JP2015048842A - Exhaust purification device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a further positive protection of a selective reduction type catalyst by restricting deposition of urea crystal at an input side of the selective reduction type catalyst.SOLUTION: This invention relates to an exhaust emission control device provided with a selective reduction type catalyst 4 capable of selectively reacting NOx with ammonia even under a presence of oxygen, exhaust gas 1 added with urea water as a reductant at more upstream side than the selective reduction type catalyst 4 is reversed with respect to the selective reduction type catalyst 4 and fed. The exhaust emission control device comprises a gas dispersion chamber 7C covering an input side end surface of the selective reduction type catalyst 4, reversing the exhaust gas 1 fed in a direction opposite to the exhaust gas flow of the selective reduction type catalyst 4 through a curved pipe part 11 and feeding it to the input side end surface of the selective reduction type catalyst 4 while being dispersed from a slant side part, and the inside part of the curved pipe part 11 in the bending direction is provided with a cylinder cowling 15 for guiding a flow of the exhaust gas 1 to the input side end surface of the selective reduction type catalyst 4 while restricting peeling of the flow of the exhaust gas 1 and rectifying the flow.

Description

  The present invention relates to an exhaust emission control device.

  2. Description of the Related Art In recent years, a selective reduction catalyst that includes a particulate filter that collects particulates in exhaust gas in the middle of an exhaust pipe, and that can selectively react NOx with ammonia even in the presence of oxygen on the downstream side of the particulate filter. It is proposed that urea water is added as a reducing agent between the selective reduction catalyst and the particulate filter to simultaneously reduce particulates and NOx.

  In this case, since the urea water is added to the selective reduction catalyst between the particulate filter and the selective reduction catalyst, the urea water added to the exhaust gas is added to ammonia and carbon dioxide. In order to secure sufficient reaction time until decomposition, it is necessary to increase the distance from the urea water addition position to the selective catalytic reduction catalyst. However, there is a sufficient distance between the particulate filter and the selective catalytic reduction catalyst. If they are spaced apart from each other, the mountability on the vehicle is significantly impaired.

  For this reason, a compact exhaust gas purification device as shown in FIG. 4 has already been proposed by the same applicant as the present invention. In the exhaust gas purification device shown here, an exhaust pipe 2 through which exhaust gas 1 from the engine flows is provided. In the middle of the process, a particulate filter 3 for collecting particulates in the exhaust gas 1 and selective reduction having the property of allowing NOx to selectively react with ammonia even in the presence of oxygen on the downstream side of the particulate filter 3. The catalyst 4 is held in parallel by the casings 5 and 6 and arranged in parallel, and the S-structured communication flow is provided between the outlet end of the particulate filter 3 and the inlet end of the selective catalytic reduction catalyst 4. The exhaust gas 1 connected through the passage 7 and exhausted from the outlet end of the particulate filter 3 is folded in the reverse direction and introduced into the inlet end of the adjacent selective catalytic reduction catalyst 4. The

  Here, the communication channel 7 surrounds the outlet side end of the particulate filter 3 and collects the exhaust gas 1 immediately after exiting from the outlet side end while changing the direction in a substantially perpendicular direction. Chamber 7A, a mixing pipe 7B for extracting the exhaust gas 1 collected in the gas collecting chamber 7A in a direction opposite to the exhaust flow direction of the particulate filter 3, and a bent pipe portion for the exhaust gas 1 guided by the mixing pipe 7B 11 so as to form an S-shaped structure with the gas dispersion chamber 7C surrounding the inlet side end so that it can be introduced while being dispersed obliquely from the inlet side end face of the selective catalytic reduction catalyst 4 through the inlet 11. An injector 8 for adding urea water into the mixing pipe 7B is provided at the center position of the inlet end of the mixing pipe 7B toward the outlet end of the mixing pipe 7B. Only and is equipped.

  In the example shown here, an oxidation catalyst 9 that oxidizes unburned fuel in the exhaust gas 1 is provided in the front stage in the casing 5 in which the particulate filter 3 is held, In addition, an ammonia reduction catalyst 10 that oxidizes surplus ammonia is provided at the rear stage in the casing 6 in which the selective catalytic reduction catalyst 4 is held.

  If such a configuration is adopted, particulates in the exhaust gas 1 are collected by the particulate filter 3, and urea water is fed from the injector 8 into the exhaust gas 1 in the middle of the mixing pipe 7 B on the downstream side. And is decomposed into ammonia and carbon dioxide, and the NOx in the exhaust gas 1 is reduced and purified well by ammonia on the selective catalytic reduction catalyst 4, so that simultaneous reduction of particulates and NOx in the exhaust gas 1 is achieved. Will be.

