JP2014015909A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device that efficiently heats a whole fuel reforming catalyst, can regenerate a particulate filter by early increasing temperatures of an oxidation catalyst and the particulate filter even at a low exhaust temperature, shortens a rise time of a selective reduction type catalyst inlet temperature and can improve a NOx reduction ratio by early adding a reduction agent to the upstream side of the selective reduction type catalyst.SOLUTION: When a temperature of an oxidation catalyst 2 is an oxidation catalyst set temperature, microwaves generated by a microwave generating device 9 are emitted to a fuel reforming catalyst 8, so as to heat the fuel reforming catalyst 8 uniformly. When the temperature of the oxidation catalyst 2 is equal to or higher than the oxidation catalyst set temperature, in a temperature region in which generation of reformed gas is not required, the microwaves are emitted to the oxidation catalyst 2 and a particulate filter 3 switching from the fuel reforming catalyst 8.

Description

  The present invention relates to an exhaust emission control device.

  Conventionally, a diesel engine is equipped with a selective reduction catalyst having a property of selectively reacting NOx with a reducing agent even in the presence of oxygen in the middle of an exhaust pipe through which exhaust gas flows, and upstream of the selective reduction catalyst. The required amount of reducing agent is added to the side from the reducing agent addition means, and the reducing agent is allowed to undergo a reduction reaction with NOx (nitrogen oxide) in the exhaust gas on the selective reduction catalyst, thereby reducing the NOx emission concentration. There is something like that.

In addition, in the field of industrial flue gas denitration treatment in plants and the like, the effectiveness of a method for reducing and purifying NOx using ammonia (NH ₃ ) as a reducing agent is already widely known. In recent years, there is a problem with traveling with ammonia itself, and in recent years, research on a so-called urea SCR (Selective Catalytic Reduction) system using non-toxic urea water as a reducing agent has been advanced. .

  That is, if urea water is added to the exhaust gas upstream of the selective catalytic reduction catalyst, the urea water is thermally decomposed into ammonia and carbon dioxide gas in the exhaust gas, and the NOx in the exhaust gas is better on the selective catalytic reduction catalyst due to ammonia. Will be reduced and purified.

  On the other hand, when purifying exhaust gas from a diesel engine, it is not enough to remove NOx in the exhaust gas. It is also necessary to collect particulate matter (particulate matter) contained in the exhaust gas through the particulate filter. However, in normal diesel engine operating conditions, there are few opportunities to obtain exhaust temperatures that are high enough for the particulates to self-combust, so an oxidation catalyst with Pt, Pd, etc. as the active species is integrated with the particulate filter. It is made to carry on.

  That is, if such a particulate filter carrying an oxidation catalyst is employed, the oxidation reaction of the collected particulates is promoted to lower the ignition temperature, and the particulates are burned and removed even at a lower exhaust temperature than in the past. It becomes possible.

  However, even when the particulate filter is employed, the trapped amount exceeds the processing amount of the particulates in the operation region where the exhaust temperature is low. If it continues, there exists a possibility that this particulate filter may fall into an over trapping state, without the reproduction | regeneration of a particulate filter progressing favorably.

  Therefore, a flow-through type oxidation catalyst is attached to the front stage of the particulate filter, and when the accumulated amount of particulates has increased, fuel is added from the fuel addition means to the exhaust gas upstream of the oxidation catalyst. It is considered to forcibly regenerate the filter.

  In other words, if fuel is added to the exhaust gas upstream of the oxidation catalyst, the added fuel (HC) undergoes an oxidation reaction while passing through the preceding oxidation catalyst. The catalyst bed temperature of the particulate filter is raised, the particulate is burned out, and the particulate filter is regenerated.

