Post on 07-Nov-2021
Hindawi Publishing CorporationJournal of Renewable EnergyVolume 2013 Article ID 209364 8 pageshttpdxdoiorg1011552013209364
Research ArticlePretreated Landfill Gas Conversion Process viaa Catalytic Membrane Reactor for Renewable CombinedFuel Cell-Power Generation
Zoe Ziaka and Savvas Vasileiadis
Department of Catalysis and Environmental Protection Hellenic Open University 26335 Patras Greece
Correspondence should be addressed to Zoe Ziaka bookenghotmailcom
Received 5 December 2012 Accepted 8 March 2013
Academic Editor Wei-Hsin Chen
Copyright copy 2013 Z Ziaka and S Vasileiadis This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited
A new landfill gas-based reforming catalytic processing system for the conversion of gaseous hydrocarbons such as incomingmethane to hydrogen and carbon oxide mixtures is described and analyzed The exit synthesis gas (syn-gas) is fed to powereffectively high-temperature fuel cells such as SOFC types for combined efficient electricity generation The current research workis also referred on the description and design aspects of permreactors (permeable reformers) carrying the same type of landfill gas-reforming reactions Membrane reactors is a new technology that can be applied efficiently in such systems Membrane reactorsseem to perform better than the nonmembrane traditional reactors The aim of this research includes turnkey system and processdevelopment for the landfill-based power generation and fuel cell industries Also a discussion of the efficient utilization of landfilland waste type resources for combined green-typerenewable power generation with increased processing capacity and efficiencyvia fuel cell systems is taking place Moreover pollution reduction is an additional design consideration in the current catalyticprocessors fuel cell cycles
1 Introduction
During our earlier IASTED papers (PGRES lsquo02 Marina DelRay CA modeling and simulation lsquo03 Palm Springs CA)we had the opportunity to describe and analyze preliminaryresults on catalytic processors for the steam-reforming reac-tion of methane and natural gas for use in fuel cell systemssuch as SOFC units [1 2]
The current paper is a continuation of that research effortby giving emphasis in the so-called ldquolandfill gas powerrdquo andldquobioenergyrdquo systems We study the use of landfill gases(landfill-generated feedstocks) as sources for electricity andheat generation using fuel cells of the SOFC type
With the introduction of landfill-based gases rich inmethane for the production of intermediate synthesis gaswe propose an attractive process in ldquogreen powerrdquo andldquobiogaslandfill energyrdquo based systems
A current emphasis on the development and commer-cialization of such systems for electricity and heat generationapplications is observed Such installations start to exist
currently mainly in US Europe Japan China and otherdeveloping countries
The above presented energy systems require the develop-ment and use of an effective catalytic reformer utilizing activemetals such as Ni Ru Rh Cr or bimetallic combinations ofthose Earthmetal enrichment in the catalyst such as with CaMg La and K promotes the catalyst stability on stream andminimizes deactivation from carbon deposition especially inthe reactor inlet (deactivation propensity is especially highat the reactor inlet due to the lack of hydrogen gas which isgenerated during the course of the reaction) [3ndash9]
The aforementioned reformer can be a fixed-bed catalyticreactor or a permreactor using membrane-type materials asreactor walls The introduction of a permreactor leads to atwo-outlet reaction system which carries the synthesis gasproduct at different compositions The permeate stream isricher in hydrogen and less rich in carbon oxides by the useof hydrogen selective membranes such as microporous inor-ganics (eg alumina titania based) or metal alloys (PdAgPdCu) Moreover one or both of the outlet gas streams
2 Journal of Renewable Energy
can be used as feed in the accompanied fuel cellSOFC Theutilization of the permreactor increases the conversion of thereactant landfill gases in the reactor due to the separationof products This increased shift in conversion yields therequired quantity of synthesis gas product for the fuel cellat a lower operation temperature than the counterpart fixed-bed (impermeable) reactor [10 11] Process operation at alower temperature is beneficial for increasing the reactor andcatalyst life times and for reducing the endothermic heatingload (Btuhr) of the endothermic reformer
Following we present a design with emphasis in bothreformer configurations for the generation and delivery ofhydrogen-rich synthesis gas from landfill gas resources intothe accompanied solid oxide fuel cell
2 Process and Fuel CellAnalysis and Description
The catalytic reaction of reformingmethane or higher hydro-carbonswith the steam is a key catalysis process for producinghigh-quality hydrogen or synthesis gas in an economicalway [3ndash6 8 12 13] As it is known synthesis gas containshydrogen mixed with carbon monoxide and possibly carbondioxide as well The aforementioned reforming processes areendothermic taking place under similar catalysis metals asthose described before
Utilization of landfill-based feedstocks as the reactinggases provides a methane- (CH
4-) rich feed in the reformer
which is converted with steam into an H2- and CO-rich
mixture Moreover the exit hydrogen-rich gas is going as fuelin the anode of the solid oxide fuel cell The reactions belowtake place in the reformer by adding steam in the landfillfeedstock as the oxidant as shownCH4+H2Olarrrarr CO + 3H
2(ΔHo298
= +2061 kJmol)
(methane-steam reforming reaction)(1)
CO +H2Olarrrarr CO
2+H2
(ΔHo298
= minus4115 kJmol)
(water-gas shift reaction)(2)
However it is assumed that the landfill gas has beenpurified before entering into the reformer from the variousimpurities and the contained carbon dioxide gas The carbondioxide gas can be separated using several options such asmembrane-based separations or pressure-swing adsorption[10 11] However some CO
2can be flown within the reactor
and reformed catalytically with the methaneIn continuation the interconnected solid oxide fuel cell
(SOFC) produces electricity by the following dual electro-chemical reaction
In the SOFC anodeH2+O2minus 997888rarr H
2O + 2eminus
CO +O2minus 997888rarr CO2+ 2eminus
(3)
In the SOFC cathode
O2+ 4eminus 997888rarr 2O2minus (4)
The overall reaction is
H2+ CO +O
2997888rarr CO
2+H2O (5)
A portion of the hot gas exiting from the fuel cell can bediverted in the shellside of the membrane reactor to providethe endothermic heat for running the reformer
The corresponding mathematical modeling of themethane-steam reformer for a steady-state fixed-bed catalyticreactor including the species reaction terms in the massbalance equation is as it is presented
119889119883119860
119889119911
= (
1205871198892
119879
4119899119860119900
)120588119861119877119860 (6)
Species 119860 can be any of the reactants and products of thereactions (1) and (2)
with
119877CH4
= minus 1198771
119877CO2
= 1198772 119877CO = 1198771 minus 1198772
119877H2
= 31198771+ 1198772 119877H
2O = minus 1198771 minus 1198772
(7)
where 1198771and 119877
2are the heterogeneous reaction rates of the
reactions (1) and (2) given aboveIn addition the thermal balance in a nonisothermal refor-
mer is given as follows
119889119879119879
119889119911
= (
1205871198892
119879
4
)(
1
1198981015840119888119901
)120588119861[(minusΔ119867
1
119903) 1198771+ (minusΔ119867
2
r ) 1198772]
minus4 (
119880
119889119879
) (119879119879minus 119879119878)
(8)
Moreover the reformer pressure balance which describesthe pressure drop along the fixed bed of catalyst is given asfollows
minus119889119875119879
119889119911
=
21198911205881198921199062
119904
119892119888119889119901
(9)
and the above equations are complemented by initial condi-tions as shown at 119911 = 0 (reactor inlet)
119883119860= 0 119879
119879= 119879119900 119875119879= 119875119879119900
(10)
Amore specific analysis of the model its parameters andtheir variation is discussed in earlier communications [10ndash12]
The above system of governing (6) (8) and (9) is inte-grated numerically as an initial value problem to providethe reactant conversions product yields reactor temperatureand pressure along the axial length and to obtain the axialprofiles of these variables and their values at the reactor exit
With the use of an inorganic permreactor as the maincatalytic processing unit to convert landfill gas feedstocks
Journal of Renewable Energy 3
into fuel cell gas the above design equations are modifiedaccordingly to include the permeation effects via the mem-brane of the different components Moreover the followingmathematical part has to be added at the right hand side of (6)to account for the permeation effects within themass balanceequations
minus(
2120587
119899119879
119860119900
)119875119860119890[
119901119879
119860minus 119901119878
119860
ln (11990311199032)
] (11)
wherein 119875119860119890
(gmolssdotcmsdotatm) is the effective permeabilitycoefficient of species 119860 via the catalytic or noncatalytic(blank) membrane It is worthy to declare that in ourearlier experimental reaction studies we utilized mesoporousaluminum oxide membranes having a thin permselectivelayer (3ndash5120583m thickness 50 porosity) with 40ndash50 A porediameter [3 10 11 14]Themembrane is amultilayer structuresupported on an a-alumina support (15ndash20mm thickness40ndash45 porosity and 10ndash15 120583m pore diameter) When apermreactor is used the corresponding mass temperatureand pressure variation equations are written as well for thegas which permeates via the membrane wall material andflows in the permeate side (119878) of the membrane reactor It isassumed that there are no reactions occurring in the permeatemembrane side An analysis of themodel for the permreactorhas been described as well in earlier communications [10ndash12]
By employing (6) (8) (9) and (11) within the modelingprocedure a complete reactor analysis is obtained for the twodifferent reformer configurations Solution of the equationsis obtained numerically by using an initial value integrationtechnique for ordinary differential equations with variablestepsize to ensure higher accuracy (implicit Adams-Moultonmethod) [10 11]
In our earlier papers we have described and analyzedthe reaction separation (ie permeation) and process (con-version yield) characteristics of permreactors (membranebased catalytic reactors) and related processes for methane-steam reforming water-gas shift and methane carbon diox-ide reforming reactions including catalysis and membranematerials characteristics The main categories of reactorsdescribed were membrane reformers which were utilized assingle permreactor [10] permreactor-separator in series orreactor-separator in series and permeactor-permeactor inseries [3 10 13 14]
These effective and versatile catalytic processes wereapplied for pure hydrogen (H
2) H2and CO
2 or H
2and
CO (syn-gas) generation to be used as fuel gas for powergeneration or as synthesis gas for the production of specialtychemicals (such as methanol and higher hydrocarbons) [10]Several key types of membrane reformers were examinedbased on the location of the fixed catalytic bed and the inert orcatalytic nature of the inorganic (alumina-based) membranetube Computationalmodeling of the described permreform-ers was running indicating performance measures (reactantconversion product yield) versus variation of intrinsic modelparameters (reactor space time reaction temperature andpressure feed composition sweep gas to feed gas ratio)Through the models we also obtain performance measures
Table 1 Specifications of a representative small landfill gas-reforming SOFC system for electricity and heat cogeneration
Landfill gas production volume 3600m3dayMethane production volumeabout 2520m3 CH4dayTotal energy generation 26100 kWhdayElectricity generationSOFC (60min) 15660 kWhdayHeat generation (30min) 7830 kWhdayWaste heat (about 10) 2610 kWhdayAnnual electricity generation 5716 MWhyearSale price per MWh (to DEH GreekElectricity Authority) 73 EuroMWh
Income about 417000 EuroyearAnnual heat generation 2858MWhyear
under new operating conditions leading to new energy andchemical process applications [3 10 14]
Moreover the interconnected or integrated solid oxidefuel cell is fed directly by the fuel gas generated by thedescribed reformers The focus of our studies goes to solu-tions in a number of problems associated with the installa-tion operation and mass energy conservation of the entirefuel cell and membrane-processing unit
The economic feasibility of the overall fuel cell installationis correlatedwith high efficiency (eg 45ndash65 for advancedunits) and high current density output (Acm2) increasedsystem reliability for continuous dispersed power generationand reduced plant installation operation and maintenancecost Such goals combined with virtual elimination of pol-lution by the use of fuel cells in stationary (eg centraland remote power stations) and mobiletransportation (egautomobile) sources make this technology highly applicableand attractive Finally clean fuel cell power minimizes NOxCO and hydrocarbon species in the emissions
3 Results and Discussion
Proper utilization of landfill gas in the reformer comingfrom landfill sites presents an innovative approach for directuse of those feedstocks for power generation [15] Thereare essential resources of these feedstocks today and theiraccumulation in land is growing Gas coming out from theproper treatment of landfills and frommunicipal sewage andsludge sites is rich in methane and constitutes the propermixture for direct conversion into the described reformer-SOFC systemThrough the catalytic conversion of these gasesin the reformerwe can obtain yields of hydrogen-richmixturefor properly powering the interconnected SOFC As the flowrates of the landfill gas increase (for larger sites and treatmentsystems) a larger capacity reformer and fuel cell are requiredto handle the conversion consecutively the final SOFCpoweroutput (kWcm2) increases as well
The catalyst used in the experiments described below is a15 NiOmixed with calcium and magnesium and supportedon aluminaThe catalyst characteristics are shown in Table 3
4 Journal of Renewable Energy
Table 2 Membrane characteristics
Layer Pore diameter Thickness1 40 A 5120583m2 020 120583m 30 120583m3 08 120583m 50 120583m4 support 10ndash15 120583m 15ndash20mm
Table 3 Catalyst characteristics
Pore volume 03 ccgSurface area 50m2gPorosity 55Composition 15wt
90
80
70
60
50
40
30
20
10
0
350 400 450 500 550 600 650
Met
hane
conv
ersio
n (
)
Membrane reactor experiment sweep Ar 011 gmolehrMembrane reactor modelPlug flow reactor experimentEquilibrium conversion
Temperature (∘C)
Figure 1 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous operationTotal methane conversion data (119875
119879119900
= 168 atm space time =480 gcatsdothrgmoleCH4)
