JP2009115022A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively reduce NOx by positively supplying a sufficient amount of HC gas for reducing and controlling NOx to a selective reduction type catalyst in an exhaust emission control device that reduces both of NOx and particulates by using both of a particulate filter and the selective reduction type catalyst. <P>SOLUTION: This exhaust emission control device includes, in mid-way of an exhaust pipe 9, the particulate filter 11 for collecting particulates in exhaust gas 7, an oxidation catalyst 12 for oxidizing unburned HC in the exhaust gas 7 at a further upstream side than the particulate filter 11, and an injector 14 (fuel addition device) for adding fuel to the exhaust gas 7 at a further upstream side than the oxidation catalyst 12. The selective reduction type catalyst 13 for selectively reacting NOx with HC even under coexistence of oxygen is interposed between the oxidation catalyst 12 and the particulate filter 11. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device.

  Particulate matter (particulate matter) discharged from a diesel engine is mainly composed of a soot fraction composed of carbon and a SOF fraction (Soluble Organic Fraction) composed of a high-boiling hydrocarbon component. Furthermore, the composition contains a small amount of sulfate (mist-like sulfuric acid component). As a measure to reduce this type of particulates, a particulate filter is installed in the middle of the exhaust pipe through which the exhaust gas flows. Has been performed conventionally.

  The particulate filter has a porous honeycomb structure made of a ceramic such as cordierite, and the inlets of the respective channels partitioned in a lattice shape are alternately sealed, and the channels are not sealed. The outlet is sealed, and only the exhaust gas that has permeated through the porous thin wall that defines each flow path is discharged downstream.

  Then, the particulates in the exhaust gas are collected and deposited on the inner surface of the porous thin wall, so that the particulates are appropriately burned and removed before the exhaust resistance increases due to clogging. It is necessary to regenerate, but in normal diesel engine operation conditions, there are few opportunities to obtain exhaust temperatures that are high enough for particulates to self-combust, so a catalyst regeneration type that integrally supports an oxidation catalyst. Adoption of a particulate filter is being studied.

  That is, if such a catalyst regeneration type particulate filter is employed, the oxidation reaction of the collected particulates is promoted to lower the ignition temperature, and the particulates can be burned and removed even at an exhaust temperature lower than the conventional one. It becomes possible.

  However, even when such a catalyst regeneration type particulate filter is used, the trapped amount exceeds the particulate processing amount in the operation region where the exhaust temperature is low, so such a low exhaust gas. If the operation state at the temperature continues, there is a possibility that the particulate filter will fall into an over trapped state without the regeneration of the particulate filter proceeding well.

  Therefore, a flow-through type oxidation catalyst is separately arranged in front of the particulate filter, and fuel is added to the exhaust gas upstream of the oxidation catalyst at the stage where the amount of particulate accumulation has increased. It is considered to perform forced regeneration.

  That is, the fuel (HC) added on the upstream side of the particulate filter undergoes an oxidation reaction while passing through the preceding oxidation catalyst, and the catalyst bed of the particulate filter immediately after the inflow of exhaust gas heated by the reaction heat. The temperature is raised, the particulates are burned out, and the particulate filter is regenerated (see, for example, Patent Document 1 below).

  However, when purifying exhaust gas from a diesel engine, it is not sufficient to remove particulates in the exhaust gas as described above, and it is also necessary to remove NOx (nitrogen oxide) contained in the exhaust gas. In general, a part of the exhaust gas extracted from the exhaust system is returned to the intake system, and the exhaust gas returned to the intake system is used to suppress combustion of the fuel in the engine to lower the combustion temperature. An EGR device (EGR: Exhaust Gas Recirculation) that reduces the generation of (nitrogen oxides) is used together. However, in recent years, exhaust gas regulations have been strengthened. It has become difficult to reduce to the target value only by circulation.

For this reason, the present inventor has additionally provided a selective reduction type catalyst that selectively reacts NOx with HC even in the presence of oxygen immediately after the particulate filter, and upstream of the oxidation catalyst in an operating state with a low exhaust temperature. The inventors have come up with the idea of reducing and purifying NOx by introducing a part of the added fuel to the selective catalytic reduction catalyst without any treatment.
JP 2003-193824 A

  However, when the selective reduction type catalyst is additionally provided immediately after the particulate filter in this way, even if fuel is added as a reducing agent for reducing and purifying NOx on the upstream side, HC generated from the added fuel Since most of the gas is consumed while passing through the preceding oxidation catalyst and particulate filter, a sufficient amount of HC gas to reduce and purify NOx reaches the final selective reduction catalyst. There is a problem that the selective catalytic reduction catalyst cannot be effectively used.

  The present invention has been made in view of the above-described circumstances, and relates to an exhaust emission control device that simultaneously reduces NOx and particulates by using a particulate filter and a selective reduction catalyst, and is sufficient to reduce and purify NOx. The object is to reliably supply an amount of HC gas to the selective catalytic reduction catalyst so that NOx can be effectively reduced.

