Continuous pressure filters

Batch, semi-batch vacuum filters Continuous vacuum filters Batch, semi-batch pressure filters Continuous pressure filters Compression filters Filtering centrifuges Precoat filters... 

Horizontal vessel filters with vertical rotating elements have been under rapid development with the aim of making truly continuous pressure filters, particularly for the filtration of fine coal. 

Membrane plate and tube presses are dealt with here belt and screw presses are included in the discussion of continuous pressure filters. 

A continuous pressure filter may be defined as a filter that operates at pressure drops greater than 100 kPa and does not require intermption of its operation to discharge the cake the cake discharge itself, however, does not have to be continuous. There is Htfle or no downtime involved, and the dry soHds rates can sometimes be as high as 1750 kg/m h with continuous pressure filters. 

Most continuous pressure filters available (ca 1993) have their roots in vacuum filtration technology. A rotary dmm or rotary disk vacuum filter can be adapted to pressure by enclosing it in a pressure cover however, the disadvantages of this measure are evident. The enclosure is a pressure vessel which is heavy and expensive, the progress of filtration cannot be watched, and the removal of the cake from the vessel is difficult. Other complications of this method are caused by the necessity of arranging for two or more differential pressures between the inside and outside of the filter, which requires a troublesome system of pressure regulating valves. 

Despite the disadvantages, the advantages of high throughputs and low moisture contents in the filtration cakes have justified the vigorous development of continuous pressure filters. 

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. 

Continuous Pressure Filter for the Process Industries, IngersoU-Rand, Nashua, N.H., 1992. 

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. 

Two methods are used to remove the dust cake, both of which require interruption of the airflow. The difference in dust-cake removal conveniently divides filters into intermittent and continuous rating. In the intermittent type the pressure increases (with time) up to a pre-arranged level. The airflow is then stopped and the fabric is mechanically shaken. In the continuously rated filter the pressure drop rises to a low set point, after which it remains constant across the filter as a whole. The cleaning is done by isolating a part of the filter from the air stream and that section is cleaned. 

KCl-langbeinite ore, 20 628. See also Potassium chloride KDF continuous pressure filter,... 

Fig. 40. Production diagram of oligoethylsiloxanes by the continuous technique 1-4, 9, 14, 17 - batch boxes 5, 21 - agitators 6, 36- reactors 7, 10, 11, 19, 26 - coolers 8 - forehydrolyser 12, 18, 23 - settling boxes 13 - neutraliser 15, 20, 24, 29, 40 - collectors 16 - hydrolyser 22 - heat exchanger 25 - distillation tank 27, 30, 33 - receptacles 28 - flusher 31 - purification apparatus 32 - nutsch filter 34 - pressure container 35 - circulation tube 37 - bubble tube 38 - separator 39 - trap 41 - container...

Procedures to run an SDI test call for a 0.45-micron filter pad to be placed with the shiny side up in the filter holder. A small squirt of water from a water bottle is used to wet and completely seat the filter pad. (If the pad shows signs of air bubbles or erratic coverage of foulant of the pad upon removal from the filter holder, the filter was not seated properly and the SDI test is invalid). The isolation valve is opened and the pressure regulator is set to 30 psi. The time it takes to collect 500 ml of water through the 0.45-micron filter pad is then recorded. After this volume of water has been collected, water is allowed to run through the filter continuously for a total time of 15 minutes. If necessary, the pressure should be adjusted to remain at 30 psi. At the end of 15 minutes, the time it takes to collect another... 

In this type of filter, the pressure differential across the filter is achieved by imposing a vacuum on the downstream side, rather than pressure on the upstream side. Both batch and continuous vacuum filters are widely used in... 

Figure 3-3. Pressure ultrafiltration. The solution to be concentrated is placed in the ultrafiltration chamber which is fitted with a semi-permeable membrane on the lower surface, and filtered under pressure. Membrane clogging is prevented by continuous stirring of the solution.

It may be noticed that some of the filters discussed are operated continuously and some are not. For example, the rapid sand filter, the slow sand filter, the pressure filter, and the rotary vacuum filter are all operated continuously. The plate-and-frame press is operated as a batch. Thus, filters may also be classified as continuous and discontinuous. Only the plate-and-frame press is discussed in this chapter as a representation of the discontinuous type, but others are used, such as the shell-and-leaf filters and the cartridge filters. The first operates in a mode that a leaf assembly is inserted into a shell while operating and retracted out from the shell when it is time to remove the cake. The second looks like a cartridge in outward appearance with the filter medium inside it. The medium could be thin circular plates or disks stacked on top of each other. The clearance between disks serves to filter out the solids. 

While the designs of commercially available crystallizer cells have some variances, all are intended to cool and agitate the oil as a batch more or less in the same manner. There are, however, several types of filters in use based on the products and style of operation. These basic designs include plate and frame filters, continuous vacuum systems, membrane systems, and pressure leaf designs. 

Each group may be further subdivided into filters employed in continuous or batch processes although, due to technical difficulties, continuous pressure filters are uncommon and expensive. Centrifugation is another means of removing filtrate. Extensive surveys can be found in the literature. ... 

Vorious pressure filters — Continuous drum Botch leof Botch ptote Botch tubulor element Botch cartridge Batch plote ond frame... 

Various pressure filters — Continuous drum Botch leaf Botch ptote Botch tubular element Batch cortridge Botch plote ond frome... 

The solution photooxidations were performed on 2% solutions of polymer in benzene at 25°C under pure O2 irradiated with a Pyrex-filtered high pressure mercury lamp. Oxygen consumption was monitored continuously by a self-leveling gas buret maintained at atmospheric pressure. Typically, 2.4 g of polymer (20 mmol of repeating units) would consume 0.7 cc of O2 per hour and an experiment would run 24-48 hours. Aliquots could be removed and analyzed by standard methods. 

Spray drying processes can be batch or continuous depending on production needs and the stability of the solutions to be spray dried. Because of reduced product manipulation, microbial and particulate burden can be reduced. Normally there is a solution vessel, a filtration system with prefilters and sterile filters, a pressure vessel to feed the spray dryer at a controlled rate, the spray dryer itself, and bulk containers. 

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