Liquefaction and Storage

The central part of the project infrastructure — the Prigorodnoye production facility, consisting of the LNG plant and the oil export terminal (OET) — is situated in the south of Sakhalin, near Korsakov. LNG and oil export capacities are a part of the Prigorodnoye port established in 2008.

The complex includes the following equipment and infrastructure:

• two LNG processing trains, each with a capacity of 4.8 million tonnes of LNG per year;
• two 100,000 cubic meters storage tanks;
• an LNG jetty;
• two refrigerant storage spheres with a gross capacity of 1,600 cubic meters each for propane and ethane storage;
• a heat transfer fluid (HTF) system to supply heat to process consumers;
• five gas turbine-driven generators with a total power capacity of around 129 MW;
• utility systems, including instrument air and nitrogen plants and diesel fuel systems;
• a wastewater treatment plant to treat both sewage water and coil-containing water.

An 800-kilometre pipeline takes natural gas from the OPF to the LNG plant at the Prigorodnoye facility where the gas is liquefied at two trains with the capacity of 4.8 million tonnes of LNG per year. The plant is expected to reach its design capacity of 9.6 million tonnes a year in 2010.

The LNG plant uses Shell proprietary double mixed refrigerant (DMR) process which improves energy efficiencies of the liquefaction process by exploiting the benefits of the cold Sakhalin climate.

The mixed refrigerant used in the trains is a mixture of nitrogen, methane, ethane and propane. It cools gas to −162°C, at which temperature the gas becomes a liquid and is reduced in volume by a factor of around 600 times, making its transportation and storage more efficient.

Storage

LNG produced at the plant is initially stored in two cryogenic tanks with the capacity of 100,000 cubic meters each.

The LNG storage tank includes an outer tank and two inner tanks.

The outer tank is made of concrete with walls varying from 1 metre to 0.5 metre thick from bottom to top. The second tank has a carbon steel wall to insulate the inner tank from oxygen or moisture and to contain gas vapour. The inner tank made of 9% nickel steel is designed to withstand low temperatures of down to −165°C. A layer of one metre of insulation is inserted between the inner tank and the vapour containment wall.

LNG tanks have roofs made of a layer of 0.4 metre of concrete with a vapour containment wall below. The weight of each roof is 600 tonnes.

During storage, LNG is constantly evaporating. This vaporised gas is removed from the tanks to maintain the constant pressure and is used as fuel.

Flare

A key element of the plant safety system is the flare. Flaring is a method by which unwanted gas is quickly and safely disposed of by burning through a high vertical pipe (called a flare stack, which is 125-metre high) with a burner.

The flare is “a safety valve” of the plant. A pilot burner at the top of the flare stack is constantly burning, indicating normal operation. The pilot burner ignites the gas when it reaches the top of the flare stack if excess gas from the process units of the plant needs to be disposed of.

Flaring minimises impacts on the environment and is considered a more environmentally friendly option compared to releasing un-burnt gas directly into the atmosphere.