Frederick Gardner Cottrell’s development of the electrostatic precipitator led to the use of this technology to remove particulates and fumes from atmospheric emissions for pollution control.
The advent of the Industrial Revolution led to the development of severe air-pollution problems in industrializing nations. Prior to that time, there were periods when coal burning was forbidden in some urban areas, but these restrictions came about mainly for aesthetic reasons. Large-scale industrialization resulted in much more serious environmental problems.
By the early 1900’s, various methods of pollution control were available, including the use of “tall stacks” to dissipate pollutants and the use of baghouses to contain particulates through the use of filtering mechanisms very similar to those in vacuum cleaners. Although some success was achieved using these techniques, many pollutant streams could not be treated successfully through these methods. It was evident that new techniques were needed.
In 1824, M. Hohlfeld, a German mathematics teacher, first suggested the precipitation of smoke particles by electricity. In the 1880’s, Sir Oliver Joseph Lodge
As a youth, Frederick Gardner Cottrell exhibited a wide range of interests. During the early 1890’s, when he was in his young teens, he advertised himself as a landscape photographer, printer, electrician, chemist, and telegraph operator. These early enthusiasms, particularly his interest in electricity and electrical apparatus, provided Cottrell with the seed of an idea for one of his most important contributions to science and technology, electrostatic precipitation. The Christmas, 1890, issue of the Boys’ Workshop (a weekly publication that Cottrell edited) contained an article titled “The Progress of Science” that referred to “two very important applications of electricity.” The first application was welding, and the second, alluded to only briefly, was “the deposition of smoke and dust by electrical aid.”
Cottrell’s later interest in air-pollution control was sparked in 1905 by the difficulties experienced by the Du Pont plant near Pinole, California, which produced explosives and acids. Sulfuric acid was produced by the newly developed “Mannheim process,” a contact method in which gaseous sulfur dioxide and oxygen are passed through an iron oxide catalyst to produce sulfur trioxide, which is converted to concentrated sulfuric acid. An undesired by-product was arsenic, which poisoned the catalyst. Cottrell’s first solution was to develop a centrifuge, a tube 76 centimeters (about 30 inches) long and 3.8 centimeters (about 1.5 inches) in diameter that was rotated at high speed to separate the arsenic from an acid mist. In spite of the success attained in the laboratory, the pilot plant using the centrifuge at Pinole was a dismal failure.
Frederick Gardner Cottrell.
Working in his laboratory at the University of California, Berkeley, Cottrell pursued another idea. In early 1906, he applied electricity to the problem of sulfuric acid mists. Cottrell’s efforts differed from Lodge’s previous attempts in three major ways: the use of rectified alternating current (AC), the introduction of a “pubescent” discharge electrode, and the application of a negative polarity to the discharge electrode. Cottrell’s first tests required that one of his students learn to smoke a pipe. The pipe smoke was blown into a glass jar containing a pubescent discharge electrode, a cylindrical wire screen around which were wrapped several turns of asbestos sewing twine. The walls of the jar served as the collecting electrode. Subsequently, Cottrell made a miniature sulfuric acid plant from odds and ends around his laboratory and tested the process on acid mist.
When a high voltage was applied across the electrode and the jar sides, electrons were emitted from the highly charged discharge electrode. These electrons then collided with the surrounding gas molecules, ionizing them. The negative gas molecules migrated to the relatively positive collection electrode and, in doing so, collided with and transferred their negative charge to the entrained smoke or sulfuric acid mist particles. The negative smoke, or mist particles, then migrated to the collection electrode, where they were neutralized and collected at the sides and bottom of the jar.
Cottrell soon discovered that to handle large volumes of moving gases, it was necessary to use a direct current (DC) rather than alternating current. To attain the high voltages necessary for these tests, he transformed the 120-volt lighting system in the chemistry building to 10,000 volts, then commutated the AC to intermittent DC through a homemade rotating contact maker.
To develop and commercialize the process, Cottrell, along with Henry East Miller, E. S. Heller, and Edmond O’Neill, formed two companies, International Precipitation Company and Western Precipitation Company. The former obtained and held all the patents, and the latter was the operating unit. Cottrell then returned to the Du Pont powder works at Pinole for pilot tests, to redeem his failure with the centrifuge. The new precipitator was able to treat successfully 30-60 cubic meters (about 1,059-2,119 cubic feet) per minute of gas.
Before negotiations regarding licensing of the process could be concluded with the Du Pont plant, Selby Smelting and Lead Company
The Selby smelter had three separate stacks with three separate problems. Each had to be handled individually. The first stack emitted lead fumes from the lead blast furnace. These emissions were collected successfully by a known process, a baghouse. The second stack emitted sulfuric acid mists from the refinery, where the acid was used to dissolve silver from the gold/silver alloy extracted from the lead. Cottrell developed a lead flue, 1 meter by 1 meter (3.28 feet by 3.28 feet) in size, in which several rows of vertical lead plates were suspended. Each was 10 centimeters (about 3.94 inches) wide and 1 meter long, and the plates were placed 10 centimeters apart. Between every two plates was a lead-covered iron bar with pointed projections of mica, which served as the negative discharge electrode. By October, 1907, the precipitator was declared a success. A heavy white plume was converted into an occasional, almost imperceptible, thin white puff. The third stack discharged 15,240 cubic meters (about 538,196 cubic feet) per minute of a dense white mixture of sulfur dioxide gas, sulfuric acid fumes, and arsenic and lead salts from the roasters. Cottrell and his colleagues spent more than two years attempting to solve this problem, with no real success. Eventually, the smelter had to install new roasters.
