- 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.
- 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.
- 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.
- 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]
- 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.
- 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.