Gravity seperation and desliming of fine coal: pilot-plant study using Reflux Classifiers in series

Two pilot-scale Reflux Classifiers (600 mm × 600 mm cross-section) arranged in a cascading sequence were used to beneficiate fine -2 mm coal. The first Reflux Classifier performed a density separation that produced a coal product contaminated with fine high-ash slimes. This was then washed in the second Reflux Classifier to remove the fine clays and mineral matter. This combination reliably produced a clean coal product and allowed gravity separation performance to be extended from the usual eight-fold limit of upper to lower size to a much broader size range. Performance was similar to previous laboratory-scale results units with cross-sectional areas of only 100 mm × 80 mm each. Hence, full-scale desliming units can be confidently designed based on laboratory trials. The cut size varied linearly from 0.04 to 0.24 mm with increases in the overflow channel velocity from 25 to 55 m³/(m² h). The Ep values increased from 0.02 to 0.07 mm (Whitten factor α from 2 to 6) over the same range. The linear dependence of the cut size on velocity in the Reflux Classifier was consistent with the theory and with the significant throughput advantage of the technology