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Research Papers

Dynamic Modeling of a Compact Heat Exchange Reformer for High Temperature Fuel Cell Systems

[+] Author and Article Information
Jeongpill Ki

 Mechanical and Aerospace Engineering, 500 W. 1st Street, The University of Texas at Arlington, Arlington, TX 76019jeong.ki@mavs.uta.edu

Daejong Kim1

 Mechanical and Aerospace Engineering, 500 W. 1st Street, The University of Texas at Arlington, Arlington, TX 76019daejongkim@uta.edu

Srikanth Honavara-Prasad

 Mechanical and Aerospace Engineering, 500 W. 1st Street, The University of Texas at Arlington, Arlington, TX 76019srikanth.honavaraprasad@mavs.uta.edu

1

Corresponding author.

J. Fuel Cell Sci. Technol 9(1), 011013 (Dec 22, 2011) (16 pages) doi:10.1115/1.4004709 History: Received January 13, 2011; Revised July 20, 2011; Published December 22, 2011; Online December 22, 2011

Solid oxide fuel cells (SOFC) are the most advanced energy system with the highest thermal efficiency. Current trend of research is on less than 10 kW scale, which requires compact fuel processing systems. Even if internal reforming in the stack is also a possible option, it causes significant temperature gradients and thermal stress. As an alternative, a compact heat exchange reformer (CHER) with a plate-fin co-flow or counter-flow configuration is proposed. Such a system integrates the heat management and reforming in one compact unit. This paper focuses on simulation of transient characteristics of CHER during the initial phase of start-up of small SOFC systems. Steam reforming (SR) and water-gas shift (WGS) reactions are chosen as the most appropriate reforming model. CHER is modeled as two-dimensional array of finite control volumes, and they are modeled with transient energy equations and dynamic molar balance equations. In addition, both reaction enthalpy and convection heat transfer between the catalyst-coated fins and fuel-steam mixture channels are considered. Several parametric simulations are performed as methane steam as a primary fuel mixture as a function of different operating temperature, steam-to-carbon ratio at the inlet, pressure gradient across the CHER, channel length, and flow configuration (co-flow and counter-flow).

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Stages of a dynamic SOFC system. CHER: compact heat exchange reformer, CI: cathode inlet plenum, CE: cathode exit plenum, AI: Anode inlet plenum, AE: anode exit plenum, COMB: combustor, M/C: mixing chamber, HEX: heat exchanger

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Figure 2

Configuration of CHER and flow directions of gases

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Figure 3

Cross section of CHER flow passages with fins and plates, simplified model and model of thermal circuit

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Figure 4

System layout for simulation of co-flow CHER

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Figure 5

Coordinate system for model discretization (y is along the flow direction), Nx  = 10, Ny  = 30

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Figure 6

Schematic diagrams of heat transfers in CHER stack

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Figure 7

Temperature distributions in each channel and plate (90 s) Tair  = 600 °C, TFSM  = 500 °C, Tinitial  = 500 °C, SCR = 2.5, ΔP = 1000 Pa, L = 762 mm

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Figure 8

Temperature distributions in each channel and plate (90 s) Tair  = 700 °C, TFSM  = 600 °C, Tinitial  = 600 °C, SCR = 2.5, ΔP = 1000 Pa, L = 762 mm

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Figure 9

Molar fractions of each species with different temperature sets at steady state in the central channel, SCR = 2.5, ΔP = 1000 Pa, L = 762 mm

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Figure 10

Mass flow rate of FSM and H2 in central channel at different temperature

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Figure 11

Temperature of FSM at various SCRs in the central channel

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Figure 12

Molar fraction of each species inside FSM channel (SCR: 2.0, 90 s)

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Figure 13

Molar fraction of each species inside FSM channel (SCR: 2.5, 90 s)

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Figure 14

Molar fraction of each species inside FSM channel (SCR: 3.0, 90 s)

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Figure 15

Molar fractions of each species at various SCRs in the central channel

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Figure 16

Mass flow rate of FSM, H2 and CO in central channel with different ΔP

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Figure 17

Temperature distributions in the central channel at different ΔP

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Figure 18

Mass flow rate of H2 in central channel and temperatures of FSM and catalytic fin at outlet with different channel lengths

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Figure 19

Temperatures and chemical compositions with different flow directions

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