Absorption in air handling

Among pollutant-laden air treatment processes, the unit operation – absorption – performed within gas-liquid contactors, falls into the category of processes based on transfer with direct recovery, and is comparable to gas-solid adsorption or condensation . The aim is to offer solutions for the treatment of contaminated gaseous effluents such as :

• atmospheres containing volatile organic compounds (VOCs) of the oxygenated type: volatile fatty acids, alcohols, ketones, chlorine derivatives. Emitters of VOCs are mainly transport and solvent-using industries ;

• combustion fumes from incinerators containing NO_x , SO₂ , HCl ;

• acid gases based on HCl, HF, H₂ S and CO₂ ;

• effluents containing odorous compounds of the sulfurous (H₂ S, CH₃ SH), nitrogenous (NH₃ , CH₃ NH₂ ) or oxygenated (acetone, acetic acid) type. The main sources are wastewater treatment plants, food processing industries (canneries, rendering plants), paper mills and chemical industries.

As we understand it in this article, absorption is a unitary operation whose principle is based on the passage of one or more constituents from a gaseous phase into a liquid phase. Matter is exchanged (or transferred) between a gaseous phase and a liquid phase with different chemical compositions. This transfer of matter takes place within gas-liquid contactors (or reactors) in which the two phases are brought into contact to promote the exchange of matter.

The sizing of these devices is based on a number of fundamental concepts that need to be recalled here, without going into the details of certain demonstrations that have been the subject of numerous publications.

The following points will be addressed:

• the different types of gas-liquid contactors ;

• basic concepts of gas-liquid mass transfer ;

• principles of absorber sizing ;

• the use of absorbers through case studies.

We assume that :

• the concentrations of constituents present in the gas phase and likely to be absorbed into the liquid phase are relatively...