Effective filter area

Reliable enclosed filters of ample effective filtering area should be used for both stages. The filter design should not allow the pressure drop to exceed 7kN/m (1 Ibf/in ) across second-stage fine filters in clean conditions. Filters should preferably be of the duplex or self-cleaning type, and installed so that oil spillage will not occur during operation. 

Disc filters are similar in principle to rotary filters, but consist of several thin discs mounted on a shaft, in place of the drum. This gives a larger effective filtering area on a given floor area, and vacuum disc filters are used in preference to drum filters where space is restricted. At sizes above approximately 25 m2 filtration area, disc filters are cheaper but their applications are more restricted, as they are not as suitable for the application of wash water, or precoating. 

The disposable microfilters, CRC thimbles (W. R. Ralston Ltd., Maidstone, Kent, U. K.) shown in Fig. 2 consist of a glass fiber filter disk 1 cm in diameter with an effective filter area of 33 mm, sealed between two polypropylene cylinders. The outer cyclinder has a base perforated... 

Drum, gravity cake formation rate > 3 mm/s solids flux 0.15-0.47 kg/s m of effective filter area. Actual filter area 0.7-15 m. ... 

Filter, plate and frame cast iron, with frames, plates, stand excluding filter medium. FOB cost = 16000 for an effective filter area = 10 m with n = 0.55 for the range 1-150. L+M = 1.8. L/M = 0.42. Alloy factors cast iron, X 1.00 bronze, X 3.0 lead, X 2.4 rubber lined, X 2.7 PVC, X 2.0. 

Filter, plate and frame yellow pine, with frames, plates, stand excluding filter medium. FOB cost = 14 200 for an effective filter area = 10 m with n = 0.50 for the range 1-150. 

Rotary drum filter, vacuum, c/s with swing agitator, panel or wire-wound drum, wash apparatus, variable speed drum drive, trunions, stuffing boxes, scraper discharge, motor and drive excluding vacuum system and vacuum receiver. FOB cost = 210000 for a total drum, nDL, area = 22 m with n = 0.25 for the range 2-22 and n = 0.7 for the range 22-200. FOB cost = 210 000 for an effective filter area =... 

Belt filter, horizontal vacuum 316 s/s for parts contacting the liquid, including drive and motor but excluding vacuum equipment, platforms, tanks, pumps and piping for feed and wash. FOB cost = 400000 for an effective filter area = 9 m with n = 0.64 for the range 10-60. L-i-M = 2.2-3.2. L/M = 0.42. Alloy factors 316 s/s, X 1.00 rubber-coated, X 1.0 c/s, X 0.60. Complexity factors excluding vacuum auxiliaries, X 1.00 including vacuum auxiliaries, X 1.3. 

Example 14-2 A 20-frame (plate and frame filter) has dimensions (per frame) of 0.75 by 0.75 m and a thickness of 0.064 m. If this system is used for the slurry of Example 14-1 find the volume of slurry and time for filtration at a constant pressure of 2.76 x 10 pascals. Effective filtering area per frame is 0.87 m. ... 

Instead of a fiat traverse, the filter cloth may run in a V-shaped path to increase the effective filter area. The units may also operate vertically face downwards, and they may, of course, also be made self-cleaning by continuous recirculation of the filter medium. 

---