  However, the catalyst bed in which the oxidation catalyst in the previous stage can exhibit sufficient catalytic activity in a vehicle with an operation state in which the operation state with a low exhaust temperature continues for a long time such as an urban route bus traveling only on a congested road It is difficult to raise the temperature to the temperature, and the oxidation reaction of the added fuel in the oxidation catalyst is not activated, so that it is difficult to efficiently regenerate the particulate filter in a short time, and the selective reduction catalyst is also a catalyst. There was a problem that the NOx emission concentration increased because it was not possible to add urea water without raising the temperature to a catalyst bed temperature at which activity could be exhibited.

Therefore, in recent years, a fuel reforming catalyst capable of decomposing the added fuel into H ₂ and CO is disposed on the inlet side of the oxidation catalyst, and the fuel reforming catalyst is heated using a heater or a glow plug to be added. reforming the reformed gas of highly reactive H ₂ and CO fuel, the H ₂ and CO in the reforming gas, even low exhaust gas temperature region, the oxidation catalyst and temperature of the particulate filter It is considered that the particulate filter can be regenerated early and the urea water can be added upstream of the selective catalytic reduction catalyst so that a high NOx reduction rate can be obtained. .

  For example, Patent Document 1 discloses a general technical level of an exhaust purification device that heats a catalyst device by microwave irradiation.

JP 2004-169665 A

  However, as described above, when a heater or a glow plug is used as a heating source, the heating is not uniform, and as shown in FIG. 5, the temperature at which the entire fuel reforming catalyst can reform the fuel (for example, 400) [° C.]) takes a long time to rise, and it becomes difficult to raise the temperature of the oxidation catalyst and the particulate filter at an early stage, making it difficult to regenerate the particulate filter. As a result, the rising time is prolonged, and urea water cannot be added to the upstream side of the selective catalytic reduction catalyst at an early stage, which makes it difficult to obtain a high NOx reduction rate.

  In FIG. 5, A ′ is a conventional reformed gas in which the fuel reforming catalyst temperature reaches the reforming set temperature (for example, 400 [° C.]) and fuel and air are supplied to the fuel reforming catalyst. The timing when it becomes possible to generate is shown.

  Further, B ′ has conventionally been such that the oxidation catalyst temperature reaches an oxidation catalyst set temperature (for example, 200 [° C.]), stops the supply of fuel and air to the fuel reforming catalyst, and is upstream of the oxidation catalyst. The timing at which the particulate filter can be forcibly regenerated by adding fuel from the fuel addition means to the exhaust gas is shown.

  Furthermore, C ′ has conventionally been subjected to selective reduction-type catalyst temperature reaching a selective reduction setting temperature (for example, 200 [° C.]), and urea water as a reducing agent is added from the reducing agent adding means to perform selective reduction. The timing at which NOx in the exhaust gas can be reduced and purified with ammonia on the type catalyst is shown.

  The present invention has been made in view of the above-described conventional problems, and efficiently heats the entire fuel reforming catalyst and raises the temperature of the oxidation catalyst and the particulate filter at an early stage even at a low exhaust temperature. An exhaust emission control device capable of regenerating a filter, shortening the rise time of the selective catalytic reduction catalyst inlet temperature, and quickly adding a reducing agent upstream of the selective catalytic reduction catalyst to improve the NOx reduction rate It is something to be offered.

The present invention includes an oxidation catalyst and a particulate filter disposed in an exhaust pipe through which exhaust gas flows,
Fuel addition means for forcibly regenerating the particulate filter by adding fuel to the exhaust gas upstream of the oxidation catalyst;
A selective reduction catalyst disposed in the exhaust pipe;
A reducing agent adding means for adding a reducing agent upstream of the selective catalytic reduction catalyst to cause a reduction reaction with NOx in the exhaust gas on the selective catalytic reduction catalyst;
A fuel reforming catalyst for supplying a reformed gas of fuel to the inlet side of the oxidation catalyst;
A microwave generator that irradiates microwaves to any one of the fuel reforming catalyst, the oxidation catalyst, and the particulate filter;
When the oxidation catalyst temperature is lower than the oxidation catalyst set temperature, the microwave generator is switched to irradiate the fuel reforming catalyst with microwaves, while the oxidation catalyst temperature is equal to or higher than the oxidation catalyst set temperature. And a control device for switching the microwave generator so as to irradiate the fuel reforming catalyst with microwaves and irradiate the oxidation catalyst and the particulate filter with microwaves. It concerns the purification device.

