Filtration 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. 

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

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... 

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

A wide variety of filters are available for the cell recovery. There are generally two major types of filters pressure and vacuum filters. The detailed descriptions of those filter units can be found in Chemical Engineers Handbook (Perry and Chilton, 1973). The two types of filters most used for cell recovery are the filter press and rotary drum filters. A filter press is often employed for the small-scale separation of bacteria and fungi from broths. For large-scale filtration, rotary drum filters are usually used. A common filter medium is the cloth filter made of canvas, wool, synthetic fabrics, metal, or glass fiber. 

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. 

As a member of a design group working on the design of a recovery system for SO, you have been asked to estimate the area necessary for a rotary vacuum filter to handle a zinc sulfite filtration. You are also to determine the horsepower of the motor necessary for the vacuum pump. Do not include any safety factors in your results. 

Laboratory data compiled at the request of the SO,-recovery design group (results of filtration of zinc sulfite slurry on an Oliver rotary vacuum filter) are as follows ... 

Figures 7.5 to Figure 7.7 pertain to the use of rotary vacuum filters in vacuum filtration. In vacuum filtration, a drum wrapped in filter cloth rotates slowly while the lower portion is submerged in a sludge tank (Figure 7.7a). A vacuum applied in the underside of the drum sucks the sludge onto the filter cloth, separating the filtrate and, thus, dewatering the sludge.

FIGURE 7.7 (a) Cross section of a rotary vacuum filter (b) flow sheet for continuous vacuum filtration. 

Holdich, R. G. (1990). Rotary vacuum filter scale-up calculations—and the use of computer spreadsheets. Filtration and Separation. 27, 435-439. 

Continuous filters are most attractive when the process application is a steady-state continuous one, but the rate at which cake forms and the magnitude of production rate are sometimes overriding factors. A rotary vacuum filter, for example, is a dubious choice if a 3-mm (0.12-in) cake will not form under normal vacuum in less than 5 min and if less than 1.4 m /h (50 ft /h) of wet cake is produced. Upper production-rate limits to the practicality of batch units are harder to establish, but any operation above 5.7 m /h (200 ft /h) of wet cake should be considered for continuous filtration if it is at all feasible. Again, however, other factors such as the desire for flexibility or the need for high pressure may dictate batch equipment. 

At the end of the fermentation, protein is separated from cell mass by filtration, typically with a rotary vacuum filter. The crude enzyme concentration is often lower than suitable for commercial applications, so the concentration of enzyme is increased by ultrafiltration. Most cellulase enzymes have a molecular weight of 25,000 to 75,000 and are retained by ultrafiltration membranes of 5000 molecular weight cutoff. The membranes permit the passage of low molecular weight salts, sugars and other impurities, and are sometimes operated in a diafiltration mode to increase the purity of the enzymes. The crude broth at this point is dark brown. 

With the exception of the precoat applications, RVF s do not usually yield absolutely clear filtrate. Although still widely used, rotary vacuum filters are, in some cases, being replaced by membrane separation technology as the method of choice for clarification of fermentation broths and concentrating cell mass. Membranes can yield more complete filtration clarification, but often a wetter cell paste. 

Continuous rotary vacuum filters are sometimes adapted to operate under positive pressures up to about 15 atm for situations in which vacuum filtration is not feasible or economical. This may be the case when the solids are very fine and filter very slowly or when the liquid has a high vapor pressure, has a viscosity greater than 1 P, or is a saturated solution that will crystallize if cooled at all. With slow-filtering slurries the pressure differential across the septum must be greater than can be obtained in a vacuum filter with liquids that vaporize or crystallize at reduced pressure, the pressure on the downstream side of the septum cannot be less than atmospheric. However, the mechanical problems of discharging... 

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