JP2009138627A - Urea water addition nozzle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an urea water addition nozzle capable of avoiding risk of building up of a large cylindrical solid around an injection hole. <P>SOLUTION: In the urea water addition nozzle 2 adding urea water 1 as reducer at an upstream side of a selective reduction type catalyst for reducing and eliminating NOx, a nozzle body 7 provided with an injection hole 6 on its tip is disposed on an outer circumference part of an exhaust pipe 3 and is made face the exhaust pipe 3 in such a manner that the same is not directly exposed to flow of exhaust gas 5, a water cooling jacket 15 is provided around the top side of the nozzle body 7 as a cooling structure for protecting the nozzle body 7 from heat of the exhaust gas 5, and heat insulating material 19 is coated on a surface facing an inside of the exhaust pipe 3 of the water cooling jacket 15 to surround the injection hole 6 of the nozzle body 7. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a urea water addition nozzle for mixing urea water added as a reducing agent upstream of a selective reduction catalyst for reducing and purifying NOx with exhaust gas.

  Conventionally, a diesel engine is equipped with a selective reduction catalyst having a property of selectively reacting NOx with a reducing agent even in the presence of oxygen in the middle of an exhaust pipe through which exhaust gas flows, and the selective reduction catalyst A required amount of a reducing agent is added to the upstream side of the catalyst so that the reducing agent undergoes a reduction reaction with NOx (nitrogen oxide) in the exhaust gas on the selective catalytic reduction catalyst, thereby reducing the NOx emission concentration. There is what I did.

On the other hand, in the field of industrial flue gas denitration treatment in plants and the like, the effectiveness of a method for reducing and purifying NOx using ammonia (NH ₃ ) as a reducing agent is already widely known. Since it is difficult to ensure safety with respect to traveling with ammonia itself, in recent years, the use of non-toxic urea water as a reducing agent has been studied (see, for example, Patent Document 1). .

That is, if urea water is added to the exhaust gas upstream of the selective catalytic reduction catalyst, the urea water in the exhaust gas is thermally decomposed into ammonia and carbon dioxide gas by the following formula, and the exhaust gas is exhausted on the selective catalytic reduction catalyst. NOx is reduced and purified well by ammonia.
[Chemical 1]
(NH ₂ ) ₂ CO + H ₂ O → 2NH ₃ + CO ₂

  FIG. 5 shows an example of a conventional urea water addition nozzle 2 for adding urea water 1 as a reducing agent of the selective catalytic reduction catalyst. In the example shown here, the outer periphery of the exhaust pipe 3 is disposed upstream. A boss part 4 projecting obliquely toward the surface is provided, and the urea water addition nozzle 2 is attached to the boss part 4 from the outside of the exhaust pipe 3 so as to face the exhaust pipe 3. The urea water 1 is added while protecting it from being directly exposed to the flow of the exhaust gas 5.

  The urea water addition nozzle 2 includes a nozzle body 7 that injects urea water 1 fed from a supply pump (not shown) from a tip injection port 6, and moves a plunger 8 built in the nozzle body 7 forward and backward. By doing so, the injection port 6 can be opened and closed.

  That is, the plunger 8 is pushed out by the valve springs 9 and 10 and is urged in the advancing direction toward the exhaust pipe 3, and is lifted by the electromagnetic force of the solenoid 11 against the urging force of the valve springs 9 and 10. Retreating, the ball seal 12 at the tip and the flange portion 13 in the middle are separated from the valve seat, and the injection port 6 is opened.

Here, since a seal rubber 14 for enhancing liquid tightness is mounted at a position where the flange portion 13 of the plunger 8 is seated, in order to protect the seal rubber 14 and the like from heat, the front end side of the nozzle body 7 is used. A water cooling jacket 15 is provided as a cooling structure around the water cooling port 15, and a water suction port 17 and a drainage port 18 are provided so that the cooling water 16 can be sucked into and discharged from the water cooling jacket 15.
JP 2005-273614 A

  However, in the conventional urea water addition nozzle 2 as shown in FIG. 5, since the periphery of the injection port 6 of the nozzle body 7 is cooled by the water cooling jacket 15, the injection flow of the urea water 1 injected from the injection port 6 When some of the spray particles are returned to and adhered to the periphery of the injection port 6 due to the entrainment of water, only the water evaporates and the urea crystallizes without the thermal decomposition proceeding well, and the periphery of the injection port 6 However, there is a problem that the cylindrical solid material grows greatly.

