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

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.