JP2008014213A - Exhaust treatment device - Google Patents

Abstract

[Object] To quickly supply urea as a reducing agent to a denitration catalyst without depositing it in a flue.
An exhaust treatment apparatus includes a denitration catalyst reactor 19 provided in a flue 52 through which exhaust gas flows to reduce nitrogen oxide in exhaust gas, and urea in the flue upstream of the denitration catalyst reactor. An injection valve 76 for injecting water is provided, and an evaporation cylinder 100 surrounding the spray of urea water injected from the injection valve is arranged so as to extend from the wall surface of the flue into the flue. According to this configuration, even if a liquid flow due to the urea water is generated as the urea water sprayed from the injection valve 76 is sprayed, the liquid flow flows into the inner wall of the evaporation cylinder 100 and is efficiently vaporized. The urea precipitation in the flue can be suppressed.
[Selection] Figure 4

Description

  The present invention relates to an exhaust treatment device, and more particularly to a technique for suppressing the deposition of a reducing agent (urea water) sprayed in a flue through which exhaust gas discharged from an engine flows.

  As a method for removing nitrogen oxides (hereinafter referred to as NOx) contained in exhaust gas from a diesel engine or the like, a selective reduction catalyst that selectively reacts NOx with a reducing agent is disposed in a flue through which exhaust gas flows, A technology is known in which a reducing agent (for example, hydrocarbon, ammonia or a precursor thereof) is added to the upstream exhaust gas, and the reducing agent is subjected to a reduction reaction with NOx on a selective reduction catalyst to reduce the NOx emission concentration. It has been.

  The NOx reduction method using this selective reduction catalyst is called SCR (Selective Catalytic Reduction), and the one using urea as a reducing agent is called urea SCR.

  As an example of applying this urea SCR to a vehicle, there is a technique in which urea water is injected into a flue from an injection nozzle, urea is hydrolyzed using exhaust heat, and NOx is reduced using generated ammonia. It is known (for example, refer nonpatent literature 1). In this case, for example, urea water is stored in the tank, urea water supplied from the tank and compressed air supplied from the vehicle side are mixed in the mixing chamber, and this is exhausted from the injection nozzle in the flue. To spray. Here, the urea water amount is adjusted by controlling the drive pulse width of the solenoid valve, and the compressed air amount is regulated by electronic control.

  Further, hydrolysis that promotes hydrolysis of urea water in at least one of the inner wall of the flue between the NOx reduction catalyst and the upstream injection nozzle, the inner wall of the injection nozzle, and the diffusion plate that diffuses the exhaust gas A technique is disclosed in which urea water is efficiently hydrolyzed to generate ammonia by applying a catalyst to improve denitration efficiency (see, for example, Patent Document 1).

  By the way, in such an SCR device, a predetermined amount of urea water commensurate with the amount of NOx generated from the engine is rapidly hydrolyzed to generate ammonia, which is uniformly dispersed in the exhaust gas, and then on the denitration catalyst. To be supplied to That is, in order to supply a predetermined amount of urea water (including ammonia) corresponding to the amount of NOx generated onto the denitration catalyst, all urea water is supplied promptly without precipitating the injected urea water along the route. There is a need to.

  For example, in Patent Document 1, urea water mixed with compressed air is injected from an injection nozzle at the tip of a pipe provided extending in a flue. For this reason, when the exhaust gas flowing in the flue is at a low temperature (when the engine is started), the urea water passing through the pipe is cooled, so that urea may be deposited in the injection nozzle, for example. In addition, since the outer wall portion of the flue is cooled by being exposed to the outside air, urea water injected into the flue may adhere to the inner wall surface of the flue, so that urea may be deposited on the inner wall surface of the flue .

  As described above, when urea is deposited in the injection nozzle, in the worst case, the injection nozzle is clogged, and it is difficult to supply urea into the flue. Further, when urea is deposited on the inner wall surface of the flue, the flow path pressure loss of the flue increases, and the fuel consumption of the engine is reduced. In addition, if urea precipitates before reaching the denitration catalyst, the amount (urea vapor and ammonia gas) reaching the denitration catalyst is less than the supply amount of urea water corresponding to the amount of NOx generated from the engine. Therefore, the denitration efficiency decreases.

  Moreover, in patent document 1, there exists a fixed effect in suppression of urea precipitation at the point which has apply | coated the hydrolysis catalyst to the inner wall of the exhaust pipe between an injection nozzle and a NOx reduction catalyst, the inner wall of an injection nozzle, etc. . However, the injection nozzle at the tip of the pipe arranged in the flue and the reducing agent supply device for supplying urea water arranged outside the flue are connected by the pipe and supplied from the reducing agent supply device. A certain time delay occurs until urea water is supplied into the flue through the injection nozzle. Further, the temperature distribution in this piping path may cause urea precipitation in a part of the piping.

  Therefore, as a method for solving such a problem, for example, a space retracted by a predetermined distance outside the inner wall surface of the flue is formed, and urea water is injected into the flue from an injection nozzle arranged in the space. The method of making it be studied.

  According to this, for example, as in Patent Document 1, it is not necessary to arrange the urea water supply pipe so as to extend into the flue, and the injection nozzle is not directly exposed to the high-temperature exhaust gas. Since the boiling of urea water can be suppressed in the inside, precipitation of urea can be suppressed in the urea water supply path including the injection nozzle.

