JP2007009718A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device adapted for suppressing deterioration of fuel consumption, and making added fuel react in a post-treatment device from a relatively low temperature zone. <P>SOLUTION: The exhaust emission control device is provided with a pair of NOx storage reducing catalysts 5A and 5B in an exhaust pipe 4 as the post-treatment device requiring addition of fuel, and a fuel adding device 23 for adding fuel into exhaust gas 3 on the upstream sides of the respective NOx storage reducing catalysts 5A and 5B. This device also includes an additive tank 14 independent of a fuel tank 20 for supplying light oil 19 as fuel to a diesel engine 1, and is configured so as to supply kerosene 18 from the additive tank 14 to the fuel adding device 23 through a supply line 15. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device.

Conventionally, it has been practiced to provide an aftertreatment device that requires fuel addition in the middle of the exhaust pipe to purify exhaust gas. As this type of aftertreatment device, when the exhaust air-fuel ratio is lean, NOx occluded with the ability to oxidize and temporarily store NOx in the form of nitrate, and to reduce and purify NOx by decomposing and releasing it through the presence of unburned HC, CO, etc. when the O ₂ concentration in the exhaust gas decreases Reduction catalysts are known.

In this NOx occlusion reduction catalyst, when the occlusion amount of NOx increases and reaches the saturation amount, no more NOx can be occluded, so the O ₂ concentration of the exhaust gas flowing into the NOx occlusion reduction catalyst periodically. Needs to be reduced to decompose and release NOx.

For example, when used in a gasoline engine, the operating air-fuel ratio of the engine is reduced (the engine is operated at a rich air-fuel ratio), thereby reducing the O ₂ concentration in the exhaust gas and unburned HC in the exhaust gas. It is possible to promote the decomposition and release of NOx by increasing reducing components such as CO and CO. However, when the NOx storage reduction catalyst is used as an exhaust purification device of a diesel engine, it is difficult to operate the engine at a rich air-fuel ratio. is there.

For this reason, by adding fuel (HC) to the exhaust gas upstream of the NOx storage reduction catalyst, the added fuel is used as a reducing agent to react with O ₂ on the NOx storage reduction catalyst. ₂ It is necessary to reduce the concentration (see, for example, Patent Document 1).

Further, since SO ₂ derived from the sulfur content in the fuel exists in the exhaust gas of the diesel engine, there is a possibility that the NOx storage reduction catalyst may be poisoned by this SO ₂ , as described above. If fuel (HC) is added to the exhaust gas upstream of the NOx storage reduction catalyst and an oxidation reaction is carried out on the catalyst, the heat of reaction raises the catalyst bed temperature of the NOx storage reduction catalyst to about 600 ° C. or higher. It is also possible to desulfurize the components.

  On the other hand, as a measure to reduce particulate matter (particulate matter) emitted from diesel engines, a particulate filter carrying an oxidation catalyst is installed in the middle of the exhaust pipe to collect particulates in the exhaust gas. However, it has already been proposed that the oxidation reaction of the collected particulates is promoted by an oxidation catalyst to achieve efficient combustion removal of the particulates.

  However, this type of oxidation catalyst has an active temperature range, and if the operation state continues at an exhaust temperature that falls below its lower activation limit temperature, the oxidation catalyst will not be activated and the particulates will not be burned and removed well. If necessary, fuel is added to the exhaust gas on the upstream side, and the added fuel is thermally decomposed in high-temperature exhaust gas to produce high-concentration HC gas. It has been proposed that the catalyst bed temperature is positively increased by the reaction heat by oxidizing the catalyst on the oxidation catalyst.

As described above with some examples, fuel is added to the upstream side of the aftertreatment device (NOx storage reduction catalyst, oxidation catalyst, or particulate filter carrying these) installed in the middle of the exhaust pipe. The idea itself has been proposed previously.
JP 2000-356127 A

  However, in the past, since light oil fuel used for driving the diesel engine was diverted from the fuel tank and added to the upstream side of the aftertreatment device, the fuel consumption was greatly deteriorated, Under operating conditions where the exhaust temperature required to react (combust) the added fuel with the aftertreatment device cannot be obtained (for example, slow driving in a city with heavy traffic), the performance of the aftertreatment device is efficiently extracted. There was a problem that I could not.

  The present invention has been made in view of the above-described circumstances, and provides an exhaust emission control device that can suppress the deterioration of fuel consumption as compared with the prior art and allow the added fuel to react with the aftertreatment device from a relatively low temperature range. It is an object.

