Internal rotary drum filters

Internal Rotary-Drum Filters An example of an internal rotary-drum filter is illustrated in Figure 14. The filter medium is contained on the inner periphery. This design is ideal for rapidly settling slurries that do not require a high degree of washing. Tankless filters of this design consist of multiple-compartment drum vacuum filters. 

Figure 11.12 represents the main kinds of rotary drum filters. Commercial sizes are listed in Table 11.14. The fiowsketch of Figure 11.12(a) identifies the main auxiliaries required for this kind of filtration process. Feed to the drum may be dip-type as in Figure 11.12(b), but top feed designs also are widely used. The unit with internal filtering surface of Figure 11.12(c) is suited particularly to rapidly settling solids and has been adapted to pressure operation. 

Rotary-drum filter. The most common type of continuous vacuum filter is the rotary-drum filter illustrated in Fig. 30.8. A horizontal drum with a slotted face turns at 0.1 to 2 r/min in an agitated slurry trough. A filter medium, such as canvas, covers the face of the drum, which is partly submerged in the liquid. Under the slotted cylindrical face of the main drum is a second, smaller drum with a solid surface. Between the two drums are radial partitions dividing the annular space into separate compartments, each connected by an internal pipe to one hole in the rotating plate of the rotary valve. Vacuum and air are alternately applied to... 

A rotary drum filter (area 3 m, 30 percent submergence internal pressure of 30 kN/m ) operates at 0.5 rpm. If the filter cake is incompressible and the filter cloth has a resistance equal to 1 nun of cake, find the rate of production of filtrate and the cake thickness. 

All drum filters (except the single-compartment filter) utilize a rotary-valve arrangement in the drum-axis support trunnion to facih-tate removal of filtrate and wash hquid and to allow introduction of air or gas for cake blowback if needed. The valve controls the relative duration of each cycle as well as providing dead portions of the cycle through the use of bridge blocks. A typical valve design is shown in Fig. 18-121. Internal piping manifolds connect the valve with various sections of the drum. 

Bird-Young filter. This filter (Bird Machine Co.) differs from most drum filters in that the drum is not compartmented and there is no internal piping or rotary valve. The entire inside of the drum is sub-... 

Figure 1.26 Representations of rotary vacuum drum filters, (a) bottom fed, knife/scraper discharge (Filtration Services) (b) bottom fed, roller discharge (c) bottom fed, string discharge (d) bottom fed, belt discharge (Dorr-Oliver Eimco) (e) top fed (Filtration Services) (f) internal drum.

The filter drums used in ketone dewaxing (rotary vacuum) and in propane dewaxing (Rotary pressure) have filter cloths secured to the drum surface. The filter cloth retains the wax crystals while allowing the filtrate to pass through the filter cake, through the filter cloth and into the internals of the filter drum and eventually to the filtrate receiver drum. 

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