JP3919407B2 - Exhaust purification device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust purification device used for an internal combustion engine such as a diesel engine.
[0002]
[Prior art]
Conventionally, in a diesel engine, a NOx reduction catalyst is provided in the middle of an exhaust pipe through which exhaust gas flows, and a necessary amount of a reducing agent is added upstream of the NOx reduction catalyst so that the reducing agent is placed on the NOx reduction catalyst. The exhaust concentration of NOx can be reduced by a reduction reaction with NOx (nitrogen oxide) in the exhaust gas.
[0003]
On the other hand, it is widely known that lean combustion can be performed at an air / fuel ratio thinner than the stoichiometric air / fuel ratio, so that significant improvement in fuel efficiency can be achieved. However, it is assumed that such lean combustion operation is performed. Reducing the NOx emission concentration is also an important issue for diesel engines.
[0004]
However, in general, in the presence of excess oxygen during lean combustion operation, since the reducing agent reacts with oxygen before reacting with NOx on the NOx reduction catalyst, the practical use level during lean combustion operation It was difficult to obtain a high NOx reduction effect.
[0005]
Therefore, as a catalyst capable of reducing NOx even during lean combustion operation, NOx is oxidized during lean combustion operation where the oxygen concentration in exhaust gas is high, and is temporarily stored in the form of nitrate, and the oxygen concentration in exhaust gas is The practical application of a NOx occlusion reduction catalyst having the property of decomposing and releasing NOx through the reduction agent during low stoichiometric air-fuel ratio operation to reduce and purify is currently under investigation.
[0006]
As this type of NOx occlusion reduction catalyst, platinum / barium / alumina catalyst, iridium / platinum / barium / alumina catalyst, etc. are already known as having the above-mentioned properties.
[0007]
[Problems to be solved by the invention]
However, when the NOx occluded by the NOx occlusion reduction catalyst is released to regenerate the NOx occlusion reduction catalyst, the operation state is switched from the lean combustion operation to the stoichiometric air fuel ratio operation every time. There is a problem that the merit of improving fuel efficiency by driving is impaired.
[0008]
For this reason, it is desired that the NOx occlusion reduction catalyst can be favorably regenerated while maintaining the lean combustion operation. However, in the presence of excessive oxygen during the lean combustion operation, the oxygen concentration in the exhaust gas is reduced. Therefore, as in the case of the NOx reduction catalyst described above, a reducing agent such as HC is consumed by reacting with oxygen before reacting with NOx, and thereby the reaction selectivity between the reducing agent and NOx. As a result, the NOx occlusion reduction catalyst cannot be successfully regenerated.
[0009]
The present invention has been made in view of the above circumstances, and uses a NOx occlusion reduction catalyst having a high NOx reduction effect at the time of lean combustion operation, and can successfully regenerate the NOx occlusion reduction catalyst even in a lean combustion operation state. An object of the present invention is to provide a highly practical exhaust gas purification device.
[0010]
[Means for Solving the Problems]
The present invention provides a reducing agent that oxidizes NOx when the oxygen concentration in the exhaust gas is high and temporarily stores it in the form of nitrate in the middle of the exhaust pipe through which the exhaust gas circulates and when the oxygen concentration in the exhaust gas is low Is equipped with a NOx occlusion reduction catalyst that decomposes and releases NOx through reduction and purifies it, and a regeneration gas flow path is provided so that air can be separately guided from the atmosphere to the NOx occlusion reduction catalyst. Equipped with an oxygen absorber in the middle of the path, a reducing agent is appropriately added to the NOx storage reduction catalyst, and nitrogen-rich gas generated by absorbing oxygen from the air by the oxygen absorption material is supplied to the NOx storage reduction catalyst. On the other hand, the present invention relates to an exhaust emission control device characterized in that it can be appropriately introduced.
[0011]
Therefore, according to such an exhaust purification device, during lean combustion operation in which the oxygen concentration in the exhaust gas is high, NOx in the exhaust gas is occluded in the form of nitrate by flowing the exhaust gas through the NOx storage and reduction catalyst. After that, when a sufficient amount of NOx is occluded in the form of nitrate and the storage capacity of the NOx occlusion reduction catalyst is reduced, air is separately supplied from the atmosphere through the regeneration gas flow path. Introducing nitrogen rich gas generated by absorbing oxygen from the air with an oxygen absorber into the NOx storage reduction catalyst to enhance the reducing atmosphere in the NOx storage reduction catalyst, and adding a reducing agent thereto The reaction selectivity between the reducing agent and NOx is improved, whereby NOx is actively decomposed and released from the NOx occlusion reduction catalyst to achieve good regeneration of the NOx occlusion reduction catalyst, and the released NOx On the NOx storing and reducing catalyst is reacted with the reducing agent it is possible to reduce and purify by.
