JP2013087745A - Reducing agent supply device and exhaust gas purifying apparatus including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reducing agent supply device capable of improving reduction efficiency of No, and an exhaust gas purifying apparatus including the device.SOLUTION: Respective ejection pipes 12 form a spoke shape in which they intersect at one location at the center radially inside an annular flow path 11. Each ejection pipe 12 has a plurality of ejection holes 25 formed. A distance between adjacent ejection holes 25 is constant in each ejection pipe 12. In addition, a flat fin 30 with a sectorial shape is mounted on each ejection pipe 12.

Description

  The present invention relates to a reducing agent supply device and an exhaust gas purification device including the same.

A urea SCR (Selective Catalytic Reduction) system has been developed to reduce nitrogen oxide (NOx) contained in exhaust gas of a diesel engine. The basic configuration of the urea SCR system includes an oxidation catalyst for oxidizing nitrogen monoxide (NO) to nitrogen dioxide (NO ₂ ), and ammonia and NOx generated from urea water provided downstream of the oxidation catalyst. The SCR catalyst for reducing NOx to nitrogen and water, the urea addition system for adding urea water to the SCR catalyst, and the downstream of the SCR catalyst are consumed by the chemical reaction in the SCR catalyst. And an oxidation catalyst for oxidizing the remaining ammonia.

  Such a urea SCR system is described in Patent Document 1, for example. In this urea SCR system, a grid-like pipe having a plurality of jet holes is provided on the upstream side of the catalyst carrier, and urea water is sent to the grid-like pipe by a pump and directed from the jet hole to the catalyst carrier. Therefore, urea water is supplied. Since the ejection holes are provided at equal intervals in the pipes provided in a lattice shape, the urea water is uniformly supplied to the entire end face of the catalyst carrier.

JP 2007-107450 A

  However, when the exhaust gas flows through the exhaust pipe, the exhaust gas generally has a speed distribution that increases in speed from the wall surface of the exhaust pipe toward the center portion, so that urea is uniformly distributed over the entire end face of the catalyst carrier. When water is supplied, the urea water is insufficient in the region near the center portion even though the urea water is excessive in the region near the wall surface of the exhaust pipe, resulting in a reduction in NOx reduction efficiency. was there.

  The present invention has been made to solve such problems, and an object of the present invention is to provide a reducing agent supply device capable of improving the reduction efficiency of NOx and an exhaust gas purification device provided with the same.

A reducing agent supply device according to the present invention is a reducing agent supply device that supplies a reducing agent to a catalyst carrier on which an SCR catalyst for reducing NOx in exhaust gas discharged from an internal combustion engine and flowing through an exhaust pipe is supported. And a plurality of ejection holes through which the reducing agent is ejected, and the plurality of ejection holes are provided so that an opening ratio of the ejection holes with respect to a flow passage cross section of the exhaust pipe increases from the wall surface of the exhaust pipe toward the center. It has been. Since the supply amount of the reducing agent increases from the wall surface of the exhaust pipe toward the center, an appropriate amount of urea water is supplied according to the velocity distribution of the exhaust gas flowing through the exhaust pipe.
An annular annular passage through which the reducing agent flows, and a plurality of ejection pipes provided on the radially inner side of the annular passage and formed with a plurality of ejection holes. You may communicate with the road. The plurality of ejection pipes may constitute a spoke shape that intersects at one place in a portion other than their both ends. The ejection pipe may be made of a porous material.
The ejection pipe may have a mixer section that changes the flow of the exhaust gas.

