JP2020076326A - Catalyst structure and purification system - Google Patents

Abstract

To provide a catalyst structure capable of appropriately managing an adsorption amount and desorption amount of a nitrogen oxide and suppressing deterioration.SOLUTION: A tubular catalyst structure 50 capable of adsorbing and desorbing NOx in exhaust gas comprises: a cavity part 52 provided along an axial direction in a central part; a catalyst part 53 provided so as to surround the cavity part 52; and an opening/closing valve 55 provided on the outlet side of the cavity part 52.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a catalyst structure and a purification system.

  In the exhaust passage of vehicles such as trucks, a purifying device that purifies the nitrogen oxides (NOx) in the exhaust gas by reduction reaction is mounted. Further, in recent years, it has been considered to provide a tubular catalyst structure capable of adsorbing and desorbing NOx on the upstream side of SCR (Selective Catalytic Reduction) in the exhaust passage as an auxiliary device of the purifying device. The catalyst structure adsorbs NOx when the temperature of the exhaust gas is low, and desorbs the adsorbed NOx when the temperature of the exhaust gas exceeds the temperature at which purification is started in the purifying device. Then, the desorbed NOx is purified by the purification device.

JP, 2005-151887, A

  In the above catalyst structure, the exhaust gas usually continues to pass through the catalyst portion, which may deteriorate the catalyst portion. Moreover, since the desorption amount of NOx depends on the temperature change of the exhaust gas, it is difficult to manage the desorption amount of NOx. As a result, there is a risk that an amount of NOx that exceeds the purification capacity of the purification device will be desorbed.

  Therefore, the present invention has been made in view of these points, and an object thereof is to provide a catalyst structure capable of appropriately controlling the adsorption amount and desorption amount of nitrogen oxides and suppressing deterioration.

  In the first aspect of the present invention, a tubular catalyst structure capable of adsorbing and desorbing nitrogen oxides in exhaust gas, wherein a hollow portion is provided in a central portion along an axial direction, and the hollow portion. There is provided a catalyst structure including a catalyst portion provided so as to surround the portion, and an opening / closing valve provided on the outlet side of the hollow portion.

  The catalyst portion may have a honeycomb structure, and the catalyst structure may further include a partition wall provided between the hollow portion and the catalyst portion.

  In a second aspect of the present invention, there is provided an exhaust passage through which exhaust gas flows, and a tubular catalyst structure provided in the exhaust passage and capable of adsorbing and desorbing nitrogen oxides in the exhaust gas. A catalyst structure having a hollow portion provided along the axial direction of the hollow portion, a catalyst portion provided so as to surround the hollow portion, and an opening / closing valve provided on the outlet side of the hollow portion; A control system that operates a valve and adjusts a flow rate of exhaust gas flowing through the hollow portion and the catalyst portion.

  Further, the purification system is provided on a temperature detection unit that detects the temperature of the exhaust gas and on a downstream side of the catalyst structure in the exhaust passage, and the nitrogen gas is provided when the temperature of the exhaust gas becomes equal to or higher than a first temperature. A purification unit for purifying oxides is further provided, and the control unit closes the on-off valve and passes through the catalyst unit when it is detected that the temperature of the exhaust gas is lower than the first temperature. When the temperature of the exhaust gas is detected to be equal to or higher than the first temperature, the nitrogen oxide in the exhaust gas is adsorbed to the catalyst portion, and the opening / closing valve is opened to allow the exhaust gas to pass through the cavity. It may be allowed to pass through the section.

  The catalyst unit desorbs the adsorbed nitrogen oxides when the temperature of the exhaust gas is equal to or higher than a second temperature higher than the first temperature, and the control unit controls the temperature of the exhaust gas. Is detected to be equal to or higher than the second temperature, the on-off valve may be closed to allow the exhaust gas to pass through the catalyst portion.

  Further, the purification system further includes a nitrogen detection unit that is provided between the catalyst structure and the purification unit in the exhaust passage, and detects a nitrogen oxide amount, and the control unit includes the nitrogen detection unit. When the detected amount of the part exceeds a predetermined threshold value, the opening degree of the opening / closing valve may be adjusted according to the detected amount.

  According to the present invention, it is possible to appropriately control the adsorption amount and desorption amount of nitrogen oxides in the catalyst structure and suppress deterioration.

It is a schematic diagram for explaining the composition of the purification system 1 concerning one embodiment of the present invention. 3 is a schematic diagram for explaining the configuration of a catalyst structure 50. FIG. FIG. 3 is a schematic sectional view taken along the line AA of FIG. 2. It is a flow chart for explaining an example of operation of purification system 1.

<Structure of purification system>
The configuration of the purification system according to one embodiment of the present invention will be described with reference to FIG.

