Exhaust gas purifying apparatus and method for regenerating particulate filter thereof

Abstract

An exhaust gas purifying apparatus includes an exhaust pipe, a first oxidation catalyst, a selective catalytic reduction (SCR) catalyst, a urea water supply system, a particulate filter (PF) and a controller. Exhaust gas discharged from an internal combustion engine flows through the exhaust pipe. The first oxidation catalyst is disposed in the exhaust pipe. The SCR catalyst is disposed in the exhaust pipe downstream of the first oxidation catalyst. The urea water supply system supplies urea water to the SCR catalyst. The PF is disposed in the exhaust pipe downstream of the SCR catalyst. The controller stops supplying the urea water from the urea water supply system during regeneration of the PF, so as to supply the NO 2 formed in the first oxidation catalyst to the PF, wherein the NO 2 functions as an oxidizing agent to oxidize particulate matter (PM) deposited on the PF for regenerating the PF.

1 . An exhaust gas purifying apparatus comprising;
 an exhaust pipe through which exhaust gas discharged from an internal combustion engine flows;   a first oxidation catalyst disposed in the exhaust pipe, the first oxidation catalyst generates nitrogen dioxide;   a selective catalytic reduction catalyst disposed in the exhaust pipe downstream of the first oxidation catalyst;   a urea water supply system supplying urea water to the selective catalytic reduction catalyst;   a particulate filter disposed in the exhaust pipe downstream of the selective catalytic reduction catalyst; and   a controller for controlling the urea water supply system,   wherein the controller stops supplying the urea water from the urea water supply system during regeneration of the particulate filter, so as to supply the nitrogen dioxide formed in the first oxidation catalyst to the particulate filter, wherein the nitrogen dioxide functions as an oxidizing agent to oxidize particulate matter deposited on the particulate filter for regenerating the particulate filter.   
   
   
       2 . The exhaust gas purifying apparatus according to  claim 1 , wherein the exhaust gas purifying apparatus further includes a second oxidation catalyst disposed in the exhaust pipe between the selective catalytic reduction catalyst and the particulate filter. 
   
   
       3 . The exhaust gas purifying apparatus according to  claim 1 , wherein the exhaust gas purifying apparatus further includes a pressure sensor and the controller receives a signal outputted from the pressure sensor for detecting pressure differential between the upstream and downstream of the particulate filter, wherein the controller stops supplying the urea water from the urea water supply system when the pressure differential reaches a predetermined value. 
   
   
       4 . The exhaust gas purifying apparatus according to  claim 1 , wherein the urea water supply system is activated to supply urea water to the selective catalytic reduction catalyst when the regeneration of the particulate filter is completed. 
   
   
       5 . The exhaust gas purifying apparatus according to  claim 1 , wherein the urea water supply system includes;
 an injection nozzle injecting urea water;   a urea water tank storing urea water;   a piping through which the injection nozzle is in communication with the urea water tank; and   a urea water supply device supplying urea water in the urea water tank to the injection nozzle and is disposed in the piping.   
   
   
       6 . The exhaust gas purifying apparatus according to  claim 1 , wherein the controller stops supplying the urea water from the urea water supply system in a condition where the temperature of the exhaust gas is as high as the temperature that the nitrogen dioxide functions as the oxidizing agent in the particulate filter. 
   
   
       7 . The exhaust gas purifying apparatus according to  claim 1 , wherein the internal combustion engine is a diesel engine, and the particulate filter is a diesel particulate filter. 
   
   
       8 . A method for regenerating a particulate filter of an exhaust gas purifying apparatus, the apparatus includes an exhaust pipe through which exhaust gas discharged from an internal combustion engine flows, a first oxidation catalyst disposed in the exhaust pipe, the first oxidation catalyst generates nitrogen dioxide, a selective catalytic reduction catalyst disposed in the exhaust pipe downstream of the first oxidation catalyst, a urea water supply system supplying urea water to the selective catalytic reduction catalyst and a particulate filter disposed in the exhaust pipe downstream of the selective catalytic reduction catalyst,
 the method comprising:   stopping supplying the urea water from the urea water supply system during regeneration of the particulate filter; and   supplying the nitrogen dioxide formed in the first oxidation catalyst to the particulate filter, wherein the nitrogen dioxide functions as an oxidizing agent to oxidize particulate matter deposited on the particulate filter.