Optimal design of different reforming processes of the ...
Transcript of Optimal design of different reforming processes of the ...
ww.sciencedirect.com
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 4 2 ( 2 0 1 7 ) 1 9 7 7e1 9 8 8
Available online at w
ScienceDirect
journal homepage: www.elsevier .com/locate/he
Optimal design of different reforming processesof the actual composition of bio-oil forhigh-temperature PEMFC systems
Suthida Authayanun a,*, Dang Saebea b, Yaneeporn Patcharavorachot c,Suttichai Assabumrungrat d, Amornchai Arpornwichanop e
a Department of Chemical Engineering, Faculty of Engineering, Srinakharinwirot University, Nakhon Nayok 26120,
Thailandb Department of Chemical Engineering, Faculty of Engineering, Burapha University, Chonburi 20131, Thailandc School of Chemical Engineering, Faculty of Engineering, King Mongkut's Institute of Technology Ladkrabang,
Bangkok 10520, Thailandd Center of Excellence in Catalysis and Catalytic Reaction Engineering, Department of Chemical Engineering, Faculty
of Engineering, Chulalongkorn University, Bangkok 10330, Thailande Computational Process Engineering Research Unit, Department of Chemical Engineering, Faculty of Engineering,
Chulalongkorn University, Bangkok 10330, Thailand
a r t i c l e i n f o
Article history:
Received 24 July 2016
Received in revised form
18 October 2016
Accepted 21 October 2016
Available online 14 November 2016
Keywords:
Bio-oil
High-temperature PEMFC
Steam reforming
Autothermal reforming
Partial oxidation
* Corresponding author. Fax: þ66 3 732 2608E-mail address: [email protected] (S.
http://dx.doi.org/10.1016/j.ijhydene.2016.10.10360-3199/© 2016 Hydrogen Energy Publicati
a b s t r a c t
Hydrogen production from bio-oil, a by-product of the pyrolysis of palm empty fruit
bunches, using different reforming processes, i.e., steam reforming (SR), partial oxidation
(POX) and autothermal reforming (ATR), is theoretically investigated using the actual
composition of bio-oil. The effect of the reaction temperature, steam to carbon (S/C) ratio
and oxygen to carbon (O/C) ratio on the hydrogen production and coke formation of the
reformers is analysed. Favourable operating conditions to inhibit carbon formation, to
produce low CO concentrations and to achieve high hydrogen yields for the hydrogen
production processes coupled with a high-temperature water-gas shift reactor (HT-WGSR)
in a high-temperature proton exchange membrane fuel cell (PEMFC) system is also
investigated. The results show that an S/C ratio above two is preferred for the bio-oil steam
reformer to keep the CO concentration below the maximum allowable limit of the high-
temperature PEMFC. However, the CO concentration in the product gas from an HT-
WGSR integrated with an autothermal reformer and a partial oxidation reactor is lower
than the 5% limit at all temperatures (300e1000 �C), S/C ratios (1e2) and O/C ratios (0.3e1)
considered. The efficiency of different bio-oil reforming processes integrated with high-
temperature PEMFC systems is studied. The highest system efficiency is achieved from
the integrated system consisting of a bio-oil steam reformer, an HT-WGSR and a high-
temperature PEMFC with heat integration.
© 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
.Authayanun).25ons LLC. Published by Els
evier Ltd. All rights reserved.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 4 2 ( 2 0 1 7 ) 1 9 7 7e1 9 8 81978
Introduction
Hydrogen is an energy carrier that is used to produce elec-
tricity via fuel cell applications. Most hydrogen is produced
from natural gas through a steam reforming process due to
the high performance and cost-effectiveness of this process.
Biomass is one of the most interesting fuels for hydrogen
production when environmental and availability aspects are
considered [1]. Sources of biomass can be plants, residues
from agriculture or forestry, and the organic components of
household and industrial wastes. The best-known thermo-
chemical processes for producing hydrogen from biomass are
the pyrolysis and gasification processes. For the biomass
gasification process, solid biomass is transformed to mainly
gas phase products in a gasifier in the presence of oxygen or
air. Alternatively, the biomass can be converted to hydrogen
by using pyrolysis followed by the reforming process [2]. In the
pyrolysis reactor, biomass is decomposed to liquid, gas and
char in the absence of oxygen. The liquid product is called bio-
oil and can be reformed to reformate gas in the reformer. The
low energy density and high transportation cost of biomass
are the main problems of hydrogen production from biomass
gasification [3]. Because bio-oil is easier and less expensive to
transport than biomass, the use of the biomass pyrolysis
process to produce bio-oil, which is in turn reformed to
hydrogen via reforming processes, is a promising way to
produce hydrogen from biomass from different locations [3,4].
Many works focus on the development of bio-oil reforming
processes using model compounds [5e7]. Gil et al. [8] studied
the sorption-enhanced steam reforming using acetic acid as
the model compound. They revealed that high steam to car-
bon ratio and low weight hourly space velocity (WHSV) in the
feed stream can enhance hydrogen production and suppress
methane, CO and CO2 formation in the product gas. High
hydrogen purities of up to 99.8% were obtained. Goicoechea
et al. [9] analysed steam reforming using acetic acid as the
model compound for bio-oil for a solid oxide fuel cell (SOFC)
system. They revealed that steam reforming of acetic acid is
thermodynamically feasible even at low steam to acetic acid
ratios. To obtain a high hydrogen yield for the SOFC, a steam
reformer should be operated at high temperatures and high
steam to acetic acid ratios. However, lower steam to acetic
acid ratios reduce the energy usage and improve the system
efficiency. Zhang et al. [10] developed catalysts for steam
reforming of acetic acid from bio-oil. They concluded that
Ni0:2Co0:8Mg6O7±d has more resistance to both carbon forma-
tion and oxidation of activemetals compared tomonometallic
catalysts. Most previousworks investigated only acetic acid as
the model compound. However, actual bio-oil has a wide va-
riety of components in addition to acetic acid. Many experi-
mental studies of reforming of actual bio-oil have already
been carried out [11e13]. Valle et al. [11] studied steam
reforming of the aqueous fraction of bio-oil with pyrolytic
lignin retention in a two-step reaction unit. For the first step, a
pyrolytic lignin is deposited by repolymerization of certain
bio-oil components, and the treated bio-oil is reformed in the
second step. These authors concluded that the catalyst
deactivation is low and the hydrogen yield and selectivity are
improved by using a Ni/La2O3ea Al2O3 catalyst. Additionally,
the steam reforming of raw bio-oil in a fluidized bed reactor
with CO2 capture was studied by Remiro et al. [12] CO2 was
effectively captured by using dolomite as an adsorbent in the
reforming reactor. The raw bio-oil was reformed at 600 �Cwithout adding water. In addition, Remiro et al. [13] investi-
gated the catalyst deactivation by coke deposition in the
steam reforming of the bio-oil aqueous fraction. They
concluded that the coke is gasified and Ni does not undergo
sintering at 700 �C.However, the theoretical study of hydrogen production
from the mixture of different oxygenated components of real
bio-oil is limited. Montero et al. [14] thermodynamically ana-
lysed the steam reforming of model compounds of real bio-oil
and ethanol. They used components in the bio-oil resulting
from the fast pyrolysis of pine sawdust as the model com-
pounds. However, the performance analysis and comparison
of different bio-oil reforming processes, steam reforming,
partial oxidation and autothermal reforming has not been
reported yet. In addition, the high molecular weight compo-
nents in bio-oil tend to be reformed to carbon, which causes
catalyst deactivation. Therefore, the study of reforming of
actual bio-oil with consideration of carbon formation is an
interesting topic.
