JP2013104396A - Urea water mixing structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a urea water mixing structure which enables conversion to ammonia from urea water to be more efficiently performed than ever.SOLUTION: The urea water mixing structure includes: a selective reduction catalyst 4 which makes ammonia react with NOx contained in exhaust gas 1; an injector 8 (urea water adding means) which adds the urea water into the exhaust gas 1 on an upstream side with respect to the selective reduction catalyst 4; and a mixing pipe 7B which connects portions from the injector 8 to the selective reduction catalyst 4. In the urea water mixing structure, injector 8 makes the urea water added to the exhaust gas 1 flowing through the mixing pipe 7B, and the urea water is mixed therewith. A spiral protrusion 16 is formed along a spiral orbit coaxial with the central axis of the mixing pipe 7B on the inner peripheral surface of the mixing pipe 7B, and a swirl flow of the exhaust gas 1 can be formed in the mixing pipe 7B.

Description

  The present invention relates to a urea water mixing structure.

  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, the same applicant as the present invention has already proposed a compact exhaust emission control device as shown in FIG. 3 (see Patent Document 1 below). In the exhaust emission control device shown in FIG. In the middle of the exhaust pipe 2 through which the exhaust gas 1 circulates, a particulate filter 3 that collects particulates in the exhaust gas 1, and NOx is selectively exchanged with ammonia on the downstream side of the particulate filter 3 even in the presence of oxygen. The selective catalytic reduction catalyst 4 having a property capable of reacting is held in parallel by the casings 5 and 6, and the outlet side end of the particulate filter 3 and the inlet side end of the selective catalytic reduction catalyst 4 are arranged. Are connected by an S-shaped connecting flow path 7, and the exhaust gas 1 discharged from the outlet end of the particulate filter 3 is folded back in the opposite direction to the inlet end of the adjacent selective catalytic reduction catalyst 4. To be introduced.

  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.

  As disclosed in Patent Document 1 below, the location where the urea water is added by the injector 8 is provided at the end of the inlet side of the cylindrical mixing pipe 7B as shown in detail in FIGS. A mixer structure 15 is adopted in which the exhaust gas 1 from the gas collecting chamber 7A is introduced into the opening 11 from the tangential direction by the guide fins 12, 13, and 14, thereby giving a swirl flow (swirl) to the exhaust gas 1. The urea water is added from the injector 8 to the center of the swirling flow, thereby improving the mixing property of the urea water with respect to the exhaust gas 1 and promoting the conversion to ammonia.

JP 2008-196328 A

  However, the exhaust gas 1 generated at the inlet end of the mixing pipe 7B is simply introduced into the opening 11 at the inlet end of the mixing pipe 7B from the tangential direction by the guide fins 12, 13, and 14. It is difficult to effectively maintain the momentum of the swirling flow up to the exit end, and the momentum of the swirling flow declines before reaching the exit end of the mixing pipe 7B. When the amount of urea water added is increased in order to obtain the above, there is a concern that it is impossible to efficiently convert all of the added urea water into ammonia.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a urea water mixing structure capable of efficiently converting urea water into ammonia as compared with the prior art.

  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 And a selective pipe for connecting to the selective catalytic reduction catalyst, and urea water mixing structure in which urea water is added to the exhaust gas flowing through the mixing pipe by the urea water addition means and mixed. A spiral projection is formed on the inner peripheral surface of the mixing pipe along a spiral trajectory concentric with the central axis of the mixing pipe, and a swirl flow of exhaust gas can be formed in the mixing pipe. It is a feature.

  Thus, when the exhaust gas flows in the mixing pipe, the flow is guided in the direction along the spiral trajectory by the spiral protrusion in the mixing pipe. And the swirling flow continues to be formed until it reaches the outlet end of the mixing pipe, so that the swirling flow of the exhaust gas is sustained vigorously over the entire length of the mixing pipe, The mixing ability of the urea water added from the adding means is remarkably improved, and the flow of the exhaust gas becomes a flow along the spiral orbit, thereby increasing the moving distance of the urea water and ensuring a long reaction time. Conversion to ammonia is performed more efficiently than before.

