air or gas strippers, removing CO2

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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.

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