JP2010036083A - Exhaust gas cleaning apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas cleaning apparatus with improved temperature rise efficiency of a catalyst. <P>SOLUTION: A catalyst carrier 12 is covered with a side face covering member 21, an upstream end covering member 22, and a downstream end covering member 23. In each of the side face covering member 21, upstream end covering member 22 and downstream end covering member 23, a stainless steel rod-like member 25 is coated with a microwave absorbing body 26 consisting of carbon being a material absorbing microwaves, and further a mesh is formed by covering a protective film 27 consisting of silica with the microwave absorbing body 26. One end of a microwave introducing path 15 with the other end connected to a magnetron 16 penetrates through a converter casing 11 and a heat insulation member 17 and insertedly connected to a microwave introducing hole 24 provided on the side face covering member 21. A dielectricity member 29 made of mica is formed in the microwave introducing path 15 so as to be located outside the converter casing 11. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification device, and more particularly, to a temperature rise of a catalyst constituting the exhaust gas purification device.

A urea SCR (Selective Catalytic Reduction) system has been developed to reduce nitrogen oxides (NOx) contained in exhaust gas from diesel engines. The basic structure of the urea SCR system is provided by oxidizing nitrogen monoxide (NO) into nitrogen dioxide (NO ₂ ) and a downstream side of the oxidation catalyst, which is generated by reacting water with urea. An SCR catalyst for converting NOx into nitrogen and water by a chemical reaction between ammonia and NOx, a urea addition system for adding urea to the SCR catalyst, and a chemical reaction in the SCR catalyst are provided downstream of the SCR catalyst. And an oxidation catalyst for oxidizing the remaining ammonia without being consumed.

  In general, both the oxidation catalyst and the SCR catalyst exhibit sufficient catalyst performance when the temperature is higher than a certain temperature, but the catalyst performance is extremely deteriorated when the temperature is lower than a certain temperature. For this reason, for example, when the exhaust gas temperature is low immediately after the engine is started, the catalyst temperature is low and sufficient catalyst performance cannot be obtained, so that the temperature of the catalyst needs to be increased. As a catalyst temperature raising technique, Patent Document 1 discloses a catalyst in which a mixture of an electromagnetic wave absorber and a catalyst is supported on the surface of a ceramic wall. When the catalyst is irradiated with microwaves, the electromagnetic wave absorber absorbs the microwaves to generate heat, and the catalyst is heated.

JP-A-5-49939

  However, in the exhaust gas purifying apparatus of Patent Document 1, a heating chamber for accommodating the catalyst is formed by providing a metal plate having a number of punching holes on the upstream side and the downstream side of the catalyst, and the upstream side of the heating chamber. Although the microwaves are prevented from spreading to the downstream side, not all the microwaves irradiated in the heating chamber are used for raising the temperature of the catalyst, so the temperature raising efficiency of the catalyst is not so high. There was a problem.

  The present invention has been made to solve such problems, and an object of the present invention is to provide an exhaust gas purifying apparatus in which the temperature rise efficiency of the catalyst is improved.

An exhaust gas purifying apparatus according to the present invention is provided so as to cover a catalyst carrier provided in an exhaust pipe through which exhaust gas flows, a microwave generator for generating microwaves to irradiate the catalyst carrier, and the catalyst carrier. A microwave blocking member that blocks the microwave, a microwave absorber that is made of a material that can absorb the microwave, is in contact with the surface of the catalyst carrier and covers the catalyst carrier, and A microwave introduction hole provided in the microwave blocking member, a microwave introduction passage having one end connected to the microwave generator and the other end connected to the microwave introduction hole, and the microwave introduction passage A dielectric member provided, and the microwave blocking member and the microwave absorber include an exhaust gas for supplying the exhaust gas to the catalyst carrier. A supply hole, and an exhaust gas outflow hole for discharging the said exhaust gas which has passed through the catalyst support is provided. Since the microwave blocking member covers the catalyst carrier, the microwave generated by the microwave generator is confined in the microwave blocking member, so that the microwave provided in contact with the surface of the catalyst carrier and covering the catalyst carrier is provided. It becomes easy to be absorbed by the wave absorber.
The microwave absorber may be coated on the surface of the microwave blocking member.
The microwave absorber may be covered with a protective film. The protective film may be a silica film.
The microwave blocking member may be configured such that the conductive material forms a mesh.
The dielectric member may be provided in the microwave introduction passage so as to be located outside the exhaust pipe.

