JP6718137B2 - Exhaust purification device - Google Patents

Description

The present invention relates to an exhaust gas purification device, particularly a particulate filter, and more particularly to a particulate filter for treating particulates contained in exhaust gas of a diesel engine.

Exhaust gas emitted from a diesel engine contains a large amount of particulates in addition to HC, CO, NOx, etc. In order to process the particulates, an exhaust system of the engine has a diesel particulate filter (hereinafter, Simply called a filter) is provided. This kind of filter is configured as a wall flow type, and a large number of cells are divided by porous partition walls, and the inlet side and the outlet side of adjacent cells are alternately plugged, so that the pores of the partition walls are Particulates are collected when the exhaust gas is distributed.

In order to improve the collection efficiency of such particulates, for example, the filter described in Patent Document 1 is known. In the filter of Patent Document 1, a carrier that connects the inlet side and the outlet side of the exhaust gas to each other via a large number of cells partitioned by porous partition walls is provided, and the inlet side and the outlet side of the first cell group are formed. Each is plugged with an inlet plug and an outlet plug, and the intermediate portion in the longitudinal direction of the carrier of the second cell group adjacent to the first cell group is also plugged with an intermediate plug.

As a result, the exhaust gas flows into each cell of the second cell group of the filter and flows to each cell of the first cell group through the pores of the partition wall while being stopped by the intermediate plug in the cell. Exhaust gas in each cell of the first cell group passes through the pores of the partition wall again while being restrained by the outlet plug, and then flows back to each cell of the second cell group, and then flows out of each cell of the second cell group. To do. That is, the collection efficiency of particulates is improved by doubling the number of times exhaust gas flows through the partition wall, which was only once in the conventional filter.

JP, 2005-262210, A

By the way, as particulate matter is gradually accumulated on the partition walls of the filter as the particulate matter is collected, the increase in pressure loss of the filter due to this phenomenon causes a decrease in engine performance. A so-called forced regeneration of a filter for processing the particulates deposited on the surface is carried out. For example, in forced regeneration, post-injection is performed in the expansion stroke after main injection of the engine to increase HC in the exhaust gas, and the HC is oxidized by a pre-stage oxidation catalyst provided on the upstream side of the filter. The particulate heat on the filter on the downstream side is incinerated and removed by the reaction heat of.

During such forced regeneration of the filter, neither the oxidation reaction of HC on the pre-stage oxidation catalyst nor the combustion of particulates on the filter is completely performed, and some of the HC does not react and the pre-stage oxidation catalyst is removed. In addition to passing through, CO may be generated by incomplete combustion of some of the particulates on the filter. As a measure to prevent the emission of these HC and CO into the atmosphere, a post-stage oxidation catalyst for purifying HC and CO is provided on the downstream side of the filter, but in place of this, a catalytic function may be added to the filter. is there.

The filter described in Patent Document 1 is also provided with a catalytic function, so that the carrier of the filter is loaded with a noble metal and also a combustion promoter is loaded to accelerate the combustion of particulates during forced regeneration. There is. In the filter of Patent Document 1, although the internal structure of the filter is changed in order to improve the collection efficiency of particulates, the collection/combustion of particulates and the purification of HC and CO are still performed in the common region. Since it is based on the same idea as that of a general filter, a noble metal and a combustion promoter are respectively supported on the entire carrier.

However, the actual collection and combustion of particulates and the purification of HC and CO are mainly limited to the downstream side of the partition wall. Therefore, it is hard to say that the noble metal and the combustion accelerator carried on the portion other than the downstream portion are effectively used for promoting the combustion of particulates and for purifying HC and CO. As a result, there is a problem in that the manufacturing cost of the filter rises due to the useless use of precious metals and combustion promoters that do not contribute to the purification performance.

The present invention has been made in order to solve such a problem, and the purpose thereof is to effectively utilize the limited capacity of the filter to appropriately carry the precious metal and the combustion accelerator, An object of the present invention is to provide an exhaust gas purification device that can reduce manufacturing costs while maintaining high purification performance.

