Dissolved Air Flotation as a Floe Separation Technique in the Cleaning of Coal by Selective Flocculation

Abstract

The work defined the feasibility of using dissolved air flotation as a separation technique for coal flocs produced from a coal slurry by selective flocculation. The dissolved air flotation experiments determined the optimum air to solids ratio, which was correlated with the solids content of the flocculated suspension. For a single step selective flocculation process at predetermined conditions, the ash content of a pre-cleaned coal was reduced from 12.5% to 4.6% with 95% coal recovery. The total sulfur content of the cleaned coal was reduced from 1.1% to 0.9%. The use of dissolved air flotation for floc separation produced comparable ash rejection and recovery to floc separation by sedimentation, but reduced the total sulfur content to 0.7%. The optimum air to solids ratio was 0.8 mg air/g of solids. The air to solids ratio was a linear function of the solids content of the flocculated suspension. Two step selective flocculation/dissolved air flotation gave further cleaning. The ash content in the coal flocs was reduced to 2.7%, at a coal recovery over 90%. In some tests, over 90% of the pyrite was removed