Page 39 - Hub-4 Magazine Issue 67
P. 39

 Washing &
Screening
  How does a thickener tank work?
Thickener tanks are circular in design with a conically shaped- centre. The tanks vary considerably in size. Fluid enters the thickener tank via an overhead pipe and down into the centre of the tank.
At the bottom of the tank rotating rakes help the solids settle and draw the silt towards the centre of the tank. The water meanwhile flows over the edge of the tank and into an overflow before exiting at the side via a pipe. This is pumped away and reintroduced to the wash plant process.
The silt eventually exits the tank at the centre point underneath and is pumped away.
What pumps would you use in conjunction with a thickener tank?
While a light duty slurry pump can be used to pump the overflow water away from the thickener tank, there are three types of pump that can be used to remove the thickener underflow:
Centrifugal pump
Currently the most common pump to be used to remove the thickener underflow, a centrifugal pump is not necessarily the best option. Spares are relatively cheap and easy to obtain, however using a centrifugal pump carries a number of issues.
Firstly, the slurry has to be watered down to go through the pump, which is somewhat counter-productive. Also, as it is a batch process, solids can settle in the pump when it is switched off. Stray solids can also jam the pump; if blockages occur, they are very difficult to rectify.
These pumps are not self-priming, meaning they have to be located directly below the tank to ensure suction, this makes access more difficult. Seal leakage is also a common issue due to back pressure which can in turn cause premature bearing failure.
Screw pump
Not as common as centrifugal pumps, screw pumps would appear to be very suited to this application. Unlike centrifugal pumps, the slurry doesn’t have to be watered down. The pumps however carry the shortest lifespan and spares can be very expensive. The pumps also have narrow tolerances so extraneous solids are catastrophic.
Peristaltic Pumps
Peristaltic pumps are by far and away the best pump option to use with this type of application.
Although reasonably expensive to purchase, they are the most cost-effective option, are long-lasting, easy to repair and spares are relatively cheap to purchase.
Unlike centrifugal pumps, peristaltic pumps are self-priming, so can be located further away from the tank and the slurry doesn’t need to be watered down.
Peristaltic pumps also have the ability to run backwards allowing blockages to be cleared, they can pump a higher solids percentage and the flow rate of the pump can easily be controlled.
Furthermore, peristaltic pumps offer the lowest energy consumption of the three types of pump we feature.
Danish based LSM Pumps are one of the world’s leading peristaltic pump manufacturers with Atlantic Pumps being the companies’ exclusive UK distributor.
The company produces a range of different sized peristaltic pumps and the pumps are known for their low energy consumption, low and easy maintenance, and their exceptional build quality.
LSM pumps are also available for hire. Atlantic’s hire fleet gives you a low risk and capital free way of trialing the cost and downtime savings that are available to you.
For all enquiries regarding pumps for thickener tanks, please contact Atlantic Pumps on 01246 284 420.
 www.hub-4.com Mar-Apr 21 - Issue 67
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