JP4717755B2 - Nitrogen oxide treatment apparatus and method - Google Patents

Description

  The present invention relates to a nitrogen oxide treatment apparatus and method, and more particularly to a nitrogen oxide treatment apparatus and method for reducing and removing nitrogen oxide from automobile exhaust gas.

  Exhaust gas emitted from gasoline and diesel engines contains harmful substances such as nitrogen oxides (NOx), hydrocarbons (HC), and carbon monoxide (CO), and technology to remove these harmful substances As a conventional method, a reduction method using a three-way catalyst is known. In this three-way catalyst method, platinum, palladium, and rhodium are added on the basis of alumina and a catalyst is used to simultaneously perform an oxidation reaction of HC and CO and a reduction reaction of NOx, respectively.

  In a diesel engine, an EGR device (exhaust gas recirculation device) is used to reduce the amount of NOx emissions. This EGR device suppresses the combustion temperature by recirculating a part of the exhaust from the engine to the intake system, thereby reducing the amount of NOx emission.

  Recently, as a technique for removing NOx from exhaust gas, a reduction treatment technique for NOx by an electrochemical method using a solid electrolyte has attracted attention. As this type of prior art, for example, Patent Document 1 can be cited.

  In Patent Document 1, a cylindrical substrate made of a solid electrolyte that transmits oxygen ions is used, a cathode electrode is disposed on the inner surface of the substrate, an anode electrode is disposed on the outer surface, and a voltage source is connected to the anode and the cathode. Has been.

  When a voltage is applied, an electric field is generated in the substrate, and oxygen ions move from the inner surface to the outer surface of the substrate. When exhaust gas is introduced into the substrate, NO2 contained in the exhaust gas is reduced using the inner surface of the substrate as a cathode.

On the other hand, oxygen ions that have reached the anode side of the outer surface emit electrons and become oxygen gas.
JP 2000-516678 Gazette

When applying a method of reducing NOx electrochemically using a solid electrolyte in this way to purify the exhaust gas of an automobile, a power source is required to apply an electric field to the electrolyte, and usually a car battery is used. become. For this reason, the battery consumption during operation increases, and the alternator load for replenishment increases, so that there is a problem that the fuel consumption decreases.
Accordingly, an object of the present invention is to solve the problems of the prior art, reuse the heat energy of the exhaust gas, apply an electric field to the electrolyte by thermoelectric power generation, and effectively use the heat energy of the exhaust gas. It is an object of the present invention to provide a nitrogen oxide treatment apparatus that can effectively reduce NOx in exhaust gas.

In order to achieve the above object, the present invention provides:
A nitrogen oxide treatment apparatus for decomposing NOx contained in exhaust gas of an internal combustion engine by an electrochemical reduction reaction,
It is made of a solid electrolyte in which oxygen ions move under an electric field, forms an exhaust gas passage through which exhaust gas is introduced, and a reduction region for reducing NOx in the exhaust gas on the high temperature side surface forming the exhaust gas passage. An electrolyte body to be formed;
A temperature difference between the inside and outside of the electrolyte body to generate a voltage for placing the solid electrolyte under an electric field, and a thermoelectric element portion integrally incorporated in the electrolyte body,
The thermoelectric element portion is made of a p-type thermoelectric element, and is characterized in that the p-type thermoelectric element is sandwiched between two catalytic metals that serve as an anode and a cathode, respectively, and sandwich a solid electrolyte .

  According to the present invention, the heat energy of the exhaust gas is reused, and an electric field is applied to the electrolyte by thermoelectric power generation. Therefore, NOx in the exhaust gas is effectively used by effectively using the heat energy of the exhaust gas. In addition, since the structure of the apparatus is a structure in which the solid electrolyte and the thermoelectric element are integrated, a power source, wiring, and the like are not required.

Hereinafter, embodiments of a nitrogen oxide treatment apparatus according to the present invention will be described with reference to the accompanying drawings.
First embodiment
FIG. 1 shows a nitrogen oxide processing apparatus according to a first embodiment of the present invention. In FIG. 1, reference numeral 10 indicates an electrolyte body that reduces NOx in gas.
In this embodiment, the electrolyte body 10 is formed into a tubular body using, for example, a solid electrolyte such as ZrO2 (zirconium dioxide) or YSZ (Y2O2 stabilized zirconia). This type of solid electrolyte has the property that oxygen ions move in the electrolyte when an electric field is applied. By using this property, NOx contained in exhaust gas from internal combustion engines such as diesel engines and gasoline engines is reduced. To do.

