JP2005042687A - Exhaust emission control device and emission control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact exhaust emission control device and an exhaust emission control method, which efficiently remove NOx and particulate substance contained in exhaust gas, in the exhaust emission control device of a diesel engine and which can reduce pressure loss in the whole exhaust emission control device. <P>SOLUTION: The exhaust emission control device is constructed such that a filter and a SCR (Selective Catalytic Reduction) catalyst are arranged in this order from an upstream side in an exhaust passage of the diesel engine. The ceramic honeycomb filter has a porous ceramic honeycomb structure in which desired flow passages are sealed. At least one sealed portion on an exhaust gas inflow side of the filter is arranged apart from an exhaust gas inflow side end surface. Catalyst material is carried on at least a part of partition walls and/or the sealed portions. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention is discharged from a diesel engine, to a exhaust gas purifying device for a diesel engine for purifying nitrogen oxides (also hereinafter NO _x abbreviated) and an exhaust gas containing particulate matter.

Demand for diesel engines is increasing mainly in Europe due to its high fuel efficiency. However, since PM (Particulate Matter) and nitrogen oxide (NO _x ) contained in the exhaust gas of diesel engines have a great influence on human health, this PM and NO _x reduction technology Various studies have been made. As an exhaust gas purifying device for reducing PM and NO _x in the exhaust gas, for example, the invention described in Patent Document 1 includes an improved SCR (Selective Catalytic) for treating combustion exhaust gas containing NO and particulate matter. Reduction mechanism, in which an oxidation catalyst that effectively converts at least a portion of NO in the NO _x into NO ₂ , a particulate matter trap, a source of reducing agent fluid, and an SCR catalyst in this order. A combined SCR mechanism is disclosed. Here, SCR refers to selective catalytic reduction, which is a method in which high-temperature exhaust gas is passed over a catalyst in the presence of a nitrogen-based reducing agent, particularly ammonia or urea. In the present invention, NO in the exhaust gas is effectively converted to NO ₂ by the oxidation catalyst, and at least a part of the particulate matter in the exhaust gas is at a relatively low temperature in the presence of NO ₂ by the particulate matter trap. Burned away. Further, a nitrogen-based reducing agent is added to the exhaust gas having a high NO ₂ content to form a gas mixture, and this gas mixture is passed over the SCR catalyst, so that NO _x is converted to N ₂ . Is done. According to the present invention, the oxidation catalyst disposed upstream of the SCR catalyst and the particulate matter trap are considered to be particularly effective in increasing the conversion rate from NO _x to N ₂ by the SCR mechanism. In this invention, a platinum catalyst supported on a through-flow honeycomb carrier made of, for example, ceramic or metal is particularly suitable as the oxidation catalyst, and the particulate matter trap is generally manufactured from ceramic. The wall-flow filter is preferred, and the SCR catalyst is preferably a V ₂ O ₅ / WO ₃ / TiO ₂ catalyst supported on a through-flow honeycomb carrier.

Further, in the invention described in Patent Document 2, the exhaust passage 2 of the diesel engine is shown in FIG. 4 as a configuration diagram of the exhaust system of the engine showing the exhaust gas purifying device of the diesel engine of the embodiment according to the present invention. In addition, an SCR catalyst 5 for reducing and purifying NO _x is disposed, and the upstream side of the SCR catalyst is oxidized in order from the upstream side, and the sulfur content in the exhaust gas is oxidized by the catalytic action of the oxidation catalyst 3. An exhaust gas purification device for a diesel engine is disclosed, in which a filter 4 capable of collecting the generated sulfate is arranged in series. A reducing agent supply device 6 is provided in the exhaust passage 2 between the filter 4 and the SCR catalyst 5. According to the configuration of the present invention, the sulfur content contained in the exhaust gas can be collected together with the dust in the exhaust gas, and the downstream SCR catalyst 5 can be prevented from being poisoned by dust such as the sulfur content and PM. so it can be efficiently reduce and purify NO _x, are the pollution can be reduced by the exhaust gas. In the present invention, the oxidation catalyst 3 is, for example, a cordierite monolith support formed by coating a catalyst support layer of alumina and supporting a catalyst component such as platinum on the support layer. A cordierite honeycomb filter in which a large number of exhaust passages are formed in parallel with each other, a filter made of a ceramic nonwoven fabric such as alumina, or the like can be used. Further, the SCR catalyst 5 uses Al ₂ O ₃ , TiO _{2 as} a carrier. The catalyst metal is formed of Pt, V ₂ O ₅ , Fe ₂ O ₃ , CuO, Mn ₂ O ₃ , Cr ₂ O ₃ , MoO ₃ or the like as an active substance.