An exhaust gas purifying apparatus according to the present invention comprises a catalyst carrier carrying an SCR catalyst for reducing NOx in exhaust gas discharged from an internal combustion engine and flowing through an exhaust pipe, and a catalyst carrier for reducing NOx by the SCR catalyst. A reducing agent supply device that supplies a reducing agent to the reducing agent supply device, the reducing agent supply device includes a plurality of ejection holes from which the reducing agent is ejected, and the plurality of ejection holes are directed from the wall surface of the exhaust pipe toward the center portion. It is provided so that the opening ratio of the ejection holes with respect to the flow passage cross section of the exhaust pipe increases. Since the supply amount of the reducing agent increases from the wall surface of the exhaust pipe toward the center, an appropriate amount of urea water is supplied according to the velocity distribution of the exhaust gas flowing through the exhaust pipe.
An annular annular passage through which the reducing agent flows, and a plurality of ejection pipes provided on the radially inner side of the annular passage and formed with a plurality of ejection holes. You may communicate with the road. The plurality of ejection pipes may constitute a spoke shape that intersects at one place in a portion other than their both ends. The ejection pipe may be made of a porous material.
The ejection hole may be provided in a direction in which the reducing agent is ejected toward the upstream side with respect to the direction in which the exhaust gas flows in the exhaust pipe.
The ejection pipe may have a mixer section that changes the flow of the exhaust gas.
The reducing agent supply device may be disposed on an upstream end surface of the catalyst carrier.

  According to this invention, the amount of reducing agent supplied from the wall surface of the exhaust pipe increases toward the center, so that an appropriate amount of urea water is supplied according to the velocity distribution of the exhaust gas flowing through the exhaust pipe. Therefore, NOx reduction efficiency can be improved.

1 is a schematic configuration diagram of an exhaust gas purification device according to an embodiment of the present invention. It is sectional drawing of the catalyst carrier of the exhaust gas purification apparatus which concerns on this embodiment. It is a top view of the reducing agent supply apparatus of the exhaust gas purification apparatus which concerns on this embodiment. It is sectional drawing of the modification of the ejection pipe | tube of the reducing agent supply apparatus of the exhaust gas purification apparatus which concerns on this embodiment.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
As shown in FIG. 1, an exhaust gas purification filter 4 having an oxidation catalyst 3 and a wall flow type catalyst carrier 6 is provided in an exhaust pipe 2 through which exhaust gas discharged from a diesel engine 1 which is an internal combustion engine flows. The oxidation catalyst 5 is provided. Between the exhaust gas purification filter 4 and the oxidation catalyst 5, a NOx sensor 7 for detecting the NOx concentration in the exhaust gas is provided. On the upstream end face 6 a of the catalyst carrier 6, a reducing agent supply device 10 that ejects urea water as a reducing agent is provided. The reducing agent supply device 10 includes an annular flow path 11 having the same outer diameter as the outer diameter of the catalyst carrier 6 and a plurality of ejection pipes 12 whose both ends communicate with the annular flow path 11. The annular flow path 11 is communicated via a pipe 13 to a urea water tank 14 in which urea water is stored. The pipe 13 is provided with a pump 15 for pumping urea water stored in the urea water tank 14 to the annular flow path 11 and an electromagnetic valve 16. The NOx sensor 7, the pump 15, and the electromagnetic valve 16 are each electrically connected to an ECU 17 that is a control device.

  As shown in FIG. 2, the catalyst carrier 6 is composed of a porous base material 21. As a material of the base material 21, a ceramic material used as a normal filter base material such as cordierite, alumina, silicon carbide, or the like can be used. An SCR catalyst for reducing NOx is supported in the pores inside the substrate 21. The surface 21a of the base material 21 on the diesel engine 1 side is coated with a collection layer 22 for collecting particulate matter (PM) in the exhaust gas. As the material of the collection layer 22, the same material as that of the substrate 21 can be used. A plurality of exhaust gas passages 23 extending in the axial direction of the catalyst carrier 6 are formed inside the catalyst carrier 6. Since the catalyst carrier 6 is a wall flow type catalyst carrier, each exhaust gas passage 23 is Either one of the end face 6a side and the other end face 6b side constitutes an opening 23a, and the other end constitutes a sealing part 23b.

  As shown in FIG. 3, each of the ejection pipes 12 has a spoke shape that intersects at one place in a portion other than the both end portions (a central portion in this embodiment) on the radially inner side of the annular flow path 11. It is composed. Each ejection pipe 12 has a plurality of ejections so that when the reducing agent supply device 10 is viewed in a direction facing the end face 6a (see FIG. 1) of the catalyst carrier 6, the ejection holes 25 for ejecting urea water can be seen. A hole 25 is provided. Thereby, urea water comes to be ejected from the ejection hole 25 toward the upstream side with respect to the direction in which the exhaust gas flows in the exhaust pipe 2 (see FIG. 1). However, the urea water does not need to be jetted in a direction completely opposite to the exhaust gas flow (parallel to the exhaust gas flow), and is oblique to the exhaust gas flow direction, that is, at an angle. However, it may be ejected toward the upstream side in the direction in which the exhaust gas flows.

