JP2004263600A - Exhaust gas purification equipment - Google Patents

Abstract

An exhaust gas purifying apparatus capable of sufficiently exerting a catalytic action even at a low exhaust gas temperature such as at a cold start.
In an exhaust gas purifying apparatus provided in the middle of an exhaust gas pipe, a cylindrical HC adsorption cylinder having a hollow portion provided in a tubular container, and an exhaust gas flow inside the container that is higher than the HC adsorption cylinder. A three-way catalyst provided downstream of the HC adsorption column, a discharge electrode provided in the hollow portion of the HC adsorption column so as to extend in the direction of the exhaust gas flow, and a ground provided on the outer surface of the HC adsorption column. And a plasma discharge part formed by the electrode.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purifying apparatus for purifying exhaust gas discharged from an engine of an automobile or the like.
[0002]
[Prior art]
In recent years, demands for lower emission of exhaust gas from engines of automobiles and the like have been rapidly increasing due to resource saving and increasing interest in environmental issues.
[0003]
In particular, exhaust gases from internal combustion engines (gasoline engines, diesel engines, etc.) contain harmful substances such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). With regard to emission reductions, emission regulations on a global scale are being rapidly strengthened due to JULEV regulations in Japan, LEV regulations in the United States, STEP regulations in Europe, and the like.
[0004]
Based on such a background, development of various exhaust gas purifying devices for realizing low emission and clean exhaust gas has been promoted.
[0005]
For example, a purifying apparatus has been proposed in which a high-voltage field is used for purifying exhaust gas, and the amount of charged electric power is controlled in accordance with the operation state of the engine, thereby optimizing the purifying performance of the exhaust gas. And Patent Document 1).
[0006]
Similarly, there has been proposed an exhaust gas purifying apparatus using a high voltage field for purifying exhaust gas, to which a safety means for preventing an electric leakage accident or an electric shock accident at the time of abnormality of the apparatus has been added (for example, Patent Reference 2).
[0007]
[Patent Document 1]
JP-A-5-59934 [Patent Document 2]
Japanese Patent Application Laid-Open No. 2002-21541
[Problems to be solved by the invention]
However, in the exhaust gas purifying devices disclosed in the above-mentioned patent documents, it is assumed that the catalyst for purifying exhaust gas components has reached an activation temperature (reaction temperature), and the catalyst is not activated. As for purification of exhaust gas components in a warm-up state where the temperature has not reached or when the exhaust gas is in a low temperature state, there has been a problem that the function cannot be sufficiently exhibited.
[0009]
That is, for example, in a cold state such as when the engine of a car is started, the catalyst is in a warm-up state in which the catalyst has not reached the activation temperature, and in this state, a sufficient catalytic reaction cannot be performed. Of the exhaust gas flow, the flow near the pipe wall has a lower exhaust gas temperature than the flow of the exhaust gas in the central portion, so that there has been a problem that the catalytic reaction is more difficult to proceed.
[0010]
Accordingly, an object of the present invention is to provide an exhaust gas purifying apparatus capable of sufficiently exerting a catalytic action even when the exhaust gas is at a low temperature, such as at the time of a cold start, in view of the above-mentioned problems of the related art.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, an exhaust gas purifying apparatus of the present invention includes an exhaust gas purifying apparatus provided in the middle of an exhaust gas pipe, a cylindrical HC adsorption cylinder having a hollow portion provided in a tubular container, A three-way catalyst provided in the vessel at a downstream portion of the exhaust gas flow from the HC adsorption column, and a discharge electrode provided in the hollow portion of the HC adsorption column so as to extend in the direction of the exhaust gas flow. A plasma discharge unit formed by a ground electrode provided on the outer surface of the HC adsorption cylinder.
[0012]
In the exhaust gas purifying apparatus of the present invention configured as described above, the HC component is temporarily collected in the HC adsorption column until the three-way catalyst reaches the activation temperature with respect to the flow at the peripheral portion where the exhaust gas temperature is low. Along with this, with respect to the flow in the central portion where the exhaust gas temperature is high, the HC molecules are cationized by the plasma discharge and are guided to the ground electrode side, and are similarly collected in the HC adsorption column. The collection rate is improved. Furthermore, the exhaust gas flow in the central part, which has passed through the hollow part of the HC adsorption cylinder and has a high temperature, heats the three-way catalyst and promotes warm-up. The catalytic reaction by the source catalyst is promoted, whereby the purification action of the exhaust gas can be promoted even in a cold state.
