Method and a device for removing nitrogen oxides and sulphur trioxide from a process gas

A gas cleaning system operative for removing, at least partially, nitrogen oxide from a hot process gas, said gas cleaning system including a catalytic reactor embodying catalytically active material, said catalytic reactor comprising a catalyst bed comprising at least two catalyst bed segments, which are arranged in parallel relation with respect to the direction of flow of the hot process gas, each of said at least two catalyst bed segments being provided with a closing device, such that each of said at least two catalyst bed segments can be individually isolated from the flow of said hot process gas, characterized in that said catalytic reactor is operative for purposes of causing said hot process gas to flow through at least a first catalyst bed segment of said at least two catalyst bed segments, said hot process gas being at a first temperature at which the sulphur trioxide entrained in said hot process gas is at least partially precipitated out on to the catalytic material that said first catalyst bed segment embodies, and for periodically effecting the operation of said closing device in order to thereby isolate said first catalyst bed segment from the flow therethrough of said hot process gas, while a second one of said at least two catalyst bed segments remains operative for purposes of effecting the removal therewith of the sulphur trioxide and of the nitrogen oxide from said hot process gas,

• said gas cleaning system further includes a regeneration system, which is operative for purposes of causing a regenerating gas to flow through said first catalyst bed segment when said first catalyst bed segment is isolated from the flow of said hot process gas, as well as a sulphur trioxide removal device, which is separate from said catalytic reactor, and which is operative for purposes of effecting therewith the removal of the sulphur trioxide from said regenerating gas that has been made to flow through said first catalyst bed segment.