JPH06146852A - Diesel engine exhaust gas purifying device - Google Patents

Abstract

PURPOSE:To improve purifying efficiency for exhaust gas while preventing increase of pressure loss caused by adhesion of soot and lowering of engine efficiency by applying oxidation decomposition to soot stuck on the filter element of a collective ceramic filter by plasma treatment. CONSTITUTION:A casing 5 having the inlet 3 of exhaust gas and the outlet 4 of purifying gas is connected to the exhaust duct 2 of a diesel engine. A ceramic filter 6 is arranged inside the casing 5, and also plasma treatment electrodes 8, 9 are arranged respectively in vertical direction in a filter element 7. Discharge interposed the filter element 7 as dielectric is generated by applying a high frequency voltage and the like from A.C. power supply between each plasma treatment electrode 8, 9. And plasma and radical which is rich to reaction of oxidizing performance and reducing performance are generated in association with discharging so as to discharge soot stuck on the filter element 7 as CO2 or CO.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention efficiently collects soot contained in combustion exhaust gas, particularly exhaust gas from a diesel engine using a ceramic filter, and at the same time collects soot at a low temperature by a discharge plasma. By oxidizing and gasifying, the clogging of the ceramic filter is prevented, the increase in pressure loss of the filter caused by soot is prevented, and the gas such as NOx in the exhaust gas due to the action of radicals generated by the plasma. The present invention also relates to a device for preventing air pollution by oxidizing and reducing pollutants as well.

[0002]

2. Description of the Related Art Conventionally, when soot in exhaust gas of a diesel engine is collected using a ceramic filter, the collected soot causes the filter to be clogged, and the pressure loss of the filter is significantly increased in a short time. The efficiency will decrease.

Therefore, a burner is placed on the upstream side of the ceramic filter, or a heater is placed in the ceramic filter itself so that the collected soot is gasified by combustion to prevent clogging.

However, in this case, it is difficult to combust evenly, and more gas is introduced into the first combusted portion due to the reduction in ventilation resistance, the amount of oxygen supplied is increased, the combustion speed is increased, and more and more gas is increased. Will flow in. As a result, excessive combustion heat is generated in that part, an abnormal rise in temperature occurs, the ceramic filter wears,
It had shortened its life significantly.

In addition, a method using a catalyst is used to remove NOx which is another problem of the exhaust gas of a diesel engine.

However, a highly efficient and long-life NOx removal catalyst for a diesel engine exhaust containing soot has not yet been completed, and when the above-mentioned ceramic filter for collecting soot and the catalyst are used in duplicate, the pressure on the exhaust side is increased. The losses are increasing and the loss of engine efficiency is inevitable.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to prevent the clogging of a soot trapping ceramic filter without overheating or damage by uniformly oxidizing the soot trapped in the ceramic filter at a low temperature. It is to be.

Yet another object is to simultaneously remove gaseous pollutants, especially NOx, in the exhaust gas.

[0009]

DISCLOSURE OF THE INVENTION A diesel engine exhaust gas purifying apparatus of the present invention is provided with a casing connected to an exhaust duct of a diesel engine and having an inlet for exhaust gas containing soot and an outlet for clean gas. A ceramic filter is provided so as to block the gas flow inside, and two sets of plasma processing electrodes, each of which is composed of at least one electrode element having a structure that does not impede the gas flow, are mutually insulated by sandwiching the filter element of the ceramic filter. An AC power supply is provided to connect both plasma processing electrodes and to apply an AC voltage between them, and an electric discharge is generated between both plasma processing electrodes via at least a part of the filter element. .

In this case, both of the plasma treatment electrodes are constructed by providing wire mesh or perforated plate electrode elements on the upstream and downstream sides of the electrodes in the vicinity of the ceramic filter.

If desired, the ceramic filter is composed of a large number of elongated gas passages having a honeycomb structure, and the upstream and downstream ends of the gas passages are alternately closed to communicate with the upstream gas passages. And a group of downstream gas passages communicating with the downstream side, and a partition wall between the two adjacent gas passages uses a honeycomb ceramic filter in which the filter element constitutes the filter element. The upstream electrode is composed of any one of electrode elements of a wire mesh or a perforated plate which is provided close to the upstream side of the closed end of the honeycomb ceramic filter, and the downstream electrode is the honeycomb ceramic filter. It is composed of a wire-shaped electrode element inserted from the downstream side into the downstream gas passage group.

Alternatively, in this case, of the two sets of plasma processing electrodes, the upstream processing electrode is provided with a wire-shaped electrode element on the upstream side of the honeycomb type ceramic filter, and the downstream end portion thereof is the upstream side. The processing electrode is located near the inlet of the side gas passage group, and the downstream processing electrode is configured by inserting a wire-like electrode element from the downstream side into the downstream gas passage group.

