Stockpiling methods

For the national petroleum stockpiling bases, different stockpiling methods are utilized depending on the characteristics of each site. National LP gas stockpiling bases are required by law to be constructed adjacent to private LP gas importing bases, to reduce costs by effectively using existing facilities and commissioning operations and so on. Suitable stockpiling methods are selected for each base, as with national petroleum stockpiling bases.

Petroleum stockpiling methods

Aboveground tank system

Shibushi National Petroleum Stockpiling Base

This is the most commonly used stockpiling method at national petroleum stockpiling bases. It is a common type of petroleum storage tank and has a proven track record including safety performance and advantages such as relatively low construction cost, and less vaporization loss during long term storage.

In-ground tank system

In this stockpiling method, most of the tank body is buried in the ground. The risk of petroleum leakage or penetration into the ground is very low, and the structure has excellent earthquake resistance because the tank is made by reinforced concrete. This type of tank has approximately three times the capacity of an aboveground tank, because the tank diameter and depth of the tank can be made larger.

Structure of the in-ground tank system(Akita National Petroleum Stockpiling Base)

Water-sealed type underground rock cavern tank system

This system is called an underground rock cavern which was excavated and used to store petroleum. This type of tank has advantages of low risk petroleum leakage and has resistantance to natural disasters such as earthquake, lightning, etc. In addition, there is minimal effect on the surrounding scenery because the storage facility requires only limited space for incidental facilities.

Inside of a rock cavern tank (Kushikino National Petroleum Stockpiling Base)

Floating tank system

In this stockpiling method, storage facilities are installed in offshore to utilize the available ocean space. Each “storage vessel,” which has a double hull structure, is set afloat on the sea and surrounded by double petroleum fences and breakwaters to provide maximum protection against petroleum leakage or diffusion.

Shirashima National Petroleum Stockpiling Base has eight “storage vessels” floating on the sea.

LP gas stockpiling methods

On-ground low-temperature tank system

In this stockpiling method, LP gas, which is liquefied by cooling, is stored at low temperature in a cylindrical double-shell tank with a flat bottom. The double-shell tank consists of an inner tank and an outer tank is made of low temperature resistant steel, and the space between inner and outer tanks is filled with insulator (cold insulator). The principle is the same as that of a thermos flask. This is the most common storage method used at LP gas importing bases.

Structure of On-ground low-temperature tank system

Water-sealed type underground rock cavern tank system

In this system, LP gas at normal temperature is sealed in a rock cavern by groundwater pressure. The storage tank is installed underground at a depth where the groundwater pressure is slightly higher than the pressure of the LP gas, preventing leakage of the gas and liquid to the outside. Water is supplied to the bedrock from water-sealing tunnels and water-sealing boring in order to stabilize the groundwater pressure.

Structure of underground rock cavern tank system

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