Parametric analysis of a circulating fluidized bed biomass gasifier for hydrogen production

Energy xxx (2015) 1e8

Contents lists available at ScienceDirect

Energy
journal homepage: www.elsevier.com/locate/energy

Parametric analysis of a circulating fluidized bed biomass gasifier for
hydrogen production
Bhawasut Chutichai a, Yaneeporn Patcharavorachot b, Suttichai Assabumrungrat c,
Amornchai Arpornwichanop a, *
a

Computational Process Engineering Research Unit, Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University,
Bangkok 10330, Thailand
School of Chemical Engineering, Faculty of Engineering, King Mongkut's Institute of Technology Ladkrabang, Bangkok 10520, Thailand
c
Center of Excellence in Catalysis and Catalytic Reaction Engineering, Department of Chemical Engineering, Faculty of Engineering,
Chulalongkorn University, Bangkok 10330, Thailand
b

a r t i c l e i n f o

a b s t r a c t

Article history:
Received 16 September 2014
Received in revised form
12 January 2015
Accepted 16 January 2015
Available online xxx

Biomass is considered a potential energy source which can be efficiently converted to useful gaseous
products via a gasification process. Circulating fluidized bed (CFB) gasifiers have attracted significant
attention due to their high reaction rates and thermal efficiency. This study aims to investigate the CFB
biomass gasification process to generate H2-rich synthesis gas. A process simulator is used to analyze the
gasifier performance by assuming that the gasification is fast and reach equilibrium. Parametric analysis
of the CFB gasifier shows that steam gasification generates the synthesis gas attained the highest H2
content (50e65 vol.%) and the highest product gas quality (higher heating value, HHV ¼ 10e13 MJ/Nm3)
at operating temperatures approximately 650e700  C. High-temperature steam cannot provide enough
energy for the gasifier, reducing the gross cold gas efficiency of this process to only 16%. The biomass airsteam gasification process is investigated while avoiding high energy consumption, but less H2 is produced under these conditions.
© 2015 Elsevier Ltd. All rights reserved.

Keywords:
Biomass
Circulating fluidized bed gasifier
H2-rich synthesis gas
Performance analysis

1. Introduction
Energy security becomes the most important issue because
energy demand continuously increases while fossil fuel supply
declines. Presently, renewable energy sources have been explored
to reduce the global dependence on fossil fuels and the emission of
greenhouse gases. Consequently, future energy solutions should
provide sufficient amounts of sustainable energy with minimal
environmental impact.
Hydrogen has been widely discussed as a promising energy
carrier because it provides clean and highly efficient energy conversion. This gas can also be used to drive fuel cells for power
generation. Currently, many technologies have been developed to
produce hydrogen from various sources [1e4]. Agricultural residue

is a major resource for renewable energy; it can be converted into

* Corresponding author. Tel.: þ66 2 218 6878; fax: þ66 2 218 6877.
E-mail address: (A. Arpornwichanop).

various forms of energy through thermochemical or biological
processes [5]. The thermochemical processes, including combustion, pyrolysis and gasification, have some advantages over the
biological methods because they are more flexible when selecting a
feedstock, faster and more efficient [6].
Currently, combustion-based processes are the conventional
methods used to convert biomass into heat and electricity; however, the energy efficiency of this process is quite low (20e40%)
[7]. Pyrolysis is based on cracking biomass in the absence of oxygen, and the major products are in the liquid phase (“bio-oil”) [8].
The commercial application of bio-oil is restricted by their limited
use and difficulty during downstream processing [9]. Alternatively, gasification is an attractive means to convert solid fuels
(e.g., biomass and coal) to a combustible or synthesis gas [10,11].
This process involves drying, devolatilization and a gasification/
combustion process. Currently, different designs for gasification
reactors or gasifiers have been proposed. A circulating fluidized
bed (CFB) gasifier is a type of gasifier that is currently undergoing
rapid commercialization for biomass [12]. This apparatus exhibits

/>0360-5442/© 2015 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Chutichai B, et al., Parametric analysis of a circulating fluidized bed biomass gasifier for hydrogen production,
Energy (2015), />

