Process for purifying exhaust gases and apparatus for purifying exhaust gases

Abstract

A process for purifying exhaust gases includes the steps of collecting PMs, forcibly exhausting PMs, and purifying PMs. In the step of purifying PMs, PMs in exhaust gases are collected with a filter. In the step of forcibly exhausting PMs, PMs, which are collected on the filter, are exhausted by blowing a pressurized gas onto the filter, thereby forming PMs-containing gases. In the step of purifying PMs, PMs, which are contained in the PMs-containing gases, are purified by contacting an oxidizing agent with the PMs-containing gases, thereby removing the PMs from the PMs-containing gases by means of oxidation.

1 . A process for purifying exhaust gases, the process comprising the steps of:
 collecting particulate matters (hereinafter abbreviated to as “PMs”) in exhaust gases with a filter;   forcibly exhausting PMs, which are collected on the filter, by blowing a pressurized gas onto the filter, thereby forming PMs-containing gases; and   purifying PMs, which are contained in the PMs-containing gases, by contacting an oxidizing agent with the PMs-containing gases, thereby removing the PMs from the PMs-containing gases by means of oxidation.   
   
   
       2 . The process set forth in  claim 1 , wherein:
 the exhaust gases have a predetermined temperature, and the pressurized gas has a temperature lower than the predetermined temperature of the exhaust gases; and   the oxidizing agent comprises ozone.   
   
   
       3 . The process set forth in  claim 1 , wherein the step of forcibly exhausting PMs comprises the steps of:
 supplying pressurized air from an exhaust-gas-flow downstream side with respect to the filter to an exhaust-gas-flow upstream side with respect thereto;   supplying the formed PMs-containing gas to a sub-filter, thereby collecting PMs on the sub-filter; and   supplying the oxidizing agent toward the sub-filter.   
   
   
       4 . The process set forth in  claim 2 , wherein the pressurized gas has a temperature falling within a range of from room temperature to 300° C. 
   
   
       5 . The process set forth in  claim 1 , wherein the pressurized gas is compressed to a pressure of from 0.2 to 15 Pa. 
   
   
       6 . The process set forth in  claim 1 , wherein the pressurized gas is supplied for a time period of from 1 to 20 minutes. 
   
   
       7 . The process set forth in  claim 1 , wherein the oxidizing agent is supplied at a flow rate of from 1 to 30 g/min. for a time period of from 1 to 20 minutes. 
   
   
       8 . An apparatus for purifying exhaust gases, the apparatus comprising:
 a main flow passage equipped with a filter for collecting PMs;   a back-flowing device for supplying a pressurized gas from an exhaust-gas-flow downstream side with respect to the filter to an exhaust-gas-flow upstream side with respect thereto, and blowing out PMs, which are collected on the filter, onto an exhaust-gas-flow upstream side with respect to the filter as PMs-containing gases;   an auxiliary flow passage disposed on an exhaust-gas-flow upstream side with respect to the filter, branched from the main flow passage to extend away therefrom, equipped with a sub-filter for filtering PMs, and enabling the PMs-containing gas to distribute therethrough when the back-flowing apparatus is actuated;   means for supplying an oxidizing agent to the auxiliary flow passage, the oxidizing-agent supplying means disposed on an exhaust-gas-flow upstream side with respect to the sub-filter;   a bypass flow passage disposed on an exhaust-gas-flow upstream side with respect to the filter, branched from the main flow passage to extend away therefrom, and enabling exhaust gases to distribute therethrough when the back-flowing device is actuated; and   a switching valve for switching the flow of exhaust gases from the main flow passage to the bypass flow passage, or vice versa;   when the back-flowing device is actuated, the switching valve further leading the exhaust gases from the main flow passage to the bypass flow passage; PMs, which are contained in the PMs-containing gases blown out onto the exhaust-gas-flow upstream side with respect to the filter, flowing in the auxiliary passage to be collected onto the sub-filter; and the oxidizing agent, which is supplied from the oxidizing-agent supplying means, removing the PMs, which are collected on the sub-filter, by means of oxidation.   
   
   
       9 . The apparatus set forth in  claim 8  further comprising a second filter and a second back-flowing device, which are disposed in the bypass flow passage and which operate in the same manner as the filter and the back-flowing device. 
   
   
       10 . The apparatus set forth in  claim 9  further comprising an opening-and-closing valve for opening and closing the auxiliary flow passage, the opening-and-closing valve disposed on an exhaust-gas-flow downstream side with respect to the auxiliary passage, wherein the exhaust gases flow in both of the main flow passage and the bypass passage when the opening-and-closing valve closes the auxiliary flow passage. 
   
   
       11 . The apparatus set forth in  claim 8 , wherein the filter comprises a catalytic coating layer. 
   
   
       12 . The apparatus set forth in  claim 8 , wherein the back-flowing device supplies a pressurized gas whose temperature falls within a range of from room temperature to 300° C. 
   
   
       13 . The apparatus set forth in  claim 8 , wherein the back-flowing device compresses the pressurized gas to a pressure of from 0.2 to 15 MPa. 
   
   
       14 . The apparatus set forth in  claim 8 , wherein the back-flowing device supplies the pressurized gas for a time period of from 1 to 20 minutes. 
   
   
       15 . The apparatus set forth in  claim 8 , wherein the oxidizing-agent supplying means supplies the oxidizing agent at a flow rate of from 1 to 30 g/min. for a time period of from 1 to 20 minutes.