Apparatus for treating diesel engine exhaust gas

Abstract

An apparatus for treating Diesel engine exhaust gas includes a filter unit which is located in the upstream side of a flow passage in a Diesel engine exhaust duct, the filter unit being composed of a plural number of filter chambers which are thermally insulated from each other and selectively opened for admission of the exhaust gas. Located in the downstream side is a nitrogen oxide treatment section to induce reactions between nitrogen oxides and reductant gas components of the exhaust gas. The exhaust gas is admitted into one of the filter chambers in one time period to trap particulate material on a filter in a filter chamber while letting reductant gas components of the exhaust gas pass through toward the nitrogen oxide treatment section which is located in the downstream side. In the nitrogen oxide treatment section, reducing reactions are induced between nitrogen oxides and reductant gas components of the exhaust gas in the presence of a nitrogen oxide reduction catalyst. Concurrently, in a filter chamber which is disconnected from an exhaust gas inlet passage, a heater is turned on to burn off particulate matter trapped on a filter in a filter chamber.

1 . An apparatus for treating Diesel engine exhaust gas, into which Diesel engine exhaust gas is introduced to get rid of particulate matter and to reduce nitrogen oxides in said exhaust gas to harmless nitrogen gas, characterized in that said apparatus comprises:
 a filter unit located in an upstream side of a Diesel engine exhaust gas duct and composed of a plural number of filter chambers each encasing a permeable filter member capable of trapping particulate matter in said exhaust gas while permitting passage therethrough of reductant gas components in said exhaust gas, and a nitrogen oxide treatment section located in a downstream side of said Diesel engine exhaust gas duct and encasing a nitrogen oxide reduction catalyst to induce reducing reactions between nitrogen oxides and said reductant gas components in said exhaust gas;   said filter chambers of said filter unit being thermally insulated from each other and each provided with a heater to burn off trapped particulate matter; and   a control means for the control of exhaust gas feed to the respective filter chambers of said filter unit, said control means being adapted to feed exhaust gas successively to said filter chambers, making an exhaust gas feed to one filter chamber in one time period while suspending an exhaust gas feed to other filter chambers during that time period.   
     
     
         2 . An apparatus for treating Diesel engine exhaust gas as set forth in  claim 1 , wherein each one of said filter chambers of said filter unit is packed with a permeable filter of ceramic fiber capable of filtering out particulate matter in said exhaust gas while permitting passage of reductant gas components including at least carbon monoxide and hydrocarbons. 
     
     
         3 . An apparatus for treating Diesel engine exhaust gas as set forth in  claim 2 , wherein said filter is packed between tubular inner and outer casings, of which said inner casing having an inlet opening at one end of a closed porous tube, said heater being located within said inner casing and extended forward toward said inlet opening from a closed bottom end, and said outer casing being formed of a heat insulating material. 
     
     
         4 . An apparatus for treating Diesel engine exhaust gas as set forth in  claim 1 , wherein said filter unit further comprises a shutter for covering and uncovering inlet openings of the respective filter chambers under control of said control means, in such a way as to uncover an inlet opening of one of said filter chambers to let said exhaust gas in, and turning on a heater in other filter chamber to burn off trapped particulate matter on said filter while said inlet opening is closed by said shutter. 
     
     
         5 . An apparatus for treating Diesel engine exhaust gas as set forth in  claim 4 , wherein said control means is adapted to turn on a heater of a filter chamber in a phase of trapping particulate material, and to heat said exhaust gas up to a temperature range suitable for activation of said nitrogen oxide reduction catalyst in said nitrogen oxide treatment section. 
     
     
         6 . An apparatus for treating Diesel engine exhaust gas as set forth in  claim 1 , wherein said filter chambers of said filter unit are arranged in a circular formation and said shutter is in the form of a rotary shutter adapted to uncover an inlet opening of one of said filter chambers selectively in one time period and provided with a communication passage for introduction of said exhaust gas through the uncovered inlet opening. 
     
     
         7 . An apparatus for treating Diesel engine exhaust gas as set forth in  claim 1 , wherein said nitrogen oxide reduction catalyst is constituted by an occlusion material of a honeycomb structure. 
     
     
         8 . An apparatus for treating Diesel engine exhaust gas as set forth in  claim 7 , wherein said occlusion material employs iridium or rhodium as a nitrogen oxide reduction catalyst on a porous carrier of silica.