Bowls, centrifugal sedimentation

Centrifugal Sedimentation Equipment. Commercial sedimentation centrifuges are characterized priacipaHy by how soHds are discharged, and the general dryness of these soHds. There are batch and automatic batch soHd bowl machines which coUect the soHds at the bowl wall. SoHds are removed very dry. Almost any soHd is coUectable, even those that are very soft and compressible. 

The principle of the solid bowl centrifuge is illustrated in Figure 4.19. It is essentially a device for enhancing the rate of sedimentation. The application of high G, however, creates stress in the machine and is equivalent to the application of pressure (cf. pressure filtration). There is therefore a balance to be struck between separating effect and stress. 

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" ) ... 

Using a tubular-bowl centrifuge, calculate the sedimentation velocity of a 70S ribosome (from E. coli, diameter 0.02 pm) in water at 20 °C. The rotational speed and distance from the center are 30 000 rpm and 10 cm, respectively. 

Sedimenting and Filtering Centrifuges Under centrifugal force, the solid phase assumed to be denser than the liquid phase settles out to the bowl wall—sedimentation. Concurrently, the lighter, more buoyant liquid phase is displaced toward the smaller diameter—flotation. This is illustrated in Fig. 18-149a. Some centrifuges run with an air core, i.e., with free surface, whereas others run with slurry filled to the center hub or even to the axis in which pressure can be sustained. 

PRINCIPLES OF CENTRIFUGAL SEDIMENTATION. In a sedimenting centrifuge a particle of given size is removed from the liquid if sufficient time is available for the particle to reach the wall of the separator bowl. If it is assumed that the particle is at all times moving radially at its terminal velocity, the diameter of the smallest particle that should just be removed can be calculated. 

Cartridge Centrifuges Solid bowl Filtering Sedimenting... 

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. 

The separation of biomass from growth media is a difficult operation, as cells have almost the same density as their surrounding medium, are small, are able to form stable colloids and are cohesive. Sedimentation of cell debris presents an even more difficult problem for biotechnologists and the choice of separation technique is limited. Solid bowl and tubular bowl centrifuges are relatively inexpensive and have in the past been chosen for... 

A low-concentration suspension of clay (density 2640 kg m ) in water with a viscosity of 0.001 Ns m and density 1000 kg m is to be separated by centrifugal sedimentation. Pilot runs on a laboratory tubular bowl centrifuge operating at 20000 rev. min indicate that satisfactory overflow clarity is obtained at a throughput of 8 x lO- m s-. ... 

A centrifuge can offer an alternative accelerated process via the increased force of gravity. A solid bowl centrifuge operates as the sedimentation vessel and there are numerous... 

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. 

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. 

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