JP2007321647A - Exhaust treatment equipment for engines - Google Patents

Abstract

An engine exhaust treatment apparatus that uses a fuel injection valve to supply a reducing agent to an exhaust gas is capable of stably maintaining the internal temperature of the fuel injection valve at an appropriate temperature.
SOLUTION: A reducing agent 16 is supplied into exhaust 4 discharged from an engine and flowing down an exhaust flue 5, and nitrogen oxides in the exhaust are reduced and reacted with the reducing agent on a selective reduction catalyst. An exhaust treatment apparatus for an engine that is removed from the exhaust gas and that supplies the reducing agent into the exhaust by the injection valve 17 is provided with a cooling chamber 24 that surrounds the periphery of the injection valve. The injection valve can be cooled by circulating a cooling medium in the cooling chamber.
[Selection] Figure 2

Description

  The present invention relates to an exhaust treatment apparatus for an engine, and more particularly, to an exhaust treatment apparatus that removes a reducing agent supplied in exhaust gas by reduction reaction with nitrogen oxide in exhaust gas on a selective catalytic reduction catalyst.

  As a promising technique for removing nitrogen oxides (hereinafter referred to as NOx) from engine exhaust, there is a method using a selective catalytic reduction / SCR (Selective Catalytic Reduction). This is temporarily called the SCR method. In the SCR method, a reducing agent is added to the exhaust gas, and the reducing agent is selectively reduced with NOx in the exhaust gas in the presence of oxygen on the selective catalytic reduction catalyst to reduce NOx to nitrogen and from the exhaust gas. Remove. As the reducing agent, ammonia is generally used. Specifically, urea water (urea aqueous solution) in which urea is dissolved in water is supplied into the exhaust as a precursor, and the urea water is hydrolyzed by the heat of the exhaust to generate ammonia, which is used as a reducing agent. Work. Hereinafter, the term “reducing agent” may include urea water, which is a precursor of ammonia.

  In such an SCR method, it is important to supply a reducing agent into the exhaust gas. That is, the supply of the reducing agent needs to be appropriately controlled so as to be an amount commensurate with NOx discharged from the engine. An injection nozzle method and an injection valve method are known as methods for supplying a reducing agent, specifically urea water, into the exhaust gas.

  In the injection nozzle method, an elongate tubular injection nozzle whose front end is bent in an L-shape is placed in the exhaust flue, and urea water mixed with compressed air is sprayed from the injection nozzle into a mist and supplied into the exhaust. (For example, Non-Patent Document 1, Patent Document 1, and Patent Document 2). Such nozzle systems have problems related to exhaust temperature. It is a problem that when the exhaust gas temperature is below a certain level, urea is liable to precipitate from the urea water, which makes it impossible to effectively remove NOx in a low exhaust gas temperature state. This problem is derived from the relationship between the temperature in the injection nozzle that correlates with the exhaust gas temperature and the state of urea water in the injection nozzle. That is, in a state where the exhaust temperature is high and the temperature in the injection nozzle is also high, urea water flowing down in the injection nozzle is repelled in the form of droplets on the inner wall of the injection nozzle, so urea precipitation is unlikely to occur. On the other hand, when the exhaust gas temperature is low and the temperature in the injection nozzle is lowered accordingly, the urea water adheres to the inner wall of the injection nozzle and is boiled, so that urea is likely to precipitate. When urea is precipitated, effective NOx removal cannot be stably performed because the injection nozzle is clogged or a necessary amount of ammonia cannot be generated.

  On the other hand, in the injection valve system, urea water is sprayed into the exhaust flue from an injection valve attached to the side surface of the exhaust flue and supplied into the exhaust (for example, Patent Document 3 and Patent Document 4). Such an injection valve system has fewer problems of urea precipitation than the injection nozzle system, and enables effective NOx removal in a wide exhaust temperature range.

JP 2005-105970 A JP 2005-127318 A JP 2004-353523 A JP 2005-344597 A Automotive technology Vol57.No. 9 (2003) p94-99

  As described above, the injection valve method has the advantage that there is less problem of urea precipitation than the injection nozzle method, and it is possible to perform effective NOx removal in a wide exhaust temperature range. However, urea injection cannot be completely suppressed even with the injection valve system. In other words, a certain amount of urea precipitation cannot be avoided depending on the temperature state inside the injection valve. If urea precipitation occurs, problems such as changes in the injection characteristics of the injection valve and clogging may occur. For these reasons, there is room for further improvement in the injection valve system.

  The injection valve method also has an advantage that the supply amount of urea water can be performed with higher accuracy than the injection nozzle method. In order to make more effective use of the controllability of the supply amount in this injection valve system, it is effective to use a high-performance electromagnetic valve for the injection valve. However, this has the problem of heat resistance of the solenoid valve, more specifically, heat resistance of the electromagnetic drive mechanism of the solenoid valve. That is, the heat resistance of the electromagnetic coil and the magnetic circuit in the electromagnetic drive mechanism is, for example, about 120 ° C., which is in a considerably lower range than the exhaust temperature that reaches 500 ° C. at the maximum. For this reason, there is room for improvement in making it possible to more effectively utilize the supply amount controllability of the injection valve system.

  In other words, the urea precipitation problem in the injection valve system and the heat resistance problem of the injection valve using the electromagnetic valve can be paraphrased as problems that allow the inside of the injection valve to be maintained at an appropriate temperature. That is, if the inside of the injection valve can be stably maintained at an appropriate temperature, both the urea precipitation problem and the heat resistance problem can be solved, and the advantages of the injection valve system can be utilized more effectively. It will be like that.

  The present invention has been made on the basis of the above-described knowledge, and the internal temperature of the injection valve is stable for the SCR engine exhaust treatment device that supplies the reducing agent into the exhaust gas by the injection valve. The problem is to be able to keep the temperature at an appropriate temperature.

  In the present invention, in order to solve the above-mentioned problem, a reducing agent is supplied into the exhaust discharged from the engine and flowing down the exhaust flue, and the nitrogen oxidation in the exhaust is performed on the selective reduction catalyst installed in the exhaust flue. In the exhaust treatment apparatus for an engine, the object is removed from the exhaust gas by a reduction reaction with the reducing agent, and the supply of the reducing agent into the exhaust gas is performed by the injection valve. A cooling chamber is provided so as to surround the periphery of the nozzle, and the injection valve can be cooled by circulating a cooling medium in the cooling chamber.

