Stress Analysis And Transient Simulation On Heating And Filling Process Of Large Molten-salt Storage Tank

The core advantage of solar-thermal power generation technology is that the power station is equipped with a large energy storage system,which can make up for intermittent and unstable sunlight.Molten-salt storage tank is used as key equipment in energy storage system of solar-thermal power generation station.Numerical simulation of the molten-salt storage tank under all working conditions is of great significance to the safety of the equipment as well as the whole solar thermal power station.In this thesis,strength analysis and creep-fatigue assessment and transient thermal analysis on heating and filling process of a high temperature molten-salt storage tank were performed based on finite element method.Some reasonable suggestions for the structural design of the storage tank and the design of the heating and filling schemes were provided.The main contents and conclusions are as follows:(1)The finite element model of the high temperature molten-salt storage tank and its foundation was established.Nine loads including wind load,seismic load and thermal load were considered and four load cases were specified.The stress analysis of the high temperature molten-salt storage tank was performed and strength assessment was conducted according to JB4732.The results show that the high temperature molten-salt storage tank meets the strength requirements of JB4732 under the four load cases.As working under high temperature and having a large thermal expansion,the pipelines and accessories of the storage tank should be reasonably arranged to ensure the free deformation of the tank and avoid strength failure of the tank due to constraint of the thermal deformation.(2)Based on the theory of cumulative fatigue damage,creep-fatigue analysis was carried out on the tank.The creep-fatigue assessment was conducted according to ASME NH.The results show that the creep-fatigue assessment is qualified and the design of the tank meets the requirements.Moreover,the creep damage of the molten-salt storage tank is far greater than the fatigue damage,indicating that creep deformation poses a greater threat to the safety of the tank in service.(3)Three calculation models having nozzles with different angles were established,and the effects of different angles on the uniformity of internal flow field and heating effect of the tank were compared.The results show that the flow field of the model with 45° nozzles is most uniform.In addition,under the disturbance of the circulating wind,the maximum temperature difference of the tank is the quickest to be shortened to 50? with each holding time is about 0.25 hour.The temperature rising rate of the tank with 45°nozzles is the highest and the heating effect is the best.(4)The transient analysis on heating process of the high temperature molten-salt storage tank was carried out.It is found that after heating for 104 hours,the temperature of whole storage tank has reached 300?.The temperature of the heating shell is the highest and the temperature in the middle of the roof is the lowest as there is a flow dead zone inside the roof.With the heating process going on,the temperature field of the tank is gradually uniform.The temperature gradient appears in the thickness direction of the outer insulation layer and the foundation,implying that the insulation effect of the insulation layer and the foundation is good.(5)The finite element model of the solid domain and internal fluid domain of the high temperature molten-salt storage tank with input tubes was established.Based on VOF multiphase flow model,the transient analysis on the salt-filling process of the tank was performed and the law of temperature drop of the bottom was summarized.The temperature of the bottom under the inner distribution tubes drops first.Subsequently,the low temperature molten-salt flows into the outer distribution tubes and the temperature of the bottom under the outer distribution tubes drops.With the salt-filling process going on,the low-temperature area of the bottom expands gradually.The temperature of the monitoring points on the bottom under the inner and outer distribution tubes drops faster in the early stage and the maximum temperature drop rate of the monitoring points is 55.2?/min.With the salt-filling process going on,the temperature drop rate of the metal gradually decreases and the average temperature drop rate of the monitoring points is 27?/min.The rational design of the input tubes enables that molten-salt enters the tank safely and is mixed with internal molten-salt evenly,which is conducive to reducing the thermal shock effect of the salt-filling process on the bottom and ensuring the service life of the storage tank.