JP2011157825A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent corrosion of a mixing pipe without causing a remarkable increase in installation cost. <P>SOLUTION: This exhaust emission control device includes: a selective reduction type catalyst reacting NOx contained in exhaust gas 1 with ammonia; a urea water adding injector 8 (a urea water adding means) adding urea water into the exhaust gas 1 on the upstream side of the selective reduction type catalyst; and the cylindrical mixing pipe 7B connecting a portion between the urea water adding injector and the selective reduction type catalyst. A covering piece 16 having at least a surface portion formed of material having higher corrosion resistance against a substance generated by adding the urea water than the mixing pipe 7B is arranged in the vicinity of a position for adding the urea water in the mixing pipe 7B, thus covering the partial inner peripheral surface of the mixing pipe 7B. <P>COPYRIGHT: (C)2011,JPO&INPIT

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 considered 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 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 ammonia and carbon dioxide. In order to secure a sufficient reaction time until thermal decomposition, it is necessary to increase the distance from the urea water addition position to the selective catalytic reduction catalyst. If they are spaced apart from each other by a large distance, there is a problem that the mountability on the vehicle is significantly impaired.

  Therefore, as shown in FIG. 7, in the middle of the exhaust pipe 2 through which the exhaust gas 1 from the engine flows, a particulate filter 3 for collecting particulates in the exhaust gas 1 and a downstream side of the particulate filter 3. A selective reduction catalyst 4 having the property of selectively reacting NOx with ammonia even in the presence of oxygen is held in parallel by the casings 5 and 6, and arranged in parallel with the outlet end of the particulate filter 3. The inlet side end portion of the selective catalytic reduction catalyst 4 is connected by a communication channel 7 having an S-shaped structure, and the exhaust gas 1 discharged from the outlet side end portion of the particulate filter 3 is folded back in the reverse direction. An exhaust emission control device introduced into the inlet side end of the selective catalytic reduction catalyst 4 has been devised.

  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. In the center position of the inlet end of the mixing pipe 7B, a urea water addition injector 8 (urea water addition means) for adding urea water into the mixing pipe 7B There is equipped toward the outlet end side of the mixing pipe 7B.

  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 supplied from the urea water addition injector 8 in the middle of the mixing pipe 7B on the downstream side thereof. As a result of being added to the exhaust gas 1 and thermally decomposed into ammonia and carbon dioxide gas, the NOx in the exhaust gas 1 is reduced and purified well by ammonia on the selective catalytic reduction catalyst 4, so that the particulates and NOx in the exhaust gas 1 are reduced. Are simultaneously reduced.

  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.

  Prior art document information relating to an exhaust gas purification apparatus in which this type of particulate filter 3 and selective reduction catalyst 4 are arranged in parallel and connected by an S-shaped connecting flow path 7 is disclosed in Patent Document 1 below. Etc.

JP 2008-215286 A

  However, as disclosed in the above-mentioned Patent Document 1, an opening at the entrance end of a cylindrical mixing pipe 7B as shown in FIG. 8 is provided at a location where urea water is added by the urea water addition injector 8. The mixer structure 15 is adopted in which the exhaust gas 1 from the gas collecting chamber 7A is introduced into the section 11 from the tangential direction by the guide fins 12, 13, and 14, thereby giving the exhaust gas 1 a swirl flow. Since the urea water was added from the urea water addition injector 8 to improve the mixing ability of the urea water with respect to the exhaust gas 1, the amount of urea water added was determined in order to obtain a higher NOx purification performance than before. When increased, the urea water that cannot be vaporized forms a flow along the swirling flow of the exhaust gas 1 along the inner peripheral surface of the mixing pipe 7B, and is generated by the addition of the urea water. There was a problem that the corrosion caused by the substances to be induced was caused by rapid progress.

  The inlet end of the mixing pipe 7B is encapsulated by a downstream end of the gas collecting chamber 7A with a required space therebetween and the opening end face thereof is closed, and the downstream end of the gas collecting chamber 7A is closed. The welded part is located near the urea water addition position, but in such a welded part, the crystal grains of the material are coarsened by the heat input during welding, and it is more corrosive than the general part. When the sensitivity is high, particularly when the sensitization is occurring, the intergranular corrosion sensitivity is further increased. Therefore, the entrance end portion of the mixing pipe 7B is likely to be easily corroded.

