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

Process for removing nitrogen oxides from the flue gases of a soda recovery boiler of a pulp mill. In the method, to the flue gases of the soda recovery boiler is at first fed an oxidizing agent, such as chlorine dioxide or ozone, which oxidizes nitrogen oxide to nitrogen dioxide. Subsequently, the flue gases are led into a flue gas scrubber, in which a reagent coming from the circulation of chemicals of the pulp mill is injected into the flue gases, which reagent brought into contact with the nitrogen dioxide reduces the nitrogen dioxide to nitrogen. The flue gas containing nitrogen is led out of the scrubber and the oxidized reagent is led back to the circulation of chemicals of the pulp mill.