Thermodynamic Analysis of Solid Oxide Fuel Cell-Gas Turbine Systems Operating With Various Biofuels...

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Thermodynamic Analysis of Solid Oxide

Fuel Cell Gas Turbine Systems Operating with Various BiofuelsH. C. Patel1*, T. Woudstra1, P. V. Aravind1

1 Process and Energy Laboratory, Delft University of Technology, Section Energy Technology, Leeghwaterstraat 44, 2628CA Delft, TheNetherlands

ReceivedApril 20, 2012; acceptedAugust 27, 2012

1 Introduction

Solid oxide fuel cell (SOFC) systems hold great promise as

a sustainable power source because of their high efficiency,

fuel flexibility and ability to be combined with other systems

to make hybrids with even higher efficiency. The SOFC can

be operated with various fuels because of the high operation

temperature and with the catalyst used some fuels can be

even internally reformed. Thus, there is an opportunity to usecarbonaceous biofuels in the SOFC wherein they can be

internally or externally reformed to give hydrogen for the

electrochemical reaction [1, 2]. Biomass can be a sustainable

fuel with correct regulations but biomass in itself is not very

easy to burn without environmental impact. It can be benefi-

cial to convert raw biomass into secondary liquid or gaseous

fuels with better properties like density, energy density,

transportability, etc. Biomass can be easily converted into

methanol, ethanol, and synthesis gas (CO + H2). Ammonia

and methane can be obtained from biological sources or from

waste in a sustainable manner and eventually hydrogen can

also be produced from biomass using thermal or biological

processes [2–7]. SOFC-gas turbine (SOFC-GT) systems offer

an opportunity for using biomass to meet energy require-

ments with highest possible efficiency and hence least envir-

onmental impact.

The fuel flexibility of the SOFC is a topic of growing inter-

est and various experimental as well as theoretical studies are

available in literature about SOFCs operating on fuels like

methanol, ethanol, and methane etc. [3, 5–9]. Considering the

present scenario it is not very clear what fuel would even-

tually be used if at all a single fuel is used as the futureenergy carrier. Economic, safety, and environmental concerns

would rule out some of the fuels and phase in others. All such

fuels are explored as energy carriers for the future as all of

them provide some advantages but their use in an SOFC

environment is not fully explored on a thermodynamic basis

especially when compared to each other.

A comprehensive thermodynamic analysis of an SOFC

system operating with various fuels can give invaluable infor-

mation on the operating characteristics of each fuel, the ther-

modynamic limitations, the effect on the balance of plant sys-

[*] Corresponding author, h.c.patel @tudelft.nl

Abstract

Solid oxide fuel cell–gas turbine (SOFC-GT) systems provide

a thermodynamically high efficiency alternative for power

generation from biofuels. In this study biofuels namely

methane, ethanol, methanol, hydrogen, and ammonia are

evaluated exergetically with respect to their performance at

system level and in system components like heat exchan-

gers, fuel cell, gas turbine, combustor, compressor, and the

stack. Further, the fuel cell losses are investigated in detail

with respect to their dependence on operating parameters

such as fuel utilization, Nernst voltage, etc. as well as fuel

specific parameters like heat effects. It is found that the heateffects play a major role in setting up the flows in the system

and hence, power levels attained in individual components.

The per pass fuel utilization dictates the efficiency of the fuel

cell itself, but the system efficiency is not entirely dependent

on fuel cell efficiency alone, but depends on the split

between the fuel cell and gas turbine powers which in turn

depends highly on the nature of the fuel and its chemistry.

Counter intuitively it is found that with recycle, the fuel cell

efficiency of methane is less than that of hydrogen but the

system efficiency of methane is higher.

Keywords: Biofuels, Exergy, SOFC-GT, Solid Oxide FuelCell, Solid Oxide Fuel Cell Gas Turbine, System Studies

FUEL CELLS 12, 2012, No. 6, 1115–1128 © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1115

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DOI: 10.1002/fuce.201200062



Patel et al.: Thermodynamic Analysis of Solid Oxide Fuel Cell Gas Turbine Systems Operating

tem and resulting thermodynamic effects. Optimization of

such a system with individual fuels will point out the effects

of the fuel chemistry on the overall systems as well as each

component.

The energy efficiency of systems is better understood withthe help of the exergy concept. The second law of thermody-

namics defines a difference in the quality of energy. Exergy

refers to the part of heat (or any other form of energy) which

is available for useful work. Maximum work can be obtained

in a thermodynamically reversible process and non-idealities

in a system cause a departure from reversibility resulting in

lower efficiency. Combustion is always associated with large

exergy destruction. In fuel cells electrochemical processes of

electron transfer is nearer to reversibility and hence has much

higher thermodynamic efficiency depending on temperature.

Among the various fuel cell types we consider the SOFC

because of its high thermodynamic efficiency [10–12]. The

main advantage lies in the high grade heat available at the

fuel cell exhaust (1,073–1,273 K). This can be used to drive a

bottoming cycle like a steam cycle or GT cycle to utilize the

heat and unused fuel to produce power. Such hybrid systems

have been studied extensively in literature and pros and cons

of various bottoming cycles have been detailed [9, 13].

We choose the GT cycle because of its relative simplicity,

high power to weight ratio and ability to use high tempera-

ture and pressure gas to produce electricity efficiently. Also,

the fuel cell benefits from the increased pressure, increasing

overall efficiency.

In the combined system the fuel cell exhaust gas is burnt

and the flue gas is passed through a GT. The high tempera-ture GT exhaust gas is used to preheat inlet streams of the

fuel cell resulting in good heat recovery. There is still residual

heat which can be used to generate steam used for the

reforming reaction of the hydrocarbon to form hydrogen.

These options are considered in sections below and described

in more detail.

With this arrangement we reduce the stack losses and uti-

lize the SOFC exhaust completely resulting in a more efficient

system than either of the above alone. Efficiencies of the order

of 70–80% are expected from such a hybrid system [4, 5, 10–

12, 14]. Optimization strategies have also been studied for

SOFC-GT integration mostly dealing with system configura-

tion [15, 16]. Scupita et al. [17] studied the effect of fuel com-

position limited to varying the composition between CH4,CO,

CO2, N2, a n d H2 mainly targeting biomass derived gas

streams. Some authors have focused on a fixed GT design as

commercially available “off the shelf” designs may not be

able to perform optimally in the hybrid system not specifi-

cally designed for a particular turbine [18, 19].

Previous studies on SOFC-GT systems have been mostly

focusing on optimizing a system for a particular fuel or two

fuels, providing a comparison of systems based on parame-

ters like operating pressure, temperature, steam to carbon

ratio, etc. [4, 10–12]. Leucht et al. [20] studied the dynamic

performance of an SOFC-GT system through various opera-tion strategies in order to be able to follow a particular load

for the system. They concluded that pressurizing the fuel cell

rather than operating at normal pressures is advantageous.