  The present invention relates to an exhaust purification apparatus equipped with an aftertreatment device that requires fuel addition in the middle of an exhaust pipe and a fuel addition device that adds fuel into exhaust gas upstream of the aftertreatment device. The fuel tank is provided with an additive tank independent from the fuel tank for supplying the fuel, and the fuel can be supplied from the additive tank to the fuel adding device.

  Thus, in this way, the fuel is introduced from the additive tank different from the fuel tank to the fuel addition device and added to the exhaust gas. Makes it possible to use different types of light and inexpensive fuels, reducing the total fuel consumption by the amount of fuel tank fuel that is relatively expensive and not having to be used for addition to the aftertreatment system. By using an additive fuel that is softer than the fuel used to drive the vehicle, the reactivity in the low temperature range can be increased.

Further, in the present invention, a reforming catalyst for decomposing HC components in the fuel into H ₂ and CO in the exhaust gas is provided between the fuel addition position by the fuel addition device and the aftertreatment device, An electric heater is preferably provided between the addition position and the reforming catalyst and around the reforming catalyst.

In this way, the fuel added by the fuel addition device is heated by the electric heater to generate high-concentration HC gas, and the HC gas is used as the reforming catalyst whose catalyst bed temperature is increased by the heating of the electric heater. Since it is decomposed into highly reactive H ₂ and CO when passing through, it is lower than the case where HC gas is introduced as it is with highly reactive H ₂ and CO in the post-treatment device arranged in the subsequent stage. The reaction starts from temperature. At this time, if an additive fuel that is lighter than the fuel in the fuel tank is employed, it goes without saying that the decomposition of the HC gas into H ₂ and CO in the reforming catalyst proceeds efficiently.

  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, a light and inexpensive fuel different from the fuel in the fuel tank can be adopted as the added fuel, so that the fuel tank is relatively expensive. The fuel consumption can be reduced by reducing the total fuel consumption as much as it is not necessary to use it as an additive to the aftertreatment device, and it is also softer than the fuel used to drive the engine. By employing the fuel, the added fuel can be reacted in the aftertreatment device from a relatively low temperature range.

(II) According to the invention described in claim 2 of the present invention, the fuel added by the fuel adding device is decomposed into H ₂ and CO by the reforming catalyst, and compared with these highly reactive H ₂ and CO. Since the reaction can occur in the post-treatment device from a low temperature range, for example, operating conditions where low exhaust temperatures and low exhaust temperatures are likely to be continued, such as slow driving in cities with heavy traffic congestion. However, the performance of the post-processing apparatus can be efficiently extracted.

  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, the exhaust pipe 4 through which the exhaust gas 3 discharged from the diesel engine 1 through the exhaust manifold 2 flows is shown. Further, a pair of NOx occlusion reduction catalysts 5A and 5B having a flow-through type honeycomb structure are mounted in parallel by being held in the casings 6A and 6B, and are upstream of the inlet sides of the casings 6A and 6B. The exhaust pipe 4 is branched and connected in a bifurcated manner, and the exhaust pipes 4 are joined again on the outlet side of the casings 6A and 6B to form a tail pipe.

  Further, in the example shown here, the particulate filters 7A and 7B carrying the oxidation catalyst are accommodated in the subsequent stage of the NOx storage reduction catalysts 5A and 5B in the casings 6A and 6B. The exhaust gas 3 that has passed through the NOx storage reduction catalysts 5A and 5B is passed through the particulate filters 7A and 7B, and the particulates in the exhaust gas 3 are collected.

  An exhaust distribution valve that distributes the main flow of the exhaust gas 3 to one of the NOx storage reduction catalysts 5A and 5B and narrows the flow rate of the other exhaust gas 3 at a branch portion on the inlet side of the casings 6A and 6B. 8 is rotatably provided.

  Here, on the back side of the exhaust distribution valve 8, a bypass pipe 11 that extracts and guides a part of the exhaust gas 3 from the outlet of the turbine 10 of the turbocharger 9 is connected from a direction perpendicular to the drawing. The exhaust gas 3 from the bypass pipe 11 is introduced into one of the NOx storage reduction catalysts 5A and 5B, in which the main flow of the exhaust gas 3 from the upstream exhaust pipe 4 is narrowed by the exhaust distribution valve 8. It is supposed to be.