[0013]
Also, the exhaust gas purifying apparatus of the present invention is an exhaust gas purifying apparatus provided in the middle of an exhaust gas pipe, wherein a cylindrical HC adsorption cylinder having a hollow portion provided in a tubular container, A composite catalyst formed of at least two catalysts filled and supported in a hollow portion, a three-way catalyst provided downstream of the HC adsorption cylinder in the exhaust gas flow in the container, and a composite catalyst. A plasma discharge portion formed by a discharge electrode provided at a central portion so as to extend in the direction of the flow of the exhaust gas and a ground electrode provided on an outer surface of the HC adsorption cylinder. .
[0014]
In the exhaust gas purifying apparatus of the present invention configured as described above, the HC component is temporarily collected in the HC adsorption column until the three-way catalyst reaches the activation temperature with respect to the flow at the peripheral portion where the exhaust gas temperature is low. Regarding the flow in the central part where the exhaust gas temperature is high, the exhaust gas molecules are positively ionized by plasma discharge and guided to the ground electrode side while promoting the warm-up of the composite catalyst arranged in the central part of the flow. Therefore, the collection rate of the exhaust gas component is improved. Furthermore, since the exhaust gas component activated by the plasma discharge is rich in reactivity, the catalytic reaction by the composite catalyst is promoted, and the exhaust gas can be efficiently purified even in a cold state.
[0015]
Here, the composite catalyst has a concentric cross section orthogonal to the longitudinal center axis of the HC adsorption cylinder, and the first catalyst and the second catalyst arranged in the order of increasing activation temperature from the center axis toward the outer peripheral direction. And a second catalyst.
[0016]
In this case, since the catalysts are arranged concentrically from the center of the exhaust gas flow in the order of higher activation temperature, efficient warm-up of the catalyst according to the temperature distribution of the exhaust gas flow can be promoted. Thus, it is possible to purify the exhaust gas more efficiently.
[0017]
Here, the first catalyst may be a three-way catalyst, and the second catalyst may be a NOx storage reduction catalyst.
[0018]
In this case, the HC component can be trapped by the HC adsorption column and the NOx component can be trapped by the NOx storage reduction catalyst until the three-way catalyst reaches the activation temperature, and the purification of harmful components in the exhaust gas can be performed more efficiently. Can be done
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0020]
FIG. 1 is a sectional view showing an exhaust gas purifying apparatus according to the first embodiment of the present invention.
[0021]
An exhaust gas purifying apparatus 1 according to the present embodiment includes an engine (not shown) mounted on a vehicle and a tubular exhaust gas treatment container 2 located in the middle of a muffler, and has a cylindrical shape having a hollow portion 14 in the exhaust gas treatment container 2. And a discharge electrode (anode) 16 is disposed at the center of the hollow portion 14 so as to extend in the direction of exhaust gas flow. A ground electrode (cathode) 18 is arranged on the outer peripheral portion of the HC adsorption cylinder 12 so as to face the discharge electrode 16, and the discharge electrode 16 and the ground electrode 18 are connected to a high-voltage power supply 20. Further, in the exhaust gas treatment container 2, a three-way catalyst 22 is disposed in a downstream portion 2d of the HC adsorption cylinder 12 in the exhaust gas flow.
[0022]
Here, the activation temperature (reaction temperature) of the three-way catalyst 22 is about 300 ° C. to 700 ° C., for example, with a coating layer obtained by coating a honeycomb-shaped cordierite carrier with alumina, platinum, palladium, rhodium, ceria, or the like. Is formed.
[0023]
Further, the HC adsorption cylinder 12 plays a role of collecting HC components in the exhaust gas, desorbs the HC components collected at a low temperature at about 100 ° C., and is formed of, for example, alumina, platinum, etc. carrying zeolite. ing.
