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

Abstract

A catalytic reactor ( 16 ) is provided for purposes of effecting therewith the removal of nitrogen oxides from a process gas (F) that includes at least two catalyst bed segments ( 48, 50, 52 ), each of which is provided with a closing device ( 60, 62, 64 ). The catalytic reactor ( 16 ) is operative for causing said process gas (F) to flow through a first catalyst bed segment ( 48 ). Said process gas (F) is at a first temperature at which the sulphur trioxide that is entrained in said hot process gas is at least partially precipitated out on to the catalytic material that said first catalyst bed segment ( 48 ) embodies. Periodically said closing device ( 60 ) is operated in order to thereby isolate said first bed segment ( 48 ) from the flow therethrough of said hot process gas (F). A regeneration system ( 34, 36, 38 ) is also provided that is operative for purposes of causing a regenerating gas to flow through the first bed segment ( 48 ). In addition, a sulphur trioxide removal device ( 20 ) is provided, which is separate from said catalytic reactor ( 16 ), and which is operative for purposes of effecting therewith the removal of the sulphur trioxide from said regenerating gas.

1 . 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.   
     
     
         2 . The gas cleaning system as claimed in  claim 1 , further including a regenerating gas supply device, which is operative for purposes of supplying said regenerating gas at a second temperature, said second temperature being higher than said first temperature. 
     
     
         3 . The gas cleaning system as claimed in  claim 1 , wherein said sulphur trioxide removal device is a sulphur trioxide removal device selected from the group of devices consisting of wet scrubbers, dry scrubbers, fabric filters, and electrostatic precipitators. 
     
     
         4 . The gas cleaning system as claimed in  claim 3 , wherein said sulphur trioxide removal device is located at a point downstream of the catalytic reactor with respect to the direction of flow of said hot process gas, and said sulphur trioxide removal device is operative for purposes of effecting the removal therewith of the sulphur species that are entrained in said hot process gas and in said regenerating gas. 
     
     
         5 . The gas cleaning system as claimed in  claim 1 , further including a gas cooler which is operative for purposes of effecting therewith the cooling of said regenerating gas after said generating gas has flowed through said first catalyst bed segment and before said regenerating gas is made to flow through said sulphur trioxide removal device. 
     
     
         6 . The gas cleaning system as claimed in  claim 1 , further being operative for purposes of effecting the mixing of at least a portion of said regenerating gas that has flowed through said first catalyst bed segment with an absorption medium that is made to circulate in said sulphur trioxide removal device for the purpose of effecting the removal of the sulphur dioxide from said hot process gas.