JP2008267269A - Exhaust treatment device for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust treatment device supplying urea as a reducer for reducing NOx discharged from a diesel engine, vaporizing it and then facilitating hydrolysis by efficiently supplying heater heat, and supplying generated ammonia gas to a NOx removal catalyst. <P>SOLUTION: For gasifying an urea water spray 35 serving as the reducer into the ammonia gas with a heater 43, a swirling flow is formed in a heat transfer tube 42, and a heat transfer tube throttle 48, a collision member 49 and a hydrolysis catalyst 44 are arranged. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust treatment apparatus for an engine, and in particular, in an exhaust treatment apparatus for efficiently removing nitrogen oxides in exhaust using urea water as a reducing agent, urea water is removed by heater heat as a heating element. It relates to technology that promotes efficient vaporization.

  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, and this upstream A technique is known in which a reducing agent (for example, hydrocarbon, ammonia or a precursor thereof) is added to the exhaust on the side, and the reducing agent is subjected to a reduction reaction with NOx on a selective reduction catalyst to reduce the NOx emission concentration. .

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

  As an example of applying this urea SCR to a vehicle, a technique is known 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. (See, for example, Non-Patent Document 1). In this case, for example, the urea water is stored in a tank, the urea water supplied from the tank and the compressed air supplied from the vehicle side are mixed in the mixing chamber, and this is discharged into the exhaust from the injection nozzle in the flue. 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, an exhaust treatment device comprising an exhaust flue of an engine, a denitration catalyst reactor provided in the exhaust flue, and an injection valve for injecting and supplying urea water, provided with an exhaust gas diversion means, The first injection valve that injects urea water into the flow path of the split flow exhaust gas is provided with a vaporizer that heats the injected urea water to form urea vapor, and the second injector injects urea water downstream of the vaporizer. An injection valve is installed, urea vapor generated from urea water spray injected from the first injection valve at low exhaust temperature is supplied to the exhaust flue, and injection from the second injection valve at high exhaust temperature There is an engine exhaust treatment device configured to supply the urea water spray that has been supplied to the exhaust flue (see, for example, Patent Document 1).

JP 2006-170013 A Automotive Technology Vol. 57, no. 9 (2003) p. 94-99

  By the way, in the SCR device as described above, a predetermined amount of urea water commensurate with NOx discharged from the engine is almost uniformly added to the denitration catalyst and rapidly hydrolyzed to produce ammonia, and NOx and NOx on the denitration catalyst. It is required to be able to react. In order to reduce NOx more efficiently, it is preferable to ammonia the urea water before reaching the denitration catalyst and to disperse the ammonia almost uniformly in the denitration catalyst.

  For example, in Non-Patent Document 1, the urea water mixed with compressed air is disposed in the vicinity of the center of the flue upstream of the denitration catalyst by placing an injection nozzle at the tip of a pipe provided extending in the flue. The dispersibility of urea water in the denitration catalyst is improved. Here, the spray sprayed hydrolyzes urea water using exhaust heat, and NOx is reduced by ammonia generated thereby. This can be said to be effective in terms of NOx reduction at high exhaust temperatures. However, in the case of low exhaust temperatures, hydrolysis due to the exhaust heat of urea water injected into the flue cannot be promoted. There is a concern about the decline.

  Further, in Patent Document 1, urea water spray injected from a first injection valve at a low exhaust temperature is supplied into an exhaust flue after generating urea vapor by a vaporizer, and the urea spray is supplied at a high exhaust temperature. There are some which supply urea water spray injected from the injection valve 2 directly into the exhaust flue. This presumes that high NOx removal performance can be obtained in the entire engine operating range from the low exhaust temperature to the high exhaust temperature of the engine. The carburetor is composed of a heat transfer tube and a heater, and forms a swirl flow in the exhaust gas flowing into the heat transfer tube to promote vaporization of urea water, and urea water injected from the first injection valve during this swirl flow Supplying spray. As a result, urea water droplets during the spraying of urea water are guided to the inner wall surface of the heat transfer tube, and the time for contacting the droplets on the inner wall surface of the heat transfer tube is secured to promote vaporization.

  However, there is a distribution in the spray particle size in the urea water spray injected from the first injection valve. Since spray droplets having a distribution exist from minute droplets to coarse droplets, all the spray droplets do not always pass along the inner wall surface of the heat transfer tube along with the swirling flow flowing in the heat transfer tube. That is, coarse droplets (droplets with heavy mass) injected from the first injection valve at a predetermined pressure do not accompany the swirl flow and are downstream in the injection direction when injected at a predetermined flow velocity. There is a concern that it will be sprayed linearly to the side and pass through the vaporizer without contacting the inner wall surface of the heat transfer tube. As a result, vaporization of coarse droplets during spraying is not promoted, and there is a concern that the promotion of vaporization of urea water is reduced.

