JP2010248955A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the mountability of an exhaust emission control device reducing particulates and NOx all together, more than ever before. <P>SOLUTION: An oxidation catalyst 2 for oxidation-treating HC in exhaust gas 5 and a particulate filter 1 for letting the exhaust gas 5 through the filer after passage through the oxidation catalyst 2, and collecting particulates are arranged in series at predetermined intervals in a single casing 13 interposed in the middle of an exhaust pipe 4. A selective reduction catalyst 3' having a property of selectively reacting NOx with ammonia even under the coexistence of oxygen is integrally carried by the particulate filter 1, and also just after that, a selective reduction catalyst 3 is additionally equipped with a flow-through type carrier carrying the same. A mixer 14 for agitating the flow of the exhaust gas 5 is arranged near the outlet of the oxidation catalyst 2. An urea water adding device 6 for injecting urea water 7 toward the mixer 14 is arranged between the mixer 14 and the particulate filter 1. <P>COPYRIGHT: (C)2011,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.

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

  On the other hand, when purifying exhaust gas from a diesel engine, it is not enough to remove NOx in the exhaust gas, and particulates contained in the exhaust gas are also collected through the particulate filter. However, when this type of particulate filter is employed, it is necessary to regenerate the particulate filter by appropriately burning and removing the particulate before the exhaust resistance increases due to clogging.

  For this reason, a flow-through type oxidation catalyst is attached to the preceding stage of the particulate filter, and fuel is added to the exhaust gas upstream from the oxidation catalyst when the amount of particulate accumulation increases. It is considered to force playback.

  In other words, if fuel is added to the exhaust gas upstream of the oxidation catalyst, the added fuel (HC) undergoes an oxidation reaction while passing through the preceding oxidation catalyst. The catalyst bed temperature of the particulate filter immediately after that is raised, the particulates are burned out, and the particulate filter is regenerated.

  In general, as a specific means for performing the fuel addition as described above, the post-injection is executed at the timing of non-ignition later than the compression top dead center following the main injection of fuel performed near the compression top dead center. It is considered that the fuel is added to the exhaust gas, and in order to efficiently use the added fuel for the forced regeneration and oxidize the added fuel while the exhaust gas does not decrease in temperature as much as possible, for example, As shown in FIG. 3, it is considered preferable to dispose the particulate filter 1 and the preceding oxidation catalyst 2 upstream of the selective catalytic reduction catalyst 3.

In FIG. 3, reference numeral 4 is an exhaust pipe, 5 is exhaust gas, 6 is a urea water addition device that injects urea water 7, 8 is a diesel engine, and 9 is an NH that oxidizes surplus ammonia as a measure against leaked ammonia. ₃ shows a slip catalyst.

In such a conventional structure, in order to promote uniform mixing of the urea water 7 with the exhaust gas 5, the oxidation catalyst 2 and the particulate filter 1 are held by the casing 11, and the selective reduction catalyst 3 and NH _{The three-} slip catalyst 9 is held by the casing 12, and the space between the casings 11, 12 is narrowed to form the small-diameter portion 10, and the urea water addition device 6 can be arranged here to add the urea water 7. I have to.

  That is, in this way, it becomes possible to inject the urea water 7 over the entire area in the small diameter portion 10, so that the urea water 7 is mixed well with the exhaust gas 5 and then the flow is expanded. Ammonia generated from the water 7 can be efficiently reacted in the entire region of the selective catalytic reduction catalyst 3.

  In addition, as prior art document information related to this type of particulate filter and an exhaust purification device in which the preceding stage oxidation catalyst is arranged upstream of the selective reduction catalyst, for example, the following patent documents by the same applicant as the present invention are as follows: 1 etc. already exist.

JP 2007-2697 A

  However, even if the small-diameter portion 10 as shown in FIG. 3 is formed, in order to secure a sufficient reaction time until the urea water 7 is decomposed into ammonia and carbon dioxide, selective reduction is performed from the addition position of the urea water 7. The distance from the particulate filter 1 to the selective catalytic reduction catalyst 3 becomes long because a sufficient distance must be taken to the type catalyst 3 and a taper part must be interposed before and after the small diameter part 10. Therefore, there has been a problem that the overall length of the exhaust gas purification device becomes longer and the mounting property on the vehicle becomes worse.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to improve the mountability of an exhaust gas purification apparatus capable of simultaneously reducing particulates and NOx as compared with the related art.

