JP2001140635A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly practical exhaust emission control device capable of well recovering a NOx storage reducing catalyst even in a lean-burn operating condition by using the NOx storage reducing catalyst highly effective for reducing NOx in lean-burn operation. SOLUTION: The NOx storage reducing catalyst 11 is mounted on the way of an exhaust pipe 9, in which exhaust gas 7 is distributed, for oxidizing NOx to be temporarily stored in the form of nitrate when the concentration of oxygen in the exhaust gas 7 is high and for decomposing and releasing NOx to be reduced and purified via a reducer 10 when the concentration of oxygen in the exhaust gas 7 is low. The reducer 10 is properly added to the NOx storage reducing catalyst 11 and the NOx storage reducing catalyst H is properly bypassed, whereby the flow rate of the exhaust gas 7 passing through the NOx storage reducing catalyst 11 is restricted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust emission control device used for an internal combustion engine such as a diesel engine.

[0002]

2. Description of the Related Art Conventionally, in a diesel engine, a NOx reduction catalyst is provided in an exhaust pipe through which exhaust gas flows, and a required amount of a reducing agent is added upstream of the NOx reducing catalyst to reduce the amount of the reducing agent. Is reduced on the NOx reduction catalyst with NOx (nitrogen oxide) in the exhaust gas to produce NOx.
Some of them are capable of reducing the emission concentration of methane.

[0003] On the other hand, it is widely known that lean burn can be performed at a leaner air-fuel ratio than the stoichiometric air-fuel ratio to greatly improve fuel efficiency. It is also an important issue to reduce the NOx emission concentration for a diesel engine that assumes the following.

[0004] However, in general, in the presence of excess oxygen during the lean burn operation, the reducing agent reacts with oxygen on the NOx reduction catalyst before reacting with NOx. It was difficult to obtain a high NOx reduction effect at a practical level.

Therefore, even during lean burn operation, NOx
As a catalyst that can reduce NOx, NOx is oxidized during lean burn operation in which the oxygen concentration in the exhaust gas is high to temporarily store NOx in the state of nitrate, and the reducing agent is used during stoichiometric air-fuel ratio operation in which the oxygen concentration in the exhaust gas is low. At present, practical use of a NOx storage reduction catalyst having a property of decomposing and releasing NOx to reduce and purify is being studied.

As this type of NOx storage reduction catalyst, a platinum-barium-alumina catalyst, an iridium-platinum-barium-alumina catalyst, etc. are already known as having the above-mentioned properties.

[0007]

SUMMARY OF THE INVENTION However, NOx
When releasing the NOx stored in the storage reduction catalyst to regenerate the NOx storage reduction catalyst, if the operation state is switched from lean combustion operation to stoichiometric air-fuel ratio operation each time, the fuel consumption due to the precious lean combustion operation There is a problem that the merit of improvement is impaired.

For this reason, the NO.
It is desired to be able to achieve good regeneration of the x-storage reduction catalyst, but in the presence of excess oxygen during the lean burn operation, the oxygen concentration in the exhaust gas is high, so As in the case described above, the reducing agent such as HC reacts with oxygen before reacting with NOx and is consumed, whereby the reaction selectivity between the reducing agent and NOx is reduced and the NOx storage reduction catalyst is improved. There is a problem that a proper reproduction cannot be achieved.

The present invention has been made in view of the above-described circumstances, and uses a NOx storage reduction catalyst having a high NOx reduction effect during lean combustion operation, and makes the NOx storage reduction catalyst excellent even in lean combustion operation. It is an object of the present invention to provide a highly practical exhaust gas purification device that can be regenerated.

[0010]

SUMMARY OF THE INVENTION According to the present invention, there is provided an exhaust pipe through which exhaust gas flows, when NOx is oxidized when the oxygen concentration in the exhaust gas is high, the NOx is temporarily stored in a nitrate state and the exhaust gas is temporarily stored. When the oxygen concentration in the medium is low, N
A NOx storage reduction catalyst that decomposes and releases Ox to reduce and purify is provided, a reducing agent is appropriately added to the NOx storage reduction catalyst, and exhaust gas is caused to flow by appropriately bypassing the NOx storage reduction catalyst. The present invention relates to an exhaust gas purification apparatus characterized in that the flow rate of exhaust gas passing through a NOx storage reduction catalyst can be restricted.

