JP3545712B2 - Exhaust gas purification device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification device.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a diesel engine vehicle is provided with a NOx reduction catalyst (selective reduction type catalyst) having a property of selectively reacting NOx with a reducing agent even in the presence of oxygen, in the middle of an exhaust pipe through which exhaust gas flows. Adding a reducing agent such as light oil upstream of the NOx reduction catalyst to cause the reducing agent to undergo a reduction reaction with NOx (nitrogen oxide) in exhaust gas on the NOx reduction catalyst, thereby reducing the NOx emission concentration. There is something we can do.
[0003]
As this type of NOx reduction catalyst, noble metal catalysts such as platinum and palladium and base metal catalysts such as oxides of vanadium, copper and iron are already known as having the above-mentioned properties.
[0004]
FIG. 4 schematically shows an example of an exhaust gas purifying apparatus equipped with the above-mentioned NOx reduction catalyst. An outer cylinder of a muffler of an exhaust pipe 3 through which exhaust gas 2 discharged from a diesel engine 1 of an automobile flows. Is a filter case 4.
[0005]
That is, the NOx reduction catalyst 5 is accommodated in the filter case 4. The NOx reduction catalyst 5 has an outer peripheral portion held by the cushion material 6, and is provided at an intermediate portion of the cushion material 6 in the axial center direction. Is provided with a sealing material 7 so as to prevent the exhaust gas 2 from being bypassed. The specific structure of the NOx reduction catalyst 5 is as shown in FIG. 5, and is formed as a flow-through type catalyst monolith.
[0006]
On the upstream side of the NOx reduction catalyst 5, an injection nozzle 9 for injecting a reducing agent 8 such as light oil and adding it to the exhaust gas 2 is provided, and the reducing agent 8 injected from the injection nozzle 9 reduces the NOx. The catalyst 5 performs a reduction reaction with NOx in the exhaust gas 2.
[0007]
[Problems to be solved by the invention]
However, in the example shown here, the injection nozzle 9 is inserted immediately before the NOx reduction catalyst 5 from the outer peripheral side of the filter case 4, and the tip of the injection nozzle 9 faces the upstream end face of the NOx reduction catalyst 5. However, in such a structure, the injection nozzle 9 is exposed to the flow of the high-temperature exhaust gas 2 and becomes hot, and the reducing agent 8 is carbonized and clogged in the injection nozzle 9. In addition, a bent portion or the like may be provided in the exhaust pipe 3 on the upstream side as compared with the example shown here, and the projection amount of the injection nozzle 9 into the gas flow path may be reduced as much as possible. Alternatively, it is conceivable to arrange the exhaust manifold 10 so that the amount of protrusion to the inside of the exhaust manifold 10 is minimized with respect to the longitudinal end of the exhaust manifold 10, but it goes back to the upstream side of the NOx reduction catalyst 5. Ho So that thereby causing a new problem that the addition amount of the middle of the channel the amount of reducing agent 8 which adhere to the walls increases the reducing agent 8 becomes much than necessary.
[0008]
The present invention has been made in view of the above-described circumstances, and is intended to avoid a risk that a reducing agent to be added to a NOx reduction catalyst is exposed to high-temperature exhaust gas and carbonized in a nozzle. It is intended to be.
[0009]
[Means for Solving the Problems]
The present invention is an exhaust gas purifying apparatus equipped with a NOx reduction catalyst in a filter case interposed in the middle of an exhaust pipe, wherein an exhaust gas inlet is provided at a position shifted from an axial center position on an upstream end surface of the filter case. A guide nozzle projecting in a direction away from the NOx reduction catalyst at an axial center position on an upstream end face of the filter case, and an injector for injecting a reducing agent toward the NOx reduction catalyst at a tip of the guide nozzle. The NOx is extended from the opening at the base end of the guide nozzle in the filter case toward the upstream end face of the NO x reduction catalyst while expanding in a conical shape so as to cover substantially the entire area of the end face, and its NO x the guide cone having a communication hole for taking the exhaust gas from the inlet to the circumferential surface of the reduction catalyst near provided, catalyst regeneration type particulate downstream of the NO x reduction catalyst in the filter casing It is characterized in the provision of the Interview filter.