In order to achieve the above object, the exhaust gas purifying apparatus of the present invention comprises a carrier that connects the exhaust gas inlet side and the exhaust gas side through a plurality of cells partitioned by porous partition walls, and the first cell The inlet side and the outlet side of the group are plugged by inlet plugging and outlet plugging, respectively, and an intermediate portion in the longitudinal direction of the carrier of the second cell group adjacent to the first cell group is sealed by an intermediate plugging. plugged, the intermediate plugging upstream side of the first partition wall, and the exhaust gas purification device you collecting particulates by circulating exhaust gas through the downstream side of the second partition wall from the intermediate plugging, the the combustion promoter to promote combustion of the particulates in the forced regeneration processing the particulates deposited on the carrier is supported on the first partition, it is supported noble metal for purifying HC and CO in the second partition The porosity of the first partition wall is lower than the porosity of the second partition wall .

According to the exhaust purification apparatus configured, particulates in the exhaust gas are more reliably collected in the first partition wall having reduced porosity, particulates deposited on the first partition wall, at the time of forced regeneration The HC is burned by the heat of the oxidation reaction of HC on the upstream oxidation catalyst on the upstream side. As a result, it becomes almost unnecessary to support the precious metal for oxidizing the HC on the first partition wall, and the effect of the combustion promoter supported on the first partition wall is maximized to efficiently incinerate the particulates. To be removed. Further, since the second partition wall is not required to have the function of burning particulates, HC and CO are efficiently purified by the noble metal without being hindered by the combustion accelerator , and the second partition wall captures particulates. Since it is not necessary to collect, pressure loss can be reduced by increasing the porosity .

Then, while maintaining such high purification performance, since the combustion promoting agent is carried on the first partition wall and the noble metal is carried on the second partition wall, the carrying amount of each is halved and the filter is manufactured. The cost can be reduced.
As another aspect, the amount of the noble metal carried on the second partition is set such that a portion having a large exhaust gas flow rate existing in a range connecting an inlet and an outlet of a casing accommodating the carrier in the inward and outward directions of the carrier is large It is preferable to increase the exhaust gas flow rate and decrease the exhaust gas flow rate from the large area toward the outer area.

According to this aspect, when the inlet or outlet of the casing is eccentrically located from the center of the filter, the portion where the exhaust gas flow rate is the largest within the range connecting the inlet and outlet of the casing in the inner and outer directions of the carrier. Exists. Further, a large amount of HC and CO are transferred to a portion where the exhaust gas flow rate is large, and higher purification capacity is required. However, by increasing the amount of such a portion carried, it is possible to reliably perform purification, and the exhaust gas flow rate is small. A portion outside the filter that does not require so much purification ability can reduce the supported amount accordingly and contribute to cost reduction.

As another aspect, it is preferable that the inlet and the outlet of the casing are respectively arranged at the center portions in the inner and outer directions of the carrier, and the amount of the precious metal carried at the center portion is increased most.
According to this aspect, since the exhaust gas flow rate in the center portion of the carrier in the inward and outward directions is the largest, it is possible to purify HC and CO in the exhaust gas by increasing the supported amount of the noble metal in the center portion.

As another aspect, it is preferable to increase the porosity of the first partition wall toward the inlet side of the carrier.
According to this aspect, since the exhaust gas flows through the first partition while being blocked by the intermediate plug, the amount of distribution tends to increase toward the downstream side of the first partition and the amount of particulate accumulation also tends to increase. In the present invention, since the porosity of the first partition wall increases toward the inlet side of the carrier and the exhaust gas easily flows, the tendency of the deposition amount is alleviated. Therefore, the exhaust gas is substantially evenly distributed to all parts of the first partition wall, and the pores of the entire first partition wall are effectively utilized for collecting particulates.

According to the exhaust gas purification apparatus of the present invention, by effectively utilizing the limited capacity of the filter to properly carry the precious metal and the combustion accelerator, it is possible to reduce the manufacturing cost while maintaining high purification performance. it can.

It is sectional drawing which shows the particulate filter of embodiment. It is a schematic diagram which shows the setting amount of a noble metal and a cocatalyst on a particulate filter, and porosity. FIG. 6 is a cross-sectional view showing another example of a particulate filter having a different casing shape. It is sectional drawing which shows the particulate filter of another example which extended the 1st partition and shortened the 2nd partition.

