Classifier hydrocyclone

Density methods the density of commonly-used plastics varies between 0,9 and 1,7 g/cm [5], but the most common contaminants, such as paper and metal, have densities outside this range. Density-related methods can thus be used for both purifying and sorting plastics. Commonly-used techniques are air classifiers, hydrocyclones, and float/sink baths. Often, air classifiers are used to separate light contaminants such as paper, while hydrocyclones or float/sink baths take care of the heavier fractions. 

Particle classification technologies include impoundment basins, hydraulic classifiers, hydrocyclones, grizzlies, and screens. Following is a descrqition of these technologies. Applications, limitations, and relative costs for the first three listed particle classification technologies are identified in Table 2. 

The hydrocyclone, commonly referred to simply as cyclone, is a nonmechanical sedimentation-type classifier (2,6,10,27) (Fig. 7). It has no moving parts or power attachments directly connected to it. The hydrocyclone has become the workhorse of most mineral processing operations because of its simplicity, short residence time, compactness, and low cost of operation. It is, however, characterized by lack of sharpness of separation. Equipment... 

Centrifuges. Sohd-bowl centrifuges have been proposed as an alternative classifying device to hydrocyclones for cut sizes below 10 pm. The results appear to be mixed (21). In one apphcation, where the cut size was 6.5 pm and the sharpness index 0.7, there was essentially no apparent bypass. However, in other apphcations operating at higher feed concentrations, the cut size ranged from 5—8 pm, but the sharpness index was between 0.3—0.5 and the apparent bypass between 10—30% or higher (22). Smaller cut sizes have also been reported (23). 

Classified removal of course material also can be used, as shown in Figure 16. In a crystallizer equipped with idealized classified-product removal, crystals above some size ate removed at a rate Z times the removal rate expected for a perfecdy mixed crystallizer, and crystals smaller than are not removed at all. Larger crystals can be removed selectively through the use of an elutriation leg, hydrocyclones, or screens. Using the analysis of classified-fines removal systems as a guide, it can be shown that the crystal population density within the crystallizer magma is given by the equations... 

As representative examples of the various machineries used for classification mention may be made of mechanical classifiers, hydraulic classifiers, and hydrocyclones. Simplified sketches of these have been shown in Figure 2.12 (A-C). 

A) crossflow classifier (B) hydraulic classifier (C) hydrocyclone (D) cyclone. 

There is a clear need for other size classifiers which combine a high separation efficiency with flexibility and compactness. Hydrocyclones have a small volume, are simple in operation and are standard size classification equipment, for example in closed circuit grinding applications. The recent development of the flat-bottom hydrocyclone, which permits classification in the coarse size range, creates an additional motive to study the use of hydrocyclones for Crystal Size Distribution (CSD) control. Furthermore, throttling of a flat botom hydrocyclone does not necessarily provoke blockage but allows continuous control of its cut size when a controlled throttling valve is used. There is a clear incentive for its use in this application since it may provide an additional process input. 

These are used to make two product size ranges, oversize and undersize, with some overlap. The break commonly is between 28 and 200 mesh. A considerable variety of equipment of this nature is available, and some IS kinds are described by Kelly and Spot-tiswood (1982, pp. 200-201). Two of the most important kinds, the drag rake classifier and the hydrocyclone, will be described here. 

A machine used to separate particles of specified size ranges. Wet classifiers include settling tanks, centrifuges, hydrocyclones, and vibrating screens. Dry classifiers, also termed air classifiers , use gravity or centrifugal settling in gas streams. 

In the grinding operation of Fig. 13.3, a ball mill is in closed circuit with a hydrocyclone classifier. The mass flow rates of the classifier feed, oversize, and undersize are denoted by the symbols A, O,... 

The hydrocyclone has mostly replaced other classifiers in closed-circuit grinding. 

Hydrocyclones are rapidly taking over the functions formerly handled by bowl classifiers because of lower capital costs and floor-area requirements. 

An essential factor for good table operation is that the rate of feed must be uniform, both as to tonnage and as to physical properties. No one factor will cause more trouble to the table operator than to have a surging feed. The feed to tables may be unsized, or it may be either screened or hydraulically classified. For treating fine coals a common procedure is to use hydrocyclones both to deslime the material and to give a cyclone underflow of about 40 percent solids, which constitutes the table feed. 

Particle size distribution and classifier selectivity have been determined, using kernel density estimations, to data from (two) classifier flow streams. The procedure has been applied to hydrocyclones using platey particles whose sizes were determined with a Sedigraph 5100 and spheroidal particles whose size distributions were determine using the Malvern Mastersizer and the Coulter Counter [8] Svarovsky s equation was used [9,10]. 

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