The working pressure of LNG cryogenic storage tank is 0.6-1.44MPa, and the working temperature is -162℃ (divided into vertical or horizontal), and its tank body is composed of two layers inside and outside to reduce the external heat transfer into the tank, and between the two layers, the vacuum-filled pearlescent sand cold-retaining material adiabatic structure is adopted to reduce the inflow of heat from outside into the tank, and the cold-retaining layer between the outer and inner tanks is adopted to avoid the influence of atmospheric pressure or temperature change on the atmosphere, thus effectively guaranteeing and improving the effect of the use of the cold-retaining material. The adiabatic structure of the material avoids the influence of atmospheric pressure or temperature change on the atmosphere, so as to effectively guarantee and improve the use effect of the cold-preservation material.

I. Purification of LNG cryogenic storage tank.
LNG cryogenic storage tanks should be purified before LNG sub-filling, or after decommissioning due to the need for internal maintenance. The purpose of purification is to replace the air or natural gas in the tank with an inert gas, to avoid the formation of an explosive mixture of natural gas and air. This purification process is also called “inerting”. Inerting gas is usually used nitrogen or carbon dioxide.
Second, the pressure control of LNG cryogenic storage tanks.

LNG cryogenic storage tank internal pressure must be controlled within the allowable range, the tank pressure is too high or negative pressure, will bring potential harm to the tank. There are many factors that can affect the tank pressure, such as evaporation of liquid due to heat entry, liquid flash vaporization during filling, drop in air pressure or incorrect operation, etc., which can lead to an increase in pressure inside the tank. In addition, draining, pumping, and low liquid temperatures at very high velocities can also cause negative tank pressures.LNG cryogenic storage tanks shall have tank pressure control devices to ensure that the tank pressure is within the allowable range. In addition, the tank must be equipped with pressure safety valve and vacuum safety valve. Decompression safety valve to prevent overpressure phenomenon in the tank, vacuum safety valve can feel the local atmospheric pressure, to determine whether there is a vacuum in the tank, generating negative pressure.

LNG cryogenic storage tank instructions for use:

1, cold storage explosion-proof port (r) and vacuum port (m) is strictly prohibited collision, private opening.

2, lng cryogenic storage tanks should be used pressure value than the tank design pressure is lower than 0.2MPa. tanks of the ascending value is lower than the value of the starting pressure of the safety valve 0.05MPa, shall be manually discharged or the use of BOG gas.

3, lng cryogenic storage tank process valve can not be used as an operating valve, can not be opened and closed frequently.

4, in the unloading, should pay attention to the liquid level, to avoid overfilling, in the absence of confirmation can open the relief valve (GJ-105) for observation.

5, should be regularly checked with lng cryogenic storage tanks related to the pressure gauge and liquid level meter pipeline, so as to avoid the pipeline leakage and lead to measurement inaccuracy, which will lead to danger.

6、On-site operators must be qualified training, licensed to operate, so as to avoid the danger caused by misoperation.

7. Smoking is prohibited within a radius of 40 meters from the cryogenic storage LNG tank, and the station should be equipped with fire fighting equipment according to regulations.

In the LNG cryogenic storage tank pressure safety valves and vacuum safety valves and tanks also need to set a manual switch between the shut-off valve, in order to facilitate maintenance. In the event of a fire, the safety exhaust device should also give full consideration to how to realize safe discharge. For tanks of double-wall construction, in order to prevent the internal LNG from leaking between the internal and external tank walls to the insulation layer, the external tank shall be fitted with an adequate safety venting device. The working pressure of the venting channel must not exceed the design pressure of the tank, which shall not be less than 0.0034 c/kg according to NFPA 59A, but not more than 2000 MPa; the working pressure of the safety venting device of this external tank must not exceed any of the design internal pressure and design external pressure of the external tank.