CN108368760A - Internal combustion engine exhaust gas purification system and internal combustion engine exhaust gas purification method - Google Patents

Abstract

In an exhaust gas purification system (1) for an internal combustion engine, in which a catalyst-carrying particulate collection unit (21) is disposed in an exhaust passage (15) of the internal combustion engine (10), wherein an exhaust gas purification unit carrying an oxidation catalyst is not disposed on the upstream side of the catalyst-carrying particulate collection unit (21) in the exhaust passage (15), the filter of the catalyst-carrying particulate collection unit (21) is constituted by a particulate filter (21a), and a catalyst (21b) carried by the particulate filter (21a) is a non-noble metal catalyst containing no noble metal.

Description

Internal combustion engine exhaust gas purification system and internal combustion engine exhaust gas purification method

technical field

This patent relates to an internal combustion engine exhaust gas purification system and an internal combustion engine exhaust gas purification method. More specifically, an internal combustion engine exhaust gas purification system and an internal combustion engine exhaust gas purification method are disclosed, in which pressure loss in an exhaust gas purification unit for purifying PM (particulate matter) is reduced, thereby making regeneration of PM zero or regenerating PM The frequency of PM is significantly reduced, even if the fuel used has a high content of sulfur, the incidence of sulfur poisoning caused by noble metal catalysts will be reduced, and thus the amount of fuel consumed to purify PM will also be reduced.

Background technique

Generally, in a vehicle equipped with an internal combustion engine such as a diesel engine, as shown in FIG. The oxidation catalyst unit 31 and the particulate trapping unit 32 carrying the catalyst are constituted.

In general, the oxidation catalyst unit 31 oxidizes CO (carbon monoxide) and HC in exhaust gas Ga using a noble metal catalyst 31b which is placed on a carrier 31a and contains a noble metal, thereby performing various functions such as a temperature raising function so that the temperature of the exhaust gas Ga Lifting; the function of removing SOOT, which is a kind of oxidation of PM; and the function of generating NO ₂ (nitrogen dioxide), which is the function of oxidizing NO (nitrogen monoxide) into nitrogen dioxide. Moreover, the catalyst-loaded particulate trap unit 32 disposed on the downstream side can relatively easily operate various processes, for example, the process of removing PM in normal combustion; the process of removing it by combustion when PM is regenerated; and carrying Catalyst particulate trap unit 32 related to desulfurization treatment of sulfur poisoning regeneration.

Meanwhile, the oxidation catalyst unit 31 uses a noble metal catalyst 31b containing a platinum group noble metal such as rhodium (Rh), palladium (Pd), platinum (Pt), and thus results in high cost. As a result, a noble metal catalyst 31b that reduces the amount of noble metal used was developed.

In addition, if only the catalyst unit 31 is oxidized, the SOF (soluble organic fraction) adhering to the SOOT of PM can be purified by the low noble metal catalyst coating with a small amount of the noble metal catalyst 31b. However, since there is no filtering function, the purification rate of PM is very low.

Therefore, although the catalyst-loaded particulate trap unit 32 is provided, in order to achieve a very small particulate filtration efficiency of, for example, less than 10% on a mass basis, the filter of the catalyst-loaded particulate trap unit 32 is Inlets and outlets of porous ceramic honeycomb channels are alternately sealed as integral wall-flow filters 32 a and the like, thereby suppressing PM from flowing downstream.

In addition, by supporting the catalyst 32b such as a noble metal catalyst, a combination of platinum and a basic NOx absorbing material, a PM oxidation catalyst such as ceria (CeO ₂ ), it acts to promote combustion to remove trapped PM.

Furthermore, when the amount of PM trapped in the catalyst-loaded particulate trap unit 32 increases due to the continued low temperature of the exhaust gas Ga, the pressure difference across the catalyst-loaded particulate trap unit 32 also increases. Therefore, in order to keep the pressure difference between front and back at a predetermined level or less, it is necessary to perform a PM regeneration process that periodically burns and removes PM. Moreover, when the catalyst 32b carried on the particulate trapping unit 32 carrying the catalyst degrades the catalytic function related to the combustion and removal of PM due to sulfur poisoning, it is necessary to perform the treatment of sulfur poisoning regeneration. In the sulfur poisoning regeneration treatment, the catalyst temperature is set to Desulfurization is performed at a high temperature of 600 degrees Celsius or higher and in a rich combustion state.

