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The removal of acid gas pollutants from combustion sources like waste incinerators and small industrial boilers can be achieved by dry sorption.
In this process the absorption agent is usually a dry powder of Lime or Sodium Bicarbonate.
The reagent is fed into a dedicated reactor, used to increase the contact time and mixing between the reagent itself and the flue gas.
The dose rate of reagent as well as the reagent type depends on process consideration like pollutant reduction efficiency, flue gas temperature, etc..
The reaction by-products are solid and need to be deposited from the flue-gas as dust in a bag filter.
The cake of reagent that forms on fabric filters gives effective contact between flue-gas and absorbent and is the place where the absorption is completed.
The adding of moderate amounts of activated carbon or lignite coke, also injected dry with the dry sorbent, generally makes it possible to meet the most stringent emission standards in Waste Incineration.
The use of two reagents has found expensive commercial application: Lime and Sodium Bicarbonate.
LIME
Dry scrubbing with Lime methods have improved significantly in recent years, resulting in excellent removal efficiencies. Lime with very high specific surface is available on the market and this method is now a standard for Flue Gas Treatment on glass plants and Waste Incinerators , where it is basically used to reduce HCl,
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and HF. |
The reaction mechanism is the following:
In the attached picture a typical block diagram of a Dry-Lime System is represented.
BICAR
Dry sorption by injection of Sodium Bicarbonate is very similar to the one making use of Lime. In this case the process is based on the injection of dry, finely ground Sodium Bicarbonate into the “dirty” flue gas.
The overall chemical reactions of acid neutralisation using sodium bicarbonate are presented below:
Termokimik apply this process mainly on Waste-to-Energy Plants and small size Industrial Boilers. |
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