Fuels - Part III

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Coal : Coal is one of the important fossil fuels that we can obtain from deep within the earth’s surface. Coal is formed by thousands and millions of years of decomposition of plants that got buried deep inside the earth due to various natural phenomena like earthquakes and volcanoes.  Bacteria, high temperature and high pressure caused the slow conversion of wood into coal. This process is called carbonization. Coal is mainly carbon. If the carbonization is not complete, we get inferior verities of coal. Different verities of coal are peat (60%carbon), lignite (70% carbon), bituminous (80%carbon) and anthracite (90% carbon). Bituminous and anthracite are generally used in households and industries.  

Uses of coal :  

  • Coal is used as fuel because it burns easily and has high calorific value.

  • Coal is used to make other fuels like coal gas, synthetic petrol, methane and coke.

  • Coal is used for the manufacture of industrially useful organic compounds like benzene, naphthalene, etc.  

On strongly heating coal in air, destructive distillation occurs. Coal breaks down in different components such as coal gas, ammoniacal liquor, coal tar and coke.

Coal gas : Coal gas is a composite of gases such as hydrogen, methane and carbon monoxide. These gases are good fuels with high calorific value. Coal gas finds its use as cooking gas and for lights. These days it is used in industries as fuel. Because of the presence of hydrogen, it is also used in industries for obtaining reducing environment for many chemical and metallurgical processes.

Ammoniacal liquor : A solution of ammonia in water is called ammoniacal liquor. Ammoniacal liquor when reacted with sulphuric acid gives rise to ammonium sulphide, which is used as a fertilizer.

Coal tar : Coal tar is a mixture of as many as two hundred carbon compounds. These compounds can be separated by fractional distillation. Compounds such as benzene, toluene, phenol or carbolic acid, naphthalene, anthracene, etc. These compounds are used to make medicines, dyes, explosives, paints, plastics, synthetic fibers, pesticides, etc. The residue left behind after destructive distillation of coal tar is called tar. This is used to surface roads, waterproof roofs.

Coke : Coke consists of carbon only. Uses of coke are many. Coke is a very good fuel. It has a higher calorific value than coal itself. Coke is also used to make water gas (CO + H2) and producer gas (CO + N2). These gases have many applications in chemical industries. Coke is also a very useful reducing agent in industries. Coke is a good starting material for the preparation of acetylene, acetic acid and plastics like polyvinyl chloride.  

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