LIQUIFIED PETROLEUM GAS (LPG)

8.0 LIQUIFIED PETROLEUM GAS (LPG)

LPG is a by-product of natural gas processing or a product that comes from crude oil refining and is composed primarily of propane and butane with smaller amounts of propylene and butylenes. Since LPG is largely propane, the characteristics of propane sometimes are taken as a close approximation to those of LPG. Composition of LPG and CNG is given in Table-10.

8.1 Production:

LPG is a by-product of two sources: natural gas processing and crude oil refining. When natural gas is produced, it contains methane and other light hydrocarbons that are separated in a gas processing plant. Because propane boils at -44 degrees F and ethane boils at -127 degrees F, separation from methane is accomplished by combining increasing pressure and decreasing temperature. The natural gas liquid components recovered during processing include ethane, propane and butane and other heavier hydrocarbons. Propane and butane along with other gases are also produced during crude refining as a by-product of the process that rearrange or break down the molecular structure to obtain more desirable petroleum compounds.

8.2 Emissions:

The main constituent of LPG is propane. Lower carbon-to-hydrogen ratio, higher octane rating and its ability to form a homogeneous mixture inside the combustion chamber enable it to produce lesser emissions compared to conventional fuels. Table-11 gives a comparative emissions status from Euro-II diesel and LPG buses. LPG outperforms conventional fuels in both regulated and non-regulated emissions. Comparison of non-regulated components of emissions between diesel and LPG vehicles is given in Table-12. Non-regulated components of emissions like aldehydes and poly-aromatic hydrocarbons are much lower from CNG vehicles compared to that of diesel vehicles.

8.3 Advantages of LPG:

Some of the benefits of LPG as automotive fuel are:
- Reduction in emissions.
- Very less carbon build-up increases life of engine parts like spark plugs.
- Fueling is akin to that of conventional diesel or gasoline and time needed is also similar.
- Service life of a vehicle increases with LPG.
- Little or no damage to soil and water if it is spilled, due to its rapid evaporation.
- Higher octane number.

8.4 Disadvantages of LPG:

Many countries in the world are using LPG as automotive fuel. Many years of experience of successful use of LPG in vehicles and the emission benefits it offers really support it to outperform the associated disadvantages of the fuel, if any. Moreover, familiarity with LPG in household application like cooking makes it more acceptable to the users. However, in the initial stages of introduction of this fuel, issues like safety, storage & handling, extreme volatility of the fuel, etc. needs proper attention.

8.5 Safety Issues:

Safety is an issue with LPG, however, standards for application, storage and distribution already exists. The hazard associated with on-board storage should be similar to that of gasoline, especially if reinforced cylinders similar to that of CNG tanks are used. LPG fuel systems have many built-in safety features and they generally maintain their integrity in severe collisions and do not permit massive leaks. LPG is about twice as heavier than air and unlike CNG does not disperse easily in air. Its flammability limits (2.1-9.5 vol.%) and auto ignition temperature (450 degrees C) are also lower than natural gas and as such should not be handled carelessly. Accident statistics, though limited, indicate that LPG or propane is as safe as gasoline.

8.6 Indian Initiative on LPG:

In India, initiatives for evaluating the performance of LPG as automotive fuel dates back to 80s and mid-80 when IIP, Dheradun carried out some field studies on bus and tractor engines using commercially available duel-fuel engine kits. Studies on diesel engines were also conducted at IIT Madras and Anna University, Madras. Some manufacturers in India already acquired the technology for producing LPG version of their products, especially two wheelers but huge demand of LPG for domestic cooking seems to discourage its lunch in the automobile sector in a big way.

In India, the Committee of experts appointed to study introduction of LPG as an auto fuel has submitted its recommendations and Government of India has already passed legislation enabling use of LPG as automotive fuel. Government has accorded approval for developing 201 Auto LPG dispensing facilities in the existing retail networks. Bharat Petroleum Corporation (BPC) has developed one auto LPG dispensing facility in Delhi as a pilot project. Moreover, comprehensive regulatory and safety framework for the fuel is under development.

Moreover, a pilot project was also initiated in Delhi for conversion of two-stroke petrol three-wheelers to Propane. Accordingly, three propane-dispensing stations were set up in Delhi (Vinodnagar, Mayurvihar, Okhla) with the assistance of G&T Resources Worldwide (USA). However, this project was withdrawn at a later stage.