  Therefore, urea water injected into the flue is efficiently hydrolyzed and ammonia is generated in the entire operation range from low exhaust temperature to high exhaust temperature of the engine, and a high NOx reduction rate (denitration rate) is ensured. In order to achieve this, it is important to secure a NOx reduction rate at a low exhaust temperature. In order to secure a NOx reduction rate at a low exhaust temperature, it is important to convert urea water into ammonia gas by hydrolysis and supply it to the denitration catalyst.

  An object of the present invention is to provide a heater heat for spraying (mainly sprayed coarse droplet group) that does not contact the inner wall surface of the heat transfer tube during the urea water spray injected into the vaporizer composed of the heat transfer tube and the heater. It is an object of the present invention to provide an exhaust treatment apparatus that can efficiently supply and vaporize and then promote hydrolysis and supply the generated ammonia gas to a denitration catalyst.

  In order to achieve the above object, an exhaust treatment apparatus for an engine according to the present invention is an exhaust treatment apparatus for an engine for reducing nitrogen oxide in exhaust gas, and an injection valve for injecting urea water into the exhaust gas. And a vaporizer with a heater for vaporizing the urea water injected from the injection valve, and the vaporizer is configured such that a heater is disposed on the outer periphery of the heat transfer tube, and the urea water is contained in the heat transfer tube. In the engine exhaust treatment apparatus for supplying urea water vaporized by the carburetor into the flue, a collision member which is a perforated plate is disposed in the heat transfer tube.

  At this time, it is preferable to arrange a throttle in the heat transfer tube and arrange the collision member downstream thereof.

  Moreover, it is good to arrange | position the fixed swirl | blade for swirling exhaust gas in a heat exchanger tube in the heat exchanger tube upstream end part.

  The throttle and the impingement member have a parallel portion having a predetermined length in the axial direction of the heat transfer tube as they come into contact with the inner wall surface of the heat transfer tube, and the constriction or the collision member is brought into the heat transfer tube by the parallel portion. While fixing, it is good to enlarge the contact area which contacts a heat-transfer tube inner wall surface, the said aperture_diaphragm | restriction, and the said collision member.

  In addition, an outer cylinder is disposed on the outer periphery of the heater disposed on the outer periphery of the heat transfer tube, which is a vaporizer, and a heat insulating layer that is a space is formed between the outer periphery of the heater and the inner wall surface of the outer cylinder, and the heat insulating layer It is good to communicate with the inside of the heat transfer tube and the heat transfer tube outlet.

  Moreover, it is good to arrange | position a hydrolysis catalyst in the said heat exchanger tube downstream of the said collision member or the said aperture | diaphragm, or its downstream side.

  The temperature of the inner wall surface of the vaporizer may be adjusted to a temperature at which the urea water boils in the vaporizer with the heater.

  According to the present invention, it is possible to efficiently supply heater heat to the urea water spray that passes through the heat transfer tube, which is a vaporizer, at a low exhaust temperature, and ammonia is generated by efficiently vaporizing the urea water spray. After that, since it is supplied to the denitration catalyst, high denitration performance at a low exhaust temperature can be ensured. Therefore, a high denitration rate can be ensured in the entire operation region from the low exhaust temperature to the high exhaust temperature of the engine.

  Examples of the present invention will be described below.

  FIG. 1 is a diagram showing an overall configuration of an exhaust treatment device according to an embodiment of the present invention and its peripheral configuration, and FIG. 2 is an external perspective view of a urea addition device 70 shown in part A of the exhaust treatment device shown in FIG. The figure is shown. FIGS. 3A and 3B are views in the B direction and the C direction of the external perspective view of the urea addition device 70 shown in FIG. 2, respectively. FIG. 4 is an EE cross-sectional view of the urea addition device 70 shown in FIG. FIG. 5 is a DD cross-sectional view of the urea addition device 70 shown in FIG. FIG. 6 is an enlarged view of a portion F of the urea addition device 70 shown in FIG. FIGS. 7A, 7B, and 7C are perspective views of the heat transfer tube throttle 48, the heat transfer tube impingement member 49, and the heat transfer tube swirl blade 30 disposed in the heat transfer tube 42 of the urea addition device 70, respectively. . Moreover, FIG. 8 is a figure which shows the urea treatment rate of the heat exchanger tube part of the urea addition apparatus 70 of this invention.

The exhaust treatment device of the present embodiment includes, for example, a urea addition device 70 for supplying urea water as a reducing agent into a flue through which the exhaust 12 discharged from the diesel engine 1 flows, and a black upstream. Fine particle removal device DPF (Diesel) for removing fine particles such as smoke particles
Particulate Filter) 17 and a denitration catalyst (SCR: Selective Catalytic Reduction) 18 for treating NOx in the exhaust gas, which is disposed on the downstream side of urea addition device 70, is configured.

