Coal - Formation, Types, Effect of Sulphur in Coal, Coal Distribution in World & India

Coal-  Also called as Black gold, second largest fuel source in global energy resources. Non-renewable sources, which include coal, oil and natural gas, have been the traditional sources of power for industry, transport and domestic users. Coal originates from the remains of trees, bushes. ferns, mosses, and other forms of plant life that flourished in  swamps and marshes millions of years ago. Important products are derived from coal by a process called pyrolysis-heating of coal in the absence of air which produces coke (a residue) and volatile matter such as coal gas, and a liquid known as coal tar.

Coal varies widely in important physical characteristics such as energy content, carbon percentage, moisture content, presence of contaminants such as sulfur, etc.

High-rank coals are high in carbon and therefore heat value, but low in hydrogen and oxygen. Low-rank coals are low in carbon but high in hydrogen and oxygen content.

Types of Coal and Their Characteristics
Coal Type	Percent Carbon	Heating Range Values (MMBtu/ton)	Heating Avg. (MMBtu/ton)	Moisture Content by Weight	Sulfur Content by Weight
Anthracite (hard coal)	86-97%	22 to 28	25	usually < 15%	0.6%
Bituminous (soft coal)	86-45%	21 to 30	24	usually < 20%	1.4%
Subbituminous (black lignite)	35-45%	17 to 24	18	20-30%	0.4%
Lignite (brown coal)	< 35%	9 to 17	13	as much as 45%	1.0%

Peat: Peat is the layer of vegetable material directly underlying the growing zone of a coal forming environment. The vegetable material shows very little alteration and contains the roots of living plants. Peat being the lowest rank coal and Anthracite the highest. It represents the first stage of Coal Formation.

Lignite(Brown Coal): Initially the peat is converted into lignite or 'brown coal'. In comparison to other coals, lignite is quite soft.

This is the softest, youngest, and wettest rank of coal, often referred to as "brown coal".

Lowest energy content,

Carbon content between 25-30%

Higher moister content.

Tendency to crumble

Lignite is used almost exclusively for electricity generation

Bituminous Coal(Black Coal):

Medium hard. Contains very little moisture. Carbon content between 60-86%

Widely used for power generation and in the steel and iron industries

Anthracite:

Hard. Highest carbon content.

Carbon content between 86-97%

Burns slowly.

What is the impact of Sulphur in Coal? Which Coal we should we choose based on Sulphur Content? How to reduce sulphur content in coals?

Sulfurous gases (primarily sulfur dioxide) produced by the combustion of fossil fuels are the major cause of acid rain and contribute to other pollution related health problems.

There are three ways to reduce sulfur emissions from burning coal; the first is through crushing/washing the coal which physically separates some of the sulfur from the coal. The second method is through the use of "scrubbers" which remove most of the sulfur from the combustion gases before they are released into the atmosphere. Lastly, plants can burn younger coals that contain less sulfur

World Distribution of Coal

l. China: Shansi, Shensi, Inner-Mongolia, Fenhe valley, Henan, etc.

2. USA: Pennsylvania (Anthracite field contributing 50 per cent of world`s anthracitc production). Appalachian-bituminous field, largest coal region of USA.

3. CIS: Donbas region (Ukraine), Kuzbas (Russia), Karaganda (Kazakhstan),

4. UK: Northumber Land, Durham, Yokshire, Midland

5. Germany: Ruhr, Westphalia region, Saar coat-field, Sexony

6. France: Alsace, Saar region

7. Poland: Siberia valley

8. Australia: New South Wales (largest coal producing region in the Southern Hemisphere)

Coal Distribution in India:

(I) Gondwana coals

In India 99% of our coal production comes from the Gondwana coals which are found in three geological units:

Upper Permian - a) Raniganj Formation               

Lower Permian- a) Barkar Formation b) Karharbari Formation

Karharbari Formation is the oldest formation in India where coal has been found. The Gondwana coals of Permian times are mainly found in the Peninsular Gondwana basins of India .

