Electrical precipitators collection efficiency

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. 

Electrical precipitators are probably the most versatile of all types of dust collectors. Veiy high collection efficiencies can be obtained regardless of the fineness of the dust, provided that the precipitators are given proper maintenance. The chief disadvantages are the high initial cost and, in some cases, high maintenance costs. Furthermore, caution must be exercised with dusts that are combustible in the carrier gas. 

The development of electrostatic precipitators was based mostly on empirical work, and it has produced more than 1000 patents covering all aspects of electrostatic air cleaning. From the theoretical point of view, important milestones were papers published by Deutsch as well as White.These papers deal with the collection efficiency of the electrostatic precipitator. The most important early papers dealing with the electrical charging of particles are the ones published by Arendt and Kallmann, Pautheniet and Moreau-Hanot, and White. ... 

For two-stage precipitators with close collecting-plate spacings (Fig. 17-76), the gas flow is substantially streamline, and no electric wind exists. Consequently, with reentrainment neglected, collection efficiency may be expressed as [Penny, Electr. Eng, 56, 159 (1937)]... 

Example 7.2 Consider a dust-laden gas passing through an electrostatic precipitator. Assume that all particles have the same charge-to-mass ratio, q/m, and the electric field is uniform. Use the Deutsch equation to estimate the overall collection efficiency if the particle size distribution based on weight percentage (wt%) can be expressed by the mass density function, /M, as... 

Ideally, electrical precipitators generally achieve collection efficiencies of more than 99% for a full range of particle size. The efficiency depends on the ratio of the collector surface area particle size and dielectric properties and the volumetric gas flow rate times the charged particle migration speed induced by the applied electrical field. 

For single-stage precipitators, %t and %j, may be considered as essentially equal. It is apparent from Eq. (17-31) that the mobility in an electric field will Be almost the same for all particles smaller than about l- dm diameter, and hence, in the absence of reentrainment, collection efficiency should be almost independent of particle size in this range. Very small particles will actually have a greater mobility because of the Stokes-Cunningham correction factor. Values of are listed in Table 17-14 for 70°F, = 2, and % = %, = %j,= 0 statV/cm. 

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