JP6285255B2 - Exhaust purification device - Google Patents

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 in the exhaust gas is heated 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 purification device as shown in FIG. 3 has already been proposed by the same applicant as the present invention. In the exhaust 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. A 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 of the particulate filter 3, and a direction in which the exhaust gas 1 guided by the mixing pipe 7B is substantially perpendicular The S-shaped structure is formed by the gas dispersion chamber 7C surrounding the inlet side end so that the dispersed exhaust gas 1 can be introduced into the inlet side end of the selective catalytic reduction catalyst 4 while being dispersed. The injector 8 for adding urea water into the mixing pipe 7B is provided at the central position of the inlet side end of the mixing pipe 7B. It is equipped toward the side end portion side.

  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. Is added to the catalyst and thermally decomposed into ammonia and carbon dioxide, and the NOx in the exhaust gas 1 is reduced and purified well by the ammonia on the selective catalytic reduction catalyst 4, so that simultaneous reduction of particulates and NOx in the exhaust gas 1 is achieved. It will be illustrated.

  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.

  Then, at the location where urea water is added by the injector 8, the exhaust gas from the gas collecting chamber 7A with respect to the opening 11 at the inlet end of the cylindrical mixing pipe 7B as shown in detail in FIGS. 1 is introduced in a tangential direction by guide fins 12, 13, and 14, thereby adopting a mixer structure 15 that gives a swirling flow (swirl) to the exhaust gas 1. At the center of this swirling flow, urea water is injected from the injector 8. By performing the addition, the mixing property of the urea water with respect to the exhaust gas 1 is enhanced, and the conversion to ammonia is promoted.

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

JP 2008-196328 A

  However, when the swirl flow is given to the exhaust gas 1 and urea water is added as described above, the exhaust gas 1 flowing into the gas dispersion chamber 7C while swirling from the mixing pipe 7B is shown in FIG. Thus, it is easy to form a biased flow along the inner wall w on one side of the gas dispersion chamber 7C by virtue of the swirling flow, and the exhaust gas 1 is introduced non-uniformly to the selective catalytic reduction catalyst 4, There was a possibility that the catalyst performance to be exhibited could not be drawn out sufficiently.

  More specifically, when the selective reduction catalyst 4 and the mixing pipe 7B are arranged as shown in FIG. 4, if the swirling flow of the exhaust gas 1 is formed counterclockwise, the gas in FIG. A biased flow along the right inner wall w in the dispersion chamber 7C is likely to be formed, and as a result of the exhaust gas 1 being introduced together with the ammonia gas only on the right side of the selective catalytic reduction catalyst 4, all of the selective catalytic reduction catalyst 4 is obtained. There is a concern that the volume is not effectively used, and that the reduction and purification reaction of NOx proceeds with only a part of the selective catalytic reduction catalyst 4.

  If the distance from the gas dispersion chamber 7C indicated by the symbol L in FIG. 3 to the inlet side end face of the selective catalytic reduction catalyst 4 is sufficiently large, the above-described flow deviation of the exhaust gas 1 can be improved. However, there is a situation that this distance L is to be kept as small as possible because it may result in the end-to-end fall that causes deterioration of the mountability.

  The present invention has been made in view of the above circumstances, and an object thereof is to make it possible to introduce a flow distribution of exhaust gas into a selective reduction catalyst with a uniform distribution.

The present invention relates to a selective reduction catalyst for reacting NOx contained in exhaust gas with ammonia, urea water addition means for adding urea water to the exhaust gas upstream from the selective reduction catalyst, and urea water addition means A mixing pipe that is interposed between the catalyst and the selective reduction catalyst and guides the exhaust gas, and the exhaust gas is introduced into the mixing pipe from the tangential direction to the inlet side end of the mixing pipe, and the exhaust gas is swirled into the mixing pipe. The exhaust gas guided by the mixing pipe and the mixing pipe can be dispersed in a direction perpendicular to the mixer structure, and the dispersed exhaust gas can be introduced into the inlet side end portion of the selective catalytic reduction catalyst. An exhaust gas purifying device comprising a gas dispersion chamber surrounding the inlet side end portion, wherein urea water is added to and mixed with the swirling flow of the exhaust gas by the urea water adding means. A baffle plate that guides exhaust gas flowing in while turning from the mixing pipe toward the center of the inlet side end face of the selective catalytic reduction catalyst at a position where the mixing pipe is opened in the gas dispersion chamber. And the air guide plate is provided on the inner wall on the side where a biased flow along the inner wall in the gas dispersion chamber is likely to be formed, on the side where the biased flow in the outlet opening of the mixing pipe is likely to be formed. A running portion is formed in a straight line in a tangential direction from the edge toward the center of the entrance side end surface of the selective catalytic reduction catalyst, and the running portion reaches the position facing the entrance side end surface of the selective catalytic reduction catalyst. A retraction portion that is bent toward the inner wall on the side where a biased flow is easily formed is formed .