(a) COALFIELDS OF WEST BENGAL

RANIGANJ COALFIELD In west Bengal Raniganj coalfield is the important coalfield. This coalfield is the easternmost of the Damodar Valley Coalfields. The coalfields lie mostly in the West Bengal and partly (western portion) in Bihar . Next to Jharia coalfields, this is the most important coalfield in India . It is situated about 185 km north-west of Calcutta . The field is named after the town Raniganj which is situated in the south-eastern part of this field. The coalfield is surrounded by the Archean rocks on all sides except in the east. Coal bearing Gondwana strata lie beneath the alluvium cover.   Coals of the Barkar Measures are low in moisture (1-3%), low in volatile matter (20-30%)whereas coals of Raniganj Measures are high in moisture (3-10%) and high in volatile matter (30-36%). Other coalfields found in West Bengal are Barjora coalfield, Birbhum coalfield and Darjeeling coalfield.

(B) COALFIELDS OF JHRKAHND AND BIHAR

About one-third of the estimated coal reserves are distributed in the coalfields of Jharkhand and Bihar . Important coalfields of this state are Jharia, Bokaro, Giridih, Karanpura, Ramgarh, Daltonganj, Auranga and Hutar. Part of the Raniganj coalfield of West Bengal falls in this state. Coalfields of the Damodar valley are the chief source of metallurgical coal in the country and most of the iron and steel plants get coking coal from these fields. Relative significance has declined drastically from 47 per cent of total coal production of the country in 1970 to 26 percent in 1998-99. Consequently, it has come to second place among the coal producing states.

1. Damodar Valley Coalfields:

1. JHARIA COALFIELD Jharia coalfield is the most important coalfield in India . This is because this coalfield is now the sole is the prime depository of prime cocking coal. This coalfield is situated about 260 km northwest of Calcutta in the heart of Damodar Valley mainly along the north of this river. The coalfield lies within the district of Dhanbad. The field is roughly sickle shaped. The coal basin extends for about 38 km in an east-west direction and a maximum of 18 km in north-south direction and covers an area of about 456 sq. km. The general stratigraphic succession of the area is that the basement metamorphic rocks are overlain by the Talchir formation followed by the Barkar Formation which is the main coal bearing horizon. Above it comes the Barren Measures which is followed by the coal-bearing Raniganj Formation. The Raniganj Formation is the uppermost coal bearing formation in the Jharia coalfield. The coals of the Barkar Formation may be divided in to (i) low volatile coals containing upto 26% volatiles (ii) medium volatile coals containing 26-28% volatiles (iii) high volatile coals containing over 28% volatiles. The coals of the Raniganj Formation have slightly higher moisture content than the coals of Barkar Formation. 2. BOKARO COALFIELD This coalfield is in the form of a long narrow strip extending for about 64 km in an east-west direction with a maximum width of about 11 km in the north-south direction. The Barkar Formation is the chief coal bearing horizon. This field is divided in to two parts by Lugu Hills- East Bokaro and West Bokaro . East Bokaro coalfield: There are several coal seams with in the Barkar Formation. Lower coal seams are grouped as Karo Group in which there are 11 coal seams. Out of these seams Karo Lower Measures (19-64m) and Karo Upper Measures (8-16m) are worth mentioning. The moisture content of this coal is low and the coals are medium quality cocking coals. West Bokaro coalfield: The Barkar Formation is coal bearing and embodies 13 seams. The quality of the coal varies widely in this field. In most of the seams the ash content is high- greater than 25%. Most of the coals are medium cocking coals. 3. KARANPURA COALFIELD Just to the west of Bokaro coalfield lies the Karanpura coalfield. This coalfield is divided in to two parts – North Karanpura and South Karanpura . In Karanpura coalfield there is full development of Lower Gondwana and the younger rocks. In the North Karanpura a number of coal seams occur. The ash content of these coal seams is high. In South Karanpura there is good development of Talchir and Barkar Formation. Most of the coals of this area are non-coking.

