Submerged filters

TABLE 25-44 Anaerobic Process Performance on Industrial Wastewater UASB/ Submerged filter (SF)/ FBR... 

The stuffing boxes on high submergence filters should be Inspected for leakage and, if necessary, the stud nuts should be tightened. It should be noted that excess tightening can increase substantially the load on the drum drive so the use of a torque wrench is recommended. 

Drum, rotary vacuum cake formation rate 0.01-17 mm/s solids flux 0.008-0.16 kg/s m of submerged filter area filtrate flux 0.08-1 L/s m of submerged... 

G. Koether, H. Bergmann and H. Oumeraci, Wave attenuation by submerged filter systems, Proc. 4th Int. Conf. Hydrodynamics (ICHD 2000), Yokosuka, Japan, Vol. 2... 

J. Recio and H. Oumeraci, Preliminary experiments and numerical simulations of solitary wave acting on a submerged-filter-reef, Leichtweiss-Institute for Hydraufic Engineering and Water Resources, LWI Report No. 945 (2006). 

A filter cake from the wringer is washed to remove absorbed acid, transferred to a slurry tank of water, and quickly submerged, after which the nitrocellulose is pumped to the stabilization operation as a diluted water slurry. Exhaust systems are installed to protect personnel and equipment from acid fumes, and water sprays and cyclone separators are used for acid fume recovery before venting to the air. 

For given operating conditions and submergence, the dry cake production rate increases with the speed of rotation (eq. 10) and the limiting factor is usually the minimum cake thickness which can stiU be successfiiUy discharged by the method used in the filter. Equation 11 shows the dependence of the sohds yield on cake thickness ... 

In most rotary dmm filters, the submergence of the dmm is usually about one-third of its circumference. Greater submergence is achieved in units equipped with submerged bearings, although this is more cosdy. 

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. 

A test unit has been developed of a small dmm filter, total filter area of 0.7 m with 30% submergence, housed in a large horizontal pressure vessel. 

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. 

The most effective phosphoms production technology uses a submerged arc furnace. The submerged arc furnace performs three functions chemical reactor, heat-exchanger, and gas—soHd filter, respectively, each of which requires a significant amount of preparation for the soHd furnace feed materials. 

Anaerobic Filter. The anaerobic filter is similar to a trickling filter ia that a biofilm is generated on media. The bed is fully submerged and can be operated either upflow or downflow. For very high strength wastewaters, a recycle can be employed. 

Cake Thickness Control Sometimes the rate of cake formation with bottom feed-type filters is rapid enough to create a cake too thick for subsequent operations. Cake thickness may be controlled by adjusting the bridge-blocks in the filter valve to decrease the effective submergence, by reducing the slurry level in the vat, and by reducing the vacuum level in the cake formation portion of the filter valve. If these measures are inadequate, it may be necessaiy to use a toploading filter. 

Example 1 Sizing a Dish Filter Eqiiipmeut physical factors, selected from Table 18-9 Maximum effective siihmergeuce = 28% maximum portion of filter cycle available for dewatering = 45%. (High submergence versions require tninnion seals, and their use is hmited to specific apphcations.)... 

Example 2 Sizing a Drum Belt Filter with Washing Equipment physical factors, selected from Table 18-9 Maximum effective submergence = 30% max. apparent suhm. = 35% max. arc for washing = 29% portion of cycle under vacuum = 75%. 

Since (c) is larger than (a) in the previous step, too thick a cake will be formed and it will not wash or dry adequately unless the effective submergence is artificially restricted to yield the design cake thickness. This may be accomplished by proper bridge-block adjustment or by vacuum regulation within the form zone of the filter valve. 

Rotation speeds to 40 r/min are possible with cakes typically 3 to 6 mm (0.12 to 0.24 in) thick. Filter sizes range from 930 cm to 19 m (1 to 207 ft") with 93 percent of the area active. The slurry is fed into a conical feed tank designed to prevent solids from settling without the use of mechanical agitators. The proper hquid level is maintained by overflow, and submergence ranges from 5 to 70 percent of the drum circumference. 

Packed-Bed Fixed-Film Systems These systems were originaUy termed anaerobic trickhng filters because the first systems were submerged columns filled with stones run under anaerobic conditions (Fig. 25-57). A wide variety of packed media is now used ranging in size from graniiles 40 mesh to 7.5-cm (3—in) stones. Many systems use open structure plastic packing similar to that used in aerobic trickhng filters. 

---