Process for removing nitrogen oxides from the flue gases of a pulp mill

A process for removing nitrogen oxides from flue gases of a soda recovery boiler of a pulp mill, the method comprising the steps of

• adding to said flue gases an oxidizing agent selected from the group consisting of chlorine dioxide and ozone wherein the nitrogen oxides are oxidized to nitrogen dioxide thereby forming a nitrogen dioxide-containing gas stream;
• leading said nitrogen dioxide-containing gas stream to a flue gas scrubber;
• treating a reagent selected from the group consisting of white liquor and sodium hydroxide, where said reagent is from the chemical circulation of the pulp mill, with an additional reagent of sulphur dioxide produced from the odor gas combustion in the pulp mill to form a sodium sulphite reducing scrubbing solution;
• injecting said reducing scrubbing solution into said nitrogen dioxide-containing gas stream wherein the scrubbing solution reduces the nitrogen dioxide to nitrogen thereby forming a nitrogen-containing gas stream and an oxidized reagent;
• and
• removing said nitrogen containing gas stream from the flue gas scrubber and leading said oxidized reagent back to the circulation of chemicals of the pulp mill.