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Spray dryer absorber for SO2, HCl, HF removal


A dry or semi-dry scrubbing system, unlike the wet scrubber, does not saturate the flue gas stream that is being treated with moisture.

In some cases no moisture is added, while in other cases only the amount of moisture that can be evaporated in the flue gas without condensing is added.

Therefore, dry scrubbers generally do not have a stack steam plume or wastewater handling/disposal requirements.

There are different types of dry scrubbing system designs and all of them consist of two main sections or devices:

  1. Device to introduce the acid gas sorbent material into the gas stream (AWS atomizing nozzle)
  2. Particulate matter control device to remove reaction products, excess sorbent material as well as any particulate matter already in the flue gas.

Spray dryer absorbers are also called semi-dry scrubbers or spray dryers.

Dry scrubbing systems are often used for the removal of odorous and corrosive gases from wastewater treatment plant operations.

The medium used is typically an activated alumina compound impregnated with materials to handle specific gases such as hydrogen sulfide.
Media used can be mixed together to offer a wide range of removal for other odorous compounds such as methyl mercaptans, aldehydes, volatile organic compounds, dimethyl sulfide, and dimethyl disulfide.

The sorbent can be injected directly into several different locations:

  • the combustion process
  • the flue gas duct (ahead of the particulate control device)
  • open reaction chamber (if present).

The acid gases react with the alkaline sorbents to form solid salts, which are removed in the particulate control device.

Dry scrubbing systems are used to remove acid gases (such as SO2, SO3, HCl, Hg, and dioxins) into a slaked lime Ca(OH)2 absorbent by means of  AWS atomizing nozzle to form a stable and dry powdery product that is easy to store and transport.

Acid gases are absorbed by the slurry mixture and react to form solid salts, which are removed by the particulate control device installed downstream.

The heat of the flue gas evaporates all the water droplets, leaving a non-saturated flue gas to exit the absorber tower. Spray dryers are capable of achieving high (80+ %) acid gas removal efficiencies.

The Spray Drying Absorption technology features excellent performance for absorption, not only of primary pollutants such as SO2 and HCl.

Due to finely atomized absorbent sprayed into the flue-gas stream and the subsequent dust removal, pollutants such as SO3, HF, etc. will be completely removed.

This facilitates the use of carbon steel as construction material throughout the flue-gas path.


  • High acid-gas removal efficiency
  • Low capital, operating and maintenance costs
  • Low power and water consumption – operates on low-quality water
  • High plant availability