Comparative analysis between a PEM fuel cell and an internal combustion engine driving an electricity generator: Technical, economical and ecological aspects Lúcia Bollini Braga * ,1 , Jose Luz Silveira 1 , Marcio Evaristo da Silva 1 , Einara Blanco Machin 1 , Daniel Travieso Pedroso 1 , Celso Eduardo Tuna 1 Sao Paulo State University (UNESP), Guaratinguetá 12516-410, SP, Brazil highlights The exergetic efficiency of ICE-G was 22% and for the fuel cell was 40%. The PEM fuel cell at long-term become economically competitive compared to ICE-G. The ecological efficiency of PEM fuel cell was 96% and Diesel ICE-G was 51%. article info Article history: Received 25 June 2013 Accepted 28 October 2013 Available online 7 November 2013 Keywords: Economic analysis Ecological analysis Technical analysis Internal combustion engine Proton exchange membrane fuel cell abstract In the recent years the fuel cells have received much attention. Among various technologies, the Proton Exchange Membrane Fuel Cell (PEMFC) is currently the most appropriate and is used in several vehicles prototype. A comparative technical, economical and ecological analysis between an Internal Combustion Engine fueled with Diesel driving an electricity Generator (ICE-G) and a PEMFC fed by hydrogen pro- duced by ethanol steam reforming was performed. The technical analysis showed the advantages of the PEMFC in comparison to the ICE-G based in energetic and exergetic aspects. The economic analysis shows that fuel cells are not economic competitive when compared to internal combustion engine driving an electricity generator with the same generation capacity; it will only be economically feasible in a long term; due to the large investments required. The environmental analysis was based on concepts of CO 2 equivalent, pollution indicator and ecological efficiency. Different to the ICE-G system, the Fuel Cell does not emit pollutants directly and the emission related to this technology is linked mainly with hydrogen production. The ecological efficiency of PEMFC was 96% considering the carbon dioxide cycle, for ICE-G system this parameter reach 51%. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The criteria that influence the evolution of the world’s energy sector in the present century are complex. Typical objectives are safety in supply and exploitation of resources, competitiveness of companies and the necessity to preserve the environment (locally and globally) through the use of new technologies and the sus- tainable use of existing resources [1,2]. In the energy field, the main worldwide preoccupation is focused on environmental problems. Recently, the pollutant in- dicators reduction of toxic substances in the environment, pro- duced by the industrial and the automotive transportation sectors, is one of the most important targets that are being taken into ac- count in the majority of the industrialized countries. Both sectors must adopt future strategies for the reduction of pollutant emission into the atmosphere, with the purpose of reducing the hazardous concentrations in the air [3,4]. One factor that influences the feasibility analysis to apply technologies that use alternative fuels is the environmental impact that such technology could cause. Many researchers have devoted themselves to decrease the emission of pollutant materials by these * Corresponding author. Energy Department, Av. Dr. Ariberto Pereira da Cunha, 333, Pedregulho, Guaratinguetá 12516-410, São Paulo, Brazil. Tel.: þ55 12 31232239; fax: þ55 12 31232835. E-mail addresses: [email protected], [email protected](L.B. Braga), [email protected](J.L. Silveira), [email protected](M. Evaristo da Silva), [email protected](E.B. Machin), [email protected](D.T. Pedroso), [email protected](C.E. Tuna). 1 Energy Systems Optimization Group (www.feg.unesp.br/gose). Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng 1359-4311/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.applthermaleng.2013.10.053 Applied Thermal Engineering 63 (2014) 354e361
Comparative analysis between a PEM fuel cell and an internalcombustion engine driving an electricity generator: Technical,economical and ecological aspects
Sao Paulo State University (UNESP), Guaratinguetá 12516-410, SP, Brazil
h i g h l i g h t s
� The exergetic efficiency of ICE-G was 22% and for the fuel cell was 40%.� The PEM fuel cell at long-term become economically competitive compared to ICE-G.� The ecological efficiency of PEM fuel cell was 96% and Diesel ICE-G was 51%.