[0010]
Thus, in this way, the reducing agent injected from the injector is added to the NOx reduction catalyst through the guide nozzle outside the filter case, and the NOx in the exhaust gas introduced from the inlet and the NOx on the NOx reduction catalyst At this time, the guide nozzle that guides the reducing agent from the injector into the filter case is disposed outside the filter case and is air-cooled. The possibility that the agent is carbonized is avoided beforehand, and clogging of the guide nozzle due to carbonization of the reducing agent is prevented.
Further, the exhaust gas introduced from the inlet into the filter case is guided to the NO x reduction catalyst flows from the communication hole that opens to the peripheral surface of the NO x reduction catalyst near the guide cone in the guide cone , NO x towards the reduction catalyst side is the amount corresponding pressure in the flow of the exhaust gas relatively lower than the guide nozzle side in the guide cone, soot guide nozzle to be associated to the exhaust gas and the exhaust gas having a high temperature Since it is no longer guided to the side, the risk that the reducing agent is carbonized in the flow path of the guide nozzle can be more reliably avoided, and contamination of the guide nozzle by soot can be avoided.
Moreover, the reducing agent that has passed through the NO x reduction catalyst without being used for the reduction of NO x causes an oxidation reaction (combustion) on the oxidation catalyst on the surface of the subsequent particulate filter, and the heat of the reaction causes the particulate filter Since the combustion of the particulates collected in the fuel cell is assisted, it is possible to efficiently burn and remove the particulates at a relatively low ignition temperature.
[0013]
Further, in the present invention, the guide nozzle may have a bell mouth shape whose diameter gradually increases toward the reducing agent injection direction, or the guide nozzle may have a taper shape whose diameter gradually increases toward the reducing agent injection direction. Preferably, in this manner, the reducing agent injected from the injector can be smoothly diffused, introduced into the filter case, and satisfactorily dispersed over substantially the entire upstream end surface of the NOx reduction catalyst.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0016]
FIG. 1 shows an example of an embodiment of the present invention. As shown in the drawing, in the exhaust gas purifying apparatus of the present embodiment, as in the case of FIG. Is illustrated as a filter case 4. A flow-through type NOx reduction catalyst 5 is accommodated between an inlet pipe 11 and an outlet pipe 12 in the filter case 4. The catalyst regeneration type particulate filter 13 is also accommodated in the case 4 after the NOx reduction catalyst 5.
[0017]
The particulate filter 13 has a porous honeycomb structure made of a ceramic such as cordierite, and the inlets of the flow paths 14 partitioned in a lattice are alternately plugged, and the inlets are not plugged. The outlet of the flow path 14 is plugged, and only the exhaust gas 2 that has passed through the porous thin wall 15 that defines each flow path 14 is discharged to the downstream side. The particulates are collected on the inner surface of the wall 15.
[0018]
The catalyst regeneration type particulate filter 13 referred to herein is, for example, a filter obtained by adding an appropriate amount of a rare earth element such as cerium to alumina on which platinum is supported, and integrally supporting the oxidation catalyst. The integrated oxidation catalyst promotes the oxidation reaction of the collected particulates to lower the ignition temperature, so that the particulates can be burned and removed at a lower exhaust temperature than before. pointing.
[0019]
The particulate filter 13 also has an outer peripheral portion held by the cushion material 6 like the NOx reduction catalyst 5 at the preceding stage, and a bypass of the exhaust gas 2 is provided at an intermediate portion of the cushion material 6 in the axial direction. A sealing material 7 is interposed so as to be able to block.
[0020]
The inlet pipe 11 connected to the exhaust pipe 3 on the upstream side and forming an inlet for the exhaust gas 2 is disposed at a position shifted from the axial center position on the upstream end face of the filter case 4. A guide nozzle 16 protruding from the NOx reduction catalyst 5 in a direction away from the NOx reduction catalyst 5 is provided at an axial center position on the upstream end surface so that the reducing agent 8 can be injected toward the NOx reduction catalyst 5 at the tip of the guide nozzle 16. An injector 17 is provided.
