Natural Gas:

• Natural gas is a naturally occurring hydrocarbon gas mixture consisting primarily of methane along with other higher alkanes and a small percentage of carbon dioxide, nitrogen and hydrogen sulphide (H₂S). If the natural gas contains lower hydrocarbons like methane and ethane, it is called dry gas. If higher hydrocarbons like propane and butane are also present in the gas, it is called wet gas.
• Natural gas is always found above the oil in the oil wells. This gas is trapped inside the small spaces in underground rocks called reservoirs. Conventional natural gas can be extracted through drilling wells. Natural gas can also be found in reservoirs with oil and is extracted along with oil. This is called associated gas.
• Natural gas is a fossil fuel used as a source of energy for heating, cooking and electricity generation. Natural gas occurs in Tripura, Rajasthan, Maharashtra, Andhra Pradesh (Krishna, Godavari Basins) and Tamil Nadu (Cauveri Delta). It is also formed by the decomposition of organic matter in marshy areas and waste sewages. The natural gas formed by this way contains mainly methane.

Uses of Natural Gas:

• Natural gas is used as an industrial and domestic fuel.
• It is used in thermal power stations.
• It is used as fuel in vehicles as an alternative for petrol and diesel.
• When heated it decomposes and forms hydrogen and carbon. Hydrogen thus formed is used in the manufacture of fertilizers.
• It is used to manufacture chemicals, fabrics, glass, steel, plastics and paints.
• It is also used in electricity generation.

Advantages of Natural Gas:

• It produces lot of heat as it can be easily burnt.
• It does not leave any residue.
• It burns without smoke and so causes no pollution.
• This can be easily supplied through pipes.
• It can be directly used as fuel in homes and industries.

Compressed Natural Gas:

• When the natural gas is compressed at high pressure, it is called Compressed Natural Gas (CNG). Nowadays it is used as fuel in automobiles. The primary hydrocarbon present in CNG is methane (88.5%). Natural gas is liquefied for shipping in large tankers. This is called Liquefied Natural Gas (LNG). CNG is stored at high pressure whereas LNG is stored in ultra cold liquid form. CNG has the following properties.
• It is the cheapest and cleanest fuel.
• Vehicles using this gas produce less carbon dioxide and hydrocarbon emission.
• It is less expensive than petrol and diesel.

The average composition of CNG:

Other Gases:

• Apart from natural gas, there are some other gases which are used as fuel. Producer gas, coal gas, bio gas and water gas are some of them.

Producer Gas:

• Producer gas is a gaseous mixture of carbon monoxide and nitrogen. It is produced by passing air mixed with steam, over red hot coke at a temperature of 1100 ˚C. It is used as an industrial fuel for iron and steel manufacturing.

Coal Gas:

• It is a mixture of gases like hydrogen, methane and carbon monoxide obtained by the destructive distillation of coal. Heating coal in the absence of air is called destructive distillation. It is used in heating open hearth furnace in the manufacture of steel. It is also used as a reducing agent in certain metallurgical operations.

Water Gas:

• It is a gaseous mixture of carbon monoxide and hydrogen. It is made by passing steam over incandescent coke at a temperature of 1000°C.
• It is also called as syngas or synthesis gas as it is used to synthesize methanol and simple hydrocarbons. It is used as an industrial fuel also.

Bio-Gas:

• Bio-gas is a mixture of methane and carbon dioxide. It is produced by the decomposition of plant and animal waste which form the organic matter. The breaking down of organic matter in anaerobic condition (ie., in the absence of oxygen) leads to the formation of biogas. It is an example for renewable source of energy.

Petroleum:

• The term ‘petroleum’ is derived from the Latin words ‘petra’ meaning rock and ‘oleum’ meaning oil. It is a fossil fuel formed from the remains of ancient marine organisms through decaying process. Petroleum is a complex mixture of hydrocarbons that occur in Earth in liquid, gaseous, or solid form. The term petroleum commonly denotes the liquid form, crude oil. But technically petroleum also includes natural gas and bitumen, a solid form. The natural gas and the crude oil constitute the primary fossil fuels.

Occurrence of Petroleum:

• The chief petroleum producing countries are U.S.A, Kuwait, Iraq, Iran, Russia and Mexico. In India, petroleum is found in Assam, Gujarat, Maharashtra (Mumbai), Andhra Pradesh (Godavari and Krishna basin) and Tamil Nadu (Cauveri Basins). By drilling through the earth the crude oil is pumped out from the well as a black liquid.

Refining of crude petroleum:

• The crude petroleum obtained from the well is a dark colored viscous liquid which contains many impurities such as water, solid particles and gases like methane and ethane. To make it useful for different purposes, it must be separated into various components. The process of separating petroleum into useful by-products and removal of undesirable impurities is called refining. The steps involved in this process are given below.

Separation of water:

• The crude oil obtained from the oil wells will have salt water mixed with it. As the first step the water is removed from the crude oil.

Removal of sulphur compounds:

• The crude oil will have harmful sulphur compounds as impurities. In this step these impurities are removed.

