Tubular bowl centrifuge liquids

High-speed, vertical axis, tubular bowl centrifuges are used for the separation of immiscible liquids, such as water and oil, and for the separation of fine solids. The bowl is driven at speeds of around 15,000 rpm (250 Hz) and the centrifugal force generated exceeds 130,000 N. 

In order to separate the particles in a suspension, the maximum allowable flow rate through the tubular-bowl centrifuge, as shown schematically in Figure 9.3a, can be estimated as follows [1]. A suspension is fed to the bottom of the bowl at a volumetric flow rate of Q (m" s" ) and the clarified liquid is removed from the top. The sedimentation velocity of particles in the radial direction (v = dr/di ) can be given by Equations 9.7 and 9.8 with the use of the terminal velocity under gravitational force v (m s" ) and the gravitational acceleration (m s" ) ... 

To recover liquid in order of preference of settlers, Section 5.8, thickeners. Section 5.10 and sedimentation centrifuges. Section 5.12 clarifier, settler, washing tray thickener, reactortubular bowl centrifuge, batch automatic (horizontal or vertical bowl, disc with intermittent nozzle discharge) continuous disc bowl centrifuge with nozzle discharge. 

In Fig. 14.4-2 a schematic of a tubular-bowl centrifuge is shown. The feed enters at the bottom and it is assumed all the liquid moves upward at a uniform velocity, carrying solid particles with it. The particle is assumed to be moving radially at its terminal settling velocity o,. The trajectory or path of the particle is shown in Fig. 14.4-2. A particle of a given size is removed from the liquid if sufficient residence time is available for the particle to reach the wall of the bowl, where it is held. The length of the bowl is b... 

In Fig. 14.4-3 a tubular-bowl centrifuge is shown in which the centrifuge is separating two liquid ph es, one a heavy liquid with density kg/m and the second a light liquid with density pi. The distances shown are as follows r, is radius to surface of light liquid layer, r2 is radius to liquid-liquid interface, and r/ is radius to surface of heavy liquid downstream. 

Figure 14-15. Tubular bowl centrifuge internal configurations for solid-liquid and liquid-liquid separations. (Adapted with permission from reference 2. Copyright 1960, John Wiley and Sons, Inc.)...

Figure 7.3.12. Schematic for particle separation from a liquid in a tubular bowl centrifuge.

We calculate now the grade efficiency function G Vp) of the tubular bowl centrifuge. Since the z-directional liquid motion is assumed to be of the plug flow type, the following equality holds ... 

A tubular bowl centrifuge can be used to separate continuously two immiscible liquids having different densities. Near the top of the rotating bowl in such a centrifuge (Figure 7.3.13), two liquid outlets are provided at different... 

Disc stack, decanter and tubular bowl centrifuges are used for a wide range of separation duties in the pharmaceutical and fermentation industries, including liquid-solid, liquid-liquid, liquid-liquid-soUd separations, and liquid-solid extraction. Typical process steps include cell harvesting, concentration and washing, cell debris removal, inclusion body recovery and purification, solvent extraction, dewatering and recovery. 

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. 

In their liquid-liquid separation duty, the tubular bowl centrifuges can operate without stopping, but there is always a small amount of solid particulate suspended in the liquids, which is denser than either, and so settles to the bowl wall, where it stays until the centrifuge operation is stopped, and the machine is dismantled for manual cleaning. 

A sedimenting centrifuge is formed if the drum-shaped perforated basket centrifugal filter, described in Section 31, is run instead without any perforations in its bowl (basket) walls. Its behaviour mirrors that of the tubular bowl centrifuge, with feed entering below a lip at the top of the bowl, separating liquids forming two layers as they flow down the bowl, to overflow at the bottom from two levels. As with its perforate basket equivalents, the basket can be under driven or over driven, and can have a three-column suspension. 

The Imperforate Bowl Centrifuge. In an imperforate bowl centrifuge the flow of the continuous liquid phase is nominally axial, except for areas immediately adjacent to the feed inlet and effluent oudet. Tubular solid-bowl basket and imperforate bowl conveyor-discharge centrifuges satisfy this definition. 

Imperforate basket centrifuges are vertical baskets that make up a relatively small portion of those sold. They are most often used to collect fine or amorphous solids, especially slimy or sticky ones. The solids are fed into the basket and those that are heavier than the liquid accumulate on the wall, much as they do in the tubular bowl. Because the diameter of the basket is at least an order of magnitude larger than that of the tubular bowl, there is usually space for a discharge mechanism inside the basket. Imperforate bowls often have two instruments a skimmer for liquids and a plow for solids. The clear, less dense liquid supernates... 

High-speed centrifugals include tubular-bowl and disk-bowl machines, used for both liquid-liquid and litiuid-solid separations. Capacities are particularly difficult to anticipate for application of the types carried out in such machines. Approximate capacities for several materials are... 

The tubular bowl would make a good clarifying device for a single liquid, but the disc-stack centrifuge is more efficient for this purpose. 

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