How does a scrubber work? Focus on pollutants removal
As we have already seen, industrial scrubbers clean the gas flow neutralising the pollutants there. In order to do this, at the base of the vertical wet scrubber there is a tank containing the water solution, which is then pumped in the upper part of the scrubber by the recirculation pumps and the vaporizer nozzles. They spray this liquid inside the scrubber, in order to allow the pollutants to be reduced.
This form facilitates the exchange between the water solution and the gas flow, which comes upstream from the scrubber’s lower part.
The water solution must have suitable pH and Redox, in order to provide the pollutants’ correct treatment: the acidic pollutants are treated with base solutions (caustic soda), on the other hand the base pollutants are treated with acidic solutions (sulphuric acid). In order to reduce the bacterial flora and the potential pollutant’s pathogenic load, a tank with oxidizing solutions such as sodium hypochlorite, hydrogen peroxide, peracetic acid and similar could be added.
The storage tanks containing the water solutions are provided with dosing stations with metering pumps needed to compensate for reagents values in order to provide a suitable reduction-effectiveness.
After having been treated inside the vertical wet scrubber, the gas flow seeps into the droplet separator, which recovers the leftover droplets flow or they would be released into the atmosphere.
The scrubbers for air treatment can be made up of one, two or more stages. The stages quantity varies according to the types of pollutants there and their concentration. For example, the scrubbers with two stages can be used when the gas flow includes both base pollutants (hydrogen sulphide, mercaptans) and acidic ones (ammonia, organic nitrogen).
The functioning principle of the vertical wet scrubbers is the same one used in the horizontal wet scrubber but it has differences in its own structure. In it, rather than an upstream gas flow, it is cross-flow: the gas comes in sideways, whereas the liquid comes from the top. The horizontal wet scrubbers can be designed with two or more abatement stages and they are recommended in case the vertical ones are not allowed due to the available area.