COAL RESOURCES OF INDIA
     
 

Based on TEXT BOOK OF COAL (Indian Context) First Edition (2000) by D. Chandra, R, M. Singh & M.P. Singh, Published by- The Book Agency, Kamachha, Varanasi .
COAL AND LIGNITE RESOURCES OF INDIA – AN OVERVIEW by S. K. Acharyya, Geological society of India , Bangalore , 2000, Websites- www.wikipedia.com and other websites.

 
     
   
 

Coal is “ Black Diamond” in more sense than one! Coal is the main source of energy not only in our country but also for most of the countries of the world. The energy requirement of India is increasing every year and to meet this demand the country has to depend to a large extent on coal. At present more than 60% of the total commercial energy requirement is met from the coal.

The word coal is a very common term. It was formerly written as “Cole” and could be traced to the Sanskrit root “Kala” which means black. According to Stopes and Wheeler (1918), “ordinary coal is a compact, stratified mass of mummified plants which have in part suffered arrested decay to varying degrees of completeness.” Arber (1918) has defined coal, as a solid, stratified rock, composed mainly of hydrocarbons and capable of being used as a fuel to supply heat or light or both.


Coal is a fossil fuel extracted from the ground by underground mining or open-pit mining (surface mining). It is a readily combustible black or brownish-black sedimentary rock. It is composed primarily of carbon along with assorted other elements, including sulfur. Often associated with the Industrial Revolution, coal remains an enormously important fuel and is the largest single source of electricity worldwide .
 
  COMPOSITION OF COAL  
 

Carbon forms more than 50 percent by weight and more than 70 percent by volume of coal (this includes inherent moisture). This is dependent on coal rank , with higher rank coals containing less hydrogen, oxygen and nitrogen, until 95% purity of carbon is achieved at Anthracite rank and above. Graphite formed from coal is the end-product of the thermal and diagenetic conversion of plant matter (50% by volume of water) into pure carbon.

Coal usually contains a considerable amount of incidental moisture, which is the water trapped within the coal in between the coal particles. Lignite and other low-rank coals still contain a considerable amount of water and other volatile components trapped within the particles of the coal, known as its macerals. This is present either within the coal particles, or as hydrogen and oxygen atoms within the molecules.

Other constituents of coals include mineral matter, usually as silicate minerals such as clays, illite, kaolinite and so forth, as well as carbonate minerals like siderite, calcite and aragonite. Iron sulfide minerals such as pyrite are common constituents of coals. Sulfate minerals are also found, as is some form of salt, trace amounts of metals, notably iron, uranium and cadmium, and rarely gold.

Methane gas is another component of coal, produced not from bacterial means but from methanogenesis. Methane in coal is dangerous as it can cause coal seam explosions especially in underground mines, and may cause the coal to spontaneously combust. It is, however, a valuable by-product of some coal mining, serving as a significant source of natural gas (see the Note on Coal Bed Methane-CBM at the end of this section).

 
     
 

TYPES OF COAL

 
 

Depending on the origin, coals have been grouped in to (a) Sapropelic coal, and (b) Humic coals.

(a) Sapropelic Coal:
Sapropelic coals are formed by putrefaction process. These coals are essentially non-banded in character and are rich in resins, waxes or fats and therefore richer in hydrogen than the humic coals. They are usually lenticular in shape, local in extent and occur at the top of a coal bed. Two types of Sapropelic coals have been recognized: (i) Boghead (Torbanite) (ii) Cannel.

(b) Humic Coal:
Unlike Sapropelic coals the humic coals are banded in character and the constituent bands are distinct in their physical appearance. Humic coals have a series of rank starting from wood-peat-lignite-bituminous coal to anthracite. In humic coals, the remains of wood and bark predominate.

Over the time, geological processes apply pressure to peat , which is transformed successively into the following ranks:

Lignite - also referred to as brown coal, is the lowest rank of coal and used almost exclusively as fuel for steam-electric power generation. Jet is a compact form of lignite that is sometimes polished and has been used as an ornamental stone since the Iron Age .

Sub-bituminous coal - whose properties range from those of lignite to those of bituminous coal and are used primarily as fuel for steam-electric power generation.

Bituminous coal - a dense coal, usually black, 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 - the highest rank, used primarily for residential and commercial space heating.

(c) Unusual coal types:
These coal types include paper coal and colored coal. Paper coal look like accumulated sheets of soiled light brown semitransparent papers. These coals consist almost entirely of cuticles (outerskins of plants). The coals being carboniferous in age are of lignite rank. Humic coals may show bright variegated colors like peacock, a mixture of blue, green yellow or red. Miners call this as Peacock coal.

 
     
  ORIGIN OF COAL  
 

Coal is formed from plant remains that have been compacted, hardened, chemically altered, and metamorphosed by heat and pressure over geologic time.

Coal was formed in swamp ecosystems which persisted in lowland sedimentary basins. These swamp environments were formed during slow subsidence of passive continental margins, and most seem to have formed adjacent to estuarine and marine sediments suggesting that they may have been in tidal delta environments.

When plants die in these peat swamp environments, their biomass is deposited in anaerobic aquatic environments where low oxygen levels prevent their complete decay by bacteria and oxidation. For masses of undecayed organic matter to be preserved and to form economically valuable coal the environment must remain steady for prolonged periods of time, and the waters feeding these peat swamps must remain essentially free of sediment. This requires minimal erosion in the uplands of the rivers which feed the coal swamps, and efficient trapping of the sediments.