a r t i c l e i n f o
Article history:Received 25 June 2013Accepted 28 October 2013Available online 7 November 2013
1359-4311/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.applthermaleng.2013.10.05
a b s t r a c t
In the recent years the fuel cells have received much attention. Among various technologies, the ProtonExchange Membrane Fuel Cell (PEMFC) is currently the most appropriate and is used in several vehiclesprototype. A comparative technical, economical and ecological analysis between an Internal CombustionEngine fueled with Diesel driving an electricity Generator (ICE-G) and a PEMFC fed by hydrogen pro-duced by ethanol steam reforming was performed. The technical analysis showed the advantages of thePEMFC in comparison to the ICE-G based in energetic and exergetic aspects. The economic analysisshows that fuel cells are not economic competitive when compared to internal combustion enginedriving an electricity generator with the same generation capacity; it will only be economically feasiblein a long term; due to the large investments required. The environmental analysis was based on conceptsof CO2 equivalent, pollution indicator and ecological efficiency. Different to the ICE-G system, the FuelCell does not emit pollutants directly and the emission related to this technology is linked mainly withhydrogen production. The ecological efficiency of PEMFC was 96% considering the carbon dioxide cycle,for ICE-G system this parameter reach 51%.
� 2013 Elsevier Ltd. All rights reserved.
1. Introduction
The criteria that influence the evolution of the world’s energysector in the present century are complex. Typical objectives aresafety in supply and exploitation of resources, competitiveness ofcompanies and the necessity to preserve the environment (locally
r. Ariberto Pereira da Cunha,Paulo, Brazil. Tel.: þ55 12
[email protected] (L.B. Braga),esp.br (M. Evaristo da Silva),feg.unesp.br (D.T. Pedroso),
esp.br/gose).
All rights reserved.3
and globally) through the use of new technologies and the sus-tainable use of existing resources [1,2].
In the energy field, the main worldwide preoccupation isfocused on environmental problems. Recently, the pollutant in-dicators reduction of toxic substances in the environment, pro-duced by the industrial and the automotive transportation sectors,is one of the most important targets that are being taken into ac-count in the majority of the industrialized countries. Both sectorsmust adopt future strategies for the reduction of pollutant emissioninto the atmosphere, with the purpose of reducing the hazardousconcentrations in the air [3,4].
One factor that influences the feasibility analysis to applytechnologies that use alternative fuels is the environmental impactthat such technology could cause. Many researchers have devotedthemselves to decrease the emission of pollutant materials by these
technologies, trying to reverse the current environmental situation.The control of emission substances, such as: particulate matter(PM), CO2, SO2, and NOx represents a major concern all over theworld [5,6].
Brazil has developed many sustainable energy programs in or-der to reduce carbonic gas emission. Those programs use technol-ogies that not only are respectful to the environment but alsotechno-economically competitive; for instance: hydrogen produc-tion, biodiesel production, ethanol production, and producer gasgeneration from biomass gasification, especially micro-scale sys-tem gasifiers, associated to an internal combustion engine. Some ofthese fuels could be used directly in conventional combustionsystems; however, others need some kind of conditioning toreplace the conventional fuels [6].
Among several technologies nowadays, Fuel Cell (FC) appears asa promising alternative for electricity generation, principally insubstitution of the Internal Combustion Engine fueled with Dieseldriving an electricity Generator (ICE-G) [7,8]. The FC is a very effi-cient system that converts the chemical energy from a fuel intoelectricity through a chemical reaction rather than combustion. Asresidual of the process water, electricity, and heat are generatedthrough the combination of hydrogen and oxygen in the FC [7].