  According to the above means, the following operation can be obtained.

  Compared to the case of using a heater or a glow plug as a heating source as in the past, the microwave generated by the microwave generator when the oxidation catalyst temperature is lower than the oxidation catalyst set temperature as in the present invention is fuel reformed. When the catalyst is irradiated, the fuel reforming catalyst is uniformly heated, and the time until the entire fuel reforming catalyst rises to a temperature at which the fuel can be converted into reformed gas is shortened. The oxidation catalyst and the particulate filter It is easy to raise the temperature early, the regeneration of the particulate filter is facilitated, and the rise time of the inlet temperature of the selective catalytic reduction catalyst is not prolonged, so that the reducing agent can be added to the upstream side of the selective catalytic reduction catalyst. It becomes possible to carry out at an early stage, and a high NOx reduction rate can be obtained.

  Further, in a temperature range where the temperature of the oxidation catalyst is equal to or higher than the oxidation catalyst set temperature and it is not necessary to generate reformed gas, the microwave generated by the microwave generator is transferred from the fuel reforming catalyst to the oxidation catalyst and the particulate filter. In order to irradiate and switch to, the microwave can be used as an aid for raising the temperature of the oxidation catalyst and the particulate filter, and the temperature of the oxidation catalyst and the particulate filter is kept high even under operating conditions where the exhaust temperature is lowered, It is very effective in maintaining high activity. Incidentally, what is disclosed in Patent Document 1 is to heat the catalyst device by microwave irradiation, but is different from that to switch the heating target according to the temperature as in the present invention.

In the exhaust emission control device, when the fuel reforming catalyst temperature becomes equal to or higher than a reforming set temperature due to microwave irradiation to the fuel reforming catalyst, fuel and air are supplied to the fuel reforming catalyst to generate reformed gas. Generate
When the oxidation catalyst temperature becomes equal to or higher than the oxidation catalyst set temperature, supply of fuel and air to the fuel reforming catalyst is stopped and fuel is added from the fuel addition means,
The controller is configured to stop the microwave irradiation to the particulate filter and stop the fuel addition from the fuel addition means when the inlet temperature of the particulate filter becomes equal to or higher than a filter set temperature. Can do.

Further, when the selective reduction catalyst temperature becomes equal to or higher than the selective reduction set temperature due to fuel addition from the fuel addition means, a reducing agent is added from the reducing agent addition means,
The control device can also be configured to stop the addition of the reducing agent from the reducing agent addition means when the NOx concentration in the exhaust gas becomes below a reference value.

  In the exhaust gas purification apparatus, the reducing agent can be urea water.

  According to the exhaust emission control device of the present invention, the entire fuel reforming catalyst can be efficiently heated, and the temperature of the oxidation catalyst and the particulate filter can be increased at an early stage even at a low exhaust temperature to regenerate the particulate filter. In addition, it is possible to achieve an excellent effect that the time for raising the selective reduction catalyst inlet temperature is shortened and the reducing agent is added to the upstream side of the selective reduction catalyst at an early stage to improve the NOx reduction rate.

1 is an overall schematic configuration diagram showing an embodiment of an exhaust emission control device of the present invention. It is a perspective view which shows the waveguide in the Example of the exhaust gas purification apparatus of this invention. It is a flowchart which shows the flow of control in the Example of the exhaust gas purification apparatus of this invention. It is a flowchart which shows the flow of control in the Example of the exhaust gas purification apparatus of this invention. It is a diagram which shows the temperature rise of the fuel reforming catalyst, oxidation catalyst, and selective reduction catalyst in the embodiment of the exhaust gas purification apparatus of the present invention in comparison with the conventional case.

