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Energy and exergy analyses of an integrated SOFC and coalgasification system

Rami Salah El-Emama,b,*, Ibrahim Dincer a, Greg F. Naterer a

a Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, 2000 Simcoe Street North, Oshawa,

Ontario L1H 7K4, Canadab Faculty of Engineering, Mansoura University, Mansoura, Egypt

a r t i c l e i n f o

Article history:

Received 16 August 2011

Received in revised form

17 September 2011

Accepted 20 September 2011

Available online 27 October 2011

Keywords:

SOFC

Hydrogen

Coal gasification

Energy

Exergy

Efficiency

* Corresponding author. Faculty of EngineeriNorth, Oshawa, Ontario L1H 7K4, Canada. T

E-mail addresses: rami.elemam@uoit.ca,0360-3199/$ e see front matter Copyright ªdoi:10.1016/j.ijhydene.2011.09.139

a b s t r a c t

This paper examines an integrated gasification and solid oxide fuel cell (SOFC) system with

a gas turbine and steam cycle that uses heat recovery of the gas turbine exhaust. Energy

and exergy analyses are performed with two different types of coal. For the two different

cases, the energy efficiency of the overall system is 38.1% and 36.7%, while the exergy

efficiency is 27% and 23.2%, respectively. The effects of changing the reference temperature

on the exergy destruction and exergy efficiency of different components are also reported.

A parametric study on the effects of changing the pressure ratio on the component

performance is presented.

Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights

reserved.

1. Introduction The combination of two or more power cycles into one

Integrated energy conversion systems are promising alterna-

tives to fulfill the increasing need for energy sustainability.

There is a wide variety of integrated systems which are very

efficient and have fuel flexibility for combined production of

electricity, hydrogen and heat [1]. An attractive integrated

energy conversion system is one that operates based on

syngas. Coal is a common source of producing syngas [2]. The

composition of syngas generated froma gasification process is

different depending on the gasification method, type of coal

and oxygen purity. Gasification conditions, such as tempera-

ture and pressure, affect the syngas composition [3,4].

ng and Applied Science,el.: þ1 2892004658.elemam@hotmail.com (R2011, Hydrogen Energy P

system is a viable option for efficient power generation [5]. It

can also be useful for improving the overall performance of

the energy conversion system and the energy efficiency [6].

One of the current fields of coal gasification is the application

of integrated gasification combined cycles (IGCC). The tech-

nology of coal gasification is well suited to the co-production

of hydrogen and electricity, which may increase the overall

efficiency of the process and provide other economic benefits

[7]. Fig. 1 shows the main elements of a coal based IGCC plant.

Also, solid oxide fuel cell (SOFC) technology is a promising

technology to work in integrated plants because of its high

operating efficiency, solid state design, operating conditions

University of Ontario Institute of Technology, 2000 Simcoe Street

.S. El-Emam).ublications, LLC. Published by Elsevier Ltd. All rights reserved.

Fig. 1 e Typical plant components of an IGCC system.

Fig. 2 e A schematic diagram of the modified integrated

system, as given in Ref. [13].

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 7 ( 2 0 1 2 ) 1 6 8 9e1 6 9 71690

and high temperature capability, as well as the potential for

gas and liquid fuel internal reforming [8e10].

An investigation of the processes of system integration for

combined hydrogen and electricity co-production was per-

formed by Cormos [11]. The hydrogen production from coal

gasification with carbon dioxide capturing technology was

studied by Cormos et al. [12] with a commercial ChemCAD

package. Ghosh and De [13] performed an energy analysis for

a cogeneration gasification and SOFC system. They studied

the effects of the pressure ratio on the performance of the

system at different values of the SOFC operating temperature.

An exergy analysis performed on the cogeneration system [14]

showed the exergy destruction in different components of the

system and how it is affected by the pressure ratio. Jin et al.

[15] and Li et al. [16] developed a thermodynamic model for

a coal gasification process in supercritical water for hydrogen

production with a fluidized bed reactor.

This paper is concerned with the thermodynamic perfor-

mance of an integrated system based on the production of

syngas using coal gasification, which is directed to a solid

oxide fuel cell. The fuel cell outlet gas mixes with natural gas

and then feeds the combustion chamber of a bottoming gas

turbine system. A heat recovery steam generator is used to

produce steam for a steam turbinewith heat of the gas turbine

exhaust. Exergy analysis is performed for different compo-

nents of the system. Different values of the reference

temperature, which directly affect the exergy performance,

and their effects on the system performance are studied. A

parametric study of the effects of the pressure ratio with

varying fuel cell temperature is performed on selected

components of the system.

