JP2011099341A - Plasma reactor and exhaust emission control device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma reactor which eliminates hazardous substances such as NOx and particulates in an emission through an oxidation/reduction reaction by employing plasma discharge and which can be inexpensively manufactured with a simple structure and with high durability, and an exhaust emission control device using the same. <P>SOLUTION: A plasma reactor keeps honeycomb members 10H in a plurality of rows and columns, embeds even rows in a honeycomb gas passage 25 and odd rows in a conductive member 3 taken as an electrode, produces plasma discharge by independently applying high voltage to the conductive member 3 divided into an upstream side and downstream side sandwiching the honeycomb gas passage 25 therebetween, oxidises to eliminate particulates by ozone and active oxygen generated through the plasma discharge, makes a wall surface absorb NOx under the plasma discharge at low temperature and reduces to eliminate NOx discharged at high temperature. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention adsorbs harmful substances such as NO _x and particulate matter (PM) contained in exhaust gas discharged from a prime mover such as a diesel engine and a gasoline engine, or combustion equipment such as a burner and a boiler. The present invention relates to a plasma reactor for eliminating exhaust gas and purifying exhaust gas, and an exhaust gas purifying apparatus using the plasma reactor.

Diesel engines have high thermal efficiency, and as a result, the spread of diesel vehicles will contribute to the prevention of global warming. In addition, harmful substances such as carbon-based particulate matter (PM), NO _x , and organic compounds emitted from diesel engines are harmful to the human body and have been regulated in recent years to further reduce their emissions. ing. Because the temperature of exhaust gas discharged from diesel vehicles is low, the technology for reducing harmful substances by plasma reaction is said to be effective for removing PM. Conventionally, it is known that it is effective to reduce PM discharged from an engine or a combustor using a plasma reaction in an exhaust gas purification device.

As an under-plasma NO _x purification method and apparatus therefor, it is known that exhaust gas can efficiently remove NO _x from a low temperature to a high temperature. The plasma under NO _X purification method, when the exhaust gas temperature is below operating temperature of the NO _X purification catalyst, discharged near the surface of the plasma under NO _X adsorbent exhibiting a weakly basic, with a reducing agent-containing exhaust gas atmosphere by generating plasma by adsorbing NO _X in the plasma under NO _X adsorbent, it stops discharging when the exhaust gas temperature is operating temperatures more of the NO _X purification catalyst. To release plasma under NO _X NO _X which has been adsorbed by the adsorbent leads to a NO _X that was released from the plasma under NO _X adsorbent and NO _X in the exhaust gas in the NO _X purification catalyst, purification process of the NO _X (For example, refer to Patent Document 1).

  Conventionally known plasma reactors have a case body having a plasma generating electrode and a gas flow path containing a predetermined component inside, and when the gas is introduced into the gas flow path of the case body, the plasma reaction is performed. The predetermined component contained in the gas reacts with the plasma generated by the generator electrode. The plasma generating electrode includes two or more plate-like unit electrodes opposed to each other, can generate plasma by applying a voltage between the unit electrodes, and the unit electrode is a ceramic that is a dielectric. A body, a conductive film disposed on one surface of the ceramic body, and a first protective film composed of a metal film disposed to cover the exposed surface of the conductive film Yes (see, for example, Patent Document 2).

  As a method of manufacturing a plasma electrode, a plasma electrode for producing plasma by applying a voltage is prepared, and a dielectric is formed by coating glass on the electrode body by dip coating. (See, for example, Patent Document 3).

As an exhaust gas purification method and apparatus therefor, an efficient one that effectively purifies NO _{x in} exhaust gas and causes no energy loss is known. In the exhaust gas purification method, when the exhaust gas temperature is lower than the operating temperature of the NO _x storage reduction catalyst, a discharge is performed by applying a high voltage between the electrodes by a signal from the control device based on a signal from the temperature sensor, A plasma state is generated, and the generated plasma is brought into contact with the base component and / or the surface of the noble metal supported on the NO _x storage reduction catalyst so that NO _x is adsorbed in the lean state and NO in the rich state. _{When X} is reduced and the exhaust gas temperature from the internal combustion engine is equal to or higher than the operating temperature of the NO _X storage reduction catalyst, no voltage is applied between the electrodes, discharge and plasma generation are stopped, and NO _X is stopped. The exhaust gas purification process is performed in the presence of HC by the storage reduction catalyst (see, for example, Patent Document 4).

