JP4329466B2 - Exhaust purification equipment - Google Patents

Description

  The present invention relates to a purification device for exhaust gas from an internal combustion engine or the like, and more particularly to an exhaust gas purification device for removing particulate matter (particulate: hereinafter referred to as “PM”) discharged from a diesel engine. .

  Diesel engines are often installed in automobiles, particularly large vehicles. Recently, it has been strongly desired to reduce PM emissions together with nitrogen oxides, carbon monoxide, hydrocarbons, and the like in the exhaust gas in recent years. Therefore, it is desired to establish a technique for efficiently removing PM in the exhaust gas as well as technical development for fundamentally reducing PM by improving the engine or optimizing combustion conditions.

  Generally, a ceramic honeycomb filter, an alloy filter, and a ceramic fiber filter are used for removing PM in the exhaust gas. However, with these methods, as the usage time elapses, the trapped particulate matter causes the filter to become clogged, increasing the airflow resistance, resulting in a burden on the engine. In addition, the nano-sized PM has a high probability that it will not be collected by escaping the physical collision collection in the base material communication hole. Further, even when PM is collected by a conventional filter, sufficient oxidation removal of PM cannot be expected by the action of exhaust heat alone.

  As an exhaust gas purification device for a diesel engine, a device using discharge is known. For example, as shown in Patent Document 1, a collection electrode is provided that surrounds a needle electrode and a deflection electrode, and PM in the diesel engine exhaust is charged by discharge between the electrodes, and the PM is collected on the collection electrode. There has been proposed an exhaust emission control device. However, this device only collects PM, and is not a device that actively burns and removes PM, but requires a separate treatment of the collected PM. I can't expect. Moreover, even if a catalyst having an exhaust purification activity is coated on the surface of the metal honeycomb, it tends to peel off.

  As an exhaust purification device using discharge, the one shown in FIG. 3 can be considered. FIG. 3A is a perspective view of the exhaust purification device 30, and FIG. 3B is a cross-sectional view of the exhaust purification device 30. In FIG. 3, the exhaust purification device 30 is disposed on the insulating honeycomb structure 32, the outer peripheral electrode 36 such as a mesh electrode disposed on the outer periphery of the insulating honeycomb structure 32, and the central axis of the honeycomb structure. A rod-shaped electrode 34 is provided, and a voltage is applied between the electrodes 34 and 36 by the power source 18.

  According to the exhaust gas purification apparatus of FIG. 3, PM in the exhaust gas flow is deposited on the honeycomb structure by the electric field between the outer peripheral electrode 36 and the rod-shaped electrode 34, and the discharge plasma generated between these electrodes and the honeycomb structure The catalyst on the body can promote the combustion removal of the deposited PM.

  However, in this exhaust purification device 30, since a high electric field can be generated only in the vicinity of the rod-shaped electrode 34, the PM collection efficiency is reduced on the outer peripheral side of the honeycomb structure, and the exhaust purification capability is also reduced.

Japanese Patent No. 2698804

  That is, a conventionally known exhaust purification device using discharge is not necessarily sufficient for PM collection and combustion removal. Therefore, it is necessary to increase the combustion removal efficiency and collection efficiency of PM in the exhaust discharged from a diesel engine or the like.

Exhaust purification system of the present invention includes a conductive honeycomb electrode and the counter electrode, the conductive honeycomb electrode, a ceramic honeycomb substrate der having a coating of conductive material is, counter electrode, a conductive honeycomb electrode The counter electrode has a plurality of acicular electrode portions, and the acicular electrode portions are disposed in each cell of the conductive honeycomb electrode .

  According to the exhaust emission control device of the present invention, since the honeycomb itself through which the exhaust gas circulates functions as an electrode, deposition of charged PM on the conductive honeycomb electrode can be promoted by Coulomb force. Further, since the ceramic honeycomb substrate is porous, the coating is hardly peeled off.

Further , according to the exhaust emission control device of the present invention, the counter electrode is disposed on the upstream side of the exhaust flow of the conductive honeycomb electrode , whereby PM can be charged before reaching the conductive honeycomb electrode. It is possible to promote the collection of PM by the Coulomb force at the conductive honeycomb electrode.

Furthermore, according to the exhaust gas purifying apparatus of the present invention, the counter electrode has a plurality of needle-like electrode portion, and the needle-like electrode portion is disposed within each cell of the conductive honeycomb electrode, whereby acicular Since the distance between the electrode portion and the cell wall of the conductive honeycomb electrode acting as an electrode is close and a strong electric field can be obtained, purification of exhaust components, and collection and combustion removal of PM can be improved.

  In one aspect of the exhaust purification device of the present invention, the coating of the conductive material is a porous coating. According to this, the surface area which can be utilized for accumulation and purification of PM in the exhaust gas can be increased.

  In one aspect of the exhaust emission control device of the present invention, the conductive material has catalytic activity. According to this, combustion removal of the collected PM can be promoted by the catalytic activity of the conductive material coating itself.

