Research Article Pretreated Landfill Gas Conversion ...

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


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


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


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 )


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


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


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



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


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


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


[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

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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



minus(

2120587

119899119879

119860119900

)119875119860119890[

119901119879

119860minus 119901119878

119860

ln (11990311199032)

] (11)

wherein 119875119860119890





2) H2and CO

2 or H

2and
















90

80

70

60

50

40

30

20

10

0

350 400 450 500 550 600 650

Met

hane

conv

ersio

n (

)


Temperature (∘C)


119879119900




80

70

60

50

40

30

20

10

0

Carb

on d

ioxi

de y

ield

()

350 400 450 500 550 600 650


Temperature (∘C)


119879119900













90

80

70

60

50

40

30

20

10 15 20 25 30 35 40 45 50

Met

hane

conv

ersio

n (

)


119879 = 550∘C



119879119900





2yield data


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


119879 = 550∘C



119879119900



2yields





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





119879119900


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





119879119900




055

05

045

04

035

03

025

02

015

01

350 400 450 500 550 600 650

Temperature (∘C)


Tota

l hyd

roge

n yi

eld

(gm

ole

hr)





4 Conclusions



2 CO





Thermocouples

Sweep gas in

Compression fitting

Product gases out

Graphitized string


gases out





References

























FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of



















minus(

2120587

119899119879

119860119900

)119875119860119890[

119901119879

119860minus 119901119878

119860

ln (11990311199032)

] (11)

wherein 119875119860119890





2) H2and CO

2 or H

2and
















90

80

70

60

50

40

30

20

10

0

350 400 450 500 550 600 650

Met

hane

conv

ersio

n (

)


Temperature (∘C)


119879119900




80

70

60

50

40

30

20

10

0

Carb

on d

ioxi

de y

ield

()

350 400 450 500 550 600 650


Temperature (∘C)


119879119900













90

80

70

60

50

40

30

20

10 15 20 25 30 35 40 45 50

Met

hane

conv

ersio

n (

)


119879 = 550∘C



119879119900





2yield data


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


119879 = 550∘C



119879119900



2yields





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





119879119900


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





119879119900




055

05

045

04

035

03

025

02

015

01

350 400 450 500 550 600 650

Temperature (∘C)


Tota

l hyd

roge

n yi

eld

(gm

ole

hr)





4 Conclusions



2 CO





Thermocouples

Sweep gas in

Compression fitting

Product gases out

Graphitized string


gases out





References

























FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of






















90

80

70

60

50

40

30

20

10

0

350 400 450 500 550 600 650

Met

hane

conv

ersio

n (

)


Temperature (∘C)


119879119900




80

70

60

50

40

30

20

10

0

Carb

on d

ioxi

de y

ield

()

350 400 450 500 550 600 650


Temperature (∘C)


119879119900













90

80

70

60

50

40

30

20

10 15 20 25 30 35 40 45 50

Met

hane

conv

ersio

n (

)


119879 = 550∘C



119879119900





2yield data


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


119879 = 550∘C



119879119900



2yields





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





119879119900


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





119879119900




055

05

045

04

035

03

025

02

015

01

350 400 450 500 550 600 650

Temperature (∘C)


Tota

l hyd

roge

n yi

eld

(gm

ole

hr)





4 Conclusions



2 CO





Thermocouples

Sweep gas in

Compression fitting

Product gases out

Graphitized string


gases out





References

























FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of




















90

80

70

60

50

40

30

20

10 15 20 25 30 35 40 45 50

Met

hane

conv

ersio

n (

)


119879 = 550∘C



119879119900





2yield data


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


119879 = 550∘C



119879119900



2yields





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





119879119900


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





119879119900




055

05

045

04

035

03

025

02

015

01

350 400 450 500 550 600 650

Temperature (∘C)


Tota

l hyd

roge

n yi

eld

(gm

ole

hr)





4 Conclusions



2 CO





Thermocouples

Sweep gas in

Compression fitting

Product gases out

Graphitized string


gases out





References

























FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of


















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





119879119900


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





119879119900




055

05

045

04

035

03

025

02

015

01

350 400 450 500 550 600 650

Temperature (∘C)


Tota

l hyd

roge

n yi

eld

(gm

ole

hr)





4 Conclusions



2 CO





Thermocouples

Sweep gas in

Compression fitting

Product gases out

Graphitized string


gases out





References

























FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of



















Thermocouples

Sweep gas in

Compression fitting

Product gases out

Graphitized string


gases out





References

























FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of
























FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of

















Research Article Pretreated Landfill Gas Conversion ...

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