There are some researches considering several aspects of thefuel cells and internal combustion engines behavior. Barelli et al.[8], developed a study in combined heat power systems based on a(PEMFC), Rakopoulos et al. [9] performed research about energyand exergy analysis of an ICE and Zamel et al. [10] published a full
analysis of the impact of the difference between the Canadian andAmerican energy realities on the lifecycle of fuel cell vehicles andinternal combustion engine vehicles. The PEMFC could substitutethe ICE in several kinds of situations, such as: in the transportsector, in the stationary or distributed generation, among others;however there are not papers published in the literature with acomprehensive comparison of technical, economical and ecologicalaspects between both systems, to help decision makers choosewhich is in fact, the best device for a specific application.
On this background, the goal of this paper is to perform thecomparative analysis between the PEMFC and the ICE-G based onthe technical, economical and ecological aspects. Firstly, it wasperformed the technical analysis, based on the exergetic efficiency,in order to have the true efficiency of both systems. Afterward, aneconomical analysis was realized in order to have the economicfeasibility of the implementation of both systems; finally was per-formed an ecological analysis based on concepts of equivalentcarbon dioxide, pollutant indicator, and ecological efficiency.
2. Methodology
2.1. Systems description
In the present work, it was analyzed an ICE-G and a PEMFC, bothsystems with a generation capacity of 5 kW of electricity; the heatproduced by both systems was despised.
Figs. 1 and 2 shown a representation of the physical configura-tion of the ICE-G and the PEMFC systems respectively, indicating allthe flows, as well as the operation parameters (temperature,pressure, etc.).
For the thermodynamic analysis of the ICE-G, the Eqs. (1) and (2)were applied as follows:
helc ¼ EpESfuel
(1)
ESfuel ¼ _mdiesel � LHVdiesel (2)
where:
Ep ¼ 5 kW
he ¼ 0.27 [11] (considering a thermal efficiency equal to 0.30 andthe electricity generator efficiency equal to 0.9)
LHVdiesel ¼ 42;490 kJ=kg ½7�Through these values, was determinate the mass flow rate
ð _mdieselÞ of Diesel equals to 0.000436 kg/s, and through Eq. (3)(stoichiometric equation of Diesel combustion), considering 100%of air excess (a), was possible to calculate the mass flow rate of inletair and the mass flow rate of exhaust gases.
In order to calculate the inlet and outlet streams of the PEMFC,the Equations (4)e(7), were considered according to Larminie andDick [12]:
_mair;reactant ¼ 3:57� 10�7�lWV
�(4)
_mH2;reactant ¼ 1:05� 10�8�WV
�(5)
_mair;product ¼ 3:57� 10�7�lWV
�� 8:29� 10�8
�WV
�(6)
_mH2;product ¼ 9:34� 108�WV
�(7)
Where:
W ¼ 5 kWV ¼ 0.5 V [13]l ¼ 3
Fig. 1. Internal Combustion Engine fueled with Diesel driving an electricity Generator(ICE-G).
The equations to calculate the mass flow rate of the productsand the reactants in the fuel cell (Eqs. (4)e(7)) dependent on thepower output (W), on the fuel cell voltage (V) and on the stoi-chiometric air coefficient (l). The mass flow of one product, the air,can be defined as the difference between the amount of oxygen thatenters into the PEMFC and the oxygen that is consumed by thereaction with hydrogen to produce water. The efficiency of the fuelcell can be greatly improved if l is increased; however is recom-mended that the l value ranges between 2 and 4, in order tomaintain the relative humidity level in the product air to avoiddrying of the fuel cell membrane at the high operating tempera-tures [13].
2.2. Exergetic balance
An important tool to evaluate the performance of the thermalsystem is the exergetic balance. This analytical procedure is verysimilar to the energy balance. The energy balance is based on theFirst Law of thermodynamics (energy conservation), whilst theexergetic balance is based on the Second Law of thermodynamics.The exergetic balance is performed considering that the energydegradation being equivalent to the energy loss, due to the fact thatreal processes are irreversible [14].
According to Nogueira et al. [15], the exergetic calculation ismainly determined by the thermodynamic balance, by the differ-ence between the concentration of chemical species, by chemicalpotential associated to the reactions and also by other factors withminimal contributions.
