Application Research Of Low Vacuum Circulating Water Heating Reform Technology In Thermal Power Plant

The use of circulating water heating can improve the thermal efficiency of steam turbine units and achieve better energy-saving effect.Since the 1970s,some steam turbines with installed capacity less than 50MW have been used in low vacuum operation in some power plants in northern China.In recent years,the retrofit of units below 200MW has been attempted,and some results have been achieved.Using exhaust steam heating circulating cooling water as direct heating or as primary heater heat source for heating in winter,the operation practice of several power plants shows that the technology is reliable and the unit runs steadily from a technical point of view.When the pumping unit uses low vacuum circulating water for heating,the steam turbine does not need large-scale renovation,only the inlet and outlet pipes of the circulating cooling water of the condenser are connected to the heating system.From the point of view of steam turbine operation,it is a kind of off-design operation.The condenser is used as a primary heater to heat the circulating water by using the latent heat of vaporization of exhaust steam,and the circulating water is used to replace the heating water of the heat network,so that the latent heat of exhaust vaporization can be utilized.The heat user in the heat network is equivalent to the cooling tower in the circulating cooling system,and the circulating water absorbs heat in the condenser and sends it to the heat user for heat dissipation,and then returns to the condenser for heat absorption and circulation.In order to ensure the safe operation of the condenser in low vacuum,the water side pressure should not exceed 0.196 MPa under normal conditions.Therefore,it is necessary to strengthen the condenser so that its pressure can reach 0.4 MPa,and its supply and return temperatures should be 60—500C.Since the low vacuum operation is only the special variable working conditions of the steam turbine,there is no change to the steam turbine itself,but during the operation of the condenser in Iow vacuum,the generating capacity of the steam turbine is directly heated.Therefore,the reasonable determination of heating area has great influence on the economic operation of steam turbine.In this paper,the technology of waste heat utilization of circulating cooling water in Dalian Taishan Thermal Power Plant and Chifeng Thermal Power Plant is studied.Dalian Taishan Thermal Power Plant has 8400 t/h flow circulating cooling water,and Chifeng Thermal Power Plant has 6000 t/h flow circulating cooling water.In winter,the water temperature is stable between 18?26? This part of heat energy is lost in the spray cooling process of cooling tower,and the evaporation of cooling water also loses a lot of water(Dalian Taishan Power Plant loses 824448 tons of water in heating period every year,Chifeng Thermal Power Plant loses 824448 tons of water in heating period,Chifeng Thermal Power Plant loses a lot of water in spraying cooling The plant loses 127 368 tons of water during the heating period every year.Using high temperature heat punp technology and heat network switching technology and related equipment,the circulating cooling water of thermal power plant is used as low temperature heat source to extract and recover a large amount of low temperature heat energy.After transformation,Dalian Taishan Power Plant saves 36 949 tons of standard coal per year,Chifeng Thermal Power Plant saves 28 480 tons of standard coal per year,effectively saving energy,reducing air pollution and CO2 emissions.Various schemes can be used in the renovation project:using high temperature heat punp and circulating water to achieve centralized heating;using heat network switching to improve heating capacity;using series heating system to maximize comprehensive energy efficiency.The calculation results show that the scheme of heat recovery combined with high temperature heat pump and circulating water and the scheme of switching heat network have their own ad'vantages and disadvantages,which are suitable for popularization and application in different regions.