JP2014001664A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of rising a temperature of an aftertreatment device of a selective reduction type catalyst and the like at an earlier stage than conventional.SOLUTION: An exhaust pipe 2 upstream of an oxidation catalyst 9 is provided with: a fuel addition device 10 (fuel addition means) for directly injecting fuel 8 in the exhaust pipe 2; and a modified gas addition device 12 (modified gas addition means) for dissolving the fuel 8 into modified gas 11 with high response and introducing it in the exhaust pipe 2. The modified gas 11 is introduced by the modified gas addition device 12 when a temperature of the oxidation catalyst 9 is not less than a first temperature that is an active lower limit temperature at which the modified gas 11 from the modified gas addition device 12 can be oxidized, and lower than a second temperature that is an active lower limit temperature at which the added fuel 8 from the fuel addition device 10 can be oxidized. The fuel 8 can be directly injected by the fuel addition device 10 when the temperature of the oxidation catalyst 9 is not less than the second temperature.

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. In recent years, it has been difficult to ensure the safety of traveling with ammonia itself, and in recent years, the use of urea water as a reducing agent has been studied.

That is, if urea water is added into the exhaust gas upstream of the selective catalytic reduction catalyst, the urea water is thermally decomposed 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

  As prior art document information related to this type of exhaust purification device, there is the following Patent Document 1 and the like.

JP 2002-161732 A

  However, in such an exhaust purification device, sufficient catalytic activity cannot be obtained unless the temperature of the selective catalytic reduction catalyst reaches about 200 ° C. Therefore, the temperature of the selective catalytic reduction catalyst is about 200 at the time of cold start. The urea water cannot be added until the temperature reaches about 0 ° C., and during this time, NOx is discharged without being purified, and the NOx reduction rate is greatly reduced.

  By the way, during such cold start, the engine warm-up is given priority and exhaust gas recirculation (EGR) is also stopped, so NOx is suppressed by exhaust gas recirculation. There was also a circumstance that it was not possible.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide an exhaust purification device that can raise the temperature of an aftertreatment device such as a selective catalytic reduction catalyst earlier than before.

  The present invention includes an oxidation catalyst upstream of a post-treatment device in the middle of an exhaust pipe, and fuel is added to the oxidation catalyst, and the heat of the post-treatment device is generated by reaction heat when the fuel undergoes an oxidation reaction on the oxidation catalyst. An exhaust emission control device that can increase the temperature of the exhaust gas, the fuel adding means for directly injecting the fuel into the exhaust pipe upstream of the oxidation catalyst, and the fuel is decomposed into a highly reactive reformed gas. And a reformed gas adding means for introducing the fuel into the exhaust pipe, and the temperature of the oxidation catalyst is equal to or higher than a first temperature that forms a lower limit activation temperature at which the reformed gas from the reformed gas adding means can be oxidized, and the fuel The reformed gas is introduced by the reformed gas adding means when the added fuel from the adding means is lower than a second temperature that constitutes a minimum active temperature at which oxidation treatment is possible, and the temperature of the oxidation catalyst is set to the second temperature. When it is over temperature, add fuel It is characterized in that it has configured to be able to implement the direct injection of fuel by.

  Thus, in this way, even when the temperature of the oxidation catalyst is lower than the second temperature at which the added fuel can be oxidized, the reformed gas is added when the temperature reaches the first temperature lower than the second temperature. The reformed gas is introduced by the means, the highly reactive reformed gas is oxidized by the oxidation catalyst disposed downstream thereof, and the temperature of the oxidation catalyst is rapidly raised by the heat of reaction. As a result, the fuel is switched from the introduction of the reformed gas by the reformed gas adding means to the direct injection of the fuel into the exhaust pipe by the fuel adding means, and the added fuel is directly oxidized by the activated oxidation catalyst. The exhaust gas heated by the reaction heat further passes through the downstream aftertreatment device, so that the temperature of the aftertreatment device is raised earlier than before.

  Also, in the present invention, the reformed gas adding means accommodates a reforming catalyst having a ventilation structure having the property of decomposing fuel into a reformed gas having high reactivity and one end side containing the reforming catalyst. A casing opened in the exhaust pipe, a carrier air supply pipe connected to the other end side of the casing to guide the carrier air for scavenging the reformed gas to one end side, and a fuel connected to the other end side of the casing It is preferable that a fuel supply pipe that supplies the reforming catalyst and a heating unit that heats the reforming catalyst are provided.

