JP2010019229A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of raising a catalyst temperature without affecting catalyst performance. <P>SOLUTION: An SCR catalyst 5 comprises a converter case 11 and a column-shaped catalyst support 12 provided in the converter case 11. The SCR catalyst 5 is connected with a magnetron 16 which is a microwave generating device via a hole 15 partially formed at the converter case 11. Plate-like microwave absorbers 23 formed of carbon are provided on four outer peripheral surfaces 20a of a honeycomb piece 20 which composes the catalyst support 12. The microwave absorbers 23 are coated with protection films 24 formed of silica. <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, since the electromagnetic wave absorber and the catalyst are supported in a mixed state, there is a problem that the electromagnetic wave absorber may affect the catalyst performance.

  The present invention has been made to solve such problems, and an object thereof is to provide an exhaust gas purifying apparatus capable of raising the catalyst temperature without affecting the catalyst performance.

An exhaust gas purifying apparatus according to the present invention comprises a catalyst carrier comprising a plurality of honeycomb pieces each having a plurality of holes and a catalyst supported on the inner surface of the holes, and a microwave for generating microwaves for irradiating the catalyst carrier. And a microwave generator made of a material capable of absorbing the microwave is provided on the outer periphery of the honeycomb piece. When the microwave generated by the microwave generator is irradiated onto the catalyst carrier, the microwave absorber absorbs the microwave and generates heat.
The microwave absorber may be covered with a protective film. The protective film may be a silica film.
You may provide the at least 1 temperature sensor for measuring the temperature of waste gas, and the microwave interruption | blocking means for interrupting | blocking the said microwave with respect to the said at least 1 temperature sensor.

  According to the present invention, when the microwave generated by the microwave generator is irradiated onto the catalyst carrier, the microwave absorber provided on the outer periphery of the honeycomb piece absorbs the microwave and generates heat. The catalyst temperature can be raised without affecting the catalyst.

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 and a columnar catalyst carrier 12 provided in the converter case 11. A magnetron 16 that is a microwave generator is connected to the SCR catalyst 5 through a hole 15 partially provided in the converter case 11. A pair of metal meshes 17a and 17b are provided at both ends of the converter case 11 as microwave blocking means. Exhaust gas flows from left to right in the figure. A temperature sensor 13a for measuring the exhaust gas temperature is provided upstream of the upstream metal mesh 17a. Further, a temperature sensor 13b for measuring the exhaust gas temperature after passing through the catalyst carrier 12 is provided downstream of the downstream metal mesh 17b. 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 composed of a plurality of rectangular parallelepiped honeycomb pieces 20 made of silicon carbide (SiC). A plurality of holes 21 are provided in the honeycomb piece 20 so as to penetrate the honeycomb piece 20 in the axial direction of the honeycomb piece 20. A selective reduction catalyst 22 is carried on the inner peripheral surface 21 a of the hole 21.

As shown in FIG. 4, plate-like microwave absorbers 23 made of carbon are provided on each of the four outer peripheral surfaces 20 a of the honeycomb pieces 20. The microwave absorber 23 is covered with a protective film 24 made of silica (SiO ₂ ) formed by curing polysilazane after coating. The honeycomb pieces 20 covered with the protective film 24 are bonded to each other with an adhesive, whereby the columnar catalyst carrier 12 is formed.

2 to 4 show the structure of the SCR catalyst 5 in detail, but the oxidation catalysts 3 and 6 have the same structure and are supported on the inner peripheral surface 21a of the hole 21 of the honeycomb piece 20 in the SCR catalyst 5. The selected selective reduction catalyst 22 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, the operation of the exhaust gas purification apparatus according to this embodiment will be described.
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 temperature does not rise to the temperature required to exhibit 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 enters the converter case 11 through the hole 15 and is irradiated to the catalyst carrier 12. At this time, the microwave is blocked by the pair of metal meshes 17a and 17b, thereby preventing the exhaust pipe 2 from spreading to the upstream side of the metal mesh 17a and the downstream side of the metal mesh 17b. As a result, the microwave is blocked with respect to the temperature sensors 13a and 13b.

