8th Class Science Coal and Petroleum Coal

      Coal

Coal is a fossil fuel formed in ecosystems where plant remains were preserved by water and mud from oxidization and biodegradation, and by which its chemical and physical properties have been changed as a result of geological action over time, thus sequestering atmospheric carbon. Coal is a readily combustible black or brownish-black rock.

It is composed primarily of carbon and hydrogen along with small quantities of other elements, notably sulphur. Coal is extracted from the ground by coal mining, either underground mining or open pit mining (surface mining).It is a nonrenewable resource.

         Coal Formation

Coal is a sedimentary rock formed from plants that flourished millions of years ago when tropical swamps covered large areas of the world. Lush vegetation, such as early club mosses, horsetails, and enormous ferns, thrived in these swamps. Generations of this vegetation died and settled to the swamp bottom, and over time the organic material lost oxygen and hydrogen, leaving the material with a high percentage of carbon. Layers of mud and sand accumulated over the decomposed plant matter, compressing and hardening the organic material as the sediments deepened. Over millions of years, deepening sediment layers, known as overburden, exerted tremendous heat and pressure on the underlying plant matter, which eventually became coal.

            Types of Coal

As geological processes apply pressure to dead biotic matter over time, under suitable conditions it is transformed successively into

Peat: It is considered to be a precursor of coal, has industrial importance as a fuel in some regions, for example, Ireland and Finland.

Lignite: It also referred to as brown coal, is the lowest rank of coal and used almost exclusively as fuel for electric power generation. Bituminous: It is dense mineral, black but sometimes dark brown, often with well-defined bands of bright and dull material, used primarily as fuel in steam-electric power generation, with substantial quantities also used for heat and power applications in manufacturing and to make coke.

Anthracite: It is the highest rank of coal; a harder, glossy, black coal used primarily for residential and commercial space heating.

           Coalmine Fires

Coalmine fires can be triggered during routine mining operations. For example, sparks generated by mining equipment can ignite explosive gases, coal dust, and even the coal bed itself. Because coal beds provide an almost inexhaustible fuel source, once a coal seam is ignited, it can be extremely difficult to extinguish. The intense heat generated by burning coal can rupture the overlying rock strata, sometimes causing the roof to collapse. Uncontrollable fires in some coal deposits have continued burning for years, posing a danger to local communities..