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

1 to 5 show an embodiment of the exhaust gas purification apparatus of the present invention, in which an oxidation catalyst 2 and a particulate filter 3 are arranged in an exhaust pipe 1 through which exhaust gas flows, and as a reducing agent downstream thereof. A selective reduction catalyst 4 using urea water and an ammonia slip catalyst 5 for oxidizing excess ammonia (NH ₃ ) leaking from the selective reduction catalyst 4 are provided.

  A fuel addition means 6 for forcibly regenerating the particulate filter 3 by adding fuel to the exhaust gas is provided upstream of the oxidation catalyst 2, and a reducing agent is added upstream of the selective catalytic reduction catalyst 4. A reducing agent addition means 7 is provided for reducing the NOx emission concentration by causing the reducing agent to undergo a reduction reaction with NOx in the exhaust gas on the selective catalytic reduction catalyst 4. Here, the fuel addition means 6 has a configuration in which a fuel addition nozzle 6c for injecting fuel into the exhaust pipe 1 is connected to the tip of a fuel pipe 6a provided with a shutoff valve 6b in the middle. Yes. The reducing agent addition means 7 has a configuration in which a reducing agent addition nozzle 7c for injecting a reducing agent into the exhaust pipe 1 is connected to the tip of a reducing agent pipe 7a provided with a shutoff valve 7b in the middle. Have.

  A fuel reforming catalyst 8 for supplying a reformed gas of fuel is provided on the entry side of the oxidation catalyst 2, and the fuel reforming catalyst 8 and any one of the oxidation catalyst 2 and the particulate filter 3 are micro-connected. A microwave generator 9 for irradiating a wave is provided outside the exhaust pipe 1. The microwave generator 9 includes a high voltage generator 9a and a magnetron 9b that generates a microwave when a high voltage is applied from the high voltage generator 9a.

  The fuel reforming catalyst 8 is disposed in a casing 13 having a fuel pipe 10a and an air pipe 11a connected to one end face and a reformed gas blowing pipe 12 connected to the other end face. Is provided with an electromagnetic shielding member 14 such as a punching metal so as to sandwich the upstream side and the downstream side of the fuel reforming catalyst 8 from both sides, and the microwave generator is disposed in a space sandwiched by the electromagnetic shielding member 14. 9, a waveguide 15 extending from the magnetron 9b and irradiating the fuel reforming catalyst 8 with microwaves is inserted, and shut-off valves 10b and 11b are provided in the middle of the fuel pipe 10a and the air pipe 11a, respectively. is there.

  An electromagnetic shielding member 16 such as punching metal is disposed in the exhaust pipe 1 so as to sandwich the upstream side and the downstream side of the oxidation catalyst 2 and the particulate filter 3 from both sides, and is sandwiched by the electromagnetic shielding member 16. A waveguide 17 extending from the magnetron 9b of the microwave generator 9 and irradiating the oxidation catalyst 2 and the particulate filter 3 with microwaves is inserted into the space.

  The electromagnetic shielding members 14 and 16 are provided with a large number of small-diameter holes (not shown) through which microwaves cannot pass, and the microwaves are shielded by the electromagnetic shielding members 14 and 16. The fuel, air, and exhaust gas can pass through the holes of the electromagnetic shielding members 14 and 16, respectively.

  Furthermore, a temperature detector 18 for detecting the temperature of the fuel reforming catalyst 8, a temperature detector 19 for detecting the temperature of the oxidation catalyst 2, and a temperature detector 20 for detecting the inlet temperature of the particulate filter 3; The temperature detector 21 for detecting the temperature of the selective catalytic reduction catalyst 4 and the NOx detector 22 for detecting the NOx concentration in the exhaust gas are provided and detected by the temperature detectors 18, 19, 20, 21. Based on the temperature and the NOx concentration detected by the NOx detector 22, a control device 23 is provided for outputting a switching control signal to the microwave generator 9 and outputting an opening / closing control signal to the shutoff valves 6b and 7b. .

