JP2015048715A - Urea water mixing structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a more efficient conversion from urea water into ammonia than that of the prior art.SOLUTION: There is provided urea water mixing structure which includes: a selective reduction type catalyst 4 causing NOx contained in exhaust gas 1 to react with ammonia; an injector 8 (urea water adding means) placed upstream of the catalyst 4 and adding urea water into the exhaust gas 1; a mixing pipe 7B connecting between the injector 8 and the selective reduction type catalyst 4; and mixer structure 15 for feeding the exhaust gas 1 from its tangential direction against an input end part of the mixing pipe 7B to form a swirl flow of the exhaust gas 1 within the mixing pipe 7B, and in which the injector 8 adds the urea water to the swirl flow of exhaust gas and mixes them with each other. In the urea water mixing structure, a spiral rail 16 is installed in the inner circumferential surface of the mixing pipe 7B in such a way that the spiral rail 16 forms a helical railway concentric with a central axis of the mixing pipe 7B, and the helical railway of the spiral rail 16 corresponds to the swirl flow of the exhaust gas 1.

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 an exhaust gas 1 guided by the mixing pipe 7B in a substantially perpendicular direction 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, although the swirl flow is imparted to the exhaust gas 1 in this way to successfully improve the urea water mixing property with the exhaust gas 1, no matter how much the urea water mixing property is improved, it is expected. The present inventors have confirmed that the conversion from urea water to ammonia does not proceed efficiently, and in order to promote the conversion from urea water to ammonia more efficiently, the vaporization of urea water must be actively carried out. It was concluded that it was necessary to promote the substantial chemical reaction of ammonia production, but the actual solution has not yet been devised.

  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 A mixing pipe that connects between the gas and the selective reduction catalyst, and a mixer structure that introduces exhaust gas 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; A urea water mixing structure in which urea water is added and mixed with the swirling flow of exhaust gas by the mixer structure by the urea water adding means, and the mixing pipe has a center on the inner peripheral surface of the mixing pipe. A spiral rail is laid to form a spiral track concentric with the shaft, and the spiral track of the spiral rail is configured to correspond to the swirl flow of the exhaust gas. It is characterized by that.

  Thus, with this configuration, exhaust gas is introduced from the tangential direction to the inlet end of the mixing pipe by the mixer structure, and a swirling flow is formed in the mixing pipe. When urea water is added by the urea water addition means, the mixing ability of the urea water with respect to the exhaust gas is remarkably improved, and the movement distance of the urea water is increased due to the flow of the exhaust gas along the spiral trajectory. Long time is secured.

  At this time, since the swirling flow of the exhaust gas flows along the spiral rail on the inner peripheral surface of the mixing pipe, the mist of urea water is frequently repeated on the spiral rail that is constantly exposed to the exhaust gas and is heated. By contacting, effective heat reception is achieved, whereby the vaporization of urea water is remarkably accelerated, and conversion to ammonia is performed more efficiently than before.

  That is, while the spiral rail is laid on the inner peripheral surface of the mixing pipe, the heat receiving area is increased, while it takes a sufficient amount of time along the spiral track that is significantly longer than the total length of the original mixing pipe. Since the mist of urea water repeatedly contacts the spiral rail, the heat receiving time is ensured for a long time, so that the vaporization of the urea water is remarkably promoted and the conversion to ammonia proceeds.

  In addition, since the spiral track of the spiral rail is configured to correspond to the swirling flow of the exhaust gas, the laying of the spiral rail contributes to maintaining the swirling flow of the exhaust gas, The momentum of the swirling flow of the exhaust gas formed by the mixer structure at the inlet side end of the mixing pipe is maintained so as not to decay.

  Since the swirling flow of the exhaust gas formed by the mixer structure swirls on the same spiral track only by changing the swirl speed even if the flow rate of the exhaust gas increases or decreases, the spiral track of the spiral rail becomes the exhaust gas. If it is configured to cope with the swirling flow, the increase in pressure loss due to the laying of the spiral rail can be suppressed to a slight extent.

  Further, in the present invention, an opening formed at an appropriate position in the circumferential direction of the inlet end of the mixing pipe, and exhaust gas is provided to the opening from the tangential direction of the inlet end. It is preferable to form a mixer structure with the guide fins, and in this way, the exhaust gas is introduced from the tangential direction by the guide fins to the opening at the entrance end of the mixing pipe, so that the swirl flow is effective. Will be formed.

  According to the urea water mixing structure of the present invention described above, urea water is added by the urea water adding means to the swirling flow of the exhaust gas formed in the mixing pipe by the mixer structure, and the swirling flow including the mist of the urea water is added. By flowing along the spiral rail, urea mist can be repeatedly contacted with high frequency and effectively received heat to the spiral rail that has already been exposed to the flow of exhaust gas and heated to high temperature. It is possible to achieve an excellent effect that the vaporization of water is remarkably promoted and the conversion to ammonia can be performed more efficiently than before.

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 rail 16 is laid so as to form a spiral track concentric with the central axis of the pipe 7B, and the spiral track of the spiral rail 16 corresponds to the swirl flow (swirl) of the exhaust gas 1 formed by the mixer structure 15. Is configured to do.

