Centrifuges solids retaining separators

Solids-retaining separators (Fig. 2) are batch centrifuges. They are generally larger in diameter than tubular bowls. Therefore, they are large enough to contain a disk stack but are dependent on at least partial disassembly for manual removal of solids. The larger... 

Filtration is the separation of undissoived particulate solids from a mixture of fluid and solid. The separation is brought about by passage of the fluid thru a pervious septum (filter medium) in or on which the solids are retained. A driving force (gravity, vacuum, pressure, or centrifugal force) produces the flow. Filter aids may be added to the fluid before filtering to counterbalance the unfavorable characteristics of badly filtering materials... 

Disk stack separators are vertical bowl centrifuges that are characterized by the presence of a nested conical stack of disks. The centrifuges are usually categorized by the method of solid removal from the bowl and include solids-retaining, solids-ejecting, and nozzle-discharge units. The feed enters the bowl at... 

The term in dJ/dt has been retained, since it is needed routinely in, for example, the modelling of solids-liquid separation centrifuges and it may be needed to model other rotating components in fault situations where change of geometry is possible. 

The original type of disc-stack centrifugal separator is the solids-retaining machine, used on liquid-liquid or Uquid-solids separation when the solids content in the feed... 

In a filtering centrifuge, separating sohds from liquid does not require a density difference between the two phases. Should a density difference exist between the two phases, sedimentation is usually at a much more rapid rate compared to filtration. In both cases, the solid and liquid phases move toward the bowl under centrifugal force. The sohds are retained by the filter medium, while the liqmd flows through the cake solids and the filter. This is illustrated in Fig. 18-138/ . 

Instant tea produced as described above will dissolve completely in hot water but not in cold water, as the caffeine-polyphenol complexes are insoluble under those conditions. Since virtually all instant tea manufacture in the U.S. is for iced tea preparation, process modification is required. This initial extract may be cooled to 5 to 10°C and the cold water insoluble material or cream be allowed to precipitate. Under these conditions, 20 to 35% of the extract solids may be separated by centrifugation. The supernatant solids will reconstitute in cold water after concentration and drying.105 It is also possible to process the cream to make a portion of it compatible with the product and thereby retain the caffeine and some polyphenolic components that are present in this fraction.106 Commercial use of the enzyme Tannase, which removes gallic acid from gallated tea polyphenols107 and reduces cream formation108 can be used to reduce cream losses and manufacture instant teas retaining more of the natural polyphenol content. 

Although the crystals are likely to be pure, the mass of crystals will retain some liquid when the solid crystals are separated from the residual liquid. If the adhering liquid is dried on the crystals, this will contaminate the product. In practice, the crystals will be separated from the residual liquid by filtration or centrifuging. Large uniform crystals separated from a low-viscosity liquid will retain the smallest proportion of liquid. Nonuniform crystals separated from a viscous liquid will retain a higher proportion of liquid. It is common practice to wash the crystals in the filter or centrifuge. This might be with fresh solvent, or in the case of melt crystallization, with a portion of melted product. 

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