Disk filters

Compared to disk thickeners disk filters (Fig. 4.48) additionally apply vacuum to further increase the consistency, production, and retention. They are used for white water cleaning in the paper machine water circuit (save-all) and for dewatering of pulp suspensions in pulping. Typical consistencies are 0.5-1.3 % at the inlet 

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Rotary Vacuum Disk Filters. An alternative to the dmm filter is the disk filter, which uses a number of disks mounted vertically on a horizontal shaft and suspended in a slurry reservoir. This arrangement provides a greater surface area for a given floor space, by as much as a factor of 4, but cake washing is more difficult and cloth washing virtually impossible. 

Total submergence is used in the vacuum disk filter thickener (Eig. 13) in which the cake discharge, by backwashing with filtrate, occurs as each sector passes through the lowest point of the slurry tank. 

In conventional disk filters, cake discharge is usually performed by a scraper blade, for cakes thicker than 10 mm, or sometimes by a tapered roU air blowback is often used to assist the discharge. High pressure sprays also have been used for cake discharge. 

Horizontal or vertical vessel filters, especially those with vertical rotating elements, have undergone rapid development with the aim of making truly continuous pressure filters, particularly but not exclusively for the filtration of fine coal. There are basically three categories of continuous pressure filters available, ie, disk filters, dmm filters, and belt filters including both hydrauHc and compression varieties. 

There are many technical problems to be considered when developing a new commercial and viable filter. However, the filtration hardware in itself is not enough, as the control of a continuous pressure filter is much more difficult than that of its equivalents in vacuum filtration the necessary development may also include an automatic, computerized control system. This moves pressure filtration from low to medium or even high technology. Disk Filters. 

The Gaudfrin disk filter, designed for the sugar industry and available in Prance since 1959, is also similar in design to a vacuum disk filter but it is enclosed in a pressure vessel with a removable Hd. The disks are 2.6 m in diameter, composed of 16 sectors. The cake discharge is by air blowback, assisted by scrapers if necessary, into a chute where it may be either reslurried and pumped out of the vessel or, for pasty materials, pumped away with a monopump without reslurrying. 

The Gaudfrin disk filter is designed for only relatively low pressures of 100 kPa on average and it provides for cake washing in two stages, in two separate compartments within the same vessel. 

The KDF Filter. The KDP filter (Pig. 23) (Amafilter, Holland) is based on the same principle as disk filters. It was developed for the treatment of mineral raw materials, like coal flotation concentrates or cement slurries, and can produce a filter cake of low moisture content at very high capacities, up... 

The KHD Pressure Filter. Another development of the disk filter has been reported (KHD Humboldt Wedag AG, Germany). A somewhat different system, probably a predecessor, was patented (15). 

The disk filter is similar to the dmm in operation, but filtration is conducted using a series of large diameter filter disks that carry the filter medium on both sides of the disk. They are connected to the main horizontal shaft and partly immersed in the feed slurry. The central shaft is connected by a set of valves which serve to provide vacuum and air as in dmm filters. As the disk sections submerge during rotation, vacuum is appHed to form a cake on both sides of the disk. The cycle of operation is similar to that in a dmm filter. One unit can have as many as 12 disks of up to 5-m diameter. Disk filters, both compact and cost effective, are used extensively in the iron ore industry to dewater magnetite concentrates. 

There are, however, certain special applications where the filter medium around the edge of the section may be dehberately blinded by painting in order to improve cake discharge. This technique is most frequently used on disk filters, with the result that the actual area may be only 75 to 85 percent of the nominal area. This is a significant deviation from the nominal area and must be considered separately. 

Continuous Pressure Filters These filters consist of conventional drum or disk filters totally enclosed in pressure vessels. Filtration takes place with the vessel pressurized up to 6 bar and the filtrate discharging either at atmospheric pressure or into a receiver maintained at a suitable backpressure. Cake discharge is facilitated through a dual valve and lock-hopper arrangement in order to maintain vessel pressure. Alternatively, the discharged filter cake can be reslurried within the filter or in an adjoining pressure vessel and removed through a control valve. 

Disk Filters A disk filter is a vacuum filter consisting of a number of vertical disks attached at intervals on a continuously rotating horizontal hollow central shaft (Fig. 18-127). Rotation is by a gear drive. Each disk consists of 10 to 30 sectors of metal, plastic, or wood, ribbed on both sides to support a filter cloth and provide drainage via an outlet nipple into the central shaft. Each sector may be replaced individually. The filter medium is usually a cloth bag slipped over the sectors and sealed to the discharge nipple. For some heavy-duty applications on ores, stainless-steel screens may be used. 

