Process for removal or mercury vapor and/or vapor of noxious organic compounds and/or nitrogen oxides from flue gas from an incinerator plant

A process for removal of mercury vapor and/or vapor of noxious organic compounds and/or nitrogen oxides from a stream of hot flue gas exhausted from an incinerator plant and possibly containing fly ash, combined with a simultaneous removal of acidic components of the flue gas, by passing said stream at a temperature of 135.degree.-400.degree. C. into a spray absorption chamber wherein an aqueous liquid containing a basic absorbent is atomized to cool the flue gas at a temperature between 180.degree. C. and 90.degree. C. and to absorb acidic components from the flue gas, and simultaneously to evaporate the water in said aqueous liquid, thereby forming a particulate material containing reaction products of the basic absorbent with acidic components of the flue gas, and nonreacted absorbent, which particulate material together with the fly ash, if any, is separated from the flue gas in a particle separator downstream of the spray absorption chamber, comprising injecting powdery activated carbon in an amount of 1-800 mg per Nm.sup.3 flue gas into the stream of flue gas at least one location selected from locations upstream of the spray absorption chamber, locations within the spray absorption chamber and locations downstream the spray absorption chamber but upstream of the particle separator, and separating said powdery carbon in the particle separator together with said particulate material.