JP2009264148A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of showing high NOx reduction performances right after a stage where exhaust gas temperature reaches activation temperature zone of selective reduction type catalyst even under a condition where exhaust gas temperature is low such as in the case of engine start and low speed travel. <P>SOLUTION: The exhaust emission control device is provided with the selective reduction type catalyst 11 provided with a characteristics making NOx selectively react with ammonia even under existence of oxygen, and an urea water adding valve 14 (urea water adding means) adding urea water 13 as reducer to an upstream side of the selective reduction type catalyst 11, in the middle of an exhaust pipe 10 in which exhaust gas 8 from an engine 1 flows. The device is additionally equipped with an urea water discharge decomposition reactor 18 forcibly decomposing solid of urea to ammonia by discharge plasma and introducing the same to the exhaust pipe 10 at an upstream side of the selective reduction type catalyst 11. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device.

  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 is hydrolyzed into ammonia and carbon dioxide gas by the following equation by the heat of the exhaust gas, and the exhaust gas is exhausted on the selective catalytic reduction catalyst. The NOx contained therein is reduced and purified well by ammonia.
[Chemical 1]
(NH ₂ ) ₂ CO + H ₂ O → 2NH ₃ + CO ₂
JP 2002-161732 A

  In such an exhaust purification device, it has been confirmed by experiments that an NOx reduction effect can be obtained from an exhaust temperature of about 100 ° C. or more by adding ammonia to the selective catalytic reduction catalyst. Since an exhaust temperature of at least about 150 to 160 ° C. is required to hydrolyze it into carbon dioxide, urea water can be added to some extent when starting an engine at a lower exhaust temperature or when driving at a low speed. However, there is a problem that the NOx reduction performance is not easily improved because ammonia is not sufficiently generated.

  The present invention has been made in view of the above circumstances, and even when the engine temperature is low or when the engine is running at low speed, the NOx reduction performance is high immediately after the exhaust temperature reaches the active temperature range of the selective catalytic reduction catalyst. An object of the present invention is to provide an exhaust emission control device that can exhibit the above.

  The present invention provides a selective reduction catalyst having a property of selectively reacting NOx with ammonia even in the presence of oxygen in the middle of an exhaust pipe through which exhaust gas from an engine flows, and an upstream side of the selective reduction catalyst. In the exhaust gas purification apparatus equipped with urea water addition means for adding urea water as a reducing agent, the urea discharge decomposition reactor that forcibly decomposes urea solids into ammonia by discharge plasma and introduces it into the exhaust pipe is selectively reduced. It is characterized by additional equipment upstream of the type catalyst.

  Thus, in this way, even if the exhaust temperature does not reach a temperature sufficient to efficiently hydrolyze urea water into ammonia and carbon dioxide, the exhaust temperature is within the active temperature range of the selective catalytic reduction catalyst. When the urea discharge decomposition reactor is activated, the urea discharge decomposition reactor forcibly decomposes urea solids into ammonia by the discharge plasma and introduces it into the exhaust pipe, and this ammonia is used as a reducing agent in the exhaust gas. NOx can be reduced and purified well on the selective catalytic reduction catalyst.

  If the urea solid is decomposed into ammonia by discharge plasma in this way, the weight and volume of urea required to add the same amount of ammonia is urea water (usually about 32.5% by weight). 1) compared to the aqueous solution of (2), and it is possible to produce concentrated ammonia from a small amount of urea solids.

  In addition, when the exhaust gas temperature has shifted to an operating state where the urea water exceeds the temperature sufficient to efficiently hydrolyze the urea water into ammonia and carbon dioxide, the urea water addition means is switched to start the urea water addition. The urea water may be added by controlling the addition amount so that there is no excess or deficiency corresponding to the NOx generation amount estimated from the operating state.

  Furthermore, in more concrete implementation of the present invention, the urea discharge cracking reactors are arranged to face each other at a required interval, and a dielectric is arranged on the opposite surface with respect to the other, so that a high voltage is generated between them. Electrodes, dielectric pellets filled in the discharge space formed between the electrodes, and urea cutting in which the solid matter of urea is cut into the discharge space and then refined It is preferable that a charging means and a carrier gas line for guiding a carrier gas for sending ammonia generated in the discharge space into the exhaust pipe are provided.