[0021]
Here, the injector 17 is configured such that a reducing agent 8 is guided from a reducing agent tank (not shown) by a supply line 19 provided with a feed pump 18, and an electromagnetic valve 20 provided in the injector 17 is connected to the injector 17. By electrically opening and closing, the reducing agent 8 can be appropriately injected.
[0022]
Also, between the opening 21 at the base end of the guide nozzle 16 and the NOx reduction catalyst 5 in the filter case 4, substantially the entire area of the end face is covered from the opening 21 toward the upstream end face of the NOx reduction catalyst 5. A guide cone 23 having a communication hole 22 which extends while expanding in a conical shape and has a communication hole 22 for taking in the exhaust gas 2 from the inlet pipe 11 is provided on the peripheral surface near the NOx reduction catalyst 5.
[0023]
Here, the inlet pipe 11 extends to a position where it abuts on the guide cone 23 and is welded to an appropriate position in the circumferential direction of the guide cone 23, and is inserted into the filter case 4 of the inlet pipe 11. A large number of communication holes 24 are also opened at the set portion.
[0024]
The outlet pipe 12 is attached to the downstream end surface of the filter case 4 at the axial center position thereof and is fixed to the separator 25. The outlet pipe 12 and the portion of the outlet pipe 12 inserted into the filter case 4 are connected to the separator 25. Also, many communication holes 26 and 27 are opened.
[0025]
Thus, in this manner, the reducing agent 8 injected from the injector 17 is added to the NOx reduction catalyst 5 through the guide nozzle 16 outside the filter case 4, and the reducing agent 8 in the exhaust gas 2 introduced from the inlet pipe 11 The NOx and the NOx reduction catalyst 5 undergo a reduction reaction. At this time, a guide nozzle 16 that guides the reducing agent 8 from the injector 17 into the filter case 4 is disposed outside the filter case 4 and air-cooled. Therefore, the risk that the reducing agent 8 is carbonized in the flow path of the guide nozzle 16 is avoided beforehand, and the clogging of the guide nozzle 16 due to the carbonization of the reducing agent 8 is prevented.
[0026]
Therefore, according to the above embodiment, the risk that the reducing agent 8 to be added to the NOx reduction catalyst 5 is exposed to the high-temperature exhaust gas 2 and carbonized in the guide nozzle 16 can be avoided beforehand. Therefore, clogging due to carbonization of the reducing agent 8 can be prevented, and the reducing agent 8 can be stably added over a long period of time.
[0027]
Further, in this embodiment, in particular, the exhaust gas 2 introduced into the filter case 4 from the inlet pipe 11 passes through the guide cone 23 through each of the communication holes 22 opened on the peripheral surface of the guide cone 23 near the NOx reduction catalyst 5. The NOx reduction catalyst 5 flows into the NOx reduction catalyst 5 and is guided to the NOx reduction catalyst 5. The NOx reduction catalyst 5 side in the guide cone 23 has a relatively lower pressure than the guide nozzle 16 side by the amount of the flow of the exhaust gas 2, Since the high-temperature exhaust gas 2 and soot accompanying the exhaust gas 2 are not guided to the guide nozzle 16 side, the possibility that the reducing agent 8 is carbonized in the flow path of the guide nozzle 16 is further reliably avoided. The contamination of the guide nozzle 16 by soot can also be avoided.
[0028]
Further, in the present embodiment, since the catalyst regeneration type particulate filter 13 is provided at the subsequent stage of the NOx reduction catalyst 5 in the filter case 4, the NOx reduction catalyst 5 has passed without being used for NOx reduction. Since the reducing agent 8 causes an oxidation reaction (combustion) on the oxidation catalyst on the surface of the subsequent particulate filter, the heat of the reaction can assist combustion of the particulates collected by the particulate filter 13. Particulates can be efficiently burned and removed at a relatively low ignition temperature.
