Investigation Of Thermal Performance Of High-Temperature Molten-Salt Receiver In The Concentrated Solar Tower Power Plant

With the rapid development of the world in recent decades,the shortage and exhaustion of traditional energy sources have begun to appear,which will not be enough to support the rapid development of mankind in the future.To solve this problem,solar thermal power generation is considered a competitive candidate.Solar thermal power generation has its own heat storage system,which can achieve continuous power generation for 24 hours in one day,and has become one of the most potential renewable energy applications.Based on the above background,this thesis focused on and carried out related researches on the thermal performance,thermal stress and preheating process of the high-temperature molten salt receiver,the key equipment in the CSP plant.First,the corrosion characteristics of commonly used materials in CSP stations in high-temperature solar salt were studied.The study found that nickel-chromium alloy Inconel 625 and stainless steel 347 H have good corrosion resistance to hightemperature molten salt,and can be used to manufacture the high-temperature molten salt receiver and receiver hot salt tank its accessory pipes.Carbon steel 20# only has corrosion resistance to low-temperature molten salt,and can only manufacture the cold salt tanks and nearby pipelines in CSP stations.Secondly,a small-scale external molten salt receiver system with an electric power of 150 k W xenon lamp group as the light source was designed and built,and the optical and thermodynamic characteristics of the small-scale receiver were studied.The measurement method is provided for the parameters of the receiver in the operation.At the same time,experimental and simulation methods were used to study the thermal performance of the lab-scale receiver under the reference conditions.The result of experiments and simulations show that the temperature rise of the molten salt in the receiver is about 4 ? and 4.2 ?,respectively.The deviation of the back wall temperature of the receiver obtained by numerical simulation and experimental measurement is basically within 5%,indicating that the two methods are in good agreement.Finally,the thermal efficiency of the lab-scale receiver was studied,and the thermal efficiency of the lab-scale receiver was about 85%.Third,a series of the off-design tests were carried out on the lab-scale receiver.At the same time,based on the heat transfer characteristics of the receiver,the net heat flux method was used to combine the heat convection and heat radiation characteristics of the receiver to develop a fast thermal performance evaluation code for the receiver.The deviation between the results obtained by using this procedure and the measured value of the thermocouple was only 0.22%,which proved the reliability and accuracy of the code.Then experiment and simulation methods were used to explore the performance of the lab-scale receiver under different working conditions.The test and simulation results showed that when the molten salt mass flow rate in the receiver increases,the electric power of the xenon lamp decreases or the wind speed increases,the temperature rise of the molten salt in the receiver will all decrease.Besides,a transient performance calculation code of the receiver was also developed,and the transient characteristic of the lab-scale receiver's temperature distribution was analyzed when its working condition was changed.Fourth,on the basis of the previously developed receiver thermal performance calculation program,the thermal stress calculation module of the receiver was added,and a set of programs that can quickly evaluate the thermal performance and thermal stress of the receiver was obtained.Then the program was applied to the Yumen 600 MWth receiver to study its thermal performance and thermal stress properties.Through the numerical calculation,the three-dimensional temperature and thermal stress distribution of the receiver was presented,and it was found that the highest temperature and the maximum stress of the receiver appeared on the last and first panel,respectively.At the same time,the tangential,radial and axial component stresses of the heat absorption tube were analyzed,and it was found that the tangential and axial thermal stresses all have a transition from compressive stress to tensile stress in the radial direction,while the radial thermal stress is too small and can be almost directly ignore.Finally,the thermal stress change of the receiver during the vernal equinox day was studied.The results showed that the average maximum thermal stress and the maximum thermal stress change ratio of the receiver were 145 MPa and 1.843,respectively.The maximum thermal stress of the receiver was 145 MPa and 1.843.The stress dropped by45.74% from 12:00 to 18:00 on the vernal equinox.Fifth,the Monte Carlo ray-tracing algorithm was introduced to evaluate the thermal performance properties of a 50 MWe receiver in northwest China.The algorithm could simultaneously calculate the heat flux distribution on the receiver and the radiation heat transfer between the tubes.Finally,a set of receiver calculation program based on Monte Carlo ray-tracing algorithm is developed,which includes 4modules such as heat flux,view factor,thermal performance and thermal stress calculation.After studying the thermal performance and thermal stress of the 50 MWe receiver,the overheating problem of the receiver was finally discussed,and an optimization algorithm to solve the overheating problem was introduced.It is found that after the algorithm optimization,the temperature of the back and frontal tube walls of the over-heated area of the receiver met the safety standards,and the temperature of the outlet molten salt of the receiver still reached 563 ? after the optimization process,which only dropped by 2 ?.Finally,the lab-scale receiver was used to study the receiver preheating process,and a set of receiver preheating transient performance calculation program based on unsteady heat conduction was developed,too.The preheating process of the lab-scale receiver under different constant heat flux was studied,and it was found that the larger the heat flow used during preheating process,the shorter the preheating time,but only using the constant heat flux preheating cannot meet the preheating requirements.Therefore,a preheating test based on the real-time negative feedback control on the heat flux according the surface temperature of the receiver was carried out.After preheating process completed using this method,the surface temperature distribution of the lab-scale receiver was uniform and reached the preheating requirement.Finally,a related study was conducted on the influence of ambient temperature on the preheating process,and it was found that when the ambient temperature is-2 ?,the preheating time of the lab-scale receiver under the same heat flux will be longer than the preheating time when the ambient temperature is 13 ?,and It was extended by about 30 s.