  The present invention relates to a particulate filter that collects particulates in exhaust gas, an oxidation catalyst that oxidizes unburned HC in exhaust gas upstream of the particulate filter, and an exhaust gas upstream of the oxidation catalyst. In the exhaust gas purification apparatus provided with a fuel addition apparatus for adding fuel to the gas in the middle of the exhaust pipe, selection is made to selectively react NOx with HC even in the presence of oxygen between the oxidation catalyst and the particulate filter. It is characterized in that a reduced catalyst is interposed.

  In this way, when the fuel is added to the exhaust gas by the fuel addition device, the selective reduction catalyst is disposed in front of the particulate filter, so that the amount consumed by the particulate filter is reduced. HC gas is supplied as it is to the selective catalytic reduction catalyst, and the amount of HC gas supplied to the selective catalytic reduction catalyst is increased as compared with the case where the selective catalytic reduction catalyst is arranged immediately after the particulate filter. It becomes possible to satisfactorily reduce and purify NOx using this HC gas as a reducing agent.

  On the other hand, the particulate filter in the exhaust gas is collected by the particulate filter immediately after the selective catalytic reduction catalyst, so that the particulate and NOx can be simultaneously reduced, and added by the fuel addition device. The HC gas generated from the burned fuel undergoes an oxidation reaction on the front stage oxidation catalyst, and the exhaust gas heated by the reaction heat flows in, so that the catalyst bed temperature of the rear stage particulate filter is raised and trapped inside. The particulate is burned out and the particulate filter is regenerated.

  Further, in the present invention, the oxidation catalyst and the selective reduction catalyst can be supported and integrated on the same carrier, and in this way, the oxidation catalyst, the selective reduction catalyst, the particulate filter, The overall length of the device is shortened compared to the case where three are arranged individually, and the occupied space is made compact, and the number of parts for fixing the oxidation catalyst and the selective reduction catalyst in the casing is also reduced. become.

  In addition, noble metal catalysts such as platinum and palladium, which are known as selective reduction catalysts having the property of selectively reacting NOx with a reducing agent even in the presence of oxygen, use added fuel for forced regeneration of the particulate filter. The oxidation catalyst is similar in composition to the oxidation catalyst to be oxidized, and there is no particular technical problem in integrating the oxidation catalyst and the selective reduction catalyst on the same carrier.

  However, carrying the selective reduction catalyst on the particulate filter so that sufficient performance as the selective reduction catalyst can be exerted causes clogging of the particulate filter. It is difficult to integrate the particulate filter with the particulate filter, and it can be said that the integration of the oxidation catalyst and the selective reduction catalyst is realized because the selective catalytic reduction catalyst is arranged in advance of the particulate filter.

  According to the exhaust emission control device of the present invention described above, various excellent effects as described below can be obtained.

  (I) According to the invention described in claim 1 of the present invention, it relates to an exhaust emission control device that simultaneously reduces NOx and particulates by using a particulate filter and a selective catalytic reduction catalyst. A sufficient amount of HC gas can be reliably supplied to the selective catalytic reduction catalyst to effectively reduce NOx, and the cost can be reduced by improving the NOx purification performance and reducing the capacity of the selective catalytic reduction catalyst. Can do.

  (II) According to the second and third aspects of the present invention, the total length of the apparatus can be shortened compared to the case where the oxidation catalyst, the selective reduction catalyst, and the particulate filter are individually arranged in triplicate. Since downsizing can be achieved, the mountability to the vehicle can be greatly improved, and the number of parts for fixing the oxidation catalyst and the selective reduction catalyst in the casing can be reduced. Further cost reduction can be realized.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an example of an embodiment for carrying out the present invention. In FIG. 1, reference numeral 1 denotes a diesel engine equipped with a turbocharger 2, and air 4 guided from an air cleaner 3 passes through the intake pipe 5 through the turbocharger. The air 4 sent to the compressor 2a of the charger 2 and pressurized by the compressor 2a is further sent to the intercooler 6 to be cooled, and the air 4 is led from the intercooler 6 to an intake manifold (not shown) to be a diesel engine. 1 is introduced into each cylinder.

  Further, exhaust gas 7 discharged from each cylinder of the diesel engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 8, and the exhaust gas 7 driving the turbine 2b passes through the exhaust pipe 9 to the outside of the vehicle. To be discharged.

  In the middle of the exhaust pipe 9 through which the exhaust gas 7 circulates, a casing 10 forming a muffler outer cylinder is provided, and a particulate filter that collects particulates in the exhaust gas 7 is provided in a subsequent stage in the casing 10. 11 is housed, and an oxidation catalyst 12 that oxidizes unburned HC in the exhaust gas 7 is provided upstream of the particulate filter 11 in the front stage in the casing 10. And the particulate filter 11 is provided with a selective reduction catalyst 13 that selectively reacts NOx with HC even in the presence of oxygen.