2. System description

In this paper, a modified combined cogeneration system is

developed based on the system studied by Ghosh and De [13].

The system involves coal gasification and an SOFC unit

combinedwith gas and steam turbine cycles. Thermodynamic

energy and exergy analyses are performed on the proposed

system. The effects of the reference temperature are studied

for two different coal types as a fuel supply to the gasifier.

Fig. 2 shows a schematic of the combined cogeneration

power plant. Atmospheric air (1) enters the air compressor.

The compressor supplies compressed air to the gasifier, SOFC

and the combustion chamber of the gas turbine cycle. Part of

the delivered air is directed to the air separation unit where

oxygen is separated and directed to the gasifier. The syngas

produced from the gasification process is then cooled, purified

and directed to supply the SOFC anode side. Preheated water

from the heat recovery steam generator (HRSG) is used to cool

the syngas. Superheated vapor from the cooler is then

directed to the steam turbine for electricity production.

Compressed air (7) is directed to the fuel cell cathode after

being preheated through the recuperator using heat of the

exiting gas from the fuel cell. Anode and cathode exit streams

are mixed together and directed to the combustion chamber

of the gas turbine bottoming cycle. It mixes with the supply

fuel of the combustion chamber. The exhaust of the gas

turbine is recovered in the HRSG for providing steam to the

steam turbine. The additional heat recovered is used to

produce saturated steam at low pressure.

The analysis of the components in the system (Fig. 2) is

modeled by balance equations of mass, energy, entropy and

exergy. The following assumptions were used. Atmospheric

air is considered as an ideal gas with the composition of 21%

oxygen and 79% nitrogen. All flow steams are assumed as

ideal gases. No pressure losses are considered in the flow

paths. Ambient temperature and pressure are constant. A

steady state operation is assumed. Heat exchangers,

compressors and the turbine are assumed adiabatic.

3. Thermodynamic analysis

3.1. Formulation of energy and exergy efficiencies

The energy balance is formulated for the components of the

system in Fig. 2. The energy balance equation considering

each component as a control volume in steady state operation

can be written as follows:

_Qcv � _Wcv ¼Xout

_nihi �Xin

_nihi (1)

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where _ni and hi represent the molar flow rate and specific

molar enthalpy of the flow stream into and out from each

component in the system.

Exergy is defined as the maximum work that can be

extracted from a system interacting with a reference envi-

ronment [17]. The exergy balance is formulated for the system

components operating at a steady state condition as follows:

0 ¼X�

1� To

T

�_Qcv � _Wcv þ

Xin

_niexi �Xout

_niexi � _Exdi (2)

where exi is the specificmolar flow exergy for each component

of the inlet and outlet flow streams. It can be defined by

neglecting the kinetic and potential energy changes, as follows:

exi ¼ ðhi � hoÞ � Toðsi � soÞ þ exch (3)

where exch;i is the specific molar chemical exergy of the flow

streams. The specific chemical exergy of different species in

a gas mixture can be written as follows:

exch ¼X

yi:exch;i þ RTo

Xyi:ln yi (4)

where yi is the molar fraction of the gas species ‘i’ in the gas

mixture. The molar specific chemical exergies for the gas

species in the analysis are shown in Table 1 [18]. The enthalpy

and entropy values for each component of the gas are calcu-

lated using polynomial equations as a function of the

temperature [19].

The exergy destruction in component ‘i’, which appears as

‘i’ in the exergy balance equation, is proportional to the

entropy generation, _Exdi , i.e.:

_Exdi ¼ To:Sgen;i (5)

where Sgen;i denotes the entropy generation in each

component.

The energy efficiency can be expressed as a ratio of the

generated power to the lower heating value of the fuel.

hth ¼_W

_nf :LHV(6)

The energy efficiency of the integrated system based on the

heating value of the fuel can be determined as follows:

_Wnet ¼ _WSOFC þ _WGT;net þ _WST � _Wpump (7)

The exergy efficiency for each component is defined based

on the total exergy output to the total exergy input as follows:

j ¼_Exout

_Exin

(8)

Table 1 e Specific chemical exergy values for differentcomponents.