  An exhaust gas passage 12 into which exhaust gas is introduced is formed in the electrolyte body 10, and the inner peripheral surface of the electrolyte body 10 is heated to a high temperature by the heat of the exhaust gas, and becomes a NOx reduction region. The outside of the electrolyte body 10 is kept at a low temperature by being cooled by cooling fins.

  In the nitrogen oxide processing apparatus according to the present embodiment, a thermoelectric element is integrally incorporated in the electrolyte body 10 itself, and an electric field for moving oxygen ions in the electrolyte is generated by a voltage generated by the thermoelectric element.

FIG. 2 is a diagram showing an arrangement structure of thermoelectric elements.
In FIG. 2, the thermoelectric element is composed of a combination of a p-type thermoelectric element 14 and an n-type thermoelectric element 15. In this case, as described above, the inner peripheral surface of the electrolyte body 10 is on the high temperature side, and the outside of the thermoelectric element is on the low temperature side. By giving the temperature difference between the inside and outside, a thermoelectromotive force is generated in the p-type thermoelectric element 14 and the n-type thermoelectric element 15, but the voltages have opposite signs. Therefore, the p-type thermoelectric element 14 and the n-type thermoelectric element 15 are directly and alternately connected to each other and arranged on the outer periphery of the electrolyte body 10, whereby the voltages of the respective elements are added to increase the voltage for generating an electric field.

  In this embodiment, each of the p-type thermoelectric element 14 and the n-type thermoelectric element 15 is electrically connected in series to the electrolyte by a conductor insulated via an insulating layer as follows. That is, an anode side catalyst metal 16 such as platinum is interposed between the first n-type thermoelectric element 15 and the electrolyte of the electrolyte body 10. A catalytic metal 17 on the cathode side is attached to the inner peripheral surface of the electrolyte. The first p-type thermoelectric element 14 is connected to the first n-type thermoelectric element 15 via the conductor 18a. The first p-type thermoelectric element 14 and the next n-type thermoelectric element 15 are connected via a conductor 18 b, and the conductor 18 b is insulated from the electrolyte via an insulating layer 19. This n-type thermoelectric element 15 is connected to the last p-type thermoelectric element 14 via a conductor 18c. The last p-type thermoelectric element 14 is electrically connected to the catalyst metal 17 on the cathode side via the conductor 18 d and the metal wire 11.

Next, operations and effects of the first embodiment configured as described above will be described.
In FIG. 1, when the exhaust gas containing NOx is led to the exhaust gas passage 12 of the electrolyte body 10 as indicated by an arrow, a voltage is applied to the p-type thermoelectric element 14 and the n-type thermoelectric element 15 due to the temperature difference between the inside and outside. And the electrolyte of the electrolyte body 10 is placed under an electric field. The catalyst metal 17 on the inner peripheral surface side of the electrolyte body 10 becomes a cathode, and the catalyst metal on the outer peripheral surface side becomes an anode. In the electrolyte, oxygen ions move from the cathode side to the anode side, and electrons move from the anode side. It flows through the array of thermoelectric elements and moves to the cathode.

At this time, a reduction reaction occurs on the cathode side, and nitrogen dioxide in the exhaust gas is decomposed into nitrogen and oxygen.
On the other hand, on the anode side, oxygen ions emit electrons and generate oxygen gas.

  In this way, exhaust gas is introduced into the electrolyte body 10, and an electric field is applied to the electrolyte body 10 by the p-type thermoelectric element 14 and the n-type thermoelectric element 15, so that nitrogen oxides are formed on the inner peripheral surface of the electrolyte body 10. A reduction reaction can be caused. For this reason, it is no longer necessary to recycle the waste heat energy and use a battery as a voltage source. It becomes possible to remove NOx.

Second embodiment
Next, FIG. 3 shows a nitrogen oxide processing apparatus according to a second embodiment of the present invention. In the first embodiment of FIG. 2, the n-type thermoelectric elements and the p-type thermoelectric elements are arranged directly and alternately in the second embodiment of FIG. 3, whereas in the second embodiment of FIG. The type thermoelectric element 20 alone is used.

