Analysis Of Supercritical Carbon Dioxide Cycle And Comparison With Steam Cycle

The supercritical carbon dioxide(sCO2)cycle is a new type of power cycle with compact structure and simple system.After more than one hundred years of development,the steam cycle has a wide spread applicability and proven technology.Whether the efficiency of sCO2 cycle can reach that of steam cycle is the key to whether sCO2 cycle can replace steam cycle in various power generation fields.This paper begins with the structure optimization of the sCO2 cycle,and conducts an in-depth analysis of the multi-stage compression-regenerative process.On this basis,the single reheat steam cycle with multi-stage regenerative process and the single reheat sCO2 cycle with multi-stage compression-regenerative process are compared.Finally,the performance of several steam cycles and sCO2 cycles suitable for coal-fired power generation are compared under three typical parameters.The compression-regenerative process is a typical feature of sCO2 cycle.In order to explore the mechanism of compression-regenerative process on efficiency,this paper conducts a theoretical analysis on the efficiency of sCO2 cycle.It is found that the thermal efficiency of the recompression cycle(RC)can be divided into two parts:one part is equivalent to a simple recuperated Brayton cycle(SC);the other part has an efficiency of 100%,which is equivalent to the internal regenerative process,Based on this finding,it can be seen that a cycle with 100%efficiency is added to the SC to form the RC with higher efficiency.According to this idea,on the basis of the RC,a cycle with an efficiency of 100%can be added to build a three-stage compression-regenerative cycle(TC),which has higher thermal efficiency.Further,as long as the two construction conditions of the terminal temperature difference condition and the work output condition are satisfied,a compression-regenerative cycle with higher stage and higher efficiency can be obtained through this method.On this basis,the thermodynamic model and particle swarm optimization model are established.The thermodynamic theoretical analysis and comparison are made between the single-reheat steam cycle with multi-stage regenerative process and the single reheat sCO2 cycle with multi-stage compression-regenerative process.It turns out that the sCO2 cycle is more sensitive to the turbine inlet temperature,but insensitive to the turbine inlet pressure.In other words,increasing the operating temperature can obviously improve the sCO2 cycle efficiency.Under the conditions of high temperature and low pressure,the sCO2 cycle has obvious efficiency advantage compared with the steam cycle.However,the sCO2 cycle is more affected by the pressure drop of the heater and reheater,and whether the pressure drop can be effectively reduced is one of the key factors for the high efficiency of the sCO2 cycle.Further,the performance of several steam cycles and sCO2 cycles suitable for coal-fired power generation are compared under three typical parameters.The results show that the sCO2 cycle has evident efficiency advantage under the typical 600℃ single reheat parameter.The thermal efficiency of sCO2 cycle of RC+FGC structure and IC+TC+EAP structure are 1.62%and 3%higher than that of conventional steam cycle,respectively.Under the typical 600oC double reheat parameter,the efficiency of sCO2 cycle is similar to that of steam cycle.Under the typical 700℃ double reheat parameter,the sCO2 cycle has evident efficiency advantage.The thermal efficiency of the sCO2 cycle with IC+TC+EAP structure is up to 57.66%,which is 3.31%higher than that of the conventional steam cycle and 3.2%higher than that of the Master Cycle.Finally,through exergy analysis,it is found that the advantage of sCO2 cycle mainly lies in the small exergy loss of boiler.