This is a series of devices designed to remove, or rather, reduce the concentration of pollutants in the flue gas to be treated. Depending on the chemical-physical properties of the flue gas and the pollutants, the system can be composed of one or more stages. The decision on which of the systems below is most appropriate depends on the physical state of the pollutant present in the gaseous current, and its chemical properties. The options include:
Dry systems (for dust or drops) that can be either dynamic (ex. cyclones) or static (ex. bag filters);
Moist systems (for example for sulphur dioxide or chloride acid) such as scrubbing absorption towers;
Thermal and catalytic systems (for nitrogen oxides and polycyclical and/or polychlorinated organic compounds), such as combustors and catalytic reactors;
Absorption systems (for organic compounds insoluble in water) such as activated carbon columns;
Biological systems such as biofilters.
These stages are generally mixed and matched, for example, dry stages such as filtering with moist stages such as absorption units. It is also common to have a final catalytic or adsorption stage that ensures a last powerful reduction of particularly hazardous pollutants such as chlorinated organic compounds.
Source: Courtesy of Ambiente, an Eni Group Company