The proton exchange membrane fuel cell (PEMFC) is a low-
temperature fuel cell that plays a leading role in trans-
portation, portable power and residential power applications.
PEMFCs can be classified into two types, the low-temperature
PEMFC (60e80 �C) and the high-temperature PEMFC
(100e200 �C). For pure hydrogen operation, high-temperature
PEMFCs show lower performance than low-temperature
PEMFCs due to low oxygen permeability and strong phos-
phate adsorption [15]. However, high-temperature operation
allows high-temperature PEMFCs to tolerate relatively high
levels of fuel impurities. To utilize reformate gas for proton
exchange membrane fuel cells, CO removal units are required
to reduce the CO content in the reformate gas. For conven-
tional PEMFCs, complex hydrogen purification units are typi-
cally needed to achieve CO concentrations below 10 ppm. For
high-temperature PEMFCs, only a water-gas shift reactor is
necessary due to the higher CO tolerance of this type of fuel
cell [16].
Recently, the integration of the hydrogen production pro-
cess with PEMFCs has received considerable attention.
Because of increased power demand and environmental
concerns, the development of a new sustainable feedstock for
hydrogen production is necessary. Chutichai et al. [17] studied
the integration of biomass gasification with the PEMFC sys-
tem. They proposed that the system efficiency is enhanced up
to 50% when waste heat is recovered to utilize in the system.
Guan et al. [18] investigated a PEMFC system fuelled by bio-gas
to cogenerate electricity and heat for a dairy farm and a biogas
plant. They concluded that the total efficiency of the PEMFC e
based combined heat and power system is 82%. In addition,
this system can reduce CO2 emissions by approximately 416
tons/year compared with a coal-fired combined heat and
power plant. Recently, our previous work [19] analysed the
performance of bio-ethanol steam reforming integrated with
a PEMFC system by considering the environmental impact.
The system integrating mixed bio-ethanol and methane
reforming with the PEMFC system achieved a higher system
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 4 2 ( 2 0 1 7 ) 1 9 7 7e1 9 8 8 1979
efficiency and a lower environmental impact than the system
integrating dehydrated bio-ethanol reforming with the PEMFC
because of the high energy consumption of the reformer,
preheating unit and bio-ethanol distillation unit in the system
using the dehydrated bio-ethanol reformer. In addition, our
previous work also investigated the performance of a high-
temperature PEMFC system fuelled by different non-
renewable and renewable fuels (i.e., methane, methanol,
ethanol, glycerol) [20]. The effect of CO poisoning on the high-
temperature PEMFC performance and the necessity of a
water-gas shift reactor as a CO removal unit were studied for
each fuel type. The results showed that a water-gas shift is
required to reduce the CO poisoning effect and to enhance the
system efficiency. However, only limited work on high-
temperature PEMFC systems that run on biomass-derived
bio-oil has been published. In addition, the operational
design of the reforming process coupled with the CO removal
process for HT-PEMFCs should be investigated.
In this study, a thermodynamic analysis of hydrogen pro-
duction from bio-oil, a by-product of pyrolysis of palm empty
fruit bunches, using different reforming processes, i.e., steam
reforming (SR), partial oxidation (POX) and autothermal
reforming (ATR), is investigated using the Aspen Plus simu-
lator and using the actual composition of the bio-oil. Simula-
tion studies are performed to determine the influence of key
operating parameters (e.g., reaction temperature, steam to
carbon (S/C) molar feed ratio, oxygen to carbon (O/C) molar
feed ratio) on the performance of a reformer in terms of
hydrogen production and coke formation. The integration of
the bio-oil reforming processes with the high-temperature
water-gas shift reactor (HT-WGSR) to produce hydrogen for a
high-temperature PEMFC was examined. The CO concentra-
tion at different reformer operating conditions is presented to
find conditions to produce a sufficiently low CO concentration
(<5%) for the HT-PEMFC. Subsequently, the optimal conditions
for bio-oil steam reforming, autothermal reforming and par-
tial oxidation processes integrated with an HT-WGSR to
inhibit carbon formation, to achieve a low CO concentration
and to maximize the hydrogen fraction are presented. In
addition, the efficiency of the integrated high-temperature
PEMFC systems at different reforming processes is studied
and compared.
Process description
The integrated high-temperature PEMFC systems examined in
this work are shown in Fig. 1. Each system consists of a fuel
processing process and a high-temperature PEMFC. Steam
reforming, autothermal reforming and partial oxidation are
the hydrogen production processes and the high-temperature
water-gas shift reactor is only used as a hydrogen purification
process to decrease the CO concentration below 5%.
Fuel processing process
In this work, the composition of actual bio-oil produced from
empty palm fruit bunch fast pyrolysis is used [21]. The
composition of the bio-oil is shown in Table 1. The product
compositions of the reformer and the water-gas shift reactor
at equilibrium are calculated by minimization of the Gibbs
free energy, as shown in Eq. (1):
minni
ðGtÞT;P ¼XCi¼1
niGi ¼XCi¼1
ni
G
�i þ RT ln
f if �i
!(1)
where C is the total number of components in the reaction
system, and ni is the amount of each gaseous component.