Eventually, and usually due to the initial onset of orogeny or other tectonic events, the coal forming environment ceases. In the majority of cases this is abrupt, with the majority of coal seams having a knife-sharp upper contact with the overlying sediments. This suggests that the onset of further sedimentation quickly destroys the peat swamp ecosystem and replaces it with meandering stream and river environments during ongoing subsidence.

Burial by sedimentary loading on top of the peat swamp converts the organic matter to coal by the following processes;

  • compaction, due to loading of the sediments on the coal which flattens the organic matter
  • removal of the water held within the peat in between the plant fragments
  • with ongoing compaction, removal of water from the inter-cellular structure of fossilised plants
  • with heat and compaction, removal of molecular water
  • methanogenesis; similar to treating wood in a pressure cooker, methane is produced, which removes hydrogen and some carbon, and some further oxygen (as water)
  • dehydrogenation, which removes hydroxyl groups from the cellulose and other plant molecules, resulting in the production of hydrogen-reduced coals

Generally, to form a coal seam 1 metre thick, between 10 and 30 metres of peat is required. Peat has a moisture content of up to 90%, so loss of water is of prime importance in the conversion of peat into lignite, the lowest rank of coal. Lignite is then converted by dehydrogenation and methanogenesis to sub-bituminous coal. Further dehydrogenation reactions, removing progressively more methane and higher hydrocarbon gases such as ethane, propane, etcetera, create bituminous coal and, when this process is complete at sub-metamorphic conditions, anthracite and graphite are formed.

The greatest coal-forming time in geologic history was during the Carboniferous era (280 to 345 million years ago). Further large deposits of coal are found in the Permian, with lesser but still significant Triassic and Jurassic deposits, and minor Cretaceous and younger deposits of lignite.

A speculative inorganic process was proposed by Thomas Gold in his book The Deep Hot Biosphere: The Myth of Fossil Fuels. He proposes that black coal is continually created from the condensates of magma under the Earth's crust. This highly speculative hypothesis makes a distinction between brown and black coal, and upholds that brown coal is formed by the classical organic process.

 
     
 

RESERVES OF COAL (As on 1.1.2004)

 
 

The present updated total coal resources of the country as per the latest national inventory as on 1.1.2004 is 2,45,692.42 million tonnes for coal seams of 0.9m and above in thickness and upto 1200m depth from surface. The inventory is based on sub-surface data accrued from regional (including promotional) and detailed drilling carried out by GSI, CMPDI, SCCL and MECL. Out of the total resources, Gondwana coalfields contribute 2,44,785.47 million tonnes while the Tertiary coalfields account 906.95 million tonnes. Bulk of augmentation comes from Talcher Coalfield (1,783.34 Mt), the other coalfields that contribute to the enhancement are Rajmahal (683.64 Mt), Mand-Raigarh (545.79 Mt), Shohagpur (342.41Mt), Godavari (109.39 Mt), Tatapani-Ramkola (109.27 Mt), Ib-River (100.79), Birbhum (90 Mt), Korba (72.50 Mt), Raniganj (51.93 Mt) and South Karanpura (12.58 Mt). The updated ‘Proved' resources are 91,630.73 Mt and updated ‘Indicated' and ‘Inferred' resources of the country stand at 1,16,173.75 Mt and 37,887.94 Mt respectively. State-wise distribution of Indian coals shows that Jharkhand tops the list with 71.8 Bt followed by Orissa (60.9 Bt), Chhattisgarh (39.5 Bt), West Bengal (27.4 Bt) and the rest.

A glimpse at the coalfield-wise distribution of Indian coal resource suggests that nearly 42.7% of total resource of the country is shared by four coalfields – Talcher (38.65 Bt), Raniganj (25 Bt), Ib-River (22.3 Bt) and Jharia (19.4 Bt Out of the total coking coal resource of 32,073.32 Mt, the prime, medium and semi-coking types are 5,313.06 Mt, 25,053.13 Mt and 1,707.13 Mt respectively. Jharkhand (28.7 Bt) is practically the lone contributor of coking coal with minor resources from Madhya Pradesh (2.18 Bt), West Bengal (1.02 Bt) and Chhattisgarh (0.17 Bt).

The depth-wise breakup of the total resource reveals that about 65.6% of coal resource are confined within 0-300m depth level in which maximum share comes from Orissa (43.9 Bt), followed by Jharkhand (36.1 Bt) excluding Jharia coalfield, Chhattisgarh (31.4 Bt), West Bengal (12.3 Bt) and others. The superior quality non-coking Gondwana coal (belonging to Grades A, B and C) amounts to 30,677.81 Mt. The resource of intermediate quality (Grade D) stands at 31,680.38 Mt while resource of inferior quality (Grades E, F and G) coal is 1,14,945.41 Mt. Distribution of the superior quality non-coking coal depicts that Raniganj coalfield (10.2 Bt) is the major contributor (way ahead of other coalfields). The power grade coal at shallow depth (upto 300m) in the country are mainly available from Talcher, Ib-River, Mand-Raigarh, North Karanpura, Rajmahal, Korba, Godavari, Singrauli coalfields. (Coal Resources of India , Coal Wing, Geological Survey of India , Kolkata)

 
   
   
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