Therefore, according to such an exhaust gas purifying apparatus, during the lean burn operation in which the oxygen concentration in the exhaust gas is high, the exhaust gas is caused to flow through the NOx storage reduction catalyst so that the NOx in the exhaust gas is reduced.
NOx is reduced by storing NOx in the state of nitrate, and thereafter, when a sufficient amount of NOx is stored in the state of nitrate and the storage capacity of the NOx storage reduction catalyst decreases, the NOx is reduced. By restricting the flow rate of the exhaust gas passing through the NOx storage reduction catalyst by flowing the exhaust gas by bypassing the storage reduction catalyst, the reducing agent is added, and the relative excess air ratio with respect to the amount of the reducing agent added is determined. Lower the reducing agent and N
The reaction selectivity of Ox is improved, whereby NOx is actively decomposed and released from the NOx storage-reduction catalyst to achieve good regeneration of the NOx storage-reduction catalyst, and the released NOx is reduced on the NOx storage-reduction catalyst. It can be reduced and purified by reacting with an agent.

Also, the present invention provides a method for oxidizing NOx in the middle of an exhaust pipe through which exhaust gas flows, when the oxygen concentration in the exhaust gas is high, temporarily occluding NOx in a state of nitrate, and further reducing the oxygen concentration in the exhaust gas. A NOx storage-reduction catalyst that decomposes and releases NOx through the presence of a reducing agent when the pressure is low, and an oxygen-absorbing material is provided in an exhaust pipe upstream of the NOx storage-reduction catalyst. An exhaust gas purifying apparatus, wherein an exhaust gas is guided to the NOx storage reduction catalyst by appropriately adding a reducing agent to the NOx storage and reduction catalyst by appropriately bypassing the oxygen absorbent. .

Therefore, according to such an exhaust gas purifying apparatus, during the lean burn operation in which the oxygen concentration in the exhaust gas is high, the exhaust gas flows to the NOx storage reduction catalyst by bypassing the oxygen absorbing material, and the NOx in the exhaust gas is reduced. NOx is reduced by storing NOx in the state of nitrate, and thereafter, when a sufficient amount of NOx is stored in the state of nitrate and the storage capacity of the NOx storage reduction catalyst decreases, the NOx is reduced. The oxygen concentration of the exhaust gas is lowered by passing the exhaust gas through the oxygen absorbing material on the upstream side of the storage reduction catalyst to absorb oxygen, and the reducing agent in the NOx storage reduction catalyst on the downstream side is raised after the reducing atmosphere is increased. To enhance the reaction selectivity between the reducing agent and NOx, thereby actively decomposing and releasing NOx from the NOx storage-reduction catalyst, thereby achieving good regeneration of the NOx storage-reduction catalyst, and releasing the released NOx. On the NOx storing and reducing catalyst is reacted with the reducing agent it is possible to reduce and purify by.

The oxygen absorbing material may be configured to release and regenerate an oxygen component while the NOx storage / reduction catalyst is storing NOx by bypassing the exhaust gas.

Furthermore, the present invention provides a method for oxidizing NOx in the middle of an exhaust pipe through which exhaust gas flows, when the oxygen concentration in the exhaust gas is high, temporarily occluding NOx in a state of nitrate, and further reducing the oxygen concentration in the exhaust gas. A NOx storage-reduction catalyst that decomposes and releases NOx through the presence of a reducing agent to reduce and purify when the pressure is low, and a regeneration gas flow path is provided for the NOx storage-reduction catalyst so that air can be separately introduced from the atmosphere to the NOx storage-reduction catalyst. An oxygen absorbing material is provided in the middle of the regeneration gas flow path, a reducing agent is appropriately added to the NOx storage reduction catalyst, and a nitrogen-rich gas generated by absorbing oxygen from air by the oxygen absorbing material is removed. The present invention also relates to an exhaust gas purification device characterized in that it can be appropriately introduced into a NOx storage reduction catalyst.