Because of the conservation of atomic species, ni must satisfy
the element balance in Eq. (2):
Xi
niaik �Ak ¼ 0 ðk ¼ 1; 2; :::;wÞ (2)
where aik is the number of atoms of element k in component i,
Ak is the total number of atoms of element k in the reaction
mixture, and w is the total number of elements.
The reactions of oxygenates due to steam reforming, par-
tial oxidation and autothermal reforming, along with the
possible side reaction, are presented in Table 2. The compo-
nents in the steam reforming system are the mixture of the
actual components of bio-oil (see Table 1), CH4, H2, CO, CO2, C
(Graphite), C2H2, C2H4 and H2O. The O2 component is added to
the reactive system for the partial oxidation and autothermal
reforming processes. The structure and properties of the
components in bio-oil (i.e., 1-hydroxy-2-butanone, 2(5H)-fur-
anone, 2-cyclopenten-1-one, 2-hydroxy-3-methyl, 2-
methoxy-(guaiacol), 2,6-dimethyoxy-(syringol), and Levoglu-
cosan) are input to the Aspen Plus program since the ther-
modynamic properties of these components are not available
in conventional thermodynamic databases.
The Rgibbs reactor module in Aspen Plus simulator is used
to represent the steam reformer, the autothermal reformer,
the partial oxidation reactor and the water-gas shift reactors.
Methane is treated as an inert gas in the water-gas shift
reactor. The equation of state used in the calculation is based
on the SoaveeRedlicheKwong equation [9]. The HT-WGSR is
operated at a temperature of 350 �C, and the ratio of steam to
CO in the feed stream is greater than two. Additional steam is
added if the steam to CO ratio of the reforming gas is lower
than two. Table 3 shows the validation of the steam reforming
of the acetic acid model compound using a steam reformer
temperature of 800 �C, an S/C ratio of 6 and atmospheric
pressure. The simulation results agree with the experimental
data reported by Hu and Lu [22].
High-temperature PEMFCs
The high-temperature PEMFC model based on electro-
chemical reactions is coded in FORTRAN in the Aspen Plus
simulator to predict the relation between voltage and current
density. An ideal separator, Sep, is applied for the anode to
separate the hydrogen from the reformate gas, and the cath-
ode is modelled as an Rgibbs reactor. The cell temperature of
the high-temperature PEMFC is specified as 175 �C. A PBI-
doped phosphoric acid membrane is used as the electrolyte
for the high-temperature PEMFC. The actual cell potentials or
operating voltage of a fuel cell (Ecell) is always smaller than the
reversible cell potential (Er) due to irreversible losses. Ecell can
be calculated from the activation loss at the anode ðhact;aÞ, theactivation loss at the cathode ðhact;cÞ and the ohmic loss
ðhohmicÞ as shown in Eq. (3).
Fig. 1 e The integrated high-temperature PEMFC systems.
Table 1 e The composition of bio-oil from empty palmfruit bunch fast pyrolysis [21].
Components Chemicalformula
Composition(wt%)
Acetic acid C2H4O2 56.73
Propanoic acid (acetol) C3H6O2 1.09
1-hydroxy-2-butanone C4H8O2 3.49
2(5H)-furanone C4H4O2 0.33
2-cyclopenten-1-one,
2-hydroxy-3-methyl
C6H8O2 7.90
Phenol C6H6O 23.97
Phenol, 2-methoxy-(guaiacol) C7H8O2 1.70
Phenol, 2,6-dimethyoxy-(syringol) C8H10O3 2.90
Levoglucosan C6H10O5 1.88
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 4 2 ( 2 0 1 7 ) 1 9 7 7e1 9 8 81980
Ecell ¼ Er � hact;a � hact;c � hohmic (3)
The reversible cell potential is described by the Nernst
equation.
Er¼��DHT
nF� TDST
nF
�þ RT
nFln
"ðRTÞ1:5CPt;aC0:5
Pt;c
aH2O
#(4)
where aH2O is the water activity defined by the ratio of water
partial pressure to its saturation pressure ðPsatH2O
Þ, which is
given in Eq. (5). CPt,a and CPt,c are the concentrations of
hydrogen and oxygen at the anode and cathode catalyst sur-
face, which are calculated by the StefaneMaxwell equation
and Fick's law, as shown in Table 4. Deffij is calculated using the
SlatteryeBird correlation [23] and corrected to account for the
porosity/tortuosity effects using the Bruggeman correlation
[24].
Table 2 e Reactions involved in the different hydrogenproduction processes.
Steam reforming
CnHmOk þ ðn� kÞH2O/nCOþ ðnþm=2� kÞH2
CnHmOk þ ð2n� kÞH2O/nCO2 þ ð2nþm=2� kÞH2
Partial oxidation
CnHmOk þ ðn=2� kÞO2/nCOþ ðm=2ÞH2
CnHmOk þ ðn� kÞO2/nCO2 þ ðm=2ÞH2
Autothermal reforming
CnHmOk þ 12 ðn=2� kÞO2 þ 1
2 ðn� kÞH2O/nCOþ 12 ðnþm� kÞH2
CnHmOk þ 12 ðn� kÞO2 þ 1
2 ð2n� kÞH2O/nCO2 þ 12 ð2nþm� kÞH2
Additional side reactions for hydrogen production processes
Wateregas shift reaction
CO þ H2O4 CO2 þ H2
Methanation reaction
COþ 3H2/CH4 þH2O
Carbon formation reactions
2CO4CO2 þ C
CH442H2 þ C
COþH24H2Oþ C
Table 3 e The validation of the acetic acid steamreforming process at a reformer temperature of 800 �C, S/C ratio of 6 and atmospheric pressure.
