Low temperature storage tank is a vertical or horizontal double-layer vacuum insulated storage tank used to store liquid oxygen, nitrogen, argon, carbon dioxide and other media. The material of inner liner is austenitic stainless steel; the material of outer container is Q235-B, Q245R or 345r according to the national regulations according to the different user areas. The interlayer of inner and outer container is filled with pearlescent sand or aluminum foil, insulation cotton and vacuumized.

Liquid natural gas must be stored in low-temperature storage tank, which is usually composed of inner tank and outer tank and filled with thermal insulation material.

Inner tank

Inner tank, also known as "membrane tank", is a liquid tight and flexible content device made of low-temperature steel sheet. It must pass the hydraulic head to the insulation. The materials used as thin films must have the characteristics of non embrittlement at low temperature, enough toughness and good processability. Nickel steel, stainless steel or aluminum alloy are usually used.

Insulation layer

The heat insulation layer not only transfers the hydraulic head to the outer tank, but also reduces the gasification amount, the temperature difference between the inner and outer walls of the tank, and the resulting temperature difference stress. In addition, it also has the function of fixing the "film". Therefore, it is required that the thermal conductivity of the thermal insulation layer is small and has enough strength. The materials that can meet these conditions are rigid foam ethyl carbamate, foam glass, perlite and rigid foam phenolic resin. In order to improve the heat insulation performance and economy of the heat insulation materials, the heat insulation method of powder, fiber, plate and other heat insulation materials can be used.

When LNG is injected into the tank, the inner tank wall will shrink; otherwise, when LNG is completely discharged, the temperature in the tank will gradually rise, and the inner tank wall will expand accordingly. The powder thermal insulation material filled in the middle of the inner and outer tanks becomes tight due to the repeated expansion and contraction of the inner tank wall. Therefore, it is necessary to lay a layer of thermal insulation layer with strong expansibility near the inner tank. The thickness of the thermal insulation layer is suitable for the expansion and contraction of the inner tank wall, and plays a buffer role in the expansion and contraction of the inner tank wall to ensure the safe operation of the tank.

Outer tank

(also called can body)

Outer tank is the shell that can bear all kinds of loads. It must have enough strength. According to the different materials used, it can be divided into the following types: frozen soil wall, steel wall, reinforced concrete wall and prestressed concrete wall.

① Frozen soil wall. The frozen soil wall and the heat insulation cover form the airtight closed space as the outer tank, also known as the pit storage. During construction, the soil around the inner tank is frozen by cooling pipe. After the pit is put into operation, the low temperature liquid will keep the surrounding frozen state, and the frozen soil layer will expand year by year, so the evaporation loss will also reduce year by year. In addition, the bottom of the pit should be the most impermeable rock or clay layer.

② Steel wall (including alloy and aluminum). It is only applicable to the above ground low temperature storage tank of liquefied natural gas, which is different from the general normal temperature storage tank. It is necessary to consider that the ground under the tank is bulging due to the freezing and expansion of the soil, so that the tank may be damaged. Therefore, measures must be taken to prevent the ground soil from freezing. Generally, the above ground storage tank can be divided into floor type and elevated type. The floor type bottom is insulated with perlite concrete, hot air or hot water is introduced into the embedded pipes, or electric heater is preset in the foundation to prevent soil freezing. The elevated type is to support the tank chassis with columns to separate it from the ground, keep the air between the tank and the ground unblocked, prevent liquefied natural gas from absorbing a large amount of heat on the ground, and avoid soil freezing.

③ Reinforced concrete wall and prestressed concrete wall. These two kinds of outer walls are the main materials for the shell of underground tank, which have the following advantages:

a. Reinforced concrete and prestressed concrete are good low-temperature materials. Even if the membrane is damaged, the low-temperature storage fluid will not damage the outer wall when it contacts the prestressed concrete wall;

b. Good durability, not corroded by groundwater, not brittle;

c. It has good liquid tightness and good seismic performance.