development.
give
Gasitier
producer
gas.
Neither
and
have
published
iníormative

articles
and
plans
with
6
2
fur- ther
into
theprevent
hot char
althoughpyrolysis
tar cracking
nowgasiíier
thought
steady
rate
alternate
and ischar
-Cyclone
TheUnburned
heating
of
producer
varies
with
flow
rate,the
as
the
nozzles

sovalue
incoming
airgas
burns
the char
to
reduce
(10
Btu/h-ft
)that
either
by since
bed
stability
or grate
by
incipient
Vfsize
tp
power
which
otherwise
might
cause
to heat
with
excess
airon
orabout
oxygen.

At
the
bottom
of
the
second
íurtherlevel,
reactions.
However,
the
íourththe
layer
is 5
available
an
upper
limit
nozzle-fed
downdraft
gasifiers
when
fluidized
bed
nor
suspended
particle
gasiíiers
have
been
fuel

80
176
95
100
5
6.4
3.3
44
21
photographs
of
íabrication
steps.
The
plans
are
sufficiently
268/80 solids
268
256
9.0
1.19
to
occur
only
above
850°c
(Kaupp
1984b;
Diebold

operation,
which
canWorld
generate
tar ample
levels.
(We tion
haveto
shownlevel.
in Fig.Thus,
7-20.the
Notice
that overheating.
the
maximum
ef- ficiency
for
char
reaction
zone
is maintained
at the
of vacuum.
pyrolysis
=cross-sectional
600°c
fluidization,
updraỀ
vehicle
units

of the
War
IIhigh
era to
had
vibraexcessively.
zone,
theTemperature
biomass
has
been
converted
charcoal,
and all5
of a 5.7.5
to absorb
Disadvantages
heat slagging,
or
oxygen
ofand
if the
conditions
Imbert
change,
DesignLarge
it serves
5.8.1
Introduction
gas

flow
is
provided
by
engine
If
the
developed
engine
use.
100
202
100
5.5
2.7
1.00
63
8 both
30
5.2
Basic
Gasitier
Types
268/100
268
256
10.
detailed
sofor
thatsmall-scale

asized
skilled
welder
íabricate
a100
gasiíier
for
1985].
observed
higher
tar
levels
from
thiscan
pulsing
pyrolysis
process
Heat
of
pyrolysis:
hp
=
2081
J/g
rice Gas
hulls
occurs
at twice
the flow
rate slagging

that produces
the
nozzles.
gasiíiers
are
sometimes
operated
in
the
mode,
in
jar
the
carefully
wood
blocks
through.
In
fact,
an
entire
the
oxygen
from
the
air
reacted.
The256
final
gas

leaving
the = 12.
as acooling'
buffer
and 2.2
as a charcoal
storage
zone.
The
temperatures
5 Although
120
110
100
5
area
of
the
nozzles
ishas
too
small,
there
will
be
an
excessive
the
Imbert
gasiíier

has
been
the
prototype
268/120 Fig.
268
216
5.0
0.92
90
12
42
A
new
type
of
gasiíier,
which
we
have
named
the
“stratiíied
relatively
small
expense.
Heat
to
vaporize
water

to
600°C:
h
We
have
already
mentioned
that
gasifier
designs
will
differ
Fixed
bed
(sometimes
called
moving
bed)
when
using
oxygen
than
when
using
air.)
maximum
heating
value
from
rice

hulls.
This
occurs
because
The
spaces
between
theand
nozzles
(shown
Fig.
5-8)
allow
all
ashcompositions
isCo.,zone
melted
onthe
a hearth.
This
particularly
industry
emerged
for
preparing
wood
atin
that
time
(Gengas

The
stratiíied
downdraft
design
has
aeach
number
ofiszone,
advantages
5-11. Buck
Rogers
gasitier
(Source:
Walawender
1985,
p. 913.
©
1985.
Used
with
permission
of which
Eìsevier
Science
Publishing
Inc.)
0
Below
the the
air

nozzle
lies
gas-reduction
usually
zone
contains
co
Hcalled
, car
asjets;
well
the
C0
H
and
chemical
in
zone
are
shown
2air
2 and
20
pressure
drop
in
íorming
the
ifas
the

cross-sectional
300/100 second
100
300
208
100
275
115
5
10.
5.5
3.0
1.00
77
10
36
downdraft
gasiíier,
itlower
has
atemperanumber
of disadvantages.
The
downdraft
gasiíier,”
(also
“open-top”
or
“topless”
3654

J/g
for
different
íeedstocks,
and
special
gasiíiers
have
been
gasiíiers
use
a
bed
of
solid
fuel
particles
through
which
air
the
combination
of
tures
and
low
flow
rate
some
unpyrolyzed

biomass
to
pass
through.
Theina from
hearth
useíul
for
high-ash
fuels
such
ashearth
MSW;
bothfuel
the to
Purox
and
1950).
over
the5.0
Imbert
gasifier.
The
open
top
permits
be
consisting
of ain
classical

Imbert
(Fig.
5-2)
or
in fed
later
In
19
78,
a300
number
of jets
testsof
were
performed
under
SERI
5
in
the
earlier
stages
combustion,
as
shown
Fig.
schematically
Fig.
5-10.
Very

wet
fuels
inhibit
the
Aaming
pyrolysis
zone
275
115
5
11.
2.6
0.92
95
12
45
300/115 produced
115
228
105
area
is
too
large,
the
air
will
have
too
low

a
velocity
and
hearth
constriction
seriously
limits
the
range
of
biomass
fuel
gasiíier)
has
been
developed
during
the
last
few
years
through
developed
to
handle
forms
ofquantity
biomass
íeedstocks,
and

gas pass
either
up speciíic
orall
down.
They
are
thelarge
simplest
type
of 5more
íavors
methane
and
tar operate
production.
Although
the air)
change
in
constriction
then
causes
gases
to
pass
through
hot
zone
of

gasifiers
that
convert
the
maximum
ofthe
tar
to5
gas
Andco
Torax
processes
in
the
slagging
mode
(Masuda
In
his
thesis,
Groeneveld
used
cold
flowrecently,
models
easily
and
allows
easy
access

for
instruments
toinIn
principle,
the
gasiíier
can
be
scaled
to
diameters
perience
with
these
gasiíiers
(using
both
oxygen
and
have
years,
of
thecan
“V”
hearth
(Fig.
5-6).
Most
theto
flatcontract

onco
aenough
75-hp
(Imbert-type)
downdraft
130
300
248
110
275
115
12.
4.6
2.3
0.85
115
15
55
5-10.
and
Hto
mixture
already
isSERI
sufficiently
advancing
fast
keep
up
with

the
fuel,
and
2 “Hessêlman”
300/130
the
airThe
will
not
penetrate
the
bed.
The
velocity
of
the
air
blast
shapes
that
bethe
successíully
gasiíỉed
without
expensive
cooperative
efforts
among
researchers
atincoming

(Reed
1982;
The
top
zone
of
stratiíied
downdraft
gasiíier
may
beis
such
as
municipal
solid
wastes
(MSW)
and
rice
hulls.
gasiíiers
and
are
the
only
ones
suitable
for
small-scale
5.7.3

Superticial
Velocity,
Hearth
Load,
and
efficiency
is
small,
the
beneíit
of
reducing
tar
production
during
gasification.
5
at
the
constriction,
thus
giving
maximum
mixing
and
1980;
Davidson
1978).
Slagging
updraữ

gasifiers
have
both
a
vestigate
the
flow
of
gases
around
a
nozzle.
He
found
that
the
measure
conditions
within
the
bed.
Thehas
uniíorm
passage
of. air
because
it
operates
as
a

plug-flow
reactor,
and
the
air
and
fuel
uncovered
questions
that
must
be
understood
and
resolved
in
plate
hearữi
constriction
(Fig.
5-7)
been
introduced.
The
gasiíier.
This
gasifier
was
built
in

Sweden
at
the
end
of
Engine
150
to
be
a
combustible
gas
at
this
point.
the
zone
subsequently
moves
toward
the
grate,
consuming
the
300/150 concentrated
300
258
120
275
115

5
14.
4.4
2.0
0.80
140
18
67
isapplication.
shown in1984),
Table the
5-2.University of Caliíornia in Davis (Kaupp
Flamingor
cubing
pelletizing
pretreatment.
(The and
stratified-bed
1983a,b;
adjusted
toairany
depth
during
air
operation
serves
the
substantial.
Gasitier
Sizing

minimum
heat
loss.
The
highest
temperatures
arevvhether
reached
in 10.
slow
response
time
and
aaccumulate
long
startup
period
because
of
the
incoming
stream
entrains
and
burns
tarladen
gas
as
pyrolysis'
The

manner
inmixed.
which
ash
is removed
determines
the
and
fuel
down
the
gasiíier
keeps
local
temperatures
from
are
uniíormly
A
0.6
m (24
in.)
internal
diameter
suction
any
commercial
design.
latter
two

hearth
designs
a
layer
of
retained
ash
to
0
World
War
II
and
was
imported
to
this
400/13 The
130
400
258
110
370
155
7
4.6
3.1
0.85
120
17

57
dead
char
zone
at
the
bottom.
The
zone
may
become
“grategasiíĩers
currently
under
development
at SERI
andgasiíier.
other
1984a),
the so
Open
University
in
London
(Reines
1983),
hot
gases
produced
in of

theTars
ílaming
pyrolysis
zone
reactthe
same thermal
íunction
as5-9the
magazine
the
Imbert
5.9.2
Combustion
0
this
section
the
hearth
constriction
should
replaceable.
large
mass
involved.
shown
inrelated
if fuel
the
gasifier
isinaverage

properly 21
gasiíier
is atclassiíied
as
either
a choosing
dry
ash
(ash
isbe
removed
as
a 5
becoming
tooFig.
high
too
low
while
the
temperature
gasifier
has
been
operated
successíully
by
the
Buck
Rogers

Closely
toorhearth
area
is the
cross-sectionaldesigned
area of
An
important
íactor
used
in120
dimensions
of7the
any
form
a
high-quality,
self-repairing
insulation.
country
by
Proíessor
Bailie
of
400/150
135
400
258
370
155

12.
4.5
2.7
0.80
150
71
5.7.4
Turndovvn
Ratio
The
downdraft
gasiíìer
(Figs.
4-5(b),
5-1,
and
5-2)
stabilized”
this
point,
or
it
may
continue
to
move
to
the
íacilities
and through

discussed
in Sec5.8 areandfree
of
Buck
Co.
(Walawender
1985;
Chern
1985) inzone
Kansas,
with
theRogers
charcoal
in
the third,
or
char
gasiíication,
to
Fuel isUnansvvered
added
the
open
topAbout
oftion
thethe
gasifier
should
Questions
If 175

tarry
gas
is(Walawender
produced
from
this
type
of
gasifier,
common
(Groeneveld
1980a,b).
After
results,
povvder)
or
slagging
(ash
isofvolatile
removed
asthe
aA
molten
slag) 13.
0 is5.8.3
high.
The
cylindrical
construction
is

easyof
tothese
íabricate
and a
Co.
ofand
Kansas
1985;
Chern
1985].
0.77
mTable
400/17 convert
the
air4.2
nozzles
(tuyeres)
(A m). publication
Early
workers
gasifier
is
the
“superíĩcial
velocity,
V 370
ofare
gas
calculated
University

of
West
Virginia.
Proíessor
The
tar
levels
400
from
a308
number
130
gasiíiers
shown
155
in
7(30
0.74
190
26
90
s ,”
was
developed
to
convert
high
fuels
(wood,
biomass)

-Air
grate
be
extinguished.
Improved
insulation
in
the
hearth
constrictions
and2.3
promise
to broaden
the range
of nozzles
fuels
that
and
in
Florida
(LaFontaine
1984].
It
is
also
related
to
the
more
of

the
C0
to
co
and
H
,
through
the
2 and H
2 Õconcept
2in
be
replenished
beíore
the
advancing
pyrolysis
íront
Another
important
sizing
5
VVater
Pump
practice
is
to
reduce
the

hearth
constriction
area
until
a
lowstratitied
Downdraft
Gasifier
5
gasiíỉer
using
this
principle
(a
centraỉ
air
nozzle
promotes
gasiíier.
Slagging
updraít
gasiíiers
for
biomass
and
coal
have
5.7
The
Imbert

Downdraft
Gasitier
permits
continuous
fỉow
for
otherwise
troublesome
fuels
in.)
internal
diameter
gasifier
to
produce
750
kw
of
power
400/20 Boudouard
where
200
it
passes
400
through
318
the
narrowest
145

370
part
of
the
153
gasification
7
16.
3.9
2.0
0.73
230
33
110
Bailie
used
the
gasiíier
in
tests
during
which
5-5.
(One
cubic
meter
of
producer
gas
weighs

about
1
kg
at
to
low tar
gas
and
thereíore
has
proven
to beand
the most
results
*NTPbe
reíers
to the
European
lower
practice tar
ofgasifier
correcting
production
gas volumeand
measurements
a higher
to a
can
gasified.)
The

Imbert
requires
high-grade,
Chinese
rice
hull
gasiíier
(Kaupp
1984b;
Cruz
water-gas
reactions
(Eqs.
4-7
consumes
allin
of
the
available
fuol.
-Char areaction
gasiíiers
is
the
“turndown
ratio,”
the
ratio
of 4the
Thus,

control
of
reaction
zone
3 is (Graboski
very
im- m/s),
portant
0
tar
gas
isand
produced.
However,
one
should
remember
recirculation
and
combustion
produced
in
been
operated
atthe
a level
very
large
scale.
causing

bridging
or
channeling.
Finally,
the
various
has
been
developedby
Syngas
Systems,
Inc.,
zone.
Although
the
units
of detined
V
length/time
(e.g.,
one
the
gasifier
operated
on
wood,
wood
pellets,
and
NTP;

thereíore
aonly
of
1position
g/m
corresponds
tothat
a 0 without
“normal
temperature
and
pressure”
of 0
°of
c ofoperating
andthe volatiles
s are
The
foremost
question
about
the
stratiíìed
downdraft
gasiíier
successíul
design
for
power
generation.

We
concem
ourselves
eííĩciency
over
a
wider
range
conditions.
Variables
not
given
intar
íigure
are
as
follows:
usually
hardwood,
fuel,
generally
at
least
2
cm
along
the
1984)
.
The

stratiíied
downdraft
gasifier
overcomes
many
of
8).
We
call
this
process
adiabatic
char
highest
practical
gas
generation
rate
to
the
in
the
stratiíied
downdraft
gasiíier.
A
number
of
mechanisms
hearth

dimensions
also
play
a
role
in
the
gas
production
rate
5.7.1
During
Introduction
oxygen
operation,
the
advancing
pyrolysis
front
atmosphere.
In
the
United
States
it
is
conventional
to
correct
measured

volumes
to
STP,
pyrolysis)
was
designed
and
marketed
in
the
Netherlands.
strata
are
more
accessible
for
measuring
compositions
and
1985)concentration
is (Bailie
being
extensively
andproduction
oxygen
shouldand
think
ofseveral
theoperated
supervelocityonasair

gas
oxygen
1979).
of
1000
ppm
orficial
0.1%;
design
concerns
charwith
and no
ashmore
removal.
As
the
charcoal
reacts
primarily
with
forms
of Subsequently,
downdraft
gasifiers
in the
this
o
smallest
dimension
20%

moisture.
During
the
of
the
Imbert
gasifier
andturndown
may
ultimately
be
gasiíìcation
(adiabatic
means
no
heat
After
the
combustion/pyrolysís
ofthan
and
hot
char
at the
lowest
a difficulties
= inner
practical
aiameter
OT

tne
luyere.
rate.
The
ratio
of
“Standard
temperature
andstabilized
pressure,”
77"F
(or
25
°top
c) 
1 atmosphere.
Tjseem
to
be
effective
in
stabilizing
this
position
and
they
are
3 1986).
(see
below).

moves
much
íaster
and
is
at
the
ofand
the
second
temperatures
within
the
bed
so
that
itwood
is
possible
to
compare
(Graboski
expressed
in
terms
of
gas
volume/cross-sectional
area-time
gasiíier

was
sent
to
SERI
in
Colorado
for
íurther
testing
with
nozzle
(tuyere)
and
constricted
hearth
downdraft
gasiíier
1
mg/m
is
1
ppm
by
weight,
and
we
shall
use
this
The

DeLaCotte
tar-recycling
gasiíier
(Fig.
5-15)
was
the
íirst
with
the
gases
in
the
char
gasiíication
zone,
it
eventually
chapter.
War
II, (see
stringent
speciíications
were
maintained
on fuel
theA3 basis
for
improved
gasifier

designs.
However,
it hasAhnot
flows
into
or
out
of
theof section).
During
reaction,
o
.Grate
shaker
nozzle
level
below),
the
resulting
hot
combustion
World
War
gasiíiers
varied
between
3
for
Imbert-style
=2sum

ofaII
cross
sectional
areas
the
air jet openings
in the
the
tuyeres.
= cross World
discussed
in
recent
paper
(Reed
1985a).
zone soin
there
is4-5(b),
no It
íirst
zone
of
fuel
storage.
must
modeling
with
empirical
CM

/mfine
-s),Onan
athat
gas
production
rate.
Itthe
isdesigns
called
a(m
15-kW
electric
generator.
More
recently,
the
gasiíier
shown
Figs.
5-4,
andobservations.
5-5
isbreaks
equivalence
inspecific
discussing
tareventually
levels.)
It
is

important
to
note
The
char-ash
dustadvantages,
clog
the
charcoal
beda
tar-burning
gasifier.
has
two
solid-fuel
chambers
and
gasreaches
aresults
very
low
and
up Biomass
into
a adust
We
believe
these
coupled
with

production,
which
wasdensity
carried
out
atsometimes
a number
of
licensed
been
widely
commercialized
at this
point;
the18
reader
must
sensible
heat
of
gas
iscan
converted
into
chemical
energy
of
A
ò
gases

(C0
and
H
0)
pass
into
this
hot
gasiíìers
with
uninsulated
V-hearth
gasiíiers
and
for
highly
2
2
sectional
area
ofthe
the throat.
The
updraỉt
gasifier
(Figs.
4-5(a),
5-3,
and
5-4)

is
widelỵ
then be fed
regularly
onto
of theis flaming
pyrolysis
superficial
velocity
since
actual
velocities
willThe
be
has
been
used
tothe
gasiíy
peat
by
Goldhammer
that
updraft
gasiíiers
generate
5%
to 20%
tar
(50,000-200,000

r--------------------1
9
and
will
reduce
gas
unless
the
is
removed.
combustion
thethe
side.
Fuel
pyrolyzed
in the
containing
all chamber
of
the ash
aspartially
well
astop
a percentage
the
original
1
simplicity,
may
ultimately

allow
thestratiíìed
downdraft
íactories.
balance
the
proven
reliability
of Proíessor
the
gasiíiers
discussed
above
the
fuel
gas.
This
results
inflow
cooling
the
gasdust
to
about
800°c,
aas
char
where
they
areon

reduced
toconceptually
theofand
fuel
gases
insulated
V-hearth
gasiíiers.
Vehicle
operation
used
for
coal
gasification
and
nonvolatile
fuels
such
The
stratiíied
downdraft
gasiíier
is be
bothclosed
andco
A = number
of
tuyeres.
zone,
and

the
second
zone
must
insulated
three
to
six
times
higher
due
to
the
presence
of
the
charcoal
of
Lowell
University.
The
gasifier
is
now
ppm!)
(Desrosiers
1982).
The
downdraft
gasifiers

of
Table
5-5
charcoal
is
supported
by
a
movable
grate
that
can
be
shaken
upper
part
of
the
fuel
chamber.
Pyrolysis
products
are
carbon.
This
dust
may
be
carried
away

partially
by
the
gas.
gasiíier
to
supplant
the
Imbert
and other
earlier
gasifiers,
against
the
promises
of íurther
the
stratiíied
downdraft
gasiíỉer.
temperature
at
which
no
reaction
isof
possible.
and
H 2 íorming
accordingto

Eqs. section.
(4-7)
and
(4-8).
This
procedure
requires
turndown
ratios
at
least
8:1,
charcoal.
However,
the
rate
production
mathematically
easier
to scaled-up
comprehend.
Quantitative
m
Kaupp
1984a,
Tablehigh
5; Fig.
75. of tar
above,
burner

The
Imbert
design
cannot
larger
because
and
the atar
high
temperatures
existing
atthe
the
throat.
A can
closely
being
used
by
Syngas
Systems,
Inc.,
to
produce
in Ash
amounts
at
least
an order
ofgrate

magnitude
lower
at Source:
intervals.
builds
up
below
and
be
I using
aspirated
out
theaortop
to the
sidebegin
combustion
chamber
However,
sooner
later
it be
will
to to
plug
the sizes
gasifier
so the
it
and
that

number
of
design
variations
will
grow
from
the
Ash
Out
making
the
need
for
insulation
and
proper
sizing
in
highAsh
pit
Finally,
there
may
be
a
zone
of
unreacted
charcoal

descriptions
and
mathematical
models
of
gas
flows
through
Char-ashthe
air
enters
at
the
sides
and
is
incapable
of
penetrating
a
related
term
isproducer
the
maximum
hearth
Bdescribed
innow
gas
generate

gas
to
test
gasload,
cleanup
systemsare
for
use
than
thestratiSed
updraữ
gasifiers,
and
new
developments
h , expressed
removed
during
cleaning
operaflow bí:
of removed
combustion
air in an
eịector, (Imbert
where they
burn
must
by shaking
or stirring.
gasiíiers

basic
downdraft
gasifier
here.
turndown
applications
apparent.
Although
enoften
*The units
J(th)
Btu(th) refer
tozone
the thermal
or chemical
energy
produced.
This can
below
the
char
gasiíication
through
which
thegineers
gas
the
bed are thus íacilitated.
large-diameter
fuel

bed unless
the and,
fuelwhen
size used
is increased
volume/hearth
area-h,
expressed
in
practical
with
its 750-kW
power
generator.
Although
much
of the testreducing
tarsand
into
theyears
100
toof
1000
ppm
level.
completely
at
high
have
a

provision
for
shaking
the
grate
to
Nevertheless,
several
exFig.
6
)
be
to electricity
with
an
efficiency
of 10%
40%,Fig.
so 18.©
the
electrical
energy
oversize
equipment,
this
can
be
fatal
in to1974,
gasifier

design.
Heat
Fịg.converted
5-5. Diagram
of crossdratt
gasilication
(Source:
Skov
1974. Used
with
proportionally.
The
tar
level,hearth)
while
Fig.
5-2.
(nozzle
andcharcoalgasitier,
constricted
gasiũer
GengasKaupp
1950, Fig.
75) Fig.
Fig.content
5-12. SEFìl
(Source:
Reedlower.
Publishing
Corporation)

(J orBtu)
beEnergy
proportionally
5-4. Imbert
Updratt
coke and
early
World(Source:
War II (Source:
1984a,
permission
ofoxygen
Biomass
Foundation,
losses
tend
towill
begasitier
independent
of1985b, Fig. 3.4. © 1985. Used with permission oi PlenumFig.
Fìg. 76)

Chapter 5

Gasitier Designs

2

a

b

2

c

2

d

e

w

w

w

m

m

MaU

27)

4034
Handbook
ofof
Biomass

Downdraft
Gasifier
Engine
Systems
32
Handbook
of
Biomass
Downdraft
Gasitier
Engine
Systems
Handbook
Biomass
Downdraft
Gasitier
Engine
Systems
42
Handbook
of Biomass
Downdraft
Gasitier
Engine Systems
Handbook
of
Downdraft
Gasifier
Engine
Systems

30
Handbook
of Biomass
Biomass
Downdraft
Gasifier
Engine
Systems
38Handbook
36
of Biomass
Downdraft
Gasitier
Engine
Systems

Gasitier
Designs
Gasitier
Designs
33
Gasitier
41
GasiíierDesigns
31
35
Gasitier Designs 39

43

Fig. 5-14. Observed and calculated temperature and composition in abiabatic char conversion zone (Source Reed 1984, Fig. 5)

temperature in the absence of solids. (Combustion with
air generates producer gas; combustion with oxygen
could generate synthesis gas.) The hot combustion
products (1000°-1100°C) are reinjected at the center of
the gasifier. One-fourth of the gas rises through the
upper chamber to assure pyrolysis of the biomass fuel.
The remaining three-fourths travel down through the
lower chamber containing the char produced from the
biomass in the upper chamber. The char is gasiíied by
reacting with the C0 2 and H 2 0 produced by combustion, as in other gasiíiers. The high-temperature combustion
chamber
may
permit
more
thorough
destruction of the tars; in any case, this gasiíier claims
to produce very low tar levels.

