Dust deposition

Air cleaning systems are often used to remove dust or vapors from plant or process exhaust streams. Dust collecting systems such as filters or electrostatic precipitators that handle heavy loads of dust are usually designed to be self-cleaning, but it is stiU. necessary to enter the air cleaner periodically for inspection or repair. Dust deposits inside the equipment are likely to be stirred up and inhaled by unprotected workers. Baghouses are particularly likely to cause exposure because large amounts of dust may be retained in the cloth and released when the bags are handled. 

For combustible dusts, the explosibility limits do not have the same meaning as with flammable gases and flammable vapors, owing to the interaction between dust layers and suspended dust. This protective measure can, for example, be used when dust deposits are avoided in operating areas or in the air stream of clean air lines after filter installations WTiere in normal operation the lower explosibility limit is not reached. However, dust deposits must be anticipated with time. When these dust deposits are whirled up in the air, an explosion hazard can arise. Such a hazard can be avoided by regular cleaning. The dust can be extracted directly at its point of origin by suitable ventilation measures. 

FPN No. 2) Where products such as seed are handled in a manner that produces low quantities of dust, the amount of dust deposited may not warrant classification. 

Acoustical ceilings do have certain draw backs. They are fragile, porous, and attractive to dust. Areas siurounding air intakes will soon show dust deposits, but periodic vacuuming with a soft brush attachment will keep a ceiling in good shape for a long time. 

Acoustical tile was specified for all ceilings, with the engineering firm selecting the appropriate tj pe. Perfonnance was good, the tiles seemed to have a low dirt pick-up, and dust deposits near the ventilation outlets w ere minimal. 

E. Baath, A. Frostegard, and H. Fritze, Soil bacterial bioma.ss, activity, phospholipid fatty acid pattern, and pH tolerance in an area polluted with alkaline dust deposition, Appl. Environ. Microbiol. 5S 4026 (1992). 

Fig. 3.23 Left-. Calculated relationship between the thickness of an alteration rind and/or dust coating on a rock and the amount of 15.0-keV radiation absorbed in the rind/coating for densities of 0.4, 2.4, and 4.0 g cm [57]. The bulk chemical composition of basaltic rock was used in the calculations, and the 15.0 keV energy is approximately the energy of the 14.4 keV y-ray used in the Mossbauer experiment. The stippled area between densities of 2.4 and 4.0 g cm is the region for dry bulk densities of terrestrial andesitic and basaltic rocks [58]. The stippled area between densities of 0.1 and 0.4 g cm approximates the range of densities possible for Martian dust. The density of 0.1 g cm is the density of basaltic dust deposited by air fall in laboratory experiments [59]. Right Measured spectra obtained on layered laboratory samples and the corresponding simulated spectra, from top to bottom 14.4 keV measured (m) 14.4 keV simulated (s) 6.4 keV measured (m) and 6.4 keV simulated (s). All measurements were performed at room temperature. Zero velocity is referenced with respect to metallic iron foil. Simulation was performed using a Monte Carlo-based program (see [56])...

The rough duct design method may result in premature dust deposition or excessive system erosion (due to incorrect duct sizes and velocities)... 

The ash of peat forming plant species contains a predominant amount of silicon. This element is particularly abundant in the Sphagnum, where its content achieves 36% by ash weight. Iron and aluminum are the next abundant. The first is accumulated during the peat formation process. The accumulation of calcium and potash is more pronounced than sodium, and the sulfur content is also remarkable. A large amount of mechanically admixed mineral particles (40-80% by ash weight) is found in mosses. This is due to the deposition of fine dispersed mineral material from snowmelting waters and atmosphere dust deposition (Table 1). 

Compact design No filter to replace. Generates secondary pollution in form of dusts deposited around the vicinity of the appliance Ineffective against gaseous pollutants Requires constant maintenance. 

