JP7307015B2 - Plasma reactor for exhaust gas purification - Google Patents

Description

TECHNICAL FIELD The present invention relates to a plasma reactor attached to an engine of an automobile or the like and used to remove PM (particulate matter) from exhaust gas.

The exhaust gas discharged from the engine contains PM (Particulate Matter) along with CO, HC, and NOx. This PM is often generated in diesel engines, and DPF is used as a means of removing PM in diesel engines. There are many problems such as increased pressure loss due to ash (unburned ash due to sulfur components in fuel).

On the other hand, since gasoline engines generate less PM than diesel engines, three-way catalysts targeting CO, HC, and NOx have been conventionally used as a means of purifying exhaust gas. The removal of PM has emerged as an important issue, such as the adoption of GPF in gasoline engines as well as the transition to number control (PN). However, the GPF is also concerned about the same problem as the DPF.

Therefore, a plasma reactor is attracting attention as a means for removing PM. A plasma reactor consists of a large number of discharge panels arranged in parallel in a casing with a discharge gap interposed therebetween. The PM contained in the exhaust gas is oxidized (burned) and rendered harmless.

Although the plasma reactor is useful for removing PM, it has been proposed to combine the plasma reactor with the function of removing harmful components such as HC to make it hybrid. It is disclosed that an oxidation catalyst layer is provided on the surface of each discharge panel so as to overlap with the electrodes when viewed from the stacking direction of the discharge panels.

JP 2018-71404 A

It can be said that hybridizing the plasma reactor is a favorable development in terms of exhaust gas purification. Since the electric current is discharged to the discharge gap through the oxidation catalyst layer, for example, if HC or condensed water adheres to the oxidation catalyst layer, they may act as resistance, destabilizing the discharge or making it impossible to discharge. Concerned.

In addition, in the plasma reactor, if the frequency of the discharge current is increased, the PM decomposition performance is improved. There is also a risk that power will be consumed more than necessary and fuel consumption will be worsened.

The present invention was made against the background of such a situation, and hybridizing the plasma reactor is in line with Patent Document 1, while improving the stability of discharge, removing harmful substances, suppressing power consumption, etc. It is intended to

The present invention, as claimed in claim 1,
"A negative electrode discharge panel provided with a negative electrode and a positive electrode discharge panel provided with a positive electrode are alternately stacked in a casing through which the exhaust gas flows from one side to the other through a discharge gap through which the exhaust gas flows. Either or both of the positive electrode discharge panel and the negative electrode discharge panel are provided with an auxiliary treatment layer that treats the harmful components of the exhaust gas with non-plasma.”
In the basic configuration of
"At least one of the negative electrode and the positive electrode and the auxiliary treatment layer are arranged such that at least one of the negative electrode and the positive electrode is positioned on the upstream side of the exhaust gas flow, and the auxiliary treatment layer is positioned on the downstream side. are arranged separately as
It has the characteristics of

The present invention can be developed in various ways. As an example, in claim 2,
"By forming the negative electrode discharge panel with a narrow width offset to the upstream side in the flow direction of the exhaust gas, the discharge can be performed in the space sandwiched between the adjacent positive electrode discharge panels on the downstream side of the negative electrode discharge panel. A relief space is formed with an interval larger than the gap,
The auxiliary treatment layer is provided on both the front and back surfaces or on one side of the positive electrode discharge panel so as to be exposed to the escape space, and the positive electrode provided on the positive electrode discharge panel is located more than the negative electrode on the negative electrode discharge panel. is also widely formed
configuration is adopted.

In the present invention, the auxiliary treatment layer can have various functions. For example, an inorganic porous material such as zeolite can be used as an adsorption layer that collects or decomposes carbon compounds such as HC. It is also possible to form a catalyst layer in which a catalyst metal is supported on a ceramic layer.

In addition, although the width of the electrodes is small in the narrow discharge panel, the width of the electrodes provided in the wide discharge panel may be set to match the width of the electrodes provided in the narrow discharge panel. , the width of the electrode may be wider than that of the narrow electrode. Although the electrodes can be exposed on the surface of the substrate, they are preferably embedded inside the substrate.

In the invention of the present application, since the auxiliary treatment layer is arranged separately on the downstream side of the electrodes, the electric discharge between the electrodes is never hindered by the auxiliary treatment layer. Therefore, it is possible to generate stable plasma in the discharge gap and stabilize the oxidation removal performance of PM.

