Scrubber
Recently, the term has also been used to describe systems that inject a dry reagent or slurry into a dirty exhaust stream to "wash out" acid gases.
Water is the most common solvent used to remove inorganic contaminants, particularly for dust, but solutions of reagents that specifically target certain compounds may also be used.
A dry or semi-dry scrubbing system, unlike the wet scrubber, does not saturate the flue gas stream that is being treated with moisture.
The medium used is typically an activated alumina compound impregnated with materials to handle specific gases such as hydrogen sulfide.
Dry sorbent injection involves the addition of an alkaline material (usually hydrated lime, soda ash, or sodium bicarbonate) into the gas stream to react with the acid gases.
The sorbent can be injected directly into several different locations: the combustion process, the flue gas duct (ahead of the particulate control device), or an open reaction chamber (if one exists).
The acid gases react with the alkaline sorbents to form solid salts which are removed in the particulate control device.
Acid gases are absorbed by the slurry mixture and react to form solid salts which are removed by the particulate control device.
The flue gas is passed through a cartridge which is filled with one or several adsorber materials and has been adapted to the chemical properties of the components to be removed.
In July 2015, one study found that some mercury scrubbers installed on coal power plants inadvertently capture PAH (polycyclic aromatic hydrocarbons) emissions as well.
[8][9] One side effect of scrubbing is that the process only moves the unwanted substance from the exhaust gases into a liquid solution, solid paste or powder form.
As an example of reuse, limestone-based scrubbers in coal-fired power plants can produce a synthetic gypsum of sufficient quality that can be used to manufacture drywall and other industrial products.
Later, in preparation for the global 0.5% sulfur cap in 2020, the International Maritime Organization (IMO) adopted guidelines on the approval, installation and use of exhaust gas scrubbers (exhaust gas cleaning systems) on board ships to ensure compliance with the sulfur regulation of MARPOL Annex VI.
If a scrubber system is not functioning properly (and the IMO procedures for such malfunctions are not adhered to), port states can sanction the ship.
