Multotec Gravity Division says its new SX10 low density spiral further extends the benefits this innovation offers in fine coal beneficiation, with the technology able to produce both thermal and coking coal on one spiral.

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 coal industry today, according to Multotec Technology Manager, Faan Bornman.

The result, he says, is cleaner coal with less waste being achieved in a single stage. This helps achieve savings 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,” Multotec said.

The first off-take removes ash, opening up the available separation surface of the spiral and allowing the remaining material to separate more easily. This separates clean coal from less-clean coal.

“The low density spiral is essentially a primary and secondary stage on one centre column,” Bornman said. “Rejects are discarded into the centre column and the remaining product is re-pulped 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, according to the company.

Depending on the setting of the product box splitters, this new spiral has the ability to produce both thermal coal and coking coal on one spiral, Multotec claimed. Bornman said this was proven through test work done in the US where 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 Africa collieries as well as doing site test work in the US. Promising results were obtained leading to the first order for Multotec SX10 spirals from a North America-based mine, it said.