Coal Preparation » Gravity Separation
This project evaluated the performance of a large diameter (1450mm cyclone diameter) high capacity dense medium cyclone, treating a full size range of -50+1.4wwmm at cut-points in the range 1.42-1.51RD and 17-45% NG (+/-0.1RD). A range of feed solids loading / M:C ratios (3:1 to 6:1), and feed pressure conditions were tested to identify the point at which this DMC would begin to exhibit performance deterioration in a low density, high near gravity separation environment. The performance assessment encompassed both the target coarse coal fractions and the non-magnetics in the medium samples to assess the limits at very fine size fractions. The outcome of this assessment showed similar performance to that of both smaller diameter cyclones and from higher density, low near gravity separations determined on this same cyclone in earlier studies. The performance of the cyclone only began to show deterioration at size fractions below a GMS of 1mm and it is only in these size fractions where the reported "breakaway" particle size would appear to have any relevance.
The detailed Ep by size data to very fine size fractions generated by this project enabled a model for this relationship to be proposed as a replacement for existing industry models that this study and others have demonstrated as being inadequate.
Application of an alternate empirical model for determination of volumetric split in a high capacity large diameter DMC was shown to provide far better correlation to the actual determined volumetric splits than historical empirical models that were demonstrated as being inadequate.
The performance sampling program from this high capacity, large diameter DMC circuit and the associated diligence to sample mass requirements, sample point assessments and data validation technique have also been described. This methodology produced accurate and reliable data sets for this installation and provides a suitable basis for similar large diameter DMC test programs at other sites.