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Chemical desulfurization - precipitation with iron salts

Chemical desulfurization applies metal salts like FeCl2 to precipitate sulfur. Iron salts, like iron II chloride (FeCl2), help to keep hydrogen sulfide levels (H2S) low.

 

With the addition of iron II chloride (FeCl2) into the digestion process sulfure can ? due to the high chemical affinity between iron and sulfur ? be pecipitated selectively. Iron stays in solution for a long time and reacts with sulfur when it becomes present. Due to this one dosing point is sufficient to secure a complete precipitation in the whole digester.

 

    • Precipitation reaction FeCl2 + H2S    --> FeS + 2 HCl

 

Only a small amount of FeCl2 can control and keep H2S-conzentrations at less than 200ppm in order to minimize corrosion with the biogas engine burning the digester gas.

 

Molecular weight of iron und sulfur:

 

    • Fe = 55,845 g/mol
    • S = 32,065 g/mol
    • FeS = 87,91 g/mol