Table 5-5. Tar Content in
Product Gas from Downdraft Gasitiers

Throat
Specitic
Tar
Capacity
Diameter
Load

Content
Gasitier
kg/h
m kg/hm g/Nm
Kromag KS-12 15.0
0.12
1330
0.62
Kromag K-4
7.5
0.09
1180
1.90
Semmier
12.0
0.15
680
0.88
Danneberg
19.0
0.15
1075
0.70
Leobersdorier 36.0
0.42
260
1.20
TH. Tvvente 20.0
0.20
640

0.50
Forintek Canada50.0
?
?
3.00
Mini Gasitier
0.2
0.01
2550
3.00
------------------------------------------------------------Fig. 5-15. DeLaCotte tar recycíing gasitier (Source: Kaupp 1984a,
Source: Susanto 1983
FÌg.
133)
2

3

44 Handbook of Biomass Downdraft Gasitier Engine Systems


used, it Catalytic
will
necessary
to
use developed
either TIG a(tungstenand beBeenackers
have
gasiíỉer inert
that

5.9.4Susanto
Tar Cracking

ashown
later time.
unit results
has been
testedare
and
is in
in Fig.After
5-19.a The
forthoroughly
three catalysts
shown
production,
such
provisions
can
be
omitted.
gas)
or
MIG
(metal-inert
gas)
vvelding
techniques.
recycles
tars

internally
in
a
similar
manner,
as
shovvn
in
Fig.
in
Table
5-6.
The
variation
of
cracking
rate
with
temperature
Chapter
6
Recent work in Europe has íocused
on
5-16.
In this
the combustor
is
contained
centrally
inusing

the
is shown in Fig. 5-20 for a dolomite lime catalyst, a refinerỵ
All seals
mustcase,
be synthesis
made
gas-tight;
threaded
andmethanol
welded íittings
producing
gas for
making
6.5Instruments
and Controls
lower
(char)
section
of
the
gasifier
and,
thereíore,
has
very
silica-alumina cracking
catalyst, and a silicalite molecular
are preíerred
at all points,
and

gaskets
can
oxygen
and Gasitier
several
schemes
for exhaust-pipe-type
eliminating
tarsManutacture
and
methane.
Fabrication
and
little
heat
loss
(Susanto
1983).
Without
recycle,
this
gasiíier
sieve
type
catalyst.
The
gasiíiers
of
the past were crude,
be

used
if
necessary.
High-temperature,
anti-sieze
pipe
dope
In the Swedish MINO
process, the tarry
3
produced
mg/Nm
(approximately
ppm).
With aa
inconvenient devices. Today’s gasiíiers are evolving
shouldfrom
be1400
used
on all
pipe joints.1400
gas
an
oxygen
fluidized-bed
is High-temperature
passed
tHrough
gas/air
recyclewill

ratio
of 0.85,
the
tarsfiber
were
to betvveen
the
very 5.10
toward safer,
automated processes that make use of a wide
applications
require
ceramic
orreduced
asbestos
gaskets.
bed
of hydrocarbon
cracking
catalyst
at temperatures
Some ofSummary
the mild-steel components may suffer chemi- cal
6.1low
Introduction
level
of
48
ppm
of

tar
as
shown
in
Fig.
5-17.
range of present-day instruments and Controls. An extended
Silicone
appropriate
at temperatures
belowppm
300°c
950°
and sealant
1040°c, isresulting
in a gas
containing 10-100
of
A
large number
of gasiỉiers
been developed
the last
corrosion
in certain
parts. have
Corrosion
is likely over
to occur
in

Gasifier
construction
a relatively
simple
task
andisperíorm
can
discussion of the sỵstem instrumentation and control
and
rubber
or Viton
“O”
rings in
and
gaskets
will
The
high
degree
of tar is
destruction
these
two
units
due be
to
tar
(Strõm
1985).
century

using
both
experience
and intuition.
The water
most
areas where
water
condenses
or collects
since gasiíier
accomplished
in anytemperature.
well-equipped
shop
using
basic
sheet
requirements is found in Chapter 10.
excellentlỵ
room
Thepromoted
system
should
be
leakthe
high tar at
combustion
temperature
by the

positive
successíul
of thesẽ
hasacids.
beenWater
the Imbert
downdraft
gasifier,
often contains
organic
col- lection
is especially
a
D’Eglise
has
studied
the
kinetics
of
metal and
welding
assembly
techniques.
deed,
the
taskand
is
tested
before
startup,

asfrom
wellthe
asInafter
modifications.
circulation
of the
tarsinitial
upward
away
reduction
zone
which
produces
relatively
low
levels
of
tar
gas
from
problem
in
regions
such
as
the
upper
magazine
of
Imbert

Temperature
cracking
of
oilsthe generated
lower 6.5.1
so simple
waspyrolysis
possible
for
countries
ofat wartime
Leak-testing
is itaccomplished
by
plugging
the place
system
also
to the that
more
complete
combustion
that
takes
in and
the
uniíormly
high-grade
fuels.
gasiíiers, as

well(such
as in
wet-scrubber
temperatures
and
found
that
more
than
99.9%
of
these
oils
can
Thermocouples
assome
chromel-alumel
type K)systems.
should be
Europe to
onein.)
million
gasiíiers
just a few
pressurizing
it to 25almost
cm (10
of water
with in
a blower.

A
absence
of construct
solids.
In
these
instances,
the
Steel
should
be replaced
by
be
cracked
by dolomite
limeshortages
at temperatures
as1943;
low asGengas
500°c
used
to
measure
vaxious
gasiíier
temperatures,
especially
years
in
spite

of
wartime
(Egloff
We
are
in
a
new
period,
during
which
the
principles
of
thick soap solutíon is applied to all íittings and ịoints, and
corrosion-resistant
materials
such
as
copper,
brass,
epoxy
(Donnot
1985).
However,
these
low
temperature
compounds
below

the
grate,
as
a
check
for
normal
or
abnormal
operation.
1950).
Nevertheless,
a
number
of
new
materials
and
corabustion
Science
are
being
applied
to
develop
a
better
they are checked for emerging soap bubbles. Leak-testing
lined Steel, or stainless
as not

required.
Steel
are
cracked techniques
and rearranged
easily than
the
tars
Temperatures
grate Steel
should
exceedStainless
800°C;
higher
íabrication
have much
become
available
since
World
understanding atofthe
gasification.
New gasifiers,
such as
the
should
also be performed
as amore
Standard
test in

the
usually costs indicate
two to three
times
as
much
as
mild
íormed
at
high
temperatures
so
the
results
may
not
be
temperatures
abnormal
íunction.
Consequently,
the
War II, maintenance
and we shall call schedule.
attention to these improvements in
stratiíied downdraft gasiíier and the tar-reburning gasiíier,
regular
Steel
and

requires
inert
gas
welding
techniques.
representative
of
the
difficulty
of
gasifier
tar
cracking.
signal
from
the
thermocouple
can
be
used
by
a
control
sỵstem
this discussion.
promise to expand the range of usable fuels and to prõduce an
Copper
and brass cost íĩve times as much as mild
or
an alarm

even
cleanersystem.
product gas. Only time will tell whether this
6.4Sizing
and
Laying
out
the
Pipes
We
used
the
laboratory
sized
transparent
gasiíier
to
generate
Steel
but
can be will
joined
bỵ brazing or hardAccording to Kaupp (1984a), “the construction of a small
increased
understanding
result in cleaner, more versatile
When
designing
a gasifier,
it is important

to keep
the
pressure
typical
gasifier
tars
forpuriíication
testing
the system,
kinetics
of tar
Pressure
using an acetylene torch. Aluminum is particularly
gasiíier,
including
the
does
notcracking
require 6.5.2soldering
gasifiers at an acceptable cost.
drop
the system
as small
as apparatus
possible.
Because there
with
ainnumber
of catalysts
the

vulnerable toare
corrosion
its use
sophisticated
equipment
orinhighly
skilled mechanics.
It canare
be
Manometers
requiredintoalkaline
measureenvironments,
pressure dropsand
across
the
unavoidable
pressure
drops associated
withrepair
the gasifier,
the
should
be avoided
there.in producer
built in vvorkshops
comparable
to the auto
shops found
bed,
cyclone,

othergascomponents.
these
Fig.
5-17.
VVater andíilters,
tar contentand
(dry basis) versus(Usually,
recyde ratio (Source:
cyclone
separator,
the cleanup system, it is very important
in most third
worldand
countries.”
Susanto
Fig. 2.7. amount
©
1983. Used
with permission
the Beiịer
Institute)of water
pressure
drops
to particularly
only
a fewol centimeters
Some 1983,
wartime
gasiíiers,
the

stationary
ones,
to use adequately sized pipe. The pressure
drop associated
Legend:
pressure.]
The
manometers
are
available
as
tubes
íilled
with
contained
massive
but
fragile
firebrick
insulation.
We
are
Cracking
of Gasitier Tars by Several Catalysts
Fabrication
reíersTable
to
theof5-6.
construction
single

for
with
Standard
runs
pipesCatalytic
is shown
Fig. gasiíier
6-1 (Perry
Aof =a in
wood
colored
liquid
or,
more
conveniently,
bellows
manometers
íortunate today to have lightweight in- sulating materials
use
or
for
an
experiment.
Manufacture
commences
input also list the
1973). Engineering and plumbing
handbooks
Run Conditions
Tar gauge).

(such
Magnehelic
gi ve ofa
based asona Dwyer
spun alumino-silicate
thatBoth
are types
capable
B
air
inlet
when onedrops
undertakes
the construction
of a=number
ofasidentical
Concentration
pressure
associated
with pipe íittings
such
elbows
direct
reading
of
the
pressure
drop
and
can

be
equipped
with
withstanding
temperatures
up
to
1500°c,
far
beyond
the
Temp
After(C2)
Rate-k
Flow Rate c Residence
= product
Space Vel
Befor
units.
3
b
and
couplings.
.a
mg/Nm
L/S
limit
switches
that
will

alarm to silicate
warn when
preset
5.9.3
Thermal
Tarsound
Cracking
gas
outlet
requirements
of
gasiíiers.
Theanaluminoinsulation
kg/h
Time(t),
s
g/g-h
e(C1)
°c
c
1985Ơ,
Vol.other
I, p. 210)
On
the
hand,
gas
velocities
within
the

pipes
should
be
A
general
discussion
of
drilling,
welding,
and
assembly
flow
leveỉs
have
been
violated,
and/or
activate
control
valves
D
=
recycle
mg/N
Catalyst: Dolomite
also offers many
times 800°c
the durability
and heat-flow
0.34

0.33
9574
3597
2.84
Temperatures
above
rapidly
crack theresistance
primary
adequate
ứiat entrained
solids
willgas
be conveyed to their
procedures
to gasiíier
fabrication
and manuíacture
is
to
regulateoilsthose
flows. and
Also,
electrical
transducers
of íirebrick,
at to
a fraction
of
thearomatic

weight
(Perry
1973).These
It are
is
600 0.73sopertinent
pyrolysis
oleíins
compounds.
_E =weinịector
proper
point
of removal,
as
shownInin stead,
Table
6-1
rather
beyond
the
scope
of
this
manual.
shall
comment
available
that
convert
pressure

difíerence
into
an
electrical
relatively
inexpensive
and
is
available
in
a
wide
variety
of
compounds
continue
to
react
in
the
absence
of
oxygen
to
750
0.73
0.29
0.29
3169
1294

3.05
=as well as the wide
than
deposited
inside
the F
pipe.
upon
techniques
of íabrícation,
signal
suitable
readout
control
Processing.
forms.polynuclear
The 2-forto
5-cm- orcompounds
thick
felt
blankets
andeventually
vacuum
820 speciíỉc
0.73
0.28
0.27
make
18082
aromatic

2674
(PNAs)
and
6.95
combustor
range
materials
speciíically
applicable
to 0.24
gasiíiers.
preíormed
cylinders
(or
“risa
sleeves”)
are
particularly
When
laying
out pipe
connections
forGa gasiíìer
system, it is 6.5.3
960 of
0.73
0.24
8346
1113
8.26

=
soot. While
temperatures (above 800°C) can destroy
tais
Gashigh
Mixture
750
0.20to various parts1.07
recommended
for3169
in-high
sulating
the reaction
200also promote
zone. “Moldable
2.58
important
to allow access
that may require 1.04
rapidly,
these same
temperatures
reaction
Oxygen sensors 7537
have been developed
by ứie automotive
6.2 cleaning
Materials
of Construction
750 or adjustment.

0.40
2408
2.13
ceramics”
that come
as arapidly
wet putty
can bethe
shaped
corners
It is recommended 0.54
that new systems 0.52
with
char, which
in turn
quenches
gas toto800°c.
industry to measure the small changes in oxygen
d
and edges, and
thus
are
also very
be
assembled
with a large
numberfrom
of pipe
unions
íacilitate 2.02

Gasiíiers
are usually
constructed
commercially
Catalyst:
Si-AI
Catalyst
Therefore,
the time
available
for useíul.
tar4654
cracking in a bed 0.88
of hot
1.54 to available
18082
concentration required to control the air/fuel ratio for clean,
cleaning
out
theaspipes,
wellsheet,
as íuture
designWhen
modiíications.
materials
such
Steel as
pipe,
and plate.
choosing

charcoalplastics
is very can
short.
For
thisinreason,
a bed
of hot charSome
may
432 0.51
Finally,
be
used
certain
applications.
efficient combustion. They are relatively inex- pensive and, in
In
general,One
it isshould
better0.51
to use apossible)
pipe “T”select
with
a plugthat
rather
materials,
(where
are 2.02
not
be very
effective

in taracceptably
cracking 1313
as
was
originally
believed
plastic
pipe
will
períorm
up
to
the
boiling
point
of
432
1.54those
22070
1.83
principle, can be adapted to gasiíier systems for similar
than
to allow
for instrument
mounting
and other
readily
available
and0.56
use

off-the- shelf
equipment
and 1.57
(Reed
1982;
Chittick
1983).
The French
Croisot
Loire
552 an elbow,
1.20
5929
333
2.40
water,
is
more
Aexible
than
metal
pipe,
and
will
not
corrode.
íunctions (though this has not yet been done].
additions
atthat are available
materials

process
a paints,
tarry
from
415
0.48 in bulk quantities.
1.68 One should 2.19
4863
695
1.16a
Plastic liners, allows
such
as epoxy
can gas
sometimes
provide
avoid
fluidized
Automatic
bed
to
be
Controls
burned
íiưther
in
a
separate
chamber
343 exotic alloys, special

0.49 shapes, and custom
1.84 íabrication 6.5.4
2.40
4654
847
0.93
the corrosion resistance needed in critical areas, provided
Table 6-1.that
Gas
Velocity
Requirements
for Conveying
techniques
requừe
large
initial Setup 1.94
and
tooling costs, 2.54
287
0.51
5605
780
1.02
at
1300°c
(Bioenergy
1985),
resulting
in
a

final
gas
that
has
temperatures
are
not
greater
than
120°c.
The fact that an operator will be required for both largeanda
except
in casesCrystalline
where their Solids
use is justified. 0.91
very low targasiíiers
content
(Chrysostome
1985).
Catalyst:
1.68
8280
790
2.58
small-scale
is
a
fixed-cost
scale
íactor

that
naturally
Silica conveying
S-155e
causes
larger transparent
systems togasifier,
be íavored.
Automaticofunattended
The
velocities
in pipes
are
Smaller,
atmospheric-pressure
gasiíiers require
a min- imum
A laboratory
a modiíỉcation
the SERI
416
0.59
dependent
upon
the
natureotthecontaminant.
operation
is
thereíore
essential

to
the
economic
viability
406
0.39
1.40
2.57
15237
2303
1.35ofa
metal thickness of 20-gauge, with double-thick- ness
stratiíied downdraft gasiíior, shown in Fig.
5-18, has
added
Recommended
minimumgasvelocities
are:
small
gasiỄier
systems.
Automatic
fuel
feed
and
char-ash
469
0.34
1.47
2.70

15189
3359
reiníorcements extending a few centimeters (1 in.) around all
tar-cracking chamber in which small amounts of oxygen1.03
or air
removal equipment
are already welI-developed
for stoker-fed
Contaminant
Velocity 1.83
505 and íastenings
0.48
0.99maximum
11725
1.33
íittings
(Freeth 1939]. The
can be added to crack
the final trace3131
quantities of gas from
the
Smoke,
fumes,
very
dust
boilers
and could
be adapted to automatic
operation.
613

0.47light
0.89is 10
1.64
3930gasiíier
2.10
6.3
Methods
of 25305
Construction
mild-steel
Service
temperature
480°c
gasiíìer,
in the
absence of the quenching
action of
the
m/s
812 (MASEC). Although
0.42
0.81
1.50
9184
1075
A gasiíierWe
is have
built
much like
aconcentrations

water
heater, of
and
the2.64
same
(900°F)
the
metal
temperatures
encharcoal.
measured
tar
50-500
ppm
Dry medium density dust (savvdust, grain)
methods
construction
are chamber.
used. The
workshop
be
countered
in well-designed
air gasiíiers
exceed
at
the exitoffrom
the cracking
However,
thêshould

difficulty
Average
overdoanot
20usually15
cracking catalyst, and (c) silicalite cracking catalyst
Fig.
5-19. Tar crackingtemperature
apparatus (Source: Reed 1985c)
equipped
with
tools
for
períorming
tasks
such
as
shearing
the
point
mild Steel,Rate
certain stain- less steels or
of maintaining a large chamber at temperatures in excess of
m/s
cmsoữening
length
ofofturnace.
sheet metal,
cylinders
cones,
drilling,

riveting,
inconel
may
give
the
extra
temperature
resistance
necessary
900°c
caused rolling
considerable
lossand
in gas
quality
at this
scale.
Heavy
dust
(metal
turnings)
25
calculated from k = -ln(C1/C2)/t
grinding,
painting,
sawing,
tube
cutting,
and
pipe

threading.
for
critical
areas
such
as
the
grate,
hearth,
or
nozzles.
Perhaps thermal cracking alone is practical in much larger
m/s
a

b

1.03 kg of dolomite lime contained in 20 cm length of 5 cm i.d. stainless pipe. Bulk
An
torch
is valuable
for decomposes
cutting and weld- ing
(Reed 1985c).
density Kaupp
= 3346 kg/m ; void volume = 0.25 cmgasiíiers
/g.oxyacetylene
Dolomite
limestone
to

Source:
dolomite lime in1984a
the range 600-1000°C. Particle
tasks,size
but 5anmm.
arc welder is preíerred for mild-steel
Si-AI
cracking
(Davison
Chemicals,
Gr 980-13)
510
g sample,
bulk density
Fig.
5-16. Gastíier
with internal tarcatalyst
recycle (Source: Susanto
1983, Fig. 3.2.
© 1983.
When
aluminum,
stainless
Steel, or=
7655
kg/mof the
; void
volume = 0.85 cm /g. Particlevvelding.
size
1mm

d
X
5
mm
long
cylinders.
Used
with permission
Beijer Institute)
inconel
Crystalline silica catalyst S-155 (Union Carbide)
543isg charge; bulk
c

3

3

d

3

3

e

Gasitier Fabrication
and Manutacture
Gasitier
Designs 45 49

46 Handbook of Biomass Downdraft Gasitier Engine Systems
48 Handbook of Biomass Downdraft Gasitier Engine Systems
Gasitier Designs 47


Finally, we can look forward to gasiíier systems of the
íuture that will use inexpensive microprocessors to integrate the signals from these sensors into the

and unattended operation of highly efficient
Chapterautomatic
7
gasiíiers, making gasifiers as simple to use as a car or

Gas Testing

home íurnace.

