With the development of science and technology, the technology of using cryogenic tanks to store materials under normal pressure is becoming more and more mature. There are more and more reports about the construction of large liquefied natural gas (LNG) tanks and liquefied petroleum gas (LPG) tanks in China.

At present, according to the storage medium, domestic large-scale low-temperature storage tanks are mainly divided into liquid oxygen storage tanks (- 183 ℃); Liquid nitrogen storage tank (- 196 ℃); Liquid argon storage tank (- 186 ℃); Liquid natural gas storage tank (- 162 ℃); Liquid ethane storage tank (- 89 ℃); Ethylene storage tank (- 104 ℃) and other types. Compared with other storage methods, atmospheric cryogenic tank has many advantages: compared with vacuum tank and spherical tank, the safety of cryogenic tank is better because of its low storage pressure; The low-temperature storage tank has realized the large-scale, it occupies less land, reduces the storage cost, the low-temperature storage tank structure is simple, the construction is easy, reduces the construction cost.

Process flow system

Liquid inlet system; Temperature system;

Drainage system; Gas emission system;

Pump return system; Analytical sampling system;

Mezzanine nitrogen supply system; safety system;

Liquid level and pressure measurement system; Supercharging system.

Structure and principle of storage tank

At present, the low-temperature storage tanks constructed by our company are of flat bottom arch cover, vertical double wall structure, and the interlayer adopts pearlite powder accumulation insulation. The equipment consists of inner groove, outer groove, bottom insulation layer, interlayer insulation layer, equipment ladder platform, valve instrument and foundation platform, etc.

The inner tank is mainly composed of tank top, cylinder and bottom plate. All parts are made of austenitic stainless steel. The whole inner tank can be fastened on the base of the bottom through the anchor belt. At the same time, the convex deformation of the bottom of the inner tank can be prevented under the action of lifting force.

The outer groove is mainly composed of top cover, cylinder and bottom plate. Carbon steel plate is used for all parts. The bottom plate of the outer groove is laid on the foundation platform, and the outer groove is fastened on the foundation platform by embedded steel plate.

Foam glass brick and concrete load distribution board are laid between the bottom of the outer tank and the bottom of the inner tank as the bottom insulation layer. The inner tank and liquid gravity are evenly distributed through the bottom insulation layer and transferred to the foundation platform.

The interlayer of the tank is filled with pearlite powder as the insulation layer, and the interlayer is filled with dry nitrogen to keep the insulation material dry, so as to maintain the tank with good insulation performance and low daily evaporation rate. The operation platform is set outside the tank, and the valves and instrument panels are centrally set on the operation platform, which is convenient for operation.

In operation, in order to ensure the safety of the tank, the inner tank is equipped with safety devices, one is overpressure protection, the other is negative pressure protection：

① For overpressure protection, the vent valve is automatically controlled by the top pressure of the inner tank. When the pressure exceeds the set value, it will automatically discharge and relieve pressure; In terms of negative pressure protection, in order to prevent negative pressure in the tank when a large amount of low-temperature liquid is output, the tank is equipped with a self pressurization system, which can automatically replenish gas according to the pressure in the tank to maintain the positive pressure in the tank.

② The second protection is: a breathing valve is installed on the top of the inner tank, that is, when the pressure exceeds the upper limit of positive pressure, the safety valve will open to relieve pressure, and when the negative pressure in the tank exceeds the set value, the safety valve will open to inhale atmospheric protection tank. There are breathing valve and emergency vent valve on the top of the outer tank. The breathing valve is used to maintain micro positive pressure in the interlayer, and has two functions of breathing and suction. The emergency vent valve is used in emergency situations, that is, when the liquid in the inner tank leaks into the interlayer, a large amount of vaporization will occur, so that the pressure in the interlayer will rise rapidly, and the emergency vent valve will be opened for pressure relief to prevent accidents. In addition to the above safety devices, the tank is also equipped with liquid level gauge, pressure gauge, analysis sampling valve and other instruments.

Application industries of large cryogenic liquid storage tanks: aerospace, machinery industry, electronic industry, geology and mineral resources department, metallurgical industry, construction and environmental protection, transportation department, petroleum, chemical industry, electric power, energy, agriculture and forestry