An embodiment in which the present invention is embodied in a particulate filter for a vehicle will be described below.
FIG. 1 is a cross-sectional view showing an exhaust gas purification device (particulate filter) of the present embodiment, and FIG. 2 is a schematic diagram showing the amount of precious metal carried on the particulate filter and the porosity setting. First, the purpose of this embodiment will be described.

As described in [Problems to be Solved by the Invention], the filter described in Patent Document 1 is a carrier based on the idea that the collection of particulates and the purification of HC and CO are performed at a common location. Since the noble metal and the combustion accelerator are carried on the whole, wasteful noble metal and combustion accelerator that do not contribute to the respective purposes are generated, which is a factor of increasing the manufacturing cost.

In view of the above problems, in the filter of Patent Document 1, since the exhaust gas is circulated twice in different regions in the longitudinal direction of the partition wall, one of the regions is specialized for collecting and burning particulates, The inventors have found a measure to specialize the other region for purification of HC and CO and selectively carry only components required for their respective functions.
As shown in FIG. 1, the carrier 2 of the filter 1 has a cylindrical shape as a whole, and a large number of cells 4a and 4b extending in the longitudinal direction are partitioned by a porous partition wall 3 so as to be adjacent to each other. The inlet side and the outlet side of the carrier 2 are communicated with each other through the cells 4a and 4b, and these cells are separated into a first cell group 4a and a second cell group 4b. The cells of the first cell group 4a are not adjacent to each other, the cells of the second cell group 4b are not adjacent to each other, and the cells of the first cell group 4a and the cells of the second cell group 4b are adjacent to each other. It is arranged to.

Then, the inlet side and the outlet side of each cell of the first cell group 4a are plugged with an inlet plug (entrance plugging) 5 and an outlet plug (exit plugging) 6, respectively, and each cell of the second cell group 4b is An intermediate plug 7 is plugged at an intermediate point in the longitudinal direction of the cell carrier.
The carrier 2 as described above is manufactured by the following procedure.
First, powders such as kaolin, talc, silica, aluminum hydroxide, and alumina are adjusted to a cordierite composition, and a molding aid, a pore-forming agent, and a specified amount of water are added and then sufficiently mixed to produce a kneaded clay. .. Then, by extruding this kneaded material, a honeycomb structure in which a large number of cells composed of the first and second cell groups 4a and 4b are partitioned by the partition walls 3 as described above is manufactured, and dried and fired. ..

After that, the plugs 5 to 7 each having a shape corresponding to the cross section of the cells 4a and 4b are made of kneaded clay, and then the inlet plug 5 is provided on the inlet side of each cell of the first cell group 4a and the first cell group The outlet plug 6 is inserted and arranged on the outlet side of each cell of 4a, and the intermediate plug 7 is inserted and arranged in the middle of each cell of the second cell group 4b. If the carrier is dried and baked again in this state, the carrier 2 is completed. However, the manufacturing method of the carrier 2 of the present invention is not limited to the above, and can be arbitrarily changed.

The carrier 2 manufactured in this manner carries a combustion accelerator that promotes the combustion of particulates during forced regeneration, and a precious metal (including co-catalyst) that purifies HC and CO. In order to effectively use the limited capacity of the filter 1, the carrier 2 is divided into an upstream region and a downstream region with the intermediate plug 7 as a boundary, and the carried components are different from each other. Describe.

Hereinafter, for convenience of description, the partition 3 upstream of the intermediate plug 7 is referred to as a first partition 3a, and the partition 3 downstream of the intermediate plug 7 is referred to as a second partition 3b. Since the intermediate plug 7 is located in the middle of the carrier 2 in the longitudinal direction, the first partition 3a and the second partition 3b have the same length.
Then, the first partition wall 3a carries only the combustion promoter that promotes the combustion of particulates, and does not carry the noble metal. However, if it is a very small amount, a precious metal may be supported on the first partition wall 3a in addition to the combustion accelerator. Further, the second partition wall 3b carries only the noble metal and does not carry the combustion accelerator.

The carrying amount of the noble metal is set in association with the positions of the inlet and the outlet of the casing 10 in which the filter 1 is housed. That is, there is a difference in the flow rate of the exhaust gas flowing through the cells 4a, 4b of the carrier 2, and as shown in FIG. 1, the exhaust gas flows into the filter 1 from the inlet 10a of the casing 10 and from the inside of the filter 1 to the casing 10. It flows out to the outlet 10b. Further, in the present embodiment, since the inlet 10a and the outlet 10b of the casing 10 are both arranged at the center of the filter 1 in the inward and outward directions, the exhaust gas flow rate at the center of the filter 1 (shown by a virtual line C in FIG. 1). Is the largest, and the exhaust gas flow rate decreases toward the outer peripheral portion.

