Cottrell precipitators

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. 

The gases from the several furnaces treating the slimes carry bismuth, silver, gold, and other values as particulates, which are recovered via Cottrell precipitators, baghouses, or scmbbers. 

Although intended primarily for air-conditioning applications, these units have been successfully applied to the collection of relatively nonconducting mists such as oil. However, other process applications have been limited largely to experimental installations. The large cost advantage of these units over the Cottrell precipitator lies in the... 

Cottrell, Frederick G. (1877-1948). American scientist, inventor of an electrostatic precipitator, now known as Cottrell Precipitator, for smoke, dust fumes. Among other inventions are the pebble bed furnace, boiling point apparatus the Cottrell-Daniels process for fixation of atmospheric nitrogen. Cottrell was Director of US Bureau of Mines Director of the Fixed Nitrogen Research Laboratory, and founder of the Research Corporation, a nonprofit organization... 

A particle removal method commonly used in industry is electrostatic precipitation. Industrial interest in this very efficient scheme can be traced back to 1911 with the investigation of F. Cottrell. His pioneering studies of sulfuric acid mist removal from copper smelter effluents led to the production of the Cottrell precipitator. 

The catalytic oxidation of naphthalene can easily be carried out in the laboratory, although the amount of phthalic anhydride which can be prepared in one operation is insignificant. It is of great importance that the correct temperature be maintained and that a suitable catalyst be used. Special attention must be given to the apparatus if the preparation in the laboratory is to succeed. Furthermore, it is highly desirable to use a Cottrel precipitator to collect the reaction product completely. This apparatus will collect even the fine particles, which otherwise would be lost. 

The Cottrell precipitator installed in a smokestack. The charged plates attract the colloidal particles because of their ion layers and thus remove them from the smoke. 

In at least one instance, in an urban area, selective discard of catalyst fines collected by a Cottrell precipitator has been practiced in order to decrease the per cent fines in the circulating catalyst and thereby minimize dust losses to the atmosphere (288a). 

The collection efficiency of a Cottrell precipitator is much less dependent upon particle size than is the case with a cyclone separator. Thus in one comparison the efficiency only decreased from 99.7% to 98.5% as particle size was varied from 50 microns to 10 microns (288a). 

Loss of catalyst from the unit is measured by changes in inventory in the vessels and by the additions of make-up catalyst. Accuracy of the measurement from day to day is not high, but reliable data are accumulated over a period of time. An instrument has been developed for continuous recording of catalyst loss from the stack, which consists of an optical device (light source and thermopile) to measure concentration of solids, and a flowmeter to measure the flue-gas rate (268). The two devices are coupled by a mechanism which automatically multiplies catalyst concentration by the gas-flow rate. Catalyst carry-over from the regenerator of a unit equipped with a Cottrell precipitator has been measured by heat balance in the catalyst-return line from the Cottrell to the regenerator (34). 

Description of Cottrell Precipitator, The principle of Cottrell method can be learned from Fig 243, p 722 of Ref 3, which is reproduced here as Fig E28, The dirty gas enters at pipe (3), connected at right angle to the vertical pipe (2), in which.a copper or lead-covered copper wire (1) is suspended axially. The pipe (2) is 3 to 12 inches in diam and from 5 to 15 feet long. Its lower part is attached to a dust-collecting box. A hi -tension direct current passes from the wire (1) to the surrounding pipe, as shown in Fig, Ttiis causes the particles of solids present in the dirty gas to be electrified by the silent discharge of wire and then to be attracted by the pipe, which has the opposite polarity. The gas issued from the top of the pipe is known as "clean gas because it is free of... 

Cottrell precipitator in the smokestack. The charged plates of that type of precipitator attract colloidal soot particles and remove them from the air. This is how air pollution has been reduced in many industrial cities. 

Cottrell precipitators continue to benefit the environment by removing particulates from the gases routinely emitted by factory chimneys. Companies that install them find that the devices soon pay for themselves in terms of the value of the materials that are recovered from the precipitated solids. 

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