(ii) North Koel Valley Coalfields:

There are three coalfields – Auranga, Hutar and Daltonganj in the valley of Koel river, a tributary to Son river. The Auranga and Hutar coalfields are in the same alignment with those of Damodar Valley while Daltonganj coalfield is somewhat north of axial line. Hutar and Daltonganj coalfields are of economic importance. In Hutar coalfield coal seams occur in Lower Barkar . A number of coal seams have been reported. The coals are low in volatile matter (12.6%) and ash content (17.67%). (iii) Deogarh Coalfields:  The Deogarh group of coalfields comprises three isolated Lower Gondwana sedimentary basins such as Jainti, Sahrjuri and Kundit Kuraiha. These basins forms a NW-SE trending belt and are located in the Santhal Pargana districts of Bihar . The coal seams are reported to occur in the Karharbari as well as Barkar Formation. The coals are high in ash and range in rank from Sub-bituminous B to high volatile bituminous B. (iv) Rajmahal Coalfields:  The coalfields of this area are assuming importance lately. The unique location of the coalfields at the southern bank of the Ganges offers a good possibility of supplying coals to major power stations of North Bihar , North Bengal and Bangladesh . Based on the coal of this region, a Super Thermal Power Station has been built at Farakka. There are five coalfields in this area. Coals of this region are sub-bituminous to high volatile bituminous in rank. (v) Hazaribagh Coalfields:  Girdih or Karharbari coalfield is the most important coalfield amongst the Hazaribagh group of coalfields. Some of the best coking coals were extracted from this coalfield. Besides, Girdih coalfield is the type area of Karharbari Formation. The coal from the seams are low in moisture (1.40-1.80%), low in ash (9-12.6%), low in volatile, low in sulphur (0.5%) and phosphorous (0.01%). (c) COALFIELDS OF CHHATTISGARH AND MADHYAPRADESH  About one-fifth of the estimated reserves of the country are located in coalfields of these states. Coalfields of these states are traditionally put into four groups: (a) Central Indian coalfields (Singrauli, Sohagpur, Umaria, and Johilla), (b) Satpura coalfields (Pench, Kanhan and Pathakhera), (c) North Chhattisgarh coalfields (Chirimiri, Kurasia, Bisrampur, Jhilimili, Sonhat, Sendurgarh, Tatapani-Ramkola), and (d) South Chhattisgarh coalfields (Hasdo- Arand, Korba, Mand-Raigarh). Madhya Pradesh and Chhattisgarh produced 29.2 per cent of total production in India . (i) Central Indian coalfields:    1.SINGRAULI COALFIELD This field is situated mostly on the border of Uttar Pradesh and Madhya Pradesh. While most of the field is in M..P. a part of it is situated in the Mirzapur district of U.P. In this coalfield coals have been found in Barkar and Raniganj Formation, there are four coal seams. These coals are useful for thermal power generation.   2. SOHAGPUR COALFIELD Sohagpur is another important coalfield in the Son Valley . Barmni-Chilpa fault trending east-west has divided this field in two parts. In the southern part of the fault there are 5 coal seams within the Barkar Formation. The coal contains 4 -7 %moisture and 20-27 % ash. The coals on the north of this fault are characteristically different from the coals occurring south of the fault. Coking coals have been found in the north of the fault.   3. UMARIA COALFIELD This coalfield is situated on the Umrer river a tributary of the Son river. The Lower Gondwana rocks are well developed in this coalfield. Six coal seams have been found in this field. The coals are relatively high in moisture (7-10%) and high in ash (18.6-29.4%).   4. JOHILLA COALFIELD This coalfield is situated in the Valley of Johilla River. In this field, Talchirs, Barkars and beds of Raniganj age are developed. Johilla seam is the most important seam in the northern area. The seam has a high moisture (10.8%), ash (17.9%) and volatile matter content (31.7%). (ii) Satpura Coalfields:  Satpura coalfields lie within the Pench-Kanhan-Tawa valley, south of Narmada river, known as Satpura Gondwana Basin . In this region, Gondwana lie in a syncline trending ENE to WSW. Important coalfields in this region are:   1. MOHPANI COALFIELD This coalfield is one of the country's oldest coal-bearing areas. It is situated in the west of Mohpani. In this coalfield, Talchir and Barkar Formations are overlain by the Upper Gondwana rocks of Bagra Formation (Mahadeva Group) and Jabalpur Formation. The coal seams in this area are weakly coking with moisture content ranging from 4 to 6%.   