Biomass fueling of a SOFC by integrated gasifier: Study of the effect of operating conditions on system performance

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 8 ( 2 0 1 3 ) 3 2 0 e3 2 7

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Biomass fueling of a SOFC by integrated gasifier: Study of the
effect of operating conditions on system performance5
Gennaro Campitelli b, Stefano Cordiner a, Mridul Gautam b, Alessandro Mariani a,
Vincenzo Mulone a,*
a
b

Dipartimento di Ingegneria Industriale, Universita` di Roma “Tor Vergata” via del Politecnico 1, 00133 Roma, Italy
Mechanical and Aerospace Engineering, West Virginia University ESB, Evansdale Drive, Morgantown, WV 26506-6106, USA

article info

abstract

Article history:

Biomass gasification can be efficiently integrated with Solid Oxide Fuel Cells (SOFCs) to

Received 14 May 2012

properly deploy the energy content of this renewable source and increasing the ratio of

Received in revised form

electric to thermal converted energy. The key objective of this work is to analyze in

21 September 2012

a systematic and wide process the integration of a biomass gasifier process with the SOFC

Accepted 3 October 2012

operation. In particular the work aims at identifying the role of SOFC H2 utilization as

Available online 30 October 2012

a basic parameter to maximize the system output and avoid gasifier bad operation issues
such as tar production and carbon deposition. An efficient simulation framework is used to

Keywords:

that purpose allowing for a detailed analysis of the influence of key driving parameters.

Solid oxide fuel cells

The performance of the integrated system is thoroughly analyzed in the range of 1e2 kW

Biomass gasification

electric power by also varying the input biomass characteristics in terms of Moisture

Fuel cell modeling

Content (MC). Results show how a variation of the SOFC H2 utilization, a parameter whose

Thermal integration

effects are also correlated with the gasifier air requirement, affects electrical power output
also depending on the biomass Moisture Content.
Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights
reserved.

1.

Introduction

Power production from biomass may represent a significant
way to limit CO2 emissions and deploy the local availability of
energy sources. Biomass is, in fact, the fourth largest source of
energy in the world, accounting for 15% of world’s primary
energy consumption; this number is consistently higher,
reaching 38%, in the developing countries [1,2]. However, due
to the limited volumetric energy content, the high potential of
biomass is more suitable within the Distributed Generation
(DG) power production concept that foresees the use of small
size (from few to about 500 kWe) power plants. In such
a characteristic size, the combined generation of heat and
5

power is of utmost importance to guarantee the best fuel
exploitation, and reach the maximum as possible total efficiency htot ¼ hel þ hth which accounts for both thermal and
electric use of the converted energy, commonly in excess of
0.8e0.9. Depending on the specific application, different
values of the electrical to thermal power ratio may correspond
to same total efficiencies htot, depending on both technology

and system characteristic power size.
Several integration strategies are currently available,
allowing for the use of biomass for energy conversion, which
may either be based on traditional technology (i.e. microturbines, internal combustion engines or Organic Rankine
Cycles ORC turbines) having electric efficiency in the range of

Presented at the ASME 4th European Fuel Cell Technology and Applications Conference, December 14e16, 2011.
* Corresponding author. Mechanical Engineering Dept., University of Rome “Tor Vergata”, via del Politecnico 1, 00133 Rome, Italy. Tel.:
þ39 06 72597170; fax: þ39 06 2021351.
E-mail address: (V. Mulone).
0360-3199/$ e see front matter Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
/>

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 8 ( 2 0 1 3 ) 3 2 0 e3 2 7

15e20% [3,4] or use H2 as an energy vector [5]. Among the
thermo-chemical conversion technologies, biomass gasification is a popular option giving high overall electric efficiency
[2,6e8], especially as far as more complicated layouts are
concerned, such as microturbine-fuel cell hybrid [9]. An
accurate system integration would nevertheless be required
in this case to guarantee a better deployment of the biomass
energy potential.
The combination of highly efficient Solid Oxide Fuel Cells
(SOFCs) and gasification systems is an effective technology for
reaching both energy and economic feasibility of combined
heat and power production [10]. In this case, in fact, the
syngas can directly feed the fuel cell, which is tolerant to CO
and able to directly or indirectly convert the CH4 contained in
the producer gas. In the integrated biomass gasifier e SOFC
system, special attention must be given to the three main