Component % Conversion or yield % Error
Simulation Experimental [22]
Acetic acid 100 100 0.00
H2 86 88 2.27
CO 12.7 13 2.31
CO2 80.1 82 2.32
CH4 0 0 0.00
Table 4 e Diffusion models used in the simulation of the high
Diffusion models
Stefan Maxwell models
Fick' law models
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 4 2 ( 2 0 1 7 ) 1 9 7 7e1 9 8 8 1981
PsatH2O
¼ �142:07682T4 � 171026:12676T3 þ 78013638:11584T2
� 15953375633:8471Tþ 1231888491801:45�*10�10 (5)
Activation losses are governed by the ButlereVolmer
equation (Eqs. (6) and (7)).
ia ¼ i0;a
�exp
��aRd;aFRT
�hact;a
��� exp
��aOx;aFRT
�hact;a
���(6)
ic ¼ i0;c
�exp
��aRd;cFRT
�hact;c
��� exp
��aOx;cFRT
�hact;c
���(7)
where i is the current density and a is the transfer coefficient.
i0 is the exchange current density, which can be calculated
from Eqs. (8) and (9) for the anode and cathode, respectively.
i0;a ¼ iref0;aac;aLc;a
CPt;a
CrefPt;a
!g
exp
�� Ec;a
RT
�1� T
Tref ;a
��(8)
i0;c ¼ iref0;cac;cLc;c
CPt;c
CrefPt;c
!g
exp
�� Ec;c
RT
�1� T
Tref ;c
��(9)
Assuming aRd ¼ aOx ¼ a, the hyperbolic sine function can be
substituted in Eqs. (6) and (7), yielding the following
relationship:
hact ¼RTaF
sinh�1
�i2i0
�(10)
The effect of CO poisoning is included in the anode acti-
vation loss model of the high-temperature PEMFCs because
hydrogen-rich gas from the fuel processor is used at the
anode. The anode activation loss can be calculated from the
exchange current density of hydrogen and the CO coverage
-temperature PEMFC.
Equations
At the anode
dXCO2dz ¼ RT
P XCO2
0@ NH2 ;g
DeffH2 ;CO2
1A
dXH2O
dz ¼ RTP XH2O
0@ NH2 ;g
DeffH2 ;H2O
1A
dXCOdz ¼ RT
P XCO
0@ NH2 ;g
DeffH2 ;CO
1A
dXCH4dz ¼ RT
P XCH4
0@ NH2 ;g
DeffH2 ;CH4
1A
XH2 ¼ 1� XCO2 � XH2O � XCO � XCH4
At the cathode
dXN2dz ¼ RT
P XN2
0@ NO2
DeffN2 ;O2
þ NH2O;g
DeffN2 ;H2O
1A
dXH2O
dz ¼ RTP
24XH2O
0@ NO2
DeffO2 ;H2O
1A� NH2O
0@ XO2
DeffO2 ;H2O
þ XN2
DeffN2 ;H2O
1A35
XO2 ¼ 1� XN2 � XH2O
At the anodeNH2
SPt�anode¼ �DH2
ðCPt;a�CH2 ðdissolveÞ Þdanode
CH2ðdissolveÞ ¼ CdissolvedH2
$XH2 $P
At the cathodeNO2
SPt�cathode¼ �DO2
ðCPt;c�CO2 ðdissolveÞ Þdcathode
CO2ðdissolveÞ ¼ CdissolvedO2
$XO2 $P
Table 5 e Parameters used for the high-temperaturePEMFC [15].
Parameters Value
Cell temperature, T (�C) 175
Operating pressure at anode, Pa (atm) 1
Operating pressure at cathode, Pc (atm) 1
Stoichiometric ratio at anode, Sa 1.25
Stoichiometric ratio at cathode, Sc 2
Membrane thickness, lm (m) 4 � 10�5
GDL thickness, z (m) 0.0002
Anode film thickness, danode (m) 2.5 � 10�9
Cathode film thickness,dcathode (m) 1.48 � 10�9
Anode activation energy, Ec,a (J mole�1 K�1) 16,900
Cathode activation energy, Ec,c (J mole�1 K�1) 72,400
Anode reference cell temperature, Tref,a (�C) 160
Cathode reference cell temperature, Tref,c (�C) 100
Anode catalyst surface area, ac,a (m2 g�1) 64
Cathode catalyst surface area, ac,c (m2 g�1) 32.25
Anode catalyst loading, Lc,a (mg cm�2) 0.2
Cathode catalyst loading, Lc,c (mg cm�2) 0.4
Transfer coefficient at anode, aa 0.5
Transfer coefficient at cathode, ac 0.75
Reaction order at anode, ga 1
Reaction order at cathode, gc 1.375
Anode reference concentration, CrefPt;a (mol cm�3) 0.0002
Cathode reference concentration, CrefPt;c (mol cm�3) 0.0004
Temperature (oC)
300 400 500 600 700 800
H2
mol
ar fl
ow ra
te (m
ol/s)
0
2
4
6
8
S/C = 1S/C = 1.5S/C = 2S/C = 2.5S/C = 3
S/C = 0.5S/C = 1S/C = 1.5
Inhibited carbon formation
Carbon formation
Fig. 2 e Effect of the reformer temperature and S/C ratio on
the hydrogen molar flow rate of the steam reforming
process.
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 4 2 ( 2 0 1 7 ) 1 9 7 7e1 9 8 81982
(qCO) [25] as shown in Eq. (11). The bridge model of CO
adsorption on Pt and the anode activation loss of HT-PEMFC is
represented by Eq. (12).
hact;a ¼ RTaF
sinh�1
i
2i0ð1� qCOÞ2!
(11)
qCO ¼ a*ln½CO�½H2� þ b*lnðiÞ*ln ½CO�
½H2� þ c (12)
where
a ¼ �0:00012784�T2 þ 0:11717499�T� 26:62908873b ¼ 0:0001416�T2 � 0:12813608�T þ 28:852463626c ¼ �0:00034886�T2 þ 0:31596903�T� 70:11693333
The ohmic loss for a high-temperature PEMFC is described
as follows:
hohmic ¼ Rmemi ¼�sm
lm
�i (13)
where Rmem is the membrane resistance, sm is the proton
conductivity of the membrane and lm is the membrane
thickness.