Automotive Technology Vol. 57, no. 9 (2003) p. 94-99 JP 2005-105970 A

  By the way, when an injection nozzle is arranged in a space formed by retreating outward from the inner wall surface of the flue and urea water is injected, airflow is generated between the outer peripheral portion of the spray and the surface forming the space. May occur. Since this airflow is attracted by the spray and flows so as to involve a part of the fine droplets being sprayed, the fine droplets are accompanied by the airflow and adhere to the surrounding wall surface. Then, the droplets adhering to the wall surface are gradually accumulated and the droplets are combined with each other, and finally drop into the flue through the wall surface as a flow of urea water.

  That is, the liquid flow that has flowed out on the inner wall surface of the flue may cause precipitation of urea depending on, for example, the temperature condition in the flue.

  An object of the present invention is to provide an exhaust treatment apparatus that can quickly supply urea to the denitration catalyst without precipitating urea as a reducing agent in the flue.

  In order to solve the above problems, the present invention provides a denitration catalyst reactor that is provided in a flue through which exhaust flows and that reduces nitrogen oxides in the exhaust, and urea water in the flue upstream of the denitration catalyst reactor. In an exhaust treatment apparatus including an injection valve for injecting water, an evaporating cylinder surrounding a spray of urea water injected from the injection valve extends from the wall surface of the flue into the flue and is arranged.

  According to this configuration, the evaporating cylinder disposed in the flue is always exposed to the exhaust flow flowing in the flue, so that it receives heat from the exhaust and is heated to a high temperature. For this reason, for example, when a liquid flow is generated along with the spraying of urea water, the liquid flow flows into the evaporation cylinder along the inner wall surface of the evaporation cylinder, and vaporization is promoted in the process. Then, for example, urea water that has become fine droplets or vaporized urea on the inner wall surface of the evaporation cylinder is entrained in the exhaust flow and conveyed to the downstream denitration catalyst reactor.

  Thus, according to the present invention, the liquid flow of urea water is guided into the evaporation cylinder held at a high temperature using the heat of the exhaust gas, for example, after the liquid flow is vaporized by film boiling, the flow of the exhaust gas Therefore, urea water can be promptly supplied to the denitration catalyst without being precipitated in the evaporation cylinder or the flue.

  Specifically, in the present invention, the nozzle hole of the injection valve is arranged outside the inner wall surface of the flue to form a flow path that connects the nozzle hole and the inside of the flue, and this flow path is formed of the evaporation cylinder. It shall communicate with the space formed inside. That is, the urea water injected from the nozzle hole sequentially passes through the flow path and the evaporation cylinder and is introduced into the flue.

  In this case, the evaporation cylinder is formed, for example, so that the cross-sectional area in the injection direction of the urea water increases continuously or stepwise. According to this, for example, a liquid flow can be guided to the inner wall surface of the evaporation cylinder, and the liquid flow can be quickly vaporized and entrained in the exhaust flow without being deposited. In addition, since the fine droplets being sprayed can be uniformly dispersed in the exhaust gas without agglomerating, the efficiency of hydrolysis of urea water can be improved.

  The flow path is formed so that the cross-sectional area in the injection direction of the urea water increases continuously or stepwise. According to this, since the space between the outer periphery of the spray of urea water and the wall surface of the flow path can be reduced, the entrainment of the air flow due to the spray can be suppressed and the liquid flow can be hardly generated. In addition, in this way, by enlarging the cross-sectional area in the injection direction of the flow path and forming the evaporation cylinder in the same manner, the entrainment of the airflow can be effectively suppressed.

  According to the present invention, urea as a reducing agent can be quickly supplied to the denitration catalyst without precipitating in the flue.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a first embodiment of the invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining a urea supply device of an exhaust treatment device to which the present invention is applied and a flow of exhaust gas passing through the urea supply device. FIG. 2 is a configuration diagram of an injection valve that injects urea water into the flue in the urea supply device, its supply path, and cooling means. 3A, 3B, and 3C are respectively an external perspective view, a front view, and a side view of the urea supply device. 4A and 4B are cross-sectional views taken along the line BB in FIG. 3 and an enlarged view of a portion D in FIG. 4A, respectively. 5 (a) and 5 (b) are CC sectional views of FIG. 3 and an enlarged view of portion E of FIG. 5 (a), respectively. FIG. 6A shows a structure around the injection hole portion of a conventional injection valve, and FIGS. 6B and 6C show a structure around the injection hole portion of the injection valve to which the present invention is applied. .

  The exhaust treatment device of the present embodiment is installed on the upstream side of a urea supply device 50 for supplying urea water as a reducing agent into a flue through which exhaust exhausted from a diesel engine (not shown) flows, for example. A particulate removal device (DPF: Diesel Particulate Filter) 13 for removing particulates such as smoke particles and a denitration catalyst (SCR: Selective Catalytic) installed downstream of the urea supply device 50 to treat NOx in the exhaust gas Reduction: selective reduction type NOx catalyst) 19 is provided.

  The denitration catalyst 19 is a catalyst having a function of accelerating a reduction reaction of NOx in the exhaust 14 by urea water and its vapor or ammonia generated by a hydrolysis reaction and reducing the NOx emission amount. In addition, on the downstream side of the denitration catalyst 19, a flue, a muffler, and the like (not shown) are disposed and communicate with the outside air.