Meanwhile, since the combination of the oxidation catalyst unit 31 and the catalyst-loaded particulate trap unit 32 requires two exhaust gas purification units, for example, in the catalyst-loaded particulate trap using a wall flow filter without an oxidation catalyst unit, In the unit, an exhaust gas purification filter is proposed. On the partition wall on the exhaust gas inflow side, the first exhaust gas purification catalyst composed of transition metal and alkali metal salt is carried; Exhaust gas purification catalyst (For example, please refer to Patent Document 1).

Then, since the exhaust gas purification filter uses the second exhaust gas purification catalyst containing precious metals, in areas where high-sulfur fuel is used, the sulfur components removed from the exhaust gas cause sulfur poisoning, the oxidation function is weakened, and the PM purification function is also reduced. will be weakened. In addition, in the desulfurization treatment for solving sulfur poisoning, a high-temperature rich combustion environment is required, so that the fuel consumed in regeneration of sulfur poisoning increases, and thus the efficiency of fuel utilization also decreases.

With regard to the problem of sulfur poisoning, recently, a mixed catalyst composed of a complex metal oxide composed of various metals and a specific alkali metal sulfate has high activity against PM and is highly tolerant, so a method that does not require the use of a platinum group has been proposed. Diesel engine exhaust gas purification catalyst that is a metal and replaces a noble metal catalyst (refer to Patent Document 2 and Non-Patent Document 1).

Compared with the noble metal catalysts in the prior art, the diesel exhaust gas purification catalyst does not use the oxygen in _NO2 to burn PM. Specifically, it burns by directly supplying oxygen in the air to PM, and this catalyst is characterized in that the gaseous oxygen molecules in the exhaust gas are decomposed, and then the decomposed oxygen molecules are provided to PM, thereby achieving High-efficiency combustion to remove PM. Unlike noble metal catalysts, this diesel exhaust gas purification catalyst hardly causes sulfur poisoning.

At the same time, instead of the wall-flow filter that can remove more than 90% of PM in exhaust gas, a diesel engine emission treatment system is proposed that has a fine particle filtration efficiency in which less than 10% of fine particles can be filtered out, and in An SCR catalyst having a _NOx conversion effect is supported on a partial filter having a particle filtration efficiency in the range of about 30% to 60% on a mass basis (for example, see Patent Document 3).

The particle filter is composed of a metal foam filter with a porosity between 60% and 95%, metal mesh, etc. In addition, granular ceramics can also be used as a particulate filter, and the oxidation catalyst and PM oxidation catalyst are attached to the surface of the ceramic particles, whereby PM trapped and accumulated in the particulate filter can be burned by the heat of exhaust gas. In addition, there are other types of particulate filters in which the plugged portion of one end of the unit is reduced in the wall-flow filter.

<reference list>

patent documents

Patent Document 1: Japanese Patent Laid-Open No. 2009-247931

Patent Document 2: Japanese Patent Laid-Open No. 2014-508

Patent Document 3: Japanese Patent Application Publication No. 2012-528705

non-patent literature

Non-Patent Document 1: Tatsuro MIYAGAWA, Takahiro NAKAJIMA, Masahiro KUBO and Ryosuke SUGA, "Catalyst consisting of combined metal oxide and alkali metal sulfate for diesel exhaust emissions”, pp. 20-24, Vol. 57, No. 1, Panasonic Technical Journal, April 2011.

Contents of the invention

technical problem

Meanwhile, the catalyst-loaded particulate trap unit using the wall flow filter disclosed in Patent Document 2 and Non-Patent Document 1 not only easily collects PM, but also has a high purification rate for PM. However, the catalyst-loaded particulate trap unit also has some problems, such as large pressure loss, easy clogging during PM capture, and pressure difference between before and after the catalyst-loaded particulate trap unit due to clogging. become more apparent. Therefore, because of the increase in exhaust gas temperature caused by PM regeneration, the frequency of PM regeneration during _NO2 generation also increases, and thus the amount of fuel consumed for PM regeneration also increases, resulting in poor fuel efficiency.