  By thus cooling the injection valve by the cooling chamber that circulates the cooling medium, the internal temperature of the injection valve can always be kept at an appropriate temperature, and when urea water is used as the reducing agent. Therefore, it is possible to avoid both the urea precipitation problem that urea precipitation occurs in the urea water in the injection valve and the heat resistance problem when the electromagnetic valve is used as the injection valve.

  In the present invention, urea water is used as the cooling medium in the exhaust treatment apparatus as described above. If urea water is used as the cooling medium in this way, the supply system to the injection valve of urea water can be used, and the circulation system of the cooling medium can be completed with a simpler structure.

  Moreover, in this invention, about the above exhaust processing apparatuses, the said cooling chamber shall be formed so that it may become the annular space surrounding the circumference | surroundings of an injection valve. By forming the cooling chamber in this way, the cooling capacity for the injection valve can be made higher.

  In the present invention, the exhaust treatment apparatus as described above is provided with an injection valve holder that holds the injection valve, and a cooling chamber is provided in the injection valve holder.

  In the present invention, in the exhaust treatment apparatus as described above, a swirl flow is formed in the cooling medium flowing down the cooling chamber. By generating the swirl flow in this manner, it is possible to effectively prevent stagnation in the flow of the cooling medium in the cooling chamber, and more effective cooling can be performed.

  Further, in the present invention, in the exhaust treatment apparatus as described above, the cooling medium inlet and the cooling medium outlet in the cooling chamber are provided in a state where they are separated from each other in the length direction of the injection valve, and the cooling medium inlet is provided on the cooling medium inlet side. The flow rate is decreased, and the flow rate of the cooling medium is increased on the cooling medium outlet side. By giving the flow velocity distribution to the cooling medium in this manner, the injection valve can be cooled more uniformly, and as a result, the injection valve can be cooled more effectively.

  Further, in the present invention, for the exhaust treatment apparatus as described above, the injection valve is attached to the exhaust flue with the injection hole of the injection valve facing the inside of the exhaust flue from the side surface of the exhaust flue, and this attachment In this state, the cooling medium inlet is provided at a position close to the exhaust flue, and the cooling medium outlet is provided at a position away from the exhaust flue. By doing in this way, the temperature gradient which is going to be generated in the cooling chamber in relation to the exhaust flue can be suppressed, and the injection valve can be cooled more effectively.

  In the present invention, in the exhaust treatment apparatus as described above, the width of the annular space of the cooling chamber is widened at the portion near the cooling medium inlet, while the width of the annular space of the cooling chamber is narrowed at the portion near the cooling medium outlet. The annular space has a multistage structure. Such a multi-stage structure of the annular space promotes the formation of the swirling flow and is effective for forming the flow velocity distribution.

  In the present invention, in the exhaust treatment apparatus as described above, the cooling medium is caused to flow into the cooling chamber at a pressure higher than the atmospheric pressure. By doing so, when urea water is used as the cooling medium, the boiling point can be increased, and the urea precipitation problem in the cooling chamber can be effectively prevented.

  Further, in the present invention, the exhaust valve is held when the injection valve has a structure in which the injection hole is attached in a state in which the injection hole faces the inside of the exhaust flue from the side surface of the exhaust flue. A heat insulation space communicating with the exhaust flue is provided between the injection valve holder and the exhaust flue. By doing in this way, it can avoid that a cooling chamber touches the heat from an exhaust flue directly, and can improve the cooling capacity of a cooling chamber.

  Further, in the present invention, in the exhaust treatment apparatus as described above, the heat insulation space is communicated with the exhaust flue. By doing in this way, air can be sealed in the heat insulation space, and it is possible to prevent an unfavorable state such as a pressure generated when the air expands due to a temperature rise.

  According to the present invention as described above, the internal temperature of the injection valve can be stably maintained at an appropriate temperature with respect to the SCR engine exhaust treatment apparatus that uses the injection valve to supply the reducing agent into the exhaust. Become.

  Hereinafter, modes for carrying out the present invention will be described. FIG. 1 shows the overall configuration of an exhaust treatment apparatus for an engine according to the first embodiment. The exhaust treatment apparatus of the present embodiment is an example in the case of application to exhaust treatment of a diesel engine, and is configured by incorporating an exhaust treatment system 3 into an exhaust system 2 connected to the diesel engine 1.

  The exhaust system 2 has an exhaust flue 5 through which the exhaust 4 discharged from the diesel engine 1 flows down. The exhaust flue 5 includes an upstream part 5a, a midstream part 5b, and a downstream part 5c, and a particulate removal device (DPF; Diesel Particulate Filter) for removing particulates such as black smoke particulate matter from the exhaust 4 flowing down therethrough. ) 6 is disposed between the upstream portion 5a and the midstream portion 5b, and a muffler (not shown) is disposed at the tip of the downstream portion 5c.

  The exhaust treatment system 3 includes an injection system 11, a supply system 12, a selective reduction catalyst 13 and a control unit 14.

  The injection system 11 includes an injection valve 17 that injects a reducing agent supplied by the supply system 12, specifically urea water 16 into the exhaust flue 5, an injection valve holder 18 that holds the injection valve 17, and an injection valve 17 includes a collision plate 20 that collides with a spray 19 (FIG. 2) of urea water injected from 17.

  The injection valve 17 is composed of a high-performance electromagnetic valve. As shown in FIGS. 2 and 3, the injection valve 17 is held by the injection valve holder 18 in the midstream portion 5 b of the exhaust flue 5. It is attached to the outer peripheral surface of the exhaust flue 5 so as to be orthogonal to the side surface, and its nozzle hole 21 faces the inside of the exhaust flue 5 from the side surface of the exhaust flue 5.

  The injection valve holder 18 is composed of a holder inner cylinder 22 and a holder outer cylinder 23 formed of a material such as aluminum or aluminum alloy having excellent thermal conductivity, and between the holder inner cylinder 22 and the holder outer cylinder 23. A cooling chamber 24 is formed.

  The cooling chamber 24 functions to cool the injection valve 17 with the cooling medium 25 circulated therethrough to keep the inside of the injection valve 17 at an appropriate temperature. As the cooling medium 25, engine cooling water or urea water as a reducing agent can be used. In this embodiment, urea water is used as the cooling medium 25. By using urea water as the cooling medium 25 in this way, the urea water supply system can be used, and the circulation system of the cooling medium 25 can be completed with a simpler structure.