  The urea supply device 50 is provided with two main injection valves 76 and two sub injection valves 77 for supplying the urea water 4 to the flue 52 formed inside thereof. The main injection valve 76 is used when injecting the urea water 4 into the flue 52, and the sub injection valve 77 is used when injecting the urea water 4 into the heat transfer pipe 69 through which the diverted exhaust gas 64, which will be described later, passes. Used for.

  The end surface of the cylindrical taper member 124 is provided in contact with the outer wall of the flue 52. Inside the inner peripheral surface of the taper member 124, the spray 53 injected from the main injection valve 76 passes and the spray 53 does not collide directly, and the cross-sectional area of the spray 53 in the injection direction is continuous. A flow path 125 having an enlarged tapered side surface is formed.

  Further, an evaporation cylinder 100 forming a frustoconical space is connected to the wall surface of the flue 52 so as to extend into the flue 52, and the flow path 125 and the smoke are passed through the evaporation cylinder 100. The road 52 is in communication.

  A main holder 78 including a holder inner cylinder 90 and a holder outer cylinder 91 is disposed on the other end face side facing the end face of the taper member 124 in contact with the flue 52. The main holder 78 is formed with a cooling chamber 101 that is a multistage annular space in a region facing the outer peripheral portion of the main injection valve 76. The holder outer cylinder 91 is formed with a cooling water inlet 80 and a cooling water outlet 82 which are inflow / outflow openings for allowing urea water 84 to be described later to pass through the inside of the cooling chamber 101. The cooling water inlet 80 is disposed on the side close to the flue 52, the cooling water outlet 82 is disposed on the side away from the flue 52, and the center points of the respective openings are disposed at different positions. Yes.

  Between the end faces where the main holder 78 and the taper member 124 face each other, a heat insulating material 105 is disposed and a heat insulating space 107 is formed. A main injection valve 76 is disposed on the inner peripheral side of the holder inner cylinder 90 of the main holder 78.

  In the flue 52 in the injection direction of the spray 53 injected from the main injection valve 76, a plurality of collision plates 16 are disposed at positions where the spray 53 can collide. The first-stage and second-stage collision plates 16 on the side close to the main injection valve 76 are composed of perforated plates (punching plates) having a plurality of holes 36 formed therein. Further, the third-stage collision plate 16 disposed at a position farthest from the main injection valve 76 is configured by a plate in which a plurality of holes are not formed. Each of the collision plates 16 is attached at a predetermined angle with respect to the flow axial flow direction of the exhaust 14.

  Further, in the flue 52 of the urea supply device 50, a flue restriction 71 is formed in which the passage cross-sectional area is once reduced on the downstream side of the exhaust 14 from the position where the collision plate 16 is disposed. The throttle 71 is provided with swirl vanes 67 for generating a swirl flow in the flow of the exhaust 14. Further, a bypass passage is formed in the throttle 71 and the flue 52 on the upstream side thereof. In this passage, a branch pipe inlet 55 is opened on the upstream side of the throttle 71 so as to face the axial direction of the flow of the exhaust 14 flowing in the flue 52.

  The diversion pipe inlet 55 communicates with the swirl chamber 70 disposed on the downstream side thereof via the diversion pipe 56. The diversion pipe 56 is arranged eccentrically with respect to the outer wall portion of the swirl chamber 70. A heat transfer tube 69 is disposed downstream of the swirl chamber 70, and a hydrolysis catalyst 60 is disposed downstream of the heat transfer tube 69. A heating element 57 is disposed on the outer periphery of the heat transfer tube 69, and the vaporization of the spray 54 flowing in the heat transfer tube 69 is promoted by heating the heating element.

  The outlet portion 126 of the hydrolysis catalyst communicates with the dispersion chamber 61 that is a part of the annular space formed inside the wall 62 that surrounds the outer wall of the throttle 71. The dispersion chamber 61 communicates with the inside of the restrictor 71 through a nozzle hole 68 formed in the restrictor 71. That is, the inside of the flue 52 on the upstream side of the throttle 71 communicates with the nozzle hole 68 via the branch pipe inlet 55. Here, the nozzle hole 68 formed in the throttle 71 is disposed on the downstream side of the swirl vane 67.

  The sub holder 79 including the sub injection valve 77 is disposed on the outer wall of the swirl chamber 70 via the heat insulating material 106 and the heat insulation space 108, and the spray 54 injected from the sub injection valve 77 passes through the swirl chamber 70. Thus, it is injected into the heat transfer tube 69. Here, like the main holder 78 provided with the main injection valve 76, the sub holder 79 provided with the sub injection valve 77 includes a holder inner cylinder 92 and a holder outer cylinder 93, and the sub holder 79 includes A cooling chamber 102 that is a multistage annular space is formed so as to surround the sub injection valve 77. The holder outer cylinder 93 is formed with a cooling water inlet 81 and a cooling water outlet 83 which are inflow / outflow openings for allowing urea water 85 to be described later to pass through the inside of the cooling chamber 102.

  The cooling water inlet 81 is disposed on the side close to the swirl chamber 70, and the cooling water outlet 83 is disposed on the side far from the swirl chamber 70, and the opening center points are disposed at different positions. Between the end faces where the sub holder 79 and the swirl chamber 70 face each other, a heat insulating material 106 is disposed and a heat insulating space 108 is formed. A sub injection valve 77 is arranged on the inner peripheral portion of the holder inner cylinder 92 of the sub holder 79.