Song et al. [18] studied a tubular cell with a quasi 2D model

allowing prediction of temperatures and flow in a particular

direction in the cell. They concluded a co-flow arrangement ismore efficient than the counter-flow. Kuchonthara et al. [21]

studied further energy recuperation techniques in an SOFC-

GT system considering steam (through a heat recovery steam

generator) and heat recuperation and found that steam recup-

eration can improve the overall system efficiency as well as

specific power. Similarly Yi et al. [22] applied an intercooled

GT to the SOFC-GT hybrid cycle. An efficiency of 75.8% elec-

trical was achieved using natural gas (NG) as fuel. Multistage

oxidation using SOFCs in a hybrid SOFC-GT system was

found to increase the efficiency and limit the temperature gra-

dients [23]. Methanol and kerosene were investigated as fuels

by Santin et al. [9] with respect to thermodynamic as well as

economic criteria with methane as the reference fuel. For an

operating pressure of 4 bar the efficiency was found to be

64.5% for the reference case of methane. The maximum effi-

ciency obtained was 64.8% for methanol and 54.9% for kero-

sene. The economic performance was better with methanol

than with other systems. Chan et al. [24] in their study mod-

eled a tubular SOFC with the losses split into Ohmic, activa-

tion and concentration polarizations for an NG fed SOFC-GT

system coupled with a heat recovery steam generator. An

electrical efficiency of 61.9% was obtained. The effect of pres-

sure, flow rates was studied in a separate study [25].

But the exergy criterion is not considered by many. Ener-

getic criterion does not differentiate between the qualities of the various energy sources. This can be achieved using

exergy which takes into account the second law of thermody-

namics and that not all forms of energy are equal in quality.

Exergy analysis of SOFC-GT system has been provided by

Calise [26] where individual components and exergy losses

are identified for a single gas composition. Motahar and

Alemrajabi [27] studied a tubular SOFC-GT system with

steam injection. Individual components were identified and

losses in each were presented. Using steam injection it was

found that the stack losses could be brought down signifi-

cantly increasing efficiency from 58.28 to 65.34%. The system

exhaust temperature was brought down from 381 to

130.27 °C. Granovskii et al. [12] studied methane conversion

in an SOFC-GT system using exergy where the maximum

thermodynamic efficiency reached as high as 70–80%. Bavar-

sad [28] performed energy and exergy analysis of a NG fed

SOFC-GT system based on parameters like pressure ratio and

flow rates. The first and second law efficiencies achieved

were 65.62 and 59.32%, respectively. He also concluded that

higher air or fuel flow rates have a negative influence on the

efficiency. Aravind et al. [5] on the other hand found no sig-

nificant influence of pressure ratio on the efficiency of a sys-

tem comprised of a biomass gasifier with an SOFC-GT.

Excluding the gasifier the major system components contri-

buting to exergy losses were the GT and compressors. A highefficiency of 73% was obtained for a gasifier SOFC-GT system

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where multiple fuel cell stages were applied [28]. Similarly

Haseli et al. [30, 31] provide an exergy analysis of an SOFC-

GT system with the effect of operating parameters like ambi-

ent temperature and compressor pressure. An efficiency of

60.6% was obtained at the compression ratio of about 4 whichwas found to be the optimum. Douvartzides et al. [32] used

exergy analysis to analyze an SOFC power plant fed with

methane or ethanol using an external steam reformer. They

concluded that methane fed power plant was more efficient

than the ethanol fed one irrespective of temperature (within

allowable limits) and reforming factor. Efficiencies of the

order of 65–75% were obtained depending on temperature

and fuel. Chan et al. [33] performed exergy analysis of the

SOFC without the GT cycle exploring the effect of current

density and temperature for hydrogen and methane fuels.

The first and second law efficiencies for hydrogen and

methane are 50.97 and 52.8% and 62.19 and 59.96%, respec-

tively.

Other studies mainly focus on single fuels and optimizing

of components like GTs, steam turbines, and various types of

fuel cells or operating conditions and parameters like fuel uti-

lization, operating pressure, etc. [2, 4, 5, 11, 12, 14, 34–37].

Though these are important in identifying operating con-

ditions, to gain deeper insight into operating characteristics

of different fuels, it is required that various fuels be compared

at a particular operating condition and individual compo-

nents of the system be identified and losses within each com-

ponent be quantified. A comprehensive study across such

broad range of fuels based on exergy by identifying individu-

al components is absent as far as the authors knowledge goes.In this study various fuels are compared based on exer-

getic criteria as it provides a truer measure of work obtain-

able. The influence of individual components on the overall

efficiency for different fuels, when judged with the exergy cri-

teria is an important method for arriving at more refined sys-

tem concepts with high efficiency and optimal operating con-

ditions. Thus, in this study it is aimed at arriving at a high

efficiency SOFC-GT system and identifying parameters cru-

cial to its operation. Individual components are identified in

addition to the operating parameters and the efficiency of

each component is discussed for the fuel considered using

exergy.

2 Fuel Options

Hydrogen is considered in this study because of the basic

reaction of the fuel cell being hydrogen oxidation to produce

water. Hydrogen is studied on a large scale by many organi-

zations toward the development of a sustainable hydrogen

economy and thus serves as an ideal case.

Since cost of hydrogen and its storage is an issue NG is a

viable alternative. NG is readily available through pipe net-

work or through tanks (liquefied NG). Further, NG is cheap

and has lesser pollutants than diesel oil. Another advantage

with NG is that in the SOFC it is internally reformed, so aseparate reformer is not always required. In the SOFC, NG

components (CH4 mainly with some higher hydrocarbons)

undergo reforming internally as this reaction is supported by

the electro-catalyst used in the anode. Thus NG (with steam

addition) can be used directly as a feedstock in the SOFC

leading to a more simple and feasible system for the time being. It is interesting to note that this change in fuel will

already bring about a reduction in CO2 emissions resulting

from the lower C content of the fuel as compared to diesel oil.

For the purpose of modeling NG is considered as methane

[1, 14]. Methane is taken as the basis for comparison of other

fuels.

Biomass-based fuels are under a lot of discussion. Because

of the high temperatures in the SOFC it is possible to use a

variety of fuels. With proper legislation and production tech-

niques, biomass and waste derived fuels like ammonia,

dimethyl ether (DME), ethanol, methanol, biodiesel can all be

considered as sustainable carbon neutral sources [8, 26, 38, 39].