2. PATHAKHERA COALFIELD This is an important coalfield in the Tawa valley. In the vicinity of Pathakhera three coal seams have been encountered by boring. The top seam is of poor quality and the other seams are comparatively better in quality.   3. KANHAN VALLEY COALFIELD There are the most important coalfields of Satpura region. Coals of Kanhan valley are characteristically coking particularly in Damua, Kalichhapar and Rahikol collieries. The area is covered by Barkars. The area is intersected by number of faults. The coal in this region generally is of low moisture and ash content and is of coking quality.   4. PENCH VALLEY COALFIELD This area is situated in the north-west of Chindwara and lies in the east of Kanhan valley coalfields. The rocks of Barkar Formation are exposed in the area. Important coal seams are exposed in Gajandoh area, Barkuhi area, Chandamata - Dongar Chikhli area etc. (iii) North Chhattisgarh Coalfields:   1. TATAPANI RAMKOLA COALFIELD This coalfield is located in the Surguja District of Chhattisgarh and covers an area of about 260 sq.km.. It consists of two separate areas – the eastern and western. The eastern portion is called Tatapani area where 5 coal seams occur in the Barkar Formation. The coals in the area are non-coking with low ash content. The western part or Ramkola area is separated from eastern part by a patch of Upper Gondwana rocks called the Rajkhatra tract. There are 5 coal seams in the Barkar Formation. The ash content varies between 17 and 34%.  2. JHILIMILI COALFIELD This village is situated around village Jhilimili. The Lower Gondwana is represented by Talchir and Barkar rocks. The Talchir rocks are exposed towards the south of the field. Barkar rocks, consisting of sandstone, shale and coal seams mainly occupy the northern area. The coalfield may be divided in to three areas: (i) Northern area; (ii) Central area; (iii) Southern area. In the Southern area good exposures of coals have been noted from several parts Out of which Manikmara is important.  3. SONHAT COALFIELD This coalfield lies west of the Jhilimili coalfield forming the eastern extension of Sohagpur coalfield. The Barkar rocks which occupy the Sonhat plateau have been broadly divided in to three divisions. The lower division consists of more than 15 coal seams. The middle division is devoid of coal seams. In the Upper division although Barkar strata is of considerable thickness in the field, the number of coal seams and their thickness is poor.  4. CHIRIMIRI AREA Three seams of the Karakot horizon are the most important seams in this area. The composite seam is being worked in the collieries of Chirimiri, New Pouri (New Chirimiri) and Kurasia. 5. KURASIA AREA In the eastern sector drilling has proved the existence of workable coal horizon in this area. These are: Duman seam; Kaperti seam; Shorgela seam; and Kotmi seam. 6. BISRAMPUR COALFIELD This coalfield covers an area of about 1036 sq.km. Coal bearing Barkar rocks are developed to a thickness of about 150 metres. Several coal seams have been reported from different localities. In the south-western part of the field detailed prospecting conducted by Indian Bureau of Mines has indicated more than one horizon of coal. Pasang seam is the thickest seam in the horizon. The coal is of non- coking type in this seam. (iv) South Chhattisgarh Coalfields: 1.HASDO – RAMPUR OR ARAND (SURGUJA) COALFIELD This coalfield extends from Rampur and Paharbula Lappas in Arand valley to Hasdo river in Bilaspur district. This coalfield is divided in to four parts: The eastern or Rampur section in Rer (Arand) valley North central (Paharbula) area South Central (Uprora) area Western (or Mation) area beyond the Gej and Hasdo rivers The quality of coal in this field varies widely. The contents of moisture varies from 1.56 to 7.40% and ash from 11.26 to 25%. 2. KORBA COALFIELD Korba coalfield is located in Korba district of Chhattisgarh and covers an area of about 530 Sq.Km. The coalfield is named after the village Korba on the eastern bank of the Hasdo river which is tributary of the Mahanadi river. The Barkar Formation is the coal bearing measures. As per GSI a total of 10075 Mt. coal reserves available in Korba coalfield.  The deposits are restricted into two distinct zones: Thick seam/qurriable power grade zone comprising of grade E, F, & G having reserves of approx. 