Research On Engineering Application Of Waste Heat Heating Of Auxiliary Units In Power Plants

Coal accounts for the largest proportion of primary energy structure in China.Although renewable energy such as photovoltaic power generation,wind power generation and hydroelectric power generation have increased in recent years,and natural gas utilization has also increased rapidly,primary energy consumption in China is still dominated by coal,so thermal power generation is still the main mode of power generation in China.At present,the single power of thermal power plant is increasing,and the driving power of auxiliary engine is increasing.In order to reduce the power consumption rate,the auxiliary machines of large power plants are driven by steam or revamped by steam.However,due to the limitations of season,operation mode and site layout,there is a loss of residual heat cold source of small steam turbines.In this dissertation,the efficient utilization of waste heat of small steam turbines for driving auxiliary machines is studied.During heating period,the auxiliary heat is heated by heating network water for heating,and during non-heating period,the auxiliary heat is heated by condensate water to ensure the efficient operation of small steam turbines throughout the year.In the case of insufficient utilization of exhaust steam or failure to meet the heating requirements,the recovery and utilization of waste heat by compressed upgrading is discussed.The heat supply system of back pressure type and back pumping type small steam turbines and the process of heat supply system of small steam turbines are given respectively.Based on the actual high back pressure heat supply unit,the thermal system model of auxiliary heat supply is built,and the thermal economy of the unit after adding auxiliary heat supply is calculated and analyzed by the second law of thermodynamics.At the same time,the thermal economy of condensate water system heated by auxiliary heat in non-heating condition in summer is qualitatively calculated.The results show that:After heat-supply with auxiliary heat during heating period,the heat-supply capacity of the unit increases under different conditions.Under design conditions,the heat-supply load of the unit increases by 11.76%,the rolling efficiency increases by 0.9%,the coal consumption rate of power generation decreases by 8.37 g/kW h.The condensate water heated by auxiliary heat during non-heating period reduces the extraction capacity of main steam turbine and increases the generating power.Under rated intake condition,the generating power increases by 1.42MW,the generating efficiency increases by 0.14%,and the coal consumption rate of power generation decreases by 1.21 g/kW·h,which realizes the efficient operation of small steam turbines throughout the year,and solves the problem of cold end loss of small steam turbines driving auxiliary machines.In order to adapt to wider heating conditions and realize efficient recovery and utilization of waste heat from exhaust steam of small steam turbines,a preliminary discussion is made on the auxiliary turbocharging and upgrading system of waste heat.The steam compressor is installed to compress and upgrade the exhaust steam of small steam turbines for external heating,so as to realize energy cascade utilization.