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Title: Analysis of Percent On-Cell Reformation of Methane in SOFC Stacks and the Effects on Thermal, Electrical, and Mechanical Performance

Abstract

Numerical simulations were performed to determine the effect that varying the percent on-cell steam-methane reformation would have on the thermal, electrical, and mechanical performance of generic, planar solid oxide fuel cell stacks. The study was performed using three-dimensional model geometries for cross-, co-, and counter-flow configuration stacks of 10x10- and 20x20-cm cell sizes. The analysis predicted the stress and temperature difference would be minimized for the 10x10-cm counter- and cross-flow stacks when 40 to 50% of the reformation reaction occurred on the anode. Gross electrical power density was virtually unaffected by the reforming. The co-flow stack benefited most from the on-cell reforming and had the lowest anode stresses of the 20x20-cm stacks. The analyses also suggest that airflows associated with 15% air utilization may be required for cooling the larger (20x20-cm) stacks.

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
921399
Report Number(s):
PNNL-SA-53556
AA2530000; TRN: US200804%%797
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: ECS Transactions, 5(1):473-480; Journal Volume: 5; Journal Issue: 1
Country of Publication:
United States
Language:
English
Subject:
03 NATURAL GAS; 30 DIRECT ENERGY CONVERSION; AIR; ANODES; CONFIGURATION; METHANE; PERFORMANCE; POWER DENSITY; SOLID OXIDE FUEL CELLS; STRESSES; solid oxide fuel cell; stack; modeling; on-cell; reformation; electrochemistry

Citation Formats

Recknagle, Kurtis P., Koeppel, Brian J., Sun, Xin, Khaleel, Mohammad A., Yokuda, Satoru T., and Singh, Prabhakar. Analysis of Percent On-Cell Reformation of Methane in SOFC Stacks and the Effects on Thermal, Electrical, and Mechanical Performance. United States: N. p., 2007. Web. doi:10.1149/1.2729027.
Recknagle, Kurtis P., Koeppel, Brian J., Sun, Xin, Khaleel, Mohammad A., Yokuda, Satoru T., & Singh, Prabhakar. Analysis of Percent On-Cell Reformation of Methane in SOFC Stacks and the Effects on Thermal, Electrical, and Mechanical Performance. United States. doi:10.1149/1.2729027.
Recknagle, Kurtis P., Koeppel, Brian J., Sun, Xin, Khaleel, Mohammad A., Yokuda, Satoru T., and Singh, Prabhakar. Mon . "Analysis of Percent On-Cell Reformation of Methane in SOFC Stacks and the Effects on Thermal, Electrical, and Mechanical Performance". United States. doi:10.1149/1.2729027.
@article{osti_921399,
title = {Analysis of Percent On-Cell Reformation of Methane in SOFC Stacks and the Effects on Thermal, Electrical, and Mechanical Performance},
author = {Recknagle, Kurtis P. and Koeppel, Brian J. and Sun, Xin and Khaleel, Mohammad A. and Yokuda, Satoru T. and Singh, Prabhakar},
abstractNote = {Numerical simulations were performed to determine the effect that varying the percent on-cell steam-methane reformation would have on the thermal, electrical, and mechanical performance of generic, planar solid oxide fuel cell stacks. The study was performed using three-dimensional model geometries for cross-, co-, and counter-flow configuration stacks of 10x10- and 20x20-cm cell sizes. The analysis predicted the stress and temperature difference would be minimized for the 10x10-cm counter- and cross-flow stacks when 40 to 50% of the reformation reaction occurred on the anode. Gross electrical power density was virtually unaffected by the reforming. The co-flow stack benefited most from the on-cell reforming and had the lowest anode stresses of the 20x20-cm stacks. The analyses also suggest that airflows associated with 15% air utilization may be required for cooling the larger (20x20-cm) stacks.},
doi = {10.1149/1.2729027},
journal = {ECS Transactions, 5(1):473-480},
number = 1,
volume = 5,
place = {United States},
year = {Mon Apr 30 00:00:00 EDT 2007},
month = {Mon Apr 30 00:00:00 EDT 2007}
}
  • This report summarizes a parametric analysis performed to determine the effect of varying the percent on-cell reformation (OCR) of methane on the thermal and electrical performance for a generic, planar solid oxide fuel cell (SOFC) stack design. OCR of methane can be beneficial to an SOFC stack because the reaction (steam-methane reformation) is endothermic and can remove excess heat generated by the electrochemical reactions directly from the cell. The heat removed is proportional to the amount of methane reformed on the cell. Methane can be partially pre-reformed externally, then supplied to the stack, where rapid reaction kinetics on the anodemore » ensures complete conversion. Thus, the thermal load varies with methane concentration entering the stack, as does the coupled scalar distributions, including the temperature and electrical current density. The endotherm due to the reformation reaction can cause a temperature depression on the anode near the fuel inlet, resulting in large thermal gradients. This effect depends on factors that include methane concentration, local temperature, and stack geometry.« less
  • This paper examines the electrochemical and on-cell steam-methane reforming performance of the solid oxide fuel cell when subjected to pressurization. Pressurized operation boosts the Nernst potential and decreases the activation polarization, both of which serve to increase cell voltage and power while lowering the heat load and operating temperature. A model considering the activation polarization in both the fuel and air electrodes was adopted to address this effect on the electrochemical performance. Both the increase in methane conversion kinetics and the increase in equilibrium methane concentration, which are competing effects of pressurization on steam-methane reforming, are considered in a newmore » rate expression. The models were then applied in simulations to preview how the distributions of reforming rate, temperature, and current density can potentially be changed within stacks operating at elevated pressure. A generic 10 cm counter-flow stack model was created and used for the simulations of pressurized operation. The predictions showed improved thermal and electrical performance with increased operating pressure. The average and maximum cell temperatures decreased by 3% while the cell voltage increased by 9% as the operating pressure was increased from 1 to 10 atmospheres.« less
  • This paper examines the electrochemical and direct internal steam-methane reforming performance of the solid oxide fuel cell when subjected to pressurization. Pressurized operation boosts the Nernst potential and decreases the activation polarization, both of which serve to increase cell voltage and power while lowering the heat load and operating temperature. A model considering the activation polarization in both the fuel and air electrodes was adopted to address this effect on the electrochemical performance. The pressurized methane conversion kinetics and the increase in equilibrium methane concentration are considered in a new rate expression. The models were then applied in simulations tomore » predict how the distributions of direct internal reforming rate, temperature, and current density are effected within stacks operating at elevated pressure. A generic 10 cm counter-flow stack model was created and used for the simulations of pressurized operation. The predictions showed improved thermal and electrical performance with increased operating pressure. The average and maximum cell temperatures decreased by 3% (20ºC) while the cell voltage increased by 9% as the operating pressure was increased from 1 to 10 atmospheres.« less
  • Planar Solid Oxide Fuel Cells (SOFC) stacks are multi-material layered systems with different thermo-mechanical properties. Due to their severe thermal loading, these layers have to meet high demands to preserve their mechanical integrity without initiation and propagation of fracture. Here, we focus on a typical unit cell of the stack which consists of positive electrode-electrolyte-negative electrode (PEN). Based on the mechanical properties of each layer and their interfaces, an energy criterion as a function of crack length is used for the prediction of possible crack extensions in the PEN. This criterion is a pure local criterion, independent of applied loadsmore » and geometry of the specimen. An analysis of the competition between crack deflections in the interfaces and crack penetration in layers is presented.« less