Dewatering: Thickening, Filtering, CCD, Water Treatment & Tailings Disposal

Dewatering: Thickening, Filtering, CCD, Water Treatment & Tailings Disposal 2017-03-23T09:42:05+00:00
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Sizing a high rate thickener (8 replies)

Zander Barcalow
1 year ago
Zander Barcalow 1 year ago

During the last decade, various methods have been utilized in sizing a thickener such as Coe and Clevenger, Talmage and Fitch and Wilhem-Naide. Which method is superior (recommended) in sizing a high rate thickener? Which value of impact factor is recommended in sizing a high rate thickener?

OberstGruppen
1 year ago
OberstGruppen 1 year ago

Firstly, let’s define Hi-Rate Thickening. The development of modern polymers which could achieve settling rates one or more orders of magnitude higher than lime, starch or other agglomeration additives in common use at the time came with a twist - an optimum feed concentration operating window. In this window, the floc dose is minimized, the solids loading onto the polymer chain and flux rate are maximized. These factors are critical to performance so in order to model/size a Hi-Rate Thickener, first you need to know the optimum feed solids concentration for flocculation and settling. Once you have the right set of data, you can consider how to predict behavior.

Regardless of which model you use, if you are not doing your test work at the optimum solids concentration - which can quickly be determined - you are starting from the wrong place.

Of the models you list, these were developed to predict underflow density as a function of time using a jar settling curve. The models are based on flux (area) and do not take into account bed depth or raking which are beneficial to the de-watering of the bed and the underflow solids concentration. These models will oversize the thickener - C&C being the most conservative, W-N the least.

Some OEM's (FLSmidth, Outotec - perhaps others) uses a dynamic testing as well as / in place of static tests. There are models for these but they are proprietary!

AMIRA have spent quite some time looking into thickener modeling and prediction - there have been some good papers published.
However, in very simple, practical and boring terms, if you want to know how big a thickener should be, you are best asking someone who supplies thickeners. They have to live by their track record.

Final point - as long as the thickener is designed in the knowledge that it is oversized, you should always think about the downstream process. While a thickener should never be treated as a storage tank (but a tank with an agitator) some "upside" in the thickener size has got many a metallurgist out of jail.

Unterstarm
1 year ago
Unterstarm 1 year ago

If I were you, I will not read literature/talk to people and start selecting a thickener (high rate or otherwise); the material/pulp characteristics and reagent type etc have to be established based on experimental studies and also discussions with manufacturers. Wrong selection can lead to disaster in all the other operations.

Zander Barcalow
1 year ago
Zander Barcalow 1 year ago

Thanks a lot for your valuable comment

you mentioned that these methods of thickener sizing would led to oversize a thickener. Can we utilize these methods along with smaller values of safety factors? Which values of safety factors do you recommend?
Also is there any especial method to predict the underflow solids concentration precisely?

About conventional thickener sizing methods(C-C, T-F, W-N):
these methods use the desired underflow solids concentration while in an especial case, accurate prediction of underflow solids concentration in a green field project may be not possible in practical point of view.
Furthermore, in conventional methods lowest settling flux is considered with the aim of handling the worst condition. To my mind in a high rate thickener, solids concentration during flocculation is a powerful tool and we have to choose the solids concentration to achieve maximum flux concentration. In this condition selecting a safety factor would led to overcome variation in feed properties (e.g. solids concentration) and a wise design would be achieved.

Do you agree with choosing the optimum solids concentration during flocculation contributing to maximum settling flux in sizing high rate thickener?

Alan Carter
1 year ago
Alan Carter 1 year ago

Your last question is the main point in thickening. Under flowing solid concentration demand from the highest thickener. More high thickener will be more solid concentration. Now highest thickener has 20 meters that solid concentration is 65...70%.

Obergruppenfuhrer
1 year ago

Your best option is to invite a thickener vendor to come and test your slurry using their dynamic test rig. Most vendors have such rigs available in every office and they can be transported in a specialized suitcase. These rigs simulate the bed filtration behavior of a high rate thickener and generate settling flux rate data that can be used for accurate sizing. If you are not too remote they will often visit at no charge in anticipation of obtaining an order for the equipment.

Unterstarm
1 year ago
Unterstarm 1 year ago

The vendors have data bank and also can take a total view.

We should have basic data and also have to be able to interact with the vendors with knowledge of what we want / and what is being offered by vendors.

David
1 year ago
David 1 year ago
David
1 year ago
David 1 year ago

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