In this way, exergy can be defined as the maximum obtainablework from a given form of energy, using environmental parametersas the reference state. One of the main uses of this concept is in theexergy balance, which may be analyzed as a measure of the energydegradation. In the absence of magnetic, electrical and nuclear ef-fects, the exergy of a system, if the changes in kinetic and the po-tential exergies are neglected, is given by Eq. (8) [16].
ex ¼ exTM þ exCH (8)
where the first term represents the portion of exergy associated toheat transfer on the control surface. In this work, is important thatthe air and the gases are considered ideal gases; in that case thefirst term of Eq. (8) can be evaluated through Eq. (9), which con-siders constant Cp (specify heat at constant pressure) [16], andwhen they cannot be considered as ideal gases like the water vaporproduced by a PEMFC, the Eq. (10) is used [6].
exTM ¼ZTT0
Cp�1�
�T0T
��dT þ RT0ln
�PP0
�(9)
exTM ¼ ðh� hoÞ � Toðs� soÞ (10)
To calculate the second term of Eq. (8), that represents theportion of chemical exergy, is used the Eq. (11) [13], unless in thecase of Diesel fuel, where is used the Eqs. (12) and (13) [6].
Finally, the total exergy of the system is shown in Eq. (14) [16].
Ex ¼ _mðexTM þ exCHÞ (14)
The temperature and the pressure of the environment were setequal to the reference values, 25 �C and 1 atm respectively. Theatmosphere was modeled as an ideal-gas mixture with thecomposition shown in Table 1 [8].
The efficiencies (mechanical, thermal, etc.) are not traditionallybased on the Second Law of thermodynamics. Recent de-velopments of the exergetic analysis allow the definition of newperformance criteria, offering advantages over the traditional cri-terions. According to Kotas [17], the rational efficiency, shown in Eq.(15), is based on the following scheme:
I ¼ Exi � ExE � 0 1� ExEExi
� 0 j ¼ ExEExi
< 1 (15)
3. Economical analysis
This section economically compares the electricity cost pro-duced by the PEMFC and the ICE-G systems. The PEMFC in this workis fueled with hydrogen produced by the sugar cane ethanol steamreforming and the ICE is fueled with Diesel. For the calculation ofthe electricity cost (Ctel) generated by the PEMFC system, thefollowing considerations were used: the cost of hydrogen produc-tion by the ethanol steam reforming was considered 0.09 US$/kWh[18]. The investment cost in a PEMFC will probably decrease insome years. With the technological evolution and the increase ofproduction units, the cost of a PEMFC ranges between 1000 US$/kW and 5000 US$/kW [19]; according to that in this paper threedifferent values of investment ({FC) were considered for this tech-nology, which are: 1000 US$/kW, 2500 US$/kW and 5000 US$/kW.
Other parameters that were considered for the calculus in thePEMFC system are: W ¼ 5 kW (electric power); LHV(hydrogen) ¼ 119,742.48 kJ/kg [7]; Hp ¼ 6570 h/year (18 h/day,during 1 year).
For the calculation of the electricity cost (Ctel) using the ICE-Gsystem, the following considerations were used: the cost of Dieselwas 0.06 US$/kWh [20]; the investment cost in an ICE-G ({ice) wasconsidered 500 US$/kW [20e22]. Other parameters that wereconsidered for ICE-G system are: W ¼ 5 kW (electric power); LHV(Diesel) ¼ 42,490 kJ/kg [7] and Hp ¼ 6570 h/year.
The Equations (16) and (20) [23] were used for the calculation ofthe cost of the electricity generated in both systems.
Table 1Mole Fractions and chemical exergy (kJ/kmol) of reference components in the at-mospheric air [8].
Component Mole Fraction, xn Chemical exergy, e�CHn (kJ/kmol)
N2 0.79 720O2 0.21 3.970
_m ¼ Wh� LHV
� 100 (16)
q ¼ 1þ r100
(17)
f ¼ qkðq� 1Þqk � 1
(18)
The global equation for the electricity cost was considered as Eq.(19) [23].
