Coarse dust

Zinc dust is smaller in particle size and spherical in shape, whereas zinc powder is coarser in size and irregular in shape. The particle size of zinc dust, important in some appHcations, is controUed by adjusting the rate of condensation. Rapid cooling produces fine dust, slower condensation coarse dust. In the case of zinc powder, changes in the atomization parameters can be employed to change particle size to some degree. The particle size distributions for commercial zinc powders range from 44 to 841 p.m (325—20 mesh). The purity of zinc powders is 98—99.6%. 

The particles to be removed may range in size from large molecules, measuring a few hundredths of a micrometre, to the coarse dusts arising from the attrition of catalysts or the fly ash from the combustion of pulverised fuels. 

The lower explosive limit and minimum explosive concentrations of flax, wool, cotton, jute, hemp and sisal fibres are of the same order of magnitude as those of highly explosive dusts [15], The explosibility of pyrites dusts with sulfur contents above 20% was evaluated experimentally. Dusts of 30% sulfur content gave explosion pressures of 3 bar at pressure rise rates of 16 bar/sec. Mixtures of 60% pyrites and 40% powdered limestone still showed significant pressure effects, and the proportion of limestone actually needed to suppress explosions was considerably above the values currently accepted by mining industries [16], Effects of mixtures of particle sizes in combustible dusts upon minimum ignition temperature (T ") and upon presence or absence of explosion were studied. Presence of 30% of fines in a coarse dust lowers Tf significantly [17], Experimental explosions of polyethylene,... 

Scroll collectors, Removal of fairly coarse dusts down to... 

Of 27 workers with heavy exposures to aluminum powder in the same plant as the above-mentioned case, 6 were found to have evidence of pulmonary fibrosis. The finer dust was more dangerous than the coarse dust Of the 12 men exposed to fine aluminum powder, 2 died and 2 others were affected, and of 15 men who worked exclusively with coarser powder, 2 had radiological changes but no symptoms. ... 

Industrial production is a major economic sector in Germany and so industry emissions were and still are important regarding air quality. However, since the 1960s mitigation actions based on national and EU regulations have led to considerable emission reductions, most prominently for (coarse) dust, soot and sulphur dioxide [89], toxic compounds like heavy metals [70] and dioxins [71]. 

The dustiness index of coal is a means of determining the relative values that represent the amount of dust produced when coal is handled in a standard manner. Thus, a 50-lb sample of coal is placed on a slide plate in a metal cabinet of prescribed size. When the plate is withdrawn, the sample falls into a drawer, and after 5 seconds, two slides are inserted into the box. The slides collect suspended dust particles for 2 minutes (coarse dust) or for 10 minutes (fine dust). The dustiness index is reported as 40 times the gram weight of dust that has settled after either 2 minutes or after an additional 8 minutes. 

The overall efficiency is 98.51%. As expected, the efficiency is high because of the coarse dust and the size of the unit. The reader should also check to ensure that... 

In the inflammable gas recovery system, the gas is cleaned first by collecting coarse dust with a dry dust collector, then... 

Diethyl zinc, diethylamine, hydrazine, methyl parathion in xylene and sodium hydride are in degree three (3). This degree includes liquids with a flash point below 73°F and a boiling point at or above 100°F, and liquids with a flash point at or above 73°F but below 100°F. It includes coarse dusts which will bum rapidly, but do not form explosive mixtures with air as well as materials which bum with extreme rapidity often by reason of self-contained oxygen. 

Coarse dust particles Particles larger than 5 pm... 

Fig. 6.33 Particle-filtering half masks, (a) Mouth protection against coarse dusts (b) protection level FFPl without exhalation valve (c) protection level FFPl with exhalation valve (d) protection level FFP3 with an exhalation valve (e) FFP3 with an exhalation valve.

Section 6.9). The filters for coarse dusts (see Fig. 6.33a), which are quite commonly used in some industrial sectors, do not meet the general requirements for respiratory devices therefore they are not to be used against hazardous particles. Whereas particle filters of type PI and FFPl are not to be used for protection against aerosols, the higher filter classes can be used against fog and droplet-aerosols. 

Because of the differing human health effects caused by fine and coarse dust particles, these two types of particles have to be assessed separately. In the soparticle size fractions can be identified, which are further defined in the international standards ISO 7708 and EN 481 [6-103] ... 

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