Table 6 e The models of efficiency of high-temperature PEMFC
Efficiency
Reformer efficiency ðhRÞFuel processor efficiency ðhFP ÞFuel cell efficiency ðhFCÞSystem efficiency without heat integration ðhSÞSystem efficiency with heat integration ðhSCÞ
The proton conductivity as a function of temperature and
relative humidity [26] can be calculated from Eqs. (14)e(16).
sm ¼ ATexp
� �BRðTÞ
�(14)
A ¼ exp��ka1RH
3�þ �ka
2RH2�þ �ka
3RH�þ ka
0
�(15)
B ¼�kb1RH
3þ�kb2RH
2þ�kb3RH
þ kb
0 (16)
The parameters used for the simulation of high-
temperature PEMFCs are shown in Table 5. In addition, the
detailed calculations of reformer efficiency, fuel processor
efficiency, fuel cell efficiency and system efficiency can be
found in Table 6. To calculate the system efficiency with heat
integration, heat recovered from the high-temperature PEMFC
is used to preheat the reactants for the fuel processing
processes.
Results and discussion
Reforming processes
For the steam reforming process, the effect of the reformer
temperature and S/C ratio on the hydrogen molar flow rate is
shown in Fig. 2. The dashed lines showoperating conditions to
systems.
Equations
hR ¼ LHVH2$ð _mH2
ÞLHVfuel $ð _mfuelÞþQT
QT ¼ QR1 þ QR2 �QR3
hFP ¼ LHVH2$ð _mH2
ÞLHVfuel $ð _mfuelÞþQT
QT ¼ QR1 þQR2 �QR3 þQP1
hFC ¼ PFCð _mH2
Þ$LHVH2
hS ¼ PFCLHVfuel $ð _mfuelÞþQT
QT ¼ QR1 þQR2 � QR3 þQP1 �QP2 þQF1
hSC ¼ PFCLHVfuel $ð _mfuelÞþQT
QT ¼ QR1 þ QR2 �QR3 þQP1 �QP2 þ QF1 �QF2
Temperature (oC)
300 400 500 600 700 800 900 1000
H2
mol
ar fl
ow ra
te (m
ol/s)
0
1
2
3
4
O/C = 0.6O/C = 0.7O/C = 0.8
O/C = 0.1O/C = 0.2O/C = 0.3O/C = 0.4O/C = 0.5O/C = 0.6 O/C = 0.7O/C = 0.8
Carbon formation Inhibited carbon formationO/C = 0.3O/C = 0.4O/C = 0.5
Fig. 3 e Effect of the reformer temperature and O/C ratio on
the hydrogen molar flow rate of the partial oxidation
process.
Fig. 4 e Effect of the reformer temperature and O/C ratio on the
process at different S/C ratios: (a) S/C ¼ 0.5, (b) S/C ¼ 1, (c) S/C ¼
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 4 2 ( 2 0 1 7 ) 1 9 7 7e1 9 8 8 1983
be avoided because carbon formation occurs, whereas the
solid lines show the hydrogen production rate where carbon
formation does not occur. The steam reformer should be
operated at temperatures of 650e700 �C to maximize the
hydrogen molar flow rate. Carbon formation is unfavourable
at S/C ratios higher than two at all reformer temperatures
considered. Compared to the steam reforming of the acetic
acid model compound, higher S/C ratios are required for bio-
oil steam reformer to prevent carbon formation due to the
higher molecular weight compounds contained in actual bio-
oil [27]. In addition, the simulation predictions of carbon for-
mation for bio-oil steam reforming are in agreement with the
results of Montero et al. [14]. Although carbon formation can
be avoided by adding excess steam into the reformer, it still
occurs at high temperatures, as observed from experimental
data [13]. This is because the assumed graphite carbon in the
simulation is not the complete representation of the carbon
that is deposited, and it is a very complex task to thermody-
namically model carbon deposition [14,28]. However, Hu and
Lu [29], who experimentally investigated bio-oil steam
hydrogen molar flow rate of the autothermal reforming
1.5 and S/C ¼ 2.
Fig. 5 e Effect of the reformer temperature and S/C ratio on
the performance of the bio-oil steam reformer integrated
with HT-WGSR at the carbon formation-inhibiting
condition: (a) %CO (dry basis) and (b) Hydrogen mole
fraction (dry basis).
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 4 2 ( 2 0 1 7 ) 1 9 7 7e1 9 8 81984
reforming, partial oxidation and oxidative steam reforming
with CO2 utilization, proposed that high temperature has a
positive effect on reducing coke formation. Therefore, further
study and characterization of carbon is necessary, and it is an
interesting topic for furthering the understanding of carbon
formation in real systems [30]. In addition, it is noted that a
high S/C ratio and high temperature are required to enhance
hydrogen production and to prevent carbon formation.
Furthermore, the effect of reformer temperature and the O/
C ratio on the hydrogen molar flow rate for the partial oxida-
tion of actual bio-oil is presented in Fig. 3. The partial oxidation
reactor is operated at atmosphere pressure and isothermal
conditions. Additionally, the operating conditions represented
by the dashed line and by the solid line show the hydrogen
production with carbon formation and with inhibited carbon
formation, respectively. According to the simulation results,
carbon is formed at all O/C ratios (0.1e0.8) studied. At high O/C
ratios (O/C ratio � 0.3), the dashed lines become solid lines at
higher temperatures. However, the hydrogen content de-
creases with increasing O/C ratio. From Fig. 3, the hydrogen
molar flow rate increases with increasing temperature until
reaching a maximum. Beyond that point, further increase in
temperature slightly reduces the hydrogen production rate.
The maximum hydrogen molar flow rate is observed at tem-
peratures greater than 900 �C and O/C ratios of 0.1 and 0.2, but
carbon formation is promoted at these conditions. Therefore,
the optimal condition with inhibited carbon formation for
partial oxidation of actual bio-oil is an O/C ratio of 0.3 and a
temperature above 800 �C. Compared to the steam reforming
process, the partial oxidation process provides a lower
hydrogen content and needs to be operated at a higher
temperature.
Next, the performance of autothermal reforming of actual
bio-oil for hydrogen production is thermodynamically ana-
lysed under atmospheric pressure and at isothermal condi-
tions. The effect of the operating parameters of autothermal
reforming of actual bio-oil on the hydrogen molar flow rate is
shown in Fig. 4. In this process, both steam and oxygen are
used as agents to reform bio-oil into reformate gas. In Fig. 4(a),
which shows the performance of autothermal reforming of
the actual bio-oil composition at an S/C ratio of 0.5, the dashed
lines appear at all operating O/C ratios. This means carbon
formation is favourable at these conditions. However, the
maximum hydrogen molar flow rate can be achieved at a
reformer temperature of 800 �C and an O/C ratio of one with
inhibited carbon formation.
