Dust collection cyclone

For dust-collecting cyclones (particles 100 /on), SF = 200, whereas conventional centrifuges used in precipitation of submicrometer particles and large molecules in liquid suspension have SF = 5000. 

The separation step requires (1) application of a force that produces a differential motion of the particles relative to the gas, and (2) sufficient gas-retention time for the particles to migrate to the collecting surface. Most dust-collections systems are comprised of a pneumatic-conveying system and some device that separates suspended particulate matter from the conveyed air stream. The more common systems use either filter media (e.g., fabric bags) or cyclonic separators to separate the particulate matter from air. 

A widely used type of dust-collection equipment is the cyclone separator. A cyclone is essentially a settling chamber in which gravitational acceleration is replaced by centrifugal acceleration. Dust-laden air or gas enters a cylindrical or conical chamber tangentially at one or more points and leaves through a central opening. The dust particles, by virtue of their inertia, tend to move toward the outside separator wall from where they are... 

Within the range of their performance capabilities, cyclones are one of the least expensive dust-collection systems. Their major limitation is that, unless very small units are used, efficiency is low for particles smaller than five microns. Although cyclones may be used to collect particles larger than 200 microns, gravity-settling chambers or simple inertial separators are usually satisfactory and less subject to abrasion. 

Cyclone Separators The most widely used type of dust-collection equipment is the cyclone, in which dust-laden gas enters a cylindrical or conical chamber tangentially at one or more points and... 

Reentrainment from the bottom of the cyclone can be prevented in several ways. If a typical long-cone dry cyclone is used and liquid is kept continually drained, vortex entrainment is unlikely. However, a vortex breaker baffle in the outlet is desirable, and perhaps a flat disk on top extending to within 2 to 5 cm (0.8 to 2 in) of the walls may be beneficial. Often liquid cyclones are built without cones and have dished bottoms. The modifications described earlier are definitely needed in such situations. Stern, Caplan, and Rush (Cyclone Dust Collectors, American Petroleum Institute, New York, 1955) and Rietema and Verver (in Tengbergen, Cyclones in Industry, Elsevier, Amsterdam, 1961, chap. 7) have discussed liquid-collecting cyclones. 

Because most of the ash is removed as molten slag, addition of a bottom grate is not necessary.7 However, small TDF is required, because much of the combustion must occur in suspension.7 TDF that is too large to combust completely can get carried over into the boiler or dust collection system, and cause blockage problems.9 Therefore, particle size may inversely determine the amount of TDF that can be used in a cyclone boiler.11 Three cyclone-fired boilers at utilities have burned 1M x 1" TDF in test operation, one at the 2 percent, one at the 5 percent, and one at up to a 10 percent level.3,9,12 One pulp and paper mill plans the use of TDF in a cyclone-fired hog-fuel boiler.13... 

Separation based on rotating flow principles is one of the most common operations involved in gas-solid flows. This section describes the fundamental rotating flow principles and their applications to cyclone operation. The efficiency of dust collection in cyclones is also described. 

Current industry trends are toward the installation of enclosed conveyors and the construction of enclosed areas with negative pressure aspiration for oilseed unloading and meal load-out. Highly efficient dust collection systems and control equipment (cyclones and bag houses) are used throughout the processes to control both fugitive and point source emissions. 

Vatavuk (1990) pointed out that a key dimension in the sizing of a cyclone is the inlet area. Properly designed cyclones can remove nearly every particle in the 20-30 micron range. Typically, cyclone separators have efficiencies in the range of 70-90%. Because of the low efficiency of these units, they are often used as a first stage of dust collection, or are referred to as primary collectors. 

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