Fuels such as ammonia have received attention lately as alter-

natives to conventional diesel oil for fuel cell applications

[40]. These if properly regulated can indeed be sustainable

and have zero emissions by being conserved in the carbon

cycle. Ammonia is an interesting alternative as it is actually

commercially available in large quantities. It is carbon free

and has very high hydrogen content in addition to being

almost non-flammable [6]. The products of ammonia reaction

in the SOFC are merely nitrogen and water and thus no

greenhouse gas emissions [6–8, 10]. Ammonia is converted

into its constituent N2 and H2 and the H2 is further utilized in

the normal H2–H2O cell reaction [41]. There is minimal

production of NOx at operating conditions showing that theN2 is mostly inert in the cell. On the other hand ammonia is

toxic and can be detected by its smell even at levels of few

ppms [6, 7].The technology of the cell itself is not yet well

developed and accepted.

Ethanol and methanol are biomass derivatives which can

be obtained from synthesis gas as well as biomass conversion

through biological processes. Compared to NG the reforming

requirement is different as the major component of NG is

methane, the simplest of hydrocarbons, while methanol is

also a C1 compound, while ethanol is possibly more difficult

to break. Energy density of methanol is high and this might

provide an interesting option for fuel supply if methanol can

be commercially produced and distributed [39]. Ethanol is

already produced on a large scale biologically but competi-

tion with the current feedstock, which is mainly from food

needs to be considered. A broad comparison is given in Table

1 for the various fuels which will be considered in this study

[8].

Synthesis gas, which will be produced by reforming of the

above fuels, has been studied extensively as a fuel. With the

SOFC there is no need to remove CO. With steam addition

this can be converted to H2 using the water gas shift (WGS)

reaction. At the temperatures used in SOFC this reaction is

quite favorable. This is desirable as the OCV of CO–CO2 is

lower than that of H2–H2O [1]. It is assumed here that only

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WGS reaction occurs and all CO is converted to CO2 through

the shift reaction.

3 Modeling and Input Parameters

For the purpose of this study four fuels have been chosen

as all of these can be sustainably manufactured from biologi-

cal sources and it would be of importance to explore these in

context of SOFC systems.

The fuels studied are

(i) Methane

(ii) Ammonia

(iii) Hydrogen

(iv) Ethanol

(v) Methanol

The Lower Heating Value(LHV) and Exergy values are

provided in Table 1 for the above fuels. Cycle Tempo is a in-

house software developed at TU Delft which can be used for

thermodynamic analyses and optimization of power cycles

including fuel cells [42]. Cycle Tempo employs a Gibbs free

energy minimization based routine for equilibrium calcula-

tions in the fuel cell and combustor. For more details about

these models the reader is referred to the manual of Cycle

Tempo [42].

A model was developed in Cycle Tempo for a combined

SOFC-GT system considering internal reforming for various

fuels keeping the heat exchanger network same at same val-

ues. In the model a choice is made to fix the GT power at

30 kW and let the fuel cell output vary. The GT is not the

same in all cases but has the same power rating. The conse-quence of the fuel cell power varying is that the fuel cell will

be of a different size (area) for different fuels. For the purpose

of this study the systems are compared at design load only.

The pressure of 3 bar is chosen keeping into mind that this is

similar to a recuperating turbine and is more efficient at

around this pressure ratio [2]. Also previous studies have

shown that this is more or less near to an efficient point of

operation for the combined system [26, 30].

Methane, ethanol, methanol, ammonia and hydrogen are

all available in the library of FluidProp [43] which is used by

Cycle Tempo. For the detailed equations and properties the

reader is referred to the manual of Cycle Tempo and Fluid-

Prop [42, 43].

The model used is depicted in Figure 1 along-with various

subsystems considered for the analysis in later sections. It is

assumed here that all the fuels are completely internally

reformed at the SOFC anode. This is based on the assumption

that no carbon deposition occurs in the pipes upstream the

fuel cell. The feed is 20% water, alongwith the respective fuel

at 288 K, 1.013 bar. Because of the recycle there is always

enough steam in all cases. The steam to carbon ratios

achieved at the inlet of the fuel cell are 6.2, 6.9, and 3.8 for

methane ethanol and methanol, respectively. The fuel and

water is compressed to 3.065 bar in the compressor and

passed through successive heat exchangers to recover heatfrom the exhaust stream of the GT. The exact outlet tempera-

ture for the heat exchangers for each fuel is different based on

the heat available after the exhaust of GT. This fresh fuel is

mixed with recycled stream from the anode in order to obtain

a temperature of 1,173 K. On the air side fresh air is com-

pressed from 1.013 to 3.04 bar and preheated in heat exchan-ger and mixed with the recycle stream to again obtain a tem-

perature of 1,173 K. The exhaust streams from the fuel cell

are mixed and combusted in the combustor and subsequently

fed to the GT. As mentioned before the exhaust from the GT

is used to preheat the incoming streams and then given out in

the stack.

3.1 Calculation and Model Rules

Cycle Tempo utilizes Gibbs free energy minimization to

determine equilibrium conditions in the Fuel Cell and Com-

bustor. For this particular model the power level of the tur-

bine (fixed at 30 kW) is in turn used to calculate the mass

flow through the turbine and other equipment. Current in the

fuel cell is determined by the specified fuel utilization and

mass flow determined from GT/Combustor as well as set

temperatures. The mass flow ratio at cathode and anode is

determined by energy balance to obtain specified tempera-

tures. The current is then calculated from the mass flows and

the fuel utilization specified. Hence, active area of the cell

and the equivalent resistance is also calculated from the volt-

age and the current density. The enthalpy at turbine and com-

pressor outlet is calculated from the isentropic efficiency.

Other parameters used, common to all fuels are given in

Table 2.In each case the cell voltage is adjusted to obtain an

equivalent resistance of 5 × 10–5Xm2. Heat exchangers are

provided to ensure an inlet temperature of 1,173 K to cathode

and anode. Since this is not fully possible utilizing only the

GT exhaust, the exhaust gases from fuel cell are re circulated

to obtain the required inlet temperature. This recirculation is

also used in order to prevent large thermal gradients across

the cell and also equilibrate composition. It is noted here that

because of the recycle even though the overall utilization is

fixed it can vary per pass. The utilization based on fuel used in

the cell is called the per-pass utilization and the utilization

based on fresh fuel is called the overall utilization. The

amount of recycle is calculated on the basis of the inlet tem-

perature (which is specified) and the temperature at the out-

let of the heat exchangers. Practically also maintaining of a

steady operating temperature is essential.

The fuels are used as available from the library of Cycle

Tempo and are fed alongwith 20% water. The enthalpy for

vaporization is provided in subsequent heat exchangers.

Internal reforming of methane to CO and H2 and subsequent

WGS is calculated by Cycle Tempo based on equilibrium

under those conditions of temperature and pressure. In inter-

nal reforming SOFC module of Cycle Tempo, the equilibrium

compositions are calculated first and then the fuel cell param-

eters are calculated based on this composition as shown inFigure 2. T react and Preact are the temperature at which

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reforming and WGS reaction equilibrium compositions are

calculated and T fcel and Pfcel are fuel cell temperature and

pressures.

