Study Of A Novel District Heating System Based On Energy-saving Potential Exploration

The severe winters of North China make the heating project relate to everyone’s livelihood.Heating by coal has led to a large number of pollutants discharged,seriously affecting the health and life quality of the people.Therefore,in order to realize the coordinated development of heating and energy saving and emission reduction,clean heating is being launched in northern China.District heating system is the dominant heating source in northern cities,its further energy saving and emission reduction is the key direction of clean heating.This paper is devoted to exploring the energy-saving potential of the district heating system and constructing a new clean dominated heating mode of cities.The main ideas include:(1)Further exploring the energy-saving potential of the existing coal-fired cogeneration district heating system,realizing high-efficiency recovery of waste heat from power plant and large-temperature difference transmission of water by heating network,making the cogeneration the most energy-efficient,lowest-cost and basic heat source;(2)Rationally developing natural gas heating,making it the auxiliary heat source to undertake the peak load of district heating system,while further improving the whole performance of the system by making full use of its high grade.According to the first law of thermodynamics and the exergy analysis method of second law of thermodymanics,the irreversible losses in the conventional cogeneration district heating system are quantitatively analyzed,and the utilization methods of the exergy losses in the heat exchange links of the system are explored.Then novel heat exchange modes both on the heating network and in the CHP plant are proposed: On the heating network,the capacity of high temperature water and natural gas to do work is used for driving the absorption heat exchangers(AHEs),by which the return water temperature of primary heating network can be greatly reduced.While in the CHP plant,a cascaded heating process with absorption heat pump(AHP)is constructed for efficient utilization of the condensed waste heat,which significantly improves both the heating capacity and the energy efficiency of heating system.This paper proposes a novel cogeneration district heating system and builds corresponding models based on a CHP plant with 2×330MW turbine units.According to the comprehensive evaluation indexes and methods of themodymanic,energy efficiency,environmental protection and economy,the novel system is compared with the typical conventional system(coal-fired cogeneration with gas-fired boiler as peak shaving heat source).The new system has a higher degree of thermodynamic perfection,a significant reduction in energy consumption,a significant reduction in pollutant emissions,and a remarkable economic benefit with an annual return of 22% of the project.The new system proposed in this paper provides a new idea for the construction of clean heating system in northern China.