JP2010048111A - Exhaust emission control system and exhaust emission control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control system and an exhaust emission control method making purification performances of catalysts quickly and efficiently usable with temperature dependence of purification performances of the catalysts and desulfurization treatment required for high temperature process considered in the exhaust emission control system provided with an exhaust emission control device using catalyst action of an NOx conversion catalyst device, an oxidation catalyst device, and a filter device with a catalyst. <P>SOLUTION: In the exhaust emission control system 1 provided with the exhaust emission control device 10 carrying catalyst converting harmful components in exhaust gas G, a section carrying catalyst of the exhaust emission control device 10 is divided into two of an outer circumference part 11 and a canter tube part 12 by a tubular partition wall 13, the exhaust gas G is made to flow to the outer circumference part 11 by opening a first valve 16 disposed between the outer circumference part 11 and an exhaust passage 2 of an internal combustion engine, the exhaust gas G is made to flow to the center tube part 12 by opening a second valve 18 disposed between the center tube part 12 and the exhaust passage 2, and the tubular partition wall 13 is formed in a heat insulating structure. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas in which a catalyst carrying part of an exhaust gas purifying device is divided into an outer peripheral part and a central cylindrical part, and a cylindrical partition wall having a heat insulating structure is formed between the outer peripheral part and the central cylindrical part. The present invention relates to an exhaust gas purification system provided with a gas purification device and an exhaust gas purification method.

  One device for purifying exhaust gas from an internal combustion engine is a NOx purification catalyst device for purifying NOx (nitrogen oxide) in the exhaust gas. In one of these NOx purification catalyst devices, an alkali metal or alkaline earth metal is supported together with a noble metal, NO (nitrogen monoxide) in exhaust gas containing excess oxygen is oxidized and adsorbed on the catalyst as a nitrate, There is an apparatus carrying a NOx occlusion reduction type catalyst for purifying NOx. This NOx occlusion reduction type catalyst occludes NOx when the exhaust gas is in a lean air-fuel ratio state with excess oxygen, and releases the occluded NOx in a rich air-fuel ratio state where the oxygen concentration is low or the air-fuel ratio is less than 1. The released NOx is reduced in a reducing atmosphere to reduce NOx.

  Moreover, as another device of the exhaust gas purification device, it cannot occlude NOx, but mainly carries precious metals and oxidizes and removes CO (carbon monoxide) and HC (hydrocarbon) by its oxidation action. There is an oxidation catalyst device. Furthermore, there is a filter device with a catalyst that collects PM (particulate matter) in exhaust gas and oxidizes and removes it with an oxidation catalyst supported on a filter or a PM oxidation catalyst.

  Using these catalytic devices and filter devices with catalysts, the harmful gases such as NOx, CO, HC and PM in the exhaust gas discharged from the internal combustion engine are purified, and these harmful components are released into the atmosphere. The amount is reduced below the emission standard.

  However, in an exhaust gas aftertreatment system using these catalysts, it is necessary to raise the catalyst to a temperature at which the catalyst is activated and a purification reaction is possible. Although it depends on the type of the catalyst, when the temperature reaches approximately 200 ° C. to 250 ° C., the purification reaction is started. However, until the activation temperature is reached, harmful components in the exhaust gas cannot be removed by catalytic reaction, and there is a problem that the harmful components are discharged into the atmosphere as they are. In other words, in the aftertreatment system using a catalyst, if the time to reach the temperature at which the catalyst starts the purification reaction is short, the amount of harmful components released into the atmosphere can be reduced accordingly.

  In this connection, a flow path control mechanism is provided upstream of the catalyst, and when the exhaust gas temperature is low, the exhaust gas flow is concentrated at the center of the catalyst so that the catalyst temperature reaches the activation temperature quickly. In addition, when the exhaust gas temperature is high, the exhaust gas is concentrated in the periphery of the catalyst, and even if the exhaust gas becomes hot, a catalytic converter for a diesel engine that prevents the formation and accumulation of sulfate in the catalyst is proposed. (For example, refer to Patent Document 1).

  In this diesel engine catalytic converter, it is considered effective to provide a plurality of cooling fans on the outer surface of the catalytic converter housing, and in order to suppress the generation of sulfate, the exhaust gas is discharged when the exhaust gas reaches a high temperature. Instead of flowing in the central part of the catalyst, the catalyst is passed through in a concentrated manner at the periphery of the catalyst having a low temperature.

  However, maintaining the temperature of the outer peripheral portion at a low temperature seems to be effective for suppressing the formation of sulfate, but in terms of NOx purification, the temperature of the entire catalyst needs to be raised above the activation temperature of the catalyst. Therefore, lowering the temperature of the outer peripheral portion is not preferable from the viewpoint of NOx purification. Further, when desulfurization is performed by raising the temperature of the outer peripheral portion in order to remove the sulfate generated in the catalyst, there is a problem that it is difficult to increase the temperature of the outer peripheral portion of the catalyst and desulfurization regeneration is difficult.

  If the exhaust gas temperature is lower than the oxidation catalyst activation temperature, a high-temperature exhaust gas treatment unit carrying the oxidation catalyst is provided in the center and a low-temperature exhaust gas treatment unit equipped with heating means is provided in the periphery. The exhaust gas is heated above the oxidation catalyst activation temperature and flowed to the low temperature exhaust gas processing section to improve the exhaust gas purification efficiency at start-up and when the exhaust gas temperature decreases, and the exhaust gas When the temperature is equal to or higher than the oxidation catalyst activation temperature, an automobile exhaust gas treatment device that stops the operation of the heating means and flows exhaust gas to the high-temperature exhaust gas treatment unit to purify harmful components by the oxidation catalyst. It has been proposed (see, for example, Patent Document 2).

  In this automobile exhaust gas treatment device, when the exhaust gas temperature is high, the exhaust gas is flowed through the high temperature exhaust gas treatment unit and the low temperature exhaust gas treatment unit to purify it. In such a case, the path is switched to flow into the peripheral low temperature exhaust gas processing section via the heating means. As a result, the exhaust gas is heated to a temperature higher than the catalyst activation temperature by the heating means, and the heated exhaust gas flows into the low-temperature exhaust gas processing section for purification.

