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A METHOD FOR PREVENTING FROTH FROM A FLOTATION PROCESS TO CONTAMINATE THE OVERFLOW CLARITY OF A THICKENER

TOP OF TANK

Froth forming above

liquid level

Extended tank

above overflow

level

Liquid level

Mixing chamber

extended above

centre of holes

Overflow

launder

Conical baffle

Annular opening

between mixing

chamber & conical

baffle opens a vertical

upward path for froth.

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A NOVEL WAY TO PREVENT FROTH FROM ENTERING THICKENER OVERFLOW

Conventional and High-rate thickeners are typically equipped with peripheral overflow launders.

The feed pulp to a thickener flows into a central feed well and liquid separated from the pulp then move radially outwards towards and over the periphery or through V-notches cut into the priphery. An overflow launder is provided to remove the recovered liquid.

Should froth form on top of the thickener this is carried over the V-notches and contaminates the overflow.

This ultimately culminates in great losses of sometimes very valuable concentrate.

In other cases it can lead to unacceptable dirty recovered process liquid which in turn can adversely affect the quality of the final product.

With the Magra-Ultrasep 2000 design the cylindrical tank section is extended around 600 mm above the ‘normal’ overflow level. and the feed well is raised around 200 mm above the ‘normal ‘ overflow level.

Multiple holes are now created where the V-notches were. Sizing of the holes are such that at maximum flowrate a level of about 200 mm above the hole centres is maintained.

Froth follows a path which extends vertically above the throat area surrounding the feedwell and when it surfaces spreads away from the centre to the outer periphery of the thickener floating on top of the liquid.

This means that froth does not interfere with the clear liquor flowing through the holes.

Froth now builts up and the tank wall being higher than the top of the feedwell allows the collapse of froth towards and into the feedwell.

Flow from the central dewatering pipe continues to wash away at the froth entering the feedwell effectively collapsing the air bubbles to which the concentrate adheres. Concentrate particles are now freed and settles out under gravity.

.

Outer thickener tank wall

Overflow launder

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Should the liquid level drop during low feed flowrates or during shut down or after starting up with a low liquid level exposing the discharge holes or part of it froth would also exit the holes.

In order to prevent froth from entering the holes during shutdown or low feed flowrates a pipe arrangement is installed which now allows overflow to be taken from the clear liquid zone below the holes and maintain clear overflow devoid from concentrate.

The height of the feedwell is adjustable by means of adjuster bolts in order to prevent overflow entering the top of the feedwell at maximum feed flowrate.

Adjustment of the feedwell is normally done during commissioning or when feed flow parameters necessitates it.

The feedwell could also have entry holes similar to the above and discharging at any determined level similar to the extended discharge below overflow level in order to introduce secondary feed dilution in addition to the dewatering dilution from the central dewatering pipe.

PROTECTED BY PROVISIONAL PATENT NO. 2005/02450