2

B. Chutichai et al. / Energy xxx (2015) 1e8

many advantages during biomass gasification, including a high
degree of solid mixing, a high thermal efficiency and good scalability [13].
When operating the gasifier, the quality of synthesis gas is
strongly affected by types of used gasifying agents, such as air,
oxygen and steam. Air gasification is feasible for industrial applications; however, the synthesis gas produced using this technology has a low H2 content, which ranges from 8 to 14 vol.%, and
a low higher heating value (HHV) approximately 4e6 MJ/m3 [14].
Although using pure oxygen during gasification can produce gas
with a higher heating value (10e18 MJ/m3), the high cost of pure
oxygen generated using current technology, such as a cryogenic
air separation, makes the gasification process impractical
[9,14,15]. To obtain H2-rich gas for internal combustion engines,
gas turbine systems or fuel cells for electricity and heat generation, steam gasification might be an interesting alternative
[16e19] because this process can produce synthesis gas with high
H2 contents (30e60 vol.%) and higher heating values (10e16 MJ/
m3) [14]. However, steam gasification reactions are endothermic,
requiring large amounts of energy for the gasifier [20]. Adding air
to steam gasification, which is called air-steam gasification, is an
alternative for supplying energy based on the partial combustion
of biomass with air; however, the quality of the product gas may
be lower [11,21].
In general, the composition of the synthesis gas is the major
parameter affecting the performance during biomass gasification
because it directly affects the heating value of the product gas and
the gasification efficiency [6,9]. However, making exact predictions
of synthesis gas compositions is not easy because these models
depend on many parameters, such as the biomass composition,
operating conditions and gasifying agent. Umeki et al. [20] studied
on the performance of a high temperature steam gasification process for woody biomass and found that the obtained synthesis gas,
which contained 35e55 vol.% H2, was generated by wateregas and
steam reforming reactions. The cold gas efficiency was 60.4%, but

the gross cold gas efficiency was 35% due to the heat supplied by
high-temperature steam. Mehrdokht and Mahinpey [22] performed a sensitivity analysis of a biomass fluidized bed gasifier,
finding that the H2 content in the product gas increased when
increasing the operating temperature. Adding more steam to the
gasifier increases the H2 and CO production while decreasing the
CO2 and carbon conversion. Kumar et al. [23] also studied the effect
of operating parameters of fluidized bed gasification, such as
gasification temperatures and gasifying agent feed rates, on the
energy conversion efficiencies. The results showed that the gasification temperature is the most influential parameter while the
gasifying agent feed rates has the strong effect on the carbon
conversion and energy efficiencies. The balance between air and
steam feed rates was the way to achieve H2-rich gas production.
Doherty et al. [15] developed a model of a CFB biomass gasifier to
predict its performance under various operating conditions. The
heating value of the synthesis gas increased with the equivalent
ratio of the air supply. Preheating the air increased the H2 and CO
contents. Steam was introduced to promote H2-rich synthesis gas
production.
The aim of this study is focused on improving the CFB biomass
gasification process to produce a H2-rich synthesis gas. A model of
the CFB gasifier is developed using a commercial process simulator
to investigate the effect of key operating parameters, such as the
gasifier temperature, steam temperature, steam-to-biomass ratio
(S/B), equivalent ratio (ER) and type of gasifying agents, on the
performance of the CFB gasifier. The synthesis gas composition and
heating value, as well as the biomass gasification process efficiency,
are the criteria used to determine suitable operating conditions for
the CFB gasifier.

2. Methods

2.1. Model of a circulating fluidized bed (CFB) gasifier
The fluidized bed reactor has been broadly utilized for coal and
biomass combustion and gasification. A traditional bubbling fluidized bed gasifier has a lower carbon conversion efficiency; therefore, the design of fluidized bed gasifiers has shifted from low
velocity bubbling beds to high velocity circulation-based designs
because a circulating fluidized bed gasifier (CFB) has a higher char
circulation rate, improving the overall efficiency [24].
Circulating fluidized bed gasifiers might improve biomass
gasification by using higher gasifying agent flow rates to entrain
and move the bed material, which can be either sand or char; in
addition, these apparatuses recirculate nearly all of the bed material and char with a cyclone separator. A schematic diagram of a CFB
biomass gasifier is shown in Fig. 1(a). When the biomass is added to
the gasifier, it is rapidly dried and pyrolyzed, releasing all of the
gaseous portions of the biomass at a relatively low temperature.
The remaining char is oxidized within the bed to provide a heat
source for the drying and gasification processes. The large thermal
capacity of the inert bed material plus the intense mixing associated with the fluid bed allow this system to handle a much greater
quantity of material with a much lower quality fuel.
2.2. Process workflow
The CFB gasifier is modeled using a commercial process simulator
(Aspen Plus). The model is divided into three stages including
devolatilization, gasification and solid recirculation, as shown in
Fig. 1(b). The main assumptions made to develop the CFB model are
as follows: the process is operated under steady state conditions; the
gases are treated as ideal gases; the ash is treated as an inert solid,
and tar formation is ignored because of the relatively high operating
temperature [25]; the syngas is produced by the gasifier at the
chemical equilibrium; heat losses are ignored, the cyclone separation
efficiency is 90% [26], and 2% of the carbon is lost to the ash [27].
In Fig. 1(b), the ‘BIOMASS’ stream was treated as a nonconventional stream whose proximate and ultimate analyses are defined
in Table 1 (pine sawdust). The standard operating conditions of this

