Performance optimization of a compound spiral for fine and ultrafine coal cleaning.

摘要

piral concentrators have been widely used in coal preparation plants to clean 1 mm x 150 micron particle size coal fraction, which is too fine to be effectively cleaned by heavy medium cyclones and too coarse for froth flotation cells or flotation columns. Conventional spirals are capable of providing excellent clean coal recovery, although at a relatively high ash content. Compound spirals, which provide two stages (rougher-cleaner) of spiral cleaning in a single taller unit, have been commercialized in recent years to improve upon the cleaning performance obtained from conventional spirals. The present study aimed at optimizing the performance obtained from a compound spiral for cleaning especially high sulfur fine and ultrafine coal.;Industrial-scale spiral units were utilized for this study in a pilot-scale facility at the Illinois Coal Development Park. A statistically designed experimental program was conducted to optimize ash and sulfur cleaning performance of the compound spiral. It was found that significant cleaning of ultrafine coal (i.e., 150 x 45 micron and even 45 x 25 micron size coal) is achievable with the compound spiral. However, operating conditions for cleaning finer coal fractions (-150 micron size coal) have to be significantly different from those used to clean coarser coal fractions (+150 micron size coal). The sulfur rejection trends were different from ash separation efficiency trends in all size fractions except 45 x 25 micron particle size fraction. The probable error (Ep) and effective specific gravity of separation (SG 50c) determined for the compound spiral cleaning of the overall particle size were as low as 0.07 and 1.62, respectively. However, the bypass of a small percentage of clean coal to the tailings stream of the compound spiral, may need further adjustment of the key process parameters. A preliminary economic analysis conducted in this investigation indicated that an annual profit of