Why is gas replacement still necessary after installing an insulation layer between the inner and outer tanks of LNG?
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Why is gas replacement still necessary after installing an insulation layer between the inner and outer tanks of LNG?
There is air between the layers, and water vapor is present in that air; when it cools down, ice will form. Therefore, it is necessary to replace that air, and the dew point also needs to be measured. Replacing the air in the layers takes a long time – 15 to 60 days may be required!
This is necessary in order to convert the water vapor in the air, maintain the inertness of the annular space, and control the oxygen concentration in that space before LNG is fed in, thereby ensuring the safety of the tank and preventing the water vapor in the air from corroding the steel plates lining the outer part of the tank.
The main purposes of the interlayer replacement in LNG storage tanks are: oxygen displacement and drying. Large LNG storage tanks are usually designed with a suspended ceiling structure, and the gas space between the inner tank and the outer tank is not completely sealed; therefore, inert gases are used for purging in order to keep the oxygen content in the interlayer at a certain level, primarily for safety reasons. Additionally, the purpose of replacement is water removal and drying; this is mainly to prevent water vapor from precipitating and freezing at low temperatures, thereby avoiding a reduction in the insulation effect.
My main function is to act as a desiccant; the interlayer has been filled with perlite, and the oxygen content there is already very low. Is it still within the range that could lead to an explosion? With the guidance of an expert!
Perlite is conveyed using compressed air; then how can the oxygen content in the annular space decrease? ? ? The lower explosion limit for LNG is 5%; an explosion is possible as long as the conditions are met. Safety first at all times!
Firstly, insulation materials (such as perlite) have strict requirements regarding water; a high moisture content reduces their strength and affects their insulating performance. The interlayer space must be dry and filled with an inert gas to maintain a slight positive pressure in the space.
Replying to floor 6: It is dried with nitrogen after filling it with expanded perlite! At the bottom of the interlayer between the inner and outer tanks, there is a nitrogen circulation pipeline for displacement purposes!
The cycle for lowering the dew point and removing oxygen is very long~~~