366 with difficult cleaning characteristics. Indian coals are drift origin and hence tend to have high ash and difficult washability characteristics because of the presence of high neargravity material (NGM) since the impurities are intimately present in the coal matrix. NGM possesses a relative density close to that of the separating liquid or dense medium employed to separate the coal and the impurities present in raw coal. NGM becomes more difficult to separate due to the fact that it takes very long to settle in the dense-medium because its density is similar to that of the medium. This enhances the likelihood of material that is supposed to report to float incorrectly reports to sinks and vice versa, thus adding up to more misplaced material". It is the amount (%) of material with relative density in + 0.1 of separation density. The modern high efficiency plants are able to separate quite easily even when NGM (RD50±0.1) is as high as 25 wt%. In LVMC coals, NGM content is usually high (~50%) at the preferred specific gravity of cut, mean raw coal ash is up to 35-50%. Owing to close mixing of finely disseminated coal and shale such coals possess very poor liberation properties; even progressive crushing to 15/13 mm does not yield much to clean coal. The washability potential of such coals are so low that the available old washeries with conventional washing technologies cannot provide coals of ash 17-18% as required by indigenous metallurgical industries and cannot compete with foreign coals due to poor yield of clean coal at 17-18% ash. Therefore, such coals are supplied to other industry, contrary to increasing metallurgical coal demand for coke production and hence wasting of limited coking coal reserves. Subsequently, it was found that washed LVMC coal possess coking potential and can be used for coke making in steel industry through blending. Observing this, these LVMC coals are placed under coking coal category as washery grade, W-V (ash- above 35% up to 42%) & W-VI (ash- above 42% up to 49%). The country has a moderate reserve of LVC coal, about 40% of the total coking coal reserve. In the year 2024-25, production of LVMC coals (W-V &VI) in India was 26.5 Mt, about 40% of the total coking coal production (66.5 Mt). However, out of 66.5 Mt of coking coal produced in FY 202425, only 18 Mt of coking coal was feed to washery for beneficiation to produce about 5.9 Mt of metallurgical washed coal and imported 57.6 Mt to meet the demand of coking coal to produce metallurgical coke. Over the last 5 years, about 20-25% of coking coal produced was washed before utilisation with average yield of 40%. The reason for diversion of coking coal to the non-metallurgical sector is gradual deterioration in the quality of raw coal over the years due to depletion of good quality coking coal reserves leading to poor performance of old washeries. The conventional washing technologies of old washeries are unable to supply coals of ash 17-18% as desired by steel industries. Advance beneficiation has been identified as a requirement to cater the deteriorating raw coal quality (LVMC coal) and meet the increasing demand of metallurgical coal in India. This will reduce import of coking coal and saves exodus of FOREX Reserves. New research has emphasised the implementation of new technologies of beneficiation in order to have improved clean-coal recovery from high ash coal. Most of the Indian coking coal washeries are already operating at 13 mm as top size of coal for coarse coal washing, at the same top size the yield of clean coal with 18% ash is poor. Decreasing the top size to below 13 mm enhances the liberation and hence the recovery of clean coal and ease of washing also enhanced due to distribution of NGM to higher gravity section. Intermediate Size Beneficiation (ISB) and Advanced flotation cell technologies have identified reducing ash % without sacrificing yield. ISB utilizes intermediate circuit (3rd circuit) versus the standard two-circuit layout (coarse and fines circuit) for processing fine coal of size range (1/0.5mm – 0.25/0.15 mm) and is able to enhance 2-4% clean coal yield with same ash level.
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