Study On A Large Temperature Difference District Heating System With Multiple Clean Energy Complementary Synergy

With the continuous development of the district heating system in China,the coalbased heating pattern has brought serious air pollution problems.In order to ensure people's livelihood heating and achieve energy conservation and emission reduction,a clean and efficient district heating method must be implemented.This paper puts forward an urban district heating system based on coal-fired cogeneration,with multiple clean energy complement such as natural gas,electricity,and industrial waste heat,and the system integration and operation issues are profoundly studied.1)The large temperature-difference district heating system with multiple clean energy complementary synergy is constructed from heat network and heat source.The ideas of the low-temperature heat network return water technology are analyzed,and a novel heat network large temperature-difference heat exchange process is proposed.With three different heat pumps set in the substation and the main pipeline of heat network,the primary return water temperature is greatly decreased.The heat source cascade heating process is built,including the cogeneration and the industrial waste heat,which can realize the recovery of low-temperature waste heat and the cascade use of energy.2)The heat network and heat source thermal equilibrium models of the novel district heating system is established,and the thermodynamic models of absorption heat pumps and electric heat pumps are built for system optimization study.The “equivalent electricity of heating” is introduced as the indicator and method of energy consumption evaluation,which is an important basis of system optimization.3)With the goal of reducing the comprehensive energy consumption of the system,the optimization study of heat network and heat source is carried out.The effects of supply water temperature and peak-shaving ratio on the return water temperature and energy consumption are analyzed,it's considered that the supply water temperature of 120? and the peak-shaving ratio of around 0.2 is reasonable.The impact of bypass water flow rate on system key parameters and comprehensive energy consumption are studied,and the system optimization direction is figured out.In addition,according to the variable working condition characteristics of heat pumps,the system full working condition operation strategy was formulated,and the heat supply composition is analyzed.For the entire heating season,the system heating comprehensive equivalent electricity is 64.4kW·h/GJ,which is 15.9% lower than that of extraction steam heating.4)Taking a city as an example,the theoretical study results of this paper are used to guide the construction of a novel district heating system in actual project,and the energy saving,environmental protection as well as economic performance of the novel system are analyzed,the feasibility of the new system is verified.