Ammonia also undergoes thermal decomposition to form

constituent N2 and H2. The hydrogen is utilized as fuel in the

normal fuel cell reaction to produce water. In Cycle Tempo

calculations, all the fuels are completely reformed into hydro-

gen and constituent molecules (CO/CO2/N2).

Mass flows in each apparatus is calculated by mass and

energy balance. Overall the number of equations must be

equal to number of pipes. In this case the oxidant to fuel ratio

in the combustor is determined by the airflow and hence cool-

ing requirement of the fuel cell.

In the fuel cell module in Cycle Tempo the inlet gas is first

taken to equilibrium. The current flow I , voltage V , and

power Pe are then calculated. The current can be calculatedfrom the flow to the anodeUm,a,in andthe fuelutilization U f as

I main

Ma2F yH2O yCO 4 yCH4

U f (1

where Ma is the molar mass, y i are the respective mole frac-

tions of the species and F is the Faradays constant. From this

the flow of oxygen from the cathode is calculated. Since the

temperature at the outlet is set, the airflow can be calculated.

Further to calculate the voltage V , power Pe, and current den-

sity im a one dimensional model is used. The temperature is

assumed constant in the cross section perpendicular to the

direction of fuel flow. Local variables of current density ix,

voltage V x, and concentrations yx are calculated.

The local Nernst voltage V rev,x is calculated as

V revx V 0rev RT

2F

ln y

12

02 c yH2

yH2O

p12

cell (2

Fig. 1 Model in Cycle Tempo with subsystems.

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where T is the temperature, V 0rev the standard reversible vol-

tage, R the universal gas constant yi the mole fraction, and

pcell is the pressure. If the voltage losses are assumed to be

negligible in the x direction then the cell voltage would be

constant over the fuel cell. Hence

DV x V revx V (3

where D

V x

is the loss in voltage. If Req is the equivalent cellresistance then the current density can be calculated as

ix DV xReq

(4

Over the complete area A of the cell we can use

I

A

U f

Req

U f

0

1

V revV dk

(5

where k is the reaction ordinate. Hence, the power can be cal-

culated.

For a known power of GT, the mass flow can be calculatedfrom the specific enthalpy as given below.

The outlet enthalpy for a compressor is obtained from

ho hi hos hi

gs(6

And for a GT it is found as

ho hi gshi hos (7

where ho is the specific enthalpy at the outlet, h i the specific

enthalpy at the inlet, ho,s the specific enthalpy at the outlet for

an isentropic process, and gs the isentropic efficiency.

Exergy efficiency can be defined as

gEx RExproducts

RExsource(8

where, RExproducts is the exergy flow that can be considered a

product of the system while RExsource is the exergy of that

part of the ingoing process that can be considered as neces-

sary to form the product. Depending on particular problemthe Exproducts and Exsource need to be specified. In the case of a

Fig. 2 Cycle Tempo calculations for fuel cell.

Fig. 3 Exergy loss distribution in heat exchanger, fuel cell, combustor, GT,stack and compressor (exergy losses as% of total input).

Table 1 Comparison of fuels

Fuel LHV (MJ kg–1) Exergy values (MJ kg–1)

Methane 50.0 51.4

Hydrogen 121.4 117.5

Ammonia 18.6 19.8

Ethanol 26.8 27.6

Methanol 19.9 22.5

Table 2 Input parameters for the models.

Parameter Value

Fuel utilization (based on fresh fuel) 85%

Current density 2,500 Am–2

Inlet pressure 1 bar

Resistance 5 × 10–5Xm2

Cell temperature 1,223 K

Inlet temperatures 1,173 K

Outlet temperatures 1,273 K

Fuel cell pressure 2.97 bar

Compressor pressure ratio 3Isentropic efficiency of compressor and

turbine

78%

Mechanical efficiency of compressor and

turbine

98%

Efficiency of generator 90%

Table 3 Efficiencies for various fuels.

Fuel Energy efficiency Exergy efficiency

Methane 78.3 75.5

Hydrogen 69.0 70.4

Ammonia 74.7 70.0

Ethanol 75.5 70.8

Methanol 73.1 68.5

Table 4 Power produced in fuel cell and GT.

Fuel Gas turbine power (kW) Fuel cell power (kW)

Methane 30 139

Hydrogen 30 81

Ammonia 30 112

Ethanol 30 117

Methanol 30 100

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power plant, the electrical exergy efficiency of the system is

given as

gExel RPelout RPelin

Exfuelin(9

where RPel,out is the electrical output of the system and RPel,in

is the input electrical power. Exfuel,in is the exergy of the fuel

that is fed to the system.

For more details, the reader is referred to the work of Ara-

vind et al. [5] and the manual of Cycle Tempo [42].

4 Results and Discussion

The system with methane is taken as a basis and is

explained in detail while results are presented for the other

systems for comparison. With the GT power fixed at 30 kW

the fuel cell produces 139 kW based on the temperatures spe-

cified and recycle ratios obtained. The air compressor con-

sumes 29.6 kW while the recirculation fans consume 1.4 kW

of power. The fuel cell operating voltage for a resistance of

5 × 10–5Xm2 is 0.795 V. The corresponding area of the fuel

cell is 70.134 m2. The overall utilization is fixed at 85% while

the per pass utilization achieved, because of the recycle is

76.5%. The air recycle ratio is 0.1 and the fuel recycle ratio is

0.7. With this system the energy efficiency attained is 78.3%

and the exergy efficiency is 75.5%.

Efficiencies are obtained for all the fuels using the model

and input parameters are shown in Table 3.

The (system using) methane is clearly most efficient fol-

lowed by ammonia and ethanol. This trend is not followed bythe exergy efficiency. The exergy efficiency of methane is

highest but ammonia has a much lower exergy efficiency

compared to its energy efficiency and the exergy efficiency of

hydrogen is almost similar to that of ethanol even though the

energy efficiency of ethanol is around 6.5% more than that of

hydrogen.

The distribution of energy and exergy efficiencies can be

because of flows, the heat exchangers, the combustor or the

fuel cell itself. Another significant factor is the split between

the fuel cell and GT power as we expect that higher fraction

of power produced in the fuel cell would lead to higher effi-

ciency.

As shown in Table 4 the fuel cell produces most power in

the methane system and immediately points toward its high

energy and exergy efficiency. The low energy efficiency of

hydrogen is also clearer because of the relatively lower frac-

tion of power produced in the fuel cell. The energy efficiency

follows from the split in the GT and SOFC power but the

exergy efficiency of the various fuels do not follow this trend.

Losses in various subsystems can be quantified and a dis-

tribution is presented based on the following subsystems –

heat exchangers, combustor, fuel cell, GT, and compressor

(recirculation fans in addition to air and fuel compressors).

Each of these subsystems shows a different pattern in losses

for each fuel and based on the operating parameters the behavior can be understood better. It is noted here that losses

Fig. 4 Fuel utilization per pass of fuel cell alongwith exergy loss in fuel cell

for all fuels.