  In one aspect of the exhaust emission control device of the present invention, the conductive material is ceramic. According to this, since both the coating and the base material are ceramic, peeling of the coating due to a difference in thermal expansion coefficient can be suppressed.

In one aspect of the exhaust emission control device of the present invention, the conductive material is Fe ₂ O ₃ . According to this, collection of PM and combustion removal of the collected PM can be promoted by the conductivity and catalytic activity of Fe ₂ O ₃ .

  In one aspect of the exhaust emission control device of the present invention, the conductive material is a metal. According to this, the conductivity of the conductive honeycomb electrode can be ensured.

  According to the exhaust emission control device of the present invention, it is possible to improve the combustion removal efficiency and collection efficiency of PM in exhaust gas discharged from a diesel engine or the like.

Hereinafter, the present invention will be specifically described based on the embodiment shown in FIG. 2 , but FIG. 2 is a diagram showing an example of an exhaust emission control device constituting the present invention, and the present invention is limited to this embodiment. It is not something.

An exhaust gas purification apparatus of a reference example will be described with reference to FIG. Here, FIG. 1 (a) is a side view of the exhaust gas purifying apparatus of the reference example, FIG. 1 (b) is a cross-sectional view of the exhaust gas purifying apparatus of this embodiment.

The exhaust emission control device 10 of the reference example includes a conductive honeycomb electrode 12 that is grounded, and a mesh-like counter electrode 14 that is electrically connected to a power source 18. An arrow 19 indicates the direction in which the exhaust gas containing PM flows.

In the use of the exhaust purification apparatus of the reference example shown in FIG. 1, an electric field is created between the conductive honeycomb electrode 12 and the mesh counter electrode 14 by applying a power source 18. The PM contained in the exhaust flow is charged between the mesh electrode 14 and the conductive honeycomb electrode 12, thereby promoting the deposition of PM on the conductive honeycomb electrode 12 by Coulomb force.

For implementation of the invention will be described with reference to FIG. Here, FIG. 2 (a) is a side view of the implementation of the invention, a cross-sectional view of the implementation form shown in FIG. 2 (b) Yoko.

Exhaust purification apparatus 20 of the implementation form of the present invention includes an electrically conductive honeycomb electrode 12 which is grounded, the counter electrode 24 that is electrically connected to a power source 18. The counter electrode 24 includes a mesh electrode portion 23 and a plurality of needle electrode portions 25 that are electrically connected to the mesh electrode portion 23 and extend into each cell of the conductive honeycomb electrode 12. Has been. An arrow 19 indicates the direction of the exhaust flow containing PM.

  In the use of the exhaust emission control device 20 shown in FIG. 2, an electric field is created between the conductive honeycomb electrode 12 and the counter electrode 24 by applying the power source 18. The PM contained in the exhaust flow is charged between the mesh electrode 23 and the conductive honeycomb electrode 12, thereby promoting the deposition of PM on the conductive honeycomb electrode 12 by Coulomb force. In addition, since the cell wall of each cell of the conductive ceramic electrode 12 and the needle electrode portion 25 in the cell of the conductive honeycomb electrode 12 are close to each other, a strong electric field is generated between these electrodes 12 and 25. It is made. This strong electric field promotes PM deposition.

Incidentally, in any of the reference examples and the implementation form of the exhaust gas purifying device 10 and 20 of the present invention also has conductive honeycomb electrode 12 is grounded, but counter electrode 14 or 24 is connected to a power supply 18, which Can be reversed or each electrode can be electrically connected to the opposite pole of the power supply 18. However, grounding the conductive honeycomb electrode is preferable in order to suppress erroneous discharge between the conductive honeycomb electrode and the case holding the conductive honeycomb electrode. The conductive honeycomb electrode can also have a conductor such as the outer peripheral electrode 36 of FIG. 3 in order to ensure electrical contact.

Also, although the coating of conductive material can itself have exhaust purification catalytic activity, an additional catalyst having exhaust purification activity can also be supported on the conductive material coating. Examples of the additional catalyst include catalysts having catalytic activity for PM combustion removal, such as CeO ₂ , Fe / CeO ₂ , Pt / CeO ₂ , and Pt / Al ₂ O ₃ .

When discharging between the electrodes of the exhaust emission control device of the present invention, not only the charging of PM for collecting PM on the conductive honeycomb electrode is promoted, but also active oxygen and ozone generated in the exhaust component by the discharge. Combustion of PM in the collected exhaust gas can be promoted by the action of gas components having strong oxidizing power such as NO _x , oxygen radicals, and NO _x radicals. Moreover, plasma can be generated by a high voltage to promote PM collection and combustion.

  Below, each part which comprises the exhaust gas purification apparatus of this invention is demonstrated more concretely.

  The ceramic honeycomb substrate coated with a conductive material and constituting the conductive honeycomb electrode of the present invention may be, for example, a cordierite honeycomb structure. The ceramic honeycomb substrate may be a straight flow type or a wall flow type, but from the viewpoint of ventilation resistance, a straight flow type is preferable, and a straight flow type ceramic honeycomb substrate may be used. Collection efficiency can be achieved.