  The present invention provides a single oxidation catalyst that oxidizes HC in exhaust gas and a particulate filter that passes exhaust gas that has passed through the oxidation catalyst and collects particulates in the middle of the exhaust pipe. A selective reduction catalyst that has a property of selectively reacting NOx with ammonia even in the presence of oxygen is arranged in series in the casing with a predetermined interval, and is supported on the particulate filter integrally with the particulate filter, and the particulate filter Immediately after that, a flow-through type carrier is additionally provided by being mounted, and a mixer for agitating the flow of the exhaust gas is disposed near the outlet of the oxidation catalyst, and the mixer and the particulate filter are disposed between A urea water addition device for injecting urea water toward the mixer is arranged.

  Thus, when urea water is injected toward the mixer on the upstream side by the urea water addition device, the urea water is injected against the flow of the exhaust gas, and the flow of the exhaust gas and the injection of the urea water The urea water is easily dispersed by the collision with the flow, and the reaction time of the urea water is more easily secured than in the case of injecting in the flow direction of the exhaust gas.

  Moreover, since the urea water from the urea water addition device is injected to the place where the flow of the exhaust gas is turbulent on the outlet side of the mixer, the dispersibility of the urea water is further improved and the exhaust gas is improved. It is possible to achieve good mixing with.

  As a result, the entire range of the selective catalytic reduction catalyst in which urea water is well mixed with the exhaust gas to promote ammoniation without forming a small-diameter portion as in the prior art, and the ammonia is supported on the particulate filter. Therefore, it is possible to reduce the overall length of the exhaust emission control device by the amount that does not require the formation of the small diameter portion.

  In addition, since the selective reduction catalyst is supported on the particulate filter, the selective reduction catalyst that is additionally provided immediately after that reduces the processing capacity of the selective reduction catalyst supported on the preceding particulate filter. The capacity is small enough to be compensated, and the size of the exhaust gas purification device can be further reduced and the overall length of the exhaust emission control device can be further shortened.

  In addition, since the selective reduction catalyst is supported on the particulate filter, it must be supported with a degree that does not adversely affect the filter performance of the particulate filter, so the same NOx treatment as that of the conventional selective reduction catalyst is performed. Although it is impossible to have all the capacity on the particulate filter side, supporting the selective reduction catalyst on the particulate filter greatly contributes to downsizing of the selective reduction catalyst in the subsequent stage.

  On the other hand, the particulates in the exhaust gas are collected while passing through the particulate filter. When this particulate filter is forcibly regenerated, the post on the engine side is the same as before. HC is added to the exhaust gas by injection, etc., the added HC is oxidized with an oxidation catalyst, and the temperature of the exhaust gas is raised by reaction heat, thereby raising the catalyst bed temperature of the particulate filter and collecting the collected particulates. What is necessary is just to aim at the combustion removal of curate.

Further, in the present invention, it is preferable to add a further mixer between the particulate filter and the flow-through type selective reduction catalyst, and a leak is immediately after the flow-through type selective reduction catalyst. It is possible to arrange an NH ₃ slip catalyst that oxidizes surplus ammonia as a countermeasure against ammonia, or NH ₃ that oxidizes surplus ammonia as a countermeasure against leaked ammonia in a part of the flow-through type selective reduction catalyst. It is also possible to carry a slip catalyst.

  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, urea water can be mixed well with exhaust gas without forming a small diameter portion between the particulate filter and the selective catalytic reduction catalyst. Ammonia is promoted, and the ammonia can be reacted efficiently in the entire range of the selective catalytic reduction catalyst supported on the particulate filter. In addition, since the selective reduction catalyst is supported on the particulate filter, the selective reduction catalyst that is additionally provided immediately after that can be greatly reduced in size, and the exhaust purification device can be further reduced. Therefore, the mountability of the exhaust gas purification device capable of simultaneously reducing particulates and NOx can be greatly improved.

  (II) According to the invention described in claim 2 of the present invention, the urea water remaining in the exhaust gas that has passed through the particulate filter is further stirred by a mixer to enhance dispersibility, and good mixing with the exhaust gas is achieved. As a result, ammoniating of the urea water can be promoted, so that the ammonia can be efficiently reacted in the entire region of the selective catalytic reduction catalyst immediately after the particulate filter.

(III) According to the invention described in claim 3 of the present invention, the excess ammonia which has not been treated with the selective reduction catalyst immediately after the particulate filter and has passed through untreated is passed through the NH ₃ slip catalyst in the subsequent stage. Thus, it is possible to prevent the possibility that excess ammonia is discharged to the outside of the vehicle together with the exhaust gas without being treated.