  The cooling chamber 24 is an electromagnetic drive mechanism 27 for driving a valve body disposed inside the nozzle from the vicinity of the injection valve 17, in particular, the main part of the injection valve 17 (the vicinity of the injection hole 21 at the tip of the injection valve 17 nozzle portion). A structure is provided to cool the injection valve 17 more effectively, that is, to enhance the cooling performance of the injection valve 17.

  The first structure is an arrangement structure in the relationship between the cooling medium inlet 28 provided in the cooling chamber 24 and the exhaust flue 5 of the cooling medium outlet 29. Specifically, the cooling medium inlet 28 and the cooling medium outlet 29 are provided in a state separated from each other in the length direction of the injection valve 17. In this state, the cooling medium inlet 28 is close to the exhaust flue 5. The cooling medium outlet 29 is disposed on the side of the injection valve 17, that is, on the side away from the exhaust flue 5, that is, on the rear end side of the injection valve 17. By arranging the cooling medium inlet 28 and the cooling medium outlet 29 in this way, the temperature gradient in the cooling chamber 24 can be further reduced. That is, the cooling chamber 24 is in a state in which a temperature gradient is likely to be generated, such that the temperature near the exhaust flue 5 becomes high due to the heat from the exhaust flue 5 and the temperature decreases as the distance from the exhaust flue 5 increases. In such a state, the low-temperature cooling medium 25 is caused to flow from the cooling medium inlet 28 disposed close to the exhaust flue 5 to the side close to the exhaust flue 5, while the raised cooling medium 25 is supplied to the exhaust flue 5. By causing the coolant to flow out from the cooling medium outlet 29 on the side away from 5, the occurrence of the temperature gradient as described above can be suppressed. As a result, the injection valve 17 can be cooled more effectively.

  The second structure is a structure that generates a swirling flow in the cooling medium 25 inside the cooling chamber 24. Specifically, the center positions of the cooling medium inlet 28 and the cooling medium outlet 29 are made different in the circumferential direction of the cooling chamber 24 (FIG. 3), and the annular space of the cooling chamber 24 surrounding the injection valve 17 is tapered in a multistage manner. Is formed. Here, the multi-stage tapered structure of the annular space means that in the example of FIG. 2, the width of the annular space is widened at the portion near the cooling medium inlet 28 and the width of the annular space is widened at the portion near the cooling medium outlet 29. The structure is narrow, and in the example of FIG. By doing so, a swirl flow can be efficiently generated in the cooling medium 25 in the cooling chamber 24. By generating the swirl flow, it is possible to effectively prevent stagnation in the flow of the cooling medium 25 in the cooling chamber 24, and the injection valve 17 can be cooled more effectively.

  The third structure is a structure that gives a flow velocity distribution to the cooling medium 25 in the cooling chamber 24. Although the cooling medium 25 flowing from the cooling medium inlet 28 is at a low temperature, the temperature rises while it passes through the cooling chamber 24 and cools the injection valve 17. That is, the temperature of the cooling medium 25 at the cooling medium outlet 29 is higher than that of the cooling medium 25 at the cooling medium inlet 28. Therefore, the cooling effect of the cooling medium 25 in the cooling chamber 24 tends to decrease as it goes near the cooling medium outlet 29. Therefore, the flow rate of the cooling medium 25 is decreased at a portion near the cooling medium inlet 28 where the temperature of the cooling medium 25 is relatively low, and the cooling is performed at a portion near the cooling medium outlet 29 where the temperature of the cooling medium 25 is relatively high. The flow rate of the medium 25 is increased. This flow velocity distribution is provided by the multi-stage tapered structure described above. That is, the multi-stage tapered structure functions not only for the generation of the swirling flow but also for the generation of the flow velocity distribution. Specifically, the flow rate of the cooling medium 25 is relatively slow at the portion near the cooling medium outlet 28 due to the wide annular space of the cooling chamber 24, and the portion of the cooling chamber 24 near the cooling medium outlet 29 is relatively close. The flow velocity distribution is formed so that the flow velocity of the cooling medium 25 becomes relatively fast due to the narrow width of the annular space. By doing so, the heat transfer coefficient of the cooling medium 25 correlates with the flow rate, and the higher the flow rate, the larger the cooling medium 25. Therefore, even if the cooling medium 25 in the cooling chamber 24 has a temperature distribution, As a result, the injection valve 17 can be cooled more effectively.

  FIG. 4 shows an example of the result of analyzing the flow of the cooling medium in the cooling chamber 24. In the figure, the flow of the cooling medium is indicated by a flow line S. According to this result, a desirable swirl flow is formed in the cooling chamber 24. Further, the number of swirling flows in the portion corresponding to the nozzle portion of the injection valve 17 is increased, and the swirling flow in this portion is relatively low. Further, the flow is relatively fast on the side close to the cooling medium outlet 29, that is, on the side where the temperature of the cooling medium is relatively high, so that the heat transfer coefficient becomes relatively large. With such a swirl flow and flow velocity distribution, the injection valve 17 can be cooled more effectively by the cooling chamber 24.

  As described above, the injection valve holder 18 is preferably formed of a material such as aluminum or aluminum alloy having excellent thermal conductivity. However, these materials have difficulty in corrosion resistance due to the relationship with urea water (the hydrogen ion concentration is around 9) used for the cooling medium 25. There is also a problem of corrosion of any metal material due to contact between the material metal (such as stainless steel) of the injection valve 17 and the material metal (such as aluminum or aluminum alloy) of the injection valve holder 18. Therefore, it is preferable to perform an appropriate surface treatment on the injection valve holder 18. As the surface treatment, electroless nickel plating or a synthetic resin material excellent in chemical resistance, for example, coating with a fluororesin or glass coating is suitable. Corrosion resistance can also be improved by forming an anodic oxide film that oxidizes aluminum by electrolysis to form a film on the surface.

