An aqueous solution containing both pentavalent vanadium and divalent manganese compounds has been found to be useful for autoxidation of sulfur dioxide.
Thus, a flue gas desulfurization process using the new catalyst, comprising absorption, oxidation and neutralization (producing gypsum), has been developed by means of a laboratory equipment (Fig. 1) with simulated gas.
Introducing sulfur dioxide into an aqueous solution of pentavalent vanadium compounds, vanadium was rapidly reduced to tetravalent state and deactivated; therefore the solution could not be provided as catalyst.
Reduction of vanadium was extremely suppressed by a little amount of divalent manganese compounds; moreover, the catalyst activity was remarkably increased.
Pentavalent vanadium needed for preparing the catalyst and making up for the circulation loss could be readily obtained by oxidizing washings of fly ash from residual oil-fired boilers.
In comparison with the well-known conventional catalyst "aq-Solution of Ferric Sulfate", the new catalyst has higher activity and therefore causes more autoxidation of sulfur dioxide in absorber, and results in superior sulfur dioxide removal.
Neutralizing the sulfuric acid in the catalyst solution by means of limestone, gypsum was produced and tetravalent vanadium was oxidized with air. After separating the catalyst solution from gypsum, it was recycled to absorb sulfur dioxide.
All kind of anticipated catalyst contaminants proved to be nonpoisonous.
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