Fig. 5 Nernst voltage (V) based on compositions at the end of the cell andactual cell voltage.

Fig. 6 IV characteristics for fuel utilization of 76.5% for H2 and methane with no recirculation.

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such as nodes are not included in the distribution depicted in

Figure 3.

Methane has high system efficiency with higher losses in

stack, GT combustor and fuel cell than compressor or heat

exchangers. The higher loss in the fuel cell can be attributedto the high fraction of power that is produced by the fuel cell.

Ammonia, methanol, and ethanol all have high fuel cell losses

inspite of the internal reforming reactions to remove heat

from the cell. Hydrogen is the most efficient exergetically as

far as the fuel cell itself is concerned with methanol being the

least efficient. The auxiliary power consumption (compres-

sors) is also very indicative of the reasons for the losses. The

auxiliary power consumption of hydrogen is highest fol-

lowed by methanol, ethanol, ammonia and the lowest is for

methane. This is because of larger airflows and compressors

required for both ammonia and hydrogen which mostly also

is followed by large fraction of GT power. A high GT power

fraction means that the combustor as well as the compressor

has higher flows leading to higher losses. The hydrogen sys-

tem has the highest losses in GT, compressor, and combustor.

From the distribution it seems likely that the internal

reforming reaction of ammonia, ethanol, and methanol influ-

ences the distribution of the losses especially the high losses

in the fuel cell. The above picture presents questions about

the source of these losses and corresponding influence on the

system performance.

Calculation of the flows in the system is based on the

power and temperatures and hence heat effects play an

important part in determining the flow through each of the

components. In addition to the normal heat exchangers thereis an additional source of heat in the fuel cell as well as a sink.

The fuel cell produces heat with fuel oxidation, while the

reforming reactions consume heat. Based on this balance the

flows in the system are set. The recycle adds some more com-

plexity as the flows are adjusted for maintaining temperature

at the fuel cell inlet which in turn sets the per pass utilization

in the fuel cell.

For each mole of H2 in an ideal fuel cell if we neglect all

other irreversibilities, there is around 65 kJ mol–1 of heat pro-

duced (using simply the difference between change in

enthalpy and Gibbs free energy) at around 1,223 K. For an

operating cell this will of course be higher with other irrever-

sibilities like Ohmic, activation, etc. Now, if we consider sim-

ple steam reforming reactions for each fuel then we may be

able to look at the losses qualitatively from the point of view

of heat utilization. For methanol and ammonia decomposi-

tion is considered. Reaction enthalpies are calculated for each

fuel at 1,223 K according to stoichiometric quantities, as

shown in Table 5.

Methane requires 227.2 kJ mol–1 of heat for reforming

while producing 3 moles of H2 at 1,223 K. Thus, per mole of

hydrogen the amount of heat required is large and if we con-

sider other irreversibilities in the cell the heat can for a large

part be easily taken away from the cell by the reforming reac-

tion of methane. The air to fuel ratio is least for the fuel cellwith methane fuel is the least showing very good heat use

within the cell. Ethanol however produces 4 moles H2 requir-

ing 308.2 kJ mol–1 heat. However, the air to fuel ratio is much

higher than methane. In case of Ammonia the reaction

requires 55.8 kJ mol–1 producing 1.5 moles of H2. This still

serves to remove heat, but is very low compared to the otherfuels corresponding air factor and GT powers are higher

when compared to other fuels. The nitrogen is not further

used in the WGS reaction which provides for another heat

sink within the cell as compared to the other fuels where the

WGS would tend to increase the heat release. Thus, the heats

from electrochemical and reforming reactions would tend to

be even more imbalanced. The nitrogen which is produced

does act as a diluent but serves to remove heat from the cell

as well. Methanol has an intermediate heat requirement

which is clear from its low heat requirement for reforming.

Now the picture is much clearer as to the reasons for exergy

losses in the system. There is a lot of excess heat in case of

ammonia ethanol and methanol which leads to much higher

cathode air flows and thus higher exergy losses. The WGS

reaction also plays a part in determining the heat released as

it is exothermic and will decrease the heat sink that is pro-

vided by the reforming reactions. In Cycle Tempo, as men-

tioned in Section 3, equilibrium compositions are calculated

based on reforming as well as WGS reactions. For the sake of

the discussion in the next two paragraphs only, we neglect

the WGS reaction which is not entirely accurate, but as can be

seen the comparison remains more or less similar qualita-

tively. We would like to point out again that in the calcula-

tions done by Cycle Tempo, the WGS reaction included for

heat as well as mass balances.If we now consider the recycle ratios for each of the fuels

then we can also explain why there is a distribution of recycle

ratios for fuel and air. This will indicate the amount of heat

which is recycled compared to fresh air/fuel which is taken

in. The recycle ratio is set by the inlet temperature which is

prescribed and heat recovery which is achieved from the GT

exit.

Methane and ammonia have low air recycle ratios while

methanol and ethanol have higher recycle ratios thus requir-

ing more recycle to maintain the cathode inlet temperature.

Less recycle is required to maintain the anode inlet tempera-

ture with methanol than with methane or ethanol while for

hydrogen, the recycle is very high. This distribution of recycle

ratios for various fuels brings to the front another parameter,

the per pass fuel utilization. Because of the different recycle

ratios the per-pass utilization in the fuel cell is different than

the overall utilization (which is fixed at 85%). This results in

different operating characteristics of each fuel cell and hence

different efficiencies.

In Figure 4 fuel utilization per pass is plotted for each fuel

alongwith the exergy loss in the fuel cell.

The per-pass utilization of hydrogen is the lowest and is

highest for methanol which is in agreement with the anode

recycle. From Figure 4 we can deduce that high per-pass utili-

zations is accompanied by higher exergy losses in the fuel celland hence a lower fuel cell efficiency even though the system

ORIGINALRESEARCH

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efficiency can go up if a higher fraction of power is derived

from the fuel cell. If the fuel utilization is increased the volt-

age will drop significantly toward the exit of the fuel cell

(where there is less fuel) and the local Nernst voltage drops.

Thus, for higher per pass utilizations the fuel cell itself is less

efficient.

Thus, we see that the utlization set by the recycle is a very

important factor governing the efficiency of the fuel cell. This

sets the operating efficiency of the fuel cell. Since the heat

recovery after the GT is set by the temperature which in turn

depends on the flows set by the fuel cell, the basic chemistry

of the fuel, i.e., the heats of formation, reforming as well as

the composition of the fuel plays an important part in deter-

mining the overall system as well as component efficiency.

The Nernst voltages are calculated for each fuel and

plotted in Figure 5. The Nernst voltages are based on compo-

sitions at the exit of the fuel cell considering only hydrogen

using Eq. (2).

