Fines particles

Fluidized-bed catalytic reactors. In fluidized-bed reactors, solid material in the form of fine particles is held in suspension by the upward flow of the reacting fluid. The effect of the rapid motion of the particles is good heat transfer and temperature uniformity. This prevents the formation of the hot spots that can occur with fixed-bed reactors. 

Figure 11.3 Electrostatic precipitation can be used to remove fine particles. (Reproduced with permission from Stenhouse, Pollution Control, in Teja, Chemical Engineering and the Enuironment, Blackwell Scientific Publications, Oxford, U.K., 1981.)...

Solids materials that are insoluble in hydrocarbon or water can be entrained in the crude. These are called bottom sediments and comprise fine particles of sand, drilling mud, rock such as feldspar and gypsum, metals in the form of minerals or in their free state such as iron, copper, lead, nickel, and vanadium. The latter can come from pipeline erosion, storage tanks, valves and piping systems, etc. whatever comes in contact with the crude oil. 

Earlier on when we described the cutting action of the drill bit we learned about the drilling fluid or mud. The mud cools the bit and also removes the cuttings by carrying them up the hole outside the drill pipe. At the surface the mud runs over a number of moving screens, the shale shakers (Fig. 3.11) which remove the cutting for disposal. The fine particles which pass through the screens are then removed by desanders and desilters, usually hydrocyclones. 

For the revelation of the small width particle, reveler products of fine particles give good results (1-2 micron) and inversely for defects of important dimensions (10-50 micron). 

Kitakami O et al 997 Size effect on the crystal phase of cobalt fine particles Phys. Rev. B 56 13 849 Cullity B D 1978 Elements of X-ray Diffraction (Reading, MA Addison-Wesley)... 

The solid in the tower may be supported on a Witt filter plate, but a plug of glass wool is satisfactory the plug of glass wool above the solid acts as a filter for fine particles of the desiccant. 

An interesting example of a large specific surface which is wholly external in nature is provided by a dispersed aerosol composed of fine particles free of cracks and fissures. As soon as the aerosol settles out, of course, its particles come into contact with one another and form aggregates but if the particles are spherical, more particularly if the material is hard, the particle-to-particle contacts will be very small in area the interparticulate junctions will then be so weak that many of them will become broken apart during mechanical handling, or be prized open by the film of adsorbate during an adsorption experiment. In favourable cases the flocculated specimen may have so open a structure that it behaves, as far as its adsorptive properties are concerned, as a completely non-porous material. Solids of this kind are of importance because of their relevance to standard adsorption isotherms (cf. Section 2.12) which play a fundamental role in procedures for the evaluation of specific surface area and pore size distribution by adsorption methods. 

Prepared feeds are marketed in various forms from very fine particles through cmmbles, flakes, and pellets. Pelleted rations may be hard, semimoist, or moist. Hard pellets typically contain less than 10% water and can be stored under cool, dry conditions for at least 90 days without deterioration of quahty. Semimoist pellets are chemically stabilized to protect them from degradation and mold if they are properly stored, while moist pellets must be frozen if they are not used immediately after manufacture. Moist feeds are produced in machines similar to sausage grinders. 

D. L. Dauplaise and M. F. Wemeke, Proceedings of the Consolidation and Dewatering of Fine Particles Conference, University of Alabama, Tuscaloosa, Ala., 1982, pp. 90-113. 

The copolymer latex can be used "as is" for blending with other latexes, such as in the preparation of ABS, or the copolymer can be recovered by coagulation. The addition of electrolyte or free2ing will break the latex and allow the polymer to be recovered, washed, and dried. Process refinements have been made to avoid the difficulties of fine particles during recovery (65—67). 

Homogeneous distribution can be attained by controlled coprecipitation of hydroxides which are then decomposed by calciaation yielding powders of fine particle si2es. Active siaterable powders are produced commercially, usually by hydrolysis of a mixture of ZrOCl2 and YCl to precipitate the mixed... 