In addition, the results further show that no dashed lines
(meaning carbon formation did not occur) are found at high O/
C ratios when the S/C ratio increases to 1 and 1.5, as shown in
Fig. 4(b) and (c), respectively. For an autothermal reformer
operated at an S/C ratio of one in Fig. 4(b), carbon did not
appear in the products of the autothermal reformer at all
operating temperatures when the O/C ratio was greater than
0.6. In addition, the O/C ratio needed to prevent carbon for-
mation at all reformer temperatures should be greater than
0.3 when an S/C ratio of 1.5 is specified, as shown in Fig. 4(c).
For an autothermal reformer operated at an S/C ratio of two,
as shown in Fig. 4(b), carbon formation is avoided at all
operating temperatures and O/C ratios studied. The hydrogen
production of the autothermal reformer of actual bio-oil is
enhanced at high S/C ratios, reformer temperatures of
700e800 �C and anO/C ratio of 0.1. However, it should be noted
that operation at higher O/C ratios can reduce the require-
ment of external heat for the reformer.
Reforming processes integrated with a CO removal unit
The CO and hydrogen concentrations at different operating
parameters of a steam reformer, a partial oxidation reactor
and an autothermal reformer are investigated when the
hydrogen production processes are integrated with a high-
temperature water-gas shift reactor (HT-WGSR). It is noted
that the optimal operating conditions for hydrogen produc-
tion processes should not only maximize hydrogen concen-
tration but also achieve a CO fraction lower than 5%.
Therefore, the CO concentration in the product gases at
various operating conditions is first studied and then the ef-
fect of operating conditions on the hydrogen fraction while
avoiding carbon formation and achieving CO fractions <5% is
investigated. For the bio-oil steam reformer integratedwith an
Fig. 6 e Effect of the reformer temperature and O/C ratio on
the performance of the bio-oil partial oxidation reactor
integrated with HT-WGSR at the carbon formation-
inhibiting condition: (a) %CO (dry basis) and (b) Hydrogen
mole fraction (dry basis).
(a)
(b)
Temperature (oC)
300 400 500 600 700 800
%C
O (d
ry b
asis)
0
1
2
3
4
5
6
O/C = 0.1O/C = 0.2O/C = 0.3
CO limitation
Inhibited carbon formation
Temperature (oC)
300 400 500 600 700 800
H2 m
ole
frac
tion
(dry
bas
is)
00.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
O/C = 0.1O/C = 0.2O/C = 0.3
Inhibited carbon formation and CO < 5%
Fig. 7 e Effect of the reformer temperature and O/C ratio on
the performance of the bio-oil autothermal reformer
integrated with HT-WGSR at the carbon formation-
inhibiting condition: (a) %CO (dry basis) and (b) Hydrogen
mole fraction (dry basis). Dotted line e S/C ¼ 1; Dashed line
e S/C ¼ 1.5; Solid line e S/C ¼ 2.
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 4 2 ( 2 0 1 7 ) 1 9 7 7e1 9 8 8 1985
HT-WGSR, the CO fraction increases with increasing temper-
ature andwith decreasing S/C ratio, as shown in Fig. 5(a). At S/
C ratios of 1 and 1.5, the CO concentration is greater than 5% at
almost all reformer temperatures studied. Therefore, the
steam reformer should be operated at an S/C ratio �2 to keep
the CO concentration below the maximum allowable limit of
an HT-PEMFC. To find the optimal condition that maximizes
hydrogen concentration, the effect of the S/C ratio and the
reformer temperature on the hydrogenmolar fraction from an
HT-WGSR is studied at operating conditions that inhibit car-
bon formation and produced a CO concentration below 5%.
The simulation results are presented in Fig. 5(b). The highest
hydrogen concentration is obtained at reformer temperatures
of 700e800 �C and S/C ratios of 2 or higher. However, it should
be noted that operation at high temperature (above 700 �C)causes catalyst deactivation by sintering [2].
The partial oxidation reactor integrated with an HT-WGSR
is examined next. The effect of the reformer temperature and
the O/C ratio on CO fraction and hydrogen fraction in the
product gas from theHT-WGSR is presented in Fig. 6(a) and (b).
Fig. 6(a) shows that increasing the temperature from 300 to
600 �C increases the CO concentration. Further increase in
temperature results in only small changes of the CO fraction.
When the O/C ratio is lower than 0.9, the CO fraction increases
with increasing O/C ratio. However, the CO concentration
decreases when the O/C ratio increases from 0.9 to 1. The
lowest CO concentration for a partial oxidation reactor inte-
grated with an HT-WGSR is obtained at an O/C ratio of 1. This
is because under conditions with a high amount of oxygen,
fuel is converted to CO2 instead of CO. The reactions for partial
oxidation with different products (CO and CO2) are shown in
Table 2. Fig. 6(b) shows that a low O/C ratio is preferred to
enhance hydrogen production. Increasing temperature im-
proves the hydrogen concentration until it reaches an optimal
value for each O/C ratio. In addition, it can be concluded that
the CO fraction is below the limitation of the HT-PEMFC at all
of the operating conditions studied.
The effect of temperature, the S/C ratio and the O/C ratio of
an autothermal reformer integrated with an HT-WGSR on the
fuel processor performance is shown in Fig. 7. These operating
conditions have a significant effect on the CO and hydrogen
Table 7 e The optimal operating conditions and productcompositions of the different reformers for high-temperature PEMFC systems at inhibited carbonformation and CO < 5%.
Steamreformer
Autothermalreformer
Partialoxidation reactor
Temperature (�C) 700 700 850
S/C 2 1 e
O/C e 0.1 0.3
Hydrogen fraction 0.67 0.64 0.61
%CO 4.15 2.82 2.58
Fig. 8 e The efficiency of the different high-temperature
PEMFC systems.