The Nernst voltage at the outlet is highest for methane fol-

lowed by ethanol, hydrogen, ammonia, and lowest for metha-nol. The actual operating voltage is also highest for methane

and is lowest for hydrogen. While the low efficiency obtained

with methanol can be partly attributed to the low Nernst volt-

age the same is not the case with methane and hydrogen. In

the case of hydrogen inspite of the low per pass utilization

the high hydrogen fraction is offset by the fraction of waterlowering the Nernst voltage. Somewhat counter-intuitively

even though the system efficiency is the highest with

methane, it is not the most efficient fuel as far as only the fuel

cell is concerned in the configuration currently employed.

The parameter of per pass fuel utilization is responsible for

this seeming anomaly as a higher per pass utilization would

lead to higher drop of voltage across the cell and hence higher

loss. This high fuel utilization shows a more extended region

of operation for methane than hydrogen.

In order to verify this particularly in the case of hydrogen

and methane the fuel cells alone are operated under the same

fuel utilization without recycle and the IV curves are plotted

for a set utilization of 76.5%.

From Figure 6, it is clear that the methane system is much

more efficient than the hydrogen fuel cell for the same per

pass fuel utilization. The effect of per pass higher fuel utiliza-

tion is highlighted if we calculate the inlet and exit voltages

for hydrogen and methane.

Figure 7 shows the inlet and exit Nernst voltages for

hydrogen and methane for 70 and 76.5% utilizations, respec-

tively. Clearly, the methane fuel cell has a much higher volt-

age drop across the cell. This indicates a lower operating

point in the efficiency and hence the fuel cell losses are also

higher for methane than hydrogen. The Nernst voltages at

the beginning and end have a large influence on efficiency of the fuel cell and a larger drop across the fuel cell indicates a

higher loss. The difference between the voltages at the begin-

ning and end are indicative of a wider operating window of

local current densities. Thus inspite of having a large heat

sink in the reforming reaction, methane as fuel has slightly

lower fuel cell efficiency as compared to hydrogen because of

higher drop in Nernst voltage caused by the higher fuel utli-

zation.

5 Discussion

In previous studies, the combustor and SOFC have been

found to be major contributors to the exergy losses [12, 27, 28,

30, 31]. For the combustor, these have been attributed mainly

to the irreversible nature of combustion reactions in the com-

bustor. This is true in this work as well with the combustor

losses being in general high for almost all fuels. Granovskii et

al. [12] found that the maximum thermodynamic efficiency of

the system can reach as high as 70–80% for methane conver-

sion, similar to the efficiency obtained here. The reasons for

the high losses in the combustor and SOFC are not discussed

in detail, but are said to be related to methane oxidation in

the SOFC. Motahar and Alemrajabi [27] also found the com-

bustor and SOFC to be the dominant contributors to the

losses. SOFC losses were attributed to most of the reactionsoccurring in the SOFC and associated irreversibilities with

Fig. 7 Nernst voltage at begin and end of cell for methane and H2 for sys-

tem under consideration (see Figure 5).

Fig. 8 Fuel and air recycle ratios of the fuel cell for all fuels.

ORI GI N






the reactions. Haseli et al. [30, 31] pointed out that the high

temperatures in the combustor and SOFC could be a possible

cause for the high exergy destruction in these apparatuses.

The highest temperatures occurred in the combustor followed

by the SOFC in their work. While previous work was instru-

mental in pointing out that the SOFC is among the major con-

tributors to the exergy losses of the system, the reason for the

high loss in the SOFC is not very clear. It is attempted in this

study to understand the reasons for the exergy losses occur-

ring in various components and gain a deeper insight into

operating characteristics of different fuels. In this study a step

further is taken to attempt to analyze the distribution of the

exergy losses across various fuels. Also the effect of recycling

the anode and cathode flows is studied with respect to its

effect on the overall system performance. When comparing

between two or more fuels it is important to identify various

components which dictate the overall efficiency of the system

and define the system behavior for a set of fixed parameters.

If sufficient information is obtained about the losses in indi-

vidual components it will help in optimizing the overall sys-

tem and eventually tailor the system based on the fuel. Such acomparison across fuels for this particular set of conditions is

missing in literature as far as the authors know. It is found

here that heat effects are important in setting up the flow con-

figuration and hence determining the cathode and anode air-

flows which determine the component as well as system effi-

ciency. Heat effects have also been discussed by Liu et al. [39]

in an experimental study of methanol, hydrogen and ammo-

nia in an SOFC, where a drop in the cell temperature because

of the internal reforming/decomposition reactions is sug-

gested to cause an increase in the resistance. This is signifi-

cant as it points to the heat effects being a contributor to the

overall response of the cell. At system level like in this study

it becomes important how well the heat is utilized in the sys-

tem for each fuel and the losses arising out of the same. If we

consider only reforming reactions for all the fuels considered

in this study then we can form a clear trend as to the heat bal-

ance between the electrochemical, reforming, and WGS reac-

tions. The reforming and WGS reactions influence the excess

air required which has a large influence on the split between

GT and fuel cell power. The recycle ratios determine the perpass utilization which has an effect on the efficiency of the

Fig. 9 Exergy flow diagram methane.

Fig. 10 Exergy flow diagram hydrogen.

ORIGINALRESEARCH

PAPER





fuel cell. Based on exergy flow diagrams we can try and ana-

lyze the results obtained and provide a basis for comparison.

Methane reforming (Exergy flow diagram Figure 9) is

highly endothermic and provides an excellent heat sink for

electrochemical as well as WGS reactions. The low air to fuel

ratio with methane makes the fuel cell power high compared

to the GT and correspondingly parasitic losses are small.

Moreover, GT power is small while the fuel cell produces

most of the power and so system efficiency is high. The

exergy loss in the fuel cell is higher because of the higher per

pass utlization.

The Nernst voltage for hydrogen as fuel (Exergy flow dia-

gram Figure 10) is low at the end of the cell (Figure 5). With

pure hydrogen we would expect an even higher Nernst volt-

age at the beginning of the cell but the high hydrogen mole

fraction is offset by the high water mole fraction because of

the high recycle (Figure 8) lowering the Nernst potential.

Thus, the voltage drop across the cell is low leading to higher

fuel cell efficiency. For hydrogen there is no reforming and so

all the heat has to be carried away by the incoming flows.This results in high cathodic flows and correspondingly high

parasitic losses. The high fuel recycle causes low fuel utiliza-

tion per pass and hence a higher fuel cell efficiency is

achieved. But the main detriment in system efficiency in this

case is the excess air required for cooling the cell which

causes higher power through the GT. Consequently losses in

combustor are high because of large amount of excess air.

This results in lower efficiency on the system level although

fuel cell losses are small because of the low utilization. The

fraction of GT power is highest in hydrogen with the per pass

utilization being the lowest.

