Centrifugal Separation Processes

Introduction. Centrifugal separators make use of the common principle that an object whirled about an axis or center point at a constant radial distance from the point is acted on by a force. The object being whirled about an axis is constantly changing direction and is thus accelerating, even though the rotational speed is constant. This centripetal force acts in a direction toward the center of rotation. 

If the object being rotated is a cylindrical container, the contents of fluid and solids exert an equal and opposite force, called centrifugal force, outward to the walls of the container. This is the force that causes settling or sedimentation of particles through a layer of liquid or filtration of a liquid through a bed of filter cake held inside a perforated rotating chamber. 

In Fig. 14.4-lc two liquids having different densities are being separated by the centrifuge. The more dense fluid will occupy the outer periphery, since the centrifugal force is greater on the more dense fluid. 

The centrifugal force in N (Ibf) acting on the particle is given by Fj = ma = mrco (SI) 

the force developed in a centrifuge is rco Jg or v /rg times as large as the gravity force. This is often expressed as equivalent to so many g forces. 

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To evaluate the performance of a centrifugal separation process, a dimensionless separation factor, SF, defined as the ratio of centrifugal acceleration to gravitational acceleration, is used... 

Centrifugal filtration. In this second type of centrifugal separation process, centrifugal filtration occurs which is similar to ordinary filtration where a bed or cake of solids builds up on a screen, but centrifugal force is used to cause the flow instead of a pressure difference. 

Figure 14.4-3. T ubular bowl centrifuge for separating two liquid phases. Sec. 4.4 Centrifugal Separation Processes...

Deffense [25] also patented a centrifugal separation process for fat crystals, based on a hydroejector, and Breeding and Marshall [26] successfully fractionated AMF using a filter centrifuge. 

Industrial separations are conducted in gravity or bath separators for a coarse feed, and in centrifugal separators for a fine feed (2,6,10). In gravity-type separators the feed and medium are introduced to the surface of a large quiescent pool of the medium. The float material overflows or is scraped from the pool surface. The heavy particles sink to the bottom of the separator and are removed using a pump or compressed air. The dmm separator (Fig. 13), up to 4.6 m dia and 7 m long, processes approximately 800 t/h, and treats feed of size up to 30 cm dia, operates in the gravity or the... 

Centrifugal separators are used in many modem processes to rapidly separate the hydrocarbon and used acid phases. Rapid separation greatly reduces the amounts of nitrated materials in the plant at any given time. After an explosion in a TNT plant (16), decanters (or gravity separators) were replaced with centrifugal separators. In addition, rapid separation allows the hydrocarbon phase to be quickly processed for removal of the dissolved nitric acid, NO, etc. These dissolved materials lead to undesired side reactions. The organic phase generally contains some unreacted hydrocarbons in addition to the nitrated product. 

Reversible Processes. Distillation is an example of a theoretically reversible separation process. In fractional distillation, heat is introduced at the bottom stiUpot to produce the column upflow in the form of vapor which is then condensed and turned back down as Hquid reflux or column downflow. This system is fed at some intermediate point, and product and waste are withdrawn at the ends. Except for losses through the column wall, etc, the heat energy spent at the bottom vaporizer can be recovered at the top condenser, but at a lower temperature. Ideally, the energy input of such a process is dependent only on the properties of feed, product, and waste. Among the diffusion separation methods discussed herein, the centrifuge process (pressure diffusion) constitutes a theoretically reversible separation process. 

Cascade Design. The efficiency of a Zippe-type centrifuge, separating uranium isotopes when UF is the process gas, operating at a peripheral speed of 350 m/s and at a temperature of 320 K A = 2.85), would be expected to be... 

Differences in mobilities of ions, molecules, or particles in an electric field can be exploited to perform useful separations. Primary emphasis is placed on electrophoresis and dielec trophoresis. Analogous separation processes involving magnetic and centrifugal force fields are widely apphed in the process industiy (see Secs. 18 and 19). 

Centrifuging of Test material for impact/shock sensitivity and unstable material, thermal hazards shock sensitive, alternate (low energy) separation process for material could shock sensitive/unstable material result in decomposition. CCPS G-13... 

Cyclone collectors are popularly used both for particle removal and for particle sampling (Fig. 13.1). The separation process of a cyclone relies on the centrifugal accelerations that are produced when particle-laden fluid experi-... 

Centrifugation is a well-established liquid-solid separation process popular in commercial and municipal waste treatment facilities. It is usually used to reduce slurry and sludge volumes and to increase the solids concentration in these waste streams. It is a technically and economically competitive process and is commonly used on waste sludges produced from water pollution control systems and on biological sludges produced in industry and municipal treatment facilities. 

Separation processes are based on some difference in the properties of the substances to be separated and may operate kinetically, as in settling and centrifugation, or by establishing an equilibrium, as in absorption and extraction. Typical separation processes are shown in Table 6.1. Better separations follow from higher selectivity or higher rates of transport or transformation. The economics of separation hinges on the required purity of the separated substance or on the extent to which an unwanted impurity must be removed (Figure 6.13). 

Production of the color involves centrifugal separation of the biomass, cell breakage, and extraction. Use of a salt solution rather than water as an extraction medium increases stability of the color during extraction. Methods for partial exclusion of the polysaccharide from the color extract in order to enhance resolubilization of the dried color were developed. These processes include either microfiltration or co-precipitation of the polysaccharide with an added positively charged polysaccha-... 

HSCCC is attracting attention based on its high separation scale, 100% recovery of sample, and mild operating conditions. It is a chromatographic separation process based on the partition coefficients of different analytes in two immiscible solvent systems (mobile phase and stationary phase) subjected to a centrifugal acceleration field. 

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