Exhaust gas treatment system and exhaust gas treatment method

Abstract

There is provided an exhaust gas treatment system for removing nitrogen oxide and sulfur trioxide in exhaust gas by using a catalyst characterized in that a SO 3 reducing catalyst on the upstream side and a denitrifying catalyst on the downstream side are arranged in series with respect to the flow direction of exhaust gas. Also, there is provided an exhaust gas treatment method characterized by including a SO 3 reducing process for reducing SO 3 using a SO 3 reducing catalyst on the upstream side and a denitrifying process for removing nitrogen oxides using a denitrifying catalyst on the downstream side with respect to the flow direction of exhaust gas.

1 . An exhaust gas treatment system for removing nitrogen oxide and sulfur trioxide in exhaust gas by using a catalyst, characterized in that a SO 3  reducing catalyst on the upstream side and a denitrifying catalyst on the downstream side are arranged in series with respect to the flow direction of exhaust gas.  
     
     
         2 . The exhaust gas treatment system according to  claim 1 , characterized in that said SO 3  reducing catalyst is a catalyst in which Ru is carried as an active metal on a carrier.  
     
     
         3 . The exhaust gas treatment system according to  claim 1 , characterized in that the carrier used for said SO 3  reducing catalyst is at least one kind selected from a group consisting of titania, alumina, zirconia, silica, and zeolite.  
     
     
         4 . The exhaust gas treatment system according to  claim 2 , characterized in that said SO 3  reducing catalyst contains at least one kind selected from a group consisting of Mo, W and V as a co-catalyst in the carrier.  
     
     
         5 . The exhaust gas treatment system according to  claim 1 , characterized in that said denitrifying catalyst carries at least one kind selected from a group consisting of Mo, W and V as an active metal on a carrier containing titania.  
     
     
         6 . The exhaust gas treatment system according to  claim 1 , characterized in that both of said SO 3  reducing catalyst and said denitrifying catalyst are a catalyst formed into a honeycomb shape.  
     
     
         7 . An exhaust gas treatment method for removing nitrogen oxide and sulfur trioxide in exhaust gas by using a catalyst, characterized in that said treatment method includes a SO 3  reducing process for reducing SO 3  using a SO 3  reducing catalyst on the upstream side and a denitrifying process for removing nitrogen oxides using a denitrifying catalyst on the downstream side with respect to the flow direction of exhaust gas.  
     
     
         8 . The exhaust gas treatment method according to  claim 7 , characterized in that said treatment method includes an NH 3  adding process for adding ammonia NH 3 , which is a reducing agent for nitrogen oxides and SO 3 , in a mole ratio of NH 3 /NOx not lower than the equivalent at the preceding stage of said SO 3  reducing process.  
     
     
         9 . The exhaust gas treatment method according to  claim 7 , characterized in that the concentration of NH 3  at the downstream outlet of the SO 3  reducing catalyst is 3 ppm or higher in said SO 3  reducing process.