  According to the present invention, the microwave blocking member covers the catalyst carrier, so that the microwave generated by the microwave generator is confined in the microwave blocking member, contacts the surface of the catalyst carrier, and covers the catalyst carrier. Therefore, most of the microwaves are used only for raising the temperature of the catalyst, and as a result, the temperature raising efficiency of the catalyst can be improved.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 shows a schematic configuration diagram of an exhaust gas purifying apparatus according to an embodiment of the present invention. In an exhaust pipe 2 through which exhaust gas discharged from the diesel engine 1 flows, an oxidation catalyst 3, a diesel particulate filter (DPF) 4, an SCR catalyst 5, and an oxidation catalyst 6 are provided. An injection nozzle 7 for injecting urea water is provided between the DPF 4 and the SCR catalyst 5, and the injection nozzle 7 communicates with a urea water tank 9 for storing urea water through a pipe 8. . The pipe 8 is provided with a urea water addition system 10 for supplying urea water in the urea water tank 9 to the injection nozzle 7. The urea water addition system 10 is electrically connected to an ECU 14 that is a control device.

  FIG. 2 shows a detailed view of the SCR catalyst 5. The SCR catalyst 5 includes a converter case 11 constituting a part of the exhaust pipe 2, a columnar catalyst carrier 12 provided in the converter case 11, and a heat insulating member 17 that covers the catalyst carrier 12 in the converter case 11. Have. The SCR catalyst 5 is connected to a magnetron 16 that is a microwave generator through a microwave introduction passage 15. Exhaust gas flows from left to right in the figure. A temperature sensor 13 a for measuring the exhaust gas temperature is provided upstream of the catalyst carrier 12. Further, a temperature sensor 13 b for measuring the exhaust gas temperature after passing through the catalyst carrier 12 is provided on the downstream side of the catalyst carrier 12. The temperature sensors 13a and 13b and the magnetron 16 are each electrically connected to the ECU 14.

As shown in FIG. 3, the catalyst carrier 12 is provided with a cylindrical side surface covering member 21 so as to be in contact with the side surface of the catalyst carrier 12, and a disk-like shape so as to be in contact with the upstream end surface of the catalyst carrier 12. An upstream end face covering member 22 is provided, and a disc-shaped downstream end face covering member 23 is provided so as to contact the downstream end face of the catalyst carrier 12. The side surface covering member 21 is provided with a microwave introduction hole 24 formed so as to penetrate the side surface covering member 21. Each of the side surface covering member 21, the upstream end surface covering member 22, and the downstream end surface covering member 23 has a lattice mesh configuration. That is, a stainless steel rod-like member 25 is coated with a microwave absorber 26 made of carbon, which is a material capable of absorbing microwaves, and further, a protection made of silica (SiO ₂ ) formed by curing after applying polysilazane. Each of the side surface covering member 21, the upstream end surface covering member 22, and the downstream end surface covering member 23 is configured so as to form a mesh by coating the film 27 on the microwave absorber 26. The mesh interval is preferably 10 mm or less. Of the side surface covering member 21, the upstream end surface covering member 22, and the downstream end surface covering member 23, the rod-shaped member 25 formed in a mesh shape constitutes a microwave blocking member. Moreover, since each of the side surface covering member 21, the upstream end surface covering member 22, and the downstream end surface covering member 23 is configured in a mesh shape, a plurality of holes are provided in each. Here, the plurality of holes 22a provided in the upstream end surface covering member 22 constitute exhaust gas supply holes, and the plurality of holes 23a provided in the downstream end surface covering member 23 constitute exhaust gas outflow holes.

  As shown in FIG. 4, the other end of the microwave introduction passage 15 having one end connected to the magnetron 16 penetrates the converter case 11 and the heat insulating member 17 and is provided in the side surface covering member 21. 24 to be inserted. With such a configuration, the catalyst carrier 12 is connected to the magnetron 16 via the microwave introduction passage 15. A dielectric member 29 made of mica is provided in the microwave introduction passage 15 so as to be located outside the converter case 11, and the dielectric member 29 blocks communication between the catalyst carrier 12 and the magnetron 16. .

