Abstract: An apparatus for purifying a process gas containing at least one pollutant gas, having a reactor vessel, has a cylindrical region and a tapering region, and into which oxygen or an oxygen-containing gas can be introduced as a reaction gas into at least one gas inlet and can be discharged through at least one gas outlet. The at least one gas inlet introduces a defined volumetric flow of the reaction gas into the reactor vessel tangentially to a circumferential surface of the cylindrical region. The apparatus may have a pollutant gas inlet, which introduces a defined volumetric flow of the process gas containing at least one pollutant gas into the reactor vessel, so that the at least one pollutant gas and the reaction gas are mixed with each other in the direction of the gas outlet and chemically react with each other on their way through the reactor vessel.