Cryogenic storage tank is a vertical or horizontal double-layer vacuum insulated storage tank for storing liquid oxygen, nitrogen, argon, carbon dioxide and other media. Generally, it consists of an inner tank and an outer tank, and the middle is filled with heat insulation materials.
2. What is the structure of the cryogenic storage tank?
Cryogenic storage tanks usually consist of three parts:
1, inner tank
The inner container, also known as the "membrane tank", is a liquid-tight flexible inner container made of thin low-temperature steel plate. It must transfer the hydraulic head to the insulating material. The materials used as thin films must have the characteristics of non-embrittlement at low temperature, sufficient toughness and good processability. Nickel steel, stainless steel or aluminum alloy are usually used.
2. Thermal insulation layer
The insulation layer not only transfers the water pressure head to the outer tank, but also plays a role in reducing the gasification amount, reducing the temperature difference between the inner and outer walls of the tank and alleviating the resulting temperature difference stress. In addition, it also has the function of fixing the "film". Usually, the thermal insulation layer is made of rigid foamed polyurethane, foamed glass, perlite and rigid foamed phenolic resin.
3. External storage tank
The outer tank is a shell that can bear various loads and must have sufficient strength. According to the different materials used, it can be divided into the following categories:
(1) Frozen soil wall: Frozen soil wall and heat shield form a closed space as an outer tank, also called cellar storage. During construction, the soil around the inner tank is frozen by the cooling pipe. After the pit is put into production, the low-temperature liquid will keep the surrounding frozen, and the frozen soil layer will expand year by year, so the evaporation loss will also decrease year by year. High groundwater level is the premise of building a pit, and the bottom of the pit should be a rock or clay layer with the least permeability.
(2) Steel wall: only applicable to the construction of above-ground low-temperature storage tanks. Above-ground low-temperature storage tanks are different from ordinary normal-temperature storage tanks. It must be considered that the ground under the storage tank will expand due to the freezing and expansion of soil, which makes the storage tank in danger of damage. So measures must be taken to prevent the soil from freezing.
(3) Reinforced concrete wall and prestressed concrete wall: These two kinds of external walls are the main materials of underground storage tank shell, and they are very good low-temperature materials. Even if the membrane is damaged, the external wall will not be damaged when the cryogenic liquid comes into contact with the prestressed concrete wall.
Three, low temperature storage tank vacuum standard
The use of cryogenic storage tanks needs to be evacuated, and the interlayer vacuum degree is destroyed, so the low temperature environment cannot be maintained, which may lead to "sweating" and "frosting" in a large area of cryogenic storage tanks. So what is the vacuum standard of cryogenic storage tank?
Generally speaking, the vacuum degree of cryogenic storage tanks should be no less than 65438±0pa. If the vacuum degree is found to be unqualified, find out the fault and handle it in time. Vacuum again if necessary.