Thickener Underflow

What is a thickener tank?

 

Thickener tanks are a time and space-saving way of de-watering slurry, removing the waste silt and allowing the water to be recycled.

 

In the quarry environment, thickener tanks are used at the end of the wash plant process, after the cyclones. 

 

A lagoon on site can serve the same purpose, but these take up space, require maintenance, and are much slower as it takes a long time for the silt to settle out. 

 

Thickener tanks are becoming more and more popular and are now regularly seen on inner-city sites, wharfs, quarries and on sites that are no longer able to use their lagoons.  


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 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. From a spares perspective they are the most cost effective pump 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 are the most cost effective of the three types of pump we feature here and unlike centrifugal pumps, the slurry doesn’t have to be watered down. 

 

The pumps however carry the shortest lifespan while 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, peristaltics 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. 

 

For an overview of how a peristaltic pump works, please see here.


LSM – the only peristaltic pump brand you need!

 

Danish based LSM Pumps are one of the world’s leading peristaltic pump manufacturers and Atlantic Pumps are 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 now available for hire. Our hire fleet gives you a low risk and capital free way of trialing the cost and downtime savings that are available to you.

 

A full overview of the LSM range, can be found here.

 

For all enquiries regarding pumps for thickener tanks, please call +44 (0)800 118 2500.