Research On Application Of Cascade Heating Technology For 350MW Cogeneration Units

China clearly put forward the "double carbon" goal in 2020,and the State Council issued the "Action Plan for Carbon Peak by 2030" in 2021,which proposed to accelerate the energy-saving upgrading and flexibility transformation of coal-fired power generation units and promote the transformation of coal-fired power generation.Coal-fired cogeneration units reduce the emission of combustion pollutants while recycling a large amount of low-grade waste heat,which has significant economic and social benefits of energy conservation and emission reduction.By reforming the existing coal-fired power generation units and making full use of their heating capacity as the basic heat source for central heating,the current situation of high energy consumption and high pollution in winter heating in the north can be effectively changed.With the proposal of the "double carbon" goal,the installed capacity of renewable energy power generation has increased rapidly.However,in order to meet the heating demand in the heating season,coal-fired cogeneration units cannot effectively participate in peak shaving when they adopt the operation mode of"determining power by heat",thus squeezing the space for grid connection of renewable energy power generation.Through the recovery of waste heat from auxiliary equipment,combined with high back pressure,cylinder cutting and other heating transformation technologies,the construction of a cascade heating system can further expand the heating capacity of the unit and enhance the deep peak shaving capacity of the unit,and can effectively improve the comprehensive energy utilization efficiency of the unit.This paper focuses on the engineering application of the cascade heating transformation technology of 350MW cogeneration units,uses Ebsilon software to establish the off-design calculation model of the cogeneration units,and combines the characteristics of high energy comprehensive utilization efficiency of high back pressure heating and good deep peak shaving ability of cylinder cut heating,and proposes the recovery of low temperature flue gas waste heat,high back pressure unit exhaust steam waste heat,and high temperature flue gas waste heat,The multi-stage heat supply system with multiple heat sources and residual heat is supplemented by steam extraction of the cylinder cutting unit.Based on the off-design calculation model,the change characteristics of high backpressure heat supply,cylinder cutting heat supply,low temperature flue gas heat supply and high temperature flue gas heat supply in the cascade heating system are analyzed.The results show that the utilization of high backpressure exhaust steam is affected by the circulating water flow and return water temperature of the heating network,and the recovery of low temperature flue gas heat will reduce the utilization rate of exhaust steam,while the utilization of high temperature flue gas heat can increase the utilization rate of exhaust steam;The heat supply of cylinder cutting can further reduce the power generation load and expand the heat supply capacity through the steam inlet bypass regulation of low pressure cylinder;The cascade heating system improves the comprehensive utilization efficiency of energy and expands the regulation range of power generation load.Through the processing and analysis of the historical heating season heating data of a cogeneration unit in Yangquan City,a local temperature-heat index model can be established.The heating load prediction model is built based on LSTM long and short time memory neural network.By comparing the influence of different training methods on the heating load prediction value,the reliability of the application of the temperature-heat index model can be further verified.According to the case unit,a multi-step heat supply reconstruction scheme with residual heat of multiple heat sources is designed,and the heating boundary conditions are obtained based on the temperature-heat index model,and the economy of deep peak shaving in the heating season before and after the step heating reconstruction is calculated.The results show that when the typical daily deep peak shaving operation in the heating season,the modified step heating system can reduce the average standard coal consumption rate for power generation from 213.86g/(kW·h)to 150.24g/(kW·h),It can improve the comprehensive energy utilization efficiency from 74.63%to 87.35%,enhance the capacity of deep peak shaving of the unit,and have a high economy of deep peak shaving.