  When the catalyst carrier 12 is irradiated with microwaves, the microwave absorber 23 provided on the outer peripheral surface 20a of the honeycomb piece 20 constituting the catalyst carrier 12 absorbs the microwaves and generates heat. Due to the heat generated by the microwave absorber 23, the honeycomb piece 20 is heated, and the selective reduction catalyst 22 supported on the inner peripheral surface 21 a of the hole 21 of the honeycomb piece 20 is heated.

When the temperature 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 23 is not generated, the microwave absorber 23 does not generate heat. Thereafter, the ECU 14 starts and stops the magnetron 16 based on the measured values of the temperature sensors 13a and 13b, whereby the selective reduction catalyst 22 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.

As described above, when the microwave generated by the magnetron 16 is irradiated onto the catalyst carrier 12, the microwave absorber 23 provided on the outer peripheral surface 20a of the honeycomb piece 20 absorbs the microwave and generates heat. The temperature of the selective reduction catalyst 22 can be raised without affecting the catalyst performance of the catalyst 22. The same applies to the oxidation catalysts 3 and 6.
Further, since the microwave absorber 23 is made of carbon, it will not oxidize when directly contacted with high-temperature exhaust gas, but it can be prevented because it is covered with the protective film 24 made of silica. . Since silica transmits microwaves, the microwave absorption by the microwave absorber 23 is not hindered.
Moreover, since the microwave absorber 23 is provided on the outer peripheral surface 20a of each honeycomb piece 20, the catalyst carrier 12 can be heated uniformly.

  In this embodiment, a plate-like member made of carbon is used as the microwave absorber 23, but the present invention is not limited to this form. It may be a carbon powder or a small piece of any shape. Also, the material is not limited to carbon, and any material that can absorb microwaves may be used, such as carbon fiber, graphite, SiC, or the like.

  In this embodiment, polysilazane-derived silica is used as the material of the protective film 24, but the present invention is not limited to this. Any material may be used as long as it is capable of transmitting microwaves and can protect the microwave absorber from exhaust gas. For example, any ceramic material such as alumina may be used.

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.
Also, the number of temperature sensors is not limited to two. At least one temperature sensor is provided on the upstream side of the metal mesh 17a or the downstream side of the metal mesh 17b, and based on the measured value of the temperature sensor. The operation of the magnetron 16 may be adjusted.

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.
In this embodiment, the microwave absorber 23 is provided on the entire outer peripheral surface 20a of each honeycomb piece 20. However, for example, the microwave absorber 23 may be provided on one of the outer peripheral surfaces 20a bonded to each other. .

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 the elements on larger scale of the catalyst support | carrier 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

  12 catalyst carrier, 13a, 13b temperature sensor, 16 magnetron (microwave generator), 17a, 17b metal mesh (microwave blocking means), 20 honeycomb piece, 20a (honeycomb piece) outer peripheral surface (honeycomb piece outer periphery), 21 pores, 22 selective reduction catalyst (catalyst), 23 microwave absorber, 24 protective film.

Claims (4)

A catalyst carrier comprising a plurality of honeycomb pieces each having a plurality of holes therein and supporting a catalyst on the inner surface of the holes;
A microwave generator for generating microwaves to irradiate the catalyst carrier,
An exhaust gas purification apparatus in which a microwave absorber made of a material capable of absorbing the microwave is provided on an outer periphery of the honeycomb piece.   The exhaust gas purification apparatus according to claim 1, wherein the microwave absorber is covered with a protective film.   The exhaust gas purification apparatus according to claim 2, wherein the protective film is a silica film. At least one temperature sensor for measuring the temperature of the exhaust gas;
The exhaust gas purification apparatus according to any one of claims 1 to 3, further comprising: a microwave blocking unit configured to block the microwave with respect to the at least one temperature sensor.

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