  The injection valve holder 18 functions to cool the injection valve 17 in the cooling chamber 24 as described above. In order to make the cooling function of the injection valve holder 18 more effective, a heat insulating structure is provided between the injection valve holder 18 and the exhaust flue 5. Specifically, an annular heat insulating material 31 is disposed between the injection valve holder 18 and the side wall of the exhaust flue 5, thereby reducing the amount of heat conducted from the exhaust flue 5 to the injection valve holder 18. Further, in order to reduce the amount of heat transmitted from the exhaust 4 flowing down the exhaust flue 5 to the injection valve holder 18, a heat insulating space 32 is formed in a portion where the injection valve holder 18 and the exhaust 4 are in contact (see FIG. 2). ). The heat insulating space 32 is formed by combining a recess provided on the outer surface of the side wall of the exhaust flue 5 and a recess provided on the bottom surface of the holder inner cylinder 22 of the injection valve holder 18. The heat insulating space 32 is formed as a flat annular space surrounding the tip of the injection valve 17, and the inner peripheral side thereof is a flue side protrusion 33 protruding from the side wall of the exhaust flue 5 and the inside of the holder. It is defined by a holder-side protrusion 34 protruding from the bottom surface of the tube 22. A narrow gap 35 is provided between the flue-side protrusion 33 and the holder-side protrusion 34 so that the heat insulating space 32 communicates with the inside of the exhaust flue 5.

  Here, if the flue-side protrusion 33 and the holder-side protrusion 34 are in direct contact with each other, the heat transferred from the high-temperature exhaust 4 to the side wall of the exhaust flue 5 via the flue-side protrusion 33 is the holder-side protrusion. 34 will be transmitted directly. For this reason, the temperature of the injection valve holder 18 increases in the vicinity of the holder-side protrusion 34, that is, in the vicinity of the tip of the injection valve 17, and as a result, the temperature of the tip of the injection valve 17 increases. It becomes easy. This is not preferable because the tip of the injection valve 17 dislikes urea precipitation. Moreover, when the heat insulation space 32 is a sealed space, there is a possibility that an undesired state may be caused by the pressure generated when the air to be sealed therein expands as the temperature rises. In order to prevent the occurrence of such an unfavorable state, the above-described gap 35 and the communication structure of the heat insulating space 32 to the exhaust flue 5 are thereby prevented.

FIG. 5 shows a temperature distribution obtained by thermal fluid analysis in the vicinity of the injection hole 21 of the injection valve 17s. Fig.5 (a) is a comparative example and is temperature distribution about the injection valve holder produced for the comparison. In the injection valve holder for comparison, the material is stainless steel, and no element corresponding to the heat insulating space 32 is provided. On the other hand, FIG.5 (b) is temperature distribution about the injection valve holder 18s in 2nd Embodiment mentioned later. The analysis conditions were as follows: 400 ° C. air was used as the diverted exhaust 63, the flow rate was 0.25 m ³ / min, 60 ° C. water was used as the cooling medium supplied to the cooling chamber 24, and the flow rate was 0.5 liter / liter. It was set to min.

  Here, it is known from the experiments by the inventors that urea precipitation occurs when the urea water boils in a space filled with the urea water (for example, inside the injection valve and the cooling chamber). Therefore, it is important for preventing precipitation that urea water does not boil. However, urea water has a higher boiling point than water because it is an aqueous solution of urea. In addition, the urea water is set to a pressure higher than the atmospheric pressure in the injection valve 17s, and the boiling point increases accordingly. Based on these facts, it can be said that urea precipitation does not occur in the urea water if the inside of the injection valve 17s can be cooled so as to be kept below the boiling point of water.

  The pressure in the cooling chamber 24 does not become so high because the cooling medium circulates. If the pressure in the cooling chamber 24 is 0.1 MPa and the cooling medium is water, the boiling point (boiling point temperature) is 120 ° C. If the supply pressure to the injection valve 17 is 0.5 MPa and the working fluid is water, the boiling point is 159 ° C.

  According to the analysis result seen in FIG. 5, in the comparative example (a), the temperature in the vicinity of the injection hole 21c of the injection valve 17c is 140 ° C. or higher (162 ° C.). For this reason, the urea water is boiled in the vicinity of the injection hole 21c to cause precipitation of urea, and the possibility of causing malfunction of the injection valve 17s due to the urea precipitation increases. Moreover, in the comparative example of (a), the highest reached temperature of the inner wall of the cooling chamber 24c is 110-130 degreeC (120 degreeC). For this reason, there is a possibility that the cooling medium will boil, and when boiling occurs, when urea water is used as the cooling medium, urea precipitation occurs in the urea water, and the urea precipitation causes the swirling flow as described above. There is a possibility that the cooling capacity of the cooling chamber 24 is lowered due to the inhibition of the formation.

  On the other hand, in the present invention of (b), the temperature in the vicinity of the injection hole 21 of the injection valve 17s is 90 to 110 ° C. (100 ° C.), and the maximum temperature reached on the inner wall of the cooling chamber 24s is 70 to 90 ° C. 80 ° C.). That is, the temperature inside the injection valve 17 is kept at 110 ° C. or lower, and the temperature of the cooling medium does not exceed 90 ° C. in the cooling chamber 24 s. This is a result that the heat insulation of the cooling chamber 24s by the heat insulating space 32 with respect to the heat from the swirl chamber 66 works effectively, and the cooling of the injection valve 17s by the cooling chamber 24s is effectively performed. Therefore, according to the present invention, it is possible to effectively prevent the occurrence of urea precipitation due to the boiling of urea water in both the injection valve 17s and the cooling chamber 24s, and to make the supply of the reducing agent by the injection valve 17s more stable. It becomes possible. Here, the temperature in parentheses is a value obtained by increasing the temperature display resolution.

  The impingement plate 20 is formed of a perforated plate having a plurality of holes 36, and is installed in multiple stages (two stages in the example of FIG. 1) in the midstream portion 5b of the exhaust flue 5. The collision plate 20 is installed so as to face the injection hole 21 of the injection valve 17 at a predetermined angle for the first stage, and parallel to the flow of the exhaust 4 in the exhaust flue 5 for the second stage. It is installed in a state. Here, the “predetermined angle” is an angle at which the spray 19 injected from the injection valve 17 can be directed in the exhaust flow direction in the exhaust flue 5 by the collision with the collision plate 20.