JP 2001-182525 A Japanese Patent Laying-Open No. 2005-93107 JP 2009-117175 A JP 2001-164927 A

Incidentally, the exhaust gas purifying apparatus, a plasma reaction utilizing an exhaust gas particulate matter contained in the (PM), in order eliminate harmful substances such as NO _X, and the active oxygen species generated by the plasma discharge PM efficiency It was necessary to make contact and oxidize. In the plasma reactor, it is necessary to generate a plasma discharge in a discharge space at a predetermined location. The exhaust gas purification devices that have been developed so far incorporate a plasma reactor with a ceramic honeycomb structure in the exhaust gas passage to remove and eliminate PM and NO _x in the exhaust gas using plasma discharge. The structure was complicated, the strength could not be secured, the honeycomb structure was damaged, the plasma discharge could not be generated stably, and most of them were not practical.

An object of the present invention is to solve the above-mentioned problem, in which a large number of honeycomb passages are arranged in a plurality of rows by ceramic honeycomb members, and even-numbered honeycomb passages are configured as honeycomb gas passages and are odd-numbered. Conductive members serving as electrodes are embedded in the honeycomb passages in a row, and a high voltage is independently applied to the conductive members separated on the upstream side and downstream side across the honeycomb gas passages to generate plasma discharges. Either the upstream side or the downstream side of the gas, the particulate matter contained in the exhaust gas is oxidized and disappeared by ozone or active oxygen generated by plasma discharge, and on the other hand, NO _x is adsorbed on the wall surface in the plasma discharge environment, and plasma discharge It is intended to release the NO _X in the stop reduced loss, a plasma discharge with stably generate the discharge space of the honeycomb gas passage, high honeycomb member It has a simple and strong honeycomb structure, can withstand repeated loads of high vibrations and temperature changes in automobiles, etc., ensures high durability, and can be manufactured very easily, inexpensively, and at a significantly reduced cost. It is an object to provide a plasma reactor and an exhaust gas purification apparatus using the plasma reactor.

The present invention is disposed in an exhaust gas passage for discharging exhaust gas from the engine or combustion equipment, NO _X contained in the exhaust gas, said harmful substances such as particulate matter abolished by plasma discharge In a plasma reactor that purifies exhaust gas,
In the honeycomb member made of ceramics in which a plurality of honeycomb passages having a polygonal, elliptical, or circular cross section are arranged in a plurality of rows and in a plurality of rows, the even-numbered honeycomb passages are configured as honeycomb gas passages and the odd-numbered honeycombs Embed a conductive member constituting the electrode in the passage,
Forming a honeycomb structure that can be applied to a high voltage capable of plasma discharge by electrically insulating the conductive members sandwiching the honeycomb gas passage;
The conductive member of the honeycomb structure is divided into upstream and downstream conductive members that can individually apply the high voltage to the upstream side and the downstream side of the honeycomb gas passage,
When the exhaust gas temperature is low, the high voltage is applied between both electrodes of the conductive member, and at least one of the upstream side and the downstream side of the honeycomb gas passage adsorbs the NO _x , and the other side Oxidized and burned by active oxygen or ozone generated by the plasma discharge by adsorbing particulate matter,
The exhaust gas temperature at high temperatures of not discharged the NO _X which stops the application of a high voltage for between one of the electrodes on the upstream side or downstream side of the conductive member was adsorbed at low temperatures, is between the other of said electrodes subsequently continuing the adsorption and oxidative combustion of the high voltage the particulate material was applied was discharged from the wall surface of the honeycomb gas passage and the NO _X in the exhaust gas in response to the supply of the NO _X reducing agent The present invention relates to a plasma reactor characterized in that the exhaust gas is purified by reducing the NO _x to N ₂ .

  The central portion of the rib constituting the honeycomb member is made of a dense ceramic having an insulating property and a high dielectric constant selected from alumina, cordierite, aluminum nitride, aluminum titanate, and zeolite, and the honeycomb gas passage The inner surface of is made of porous ceramics. Further, the dense ceramic constituting the central portion of the rib constituting the honeycomb member and the porous ceramic constituting the inner surface of the honeycomb gas passage are made of the same ceramic material.

  Further, a part of the inner surface of the honeycomb gas passage is wash-coated with γ-alumina, zeolite, or a wash-coat material made of γ-alumina and zeolite. Further, an oxidation catalyst is supported on the washcoat material.

  In addition, the conductive member is fired by applying a conductive paste to a metal plate, a metal mesh, or a wall surface of the honeycomb passage inserted into the honeycomb passage. Further, the conductive member contains 50 wt% or more of tungsten or molybdenum. The honeycomb passage in which the conductive member is disposed is sealed with a sealing material such as a non-breathable ceramic material.

