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What is LPG (LIQUIFIED PETROLEUM GAS)? LPG may be defined as those hydrocarbons, which are gaseous at normal atmospheric
pressure, but may be condensed to the liquid state at normal temperature, by the application
of moderate pressures. Although COMPOSITION LPG is a predominant mixture of propane and Butane with a small percentage of unsaturated (Propylene and Butylene) and some lighter C2 as well as heavier C5 fractions. Included in the LPG range are propane (C3H8), Propylene(C3H6), normal and iso-butane (C4H10)and Butylene(C4H8). Commercial LP gases invariably contains traces of lighter hydrocarbons like ethane (C2H6) and ethylene (C2H4) and heavier hydrocarbons like pentane (C5H12). MANUFACTURE OF LPG: There are two main sources from which LP gases are produced, namely: (A) Wet Natural Gas or Associated Gas & (B) Refinery Operations. LP gases prepared from wet natural gas consist entirely of "saturated" hydrocarbons i.e. propane and butane . LP Gases produced from straight distillation process will have "saturated" hydrocarbons i.e. propane and butane (both normal and iso) LP Gases produced by both cracking and reforming processes will have, in addition to saturated hydrocarbons, some quantities of unsaturated hydrocarbons also ( i.e. propylene and butylene) LP Gases produced will have impurities like moisture & sulphur compounds like hydrogen sulphide and mercaptans. Moisture may lead to clogging of regulators, valves, etc. and sulphur compounds cause corrosion. Moisture and sulphur compounds are, therefore, removed by suitable treatment at the refinery. However, to alert the user of LPG in case of a leak takes place, "ethyle mercaptan" which has a distinctive odour is added in minute quantities at the refinery. LPG marketed in India confirms to Indian Standard Specification IS-4576. Some of the important properties and their bearings are : Important Properties: 1. Specific Gravity: Definition: It is the ratio of density of a substance to that of water in case of liquid specific gravity and air in case of gaseous specific gravity at same temperature and pressure conditions. Values:
Importance: It can be seen that LPG is heavy twice than air and hence in case of any leakage it settles down at floor level, and can be hazardous if it accumulates in pits, drains, depressions. Hence ground level ventilation is very necessary. 2. Liquid to gas Ratio: Definition: It is the ratio of volume of gas of certain mass to that of Volume of liquid of same mass at the same temperature. Value:
Importance: Any leakage of LPG liquid can cause expansion in vapour, which occupies 246 times, volume to that of liquid and can be very hazardous. 3. Specific Volume: Definition: It is the reciprocal of Liquid density. Value:
4. Vapour Pressure: Definition: Vapour pressure is the pressure exerted on the walls of the container when the gas is enclosed in it. When liquid exists with the gas the pressure is called as Saturated Vapour pressure at that temperature. Vapour pressure depends of temperature and is independent on the quantity of liquid present in the container. 5. Boiling Point: Definition: It is the temperature at which the first bubble will form and has the same Vapour pressure as that at the surface of liquid.
6. Flammability Limit: Explanation: Fuel gases will burn only when mixed with air in the in the certain proportion. The minimum and maximum concentrations of a fuel gas in a fuel/air mixture between which the mixture between can be ignited are termed as the lower and upper limit of inflammability. These limits are narrower in LPG than other fuel gases, making LPG relatively safer in use. Value:
7. Calorific Value: Definition: Calorific value is defined as the amount of heat released when a unit quantity of gas is burned at atmospheric pressure and ambient temperature. Gross calorific value (GCV) is obtained when the contribution from the latent heat of condensation of water vapour formed is recovered The net calorific value is obtained from GCV by subtracting the heat of condensation of water vapour. Value:
Importance: Depending on the composition of the LPG the calorific value of fuel will change and in turn it will change the net heating value also. 8. Dew Point: Explanation: It is the maximum temperature at which the first drop of liquid is formed when a saturated gas is cooled or is brought on contact with a cool surface. As the pressure increases the dew point of LP Gases decreases. Value: in deg C
Importance: In cold climatic condition when outside temperature is low the LPG tends to condense down which can be very hazardous. Hence by reducing the pressure of gas the dew point can be depressed and the condensation phenomenon can be avoided. When a customer uses a vaporizer the vapour coming out of the vaporizer is in saturated vapour at high temperature and it can reach dew point if cooled to atmospheric temperature at high pressure . 9. Toxicity: LPG contains no toxic material, In case of heavy leakage asphyxiation due to lack of oxygen can be caused. LPG is slightly anesthetic when high concentrations are breathed in for sufficiently long time. 10. Odour: LPG is purposefully odorized by adding Ethyl/Methyl Mercaptan. Its smell is detectable in air at 11. Air to fuel Ratio: Air required for complete combustion of a particular amount of fuel. Value:
Other Properties:
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