A Perspective on Indian Coal Resources

By M.K. Sinha

Technical Director, Coal India Limited, Kolkata, India.

Introduction

India has fairly large coal resources, but they are small per capita compared to those of other countries. Efforts have been made in the last three decades to exploit the resources at a fast pace to meet the bulk of the energy required in the country. This paper outlines the Indian energy scene, the coal resource endowment, general coal classification and characteristics of Indian coals. The paper also develops an overall outlook for Indian coal. The resource status of different quality coal deposits is reviewed, the geo-mining conditions are highlighted and environmental and beneficiation issues are discussed. Finally, trends in development of Indian coal and the Indian coal industry are discussed in the context of the quality of coal resources and their exploitation.

Indian Energy Scene

The coal resources of India are estimated at 214 Bt coal as of January 2001, about 1% of the total world resources for 16% of the global population. Because of this resource abundance, coal has a prominent role in the energy scenario of the country. About 60% of the total energy consumption of India during the last three decades has been coal.

Coal production in India has risen consistently and dramatically from 72 Mt in the early 1970’s and is expected to reach 328 Mt in 2001-02 (88% being contributed by the State-owned Coal India Limited), making India the third largest coal producing country in the world. The Power Sector is expected to consume 76% of this production, Steel 5%, Cement 2.6%, and others the rest. The demand for coal in India is expected to increase further in the coming years, to about 510 Mt in 2006-07 and 775 Mt in 2011-12.

Indian Coal Resources

The workable coal deposits in India occur in only two geological formations. The Permian Gondwanas in the southeast quadrant of the country, bounded by 78o E longitude and 24o N latitude contain almost 99.5% of the total resources. There are minor deposits in the Tertiary age formations in the north-eastern Himalayas.

The Permian coalfields are generally aligned along prominent river valleys (e.g. Damodar-Koel, Son-Mahanadi, Pranhita-Godavari and Satpura). The individual coal basins represent a half-graben structural configuration. The beds have generally low to moderate dips and in places they are folded to form low amplitude sub-basins. Most of the faults are normal, but the density of faulting varies from coalfield to coalfield and from project to project. In general, the density of faulting is high in the Damodar Valley Coalfields and in parts of Satpura coalfields.

The estimated coal resources in 45 Permian and 17 north-eastern Tertiary coalfields are given in table 1. The coal resource estimations in India are based on the Indian Standard Procedure (ISP) for coal reserve estimation. According to the ISP, the reserves estimated within 200m of a bore hole or surface measurement are considered Proved, those within the radius of 200m to 500m from the observation point are Indicated and those within 500m to 1 Km of the observation point are Inferred. The reserves are further broken down into depths and grades (for Proved and Indicated categories) for individual coal seam with thicknesses >1 m to a maximum depth of 1200m.

Quality Classification of Indian Coal

The classification of Indian coals and lignites utilizes the three basic parameters of calorific value (CV), VM%, and Coke Type (Gray-King categories) Moisture % (M), Carbon % (C) and Hydrogen % (H). This classification scheme is summarized in table 2.

The general commercial classification of coals in India adopts a simple two-track approach. For coking coals, the ash content indexes the different coal grades. For non-coking coals, the Useful Heat Value (UHV) is utilized for grading. The UHV is a concept evolved for typically high ash Indian coals. This concept allows for deduction of heat value from the determined Gross Calorific Value (GCV) for ash content. The deduction increases with increasing ash content to reflect the heat practically lost in mineral matter combustion, in cinders, etc. The deduction is computed generally through the Ash and Moisture determination as UHV (Kcal/Kg) = 8900-138 (A+M) for non-coking coals.

The grading of coking coal and non-coking coal in India are shown below in table 3 and table 4.

Quality Characteristics of Indian Coals

There are three coal-bearing stratigraphic horizons of Permian age in India: the lower Karharbari Formation, the middle Barakar Formation, and the upper Ranigunj Formation. The coal in these formations is sub-bituminous to bituminous in rank, and usually contains high amounts of mineral matter. In addition, most coal in the Barakar Formation contains greater ash content than the other Permian coals. The lower ash coals of the Barakar formation are limited and are found generally in the Sohagpur, Chirimiri, Sonhat, and Bisrampur coalfields. The Ranigunj Formation, particularly in the Ranigunj Coalfield, has coals with relatively greater Vitrinite and VM content. The rest of the Permian coals generally contain high amounts (30% to 40%) of Inertinites. This, together with finely disseminated clay minerals, makes Indian Gondwana coals difficult to wash with poor yields of cleans.

In the Damodar Valley Coalfields of Jharia, Ranigunj, East & West Bokaro, Ramgarh and North and South Karanpura, the coals have coking properties. Some coals in the outlying Sohagpur and Pench-Kanhan coalfields also develop coking properties. The Jharia coalfield, however, is the only store-house of “Prime” coking coals in the country.

The Tertiary coals of the north-eastern Himalayas are limited reserves with different characteristics from the Permian coals. The Tertiary coals have higher sulphur contents (1.3% to 6.0%) compared to Permian coals (0.5%-0.7%). More importantly, their Hydrogen content (5.3%-6.6%), Atomic H/C ratio (0.86-0.74), VM content (41.2%-51.7%), and content of reactives (87.0%-98.0%) are greater than those of Permian coals.

The Indian coal resource estimation of 214 Bt is only for the reserves falling in the Proved and Indicated categories. An additional estimation that includes the Inferred reserves as well is presented in tables 5a and 5 b.