  At this time, the exhaust gas 1 discharged from the outlet end portion of the particulate filter 3 is folded in the reverse direction by the connecting flow path 7 and then introduced into the inlet end portion of the adjacent selective catalytic reduction catalyst 4. Therefore, a long distance from the urea water addition position to the selective catalytic reduction catalyst 4 is secured, and a sufficient reaction time is secured for ammonia to be generated from the urea water.

  In addition, the particulate filter 3 and the selective catalytic reduction catalyst 4 are arranged in parallel, and the communication flow path 7 is arranged between the particulate filter 3 and the selective catalytic reduction catalyst 4, so that the whole The configuration becomes compact, and the mountability to the vehicle is greatly improved.

  On the other hand, when the exhaust gas 1 is inverted and introduced to the selective catalytic reduction catalyst 4 in this way, when the exhaust gas 1 is inverted, the exhaust gas 1 tends to flow unevenly on the outside in the bending direction. There is a concern that the exhaust gas 1 is introduced non-uniformly with respect to the reduction catalyst 4, and the catalyst performance that should be originally exhibited cannot be sufficiently extracted.

  For this reason, in the gas dispersion chamber 7C, the inlet side of the selective catalytic reduction catalyst 4 warps in a direction away from the inlet side end surface of the selective catalytic reduction catalyst 4 and moves away from the curved pipe portion 11 in the direction of introducing the exhaust gas 1. A recess 12 is formed so as to be close to the end surface, and the flow of the exhaust gas 1 is suppressed by the recess 12, so that a relatively large amount of the exhaust gas 1 flows in an uneven manner outside the bending direction. The trend is corrected.

  In addition, a recess 13 is formed at a position immediately before the bent tube portion 11, and a portion on the inner side in the bending direction at the position immediately before the bent tube portion 11 is once swung outward by the recess 13 so that the bent portion is The curvature is made small to make the curve gentle, and the flow of the exhaust gas 1 can be bent as smoothly as possible and led to the inlet side end face of the selective catalytic reduction catalyst 4.

  As prior art document information related to this type of exhaust purification device, there is the following Patent Document 1 and the like.

JP 2009-68415 A

  However, even if the distribution of the flow of the exhaust gas 1 can be improved by the formation of the depressions 12 and 13, the pressure difference of the exhaust gas 1 cannot be equalized. 4, the flow is separated inside the bending direction of the exhaust gas 1, which is reversed in the opposite direction to the exhaust flow direction, and a pressure drop occurs, and the pressure drop portion x includes the mist content of urea water from the high pressure side. There remains a problem that the exhaust gas 1 is circulated and urea crystals are likely to precipitate.

  That is, the pressure drop portion x is not directly exposed to the flow of the high-temperature exhaust gas 1, and the flow of the exhaust gas 1 is stagnated and the relative temperature is also lowered. The mist content of urea water accompanying the exhaust gas 1 flowing from the high temperature side is easy to accumulate, and only the water is contained before the accumulated urea water is sufficiently hydrolyzed to ammonia. There is a concern that it evaporates and precipitates as urea crystals, which gradually accumulates to form a lump and then desorbs to jump into the selective catalytic reduction catalyst 4 and damage the selective catalytic reduction catalyst 4. there were.

  Therefore, a cover 14 that covers the pressure drop portion x is provided on the inlet side of the selective catalytic reduction catalyst 4 in the casing 6, and urea crystals that have precipitated in the pressure drop portion x are prevented from being detached by the cover 14. Although it is considered that the selective catalytic reduction catalyst 4 is protected, it is not a measure for preventing the precipitation of urea crystal itself, so that the selective catalytic reduction catalyst 4 can be reliably prevented from being damaged. Measures are required.

  The present invention has been made in view of the above circumstances, and an object thereof is to suppress the precipitation of urea crystals on the inlet side of the selective catalytic reduction catalyst and to further protect the selective catalytic reduction catalyst.

  The present invention includes a selective reduction catalyst that can selectively react NOx with ammonia even in the presence of oxygen, and the exhaust gas to which urea water is added as a reducing agent upstream of the selective reduction catalyst is used as the selective reduction catalyst. An exhaust gas purification apparatus that is inverted with respect to a catalyst and introduces exhaust gas that encloses an inlet side end face of the selective catalytic reduction catalyst and that is led in a direction opposite to an exhaust flow direction of the selective catalytic reduction catalyst. A gas dispersion chamber that is reversed and introduced from the oblique side to the inlet side end face of the selective catalytic reduction catalyst through a curved pipe portion, and the flow of exhaust gas is separated inside the curved pipe portion in the bending direction. An air guide plate is provided that leads to the inlet side end face of the selective catalytic reduction catalyst while suppressing and rectifying.