  When the reformed gas adding means is configured in this way, the reforming catalyst is heated by the heating means to increase the catalytic activity, and then the fuel is supplied to the reforming catalyst from the fuel supply pipe, and the other end of the casing is provided. When the carrier air is guided from the carrier air supply pipe, the fuel is decomposed into the reformed gas having high reactivity by the reforming catalyst and is sent out into the exhaust pipe by the carrier air.

  In the present invention, the reformed gas adding means includes an ignition means for igniting the reformed gas, and a combustion air supply pipe for guiding combustion air for assisting the combustion of the reformed gas. It is preferable that when the temperature is lower than the first temperature, a reformed gas is generated by the reformed gas adding means, and the reformed gas is ignited to perform burner combustion.

  When the reformed gas addition means is configured in this way, even if the temperature of the oxidation catalyst is lower than the first temperature, the reformed gas generated by the reformed gas addition means is ignited by the ignition means and the combustion air is supplied. Burner combustion is performed by supplying combustion air through the pipe, so that the oxidation catalyst is quickly heated by the burner combustion and reaches the first temperature.

  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 first and second aspects of the present invention, when the temperature of the oxidation catalyst is lower than the second temperature at which the added fuel can be oxidized, the first temperature lower than the second temperature. The reformed gas is introduced by the reformed gas adding means from the stage of reaching the temperature, and the reformed gas is oxidized with the downstream oxidation catalyst to rapidly raise the temperature of the oxidation catalyst with the reaction heat. The temperature can be reached, and after that, by adding the reformed gas by the reformed gas adding means to the direct injection into the exhaust pipe of the fuel by the fuel adding means, it is added by the oxidation catalyst having increased activity. By directly oxidizing the fuel, the exhaust gas is heated using the maximum amount of heat generated by the fuel, and the exhaust gas is further passed through the downstream post-treatment device, thereby making the post-treatment device earlier than before. For example, after treatment When the apparatus is a selective reduction catalyst using urea water as a reducing agent, the selective reduction catalyst can be activated at an early stage even at the time of cold start so that the addition of urea water can be started at an earlier stage than before. The NOx reduction rate at the time of cold start can be greatly improved, and when the aftertreatment device is a particulate filter, the particulate filter can be particulated at an early stage even under operating conditions where the exhaust temperature is low. It is possible to reach a regeneration temperature at which (apportioned) can be removed by combustion, and the regeneration time of the particulate filter can be greatly shortened.

  (II) According to the invention described in claim 3 of the present invention, when the temperature of the oxidation catalyst is lower than the first temperature, the reformed gas generated by the reformed gas addition means is ignited by the ignition means. As a result, burner combustion can be performed, and the oxidation catalyst can be quickly heated to the first temperature by the burner combustion, so that the start timing of introduction of the reformed gas by the reformed gas adding means can be advanced. As a result, the timing for switching to direct injection of fuel into the exhaust pipe by the fuel addition means can be advanced, so that the temperature of the post-treatment device can be raised even more quickly.

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 reformed gas addition apparatus of FIG. It is a graph which shows the time transition of the exit temperature of the oxidation catalyst in the example of FIG. It is the schematic which shows another form example of this invention. It is a graph which shows temporal transition of the exit temperature of the oxidation catalyst in the example of FIG.

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

  FIG. 1 shows an example of an embodiment of the present invention. A selective reduction type having the property of selectively reacting NOx with ammonia even in the presence of oxygen in the middle of an exhaust pipe 2 through which exhaust gas 1 flows. A catalyst 3 (post-treatment device) is provided, and a urea water addition device 5 for adding urea water 4 as a reducing agent is disposed on the inlet side of the selective reduction catalyst 3. On the side, an ammonia reduction catalyst 6 that oxidizes excess ammonia that is generated from the urea water 4 and passes through the selective reduction catalyst 3 without reacting is provided.

  Further, the exhaust pipe 2 upstream of the urea water addition device 5 is equipped with a particulate filter 7 (post-treatment device) that collects particulates in the exhaust gas 1. On the inlet side, an oxidation catalyst 9 capable of oxidizing the fuel 8 added to the exhaust gas 1 is equipped.

