Wet scrubbers are designed to remove pollutants from a gaseous stream with a scrubbing liquid. Contaminants are absorbed out of the air stream and dissolved in the liquid. In certain cases, contaminants which are low in solubility require the addition of chemical additives to improve absorption.
In a single-stage, vertical packed scrubber, the tower contains randomly dispersed packing to improve contact between the gas and liquid phases. The polluted air stream flows upwards through the bottom of the packed tower counter-currently to the flow of a scrubbing liquid. The cleaned gas then passes through a mist eliminator to remove any entrained liquids. As the scrubbing liquid is re-circulated, the addition of fresh water and removal of old liquid is necessary to purge contaminants that accumulate. Fresh water may be added to the recycle reservoir either continuously or on a periodic basis.
Multiple scrubber stages may be employed for the removal of different compounds. For example, use of a caustic solution may be used in one stage to neutralize and absorb acids, and a sulfuric acid solution in the other to remove ammonia.