Thickener Control using Turbidity measurement.

A

Thread Starter

Anonymous

Hello to all.

Could anyone tell me any experience about controlling a thickener (minerals industry, tailings or concentrate) using turbidity measurements (or solids% measurements in the overflow)? In theory, this measurement could be used to modify the flocculant dosage (instead of using a ratio control: flocculant/mineral pulp) in order to optimize the agglomeration/sedimentation process and reduce the solids in the overflow. I believe there are some experiences using bed level measurement, but couldn't find anything about turbidity.

Thanks in advance!
 
W
Turbidity isn't likely to work. Density, on the other hand, should work fine, and there is a long history of density control of thickener underflow in the mining industry. You can use nuclear density or any other density meter that will stand up to the abrasion in the underflow.

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Derrick Stableford

Most thickener controls are based on Sludge Blanket Detectors, for the feedback of sludge build up. It's a slow process, so expect a reasonable length of time before getting a reasonable value back.

Also your process lab should be doing jar tests for the thickener polymer addition rates, and at what percentage strength of polymer. Also note that different makes and types of polymer react differently. You can't just plug in an equation.

Thickening is often an open loop system based on the lab results, and dosed proportionally to the volume of dirty water, with the sludge blanket detector used to draw down the thickened sludge to a sludge storage tank for further dewatering, and the resultant supernatant further processed.

Regards

Derrick Stableford
stablefordd @ ae. ca
 
P

Pierre Cochelin

I heard of turbidity measures being used for floc addition in wastewater treatment but I have no direct experience with it. I work in mining application where the important factor is sludge density instead of overflow clarity, and we typically use ultrasonic bed level measurement, and underflow density nuclear gauges.

But on a recent project the plant installed a settling time measurement device. It basically takes a sample of the water in the thickener, let it settles for a while and measures the thickness of the precipitate. This is guaranteed to minimize the amount of expensive floc added to the mix. Because when you think about it for a minute, the amount of floc should be inversely proportional to the settling time of the material in suspension, since you are adding floc to hasten the settling.

I found the instrument name in my archives:
Ciba Alcotech TC Micro, Automatic Flocculant Control for Thickeners. The contact at the bottom of the data sheet is:
PO BOX 38
Bradford
West Yorkshire
BD12 0JZ
Tel: +44 1274 417000
Fax: +44 1274 417779

Regards,

Pierre Cochelin, P. Eng.
Senior Automation Engineer
Met-Chem Canada Inc.
 
Hello to all.

I agree with Mr Cochelin for semi-feed-forward control, however feed back control is still a must, even if used in cascade with the Alcatech. There are faster and more precise methods of controlling overflow clarity than measuring it once it has flared. Try http://www.plapl.com.au and the "SmartDiver" that we manufacture. The device sends a turbidity (or other) probe diving down to profile the tank. You can then accurately see the solids profile and see a flare happening as it occurs. You obviously get a turbidity, settling zone and mud level reading at the same time. Try also http://www.mantacontrols.com.au who specialise in Thickener and CCD control. John Karageorgous from Manta is a well respected authority on this application.

Regards,
Nic Waugh
Precision Light and Air Australia
[email protected]
 
J

John Karageorgos

Hi,

Please let me know if you need any further information on thickener control. Glad to talk about it.

You can contact me at john.karageorgos @ mantacontrols. com. au

Regards,
John K.
 
C

Colin Howard

Oscillation has been manufacturing the Clarometer for over 20 years. It samples the centre well for settling time and so closely controls flocc addition. This helps stabilise the bed and control overflow turbidity.

Our bed level device, the VBI, measures bed height through a turbidity probe mud diver. Generally this is more of an assistance to under flow density control rather than flocc addition.
For photos, etc. of these devices, visit http://www.clarometer.com

Regards
Col Howard
 
B
Hello,

I want the total control system of thickener, i.e. how to control

1. Over Flow Clarity of thickener
2. Flocculant Dosing rate
3. UnderFlow Density and Flow Rate
4. BedLevel, Torque of Thickener
5. MassBalance of Thickener

Regards,
Badiujzama
 
Hello to all.

Could anyone tell me any experience about controlling a thickener (minerals industry, tailings or concentrate) using turbidity measurements (or solids% measurements in the overflow)? In theory, this measurement could be used to modify the flocculant dosage (instead of using a ratio control: flocculant/mineral pulp) in order to optimize the agglomeration/sedimentation process and reduce the solids in the overflow. I believe there are some experiences using bed level measurement, but couldn't find anything about turbidity.

Thanks in advance!
Hi,
We have a Settling Rate Monitor that measures turbidity in the thickener center-well to determine settling rate; and control both Flocculant & Coagulant dosing.
Talk to your local Nalco Water (Ecolab) representative and ask for the STORM Settling Rate Monitor.
 
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