Coal Beneficiation

A key priority for power producers to reduce ash content

Owing to its drift origin, Indian coal  is of poor quality and often contains 30-50 per cent ash when shipped to power stations. Over time, the ash content of Indian coal has increased with the depletion of good quality coal reserves, expansion in surface mining and mechanisation in coal mining. This has led to a growing thrust on coal washing in the country. Further, ensuring compliance with the Ministry of Environment, Forest and Climate Change’s (MoEFCC)  directive of limiting ash content to 34 per cent for plants situated over 500 km from the pithead has led to an increased thrust on using washed coal by power producers.

Besides ensuring compliance, the use of washed coal at thermal power plants (TPPs) offers a host of advantages to power producers. Burning of washed coal significantly reduces smoke (greenhouse gases), dust and ash emissions from the plant. It also improves the plant load factor and plant availability, and reduces specific coal consumption and wear and tear of the coal handling plant, and other equipment. Apart from this, the transportation of washed coal lowers the rail and port requirement. It also mitigates harmful environmental impacts and energy wastage.

Policy and regulation

In order to restrict the transportation of high ash coal for power, the MoEFCC, in November 2014, issued a directive for supplying coal of not more than 34 per cent ash content for TPPs located beyond 750 km from the pithead with effect from January 1, 2015 and those located beyond 500 km from the pithead with effect from June 5, 2016. Further, the notification mandates that all new (as well as expansion) opencast projects of 2.5 million tonnes per annum (mtpa) and above capacity, which are not linked to pithead power stations, should be designed with integrated washeries. The MoEFCC’s notification is applicable to coal producers and consumers and, therefore, both power plant developers and coal mine owners are required to submit a quarterly report on the quality of coal supplied and used.

Notably, industry experts suggest that in the coming years, the transportation of coal with over 34 per cent ash content is likely to be allowed only up to 250 km. This would curtail the use of unwashed coal to a large extent.

Existing coal washing capacity

As per Power Line Research, the coal washing capacity in India is around 184.82 mtpa across 60 washeries. While in the non-coking coal segment, there are a total of 41 washeries aggregating 151.42 mtpa of capacity, in the coking segment, there are 19 washeries aggregating 33.4 mtpa.

In terms of ownership of washeries, of the 60 washeries, 15 are owned by Coal India Limited (CIL) and the remaining 45 are owned by the private sector and PSUs. In the coking coal segment, CIL operates 12 coal washeries aggregating 23.3 mtpa and the PSUs operate seven washeries aggregating 10.01 mtpa. On the other hand, in the non-coking coal segment, CIL operates three washeries aggregating 13.5 mtpa and private players operate 38 washeries aggregating 137.92 mtpa. The key private players operating in the non-coking coal washing segment are ACB India Limited (19 washeries with 76.71 mtpa capacity) and Gupta Coalfield & Washeries Limited (10 washeries with 35.05 mtpa capacity). Some of the other private players in the coal washing segment are Bhatia International Limited, Jindal Steel & Power Limited, Indo Unique Flame Limited, ST-CLI Coal Washeries Limited and BLA Industries.

Coal washing technology

In India, the popular technology for coal washing is wet washing. Broadly, wet washing of coal is undertaken with jigs and other dense medium separation (DMS) methods such as cyclone and baths. Jigs are gravity separators mostly used for coarse coal. On the other hand, dense medium gravity separation methods use a material such as magnetite to form a medium denser than water to assist in separation. In coal washing undertaken through cyclone, which works on the principle of DSM, the higher specific gravity fractions that are subject to greater centrifugal forces pull away from the central core and descend downwards and pass out as rejects/middling. Meanwhile, the lighter particles are caught in an upward stream and pass out as clean coal.

An emerging technology for coal washing is dry washing, which is done with the use of blowers. This is best done at the mine face, with the use of optical analysers and air blast separators. This technology is yet to witness uptake in India and is currently used in countries like Australia.

An important aspect with regard to coal washing is the partial washing of non-coking coal. Under this, less than 13 mm particles are left unwashed and only over 13 mm coal are washed. The washed product (from +13 mm washing) is then blended with unwashed coal to obtain an overall ash content of 34 per cent in coal. However, this is not always successful in meeting the less than 34 per cent ash content criterion as the run-of-the-mine coal has varying quality seam-wise.

Upcoming coal washery capacity

CIL has planned to set up 15 coal washeries with a total capacity of 94.1 mtpa – six coking coal washeries aggregating 18.6 mtpa of capacity and nine non-coking coal washeries with a total capacity of 75.5 mtpa. Of the total 15 washeries planned under Phase I, three are already under construction – Madhuband (5 mpta), Paterdih (5 mtpa) and Dahibari (1.6 mtpa) – with a total capacity of 11.6 mtpa and expected to be commissioned in 2017-18. In addition to this, five new washeries, one of 2.5 mtpa capacity by Bharat Coking Coal Limited (BCCL) and four aggregating 16.25 mtpa by Central Coalfields Limited, and two deshaling plants aggregating 4 mtpa by BCCL have been planned for coking coal. Apart from this, BCCL plans to undertake the renovation of five existing coking coal washeries aggregating 6.83 mtpa to improve capacity utilisation.

Issues and challenges

One of the biggest challenges faced in the development of coal washeries is the non-availability of non-coal-bearing and non-forest land in the vicinity of coal mines. Besides, legacy issues such as problems in land acquisition and delays in obtaining land and environmental clearances hamper the development of coal washeries. The paucity of water for washing purposes during the operations of the washery is also a challenge. Another challenge in the coal washery operations pertains to the handling of coal washery rejects. In the absence of sufficient land in the vicinity of the mines for setting up a reject-based plants, the utilisation of washery rejects in an environment-friendly manner becomes difficult. In this regard, some of the steps undertaken by CIL include the setting up of washery reject-based fluidised bed combustion (FBC) power plants with NTPC, the signing of a long-term MoU with FBC-based producers for the utilisation of rejects, and the sale of unused washery rejects through the e-auction route.

With regard to the uptake of washed coal by TPPs developers, a key challenge pertains to the misleading perception that coal washing increases the cost of electricity generation. This notion is linked to issues with coal quality. The quality/ grade of the raw coal received by coal washeries from the coal companies does not correspond to the quality of coal for which the consumer has been charged by the coal company. Notably, the yield of washed coal is directly proportional to the quality of the raw coal received from the mines. This issue can be tackled by the installation of auto samplers at the coal mine, which would track the quality of coal produced at the mine and that supplied to the washery. Overall, it is essential to incentivise the power plant developer to opt for washed coal, as the existing coal washing capacity is not being utilised fully.

To conclude, in the coming years, the coal washing industry is expected to expand significantly, primarily on the back of growing environmental awareness, the need for enhancing the operational efficiency of TPPs and the imposition of stringent environmental norms. Industry estimates suggest that there is a gap of around 267 mtpa in the country’s washing capacity. This gap is expected to widen further with the implementation of the MoEFCC’s stipulations.

Going forward, the setting up of upcoming and under-construction coal washeries needs to be expedited. It is also necessary to ensure that the mode of execution of future coal washeries is in the best interests of all stakeholders, including power plant developers, coal mine owners and electricity consumers.

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