JP2005105940A - Engine exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the rejection rate of NOx by suppressing reducing agent from precipitating in an exhaust passage even when the exhaust temperature from an engine is low. <P>SOLUTION: The exhaust gas in the exhaust gas 3 is heated up to the temperature above the melting temperature of the reducing agent with an electric heat carrier 11 installed at the upstream side of an injection nozzle 7 to supply the reducing agent to the exhaust gas upstream side of the reducing catalyst 5 in the exhaust pipe 3. This prevents the reducing agent from precipitating on the inner wall of the exhaust pipe 3 even when the exhaust temperature from the engine 1 is lower than the melting point of a reducing agent to make it possible to effectively use the reducing agent fed from the ejection nozzle 7 for catalyst reduction reaction. This makes it possible to purify NOx in the exhaust gas into an innocent component and improve the rejection rate of NOx. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an exhaust emission control device that reduces and removes nitrogen oxides (NOx) discharged from a diesel engine, a gasoline engine, or the like mounted on a moving vehicle by supplying a reducing agent to an exhaust upstream side of a reduction catalyst. The present invention relates to an engine exhaust gas purification device that improves the NOx removal rate by suppressing the precipitation of the reducing agent in the exhaust passage even when the exhaust gas temperature from the engine is low.

Several exhaust emission control devices have been proposed as a system for purifying exhaust gas by removing NOx from particulate matter (PM) in exhaust gas discharged from the engine. This exhaust purification device places a reduction catalyst in an exhaust system of an engine, and injects and supplies a reducing agent into an exhaust passage upstream of the reduction catalyst, thereby causing NOx and reducing agent in the exhaust to undergo a catalytic reduction reaction, thereby reducing NOx. Is purified to harmless components. The reducing agent is stored in a storage tank in a liquid state at room temperature, and a required amount is injected and supplied from an injection nozzle. In the reduction reaction, ammonia having good reactivity with NOx is used, and as the reducing agent, an aqueous urea solution, an aqueous ammonia solution, or other reducing agent aqueous solution that easily generates ammonia by hydrolysis is used (for example, patents). Reference 1 and Non-Patent Document 1).
JP 2000-27627 A "Catalyst" Vol.45 No.3 2003, Catalysis Society of Japan, April 10, 2003, page 227

  However, in the above-described conventional exhaust purification device, when the exhaust temperature from the engine is lower than, for example, 132 ° C., a urea aqueous solution (hereinafter referred to as “urea water”) as a reducing agent injected and supplied into the exhaust passage. Urea may be deposited on the inner wall surface of the exhaust pipe. This is because urea water condenses in the vicinity of 100 ° C., and the melting point of urea is 132 ° C., so the temperature of the exhaust discharged from the engine is 100 ° C. or higher at which urea water condenses, but it is the melting point of urea. This is because urea remains deposited in a temperature range of less than 132 ° C. In such a case, the urea water is reduced by the amount of urea precipitation and the urea water injected and supplied from the injection nozzle is not effectively used for the catalytic reduction reaction, and NOx may not be sufficiently reduced and removed. The removal rate may decrease.

  Accordingly, the present invention addresses such problems and suppresses the precipitation of reducing agent in the exhaust passage even when the exhaust temperature from the engine is low, thereby improving the NOx removal rate of the engine. The purpose is to provide.

  The exhaust emission control device according to claim 1, which is disposed in an exhaust system of the engine and reduces an amount of nitrogen monoxide in the exhaust gas by an oxidation reaction, and is disposed in the exhaust system and includes nitrogen oxides in the exhaust gas. Exhaust gas from an engine comprising: a reduction catalyst that reduces and purifies gas with a reducing agent; and a reducing agent supply means that has an injection nozzle that supplies the reducing agent to the exhaust upstream side of the reduction catalyst in an exhaust passage of the exhaust system. The purification apparatus is characterized in that heating means for heating the exhaust gas in the exhaust passage to a temperature equal to or higher than the melting point of the reducing agent is provided on the exhaust upstream side of the injection nozzle.

  With such a configuration, the exhaust in the exhaust passage is made to exceed the melting point of the reducing agent by the heating means provided on the upstream side of the injection nozzle that supplies the reducing agent to the exhaust upstream side of the reduction catalyst in the exhaust passage of the exhaust system. Heat to the temperature of. Thereby, precipitation of a reducing agent is suppressed.

