SYSTEM DESIGN AND THERMODYNAMIC ANALYSIS ON A COAL SUPERCRITICAL WATER GASIFICATION POWER GENERATION SYSTEM INTEGRATED WITH SUPERCRITICAL CARBON DIOXIDE CYCLE

Coal supercritical water gasification (SCWG) is a potential clean coal technology. To enhance the efficiency and reduce carbon emissions of SCWG coal power, a novel coal SCWG power generation system with supercritical CO2 (S-CO2) circulating is proposed in this study. The system achieves autothermal gasification by partial oxidation of coal. Syngas combusts with pure oxygen, and mixes with circulating S-CO2 to form the CO2-dominated mixed working medium for power generation. Turbine exhaust is split into three streams to preheat oxygen, water and S-CO2 in the heat exchanger (HEX), respectively. With an appropriate flow rate of circulating S-CO2, HEX has a good temperature difference matching, which decreases the heat transfer exergy destruction. The system simulation and exergy analysis models are developed. Results show the energy and exergy efficiency of system with benchmark conditions are 50.23% and 49.00%, respectively. Exergy destruction of combustor accounts for 52.61% of the total exergy loss, and that of HEX accounts for 19.30%. Additionally, effects of key parameters are investigated. The optimal water coal ratio (WCR) is 1.7, the optimal gasification pressure is 26 MPa (WCR is 1.7), higher gasification pressure (WCR is 1.8), and higher turbine inlet temperature can improve the system efficiency.