How Do Scrubbers Work?
The Clean Coal Technology Program began in 1985, according to the U.S. Department of Energy. The program was founded because Canada and the United States wanted to find a solution to acid rain. Many of the pollutants that are found in acid rain come from coal-burning power plants. One of their solutions to acid rain was scrubbers.
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Function
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Scrubbers use limestone, one of the most commonly found substances in nature to clean air. Limestone is crushed, processed and turned into a white powder for scrubbers. Limestone can absorb sulfur gases under proper conditions, according to the U.S. Department of Energy. Limestone is readily accessible as the United States has mountains made entirely of limestone.
Crushed limestone is typically mixed with water and sprayed into gases from burning coal. This limestone and water solution captures the toxic sulfur gases and pulls them out of the gas. The result is a wet paste or, on newer scrubbers, a dry powder. This prevents sulfur molecules from being released into the atmosphere.
Types
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The two main types of scrubbers include wet scrubbers and dry scrubbers, according to the Federal Remediation Technologies Roundtable. With wet scrubbers, polluted gas is forced to pass through a liquid solution of atomized gas that traps sulfur particles. Venturi scrubbers are another type of wet scrubber that forces gas through a liquid solution at a higher speed to more efficiently clean gas.
Fiber-bed scrubbers are another type of gas scrubber where gas particles pass through a fiber-based material such as fiberglass, steel or glass fibers to be cleaned. Mechanical scrubbers use a power-driven rotor that uses a fine spray to trap sulfur particles. Impingement-plate scrubbers use a vertical chamber with plates that have water trickling down them. As gas passes up the chamber, water flows down the sides of the chamber and traps sulfur particles. Spray scrubbers use sprayers that spray liquid through gas as it passes up a chamber to trap sulfur particles. Condensation scrubbing involves spraying a gas solution into the polluted gas stream. The pollutants then condense and are removed. Condensation scrubbing is the most efficient form of scrubbing. Dry scrubbers are used in small- to medium-sized power plants, use limestone and can only handle smaller loads of gas.
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Cost
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The cost of scrubbing ranges from $3,000 to $172,000 per cubed meter per second, according to the Federal Remediation Technologies Roundtable.
Considerations
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Most scrubbers are made of the cheapest acid proof materials such as polypropylene and are extremely sensitive to high temperatures, according to the Federal Remediation Technologies Roundtable. As a result, hot flue gas must be cooled before scrubbing.
Fun Fact
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Scrubbers are also referred to as caustic scrubbers, according to the Federal Remediation Technologies Roundtable.
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References
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- Photo Credit pollution image by Joseph Chiapputo from Fotolia.com
