Dust collection structure

In this process EAF dust, other zinc-bearing wastes, recycled materials, coke or coal, lime, and silica are mixed and fed to a rotary furnace. The zinc and other volatile nonferrous metals in the feed are entrained in the furnace off-gas and are carried from the furnace to an external dust collection system. The resulting oxide (zinc calcine) is a crude zinc-bearing product that is further refined at zinc smelters. A byproduct of the process is a nonhazardous, iron-rich slag that can be used in road construction. Solidification technologies change the physical form of the waste to produce a solid structure in which the contaminant is mechanically trapped. 

Fib er-Bed Scrubbers Fibrous-bed structures are sometimes used as gas-liquid contactors, with cocurrent flow of the gas and liquid streams. In such contactors, both scrubbing (particle deposition on droplets) and filtration (particle deposition on fibers) may take place. If only mists are to be collected, small fibers may be used, but if solid particles are present, the use of fiber beds is limited by the tendency of the beds to plug. For dust-collection service, the fiber bed must be composed of coarse fibers and have a high void fraction, so as to minimize the tendency to plug. The fiber bed may be made from metal or plastic fibers in the form of knitted structures, multiple layers of screens, or random-packed fibers. However, the bed must have sufficient dimensional stability so that it will not be compacted during operation. 

If ultrafme particles can be agglomerated, the mass of the new entity is equal to the sum of aU particles in the structure and mass related forces as well as inertia increase proportionately. After agglomeration, ultrafine particles, in their new form, can be removed in standard dust collection devices such as cyclones and packed bed filters. 

Conversely, by constructing the filter medium with a blend of fibres of widely contrasting triboelectric properties, it is claimed by a fibre manufacturer that superior collection efficiency can be obtained. It is further claimed that, by virtue of this enhanced efficiency, a more open structure can be used with consequent advantages in respect of the reduced power consumption required to pull the dust-laden air through the collector. However, although this effect has been used to some advantage in clean air room filtration applications, considerably more research is necessary if the triboelectric effects in industrial dust collection are to be fully understood and exploited. 

As in dust collection, where surface coatings have been available for many years, the treatments are designed to present a microporous structure to the slurry which effectively restricts the penetration of particles to all but a few micrometres in depth. Consequently, a filter cake quickly forms on the surface of the coating and by restricting the particles to the surface, the same cake can be easily discharged at the end of the filtration cycle. Unlike the coatings in dust collection, however, the microporous structure in liquid applications has to withstand much higher pressures. Failure to do so will result in structural collapse and premature pressurisation of the filter. 

Electrical forces may also act on dust particles before they come into contact with the surface (see Section 16) i.e., it is possible in principle to make coatings that are dust repellent, principally with reference to atmospheric dust. An example may be found in alkyd-styrene structural paints with a low binder content [221]. A similar result can be achieved by treatment of various particles with a 1% aqueous solution of the cationic substance Arquad 18, which, according to data furnished by Armour (USA), prevents dust accumulation on the articles for a period of several months. In this particular case, the dust-retention tendency is reduced by removal of the electric charges from plastic articles by a process that is analogous to the action of antistatic agents [222]. Also available are dust-collecting paints and enamels, which create their own electric field. 

A variety of fabrics styles are employed in dust collection, these being chosen according to the physical forces that will be imposed by the filter and the quantity and abrasive nature of the dust being collected. As a consequence, for reverse air and pulsejet filters needlefelts are preferred whereas for shake filters both woven and needlefelt structures are used. By comparison for cartridge filters spunbonded, meltblown and electrospun fabrics are more likely to be found. 

A) Where lead containing coatings or paint are present manual demolition of structures (e.g., dry wall), manual scraping, manual sanding, heat gun applications, and power tool cleaning with dust collection systems ... 

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