When gases that are somewhat soluble in a Hquid concentrate are used, both concentrate and dissolved gas are expeUed. The dissolved gas then tends to escape into the atmosphere, dispersing the Hquid into fine particles. The pressure within the container decreases as the product is dispersed because the volume occupied by the gas increases. Some of the gas then comes out of solution, partially restoring the original pressure. This type of soluble compressed gas system has been used for whipped creams and toppings and is ideal for use with antistick cooking oil sprays. It is also used for household and cosmetic products either where hydrocarbon propeUants cannot be used or where hydrocarbons are undesirable. 

Whenever unvented combustion occurs iadoors or when venting systems attached to combustion units malfunction, a variety of combustion products win be released to the iadoor environment. Iadoor combustioa units include nonelectric stoves and ovens, furnaces, hot water heaters, space heaters, and wood-burning fireplaces or stoves. Products of combustion include CO, NO, NO2, fine particles, aldehydes, polynuclear aromatics, and other organic compounds. Especially dangerous sources are unvented gas and kerosene [8008-20-6] space heaters which discharge pollutants directly into the living space. The best way to prevent the accumulation of combustion products indoors is to make sure all units are properly vented and properly maintained. 

Fig. 4. Terminal velocities in air of spherical particles of different densities settling at 21°C under the action of gravity. Numbers on curves represent tme (not bulk or apparent) specific gravity of particles relative to water at 4°C. Stokes-Cunningham correction factor is included for settling of fine particles.

Eig. 6. Penetration and fractional efficiency for fine particles. Erom ref. 152,... 

Precipitators are currently used for high collection efficiency on fine particles. The use of electric discharge to suppress smoke was suggested in 1828. The principle was rediscovered in 1850, and independently in 1886 and attempts were made to apply it commercially at the Dee Bank Lead Works in Great Britain. The installation was not considered a success, probably because of the cmde electrostatic generators of the day. No further developments occurred until 1906 when Frederick Gardiner Cottrell at the University of California revived interest (U.S. Pat. 895,729) in 1908. The first practical demonstration of a Cottrell precipitator occurred in a contact sulfuric acid plant at the Du Pont Hercules Works, Pinole, California, about 1907. A second installation was made at Vallejo Junction, California, for the Selby Smelting and Lead Company. 

Chaiacteiistics of tfie pads vaiy slighdy witfi mesh density, but void space is typically 97—99% of total volume. Collection is by inertial impaction and direct impingement thus efficiency will be low at low superficial velocities (usually below 2.3 m/s) and for fine particles. The desireable operating velocity is given... 

W. Auyeung and co-workers. Pin Evaluation of Technologies to Produce Fine Particle Si e EDX, ARLCD-TR-85024, ARDEC, Dover, N.J., Sept. 1985. 

Moving-bed percolation systems are used for extraction from many types of ceUular particles such as seeds, beans, and peanuts (see Nuts). In most of these cases organic solvents are used to extract the oils from the particles. Pre-treatment of the seed or nut is usually necessary to increase the number of ceUs exposed to the solvent by increasing the specific surface by flaking or rolling. The oil-rich solvent (or misceUa) solution often contains a small proportion of fine particles which must be removed, as weU as the oil separated from the solvent after leaching. 

Nonnutrient Additives. Nonnutritional dietary additives provide antioxidants to preserve freshness, flavor enhancers to stimulate food selection, color to meet the owner s expectations, pellet biaders to minimi2e fine particles, mycostats to minimi2e mold growth, and iagredient-flow enhancers. Pet foods do not iaclude coccidiostats, antibiotics, added hormonal materials, and fly-larval iasecticides used ia other animal feeds. 

The particle sizes of fillers are usually collected and ordered to yield size distributions which are frequendy plotted as cumulative weight percent finer than vs diameter, often given as esd, on a log probabiUty graph. In this manner, most unmodified fillers yield a straight-line relationship or log normal distribution. Inspection of the data presented in this manner can yield valuable information about the filler. The coarseness of a filler is often quantified as the esd at the 99.9% finer-than value. Deviations from linearity at the high and low ends of the plot suggest that either fractionation has occurred to remove coarse or fine particles or the data are suspect in these ranges. 

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