Study On Multi-Dimensional Operation Mode Of Cogeneration Of Gas-Steam Combined Cycle Unit

In recent years,under the influence of environmental protection requirements such as energy saving and emission reduction,air pollution control,Beijing has planned to build four gas thermal power centers and regional gas energy centers,and put a large number of gas-steam combined cycle power plants into operation.Compared with the traditional coal-fired units,the gas-steam combined cycle units have smaller thermal power ratio and more power generation,which have good equipment performance and economic benefits.Although the combined cycle reduces the emission of pollutants after replacing the coal-fired units,it brings about a sharp increase in the consumption of natural gas.Considering the fact that natural gas depends on imports in China,the natural gas consumption rate of power generation in gas-fired power plants should be reduced as much as possible.In addition,from the point of view of peak shaving,in order to solve the problem of renewable energy generation,on the premise of guaranteeing heat load in the heating season,the thermal power ratio of units should be increased to make room for renewable energy to access the grid.Taking the combined cycle unit of Shenhua Guohua(Beijing)Gas Thermal Power Company as the research object,this dissertation establishes the off-design model of 9FB gas-steam combined cycle unit by using the thermal cycle simulation software Ebsilon.The thermal economy and peak shaving ability of the combined cycle unit under multi-dimensional operation mode are analyzed with the heat-power ratio and natural gas consumption rate as the indexes respectively,and the heat supply performance and peak shaving performance of the combined cycle unit are obtained.It can be seen that under the back pressure mode,the heat supply of the unit corresponds to the output of the unit one by one,which does not have peak-shaving ability,while the condensation mode has a certain peak-shaving ability,and with the increase of heating demand,its peak-shaving ability gradually becomes worse.Because the case unit operates in NCB,it operates in pure condensation during non-heating season,and operates in condensation and back pressure modes switched by SSS clutch during heating season.Besides,when the heating load and power load change,it can also switch between "two drag one" operation and "one drag one”operation.So the operation mode is multi-dimensional.Aiming at the heat load demand in the heating season of 2017-2018,this dissertation calculates the heat economy index under different operation modes in the heating season,and puts forward suitable operation modes for the case units,so as to facilitate the rational and economic dispatch of generation and heating by the power grid and the heating network.Under the premise of guaranteeing the heating demand,the back pressure mode "two drags one" operation with large thermal power ratio should be chosen as far as possible,which can provide access space for renewable energy.Because of less power generation,the natural gas consumption rate of power generation is low,which has better economic and environmental benefits.It can be flexibly switched to the condensation mode when the power demand increases.In the end of March,the heat load is small,which is lower than the minimum heating capacity of the back pressure mode "two tows one" operation.In order to ensure the safety and stability of the unit,the extraction mode "two tows one" operation should be selected.