  However, in general, because of the heat dissipation, the central part of the catalyst is likely to be at a high temperature, and the peripheral part is likely to be at a low temperature. The configuration of the processing apparatus has a problem of poor thermal efficiency.

In contrast, as a means of shortening the temperature raising time for heating the catalyst, the present inventor changes the heat capacity of the portion where the catalyst is supported, and supports the catalyst when the exhaust temperature is low, such as immediately after starting the engine. It was considered that the exhaust gas is allowed to flow only in the central part of the part that has been made to reduce the heat capacity of the part carrying the catalyst to be heated, thereby shortening the temperature raising time.
JP-A-10-299465 JP 2002-295233 A

  The present invention has been made in view of the above situation, and an object of the present invention is to purify an exhaust gas provided with an exhaust gas purification device that uses a catalytic action such as a NOx purification catalyst device, an oxidation catalyst device, and a filter device with a catalyst. Provided is an exhaust gas purification system and an exhaust gas purification method capable of quickly and efficiently using catalyst purification performance in consideration of temperature dependency of catalyst purification performance and desulfurization treatment that requires high-temperature treatment. There is.

  In order to achieve the above object, an exhaust gas purification system of the present invention is an exhaust gas purification system comprising an exhaust gas purification device carrying a catalyst for purifying harmful components in the exhaust gas, the catalyst of the exhaust gas purification device. Is divided into an outer peripheral portion and a central cylindrical portion by a cylindrical partition wall, and a first valve is provided between the exhaust passage and the outer peripheral portion of the internal combustion engine, and the exhaust passage and the central cylindrical portion. A second valve is provided between the first and second valves, and exhaust gas is caused to flow to the outer peripheral portion by opening the first valve, and exhaust gas is caused to flow to the central cylinder portion by opening the second valve; The cylindrical partition wall is formed in a heat shield structure.

  According to this configuration, the part carrying the catalyst is divided into two parts by the cylindrical partition wall of the heat-shielding structure, and the heat capacity in each part is reduced. When it is necessary to raise the temperature above the activation temperature, the exhaust gas is flowed only to one catalyst side (for example, the central cylinder side) whose heat capacity has decreased compared to the whole catalyst, thereby quickly The catalyst can be activated by increasing the temperature.

  At this time, a cylindrical partition wall between the outer peripheral portion and the central cylindrical portion is formed in the heat shield structure so as to suppress heat transfer and reduce the amount of heat lost by heat transfer to the outer peripheral portion. Since it comprises, the heat | fever of exhaust gas can be utilized efficiently for temperature rising of a center cylinder part, and the catalyst of a center cylinder part can be heated up rapidly.

  Further, when the exhaust gas temperature increases and the volumetric flow rate of the exhaust gas increases, the volume of the portion through which the exhaust gas passes is also caused by flowing the exhaust gas through the other catalyst (for example, the outer peripheral side). To reduce the space velocity with respect to the exhaust gas of the exhaust gas purification device, and to increase the contact time with the catalyst to promote the catalytic reaction. Can be purified.

  As an exhaust gas purifying device carrying a catalyst for purifying this harmful component, a NOx occlusion reduction type catalyst, a NOx direct reduction type catalyst, a selective reduction type NOx catalyst (SCR catalyst), an oxidation catalyst, a three-way catalyst, with a catalyst There are filters.

  In the exhaust gas purification system described above, when the first index temperature indicating the temperature of the catalyst in the central cylinder portion is equal to or lower than a preset first determination temperature, the first valve is closed and the second valve is opened to exhaust gas. When the first index temperature exceeds the first determination temperature, the first valve is opened while the second valve is open, and exhaust gas is exhausted from the central cylinder portion and the outer periphery. Configured to flow to both of the parts.

  The “first index temperature” refers to the temperature of the catalyst in the central cylinder portion itself or a temperature indicating the temperature. This is because it is often difficult to directly measure the temperature of the catalyst. Instead, a temperature closely related to the temperature of the catalyst, for example, the temperature of the exhaust gas flowing into the central cylinder or the central cylinder is used. The temperature of the exhaust gas flowing out may be used. Therefore, “first index temperature” is expressed as an expression including the temperature used instead.

  The first determination temperature is a temperature equal to or higher than the activation temperature of the catalyst, and is a temperature within a range of 200 ° C. to 300 ° C., for example, set to 250 ° C., depending on the type of catalyst. Until the first index temperature reaches the first determination temperature, the exhaust gas does not flow in the outer peripheral portion.

  According to this configuration, at the time of warm-up operation or low-load operation immediately after engine startup, the first index temperature is low and the exhaust gas volumetric flow rate is also small, so the exhaust gas is caused to flow through the central cylinder portion with good heat retention, It is possible to quickly raise the temperature of the catalyst in the tube portion and shorten the time until activation. In addition, when the first index temperature is high and the exhaust gas volume flow rate is large, the exhaust gas is flowed through both the central tube portion and the outer peripheral portion, the volume of the portion through which the exhaust gas passes is increased, and the space velocity relative to the exhaust gas is increased. The catalyst reaction can be promoted by increasing the time during which the exhaust gas contacts the catalyst.

  In the above exhaust gas purification system, a NOx occlusion reduction type catalyst is used as the catalyst, potassium is supported as a NOx occlusion material in the central cylinder portion, and barium is carried as an NOx occlusion material in the outer peripheral portion. Configure.

  According to this configuration, high-temperature (450 ° C. to 550 ° C.) potassium is often passed through a high-temperature exhaust gas, and is provided in the central cylinder portion having a high average temperature during the NOx purification treatment. ˜450 ° C.) is provided in the outer peripheral portion where the passage of low-temperature exhaust gas is frequent and the average temperature is low during the NOx purification treatment, so that different catalyst components are arranged according to the temperature characteristics. Thus, the NOx occlusion performance can be exhibited more efficiently.