An NO _x reduction catalyst is supported on at least a part of the wall surface constituting the honeycomb gas passage.

  The plasma generating power source for applying a high voltage to the electrodes of the upstream conductive member and the downstream conductive member is a high frequency pulse power source.

Further, the present invention is disposed in the exhaust gas passage for discharging exhaust gas from the engine or combustion equipment, NO _X contained in the exhaust gas, and the harmful substances such as particulate matter abolished by plasma discharge In the exhaust gas purification device for purifying the exhaust gas,
In the exhaust gas passage, the plasma reactor according to any one of claims 1 to 10 is disposed,
Wherein and plasma reactor NO _X reduction device for supplying NO _X reducing agent to the exhaust gas passage upstream of is disposed, the NO _X is by the NO _X reducing agent supplied from the NO _X reduction device The present invention relates to an exhaust gas purification apparatus using plasma discharge, wherein the exhaust gas is purified by being reduced.

Further, the plasma generation power source is ON / OFF in response to the exhaust gas temperature is controlled, the NO _X given temperature the electrodes of the conductive member of the suction side of the exhaust gas temperature is predetermined in the following It is turned on in the low temperature region and turned off in the higher temperature region, and the electrode of the conductive member on the side where the particulate matter is oxidized and burned is controlled to be always turned on. Further, the NO _x reduction device is controlled to be turned on / off in response to the exhaust gas temperature, and is turned off in a low temperature region where the exhaust gas temperature is lower than a predetermined temperature, and is turned on in a higher temperature region. Is controlled.

  The reducing agent is ammonia, urea, or a hydrocarbon such as light oil, gasoline, or alcohol. The temperature of the exhaust gas flowing into the plasma reactor is controlled by operation of an intake throttle, post-injection, a fuel injection device disposed upstream of the oxidation catalyst device, or an exhaust shutter.

Since the plasma reactor and the exhaust gas purification apparatus using the plasma reactor according to the present invention are configured as described above, the exhaust gas discharged from the engine, the combustion equipment, etc. flows from the inlet at one end and is formed in the honeycomb member. The purified exhaust gas flows out from the outlet of the other end, and when the exhaust gas is at a low temperature, a high voltage is applied between the high-voltage side electrode and the ground-side electrode made of a conductive member. Is applied to the discharge space of the honeycomb gas passage to form a plasma discharge atmosphere. Particulate matter adhering to the inner surface, which is one of the upstream or downstream wall surfaces of the honeycomb gas passage, or particulate matter in the exhaust gas is removed. ozone was generated by plasma reaction, together with the exhaust gas become the carbon dioxide is purified by active oxygen adsorption and discharge failure of the NO _X in the exhaust gas to the inner surface which is the other wall NO _X by repeating the out is reduced to N ₂ in the presence of the NO _X reducing agent, thereby being purified exhaust gas, also in one of the conductive members on the upstream side or downstream side at all times high voltage Because of the plasma discharge atmosphere, particulate matter in the exhaust gas is constantly purified by the plasma reaction. Specifically, when the exhaust gas is at a low temperature, NO _x is adsorbed on the wall of the honeycomb gas passage such as γ aluminum in the plasma discharge atmosphere. is, when the exhaust gas temperature becomes high, the plasma discharge is to OFF, since the NO _X which has been adsorbed on the wall surface ever is released, NO _X by here supplying NO _X reducing agent reduction to N ₂ The exhaust gas is purified, the structure itself is simplified, and the plasma discharge is surely generated in response to the exhaust gas temperature between the electrodes of the conductive member. The device itself can be configured with a simple structure with high strength, and the manufacturing cost can be reduced.

It is explanatory drawing which shows one Example which comprises the exhaust gas purification apparatus using the plasma reactor by this invention. FIG. 2 is a front view showing an end face on the exhaust gas inflow side showing a ceramic honeycomb member in the exhaust gas purifying apparatus in FIG. 1. FIG. 3 is a cross-sectional view taken along the line AA of FIG. The plasma reactor shows the exhaust gas purifying state of the exhaust gas purification apparatus using the a graph exhaust gas temperature indicates the characteristics of the proportion discharging the adsorption rate of the NO _X on the wall surface of the honeycomb gas passage. 3 is a graph showing NO _X reduction characteristics with respect to the exhaust gas temperature of a NO _X reduction catalyst or NO _X reducing agent.