  Next, the urea water supply path to the main injection valve 76, the sub injection valve 77, the main holder 78, and the sub holder 79 and the cooling means for each injection valve according to this embodiment will be described with reference to FIG.

  First, the supply path of the urea water 4 will be described. The urea water 4 stored in advance in the urea water tank 3 is sucked by the pump 6 through the filter 5, and then the urea water 4 discharged from the pump 6 is supplied into the pipe 97. The pipe 97 is branched into pipes 98 and 99, and communicates with the main injection valve 76 and the sub injection valve 77 through the injection valve inlets 88 and 89. Thereby, the urea water 4 is supplied to the main injection valve 76 and the sub injection valve 77 as urea water 109 and 110 by a predetermined pressure, respectively.

  Here, the pressure adjustment to the main injection valve 76 and the sub injection valve 77 is performed by opening and closing the pressure adjusting valve 7 disposed in the pipe 94 branched from the pipe 97. By the opening / closing operation of the pressure regulating valve 7, the urea water 84 that has passed through the pressure regulating valve 7 is supplied into the cooling chamber 101 through the cooling water inlet 80 of the main holder 78 after passing through the pipe 94.

  The urea water 84 supplied into the cooling chamber 101 flows into the pipe 95 using the cooling water outlet 82 as the urea water 85, and then supplied into the cooling chamber 102 via the cooling water inlet 81 of the sub holder 79. The urea water 85 supplied into the cooling chamber 102 is configured to flow into the pipe 96 using the cooling water outlet 83 as the urea water 87 and return to the urea water tank 3. The circulation path of the cooling water that has passed through the pressure regulating valve 7 passes through the cooling chambers 101 and 102 of the sub-holder 79 via the main holder 78, but the reverse is also possible.

  In the present embodiment, urea as a reducing agent is used in a relatively wide operating range from a low load region with a low exhaust temperature and small displacement, such as when the engine is started, to a high load region with a high exhaust temperature and a large displacement. Since the water can be quickly supplied to the denitration catalyst 19 without precipitating water, the supply form of urea water supplied from the urea supply device 50 into the flue 52 can be changed.

  That is, at the time of high exhaust temperature, the supply of the urea water spray 53 from the main injection valve 76 is mainly performed, and the spray 53 is collided with the plurality of collision plates 16 to promote dispersion in the flue 52 and the high temperature. After the vaporization is promoted by the collision with the collision plate 16 disposed in the exhaust 14 and the heat of the exhaust 14, the denitration catalyst 19 is supplied to obtain high denitration performance.

  On the other hand, when the exhaust gas temperature is low, the spray 54 is actively vaporized mainly by the supply of the urea water spray 54 from the sub-injection valve 77 by the heat of the heating element 57 disposed on the outer periphery of the heat transfer tube 69. Then, by allowing the hydrolysis catalyst 60 to pass through, the ammonia gasification of the urea water spray 54 is promoted, followed by promoting the mixing with the exhaust 65, and then supplying the denitration catalyst 19 to obtain high denitration performance. .

  As described above, in this embodiment, by changing the supply form of the urea water supplied from the urea supply device 50 into the flue 52 according to the operation state of the engine, high denitration performance is achieved in the entire operation region of the engine. Is to secure.

  Next, the supply of the urea water spray 53 supplied from the main injection valve 76 mainly used at the high exhaust temperature to the denitration catalyst 19 will be described.

  In the exhaust treatment device of the present embodiment, the exhaust 14 that has passed through the DPF 13 is supplied into the flue 52 of the urea supply device 50. Here, the plurality of collision plates 16 disposed in the flue 52 do not cause the urea water spray 53, which is a reducing agent of NOx injected from the main injection valve 76, to deposit in the flue 52, This is to efficiently distribute and supply the catalyst to the denitration catalyst 19.

  In other words, the plurality of collision plates 16 disposed in the exhaust 14 having a high exhaust temperature receive heat from the exhaust 14 and have the same temperature as the temperature of the exhaust 14. Here, from the main injection valve 76 built in the main holder 78, urea water 109 corresponding to the amount of NOx contained in the exhaust 14 is sprayed as the spray 53 toward the plurality of collision plates 16. At this time, the droplets in the spray 53 that have collided with the high-temperature collision plate 16 take the form of film boiling on the collision plate 16 to promote evaporation. Therefore, an air layer is interposed between the droplets in the spray 53 and the collision plate 16, and the spray 53 does not adhere to the collision plate 16, so that precipitation of urea can be prevented without generating a liquid flow.

  Further, the spray 53 injected toward the plurality of collision plates 16 is collided with the collision plates 16 to promote dispersion in the flue 52. That is, the droplet group of the spray 53 collides according to the opening ratio of the collision plate 16 in which the plurality of holes 36 in the first stage are drilled, and is reflected toward the downstream direction of the flue 52 while being promoted to vaporize. The droplet group in the spray 53 that has passed through the hole 36 formed in the first stage collision plate 16 without colliding with the first stage collision plate 16 collides with the second stage collision plate 16, and vaporization is promoted. Reflects in the downstream direction of the road 52. Further, the remaining droplet group in the spray 53 that does not collide with the second-stage collision plate 16 and passes through the hole 36 formed therein has a plate-like shape in which the third-stage hole 36 is not formed. It collides with the collision plate and promotes vaporization. In this way, each collision plate 16 is responsible for vaporizing and reflecting the droplets of the spray 53. In addition, the collision plate 16 disposed in the flue 52 can suppress the collision of the droplets of the spray 53 onto the inner wall surface of the flue 52 and prevent urea precipitation on the inner wall surface of the flue 52.

