The natural gas storage tank is a double-layer structure inner tank to store low-temperature liquid and bear the pressure of medium. The low-temperature resistant alloy steel (0Crl8Ni9) shell is used as the material of the inner tank. A certain distance is maintained between the protective layer of the inner tank and the inner tank to form an insulating space to bear the gravity load of the inner tank and medium and the vacuum negative pressure of the insulating layer. The shell is not in contact with low temperature and is made of container steel. The insulation layer is mostly filled with pearlescent sand to pump high vacuum. The evaporation rate of low-temperature storage tank is generally lower than 0.2%.

Schematic diagram of decompression and pressurization of low temperature storage tank:

The outlet of natural gas storage tank is powered by the self pressure of the storage tank. After the liquid is sent out, the liquid level drops and the gas phase space increases, resulting in the pressure drop in the tank. Therefore, it is necessary to continuously supplement gas to the tank and keep the pressure in the tank unchanged in order to meet the process requirements. As shown in Figure 2, a pressurized gasifier and a pressurized valve are arranged under the storage tank. Pressurized gasifier is an air temperature gasifier, and its installation height shall be lower than the minimum liquid level of natural gas storage tank. The action of the booster valve is opposite to that of the pressure reducing valve. When the outlet pressure of the valve is lower than the set value, it opens and the pressure rises above the set value, it closes. The pressurization process is as follows: when the pressure in the tank is lower than the set value of the pressurization valve, the pressurization valve is opened, and the liquid in the tank flows into the pressurization gasifier slowly by the liquid level difference. The gas generated by liquid gasification flows through the pressurization valve and gas phase pipe to supplement to the tank. The continuous supplement of gas makes the pressure in the tank rise. When the pressure rises above the set value of the booster valve, the booster valve is closed. At this time, the pressure in the pressurized gasifier will prevent the liquid from continuing to flow into the end of the pressurization process.