  In the exhaust gas purification system, when the desulfurization process is performed, the first valve is closed when the first index temperature indicating the temperature of the catalyst in the central cylinder portion is equal to or lower than a preset second determination temperature. When the second valve is opened and exhaust gas is allowed to flow only through the central tube portion, the first index temperature exceeds the second determination temperature, and the first index temperature exceeds the second determination temperature. The first valve and the second valve are kept open and closed until the first determination time set in advance, which is the sum, elapses, and the first desulfurization time is the first time. When the determination time has elapsed, the first valve is opened, the second valve is closed, exhaust gas is allowed to flow only to the outer peripheral portion, and a second index temperature indicating the temperature of the catalyst in the outer peripheral portion is preliminarily set. Set the third judgment temperature In other words, the first valve and the second valve until the second desulfurization treatment time, which is the sum of the times when the second index temperature exceeds the third determination temperature, passes a preset second determination time. The open / close state is continued as it is, and when the second desulfurization processing time has passed the second determination time, the desulfurization processing is terminated.

  The “first index temperature” refers to the temperature of the catalyst in the central cylinder portion itself or a temperature indicating the temperature thereof. The “second index temperature” refers to the temperature of the catalyst in the outer peripheral portion itself or the temperature thereof. Say the temperature to do. This is because it is often difficult to directly measure the temperature of the catalyst. Instead, a temperature closely related to the temperature of the catalyst, for example, the temperature of the exhaust gas flowing into the central cylinder or the outer periphery or the center The temperature of the exhaust gas flowing out from the cylinder part or the outer peripheral part may be used. Therefore, the expression including the temperature used instead is expressed as “first index temperature” and “second index temperature”.

  The second determination temperature and the third determination temperature are temperatures equal to or higher than the temperature at which the desulfurization treatment of the catalyst in the central cylinder portion or the outer peripheral portion can be performed, and depending on the type of the catalyst, a range of 650 ° C to 750 ° C For example, 700 ° C. and 650 ° C. Note that the third determination temperature is usually set lower than the second determination temperature because of thermal degradation.

  The first determination time is the time until the desulfurization treatment of the catalyst in the central cylinder portion is completed, and the second determination time is the time until the desulfurization treatment of the catalyst in the outer peripheral portion is completed. These times are set based on the results of experiments conducted in advance. In general, the second determination time is longer than the first determination time because barium used in the NOx occlusion reduction catalyst for low temperature is more easily desorbed than potassium used in the NOx occlusion reduction catalyst for high temperature. Set short.

  According to this configuration, in the desulfurization treatment that requires the catalyst to be at a high temperature, from the first index temperature exceeding the second determination temperature until the first determination time is exceeded, the heat insulating structure of the cylindrical partition wall Exhaust gas is allowed to flow through the central tube portion where heat retention is high and the temperature rises quickly, and the desulfurization process of the central tube portion is completed. Further, when the desulfurization process of the central cylinder part is completed, the exhaust gas is flowed to the outer peripheral part where the temperature rise of the catalyst is likely to be delayed as compared with the central cylindrical part, and the desulfurization process of the outer peripheral part is concentrated. Therefore, desulfurization of the entire catalyst can be performed efficiently.

  For example, in a NOx occlusion reduction type catalyst, the NOx purification performance deteriorates due to sulfur adsorption. This sulfur adsorption occurs at temperatures below about 600 ° C, while desulfurization requires high temperatures above about 650 ° C. Therefore, the adsorption of sulfur extends to the outer periphery of the catalyst which does not easily reach a high temperature. However, in the desulfurization, the catalyst temperature needs to be further increased. However, since the outer peripheral portion does not easily reach a high temperature, there is a problem that sulfur tends to remain.

  In order to solve this problem, in the present invention, a cylindrical heat shield structure (partition wall) is provided between the inner side and the outer side in the radial direction of the portion supporting the catalyst to form a central cylindrical portion and an outer peripheral portion, and desulfurization is performed. In the latter half of the treatment, only the outer periphery is desulfurized, and the exhaust gas is difficult to pass through and the outer periphery where the temperature is difficult to rise is persistently desulfurized, so that sufficient desulfurization can be performed over the entire catalyst. It becomes like this.

  As a result, it is possible to reduce the time and number of reduction processes necessary for maintaining the purification performance of the catalyst, in other words, the regeneration process for recovering the purification capacity of the catalyst, thereby reducing the fuel consumption required for the regeneration process. . Therefore, the capacity of the catalyst mounted on the vehicle can be reduced to ensure the mountability and reduce the cost. In addition, in the desulfurization treatment, it is possible to suppress the deterioration of the catalyst due to the central cylinder portion being exposed to an excessively high temperature by heating only the outer peripheral portion of the catalyst that is easily cooled to a high temperature.

  Furthermore, if a heat retaining structure is provided around the outer periphery, the temperature of the catalyst at the outer periphery can be raised more efficiently during the desulfurization process.

  Further, the desulfurization treatment can be performed separately for the outer peripheral portion and the central cylindrical portion, and the number of desulfurization treatments of the outer peripheral portion and the central cylindrical portion can be changed. In this case, it is relatively difficult to adsorb sulfur. It is also possible to reduce the amount of fuel used for the desulfurization process by reducing the number of treatments in the outer peripheral part and reducing the heat treatment time of the central cylinder part.

  And the exhaust gas purification method of the present invention for achieving the above object is an exhaust gas purification method of an exhaust gas purification system comprising an exhaust gas purification device carrying a catalyst for purifying a harmful component in the exhaust gas. A portion of the exhaust gas purifying device that supports the catalyst is divided into an outer peripheral portion and a central cylindrical portion by a cylindrical partition wall, and the cylindrical partition wall is formed in a heat shield structure to form the outer peripheral portion and the central portion. Provided between the exhaust passage of the internal combustion engine and the outer peripheral portion when the first index temperature that shields heat from the cylinder portion and the first index temperature that indicates the temperature of the catalyst in the central cylinder portion is equal to or lower than a preset first determination temperature. While closing a 1st valve, the 2nd valve provided between the said exhaust passage and the said center cylinder part is opened, exhaust gas is flowed only to the said center cylinder part, and the said 1st parameter | index temperature uses the said 1st determination temperature. When exceeded, the second valve was opened Or is the exhaust gas by opening the first valve and wherein the flow into both of the outer peripheral portion and the central cylindrical portion. The first index temperature and the first determination temperature are the same as the first index temperature and the first determination temperature.