Now, the ability to remove PM is proportional to the frequency of the current discharged between the electrodes. Therefore, it can be said that PM removal performance can be remarkably improved by increasing the frequency of the current applied between the electrodes, for example, from the usual 1 KHz to about 20 KHz. However, there is a problem that power consumption increases as the frequency of the current increases. In this regard, in the present invention, by increasing the discharge voltage while reducing the width of the electrode (negative electrode), it is possible to obtain a high PM removal effect while suppressing an increase in power consumption.

If the electrode is formed narrow, it is possible to create a margin in the area of the discharge panel. It is possible to improve the reliability of removal of PM and removal of gaseous components such as HC without increasing the size.

In the invention of claim 2, since a relief space with a distance far larger than the discharge gap is formed on the downstream side of the negative electrode discharge panel, the area of the auxiliary treatment layer is increased without causing an increase in pressure loss, thereby purifying gas components such as HC. can ensure

(A) is a schematic vertical cross-sectional side view of the plasma reactor according to the first embodiment, (B) is a partially enlarged view of (A), (C) is a CC cross-sectional view of (B), (D) is ( B) is a cross-sectional view taken along line DD. FIG. 11 is a partial longitudinal side view of the second embodiment; FIG. 11 is a partial longitudinal side view of the third embodiment; It is a partial longitudinal side view of a 4th embodiment.

Next, embodiments of the present invention will be described based on the drawings. This embodiment is used as an accessory for an automobile engine.

(1). Structure of First Embodiment First, the first embodiment shown in FIG. 1 will be described. (A) of FIG. 1 schematically shows the entire plasma reactor 1 . This plasma reactor 1 is arranged in the middle of an exhaust pipe 2 (for example, downstream of a catalytic purification device) to remove PM and the like from exhaust gas discharged from an automobile engine.

The plasma reactor 1 includes a casing (housing) 3 having a front cone portion 3a and a rear cone portion 3b, and a group of a large number of negative electrode discharge panels 4 and positive electrode discharge panels 5 arranged in parallel on a straight portion 3c of the casing 3. I have. The negative electrode discharge panels 4 and the positive electrode discharge panels 5 are alternately arranged with a discharge gap (exhaust gas passage space) 6 interposed therebetween.

The discharge panels 4 and 5 may be formed in a rectangular shape elongated in the flow direction of the exhaust gas, or formed in a square having the same length in the flow direction of the exhaust gas and a width orthogonal to the flow direction of the exhaust gas. It is possible. The casing 3 is made of a metal plate such as a stainless steel plate, and has a rectangular shape when viewed from the exhaust gas flow direction. Therefore, the cone portions 3a and 3b are in the shape of a pyramid.

The discharge panels 4 and 5 have a structure in which electrodes 8 and 9 are embedded in a dielectric substrate 7 . The substrate 7 is made of ceramic such as alumina, while the electrodes 8 and 9 are made of a metal film having low electric resistance such as tungsten. The substrate 7 has a laminated structure of a surface layer and a back layer at the manufacturing stage. It is a single plate product in which electrodes 8 and 9 are embedded.

The negative electrode discharge panel 4 and the positive electrode discharge panel 5 have a rectangular shape elongated in a direction perpendicular to the flow direction of the exhaust gas (a direction perpendicular to the paper surface). They are alternately arranged in parallel in a direction perpendicular to the exhaust gas flow direction via an exhaust gas passage space 6 .

The negative electrode discharge panel 4 and the positive electrode discharge panel 5 are formed in a rectangular shape when viewed from the stacking direction, and therefore each have a width in the exhaust gas flow direction. The width dimension W1 of the negative electrode discharge panel 4 is It is a fraction of the width W2 of the positive electrode discharge panel 5 . Therefore, the negative electrode discharge panel 4 has a rectangular shape elongated in the direction perpendicular to the flow direction of the exhaust gas.

On the other hand, the positive electrode discharge panel 5 can be formed in a rectangular shape whose width W2 is greater than the length in the direction perpendicular to the flow direction of the exhaust gas, or can be formed in a square whose width W2 is equal to its length. Furthermore, it can also be formed in a rectangular shape in which the width dimension W2 is greater than the length.

The negative electrode 8 of the negative electrode discharge panel 4 has its front end and rear end exposed to the end surface of the substrate 7 facing the flow direction of the exhaust gas. Therefore, the width dimension of the negative electrode 8 is the same width as the width dimension W1 of the negative electrode discharge panel 4 .

On the other hand, the positive electrode 9 of the positive electrode discharge panel 5 has the same width dimension as the negative electrode 8, and therefore faces the flow direction of the exhaust gas, and the rear end thereof is exposed on the end surface of the substrate 7, but the direction of the flow of the exhaust gas is exposed. , the front end is embedded in the substrate 7 . Both the negative electrode 8 and the positive electrode 9 can be entirely embedded in the substrate 7 .