  That is, the electrolyte of the electrolyte body 10 is sandwiched between the catalyst metal 21 and the catalyst metal 22, and a p-type thermoelectric element 20 that forms a thermoelectric element portion is interposed between the two catalyst metals 21 and 22. It is sandwiched.

  According to such a thermoelectric element portion, the inner catalytic metal 21 side in contact with the exhaust gas becomes high temperature, the outer catalytic metal 22 side becomes low temperature, and a voltage is applied to the p-type thermoelectric element 20 due to the temperature difference between the inside and outside. And the electrolyte of the electrolyte body 10 is placed under an electric field. The catalytic metal 21 serves as a cathode, and the catalytic metal 22 serves as an anode. Within the electrolyte, oxygen ions move from the cathode side to the anode side, and electrons flow from the anode to the cathode inside the p-type thermoelectric element.

At this time, a reduction reaction occurs on the cathode side, and nitrogen dioxide in the exhaust gas is decomposed into nitrogen and oxygen.
On the other hand, on the anode side, oxygen ions emit electrons and generate oxygen gas.

  According to the second embodiment, the p-type thermoelectric element 20 is sandwiched between the electrolyte and the catalytic metals 21 and 22 so that the heat energy of the exhaust gas can be used more efficiently than when combined with the n-type thermoelectric element. Thus, an electric field can be applied to the electrolyte body 10. That is, in general, the p-type thermoelectric element 20 has higher energy conversion efficiency in a high temperature region than the n-type thermoelectric element, so that the cathode side is heated to a high temperature and the anode side is cooled by the heat of the exhaust gas. By increasing the temperature difference by lowering the temperature, the heat energy of the exhaust gas can be efficiently converted into electric energy necessary for the reduction reaction of nitrogen oxides. Further, in comparison with the first embodiment, there is an advantage that it is not necessary to use a metal wire for wiring to form a circuit through which electrons flow. In FIG. 3, an insulator may be interposed between the electrolyte and the p-type thermoelectric element 20.

Third embodiment
FIG. 4 shows a nitrogen oxide processing apparatus according to a third embodiment of the present invention. Both the first embodiment and the second embodiment described above are forms using thermoelectric elements separately from the electrolyte, but in the third embodiment, the electrolyte itself of the electrolyte body 10 is operated as a p-type thermoelectric element. I have to.

  In the third embodiment, a doping process is performed on a solid electrolyte such as ZrO2 (zirconium dioxide) or YSZ (Y2O2 stabilized zirconia) to operate as a p-type thermoelectric element when a temperature difference is given.

  Therefore, the temperature of the inner catalytic metal 21 in contact with the exhaust gas becomes high, the temperature of the outer catalytic metal 22 becomes low, and a voltage is generated in the electrolyte of the electrolyte body 10 due to the temperature difference between the inside and outside, so I'm left. The catalytic metal 21 serves as a cathode, and the catalytic metal 22 serves as an anode. Within the electrolyte, oxygen ions move from the cathode side to the anode side, and electrons flow from the anode to the cathode inside the p-type thermoelectric element. Thereby, the function substantially the same as 2nd Embodiment using a p-type thermoelectric element is realizable, without using an independent thermoelectric element.

Fourth embodiment
Next, a nitrogen oxide processing apparatus according to a fourth embodiment of the present invention will be described with reference to FIG. The fourth embodiment is an embodiment in which the second embodiment is applied to a honeycomb structure 30 in which a plurality of exhaust gas passages 32 are partitioned. In the fourth embodiment, the outer peripheral portion of the honeycomb structure 30 and the partition walls that define the exhaust gas passage 32 are formed of a solid electrolyte. In addition, the solid electrolyte is sandwiched between the catalyst metal 33 on the outer surface of the outer peripheral portion and the catalyst metal 34 on the surface of the partition wall 33. The p-type thermoelectric element 35 is also sandwiched between the catalyst metals 33 and 34, and the outer peripheral portion of the honeycomb structure is on the low temperature side. The exhaust gas passage 32 side becomes the high temperature side, and a voltage is generated in the p-type thermoelectric element 35 due to this temperature difference, so that the solid electrolyte is placed in an electric field.

  According to the fourth embodiment, by adopting a structure in which the exhaust gas passage 32 is formed using the honeycomb structure 30 and the p-type thermoelectric element 35 is incorporated, the area of the region where nitrogen oxides are reduced is reduced. Since it can be increased, it is possible to increase the decomposition efficiency.