9068 Mt. Thin seam /underground superior grade zone comprising of grade B to D having reserves of approx.1007 Mt. 3. MAND-RAIGARH COALFIELDS These coalfields are situated in Raigarh district of Chhattisgarh and covers an area of about 520 sq. km. This coalfield comprising of grades A to G and having reserves of 18522.93 Mt. Here large potential for power grade coal are present and may be exploited through open-cast mining. (e) COALFIELDS OF MAHARASHTRA   (i) Coalfields of Nagpur region:    1. KAMPTEE COALFIELD  This coalfield is situated about 19 km NNE of Nagpur. This coalfield can be called as a hidden coalfield as the coal bearing rocks are not exposed anywhere. Later on geophysical prospecting technique was applied in this coalfield for the first time for exploration of coal in India . Detailed exploration has proved a large deposit of coal in the following three blocks: Ghatrohan area to the east of the Kanhan river Silewara area to the west of the Kanhan river Bina area to the south of the Kanhan river Five workable seams have been proved over the three blocks. The moisture content of the coals varies from 8 to 11% and the volatile matter from 33 to 43 %. The coals are non-coking.   2. BOKHARA COALFIELD  This field is situated 9 km north-west of Nagpur railway station. Seven coal seams have been proved. The moisture content of the coal seams varies from 8 to 11% and the volatile matter from 24 to 29 %. The coals are non-coking.   3. UMRER COALFIELD  Umrer is a small town situated about 44 km south-east of Nagpur . The coal bearing strata is nowhere exposed at the surface. The coal bearing Barkars rocks lie over Talchirs. There are four workable seams in the area. (ii) Wardha Valley Coalfields: The Wardha valley coalfields are situated in the valley of Wardha river, lying mainly in the Chandrapur district. The coalfields extend in a NW-SE direction extending over a distance of 115 km and cover an area of about 4130 sq. km. The coal bearing Barkar rocks are only 76 metres thick and occur in patches. Rarely coals are found in the outcrops. (f) COALFIELDS OF ANDHRA PRADESH In Andhra Pradesh important Coalfields lie in the Pranhita – Godavari Valley . In continuation of the Wardha valley there are coalfields in the Pranhita-Godavari valleys covering an enormous area of over 9000 sq. km. The Lower Gondwana rocks consisting of Talchir, Barkar and Kamthi are well developed in the area. The exposures of Barkar rocks are few. The coalfields are traversed by post-Kamthi faults. The characteristic of the coalfields is that these are devoid of igneous intrusions. Based on geographical and geological considerations, the Godavari valley coalfield is divided in to twelve coal belts. Ramagundam Coal belt is one of such coal belts located along the western margin of the Godavari valley coalfield. Important coalfields of the area Tandur Coalfield; North Godavari and South Godavari Coalfield; Karlapalli or Kamaram Coalfield; Ramagundam Coalfield etc.   (g) COALFIELDS OF ORISSA Out of 57 Gondwana and 14 Tertiary coalfields considered for the national inventory of the coal, Orissa state has only two-intact geologically only one and half coalfields. Yet its share in the reserve so far established in the country amounts to 23.6%. The famous coal bearing basins are Ib-River coalfields & Talcher coal fields and as a sequel to which these coal fields have been added advantage of being accorded most favored coal fields status by nature as far as qurriable potentiality is concerned. A substantial qurriable reserve has been located in northern part of Ib-River coalfield (Gopalpur area) and towards its south-eastern extremity in Khinda-Talabira area. Occurrence of coal seems has also been reported from Raniganj Formation of Ib-River coalfield very recently. The importance of Orissa coalfields is further enhanced due to their proximity to the east coast. Gondwana Coals occur in India mainly along the three master Gondwana basins, viz. Damodar Valley , Son-Mahanadi Valley and Gondwana Valley . Coalfields of Orissa constitute the southern part of the Son-Mahanadi Valley basin. Except the Ib-River coalfield and Talcher coalfield, there are Four more Gondwana basins in Orissa: a) ATHAGARH basin b) GAISILAT basin c) ATHAMALIK basin d) KATRANJIA basin. (h) UPPER GONDWANA COALS It includes coalfields of Gujarat . Sub-bituminous type of coal is found in association with Upper Gondwana sediments (Cretaceous) in the district of Kutch, Surendranagar and Mehsana district.