  In this way, the exhaust gas is introduced from the tangential direction to the inlet end of the mixing pipe by the mixer structure, thereby forming a swirling flow of the exhaust gas in the mixing pipe. When urea water is added to the stream by means of urea water addition, the urea water is effectively mixed to produce ammonia, and the exhaust gas containing ammonia advances through the mixing pipe while turning to reach the gas dispersion chamber. Here, it is dispersed while being redirected in a substantially right-angle direction and introduced into the inlet end of the selective catalytic reduction catalyst, and NOx in the exhaust gas is reduced and purified well by ammonia by the selective catalytic reduction catalyst. However, at this time, the exhaust gas flowing into the gas dispersion chamber while turning from the mixing pipe is directed toward the center of the inlet side end face of the selective catalytic reduction catalyst by the air guide plate. Therefore, the tendency of the exhaust gas to flow unevenly along the inner wall on one side of the gas dispersion chamber is corrected, and the flow distribution of the exhaust gas introduced to the inlet side end face of the selective catalytic reduction catalyst is made uniform. Will be.

Further, in the present invention, the particulate filter is arranged in parallel so that the entrance ends of the selective reduction catalyst are directed in the same direction, and the particulate filter is discharged from the exit end of the particulate filter. Preferably, the exhaust gas is applied to an exhaust gas purification apparatus configured to introduce exhaust gas to the inlet side end portion of the mixing pipe through the mixer structure and fold back in an opposite direction to the exhaust flow of the particulate filter. It is possible to make the whole compact in a compact manner while keeping the distance to the entry side end face of the selective catalytic reduction catalyst small.

  According to the exhaust purification apparatus of the present invention described above, the exhaust gas flowing into the gas dispersion chamber while turning from the mixing pipe is guided toward the central portion of the inlet side end face of the selective catalytic reduction catalyst by the air guide plate. Therefore, the flow distribution of the exhaust gas can be introduced to the inlet side end face of the selective catalytic reduction catalyst, and the catalyst performance that should be originally exhibited can be achieved by efficiently using the entire volume of the aftertreatment device. Various excellent effects can be obtained, such as being able to draw out sufficiently, and reducing the distance from the gas dispersion chamber to the inlet side end face of the selective catalytic reduction catalyst, and making the entire structure compact.

It is the top view which notched a part which shows an example of the form which implements this invention. It is sectional drawing of the II-II arrow of FIG. It is the top view which notched a part which shows a prior art example. It is sectional drawing of the IV-IV arrow of FIG. It is sectional drawing which shows the detail of the principal part of FIG. It is a perspective view which expands and shows the principal part of FIG.

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

  FIG. 1 and FIG. 2 show an example of an embodiment for carrying out the present invention. In this embodiment, the exhaust purification apparatus constructed in substantially the same manner as that of FIG. 3 and FIG. Is provided with a wind guide plate 16 that guides the exhaust gas 1 flowing in from the mixing pipe 7B toward the center of the inlet side end face of the selective catalytic reduction catalyst 4 at a position where the mixing pipe 7B is opened. However, it is characterized.

  That is, in the example shown in FIG. 2, the gas dispersion chamber 7 </ b> C has a teardrop shape (shown in an inverted teardrop shape in FIG. 2) that widens from the mixing pipe 7 </ b> B side to the selective reduction catalyst 4 side. Since the swirl flow of the exhaust gas 1 is formed counterclockwise when viewed from the front, the flow is biased along the right inner wall w in the gas dispersion chamber 7C in FIG. (See FIG. 4) tends to be formed easily.

  Therefore, on the inner wall w on the right side of the gas dispersion chamber 7C, the baffle plate is tangentially directed from the right edge of the outlet opening 17 of the mixing pipe 7B toward the center of the inlet side end face of the selective catalytic reduction catalyst 4. The sixteen run-up portions 16a are formed in a straight line shape, and are bent toward the inner wall w on the right side when they reach a position facing the entry-side end surface of the selective catalytic reduction catalyst 4, thereby forming a retracting portion 16b.

  What is important in forming such a baffle plate 16 is to prevent the baffle plate 16 from reaching the position facing the entry side end face of the selective catalytic reduction catalyst 4 as much as possible. This is because if the air guide plate 16 protrudes to a position facing the entrance end surface of the selective catalytic reduction catalyst 4, the exhaust gas 1 wraps around the air guide plate 16 and enters the selective catalytic reduction catalyst 4. This is because there is a concern that the air flow must be directed toward the end face, and the flow distribution of the exhaust gas 1 may have another tendency to be biased.

