Rotary vacuum filter

Filtration is the separation of two phases, particulate form, ie, soHd particles or Hquid droplets, and continuous, ie, Hquid or gas, from a mixture by passing the mixture through a porous medium. This article discusses the more predominant separation of soHds from Hquids. Filtration of soHd particles or Hquid droplets from gases is dealt with elsewhere (see Airpollution controlmethods). The oldest recorded appHcations of filtration are the purifications of wine and water practiced by the ancient Greeks and Romans. Cake filters, such as the rotary vacuum filter and the filter press, were developed much later from the necessity to filter sewage. 

Insofar as they are used to purify other products, several processes used in the refinery fall under the classification of dewaxing processes however, such processes must also be classified as wax production processes (2). Most commercial dewaxing processes utilize solvent dilution, chilling to crystallize the wax, and filtration (28). The MEK process (methyl ethyl ketone—toluene solvent) is widely used. Wax crystals are formed by chilling through the walls of scraped surface chillers, and wax is separated from the resultant wax—oil—solvent slurry by using fliUy enclosed rotary vacuum filters. 

Following carbonation, the product can be further purified by screening. This screening, also used to control the maximum size of the product, is followed by dewatering (qv). Rotary vacuum filters, pressure filters, or centrifuges are used in the mechanical removal of water. Final drying is accompHshed as with natural calcium carbonate in either a rotary, spray, or flash dryer. Products having mean particle sizes from submicrometers (- O-OS fiTo) to several micrometers are available. 

There are two commercial solvent crystaUi2ation processes. The Emersol Process, patented in 1942 by Emery Industries, uses methanol as solvent and the Armour-Texaco Process, patented in 1948, uses acetone as solvent. The fatty acids to be separated are dissolved in the solvent and cooled, usually in a double-pipe chiller. Internal scrapers rotating at low rpm remove the crystals from the chilled surface. The slurry is then separated by means of a rotary vacuum filter. The filter cake is sprayed with cold solvent to remove free Hquid acids, and the solvents are removed by flash evaporation and steam stripping and recovered for reuse (10). 

Modem manufacturing processes quench the roast by continuous discharge into the leach water held in tanks equipped with agitators. At this point the pH of the leach solution is adjusted to between 8 and 9 to precipitate aluminum and siHcon. The modem leaching operations are very rapid because no or htde lime is used. After separation of the ore residue and precipitated impurities using rotary vacuum filters, the cmde Hquid sodium chromate may need to be treated to remove vanadium, if present, in a separate operation. The ore residue and precipitants are either recycled or treated to reduce hexavalent chromium to Cr(III) before disposal. 

Comparisons are available on the relative performance and costs for dewatering municipal sludges (2). The relative performance of different filters and conditioners on waste sludges is shown in Table 3. The same sludge was treated on two belt-filter presses, two different centrifuges, and rotary vacuum filter (75). In another study, a variable chamber filter press, fixed-volume filter press, continuous belt-filter press, and rotary vacuum filter were compared for performance, capacity, and capital and operating costs (69). 

Property Belt-filter Standard press Vacuum-a ssisted Filter Plates press Cloth Rotary vacuum filter Centrifuge... 

Thixotropic filter cakes from rotary vacuum filters that cannot be preformed by any of the above methods can often be scored by knives on the filter, the scored cake discharging in pieces suitable for through-circulation diying. 

Leakage of flammable or toxic chemical from rotary vacuum filter. 

R.G. Holdich, 1990, Rotary Vacuum Filter Scale-up Calculations - and the use of Computer Spreadsheets, Filtration and Separation, 27, pp 435-439... 

Determine the blower requirements for a rotary vacuum filter used for filtering solids from a liquid suspension under the following set of conditions ... 

Filtration of suspensions, e.g. in filter presses, rotary vacuum filters Sedimentation, gravity settling... 

Pharmaceutical Removal of suspended matter is a frequent application for MF. Processes may be either clarification, in which the main product is a clarified liquid, or solids recovery. Separating cells or their fragments from broth is the most common application. Clarification of the broth in preparation for product recovery is the usual objective, but the primary goal may be recovery of cells. Cross-flow microfiltration competes w l with centrifugation, conventional filtration by rotary vacuum filter or filter press and decantation. MF delivers a cleaner permeate, an uncontaminated, concentrated cell product... 

The most important factors in filter selection are the specific resistance of the filter cake, the quantity to be filtered, and the solids concentration. For free-filtering materials, a rotary vacuum filter is generally the most satisfactory since it has a very high capacity for its size and does not require any significant manual attention. If the cake has to be washed, the rotary drum is to be preferred to the rotary leaf. If a high degree of washing is required, however, it is usually desirable to repulp the filter cake and to filter a second time. 

Band filters have several advantages over rotary vacuum filters which are described in the following section. These include ... 

Table 7.4. Filtration cycles for drum-type rotary vacuum filter (times in seconds)... 

Coprecipitation of special cations such as antimony or cerium can improve lightfastness further [2.45]. After treatment in aqueous media, the pigments are washed on a rotary vacuum filter or a filter press until they are free of salt, and then dried using, e.g., belt, spray, or fluidized-bed dryers. 

The equations of this section are applied in Example 11.3 to the sizing of a continuous rotary vacuum filter that employs a washing operation. 

If the peripheral speed were made 1.22m/min, a drum 1.0 m dia would meet the requirements with AP = 0.8 bar. Another controllable feature is the extent of immersion which can be made greater or less than 1/3. Sketches of a rotary vacuum filter are in Figure 11.12. 

TABLE 11.18. Typical Performance Data of Rotary Vacuum Filters... 

Slurry drawn from the crystallizing columns is filtered in rotary vacuum filters where the NaHC03 crystals are water-washed. The filtered liquor then flows to the distillation unit for recovery of ammonia. The crude bicarbonate filter cake contains 3 percent... 

For recovery, the broth is clarified by means of rotary vacuum filters. The penicillin, being acidic, is extracted from the aqueous phase into a solvent, such as methyl isobutyl ketone or amyl acetate, at a pH of 2.5 by means of a continuous countercurrent extractor, such as a Podbielniak. The penicillin is then reextracted with an aqueous alkaline solution or a buffer at a pH of 6.5-7.0. About 90 percent recovery yield is typical at this step. The... 

Scums and Muds. Both phosphatation and carbonatation produce scums or muds that have a moderate level of entrained sucrose, which must be recovered. Various schemes exist for removing the sugar, such as secondary clarification of phosphatation scums and sluicing of car-bonation muds with dewatering on rotary vacuum filters. 

A new plant requires a large rotary vacuum filter for the filtration of zinc sulfite from a slurry containing 1 kg of zinc sulfite solid per 20 kg of liquid. The liquid contains water, sodium sulfite, and sodium bisulfite. The filter must handle 8000 kg of slurry per hour. What additional information is necessary to design the rotary vacuum filter How much of this information could be obtained from laboratory or pilot-plant tests Outline the method for converting the test results to the conditions applicable in the final design. 

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