Pressure drop
due to triction
Based
on
of Producer
Gas
pipeand Its
7.1 Introduction
Ap> 7.3Description
õ
Liquids:
-----o
Contaminants

It is relatively simple to build a gasiíier and operate an engine
<
L
clean
Steel
for a short time. However, the commercial suc- cess of
7.3.1
The Gas
Analysis
Ap'
gasification Turbulent
ultimately depends
reliable
regionon long-term,
raw gas analysis from a recent SERI test of corncob
Gases:
---- (P )A typical
Lb/ft
at 1
operation of gasiíier systems. Many gasiíier systemsL have
Centipoises
gasification
is gìven in Table 7-1. This analysis includes
íailed
after
less
than
100
h
of

operation
because
of
tar
buildup
Weight Mass
Diam
volume concentrations
of each major chemi- cal constituent,
atm.
velocity,
ineter,
either the systemflow,
or the engine. Desừoying an engine is a
Vcphysical contaminants ofTemperature,
as well as the
the gas. The energy°c
thousands
actua
Pg= absolute pressurel
,0gas
. 1can
6 be calculated from the energy content
costly
method for determining whether a gas is sufficiently
content
of
the
thousands
l for engine operation.

of gas,
J
clean
A quantitative knowledge
ofatmospheres
gas
1
of the components
using the high or low heating
tb/hf
lb/(h)(ft
)
■lò "
insid
w
-100- values (HHV
quality and cleanliness is necessary for the designer,
0for each gas, as shown in Tables
or
LHV)
7-1 and 7-2. The
lb/in
.
in.
e
[
DI
-user
100,000
0

2n
developer,
of gasiíier equipment.
-50
water
'o
diamebuyer, and 50.00
LHV
also
can
be
determined
graphically
from
Fig. 7-1.
ì
■1
10,000
0 simple -and
/ft. pipe
pipe 50
4~
ter,
This
chapter will describe
inexpensive
tests ofỊ/ft.
the 7.3.2
V—
Gases

Particulates
14
1000
20.1 -1
100
- these500
in.
60- and charcoal
500
physical and chemical0,0
properties of
Using
m levels reported for wood
^_ioon Some particulate
0 pioducer5gas. 50
820
1suitable
0tests will- allow One to
determine
whether
the
gas
is
gasiíiers are listed
in Figs. 7-2 and 7-3.
D
00
o
5 -10
50 :

for its intended
purpose.
2000
5
10
5
10t
In order to remove
particles with the appropriate equip- ment,
03
0
0
- their nature and size dis- tribution.
10
it is necessary
oto know
.5
100 1000
10.5
r
20
0
/
1
Particle size distributions
shown in Fig. 7-4, Table 7-3, and
5
4
5
0

200-r30
-30= by mechanical screen
01 0
500
Fig. 7-5 were
obtained
separation
of the
2
0
0
2
0.0
4
40cyclone
contents
for
SERI
and
Imbert
tests.
The
results
of
5
-30
300“ -250
0
1 aie plotted
ị60 in Fig. 7-4 on log probability

2
both
tests
paper
for
7.2Gas-Quality Measurements
and0
1 /■
.803
displaying the distinctive slope common to
0.01 0.5 ease of analỵsis,
-9
0
Requirements 0
0
100
0.1
most
fine
powders
produced
by fragmentation.
0.00
-1
400- 200
20
During gasifier
system development, one may need to
.
200

5
r
8
be able to measure: 0
The potential particle-size range of a wide600variety- of particles
0
500
0.0011
150
0 volume percent of/r -co,
and
their
characteristics
are
shown
in
Fig.
7-6,
• Gas composition: The
C0
,
H
,
H
0,
0.05 2 2 2
-1
0
52 and higher hydrocarbons, and N 2 to calculate the
0.2

CH 4 , C
700
5
/0.0005 ^
gas energy content or to analyze00
gasiíier :operation.
0
-7/
:
800 J -.10
• Gas eneTgy
content: Can be calculated
from gas com1
r-0.01
0
1000
— 0
0
'5
0.1position, or it can also
without
2 be measured calorimetrically
-9
Ị / have an energy
the need
The gas must
0
“ to know composition.
0.0001-50
03 (1000 r0.Q05

content
4
MJ/Nm
Btu/scf) for most
8 greater than
0
c
3
-7
0.05applications. (See Appendix
for deíìnition
of scf and Nm .)
o í6
-1
Table
7-1. Composition of Producer Gas from Corn
- of tars: The
• Quantity
q
or- ganics in
0.00005 -= Cobs after Cyclone Separation
0 quantity of condensible
6
-0.001
-5 is a measure
>
raw gas
ofL 1 gasiíier
and
2

-0
0
,L 3performance
Physical
-4 whether the gas can be cleaned.
0.002-Composition
determines
Above 5000
3
a
_ r
Tarcontent
1300mg/m3 1300ppm
3
-30
„ >Mercury
mg/Nm
-3 tars, the gas is difficult to clean
C up1 and is suitable
0.00001-3
Particulate
330 mg/m
330 ppm 3
0.001-T*
only for close coupled direct com- bustion.
Gas cleanup
f- 0.0005
Ash
content
of

particulate
30
mg/m
0.023
equipment should reduce the tar level to -below
5 10 mg/Nm . 0.000005 ^
30
ppm
• Quantity and size of particulates: The nature
and quantitỵ of
-0.0001
H2O
7.1 wt%
71,000 ppm
char-ash and soot entrained in the gas stream can help to
Fig.6-1. Piping flow chart (Source: Adapted from Perry 1973, Fig. 5-27)
Chemical
Composition
•
design tiltcrs. Particles larger than 10 |iin
be removed
z must
0.00005
CO 0.0119 Vol% X 322 Btu/scf
= 61
to a level below 10 mg/Nm 3 for engine applications.
l ‘4
CO2
14
Vol%

X
0
• Water content of gas: The vvater content of the gas helps to
0.000001^
H
17 Vol
Btu/scf
=
55
calculatc cooling requirements.
-Vol%%XX 325
CH4
2
1031
Btu/scf=
20
L
N
48
Vol
%
X
0
_
_
_
2
-0.00001
136
0.005"

b
Dry Gas (HHV) 136 Btu/scf (60°F, 30 in. Hg
Dry)
1 Nm of gas vveighs about 1 kg, so that
1 mg/Nm = 1 ppm
The gas heating value may be
F

G

3

01 6

2

2

r

.

-

Ui

L

2

a

3

3

b

50

Handbook of Biomass Downdraft Gasitier Engine Systems

Gas Testing 51


along with
theboth
equipment
appropriate
for separation
each
removed
from
the suríace
and interior
of the char of
particle
sizemotion
range. of the hot gases. The char particle cracks and
by

crumbles as carbon is converted to ash.
It is important to distinguish between the various forms of
The term char-ash reíers to the black dust that falls naturally
particulates that result from biomass combustion and
through the grate in a downdraft gasiíier when gasiíication is
gasiíìcation. Starting with full-sized biomass fuel and 0.5%
as complete as it will go. Char-ash is produced during the
ash, we can use this ash as a tracer to follow conversion in the
final breakdown of the charcoal mechanical structure as the
gasiíication process.
charcoal reacts with pyrolysis gases. Chai-ash from downdraft
gasiíiers still contains 50% to 80% carbon (Fig. 3-3), which is
enough carbon to give char-ash a black color. Char-ash
usually is collected below the grate or in the cyclone
separators.

If the finecombustion
char-ash from
downdraft
gasiíiers
Although
and updraít
gasiíiers
leaveis a about
white 20%
ash,
ash, then this
represents
a 95%
mass this

conversion
of the fuel
downdraft
gasifiers
do not
produce
white mineral
ash
since we there
startedis with
0.5% ash
biomass.
Wethe
canfinal
also see
from
because
no oxygen
present
when
charcoal
Fig. 3-3 that
it isFreshly
desirable
to keep charcoal,
the char larger
than it500
breakup
occurs.
produced

just after
has|
im (0.5mm)
in thepyrolysis,
gasiíier toisboost
Also, particles
íinished
Aaming
onlyefficiency.
slightly smaller
than it
under 500
|im should
have completed
taskthrough
and should
be
started
out and
not be able their
to pass
the grate.
removed
as thoroughly
as possible.
As
gasiíication
of the charcoal
proceeds, carbon is

Fig. 7-5. Residue curve for the screening of Imbert generator gas (Source: Gengas 1950,
Fig.
)

88

Although the unconverted carbon found in char-ash represents
an energy loss, it also has several benefits. The final ash from
combustion is less than 1 |i.m in size and can be captured only
in expensive bag house íilters. The char-ash holds the ash in a
10 um matrix which is captured by cyclones. The char-ash
may have considerable value as a charcoal or as a soil
conditioner.

Fig. 7-1. Nomogram for lower heating value of producer gas (Source: Kaupp 1984a)

Char-ash particles smaller than the cyclone separator’s cutpoint pass through the cyclone separator. Smaller particles
normally are higher in ash content, as shown by Fig. 3-3.
Higher ash content is more abrasive; however, solids smaller
than the oil film thickness do not cause major engine wear.
Ash that has been sub- ịected to slagging is much harder and
Totalsoot
more abrasive than nonslagging ash, which crumbles
easily.5

quantity o o

Fig. 7-4. Imbert and SERI downdraft parỉicle size distribution of producer gas char dusts

o

All biomass contains some ash (typically a few per- cent), but
Removed
some fuels, such as rice hulls or MSW, can
by1 <
c Tarcoal
m
c
cyclone
gas o

Total soot
quantity
y'
)
b
3
C
Removed
Component
Symbol HHVb (MJ/Nm3) HHVC (Btu/scf)
LHV
(MJ/Nm
)
LHV
(Btu/scf)
o
c
by
cyclone
o

>
Dd
gas
o
Hydrogen
H2
13.2
325
11.2
275
ọ
Carbon
CO
13.1
322
13.1
322
ọ
monoxide
<
Methane
CH4
41.2
1013
37.1 - -1—
913
0
20
40
60

80
100
20
40
60
80
1 Btu/scf = 8.26 kcal/Nm
=
Lo
Load Nm3/h
ad
40.672 kJ/Nm Standard
conditions,
0°cfor and
mm
Fig. 7-3. Dust concentration relateơ to the load in wood and charcoal gas generators
Fig. 7-2. Dust concentrations
wood gas760
generators
of various makes as a tunction of
load (Source:
1950, Fig. 87)
(Source: Gengas 1950, Fig. 86)
Hg
DryGengas
Slandard
conditions, 60°F and 30 in.
Table 7-2. High Heating Value and Low
c
3

<
Heating Value of Gas Components
1

/V

3

a

3

b

c

52 Handbook of Biomass Downdraft Gasiíier Engine Systems

Gas Testing 53


Approximate
be obtained
by comparing
the
Table 7-3. Analysis of Wood Gas Dust
distribution asresults
well can
as the
total quantity

of particles.
volume
of
sample
required
for
a
particular
depth
of
color
Relatively little iníormation is available in the litera- ture
Particle diameter,
(Ị

deposit
as 50%
grey measured
on a Standard
grey scale
(Gengassuch
1950),
so complete
gas cleanup
design necessitates

0.0001

0.01
Over 1000 |im (1 nim screen) m*»l

1.7
0.0
256
3 0.14
such
as that used
for smoke testing
(Dwyersize
1960).
Tests at
measurement
or knowledge
of particledistribution.
ẹ
1 1
■M on
1 Va T47-mm
1 1 11 1 1 1 fíilter
SERI
found that
a color of 50%
grey
1000-250 Ịim
24.7
1250
Particle-size
measurement
is
discussed
further

i'
V
I in
10 lóo
IOÒOdisc,
—/—■
250- Equiva
102
um
23.7
taken
ửom
a
Standard
grey
scale,
10,000
I
3S
I
20
I
10
Section
7.8.
ì'
1
I
11
J

lent
Ẳngstròm
25001 approximately
625
102 -75
um
7.1
represented
0.12I
0.5ỉ
sizes
units Â.
I to40
12
I mg
6 2Ó|
Iof collected
3
i’
Theoretica
75 - 60 )im
8.3
contaminants
(Das 1985). A quantity
ofscreen
gas for chemi- cal
U.S.
l Tars
mesh
mesh

I „1
Under 60 |xm
30.3 7.3.3analysis
can be
collected at the same
time I..I
as the
sample to be
Initial biomass pyrolysis can produce up to 60% VB
“wood oil,”
Losses
4.2
used for physical analysis.
composed
of
the
monomers,
oligomers,
and
fragments
of the
100.0
Gas
biomass
polymers
cellulose,
hemicellulose,
and
disp
WaterTechni

content
3.2
erso
ids Att«rb«rg
lignin.
Subsequent
high-temperature
cal
def
or
Sampling
Ash content,
10.6 7.4.2crackingIsokinetic
inition dry sampleIntarnoltonol Std.
(over 700°C) of these large molecules results mostly
Isokinetic
(equal
----------------(—(V—I
gas-velocity)
conditions in the flow chamber
Clo*»tflcotion
LossCommon
due to burning, dry
sample
15.7
- - -Smog - in gas, but also
gyy.
polymerization to form 5%
to 10% of heavier
atmospheri

and the sampling
tube
should
be
ensured
where particle sizes
Clouds
and
fog- 'Rainl*Fertilizer,
Content of
11.0
aromatic
molecules that are similar to coal tars.
c Fe2C>3 in the ashes
—Rosinpolynuclear
qroundparticle- size distribution will not
exceed 10 |iim. Otherwise
smokeUp- to 20%—
of these
tars and oils can be carried through with
Content of SiC>2 in the ashes
7.7
limestone*
H—Oil -Coal
dusĩ
be the same
in the chamber and sampling tube. The design of
-dusts Metallurgical
smokesthe gas from updraít gasiíiers.
Source: Gengas 1950, Table 2-9

sampling-tube
parts and their placement within the gas stream
and
fumes
^mmonium
cloride^Cement
In
downdraft
gasiíication,
oxỵgen
is
available
toFigure
burn these
-Beach
sandare
shown
in
Figs.
and
7-9,
respectively.
7-10
dustfume
L 7-8
lconcentraĩor
oils during
pyrolysis.
Although
flaming

pyrolysis
burns
contain 20% ash or more. During ílaming pyrolysis -Carbon
of the
blackshows
velocity
streamlines
for
a
sampling
tube
in a most
flow
■H
mist
sultụric
Jof
the tarsPart
and“a”
oils,
0.1% toisokinetic
1% (depending
on the
original biomass, the organic molecules break down tomist
form a
Flota1ion
ores-H
chamber.
illustrates
conditions;

thatgasiíier
is, the
—•*'
Typical
h—Paint
pigments
design]
can
be
expected
to
survive.
These
tars
and
oils are
very particles
finely divided soot (carbon black), such as Coll
that
streamlines
are
equally
spaced
within
the
duct
and
tube.
In
H—t-Ground

talc
oxide
fume-*iin the Plant
oida
troublesome
gas-processing
system
and duct
the engine,
so
seen and
in oil or candle flames. ‘Zinc
Soot
“b,”
sampling-tube
velocity
is
less
than
in
the
(indicated
-Spray
"lế
l
sp removed by scrubbing.
they
must wider
be ores
thoroughly

gas are port
particles
much
dried
by the
streamline
spacing in the tube), and
silic
Fig. 7-7. Static tap sampling
(Source:smaller
ASME 1969,than
Fig. 1) char-ash particles
a
Pol
(ordinarily less ứian 1 um). The soot is so fine that it can Atmospheric
be
milk
proportionately
more
gas
must
around oftho
than
Tars
occur
mostly
as
a
mist
or

fogflow
composed
finetube
droplets
dust
len
Ait_
OUST- - - -1—H
------------------------ex- pected to pass harmlessly with the gas and burn in the
Hydraulic
nozzle
drops^
through
it.
of (see
largeFig.
particles
impedes
that may
be However,
less 1—
than 1thein inertia
diameter
7-6). Tar
mists
* h-Nebulizer
H
The temperature, pressure, and moisture content of gas at the
dróps-*
►*-!+

►»Seatheir
salt
nucleH
engine without harm.
being
carried
by theinto
around
tube.
continually
agglomerate
largerdeũects
droplets
and the
tend
to
Lunq
damaqinq
-gas that
nozzle must be accounted for when designing a sampling
n
h-Nebulizer
dróps-*
I,
Pneumotic
,
i'
Large
particles
in

line
with
and
immediately
upstream
of
the
saturate
and
coat
solid
particles.
If
not
removed,
tar
mist
Carbon
monoxide
is
unstable
below
700°c
and,
given
enough
train, and measurements should be reduced to Standard
dusttube
T I continue
nozzle en- gine

uclei
sampling
ílight intake
into the
tube.
forms deposits
that causetheir
valves
andHence,
other
dropsl
time,
will decompose
in the presence
of certain
pectroformetj
conditions.
For average
samples,
thecatalytic
test
-Sieving
- the
-Impmgersproportionately
more
large
particles
exist
in
tube

than
moving
parts
to
stick.
Beíore
a
gasiíier
is
considered
suitable
metal
surfaces
carbon the
dioxide,
according
duration
shouldtobeform
long carbon
enoughand
to average
reading
over
at
>•-flow
in the chamber.
Theit opposite
holds that
true one
where

for operating
an engine,
is imperative
test tube
the
Ultramicr
to
the reaction
least
one
cycle
of
the
equipment
being
tested—
for
Metho
Elutriati
ovape'
'
velocity
is
greater
than
the
velocity
in
the
chamber

(Fig.
7producer
gas
for
tars
and
particulates.
ds 2for
instance,
theCOfuel-feed
—> c + C0 2 .cycle, the scrubber
(7-1)
on— UHracen1
particl
10(c));
i.e.,
large
particles
are
underrepresented
in
the
tube.
Sedimentat
Service
cycle. ForK-Xsnap samples
or
Permeability *- -Visible to eyerifuge
e cycle,- or the shaking
This

as Boudouard
carbon,
is
Adsorption
*— --------NonisokineticsamplingerrorisplottedinFig.
7-11.
We can see
where carbon,
a ừansient known
phenomenon
is being observed,
then-----------the
"Machine
tools
1
--Scanners
ray
slippery
to the touch and nonabrasive. Below 7.4Gas
Sampling
(micrometers,
Light
scattering
*
that for
under 10 |im-particles,
thecalipers,
concentra- tion
most rapid sampling method and small samples should be
etcerror is

about
500°c, the reaction is very —slow.
- Ultrosonics
- - - - - within ±10% over a wide range
of sampling
velocity from
used.
Setting
chambers(vcry
limittd
induitriol
applicotion)
Sample
Ports
Normally, Boudouard carbon does not form in 7.4.1half to-+—
double the gas velocity for a velocity ratio U s /Ug
Hot, raw gas
emerging
gasiíier
will contain
tar,
gasiíiers
because
thefrom
gasany
cools
quickly
through
Centritugal
A

temporary
or
permanent
port must be provided at each point
between
1/2 and 2.
Types
of water
char-ash,
soot, and
vapor, and it is relatively simple to
Cloth
this
temperature
range.
on
the separators
gasiíier where samples are desired, as shown in Fig. 7collectors
gos
—
“'■''"'7*--Common
air separator of a gasifier
In- practice,
the high
efficiency cyclone
measure
these quantities in a small sample of raw gas. After
cleaning
7, íillers"
such as downstream from the cvclone and beíore the burner

Char-ash,
because of its high mineral
system will remove
most particles
larger than 10 |im, so for
the gas
has been cleaned and condi- tioned, the measurements
equipme
—High
efficiency
air
filters
■«+»--ịI
or engine, as well asMechanical
at eachseporalorst*
stage along the gas cleanup train
content
and abrasive potential, is the main cause
Thermal
of
the smaller particles remaining
in the gas stream, the error
become more difficult. Im- purity levels are much lower,
so it
precipitatio
when it is desired to determine the effectiveness of each
engine wear in engine systems and understandably is a main
n
-Electricaí
due to nonisokinetic sampling can be ignored.

is necessary to handle much larger gas samples in order to
precipitotor
system component. It is important that the gas sample is
focus in gas cleanup. Similarly,
soot
and
s
Rey
l nonisokinetic sampling condi- tions
accumulate a measurable-sized
sample.
The
principles
l
nol
The
sampling of
error
In
representative
the for
gas
ũ at each point. The port and tap may
Boudouard
carbon
are
inherentlỵ
ash
free,
ds

ộ
Terminal
al
núming.
ofmeasure- ment remain the same,
but the "measurements
Set
also
canbe be
tar' premature
mists and condensation
other very (see
fine
need to
heatneglected
traced to for
prevent
gravitati
r
nonabrasive,
and possibly
lubricatDespite
their
tlm
9
oỉ
require more
time to accomplish.
g
onal

aerosols.
In
fact,
the
sampling
port
of
Fig.
7-7
can
serve
as
a
below).
L
small
size and difficulty
vel of capture, they
settling**
convenient
10-)j.m
coarse
inertial
preíĩlter.
The
particleThe
physical
analysis
of
producer

gas
is
based
on
the
weight
are not seen
as a signiíicant factor in engine wear.
/for
Permanent sampling ports should be closed off with gate or
sample probe of Fig. 7-9 tends to accumu- late impacted
of tar,
particulates, and water in a measured quantity ofgas.
spheres\
ball valves, which provide a straight through passage. Needle
Typically,
the
largest
particles
that
pass
through
the
grate
can
specitic
\
large-particle deposits and eventually clogs, so it should be
Thereíore,
a positive-displacement

gas- testing meter (such as
valves and sill cock type 4water
3 2valves
654
2I'Ỹ be avoided,
be extracted mechanically,
for
instance,
with
an
auger.
3 periods
23should
adjusted
to face downstream
during
that it1is- not in
those made by Singer,I
Rockwell, and the American
Gas
5
3
2
'?
5
3 2much
'9
n
T
I

I
i_L-L-l--l
since
of the materialỊbeing
sampleđ
will deposit
within
Subsequent
to
that
step,
removing
the
Particle
1
use.
Association)
should be ạ
available for calibrating flowmeters,
t
diffusi
the twisted passages of these
types in
of valves.
I is the2 principal
10
io"*^
suspended small particles
problem
in gas

'ộ
6
5
4
3
654
3 2
n ponents.
pumps, on
and coef
similar comAn analytical balance
2
7*
„ 654
3 1
26541 3 2 !
cleanup.
The particulates
in' 'Table
7-1
n
T
,
I
lui!
Ị
I
'
^HìH-v-r-ĩ
' ' 1 1 I Vmrị

capable ficientĩ
of weighing to r
Ivũiseparator,
‘
were collected after theaccurate
cyclone
which
caught
0.4 56 8ị
|‘
2 3measurement
2tars
1 mg is also required for0.0001
of
and
68 i 34 56 81 2 3
3 4 00
56 0 1are composed
50% of 50-|am particles. These smaller
particles
Particle diometer,/i
particulates.
1
of very fine char-ash, soot, and tar mists.
Con,act

:

1

1

1

654

10

11

5

6541

1

1

456

The type of gas cleanup equipment required is deter- mined
by the particle sizes that must be removed, and thereíore it is
important to determine the particle-size

Fig. 7-6. Characteristics of particles and particle dispersoids (Source: Adapted from Perry 1973, Fig. 20-92)

54 Handbook of Biomass Downdraft Gasitier Engine Systems
56 Handbook of Biomass Downdraft Gasitier Engine Systems

Gas Testing 55

The isokinetic flow rate can be calculated as
2

2

Qn = Qp (D n /Dp )

where
Q = flow rate, D

(7-2)

= diameter.
The subscripts n and p reíer to nozzle and pipe, respectively.
The flow rate of a dirty-gas stream can be measured irrespective of temperature and molecular weight of the gas by
using a balanced-tube, null-type apparatus. Such a system in
eữect measures chamber flow by col- lecting a portion of the
gas ũow through a sampling tube, cleaning it, and measuring
it. The mass flow through the entire chamber is then
calculated, using the ratio of chamber area to sampling tube
area. Measurements are made once the velocity in the sampling tube has been adjusted (via a vacuum pump in the
system) to be equal to that in the flow chamber. Velocities
vvithin the tube and chamber are equilibrated bỵ using a
differential manometer to balance the static pressures for the
tube and chamber. The best placement for the probe vvithin
the chamber can be checked by testing the flow proíile across
the chamber. The probe should be located where the flow is
average for the chamber. Where necessary, flow straighteners

should be used to ensure accurate readings. Balance-tube,
null-type sampling, without gas-cleanup equipment, can be
used for clean gas.

