Liquid-solid particle, separators Centrifugal

Lines in vacuum service, 135—141 Line symbols, 17, 23 Numbering, 23 Lined centrifugal pumps, 171 Liquid-solid particle, separators, 228 Baffle type specifications, 248 Baffle type, 247, 248 Centrifugal, 256, 259-261 Chcvron-vanc, 248, 235 Comparison chart, 230 Cyclone, 259 Specification form, 268 Vane, 259 Wire mesh, 246 York-vane, 248 Low pressure storage... 

Centrifugal Separation Centrifugal force can be utilized to enhance particle collection to several hundredfold that of gravity. The design of cyclone separators for dust removal is treated in detail in Sec. 17 under Gas-Solids Separations, and typical cyclone designs are shown in Fig. 17-43. Dimension ratios for one family of cyclones are given in Fig. 17-36. Cyclones, if carefully designed, can be more efficient on hquids than on solids since liquids coalesce on capture and are easy to drain from the unit. However, some precautions not needed for solid cyclones are necessary to prevent reentrainment. 

In general, when sepiarating two liquids, they must be immiscible and have different spiecific gravities before a separation technique-such as oil/water separation-would be effective. In the case of finely dispersed liquids or finely dispersed solids, if the dispersed material is below one micron in particle size, centrifuging should be considered. The use of centrifugal force on the differing densities of the material can facilitate the separation technique. 

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. 

Figure 4-55. Specification Sheet, gas phase centrifugal entrainment Figure 4-57. Inertial centrifugal dust separator. Courtesy of Univer-separator (liquid or solid particles). sal Road Machinery Co.

The need to separate solid and liquid phases is probably the most common phase separation requirement in the process industries, and a variety of techniques is used (Figure 10.9). Separation is effected by either the difference in density between the liquid and solids, using either gravity or centrifugal force, or, for filtration, depends on the particle size and shape. The most suitable technique to use will depend on the solids concentration and feed rate, as well as the size and nature of the solid particles. The range of application of various techniques and equipment, as a function of slurry concentration and particle size, is shown in Figure 10.10. 

Centrifugal force can also be used to separate solid particles from fluids by inducing the fluid to undergo a rotating or spiraling flow pattern in a stationary vessel (e.g., a cyclone) that has no moving parts. Cyclones are widely used to remove small particles from gas streams ( aerocyclones ) and suspended solids from liquid streams ( hydrocyclones ). 

For fine suspended solids with particles that are too small to be separated from the liquid by gravitational or centrifugal methods, a barrier method such as a filter may be used. The liquid is passed through a filter medium (usually a cloth or screen) that provides a support for the solid particles removed from the slurry. In actuality, the pores in the filter medium are frequently larger than the particles, which penetrate some distance into the medium before being trapped. The layer of solids that builds up on the surface of the medium is called the cake, and it is the cake that provides the actual filtration. The pressure-flow characteristics of the porous cake primarily determine the performance of the filter. 

The determination of adsorption isotherms at liquid-solid interfaces involves a mass balance on the amount of polymer added to the dispersion, which requires the separation of the liquid phase from the particle phase. Centrifugation is often used for this separation, under the assumption that the adsorption-desorption equilibrium does not change during this process. Serum replacement (6) allows the separation of the liquid phase without assumptions as to the configuration of the adsorbed polymer molecules. This method has been used to determine the adsorption isotherms of anionic and nonionic emulsifiers on various types of latex particles (7,8). This paper describes the adsorption of fully and partially hydrolyzed PVA on different-size PS latex particles. PS latex was chosen over polyvinyl acetate (PVAc) latex because of its well-characterized surface PVAc latexes will be studied later. 

Batch centrifuges with imperforate bowls are used either for producing an accelerated separation of solid particles in a liquid, or for separating mixtures of two liquids. In the former case, the solids are deposited on the wall of the bowl and the liquid is removed through an overflow or skimming tube. The suspension is continuously fed in until a suitable depth of solids has been built up on the wall this deposit is then removed either by hand or by a mechanical scraper. With the bowl mounted about a horizontal axis, solids are more readily discharged because they can be allowed to fall directly into a chute. 

Very fine dispersions can be separated effectively with disk-type centrifuges. Commercial units have capacities of 5-500 gpm and are capable of removing water from hydrocarbons down to the ppm range. A mild centrifugal action is achieved in hydrocyclones. They have been studied for liquid-liquid separation by Sheng, Welker, and Sliepcevich (1974), but their effectiveness was found only modest. The use of hydrocyclones primarily for the recovery of solid particles from liquids is described in the book of Bradley (1965). A symposium on coalescence has papers by Belk (1965), Jordan (1965), Landis (1965), and Waterman (1965). 

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