[0012]
Note that the oxygen absorber absorbs oxygen during the NOx occlusion by the NOx occlusion reduction catalyst, or while the nitrogen-rich gas is stored in some storage means and is not in use. It can be released and regenerated.
[0013]
In the present invention, oxygen absorbers may be provided in pairs in parallel so that both oxygen absorbers can be regenerated alternately. In this way, one oxygen absorber has an oxygen content. Since the other oxygen absorbing material can be regenerated while the absorption is performed, any one of the oxygen absorbing materials can always be kept in a usable state.
[0014]
Furthermore, in the present invention, the NOx storage reduction catalyst may be provided in parallel as a pair so that both the NOx storage reduction catalysts can be regenerated alternately. While the NOx occlusion is being performed, the other NOx occlusion reduction catalyst can be regenerated, so that any NOx occlusion reduction catalyst can always be used and NOx can be continuously reduced. It becomes possible to plan.
[0015]
Further, in the present invention, the exhaust pipe upstream of the NOx storage reduction catalyst is equipped with a selective reduction catalyst that selectively reacts the reducing agent with NOx, and the reducing agent can be appropriately added to the selective reduction catalyst. In this way, a part of the NOx in the exhaust gas is reduced and purified in advance by the selective reduction catalyst. Therefore, the NOx occlusion in the NOx occlusion reduction catalyst on the downstream side thereof is performed. Thus, the time required for the NOx occlusion reduction catalyst to reach the occlusion limit can be lengthened to extend the regeneration cycle.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0017]
FIG. 1 shows an example of an embodiment of the present invention. In the figure, reference numeral 1 denotes an engine that is a diesel engine. In the engine 1 shown here, a turbocharger 2 is provided. The guided air 4 is sent to the compressor 2a of the turbocharger 2 through the intake pipe 5, and the air 4 pressurized by the compressor 2a is further sent to the intercooler 6 to be cooled, from the intercooler 6 not shown. Air 4 is guided to the intake manifold and introduced into each cylinder of the engine 1.
[0018]
In each cylinder of the engine 1, liquid fuel (light oil) from a fuel tank (not shown) is injected into each cylinder of the engine 1 and burned, and discharged from each cylinder of the engine 1. Exhaust gas 7 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 8, and the exhaust gas 7 that has driven the turbine 2b is discharged outside the vehicle through the exhaust pipe 9.
[0019]
In the middle of the exhaust pipe 9 through which the exhaust gas 7 circulates, when the oxygen concentration in the exhaust gas 7 is high, NOx is oxidized and temporarily stored in the form of nitrate, and the oxygen concentration in the exhaust gas 7 is low. A NOx occlusion / reduction catalyst 11 that decomposes and releases NOx through reduction agent 10 (light oil), which will be described later, to reduce and purify the exhaust gas is provided. A bypass passage is provided in the exhaust pipe 9 to bypass the NOx occlusion reduction catalyst 11. 12 is attached.
[0020]
Here, the exhaust gas 7 flowing through the exhaust pipe 9 is appropriately distributed to the bypass flow path 12 at the branching point and the joining point of the bypass flow path 12 with respect to the exhaust pipe 9, and the exhaust gas 7 passing through the NOx storage reduction catalyst 11. Opening variable valves 13, 14, 15, and 16 are provided to limit the flow rate, respectively.
[0021]
Further, the inlet side of the NOx occlusion reduction catalyst 11 in the exhaust pipe 9 and a reducing agent tank 17 (which can also be used as a fuel tank) provided at a required place are connected by a reducing agent supply pipe 18. The reducing agent 10 in the reducing agent tank 17 can be added to the inlet side of the NOx occlusion reduction catalyst 11 through the injection nozzle 20 by driving a feed pump 19 provided in the middle of the reducing agent supply pipe 18.
