| Energy storage technology can effectively alleviate the problem of time-space mismatch between energy supply and demand.With the characteristics of wide operating temperature range,high energy storage density and high safety and reliability,molten salt heat storage technology has received great attention in achieving carbon peaking and carbon neutrality goals.Compared with the mature two-tank molten salt heat storage process,single-tank energy storage system has the advantages of small occupied area and low investment cost.The optimization of materials and equipment of this process is the research focus of the academic world at present.Therefore,this paper designs a new single-tank of electrothermic molten salt with heat storage,heat release and heating integrated in one.The design method,structure optimization and heat release characteristics of molten salt in the tank are studied.The specific research contents are as follows:Firstly,taking a non-woven energy storage heating project of the research group as reference,the design proposal of a single tank of electrothermic molten salt was studied,and a single tank of electrothermic molten salt integratin heat storage,heat release and heating was designed.The following details should be paid attention to in the design: 1)in order to maintain the stability of the system,the heat storage medium should use Hitec ternary molten salt;2)when the corrosive heat storage medium in the tank is strong,the storage tank material should be stainless steel 316L;3)the design method of welded oil storage tank in API 650 is adopted for tank structure,but the design method of welded atmospheric pressure vessel with steel NB-T 47003 should be adopted for tank wall thickness for temperature correction.Secondly,ANSYS Workbench software was used to establish a finite element model for a single tank of electrothermic molten salt,and the influences of the number of electric heaters,position of electric heaters,tank bottom constraint and tank height-diameter ratio on the thermal stress of a single tank of electrothermic molten salt under the same heating power were studied.The research results are as follows: 1)when the number of electric heaters increases from 4 to 8,the maximum equivalent stress of the heat storage tank increases from 105.38 MPa to 114.12 MPa;2)the maximum equivalent stress of the heat storage tank decreases from 110.11 MPa to 95.26 MPa when the distance between the sleeve position of the electric heater and the tank bottom increases from 400 mm to 800 mm;3)the maximum equivalent stress of the heat storage tank increases from 105.38 MPa to1027.92 MPa when the friction coefficient of the tank bottom increases from 0.3 to the fixed constraint;4)when the height-diameter ratio of the heat storage tank increases from 1 to 1.4,the maximum equivalent stress of the heat storage tank decreases from 117.96 MPa to105.38 MPa.At the same time,the structural strength of the heat storage tank was checked according to the method in JB 4732,and the checking results of the single tank of electrothermic molten salt all met the strength requirements.Finally,Fluent software was used to analyze the influence of inlet and outlet velocity and temperature difference on the variation law of the thermocline layer in the heat release process of molten salt.The research results indicate that: 1)when the heat release condition of molten salt is determined,the thermocline layer could move stably in the tank,and the temperature of molten salt outlet is constant;2)when the molten salt flow rate increases from 0.1 m/s to 0.4 m/s,the maximum thermocline thickness increases from 1.02 m to 1.29m;3)when the temperature difference increases from 50 K to 200 K,the maximum thermocline thickness increases from 0.68 m to 1.29 m.In a word,the design method of a new single molten salt tank and the law of heat release in operation are studied with the aim of providing some theoretical support for the application of molten salt heat storage in distributed energy-using enterprises. |
