Coal – Formation of Coal – Types of Coal – Peat, Lignite, Bituminous Coal & Anthracite Coal. Carbon content in different types of coal. Importance of each type.

Coal

• Also called black gold.
• Found in sedimentary strata [layers of soil].
• Contains carbon, volatile matter, moisture and ash [in some cases Sulphur and phosphorous]
• Mostly used for power generation and metallurgy.
• Coal reserves are six times greater than oil and petroleum reserves.

Carboniferous Coal

• Most of the world’s coal was formed in Carboniferous age [350 million years ago][Best quality coal].
• Carboniferous age: In terms of absolute time, the Carboniferous Period began approximately 358.9 million years ago and ended 298.9 million years ago. Its duration is approximately 60 million years.
• The name Carboniferous refers to coal-bearing strata.

Formation of Coal

Amount of oxygen, nitrogen and moisture content decreases with time while the proportion of carbon increases [The quantity of carbon doesn’t increase, only its proportion increases due to the loss of other elements].

Capacity of coal to give energy depends upon the percentage or carbon content [Older the coal, much more is its carbon content].

Percentage of carbon in coal depends upon the duration and intensity of heat and pressure on wood. [carbon content also depends on depth of formation. More depth == more pressure and heat == better carbon content].

• Coal formed millions of years ago when the earth was covered with huge swampy [marshy] forests where plants – giant ferns and mosses – grew.
• As the plants grew, some died and fell into the swamp waters. New plants grew up to take their places and when these died still more grew.
• In time, there was thick layer of dead plants rotting in the swamp. The surface of the earth changed and water and dirt washed in, stopping the decaying process.
• More plants grew up, but they too died and fell, forming separate layers. After millions of years many layers had formed, one on top of the other.
• The weight of the top layers and the water and dirt packed down the lower layers of plant matter.
• Heat and pressure produced chemical and physical changes in the plant layers which forced out oxygen and left rich carbon deposits. In time, material that had been plants became coal.
• Coals are classified into three main ranks, or types: lignite, bituminous coal, and anthracite.
• These classifications are based on the amount of carbon, oxygen, and hydrogen present in the coal.
• Coals other constituents include hydrogen, oxygen, nitrogen, ash, and sulfur.
• Some of the undesirable chemical constituents include chlorine and sodium.
• In the process of transformation (coalification), peat is altered to lignite, lignite is altered to sub-bituminous, sub-bituminous coal is altered to bituminous coal, and bituminous coal is altered to anthracite.

Types of Coal

• Peat, Lignite, Bituminous & Anthracite Coal.
• This division is  based on carbon, ash and moisture content.

Peat

• First stage of transformation.
• Contains less than 40 to 55 per cent carbon == more impurities.
• Contains sufficient volatile matter and lot of moisture [more smoke and more pollution].
• Left to itself, it burns like wood, gives less heat, emits more smoke and leaves a lot of ash.

Lignite

• Brown coal.
• Lower grade coal.
• 40 to 55 per cent carbon.
• Intermediate stage.
• Dark to black brown.
• Moisture content is high (over 35 per cent).
• It undergoes SPONTANEOUS COMBUSTION [Bad. Creates fire accidents in mines]

Bituminous Coal

• Soft coal; most widely available and used coal.
• Derives its name after a liquid called bitumen.
• 40 to 80 per cent carbon.
• Moisture and volatile content (15 to 40 per cent)
• Dense, compact, and is usually of black colour.
• Does not have traces of original vegetable material.
• Calorific value is very high due to high proportion of carbon and low moisture.
• Used in production of coke and gas.

Anthracite Coal

• Best quality; hard coal.
• 80 to 95 per cent carbon.
• Very little volatile matter.
• Negligibly small proportion of moisture.
• Semi-metallic lustre.
• Ignites slowly == less loss of heat == highly efficient.
• Ignites slowly and burns with a nice short blue flame. [Complete combustion == Flame is BLUE == little or no pollutants. Example: LPG]
• In India, it is found only in Jammu and Kashmir and that too in small quantity.

Primary References: NCERT Geography, Indian Geography by Kullar [Amazon and Flipkart]