In-plant testing of a novel coal cleaning circuit using advanced technologies. Technical report, September 1--November 30, 1995

A circuit utilizing hindered-bed classifiers, enhanced gravity concentrators and column flotation has been found to provide a highly efficient cleaning of fine coal in which both ash and total sulfur contents are significantly reduced while maximizing the recovery of coal. In this study, a circuit comprised of the three technologies will be tested in an operating preparation plant to evaluate circuit performance and to compare the performance with the current technologies used to treat fine coal. Prior to the in-plant testing, the effect of changing feed characteristics on the performance of the enhanced gravity concentrator was evaluated for process control purposes. During this reporting period, a {minus}16 mesh Illinois No. 6 coal sample containing about 30% ash and 8.0% total sulfur was collected from a refuse pond. The ash and total sulfur contents of the sample were depleted by withdrawing a controlled amount of tailings produced by the unit to determine the effect of changing feed compositions. It was found that higher combustible recovery values are achieved when the feed ash content is decreased and slightly lower product sulfur content values are obtained when the pyritic sulfur content in the feed is decreased. The lower total sulfur contents are most likely due to the natural by-pass to the product stream of 5--10% of the heavy particles. In other words, an increase in the feed sulfur content results in an incremental increase in the sulfur content of the product. The higher combustible recovery values obtained with decreasing feed ash contents are likely due to a reduction in the amount of entrapped coal particles within the bed of heavy-particles formed contiguous to the bowl wall in the Falcon unit. Higher bowl speeds and adjustment of the tailings rate have been found to counter the negative effects caused by the increase in feed ash and total sulfur contents