Centrifugal clarification

Within the context of particle technology, the most relevant application of centrifugation is centrifugal clarification since it follows theoretical principles of dynamics of particles submerged in fluids as discussed in this book. Those principles are used to describe centrifugal clarification as a unit operation. 

Assuming that half of all those particles present in the feed with a particular diameter are removed during their transit through the bowl, those particles with diameters greater than x will be mostly removed from the liquid, whereas those particles with diameters smaller than x will be likely to remain in the liquid. In this context as here defined is known as the cut-point or critical diameter. 

Schematic diagram of radial separation zones in the cross section of a centrifugal clarifier. 

Integrating Equation 10.70 and substituting limits the following relation is obtained  

The minimum residence time for a particle in the bowl is V/Q, where V is the volume of liquid held in the bowl at any time and Q is the volumetric flow rate of liquid through the bowl. Thus, for a particle of diameter to be separated out 

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The expanded-bed adsorption process replaces the centrifugation, clarification, and concentration steps and allows the direct adsorption of the... 

CRM 9 is a mutant diphtheria toxin with a molecular weight of 60,000 secreted extracellularly from C. diphtheriae under certain growth conditions.7 Traditionally, this protein is captured on an anion-exchanger only after centrifugation, clarification, and extensive diafiltration, since the ionic strength of the medium is too high for direct adsorption (Fig. 6). When using the... 

Nordestgaard, S., Chuan, Y.R., O Neill, B., Waters, E., Deans, L., Rohcki, R, Colby, C. (2006). In-line Dosing of White Wine for Bentonite Eining with Centrifugal Clarification. Am. J. Enol. Vitic., 58, 283-285... 

Still existing turbidities will be eliminated by appropriate methods of clarification and stabilisation of the wine. Turbidity-causing matters are mostly proteins as well as oxidized and condensated polyphenols. Moreover, metal ions may lead to discolouring and sedimentation. Common methods of wine clarification are precipitation (fining), filtration or centrifugation. Clarification by means of filtration is achieved with cellulose or diatomaceous earth. 

In the precoat and body feed mode, filter aids allow appHcation of surface filtration to clarification of Hquids, ie, filtration of very dilute suspensions of less than 0.1% by volume, such as those normally treated by deep bed filters or centrifugal clarifiers. Filter aids are used in this mode with pressure filters. A precoat is first formed by passing a suspension of the filter aid through the filter. This is followed by filtration of the feed Hquid, which may have the filter aid mixed with it as body feed in order to improve the permeabiUty of the resulting cake. The proportion of the filter aid to be added as body feed is of the same order as the amount of contaminant soHds in the feed Hquid this limits the appHcation of such systems to low concentrations. Recovery and regeneration of filter aids from the cakes normally is not practiced except in a few very large installations where it might become economical. 

Other modifications have special but more limited apphcations. A centrifugal bowl may contain, instead of disks, several aimular baffles that take the hquid through a labyrinth path before discharge. The multiple cylinders increase cake capacity to as much as 70 L for easily sedimented sohds. This centrifuge is used for clarification of food symps and antibiotics (qv), and for recovery of heavy metallic salts and catalysts (see Fig. 14c). 

The cyliudricaTsection provides clarification under high centrifugal gravity. In some cases, the pool should be shallow to maximize the G-force for separation. In other cases, when the cake layer is too thick inside the cylinder, the settled solids—especially the finer particles at the cake surface—entrain into the fast-moving liqmd stream above, which eventually ends up in the centrate. A slightly deeper pool... 

These scale-up factors are relative capacities of centrifuges of the same type hut different sizes when performing at the same level of separation achievement (e.g., same degree of clarification). These factors must not he used to compare the capacities of different types of centrifuges, f Approaches 2.5 at rates helow mL/min. fLong howl configuration. 

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