About LNG and LPG

 Is LNG always refrigerated?

Yes, Liquefied Natural Gas (LNG) must always be kept at cryogenic, refrigerated temperatures to remain a liquid. [1, 2]

Because natural gas is primarily composed of methane, it has a critical temperature of -82.6°C (-116.7°F). Above this temperature, methane cannot exist as a liquid, no matter how much pressure is applied. To maintain its liquid state and keep its volume shrunk by 600 times, LNG is strictly stored and transported at approximately -162°C (-260°F). [1, 2, 3, 4, 5]

How LNG Stays Cold (Without Active Refrigeration)

While LNG must always be refrigerated, it does not always require a mechanical refrigerator (like a kitchen freezer) while it is being stored or shipped. Instead, the industry relies on two primary mechanisms: [1, 3, 4]

• Extreme Insulation: LNG is held in massive, double-walled tanks with high-grade vacuum or powder insulation that drastically slows down heat from entering the tank. [1, 2, 3, 4, 5]
• Autorefrigeration: LNG is stored as a "boiling cryogen". Just like boiling water stays at exactly 100°C because evaporating steam carries heat away, LNG stays at a constant -162°C because a tiny amount of the liquid is allowed to evaporate into Boil-Off Gas (BOG). [1, 2, 4, 5]

What Happens to the Boil-Off Gas?

Because tanks cannot simply vent natural gas into the atmosphere for environmental and safety reasons, the BOG must be managed: [, 2]

1. Fuel Source: On⁠LNG carrier ships, the boiled-off gas is captured and piped directly to the ship's engines to power the vessel.
2. Reliquefaction: On modern ships or at large land-based ⁠LNG terminals, active mechanical refrigeration units compress and re-cool the BOG, turning it back into a liquid and pumping it back into the tank. [1, 2]

LNG vs. LPG (A Common Confusion)

People frequently confuse LNG with LPG (Liquefied Petroleum Gas, which is propane and butane). [1]

• LPG can be liquefied simply by applying moderate pressure at normal room temperatures (like a backyard grill propane tank).
• LNG cannot be kept at room temperature using pressure; if you seal it in a tank without refrigeration or BOG venting, the pressure will skyrocket until the tank ruptures. [1, 2, 4, 5]