Research On A Cold-End Optimization For Supercritical Coal-Fired Power Generation Incorporating A Supplementary Supercritical CO₂ Cycle

Recently,the thermal power plants are developing rapidly for large-scale and high-parameters,and a large number of supercritical power plants have been built,which has effectively reduced the average coal consumption level.However,it has also brought some problems.In the supercritical power plants,the increased steam parameters have led to the increase of the steam bleeds parameters,and the superheat of the steam bleeds is also increased.This will lead to the increase of the heat exchange temperature difference of the regenerative system and the energy utilization is not efficiently.Therefore,how to reduce the superheat of steam bleeds is an important issue for supercritical power plants.In addition,during the air preheating process within the boiler tail flue,the boiler exhaust temperature is generally 120-140?,while the ambient temperature is generally 20-30?,so the heat exchange temperature difference between the flue gas and the air can reach over 100?,and the energy utilization is also unreasonable.Therefore,effective utilizing the energy within the boiler tail flue is also an important way to improve the efficiency of the power plants.This paper proposed a coal-fired power plant integrated with a supercritical CO2 cycle.Before regenerative heaters,the superheat of the steam bleeds is utilized to heat CO2 to drive the supercritical CO2 cycle.The superheat of the steam bleeds is significant decreased.In addition,the exhaust of the CO2 turbine can be used to heat part of the ambient air.Within the tail flue of the boiler,the air preheater is divided into two stages,part of the ambient air is heated within the low temperature air preheater,and the air further heated within the high temperature air preheater to the combustion temperature.Between the two-stage air preheaters,A low-temperature economizer is arranged to heat feedwater/condensate to save steam extraction.In this paper,a system integrated with a supercritical CO2 cycle based on a typical 1000 MW supercritical coal-fired power plant is proposed and simulated by the EBSILON software.The energy-saving effects of regenerative system and air preheating process in the proposed system were analyzed through the exergy diagram utilization.Finally,the sensitivity analysis to the power load and the CO2 turbine inlet pressure were carried out.And the economic analysis was briefly discussed.Results showed that the total power generation of the integrated system could reach 1007.79 MW.and the system efficiency could reach 46.0%,0.4%higher than that of the reference power plant.The power supply coal consumption decreased by 2.6 g/kWh and the energy saving effect is remarkable.