Thermodynamic analysis of a novel high-efficiency coal-based sCO2 power cycle combining semi-closed oxy-combustion cycle with sCO2 Brayton cycle

Abstract

The semi-closed oxy-combustion cycle (SCOCC) is a highly promising low-carbon power generation technology. When it is applied to coal-based fuels, the inefficient recovery of raw syngas heat during coal gasification constrains the cycle performance due to the limitation of the allowable temperature of heat exchangers. This study develops a novel coal-based supercritical CO₂ (sCO₂) power cycle that thermally integrates the sCO₂ Brayton cycle into the SCOCC to make full use of the raw syngas heat. The thermodynamic analysis reveals that the sCO₂ Brayton cycle recovers 71 % of the raw syngas heat and contributes 12 % to the total net output power. The proposed power cycle achieves a system efficiency of 48.69 %, representing an 8.11 % improvement over the basic cycle. The system exergy efficiency rises from 37.69 % to 45.22 %, with the gasifier and combustor identified as the primary sources of exergy losses. Sensitivity analysis reveals that cold gas efficiency has the greatest impact on system performance, with a 1 % increase leading to a 0.62 % efficiency gain. Turbine isentropic efficiency ranks as the second most significant factor, whereas compressor isentropic efficiency and pinch point temperature difference (PPTD) have comparatively minor influences. After parameter optimization, the coal-based sCO₂ power cycle attains a system efficiency of 51.28 % under conditions of a 5 °C PPTD, 84 % cold gas efficiency, and turbine and compressor isentropic efficiencies of 0.93 and 0.91, respectively.