Non-Conventional sources of energy.Fossil fuels – solid, liquid and gaseous fuels.

TOPIC: Non-Conventional sources of energy. Fossil fuels – solid, liquid and gaseous fuels. n INTRODUCTION What is energy? Simply stated, energy is the ability to do work. we use energy to do work and make all movements. When we eat, our bodies transform the food into energy to do work. When we run or walk or do some physical work, we use this energy. Sources of energy and its characteristics: A source of energy is that which is capable of providing enough useful energy at a steady rate over a long period of time. A good source of energy should be: (1)safe and convenient to use. (2)Easy to transport. (3)Easy to store. Sources of energy is classified into two 1.Renewable and non renewable. 2.Conventional and non conventional. n Non conventional sources of energy n The growing consumption of energy has resulted in the country becoming increasingly dependant on fossil fuels such as coal, oil and gas . Rising prices of oil and gas and their potential shortages have raised uncertainties about the security of energy supply in future, which in turn has serious repercussions on the growth of the national economy. Moreover, increasing use of fossil fuels also causes serious environmental problems. Hence, there is a pressing need to use renewable energy sources like solar energy, wind, tide, biomass, and energy from waste material. These are called non conventional energy sources. Sources of energy which are not extensively as the conventional energy sources and meet our energy demands only on a limited scale are called non-conventional sources of energy. Examples of non conventional sources of energy are solar energy, ocean energy (tidal energy, wave energy, ocean thermal energy), geothermal energy and nuclear energy. These sources which have been tapped with the aid of advances in technology to meet our growing energy needs are also called Alternative energy sources Sun is the main inexhaustible source of energy. Strictly speaking, all forms of energy on the earth are derived from the sun. The more conventional energy sources, viz. the fossil fuels, received their solar input decades ago and possesses the energy in a greatly concentrated form. Other conventional and non conventional forms of energy are also different forms of solar power or solar related power. Here we will look more about the conventional energy sources like fossil, solid, liquid and gaseous fuels. n Fossil fuels Fossil fuels are the remains of prehistoric plants and animals which got buried deep inside the earth millions of years ago due to some natural processes. The energy of fossil fuels is, in fact, the solar energy which was trapped by natural processes a very long time ago. Fossil fuels are mainly classified as follows: 1.Solid fuels 2.Liquid fuels 3.Gaseous fuels n Solid fuels n Solid fuels can be natural solid fuels or prepared solid fuels. Natural solid fuels include wood, peat, lignite, bituminous coal and anthracite coal. The prepared solid fuels include charcoal, coke and pulverized coal. n Coal: it is the most abundant fossil fuel on the earth. It is essentially carbon and is mainly used as combustion fuel. The large scale use of coal began with the industrial revolution in the 19th century. Coal provides 27% of the World’s energy. n How coal was formed? : Coal is a product of plants, mainly trees, which died tens or hundreds of millions of years ago. These dead plants and trees did not decompose in a normal way as they were covered with water and protected from oxidizing effect of air. the action of certain bacteria released oxygen and hydrogen, making the residue richer and richer in carbon. Thick layers of this carbon-rich(27%)substance called peat, built up over thousands of years. As more material accumulated above peat, water was squeezed out. Pressure and temperature further compressed peat and gases were expelled. The proportion of carbon continued to increase till it slowly changed into coal over a period of millions of years. Peat, lignite, bituminous coal and anthracite coal are various forms of coal. Peat consists of partly decomposed vegetable matter. Even though peat is a cheap and locally available fuel, it presents severe problems because of its high moisture content (as high as 90%). The calorific value of air dried peat is about 3500kcal/kg. The brown coal or lignite is a more decomposed vegetable matter than peat. It is characterized by a moisture content of 30 to 50% and it contains nearly 60% carbon. After drying, its calorific value is about 5000kcal/kg. Bituminous coal contains moisture less than 10%. Its carbon content varies from 80 to 90%. The calorific value of this fuel varies from 7500 to 9000kcal/kg. this variety of coal forms the major portion of the coal used in industries. Anthracite coal contains very low moisture content. Also the carbon content of this fuel is more than 92% with the calorific value of about 8500kcal/kg. Wood, even though is an important domestic fuel, is relatively unimportant as an industrial fuel. But, under certain circumstances it is also used as industrial fuel along with coal. Charcoal is an artificial or prepared solid fuel made by heating wood out of contact with atmosphere. Dry charcoal contains 80 to 90% carbon and its calorific value is about 6700kcal/kg. Pulverized coal is made from ordinary coal by crushing into powder form of such fineness that it will float in air. Many important power plants are now working on pulverized fuel. Coke is made from bituminous coal by driving out its volatile elements. It contains 85 to 95% carbon and its calorific value is about 7800kcal/kg. n Liquid fuels. Naturally available liquid fuel is the crude petroleum. Petroleum literally means rock oil (Petra stands for rock and oleum for oil). It is a complex mixture of many compounds of hydrogen and carbon which are called hydrocarbons. Small amounts of other compounds of carbon containing oxygen, nitrogen and sulphur are also present in petroleum. How was petroleum formed? : Millions of years ago, sea covered much of what is now dry land. In prehistoric times, tiny plants and animals lived in the sea. When these died, they sank to the bottom of the sea and got buried in the layers of mud and sand. As the ages passed, this organic material sank deeper and