System for processing combustion exhaust gas containing soot particles and NOx

Abstract

The invention relates to a system and a method for processing exhaust gas of an internal combustion engine such as a diesel engine. The disclosed system and method can be particularly suitable to the diesel engine that usually operates in a lean burn condition without the occurrence of a periodic high-load condition in view of its combustion characteristics. According to the system and method, an exhaust composition containing soot particles and gaseous components are processed to remove the soot particles and to reduce the amount of NOx compounds. The soot particles are first filtered with a filter that passes gaseous components of the composition and collecting the soot particles. The collected soot particles are oxidized in the presence of a light-activated redox catalyst to turn to smaller molecules that can pass through the filter. The NOx compounds are temporarily adsorbed by an adsorber and reduced in the presence of a light-activated redox catalyst to turn to N 2 .

1 . A system for processing a composition comprising soot particles and NOx, the system comprising: 
 an inlet configured to receive a composition comprising soot particles and gaseous components, the gaseous components comprising NOx compounds, which comprise NO and NO 2 ;    an outlet configured to discharge a processed composition;    a soot remover located between the inlet and outlet, the soot remover comprising a filter, a first light-activated redox catalyst and a first light source, the filter being configured to filter soot particles while passing most of the gaseous components therethrough, the soot particles comprising hydrocarbons that may not pass the filter, the first light source being configured to generate light so as to activate the first light-activated redox catalyst, wherein at least part of the filtered soot particles is removed by an oxidation reaction thereof in the presence of the first redox catalyst, and wherein some or all of the hydrocarbons are broken into smaller molecules that can pass through the filter; and    a NOx converter located between the inlet and outlet, the NOx converter comprising an adsorber, a second light-activated redox catalyst and a second light source, the adsorber being configured to adsorb at least part of the NOx compounds, the second light source being configured to generate light so as to activate the second light-activated redox catalyst, wherein at least part of the NOx compounds is adsorbed in the adsorber and converted to N 2  by a reduction reaction thereof in the presence of the second redox catalyst.    
   
   
       2 . The system of  claim 1 , wherein the filter is made of a porous ceramic material.  
   
   
       3 . The system of  claim 1 , wherein at least one of the first and second light-activated redox catalysts is selected from the group consisting of TiO 2 , ZnO, CdS, ZrO 2 , SnO 2 , V 2 O 2 , WO 3 , SrTiO 3 , and a mixture comprising one or more of the foregoing compounds.  
   
   
       4 . The system of  claim 1 , wherein at least one of the first and second light sources comprises a plasma generator comprising two discharge electrodes configured to create a plasma discharge state upon application of a voltage therebetween.  
   
   
       5 . The system of  claim 1 , further comprising a controller configured to change intensity of the light generated by at least one of the first and second light sources, and wherein the degree of at least one of the removal of soot particles and the conversion of NOx is attributable to the change of the intensity of the light.  
   
   
       6 . The system of  claim 1 , wherein at least part of the smaller molecules broken from hydrocarbons participates in the reduction reaction of NOx compounds as a reducing agent.  
   
   
       7 . The system of  claim 1 , further comprising a control circuit configured to control intensity of the light generated by at least one of the first and second light sources.  
   
   
       8 . The system of  claim 1 , wherein at least part of the NOx compounds participates in the oxidation reaction of hydrocarbons as an oxidizing agent.  
   
   
       9 . The system of  claim 1 , further comprising a pre-oxidizer located between the inlet and the soot remover, wherein the pre-oxidizer is configured to oxidize at least part of components of the composition passing therethrough.  
   
   
       10 . A system for processing a combustion exhaust composition, the system comprising: 
 an inlet configured to receive an exhaust composition comprising soot particles and gaseous components, the gaseous components comprising NOx compounds;    an outlet configured to discharge a processed composition;    a soot remover located between the inlet and outlet, the soot remover comprising a filter configured to filter soot particles while passing most of the gaseous components, the soot remover being configured to provide an oxidizing agent to the filtered soot particles such that at least part of the filtered soot particles is oxidized and broken into smaller molecules that can pass through the filter; and    a NOx converter located between the soot converter and outlet, the NOx converter comprising an adsorber configured to adsorb at least part of the NOx, the NOx converter being configured to provide a reducing agent to the adsorbed NOx such that at least part of the adsorbed NOx is reduced and converted to N 2 .    
   
   
       11 . The system of  claim 10 , further comprising a pre-oxidizer located between the inlet and the soot remover, wherein the pre-oxidizer is configured to oxidize at least part of components of the composition, thereby converting the at least part of the components to oxidized species thereof.  
   
   
       12 . The system of  claim 11 , wherein the pre-oxidizer comprises a light-activated redox catalyst and a light source configured to generate light for activating the light-activated redox catalyst.  
   
   
       13 . The system of  claim 11 , wherein the pre-oxidizer comprises a plurality of channels elongated in a general direction from the inlet toward the soot remover, and wherein the redox catalyst is provided in at least one of the channels.  
   
   
       14 . The system of  claim 11 , wherein the oxidizing agent provided to the filtered soot particles comprises at least part of the oxidized species converted in the pre-oxidizer.  
   
   
       15 . The system of  claim 10 , wherein at least one of the soot remover and the NOx converter further comprises a light-activated redox catalyst and a light source configured to generate light for activating the light-activated redox catalyst.  
   
   
       16 . The system of  claim 10 , wherein the soot remover comprises a first cell having an opening toward the inlet and a second cell having an opening toward the NOx converter, wherein the filter is located between and separates the first and second cell.  
   
   
       17 . The system of  claim 16 , wherein the soot remover further comprises a plasma-activated redox catalyst and a pair of discharge electrodes configured to create a plasma discharge in the vicinity of the filter.  
   
   
       18 . The system of  claim 10 , wherein the reducing agent provided to the adsorbed NOx comprises at least part of the small molecules broken from soot particles.  
   
   
       19 . The system of  claim 10 , wherein the NOx converter comprises a plurality of channels elongated in a general direction from the soot remover toward the outlet, and wherein a redox catalyst is provided in at least part of the channels.  
   
   
       20 . The system of  claim 10 , further comprising an automobile comprising an internal combustion engine, wherein the inlet is connected to an exhaust of the internal combustion engine of the automobile.  
   
   
       21 . The system of  claim 10 , wherein no additional oxidizing agent or reducing agent is supplied to the system other than the exhaust composition and air from the surrounding.  
   
   
       22 . A system for processing exhaust gas of an engine, comprising: 
 a first reactor configured to oxidize at least part of hydrocarbons, CO, NO and particulate matters contained in an exhaust gas;    a second reactor configured to collect the particulate matters with a filter and oxidizing the collected particulate matters;    a third reactor comprising a light source, a light-activated redox catalyst and an adsorber configured to adsorb NOx contained in the exhaust gas, the third reactor being configured to remove at least part of the adsorbed NOx by a reduction reaction thereof;    a controller for controlling intensity of light from the light source; and    wherein the first, second and third reactors are located in a conduit for flowing exhaust gas of an engine.