[0029]
Further, in the embodiment of FIG. 1 described above, the guide nozzle 16 has a straight pipe shape. However, as shown in FIG. As shown in FIG. 3, the guide nozzle 16 can have a gradually increasing bell-mouth shape, or a tapered shape in which the diameter gradually increases toward the injection direction of the reducing agent 8, as shown in FIG. The reducing agent 8 injected from the device 17 is smoothly diffused into the filter case 4, and can be satisfactorily dispersed over substantially the entire upstream end surface of the NOx reduction catalyst 5.
[0030]
It should be noted that the exhaust gas purification apparatus of the present invention is not limited to the above-described embodiment, and it goes without saying that various changes can be made without departing from the spirit of the present invention.
[0031]
【The invention's effect】
According to the exhaust gas purification apparatus of the present invention described above, various excellent effects as described below can be obtained.
[0032]
(I) According to the first aspect of the present invention, it is possible to avoid the possibility that the reducing agent to be added to the NOx reduction catalyst is exposed to high-temperature exhaust gas and carbonized in the guide nozzle. Therefore, clogging due to carbonization of the reducing agent can be prevented, and the reducing agent can be stably added over a long period of time.
[0033]
(II) According to the first aspect of the present invention, the high-temperature exhaust gas and the soot accompanying the exhaust gas are not guided to the guide nozzle side. The risk of carbonization can be more reliably avoided, and contamination of the guide nozzle by soot can also be avoided.
[0034]
(III) According to the invention of claim 1 of the present invention, the reducing agent that has passed without being used for the reduction of NO x by the NO x reduction catalyst is oxidized on the oxidation catalyst on the surface of the subsequent particulate filter. The reaction allows the reaction heat to assist the burning of the particulates collected by the particulate filter, so that the particulates can be efficiently burned and removed at a relatively low ignition temperature .
[0035]
According to the invention described in claim 2 or 3 (IV) present invention, substantially the upstream end face of the injector while smoothly diffuse the injected reducing agent from led into the filter case put the NO x reduction catalyst It can be spread well over the entire area .
[Brief description of the drawings]
FIG. 1 is a sectional view showing an example of an embodiment of the present invention.
FIG. 2 is a sectional view showing a modification of the guide nozzle of FIG.
FIG. 3 is a sectional view showing another modified example of the guide nozzle of FIG.
FIG. 4 is a schematic view showing a conventional example.
FIG. 5 is a perspective view showing the details of the NOx reduction catalyst of FIG. 4 with a part thereof cut away.
[Explanation of symbols]
2 Exhaust gas 3 Exhaust pipe 4 Filter case 5 NOx reduction catalyst 8 Reducing agent 11 Inlet pipe (inlet)
13 Particulate filter 16 Guide nozzle 17 Injector 21 Opening 22 Communication hole 23 Guide cone

Claims (3)

An exhaust purification device equipped with a NOx reduction catalyst in a filter case interposed in the middle of an exhaust pipe, wherein an exhaust gas inlet is provided at a position shifted from an axial center position on an upstream end surface of the filter case, and a filter case is provided. together with the guide nozzle protruding in a direction away from the NOx reduction catalyst projecting from the axial position at the upstream side end face, equipped with injectors that can inject a reducing agent for the NOx reduction catalyst at the tip of the guide nozzle , in the filter case of the guide nozzle from the opening of the proximal end NO x reducing catalyst upstream end surface facing the end face a conical manner capable of covering substantially the entire area in the increased diameter while extending and the the NO x reduction catalyst near the the guide cone having a communication hole for taking the exhaust gas from the inlet to the peripheral surface provided, particulate catalyst regeneration type downstream of the NO x reduction catalyst in the filter casing Exhaust purification apparatus characterized in that a filter. 2. The exhaust gas purifying apparatus according to claim 1 , wherein the guide nozzle has a bell-mouth shape whose diameter gradually increases in the reducing agent injection direction. 2. The exhaust gas purifying apparatus according to claim 1 , wherein the guide nozzle has a tapered shape whose diameter gradually increases in the reducing agent injection direction.

Images