  In the present invention, the guide fin is formed so that an opening is formed at an appropriate position in the circumferential direction of the inlet end of the mixing pipe and exhaust gas is introduced into the opening from the tangential direction of the inlet end. And the urea water adding means is disposed at the center of the inlet end of the mixing pipe so that urea water can be added into the swirling flow of exhaust gas by the mixer structure. It is preferable to dispose toward the end side.

  In this way, a swirling flow is immediately formed by introducing exhaust gas from the tangential direction to the opening at the inlet end of the mixing pipe by the guide fins, and the momentum of the swirling flow is more effective by the spiral protrusion. Therefore, when urea water is added from the center position of the inlet end of the mixing pipe through the urea water addition means, the urea water is well dispersed in the swirling flow of the exhaust gas, and urea is added. The water mixing property is further improved, and the conversion of urea water to ammonia is further promoted.

  According to the urea water mixing structure 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 swirl flow can be formed by guiding the flow of the exhaust gas in the direction along the spiral orbit by the spiral protrusion in the mixing pipe. Since the momentum of the swirling flow can be maintained over the entire length of the mixing pipe, the urea water added from the urea water addition means can be well dispersed to greatly improve the mixing with the exhaust gas and the exhaust gas. The reaction time can be secured long by increasing the moving distance of the urea water by making the gas flow along the spiral trajectory, whereby the urea water can be converted into ammonia more efficiently than before.

  (II) According to the invention described in claim 2 of the present invention, the swirl flow of the exhaust gas is formed immediately after the introduction to the inlet side end of the mixing pipe, and the momentum of the swirl flow is maintained by the spiral protrusion. The urea water can be satisfactorily dispersed in the swirling flow of the exhaust gas by adding the urea water from the center position of the inlet side end of the mixing pipe via the urea water addition means. The mixing property can be further improved, and the conversion of urea water to ammonia can be further promoted.

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 principal part of FIG. It is the schematic which notched a part which shows a prior art example. 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.

  FIGS. 1 and 2 show an example of an embodiment for carrying out the present invention. In this embodiment, urea water is applied to an exhaust gas purification apparatus configured substantially the same as that shown in FIGS. As a mixing structure, the mixing pipe 7B of the S-shaped connecting flow path 7 connecting the outlet side end of the particulate filter 3 and the inlet side end of the selective catalytic reduction catalyst 4 is mixed on the inner peripheral surface of the mixing pipe 7B. A spiral protrusion 16 is formed along a spiral trajectory concentric with the central axis of the pipe 7B (in the drawing, the spiral protrusion 16 is formed as an inverted shape by denting the outer peripheral surface side of the mixing pipe 7B into a groove shape. The swirl flow of the exhaust gas 1 can be formed in the mixing pipe 7B.

  Here, as described in detail with reference to FIGS. 3 to 5 above, an injector 8 for adding urea water into the mixing pipe 7B (addition of urea water) is provided at the central position of the inlet side end of the mixing pipe 7B. Means) is provided toward the outlet end side of the mixing pipe 7B, and the opening 11 at the inlet end of the cylindrical mixing pipe 7B is provided at a location where urea water is added by the injector 8. On the other hand, the mixer structure 15 is adopted in which the exhaust gas 1 from the gas collecting chamber 7A is introduced from the tangential direction by the guide fins 12, 13, and 14, thereby giving the swirl flow (swirl) to the exhaust gas 1.

  Thus, if the urea water mixing structure is configured in this way, when the exhaust gas 1 flows in the mixing pipe 7B, the flow is guided in the direction along the spiral trajectory by the spiral protrusion 16 in the mixing pipe 7B. As a result, a swirling flow of the exhaust gas 1 is formed in the mixing pipe 7B, and this swirling flow continues to be formed until reaching the outlet end of the mixing pipe 7B. Therefore, the exhaust gas 1 extends over the entire length of the mixing pipe 7B. The swirl flow of the exhaust gas 1 is maintained vigorously, the mixing ability of the urea water added from the injector 8 to the exhaust gas 1 is remarkably improved, and the flow of the exhaust gas 1 becomes a flow along the spiral trajectory. The moving distance is increased, the reaction time is ensured longer, and the conversion of urea water to ammonia is performed more efficiently than before.

