| Liquefied Petroleum Gas(LPG) |
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LPG at atmospheric pressure and temperature is a gas which is 1.5 to 2.0 times heavier than air. It is readily liquefied under moderate pressures and the density of the liquid is approximately half that of water and ranges from 0.525 to 0.580 @ 15 deg. C. Since LPG vapour is heavier than air, it would normally settle down at ground level/ low lying places, and accumulate in depressions. Under still conditions the dissipation of accumulated vapour can be slow. The pressure inside a LPG storage vessel/ cylinder will be equal to the vapour pressure corresponding to the temperature of LPG in the storage vessel. The restriction on vapour pressure is stipulated by IS-4576 which in turn regulates the lighter ends of hydrocarbons and this governs the design parameters for storage vessels.
The vapour pressure is dependent on temperature as well as on the ratio of mixture of hydrocarbons. At liquid full condition any further expansion of the liquid, the cylinder pressure will rise by approx. 14 to 15 kg./sq.cm. for each degree centigrade. This clearly explains the hazardous situation that could arise due to overfilling of cylinders. LPG has an explosive range of 1.8% to 9.5% volume of gas in air. This is considerably narrower than other common gaseous fuels. This gives an indication of hazard of LPG vapour accumulated in low lying area in the eventuality of the leakage or spillage. The auto-ignition temperature of LPG is around 410-580 deg. C and hence it will not ignite on its own at normal temperature. The combustion reaction of LPG increases the volume of products in addition to the generation of heat. LPG requires upto 50 times its own volume of air for complete combustion and at the same time yields 3 or 4 times its own volume of carbon-dioxide yielding approx. 10,900 kcal heat per kg.
When pressure is released, LPG vapourizes rapidly lowering the surrounding temperature. This may lead to frost burns by contact of LPG with the skin. Protective clothing such as gloves and goggles shall therefore be worn when there is any possibility of contact with LPG. Auto refrigeration effect of the vapourisation of LPG freezes the water vapour in the atmosphere, which makes the escaping LPG vapour visible as a whitish cloud. Even if this cloud disappears, it is not a sign that the inflammable gas/ air mixture has been dispersed. Leaking liquid phase LPG will rapidly expand around 250 times its own volume thereby creating a greater risk than would occur with a similar sized vapour leakage. Sufficient ullage space for the expansion of liquid when the temperature rises must therefore be left in all storage/ transport containers.
LPG has only a very faint smell, and consequently, it is necessary to add some odourant, so that any escaping gas can easily be detected. Ethyl Mercaptan is normally used as stenching agent for this purpose. The amount to be added should be sufficient to allow detection in atmosphere 1/5 of lower limit of flammability or odour level 2 as per IS : 4576. LPG is colourless both in liquid and vapour phase. During leakage the vapourisation of liquid cools the atmosphere and condenses the water vapour contained in them to form a whitish fog which may make it possible to see an escape of LPG. LPG liquid has low viscosity of around 0.3 CS @ 45 deg. C and can leak when other petroleum products normally cannot, thus demanding a very high integrity in the pressurised system to avoid leakage. It is also a poor lubricant and leaks are therefore likely to occur at pump seals and glands. In view of this a special attention to the given, for example to the selection of mechanical seals for pumps and also seals at the carousel centre column.
LPG even though slightly toxic, is not poisonous in vapour phase, but can, however, suffocate when in large concentrations due to the fact that it displaces oxygen. In view of this the vapour posses mild anaesthetic properties. Caustic soda treatment employed for the removal of hydrogen sulphide could leave traces of caustic in LPG. This may lead to corrosion on the storage vessel and other LPG handling equipment with predominant effect on aluminium alloys. Hence stipulating absence of caustic is essential in addition to IS-4576 specification.
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| Prices in Metros (Rs./14.2 kg cylinder) |
| Applicable in: March 01, 2007 |
| Delhi | 294.75 |
| Kolkata | 300.50 |
| Mumbai | 298.00 |
| Chennai | 288.10 |
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| Previous Prices |
| Prices in Metros (Rs./19 kg cylinder) |
| Applicable from: May 01, 2008 |
| Delhi | 975.46 |
| Kolkata | 1036.10 |
| Mumbai | 1021.05 |
| Chennai | 1105.55 |
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| Previous Prices |
| Specifications |
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| prdeodhar@indianoil.co.in. |
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