What is LPG or LP Gas?

What is LPG or LP Gas?
LPG or LP Gas is the abbreviation of Liquefied Petroleum Gas. This group of products includes saturated Hydrocarbons - Propane (C3H8) and Butane (C4H10), which can be stored/transported separately or as a mixture. They exist as gases at normal room temperature and atmospheric pressure.

Why is it called Liquefied Petroleum Gas?
This is because these gases liquefy under moderate pressure. They liquefy at moderate pressures, readily vaporizing upon release of pressure. It is this property that permits transportation of and storage of LP Gas in concentrated liquid form.

Where does LPG come from?
LPG comes from two sources. It can be obtained from the refining of crude oil. When produced this way it is generally in pressurized form. LPG is also extracted from natural gas or crude oil streams coming from underground reservoirs. 60% of LPG in the world today is produced this way whereas 40% of LPG is extracted from refining of crude oil.

What is commercial Propane & Butane?
Ideally products referred to as "propane" and "butane" consist very largely of these saturated hydrocarbons; but during the process of extraction/production certain allowable unsaturated hydrocarbons like ethylene, propylene, butylenes etc. may be included in the mixture along with pure propane and butane. The presence of these in moderate amounts would not affect LPG in terms of combustion but may affect other properties slightly (such as corrosiveness or gum formation).

How is LPG seen & felt?
-It is colorless and cannot be seen
-It is odorless. Hence LPG is odorized by adding an odorant (Mercaptans) prior to supply to the user, to aid the detection of any leaks.
-It is slightly heavier than air and hence if there is a leak it flows to lower lying areas.
-In liquid form, its density is half that of water and hence it floats initially before it is vaporized.
-It is non-toxic but can cause asphyxiation in very high concentrations in air.

"LPG expands upon release and 1 liter of liquid will form approximately 250 liters of vapor"

What is LPG used for?
LPG is used as a fuel for domestic (cooking), industrial, horticultural, agricultural, heating and drying processes. LPG can be used as an automotive fuel or as a propellant for aerosols, in addition to other specialist applications. LPG can also be used to provide lighting through the use of pressure lanterns.

Why are Butane and Propane used in combination?
While butane and propane are different chemical compounds, their properties are similar enough to be useful in mixtures. Butane and Propane are both saturated hydrocarbons.

They do not react with other. Butane is less volatile and boils at 0.6 deg C.

Propane is more volatile and boils at - 42 deg C.

Both products are liquids at atmospheric pressure when cooled to temperatures lower than their boiling points. Vaporization is rapid at temperatures above the boiling points.

The calorific (heat) values of both are almost equal.

Both are thus mixed together to attain the vapor pressure that is required by the end user and depending on the ambient conditions.

If the ambient temperature is very low propane is preferred to achieve higher vapor pressure at the given temperature.

What are the advantages of LPG?
The advantages of LPG are as follows :- Because of its relatively fewer components, it is easy to achieve the correct fuel to air mix ratio that allows the complete combustion of the product. This gives LPG its clean burning characteristics.

Both Propane and Butane are easily liquefied and stored in pressure containers. These properties make the fuel highly portable, and hence, can be easily transported in cylinders or tanks to end-users.

LPG is a good substitute for petrol in spark ignition engines. Its clean burning properties, in a properly tuned engine, give reduced exhaust emissions, extended lubricant and spark plug life.
As a replacement for aerosol propellants and refrigerants, LPG provides alternatives to fluorocarbons, which are known to cause deterioration of the earth's ozone layer.

The clean burning properties and portability of LPG provide a substitute for traditional fuels such as wood, coal, and other organic matter. This provides a solution to de-forestation and the reduction of particulate matter in the atmosphere (haze), caused by burning the traditional fuels.

What are LPG properties?
Property---------------------Units-----Com-Propane------Com-Butane-----Mixture 50% each
Specific gravity of Liquid

at 15 deg C (Water=1)------------------ 0.504--------------0.582-----------0.543
Specific gravity of Vapor

at 15 deg C(Air=1)----------------------1.5------------------2.01------------1.75
Vapor pressure at 38 deg C--Kg/sq.cm--13.8-----------------2.6-------------8.0
Boiling point at atm pressure-Deg C------(- 42)---------------(9)------------+ 9 to - 42
Ignition temperature in air---Deg C------495-605-----------480-535-------480-605
Latent Heat of Vaporization--Btu/lb------184----------------167------------175