Pressure vessel filter

Pressure Vessel Filters. The several designs of pressure vessel filters all consist of pressure vessels housing a multitude of leaves or other elements which form the filtration surface and which are mounted either horizontally or vertically. With horizontal leaves most suitable where thorough washing is required, there is no danger of the cake falling off the cloth with vertical elements, a pressure drop must be maintained across the element to... 

AUS105 AUS205 Type 3 Type D-3 Good thermal shock resistance high resistance to erosion particularly in alkaline media Pumps, valves, pressure vessels, filter parts, exhaust gas manifolds... 

Pressure filters are usually operated batch-wise. The batch pressure filters can be classified as tank (pressure vessel) filters or presses. Tank filters have different types of filter elements in pressure vessels. Presses consist of a series of filter surfaces (plates). The elements are mounted on a frame and are pressed together mechanically. 

Tank (pressure vessel) filters are useful where noxious vapors are involved, and a completely closed system is desirable. Pressure vessel filters are divided into the following types ... 

Sedimenting centrifuges Filtering centrifuges Hydrocyclones Deep-bed filters Cartridge filters Pressure vessel filters Filter presses Continuous filters Gravity separation equipment... 

These units are sometimes described as pressure vessel filters the vessels used to contain the filter dements are cylindrical designs, positioned vertically or horizontally. These vessels operate in batch mode, with filter cycles similar to plate and fimne filters. The variations available in the type of elements (leaf or candle) and its position in the pressure vessel, lead to a large number of available designs [Purchas, 1981], General operating features of pressure vessel filters have been described [Bosley, 1986] these units are considered to be cleaner and more reliable than other pressure filters, provided adequate attention is given to filter cake properties. 

Thus, Figure 4.4 shows a pressure vessel filter, operating in upflow mode, and developed for the removal of dissolved iron from water supplies. The filter medium takes the form of a bed of catalysed manganese dioxide in grannlar form, approximately 1 m deep. This medium has the ability to cause dissolved iron to react with the oxygen present in the water to form insoluble iron oxides, which will precipitate and be retained by the bed. Cleaning is then undertaken by a high velocity backwash process which fluidizes the bed medium and removes the precipitated iron. 

P. Simard M. Piriou B. Benoist, A. Masia. Wavelet transformation Filtering of eddy current signals. In l th International Conference on NDe in the nuclear and Pressure Vessel Industries, pages 313-317, 1997. 

Optimization of Cycle Times. In batch filters, one of the important decisions is how much time is allocated to the different operations such as filtration, displacement dewatering, cake washing, and cake discharge, which may involve opening of the pressure vessel. Ah. of this has to happen within a cycle time /. which itself is not fixed, though some of the times involved may be defined, such as the cake discharge time. 

Another option available with rotary vacuum dmm filters is fiiU enclosure. This enables operation under nitrogen or other atmospheres, for reasons such as safety, prevention of vapor loss, etc. Enclosure may also be used to prevent contamination of the material being filtered or to confine the spray from washing nozzles. The rotary dmm filter also can be enclosed in a pressure vessel and operated under pressure. 

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. 

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. 

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. 

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. 

Drum Filters. The rotary dmm filter, also borrowed from vacuum filtration, makes relatively poor use of the space available in the pressure vessel, and the filtration areas and capacities of such filters cannot possibly match those of the disk pressure filters. In spite of this disadvantage, however, the pressure dmm filter has been extensively developed. 

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. 

TDF Drum Filter. This is a fairly conventional dmm filter housed in a vertical pressure vessel. Test data, obtained with the smallest model of only 0.75 m filtration area, is available (18). Larger models have also been announced, ranging up to the filtration area of 46 m and very large vessels. The operating pressures are moderate, up to 25 or 35 kPa, and the dmm speeds fairly conventional from 0.3 to 1.5 rpm. The range of dry cake production quoted is from 250 to 650 kg/m h for fine coal. 

A plate-type filter, the PDF filter (18), uses a paddle wheel with radial, longitudinal plates coveted with filter cloth and manifolded to the filter valve at one end of the vessel, instead of a dmm. This filter uses a horizontal pressure vessel, was built to have only 0.75 or 1.5 m area, and operates at 25 kPa. A central screw conveyor collects the cake blown off the plates and conveys it to the discharge end of the vessel. 

A horizontal belt filter has been used in place of the small dmm filter in filtration studies (17). The entire filter was placed in a large pressure vessel with no moving parts passing through the filter shell. There is no commercial filter based on this principle the utilization of the space inside the pressure vessel would be poor and the filtration areas limited. 

Since its conception, the dynamic filter has been widely reported and further developed. Most European designs are comprised of a multistage disk arrangement (Fig. 28) with both the rotating and stationary elements covered with filter cloth, thus utilising the space inside the pressure vessel. Such filters have been found (29) to be from 5 to 25 times more productive in mass of dry cake per unit area and time than filter presses for the same moisture content of the final slurry. In some cases, the moisture content with the dynamic filter was actually lower than with a filter press. The maximum productivity was achieved with peripheral disk speeds from 2.8 to 4.5 m/s. 

The axial filter (Oak Ridge National Laboratory) (30) is remarkably similar to the dynamic filter in that both the rotating filter element and the outer shell are also cylindrical. An ultrafiltration module based on the same principle has also been described (31). Unlike the disk-type European dynamic filters described above, the cylindrical element models are not so suitable for scale-up because they utilize the space inside the pressure vessel poorly. 

Carbonates. Basic zirconium carbonate [37356-18-6] is produced in a two-step process in which zirconium is precipitated as a basic sulfate from an oxychloride solution. The carbonate is formed by an exchange reaction between a water slurry of basic zirconium sulfate and sodium carbonate or ammonium carbonate at 80°C (203). The particulate product is easily filtered. Freshly precipitated zirconium hydroxide, dispersed in water under carbon dioxide in a pressure vessel at ca 200—300 kPa (2—3 atm), absorbs carbon dioxide to form the basic zirconium carbonate (204). Washed free of other anions, it can be dissolved in organic acids such as lactic, acetic, citric, oxaUc, and tartaric to form zirconium oxy salts of these acids. 

Internal Cake Tube Filters or Liquid Bag Filters This type of filter, such as manufactured by Industrial Filter and Pump Mfg. Co., Rosedale, Illinois, and many others, utihzes one or more perforated tubes supported by a tube sheet or by the hp of the pressure vessel. A cyhndrical filter bag sealed at one end is inserted into the perforated... 

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. 

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