Operational behavior and reforming kinetics over Ni/YSZ of a planar type pre-reformer for SOFC systems

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1 Mitglied der elmholtz-gemeinschaft nd World Congress on Petrochemistry and Chemical Engineering ctober 9 th, 01 Las Vegas, USA erational behavior and reforming kinetics over Ni/YSZ of a lanar tye re-reformer for SFC systems Van Nhu Nguyen, Ludger Blum, Roland Peters Forschungszentrum Jülich Gmb, Germany va.nguyen@fz-juelich.de

2 utline Introduction Global reaction kinetics Exerimental setu Results Modeling Conclusions Institute of Energy and Climate Research Electrochemical Process Engineering (IEK-3)

3 Basic layout of the SFC system Reaction in the Cathode: + e - - Reactions in the Anode: e - C + - C + e -, C, C, C, Institute of Energy and Climate Research Electrochemical Process Engineering (IEK-3) 3

4 Steam reforming reactions of methane Reaction - (5 C) [kj/mol] R1 C + C R C + C R3 C + C C + -7 R C + C + 1 R5 C C R6 C C + C 17 R7 C + C Institute of Energy and Climate Research Electrochemical Process Engineering (IEK-3)

5 Models for global reaction kinetics T R E ex F r a β α C Arr r, ( ) C C C C Lang r, K K 1 K K k r + + 1) Arrhenius tye ) Langmuir-inshlewood tye Institute of Energy and Climate Research Electrochemical Process Engineering (IEK-3) 5 C e,str 3 C C eq r, K 1 k r C e,s C C s s K 1 k r 3) Equilibrium aroach ) Water shift reaction aroach

6 Global reaction kinetics (Arrhenius tye) r k α β r, Arr C where k F ex R E a T Literature data review: inconsistent results of kinetics * : ( 1 was used very often) * Andersson M, Yuan J, Sunden B, Alied Energy 010; 87:161 : negative and ositive values Ea : - 08 kj/mol Motivation: Find the real global kinetics of steam reforming reactions timization of re-reformer for SFC-system Institute of Energy and Climate Research Electrochemical Process Engineering (IEK-3) 6

7 Design of a 5-layer re-reformer using air heater Catalyst: Ni/YSZ (Ni + 8 mol% Y3-stabilized Zr) Catalyst s Institute of Energy and Climate Research Electrochemical Process Engineering (IEK-3) 7

8 Flow scheme of the exerimental setu Institute of Energy and Climate Research Electrochemical Process Engineering (IEK-3) 8

9 Results The comarison between the comositions for equilibrium and measurement as function of temerature and sace-time Analytical methods dew-oint-measurement gas-chromatograhic method τ V v o reactor volume volumetric feed rate Institute of Energy and Climate Research Electrochemical Process Engineering (IEK-3) 9

10 Grahs of concentration versus sace time The exerimental data fit not first order kinetics for methane concentration C S/C, k 6 70% AGR, k % AGR, k 37 x C / x C,inlet y e -1,861x 1-layer-reformer, S/C 5-layer-reformer, S/C 70% Recycle 0. y e -.5x 80% Recycle y e -3.09x root (τ/s) τ V v o reactor volume volumetric feed rate Institute of Energy and Climate Research Electrochemical Process Engineering (IEK-3) 10

11 Modeling (Arrhenius tye) Integrated reaction rate τ layer-reformer ; 1 k 106 k 66 k 35 k 1 k 6, d Sace time / s ( ξ) ( x ξ) ( x ξ) 0 0, C 0, ξ: Progress variable of reforming reaction k τ 60 C 500 C 580 C 660 C 70 C Integrated reaction rate τ V v o reactor volume volumetric feed rate Integrated reaction rates from ex. data of the both reformers 1- and 5-layer-reformer ; 1 k 35 k Sace time /s 500 C 1-layer 500 C 5-layer 580 C 1-layer 580 C 5-layer Institute of Energy and Climate Research Electrochemical Process Engineering (IEK-3) 11

12 Temerature deendency of reaction rate ln(k) layer-reformer ln(k) -6,31 * (1000/T) + 10, Ea 50 kj/mol** (1/T) * 1000 ** Drescher I. Kinetik der Methan-Damf- Reformierung. Diss RWT Aachen Ea kj/mol*** *** Liu, K., Song, C., Subramani, V. (Eds.) Wiley & Sons Publication; 010. ln(k) Temerature: 350 C 60 C Ea 53 kj/mol* S/C,0 S/C,5 S/C3,0 * Nguyen,V.N., Blum, L., Peters, Ro., Int. J. ydrogen Energy (01) 39: 7131 Temerature: 60 C 70 C 1-layer-reformer ln(k) -6,5 *(1000/T) + 11, (1/T) *1000 Ea 5 kj/mol S/C.0 S/C.5 S/C3.0 Institute of Energy and Climate Research Electrochemical Process Engineering (IEK-3) 1

13 Effect of anode off-gas recycling (AGR) Integrated reaction rate % AGR ; 1 k 37 k 6 k Sace time / s 80 C 50 C 610 C AGR at 70% fuel utilization Examle at 610 C: Without AGR, k 6 70% AGR, k % AGR, k 37 ln(k) -1,09 * (1000/T) + 1,80 Ea 117 kj/mol τ ( ξ) ( x ξ) ( x ξ) 0 0, C 0, d ξ: Progress variable of reforming reaction k τ ln(k) 3 ln(k) -1,15*(1000/T) + 1, /T 80% AGR 70% AGR Institute of Energy and Climate Research Electrochemical Process Engineering (IEK-3) 13

14 Conclusions Two different lanar re-reformers containing Ni/YSZ catalyst were tested for oerational behavior and kinetics of methane steam reforming reactions in a temerature-range of 350 C - 70 C. Exerimental results for the two reformers are close to each other. The develoed kinetic exression of Arrhenius tye (second order with resect to mole fraction of methane and first order with resect to mole fraction of water) gives a good agreement with the exerimental results. This kinetic exression ( ; 1) is universally alicable for different steam to carbon ratios and also for the case of anode off-gas recycling (AGR). In the case of anode off-gas recycling the reaction rate constant is larger than that without AGR. Understanding of the methane steam reforming reactions is exected to be of significant imortance for the further develoment of SFC systems. Institute of Energy and Climate Research Electrochemical Process Engineering (IEK-3) 1

15 Acknowledgement goes to all staff members of JÜLIC for their excellent work and to the elmholtz Society for financing these activities Thank you for your attention! Institute of Energy and Climate Research Electrochemical Process Engineering (IEK-3) 15