Chemical Exergy, [kJ/kmol]

CH4 836,510 H2O 9340

C2H6 1,504,360 H2 20,340

C3H8 2,163,190 O2 253,680

CO2 27,900 N2 720

CO 275,000

Source: [18].

The total exergy efficiency of system is defined based on fuel

exergy as follows:

j ¼ 1�P _Exd;iP _Exfuel þ _Exair;in

(9)

3.2. Coal gasification

Two different types of coal have been used in the gasifier. The

gasification process occurs at elevated temperatures, and the

pressure was limited to 15 bars. The composition of the coal,

heating value and water content are shown in Table 2.

The chemical exergy of the coal is calculated based on the

following formulawhich is used for solid industrial fossil fuels

[17]:

Exch;fuel ¼�CV0 þw:hfg

�4dry þ 9; 417s (10)

where CV0 is the net calorific value of the fuel, w is the

moisture content of the fuel, hfg is the latent heat of water at To

and s denotes the mass fraction of sulphur in the fuel. Also,

4dry can be defined in terms of the dry organic substances

contained in the coal as follows [18]:

4dry ¼ 0:1882hcþ 0:061

ocþ 0:0404

ncþ 1:0437 (11)

where c, h, o and n represent the mass fractions of carbon,

hydrogen, oxygen and nitrogen in the fuel, respectively. This

formula is applicable with a mass ratio of oxygen to carbon

less than 0.667 [18]. The typical syngas composition exiting

the gasifier as percentage molar compositions is 10.6% CO2,

51.6% CO, 0.1% CH4, 35.1% H2, and 2.6% N2 and others [22]. The

reaction occurs in the gasifier using compressed oxygen,

separated from air in the air separation unit, and it can be

presented as

�ycCþ yH2

H2 þ yH2H2 þ yO2

O2 þ yH2OH2Oþ yN2N2 þ ysSþ ash

�þ X:O2/Y:

�yCO2

CO2 þ yCOCOþ yCH4CH4 þ yH2

H2 þ yN2N2

�þ yH2OH2Oþ Z:Cþ ash

(12)

where yi is the molar fraction of the composition ‘i’, and X, Y

and Z are the mole fractions of oxygen, syngas and char,

which can be calculated from the molar balance equations for

individual elements in the chemical reaction. The syngas

temperature can be determined from the energy balance of

the gasifier.

Table 2 e Ultimate analysis of the coal types in the study.

Coal ultimate analysis wt.% Case 1 Case 2

C 58.8 63.75

H 3.80 4.50

O 12.2 6.88

N 1.30 1.25

S 0.30 2.51

Moisture content 19.6 11.12

LHV (kJ/kg) 21,920 25,886

HHV (kJ/kg) 23,200 27,135

Source: [20,21].

Table 3 e Values of constants for the equilibriumconstant equation.

Reforming Shifting

a �2.6312 � 10�11 5.47 � 10�12

b 1.2406 � 10�7 �2.547 � 10�8

c �2.2523 � 10�4 4.6374 � 10�5

d 0.195027 �3.915 � 10�2

e �66.139488 13.209723

Source: [23].

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3.3. Solid oxide fuel cell (SOFC)

The solid oxide fuel cell unit, Fig. 3, uses the syngas produced

from the gasification process. The supply fuel is mixed with

circulated gas that exists from the anode side. The steam

reforming process ofmethane and thewater gas shift reaction

occurs in the anode side where the electrochemical reaction

also occurs. The compressed air is directed to the cathode side

as it works as an oxidant. The electrons, which are produced

at the anode side, are directed to the cathode side and reacted

with the oxygenmolecules. The oxide ions produced from this

reaction at the cathode side diffuse to the anode through the

electrolyte layer. The electric current is produced by the flow

of electrons. The SOFC is assumed to be internally reforming,

and the reforming and shifting reactions maintain equilib-

rium conditions.

