JP2010185347A - Exhaust gas purifying apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas purifying apparatus capable of surely removing NOx regardless of the operation condition of an internal combustion engine. <P>SOLUTION: A diesel engine 1 has an exhaust pipe 2 through which an exhaust gas discharged from the engine 1 flows. The exhaust pipe 2 is provided with an electrochemical reactor 3 in which gold or silver is used as a catalyst, and an alkaline earth metal salt as an auxiliary catalyst. Further, an NOx removing apparatus 4 is provided at a downstream side of the reactor 3. When an exhaust gas temperature measured by a temperature sensor 9 is lower than the set value previously set to an ECU 11, ECU 11 operates a power supply 10 and voltage is applied to the reactor 3. Thereby, NOx in the exhaust gas is occluded into the reactor 3. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification device, and more particularly to an exhaust gas purification device equipped with an electrochemical reactor.

  An exhaust gas purification apparatus using an electrochemical reactor is described in Patent Document 1. In the electrochemical reactor of this exhaust gas purification device, a noble metal surface that selectively stores nitrogen oxides (NOx) and NOx reducing agents (hydrocarbon compounds (HC), carbon monoxide (CO), etc.) are selected. Since the surface of the noble metal adsorbed on the surface is joined with the solid electrolyte and the electron conductive material, ions and electrons are conducted between the noble metals, the oxidation-reduction reaction is promoted, and the exhaust gas is purified. In order to cause this electrochemical reaction, it is necessary to selectively store and adsorb NOx and HC as a NOx reducing agent on separate noble metal surfaces. Therefore, the electrochemical reactor includes a NOx storage material and HC adsorption. Material is provided.

JP 2002-188431 A

  However, depending on the operating conditions of the internal combustion engine, the NOx purification ability of the electrochemical reactor may not be fully exhibited, and there has been a problem that exhaust gas purification may be incomplete.

  The present invention has been made to solve such problems, and an object of the present invention is to provide an exhaust gas purification device that can reliably purify NOx regardless of the operating conditions of the internal combustion engine.

An exhaust gas purifying apparatus according to the present invention includes an exhaust pipe through which exhaust gas discharged from an internal combustion engine flows, at least one electrochemical reactor provided in the exhaust pipe, and a power source for applying a voltage to the electrochemical reactor And a NOx purification device provided in the exhaust pipe downstream of the electrochemical reactor, and the power supply device applies a voltage to the electrochemical reactor so that the electrochemical reactor is in the exhaust gas. After the NOx is occluded, by stopping the application of voltage by the power supply device, the NOx occluded in the electrochemical reactor is desorbed from the electrochemical reactor and flows into the NOx purification device. Some electrochemical reactors have a function of occluding NOx when a voltage is applied. Using this function, when the purification capability of the NOx purification device is low, NOx is occluded in the electrochemical reactor, and after the purification capability of the NOx purification device is increased, voltage is applied to the electrochemical reactor. And the stored NOx is desorbed and purified by the NOx purification device.
In the electrochemical reactor, gold or silver may be used as a catalyst and an alkaline earth metal salt may be used as a promoter.
The exhaust pipe is provided with at least one bypass pipe that bypasses the electrochemical reactor provided in the exhaust pipe, and the bypass pipe is provided with an electrochemical reactor, and at least one of the electrochemical reactors Switching means for preventing the exhaust gas from flowing through the chemical reactor, and when the electrochemical reactor through which the exhaust gas does not flow is changed by the switching means, a voltage is applied to the electrochemical reactor in which the exhaust gas flows. In addition, the addition of voltage may be stopped for the electrochemical reactor in which the exhaust gas has stopped flowing.
A temperature sensor for measuring the temperature of the exhaust gas is provided in the exhaust pipe, and when the value measured by the temperature sensor is lower than a preset set value, the power supply device is connected to the electrochemical reactor. When a voltage is applied and the value measured by the temperature sensor is equal to or greater than the set value, the voltage application by the power supply device may be stopped.
A map representing a relationship between the operating condition of the internal combustion engine and the temperature of the exhaust gas, the temperature of the exhaust gas is estimated from the operating condition based on the map, and the estimated value of the temperature of the exhaust gas is When the set value is lower than a preset value, the power supply device adds a voltage to the electrochemical reactor, and when the estimated value is equal to or higher than the set value, the voltage is added by the power supply device. You may stop.

  According to the present invention, when the purification capability of the NOx purification device is low by using the electrochemical reactor, NOx is stored in the electrochemical reactor, and after the purification capability of the NOx purification device is increased, By stopping the application of voltage to the chemical reactor, the stored NOx can be desorbed and purified by the NOx purification device, so that NOx can be reliably purified regardless of the operating conditions of the internal combustion engine. it can.

