Study On Variation Of Interspace Pressure Of Cryogenic Tanks After Liquid Filling

Cryogenic tank as an equipment for storaging and shipping liquids of low temperature, can be used in the cryogenic field wildly, such as air-separation operation, cryogenic gasification, LNG station, peak-shaving station, etc. Cryogenic tank should have good heat insulation property to ensure the normal work, since its storage medium temperature is far below the environment temperature. The insulation property of vacuum insulation cryogenic tank mainly depends on the interspace vacuum degree in the cryogenic tank. Engineering practice shows that liquid filling could cause the change of the interspace vacuum degree and affect insulation property of the cryogenic tank. Therefore, it is greatly significant for us to study the change of the cryogenic tank interspace vacuum degree for evaluating the insulation property of cryogenic tank.Filling cryogenic tanks with cryogenic liquids will cause interspace volume to enlarge with the inner vessels to contract, interspace gas mass to decrease with the adsorption capacity of adsorbent to increase and steam condense in the interspace as well as interspace temperature to decrease, and finally result in the change of interspace pressure. Therefore, firstly, this paper theoretically analyzed the contraction of inner vessels of the cryogenic tank after filling, put forward the concept of equivalent length of inner vessel and get the calculating model of the interspace volume change. Secondly, through deep-analyzing the heat transfer process of cryogenic tank, put forward the calculation method of the interspace average temperature assuming that the apparent thermal conductivity is a constant. Thirdly, analyzing the adsorption mechanism, and steam condense, interlayer gas mass will decrease because of the combined action of adsorption and condensation under low-temperature conditions. Finally, using the Ideal-Gas Equation, comprehensively analyzed the change of the interspace volume, average temperature, air mass after filling, get the law of pressure variation. According to the calculation model, taking a 50m3 cryogenic tank with vacuum powder insulation, the interspace pressure drops to 32% of the initial pressure after liquid filling. Then, using the method of computer simulation for the changes of the inner vessel to contract and interspace temperature after filling, the simulation result and theoretical analysis are matched.Through the research, the interspace vacuum degree of cryogenic tank will be raised, that is, the absolute pressure will drop. This counterbalance the pressure increase caused by the interspace leakage at a certain extent, and maintains the insulation propertly. It is beneficial for cryogenic tanks.