system components (gasifier, gas processing unit and fuel cell)
while still maintaining the system complexity minimum as
possible not compromising the long-term stability of the fuel
cell at the same time [11].
The coupling of SOFCs to gasifiers is discussed in several
studies [12e16]. Experimental and modeling activities are reported aiming at identifying the most efficient configuration
of key operating parameters on the performances of the
different components and at analyzing the influence of syngas
composition on the fuel cell performance [17,18].
From the modeling point of view, some papers describe the
effect of basic syngas fueling on cell performance by using a 0D representation [16], whereas the influence of Fuel Cell
design parameter is also evaluated in detail (either by multidimensional modeling or direct experimental testing) to
understand the difference in operation when feeding the cell
with hydrogen or methane or with syngas characterized by
different composition.
Among the others, thermal integration of the different
components is a key aspect in the development of sustainable
solutions as it potentially allows for a considerable increase of
electric efficiency hel [19,20]. Depending on the design, gasification may be autothermal or allothermal whereas the SOFC
may be operated under different fuel utilization conditions. To
the aim of sustaining the gasifier operation and producing
syngas characterized by high energy content (e.g. Lower
Heating Value e LHV) as well as a more favorable H2/CO ratio
[19e22], system optimal configuration may be different from
what is required for the single component. Moreover, solid
carbon deposition issues may arise thus requiring the use of
steam to avoid the rapid clogging of FC channels. This issue
may be the target of a specific optimization strategy while
operating with standard biomass feedstock, which may
generally be characterized by high Moisture Content (MC) and

contain enough water to face with the cited issues. The correct
use of this water content is nevertheless a function of required
energy for steam production to sustain the steam reforming
regime. This energy may be recovered from the SOFC off-gas
cooling but requires specific design and control of the integrated systems. However, in the cited papers, a key parameter,
such as fuel utilization, and more specifically the utilization of
H2 that is the main gaseous reactant responsible of electrochemical reactions especially at average (e.g. 0.6e0.7 V) voltage
operating conditions [23], is imposed as a constant [24], or the

321

impact of its variation is not even discussed [21]. In this paper
the role of this parameter is studied from the point of view of
system efficiency and has been varied accordingly in order to
evaluate the combined effects on fuel cell efficiency (which
may increase if more H2 is available to the electrochemical
reaction) and the corresponding losses at a system level.
Special focus has also been given to the analysis of the variation of feedstock characteristics, in terms of biomass MC, that
may easily change during normal operation for biomass fueled
power production systems.
To the presented aim, a 0-D model describing the power
plant, including a gasifier, a SOFC and all the thermal
exchangers providing integration heat, has been developed
and implemented under the Matlab/Simulink environment.
The model has been used to make a wide screening of operating conditions and identify the most efficient ones. The
details of the used models for the single components and the
overall system are given in the next section whereas results
are illustrated in a specific section.

2.

SOFC-gasifier integrated 0-D model

A numerical model, that comprises two main sub-modules,
has been implemented to represent the behavior of a SOFC
coupled to an integrated downdraft gasifier. In fact, updraft
and downdraft technologies are usually preferred to fluidized
bed for small size applications especially for temperature
control issues [25]. The downdraft technology was moreover
selected for the low tar yield, that is particularly important for
SOFC fueling [26,27]. According to the system schematic
provided in Fig. 1, the downdraft gasifier is directly fed with
wet biomass, and is thermally integrated by the SOFC offgases after combustion in the burner. The system includes
another heat exchanger to pre-heat the SOFC feeding air.
The 0-D approach has been selected, as it is characterized by
affordable computational timings for optimization analyses.
The overall model has been implemented in MatlabSimulink computational environment. Synthetic details of
the two modules are given in the following two sub-sections.

2.1.

Gasifier module

This module predicts the syngas chemical composition
downstream of the gasifier in terms of gaseous species mass

Fig. 1 e Schematic of the system: SOFC fed by integrated
biomass gasifier.