  The denitration catalyst 18 is a catalyst having a function of promoting NOx reduction reaction in the exhaust 12 by urea water, its vapor, and ammonia generated by a hydrolysis catalytic reaction to reduce NOx emission. In addition, on the downstream side of the denitration catalyst 18, a flue, a muffler, and the like (not shown) are disposed and communicate with the outside air.

  The urea addition device 70 is provided with two main injection valves 26 for supplying urea water 4 into the flue 10 formed therein and two sub injection valves 27. The main injection valve 26 is used when injecting the urea water 4 into the flue 10, and the sub injection valve 27 is used when injecting the urea water 4 into the heat transfer pipe 42 through which the diverted exhaust gas 14 which will be described later passes. Used.

The spray 34 injected from the main injection valve 26 is injected into a relatively large space 36 formed in the flue 10.

  Further, in the flue 10 of the urea addition device 70, a flue restriction 20 having a passage sectional area once reduced is formed on the downstream side of the space 36. The throttle 20 is provided with a mainstream swirl vane 19 for generating a swirl flow in the exhaust 13 flow. A diversion passage 41 that is a bypassed passage is communicated with the throttle 20 and the space 36 in the flue 10 on the upstream side thereof. The diversion passage 41 is provided with an opening 40 for the diversion passage so as to oppose the axial flow direction of the flow of the exhaust gas 12 flowing in the flue 10 on the upstream side of the throttle 20. The diversion passage inlet 40 communicates with the swirl chamber 33 disposed on the downstream side thereof via the diversion passage 41. A heat transfer tube swirl blade 30 is disposed in the swirl chamber 33. A heat transfer tube 42 is disposed on the downstream side of the heat transfer tube swirl blade 30, two heat transfer tube throttles 48 are disposed inside the heat transfer tube 42, and two heat transfer tube collision members 49 are disposed on the downstream side. Has been.

  The heat transfer tube restrictor 48 has a parallel portion 61 having a cylindrical predetermined length, and a protrusion having a predetermined height toward the center of the cylindrical parallel portion 61 at the cylindrical end portion. 60 is formed. On the other hand, the heat transfer tube collision member 49 has a parallel portion 63 having a cylindrical predetermined length, and has a shape in which the end of the cylindrical parallel portion 63 is closed. Further, the heat transfer tube collision member 49 has a porous (hole) structure in which a plurality of holes 62 are formed.

  Further, a hydrolysis catalyst 44 is disposed inside the heat transfer tube 42 on the downstream side of the heat transfer tube collision member 49. A heater 43, which is a heating element, is disposed on the outer peripheral portion of the heat transfer tube 42, and vaporization of the spray 35 flowing in the heat transfer tube 42 is promoted by heating the heater 43, which is a heating element. An outer cylinder 47 is disposed on the outer periphery of the heater 43 so that the heater 43 does not come into direct contact with the outside air. A heat insulating layer 53 that is a gas phase is formed between the heater 43 and the inner wall of the outer cylinder 47. The heat insulating layer 53 has a structure communicating with an outer cylinder bottom 50 described later.

  An outer cylinder bottom 50 communicating with the outer cylinder 47 is disposed downstream of the hydrolysis catalyst 44, and a hydrolysis catalyst 51 is disposed at the outlet of the outer cylinder bottom 50.

  The outlet of the hydrolysis catalyst 51 communicates with a pressure regulation chamber 45 in an annular space formed inside the wall 21 provided surrounding the outer wall of the throttle 20. The pressure regulating chamber 45 communicates with the inside of the throttle 20 through an ammonia ejection hole 46 formed in the throttle 20 portion. That is, the space 36 in the flue 10 on the upstream side of the throttle 20 communicates with the ammonia ejection hole 46 via the branch passage entrance 40. Here, the ammonia ejection hole 46 formed in the throttle 20 is disposed on the downstream side of the mainstream swirl vane 19.

  Next, the supply path | route to each part of the urea water 4 is demonstrated. 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 applied to the main injection valve 26 and the sub injection valve 27 with a predetermined pressure. Supplied at Here, the pressure adjustment to the main injection valve 26 and the sub injection valve 27 is performed by the pressure adjusting valve 7 disposed in the middle of the flow path communicating with the tank 3 on the downstream side of the pump 6.

  In this embodiment, urea water, which is a reducing agent, is used in a relatively wide operating range from a low exhaust temperature and a low load region with a small exhaust amount to a high exhaust temperature and a high load region with a large exhaust amount. In order to quickly supply a predetermined amount to the denitration catalyst 18, it is possible to change the supply form of urea water supplied from the urea addition device 70 into the flue 10.