7.5Physical Gas-Composition Testing
7.5.1

Raw Gas

Sampling train options for measuring the range of levels of
tar, char-ash, and water are shown in Fig. 7-12, and gasifier
test-train component options are presented in Tables 7-4, 7-5,
and 7-6.
Certain basic procedures must be followed whenever
sampling producer gas—be it for tar, particulates, heat
content, etc.:

(b)
Notes:
2.
The area upstream of this 90°
sector
shall
be
free
of
obstructions between planes AA and B-B.
3.
No portion of probe shall
proịect upstream of nozzle

entrance within a distance from
nozzle centerline of 15 cm or 5
nozzle diameters, vvhichever is
greater.
Fig. 7-8. (a) Typical holder for flat round tìlters and (b) recommended design for sampling
nozzle tip (Source: ASME 1980)

Fig. 2.9.

©

1975. Used with permission of Pergamon Press)

Gas Testing 57


being tonoxious,
off or
also The
can gas,
be used
measureshould
gas be
floweither
and burned
to collect
returned to the pipe downstream from the sam- pling point.
moisture and tars and particulates over a measured
time.The gas should be cleaned.
The gas should be dried.

Figure 7-12(c) shows a system train for measuring gas
flow and tars and particulates.

shows a Setup for measuring
particulates and tar, or moisture, or gas composition,
Figure 7- 12(a)

or gas production rate.
Figure 7- 12(b) is a Setup for continuously measuring change
in vvater content and change in heat content. It

The ball valve at the sample port (Fig. 7- 12(a) and (c))
permits changing the íilter disc without danger of
releasing gas or admitting air. The íilter holder in
Fig. 7- 12(a) and (c) must be maintained, by electric
heating or locating close to the hot gas pipe to keep the
íilter hot enough, above the water dew point, typically
80°c, to avoid water condensation in the filter disc.
The desiccant-drying section (Fig. 7-12(a)-(c)) should
be constructed so that it can be disconnected for weighing. We have found that an indicating desiccant assembly can be íabricated by containing the desiccant
between two glass-wool plugs in Tygon or glass “U”tubes (Fig. 7-12(b]). (Drierite is a commercial forin of
anhydrous
CaS0 4
containing
cobalt
sulíate,
which
changes from blue to pink when it becomes hydrated.)

Fíg. 7-11. Errors in concentrations of 5 and 10 ịim particles (Source: Strauss 1975, Fig. 2.13.

© 1975. Useơ with permission of Pergamon Press)

Table 7-5. Additional Components for Continuous Gas Quality Test Train

Function
Sample Port

Specitications
1/4 in. FPT Fitting
1/4 in. MPT —>1/4 in. tube compression

Manutacturer
Common
compression
tittings (e.g., Swagelock)
User íabricated
Hygrometer
Cross íitting bushed down to accept 1/4 in.
Sampling
too low
(c) Sampling velocity too high
Dry Bulb wét
tubing Water reservoir
in bottom velocity
2 hole stopper
with
Bulb
thermometers Dry bulb bare
Wet bulb wrapped with vvicking that dips into water
reservoir

Fig. 7-10. Gas stream lines at the entrance to sampling probes (Source: Adapted from Strauss 1975, Fig. 2.12. © 1975. Useơ with permission of Pergamon Press)
Dryer
User tabricated
Indicating desiccant Drierite or silica gel in a Container large
enough for several hours sample time 1.5 cm dia X 40
cm U-tube Table 7-4. Components for Raw Gas Contaminant Test Train
Requirements
Item
Price
Rank (1
Pump
Whisper (User
moditied)
Aquarium
pump modified for suction and
=Lowest)
Tar-only
measurements
titting
Service
capable
of 50permit
in. WG,any
0.01suitable
scfm
Sample Probe pressure
1
with pipe
thread
access

Tar
and
particulates
require
tubing
with
90°
bend
2
Flow Meter
Floating
ball the
rotameter—RMA
Dwyer
íacing
gas stream
Ball Valve 1/4 in.
—
Shut
Off
Valve
Burner
Diffusion flame non-mixed
See Fig. 7-16 or user
tabricated
Filter Holder 1/4 in.
47tubing
mm reusable
holder
with 1/8 in. ID opening

Polycarbonate
1
Chromel-alumel
thermocouple
Readout
Omega,
Aluminum
2 etc.
Stainless
Table 7-6. Additional
Components for Condensible Collection Test Train 3
Glass íibers 99.9% efficiency at 0.3 |um
—
Filter Discs
Gas
Sample Purpose
Hand operated rubber bulb
Item
Price1 Rank
Pump
Plastic piston pumps (36 cm/stroke)
3
Gas Dryer
For Water-powered
small sample moisture
1 8 in. length of 3/8 in. tubing
aspiratordetermination
pump
2
withMotor

tittings
tilledvacuum
with indicating
driven
pump desiccant weighed betore and after4 each
test 2
Gas Sample
meter,
2 in.
scale,
4% full scale
2
For Flow
largeflow
sample
pump
protection
250 ml flask tilled with indicating desiccant
Flow
Gas
indicator
1
or ice bath, bubbler, impinger, condenser 3
Positive
displacement
meter
to
indicale
Gas Test Meter To prevent
1

accumulated
sample volume
condensation
probe
Filter Heater
1
Heater tape around
sample at
lines
and
tilter
holder
heated chamber

58 Handbook of Biomass Downdraft Gasiíier Engine Systems

Gas Testing 59


The
desiccant
Container
should be sealed
for transport
sample
containers
are unavailable,
gas samples
can and
be

weighing.
Raw-gas
moisture
measurement
is essential
mass
collected in
glass bottles
by water
displacement,
insert-to ing
a
balance
calculations.
stopper while
the bottle is submerged and sealing by dipping
the stoppered
openingisinmeasured
paraffin.(Fig.
Whichever
is
Finally,
where volume
7- 12(a) Container
and
used,
the
samples
should
be

tested
as
soon
as
possible,
since
), means must be provided to pull a known quantity of gas
hydrogenthiscan
rapidly
diffuse
through
rubberment
seals
and
through
train.
Hand-held
positive
displacevacuum
stopcocks,
thereby
changing
the
gas
composition
in
a
few
pumps are made by a number of sup- pliers (e.g., Mine Saíety,
hours. and Gelman). We have also used a hand-held rubber

Draeger,

7.6.2

Methods of Analysis

7.6.2.1

Gas Chromatography

p
Gas chromatography (GC) is the most widely used method ofo
gas analysis. It depends on the ability of cer- tain adsorbent<
materials to selectively slow the rate of gas passage through a
column packed with the adsor- bent. Hydrogen is slovved
least, co, N 2 , and 0 2 are

aspirator bulb and found ứiat 70 strokes collected 3 L of gas
(0.1 ft 3 ). We also have used a Dwyer smoke test pump. The
gas meter is required only for initiallỵ calibrating the
sampling train and pump, since counting strokes yields
adequate precision for measuring the test-gas volume. A
decision on the amount of gas to be sampĩed should be based
on the anticipated impurities in the gas and the con- taminant
sample quantity required for the speciíic analysis methods
available. For instance, 50% grey scale analysis requires a 0.5
mg sample on a 47 mm íilter disc.
VVeighed samples require a 5 to 30 mg sample size for
analytical balances with 0.1 mg readability.

7.5.2

Cleaned Gas

Fig. 7-13. Gas sample corttainers (Source: Strauss 1975, p. 13. © 1975. Used with

If the gas is cleaned sufficiently for engine use, it will be
Tw (usually
necessary to pass a much largerTo
sample
3
m ] through the íỉlter. A mechanical pump capable of pulling a
moderate vacuum, such as: a motor-driven vacuum pump or a
H|isjB’
^BT~!BỊ The
^ ỊJ=|
calibrated air-sample pump,
recommended.
positivedisplacement meter can also be located in the collection trainFine
J V if the system pressure is
between the pump and the gas1return
close to atmospheric
Gas pressure. It is imperative to protect the
pump and meter with a large absolute íilter because any tar or
particulates entering the pump or meter will rapidly affect
their períormance.
Dry bulb Desiccant

and wet bulb
7.6Chemical Gas Composition

thermometer
7.6.1

Gas Samples for Chemical Analysis
b. Continuous Readout Sampling Train

The gas composition can be measured either con- tinuously
(on-line) or through discrete samples taken periodically from
the gas stream. These methods will be discussed separately.
Beíore the gas is analyzed, it must be drawn from the system
and cleansed of tar and particulate contaminants, as described
previously.
Batch-sampling requires collecting a sample of gas in a

suitable Container (e.g., glass cylinder,
metal cylinder, Tedlar gas sample bag or syringe), as
shown in Fig. 7-13. The subsequent analysis is only as good
as the sample, and it is easy for gas leaks to spoil a sample
after it has been taken. Thereíore, it is important to use extra
care to avoid leaks either into the sampling train while the
sample is being taken or out of the sample bulb beíòre the
analysis is made.
(b)

permission ol Pergamon Press)

When possible, the sample cylinder should be evacuated or,
alternatively, should be very thoroughlỵ Aushed. The cylinder
shouldbe filled to at least a small positive pressure from the
filter

1 Burner
pumpGassampleFlowmeter
(Fig. 7-14), so that air cannot leak in beíore analysis. A
positive pressure
sample can be collected without a pump by
chilling the>■<
cylinder beíore the gas is taken, so that a positive
pres- sure develops
as the gas in Readout
the cỵlinder warms to room
.
temperature. Gas samples should be drawn from a point as
close as practical
^^ to the gasiíier outlet, in order to avoid errors
due to air leaks in the gasiíier piping.

Usually, any oxygen found in the gas can be attributed to air
leaks, since oxygen is completely removed in the gasiíier.
forWhen
Gasoxygen
Quality
andinMoisture
is found
the gas, the (clean
composi-gas
tion can be
only)
converted to an “air-free” basis by subtract- ing the oxygen
and the corresponding ratio of niừogen (the N 2 /0 2 ratio in air
is 79/21).

Some gas sample containers are shown in Fig. 7-13. A

rubber septum is a desirable feature that
permits one to extract the gas sample with a
hypodermic syringe for inịection into a gas-chromatograph
without opening the stopcocks. The hypodermic syringe for
injecting samples into the gas chromatograph should have a
valve at the needle that can be closed between íilling the
syringe and analysis. Valved syringes are available as
accessories from gas chromatograph manuíacturers. The metal
cylinder of Fig. 7-13 can contain gas at a much higher
pressure than the glass system. It is im- portant to use leakproof valves rather than needle valves on this
Container and to avoid stopcock grease, which
has a high hydrogen solubility. A syringe also can be used

to collect a gas sample. If Standard gas

Fig. 7-14. Apparatus fordrawing gas samples: (a) Filling sample containers byliquiddisplacement; (b) hand-operaledpiston vacuum pump; (c) motor- driven rotarỳ vacuum pump; (d) rubber bulb
hẩnd aspìrator; (e) Chapman tiíter pump (Source: (à, d, e) ASME 1969, Figs.
and 7)

6

Fig. 7-12. Sampling train coníigurations

62 Handbook of Biomass Downdraft Gasitier Engine Systems
60 Handbook of Biomass Downdraft Gasifier Engine
Systems

Gas Testing 61

The Orsat analysis depends on the ability of certain chemicals
The most common GC detector períorms
ato peak.
quantity with
of that
then determined
by
slowed
to a greater
and water andthe
C0 2 arethermal
slowed to
react The
selectively
eachgas
gasis component
of the
analyses
by extent,
measuring
integrating
the
area
under
the
peak
in
the

curve
and
compared
the
greatest
degree.
The
gas
sample
is
mixed
with
a
carrier
producer gas mixture. The components
conductivity of the gas (TC detector) and is the
with
a calibration
known composition.
More
gas;
helium
is used
because it With
does this
not tỵpe
occur
are that
ab-in sorbed
in gas

theof order
of C0
most usually,
suitable for
producer
gas measurement.
of
2 , 0 2 , co,
advanced
automati- cally controlled
naturally
in the sample.
A detector, which
is inserted
into the
then H 2 recorders
and CHinclude
detector, helium
(or a hydrogen-helium
mixture,
see below)
is
4 , and the analysis reports the volume
valving,
integration
of the response
gas
the end of
of the
records

on athermal
chart
percent of
each component
directly. curves, calculation of gas
oftenstream
used at because
its column,
abnormally
high
quantity
from
calibration
fac- tors, and a printout of the
recorder
both
the
time
of
passage
and
the
quantity
of
each
conductivity relative to other gases.
Orsat analysis equipment is portable, does not require AC
composition results. Such a printout is shown in Fig. 7-15.
component. The presence of a particular gas component is
power, has no warmup time, and can be purchased (along with

The flame-ionization detector (FID) measures the num- ber of
indicated by
the required chemicals] from scientiíic supply houses for
ions produced in a ílame and is particularly use- ful for
$500 to $1000.
detecting hydrocarbon species. The FID is not particularly
useíul for producer gas,
I- since producer gas contains few 7.6.2.3
On-Line Gas Measurement
hydrocarbons other than-methane.
It is convenient to have continuous “on-line” measure- ment
rả
of all the gas components to show instantaneous changes in
The response of the TC detector to low levels of hydrogen in
composition that otherwise would not be shown by batch
the inert carrier gas is nonlinear, and this leads to ambiguous
sampling. Methods for on-line gas analysis include flame
results. There are two effective solutions to this problem. A
observation, combustion calorimetry, inírared absorption,
heated palladium tube at the inlet can be used to selectively
thermal conductivity, and mass spectrometry.
diffuse the hydrogen out of the sample into a separate
nitrogen gas stream; in this secondary stream, hydrogen yields
The heat content of the gas is a measure of a gasifier’s
a
linear
response
(Carle
method).
performance and can be calculated from the gas com- position

Alternatively, adding hydrogen to the helium
(see Fig. 7-1 and Table 7-2). Most gasiíier facilities, if they
carrier gas will move the baseline onto the linear region of the
have gas analysis equipment, use an Orsat analyzer or a gas
TC-detector response curve.
chromatograph, so that normal- ly a value is available only
after a considerable time delay (10-30 min). It is desirable to
The position of a peak on the time scale of the recorder chart
have a continuous indication of gas quality.
indicates the time of retention and is characteris- tic of

each particular gas component. The area
under the peak, obtained by analog or digital integration,

in- dicates the volume of each gas present. Although retention times and sensitivities are listed for each adsorbent
material, aging and drift are common to column pack- ings, so
it is necessary to calibrate the instrument daily to obtain an
accuracy on the order of 1%. For this pur- pose, it is
necessary to have a cylinder of previously analyzed Standard
gas. These cylinders are available from
GC

equipment manuíacturers.

Although samples are usually collected as needed, it is
possible to use automatic sampling with the GC to give a
measurement of gas composition at regular intervals. The

GC analysis cycle time depends on both
the reten- tion time of the columns used and the number

Continuous

immediate

readout

of

producer

gas

com-

position, however, has been achieved
intwo ways. One method, used at u. c. Davis, uses
inírared (IR) absorp- tion for continuous co,
C0 2 , and CH 4 analysis with a thermal
conductivity detector for continuous H 2
deter- mination. The second method uses a mass specữometer to give immediate on-line digital readout of all gases
present, co, C0 2 , H 2 , 0 2 , H 2 0, CH 4 , and
high hydrocarbons (Graboski 1986).
The calorimeter shown in Fig. 7-16 is a precise primary

Standard for measuring HHV of the gas.
Combustion air, fuel rates, delivery temperatures, and

pressures are careíully measured. Heat-transfer air is also
metered for inlet flow, temperature, and pressure. A

of species analyzed. This time is typically 30 minutes, but
counterflow heat exchanger cools the combustion products to
[HP]
27:is oneMANUALINƠECTION
AT 15:49 FEB 7, 1984
noie that the warmup time for
the GC
day.
the air inlet temperature (60°F) and simultaneously conRUN
E7
SAMPLE
W6
denses water vapor to a liquid. The temperature rise of the
A number of companies, including Carle, Hewlett- Packard,
heat-transfer air is directly proportional to the HHV of the
and Perkin-Elmer, manuíacture satisíactory units for $3000 to
RUN TIME
AMOUNT
NAME
fuel gas. The equipment
pictured in Fig. 7-16 was designed
$30,000 and provide excellent insửuction and Service.
2.87
25.723
HYDROGE
for gas with a HHV
of
1000 Btu/scf and may require
N
4.25

0.15of PROPYLENE
modification
the burner to use producer gas with a HHV of
7.6.2.2
Orsat Gas Analysis
9.46
0.08219
TRANSBUTE
150
Btu/scf.
The Orsat gas analysis system
was developed to measure
NE
15.26
14.592
C02
the gases C0 2 , co, 0 2 , H 2 , and CH 4 . It was
Other simpler, more relative methods are available and may
1.318
the principal measurement15.84
method used beíore the GC was
be sufficient forETHYLENE
manỵ applications. It is informa- tive simply
0.136
ETHANE
developed in the 1950s and16.37
is more reliable and less costly
to observe
the gas
flame during operation.

17.09it requires more
than GC; hovvever,
time (typi- cally 30 18.41
minutes of full operator attention
per analysis) and more skill.18.76
19.58
23.92

0.367 ACETYLENE

Flame length tends to increase with the gas heating value;
0.49 OXYGEN
flame luminance increases with hydrocarbon and tar content.
1.949
NITROGEN
After the operator has gained

3.9303 METHANE
0.002827 BACKFLUSH

Fig. 7-15. Typical gas chromatography printout

64

Handbook of Biomass Downdraft Gasitier Engine Systems

Gas Testing 63

0J
cu
t

o
_
adequate
capacity for prolonged use and adequate efficiency
Table 7-7. Mass
Balance
u->
Q 1 .o hhoỵ o
IỌ LỌ
for
equipment
protection.
o Inputs
%'S- CO
(M
ò cô
(kg/h)
Outputs
(kg/h)
Closure (%)
CvJ
h- 7C\J
ọ o 00
Water
Vapor Analysis
Wet Chips Dry Airr^

Total Dry7.6.3
Gas
Cha Tar
H20
Total
co H20
r can0.09
co
OJ
Water
vapor
be
determined
by
many
methods. 98.9
The three
98
32.0
43.1
0.5
75.6
66.3
0.9
7.4
74.7
8 gig ư>
LO 0.5
most suited
to 0.14

producer
gas
condenser
cọ LỌ
ƠỊ are psychrometry,
910
32.0
45.2
77.7
68.0
0.9
7.4
76.4
98.3
0,5 co
cộand gravimetric
1methods.
920
35.7
62.1 CM 0.4
98.2
92.9 outlet temperature,
1.4
0.09
7.1
101.5
96.6
I<
o'-'
cọ

101
52.4
76.9 LO 0.8
130.1
116.97.6.3.1
1.7Psychrometry
0.09
13.3 132.0
98.6
« £74.0
ễ * cọ 1.0
929
52.7
127.7
113.0
1.8
0.14
12.2
127.1
99.5
cọ
ẵ ®
® h- 0.5
be determined
measuring the95.4
wet- and
106
58.1
76.8
135.4

117.0Water content
1.2 can
0.09
10.8 by129.1
_ơ)
I I as in196.8
dry-bulb
temperature
of the19.7
gas
Fig. 7-17. The97.3
moisture
ầ 112.1
* > io
111
89.1
1.0
202.2
173.8
3.0
0.27
00
cọ
9111
ơ) 0.7
is then calculated
from
a psychromeửic
(Fig. 796.2
237.3

218.9content2.5
0.18
22.9
244.5 chart97.0
®140.4
g _ r-Ô
7
122
140.5
202.1 ư)
1.1
343.7
302.1
4.1
0.54
43.3
350.0
98.2
18
or
7-19,
depending
on
gas
temperature)
to
find
the
ócô
1

CD
moisture
as
absolute
humidity.
co
Source: Walawender 1985,
p. 918.
Cỏ
cô
co
cọ LO
LÔ
Moisture wt % = Absolute ọr^
humidity X 100
(7-3)
<Ó
cò
Mass and energy balances have only been applied ocfuel economy should be sized with higher hearth load to
oò
c\ibecause of the dif- íiculty
ơ>
casionally to gasiíier development
coincide with the peak efficiency curve. Engine ap- plications
Csĩ
ò
00 maximum
cọ hearth load to coincide vvith
cô
and expense of measuring

all
flow
streams.
Detailed
mass
and
should be sized for
9.3
cvi
cp cp
^íCM
ơ
energy balances usually5*0
can be percô íormed at universities in
peak of the efficiency
curve in
o
)< order to allovv maximum room
cõ
chemical engineering Xlaboratories
or
at
major
research
for
turndown.
GÔ
cô
cvi
laboratories, and only a few have

c\i been períormed on air
ló
gasiíiers. If gasiíica- tion is to become
<6 a developed field, it is 7.8Particle-Sizer-Measurement
To
>.
Ẽ ơi
C\
necessary to períorm mass and energy balances.
co distribution
Knowledge of theinsize
and other charac- teristics
J
<Ó
ìs.y
CM
CvJ
of
gas
contaminants
is
helpful
for
cleanup
design. Table 7-9
T^
í'“
0)0
7.7.2
Flow Rate

Ta Characterization
có
ơ)
presents particle-size analysis methods and examples of
ble
The variation of gas qualitỵ of aÒ
gasiíier with flow rate helps
<
7equipment available
for
particle size.
C
o
T*characterizing
determine optimum
sizing
parameters.
Note that in Fig. 7-20
D
cọ C\J
8.
C
/>
_
co Tt
ì'*.
Ọ
total hydrocarbonsEnand tars steadily
Typical Particle-Size
Distributions

Co
h- decrease with increased 7.8.1
k. 2. ìỏ
flow. In Fig. 7-21erg
we see that maximum
LÒ
heating
value,
peak
The
particle-size
distribution
of
solid
char
and ash for raw gas
hLÒ
y
ló
co and H 2 , and maximum efficiency
do not coincide. Peak
GO
shown
in
Fig.
7-12
was
produced
by
mechanical screen

Ba
CD
eữiciency occurs lan
at more than twice the flow rate for
o
Ợ)
ỌJ
separation
for
both
the
Imbert
(tuyere
and
hearth
constriction)
ị- 2 § r^
hC\I aị
O)
maximum heating ce
value.Ũ
cô õ
and the SERI unconstricted
1^0 gas producers. The difference
co
between the two gasiíỉers is 5caused by the grate design. Gas
4) co
Actual hearth load (see <2
Section
5.7.3) for sizing depends on