  Further, the waveguides 15 and 17 are rectangular cylinders having a rectangular cross section as shown in FIG. 2 and closed at the front end side (the lower end side in FIG. 2), so that the fuel reforming catalyst 8 or the oxidation catalyst 2 and Openings 15a and 17a are formed on the surface facing the particulate filter 3 (see FIG. 1), and the microwaves generated by the magnetron 9b of the microwave generator 9 are reflected internally while the openings 15a and 17a are reflected. It can be irradiated from.

  Next, the operation of the above embodiment will be described.

  During operation of the diesel engine, it is determined whether or not the temperature of the oxidation catalyst 2 detected by the temperature detector 19 is lower than the oxidation catalyst set temperature (for example, 200 [° C.]) (see step S1 in FIG. 3). ) When the temperature of the oxidation catalyst 2 is lower than the oxidation catalyst set temperature, the magnetron 9b of the microwave generator 9 is switched by the switching control signal output from the control device 23 to the fuel reforming catalyst 8. Microwaves are irradiated from the waveguide 15 and heated (see step S2 in FIG. 3).

Subsequently, it is determined whether or not the temperature of the fuel reforming catalyst 8 detected by the temperature detector 18 has become equal to or higher than a reforming set temperature (for example, 400 [° C.]) by microwave irradiation (FIG. 3). In step S3), when the temperature of the fuel reforming catalyst 8 becomes equal to or higher than the reforming set temperature, the shutoff valves 10b and 11b are opened by the open / close control signal output from the control device 23, and the fuel reforming catalyst. Fuel and air are supplied to 8 to generate reformed gas (see step S4 in FIG. 3), and the reformed gas is blown out from the reformed gas blowing pipe 12 toward the oxidation catalyst 2 and the particulate filter 3, the H ₂ and CO in the reformed gas, even at a low temperature region the exhaust gas, it is conducted to said early raises the oxidation catalyst and temperature of the particulate filter to allow regeneration of the particulate filter That. If the temperature of the fuel reforming catalyst 8 is not equal to or higher than the reforming set temperature, the process returns to step S2, and heating of the fuel reforming catalyst 8 by microwave irradiation is continued.

  When the temperature of the oxidation catalyst 2 is not lower than the oxidation catalyst set temperature but is already equal to or higher than the oxidation catalyst set temperature in the step S1, the microwave irradiation to the fuel reforming catalyst 8 is not performed and the step S4 is performed as it is. It becomes a form to go to.

  It is determined whether or not the temperature of the oxidation catalyst 2 is equal to or higher than the oxidation catalyst set temperature (see step S5 in FIG. 3). If the temperature of the oxidation catalyst 2 is equal to or higher than the oxidation catalyst set temperature, control is performed. The magnetron 9b of the microwave generator 9 is switched by the switching control signal output from the device 23, the microwave irradiation to the fuel reforming catalyst 8 is stopped, and the heating is stopped (see step S6 in FIG. 3). The shutoff valves 10b and 11b are closed by the open / close control signal output from the control device 23, the supply of fuel and air to the fuel reforming catalyst 8 is stopped, and the generation of reformed gas is stopped (step of FIG. 3). S7), the particulate filter 3 is irradiated with microwaves from the waveguide 17 and heated (see step S8 in FIG. 3).

  Thereafter, the shutoff valve 6b is opened by an open / close control signal output from the control device 23, fuel injection from the fuel addition nozzle 6c of the fuel addition means 6 is started (see step S9 in FIG. 4), and the temperature detector 20 It is determined whether or not the inlet temperature of the particulate filter 3 detected in (1) is equal to or higher than the filter set temperature (for example, 600 [° C.]) (see step S10 in FIG. 4). If the inlet temperature is not equal to or higher than the filter set temperature, the process returns to step S9, and the fuel addition means 6 adds fuel while the particulate filter 3 is continuously heated by microwave irradiation. When the fuel injection from the nozzle 6c is continued and the inlet temperature of the particulate filter 3 becomes equal to or higher than the filter set temperature. The microwave irradiation to the particulate filter 3 is stopped (see step S11 in FIG. 4), and the fuel injection from the fuel addition nozzle 6c of the fuel addition means 6 is stopped (see step S12 in FIG. 4). .

