Tubular filter

The following pressure filters, varying in type and arrangement of elements, are those in which the elements are contained in a pressure vessel. They offer the advantages of lower labor costs and less opportunity for leakage, when compared to plate and frame filters. 

Tubular filters (Fig. 10) offer low cost construction and high hydraulic capacities. They are made with both rigid and flexible tubes. Celite is used on the rigid tube filters in the usual combination of precoat and body feed. With flexible tube filters, instead of body feed, an extra heavy precoat [25-30 lb (11.4-13.6 kg) filter aid per 100 ft (9.29 m ) filter area] is used. After filter pressure has reached a maximum, the precoat is bumped from the tubes, re-slurried, then re-deposited. This sequence is repeated until pressure is no longer reduced significantly, at which time the precoat is discarded and a new one applied. 

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The advantages of the tubular filter are that it uses an easily replaced filter medium, its filtration cycle can be interrupted and the shell can be emptied of prefilt at any time without loss of the cake, the cake is readily recoverable in dry form, and the inside of the filter is conveniently accessible. There is also no unfiltered heel. Disadvantages are the necessity and attendant labor requirements of emptying by hand and replacing the filter media and the tendency for neavy solids to settle out in the header chamber. Applications are as a scavenger filter to remove fines not removed in a prior-filtration stage with a different land of equipment, to handle the runoff from other filters, and in semiworks and small-plant operations in which the filter s size, versatility, and cleanliness recommend it. 

External-Cake Tubular Filters Several filter designs are available with vertical tubes supported by a filtrate-chamber tube sheet in a vertical cylindrical vessel (Fig. 18-115). The tubes may be made of wire cloth porous ceramic, carbon, plastic, or metal or closely wound wire. The tubes may have a filter cloth on the outside. Frequently a filter-aid precoat will be applied to the tubes. The prefilt slurry is fed near the bottom of the vertical vessel. The filtrate passes from the outside to the inside of the tubes and into a filtrate chamber at the top or the bottom of the vessel. The sohds form a cake on the outside ofthe tubes with the filter area actually increasing as the cake builds up, partially compensating for the increased flow resistance of the thicker cake. The filtration cycle continues until the differential pressure reaches a specified level, or until about 25 mm (1 in) of cake thickness is obtainea... 

FIG. 18-115 Top -outlet tubular filter. (Indust7ial Filter h- Pump Mfg. Co)... 

Candle FilterS Tubular filter elements contained in a matching vessel are known as candle filters. The actual filter vessel may contain one or more filter candles, and may be used as pressure or suction filters for the filtration of liquids and gases. A particular advantage offered is that candles may readily be changed to different types, to suit particular requirements or applications. A typical candle filter is shown in Fig. 11. Materials of candles are selected to fit a particular process. 

Pressure filters are usually operated batch-wise. The batch pressure filters can be classified as tank (pressure vessel) filters or presses. Tank filters have filter elements of different types mounted in pressure vessels. Tank filters are divided into pressure nutsches, leaf filters, candle or tubular filters, bag filters, and cartridge filters. Presses (see Figure 22.38) consist of a series of filter surfaces (plates). The elements are mounted on a frame and are pressed together mechanically. 

FIGURE 58.7 Tubular filter. (From Shirato, M. et al., Filtration— Principles and Practice, eds. M.J. Matteson and C. Orr, Marcel Dekker, New York, pp. 299-423, 1987. With permission.)... 

FIGURE 3.4>14 Tubular filter. Courtesy of the Industrial Filter and Pump Manufacturing CO. 

Tube Press. A high pressure tubular filter... 

A very interesting development of a tubular filter press as a variation of the cross-flow filter took place in the Chemical Engineering Department of the University of Natal in around 1990 . A prototype of this filter was first constructed and operated at Umgeni Water s Hill Water Treatment Plant near Pietermaritzburg. The filter was later available in Britain from Crossflow Microfiltration Ltd (as Exxflow ), further prototypes were tested by Yorkshire Water and an installation made at a new plant at Harrogate, North Yorkshire. The filter consists of several arrays of horizontal tubes hung in... 

Rencken, G. E., Performance studies of the Tubular Filter Press , PhD Thesis, Faculty of Engineering, University of Natal, South Africa (1992)... 

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