  Thus, in this case, the exhaust gas to which urea water is added as a reducing agent upstream from the selective catalytic reduction catalyst is reversed through the curved pipe portion and introduced into the inlet side end face of the selective catalytic reduction catalyst. Then, the flow of the exhaust gas is rectified by the baffle plate on the inner side in the bending direction of the bent pipe portion so as not to cause separation, and is guided to the inlet side end surface of the selective catalytic reduction catalyst, and the pressure is applied to the inner side in the bending direction of the exhaust gas. Since the descending portion is difficult to occur, the phenomenon that the exhaust gas containing the mist content of urea water circulates from the high pressure side to the pressure dropping portion and urea crystals are precipitated on the entrance side of the selective catalytic reduction catalyst is remarkably suppressed. Become.

  Further, in the present invention, the curved pipe portion of the gas dispersion chamber is formed in a cross-sectional shape having a straight portion on the inner side in the bending direction of the curved pipe portion, and the base end portion of the wind guide plate is attached along the straight portion. Preferably, the air guide plate can be easily attached and the flow of exhaust gas along the inside of the bent pipe portion in the bending direction can be smoothly guided to the air guide plate. Become.

  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, the selective catalytic reduction catalyst is obtained by inverting the exhaust gas to which urea water is added as a reducing agent upstream of the selective catalytic reduction catalyst through a curved pipe portion. When the gas is introduced to the inlet side end surface of the exhaust gas, it is possible to make it difficult for a pressure drop portion on the inner side of the exhaust gas to be bent, and the exhaust gas containing the mist content of urea water circulates from the high pressure side to the pressure drop portion and selectively reduces Since the phenomenon of urea crystals precipitating on the entrance side of the type catalyst can be remarkably suppressed, it is possible to greatly reduce the situation in which the urea crystals grow in a lump and then detach and jump into the selective catalytic reduction catalyst. Further reliable protection of the selective catalytic reduction catalyst can be achieved.

  (II) According to the invention described in claim 2 of the present invention, the curved pipe part of the gas dispersion chamber is formed in a cross-sectional shape having a straight part on the inside in the bending direction of the curved pipe part, and along the straight part. Since the base end portion of the air guide plate is attached, the air guide plate can be easily attached, and the flow of exhaust gas along the bending direction inside of the curved pipe portion is smoothly applied to the air guide plate. You can also go along.

It is the schematic which notched one part which shows an example of the form which implements this invention. It is a perspective view which expands and shows the attachment state of the baffle plate of FIG. It is an arrow view of the III-III direction of FIG. It is the schematic which notched a part which shows a prior art example.

  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 this embodiment, a gas dispersion that forms a downstream portion of a communication flow path 7 is related to an exhaust gas purification device configured substantially the same as that of FIG. The chamber 7C encloses the entrance-side end face of the selective catalytic reduction catalyst 4 and led in the direction opposite to the exhaust flow direction of the selective catalytic reduction catalyst 4 (right direction in FIG. 1) (left direction in FIG. 1). The exhaust gas 1 is inverted through the curved pipe portion 11 and is introduced while being dispersed from the oblique side to the inlet side end face of the selective catalytic reduction catalyst 4. Is provided with an air guide plate 15 that leads to the inlet side end face of the selective catalytic reduction catalyst 4 while suppressing flow separation of the exhaust gas 1 and rectifying.

  The air guide plate 15 has a base end portion that is in a direction substantially perpendicular to the axial center direction of the selective catalytic reduction catalyst 4 in the vicinity of the middle of the folding at the bent tube portion 11, and a straight portion on the inner side in the bending direction. 16 and is bent and extended toward the entrance end surface of the selective catalytic reduction catalyst 4 so as to wrap around the inside in the bending direction of the curved pipe portion 11 to the outside, and the bending state of the curved pipe portion 11 is extended. By making it gentler than the inside in the bending direction, the flow of the exhaust gas 1 can be guided in a laminar flow without being separated.