  Concurrently with the comparison judgment with respect to the filter set temperature of the inlet temperature of the particulate filter 3 in the step S10, the temperature of the selective catalytic reduction catalyst 4 detected by the temperature detector 21 is the selective reduction set temperature (for example, 200 [° C.]). ) Is determined (see step S13 in FIG. 4). If the temperature of the selective catalytic reduction catalyst 4 is not equal to or higher than the selective reduction set temperature, the process returns to step S9, Fuel injection from the fuel addition nozzle 6c of the fuel addition means 6 is continued in a state in which the particulate filter 3 is continuously heated by microwave irradiation, and from the fuel addition nozzle 6c of the fuel addition means 6 When the temperature of the selective reduction catalyst 4 becomes equal to or higher than the selective reduction set temperature due to the fuel injection, the reducing agent addition nose of the reducing agent addition means 7 is reduced. Urea water is injected as a reducing agent from 7c (see step S14 in FIG. 4).

  Judgment is made as to whether or not the NOx concentration in the exhaust gas detected by the NOx detector 22 has fallen below the reference value due to the injection of urea water as the reducing agent from the reducing agent addition nozzle 7c of the reducing agent addition means 7. If the NOx concentration in the exhaust gas is not below the reference value, the process returns to step S14 and the reducing agent from the reducing agent addition nozzle 7c of the reducing agent addition means 7 is performed. When the NOx concentration in the exhaust gas becomes equal to or less than a reference value, the addition of urea water as a reducing agent from the reducing agent addition nozzle 7c of the reducing agent addition means 7 is continued. Stopped (see step S16 in FIG. 4).

  In FIG. 5, A indicates that the temperature of the fuel reforming catalyst 8 reaches the reforming set temperature (for example, 400 [° C.]) and supplies fuel and air to the fuel reforming catalyst 8 in this embodiment. The timing at which the reformed gas can be generated is shown.

  In the present embodiment, B indicates that the temperature of the oxidation catalyst 2 reaches the oxidation catalyst set temperature (for example, 200 [° C.]), stops the supply of fuel and air to the fuel reforming catalyst 8, and The timing at which fuel can be added from the fuel addition means 6 to the exhaust gas upstream of the oxidation catalyst 2 and the particulate filter 3 can be forcibly regenerated is shown.

  Furthermore, in the present embodiment, C, when the temperature of the selective catalytic reduction catalyst 4 reaches a selective reduction setting temperature (for example, 200 [° C.]), urea water as a reducing agent is added from the reducing agent adding means 7. The timing at which NOx in the exhaust gas can be reduced and purified with ammonia on the selective catalytic reduction catalyst 4 is shown.

  As a result, as compared with the conventional case where a heater or a glow plug is used as a heating source, the fuel reforming catalyst 8 is irradiated with the microwave generated by the magnetron 9b of the microwave generator 9 as in this embodiment. The time until the fuel reforming catalyst 8 is uniformly heated and the whole fuel reforming catalyst 8 rises to a temperature at which the fuel can be converted into reformed gas (for example, 400 [° C.]) as shown in FIG. The temperature of the oxidation catalyst 2 and the particulate filter 3 can be easily raised early, the regeneration of the particulate filter 3 is facilitated, and the rise time of the inlet temperature of the selective catalytic reduction catalyst 4 is prolonged. Therefore, urea water can be added to the upstream side of the selective catalytic reduction catalyst 4 at an early stage, and a high NOx reduction rate can be obtained.