  The impingement plate 20 functions to uniformly disperse the spray 19 of urea water from the injection valve 17 in the exhaust 4 while effectively preventing precipitation of urea, and ammonia gas by hydrolysis of urea water. It also works to promote the generation of. The function is demonstrated as follows. Since the collision plate 20 is installed in the exhaust flue 5, it is in a high temperature state substantially the same as the temperature of the exhaust 4. When the spray 19 from the injection valve 17 collides with the high-temperature impingement plate 20, the droplets in the spray 19 take the form of film boiling on the impingement plate 20 and diffuse into the exhaust 4 while promoting evaporation. Here, the film boiling means that a droplet receiving heat conduction from the collision plate 20 boils in a state where an air layer is interposed between the collision plate 20 and the surface of the collision plate 20, and has the characteristic that precipitation of urea hardly occurs. is there. That is, by supplying the urea water in the sprayed state into the exhaust 4 through the collision with the collision plate 20, the urea water can be uniformly dispersed in the exhaust 4 while effectively preventing the precipitation of urea. Further, the supply of the sprayed urea water via the collision to the collision plate 20 promotes the generation of ammonia gas by hydrolysis of the urea water by giving and receiving heat in the collision to the collision plate 20. Here, since the collision plate 20 has a plurality of holes 36, a part of the spray 19 passes through the holes 36 by the first-stage collision plate 20, and the second-stage collision plate 20 (in FIG. 2). The second-stage collision plate 20 is subjected to the same action as that of the first-stage collision plate 20. In addition to the above functions, the collision plate 20 also prevents urea deposition on the inner surface of the exhaust flue 5 by suppressing the spray 19 from colliding with the inner surface of the exhaust flue 5. Function.

  As described above, in the present embodiment, the collision plate 20 is configured in two stages, but is not limited thereto, and may be configured in two or more stages. It is also possible to adopt a configuration in which the opening rate of the hole 36 formed in the collision plate 20 is changed for each step to adjust the collision rate of the spray 19 in each step. When such a collision rate adjusting structure is employed, the degree of dispersion of urea water in the exhaust flue 5 can be adjusted, and the selective catalytic reduction catalyst 13 can be operated more efficiently.

  The supply system 12 supplies urea water 16 to the injection valve 17 and also supplies a cooling medium 25 that circulates to the cooling chamber 24. As the cooling medium 25, the urea water 16 is used as described above. For this purpose, the supply system 12 includes a storage tank 41. The urea water 16 stored in the storage tank 41 is pumped up by the pump 43 downstream of the filter 42 and discharged to the reducing agent supply pipe 44, and the injection valve inlet 45 in a predetermined pressure state through the reducing agent supply pipe 44. (Fig. 2) is supplied to the injection valve 17.

  A cooling medium supply pipe 46 is branched from the reducing agent supply pipe 44 immediately after the pump 43. The cooling medium supply pipe 46 is provided with a pressure adjustment valve 47. The pressure adjustment valve 47 adjusts the supply pressure of the urea water 16 to the injection valve 17 through adjustment of the flow rate of the cooling medium 25, that is, the urea water 16 that flows through the cooling medium supply pipe 46. The urea water 16 branched from the reducing agent supply pipe 44 by the cooling medium supply pipe 46 flows down the cooling medium supply pipe 46 as the cooling medium 25 and flows into the cooling chamber 24 from the cooling medium inlet 28. A cooling medium return pipe 48 is connected to the cooling medium outlet 29 of the cooling chamber 24, and the cooling medium 25 that has cooled the injection valve 17 in the cooling chamber 24 is returned to the storage tank 41 by the cooling medium return pipe 48. It is.

  The selective catalytic reduction catalyst 13 functions to selectively reduce NOx in the exhaust gas 4 in the presence of oxygen and oxygen, which are produced by hydrolysis of a reducing agent, specifically urea water 16. This selective catalytic reduction catalyst 13 is disposed in the exhaust flue 5 between the midstream portion 5b and the downstream portion 5c, and is ammonia generated by hydrolysis of urea water 16 supplied into the exhaust 4 by the injection valve 17. Exhaust gas 4N containing the gas efficiently contacts.

  The control unit 14 controls the operation of the injection valve 17 according to the amount of NOx contained in the exhaust 4. Specifically, the control unit 14 inputs the temperature of the exhaust 4 detected by the exhaust temperature sensor 51, the NOx concentration in the exhaust 4 detected by the NOx sensor 52, and the ammonia concentration in the exhaust 4 detected by the ammonia sensor 53. Based on these data, the operation of the injection valve 17 is controlled so that the urea water 16 can be supplied to the exhaust gas 4 with an optimum supply amount.

  Hereinafter, the second embodiment will be described. FIGS. 6-14 shows the structure of the principal part of the exhaust processing apparatus by 2nd Embodiment. 6 shows the relationship between the flow of exhaust gas and the mounting position of the injection valve in the exhaust treatment apparatus of this embodiment, FIG. 7 shows the supply path of urea water to the injection valve and the circulation path of the cooling medium, and FIG. Is a perspective view of a portion C in FIG. 6, FIG. 9 is a front view of the portion C in FIG. 6, FIG. 10 is a side view of the portion C in FIG. 6, and FIG. FIG. 12 is an enlarged view of a portion F in FIG. 11, FIG. 13 is a sectional view taken along a line EE in FIG. 10, and FIG. 14 is a perspective view of a portion C in FIG.

  The present embodiment is basically the same as the first embodiment, and is different in that a reducing agent supply unit 60 at the time of exhaust gas low temperature is added and a swirl vane 61 is added. In the following, the same components as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and description thereof is omitted.

  First, the exhaust gas low temperature reducing agent supply unit 60 will be described. The exhaust gas low temperature reducing agent supply unit 60 operates when the temperature of the exhaust gas 4 flowing down the exhaust flue 5 is lower than a certain level and supplies the reducing agent into the exhaust gas 4. The specific configuration is as follows.

  A throttle portion 62 having a partially reduced cross-sectional size is formed in the middle flow portion 5 b of the exhaust flue 5. The throttle 62 functions to guide a part of the exhaust 4 to the exhaust low-temperature reducing agent supply unit 60 as the shunt exhaust 63. That is, the inlet 65 of the branch pipe 64 faces the upstream end of the throttle portion 62 so as to face the flow of the exhaust 4, and the branch exhaust 63 can be guided from the inlet 65 to the branch pipe 64. ing. A swirl chamber 66 for generating a swirling flow in the diverted exhaust gas 63 guided by the diverter pipe 64 is provided downstream of the diverter pipe 64 so as to communicate with the diverter pipe 64. 67 is connected. An injection valve 17 s held by an injection valve holder 18 s is attached to the swirl chamber 66, and urea spray 19 injected from the injection valve 17 s is injected into the heat transfer tube 67 through the swirl chamber 66. It is like that.

