Application Study On The Distributed Heat Storage Tank In The District Heating System With Cogeneration Units

At present,the mismatch between supply and demand of the thermal and electrical loads is a serious problem,which is caused by the thermoelectric coupling relationships of the cogeneration units in the district heating system.Fortunately,the application of the heat storage technology can effectively alleviate the problem.On the one hand,when the electrical and thermal loads is lower,the heat storage technology can solve the shutdown problem of the cogeneration units under small load.Inversely,the heat release of the heat storage tank can solve the problem of inadequate unit capacity under large load.On the other hand,the heat storage technology can be used as the peak-regulating heat source to reduce the capacity of the peak regulating equipment.However,the thermoelectric decoupling and the economy of system operation are significantly impacted by the capacity of the heat storage tank.Hence,this study mainly investigates the thermal and electric characteristics,the hydraulic conditions of the pipe network,and system economy of the cogeneration district heating system with heat storage tank.The main contents of this paper is as follows:Firstly,in this paper,the characteristic day method was used to calculate the volume of the heat storage tank with different heat storage ratios during the most typical heating hours,according to the analysis of the hourly load throughout the year.The model of the heating system is built by using the TRNSYS software,and the volume range of the heat storage tank for the system is studied.Moreover,the thermoelectric power relationships of the system are analyzed under different heat storage ratios.Besides,compared with the original heating system,the hydraulic conditions,the system economy,and the environmental cost of the distributed heating system with the distributed heat storage tank are also analyzed.The study shows that the thermoelectric decoupling can be enhanced with increasing the volume of the heat storage tank,the influence of the system is larger on the secondary pipe network than the primary network,and compared with the peak regulating boiler,the initial cost is the largest but the operating cost is the least when the heat storage tank is selected as the peak regulating equipment.Because the heat storage tank cannot run at full load in certain time,when the payback period is considered,on basis of the peak regulating heat of the heat storage tank,the economy of each peak regulating style is compared and analyzed to ensure the rationality of economic analysis.When the heat storage tank cannot run at full load all the time,the payback period gradually increases with the increase of the heat storage ratio.In addition,the cogeneration units can reduce greenhouse gas emissions such as carbon dioxide compared to the coal-fired boilers for the district heating system.Secondly,this study investigates the thermal characteristics of the heat storage tank by using the FLUENT software.Besides,the temperature field of the heat storage tank is analyzed in detail by varying the inlet parameter of the heat storage tank.The simulation results indicate that the heat storage process of the heat storage tank is significantly affected by the parameters of the height-diameter ratio,the inlet flow,the opening size and angle of the water distributor.The studies on the peak regulation and thermoelectric decoupling by utilizing the heat storage technology are still in the preliminary stage,and the relevant theory system is not mature yet.Therefore,it is hoped that the study on the application of the distributed heat storage tank in the district heating system with cogeneration units can give some references value for the relevant investigation in the future.