  That is, at the time of a high exhaust temperature, the spray 34 of the urea water 4 injected from the main injection valve 26 is mainly supplied to the relatively large space 36 in the flue 10, and then the exhaust 20 and the throttle 20. By passing through the mainstream swirl vane 19 disposed inside it, the heat of the exhaust 13 is exchanged to promote vaporization, and after mixing is promoted, it is supplied to the denitration catalyst 18 and has high denitration performance. Get.

  On the other hand, at the time of low exhaust temperature, the supply of the spray 35 of the urea water 4 injected from the sub injection valve 27 is mainly used, and the spray 35 is heated by the heat of the heater 43 which is a heating element disposed on the outer peripheral portion of the heat transfer tube 42. After positively evaporating inside the heat transfer pipe 42 and passing the hydrolysis catalysts 44 and 51, the ammonia gasification of the spray 35 of the urea water 4 is promoted, and then the mixing with the exhaust 13 is promoted. The denitration catalyst 18 is supplied to obtain high denitration performance.

  As described above, in this embodiment, by changing the supply form of the urea water supplied from the urea addition device 70 into the flue 10 according to the operation state of the engine, high denitration performance is achieved in the entire operation region of the engine. It is to secure.

Next, the supply of the urea water spray 34 supplied from the main injection valve 26 mainly used at the high exhaust temperature to the denitration catalyst 18 will be described.

In the exhaust treatment apparatus of the present embodiment, the exhaust 13 that has passed through the DPF 17 is supplied to the space 36 in the flue 10 of the urea addition apparatus 70. At this time, the urea water spray 34 injected into the space 36 in the flue 10 is promoted to hydrolyze along with the evaporation of the droplets in the spray 34 by the transfer of heat of the exhaust gas 13, thereby promoting the generation of ammonia gas. Is done.

  Further, a throttle 20 having a reduced passage cross-sectional area is disposed in the flue 10 on the downstream side of the space 36, and a mainstream swirl vane 19 is disposed in the throttle 20 portion. Therefore, the flow rate of the exhaust gas 13 is increased by passing through the throttle 20 part along with the air flow of the exhaust gas 13, and the turbulence of the flow at the throttle 20 due to passing through the mainstream swirl blade 19 causes the exhaust gas 13 and the spray. 34 is promoted.

  Due to the effects of the exhaust 13 flow, the throttle 20 and the mainstream swirl vane 19, the spray 34 injected from the main injection valve 26 has a hydrolysis reaction accelerated by the high-temperature exhaust 13 and moisture contained in the exhaust, and ammonia gas. As the catalyst is promoted, urea spray droplets, steam and ammonia can be supplied almost uniformly to the denitration catalyst 18, and high denitration performance can be obtained.

  Next, the supply of the urea water spray 34 supplied from the sub-injection valve 27 mainly used at the low exhaust temperature to the denitration catalyst will be described.

  The diverted exhaust gas 14 diverted from the exhaust 12 flowing into the diversion passage 41 from the diversion passage entrance 40 flows into the swirl chamber 33 via the diversion passage 41. A heat transfer tube swirl vane 30 is disposed in the swirl chamber 33. The heat transfer tube swirl blade 30 has a structure in which a plurality of blade 37-shaped protrusions are formed on the end face of a cylindrical ring 38 portion. A space is formed between the side wall surface of the swirl chamber 33 and the heat transfer tube swirl blade 30, and the diverted exhaust gas 14 flowing from the diversion passage 41 flows into the space. The diverted exhaust gas 14 flowing into the space flows into the heat transfer tube 42 while forming a swirl flow when passing through the heat transfer tube swirl blade 30. It is preferable that the diverted exhaust gas 14 flowing into the heat transfer tube 42 via the heat transfer tube swirl blade 30 flows uniformly from the circumferential direction of the inlet portion of the heat transfer tube 42.

  Further, the spray 35 of urea water is injected from the sub injection valve 27 toward the inside of the heat transfer tube 42 through the inside of the ring 38 of the heat transfer tube swirl vane 30 disposed in the swirl chamber 33.

  Here, since the shunt exhaust 14 passes through the heat transfer tube swirl blade 30 and flows while forming a swirl flow in the heat transfer tube 42, the passage pressure loss is smaller than that when the flow passes through the right angle bend tube. This makes it possible to reduce the flow rate and efficiently flow the diverted exhaust gas 14 into the heat transfer tube. Furthermore, since the spray 35 injected into the heat transfer tube 42 is accompanied by the swirl flow by the swirl flow formed in the heat transfer tube 42, it is possible to forcibly contact the inner wall surface of the heat transfer tube 42, The time for which the droplets in the spray 35 are brought into contact with the inner wall surface in the heat transfer tube 42 can be extended, and the spray 35 can be efficiently vaporized.