00
cvi
from the Imbert gasiỉier exits upward through a settling space
the application. Heating applications
LO
00 ứiat need maximum
■C
2
that retains largercọ particles.coOn
ũarne temperature should be sized
lò the other hand, the SERI
cowith lower hearth rate load
CVJ
o 5.0,0, o
oxygen
gasiíier
passes
all
solids
through the gas outlet. Note
có
co
to 7-19,
provide
maximum
heating o
value.
Fig.
Psychrometric
chart for high

temperatures
(Source:Heating
ASME 1980,applications
Fig. K-3)
that
the
overall
slope
is
the
same
for
both size distributions.
co
r-.
that need maximum
C\J
ơ)
7.8.2
Sieve Analysis
<n 2 ơ>
r- Tơ> ^
h7.6.3.2
Gravimetric ■SV' LO
1- Tfr
an
exact
balance indicates
either
an error in

measureor
60 50thanment,
c\i Ôparticles
The
distribution
of
large
solid
greater
40 |im
,N.
CO
that
some
important
flow
has
been
overlooked.
may
be
determined
using
sieves.
Table
7-10
lists
actual

sieve
Gas moisture also can ò~
be determined
o CO
co by passing a measured
ơ)
The
total
inlet and
size
for
various
meshoutlet
size. mass flows must not only balance
volume of gas through a preweighed
dryer assembly
Wet
bulb
^ co
T- the
LO inlet
temperature,
7Zand outlet mass flows of each
Neach
other,
but
also
containing desiccant. Moisture can
be
calculated

as
LỌ
Tơ>
7.8.3elementMicroscopic
Size Analysis
ư>
Dew
point
(in this case, carbon, hydrogen, and oxygen) must
í^.
o
05 XWeight
hParticles
captured
on mass
a íilter
disc iscan
be rigorous
counted test
by
temperatu
Moisture wt % =
100
gain
balance. This
elemental
balance
a more
ơ>X Cas density
Sampie T“

vol.
re,
microscopic
examination.
However,
particles
smaller
than
10 |
O)
of
measurement
procedure;
the
sources
of
error
in
the
global
CM
a>
co
j.m
are
difficult
see under
light microscope,
and liquid(overall
inlet andtooutlet)

massabalance
may be pinpointed
by
C\J
Relative
Fig. 7-16. Gas calorìmeter combustion
chamber
(Source: Adapted from ASTM 1977)
fl>
io
droplet
sizes
cannot
be
determined
by
this
method
because
ÒJ
the
elemental
mass
balance.
humidity,
7.7Analysis of Test Data
_;
5CNJ
droplets,
once captured, coalesce, leaving no evidence of their

<jỹ>
ư)
Table%7-8
shows an energy balance, vvhich is obtained by
1—
_ and
theBalances
flame a>can
reveal
a
good
deal
on
the
7.7.1experience,
Mass
Energy
Balances
-o
original
size.
•Ỵ—
ơ)
tabulating the energy associated with d8all input and output
c\l
íunctioning or malíunctioning
system.
LO
The law of conservation
of energy,

which requires
A typical gasiíier mass“■
balance,o
shown in Table 7-7, is an 7.8.4streams.Aerodynamic
Size Analysis
5 LÕ
ÒJ
osmall
One author of
(Das)
has 3used
burner/thermocouple
that
energy
be
conserved,
thereíòre
provides
a means
accounting
all mass
inputs
to
the
gasiíier
(or
gasiíier
> a oõú
C\J
c

Aerodynamic sizing can be accomplished
with
eitherfor
0.003
Ia
monitor and
shown
Fig.ouputs
7-12(b),
which
produces
a temperature
oj
evaluating
efficiency,
finding
instrumental
errors,
or
system)
all in
mass
over
a
given
time.
Since
the
law
T—

cascade impactor or a cascade cyclone. Particles
and
®
00
signal
roughly proportional
to thethat
heatmass
content
of the clean
calculating quantities that cannot be measured directly.
of
conservation
of mass requires
be
conserved
in
5'
o
1—
.- 100 110
gas. process, the total mass
50
60
70
80
any
input
must equal
the total mass

CM
£ flow
cvj
Producer
gas
rate,
m 3/h (25°
c, 1 atm)
Q
output.
Any deviation
from sampling
The accuracy
of continuous
equipment
is
subject
to
o
co
Dry
bulb ơ
ỡ)
ơ>
ổ>
accumulation of gas contaminants,
so
preíiltration
should
be

Ờ5
s
>.3p Adapted from ASHRAE
Củ
ÒS
Fíg. 7-18. Psychrometric
chan
for mediumO
temperatures
Fig. 7-20. Tarversusflowforricehullgasifier (Source:
Kaupp 1984b, FÍg. 10-88)
o
c(Source:
temperature,
c
used as in Fig. 7-12(b) of
òì
|l £
T—
1981)
cã
cô
J
Ờ5
o
o
ơ)
05
1—
cô

1—
Gas Testing
Testing67
65
Gas
66 Handbook68
of Biomass
Gasitier
Engine
Systems
côDowndraft
Handbook
of Biomass
Downdraft
Gasitier
Engine Systems
‘T—
ò
ỊI
cô
(Ỏ
ÒJ
<0
a

a>
ưS ó

05

lO T-

0

c

05


Table 7-10. Sieve Number Versus Mesh Size cyclone cut diameter, dp 5 0 , with a Standard
7.8.5
Graphic
Sizeis Distribution
deviation,
ơg Analysis
equal to 2.5,of
which
characteristic of

droplets
are Number
collected inertially as
a íunction
of their
Sieve
Mesh
Size, ụm
aerodynamic size. Once they have been separated by size,

80
180
there is no need to prevent the droplets from coalescing.
100
150
Quantities, and therefore distributions, are subsequently
120
125
determined by the relative masses represented in each size
140
106
grade.

170
200
230
270
325
400

90
75
63
53
45
38

Standard deviation ơ as indicated by the
slope. Note that both distributions shown in Fig. 7-4 have
the same overall slope. This slope is typical of large materials

70 been broken up into a wide range of smaller
that have
particles. It will be helpful for us to express this slope as
the>N geometric Standard deviation, ơg
o
ơ
=
=
c
(7-5)
0) 65 g ^p84^p50 dp5o/dp 16
where
< dp 50 is the0 diameter for which 50% of the total particles
Õ
are 1)
captured. The other subscripts denote similar cumulative
c
percentages
of 1
particles smaller than the respective particle
> 60
_3
diameter
d.
c
o
>
Theo solid particles
that pass through a cyclone can be
o

expected
to
have
a
mean
particle diameter near the
bì 55
<
1)

cyclones, gravity separators, and all Stokes’ law particle
The
cumulative particle-size distribution shown in Fig. 7-4
movement.
plots as a straight line on probability paper, thereby indicating
log normal distribution about a mean particle diameter, dp at
50%, with a geometric

7.8.6

Physical Size Analysis

The major methods for particle-size measurement are shown
inTable 7-9. Screeningand microscopy areused to determine
linear dimensions. The Stokes’ radius, r g) is the radius of a
Ợ
hypothetical spherical particle with the same íalling velocity
(
and bulk density as the particle. The aerodynamic diameter,
D

cỊpa, is the diameter of a hypothetical sphere of densrty 1
g/cm 3 that will attain the same íalling velocity as the particle
E
in question.
cố

The number mass and area distributions all have the 5.5
same
õ
geometric Standard deviation, ơg.
o
ữ?
Á by the
Scrubber períormance can be characterized similarly
c
size particle diameter which is captured at o50%. The
5.0
preciseness of the size cutoff point is characterized
C
”5 by the
value of ơ„. Various scrubbers and separatorsDare compared
in
Tabìe 8-1 for cut diameter and sharpness. INote Ó
how many
D _ those that
have a Standard deviation near 2.5. Consider
3 4.5
o
have a sharper orbroader deviation and why.
&

>
ơ)
c
O
)
X

50

4.0

3.5L

Producer gas flow rate,m /h (25°c,1atm)
3

Fig. 7-21. Flow rate effects on efficiency, heating vaiue, and gas composition for rice hulls (Source: Compiled from Kaupp 1984b data)

Table 7-9. Examples of Size-Analysis Methods and Equipment

General Method
Particle Size, |im
Examples of Speciíic
Instruments*
37 and larger
Dry-sieve analysis
Tyler Ro-Tap, Alpine Jet sieve
10 and larger
Wet-sieve analysis
Buckbee-Mears sieves

1-100
Optical microscope Microscope
Zeiss, Bausch & Lomb, Nikon microscopes
with
scanner
and
counter
Dry
Millipore
0.2-20
Royco IIMC system
Light scattering
Brink, Anderson, Casella, Lundgren impactors
Cascade impactor
M.S.A.-VVhitby analyzer
Wet centriíugal sedimentation
0.01-10

Ultracentriíuge
Transmission electron

Goetz aerosol spectrometer Phillips, RCA, Hitachi,
Zeiss, Metropolitan-Vickers, Siemens microscopes
Reist & Burgess system

microscope Scanning electron
*This table gives examples of specitic equipment. It is not intended to be acomplete
listing, nor is it intended to be an endorsementoí any instrument. Source: Perry
1973, Table 20-33.
70 Handbook of Biomass Downdraft Gasitier Engine Systems

Gas Testing 69


Chapter 8
Gas Cleaning and Conditioning
8.1Introduction
If the gas is to be used in a burner
application, an updraít gasiíier can be used,
and no cleanup will be needed. However, if
the fuel gas will be fed to an engine, then a
downdraft or other tar cracking gasiíier must
be used; and the gas must be cleaned and
conditioned before it is fed to the engine.
The gas emerging from a downdraft gasifier is
usually hot and laden with dust, containing
up to 1% tars and particulates. If these
materials are not removed proper- ly, they
can cause maintenance, repair, and reliability
problems much more costly and troublesome
than operation of the gasifier itselí. In fact, it
is likely that more gasiíier engine systems
have íailed because of im- proper cleanup
systems than for any other cause. In
particular, the gas is very dirty during startup
and should be burned at the gasiíier until the
system is fully operational. (See Sections 9.3.3,
9.3.4 and 9.4.1 for blowers, ejectors, and
ílares.)
In 1983, the Minneapolis Moline Engine Company be-

came the first contemporary engine
manufacturer to offer a 5000-h warranty on its
engine—based on a fuel gas at the engine containing less than
5 mg/Nm 3 of total combined tars and particulates (Mahin,
June 1983). This amounts to 99% removal of all dust
particles.

Prior to 1950, manuíactured gas was widely
disừibuted to homes, and the technology for
gas cleanup was used extensively and well
understood at that time. The chemical and
energy industries of today routinely use the
methods that will be described in this chapter.
In order to design effective gas cleanup
systems, one must determine the magnitude,
T > 700 °c

T > 300°c

T>80°c

respective capabilities and suitability, and
some approaches for overall cleanup systems.
The basic cleanup system design strategy
should be based on the required cleanliness
goals (determined by the application), the
order of removal, temperature, and the
intended deposit site for collected materials.
In addition, size, weight, cost, reliability, the

need for ex- otic materials, water
consumption, effluents disposal, the time
between cleaning cycles, and the ease of
equipment servicing must be considered.
The íìrst step toward producing clean gas is to
choose a gasiíier design that minimizes
production of tars and particulates to be
removed, such as a downdraft or other lowtar gasifier, and to make sure that the gasifier
is operated in a manner that will minimize
particulate production by proper sizing (see
Chapter 5). Develop- ment of cleaner gasiíiers
is proceeding in the United States and Europe
at a good pace (see Chapter 5).
The next step, which simpliíies the handling
of cap- tured contaminants, is to remove
particulates, tars, and water in the proper
order and at the right temperature. If the gas
is immediately cooled and quenched in one
operation, then char, tars, and water all are
removed at one location to form a stickỵ,
tarry mess. If particulates are removed íirst at
a temperature above the dewpoint of the tars
(~300°C), tars are removed next at intermediate temperatures (above 100°C), and
water is removed last at 30°-60°C, then each
separated con- taminant can be handled much
more easily. The rela- tion between gas
temperature and each operation is shown in
Fig. 8-1.
The final step of effective gas cleanup is to
O

co

r~-

O
c\
l

<

CŨ

Fig. 8-1. Schematic relationship oígas temperature to contaminant removal

Gas Cleaning and Conditioning 71


BA-G0201774

of99.9
Particle
Collection
Methods
capture
element
is during
the
dynamic
that and
íorms

the íilter
ash
that
otherwise
was
present
inTable
condensate
orSharpness
scrub can
water.
gasiíier,
especially
idling,
wet
fuel
The
details,
including
the
mathematics,
of8-1.
separation
be 8.6.2
sharpness
indicates
that
particle
separation
is

degraded
by
cyclone Cyclone
inlet
width
bSeparators
for
astartup,
given
pressure
dropwhen
asonshovvn
in
8.6.2.1
Cyclone
Operating
Principles
o
// ocake
captured.
The
pressure
drop
across
the
cleanup
sỵstem

8.2The
Povver

Theory
ofconsists
Gas
Cleanup
surface.
This
which
of captured
The
íabric
filter issuch
noimparts
doubt
the
mostitmotion
efficient
for
fine
Sharpness
Size
found
in rises
Strauss
(1975).
However,
is
ing
to note
Cut
is

used.
some
mechanism
reentrainment
orinterestfragmentation.
Fig.
8-6. Notice
that of
the
effect
of
temperature
99.5
Cyclones
are cake,
simple
and
inexpensive
dustReíerence
and particles,
droplet
A
cyclone
separator
a rotary
todevice
the
gases
and
steadily

with
theasaccumulation
of
captured
materials,
Ak
!
°
According
to
the
contact-power
theory
of gas cleanup
(Perry
Separation
Standard
rCL
ỵ//
presents
a
circuitous
path
that
effectively
captures
fine
cleaning;
but
for

wood
gas,
extensive
precautions
against
that
the
relation
between
any
separator’s
50%
capture
cutDiameter
thereby
enhances
theorsettling
rate to
many pressure
times
thatdrops
induced
they
are
widely
used
on
gasiíiers
and
will

be
The
requiring
minimum
írequent
particle
automatic
size and
typical
cleaning
or replacement.
are 8.3.4
oseparators;
98
ơ
Cleanup
Design
Target
1973),
for
a
given
power
consumption,
as
measured
by
the
Deviation
g

=
dp84/dp50
particles,
while
coarser
captured
particles
maintain
an
open
condensation
of
tar
or
water
are
necessary
(Gengas
1950).
(dpso)
um
particle
diameter
and
the
capture
rate
for
other
sized

particles
by
gravity
alone.
A
cyclone
separator
is
essentially
a
discussed
in
extra
detail
in
this
section.
o"
shown
for efficiency
various scrubbers
in aTable
The filter
scrubber
Collection
is low for
clean,8-2.
in-line
but
gas

drop
water flow
rate,gas
devices
give
Requirements
for
solid-particle
removal
may
be determined
cakepressure
structure
to or
promote
high
permeability.
xall cleaning
is:
Note
Table
8-3
that
cylinder
wear
less
for
gravitational
separator
that

has pressure
been
a
»tion
-V
selection
parameters
arethe
the
particle
size istoenhanced
be removed,
the
climbsin steadily
with
the
increasing
drop
as producer
theby
iìlter
0Hot
90 gas
substantially
the
same
collecefficiency,
and
cyclone
separators

are
well
suited
to
remove
solid
,.^y
from
knowledge
of
average
particle
diameter
dp,
and
the
When
a
new
íilter
íabric
is
inserted,
the
main
Gravity
Settling
50of
2.5
Perry 1973

gas
withcollection
aplugged.
íabric
íilter
than
forand
diesel
oil alone.
centrifugal
íorce
component.
The
cyclone
separator
grade
desired
eữiciency,
the
maximum
pressure
drop.
becomes
Collection
efficiency
measurements
indp50
(1/2)
dp
0Chamber

(1/3)
rìp90
= (1/4)
dp
(8ữ>
collection
efficiency
increases
with
power.
Some
particles
larger
than
10
|im
as
a
preỉilter
for
the
gas
cooler
and
worst-case
char-ash
dust
content
(c
This

iníormation
can
mechanism
*—1
of
1
1
particle
collection
d ).increasing
is
physical
sizing
as
'õ
efficiency
curve,
Fig.
8-4,
applies
to all loading
cyclone
as
line
filters
should
clearly indicate
effects
or 4)
be

During
operation,
the
previously
described
íilterseparators,
cake1grows
Single
Cyclone
2.5
Kaupp1984
improvement
over
conlimitations
can
be
ỈỄ70
fine
particleusing
removal,
astact-power
shown
intheory
Fig.
8-3,
forto
acollect
vehicle
be
gathered

isokinetic
sampling
techniques
a
determined
by
the
openings
in
the
weave.
At
first,
small
8.3Gas
Cleanup
Goals
well
as toinover
inertial
andcleaning
gravitational
collectors.
averaged
ausing
full
cycle
in order
toclimbs,
be meaningíul.

steadily
thickness,
collection
efficiency
and
All
collectors
the
same
capture
mechanism
will the
be
Dgasiíier
gained
using
designs
for
reduced
power
consumption
that
ofmay
the
1939-1945
era.parrepresentative
sample
of all
ticle
sizes.

If
ca
represents
paiticlesby
pass
uncaptured
until
some
buildup
dmax
accumulates
Das1986
Cascade
Cyclones
n
in
series
0.67*
1.8
^50
pressureGas
drop by
across
the filter
rises.
When
the
has
characterized
the same

slope
(Fig.
8-2)
and íìlter
Standard
8.3.1Cyclone
Contaminant
Characteristics
períormance
of
particle
cut cake
diameter
use
small
parallel
streams,
multiple
in series,
the
maximum
permisdust
formust
engine
use,diffusion,
thenpass
the
on the
íilter.
From

thissible
point
on, level
thestages
gas
effectively
identical
n thickness
=such
2 isnasrated
=cyclone
3 ninremoval,
=terms
4separators,
0.53*
0.65
separators
are also used widely in industrial
Off-line
devices,
wet
scrubbers,
2Cyclone
30 transíer,
reached
optimal
for
the
íỉlter
cake

must
be
deviation
(Table
8-1).
or
cut
size.
The
cut
size,
dp
Q,
is
the
particle
size
which
is
mass
or
condensation.
5
maximum
permissible
dust
penetration
a
is
given

by:
through
a
packed
bed
of
micrometer-sized
particles.
Gas
goals should be based
on the
degreematerials
of
con0.48*
oprocesses.
>
The 0.55
principles are well-developed, and designs are
and cleanup
electrostatic
captured
removed
by one ofprecipitators,
the followingdeposit
methods:
momentary
flow
captured
50%.
Interception

and and
impaction
then
emerge
as of
significant
tamination,
the flow
size, path.
distribution,
and nature
of the
the
The
períormance
sharpness
of size
separation
various
easily
scaled
to
the necessary
size.
High-eữiciency
cyclone
®
^dmax
* 100 ^^dmeasured
(8-3)

outside
of
the
These
devices
separate
reversal
collapse
the bag and dislodge the cake as shown in
8.6toDry
Collectors
collection
mechanisms.
contaminants,
as
well
as
the
degree
of
cleanliness
required
The
relationship
particle
cut gas
diameters
forcreate
this
type

cleanup
components
are
compared
in
Table
8-1
and
Fig.
8-2.
separators
can
be
íabricated
readily
by
a
sheet-metal
or
contaminants
intobetween
one
stream
and the
into
another
stream.
Fig.
8-10, a pulse
jet of

compressed
or air
to
the
On a probability
plot of the size distribution of the dust
0.12.5
1 10
by
the
equipment.
Both
solid
and cies
liquid
contaminants
are
separator
is bag
given
by
(8-4),
where
dp is
particle
Particle
cut
diameter
(as
vvritten

dp
or
dp
)
is
the
particle
Disintegrator
0.6these
Perry
1973
vvelding
shop.
Cyclone
design
parameters
are
presented
in
C
50
The
pressure
drops
andEq.
eữicienassociated
with
8.6.1
Gravity
Settling

Õ.6.3.3
Application
of
Baghouse
Filters
momentary
collapse,
orChambers
dismantling
andthe
manually
shown, for example, in Fig. 7-4, we then find the par- ticle
present
in
producer
gas. and
Thesubscript
solids are
char,
ash,
and soot,
Particle
size,
/um
diameter
and
the
numerical
denotes
the

collection
diameter
at
which
50%
of
particles
are
captured.
A
capture
this
section
and
at
greater
length
in
Perry
(1973),
Calvert
devices
are
predictable
independent
of
the
amount
of
shaking

the
bag
(Breag
1982).
size
dp
where
cumulative
mass
%
less
than
As
long as1unlimited
space and materials are provided,
a
Baghouse 1.3
fiIters have been used
with
Karbate
in.a size
Ap
5
Perry
1973
and
they cover
wide
range of sizes.
Thebuildup

liquid isofinitially
a
efficiency
of thatchamber
particle.
rate other
than
50%
may
beisUníortunately,
noted
as
a cyclone
different
subscript.
A
(1972),
and
Strauss
the successíul
small
cyclones
captured
materials,
eliminating
the is
slow
pressure
dp
equals

a.
Tnis(1975).
dp 50 many
then
the
cut
diameter
gravity
settling
theoretically
can
achieve
any
level
of
good
success
in
of
the
more
and
After
cleaning,
the
íilter
efficiency
lower
until
the

filter
o
Cyclone-cloth
(loaded)
fine
mist
or
fog
composed
of
droplets
smaller
than
1
Ị
0
.m,
convenient
relationship
exists
for
particle
collectors
with
2.4
2.5
Perry
1973
required
for

small
gasiíiers
are
not
available
commercially,
so
drop
with
use. Off-line
methods
are
applications
Wire
Mesh
2 layers
in.
required for
solids
cleanup.systems (Breag
particle
separation
to(0.011
theuse
Stokes’
limit of in
about
1 |im. In
reliable
engine

gasifier
1982; Kjellstrom
cake
reíorms.
It
isdown
wise
to
a preíerable
conservatively
8.6.2.2
Cyclone
Design
Principles
□
Cyclone-cloth
(partially
but
the
agglomerate
to increase
in size asdesigned
the gas
Standard
deviation
2.5. Particles
with
diameters
that the
are

they
must
be
custom
designed
andhas
fabricated.
2.5
wire)
3droplets
layers
where
they
can
be
used.
2 gasworks used gigantic 1.5
loaded)
fact,
many
of
the
earliest
settling
1981).
The
use
of
fabric
íilters

virtually
eliminated
íabric
íilter
(5-10
cfm/ft
),
or
even
larger
bag
area,
to
The
cools.proportions for high-efficiency cyclone separators are
A
useíul ruleA
of Cyclone-cloth
thumb is that the cut(clean)
diameter (dp 50 ) required
double
chambers.
However,
evendeep
though
is effective,
method
corrosive
maximize
the

interval
between
cleaningsthis
so 2.3
as to
Packed
Bed
6 in.
1/2itbag
shown
in Fig.
8-5.
for a cyclone
or scrubber will be about thePerry
same 1973
as the
• 1.65
Cyclone-alone
be
a+bitSaddles
cumbersome.
maintain
clean
gas
flow.
Fig.
8-9. to
Wet
cyclone
(Source:

Calvert
1972,
Fig. 3.1-6)
Spheres
Velocity
5
0.95
1.8
8.3.2tends
Typical
Dirty
Gas
diameter at the cumulative íraction cor- responding to the
The particle
size that can
be
separated with 50% ef- íiciency
fpsare
Velocity
fps
Fig. 8-11. Fractional efficiency curves o1 cyclone-alone and cyclone- cioth collectors
3
Bag
íilters
suitable 30
only
for gas
removing
dry100
particulates;

maximum permissible penetration (Calvert 1972).
A typical
speciíication
dirty
be
mg/Nm
of
is
predicted
for generalfor
cyclones
andmight
for the
high-efficiency
(Source:
Gas temperature
(°C)Peterson 1965, p. 48)
sticky
or
tacky
materials
do
not
release
from
filterbags.
particulates
with
mean
diameter

dp
=
100
|im,
a
geometric
50
Collecting
enữained
cyclone
proportions
of Fig. 8-6 bydroplets from wet
Therefore,
special provisions
precautions
areversus
required
to
Venturideviation
Scrubber
in. and
ApWG
0.3
1.8 low-temperature operations
Perry
1973
8-8. contamination
Gas viscosity
temperature
Standard

ơg 40
=a 3.5,
andFig.
tar
of
1000
scrubbers
with
cyclone
separator
requires
an
outlet
are limited toof
re- quiring
8.4 íilters
Classitication
Particles
3 the
maintain
bag
íiltnr
temperature
in
order
to
prevent
water
dpc
=

V
9
H
b/[27C
N
Vj
(p
P
)]
(8-5)
G
e
p
G
mg/Nm
0.625
2 gas cooling.
Calvert
skirt
to .prevent
reentrainment
ofHole
liquids that have impinged
accurately
controlled
Various
íilters
were
Sieve
Platefrom

1.5
in. ApWG
Solid particles
with diameters
greater
than 1cloth
|im
are
called
vapor Eq.
or tars
condensing
onthetherelationship
íilter bag. In
partỉcular,
1972
3
From
(8-5)
we
can
derive
between
the
on
the
outlet
tube,
as
shown

in
Fig.
8-9.
used
on
gasiíiers
between
1939
and
1945,
but
these
proved
to
Velocity
Vh
=
75
fps
density 0.2 (200 kg/m ), that the cyclone cut size will
dust,
removal.
and
Also,
those
any
tars
with
in
the

diameters
gas
stream
must
below
still
be
1
since tar-laden
start-up
gasGoals
should
not
be drawn through a
8.3.3cyclone
Gas
Cleanup
separator’s
particle
cut
size dp
50 and the
be
a
continual
source
of
difficulty
because
they

could
catch
be
ỊÌ.IĨ1
aie
reíerred
to
as
fume.
Liquid
droplets
over
10
removed
by
other
means.
Kaupp
cold
bagRecent
filter, the
designDevelopment
outlet
Impingement
Scrubber
4should locate the flare1.5
8.6.2.6
Cyclone
6.7 too hot, or would get wet (from
fire

if diameter
they became
The solids can be quite abrasive, and the tar mist can cause
|i.m in
are called spray, and droplets 1984a
with dỉameters
mbar/stage
upstream
from
the
bag versus
íilter
and
provide
means
for1965,
preheating
0.076
8.5
Fig.
8-7.
Particle
settling
velocity
size
and
ơensity
(Source:
ASME
Fig.