  As shown in FIG. 5, the catalyst carrier 12 is composed of a plurality of rectangular parallelepiped honeycomb pieces 30 made of silicon carbide (SiC). In the honeycomb piece 30, a plurality of holes 31 are provided so as to penetrate the honeycomb piece 30 in the axial direction of the honeycomb piece 30. A selective reduction catalyst 32 is supported on the inner peripheral surface 31 a of the hole 31.

2 to 5 show the structure of the SCR catalyst 5 in detail, but the oxidation catalysts 3 and 6 have the same configuration and are supported on the inner peripheral surface 31a of the hole 31 of the honeycomb piece 30 in the SCR catalyst 5. The selected selective reduction catalyst 32 is an oxidation catalyst for oxidizing NO into NO ₂ in the oxidation catalyst 3, and an oxidation catalyst for oxidizing ammonia in the oxidation catalyst 6.

Next, operation | movement of the exhaust gas purification apparatus which concerns on this embodiment is demonstrated based on FIGS.
When the diesel engine 1 is started or idling, the temperature of the exhaust gas discharged from the diesel engine 1 is low. Therefore, even if exhaust gas flows through each of the oxidation catalyst 3, the SCR catalyst 5, and the oxidation catalyst 6, sufficient The catalyst temperature does not increase to the temperature required to exhibit the catalyst performance. Therefore, the temperature raising operation for the SCR catalyst 5 will be described. When the temperature measured by the temperature sensor 13a is lower than a preset temperature (hereinafter referred to as “set temperature”), the ECU 14 activates the magnetron 16 to generate a microwave.

  The generated microwave propagates through the microwave introduction passage 15, passes through the dielectric member 29, and is in a space surrounded by the side surface covering member 21, the upstream end surface covering member 22, and the downstream end surface covering member 23, that is, the catalyst carrier. 12 is irradiated. The microwave is blocked by a bar-like member 25 (microwave blocking member) formed in a mesh shape of the side surface covering member 21, the upstream end surface covering member 22, and the downstream end surface covering member 23, and the side surface covering member 21 and the upstream end surface covering member 22. , It is confined in the space surrounded by the downstream end face covering member 23. Then, the microwave absorber 26 absorbs and heats the confined microwave, and the catalyst carrier 12 is heated by the heat. As the temperature of the catalyst carrier 12 is increased, the temperature of the selective reduction catalyst 32 supported on the inner peripheral surface 31a of the hole 31 of the honeycomb piece 30 is increased.

  The exhaust gas flowing through the exhaust pipe 2 passes through a plurality of holes 22 a formed in the upstream end surface covering member 22 and is in a space surrounded by the side surface covering member 21, the upstream end surface covering member 22, and the downstream end surface covering member 23. It flows in and flows through the holes 31 of the honeycomb pieces 30 constituting the catalyst carrier 12. Since the temperature of the catalyst carrier 12 is raised, the temperature of the exhaust gas rises when flowing through the holes 31. After the exhaust gas circulates through the holes 31, the exhaust gas passes through a plurality of holes 23 a formed in the downstream end surface covering member 23, and from the space surrounded by the side surface covering member 21, the upstream end surface covering member 22, and the downstream end surface covering member 23. leak. Although the microwave introduction hole 24 is provided in the side surface covering member 21, the microwave introduction passage 15 is blocked by the dielectric member 29, so that the exhaust gas enters the magnetron 16 through the microwave introduction passage 15. Prevents inflow.

When the temperature of the exhaust gas measured by the temperature sensor 13b becomes equal to or higher than the set temperature, the ECU 14 stops the operation of the magnetron 16. Thereby, since the microwave absorbed by the microwave absorber 26 is not generated, the microwave absorber 26 does not generate heat. Thereafter, the ECU 14 starts or stops the magnetron 16 based on the measured values of the temperature sensors 13a and 13b, whereby the selective reduction catalyst 32 is maintained at an appropriate temperature.
The oxidation catalysts 3 and 6 are also kept at an appropriate temperature in the same manner as the temperature raising operation for the SCR catalyst 5 although the set temperatures are different.