  Further, between each collision plate 16, the exhaust 14 flows toward the denitration catalyst 19, and droplets reflected by the collision plate 16 ride on the air flow of the exhaust 14 and are efficiently conveyed to the denitration catalyst 19. The At this time, the spray 53 of urea water injected into the flue 52 is accelerated by hydrolysis along with evaporation of the droplets of the spray 53 due to collision with the collision plate 16 and transfer of heat from the exhaust heat, and ammonia gas. Generation is promoted.

  Further, the flue 52 on the downstream side of the collision plate 16 communicates with a restriction 71 having a reduced passage cross-sectional area, and a swirl vane 67 is disposed in the restriction 71. The spray 53 dispersed by the impingement plate 16 is accompanied by the air flow of the exhaust gas 14 and passes through the throttle 71 part, so that the flow velocity increases, and the disturbance of the flow at the throttle 71 due to passing through the swirl vane 67 causes Mixing of the exhaust 14 and the spray 53 is promoted.

  Due to the effects of the collision plate 16, the throttle 71 and the swirl vane 67, the spray 53 injected from the main injection valve 76 is accelerated by the hydrolysis reaction by the high-temperature exhaust gas 14 and moisture contained in the exhaust gas, and is converted into ammonia gas. As a result, the spray of urea water, steam and ammonia can be supplied almost uniformly to the denitration catalyst 19, and high denitration performance can be obtained.

  In the present embodiment, the collision plate 16 is configured in three stages, but is not limited thereto. For example, the collision plate 16 may be composed of three or more stages. Furthermore, the ratio of the spray 53 reflected by the collision with the collision plate 16 may be adjusted by changing the aperture ratio of the hole 36 formed in the collision plate 16 for each step number. Moreover, although the plate | board without the hole 36 was arrange | positioned in the lowest step of the collision board 16 comprised in multiple steps, this is good also as the collision board 16 which is a perforated board.

  By setting them appropriately, the degree of dispersion of the reducing agent in the denitration catalyst 19 can be adjusted, and the denitration catalyst 19 can be used efficiently.

  Next, the flow until the urea water spray 54 injected from the sub injection valve 77 reaches the denitration catalyst 19 will be described.

  The diverted exhaust gas 64 flowing in from the diverter tube inlet 55 flows into the swirl chamber 70 through the diverter tube 56 and flows into the heat transfer tube 69 while forming a swirl flow. On the other hand, the spray 54 of urea water is injected from the sub injection valve 77 toward the heat transfer tube 69 through the inside of the swirl chamber 70. Here, since the shunt exhaust 64 forms a swirl flow and flows into the heat transfer tube 69, the passage pressure loss can be reduced as compared with the case where the flow is bent at a right angle and passes through the tube, and the shunt exhaust 64 is efficiently transferred into the heat transfer tube 69. It becomes possible to flow into. Furthermore, since the spray 54 injected into the heat transfer tube 69 can be forcibly brought into contact with the inner wall of the heat transfer tube 69 by the swirling flow, the time for which the droplets in the spray 54 are brought into contact with the inner wall surface of the heat transfer tube 69 is expanded. Therefore, the spray 54 can be efficiently vaporized.

  The urea vapor 58 promoted to vaporize in the heat transfer tube 69 is promoted to be hydrolyzed by the heat of the divided exhaust 64 and the heat supplied from the heating element 57 into the heat transfer tube 69. Furthermore, by passing through the hydrolysis catalyst 60, the hydrolysis reaction is further promoted, and ammonia gasification of urea water can be achieved. The mixed gas 59 that promotes the ammonia gasification of the spray 54 is supplied into the dispersion chamber 61, attracted to the mainstream exhaust 65 from the plurality of nozzle holes 68, and supplied into the throttle 71. This is because the static pressure on the throttle 71 side is lowered by the amount of pressure loss of the heat transfer tube 69 due to the throttle 71 through which the main flow exhaust 65 passes, and the flow rate of the split exhaust 64 in the heat transfer tube 69 is ensured.

  By passing through the throttle 71, the flow velocity of the main exhaust 65 is faster than the flow velocity of the exhaust 14. Further, by passing through the arranged swirl vane 67, the flow of the main exhaust 65 downstream of the swirl vane 67 is locally disturbed to form a swirl flow and promote mixing with the mixed gas 59. Then, high NOx removal performance can be obtained by passing the exhaust gas 66 in which the mainstream exhaust gas 65 and the mixed gas 59 containing ammonia gas are promoted to the NOx removal catalyst 19.

  The temperature of the exhaust 14 from the engine changes depending on the engine load, and when the temperature of the exhaust 14 is high, the urea water is rapidly vaporized and hydrolyzed by the heat obtained from the exhaust 14 even if the urea water is directly injected. Then, a necessary amount of ammonia gas as a reducing agent is supplied to the denitration catalyst 19, but when the temperature of the exhaust 14 is low, ammonia gasification of urea water does not proceed and the reduction reaction at the denitration catalyst 19 is sufficient. Will not advance. For this reason, generally, when the temperature of the exhaust 14 is low, the NOx reduction rate deteriorates.