  According to this method, at the time of warm-up operation or low load operation immediately after engine start, the first index temperature is low and the exhaust gas volumetric flow rate is also small. It is possible to quickly raise the temperature of the catalyst in the tube portion and shorten the time until activation. In addition, when the first index temperature is high and the exhaust gas volume flow rate is large, the exhaust gas is flowed through both the central tube portion and the outer peripheral portion, the volume of the portion through which the exhaust gas passes is increased, and the space velocity relative to the exhaust gas is increased. The catalyst reaction can be promoted by increasing the time during which the exhaust gas contacts the catalyst.

  In the above exhaust gas purification method, when the desulfurization process is performed, the first valve is closed when the first index temperature indicating the temperature of the catalyst in the central cylinder portion is equal to or lower than the preset second determination temperature. When the second valve is opened and exhaust gas is allowed to flow only through the central tube portion, the first index temperature exceeds the second determination temperature, and the first index temperature exceeds the second determination temperature. The first valve and the second valve are kept open and closed until the first determination time set in advance, which is the sum, elapses, and the first desulfurization time is the first time. When the determination time has elapsed, the first valve is opened, the second valve is closed, exhaust gas is allowed to flow only to the outer peripheral portion, and a second index temperature indicating the temperature of the catalyst in the outer peripheral portion is preliminarily set. Exceeds the set third judgment temperature And until the second desulfurization processing time, which is the sum of the times when the second index temperature exceeds the third determination temperature, has passed a second determination time set in advance, the first valve and the second valve The open / close state is continued as it is, and when the second desulfurization processing time has passed the second determination time, the desulfurization processing is terminated.

  According to this method, since the desulfurization process can be performed completely, it is possible to reduce the time and number of times for the regeneration process to recover the purification ability of the catalyst. Therefore, the fuel consumption necessary for this regeneration process can be reduced. Therefore, the capacity of the catalyst mounted on the vehicle can be reduced to ensure the mountability and reduce the cost. Further, in the desulfurization treatment, only the outer peripheral portion of the catalyst that is easily cooled is heated to a high temperature, so that the central cylinder portion is exposed to an excessively high temperature and the catalyst can be prevented from deteriorating.

  According to the exhaust gas purification system and the exhaust gas purification method of the present invention, in the exhaust gas purification device using a catalyst such as a NOx purification catalyst device, an oxidation catalyst device, and a filter device with a catalyst, the temperature dependence of the purification performance of the catalyst. Therefore, the purification performance of the catalyst can be utilized quickly and efficiently.

  In other words, the part carrying the catalyst is divided into two parts by the cylindrical partition wall of the heat shield structure, and the heat capacity of the divided part is reduced, so it is necessary to quickly raise the temperature of the catalyst in the case of warm-up operation, etc. If there is, the temperature of the catalyst can be quickly raised and activated by flowing the exhaust gas through a portion having a small heat capacity.

  At this time, a cylindrical partition wall is formed in the heat-insulating structure between the central tube portion and the outer peripheral portion to suppress heat transfer and lost due to the heat transfer between the central tube portion and the outer peripheral portion. Since the amount of heat is reduced, the heat of the exhaust gas can be efficiently used to raise the temperature of the catalyst supporting portion. Therefore, the temperature of the catalyst can be raised quickly, and harmful components in the exhaust gas can be efficiently purified with the activated catalyst.

  In addition, when the exhaust gas temperature rises and the volume of the exhaust gas flow increases, the exhaust gas flows through all the catalysts to increase the catalyst volume and reduce the space velocity of the catalyst with respect to the exhaust gas. As a result, the time during which the exhaust gas contacts the catalyst can be lengthened to promote the catalytic reaction.

  Hereinafter, an exhaust gas purification system and an exhaust gas purification method according to embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a configuration of an exhaust gas purification system 1 according to an embodiment of the present invention. This exhaust gas purification system 1 is one of a NOx purification catalyst device, an oxidation catalyst device, a catalyst-equipped filter device in which an exhaust passage 2 of an engine (internal combustion engine) carries a catalyst that purifies harmful components in the exhaust gas G, or The exhaust gas purification device 10 formed by several combinations is arranged and configured.

When the exhaust gas purification device 10 is an oxidation catalyst device that supports an oxidation catalyst, the exhaust gas temperature is increased by oxidizing HC (hydrocarbon) in the exhaust gas, or NO (monooxide) in the exhaust gas. In order to facilitate the purification of NOx (nitrogen oxide) by oxidizing (nitrogen) to NO ₂ (nitrogen dioxide), an oxidation catalyst such as platinum is supported on a support such as a porous ceramic honeycomb structure. Formed.

  When the exhaust gas purification device 10 is a NOx purification catalyst device carrying a NOx occlusion reduction type catalyst, the exhaust gas purification device 10 is formed of a monolith catalyst to purify NOx in the exhaust gas. A catalyst coat layer of aluminum oxide, titanium oxide or the like is provided on a carrier such as a cordierite honeycomb of the monolith catalyst. This catalyst coat layer is configured to carry a NOx occlusion reduction catalyst comprising a catalyst metal such as platinum (Pt) or palladium (Pd) and a NOx occlusion material (NOx occlusion material) such as barium (Ba).

  This NOx occlusion reduction type catalyst purifies NOx in the exhaust gas by the NOx occlusion material storing NOx in the exhaust gas when the oxygen concentration is in a high exhaust gas state, that is, in an air-fuel ratio lean state, When the oxygen concentration is low, the air-fuel ratio is less than 1 or the air-fuel ratio is rich, or the air-fuel ratio is in the air-fuel ratio stoichiometric state, the stored NOx is released, and the released NOx is also catalyzed by the catalytic metal. By reducing with NO, the outflow of NOx to the atmosphere is prevented.

  When the air-fuel ratio lean state continues, the NOx occlusion reduction catalyst changes the NOx occlusion material to nitrate, and therefore performs regeneration control to make the exhaust gas rich in the air-fuel ratio before the NOx occlusion capacity is saturated. The NOx occlusion capacity is recovered by releasing and reducing the occluded NOx.