6)
Recent
work
has
been
done
on
cyclone
design
d
A/
-----------n
= inlet valves, rings, throttle shaíts, and other moving parts
condensate)
if are
theycalled
became
tooAerosols
cold. Polyester
felt or
bags,
the
the
1the
Stage
below
10
|j,m
mist.
are

solids
liquids
0.015
20
bag
filter
assembly.
c
speciíically
applied
to gasiíiers
by thoroughly
LePori
P stick.
V
2N e Vj
(pp - PQ)
71
most
widely
available,
are
rated
for
135°c
continuous
Service
to
Therefore,
both

contaminants
must
be
2(1983).
Stage that have been used for bag íilters include natural
suspended in a gas (Calvert 1972).
Materials
8-6. High-efficiency
cyclone engine
—
cut size
inlet width 1950; Freeth 8.6.2.5
other
Factors
temperature.
Stainlessin Cyclone
Steel, Pertormance
glass-íiber, and
for
tion
(Gengas
ạ?Fig.
3 reliable
= 63cyclone
m3 opera3versus
3removed
Stage
30
Nm
/h

273
10
K
/h
(37
ft
/min)
(8-6)
Table
8-4.
Filter
Fabric
Characteristics
A
pipe 2.5
cm (1 in.) inside diameter should provide a gas
organic
fiber,
glass1984a;
fiber,
ceramic
íiber,
and
roand
Dispersion
aerosols
are
v
The
most

common
errors
encountered
inmaterials
cyclone
are
ceramic-fiber
bag
filters
have design
been that
useda
1939;synửietic
Goldman
1939;
Kaupp
Kjellstrom
1981).
9(255 X 10~ kg/m-s)(0.025
m)
velocity of
Fabric Baghouse
Filter
1.8
Peterson
Steel.
The properties
of these materials
are outlined
3** gas

begin
as
large
particles
and
subsequently
are
broken
into
low
intake
velocity
caused
by
an
oversized
cỵclone,
and
Operating
Air
8.6.3stainless
Filter
successfully
at
higher
temperatures
and
show
good
promise

Successíul
gasifier-engine
systems
have
required
2(5)(14 m/s](2000 0.489 kg/m ) (3.14)
1965
quate
solids-conveying
velocity
within
the
pipe.
onTable
cyclone
cut size
is bag
minimal.
This Permeabilỉty
is due to
the 3
bTypi- cal
in
8-4.
Organic-fiber
smaller
sizes.
They
tend
to

be
coarse
with
a
wide
size-range,
reentrainment
of
solid
particles
caused
by
improper
cone
Exposure
(°F)
Supports
_____________
Resistance
to
__________
(Ịohansson
1980].
Uníortunately,
the
abrasion
and
ílexing
H
cleanliness

standards
from
2
3
Perry
1973
Spray
Cyclone
Dia.
24
in.
8.6.3.1
Principle
of Baghouse Filters
V=
solids-conveying
velocities
for light
materials range
from 10
2.5
|am (8-9)
counterbalancing
variations
of
and viscosity
2with
composed
of
particles

andfibers
aggregates
(i.e.,low;
char-ash
design or7lD
faulty
design
ofMineral
the
discharge
receiver.
resistance
of
glass
and
ceramic
can Organic
be
after
Fiber a
Long
Short
Combustion
(cfm/ft
3
)Composition
Abrasion
Acids
Acids Alk
mg/Nm

totoless
than
120mg/Nm
. density
2 irregular
Apwish
=3 2-10
in.
H
Vị
= 357
fpsasto 10
We
reduce
solid
particulates
mg/Nm
from
raw
Baghouse
íilters
(such
shown
in
Fig.
to
15
m/s
(30-50
ft/s),

as
shown
in
Table
6-1.
One
should
n
temperature.
,13
'
dust).
Condensatỉon
aerosols
are heated,
ỉormed
from
installation,
and
especially
once
they
have
been
the
se
Droplet
40-200
um
3

Rankc d Many
for
ash,
and
180
225
Yes
10-20
Cellulose
G
p
G
G
Reducing
the
flow
rate
decreases
the
separator’s
perforgasiíiers
can
produce
very
clean
tar-free
gas
under
gas that exits
gasifier widely

at 700°c.
The gas
within
few
4(63width
m /h) (b) equal to the gasiíier
8-10)
aretheused
today
to cools
capture
fine a dust
select
the cyclone
inlet such
pipe
supersaturated
vapors,
as2astar
and as
water
mist Highfrom
Scrubber
Tỵpe
materials
should
beonly
han-a dled
little
possible.

b
mance,
but
it
has
slight
effect
on
gas
cleanliness
If
coarse
particles
are
introduced
into
a
fine-particle
cyclone
certain
conditions.
However,
it
is
best
to
design
the
gas
feet

of
pipe
to
300°c,
which
we
will
consider
as
the
and
separate
Ayash
from combustion
gases.
3.14
(2.5
cm/100
cm/m)
(3600
s/h) velocity
5 A Protein
2.5
Perry
1973
outlet
pipe
diameter
the cyclone
inlet

to
Wool o particles
200
250
No
20-60
Gor set
Fwidely
F equal
p
SprayTovver
2-4
fpsXDróplet
7
chemical
reactions,
and
íormed
fromgas
cracked
9(259
10“capability
kg/m-s)(0.025
m) First,
d _ ,. /
temperature
bag
materials
are soot
not as in

available
as
other
because
the
dust
loaddesign
entrained
thecloth
inlet
to
the
Cyclone
and
then
two
detrimental
effects
may
occur.
the
cleanup
system
with
adequate
for íibrous
the
very
dirtybags
gas

cyclone
inlet
temperature.
Screening
analysis
of Polyamide
c_
3more
baghouse
filter
consists
of one
or
íilter
Nylond o separator,
200
250
Yes
15-30
E
p
F
G
(J,m
53
ft- 0.489
high
the
pipe
velocity

and
the
cyclone
according
to
the
P500-1000
V 2(5)(14
m/s)(200
kg/m
) (3.14]
hydrocarbon
molecules.
Theyreduced
tend toflow
be rate.
very The
fineresulting
and
of
materials.
m/s (7000atfpm)
(8-7)
separator=is35also
may produced
block
the
the
high Polyacrylonitrile
that

isparticles
occasionally
bysmall
airbome_char
7-4)
shows
aevery
mass
mean
particle
diameter
supported
metal
cages
enclosed
in
a Second,
chamber
through
loaded
Orlon k large
240on (Fig.
275
Yesinlet.
20-45
G 8-5.the The
G
F
proportions
in lower

Fig.
equations
that Gappeared
uniỉorm
size.
dof velocities
=
8
I^m
(8-10)
effect
is
that
this
outlet
dust
load
slowly
increases
with
vvithin
the
separator
may break
the coarse
which well
above
the
minimum.
dp = 100

|im
with
a geometric
Standard
deviation
ơg
= Polyestẽr
Dacron Bi which
the
275
gases
must
325
pass.
A deposit
Yes
of the up
separated
10-60
parE
G
G
2 —
Part
previously
then
can
be loaded
used to predict
particle

cutGsize
anda
5
11
Perry
1973
Wave
Plate
90°
decreased
flow
rate
inverse
square
rootto
ofthe
gas
flow pipe
rate
bybuilds
erosion,
impact,
and
attrition.
latter
effect
2.5.
Particulate
sampling
indicates

that
total This
dusta7-30
load
peak
Polypropylen
200
Yes
Eby theinlet
E equal
E
ticles
soon
up250
on
the
bag
and
establishes
dust at
cake
of Oleíin
Selectingdrop.
the
cyclone
widửi
pressure
3 —
Venturi
scrubber

(40
in.
wgEgas
o particles
for
char.
7
waves
7/16
in.
radius
0.15
in.
3
e
425
No
25-54
F
E
(Gengas
1950;
Calvert
1972;
Perry
1973).
generate
fine
particles
that

may
be
harder
to
capture
than
m .can
flow is 5000pore
mg/Nm
. through
For a turndown
ratio requirement
of Polyamide
appropriate
size
which
additional
particles
500
E
G
8.5
Particle
Movement
and
Capture
diameter,
the
cyclone
is

designed
by
the
proportions
from
4
—
Packed
bed
(6
in.
deep,
30
Table
8-3.be
Cylinder Wear for Gas Cleaned
with WetCyclone
CleaningDesign
and Fabrics
Filters
spacing
Nomex°
8.6.2.4
Example
a anything
The
cyclone
pressure
drop is
will

previously
present
inaccumulated,
theNo
gas penetration
(Perry
1973).
For this
Fiberglass
550
600
10-70
P-F
E an 5inlet
p
4:1,
the
maximum
dust
at Glass
cannot
pass.
As
more
dust
the
pressure
It
is 8-5.
tempting

tofps
reduce
inlet
Fig.
For inlet
width
2.5 cyclone
cm (1 E
in.)
andwidth
inlet with
height
cm
,1 the
Mechanisms
d ss
Diesel
3
Oil
2
2
Teflon D reason
500
No
15-65
Polytluoroethyle
F
E
E
E

it450
is preíerable
to
provide
a
gas-disengagement
space
Dual
Fuel
—
Diesel
Oil/Producer
Gas
Wet
For
example,
let
us
design
a
high
efficiency
cyclone
for
a
10
peak
flow
rate
is

P’
=
100
X
[(10
mg/Nm
)/(5000
'Cyclone
cut
diameter
(•065)(p
)(V
is
determined
)A
De
drop
increases.
When
D
the
cake
is
an
op=
G
i
d
vane;
the upset

cyclone
proportions
beenstream
found
(2 in.)however,
thenfortheseparating
cyclone
inlet
will
be have
/2
in.velocity
spheres)
Methods
particulates
from
the gas
3
Cleaning
System
Fabric
Filter
within
theby
thaneither
two by
stages
Table
Minimum
Particle

Size
(13.4 hp)
engine
system.
o for
mg/Nm
)]cfm/ft
=settling
0.2%.
Derating
root
the ne kw
2 8-2.
timal
thickness
for
removal,
the
bag
israther
agitated
gas
bygravity
design,
down
to
1gasifier
um.
**Fabric
to reduce

the
effective
number
of gas
rotations
NThe
t to as low as
3square
2of turndown,
5 gasiíier
—
Wet
impingement
scrubber
at
0.5
in.
water
usually
depend
on
the
mass
of
the
particles.
simplest
_
(.065)(0.489
kg/m

)(14
m/s)
(O
.Ũ25
m)
w of
cyclones.
This
will
allow
the of
coarser
particles
to settle
out
for
Various
Types
Scrubbers
maximum
for
is=Pfair,
= 0.2%/VÌ"=
0.1%.
pressure
orpenetration
by
mechanical
means,
causing

Dis
the
excess
cake
to
6increase
—
tilter
collection
efficiency
above
two and
to
reentrainment
1973).
Thereíore,
Cylinder
wear
1000
hturndown
gauge
P=
poor,
Fm)
method
theKarbate
particles
settle
under
thea inAuence

of
n prior
First
we allows
must
determine
the to
gas
flow(Perrỵ
rate for
typical
22%
(0.05
(0.05
m) 2 are related to
to
the
cyclone
separator.
Settling
velocities
7 — particles
Disintegrator
to 7-4
the
bottom
of
the
housing
where

it
is
eventually
to
remove
finer
using
cyclones
at
a
lower
pressure
dr drop
On
Fig.
we
follow
the
particle
size
distribution
line
for
an
Minimum
G
=
good,
E
=

excellent.
gravity,
with
the
gas
stream
flowing
vertically
upward
or
engine
efficiency
and
an
assumed
heating
value
of
1300
aerodynamic
diameter,
80%
of
particles
dp
=
20
|i.m,
and
the dp

are captured
with
80%
eữiciency, and (8-11)
those
8 — Packed bed (6 in. deep, 5
C value
size
as shown
in Figs.
7-6
and
8-7.
af particle
=gasifier
31 01
mm
(1.22
H
removed.
20
drop, it is
to reduce
theBtu/scf).
individual
cyclone
diameter
3 preíerable
3
Particle

Size,
Imbert
to
the in.)
data
point
where
the cumulative
fraction
T
ractor
0.015
mm
0.05
Cost
rank,
1
=
lowest
horizontally.
For
horizontal
separation,
the
process
can
be
fps
kcal/Nm
(5.44

MJ/Nm
,
157
Then
speciíic
gas
90%
of
particles
dp
=
30
um.
with
diameters
triple
the
d
value
are
captured
t equals 02
pc
(im
using multiple
parallel
cyclones
(multi-clones)
if necessary.
3

the
maximum
penetration
allowing
for
turndown
0.028
0.05
8.6.2.3
Cyclone
Strategy
cost,
9of
=the
highest
cost.
accelerated
byism
providing
multiple
Particles
3
4 /hp-h
2 spheres)
2
G Spray
tovvers
0.5-1.5
10
consumption

2.2
Nm
Ví
in.
scfm/hp) plates.
per
horsepower
We
can
see
that
cycloneshould
achieve
the
desired
*.l
rm
r\/ this
f>r*
•Design
T wofds
.
1in the
r Operation
1 PofD
8.6.3.2
Action
Filter
Cake
with

90%
efficiency.
In
other
(63
/h](10
/m(1.43
) horizontal
Note that_3 gravity
settlingcmchamber,
cyclone, disintegrator,
03
0.031
0.06
0.007
a In
(0.1%).
The
corresponding
particle
diameter
dp
=
3
|im
is
the
Air
leaking
into

the
char-ash
hopper
at
the
bottom
of a
also
can
be
separated
from
the
gas
on
the
basis
their mass
or 3 Nm(2.5
/kwh
(25cm)(3600
cfm/kW)s/h)
(Gengas
1950). of
Du
particulate
Pont
removal
registered
without

excessive
pressure
drop.
9 cm)(5
—
Impingement
scrubber
Fabric
Filters
our
experience,
the
cyclones
íitted
to
gasiíiers
aie
too
large
Cyclone
spray
2-10
2-10
wire m'esh separator, and spray tower all have0.019
the same
sitcut
2dpd50 p50>
06
0.005-0.010
(8the

-1)
point
we
wi.ll
require.
=
3
^m,
as
shown
by
p80
cyclone
separator
deteriorates
períormance
substantially.
by
using
the
centripetal
íorce
provided
by
a
centriíugal
scrubbers
optimum
particle
removal.

Thereíore,
present
here
an
10 — Cyclone
Impingemenl
2-50beenwe
1-5
ie for
However,
there
is íilters
still
a finite
possibility
ofíòund
large
parStandard
of scfm)
inertial
and
A
10 kw =engine
require
30 Nm 3 /h
(20
of producer
Fibrous
bag
have

toticles
be
08
0.020
0.011
14deviation—characteristic
m/swill
(2755
fpm)
(8-8)
dotted
Similarly,
removing
the
gas
through
bottom improves
the
scrubbers
separator.
r example
Packedand
and line.
of
detailed
cyclone
design.
11
—
Wire

mesh
(n
=the
2)outpassing
through
a
cyclone,
so
it
is
not
advisable
to
use
a
gravitational
separation
mechanisms.
Sharper
particle
gas,
which
corresponds
to
a
gas
energy
put
of
163

MJ/h
in
the
removal
of
particles
down
to
E outstanding
Oil
contamination
expressed
0.2%
0.3%
0.54%
-1.97%
0.12%-0.25%
fluidized-bed
efficiency
of
the
cyclone
separator.
Cyclone
cut
size
is
the
size
particle

that
will
be
collected
scrubbers
2-50
1-10
The
recommended
minimum
gas
velocity
for
conveying
12 indicated
—
(nStandard
=at1)the cyclone
cyclone
as the
method
of- particulate
separation
as
by mesh
smaller
devia- tion
n The
dp90
dp50■

(188
kBtu/h).
TheWire
volume
gas
inlet
submicron
sizes,
as shown
in
thedust
diameter
ofsole
pipe
from
thefor
gasiíier
to(8the
-2 )
withaverage
50%
efficiency.
Then
weofcalculate,
using the
Oritice
scrubbers
5-100
1 grade
medium

density
dust leading
is 15 m/s,
and
heavyoutlet
(metal
(2viscosity
tests)
as amount
of
insoluble
0.75%
(9tests)
gi cyclone
13
—
Wave
plate
involves
the
beneíit
of
other
or
additional
capture
temperature
of
300°c
will

be
efficiency
curve
of
Figs.
8-2
and
8-11.
Highinlet
should
be selected 5-100
to allow an ade- 0.8
Venturi
scrubbers
and density of producer gas from Fig. 8-8 and
assuming100
ash
50
is
25
m/s.
n turnings)
Products
in
benzene
after
100
mechanisms
suchcyclone
as condensation,

cascading
dif- íusion, or
efficiency
capture
ofcurve
small
particles
isum
surprisingly
3proportions (Source:
For
example,
agasitier
cyclone
rated
at
d p5Q
=gas10
can
be ex-ừom Skov 1974)
e Fig.
Fig. 8-5. High-efficiency
Perry 1973, Fig. 20-96. © 1973.
Fibrous-bed
5-110
0.5
Fig.
8-3.
8-4.
Typical

Cyclone
vehicle
grade
efficiency
system
showing
(Source:
cyclone
Kaupp
and
1984a,
Fig.
cooler
138)
(Source:
Adapted
density
2.0
(2000
kg/m
)
and
char
hpected to capture
size
(dp)
/im
Source:
Kjellstrom
1981,

2.4.
mass
Fig. 8-10.
transíer.
Cloth bag
Similarlỵ,
filter
with intermittent
reverse
separation
pulse
cleaning
(Source: Work 1955, p.
independent
of
the50%
sizeofofparticles
openings
inTable
the10íilter
weave.Particle
The
Used
with
permission
of McGraw
Hillpoorer
Book Co.;
Kaupp
1984a,

Fig. 134)
scrubbers
having
|i.m
Source:
Perry
1973,
Table
20-41.
483)
reason
for
this
is
that
the
primary
Fig. 8-2. Scrubber pedormance and sharpness comparison (Source: See reíerence in Table 8-1) 72 Handbook of
=

8

=

95

a

b

c

d

3

78
80
of
Downdraft
Gasiỉier
76
74 Handbook
Handbook
of Biomass
Biomass
Downdraft
Gasifier Engine
Engine Systems
Systems
Biomass
Downdraft
Gasitier
Engine Gasitier
Systems

79
Gas
Gas Cleaning
Cleaning and

and Conditioning
Conditioning 73
81
77
75


8.6.3.4

Safety Filter
—-ị ụ

If the íĩlter bag ruptures, contaminants harmíul to the engine
will be released. Thereíore, a saíety íilter or other effective
warning means should always be used in conjunction with bag
íìlters. The saíety íilter acts by plugging quickly and shutting
down the system in the event of an upstream equipment
íailure. A 200-mesh screen is suitable for a saíety íilter, as
shown in Fig. 8-12

8.6.4

Wire
netting
Supporti
ng
tilter

Electrostatic (Cottrell) Precipitators

í
--------- To
-

the
§
mixer

From the cloth cleaner

Electrostatic precipitators have a long history of in- dustrial
use to produce exceptionallỵ clean gas. During operation, the
gas passes through a chamber (as shown in Fig. 8-13)
containing a Central high-voltage (10- 30 kv) negative
electrode. A corona discharge forms around the Central
electrode, which imparts a negative charge to all particles
and droplets. The negatively charged particles then migrate to
the positive electrode, which may be vvashed by a continuous
water stream to remove these particles. The electrostatic
precipitator ís effective for all drop and particle sizes.