  As a countermeasure, the heat transfer tube 69 is used to promote the ammoniation of urea water by two functions of heating by the heating element 57 and promotion of the reaction by the hydrolysis catalyst 60, and assist in removing NOx at a low temperature. Further, when the temperature of the exhaust 14 is high, the main injection that injects the urea water spray 53 directly into the exhaust 14 without performing the injection of the urea water spray 54 from the sub-injection valve 77 disposed in the branch pipe 56. By adding urea water using only the valve 76, the heating element 57 is prevented from consuming extra energy. Further, with regard to reaction assistance by heating at low temperatures, the energy consumed by the heating element 57 is reduced by heating only the divided exhaust 64 instead of heating the entire exhaust 14.

  Next, the taper member 124 disposed on the outer wall portion of the flue 52, the main holder 78 disposed in the swirl chamber 70, the main injection valve 76 of the sub holder 79, and the heat insulation and cooling means of the sub injection valve 77 will be described. To do. Since the basic cooling means is the same for both the main holder 78 and the sub holder 79, the main holder 78 incorporating the main injection valve will be described here, and the description regarding the sub holder 79 will be omitted.

  Direct injection of the urea water 109 from the main injection valve 76 into the flue 52 of the urea supply device 50 as the spray 53 is very effective in quickly supplying the reducing agent into the flue 52. However, the hot exhaust 14 flows in the flue 52. The outer wall portion of the flue 52 is also hot. Therefore, if the main injection valve 76 is directly disposed on the outer wall portion of the flue 52, the operating environment of the main injection valve 76 may be significantly exceeded. That is, when the main injection valve 76 is a solenoid valve, a coil or a magnetic circuit for driving the solenoid valve may be damaged by heat and cause malfunction. Further, when urea water boils in the injection hole (hereinafter, referred to as a nozzle as appropriate) of the main injection valve 76, urea precipitation occurs. Urea precipitation in the nozzle results in a change in the injection amount characteristic of the main injection valve 76, a change in the shape of the spray 53, and the like, so that the predetermined performance with respect to the main injection valve 76 cannot be maintained. In addition, the NOx reduction rate (denitration rate) in the exhaust 14 discharged from the engine is significantly deteriorated. If the nozzle is completely clogged by precipitation, the spray 53 cannot be supplied into the flue 52.

  In order to improve them, in this embodiment, means for suppressing heat transfer from the exhaust 14 and the flue 52 to the main injection valve 76 and means for cooling the main injection valve 76 are provided.

  The means will be described below. First, urea water 84 that is a cooling fluid passing through the cooling chamber 101 formed in the main holder 78 is supplied from the high temperature side to the low temperature side of the cooling chamber 101. That is, the cooling water inlet 80 is disposed on the side close to the flue 52, and the cooling water outlet 82 is disposed at a position away from the flue 52. Therefore, it is possible to supply the lower temperature urea water 84 to a higher temperature portion in the cooling chamber 101, and each temperature gradient becomes steep, which is effective in reducing the temperature of the high temperature portion in the cooling chamber 101.

  Second, the center positions of the openings of the cooling water inlet 80 and the cooling water outlet 82 are made different, and the cooling chamber 101 that is a multistage annular space is formed so as to surround the main injection valve 76, and passes through the cooling chamber 101. A swirling flow is efficiently generated in the urea water 84. As a result, stagnation is less likely to occur due to the flow of the urea water 84 in the cooling chamber 101, and a local temperature increase in the cooling chamber 101 can be prevented. Furthermore, a swirl flow is formed along the outer periphery of the main injection valve 76, and the cooling performance of the nozzle, coil part, magnetic circuit part, etc. of the main injection valve 76 is enhanced.

  Thirdly, the urea water 84 flowing from the cooling water inlet 80 is low in temperature, but the temperature rises in the cooling chamber 101 by passing through the cooling chamber 101. The temperature of the urea water 85 at the cooling water outlet 82 is higher than the temperature of the urea water 84 at the cooling water inlet 80. Therefore, the cooling effect by the urea water 84 in the cooling chamber 101 tends to decrease as it goes near the cooling water outlet 82. Therefore, when the temperature of the urea water 84 near the cooling water inlet 80 is relatively low, for example, in order to reduce the flow rate of the urea water 84 flowing through the cooling chamber 101, the urea water is supplied to a relatively wide space and the cooling water is supplied. In the place where the urea water temperature near the outlet 82 rises, the urea water 84 flows in a relatively narrow space in order to increase the flow rate of the urea water 84 flowing through the cooling chamber 101.

  That is, urea having a relatively high temperature on the cooling water outlet 82 side by increasing the flow velocity by reducing the passage cross-sectional area through which the urea water 84 passes through the cooling chamber 101 and increasing the heat transfer coefficient. Water 84 can also promote cooling.

  Further, in order to protect the main injection valve 76 from the high-temperature exhaust 14 and the flue 52, in this embodiment, the heat insulating material 105 and the taper member 124 are disposed between the outer wall portions of the main holder 78 and the flue 52 facing each other. . By disposing the heat insulating material 105 and the tapered member 124, the amount of heat conducted from the flue 52 to the main holder 78 can be reduced.