  FIG. 1 is a schematic diagram for explaining the configuration of a purification system 1 according to one embodiment. The purification system 1 is a system for purifying engine exhaust gas, and is installed in a vehicle such as a truck here. As shown in FIG. 1, the purification system 1 includes an exhaust passage 10, a DOC (Diesel Oxidation Catalyst) 30, a DPF (Diesel Particulate Filter) 32, an injection unit 40, an SCR 42, a catalyst structure 50, and NOx. It has a sensor 60, a temperature detector 80, and a controller 90.

  The exhaust passage 10 is an exhaust pipe connected to an engine (not shown) of the vehicle and through which exhaust gas of the engine flows. The engine is a diesel engine here.

The DOC 30 is an oxidation catalyst for diesel, and efficiently oxidizes hydrocarbons in exhaust gas to raise the temperature of exhaust gas.
The DPF 32 is a filter that collects particulate matter (PM) in exhaust gas.

The injection unit 40 injects urea water, which becomes ammonia, into the exhaust passage 10.
The SCR 42 reacts nitrogen oxides (NOx) in the exhaust gas with ammonia to reduce harmless nitrogen and water. In the present embodiment, the SCR 42 corresponds to the purification unit that purifies NOx. When the temperature of the exhaust gas passing through becomes equal to or higher than the purification temperature T1 (the purification temperature T1 corresponds to the first temperature), the SCR 42 reduces NOx and purifies it. The purification temperature T1 is, for example, 160 to 200 ° C.

  The catalyst structure 50 is an auxiliary device of the SCR 42, and is provided on the upstream side of the SCR 42 in the exhaust passage 10. In the present embodiment, the catalyst structure 50 is provided on the upstream side of the DOC 30. However, the present invention is not limited to this, and the catalyst structure 50 may be provided between the DPF 32 and the SCR 42. The catalyst structure 50 has a catalyst capable of adsorbing and desorbing NOx in the exhaust gas.

  FIG. 2 is a schematic diagram for explaining the structure of the catalyst structure 50. FIG. 3 is a schematic cross-sectional view taken along the line AA of FIG. The catalyst structure 50 has a cavity portion 52, a catalyst portion 53, a partition wall 54, and an opening / closing valve 55. The hollow portion 52, the catalyst portion 53, the partition wall 54, and the opening / closing valve 55 are provided inside the housing 51 (FIG. 3) of the catalyst structure 50.

  The cavity portion 52 is provided in the central portion along the axial direction (see FIG. 2). The cavity 52 is a circular cavity here as shown in FIG. The hollow portion 52 also functions as a passage through which exhaust gas passes. Specifically, the exhaust gas passes through the cavity 52 when the open / close valve 55 is open.

  As shown in FIG. 3, the catalyst portion 53 is provided so as to surround the hollow portion 52. The catalyst portion 53 has a honeycomb structure, and exhaust gas can pass through the inside. Specifically, the exhaust gas passes through the catalyst portion 53 when the open / close valve 55 is closed. Due to the structure of the catalyst portion 53, the pressure loss when the exhaust gas passes through the cavity 52 is smaller than that when the exhaust gas passes through the catalyst portion 53.

  The catalyst part 53 is composed of, for example, an Fe-zeolite catalyst or a Cu-zeolite catalyst, and can maintain high activity from a low temperature region to a high temperature region. The catalyst unit 53 switches between adsorption and desorption of NOx in the exhaust gas according to the temperature of the exhaust gas passing through. For example, when the temperature of the exhaust gas is lower than the purification temperature T1, NOx in the exhaust gas is adsorbed by the catalyst unit 53. On the other hand, when the temperature of the exhaust gas becomes equal to or higher than the desorption temperature T2 (the desorption temperature T2 corresponds to the second temperature) higher than the purification temperature T1, the catalyst unit 53 desorbs the adsorbed NOx. The desorption temperature T2 is, for example, 300 to 500 ° C.

  The partition wall 54 is provided between the cavity portion 52 and the catalyst portion 53. For example, the partition wall 54 is made of metal and is provided in a ring shape. By providing such a partition wall 54, the strength of the catalyst structure 50 can be increased.

  As shown in FIG. 2, the open / close valve 55 is a valve provided on the outlet side of the hollow portion 52 so as to be openable and closable. For example, when the open / close valve 55 is closed, the exhaust gas flows through the catalyst portion 53, and when the open / close valve 55 is open, the exhaust gas flows through the hollow portion 52. The on-off valve 55 opens and closes based on a command from the control device 90. The opening / closing valve 55 is, for example, a butterfly valve, and the opening may be adjustable. By adjusting the opening degree in this way, the flow rate of the exhaust gas flowing through the cavity portion 52 and the flow rate of the catalyst portion 53 can be adjusted respectively. The on-off valve 55 may be a valve other than the butterfly valve.

