Solid/liquid separation continuous filters

The solid-liquid separation of shinies containing particles below 10 pm is difficult by conventional filtration techniques. A conventional approach would be to use a slurry thickener in which the formation of a filter cake is restricted and the product is discharged continuously as concentrated slurry. Such filters use filter cloths as the filtration medium and are limited to concentrating particles above 5 xm in size. Dead end membrane microfiltration, in which the particle-containing fluid is pumped directly through a polymeric membrane, is used for the industrial clarification and sterilisation of liquids. Such process allows the removal of particles down to 0.1 xm or less, but is only suitable for feeds containing very low concentrations of particles as otherwise the membrane becomes too rapidly clogged.2,4,8... 

The solids-liquid separation of slurries containing particles below 10 xm is difficult by conventional filtration techniques. A conventional approach would be to use a slurry thickener in which the formation of a filter cake is restricted and the product is discharged continuously as a concentrated slurry. Such filters use filter cloths as the filtration medium... 

Figure 4.15. Solid-liquid separation in industrial scale using centrifugation in continuous mode (A) or passage of the suspension through manifolds such as those shown in (B) mounted with filter cartridges (C) designed for tangential or cross-flow of liquid suspension. Panel A NIH Fredrick facility, with permission Panels B and C Milipore, MA, with permission.

Svarovsky, Ladislav. 1990. Solid-liquid separation. 3rd ed. London, Boston Butterworth Co., 29-30. Tiller, F.M. 1978. Characteristics of staged, delayed-cake filters. Filtration and Separation May/June XXX. Tiller, F.M. 1974. Continuous processes for cake filtration. Chemical Engineering April 29. 

As shown in Fig. 11.1-1, the solids—liquid separation device is the link between the solids formation equipment and the diying operation, Thus, predictable and reliable operation is essential in this stage of the processing sequence. Continuous or baich-automatic centrifuges nad continuous vacuum filters are typically used to recover solid material from continuous crystal I ization operations. Many factors are considered in [ha final selection of the device. In any case, an equipment testing program is always essential to determine the capacity and performance of solids separation equipment. 

One of the most commonly used solid-liquid separation methods in crystallization processes is centrifugal filtration, such as continuous pusher and batchwise peeler centrifuges shown schematically in Figure 64.10. A manufacturer of centrifuges used in crystallization processes is KMPT AG [52]. In addition, Nutsche filters, frame pressure filters, and belt filters have also been used. Most of these filters have a possibility of cake washing which is important for the final purity as discussed earlier. 

Efficient and rapid removal of solvent and antisolvent is a vital component of the successful MBPprocess. Once the precipitation has been completed (concurrently for continuous process and at the end of the solvent addition for the semi-batch process), the MBP is filtered from the suspension. This is generally performed by any of the standard filtration processes such as vacuum filtration ranging from Buchner funnel to Nutsche filter or centrifugal filter. Centrifugal filters are preferred for filtration of MBP suspension because of the particle size, the hydrogel nature of the polymer, and the effectiveness in solid/liquid separation... 

Depending on the task of the separation process, a large number of different types of equipment for the solid-liquid separation are available. Criteria for the selection are, inter alia, the filtration properties of the crop and the size of the particles, the suspension density, and the mode of operation, batchwise or continuous. Two main types of solid-liquid separations can be distinguished, cake forming filtration under pressure and centrifugation. In both cases, the crystals form a filter cake on a medium through which the mother liquor has to pass. The resistance is the rate-limiting step for the filtration and the characteristic property of the suspension. 

As a filtration process proceeds, generally under an applied driving force of pressure, solids are removed by and begin to accumulate on the filter medium. The liquid portion continues to move through the filter medium and out of the filter system. The separated liquid is referred to as the filtrate. The amount of pressure applied to accomplish the filtration depends on the filtration resistance. Filtration resistance is a result of the frictional drag on the filtrate as it passes through the filter medium and the accumulated solids. In equation form,... 

Liquid waste streams with a high-suspended solids content can be cleaned up by solids removal in clarifiers, thickeners, and liquid cyclones and by accelerated settling by inclined Chevron settlers or the like [73]. For waste streams with very finely divided solids in suspension (i.e., less than about 100 pm) dissolved air flotation techniques have been shown to be more efficient than methods employing sedimentation. Final dewatering of the sludges obtained may be carried out on a continuous filter or a centrifuge. The clarified water product can be accepted for more potential options of reuse or final disposal options than untreated water, and the separated solids may be burned or discarded to landfill, as appropriate [74]. 

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