A Thermodynamic Analysis of Electricity and Hydrogen Co-Production Using a Solid Oxide Fuel Cell

[+] Author and Article Information
Elisângela M. Leal

Combustion and Propulsion Laboratory, National Institute for Space Research (INPE), Cachoeira Paulista, SP, Brazil 12630-970elisangelaleal@yahoo.com

Jack Brouwer

National Fuel Cell Research Center, University of California, Irvine CA 92697jb@nfcrc.uci.edu

J. Fuel Cell Sci. Technol 3(2), 137-143 (Sep 29, 2005) (7 pages) doi:10.1115/1.2173669 History: Received July 18, 2005; Revised September 29, 2005

This paper presents the electricity and hydrogen co-production concept, a methodology for the study of SOFC hydrogen co-production, and simulation results that address the impact of reformer placement in the cycle on system performance. The methodology is based on detailed thermodynamic and electrochemical analyses of the systems. A comparison is made between six specific cycle configurations, which use fuel cell heat to drive hydrogen production in a reformer using both external and internal reforming options. SOFC plant performance has been evaluated on the basis of methane fuel utilization efficiency and each component of the plant has been evaluated on the basis of second law efficiency. The analyses show that in all cases the exergy losses (irreversibilities) in the combustion chamber are the most significant losses in the cycle. Furthermore, for the same power output, the internal reformation option has the higher electrical efficiency and produces more hydrogen per unit of natural gas supplied. Electrical efficiency of the proposed cycles ranges from 41 to 44%, while overall efficiency (based on combined electricity and hydrogen products) ranges from 45 to 80%. The internal reforming case (steam-to-carbon ratio of 3.0) had the highest overall and electrical efficiency (80 and 45% respectively), but lower second law efficiency (61%), indicating potential for cycle improvements.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Results of production of hydrogen from methane as a function of temperature and steam-to-carbon ratio (solid line (S=3) and dashed line (S=2)

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Figure 2

Cases 1–4: placement of a reformer in different locations (those four configurations consist of the placement of a reformer): (1) after the air preheater, (2) after the water preheater, (3) after the methane preheater, and (4) after the combustion

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Figure 3

SOFC configurations: (a) external reforming with combustion chamber after the air preheater (configuration 5); and (b) internal reforming option (configuration 6)

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Figure 4

Results of energy performance analysis

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Figure 5

Sankey diagram of the first configuration

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Figure 6

Results of exergy performance analyses (lines for efficiency, bars for irreversibilities)



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