Quality of coal for Indian Cement Industry
Coal is the main fuel for the manufacture of cement in India, given the high cost and inadequate availability of oil and gas. The consumption of coal in dry process system ranges from 20-25per cent of clinker production. That means 0.20-0.25 T of coal is consumed to produce one tonne of clinker. The cement industry consumes about ten million tonnes of coal annually. Since coalfields like Bharat Coking Coal Limited (BCCL), Central Coalfields Limited (CCL) supply poor quality coal, the industry has to blend high-grade coal with it; imported coal attracts a customs duty. The power sector is the largest consumer of coal followed by the iron and steel and cement industry. The current coal consumption is about 600x106 T, out of which about 85x106 T is imported.
Coal is a type of combustible carbonaceous rock, with different organic and inorganic constituents, formed from accumulated vegetable matter that has been altered by decay and various amounts of heat and pressure, over millions of years. Coal varies widely in its composition. It is composed chiefly of rings of six carbon atoms joined together in an extremely complex composition of layered arrangements that have in them, not only hydrogen but significant amounts of oxygen and nitrogen. The structure also includes varying amounts of sulphur and other environmental pollutants. Coal is usually analysed for moisture, volatile matter, fixed carbon and ash. The sulphur and nitrogen content are important, as emissions of their chemical oxides during coal combustion pollute air.
Typically, Indian coal is characterised by the following quality aspects:
- Lower to medium grade.
- High ash.
- Low moisture.
- Low sulphur.
The major issues faced by the coal industry since last few decades, leading to further quality deterioration, are as follows:
- Increased production from lower seams.
- Lower liberation size (coal is required to be reduced to relatively small size to improve yield).
- Low washability index (coal is difficult to wash when the index is low).
- Enhanced production from mechanical open cast mines consisting of larger dirt particles and foreign Materials.
- Depletion of good quality coal seams (coking as well as thermal coal).
As a result, the calorific value of coal has come down from nearly 5,250 to 3,500 Kcal/kg, in the last fifty years.
Owing to a very wide spectrum of coal usage, ranging from power generation to steel production to infrastructure and commercial usage, the technology of coal by washing needs to be improved, to reduce the environmental impact, enhance coal quality and increase process efficiency. The Central Institute of Mining and Fuel Research (the erstwhile Central Fuel Research Institute, CFRI) have developed the following processes for coal beneficiation:
- Improved froth floatation process.
- Oleo flotation process.
- Oil agglomeration process.
Coal washing and coal beneficiation processes require major thrust in terms of developing strong research cells for developing better practices, suiting requirements of all the coalfields of India.
1. The Indian coal sector: Challenges and future outlook, Indian Chamber of Commerce, 2012
2. Technologies for Coal Beneficiation in India, Haldar D. D., Central Institute of Mining and Fuel Research, Dhanbad, India.