Fifth embodiment
Next, FIG. 6 shows a nitrogen oxide processing apparatus according to a fifth embodiment of the present invention. The first to fourth embodiments described so far are all embodiments in which the electrolyte body is integrated with the thermoelectric element portion, whereas the fifth embodiment uses a power generation element. In this embodiment, the thermoelectric power generation unit 40 is an independent unit separated from the electrolyte body 41.

  As shown in FIG. 6, a thermoelectric power generation unit 40 and an electrolyte body 41 are accommodated in a case 44 having an inlet 42 and an outlet 43. The thermoelectric power generation unit 40 is hollow so that exhaust gas flows through the center. The electrolyte body 41 is a tubular body.

  The thermoelectric power generation unit 40 has a cooling surface on the outer peripheral surface, and a temperature difference is generated between the inside of the high temperature side through which the exhaust gas flows and the low temperature outer peripheral surface. The thermoelectric power generation unit 40 is electrically connected to the electrolyte body 41 by metal wires 45 and 46, and the inner peripheral surface of the electrolyte body 41 is a cathode and the outer peripheral surface is an anode.

  According to the fifth embodiment, in the thermoelectric power generation unit 40, a voltage generated due to the temperature difference between the inside and outside is applied to the electrolyte body 41. In the electrolyte body 41 placed under an electric field, the inner peripheral surface of the cathode is the reduction region. Thus, the nitrogen oxides contained in the exhaust gas are decomposed.

  Thus, it is necessary to distribute power from the battery by reusing the thermal energy of the exhaust gas by using the thermoelectric generator unit 40 using the power generation element that converts the heat of the exhaust gas into electric energy as a voltage source. Therefore, nitrogen oxides in the exhaust gas can be processed efficiently without reducing fuel consumption. The electrolyte body 41 is not limited to a normal tube body, and may be a tube body having a honeycomb structure. Moreover, although the arrangement position of the thermoelectric generator unit 40 is arranged immediately upstream of the air quality charge 41 in FIG. 6, it may be a downstream position.

The figure explaining the structure of the nitrogen oxide processing apparatus by 1st Embodiment of this invention. The schematic diagram which shows the thermoelectric element part of the nitrogen oxide processing apparatus by said 1st Embodiment. The schematic diagram which shows the thermoelectric element part in the nitrogen oxide processing apparatus by 2nd Embodiment of this invention. The schematic diagram which shows the electrolyte body used for the nitrogen oxide processing apparatus by 3rd Embodiment of this invention. The schematic diagram which shows the honeycomb structure which comprises the nitrogen oxide processing apparatus by 4th Embodiment of this invention. The schematic diagram which shows the nitrogen oxide processing apparatus by 5th Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electrolyte body 12 Exhaust gas passage 14 P-type thermoelectric element 15 N-type thermoelectric element 16, 17 Catalytic metal 20 P-type thermoelectric element 21, 22 Catalytic metal 30 Honeycomb structure 35 P-type thermoelectric element 40 Thermoelectric power generation unit 41 Electrolyte body 42 Introduction Mouth 43 Outlet 44 Case

Claims (2)

A nitrogen oxide treatment apparatus for decomposing NOx contained in exhaust gas of an internal combustion engine by an electrochemical reduction reaction,
It is made of a solid electrolyte in which oxygen ions move under an electric field, forms an exhaust gas passage through which exhaust gas is introduced, and a reduction region for reducing NOx in the exhaust gas on the high temperature side surface forming the exhaust gas passage. An electrolyte body to be formed;
A temperature difference between the inside and outside of the electrolyte body to generate a voltage for placing the solid electrolyte under an electric field, and a thermoelectric element portion integrally incorporated in the electrolyte body,
The said thermoelectric element part consists of a p-type thermoelectric element, respectively, The nitrogen oxide processing apparatus characterized by sandwiching the said p-type thermoelectric element between the two catalyst metals which become an anode and a cathode, respectively, and sandwich a solid electrolyte. 2. The nitrogen oxide processing apparatus according to claim 1 , wherein a honeycomb structure in which a plurality of exhaust gas passages are partitioned by the electrolyte body, the thermoelectric element portion, and a catalyst metal sandwiching them is formed.

Images