Natural gas is widely recognized as a clean, environmentally friendly, and safe high-quality energy source. After liquefaction, the volume of natural gas is reduced by approximately 600 times, which greatly benefits storage. Storage of liquefied natural gas (LNG) is done in atmospheric pressure, low-temperature tanks. Let's discuss the unique features of these LNG storage tanks.

What are the special requirements for LNG low-temperature storage tanks?

1.Low-temperature resistance

The boiling point of liquefied natural gas (LNG) at atmospheric pressure is -160°C. LNG is stored at low temperatures and atmospheric pressure, lowering the gas temperature below its boiling point, which results in the storage tank operating at slightly higher pressure than atmospheric. Compared to high-pressure, high-temperature storage, this method significantly reduces the tank wall thickness and enhances safety performance.

Therefore, LNG requires storage tanks with excellent low-temperature resistance and superior insulation properties.

2.High safety requirements

Due to the storage of low-temperature liquids inside the tank, in the event of an accident, the refrigerated liquid would volatilize in large quantities, with the vaporization amount being approximately 300 times that of the original refrigerated state, forming explosive gas clouds in the atmosphere.

Therefore, standards like API and BS require the use of double-walled tank structures and the application of sealing concepts. In the event of a leak in the first layer, the second layer can completely seal off the leaking liquid and evaporated gas, ensuring storage safety.

3.Special Material

The inner tank wall must withstand low temperatures, typically made of materials like 9Ni steel or aluminum alloys, while the outer tank wall is constructed of pre-stressed reinforced concrete.

4.Insulation measures are stringent

The temperature difference between the inside and outside of the tank can reach up to 200°C. To maintain a temperature of -160°C inside the tank, the tank must have excellent insulation properties, filled with high-performance insulation material between the inner and outer tanks. The insulation material at the bottom of the tank must also have sufficient pressure-bearing capacity.

5.Good seismic performance

General building seismic requirements are to crack but not collapse under specified seismic loads. To ensure the safety of storage tanks under unexpected loads, they must have excellent seismic performance. For LNG storage tanks, it is required that they neither collapse nor crack under the specified seismic loads.

Therefore, the selected construction site usually avoids seismic fault zones, and anti-seismic tests must be conducted on the storage tanks before construction. This analysis evaluates the structural performance of the tanks under dynamic conditions, ensuring that the tank body remains undamaged under the given seismic intensity.

6.Construction requirements are stringent.

Tanks must undergo 100% magnetic particle testing (MT) and 100% vacuum leak testing (VBT). Strict selection of insulation materials is required, and construction should follow the prescribed procedures. To prevent concrete cracking, post-tensioned prestressed construction is used uniformly, with strict control over the verticality of the tank walls.

LNG Low-Temperature Storage Tank Detailed Description:

The LNG storage tank is a horizontal double-walled structure, consisting of the inner tank, outer tank, internal and external supports, insulation layer, pressure safety system, vacuum pump, pipeline system, etc. All vacuum-insulated structures rely on vacuum. Due to the high degassing rate and suction resistance of the insulation space materials, and the inability of the sealing material to withstand high baking temperatures and slow degassing, suction is difficult. To achieve the required vacuum level within the design-specified suction time, in addition to the vacuum pump and suction process, it also depends on the flow area of the annular suction pipes. To ensure a high vacuum level and improve the suction rate, a vacuum pump is installed at both ends of the equipment. One pump is composed of three suction pipes, placed in the lower annular space and leading out from the bottom, while the other is also made up of three suction pipes, positioned in the upper annular space and leading out from the top, with the two sets of suction pipes crossing and overlapping along the tank's length. By increasing the flow area of the suction pipes and employing various auxiliary methods such as heating and nitrogen displacement, the vacuum achievement time for the 100m3 annular insulation space is reduced to one-third of the conventional structure.