In addition, the particulate filter disclosed in Patent Document 3 has a smaller pressure loss in the initial stage and a smaller increase in pressure loss during PM capture than a wall-flow filter. Therefore, the use of particulate filters is an effective way to reduce the pressure loss of particulate trapping units loaded with catalysts. At the same time, the fine particle filtering efficiency of PM is also high, so PM may not be completely purified.

The internal combustion engine exhaust gas purification system and the internal combustion engine exhaust gas purification method disclosed in this patent can not only reduce the increase in pressure loss caused by the catalyst-loaded particle trapping unit that traps PM, but also avoid the use of fuels containing high concentrations of sulfur. Sulfur poisoning in precious metals at that time, so it is possible to maintain the ability of PM purification for a longer period of time. As a result, the PM regeneration of the catalyst-loaded particulate trap unit may be zero or the PM regeneration frequency may be significantly reduced.

means of solving problems

The internal combustion engine exhaust gas purification system of the present invention includes: a catalyst-loaded particulate trap unit arranged in an exhaust passage of the internal combustion engine, wherein the exhaust gas purification unit loaded with a noble metal catalyst is not arranged upstream of the catalyst-loaded particulate trap unit In the exhaust passage on the side, wherein the filter of the catalyst-loaded particulate trap unit is composed of a partial filter, and the catalyst carried by the particulate filter is a non-precious metal catalyst that does not contain noble metal.

That is, the performance of the PM purification function in the exhaust gas is not performed based on the cooperation of the oxidation catalyst unit arranged on the upstream side and the catalyst-carrying particulate trap unit arranged on the downstream side, and its operation is based on such a structure that In this structure, no oxidation catalyst unit is included but only a catalyst-loaded particle trap unit. In addition, the non-precious metal catalyst supported on the particulate filter is composed of a compound that does not contain noble metal, whereby oxidation and combustion of PM are performed by the non-precious metal catalyst.

Here, the particle filter refers to a filter having a particle filtration efficiency at which particles between 30% and 60% by mass can be filtered. The particle filter can be composed of metal foam, metal mesh, granular ceramics, and the like. In addition, the initial pressure loss of the particulate filter is less than that of the wall-flow filter, and the increase rate of the pressure loss is lower when trapping PM. Therefore, in the particulate filter, the oxidation catalyst and the PM oxidation catalyst are supported on the surfaces of the pores of the metal foam, the metal mesh, and the granular ceramics.

According to the above structure, since the particulate filter is used as the filter structure for trapping PM, it is comparable to the case of using a monolithic honeycomb type wall flow filter in which the inlet and outlet of the honeycomb flow path of porous ceramics are alternately sealed. ratio, the increase ratio of pressure loss caused by pressure loss and PM trapping can be significantly reduced. Accordingly, PM regeneration for addressing the increase in pressure loss may be zero or its frequency may be significantly reduced, and thus the amount of fuel consumed for generating PM may be reduced, thereby improving fuel utilization efficiency.

In addition, the catalyst carried on the particulate filter is a non-precious metal catalyst that does not contain noble metals. Therefore, even if the sulfur content in the exhaust gas is relatively high due to the use of fuel with a high sulfur content, the catalyst does not contain noble metals. It is possible to avoid the occurrence of sulfur poisoning. In addition, since the non-noble metal catalyst contains a very small amount of sulfur poisoning, it is possible to suppress the weakening of the PM oxidation function to maintain the PM purification function, thereby compensating for the weakening of the PM purification rate due to the use of the particulate filter.

In addition, the exhaust gas purification system of an internal combustion engine does not contain an exhaust gas purification unit carrying a noble metal catalyst, that is, an oxidation catalyst unit, so that the pressure loss caused by the use of the oxidation catalyst unit can be reduced.

Furthermore, in this internal combustion engine exhaust gas purification system, the non-noble metal catalyst may be a mixed catalyst composed of a composite metal oxide composed of a plurality of metals and an alkali metal sulfate.

According to the structure described above, this mixed catalyst composed of composite metal oxide composed of multiple metals and alkali metal sulfate does not use platinum metal catalyst. Moreover, unlike noble metal catalysts, this hybrid catalyst does not use oxygen in _NO2 to burn PM, but burns PM by directly supplying atmospheric oxygen to PM, so the incidence of sulfur poisoning can be suppressed, and it makes PM has better purification efficiency. As a result, it is possible to compensate the low PM collection rate of the particulate filter and improve the PM purification rate as the catalyst-loaded particulate trap unit.