Mechanical Scrubbers Mechanical scrubbers comprise those devices in which a power-driven rotor produces the fine spray and the contacting of gas and liquid. As in other types of scrubbers, it is the droplets that are the principal collecting bodies for the dust particles. The rotor acts as a turbulence producer. An entrainment separator must be used to prevent carry-over of spray. Among potential maintenance problems are unbalancing of the rotor by buildup of dust deposits and abrasion by coarse particles. 

Evidence in support of the Iron Hypothesis has been obtained from ice cores that contain records of past dust deposition, atmospheric CO2 levels and global temperatures. As shown in Figure 5.13, during the past 160,000 years, periods during which dustborne iron levels have been high coincide with lower atmospheric CO2 levels and global temperatures, i.e., the most recent Ice Ages. 

The southern flank of the upwelling CDW sinks around the continent of Antarctica to become AABW The northern flank of upwelling CDW is transported by surface currents, first into the polar frontal zone (PFZ) where AAIW forms, and then into the subantarctic zone (SAZ ) where SAMW forms. At these latitudes, dust deposition is high enough to reduce iron limitation of the diatoms. As the surfece waters move northward. 

The micrometeorites that melt during passage through Earth s atmosphere tend to solidify as spheres. These are termed cosmic spherules. The mineralogy of these spherules is given in Table 13.2. Their high iron and nickel content make them much denser (3 to 6g/cm ) than continental rock ( 2.7g/cm ). Like aeolian particles, cosmic dust deposited on the sea surface eventually settles to the seafloor via pelagic sedimentation. 

Fig. 1 Climbers ascending Weissmies (4,023 m) in the Swiss Alps. The crevasse wall clearly shows the layering of snow. The most prominent layers confine the accumulation of individual years. The yellowish layer is a Saharan dust deposit, a phenomenon commonly occurring in the Alps. Photo Jtirg Alean, Glaciers online http //www.glaciers-online.net...

Fine metallic aluminum powders inhaled by hamsters and guinea pigs caused no pulmonary fibrosis in rats that inhaled the dust, small scars resulted from foci of lipid pneumonitis. Alveolar proteinosis developed in all three species it resolved spontaneously, and the accumulated dust deposits cleared rapidly from the lungs after cessation of the exposure. The failure of inhaled aluminum powder to cause pulmonary fibrosis in experimental animals parallels the clinical experience in the United States, where pulmonary fibrosis has not been observed in aluminum workers. ... 

Exposures to relatively low concentrations of silica for a prolonged period may be capable of causing hilar node fibrosis, impairing the clearance of any silica inhaled subsequently. In one case, 30 years of exposure to <0.1mg/m led to hilar node fibrosis and calcification in an exposed stonemason subsequent exposure for 5 years to about 2 mg/m led to rapid, progressive silicosis that proved fatal. Estimates of exposure tallied with postmortem measurement of lung burden, suggesting retention of all dust deposited in the lungs over his final period of work. ... 

The industrial dust deposited in the metropolitan area of Shanghai consisted of high-coercivity (hematite) and low-coercivity (magnetite/maghemite) particles, usually < 10 pm in size. Four different dust sources could be distinguished on the basis of magnetic properties (Shu et al. 2000). Given previously reported links between... 

Under dirty operating conditions it is possible for dust deposits to form a crusf in the pump chamber. These contaminants will deposit in part in the pumping chamber and in part on the pump s impellers. They may be removed, once the two connection lines have been detached, either by blowing out the system with dry compressed air or by rinsing with a suitable cleaning agent, such as petroleum ether (naphtha). 

The mass flux ms,Gr is the sum of the reaction product deposited on the liquid film and non-converted material flux, of the dust deposited on the particles coming from separator into granulator and of the attrition mass flux coming from separator into granulator, which leads to the growth of particles. 

A representative section (one fourth wedge) of the Millipore filter, with dust deposition side up, was placed on each of the pads for two minutes. Between each treatment the bottom side of the filter was blotted on a paper towel to remove access solution. After the final treatment the filter was dried for one hour at roan temperature. The dry, stained filter was then placed on a clear microscope slide and made translucent with immersion oil. Permanent slides were made by sealing the coverslips to the slides with clear fingernail polish. 

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