In most cases the gas is composed of a polluted air stream air and the absorber liquid is water with the addition of chemical reagents which oxidise the polluting substances.

The use of this technology is as easiest on soluble polluting compounds which are easily oxidised. A typical application is the removal of inorganic chemical compounds such as hydrogen sulphide (compound responsible for bad odours in wastewater treatment plants) and ammonia (compound found in solid waste treatment plants).

Absorbers came in two design: counter-current wash (vertical washing towers) or crossing flow (horizontal washing towers). Different kind of materials are utilized for the replenishment based on the kind of application. Reactors can be made of polypropylene, fiberglass or stainless steel. Air Clean can offer the suitable treatment based on the specific treatment required.

Chemical washing towers

In chemical washing towers pollutants are transferred into the water in a mass transfer column and chemically oxidized.

The washing towers are normally constructed using a reactor column in which the washing liquid is recirculated counter-current through the mass transfer packing which brings the airborne pollutants in to close contact with the chemical reagent.The transfer of pollutants from the air to the washing solution is helped by the use of mass transfer packing with high specific surface.

The packing can be either fixed (static scrubber) or can be kept in continuous movement (fluidized) by the contaminated air (floating bed scrubber). The latter mode of operation is especially useful in the presence of dust laden airstreams.


Air washing towers can be used for air humidification (Humidifiers).

An example of a typical application is the pre-treatment of air prior to a biological purification system, usually biofilter is containing organic media.

Since the air humidification process involves loss of heat due to humidification, an indirect effect consists of the reduction of the gas temperature.

Stripping towers

Stripping towers are used to transfer gaseous chemicals from a liquid into an air or gas stream. This is the reverse process of absorption.

Physically stripping towers are similar to the chemical scrubber, however recirculation of the liquid solution from which the gaseous are released is not normally not provided for. The liquid passes through on a once through basis in a counter-current format used for gas stripping.

A typical application would be NH3 stripping from landfill leachates. In this case the process will be enhanced by a rise in temperature and a change of Ph.

Direct air to water heat exchangers

In addition to the chemical absorption of pollutants packed column scrubbers can be used for cooling or heat recovery.

In these systems the washing liquid is used to remove heat from the gas to be cooled. Liquid obtained can in turn be cooler in a water/water exchanger.

This technology has application when there are dusty emissions for which the use of air exchangers is problematic.

Chemical scrubber