(IV) According to the invention described in claim 4 of the present invention, surplus ammonia that is not completely treated with the selective reduction catalyst and tries to pass through untreated is supported on a part of the selective reduction catalyst. It can be oxidized with an NH ₃ slip catalyst, and it is possible to prevent the possibility that excess ammonia will be discharged out of the vehicle together with the exhaust gas without being treated. It can be realized with a compact configuration.

It is the schematic which shows an example of the form which implements this invention. It is the schematic which shows another form example of this invention. It is the schematic which shows a prior art example.

  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. In the exhaust purification apparatus of this embodiment, HC in the exhaust gas 5 is oxidized in a single casing 13 interposed in the middle of the exhaust pipe 4. An oxidation catalyst 2 to be treated and a particulate filter 1 that collects particulates through exhaust gas 5 that has passed through the oxidation catalyst 2 are arranged in series at a required interval. Instead of supporting an oxidation catalyst such as platinum, a selective catalytic reduction catalyst 3 'having the property of selectively reacting NOx with ammonia even in the presence of oxygen is supported.

  Further, a selective reduction catalyst 3 is additionally provided immediately after the particulate filter 1 by being carried on a flow-through type carrier, and this selective reduction catalyst 3 is carried on the particulate filter 1 at the preceding stage. Further, the capacity of the selective catalytic reduction catalyst 3 ′ is small enough to compensate for the shortage of the processing capacity, and it is much smaller than the conventional selective catalytic reduction catalyst.

  That is, when the selective reduction catalyst 3 'is supported on the particulate filter 1, it must be supported with a degree that does not adversely affect the filter performance of the particulate filter 1. It is impossible to have the same NOx treatment capacity as that of the catalyst on the particulate filter 1 side, and it is necessary to additionally equip the selective reduction catalyst 3 immediately after the particulate filter 1.

  Further, a mixer 14 for stirring the flow of the exhaust gas 5 is disposed in the vicinity of the outlet of the oxidation catalyst 2. Between the mixer 14 and the particulate filter 1, urea water 7 is directed toward the mixer 14. In the example illustrated here, a further mixer 15 is also provided between the particulate filter 1 and the flow-through type selective reduction catalyst 3. Separately arranged.

As in the case of the conventional example of FIG. 3 described above, immediately after the flow-through type selective reduction catalyst 3 in the casing 13, an NH ₃ slip catalyst 9 that oxidizes surplus ammonia as a countermeasure for leaked ammonia is provided. However, the NH ₃ slip catalyst 9 may be provided as necessary.

  Thus, when urea water 7 is injected toward the upstream mixer 14 by the urea water addition device 6, the urea water 7 is injected against the flow of the exhaust gas 5. When the flow and the jet flow of the urea water 7 collide with each other, the urea water 7 is easily dispersed, and the reaction time of the urea water 7 is more easily ensured than when jetting in the flow direction of the exhaust gas 5.

  Moreover, since the urea water 7 from the urea water addition device 6 is injected to the place where the flow of the exhaust gas 5 is turbulent on the outlet side of the mixer 14, the dispersibility of the urea water 7 is further increased. Thus, good mixing with the exhaust gas 5 is achieved.

  As a result, even if the conventional small diameter portion 10 (see FIG. 3) is not formed, the urea gas 7 is mixed well with the exhaust gas 5 to promote ammoniating, and the ammonia is supported on the particulate filter 1. Since the reaction can be efficiently performed in the entire range of the selective catalytic reduction catalyst 3 ′, the entire length of the exhaust purification device can be shortened by the amount that the small diameter portion 10 (see FIG. 3) is not required to be formed. It becomes possible.

Further, the urea water 7 remaining in the exhaust gas 5 that has passed through the particulate filter 1 is further stirred by the mixer 15 to enhance dispersibility, and good mixing with the exhaust gas 5 is achieved, so that the ammonia of the urea water 7 can be obtained. The ammonia is reacted efficiently in the entire region of the selective catalytic reduction catalyst 3 immediately after the particulate filter 1, and the ammonia cannot be completely treated by the selective catalytic reduction catalyst 3 immediately after the particulate filter 1. Excess ammonia that has passed through untreated is oxidized by the NH ₃ slip catalyst 9.

  On the other hand, the particulates in the exhaust gas 5 are collected while passing through the particulate filter 1, and when this particulate filter 1 is forcibly regenerated, the engine side, HC is added to the exhaust gas 5 by post-injection in the catalyst, and the added HC is oxidized by the oxidation catalyst 2 to raise the temperature of the exhaust gas 5 by reaction heat, whereby the catalyst bed temperature of the particulate filter 1 is increased. Is raised to burn and remove the collected particulates.