  Thus, when a urea discharge decomposition reactor is configured in this way, a high voltage is applied between the electrodes to generate discharge plasma in the discharge space, while urea solids are cut by the urea cutting input means. Then, when it is made finer and then introduced into the discharge space, the solid matter of urea is decomposed into ammonia by the discharge plasma in the discharge space, and the ammonia is sent out into the exhaust pipe by the carrier gas guided by the carrier gas line.

  At this time, if the discharge space is filled with dielectric pellets, the electric field is concentrated at the contact points between the dielectric pellets, and a strong discharge plasma is likely to be generated. In this case, the decomposition of urea into ammonia is easier to proceed, so that the solid substance of urea is efficiently decomposed into ammonia by the strong discharge plasma in the discharge space.

  Furthermore, it is preferable that a urea decomposition catalyst that promotes the decomposition of urea into ammonia is supported on the surface of the dielectric pellet. In this way, the decomposition of urea into ammonia is further promoted. Is possible.

  According to the exhaust emission control device of the present invention described above, various excellent effects as described below can be obtained.

  (I) According to the invention described in claim 1 of the present invention, the urea discharge decomposition reactor is operated to forcibly discharge the urea solid matter by the discharge plasma even when the engine having a low exhaust temperature is started or at low speed. It can be decomposed into ammonia, and this ammonia can be introduced into the exhaust pipe as a reducing agent for the selective catalytic reduction catalyst, so that it exhibits high NOx reduction performance immediately after the exhaust temperature reaches the active temperature range of the selective catalytic reduction catalyst. Can be made.

  (II) According to the invention described in claim 2 of the present invention, the solid matter of urea is cut and refined by urea cutting and charging means to promote decomposition into ammonia and strong discharge by filling the dielectric pellets. By generating plasma and causing decomposition on a solid surface such as a dielectric pellet, decomposition from urea to ammonia can be facilitated, and decomposition from urea to ammonia can be efficiently realized.

  (III) According to the invention described in claim 3 of the present invention, the urea decomposition catalyst for promoting the decomposition of urea into ammonia is supported on the surface of the dielectric pellet, so that the decomposition of urea into ammonia is further improved. It can be further promoted.

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

  1 to 3 show an example of an embodiment of the present invention. Reference numeral 1 in FIG. 1 denotes an engine that is a diesel engine. In the engine 1 shown here, a turbocharger 2 is provided. The intake air 3 guided from an air cleaner (not shown) is sent to the compressor 2a of the turbocharger 2 through the intake pipe 4, and the intake air 3 pressurized by the compressor 2a is further sent to the intercooler 5 for cooling. The intake air 3 is guided from the intercooler 5 to the intake manifold 6 and introduced into each cylinder 7 of the engine 1.

  Further, exhaust gas 8 discharged from each cylinder 7 of the engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 9, and the exhaust gas 8 driving the turbine 2b passes through the exhaust pipe 10 to the outside of the vehicle. In the middle of the exhaust pipe 10, a selective catalytic reduction catalyst 11 having a property of selectively reacting NOx with ammonia even in the presence of oxygen is provided via a casing 12. .

  Further, a urea water addition valve 14 is provided near the inlet of the casing 12 as urea water addition means for adding urea water 13 to the exhaust gas 8. The urea water addition valve 14 is provided at a required place. A urea water supply line 16 led from the disposed urea water tank 15 is connected, and the urea water 13 in the urea water tank 15 is extracted by driving a pump 17 provided in the middle of the urea water supply line 16. The urea water addition valve 14 is supplied to the urea water addition valve 14 and is injected into the exhaust pipe 10 from the nozzle tip of the urea water addition valve 14.

  In this embodiment, the urea discharge decomposition in which the solid substance of urea is forcibly decomposed into ammonia by discharge plasma and introduced into the exhaust pipe 10 in contrast to the configuration of the conventionally known exhaust purification device as described above. A reactor 18 is additionally provided near the inlet of the casing 12 (upstream of the selective catalytic reduction catalyst 11).

  As shown in detail in FIG. 2, the urea discharge decomposition reactor 18 is arranged so as to stand upright above the exhaust pipe 10, and a rod-shaped high-voltage electrode 19 is arranged in an upright state at the lower stage inside thereof. A cylindrical ground electrode 20 is concentrically disposed so as to surround this, and a dielectric 21 is fitted on the inner peripheral surface of the ground electrode 20 (the surface facing the high voltage electrode 19). A high voltage is applied between the voltage electrode 19 and the ground electrode 20.