It is a schematic diagram which shows the structure of the exhaust-gas purification apparatus which concerns on Embodiment 1 of this invention. 6 is a schematic diagram showing a configuration of an exhaust gas purification apparatus according to Embodiment 2. FIG.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
Embodiment 1 FIG.
The configuration of the exhaust gas purifying apparatus according to Embodiment 1 is shown in FIG. A diesel engine 1 that is an internal combustion engine has an exhaust pipe 2 through which exhaust gas discharged from the diesel engine 1 flows. The exhaust pipe 2 is provided with an electrochemical reactor 3, and further, a NOx purification device 4 is provided downstream of the electrochemical reactor 3. Between the diesel engine 1 and the electrochemical reactor 3, a temperature sensor 9 for measuring the temperature of the exhaust gas flowing through the exhaust pipe 2 is provided.

  The NOx purification device 4 is a urea SCR system, and includes an oxidation catalyst 5, an SCR catalyst 6, and an oxidation catalyst 7, and an injection nozzle 8 that injects urea water between the oxidation catalyst 5 and the SCR catalyst 6. Is provided.

  The electrochemical reactor 3 is composed of an electrochemical cell having a cathode, an anode, and an electrolyte disposed between the cathode and the anode. Gold or silver is used as a catalyst, and an alkaline earth metal salt is used as a promoter. The electrochemical reactor 3 is provided with a power supply device 10 for applying a voltage between the cathode and the anode. When a voltage is applied to the electrochemical reactor 3 having such a configuration, NOx is occluded on the electrode while the voltage is applied, and the occluded NOx is desorbed when the voltage is not applied. .

  Each of the temperature sensor 9 and the power supply device 10 is electrically connected to an ECU 11 that is a control device.

Next, the operation of the exhaust gas purification apparatus according to Embodiment 1 will be described.
At the time of starting the diesel engine 1 and the like, since the temperature of the exhaust gas discharged from the diesel engine 1 is low, even if the exhaust gas flows through each of the oxidation catalyst 5, the SCR catalyst 6, and the oxidation catalyst 7, The catalyst temperature does not rise to a temperature necessary for exhibiting sufficient catalyst performance. Therefore, when the temperature of the exhaust gas measured by the temperature sensor 9 is lower than a preset value set in the ECU 11, the ECU 11 applies a voltage to the electrochemical reactor 3 by operating the power supply device 10. . Then, NOx in the exhaust gas is occluded in the electrochemical reactor 3, and the exhaust gas having a reduced NOx concentration flows out of the electrochemical reactor 3 and flows into the NOx purification device 4.

In the NOx purification device 4, first, the oxidation catalyst 5 oxidizes nitrogen monoxide (NO) in the exhaust gas to nitrogen dioxide (NO ₂ ). Subsequently, the exhaust gas flows into the SCR catalyst 6, but the urea water supplied from the injection nozzle 8 is hydrolyzed in the SCR catalyst 6 at an appropriate timing to become ammonia and carbon dioxide, and the generated ammonia and NOx in the exhaust gas. React with nitrogen and water. Ammonia remaining without being consumed in the SCR catalyst 6 is oxidized in the oxidation catalyst 7, and the exhaust gas from which NOx has been purified is discharged into the atmosphere. Even when the NOx purification function of the NOx purification device 4 is not fully exhibited, exhaust gas with a reduced NOx concentration is processed, so exhaust gas with a sufficiently reduced NOx concentration is discharged into the atmosphere. Will be.

  Thereafter, when the temperature of the exhaust gas rises and the measured value by the temperature sensor 9 becomes equal to or higher than the set value, the ECU 11 stops the operation of the power supply device 10 to add voltage to the electrochemical reactor 3 Stop. Then, the NOx stored in the electrochemical reactor 3 is desorbed and flows into the oxidation catalyst 5 together with the exhaust gas flowing through the exhaust pipe 2. Since the temperatures of the oxidation catalyst 5, the SCR catalyst 6, and the oxidation catalyst 7 are sufficiently high, the NOx purification device 4 can exhibit a sufficient NOx purification function, and only NOx in the exhaust gas can be exhibited. Instead, NOx desorbed from the electrochemical reactor 3 can also be purified.

  Further, when the temperature of the exhaust gas decreases due to a change in the operating condition of the diesel engine 1 and the measured value by the temperature sensor 9 falls below the set value, the ECU 11 causes the power supply device 10 to operate again to the electrochemical reactor 3. A voltage is applied to cause the electrochemical reactor 3 to store NOx in the exhaust gas. Thereafter, when the measured value by the temperature sensor 9 becomes equal to or higher than the set value, the ECU 11 stops the operation of the power supply device 10 to stop the application of voltage to the electrochemical reactor 3.

