JP5582122B2 - Apparatus and method for exhaust purification of internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus and method for an internal combustion engine for purifying harmful components in exhaust gas from the internal combustion engine.

  Conventionally, in order to purify harmful components such as hydrocarbons (HC), nitrogen oxides (NOx) and carbon monoxide (CO) contained in exhaust from internal combustion engines, oxidation catalysts, reduction catalysts, three-way catalysts, etc. These catalysts are used. However, in a low temperature range where the catalyst is difficult to activate, such as immediately after the start of the internal combustion engine, hydrocarbons and nitrogen oxides, which are harmful components in the exhaust, are strongly adsorbed on the surface of the catalyst and inhibit the purification reaction of the harmful components ( Adsorption poisoning). For this reason, the catalyst tends to deteriorate the purification performance of harmful components, particularly in a low temperature range.

  In the following Patent Document 1, the HC adsorbent and the NOx adsorbent are provided at a position upstream of the lean NOx catalyst in the exhaust passage of the internal combustion engine. For example, in a low temperature range where the lean NOx catalyst is difficult to activate, such as immediately after starting the internal combustion engine, the HC adsorbent adsorbs HC in the exhaust from the internal combustion engine, and the NOx adsorbent adsorbs NOx in the exhaust from the internal combustion engine. Therefore, a reduction in purification performance due to adsorption of HC and NOx to the lean NOx catalyst is suppressed. After reaching the temperature range where the lean NOx catalyst is activated, HC and NOx adsorbed by the HC adsorbent and the NOx adsorbent are respectively released and purified by the lean NOx catalyst.

Further, in Patent Document 2, in an exhaust passage of an internal combustion engine, from the upstream, HC trapping agent for temporarily trapping HC in the exhaust gas temporarily trapping of H ₂ O in the exhaust H ₂ O trapping agent The CO oxidation catalyst that oxidizes CO from a low temperature is arranged in this order, and the H ₂ O trapping agent is arranged close to the upstream side of the CO oxidation catalyst. As a result, when CO is oxidized by the CO oxidation catalyst, H ₂ O and HC, which are the activity hindering components, are removed, and the temperature rising effect due to the heat of adsorption and condensation of H ₂ O is utilized to reduce the CO oxidation catalyst. Early activity is planned.

JP 2000-345832 A JP 2002-138824 A Japanese Patent Laid-Open No. 5-23553 Japanese Patent Laid-Open No. 11-227087

  In Patent Documents 1 and 2, harmful components such as HC and NOx can be adsorbed by the adsorbent or trapping agent until the adsorbent or trapping agent reaches saturation in a low temperature range where the catalyst is difficult to activate. However, after the adsorbent and trap agent reach saturation adsorption, harmful components such as HC and NOx are released without being adsorbed by the adsorbent and trap agent, and the purification performance is lowered by adsorbing to the catalyst. Therefore, when the low temperature range where the catalyst is difficult to activate continues for a long time, it becomes difficult to prevent the exhaust purification performance from being deteriorated.

  An object of the present invention is to prevent a decrease in exhaust purification performance even when a low-temperature region where the catalyst is difficult to activate continues for a long time.

  The exhaust gas purification apparatus and method for an internal combustion engine according to the present invention employs the following means in order to achieve the above-described object.

An exhaust gas purification apparatus for an internal combustion engine according to the present invention is an exhaust gas purification apparatus for an internal combustion engine for purifying harmful components including nitrogen oxides, hydrocarbons, and carbon monoxide in exhaust gas from the internal combustion engine. A reformer that reforms nitrogen monoxide and hydrocarbons contained in harmful components in exhaust gas from water into a water-soluble gas, and an absorbent containing water containing the harmful components reformed into water-soluble gas by the reformer An absorption device for absorbing and separating and absorbing, and an exhaust purification catalyst for purifying harmful components including carbon monoxide that has passed through the absorption device, a reforming process by the reformer, and a separation by the absorber The gist is to sequentially perform the removal process and the purification process by the exhaust purification catalyst .

  In one aspect of the present invention, it is preferable that the absorption device includes a gas-liquid contact device that absorbs a harmful component that has been modified into a water-soluble gas by the reforming device through contact with the absorption liquid through the porous membrane. is there.

