Performance Analysis And Parameter Optimization Of Semi-closed SCO₂ Cycle For Integrated Coal Gasification

With the orderly promotion of peaking carben dioxide emissions and achieving carbon neutralization in China,it is becoming more and more urgent to strengthen the clean and efficient utilization of coal and promote the low-carbon transformation of energy.The integrated coal gasification semi-closed sCO₂cycle power generation system,by coupling the coal gasification system,air separation system and semi-closed sCO₂cycle,can capture CO₂ while improving the power generation efficiency of coal-fired thermal power plants and realize near zero CO₂emission.In recent years,it has attracted more and more attention and research.The integrated coal gasification semi-closed sCO₂cycle is constructed,and the key processes of coal gasification system,air separation system and semi-closed sCO₂ cycle are simulated.On this basis,a semi-closed sCO₂ recompression cycle for integral coal gasification is proposed,and its thermal performance is compared with that of no recompression cycle.The effects of turbine inlet temperature,split ratio,turbine inlet pressure,minimum cycle temperature,compressor isentropic efficiency,turbine isentropic efficiency and minimum temperature difference of regenerator on the performance of integrated coal gasification semi closed sCO₂ recompression cycle were studied.The results show that the performance of the improved overall coal gasification semi closed sCO₂ cycle is significantly improved by adding the recompression process,the net cycle efficiency increases from 38.00%to 41.32%,and the CO₂ capture per unit power generation decreases from 0.935 kg/k W·h to 0.898 kg/k W·h.The comparison of multiple working conditions between recompression cycle and no recompression cycle shows that after the change of cycle structure,the conditions corresponding to the optimal efficiency of recompression cycle and no recompression cycle change.The non recompression cycle achieves the maximum net efficiency of 39.85%when the turbine inlet pressure is 32 MPa,the turbine inlet temperature is 1200℃and the turbine outlet pressure is 3.2 MPa.With recompression cycle,the maximum net efficiency is 41.95%when the turbine inlet pressure is 32 MPa,the turbine inlet temperature is 1150℃and the turbine outlet pressure is 3.2 Mpa.With the increase of turbine inlet temperature,turbine outlet pressure and split ratio,the cycle net efficiency increases monotonically.The system optimization results show that when the turbine inlet temperature is 1100℃,the turbine outlet pressure is 3.6MPa and the split ratio is 0.3,the net efficiency of the overall coal gasification semi closed sCO₂ recompression cycle is the highest,and the net efficiency can reach 42.49%after capturing nearly 100%sCO₂.When the minimum circulating temperature increases by 1℃,the net efficiency decreases by 0.23%.When the isentropic efficiency of the compressor increases by 1%,the net efficiency increases by 0.102%.When the isentropic efficiency of the turbine increases by 1%,the net efficiency of the cycle increases by 0.325%.When the minimum temperature difference of the heat exchanger increases by 1℃,the net efficiency of the cycle decreases by 0.178%.When the minimum temperature difference of the regenerator increases from 5℃to 20℃,the heat exchange area of the heat exchanger decreases by 64%.