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 4 2 ( 2 0 1 7 ) 1 9 7 7e1 9 8 81986
fractions, as shown in Fig. 7(a) and (b), respectively. At an S/C
ratio of two, increasing the O/C ratio decreases the CO con-
centration. However, the CO fraction decreases with
increasing O/C ratio at an S/C ratio lower than two. This is
because the CO is still high at low S/C ratios, as seen in
Fig. 5(a); therefore, the addition of oxygen has a significant
effect on the CO concentration and can considerably reduce
the CO content in the product gas. From Fig. 7(b), a high S/C
ratio and a low O/C ratio are preferred for hydrogen produc-
tion with a high hydrogen fraction (dry basis). The optimal
operating temperature is 700 �C or higher. To apply the
product gas for an HT-PEMFC, the optimal operating param-
eters of the steam reformer, autothermal reformer and partial
oxidation reactor for an HT-PEMFC system to inhibit carbon
formation, obtain a CO fraction <5%, and maximize the
hydrogen fraction are shown in Table 7.
HT-PEMFC systems
The efficiency of the system and the efficiency of each unit of
the different hydrogen production processes and HT-WGSR
integrated with an HT-PEMFC are also studied, as shown in
Fig. 8. The steam reforming process achieves the highest
reformer efficiency (66%) and the partial oxidation process
shows the lowest reformer efficiency (34%), whereas the
reformer efficiency of the autothermal reforming process is
approximately 51%. However, the fuel processor efficiency
(efficiency of hydrogen production processes integrated with
HT-WGSR) is enhanced from the reformer efficiency because
additional hydrogen is produced from the HT-WGSR. The fuel
processor efficiencies of the steam reformer, autothermal
reformer and partial oxidation reactor are 75%, 71% and 66%,
respectively. However, the fuel cell efficiency of each
reforming process is quite similar due to the comparable
hydrogen fraction, as seen in Table 7. In should be noted that
the oxidant used in the autothermal reformer and the partial
oxidation reactor is oxygen, and thus no nitrogen dilution
effect occurs. The system efficiency improves when heat re-
covery from the HT-PEMFC is applied to the hydrogen pro-
duction processes. The system using a steam reformer, HT-
WGSR and HT-PEMFC with heat integration achieves the
highest system efficiency (41%).
Conclusions
This study is focused on hydrogen production for HT-PEMFC
systems to inhibit carbon formation and achieve a low CO
concentration (CO < 5%). The actual components of bio-oil
from fast pyrolysis of empty palm fruit bunch are used as
the fuel for hydrogen production from steam reforming, par-
tial oxidation and autothermal reforming processes. High re-
action temperatures and high S/C ratios enhances hydrogen
production, but hydrogen production decreases with
increasing O/C molar ratio. However, reformer operation at
high S/C molar ratios, high O/C molar ratios and high tem-
peratures is required to prevent coke formation. It should be
noted that graphite carbon does not fully represent carbon
deposition and that further study of this critical issue is
necessary. For a steam reformer integrated with HT-WGSR,
the steam reformer should be operated at S/C � 2 to keep
the CO fraction below 5%, which is the requirement for HT-
PEMFC. However, the CO concentration in the product gas
fromHT-WGSR is lower than 5% at all temperatures, S/C ratios
and O/C ratios considered for the autothermal reformer and
the partial oxidation reactor. In addition, the optimal oper-
ating conditions of the steam reformer, autothermal reformer
and partial oxidation reactor for the HT-PEMFC system to
maximize the hydrogen concentration, to inhibit carbon for-
mation, and to maintain the CO fraction <5% are presented as
well. When the different reforming options are compared, the
HT-PEMFC system based on the steam reforming process
achieved the highest system efficiency (41%), followed by the
HT-PEMFC system based on autothermal reforming (38%) and
the partial oxidation processes (35%).
Acknowledgements
Support from the Srinakharinwirot University and the Chu-
lalongkorn Academic Advancement into its 2nd Century
Project and the Thailand Research Fund (DPG5880003), is
gratefully acknowledged.
Nomenclatures
ac Catalyst surface area, m2 g�1
aH2O Water activity
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 4 2 ( 2 0 1 7 ) 1 9 7 7e1 9 8 8 1987
Cdissolve Equilibrium concentration, mol cm�3
CPt Concentration on the catalyst surface, mol cm�3
CrefPt Reference concentration on the catalyst surface,
mol cm�3
Deffij Binary diffusion coefficient, m2 s�1
Ec Activation energy, J mol�1 K�1
Ecell Cell voltage, V
Er Reversible cell potential, V
F Faraday constant, 96,485 C mol�1
H Enthalpy, J mol�1
i Current density, A m�2
i0 Exchange current density, A m�2
iref0 Reference exchange current density, A m�2
Lc Catalyst loading, mg cm�2
lm Membrane thickness, m
m Molar flow rate, mol s�1
LHV Lower heating value, kJ mol�1
N Molar flux, mol s�1 m�2
P Pressure, atm
PFC Power output of fuel cell, W
Q Heat flow, J s�1
QT Total heat required for the hydrogen production
process, J s�1
R Gas constant (¼8.314), J mol�1 K�1
SPt Real platinum surface area
T Cell temperature, K
X Mole fraction
Greek letters
d Average film thickness, m
a Transfer coefficient
g Reaction order
qCO CO coverage
qH H2 coverage
sm Proton conductivity, S cm�1
hFP Fuel processor efficiency
hact Activation loss, V
hohmic Ohmic loss, V
hS System efficiency without heat integration
hSC System efficiency with heat integration
hR Reformer efficiency
hFC Fuel cell efficiency
Subscripts and superscripts
a Anode
c Cathode
m Membrane
i,j Components “i” and “j”
in Inlet stream
out Outlet stream
r e f e r e n c e s
[1] Kan T, Xiong J, Li X, Ye T, Yuan L, Torimoto Y, et al. Highefficient production of hydrogen from crude bio-oil via anintegrative process between gasification and current-enhanced catalytic steam reforming. Int J Hydrogen Energy2010;35:518e32.
[2] Medrano JA, Oliva M, Ruiz J, Garcia L, Arauzo J. Hydrogenfrom aqueous fraction of biomass pyrolysis liquids by
catalytic steam reforming in fluidized bed. Energy2011;36:2215e24.
[3] Braimakis K, Atsonios K, Panopoulos KD, Karellas S,Kakaras E. Economic evaluation of decentralized pyrolysisfor the production of bio-oil as an energy carrier forimproved logistics towards a large centralized gasificationplant. Renew Sust Energ Rev 2014;35:57e72.
