NATURAL GAS
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7.0 NATURAL GAS India's recoverable resources of more than 690 billion cubic meters make it a long-term substituted fuel for use in petrol and diesel engines. Low exhaust emissions, low noise, less maintenance, not prone to adulteration, driver's comfort, etc. are some of the attractive features of CNG as an automotive fuel. |
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Natural gas can be produced domestically. Gas streams produced from reservoirs or wells contain natural gas liquids and other materials. Processing is required to separate the gas from petroleum liquids and to remove contaminants. First the gas is separated from free liquids such as crude oil, hydrocarbon condensate, water and entrained solids. The separated gas is further processed to meet specified requirements. Natural gas when stored and distributed in the liquid phase is called Liquefied Natural Gas or LNG. LNG essentially facilitates storage and transportation of natural gas. This LNG is again reheated to CNG and filled on-board a vehicle for use as fuel. Vehicles running on LNG are also available in many parts of the world.
7.2 Emissions:
Given the availability and the infrastructure, CNG qualifies to be one of the most prominent alternative fuels. It stands substantially better than conventional fuels both in life cycle emissions and vehicle exhaust emissions. Table-4 gives the comparative emissions from CNG and conventional diesel. Emission results as tested by the Indian manufacturers are given in Table-5, 6, 7 and 8.
7.3 Advantages of CNG:
Following are some of the benefits of CNG when used as an automotive fuel:
- No visible tail pipe emissions.
- Eliminates sulphur and lead from the exhaust emissions.
- Reduction in CO, NOx and Particulate emissions.
- Significant reduction in benzene and other toxic emissions.
- Higher octane value of CNG reduces knocking problems of a vehicle.
- Reduces noise from running vehicles.
- CNG cannot be adulterated.
- Reduce noise in operation.
7.4 Disadvantages of CNG:
CNG is now established as a very successful alternate fuel for automobiles throughout the world. The disadvantage of this fuel, if any is easily overruled by the advantages associated with this fuel. Nevertheless, infrastructure, on-board storage and issues on safety need proper attention for this fuel.
7.5 Safety Issues:
Natural gas is neither corrosive nor toxic, its ignition temperature is high, it is lighter than air, and it has a narrow flammability range, making it an inherently safe fuel compared to other fuel sources. Natural gas cannot contaminate soil or water. It will always rise to the atmosphere out of doors, unlike other fuels, which are heavier than air and can pool, either as a liquid or a vapor, upon the ground. Natural gas contains a distinctive odorant (mercaptan), which allows natural gas to be detected at 0.5% concentration in air, well below levels that can cause drowsiness due to inhalation and well below the weakest concentration that can support combustion. Due to high ignition temperature of natural gas (540 degree C), simple exposure to a hot surface (such as exhaust manifold) is unlikely to lead a fire.
7.6 Indian Initiative on CNG:
After several trails and field studies by various institutions and taking stock from the experience of other countries, India too initiated to introduce CNG as automobile fuel. Recently large numbers of buses, autos and taxis in Delhi have been switched over to CNG (Table-9). Initially there have been problems of infrastructure and dispensing stations but slowly things are getting back to normal in Delhi. At present there are 97 dispensing stations in Delhi with a total compression capacity of 7.9 lakhs kg/day and dispensing capacity of 6.0 lakhs kg/day. CNG vehicles are also present in Mumbai and Baroda. Acknowledging the impact of CNG on the air quality of Delhi other cities of India are also taking up plans for introducing CNG in a phased manner.
