| The development of renewable energy is the key to the realization of China’s"3060double carbon goal",and it is also China’s energy strategy for a long time in the future.However,solar energy,wind energy and other renewable energy are affected by natural factors and have the characteristics of intermittence and instability.It is an effective way to solve this problem by using thermal energy storage technology to store garbage electricity that cannot be connected to the network,such as wind and photoelectric power or low valley power in the form of heat energy for heating.Compared with the technology of double tank heat storage,single tank heat storage technology has the advantages of simple structure and low cost and is suitable for small place heating.However,the molten salt heat storage system with heat exchanger arranged in a single tank,the molten salt temperature will gradually decrease with the heat discharging,resulting in the inability to provide stable heat for users.Therefore,solving the stability of heat output in the process of heating has become an urgent problem to be solved.Based on the original small single tank heat storage system in the laboratory,PID control technology is added,and the principle verification system of stable heat discharging of single tank molten salt is set up.Different PID setting methods are used to realize the continuous adjustment of the heat exchange area of the coil heat exchanger in a single tank.By increasing the heat exchange area to make up for the decrease of molten salt temperature,and finally achieve the purpose of stabilizing the water temperature at the outlet of the heat exchanger.Through the verification test,the best PID regulation method of heat exchanger area is obtained.In order to verify the effectiveness of the regulation method,a single tank heat storage amplification experimental system is built in this thesis,and a single tank molten salt heating system is designed for 72 m~2 building heating.The experiment shows that the heating water temperature is stable by continuously adjusting the heat exchange area,and the molten salt temperature in a single tank in the heat discharging process is analyzed.The results show that at the same vertical height in a single tank,the molten salt temperature in the center of the tank is higher than that in the annular channel.At different vertical heights,the molten salt temperature at the higher position is higher than that at the lower position,indicating that the heat discharging process in the tank has formed a stable natural convection.At the same time,the heat discharging effects of continuous adjusting heat exchanger and fixed heat exchanger are compared and analyzed.The results show that the method of continuously adjusting the heat exchange area can not improve the heat release and heat discharging efficiency,but can significantly prolong the heat discharging time of single tank molten salt system.In order to analyze the distribution of molten salt temperature field and flow field in a single tank under the adjustment of heat exchanger in the process of heat discharging,it is studied by numerical simulation in this thesis.The results show that the molten salt is evenly distributed during the heat discharging process,there is no obvious temperature stratification,and the molten salt temperature in the center of the tank is basically the same as that in the annular channel.In the process of heat release,the molten salt flows regularly in a single tank,which proves that the cylindrical diaphragm has the effect of enhancing the natural convection heat transfer on the molten salt side and reducing the temperature stratification.In addition,the natural convection heat transfer coefficient on the molten salt side is analyzed and studied.The results show that the continuous regulation of the heat exchanger enhances the disturbance of the molten salt,so that the convection heat transfer coefficient on the molten salt side always fluctuates up and down in a certain range.On this basis,this thesis applies this technology to the demonstration heating project funded by the major special project of Inner Mongolia"optimization of wind power storage and load multi energy complementary system based on decentralized wind power consumption",and realizes the demonstration of building heating engineering with clean energy.While designing the single tank molten salt heat storage system,the economic analysis of the system is carried out.The results show that in this demonstration project,the initial investment cost of the single tank molten salt heat storage system is 594800 Yuan and the operation cost is 32.1 Yuan/m~2,which has high economy and promotion value. |