322

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 8 ( 2 0 1 3 ) 3 2 0 e3 2 7

fraction and overall HHV as functions of the inlet MC of the
woody biomass.
Chemical equilibrium is assumed for all reactions and
implies that pyrolysis products are all consumed into the
reduction zone before they leave it. The global gasification
reaction taken into account [28] may be written for woody
material (CH1.44O0.66) as
CH1:44 O0:66 þ wH2 O þ mO2 þ 3:76mN2 /x1 H2 þ x2 CO þ x3 CO2

Table 1 e Volumetric heating value [MJ/m3] as a function
of temperature [K]: experimental-numerical comparison
in the case of MC [ 0.2.
T
1023
1073
1123
1173

Model

Experiment

Error %

4.812
4.739

4.638
4.517

4.9
4.8
4.5
4.6

1.8
1.3
3.0
1.8

þ x4 H2 O þ x5 CH4 þ 3:76mN2
(1)
where w is the amount of water per mol wood, related to the
biomass MC as shown below
w¼

24MC
18ð1 À MCÞ

m is the amount of oxygen per mol wood, and xi are the molar
fractions of gaseous product unknowns.
The energy balance may be written instead as follows:
dHfwood þ wdHH2 OðlÞ þ dHint ¼ x1 dHH2 þ x2 dHCO þ x3 dHCO2
þ x4 dHH2 OðvapÞ þ x5 dHCH4
þ 3:76mdHN2

(2)

where dHfwood is the wood standard enthalpy of formation,
while dHint is the integration heat term given by the burner
under the assumption of exploiting the residual heating value
of the syngas composed by H2, CO and CH4. The energy
balance, along with elemental balances, equilibrium
constants, and further chemical reactions such as methane
formation and water gas shift reactions, constitute a three
non-linear equation set.
Experimental data [29] in the case of adiabatic condition
(dHint ¼ 0) have been used to validate this module. The effect
of the input biomass MC on the syngas composition in terms
of dry basis volume fractions is shown in Fig. 2. First, CO
decreases with MC increment as expected. Hydrogen and
carbon dioxide increase with MC, while methane fraction is
negligible (1%). High N2 fraction is observed all over the entire
MC range [30].

Table 1 shows the validation of this module against
experimental data [29]. This has been performed in terms of
syngas heating value for different operating temperatures and
MC equal to 0.2. For a wide temperature range where the SOFC
is expected to operate, the heating value leads to appreciable
predictive accuracy. The availability of enough residence time
(that is a function of the gasifier specific design) and temperature, allow chemical reactions to almost reach equilibrium,
thus giving relatively low errors overall. In summary, this
module is capable of evaluating the amount of air required for
gasification of the selected biomass and the syngas composition by only using biomass water content w, operating
temperature and integration heat (dHint) as input data.

2.2.

SOFC module

The SOFC module, that is based as mentioned on a 0-D
approach, is capable of representing a planar stack under
steady state operating conditions [19,20]. The main assumptions are that the cell is isothermal, H2 is the only gaseous
species participating to electrochemical reactions, and the
SOFC H2 fuel utilization is a constant input parameter. Water
Gas Shift (WGS) reaction is also taken into account to calculate
further H2 production via H2O in the SOFC anode. This has
been modeled at its equilibrium state with an operating
temperature equal to the SOFC, and atmospheric pressure.
The equilibrium constant of reaction is evaluated by van’t
Hoff isothermal assumption and according to reactants and
products molar fractions

Fig. 2 e MC effect on outlet gasifier composition (T [ 1073 K).


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Kp ¼ Kc ¼

À Á0:25 À120$103 =RT Â
Ã
J0 CAT ¼ 5:5$108 xO2
e

A=m2

½CO2 Š½H2 Š
½COŠ½H2 OŠ

with

Since residual moles may be computed as follows:

xO2 ¼

nCO res ¼ nCO init ð1 À a1 Þ
nH2 O res ¼ nH2 O init ð1 À a2 Þ

l À mf
¼ nH,
l
2
À mf
0:21

xH2 O ¼ n ,

moles of H2 yielded with the WGS are

H2 O init

nH2 ¼ nCO init a1 ¼ nH2 O init a2

þn ,

init

H2 init

1 À mf
_ TOT
m

_ TOT
$mf m

By solving this equation set and applying Hesse’s law, the
new syngas composition available for the SOFC is obtained as
well as enthalpy balance of the WGS reaction.
The cell voltage is defined as

In the presented equations l is the air fuel ratio, which is
usually in the range 2 < l < 4 [36,37] for syngas fueled SOFCs,
_ TOT is the minimum syngas molar flow rate at the inlet
while m
SOFC section to allow for H2 oxidation. nH, init and nH, O init are
2
2
the molar flow rates, for H2 and H2O respectively.
Concentration losses due to mass transfer limitations are
taken into account according to the 0-D modeling approach
and the fuel utilization. The whole phenomenon has been
represented by using two different formulas