  Although it is possible to take measures to change the entire mixing pipe 7B to a material with high corrosion resistance such as a high Cr material, even if the material is changed to such a material, the grain size and sensitivity of the welded part are increased. Corrosion susceptibility due to corrosion becomes high, and there is a concern about corrosion resistance. Moreover, since a high corrosion resistance material such as a high Cr material is expensive, changing the entire mixing pipe 7B significantly increases the equipment cost of the exhaust purification device. It will cause a surge.

  The present invention has been made in view of the above circumstances, and an object thereof is to prevent the mixing pipe from being corroded without causing a significant increase in equipment cost.

  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 An exhaust purification device having a cylindrical mixing pipe connecting between the selective reduction catalyst and the selective reduction catalyst, wherein at least a surface portion of the mixing purification pipe is located near the urea pipe addition position in the mixing pipe than the mixing pipe. A coating piece made of a material having high corrosion resistance to a substance generated by adding water is disposed to cover a part of the inner peripheral surface of the mixing pipe.

  Thus, by covering the inner peripheral surface of a part of the mixing pipe with the covering piece disposed in the vicinity of the urea water addition position, direct adhesion of urea water that cannot be completely evaporated is avoided. Therefore, a situation in which rapid progress of corrosion is induced by the substance generated by the addition of urea water does not occur in the mixing pipe.

  On the other hand, when the amount of urea water added is increased in order to improve NOx purification performance, urea water that cannot be completely evaporated can occur on the inner peripheral surface of the coated piece. Since it is made of a material that has higher corrosion resistance to substances generated by adding urea water than mixing pipes, it is difficult to corrode, and in order to fix itself, it is possible to select and weld parts that are not sprayed with urea water Because there is no need to have other welds that are highly susceptible to corrosion, there is no fear of rapid corrosion such as when urea water that cannot be vaporized flows along the inner peripheral surface of the inlet end of the mixing pipe. .

  Further, in carrying out the present invention more specifically, for example, an opening is formed at an appropriate position in the circumferential direction of the inlet end of the mixing pipe, and exhaust gas is supplied to the inlet end with respect to the opening. The mixer fin is arranged by introducing guide fins to be introduced from the tangential direction, and the urea water addition means is arranged on the inlet side 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 arrange | position toward the output side edge part side in the center position of an edge part.

  In this way, by adding urea water into the swirling flow of the exhaust gas formed by the mixer structure, the urea water can be mixed with the exhaust gas while the urea water is added to improve the NOx purification performance. When the amount is increased, urea water that cannot be vaporized easily forms a flow along the swirling flow of the exhaust gas along the inner peripheral surface of the mixing pipe, but the inner peripheral surface of the mixing pipe is covered by the covering piece. Therefore, it is possible to prevent the mixing pipe from being corroded while improving the mixing ability of the urea water with respect to the exhaust gas.

  In addition, it is preferable that at least a part of the guide fins be integrally formed on the covering piece, and in this way, when the covering piece and the guide fin are assembled as separate parts, there is no level difference between the two. In addition, it is possible to smoothly introduce exhaust gas into the mixing pipe, and it is also possible to prevent a gap from being formed between the covering piece and the guide fin, so that the urea water can be prevented from entering the gap. Therefore, crevice corrosion can be prevented.

  In order to integrally form the guide fin on the covering piece, it is only necessary to cut and raise a part from the cylindrical covering piece to make a guide fin. The opening portion is combined with the opening portion at the inlet side end portion of the mixing pipe to serve as an exhaust gas introduction port, and the whole can be easily manufactured with good yield.

  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 mixing pipe is inserted only by covering a part of the inner peripheral surface of the mixing pipe with a covering piece having at least a surface portion made of a highly corrosive material. Since the corrosion of the side end can be prevented, the equipment cost can be greatly reduced as compared with the case where the entire mixing pipe is changed to a material having high corrosion resistance such as a high Cr material.

  (II) According to the invention described in claim 2 of the present invention, the urea water is added to the swirling flow of the exhaust gas formed by the mixer structure, thereby improving the mixing property of the urea water with respect to the exhaust gas. The flow of urea water that is likely to be formed along the swirling flow of the exhaust gas can be separated from the inner peripheral surface of the mixing pipe by the covering piece to prevent corrosion of the mixing pipe.