[0022]
Further, another NOx occlusion reduction catalyst 22 that is paired with the NOx occlusion reduction catalyst 11 is provided in the middle of the bypass passage 12, and the inlet side of the NOx occlusion reduction catalyst 22 and the reducing agent tank are provided. 17 is connected by a reducing agent supply pipe 23, and the reducing agent 10 in the reducing agent tank 17 is stored in the NOx occlusion through the injection nozzle 25 by driving a feed pump 24 installed in the middle of the reducing agent supply pipe 23. It can be added to the inlet side of the reduction catalyst 22.
[0023]
In addition, the compressor 2a and the intercooler of the turbocharger 2 are respectively connected to the inlet side of the NOx storage reduction catalyst 11 installed in the middle of the exhaust pipe 9 and the NOx storage reduction catalyst 22 installed in the middle of the bypass passage 12. A regeneration gas flow path 40 is connected so that the air 4 can be separately guided from the intake pipe 5 to 6 via the opening variable valve 39.
[0024]
Here, an air compressor 41 and a reservoir tank 42 are provided on the upstream side of the regeneration gas flow path 40, and the air 4 guided from the middle of the intake pipe 5 through the opening degree variable valve 39 is supplied to the air. The compressor 41 is pressurized and the pressurized air 4 can be stored in the reservoir tank 42.
[0025]
The regeneration gas flow path 40 is configured such that the downstream side of the reservoir tank 42 is branched into two branch flow paths 40A and 40B via a three-way valve 43 and then merges again. Each of 40A and 40B is equipped with oxygen absorbers 44 and 45 such as porous carbon in parallel, and the casing holding each oxygen absorber 44 and 45 is opened to the atmosphere. Relief channels 46 and 47 are connected.
[0026]
Here, stop valves 48, 49 and 50, 51 which can appropriately close the flow paths on the outlet side of the oxygen absorbing materials 44, 45 in the relief flow paths 46, 47 and the branch flow paths 40 A, 40 B, respectively. Are also provided, and furthermore, a similar stop valve 52 is provided at the junction of each branch flow path 40A, 40B.
[0027]
A pressure reducing valve 53 and a three-way valve 54 are provided on the downstream side of the stop valve 52. The three-way valve 54 is branched into two branch passages 40C and 40D, and the NOx occlusion reduction of the exhaust pipe 9 is performed. The catalyst 11 and the bypass passage 12 are connected to the respective inlet sides of the NOx storage reduction catalyst 22.
[0028]
Further, particularly in the present embodiment, the selective reduction catalyst 26 that selectively reacts the reducing agent 10 with NOx in the exhaust pipe 9 upstream from the branch point of the bypass passage 12 (if the reducing agent 10 is light oil). Copper / zeolite catalyst, platinum / alumina catalyst, etc.), and the inlet side of the selective reduction catalyst 26 and the reducing agent tank 17 are connected by a reducing agent supply pipe 27. The reducing agent 10 in the reducing agent tank 17 can be added to the inlet side of the selective reduction catalyst 26 through the injection nozzle 29 by driving the feed pump 28 installed in the middle.
[0029]
In the figure, reference numeral 21 denotes a muffler provided on the downstream side of the exhaust pipe 9.
[0030]
Thus, when the exhaust emission control device is configured in this manner, the opening variable valves 13 and 14 are opened and the opening variable valves 15 and 16 are closed during the lean combustion operation in which the oxygen concentration in the exhaust gas 7 is high. Then, the exhaust gas 7 is caused to flow through the NOx occlusion reduction catalyst 11, whereby NOx in the exhaust gas 7 is occluded in the form of nitrate to reduce NOx.
[0031]
Thereafter, when a sufficient amount of NOx is occluded in the form of nitrate and the occlusion capacity of the NOx occlusion reduction catalyst 11 decreases, the opening variable valves 15 and 16 are opened and the opening variable valves 13 and 14 are opened. Is closed to bypass the exhaust gas 7 to the bypass flow path 12 side, so that the NOx occlusion reduction catalyst 22 on the bypass flow path 12 side can take over the NOx occlusion, while the NOx occlusion reduction catalyst 11 having a reduced occlusion capacity is used. Play as follows.