deeper. The earth’s crust changed its shape and put intense pressure and heat on what were once only plants and tiny animals. Heat from the earths interior and the weight of the overlying rocks gradually changed these energy containing substances into oil. Bacterial anaerobic reactions also played their role in the formation of oil. Oil being light and mobile, moved upwards through the rocks but eventually got trapped beneath impermeable rocks in the Earth’s crust and that is where the present oil reserves are located. Petroleum is extracted from such reserves through wells driven in them by cutting through the impervious rocks. n Refining of petroleum : petroleum (also known as crude oil) is a thick black liquid and is not used as a fuel in its natural form. It is refined to obtain a number of useful components (products). The refining of petroleum is the process of separating the crude oil into different useful fractions which is carried out by fractional distillation. The process of fractional distillation is based on the fact that different components of crude oil have different boiling point ranges. Fractional distillation is carried out in a distillation tower or fractionating tower. n The series of products obtained by distillation are: 1.Motor spirit or petrol (gasoline) which is the source of power for road traction, aviation and for small industrial installations. 2.Solvent spirit (paint thinner) and industrial solvent of various distillation ranges. 3.Burning oil or kerosene, useful for domestic purposes. 4. Diesel oil which are used in diesel engines and oil fired furnaces. 5.Lubricating oil-from the lightest spindle oil to the most viscous steam cylinder oil. 6.Paraffin wax-useful in candle manufacturing , water proofing of papers etc 7.Bitumens – which are used for road surfacing and for water proofing purpose. 8.Distillates and residual oils which are used as fuel oil for furnaces. If the distillation is continued to the extreme extent, a solid residue of nearly pure carbon known as petroleum coke remains. This is used principally in electro-metallurgical industries. n Gaseous fuels n Like solid fuels, gaseous fuels may be divided into two classes, viz., natural gas and prepared gas. n Natural gas is an important fossil fuel and is usually found underground near an oil source. However, there are some oil wells which give only natural gas. The process by which natural gas was formed millions of years ago is the same as that of oil. Natural gas is lighter than air and is a mixture of methane (about 95%), ethane, propane and butane. Other components found in natural gas include carbon dioxide, helium, hydrogen sulphide and nitrogen. It is highly inflammable and has no odour and cannot be seen. Therefore, before it is sent to the pipelines or storage tanks, it is mixed with a chemical that gives it a strong odour which is almost like that of rotten eggs. This makes it easy to detect any leakage. Natural gas is the cleanest burning fossil fuel as it gives off 50%of the carbon dioxide released by coal and 25% less carbon dioxide than oil for the same amount of energy produced. It virtually gives no sulphur dioxide and only small amount of nitrous oxide. Thus, natural gas is an environment- friendly fuel. Uses of natural gas: 1.It is used as a domestic and industrial fuel. 2.It is used as a fuel in Thermal Power Plants to generate electricity. 3.It has been a source of hydrogen in the manufacture of fertilizers. 4.Compressed Natural Gas (CNG), which is in the liquid form, is used as a fuel in transport vehicles as being pollution free, it is a good alternative to petrol and diesel. n Advantages of Natural gas: 1.It is a complete fuel and can be used directly for household and industrial purposes. 2.There is no problem of transportation as it can be supplied directly through gas pipelines. 3.It has a high calorific value of about 55kj/g. n The prepared gases include coal gas, producer gas, water gas, blast furnace gas and marsh gas. n Coal gas is obtained by distilled coal in retorts. Its constituents are hydrogen, methane, carbon monoxide, carbon dioxide and nitrogen. Its calorific value ranges from 5000 to 6000kcal/m3. n Producer gas is a mixture of carbon monoxide, hydrogen, nitrogen and carbon dioxide. It is produced by passing air and steam over fuel (coal or coke) bed. Its calorific value varies from 1000 to 1600kcal/m3. n Water gas is produced by the action of steam on red hot coal or coke. Its main constitutes are hydrogen and carbon monoxide with little traces of nitrogen and methane. As this fuel burns with a blue flame it is known as ‘blue gas’. Its calorific value ranges from 2800 to 5500 kcal/m3. n Blast furnace gas is produced during the extraction of iron from its ores, and is extensively used as a fuel in metallurgical industries. Its calorific value is about 900 kcal/m3. n Marsh gas is produced by the decomposition of vegetable matter. Its calorific value is about 5500 kcal/m3. n Disadvantages of fossil fuels n These are non-renewable sources of energy. n Air pollution is caused by burning fossil fuels. n Carbon dioxide produced by burning these fuels produces greenhouse effect. n The oxides of carbon, nitrogen and sulphur which are released on burning these fuels lead to acid rain which affects our water and soil resources. n Environmental consequences of exploiting energy sources. Environment is disturbed whenever a source of energy is used to derive energy from it. 1.Burning of fossil fuels causes air-pollution. 2.Using wood as fuel results in deforestation which affects environment. n How long will an energy source last us? n Fossil fuels (coal, petroleum, and natural gas) will get depleted some day as these are exhaustible sources of energy. It has been estimated that coal will last for another 200 years whereas known reservoirs of petroleum for another 60 years and those of natural gas for about 40 years. n Steps to reduce energy consumption. n Fossil fuels should be used with care and caution to derive maximum benefit out of them. n Fuel saving devices such as pressure cookers etc. should be used. n Efficiency of energy sources should be maintained by getting them regularly serviced. n And last of all, we should be economical in our energy consumption as energy saved is energy produced. by, Greeshma S Saintgits College Of Engineering