  In each ejection pipe 12, the distance between adjacent ejection holes 25 is constant. However, since each ejection pipe 12 intersects at one place in the central portion thereof, the distance between the adjacent ejection pipes 12 becomes shorter from the annular flow path 11 toward the intersection of each ejection pipe 12. ing. Thus, the ejection holes 25 are provided so that the ejection holes 25 become dense from the annular flow path 11 toward the intersecting portions of the ejection pipes 12, that is, the number of the ejection holes 25 per unit area increases. It has been. That is, the ejection holes 25 are provided so that the opening ratio of the ejection holes 25 with respect to the flow path cross section of the exhaust pipe 2 increases from the wall surface of the exhaust pipe 2 toward the center. Thereby, when the reducing agent supply device 10 is installed in the exhaust pipe 2 (see FIG. 1), the amount of urea water supplied increases from the wall surface of the exhaust pipe 2 toward the center.

  In addition, a flat fin 30 having a fan shape is attached to each ejection pipe 12. The fins 30 are oblique to the back side of the paper surface of FIG. 3, that is, when the reducing agent supply device 10 is installed in the exhaust pipe 2 (see FIG. 1), the end surface 6a of the catalyst carrier 6 (see FIG. 1). It inclines so that it may incline toward. Here, since the flow direction of the exhaust gas flowing through the exhaust pipe 2 is bent along the inclination of the fin 30, the fin 30 constitutes a mixer unit that changes the flow of the exhaust gas.

Next, the operation of the reducing agent supply device according to this embodiment and the exhaust gas purification device including the same will be described.
As shown in FIG. 1, after starting the diesel engine 1, the exhaust gas flows through the exhaust pipe 2. By the exhaust gas flows through the oxidation catalyst 3, a portion of the NO in the exhaust gas is oxidized into NO _2. Subsequently, the exhaust gas flows into the exhaust gas purification filter 4. In the exhaust gas purification filter 4, the exhaust gas passes through the reducing agent supply device 10. At this time, the flow of the exhaust gas changes along the fins 30 and is disturbed, and an exhaust gas vortex is generated. In this state, the exhaust gas flows into the catalyst carrier 6.

  As shown in FIG. 2, the exhaust gas that has flowed into the catalyst carrier 6 through the opening 23 a flows through the exhaust gas passage 23. The exhaust gas passage 23 provided with the opening 23a at the end portion on the end surface 6a side is provided with the sealing portion 23b at the end portion on the end surface 6b side. Then, the gas passes through the wall of the exhaust gas passage 23, that is, the collection layer 22 and the base material 21, and moves to the adjacent exhaust gas passage 23. Since the adjacent exhaust gas passage 23 has an opening 23a at the end on the end face 6b side, the exhaust gas passage 23 flows out of the catalyst carrier 6 through the opening 23a.

When the exhaust gas passes through the wall of the exhaust gas passage 23, PM contained in the exhaust gas is collected by the collection layer 22. The exhaust gas that has passed through the collection layer 22 passes through the substrate 21 while diffusing through the pores inside the substrate 21. At this time, the urea water supplied by the operation described later becomes hydrolyzed ammonia and carbon dioxide (CO ₂ ), and the generated ammonia and exhaust gas in the SCR catalyst supported in the pores inside the base material 21. The inside NOx reacts to form nitrogen (N ₂ ) and water (H ₂ O). As shown in FIG. 1, the ammonia that remains without being consumed in the exhaust gas purification filter 4 is oxidized in the oxidation catalyst 5. The exhaust gas from which NOx has been purified in this way flows through the exhaust pipe 2 and is exhausted to the atmosphere.