[0032]
That is, the air 4 is led from the intake pipe 5 between the compressor 2a of the turbocharger 2 and the intercooler 6 through the opening degree variable valve 39 to the regeneration gas flow path 40, and the air 4 is pressurized by the air compressor 41 to be stored in the reservoir. After storing in the tank 42 and closing all the stop valves 48, 49, 50, 51, 52, the used portion of the compressed air 4 ′ is taken out from the reservoir tank 42, and this is taken out through the three-way valve 43 to When the oxygen absorbing material 44 is guided, the oxygen content in the compressed air 4 'is absorbed by the oxygen absorbing material 44 and nitrogen rich gas 4 "is generated. Therefore, the nitrogen rich gas 4" is opened by the stop valves 50 and 52. Then, the pressure is reduced by the pressure reducing valve 53, and then led to the branch flow path 40C via the three-way valve 43 and introduced into the inlet side of the NOx storage reduction catalyst 11, whereby the NOx storage reduction catalyst 11 By increasing the reducing atmosphere and adding the reducing agent 10 through the reducing agent supply pipe 18 here, the reaction selectivity of the reducing agent 10 and NOx is improved, and NOx is actively decomposed and released from the NOx storage reduction catalyst 11. Thus, the NOx occlusion reduction catalyst 11 is favorably regenerated, and the released NOx is reacted with the reducing agent 10 on the NOx occlusion reduction catalyst 11 to be reduced and purified.
[0033]
When the nitrogen rich gas 4 ″ is introduced into the NOx occlusion / reduction catalyst 11 having a reduced occlusion capacity to regenerate the NOx occlusion / reduction catalyst 11, the temperature of the NOx occlusion / reduction catalyst 11 does not deviate from the catalyst activation temperature range. The opening variable valves 13 and 14 may be slightly opened at an appropriate opening so that a part of the exhaust gas 7 is mixed.
[0034]
Then, if the three-way valve 43 is switched and the compressed air 4 ′ is led from the reservoir tank 42 to the oxygen absorbing material 45 of the branch flow path 40B, the nitrogen rich gas 4 ″ is generated in the same manner as described above. In the closed state, the stop valve 48 of the relief flow path 46 is opened, and the oxygen absorbing material 44 is opened to the atmosphere to reduce the pressure, thereby releasing the oxygen component absorbed in the oxygen absorbing material 44 and the oxygen absorbing material. 44 playback is planned.
[0035]
In this way, if one of the oxygen absorbing materials 44 and 45 is made to absorb the oxygen content while the other of the oxygen absorbing materials 44 and 45 is regenerated, the oxygen absorbing material 44, It is possible to wait for any of 45 in a usable state.
[0036]
Further, when the NOx storage / reduction catalyst 22 has reduced its storage capacity by storing a sufficient amount of NOx in the form of nitrate, the opening variable valves 13 and 14 are opened and the opening variable valves 15 and 16 are closed. Thus, the exhaust gas 7 is prevented from detouring to the bypass flow path 12 side, so that the NOx occlusion reduction catalyst 11 on the regenerated exhaust pipe 9 side can take over the NOx occlusion, while the NOx occlusion reduction catalyst having a reduced occlusion capability. 22 may be reproduced in the same manner as described above.
[0037]
Thus, if the other of the NOx storage reduction catalysts 11 and 22 is regenerated while one of the NOx storage reduction catalysts 11 and 22 is storing NOx, the NOx storage and reduction catalyst is always stored. It becomes possible to continuously reduce NOx in a state where any one of the reduction catalysts 11 and 22 can be used.
[0038]
Here, in the present embodiment, the air 4 is guided from the intake pipe 5 between the compressor 2a of the turbocharger 2 and the intercooler 6, but the regeneration gas flow path is completely different from the intake system. And a dedicated blower for taking in air 4 from the atmosphere may be provided in the regeneration gas flow path. In such a case, the blower is driven using engine power. It is good to make it.
[0039]
Therefore, according to the present embodiment, since the NOx storage reduction catalysts 11 and 22 can be regenerated well even in the lean combustion operation state, the exhaust using the NOx storage reduction catalyst 11 having a high NOx reduction effect during the lean combustion operation. The purification device can be put into practical use, and the other of the oxygen absorbing materials 44 and 45 can be regenerated while one of the oxygen absorbing materials 44 and 45 is absorbing oxygen. Therefore, one of the oxygen absorbents 44 and 45 can always be kept in a usable state, and one of the NOx occlusion reduction catalysts 11 and 22 is made to occlude NOx. In the meantime, since the other of the NOx storage reduction catalysts 11 and 22 can be regenerated, it is always possible to use either of the NOx storage reduction catalysts 11 or 22 and continuously reduce NOx. Can also .
