Centrifugal filtration installation

The only exception to this is the Oslo crystallizer, which due to the system properties can also be operated at higher suspension densities. It is not unusual for the mass balances, however, to show suspension densities that are below the limit of 15% by mass. This can be easily remedied by the installation of a dear liquor outlet (Figure 11.25). The suspension in the crystallizer is concentrated as a result. Figure 11.26 shows the opposite measure, which is necessary when the suspension density is too high. In this case, the suspension is diluted by returning mother liquor (centrifuged filtrate). 

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. 

If a screen is installed at the bottom of the tank, the solid-liquid separation can take place within the extraction equipment. The extract drains out of the tank, leaving the solids behind. Water can then be added to reslurry the solids, washing solvent from the marc. However, some means of removing the washed marc from a tank equipped with a screen is needed. Where external filtration or centrifuging equipment is used, solvent can be removed from the marc by water washing or conveying to an external dryer. 

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