  Furthermore, since the heat transfer tube constriction 48 having the circumferentially continuous protrusion 60 is disposed inside the heat transfer tube 42, a constricted shape is formed in the heat transfer tube 42. Further, in the heat transfer tube 42, since the heat transfer tube swirl vane 30 is disposed at the inlet of the heat transfer tube 42, a swirl flow of the diverted exhaust 14 is formed, and droplets of the spray 35 injected from the sub-injection valve 27 are projected 60 parts. It is possible to trap in the upstream and downstream regions of the inner wall surface in the axial flow direction of the heat transfer tube 42 and the residence time of the spray 35 droplets in the upstream and downstream regions of the protrusion 60 can be greatly increased. The vaporization of the spray 35 can be promoted.

Here, since the spray droplets in the upstream and downstream regions of the projection 60 are trapped and concentrated, the amount of heat transfer from the heater 43 to the spray 35 droplet in the projection 60 increases, and the smooth portion of the inner wall portion of the heat transfer tube 42 As compared with the above, the inner wall surface temperature of the heat transfer tube 42 in the upstream / downstream region of the protrusion 60 tends to decrease. The point to be considered is that the form of boiling of the spray 35 droplets of the heat transfer tube throttle 48 disposed in the heat transfer tube 42 is not nucleate boiling but film boiling in the heat transfer tube 42 including the upstream and downstream regions of the protrusion 60 part. It is a point to form. For this purpose, a predetermined heat generation amount is supplied from the heater 43, the height of the projection 60 is optimized, and the trap amount of the spray 35 droplets in the upstream and downstream areas of the projection 60 is optimized. Here, when the spray 35 droplets are nucleate boiled on the inner wall surface of the heat transfer tube 35, the heat transfer between the inner wall surface of the heat transfer tube 42 and the urea water is promoted, and the inner wall surface temperature of the heat transfer tube 42 rapidly decreases. Urea precipitates on the inner wall surface, but if the boiling form of the sprayed 35 droplets in the heat transfer tube 42 is the film boiling form, the heat transfer rate from the heater 43 compared to the nucleate boiling form. However, since the sprayed 35 droplets are vaporized in the form of droplets in the heat transfer tube 42, urea precipitation can be prevented.

  Further, the heat transfer tube throttle 48 has a parallel portion 61 formed along the inner wall surface of the heat transfer tube 42. Therefore, since the contact area between the inner wall surface of the heat transfer tube 42 and the parallel portion 61 is enlarged, the heat of the heater 43 is likely to be input to the protrusion 60 portion of the heat transfer tube restrictor 48, It is possible to prevent a temperature drop due to vaporization of the sprayed 35 droplets.

  As described above, since the heat transfer tube restrictor 48 is disposed on the inner wall surface of the heat transfer tube 42, the time and heat to apply the heat of the heater to the droplets in the spray 35 trapped in the upstream and downstream areas of the protrusion 60 as the restrictor 48 are sufficient. It is possible to secure vaporization and promote vaporization. In this embodiment, a two-stage heat transfer tube restrictor 48 is provided, but by further increasing the number of stages, the trap amount of the spray 35 on the inner wall surface of the heat transfer tube 42 can be leveled, and the trap amount and residence time can be reduced. Since it can be increased, further vaporization is promoted.

Furthermore, a heat transfer tube collision member 49 having a porous (hole) structure in which a plurality of holes 62 are formed is disposed on the downstream side of the heat transfer tube constriction 48 inside the heat transfer tube 42. Here, in the spray 35 injected from the sub-injection valve 27 into the heat transfer tube 42, the sub-injection is not accompanied by the swirling flow of the diverted exhaust gas 14 in the heat transfer tube 42 formed by the heat transfer tube swirl blade 30. There are coarse droplets flying along the injection direction from the valve 27. Here, the coarse droplet collides with the heat transfer tube collision member 49. By colliding with the collision member 49, the coarse droplet is split into fine droplets, and the collided coarse droplet is promoted to be vaporized by the heat of the collision member 49 and the shunt exhaust 14 heated by the heater. Here, the temperature of the collision member 49 tends to decrease due to the promotion of vaporization of the spray 35. The point that should be considered in the same manner as the inner wall of the heat transfer tube 42 including the upper and lower regions of the protrusions 60 with respect to the spray 35 droplets of the heat transfer tube constriction 48 disposed in the heat transfer tube 42 described above is the spray on the impingement member 49. 35 boiling forms are film boiling. For this purpose, a predetermined heat generation amount is supplied from the heater 43 and the aperture ratio of the porous collision member 49 is optimized so as to optimize the collision amount of the sprayed 35 droplets colliding with the collision member 49. . Thus, since the sprayed 35 droplets can boil on the collision member 49, urea precipitation on the collision member 49 can be prevented.

  Further, the heat transfer tube collision member 49 is formed with a parallel portion 63 along the inner wall surface of the heat transfer tube 42. Therefore, since the contact area between the inner wall surface of the heat transfer tube 42 and the parallel portion 63 is enlarged, the heat of the heater 43 is easily input to the heat transfer tube collision member 49, and the spray 35 liquid of the collision member 49 It is intended to prevent temperature drop due to vaporization of droplets.

