‘Low cut’ spiral technology has been taken to a new level thanks to Multotec Gravity Division and its new SX10 low density spiral. This further extends the benefits this innovation offers in fine coal beneficiation.
According to Multotec technology manager Faan Bornman, the Multotec SX10 low density spiral’s reduced cut point of 1.55 g/cm3 delivers considerable advantages over the cut points of between 1.6 and 1.8 g/cm3 typically achieved in the industry today.
The result, he says, 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 off-takes.
The first off-take 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,” Bornman says. “Rejects are discarded into the centre column and the remaining product is repulped before being sent to a secondary off-take.”
Facilitating the two off-takes is a longer spiral on the Multotec SX10. 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 has the ability to produce a thermal coal and a coking coal on one spiral. Bornman says this was proven through test work done in the USA. The two offtakes enable the removal of most of the gangue leaving a 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 test work in the USA. Promising results were obtained leading to the first order for Multotec SX10 spirals from a North America-based mine.
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