When the oxidation catalysts 3 and 6 and the SCR catalyst 5 reach appropriate temperatures, the exhaust gas flows through the oxidation catalyst 3, so that NO in the exhaust gas is oxidized to NO ₂ . Subsequently, the exhaust gas flows through the DPF 4, whereby particulate matter (PM) in the exhaust gas is captured by the DPF 4. The ECU 14 operates the urea water addition system 10 at an appropriate timing, supplies the urea water in the urea water tank 9 to the injection nozzle 7 via the pipe 8, and the urea water is added to the SCR catalyst 5 from the injection nozzle 7. The The urea water added to the SCR catalyst 5 is hydrolyzed to become ammonia and carbon dioxide, and the produced ammonia reacts with NOx in the exhaust gas to become nitrogen and water. Ammonia remaining without being consumed in the SCR catalyst 5 is oxidized in the oxidation catalyst 6.

In this way, the stainless steel rod-shaped member 25 (microwave blocking member) configured in a mesh shape covers the catalyst carrier 12, so that the microwave generated by the magnetron 16 is confined in the microwave blocking member, Since it becomes easy to be absorbed by the microwave absorber 26 provided so as to contact the surface of the catalyst carrier 12 and to cover the catalyst carrier 12, most of the microwaves are used only for raising the temperature of the catalyst. Thermal efficiency can be improved. The same applies to the oxidation catalysts 3 and 6.
In addition, the microwave absorber 26 is easily damaged or deteriorated because it is in direct contact with high-temperature exhaust gas. However, since the microwave absorber 26 is covered with the protective film 27 made of silica, damage and deterioration due to the exhaust gas can be prevented. it can. Since silica transmits microwaves, the microwave absorption by the microwave absorber 26 is not hindered.
Each of the side surface covering member 21, the upstream end surface covering member 22, and the downstream end surface covering member 23 has a triple structure of a rod member 25 made of stainless steel, a microwave absorber 26, and a protective film 27. Since it plays the role of a skeleton, the strength of each of the side surface covering member 21, the upstream end surface covering member 22, and the downstream end surface covering member 23 can be increased.
Furthermore, the dielectric member 29 is provided in the microwave introduction passage 15 so as to be located outside the exhaust pipe 2, but the portion of the microwave introduction passage 15 where the dielectric member 29 is provided surrounds the periphery thereof. Since the outside air surrounds, it is possible to cool the dielectric member 29 that is in contact with the high temperature exhaust gas.

In this embodiment, the side surface covering member 21, the upstream end surface covering member 22, and the downstream end surface covering member 23 are each covered with a stainless steel mesh-like rod-shaped member 25 and a microwave absorber 26 and a protective film 27. However, the present invention is not limited to this structure. A microwave absorber may be provided between the plate-like microwave blocking member and the catalyst carrier 12 so as to contact the catalyst carrier 12. In this case, the microwave introduction hole 24, the exhaust gas supply hole 22a, and the exhaust gas outflow hole 23a may be provided so as to penetrate the plate-shaped microwave blocking member. In addition, the microwave blocking member is configured by forming the rod-shaped member 25 in a lattice-shaped mesh, but is not limited to this configuration, and may be configured from a mesh such as punching metal or expanded metal. .
In addition, the upstream end surface covering member 22 and the downstream end surface covering member 23 need to be provided with a plurality of holes 22a and 23a for the exhaust gas to circulate, but the side surface covering member 21 may not have any holes. Good. Furthermore, although the microwave introduction hole 24 is provided in the side surface covering member 21, it is not limited to this configuration, and may be provided in the upstream end surface covering member 22 or the downstream end surface covering member 23.

  The material of the rod-shaped member 25 is not limited to stainless steel, and other metals may be used. The material of the microwave absorber 26 is not limited to carbon, and any material that can absorb microwaves may be used, such as carbon fiber, graphite, SiC, or the like. Further, although silica derived from polysilazane is used as the material of the protective film 27, the present invention is not limited to this. Any material can be used as long as it is capable of transmitting microwaves and can protect the microwave absorber 26 from exhaust gas. For example, a ceramic material such as alumina may be used. Furthermore, the material of the dielectric member 29 is not limited to mica, and any material can be used as long as it is difficult to be damaged by contact with high-temperature exhaust gas and can transmit microwaves (relative permittivity is less than 30). For example, glass, alumina, quartz, asphalt, diamond and the like can be mentioned.

