Characteristics and economic evaluation of a CO_2-capturing repowering system with oxy-fuel combustion for utilizing exhaust gas of molten carbonate fuel cell (MCFC)

摘要

A scale of 2.4 MW molten carbonate fuel cell (MCFC) was taken to construct a high-efficiency and economic power generation system without CO_2 emission for utilizing its exhaust gas. A conventional steam turbine power generation system (STPS) is evaluated and the net generated power (NGP) is estimated to be only 131 kW and the STPS is not economically feasible. A CO_2-caputuring repowering system is proposed, where low temperature steam produced at heat recovery steam generator (HRSG) by using the MCFC exhaust gas is utilized as a main working fluid of a gas turbine, and the temperature of the steam is raised by combusting fuel in a combustor by using pure oxygen, not the air. It is estimated that NGP of the proposed system is 253 kW, and CO_2 reduction amount is 583 t-CO_2/y, compared to 302 t-CO_2/y for the STPS and that the proposed system becomes economically feasible if a CO_2 emission credit higher than 20 $/t-CO_2 can be granted. It is also estimated, when its turbine inlet temperature is increased from 850℃ to 1000℃, CO_2-capturing is not cost-consuming but becomes to be profitable, owing to improved power generation characteristics.