The internal combustion engine exhaust gas purification of the present invention is a method for internal combustion engine exhaust gas purification, wherein the particulate matter in the exhaust gas is purified by a catalyst-loaded particle trapping unit arranged in the exhaust gas exhaust passage, including exhaust gas discharged from the exhaust passage of the internal combustion engine passing through A catalyst-loaded particulate trap unit, which is a particulate filter that carries a non-precious metal catalyst that does not contain heavy metals, instead of passing exhaust gas through an exhaust gas purification unit that carries a noble metal catalyst. According to the internal combustion engine exhaust gas purification method, the same effect as that of the internal combustion engine exhaust gas purification system can be obtained.

outstanding effect

According to the disclosed content of the internal combustion engine exhaust gas purification system and the internal combustion engine exhaust gas purification method of the present invention, the particle filter is used as the filter structure for trapping PM (particulate matter), and the pressure loss and the increase of the pressure loss can be significantly reduced, thereby enabling to solve the problem of pressure loss The increase in the problem of PM regeneration is zero or its frequency can be significantly reduced. As a result, the amount of fuel consumed for generating PM can be reduced, thereby improving fuel utilization efficiency.

In addition, since the catalyst carried on the particulate filter is a non-precious metal catalyst, sulfur poisoning can be avoided even when fuel with a high sulfur concentration is used. Thereby, deterioration of the PM oxidation function can be suppressed and the PM purification function can be maintained, thus compensating for the deterioration of the PM purification rate due to the use of the particulate filter.

In addition, since an exhaust gas purification unit carrying a noble metal catalyst is not provided, pressure loss can be reduced.

That is, by this combination of not using the oxidation catalyst unit and using the particulate filter, the pressure loss in the exhaust gas purification unit for purifying PM and the increase in pressure loss therein can be reduced. In addition, by using this combination of particulate filter and non-precious metal catalyst, not only sulfur poisoning can be avoided, but also a low degree of pressure loss and a high degree of PM purification rate can be maintained. According to the two effects produced by the above three combinations, not only the frequency of PM regeneration can be reduced, but also the increase in fuel consumption due to maintaining the PM purification rate can be reduced by eliminating the regeneration of sulfur poisoning.

Description of drawings

FIG. 1 is a configuration diagram showing an exhaust gas purification system of an internal combustion engine according to an embodiment disclosed in the present invention.

FIG. 2 is a configuration diagram showing a PM purification unit composed only of a catalyst-carrying particulate trap unit.

FIG. 3 is a configuration diagram showing a PM purification unit composed of a combination of an oxidation catalyst unit and a catalyst-carrying fine particle trap unit.

Detailed ways

The following is a detailed description of the embodiments of the disclosed internal combustion engine exhaust gas purification system and internal combustion engine exhaust gas purification method with reference to the accompanying drawings.

As shown in FIG. 1 , an internal combustion engine exhaust gas purification system 1 will be described. In the engine (internal combustion engine) 10 equipped with the internal combustion engine exhaust gas purification system 1, the fresh air A introduced from the atmosphere passes through the air cleaner 17 in the intake passage 14, the turbocharger (turbocharger) 18 in the Compressor 18b, intercooler 19a and intake throttle valve 19b, after which fresh air A enters cylinder 10a from intake valve 12. Exhaust gas Ge (EGR gas) flows from the EGR passage 16 into the intake passage 14 along with the fresh air A as required.

The intake gas (A+Ge) is compressed by the piston 10 b provided in the cylinder 10 a, and the fuel injected from the fuel injection device 11 starts to combust, thereby generating power of the engine 10 . Exhaust gas G generated by fuel combustion flows out into exhaust passage 15 through exhaust valve 13, and a part of exhaust gas G flows into EGR passage 16 as EGR gas Ge. At this time, the remaining exhaust gas Ga (=G-Ge) is purified after passing through the exhaust purification device 20 via the turbine 18a of the turbocharger 18, and then the remaining exhaust gas Ga is discharged as purified exhaust gas Gc through a muffler (not shown). into the air.