For the reforming reaction:

CH4 þH2O4COþ 3H2 (13)

For the shifting reaction:

COþH2O4CO2 þH2 (14)

The net electrochemical reaction of the fuel cell is given by:

H2 þ 1=2O2/H2O (15)

where the equilibrium constants can be determined as

a function of the operating temperature. They can also be

formulated as a function of the partial pressure of reactants

and products according to the reactions above as:

Kreform ¼ P3H2PCO

PCH4PH2O

(16)

KShift ¼ PH2PCO2

PCOPH2O(17)

The component partial pressures can be expressed as

a function of their concentrations. The equilibrium constants

can be determined from the following polynomial which

presents the equilibrium constant as a function of the oper-

ating temperature. The values of the constants are shown in

Table 3 for the reforming and shifting reaction [23].

log K ¼ aT4 þ bT3 þ cT2 þ dTþ e (18)

Fig. 3 e Schematic diagram of IR- SOFC.

The equilibrium constants can also be expressed in terms of

the molar composition as follows:

Kreform ¼ y3eq;H2

:yeq;CO

yeq;CH4:yeq;H2O

x

�PPO

�2

(19)

KShift ¼ yeq;H2:yeq;CO2

yeq;CO:yeq;H2O(20)

where yeq;i represents the equilibrium molar concentration of

the compositions. This can be expressed as the ratio of the

equilibrium number of moles of the component to the total

number of moles at equilibrium as follows:

yeq;i ¼_nf3;i

_nf3(21)

For the equilibrium number of moles for each composition,

the following relations are used based on the equilibrium

reactions of reforming, shifting and electrochemical reactions

as follows:

_nf3;CH4¼ _nf2;CH4

� a (22)

_nf3;CO ¼ _nf2;CO þ a� b (23)

_nf3;CO2¼ _nf2;CO2

þ b (24)

_nf3;H2¼ _nf2;H2

þ 3aþ b� c (25)

_nf3;H2O ¼ _nf2;H2O � a� bþ c (26)

The total number of moles at equilibrium can be found by

adding the right sides of the equilibrium number of the

previous molar equations, yielding:

_nf3 ¼ _nf2 þ 2a (27)

where _nf2;i represents the number ofmoles of fuel composition

flowing into the fuel cell at state 2, which is indicated in Fig. 3.

Here a and b represent the extent of conversion of CH4 and CO

in the reforming and shifting reactions, respectively, and c

represents the hydrogen conversion during the electro-

chemical reaction. This is the molar flow rate of hydrogen

utilized in the fuel cell. The value of c can be calculated from

the following equation [24]:

c ¼ Uf :�_nf1;H2O þ 3aþ b

���1� rþ r:Uf

�(28)

where r is the recirculation ratio of the anode outlet, and Uf is

the fuel utilization ratio. The number of moles for the fuel

Fig. 4 e Exergy destruction in the system components for

case 1.

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composition entering the fuel cell at state 2 can be calculated

from the following equation:

_nf2;i ¼ _nf1;i þ yeq;i:r: _nf3 (29)

The electric current produced can be expressed as

j ¼ 2F:c (30)

The fuel cell reversible potential can be calculated from the

Nernst equation [8] as follows:

V ¼ 1:19þ R:T2:F

ln

PH2

:PO21=2

PH2O

!(31)

The potential estimated from the Nernst equation is reduced

because of fuel cell ohmic, activation and concentration losses.

In this study, these losses are neglected [13]. The electric work

produced by the fuel cell can be obtained as follows:

Wel ¼ j:V (32)

In the analysis of the solid oxide fuel cell, it is assumed to be

insulated [24], and the following assumptions are used. The

solid oxide fuel cell works at a steady state condition. The

pressure drop across the fuel cell is neglected. The gasmixture

is leaving the fuel cell at a chemical equilibrium condition.

Finally, the fuel cell is insulated and there is no heat exchange

with the surroundings.

3.4. Gas turbine cycle

The mixed gas exiting from the fuel cell is directed to the

combustionchamberafter itflowsthroughtherecuperator.The

gas is thenmixedwithnatural gas.Theexhaust gas isexpanded

then in the gas turbine, it produces mechanical work. The

natural gas has the following composition: 93.9% CH4, 3.2%

C2H6, 1.1% C3H8, 1% CO2 and 0.8% N2 [20]. Compressed air is

added for thecombustionprocess.Theseparatednitrogen from

theair separationunit is alsomixed in thecombustionchamber

for limiting the temperature at the gas turbine inlet to 1250 �C,and to help reduce the formation of nitrous oxides.

