| In order to meet the increasing demand for heat and achieve clean heating,the large-scale pure condensing unit in northern China implements heating reform and recycling of waste heat.And through large temperature difference long-distance heating,it can effectively achieve energy saving and emission reduction,and prevent pollution problems caused by coal-fired heating in winter.However,because the heating system is different from the traditional cogeneration heating system,the operation adjustment and control methods are very different,and the research in this area is still insufficient.Therefore,it is necessary to carry out research on the operating characteristics of the heating system under variable working conditions to meet the needs of the heating load change in the heating season and achieve efficient and economical heating.In this thesis,the heating system of 300 MW heating unit adopting absorption heat pump to recover the residual heat of circulating cooling water is taken as the research object.By establishing a thermal load prediction model,as well as mathematical models of absorption heat pumps,conventional heat exchangers,steam turbine low pressure cylinders and condensers,the characteristics of the operation of the unit and the first station of the heat exchanger under different heating and heating loads are studied,and optimized the operation mode of the heating system under variable working conditions.The details are as follows:Firstly,according to the operating parameters of the main components of the cogeneration unit,as well as the meteorological conditions and heating heat load during local heating,a mathematical prediction model between outdoor temperature and heating heat load is established by fitting and parameter correction.Secondly,the cyclic process and thermal process of lithium bromide absorption heat pump and conventional heat exchanger are analyzed in detail.A mathematical model was established for the absorption heat pump and the conventional heat exchanger in the first station of the heat exchange using excel software to calculate the operating parameters of each unit in the first station of the heat exchanger under different working conditions.Then,according to the Fruger formula,the mathematical model of pressure and flow rate applicable to the low pressure cylinder of the steam turbine of the heating unit is derived,and the operating parameters of each group and each extraction port of the low pressure cylinder of the steam turbine under different steam inlets arecalculated.The mathematical relationship between the amount of steam entering the low pressure cylinder and the amount of steam exhausted is obtained by the fitting method,and the flow rate of the condenser circulating water under different steam exhaust amounts is calculated.Finally,according to the mathematical model established above,the adjustment mode of different central heating operation is obtained,and the variation law of COP in different outlet water temperature,circulating water flow and different extraction amount is obtained,and the difference is further analyzed.Under the working conditions,the unit load change in the first station of the heat exchange and the economics of the unit.The results show that: 1)When the temperature of the heat pump outlet water rises,the extraction pressure rises,the temperature of the hot network circulating water increases,and the steam extraction increases,the COP of the heat pump increases;2)When the heat load of the user changes and the heating system adopts different adjustment modes,the heating ratio curve of the first station of the heat exchange shows different trends.The heat pump outlet temperature is different,and the heating ratio of the first station of the heat exchange is also different;3)From the economic analysis of the heating system,when the heat pump outlet temperature is set to 80 °C,the heating system adopts the quality adjustment mode to recover more waste heat than the quantity adjustment mode,which is more energy-saving. |
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