Ptdp) filtei. s. These filters employ one or more packs of filtermasse (cellulose fibers compressed to a compact cylinder) stacked into a pressure case. The packs are sometimes supported in individual trays which provide drainage channels and sometimes rest on one another with a loose spacer plate between each two packs and with a drainage screen buried in the center of each pack. The liquid being clarified flows under a pressure of 345 kPa (50 psig) or less through the pulp packs and into a drainage manifold. Flow rates are somewhat less than for disk filters, on the order of 20 L/(min-m ) [0.5 gal/ (min-ft")]. Pulp filters are used chiefly to polish beverages. The filtermasse may be washed in special washers and re-formed into new cakes. 

Plate pr esses. Sometimes called sheet filters, these are assemblies of plates, sheets of filter media, and sometimes screens or frames. Thev are essentially modified filter presses with practically no cakeholding capacity. A press may consist of many plates or of a single filter sheet between two plates, the plates may be rectangular or circular, and the sheets may lie in a horizontal or vertical plane. The operation is similar to that of a filter press, and the flow rates are about the same as for disk filters. The operating pressure usually does not exceed 138 kPa (20 psig). The presses are used most frequently for low-viscosity liqmds, but an ordinaiy filter press with thin frames is commonly used as a clarifier for 100-Pa s (1000-P) rayon-spinning solution. Here the filtration pressure may be 6900 kPa (1000 psig). 

Disk Filters Disk filters consist of a number of concentric disks mounted on a horizontal rotary shaft. The operating principle is the same as that of rotary-drum vacuum filters. The basic design is illustrated in Figure 22. The disks are formed by using V-shaped hollow sectors assembled radially about a central shaft. Each sector is covered with filter cloth and has an outlet nipple coimected to a manifold... 

Continuous vacuum filters are mostly of the constant pressure type and are mainly used in dewatering concentrated slurries such as concentrates. These filters are classified into disk, drum, and horizontal filters. The drum and the disk filters are the mainstay for most final detwatering, the drum filters being used to a lesser extent than the disk filters. These two groups of filters remove most fine particles from a process stream. 

Disk filters, 11 374-377 16 658. See also Rotary disk vacuum filters Disk flat blade turbine, 16 701 Disk meters, nutating, 11 655 Disk pumps, 21 69 Dislocation density, 13 496 Disodium 5 -guanylate (GMP), 12 49 Disodium 5 -inosinate (IMP), 12 49 Disodium acetylide, 22 765 Disodium cocoamphodiacetate, cosmetic surfactant, 7 834t Disodium decacarbonyldichromide, 6 528-529... 

Other filter designs such as the stacked-disk filter exist, but are not common. 

The double drum filter of Figure 11.12(e) has obvious merit particularly when top feeding is desirable but it is not used widely nowadays. Disk filters of the type of Figure 11.12(f) are the most widely used rotary type when washing of the cake is not necessary. 

The American filter, a similar disk filter, also available in 4ft diameter, with 20 sqft disk. 

Vacuum filters include the nulschc filter, enclosed agitated vacuum fillers, the vacuum leaf filter, the tipping pan filter, horizontal rotating pan filters, horizontal belt vacuum fillers, rotary vacuum drum lilters. and rotary vacuum disk filters. 

Disk tillers include the McGaskell and Gaudfrin disk filters, the KDF tiller, and the KHD pressure litter. 

Sterilize the filter system. Figure 13 shows a hypothetical test system for a disk filter medium. 

Figure 13 Hypothetical disk-filter bacterial challenge test appartus.

For example, if a 293-mm-diameter disk filter system having an EFA of 530 cm2 is challenged and the 107/cm2 level is used, the total challenge to the filter is 5.3 x 109 organisms. If a sterile filtrate is assumed the LRV would be calculated and reported as follows ... 

Figure 10.5 Principle of photoDSC. (a) The sample (solid or liquid film) is placed in the DSC pan. Light is introduced by two optical fibers. Two sapphire disks filter the wavelength and complete the thermal insulation of the DSC furnace.

Serra CA, Wiesner MR, Laine JM (1999), Rotating membrane disk filters design evaluation using computational fluid dynamics, Chem. Eng. J. 72 1-5. 

Many types of continuous filters, such as rotary-drum or rotary-disk filters, are employed in industrial operations. Development of the general design equations for these units follows the same line of reasoning as that presented in the development of Eq. (38). The following analysis is based on the design variables for a typical rotary vacuum filter of the type shown in Fig. 14-61. 

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