Performance evaluation with impurity effects as a part of conceptual design of oxy-coal combustion power generation system

Abstract

Global warming is critical issue for the sustainability of human being these days. The cause of this unnatural phenomenon is known to be the increase of $CO_2$ concentration in the air and the inter-governmental efforts to reduce $CO_2$ have been underway since the early 21centrury. Given the worsening environmental problem, oxy-fuel combustion is one of the viable methods to capture $CO_2$ from fossil fuel power plant. In the ideal oxy-fuel combustion system, pure oxygen is supplied to the boiler or furnace and the resulting gases from this combustion are expected to be $CO_2$ and $H_2O$ only. The $H_2O$ can be removed by the processes of cooling, compression and dehydration in sequence and the highly concentrated $CO_2$ stream, which is obtained from oxy-fuel combustion, is transported and stored in proper storage site. The feasibility study has been conducted on the retrofit project of Youngdong power station unit 1. The conventional power plant, capacity of 125MWe, was examined to be converted to the 100MWe oxy-coal combustion system, and the one of the critical issues analyzed were impurity impacts in the aspect of optimizing the oxygen supplied power generation system. Impurities mainly consist of non-condensable gases including $N_2$, Ar and $O_2$. Existence of these impurities requires additional separation work for sequestration of $CO_2$, which degrades net plant efficiency. The aim of this study is to examine the effects of impurity and to suggest ways to deal with impurities as a part of conceptual design of oxy-coal combustion power generation system. The scope of impurity sources considered in this research is $O_2$ purity, excess $O_2$ and air ingress. In order to simulate the whole process, cryogenic separation technology with two stage flash was assumed in the $CO_2$ stream purification process, and $CO_2$ purity, $CO_2$ recovery rate and power cost were compared to find out optimized operational mode. Flue gas compositions attained from...