Properties of Liquefied Petroleum Gas (LPG)

Liquefied petroleum gas or liquid petroleum gas (LPG or LP gas), a mixture of propane and butane, is a flammable mixture of hydrocarbon gases used as a fuel in heating appliances, cooking equipment, and vehicles.

It is also increasingly used as an aerosol propellant and a refrigerant, replacing chlorofluorocarbons in an effort to reduce damage to the ozone layer. When specifically used as a vehicle fuel it is often referred to as auto gas.

Varieties of LPG bought and sold include mixes that are primarily propane (C₃H₈), primarily butane (C₄H₁₀) and, most commonly, mixes including both propane and butane. In winter, the mixes contain more propane, while in summer, they contain more butane.

Properties of Liquefied Petroleum Gas (LPG)

The properties of LPG gas are discussed below.

Chemical Identity

Chemical Name: LIQUEFIED PETROLEUM GAS
Chemical Classification: Hydrocarbon Mixture
Synonyms: LPG, Propane, Butane, Propylene
Trade Name: LPG, Purofax, Bottled Gas.
Formula: C₃H₈, C₄H₁₀ (Mixture)
Regulated Shipping Name: Petroleum Gases, Liquefied.
Max. Vapour pressure @650C 16.87kg/cm2
Volatility: evaporation at 20C for 95% by vol. At 760mm hg Pressure

The density of liquid (0.525 to 0.580 at 15°C)

Remain over water in drain etc.
LPG Fire cannot be extinguished with water
Water is used only for cooling

Density of LPG vapour (1.5 to 2.0)

Heavier than Air
Settles down in low lying area /Ground level
Accumulates in depression
Under still condition dissipation is low
Accumulation can give rise to potential Fire & explosion Hazards
Hot plate (Gas stove) shall always be at higher level compared to Cylinder

Co-efficient of volumetric expansion

LPG liquid expands 250 times by volume to vapour
At liquid full condition, any further expansion of liquid Cylinder pressure will rise by 14 -15 kg/cm2
In case of fire it is essential to cool all adjacent vessels to avoid BLEVE
Expansion is 100 times more than steel
Vapour pressure depends on temperature & has no relation to the quantity of LPG
Minimum allowable space 5%

Flammability (1.8 % – 9.5 %)

Small leakage can cause Fire.
Major leakages are with high concentrations initially, but in contact with air LPG dissipates very fast and forms flammable mixture
Auto Ignition Temperature (410 – 580 °C)

Latent heat (10,900 Kcal /Kg)

Causes formation of ice during gushing out of LPG
If venting is done in uncontrolled condition, shall lead to jamming of valves
Results in cold burn/ Frost bite if exposed to body

Colour

Colourless in both Liquid & Vapour Phase
Leakage cannot be detected by naked eye

Odour

Very Faint Smell (Odourless)
Leakage cannot be detected by smell. For Detection by smell a chemical is added to LPG
Ethyl Mercaptan – 20 ppm/odour level 2

Combustion properties

Oxidation of LPG vapour with air/oxygen
LPG requires @ 50 times its own volume of air for combustion yielding 3 to 4 times its own volumes of carbon dioxide & 10,900 kcal heat
Results in loss of air after combustion
Limit of flammability
Calorific value – ideal fuel

The behaviour of LPG in a closed container

If no ullage, exerts a pressure of 14 to 15kg /cm2 on the container per degree rise of temperature •Vapour pressure depends on temperature & has no relation to the quantity of LPG
Adequate vapour must be present
Minimum allowable space 5%