Research Papers

Kawagoe 300kW Class MCFC/TCG Compact System: Thermal Efficiency and Endurance Test Results

[+] Author and Article Information
Fumihiko Yoshiba

Energy Engineering Research Laboratory, Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka 240-0196, Japanyoshiba@criepi.denken.or.jp

J. Fuel Cell Sci. Technol 5(2), 021010 (Apr 18, 2008) (16 pages) doi:10.1115/1.2784281 History: Received November 24, 2005; Revised June 26, 2006; Published April 18, 2008

A 300kW class molten carbonate fuel cell (MCFC)/gas turbine combined compact system has been designed; the system has a 250-cell MCFC stack and a turbocharger generator (TCG) as part of its gas turbine. The 250-cell stack had trouble with a gas leakage; thus, a modified 125-cell stack was refabricated and operated in the system. Using the operation results of the 125-cell+TCG system, the thermal efficiency was estimated for the 250-cell+TCG system of the original design. The estimated thermal efficiency is 41.0% high heating value (HHV) (45.4% low heating value); the efficiency is 2% lower than the expected value of the original design. The difference of the thermal efficiency between the estimated and expected values of the 250-cell MCFC stack is due to the increase of the internal resistance caused by the stacking procedure. The 125-cell stack was operated for 1700h with the TCG and 3200h with an external air supply system at an operating current density of 1500Am2; the maximum thermal efficiency of the 250-cell+TCG system was estimated (43.0% HHV) at an operating current density of 1500Am2. The cell voltage degradation rate was converted to be 0.39%1000h at an operating current density of 2000Am2. The thermal efficiency, the stack performance, the temperature distribution of the stack, the performance of the TCG, etc., are discussed in detail.

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 1

Configuration of the MCFC/GT compact system

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Figure 2

Schematic structure of the MCFC stack

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Figure 3

OCV and cell voltage of each cell in the stack

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Figure 4

Measured and estimated I-V curve

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Figure 5

Measured and estimated cell voltage versus operating pressure

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Figure 6

Measured temperature distribution of the stack. Operating pressure=0.0952MPa(1.97atm(absolute)), current density=1835A∕m2, fuel utilization=79.9%, supplied anode gas composition: H2∕CO2∕CO∕CH4∕H2O=54.1∕6.3∕10.4∕0.5∕28.6, CO2∕O2utilization=36.0% and 24.7%, supplied cathode gas composition: CO2∕O2∕N2∕H2O=7.4∕9.8∕60.6∕22.2, anode/cathode inlet gas flow rate=190Nm3∕h∕3620Nm3∕h, anode/cathode pressure drop=750Pa∕4588Pa (calculated), average voltage=688mV (stand-alone efficiency=54.9%̱H2̱LHV), standard deviation=12mV.

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Figure 7

Measure and estimation procedure of the system performance

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Figure 8

Measured temperature and pressure of the 125-cell+TCG system. Fuel utilization=80% and current density=1800A∕m2; the heat unbalance of the MCFC stack and BOP is adjusted by supplying additional natural gas from stream 46.

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Figure 9

Estimated system temperature and pressure of the 250-cell+TCG system

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Figure 10

Mass and heat balance in TCG in the measured 125-cell+TCG system (75,000rpm)

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Figure 11

Mass and heat balance of TCG in the estimated 250-cell+TCG system (90,000rpm)

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Figure 12

Average cell voltage, and difference between designed and observed voltages, versus operating time in endurance test

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Figure 13

Change of reforming efficiency of the reformer during the endurance test

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Figure 14

Thermal efficiency change by the stack performance degradation during the 5000h operation (estimated value). The operating current density in the endurance test was fixed at the same value as in the maximum efficiency case.

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Figure 15

Thermal efficiency at partial load operating conditions




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