Research On District Cooling Systems Driven By Surplus Steam In Power Plant

The cogeneration system improves the rate of energy utilization and reduces the adverse impact on the environment; but in winter, for heat load no longer exists, cogeneration plant starts to operate in a coal-fired power plant way. This shift may cause some bad effects, such as wasting low-grade energy and increasing the adverse impact on the environment. Additionally, there is so much surplus steam in cogeneration plants in summer. It proves to be important to find out the reasonable way to use the surplus steam and the proper method which cogeneration plants operate in summer.This paper puts forward some district cooling systems such as Li-Br absorption refrigeration system, steam-driving compression refrigeration system and combined cycle system, which can be used to consume surplus steam in Fengyuan cogeneration plant. This paper also analyzes the feasibilities of each system qualitatively.On the basis of the principles of compression refrigeration and absorption refrigeration, this article selects the proper calculation models for every system and carries on the thermal calculation of the absorption system, steam-driven compression system and combined-cycle system with the mid-pressure of 0.8MPa, 0.6MPa, 0.4MPa. Further, the heat loads and heat transfer areas are calculated and the amount of surplus steam consumption is compared and analyzed.Since the thermal calculation of every system is carried on, the impacts on absorption system caused by chilled water temperature, cooling water temperature and parameters of surplus steam are analyzed; the impacts on steam-driven compression system and combined-cycle system caused by chilled water temperature, cooling water temperature, parameters of surplus steam and transfer efficiency of the turbine are analyzed. The levels of effect to each system as well as the amount of surplus steam consumption in each system are compared.On the basis of selecting the equipments of all the systems, the initial investments and annual operating costs are calculated. The thermal economy indexes are evaluated by means of comparing the energy efficiency ratio of each system, and the economic indexes are evaluated by means of comparing the annual costs, net present values (NPV) and dynamic recovery periods. The system's advantages and disadvantages of thermal economy and economy are concluded.Nowadays, district cooling in cogeneration plant are always achieved by means of absorption refrigeration driven by surplus steam in power plants. The development of district cooling in power plants is limited by the lack of flexibility. This paper is to propose several new centralized steam-driven cooling systems and compare these systems with traditional absorption system. This article contributes to the development of CCHP by providing some new ideas and methods for district cooling in power plants.