  Further, by providing the taper member 124, the nozzle hole of the spray 53 injected from the main injection valve 76 can be arranged at a position away from the flue 52, and the exhaust 14 flowing in the flue 52 The influence of heat can be reduced. Further, a heat insulating space 107 is formed between the main holder 78 and the taper member 124 for the purpose of reducing the amount of heat transferred from the exhaust 14 to the main holder 78. The heat insulating space 107 is formed by a part of the outer wall of the taper member 124 and a part of the outer wall of the holder inner cylinder 90 of the main holder 78. Further, the protrusion 122 formed on the holder inner cylinder 90 does not contact the taper member 124, forms an annular narrow gap 120, and the heat insulating space 107 and the internal space of the taper member 124 and the inside of the flue 52 communicate with each other. It is. Accordingly, heat conduction from the taper member 124 to the protrusion 122 formed on the holder inner cylinder 90 is suppressed, so that the temperature rise of the nozzle of the main injection valve 76 disposed in the protrusion 122 can be suppressed.

  Here, in the case where the taper member 124 and the protrusion 122 are in contact with each other, the heat from the high-temperature exhaust 14 is transferred to the flue 52 and then thermally conducted through the wall surface of the flue 52, via the taper member 124. The heat is conducted to the protrusion 122 of the holder inner cylinder 90. And since the temperature around the protrusion 122 of the holder inner cylinder 90 rises, the temperature of the nozzle tip of the main injection valve 76 is raised. As a result, the urea water temperature in the nozzle is raised and there is a concern about urea precipitation due to boiling of the urea water. Further, if the heat insulating space 107 is a sealed space and the sealed space is filled with air, the pressure in the sealed space increases due to the expansion of the air in the sealed space as the temperature of the exhaust gas 14 rises. Since a useless force is generated inside, it is not preferable from the viewpoint of safety. For this reason, even when the annular gap 120 cannot be formed, for example, it is preferable to make a small hole and communicate with the inside or outside of the exhaust 14.

  Next, a technique for preventing urea precipitation in the flue due to generation of a liquid flow accompanying the urea water spray 53 will be described with reference to FIG.

  First, in the conventional example, as shown in FIG. 6A, the nozzle of the main injection valve 76 is arranged outside the inner wall surface of the flue 52, and a cylindrical flow that communicates with the nozzle and the inside of the flue 52. The path 133 is formed on the inner peripheral side of the cylindrical member 134 and has a uniform cross-sectional area in the urea water injection direction. By disposing the cylindrical member 134 between the main holder 78 and the outer wall surface of the flue 52, the main injection valve 76 can be thermally protected, and the boiling of urea water in the nozzle is suppressed, Urea precipitation can be prevented. Furthermore, since the coil portion and the magnetic circuit portion of the main injection valve 76 that is an electromagnetic valve can be protected, a predetermined amount of the urea water spray 53 can be stably supplied.

  The spray 53 injected from the main injection valve 76 is injected into the flue 52 through the flow path 133. However, when the spray 53 injected from the main injection valve 76 is injected into the flow path 133, an air flow is generated around the spray 53 as shown by the arrows in the drawing.

  This is because the spray 53 is ejected at a relatively high flow rate, so that the airflow around the spray 53 is attracted to the spray 53 and a flow of airflow as indicated by an arrow is generated. Then, when some of the fine droplets in the spray 53 are involved in the flow of the air flow, a phenomenon of entrainment of the fine droplets occurs around the spray 53. Here, a space in which this entrainment phenomenon occurs is called an entrainment space. Due to this phenomenon, the entrained fine droplets adhere to the periphery of the nozzle of the main injection valve 76, the wall portion 135 of the flow path 133, and the like. The adhering fine droplets are gradually accumulated, and the droplets are combined to finally form a liquid flow 136 of urea water, which drips into the flue 52 from the wall 135 or the like. The urea water dripping into the flue 52 evaporates only the water of the urea water on the inner wall surface of the flue 52 and precipitates urea.

  As a countermeasure, in this embodiment, as shown in FIG. 5B, the nozzle of the main injection valve 76 is arranged outside the inner wall surface of the flue 52, and the cone communicates with the inside of the flue 52. The trapezoidal flow path 125 is formed on the inner peripheral side of the taper member 124 so that the cross-sectional area in the injection direction of the urea water continuously increases. By disposing the taper member 124 between the main holder 78 and the outer wall surface of the flue 52, the main injection valve 76 can be thermally protected.

  Here, the spray 53 injected from the main injection valve 76 is injected into the flue 52 via the flow path 125. The flow path 125 has, for example, a tapered shape that follows the outer periphery of the spray 53. Therefore, the entrainment space of the spray 53 can be reduced, and even when the spray 53 is ejected at a relatively high flow rate, the airflow around the spray 53 is not attracted as compared with the conventional example, and the phenomenon of entrainment of fine droplets is caused. Can be reduced. Therefore, the adhesion of fine droplets to the inner wall surface of the flow path 125 can be greatly reduced.

  In addition, although the flow path 125 of this embodiment is formed so that the cross-sectional area of the injection direction of urea water may become large continuously, for example, even if it is formed so that a cross-sectional area may become large in steps. Good.

  An evaporation cylinder 100 is disposed downstream of the flow path 125 in the injection direction, and the flow path 125 communicates with a space 104 formed inside the inner wall surface of the evaporation cylinder 100. That is, the evaporation cylinder 100 is formed to extend from the wall surface of the flue 52 into the flue, is in contact with the exhaust 14 that passes through the flue 52, and the spray 53 passes through the space 104. The space 104 is formed so that the cross-sectional area in the spraying direction of the spray 53 is enlarged, and is formed of, for example, a thin plate in consideration of heating efficiency.