By 1910, Cottrell discarded the pubescent electrode idea. The Riverside Portland Cement Company, emitting 100 metric tons per day of high-temperature, partially processed cement dust, was under an injunction for destroying the nearby orange groves. In an attempt to handle these dusts, the pubescent electrode was replaced by a bare wire of moderate diameter developed by Walter A. Schmidt, one of Cottrell’s former pupils. In 1912, Cottrell founded the Research Corporation, a nonprofit organization that supported basic research at colleges and universities. He assigned his precipitator patents to the corporation as an endowment.
The electrostatic precipitator had an immediate impact on many industries, not only regarding their emissions but also in a completely unexpected way. Prior to World War I, the United States imported from Germany about 1 million tons of potash annually for fertilizer.
Over the years, the value of the by-products in the materials collected proved to be a major incentive for the use of precipitators. Although other collection devices, such as wet scrubbers, can collect more than 99 percent of the particulates or fumes emitted from a stack, for many applications, a dry process is preferred. In the cement industry, for example, on the average one-third of the raw materials are converted to dust. Without recycling, this would result in losses of approximately 150 metric tons per day per kiln of partially processed materials. Even at the Riverside plant, it is estimated that Cottrell’s original precipitator, during its thirty-eight-year lifetime, collected more than 1 million tons of dust. A dry process, such as a precipitator, produces a dust product that is eminently suitable for recycling directly back to the kiln.
The same situation exists for many other industries. Many times, the emissions contain substances that have significant economic value and can be recovered. For example, many years after an older smelting plant in Montana closed, the soil surrounding it was stripped off and processed at a nearby newer plant of the Anaconda Smelting and Refining Company. The topsoil was sent through the concentrator and smelted at the new plant with a reported recovery of more than $1 million in copper and other metals. Today, many of the metals and sulfur oxides in smelter emissions can be collected on-site and reprocessed immediately.
The impacts of the use of precipitators are not restricted to the value of the collected particulates. Reducing the quantity of air emissions not only improves the environment aesthetically but also has major economic impacts. It has been estimated that for every $90 spent on air-pollution control in the United States, $240 is saved in damages to health and property. Further, if air pollution could be reduced to safe levels in all U.S. factories and power plants, the result would be a 75 percent decline in illness and, consequently, a savings of $16 billion in health costs annually.
Precipitators are the pollution control method of choice in many industries. They are versatile and efficient, often approaching 99.9 percent efficiency. They permit collection of very fine, hot, and/or corrosive particles. In addition, the costs of operating and maintaining precipitators are low in comparison with the costs associated with other high-efficiency collectors.
The 1970 Clean Air Act forced many U.S. industries to reduce their air emissions. Nevertheless, even with the increased emphasis on new, efficient, and economical techniques of pollution control, no significant innovations in air-pollution control have been developed in the years since Cottrell’s work. Iron and steel companies, nonferrous smelters, foundries, power plants, cement and lime kilns, and pulp and paper mills are merely a few of the industries that often employ electrostatic precipitators for collection of their dusts, fumes, and/or mists.
-
Cameron, Frank. Cottrell: Samaritan of Science. Garden City, N.Y.: Doubleday, 1952. Well-researched biography provides insights into Cottrell’s life, work, and personality. Includes index. -
Colls, Jeremy. Air Pollution. 2d ed. New York: Spon Press, 2002. Comprehensive textbook covers all aspects of the causes, effects, and control of air pollution. Provides a brief description of electrostatic precipitation. Includes index. -
Cottrell, Frederick. “Electrical Precipitation: Historical Sketch.” Transactions of the American Institute of Electrical Engineers 34 (January, 1915): 387-396. Focuses on the early history and development of the precipitation process, including the work of Hohlfeld and Lodge, and on Cottrell’s smoke abatement work at the Mellon Institute. Discusses Cottrell’s preliminary ideas of using precipitation for fog abatement. -
Sell, Nancy J. Industrial Pollution Control: Issues and Techniques. 2d ed. New York: John Wiley & Sons, 1992. Explains in relatively nontechnical language not only the advantages, limitations, and operating principles of precipitators but also their uses in a variety of industries. Suitable for readers with some minimal background in physical science. Includes index. -
Weiner, Ruth F., and Robin Matthews. Environmental Engineering. 4th ed. Burlington, Mass.: Elsevier Science, 2003. Textbook intended for use by students with some physical science or engineering background provides a brief but informative section on electrostatic precipitator design. Includes illustrations, useful appendixes, bibliography, and index. -
Yost, Edna. Modern Americans in Science and Technology. New York: Dodd, Mead, 1962. Collection of nontechnical essays on thirteen American scientists devotes a chapter to Cottrell. Provides a good summary of the early applications of the precipitation process, the savings attained through dust recovery, and the establishment of Cottrell’s Research Corporation. Includes index.
International Association for the Prevention of Smoke Is Founded
Steinmetz Warns of Pollution in “The Future of Electricity”
Oil Pollution Act Sets Penalties for Polluters
Wolman Begins Investigating Water and Sewage Systems
Arbitration Affirms National Responsibility for Pollution