  The heat transfer tube 67 is heated by a heating element 68 disposed on the outer peripheral portion thereof, and urea water supplied as the spray 19 by the injection valve 17s and flowing down together with the diverted exhaust gas 63 is promoted for vaporization thereof. To be heated. Further, the heat transfer tube 67 is provided with a hydrolysis catalyst 69 in a portion near the downstream end thereof, and the urea vapor 71 generated by the urea water being vaporized by being heated by the heat transfer tube 67 is hydrolyzed. By contacting the catalyst 69, hydrolysis of urea to ammonia is promoted.

  A dispersion chamber 72 is connected to the downstream end of the heat transfer tube 67. The dispersion chamber 72 is formed as an annular space surrounding the side wall of the throttle part 62 and communicates with the inside of the exhaust flue 5 through a plurality of injection holes 73 formed in the side wall of the throttle part 62. Has been. The dispersion chamber 72 functions to uniformly return the diverted exhaust 63N containing ammonia generated by the hydrolysis of urea water and flowing out from the heat transfer pipe 67 into the exhaust flue 5.

  Next, the swirl blade 61 will be described. The swirl vane 61 is disposed inside the throttle unit 62 so as to be positioned upstream of the nozzle hole 73 of the dispersion chamber 72 near the downstream end of the throttle unit 62. The swirl vane 61 functions to promote mixing of the split flow exhaust 63N and the exhaust 4 by generating local turbulent flow and swirl flow in the exhaust 4 flowing down the throttle portion 62.

  Below, the operating state and effect of the exhaust gas low temperature reducing agent supply unit 60 will be described. The diverted exhaust gas 63 that has flowed into the diverter pipe 64 from the introduction port 65 flows down the diverter pipe 64 and flows into the swirl chamber 66, where it flows into the heat transfer pipe 67 while forming a swirl flow. Meanwhile, the spray 19 of urea water is injected from the injection valve 17 s toward the heat transfer tube 67 through the swirl chamber 66.

  Here, since the diverted exhaust 63 forms a swirling flow and flows into the heat transfer pipe 67, the passage pressure loss in the flow of the diverted exhaust 63 flowing down from the diverted pipe 64 to the heat transfer pipe 67 in a state orthogonal thereto. Therefore, the divided exhaust 63 can be efficiently introduced into the heat transfer tube 67. Further, the spray 19 injected to the heat transfer tube 67 can be forcibly brought into contact with the inner peripheral surface of the heat transfer tube 67 by the swirling flow. As a result, the time during which the droplets in the spray 19 are in contact with the inner peripheral surface of the heat transfer tube 67 can be increased, and the droplets can be heated more efficiently by the heat transfer tube 67. That is, the vaporization promotion of the spray 19 by the heat transfer tube 67 can be made more efficient.

  The urea vapor 71 generated by the vaporization of the spray 19 by heating by the heat transfer tube 67 passes through the hydrolysis catalyst 69 while being heated from the diverted exhaust 63 and the heat transfer tube 67, whereby the hydrolysis reaction is promoted and ammonia ( Ammonia gas) is generated efficiently. The split flow exhaust 63N containing ammonia thus generated flows into the dispersion chamber 72, and flows into the exhaust flue 5 at the throttle portion 62 while being attracted by the flow of the exhaust 4 from the nozzle hole 73 therein.

  In the throttle portion 62, the flow of the exhaust 4 is fast. Further, passing through the swirl blade 61 causes a local turbulent flow in the flow of the exhaust 4 and forms a swirl flow. For this reason, the mixing of the split flow exhaust 63N and the exhaust 4 can be promoted more effectively. Therefore, the exhaust 4N in which ammonia is sufficiently mixed can be brought into contact with the selective catalytic reduction catalyst 13, and NOx can be efficiently removed.

  The temperature of the exhaust 4 changes depending on the load of the diesel engine 1. When the temperature of the exhaust gas 4 is high, even if urea water is directly injected into the exhaust gas 4, vaporization and hydrolysis of the urea water proceeds rapidly by the heat obtained from the exhaust gas 4, and a predetermined amount of ammonia as a reducing agent is obtained. Is supplied to the selective catalytic reduction catalyst 13. However, when the temperature of the exhaust 4 is low, ammonia gasification of urea water is difficult to proceed, and the NOx reduction reaction at the selective catalytic reduction catalyst 13 does not proceed sufficiently. That is, the NOx removal rate deteriorates when the temperature of the exhaust 4 is low.

  The exhaust gas low temperature reducing agent supply unit 60 can effectively cope with such a problem. That is, as described above, the temperature of the diverted exhaust 63 is increased by heating with the heat transfer tube 67, the vaporization of urea water and the hydrolysis of urea into ammonia are promoted, and in addition to these, the hydrolysis catalyst 69 further increases urea. By promoting the hydrolysis of ammonia into ammonia, even when the temperature of the exhaust 4 is low, the exhaust 4N in which ammonia is sufficiently mixed can be brought into contact with the selective catalytic reduction catalyst 13, thereby improving the efficiency of NOx. Allows removal.

  Since the exhaust gas low temperature reducing agent supply unit 60 has the above functional purpose, the exhaust cold temperature reducing agent supply unit 60 is not operated when the temperature of the exhaust 4 is sufficiently high, and directly into the exhaust flue 5. Only the injection valve 17 that injects urea water is used. By appropriately using such a method, it is possible to minimize the energy consumption associated with the exhaust processing. It should be noted that the suppression of energy consumption also contributes to the fact that the diverted exhaust 63 is taken out from the exhaust 4 and the small amount of the diverted exhaust 63 is subjected to heat treatment.

  Here, as the heating element 68 that heats the heat transfer tube 67, for example, a sheath heater, a ceramic heater, a PTC (Positive Temperature Coefficient Thermistor) heater, or the like can be used. A PTC heater generates heat by applying an electric current to an electrode. When the temperature of the heater exceeds a predetermined temperature, the electric resistance rapidly increases and the current decreases to keep the temperature constant. This is a ceramic heater. When such a PTC heater is used for the heating element 68, since the heater can adjust its temperature, the temperature sensor for adjusting the heater temperature can be omitted, and the apparatus can be downsized.