[0040]
Moreover, particularly in this embodiment, the reducing agent 10 can be added to the inlet side of the selective reduction catalyst 26 through the reducing agent supply pipe 27 to selectively react the reducing agent 10 with NOx. Even in the presence of excess oxygen during lean combustion operation, about 20 to 30% of NOx in the exhaust gas 7 can be reduced and purified in advance by the selective reduction catalyst 26, so that the NOx in the NOx storage reduction catalyst 11 on the downstream side thereof can be reduced. The burden of occlusion can be greatly reduced, and the time required for the NOx occlusion reduction catalyst 11 to reach the occlusion limit can be lengthened to prolong the regeneration cycle.
[0041]
The exhaust emission control device of the present invention is not limited to the above-described embodiment.For example, a configuration in which a pair of oxygen absorbers and NOx occlusion reduction catalysts in the illustrated example are provided alone, Of course, a configuration in which the selective reduction catalyst on the upstream side of the NOx occlusion reduction catalyst is omitted may be adopted, and various changes may be made without departing from the scope of the present invention.
[0042]
【The invention's effect】
According to the exhaust emission control device of the present invention described above, various excellent effects as described below can be obtained.
[0043]
(I) According to the invention described in claim 1 of the present invention, the NOx occlusion reduction catalyst can be regenerated well even in the lean combustion operation state, so the NOx occlusion reduction catalyst having a high NOx reduction effect during the lean combustion operation. Practical application of an exhaust gas purification apparatus using the above can be achieved.
[0044]
(II) According to the invention described in claim 2 of the present invention, while the oxygen content of one oxygen absorber is absorbed, the other oxygen absorber can be regenerated. Any one of the oxygen absorbers can be kept ready for use.
[0045]
(III) According to the invention described in claim 3 of the present invention, while the NOx occlusion reduction catalyst is performing NOx occlusion, the other NOx occlusion reduction catalyst can be regenerated. It is possible to continuously reduce NOx by always using one of the NOx storage reduction catalysts in a usable state.
[0046]
(IV) According to the invention described in claim 4 of the present invention, a part of NOx in the exhaust gas can be reduced and purified in advance by the selective reduction catalyst, and the NOx in the NOx occlusion reduction catalyst downstream thereof Since the burden of occlusion can be greatly reduced, it is possible to lengthen the time required for the NOx occlusion reduction catalyst to reach the occlusion limit and prolong the regeneration cycle.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of an embodiment of the present invention.
[Explanation of symbols]
4 Air 4 ”Nitrogen rich gas 7 Exhaust gas 9 Exhaust pipe 10 Reducing agent 11 NOx occlusion reduction catalyst 22 NOx occlusion reduction catalyst 26 Selective reduction catalyst 40 Gas passage for regeneration 44 Oxygen absorber 45 Oxygen absorber

Claims (4)

  In the middle of the exhaust pipe through which the exhaust gas circulates, NOx is oxidized when the oxygen concentration in the exhaust gas is high and temporarily stored in the form of nitrate, and when the oxygen concentration in the exhaust gas is low, the NOx is interposed by the intervening reducing agent. Is equipped with a NOx occlusion reduction catalyst that decomposes and discharges and reduces and purifies, and a regeneration gas passage is provided in the middle of the regeneration gas passage so that air can be separately guided from the atmosphere to the NOx occlusion reduction catalyst. Equipped with an oxygen absorber, a reducing agent is appropriately added to the NOx storage reduction catalyst, and nitrogen-rich gas generated by absorbing oxygen from the air by the oxygen absorption material is appropriately introduced to the NOx storage reduction catalyst. An exhaust emission control device characterized in that it can be configured.   The exhaust emission control device according to claim 1, wherein the oxygen absorbing material is provided in parallel as a pair so that both oxygen absorbing materials can be regenerated alternately.   The exhaust emission control device according to claim 1 or 2, wherein NOx occlusion reduction catalysts are provided in parallel as a pair so that both NOx occlusion reduction catalysts can be regenerated alternately.   The exhaust pipe upstream of the NOx storage reduction catalyst is equipped with a selective reduction catalyst that selectively reacts the reducing agent with NOx, and the reducing agent can be appropriately added to the selective reduction catalyst. The exhaust emission control device according to claim 1, 2, or 3.

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