  Thus, by using the electrochemical reactor 3 in which gold or silver is used as a catalyst and an alkaline earth metal salt is used as a cocatalyst, when the temperature of the exhaust gas is lower than a set value, the electrochemical reactor NOx is stored in the NOx 3, and after the temperature of the exhaust gas rises to a set value or higher, the addition of voltage to the electrochemical reactor 3 is stopped to desorb the stored NOx and the NOx purification device Therefore, NOx can be reliably purified regardless of the operating conditions of the diesel engine 1.

  In the first embodiment, the temperature of the exhaust gas is directly measured by the temperature sensor 9, but the present invention is not limited to this embodiment. The ECU 11 incorporates a map of the operating conditions (rotation speed, fuel injection amount, etc.) of the diesel engine 1 and the exhaust gas temperature, and estimates the exhaust gas temperature from the operating conditions of the diesel engine 1 based on this map. It may be.

Embodiment 2. FIG.
Next, an exhaust gas purification apparatus according to Embodiment 2 of the present invention will be described. In the second embodiment, the same reference numerals as those in FIG. 1 are the same or similar components, and detailed description thereof is omitted.
The exhaust gas purification apparatus according to Embodiment 2 of the present invention is different from Embodiment 1 in that a bypass pipe is provided in the exhaust pipe 2 so as to bypass the electrochemical reactor 3, and the electrochemical reactor is also provided in this bypass pipe. It is provided.

  As shown in FIG. 2, the exhaust pipe 2 is provided with a bypass pipe 20 so as to bypass the electrochemical reactor 3. The bypass pipe 20 is also provided with the same electrochemical reactor 3 ′ as the electrochemical reactor 3. A three-way valve 21 serving as switching means is provided at a connection portion between the upstream end of the bypass pipe 20 and the exhaust pipe 2. Each of the electrochemical reactors 3 and 3 ′ is provided with a power supply device 10 and 10 ′ for applying a voltage between the cathode and anode thereof. Each of the three-way valve 21 and the power supply devices 10 and 10 ′ is electrically connected to the ECU 11. Other configurations are the same as those in the first embodiment except that the temperature sensor 9 is not provided.

Next, the operation of the exhaust gas purification apparatus according to Embodiment 2 will be described.
It is assumed that the exhaust gas flows through the electrochemical reactor 3 in the three-way valve 21 when the diesel engine 1 is started. When the diesel engine 1 is started, the ECU 11 applies a voltage to the electrochemical reactor 3 by operating the power supply device 10. Then, as in the first embodiment, NOx in the exhaust gas is occluded in the electrochemical reactor 3, and the exhaust gas having a reduced NOx concentration flows into the NOx purification device 4.

  When a preset time (hereinafter referred to as “set time”) elapses, the ECU 11 switches the three-way valve 21 so that the exhaust gas flows through the electrochemical reactor 3 ′, and further stops the operation of the power supply device 10. At the same time, the power supply device 10 'is operated to apply a voltage only to the electrochemical reactor 3'. Then, the exhaust gas discharged from the diesel engine 1 flows into the electrochemical reactor 3 ′ through the bypass pipe 20. Similar to the electrochemical reactor 3, the electrochemical reactor 3 ′ occludes NOx in the exhaust gas, and the exhaust gas having a reduced NOx concentration flows into the NOx purification device 4.

  On the other hand, since no voltage is applied in the electrochemical reactor 3, the stored NOx is desorbed, and the desorbed NOx flows into the NOx purification device 4 together with the exhaust gas flowing into the NOx purification device 4 through the bypass pipe 20. To do. The NOx purification operation in the NOx purification device 4 is the same as that in the first embodiment.

  After this, when the set time has elapsed, the ECU 11 switches the three-way valve 21 so that the exhaust gas flows through the electrochemical reactor 3 and stops the application of voltage to the electrochemical reactor 3 ′. Apply voltage to only. Thereafter, these operations are repeated.

  Thus, in addition to the electrochemical reactor 3 provided in the exhaust pipe 2, another electrochemical reactor 3 ′ is provided in the bypass pipe 20 that bypasses the electrochemical reactor 3, and the electrochemical reactors 3 and 3 ′ are alternately arranged. When the diesel engine 1 is in operation, NOx in the exhaust gas is always occluded in one electrochemical reactor, and the NOx occluded in the other electrochemical reactor is desorbed and the NOx purification device 4 is applied. To flow into. As a result, not only when the diesel engine 1 is started, but also when the NOx purification function of the NOx purification device 4 is lowered due to fluctuations in operating conditions during operation, etc., the electrochemical reactor 3 or 3 ′ temporarily. When NOx is occluded and the NOx purification function returns, the occluded NOx can be purified, so that NOx can be reliably purified regardless of the operating conditions of the diesel engine 1.

