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Dust Collectors: Wet Scrubbers

Industrial dust that arises as a result of reductive manufacturing processes, such as certain types of wood-working, can range from relatively harmless particles to more toxic and potentially dangerous variants. As a result of the range in size and content of industrial dust, several dust control devices were developed to either contain dust or remove it completely from an air stream. Devices such as centrifugal collectors and inert separators are often effective ways to remove large particles, while other types of filters, such as fabric collectors, can be used to further control dust by removing smaller particles. However, occasionally the dust removed by large particle filters escape back into the air stream. Other types of dust collectors, such as wet scrubbers, can help remove dust that manages to evade other kinds of collectors.

Wet Scrubbers

Wet scrubbers rely on liquid, usually water, in order to remove dust from an air stream. Depending on the particular application, one of several wet scrubber variants may be appropriate, such as a wet cyclone scrubber, a spray scrubber, a venture scrubber, or an orifice scrubber.

A wet cyclone scrubber highly resembles a traditional dry cyclone collector, wherein one rotating spiral circles downward carrying larger particles, while another rotating spiral creates an inner vortex, moving upwards and carrying smaller particles. In a wet cyclone scrubber, however, spray nozzles release atomized water as the dust moves along the spirals. The environment is kept humid so that dust particles expand, becoming easier to trap. Dust and water then combine to create larger particles, which settle into a separate collector. As the dust-laden particles of water separate from the cleaner mist, the mist is then passed into a chamber where the water and air are separated. The dirty water, containing dust, is either cleaned or removed from the system.

Spray scrubbers essentially use nozzles to release mist into an empty chamber. As the mist is released, the dust-laden air is fed into the bottom of the chamber. As the mist and dusty air make contact, the dust-laden particles are weighed down by the water while the clean mist is free to escape through a filter in the top of the chamber, where it renters the air stream.

Venturi scrubbers serve a more specialized purpose because the remove dangerous solids from an air stream. Because the air in Venturi scrubbers operate at an extremely high velocity, the air inside is moving so fast it generates very small water droplets, which collect very small dust particles. Additional water is fed into the chamber, which also latches on to dust particles which are large and create a slush or slurry. As the air exits the chamber it is passed into a mist eliminator where the stream of mist is forced to change directions, which helps to separate the clean air from the water before returning the clean air to the air stream. In order for venture scrubbers to operate at a high level of efficiency, which ranges between 90 and 95 percent, the air velocity must be fast enough for the majority of dust to make contact with the water.

Orifice scrubbers depend on centrifugal, impingement, and turbulence forces to force contact between water and dust particles. The air stream, as in a venture scrubber, is fed into the chamber at a high velocity to allow for maximum contact with the water. As the dust particles are wetted, the air stream changes directions to filter out the heavy, dust-laden particles from the air stream. Sometimes the air stream can be routed to change direction several times, increasing the efficiency of the process. Although large amounts of water are used, most of the water can be cleaned and re-circulated.

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