An appropriate position of the bypass pipe 11 is equipped with a reforming catalyst 12 that decomposes an HC component obtained by fuel addition, which will be described later, into H ₂ and CO in the exhaust gas 3. For example, it is possible to use an oxide such as alumina or silica or a composite oxide such as zeolite that supports Pd, Pt, Rh, or the like as an active metal.

  Further, an injection nozzle 13 is provided through the bypass pipe 11 on the inlet side of the reforming catalyst 12, and the supply line 15 connects between the injection nozzle 13 and the additive tank 14 provided at a required location. The kerosene 18 (fuel as the reducing agent) in the additive tank 14 is supplied to the reforming catalyst 12 through the injection nozzle 13 by driving the supply pump 16 provided in the middle of the supply line 15 and opening the addition valve 17. The fuel addition device 23 is constituted by the injection nozzle 13, the supply line 15, the supply pump 16, and the addition valve 17.

  Here, the additive tank 14 described above is independent from the fuel tank 20 for supplying the diesel engine 1 with the light oil 19 as a fuel. Here, a case where kerosene 18 is stored as an additive is illustrated. However, the fuel is not necessarily limited to kerosene 18 as long as it is lighter than light oil 19.

  Further, electric heaters 21 and 22 are provided between the injection nozzle 13 forming the addition position of kerosene 18 and the reforming catalyst 12 and around the reforming catalyst 12, and exhaust temperatures are provided by these electric heaters 21 and 22. And the catalyst bed temperature can be increased.

Thus, as shown in FIG. 1 as an example, the main flow of the exhaust gas 3 from the diesel engine 1 is distributed to one NOx occlusion reduction catalyst 5A by the exhaust distribution valve 8, and the reforming catalyst by the bypass pipe 11 When the exhaust gas 3 guided through 12 is distributed to the other NOx occlusion reduction catalyst 5B and the kerosene 18 is added to the inlet side of the reforming catalyst 12 by the fuel addition device 23, the kerosene 18 is heated by the electric heater 21. When the HC gas passes through the reforming catalyst 12 in which high-concentration HC gas is generated and the catalyst bed temperature is increased by the heating of the electric heater 22, it reacts with O ₂ coexisting in the atmosphere to react with the ambient temperature. And after O ₂ is consumed, it is decomposed into highly reactive H ₂ and CO and introduced into the NOx occlusion reduction catalyst 5B in the subsequent stage.

As a result, the concentration of O ₂ in the atmosphere becomes almost zero from the introduction stage, and the decomposition and release of NOx is immediately started, and the conventional light oil is directly reacted with H ₂ and CO which are highly reactive on the surface of the NO x storage reduction catalyst 5B. The NOx is efficiently reduced to N ₂ from a temperature lower than the combustion temperature in 19 addition.

  Note that the addition of kerosene 18 by the fuel addition device 23 is mainly performed only for the exhaust gas 3 having a relatively small flow rate guided by the bypass pipe 11, and therefore, the excess air ratio in the exhaust gas 3 even when the addition amount is smaller than the conventional amount. Is effectively reduced, and the NOx occlusion reduction catalyst 5B can be efficiently regenerated by adding the minimum amount of kerosene 18.

Further, since kerosene 18 that is lighter than the light oil 19 in the fuel tank 20 is used as an additive, the light oil 19 that is the fuel of the diesel engine 1 is also used for the decomposition of the kerosene 18 into H ₂ and CO. The process proceeds more efficiently than when the catalyst 12 is decomposed into H ₂ and CO.

  If the other NOx occlusion reduction catalyst 5B is regenerated while the NOx occlusion reduction catalyst 5A performs NOx occlusion in this way, one of the NOx occlusion reduction catalysts 5A, 5B is always used. It is possible to regenerate the pair of NOx storage reduction catalysts 5A and 5B alternately one by one while continuously reducing NOx as possible.

  Therefore, according to the above embodiment, the kerosene 18 is led from the additive tank 14 different from the fuel tank 20 to the fuel addition device 23 and added to the exhaust gas 3. Light and inexpensive kerosene 18 that is different from the light oil 19 in the fuel tank 20 can be used, and the light oil 19 in the fuel tank 20 that is relatively expensive is used for addition to the NOx storage reduction catalysts 5A and 5B. By reducing the total fuel consumption by the amount that is not required, the deterioration of the fuel consumption can be suppressed as compared with the prior art, and the use of kerosene 18 that is softer than the light oil 19 used to drive the diesel engine 1 is relatively From the low temperature range, the added fuel can be reacted with the NOx storage reduction catalysts 5A and 5B to obtain the NOx reduction effect.