  In addition, as illustrated in FIG. 2, the run-up portion 16 a of the air guide plate 16 is formed so that induction can be started from the outlet side opening 17 of the mixing pipe 7 </ b> B immediately after the exhaust gas 1 comes out. Preferably, the retracting portion 16b of the air guide plate 16 is formed at a gentle angle as much as possible with respect to the running portion 16a so as not to cause turbulence of the exhaust gas 1 due to a sudden shape change. Is preferred.

  Thus, if the exhaust gas purification device is configured in this way, the exhaust gas 1 is introduced from the tangential direction to the inlet side end portion of the mixing pipe 7B by the mixer structure 15, whereby the exhaust gas 1 is introduced into the mixing pipe 7B. Since a swirling flow is formed, when urea water is added to the swirling flow by the injector 8, the urea water is effectively mixed to generate ammonia, and the exhaust gas 1 containing ammonia swirls while mixing the mixing pipe. The gas travels through 7B to reach the gas dispersion chamber 7C, where it is dispersed while being redirected in a substantially perpendicular direction, introduced into the inlet end of the selective catalytic reduction catalyst 4, and exhausted by the selective catalytic reduction catalyst 4. The NOx in the gas 1 is reduced and purified well by ammonia. At this time, the exhaust gas 1 flowing into the gas dispersion chamber 7C while turning from the mixing pipe 7B Since the air guide plate 16 is guided toward the center of the inlet side end face of the selective catalytic reduction catalyst 4, the tendency of the exhaust gas 1 to flow unevenly along the inner wall w on one side of the gas dispersion chamber 7C is corrected. Thus, the flow distribution of the exhaust gas 1 introduced into the inlet side end face of the selective catalytic reduction catalyst 4 is made uniform.

  Therefore, according to the above embodiment, the exhaust gas 1 flowing into the gas dispersion chamber 7C while turning from the mixing pipe 7B is directed toward the central portion of the inlet side end face of the selective catalytic reduction catalyst 4 by the air guide plate 16. Therefore, the flow distribution of the exhaust gas 1 can be introduced to the inlet side end face of the selective catalytic reduction catalyst 4 in a uniform manner, and the entire volume of the selective catalytic reduction catalyst 4 can be used efficiently. The catalyst performance to be achieved can be sufficiently drawn, and the distance L from the gas dispersion chamber 7C to the inlet side end face of the selective catalytic reduction catalyst 4 can be kept small, and the overall structure can be made compact.

  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, if a configuration is adopted in which a mixing pipe is connected between the urea water addition means and the selective reduction catalyst, the present invention can be applied to an exhaust purification device having various layouts different from those shown in the figure. Of course, various modifications can be made without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Exhaust gas 3 Particulate filter 4 Selective reduction type catalyst 7B Mixing pipe 7C Gas dispersion chamber 8 Injector (urea water addition means)
15 Mixer structure 16 Air guide plate

Claims (2)

A selective reduction catalyst for reacting NOx contained in exhaust gas with ammonia, urea water addition means for adding urea water to the exhaust gas upstream from the selective reduction catalyst, and selective reduction from the urea water addition means A mixing pipe that is interposed between the catalyst and the exhaust pipe and guides the exhaust gas, and an exhaust gas is introduced from the tangential direction to the inlet side end of the mixing pipe to form a swirling flow of the exhaust gas in the mixing pipe. Mixer structure and exhaust gas guided by the mixing pipe are dispersed while being redirected in a right angle direction, and the dispersed exhaust gas can be introduced into the inlet side end of the selective catalytic reduction catalyst. An exhaust gas purifying device comprising a gas dispersion chamber surrounding a portion, wherein urea water is added to the swirling flow of the exhaust gas by the urea water addition means and mixed.
An air guide plate is provided at the position where the mixing pipe is opened in the gas dispersion chamber to guide the exhaust gas flowing in while turning from the mixing pipe toward the center of the inlet side end face of the selective catalytic reduction catalyst. ,
The air guide plate is formed on the inner wall on the side where a biased flow along the inner wall in the gas dispersion chamber is easily formed, from the edge on the side where the biased flow is easily formed in the outlet side opening of the mixing pipe. A running portion is formed linearly in a tangential direction toward the center of the entrance-side end surface of the selective catalytic reduction catalyst, and the biased portion approaches the position where the running portion faces the entrance-side end surface of the selective catalytic reduction catalyst. An exhaust emission control device, characterized in that a retraction portion that is bent toward the inner wall on the side where a flow is easily formed is formed . A particulate filter is arranged in parallel so that the inlet ends of the selective catalytic reduction catalyst are directed in the same direction, and the exhaust gas discharged from the outlet end of the particulate filter is mixed with the mixer structure. 2. The exhaust emission control device according to claim 1 , wherein the exhaust gas purification device is configured to be introduced to an inlet side end portion of the mixing pipe and to be turned back in a direction opposite to the exhaust flow of the particulate filter.

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