Research On Operating Characteristics And Strategies Of Molten Salt Receriver For Concentrating Solar Power

Concentrating Solar Power(CSP)is one of the primary development directions in the future because of its high efficiency and stable electricity output.Molten salt receiver is a crucial part of the whole system.In order to enhance the safety and economic benefit of CSP,and to make it better adapt to the climate in Northwest China,it is necessary to investigate the operating characteristics of a molten salt receiver and to optimize its operating strategies.Full-scale numerical simulation is implemented to study the overall heat loss and thermal efficiency of the molten salt receiver under typical operating conditions.Local flow and heat transfer characteristics of the receiver are analyzed.In addition,a physical protection method is proposed and its protective effect is validated.Based on comprehensive analysis of the thermal efficiency,exergy efficiency and system efficiency,as well as typical weather conditions in Northwest China,an integral averaging method for DNI data and operating strategies for receiver are proposed.The results show that the wind velocity and the concentrated incident energy can affect the heat loss and thermal efficiency of the receiver greatly,while the wind direction and the environmental temperature make little influence.Local convective heat loss of the receiver is significantly affected by both wind direction and wind velocity.Based on typical design,the thermal efficiency,exergy efficiency and system efficiency are around 87%,55% and 18% respectively when running at full load under normal wind velocity.All of the above three efficiencies decrease with concentrated incident energy decreasing or with wind velocity increasing.The total convective heat loss of the receiver surpasses the radiative one if wind velocity is over 7m/s.When operating under rated outlet temperature mode,the thermal efficiency of the molten salt receiver is lower than that of rated mass flow rate mode,while the exergy efficiency of the receiver and energy efficiency of the whole system are higher.When the concentrated incident energy decreases from 100% to 30% of the designed value,system efficiency decreases from 18.45% to 16.20% for rated outlet temperature mode,and from 18.36% to 7.10% for rated mass flow rate mode respectively under normal wind velocity.The core of operating strategies proposed in this study is to provide a method for determining the mass flow rate of molten salt based on concentrated incident energy,so that the receiver can operate close to rated outlet temperature mode.When DNI is steady,the rated outlet temperature mode should be implemented.It should be smoothed when DNI fluctuates,after which equivalent rated outlet temperature mode can be employed.If cloud blocks the radiation for a short period,molten salt should be provided continously and physical protection measures should be taken so that the receiver is preprared to absorb energy after cloud disappears.The difference of both modes in terms of thermal efficiency and exergy efficiency is no more than 1%,and difference of system efficiency no more than 2% if concentrated incident energy is no less than 80% of the designed value.Compared to rated mass flow rate mode,the system efficiency can be enhanced by 2%-7% under rated outlet temperature mode when concentrated incident energy is between 40%-80% of the designed value.relevant research in this study is expected to provide reference for operating optimization of molten salt receiver for CSP.