The system of the apparatus used in the experimentsreported here consists of mass-flow controllers a bubblerto generate steam for the reaction and the reactor housingwherein the plug-flow reactor or the membrane reactor wasplaced The reactor is accompanied with thermocouples toread the temperature and pressure transducers to read thepressure At the exit of the reactor apparatus there are steamtraps and a gas chromatograph to analyze the exit streamThe gas chromatograph operates in the TCD mode and isequipped with a porapack Q column for the gas analysis
Figure 1 below describes a set of experiments for thetwo reformer configurationsThemembrane reformer showsbettermethane conversions than the nonmembrane reformerfor all the range of temperatures examined experimentally(ie 400ndash600∘C) At low temperatures we avoid coke for-mation and prolong the catalyst activity The membranecharacteristics are shown in Table 2
80
70
60
50
40
30
20
10
0
Carb
on d
ioxi
de y
ield
()
350 400 450 500 550 600 650
Membrane reactor experiment sweep Ar 011 gmolehrMembrane reactor modelPlug flow reactor experimentEquilibrium yield
Temperature (∘C)
Figure 2 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous opera-tion Carbon dioxide yield data (119875
119879119900
= 168 atm space time =480 gcatsdothrgmoleCH4)
Ar gas was flown in the permeate side of the membranereactor to sweep the permeating gas The feed compositionis CH
4 H2O H2= 1 4 020 The residence time of the
reactor remained constant at 480 gsdothrgmolCH4 for all theexperiments reported here The pressure at the reaction sidewas kept constant at 119875
119879= 10 plusmn 05 psig There is also a good
agreement of the developed model with the experimentalmembrane-reactor conversions Moreover most of the con-versions obtained with the membrane reformer are betterthan the ones calculated at the equilibrium state
The equilibrium calculations are based on the maximumthermodynamic equilibrium conversion that the specificreaction system can achieve according to the operatingparameters and conditions given They are calculated bythe corresponding thermodynamic equilibrium equationsThe results are shown in the figures as equilibrium yieldsand conversionsThe permeability (permeability coefficienttimes102 molmsdotssdotPa) is given in Table 4 They are experimentalmeasurements at 35∘C for unmodified alumina membrane
The reactor is a tubular one with the ceramic membraneinside Its length is 20 cm and the diameter is 1 cm with feedflow rate 011 gmolehr The reactor schematic is shown inFigure 8
Figure 2 is indicative of the carbon dioxide yieldsobtained with the membrane reformer as function of thereaction temperature These yields are better than thoseobtained with the nonmembrane type reformer and theequilibrium calculated yields The results of Figure 2 areindicative of the yield of the water-gas shift reaction (reaction(2)) However our future efforts seek to minimize the effectof reaction (2) and promote the effect of reaction (1) only In
Journal of Renewable Energy 5
Table 4 Permeability coefficient times 102 molmsPa Experimental measurements at 35∘C for unmodified alumina membrane
Average transmembrane pressure KPa Hydrogen Methane Carbon monoxide Carbon dioxide Argon105 168 76 54 50 42117 179 81 57 56 45135 181 83 60 59 52
90
80
70
60
50
40
30
20
10 15 20 25 30 35 40 45 50
Met
hane
conv
ersio
n (
)
Membrane reactor experiment no sweep gasMembrane reactor modelPlug flow reactor experimentPlug flow reactor modelEquilibrium conversion
119879 = 550∘C
Space time (gr(cat)middothrgmoleCH4 )
Figure 3 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous operationTotal methane conversion data (119875
119879119900
= 168 atm feed compositionCH4 H2O H2= 1 4 02
this way the flow rate of the fuel-gas product going into thefuel cellSOFC system is maximized based on reactions (5)
Figure 3 next shows the effect of the space time of thereactor on the methane conversion
The temperature is fixed at 550∘CThemembrane reactoroffers better conversions and yields than the nonmembranereactor as also shown in Figures 3 and 4 The membranereactor conversions are showed to exceed the conventionalcatalytic plug-flow-reactor conversions for all the space timesexamined in this experimentThis is attributed to the effect ofthemembraneThemembrane offers primarily the separationof hydrogen an effect that increases the conversion above theequilibrium conversionThe computational model describedabove agrees well with the membrane reactor data andthe conventional catalytic plug-flow reactor data Both theexperimental membrane reactor yield data and the model arehigher than the plug-flow reactor data and the equilibriumcalculated CO
2yield data
It is characteristic that most of the points taken with themembrane reactor operation exceed in methane conversionmeasure the corresponding points taken under regular plugflow reactor operationWe should point out that both reactors
90
80
70
60
50
40
30
20
10
0
Carb
on d
ioxi
de y
ield
()
10 15 20 25 30 35 40 45 50
Membrane reactor experiment no sweep gasMembrane reactor modelPlug flow reactor experimentPlug flow reactor modelEquilibrium yield
119879 = 550∘C
Space time (gr(cat)middothrgmoleCH4 )
Figure 4 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous operationCarbon dioxide yield data (119875
119879119900
= 168 atm feed compositionCH4 H2O H2= 1 4 020)
are catalytic and are filled with catalyst particles Also weshould point out that the alumina-based membrane used inthese experiments was blank (not rendered catalytic) It isalso characteristic that the membrane reactor points exceedthe equilibrium conversion calculated at the respective reac-tion side conditions Moreover the computational modeldescribed earlier which simulates the membrane-reactoroperation shows a good agreement with the experimentallymeasured membrane methane conversions and CO
2yields
under the same reaction conditions Thus the membranereformer is operation show to be beneficial in producingmore synthesis gas (amixture of hydrogen and carbon oxides)than the counterpart conventional plug flow reformer
We are also presenting below two figures relating with themodeling and simulation of the methanelandfill gas-steamreforming reactor We have used the model of (6) (8) (9)and (11) to simulate the permeable reformer [10] PBMR inthese plots stands for a packed bed membrane reactor
Next Figure 5 shows the dimensionless molar flow rateof hydrogen steam and methane along the reaction side ortubeside of the membrane reactor The molar flow rate forhydrogen passes through a maximum at about the middle
6 Journal of Renewable Energy
08
07
06
05
04
03
02
01
0
Dim
ensio
nles
s mol
ar fl
owra
te
0 01 02 03 04 05 06 07 08 09 1
MethaneSteamHydrogen
Dimensionless distance (zL)
Reaction side (119879 = 450∘C)
Figure 5Modeling results of landfill gas-steam reformers for syngasproduction and SOFC continuous operation Molar flowrate data inthe reaction side (tubeside) (119875
119879119900
= 168 atm feed composition CH4
H2O H2= 1 4 020)
0 01 02 03 04 05 06 07 08 09 1
045
04
035
03
025
02
015
01
005
0
Dim
ensio
nles
s mol
ar fl
owra
te
MethaneSteamHydrogen
Dimensionless distance (zL)
Separation side (119879 = 450∘C)
Figure 6 Modeling results of landfill gas-steam reformers forsyngas production and SOFC continuous operation Molar flowratedata in the separation side (119875
119879119900
= 168 atm feed compositionCH4 H2O H2= 1 4 020)
axial length of the reactor The molar flowrates for steam andmethane decreasemonotonically along the axial length of thereactor
Figure 6 shows the dimensionless molar flow rate ofhydrogen steam and methane along the separation side orshellside of themembrane reactor In this case themolar flow
055
05
045
04
035
03
025
02
015
01
350 400 450 500 550 600 650
Temperature (∘C)
Calculated equilibrium yieldReactor with shellside closedMembrane reactor (no sweep gas)Membrane reactor model
Tota
l hyd
roge
n yi
eld
(gm
ole
hr)
Figure 7 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous operationTotal hydrogen yield data
rates for hydrogen steam and methane increase monotoni-cally along the axial length of the reactor
Finally Figure 7 shows the combined hydrogen yieldobtained with the two types of reactors The membranetype reformer offers better hydrogen yields than the non-membrane type reformer This is shown both with theexperimental and modeling results in Figure 7 It is thereforebeneficial to use the membrane reformer in the flow chart ofthis process to accomplish the operation
Moreover Table 1 below shows a summary of spec-ifications from a landfill-gas-processing plant for energycogeneration (landfill gas is coming from a concentratedlandfill site [16]) The table provides details on the energeticdistribution outcome of the entire plantThis table is given forcomparison purposes in order to evaluate the potential of thenewly described landfill gas to SOFC unit using the describedmembrane reactor and conventional reactor technologies Itis characteristic that the installed fuel cellSOFC can provideelectricity at a higher degree of efficiency than the respectivegas engine or gas turbine
4 Conclusions
It is shownhere that high temperature SOFCsfuel cells can becombined with reforming operations of landfill-based gasesThe referred SOFCs systems can operate in series or areintegrated with a catalytic reformer or membrane reformerwhich convert landfill gas into fuel-gas product at variousoperating conditions To be more specific these feedstockgases are rich in CH
4and are converted into an H
2 CO
and CO2mixture suitable for the continuous operation
of the SOFC unit The reformers studied here have been
Journal of Renewable Energy 7
Stainless steel casing ThermocoupleThermocouple
Thermocouples
Sweep gas in
Compression fitting
Product gases out
Graphitized string
Feedgases in Product
gases out
Alumina tube(membrane + support)
Figure 8 Ceramic membrane reactor
also studied by computational models taking into accountthe reaction and hydrogen separation in the permeablereformers Essential operating conditions in the permeablereformers have been simulated by the mathematical modelsThe experimental membrane reformer shows to offer higheryields than the nonmembrane type reformer for a number ofoperating conditions
It is worthy to notice that important distributed powergeneration within a wider power grid can be accomplishedwith this operation being able to cover the local needsof municipal and remote areas Fuel cell power relates tothe reformer conversion and the efficient utilization of thesyngas by the fuel cell The waste heat from the conversionof syngas to electricity can be descreased through the fuelcell operation and specifically through the operation of highefficiency SOFCs Fuel cell (SOFCs) continuous operationand power generation from landfill gas can lead to pollutionminimization higher power density and increased efficiency(reduced waste heat) in comparison with conventional powersystems
References
[1] Z Ziaka and S Vasileiadis ldquoCatalytic reforming -shift proces-sors for hydrogen generation and continuous fuel cell opera-tionrdquo in Proceedings of IASTED-Power and Energy Systems pp360ndash365 Marina Del Ray Calif USA May 2002
[2] S Vasileiadis and Z Ziaka-Vasileiadou ldquoBiomass reformingprocess for integrated solid oxide-fuel cell power generationrdquoChemical Engineering Science vol 59 no 22-23 pp 4853ndash48592004
[3] S Vasileiadis and Z Ziaka ldquoAlternative generation of H2 CO
and H2 CO2mixtures from steam-carbon dioxide reforming
of methane and the water gas shift with permeable (membrane)reactorsrdquo Chemical Engineering Communications vol 176 pp247ndash252 1999
[4] J Xu and G F Froment ldquoMethane steam reforming methana-tion and water-gas shift I Intrinsic kineticsrdquo AIChE Journalvol 35 no 1 pp 88ndash96 1989
[5] J P van Hook ldquoMethane-steam reformingrdquo Catalysis ReviewsScience and Engineering vol 21 no 1 pp 1ndash51 1980
[6] J R Rostrup-Nielsen ldquoSulfur-passivated nickel catalysts forcarbon-free steam reforming of methanerdquo Journal of Catalysisvol 85 no 1 pp 31ndash43 1984
[7] J R Rostrup-Nielsen ldquoCoking on nickel catalysts for steamreforming of hydrocarbonsrdquo Journal of Catalysis vol 33 no 2pp 184ndash201 1974
[8] J T Richardson and S A Paripatyadar ldquoCarbon dioxidereforming of methane with supported rhodiumrdquoApplied Catal-ysis vol 61 no 1 pp 293ndash309 1990
[9] E Ruckenstein and Y H Hu ldquoCombination of CO2reforming
and partial oxidation of methane over NiOMgO solid solutioncatalystsrdquo Industrial amp Engineering Chemistry Research vol 37no 5 pp 1744ndash1747 1998
[10] Z D Ziaka and S P Vasileiadis Reactors for Fuel Cells andEnvironmental Energy Systems Xlibris Publishing IndianapolisInd USA 2009
[11] S P Vasileiadis and Z D Ziaka ldquoEnvironmentally benignhydrocarbon processing applications of single and integratedpermreactorsrdquo in Reaction Engineering for Pollution Preventionpp 247ndash304 Elsevier Science Philadelphia Pa USA 2000
[12] Z D Ziaka and S P Vasileiadis ldquoReactor-membrane permeatorcascade for enhanced production and recovery of H2 andCO2 from the catalytic methane-steam reforming reactionrdquoChemical Engineering Communications vol 156 pp 161ndash2001996
[13] D L Klass Biomass for Renewable Energy Fuels and ChemicalsAcademic Press San Diego Calif USA 1988
[14] S Vasileiadis and Z Ziaka ldquoEfficient catalytic reactors-pro-cessors for fuel cells and synthesis applicationsrdquo in Proceedingsof the 17th International Symposium on Chemical ReactionEngineering Hong Kong August 2002 paper no 13
8 Journal of Renewable Energy
[15] R Rautenbach and K Welsch ldquoTreatment of landfill gas bygas permeationmdashpilot plant results and comparison to alterna-tivesrdquo Journal of Membrane Science vol 87 no 1-2 pp 107ndash1181994
[16] M Tsimpa Biogas usages in Greece for energy generationtrends and opportunities [MS thesis] HellenicOpenUniversityPatras Greece 2010
TribologyAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
FuelsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofPetroleum Engineering
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Industrial EngineeringJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Power ElectronicsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
CombustionJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Renewable Energy
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
StructuresJournal of
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nuclear InstallationsScience and Technology of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solar EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Wind EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nuclear EnergyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
High Energy PhysicsAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
2 Journal of Renewable Energy
