Supercritical CO2 Brayton cycles for coal-fired power plants

Abstract

This paper investigates the supercritical CO2 cycles performance, from thermodynamic consideration and within realistic industrial modeling hypotheses, for coal power plant application. It proposes a design of such a power cycle for a first step implementation of the technology. Main findings are the following: even with the low temperature heat available in the coal combustion flue gas, a recompression cycle is mandatory for this application: the difference between this option and a standard Brayton cycle is more than 4.5%pt efficiency. Compared to no-reheated cycle, single reheat is an effective configuration with 1.5%pt efficiency increases. Another process improvement such as double reheat cycle, double recompression cycle and an advanced flue gas economizer configuration induce efficiency gain between 0.3 and 0.5%pt. Influence of the heat sink temperature stability has been quantified: 1.5%pt reduction for 5 °C increase with a minimal cycle pressure of 7 MPa; however, performance stability could be improved by adapting the main compressor inlet pressure. As a conclusion, CO2 supercritical coal-fired power plant theoretically offers interesting performances, of 47.8%-LHV efficiency, with existing materials at current operating conditions in a relatively near timeframe.