Table of Contents

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.