[4] Czernik S, Evans R, French R. Hydrogen from biomass-production by steam reforming of biomass pyrolysis oil.Catal Today 2007;129:265e8.
[5] Wiranarongkorn K, Authayanun S, Assabumrungrat S,Arpornwichanop A. Analysis of thermally coupling steamand tri-reforming processes for the production of hydrogenfrom bio-oil. Int J Hydrogen Energy 2016;41:18370e9.
[6] Esteban-Dı́ez G, Gil MV, Pevida C, Chen D, Rubiera F. Effect ofoperating conditions on the sorption enhanced steamreforming of blends of acetic acid and acetone as bio-oilmodel compounds. Appl Energy 2016;177:579e90.
[7] Mei Y, Wu C, Liu R. Hydrogen production from steamreforming of bio-oil model compound and byproductselimination. Int J Hydrogen Energy 2016;41:9145e52.
[8] Gil MV, Fermoso J, Pevida C, Chen D, Rubiera F. Production offuel-cell grade H2 by sorption enhanced steam reforming ofacetic acid as a model compound of biomass-derived bio-oil.Appl Catal B Environ 2016;184:64e76.
[9] Goicoechea S, Ehrich H, Arias P, Kockmann N.Thermodynamic analysis of acetic acid steam reforming forhydrogen production. J Power Sources 2015;279:312e22.
[10] Zhang F, Wang N, Yang L, Li M, Huang L. Ni-Co bimetallicMgO-based catalysts for hydrogen production via steamreforming of acetic acid from bio-oil. Int J Hydrogen Energy2014;39:18688e94.
[11] Valle B, Remiro A, Aguayo AT, Bilbao J, Gayubo AG. CatalystsNi/a-Al2O3 and Ni/La2O3-a Al2O3 for hydrogen productionby steam reforming of bio-oil aqueous fraction withpyrolytic lignin retention. Int J Hydrogen Energy2013;38:1307e18.
[12] Remiro A, Valle B, Aguayo AT, Bilbao J, Gayubo AG. Steamreforming of raw bio-oil in a fluidized bed reactor with priorseparation of pyrolytic lignin. Energy Fuels2013;27:7549e59.
[13] Remiro A, Valle B, Aguayo AT, Bilbao J, Gayubo AG. Operatingconditions for attenuating Ni/La2O3-a Al2O3 catalystdeactivation in the steam reforming of bio-oil aqueousfraction. Fuel Process Technol 2013;115:222e32.
[14] Montero C, Oar-Arteta L, Remiro A, Arandia A, Bilbao J,Gayubo AG. Thermodynamic comparison between bio-oiland ethanol steam reforming. Int J Hydrogen Energy2015;40:15963e71.
[15] Authayanun S, Mamlouk M, Scott K, Arpornwichanop A.Comparison of high-temperature and low-temperaturepolymer electrolyte membrane fuel cell systems withglycerol reforming process for stationary applications. ApplEnergy 2013;109:192e201.
[16] Authayanun S, Saebea D, Patcharavorachot Y,Arpornwichanop A. Evaluation of an integrated methaneautothermal reforming and high-temperature protonexchange membrane fuel cell system. Energy 2015;80:331e9.
[17] Chutichai B, Authayanun S, Assabumrungrat S,Arpornwichanop A. Performance analysis of an integratedbiomass gasification and PEMFC (proton exchangemembrane fuel cell) system: hydrogen and powergeneration. Energy 2013;55:98e106.
[18] Guan T, Alvfors P, Lindbergh G. Investigation of the prospectof energy self-sufficiency and technical performance of anintegrated PEMFC (proton exchange membrane fuel cell),dairy farm and biogas plant system. Appl Energy2014;130:685e91.
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 4 2 ( 2 0 1 7 ) 1 9 7 7e1 9 8 81988
[19] Authayanun S, Suwanmanee U, Arpornwichanop A.Enhancement of dilute bio-ethanol steam reforming for aproton exchange membrane fuel cell system by usingmethane as co-reactant: performance and life cycleassessment. Int J Hydrogen Energy 2015;40:12144e53.
[20] Authayanun S, Saebea D, Patcharavorachot Y,Arpornwichanop A. Effect of different fuel options onperformance of high temperature PEMFC (protonexchange membrane fuel cell) systems. Energy2014;68:989e97.
[21] Do TX, Lim Y, Yeo H. Techno-economic analysis of biooilproduction process from palm empty fruit bunches. EnergyConvers Manage 2014;80:525e34.
[22] Hu X, Lu G. Investigation of the steam reforming of a series ofmodel compounds derived from bio-oil for hydrogenproduction. Appl Catal B Environ 2009;88:376e85.
[23] Slattery JC, Bird RB. Calculation of the diffusion coefficient ofdilute gases and of the self-diffusion coefficient of densegases. AIChE J 1958;4:137e42.
[24] Scott K, Pilditch S, Mamlouk M. Modelling and experimentalvalidation of a high temperature polymer electrolyte fuelcell. J Appl Electrochem 2007;37:1245e59.
[25] Authayanun S, Mamlouk M, Arpornwichanop A. Maximizingthe efficiency of a HT-PEMFC system integrated with glycerolreformer. Int J Hydrogen Energy 2012;37:6808e17.
[26] Mamlouk M, Sousa T, Scott K. A high temperature polymerelectrolyte membrane fuel cell model for reformate gas. Int JElectrochem 2011;2011:1e18.
[27] ECh Vagia, Lemonidou AA. Thermodynamic analysis ofhydrogen production via steam reforming of selectedcomponents of aqueous bio-oil fraction. Int J HydrogenEnergy 2007;32:212e23.
[28] Vicente J, Montero C, Erena J, Azkoiti MJ, Bilbao J, Gayubo AG.Coke deactivation of Ni and Co catalysts in ethanol steamreforming at mild temperatures in a fluidized bed reactor. IntJ Hydrogen Energy 2014;39:12586e96.
[29] Hu X, Lu G. Bio-oil steam reforming, partial oxidation oroxidative steam reforming coupled with bio-oil dryreforming to eliminate CO2emission. Int J Hydrogen Energy2010;35:7169e76.
[30] Alvarado FD, Gracia F. Steam reforming of ethanol forhydrogen production: thermodynamic analysis includingdifferent carbon deposits representation. Chem Eng J2010;165:649e57.