In addition, the exhaust purification device 20 is not equipped with a pre-stage oxidation catalyst unit, but is sequentially equipped with a catalyst-loaded particulate trap unit 21, a selective reduction catalyst unit (SCR) 22, and a post-stage oxidation catalyst unit on the upstream side. A rear-stage oxidation catalyst unit (DOC) 23 is installed. In addition, it also has a pressure sensor 24 and a temperature sensor 25, through which the pressure difference before and after the particle trapping unit 21 loaded with catalyst can be detected; The temperature of the exhaust gas Ga.

In addition, a fuel nozzle 26 for injecting fuel F into the exhaust gas Ga is provided to assist PM regeneration in the catalyst-loaded particulate trap unit 21 when necessary, and this process occurs in the catalyst-loaded particulate trap unit 21. In the exhaust passage 15 on the upstream side. In addition, on the upstream side of the selective reduction catalyst unit 22, there is a urea injection device 27 for supplying urea as a NOx reducing agent to the selective reduction catalyst unit 22 for NOx purification.

A controller 41 is provided which controls fuel injection in the fuel nozzle 26 and urea injection in the urea injection device 27 . The controller 41 may be integrated into the overall system controller 40 that controls the overall operating state of the engine 10, or the controller may be provided separately.

As shown in FIG. 2, the filter structure of the catalyst-loaded particulate trap unit 21 is formed of a particulate filter 21a on which the catalyst is a non-precious metal catalyst 21 that does not contain noble metal.

The particle filter 21a is a filter having a particle filtration efficiency at which particles between 30% and 60% by mass can be filtered. Compared with the wall-flow filter, the initial pressure loss of the particulate filter 21 is lower, and the increase in pressure loss when collecting PM is also lower.

The particulate filter 21a may be formed of metal foam, metal mesh, granular ceramics, or the like. Formed by partially removing the seal at the end of the wall flow filter. In the particulate filter 21a, the non-precious metal catalyst 21b is supported on the surface of the pores of the metal foam, the surface of the metal mesh, the surface of granular ceramics, and the like.

The non-noble metal catalyst 21b may be embodied in the form of a mixed catalyst composed of a composite metal oxide with multiple metals and an alkali metal sulfate. The mixture of transition metal sulfate or transition metal oxide and alkali metal sulfate has ideal PM combustion activity, the mixture of vanadium pentoxide (V ₂ O ₅ ) and potassium sulfate (K ₂ SO ₄ ) and vanadyl sulfate (VOSO ₄ ) and cesium sulfate (Cs ₃ SO ₄ ) can also achieve the above effects.

That is, the PM purification function in the exhaust gas Ga is not performed based on the combination of the oxidation catalyst unit located on the upstream side and the catalyst-carrying particulate trap unit 21 located on the downstream side, but only based on the abolished oxidation catalyst unit Such a configuration of the catalyst-loaded particulate trapping unit 21 is completed. In addition, a non-noble metal catalyst as a purification catalyst, composed of a compound that does not contain noble metals such as platinum (Pt), palladium (Pd), is loaded on the particulate filter 21a, thereby passing through the catalytic action of the above non-noble metal catalyst 21b to oxidize and burn PM.

As shown in the implementation of the disclosed embodiments of the present invention, the exhaust gas purification method of the internal combustion engine is to purify the PM in the exhaust gas Ga in the particulate trap unit 21 loaded with the catalyst, wherein the particulate trap unit 21 loaded with the catalyst is located in the engine 10 in the exhaust passage 15. In addition, the internal combustion engine exhaust gas purification method is operated so that the exhaust gas Ga exhausted from the engine 10 does not pass through the exhaust gas purification unit carrying the noble metal catalyst, but passes through the filter structure having a particulate filter 21a and the carried catalyst does not contain the noble metal The catalyst-loaded particulate trapping unit 21 of the non-noble metal catalyst 21b. The above is the purification treatment process of exhaust gas Ga.

According to the internal combustion engine exhaust gas purification system 1 and the internal combustion engine exhaust gas purification method disclosed in the present invention, compared with the wall flow filter 32a, since the particle filter 21a is used as the structure for trapping PM, the pressure loss and the pressure loss caused by the PM can be significantly reduced. Increased pressure loss from PM collection. As a result, PM regeneration to account for increased pressure loss may be zero, or the frequency of PM regeneration may be significantly reduced. Therefore, it is possible to reduce the amount of fuel consumed to generate PM and improve the efficiency of fuel utilization.