Embodiments of an exhaust gas purifying apparatus using a plasma reactor according to the present invention will be described below. This exhaust gas purification device generally uses plasma discharge for harmful substances such as NO _x and particulate matter contained in exhaust gas G discharged from combustion engines such as prime movers such as diesel engines and gasoline engines, boilers, and burners. And exhaust gas G is purified.

Hereinafter, an embodiment of an exhaust gas purification apparatus using a plasma reactor according to the present invention will be described with reference to the drawings.
As shown in FIGS. 1 to 3, this exhaust gas purification device is accommodated in a housing 17, and the housing 17 is exhaust gas from an engine such as a diesel engine or a gasoline engine or combustion equipment such as a boiler or a burner. It is used by being disposed in an exhaust gas passage that discharges gas. An exhaust gas passage 21 communicating with the exhaust gas passage is formed in the housing 17 in the axial direction, that is, in the flow direction, an inlet 22 through which exhaust gas G flows is formed at one end, and the plasma reactor 6 is disposed in the middle. , An outlet 23 through which the exhaust gas G flows out is formed at the other end. This exhaust gas purification device adsorbs NO _x , particulate matter (PM), soot and other harmful substances contained in the exhaust gas G on the inner wall surface 8 of the honeycomb gas passage 25 formed in the honeycomb passage 7, These harmful substances are oxidized and reduced with the help of plasma discharge to disappear, and the exhaust gas G is purified. As shown in FIG. 2, the plasma reactor 6 has a plurality of stages (7 stages in FIGS. 1 and 2) of honeycomb passages 7 having a polygonal, elliptical, or circular cross section (in FIG. 2, the cross section is square). The ceramic honeycomb members 10H are arranged in a plurality of rows (four rows in FIG. 2), and are housed in the housing 17 via the heat insulating material 16 as shown in FIG.

  As shown in FIG. 1, this exhaust gas purifying apparatus is configured such that the exhaust gas passage 21 in the housing 17 has a plasma reactor 6 made of a honeycomb structure 10 and a hydrocarbon in the exhaust gas passage 21 upstream of the plasma reactor 6. A reducing agent supply device 28 for supplying a reducing agent 14 such as system gas, fuel, ammonia, urea or the like is disposed. The plasma generator 12, which is a high-pressure pulse power supply, and the reducing agent supply device 28 are ON / OFF controlled by the controller 20 in response to the exhaust gas temperature of the exhaust gas G flowing through the exhaust gas passage 21. It is configured. The exhaust gas temperature can be detected by the temperature sensor 11 installed at the inlet 22 in the housing 17.

The plasma reactor 6 includes a honeycomb structure 10 composed of a honeycomb member 10H and a conductive member 3 that serves as an electrode. When the exhaust gas G flows through the honeycomb gas passage 25 formed in the honeycomb member 10H, harmful substances disappear. Thus, the exhaust gas G is purified. The honeycomb gas passage 25 in the honeycomb structure 10 is formed in a high-strength open type with a simple structure in which both ends penetrate from the upstream side to the downstream side. The plasma reactor 6 has a honeycomb structure 10 in which the even-numbered honeycomb passages 7 in the honeycomb member 10H are configured as the honeycomb gas passages 25 and the conductive member 3 is embedded in at least a part of the odd-numbered honeycomb passages 7. ing. The honeycomb passage 7 constituting the honeycomb gas passage 25 has a larger cross-sectional area than the honeycomb passage 7 in which the conductive member 3 is embedded, and is formed, for example, about 7 to 20 times. The conductive members 3 arranged in the honeycomb passages 7 are individually insulated by being surrounded by a sealing material 27 made of dense ceramics, that is, non-breathable ceramics. In the plasma reactor 6, the conductive members 3 sandwiching the honeycomb gas passage 25 are electrically insulated and can be applied to a high voltage capable of plasma discharge. with adsorbed to oxidative combustion of substances like, it is intended to eliminate by reducing NO _X to N ₂ by supplying NO _X reducing agent 14 by adsorbing NO _X.