  Then, a fuel addition device 10 for directly injecting fuel 8 into the exhaust pipe 2 to the exhaust pipe 2 upstream from the oxidation catalyst 9 and a reformed gas 11 having high reactivity are decomposed into the exhaust pipe 2. A reformed gas addition device 12 to be introduced into the fuel is provided, and the operations of the fuel addition device 10, the reformed gas addition device 12, and the urea water addition device 5 are controlled by the control device 13 via a control signal 13a. It has become so.

  The control signal 13a in FIG. 1 extends directly toward the fuel addition device 10, the reformed gas addition device 12, and the urea water addition device 5 for convenience of explanation. Of course, it is output as an electrical signal to the equipment responsible for the operation.

  Here, a temperature sensor 14 for detecting the temperature of the exhaust gas 1 as a substitute value for the temperature of the oxidation catalyst 9 is disposed on the outlet side of the oxidation catalyst 9, and the inlet side of the selective catalytic reduction catalyst 3. Is provided with a temperature sensor 15 for detecting the temperature of the exhaust gas 1 as a substitute value for the temperature of the selective catalytic reduction catalyst 3, and detection signals 14 a and 15 a of these temperature sensors 14 and 15 are used as the control device 13. To be input.

  In the control device 13, based on the detection signals 14 a and 15 a of the temperature sensors 14 and 15, the lower limit of the activity at which the temperature of the oxidation catalyst 9 can oxidize the reformed gas 11 from the reformed gas addition device 12. When the temperature is lower than the first temperature (about 80 ° C.) that is higher than the first temperature (about 80 ° C.) and lower than the second temperature (about 200 ° C.) that constitutes the lower limit temperature of activation of the added fuel 8 from the fuel addition device 10 When the reformed gas 11 is introduced by the reformed gas adding device 12 and the temperature of the oxidation catalyst 9 is equal to or higher than the second temperature, the fuel adding device 10 can directly inject the fuel 8. It is.

Further, with reference to FIG. 2, the specific structure of the reformed gas addition device 12 will be supplemented. This reformed gas addition device 12 is a vent having the property of decomposing the fuel 8 into H ₂ and CO. A reforming catalyst 16 having a structure, a casing 17 containing the reforming catalyst 16 and having one end opened into the exhaust pipe 2, and connected to the other end of the casing 17 to connect the reformed gas 11 to one end. A carrier air supply pipe 19 that guides the carrier air 18 for scavenging, a fuel supply pipe 20 that is connected to the other end of the casing 17 and supplies the fuel 8 to the reforming catalyst 16, and the reforming catalyst 16 A glow plug 21 (heating means) for heating is provided.

  Here, the reforming catalyst 16 having the ventilation structure can be configured by coating a metal mesh with a catalyst raw material, for example, and an appropriate number of glow plugs 21 are inserted into the casing 17 from the other end side. The reforming catalyst 16 can be heated by energizing each glow plug 21 to generate heat.

  When the reformed gas 11 is introduced into the exhaust pipe 2 by the reformed gas addition device 12, the reforming catalyst 16 is heated by the glow plug 21 to increase the catalytic activity, and the reforming catalyst 16 is supplied with fuel. When the fuel 8 is supplied from the supply pipe 20 and the carrier air 18 is guided from the carrier air supply pipe 19 to the other end side of the casing 17, the fuel 8 is decomposed into a highly reactive reformed gas 11 by the reforming catalyst 16. Then, it is sent out into the exhaust pipe 2 by the carrier air 18.