  As shown in FIG. 1, the NOx sensor 60 is a nitrogen detection unit that is provided between the catalyst structure 50 and the SCR 42 in the exhaust passage 10 and that detects the amount of NOx. For example, the NOx sensor 60 detects the amount of NOx desorbed from the catalyst section 53. The detection result of the NOx sensor 60 is output to the control device 90.

  The temperature detector 80 detects the temperature of exhaust gas. The temperature detection unit 80 includes, for example, a temperature sensor provided in the exhaust passage 10 to measure the temperature of the exhaust gas. The detection result of the temperature detection unit 80 is output to the control device 90.

  The control device 90 is an electronic control device (Electric Control Unit) including a microcomputer having, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The control device 90 controls the operation of each device described above.

  The control device 90 operates the opening / closing valve 55 to adjust the flow rate of the exhaust gas flowing through the hollow portion 52 and the catalyst portion 53. That is, the controller 90 adjusts the flow rate of the exhaust gas flowing through the hollow portion 52 and the catalyst portion 53 by controlling the opening / closing of the open / close valve 55 and switching the flow path of the exhaust gas to the hollow portion 52 or the catalyst portion 53. .

  When it is detected that the temperature of the exhaust gas (exhaust temperature) is lower than the purification temperature T1, the control device 90 closes the opening / closing valve 55 and allows the catalyst portion 53 to pass. When the exhaust gas passes through the catalyst portion 53, NOx in the exhaust gas is adsorbed by the catalyst portion 53. As a result, when the exhaust temperature is lower than the purification temperature T1, NOx is adsorbed by the catalyst portion 53, so that NOx can be suppressed from going to the SCR 42.

  On the other hand, when it is detected that the temperature of the exhaust gas is equal to or higher than the purification temperature T1, the control device 90 opens the open / close valve 55 to allow the exhaust gas to pass through the hollow portion 52. As a result, the NOx that has passed through the cavity 52 is purified by the SCR 42. The control device 90 may suppress the inflow of NOx into the SCR 42 all at once by opening the on-off valve 55 little by little and adjusting the amount of NOx passing through the cavity 52. As a result, the purification rate of the SCR 42 can be increased.

  When it is detected that the temperature of the exhaust gas is equal to or higher than the desorption temperature T2, the control device 90 closes the open / close valve 55 and allows the exhaust gas to pass through the catalyst portion 53. As a result, the exhaust gas passing through the catalyst portion 53 promotes the desorption of NOx adsorbed by the catalyst portion 53 up to that point. The desorbed NOx flows toward the SCR 42 together with the exhaust gas.

  The controller 90 may operate the opening / closing valve 55 based on the detection result of the NOx sensor 60. For example, when the detected amount of the NOx sensor 60 exceeds a predetermined threshold value, the control device 90 adjusts the opening degree of the opening / closing valve 55 according to the detected amount. As a result, the amount of NOx desorbed from the catalyst portion 53 can be appropriately controlled, and the purification by the SCR 42 can be appropriately performed.

<Operation example of purification system>
An operation example of the above-described purification system 1 will be described with reference to FIG.

  FIG. 4 is a flowchart for explaining an operation example of the purification system 1. The processing illustrated in FIG. 4 is realized by the CPU of the control device 90 executing a program.

  The process of FIG. 4 starts when the engine starts rotating and exhaust gas of the engine flows through the exhaust passage 10. Although the temperature of the exhaust gas is low immediately after the engine starts rotating, the temperature of the exhaust gas rises as the engine continues to rotate.

  First, the control device 90 detects the temperature of the exhaust gas flowing through the exhaust passage 10 (step S102). That is, the control device 90 detects the temperature of the exhaust gas by the temperature detection unit 80. In addition, the temperature detection of the exhaust gas by the temperature detection unit 80 is continued at a predetermined interval thereafter.

  Next, the control device 90 determines whether the detected temperature of the exhaust gas (hereinafter, simply referred to as the exhaust temperature) is lower than the purification temperature T1 (step S104). Here, since the engine has just been rotated, the exhaust temperature is lower than the purification temperature T1.

  When it is determined in step S104 that the exhaust temperature is lower than the purification temperature T1 (Yes), the control device 90 closes the opening / closing valve 55 of the catalyst structure 50 (step S106). If the open / close valve 55 has already been closed, the control device 90 maintains the closed state of the open / close valve 55. As a result, the exhaust gas passes through the catalyst portion 53 of the catalyst structure 50. At this time, NOx in the exhaust gas is adsorbed by the catalyst portion 53. As a result, NOx can be suppressed from flowing into the SCR 42 before the purification is started.

  After that, although the temperature of the exhaust gas rises, the control device 90 determines whether the exhaust temperature is equal to or higher than the purification temperature T1 (step S108). When the exhaust gas temperature is equal to or higher than the purification temperature T1 in step S108 (Yes), the control device 90 opens the opening / closing valve 55 (step S110). As a result, the exhaust gas reaches the SCR 42 through the hollow portion 52 having a smaller pressure loss than the catalyst portion 53. Since the exhaust temperature is the purification temperature T1, the NOx in the exhaust gas is purified by the SCR 42.