Corresponding to such a distribution of the exhaust gas flow rate, the amount of the precious metal carried on the second partition wall 3b is increased at the center of the filter 1 where the exhaust gas flow rate is large as shown in FIG. It is set so as to decrease at a predetermined gradient toward the outer peripheral side portion. The total carrying amount is smaller than that of the filter of Patent Document 1 shown by a virtual line in FIG.

On the other hand, the first partition wall 3a and the second partition wall 3b have a difference in porosity of the carrier 2, and the porosity of the first partition wall 3a is lower than that of the second partition wall 3b. I am making it. Further, while the porosity of the second partition wall 3b is uniform in the longitudinal direction of the filter 1, the porosity of the first partition wall 3a increases toward the inlet side of the filter 1 with a predetermined gradient. .. Regarding the particulate collecting function, the porosity of the first partition wall 3a is set so that the particulate matter can be reliably collected even on the inlet side having the highest value, whereas the porosity of the second partition wall 3b is set. The porosity is set to a large value without considering the collection of particulates.

In summary, the first and second partition walls 3a and 3b have the following features.
The first partition wall 3a corresponding to the upstream side of the filter 1 does not carry a noble metal and therefore cannot purify HC and CO. On the other hand, since it has a low porosity, it has an excellent function of collecting particulates, and also has a function of burning the particulates during forced regeneration by carrying a combustion accelerator. Therefore, the first partition 3a can be regarded as a region specialized for collecting and burning particulates.

Second partition 3b corresponding to the downstream side of the filter 1, because a large porosity with unsuitable for collecting particulates, even if the collecting particulates, not carrying a combustion promoter Therefore, efficient combustion of particulates cannot be expected during forced regeneration. On the other hand, since the second partition wall 3b can purify HC and CO by supporting the noble metal, it can be regarded as a region specialized for purifying HC and CO.

Next, the function and effect of the particulate filter 1 of the present embodiment configured as described above will be described.
First, the flow state of the exhaust gas in the filter 1 will be described. The exhaust gas flows from the inlet 10a of the casing 10 into each cell of the second cell group 4b of the filter 1 and is blocked by the intermediate plug 7 in the cell while being blocked. It passes through the pores of one partition wall 3a and flows into each cell of the first cell group 4a. Exhaust gas in each cell of the first cell group 4a flows through each of the cells of the second cell group 4b again through the pores of the second partition wall 3b while being restrained by the outlet plug 6, and then the second cell Each cell of the cell group 4b flows out to the outlet 10b of the casing 10.

As will be described in detail below, while the particulate matter in the exhaust gas is collected in the first partition wall 3a, the particulate matter is incinerated and removed during the forced regeneration of the filter 1 and the second partition wall 3b is subjected to the forced regeneration. HC and CO are purified. In the present embodiment, the first partition 3a corresponding to the half of the filter 1 in the longitudinal direction carries the combustion promoter , and the second partition 3b corresponding to half of the filter 1 in the longitudinal direction also carries the noble metal. Therefore, the carrying amount of each is halved, and the manufacturing cost of the filter 1 can be reduced.

Then, the filter capacity of the filter 1 of the present embodiment is apparently halved as compared with the filter of Patent Document 1 in which the combustion promoter and the noble metal are carried on the entire carrier, but due to the factors described below, the particulates are Regarding the collection of the above, the incineration and removal of particulates during the forced regeneration, and the purification of HC and CO, the same or higher performance as the filter of Patent Document 1 can be obtained.

First, in the first partition wall 3a, when the exhaust gas flows through the pores, the particulates in the exhaust gas are collected. As described above, the first partition wall 3a can collect the particulates even on the inlet side having the highest porosity, so that the particulates in the exhaust gas are reliably collected by the first partition wall 3a. Therefore, exhaust gas containing no particulates circulates in the pores of the second partition wall 3b, and even if the porosity of the second partition wall 3b is large, there is no problem in collecting the particulates.