Thus, when the exhaust gas purification apparatus is configured in this way, as shown by the curve A in the graph of FIG. 3, the temperature of the oxidation catalyst 9 is the second temperature (about 200 ° C.) at which the added fuel 8 can be oxidized. However, the reformed gas addition device 12 introduces the reformed gas 11 at the stage T ₁ when the temperature reaches a first temperature (about 80 ° C.) lower than the second temperature, and is disposed downstream of the first temperature. The reformed gas 11 having high reactivity is oxidized by the oxidation catalyst 9 and the temperature of the oxidation catalyst 9 is rapidly raised by the reaction heat to reach the second temperature. At this stage T ₂ , the reformed gas The introduction of the reformed gas 11 by the addition device 12 is switched to the direct injection of the fuel 8 into the exhaust pipe 2 by the fuel addition device 10, and the added fuel 8 is directly oxidized by the oxidation catalyst 9 having increased activity, The exhaust gas 1 heated by the reaction heat is further selectively reduced downstream. 3, the temperature of the selective catalytic reduction catalyst 3 is raised earlier than before (if there is no prior introduction of the reformed gas 11, until the stage T _{3 that} is later than the stage T ₂ as shown by the curve B). The addition of fuel 8 cannot be started).

  Therefore, according to the present embodiment, when the temperature of the oxidation catalyst 9 is lower than the second temperature at which the added fuel 8 can be oxidized, the reformed gas starts from the stage where the first temperature lower than the second temperature is reached. The reforming gas 11 is introduced by the adding device 12, and the reforming gas 11 is oxidized with the downstream oxidation catalyst 9, whereby the oxidation catalyst 9 is rapidly heated with the reaction heat to reach the second temperature. Thereafter, by switching from the introduction of the reformed gas 11 by the reformed gas adding device 12 to the direct injection of the fuel 8 into the exhaust pipe 2 by the fuel adding device 10, the oxidation catalyst with increased activity is obtained. 9, by directly oxidizing the added fuel 8, the exhaust gas 1 is heated using the maximum amount of heat generated by the fuel 8, and the exhaust gas 1 passes through the selective catalytic reduction catalyst 3 further downstream. Therefore, the selective catalytic reduction catalyst 3 is made earlier than before. The temperature can be raised, and the selective catalytic reduction catalyst 3 can be activated at an early stage even at the time of cold start so that the addition of the urea water 4 can be started from an earlier stage than before, and the NOx reduction rate at the cold start is greatly increased. Can be improved.

  Here, as a supplementary explanation, since the fuel 8 is already decomposed into the reformed gas 11 by the reforming catalyst 16, energy loss has already occurred. It is not efficient to raise the temperature of the selective catalytic reduction catalyst 3 only by introducing the fuel, and the direct addition of the fuel 8 into the exhaust pipe 2 by the fuel addition device 10 is switched as soon as possible to maximize the heat generation amount of the fuel 8. It is important to use it.

  Further, in the example shown here, the particulate filter 7 is provided on the upstream side of the selective catalytic reduction catalyst 3. However, when the particulate filter 7 is forcibly regenerated, the above-described fuel addition device is provided. By diverting the switching control between 10 and the reformed gas addition device 12, the particulate filter 7 can reach a regeneration temperature at which particulates (prorated) can be burned and removed at an early stage even under operating conditions with a low exhaust temperature. Thus, the regeneration time of the particulate filter 7 can be greatly shortened.

  When the particulate filter 7 is forcibly regenerated, post-injection is added at a non-ignition timing later than the compression top dead center in the engine (not shown) following the main injection of fuel performed near the compression top dead center. Therefore, it is common to add fuel to the exhaust gas 1, because it takes time to reach a temperature at which post injection can be used, and the amount of fuel added cannot be controlled independently of the engine side. There is a problem that temperature control is difficult, but there is also an advantage that these problems can be eliminated.

  FIG. 4 shows another embodiment of the present invention. In this embodiment, the reformed gas adding device 12 is provided with a glow plug 22 as an ignition means for igniting the reformed gas 11. A configuration in which a combustion air supply pipe 24 that guides combustion air 23 that assists combustion of the reformed gas 11 is connected to a position immediately before the glow plug 22 in the casing 17 is disposed at the gas outlet portion 17a on one end side. In addition to the switching control between the fuel addition device 10 and the reformed gas addition device 12 described above, the reformed gas 11 is generated by the reformed gas addition device 12 when the temperature of the oxidation catalyst 9 is lower than the first temperature. In addition, the reformed gas 11 can be ignited to perform burner combustion.