can be used as feed in the accompanied fuel cellSOFC Theutilization of the permreactor increases the conversion of thereactant landfill gases in the reactor due to the separationof products This increased shift in conversion yields therequired quantity of synthesis gas product for the fuel cellat a lower operation temperature than the counterpart fixed-bed (impermeable) reactor [10 11] Process operation at alower temperature is beneficial for increasing the reactor andcatalyst life times and for reducing the endothermic heatingload (Btuhr) of the endothermic reformer
Following we present a design with emphasis in bothreformer configurations for the generation and delivery ofhydrogen-rich synthesis gas from landfill gas resources intothe accompanied solid oxide fuel cell
2 Process and Fuel CellAnalysis and Description
The catalytic reaction of reformingmethane or higher hydro-carbonswith the steam is a key catalysis process for producinghigh-quality hydrogen or synthesis gas in an economicalway [3ndash6 8 12 13] As it is known synthesis gas containshydrogen mixed with carbon monoxide and possibly carbondioxide as well The aforementioned reforming processes areendothermic taking place under similar catalysis metals asthose described before
Utilization of landfill-based feedstocks as the reactinggases provides a methane- (CH
4-) rich feed in the reformer
which is converted with steam into an H2- and CO-rich
mixture Moreover the exit hydrogen-rich gas is going as fuelin the anode of the solid oxide fuel cell The reactions belowtake place in the reformer by adding steam in the landfillfeedstock as the oxidant as shownCH4+H2Olarrrarr CO + 3H
2(ΔHo298
= +2061 kJmol)
(methane-steam reforming reaction)(1)
CO +H2Olarrrarr CO
2+H2
(ΔHo298
= minus4115 kJmol)
(water-gas shift reaction)(2)
However it is assumed that the landfill gas has beenpurified before entering into the reformer from the variousimpurities and the contained carbon dioxide gas The carbondioxide gas can be separated using several options such asmembrane-based separations or pressure-swing adsorption[10 11] However some CO
2can be flown within the reactor
and reformed catalytically with the methaneIn continuation the interconnected solid oxide fuel cell
(SOFC) produces electricity by the following dual electro-chemical reaction
In the SOFC anodeH2+O2minus 997888rarr H
2O + 2eminus
CO +O2minus 997888rarr CO2+ 2eminus
(3)
In the SOFC cathode
O2+ 4eminus 997888rarr 2O2minus (4)
The overall reaction is
H2+ CO +O
2997888rarr CO
2+H2O (5)
A portion of the hot gas exiting from the fuel cell can bediverted in the shellside of the membrane reactor to providethe endothermic heat for running the reformer
The corresponding mathematical modeling of themethane-steam reformer for a steady-state fixed-bed catalyticreactor including the species reaction terms in the massbalance equation is as it is presented
119889119883119860
119889119911
= (
1205871198892
119879
4119899119860119900
)120588119861119877119860 (6)
Species 119860 can be any of the reactants and products of thereactions (1) and (2)
with
119877CH4
= minus 1198771
119877CO2
= 1198772 119877CO = 1198771 minus 1198772
119877H2
= 31198771+ 1198772 119877H
2O = minus 1198771 minus 1198772
(7)
where 1198771and 119877
2are the heterogeneous reaction rates of the
reactions (1) and (2) given aboveIn addition the thermal balance in a nonisothermal refor-
mer is given as follows
119889119879119879
119889119911
= (
1205871198892
119879
4
)(
1
1198981015840119888119901
)120588119861[(minusΔ119867
1
119903) 1198771+ (minusΔ119867
2
r ) 1198772]
minus4 (
119880
119889119879
) (119879119879minus 119879119878)
(8)
Moreover the reformer pressure balance which describesthe pressure drop along the fixed bed of catalyst is given asfollows
minus119889119875119879
119889119911
=
21198911205881198921199062
119904
119892119888119889119901
(9)
and the above equations are complemented by initial condi-tions as shown at 119911 = 0 (reactor inlet)
119883119860= 0 119879
119879= 119879119900 119875119879= 119875119879119900
(10)
Amore specific analysis of the model its parameters andtheir variation is discussed in earlier communications [10ndash12]
The above system of governing (6) (8) and (9) is inte-grated numerically as an initial value problem to providethe reactant conversions product yields reactor temperatureand pressure along the axial length and to obtain the axialprofiles of these variables and their values at the reactor exit
With the use of an inorganic permreactor as the maincatalytic processing unit to convert landfill gas feedstocks
Journal of Renewable Energy 3
into fuel cell gas the above design equations are modifiedaccordingly to include the permeation effects via the mem-brane of the different components Moreover the followingmathematical part has to be added at the right hand side of (6)to account for the permeation effects within themass balanceequations
minus(
2120587
119899119879
119860119900
)119875119860119890[
119901119879
119860minus 119901119878
119860
ln (11990311199032)
] (11)
wherein 119875119860119890
(gmolssdotcmsdotatm) is the effective permeabilitycoefficient of species 119860 via the catalytic or noncatalytic(blank) membrane It is worthy to declare that in ourearlier experimental reaction studies we utilized mesoporousaluminum oxide membranes having a thin permselectivelayer (3ndash5120583m thickness 50 porosity) with 40ndash50 A porediameter [3 10 11 14]Themembrane is amultilayer structuresupported on an a-alumina support (15ndash20mm thickness40ndash45 porosity and 10ndash15 120583m pore diameter) When apermreactor is used the corresponding mass temperatureand pressure variation equations are written as well for thegas which permeates via the membrane wall material andflows in the permeate side (119878) of the membrane reactor It isassumed that there are no reactions occurring in the permeatemembrane side An analysis of themodel for the permreactorhas been described as well in earlier communications [10ndash12]
By employing (6) (8) (9) and (11) within the modelingprocedure a complete reactor analysis is obtained for the twodifferent reformer configurations Solution of the equationsis obtained numerically by using an initial value integrationtechnique for ordinary differential equations with variablestepsize to ensure higher accuracy (implicit Adams-Moultonmethod) [10 11]
In our earlier papers we have described and analyzedthe reaction separation (ie permeation) and process (con-version yield) characteristics of permreactors (membranebased catalytic reactors) and related processes for methane-steam reforming water-gas shift and methane carbon diox-ide reforming reactions including catalysis and membranematerials characteristics The main categories of reactorsdescribed were membrane reformers which were utilized assingle permreactor [10] permreactor-separator in series orreactor-separator in series and permeactor-permeactor inseries [3 10 13 14]
These effective and versatile catalytic processes wereapplied for pure hydrogen (H
2) H2and CO
2 or H
2and
CO (syn-gas) generation to be used as fuel gas for powergeneration or as synthesis gas for the production of specialtychemicals (such as methanol and higher hydrocarbons) [10]Several key types of membrane reformers were examinedbased on the location of the fixed catalytic bed and the inert orcatalytic nature of the inorganic (alumina-based) membranetube Computationalmodeling of the described permreform-ers was running indicating performance measures (reactantconversion product yield) versus variation of intrinsic modelparameters (reactor space time reaction temperature andpressure feed composition sweep gas to feed gas ratio)Through the models we also obtain performance measures
Table 1 Specifications of a representative small landfill gas-reforming SOFC system for electricity and heat cogeneration
Landfill gas production volume 3600m3dayMethane production volumeabout 2520m3 CH4dayTotal energy generation 26100 kWhdayElectricity generationSOFC (60min) 15660 kWhdayHeat generation (30min) 7830 kWhdayWaste heat (about 10) 2610 kWhdayAnnual electricity generation 5716 MWhyearSale price per MWh (to DEH GreekElectricity Authority) 73 EuroMWh
Income about 417000 EuroyearAnnual heat generation 2858MWhyear
under new operating conditions leading to new energy andchemical process applications [3 10 14]
Moreover the interconnected or integrated solid oxidefuel cell is fed directly by the fuel gas generated by thedescribed reformers The focus of our studies goes to solu-tions in a number of problems associated with the installa-tion operation and mass energy conservation of the entirefuel cell and membrane-processing unit
The economic feasibility of the overall fuel cell installationis correlatedwith high efficiency (eg 45ndash65 for advancedunits) and high current density output (Acm2) increasedsystem reliability for continuous dispersed power generationand reduced plant installation operation and maintenancecost Such goals combined with virtual elimination of pol-lution by the use of fuel cells in stationary (eg centraland remote power stations) and mobiletransportation (egautomobile) sources make this technology highly applicableand attractive Finally clean fuel cell power minimizes NOxCO and hydrocarbon species in the emissions
3 Results and Discussion
Proper utilization of landfill gas in the reformer comingfrom landfill sites presents an innovative approach for directuse of those feedstocks for power generation [15] Thereare essential resources of these feedstocks today and theiraccumulation in land is growing Gas coming out from theproper treatment of landfills and frommunicipal sewage andsludge sites is rich in methane and constitutes the propermixture for direct conversion into the described reformer-SOFC systemThrough the catalytic conversion of these gasesin the reformerwe can obtain yields of hydrogen-richmixturefor properly powering the interconnected SOFC As the flowrates of the landfill gas increase (for larger sites and treatmentsystems) a larger capacity reformer and fuel cell are requiredto handle the conversion consecutively the final SOFCpoweroutput (kWcm2) increases as well
The catalyst used in the experiments described below is a15 NiOmixed with calcium and magnesium and supportedon aluminaThe catalyst characteristics are shown in Table 3
4 Journal of Renewable Energy
Table 2 Membrane characteristics
Layer Pore diameter Thickness1 40 A 5120583m2 020 120583m 30 120583m3 08 120583m 50 120583m4 support 10ndash15 120583m 15ndash20mm
Table 3 Catalyst characteristics
Pore volume 03 ccgSurface area 50m2gPorosity 55Composition 15wt
90
80
70
60
50
40
30
20
10
0
350 400 450 500 550 600 650
Met
hane
conv
ersio
n (
)
Membrane reactor experiment sweep Ar 011 gmolehrMembrane reactor modelPlug flow reactor experimentEquilibrium conversion
Temperature (∘C)
Figure 1 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous operationTotal methane conversion data (119875
119879119900
= 168 atm space time =480 gcatsdothrgmoleCH4)
The system of the apparatus used in the experimentsreported here consists of mass-flow controllers a bubblerto generate steam for the reaction and the reactor housingwherein the plug-flow reactor or the membrane reactor wasplaced The reactor is accompanied with thermocouples toread the temperature and pressure transducers to read thepressure At the exit of the reactor apparatus there are steamtraps and a gas chromatograph to analyze the exit streamThe gas chromatograph operates in the TCD mode and isequipped with a porapack Q column for the gas analysis
Figure 1 below describes a set of experiments for thetwo reformer configurationsThemembrane reformer showsbettermethane conversions than the nonmembrane reformerfor all the range of temperatures examined experimentally(ie 400ndash600∘C) At low temperatures we avoid coke for-mation and prolong the catalyst activity The membranecharacteristics are shown in Table 2
80
70
60
50
40
30
20
10
0
Carb
on d
ioxi
de y
ield
()
350 400 450 500 550 600 650
Membrane reactor experiment sweep Ar 011 gmolehrMembrane reactor modelPlug flow reactor experimentEquilibrium yield
Temperature (∘C)
Figure 2 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous opera-tion Carbon dioxide yield data (119875
119879119900
= 168 atm space time =480 gcatsdothrgmoleCH4)
Ar gas was flown in the permeate side of the membranereactor to sweep the permeating gas The feed compositionis CH
4 H2O H2= 1 4 020 The residence time of the
reactor remained constant at 480 gsdothrgmolCH4 for all theexperiments reported here The pressure at the reaction sidewas kept constant at 119875
119879= 10 plusmn 05 psig There is also a good
agreement of the developed model with the experimentalmembrane-reactor conversions Moreover most of the con-versions obtained with the membrane reformer are betterthan the ones calculated at the equilibrium state
The equilibrium calculations are based on the maximumthermodynamic equilibrium conversion that the specificreaction system can achieve according to the operatingparameters and conditions given They are calculated bythe corresponding thermodynamic equilibrium equationsThe results are shown in the figures as equilibrium yieldsand conversionsThe permeability (permeability coefficienttimes102 molmsdotssdotPa) is given in Table 4 They are experimentalmeasurements at 35∘C for unmodified alumina membrane
The reactor is a tubular one with the ceramic membraneinside Its length is 20 cm and the diameter is 1 cm with feedflow rate 011 gmolehr The reactor schematic is shown inFigure 8
Figure 2 is indicative of the carbon dioxide yieldsobtained with the membrane reformer as function of thereaction temperature These yields are better than thoseobtained with the nonmembrane type reformer and theequilibrium calculated yields The results of Figure 2 areindicative of the yield of the water-gas shift reaction (reaction(2)) However our future efforts seek to minimize the effectof reaction (2) and promote the effect of reaction (1) only In
Journal of Renewable Energy 5
Table 4 Permeability coefficient times 102 molmsPa Experimental measurements at 35∘C for unmodified alumina membrane
Average transmembrane pressure KPa Hydrogen Methane Carbon monoxide Carbon dioxide Argon105 168 76 54 50 42117 179 81 57 56 45135 181 83 60 59 52
90
80
70
60
50
40
30
20
10 15 20 25 30 35 40 45 50
Met
hane
conv
ersio
n (
)
Membrane reactor experiment no sweep gasMembrane reactor modelPlug flow reactor experimentPlug flow reactor modelEquilibrium conversion
119879 = 550∘C
Space time (gr(cat)middothrgmoleCH4 )
Figure 3 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous operationTotal methane conversion data (119875
119879119900
= 168 atm feed compositionCH4 H2O H2= 1 4 02
this way the flow rate of the fuel-gas product going into thefuel cellSOFC system is maximized based on reactions (5)
Figure 3 next shows the effect of the space time of thereactor on the methane conversion
