Electrostatic Precipitator (ESP)

LeeAnn Yao 9C

History Overview

The electrostatic precipitator was invented by Frederick Cottrell, a professor of chemistry at the University of California at Berkeley. It is an application that uses electric forces to remove unwanted particles and liquid droplets from gases (Mill, Milligan). The concept of the electrostatic precipitator was first introduced in 1824 by M. Holfeld, a German mathematics teacher, but was only made a reality when Cottrell constructed and patented the invention in 1907 (ON Science 9). The electrostatic precipitator was the first industrial device that utilized the principles of electrostatics.


At the time, many companies were faced with strict new regulations for air pollution control. The electrostatic precipitator was a rapidly increasing success that was adopted by ore smelters, coal-burning plants, and cement industries as it was very effective for reducing pollution from smokestacks. The electrostatic precipitator was capable of minimizing the emission of harmful by-products such as sulfuric acid, smoke, and ash produced by these heavy industries. It collects approximately 99 percent of the pollutants in the gas stream that otherwise would have been released into our atmosphere (U.S. Environmental Protection Agency). Over 100 million tons of potentially harmful particles are collected by this device in the United States annually (Gale Science in Context).

The Electrostatic Precipitator

Electrostatic Precipitator System Working.avi
An electrostatic precipitator is constructed like an input-output machine. Polluted gas is inserted through one end of the precipitator, cleansed, then dispensed out the other end. There are essentially six steps that take place in the process: Ionization, migration, collection, dissipation, dislodging, particle removal (Electrostatic Precipitator KnowledgeBase).

Ionization

Precipitators operate by electrically charging the unwanted particles in a stream of gas. This is accomplished by the highly charged ionizing wires that are connected to the electrical energy source located on the top of the unit. The ionizing wires are located within a series of metal collection plates within the precipitator. The wires convey on to the particles the same charge of which they possess when they come in contact. Additionally, the ions produced collide with other suspended particles in the gas and also bestow an electric charge upon them (Mill, Milligan). Common types of Ionizing wires include straight round wires, twisted wire pairs, and barbed discharge wires. The charging of the particles is called ionization (Electrostatic Precipitator KnowledgeBase).

Migration

The metal collection plates bear the opposite charge of the ions. According to the Law of Electrostatic Charges stating that opposite charges attract, the ions will be attracted to the oppositely charged metal collection plates (Mill, Milligan). The transporting of the charged particles to the collecting surfaces is called migration (Electrostatic Precipitator KnowledgeBase).

Collection

The accumulation of the of the particles from the gas on to the collecting surfaces is called the collection. The collecting plates are designed to receive the precipitated particles until they are removed into the hopper (Electrostatic Precipitator KnowledgeBase).

Charge Dissipation

This stage occurs when the charged particles are neutralized (Mill, Milligan).

Particle Dislodging

When the particles become accumulative, the collectors are shaken to dislodge them where they are deposited to large containers called hoppers below the unit (Hanna, Samson, Walsh, Ponder, Plaks, Sedman, Oren). This stage is called the particle dislodging (Electrostatic Precipitator KnowledgeBase).

Particle Removal

In this last stage, the unwanted material is disposed of using a conveying system (Electrostatic Precipitator KnowledgeBase).

References

Blake, Leesa, et al. ON Science 9. McGraw-Hill Ryerson, 2009. Print

“Electrostatic Precipitator KnowledgeBase.” Neundorfer Particulate Knowledge. Neundorfer, Inc. Web. 11 Feb. 2013. http://www.neundorfer.com/knowledge_base/electrostatic_precipitators.aspx

"Frederick Gardner Cottrell." World of Invention. Gale, 2006. Gale Science In Context. Web. 9 Feb. 2013.

George S. Mill, W. O. Milligan, "Electrostatic precipitator," in AccessScience, ©McGraw-Hill Education, LLC, 2012, http://www.accessscience.com

“Particulates - Electrostatic Precipitators (ESPs).“ Air Pollution Control Orientation Course. U.S. Environmental Protection Agency, 29 Jan. 2010. Web. 11 Feb. 2013.
http://www.epa.gov/eogapti1/course422/ce6a1.html

Steven R. Hanna, Perry J. Samson, Michael P. Walsh, Wade H. Ponder, Norman Plaks, Charles B. Sedman, Craig N. Oren, "Air pollution," in AccessScience, ©McGraw-Hill Education, LLC, 2012, http://www.accessscience.com

Images & Videos

http://www.youtube.com/watch?v=A0tDieiia_c

http://www.britannica.com/EBchecked/media/9655/Cottrell

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