study are shown in Table 2. The ‘DECOMP’ block is used to represent
the devolatilization process, which is a thermal decomposition
process for the biomass; the biomass is converted to volatile materials and solids, such as H2, N2, O2, C (carbon), S (sulfur), and ash.
The RYield module is ASPEN Plus is used for modeling at this stage
after specifying the yield distribution, which is determined based
on the ultimate analysis of the pine sawdust (Table 1). The enthalpy
of the ‘DECOMP’ product stream does not equal that of the feed
stream. Consequently, the ‘Q-DECOMP’ heat stream is inserted to
balance the enthalpy of the biomass stream.
The product of the thermal decomposition process (‘DECOMP’
stream) and the recirculating solid carbon (‘CRECYCLE’ stream) reacts
with steam (‘STEAM’ stream) in the gasification reaction block, which
is called ‘GASIF1’. The gasification mechanism involves a complex
collection of various reactions during a real gasification process;
however, the gasification reactions are simplified to 8 major reactions
in the present model. These reactions are summarized in Eqs. (1)e(8)
[15]. Reactions (1)e(4) are the gasification processes for char particles
that produce CO, H2 and CH4. Reaction (1) is the partial combustion of
C. The generated heat from first reaction is supplied to the endothermic reaction (2), which is the Boudouard reaction, and reaction
(3), which is the heterogenous shift reaction. Reaction (4) describes
the equilibration of the hydro gasification reaction process, which
depends on the volatile matter in the feedstock. The reaction rates of
(2)e(4) are known to be slower than that of reaction (1) [31].

Please cite this article in press as: Chutichai B, et al., Parametric analysis of a circulating fluidized bed biomass gasifier for hydrogen production,
Energy (2015), />

B. Chutichai et al. / Energy xxx (2015) 1e8

3

Fig. 1. (a) Schematic diagram of a circulating fluidized bed (CFB) biomass gasifier and (b) biomass CFB gasifier process workflow.

C þ 0:5O2 ⇔CO
C þ CO2 4CO

DH0298 ¼ À111 kJ=mol
DH0298 ¼ þ172 kJ=mol

C þ H2 O4CO þ H2
C þ 2H2 4CH4

DH0298 ¼ þ131 kJ=mol

DH0298 ¼ À75 kJ=mol

(1)

partial combustion reaction of combustible gases (CO, H2), the
wateregas shift reaction and the steamemethane reforming reaction.

(2)

CO þ 0:5O2 ⇔CO2

DH0298 ¼ À283 kJ=mol

(5)

(3)

H2 þ 0:5O2 ⇔H2 O

DH0298 ¼ À242 kJ=mol

(6)

(4)

CO þ H2 O4CO2 þ H2

Reactions (5)e(8) are gas phase reactions that occur during the
gasification of char particles. Those reactions are, respectively, the

CH4 þ H2 O4CO þ 3H2

DH0298 ¼ À41 kJ=mol
DH0298 ¼ þ206 kJ=mol

(7)
(8)

Please cite this article in press as: Chutichai B, et al., Parametric analysis of a circulating fluidized bed biomass gasifier for hydrogen production,
Energy (2015), />

4

B. Chutichai et al. / Energy xxx (2015) 1e8

Table 1

Proximate and ultimate analyses of the biomass.
Biomass
Pine sawdusta

Japan cedarb

Proximate analysis (dry basis, wt.%)
Volatile matter
79.5
Fixed carbon
16.8
Ash
3.7
Moisture content (wt.%)

52.8
33.7
13.5

6.1

and Zhong [28] which the gasifer was run at the temperature of
700  C, S/B of one and steam temperature of 400  C. Table 3 presents the synthesis gas compositions obtained from the simulation
model as well as from the references with the same feedstock and
operating conditions. The model predictions agree with the reference data with small percentages of deviation because more
complications may arise during the experimental processes.
3. Results and discussion

5.0

3.1. Effect of the gasifier temperature
Ultimate analysis (dry basis, wt.%)
Carbon
Hydrogen
Oxygen
Nitrogen
Sulfur

45.8
6.7
47.4
0.1
0.0

39.2
5.0
52.4
1.9
1.5

HHV (dry basis, MJ/kg)c

18.5

12.9

a
b
c

Tan and Zhong [28].
Keawpanha et al. [29].
Calculated by modified Dulong's equation [30].