The coating of the conductive material on the ceramic honeycomb substrate can be performed by any method. For example, a ceramic coating on a ceramic honeycomb substrate is obtained by a general washcoat method, i.e. providing a ceramic material fine powder of the desired composition, coating the substrate with a slurry containing this ceramic material fine powder, as well as This can be done by drying and sintering the coating. Examples of the conductive ceramic used in the present invention include SiC, iron group oxide, vanadium oxide, SnO _{2 and the} like. Fe ₂ O ₃ is preferable in that it also has catalytic activity. The thickness of the conductive ceramic coating may be a typical thickness for a normal catalyst support layer, for example, 1000 μm or less, particularly 500 μm or less, but is determined so as to obtain a coating having a desired conductivity and / or durability. You can also

  The metal coating on the ceramic honeycomb substrate can be performed by sintering metal powder, dipping in molten metal, electroless plating, or the like. Examples of the metal used in the present invention include Cu, W, stainless steel, Fe, Pt, and Al. The metal coating thickness can be, for example, 1000 μm or less, in particular 500 μm or less, but can also be determined so as to obtain a coating having the desired conductivity and / or durability.

  The counter electrode can be manufactured from a material capable of applying a voltage between the counter electrode and the conductive honeycomb electrode. As the material, a conductive material or a material such as a semiconductor can be used, and a metal material is particularly preferable. Specifically, Cu, W, stainless steel, Fe, Pt, Al or the like can be used as this metal material, and stainless steel is particularly preferable from the viewpoint of cost and durability.

  The counter electrode that can be used in the present invention is generally a mesh electrode that circulates exhaust gas upstream of the conductive honeycomb electrode, particularly a metal mesh electrode. The shape is not particularly limited as long as a voltage can be applied.

  The acicular electrode portion that the counter electrode can have may be included in all the cells of the conductive honeycomb electrode, or may be included in some cells, for example, alternately in every other cell. . Further, the needle-like electrode portion may enter the entire cell length of the conductive honeycomb electrode, or may enter only partway.

  The outer peripheral electrode that can be used to ensure electrical connection to the ground or power source of the conductive honeycomb electrode may be similar to the outer peripheral electrode 36 of FIG. This outer peripheral electrode can be made by wrapping the same material as shown for the counter electrode around the conductive honeycomb electrode as a metal mesh or metal foil, and by applying a conductive paste to the conductive honeycomb electrode. Can do.

  The power source may generate a pulsed or steady DC or AC voltage. As the applied voltage and the pulse period, general values for generating plasma can be used. For example, a pulse voltage of 50 kV and a pulse period of 2,000 Hz can be used.

  In order to cause a discharge between the counter electrode and the conductive honeycomb electrode, a DC voltage, an AC voltage, a periodic waveform voltage, or the like can be applied between both electrodes. It is preferable because discharge can be caused satisfactorily. When a DC pulse voltage is used, the applied voltage, pulse width, and pulse period can be arbitrarily selected as long as corona discharge can occur between both electrodes. The voltage of the applied voltage may be subject to certain restrictions from the design of the device and economy, but a high voltage and a short pulse period voltage are desirable from the viewpoint of generating corona discharge satisfactorily. .

FIG. 1 is a perspective view and a cross-sectional view showing an exhaust purification apparatus of a reference example . Figure 2 is a perspective view and a sectional view representing the exhaust gas purifying apparatus for an actual embodiments with the present invention. FIG. 3 is a perspective view and a cross-sectional view showing a conventional exhaust purification device to be considered.

Explanation of symbols

10: Exhaust gas purification device of reference example
2 0 ... exhaust purification device 12 ... conductive honeycomb electrodes 14 and 24 ... counter electrode 18 ... power supply 19 ... exhaust gas flow direction 23 ... meshed electrode portions 25 ... needle electrode portion 32 ... insulating honeycomb support 34 ... rod-like of the present invention Electrode 36 ... outer peripheral electrode

Claims (6)

An exhaust purification device having a conductive honeycomb electrode and a counter electrode ,
Before Kishirube conductive honeycomb electrode, Ri ceramic honeycomb substrate der having a coating of electrically conductive material,
The counter electrode is disposed upstream of the exhaust flow of the conductive honeycomb electrode; and
The counter electrode has a plurality of needle-like electrode portions, and the needle-like electrode portions are disposed in each cell of the conductive honeycomb electrode.
Exhaust purification device. The exhaust emission control device according to claim 1 , wherein the conductive material has catalytic activity. The exhaust emission control device according to claim 1 or 2 , wherein the conductive material coating is a porous coating. The exhaust emission control device according to any one of claims 1 to 3 , wherein the conductive material is ceramic. The exhaust emission control device according to claim 4 , wherein the conductive material is Fe ₂ O ₃ . The exhaust emission control device according to any one of claims 1 to 3 , wherein the conductive material is a metal.

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