The temperature is fixed at 550∘CThemembrane reactoroffers better conversions and yields than the nonmembranereactor as also shown in Figures 3 and 4 The membranereactor conversions are showed to exceed the conventionalcatalytic plug-flow-reactor conversions for all the space timesexamined in this experimentThis is attributed to the effect ofthemembraneThemembrane offers primarily the separationof hydrogen an effect that increases the conversion above theequilibrium conversionThe computational model describedabove agrees well with the membrane reactor data andthe conventional catalytic plug-flow reactor data Both theexperimental membrane reactor yield data and the model arehigher than the plug-flow reactor data and the equilibriumcalculated CO
2yield data
It is characteristic that most of the points taken with themembrane reactor operation exceed in methane conversionmeasure the corresponding points taken under regular plugflow reactor operationWe should point out that both reactors
90
80
70
60
50
40
30
20
10
0
Carb
on d
ioxi
de y
ield
()
10 15 20 25 30 35 40 45 50
Membrane reactor experiment no sweep gasMembrane reactor modelPlug flow reactor experimentPlug flow reactor modelEquilibrium yield
119879 = 550∘C
Space time (gr(cat)middothrgmoleCH4 )
Figure 4 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous operationCarbon dioxide yield data (119875
119879119900
= 168 atm feed compositionCH4 H2O H2= 1 4 020)
are catalytic and are filled with catalyst particles Also weshould point out that the alumina-based membrane used inthese experiments was blank (not rendered catalytic) It isalso characteristic that the membrane reactor points exceedthe equilibrium conversion calculated at the respective reac-tion side conditions Moreover the computational modeldescribed earlier which simulates the membrane-reactoroperation shows a good agreement with the experimentallymeasured membrane methane conversions and CO
2yields
under the same reaction conditions Thus the membranereformer is operation show to be beneficial in producingmore synthesis gas (amixture of hydrogen and carbon oxides)than the counterpart conventional plug flow reformer
We are also presenting below two figures relating with themodeling and simulation of the methanelandfill gas-steamreforming reactor We have used the model of (6) (8) (9)and (11) to simulate the permeable reformer [10] PBMR inthese plots stands for a packed bed membrane reactor
Next Figure 5 shows the dimensionless molar flow rateof hydrogen steam and methane along the reaction side ortubeside of the membrane reactor The molar flow rate forhydrogen passes through a maximum at about the middle
6 Journal of Renewable Energy
08
07
06
05
04
03
02
01
0
Dim
ensio
nles
s mol
ar fl
owra
te
0 01 02 03 04 05 06 07 08 09 1
MethaneSteamHydrogen
Dimensionless distance (zL)
Reaction side (119879 = 450∘C)
Figure 5Modeling results of landfill gas-steam reformers for syngasproduction and SOFC continuous operation Molar flowrate data inthe reaction side (tubeside) (119875
119879119900
= 168 atm feed composition CH4
H2O H2= 1 4 020)
0 01 02 03 04 05 06 07 08 09 1
045
04
035
03
025
02
015
01
005
0
Dim
ensio
nles
s mol
ar fl
owra
te
MethaneSteamHydrogen
Dimensionless distance (zL)
Separation side (119879 = 450∘C)
Figure 6 Modeling results of landfill gas-steam reformers forsyngas production and SOFC continuous operation Molar flowratedata in the separation side (119875
119879119900
= 168 atm feed compositionCH4 H2O H2= 1 4 020)
axial length of the reactor The molar flowrates for steam andmethane decreasemonotonically along the axial length of thereactor
Figure 6 shows the dimensionless molar flow rate ofhydrogen steam and methane along the separation side orshellside of themembrane reactor In this case themolar flow
055
05
045
04
035
03
025
02
015
01
350 400 450 500 550 600 650
Temperature (∘C)
Calculated equilibrium yieldReactor with shellside closedMembrane reactor (no sweep gas)Membrane reactor model
Tota
l hyd
roge
n yi
eld
(gm
ole
hr)
Figure 7 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous operationTotal hydrogen yield data
rates for hydrogen steam and methane increase monotoni-cally along the axial length of the reactor
Finally Figure 7 shows the combined hydrogen yieldobtained with the two types of reactors The membranetype reformer offers better hydrogen yields than the non-membrane type reformer This is shown both with theexperimental and modeling results in Figure 7 It is thereforebeneficial to use the membrane reformer in the flow chart ofthis process to accomplish the operation
Moreover Table 1 below shows a summary of spec-ifications from a landfill-gas-processing plant for energycogeneration (landfill gas is coming from a concentratedlandfill site [16]) The table provides details on the energeticdistribution outcome of the entire plantThis table is given forcomparison purposes in order to evaluate the potential of thenewly described landfill gas to SOFC unit using the describedmembrane reactor and conventional reactor technologies Itis characteristic that the installed fuel cellSOFC can provideelectricity at a higher degree of efficiency than the respectivegas engine or gas turbine
4 Conclusions
It is shownhere that high temperature SOFCsfuel cells can becombined with reforming operations of landfill-based gasesThe referred SOFCs systems can operate in series or areintegrated with a catalytic reformer or membrane reformerwhich convert landfill gas into fuel-gas product at variousoperating conditions To be more specific these feedstockgases are rich in CH
4and are converted into an H
2 CO
and CO2mixture suitable for the continuous operation
of the SOFC unit The reformers studied here have been
Journal of Renewable Energy 7
Stainless steel casing ThermocoupleThermocouple
Thermocouples
Sweep gas in
Compression fitting
Product gases out
Graphitized string
Feedgases in Product
gases out
Alumina tube(membrane + support)
Figure 8 Ceramic membrane reactor
also studied by computational models taking into accountthe reaction and hydrogen separation in the permeablereformers Essential operating conditions in the permeablereformers have been simulated by the mathematical modelsThe experimental membrane reformer shows to offer higheryields than the nonmembrane type reformer for a number ofoperating conditions
It is worthy to notice that important distributed powergeneration within a wider power grid can be accomplishedwith this operation being able to cover the local needsof municipal and remote areas Fuel cell power relates tothe reformer conversion and the efficient utilization of thesyngas by the fuel cell The waste heat from the conversionof syngas to electricity can be descreased through the fuelcell operation and specifically through the operation of highefficiency SOFCs Fuel cell (SOFCs) continuous operationand power generation from landfill gas can lead to pollutionminimization higher power density and increased efficiency(reduced waste heat) in comparison with conventional powersystems
References
[1] Z Ziaka and S Vasileiadis ldquoCatalytic reforming -shift proces-sors for hydrogen generation and continuous fuel cell opera-tionrdquo in Proceedings of IASTED-Power and Energy Systems pp360ndash365 Marina Del Ray Calif USA May 2002
[2] S Vasileiadis and Z Ziaka-Vasileiadou ldquoBiomass reformingprocess for integrated solid oxide-fuel cell power generationrdquoChemical Engineering Science vol 59 no 22-23 pp 4853ndash48592004
[3] S Vasileiadis and Z Ziaka ldquoAlternative generation of H2 CO
and H2 CO2mixtures from steam-carbon dioxide reforming
of methane and the water gas shift with permeable (membrane)reactorsrdquo Chemical Engineering Communications vol 176 pp247ndash252 1999
[4] J Xu and G F Froment ldquoMethane steam reforming methana-tion and water-gas shift I Intrinsic kineticsrdquo AIChE Journalvol 35 no 1 pp 88ndash96 1989
[5] J P van Hook ldquoMethane-steam reformingrdquo Catalysis ReviewsScience and Engineering vol 21 no 1 pp 1ndash51 1980
[6] J R Rostrup-Nielsen ldquoSulfur-passivated nickel catalysts forcarbon-free steam reforming of methanerdquo Journal of Catalysisvol 85 no 1 pp 31ndash43 1984
[7] J R Rostrup-Nielsen ldquoCoking on nickel catalysts for steamreforming of hydrocarbonsrdquo Journal of Catalysis vol 33 no 2pp 184ndash201 1974
[8] J T Richardson and S A Paripatyadar ldquoCarbon dioxidereforming of methane with supported rhodiumrdquoApplied Catal-ysis vol 61 no 1 pp 293ndash309 1990
[9] E Ruckenstein and Y H Hu ldquoCombination of CO2reforming
and partial oxidation of methane over NiOMgO solid solutioncatalystsrdquo Industrial amp Engineering Chemistry Research vol 37no 5 pp 1744ndash1747 1998
[10] Z D Ziaka and S P Vasileiadis Reactors for Fuel Cells andEnvironmental Energy Systems Xlibris Publishing IndianapolisInd USA 2009
[11] S P Vasileiadis and Z D Ziaka ldquoEnvironmentally benignhydrocarbon processing applications of single and integratedpermreactorsrdquo in Reaction Engineering for Pollution Preventionpp 247ndash304 Elsevier Science Philadelphia Pa USA 2000
[12] Z D Ziaka and S P Vasileiadis ldquoReactor-membrane permeatorcascade for enhanced production and recovery of H2 andCO2 from the catalytic methane-steam reforming reactionrdquoChemical Engineering Communications vol 156 pp 161ndash2001996
[13] D L Klass Biomass for Renewable Energy Fuels and ChemicalsAcademic Press San Diego Calif USA 1988
[14] S Vasileiadis and Z Ziaka ldquoEfficient catalytic reactors-pro-cessors for fuel cells and synthesis applicationsrdquo in Proceedingsof the 17th International Symposium on Chemical ReactionEngineering Hong Kong August 2002 paper no 13
8 Journal of Renewable Energy
[15] R Rautenbach and K Welsch ldquoTreatment of landfill gas bygas permeationmdashpilot plant results and comparison to alterna-tivesrdquo Journal of Membrane Science vol 87 no 1-2 pp 107ndash1181994
[16] M Tsimpa Biogas usages in Greece for energy generationtrends and opportunities [MS thesis] HellenicOpenUniversityPatras Greece 2010
TribologyAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
FuelsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofPetroleum Engineering
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Industrial EngineeringJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Power ElectronicsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
CombustionJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Renewable Energy
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
StructuresJournal of
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nuclear InstallationsScience and Technology of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solar EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Wind EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nuclear EnergyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
High Energy PhysicsAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of Renewable Energy 3
into fuel cell gas the above design equations are modifiedaccordingly to include the permeation effects via the mem-brane of the different components Moreover the followingmathematical part has to be added at the right hand side of (6)to account for the permeation effects within themass balanceequations
minus(
2120587
119899119879
119860119900
)119875119860119890[
119901119879
119860minus 119901119878
119860
ln (11990311199032)
] (11)
wherein 119875119860119890
(gmolssdotcmsdotatm) is the effective permeabilitycoefficient of species 119860 via the catalytic or noncatalytic(blank) membrane It is worthy to declare that in ourearlier experimental reaction studies we utilized mesoporousaluminum oxide membranes having a thin permselectivelayer (3ndash5120583m thickness 50 porosity) with 40ndash50 A porediameter [3 10 11 14]Themembrane is amultilayer structuresupported on an a-alumina support (15ndash20mm thickness40ndash45 porosity and 10ndash15 120583m pore diameter) When apermreactor is used the corresponding mass temperatureand pressure variation equations are written as well for thegas which permeates via the membrane wall material andflows in the permeate side (119878) of the membrane reactor It isassumed that there are no reactions occurring in the permeatemembrane side An analysis of themodel for the permreactorhas been described as well in earlier communications [10ndash12]
By employing (6) (8) (9) and (11) within the modelingprocedure a complete reactor analysis is obtained for the twodifferent reformer configurations Solution of the equationsis obtained numerically by using an initial value integrationtechnique for ordinary differential equations with variablestepsize to ensure higher accuracy (implicit Adams-Moultonmethod) [10 11]
In our earlier papers we have described and analyzedthe reaction separation (ie permeation) and process (con-version yield) characteristics of permreactors (membranebased catalytic reactors) and related processes for methane-steam reforming water-gas shift and methane carbon diox-ide reforming reactions including catalysis and membranematerials characteristics The main categories of reactorsdescribed were membrane reformers which were utilized assingle permreactor [10] permreactor-separator in series orreactor-separator in series and permeactor-permeactor inseries [3 10 13 14]
These effective and versatile catalytic processes wereapplied for pure hydrogen (H
2) H2and CO
2 or H
2and
CO (syn-gas) generation to be used as fuel gas for powergeneration or as synthesis gas for the production of specialtychemicals (such as methanol and higher hydrocarbons) [10]Several key types of membrane reformers were examinedbased on the location of the fixed catalytic bed and the inert orcatalytic nature of the inorganic (alumina-based) membranetube Computationalmodeling of the described permreform-ers was running indicating performance measures (reactantconversion product yield) versus variation of intrinsic modelparameters (reactor space time reaction temperature andpressure feed composition sweep gas to feed gas ratio)Through the models we also obtain performance measures
Table 1 Specifications of a representative small landfill gas-reforming SOFC system for electricity and heat cogeneration
Landfill gas production volume 3600m3dayMethane production volumeabout 2520m3 CH4dayTotal energy generation 26100 kWhdayElectricity generationSOFC (60min) 15660 kWhdayHeat generation (30min) 7830 kWhdayWaste heat (about 10) 2610 kWhdayAnnual electricity generation 5716 MWhyearSale price per MWh (to DEH GreekElectricity Authority) 73 EuroMWh
Income about 417000 EuroyearAnnual heat generation 2858MWhyear
under new operating conditions leading to new energy andchemical process applications [3 10 14]
Moreover the interconnected or integrated solid oxidefuel cell is fed directly by the fuel gas generated by thedescribed reformers The focus of our studies goes to solu-tions in a number of problems associated with the installa-tion operation and mass energy conservation of the entirefuel cell and membrane-processing unit
