Study on CO2 capture upgrading of existing coal fired power plants with gas steam mixture cycle and supercritical water coal gasification

Abstract Upgrading instead of phasing out the existing coal fired power plants for CO2 capture with high efficiency is an alternative to the tough task for realizing the commitment for Paris Agreement and carbon neutrality. A gas steam mixture power cycle with syngas from supercritical water coal gasification (GSMC-C) is proposed and studied, using syngas fuel/O2 combustion products mixed with feedwater as working medium to realize power generation with CO2 capture in internal process from the non-condensable gases of condenser. A top-turbine is set before the existing turbine unit for increasing the cycle efficiency with higher turbine inlet parameters and the working medium from the reheating combustor is used for coal gasification heating first. The effects of some key parameters on the performances of the cycle such as net efficiency, specific turbine output and percentage of auxiliary power were studied. The results show that the net efficiency and gross efficiency of GSMC-C system were 41.96% and 48.67% respectively under the conditions of top-turbine inlet parameters of 30 MPa/650°C, condenser parameters of 30 kPa/30°C and ASU specific power consumption of 0.245 kWh·kg−1(O2). The GSMC-C system can provide a reference for retrofitting coal-fired power plants into clean and efficient power plants with nearly zero emissions of CO2 and other pollutants.