  Moreover, in the discharge space 22 formed between the high voltage electrode 19 and the ground electrode 20, a number of urea decomposition catalysts such as titanium oxide having the property of promoting the decomposition of urea into ammonia are supported. A dielectric pellet 23 is filled, and the dielectric pellet 23 is supported by a bottom plate of a ceramic punching plate 24 so as not to fall off.

  Furthermore, a urea cutting charging device 26 (urea cutting charging means) for cutting and solidifying urea solids 25 into the discharge space 22 is provided in the upper stage of the urea discharge decomposition reactor 18, The urea cutting input device 26 includes a disk-shaped cutting blade 27 for cutting the urea solid material 25, a drive device 28 for rotationally driving the cutting blade 27, and the urea solid material 25 on the upper surface of the cutting blade 27. It is comprised with the supply apparatus 29 to press.

  The disk-shaped cutting blade 27 is rotatably held by a shaft support means (not shown) so as to be able to rotate horizontally around a vertical axis, and as shown in FIG. The cutting edge 27a such as a tooth of a spear rises diagonally at four positions in the drawing, and the cutting powder falls into the discharge space 22 below from a gap (a portion hidden by the cutting edge 27a in FIG. 3) that opens along the cutting edge 27a. In this manner, the cutting blade 27 is rotationally driven by the driving device 28 via a pinion 30 that meshes with gear teeth 27b formed on the outer peripheral portion of the cutting blade 27.

  The supply device 29 includes a guide cylinder 31 that holds a plurality of urea solids 25 formed in a columnar shape in multiple stages so as to face the cutting edge 27 a on the upper surface side of the cutting blade 27, and the guide cylinder 31. The piston 33 is inserted into the upper opening and biased downward by the compression spring 32. The piston 33 presses the solid material 25 of the urea against the upper surface of the rotating cutting blade 27 and cuts it. It is made to do.

  Further, a carrier gas line 37 that guides the compressed air 36 from the air tank 34 (see FIG. 1) mounted on the vehicle via the opening / closing valve 35 is drawn into a position where the upper surface of the cutting blade 27 does not interfere with the guide cylinder 31. The ammonia generated in the discharge space 22 is sent into the exhaust pipe 10 using the compressed air 36 from the carrier gas line 37 as a carrier gas.

  This type of air tank 34 is well-known for storing compressed air 36 used for brake systems and suspension systems in large vehicles such as trucks. If the vehicle is not used, the intake air 3 may be extracted from the outlet of the compressor 2a of the turbocharger 2 and guided.

  Thus, in this way, the exhaust temperature is a temperature sufficient to efficiently hydrolyze the urea water 13 into ammonia and carbon dioxide (about 200 ° C .: the urea water 13 is hydrolyzed into ammonia and carbon dioxide. However, at least when the exhaust gas temperature reaches the activation temperature range (about 100 ° C.) of the selective catalytic reduction catalyst 11, the urea discharge decomposition reactor 18 is turned on. When the urea solid matter 25 is forcedly decomposed into ammonia by the discharge plasma in the urea discharge decomposition reactor 18 and introduced into the exhaust pipe 10, NOx in the exhaust gas 8 is selected using this ammonia as a reducing agent. The reduction catalyst 11 is reduced and purified satisfactorily.

  That is, a high voltage is applied between the electrodes in the urea discharge decomposition reactor 18 to generate discharge plasma in the discharge space 22, while the cutting blade 27 is rotationally driven by the drive device 28 of the urea cutting input device 26 to urea. When the solid material 25 is cut, and the finely divided cutting powder is dropped from the gap of the cutting edge 27a of the cutting blade 27 and put into the discharge space 22, the urea solid material 25 is converted into ammonia by the discharge plasma in the discharge space 22. The ammonia is sent into the exhaust pipe 10 by the compressed air 36 that is decomposed and guided by the carrier gas line 37.