Table 2
Standard operating conditions during the biomass gasification process.
Gasification operating condition
Biomass input condition
Steam input condition
Air input condition

T
T
T
T

¼
¼
¼
¼

700  C
25  C
400  C
25  C

P
P
P
P

¼
¼
¼
¼

1
1
1
1

bar
bar
bar
bar

These reactions are simulated by minimizing the Gibbs free
energy in the RGibbs blocks: ‘GASIF1’ and ‘GASIF’2. The ‘GASIF2’
block is added to control the temperature of the system.
The ‘ASHSEP’ block accounts for ash removal through an SEP
block in which all ash is removed. The ‘PROD-GAS’ stream is fed to
the ‘CYCLONE’ block, which represents a cyclone separator with a
90% efficiency. In addition, 90% of the solid carbon from the gas
stream is removed as the ‘SOLID’ stream, which is fed into the
separator block (‘CSEP’). The remainder makes up the product-gas
stream, which is ‘SYNGAS’. The separator block ‘CSEP’ is set using
a calculator block while assuming that 2% of the solid carbon in
biomass is lost with the ash. The ‘CRECYCLE’ stream circulates the
solid carbon back to block ‘GASIF1’. The ‘CWASTE’ stream carries 2%
of the solid carbon from the biomass, mixing it with ash at a mixer

block called ‘ASH-C’ to generate the ‘ASH’ stream.
The gasification model used in this study was validated against
the experimental data of Keawpanha et al. [29] using Japan cedar as
a biomass. The gasifier was operated at the temperature of 700  C,
S/B of one and steam temperature of 250  C. The proximate and
ultimate analysis of Japan cedar is reported in Table 1. The gasification model was also compared with the simulation model of Tan

The temperature of the gasifier is crucial for producing H2-rich
synthesis gas from biomass. The gasifier temperature varies from
500 to 1000  C while the other parameters are maintained at the
standard values. During the gasification process, the alkali species
contained in biomass can be melted and coated the surfaces of ash
particles, which make ash particles sticky. Consequently, the fluidized bed system is changed to a fixed-bed system with the increase of bed temperature. In this study, the fluidized bed biomass
gasifier should not be operated above 1000  C to ensure that the
ash does not melt, which would induce agglomeration and
defludization [32,33]. The gas composition is shown as a function of
the gasifier temperature, as indicated in Fig. 2. The H2 content increases significantly as the gasifier temperature increases, peaking
at 61% H2 at approximately 700  C before remaining nearly constant. Additionally, the CO content obviously increases with the
gasifier temperature, while the CO2 and CH4 contents decreased
correspondingly. The gas composition of the biomass in the gasifier
is generated by a series of complex and competing reactions, as
shown in reactions (1)e(8). The major reactions are the Boudouard
(2) and wateregas shift reaction (7); the Boudouard reaction is an
intensive endothermic process, similar to the reforming reaction
(8), while the wateregas shift reaction (7) is an exothermic reaction. The partial combustion of the char (1) and the combustible
gases (5), (6) also release heat.
Higher temperatures favor the reactants during exothermic reactions, while the same conditions favor the products in endothermic reactions. Therefore, endothermic reactions (2), (3), and (8)
have a stronger effect when increasing the gasifier temperature,
increasing the H2 and CO contents and decreasing the CO2 and CH4

Table 3
Comparison of the gas compositions obtained from the predictive model and the
reference data of Keawpanha et al. [29] and Tan and Zhong [28].
No.

Sources

HHVa

Gas composition (vol. %, dry basis)
H2

CO

CO2

CH4

1

Keawpanha et al. [29]
Model prediction
Tan and Zhong [28]
Model prediction

10.9
10.6
10.4
10.4

44.4
45.9
61.2
61.0

18.5
21.3
18.9
19.0

29.6
27.6
19.4
19.5

7.4
5.2
0.5
0.5

2
a

Calculated in dry basis at 0  C and 1 bar (MJ/Nm3).

Fig. 2. Effect of the gasifier temperature on the composition of the product gas (S/
B ¼ 1, ER ¼ 0).

