Application Of Heat Storage Tanks In CHP Heating System

Energy storage has been included in Energy and Environmental Technology Innovation Strategy(EETIS) resently. Chinese NDRC and Energy Bureau issued a number of regulations on energy storage to improve the safety of energy supply, encourage the development of clean energy and increase the conversion efficiency of fossil fuels. The main function of thermal storage technology, "peak load shifting", not only can reduce the daily heat load fluctuations and units’ load fluctuations, but also can allow more renewable energy to be used in power grid and district heating system. In other words, thermal storage technology plays an important role in improving units’ efficiency and the net profit of cogeneration power plants. In spite of the discontinuity and instability, renewable energy(such as solar, wind) could be used widely in China’s energy structure because of the thermal storage technology and China could achieve sustainable development in terms of economy and environment. Research on heat storage tanks(HSTs) in district heating system could lay a solid theoretical foundation for real projects when the thermal performances of HSTs and combined operation strategys of HSTs and cogeneration units are figured out.After a review on heat storage technology and HSTs, the thermal characteristics of HSTs were studied in the second part. At first, mathematical models related to water flow rates and operation periods during charge process or discharge process were built and then numerical simulation were performed. Some software, such as Solid Works, ICEM, and fluent, was used to simulate the velocity field and temperature field in the tank. Then further research was carried on to figure out the characteristics of thermocline, which has a profound influence on the performance of HSTs. The simulation results showed that the heat characteristics of accumulators were affect greatly by the shape of water distributors, the velocity in the distributors’ outlet and inlet,and the temperature difference between outlet and inlet, etc.In the third part of this paper, Genetic Algorithm(GA) was used to find the optimal size of a HST and optimal combined operation of accumulators and cogeneration units. During the optimization process, maximum net profits of a plant were set as objective functions which were constrained by limitations’ of HSTs’ thermal capacity, hourly heat load during a day, and generated energy by CHP units. Based on the mathematical model and optimization process, this paper took a CHP plant as an example to design a HST with optimal capability. Compared with a cogeneration plant without heat storage technology, the cogeneration plant with HSTs performed well in energy saving, heat and power fluctuations reduction, with higher efficiency and lower carbon emission. Meanwhile, the ideal optimal combined operation strategy was more feasible than the optimal combined operation strategy under current automation level and management level.