  In one embodiment of the present invention, a reformer reforms nitrogen monoxide into higher-order nitrogen oxides by an oxidation reaction, and reforms hydrocarbons into partially oxidized hydrocarbons by an oxidation reaction, thereby providing a water-soluble gas. It is preferable to modify it.

  In one aspect of the present invention, the reformer adds oxidant to harmful components in the exhaust gas from the internal combustion engine, thereby reforming nitrogen monoxide to higher-order nitrogen oxides and partially oxidizing hydrocarbons. It is preferred to reform to a hydrocarbon.

  In one embodiment of the present invention, it is preferable that the oxidizing agent is ozone.

  In one aspect of the present invention, the exhaust purification catalyst is preferably purified by reacting carbon monoxide with the oxidant.

  An exhaust gas purification method for an internal combustion engine according to the present invention is an exhaust gas purification method for an internal combustion engine for purifying harmful components including nitrogen oxides, hydrocarbons, and carbon monoxide in exhaust gas from the internal combustion engine, A process of reforming nitrogen monoxide and hydrocarbons contained in harmful components in the exhaust gas from the internal combustion engine into a water-soluble gas, and absorbing the harmful components modified into the water-soluble gas into an absorption liquid containing water. The gist is to sequentially perform a process of separating and removing, and a process of purifying harmful components including carbon monoxide that has not been absorbed by the absorbent.

  According to the present invention, nitrogen monoxide and hydrocarbons contained in harmful components in exhaust gas from an internal combustion engine are reformed into a water-soluble gas, and then absorbed into an absorption liquid containing water and separated and removed. Nitrogen oxides and hydrocarbons that inhibit the oxidation reaction of carbon monoxide can be prevented from flowing into the exhaust purification catalyst. As a result, even when a low temperature range in which the exhaust purification catalyst is difficult to activate continues for a long time, it is possible to prevent a decrease in exhaust purification performance.

1 is a diagram showing a schematic configuration of an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention. An internal combustion engine (engine) 10 generates power by burning fuel in a cylinder. The internal combustion engine 10 here may be a spark ignition engine such as a gasoline engine, or may be a compression ignition engine such as a diesel engine. Exhaust gas after combustion in the internal combustion engine 10 is discharged into the exhaust pipe 12. The exhaust gas discharged from the internal combustion engine 10 into the exhaust pipe 12 contains harmful components such as hydrocarbons (HC), nitrogen oxides (NOx), and carbon monoxide (CO). In order to purify harmful components including nitrogen oxides, hydrocarbons, and carbon monoxide in the exhaust gas from the internal combustion engine 10, an exhaust gas purification catalyst 16 is provided in the exhaust pipe 12, and further absorbs water-soluble gas. The device 15 is provided at a position upstream of the exhaust purification catalyst 16 in the exhaust pipe 12, and the reformer 14 is provided at a position upstream of the water-soluble gas absorption device 15 in the exhaust pipe 12.

The reformer 14 has a reforming catalyst 14a and reforms nitrogen monoxide (NO) and hydrocarbons contained in harmful components in the exhaust from the internal combustion engine 10 into a water-soluble gas. In the reformer 14, water-insoluble nitric oxide is converted into water-soluble higher-order nitrogen oxides (NO ₂ , NO ₃ , N ₂ O _5, etc.) by an oxidation reaction, and water-insoluble hydrocarbons are oxidized. The reaction converts to water-soluble partially oxidized hydrocarbons (aldehyde, carboxylic acid, etc.). An ozone addition valve 24 is provided at a position upstream of the reformer 14 in the exhaust pipe 12 (position between the internal combustion engine 10 and the reformer 14) for the oxidation reaction in the reformer 14. ing. By injecting ozone (O ₃ ) as an oxidizing agent from the ozone addition valve 24 toward the reforming device 14, ozone is added to harmful components flowing into the reforming device 14. By oxidizing harmful components using high oxidizing power of ozone, water-insoluble NO is oxidized and reformed into water-soluble NO ₂ , and further oxidized and reformed into water-soluble NO ₃ and N ₂ O _5, etc. . Then, propylene (C ₃ H ₆ ) having an unsaturated bond is oxidized and modified to water-soluble formaldehyde (HCHO) and acetaldehyde (CH ₃ CHO), and further water-soluble formic acid (HCOOH) and acetic acid (CH ₃ COOH) Oxidative reforming. Similarly, ethylene (C ₂ H ₄ ) having an unsaturated bond is oxidized and modified to a water-soluble aldehyde or carboxylic acid. The high oxidation activity of ozone makes it easy to convert to a water-soluble gas even at low temperatures. In that case, since nitrogen oxide and hydrocarbon have a higher reaction rate with ozone than carbon monoxide, the added ozone is mainly used for reaction with nitrogen oxide and hydrocarbon. Exhaust gas containing harmful components converted into water-soluble gas is supplied to the downstream water-soluble gas absorber 15. Note that any means for converting the harmful component in the exhaust gas into the water-soluble gas may be used as the means for converting the water into the water-soluble gas by the reformer 14, and there is no need for the reforming catalyst 14a and only ozone addition. Although only a phase reaction may be used, a water-soluble gas can be generated more efficiently by combining a gas phase reaction and a catalytic reaction. Examples of the reforming catalyst 14a include H-BEA zeolite and ion-exchanged BEA zeolite such as Ag, Fe, and Cs.