  At this time, as shown in the present embodiment, when the discharge space 22 is filled with the dielectric pellets 23, the electric field is concentrated at the contact points between the dielectric pellets 23, and strong discharge plasma is easily generated. In addition, since the decomposition of urea into ammonia is facilitated on the solid surface such as the dielectric pellet 23, the urea solid matter 25 is efficiently decomposed into ammonia in the discharge space 22 by the strong discharge plasma. become.

  Particularly in the case of this embodiment, since a urea decomposition catalyst such as titanium oxide having the property of promoting the decomposition of urea into ammonia is supported on the surface of the dielectric pellet 23, the decomposition of urea into ammonia is prevented. This can be further promoted.

  If the urea solid material 25 is decomposed into ammonia by discharge plasma in this way, the weight and volume of urea required to add the same amount of ammonia is the urea water 13 (usually 32.5 weight). 1% as compared with an aqueous solution of about%), and since concentrated ammonia can be generated from a small amount of urea solids 25, it can be integrated as an extremely compact apparatus.

  In addition, when the exhaust gas temperature shifts to an operation state in which the urea water 13 exceeds the temperature sufficient for hydrolyzing the urea water 13 into ammonia and carbon dioxide (about 200 ° C.), the urea water addition valve 14 is switched to the urea water. The addition of the urea water 13 may be performed by starting the addition of 13 and controlling the addition amount so that there is no excess or deficiency corresponding to the NOx generation amount estimated from the current operating state.

  Therefore, according to the above embodiment, the urea discharge decomposition reactor 18 is operated to forcibly decompose the urea solid matter 25 into ammonia by the discharge plasma even when the engine is started at a low exhaust temperature or at low speed, etc. Since this ammonia can be introduced into the exhaust pipe 10 as a reducing agent for the selective catalytic reduction catalyst 11, a high NOx reduction performance is immediately exhibited from the stage when the exhaust temperature reaches the active temperature range of the selective catalytic reduction catalyst 11. Can do.

  Further, the urea solid material 25 is cut and refined by the urea cutting and feeding device 26 to promote decomposition into ammonia, and when the dielectric pellet 23 is filled, a strong discharge plasma is generated. By causing the decomposition on the solid surface, the decomposition of urea into ammonia can be facilitated, and furthermore, the urea decomposition catalyst that promotes the decomposition of urea into ammonia is supported on the surface of the dielectric pellet 23. In addition, decomposition of urea to ammonia can be further promoted.

  The exhaust emission control device of the present invention is not limited to the above-described embodiment, and the specific configuration of the urea discharge decomposition reactor is not necessarily limited to the illustrated example, and does not depart from the gist of the present invention. Of course, various changes can be made within the range.

It is the schematic which shows an example of the form which implements this invention. It is sectional drawing which shows the detail of the urea discharge decomposition reactor of FIG. It is the top view which looked at the cutting blade of FIG. 2 from upper direction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 8 Exhaust gas 10 Exhaust pipe 11 Selective reduction type catalyst 13 Urea water 14 Urea water addition valve 18 Urea discharge decomposition reactor 19 High voltage electrode 20 Ground electrode 21 Dielectric 22 Discharge space 23 Dielectric pellet 25 Urea solid matter 26 Urea Cutting input device 36 Compressed air (carrier gas)
37 Carrier gas line

Claims (3)

  A selective reduction catalyst having the property of selectively reacting NOx with ammonia even in the presence of oxygen in the middle of an exhaust pipe through which exhaust gas from the engine flows, and urea water is reduced upstream of the selective reduction catalyst And a urea water addition means to be added as an agent, wherein a urea discharge decomposition reactor that forcibly decomposes urea solids into ammonia by discharge plasma and introduces it into the exhaust pipe is provided upstream of the selective catalytic reduction catalyst. An exhaust purification system characterized by additional equipment on the side.   A urea discharge cracking reactor is disposed opposite to each other with a required interval between them, and a dielectric is coated on a surface facing one of the other so that a high voltage is applied between the electrodes, and between the electrodes Dielectric pellets filled in the discharge space to be formed, urea cutting charging means for cutting and solidifying urea solids into the discharge space, and feeding ammonia generated in the discharge space into the exhaust pipe The exhaust gas purification apparatus according to claim 1, further comprising a carrier gas line for guiding a carrier gas for the purpose.   The exhaust emission control device according to claim 2, wherein a urea decomposition catalyst that promotes decomposition of urea into ammonia is supported on a surface of the dielectric pellet.

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