Parameters Optimization Of Ultra-supercritical Thermodynamic System With Ultra-high Temperature

The pattern of coal-fired primary energy in China will not change in a short period of time.Thermal power generation still accounts for 68.9%of the total power generation.The development of efficient and clean coal-fired power generation technology is the main direction to reduce coal consumption and CO₂ emissions in China.Increasing the initial parameters of live steam is an important way to improve the efficiency and emission reduction of coal-fired power plants.With the development of material technology,the conditions to raise the temperature of live steam and reheat steam to 650^oC have been met.This thesis discusses the design analysis and parameters optimization for single reheat and double reheat units with the live and reheat steam temperatures from 600 to650^oC.It also discusses the efficiency changes after the steam temperature rises in different reheat systems.It also studies the influence of the different arrangement of regenerative system and the key parameters of the units on the thermodynamic performance of the cycle in different reheat units.The superheated steam temperature of the single reheating unit is increased from600 to 650^oC,and the absolute internal efficiency of the steam turbine can be increased by 3.67%.The efficiency of the steam system boiler is increased by 3.06%,the overall efficiency of the unit is increased by 3.68%.The efficiency of the external steam cooler system is increased more obviously when the steam temperature is higher.the adding of two-stage out steam coolers in the regenerative system can increase the feed water temperature by 6 to 9^oC,and the absolute internal efficiency of the steam turbine can be increased by 0.25 to 0.31%.When the live steam temperature of the double reheating unit is increased from 600to 650^oC,the absolute internal efficiency of the system can be increased by 2.80%;the absolute internal efficiency of the unit can be increased by 0.29%and 0.53%respectively by adding two-stage and four-stage out steam coolers.When the four-stage out steam coolers is used,the feed water temperature can be increased by 12.8^oC at650^oC of the live steam,and the extraction capacity of the#1 can be reduced by 23.3%,At the same time,the superheat degree of extraction steam of#2～#5 regenerator are effectively reduced.The relation equation was parabola equation between the steam pressure ratio of the double reheats and the absolute internal efficiency of the unit.The unit efficiency is the highest respectively when the ratio of the two reheats is 0.4536 and0.2788.The absolute internal efficiency of the system can be improved by properly increasing the single reheat pressure and the double reheat pressure in the conventional unit.Compared with the conventional double reheat system,the superheat of high-pressure extraction steam is reduced when extraction back pressure auxiliary turbine was used.Under the same temperature of live steam and reheat steam,the exergy loss of feed-water heater is minimal when the extraction back pressure auxiliary steam turbine is connected with generator.when the extraction back pressure auxiliary steam turbine is connected with feed pump and generator at the same time,the thermal performance of the double reheat unit is better.