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:
- Device to introduce the acid gas sorbent material into the gas stream (AWS atomizing nozzle)
- 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.
