Also known as: Liquefied petroleum gas, commercial propane
LPG refers to the lightest (lowest density) liquid fuels produced by a refinery, primarily C3s (propane) and some 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 underdeveloped 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.
LPG is also often used as refinery fuel if there is a limited ability to separate the LPG from refinery gas, or if there is 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.
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 steam 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 refinery 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: 124 psig at 70F; 192 psig at 100F; 286 psig at 130F
- Specific gravity: 0.509 at 60F
- Initial boiling point: -51F at 1 bar
- Dew point: -46F at 1 bar
- Specific heat: 0.588 Btu/lb at 60F; 2.462 kJ/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
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