Natural gas is recognized as a clean, environmentally friendly and safe high-quality energy. The volume of natural gas produced by liquefaction filtration device is reduced by 600 times, which brings great benefits to storage. Liquefied natural gas is stored in atmospheric and low temperature tanks. Let's talk about the unique features of these tanks.
Low temperature resistance: the boiling point of LNG under normal pressure is - 160 ℃. LNG can be stored at low temperature and normal pressure to reduce the temperature of natural gas below the boiling point, so that the operating pressure of the storage tank is slightly higher than that of normal pressure. Compared with high pressure and normal temperature storage mode, the thickness of tank wall can be greatly reduced and the safety performance can be improved. Therefore, LNG tank is required to have good low temperature resistance and excellent cold insulation performance.
High safety requirements: as the tank stores low-temperature liquid, once there is an accident in the tank, the refrigerated liquid will volatilize in a large amount, and the gasification amount is about 300 times of the original refrigerated state, forming an air mass that will detonate automatically in the atmosphere. Therefore, API, BS and other specifications require the tank to adopt double wall structure and the concept of blocking. When the first layer tank leaks, the second layer tank can completely block the leaked liquid and evaporation gas to ensure the storage safety.
Special materials: the inner tank wall is required to be resistant to low temperature, generally 9Ni steel or aluminum alloy and other materials are selected, and the outer tank wall is prestressed reinforced concrete.
Strict insulation measures: since the maximum temperature difference inside and outside the tank can reach 200 ℃, to keep the temperature inside the tank at - 160 ℃, the tank body must have good cold insulation performance, and high-performance cold insulation materials shall be filled between the inner tank and the outer tank. The cold insulation material at the bottom of the tank shall also have sufficient pressure bearing performance.
Good anti-seismic performance: the anti-seismic requirements of general buildings are to crack under the specified earthquake load without collapse. In order to ensure the safety of the tank under the unexpected load, the tank must have good seismic performance. For LNG storage tank, it is required not to collapse or crack under the specified earthquake load.
What are the characteristics of LNG cryogenic tank?
Inner tank wall: the inner tank wall is the main component of low-temperature tank, which is welded by low-temperature resistant steel plate with good mechanical properties. Generally, a5372 grade, A516 gr.60, gr18ni9, ASME 304 and other special steels are selected.
For example, 16 mm thick steel plate with A537 Cl2 material can be used as the bottom plate and ring plate of a tank, and 6.35 mm thick steel plate with A537 CL1 material can be used as the other plates.
What are the types of LNG tanks?
Cylindrical: for industrial gas gasification station, small-scale LNG production device, liquefaction filtration device, civil gas gasification station, LNG truck filling station.
Large cylindrical: used for basic load type, filtration device, liquefaction device, LNG terminal.
Spherical: used in civil gas gasification station and LNG truck filling station.
Different capacity
5-50m3: commonly used in filling points of civil LNG vehicles and civil gas liquefaction stations.
50-100m3: mostly used in industrial gas liquefaction station.
100-1000m3: suitable for small LNG production unit.
10000-40000m3: used for basic load type and peak regulation type liquefaction device.
40000-200000m3: for LNG terminal.