The economic feasibility of the overall fuel cell installationis correlatedwith high efficiency (eg 45ndash65 for advancedunits) and high current density output (Acm2) increasedsystem reliability for continuous dispersed power generationand reduced plant installation operation and maintenancecost Such goals combined with virtual elimination of pol-lution by the use of fuel cells in stationary (eg centraland remote power stations) and mobiletransportation (egautomobile) sources make this technology highly applicableand attractive Finally clean fuel cell power minimizes NOxCO and hydrocarbon species in the emissions
3 Results and Discussion
Proper utilization of landfill gas in the reformer comingfrom landfill sites presents an innovative approach for directuse of those feedstocks for power generation [15] Thereare essential resources of these feedstocks today and theiraccumulation in land is growing Gas coming out from theproper treatment of landfills and frommunicipal sewage andsludge sites is rich in methane and constitutes the propermixture for direct conversion into the described reformer-SOFC systemThrough the catalytic conversion of these gasesin the reformerwe can obtain yields of hydrogen-richmixturefor properly powering the interconnected SOFC As the flowrates of the landfill gas increase (for larger sites and treatmentsystems) a larger capacity reformer and fuel cell are requiredto handle the conversion consecutively the final SOFCpoweroutput (kWcm2) increases as well
The catalyst used in the experiments described below is a15 NiOmixed with calcium and magnesium and supportedon aluminaThe catalyst characteristics are shown in Table 3
4 Journal of Renewable Energy
Table 2 Membrane characteristics
Layer Pore diameter Thickness1 40 A 5120583m2 020 120583m 30 120583m3 08 120583m 50 120583m4 support 10ndash15 120583m 15ndash20mm
Table 3 Catalyst characteristics
Pore volume 03 ccgSurface area 50m2gPorosity 55Composition 15wt
90
80
70
60
50
40
30
20
10
0
350 400 450 500 550 600 650
Met
hane
conv
ersio
n (
)
Membrane reactor experiment sweep Ar 011 gmolehrMembrane reactor modelPlug flow reactor experimentEquilibrium conversion
Temperature (∘C)
Figure 1 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous operationTotal methane conversion data (119875
119879119900
= 168 atm space time =480 gcatsdothrgmoleCH4)
The system of the apparatus used in the experimentsreported here consists of mass-flow controllers a bubblerto generate steam for the reaction and the reactor housingwherein the plug-flow reactor or the membrane reactor wasplaced The reactor is accompanied with thermocouples toread the temperature and pressure transducers to read thepressure At the exit of the reactor apparatus there are steamtraps and a gas chromatograph to analyze the exit streamThe gas chromatograph operates in the TCD mode and isequipped with a porapack Q column for the gas analysis
Figure 1 below describes a set of experiments for thetwo reformer configurationsThemembrane reformer showsbettermethane conversions than the nonmembrane reformerfor all the range of temperatures examined experimentally(ie 400ndash600∘C) At low temperatures we avoid coke for-mation and prolong the catalyst activity The membranecharacteristics are shown in Table 2
80
70
60
50
40
30
20
10
0
Carb
on d
ioxi
de y
ield
()
350 400 450 500 550 600 650
Membrane reactor experiment sweep Ar 011 gmolehrMembrane reactor modelPlug flow reactor experimentEquilibrium yield
Temperature (∘C)
Figure 2 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous opera-tion Carbon dioxide yield data (119875
119879119900
= 168 atm space time =480 gcatsdothrgmoleCH4)
Ar gas was flown in the permeate side of the membranereactor to sweep the permeating gas The feed compositionis CH
4 H2O H2= 1 4 020 The residence time of the
reactor remained constant at 480 gsdothrgmolCH4 for all theexperiments reported here The pressure at the reaction sidewas kept constant at 119875
119879= 10 plusmn 05 psig There is also a good
agreement of the developed model with the experimentalmembrane-reactor conversions Moreover most of the con-versions obtained with the membrane reformer are betterthan the ones calculated at the equilibrium state
The equilibrium calculations are based on the maximumthermodynamic equilibrium conversion that the specificreaction system can achieve according to the operatingparameters and conditions given They are calculated bythe corresponding thermodynamic equilibrium equationsThe results are shown in the figures as equilibrium yieldsand conversionsThe permeability (permeability coefficienttimes102 molmsdotssdotPa) is given in Table 4 They are experimentalmeasurements at 35∘C for unmodified alumina membrane
The reactor is a tubular one with the ceramic membraneinside Its length is 20 cm and the diameter is 1 cm with feedflow rate 011 gmolehr The reactor schematic is shown inFigure 8
Figure 2 is indicative of the carbon dioxide yieldsobtained with the membrane reformer as function of thereaction temperature These yields are better than thoseobtained with the nonmembrane type reformer and theequilibrium calculated yields The results of Figure 2 areindicative of the yield of the water-gas shift reaction (reaction(2)) However our future efforts seek to minimize the effectof reaction (2) and promote the effect of reaction (1) only In
Journal of Renewable Energy 5
Table 4 Permeability coefficient times 102 molmsPa Experimental measurements at 35∘C for unmodified alumina membrane
Average transmembrane pressure KPa Hydrogen Methane Carbon monoxide Carbon dioxide Argon105 168 76 54 50 42117 179 81 57 56 45135 181 83 60 59 52
90
80
70
60
50
40
30
20
10 15 20 25 30 35 40 45 50
Met
hane
conv
ersio
n (
)
Membrane reactor experiment no sweep gasMembrane reactor modelPlug flow reactor experimentPlug flow reactor modelEquilibrium conversion
119879 = 550∘C
Space time (gr(cat)middothrgmoleCH4 )
Figure 3 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous operationTotal methane conversion data (119875
119879119900
= 168 atm feed compositionCH4 H2O H2= 1 4 02
this way the flow rate of the fuel-gas product going into thefuel cellSOFC system is maximized based on reactions (5)
Figure 3 next shows the effect of the space time of thereactor on the methane conversion
The temperature is fixed at 550∘CThemembrane reactoroffers better conversions and yields than the nonmembranereactor as also shown in Figures 3 and 4 The membranereactor conversions are showed to exceed the conventionalcatalytic plug-flow-reactor conversions for all the space timesexamined in this experimentThis is attributed to the effect ofthemembraneThemembrane offers primarily the separationof hydrogen an effect that increases the conversion above theequilibrium conversionThe computational model describedabove agrees well with the membrane reactor data andthe conventional catalytic plug-flow reactor data Both theexperimental membrane reactor yield data and the model arehigher than the plug-flow reactor data and the equilibriumcalculated CO
2yield data
It is characteristic that most of the points taken with themembrane reactor operation exceed in methane conversionmeasure the corresponding points taken under regular plugflow reactor operationWe should point out that both reactors
90
80
70
60
50
40
30
20
10
0
Carb
on d
ioxi
de y
ield
()
10 15 20 25 30 35 40 45 50
Membrane reactor experiment no sweep gasMembrane reactor modelPlug flow reactor experimentPlug flow reactor modelEquilibrium yield
119879 = 550∘C
Space time (gr(cat)middothrgmoleCH4 )
Figure 4 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous operationCarbon dioxide yield data (119875
119879119900
= 168 atm feed compositionCH4 H2O H2= 1 4 020)
are catalytic and are filled with catalyst particles Also weshould point out that the alumina-based membrane used inthese experiments was blank (not rendered catalytic) It isalso characteristic that the membrane reactor points exceedthe equilibrium conversion calculated at the respective reac-tion side conditions Moreover the computational modeldescribed earlier which simulates the membrane-reactoroperation shows a good agreement with the experimentallymeasured membrane methane conversions and CO
2yields
under the same reaction conditions Thus the membranereformer is operation show to be beneficial in producingmore synthesis gas (amixture of hydrogen and carbon oxides)than the counterpart conventional plug flow reformer
We are also presenting below two figures relating with themodeling and simulation of the methanelandfill gas-steamreforming reactor We have used the model of (6) (8) (9)and (11) to simulate the permeable reformer [10] PBMR inthese plots stands for a packed bed membrane reactor
Next Figure 5 shows the dimensionless molar flow rateof hydrogen steam and methane along the reaction side ortubeside of the membrane reactor The molar flow rate forhydrogen passes through a maximum at about the middle
6 Journal of Renewable Energy
08
07
06
05
04
03
02
01
0
Dim
ensio
nles
s mol
ar fl
owra
te
0 01 02 03 04 05 06 07 08 09 1
MethaneSteamHydrogen
Dimensionless distance (zL)
Reaction side (119879 = 450∘C)
Figure 5Modeling results of landfill gas-steam reformers for syngasproduction and SOFC continuous operation Molar flowrate data inthe reaction side (tubeside) (119875
119879119900
= 168 atm feed composition CH4
H2O H2= 1 4 020)
0 01 02 03 04 05 06 07 08 09 1
045
04
035
03
025
02
015
01
005
0
Dim
ensio
nles
s mol
ar fl
owra
te
MethaneSteamHydrogen
Dimensionless distance (zL)
Separation side (119879 = 450∘C)
Figure 6 Modeling results of landfill gas-steam reformers forsyngas production and SOFC continuous operation Molar flowratedata in the separation side (119875
119879119900
= 168 atm feed compositionCH4 H2O H2= 1 4 020)
axial length of the reactor The molar flowrates for steam andmethane decreasemonotonically along the axial length of thereactor
Figure 6 shows the dimensionless molar flow rate ofhydrogen steam and methane along the separation side orshellside of themembrane reactor In this case themolar flow
055
05
045
04
035
03
025
02
015
01
350 400 450 500 550 600 650
Temperature (∘C)
Calculated equilibrium yieldReactor with shellside closedMembrane reactor (no sweep gas)Membrane reactor model
Tota
l hyd
roge
n yi
eld
(gm
ole
hr)
Figure 7 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous operationTotal hydrogen yield data
rates for hydrogen steam and methane increase monotoni-cally along the axial length of the reactor
Finally Figure 7 shows the combined hydrogen yieldobtained with the two types of reactors The membranetype reformer offers better hydrogen yields than the non-membrane type reformer This is shown both with theexperimental and modeling results in Figure 7 It is thereforebeneficial to use the membrane reformer in the flow chart ofthis process to accomplish the operation
Moreover Table 1 below shows a summary of spec-ifications from a landfill-gas-processing plant for energycogeneration (landfill gas is coming from a concentratedlandfill site [16]) The table provides details on the energeticdistribution outcome of the entire plantThis table is given forcomparison purposes in order to evaluate the potential of thenewly described landfill gas to SOFC unit using the describedmembrane reactor and conventional reactor technologies Itis characteristic that the installed fuel cellSOFC can provideelectricity at a higher degree of efficiency than the respectivegas engine or gas turbine
4 Conclusions
It is shownhere that high temperature SOFCsfuel cells can becombined with reforming operations of landfill-based gasesThe referred SOFCs systems can operate in series or areintegrated with a catalytic reformer or membrane reformerwhich convert landfill gas into fuel-gas product at variousoperating conditions To be more specific these feedstockgases are rich in CH
4and are converted into an H
2 CO
and CO2mixture suitable for the continuous operation
of the SOFC unit The reformers studied here have been
Journal of Renewable Energy 7
Stainless steel casing ThermocoupleThermocouple
Thermocouples
Sweep gas in
Compression fitting
Product gases out
Graphitized string
Feedgases in Product
gases out
Alumina tube(membrane + support)
Figure 8 Ceramic membrane reactor
also studied by computational models taking into accountthe reaction and hydrogen separation in the permeablereformers Essential operating conditions in the permeablereformers have been simulated by the mathematical modelsThe experimental membrane reformer shows to offer higheryields than the nonmembrane type reformer for a number ofoperating conditions
It is worthy to notice that important distributed powergeneration within a wider power grid can be accomplishedwith this operation being able to cover the local needsof municipal and remote areas Fuel cell power relates tothe reformer conversion and the efficient utilization of thesyngas by the fuel cell The waste heat from the conversionof syngas to electricity can be descreased through the fuelcell operation and specifically through the operation of highefficiency SOFCs Fuel cell (SOFCs) continuous operationand power generation from landfill gas can lead to pollutionminimization higher power density and increased efficiency(reduced waste heat) in comparison with conventional powersystems
References
[1] Z Ziaka and S Vasileiadis ldquoCatalytic reforming -shift proces-sors for hydrogen generation and continuous fuel cell opera-tionrdquo in Proceedings of IASTED-Power and Energy Systems pp360ndash365 Marina Del Ray Calif USA May 2002
[2] S Vasileiadis and Z Ziaka-Vasileiadou ldquoBiomass reformingprocess for integrated solid oxide-fuel cell power generationrdquoChemical Engineering Science vol 59 no 22-23 pp 4853ndash48592004
[3] S Vasileiadis and Z Ziaka ldquoAlternative generation of H2 CO
and H2 CO2mixtures from steam-carbon dioxide reforming
of methane and the water gas shift with permeable (membrane)reactorsrdquo Chemical Engineering Communications vol 176 pp247ndash252 1999
[4] J Xu and G F Froment ldquoMethane steam reforming methana-tion and water-gas shift I Intrinsic kineticsrdquo AIChE Journalvol 35 no 1 pp 88ndash96 1989
[5] J P van Hook ldquoMethane-steam reformingrdquo Catalysis ReviewsScience and Engineering vol 21 no 1 pp 1ndash51 1980
[6] J R Rostrup-Nielsen ldquoSulfur-passivated nickel catalysts forcarbon-free steam reforming of methanerdquo Journal of Catalysisvol 85 no 1 pp 31ndash43 1984
[7] J R Rostrup-Nielsen ldquoCoking on nickel catalysts for steamreforming of hydrocarbonsrdquo Journal of Catalysis vol 33 no 2pp 184ndash201 1974
[8] J T Richardson and S A Paripatyadar ldquoCarbon dioxidereforming of methane with supported rhodiumrdquoApplied Catal-ysis vol 61 no 1 pp 293ndash309 1990
[9] E Ruckenstein and Y H Hu ldquoCombination of CO2reforming
and partial oxidation of methane over NiOMgO solid solutioncatalystsrdquo Industrial amp Engineering Chemistry Research vol 37no 5 pp 1744ndash1747 1998
[10] Z D Ziaka and S P Vasileiadis Reactors for Fuel Cells andEnvironmental Energy Systems Xlibris Publishing IndianapolisInd USA 2009
