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Research Papers

Development of Direct Carbonate Fuel Cell Systems for Achieving Ultrahigh Efficiency

[+] Author and Article Information
Hossein Ghezel-Ayagh, Ramki Venkataraman, Mohammad Farooque, Robert Sanderson

 FuelCell Energy, Inc., 3 Great Pasture Road, Danbury, CT 06810

Joseph McInerney1

 FuelCell Energy, Inc., 3 Great Pasture Road, Danbury, CT 06810jmcinerney@fce.com

1

Corresponding author.

J. Fuel Cell Sci. Technol 8(3), 031011 (Feb 22, 2011) (10 pages) doi:10.1115/1.4002905 History: Received July 09, 2010; Revised July 21, 2010; Published February 22, 2011; Online February 22, 2011

FuelCell Energy, Inc. (FCE) has developed products based on its Direct FuelCell® (DFC® ) technology with efficiencies near 50% based on lower heating values of natural gas. DFC is an internally reformed molten carbonate fuel cell, which operates in the 550700°C range. The combination of the internal reforming of methane and atmospheric pressure and moderately high temperature of operation has resulted in very simple power plant system configurations. Recently, FCE has developed system concepts to further increase the net electric efficiency to beyond 60% efficiency in sub-MW and MW class power plants. One of these system concepts is the arrangement of the fuel cell stacks in series for very high utilization of fuel in the stacks. Although, in principle, the concept of fuel cell stacks in series is very simple, the implementation of the concept in the actual hardware poses challenges requiring innovative solutions. These challenges include concerns with thermomechanical issues, flow and utilization patterns within the fuel cell stacks, and management of the pressure balance between the anode and the cathode. To address these issues, various analytical tools, including system-level modeling and simulation and computational fluid dynamics (CFD), were utilized. FCE has developed a comprehensive fuel cell stack operation simulation model including hydrodynamics, kinetics, electrochemical, and heat transfer mechanisms to investigate and optimize the design for performance as well as endurance. Various system configurations were developed, which included methods for fueling the second tier stacks in the series. System simulation studies using first principle mass and energy conversation laws were performed. Parametric studies were completed. Subsequent to the system modeling results, the fuel cell stack operations were analyzed using the comprehensive stack simulation model. The CFD modeling of the fuel cell stacks was performed in support of the system simulation parametric studies. The results of the CFD modeling provided insight to the thermal and flow profiles of both first and second tier stacks in series. The net outcome of the investigation was the design of the system, which met the goals of ultrahigh efficiency and yet complied with the thermomechanical requirements of the fuel cell stack components. In this paper, FCE will describe various system options for the very high efficiency systems, the issues related to the design, and the practical solutions to overcome the issues.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

DFC3000 system with parallel fuel and air to two fuel cell modules

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Figure 2

The arrangement of the fuel cell stacks in one of the stack modules used in DFC3000

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Figure 3

System with cascaded fuel cells (DFC2)

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Figure 4

Effect of module 2 current on DFC2 plant efficiency

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Figure 5

DFC2 plant efficiency versus net power

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Figure 6

DFC stacks employ both DIR and IIR for stack cooling

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Figure 7

Typical fuel path through a RU

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Figure 8

Typical fuel path through an ACC

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Figure 9

Typical oxidant path through a CCC; cross flow cathode

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Figure 10

Stack 1 RU/IIR reforming reaction rate (mol/s)

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Figure 11

Stack 1 ACC/DIR reforming reaction rate (mol/s)

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Figure 12

Stack 2 DIR reforming reaction rate (mol/s)

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Figure 13

Temperature profile for stack 1 (K)

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Figure 14

Temperature profile for stack 2 (K)

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Figure 15

Stack 2 DIR reforming reaction rate (mol/s) near end of life

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Figure 16

Temperature profile for stack 2 near end of life (K)

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