C. Ozgur Colpan Ibrahim Dincer Feridun Hamdullahpur

Transcription

1 THERMODYNAMIC MODELING O DIRECT INTERNAL REORMING PLANAR SOLID OXIDE UEL CELLS WITH ANODE RECIRCULATION C. Ozgur Clpan Ibrahm Dncer erdun Hamdullahpur

2 OUTLINE INTRODUCTION TO SOCs Advantages, dsadvantages Operatn prncple Classfcatn Refrmng MODELING Carbn depstn prblem 0-D D mdelng (Thermdynamcselectrchemstry( Thermdynamcselectrchemstry) RESULTS NCLUSIONS

3 SOLID OXIDE UEL CELL Hgh temperature fuel cell ( C) Applcatn areas: Statnary pwer and heat generatn Transprtatn applcatns Prtable applcatns 3

4 SOLID OXIDE UEL CELL Hgh temperature fuel cell ( C) Applcatn areas: Statnary pwer and heat generatn Transprtatn applcatns Prtable applcatns Advantages: N need fr precus metal electrcatalysts uel fleblty Internal refrmng Gd thermal ntegratn wth ther systems Dsadvantages: Degradatn due t carbn depstn and sulphur psnng Challenges wth cnstructn and durablty 4

5 WHY PORTABLE SOCs? Operatn n hydrcarbn fuels Hgh energy densty fuel Safe, readly avalable fuels Smple fuel refrmng Lghter than batteres Quter than IC engnes Mre effcent than IC engnes Surce: Messcpc Devces, 006 5

6 SOLID OXIDE UEL CELL H H Ande Electrlyte Cathde H O H O e - e - e - e - O - O - Lad e - e - e - e - O O 6

7 SOLID OXIDE UEL CELL Classfcatn crtera Temperature level Cell and stack desgn Type f supprt lw cnfguratn uel refrmng type Types Lw temperature SOC (LT-SOC) (500 C 650 C) Intermedate temperature SOC (IT-SOC) (650 C 800 C) Hgh temperature SOC (HT-SOC) (800 C C) Planar SOC (lat-planar, radal-planar) Tubular SOC (Mcr-tubular, tubular) Segmented-n-Seres SOC (r Integrated-planar SOC) Mnlthc SOC Self-supprtng (Ande-supprted, cathde-supprted, electrlyte-supprted) Eternal-supprtng (Intercnnect supprted, prus substrate supprted) C-flw Crss-flw Cunter-flw Eternal refrmng SOC (ER-SOC) Drect nternal refrmng SOC (DIR-SOC) Indrect nternal refrmng SOC (IIR-SOC) 7

8 REORMING If the refrmatn f the gas ccurs utsde the stack Eternal refrmng If the refrmatn f the gas ccurs nsde the stack Internal refrmng If there s anther sectn whch s respnsble fr refrmng and a thermally n cntact wth sme f the ther cmpnents f the fuel cell Indrect I.R. If the refrmng and electrchemcal reactns take place at the ande catalyst Drect I.R. Reactns: 1 H O H O 1 O H O H CH 4 HO 3H Electrchemcal reactn f H Electrchemcal reactn f Water-gas shft reactn Steam refrmng reactn 8

9 SCHEMATIC f f1 f3 f6 UEL CHANNEL f4 f5 ANODE e - ELECTROLYTE CATHODE e - LOAD a1 AIR CHANNEL a 9

10 ASSUMPTIONS uel cell perates at steady state. Gas mture at the fuel channel et s at chemcal ulbrum. Pressure drps alng the fuel cell are neglected. Temperature at the channel nlets s same. Temperature at the channel ets s same uel cell s nsulated whch means that there s n heat nteractn wth envrnment. Only hydrgen s electrchemcally reacted. s cnverted t and H by water-gas shft reactn. Cntact resstances are gnred. Radatn transfers are gnred. 10

