Gravity sedimentation thickening

Filters generally achieve a lower final moisture content than obtained by gravity sedimentation and are often fed from thickeners, as indicated in the schematic particulate process shown in Figure 9.2. In this chapter the principles of slurry filtration will be described and certain simplified filter design equations derived. For more complex derivations the reader is referred to specialist texts e.g. Coulson and Richardson (1991), Wakeman (1990a) and Purchas (1981). 

Gravity sedimentation tests were conducted by a modified AEEP method (8) in which a 400-ml sample of effluent was examined in a 1-/ graduated cylinder giving a fluid depth of 140 mm. The height of the interface between the thickened sludge and clarified supernatant is plotted versus time. Vacuum filtration tests were conducted by a modified AEEP method ]9) in which a 0.05 ft circular Lucite leaf covered with an Eimco No. NY-415 monofilament filter cloth was used in a 1-/ beaker containing 417 ml of effluent sample. 

Sedimentation thickener. The separation of a dilute slurry by gravity settling into a clear fluid and a slurry of higher solids concentration is called sedimentation. Industrially, sedimentation operations are often carried out continuously in equipment called thick-... 

The available gravity sedimentation equipment can be divided into batch operated settling tanks and continuously operated thickeners or claiiiiers. The batch settling tanks are still used where relatively small quantities of liquids are to be treated such as, for example, in spent lubrication oil reclamation and cleaning. The bulk of the processing by gravity sedimentation is, however, in continuously operated thickeners and clarifiers. 

Sedimentation is the separation of suspended solid particles from a fluid stream by the action of a body force on the settling behavior of the particle. The body force may be either gravitational or centrifugal force. This section covers gravity sedimentation, represented by clarification and thickening. The equipment used for these two operations are called clarifiers and thickeners, respectively. Centrifugal sedimentation will be discussed in the next section. 

Gravity sedimentation is classified as thickening or increasing the concentration of the feed stream, or clarification or the removal of solids from relatively dilute streams. The former is used to prepare the feed for tailings and concentrate pipeline flow, or for the removal of tailings on trucks. The latter is more frequently used in sewage and waste treatment plants, where the volume of solids is considerably smaller than in tailings and concentrate flows. 

Prethickening of filter feeds can be done with a variety of equipment such as gravity thickeners, hydrocyclones, or sedimenting centrifuges. Even cake filters can be designed to limit or completely eliminate cake formation and therefore act as thickening filters and be used in this thickening duty. 

Sedimentation is the partial separation or concentration of suspended solid particles from a liquid by gravity settling. This field may be divided into the functional operations of thickening and clarification. The primaiy purpose of thickening is to increase the concentration of suspended sohds in a feed stream, while that of clarification is to... 

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