Fractional distillation:

• Petroleum is a mixture of various constituents such as petroleum gas, petrol, diesel, kerosene, lubricating oil, paraffin wax, etc. The process of separation of various constituents or fractions of petroleum is done by fractional distillation in fractionating columns. The process of heating a mixture of liquids having different boiling points and then separating them by cooling is called fractional distillation.
• Crude petroleum is first heated to about 400°C in a furnace. As the vapours of crude oil move up the tower, the various fractions condense according to their boiling point ranges. Many useful substances are obtained from petroleum and natural gas. These are termed as ‘petrochemicals’. These are used in the manufacture of detergents, fibres, and other man-made plastics like polythene. Hydrogen gas obtained from natural gas, is used in the production of fertilizers. Due to its great commercial importance, pertoleum is also called ‘black gold’.

Uses of Petroleum:

Products obtained from crude oil have a number of uses.

• Liquefied Petroleum Gas or LPG is used in houses as well as in the industry.
• Diesel and petrol are used as fuels for vehicles. It is also used to run electric generators.
• Petrol is used as a solvent for dry cleaning.
• Kerosene is used as a fuel for stoves and also in jet planes.
• Lubricating oil reduces wear and tear and corrosion of machines.
• Paraffin wax is used to make candles, ointments, ink, crayons, etc.
• Bitumen or asphalt is mainly used to surface roads.

Fuel:

• Any substance that can produce heat and energy on burning is called fuel. We use this heat for various purposes such as cooking, heating and many industrial and manufacturing purposes. Some of the fuels that we use in our daily life are wood, coal, petrol, diesel and natural gas.

Types of fuel:

• Fuels are classified into different types according to their physical state. They are classified into solid, liquid and gaseous fuels.

Solid fuels:

• Fuels like wood and coal are in solid state and they are called solid fuels. This type of fuel was the first one to be used by man. These fuels are easy to store and transport. The production cost is also very low.

Liquid fuels:

• Most of the liquid fuels are derived from the fossil remains of dead plants and animals. Petroleum oil, coal tar and alcohol are some of the liquid fuels. These fuels give more energy on burning and burn without ash.

Gaseous fuel:

• Coal gas, oil gas, producer gas and hydrogen are some of the gaseous fuels. These fuels can be easily transported through pipes and they do not produce pollution.

Characteristics of fuel:

An ideal fuel should have the following characteristics.

• It should be readily available
• It should be easily transportable
• It should be less expensive
• It should have high calorific value
• It should produce large amount of heat
• It should not leave behind any undesirable substances

Efficiency of Fuel:

• Any fuel contains carbon as its main constituent. During the combustion of fuel carbon combines with oxygen and liberates large amount of heat. It is expected that a fuel liberates maximum amount of heat in the short time. The efficiency of a fuel can be understood from the following terms.

Specific Energy:

• Specific energy is the amount of energy produced by unit mass of a fuel. It is defined as the energy per unit mass. It is used to measure the stored energy in certain substances. Its unit is Jkg^-1.

Calorific Value:

• It is the quantity of heat produced by the complete combustion of fuel at constant pressure and normal conditions. It is measured in terms of KJkg^-1.

Calorific value of some fuels:

 Alternative Fuel:

• The natural resources in the world have been used by man in a rapid way and they will be exhausted soon. The traditional fuel that we use today including petroleum are nonrenewable and they would be depleted soon. It is estimated that coal will last for 148 years, petroleum for 40 years and natural gas for 61 years. So we need to find alternative sources of energy. More over fossil fuels emit harmful gases like carbon dioxide, carbon monoxide and sulphur dioxide which pollute the atmosphere. Burning fossil fuels also cause temperature rise in the earth’s atmosphere. Many believe that fuel which does not cause pollution is needed to enhance the quality of our environment. Some of the alternative fuels are given below.

Bio diesel:

• Bio diesel is a fuel obtained from vegetable oils such as soya bean oil, jatropha oil, corn oil, sunflower oil, cotton seed oil, rice-bran oil and rubber seed oil.

Wind energy:

• Wind energy is obtained with the help of wind mills. When wind blows, they rotate the blades of the wind mills and electricity is produced by the dynamo. Wind mills are mostly located at Kayathar, Aralvaimozhi, Palladam and Kudimangalam in Tamil Nadu.

Gobar Gas:

• Gobar gas is obtained by the fermentation of cow dung in the absence of air (anaerobic conditions). It mainly contains methane and a little ethane. It is widely used in rural areas for cooking and operating engines.

Solar Energy:

• Sun is the first and foremost energy source that makes life possible on the earth. Solar energy is the only viable fuel source of non-depleting nature for sun provides a free and renewable source of energy. It is the renewable type of energy without endangering the environment. It is the potential source to replace the fossil fuel in order to meet the needs of the world. With the advancements in science and technology, solar energy has become more affordable, and it can overcome energy crisis. Solar energy is a clean energy. With the minimum efforts maximum energy can be harnessed using various equipment’s.

Applications of Solar Energy:

• It is used in solar water heater.
• It is used in drying of agricultural and animal products.
• It is used in electric power generation.
• It is used in solar green houses.
• It is used in solar pumping and solar distillation. It is used for solar cooking and solar furnaces also.