Furthermore, since the parallel part 63 has a porous (hole) structure, an uneven shape that easily traps urea droplets can be formed on the inner wall surface of the heat transfer tube 42. Moreover, since the unevenness can be formed on the inner wall surface of the heat transfer tube 42 by the parallel part 63 having a porous (hole) structure on the inner wall surface of the heat transfer tube 42, the heat of the heater 43 is easily transmitted into the heat transfer tube 42 (from the heater 43). The heat transfer rate to the shunt exhaust 14 passing through the heat transfer tube 42 is improved). Therefore, vaporization promotion of the spray 35 in the heat transfer tube 42 is achieved.

  By arranging the heat transfer tube collision member 49 in the heat transfer tube 42 as described above, sufficient heat can be secured to break up coarse droplets in the spray 35 colliding with the collision member 49 and promote vaporization. In this embodiment, the two-stage heat transfer tube collision member 49 is provided. However, since the number of collisions of the spray 35 against the heat transfer tube collision member 49 can be increased by further increasing the number of stages, the coarse liquid of the spray 35 is increased. Microdroplet generation and vaporization are promoted by droplet breakup.

  Further, a hydrolysis catalyst 44 having a cylindrical shape along the inner wall surface of the heat transfer tube 42 and having a cylindrical vertical cross section is disposed downstream of the heat transfer tube collision member 49 inside the heat transfer tube 42. The hydrolysis catalyst 44 is preferably made of a metal base material so that the heat of the heater 43 can be easily transferred. By disposing the hydrolysis catalyst 44, the spray 35 droplets that could not be vaporized by the heat transfer tube throttle 48 and the collision member 49 disposed upstream thereof are promoted to vaporize, and the vaporized urea vapor and urea liquid are promoted. The droplet can be hydrolyzed to produce ammonia. In addition, since the heater 43 is disposed on the outer periphery of the heat transfer tube 42 and the hydrolysis catalyst 44 is disposed inside the heat transfer tube 42, the activation temperature of the hydrolysis catalyst 44 can be easily formed. Even if the temperature is equal to or lower than the activation temperature of the hydrolysis catalyst 44, the ammonia gas 15 can be efficiently generated.

  Furthermore, by disposing the heat transfer tube restrictor 48 and the collision member 49 in the heat transfer tube 42, the vaporization of the urea spray 35 in the heat transfer tube 48 can be promoted, so that the heat transfer tube 42 can be reduced in size. That is, when compared with the same heat transfer tube size, when the heat transfer tube restrictor 48 and the collision member 49 are not disposed in the heat transfer tube 42, the spray 35 that does not vaporize concentrates on the hydrolysis catalyst 44. The spray 35 is not completely vaporized on the liquid 44 and forms a liquid flow, forms a nucleate boiling state, rapidly loses heat, only urea remains, and urea precipitation may occur. In addition, the liquid flow may flow directly downstream of the hydrolysis catalyst 44 and cause urea precipitation. Therefore, a predetermined amount of ammonia gas 15 cannot be supplied to the denitration catalyst 18, and the denitration performance is reduced. Furthermore, when urea is precipitated in the hydrolysis catalyst 44 or downstream thereof, the passage through which the ammonia gas 15 passes may be blocked, and the ammonia gas 15 may not be supplied to the denitration catalyst 18.

  However, by arranging the heat transfer tube restrictor 48 and the collision member 49 in the heat transfer tube 42, the region where the urea spray 35 evaporates in the heat transfer tube 42 can be dispersed, so that the urea spray 35 is efficiently vaporized. Thus, the heat transfer tube 42 can be downsized.

In this embodiment, when the heat transfer tube restrictor 48 and the collision member 49 are disposed in the heat transfer tube 42, the heat transfer tubes in the axial flow direction in the heat transfer tube 42 are determined by the lengths of the parallel portions 61 and 63 in the axial flow direction. The diaphragm 48 and the collision member 49 are positioned. That is, the end portions on the downstream side in the axial flow direction of the parallel portion 61 of the heat transfer tube constriction 48 and the collision member 49 are in contact with the end portions on the upstream side in the axial flow direction of the heat transfer tube constriction 48 and the collision member 49, respectively. The position of each axial flow direction is determined. Further, the downstream end of the parallel part 63 of the collision member 49 located on the most downstream side is fixed in the heat transfer tube by contacting the hydrolysis catalyst 44. Here, the hydrolysis catalyst 44 is fixed in contact with the heat transfer tube 42.