  Next, the supply system 80 (FIG. 7) in 2nd Embodiment is demonstrated. The urea water 16 stored in the storage tank 41 is pumped up by the pump 43 downstream of the filter 42 and discharged to the reducing agent supply pipe 44. A reducing agent supply branch pipe 81 is connected to the reducing agent supply pipe 44, and the urea water 16 is supplied to the injection valve 17 and the injection valve 17 s through the reducing agent supply branch pipe 81 in a predetermined pressure state. The pressure adjustment at this time is performed by the pressure adjustment valve 47 installed in the cooling medium supply pipe 46 as in the case of the first embodiment. Further, the cooling medium 25 is supplied to the cooling chamber 24 of the injection valve holder 18 of the injection valve 17 through the cooling medium supply pipe 46 branched from the reducing agent supply pipe 44, as described in the first embodiment. is there.

  The cooling medium 25 discharged from the cooling chamber 24 of the injection valve holder 18 is supplied to the cooling chamber 24s of the injection valve holder 18s. That is, the cooling medium outlet 29 of the cooling chamber 24 and the cooling medium inlet 28 s of the cooling chamber 24 s are connected by the connecting pipe 82, and the cooling medium 25 discharged from the cooling chamber 24 is supplied to the cooling chamber 24 s through the connecting pipe 82. I have to. A cooling medium return pipe 48 is connected to the cooling medium outlet 29 s of the cooling chamber 24 s, and the cooling medium 25 that has cooled the injection valve 17 s in the cooling chamber 24 s is returned to the storage tank 41 by the cooling medium return pipe 48. It is.

  In the above, the cooling medium flows from the injection valve holder 18 to the injection valve holder 18s. Alternatively, the cooling medium may flow from the injection valve holder 18s to the injection valve holder 18. Is possible. Here, the injection valve 17 s is basically the same as the injection valve 17, and the injection valve holder 18 s is basically the same as the injection valve holder 18.

  Hereinafter, the third embodiment will be described. FIG. 15 shows the configuration of the supply system in the exhaust treatment apparatus according to the third embodiment. This embodiment is a modification of the second embodiment, and the main difference from the second embodiment is that urea water that has been used for cooling the injection valve 17 as a cooling medium is injected as urea water as a reducing agent. Along with this, the supply path of urea water to the injection valve 17 and the injection valve 17s, the circulation path of the cooling medium to the cooling chamber 24 and the cooling chamber 24s, and The arrangement position of the pressure regulating valve 47 is changed. Since other configurations are the same as those of the second embodiment, the same components as those of the second embodiment are denoted by the same reference numerals as those of the second embodiment, and the description thereof is omitted. .

  This embodiment is characterized by its supply system 90. In the supply system 90, the urea water 16 stored in the storage tank 41 is pumped up by the pump 43 downstream of the filter 42 and discharged to the cooling medium supply pipe 91. The urea water 16 flowing down the cooling medium supply pipe 91 first flows into the cooling chamber 24 of the injection valve holder 18 as the cooling medium 25. The urea water 16 that has worked for cooling the injection valve 17 in the cooling chamber 24 flows out to the common pipe 92 connected to the cooling medium outlet 29. A reducing agent supply pipe 93 and a connecting pipe 94 are branchedly connected to the end of the common pipe 92, and a part of the urea water 16 flowing down the common pipe 92 is a reducing agent in the reducing agent supply pipe 93. The urea water 16 flows in, and the remainder flows into the connecting pipe 94 as the cooling medium 25. The urea water 16 flowing down the reducing agent supply pipe 93 is supplied to each of the injection valve 17 and the injection valve 17s, and the cooling medium 25 flowing down the connection pipe 94 flows into the cooling chamber 24s. A cooling medium return pipe 48 is connected to the cooling medium outlet 29 s of the cooling chamber 24 s, and the cooling medium 25 that has cooled the injection valve 17 s in the cooling chamber 24 s is returned to the storage tank 41 by the cooling medium return pipe 48. It is. A pressure adjustment valve 47 is installed in the cooling medium return pipe 48. The pressure adjusting valve 47 adjusts the pressure of urea water as a cooling medium or a reducing agent by acting on the cooling medium flowing down the cooling medium return pipe 48, that is, urea water. For this reason, urea water and a cooling medium are supplied to the injection valve 17, the injection valve 17s, the cooling chamber 24, and the cooling chamber 24s with the same pressure.

  According to the present embodiment, the pressure of the cooling medium in the cooling chamber 24 and the cooling chamber 24s can be increased compared to the case of the second embodiment. That is, the boiling point of the cooling medium in the cooling chamber 24 and the cooling chamber 24s can be increased. Such a configuration of the present embodiment is useful in a condition where it is necessary to increase the boiling point of the cooling medium in the cooling chamber 24 or the cooling chamber 24s. For example, when the injection valve holder 18 or the injection valve holder 18s is made of a stainless material that is excellent in corrosion resistance but inferior in heat conduction as compared with an aluminum material, the surface treatment for improving the corrosion resistance described above is omitted to increase productivity. It is useful for such cases.

  Hereinafter, the fourth embodiment will be described. FIG. 16 shows the configuration of the supply system in the exhaust treatment apparatus according to the fourth embodiment. The present embodiment is a modification of the second embodiment, and the main difference from the second embodiment is that the cooling medium supply pipe 46 is provided with a first pressure regulating valve 96 and the cooling medium return pipe 48 is provided. The second pressure regulating valve 97 is provided. Since other configurations are the same as those of the second embodiment, the same components as those of the second embodiment are denoted by the same reference numerals as those of the second embodiment, and the description thereof is omitted. .

  In the supply system 98 of the present embodiment, the first pressure adjustment valve 96 is set to a high pressure adjustment setting such as 1 MPa, and the second pressure adjustment valve 97 is set to a low pressure adjustment setting such as 0.5 MPa. By doing so, the pressure of the urea water supplied to the injection valve 17 and the injection valve 17s can be increased, while the pressure of the cooling medium supplied to the cooling chamber 24 and the cooling chamber 24s is within a necessary range. Can be maintained.