  Here, the spiral rail 16 can be manufactured by, for example, a stainless steel angle material having high corrosion resistance, and one surface of this type of angle material is a mounting surface along the inner peripheral surface of the mixing pipe 7B. Further, the entire surface may be formed in a spiral shape with the other surface as an upright surface and sandwiched between the half-mixed mixing pipes 7B.

  However, when the spiral rail 16 is laid on the inner peripheral surface of the mixing pipe 7B, the above-described manufacturing method is not necessarily adopted, and the spiral rail 16 is not necessarily manufactured from an angle material. Of course, it is not done.

  Further, as described in detail with reference to FIGS. 3 to 5 above, an injector 8 (urea water addition means) 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. ) Is provided toward the outlet end side of the mixing pipe 7B, and the urea water is added by the injector 8 to the opening 11 at the inlet end of the cylindrical mixing pipe 7B. On the other hand, the mixer structure 15 is employed 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 a swirl flow to the exhaust gas 1.

  Thus, if the urea water mixing structure is configured in this way, the exhaust gas 1 is introduced from the tangential direction by the guide fins 12, 13, 14 into the opening 11 at the inlet side end of the mixing pipe 7B. Since the swirl flow is effectively formed, when urea water is added to the swirl flow by the injector 8, the mixing ability of the urea water with respect to the exhaust gas 1 is remarkably improved and the flow of the exhaust gas 1 is changed to the spiral trajectory. Therefore, the moving distance of the urea water is increased and the reaction time is ensured longer.

  At this time, the swirling flow of the exhaust gas 1 flows along the spiral rail 16 on the inner peripheral surface of the mixing pipe 7B, so that the mist of urea water against the spiral rail 16 constantly exposed to the exhaust gas 1 and heated. Are repeatedly contacted with high frequency and effective heat reception is achieved. As a result, the vaporization of urea water is remarkably promoted, and the conversion to ammonia is performed more efficiently than before.

  That is, while the spiral rail 16 is laid on the inner peripheral surface of the mixing pipe 7B, the heat receiving area is increased. On the other hand, sufficient time is taken along a spiral track that is significantly longer than the entire length of the original mixing pipe 7B. Since the mist of urea water repeatedly contacts the spiral rail 16 during the flow, the heat receiving time is ensured for a long time, so that the vaporization of the urea water is remarkably promoted and the conversion to ammonia proceeds.

  Further, since the spiral trajectory of the spiral rail 16 is configured to correspond to the swirling flow of the exhaust gas 1, the laying of the spiral rail 16 contributes to maintaining the swirling flow of the exhaust gas 1. In other words, the momentum of the swirling flow of the exhaust gas 1 formed by the mixer structure 15 at the inlet side end of the mixing pipe 7B is maintained so as not to decline.

  The swirl flow of the exhaust gas 1 formed by the mixer structure 15 swirls on the same spiral track only by changing the swirl speed even if the flow rate of the exhaust gas 1 increases or decreases. If the track is configured to correspond to the swirling flow of the exhaust gas 1, an increase in pressure loss due to the laying of the spiral rail 16 can be suppressed to a slight extent.

  Therefore, according to the above embodiment, urea water is added by the injector 8 to the swirling flow of the exhaust gas 1 formed in the mixing pipe 7B by the mixer structure 15, and the swirling flow including the mist of the urea water is converted into the spiral rail 16 , It is possible to receive heat effectively by repeatedly contacting the mist of urea water with the spiral rail 16 that has already been exposed to the flow of the exhaust gas 1 and being heated to a high frequency. The vaporization of water can be remarkably promoted and the conversion to ammonia can be performed more efficiently than before.

  Here, if it explains supplementarily, even if it replaces with the spiral rail 16 in this embodiment, even if it forms a spiral projection as an inverted shape by denting the outer peripheral surface side of the mixing pipe 7B into a groove shape, Since the formation of such spiral projections also increases the heat radiation surface, it is always provided in the exhaust gas 1 by laying it on the inner peripheral surface of the mixing pipe 7B as a separate part like the spiral rail 16 of this embodiment. You can't get the same heat-receiving effect that you can expose and heat up.

  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 rail

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 connects the catalyst up to the type catalyst, and a mixer structure that introduces exhaust gas from a tangential direction to the inlet side end of the mixing pipe to form a swirling flow of exhaust gas in the mixing pipe, In the urea water mixing structure in which urea water is added and mixed with the swirling flow of exhaust gas by the mixer structure by the urea water adding means, the inner peripheral surface of the mixing pipe is concentric with the central axis of the mixing pipe The spiral rail is laid so as to form a spiral track, and the spiral track of the spiral rail is configured to correspond to the swirling flow of the exhaust gas. Characteristic urea water mixing structure.   A mixer structure comprising an opening formed at an appropriate position in the circumferential direction of the inlet end of the mixing pipe, and a guide fin provided to introduce exhaust gas into the opening from the tangential direction of the inlet end. The urea water mixing structure according to claim 1, wherein:

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