Hydrocyclones arrangement

Figure 6.22 Types of multiple hydrocyclone arrangements, (a) Plan view (b) Elevation (c) Plan view (d) Plan view (e) Cross-section...

The nomographs by Zanker can be used to make a preliminary estimate of the size of cyclone needed. The specialist manufacturers of hydrocyclone equipment should be consulted to determine the best arrangements and design for a particular application. 

Liibberstedt [64] tested three different hydrocyclones for HeLa cell separation a 7 mm Bradley [67], a 10 mm Mozley (Richard Mozley Ltd., Redruth, UK), and a 10 mm Dorr-Oliver (Dorr-Oliver GmbH, Wiesbaden, Germany) (the dimension quoted here is the diameter of the cylindrical part of each hydrocyclone). The best results were obtained with the Dorr-Oliver hydrocyclone (Fig. 3), which produced a cell separation efficiency of 81 % when working at a pressure drop of 300 kPa and a flow rate of 2.8 L min When operating with two 10 mm Dorr-Oliver connected in series (the overflow of the first as feed for the second) at 200 kPa, the global efficiency of the arrangement was 94% [65]. These experimental values confirm the computational fluid dynamics (CFD) predictions that high levels of efficiencies for mammalian cells could be achieved with small diameter hydrocyclones [46]. 

Figure 14.19. General arrangement of a hydrocyclone useful in high-throughput plastic-plastic separations [77].

Diagram of radial (spider) arrangement of hydrocyclones for industrial scale. 

Hydrocyclones can also be used for washing of solids by arranging several stages in a counter-current arrangement similar to that used with gravity thickeners, see chapter 15. Such systems are found in the production of potato or com starch, or in the chemical industry. 

In order to make use of the high efficiency of separation of small diameter hydrocyclones, most manufacturers offer multiple arrangements of varying design. Series arrangements, with or without recycles, can be used to improve any performance characteristic of hydrocyclones, see chapter 16. 

Series connections of separators are a common way of improving the performance of single units. In the case of hydrocyclones, due to their low capital and running costs, multiple series arrangements are quite frequently used. As to which particular layout and arrangement should be used depends on the actual application in question. 

Countercurrent separator systems can be found in many diverse industries. One example is in the production of potato, com or wheat starch. Here, washing usually means removal of one sohd from another, i.e. gluten from starch. The gluten has to be sheared off the starch particles and hydrocyclones are ideally suited to this duty. The density of the sohds is low, however, (around 1500 kg/m ) and this combined with low particle size necessitates the use of small diameter (10 mm) cyclones in parallel arrangements. The number of stages used is often high (eight or nine, up to 24 in extreme cases). 

Figure 15.18 gives a summary of one experiment from this study that demonstrates well the capability of the arrangement in this application. The required near-complete separation of solids in the 44 mm hydrocyclones used was not a problem and therefore no additional separator on system overflow was needed in this case. Furthermore, all three stages could be set to have the same split ratios Rf of 26% (underflow to feed). The washing efficiency was about 97% but intermediate sumps had to be provided for mass transfer from within the porous solids to take place. 

The reduction in the cut size of the whole arrangement, as opposed to that of the single-pass arrangement, is clearly a function of the recycle ratio Qlq if the cut size of the hydrocyclone remains the same (i.e. greater recycle ratios are matched by a greater number of identical cyclones in parallel), the flow ratio Rf is low (which is often the case in clarification duties) and the geometric standard deviation (i.e. the steepness) of the grade efficiency curve is 1.8 (a typical value for hydrocyclones), then the rate of decrease in cut size with the recycle ratio Qlq is as shown in Table 16.3. 

As would be expected, the increased recycle flow improves overall recovery of the system but at the cost of increased size of the separator and also proportionately greater pumping costs. Figure 16.26 demonstrates this in a plot of system recovery against feed flow to the hydrocyclone (this is directly related to the installed cost of the separator). It should be noted that this arrangement, if a hydrocyclone is used as the separator, leads to... 

The modification of hydrodynamic aspects is exploited in the falling-film cell [12], where the electrolyte flows as a thin fllm in the channel between an inclined plane plate and a sheet of expanded metal which work as electrodes. Other proposal is to include turbulence promoters in the interelectrode gap in conventional parallel plate electrochemical reactors [13-16], or the use of expanded metal electrodes immersed in a fluidized bed of small glass beads, called Qiemelec cell [17]. Likewise, the Metelec cell [18] incorporates a cylindrical foil cathode concentric arranged around an inner anode, with a helical turbulent electrolyte flow between the electrodes. The electrochemical hydrocyclone cell [19] makes use of the good mass-transfer conditions due to the helical downward accelerated flow in a modified conventional hydrocyclone. 

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