E ¼ EMF À DEOHM À DEACT À DECONC

DECONC ¼

and the equilibrium constant can be expressed as
KC ¼

nCO init a21
nH2 O init ð1 À a1 À a2 þ a1 a2 Þ

(3)

where EMF is the open circuit ideal voltage according to the
Gibbs free energy at the imposed temperature, whereas
modeling of the three losses is implemented via electrolyte
resistance and thickness (DEOHM), Tafel equation (DEACT) and
as a function of H2 partial pressure via the SOFC H2 utilization
(DECONC) [19,20].
Ohmic losses are computed as follows:
DEOHM ¼ RE $Jt
where Jt is the current density and RE is the electrolyte resistance defined as
RE ¼

le
se

with le and se equal to electrolyte thickness and conductivity
respectively. The last one is evaluated by using the formula
se ¼ b1 eÀb2 =T ½U$mŠÀ1
where b1 and b2 are coefficients describing the YSZ electrolyte

behavior [22,31e35].
Overpotential losses have been modeled for anode and
cathode according to Tafel’s law.

DEACT ¼ ACAT $ln

Jt

J0 CAT





Jt
þ AAN $ln
J0 AN

where the cathode gives the main contribution, and ACAT/AAN
are defined as
ACAT ¼

AAN ¼

RT
2FgCAT

RT
2FgAN

Exchange current density values J0 are affected by molar
fractions of species evolving at the anode and cathode
respectively and thus the fuel utilization mf factor plays a key
role for their evaluation.
À100$103 =RT

J0 AN ¼ 1$10 xH2 xH2 O e
8

Â
Ã
A=m2

RT À
$ln PH2
2F

init =PH2 final

Á

DECONC ¼ m$en$Jt
The first equation better represents concentration losses
when current density is low and the major part of the H2 is still
available. The second equation instead is empirical and
represents fairly well the partial pressure decrease effect at
high current density due to mass transfer limits.
Data of a SOFC modeled with 1-D approach and fed with
pure H2 [21] have been used for validation. Voltage and current
density at different temperatures and mf’s have been investigatedand are provided in Table 2. It can be observed how the

maximum power density [W/m2] output at isothermal
condition (T ¼ 1073 K) matches reasonably well with the lower
mf cases, while, for fixed mf cases (at 0.8), better results have
been obtained at lower operating temperatures.
In summary, given the satisfactory agreement with a 1-D
model, the SOFC 0-D module here presented has been
considered capable of evaluating cell voltage, current density
and H2, CO, CH4, residual molar fractions for a unit cell unit in
planar configuration once given as inputs the electrolyte
characteristics, operating temperature and syngas characteristics in terms of species molar fractions.

Table 2 e Comparison of the 0-D SOFC model (current
work) with a literature available [21] 1-D SOFC model in
terms of power density [W/m2] as a function of
temperature T [K] (at fuel utilization[0.8) and fuel
utilization [$] (at temperature[1073K).
T

0-D model

1-D model

Error %

1023
1123
1223
mf

578.4

1602
2997
0-D model

600
1720
3250
1-D model

3.6
6.92
7.78
Error %

0.85
0.95

759.8
396.3

750
430

1.29
7.84


324

2.3.

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 8 ( 2 0 1 3 ) 3 2 0 e3 2 7

Algorithm of the numerical model

The presented numerical model is composed by several
modules interacting until the steady Gasifier-Solid Oxide Fuel
Cell energy system operating point is attained. A flow diagram
of the numerical model is provided in Fig. 3 to better understand the solution algorithm.
Fig. 3 shows how air pre-heating and reforming require
a certain amount of heat which has to be assured for the
energy system sustainability. If these two requirements are
not satisfied, the input setting imposed is considered by the
model as invalid to run the whole energy system. Conversely,
with an input setting which yields extra heat at the burner, the
integration process at the gasifier is considered physically
consistent.

3.