  In the temperature range where the temperature of the oxidation catalyst 2 is equal to or higher than the oxidation catalyst set temperature and the generation of reformed gas is not necessary, the microwave generated by the magnetron 9b of the microwave generator 9 is sent from the fuel reforming catalyst 8. Since the irradiation is switched to the oxidation catalyst 2 and the particulate filter 3, the microwave can be used as an auxiliary for raising the temperature of the oxidation catalyst 2 and the particulate filter 3, and the oxidation catalyst 2 even under operating conditions where the exhaust temperature is lowered. And it is very effective in keeping the temperature of the particulate filter 3 high and maintaining high activity. Incidentally, what is disclosed in Patent Document 1 is for heating the catalyst device by microwave irradiation, but is different from that for switching the heating target according to the temperature as in this embodiment.

  It is preferable to use a material having a large dielectric loss that is easily heated by microwaves for the carrier of the fuel reforming catalyst 8, the oxidation catalyst 2, and the particulate filter 3, but the catalyst carrier having a small dielectric loss has a low dielectric loss. Large materials may be embedded and used.

  In this way, the entire fuel reforming catalyst 8 can be efficiently heated, and the temperature of the oxidation catalyst 2 and the particulate filter 3 can be increased at an early stage even at a low exhaust temperature to regenerate the particulate filter 3. The rise time of the inlet temperature of the catalyst 4 can be shortened, and the reducing agent can be added to the upstream side of the selective catalytic reduction catalyst 4 at an early stage to improve the NOx reduction rate.

  The exhaust emission control device of the present invention is not limited to the above-described embodiment, and various changes can be made without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Exhaust pipe 2 Oxidation catalyst 3 Particulate filter 4 Selective reduction type catalyst 6 Fuel addition means 7 Reducing agent addition means 8 Fuel reforming catalyst 9 Microwave generator 10a Fuel piping 11a Air piping 12 Reformed gas outlet piping 18 Temperature detector DESCRIPTION OF SYMBOLS 19 Temperature detector 20 Temperature detector 21 Temperature detector 22 NOx detector 23 Control apparatus

Claims (4)

An oxidation catalyst and a particulate filter disposed in an exhaust pipe through which exhaust gas flows;
Fuel addition means for forcibly regenerating the particulate filter by adding fuel to the exhaust gas upstream of the oxidation catalyst;
A selective reduction catalyst disposed in the exhaust pipe;
A reducing agent adding means for adding a reducing agent upstream of the selective catalytic reduction catalyst to cause a reduction reaction with NOx in the exhaust gas on the selective catalytic reduction catalyst;
A fuel reforming catalyst for supplying a reformed gas of fuel to the inlet side of the oxidation catalyst;
A microwave generator that irradiates microwaves to any one of the fuel reforming catalyst, the oxidation catalyst, and the particulate filter;
When the oxidation catalyst temperature is lower than the oxidation catalyst set temperature, the microwave generator is switched to irradiate the fuel reforming catalyst with microwaves, while the oxidation catalyst temperature is equal to or higher than the oxidation catalyst set temperature. And a control device for switching the microwave generator so as to irradiate the fuel reforming catalyst with microwaves and irradiate the oxidation catalyst and the particulate filter with microwaves. Purification equipment. When the fuel reforming catalyst temperature becomes equal to or higher than the reforming set temperature by microwave irradiation to the fuel reforming catalyst, fuel and air are supplied to the fuel reforming catalyst to generate reformed gas,
When the oxidation catalyst temperature becomes equal to or higher than the oxidation catalyst set temperature, supply of fuel and air to the fuel reforming catalyst is stopped and fuel is added from the fuel addition means,
The control device is configured to stop microwave irradiation to the particulate filter and stop fuel addition from the fuel addition means when the inlet temperature of the particulate filter becomes equal to or higher than a filter set temperature. Item 2. An exhaust emission control device according to Item 1. When the selective catalytic reduction catalyst temperature becomes equal to or higher than the selective reduction set temperature due to fuel addition from the fuel addition means, a reducing agent is added from the reducing agent addition means,
The exhaust emission control device according to claim 2, wherein the control device is configured to stop the addition of the reducing agent from the reducing agent addition means when the NOx concentration in the exhaust gas becomes a reference value or less.   The exhaust emission control device according to any one of claims 1 to 3, wherein the reducing agent is urea water.

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