Coal-sand attrition system and its` importance in fine coal cleaning. Seventh quarterly report, March 1, 1993--May 31, 1993

Abstract

For the four coals employed in this work, it was not possible to effectively grind the minus 50 mesh feed even at the lowest solids concentration range tried. The reason for this is the low feed rate which makes it impossible to obtain a uniform flow as the coarse particles in the feed tend to settle down and form sediment in either the tubing system or the grinding chamber. Besides, only moderate levels of solids concentration could be employed as high solids concentration are also fraught with sedimentation problem. Attempts to increase the flow rate resulted in the grinding media being taken out of the mill together with the slurry. As a result of these limitations posed by the instrument, further tests were restricted to using minus 100 mesh feed size and moderate levels of feed rate and Pulp density. Some of the results obtained are given in Tables I - 4 for the different coals used. It can be seen from the tables that the softest coal (Pocahontas No. 3 in this case) requires about 2 or 3 passes in order to obtain very fine product while the harder coals would require 4 or more passes. The number ofmore » passes required for the harder coals can be reduced either by increasing the residence time of the slurry in the mill by decreasing the feed rate or preferably by increasing the stirring speed. Both of these actions will inevitably lead to a slight increase in the media wear. The media wear observed in grinding Pocahontas No. 3 in three cycles was 1.3% while the corresponding values for grinding both Illinois No. 6 and Black Creek coals in four cycles were 0.5% and 1.5% respectively.« less