Ctel ¼�isystem � f
Hp
�þ�Ctfuel � LHV� _m
W
�þ Ctmain (19)
where the maintenance cost (Ctmain) was considered as 3% of in-vestment cost and is shown in Eq. (20).
Ctmain ¼ 0:03��isystem � f
Hp
�(20)
4. Ecological analysis
In order to make possible to compare the ecological efficiencybetween an ICE-G and a PEMFC, was necessary to calculate theecological efficiency of hydrogen production that feeds the fuel cell,due to the only products of a PEMFC are steam and electricity. ThePEMFC cannot be considered a pollutant system, but the hydrogenthat feeds it is not found already isolated in nature, so it must beproduced and consequently it consumes energy and emits pollut-ants. In this paper, the hydrogen that feeds the PEMFC was pro-duced by an ethanol steam reforming, and the energy consumedduring the hydrogen production was obtained from sugar canebagasse. In the case of the ICE-G, was necessary to take into accountthe emissions to produce the Diesel fuel in the refinery (Diesel frompetroleum). Moreover, was necessary to consider the emissionwhen consumed by ICE-G (combustion process). The emissions inthe combustion process of Diesel in an internal combustion engineare based on the value reported by Taylor [24].
4.1. The equivalent carbon dioxide and pollutant indicator
The equivalent carbon dioxide (CO2)e is composed by a hypo-thetical pollutant concentration factor that can be determined bythe Equation (21). For the calculation of this coefficient, themaximum value for the CO2 concentration is divided by the cor-responding air quality standard for NOx, SO2 and PM in 1 h [6].
ðCO2Þe ¼ CO2 þ 80 SO2 þ 50 NOx þ 67PM (21)
The best fuel from the ecological standpoint is the one whichpresents a minimum amount of (CO2)e. In order to quantify thisenvironmental impact, the pollutant indicator (pg) is defined byEq. (22) [6].
pg ¼ ðCO2ÞeLHV
(22)
where (CO2)e is taken in kg per kg of fuel (kg/kg), the LHV of the fuelis expressed in MJ/kg, and pg is expressed in kg/MJ.
4.2. Ecological efficiency
The ecological efficiency is defined as an indicator which allowsthe evaluation of the systems performance, according to pollutants
Fig. 4. Electricity production by an ICE-G, considering the emissions in a refinery andin the combustion process.
emissions, by comparing the hypothetically integrated pollutantsemissions (CO2 equivalent emissions) with the existing air qualitystandards. The conversion efficiency is also considered as a deter-mining factor on the specific emissions, expressed by a number. Eq.(23) can be used for determining the ecological efficiency [6]:
ε ¼"0:204� hsystem � ln
�135� pg
�hsystem þPg
#0:5(23)
where ‘‘ε” comprises in a single coefficient, the aspects that definethe environmental impact intensity; and ranges between 0 and 1.The situation that is considered unsatisfactory from the ecologicalpoint of view is when ε ¼ 0; however, ε ¼ 1 indicates an ideal sit-uation from the ecological efficiency point of view [6].
4.3. Calculation methodology of the ecological efficiency
The ecological efficiency of a PEM fuel cell considered the pol-lutants emission of the hydrogen production by the ethanol steamreforming; it was based on Fig. 3.
For the purpose of calculate the ecological efficiency of a DieselICE-G, was considered the ecological efficiency factor of Dieselproduction in the refinery and the combustion process in an ICE-G,as shown in Fig. 4.
