air or gas strippers, removing CO2Reading time:
The main function of these "strippers" is the removal of CO2:
- on drinking water: in order to raise pH and to reduce the aggressive nature of the water (see section neutralisation – remineralisation) ;
- in industrial water: downstream cationic ion exchangers, in order to reduce conductivity and to avoid overloading anionic ion exchangers (see chapter using ion exchangers) ;
- in wastewater: in order to increase pH in heavy loading biological systems, for instance, when using pure O2 ;
Only appliances using packing are described in the following. Nevertheless, when the sole aim is to achieve partial elimination of dissolved CO2, this can be undertaken (see section air oxidation):
- by simple spraying;
- by bubbling;
- by mechanical dispersion (cascades …).
All stripping systems are counter current systems, governed by the law of mass transfer (see section gas-liquid exchange), and, by increasing the transfer surface area, packing enables the system to achieve content levels that are close to equilibrium while minimising system footprints.
They all assume that:
- water is properly distributed over the entire surface of the column (spray, perforated flow splitting system or plates);
- stripping gas (atmospheric air, steam, etc.) is properly distributed at the base of the packing, usually via a perforated floor, grating ...;
- the carrier gas is sufficiently pure, thus avoiding secondary contamination (gas washed using water).
Depending on their primary application, these appliances are designated CO2 eliminators, air strippers or gas strippers , or atmospheric degasifiers.