Research On Cooler Heat Recovery Method And Optimization In S-CO₂ Coal-fired Power Generation System

Supercritical carbon dioxide(S-CO2)cycle is simple,flexible and efficient.Under the background of "carbon peak and carbon neutralization",it is important to explore the performance potential of S-CO2 cycle.However,there are still shortcomings in cycle cooling optimization.This paper focuses on the study of S-CO2 coal fired power generation system and performs innovative research around important issues of coupling mechanism between dry cooler heat recovery(DCHR)and flue gas heat absorption in full temperature zone by using the recompression cycle and the threestage compression cycle as examples.In terms of cycle cooling optimization and flue gas residual heat absorption,this study starts from the recompression+reheating+intercooling,and applies the DCHR and the arrangement of double flue gas channels to improve the cycle efficiency.Then,the cooler flow reduction method(CFR)is proposed.The inlet temperature of the air preheater(AP)is further increased by paralleling the dry cooler at the low-temperature regenerator,so the thermal efficiency of the cycle is improved.When the cycle main parameters are 620℃/30 MPa,the circulating thermal efficiency is up to 52.50%and the net power generation efficiency is 48.13%.The split method is first applied to the performance analysis of S-CO2 coal-fired complicated power generation system.Our work starts from the analysis of tricompressions S-CO2 cycle with reheating process(TC+RH).Based on the split method,TC+RH+FGC can be equivalent to adding a new sub-cycle to TC+RH.Compared with TC+RH,the thermal efficiency of new sub-cycles determines whether the thermal efficiency of TC+RH+FGC increases or decreases.The finding inspires us to optimize the cold side of the cycle.When positive gains are brought through the new sub-cycle,the cycle efficiency will be improved.Then,the DCHR is introduced to further construct TC+RH+FGC+DCHR.The results show that the cycle can be equivalent to adding a new waste heat recovery sub-cycle to TC+RH.The waste heat of the cooler can be regarded as the heat source of these sub-cycles.Therefore,the effect of the waste heat recovery sub cycle is superimposing net power output on the basis of TC+RH.And the total heat absorption of the system remains constant.Therefore,the thermal efficiency of TC+RH+FGC+DCHR is higher than that of TC+RH with the same parameters.When the main parameters is 620℃/28 MPa,the final cycle efficiency is 52.41%,which reflects the advantages of the splitting method in analyzing complex power generation systems.In terms of efficiency improvement of coal-fired power generation system coupled with organic Rankine cycle(ORC)and S-CO2 cycle,this paper focuses on the TC+RH cycle to solve the problem of high exhaust gas temperature by introducing ORC with R123 as the working fluid to build a combined cycle.By optimizing the energy flow process between the system and the environment,the system performance is gradually improved.The air and ORC jointly absorb the heat in high temperature range of the cooler,and then the net power efficiency is further improved.When the main parameters of S-CO2 and ORC are 620℃/30 MPa and 170℃/2.9 MPa respectively,the thermal efficiency of the combined cycle with integrated cooler heat recovery(TC+RH+ORC+DCHR)increases from 51.45%to 52.06%,and the power generation efficiency increases from 47.13%to 47.90%.For the recompression and three-compression cycles,three high-efficiency coalfired power generation systems are constructed in this paper.Then,the relationship between cooler heat recovery method and boiler flue gas waste heat absorption is optimized.By analyzing the performance of complex coal-fired power generation system,the application scope of the split method is further expanded.The optimization method proposed in this paper is not limited to specific cycle configurations,but can be applied to various thermal power generation systems with multi-working fluid coupling.