Air | Dry scrubber

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Dry scrubber / adsorption filter

Application

  • Removal of various volatile compounds:
    • volatile nitrogen compounds (NH3, amines,…)
    • volatile sulphur compounds (H2S, mercaptans,...)
    • acid gases (NO, NO2, SO2,…)
    • halogen compounds (Cl2, HCl, HBr, F2, HF, SiCl4,…)
    • solvents
    • odour

Principle

In a dry scrubber, the gases to be treated are blown through a bed of solid adsorbents/reactants/catalysts. The volatile compounds to be removed will show a physical adhesion on or a chemical reaction with the solid sorbent in the dry scrubber. 

Very high (> 99%) removal efficiencies can be obtained upon selection of the correct sorbent material for the specified waste gas and maintaining the correct gas contact time. Due to the cost of the sorbent material, this technique is mainly suited for rather small gas flows with low to moderate concentrations of volatile compounds.

While activated carbon can be used for the adsorption of numerous volatile organic compounds, other sorbents as e.g. Chemisorb S and Chemisorb P are suited for the removal of e.g. acid, alkaline and halogen gases. Advantage of these inorganic sorbents is that they are non-flammable and that their saturation can be checked visually since they change colour upon saturation. As a result of this, a sight glass on top of the bed is usually provided.

For gas mixtures, different layers of sorbents can be provided in a dry scrubber as e.g. a lower layer of impregnated carbon, a middle layer of Chemisorb S and a top layer of Chemisorb P.

A good characterisation of the waste gas is crucial for selection of the most appropriate sorbents since e.g. some of them require O2 for working, others get saturated by CO2, some require water vapour for optimal performance while others get inactivated by water vapour,…

Attention should be paid to prevent overheating of the reactor upon input of high mass loads of volatile compounds towards the dry scrubber in small gas flows. Next to that, the pressure drop over some sorbents can gradually increase upon saturation, resulting in the need to provide a pressure transmitter and/or a pressure relief device as e.g. a bursting disc.

Scheme

dry-scrubber_schemeDry scrubber - scheme

Realisations

dry scrubber

Dry scrubber with impregnated carbon and Chemisorb P for the removal of alkaline gases

Dry scrubber with Chemisorb S and Chemisorb P for removal of NO and NO2