Japanese translation of PCT publication No. 2002-502927 JP 2000-303826 A

  In the apparatus for purifying exhaust gas discharged from the diesel engine described in Patent Documents 1 and 2 which are the above-described prior art, each of the oxidation catalyst, the filter, the reducing agent fluid supply source, and the SCR catalyst is provided in the exhaust gas passage. The devices are arranged in series. In many cases, the oxidation catalyst and the SCR catalyst have a ceramic honeycomb structure in which a catalyst material is supported, and the filter has a desired flow path of the ceramic honeycomb structure at both ends. Sealed ceramic honeycomb filters or filters made of ceramic nonwoven fabric are used. For this reason, the pressure loss of the exhaust gas purification device is the sum of the pressure loss of two types of honeycomb structures, the pressure loss of a filter made of a ceramic honeycomb filter or a ceramic nonwoven fabric, and the pressure loss of the entire device increases. As a result, there is a problem that the engine output and fuel consumption are reduced. Further, in the conventional exhaust gas purifying apparatus as described in FIG. 2 of Patent Document 2, for example, the oxidation catalyst and the filter are arranged in series by the exhaust passage, so that a high temperature is caused by the catalytic reaction in the oxidation catalyst. When the exhaust gas that has become lower in temperature passes through the exhaust passage between the oxidation catalyst and the filter and flows into the filter, especially when the exhaust gas temperature itself flowing into the purification device is low, such as during low-speed running In some cases, the temperature in the filter may not reach the temperature at which the particulate matter is sufficiently combusted, and unburned particulate matter may remain in the filter, resulting in an increase in the pressure loss of the filter. there were.

In addition, a device such as a honeycomb structure, a ceramic honeycomb filter or a filter made of a ceramic nonwoven fabric requires a certain amount of volume in order to ensure purification performance. When four types of devices, a ceramic honeycomb filter or a filter made of ceramic nonwoven fabric, and a reducing agent supply device are arranged in series, the mounting space becomes enormous, and there is a problem that mounting on a diesel vehicle becomes difficult, for example. Therefore, there has been a demand for an exhaust gas purifying apparatus with low pressure loss and high efficiency.
An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a small exhaust gas purifying device with low pressure loss.

As a result of diligent research on reducing the pressure loss and downsizing of the entire exhaust gas purification device while effectively reducing NO _x and particulate matter in the exhaust gas, the present inventors have found that the upstream of the SCR catalyst. The present inventors have found that it is effective to optimize the structure of the filter arranged in the above, and have arrived at the present invention.

  The exhaust gas purifying apparatus of the present invention is an apparatus for purifying exhaust gas containing nitrogen oxides and particulate matter discharged from a diesel engine, and plugs a desired flow path of a porous ceramic honeycomb structure. In the ceramic honeycomb filter, at least one exhaust gas inflow side plugged portion is disposed away from the end surface of the exhaust gas inflow side, and a catalyst substance is supported on at least a part of the partition wall and / or the plugged portion. The filter and the SCR catalyst are arranged in this order.

  Furthermore, in the exhaust gas purifying apparatus of the present invention, the end face of the exhaust gas inflow side plugging portion of the ceramic honeycomb filter is a section having a length not more than 0.7 times the total length of the ceramic honeycomb filter from the inflow side end face of the ceramic honeycomb filter. It is preferable to arrange | position. Further, it is preferable that the catalyst material supported on the ceramic honeycomb filter contains a platinum group metal. Furthermore, it is preferable that a larger amount of the catalyst material supported on the ceramic honeycomb filter is carried on the exhaust gas inflow side than on the exhaust gas outflow side.

The exhaust gas purification method of the present invention includes at least one exhaust gas inflow side plugging of a ceramic honeycomb filter disposed in a device for purifying exhaust gas containing nitrogen oxides and particulate matter discharged from a diesel engine. The stop portion is disposed away from the end surface on the exhaust gas inflow side, and a catalyst substance is supported on at least a part of the partition wall and / or the plugging portion, and particulate matter in the exhaust gas is contained in the ceramic honeycomb filter. And the molar ratio of NO / NO ₂ in the exhaust gas introduced into the SCR catalyst disposed on the exhaust gas discharge side of the filter is set to 1/2 to 2/1.