Chan et al. [25] also found that the methane fed system

was more efficient than the hydrogen fed one. It was pointed

out that the heat transfer loss to the environment was lower

with methane because of the demand of vaporizer and refor-

mer. Even though this is not directly comparable as the sys-

tem is an SOFC system not an SOFC-GT system, better heat

utilization in the system similar to the internal reforming in

this study, results in higher system efficiency.

Ammonia (Exergy flow diagram Figure 11) presents an

interesting choice for the fuel. The system efficiency forammonia as fuel is high and comparable to the other fuels.

Fig. 11 Exergy flow diagram ammonia. Fig. 12 Exergy flow diagram ethanol.

ORI GI N






The nitrogen formed on one hand dilutes the anode stream

but on the other hand can serve to remove heat from the cell

as opposed to the exothermic WGS reactions in case of other

fuels. The heat sink in ammonia reforming is not high; the

resulting high cathodic airflow makes the fraction of GT

power higher resulting in lower system exergy efficiency than

methane. Ishak et al. [44] have also found high exergy losses

in the fuel cell working on ammonia and have attributed the

losses to the irreversibilities of the electrochemical process

and also to the large thermal gradient between the fuel celland surroundings. While similar high losses have been found

in the fuel cell, the heat effects which set up the flows in the

system are found to be responsible for the exergy losses in

this study.

Ethanol (Exergy flow diagram Figure 12) is similar to

ammonia in efficiency with slightly higher exergy and energyefficiency. High Nernst voltage gives higher fuel cell effi-

ciency in addition to the endothermic internal reforming reac-

tion which serves to remove heat from the system. The sys-

tem efficiency for ethanol is lower than methane mainly

because of the lower per pass utlization as compared to

methane and so higher power is processed by the relatively

less efficient GT.

Douvartzides [32] have also found methane to be more

efficient than ethanol in their studies of the SOFC system

alone. This was attributed to methane’s exergy content

expressed as a ratio of hydrogen to carbon being higher than

that of ethanol. They reported the after burner to be the major

contributor to the losses barring the stack (exhaust) which

was attributed to the irreversible combustion process. As far

as the fuel cell itself is concerned, this is similar to our find-

ings here that the fuel cell is more efficient in case of methane

than in case of ethanol. Similarly Casas et al. [45] report high

SOFC losses which are attributed mainly to the high amount

of heat rejected by the chemical reaction.

Methanol (Exergy flow diagram Figure 13) is the least effi-

cient among the fuels considered in this particular study. The

heat of reforming is not that large, but it can provide some

heat recovery within the cell. The per pass fuel utilization is

the highest among all the fuels which results in low Nernst

voltage and low fuel cell efficiency. Correspondingly, the fuelrecycle is lowest among all the fuels. With the high utilization

in the cell should produce more power, but the low efficiency

means the power produced in the fuel cell is comparable to

that of ammonia but still higher than hydrogen, with high

parasitic losses.

From the above discussion it seems that methane is ideally

suited for a high temperature SOFC-GT system followed by

ethanol and ammonia. Even though methanol is more readily

reformed than most fuels it is less efficient than any of the

other fuels in this study but this is a reflection on the partic-

ular operating conditions than the applicability of the fuel

itself. As pointed out by Liu et al. [39] that compared to

ammonia and hydrogen, methanol was found to be a much

better performing fuel in the conditions that were used in

their study. Ammonia especially when sourced from waste

promises to be an exciting alternative, with decomposition to

produce hydrogen, without the need of an external reformer.

The high efficiency reached for all the fuels is indicative of

the potential of such combined systems to provide a sustain-

able and viable alternative.

5 Conclusion

With the system configuration considered in this study wecan conclude that methane is the most efficient fuel with

Fig. 13 Exergy flow diagram methanol.

Table 5 Heat of reaction for reforming with and without WGS reaction.

Fuel DHr (kJ mol–1) With WGS

(kJ mol–1)

DHr per mol H2

without WGS

(kJ mol–1)

Methane 227.2 194.4 75.7

Methanol 124.2 91.4 62.1Ethanol 308.2 242.6 77.0

Ammonia 55.8 55.8 37.2

ORIGINALRESEARCH

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respect to both energy and exergy efficiency (78 and 75.5%).

The energy as well as exergy efficiency of ethanol is slightly

higher than ammonia (76.48 and 70.8 vs. 74.7 and 70%).

Hydrogen has lower energy and exergy efficiency (70 and

69%) but is still similar to that of ethanol or ammonia forexergy but the energy efficiency is much lower than both

these fuels. Methanol is more efficient than hydrogen energe-

tically (73.5%) though the exergy efficiency is lowest (68.5%)

among all the fuels in this study.

The causes of exergy losses for various fuels are quite dif-

ferent. The high fuel cell losses are not entirely because of low

Nernst potentials. Using global reactions for reforming we

can conclude that the imbalance between heats from electro-

chemical and reforming reactions influences in a large way

the flows and hence the split between fuel cell and GT power.

The recycle ratios which are set by the inlet temperatures and

heat recovery, in turn determine the per pass utilization

across the fuel cell. The high per pass utilization of methane

makes the voltage drop across methane higher and hence the

fuel cell less efficient than hydrogen which has low per pass

utilization and high fuel cell efficiency although system effi-

ciency is lower. Ethanol is highly efficient and is similar to

ammonia in terms of both energy and exergy efficiency. High

per pass utilization also causes lower exergy efficiency of the

fuel cell itself though higher power is processed in the fuel

cell hence the system efficiency is higher. Methanol is least

efficient among the fuels considered here. Methanol has the

highest per pass utilization resulting in lower fuelcell efficiency.

In addition to this theexitNernst voltageis verylow and the fuel

cellbecomes a veryhigh contributorto theexergylosses.An important conclusion to draw from this is that at sys-

tem level, the efficiency of the fuel cell alone does not dictate

overall efficiency but it is dependent on other effects mostly

attributable to the nature of the fuel. The heat effects play a

major part in deciding flow distribution and setting of flows

for all equipment. Based on the per pass utilization that can

be achieved in the cell the efficiency of the fuel cell changes

but the overall efficiency does not always follow the fuel cell

efficiency. So, counter intuitively we find that hydrogen is

more efficient as far as the fuel cell alone is concerned though

the system efficiency of methane is higher for this particular

configuration. This is important for design at system level

where we need to accommodate each fuel uniquely.

It is seen from this study that heat effects play a major role

in determining the overall system efficiency. It can happen

that at different SOFC parameters like temperature, a com-

pletely different set of results is obtained for different fuels.

Thus, in order to truly tailor a system for any fuel, further

optimization with temperature as a parameter is required. In

addition to this, the fuel utilization is also another parameter

which needs to be optimized uniquely for each fuel. This is

ongoing work here at Delft and is being studied.

