Aerosols electrostatic precipitation

Dry aerosols, or particulate matter, differ so much from the carrying gas stream that their removal should present no major difficulties. The aerosol is different physically, chemically, and electrically. It has vastly different inertial properties than the carrying gas stream and can be subjected to an electric charge. It may be soluble in a specific liquid. With such a variety of removal mechanisms that can be applied, it is not surprising that particulate matter, such as mineral dust, can be removed by a filter, wet scrubber, or electrostatic precipitator with equally satisfactory results. 

Care should be exercised when sampling for aerosols that are condensable. Some separating systems, such as wet impingers, may remove the condensables from the gas stream, whereas others, such as electrostatic precipitators, will not. Of equal concern should be possible reactions in the sampling system to form precipitates or aerosols which are not normally found when the stack gases are exhausted directly to the atmosphere. SO-,... 

Pipe-type electrostatic precipitators are used to collect liquid aerosols (e.g., mists and fogs). They are also used in applications which require water flushing of collection electrodes. The diameter of precipitator pipes is typically in the range of 15 0 cm, and the length is in the range of 3-6 m. The number of pipes depends on the total gas flow. The gas-flow rates in pipe-type electro static precipitators is normally much lower than in duct-type precipitators. 

Zhibin, Z. and Guoquan, Z. Investigations of the Collection Efficiency of an Electrostatic Precipitator with Turbulent Effects. Aerosol Science and Technology. 20 (1994) 2, pp. 169-176. 

Under normal household conditions the effect of electrostatic precipitators would be less dramatic than shown here, because these measurements were carried out in a closed room. With normal movement between rooms, the aerosol concentration would not be reduced by as much and the increase in unattached fraction of 218Po would be less. 

Figure 6. Change in aerosol number weighted size distributions during operation of electrostatic precipitators.

Electrostatic precipitators were effective in reducing the radon decay-product concentration below the reference level, but analysis of the room aerosol indicated that the reduction was largely offset by an increase in lung dose per unit exposure. 

Of the major components of flue gas, oxygen and water vapor influence the reactions of the oxides considerably, hut carbon dioxide does not. Under irradiation, NO is oxidized by reactions with O, OH, and H02 radicals. The resultant N02 is oxidized to HN03 by reaction with OH radicals. S02 is similarly oxidized to H2S04 by reactions with O and OH. The products can also be converted to aerosols and collected in electrostatic precipitators. 

Wet electrostatic precipitators (WESP) are used for removal of liquid contaminants such as sulfuric acid mist, aerosols, and particulate matter. The acid mist and aerosols are typically formed in a WGS by condensation of SO3. Unlike dry precipitators, wet precipitators do not require rapping to remove the dust. The collected mist and particulate matter form a liquid film that runs down a vertical collecting plate. In some cases, a continuous spray of liquid is used to prevent solids deposition on the collecting plates. 

Figure 2. Concentration vs. size curves of Fe, Al, Sc, V, U, and Se in aerosol particles collected upstream of an electrostatic precipitator of a coal utility boiler.

Composition and Distribution Characteristics of Aerosols Emitted from a Coal-Utility Boiler Equipped with a Hot-Side Electrostatic Precipitator," presented to Annual American Chemical Society Meeting, Miami Beach, Sept 10-15 (1978). 

On-line measurements of the sulfur content of atmospheric aerosols have been made by removing gaseous sulfur species from the aerosol and then analyzing the particles for sulfur with a flame photometric detector (24) or by using an electrostatic precipitator to chop the aerosol particles from the gas so that the sulfur content could be measured by the difference in flame photometric detector response with and without particles present. These and similar methods could be extended to the analysis of size-classified samples to provide on-line size-resolved aerosol composition data, although the analytical methods would have to be extremely sensitive to achieve the size resolution possible in size distribution analysis. 

SMOKE. A colloidal or microscopic dispersion of a solid in gas, and aerosol. (1) Coal smoke A suspension of carbon particles in hydrocarbon gases or in air, generated by combustion. The larger particles can be removed by electrostatic precipitation in the stack (Cottrell). Dark color, nausealing odor,... 

Tien, C. (1989). Granular Filtration of Aerosols and Hydrosols. Stoneham, Mass. Butterworths. White, H. J. (1963). Industrial Electrostatic Precipitation. Reading, Mass. Addison-Wesley. 

In an earlier study (15) we addressed some of the problems in obtaining accurate concentration-vs-particle-size distributions for elements in stack aerosols collected downstream of an electrostatic precipitator and a Venturi wet scrubber at a coal-fired power plant. The problems investigated were error associated with the use of the... 

Wall losses were estimated by comparing the mass concentrations of various elemental constituents of aerosols collected with a series of alternately collected filter and impactor samplers. For samples collected downstream of an electrostatic precipitator (ESP), where the aerosol MMAD was 11.5 pm, the average amount of mass collected in the impactors was about 60% of that collected by the filters (Table... 

Charged aerosols and aerosol charging Microcontamination electrostatic precipitation atmospheric electricity aerosol sampling and measurement ion-particle interactions. 

Fig. 2. Surface heterogeneity of a powder sample of sodium chloride computed from the adsorption of argon at 76.1 K using a two-dimensional gas model of adsorption, x, Sample prepared by electrostatic precipitation of a NaCl aerosol O, same sample but after annealing at 31(1 315°C in a dry nitrogen atmosphere at 600mmHg. (Reproduced from ref. 4 by courtesty of Academic Press, Inc.)...

The utility of the concept of aerosol particle electrical drift velocity can be shown by using it to estimate the theoretical efficiency of an electrostatic precipitator. For simplicity it is assumed that the collector is cylindrical, having a radius R (although this assumption does not affect the results), and that an aerosol is uniformly distributed across the entrance of the collector. In addition, turbulent flow in the collector is assumed such that the uncollected aerosol remains uniformly distributed at any distance from the entrance of the tube. If the electrical drift velocity is constant, the chance of a particle 4> being collected in a time At is... 

---