Particularly in the present embodiment, the kerosene 18 added by the fuel addition device 23 is decomposed into H ₂ and CO by the reforming catalyst 12, and these highly reactive H ₂ and CO are used in a relatively low temperature range. Since the reaction can be caused by the NOx occlusion reduction catalysts 5A and 5B, even under an operating condition in which an operating state where the exhaust temperature is low and the exhaust temperature is low is easily continued, such as slow driving in a city where there is a lot of traffic. The performance of the NOx storage reduction catalysts 5A and 5B can be efficiently extracted.

FIG. 2 shows another embodiment of the present invention. In the embodiment of FIG. 1 described above, a pair of NOx occlusion reduction catalysts 5A and 5B are provided in parallel as an aftertreatment device in the middle of the exhaust pipe 4. Instead, the oxidation catalyst 24 and the particulate filter 25 are installed in series in the middle of the exhaust pipe 4 as an aftertreatment device and are held by the casing 26, and are configured in the same manner as in FIG. The kerosene 18 can be decomposed into H ₂ and CO by the fuel adding device 23 and introduced into the vicinity of the inlet of the casing 26.

Thus, when it becomes necessary to perform forced regeneration of the particulate filter 25, if the kerosene 18 is added as a reducing agent to the inlet side of the reforming catalyst 12 by the fuel addition device 23, the kerosene 18 is caused to flow by the electric heater 21. When the HC gas passes through the reforming catalyst 12 that is heated to generate high-concentration HC gas and the catalyst bed temperature is increased by heating of the electric heater 22, it reacts with O ₂ coexisting in the atmosphere. After the temperature is raised and O ₂ is consumed, it is decomposed into highly reactive H ₂ and CO and introduced into the oxidation catalyst 24, and passes through the oxidation catalyst 24 by reaction heat due to the oxidation reaction on the oxidation catalyst 24. The exhaust gas 3 to be heated is heated, and the introduction of the exhaust gas 3 raises the catalyst bed temperature of the particulate filter 25, so that the collected particulates are efficiently burned and removed.

  As described above, even when the particulate filter 25 including the oxidation catalyst 24 is used as the post-treatment device, the kerosene 18 is guided from the additive tank 14 different from the fuel tank 20 to the fuel addition device 23. Since it is added into the exhaust gas 3, a light and inexpensive kerosene 18 different from the light oil 19 in the fuel tank 20 can be used as the added fuel, and the fuel tank 20 is relatively expensive. It is possible to reduce the total fuel consumption as much as it is not necessary to use the light oil 19 for the addition to the particulate filter 25, and to suppress the deterioration of the fuel consumption as compared with the conventional fuel oil 19 than the light oil 19 used for driving the diesel engine 1. In addition, by using the soft kerosene 18, the particulate filter 25 can be favorably regenerated from a relatively low temperature range.

  Note that the exhaust purification device of the present invention is not limited to the above-described embodiment, and the fuel added by the fuel addition device is not limited to kerosene, and within the scope not departing from the gist of the present invention. Of course, various changes can be made.

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.

Explanation of symbols

1 Diesel engine (engine)
3 Exhaust gas 4 Exhaust pipe 5A NOx storage reduction catalyst (post-treatment device)
5B NOx occlusion reduction catalyst (post-treatment device)
7A particulate filter (post-processing device)
7B particulate filter (post-processing device)
DESCRIPTION OF SYMBOLS 12 Reforming catalyst 13 Injection nozzle 14 Additive tank 18 Kerosene 19 Light oil 20 Fuel tank 21 Electric heater 22 Electric heater 23 Fuel addition apparatus 24 Oxidation catalyst (post-processing apparatus)
25 Particulate filter (post-processing device)

Claims (2)

  To supply fuel to an engine in an exhaust purification apparatus equipped with a post-treatment device that requires fuel addition in the middle of an exhaust pipe and having a fuel addition device for adding fuel to exhaust gas upstream of the post-treatment device An exhaust emission control device comprising an additive tank independent of the fuel tank and configured to supply fuel from the additive tank to the fuel addition device. A reforming catalyst that decomposes the HC component in the fuel into H ₂ and CO in the exhaust gas is provided between the fuel addition position by the fuel addition apparatus and the aftertreatment device, and the reforming catalyst is provided from the fuel addition position. The exhaust gas purification apparatus according to claim 1, further comprising an electric heater in the period up to and around the reforming catalyst.

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