Please cite this article in press as: Chutichai B, et al., Parametric analysis of a circulating fluidized bed biomass gasifier for hydrogen production,
Energy (2015), />

B. Chutichai et al. / Energy xxx (2015) 1e8

5

contents. The presence of steam favors the wateregas shift reaction,
increasing the H2 content. In addition, H2 is formed through CH4
reforming. Although the wateregas shift reaction also releases CO2,
the CO2 content decreases as the temperature increases because the
Boudouard reaction, which consumes CO2, becomes more dominant; consequently, the CO content increases while the CO2 content
decreases. At 700  C, which is the temperature at which the highest
H2 content is obtained, the composition of product gas is 61 vol.% H2,
19 vol.% CO, 19.5 vol.% CO2, and 0.5 vol.% CH4. The optimal temperature for this gasification process is approximately 650e700  C,
which generates the highest amount of H2.
3.2. Effect of the steam-to-biomass ratio
The steam feed rate is another important parameter that affects
the product gas compositions. This parameter is defined as the
steam-to-biomass ratio (S/B), which is the ratio between rate of
steam fed into gasifier to rate of biomass feeding. The gas composition varies with S/B, as shown in Fig. 3(a). As the biomass feeding
rate remains at standard condition, increasing the S/B has no initial
effect on the gas composition. Subsequently, the H2 and CO2 contents begin to increase at a transition when S/B is approximately
0.3, especially in the range of 0.3e1.2, while CO and CH4 decrease.
After S/B reached 1.2, the changes in the gas composition are quite
small.
Three main reactions govern the product gas composition:
hydro gasification (4), wateregas shift reaction (7), and steammethane reforming reaction (8). The reforming reaction is a
gaseous reaction that can be balanced more easily, while the hydro
gasification reaction is a relatively slow, heterogenous reaction. The
reaction integration effects decrease the CH4 concentration when
increasing the S/B ratio; consequently, the H2 and CO contents increase more. The wateregas shift reaction plays important role in

determining the CO2 content. When more steam is introduced, the
wateregas shift reaction shifts to produce more CO2 and H2. In
addition, the wateregas shift reaction has a stronger effect on the
CO content than the reforming reaction; therefore, the decreased
CO content is primarily attributed to an increase in the wateregas
shift reaction activity. Numerous studies reported optimized results
for S/B; however, Fig. 3(a) shows that the S/B ratio, which favors the
H2-rich synthesis gas, is approximately 0.8e1.2, which produces a
gas composition of 60e62 vol.% of H2, 16e22 vol.% of CO,
17e21 vol.% of CO2, and 0.3e0.7 vol.% of CH4.
The quality of the product gas is defined as its higher heating
value (HHV), which is determine by the amount of H2 and CO in the
product gas, while the performance of the gasification process is
defined by its cold gas efficiency (CGE), which is the ratio of the
HHV values for the product gas and the biomass. Moreover, the
gross cold gas efficiency (G-CGE), which is the ratio of the chemical
energy from the product gas and the total energy added to the
gasifier, is utilized to assess the overall efficiency of the process. The
energy added to the gasifier includes the chemical energy in the
biomass and the energy required for preheating and balancing
plant. CGE and G-CGE can be calculated using Eqs (9) and (10),
respectively.

CGE ð%Þ ¼

HHV of product gas ðMJ=kgÞ
 100
HHV of biomass ðMJ=kgÞ

G À CGE ð%Þ ¼

(9)

Chemical energy of product gas ðMJ=kgÞ
 100
Total input energy to gasifier ðMJ=kgÞ
(10)

When more steam has been introduced to the gasifier, the CO
content decreases faster than the increase in the H2 content. The

Fig. 3. Effect of the steam-to-biomass ratio (S/B) on (a) the composition of the product
gas and (b) the higher heating value (HHV), the cold gas efficiency (CGE), and the gross
cold gas efficiency (G-CGE) of the product gas (gasifier temperature ¼ 700  C, ER ¼ 0).

sum of the CO and H2 content decreases, decreasing the HHV of the
product gas, as presented in Fig. 3(b). The CGE and G-CGE values
show trends similar to that of the HHV. For the gross cold gas efficiency determination, the process performance is reduced due to
the strongly endothermic effect of the steam gasification process.
More energy must be added to the gasifier to maintain the gasifier
temperature when more steam is added. The G-CGE of the steam
gasification is much lower than the CGE by approximately 60e70%.
When the S/B ratio is approximately 0.8e1.2, the HHV ranges from
10.14 to 10.68 MJ/Nm3, while the CGE and G-CGE are 81e85%, and
16e18%, respectively.

