1. Exploration and Production
2. Liquefaction process
3. LNG (liquefied natural gas) transportation
4. Storing LNG (liquefied natural gas)
5. Re-gasification process
1. Exploration and Production
Natural gas is pumped to the surface through techniques commonly used world-wide whether in the North Sea or overseas.
2. Liquefaction process
This activity takes place in the producing country:
All impurities are removed from the gas, which in the industry is known as ‘sweetening’, prior to cooling.
The cooling of natural gas to -160º allows it to be transported economically by reducing the volume by 600:1. This process is called liquefaction and produces a stable liquid ready for shipping.
3. LNG (liquefied natural gas) transportation
Liquefied natural gas is transported in special double-hulled ships built using two different technologies known as Moss Rosenberg (spheres) and membrane (using material with an expansion coefficient of practically nil).
Off-loading takes approximately 24 hours and is managed using tried and tested procedures common to all international facilities.
The liquefied natural gas is off-loaded as a liquid and pumped from the jetty to storage tanks at the terminal. The liquefied natural gas remains at -160º for the duration of the process.
4. Storing LNG (liquefied natural gas)
The tanks are double wall tanks specially designed for their purpose and are well insulated to keep the natural gas at -160c (In its liquid form).
Liquefied natural gas is stored in storage tanks of around 160,000 m3 capacity at just above atmospheric pressure. The liquefied natural gas tanks are of a full containment design. In a full containment system two tanks are employed, an inner tank which contains the stored liquid, and an outer tank which provides security in the event of any loss of containment or leak from the inner tank.
The inner shell is made of a special nickel alloy, designed to resist the low temperature. The outer shell is of pre-stressed concrete with a reinforced concrete base slab and roof.
Sophisticated automatic protection systems are employed to monitor the tank levels, pressures, temperatures and any potential leakage from the inner tank.5. Re-gasification process
This is the operational work of the terminals in the receiving country:
Re-gasification is simpler than liquification, it is purely physical and not chemical.
The liquefied natural gas is pumped out of the tanks and warmed so that it returns to its natural gas state.
The natural gas is then pumped in to the UK’s natural gas transmission system, owned and operated by National Grid (formerly Transco) as required.