In the second embodiment, the two electrochemical reactors 3 and 3 ′ are provided in parallel. However, the number is not limited to two. Three or more electrochemical reactors may be provided in parallel, and voltage may be applied in order. When three or more electrochemical reactors are provided, the switching means prevents the exhaust gas from flowing into at least one electrochemical reactor and stops applying voltage to the electrochemical reactor. Thus, NOx occluded in this electrochemical reactor may be desorbed, and exhaust gas may be introduced into the other electrochemical reactors to occlude NOx.
In the second embodiment, the two electrochemical reactors 3 and 3 ′ are the same, but electrochemical reactors having different specifications may be used. Even when more than two electrochemical reactors are used, a plurality of electrochemical reactors having different specifications may be used.

  In the second embodiment, the switching of the voltage application to the electrochemical reactors 3 and 3 ′ is performed as the set time elapses. However, the present invention is not limited to this mode. A temperature sensor may be provided in the exhaust pipe 2 to switch the voltage addition based on the exhaust gas temperature, or to switch the voltage addition based on the operating conditions of the diesel engine 1. The switching of the voltage application to the electrochemical reactors 3 and 3 ′ is most effective when the storage capacity of one electrochemical reactor reaches saturation. For example, the storage capacity of the electrochemical reactor is reduced. By measuring in advance, the saturation state of the electrochemical reactor can be predicted from the operating conditions of the diesel engine, the state of the exhaust gas, and the like.

  In the first and second embodiments, the urea SCR system is used as the NOx purification device 4, but the present invention is not limited to this. Not only the urea SCR system but also other SCR catalysts may be used, or a NOx storage catalyst (NSR catalyst) and a diesel particulate NOx reduction system (DPNR) may be used. Further, the electrochemical reactors 3 and 3 ′ according to the first and second embodiments do not have a function of storing NOx, and an electrochemical reactor having a function of purifying NOx may be used. That is, any system that purifies NOx may be used.

  In Embodiments 1 and 2, although gold or silver is used as the catalyst, the present invention is not limited to these. Metals such as platinum, rhodium, and palladium may be used as a catalyst as long as they exhibit NOx storage.

  DESCRIPTION OF SYMBOLS 1 Diesel engine (internal combustion engine), 2 exhaust pipe, 3,3 'electrochemical reactor, 4 NOx purification device, 9 temperature sensor, 10, 10' power supply device, 20 bypass pipe, 21 three-way valve (switching means).

Claims (5)

An exhaust pipe through which exhaust gas discharged from the internal combustion engine flows;
At least one electrochemical reactor provided in the exhaust pipe;
A power supply for applying a voltage to the electrochemical reactor;
A NOx purification device provided in the exhaust pipe downstream of the electrochemical reactor,
The power supply device applies a voltage to the electrochemical reactor, and after the electrochemical reactor occludes NOx in the exhaust gas, the power supply device stops applying voltage to the electrochemical reactor. An exhaust gas purification device in which the stored NOx is desorbed from the electrochemical reactor and flows into the NOx purification device.   The exhaust gas purification device according to claim 1, wherein the electrochemical reactor uses gold or silver as a catalyst and an alkaline earth metal salt as a promoter. The exhaust pipe is provided with at least one bypass pipe that bypasses the electrochemical reactor provided in the exhaust pipe, and the bypass pipe is provided with an electrochemical reactor,
Switching means for preventing exhaust gas from flowing through at least one of the electrochemical reactors;
When the electrochemical reactor through which the exhaust gas does not flow is changed by the switching means, a voltage is applied to the electrochemical reactor in which the exhaust gas has circulated, and the voltage is applied to the electrochemical reactor in which the exhaust gas has ceased to flow. The exhaust gas purification device according to claim 1 or 2, wherein the addition of is stopped. A temperature sensor for measuring the temperature of the exhaust gas is provided in the exhaust pipe;
When the value measured by the temperature sensor is lower than a preset setting value, the power supply device adds a voltage to the electrochemical reactor, and the value measured by the temperature sensor is equal to or greater than the preset value. The exhaust gas purifying apparatus according to claim 1 or 2, wherein when the power supply becomes, the application of voltage by the power supply device is stopped. Comprising a map representing the relationship between the operating conditions of the internal combustion engine and the temperature of the exhaust gas;
The temperature of the exhaust gas is estimated from the operating conditions based on the map,
When the estimated value of the temperature of the exhaust gas is lower than a preset set value, the power supply device adds a voltage to the electrochemical reactor, and the estimated value becomes equal to or higher than the set value. The exhaust gas purification device according to claim 1 or 2, wherein the application of voltage by the power supply device is stopped.

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