  According to a second aspect of the present invention, temperature detection means for detecting the exhaust temperature in the exhaust passage is provided in the vicinity of the exhaust upstream side of the injection nozzle, and the operation of the heating means is controlled by a detection signal of the temperature detection means. It is characterized by doing. Thus, the temperature detecting means provided near the exhaust upstream side of the injection nozzle detects the exhaust temperature in the exhaust passage, and controls the operation of the heating means based on the detection signal.

  The invention according to claim 3 is characterized in that the reducing agent is an aqueous urea solution. Thus, nitrogen oxides in the exhaust gas are reduced and purified using an aqueous urea solution that easily generates ammonia by hydrolysis as a reducing agent.

  The invention according to claim 4 is characterized in that the temperature of the exhaust gas heated by the heating means is 132 ° C. or higher. Thereby, the exhaust in the exhaust passage is heated by the heating means to a temperature not lower than the melting point of urea in the urea aqueous solution.

  The invention according to claim 5 is characterized in that the temperature of the exhaust gas heated by the heating means is 160 ° C. or higher. Thereby, the exhaust gas in the exhaust passage is heated by the heating means to a temperature equal to or higher than the melting point of urea in the urea aqueous solution, and also heated to a temperature at which the urea aqueous solution generates more ammonia.

  The invention according to claim 6 is characterized in that the heating means is an electric heat carrier that is disposed over substantially the entire cross section of the exhaust passage, has a porous structure, and generates heat when energized. As a result, the exhaust gas in the exhaust passage is heated to a temperature equal to or higher than the melting point of the reducing agent over substantially the entire area of the passage cross section by energizing the porous heat carrier disposed over the entire area of the cross section of the exhaust passage. .

  According to the first aspect of the present invention, even if the exhaust temperature from the engine is lower than the melting point of the reducing agent, the reducing agent is prevented from depositing in the exhaust passage and the reducing agent supplied from the injection nozzle is catalytically reduced. It can be used effectively for reaction. Therefore, the NOx in the exhaust gas can be purified to harmless components, and the NOx removal rate can be improved.

  According to the second aspect of the invention, the exhaust temperature in the exhaust passage is detected, and when the temperature is lower than the melting point of the reducing agent, the heating means is operated to reduce the exhaust in the vicinity of the exhaust nozzle upstream of the injection nozzle. It can be heated to a temperature above the melting point of the agent. Therefore, precipitation of the reducing agent can be suppressed and the NOx removal rate can be improved.

  Further, according to the invention of claim 3, NOx in the exhaust gas is purified to harmless components by using a urea aqueous solution that easily generates ammonia by hydrolysis without directly using ammonia as a reducing agent. By processing, the NOx removal rate can be improved.

  Furthermore, according to the invention of claim 4, even if the exhaust temperature from the engine is lower than the melting point of urea, urea is prevented from precipitating in the exhaust passage, and the urea aqueous solution supplied from the injection nozzle is used as a catalyst. It can be used effectively for reduction reaction. Therefore, the NOx removal rate can be improved.

  According to the fifth aspect of the invention, even when the exhaust temperature from the engine is lower than 160 ° C., urea is prevented from being precipitated in the exhaust passage, and the urea aqueous solution generates more ammonia. NOx reduction reaction is promoted, and the removal rate of NOx can be improved.

  Furthermore, according to the invention which concerns on Claim 6, the exhaust_gas | exhaustion in an exhaust passage can be rapidly heated to the temperature more than melting | fusing point of a reducing agent. Therefore, precipitation of the reducing agent can be suppressed and the NOx removal rate can be improved.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 is a view showing an embodiment of an exhaust emission control device for an engine according to the present invention. This exhaust purification device is for reducing and removing NOx discharged from a diesel engine, a gasoline engine or the like mounted on a moving vehicle using a reducing agent. The exhaust of the engine 1 using gasoline or light oil as fuel is discharged from the exhaust manifold 2 into the atmosphere via an exhaust pipe 3 serving as an exhaust passage. Specifically, the exhaust pipe 3 is provided with an oxidation catalyst 4 of nitric oxide (NO), a NOx reduction catalyst 5 and an ammonia slip oxidation catalyst 6 in order from the exhaust upstream side. An exhaust system is configured by providing a NOx sensor or the like, but the detailed configuration is not shown.