[0024]
Generally, the temperature distribution of the exhaust gas flow has the highest temperature at the center of the flow, and the temperature decreases as the distance from the center increases in a direction orthogonal to the flow, and the temperature distribution near the pipe wall of the tubular exhaust gas treatment vessel 2 The temperature is the lowest at the periphery of the flow.
[0025]
In the exhaust gas purifying apparatus 1 according to the present embodiment arranged in such an exhaust gas flow, when a high voltage is applied between the discharge electrode (anode) 16 and the ground electrode (cathode) 18 by the high-voltage power supply 20, Plasma discharge is generated, and gas molecules in the exhaust gas are activated (radicalized). The exhaust gas molecules activated at the center of the exhaust gas flow are high in temperature and excellent in reactivity, pass through the hollow portion 14 of the HC adsorption column 12, and heat the three-way catalyst 22 disposed in the downstream portion 2d. In addition to promoting warm-up, a catalytic reaction is performed early by the three-way catalyst 22.
[0026]
The HC component contained in the cold exhaust gas around the pipe wall of the exhaust gas treatment container 2 is temporarily captured by the HC adsorption column, and the three-way catalyst 22 whose warm-up is promoted by the exhaust gas flow in the central portion is activated. After that, the trapped HC component is desorbed, so that the HC purification rate in a cold state can be improved. Further, the HC component activated by the plasma discharge is also attracted to the cathode side (ground electrode side), so that the adsorption efficiency of the HC component can be increased.
[0027]
Next, a second embodiment of the present invention will be described.
[0028]
FIG. 2 is a cross-sectional view illustrating an exhaust gas purification device according to a second embodiment of the present invention.
[0029]
In the present embodiment, the composite catalyst is carried in the hollow portion of the HC adsorption cylinder in the first embodiment, and the other basic components are the same as those in the first embodiment. Are given the same reference numerals.
[0030]
An exhaust gas purifying apparatus 10 according to the present embodiment includes an engine (not shown) mounted on a vehicle and a tubular exhaust gas treatment container 2 located in the middle of a muffler, and a hollow portion is formed along a pipe wall in the exhaust gas treatment container 2. The HC adsorption cylinder 12 having a cylindrical shape and having a cylindrical shape 14 is disposed. A cylindrical NOx storage reduction catalyst 30 having a hollow portion is further disposed on the inner peripheral side of the HC adsorption cylinder 12, and a three-way catalyst 22 is disposed in the hollow portion of the NOx storage reduction catalyst 30. I have.
[0031]
A discharge electrode (anode) 16 is disposed at the center of the three-way catalyst 22 so as to extend in the flow direction of the exhaust gas, and a ground electrode (cathode) 18 is disposed at the outer periphery of the HC adsorption cylinder 12. The discharge electrode 16 and the ground electrode 18 are connected to a high-voltage power supply 20. Further, in the exhaust gas treatment container 2, a three-way catalyst 22 is disposed in a downstream portion 2d downstream of the HC adsorption cylinder 12 in the exhaust gas flow.
[0032]
Note that, in the present embodiment, the amount of the three-way catalyst 22 disposed in the downstream portion 2d may be smaller than in the first embodiment described above.
[0033]
Here, the activation temperature (reaction temperature) of the three-way catalyst 22 is about 300 ° C. to 700 ° C., for example, with a coating layer obtained by coating a honeycomb-shaped cordierite carrier with alumina, platinum, palladium, rhodium, ceria, or the like. Is formed.
[0034]
Further, the HC adsorption cylinder 12 plays a role of collecting HC components in the exhaust gas, desorbs the HC components collected at a low temperature at about 100 ° C., and is formed of, for example, alumina, platinum, etc. carrying zeolite. ing.
[0035]
Further, the activation temperature (reaction temperature) of the NOx storage reduction catalyst 30 is about 200 ° C. to 500 ° C., and is made of, for example, barium, potassium, sodium, ceria, or the like.
[0036]
Therefore, in the present embodiment, the three-way catalyst 22 and the NOx storage reduction catalyst 30 that constitute the composite catalyst are arranged concentrically from the center of the exhaust gas flow in the order of increasing activation temperature.