The relatively high ash content of Indian coals calls for environmental mitigation programs. Overall, however, except for the small resources of Tertiary north-eastern coals with relatively higher sulphur contents, Indian coals can be termed eco-friendly. Detailed testing programs indicate that the Class “a” trace elements of PECH classification (e.g. As, B, Cd, Hg, Mo, Pb and Se) are found in very small amounts in Indian coals. Arsenic concentration in coal ash is reported to be generally less than 50 ppm. Boron and Molybdenum are characteristically less than 150 ppm and Cadmium is less than 17 ppm. Despite the high ash content of Indian coals, the following other characteristics are generally "eco-friendly":

• Low sulphur and phosphorus content
• Low concentration of trace elements of greatest and moderate concern
• Low chlorine content
• Low iron content in ash
• High Ash Fusion temperature
• Refractory nature of ash
• Favorable Silica-Alumina ratios, which make up favorable slag-viscosity

Outlook for Indian Coal

The coal resources of India are significant but there are issues that need to be addressed for different utilization needs. These issues are presented below.

The prime coking coals constitute only 2.5% of the total resources. These coals occur only in the Jharia coalfield, which has been mined for more than 100 years, and they have difficult washing characteristics. It is therefore clear that imports of suitable coking coals are required for supplementing domestic needs. While similar conditions prevail for the medium and semi-coking coals, these resources are sufficient for use as coal blends for metallurgical purposes.

There is a relative paucity of low-ash superior non-coking coals in the country. The A, B, and C grades of coals are estimated at about 33 Bt or about 15% of the total (down to 1200 m depth); of which less than 50% occur at shallow depths of less than 300 m. Such reserves occur mostly in thin seams amenable only to costly underground mining.

There is a relative abundance of inferior non-coking coals in the country. Large reserves are available in thick seams, amenable to opencast mining. These coals and their exploitation have enabled India to enhance its power production over the years. Environmental mitigation measures for mining and for power generation operations are in place to minimize the impact of these activities. However, not all inferior coal-based power houses are sited at the pit-heads and coals for these power houses have to be brought in from distances up to 1800 km. This led the government to legislate against movement of coals with more than 34% Ash beyond 1000 km and to environmentally sensitive locations. Because of this legislation, suitable beneficiation and blending of such coals should be considered.

While it may be possible to enhance coal production to meet increasing demands, this enhancement will call for sustained and focused efforts, because there are specific geo-mining and coal quality conditions which need to be addressed satisfactorily. There are, for example, coking and superior non-coking coal seams with thicknesses less than 1.5 m that are not being mined presently and that will require exploitation. There are also large reserves of 2.5 Bt in pillars created by the earlier Bord & Pillar mining of generally superior grade coal seams. The short-wall method for extracting coal in thee pillars is being tried with 650 tonne shield support. In addition, there are 5 m to 20 m thick coal seams which are being worked presently by the Bord & Pillar method in one or two sections with stowing. Greater recovery is being attempted with the Blasting Gallery method. There are 20-40m thick seams with gradients of about 1 in 2, in the north-eastern region of the country where extraction through Descending Shield and Sub-level stoping methods have not been very successful. These conditions, in addition to the general occurrence of hard roof and frequent small faults, make underground mass mining difficult.

In open castable reserves, the coal with up to 1:5 stripping ratios have been found to be economically mineable by deploying HEMM, up to 24/96 Draglines, 20 Cum Electric shovels and 170t dumpers. The need for exploiting deeper reserves will call for larger equipment and systems. Surface miners have already been introduced for selective mining in flat seams. Suitable technology for selective mining in steeper seams is to be identified.

The exploitation of coking coal reserves, particularly the low volatile medium coking coals, is constrained by the high ash content, the difficult washability (20-25% yield for 17% ash in cleans), and the resultant high cost of beneficiation. The viability of a four product washery with cleans for steel plants, semi-cleans for foundries, and middlings for power plants and rejects is being examined. The environmental regulation forbidding movement of more than 34% ash coal more than 1000 km and to environmentally sensitive locations is going to be effective starting 1st June, 2002. Blending is being planned to control the ash in order to meet the stipulations by the dead line. However, to meet the requirement in the long run, Coal India is considering establishing new washeries, converting existing coal handling plants for washing, constructing small modular plants at sidings, and encouraging power houses to construct their own washeries. The concerns of the power houses about the high cost of washing, however, will need to be addressed.

In view of the above factors, India imported 11.6 Mt coking coals and 9.9 Mt non coking coals in 2000-01. The demand for coal has been projected as 511 Mt and 775 Mt by 2006-07 and 2011-12, respectively. The production planned by different agencies is given below in Table 6, with the projected production gap to be met by the following:

• Capacity building with additional investment.
• Joint venture mining by CIL with private entrepreneurs
• Private mining in 113 blocks allocated for captive mining, 26 of which have already been allotted.

¹Included in SCCL

Summary

India is moderately well endowed with coal resources which stand at about 214 Bt as of January 2001. Recent programs however, have been designed to update the reserve/resource classification systems on the lines of the UNFC, in order to determine the practical mine-ability of these resources. The coal quantity characterization systems in vogue are focused on the specific resource features and they can be readily compared and indexed with Alpen type classifications.

While the requirement of coking coals in the country can only be met with suitable imports, the need for almost all other coals can be met domestically. Large efforts, however, are required for upgrading the beneficiation and blending capabilities. In certain cases, even the import of low ash superior coals may become necessary. The upgrading of mining technologies to address geo-mining conditions will also be required.

The Government of India has already embarked on the road for economic liberalization in the coal sector. Mining blocks have already been identified for private sector mining for captive steel, power, cement, and other productions. An amendment to the Coal Mines Nationalization Act, to allow for free private mining, is being considered. It is also believed that the introduction of private players will also help address the various technical and commercial issues.