  Further, the exhaust pipe 9 upstream of the casing 10 is provided with an injector 14 (fuel addition device) for adding fuel (light oil or the like) as a reducing agent to the exhaust gas 7, and is added by the injector 14. The HC gas generated from the burned fuel undergoes an oxidation reaction while passing through the oxidation catalyst 12, and the catalyst bed temperature of the particulate filter 11 at the last stage is raised by the inflow of the exhaust gas 7 heated by the reaction heat, thereby causing the particulates The particulate filter 11 is regenerated, and part of the added fuel reaches the selective catalytic reduction catalyst 13 without being treated, and is generated from the added fuel. NOx is reduced and purified by the HC gas.

  Thus, if the exhaust gas purification apparatus is configured in this way, when the fuel is added to the exhaust gas 7 by the injector 14, the selective catalytic reduction catalyst 13 is arranged ahead of the particulate filter 11. The amount of HC gas consumed by the particulate filter 11 is supplied to the selective catalytic reduction catalyst 13 as it is, and the selective catalytic reduction catalyst 13 is disposed immediately after the particulate filtering 11 compared with the case where the selective catalytic reduction catalyst 13 is arranged. The amount of HC gas supplied to the selective catalytic reduction catalyst 13 increases, and it becomes possible to satisfactorily reduce and purify NOx using this HC gas as a reducing agent.

  On the other hand, since particulates in the exhaust gas 7 are collected by the particulate filter 11 immediately after the selective catalytic reduction catalyst 13, the particulates and NOx can be simultaneously reduced. The HC gas generated from the added fuel undergoes an oxidation reaction on the preceding oxidation catalyst 12, and the exhaust gas 7 heated by the reaction heat flows, whereby the catalyst bed temperature of the latter particulate filter 11 is raised, The particulates collected in the are burned out and the particulate filter 11 is regenerated.

  Therefore, according to the above-described embodiment, the exhaust purification device that simultaneously reduces the NOx and the particulates by using the particulate filter 11 and the selective reduction catalyst 13 in combination, an amount of HC sufficient to reduce and purify NOx. The gas can be reliably supplied to the selective reduction catalyst 13 to effectively reduce NOx, and the NOx purification performance can be improved and the cost can be reduced by reducing the capacity of the selective reduction catalyst 13.

  FIG. 2 shows another embodiment of the present invention, in which the oxidation catalyst 12 and the selective catalytic reduction catalyst 13 are supported and integrated on the same carrier. The total length of the apparatus is shortened and the occupied space is made compact, compared to the case where the catalyst 12, the selective reduction catalyst 13 and the particulate filter 11 are individually arranged in triplicate. In addition, the oxidation catalyst 12 and the selective reduction catalyst 13 are reduced. The number of parts for fixing the inside of the casing 10 is also reduced.

  Incidentally, a noble metal catalyst such as platinum or palladium known as a selective reduction catalyst 13 having the property of selectively reacting NOx with a reducing agent even in the presence of oxygen is added for the purpose of forcibly regenerating the particulate filter 11. It is similar in composition to the oxidation catalyst 12 that oxidizes the fuel, and there is no particular technical problem in integrating the oxidation catalyst 12 and the selective catalytic reduction catalyst 13 on the same carrier.

  However, since the selective filter 11 is supported on the particulate filter 11 so that sufficient performance as the selective catalytic reduction catalyst 13 can be exhibited, the particulate filter 11 is clogged. It is difficult to integrate the reduction catalyst 13 and the particulate filter 11, and the oxidation catalyst 12 and the selective reduction catalyst 13 are integrated because the selective reduction catalyst 13 is arranged in advance of the particulate filter 11. It can be said that realization has been realized.

  Therefore, according to the present embodiment, the total length of the apparatus can be shortened and the occupied space can be made compact compared to the case where the oxidation catalyst 12, the selective reduction catalyst 13 and the particulate filter 11 are individually arranged in triplicate. Therefore, the mounting property on the vehicle can be greatly improved, and the number of parts for fixing the oxidation catalyst 12 and the selective catalytic reduction catalyst 13 in the casing 10 can be reduced, thereby further reducing the cost. Can also be realized.

  Note that the exhaust emission control device of the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

It is the schematic which shows an example of the form which implements this invention. It is the schematic which shows another form example of this invention.

Explanation of symbols

7 Exhaust gas 9 Exhaust pipe 11 Particulate filter 12 Oxidation catalyst 13 Selective reduction catalyst 14 Injector (fuel addition device)

Claims (2)

  A particulate filter that collects particulates in the exhaust gas, an oxidation catalyst that oxidizes unburned HC in the exhaust gas upstream of the particulate filter, and a fuel in the exhaust gas upstream of the oxidation catalyst In the exhaust emission control device provided with a fuel addition device in the middle of the exhaust pipe, a selective reduction type catalyst that selectively reacts NOx with HC even in the presence of oxygen between the oxidation catalyst and the particulate filter. An exhaust purification device characterized by being interposed.   2. The exhaust emission control device according to claim 1, wherein the oxidation catalyst and the selective reduction catalyst are supported and integrated on the same carrier.

Images