[0037]
In the exhaust gas purifying apparatus 10 according to the present embodiment configured as described above, since the three-way catalyst 22 and the NOx storage reduction catalyst 30 are arranged on the central portion of the gas flow having a high exhaust gas temperature, the NOx storage reduction catalyst 30 is disposed around the three-way catalyst 22. Adapting to the temperature gradient, these catalysts can be efficiently warmed up.
[0038]
When a high voltage is applied between the discharge electrode (anode) 16 and the ground electrode (cathode) 18 by the high-voltage power supply 20 as in the first embodiment described above, plasma discharge occurs and gas molecules in the exhaust gas are generated. Is activated (radicalized). Then, the activated gas molecules are occluded by the HC adsorption column 12 and the NOx storage reduction catalyst 30 together with the HC component and the NOx component until the three-way catalyst 22 in which the warm-up of the central portion is promoted is activated. .
[0039]
Furthermore, the HC component contained in the cold exhaust gas around the pipe wall of the exhaust gas treatment container 2 is captured by the HC adsorption column, and is desorbed after the three-way catalyst 22 has reached the activation temperature, so that the temperature during cold operation is reduced. As the HC purification rate can be improved, the activated HC component is also attracted to the cathode side (ground electrode side), so that the adsorption efficiency of the HC component can be increased.
[0040]
Furthermore, for example, even in the case of a so-called lean burn operation, even when an exhaust gas component having an insufficient catalytic reaction due to an increase in the NOx component or the like is generated, the three-way catalyst 22 disposed in the downstream portion 2d allows the exhaust gas component to be sufficiently reduced. Cleanup can be performed.
[0041]
In the present embodiment, the three-way catalyst 22 and the NOx storage reduction catalyst 30 are used as the composite catalyst. However, the present invention is not limited to this, and the activation temperature of the catalyst is adjusted according to the temperature gradient of the exhaust gas flow. The same effect can be obtained by arranging them in such a manner.
[0042]
【The invention's effect】
As described above, according to the present invention, it is possible to provide an exhaust gas purifying apparatus capable of purifying an exhaust gas by exhibiting a sufficient catalytic function even in a cold state, whereby the harmful substances contained in the exhaust gas can be provided. It can contribute to lower emission of components and cleaner exhaust gas.
[Brief description of the drawings]
FIG. 1 is a sectional view showing an exhaust gas purifying apparatus according to a first embodiment of the present invention.
FIG. 2 is a sectional view showing an exhaust gas purifying apparatus according to a second embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Exhaust gas purifier 2 Exhaust gas treatment vessel 2d Downstream part 10 Exhaust gas purifier 12 HC adsorption cylinder 14 Hollow part 16 Discharge electrode 18 Ground electrode 20 High voltage power supply 22 Three-way catalyst 30 Storage reduction catalyst

Claims (4)

In the exhaust gas purification device provided in the middle of the exhaust gas pipeline,
A cylindrical HC adsorption cylinder having a hollow portion provided in a tubular container,
A three-way catalyst provided in the vessel at a downstream portion of the exhaust gas flow from the HC adsorption column,
A plasma discharge unit formed by a discharge electrode provided in the hollow portion of the HC adsorption column so as to extend in the direction of the exhaust gas flow and a ground electrode provided on the outer surface of the HC adsorption column;
An exhaust gas purifying device comprising: In the exhaust gas purification device provided in the middle of the exhaust gas pipeline,
A cylindrical HC adsorption cylinder having a hollow portion provided in a tubular container,
A composite catalyst formed of at least two catalysts filled and supported in the hollow portion of the HC adsorption cylinder;
A three-way catalyst provided in the vessel downstream of the exhaust gas flow relative to the HC adsorption column,
A plasma discharge unit formed by a discharge electrode provided at the center of the composite catalyst so as to extend in the direction of the exhaust gas flow and a ground electrode provided on the outer surface of the HC adsorption cylinder;
An exhaust gas purifying device comprising: The composite catalyst has a concentric cross section orthogonal to a longitudinal center axis of the HC adsorption cylinder, and a first catalyst and a second catalyst arranged in the order of increasing activation temperature from the center axis toward the outer periphery. The exhaust gas purifying apparatus according to claim 2, comprising: The exhaust gas purifying apparatus according to claim 3, wherein the first catalyst is a three-way catalyst, and the second catalyst is a NOx storage reduction catalyst.

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