3.3. Effect of the steam temperature
Steam gasification is almost an endothermic reaction. Therefore,
additional heat is needed to maintain the gasifier temperature.
However, the gasifier may operate without heat from an outside

source by balancing the energy required for the gasifier with the

Please cite this article in press as: Chutichai B, et al., Parametric analysis of a circulating fluidized bed biomass gasifier for hydrogen production,
Energy (2015), />

6

B. Chutichai et al. / Energy xxx (2015) 1e8

energy supplied during steam injection. The effect of the steam
feeding rate and temperature has been investigated by varying the
S/B between 0.1 and 3.0 and the steam temperature from approximately 400e2000  C, as shown in Fig. 4. Without the supplemental heat, the gasification process utilizes steam as a heat carrier.
The additional energy comes from the higher steam feeding rate
and higher steam temperature, which increases the gasifier temperature and accelerates the gasification process. The H2 yield also
increases when the gasifier temperature increases. Injecting steam
favors H2 production, as previously reported.
However, at S/B values of approximately 0.8e1.2, the gasifier
temperature is below the optimal range, which stated in Section 3.1,
even if the steam is introduced into the gasifier at 2000  C. The
optimal gasifier temperature can be achieved by introducing steam
above 1500  C when the S/B exceeds 1.5, as shown in Fig. 4(a).
Under these conditions, a large amount of energy is required to
produce the steam. Furthermore, under the standard conditions

when the steam temperature is 400  C, no H2 is produced because
the gasifier temperature is too low, as shown in Fig. 4(b). Therefore,
heat from an external source is necessary during an optimized
biomass steam gasification process, which will be investigated in
next sections.
3.4. Effect of gasifying agent

As mentioned previously, H2 and CO are the two most important
gas species in the gaseous product; the product composition is used
to determine its quality. From Fig. 5, the H2 and CO contents between biomass steam, airesteam, and air gasification processes are
roughly compared. At the same biomass feed rate, the H2 content
for steam gasification is higher than that of air or airesteam gasification. This result occurs for two reasons. First, the near absence of
N2 during steam gasification condition reduces the gas flow,
increasing the residence time to allow the cracking and reforming
of biomass gasification gas to proceed further and yield more H2.
Second, the presence of steam enhances the effect of the steam
reforming reactions; therefore, more H2 is produced.
However, the injected steam intensifies the wateregas shift
reaction, producing a lower CO content than during air gasification.
During airesteam gasification, the CO content decreases as the
combustion reaction proceeds in air with the wateregas shift reaction, decreasing the CO content in the product gas. The product
gas quality is measured using the higher heating value (HHV) of the
gas, which is defined by heating value of H2 and CO. If the sum of
the H2 and CO contents is higher, an HHV is generated for the
product gas. The HHV of the product gas obtained from steam
gasification, which produced the highest sum of H2 and CO, is
higher than that in airesteam gasification and air gasification,
respectively.
3.5. Effect of equivalence ratio (ER)
To operate a gasifier under self-sustaining conditions, some air
must be introduced. The biomass is oxidized by the oxygen in the
air. The high amount of heat produced by this oxidation reaction is
supplied to the gasifier, balancing the exothermic and endothermic
reactions. The air feed rate is represented by the equivalence ratio
(ER) which is the ratio between the amount of air fed into gasifier

Fig. 4. Effect of the steam-to-biomass ratio (S/B) and the steam temperature on a) the

gasifier temperature and b) the H2 concentration (vol.%, dry basis) (ER ¼ 0).

Fig. 5. Effect of the gasifying agent on the H2 and CO contents and the higher heating
value of the product gas (gasifier temperature ¼ 700  C).

Please cite this article in press as: Chutichai B, et al., Parametric analysis of a circulating fluidized bed biomass gasifier for hydrogen production,
Energy (2015), />

B. Chutichai et al. / Energy xxx (2015) 1e8

and the stoichiometric amount of air needed for complete combustion. At higher ER, more heat is released from the combustion
reaction, explaining why less energy is required from external
sources to maintain the optimal gasification conditions. Fig. 6(a)
shows the effect of the ER on the amount of heat supplied to the
gasifier. A completely self-sustaining gasifier, which does not
require additional heat, can be produced when air is added to the
system at an ER of 0.38. In addition, a smaller amount of air, which
is when ER is approximately 0.28, can become self-sustainable
operation when the heat from the hot product gas is recovered
by air pre-heating.
The H2 content varies with the ER, as shown in Fig. 6(b). A higher
ER value promotes the combustion reaction, which releases heat
and accelerates the endothermic gasification reactions. Moreover,
the strong combustion reactions of char and combustible gases
produce more CO2 and some steam while lowering the H2, content.
Furthermore, the presence of air in the gasifier means that product
gas quality has been decreased by dilution with N2.