Analysis of results

The model has been applied to the analysis of the main
performance parameters of the SOFC and the integrated
system, when fueled with woody biomass. The influence of
biomass MC by varying fuel cell operating conditions has been
analyzed to define the best compromise among power density
and efficiency of SOFC and thermal balance of the system.
This is in fact directly influenced by the following operating
aspects:

 The gasifier regime, that is primarily defined, given the
operating temperature, by the air mass flow rate, whose
variation has a high impact on syngas composition and
yield;
 The SOFC H2 fuel utilization, which is an operating parameter linked to the electrochemical exploitation of the cell
active area.
The SOFC active area has been considered equal to 1 m2,
while the woody biomass inlet flow has been set to about

1 kg/h (dry basis) and constant, corresponding to an input
thermal power in the range of 4.5 kWth. The SOFC operating
voltage has been controlled in the code to lie in the range
0.6e0.65 V, that gives an optimal compromise between cell
power density and efficiency.
A first comparison between the performance of the autothermal and thermally integrated layouts has been analyzed
by means of the system model at biomass MC ¼ 0.4. Results
are given in Table 3, confirming the increase in efficiency of
the integrated system (hsys,integ ¼ 37.7% vs hsys,autoth ¼ 24.7%).
The higher system performance has been achieved despite
the lower total fuel utilization, while the SOFC efficiency has
been kept in the optimal range of 50%. System efficiency
increase has then been observed for the better gasifier operating regime, which allows for a different syngas composition,
that is reported in Table 3. A remarkable increase in terms of
H2 concentration is in fact obtained with the integrated
system (48.5% vs 17.8% on a volume basis). This has been
achieved by a drop in gasifier air flow rate, that leads to both
the decrease in N2 concentration, i.e. no related transport
losses occur in the SOFC, and to a lower O2 flow rate (almost
0 vs 0.69 kg/h) that is possible as heat is provided by the
combustion of SOFC off-gas, according to the schematic of

Fig. 1. This basically means that the gasifier, due to the high
biomass MC (0.4), is operating under “steam reforming like”
regime with no O2, that would otherwise be unfeasible
without the thermal integration. Thus, the drop in SOFC fuel
utilization is not indicative of fuel waste, but rather of better
gasifier operation that eventually leads to higher system
efficiency.
Three different MCs have then been further analyzed for
the integrated system: 0.1, 0.3 and 0.5 by further assuming
constant SOFC H2 utilization (0.8). The effect of MC is such that
a higher electric power is delivered by the SOFC going from
MC ¼ 0.1 to MC ¼ 0.3 conditions, meaning that fuel utilization
is enough to thermally sustain the gasifier and allowing for
a decrease in air (i.e. O2) flow rate (red curve in Fig. 4). The
situation radically changes going from MC ¼ 0.3 to MC ¼ 0.5
conditions: in fact, MC is so high that the integration heat
dHint is not enough to support the gasifier via the off-gas
combustion. This is also linked to the SOFC H2 utilization,
that has been thus identified as primarily important

Table 3 e Comparison of system performance parameters
between thermally integrated and autothermal gasifiers.
System performance
parameter

Fig. 3 e Whole numerical model flow diagram.

Current [A/m2]
Voltage [V]
mf

hSOFC
hSYS
O2 [kg/h]
H2 [%mol]
CO [%mol]
CO2 [%mol]
H2O [%mol]
CH4 [%mol]
N2 [%mol]

Integrated

Autothermal

3045
0.64
70
51.3
37.7
0.004
48.5
28.3
9.7
12.4
0.7
0.4

2129
0.60
95

48.0
24.7
0.690
17.8
9.4
14.0
19.8
0.1
39.0


i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 8 ( 2 0 1 3 ) 3 2 0 e3 2 7

parameter. Results are reported in Fig. 5, where the effect of
the variation of SOFC H2 utilization has been added. It may be
observed that, as a general trend, the lower SOFC H2 utilization operating conditions have to be avoided. In fact, despite
the theoretically high availability of integration heat, a high
amount of air (O2 flow rate in the Figure) is required to let the
SOFC operate at the selected operating voltage. This also leads
to a poor exploitation of the SOFC off-gas that is evident by the
analysis of Fig. 6, where dHint is reported as a function of SOFC
H2 utilization and MC. dHint represents the amount of the offgases enthalpy that is actually utilized in the biomass gasifier.
It thus appears that low energy is required by the gasifier
to operate if air flow is sufficiently high, as in the already
commented operating conditions with low SOFC H2 utilization
and MC.
An increase in the electric power output is observable with
H2 fuel utilization at any of the proposed MCs. This is directly
related to the decrease in required O2 flow rate (again Fig. 5). At
the same time, the integration heat dHint (again Fig. 6) is

increased, as an opposite effect to the decrease of O2 flow rate:
in other words, the gasifier is moving more toward a “steam
reforming like” operating regime. However, a peak in dHint is
observed, more evident for the higher MC values (e.g.
MC ¼ 0.5), as far as higher than 0.8 SOFC H2 utilizations are
approached. That peak indicates that a limit is achieved in
terms of thermal integration potential that is due to two
concurrent phenomena:

325

Fig. 5 e Electric power (kW) and required O2 mass flow (m3/h)
as functions of SOFC H2 fuel utilization and biomass MC.

the gasifier air requirement are practically equivalent to
optimize the SOFC H2 utilization.

1) The heating value presented by the off-gas is decreased by
the higher exploitation of the SOFC at higher SOFC H2
utilizations.
2) Higher MCs allow the gasifier to produce syngas characterized by higher H2/CO ratio further giving much more
favorable water gas shift behavior into the SOFC [19,20].
This is key to both have the SOFC operating much closer to
pure H2 fueling operating conditions, as well as having
much lower off-gas waste.
3) The peak in power is also obtained at the minimum in
terms of O2 request, further testifying that criteria based on

In Fig. 7, the plot of current density is given, whose trend is
exactly similar to the power curve plotted in Fig. 5. On the

other hand efficiency, again in Fig. 7, presents a slightly
different trend since the biomass LHV (being the denominator
of efficiency) is also affected by MC. Thus, the difference
between maximum efficiencies at 0.5MC and at 0.3MC is
higher than the same difference in terms of power.
Finally, the link between air (O2) requested by the gasifier
and integration heat (dHint) is extremely important, and the
capability of the gasifier to work with minimum air request
has to be sought, along with the control of SOFC operating
voltage. Among the cases reported in Fig. 5, optimal operating
conditions in terms of SOFC H2 utilization or O2 requested flow
rate may be selected depending on the specific biomass MC,
further confirming that high MC operating conditions should
be preferred in terms of electric power maximization.

Fig. 4 e Electric power of FC (kW), H2 production (%) and
required O2 mass flow (m3/h) as functions of MC at
constant SOFC H2 fuel utilization equal to 0.8.

Fig. 6 e Efficiency (%) and current density (A/m2) as
functions of SOFC H2 fuel utilization and biomass MC.


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i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 8 ( 2 0 1 3 ) 3 2 0 e3 2 7

F
J
K

l
n
n_
R
x

Faraday coefficient
current
equilibrium constant
electrolyte thickness
moles
molar flow rate
electrolyte resistance
molar coefficients

Greek symbols
b
thermal conductivity coefficients
h
efficiency
l
air fuel ratio
m
utilization
s
thermal conductivity
Fig. 7 e Integration heat as a function of SOFC H2 utilization
and biomass MC.

4.

Conclusions

The operation of a SOFC fed by an integrated biomass gasifier
has been demonstrated to highly depend on cell operating
conditions, and specifically on SOFC H2 utilization, that is also
correlated to gasifier air requirement, and the biomass Moisture Content (MC). In fact, gasifier operation, and more
specifically its steam, autothermal or intermediate operating
regime, determines a great difference in terms of SOFC flow
rate and syngas composition.
Obtained results allow to draw the following main
conclusions:
 At constant cell operating voltage and MC operating conditions, the thermally integrated system gives much better
performance in terms of power output and system electric
efficiency (37.7% vs 24.7%). The MC (i.e. available H2O) and
integration heat are thus used to operate the gasifier more in
the steam operating conditions rather than autothermal.
That is also indicated by the almost zero requirement in
terms of gasifier air flow rate.
 System performances are highly dependent on SOFC H2
utilization, that has a direct impact on gasifier operating
conditions via its thermal integration by the combustion of
the SOFC off-gases.
 SOFC H2 utilization influences the system performance
mainly by two effects: air flow rate is more important in the
low SOFC H2 utilization end, where the selected cell voltage
is achievable only with high air flow rate; the limitation in
terms of integration heat dHint is instead more evident in
the higher SOFC H2 utilization end where air is required to
thermally sustain the gasifier.

Nomenclature

dH
E

enthalpy variation
cell voltage, overpotentials

Subscripts and superscripts
c, conc concentration
e
electrolyte
el
electric
f
fuel
p
pressure
tot
total
th
thermal

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