The oxidation catalyst 4 reduces NO or the like in the exhaust gas passing through the exhaust pipe 3 by an oxidation reaction. The catalyst shell is made of a material having excellent heat resistance and corrosion resistance such as stainless steel and has a shape like a large muffler. Is filled with catalyst pellets in which the surface of a porous member such as alumina is plated with platinum. The exhaust passing through the exhaust pipe 3 flows while contacting the catalyst pellets in the catalyst shell, so that NO in the exhaust undergoes an oxidation reaction (combustion) to become NO ₂ , and NOx in the reduction catalyst 5 on the downstream side. The removal rate is improved. Simultaneously with the oxidation reaction of NO, hydrocarbons (HC), carbon monoxide (CO), etc. in the exhaust gas are reduced by the oxidation reaction.

  The NOx reduction catalyst 5 is for reducing and purifying NOx in the exhaust gas passing through the exhaust pipe 3 with a reducing agent. For example, the honeycomb-shaped cross section made of ceramic cordierite or Fe-Cr-Al heat-resistant steel is used. A zeolite-type active component is supported on a monolith type catalyst carrier having the following. Then, the active component supported on the catalyst carrier is activated by the supply of the reducing agent, and effectively purifies NOx in the exhaust gas into a harmless substance. An ammonia slip oxidation catalyst 6 is disposed downstream of the NOx reduction catalyst 5.

  An injection nozzle 7 is disposed in the exhaust pipe 3 upstream of the NOx reduction catalyst 5, and the reducing agent and the pressure air are exhausted from the reducing agent supply device 8 through the injection nozzle 7. 3 is supplied by injection. Here, the injection nozzle 7 protrudes in the exhaust pipe 3 at a substantially right angle with the flow direction A of the exhaust gas, but the tip thereof extends toward the downstream side substantially in parallel with the flow direction A of the exhaust gas. It may be a thing. The reducing agent supply device 8 is supplied with the reducing agent stored in the storage tank 9 through the supply pipe 10. The injection nozzle 7 and the reducing agent supply device 8 constitute reducing agent supply means for supplying the reducing agent to the exhaust upstream side of the NOx reduction catalyst 5.

  In this embodiment, a urea aqueous solution (urea water) is used as a reducing agent to be supplied by injection from the injection nozzle 7. In addition, an aqueous ammonia solution or the like may be used. The urea water injected and supplied from the injection nozzle 7 is hydrolyzed by the exhaust heat in the exhaust pipe 3 and easily generates ammonia. The obtained ammonia reacts with NOx in the exhaust gas in the NOx reduction catalyst 5 to be purified into water and harmless gas. The urea water is a solid or powdery urea aqueous solution, stored in the storage tank 9, and supplied to the reducing agent supply device 8 through the supply pipe 10.

  Here, in the present invention, an electrothermal carrier 11 is provided on the exhaust upstream side of the injection nozzle 7. The electric heat carrier 11 serves as a heating means for heating the exhaust gas in the exhaust pipe 3 to a temperature equal to or higher than the melting point of urea in urea water. For example, the electric heat carrier 11 is made of a material having excellent heat resistance and corrosion resistance, such as stainless steel. It has a porous structure having a surface, and generates heat when a current is supplied from a power source 12 such as a battery. The electric heat carrier 11 is disposed over substantially the entire cross section of the exhaust passage of the exhaust system, and can quickly heat the exhaust flowing from the exhaust manifold 2.

  In addition, a temperature sensor 13 is provided in the vicinity of the exhaust nozzle 7 on the exhaust upstream side. The temperature sensor 13 serves as temperature detection means for detecting the exhaust temperature in the exhaust pipe 3. In this embodiment, the temperature sensor 13 detects the exhaust temperature near the exhaust upstream side of the injection nozzle 7. Then, the operation of the electric heat carrier 11 is controlled using the exhaust temperature detection signal detected by the temperature sensor 13.