  As described above, the cause of urea precipitation is the boiling of urea water. Therefore, in order to effectively prevent urea precipitation in the injection valve 17 and the injection valve 17s, and also in the cooling chamber 24 and the cooling chamber 24s, the urea water in them. It is important not to cause any boiling. From this point of view, according to the present embodiment, the urea precipitation problem can be more effectively dealt with. That is, the portion where the temperature rises most under the influence of the exhaust 4 is the tip of the injection valve 17 or the injection valve 17s that is directly exposed to the exhaust 4, and therefore the injection valve 17 or the injection valve as in this embodiment. By making it possible to increase the pressure of the urea water in 17 s, it is possible to more effectively cope with the urea precipitation problem.

  For example, when the supply pressure of urea water to the injection valve 17 and the injection valve 17 s is 1 MPa, the boiling point of the urea water is slightly higher than the boiling point of about 180 ° C. in the case of water, and the injection valve 17 tends to become high temperature. And boiling of urea water in the injection valve 17s can be effectively prevented. On the other hand, the presence of the heat insulating space 32 does not directly affect the exhaust 4, and the cooling by the cooling medium makes it easy to maintain a lower temperature than the injection valve 17 and the injection valve 17s. For the chamber 24 and the cooling chamber 24s, for example, the boiling point of water corresponding to a pressure of 0.5 MPa can be kept at a temperature slightly higher than about 159 ° C., and the pressure of the cooling medium is as low as about 0.5 MPa. Even so, the urea precipitation problem can be effectively avoided.

  Here, the pressure of the cooling medium in the cooling chamber 24 or the cooling chamber 24s is sufficient if it is a certain level or more, and it is not always necessary to finely adjust it. From this, the pressure setting of the cooling medium in the cooling chamber 24 and the cooling chamber 24s can be sufficiently handled by a pressure setting means having a simple structure such as an orifice. That is, for the second pressure regulating valve 97, instead of this, a pressure setting means having a simple structure such as an orifice can be used. By doing so, the cost can be reduced.

1 is a diagram illustrating an overall configuration of an exhaust treatment apparatus according to a first embodiment. It is the A section expanded sectional view in FIG. It is the B section external appearance perspective view in FIG. It is a figure which shows an example of the result of having analyzed the flow of the cooling medium in a cooling chamber. It is a figure which shows the temperature distribution obtained by carrying out the thermal fluid analysis about the vicinity of the nozzle hole of an injection valve. It is a figure which shows the relationship between the flow of exhaust_gas | exhaustion in the exhaust-gas processing apparatus of 2nd Embodiment, and the attachment position of an injection valve. It is a figure which shows the supply path | route of the urea water to the injection valve in the exhaust processing apparatus of 2nd Embodiment, and the circulation path | route of a cooling medium. It is a perspective view of the C section in FIG. It is a front view of the C section in FIG. It is a side view of the C section in FIG. It is DD sectional drawing in FIG. It is the F section enlarged view in FIG. It is EE sectional drawing in FIG. It is a perspective view of the C section in FIG. It is a figure which shows the structure of the supply system in the exhaust-gas treatment apparatus by 3rd Embodiment. It is a figure which shows the structure of the supply system in the exhaust-gas treatment apparatus by 4th Embodiment.

Explanation of symbols

1 Engine 4 Exhaust 5 Exhaust flue 13 Selective reduction catalyst 16 Urea water (reducing agent)
17 Injection valve 18 Injection valve holder 21 Injection hole 24 Cooling chamber 25 Cooling medium 28 Cooling medium inlet 29 Cooling medium outlet 32 Thermal insulation space

Claims (11)

By supplying a reducing agent into the exhaust discharged from the engine and flowing down the exhaust flue, the nitrogen oxide in the exhaust is reduced with the reducing agent on the selective reduction catalyst installed in the exhaust flue. In an exhaust treatment apparatus for an engine which is removed from the exhaust and is configured to supply the reducing agent into the exhaust with an injection valve.
An exhaust treatment apparatus, wherein a cooling chamber is provided so as to surround the periphery of the injection valve, and the injection valve can be cooled by circulating a cooling medium in the cooling chamber.   2. The exhaust treatment apparatus according to claim 1, wherein urea water is used as the cooling medium.   The exhaust treatment device according to claim 1 or 2, wherein the cooling chamber is formed to be an annular space surrounding the periphery of the injection valve.   The exhaust treatment apparatus according to any one of claims 1 to 3, wherein the injection valve is held by an injection valve holder, and the cooling chamber is provided in the injection valve holder.   The exhaust treatment apparatus according to any one of claims 1 to 4, wherein the cooling chamber is configured to form a swirling flow in the cooling medium flowing down the cooling chamber.   The cooling chamber is provided with a cooling medium inlet through which the cooling medium flows and a cooling medium outlet through which the cooling medium flows out, separated from each other in the length direction of the injection valve, and on the cooling medium inlet side. The exhaust according to any one of claims 1 to 5, wherein the flow rate of the cooling medium is decreased and the flow rate of the cooling medium is increased on the cooling medium outlet side. Processing equipment.   The injection valve is attached to the exhaust flue in a state where the injection hole faces the inside of the exhaust flue from the side surface of the exhaust flue, and in this attached state, the cooling medium inlet is connected to the exhaust flue. The exhaust treatment apparatus according to claim 5 or 6, wherein the exhaust treatment apparatus is provided at a position near the flue, and the cooling medium outlet is provided at a position away from the exhaust flue.   The cooling chamber is formed so that the width of the annular space is widened at a portion near the cooling medium inlet, while the width of the annular space is narrowed at a portion near the cooling medium outlet. The exhaust treatment device according to any one of claims 5 to 7.   The exhaust treatment apparatus according to any one of claims 1 to 8, wherein the cooling medium is allowed to flow into the cooling chamber at a pressure higher than atmospheric pressure.   The said injection valve is attached to the said exhaust flue in the state which faces the inside of the said exhaust flue from the side surface of the said exhaust flue, The said injection valve holding the said injection valve in this attachment state The exhaust treatment apparatus according to any one of claims 1 to 9, wherein a heat insulating space communicating with the exhaust flue is provided between the holder and the exhaust flue.   The exhaust heat treatment apparatus according to claim 10, wherein the heat insulation space communicates with the exhaust flue.

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