Buffer storage tank

Buffer storage tanks are core equipment in LNG vaporization stations. They directly affect the normal operation of the vaporization station and account for a relatively large proportion of the total construction cost. Classified by structural type, they can be divided into underground storage tanks, above-ground metal storage tanks, and metal prestressed concrete storage tanks. For LNG storage tanks, the existing types include vacuum powder-insulated storage tanks, positive-pressure bulk-insulated storage tanks, and high-vacuum layer-insulated storage tanks. Medium and small-sized vaporization stations generally adopt vacuum powder-insulated cryogenic storage tanks. These storage tanks consist of inner and outer layers; the interlayer is filled with perlite and evacuated to minimize heat transfer from the outside, ensuring that the daily vaporization rate of LNG in the tank is less than 0.3%.

The operating pressure of the buffer storage tank ranges from 0.6 MPa to 1.44 MPa, and the operating temperature is -162°C. The tank body (available in vertical or horizontal type) is composed of inner and outer layers. To reduce external heat transfer into the tank, a vacuum-insulated structure filled with perlite insulation material is used between the two layers. This structure isolates the tank from the atmosphere, avoiding the impact of atmospheric pressure or temperature changes and the entry of moist air into the insulation layer between the inner and outer tanks, thereby enhancing the insulation performance of the material.

High safety requirements are imposed on these tanks. Since the tank stores cryogenic liquids, any accident involving the storage tank will cause a large amount of the cryogenic liquid to volatilize—its vaporization volume is approximately 300 times that of the original cryogenic state. This vapor forms an air mass in the atmosphere that can ignite automatically. Therefore, codes and standards such as API (American Petroleum Institute) and BS (British Standards) all require storage tanks to adopt a double-wall structure and apply the "containment concept". In the event of a leak in the primary tank wall, the secondary tank wall can effectively contain and hold the leaked liquid and evaporated gas.