The present invention relates to a process plant for the oxidation of SO2 to SO3 in a process gas, said process plant comprising a heat exchanger configured for heating the process gas by heat exchange with an oxidized process gas and/or a further oxidized process gas by providing thermal contact between said process gas and said oxidized process gas and/or said further oxidized process gas, a first zone of material catalytically active in oxidation of SO2 to SO3, and a boiler configured for containing steam being heated by the oxidized process gas and/or the further oxidized process after said oxidized process gas has been cooled in the heat exchanger characterized in the cooled oxidized process gas in the boiler being non-condensing with the benefit of providing the possibility for a smaller heat exchanger which may be made with only moderate corrosion resistant materials, compared to a process plant according to the prior art, as well as a related process.