Bulk bag unloading plant solves toxic dust problem 07 January 2013

An automated system that completely contains toxic dust during sodium silicofluoride powder (Na2SiF6) additions at large-scale water fluoridisation plant has been developed and implemented in Australia by ProMinent Fluid Controls.

ProMinent sales manager Neville McKee explains that the company supplied equipment for five plants in Queensland ranging in size from 125 MLD to 750 MLD, and serving more than 50% of the population of the territory.

Na2SiF6, he says, is contained in a sealed transfer system from the time it is received until the moment it enters the mixing tank. Dust control is important, because the plants use up to 875kg/day of Na2SiF6, and the substance is toxic and subject to strict regulatory control.

In operation, bulk bags of Na2SiF6 are unloaded into a transition or floor hopper, from which a flexible screw conveyor transfers the material to a storage hopper that feeds the mixing tank.

The transition hopper is small, with a capacity of only 60 litres. In contrast, storage hoppers may be as large as 8,750 litres or more for a 750 MLD plant, and designed to hold up to seven days' supply of Na2SiF6.

The major pieces of equipment are the bulk bag discharger, a dust containment system, and the screw conveyor, all supplied by Flexicon (Australia).

In brief detail, 1,000kg bulk bags are lifted into place on the discharger frame by an electric hoist and trolley on a cantilevered I-beam. Powder is then discharged into the transition hopper through a double-wall Tele-Tube telescoping tube. The tube is secured to the bag spout by a patented Spout-Lock clamp ring that creates a dust-tight seal, while the bottom of the tube is connected to a collar in the lid of the sealed hopper.

McKee explains that the open clamp ring is raised pneumatically to the bag spout, which is pulled over the rim of the tube's inner wall, with the ring being locked in place over it. Pneumatic pressure is released, causing the telescoping tube assembly to exert downward pressure on the spout, which keeps the spout taut and helps maintain steady flow.

The dust extractor remains inactive throughout the unloading process. However, air displaced by the flow of material exits via the dust collection system. A filter prevents Na2SiF6 from being entrained in the outflowing air.

Brian Tinham

Related Companies
Flexicon
Prominent Fluid Controls (UK) Ltd

This material is protected by MA Business copyright
See Terms and Conditions.
One-off usage is permitted but bulk copying is not.
For multiple copies contact the sales team.