Therefore, according to such an exhaust gas purifying apparatus, during the lean burn operation in which the oxygen concentration in the exhaust gas is high, the exhaust gas is caused to flow through the NOx storage reduction catalyst so that the NOx in the exhaust gas is reduced.
NOx is reduced by storing NOx in the state of nitrate, and thereafter, when a sufficient amount of NOx is stored in the state of nitrate and the storage capacity of the NOx storage-reduction catalyst decreases, the NOx The reducing atmosphere in the NOx storage reduction catalyst is enhanced by separately introducing air from the atmosphere through the gas flow path and introducing a nitrogen-rich gas generated by absorbing oxygen from the air with an oxygen absorbing material to the NOx storage reduction catalyst. , By adding a reducing agent thereto, the reducing agent and NO
The reaction selectivity of x is improved, whereby NOx is actively decomposed and released from the NOx storage-reduction catalyst to achieve good regeneration of the NOx storage-reduction catalyst, and the released NOx is reduced on the NOx storage-reduction catalyst. It can be reduced and purified by reacting with an agent.

The oxygen absorbing material may be used while the NOx is being stored by the NOx storage reduction catalyst or while the storage of a sufficient amount of nitrogen-rich gas in some storage means is in an unused state. What is necessary is just to make it reproduce | regenerate by releasing oxygen content.

Further, in the present invention, the oxygen absorbing material may be provided in a pair in parallel so that the two oxygen absorbing materials can be regenerated alternately. Since it is possible to regenerate the other oxygen absorbing material while the oxygen content is being absorbed, it is possible to always keep one of the oxygen absorbing materials in a usable state. .

Further, in the present invention, the NOx storage-reduction catalysts may be provided in parallel as a pair so that both the NOx storage-reduction catalysts can be regenerated alternately.
While one NOx storage reduction catalyst is storing NOx, it is possible to regenerate the other NOx storage reduction catalyst. It is possible to achieve a reduction in NOx.

In the present invention, the exhaust pipe upstream of the NOx storage reduction catalyst is provided with a selective reduction catalyst for selectively reacting the reducing agent with NOx, and the reducing agent is appropriately supplied to the selective reduction catalyst. It is preferable that the catalyst can be added. In this case, a part of the NOx in the exhaust gas is reduced and purified in advance by the selective reduction catalyst. The load on NOx storage at the time is greatly reduced, and the time required for the NOx storage reduction catalyst to reach the storage limit can be lengthened to lengthen the regeneration cycle.

[0021]

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

FIG. 1 shows a first embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an engine which is a diesel engine. In the engine 1 shown here, a turbocharger 2 is used.
The air 4 guided from the air cleaner 3 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. After being cooled, the air 4 is guided from the intercooler 6 to an intake manifold (not shown) and introduced into each cylinder of the engine 1.

Each cylinder of the engine 1 has
Liquid fuel (light oil) from a fuel tank (not shown) is injected into each cylinder of the engine 1 and burned, and exhaust gas 7 discharged from each cylinder of the engine 1 is exhausted through an exhaust manifold 8 to the turbo. The exhaust gas 7 sent to the turbine 2b of the charger 2 and driving the turbine 2b is discharged to the outside of the vehicle via the exhaust pipe 9.

In the middle of the exhaust pipe 9 through which the exhaust gas 7 flows, when the oxygen concentration in the exhaust gas 7 is high, NOx is oxidized and temporarily stored in the form of nitrate, and the exhaust gas 7 is oxidized.
A NOx storage-reduction catalyst 11 that decomposes and releases NOx by the interposition of a reducing agent 10 (light oil) to be described below when the oxygen concentration is low is provided, and the exhaust gas is bypassed so as to bypass the NOx storage-reduction catalyst 11. The pipe 9 is provided with a bypass channel 12.

Here, the bypass passage 1 for the exhaust pipe 9
The exhaust valve 7 flowing through the exhaust pipe 9 is appropriately distributed to the bypass passage 12 at the branch point and the junction point 2 so that the flow rate of the exhaust gas 7 passing through the NOx storage reduction catalyst 11 can be limited. 13, 14, 15, and 16 are provided respectively.