[11] S P Vasileiadis and Z D Ziaka ldquoEnvironmentally benignhydrocarbon processing applications of single and integratedpermreactorsrdquo in Reaction Engineering for Pollution Preventionpp 247ndash304 Elsevier Science Philadelphia Pa USA 2000
[12] Z D Ziaka and S P Vasileiadis ldquoReactor-membrane permeatorcascade for enhanced production and recovery of H2 andCO2 from the catalytic methane-steam reforming reactionrdquoChemical Engineering Communications vol 156 pp 161ndash2001996
[13] D L Klass Biomass for Renewable Energy Fuels and ChemicalsAcademic Press San Diego Calif USA 1988
[14] S Vasileiadis and Z Ziaka ldquoEfficient catalytic reactors-pro-cessors for fuel cells and synthesis applicationsrdquo in Proceedingsof the 17th International Symposium on Chemical ReactionEngineering Hong Kong August 2002 paper no 13
8 Journal of Renewable Energy
[15] R Rautenbach and K Welsch ldquoTreatment of landfill gas bygas permeationmdashpilot plant results and comparison to alterna-tivesrdquo Journal of Membrane Science vol 87 no 1-2 pp 107ndash1181994
[16] M Tsimpa Biogas usages in Greece for energy generationtrends and opportunities [MS thesis] HellenicOpenUniversityPatras Greece 2010
TribologyAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
FuelsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofPetroleum Engineering
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Industrial EngineeringJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Power ElectronicsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
CombustionJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Renewable Energy
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
StructuresJournal of
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nuclear InstallationsScience and Technology of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solar EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Wind EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nuclear EnergyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
High Energy PhysicsAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
4 Journal of Renewable Energy
Table 2 Membrane characteristics
Layer Pore diameter Thickness1 40 A 5120583m2 020 120583m 30 120583m3 08 120583m 50 120583m4 support 10ndash15 120583m 15ndash20mm
Table 3 Catalyst characteristics
Pore volume 03 ccgSurface area 50m2gPorosity 55Composition 15wt
90
80
70
60
50
40
30
20
10
0
350 400 450 500 550 600 650
Met
hane
conv
ersio
n (
)
Membrane reactor experiment sweep Ar 011 gmolehrMembrane reactor modelPlug flow reactor experimentEquilibrium conversion
Temperature (∘C)
Figure 1 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous operationTotal methane conversion data (119875
119879119900
= 168 atm space time =480 gcatsdothrgmoleCH4)
The system of the apparatus used in the experimentsreported here consists of mass-flow controllers a bubblerto generate steam for the reaction and the reactor housingwherein the plug-flow reactor or the membrane reactor wasplaced The reactor is accompanied with thermocouples toread the temperature and pressure transducers to read thepressure At the exit of the reactor apparatus there are steamtraps and a gas chromatograph to analyze the exit streamThe gas chromatograph operates in the TCD mode and isequipped with a porapack Q column for the gas analysis
Figure 1 below describes a set of experiments for thetwo reformer configurationsThemembrane reformer showsbettermethane conversions than the nonmembrane reformerfor all the range of temperatures examined experimentally(ie 400ndash600∘C) At low temperatures we avoid coke for-mation and prolong the catalyst activity The membranecharacteristics are shown in Table 2
80
70
60
50
40
30
20
10
0
Carb
on d
ioxi
de y
ield
()
350 400 450 500 550 600 650
Membrane reactor experiment sweep Ar 011 gmolehrMembrane reactor modelPlug flow reactor experimentEquilibrium yield
Temperature (∘C)
Figure 2 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous opera-tion Carbon dioxide yield data (119875
119879119900
= 168 atm space time =480 gcatsdothrgmoleCH4)
Ar gas was flown in the permeate side of the membranereactor to sweep the permeating gas The feed compositionis CH
4 H2O H2= 1 4 020 The residence time of the
reactor remained constant at 480 gsdothrgmolCH4 for all theexperiments reported here The pressure at the reaction sidewas kept constant at 119875
119879= 10 plusmn 05 psig There is also a good
agreement of the developed model with the experimentalmembrane-reactor conversions Moreover most of the con-versions obtained with the membrane reformer are betterthan the ones calculated at the equilibrium state
The equilibrium calculations are based on the maximumthermodynamic equilibrium conversion that the specificreaction system can achieve according to the operatingparameters and conditions given They are calculated bythe corresponding thermodynamic equilibrium equationsThe results are shown in the figures as equilibrium yieldsand conversionsThe permeability (permeability coefficienttimes102 molmsdotssdotPa) is given in Table 4 They are experimentalmeasurements at 35∘C for unmodified alumina membrane
The reactor is a tubular one with the ceramic membraneinside Its length is 20 cm and the diameter is 1 cm with feedflow rate 011 gmolehr The reactor schematic is shown inFigure 8
Figure 2 is indicative of the carbon dioxide yieldsobtained with the membrane reformer as function of thereaction temperature These yields are better than thoseobtained with the nonmembrane type reformer and theequilibrium calculated yields The results of Figure 2 areindicative of the yield of the water-gas shift reaction (reaction(2)) However our future efforts seek to minimize the effectof reaction (2) and promote the effect of reaction (1) only In
Journal of Renewable Energy 5
Table 4 Permeability coefficient times 102 molmsPa Experimental measurements at 35∘C for unmodified alumina membrane
Average transmembrane pressure KPa Hydrogen Methane Carbon monoxide Carbon dioxide Argon105 168 76 54 50 42117 179 81 57 56 45135 181 83 60 59 52
90
80
70
60
50
40
30
20
10 15 20 25 30 35 40 45 50
Met
hane
conv
ersio
n (
)
Membrane reactor experiment no sweep gasMembrane reactor modelPlug flow reactor experimentPlug flow reactor modelEquilibrium conversion
119879 = 550∘C
Space time (gr(cat)middothrgmoleCH4 )
Figure 3 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous operationTotal methane conversion data (119875
119879119900
= 168 atm feed compositionCH4 H2O H2= 1 4 02
this way the flow rate of the fuel-gas product going into thefuel cellSOFC system is maximized based on reactions (5)
Figure 3 next shows the effect of the space time of thereactor on the methane conversion
The temperature is fixed at 550∘CThemembrane reactoroffers better conversions and yields than the nonmembranereactor as also shown in Figures 3 and 4 The membranereactor conversions are showed to exceed the conventionalcatalytic plug-flow-reactor conversions for all the space timesexamined in this experimentThis is attributed to the effect ofthemembraneThemembrane offers primarily the separationof hydrogen an effect that increases the conversion above theequilibrium conversionThe computational model describedabove agrees well with the membrane reactor data andthe conventional catalytic plug-flow reactor data Both theexperimental membrane reactor yield data and the model arehigher than the plug-flow reactor data and the equilibriumcalculated CO
2yield data
It is characteristic that most of the points taken with themembrane reactor operation exceed in methane conversionmeasure the corresponding points taken under regular plugflow reactor operationWe should point out that both reactors
90
80
70
60
50
40
30
20
10
0
Carb
on d
ioxi
de y
ield
()
10 15 20 25 30 35 40 45 50
Membrane reactor experiment no sweep gasMembrane reactor modelPlug flow reactor experimentPlug flow reactor modelEquilibrium yield
119879 = 550∘C
Space time (gr(cat)middothrgmoleCH4 )
Figure 4 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous operationCarbon dioxide yield data (119875
119879119900
= 168 atm feed compositionCH4 H2O H2= 1 4 020)
are catalytic and are filled with catalyst particles Also weshould point out that the alumina-based membrane used inthese experiments was blank (not rendered catalytic) It isalso characteristic that the membrane reactor points exceedthe equilibrium conversion calculated at the respective reac-tion side conditions Moreover the computational modeldescribed earlier which simulates the membrane-reactoroperation shows a good agreement with the experimentallymeasured membrane methane conversions and CO
2yields
under the same reaction conditions Thus the membranereformer is operation show to be beneficial in producingmore synthesis gas (amixture of hydrogen and carbon oxides)than the counterpart conventional plug flow reformer
We are also presenting below two figures relating with themodeling and simulation of the methanelandfill gas-steamreforming reactor We have used the model of (6) (8) (9)and (11) to simulate the permeable reformer [10] PBMR inthese plots stands for a packed bed membrane reactor
Next Figure 5 shows the dimensionless molar flow rateof hydrogen steam and methane along the reaction side ortubeside of the membrane reactor The molar flow rate forhydrogen passes through a maximum at about the middle
6 Journal of Renewable Energy
08
07
06
05
04
03
02
01
0
Dim
ensio
nles
s mol
ar fl
owra
te
0 01 02 03 04 05 06 07 08 09 1
MethaneSteamHydrogen
Dimensionless distance (zL)
Reaction side (119879 = 450∘C)
Figure 5Modeling results of landfill gas-steam reformers for syngasproduction and SOFC continuous operation Molar flowrate data inthe reaction side (tubeside) (119875
119879119900
= 168 atm feed composition CH4
H2O H2= 1 4 020)
0 01 02 03 04 05 06 07 08 09 1
045
04
035
03
025
02
015
01
005
0
Dim
ensio
nles
s mol
ar fl
owra
te
MethaneSteamHydrogen
Dimensionless distance (zL)
Separation side (119879 = 450∘C)
Figure 6 Modeling results of landfill gas-steam reformers forsyngas production and SOFC continuous operation Molar flowratedata in the separation side (119875
119879119900
= 168 atm feed compositionCH4 H2O H2= 1 4 020)
axial length of the reactor The molar flowrates for steam andmethane decreasemonotonically along the axial length of thereactor
Figure 6 shows the dimensionless molar flow rate ofhydrogen steam and methane along the separation side orshellside of themembrane reactor In this case themolar flow
055
05
045
04
035
03
025
02
015
01
350 400 450 500 550 600 650
Temperature (∘C)
Calculated equilibrium yieldReactor with shellside closedMembrane reactor (no sweep gas)Membrane reactor model
Tota
l hyd
roge
n yi
eld
(gm
ole
hr)
Figure 7 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous operationTotal hydrogen yield data
rates for hydrogen steam and methane increase monotoni-cally along the axial length of the reactor
Finally Figure 7 shows the combined hydrogen yieldobtained with the two types of reactors The membranetype reformer offers better hydrogen yields than the non-membrane type reformer This is shown both with theexperimental and modeling results in Figure 7 It is thereforebeneficial to use the membrane reformer in the flow chart ofthis process to accomplish the operation
Moreover Table 1 below shows a summary of spec-ifications from a landfill-gas-processing plant for energycogeneration (landfill gas is coming from a concentratedlandfill site [16]) The table provides details on the energeticdistribution outcome of the entire plantThis table is given forcomparison purposes in order to evaluate the potential of thenewly described landfill gas to SOFC unit using the describedmembrane reactor and conventional reactor technologies Itis characteristic that the installed fuel cellSOFC can provideelectricity at a higher degree of efficiency than the respectivegas engine or gas turbine
4 Conclusions
It is shownhere that high temperature SOFCsfuel cells can becombined with reforming operations of landfill-based gasesThe referred SOFCs systems can operate in series or areintegrated with a catalytic reformer or membrane reformerwhich convert landfill gas into fuel-gas product at variousoperating conditions To be more specific these feedstockgases are rich in CH
4and are converted into an H
2 CO
and CO2mixture suitable for the continuous operation
of the SOFC unit The reformers studied here have been
Journal of Renewable Energy 7
Stainless steel casing ThermocoupleThermocouple
Thermocouples
Sweep gas in
Compression fitting
Product gases out
Graphitized string
Feedgases in Product
gases out
Alumina tube(membrane + support)
Figure 8 Ceramic membrane reactor
also studied by computational models taking into accountthe reaction and hydrogen separation in the permeablereformers Essential operating conditions in the permeablereformers have been simulated by the mathematical modelsThe experimental membrane reformer shows to offer higheryields than the nonmembrane type reformer for a number ofoperating conditions
It is worthy to notice that important distributed powergeneration within a wider power grid can be accomplishedwith this operation being able to cover the local needsof municipal and remote areas Fuel cell power relates tothe reformer conversion and the efficient utilization of thesyngas by the fuel cell The waste heat from the conversionof syngas to electricity can be descreased through the fuelcell operation and specifically through the operation of highefficiency SOFCs Fuel cell (SOFCs) continuous operationand power generation from landfill gas can lead to pollutionminimization higher power density and increased efficiency(reduced waste heat) in comparison with conventional powersystems
References
[1] Z Ziaka and S Vasileiadis ldquoCatalytic reforming -shift proces-sors for hydrogen generation and continuous fuel cell opera-tionrdquo in Proceedings of IASTED-Power and Energy Systems pp360ndash365 Marina Del Ray Calif USA May 2002
[2] S Vasileiadis and Z Ziaka-Vasileiadou ldquoBiomass reformingprocess for integrated solid oxide-fuel cell power generationrdquoChemical Engineering Science vol 59 no 22-23 pp 4853ndash48592004
[3] S Vasileiadis and Z Ziaka ldquoAlternative generation of H2 CO
and H2 CO2mixtures from steam-carbon dioxide reforming
of methane and the water gas shift with permeable (membrane)reactorsrdquo Chemical Engineering Communications vol 176 pp247ndash252 1999
[4] J Xu and G F Froment ldquoMethane steam reforming methana-tion and water-gas shift I Intrinsic kineticsrdquo AIChE Journalvol 35 no 1 pp 88ndash96 1989
[5] J P van Hook ldquoMethane-steam reformingrdquo Catalysis ReviewsScience and Engineering vol 21 no 1 pp 1ndash51 1980
[6] J R Rostrup-Nielsen ldquoSulfur-passivated nickel catalysts forcarbon-free steam reforming of methanerdquo Journal of Catalysisvol 85 no 1 pp 31ndash43 1984
[7] J R Rostrup-Nielsen ldquoCoking on nickel catalysts for steamreforming of hydrocarbonsrdquo Journal of Catalysis vol 33 no 2pp 184ndash201 1974
[8] J T Richardson and S A Paripatyadar ldquoCarbon dioxidereforming of methane with supported rhodiumrdquoApplied Catal-ysis vol 61 no 1 pp 293ndash309 1990
