Development And Optimization Of Energy Stepped Utilization Of Heat-supply Units

The demand for electricity decreases and the heating load increases.Research on heat reforming of condensing steam turbine unit is important for reducing the cost of cogeneration.Existing research based on the First Law of Thermodynamics,neglects the energy loss of extraction steam.So,based on the Second Law of Thermodynamics,the energy stepped utilization is an urgent problem to be solved in the heat supply reforming of large condensing steam turbines.The heating reform of condensing unit is studied.Thermodynamic calculation is carried out for the scheme of retrofitting the unit into backpressure turbine and back pressure extraction turbine.Reasonable transformation scheme is obtained.After investigating the demand for heat supply,considering the reliability of heat supply,the adaptability of unit load change,the influence of steam extraction on unit safety and heating economics,low temperature reheat steam is chosen as the main steam source for heat supply and #4 extraction steam as the standby steam source.Development of energy stepped utilization of heat-supply units,extraction steam is sent to the heating network after working by a bottom backpressure steam turbine.Based on EBSILON software,the simulation model of the extraction heating system is established,including electrical and thermal loads.With the decrease of main turbine load,the efficiency of bottom back pressure steam turbine increases first and then decreases.With the increase of heat supply,the heat consumption rate of the unit decreases and the net profit of heat supply increases.By calculating the influence of steam extraction on the operation safety of steam turbine and boiler reheater,the limit of extraction steam heat supply is obtained.A new type of bottom backpressure steam turbine is proposed to overcome the disadvantages of the existing.According to the load of the main steam turbine,the inlet mode of the bottom backpressure steam turbine is adjusted.The parameters of the new bottom backpressure steam turbine are optimized,including rated intake pressure and high pressure cylinder series at the switching point of intake mode.Efficiency of the new bottom backpressure steam turbine is improved and the range of intake is enlarged.