  In order to generate ozone added to harmful components flowing into the reformer 14, an ozone generator 18 is provided, and the ozone generated by the ozone generator 18 passes through the ozone conduit 20 and is added with ozone. The fuel is injected from the valve 24 toward the reformer 14. In the ozone generator 18, ozone may be produced by any method, and examples thereof include a water electrolysis device and plasma discharge. In particular, the use of a water electrolysis device makes it possible to generate and supply ozone having a high concentration and high purity, which is advantageous in terms of efficiency, cost, space, and the like. A water electrolysis device is a device that generates ozone and hydrogen by electrolysis of water, and decomposes water on the anode side separated by a cation exchange membrane to generate ozone, while positively generating on the cathode side. Hydrogen gas is generated from hydrogen ions that have passed through the ion membrane. About the water used for electrolysis with a water electrolysis apparatus, it is also possible to supply from the outside, and it is also possible to collect | recover and supply the water in exhaust_gas | exhaustion.

The water-soluble gas absorption device 15 separates and removes harmful components that have been reformed into water-soluble gas by the reforming device 14 from the exhaust gas by absorbing them into an absorption liquid containing water. The water-soluble gas absorption device 15 here may be any device as long as it can absorb the water-soluble gas into the absorption liquid. For example, a film-type gas-liquid contact device 15a can be used. In the membrane-type gas-liquid contact device 15a, the exhaust passage and the absorbing liquid are separated by a porous membrane, and harmful components modified into water-soluble gas contained in the exhaust are converted into the absorbing liquid from the exhaust passage through the porous membrane. Absorb by contact. As the porous film, a porous PTFE (polytetrafluoroethylene) film disclosed in Patent Documents 3 and 4 can be used. As the absorbing solution, water is used, and alkali salts such as potassium carbonate and sodium carbonate, alcohols and the like may be dissolved in water. The absorption liquid mainly containing water is stored in the absorption liquid tank 15b, is pumped up by the pump 15c, and is supplied into the membrane gas-liquid contact device 15a. In the membrane-type gas-liquid contact device 15a, water-soluble high-order nitrogen oxides (NO ₂ , NO ₃ , N ₂ O ₅ etc.) and partially oxidized hydrocarbons (aldehyde, carboxylic acid etc.) contained in harmful components in the exhaust gas ) Is absorbed and removed by the absorption liquid. At that time, the higher nitrogen oxides react with water (H ₂ O) to produce nitric acid (HNO ₃ ) and nitrous acid (HNO ₂ ), and the partially oxidized hydrocarbon dissolves in water. The absorption liquid in which the higher nitrogen oxides and the partially oxidized hydrocarbons are absorbed is returned to the absorption liquid tank 15b and circulated. Higher nitrogen oxides and partially oxidized hydrocarbons absorbed in the absorbing solution may be processed by periodically replacing the absorbing solution, or may be decomposed by electrolysis or the like. The harmful components in the exhaust gas that have passed through the water-soluble gas absorption device 15 (membrane-type gas-liquid contact device 15a) without being absorbed by the absorption liquid are supplied to the exhaust purification catalyst 16 on the downstream side. The harmful components in the exhaust gas that are not absorbed by the absorption liquid include poorly water-soluble carbon monoxide and the like, and ozone added as an oxidant during reforming to a water-soluble gas also remains in the exhaust gas.

