Optimization Of Large Steam Turbine Regenerative System In Coal Fired Power Plant

Nowadays the units of new-built coal-fired power station are now developing in the direction of super-high parameters,big capacity and high efficiency with capacity greater than 600MW,which mainly consisting of super-critical or ultra-supercritical units.As an important part of the turbine generator unit,regenerative system’s layout and heat loss have great influence on the efficiency of the turbine and even the entire thermal power plant.Therefore,analyzing the thermal economy of regenerative system has become indispensable for the energy-saving reform of thermal power plants.The paper analyzed the factors affecting the regenerative system’s thermal economy,and achieved the methods to determine the best feed water temperature,the best number of steam extraction,and the best distribution of feed water’s enthalpy.The basic strategy for the optitmization of the regenerative system were reached:firstly,in the premise of the best feed water temperature remaining unchanged,the optimization range of the steam extraction number of the regenerative system was determined according to the principle of isothermal distribution;secondly,the best number of regenerative steam extraction was determined by thermo-economic analysis;and thirdly,the feed water ’s enthalpy of the regenerative system heater was adjusted based on the situation that the original regenerative system was greatly deviated from the isenthalpic distribution,so as to achieve the optimal state.Besides,an application study on the regenerative system optimization was conducted based on the THA working condition data of a 660 MW ultra-supercritical unit in a domestic power plant,and three regenerative systems optimized for the steam extraction number were obtained through the optimization method constructed.In addition,the thermal economy calculation of three regenerative systems optimized for the steam extraction number was performed according to the equivalent heat drop method and the simplified calculation method of conventional calculation and the results were checked by each method,so as to ensure the correctness of the calculation results.Furthermore,the comprehensive economy of the three regenerative systems optimized for the steam extraction number was also compared to obtain the optimal heat recovery system.During the optimization process,the optimal regenerative system was compared with the original regenerative system,Through the optimization of regenerative system,the unit’s internal efficiency has increased by 0.141%,the steam rate reduced by 0.013 kg/(kWh-1),and the heat rate reduced by 22.097 kJ/(kWh-1),resulting in a reduction of 9110t for annual standard coal consumption.In the end,the paper introduced the calculation method of variable working conditions of the regenerative system,and calculated the regenerative system for the optimized 660MW ultra-supercritical unit under changing working conditions to obtain the corresponding thermal economy indicators.The paper closely integrates with the actual operation of China’s power plants,and the results can provide important theoretical basis for the design and transformation of large turbine regenerative systems in China’s coal-fired power plants.