  Further, particularly in this embodiment, the opening 11 is formed at an appropriate position in the circumferential direction of the inlet end of the mixing pipe 7B, and the exhaust gas 1 is tangential to the inlet 11 with respect to the opening 11. Guide fins 12, 13, and 14 are arranged so as to be introduced from the mixer to constitute a mixer structure 15, and the injector 8 is mixed so that urea water can be added into the swirling flow of the exhaust gas 1 by the mixer structure 15. It is preferable to dispose the pipe 7B toward the outlet side end at the center position of the inlet side end.

  In this way, the exhaust gas 1 is introduced from the tangential direction by the guide fins 12, 13, 14 to the opening 11 at the inlet side end of the mixing pipe 7 </ b> B, whereby a swirling flow is immediately formed. Therefore, when urea water is added through the injector 8 from the center position of the inlet end of the mixing pipe 7B, the urea water is swirled by the exhaust gas 1. It is well dispersed in the flow, further improving the mixing property of the urea water, and further promoting the conversion of the urea water to ammonia.

  Therefore, according to the above embodiment, the spiral projection 16 in the mixing pipe 7B can guide the flow of the exhaust gas 1 in the direction along the spiral trajectory to form the swirl flow, and the momentum of the swirl flow can be increased. Since the mixing pipe 7B can be maintained over the entire length, the urea water added from the injector 8 can be well dispersed to greatly improve the mixing with the exhaust gas 1, and the flow of the exhaust gas 1 can be improved. By increasing the travel distance of urea water as a flow along the spiral trajectory, it is possible to ensure a long reaction time, thereby making it possible to convert urea water to ammonia more efficiently than before.

  Moreover, the swirl flow of the exhaust gas 1 can be formed immediately after the introduction to the inlet end of the mixing pipe 7B, and the momentum of the swirl flow can be maintained by the spiral protrusion 16, and the inlet pipe end of the mixing pipe 7B can be maintained. Since urea water can be favorably dispersed in the swirling flow of the exhaust gas 1 by adding urea water through the injector 8 from the center position, the mixing property of urea water can be further improved. The conversion of urea water to ammonia can be further promoted.

  The urea water mixing structure of the present invention is not limited to the above-described embodiment. In the figure, the urea water mixing structure is arranged on the inlet side of the selective catalytic reduction catalyst when the particulate filter and the selective catalytic reduction catalyst are arranged in parallel. Although the case where it applies is illustrated, if the structure which connected between the urea water addition means and the selective reduction type catalyst with the mixing pipe is adopted, the exhaust purification device of various layouts different from the illustration Of course, various changes can be made without departing from the gist of the present invention.

1 Exhaust gas 4 Selective reduction catalyst 7B Mixing pipe 8 Injector (urea water addition means)
DESCRIPTION OF SYMBOLS 11 Opening part 12 Guide fin 13 Guide fin 14 Guide fin 15 Mixer structure 16 Spiral protrusion

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 urea pipe mixing structure comprising: a mixing pipe that connects between the catalyst and the catalyst; and urea water added to the exhaust gas flowing through the mixing pipe by the urea water adding means to be mixed. The urea is characterized in that a spiral projection is formed on the inner peripheral surface of the mixing pipe along a spiral trajectory concentric with the central axis of the mixing pipe, and a swirling flow of exhaust gas can be formed in the mixing pipe. Water mixing structure.   A mixer structure in which an opening is formed at an appropriate position in the circumferential direction of the inlet end of the mixing pipe, and guide fins are disposed in the opening so as to introduce exhaust gas from the tangential direction of the inlet end. And the urea water adding means is arranged at the center position of the inlet end of the mixing pipe toward the outlet end so that the urea water can be added into the swirling flow of the exhaust gas by the mixer structure. The urea water mixing structure according to claim 1, wherein the urea water mixing structure is provided.

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