Scrubber designs remove pollutants from waste streams in power generation, manufacturing and other industries. Wet, dry and combustion scrubbers are available, with regenerative or non-regenerative options. Wet scrubbers can use venturi or spray technologies, while dry scrubbers neutralize acidic drains. Combustion units work alongside other scrubbers to destroy toxic components. Regenerative scrubbers allow for chemical reuse, while non-regenerative scrubbers require disposal of by-products.
The scrubber design is directed towards the control of air pollution through the removal of harmful contaminants from waste streams created by power generation, manufacturing and other industrial applications. Types of scrubber designs include wet scrubbers that use liquids or slurries, dry scrubbers that use powdered chemicals, and combustion equipment that burns toxic components. Units can be regenerative equipment that recycles accumulated contaminants or non-regenerative equipment that collects material for disposal. The pollutants removed can include particulates, fumes, gases and vapours.
Units that use liquids, such as wet scrubbers, can be configured with a variety of technologies. Venturi scrubbers are designed to accelerate exhaust flow through a constricted cone-shaped duct into which scrubbing liquid, often water, is sprayed to maximize contact with the gas stream. The particulate residue attaches to the liquid droplets and the wet particulate passes through a centrifugal separator to separate it from the exhaust stream equilibrium.
Spray scrubbers, such as the type often used in oil-fired power plants, bathe the gas stream with a curtain of liquid or slurry within a tower or chamber. The wetting materials are chosen for their specific chemical reactions with the exhaust to recover the maximum possible amount of pollutants. Factors such as density, viscosity and temperature affect the efficiency of these units.
A newer design of scrubbers is the condensing scrubber. The vapor is injected into a saturated gas stream and condensate forms as droplets around the fine particulate matter. Droplets are separated using mechanisms such as a mist separator.
Dry scrubbers are often used to neutralize acidic drains. The dry chemical powder is injected under high pressure into the gas stream to react with the acidic elements. To maximize the chemical reaction, the flue gas temperature can be changed before treatment. The neutralized chemicals are captured through a filtration system, thus leaving a purified waste stream to discharge.
Combustion units are another stage in scrubber design. These units typically work in tandem with other types of scrubbers. The gas stream is heated and oxidized to destroy insoluble toxic components. High-temperature combustion reduces pollutants in the exhaust stream to a level that allows the use of wet or dry scrubbers to complete the cleaning process.
The design of the regenerative scrubber allows for the reuse of chemicals collected in the scrubber for secondary uses. Typically, the cost of installing a regenerative scrubber is higher, but reselling or reusing recycled chemicals can help offset operating costs. A non-regenerative scrubber is most often less expensive to install, but by-products from the scrubbing process can incur disposal costs when removed, thereby increasing operating costs.
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