Scavenging of High-Value Product from High-Ash Medium Coking Coal: A Compulsion for Less Endowed Regions

Beneficiation of a high-ash (35%) medium coking coal to obtain a low-ash (12%) clean coal product is investigated. Characterization studies indicated that this coal can be processed after reducing the size to 1.18 mm in order to achieve reasonable yield of the clean coal at such a low target-ash level. The desired ash reduction is possible only after treating different size fractions of the -1.18 mm crushed coal separately. A gravity-based processing scheme comprising of a spiral-floatex circuit along with multigravity separator for the -1.18+0.5 mm fraction is developed to generate clean coal at 12% ash with 10.3% overall yield. Mechanical cell flotation circuit for the -0.5+0.15 mm size fraction resulted in additional 5.2% yield at 12% target ash level for the clean coal. A flotation circuit for the ultrafine fraction (-0.15 mm) is also developed using Jameson cell flotation that added further 4.4% yield in the overall mass recovery of the combustibles at the desired ash level. Thus, a total of 20% yield of the clean coal with 12% ash is achieved by treating various size classes separately. Application of the clean coal is recommended for metallurgical purpose. Out of the remaining 80% material, 35% is recovered at a 27% ash level that is recommended for use in sponge iron sector. The balance 45% with an ash level of 50% is marked for use in fluidized bed combustion for power generation. A complex flowsheet such as the one described in the present article is likely to be the future requirement for processing high-ash medium coking coals to a high-value low-ash product to enhance its utilization potential for metallurgical purpose.