Clarifiers/thickeners rakes

Alternative Clarification Processes. The discussion so far has assumed the use of a single conventional clarifier, with a cylindrical body and conical bottom with a thickening rake, in continuous operation. In small plants, the rake may be eliminated the use of a conical bottom for easy removal of the sludge is then very important. In very small plants, clarification may be a batch process, often in the same tanks used for chemical treatment. Very large clarifiers, on the other hand, are sometimes rectangular... 

Sedimentation systems consist of a collection of components, each of which can be supplied in a number of variations. The basic components are the same, whether the system is for thickening or clarifying tank, drive-support structure, drive unit and lifting device, rake structure, feedwell, overflow arrangement, underflow arrangement, instrumentation, and flocculation facilities. 

Torque Rating The choice of torque rating has been discussed earlier. Torque is a function of such factors as quantity and quality of underflow (therefore, of such parameters as particle characteristics and flocculant dosage that affect underflow character), unit area, and rake speed but, in the final analysis, torque must be specified on the basis of experience modified by these factors. Unless one is experienced in a given apphcation, it is wise to consult a thickener or clarifier manufacturer. 

Thickener (settler and clarifier tanks) for settling of unreacted material as thickened slurry Clarified dilute alum solution overflows to evaporator Loss of product alum with bottom slurry if stirring at controlled rate and settling not achieved Optimise dilution, the speed and design of rake mechanism... 

In simple terms, a clarifier or a thickener is essentially a sedimentation tank. To make the sedimentation uniform, a rake or arm rotates slowly but continuously. A relatively clear layer of liquid forms at the top and is withdrawn through an overflow box feeding a launder. The slurry in the thickener is denser at lower and lower layers. The bottom of the thickener forms a shallow cone with the center feeding into an imderflow pipe to a separate launder or pump. 

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