  The present invention has been made in view of the above-described circumstances, and provides a urea water addition nozzle capable of avoiding the possibility that a cylindrical solid material will grow greatly around an injection port. The purpose is that.

  The present invention relates to a urea water addition nozzle for adding urea water added as a reducing agent to the upstream side of a selective catalytic reduction catalyst for reducing and purifying NOx, and a nozzle body provided with an injection port at the tip is connected to exhaust gas. Attaching to the outer periphery of the exhaust pipe so as not to be directly exposed to the flow, facing the exhaust pipe, and providing a cooling structure for protecting the nozzle body from the heat of exhaust gas around the tip side of the nozzle body, The surface facing the exhaust pipe of the cooling structure is covered with a heat insulating material so as to surround the injection port of the nozzle body.

  Thus, since the periphery of the nozzle body injection port is insulated by a heat insulating material and the surface temperature is maintained substantially the same as the temperature in the exhaust pipe, the exhaust gas temperature is sufficiently high. In this case, even if some of the spray particles of urea water are returned to the periphery of the injection port and adhere, the spray particles of urea water adhere well with ammonia under high temperature conditions. The possibility of thermal decomposition into carbon dioxide gas, where urea crystallizes and precipitates cylindrical solids, is avoided.

  Further, in the present invention, it is preferable that a cover plate carrying a urea water decomposition catalyst for hydrolyzing urea water into ammonia and carbon dioxide gas is coated on the surface of the heat insulating material. Ammonia of the spray particles of urea water adhering to the periphery of the mouth is promoted by the catalytic action of the urea water decomposition catalyst, so there is a risk that urea will crystallize around the injection port and precipitate a cylindrical solid. It is avoided more reliably.

  In the present invention, the cooling structure may be constituted by a water cooling jacket capable of sucking and discharging cooling water as usual, but the heat load of the cooling structure is reduced by the heat insulating material, so that the heat received from the exhaust gas is exhausted. It is also possible to configure the cooling structure with a radiant heat blocking plate provided with a heat radiating piece that radiates heat outside the tube.

  According to the urea water addition nozzle of the present invention described above, various excellent effects as described below can be obtained.

  (I) According to the first to fourth aspects of the present invention, the surface temperature around the injection port can be kept substantially the same as the temperature in the exhaust pipe by the heat insulating effect of the heat insulating material. It is possible to avoid the possibility that a part of the spray particles crystallizes around the injection port and the cylindrical solid material grows greatly.

  (II) According to the invention described in claim 2 of the present invention, the ammoniaation of the spray particles of urea water adhering to the periphery of the injection port can be promoted by the catalytic action of the urea water decomposition catalyst. It is possible to more reliably avoid the possibility that urea will crystallize around and precipitate a cylindrical solid.

  (III) According to the invention described in claim 4 of the present invention, the heat protection of the nozzle body is achieved by radiating the heat received from the exhaust gas from the heat radiating piece to the outside of the exhaust pipe while blocking the radiant heat by the radiant heat blocking plate. As a result, a large water-cooling system is not required and significant cost reduction can be achieved.

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

  FIG. 1 shows an example of an embodiment for carrying out the present invention, and relates to a urea water addition nozzle 2 configured in the same manner as the conventional example shown in FIG. 5, and in this embodiment, in the exhaust pipe 3 of the water cooling jacket 15. A surface of the nozzle body 7 is covered with a heat insulating material 19 so as to surround the injection port 6, and the flange of the water cooling jacket 15 and the periphery of the mounting port of the boss portion 4 of the exhaust pipe 3 are bolted across the heat insulating material 19. -The nut 20 is used for fastening.

  In the example shown here, the heat insulating material 19 is a material that also functions as a gasket, so that the airtightness of the fastening portion by the bolt and nut 20 is well maintained. .

  Thus, since the periphery of the nozzle 6 of the nozzle body 7 is thermally insulated by the heat insulating material 19 and the surface temperature is kept substantially the same as the temperature in the exhaust pipe 3, the exhaust temperature is sufficiently high. If the addition of the urea water 1 is executed under a high and appropriate operating condition, even if some of the spray particles of the urea water 1 are returned to the periphery of the injection port 6 and adhere, The possibility of thermal decomposition into ammonia and carbon dioxide gas under high temperature conditions, where urea crystallizes and precipitates a cylindrical solid is obviated.

  Therefore, according to the above-described embodiment, the surface temperature around the injection port 6 can be kept substantially the same as the temperature in the exhaust pipe 3 by the heat insulating effect of the heat insulating material 19, so that part of the spray particles of the urea water 1 However, it is possible to avoid the possibility that the solid crystallized around the injection port 6 and the cylindrical solid material grows greatly.