From this we also conclude that there is a need for differ-

ent system configuration for different fuels in order to accom-

modate each fuel as efficiently as possible. Also a clearerunderstanding of the thermodynamics of the fuel cell system

with respect to setting of the flows especially with recycle is

required for further refining this work and is considered

future work. In order to optimize the system for each fuel

uniquely, the dependence of system efficiency on individual

component (especially the SOFC) parameters must be studiedin more detail.

List of Symbols

Um,a,in Flow to the anode (kg s–1)

I Current (A)

V Voltage (V)

U f Fuel utilization

yi Mole fraction

Pe Power (W)

i current density (Am–2)

V rev,x Local Nernst voltage (V)V 0rev Standard reversible voltage (V)

R Universal gas constant (J mol–1 K–1)

T Temperature (K)

F Faradays constant (C mol–1)

Req Equivalent cell resistance (Xm2)

V x Loss in voltage (V)

A Area (m2)

k Reaction ordinate

h Specific enthalpy (J kg-1)

RExproducts Exergy of products (W)

RExsource Exergy at source (W)

gx Exergy efficiency

gx,el Electrical exergy efficiency

RPel,in Input electrical power (W)

Exfuel,in Exergy of the fuel input (W)

RPel,out Electrical output of the system (W)

WGS Water gas shift

References

[1] J. Larminie, A. Dicks, Fuel Cell Systems Explained, 2nd

Ed., John Wiley & Sons Ltd., West Sussex, United King-

dom, 2003, ISBN 0-470-84857-X.

[2] P. Aravind, Phd Thesis, Technical University of Delft,

2007, ISBN-13: 978-90-9022534-0.

[3] M. Cimenti, J. M. Hill, J. Power Sources 2009, 186, 377.

[4] N. Woudstra, T. P. van der Stelt, K. Hemmes, J. Fuel Cell

Sci. Technol. 2006, 3, 155.

[5] P. V. Aravind, T. Woudstra, N. Woudstra, H. Spliethoff,

J. Power Sources 2009, 190, 461.

[6] C. Zamfirescu, I. Dincer, J. Power Sources 2008, 185, 459.

[7] A. Fuerte, R. X. Valenzuela, M. J. Escudero, L. Daza,


[8] D. Cocco, V. Tola, Energy Convers. Manage. 2009, 50,

1040.

[9] M. Santin, A. Traverso, L. Magistri, A. Massardo, Energy

2010, 35, 1077.

ORI GI N






[10] A. V. Akkaya, B. Sahin, H. H. Erdem, Int. J. Hydrogen

Energy 2008, 33, 2566.

[11] K. J. Bosch, N. Woudstra, K. V. van der Nat, Proceedings

of the 4th International Conference on Fuel Cell Science, En-

gineering, and Technology, Irvine, CA, USA, Pts A and B2006, pp. 557–564, 1220.

[12] M. Granovskii, I. Dincer, M. A. Rosen, J. Fuel Cell Sci.

Technol. 2008, 5, 0310051.

[13] P. Varbanov, J. Klemes, Energy 2008, 33, 1508.

[14] W. J. Yang, S. K. Park, T. S. Kim, J. H. Kim, J. L. Sohn, S.

T. Ro, J. Power Sources 2006, 160, 462.

[15] Y. Zhao, N. Shah, N. Brandon, Int. J. Hydrogen Energy

2011, 36, 10235.

[16] Y. Zhao, J. Sadhukhan, A. Lanzinid, N. Brandon,

N. Shah, J. Power Sources 2011, 196, 9516.

[17] M. Scupita, S. Kimijima, T. W. Song, K. Suzuki, J. Fuel

Cell Sci. Technol. 2008, 5, 041006.

[18] T. W. Song, et al., J. Power Sources 2005, 142, 30.

[19] S. K. Park, K. S. Oh, T. S. Kim, J. Power Sources 2007, 170,

130.

[20] F. Leucht, W. G. Bessler, J. Kallo, A. K. Friedrich,

H. Muller-Steinhagena, J. Power Sources 2011, 196, 1205.

[21] P. Kuchonthara, S. Bhattacharya, A. Tsutsumi, J. Power

Sources 2003, 117, 7.

[22] Y. Yi, A. Rao, J. Brouwer, S. G. Samuelsen, J. Power

Sources 2004, 132, 77.

[23] A. Selimovic, J. Palsson, J. Power Sources 2002, 106, 76.

[24] S. H. Chan, H. K. Ho, Y. Tian, Int. J. Hydrogen Energy

2003, 28, 889.

[25] S. H. Chan, C. F. Low, O. L. Ding, J. Power Sources 2002,103, 188.

[26] F. Calise, M. A. Dentice d’Accadia, A. Palombo, L. Va-

noli, Energy 2006, 31, 3278.

[27] S. Motahar, A. Alemrajabi, Int. J. Hydrogen Energy 2009,

34, 2396.

[28] P. G. Bavarsad, Int. J. Hydrogen Energy 2007, 32, 4591.

[29] P. V. Aravind, C. Schilt, B. Türker, T. Woudstra, J. Re-

new. Energy Dev. 2012, 1, 51.[30] Y. Haseli, I. Dincer, G. F. Naterer, Thermochim. Acta

2008, 480, 1.

[31] Y. Haseli, I. Dincer, G. F. Naterer, Int. J. Hydrogen Energy

2008, 33, 5811.

[32] S. Douvartzides, F. Coutelieris, P. Tsiakaras, J. Power

Sources 2004, 131, 224.

[33] S. H. Chan, S. K. Ho, Y. Tian, J. Power Sources 2002, 109,

111.

[34] T. H. Lim, et al., Int. J. Hydrogen Energy 2008, 33, 1076.

[35] R. Barrera, S. De Biase, S. Ginocchio, S. Bedogni,

L. Montelatici, Int. J. Hydrogen Energy 2008, 33, 3193.

[36] R. Toonsen, et al., Int. J. Hydrogen Energy 2011, 36,

10414.

[37] R. Toonsen, et al. Fuel Cells 2010, 10, 643.

[38] T. Suther, A. S. Fung, M. Koksal, F. Zabihian, Int. J. En-

ergy Res. 2011, 35, 616.

[39] M. Liu, R. Peng, D. Dong, X. Gao, X. Liu, G. Meng,


[40] S. Ma, J. Wang, Z. Yan, Y. Dai, B. Lu, J. Power Sources

2011, 196, 8463.

[41] A. Wojcik, H. Middleton, I. Damopoulos, J. Van herle,


[42] http://www.asimptote.com/software/cycletempo ac-

cessed on 11 July 2012.

[43] http://www.fluidprop.com/ accesed on 11 July 2012.[44] F. Ishak, I. Dincer, C. Zamfirescu, J. Power Sources 2012,

212, 73.

[45] Y. Casas, L. E. Arteaga, M. Morales, E. Rosa, L. M. Per-

alta, J. Dewulf, Chem. Eng. J. 2010, 162, 1057.

______________________

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