Rotary drum filter cycle

Figure 7.2 Schematic of a bottom fed rotary drum filter cycle with knife discharge. The cycles of the alternative roller, string and belt discharge variants are similar and differ only (from the viewpoint of calculation) in the fraction of the drum devoted to cake discharge.

Figure 7.3 Illustration of a top fed rotary drum filter cycle.

Table 7.7 Data sequences for the filtration phase of a rotary drum filter cycle. ...

Table 7.10 Data sequences for the washing phase of a rotary drum filter cycle where cake deliquoring has occurred prior to the commencement of washing. Values for t , tj, q>, f and (/> are the same as those shown in Table 7.9.

Figure 7.9 Schematic representation of the example rotary drum filter cycle. Cake formation phase 0 122°, rise phase 122 -> 198°, washing phase 198 252°, deliquoring phase 252 324° and cake discharge 324 360°.

Figure 13. Cycle sequence of a rotary drum filter.

The rotary drum filter is a continuous filtration device, because it does not have to be shut down during the cycle, although the operation is still cyclic. A schematic is shown in Fig. 13-8. The drum rotates at a rate N (rpm), and the filter area is the total drum surface, i.e., A = izDL. However, if the fraction of the drum that is in contact with the slurry is /, then the length of time in the cycle during which any one point on the surface is actually filtering is f/N ... 

A rotary drum filter is used to filter a slurry. The drum rotates at a rate of 3 min/cycle, and 40% of the drum surface is submerged in the slurry. A constant pressure drop at 3 psi is maintained across the filter. If the drum is 5 ft in diameter and 10 ft long, calculate the total net filtration rate in gpm that is possible for a slurry having properties as determined by the following lab test. A sample of the slurry was pumped at a constant flow rate of 1 gpm through 0.25 ft2 of the filter medium. After 10 min, the pressure difference across the filter had risen to 2.5 psi. The filter medium resistance may be neglected. 

Filtration is carried out in a plate and frame filter press, with 20 frames 0.3 m square and 50 mm thick, and the rate of filtration is maintained constant for the first 300 s. During this period, the pressure is raised to 350 kN/m2, and one-quarter of the total filtrate per cycle is obtained. At the end of the constant rate period, filtration is continued at a constant pressure of 350 kN/m2 for a further 1800 s, after which the frames are full. The total volume of filtrate per cycle is 0.7 m3 and dismantling and refitting of the press takes 500 s. It is decided to use a rotary drum filter, 1.5 m long and 2.2 m in diameter, in place of the filter press. Assuming that the resistance of the cloth is the same in the two plants and that the filter cake is incompressible, calculate the speed of rotation of the drum which will result in the same overall rate of filtration as was obtained with the filter press. The filtration in the rotary filter is carried out at a constant pressure difference of 70 kN/m2, and the filter operates with 25 per cent of the drum submerged in the slurry at any instant. 

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. 

The cycle shown in Figure 22.42 for a rotary drum filter consists of... 

Example 30.3. A rotary drum filter with 30 percent submergence is to be used to filter a concentrated aqueous slurry of CaCOj containing 14.7 lb of solids per cubic foot of water (236 kg/ra ). The pressure drop is to be 20 in. Hg. If the filter cake contains 50 percent moisture (wet basis), calculate the filter area required to filter 10 gal/min of slurry when the filter cycle time is 5 min. Assume that the specific cake resistance is the same as in Example 30.2 and that the filter-medium resistance R is negligible. The temperature is 20°C. 

EXAMPLE 14.2-4. Filtration in a Continuous Rotary Drum Filter A rotary vacuum drum filter having a 33% submergence of the drum in the slurry is to be used to filter a CaCO slurry as given in Example 14.2-1 using a pressure drop of 67.0 kPa. The solids concentration in the slurry is = 0.191 kg solid/kg slurry and the filter cake is such that the kg wet cake/kg dry cake = m — 2.0. The density and viscosity of the filtrate can be assumed as that of water at 298.2 K. Calculate the filter area needed to filter 0.778 kg slurry/s. The filter cycle time is 250 s. The specific cake resistance can be represented by a = (4.37 x 10 ) (—Ap) , where —Ap is in Pa and a in m/kg. 

Throughput in Continuous Rotary Drum Filter. A rotary drum filter having an area of 2.20 m is to be used to filter the CaCO slurry given in Example 14.2-4. The drum has a 28% submergence and the filter cycle time is 300 s. A pressure drop of 62.0 kN/m is to be used. Calculate the slurry feed rate in kgslurry/s for the following cases. 

In Section 7.1 the principal features of common continuous filter cycles are described, while Section 7.2 presents the equations required to model these cycles. Section 7.3 provides detailed example calculations for the horizontal belt filter and the rotary drum filter as these are representative of typical continuous cycles. Section 7.4 shows how computer simulations can be used to examine in detail the effects of process variables on... 

A high value catalyst is to be separated from aqueous suspension at a temperature of 50°C using a bottom fed, knife discharge, rotary drum filter. The drum is 2.5 m in diameter, 1.4 m in width and rotates at 0.2 rpm. The filter cycle follows the conventional sequence of cake formation, displacement washing (also at 50°C) and gas deliquoring, and all phases take place at an applied vacuum of 70 kPa. The characteristics of the catalyst and suspension are shown in Table 7.6 along with other operational parameters of the filter. 

A 20-frame (0.3-m square, 50-mm frame thickness) plate and frame filter press is operated first at constant rate for 300 sec to a pressure of 350 kN/m (one-fourth total filtrate obtained). Filtration then takes place at 350 kN/m for 1800 sec until the frames are full. Total filtrate volume per cycle is 0.7 m. Breaking down and reassembly requires 500 sec. A replacement rotary drum filter (1.5 m long, 2.2-m diameter) is to give the same overall filtration rate as the plate and frame unit. Assume that resistance of the filter cloth is the same and that the filter cakes are incompressible. What is the speed of rotation if pressure difference is 70 k N/m and drum submergence is 25 percent ... 

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