Scrubber systems are one of the primary ways of removing acid gasses from exhaust before they are released into the atmosphere. There are two primary methods of scrubbing exhaust: wet and dry.
Wet scrubbers trap suspended particles by direct contact with a spray of water or other liquid. In effect, a scrubber washes the particulates out of the dirty airstream as they collide with and are entrained by the countless tiny droplets in the spray. Since this process adds so many vapors to the exhaust, if the gas is vented, it typically looks like billowing white smoke. The sprayed liquid collects in the bottom of the area. This liquid is funneled away from the spraying chamber and collected for disposal.
Dry scrubber systems spray a collection of dry reagents into the exhaust. These reagents can have a number of different effects depending on the material they target. Dry scrubbing systems are used to remove acid gases (such as SO2 and HCl) primarily from combustion sources. Dry scrubbing systems are often used for the removal of odorous and corrosive gases from wastewater treatment plant operations. The system produces very little waste material, at least when compared to a wet scrubber. As a result, the collection requirements for a dry scrubber system are much less than for a wet one.
Dry scrubbing is a more common process by far, but wet scrubbing still has its uses. Some contaminants, such as mercury, are extremely harmful and can only be removed by a wet compound. The other common use for a wet system is heat dissipation and recycling.