Combination process for separating off sulphur oxides and nitrogen oxides from flue gases

摘要

In a combination process for separating off sulphur oxides and nitrogen oxides using a scrubbing liquid which contains an iron(II) aminopolycarboxylic complex salt and alkali metal ions or alkaline- earth metal ions (according to P 3537480.2), gaseous sulphur dioxide is additionally fed to the scrubbing liquid. This measure allows the degree of NOx separation to be increased with flue gases having an SOx/NOx molar ratio less than 3. The sulphite ion concentration increased by the addition of SO2 additionally allows reduction of the oxidised iron(III) to iron(II) by metallic iron or zinc. Addition of the SO2 before or during a gypsum precipitation (63) permits the increase in pH and thus precipitation of calcium hydroxide to be avoided. <IMAGE>