Document gDdB484onpGwL37wQGpm6V9kG

274 w. n. witheridge B. TWO-STAGE CLEANING SYSTEMS A natural outgrowth of the classification shown on page 240 is a basic two stage system comprising a preparation stage and a separation stage. There are.;, number of well-known examples of this arrangement now in use: (1) two-stag electric precipitator, with particle charging preceding precipitation (Figu re 19)' (2) venturi scrubber, with simultaneous agitation and liquid injection pr cedin' cyclone separation (Figure 23), (S) sonic agglomeration systems, with simu taneous agglomeration and gravitational precipitation followed by ineftial centrifugal separation. In the third example, preparation itself may occur in tvfj stages, when fog is injected at the entrance to the sonic chamber to improve tK cohesive property of particle aggregates. C. CONCENTRATORS: SUBDIVISION OF AIR STREAMS As the air passes through a cleaning system, it may be handled as a sing' stream from inlet to outlet. There are numerous installations, however, iij whi' the air stream is subdivided one or more times in order to specialize the tasks cleaning and make each stage more effective. A common example is conveya of the small-volume high-concentration effluent from the apex or periphery oi cyclone to a secondary separator generating greater centrifugal force. In sfl cases the primary cyclone may be designated as a concentrator. The louverfed cq separator described earlier (Figure 3) is also a concentrator from which a sin1 fraction of the air flow is directed to a centrifugal separator for more compf .remaval-of.air=borne-paxticles................... .................. ........ XIV. Entrainment Prevention In dust-collecting problems, the attention of air-cleaning engineers has b focused,almost entirely upon the forces of separation, with little attempt tip brj the dust-raising or entraining forces into view. As a result, there is practicjalf^ reliable published information, at this time, on the action of separating deiliceif dust-suspending mechanisms, which most of them are to some extent. Iritiregt this problem may begin with a consideration of studies dealing with thfc df raising ability of winds in open air, and with the action of controlled air . impinging against dusty surfaces. ! I-H"th'eBbBTOF-ef"aast"-entratomt"data" forT-specifir^paratorTtK^n^ air stream. One of the easiest ways is the application of a liquid film that oarried off by gravity or centrifugal force. A. AIR TURBULENCE Although air turbulence can be quite helpful in diffusional and contact esses, it is generally damaging in inertial and impact processes where con the particle trajectory is desired. In diffusional processes, increased tur AIR CLEANING 275 -fates the approach to equilibrium at the interface or boundary between the ffd the solid or liquid separating material. In inertial processes, the probaipf resuspension or entrainment of particles increases as air velocity increases, Gits resulting increase in air turbulence. Therefore, the use of increased air IfSfty to improve separation by higher centrifugal forces makes it necessary to ngp deflecting surfaces so that air may turn at high speed over smooth1 suri||ncountering a minimum of irregularities that cause air turbulence and ||e entrainment. B. VISCOUS LIQUIDS OR ADHESIVES '.gparating surfaces may be treated continuously with liquids to improve Son and facilitate disposal of accumulated solids. They may also be treated iSically with liquids of relatively high viscosity that remain on the surfaces fremoved by cleaning or regenerating procedures. Accordingly, the desired Sties of the adhesive are influenced in large measure by the design and ling features of the separator or filter. Nevertheless, it is possible to state liirable characteristics in general terms so that application engineers may be ' 3rd in their selection of viscous liquids or adhesives for special duty. fple Characteristics of Separator Adhesives t Viscosity should vary only slightly within the specified range of operating iratures. % Viscosity should be low enough to permit a continuous flow of liquid in ag systems. I Surface tension should be sufficient to maintain an even film over the ft surfaces, prevent draining of liquid from upper portions of the medium in ^prized systems, and prevent carry-over of mist. IT; Surface tension should not be high enough to inhibit the penetration of Sgarticles. ES: Capillarity should be sufficient to keep the exposed surfaces of the deposit Volatility should be low. ^Adhesive should be odorless at the maximum operating temperature, ?iri3i?tiieating air for human consumption. mfjjjpAdhesive should be fire-resistant, and preferably nonflammable, to pre' '" Yoke panic and damage. . Adhesive should inhibit or prevent the growth of spores or bacteria. ' Si;f?olubility in water is desirable to facilitate the cleaning of collecting XV. Continuous Service Arrangements There is a growing demand for air-cleaning systems having steady and con|,,performance characteristics, and the ability to operate for long periods of Without interruption for regeneration or removal of collected materials.