| At present,the insufficient peak shaving capacity of wind power and photovoltaic power generation in China has attracted attention.In addition,the grid connection and consumption of new energy are also hindered.In response to the above problems,the goverment has actively promoted the transformation of power consumption patterns and put forward suggestions for optimizing the development of energy storage technology.The policy points out that it is necessary to give full play to the advantages of electricity storage and heat storage in various aspects.At the same time,the implementation of electric energy substitution is supported.Based on the research of molten salt heat storage technology,a small capacity electric steam boiler molten salt heat storage system is designed in this paper.The structural design and calculation of the device have been carried out.The heat transfer of the heat storage device was analyzed by numerical simulation,and the heat exchanger was optimized.The practical application of the small capacity molten salt heat storage system was investigated by means of experimental research.The main results of the thesis research are as follows:（1）Ternary mixed nitrate HTS（53%KNO3-7%Na NO3-40%Na NO2）is selected as the working medium.On the basis of meeting the heat storage requirements,the size design of the tank was carried out by comprehensively considering the relationship between heat loss of the heat storage tank and the height to diameter ratio of the tank,the relationship between exergic efficiency and the diameter to height ratio of the tank,and the relationship between total cost and the height of the tank.The size of the heat storage tank is determined to be 1.8 m in diameter,2.15 m in height,10mm in wall thickness,and 300 mm in insulation thickness.（2）A three-dimensional model of the heat storage device equipped with an immersion heat exchanger was established,and the heat exchange of the molten salt in the tank was analyzed using Fluent software.Taking temperature distribution and heat transfer as indicators,the influence of different initial temperature of molten salt and different cold fluid inlet temperature on heat transfer was analyzed.The results show that after the same exothermic time,the lower the initial temperature of the molten salt in the tank,the smaller the temperature difference in the axial direction of the molten salt in the tank,and the smaller the average heat flux value.The lower the inlet temperature of the cold fluid,the faster the temperature of the molten salt drops,and the more obvious the temperature stratification of the molten salt in the tank along the axial direction.The higher the inlet temperature,the smaller the average heat flux value.（3）The simulation analysis of the heat storage device with the optimized heat exchanger shows that the optimized heat exchanger can provide better temperature distribution,increase the heat flow density,and have higher heat exchange under the same heat exchange area and the same heat exchange conditions.The optimized heat exchanger type is selected as the heat exchanger type of the molten salt heat storage device.（4）The multi-stage heat exchanger of the heat storage device is designed.The heat exchange area of the four-stage heat exchanger is obtained as follows:the first-stage heat exchanger is 2.0 m2,the second-stage heat exchanger is 0.28 m2,the third-stage heat exchanger is 0.42 m2,and the fourth-stage heat exchanger is 1.1 m2.Among them,an air sleeve is added outside the first-stage heat exchanger,which mainly serves as a buffer to ensure the safe and stable operation of the system.（5）A small-capacity molten salt heat storage system was constructed,and the control of the heat storage system was designed.The system is equipped with complete control functions,which can set and adjust parameters according to user needs and actual conditions.（6）The experimental platform of the small-capacity molten salt heat storage system was built to study the actual operation of the device.The results show that the system operation mode with variable valve opening can effectively maintain the stability of the steam outlet.The analysis of economic benefits based on actual operation cases found that compared with the use of ordinary electric boilers,the operation scheme with molten salt thermal storage electric boilers as the mainstay and ordinary electric boilers as auxiliary can save 53.23%of daily operating costs.The investment payback period is 661 days,and it has better economic benefits under the new electricity price conditions implemented in 2021. |
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