7

4. Conclusions
The work presents a theoretical study on a biomass-feed
circulating fluidized bed gasifier. Simulations of the gasifier are
performed to investigate the effect of primary operating parameters on the production of H2-rich synthesis gas. The results show
that when increasing the gasifier temperature, the H2 content increases significantly, peaking at approximately 700  C. The CO
content also increases with the gasifier temperature, while the CO2
and CH4 contents decreased. Increasing the steam-to-biomass ratio
decreases the sum of the H2 and CO contents and decreases the
higher heating value (HHV) of the product gas and the cold gas
efficiency (CGE). The optimal gasification process occurs at a steamto-biomass ratio of 0.8e1.2. For steam gasification, additional heat
is necessary because large amounts of steam or higher temperature
steam cannot be used. It is found that the H2 content obtained from
steam gasification is higher than that from air gasification or airsteam gasification; the HHV of the product of steam gasification,
which produced the most H2 and CO, is also highest. Introducing air
into the gasifier promotes the combustion reaction that produces
energy for the gasifier; however, the H2 content and the product
gas quality decrease upon addition of N2. Self-sustaining gasifier
operation can be achieved when ER equals 0.28.
Acknowledgments
Support from the Ratchadaphiseksomphot Endowment Fund of
Chulalongkorn University (RES560530168-EN) is gratefully
acknowledged.
B. Chutichai would like to acknowledge the Dutsadiphiphat
Scholarship, Ratchadaphiseksomphot Endowment Fund, Chulalongkorn University.
References

Fig. 6. Effect of the equivalence ratio (ER) on (a) the amount of heat supplied to the
gasifier and (b) the H2 concentration (vol.%, dry basis) (gasifier temperature ¼ 700  C).

[1] Kalinci Y, Hepbasli A, Dincer I. Biomass-based hydrogen production: a review

and analysis. Int J Hydrog Energy 2009;34:8799e817.
[2] Hajjaji N, Chahbani A, Khila Z, Pons M. A comprehensive energyeexergybased assessment and parametric study of a hydrogen production process
using steam glycerol reforming. Energy 2014;64:473e83.
[3] Chen J, Lu Y, Guo L, Zhang X, Xiao P. Hydrogen production by biomass gasification in supercritical water using concentrated solar energy: system
development and proof of concept. Int J Hydrog Energy 2010;35:7134e41.
[4] Yilmaz C, Kanoglu M. Thermodynamic evaluation of geothermal energy
powered hydrogen production by PEM water electrolysis. Energy 2014;69:
592e602.
[5] Tanksale A, Beltramini J, Lu G. A review of catalytic hydrogen production
processes from biomass. Renew Sustain Energ Rev 2010;14:166e82.
[6] Parthasarathy K, Narayanan K. Hydrogen production from steam gasification
of biomass: Influence of process parameters on hydrogen yield e a review.
Renew Energ 2014;66:570e9.
[7] Caputo A, Palumbo M, Pelagagge P, Scacchia F. Economic of biomass energy
utilization in combustion and gasification plants: effects of logistic variables.
Biomass Bioenergy 2005;28:35e51.
[8] Kim J, Oh S, Hwang H, Moon Y, Choi J. Assessment of miscanthus biomass
(Miscanthus sacchariflorus) for conversion and utilization of bio-oil by fluidized bed type fast pyrolysis. Energy 2014;76:284e91.
[9] Puig-Arnavat M, Burno J, Coronas A. Review and analysis of biomass gasification models. Renew Sustain Energy Rev 2010;14:2841e51.
[10] Johansson D, Franck P, Berntsson T. Hydrogen production from biomass
gasification in the oil refining industry e a system analysis. Energy 2012;38:
212e27.
[11] Chutichai B, Authayanun S, Assabumrungrat S, Arpornwichanop A. Performance analysis of an integrated biomass gasification and PEMFC (proton exchange membrane fuel cell) system: hydrogen and power generation. Energy
2013;55:98e106.
[12] Liszka M, Malik T, Budnik M, Ziebik A. Comparison of IGCC (integrated gasification combined cycle) and CFB (circulating fluidized bed) cogeneration
plants equipped with CO2 removal. Energy 2013;58:86e96.
[13] Gomez-Barea A, Leckner B. Modeling of biomass gasification in fluidized bed.
Prog Energy Combust 2010;36:444e509.
[14] Saxena R, Seal D, Kumar S, Goyal H. Thermo-chemical routes for hydrogen rich
gas from biomass: a review. Renew Sustain Energ Rev 2008;12:1909e27.