  Here, if a small droplet adheres to the inner wall surface of the flow path 125 to some extent and a liquid flow is generated, the liquid flow flows into the space 104 along the inner wall surface of the evaporation cylinder 100. Here, the evaporation cylinder 100 is kept at a high temperature because it always receives heat from the exhaust 14 by contacting the high-temperature exhaust 14 flowing in the flue 52. That is, the liquid flow that has flowed into the space 104 of the evaporation cylinder 100 is promoted to vaporize, for example, in the form of film boiling without causing precipitation of urea. Thereby, the liquid flow of urea water does not flow into the flue 52, and urea precipitation can be prevented. The space 104 may be formed by continuously expanding the cross-sectional area of the spraying direction of the spray 53, or may be formed by expanding stepwise.

  Next, another embodiment of the present invention will be described with reference to FIG.

  In the present embodiment, the shape of the evaporation cylinder 75 is different from that in FIG. The evaporation cylinder 100 of FIG. 6B has a shape in which the cross-sectional area in the injection direction of the spray 53 is enlarged, whereas the evaporation cylinder 75 of the present embodiment has a cross-sectional area of the space formed inside the inner wall surface. Is formed in a uniform cylindrical shape in the injection direction. Thereby, the improvement of productivity and assembly property is achieved. In addition, since this embodiment has the substantially same effect as FIG.6 (b) mentioned above, description of each part is abbreviate | omitted.

  The evaporation cylinders 75 and 100 of the above-described embodiments may be formed of, for example, a perforated plate having a plurality of holes. According to this, when the exhaust gas 14 passes through the hole, an air flow is formed to promote the vaporization of the urea liquid flow, and the vaporized urea or urea water droplets are promptly accompanied by the flow of the exhaust gas 14. Can be made.

  Further, in the above-described embodiment, the flow path 125 communicating with the nozzle and the inside of the flue 52 is formed so that the cross-sectional area in the injection direction of the urea water increases continuously or stepwise. The space between the outer periphery of the spray and the wall surface of the flow path 125 can be reduced, and the entrainment of the air flow due to the spray can be suppressed and the generation of the liquid flow can be minimized. For example, even if a liquid flow is generated and flows out from the flow path 125, the heat of the exhaust 14 can be introduced into the evaporation cylinder 100 heated to a high temperature to promote vaporization. A predetermined amount of urea (including ammonia) can be rapidly supplied to the denitration catalyst without being deposited in the flue.

  In addition, according to the above-described embodiment, it is possible to prevent clogging of the injection valve for injecting urea water as a reducing agent, and to protect the coil and magnetic circuit of the injection valve from exhaust heat. A spray of urea water can be supplied directly from the injection valve into the flue. Further, NOx can be removed at a high denitration rate in a temperature range from a low temperature range to a high temperature range of the exhaust temperature.

  Further, the present invention can be widely applied in the field of development and use of diesel engines including, for example, the automobile industry.

It is a figure explaining the flow of the exhaust gas which passes through the urea supply apparatus of the exhaust-gas treatment apparatus which applies this invention, and its inside. It is a block diagram of the injection valve which injects urea water in a flue, its supply path | route, and a cooling means in the urea supply apparatus of FIG. (A), (b) and (c) show the external appearance perspective view, the front view, and the side view of a urea supply apparatus, respectively. (A), (b) shows the BB sectional view of Drawing 3, and the D section enlarged drawing of Drawing 4 (a), respectively. (A), (b) shows CC sectional drawing of FIG. 3, respectively, and the E section enlarged view of FIG. 5 (a). (A) shows the structure around the nozzle of the conventional injection valve, and (b) and (c) are diagrams showing the structure around the nozzle of the injection valve to which the present invention is applied.

Explanation of symbols

3 Urea water tank 4 Urea water 5 Filter 6 Pump 13 DPF
14 Exhaust 16 Collision plate 19 Denitration catalyst 52 Flue 53, 54 Spray 60 Hydrolysis catalyst 67 Swirling blade 69 Heat transfer tube 71 Restriction 75, 100 Evaporating cylinder 76 Main injection valve 77 Sub injection valve 78 Main holder 79 Sub holder 101, 102 Cooling Chamber 107, 108 Thermal insulation space 124 Tapered member 125 Flow path 134 Cylindrical member

Claims (4)

Exhaust gas provided with a denitration catalyst reactor provided in a flue through which exhaust flows and reducing nitrogen oxide in the exhaust gas, and an injection valve for injecting urea water into the flue upstream of the denitration catalyst reactor In the processing device,
An exhaust treatment device, wherein an evaporating cylinder surrounding the spray of urea water injected from the injection valve extends from the wall surface of the flue into the flue. The injection hole of the injection valve is arranged outside the inner wall surface of the flue, and a flow path is formed to communicate the injection hole and the inside of the flue, and the flow path is formed inside the evaporation cylinder. The exhaust treatment apparatus according to claim 1, wherein the exhaust treatment apparatus communicates with a space to be formed. The exhaust treatment device according to claim 1 or 2, wherein the evaporation cylinder is formed so that a cross-sectional area in the injection direction of the urea water increases continuously or stepwise. The exhaust treatment device according to claim 2, wherein the flow path is formed so that a cross-sectional area in the injection direction of the urea water increases continuously or stepwise.

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