  The reducing agent supply device 8, the power source 12, and the temperature sensor 13 are connected to a control circuit 14 composed of, for example, a CPU via signal lines 15a, 15b, and 15c, respectively, and operate under the control of the control circuit 14, respectively. It is like that. That is, in accordance with a control signal from the control circuit 14, the reducing agent supply device 8 is operated to inject and supply urea water from the injection nozzle 7 to the upstream side of the NOx reduction catalyst 5 and detect the exhaust temperature from the temperature sensor 13. In response to the signal, the control circuit 14 turns the power supply 12 on and off, energizes or shuts off the electric heat carrier 11, and heats the exhaust in the exhaust pipe 3 to a temperature equal to or higher than the melting point of urea.

  Specifically, the temperature of the exhaust gas in the exhaust pipe 3 heated by the heat generated by the electric heat carrier 11 is set to 132 ° C. or higher, which is the melting point of urea. Thereby, even if the exhaust temperature from the engine 1 is lower than the melting point of urea, the exhaust in the vicinity of the exhaust upstream side of the injection nozzle 7 is heated to 132 ° C. or more, and urea is deposited on the inner wall surface of the exhaust pipe 3. Can be suppressed.

  The temperature of exhaust in the exhaust pipe 3 heated by the heat generated by the electric heat carrier 11 is 160 ° C. or higher. As a result, even if the exhaust temperature from the engine 1 is lower than 160 ° C., the exhaust near the exhaust upstream side of the injection nozzle 7 is heated to 160 ° C. or more, and urea is deposited on the inner wall surface of the exhaust pipe 3. While suppressing, it can be set as the state which urea aqueous solution produces | generates more ammonia.

  Next, the operation of the exhaust emission control device thus configured will be described with reference to FIG. First, in FIG. 1, exhaust due to the operation of the engine 1 is conducted from an exhaust manifold 2 through an exhaust pipe 3 to an oxidation catalyst 4 disposed in the exhaust pipe 3 and a NOx reduction catalyst 5. Further, it passes through the ammonia slip oxidation catalyst 6 and is discharged into the atmosphere from the end discharge port of the exhaust pipe 3. At this time, urea water is injected from the injection nozzle 7 disposed on the exhaust upstream side of the NOx reduction catalyst 5 inside the exhaust pipe 3. To this injection nozzle 7, urea water is supplied from a urea water storage tank 9 through a supply pipe 10 to a reducing agent supply device 8. By operation of the reducing agent supply device 8, urea water is discharged into the exhaust together with pressure air. It is supplied by injection.

  In this state, the temperature sensor 13 provided in the vicinity of the exhaust upstream side of the injection nozzle 7 detects the exhaust temperature in the exhaust pipe 3 and sends the detection signal to the control circuit 14. When the control circuit 14 determines that the exhaust temperature detected by the temperature sensor 13 is less than 132 ° C., for example, the control circuit 14 sends an ON signal to the power supply 12 to supply current to the electric heat carrier 11 to generate heat, and the exhaust pipe 3 The exhaust flowing inside is heated. Exhaust is controlled to be heated within a predetermined temperature range by controlling on / off of energization to the electric heat carrier 11.

  In this way, the operation of the electric heat carrier 11 is controlled by the control circuit 14, and the exhaust gas upstream of the injection nozzle 7 is heated and maintained at, for example, 132 ° C. or higher, which is the melting point of urea. At this time, since the temperature sensor 13 is provided in the vicinity of the exhaust upstream side of the injection nozzle 7, as a result, the exhaust temperature in the vicinity of the exhaust upstream side of the injection nozzle 7 is maintained at 132 ° C. or higher. As a result, even if the exhaust temperature from the engine 1 is lower than the melting point of urea, urea is prevented from depositing on the inner wall surface of the exhaust pipe 3, and the urea water supplied from the injection nozzle 7 is effectively used for the catalytic reduction reaction. Can be used. Therefore, NOx in the exhaust gas can be purified to harmless components, and the NOx removal rate can be improved.

  As another temperature control example, when the control circuit 14 determines that the exhaust temperature detected by the temperature sensor 13 is lower than 160 ° C., for example, the control circuit 14 sends an ON signal to the power source 12 to the electric heat carrier 11. An electric current is supplied to generate heat, and the exhaust flowing in the exhaust pipe 3 is heated. By controlling the energization of the electric heat carrier 11 on and off, the exhaust is heated within a predetermined temperature range.

