Integrated multiscale simulation of combined heat and power based district heating system

Abstract

Many studies have been carried out separately on combined heat and power and district heating. However, little work has been done considering the heat source, the district heating network and the heat users simultaneously, especially when it comes to the heating system with large-scale combined heat and power plant. For the purpose of energy conservation, it is very important to know well the system performance of the integrated heating system from the very primary fuel input to the terminal heat users. This paper set up a model of 300MW electric power rated air-cooled combined heat and power plant using Ebsilon software, which was validated according to the design data from the turbine manufacturer. Then, the model of heating network and heat users were developed based on the fundamental theories of fluid mechanics and heat transfer. Finally the combined heat and power based district heating system was obtained and the system performances within multiscale scope of the system were analyzed using the developed Ebsilon model. Topics with regard to the heat loss, the pressure drop, the pump power consumption and the supply temperatures of the district heating network were discussed. Besides, the operational issues of the integrated system were also researched. Several useful conclusions were drawn. It was found that a lower design primary supply temperature of the district heating network would give a higher seasonal energy efficiency of the integrated system throughout the whole heating season. Moreover, it was not always right to relate low design supply temperatures to high pump power consumptions and high heat losses in the district heating network, since the results showed that the seasonal pump power consumption and the heat loss would decrease with a lower design primary supply temperature. Therefore, from the perspective of seasonal consideration, low temperature district heating has an even more bright future compared to just considering the design heat load condition. Both the combined heat and power plant and the low temperature district heating network were simulated in detail and integrated, including the part heat load conditions, which is one novelty of this article. The simulation in this paper could be considered as the basis for the further improvement and optimization of combined heat and power based district heating systems.