The exhaust purification catalyst 16 purifies harmful components including carbon monoxide that has passed through the water-soluble gas absorption device 15 (membrane-type gas-liquid contact device 15a). In the exhaust purification catalyst 16, carbon monoxide (CO) that has not been reformed by the reformer 14 into a water-soluble gas and has not been absorbed by the absorbent by the water-soluble gas absorber 15 reacts with ozone (O ₃ ). Thus, it is purified to carbon dioxide (CO ₂ ) and oxygen (O ₂ ). The exhaust purification catalyst 16 here may be any catalyst as long as it can purify harmful components. For example, an oxidation catalyst, a three-way catalyst, an NOx storage reduction catalyst, or the like can be used. In particular, by using a supported Ag catalyst in which Ag is supported on Al ₂ O ₃ or SiO ₂ , carbon monoxide and ozone in exhaust gas can be purified from a low temperature range.

For example, the exhaust purification catalyst 16 is often operated in a low temperature range where it is difficult to activate the internal combustion engine 10 immediately after the start, low load idle operation, frequent operation such as idling stop, or the like. When hydrocarbons or nitrogen oxides that inhibit the oxidation reaction of carbon monoxide flow into the exhaust purification catalyst 16 and are strongly adsorbed in a low temperature range where the exhaust purification catalyst 16 is difficult to activate, the purification reaction at the exhaust purification catalyst 16 is inhibited. (Adsorption poisoning). In particular, hydrocarbons having an unsaturated bond such as propylene (C ₃ H ₆ ) and ethylene (C ₂ H ₄ ) are likely to be adsorbed by the exhaust purification catalyst 16 and easily inhibit the oxidation reaction of carbon monoxide. Therefore, the exhaust purification catalyst 16 is liable to deteriorate the purification performance of harmful components, particularly in a low temperature range.

On the other hand, in the present embodiment, nitrogen monoxide and hydrocarbons contained in harmful components in the exhaust gas from the internal combustion engine 10 are reformed into a water-soluble gas by the reformer 14, and the reformer 14 The harmful component modified into the reactive gas is absorbed into the absorption liquid containing water by the water-soluble gas absorption device 15 and separated and removed, and the monoxide which has passed through the water-soluble gas absorption device 15 without being absorbed by the absorption liquid The process of purifying harmful components including carbon with the exhaust purification catalyst 16 is sequentially performed. Nitrogen oxide (NO) in the exhaust gas is reformed into water-soluble higher-order nitrogen oxides (NO ₂ , NO ₃ , N ₂ O _5, etc.), and hydrocarbons such as propylene and ethylene in the exhaust gas are By reforming to partially oxidized hydrocarbons (aldehyde, carboxylic acid, etc.), nitrogen oxides and hydrocarbons in the exhaust gas are absorbed into the absorbing liquid at a high absorption rate by the membrane gas-liquid contact device 15a. It is separated and removed from the exhaust with a high purification rate. This prevents nitrogen oxides and hydrocarbons (hydrocarbons having an unsaturated bond such as propylene and ethylene) that inhibit the oxidation reaction of carbon monoxide from flowing into the exhaust purification catalyst 16 provided downstream. In the exhaust purification catalyst 16, a high carbon monoxide purification rate can be obtained even in a low temperature range. Therefore, even when the low temperature region where the exhaust purification catalyst 16 is difficult to activate continues for a long time, it is possible to prevent the exhaust purification performance from being deteriorated. For example, as described in Patent Documents 1 and 2, when adsorbing nitrogen oxides and hydrocarbons with an adsorbent or trapping agent, the adsorbent or trapping agent reaches saturation adsorption in about several minutes. In this embodiment, it is possible to continue to absorb water-soluble high-order nitrogen oxides and partially oxidized hydrocarbons for about several hundred hours with an absorbing solution of about several liters. Further, surplus ozone added as an oxidant for reforming to a water-soluble gas can react with carbon monoxide from the low temperature range in the exhaust purification catalyst 16, and is purified to carbon dioxide and oxygen. Therefore, the outflow of carbon monoxide and ozone into the atmosphere can be prevented.

