Electrostatic Precipitator (ESP)
What is an Electrostatic Precipitator?
"The electrostatic precipitator is a type of cleaner that removes unwanted particles and liquid droplets from a flow of gas. The ESP is a filter for pollution in the air." (ON Science 9)
In 1907, Dr. Frederick Cottrell invented "the electrostatic precipitator also known as an electric air cleaner, that takes advantage of the principle, opposites attract." (IOWA) Although the machine does not contain actual filters, the ESP acts as filter machine designed to trap and remove particles from air flow (filters the air flow i.e. pollution) The ESP is greatly used for the lessening of pollution by smoke from power plants, dust from kilns (furnace, oven) and other industrial sources. "They are found mainly on large power plants, cement plants, incinerators and various boiler application." (MountainViewPeople) "As industrial smokestacks became a common sight at the turn of the century, valuable raw materials were vanishing into the atmosphere."(MountainVIewPeople) Smoke stacks are a type of chimney, mostly used in industrial places, and they release the byproducts of combustion into the air. "Gases emitted through smokestacks greatly consist of carbon dioxide and water vapor, and some nitrogen and oxygen are typically present." (wiseGEEK) "The ESP uses high voltage electricity to remove 90-98% of the ash, dust, and acid which industrial smokestacks spew into the air." (MountainViewPeople)
How does it work?
2. Smoke particles attract to the collecting plates (positively charged)
3. Collecting plates are knocked in order to remove smoke particles
Pros and Cons
1. Handles very large gas volumes and heavy dust loads with low pressure drop
2. Very high collection efficiencies, even for very small particles
3. Can handle corrosive materials, wet materials, and high temperatures
4. Low operating costs, except at very high efficiencies
5. Durable - has long service life requiring little maintenance
1. Not very flexible to changes in operating conditions once installed/purchased
2. Cannot control gaseous emissions
3. Very dependent on the electrical resistivity of the particulate
4. High equipment costs
5. Takes up a lot of space
Wet Electrostatic Precipitator (WESP)
The WESP's control system can be either up flow or down flow relative to where polluted air enters it during the process. -Turning vanes and perforated plate evenly distribute the gas flow inside of the wet electrostatic precipitator- Then, gas enters the WESP round collection tubes. Above collection tubes there are two sets of spray headers.- The first spray header continually mists the collection tubes with small water droplets which are immediately charged and flow down the tube in the direction of the gas flow.- It continuously wets tubes to prevent sticky particulates from sticking to the tubes during the process. Second spray header is the flushing header which periodically sprays a greater amount of water to flush collected precipitate out of collection tubes into lower plenum, during the process. As the dust and aerosol particles enter the tubes, inside the WESP, they become charged from a bombardment of electrons. The negative particles stick to the wetted tube and are periodically flushed into the WESP's lower plenum. -Lower plenum is designed to demist the gas stream and drain all of the collected precipitate to the collection system, completing process.- (All PPC)
Dry Electrostatic Precipitator (DESP)
The DESP is in simple terms, a large box. The particulate control starts when the dust laden gases are drawn to one side of the box. Then these negative particles are attracted to a grounded collecting surface. (Positively charged) The gas leaves the box at a maximum of 99.9% cleaner than when it first entered. The particulate control process then continues inside the box, as particles from the continuous flow build up on collecting plates. The plates are rapped resulting in the particles falling into the hoppers. (large containers) Particles collected during the whole process are removed from the hoppers by a rotary screw conveyor. (All PPC)
- Blake, Leesa, et al. ON Science 9. McGraw-Hill Ryerson Limited, 2009. 421-22. Print.
- How a Wet Electrostatic Precipitator Works. PPC Air Pollution Control. Web. 13 Feb. 2013.
- How a Dry Electrostatic Precipitator Works. PPC Air Pollution Control. Web. 13 Feb. 2013.
- How to Select Electrostatic Precipitators. GlobalSpec, 1999. Web. 12 Feb. 2013.
- Foster, Niki. What are Smokestacks?. WiseGEEK. Web. 12 Feb. 2013.
- Colbruno, Michael. Lives of the Dead. Mountain View People. 2008. Web. 12 Feb. 2013
- Electrostatic Precipitators. IOWA. Uknown update. Web. 12 Feb. 2013
- William, Michael. How to Prepare Sulphuric Acid Industrially. Web. 17 Feb. 2013
- Air Pollution Control. FLS Smidth. 27 Jun.2012. Web. 17 Feb. 2013
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