  When the exhaust gas purification device 10 is a filter device with a catalyst, an inlet of a porous ceramic honeycomb channel (exhaust gas passage) is used to purify PM (particulate matter) in the exhaust gas. And a monolith honeycomb wall flow type filter or the like in which the outlets are alternately sealed. A catalyst such as platinum or cerium oxide is supported on the filter so as to promote the oxidation of PM and HC at a relatively high temperature and to adsorb HC at a relatively low temperature. PM in the exhaust gas is collected by the porous ceramic wall of the catalyst-equipped filter device.

  In this filter device with a catalyst, in order to prevent the amount of collected PM from increasing and pressure loss to increase, when the collected amount of PM exceeds a predetermined collected amount or before and after the filter device with catalyst When the differential pressure exceeds a predetermined differential pressure amount, exhaust gas temperature control is performed to raise the exhaust gas temperature and raise the temperature of the catalyst-equipped filter device above the fuel temperature of PM. In the exhaust gas temperature raising control, air-fuel ratio rich control including unburned fuel supply control is performed.

  In the present invention, as shown in FIGS. 1 and 3, the portion of the exhaust gas treatment device 10 carrying the catalyst is divided into two parts, an outer peripheral part 11 and a central cylindrical part 12, and a cylindrical ring is formed in the gap. The partition wall 13 is formed in a heat shield structure and arranged. Further, a heat insulating structure 14 having a heat insulating property for heat insulation is provided around the outer peripheral portion 11. The heat retaining structure 14 is also configured to serve as a catalyst storage container.

  When the central cylindrical portion 12 is formed in a cylindrical shape, the outer peripheral portion 11 is provided in the periphery thereof, and the exhaust gas purification device 10 is formed in a cylindrical shape, the outer diameter RA of the central cylindrical portion 12 and the outer peripheral portion The ratio of the outer diameter RB is set in consideration of the use conditions of the catalyst based on the temperature raising time. In other words, the ratio of the cross-sectional area of the central cylinder part to the cross-sectional area of the outer peripheral part is set in consideration of the use conditions of the catalyst based on the temperature rise time.

  For example, the cross-sectional area of the part supporting the catalyst is made the same, and the volume of the central cylindrical part 12 and the volume of the outer peripheral part 11 are formed to be equal, and the catalyst is supported without changing the amount of heat necessary for heating the catalyst. If the exhaust gas G is allowed to flow only through the central cylinder portion 12 so that the heat capacity of the portion is halved, in this case, the catalyst temperature Tc2 is set to a predetermined temperature (for example, 200 ° C.) immediately after the engine is started. The time required to raise the temperature to about 50% is reduced to about half, and the emission of harmful components in the exhaust gas until the catalyst is activated can be reduced. Further, when the exhaust gas temperature is high and the volumetric flow rate of the exhaust gas G is increased, the exhaust gas G is also caused to flow through the catalyst on the outer peripheral portion 11. As a result, the volume of the portion carrying the catalyst through which the exhaust gas passes is increased with respect to the increased amount of harmful component to lower the space velocity, and the time for the harmful component of the exhaust gas to contact the catalyst is lengthened. Therefore, it is possible to sufficiently purify harmful components of the exhaust gas.

  As shown in FIG. 4, the cylindrical partition wall 13 is formed in a ring shape by bending a double wall structure formed by two plates 13 b and 13 c sandwiching a corrugated plate 13 a therebetween. The both ends of the exhaust gas are closed so that the exhaust gas cannot flow in and out. The ring-shaped corrugated plate 13a reduces the contact area between the two plates 13b and 13c to reduce heat transfer due to heat conduction, and is formed between the corrugated plate 13a and the double walls 13b and 13c. The space portion 13d is filled with air, and the heat shielding property is increased by the air having low thermal conductivity.

  The heat insulating structure 14 surrounding the outer peripheral portion 11 is formed of a foaming material containing a large amount of air so as to improve the heat insulating property and the heat insulating property (heat insulating property), and also serve as a container for storing the catalyst carrier. Composed. By providing the heat retaining structure 14, the temperature of the catalyst can be raised more efficiently during the activation of the catalyst and the desulfurization process.

  Further, a first valve 16 is provided in the first passage 15 between the exhaust passage 2 and the outer peripheral portion 11 of the engine, and a second valve 18 is provided in the second passage 17 between the exhaust passage 2 and the central cylinder portion 12. By opening the first valve 16, the exhaust gas G flows through the outer peripheral portion 11, and by opening the second valve 18, the exhaust gas G flows through the central cylinder portion 12.

  Further, in order to measure the temperature Tc1 of the catalyst in the central cylindrical portion 12, a thermocouple 19 as a temperature sensor is disposed at the outer peripheral portion on the downstream side of the central cylindrical portion 12, and the temperature Tc2 of the catalyst in the outer peripheral portion 11 is measured. In order to do this, the thermocouple 20 is arranged at the outer peripheral portion on the downstream side of the outer peripheral portion 11. Further, in order to measure the temperature Tg of the exhaust gas G flowing into the exhaust gas purification device 10, a thermocouple 21 is disposed in the exhaust passage 2 upstream of the exhaust gas purification device 10.

  The measured values Tc1, Tc2, and Tg of these thermocouples 19, 20, and 21 are input to an engine control unit (ECU) 3 that controls the operation of the engine. Based on these measured values Tc1, Tc2, and Tg, The opening and closing operation of the first valve 16 and the second valve 18 is performed.

  According to this configuration, the parts 11 and 12 carrying the catalyst are divided into two parts by the cylindrical partition wall 13 having a heat shielding structure, and the heat capacity of each part 11 and 12 is reduced. When it is necessary to quickly raise the temperature of the catalyst to the activation temperature or higher, the exhaust gas G is flowed only to the central cylindrical portion 12 side where the heat capacity of the portion supporting the catalyst is reduced as compared with the whole. The catalyst can be activated by increasing the temperature of the catalyst.

  At this time, a cylindrical partition wall 13 provided between the outer peripheral portion 11 and the central cylindrical portion 12 is formed in a heat shield structure, and the movement of heat is suppressed to move from the central cylindrical portion 12 to the outer peripheral portion 11. Since the amount of heat to be reduced is reduced, the heat of the exhaust gas G can be efficiently used to raise the temperature of the central cylinder portion 12, and the temperature of the catalyst in the central cylinder portion 12 can be rapidly increased accordingly. Further, the heat retaining structure 14 also indirectly contributes to the temperature rise of the central cylinder portion 12.