  In the present embodiment, when the temperature of the exhaust purification catalyst 16 is equal to or higher than the activation temperature, the exhaust purification catalyst 16 does not necessarily convert nitrogen monoxide and hydrocarbons in the exhaust into water-soluble gas. It is possible to purify harmful components. Therefore, in this embodiment, when the temperature of the exhaust purification catalyst 16 is equal to or higher than the activation temperature, ozone addition from the ozone addition valve 24 is not performed (so that nitrogen monoxide and hydrocarbons in the exhaust gas are not absorbed by the absorption liquid). It is also possible to not modify the water-soluble gas. In that case, when the temperature of the exhaust purification catalyst 16 is lower than the activation temperature, ozone addition from the ozone addition valve 24 is performed, and water is dissolved by adding ozone so that nitrogen monoxide and hydrocarbons in the exhaust are absorbed by the absorption liquid. Reform to gas.

  As mentioned above, although the form for implementing this invention was demonstrated, this invention is not limited to such embodiment at all, and it can implement with a various form in the range which does not deviate from the summary of this invention. Of course.

  DESCRIPTION OF SYMBOLS 10 Internal combustion engine, 12 Exhaust pipe, 14 Reforming apparatus, 14a Reforming catalyst, 15 Water-soluble gas absorption apparatus, 15a Membrane type gas-liquid contact apparatus, 15b Absorption liquid tank, 16 Exhaust gas purification catalyst, 18 Ozone generator, 20 Ozone Conduit, 24 ozone addition valve.

Claims (7)

An exhaust purification device for an internal combustion engine for purifying harmful components including nitrogen oxides, hydrocarbons, and carbon monoxide in exhaust gas from the internal combustion engine,
A reformer for reforming nitrogen monoxide and hydrocarbons contained in harmful components in exhaust gas from an internal combustion engine into a water-soluble gas;
An absorption device that absorbs and removes harmful components that have been modified into water-soluble gas by a reformer into an absorption liquid containing water; and
An exhaust purification catalyst that purifies harmful components including carbon monoxide that has passed through the absorber,
Equipped with a,
An exhaust gas purification apparatus for an internal combustion engine that sequentially executes a process for reforming by the reformer, a process for separating and removing by the absorber, and a process for purifying by the exhaust gas purification catalyst . An exhaust emission control device for an internal combustion engine according to claim 1,
The absorption device is an exhaust gas purification device for an internal combustion engine having a gas-liquid contact device that absorbs a harmful component reformed into a water-soluble gas by the reformer by contacting the absorbent through the porous membrane. An exhaust emission control device for an internal combustion engine according to claim 1 or 2,
An internal combustion engine that reforms nitrogen monoxide into higher-order nitrogen oxides by an oxidation reaction and reforms hydrocarbons into partially oxidized hydrocarbons by an oxidation reaction, thereby reforming the water-soluble gas. Exhaust purification equipment. An exhaust emission control device for an internal combustion engine according to claim 3,
The reformer adds oxidant to harmful components in the exhaust gas from the internal combustion engine, thereby reforming nitrogen monoxide to higher-order nitrogen oxides and reforming hydrocarbons to partially oxidized hydrocarbons. An exhaust purification device for an internal combustion engine. An exhaust emission control device for an internal combustion engine according to claim 4,
An exhaust gas purification apparatus for an internal combustion engine, wherein the oxidizing agent is ozone. An exhaust emission control device for an internal combustion engine according to claim 4 or 5,
The exhaust gas purification catalyst is an exhaust gas purification device for an internal combustion engine, which purifies carbon monoxide by reacting with the oxidant. An exhaust purification method for an internal combustion engine for purifying harmful components including nitrogen oxides, hydrocarbons and carbon monoxide in exhaust from the internal combustion engine,
A process for reforming nitrogen monoxide and hydrocarbons contained in harmful components in exhaust gas from an internal combustion engine into a water-soluble gas;
A process for absorbing and separating harmful components modified into water-soluble gas in an absorption liquid containing water;
A treatment for purifying harmful components including carbon monoxide that has not been absorbed by the absorbent;
The exhaust gas purification method for an internal combustion engine is executed in order.

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