  FIG. 2 shows another embodiment of the present invention. In the example shown here, a cover plate 22 carrying a urea water decomposition catalyst 21 for hydrolyzing the urea water 1 into ammonia and carbon dioxide is supported on the surface. The structure which coat | covered the surface of the heat insulating material 19 is employ | adopted, and it is preferable to use a titanium oxide, titanium vanadium, a ceria etc. as a raw material for the said urea water decomposition catalyst 21. FIG. Incidentally, reference numeral 25 in FIG. 2 denotes a gasket having a heat insulating function made of the same material as the heat insulating material 19.

  By doing so, the ammoniating of the spray particles of the urea water 1 adhering to the periphery of the injection port 6 is promoted by the catalytic action of the urea water decomposition catalyst 21, so that urea crystallizes around the injection port 6 and the cylinder The possibility of depositing solid solids is more reliably avoided.

  In fact, as shown in the graph of FIG. 3, in the absence of the urea water decomposition catalyst 21, as shown by the curve A, all (100%) cannot be ammoniated unless the temperature is about 530 ° C. or higher. Although fear cannot be avoided, when the urea water decomposition catalyst 21 is present, as shown by curve B, all (100%) can be ammoniated at about 220 ° C. or higher, and the possibility of urea crystallization can be avoided. It has been confirmed.

  FIG. 4 shows still another embodiment of the present invention. In the example shown here, instead of the water cooling jacket 15 in the embodiment shown in FIGS. A radiant heat blocking plate 24 having a heat radiating piece 23 that radiates heat to the outside of the exhaust pipe 3 is employed as a cooling structure. Instead of cooling with the cooling water 16, the nozzle body 7 (mainly the seal rubber 14) is cooled by air. It can be protected from the heat of the exhaust gas 5.

  That is, since the heat load of the cooling structure is reduced by insulating the periphery of the nozzle 6 of the nozzle body 7 with the heat insulating material 19, the radiation heat can be cut off without performing the water cooling using the conventional water cooling jacket 15. By dissipating heat received from the exhaust gas 5 from the heat radiating piece 23 to the outside of the exhaust pipe 3 while blocking the radiant heat by the plate 24, it becomes possible to protect the nozzle body 7 (mainly the seal rubber 14), and a large water cooling system The cost can be greatly reduced by eliminating the need for

  The urea water addition nozzle of the present invention is not limited to the above-described embodiment, and the specific structure of the cooling structure is not necessarily limited to the structure of the illustrated water cooling jacket or radiant heat blocking plate, Of course, various modifications can be made without departing from the scope of the invention.

It is sectional drawing which shows an example of the form which implements this invention. It is sectional drawing which shows another example of a form of this invention. It is a graph which shows the difference in the ammonia conversion rate by the presence or absence of a urea water decomposition catalyst. It is sectional drawing which shows another example of a form of this invention. It is sectional drawing which shows an example of the conventional urea water addition nozzle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Urea water 2 Urea water addition nozzle 3 Exhaust pipe 5 Exhaust gas 6 Injection port 7 Nozzle body 15 Water cooling jacket (cooling structure)
16 Cooling Water 19 Heat Insulating Material 21 Urea Water Decomposition Catalyst 22 Cover Plate 23 Heat Dissipation Plate 24 Radiation Heat Blocking Plate (Cooling Structure)

Claims (4)

  A urea water addition nozzle for adding urea water added as a reducing agent to the upstream side of the selective catalytic reduction catalyst for reducing and purifying NOx, and directly exposing the nozzle body having an injection port at the tip to the flow of exhaust gas And a cooling structure for protecting the nozzle body from the heat of the exhaust gas is provided around the tip of the nozzle body so as to be attached to the outer periphery of the exhaust pipe so as not to be A urea water addition nozzle characterized by covering a surface facing the exhaust pipe with a heat insulating material so as to surround an injection port of the nozzle body.   The urea water addition nozzle according to claim 1, wherein a cover plate carrying a urea water decomposition catalyst for hydrolyzing urea water into ammonia and carbon dioxide gas is coated on the surface of the heat insulating material.   The urea water addition nozzle according to claim 1 or 2, wherein the cooling structure comprises a water cooling jacket capable of sucking and discharging cooling water.   3. The urea water addition nozzle according to claim 1, wherein the cooling structure is configured by a radiant heat blocking plate provided with a heat radiating piece that radiates heat received from the exhaust gas to the outside of the exhaust pipe.

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