Solid-bowl centrifugation

Solid-Bowl Centrifuge The Bird solid-bowl centrifuge uses powder instead of gravity and can develop centrifugal forces up to 1800 times the force of gravity. It is therefore a unique type in classification practice. 

Separation Rates in Tubular-and Solid-Bowl Centrifuges To evaluate the radial velocity of a particle moving toward a centrifuge wall, the expression for particle settling in a gravitational field is applied ... 

A solid-bowl centrifuge has the following dimensions Rj = 0.30 m, Rj = 0.32 m, = 0.30 m. It is designd to operate at 5,000 rpm, separating particles from a suspension where the particle specific gravity is 7.8. Determine the required horsepower needed to set the centrifuge into operation. 

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. 

Consider a thin layer solid bowl centrifuge as shown in Figure 4.20. In this device, particles are flung to the wall of the vessel by centrifugal force while liquor either remains stationary in batch operation or overflows a weir in continuous operation. Separation of solid from liquid will be a function of several quantities including particle and fluid densities, particle size, flowrate of slurry, and machine size and design (speed, diameter, separation distance, etc.). A relationship between them can be derived using the transport equations that were derived in Chapter 3, as follows. 

Centrifuges are used for the classification of particles in size ranges below 10 /im. Two types are used solid bowl centrifuges, usually with a cylindrical, conical bowl, rotated about a horizontal axis and nozzle bowl machines, fitted with discs. 

Solid bodies, flows past, 11 753-757 Solid-bound photosensitizing dyes, 9 518 Solid bowl centrifuges, 16 659-660 Solid-burned quicklime, 15 29 Solid by-products... 

Centrifuges. Solid-bowl centrifuges have been proposed as an alternative classifying device to hydrocydones for cut sizes below 10 JJm. The results appear to be mixed (21). In one application, where the cut size was 6.5 Jim and the sharpness index 0.7, there was essentially no apparent bypass. However, in other applications operating at higher feed concentrations, the cut size ranged from 5—8 im, but the sharpness index was between 0.3—0.5 and the apparent bypass between 10—30% or higher (22). Smaller cut sizes have also been reported (23). 

A particle and a mixture introduced, confined, and rotated within a circular enclosure accelerates as it moves from a neutral center toward the maximum diameter (inner periphery) of the enclosure. Thus, if a mixture is introduced to the center of a 24-inch (61-cemiineler) diameter solid-bowl centrifuge rotating at 1500 rpm. the panicle will be caused to move at a speed of 32.2 feel (9 8 meters) per second at the center. At the maximum diameter, the particle will have a terminal velociiy of 766.8 x 32.2 feet per second, or 24.690 feet (7525 meters) per second. Essentially, the separaiion occurs at 766 8 x g. 

Solid bowl centrifuges are similar to tubular centrifuges, but with a larger diameter bowl and running at slower speeds. Feed rates can be as high as 10 m3/hr, provided that the solids concentration in the feed is not too high, as the solids hold-up is again limited. 

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