Centrifuges decanter solid-bowl

FIGURE 3.4-9 Decanter solid-bowl centrifuge with cylindrical-conical rotor ad open liquid onllet. Courtesy of Alfa-Laval Inc,... 

Decanter Centrifuges The decanter centrifuge (also known as the solid-bowl or scrtnl centrifuge) consists of a sohd bowl with a... 

Figure 9.12. Solid-bowl decanter centrifuge-principles of operation...

Fig. 5 Solid bowl decanter centrifuge. (View this art in color at www.dekker.com.)...

Solid bowl scroll decanter centrifuges have also been built vertically. The pendulum-type construction allows the bowl to expand more easily when operating at higher temperatures and makes mechanical sealing for elevated pressures less cumbersome. Although these units have been designed for operation up to 10 bars, they often operate at 5 bars or less. 

Centrifuges are operated as elassifiers, sedimentors, and filters. Centrifugal classifieation and sedimentation are carried out in solid bowl units (frequently called decanters) as illustrated in Fig. 25. Most decanters are operated on a eontinuous basis. The slurry enters as shown in Fig. 25. The solids settle out and are conveyed toward diseharge by a seroll, whieh is turning at a lower speed than the bowl. The clear liquid moves... 

In filtering centrifuges, the solids settle out as in the decanter. However, the liquid flows in the same direction and out through the perforated bowl. As the liquid flows in the same direction as the solids, it increases the rate of deposition. In addition, as the liquid flows through the cake, the frictional effect results in sharply increased stresses on the cake. At low rotation speeds, the stress due to the frictional flow may be larger than the centrifugal body forces (Tiller and Homg 1983). 

To recover liquid and solids in order of preference of settlers. Section 5.8, CCD, Section 5.11 and sedimentation centrifuges. Section 5.12 continuous countercurrent decanter circuit CCD, horizontal solid bowl centrifuge with scroll discharge. 

SoUd-howl decanters find widespread use in process industry, particularly in food processing and waste water treatment dMes. In the latter, the solid-bowl centrifuge con etes with vacuum fibers, variable diamber presses and belt presses, in situdge dewatering operations. 

The solid-bowl scroll-discharge centrifuge — now almost universally known as the decanter centrifuge — has, indeed, become the workhorse of a wide range of liquid/solid separation activities. Its application to the dewatering of waste sludges has made it a most valuable tool in combating environmental pollution. This has made the decanter a well-known and widely appreciated piece of equipment. 

The gypsum slurry is dewatered in a solid bowl decanter centrifuge. The byproduct gypsum, which is essentially dry, is taken to storage, and the centrate is recycled. A bleed stream of the precooler water is continuously circulated through a thickener to concentrate captured fly ash. The fly ash slurry is mixed with a bleed stream of centrate, neutralized with limestone slurry, and filtered. The resulting solids are discarded. A portion of the filtrate is also discarded to maintain the water balance and dispose of soluble salts while the main stream is recycled to the absorption circuit. 

Decanter centrifuges, for process applications, are typically solid bowl scroll-discharge machines, capable of continuous sohd and centrate discharge. They are ideally suited to handling high feed solids concentrations and delivering dry solid products. They are generally able to convey the soft solids often encountered in the pharmaceutical and fermentation industries. 

A variant of the decanting centrifuge is the screen bowl decanter, shown in Figures 9.13 and 9.14. In this unit a further perforated section is attached to the smaller diameter end of the conical section. This is known as the screen and allows further drying and/or washing of the solids to take place. 

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