  In addition to this embodiment, a metal rod (antenna) having a length capable of absorbing microwaves, that is, a length that is 1/2 or 1/4 of the wavelength of the microwave, is attached to the outer peripheral surface of the catalyst carrier 12. Alternatively, it may be inserted into a part of the holes 31. The antenna generates heat by absorbing the microwaves, and the catalyst carrier 12 is heated by the heat.

In this embodiment, the temperature of the exhaust gas before and after passing through the catalyst carrier 12 is measured by the temperature sensors 13a and 13b, and the operation of the magnetron 16 is adjusted based on the temperature. However, the present invention is limited to this embodiment. Not what you want. After the magnetron 16 is started, the magnetron 16 may be stopped when a certain time has elapsed.
The number of temperature sensors is not limited to two. At least one temperature sensor is provided on the upstream side of the upstream end surface covering member 22 or on the downstream side of the downstream end surface covering member 23, and measurement of this temperature sensor is performed. The operation of the magnetron 16 may be adjusted based on the value.
Further, the operation of the magnetron 16 may be adjusted from the exhaust gas temperature known in advance from the characteristics of the engine and the temperature measured by the temperature sensors 13a and 13b.

  In this embodiment, a SiC catalyst carrier is used as the catalyst carrier 12, but the present invention is not limited to this. A catalyst carrier made of ceramics, zeolite, cordierite or the like may be used. Further, the shape of the catalyst carrier 12 is not limited to a cylindrical shape, and may be any shape such as an elliptical column shape.

1 is a schematic configuration diagram of an exhaust gas purifying apparatus according to an embodiment of the present invention. It is detail drawing of the SCR catalyst which comprises the exhaust gas purification apparatus which concerns on this embodiment. It is an exploded view of the catalyst carrier of the SCR catalyst which constitutes the exhaust gas purifying apparatus according to this embodiment. It is a partial expanded sectional view of the SCR catalyst which comprises the exhaust gas purification apparatus which concerns on this embodiment. It is a front view of the honeycomb piece of the catalyst carrier of the SCR catalyst that constitutes the exhaust gas purifying apparatus according to this embodiment.

Explanation of symbols

  2 exhaust pipe, 12 catalyst carrier, 15 microwave introduction passage, 16 magnetron (microwave generator), 22a hole (exhaust gas supply hole), 23a hole (exhaust gas outflow hole), 24 microwave introduction hole, 25 rod-shaped member (micro Wave blocking member), 26 microwave absorber, 27 protective film, 29 dielectric member.

Claims (6)

A catalyst carrier provided in an exhaust pipe through which exhaust gas flows;
A microwave generator for generating microwaves for irradiating the catalyst carrier;
A microwave blocking member provided so as to cover the catalyst carrier and blocking the microwave;
A microwave absorber made of a material capable of absorbing the microwave, provided in contact with the surface of the catalyst carrier and covering the catalyst carrier;
A microwave introduction hole provided in the microwave blocking member;
A microwave introduction passage having one end connected to the microwave generator and the other end connected to the microwave introduction hole;
A dielectric member provided in the microwave introduction passage,
The microwave blocking member and the microwave absorber are provided with an exhaust gas supply hole for supplying the exhaust gas to the catalyst carrier and an exhaust gas outlet hole for allowing the exhaust gas that has passed through the catalyst carrier to flow out. Exhaust gas purification device.   The exhaust gas purification apparatus according to claim 1, wherein the microwave absorber is coated on a surface of the microwave blocking member.   The exhaust gas purification apparatus according to claim 1 or 2, wherein the microwave absorber is covered with a protective film.   The exhaust gas purification apparatus according to claim 3, wherein the protective film is a silica film.   The exhaust gas purification device according to any one of claims 1 to 4, wherein the microwave blocking member is configured such that the conductive material forms a mesh.   The exhaust gas purification apparatus according to any one of claims 1 to 5, wherein the dielectric member is provided in the microwave introduction passage so as to be located outside the exhaust pipe.

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