11 MODELING Take r0.1 Calculate mass flw rate f fuel, et and nlet gas cmpstns Step-I Yes N Is there carbn depstn pssblty? Calculate ar utlzatn rat Step-II Calculate cell vltage, pwer utput, electrcal effcency Step-III 11

12 MODELING-STEP I Et gas cmpstn f r CH 4 f 4, H f 4, N & CH 4 ( H a a a b f 4, a f 4, HO f 4, N f 4, f f 4 N & m& m& H O N & f f 4 3a b ) (1 r )(1 U a 1 r r U b a N ) ( H 3a b ) U a b 1 r r U a a f1 a1 f3 K K r s f6 ep ep UEL CHANNEL ANODE ELECTROLYTE CATHODE AIR CHANNEL [ Δg / RT ] ( I A c r [ Δg / RT ] s z z ( ( ( ( ) H O H H ( )( ) ( )( f4 1 r r U e - e - H 3 ) CH4 HO a 3a b ) U f5 LOAD P ) P ) ) 1

13 MODELING-STEP I Inlet gas cmpstn f f 3 ( CH 4 f 6, H f 6, N & CH 4 f 3 f 3 H f 3 e e 3e f 3 e f 3 e f f 6, e f 6, HO f 6, N f 6, N & f 3 f 3 f 3 H O f 3 N & f 3 f e f 3 N f 3 e e e f f r a ) 1 r K K UEL CHANNEL f1 f3 f6 ANODE ELECTROLYTE CATHODE AIR CHANNEL a1 r s ep ep [ Δg / RT ] r y [ Δg / RT ] s y ( ( ( ( ) H O H ( )( ) ( )( H 3 ) CH4 HO P ) P ) ) f4 e - e - a f5 LOAD 13

14 Carbn Depstn Prblem When methane, butane, prpane, JP-8, methanl, ethanl, etc. are fed drectly t the SOC Carbn depstn rsk Causes degradatn n the perfrmance and eventually the fuel cell s s breakdwn. Mechansms: CH 4 C H ( s ) C C H ( s ) ( s ) Slutn: Adjustng the S/C rat at the fuel channel nlet. H O Send steam frm an eternal surce Recrculate the depleted fuel Surce: Takeguch et al., 00, J. Pwer Surces, 11:

15 Mdelng f Carbn Depstn - THEORY Assume H O,, H ulbrum. (CP- )6-6 6 Thery, H,, CH 4 and C (s) are n chemcal Temperature, pressure, ne materal balance cnstrant and three ulbrum cnstant uatns Reactns: Steam-refrmng, water-gas shft reactn, crackng f methane Equatns: PCH4 α P β P δ PHO ε P H ζ ΔGrn K(T ) ep RT α β δ ε ζ P K 1 3 δ ζ α ε K β ζ δ ε K 3 ζ α 15

16 Mdelng f Carbn Depstn Slutn Methdlgy the partal pressure f ne f the gases Change the partal pressure f the fed gas between H0 and O0 Make ntal guesses fr the partal pressures f ther gases Slve the nn-lnear uatns and fnd the partal pressure f gases Calculate the C, H and O atm rats Obtan a set f data fr C-H-O rats 16

17 C-H-O O Trangular Dagram Carbn depstn pssblty at a gven temperature and pressure may be determned fr all pssble varatns f C-H-O C O systems usng ths dagram. C Carbn depstn 1400 K 100 K 1100 K 1000 K 900 K 800 K 800 K 900 K 1000 K 1100 K 100 K 1400 K H N Carbn depstn O 17

18 Carbn actvtes Carbn Actvtes CH 4 H a a a c4 c5 c6 K K K 4 C ( s ) ( H ) 5 6 H C C CH4 ( ) HO ( s ) H ( s ) H O α c 1 Carbn frmatn s bserved α c < 1 Carbn frmatn s thermdynamcally mpssble 18