  (III) According to the invention described in claim 3 of the present invention, when the covering piece and the guide fin are assembled as separate parts by integrally forming at least a part of the guide fin on the covering piece, Steps that occur at the boundary can be eliminated, exhaust gas can be smoothly introduced into the mixing pipe, variation in the swirling flow formed in the mixing pipe can be reduced, and coating Since it is also possible to avoid a gap between the piece and the guide fin, it is possible to prevent the urea water from entering the gap and prevent crevice corrosion.

  (IV) According to the invention described in claim 4 of the present invention, exhaust gas is formed by combining an opening at the entrance end of the mixing pipe with an open portion that is cut and raised from a cylindrical covering piece. Since it can be used as it is as an introduction port, a covering piece with guide fins can be easily manufactured with good yield.

It is the perspective view which notched a part which shows an example of the form which implements this invention. It is the perspective view which showed the covering piece of FIG. 1 by the single item. It is the perspective view which notched some showing the example of another form of this invention. It is the perspective view which showed the coating | coated piece of FIG. 3 with the single item. It is a perspective view which shows the state which assembled | attached the coating piece of FIG. 4 to the mixing pipe. It is sectional drawing which shows another example of a form of this invention. It is a top view which shows an example of the conventional exhaust gas purification apparatus. It is sectional drawing which shows the detail of the principal part of FIG.

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

  1 and 2 show an example of an embodiment for carrying out the present invention, and portions denoted by the same reference numerals as those in FIG. 8 represent the same items.

  As shown in FIG. 1, in this embodiment, the corrosion resistance to a substance generated by adding urea water is higher than that of the mixing pipe 7B in the entrance end portion of the mixing pipe 7B in the structure shown in FIG. A covering piece 16 made of a material is provided so that the inner peripheral surface of the mixing pipe 7B in the vicinity of the urea water addition position by the urea water addition injector 8 (urea water addition means) can be covered.

  That is, as shown in FIG. 2, the covering piece 16 has a shape including a partial cylindrical portion 16b along the inner peripheral surface of the mixing pipe 7B in a part of the ring portion 16a. The remaining inner peripheral surface facing the opening 11 at the end in the diametrical direction is covered with the partial cylindrical portion 16b.

  The material of the covering piece 16 is preferably stainless steel (high Cr material) containing Cr in a weight ratio of 20% or more, and the covering piece 16 is fixed at a portion where the urea water spray is not applied. Select and weld as appropriate.

  Here, although the case where the entire covering piece 16 is made of a material having high corrosion resistance is described, it is sufficient that at least the surface portion of the covering piece 16 is made of a material having high corrosion resistance, and the surface treatment for improving the corrosion resistance. It is also possible to employ the covering piece 16 that has been subjected to the above, or the covering piece 16 in which another material having high corrosion resistance is bonded to the surface portion.

  Thus, in the case of the example shown here, the exhaust gas 1 from the gas collecting chamber 7A is introduced from the tangential direction to the opening 11 at the inlet end of the mixing pipe 7B by the guide fins 12, 13, and 14. Then, urea water is added from the urea water addition injector 8 into the swirling flow of the exhaust gas 1 formed thereby, and good mixing property with the exhaust water 1 of the urea water can be obtained. Therefore, when the amount of urea water added is increased in order to improve the NOx purification performance, the urea water that cannot be vaporized easily forms a flow along the swirl flow of the exhaust gas 1 along the inner peripheral surface of the mixing pipe 7B. However, since the inner peripheral surface of the mixing pipe 7B is covered with the covering piece 16 and is not directly exposed to the flow of the urea water, the rapid generation of corrosion is induced by the substance generated by the addition of the urea water. Such a situation does not occur in the mixing pipe 7B.

  On the other hand, urea water that cannot be completely vaporized may adhere to the inner peripheral surface of the covering piece 16, but the covering piece 16 is a material having a higher corrosion resistance to a substance generated by addition of urea water than the mixing pipe 7B. Therefore, it is difficult to corrode, and it is possible to select and weld a part that is not sprayed with urea water to fix itself, and it is not necessary to have another weld with high corrosion sensitivity. There is no fear that corrosion that occurs rapidly such as when urea water that cannot be broken flows along the inner peripheral surface at the inlet end of the mixing pipe 7B occurs.

