Horizontal scrubbers are absorption systems that are used for the purification of fumes, mists and vapours which may be transmitted in alkaline, acidic, in oxidizing or reducing soluble substances. The working process of a horizontal scrubber is based on cleaning which involves the airflow.

Horizontal scrubbers can be of one, two or three stages depending on the nature of the substances to be absorbed and depending on the number of reagents necessary for the absorption of the substances in the fumes. Each stage of the horizontal scrubber has a containment tank for the washing liquid, from which a pump draws the liquid through a hydraulic circuit and sends it to a distribution system place situated higher than the washing section. The system soaks the filling bed of that stage which consists of elements (usually called PALL rings) which increase the exchange surface and the contact time of the precipitating drops according to the airflow.

The liquid falls into the collection tank before being pumped back into circulation. Depending on the type of horizontal scrubber and on the nature of the substances to be absorbed, water can be used alone or can be mixed with acids and bases. At the end of each stage there is a drop separator so that there can be no contamination of one stage and the next and between the last stage and the outside air.