Coal Preparation » Dewatering
This project has considered three important concepts that were shown to offer industrial potential to reduce the moisture content of horizontal vacuum belt filer cakes.
Initial bench scale testing indicated that the use of surface hydrophobicity modifying chemicals caused significant reductions in overall moisture for the coals tested compared to untreated flotation concentrate. However when compared to flocculated material the hydrophobicity modifying chemicals provided little benefit. It is noted that the coals tested were coking coals which may be considered to have a high natural hydrophobicity. A different outcome may well result for coals with lower natural hydrophobicity values.
Bench scale testing of alternate flocculent addition rates and conditioning indicated that a maximum reduction in moisture could be attained with 25g/t and one minute conditioning at 500rpm stirrer speed. However, no reduction in moisture was achieved on the plant when attempts were made to replicate these conditions industrially. A clear explanation could not be identified, but the observed results are considered related to differences in agitation regimes between the plant and bench set ups.
Significant moisture reductions were achieved on the bench scale by using a rubber flapper to manipulate the cake structure. The moisture reductions were replicated on a pilot unit installed on an industrial horizontal vacuum belt filter. For the flocculent conditioning cases tested, 0 - 4 percentage point moisture reductions were achieved. More than 2 percentage point moisture reductions were achieved in comparison to conventional plant operation.
The benefits were obtained for a 0 x 0.5mm concentrate at both bench and pilot scale. However, no benefit was determined on the bench scale for a concentrate treated by a classifying cyclone. No benefit was found for the classifying cyclone underflow or overflow samples.