Natural Gas Liquefaction Process and shipment
The volume of natural gas is reduced by 600 times by converting it into a liquid through a process called liquefaction. The resulting substance, Liquefied Natural Gas (LNG), can then be efficiently transported by ship.
The liquefaction process
The process involves three main stages that convert natural gas (primarily methane) into a super-chilled liquid.
1. Pre-treatment
Before cooling, the raw natural gas is treated to remove impurities that would freeze and clog equipment at low temperatures. This involves removing:
- Carbon dioxide (CO₂) and sulfur compounds: These are corrosive and must be removed.
- Water: Dehydration prevents ice from forming.
- Heavy hydrocarbons: Heavier, less volatile components are separated from the lighter methane.
- Mercury: Trace amounts of mercury are removed to prevent damage to the cryogenic equipment.
2. Cryogenic cooling
After purification, the clean natural gas is cooled to a temperature of approximately -162°C (-260°F). This is done using a series of heat exchangers and refrigerants, which can include propane, ethylene, and methane.
3. Liquid storage
Once liquefied, the LNG is loaded into specially designed, heavily insulated cryogenic storage tanks on ships called LNG carriers. The insulation keeps the liquid at its low temperature during transit, which can last for weeks.
Why this is necessary for shipping
- Volume reduction: The 600-fold reduction in volume makes it economically feasible to transport vast quantities of natural gas across oceans to locations without pipeline infrastructure.
- Long-distance transport: Without liquefaction, the gas would have to be transported under extremely high pressure in much larger, more expensive, and less efficient containers.
- Versatility: Converting natural gas to LNG allows it to be traded as a global commodity and delivered to any port with a regasification terminal.