A process and device for purifying flue gases in refuse incineration plants during regeneration of a catalyst which serves for reducing nitrogen oxides, by, in a first step, removing acidic pollutant gases from the flue gas in a wet or dry manner, in a second step adding ammonia for reducing nitrogen oxides to the flue gas purified in the first step, in a third step feeding the flue gas admixed with the ammonia to a catalyst, where the catalyst is heated at a controlled heat-up rate for regeneration, which leads to liberation of ammonia, where the amount of ammonia added in the second step and the heat-up rate in the third step are controlled by the amount of a pollutant gas selected from the group of ammonia, and which the purified flue gas contains.