Dry beneficiation of coal fines using air table

Abstract

Wet processing of coal requires a large quantity of water. Waste generated from wet process ties up a significant amount of water and land. The slurry ponds also pose serious problems in case of dam failure. Dry beneficiation is coming up to be considered a feasible alternative, at least in coal preparation. Air table works on shallow bed fluidization principle in combination with the principles of a settling in wet shaking table separating the particles on the basis of specific gravity. It was observed that particles above 1 mm size cannot be effectively separated in air tables. For reasonably good separation the feed must have a narrow size range. Ultrafine particles are likely to be lost. The performance is affected by several process variables such as feed flow rate, air flow rate, deck eccentric speed, side tilt and end raise. The optimization of the process in terms of the operating variables has been performed in the present work using statistically designed experiments. The separation performance is influenced by a strong interdependence of the process variables. A mathematical model for the yield and ash content of the clean product was developed. In the present work, coal from Kuju area with a feed ash of 34.2% was used as the feed material. The product ash was reduced to 30.15% with a yield of 66% at a side tilt of 30 mm and 18.3 Hz eccentric speed expressed in terms of frequency. It was found that size also plays a dominant role. A narrower size range of feed gives better separation. It was observed that a small change in side tilt and eccentric speed affects the yield significantly. The separation efficiency is governed mostly by air flow rate and end-raise. However, the characteristics of coal play a major role with respect to dry beneficiation.