LPG refers to the lightest (lowest density) liquid fuels produced by a refinery, primarily C3s (propane) and C4s (butane). As a product, it typically refers to commercial propane, which is primarily propane, with a small amount of butane.

LPG is commonly used as a fuel where it is valued for being easily transported and is easily vaporized at room temperature to form a fuel gas. In many under-developed markets, it is an important cooking fuel. In areas without infrastructure to provide natural gas, it is often used as a home heating fuel. It is also used as a specialty light-vehicle fuel in forklifts and taxi fleets.

Propane, in its purer form also has other industrial uses. Propane is a major feed to ethylene crackers. Propane is used in farming as a drying agent for grain.

LPG is also often used as refinery fuel if there is a limited ability to separate the LPG from refinery gas, or a limited local market for LPG. However, separation for use in LPG blending is almost always a more valuable use if this option is possible.

LPG production

The propane and butane blended into LPG can come from many different process units in the refinery, as well as from outside sources such as natural gas plants (from separating NGLs) or ethylene crackers (from C4 raffinates).

Major sources inside the refinery include:

Atmospheric distillation - All crude oils yield some amount of propane and butane when distilled. Typically they leave the distillation tower in a wet gas stream that is sent to the saturated gas plant for separation of propane and butane from lighter gases (methane and ethane) that are then used for fuel.

FCC - In the FCC conversion process, large amounts of C3s and C4s are produced, including both saturated propane and butane and unsaturated propylene and butylene. Often the unsaturated olefins are separated for use as feed to the alkylation unit or as feed to petrochemicals units.

Coker - Similar to the FCC, the coker conversion process generates mixed C3s and C4s containing saturated and unsaturated molecules. However, it is less common for coker C3s and C4s to have their olefins separated out.

Reformer - Reformers will yield approximately 5% (by volume) of both C3s and C4s in the conversion process.

LPG product quality

LPG (or commercial propane) typically contains ~90%+ propane, and less than 10% butane.

Typical specifications are:

Vapor pressure: 124psig at 70F; 192psig at 100F; 286psig at 130F

Specific gravity: 0.509 at 60F

Initial boiling point: -51F at 1bar

Dew point: -46F at 1bar

Specific heat: 0.588 Btu/lb at 60F; 2.462kJ/kg at 15.6C

Lower limit of flammability: 2.4 vol% gas in air

Upper limit of flammability: 9.6 vol% gas in air

Latent heat of vaporization: 185 Btu/lb; 430.3 kJ/kg

Gross heating value (liquid): 21,550 Btu/lb; 50,125 kJ/kg

Gross heating value (gas): 2,560 Btu/ft3; 9,538 kJ/m3