Research On Key Technologies Of New Medium-Low Temperature Parabolic Trough Concentrating Solar Thermal Power Generation System

With the structural transformation of energy production and consumption patterns,traditional fossil fuel energy is gradually replaced by clean energy such as solar energy and wind energy.In this era background,Concentrating Solar Power(CSP)is an emerging renewable energy utilization technology with important development value,which provides new ideas for the rational use of clean renewable energy by human beings.According to different meteorological conditions,different solar thermal power generation technology routes can effectively solve the outstanding contradiction between energy and environment.For areas with poor meteorological resources,the adoption of medium-low temperature parabolic trough solar thermal power generation technology has unique technical advantages and broad application background and it can effectively convert the energy form of solar energy with low energy density and high dispersion.As is known to us all,the parabolic trough concentrating solar thermal power generation system is mainly composed of a parabolic trough concentrating heat collecting device,a heat storage device and a thermal power conversion device.However,a series of problems such as low efficiency,high cost and long payback period under the medium and low temperature parameters need to be solved urgently.The whole system as the research object was taken in this paper and a series of in-depth research on the key technical problems existing from the whole to the local links has been conducted.The methods adopted covered theoretical calculations,simulations and experimental studies.Firstly,based on the laws of optics,the first and second laws of thermodynamics,etc.,the mathematical model of the parabolic trough concentrator,the solar vacuum collector,the heat storage tank,and the thermal power conversion system with or without the regenerative device at the back end were sequentially established.And in the Ebsilon simulation platform,the four-day simulations of the four typical solar terms including"spring equinox,summer solstice,autumn equinox,and winter solstice" were carried out,and the general scheme of the medium-low temperature parabolic trough-type solar thermal power generation system with regenerative device was established.Secondly,the core device-concentrator and vacuum collector tube in the front-end parabolic trough concentrating collector system were optimized,and two new concepts including a new parabolic trough concentrator with a Fresnel lens at the top and an interpolated spiral three-blade rotor structures were proposed.The optical propagation path of the new concentrator and the influence of the circumferential heat flux distribution on the collector tube were simulated by SolTrace software.The internal flow field of the two types of collector tubes of the rotor tube and the smooth tube were carried out by using CFD software combined with three control equations.The numerical simulation of heat transfer flow was used to compare and analyze the speed field,pressure field,temperature field and field synergistic coupling ability,and the results of comprehensive evaluation index of heat transfer performance were given.Thirdly,the research on the dynamic characteristics of the thermal power conversion system was carried out,and a new scheme using low boiling organic dry working fluid as the circulating medium was proposed.The subcritical and supercritical cyclical changes of pure working fluid R245fa and 8 non-azeotropic dry working fluids driven by medium-low temperature solar heat source were studied by Matlab programming.The comprehensive index evaluation and operating parameters were analyzed and optimized by using the method of analytic hierarchy process.Finally,based on the previous theoretical research,the experimental study of the parabolic trough-type concentrating collector circuit was carried out.The distribution law of the heat collection of the traditional and new type parabolic trough,the temperature difference of heat transfer oil inlet and outlet of the collector unit,the instantaneous efficiency,and the heat loss performance of different types of collector tubes of the smooth tube and rotor tube were compared and analyzed from the perspective of rationality and effectiveness of the design.In the end,these core problems were deeply analyzed.Meanwhile,a certain reference for the design,operation and engineering promotion of the new medium-low temperature parabolic trough solar thermal power generation system from both theoretical and experimental perspectives was provided in this paper.