Further, the exhaust pipe 9 has an inlet side of the NOx storage reduction catalyst 11 and a reducing agent tank 17 provided at a required place.
(It can also be used as a fuel tank) is connected by a reducing agent supply pipe 18, and a reduction pump in the reducing agent tank 17 is driven by driving a feed pump 19 provided in the middle of the reducing agent supply pipe 18. The agent 10 can be added to the inlet side of the NOx storage reduction catalyst 11 through the injection nozzle 20.

In the drawing, reference numeral 21 denotes a muffler provided on the downstream side of the exhaust pipe 9.

During the lean burn operation in which the oxygen concentration in the exhaust gas 7 is high, the variable opening valves 13 and 14 are opened and the variable opening valves 15 and 16 are closed to reduce the exhaust gas 7 to the NOx storage reduction catalyst 11. To thereby reduce NOx by storing NOx in the exhaust gas 7 in the form of nitrate.

Thereafter, when a sufficient amount of NOx is stored in a nitrate state and the storage capacity of the NOx storage-reduction catalyst 11 is reduced, the opening variable valves 15 and 16 are opened and the opening variable valves are opened. 13 and 14 are closed to allow the exhaust gas 7 to pass through the bypass passage 1
2, the flow rate of the exhaust gas 7 passing through the NOx storage reduction catalyst 11 is restricted, and then the feed pump 19 is driven to guide the reducing agent 10 from the reducing agent tank 17 so that the NOx storage reduction catalyst 11 To the inlet side of.

In this way, the relative excess air ratio with respect to the amount of the reducing agent 10 added decreases, and the reducing agent 10 and NO
The reaction selectivity of x is improved, so that NOx is actively decomposed and released from the NOx storage-reduction catalyst 11, whereby good regeneration of the NOx storage-reduction catalyst 11 is achieved, and the released NOx
Reacts with the reducing agent 10 on the NOx storage reduction catalyst 11 to be reduced and purified.

Here, limiting the flow rate of the exhaust gas 7 passing through the NOx storage reduction catalyst 11 by diverting the exhaust gas 7 to the bypass flow path 12 side also reduces the flow rate of the exhaust gas 7. Therefore, the reducing agent 10 and N
The contact time with the Ox storage reduction catalyst 11 becomes longer, and the NOx storage reduction catalyst 11 is efficiently regenerated.

Therefore, according to the present embodiment, the NOx storage reduction catalyst 11 can be satisfactorily regenerated even in the lean combustion operation state. Therefore, the NOx storage reduction catalyst 11 having a high NOx reduction effect during the lean combustion operation is used. Practical use of the exhaust gas purification device can be achieved.

FIG. 2 shows a second embodiment of the present invention. In this embodiment, a NOx storage reduction catalyst 22 is provided also in the bypass passage 12 in FIG.
The inlet side of the NOx storage reduction catalyst 22 and the reducing agent tank 17 are connected by a reducing agent supply pipe 23, and the feed pump 24 provided in the middle of the reducing agent supply pipe 23 is driven to drive the inside of the reducing agent tank 17. Can be added to the inlet side of the NOx storage reduction catalyst 22 through the injection nozzle 25.

Thus, the NOx storage reduction catalyst 1
In the case where the pair 1 and 22 are provided in parallel, the opening variable valve 1
The exhaust gas 7 is allowed to flow to the NOx storage reduction catalyst 11 in the exhaust pipe 9 by opening the opening degree variable valves 15 and 16 and the NOx in the exhaust gas 7 is converted to nitrate by the NOx storage reduction catalyst 11. During the occlusion, the reducing agent 10 is added through the reducing agent supply pipe 23 to the inlet side of the NOx occlusion / reduction catalyst 22 on the side of the bypass flow passage 12 where the flow rate of the exhaust gas 7 is restricted, and the NOx occlusion / reduction is performed. The regeneration of the catalyst 22 can be performed.

That is, the reducing agent 10
Since the relative excess ratio of air with respect to the amount of addition is reduced and the selectivity of the reaction between the reducing agent 10 and NOx is improved, NOx is actively decomposed and released from the NOx storage reduction catalyst 22 and the NOx storage reduction catalyst Good regeneration of the reducing agent 22 is achieved, and the released NOx is reduced on the NOx storage reduction catalyst 22 by the reducing agent
It reacts with 0 to be reduced and purified.

