Solid-liquid separation operation classifications

Hydrocyclones are used for solid-liquid separations as well as for solids classification, and liquid-liquid separation. It is a centrifugal device with a stationary wall, the centrifugal force being generated by the liquid motion. The operating principle is basically the same as that... 

The nature and sizing of equipment depends on the economic values and proportions of the phases as well as certain physical properties that influence relative movements of liquids and particles. Pressure often is the main operating variable so its effect on physical properties should be known. Table 11.1 is a broad classification of mechanical processes of solid-liquid separation. Clarification is the removal of small contents of worthless solids from a valuable liquid. Filtration is applied to the recovery of valuable solids from slurries. Expression is the removal of relatively small contents of liquids from compressible sludges by mechanical means. 

As far as possible, then, clarification aims at a complete separation of solids from the liquid stream. The next purpose, by contrast, aims specifically to leave some solids in the exit liquid. In the classification of solids by a decanter, a slurry of solid particles of mixed particle size, or, less often, of mixed densities, is treated in such a way that a specific fraction is removed as separated solid, leaving a well-defined fraction of the original solids still in suspension. This mode of operation is particularly relevant to the processing of kaolin (china clay), and it also finds a place where the decanter is used to remove oversize material, ahead of a more efficient clarifier, which might interfere with the final separator s operation (e.g. which might block the nozzles of a disc centrifuge). The decanter is a very efficient means of effecting classification by particle size. 

Tubular bowl centrifuges usually incorporate continuous centrate discharge and batch solids recovery, and operate at variable speeds up to 20,000 G. Although primarily intended for liquid-liquid separation, they can also be used for recovery or classification of ultra-fine solids. These sedimenting centrifuges (disc, decanter and tubular bowl) are described further in Section 7. 

These operations may sometimes be better kno Ti as mist entrainment, decantation, dust collection, filtration, centrifugation, sedimentation, screening, classification, scrubbing, etc. They often involve handling relatively large quantities of one phase in order to collect or separate the other. Therefore the size of the equipment may become very large. For the sake of space and cost it is important that the equipment be specified and rated to Operate as efficiently as possible [9]. This subject will be limited here to the removal or separation of liquid or solid particles from a vapor or gas carrier stream (1. and 3. above) or separation of solid particles from a liquid (item 4j. Reference [56] is a helpful review. 

In the classification scheme in Sec. 1.4.1, the first three entries under liquid-solid separation methods, i.e., ion-exchange, adsoiption, and sorbent extraction, all belong to column separation techniques. While in the batch approach, separations based on these principles may be performed either by static equilibration or by a column technique, online columns are invariably used in FI separations, both for convenience and efficiency. FI column separation systems based on different sorptive mechanisms do not differ strongly in the principles of system design and optimization of operational parameters. Therefore, the principles discussed in the following sections are generally applicable to the different approaches. 

Classification of the separation techniques according to those involving phase change or mass transfer from one phase to another, known as diffusional operations, and those that are useful in the separation of solid particles or drops of a liquid and that are generally based in the application of an external physical force, known as mechanical separations. 

There are two major appUcations for which these metallic media are primarily used the separation of solid particles by size, and the coarse screening of gas or liquid flows ahead of some finer processing stage. In the coarser, macrofiltration processes these are very versatile materials all of the dry classification (sieving, sifting) operations are covered here, as are almost all of the applications of filters for straining and coarse filtration, both of which rely upon the precise size and shape of the apertures in the mesh or sheet. 

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