JP2004190528A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To collect a particulate matter PM; and to efficiently and precisely oxidize/reduce nitrogen oxides NOx by catalytic reaction and discharge. <P>SOLUTION: This exhaust emission control device is composed of a high voltage generator 4 for generating high voltage, a discharge electrode 3 connected to the high voltage generator 4 and impressing the high voltage, a honeycomb 7 connected to the discharge electrode, capable of discharging on the inside and discharging and collecting the particulate matter included in exhaust gas flowing on the inside and a conductive layer 9 for covering the outer periphery of the honeycomb 7 and set to grounding and/or constant voltage, and efficiently and precisely purifies NOx, and burns the PM by adding pulse streamer discharge 10 even when purification by a catalyst is difficult by a low temperature. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention captures particulate matter mainly composed of carbon (hereinafter referred to as PM) contained in exhaust gas of a diesel engine or the like, and oxidizes and reduces nitrogen oxides (hereinafter referred to as NOx) by catalytic reaction and discharge. The present invention relates to an exhaust gas purification device capable of being used.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, exhaust gas from a diesel engine contains PM made of carbon, SOF (Soluble Organic Fraction), a high molecular weight organic compound, sulfuric acid mist, and the like, and the suppression of PM emission has been strengthened from the viewpoint of environmental improvement.
[0003]
Conventionally, a charge type diesel particulate filter device combining a charging device and a filter has been proposed to suppress the emission of PM (Japanese Patent Application Laid-Open No. 2001-41024).
Further, a diesel particulate filter system has been proposed in which a conductive diesel particulate filter is used and charged and collected between the conductive filters (Japanese Patent Application Laid-Open No. 2001-20721).
[0004]
[Problems to be solved by the invention]
That is, since the former charge-type diesel particulate filter device uses an electric heater to regenerate the trapping part, it is necessary to heat the entire trapping part in addition to the PM to be burned, which requires a large amount of energy. . For this reason, the former charge type diesel particulate filter device has a large fuel consumption loss and has a problem to be solved practically.
[0005]
Further, in the latter diesel particulate filter system, the regeneration of the trapping section is controlled based on a rise in the exhaust gas temperature of the internal combustion engine. For this reason, the latter diesel particulate filter system needs to heat the entire collection unit, requires a large amount of energy, and has a problem to be solved in practice.
[0006]
In any of these prior arts, since no catalyst is supported on the trapping portion, PM combustion at a low temperature cannot be realized, and a large amount of energy is required from this viewpoint. Further, even when a Pt-based oxidation catalyst is carried in these conventional techniques, PM does not burn unless the temperature is higher than 500 ° C.
[0007]
[Patent Document 1]
JP, 2001-41024, A [0003]
[0008]
[Patent Document 2]
JP-A-2001-20721 [0003]
[0009]
The present invention has been devised to solve the above problems. That is, an object of the present invention is to collect particulate matter mainly composed of carbon (hereinafter referred to as PM) contained in exhaust gas of a diesel engine or the like, and to convert nitrogen oxides (hereinafter referred to as NOx) by a catalytic reaction and discharge. It is an object of the present invention to provide an exhaust gas purification device that can be oxidized and reduced and that can efficiently and accurately recover a trapping device.
[0010]
[Means for Solving the Problems]
The exhaust gas purifying apparatus according to claim 1 includes a high voltage generator for generating a high voltage, a discharge electrode connected to the high voltage generator and applying a high voltage, and a discharge electrode connected to the discharge electrode to enable discharge inside. A collection device consisting of a porous member that charges and collects particulate matter contained in exhaust gas flowing through the device, and a conductive layer that covers the outer periphery of the collection device and is grounded and / or set to a constant voltage. It is characterized by comprising.
[0011]
An exhaust gas purifying apparatus according to a second aspect is characterized in that a catalyst for purifying particulate matter and / or nitrogen oxides is carried on the trapping device.
[0012]
[Action and Effect of the Invention]
The exhaust gas purification apparatus of the present invention having the above-described structure improves the purification rate of PM and NOx contained in exhaust gas, and applies discharge even when purification by a catalyst is difficult at low temperatures or the like, thereby purifying NOx or the like. The effect and effect of efficiently and accurately realizing the combustion of the steel are achieved.