Please cite this article in press as: Chutichai B, et al., Parametric analysis of a circulating fluidized bed biomass gasifier for hydrogen production,
Energy (2015), />

8

B. Chutichai et al. / Energy xxx (2015) 1e8

[15] Doherty W, Reynolds A, Kenedy D. The effect of air preheating in a biomass
CFB gasifier using ASPEN Plus simulation. Biomass Bioenergy 2009;33:
1158e67.
[16] Hernandez-Pacheco E, Mann M, Hutton P. A cell-level model for a solid oxide
fuel operated with syngas from a gasification process. Int J Hydrog Energy
2005;30:1221e33.
[17] Moghadam R, Yusup S, Uemura Y, Chin B, Lam H, Shoaibi A. Syngas production
from plam kernel shell and polyethylene waste blend in fluidized bed catalytic steam co-gasification process. Energy 2014;75:40e4.
[18] Loha C, Chattopadhyay H, Chatterjee P. Thermodynamic analysis of hydrogen
rich synthetic gas generation from fluidized bed gasification of rice husk.
Energy 2011;36:4063e71.
[19] Duman G, Uddin A, Yanik J. Hydrogen production from algal biomass via
steam gasification. Bioresour Technol 2014;166:24e30.
[20] Umeki K, Yamamoto Kouichi, Namioka T, Yoshikawa K. High temperature
steam-only gasification of woody biomass. Appl Energy 2010;87:791e8.
[21] Lv P, Xiong Z, Chang J, Wu C, Chen Y, Zhu J. An experimental study on biomass
air-steam gasification in a fluidized bed. Bioresour Technol 2004;95:95e101.
[22] Mehrdokht B, Mahinpey N. Simulation of biomass gasification in fluidized bed
reactor using ASPEN PLUS. Biomass Bioenergy 2008;32:1245e54.
[23] Kumar A, Eskridge K, Jones D, Hanna M. Steam-air fluidized bed gasification of
distiller grains: effect of steam to biomass ratio, equivalence ratio and gasification temperature. Bioresour Technol 2009;100:2062e8.
[24] Ju F, Chen H, Yang H, Wang X, Zhang S, Liu D. Experimental study of a commercial circulated fluidized bed coal gasifier. Fuel Process Technol 2010;91:

818e22.

[25] Anis S, Zainal Z. Tar reduction in biomass producer gas via mechanical, catalytic and thermal methods: a review. Renew Sustain Energ Rev 2011;15:
2355e77.
[26] Zhao B. Development of a new method for evaluating cyclone efficiency.
Chem Eng Process 2005;44:447e51.
[27] Li X, Grace J, Lim C, Watkinson A, Chen H, Kim J. Biomass gasification in a
circulating fluidized bed. Biomass Bioenergy 2004;26:171e93.
[28] Tan W, Zhong Q. Simulation of hydrogen production in biomass gasifier by
ASPEN PLUS. In: Proceeding of power and energy engineering conference
(APPEEC); 2010. p. 1e4.
[29] Keawpanha M, Guan G, Hao X, Wang Z, Kasai Y, Kusakabe K, et al. Steam cogasification of brown seaweed and land-based biomass. Fuel Process Technol
2014;120:106e12.
[30] Tchobanoglous B, Theisen H, Vigil S. Integrated solid waste management.
Engineering principles and management issues. In: Civil engineering
Singapore. McGraw Hill; 1993.
[31] Watanabe H, Otaka M. Numerical simulation of coal gasification in entrained
flow coal gasifier. Fuel 2006;85:1935e43.
[32] Kuo J, Lin C, Wey M. Effect of agglomeration/defluidization on hydrogen
generation during fluidized bed air gasification of modified biomass. Int J
Hydrog Energy 2012;37:1409e17.
[33] Liu H, Feng Y, Wu S, Liu D. The role of ash particles in the bed agglomeration
during the fluidized bed combustion of rice straw. Bioresour Technol
2009;100:6505e13.

Please cite this article in press as: Chutichai B, et al., Parametric analysis of a circulating fluidized bed biomass gasifier for hydrogen production,
Energy (2015), />