When the reformed gas addition device 12 is configured in this way, even if the temperature of the oxidation catalyst 9 is lower than the first temperature, as shown by the curve A ′ in the graph of FIG. Since the generated reformed gas 11 is ignited by the glow plug 22 and the combustion air 23 is supplied by the combustion air supply pipe 24, the burner combustion is performed. Therefore, the oxidation catalyst 9 is quickly heated by the burner combustion. Thus, the first temperature is reached, and the introduction of the reformed gas 11 by the reformed gas addition device 12 is started from the stage T ₁ ′ earlier than the stage T ₁ (see FIG. 3) in the embodiment of FIGS. The direct injection of the fuel 8 into the exhaust pipe 2 by the fuel addition device 10 is started from the stage T ₂ ′ earlier than the stage T ₂ (see FIG. 3) in the embodiment of FIGS. (There is no burner combustion and the reformed gas 11 Line introduction can not start addition of fuel 8 even the stage T ₂ later stage T ₃ than 'as indicated by a curve B if).

  Therefore, according to the present embodiment, burner combustion is performed by igniting the reformed gas 11 generated by the reformed gas adding device 12 by the ignition means when the temperature of the oxidation catalyst 9 is lower than the first temperature. The oxidation catalyst 9 can be quickly heated up to the first temperature by the burner combustion, so that the start timing of the introduction of the reformed gas 11 by the reformed gas addition device 12 can be advanced and extended. In this case, the timing for switching the fuel 8 to the direct injection of the fuel 8 into the exhaust pipe 2 can be advanced, so that the temperature of the selective catalytic reduction catalyst 3 can be increased more quickly to achieve further activation. It is possible to further improve the NOx reduction rate at the time of cold start.

  Further, even when the particulate filter 7 is forcibly regenerated, the temperature of the particulate filter 7 can be increased more quickly to reach a regeneration temperature at which the particulates can be burned and removed earlier. The regeneration time of the particulate filter 7 can be further greatly shortened.

  Note that the exhaust emission control device of the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

2 Exhaust pipe 3 Selective reduction catalyst (post-processing equipment)
7 Particulate filter (post-processing device)
8 Fuel 9 Oxidation catalyst 10 Fuel addition device (fuel addition means)
11 Reformed gas 12 Reformed gas addition device (reformed gas addition means)
16 reforming catalyst 17 casing 18 carrier air 19 carrier air supply pipe 20 fuel supply pipe 21 glow plug (heating means)
22 Glow plug (ignition means)
23 Combustion air 24 Combustion air supply pipe

Claims (3)

  An oxidation catalyst is provided upstream of the aftertreatment device in the middle of the exhaust pipe, and fuel is added to the oxidation catalyst, and the temperature of the aftertreatment device is increased by reaction heat when the fuel undergoes an oxidation reaction on the oxidation catalyst. An exhaust gas purification apparatus configured to obtain a fuel addition means for directly injecting fuel into an exhaust pipe upstream of the oxidation catalyst, and decomposing the fuel into a highly reformed reformed gas into the exhaust pipe. A reformed gas adding means to be introduced, wherein the temperature of the oxidation catalyst is equal to or higher than a first temperature that constitutes an activation lower limit temperature at which the reformed gas from the reformed gas adding means can be oxidized, and from the fuel adding means. When the reformed gas is introduced by the reformed gas adding means when the temperature is lower than the second temperature that is the minimum active temperature at which the added fuel can be oxidized, the temperature of the oxidation catalyst becomes equal to or higher than the second temperature. When fuel is added Exhaust gas purification apparatus characterized by being configured so as to implement the direct injection of.   A reforming catalyst having a ventilation structure in which the reformed gas adding means has a property of decomposing fuel into a highly reactive reformed gas; and a casing containing the reforming catalyst and having one end opened in the exhaust pipe; A carrier air supply pipe connected to the other end side of the casing to guide the carrier air for scavenging the reformed gas to one end side, and connected to the other end side of the casing to supply fuel to the reforming catalyst The exhaust emission control device according to claim 1, further comprising a fuel supply pipe that performs heating and a heating unit that heats the reforming catalyst.   The reformed gas adding means includes an ignition means for igniting the reformed gas, and a combustion air supply pipe for guiding combustion air for assisting combustion of the reformed gas, and the temperature of the oxidation catalyst falls below the first temperature. 3. The burner combustion can be performed by generating a reformed gas by the reformed gas addition means when turning and igniting the reformed gas. 4. Exhaust purification device.

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