Electric precipitators

Electrostatic precipitation Electric-field gradient a. Attraction h. Induction / /5,-n/K D 5,e,2 l5, + 2/l nDtV, / Surface accommodation... 

Electrostatic precipitation Electric-field gradient a. Attraction b. Induction / KaQr b 1DTV0 ) v /K Dp28 e62 U + 2/l DbV0 ) 5P, 84 ... 

Ensor, D.S. Cowen, S. Hooper, R. Markowski, G., Evaluation of the George Neal No. 6 Electrostatic Precipitator, Electric Power Research Institute Report No. EPRI FP-1145, 1979. 

Damage to materials Stone (especially acid-soluble limestone and marble) and metal used in building construction can be corroded and etched by acidic precipitation. Electrical equipment, particularly relay contacts and springs, can be corroded by acidic precipitation. 

Over the period of service the P-scan unit has proved to be a reliable system, operating in a stable manner under the conditions of strong electrical interference, natural atmospheric precipitation. The mechanical scanner of the system adapts quite... 

Preparation of silver maleate. Dissolve 65 g. of pure maleic acid (Section 111,143) in the calculated quantity of carefully standardised 3-5N aqueous ammonia solution in a 1-htre beaker and add, whilst stirring mechanically, a solution of 204 g. of silver nitrate in 200 ml. of water. Filter oflf the precipitated silver maleate at the pump, wash it with distilled water, and press well with the back of a large flat glass stopper. Dry in an electric oven at 50-60° to constant weight. The yield of the dry silver salt is 150 g. Store in a vacuum desiccator in the dark. 

An additional method for increasing particle size deserves mention. When a precipitate s particles are electrically neutral, they tend to coagulate into larger particles. Surface adsorption of excess lattice ions, however, provides the precipitate s particles with a net positive or negative surface charge. Electrostatic repulsion between the particles prevents them from coagulating into larger particles. 

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. 

When corona occurs, current starts to flow in the secondary circuit and some dust particles are precipitated. As potential is increased, current flow and electric field strength increase until, with increasing potential, a spark jumps the gap between the discharge wire and the collecting surface. If this "sparkover" is permitted to occur excessively, destmction of the precipitator s internal parts can result. Precipitator efficiency increases with increase in potential and current flow the maximum efficiency is achieved at a potential just short of heavy sparking. 

Fig. 13. Operating principle of two-stage electrical precipitator. From Ref. 205,...

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