Next, the operation of supplying urea water to the catalyst carrier 6 will be described.
As shown in FIG. 1, the NOx sensor 7 detects the NOx concentration in the exhaust gas flowing out from the exhaust gas purification filter 4, and this detected value is transmitted to the ECU 17. The ECU 17 controls the activation of the pump 15 and the opening / closing of the solenoid valve 16 based on the detection value of the NOx sensor 7. For example, an upper limit value of the NOx concentration is set in the ECU 17 in advance, and when the detected value of the NOx sensor 7 is equal to or higher than the upper limit value, it is determined that the exhaust gas purification filter 4 needs to purify NOx, and the pump 15 And the solenoid valve 16 is opened. Then, the urea water in the urea water tank 14 flows through the pipe 13 and flows into the annular flow path 11 of the reducing agent supply device 10. The urea water flowing into the annular flow channel 11 flows into the ejection pipe 12 and is ejected from the ejection holes 25 formed in the ejection pipe 12. Conversely, if the detected value of the NOx sensor 7 is less than this upper limit value, the exhaust gas purification filter 4 determines that NOx purification is not necessary, and the ECU 17 stops the pump 15 and closes the electromagnetic valve 16. Further, a map of the detected value of the NOx sensor 7 and the supply amount of urea water is incorporated in the ECU 17 in advance, and the activation of the pump 15 and the electromagnetic valve 16 are adjusted so as to adjust the supply amount of urea water based on this map. It is also possible to control the opening and closing of.

  As already described, in this embodiment, the urea water is ejected toward the upstream side with respect to the direction in which the exhaust gas flows, so that it collides with the flowing exhaust gas. It becomes easy to be dispersed in. Further, since the exhaust gas vortex is generated by the fins 30 (see FIG. 3), the urea water jetted into the exhaust gas is further stirred, so that the dispersibility of the urea water is improved.

  Further, when exhaust gas flows through the exhaust pipe 2, the exhaust gas generally has a speed distribution such that the speed increases from the wall surface of the exhaust pipe 2 toward the center. On the other hand, as already described, in this embodiment, the supply amount of urea water is increased from the wall surface of the exhaust pipe 2 toward the center portion, so that the location where the exhaust gas speed is high. As a result, a large amount of urea water is supplied to the catalyst carrier 6 and the NOx reduction efficiency in the catalyst carrier 6 is improved.

  Thus, when the supply amount of the reducing agent increases from the wall surface of the exhaust pipe 2 toward the center, an appropriate amount of urea water is supplied according to the velocity distribution of the exhaust gas flowing through the exhaust pipe 2. Therefore, NOx reduction efficiency can be improved.

  In this embodiment, the plurality of ejection pipes 12 constitute a spoke shape, but the present invention is not limited to this form. The two ejection pipes 12 may be arranged in a cross shape, the plurality of ejection pipes 12 may be arranged in a lattice shape, or the plurality of ejection pipes 12 may be arranged in parallel. However, if the intervals between the adjacent ejection holes 25 in each ejection pipe 12 are the same except in the case where they are arranged in a cross shape, the number of ejection holes 25 per unit area increases from the wall surface of the exhaust pipe 2 toward the center. Therefore, in these cases, in each of the ejection pipes 12, the interval between the adjacent ejection holes 25 is shortened from the wall surface of the exhaust pipe 2 toward the center portion, or the size of the ejection holes 25 is reduced. Just make it bigger.

  In this embodiment, the ejection pipe 12 is formed by forming a plurality of holes as the ejection holes 25 in the tubular member. However, the present invention is not limited to this form. In the case where a plurality of jet pipes form a spoke shape or two jet pipes are arranged in a cross shape, for example, a jet pipe made of a porous material such as a ceramic sintered porous body is used. Even if it uses, since the space | interval of the jet pipe which adjoins toward the center part from the wall surface of the exhaust pipe 2 becomes short, it is possible to increase the supply amount of the reducing agent from the wall surface of the exhaust pipe 2 toward the center part. it can. In this case, the pores of the porous material constitute the ejection holes.

  In this embodiment, the fan-shaped flat fins 30 are used as the mixer section. However, the present invention is not limited to this form, and the shape, size, number, etc., are determined according to the arrangement of the ejection pipes. May be changed as appropriate. Further, as shown in FIG. 4, a jet pipe 32 having a rectangular cross section is provided in the reducing agent supply device, and one of the side surfaces 32a having the larger area of the two sets of side surfaces facing each other is flowed into the exhaust gas. The flow of exhaust gas can also be changed by inclining at an angle on the downstream side. In this case, the side surface 32a constitutes a mixer section.