  Therefore, according to the above embodiment, the urea water 7 is mixed well with the exhaust gas 5 without forming the small-diameter portion 10 (see FIG. 3) between the particulate filter 1 and the selective catalytic reduction catalyst 3. As a result, the ammonia can be promoted and the ammonia can be reacted efficiently in the entire region of the selective catalytic reduction catalyst 3 supported on the particulate filter 1, so that the small diameter portion 10 (see FIG. 3) is not formed. The total length of the exhaust gas purification device can be shortened as much as necessary, and the selective reduction catalyst 3 additionally provided immediately after the particulate filter 1 is supported by the particulate filter 1 is greatly improved. Since it is possible to reduce the size and further shorten the overall length of the exhaust gas purification device, it is possible to install an exhaust gas purification device that can simultaneously reduce particulates and NOx. It can be greatly improved.

  Further, the urea water 7 remaining in the exhaust gas 5 that has passed through the particulate filter 1 is further agitated by the mixer 15 to improve dispersibility, and good mixing with the exhaust gas 5 is achieved so that the urea water 7 is ammoniated. Therefore, the ammonia can be reacted efficiently in the entire region of the selective catalytic reduction catalyst 3 immediately after the particulate filter 1.

Further, surplus ammonia that has not been treated with the selective catalytic reduction catalyst 3 immediately after the particulate filter 1 and has passed through untreated can be oxidized with the NH ₃ slip catalyst 9, and the surplus ammonia is not treated. It is possible to prevent the possibility that the exhaust gas 5 is discharged to the outside of the vehicle.

Here, in the present embodiment, the case where the NH ₃ slip catalyst 9 is separately arranged immediately after the flow-through type selective reduction catalyst 3 is illustrated, but as shown in FIG. some NH ₃ slip catalyst 9 for oxidization treatment of surplus ammonia may be carried on the.

That is, the NH ₃ slip catalyst 9 is applied to the required range in the vicinity of the downstream end of the selective catalytic reduction catalyst 3, or the selective catalytic reduction catalyst 3 is stacked on the NH ₃ slip catalyst 9 as a whole base. It can be applied to prevent leakage ammonia.

In this case, surplus ammonia that is not completely treated by the selective catalytic reduction catalyst 3 but is untreated is oxidized by the NH ₃ slip catalyst 9 supported on a part of the selective catalytic reduction catalyst 3. It can be treated, and it is possible to prevent the excess ammonia from being discharged out of the vehicle together with the exhaust gas 5 without being treated, and the measure for the surplus ammonia is realized with an extremely compact configuration. can do.

Note that the exhaust emission control device of the present invention is not limited to the above-described embodiment, and a further mixer between the particulate filter and the flow-through type selective reduction catalyst may be added as necessary. Of course, the NH ₃ slip catalyst may be added as necessary, and various modifications may be made without departing from the scope of the present invention.

1 particulate filter 2 oxidation catalyst 3 selective catalytic reduction catalyst 3 'selective reduction catalyst 4 exhaust pipe 5 exhaust gas 6 the urea water addition device 7 urea water 9 NH ₃ slip catalyst 13 casing 14 mixer 15 Mixer

Claims (4)

  An oxidation catalyst that oxidizes HC in the exhaust gas and a particulate filter that passes the exhaust gas that passes through the oxidation catalyst and collects particulates are required in a single casing interposed in the middle of the exhaust pipe. The selective reduction catalyst having the property of being arranged in series at an interval and selectively reacting NOx with ammonia even in the presence of oxygen is integrally supported on the particulate filter, and immediately after the particulate filter. A mixer that stirs the flow of the exhaust gas is arranged near the outlet of the oxidation catalyst, and is mounted on a flow-through type carrier, and urea is directed to the mixer between the mixer and the particulate filter. An exhaust gas purification apparatus comprising a urea water addition apparatus for injecting water.   2. The exhaust emission control device according to claim 1, further comprising a mixer added between the particulate filter and the flow-through type selective reduction catalyst. The exhaust emission control device according to claim 1 or 2, wherein an NH ₃ slip catalyst that oxidizes surplus ammonia is disposed immediately after the flow-through type selective reduction catalyst as a measure against leakage ammonia. The exhaust purification apparatus according to claim 1 or 2, wherein a part of the flow-through type selective reduction catalyst carries an NH ₃ slip catalyst that oxidizes surplus ammonia as a countermeasure against leakage ammonia.

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