In the plasma reactor 6, in particular, the conductive member 3 constituting the high-voltage side electrode 4 is such that at least the positive electrode side of the applied voltage is connected to the upstream conductive member 18 on the positive electrode side and the downstream conductive member 19 on the positive electrode side of the plasma reactor 6. It is characterized by being divided by the insulating member 32 and being energized individually or independently by the controller 20. Therefore, in the plasma reactor 6, the honeycomb gas passage 25 is controlled to a plasma discharge atmosphere or a plasma non-discharge atmosphere independently on the upstream side and the downstream side. In the plasma reactor 6, at least one conductive member 18 (or 19) on the upstream side or downstream side is always controlled to a plasma discharge atmosphere, and particulate matter in the exhaust gas is oxidized and burned, and the other conductive member 19 (or 18) is controlled NO _X during the exhaust gas temperature is low temperature plasma discharge atmosphere adsorbed on the inner wall surface 8 of the honeycomb gas passage 25, or the NO _X at high temperatures in the plasma non-discharge atmosphere exhaled from the inner wall surface 8 of the honeycomb gas passage 25 Is. When NO _x is discharged from the honeycomb gas passage 25, the NO _x reducing agent 14 is supplied to control NO _x to be reduced to NO ₂ . The upstream conductive member 18 is connected to the plasma generating power source 12 via a high voltage line 29, and the downstream conductive member 19 is connected to the plasma generating power source 12 via a high voltage line 30. The conductive member 3 constituting the ground side electrode 5 does not need to be divided like the high voltage side electrode 4 and is formed on the ground side conductive member 24 that is continuous in the axial direction of the honeycomb member 10H. The ground side conductive member 24 is connected to the ground 33 through the ground line 31. In the plasma reactor 6, the conductive member 3 is configured by applying a conductive paste to a metal plate inserted in the honeycomb passage 7, a metal mesh, or a wall surface of the honeycomb passage 7 and firing it. Further, the conductive member 3 is made of a material containing 50 wt% or more of tungsten or molybdenum.

  In the plasma reactor 6, the central portion of the rib 26 constituting the honeycomb member 10H is composed of a dense ceramic 1 having an insulating property selected from alumina, cordierite, aluminum nitride, aluminum titanate, and zeolite and a high dielectric constant. Further, the inner wall surface 8 of the honeycomb gas passage 25 is composed of the porous ceramic 2. The dense ceramic 1 constituting the central portion of the rib 26 constituting the honeycomb member 10H and the porous ceramic 2 constituting the inner wall surface 8 of the honeycomb gas passage 25 are made of the same ceramic material. Therefore, both the dense ceramic 1 and the porous ceramic 2 are firmly bonded to each other, and the honeycomb structure 10 is preferable in terms of strength. Further, in the honeycomb gas passage 25 made of the honeycomb member 10, a part of the porous ceramic 2 constituting the inner wall surface 8 is covered with the washcoat material 15. The wash coat material 15 is made of porous ceramics by being coated with γ-alumina, zeolite, or a material composed of γ-alumina and zeolite, on which an oxidation catalyst is supported. Further, the conductive member 3 is fired by applying a conductive paste to a metal plate, a metal mesh, or a wall surface of the honeycomb passage 7 inserted in a honeycomb passage 7 which is a cavity previously formed in ceramics, and sealing the insulating layer. It is arranged in a state embedded in the stop material 27. Further, the conductive member 3 is made of a material containing 50 wt% or more of tungsten or molybdenum.

  This exhaust gas purification device is provided with a temperature sensor 11 at the inlet 22 of the housing 17 and is configured to detect the temperature of the inflowing exhaust gas. The exhaust gas temperature measured by the temperature sensor 11 is input to the controller 20 as information. The reducing agent supply device 28 is ON / OFF controlled by the controller 20 in response to the exhaust gas temperature, and is set to be turned off when the exhaust gas temperature is lower than a predetermined temperature, and is turned on when the exhaust gas temperature is higher than that. Is done. The plasma generating power source 12 of the high voltage power source is ON / OFF controlled by the controller 20 in response to the exhaust gas temperature. In particular, the upstream conductive member 18 (or the downstream conductive member 19) is an exhaust gas. The gas temperature is controlled to be turned on at a low temperature below a predetermined temperature, and is turned off at a higher temperature, and the downstream conductive member 19 (or the upstream conductive member 18) is controlled to be always turned on. ing. Therefore, in the honeycomb gas passage 25, the plasma discharge environment is turned ON / OFF on the upstream side (or downstream side), and the plasma discharge environment is always on the downstream side (or upstream side). Further, this exhaust gas purification device is provided upstream of an intake throttle, a post-injection, and an oxidation catalyst purification device (not shown) to control the temperature of exhaust gas flowing into the plasma reactor 6, although not shown. A fuel injection device and / or an exhaust shutter are provided, and the exhaust gas temperature is controlled by these operations.