When the storage capacity of the NOx storage reduction catalyst 11 is reduced by storing a sufficient amount of NOx in the state of nitrate, the variable opening valves 15 and 16 are opened and the variable opening valves 13 and 14 to close the exhaust gas 7 to the bypass passage 12
Side, thereby restricting the flow rate of the exhaust gas 7 passing through the NOx storage-reduction catalyst 11, and passing the reducing agent supply pipe 18 to the entrance side of the NOx storage-reduction catalyst 11 through the reducing agent supply pipe 18.
Is added to regenerate the NOx storage and reduction catalyst 11, and during this regeneration, the NOx in the exhaust gas 7 may be stored by the NOx storage and reduction catalyst 22 on the side of the bypass passage 12.

Therefore, according to this embodiment, while one of the NOx storage reduction catalysts 11 and 22 is storing NOx, the other of the NOx storage reduction catalysts 11 and 22 is regenerated. Therefore, one of the NOx storage reduction catalysts 11 and 22 can always be used, and NOx can be continuously reduced.

FIG. 3 shows a third embodiment of the present invention. In this embodiment, the reducing agent 10 is supplied to the exhaust pipe 9 upstream of the branch point of the bypass passage 12 in FIG. A selective reduction catalyst 26 for selectively reacting with NOx,
That is, if the reducing agent 10 is light oil, a copper-zeolite catalyst or a platinum-alumina catalyst is provided, and a reducing agent supply pipe 2 is provided between the inlet of the selective reduction catalyst 26 and the reducing agent tank 17.
7, 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 a feed pump 28 provided in the middle of the reducing agent supply pipe 27. It is like that.

In this way, the reducing agent 10 can be added to the selective reducing catalyst 26 through the reducing agent supply pipe 27 through the inlet side thereof, and the reducing agent 10 can be selectively reacted with NOx. Even in the presence of excess oxygen during the lean burn operation, about 20 to 30% of the 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 downstream thereof
The load of occlusion can be greatly reduced, and the time until the NOx occlusion / reduction catalyst 11 reaches the occlusion limit can be lengthened to prolong the regeneration cycle.

FIG. 4 shows a fourth embodiment of the present invention. In this embodiment, the N
On the upstream side of the Ox storage reduction catalyst 11, an oxygen absorbing material 30 such as zeolite is provided, and a bypass passage 31 is provided in the exhaust pipe 9 so as to bypass the oxygen absorbing material 30.

Here, the bypass passage 3 for the exhaust pipe 9
In the first branch point and the junction point, the exhaust gas 7 flowing through the exhaust pipe 9 is appropriately distributed to the bypass flow path 31 so as to bypass the oxygen absorbing material 30 so as to bypass the NOx storage reduction catalyst 11.
Valves 32, 33, 3 so that the exhaust gas 7 can be guided to
4, 35 are provided respectively.

The inlet of the oxygen absorbing material 30 and the reducing agent tank 17 are connected by a reducing agent supply pipe 36, and the reducing agent is supplied by driving a feed pump 37 provided in the middle of the reducing agent supply pipe 36. The reducing agent 10 in the tank 17 is injected into the injection nozzle 38
Can be added to the inlet side of the oxygen absorbing material 30 through the hole.

During the lean burn operation in which the oxygen concentration in the exhaust gas 7 is high, the variable opening valves 34, 35 are opened and the variable opening valves 32, 33 are closed to pass the exhaust gas 7 into the bypass passage 3.
When the exhaust gas 7 is led to the NOx storage reduction catalyst 11 by bypassing the oxygen absorbing material 30,
The NOx in the exhaust gas 7 is stored in the state of nitrate by the NOx storage reduction catalyst 11, so that the NOx can be reduced.

Thereafter, when a sufficient amount of NOx is stored in the state of nitrate and the storage capacity of the NOx storage reduction catalyst 11 is reduced, the opening variable valves 32 and 33 are opened and the opening variable valves are opened. 34 and 35 are closed, and the exhaust gas 7 is
To reduce the oxygen concentration of the exhaust gas 7 by reducing the oxygen concentration of the exhaust gas 7 and increase the reducing atmosphere in the NOx storage reduction catalyst 11 on the downstream side thereof.
0 is added to improve the reaction selectivity between the reducing agent 10 and NOx, thereby actively decomposing and releasing NOx from the NOx storage reduction catalyst 11 to achieve good regeneration of the NOx storage reduction catalyst 11, The released NOx is made to react with the reducing agent 10 on the NOx storage reduction catalyst 11 to be reduced and purified.

