LPG (Liquefied Petroleum Gas) is primarily kept liquid by storing it under pressure in specially designed containers like gas bottles or tanks.
This method is crucial because, as the provided reference states, "LPG needs only low pressure or refrigeration to change it into liquid from its gaseous state." Storing it "under pressure, in a gas bottle" is the common and practical way to maintain its liquid state at typical temperatures encountered during storage and transportation.
Why is LPG Kept Liquid?
Storing LPG as a liquid is significantly more efficient than storing it as a gas.
- Volume Reduction: As the reference highlights, "As a gas, LPG expands to 270 times its volume as a liquid."
- Efficient Storage and Transport: Keeping it liquid allows a much larger quantity of energy to be stored in a smaller volume, making storage, handling, and transportation vastly more economical and manageable.
Methods for Keeping LPG Liquid
Based on the properties mentioned, two primary approaches can be used to keep LPG in its liquid phase:
- Applying Pressure: This is the most common method for storage and transport in cylinders and tanks. The pressure applied is sufficient to keep the LPG in a liquid state at the ambient temperature. The reference explicitly states, "it's only logical that LPG is stored and transferred as a liquid, under pressure, in a gas bottle (e.g. propane tanks)."
- Refrigeration: While less common for small bottles, large-scale storage or transportation (like in large tanks or ships) sometimes uses refrigeration to lower the temperature, reducing the pressure needed to keep the LPG liquid. The reference mentions "refrigeration" as a way to change it into a liquid state.
Practical Application
For everyday use, such as with propane tanks for BBQs or heating, the LPG is kept liquid solely by the pressure inside the tank. When you open the valve, the pressure drops, allowing the liquid LPG to boil and turn back into gas, which is then used as fuel.
In summary, LPG is kept liquid primarily by storing it under pressure in appropriate containers, which is a highly efficient method given its significant volume change between liquid and gas states.