[0013]
[Action: Reason for effect]
Specifically, the exhaust gas purifying apparatus of the present invention having the above configuration can suppress discharge that easily occurs in the gap by covering the outer periphery of the collecting apparatus with the conductive layer without any gap. Plasma can be accurately generated inside the constituting porous member. Therefore, NO in the exhaust gas can be oxidized to NO ₂ , and O ₂ can be radicalized to efficiently purify PM. In addition, NOx can be efficiently purified by radicalization of N ₂ or activation of the reducing agent by partial oxidation. By using a pulse of several hundred nsec or less by a high voltage generator, high voltage can be stopped before arc discharge, and plasma is generated by applying high voltage from low temperature to high temperature at which arc discharge easily occurs. Can be. Further, even when a DC high voltage (DC) is applied by the high voltage generator, the PM can be burned by discharging and energizing.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
As shown in FIG. 1 and FIG. 5, an exhaust purification device according to an embodiment of the present invention is configured such that a discharge electrode 3 of a trapping treatment device 2 provided in an exhaust pipe 1 of a diesel engine E includes a high-voltage generation device 4. Are connected with good conductivity. The discharge electrode 3 is formed of a rod-shaped conductor, and has an open end disposed in parallel with the flow direction of the exhaust gas. The discharge electrode 3 has a support end fixed to the collection processing device 2 by an insulator 5, and is configured so that an axial direction is orthogonal to a flow of exhaust gas. The discharge electrode 3 is connected to the negative electrode side of the pulse high voltage power supply 6 of the high voltage generator 4. Since the discharge electrode 3 is connected by the insulator 5, the discharge electrode 3 is configured to be insulated from the case of the collection processing device 2.
[0015]
On the outer periphery of the discharge electrode 3, a honeycomb 7, which is a porous member of the collecting device, is arranged in parallel with the flow direction of the exhaust gas so that the exhaust gas can flow around the discharge electrode 3. When a high pulse voltage is applied to the discharge electrode 3 inside the honeycomb 7, a pulse streamer discharge 10 is generated in a direction orthogonal to the flow of exhaust gas, as shown in FIGS. Have been. A catalyst is supported on the honeycomb 7. The outer periphery of the honeycomb 7 is covered with a conductive layer 9 having a cushioning property, which is responsible for grounding, with good airtightness.
[0016]
As shown in FIGS. 1 and 2, when the pulse high voltage is applied to the discharge electrode 3, the pulse streamer discharge 10 penetrates the honeycomb 7 in the exhaust gas purification apparatus according to the embodiment of the present invention having the above configuration. Generated. The phenomenon caused by this pulse streamer is as shown in FIG. When the exhaust gas from the diesel engine enters the exhaust gas purification apparatus according to the embodiment of the present invention, the pulse streamer discharge 10 generates O ₃ , radicalizes O, and radicalizes N. In addition, the PM is charged and easily adheres to the honeycomb 7. Then, by the generation of O ₃ , the radicalization of O, and the radicalization of N, the reaction proceeds as shown in FIG. 3 showing the PM oxidation and NOx reduction reaction mechanism.
[0017]
The charged and adhered PM burns due to the oxidizing action of O ₃ . NOx is decomposed by N radicals. Further, a part of NO is oxidized by O radicals to become NO ₂ , and NO ₂ oxidizes PM. Through a series of these reactions, PM is oxidized and disappears, and NOx is reduced. In addition, the conductive layer 9 disposed on the outer periphery of the honeycomb 7 plays an important role in generating the pulse streamer discharge 10 that causes these oxidation and reduction reactions.
[0018]
Here, FIG. 4 shows a phenomenon that occurs when the conductive layer is not provided. That is, when the honeycomb 7 is held in the case of the collection processing device 2, the honeycomb 7 and the case are held using the insulating holding material 11. In this case, a gap is formed between the honeycomb 7 and the holding member 11, and between the holding member 11 and the case. When a high pulse voltage is applied in a state where the gap is formed, no discharge occurs in the honeycomb 7 and a partial discharge occurs in the gap with the insulating holding material 11. This is because the presence of the air layer makes it easier for the outer air layer to discharge than the inside of the honeycomb 7. As a result, the pulse streamer discharge 10 does not occur in the honeycomb 7, and the reactions shown in FIGS. 2 and 3 do not occur. For this reason, the apparatus shown in FIG. 4 cannot purify PM and NOx.
[0019]
On the other hand, in the exhaust gas purifying apparatus according to the embodiment of the present invention, by providing the conductive layer 9 with good airtightness on the outer periphery of the honeycomb 7 so as not to form an air layer, the pulse streamer discharge 10 can be reliably generated in the honeycomb 7. And PM and NOx can be purified accurately. Here, according to the diagram for comparing the purification rates of PM in FIG. 6, in the exhaust gas purification apparatus according to the embodiment of the present invention, the pulse streamer discharge 10 efficiently and accurately purifies PM. In the device shown in FIG. 4, the PM cannot be purified because the pulse streamer discharge does not occur.
[0020]
[Other embodiments]
As shown in FIG. 7, an exhaust gas purification apparatus according to another embodiment of the present invention is different from the above embodiment in that a filter (DPF) 17 is provided instead of the honeycomb 7, and the other parts are the same. The same portions are denoted by the same reference numerals and description thereof will be omitted. The exhaust gas purification apparatus according to another embodiment of the present invention can efficiently collect PM by providing the filter (DPF) 17, and performs a reaction shown in FIG. 3 on PM that has sufficiently accumulated. And the purification efficiency can be further improved.