The urea vapor promoted for vaporization in the heat transfer tube 42 is hydrolyzed by the heat of the divided exhaust 14 and the heat supplied from the heater 43 as a heating element into the heat transfer tube 42. Furthermore, by passing through the hydrolysis catalysts 44 and 51 disposed in the heat transfer tube 42 and downstream thereof, the hydrolysis reaction is further promoted, and urea can be converted to ammonia gas. The ammonia gas 15 that promotes the ammonia gasification of the spray 35 flows into the pressure regulating chamber 45 disposed downstream of the hydrolysis catalyst 51, and is attracted to the mainstream exhaust 13 through a plurality of ammonia ejection holes 46 formed in the throttle 20. Then, it is supplied into the diaphragm 20. This is because the static pressure on the throttle 20 side is lowered by the amount of pressure loss of the heat transfer tube 42 due to the throttle 20 through which the mainstream exhaust 13 passes, and the flow rate of the split exhaust 14 in the heat transfer tube 42 is secured.

  By passing through the throttle 20, the flow velocity of the main exhaust 13 becomes faster than the flow velocity of the exhaust 12. Further, by passing through the disposed main flow swirl blade 19, the flow of the main flow exhaust 13 downstream of the main flow swirl blade 19 is locally disturbed to form a swirl flow and promote mixing with the ammonia gas 15. The mixed gas 16 is supplied to the denitration catalyst 18. Thereby, high denitration performance can be obtained.

  The temperature of the exhaust 12 from the engine 1 changes depending on the load of the engine 1, and when the temperature of the exhaust 12 is high, the urea water is vaporized and hydrolyzed by the heat obtained from the exhaust 12 even if the urea water is directly injected. Promptly, a necessary amount of ammonia gas as a reducing agent is supplied to the denitration catalyst 18, but when the temperature of the exhaust 12 is low, ammonia gasification of urea water does not proceed and the reduction reaction at the denitration catalyst 18 is sufficient. Will not proceed. For this reason, generally, when the temperature of the exhaust 12 is low, the NOx reduction rate (denitration rate) deteriorates.

  As a countermeasure, the heat transfer tube 42 is used to promote the ammoniating of urea water and assist the removal of NOx at a low temperature by two functions of heating by the heater 43 as a heating element and reaction promotion by the hydrolysis catalysts 44 and 51. To do. Further, when the temperature of the exhaust gas 12 is high, the urea water spray 35 is not directly injected from the sub-injection valve 27 disposed downstream of the branch passage 41, and the urea water spray 34 is directly injected into the exhaust gas 13. By adding urea water using only the main injection valve 26, the heater 43, which is a heating element, does not consume extra energy. Further, with respect to reaction assistance by heating at low temperatures, the entire exhaust 12 is not heated, but only the shunt exhaust 14 is heated, thereby reducing the power consumed by the heater 43 that is a heating element.

  Next, the result of examining the urea treatment rate of the heat transfer tube 42 is shown in FIG.

  The horizontal axis shows the heat transfer tube specifications, and the vertical axis shows the urea treatment rate. The “conventional” specification in FIG. 8 is a case where a predetermined amount of spray 35 is injected into the straight heat transfer tube 42, and “the present invention (without hydrolysis catalyst)” swirls into the straight heat transfer tube. In addition to forming a flow, the heat transfer tube restrictors 48 are arranged in two stages in the axial flow direction, and a heat transfer tube impingement member 49 is arranged downstream thereof.

  The “present invention (with hydrolysis catalyst)” is a configuration in which a hydrolysis catalyst 44 is disposed at the outlet in the heat transfer tube 42 with respect to the “present invention (without hydrolysis catalyst)”.

  The urea treatment rate on the vertical axis indicates the ratio of the urea mass contained in the injected urea spray 35 and the urea mass recovered at the heat transfer tube outlet in percentage. Therefore, if the urea treatment rate is high, it can be said that the ammonia gasification of the urea water spray 35 can be promoted. Here, the amount and temperature of the diverted exhaust gas 14 passing through the heat transfer tube 42 and the power consumption of the heater 43 were evaluated under the same conditions.

  As a result, the urea treatment rate in the case of “conventional” is about 80% by adopting “the present invention (without hydrolysis catalyst)”, and almost “in the present invention (with hydrolysis catalyst)”. It was confirmed that 100% could be realized. That is, by applying the embodiment of the present invention of “the present invention (with hydrolysis catalyst)”, the urea water spray 35 can be almost completely converted to ammonia gas.

  Next, in the first embodiment, the heat transfer tube swirl blade 30 is disposed at the inlet of the heat transfer tube 42, the heat transfer tube constriction 48 and the collision member 49 are disposed therein, and the hydrolysis catalyst is further disposed inside the downstream heat transfer tube 42. 44 is provided. However, it is not limited to that. That is, even if the heat transfer tube impingement member 49 is arranged in a plurality of stages without using the heat transfer tube swirl blade 30 and the heat transfer tube constriction 48 having the configuration of the first embodiment, the urea is sufficiently equivalent to that of the first embodiment. A processing rate can be obtained. Since the operational effects relating to the collision member 49 are the same as those in the first embodiment, the description thereof is omitted.

