Low density spiral for the coal industry

16th July 2019

     

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A low density spiral with advantages for fine coal beneficiation, is now available.

The spiral has a reduced cut point of 1.55 g/cm3  which offers a number of benefits compared to the cut points of 1.6 g/cm3 to 1.8 g/cm3 that are currently achieved in the industry.

One of the potential benefits of the spiral is cleaner coal with less waste in a single stage. This could lead to a reduction in costs, as no further spiral stages are required for cleaning down the line.

The Multotec SX10 spiral removes the gangue, or mineral containing particles, from the trough in two off-takes.

The first off-take removes ash, which then 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,” explains Multotec technology manager Faan Bornman. “Rejects are discarded into the centre column and the remaining product is repulped before being sent to a secondary off-take.”

A longer spiral facilitates the two off-takes, which increases the residence time and gives the particles sufficient time to separate.

Depending on the setting of the product box splitters, the new spiral can produce thermal coal and coking coal on one spiral. The two off-takes 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 and testing was also conducted at sites in the US. The promising results led to the first order for the spirals from a North American mine.

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