  Further, when the temperature Tg of the exhaust gas G increases and the volumetric flow rate of the exhaust gas G increases, the exhaust gas G is allowed to flow to the outer peripheral portion 11 side while flowing the exhaust gas G to the central cylinder portion 12. By increasing the volume of the portion carrying the catalyst through which the exhaust gas passes, the space velocity with respect to the exhaust gas G can be reduced, and the time for the exhaust gas G to contact the catalyst can be lengthened to promote the catalytic reaction. In this case, the heat retaining structure 14 promotes an increase in the temperature of the catalyst on the outer peripheral portion 11.

  Further, in this exhaust gas purification system 1, when the exhaust gas purification device 10 is a NOx purification catalyst device and a NOx occlusion reduction type catalyst is used as the catalyst, the central cylinder portion 12 has potassium as the NOx occlusion material. It is preferable that the outer peripheral portion 11 is configured to support barium as a NOx storage material.

  According to this configuration, high-temperature (450 ° C. to 550 ° C.) potassium is often passed through the high-temperature exhaust gas, and is provided in the central cylinder portion 12 having a high average temperature during the NOx purification treatment. Since the low temperature exhaust gas passes through the outer peripheral portion 11 where the average temperature is low during the NOx purification treatment, the NOx occlusion performance is more efficiently achieved with different catalyst components. Can be demonstrated.

  Next, an exhaust gas purification method in the exhaust gas purification system 1 having the above configuration will be described. In a normal operation state, both the first valve 16 and the second valve 18 are opened, the exhaust gas G is caused to flow through both the outer peripheral portion 11 and the central cylinder portion 12, and harmful components in the exhaust gas G are catalyzed. Purify. In addition, the exhaust gas G for warm-up operation, low-load operation, etc. is low temperature, and it is necessary to activate the catalyst quickly, and desulfurization treatment to recover the catalyst from sulfur poisoning requires the catalyst to be at a high temperature. If there is, the first valve 16 and the second valve 18 are controlled as follows according to each case.

  First, the case of warm-up operation and low-load operation will be described with reference to the control flow of FIG. When the engine is started and the control flow in FIG. 5 is called from the advanced control flow, the temperature (first index temperature) Tg of the exhaust gas G and the first determination temperature T1 set in advance are input in step S11. Is done. In step S12, it is determined whether or not the temperature Tg of the exhaust gas G is equal to or lower than the first determination temperature T1. In the control flow of FIG. 5, the temperature Tg of the exhaust gas G flowing into the central cylinder portion 11 is used as the first index temperature that indicates the temperature of the catalyst in the central cylinder portion 11. Note that the temperature Tc1 measured by the thermocouple 19 can also be used.

  If it is determined in step S12 that the temperature Tg of the exhaust gas G is equal to or lower than the first determination temperature T1 (YES), the process goes to step S13, the first valve 16 is closed, and the second valve 18 is opened. As a result, the exhaust gas G is allowed to flow only through the central cylinder portion 12. After performing this control, after a predetermined time (time related to the interval for checking the exhaust gas temperature Tg) has elapsed, the process returns to step S11.

  If it is determined in step S12 that the temperature Tg of the exhaust gas G exceeds the first determination temperature T1 (NO, go to step S14, open the first valve 16 and open the second valve 18, that is, the second valve 18 Open the first valve 16. As a result, the exhaust gas G flows through both the central cylinder portion 12 and the outer peripheral portion 11. After this control, a preset time (check of the exhaust gas temperature Tg is checked). After the elapse of (interval related time), the process returns to step S11.

  If this step S11 to step S13 or step S11 to step S14 is repeatedly executed and the engine is stopped, an interrupt is generated, the end process of step S15 is performed, and the control flow returns to the advanced control flow. With the end of the flow, the control flow of FIG. 5 is also ended.

  According to this configuration, at the time of warm-up operation or low load operation immediately after engine startup, the temperature Tg of the exhaust gas G is low and the volumetric flow rate of the exhaust gas G is small, so that the exhaust gas G is added to the central cylinder portion 12 with good heat retention. And the temperature of the catalyst in the central cylinder portion 12 can be quickly raised. Further, when the temperature Tg of the exhaust gas G is high and the volumetric flow rate of the exhaust gas G is large, the exhaust gas G is allowed to flow through both the central cylindrical portion 12 and the outer peripheral portion 11 to increase the volume of the portion through which the exhaust gas G passes. By reducing the space velocity with respect to the exhaust gas G, the time during which the exhaust gas G contacts the catalyst can be lengthened to promote the catalytic reaction.

  The first determination temperature T1 is a temperature equal to or higher than the activation temperature of the catalyst, for example, a temperature at which the NOx purification rate is 80% or higher. Although this 1st determination temperature T1 is based also on the kind of catalyst, it is the temperature in the range of 200 to 300 degreeC, for example, is set to 250 degreeC.

  Note that the control flow of FIG. 5 is effective when the engine is started or in a low load operation. However, when the temperature Tg of the exhaust gas rises from the low load operation to the high load operation, step S14 is performed. Since the first valve 16 and the second valve 18 are both opened, it is not always necessary to stop the control flow of FIG.

  Next, the case of desulfurization treatment in which the temperature of the catalyst needs to be increased will be described with reference to the control flow of FIGS. The control flow in FIG. 6 and the control flow in FIG. 7 are one control flow connected by A at the lower end of FIG. 6 and A at the upper end of FIG.

  In the exhaust gas purification system 1, when the desulfurization process is performed, the control flow in FIG. 5 is switched to the control flow in FIGS. 6 and 7 by an advanced control flow. Here, the measured temperature Tc1 of the thermocouple 19 is used as the first index temperature, and the measured temperature Tc2 of the thermocouple 20 is used as the second index temperature. However, the hot exhaust gas is used as the first index temperature and the second index temperature. The temperature Tg of G may be used.

