Air scrubbers, wet scrubbers and gas scrubbers

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Gruiz Katalin

Air scrubbers, wet scrubbers, and gas scrubbers are air pollution control devices that use a high-energy liquid spray to remove aerosol and gaseous pollutants from an air stream. The gases are removed either by absorption or chemical reaction.  In addition to fume and gas abatement, scrubbers may be used for process air cleansing and dust collection.  Dry scrubbers are available, but they are often more costly than slurry method scrubbers.

Air scrubbers, wet scrubbers, and gas scrubbers are commonly used to help control emissions of sulfur into the atmosphere. This is of particular interest to those involved with electric power generation via combustion of coal. The gases that are emitted from the combustion process are passed through tanks containing a lime substance (often a limestone slurry) that can capture and neutralize the sulfur dioxide. 

Air scrubbers, wet scrubbers, and gas scrubbers are differentiated by the manner in which they remove gases and particulates from the air; either wet or dry.  Wet scrubbers literally wash dust and particles out of the air. Exhaust air is forced into a spray chamber, where fine water particles cause the dust to drop from the air stream. The dust-laden water is then treated to remove the solid material and is often recirculated.  Dry scrubbers are used more commonly with acid gases. The pollutant is collected on or in a solid or liquid material, which is injected into the gas stream. A dry scrubber produces a dry product that must be collected downstream from this control device.

Many air scrubbers, wet scrubbers, and gas scrubbers are available with pre-filters or final filters to further reduced emissions.  Pre-filters are installed upstream of the scrubber intended to catch larger particles.  While the scrubber itself would be able to remove these larger particulates as well, their removal allows the scrubber to focus more keenly and effectively on smaller particulates.  A final filter is installed downstream of the scrubber, and is intended to catch particles that were not removed during the scrubbing process.

While the common image of air scrubbers, wet scrubbers, and gas scrubbers is at the top of a smokestack to clean the process exhaust before it leaves an industrial setting, they are available in many styles and configurations.  Air scrubbers, wet scrubbers, and gas scrubbers may be smaller, portable devices for localized cleansing, or mounted into a truck or trailer for mobile spot dust and fume abatement, in addition to the permanent mount industrial style.

How does a scrubber work? The dirty gas entering a scrubber is forced at high velocity through a venturi where it collides with scrubbing water. The tiny water droplets capture particles through impaction and diffusion. The dirty water is then removed in a cyclonic separator and discharged into a recycle tank. Some of the liquid is continuously purged to limit the solids concentration and allow recirculation back to the venturi section.

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