Investigation on the applicability of advanced gravity separation for cleaning semi coking coal fines

Abstract

The beneficiation of fine coal from Kuju area in a teeter bed separator has been studied in the present investigation. This coal is of particular interest in view of the fact that it is a high ash, semi-coking coal and the clean coal can be used as metallurgical coal after blending with coking coal. The ash content of the feed coal is 36%. Only 4% of the material is less than 150 micron while nearly 60% of the material is larger than 0.5 mm. The washability characteristics indicate that the coal may be a good candidate for beneficiation using gravity methods in spite of a high ash level. Nearly 40% yield is possible theoretically at a target product ash of 15% using gravity separation. A set of 29 experiments was performed in floatex density separator (FDS) according to the Box-Behnken design of experiments to establish the influence of operating variables such as teeter water flow rate, bed pressure, feed flow rate and pulp density on the separation performance. A target product ash of 23% was used for this feed coal in a single stage cleaning. The performance was characterized in terms of the mass yield of clean coal and its grade (ash content). It was observed that at a higher bed pressure and higher teeter water the grade was poorer due to increase in the suspension density. The optimum conditions for maximum yield were observed at 5.41 KPa of bed pressure, 15 lpm of teeter water flow rate, 80 kg/hr of feed rate and 29.7% solids in the feed pulp. The maximum mass yield at the optimum conditions was found to be 64.3% in a single stage cleaning in the FDS. The cut point density was observed to be 1.57 at the optimum conditions. The applicability of the FDS for physical beneficiation of this coal sample has been established. A second stage of cleaning in the FDS or another unit operation would bring the ash level down to 17% for blending with metallurgical coal and use in the blast furnace.