Incidentally, the oxygen absorbing material 30 circulates the exhaust gas 7 through the bypass flow path 31 to make the NOx storage reduction catalyst 11
Pump 3 during the storage of NOx by
By driving 7, the reducing agent 10 is guided from the reducing agent tank 17, added to the inlet side of the oxygen absorbing material 30, and the oxygen content is released for regeneration.

FIG. 5 shows a fifth embodiment of the present invention. In the device configuration substantially the same as that of the second embodiment of FIG. 2 described above, the NOx storage reduction catalyst 11 provided in the exhaust pipe 9 is provided. To the respective inlet sides of the NOx storage reduction catalyst 22 provided in the middle of the bypass flow path 12, from the intake pipe 5 between the compressor 2 a of the turbocharger 2 and the intercooler 6, 4 is connected to a regeneration gas flow path 40 that can be separately led.

An air compressor 41 and a reservoir tank 42 are provided on the upstream side of the regeneration gas flow path 40. The air introduced from the middle of the intake pipe 5 through the variable opening valve 39 is provided. 4 is pressurized by an air compressor 41, and the pressurized air 4 can be stored in a reservoir tank 42.

The downstream side of the reservoir tank 42 in the regeneration gas passage 40 is branched into two branch passages 40A and 40B via a three-way valve 43 and then merges again. Branch flow paths 40A, 40
Each of B has an oxygen absorbing material 44 such as porous carbon,
45 are provided in parallel, and relief casings 46 and 47 that open the inside of the casing to the atmosphere are connected to the casing holding the oxygen absorbing members 44 and 45.

Here, the oxygen absorbing material 4 in each of the relief passages 46 and 47 and each of the branch passages 40A and 40B is used.
The outlet sides of the flow passages 4 and 45 are provided with stop valves 48 and 49 and 50 and 51, respectively, which can appropriately close the flow passages. A stop valve 52 is provided.

Downstream of the stop valve 52, a pressure reducing valve 53 and a three-way valve 54 are provided. The three-way valve 54 is branched into two branch passages 40C and 40D, and is connected to the exhaust pipe 9. N of the NOx storage reduction catalyst 11 and the bypass passage 12
The Ox storage reduction catalysts 22 are connected to their respective inlet sides.

During the lean burn operation in which the oxygen concentration in the exhaust gas 7 is high, the variable opening valves 13 and 14 are opened and the variable opening valves 15 and 16 are closed to reduce the exhaust gas 7 to the NOx storage reduction catalyst 11. To thereby reduce NOx by storing NOx in the exhaust gas 7 in the form of nitrate.

Thereafter, when a sufficient amount of NOx is stored in a nitrate state and the storage capacity of the NOx storage-reduction catalyst 11 is reduced, the opening variable valves 15 and 16 are opened and the opening variable valves are opened. 13 and 14 are closed to allow the exhaust gas 7 to pass through the bypass passage 1
2 so that the NO in the bypass flow path 12
While allowing the x storage reduction catalyst 22 to take over the storage of NOx,
The NOx storage reduction catalyst 11 whose storage capacity has been reduced is regenerated as follows.

That is, the air 4 is guided from the intake pipe 5 between the compressor 2 a of the turbocharger 2 and the intercooler 6 to the regeneration gas flow path 40 via the opening degree variable valve 39, and the air 4 is added by the air compressor 41. And stored in the reservoir tank 42, and the stop valves 48, 49, 50, 51, 5
2 is closed, and the used amount of the compressed air 4 'is taken out from the reservoir tank 42 and guided to the oxygen absorbing material 44 of the branch flow path 40A via the three-way valve 43. Since the oxygen content is absorbed by the oxygen absorbing material 44 to generate the nitrogen-rich gas 4 ″, the nitrogen-rich gas 4 ″ is depressurized by the pressure reducing valve 53 by opening the stop valves 50 and 52, and then branched through the three-way valve 43. It is led to the passage 40C and introduced into the inlet side of the NOx storage reduction catalyst 11, whereby the reducing atmosphere in the NOx storage reduction catalyst 11 is increased, and the reducing agent 10 is added through a reducing agent supply pipe 18 to add the reducing agent. The reaction selectivity between the reducing agent 10 and NOx is improved,
The NOx storage reduction catalyst 11 is actively decomposed and released to promote good regeneration of the NOx storage reduction catalyst 11, and the released NOx is reacted with the reducing agent 10 on the NOx storage reduction catalyst 11 to reduce and purify. Let it.

