Scrubber systems are a diverse group of devices that are used to control air pollution, and can be used to remove some PM and/or gases from industrial exhaust-gas streams. Traditionally, the term scrubber has referred to pollution control devices that use liquid to wash unwanted pollutants from a gas stream but, more recently with the evolution of gas cleaning operations, the term has also been used to describe systems that inject a dry reagent or slurry into a dirty exhaust stream to remove acid gases, such as carbon dioxide and hydrogen sulfide which elevate scrubbers to be one of the primary devices that control gaseous emissions, especially acid gases.