Deep Geothermal Energy District Heating System Configuration Based On Absorption Heat Exchanger

With the rapid development of urbanization,both urban heating load and energy consumption for space heating is growing in the north of China.Fossil fuel consumption of district heating systems deteriorates atmospheric environmental pollution to a certain extent.Project conversing coal into natural gas is one of the main measures to reducing emission of atmospheric pollutants.At present,district heating system based on natural gas boilers faces some problems,such as higher cost,larger irreversible loss and it results in shortage of natural gas supply in winter.The deep geothermal characterized by high temperature,high energy density and good stability can be used for available heating source in northern China.Demand of large temperature difference heating and characteristics of uneven distribution of deep geothermal energy considered,this paper puts forward a new district heating system based on deep geothermal energy with absorption heat exchangers in which thermas energy is utilized by the cascade utilization principle.It is suitable for the large scale project that heat source is far away from the center of heat users.In the new heating system,absorption heat exchangers are installed in heating stations,and geothermal wells,a water-to-water heat exchanger and an absorption heat pump are set in the heat substation.The absorption heat exchanger can greatly reduce the irreversible loss in the process of energy transfer and reduce the return water temperature of the primary heating network.Thus heat transmission capability of the primary heating network results from larger temperature between supply water and return warter.The lower return water temperature of the primary heating network contributes to efficiently utilizing the geothermal energy and in the water-to-water heat exchanger and the absorption heat pump of heating station.In this paper,configuration of district heating system is firstly optimized from the prospective of thermodynamics,and then its benefits are discussed from the viewpoint of economics by a case of heating system.Results show that the primary energy efficiency and the product exergy efficiency of the new heating system are 122% and 13.4% respectively.The heating cost and payback period are about 62.3 ?/GJ and 9 years respectively when heat transmission distance of the primary heating network is 15 km.Economical heat transmission distance of the primary heating network approaches 20 km for the new heating system.Compared with the conventional district heating system based on natural gas boiler,the new heating system has high thermodynamic performance,lower heating costs,shorter payback period,and longer economical heat transmission distance.Longer economical heat transmission distance helps to effectively develop and utilize geothermal resources far away from downtown.The new district heating system would promote the development of clean district heating technology in northern China and it provides a new ideal for plan and design of heating system and prevention and control of atmospheric environment pollution in north China.