Optimal Design Of A Small Distributed Energy System

Distributed energy system has the advantages of saving energy, economic, environmental and energy supply reliability which makes distributed energy system has broad development prospects in our country, especially in the present that the country is beset by the problems of serious environmental pollution and low energy efficiency. Now, the main problems for domestic distributed energy system are difficult to connect to grid and the technology is immature.For the energy efficiency of existing distributed energy system is low and it is hard to adjust the heat, electricity and cold load of the system, this article based on the principle of energy cascade utilization, makes full use of the existing primary energy supply network of gas in the city, designs a small gas-steam combined cycle distributed energy system, which can provide the1200kW power consumption for residential and meet the need of heat and cold load throughout the year.The small distributed energy system fully considers the all kinds of waste heat utilization, analyzes the influence of pinch point, approach temperature point and main steam temperature on the performance of power system by establishing the optimization objective functions. In order to increase the total power of combined cycle, pinch point, approach temperature point and main steam temperature take lager value in the reasonable range. Increase the main steam temperature is one of the most effective measures to improve the efficiency of combined cycle, but the increase of main steam temperature is limited by the exhaust temperature of gas turbine. Through calculation and analysis, the paper also presents the theories of the gas turbine, HRSG, steam turbine and heat pump’s selection and optimal design in the distributed energy system.Small distributed energy system’s capacity and heat is small, not enough to meet the heat load and cooling load for users, additional heating refrigeration unit is required. Through the design of gas heat exchanger and direct fired absorption heat pump, in the article, the optimal design of the heating and cooling system is presented, and the integrated optimization of the system is achieved. Finally the performance of the system under heating mode and refrigeration cycle of the small distributed energy system is calculated in this article.A small distributed energy system is designed in this article. In this system, the energy efficiency is92.84%; carbon dioxide emission reduction rate and the unit energy cost reduction rate in the winter and summer are70%and57.5%,61.33%and44%, respectively.The heating and cooling system is divided into three parts:hot water is provided all the year round through the absorption heat pump which is driven by the extraction steam of a small steam turbine and the COP of heat pump is1.8;231kW heating capacity is provided by the flue gas heat exchanger. The COP of the direct fired absorption heat pump heating and cooling system in the winter is2.41, the coefficient of performance in the summer is1.25; The exhaust gas temperature of this system can be fallen to50℃.Distributed energy is one of the important developing directions of future energy technology, based on the gas-steam combined cycle, the small distributed energy system has a broad application prospect in China.