Fig. 8-12. Flame arrestor and saíety tilter (Source: Gengas 1950, Fig. 166)

dramatic, and the tar mist at the ílare could be seen to
disappear instantaneously when the voltage was applied.
However, the electrodes and insulators soon became coated
with soot and tar, and íormed a short-circuit path that
supported an arc. A means for cleaning the electrodes must be
provided, along with a means to warm the insulators to
prevent a water-condensation short-circuit. These problems

are being investigated.

A small precipitator (20 cm in diameter and 1 m in length)
was operated at SERI to clean gas produced by a 75-hp
Hesselman gas generator powering a 15-kw electric
generator. The initial results were very

For tar-mist removal, wire and tube electrostatic precipitators
are preferred over the plate-type elecừo- static precipitator
(Strauss 1975). Typical performance

Discharge
electrodes
connected to
negative
Earth
ed
plate

H.T. inlet

Outlet
Suppo
rting
insulat
ors
Collect
ing
electro
de

Precipit
ation
electro
Drain
'Weight

Front elevationSide elevation
Hexagonal tube type precipitator Two-stage
discharge electrode vertical flow tube
precipitator
Fig. 8-13. Electrostatic precipitator examples (Source: Strauss 1975, Figs. 10-19, 10-20.

©

1975. Used with permission of Pergamon Press)

Gas Cleaning and Conditioning 83


3
Table
8-5. aTypical
Períormance
Data
for
Precipitators
70% of
theElectrostatic
total
contained

the initial
fuel.
from
hot suríacethereby
and reducing
toward
suiface.
for tar acondensation,
thecold
amount
of veryThis
fine
isto
introduced
at a energy
concentration
of vvithin
0.25 L/Nm
, at 30
psig
A
typical
sieve-plate
scrubber
can
attain
90%
efficien2cy for
phenomenon
called “thermophoresis.”

and persistentisself-nucleated
tar mist (Calvert 1972).
spray
pressure,
and
in
a
high
intensity
Sonic
field
of
The
heat
losses
from
surfaces
vary
from
1
to
5
Btu/ft
-h-°F,
Dust Concentrations
l-|im
particles
using
3/16-in.
holes,

at a time
speciíic
velocity
frequency
600
tothe800
Hz. A sieve
12-s
residence
permits
the
3
depending
on
geometry
of
the
gas
cooler
and
Wetted
particles
tend
to
stick
together
better
when
they
g/m

at
Operating
Temp.Collecting
Power
The design of a good scrubber must maximize the gas- liquid
of
15 m/sto (50
ft/s). Typical
períormance
characteristics
of
particles
agglomerate
to a size
large
enough
to becooling
captured
temperatures
involved. Thus,
a great
deal
of the
at
collide,
assisting
agglomeration.
Wetdrop
scrubbers
Consumption

contact thereby
area while
minimizing
the pressure
throughhave
the
sieve-plate
scrubbers
are
discussed
in
Kaupp
(1984a).
with
94%
efficiency by
a be
5-|im
cyclone (Calvert
1972).
3
higher
temperatures
can
accomplished
in
the
pipes
and
at

been
used
widely,
especially
in
stationarỵ
applications
for
TypeotPlant
Inlet
Outlet
Efficiency(%)
w/1000m
/h
scrubber.
For instance, the gas-liquid con- tact area for a foam
Coal
Gas
the
of the gasiíier
as wellbutas the
in the
cyclone
Impingement
Plateitselí,
cleaning
and Industry
cooling
the agas.
A scrubber

operates
by creating 8.7.2.4
If asuríaces
condensation
nucleus
isScrubbers
absent,
degree
of
is much
greater
than for
spray,
gi ven equal
energy
0.008
99.85
702
Peat
gas
producer
5.34inputs.
separators
or
other
cleaning
equipment.
However,
as
the

gas
conditions for maximum contact between the gas to be
supersaturation
(S) scrubber
exceeds shown
200%in Fig.
to 8-16
400%,
then
The
impingement-plate
is
similar
99.20
120.4
Cracking
plant
for anatural
gas chamber at0.224
If a gas and
stream
enters
liquid-filled
high velocity 0.002
approaches
ambient
temperature,
cooling
suríace
cleaned

a scrubbing
liquid
medium.
homogeneous
self-nucleation
occurs.
Self-nucleation
to
a sieve-plate
scrubber,
exceptadditional
impingement
plates
are
0.20
99.47
652
Producer
gas
from
lignite
briquettes
37.7
thiough a small hole at the bottom of the cham- ber, then all
through
some
form
of
gas
cooler

is
required.
produces
extremely
small
droplet
sizes.
The
droplet
growth
arranged so that each
hole has an impinge- ment
target one
Basic scrubber
types
and
períormance characteristics
are 0.10
99.7
602
Producer
gas
from
sembituminous
lignite
of the entering gas must experience the subsequent impaction
rate diameter
is
inversely
to Gas

the the
droplet
radius,
sosurit
Gas
coolers
exchange
between
and
hole
awayproportional
fromheat
the hole.
flowgas
past
the the
edge
of
summarized in Tables 8-1, 8-2, and 8-7, and grade
28.7efficiency
0.006
99.9
903
and diffusion
environments.
When water enters
the gas
proceeds
first,
accelerating

withawhen
droplet
size.
rounding
air,
or atbetween
the
gas and
liquid.
A typithe
oriíiceslowly
produces
spray
droplets
that,
íormed,
arecal
at
Shale-gas
cleaning
plant
40.0
99.9
903
curves are shown
in Fig.
8-2. Scrubbers can be
divided into 0.010
stxeamoven
as a high

spray, only a small 24.15
ữaction of the
Coke
townpressure
gas cleaning
radiator
used
ininvehicle
applications
is shown
in Fig. self8-3.
rest,
resulting
99.9
a large
relative over
velocity
1605
between
dust
impingement-plate,
packed-bed,
sieve- plate, spray tower, and 0.003
Nucleated
condensation
dominates
homogeneous
gas
is
close

enough
to
the
nozzle
to
receive
the beneíit of 0.078
Coke
town gas cleaning
17.0
99.8
752
Here,
theand
motion
of
the vehicle
increases
flowcondenses
around
particles
these
droplets.
The gas
velocityair
usually
is abovea
Venturioven
scrubbers.
nucleation

when
nucleation
sites
are
present.
Vapor
impaction
with
high-velocity droplets. 28.0
Spray droplet 0.039
Coke
oven
gas the
cleaning
99.2
1404
gas
cooler,
so that
coolingoperating
air isfaces,
available
atdrop
the
15
m/s
(50 ft/s),
andmore
theconcave
tỵpical

pressure
is void
more
readily
within
suríilling
thehigher
Small,
difficult-to-capture
be made
grow in
agglomeration proceedsdroplets
rapidly,may
causing
the togas-liquid
Oil
0.050
99.5
1805
speeds
when
the
heat
load
is
greatest.
In
stationary
1.5 in.
water of

gauge
mbar) perSoluble
plate. An
increased
pressure
drop
fraction
solid(4particles.
aerosol
particles
nucleate
size
with
time
until
they
are
large
enough
to
be
captured
by
contact
area to drop
off sharply
within a short4.73
distance from
carburetted
water

gas Table
cleaning
applications,
íorced
ventilation
required
to solution.
move
air
raises
the collection
Theisrequired water
flow rate
even more
readily
byefficiency.
boiling point
depression
in
A
Source:
Perry
1973,
20-45.
simply
providing
adequate
residence
time
in

the
scrubber
the nozzle. This effect seriously limits the collection ability of
through
the
gas
cooler.
is
1
to
2
gpm
per
1000
cfm
of
gas
Ổow.
small droplet grows slovvly by chance agglomeration until it
volume.
Particles
grow
in
size
by
agglomeration
and
spray scrubbers.
characteristics
for electrostatic precipitators are shown in

gravitational,
or
centriíugal
means.
particles
than
reaches
critical
size;
that,
it
grows
rapidly
by acting
As
the its
gas
cools,
tars after
begin
to For
condense
at smaller
temperatures
condensation.
Agglomeration
is efficiency.
par- ticle growth through 8.7.2.5
Venturi
Scrubbers

Table
8-5, indicating
high capture
0.1
um,
motion
is
dominated
by
molecular
collisions.
They
as
a
nucleation
site.
Soluble
particles
behave
as
nucleation
below 350°c. As the temperature passes below the dew
Almost
all high-concentration clouds tend
8.7.2particle coìlision.
Scrubber
Equipment
The
scrubber
(Fig.

8-17) critical
captures
large
particles
by
follow
Brownian
motion
behave
more
like
a gas,
The
precipitator
diameter
should bewithin
small 1enough
to
sites Venturi
vvithout
to principles,
achieve
size.
The
charash
point
of the having
gas
(typically
40°-60°C),

water
also
will
to have
the sametube
particle
concentration
min after
impaction
and
impingement,
and
also
rinses
away
any
8.7.2.1
SprayTovvers
and
may
be
collected
by
difíusion
onto
a
liquid
suríace.
In
allow

the
corona
discharge
to
be
established
at
a
reasonable
dust particles
in the
gastar stream
at
condense.
Water present
condensation
helpsproducer
to remove
par- ticles
ỉormation.
deposits
thatwemight
otherwise
Some
fine
particles
are
this
section
will look

theform.
basic
mechanisms
of
particle
voltage
and large
so thatisitsthe
volume
provide
thein
The simplest
typeenough
of scrubber
spray will
tower
(shown
temperatures
below
the taratwater
dew
point
will
act
asthe
nuclei
but
yields
a
contaminated

condensate
in
process.
If
A novel method
to capture
mist islength.
to provide
water
also captured
here byfor
diffusion.
High-velocity
flow through
movement
and capture
wet scrubber
systems.
necessary
residence
with0.2-(Am
a reasonable
Low flow
Fig. 8-14),
which time
is composed
of an empty
cylinder
with
tars

and
particulates
are
removed
from
the
gas
beíore
it
enters
fog nuclei
and
residence
time. VVater
fog collection
the low-pressure throat area atomizes the droplets. The low
rates
in aample
higher
residence
and size
higher
sprayresult
nozzles.
The
optimum
spraytime
droplet
is 500 to 1000
Particles

diameters
0.1 and
fall within
the
the gas with
cooler,
then thebetween
gas cooler
will1 (im
be able
to operate
pressure at the throat causes conden- sation, and the high
efficiency.
ụ.m. Typical upward superíicial gas velocity for a gravity
so-called
“open window.”
They
are
the most difficult
particles
longer
between
cleanings.
All
heat-exchange
and
gas-cooling
Fig. 8-16. Impingement plate scrubber (Source: Kaupp 1984a, Figs. 142, 143)
relative velocity of the droplets with respect to the gas
spray tower

is precipitator
2 to 4 ft/s,tubes,
and as
particle incollection
tosuríaces
capture,ineither
bywith
diffusion or in- ertial mechanisms. They
Multiple
parallel
shown
Fig. 8-13,is
contact
captures most larger particles by impaction.
accomplished
when particles
rising
withand
theuse
gasa lower
stream
are too large to diffuse well but too small to settle. However,
permit
a more compact
precipitator
design
Table
8-7.
Scrubber
Types

and
Períormance
mon
problem
for
wetpresent
scrubbers
in small
gasiíier
systems.
Gas
impact than
with
falling
through
the
chamber
at their
scrubbers
have
no moving
parts
andThe
are sparking
especially
well-suited
they
can
be made
to grow

in size,
since
particles
collide
voltage
a droplets
single
larger
tube.
voltage
for
The
atomized
droplets
a considerable
suríace
area
for
Method
8.7.2.3
Sieve-Plate
Scrubbers
Comments
contaminant
testing
advisable
for diffusion.
allparticles
unproven
designs.

terminal
settling
velocitỵ.
The
spray
tower
is
especially
wellfor very
dirty, corrosive,
or abrasive
might
Pressure
Drop
VVater
naturally
and
agglomerate
into larger
that
are
easier
tube
precipitators
is shown
in Limit
Table materials
8-6. In that
practice,
Size

fine particles
to beis captured
by
Furthermore,
Column
(in.) inscrubber
suited as adamage
preíilter
for extremely
heavy
dust
loads (over
50
otherwise
a blower
Particle
impeller
(Calvert
Cut
Dia.
1972].
tocondensation
capture.
precipitators
are operated
at
the highest
operating
voltage
the throat

improves
captureofthrough
diffusion
Acm
sieve-plate
(Fig.
8-15) consists
a vertical
tower
(dpso)
g/Nm 3 ),excessive
which would
plug other
types of scrubbers.
Auxiliary
Equipment
without
sparking
(Perryless-open
1973). One-second
delays 8.7.3
because
theofphenomenon
Steían
motion.
The
atomized
with
a of
series

ofhigh-efficiency
horizontalof perforated
sieve
plates.
The
One
method
collection
uses
primary
8.7.2.7
Packed-Bed
Scrubbers
Ịim
Fịg.
8-17.cone
Venturí
scrubber
with centrìtugal
entrainment
(Source:
Calvert
1972,
Fullspray
nozzles
produce
500
toresult
1000
|im eữective

droplets,
between
sparks
have
been
found
toseparator
in
Gravity
Settling
>30
Low
droplets
rapidly
agglomerate
in
the
diffuser
section,
where
scrubbing
liquid
is
fed
into
the
top
of
the
column

and
flows
separator;
veryfollowed
large
collection of large particlesCoarse
by inertia
and diffusion,
Fig. 5.3.6-1)
The
packed-bed
(Fig. 8-19)
simple
open
in 8.7.3.1
Gas
which
fall with
a scrubber
settling velocity
of 13isft/s.
For aand
spray
tower
precipitator
operation.
collection
through
diffusion
continues.

Entrained
droplets
downward
viaCooling
downcomers
to plate;
the gas
to
andfrom
bulky
by
an increase
in
fine
particle
sizeplate
by agglomeration,
andbe
design,
andtheuses
spheres,
rings, or saddles as ran- dom
Water
vapor
acts
as
an
inert
dilutent
of

producer
gas,
initially
53
ft
high,
value
of
dp
50 is 5 um.
containing
captured
contaminants
are
separated
inertially
from
scrubbed
is
introduced
at
the
bottom
of
the
column
and
passes
íinally
by

collection
and
entrainment
separation.
The
rate
of
Application
of a negative (rather than
positive) voltage on the1 cm/1 Ocm of
Massive
>5contact
Freeand
draining
coarse
demister
packings toPacking
enhance the gas-liquid
area. Packed beds
lowering
thegas.
gas
heating
value
ultimately
lowering
engine
the
cleaned
Liquid

recycle
requires
cooling
and
removal
upward
through
the
sieve
holes
counter
to
the
liquid.
Contact
agglomeration
is
proportional
to
the
total
number
of
particles
center
electrode
is
íavored
because
this

arrangement
results
8.7.2.2
Cyclone
Spray
Scrubbers
column
height
are
more
for both
and zone
liquid-gas
heat
when
theeffective
gas leaves
the gas
charabsorption
gasiíication
at about
power
orAgglomeration
burner
ratìng,
shown
ìn replenishment.
Fig.by
8-21.
Much

of with
this
of
captured
materials,
orisas
disposal
and
betvveen
the
liquid
and
gas
is enhanced
by
using
plates
present.
also
assisted
the
presence
of
in a more stable corona and less sparking.
The
cyclone
spray
scrubber
combines
the

virtues
of
the
spray
exchange
than
they
are
for
particle
collection.
However,
800°c,
the sensible heat of the1gas accounts for about 15% 10droplets
Fiber
Packing
water
cm vapor
can
be
removed
by
cooling
the
producer
gas
and
Viscous
materials
can

cause
bubble
caps,
impingement
plates,
or
sieve
plates.
that
act
as
nuclei.
The
typical
through
the capelectrode
0.1particleto 0.5it
The
collectioncondensing
efficiency out
and
droplet
size are deter- mined by
tower
and
dry
improves
the
packed
bedscurrent

arecyclone
excellent
for
turing
liquids.
of the
initial
energy
in theseparator.
wood.
If It
the
gasis entrained
islow:
burned
while
subsequently
the
water.
plugging
2
Particles
tenddrop:
to scrubber
move toward
suríace
on which
mA/m
ofefficiency
collecting

suríace
(Perry
Halfwave
the
efficiencies
maya be
in- creased
by reducing
Thepressure
sieve-plate
captures
large
particles
byconimcapture
of
the
spray
droplets
in superíìcial
ordinary
spray
For
entrainment
the
optimum
gas
is still
hot,
then theseparation,
sensible

heat
can
be1973).
utilized.
However,
if
The amount
of water
vapor
remaining
afteristhe
cooling
Pretormed
Spray
Low densation
water
consumption
taking
place.
This
phenomenon
to and
asof
rectiíication
a 50in to
60
Hz>5
electric
supply
the

throatisarea
to
raise
theHigh
pressure
drop.
The referred
efficiencies
pingement
and
impaction,
and
small
particles
by
dif- íusion.
scrubbers
byof
spray-droplet
impact.
Theprovides
cyclone
velocity
packed-bed
scrubbers
using
1/2-in.
spheres
10
the gas isfor

to
beincreasing
used
an
internal-combustion
engine,
it is
must
condensation
steps
can betend
determined
readily
from the lowest
“Steían
motion.”
Particles
to
migrate
away
adequate
time
for
extinguishing
sparks.
Venturi
scrubbers
are
discussed
in

Calvert
(1972).
Gas
passes
upward
into
the
water
layer
through
holes
in
the
spray
scrubber
also
thereentrainment
advantage,
compared
the
to
ft/s.
Floodinghas
and
occur above
a gas
for sticky
materials
be 12
cooled

to prevent
preignition,
thewith
engine
Gas
Atomized
Spray
>5 to improve
0.002 (0.001)
5.7 to vvhich Good
temperature
the gas
has been
cooled. If
sieve
plate.
The
high
gas
velocity
through
the
sieve
holes
spray
scrubber,
of
being
self
cleaning,

of
collecting
more
velocity
of consumed
The
power
by
Venturi
and
Sieve
>2 gasprecipitator
volumetric
efficiency,
andantoelectrostatic
íacilitate
cleanup. is very(2.2)
8.7.2.6
Eịector
condensation
has Venturi
occurred,Scrubbers
then the lowest gas temperature is
atomizes
the scrubber liquid into fine droplets, and most
particles
regardless
of issize,
and
operating

smaller
ft/s.
The
pressure
drop
7.5
to 8.5
in.
wateratand
gauge
forpressure
a 6-in.Plate
Scrubbers
>1
(8.9)
low,
typically
1.5
w/hp
(Strauss
1975),
The thermal energy in the raw gas may be eitherthe
dis-pressure
sipated, 22.6The
of
course
the of
dew
point
of the liquid

gas mixture.pumps
The water scrubs
vapor
velocity
the
contacting
inertial particle collection takes placeboth
just as theand
bubble is
drops.
A basic
design
is shown
in
8-9;in. others
are 91 (35.9)
deep
bed.
Performance
characteristics
Submicron
of
packed
drop
verỵ
low,
at considerably
lessFig.
than
ofbeds

water.
usedalso
foris low-temperature
applications
such 1as
drying,
or
content
of thegas
gasinmay
be determined
from Fig. as
8-22,
or the
the
entrained
an
ejector
Venturi
scrubber,
shovvn
in
íormed, by impaction on the inner suríace of the
described
in Strauss
(1975).
Commercial
cyclone
scrubbers
shown

in Fig.
8-20. Packed
beds
are free-draining;
they may7.5-20being
High-voltage
requires
rigorous
saíety
measures.
Centrifugal
1-2
(3-8)
recycled intoequipment
the gasiíier
by using
the energy to
preheat In
the
psychrometric
chart
of nozzles
Fig.
7-19.
Note
that
the tangential
moisture
Compact;
good

for
Fig.
8-18.
Spiral
spray
impart
axial
and
bubble. Diffusive particle collection dominates as the bubble
are irrigated
better than
97% efficient
at removing
with
be
to remove
accumulations
with particles
water
addition,
íailures
loss
of flow
the
incominguníoreseen
air. Eachpower
method
has may
been cause
used a on

gasiíiers.
fractỉon roughly
with
each
10°c
increase
in must
the dew
preliminary
cleanup
velocities
to suríacethe doubles
liquid
jet.
The
contacting
liquid
be
rises. 8-6.
Here,
active
agents
canSparking
reduce
the
collection
diameters1972).
greater
than 1 |im.
The ability,

cut diameter
for
a cyclone
(Calvert
electrostatic
precipitator’s
cleaning
with
a
subsequent
Table
Electrostatic
Precipitator
Potentials
Airblast preheating was used exten- sively in European
point
teraperature.
We
can
calculate
that
at
the
7
0°c
dew
removed
after
the
scrubber

by
a
suitable
entrainment
Baffle
Plate
2.5-7.5
(1-3)
Large
coarse
collector
efficiency
because
of
Steían
motion,
but
a
cold
water
20
(solids)
5
spray
scrubber
is
about
an
order
of

magnitude
less
than
that
release
tars to the
vehicleofgasifiers
to engine.
improve
the gas and to permit wetter fuels
point, water
vapor represents
25%scrubber,
of the gas
Cooling
8.7.2.8
Entrainment
Separators
separator.
to a Venturi
thevolume.
ejector
Venturi
scrubbing Compared
liquid receiving
a hot aerosol
increases
the
(mist)
for either a dry cyclone or spray scrubber.

8
to
be
gasiíied
(Schlãpíer
1937;
Egloff
1941;
Lutzbe1940).
the
gas Diameter,
torequires
40°c
reduces
the
water
content
to lesstothan
8%,
Pipe
Sparking
Potential,
scrubber
both
more
liquid
and
more
power
achieve

Entrained
liquids
from
the
wet
scrubber
must
thoroughlỵ
collection
efficiency.
A
deeper
foam
reduces
inertial
effects
8.7Wet
Scrubbers
volts
Impingement
2-3
10-50the
(4-20) in.
Recoiland
bounce;
can
reentrain
resulting
inpara substantial
improvement

in gas
quality.
ticle collection
gas
movement.
Eịector
Using sensible
heatgasto stream
do more
than preheat
the aairblast
removed
from the
because
they carry
slurry or
of
Root
Mean
and same
increases
collection
byPeak
diffusion.
Inertial
collection
is
8.7.1Entrainment
Principles
of

Wet
Scrubbers
Square
5 because
(5) slightly
Can
be
clogged
heat the fuel
hopperEntrainment
is hardly justified
the gas is
dirty 32Venturi
Water
vapor
dilution
will
be
minimized
by
using
fuels
that
are
captured
materials.
droplets
are typically
greater
only

increased
by
adding
plates
or
increasing
tho
4
59,000
45,000
As
weonlỵ
havea|nm
previously
stated,
particles
diameters
Separator
and
small
quantity
of
(15%)with
is
involved.
If larger
usable
as drop.
possible and then condensing water vapor to remove
than

10
and
may
beheat
captured
using
a variety
of
pressure
Mechanically
Aided
1-2
Acts asas
adry
blovver
High
povver and 58,000
6
76,000
than
1
um
settle
by
gravity
and
inertia.
They
follow
heat is desired,

then athepacked
enginebed,
ex- ahaust
gas fiber
andStokes’
engine
it from the gas.
techniques,
including
packed
bed, a
maintenance
9
90,000
69,000
law
and can
be are
captured
by
impaction,
Moving
Bed
1 separator,
Good mass transter
coolant
fluid
much
cleaner
and

more abundant
of7.5-15(3-6)
cyclone
separator,
an impingement
a spraysources
tower, or
12
100,000
77,000
representing
aheat,
settling
chamber.60%
Poor entrainment
Fabric
Filter
0.3 separation has been a 13(5)
Excellent;
can
be
clogged
Forgases at atmospheric pressure,
coma

Source: Compiled from data in Calvert 1972. 100°F, containing water vapor, air, CŨ2
and mist, and negative-dischargeelectrode polarity.
146)

84

86Handbook
HandbookofofBiomass
BiomassDowndraft
DowndraftGasitier
GasiíierEngine
EngineSystems
Systems
88 Handbook of Biomass Downdraft Gasifier Engine Systems

Gas Cleaning
Cleaning and
and Conditioning
Conditioning 85
89
Gas
Gas Cleaning and Conditioning 87


the raw gas are subject to ash and tar buildup, so ample
cleanout ports should be provided to clean these suríaces
without requiring extensive disassembly.