[0021]
Further, as shown in FIG. 8, the exhaust gas purification apparatus according to another embodiment of the present invention is different from the above embodiment in that a conductive coat 18 made of a conductive member is provided on the outer periphery of the honeycomb 7 and the cushioning property is further maintained on the outer periphery. The difference is that the member 19 is mounted on the winding case 20, and the other parts are the same. In the exhaust gas purification apparatus according to another embodiment of the present invention, the conductive layer 9 and the case 20 are grounded by the grounding spring 21. In the exhaust gas purifying apparatus according to another embodiment of the present invention, the provision of the cushioning holding member 19 can prevent the catalyst-equipped honeycomb 7 from being damaged due to vibration and the like. The occurrence of the partial discharge can be prevented.
[0022]
Further, as shown in FIG. 9, the exhaust gas purifying apparatus according to another embodiment of the present invention is different from the above embodiment in that a ceramic foamed foam 22 is provided instead of the honeycomb 7, and the other is the same. Therefore, the same portions are denoted by the same reference numerals and description thereof will be omitted. In an exhaust gas purifying apparatus according to another embodiment of the present invention, a Pt-based catalyst is carried on a foamed foam 22, a conductive layer 9 is applied to an outer periphery thereof, and a case 23 is grounded. The high voltage generator 24 generates a DC high voltage. This voltage may be + or-, but-is more preferable. The DC high voltage generated by the high voltage generator 24 is maintained insulated from the case 23 by the insulator 5 and guided to the center of the foam 22 by the discharge electrode 3.
[0023]
When the exhaust gas is introduced from the exhaust pipe 1 according to another embodiment of the present invention having the above-described configuration, the exhaust gas purification apparatus performs a corona discharge from the discharge electrode 3 to which a high DC voltage is applied from the high voltage generator 24. , PM are charged and electrostatically collected by the foam 22. When the temperature of the foamed foam 22 measured by the thermometer 25 is higher than a certain temperature, the trapped PM is oxidized by the action of the supported catalyst. However, if the temperature of the foam 22 is not high enough, PM will be deposited in the foam 22.
[0024]
When the value of the differential pressure gauge 26 exceeds a certain value, it is determined that PM in the foamed foam 22 has accumulated, and the voltage of the DC high voltage is increased. As a result, a pulse streamer discharge is generated in the foamed foam 22, and the deposited PM is oxidized through the reaction shown in FIG. Also in this case, since the conductive layer 9 is applied to the outer periphery of the foamed foam 22, a pulse streamer discharge occurs in the foamed foam 22 and PM can be oxidized efficiently. Similarly, NOx can be removed. The control algorithm at this time is as shown in FIG.
[0025]
The exhaust gas purification device of the present invention is not limited to the diesel engine in the above embodiment, but may be a gasoline engine that performs lean combustion. The present invention can be applied to various kinds of apparatuses such as a purifying apparatus.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an exhaust gas purification device according to an embodiment of the present invention.
FIG. 2 is a diagram showing a state where PM discharged by a discharge electrode according to an embodiment of the present invention is collected.
FIG. 3 is a diagram showing a PM oxidation and NOx reduction reaction mechanism of the exhaust gas purification apparatus according to the embodiment of the present invention.
FIG. 4 is a schematic diagram showing a conventional exhaust gas purification device.
FIG. 5 is a schematic diagram showing an arrangement state of an exhaust gas purification device in an embodiment of the present invention.
FIG. 6 is a diagram showing a comparison state of a PM purification rate between an exhaust gas purification apparatus according to an embodiment of the present invention and a conventional exhaust gas purification apparatus.
FIG. 7 is a schematic diagram showing an exhaust gas purification device according to another embodiment of the present invention.
FIG. 8 is a schematic diagram showing an exhaust gas purification device according to another embodiment of the present invention.
FIG. 9 is a schematic diagram showing an exhaust gas purification device according to another embodiment of the present invention.
FIG. 10 is a schematic diagram showing a control algorithm of the exhaust gas purification device shown in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Exhaust pipe 2 ... Collection processing device 3 ... Discharge electrode 4 ... High voltage generator 5 ... Insulator 6 ... Pulse high voltage 7 ... Honeycomb 9 ... Conductive layer 10 ... Pulse streamer discharge

Claims (2)

A high voltage generator for generating a high voltage,
A discharge electrode connected to a high-voltage generator and applying a high voltage;
A collection device comprising a porous member that is connected to the discharge electrode and discharges the inside and charges and collects particulate matter contained in exhaust gas flowing through the inside,
An exhaust gas purification device comprising: a conductive layer that covers an outer periphery of a trapping device and is grounded and / or set to a constant voltage. An exhaust gas purification device, wherein a catalyst for purifying particulate matter and / or nitrogen oxides is carried on the collection device.

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