Fremgangsmåde til rensning af røggasser eller andre fugtige spildgasser

In flue gases or other humid exhaust gases which are relatively cold and contain SO2, NO2 and other gaseous pollutants, the SO2 content is oxidized to SO3 and the NO content is reduced by a catalytic treatment, the SO3 content is condensed as sulfuric acid and other gaseous pollutants are removed by being scrubbed with aqueous liquids at low temperatures. In order to heat up the flue gas to the temperature required for the catalysis, the flue gas is heated up in a first heating-up stage by an indirect heat exchange with the catalytically treated gas before the catalytic treatment, the heated-up gas is heated up further in a second heating-up stage to the temperature required for the catalytic treatment, the catalytically treated gas which has been cooled in the first heating-up stage is cooled further in an indirect heat exchanger below the dew point temperature of sulfuric acid and is subsequently fed to an SO3 condenser. The remaining sulfuric acid vapor is absorbed by sprayed dilute sulfuric acid to form a dilute sulfuric acid having a predetermined concentration, the gas leaving the SO3 condenser is scrubbed in a scrubber with a sprayed aqueous liquid and is thus cooled to 40 DEG to 60 DEG C. and the purified gas is reheated to the required chimney inlet temperature.