[9] E Ruckenstein and Y H Hu ldquoCombination of CO2reforming
and partial oxidation of methane over NiOMgO solid solutioncatalystsrdquo Industrial amp Engineering Chemistry Research vol 37no 5 pp 1744ndash1747 1998
[10] Z D Ziaka and S P Vasileiadis Reactors for Fuel Cells andEnvironmental Energy Systems Xlibris Publishing IndianapolisInd USA 2009
[11] S P Vasileiadis and Z D Ziaka ldquoEnvironmentally benignhydrocarbon processing applications of single and integratedpermreactorsrdquo in Reaction Engineering for Pollution Preventionpp 247ndash304 Elsevier Science Philadelphia Pa USA 2000
[12] Z D Ziaka and S P Vasileiadis ldquoReactor-membrane permeatorcascade for enhanced production and recovery of H2 andCO2 from the catalytic methane-steam reforming reactionrdquoChemical Engineering Communications vol 156 pp 161ndash2001996
[13] D L Klass Biomass for Renewable Energy Fuels and ChemicalsAcademic Press San Diego Calif USA 1988
[14] S Vasileiadis and Z Ziaka ldquoEfficient catalytic reactors-pro-cessors for fuel cells and synthesis applicationsrdquo in Proceedingsof the 17th International Symposium on Chemical ReactionEngineering Hong Kong August 2002 paper no 13
8 Journal of Renewable Energy
[15] R Rautenbach and K Welsch ldquoTreatment of landfill gas bygas permeationmdashpilot plant results and comparison to alterna-tivesrdquo Journal of Membrane Science vol 87 no 1-2 pp 107ndash1181994
[16] M Tsimpa Biogas usages in Greece for energy generationtrends and opportunities [MS thesis] HellenicOpenUniversityPatras Greece 2010
TribologyAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
FuelsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofPetroleum Engineering
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Industrial EngineeringJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Power ElectronicsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
CombustionJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Renewable Energy
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
StructuresJournal of
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nuclear InstallationsScience and Technology of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solar EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Wind EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nuclear EnergyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
High Energy PhysicsAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of Renewable Energy 5
Table 4 Permeability coefficient times 102 molmsPa Experimental measurements at 35∘C for unmodified alumina membrane
Average transmembrane pressure KPa Hydrogen Methane Carbon monoxide Carbon dioxide Argon105 168 76 54 50 42117 179 81 57 56 45135 181 83 60 59 52
90
80
70
60
50
40
30
20
10 15 20 25 30 35 40 45 50
Met
hane
conv
ersio
n (
)
Membrane reactor experiment no sweep gasMembrane reactor modelPlug flow reactor experimentPlug flow reactor modelEquilibrium conversion
119879 = 550∘C
Space time (gr(cat)middothrgmoleCH4 )
Figure 3 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous operationTotal methane conversion data (119875
119879119900
= 168 atm feed compositionCH4 H2O H2= 1 4 02
this way the flow rate of the fuel-gas product going into thefuel cellSOFC system is maximized based on reactions (5)
Figure 3 next shows the effect of the space time of thereactor on the methane conversion
The temperature is fixed at 550∘CThemembrane reactoroffers better conversions and yields than the nonmembranereactor as also shown in Figures 3 and 4 The membranereactor conversions are showed to exceed the conventionalcatalytic plug-flow-reactor conversions for all the space timesexamined in this experimentThis is attributed to the effect ofthemembraneThemembrane offers primarily the separationof hydrogen an effect that increases the conversion above theequilibrium conversionThe computational model describedabove agrees well with the membrane reactor data andthe conventional catalytic plug-flow reactor data Both theexperimental membrane reactor yield data and the model arehigher than the plug-flow reactor data and the equilibriumcalculated CO
2yield data
It is characteristic that most of the points taken with themembrane reactor operation exceed in methane conversionmeasure the corresponding points taken under regular plugflow reactor operationWe should point out that both reactors
90
80
70
60
50
40
30
20
10
0
Carb
on d
ioxi
de y
ield
()
10 15 20 25 30 35 40 45 50
Membrane reactor experiment no sweep gasMembrane reactor modelPlug flow reactor experimentPlug flow reactor modelEquilibrium yield
119879 = 550∘C
Space time (gr(cat)middothrgmoleCH4 )
Figure 4 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous operationCarbon dioxide yield data (119875
119879119900
= 168 atm feed compositionCH4 H2O H2= 1 4 020)
are catalytic and are filled with catalyst particles Also weshould point out that the alumina-based membrane used inthese experiments was blank (not rendered catalytic) It isalso characteristic that the membrane reactor points exceedthe equilibrium conversion calculated at the respective reac-tion side conditions Moreover the computational modeldescribed earlier which simulates the membrane-reactoroperation shows a good agreement with the experimentallymeasured membrane methane conversions and CO
2yields
under the same reaction conditions Thus the membranereformer is operation show to be beneficial in producingmore synthesis gas (amixture of hydrogen and carbon oxides)than the counterpart conventional plug flow reformer
We are also presenting below two figures relating with themodeling and simulation of the methanelandfill gas-steamreforming reactor We have used the model of (6) (8) (9)and (11) to simulate the permeable reformer [10] PBMR inthese plots stands for a packed bed membrane reactor
Next Figure 5 shows the dimensionless molar flow rateof hydrogen steam and methane along the reaction side ortubeside of the membrane reactor The molar flow rate forhydrogen passes through a maximum at about the middle
6 Journal of Renewable Energy
08
07
06
05
04
03
02
01
0
Dim
ensio
nles
s mol
ar fl
owra
te
0 01 02 03 04 05 06 07 08 09 1
MethaneSteamHydrogen
Dimensionless distance (zL)
Reaction side (119879 = 450∘C)
Figure 5Modeling results of landfill gas-steam reformers for syngasproduction and SOFC continuous operation Molar flowrate data inthe reaction side (tubeside) (119875
119879119900
= 168 atm feed composition CH4
H2O H2= 1 4 020)
0 01 02 03 04 05 06 07 08 09 1
045
04
035
03
025
02
015
01
005
0
Dim
ensio
nles
s mol
ar fl
owra
te
MethaneSteamHydrogen
Dimensionless distance (zL)
Separation side (119879 = 450∘C)
Figure 6 Modeling results of landfill gas-steam reformers forsyngas production and SOFC continuous operation Molar flowratedata in the separation side (119875
119879119900
= 168 atm feed compositionCH4 H2O H2= 1 4 020)
axial length of the reactor The molar flowrates for steam andmethane decreasemonotonically along the axial length of thereactor
Figure 6 shows the dimensionless molar flow rate ofhydrogen steam and methane along the separation side orshellside of themembrane reactor In this case themolar flow
055
05
045
04
035
03
025
02
015
01
350 400 450 500 550 600 650
Temperature (∘C)
Calculated equilibrium yieldReactor with shellside closedMembrane reactor (no sweep gas)Membrane reactor model
Tota
l hyd
roge
n yi
eld
(gm
ole
hr)
Figure 7 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous operationTotal hydrogen yield data
rates for hydrogen steam and methane increase monotoni-cally along the axial length of the reactor
Finally Figure 7 shows the combined hydrogen yieldobtained with the two types of reactors The membranetype reformer offers better hydrogen yields than the non-membrane type reformer This is shown both with theexperimental and modeling results in Figure 7 It is thereforebeneficial to use the membrane reformer in the flow chart ofthis process to accomplish the operation
Moreover Table 1 below shows a summary of spec-ifications from a landfill-gas-processing plant for energycogeneration (landfill gas is coming from a concentratedlandfill site [16]) The table provides details on the energeticdistribution outcome of the entire plantThis table is given forcomparison purposes in order to evaluate the potential of thenewly described landfill gas to SOFC unit using the describedmembrane reactor and conventional reactor technologies Itis characteristic that the installed fuel cellSOFC can provideelectricity at a higher degree of efficiency than the respectivegas engine or gas turbine
4 Conclusions
It is shownhere that high temperature SOFCsfuel cells can becombined with reforming operations of landfill-based gasesThe referred SOFCs systems can operate in series or areintegrated with a catalytic reformer or membrane reformerwhich convert landfill gas into fuel-gas product at variousoperating conditions To be more specific these feedstockgases are rich in CH
4and are converted into an H
2 CO
and CO2mixture suitable for the continuous operation
of the SOFC unit The reformers studied here have been
Journal of Renewable Energy 7
Stainless steel casing ThermocoupleThermocouple
Thermocouples
Sweep gas in
Compression fitting
Product gases out
Graphitized string
Feedgases in Product
gases out
Alumina tube(membrane + support)
Figure 8 Ceramic membrane reactor
also studied by computational models taking into accountthe reaction and hydrogen separation in the permeablereformers Essential operating conditions in the permeablereformers have been simulated by the mathematical modelsThe experimental membrane reformer shows to offer higheryields than the nonmembrane type reformer for a number ofoperating conditions
It is worthy to notice that important distributed powergeneration within a wider power grid can be accomplishedwith this operation being able to cover the local needsof municipal and remote areas Fuel cell power relates tothe reformer conversion and the efficient utilization of thesyngas by the fuel cell The waste heat from the conversionof syngas to electricity can be descreased through the fuelcell operation and specifically through the operation of highefficiency SOFCs Fuel cell (SOFCs) continuous operationand power generation from landfill gas can lead to pollutionminimization higher power density and increased efficiency(reduced waste heat) in comparison with conventional powersystems
References
[1] Z Ziaka and S Vasileiadis ldquoCatalytic reforming -shift proces-sors for hydrogen generation and continuous fuel cell opera-tionrdquo in Proceedings of IASTED-Power and Energy Systems pp360ndash365 Marina Del Ray Calif USA May 2002
[2] S Vasileiadis and Z Ziaka-Vasileiadou ldquoBiomass reformingprocess for integrated solid oxide-fuel cell power generationrdquoChemical Engineering Science vol 59 no 22-23 pp 4853ndash48592004
[3] S Vasileiadis and Z Ziaka ldquoAlternative generation of H2 CO
and H2 CO2mixtures from steam-carbon dioxide reforming
of methane and the water gas shift with permeable (membrane)reactorsrdquo Chemical Engineering Communications vol 176 pp247ndash252 1999
[4] J Xu and G F Froment ldquoMethane steam reforming methana-tion and water-gas shift I Intrinsic kineticsrdquo AIChE Journalvol 35 no 1 pp 88ndash96 1989
[5] J P van Hook ldquoMethane-steam reformingrdquo Catalysis ReviewsScience and Engineering vol 21 no 1 pp 1ndash51 1980
[6] J R Rostrup-Nielsen ldquoSulfur-passivated nickel catalysts forcarbon-free steam reforming of methanerdquo Journal of Catalysisvol 85 no 1 pp 31ndash43 1984
[7] J R Rostrup-Nielsen ldquoCoking on nickel catalysts for steamreforming of hydrocarbonsrdquo Journal of Catalysis vol 33 no 2pp 184ndash201 1974
[8] J T Richardson and S A Paripatyadar ldquoCarbon dioxidereforming of methane with supported rhodiumrdquoApplied Catal-ysis vol 61 no 1 pp 293ndash309 1990
[9] E Ruckenstein and Y H Hu ldquoCombination of CO2reforming
and partial oxidation of methane over NiOMgO solid solutioncatalystsrdquo Industrial amp Engineering Chemistry Research vol 37no 5 pp 1744ndash1747 1998
[10] Z D Ziaka and S P Vasileiadis Reactors for Fuel Cells andEnvironmental Energy Systems Xlibris Publishing IndianapolisInd USA 2009
[11] S P Vasileiadis and Z D Ziaka ldquoEnvironmentally benignhydrocarbon processing applications of single and integratedpermreactorsrdquo in Reaction Engineering for Pollution Preventionpp 247ndash304 Elsevier Science Philadelphia Pa USA 2000
[12] Z D Ziaka and S P Vasileiadis ldquoReactor-membrane permeatorcascade for enhanced production and recovery of H2 andCO2 from the catalytic methane-steam reforming reactionrdquoChemical Engineering Communications vol 156 pp 161ndash2001996
[13] D L Klass Biomass for Renewable Energy Fuels and ChemicalsAcademic Press San Diego Calif USA 1988
[14] S Vasileiadis and Z Ziaka ldquoEfficient catalytic reactors-pro-cessors for fuel cells and synthesis applicationsrdquo in Proceedingsof the 17th International Symposium on Chemical ReactionEngineering Hong Kong August 2002 paper no 13
8 Journal of Renewable Energy
[15] R Rautenbach and K Welsch ldquoTreatment of landfill gas bygas permeationmdashpilot plant results and comparison to alterna-tivesrdquo Journal of Membrane Science vol 87 no 1-2 pp 107ndash1181994
[16] M Tsimpa Biogas usages in Greece for energy generationtrends and opportunities [MS thesis] HellenicOpenUniversityPatras Greece 2010
TribologyAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
FuelsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofPetroleum Engineering
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Industrial EngineeringJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Power ElectronicsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
CombustionJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Renewable Energy
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
StructuresJournal of
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nuclear InstallationsScience and Technology of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solar EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Wind EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nuclear EnergyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
High Energy PhysicsAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
6 Journal of Renewable Energy
08
07
06
05
04
03
02
01
0
Dim
ensio
nles
s mol
ar fl
owra
te
0 01 02 03 04 05 06 07 08 09 1
MethaneSteamHydrogen
Dimensionless distance (zL)
Reaction side (119879 = 450∘C)
Figure 5Modeling results of landfill gas-steam reformers for syngasproduction and SOFC continuous operation Molar flowrate data inthe reaction side (tubeside) (119875
119879119900
= 168 atm feed composition CH4
H2O H2= 1 4 020)
0 01 02 03 04 05 06 07 08 09 1
045
04
035
03
025
02
015
01
005
0
Dim
ensio
nles
s mol
ar fl
owra
te
MethaneSteamHydrogen
Dimensionless distance (zL)
Separation side (119879 = 450∘C)
