The purpose of these plants is the purification of aeriform substances through washing in a tower that allows the abatement of various chemical, organic and particulate pollutants.
They are generally made of steel of plastic material,  with or without beds with filling bodies.
In addition, there are pumps for recirculating the washing solution, probes and instruments to monitor the operating conditions and, when deemed useful, metering pumps and tanks containing the reagent.
Usually, the contact between the aeriform substance and the washing solution occurs on the surface of the filling bodies.
The bed can be static or dynamic, it may differentiate in layers or not be present at all.
They can be single or multi-stage, both horizontal and vertical.