When the nitrogen-rich gas 4 ″ is introduced into the NOx storage-reduction catalyst 11 having a reduced storage capacity to regenerate the NOx storage-reduction catalyst 11, the temperature of the NOx storage-reduction catalyst 11 deviates from the catalyst activation temperature range. In order to prevent this, a part of the exhaust gas 7 may be mixed by slightly opening the variable opening valves 13 and 14 at an appropriate opening.

Then, by switching the three-way valve 43 to guide the compressed air 4 'from the reservoir tank 42 to the oxygen absorbing material 45 of the branch passage 40B, the nitrogen-rich gas 4 "is generated in the same manner as described above. With the stop valve 50 closed, 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 content absorbed by the oxygen absorbing material 44, The oxygen absorber 44 is regenerated.

As described above, if one of the oxygen absorbers 44, 45 is regenerated while the other is absorbing oxygen, the oxygen absorber 44, 45 is always regenerated. Either of the members 44 and 45 can be kept in a usable state.

When a sufficient amount of NOx is stored in the state of nitrate and the storage capacity of the NOx storage reduction catalyst 22 is reduced, the variable opening valves 13 and 14 are opened and the variable opening valves 15 and 16 to prevent the exhaust gas 7 from diverting to the bypass flow path 12 side.
The NOx occlusion / reduction catalyst 2 having a reduced occlusion capacity while allowing the NOx occlusion / reduction catalyst 11 on the side to take over the NOx occlusion.
2 may be reproduced in the same manner as described above.

As described above, the NOx storage reduction catalysts 11 and 12
2 while one of the two is storing NOx.
If the other one of the Ox storage reduction catalysts 11 and 22 is regenerated, it is possible to continuously reduce NOx by setting any one of the NOx storage reduction catalysts 11 and 22 to a usable state. Become.

Here, in this embodiment, the air 4 is supplied to the compressor 2 a of the turbocharger 2 and the intercooler 6.
However, the regeneration gas flow path is configured as a completely separate system from the intake system, and a dedicated blower for taking in air 4 from the atmosphere into the regeneration gas flow path is provided. The blower may be provided, and in such a case, the blower may be driven using engine power.

The exhaust gas purifying apparatus of the present invention is not limited to the above-described embodiment. For example, the oxygen absorbing material and the NOx storage reduction catalyst in the fourth embodiment are provided in pairs. Or a configuration in which the paired oxygen absorbing material and the NOx storage reduction catalyst in the fifth embodiment are individually provided, and other first, second, and second except for the third embodiment. Fourth and fifth embodiments may employ a configuration in which a selective reduction catalyst is provided on the upstream side of the NOx storage reduction catalyst. In addition, various changes may be made without departing from the gist of the present invention. Of course.

[0061]

According to the exhaust gas purifying apparatus of the present invention described above, the following various excellent effects can be obtained.

(I) According to the first, second and third aspects of the present invention, the NOx storage reduction catalyst can be satisfactorily regenerated even in the lean burn operation state, so that the NOx reduction during the lean burn operation can be achieved. An exhaust purification device using a highly effective NOx storage reduction catalyst can be put to practical use.

(II) According to the fourth aspect of the present invention, while one oxygen absorbing material is absorbing oxygen, the other oxygen absorbing material can be regenerated. Therefore, any one of the oxygen absorbing materials can always be kept in a standby state.

(III) According to the fifth aspect of the present invention, while one NOx storage reduction catalyst is storing NOx, the other NOx storage reduction catalyst is regenerated. Therefore, it is possible to continuously reduce NOx by keeping one of the NOx storage reduction catalysts in a usable state.