  The control flow in FIGS. 6 and 7 is a control in the case of performing the desulfurization process. When started, in step S21 in FIG. 6, a first index temperature Tc1 that indexes the temperature of the catalyst in the central cylinder portion 12 is preset. A second determination temperature T2 and a preset first determination time t1 are input. Next, in step S22, it is determined whether or not the first index temperature Tc1 is equal to or lower than the second determination temperature T2.

  If it is determined in step S22 that the first index temperature Tc1 is equal to or lower than the second determination temperature T2 (YES), the process proceeds to step S23, where the first valve 16 is closed and the second valve 18 is opened. As a result, the exhaust gas G is allowed to flow only through the central cylinder portion 12. After performing this control, after a lapse of a preset time (time related to the interval for checking the first index temperature Tc1), the process returns to step S21.

  If the first index temperature Tc1 exceeds the second determination temperature T2 in the determination in step S22 (NO), it is the sum of the times when the first index temperature Tc1 exceeds the second determination temperature T2 in step S24. The first desulfurization treatment time td1 is counted. In the next step S25, it is determined whether or not the first desulfurization treatment time td1 has passed a preset first determination time t1. If it is determined in step S25 that the first desulfurization treatment time td1 has not passed the first determination time t1 (NO), the preset time (the first desulfurization treatment time td1 is checked as it is). After the elapse of (interval related time), the process returns to step S21.

  If it is determined in step S25 that the first desulfurization treatment time td1 has passed the first determination time t1 (YES), the process proceeds to step S26 of FIG. 7 via A, and the first valve 16 is opened to open the second valve. 18 is closed and the exhaust gas G is allowed to flow only to the outer peripheral portion 11.

  In the next step S27, a second index temperature Tc2 that indicates the temperature of the catalyst on the outer peripheral portion 11, a preset third determination temperature T3, and a preset second determination time t2 are input. In the next step S28, it is determined whether or not the second index temperature Tc2 is equal to or lower than the third determination temperature T3. If it is determined in step S28 that the second index temperature Tc2 is equal to or lower than the third determination temperature T3 and does not exceed the third determination temperature T3 (YES), a preset time (interval for checking the second index temperature Tc2) is determined. After elapse of the valve-related time), the process returns to step S27.

  If it is determined in step S28 that the second index temperature Tc2 exceeds the third determination temperature T3 (NO), in the next step S29, the total time during which the second index temperature Tc2 exceeds the third determination temperature T3. The second desulfurization treatment time td2 is counted. In the next step S30, it is determined whether or not the second desulfurization treatment time td2 has passed a preset second determination time t2. If it is determined in step S30 that the second desulfurization treatment time td2 has not passed the second determination time t2 (NO), the preset time (check of the second desulfurization treatment time td2) is left as it is. After the elapse of (interval related time), the process returns to step S27.

  If it is determined in step S30 that the second desulfurization processing time td2 has passed the second determination time t2 (YES), the process goes to step S31 to reset the first desulfurization processing time td1 and the second desulfurization processing time td2, etc. After completing the desulfurization process, return to the advanced control throw.

  Normally, the third determination temperature is set lower than the second determination temperature, and the second determination time is set shorter than the first determination time. This is because barium used in the low-temperature NOx storage reduction catalyst is more easily desorbed than potassium used in the high-temperature NOx storage reduction catalyst. Depending on the type of catalyst and the exhaust gas purification device 10, for example, the second determination temperature T2 is set to about 700 ° C. to 750 ° C., and the third determination temperature T3 is set to about 650 ° C. to 700 ° C. The determination time t1 is set to about 480 s to 600 s, and the second determination time t2 is set to about 180 s to 300 s.

  According to the exhaust gas purification method in the case of this desulfurization process, in the desulfurization process that requires the catalyst to be at a high temperature, from when the first index temperature Tc1 exceeds the second determination temperature T2 until it exceeds the first determination time t2. The exhaust gas G is completely flowed through the central cylindrical portion 12 that has high heat retention and quick temperature rise due to the heat insulating structure of the cylindrical partition wall 13, and is performed until the desulfurization treatment of the central cylindrical portion 11 is completed, and then the thermal insulation is performed. Although the heat retaining property is good depending on the structure, the exhaust gas G can be entirely flowed to the outer peripheral portion 11 where the temperature rise of the catalyst is likely to be delayed as compared with the central cylindrical portion 12, and the desulfurization treatment of the outer peripheral portion 11 can be performed intensively.

  Therefore, in the desulfurization process of the central cylinder part 12, since the heat transfer from the central cylinder part 12 is suppressed by the partition wall 13, the heat treatment time of the central cylinder part 12 can be reduced, and the outer peripheral part 11 Since the heat transfer from the outer peripheral part 11 is suppressed by the partition wall 13 and the heat retaining structure 14 during the desulfurization process, the heat treatment time of the outer peripheral part 11 can also be reduced. Therefore, the temperature of each part can be quickly raised, the entire catalyst can be efficiently desulfurized, and the time and fuel consumption required for the desulfurization process can be reduced.

  In addition, in the first half of the desulfurization treatment, only the central cylinder portion 12 is desulfurized, and in the second half of the desulfurization treatment, only the outer peripheral portion 11 is desulfurized, and the outer peripheral portion of the catalyst, in which exhaust gas does not easily pass and the temperature does not easily rise, By performing the desulfurization treatment steadily, sufficient desulfurization can be performed over the entire catalyst. Therefore, the purification ability can be maintained in a good state.

  As a result, it is possible to reduce the time and number of reduction processes necessary for maintaining the purification performance of the catalyst, in other words, the regeneration process for recovering the purification capacity of the catalyst, thereby reducing the fuel consumption required for the regeneration process. . Therefore, the capacity of the catalyst mounted on the vehicle can be reduced to ensure the mountability and reduce the cost. In addition, in the desulfurization treatment, it is possible to suppress the deterioration of the catalyst due to the central cylinder portion being exposed to an excessively high temperature by heating only the outer peripheral portion of the catalyst that is easily cooled to a high temperature.

  In the control flow shown in FIGS. 6 and 7, the number of desulfurization treatments is the same for the central cylinder portion 12 and the outer peripheral portion 11, but further, the sulfur treatment is performed between the outer peripheral portion 11 and the central cylinder portion 12. If it is configured to perform the process separately, the number of treatments of the outer peripheral portion 11 which is relatively difficult to adsorb sulfur can be reduced, so that the fuel consumption can be further reduced.