The rear end of the negative electrode discharge panel 4 and the rear end of the positive electrode discharge panel 5 are aligned with each other when viewed from the flow direction of the exhaust gas. Therefore, an escape space 10 with a distance far larger than the discharge gap 6 is formed downstream of the negative electrode discharge panel 4 . Since the width W1 of the negative electrode discharge panel 4 is only a fraction of the width W2 of the positive electrode discharge panel 5, the width of the relief space 10 is several times the width W1 of the negative electrode discharge panel 4. Note that the upstream end of the negative electrode discharge panel 4 can be shifted downstream from the upstream end of the positive electrode discharge panel 5 .

Adsorption layers 11 made of zeolite are provided on both the front and back surfaces of each positive electrode discharge panel 5 so as to be exposed to the escape space 10 as an example of the auxiliary treatment layer described in the claims. Therefore, the substrate 7 is arranged downstream of the negative discharge panel 4 . The adsorption layer 11 is mainly for adsorbing HC, and is integrated with the substrate 7 by applying it to the panel and baking it if necessary.

Since the discharge panels 4 and 5 are elongated in the lateral direction perpendicular to the exhaust gas flow direction, the substrate 7 has one side surface 7a parallel to the exhaust gas flow direction and the other side surface 7a, as partially shown in FIG. 1(C). In this embodiment, the negative electrode 8 is exposed on one side surface 7a of the substrate 7, while the positive electrode 9 is exposed on the other side surface of the substrate 7. As shown in FIG.

Then, the negative side electrode plate 12 is inserted between one side plate of the straight portion 3c in the casing 3 and the discharge panels 4 and 5, and the negative side electrode 13 provided on the negative side electrode plate 12 and each negative electrode discharge panel While the negative electrode 8 of 4 is electrically connected, a positive side electrode plate (not shown) is inserted between the other side plate of the casing 3 and the discharge panels 4 and 5, and is provided on the positive side electrode plate. The positive side electrode (not shown) and each positive electrode 9 of the positive electrode discharge panel 5 are electrically connected, and the side electrode 13 is connected to a power supply (not shown). Reference numerals 14 and 15 shown in FIGS. 1(C) and 1(D) denote spacers for maintaining the gap between the adjacent discharge panels 4 and 5. FIG.

The substrate 7 constituting the discharge panels 4 and 5 must have a certain thickness (for example, about 0.3 to 2 mm) from the viewpoint of maintaining strength, while the discharge gap 6 is about 0.1 to 2 mm. . Therefore, the total cross-sectional area of the discharge gap 6 is set to be approximately the same as the cross-sectional area of the exhaust pipe 2 . Note that the total cross-sectional area of the discharge gap 6 may be set larger than the cross-sectional area of the exhaust pipe 2 .

(2).Summary of the first embodiment When a pulse current is passed through the negative side electrode 13 by a power supply device (not shown) and a high voltage current of several KV is applied between the negative electrode 8 and the positive electrode 9, the discharge gap 6 A plasma is generated in the exhaust gas, and the PM contained in the exhaust gas can be oxidized and removed (decomposed).

In this case, for example, by using a high-frequency current of several tens of kHz, the width of the electrodes 8 and 9 can be reduced, and the PM oxidation removal performance can be significantly improved. Since the positive electrode discharge panel 5 is formed with the adsorption layer 11 exposed in the escape space 10, harmful gases such as HC that have passed through the discharge gap 6 are adsorbed, thereby significantly improving the exhaust gas purification performance. can.

Since the adsorption layer 11 is arranged on the downstream side of the negative electrode 8, the adsorption layer 11 has no adverse effect on discharge, and the performance of removing PM by oxidation can be stabilized. In addition, since the exhaust gas passes through the adsorption layer 11, no pressure loss is generated, so that the flow of the exhaust gas can be made smooth and the reduction of the engine output can be prevented.

In addition, if a high-frequency current of several tens of kHz is used for plasma generation, the width of the electrodes 8 and 9 can be reduced to suppress power consumption while PM can be thoroughly removed. HC removal can be ensured by securing an area several times larger than that of the negative electrode discharge panel 4 in the escape space 10 .

Looking only at the plasma generation function, it is possible to expose the electrodes 8 and 9 to the surface of the substrate 7. There is concern about a problem that an abnormal discharge is likely to occur by concentrating on the electrodes 8 and 9, and a problem that PM is likely to adhere to the electrodes 8 and 9 to cause electric leakage. On the other hand, if the electrodes 8 and 9 are embedded in the substrate 7 as in the present embodiment, PM will never adhere to the electrodes 8 and 9, so that the problem of reduced discharge due to electric leakage will be completely eliminated. By widening the gap between the electrodes 8 and 9, even if there is a variation in the gap between the electrodes 8 and 9, current concentration is eliminated and abnormal discharge can be prevented.

