Other methods of sulfur removal

The following alternative chemical approaches to FGD have been proposed. 

1 Sodium hydroxide can be used to absorb SO2 from the flue gases. HS03 is oxidized. CaC03 is then added to precipitate calcium sulfate and regenerate (most of) the alkali. 

Variations of this wet regenerative technique that have been proposed and investigated include the absorption of SO2 by Na2S03, Na2C03, K2CO3 or Mg(OH)2, or by buffered citric acid or FeS slurry, from which SO2 and/or sulfur are recovered. 

Dry regenerative techniques have been suggested, including the adsorption of SO2 either on an activated carbon bed, followed by oxidation to sulfuric acid, or on CuO (----- CUSO4), which is later reduced by hydrogen, releasing SO2. 

Dry calcium carbonate or calcium hydroxide is injected into the combustion flame and the oxidized sulfur is retained by the solid particles. This process is, however, not very efficient as excess solid must be used. Ca(OH)2 is more expensive to prepare but is more efficient in sulfur removal. 

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