19 19 19 MODELING MODELING-STEP II STEP II P P RT T g V O a H O H z z N ln ) ( Δ L ρ R V k k k cntact hm c s a s c act a act act RT RT V V V, 1, 1,, snh snh cs z as O H f H f z as z c cnc a cnc cnc RT p p RT RT V V V ln ln ln a z aeff H f as L RT D P 4 c z O a ceff O a cs L RT P P P D P 4 cn act hm N V V V V V j j a f C j j a f h N h N W h N h N & & & & & V I W C &

20 MODELING-STEP III V V N V hm V act V cn Cell vltage & W C I V Pwer utput η el, cell & N W& C LHV Electrcal effcency f the cell 0

21 Eergy Destructn n SOCs S& gen W& rev W& T act I ( V V ) N T s gen S& gen [ ( V V )] H, utlzed H, utlzed H, utlzed N T s gen ( V V V hm T act cn ) e D T s gen e D ( Vhm Vact Vcn ) 1

22 INPUT VALUES Gas cmpstn: 1% CH 4, 40% H, 0%, 18%, 1% N Input Temperature f the et (T( z ) Temperature dfference between et and nlet (ΔT)( Pressure f the cell (P( cell ) Actve surface area (A)( Echange current densty f ande (( a ) Echange current densty f cathde (( c ) Effectve gaseus dffusvty thrugh the ande Effectve gaseus dffusvty thrugh the cathde Thckness f ande (L a ) Thckness f electrlyte (L e ) Thckness f cathde (L( c ) Value 850 C 100 C 1 bar 100 cm 0.65 A/cm 0.5 A/cm 0. cm /s 0.05 cm /s 500 μm 10 μm 50 μm

23 Results Carbn Depstn Gas cmpstn: 1% CH 4, 40% H, 0%, 18% and 1% N r0.1 r0. r0.3 r0.4 r0.5 r0.6 r0.7 r0.8 C Carbn depstn Syngas LT-SOC U 0.85 Carbn actvty U 0.65 U 0.75 U 0.85 H N Carbn depstn O Recrculatn rat 3

24 Results Carbn Depstn r0.1 r0. r0.3 r0.4 r0.5 C Carbn depstn Syngas IT-SOC U 0.85 Carbn actvty U 0.65 U 0.75 U 0.85 H N Carbn depstn O Recrculatn rat 4

25 Results Carbn Depstn Mnmum recrculatn rat LT-SOC IT-SOC HT-SOC Glbal fuel utlzatn rat 5

26 Termnal vltage (V) r0.1 Ar utlzatn rat r0.3 r0.1 r r0.3 r Current densty (A/cm ) Current densty (A/cm ) Pwer utput [W] Current densty (A/cm ) r0.3 r0.1 r0. Electrcal effcency Current densty (A/cm ) r0.3 r0. 6 r0.1

27 Ar utlzatn rat U f 0.85 U f 0.75 U f 0.65 Termnal vltage (V) U f 0.85 U f 0.65 U f Current densty (A/cm ) Current densty (A/cm ) Pwer utput [W] U f 0.85 U f 0.75 U f 0.65 Electrcal effcency U f 0.85 U f 0.75 U f Current densty (A/cm ) Current densty (A/cm ) 7

28 NCLUSIONS Recrculatn s an effectve methd t suppress the carbn depstn pssblty. Recrculatn rat shuld be kept as mnmum as pssble t btan a better thermdynamc perfrmance. Hgher peratng temperature and glbal fuel utlzatn rat s needed t perate the system at lw recrculatn rats. r HT-SOC peratng at fuel utlzatn rat f 0.85, the mnmum recrculatn rat s fund t be 7% fr the selected fuel. Chemcal knetcs shuld be taken nt accunt t ncrease the accuracy f the results. -D D transent mdelng f a SOC wll be dne as a future study. Addtnally, entrpy generatn mnmzatn and thermecnmc ptmzatn f several systems based n SOC wll be cnducted. 8

29 ACKNOWLEDGEMENTS The fnancal and techncal supprt f an Ontar Premer s Research Ecellence Award, the Natural Scences and Engneerng Research Cuncl f Canada, Carletn Unversty and Unversty f Ontar and Insttute f Technlgy s gratefully acknwledged. 9