Further, since the exhaust gas flows through the first partition wall 3a while being blocked by the intermediate plug 7, the flow rate tends to increase toward the downstream side of the first partition wall 3a, and the accumulated amount of particulates also tends to increase. However, in the present embodiment, since the porosity of the first partition wall 3a increases toward the inlet side of the carrier 2, the exhaust gas is more likely to flow toward the upstream side of the first partition wall 3a, and the above-described tendency of the deposition amount tends to increase. Is alleviated. Therefore, the exhaust gas circulates substantially evenly in all parts of the first partition wall 3a, and the pores of the entire first partition wall 3a are effectively utilized for collecting particulates. As a result, although the filter capacity is halved, a particulate collection amount equal to or greater than that of the filter of Patent Document 1 can be achieved, and the collection performance can be significantly improved.

In this way, the particulates in the exhaust gas are collected by the first partition walls 3a, and the forced regeneration of the filter 1 is performed before the accumulation amount increases and exceeds the collection limit. For example, exhaust gas containing a large amount of HC is supplied to the pre-stage oxidation catalyst provided on the upstream side of the filter 1 by post-injection of the engine, etc., and the particulates on the downstream side filter 1 are incinerated and removed by the oxidation reaction heat of the HC. It

Since the particulates are deposited on the first partition wall 3a, the combustion of the particulates during forced regeneration is also performed on the first partition wall 3a, but the first partition wall 3a carries a combustion accelerator. Therefore, the particulates are efficiently incinerated and removed. Basically, since it is not necessary to oxidize HC on the filter 1, it is almost unnecessary to support the noble metal or the co-catalyst on the first partition wall 3a. Therefore, since only the combustion promoter is carried on the first partition wall (or only a small amount of the noble metal is carried), the effect of the combustion promoter is maximized and the filter capacity is halved. Nevertheless, at the time of forced regeneration, it is possible to achieve a particulate combustion performance equal to or higher than that of the filter of Patent Document 1.

In addition, since the porosity is set as described above, the particulates are substantially evenly deposited on the first partition 3a. Therefore, the particulates are also efficiently burned by using the entire first partition wall 3a, which also contributes to the improvement of the particulates burning performance.
The improvement in the combustion performance of the filter 1 leads to a reduction in the amount of post-injection of the engine required during forced regeneration, which in turn has the advantage of improving the fuel efficiency of the vehicle.

On the other hand, during forced regeneration, in the pre-stage oxidation catalyst, some HC passes through the pre-stage oxidation catalyst without reaction, and CO is generated on the first partition wall 3a of the filter 1 due to incomplete combustion of some of the particulates. Is generated. These HC and CO pass through each cell of the first cell group 4a and reach the second partition wall 3b together with the exhaust gas, but since the second partition wall 3b carries the noble metal, HC and CO are purified. It

Purification of HC and CO at this time is efficiently and reliably performed by the following factors.
First, the amount of noble metal carried on the second partition wall 3b is changed in accordance with the distribution of the exhaust gas flow rate in the inner and outer directions of the filter 1. A larger amount of HC and CO are transferred to the central portion of the filter 1 where the flow rate of exhaust gas is large, and a higher purification capacity is required. However, since the carried amount of such a portion is increased, the purification can be reliably performed. Further, not so much purification performance is required on the outer peripheral side of the filter 1 where the exhaust gas flow rate is small, and the cost of the filter 1 can be reduced by reducing the amount of support accordingly.

Further, since the particulates are collected by the first partition wall 3a as described above, the second partition wall 3b is not required to have a particulate burning function, and it is not necessarily necessary to carry the combustion accelerator. .. If the combustion promoting agent is carried on the second partition wall 3b together with the noble metal, the contact between HC and CO and the noble metal or the co-catalyst may be hindered by the combustion promoting agent, which may be a factor of reducing the purification efficiency. By not supporting the combustion accelerator on the second partition wall 3b, such a situation is prevented and the purification efficiency of HC and CO is improved.

