Effective filtration velocity

The dimensions of a bag in a filter unit are 8 in. in diameter and 15ft long. Calculate the filtering area of the bag. If the filtering unit consists of 40 such bags and is to treat 480,000 ft /h of gas from an open-hearth furnace, calculate the effective filtration velocity in feet per minute and acfin per square foot of filter area. Also calculate the mass of particles collected daily if the inlet loading is 3.1 gr/ft and the unit operates at 99.99-b% collection efficiency. 

Grout et al. (1998) question the description of natural samples by simple power laws. According to these authors natural systems are often multifractal which means the fractal dimension varies for different size scales. Veerapaneni and Wiesner (1997) studied the effect of filtration velocity on the fractal dimension of deposits formed by 69 nm colloids. Fractal dimensions increased with increased velocities where a lower head loss was measured, this was attributed to columnar structures formed. 

Selection of Filter Material. The basic requirement for filter fabrics is that they should provide cleanup at the maximum filtration velocity with the lowest possible hydraulic resistance. Moreover, the fabric must be resistant to the effects of high temperatures and aggressive media it must be mechanically strong and must have an adequate dust-holding capacity, i.e., it must retain on its surface a certain quantity of adherent dust in the form of a layer that can be removed readily by mechanical action. 

Murkes has reported tests with the same American dynamic filter, except that he eliminated cake formation altogether by spinning the discs faster. No visible abrasion of the medium was observed while the filtration velocities could be maintained high even at relatively low pressures, below 5 bar. Murkes showed clearly the effect of speed and number of rotor vanes on filtration velocities and specific energy input. His results show, for any number of rotor vanes, an increase in specific energy input (kWh per m of filtrate) with rotor speed this increase can be minimized by optimization of... 

Removal of Particulate Matter. The amount of particulate entering a cooling system with the makeup water can be reduced by filtration and/or sedimentation processes. Particulate removal can also be accompHshed by filtration of recirculating cooling water. These methods do not remove all of the suspended matter from the cooling water. The level of fouling experienced is influenced by the effectiveness of the particular removal scheme employed, the water velocities in the process equipment, and the cycles of concentration maintained in the cooling tower. 

Fibrous or particulate filters are not important anymore because membrane filters are relatively compac t and perform veiy well. For filtration by straining, there is an intermediate air velocity at which filtration efficiency is a minimum because different collec tion mechanisms predominate at different ranges of velocity. At low velocities, diffusional and elec trostatic forces on the particle are important, and increased velocity shortens the time for them to operate. At high velocities, inertial forces that increase with air velocity come into play below a certain air velocity, their effect on collection is zero. Surges or brief power failures could change velocity and collection efficiency. 

Wells, S. A. and Dick, R. I. (1993) "Permeability, Solid and Liquid Velocity, and Effective Stress Variations in Compressible Cake Filtration," Proceedings, American Filtration Society Conference on System Approach to Separation and Filtration Process Equipment, Chicago, Illinois, May 3-6, pp. 9-12... 

The design of a cross-flow filter system employs an inertial filter principle that allows the permeate or filtrate to flow radially through the porous media at a relatively low face velocity compared to that of the mainstream slurry flow in the axial direction, as shown schematically in Figure 15.1.9 Particles entrained in the high-velocity axial flow field are prevented from entering the porous media by the ballistic effect of particle inertia. It has been suggested that submicron particles penetrate the filter medium and form a dynamic membrane or submicron layer, as shown in... 

To continuously separate FT wax products from ultrafine iron catalyst particles in an SBCR employed for FTS, a modified cross-flow filtration technique can be developed using the cross-flow filter element placed in a down-comer slurry recirculation line of the SBCR. Counter to the traditional cross-flow filtration technique described earlier, this system would use a bulk slurry flow rate below the critical velocity, thereby forcing a filter cake of solids to form between the filter media and the bulk slurry flow, as depicted in Figure 15.2b. In this mode, multiple layers of catalyst particles that deposit upon the filter medium would act as a prefilter layer.10 Both the inertial and filter cake mechanisms can be effective however, the latter can be unstable if the filter cake depth is allowed to grow indefinitely. In the context of the SBCR operation, the filter cake could potentially occlude the slurry recirculation flow path if allowed to grow uncontrollably. 

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