Figure 6 Modeling results of landfill gas-steam reformers forsyngas production and SOFC continuous operation Molar flowratedata in the separation side (119875
119879119900
= 168 atm feed compositionCH4 H2O H2= 1 4 020)
axial length of the reactor The molar flowrates for steam andmethane decreasemonotonically along the axial length of thereactor
Figure 6 shows the dimensionless molar flow rate ofhydrogen steam and methane along the separation side orshellside of themembrane reactor In this case themolar flow
055
05
045
04
035
03
025
02
015
01
350 400 450 500 550 600 650
Temperature (∘C)
Calculated equilibrium yieldReactor with shellside closedMembrane reactor (no sweep gas)Membrane reactor model
Tota
l hyd
roge
n yi
eld
(gm
ole
hr)
Figure 7 Experimental and modeling results of landfill gas-steamreformers for syngas production and SOFC continuous operationTotal hydrogen yield data
rates for hydrogen steam and methane increase monotoni-cally along the axial length of the reactor
Finally Figure 7 shows the combined hydrogen yieldobtained with the two types of reactors The membranetype reformer offers better hydrogen yields than the non-membrane type reformer This is shown both with theexperimental and modeling results in Figure 7 It is thereforebeneficial to use the membrane reformer in the flow chart ofthis process to accomplish the operation
Moreover Table 1 below shows a summary of spec-ifications from a landfill-gas-processing plant for energycogeneration (landfill gas is coming from a concentratedlandfill site [16]) The table provides details on the energeticdistribution outcome of the entire plantThis table is given forcomparison purposes in order to evaluate the potential of thenewly described landfill gas to SOFC unit using the describedmembrane reactor and conventional reactor technologies Itis characteristic that the installed fuel cellSOFC can provideelectricity at a higher degree of efficiency than the respectivegas engine or gas turbine
4 Conclusions
It is shownhere that high temperature SOFCsfuel cells can becombined with reforming operations of landfill-based gasesThe referred SOFCs systems can operate in series or areintegrated with a catalytic reformer or membrane reformerwhich convert landfill gas into fuel-gas product at variousoperating conditions To be more specific these feedstockgases are rich in CH
4and are converted into an H
2 CO
and CO2mixture suitable for the continuous operation
of the SOFC unit The reformers studied here have been
Journal of Renewable Energy 7
Stainless steel casing ThermocoupleThermocouple
Thermocouples
Sweep gas in
Compression fitting
Product gases out
Graphitized string
Feedgases in Product
gases out
Alumina tube(membrane + support)
Figure 8 Ceramic membrane reactor
also studied by computational models taking into accountthe reaction and hydrogen separation in the permeablereformers Essential operating conditions in the permeablereformers have been simulated by the mathematical modelsThe experimental membrane reformer shows to offer higheryields than the nonmembrane type reformer for a number ofoperating conditions
It is worthy to notice that important distributed powergeneration within a wider power grid can be accomplishedwith this operation being able to cover the local needsof municipal and remote areas Fuel cell power relates tothe reformer conversion and the efficient utilization of thesyngas by the fuel cell The waste heat from the conversionof syngas to electricity can be descreased through the fuelcell operation and specifically through the operation of highefficiency SOFCs Fuel cell (SOFCs) continuous operationand power generation from landfill gas can lead to pollutionminimization higher power density and increased efficiency(reduced waste heat) in comparison with conventional powersystems
References
[1] Z Ziaka and S Vasileiadis ldquoCatalytic reforming -shift proces-sors for hydrogen generation and continuous fuel cell opera-tionrdquo in Proceedings of IASTED-Power and Energy Systems pp360ndash365 Marina Del Ray Calif USA May 2002
[2] S Vasileiadis and Z Ziaka-Vasileiadou ldquoBiomass reformingprocess for integrated solid oxide-fuel cell power generationrdquoChemical Engineering Science vol 59 no 22-23 pp 4853ndash48592004
[3] S Vasileiadis and Z Ziaka ldquoAlternative generation of H2 CO
and H2 CO2mixtures from steam-carbon dioxide reforming
of methane and the water gas shift with permeable (membrane)reactorsrdquo Chemical Engineering Communications vol 176 pp247ndash252 1999
[4] J Xu and G F Froment ldquoMethane steam reforming methana-tion and water-gas shift I Intrinsic kineticsrdquo AIChE Journalvol 35 no 1 pp 88ndash96 1989
[5] J P van Hook ldquoMethane-steam reformingrdquo Catalysis ReviewsScience and Engineering vol 21 no 1 pp 1ndash51 1980
[6] J R Rostrup-Nielsen ldquoSulfur-passivated nickel catalysts forcarbon-free steam reforming of methanerdquo Journal of Catalysisvol 85 no 1 pp 31ndash43 1984
[7] J R Rostrup-Nielsen ldquoCoking on nickel catalysts for steamreforming of hydrocarbonsrdquo Journal of Catalysis vol 33 no 2pp 184ndash201 1974
[8] J T Richardson and S A Paripatyadar ldquoCarbon dioxidereforming of methane with supported rhodiumrdquoApplied Catal-ysis vol 61 no 1 pp 293ndash309 1990
[9] E Ruckenstein and Y H Hu ldquoCombination of CO2reforming
and partial oxidation of methane over NiOMgO solid solutioncatalystsrdquo Industrial amp Engineering Chemistry Research vol 37no 5 pp 1744ndash1747 1998
[10] Z D Ziaka and S P Vasileiadis Reactors for Fuel Cells andEnvironmental Energy Systems Xlibris Publishing IndianapolisInd USA 2009
[11] S P Vasileiadis and Z D Ziaka ldquoEnvironmentally benignhydrocarbon processing applications of single and integratedpermreactorsrdquo in Reaction Engineering for Pollution Preventionpp 247ndash304 Elsevier Science Philadelphia Pa USA 2000
[12] Z D Ziaka and S P Vasileiadis ldquoReactor-membrane permeatorcascade for enhanced production and recovery of H2 andCO2 from the catalytic methane-steam reforming reactionrdquoChemical Engineering Communications vol 156 pp 161ndash2001996
[13] D L Klass Biomass for Renewable Energy Fuels and ChemicalsAcademic Press San Diego Calif USA 1988
[14] S Vasileiadis and Z Ziaka ldquoEfficient catalytic reactors-pro-cessors for fuel cells and synthesis applicationsrdquo in Proceedingsof the 17th International Symposium on Chemical ReactionEngineering Hong Kong August 2002 paper no 13
8 Journal of Renewable Energy
[15] R Rautenbach and K Welsch ldquoTreatment of landfill gas bygas permeationmdashpilot plant results and comparison to alterna-tivesrdquo Journal of Membrane Science vol 87 no 1-2 pp 107ndash1181994
[16] M Tsimpa Biogas usages in Greece for energy generationtrends and opportunities [MS thesis] HellenicOpenUniversityPatras Greece 2010
TribologyAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
FuelsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofPetroleum Engineering
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Industrial EngineeringJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Power ElectronicsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
CombustionJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Renewable Energy
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
StructuresJournal of
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nuclear InstallationsScience and Technology of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solar EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Wind EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nuclear EnergyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
High Energy PhysicsAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of Renewable Energy 7
Stainless steel casing ThermocoupleThermocouple
Thermocouples
Sweep gas in
Compression fitting
Product gases out
Graphitized string
Feedgases in Product
gases out
Alumina tube(membrane + support)
Figure 8 Ceramic membrane reactor
also studied by computational models taking into accountthe reaction and hydrogen separation in the permeablereformers Essential operating conditions in the permeablereformers have been simulated by the mathematical modelsThe experimental membrane reformer shows to offer higheryields than the nonmembrane type reformer for a number ofoperating conditions
It is worthy to notice that important distributed powergeneration within a wider power grid can be accomplishedwith this operation being able to cover the local needsof municipal and remote areas Fuel cell power relates tothe reformer conversion and the efficient utilization of thesyngas by the fuel cell The waste heat from the conversionof syngas to electricity can be descreased through the fuelcell operation and specifically through the operation of highefficiency SOFCs Fuel cell (SOFCs) continuous operationand power generation from landfill gas can lead to pollutionminimization higher power density and increased efficiency(reduced waste heat) in comparison with conventional powersystems
References
[1] Z Ziaka and S Vasileiadis ldquoCatalytic reforming -shift proces-sors for hydrogen generation and continuous fuel cell opera-tionrdquo in Proceedings of IASTED-Power and Energy Systems pp360ndash365 Marina Del Ray Calif USA May 2002
[2] S Vasileiadis and Z Ziaka-Vasileiadou ldquoBiomass reformingprocess for integrated solid oxide-fuel cell power generationrdquoChemical Engineering Science vol 59 no 22-23 pp 4853ndash48592004
[3] S Vasileiadis and Z Ziaka ldquoAlternative generation of H2 CO
and H2 CO2mixtures from steam-carbon dioxide reforming
of methane and the water gas shift with permeable (membrane)reactorsrdquo Chemical Engineering Communications vol 176 pp247ndash252 1999
[4] J Xu and G F Froment ldquoMethane steam reforming methana-tion and water-gas shift I Intrinsic kineticsrdquo AIChE Journalvol 35 no 1 pp 88ndash96 1989
[5] J P van Hook ldquoMethane-steam reformingrdquo Catalysis ReviewsScience and Engineering vol 21 no 1 pp 1ndash51 1980
[6] J R Rostrup-Nielsen ldquoSulfur-passivated nickel catalysts forcarbon-free steam reforming of methanerdquo Journal of Catalysisvol 85 no 1 pp 31ndash43 1984
[7] J R Rostrup-Nielsen ldquoCoking on nickel catalysts for steamreforming of hydrocarbonsrdquo Journal of Catalysis vol 33 no 2pp 184ndash201 1974
[8] J T Richardson and S A Paripatyadar ldquoCarbon dioxidereforming of methane with supported rhodiumrdquoApplied Catal-ysis vol 61 no 1 pp 293ndash309 1990
[9] E Ruckenstein and Y H Hu ldquoCombination of CO2reforming
and partial oxidation of methane over NiOMgO solid solutioncatalystsrdquo Industrial amp Engineering Chemistry Research vol 37no 5 pp 1744ndash1747 1998
[10] Z D Ziaka and S P Vasileiadis Reactors for Fuel Cells andEnvironmental Energy Systems Xlibris Publishing IndianapolisInd USA 2009
[11] S P Vasileiadis and Z D Ziaka ldquoEnvironmentally benignhydrocarbon processing applications of single and integratedpermreactorsrdquo in Reaction Engineering for Pollution Preventionpp 247ndash304 Elsevier Science Philadelphia Pa USA 2000
[12] Z D Ziaka and S P Vasileiadis ldquoReactor-membrane permeatorcascade for enhanced production and recovery of H2 andCO2 from the catalytic methane-steam reforming reactionrdquoChemical Engineering Communications vol 156 pp 161ndash2001996
[13] D L Klass Biomass for Renewable Energy Fuels and ChemicalsAcademic Press San Diego Calif USA 1988
[14] S Vasileiadis and Z Ziaka ldquoEfficient catalytic reactors-pro-cessors for fuel cells and synthesis applicationsrdquo in Proceedingsof the 17th International Symposium on Chemical ReactionEngineering Hong Kong August 2002 paper no 13
8 Journal of Renewable Energy
[15] R Rautenbach and K Welsch ldquoTreatment of landfill gas bygas permeationmdashpilot plant results and comparison to alterna-tivesrdquo Journal of Membrane Science vol 87 no 1-2 pp 107ndash1181994
[16] M Tsimpa Biogas usages in Greece for energy generationtrends and opportunities [MS thesis] HellenicOpenUniversityPatras Greece 2010
TribologyAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
FuelsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofPetroleum Engineering
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Industrial EngineeringJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Power ElectronicsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
CombustionJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Renewable Energy
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
StructuresJournal of
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nuclear InstallationsScience and Technology of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solar EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Wind EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nuclear EnergyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
High Energy PhysicsAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
8 Journal of Renewable Energy
[15] R Rautenbach and K Welsch ldquoTreatment of landfill gas bygas permeationmdashpilot plant results and comparison to alterna-tivesrdquo Journal of Membrane Science vol 87 no 1-2 pp 107ndash1181994
[16] M Tsimpa Biogas usages in Greece for energy generationtrends and opportunities [MS thesis] HellenicOpenUniversityPatras Greece 2010
TribologyAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
FuelsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofPetroleum Engineering
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Industrial EngineeringJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Power ElectronicsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
CombustionJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Renewable Energy
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
StructuresJournal of
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nuclear InstallationsScience and Technology of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solar EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Wind EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nuclear EnergyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
High Energy PhysicsAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
TribologyAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
FuelsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofPetroleum Engineering
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Industrial EngineeringJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Power ElectronicsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
CombustionJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Renewable Energy
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
StructuresJournal of
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nuclear InstallationsScience and Technology of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solar EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Wind EnergyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nuclear EnergyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
High Energy PhysicsAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014