The reducing agent supply device 28 can use, for example, hydrocarbon gas, fuel such as light oil, ammonia, urea or the like as the NO _x reducing agent 14, and exhaust gas in the housing 17 on the upstream side of the plasma reactor 6. It is provided in the passage 21 and is configured to inject the reducing agent 14 such as pressurized fuel upstream of the plasma reactor 6 through the fuel injection nozzle 9 in accordance with a command from the controller 20. The pressurized fuel (reducing agent 14) injected from the fuel injection nozzle 9 into the plasma reactor 6 is pressurized with engine light oil by a pump (not shown) and sent to the fuel injection nozzle 9, for example. It is configured. The light oil injected from the fuel injection nozzle 9 is droplets or vaporized light oil. Further, in this exhaust gas purification device, an oxidation catalyst is supported on at least a part of the wall surface of the honeycomb gas passage 25. The porous ceramics 2 constituting the inner wall surface 8 is formed by firing integrally with the honeycomb member 10H. In this exhaust gas purification device, NO _x and particulate matter are adsorbed on the surface of γ-alumina or the like constituting the inner wall surface 8 of the honeycomb gas passage 25 when the exhaust gas temperature is low and plasma discharge is performed.

  The conductive member 3 of the upstream conductive member 18 and the downstream conductive member 19 constituting the high voltage side electrode 4 causes plasma discharge between the high voltage side electrode 4 and the ground side electrode 5 composed of the ground side conductive member 24. It is connected to the plasma generating power source 12 so that a high voltage for generating it is applied. The conductive member 3 is disposed with the honeycomb gas passage 25 interposed therebetween, and the positive-side conductive member 3 constituting the high-voltage side electrode 4 is divided into an upstream-side conductive member 18 and a downstream-side conductive member 19. The upstream side conductive member 18 and the downstream side conductive member 19 constituting the high voltage side electrode 4 are connected to the plasma generating power source 12 of the high voltage power source through the high voltage power source lines 29 and 30, and the ground side electrode 5 is It is connected to the earth 33 through the earth line 31.

In this exhaust gas purification device, the high voltage applied to the conductive member 3 is supplied from the plasma generating power source 12 as a high frequency pulse power source. In this exhaust gas purification device, when the conductive member 3 is applied to generate plasma discharge, NO _x and particulate matter are adsorbed on the inner wall surface 8 of the honeycomb gas passage 25, and the adsorbed particulate matter is oxidized and burned. together is to incinerate, adsorbed NO _X is caused to reduced loss is discharged by the plasma discharge is stopped, the exhaust gas G is purified.

FIG. 4 shows the exhaust gas purification state of the exhaust gas purification device, and shows the characteristics of the NO _x adsorption ratio and the discharge ratio that the exhaust gas temperature exerts on the wall surface of the honeycomb gas passage 25. The results of testing the NO _x adsorption rate in the state where the inner wall surface 8, that is, the inner surface, is washed with γ alumina are shown as a graph. During cold exhaust gas temperature is 100 ° C., the adsorption rate of the NO _X in the plasma discharge environment as high as 100%, while the adsorption rate of the NO _X exhaust gas temperature up to 300 ° C. is maintained very high, exhaust As the gas temperature rises, the adsorption ratio decreases. At 400 ° C, the molecular motion becomes active and the adsorption ratio is close to 0%. At 400 ° C and above, the adsorption ratio is almost 0%. At 350 ° C., the NO _x discharge rate was almost 0%, but when the exhaust gas temperature rose to 400 ° C., the discharge rate started to increase, and at 550 ° C., the discharge rate became nearly 100%. On the other hand, the active region of NO _x reduction catalyst and reducing agent is different depending on the type, but the reduction to N _{2 in} the low temperature range of about 200 ° C is small, and the reduction rate increases as the exhaust gas temperature rises. Yes. On the other hand, in the active region of the NO _x reduction catalyst and reducing agent shown in FIG. 5, the reduction rate is low at 300 ° C. or lower, and the ability to reduce NO _x to N ₂ is extremely high at 350 ° C. to 450 ° C. . Therefore, when the exhaust gas temperature is low, NO _x is once trapped or adsorbed on the wall surface of the honeycomb gas passage 25, the exhaust gas temperature becomes high and the plasma discharge is stopped, and NO _x is released from the wall surface of the honeycomb gas passage 25. In other words, the reducing agent is supplied to the honeycomb gas passage 25 at the same time, and the high reducing ability of NO _x to N ₂ is exhibited. That is, in view of the suction-ejecting characteristics for the wall of the porous ceramic honeycomb gas passage 25 of the NO _X, the NO _X from the exhaust gas G is adsorbed at low temperatures, the N ₂ by ejecting NO _X at a high temperature The controller 20 is configured to control to supply the reducing agent 14 from the reducing agent supply device 28 to the honeycomb gas passage 25 in response to a high temperature of the exhaust gas so as to reduce and disappear.