(3). Other Embodiments Next, other embodiments shown in FIGS. 2 to 4 will be described. FIG. 2 shows a modification of the first embodiment, in which the positive electrode 9 of the positive electrode discharge panel 5 is extended to near the downstream end of the substrate 7 . In this embodiment, as indicated by hatching, the discharge area spreads downstream of the negative electrode 8, so the performance of removing PM by oxidation can be improved without increasing current consumption.

Most of the portion of the positive electrode 9 that protrudes downstream of the negative electrode 8 does not contribute to the discharge, but the entire positive electrode 9 is heated by the discharge, which has the advantage of accelerating the decomposition of HC.

In the third embodiment shown in FIG. 3, the escape space 10 is not provided, and the negative electrode discharge panel 4 and the positive electrode discharge panel 5 are set to have the same width. Adsorption layers 11 located downstream of the negative electrodes 8 are formed on both the front and back surfaces of the discharge panels 4 and 5 . In this case, the adsorption layer 11 can be formed only on the positive electrode discharge panel 5 or only on the negative electrode discharge panel 4 . Alternatively, it is also possible to form one adsorption layer 11 on the downstream side of the discharge gap 6 by forming only one side of the negative electrode discharge panel 4 and the positive electrode discharge panel 5 .

As described above, the discharge panels 4 and 5 use a two-layer intermediate material consisting of a surface layer and a back layer at the manufacturing stage. In the fourth embodiment shown in FIG. 4, the discharge panels 4 and 5 are arranged on the upstream side where the electrodes 8 and 9 are embedded by reducing the width of one layer. It is formed in a unequal-thickness structure of a narrow thick-walled portion located at the bottom and a wide thin-walled portion located at the downstream side where the adsorption layer 11 is formed.

In the fourth embodiment, since the semi-relief space 16 is formed at the thin portion, pressure loss can be eliminated and the flow of the exhaust gas can be made smooth. In addition, since the adsorption layer 11 is also formed on the negative electrode discharge panel 4 unlike the first embodiment, there is an advantage that the total area of the adsorption layer 11 can be doubled and the collection and decomposition performance of HC and the like can be doubled. .

Although the embodiments of the present invention have been described above, the present invention can be embodied in various other ways. For example, a catalyst layer can be employed as the auxiliary treatment layer, and when an adsorption layer is employed, materials other than zeolite can be arranged. Furthermore, it is possible to arrange an adsorption layer or catalyst layer of porous structure through which the exhaust gas passes almost without resistance so as to extend over the entire escape space.

The present invention can be embodied in a plasma reactor for exhaust gases. Therefore, it can be used industrially.

REFERENCE SIGNS LIST 1 plasma reactor 2 exhaust pipe 3 casing 4 negative electrode discharge panel 5 positive electrode discharge panel 6 discharge gap (exhaust gas passage space)
7 substrate 8 negative electrode 9 positive electrode 10 relief space 11 adsorption layer (HC adsorption layer) as an example of auxiliary treatment layer

Claims (2)

A negative electrode discharge panel provided with a negative electrode and a positive electrode discharge panel provided with a positive electrode are alternately stacked in a casing through which the exhaust gas flows from one side to the other through a discharge gap through which the exhaust gas flows. A configuration in which one or both of the discharge panel and the negative electrode discharge panel is provided with an auxiliary treatment layer for treating harmful components of the exhaust gas with non-plasma,
At least one of the negative electrode and the positive electrode and the auxiliary treatment layer are arranged such that at least one of the negative electrode and the positive electrode is positioned on the upstream side of the exhaust gas flow, and the auxiliary treatment layer is positioned on the downstream side. are located separately in the
Plasma reactor for purification of exhaust gas. By forming the negative electrode discharge panel with a narrow width offset to the upstream side in the flow direction of the exhaust gas, the discharge gap is located on the downstream side of the negative electrode discharge panel in the space sandwiched between the adjacent positive electrode discharge panels. An escape space is formed with a larger interval than
The auxiliary treatment layer is provided on both the front and back surfaces or on one side of the positive electrode discharge panel so as to be exposed to the escape space, and the positive electrode provided on the positive electrode discharge panel is located more than the negative electrode on the negative electrode discharge panel. is also widely formed,
A plasma reactor for purifying an exhaust gas according to claim 1.

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