Performance Study Of Parabolic Trough Receiver Based On Coating Spectral-Spatial Optimization And Concentrated Solar Power Generation System

The high-temperature solar thermal conversion is an important direction for the efficient utilization of solar energy in the future,and concentrated solarl power(CSP)generation technology is one of the most important high-temperature solar thermal utilization technologies.Parabolic trough solar concentrated system is currently the most mature and commercialized CSP technology,and its maximum operating temperature can reach 550℃.The solar field is the main place for solar thermal conversion and energy transmission,and its performance directly determines the efficiency and economics of CSP system.With the increase of operating temperature and the application of high-temperature molten salt as heat transfer fluid(HTF),the heat loss of the parabolic trough receiver,the key component of photothermal conversion,has increased significantly.At the same time,the enormous exergy loss in molten salt/water heat exchangers caused by the high heat transfer temperature difference in water evaporation leads to a considerable decrease in electricity production.As a high-grade energy loss at the collector end,it has a serious adverse effect on the overall performance of the system.Based on above issues,in this paper the parabolic trough CSP system is employed as research object,with the goal of realizing high-efficiency energy conversion of the CSP system.Based on the basic principles of the radiation heat transfer of the collector tube and thermodynamics of the CSP system,the investigations of the parabolic troughreceiver and the thermal power generation system are carried out.The coupling relationship between the spectral distribution characteristics of the selective absorption coating and the temperature and the energy flow density of the receiver surface,as well as the exergy loss characteristics in the molten salt/water heat exchanger is explored.The double-selective-coated receiver and direct steam generation-molten salt(DSG-MS)CSP system are proposed.The influences of environmental parameters,parabolic trough receiver performance,system configuration,HTF.et.al on the performance of CSP system are analyzed.1.The spectral and spatial coupling radiation heat transfer analysis model of the receiver was established.The influence of spectral parameters of the selective absorption coating on the performance of the receiver was investigated,and the optimal cutoff wavelength of the selective absorption coating was optimized under different temperature and thermal flux conditions.The results show that spectral slope width,spectral emissivity and cutoff wavelength are the key parameters that affect the performance of receiver.The optimal cutoff wavelength increases with the increase of thermal flux,but decreases with the increase of temperature.Sensitivity analysis results of the coating optical properties indicates that the thermal efficiency significantly decreases with increasing slope width.The change range of the thermal efficiency at the temperature of 600℃ is±6.5%,resulting from a±1 μm variation in slope width.The emissivity has obviously different negative effects on the performance of the receiver under different operation conditions.2.An innovative double-selective-coated parabolic trough receiver that employs two solar selective coatings with different properties on the outer surface of the absorber is proposed.The traditional receiver and double-selective-coated receiver were designed and trial-produced,and the heat loss test of the receiver was conducted.The experimental data show that when the temperature is 550℃,the heat loss of traditional,120° and 150° double-selective-coated is 658 W/m,493 W/m and 431 W/m,respectively,and the corresponding heat loss percentage is 25.07%and 34.50%,respectively.3.The comprehensive thermodynamic and economic model of the trough solar thermal power generation system is established to predict and compare the performance of CSP plants using traditional and double-selective-coated receiver.The influences of parameters such as anti-freezing temperature and thermal performance of receiver on the performance of thermal power plants are analyzed.The simulation results show that the annual electricity productions of power plants with novel receivers in Phoenix,Sevilla,and Tuotuohe,are 8.5%,10.5%,and 14.4%higher than those with traditional receivers at the outlet temperature of 550℃.The levelized cost of electricity of power plants with double-selective-coated receivers can be decreased by 6.9%,8.5%,and 11.6%.Low heat loss receiver coupling with low melting temperature molten salt is the best configuration for improving the overall performance of the power plants.4.A novel hybrid parabolic trough power system that integrates direct steam generation and molten salt systems is proposed in this study to stably and efficiently operate solar power plants.The heat transfer model based on energy conversion and balance is applied to numerically investigate the overall performance of various power plants.This paper presents a comparative study of the effects of different locations,steam turbines,and system configurations on the outputs of the power plants.The simulation results show that the electricity production increments of novel systems in Tonopah and Lhasa are 14.0%and 14.8%,respectively,compared with those of molten salt systems.The annual thermal energy productions of the molten salt、hybrid systems with and without the reheat section in Tonopah are 639.7,685.1 and 691.7 GWh,respectively.The percentage of energy required for anti-freezing without reheating system in total heat collection is reduced from 7.6%to 2.7%.