The company stated this further extends the benefits this innovation offers in fine coal beneficiation.
Faan Bornman, Multotec technology manager, said that the Multotec SX10 low density spiral's reduced cut point of 1.55g/cm3 delivers considerable advantages over the cut points of between 1.6/cm3 and 1.8 g/cm3 that are typically achieved in the industry today.
The result, according to Bornman, is a cleaner coal with less waste being achieved in a single stage. This saves on capital costs as no further spiral stages are required for cleaning down the line. The approach taken with the Multotec SX10 spiral is to remove the gangue, or mineral containing particles, from the trough in two offtakes.
The first offtake removes ash. This opens up the available separation surface of the spiral, allowing the remaining material to separate more easily, separating clean coal from less-clean coal.
"The low-density spiral is essentially a primary and secondary stage on one centre column," explained Bornman. "Rejects are discarded into the centre column and the remaining product is re-pulped before being sent to a secondary offtake."
A longer spiral on the Multotec SX10 facilitates the two offtakes. This increases the residence time and gives the particles sufficient time to separate.
Depending on the setting of the product box splitters, this new spiral can produce a thermal coal and a coking coal on one spiral. Bornman noted that this was proven through testwork done in the US. The two offtakes enable the removal of most of the gangue, leaving middlings and cleaner coal products to be collected at the dart splitters.
Experimental work was carried out using coal from two South African collieries as well as doing site testwork in the US. Promising results were obtained, leading to the first order for Multotec SX10 spirals from a mine in North America.