In this case, inserting / extracting means for inserting / extracting the wire-like electrode elements of the upstream electrode section into the gas passages from the inlets of the upstream gas passages, the tips of which face each other, if necessary. Is provided.

Alternatively, if necessary, the upstream processing electrode of the two sets of plasma processing electrodes is a wire-like electrode element inserted from the upstream side into the upstream gas passage group of the honeycomb ceramic filter. Further, the downstream processing electrode is composed of a wire-shaped electrode element inserted from the downstream side into the downstream gas passage group.

Alternatively, if necessary, both of the two sets of plasma processing electrodes are constructed by inserting wire-like electrode elements from the downstream side into the downstream side gas passage group, and both of the plasma processing electrodes are provided. The electrode elements to which they belong are opposed to each other via one upstream gas passage.

As the AC power supply, a high-frequency high-voltage power supply for generating a high-frequency high voltage having a peak value of output voltage of 3 kV or more and an output frequency of 5 kHz or more is used.

If desired, the AC power supply may have an output voltage peak value of 5 kV or more and an output frequency of 50 Hz.
The high-voltage pulse power supply that generates the pulsed high voltage described above is used.

[0018]

An AC voltage is continuously or intermittently applied between the two sets of plasma treatment electrodes to generate a discharge through the soot-attached filter element of the ceramic filter. The radicals generated by the plasma chemistry of this discharge gasify and remove soot by low-temperature oxidation.
Prevents soot from clogging the filter element. This keeps the pressure loss of the ceramic filter low at all times and prevents the efficiency of the diesel engine from decreasing.

By the action of the radicals, gaseous pollutants such as NOx contained in the exhaust gas are simultaneously oxidized or reduced to be removed, and the exhaust gas of the diesel engine is purified.

[0020]

1 is a longitudinal sectional view of a first embodiment showing the basic concept of the present invention. A ceramic filter 6 is arranged inside the casing 5 which connects the gas inlet 3 and the gas outlet 4 by interposing the exhaust duct 2 of the diesel engine so as to block the gas flow. However, this ceramic filter 6
Is a schematic view of a ceramic filter generally having any suitable shape and structure such as plate, pleats, honeycomb, and cylinder having a porous ceramic as a filter element.

An upstream plasma processing electrode 8 comprising an electrode element (for example, a wire mesh, a metal perforated plate, a metal blind, etc.) having a structure that allows gas to pass through on the upstream side and the downstream side of the filter element 7 of the ceramic filter 6. A downstream plasma processing electrode 9 is provided, and a high frequency high voltage or a high voltage pulse voltage is continuously or intermittently applied from an AC power source 10 between them.

As a result, a discharge is generated between the two plasma processing electrodes 8 and 9 with the filter element 7 interposed as a dielectric. This discharge is caused by the plasma processing electrodes 8, 9
In the gas space between the filter element 7 and the surface of the filter element 7, there is a silent discharge, and in the void inside the filter element 7, there is a form of void discharge, both of which have a low electron temperature but a low ion temperature (low temperature plasma). (Also called equilibrium plasma) to produce abundant radicals rich in oxidizing and reducing reactivity.

This radical causes the filter element 7 to
The soot adhering to the upstream surface and the internal voids of CO 2 is oxidized at a low temperature and discharged as CO 2 or CO, so that the filter element 7 of the ceramic filter 6 can be kept clean and the pressure loss can be kept low. At the same time, the radicals oxidize or reduce gaseous pollutants such as NOx in the exhaust gas and remove them.

FIG. 2 is a perspective view of the above-mentioned honeycomb type ceramic filter 11, and FIG. 3 is a longitudinal sectional view of the main part of Embodiment 12 in which the present invention is carried out by using the same. This filter has a honeycomb structure and has a large number of elongated gas passage groups 14 separated by porous ceramic partition walls 13.

These gas passage groups 14 are adjacent to each other at the upstream end and the downstream end thereof, and are alternately adjacent to each other.
5 and the downstream ceramic blocking portion 16,
Upstream gas passage group 1 communicating with the upstream side and having a closed downstream end
7 and a downstream side gas passage group 18 communicating with the downstream side and closed on the upstream side.

The exhaust gas is supplied to the upstream side gas passage group 17
Enters through the upstream opening 19, passes through the porous ceramic partition wall 13 constituting the filter element 7, enters the downstream gas passage group 18, and is discharged through the downstream opening 20. . The soot adheres to the upstream surface of the ceramic partition 13 and the internal voids.

Reference numeral 8 is an upstream plasma processing electrode having a wire net 21 as an electrode element, which is provided on the upstream side of the upstream ceramic blocking portion 14 in close proximity thereto. Reference numeral 9 denotes a downstream plasma processing electrode having a wire 22 inserted into the downstream gas passage group 18 from the downstream opening 20 to the back as an electrode element.