  Then, in the same manner as described above, the exhaust gas upstream of the injection nozzle 7 is heated by the control of the control circuit 14 and maintained at, for example, 160 ° C. or higher. At this time, as a result, the exhaust temperature in the vicinity of the exhaust upstream side of the injection nozzle 7 is maintained at 160 ° C. or higher. As a result, even when the exhaust temperature from the engine 1 is lower than 160 ° C., urea is prevented from precipitating on the inner wall surface of the exhaust pipe 3, and the urea aqueous solution is in a state where more ammonia is generated. Is promoted, and the NOx removal rate can be improved.

  Next, in order to end the urea water injection from the injection nozzle 7 by stopping the operation of the engine 1, the supply of the urea water from the storage tank 9 is first shut off by the operation of the reducing agent supply device 8, and then for a while. Supplies only pressure air to the injection nozzle 7. Thereby, urea water is expelled from the nozzle main body and the injection hole of the injection nozzle 7, and the injection of urea water is complete | finished.

  FIG. 3 is a view showing another embodiment of the exhaust emission control device of the present invention. In this embodiment, the arrangement of the oxidation catalyst 4 and the electric heat carrier 11 is switched in the configuration of the exhaust system, and the electric heat carrier 11 is arranged on the exhaust upstream side of the oxidation catalyst 4. Other configurations are exactly the same as those of the embodiment of FIGS. 1 and 2, and the same effects can be obtained.

  In the above description, as a heating means for heating the exhaust gas in the exhaust passage to a temperature equal to or higher than the melting point of the reducing agent, the electrothermal carrier 11 having a porous structure is provided over substantially the entire cross section of the exhaust passage. However, the present invention is not limited to this, and other devices may be used as long as the exhaust in the exhaust passage can be rapidly heated to a temperature equal to or higher than the melting point of the reducing agent. For example, a heater in which a heating wire such as a nichrome wire is stretched over substantially the entire cross section of the exhaust passage may be provided.

It is a conceptual diagram which shows embodiment of the exhaust emission purification device of the engine by this invention. It is an expansion outline figure for explaining operation of the above-mentioned exhaust purification device. It is an expansion schematic diagram which shows other embodiment of the exhaust gas purification apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Engine 3 ... Exhaust pipe 4 ... Oxidation catalyst 5 ... Reduction catalyst 6 ... Oxidation catalyst for ammonia slip 7 ... Injection nozzle 8 ... Reducing agent supply device 9 ... Storage tank 10 ... Supply piping 11 ... Electric heat carrier 13 ... Temperature sensor 14 ... Control circuit

Claims (6)

An oxidation catalyst disposed in the exhaust system of the engine to reduce nitric oxide in the exhaust by an oxidation reaction;
A reduction catalyst disposed in the exhaust system for reducing and purifying nitrogen oxides in the exhaust gas with a reducing agent;
Reducing agent supply means having an injection nozzle for supplying the reducing agent to the exhaust upstream side of the reduction catalyst in the exhaust passage of the exhaust system;
An exhaust emission control device for an engine equipped with
An engine exhaust gas purification apparatus comprising heating means for heating the exhaust gas in the exhaust passage to a temperature equal to or higher than the melting point of the reducing agent on the exhaust gas upstream side of the injection nozzle.   The temperature detecting means for detecting the exhaust temperature in the exhaust passage is provided in the vicinity of the exhaust upstream side of the injection nozzle, and the operation of the heating means is controlled by a detection signal of the temperature detecting means. An exhaust emission control device for an engine according to 1.   3. The engine exhaust gas purification apparatus according to claim 1, wherein the reducing agent is an aqueous urea solution.   The engine exhaust gas purification apparatus according to claim 3, wherein the temperature of the exhaust gas heated by the heating means is 132 ° C or higher.   The engine exhaust gas purification apparatus according to claim 3, wherein the temperature of the exhaust gas heated by the heating means is 160 ° C or higher.   6. The heating device according to claim 1, wherein the heating unit is an electric heat carrier that is disposed over substantially the entire cross section of the exhaust passage and has a porous structure and generates heat when energized. An exhaust emission control device for an engine according to 1.

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