  Further, in the first embodiment, the heat transfer tube swirl blade 30 is disposed at the inlet portion of the heat transfer tube 42, the heat transfer tube constriction 48 and the collision member 49 are disposed therein, and the hydrolysis catalyst 44 is disposed inside the downstream heat transfer tube 42. Is an arranged configuration. However, it is not limited to that. That is, without using the heat transfer tube swirl blade 30 disposed at the inlet portion of the heat transfer tube 42 having the configuration of the first embodiment, the heat transfer tube throttle 48 and the collision member 49 are arranged in a plurality of stages higher than the first embodiment. This also makes it possible to obtain a urea treatment rate equivalent to that of the first embodiment. Since the operation and effect related to the heat transfer tube restrictor 48 and the collision member 49 are the same as those in the first embodiment, the description thereof is omitted.

1 is a diagram illustrating an overall configuration of an engine exhaust treatment apparatus according to a first embodiment of the present invention. It is an external appearance perspective view of the urea addition apparatus of the exhaust gas processing apparatus shown in FIG. FIG. 3 is a B direction arrow view and a C direction arrow view of the external perspective view shown in FIG. 2. It is a figure which shows EE sectional drawing in FIG. It is a figure which shows DD sectional drawing in FIG. It is a figure which shows the F section enlarged view in FIG. FIG. 4 is a perspective view of a “throttle” and a “collision member” disposed in a heat transfer tube according to the present invention, and a perspective view of a “swirl blade” disposed in a heat transfer tube upstream stage. It is a figure which shows the effect of the exhaust-gas treatment apparatus which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diesel engine 3 Urea water tank 4 Urea water 5 Filter 6 Pump 7 Pressure control valve 12, 13, 16 Exhaust 14 Divided exhaust 15 Ammonia gas 17 DPF
18 DeNOx catalyst 19 Main flow swirl 26 Main injection valve 27 Sub injection valve 30 Heat transfer tube swirl 40 Split flow passage inlet 41 Split flow passage 42 Heat transfer tube 43 Heater 44 Upstream hydrolysis catalyst 45 Pressure regulation chamber 46 Ammonia injection hole 48 Heat transfer tube Restriction 49 Heat transfer tube impingement member 51 Hydrolysis catalyst 60 Projection parts 61, 63 Parallel part 62 Hole 70 Urea addition device

Claims (7)

An exhaust treatment apparatus for an engine for reducing nitrogen oxides in exhaust, comprising an injection valve for injecting urea water into the exhaust, and a heater for vaporizing urea water injected from the injection valve The vaporizer has a heater disposed on the outer periphery of the heat transfer tube, and urea water and exhaust gas pass through the heat transfer tube, and the urea water vaporized by the vaporizer enters the flue. In the engine exhaust treatment device to be supplied,
An exhaust processing apparatus for an engine, wherein a collision member which is a perforated plate is disposed in the heat transfer tube. The engine exhaust treatment apparatus according to claim 1,
An exhaust processing apparatus for an engine, wherein a throttle is disposed in the heat transfer tube, and the collision member is disposed downstream thereof. The exhaust treatment apparatus for an engine according to claim 2,
An exhaust processing apparatus for an engine, characterized in that a fixed swirl vane for swirling exhaust gas in the heat transfer tube is disposed at an upstream end portion of the heat transfer tube. The engine exhaust treatment apparatus according to any one of claims 1 to 3,
The throttle and the collision member have a parallel portion having a predetermined length in the axial direction of the heat transfer tube as they contact the inner wall surface of the heat transfer tube, and the throttle or the collision member is fixed in the heat transfer tube by the parallel portion. In addition, an exhaust processing apparatus for an engine, wherein a contact area that contacts the inner wall surface of the heat transfer tube, the throttle, and the collision member is enlarged. The engine exhaust treatment apparatus according to any one of claims 1 to 4,
An outer cylinder is disposed on the outer periphery of the heater disposed on the outer periphery of the heat transfer tube, which is a vaporizer, and a heat insulating layer, which is a space, is formed between the outer periphery of the heater and the inner wall surface of the outer cylinder. An exhaust treatment apparatus for an engine, wherein the exhaust pipe communicates with the inside of the heat tube and the heat transfer tube outlet. The engine exhaust treatment apparatus according to any one of claims 1 to 5,
An exhaust treatment apparatus for an engine, wherein a hydrolysis catalyst is disposed in the heat transfer tube downstream of the impingement member or the throttle or on the downstream side thereof. The engine exhaust treatment apparatus according to any one of claims 1 to 6,
An exhaust treatment apparatus for an engine, characterized in that the inner wall surface temperature of the carburetor is set to a temperature at which the urea water boils in the carburetor by the heater.

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