As a result, despite the filter capacity being halved, it is possible to achieve HC and CO purification performance equivalent to or higher than that of the filter of Patent Document 1 during forced regeneration.
In addition, since the second partition wall 3b does not need to collect particulates, a large porosity is set, and there is no problem in purifying HC and CO with noble metal even if the porosity is increased in this way. There is no. Then, by increasing the porosity of the second partition wall 3b, the pressure loss of the exhaust gas when flowing through the filter 1 is significantly reduced, and as a result, it greatly contributes to the improvement of the engine performance. Moreover, since the surface area is reduced as the porosity increases, the precious metal can be saved accordingly, which contributes to the cost reduction of the filter 1.

By the way, in the present embodiment, since the inlet 10a and the outlet 10b of the casing 10 are both arranged in the center portion of the filter 1 in the inward and outward directions, the amount of precious metal carried on the second partition wall 3b is the largest at the exhaust gas flow rate. Although it was most increased in the central portion of the filter 1, the setting of this carrying amount is preferably changed according to the shape of the casing 10.
FIG. 3 is a cross-sectional view showing another example of the particulate filter in which the shape of the casing 10 is different, and the inlet 10a of the casing 10 is at a position eccentric from the center of the filter 1. In this case, the part where the exhaust gas flow rate is the largest exists in the range E connecting the inlet 10a and the outlet 10b of the casing 10 in the inner and outer directions of the filter 1 (shown by a virtual line C in the figure), and the part The exhaust gas flow rate decreases toward the outer peripheral side of the filter 1 around Therefore, the supported amounts of the noble metal and the co-catalyst on the second partition wall 3b may be set so as to correspond to the distribution of the exhaust gas flow rate.

Further, in the present embodiment, the intermediate plug 7 is arranged in the middle of the filter 1 in the longitudinal direction to make the first partition wall 3a and the second partition wall 3b have the same length, but the present invention is not limited to this. Absent. For example, in an engine that emits a large amount of particulates, the first partition wall 3a may be extended and the second partition wall 3b may be shortened by that amount in order to improve the particulate collection performance, as shown in FIG. As a result, a large amount of particulates discharged from the engine can be reliably collected and burned by the first partition wall 3a, and the second partition wall 3b has a margin for HC and CO purification performance as described above. , HC and CO can be purified without any problem. Further, since the amount of the precious metal carried is reduced by shortening the second partition wall 3b, it contributes to the cost reduction of the filter 1.

Although the description of the embodiment has been completed, the aspects of the present invention are not limited to this embodiment. For example, in the above-described embodiment, the particulate filter 1 for a vehicle is embodied, but the application is not limited to the vehicle. For example, it may be embodied as a particulate filter for a stationary engine of a power generation facility.

1 Filter 2 Carrier 3a 1st partition 3b 2nd partition 4a 1st cell group 4b 2nd cell group 5 Inlet plug (inlet plugging)
6 Outlet plug (outlet plugging)
7 Intermediate plug 10 Casing 10a inlet 10b outlet

Claims (4)

A carrier for communicating the inlet side and the outlet side of the exhaust gas through a plurality of cells partitioned by a porous partition wall is constituted, and the inlet side and the outlet side of the first cell group are respectively sealed with an inlet and an outlet. And the second cell group adjacent to the first cell group is sealed at an intermediate position in the longitudinal direction of the carrier by intermediate sealing, and the first partition wall on the upstream side of the intermediate sealing. , and in the exhaust purification apparatus by circulating the exhaust gas you collecting particulates through the downstream side of the second partition wall from the intermediate plugging,
Carrying combustion promoter to promote combustion of the particulates in the forced regeneration processing the particulates deposited on the carrier is supported on the first partition wall, a precious metal to purify HC and CO in the second partition then,
An exhaust emission control device , wherein the porosity of the first partition wall is lower than the porosity of the second partition wall . The amount of the precious metal carried on the second partition wall is increased in a region where the exhaust gas flow rate existing in the range connecting the inlet and the outlet of the casing that houses the carrier in the inner and outer directions of the carrier is large, and The exhaust emission control device according to claim 1, wherein the exhaust gas flow rate is reduced from a large portion toward an outer portion. The exhaust gas purifying apparatus according to claim 2, wherein an inlet and an outlet of the casing are arranged at central portions of the carrier in an inward/outward direction, respectively, and a carrying amount of the noble metal is most increased at the central portion. The exhaust emission control device according to any one of claims 1 to 3 , wherein the porosity of the first partition wall is increased toward the inlet side of the carrier.

Images