Rotary table filters

The horizontal rotary table filter incorporates, as its name suggests, a horizontal rotary circular table divided into segments or drainage compartments, each of which is ported to a rotary valve underneath the table. The top surface of the table is fitted with a filter medium and walls are provided around the periphery of the table and around the hub. The feed slurry is distributed across the table through a feed box and vacuum is applied to... 

Figure 11.15 Rotary table filter screw discharge (Courtesy of Dorr Oliver, Croydon, Surrey, UK)...

Table The rotary table filter shown in Figure 1.24 comprises a rotating horizontal table with an annular filter cloth. Vacua are applied over individual...

Figure 1.24 Photograph of a partially assembled horizontal rotary table filter (Dorr-Oliver Eimco). (1) Individual segments on whieh the cloth is mounted (2) feed trough (3) wrash liquor delivery or additional feed points (4) screwr conveyor for cake discharge. A schematic of the table filter cycle is shown in Figure 7.4.

Rotary Disc Filter Rotary Table Filter Rotary Tilting Pan... 

Figure 7.4 Schematic diagram of a rotary table filter cycle.

The tipping (tilting) pan filter obviously, and the rotary table filter somewhat less obviously, are developments of the simple batch vacuum filter described in the previous chapter. The single lipping pan is a batch filter, just like the Nutsche, but other versions, including the table filter, are intended to allow more or less continuous operation. 

The rotary table filter is an extension of the multi-pan filter design. The pans are replaced by segments of the annulus, which still rotates around in a circle so that each segment in turn filters and washes. The segments do not tip, however, to discharge the solid, which is instead scraped off the surface of the filter medium by a screw conveyor, over a flexible outer containing wall. 

Unlike the multi-pan filter, which can have several feed and discharge points, the rotary table filter moves continuously from one feed point to one discharge zone. Both are being supplanted in industrial usage by the horizontal belt filter. 

Comparisons are available on the relative performance and costs for dewatering municipal sludges (2). The relative performance of different filters and conditioners on waste sludges is shown in Table 3. The same sludge was treated on two belt-filter presses, two different centrifuges, and rotary vacuum filter (75). In another study, a variable chamber filter press, fixed-volume filter press, continuous belt-filter press, and rotary vacuum filter were compared for performance, capacity, and capital and operating costs (69). 

Table 7.4. Filtration cycles for drum-type rotary vacuum filter (times in seconds)... 

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. 

Cycle times, air rates, and minimum cake thicknesses in operation of rotary drum filters are stated in Table 11.13. A few special applications of horizontal belt filters are given in Table 11.14, but in recent times this kind of equipment is taking over many of the traditional functions of rotary drum filters. Belt filters are favored particularly for fieely filtering slurries with wide range of particle sizes. 

TABLE 11.18. Typical Performance Data of Rotary Vacuum Filters... 

The equations for sizing rotary-drum filters are summarized in Table 6.18. Equation 6.18.1 is the liquid mass balance. In this procedure, y is a mass fraction. Because the cake is wet, the liquid entering the filter will be less then the liquid leaving. Equation 6.18.2 is the solids mass balance, assuming that all the solids in the slurry are removed. Solve Equation 6.18.2 for the cake formation rate, me. Then, solve Equation 6.18.1 for the filtrate volumetric flow rate, V2. Next, calculate the filtration area from Equation 6.18.5 and the dmm area from Equation 7.18.6. Finally, select a standard rotary filter from Table 6.20. The calculation procedure for sizing a rotary filter is outlined in Table 6.19. Example 6.5 illustrates the sizing procedure. 

Table 6.18 Summary of Equations for Sizing Rotary-Drum Filters ...

Select a standard rotary-dram filter from Table 6.20. 

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