This exhaust gas purification device is configured as described above. Exhaust gas G exhausted from the engine or combustion equipment flows from the inlet 22 of the housing 17, and the exhaust gas flowing into the housing 17 is first exhausted. The gas G flows from the inlet of the plasma reactor 6 into the honeycomb gas passage 25. The inner wall surface 8 of the honeycomb gas passage 25, since the oxidation catalyst is supported, is oxidized convert NO in the exhaust gas to NO _2. The exhaust gas G flowing into the honeycomb gas passage 25 passes along the wall surface made of porous ceramics. At this time, if the exhaust gas temperature is high, particles trapped on the inner wall surface 8 of the porous ceramics 2 The particulate matter PM is extinguished by an oxidation reaction, passes through the honeycomb gas passage 25, and is discharged from the outlet.

In this exhaust gas purification device, when the exhaust gas temperature is low, the exhaust gas flows in from the inlet of the honeycomb gas passage 25 and then flows out along the inner wall surface 8 of the porous ceramics 2. Since the gas passage 25 is in a plasma discharge environment, when a high voltage is applied between the high-voltage side electrode 4 and the ground-side electrode 5 of the conductive member 3, plasma discharge occurs, and the inner wall surface 8 of the honeycomb gas passage 25. Particulate matter adhering to the gas becomes carbon dioxide (CO ₂ ) by ozone and active oxygen generated by plasma discharge, and is discharged from the outlet. On the other hand, as shown in the graph of FIG. 4, when the exhaust gas temperature is low, the high voltage side electrode 4 is ON, so that NO _x is applied to the inner wall surface 8 made of porous ceramics 2 such as γ alumina under plasma discharge. Adsorbed. On the other hand, when the exhaust gas temperature becomes high, the plasma discharge is turned off, and when the plasma discharge is turned off, the NO _x that has been adsorbed on the inner wall surface 8 is released, that is, exhaled. Is operated, the reducing agent 14 is supplied, NO _x is reduced to N ₂ , and the exhaust gas G is purified. Further, in this exhaust gas purification device, when the exhaust gas temperature is high, the particulate matter can be reacted and burned by the oxidation catalyst, so that it is sufficient to turn on only the downstream conductive member 19 for plasma discharge.

The plasma reactor according to the present invention and the exhaust gas purifying apparatus using the plasma reactor are particulate matter such as soot, black smoke, NO _x, etc. contained in the exhaust gas from a prime mover such as a diesel engine or combustion equipment such as a burner or boiler. These harmful substances are preferably used for oxidative combustion using ozone generated by plasma discharge or active oxygen, or for reduction and extinction.

DESCRIPTION OF SYMBOLS 1 Dense ceramics 2 Porous ceramics 3 Conductive member 4 High voltage side electrode 5 Ground side electrode 6 Plasma reactor 7 Honeycomb passage 8 Inner wall surface (porous ceramics)
9 Fuel injection nozzle 10 Honeycomb structure 10H Honeycomb member 11 Temperature sensor 12 Power source for plasma generation (high voltage power source)
14 NO _X reducing agent (light oil, fuel)
DESCRIPTION OF SYMBOLS 15 Wash-coat material 16 Heat insulating material 17 Housing 18 Upstream conductive member 19 Downstream conductive member 20 Controller 21 Exhaust gas passage 24 Ground side conductive member 25 Honeycomb gas passage 26 Rib (honeycomb member)
27 Sealing material 28 Reducing agent supply device 32 Insulating member G Exhaust gas

Claims (15)

