Gas treatment appartatus

Abstract

The invention relates to a gas treatment apparatus ( 1 ) for treating a gas stream. The gas treatment apparatus ( 1 ) comprising addition means ( 14 ) for adding a reducing agent ( 12 ) to a gas stream passing through the apparatus ( 1 ), a guide chamber ( 8 ), a mixing conduit ( 18 ) and a catalytic treatment chamber ( 16 ) containing a catalytic treatment element ( 20 ). The apparatus ( 1 ) is arranged such that gas must pass through the mixing conduit ( 18 ) to pass from the guide chamber ( 8 ) to the catalytic treatment chamber ( 16 ). The mixing conduit ( 18 ) includes an outer wall ( 22 ) surrounding a mixing axis ( 20 ) within the guide chamber ( 8 ). The outer wall ( 22 ) including at least one aperture ( 30 ) through which a gas can enter the mixing conduit ( 18 ) from the guide chamber ( 8 ). The at least one aperture includes guide means ( 32 ) associated therewith for causing at least some of a gas passing through the at least one aperture ( 30 ) to flow circumferentially about the mixing axis ( 20 ) within the mixing conduit ( 18 ) before entering the catalytic treatment chamber ( 16 ).

1 . A gas treatment apparatus for treating a gas stream, the gas treatment apparatus comprising addition means for adding a reducing agent to a gas stream passing through the apparatus, a guide chamber having an end wall, a mixing conduit within which the addition means are located and a catalytic treatment chamber containing a catalytic treatment element, wherein: 
 the mixing conduit has a smaller cross sectional area for gas flow than the catalytic treatment chamber and guide chamber such that, in use, gas flows faster within the mixing conduit than in the catalytic treatment chamber and the apparatus is arranged such that gas must pass through the mixing conduit to pass from the guide chamber to the catalytic treatment chamber;    the mixing conduit extends into the guide chamber and includes an outer wall surrounding a mixing axis therein, the mixing conduit having an outlet into a downstream chamber which is substantially coaxial with a central axis of said downstream chamber;    the outer wall includes at least one aperture through which a gas can enter the mixing conduit from the guide chamber, the at least one aperture including guide means associated therewith for causing at least some of a gas passing through the at least one aperture to flow circumferentially about the mixing axis within the mixing conduit.    
   
   
       2 . A gas treatment apparatus as claimed in  claim 1 , in which there are a plurality of apertures through the outer wall of the mixing conduit and each aperture includes guide means for causing at least some of a gas passing through the aperture to flow circumferentially about the mixing axis within the mixing conduit.  
   
   
       3 . A gas treatment apparatus as claimed in  claim 1 , in which the mixing conduit has a substantially circular cross section.  
   
   
       4 . A gas treatment apparatus as claimed in  claim 1 , in which the catalytic treatment chamber has a substantially circular cross section.  
   
   
       5 . A gas treatment apparatus as claimed in  claim 1 , in which the guide chamber has a substantially circular cross section.  
   
   
       6 . A gas treatment apparatus as claimed in  claim 2 , in which the plurality of apertures are substantially equally circumferentially spaced around the outer wall of the mixing conduit.  
   
   
       7 . A gas treatment apparatus as claimed in  claim 1 , in which the guide means comprise a deflection wall, the deflection wall being angled such that at least some of a gas passing substantially radially through the, or each, aperture is deflected by the deflection wall to flow substantially circumferentially.  
   
   
       8 . A gas treatment apparatus as claimed in  claim 1 , in which at least one aperture is substantially rectangular.  
   
   
       9 . A gas treatment apparatus as claimed in  claim 8 , in which at least one aperture is arranged such that a long axis of the rectangular aperture is substantially parallel with the mixing axis.  
   
   
       10 . A gas treatment apparatus as claimed in  claim 8 , in which the guide means associated with the, or each, aperture comprises a substantially rectangular deflection wall, the deflection wall extending from a side of the aperture into the mixing conduit.  
   
   
       11 . A gas treatment apparatus as claimed in  claim 1 , in which the guide means and aperture in the wall of the mixing region are formed by forming a cut in the wall of the mixing chamber and then deforming a region of said wall adjacent to the cut into the mixing conduit such that an aperture is opened and a guide means formed.  
   
   
       12 . A gas treatment apparatus as claimed in  claim 1 , in which the catalytic treatment chamber includes an entry portion located between the mixing conduit and the catalytic treatment element such that a gas leaving the mixing conduit can disperse across the entire cross section of the catalytic treatment chamber before entering the catalytic treatment element.  
   
   
       13 . A vehicle having a diesel engine, the vehicle being equipped with a gas treatment apparatus as claimed in  claim 1 , for treating the exhaust gas from the diesel engine.