It is a figure which shows the structure of the exhaust-gas purification system of embodiment of this invention. It is a figure which shows the structure of the inlet_port | entrance of the exhaust gas of an exhaust gas purification apparatus. It is a figure which shows the cross section of an exhaust-gas purification apparatus. It is an enlarged view of the ellipse part shown by H of FIG. 3 which shows the structure of the cylindrical partition wall of an exhaust-gas purification apparatus. It is a figure which shows an example of the control flow in the case of warm-up operation and low load operation of the exhaust gas purification method according to the present invention. It is a figure which shows the first half of an example of the control flow in the case of the desulfurization process of the exhaust gas purification method which concerns on this invention. It is a figure which shows the second half of the control flow of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exhaust gas purification system 2 Engine exhaust passage 3 Engine control apparatus (ECU)
DESCRIPTION OF SYMBOLS 10 Exhaust gas purification apparatus 11 Outer peripheral part 12 Central cylinder part 13 Partition wall 13a Corrugated sheet 13b, 13c Board (double wall)
13d Space 14 Thermal insulation structure 15 First passage 16 First valve 17 Second passage 18 Second valve 19, 20, 21 Thermocouple G Exhaust gas T1 First judgment temperature T2 Second judgment temperature T3 Third judgment temperature Tc1 First Index temperature Tc2 Second index temperature Tg Exhaust gas temperature t1 First determination time t2 Second determination time td1 First desulfurization time td2 Second desulfurization time

Claims (6)

In an exhaust gas purification system equipped with an exhaust gas purification device carrying a catalyst for purifying harmful components in exhaust gas,
A portion carrying the catalyst of the exhaust gas purifying device is divided into an outer peripheral portion and a central cylindrical portion by a cylindrical partition wall, and a first valve is provided between the exhaust passage of the internal combustion engine and the outer peripheral portion, A second valve is provided between the exhaust passage and the central cylinder part, and the exhaust gas flows into the outer peripheral part by opening the first valve, and the exhaust gas is supplied to the central cylinder part by opening the second valve. While configuring to flow,
An exhaust gas purification system, wherein the cylindrical partition wall is formed in a heat shield structure.   When the first index temperature indicating the temperature of the catalyst in the central cylinder portion is equal to or lower than the first determination temperature set in advance, the first valve is closed and the second valve is opened to allow the exhaust gas to flow only in the central cylinder portion. When the first index temperature exceeds the first determination temperature, the first valve is opened while the second valve is open, and the exhaust gas is allowed to flow through both the central tube portion and the outer peripheral portion. The exhaust gas purification system according to claim 1.   The NOx occlusion reduction type catalyst is used as the catalyst, potassium is supported as a NOx occlusion material in the central cylindrical portion, and barium is supported as an NOx occlusion material in the outer peripheral portion. The exhaust gas purification system according to 1 or 2.   When the desulfurization treatment is being performed, if the first index temperature indicating the temperature of the catalyst in the central cylinder portion is equal to or lower than the second determination temperature set in advance, the first valve is closed and the second valve is opened to exhaust the exhaust gas. A first desulfurization treatment time that is the sum of the time when the first index temperature exceeds the second determination temperature after the gas is allowed to flow only through the central cylinder portion and the first index temperature exceeds the second determination temperature. Until the first determination time set in advance has elapsed, the open and closed states of the first valve and the second valve are continued as they are, and when the first desulfurization processing time has passed the first determination time, The first valve is opened and the second valve is closed to allow the exhaust gas to flow only in the outer peripheral portion. Further, a second index temperature indicating the temperature of the catalyst in the outer peripheral portion exceeds a preset third determination temperature. And the second index temperature is the third Until the second desulfurization processing time, which is the sum of the times exceeding the constant temperature, passes the preset second determination time, the open and closed states of the first valve and the second valve are continued as they are, and the second desulfurization is continued. 4. The exhaust gas purification system according to claim 1, wherein the desulfurization treatment is terminated when the treatment time passes the second determination time. In an exhaust gas purification method of an exhaust gas purification system provided with an exhaust gas purification device carrying a catalyst for purifying harmful components in exhaust gas,
A portion of the exhaust gas purifying device that supports the catalyst is divided into an outer peripheral portion and a central cylindrical portion by a cylindrical partition wall, and the cylindrical partition wall is formed in a heat shield structure to form the outer peripheral portion and the central portion. Heat insulation between the tube,
When the first index temperature indicating the temperature of the catalyst in the central cylinder portion is equal to or lower than a first determination temperature set in advance, the first valve provided between the exhaust passage of the internal combustion engine and the outer peripheral portion is closed, and the exhaust When the second valve provided between the passage and the central cylinder part is opened to allow exhaust gas to flow only in the central cylinder part, the second valve is activated when the first index temperature exceeds the first determination temperature. An exhaust gas purification method, wherein the first valve is opened while the exhaust valve is opened, and the exhaust gas is allowed to flow through both the central cylindrical portion and the outer peripheral portion.   When the desulfurization treatment is being performed, if the first index temperature indicating the temperature of the catalyst in the central cylinder portion is equal to or lower than the second determination temperature set in advance, the first valve is closed and the second valve is opened to exhaust the exhaust gas. A first desulfurization treatment time that is the sum of the time when the first index temperature exceeds the second determination temperature after the gas is allowed to flow only through the central cylinder portion and the first index temperature exceeds the second determination temperature. Until the first determination time set in advance has elapsed, the open and closed states of the first valve and the second valve are continued as they are, and when the first desulfurization processing time has passed the first determination time, The first valve is opened and the second valve is closed to allow the exhaust gas to flow only in the outer peripheral portion. Further, a second index temperature indicating the temperature of the catalyst in the outer peripheral portion exceeds a preset third determination temperature. And the second index temperature is the third Until the second desulfurization processing time, which is the sum of the times exceeding the constant temperature, passes the preset second determination time, the open and closed states of the first valve and the second valve are continued as they are, and the second desulfurization is continued. The exhaust gas purification method according to claim 5, wherein the desulfurization treatment is terminated when the treatment time passes the second determination time.

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