Key Technology Research On Collecting System Of Molten Salt Linear Fresnel Solar Concentrating Power

Linear Fresnel Concentrating Solar Power(CSP)has a series of advantages such as pollution-free,large-scale thermal storage,stable and adjustable output and so on.It is a transformative technology to construct a modern energy system.With the implementation of the first national demonstration projects for Concentrating Solar Power,the technology is receiving widespread attention.At present,Concentrating Solar Power technology is developing towards the technical direction of low cost,high efficiency and large installed capacity.In view of this trend,this paper takes the solar field of high temperature molten salt linear Fresnel Concentrating Solar Power of Dacheng in Dunhuang as the research object,and selects several key technical aspects of the solar concentrator and collector system,such as controllable preparation of high temperature selective absorption film,optical characteristics of the concentrator,heatloss characteristics of the collectors,outlet temperature control of the collector loop and so on.The main results in this thesis are summarized as follow:(1)In order to solve the problem of low cost and controllable preparation of high temperature selective absorption films,the technological feasibility of single-target self-doping WO_x photothermal conversion coatings was studied.First of all,monolayer WO_x films and multilayer WO_x based photothermal conversion coatings were prepared by reactive sputtering,and their optical properties were analyzed.The self-doped WO_x based photothermal conversion coating prepared by this process shows excellent optical absorption performance,with the absorption rate of 93.2%and the emissivity of 5.8%.(2)In order to meet control requirements of self-doping reactive sputtering process,A scheme of process stability control was proposed by using target voltage as feedback to adjust reaction gas flow in closed loop.The fuzzy PDF control strategy is used to solve the nonlinear and stable control problems of reactive sputtering process,and the simulation research is carried out.The results show that,compared with the conventional PDF control strategy and PID control strategy,the fuzzy PDF control strategy has good dynamic response performance,strong anti-interference ability and robustness for the second-order system with time-varying parameters.Therefore,the embedded reactive sputtering controller module based on the field bus is designed and applied in the selective absorption film coating production line,and the practical value of the scheme is verified by the experiment.(3)Aiming at the problems of optical efficiency and heat loss characteristics of the linear Fresnel concentrator system in actual operation,first of all,based on the theoretical model of linear Fresnel concentrator,the cosine loss,end effect and shadow occlusion effect of the concentrator are calculated and analyzed.By using Trace Pro software,the incidence angle modifier(IAM)of the concentrator was simulated by ray tracing method,and the dynamic optical efficiency model of the concentrator was obtained.Then,the influence of ambient temperature,wind speed and direct normal irradiance on the heat loss of collector tubes in different states was simulated and tested.On this basis,three typical Collector conditions were selected on the molten salt linear Fresnel collector loop test system of Dacheng in Dunhuang.The heat collection performance test was carried out by using the quasi-dynamic method.The dynamic model parameters of the collectors under typical collector conditions were identified by multiple linear regression least square method.The test results show that,linear Fresnel concentrator system in actual operation,the actual optical efficiency of the Concentrator is about64%and the heat loss of the system presents great dispersion under different collector conditions,and the dispersion of heat loss in the high temperature section is more obvious.The research results indicate that the influence of collector conditions on the collector performance should be fully considered in the research and design of the high temperature molten salt linear Fresnel collectors.(4)The fuzzy gain scheduled MMPC was applied to the high temperature molten salt linear Fresnel collector system,which can effectively control the outlet temperature with time-delay,large inertia and time-vaying characteristics.According to the parameter set of the linear Fresnel collector system under typical cillector conditions,the linear model and the global fuzzy model of the outlet temperature of the collector system are established under typical working conditions,and the net heat collected by the collectors is selected as the scheduling variable of the MMPC.The control algorithm is simulated by MATLAB.The results show that the dynamic performance,static error and anti-disturbance performance of the control system are superior.Under complex astronomical conditions,the outlet temperature control precision of the collector system can reach±8?.This control strategy can provide reference for the outlet temperature control of the large-scale solar field of the linear focusing CSP.A collector loop flow field controller based on PLC was designed in this dissertation.Therefore,a temperature control system for outlet of collector loop is proposed,which is based on the structure of solar field distributed control system(SCS),This scheme serves as the basis for further experiments and research.