Industrial gas scrubbers or scrubbing columns as they are also known are pollution control devices designed to remove unwanted pollutants from a gas stream. These pollutants can be chemicals such as ammonia, chlorine or sulfur compounds. Gas scrubbers are often used in the chemical processing industry and gas scrubbing usually takes place in packed columns which contain packings such as raschig rings or pall rings. Gas enters the bottom of the column and travels upwards through the packing, a scrubbing liquid enters the top of the column and is distributed evenly across the packing. After the scrubbing the lean gas exists through the top of the column and the strong liquor remains in the bottom. Gas scubbers are often made from synthetic material such as glass reinforced plastic due to the aggressivity of the pollutants and chemicals used.