  Therefore, according to the above embodiment, the urea water is added to the swirling flow of the exhaust gas 1 formed by the mixer structure 15 to improve the mixing property of the urea water with the exhaust gas 1, but this exhaust gas 1. Since the flow of urea water that is easily formed along the swirling flow of the mixing pipe 7B can be isolated from the inner peripheral surface of the mixing pipe 7B by the covering piece 16, corrosion of the mixing pipe 7B can be prevented. Compared with the case of changing to a material with high corrosion resistance such as Cr material, the equipment cost can be greatly reduced.

  3 to 5 show another embodiment of the present invention. In the example shown here, the upper guide fin 12 is formed integrally with the covering piece 16, and When the guide fins 12 are integrally formed on the covering piece 16, a part is cut and raised from the cylindrical covering piece 16 to form the guide fins 12 (see FIG. 4).

  Thus, in this way, when the covering piece 16 and the guide fin 12 are assembled as separate parts, there is no level difference between the two, and the exhaust gas 1 can be smoothly introduced into the mixing pipe 7B. Therefore, it is possible to reduce the variation in the swirling flow formed in the mixing pipe 7B, and it is also possible to avoid the occurrence of a gap between the covering piece 16 and the guide fin 12. Intrusion of urea water into the gap can be prevented and crevice corrosion can be prevented.

  That is, in the conventional example shown in FIG. 8, the upper guide fin 12 is formed by cutting a part of the inlet side end portion of the mixing pipe 7B, and the upper guide fin 12 is cut and raised. The opening 11 is formed at the same time, but when the covering piece 16 as shown in FIGS. 1 and 2 is arranged here, a partial cylindrical portion of the covering piece 16 is formed on the inner peripheral surface of the upper guide fin 12. As shown in FIG. 5, the upper guide fin 12 is formed on the mixing pipe 7B side, and the step or gap is formed on the covering piece 16 side. The formation of is avoided.

  Moreover, as shown in FIG. 5, the opening part of the covering piece 16 opened by cutting and raising part is used as it is as the introduction port for the exhaust gas 1 together with the opening part 11 at the inlet side end part of the mixing pipe 7B. Therefore, the covering piece 16 with the guide fins 12 can be easily manufactured with good yield.

  FIG. 6 shows still another embodiment of the present invention. In the example shown here, an elbow pipe portion 17 is formed at the inlet end of the mixing pipe 7B, and the middle portion of the elbow pipe portion 17 is shown. In this example, the urea water injector 8 is provided with an injector 8 for the urea water addition, and even in such a configuration example having no mixer structure, the inside of the elbow pipe portion 17 that forms the inlet end of the mixing pipe 7B ( In the vicinity of the urea water addition position), a covering piece 16 made of a material having a higher corrosion resistance to the substance produced by the addition of the urea water than the mixing pipe 7B is disposed to cover the inner peripheral surface of the elbow pipe portion 17. Then, since the inner peripheral surface of the mixing pipe 7B is covered with the covering piece 16 and is not directly exposed to the urea water, corrosion of the inlet side end of the mixing pipe 7B can be prevented. Both can be achieved a significant reduction in equipment cost as compared with the case of changing the entire mixing pipe 7B to those of high corrosion resistance material such as a high Cr material.

  Note that the exhaust emission control device of the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 Exhaust gas 3 Particulate filter 4 Selective reduction type catalyst 7B Mixing pipe 8 Urea water addition injector (urea water addition means)
DESCRIPTION OF SYMBOLS 11 Opening part 12 Guide fin 13 Guide fin 14 Guide fin 15 Mixer structure 16 Covering piece

Claims (4)

  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 Exhaust gas purification device having a cylindrical mixing pipe that connects to the catalyst, and at least a surface portion is generated by adding urea water rather than the mixing pipe in the vicinity of the urea water addition position in the mixing pipe An exhaust emission control device comprising a covering piece made of a material having high corrosion resistance against a substance to be covered to cover a part of the inner peripheral surface of the mixing pipe.   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. The urea water adding means is disposed 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 exhaust emission control device according to claim 1, wherein   The exhaust emission control device according to claim 2, wherein at least a part of the guide fins is integrally formed on the covering piece.   The exhaust emission control device according to claim 3, wherein a guide fin is formed by cutting and raising a part of the cylindrical covering piece.

Images