  Here, as shown in FIG. 2, the curved pipe portion 11 of the gas dispersion chamber 7 </ b> C is formed in a substantially triangular cross-sectional shape having a straight portion 16 inside the curved pipe portion 11 in the bending direction. A base end portion of the air guide plate 15 is attached along the portion 16 by welding or the like. Note that the substantially triangular cross-sectional shape of the curved pipe portion 11 gradually becomes a circular cross-sectional shape as it moves from the curved pipe portion 11 to a portion enclosing the inlet side end face of the selective catalytic reduction catalyst 4. And the diameter is expanded to match the outer shape of the casing 6 of the selective catalytic reduction catalyst 4 (see FIG. 3), and the wind guide is adapted to the expansion of the flow path inside the gas dispersion chamber 7C. The width of the plate 15 expands in a fan shape as it goes toward the tip.

  Thus, in this case, the exhaust gas 1 to which urea water is added as a reducing agent upstream of the selective catalytic reduction catalyst 4 is reversed through the curved pipe portion 11 to enter the selective catalytic reduction catalyst 4. When introduced into the side end face, the flow of the exhaust gas 1 is rectified by the baffle plate 15 located on the inner side in the bending direction of the bent pipe portion 11 so as not to cause separation, and is guided to the inlet side end face of the selective catalytic reduction catalyst 4, Since the pressure drop portion (see FIG. 4) is less likely to occur inside the bending direction of the exhaust gas 1, the exhaust gas 1 containing the mist content of urea water enters the pressure drop portion from the high pressure side and the selective reduction catalyst 4. The phenomenon of urea crystals precipitating on the entry side is significantly suppressed.

  Accordingly, when the exhaust gas 1 to which urea water is added as a reducing agent upstream from the selective catalytic reduction catalyst 4 is inverted through the curved pipe portion 11 and introduced into the inlet side end face of the selective catalytic reduction catalyst 4, the exhaust gas. It is possible to make it difficult to generate a pressure drop portion on the inside of the bending direction of 1, and the exhaust gas 1 containing the mist content of urea water circulates from the high pressure side to the pressure drop portion, and urea crystals enter the selective reduction catalyst 4 on the entry side. Can be remarkably suppressed, so that it is possible to greatly reduce the situation where urea crystals grow into a lump and then desorb and jump into the selective catalytic reduction catalyst 4. Reliable protection can be achieved.

  Further, the curved pipe portion 11 of the gas dispersion chamber 7C is formed in a substantially triangular cross-sectional shape having a straight portion 16 on the inner side in the bending direction of the bent pipe portion 11, and the air guide plate 15 is formed along the straight portion 16. Since the base end portion is attached, the air guide plate 15 can be easily attached, and the flow of the exhaust gas 1 along the inside of the bent tube portion 11 in the bending direction smoothly follows the air guide plate 15. It can also be made.

  The exhaust emission control device of the present invention is not limited to the above-described embodiment. In the drawing, the exhaust purification device is applied to the inlet side of the selective catalytic reduction catalyst when the particulate filter and the selective catalytic reduction catalyst are arranged in parallel. However, the combined use with the particulate filter is optional, the selective reduction catalyst may be used alone or in combination with another catalyst, and the curved pipe portion of the gas dispersion chamber Is formed in a cross-sectional shape having a straight portion on the inner side in the bending direction of the bent pipe portion, it is not always necessary to have a substantially triangular shape, and various other modifications can be made without departing from the scope of the present invention. Of course.

DESCRIPTION OF SYMBOLS 1 Exhaust gas 4 Selective reduction type catalyst 7C Gas dispersion chamber 11 Curved pipe part 15 Air guide plate 16 Straight part

Claims (2)

  A selective reduction catalyst that can selectively react NOx with ammonia even in the presence of oxygen is provided, and the exhaust gas to which urea water is added as a reducing agent upstream of the selective reduction catalyst is inverted with respect to the selective reduction catalyst. An exhaust gas purification apparatus adapted to introduce an exhaust gas that encloses the inlet side end face of the selective catalytic reduction catalyst and guides the exhaust gas that is directed in the direction opposite to the exhaust flow direction of the selective catalytic reduction catalyst to a curved pipe portion. And a gas dispersion chamber that is introduced while being dispersed obliquely with respect to the inlet side end face of the selective catalytic reduction catalyst, and rectifies by suppressing separation of the exhaust gas flow inside the bending pipe portion in the bending direction. An exhaust gas purification apparatus, characterized in that an air guide plate is provided for guiding the selective reduction catalyst to the inlet side end face.   The bent portion of the gas dispersion chamber is formed in a cross-sectional shape having a straight portion on the inner side in the bending direction of the bent tube portion, and a base end portion of a wind guide plate is attached along the straight portion. Item 2. An exhaust emission control device according to Item 1.

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