Capacity Configuration And Thermal Performance Analysis Of Medium And Low Temperature Molten Salt Heat Storage System

With the large-scale access of renewable energy such as solar energy and wind energy,the energy framework in the new era needs more reliable and stable technical support.As an important way of energy storage,thermal storage technology has a unique position in the solar thermal utilization.It solves the fluctuation and intermittent shortcomings of solar resources,realizes the space-time translation of energy,thus guaranteeing the continuity and dispatch of power generation in solar-thermal power plants.The purpose of this paper is to explore the reasonable capacity configuration of molten salt heat storage system in solar-thermal power station,to study the thermodynamic characteristics of key equipment in the system and its control strategy,and to lay a theoretical foundation for the experiment and system optimization.The main research contents and conclusions are as follows:This paper describes the basic structure and operation mode of the thermal storage system.Taking the 50MW trough solar-thermal power station in Tucson,USA as the research object,the data of typical characteristic days in the four seasons are extracted.The influence of the thermal storage system on the thermal storage system is analyzed by SAM software,and the thermal storage system is quantitatively calculated after the thermal storage system is deployed.Taking solar multiple and heat storage time as independent variables,the total power generation and auxiliary power consumption of the power station are explored to find out the changing law of cost price and put forward suggestions for determining the economic capacity of heat storage system.According to the comparison of economic cost and thermodynamic characteristics between single-tank molten salt sand-gravel packed bed system and double-tank molten salt indirect heat storage system.It is found that their consumption on the structure and material purchase of heat storage tanks has their own advantages and disadvantages,and the average temperature level of heat storage medium belongs to single-tank system.Therefore,ANSI/ASHRAE Standard is used to evaluate the performance of single tank heat storage system,and the optimal inflow rate is explored according to the stratification index of molten salt in the tank.Using ANSYS FLUENT to model and imitate the high temperature molten salt tank under different operation modes,a nitrogen-molten salt two-phase model is used to study the heat dissipation of molten salt and the wall of the heat storage tank in a certain period.It is found that the total heat dissipation through the top wall of the heat storage tank is the largest.Therefore,the thermal insulation structure should be arranged reasonably to protect the shape of heat storage tank.In order to ensure the effective heat transfer between heat storage part and heat collection part,we carried out the dynamic numerical simulation of oil-salt heat exchanger.It is known that the effective heat transfer area should be enlarged as much as possible to reduce the adverse effects of heat transfer dead zone.When adopting feed-forward and feedback compound regulation mode,molten salt inlet temperature is considered for rough adjustment and heat-conducting oil inlet temperature is used for fine adjustment.By this method,we can effectively restrain the temperature fluctuation of the heat collection field,and stabilize the operation parameters of the heat storage system,finally achieve the qualified storage target,and provide a reliable guarantee for the smooth operation of the unit in rainy weather and at night.