Table 2 shows the elementary composition of sugar canebagasse in a dry base, from which was determined the stoichio-metric equation of bagasse combustion process shown in Equation(24). In this case, as there is not chemical formula defined for thiskind of fuel, it was made the equation of combustion for 100 g offuel (sugar cane bagasse) with 30% of air excess [25].
a1Cþ b1Hþ c1Oþ d1Nþ e1Sþ 3:83ðaO2 þ aN2Þ/w1CO2
þ y1H2Oþ 3:83að1� aÞO2 þ 3:83aN2
(24)
where:a ¼ 1.30 (considering 30% of air excess in the bagassecombustion);a1; b1; c1; d1; e1;w1; y1 e are the values of elementarycomponents of bagasse, determined by the ratio between theelementary composition and the molar mass of the accordingelement.
4.3.1. Calculation of carbon dioxide emissions in the combustionprocess of sugar cane bagasse
According to Villela et al. [27], the carbon dioxide emissionresult of the combustion of 1 kg of fuel, can be calculated using theEquation (25), as follows:
MCO2¼ ðw144:1ÞCO2
n(25)
Fig. 3. Electricity production by a PEMFC using
The molar mass of bagasse can be determined according to theelementary composition and the stoichiometric equation (Table 2and Equation (24)). In this way, the molar mass of sugar canebagasse can be calculated through Equation (26):
4.3.2. Emission of ethanol steam reforming systemThe emission values of NOx, SO2 and PM of the bagasse com-
bustion process are reported by Lora et al. [25], and are shown inTable 3.
Using the stoichiometric reaction of sugar cane bagasse com-bustion (Eq. (24)), the global stoichiometric reaction of ethanolsteam reforming (Eq. (27)) and the carbon dioxide lifecycle fromsugar cane plantation to ethanol production, shown in Fig. 5, it waspossible to obtain the emission of the ethanol steam reformingprocesses. For this calculation, it was considered the following ratio(1 ton of sugar cane produces 83.33 L of ethanol and 250 kg ofbagasse) [28]
C2H5OHþ 3H2O/2CO2 þ 6H2 (27)
4.3.3. Emission of DieselThe emissions values of Diesel production in a refinery and in
combustion process were based on the values reported by Ball et al.[29] and Taylor [24] respectively, and are shown in Table 7.
5. Results
5.1. Exergetic analysis
The results of exergetic analysis for the ICE-G and the PEMFC areshowed in Tables 4 and 5, respectively.
One of the major advantages of the PEMFC is that it can attainhigh efficiency, since it is not limited by the Carnot cycle. Onaverage, the electric efficiency of the PEMFC is about 20%e30%
hydrogen from ethanol steam reforming.
Table 3SO2, NOx, PM emissions of bagasse combustion [25].
higher than the combustion of fossil fuels such as Diesel, natural gasand coal [30], due to the fuel cells is based on an electrochemistryreaction.
Theoretically, the efficiency of a PEMFC and an ICE-G based onthe First Law of thermodynamics makes no reference to the bestpossible performance of both systems, and thus, could bemisleading [13]. On the other hand, the Second Law could give atrue demonstration of efficiency of the system’s performance.
According to the exergetic study shown in Tables 4 and 5, it canbe noted that the PEMFC system attain a higher value of exergeticefficiency compared to an ICE-G system, 40.34% versus 22.36%respectively. The irreversibility of the ICE-G was 13.32 kW, whilethe PEMFC was 6.64 kW. That means that, for both devices pro-ducing the same power, the electricity is generated in the fuel cellwith less exergetic losses (irreversibility); that’s means that thePEMFC system produces more useful work than the ICE-G.
5.2. Economic analysis
The results of the economic analysis are showed in Fig. 6. Theinvestment cost of the fuel cell ranges from 1000 US$/kW up to5000 US$/kW [19]. The investment cost in ICE was 500 US$/kW[20].
It is possible to observe in Fig. 6, that with both systems oper-ating 6570 h/year, the electricity cost of the ICE-G is moreeconomically feasible than when use the PEMFC for a period up to10 years, due to the high initial investment of the PEMFC and thehigher cost of hydrogen fuel. The electricity price of PEMFCwith theinvestment of 1,000 US$/kW, from the second years, is near to theprice of the electricity produced with ICE-G (difference of 12.9%),and decrease constantly until reach a difference of 4.16% in tenyears. The difference between the electricity production costs willdecrease more rapidly when some barriers are broken and beginthe PEMFC production at large scale; at that point this technologywill become more available and reliable.
