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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

## Abstract

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 $∼1500A∕m2$; the maximum thermal efficiency of the $250-cell+TCG$ system was estimated (43.0% HHV) at an operating current density of $1500A∕m2$. The cell voltage degradation rate was converted to be $0.39%∕1000h$ at an operating current density of $2000A∕m2$. The thermal efficiency, the stack performance, the temperature distribution of the stack, the performance of the TCG, etc., are discussed in detail.

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## Figures

Figure 1

Configuration of the MCFC/GT compact system

Figure 2

Schematic structure of the MCFC stack

Figure 3

OCV and cell voltage of each cell in the stack

Figure 4

Measured and estimated I-V curve

Figure 5

Measured and estimated cell voltage versus operating pressure

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.

Figure 7

Measure and estimation procedure of the system performance

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.

Figure 9

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

Figure 10

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

Figure 11

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

Figure 12

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

Figure 13

Change of reforming efficiency of the reformer during the endurance test

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.

Figure 15

Thermal efficiency at partial load operating conditions

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