  Then, the control device 90 determines whether the exhaust gas temperature is equal to or higher than the desorption temperature T2 (step S112). Then, when it is determined in step S112 that the exhaust gas temperature is equal to or higher than the desorption temperature T2 (Yes), the control device 90 closes the opening / closing valve 55 (step S114). As a result, the exhaust gas passes through the catalyst section 53. Further, at the desorption temperature T2, NOx adsorbed on the catalyst portion 53 is desorbed and flows to the SCR 42 together with the exhaust gas. As a result, the desorbed NOx is purified in the SCR 42, so that the purification rate can be increased.

<Effects of this embodiment>
As described above, the catalyst structure 50 that is provided upstream of the SCR 42 in the exhaust passage 10 and is capable of adsorbing / desorbing NOx surrounds the cavity portion 52 provided in the central portion along the axial direction and the cavity portion 52. The catalyst portion 53 thus provided and the opening / closing valve 55 provided on the outlet side of the hollow portion 52 are provided.
By providing the opening / closing valve 55, the catalyst portion 53 and the cavity portion 52 can be switched as the exhaust gas flow path, so that the flow rate of the exhaust gas flowing through the catalyst portion 53 and the cavity portion 52 can be adjusted. As a result, it is possible to prevent the catalyst portion 53 from deteriorating due to, for example, exhaust gas continuously flowing through the catalyst portion 53. Further, by adjusting the flow rates of the cavity portion 52 and the catalyst portion 53 according to the temperature of the exhaust gas, it is possible to properly manage the adsorption amount and desorption amount of NOx with respect to the catalyst portion 53, and as a result, purification of NOx by the SCR 42. Can be done effectively.

  Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist thereof. is there. For example, the specific embodiment of the distribution / integration of the device is not limited to the above-described embodiment, and all or a part thereof may be functionally or physically distributed / integrated in arbitrary units to be configured. You can Further, a new embodiment that occurs due to an arbitrary combination of a plurality of embodiments is also included in the embodiment of the present invention. The effect of the new embodiment produced by the combination has the effect of the original embodiment.

1 Purification system 10 Exhaust path 42 SCR
50 catalyst structure 52 cavity part 53 catalyst part 54 partition wall 55 on-off valve 60 NOx sensor 80 temperature detection part 90 control device

Claims (6)

A tubular catalyst structure capable of adsorbing and desorbing nitrogen oxides in exhaust gas,
A cavity provided along the axial direction in the central part,
A catalyst portion provided so as to surround the cavity,
An on-off valve provided on the outlet side of the cavity,
A catalyst structure comprising: The catalyst portion has a honeycomb structure,
Further comprising a partition wall provided between the hollow portion and the catalyst portion,
The catalyst structure according to claim 1. An exhaust path through which exhaust gas flows,
A tubular catalyst structure that is provided in the exhaust passage and is capable of adsorbing and desorbing nitrogen oxides in the exhaust gas, and has a hollow portion provided along the axial direction in the central portion and the hollow portion. A catalyst structure having a catalyst portion provided so as to surround the opening and closing valve provided on the outlet side of the cavity portion,
A controller that operates the on-off valve to adjust the flow rate of exhaust gas flowing through the cavity and the catalyst;
Purification system. A temperature detector for detecting the temperature of the exhaust gas,
A purification unit that is provided on the downstream side of the catalyst structure in the exhaust passage, and that purifies the nitrogen oxides when the temperature of the exhaust gas becomes a first temperature or higher;
The control unit is
When it is detected that the temperature of the exhaust gas is lower than the first temperature, the on-off valve is closed to adsorb the nitrogen oxide in the exhaust gas passing through the catalyst unit to the catalyst unit,
When the temperature of the exhaust gas is detected to be equal to or higher than the first temperature, the on-off valve is opened to allow the exhaust gas to pass through the cavity.
The purification system according to claim 3. When the temperature of the exhaust gas becomes equal to or higher than a second temperature higher than the first temperature, the catalyst unit desorbs the adsorbed nitrogen oxides,
When the temperature of the exhaust gas is detected to be equal to or higher than the second temperature, the control unit closes the on-off valve to allow the exhaust gas to pass through the catalyst unit,
The purification system according to claim 4. In the exhaust passage, provided between the catalyst structure and the purification unit, further comprising a nitrogen detection unit for detecting the amount of the nitrogen oxides,
The control unit adjusts the opening degree of the opening / closing valve according to the detected amount when the detected amount of the nitrogen detecting unit exceeds a predetermined threshold value,
The purification system according to claim 5.

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