| It is imperative to implement low-carbon and clean heating with high energy consumption and serious pollution in district heating in northern China.Exploiting the energy-saving potential of coal-fired Cogeneration,improving the feasibility of district heating,and complementing multiple energy sources with natural gas and electricity are critical directions to achieve the low-carbon and clean heating in northern China.In order to solve an overall problems such as recovering the low-temperature waste heat from the combined heating and power plant,achieving long-distance economic heat transfer in heat networks,realizing flexible peaking of natural gas and efficient utilization of electricity,this paper proposes a large temperature-difference heat exchange district heating system with multiple energy sources complementing waste heat,natural gas and electricity,and carries out in-depth research work around the optimization and integration of the system.Firstly,a new district heating system is constructed with the objective of improving the thermodynamic perfection of the system.In the heat source,a multi-source ladder heating process is established to recovery the waste heat and improve the overall energy efficiency;In the heat network,a heat-gas-electricity complementary large temperature difference heat exchange process is built to decrease the return water temperature of the heat network.Secondly,based on the mathematical model of variable working conditions of the heat pump,the mathematical model of thermal characteristics of each link at the heat source and the mathematical model of thermal characteristics of large temperature difference heat exchange at the heat network,as well as the mathematical model of heat supply analysis and the mathematical model of heat network parameter analysis for the full conditions of the system.In addition,the multi-objective evaluation indexes and analysis methods covering energy efficiency,environmental protection and economy of the system are established.Based on the new system mathematical analysis model and multi-objective evaluation indexes,the key parameters optimization methods of the three types of large temperaturedifference heat exchange in the system and the regulation characteristics of the full conditions of the heat network are studied,with the goal of deeply reducing the return water temperature of the primary heat networkFinally,a waste heat-gas-electricity complementary large temperature difference heat exchange central heating system is designed.Compared with the conventional natural gas and electricity combination scheme,evaluate the energy efficiency and environmental performance of the two systems,and economics of the new system. |
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