In this embodiment, the surface 21a on the diesel engine 1 side of the porous base material 21 constituting the catalyst carrier 6 is coated with a collection layer 22 for collecting PM in the exhaust gas. The form is not limited. The base material 21 may be provided with a diesel particulate filter (DPF) for collecting PM between the oxidation catalyst 3 and the catalyst carrier 6 without providing a member for collecting PM. In this embodiment, the catalyst carrier 6 is a wall flow type, but may be a flow through type.
Further, in this embodiment, the reducing agent supply device 10 is provided on the upstream end face 6 a of the catalyst carrier 6, but it may be arranged at a distance from the catalyst carrier 6.

In this embodiment, urea water is used as the reducing agent, but the present invention is not limited to this. Other reducing agents such as ammonia water and ammonia gas may be used.
Further, in this embodiment, the supply of the reducing agent is controlled based on the detection value of the NOx sensor 7, but the supply of the reducing agent is controlled by using the operating state of the diesel engine 1 or using it together. May be.

  DESCRIPTION OF SYMBOLS 1 Diesel engine (internal combustion engine), 2 exhaust pipe, 6 catalyst carrier, 6a (catalyst carrier) end surface, 10 reducing agent supply apparatus, 11 annular flow path, 12, 32 ejection pipe, 25 ejection hole, 30 fin (mixer part) ), 32a (outlet tube) side surface (mixer part).

Claims (12)

A reducing agent supply device for supplying a reducing agent to a catalyst carrier on which an SCR catalyst for reducing NOx in exhaust gas discharged from an internal combustion engine and flowing through an exhaust pipe is supported,
A plurality of ejection holes through which the reducing agent is ejected are provided, and the plurality of ejection holes increase from the wall surface of the exhaust pipe toward the center thereof the opening ratio of the ejection holes with respect to the flow passage cross section of the exhaust pipe A reducing agent supply device provided to perform. An annular annular channel through which the reducing agent flows;
A plurality of ejection pipes provided on the radially inner side of the annular flow path and formed with the plurality of ejection holes;
The reducing agent supply device according to claim 1, wherein both ends of the ejection pipe communicate with the annular flow path.   The reducing agent supply device according to claim 2, wherein the plurality of ejection pipes constitute a spoke shape that intersects at one place in a portion other than both end portions thereof.   The reducing agent supply apparatus according to claim 3, wherein the ejection pipe is made of a porous material.   The reducing agent supply apparatus according to any one of claims 2 to 4, wherein the ejection pipe includes a mixer section that changes a flow of the exhaust gas. A catalyst carrier on which an SCR catalyst for reducing NOx in exhaust gas discharged from an internal combustion engine and flowing through an exhaust pipe is supported;
A reducing agent supply device for supplying a reducing agent to the catalyst carrier for reducing NOx by the SCR catalyst;
The reducing agent supply device includes a plurality of ejection holes through which the reducing agent is ejected, and the plurality of ejection holes are ejected from a wall surface of the exhaust pipe toward a central portion with respect to a flow passage cross section of the exhaust pipe. An exhaust gas purifying device provided so that the aperture ratio of the holes is increased. The reducing agent supply device includes:
An annular annular channel through which the reducing agent flows;
A plurality of ejection pipes provided on the radially inner side of the annular flow path and formed with the plurality of ejection holes;
The exhaust gas purification device according to claim 6, wherein both ends of the ejection pipe communicate with the annular flow path.   The exhaust gas purification device according to claim 7, wherein the plurality of ejection pipes constitute a spoke shape that intersects at one place in a portion other than their both ends.   The exhaust gas purification apparatus according to claim 8, wherein the ejection pipe is made of a porous material.   The said ejection hole is provided in the direction in which the said reducing agent is ejected toward the upstream with respect to the direction in which the said exhaust gas flows through the inside of the said exhaust pipe. Exhaust gas purification device.   The exhaust gas purification device according to any one of claims 7 to 10, wherein the ejection pipe has a mixer section that changes a flow of the exhaust gas.   The exhaust gas purification device according to any one of claims 6 to 11, wherein the reducing agent supply device is disposed on an upstream end surface of the catalyst carrier.

Images