4. Results and discussion

Based on the thermodynamic model of the system, an EES

(Engineering Equation Solver) code is written to study the

Table 4 e Performance data for the system operation inthe base case.

Performance parameters (assumed)

Compressor pressure ratio 15

Gas turbine inlet temperature, K 1450

SOFC operating temperature, K 1273

Steam turbine inlet temperature, K 823

Steam turbine inlet pressure, bar 80

Coal feeding rate, tons/hr 6.69

Gas turbine isentropic efficiency, % 85

Compressor isentropic efficiency, % 85

Pump isentropic efficiency, % 96

Atmospheric air; O2, N2 (% vol.) 21, 79

performance of the system components. Table 4 shows the

performance data in the system analyses. A parametric study

is performed to investigate the effects of changing the pres-

sure ratio through the system on the exergetic performance of

different system components. Comparisons between two

Fig. 5 e Exergy efficiency in the system components for

cases (a) 1 and (b) 2.

Fig. 8 e Exergy efficiency of the system components for

cases 1 and 2 at To [ 20 �C.

Fig. 6 e Exergy destruction in the system components as

a percentage of total exergy destruction for cases (a) 1 and

(b) 2.

Fig. 7 e Exergy destruction as a percentage of the total fuel

exergy input for cases 1 and 2 at To [ 20 �C.

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different types of supply fuels to the gasifier are performed.

The exergy destruction and exergy efficiency of different

components are studied. Based on an energy analysis of the

system for the case 1 type of fuel, the power produced by the

steam turbine is 5.41 MW. The fuel cell produces 12.8 MW of

electric work at 55.8% energy efficiency. The gas turbine net

work output is 19.3MW. Under the same operating conditions,

the overall energy and exergy efficiencies of the system were

calculated as 38.1% and 27%, respectively. As a comparison

with the overall performance of the integrated system, using

the case 2 type of fuel results in overall energy and exergy

efficiencies of 36.7%, and 23.2%, respectively. The analyses

and results in Figs. 5e9 are performed at a compressor pres-

sure ratio of 15. Table 4 shows the data of systemperformance

and Table 5 shows the gas composition for case 1 at different

states corresponding to Fig. 2.

Exergy destruction in the system component for case 1 is

shown as a percentage of the total exergy destruction in the

whole system in Fig. 4. The most significant exergy destruc-

tion occurs in the fuel cell. Significant exergy destruction can

Fig. 9 e Pressure ratio effect on the performance of the

gasifier.

Table 5 e Gas state point data and composition through the system for case 1.

State Temperature[K]

Mass flowrate [tons/h]

Molar composition, %

CH4 CO2 CO H2 H2O O2 N2

1 293 84.67 0 0 0 0 0 21 79

2 733 84.67 0 0 0 0 0 21 79

3 1885 7.38 0.1 10.6 51.6 35.1 0 0 2.6

4 850 7.38 0.1 10.6 51.6 35.1 0 0 2.6

5 850 7.38 0.1 10.6 51.6 35.1 0 0 2.6

6 733 36.14 0 0 0 0 0 21 79

7 850 36.14 0 0 0 0 0 21 79

8 1273 43.52 0 14.87 0.25 3.13 5.44 8.88 67.43

9 1100 43.52 0 14.87 0.25 3.13 5.44 8.88 67.43

10 1450 117.07 0 9.844 0 0 11.57 1.202 77.38

11 746.6 117.07 0 9.844 0 0 11.57 1.202 77.38

12 435 117.07 0 9.844 0 0 11.57 1.202 77.38

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 en e r g y 3 7 ( 2 0 1 2 ) 1 6 8 9e1 6 9 7 1695

also be noticed in the gasifier, combustion chamber and the

HRSG as well. Fig. 5 shows the effect of changing the reference

temperature on the exergetic performance of different

components of the system for the two different types of coal.

The performance is characterized by the exergy efficiency of

the devices. Three different values of reference temperature

have been studied: 10, 20 and 30 �C, respectively.In Fig. 6, the devices performance are shown based on the

exergy destruction as a percentage of the total exergy

destruction within the integrated system, at different refer-

ence temperature values, for two different cases. From Fig. 6,

it appears that the exergy destruction is affected by the

change of reference temperature. Exergy destruction

increases with temperature for the gasifier, combustion

chamber and HRSG, however it decreases for the fuel cell, as it

is shown for the two cases. The results shown in Fig. 7

represent a comparison between the exergy destruction as

a percentage of the exergy of the fuels fed for different devices

in cases 1 and 2, at the reference temperature of 20 �C. Fig. 8shows a comparison between the exergy efficiency of

different devices performing in case 1 and 2.