It is disposed in the exhaust gas passage that exhausts exhaust gas from the engine or combustion equipment, and purifies the exhaust gas by using plasma discharge to eliminate harmful substances such as NO _x and particulate matter contained in the exhaust gas In a plasma reactor that
In the honeycomb member made of ceramics in which a plurality of honeycomb passages having a polygonal, elliptical, or circular cross section are arranged in a plurality of rows and in a plurality of rows, the even-numbered honeycomb passages are configured as honeycomb gas passages and the odd-numbered honeycombs Embed a conductive member constituting the electrode in the passage,
Forming a honeycomb structure that can be applied to a high voltage capable of plasma discharge by electrically insulating the conductive members sandwiching the honeycomb gas passage;
The conductive member of the honeycomb structure is divided into upstream and downstream conductive members that can individually apply the high voltage to the upstream side and the downstream side of the honeycomb gas passage,
When the exhaust gas temperature is low, the high voltage is applied between both electrodes of the conductive member, and at least one of the upstream side and the downstream side of the honeycomb gas passage adsorbs the NO _x , and the other side Oxidized and burned by active oxygen or ozone generated by the plasma discharge by adsorbing particulate matter,
The exhaust gas temperature at high temperatures of not discharged the NO _X which stops the application of a high voltage for between one of the electrodes on the upstream side or downstream side of the conductive member was adsorbed at low temperatures, is between the other of said electrodes subsequently continuing the adsorption and oxidative combustion of the high voltage the particulate material was applied was discharged from the wall surface of the honeycomb gas passage and the NO _X in the exhaust gas in response to the supply of the NO _X reducing agent A plasma reactor, wherein the exhaust gas is purified by reducing the NO _x to N ₂ .   The central portion of the rib constituting the honeycomb member is made of a dense ceramic having an insulating property and a high dielectric constant selected from alumina, cordierite, aluminum nitride, aluminum titanate, and zeolite, and the inner surface of the honeycomb gas passage The plasma reactor according to claim 1, wherein the plasma reactor is made of porous ceramics.   The dense ceramic constituting the central portion of the rib constituting the honeycomb member and the porous ceramic constituting the inner surface of the honeycomb gas passage are made of the same ceramic material. The plasma reactor according to claim 2.   4. The plasma reactor according to claim 2, wherein a part of the inner surface of the honeycomb gas passage is wash-coated with γ-alumina, zeolite, or a wash-coat material made of γ-alumina and zeolite.   The plasma reactor according to claim 4, wherein an oxidation catalyst is supported on the washcoat material.   6. The conductive member according to claim 1, wherein the conductive member is fired by applying a conductive paste to a metal plate inserted in the honeycomb passage, a metal mesh, or a wall surface of the honeycomb passage. A plasma reactor according to claim 1.   The plasma reactor according to claim 1, wherein the conductive member contains 50 wt% or more of tungsten or molybdenum.   The plasma reactor according to any one of claims 1 to 7, wherein the honeycomb passage in which the conductive member is disposed is sealed with a sealing material such as a non-breathable ceramic material. . The plasma reactor according to any one of claims 1 to 8, wherein a NO _x reduction catalyst is supported on at least a part of the wall surface constituting the honeycomb gas passage.   10. The plasma generation power source for applying a high voltage to the electrodes of the upstream conductive member and the downstream conductive member is a high frequency pulse power source. The plasma reactor as described. It is disposed in an exhaust gas passage that exhausts exhaust gas from an engine or combustion equipment, and purifies the exhaust gas by using a plasma discharge to eliminate harmful substances such as NO _x and particulate matter contained in the exhaust gas. In exhaust gas purification equipment,
In the exhaust gas passage, the plasma reactor according to any one of claims 1 to 10 is disposed,
Wherein and plasma reactor NO _X reduction device for supplying NO _X reducing agent to the exhaust gas passage upstream of is disposed, the NO _X is by the NO _X reducing agent supplied from the NO _X reduction device An exhaust gas purification apparatus using plasma discharge, wherein the exhaust gas is purified by being reduced. The plasma generation power source is controlled ON / OFF in response to the exhaust gas temperature, the NO _X of the electrode is low below the exhaust gas temperature is given to a predetermined temperature of the conductive member of the suction side 12. The plasma discharge according to claim 11, wherein the plasma discharge is controlled to be turned on in a region and turned off in a higher temperature region, and the electrode of the conductive member on the side for oxidizing and burning the particulate matter is always turned on. Exhaust gas purification device using. The NO _X reduction device is controlled to be turned on / off in response to the exhaust gas temperature, and is turned off in a low temperature region where the exhaust gas temperature is equal to or lower than a predetermined temperature, and is turned on in a higher temperature region. The exhaust gas purifying apparatus using plasma discharge according to claim 11 or 12, wherein the exhaust gas purifying apparatus uses plasma discharge.   The exhaust gas purification apparatus using plasma discharge according to any one of claims 11 to 13, wherein the reducing agent is ammonia, urea, or a hydrocarbon such as light oil, gasoline, alcohol, or the like.   The temperature of the exhaust gas flowing into the plasma reactor is controlled by operation of an intake throttle, post-injection, a fuel injection device disposed upstream of the oxidation catalyst device, or an exhaust shutter. An exhaust gas purification apparatus using the plasma discharge according to any one of 11 to 14.

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