When a high frequency high voltage or a high voltage pulse voltage is continuously or intermittently applied from the AC power source 10 between the plasma processing electrodes 8 and 9, the upstream end 23 of the wire electrode element 22 and the wire mesh electrode. Silent discharge is generated between the element 22 through the upstream ceramic closing part 15 which is a dielectric and the upstream opening 19 of the ceramic partition wall 13, and the radicals generated thereby generate the radicals in the upstream opening. The soot advancing into each upstream gas passage group 17 from 19 and adhering to the upstream surface of the ceramic partition wall 13 and its internal gap is oxidized at low temperature and removed. Also, it removes gaseous pollutants such as NOx in the exhaust gas by oxidizing and reducing them.

FIG. 4 is a longitudinal sectional view of the main part of a twenty-fourth embodiment of the present invention, which is different from FIG. 3, in which the upstream plasma processing electrode 8 is composed of a wire electrode element 25 in this embodiment, and the downstream tip 26 thereof. It is located near the center of the opening of the upstream opening 19. The names and functions of the other elements 12 to 23 are the same as those of the elements with the same numbers in the twelfth embodiment of FIG.

When the AC voltage is applied between the electrodes 8 and 9 from the AC power source 10, silent discharge is generated between the upstream side tip portion 26 and the downstream side tip portion 23 to generate radicals and the upstream side opening. The soot oxidation first starts in the vicinity of the portion 19 and successively reaches the inside of the upstream gas passage 17. In order to assist its action, the wire electrode element of the plasma processing electrode 8 not shown in the figure is inserted into the inside of the upstream gas passage 17,
Further, there is an inserting / extracting means for extracting, and the upstream end portion 26 is successively advanced as the soot is oxidized and removed, and when the soot is removed, the soot is extracted to the original position.

As described above, in this case, NOx and other gaseous pollutants are also removed by the action of radicals.

FIG. 5 is a longitudinal sectional view of the main part of a twenty-seventh embodiment of the present invention, which is different from FIGS. 3 and 4, and the upstream plasma processing electrode 8 is composed of a wire electrode element 25 as in FIG. However, in the present embodiment, the wire electrode element 25 is inserted into the upstream side gas passage group 17 from the upstream side to the back side, and the downstream side plasma inserted into the downstream side gas passage group 18 from the downstream side to the back side. It faces the wire electrode element 22 of the processing electrode 9 via the porous partition wall 13. The names and functions of the other elements 8 to 25 are the same as those in the first embodiment shown in FIGS. 3 and 4.
This is the same as the elements with the same numbers in 2 and 24.

When the AC voltage is applied between the electrodes 8 and 9 from the AC power supply 10, the wire electrode elements 2 are
A discharge is generated between the 2 and 25 through the porous partition wall 13,
As described above, the soot adhering to the upstream surface of the partition wall and the inside voids is removed, and the gaseous pollutants including NOx are also removed.

FIG. 6 is a vertical cross-sectional view of the main part of an embodiment 28 of the present invention, which is different from FIGS. 3, 4 and 4. In this embodiment, each of the two sets of plasma treatment electrodes 9 and 29 is composed of wire electrode elements 22 and 30 inserted from the downstream side to the inside in the downstream gas passage group 18, and both wire electrode elements 22 and 30 is one upstream gas passage 14 in the middle
And the porous ceramic partition walls 13 on both sides thereof are opposed to each other. The names and functions of the other elements 9 to 22 are the same as those of the elements with the same numbers in FIGS. 3 and 4 and the embodiments 12, 24, and 28.

When the AC voltage is applied from the AC power supply 10 between the plasma processing electrodes 9 and 29, the upstream gas passage 14 sandwiched between the wire electrode elements 22 and 30 and the upstream gas passage 14 therebetween. The porous ceramic partition walls 13 on both sides
As described above, the silent discharge is generated through the soot and the gaseous pollutants are removed by the soot.

[0036]

[Advantages] Since the present invention is as described above, the soot adhering to the upstream surface and internal voids of the filter element of the ceramic filter is constantly oxidatively decomposed by the plasma treatment by electric discharge, and the increase of the pressure loss due to the soot adhesion is prevented. As a result, the efficiency of the diesel engine can be prevented from decreasing and the life of the ceramic filter can be maintained for a long time.

At the same time, gaseous pollutants such as NOx contained in the exhaust gas of the diesel engine can be oxidized and reduced by the plasma treatment, and can be removed to achieve extremely economical purification of the exhaust gas of the diesel engine.

[0038]

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an embodiment showing the basic concept of the present invention.

FIG. 2 is a perspective view of a honeycomb type ceramic filter used in the present invention.

FIG. 3 is a vertical sectional view of another embodiment of the present invention.

FIG. 4 is a vertical sectional view of still another embodiment of the present invention.