5.3. Ecological analysis
Table 6 shows the emission values calculated by hydrogenproduction of ethanol steam reforming. In these calculations, two
Fig. 5. Total carbon dioxide emission f
scenarios were considered (one without considering the carbondioxide lifecycle and the other taking the carbon dioxide cycle intoaccount).
Table 7 shows the emission values of process of Diesel produc-tion in a refinery and during in its combustion process.
Using the emissions values of CO2, NOx, SO2, PM and the LVH ofsugar cane bagasse equals 17.32 MJ/kg. It was determined theequivalent carbon dioxide ((CO2)e) and the pollutant indicator (pg)of the hydrogen production system, and they were compared withthe total emission of equivalent carbon dioxide ((CO2)e) of Diesel((CO2)e from refinery þ (CO2)e from combustion process) and thepollutant indicator (pg), considering the LHV of crude oil equal to42.8 MJ/kg [31]. These values are shown in Table 8.
Analyzing the hydrogen production processes by ethanol steamreforming, it was determined the thermodynamic efficiencyequation of the ethanol steam reforming system (hEtOH steam
Legend:*PEMFC-1000 : PEMFC system with the investivement of 1000US$/kW*PEMFC-2500 : PEMFC system with the investivement of 2500US$/kW*PEMFC-5000 : PEMFC system with the investivement of 5000US$/kW*ICE-G: ICE-G system with the investivement of 500US$/kW
Fig. 6. Electricity production cost (US$/kWh) of the PEMFC and the ICE-G operating6570 h/year.
Table 8Results e equivalent carbon dioxide and pollutant indicators for the proposedsystem.
Table 9 shows the results of the global thermodynamic effi-ciency and the ecological efficiency of electricity production of bothsystems. The global thermodynamic efficiency of the fuel cell sys-tem was calculated by the product of hydrogen production effi-ciency (55.6%) times the energetic efficiency of PEMFC device (47%)[32], and for the Diesel engine was calculated by the product of theDiesel production efficiency (31%) times the ICE-G system energeticefficiency (27%) [33,19].
Table 6Results e emissions from the hydrogen producing by steam reforming of ethanolprocess.
This paper shows that the fuel cell could be a promising alter-native for electricity generation due to the high efficiency and thelower emission of pollutants in comparison with ICE-G. From theexergetic point of view, the comparison shows that the fuel cellsystem can be more efficient than the ICE-G. The ICE-G using Dieselas fuel has exergetic efficiency of 22.36%, and fuel cells have exer-getic efficiency of 40.34%.
As was showed in this economic analysis, at present time, thefuel cell technology with an investment cost ranging between1000 US$/kWand 5000 US$/kW is not economically feasible but, ina long-term, the fuel cells will become more competitive comparedto the internal combustion engine fueled with Diesel driving anelectricity generator. Bringing down some barriers and starting amarket with a sufficient scale, justifying the investments by afurther fuel cell production, and in the scaling-up of production,which will take this technology into acceptable levels of cost,availability and reliability.
Finally, according to the ecological analysis, the PEMFC usinghydrogen produced by an ethanol steam reforming, is an environ-mentally promising technology, due to its high ecological efficiencywhen considering the carbon dioxide cycle, ε ¼ 96%.
The hydrogen, the main energy carrier to fuel cells and itsproduction by the ethanol steam reforming, is the best way toguarantee the volume of production necessary to producehydrogen in sustainable way in larger sugar cane productioncountries like Brazil. The integration or association of hydrogenproduction with the sugar industry can certainly put Brazil in agood classification in the “Hydrogen Era” in the near future.
Acknowledgements
This work is financed by FAPESP (São Paulo ResearchFoundation).
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