(IV) According to the invention of claim 6 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 N
Since the load of NOx storage on the Ox storage reduction catalyst can be greatly reduced, the time until the NOx storage reduction catalyst reaches the storage limit can be lengthened, and the regeneration cycle can be lengthened.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a first embodiment of the present invention.

FIG. 2 is a schematic view showing a second embodiment of the present invention.

FIG. 3 is a schematic view showing a third embodiment of the present invention.

FIG. 4 is a schematic view showing a fourth embodiment of the present invention.

FIG. 5 is a schematic view showing a fifth embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 4 air 4 "nitrogen rich gas 7 exhaust gas 9 exhaust pipe 10 reducing agent 11 NOx storage reduction catalyst 22 NOx storage reduction catalyst 26 selective reduction catalyst 30 oxygen absorbing material 40 regeneration gas flow path 44 oxygen absorbing material 45 oxygen absorbing material

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Hirabayashi 3-1-1, Hinodai, Hino-shi, Tokyo Inside Hino Motor Co., Ltd. (72) Inventor Masatoshi Shimoda 3-1-1, Hinodai, Hino-shi, Tokyo Hino Motors Co., Ltd. (72) Inventor Mitsuru Hosoya 3-1-1, Hinodai, Hino-shi, Tokyo F-term in Hino Motors Co., Ltd. (reference) 3G091 AA10 AA18 AA28 AB06 BA01 BA14 CA13 CA16 CA18 EA30 GB01W GB06W GB09W HA08 HA11

Claims (6)

[Claims] 1. An exhaust pipe through which exhaust gas flows, oxidizes NOx when the oxygen concentration in the exhaust gas is high, temporarily stores it in the form of nitrate, and reduces it when the oxygen concentration in the exhaust gas is low. A NOx storage reduction catalyst that decomposes and releases NOx through the intervening agent to reduce and purify the exhaust gas, appropriately adding a reducing agent to the NOx storage reduction catalyst and appropriately bypassing the NOx storage reduction catalyst to reduce exhaust gas. An exhaust gas purification apparatus characterized in that the flow rate of exhaust gas passing through the NOx storage reduction catalyst can be restricted by flowing the exhaust gas. 2. In the middle of an exhaust pipe through which exhaust gas flows, NOx is oxidized when the oxygen concentration in the exhaust gas is high, temporarily stored in the form of nitrate, and reduced when the oxygen concentration in the exhaust gas is low. Equipped with a NOx storage reduction catalyst that decomposes and releases NOx through the intervening agent, and an oxygen absorbing material in the exhaust pipe upstream of the NOx storage reduction catalyst,
An exhaust gas purification apparatus characterized in that a reducing agent is appropriately added to the NOx storage reduction catalyst, and the oxygen absorbent is appropriately bypassed so that exhaust gas can be led to the NOx storage reduction catalyst. 3. In the middle of an exhaust pipe through which exhaust gas flows, NOx is oxidized when the oxygen concentration in the exhaust gas is high, temporarily stored in the form of nitrate, and reduced when the oxygen concentration in the exhaust gas is low. A NOx storage-reduction catalyst that decomposes and releases NOx through the intervening agent, and provides a regeneration gas flow path so that air can be separately guided from the atmosphere to the NOx storage-reduction catalyst. An oxygen absorbing material is provided in the middle of the flow path, and a nitrogen-rich gas generated by appropriately adding a reducing agent to the NOx storing and reducing catalyst and absorbing oxygen from air by the oxygen absorbing material is used as the NOx storing and reducing catalyst. An exhaust gas purification apparatus characterized in that it can be appropriately introduced into the exhaust gas purification apparatus. 4. The exhaust gas purification apparatus according to claim 2, wherein the oxygen absorbents are provided in pairs in parallel, and the two oxygen absorbents can be regenerated alternately. 5. A NOx storage reduction catalyst is provided in a pair in parallel,
5. The exhaust gas purification apparatus according to claim 1, wherein the two NOx storage reduction catalysts can be regenerated alternately. 6. An exhaust pipe upstream of a NOx storage reduction catalyst is provided with a selective reduction catalyst for selectively reacting a reducing agent with NOx so that the reducing agent can be appropriately added to the selective reduction catalyst. 3. The device according to claim 1, wherein
The exhaust purification device according to 3, 4, or 5.