In addition, a non-noble metal catalyst 21b containing no noble metal is supported on the particulate filter 21a. Therefore, even if fuel with a high sulfur content is used, so that a relatively high concentration of sulfur components flows into the exhaust gas Ga, that is to say, the fuel of the engine 10 has a relatively high sulfur content, but it can still be avoided because no catalyst containing noble metals is used. Sulfur poisoning often occurs with noble metal catalysts. In addition, since the non-precious metal catalyst 21b is used, it is possible to suppress the deterioration of the PM oxidation function and maintain the PM purification function, so it is also possible to compensate for the deterioration of the PM purification rate due to the use of the particulate filter 21a.

In addition, according to PM purification device 30 in the prior art shown in FIG. 3 , internal combustion engine exhaust gas purification system 1 is not equipped with oxidation catalyst unit 31 , so pressure loss due to use of oxidation catalyst unit 31 can be reduced.

That is, by the combination of not employing the oxidation catalyst unit 31 and employing the particulate filter 21, the pressure loss caused by purifying PM in the exhaust gas purifying unit 21 and the resulting increase in pressure are reduced. Furthermore, by a combination of using the particulate filter 21a and using the non-precious metal catalyst 21b, sulfur poisoning can be avoided while maintaining a low degree of pressure loss and a high degree of PM purification rate. According to the two effects produced by the above three combinations, the frequency of PM regeneration is reduced, and by eliminating sulfur poisoning regeneration, an increase in fuel consumption for maintaining PM purification capability can also be suppressed.

The priority claimed by this application is based on Japanese Patent Application (JP-2015-243228) filed on December 14, 2015, the entire contents of which are incorporated herein by reference.

Industrial Application Capability

According to the internal combustion engine exhaust gas purification system and the internal combustion engine exhaust gas purification method, the pressure loss in the exhaust gas purification unit for purifying PM is reduced, so that PM regeneration can be made zero, or the frequency of PM regeneration can be significantly reduced, even when fuel containing high sulfur is used When , the sulfur poisoning of the noble metal catalyst can be avoided, and the amount of fuel consumed to purify PM is also significantly reduced.

Explanation of reference signs

1: Internal combustion engine exhaust gas purification system

10: Engine (internal combustion engine)

15: exhaust channel

20: Exhaust gas purification device

21: Particle trapping unit loaded with catalyst

21a: Particle filter

21b: Purification Catalyst

22: Selective reduction catalyst unit (SCR)

23: Post Oxidation Catalyst Unit (DOC)

26: Fuel nozzle

27: Urea injection device

40: Overall System Controller

41: Controller

A: fresh air

A+Ge: inhaled gas

G: Exhaust gas generated

Ga: Exhaust gas entering the exhaust gas purification system (G-Ge)

Gc: Purified exhaust gas

Ge: exhaust gas (EGR gas)

Claims (3)

1. a kind of internal-combustion engines exhaust gas purifying system, including：

It is loaded with the micro particle catching unit of catalyst, is arranged in the exhaust passage of internal combustion engine,

Wherein, carrying noble metal is not arranged in the upstream side of the micro particle catching unit for being loaded with catalyst in an exhaust gas The exhaust purification unit of catalyst, and

Wherein, the filter of the micro particle catching unit for being loaded with catalyst be made of particulate filter, and

Wherein, the catalyst carried on the particulate filter is free from the non-precious metal catalyst of noble metal.

2. internal-combustion engines exhaust gas purifying system as described in claim 1, wherein

Above-mentioned non-precious metal catalyst be by with various metals metal composite oxide and alkali metal sulfates constitute it is mixed Close catalyst.

3. a kind of method of internal-combustion engines exhaust gas purifying, wherein passing through the catalyst that is loaded with being arranged in the exhaust passage of internal combustion engine Micro particle catching unit purifies the particle matter in exhaust gas, the method includes：

The exhaust gas being discharged from the internal combustion engine is set to pass through the particle filtering by being loaded with the non-precious metal catalyst for not containing noble metal The described of device composition is loaded with the micro particle catching unit of catalyst, rather than makes exhaust gas net by the exhaust gas for carrying noble metal catalyst Change unit.