FIG. 5 is a vertical sectional view of still another embodiment of the present invention.

FIG. 6 is a vertical sectional view of still another embodiment of the present invention.

[Explanation of symbols]

 2 Exhaust Duct 3 Gas Inlet 4 Gas Outlet 5 Casing 6 Ceramic Filter 7 Filter Element 8 Upstream Plasma Treatment Electrode 9 Downstream Plasma Treatment Electrode 10 AC Power Supply 11 Honeycomb Ceramic Filter 13 Porous Ceramic Partition 17 Upstream Gas Passage Group 18 Downstream Side gas passage group 21 Wire mesh electrode element 22 Wire electrode element 25 Wire electrode element 29 Downstream plasma treatment electrode

Claims (10)

[Claims] 1. A ceramic filter made of a porous ceramic filter element is provided inside a casing having an inlet for exhaust gas containing soot and an outlet for clean gas, and the filter element is sandwiched between the ceramic filters. , For arranging two sets of plasma processing electrodes consisting of at least one electrode element having a structure that does not impede the flow of gas so as to be insulated from each other, and connecting the two plasma processing electrodes to apply an AC voltage therebetween. An exhaust gas purifying apparatus for a diesel engine, characterized in that an AC power source is provided, and an electric discharge is generated between both plasma processing electrodes through at least a part of the filter element. 2. The plasma processing electrodes are composed of an electrode element, which is either a wire mesh or a perforated plate, which is provided in the upstream side and the downstream side of the ceramic filter in the vicinity of the ceramic filter. Exhaust gas purification device for diesel engine described in. 3. The ceramic filter has a honeycomb structure and is composed of a large number of elongated gas passage groups, and the upstream and downstream ends of the gas passages are alternately closed by a closed portion made of ceramic to communicate upstream. 2. A honeycomb type ceramic filter, which is divided into a side gas passage group and a downstream side gas passage group communicating with the downstream side, and a partition wall between adjacent gas passages constitutes the filter element. Alternatively, the diesel engine exhaust gas purifying device according to any one of 2 or 3. 4. Of the two sets of plasma treatment electrodes,
One is composed of an electrode element of either a wire mesh or a perforated plate provided on the upstream side of the closed end of the honeycomb type ceramic filter and adjacent thereto, and the other is the gas passage on the downstream side of the honeycomb type ceramic filter. The exhaust gas purification refurbishment of a diesel engine according to claim 3, characterized by comprising wire-shaped electrode elements inserted into the group from the downstream side to the inner side. 5. Of the two sets of plasma treatment electrodes,
One consists of wire-shaped electrode elements arranged so that the downstream tip is located near the inlet of the upstream gas passage group of the honeycomb ceramic filter, and the other consists of the downstream side in the downstream gas passage group. The exhaust gas purifying device for a diesel engine according to claim 3, wherein the exhaust gas purifying device comprises a wire-shaped electrode element inserted from the inside. 6. Of the two sets of plasma treatment electrodes,
One consists of wire-shaped electrode elements arranged so that the downstream tip is located near the respective inlets of the upstream gas passage group of the above-mentioned honeycomb type ceramic filter, and the other consists of the downstream gas passage group. Insertion consisting of wire-like electrode elements inserted from the downstream side, and inserting / extracting the wire-like electrode elements of the upstream processing electrode into the gas passages from the inlets of the upstream gas passages whose tips respectively face each other. An exhaust gas purifying device for a diesel engine according to claim 5, characterized in that extraction means is provided. 7. Of the two sets of plasma treatment electrodes,
One consists of wire-shaped electrode elements inserted from the upstream side to the inside of the upstream side gas passage group of the honeycomb ceramic filter, and the other is inserted from the downstream side to the inside of the downstream side gas passage group. The exhaust gas purifying apparatus for a diesel engine according to claim 3, wherein the exhaust gas purifying apparatus comprises a wire-shaped electrode element. 8. Both of the two sets of plasma processing electrodes are wire-like electrode elements inserted from the downstream side into the downstream gas passage group, and the electrode elements belonging to both sets of plasma processing electrodes are mutually The exhaust gas purifying apparatus for a diesel engine according to claim 3, wherein the exhaust gas purifying apparatus is opposed to each other via one of the upstream gas passages. 9. The above AC power supply has an output voltage peak value of 3 k.
A high-frequency high-voltage power supply that generates a high-frequency high voltage of V or more and an output frequency of 5 kHz or more.
8. An exhaust gas purifying device for a diesel engine according to any one of 8 above. 10. The above AC power supply has an output voltage peak value of 5 k.
2. A high-voltage pulse power supply that generates a pulsed high voltage of V or higher and an output frequency of 50 Hz or higher.
9. An exhaust gas purifying device for a diesel engine according to any one of items 1 to 8.