Figs. 9e11 show the effects of changing the pressure ratio

of the gas turbine compressor on the exergetic performance of

the gasifier, fuel cell and combustion chamber, where the

dominant exergy destruction occurred. The exergetic perfor-

mance is presented by the exergy efficiency and the exergy

destruction as a percentage of the exergy of fuel input. Two

Fig. 10 e Pressure ratio effect on the fuel cell performance

at different fuel cell operating temperatures.

different fuel cell operating temperatures are investigated for

the fuel cell and the combustion chamber. The fuel cell

operating temperature has no effect on the gasifier. Fig. 9

shows that increasing the pressure ratio enhances the

exergy efficiency of the gasifier. The output syngas will be at

a higher pressure and temperature, causing a higher exergy

output of the system. For the solid oxide fuel cell, Fig. 10,

increasing the pressure ratio decreases the exergy destruc-

tion. This is might be as a result of the increase of the fuel cell

work with the increase of the pressure ratio, so the exergy

destruction decreases and exergy efficiency increases. On the

other hand, increasing the fuel cell operating temperature

decreases the exergy efficiency of the fuel cell and the exergy

destruction increases.

Fig. 11 shows the effect of pressure ratio variation on the

combustion chamber. Increasing the pressure ratio causes

a decrease in the combustible gases in the exhaust of the

fuel cell, which is directed to the combustion chamber. This

implies a reduction in the extent of combustion, and

decrease in the exergy destruction of the combustion

chamber. However, after a pressure ratio value of 25, the

enhancements of performance become lower, due to mixing

with natural gas fuel in the combustion chamber. Increases

of the fuel cell temperature means an increase of the fuel

cell exhaust gas flow that is delivered to the combustion

chamber. This leads to higher exergy destruction in the

combustion chamber.

Fig. 11 e Pressure ratio effect on the combustion chamber

performance at different fuel cell operating temperatures.

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 7 ( 2 0 1 2 ) 1 6 8 9e1 6 9 71696

5. Conclusions

Coal gasification technology integrated with a solid oxide fuel

cell is a promising alternative for energy sustainability. This

study has performed thermodynamic analyses based on

energy and exergy to investigate the performance of the

integrated system and determine the extent of the system

components to be enhanced for higher efficiency. Two

different types of coal have been used in the gasification

process. The total energy and exergy efficiencies of the system

were calculated as 38.1% and 27%, respectively, for case 1, and

36.7% and 23.2%, respectively, for case 2. The effect of varia-

tions of pressure ratio of the gas turbine compressor on

different devices has also been studied. For the gasifier, SOFC,

and the combustion chamber, increasing the pressure ratio

enhances the performance of these devices. It decreases the

exergy destruction across the device. Increasing the fuel cell

operating temperature causes more exergy destruction in the

combustion chamber and the fuel cell. Three different refer-

ence temperature values are applied to study its effect on the

exergetic performance of different devices.

Acknowledgments

Financial support from the Natural Sciences and Engineering

Research Council of Canada is gratefully acknowledged.

Nomenclature

ex Specific molar exergy, kJ/kmol_Exd Exergy destruction, kW

F Faraday constant

h Specific molar enthalpy, kJ/kmol

j Current density, mA/cm2

K Equilibrium constant_n Molar flow rate, kmol/s

P Partial pressure, pressure, kPa_Q Heat flow rate, kW

r SOFC anode circulation ratio

R Universal gas constant, kJ/kmol K_Sgen Entropy generation, kW/K

s Specific molar entropy, kJ/kmol K

T Temperature, K

U Utilization factor, %

V Cell voltage, V_W Work rate, kW

g Mole fraction

Greek symbols

h Energy efficiency, %

J Exergy efficiency, %

Subscripts

cv Control volume

eq Equilibrium

i State, or device

f Fuel

Acronym

ASU Air separation unit

HHV Higher heating value

HRSG Heat recovery steam generator

IGCC Integrated gasification combined cycle

LHV Lower heating value

SOFC Solid oxide fuel cell

SRU Sulphur removal unit

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