8.7.3.2

Gas Drying

The diluting effect of water vapor on the wet gas heat- ing
value (HV W ) may be determined from the heating

value of the dry gas (HV fj) and the moisture ữaction (F m ) from

Packed
bed F mseparators
good
for finer
Fig.
8-22, where
= water vapor are
partial
pressure/total
droplet
removal.
For
example,
Fig.
8-24
illustxates
that a
(absolute) gas pressure.
6-in,- deep bed packed with l/2-in.-diameter spheres will
Then, HV W is found from
capture 50% of 2.5-ỊJ.m diameter droplets from a super- ficial
gas velocity at 1.5 m/s (5 ft/s). Deeper beds and íiner
packings will increase
collection
HV W = HV
(8-12)
d (l - F J períormance; however,
excessive gas velocity may cause reentrain- ment,
deteriorating overall performance. The mini- mum packing
size is limited by the fact that smaller packings more rapidly

become plugged by viscous tar deposits. In these cases flow
can be restored by stirring or replacing the packing.

o

It was common practice during VVorld War II to pass the gas
through wood chips, cork, or other íibrous materials to

remove tars. Some of these materials
subsequently can be used as fuel in the gasííier and thus
Raschig ring
Berl saddle

Liqui
d in

dispose of the pollutants. Fiberglass íilters have been used to
clean gas Qohansson 1985) as has char (Humphries 1985).

Fiber-type demisters have limited applications be- cause
viscous tar deposits on fine wire mesh do not drain freely and
are prone to plugging.

.
Packin
g

An electrostatic precipitator may be useful for entrainment separation. However, these units have not yet been
proven
reliable for continuous operation

with producer gas.
Les
Tellerette

Gas
distributor
and
Fig.8-22. Water content of saturated producer gas (Source: Gengas 1950,
Fig. 82)
packing
(The
moisture
íraction
approximately the same value

Fm

8.7.3.4

is

for either mass
íraction or volume íraction of water, since 1 Nm 3 of water and
1 Nm 3 of producer gas each
weighs approximately 1 kg.) The
Liq
uid has on the heating value of a
effect that vvater- vapor dilution
out
150-Btu gas is shown in Fig. 8-21.

sig
ringPreventing Further Condensation

The scrubbed gas may have a very high humidity (from 80%
humidity to the saturation point). Further condensation can be
expected to occur either as the pressure drops or when the
producer gas is mixed with combustion air.
To prevent íurther umvanted condensation, one may heat the
gas or secondary air (the engine ìntake air) vvith engine
exhaust heat as shown in Fig. 8-25.

Pall ring

Methods
of measuring gas moisture are
Fig.8-19. Packed tower and packings (Source: Kaupp 1984a, Fig. 151)
presented in Chapter 7. To minimize the power loss

Intal
ox
sadd
le

from water- vapor dilution, the necessary cooling suríace can
be roughly determined from Fig. 8-23. Ample ventilation must
be provided to cool and condense the gas with a 60°c dew
point from 700°c100
down to 40°c.

8.7.3.3 Collectio
Demisting/Entrainment
Separation
Reentrainment

A n common problem with
otherwise
degrades
droplet
adequate
inadequate removal
efficienc gas cleanup systems iscollection
above of
entrained
50 in. H20
y forscrubber
6 liquids.
oil 50
Theụm
gas emerging
from the gas cooler and from wet scrubbers
droplets
contains
droplets of dirty water entrained in the gas stream.
in engine6”
Most
trouble is caused when these entrainment-borne
contaminants
deep bedform deposits on the engine parts.
Therefore, they must be removed to íinish

the job of gas puriíication.

Wet cyclone separators
Fig. 8-9), with
2
5 10 20(shown
50 in 100
a max- imum spray velocity
of 45 ft/s
(15 (AP)
m/s), are
good
for
Pressure
drop
in.H
20
removing large mechanical entrainment drops more than 100 |
im
diameter
have low efficiency for fine mist particles
Fig. in
8-20.
Pertormancebut
otpackeơbed
less than 10 |xm in diameter.

c

Fig. 8-21. Power loss due to moisture saturated producer gas for 150 Btu/scídry basis gas

Fig. 8-23. Gas cooler surtace requirements for various outputs at 700°
(Source: Gengas
1950, Fig. 99)

90 Handbook of Biomass Downdraft Gasitier Engine Systems

Gas Cleaning and Conditioning 91


9.2.3

Feeding Solids

rni^ippo
During testing, fuel can be fed manually
Chapter
✓ to small gasiíiers.
However, there is the danger of running out of fuel, which in
ỉ
° / Bcharcoal
e đ d e p t h 6 burns.
turn overheats the gasifier as the
remaining
I
Pa r t i cl e Gasitier
d e n si t y 8 3 Systems
q/cc
Level alarms or other Con trols
t are strongly
o 2 5 f p s recommended

A 8 f ps
o 2 0 f p s operation
o 6 fps
for gasiíier systems intended /for continuous
(see
/
□ 10 fps
Chapter 10].
^
------ E x p e r i m e n t a l
ỵ

s

9.1The Complete Gasitier System
------T h e o r e t i c a l

stances and should be treated with due caution. Col- lected
that cannot be recycled to the gasiíier or burned on site
9tars
may need to be treated as hazardous wastes. They should not
be dumped on the ground or released into waterways.
Prevention through low-tar gasiíier designs is the best cure
for tar (see Chapters 4 and 5).

8.8.3
Condensate
can support
a shear stress, solids can bridge and arch in

The
liquid channels.
condensate
producer
gasof may
contain
Biomass fuels are only partially free flowing íram a hopper by
cylindrical
An from
important
measure
the difficulty
The previous chapters have discussed the major opera- tional
substantial
of tars
andthe
phenols.
are iswellgravity alone so bin stirrers, vibrators, or shakers may be
of íeeding amounts
a particular
solid,
angle Phenols
of repose,
tMe
components of a gasiíier-engine system. However, no system
known
and will
kill soil bacteria
spread
on the

required for even fuel delivery. Biomass can be moved
averagegermicides
angle from
a horizontal
plane ifassumed
by
is stronger than its weakest link. A complete
system requires
J____L
ground.
If biomass
releasedpieces
into waterways,
therancondensate
could
laterally and vertically
by
conveyor
belts,
chain
drags,
bucket
individual
when
they
are
domly
piled
up.
10

t
2 dry
3 the biomass,
6
means to store and possibly
to feed 20
the
damage
lifeforms
by those
elevators, augers, pneumatic
For liquids,
this supported
angle is zero;
for waterways.
some solids, it can be
Di a m eblowers,
t e r ( m i cr o n s)and vibratory íeeders
biomass, to remove char-ash,
to
push or pull the gas through
(e.g., Syntron type), widely available in agricultural handling
greater
than 90°!water,
For this
reason,
vibrators,
shakers,
and
For

condensate
as
with
tars,
prevention
is rakes
the best
the System, to clean the gas, and to burn the gas during
Fig. 8-24. Entrainment
separaỉor
otpackeớ
bedfor
removal
equipment.
Again,
thosecollection
with efficiency
experience
with
thedroplet
particular
chains,
live bottoms
(on trucks),
and a formahost oftion
ingenious
cure.
Methods
of
minimizing

condensate
should
startup,
as 1973,
shown
in the Ễront of this book and in Fig. 9-1.
(Source: Perry
Fig. 18-142)
biomass
form should
be contacted for íeeding and equipment
devices
are used
widely in the
industrial
be
considered
fullỵ
early
designand
andagricultural
selection ofsolidthe
A complete system also requires instruments to measure
suggestions.
feeding
applications.
Much
time
and
money

can bemay
wasted
system (see Chapter 5). Gas moisture content
be
pressure,
flow
and
temperatures
at 79.
crucialUsed
points,
and of McGraw
reinventing
these
devices,
so(the
thedrier,
designer
is advised
to
Fig.
9-3. Solids
íeedingrates,
devices
(Source:
Perry 1973, Fig. 20© 1973.
with permission
Hill Book Co.)
minimized
bỵ

using
dry
fuel
the
better)
and
by
8.8
Disposal
of
Captured
The
flow of solids
in the gasiíier
is also consubjectditions.
to irControls
to establish
the required
contact others
with
experience
in íeeding
the particular
form
recycling
heat
back
into
the
gasiíier

through
an
air-blast
regularity
and
andwill
can be
cause
great difficulty
Contaminants
Instruments
andinterruption
Controls
discussed
in Chapter
of biomassCondensation
being used. from the gas may be minimized by
preheater.
during
gasiíication,
resulting
in
such
problems
as
bridging,
pipeline disữibution or synsas for chemical synthesis (Reed 9.3.2limiting Fans
10.
the
amount of gas cooling so as to use the gas above

8.8.1caking, Char-Ash
1982). channelling, and rat-holing. The importance of
Propeller-type
fan blades
usuallyThe
generate
1.25
cm (0.5
its
water
dew
point
(40°-60°C).
loss inunder
engine
power
or
uniíorm
feeding
cannotfrom
be
overemphasized
experts in
The char-ash
removed
producer
gas is Solids
freeand
of dangerous
9.2Storing,

Feeding,
and
Sealing
in.)
of
water
gauge
pressure
and
are
used
in
gasiíiers
onlythe
to
the
costs
of
larger
engines
may
be
more
than
offset
by
the
field should
be consulted
(Guzdar

1982, disposed
Miles 1982).
materials
and can
be burned
or saíely
of in a
move airinthrough
heat
exchangersdisposal.
and radiators. They are not
savings
the
cost
of
condensate
landíill.Characteristics
When burned oftoSolids
white ash, char-ash contains
9.2.2 storage
9.2.1Char-ash
must be removed
from the gasiíier and stored as it is
suitable for moving gas against any resistance.
valuable
minerals
that
may
be
beneficially

retumed
to
the
A closed bin, silo, or hopper must be supplied to hold the
Solids are
many
times Eịectors,
more
difficult
to feed
and be
seal
agaỉnst
produced.
An
air-tight
char-ash
receiver
should
provided,
9.3Fans,
Blovvers,
and
soil.flow
Charcoal
is a valuable,
clean-burning
fuel, worth several
biomass íeedstock (chips, cobs, pellets, etc.), to prevent it
gas

liquids
and gases.
Because they
since
thisthan
char
material
is combustible
and may reignite
Fig. 9-2. Batch fed gasilier with lid (Source: NAS 1983, p. 68)
Compressors
times the value of wood. Alternate uses and possible markets
from getting wet. In many cases, industrial or agricultural
spontaneously. In addition, it may be necessary to cool the
deíinitely
should be examined.
containers are available in appropriate sizes at low cost.
9.3.1receiver.
Importance
ofweight
Gas-Moving
Systemmay be only 2%
Although the
of the char-ash

Design
to
5% of
the material
weight of

thebebiomass
the gasiíier,
its
Larger
char
may
saleablefedforto íurther
charcoal

volume
may combustion,
represent
a larger
fractionmethod
of the for
volume
of the
gasiíication,
orabriquetting.
It
is important
to provide
suitable
pulling
or
original the
biomass
be- cause
of
its lower

density.
The
required
pushing
gas
through
the
gasiũer,
and
since
the
mass
of
gas
In addition to valuable soil minerals, charcoal has been
receiver
volume
must is
thereíore larger
be calculated
measured
and
air being
moved
thefrom
mass
successfully
used
as a soilmuch
conditioner than

in Japan,
result-ofingfuel
in
char-ash
bulk
densities, power
which may
may be
range
from 0.064
to 0.4
being
fed,
considerable
required.
The
improved
crop yields
(Kishimoto 1985). It also has beenengine
used
3
3
g/cm íueled
(4-26 lb/ft
).
being
canfeed
serve
this purpose.
as a livestock

supplement
to reduce digestive problems
Every
internal-combustion
engine
is receivers
a compressor,
since
it
Itand
should
be
mentioned
here
that ash
can has
contain
meat
hormone
ỉevels
(Taylor
1986].
Charcoal
long
compresses
and They
fuel
toin 10
to developing
30 times

explosive
gastheeven
whenaircold.
been
known
to
been considered
aintake
premium
cooking
fuelhave
many
atmospheric
pressure
igniting
the fuel.
When
an engine
ignite
on startup,
and beíore
precautions
should
be taken
against
this.
countries.
operates on producer gas, it can also provide suction and
8.8.2
Tar for the gasiíier. However, an engine is a very

9.2.4compression
Sealing
Solid Flows
3
A
gasifier
that producesformore
than new
0.5 g/Nm
of tar
can- not
expensive
compressor
testing
(Arthayukti
Gasiíiers may operate at pressures
up togasiíiers
20 in. water
gauge
be suitably
cleaned
foris engine
applications
dueother
to the
large
1984;
Breag
1982).
It

desirable
to
use
some
method
above or below atmospheric pressure, which makes
it
amounts
of the
tar that
mustisbeless
captured
andtodisposed
of.
For
a
for
moving
gas
that
sensitive
tar,
char,
and
soot
necessary to provide a seal through which the
biomass
can
3
worst-case

tar production
scenarioalso
of 2may
g/Nm
(0.2%), up type
to 2
during
testing.
Full
engine
require
pass without
leaking
air power
or gas. Proper
seals some
are very
g compressor
of tar per hp-hmay
arise10).
with each horsepower. Thus, a
of
(see
Chapter
important, to ensure both gas quality and safe operation (see
100-hp
engineofwould
produce
up to
4.8 kgbeofpulled

tar in (suc24 hours,
The
question
whether
the gas
should
tion
Chapter
12).
or
about
5
L.
At
room
temperature,
tar
is
a
viscous,
operation) or pushed (pressurized operation) throughslowthe
Gasifiers
the World War IIItera
were
batch-fed
through a
flowing,isfrom
molasses-like
contain
carcinogenic

gasifier
important, andfluid.
one íỉndsmay
strong
advocates
of each
lid
could be sealed tightly, as shown in Fig. 9-2. The
sub-that Gas
method.
leaks from gasiíiers operating above atmospheric
spring-loaded lid would pop open in the event of an internal
pressure can be dangerous because of the possibility of
gas explosion. As long as the gasifier was íilled quickly, the
leaking carbon monoxide out of the gasiíier; air leaking into
expelled smoke could be tolerated as a nuisance.
gasifiers operating below atmospheric pressure can cause
Gas ftows ZH^Z
explosions.

Solid/liquid
flows Measuring
devices

There are two basic types of solids íeeding and sealing
dnvices—mechanical seal type where the seal mechanically
prevents gas passage, and plug seal where the íủel acts as its
own plug and seal such that fuel velocity into the gasiíìer is
greater than gas velocity out through the fuel plug. It should
be noted that rotary valves and gate valves are also good

Exha
firestops for ílash- back or explosion prevention. Inert or air
ust
purgepipe
gas should be used in pressurized gasiíiers to offset
leakage through rotary valves. Additionally, there is the
Note:
stratiíied
charge gasiíier where air enters through the top at
The. pressure such that for operation above a
atmospheric
secondar
minimum gasiíỉcation rate, all smoke is drawn down into the
y air'
fuelpipe
bed, and
a lid is unnecessarỵ. In many cases, the biomass
runs
feed
can help to act as a seal in a long auger or vertical pipe.
Secondary
air valve
However,
the pressure drop through the fuel is small, and the
technique
will not work if the gasiíier fuel inlet is under a
Gas valve
positive pressure of more than 2.5 cm (1 in.) water gauge.
Various solids íeeding devices are shown in Fig.From
9-3. Star

valves, which rotate to feed the fuel, are gasiti
eravailable
commercially.
Heatingisofsecondaryairbyexhaustgasheatfrom
theengine (Source:
Gengas
IfFig.a 8-25.
gasifier
to be operated at high pressure,
it becomes
1950, Fig. 85)
exceedingly
diữicult to feed biomass through a single seal.
Lock hoppers that use two slide or bell valves supplying a
E = ejector L =
metering íeeder as shown in Fig. 9-4 have boen used with
level control T =
biomass at pressures up to 30 atmospheres for making
thermocouple
medium-energy gas for

AP = differential pressure gauge or
control m = feed mass flow
1982)
measurement device
Fig. 9-1. Gasitier system showing means of moving solids and gases and positions for various 'Instruments and Controls
94 Handbook
of Biomass
Downdraft
Gasitier

Engine
Systems
Handbook
of Biomass
Downdraft
Gasitier
Engine
Systems
92

Gasiíier Systems 95
Gasiíier Systems 93


and mixes with the driven gas. Optimum ejector dimensions
9.3.3
Blovvers
are discussed in Perry (1973).
Centriíugal blowers (Fig. 9-5) can generate pressures on the
9.3.5
Turbochargers and Superchargers
order of 100 cm (40 in.) of water gauge pressure and are quite
The power output of internal-combustion spark and diesel
suitable for gasiíier testing. To generate these pressures, the
engines is directly proportional to the energy content of the
blowers must either rotate very fast or have a large diameter,
intake fuel-air mixture. A mixture of producer gas and air has
since it is the centriíugal force that creates the pressure. The
30% less energy than a gasoline and air mixture, resulting in a
blower can tolerate, and in fact will remove, a certain amount

minimum 30% povver loss at any given rpm. Intake pressure
of tar and particu- lates, but a means for draining and cleaning
can be in- creased to overcome this power loss by a
the blower shouldbe provided. Blowers canbeused
turbocharger using engine exhaust pressure to run a turbine,
eithertopush the air into the gasifier or to pull the hot gas
or a su-Straight-blade,
percharger
operating
from
the
engine
shaft
power.
through the system at negative pressure. Considerably more
or steel-plate, fan.
This pressure boost is widely used in diesel engines and
power is required to pull the gas through the system than to
racing cars, and is coming into wider use even for sparkpush air because there is necessarily more mass to manipulate
ignition engines.
and the gas is less dense. In addition, suction fans must be
capable of handling a higher temperature than fans pushing
Positive displacement rotary blowers (Fig. 9-7) and suair into the gasifier. Most blower breakdowns occur due to
perchargers can achieve any pressure required, but they do so
deposits on shaft seal and impeller or erosion of the case.
at higher Capital, operating, maintenance, and energy
Reliability is limited by deposits.
costs. This increased cost must be weighed against the lower
cost of using a larger engine.

9.3.4

9.4 Flares and Product-Gas Burners
Forward-ciưved-b!ade, or “Sirocco”-type fan.

9.4.1

Flares

Plares sometimes may be seen at oil wells or refineries in
which excess gas burns with a luminous flame. In order to
produce a nonluminous flame, it is necessary to provide
enough air and residence time to burn the soot in a hotter,
nonluminous flame. This is called a gas incinerator.
Raw producer gas contains up to 40% carbon monoxide and
up to 20% volatile tars, making it absolutely essential that a
reliable incinerator be available during testing to burn the gas.
The incinerator must be sized to fit the gasiíier. Most of the
principles discussed below for incinerators also apply to
developing burners for producer gas.
The three essential elements necessary to combust any gas are
residence time, temperature, and turbulence (the three “T’s”
of gas 130
combustion). Residence time re- quires a suữicently
y
large chamber
for combustion to proceed to completion. High
£120
4. \
LU

temperature
is
by—I
using a reữactory lining on the
HO " achieved
V
, can be —
burner. Turbulence
generated
by high-velocity
K I___
V,
‘V mixing
of the |com- bustion air orI fuel (for
instance,
by
passing it
^
- 'N \LV >> air with the gas.
through a nozzle)stroighỉ
or by tangentially mixing
'
70
bậQđe"''
le'
The reader
to books on
combustion and \burners for
ềio60 is reíerred
Forwarơ’

1
2-stoge
a more complete Curved
discussion
(e.g., Perry 1973).>
prvpeller
1 50
V
\ \ a pilot
40
Incinerators
for toxic chemicals and gases \require
ỉ
flame to assure combustion operated on methane or
\ propane,
3
\ down
\
an ignitor
the
s 0to start the flame, a flame sensor to shut
burner8 if■the flame is extinguished, and a control system to
I the0air mixture
20
40 and
60 stack temperature.
60
regulate
20
100 Ị20

Í4Ọ 160
Volume in Per Cerrt of Volume ot Highesl Etticie
Approximate characteristics of varioưs types of fans.

ncy

Fig. 9-5. Centritugal blovvers (Source: Perrỵ 1973, Figs. 6-37, 6-38, 6-39, 6-41. © 1973.
Used with permission of McGravv Hill Book Co.)

Ejectors

Ejectors are a very convenient and simple means for moving
dirty gas. No moving parts are exposed to gas contaminants.
Eịectors (Fig. 9-6] use the motion of a small amount of one
gas to move larger quantities of a second gas, oíten at
negative pressures. During startup, the gas produced initially
is very tarry and may quick- ly clog cleanup and engine.
Thereíore, one should use a fan or eịector during startup to
send this gas to a product-gas burner until low-tar operation is
reached. Compressed air, nitrogen, or steam can be used to
drive the ejector. VVater jets can also be used to move, cool,
and clean the gas.
Ejector design is based on the principle of the conser- vation
of momentum of the driver gas as it aspirates

sliding-vane type o( rotary blower.

Fíg. 9-7. Positive displacement rotary blovvers and compressors (Source: Perry 1973, Figs.
Fig. 9-6. Eịectorpumpíormovinggas (Source: Perry 1973, Fig. 6-73. © 1973. Used with
6-49, 6-50, 6-51. © 1973. Used with permis- sion fMcGraw Hill Book Co.)

permission of McGraw Hill Book Co.)

96 Handbook of Biomass Downdraft Gasiíier Engine Systems

0

Gasitier Systems 97