The operation and effect of the exhaust gas purification apparatus and the exhaust gas purification method of the present invention will be described with reference to FIG. 1 which is a configuration diagram of an engine exhaust system showing the exhaust gas purification apparatus of the present invention.
An apparatus for purifying exhaust gas containing nitrogen oxide (NO _x ) and particulate matter discharged from a diesel engine of the present invention is a ceramic honeycomb filter in which a desired flow path of a porous ceramic honeycomb structure is plugged. The filter 11 has at least one exhaust gas inflow side plugging portion disposed away from the exhaust gas inflow side end surface, and at least a part of the partition wall and / or the plugging portion carries a catalyst substance. And the SCR catalyst 5 are arranged in this order. For this reason, the pressure loss of the exhaust gas purification device of the prior art in which the oxidation catalyst, the filter, the reducing agent supply source, and the SCR catalyst are arranged in this order is the pressure loss of the honeycomb structure used for the oxidation catalyst, the ceramic honeycomb filter Or the pressure loss of the filter made of the ceramic nonwoven fabric and the pressure loss of the honeycomb structure used for the SCR catalyst, and the pressure loss of the entire apparatus is large, whereas the pressure of the exhaust gas purification apparatus of the present invention Since the loss is only the sum of the pressure loss of the ceramic honeycomb filter and the pressure loss of the honeycomb structure used for the SCR catalyst, the pressure loss of the entire exhaust gas passage can be reduced, and the engine output and fuel consumption are prevented from being lowered. In addition, the entire exhaust gas purification device can be reduced in size.

Here, in the exhaust gas purification device of the present invention, at least one exhaust gas inflow side plugged portion of the ceramic honeycomb filter in which a desired flow path of the porous ceramic honeycomb structure is plugged is an exhaust gas inflow side end surface. The reason, function, and effect of using the filter 11 that is disposed further apart and that has a catalytic substance supported on at least a part of the partition walls and / or plugging portions will be described below.
FIG. 2 is a schematic cross-sectional view of an example of the filter 11 used in the exhaust gas purification apparatus of the present invention. The filter 11 has a porous ceramic honeycomb having a substantially vertical or substantially elliptical cross section in the flow path direction, an outer peripheral wall 20, and a large number of flow paths 40 surrounded by partition walls 30 on the inner peripheral side of the outer peripheral wall 20. The desired portions of the flow path 40 of the structure 10 are alternately plugged by plugging portions 50 and 52. At least one exhaust gas inflow side plugging portion end surface 51 is disposed away from the inflow side end surface 12 of the ceramic honeycomb filter on the exhaust gas outflow side, and the partition wall and / or the plugging portion At least a part of the catalyst material 60 is supported.

  In the honeycomb filter having such a structure, exhaust gas flows from the flow paths 41 and 42 opened at the inflow side end face 12. Among these, the exhaust gas 91 that has flowed in from the flow path 42 passes through pores (not shown) formed in the partition wall 31 and is discharged to the adjacent flow path 41 because of the inflow side plugging portion 50. After joining the exhaust gas 90 flowing into the flow path 41 from the inflow side end face 12, the flow path 41 proceeds toward the outflow side end face 13, and the outflow side end face of the flow path has an outflow side plugging. Due to the presence of the portion 52, it passes through the pores (not shown) formed in the partition wall 32 and is discharged from the flow path 43 that is open at the outflow side end face 13 that is an adjacent flow path (indicated by an arrow 92). Is done. Note that some of the exhaust gas passes through pores (not shown) formed in the inflow side plugged portion 50 and the outflow side plugged portion 52 and is exhausted. During this time, the particulate matter in the exhaust gas is collected by the porous partition walls mainly when passing through the flow paths 41 to 43 and the partition walls 31 to 32, and at least the partition walls and / or the plugging portions. In part, the exhaust gas is efficiently purified by being burned by the action of the end-carrying catalyst substance.

  In the prior art, in addition to the problem that the exhaust gas purification device cannot be downsized, the temperature of the exhaust gas that has become high due to the catalytic reaction in the oxidation catalyst decreases when passing through the exhaust passage 2 between the oxidation catalyst and the filter. However, when the exhaust gas temperature that flows into the filter as low-temperature exhaust gas and flows into the purification device, such as when traveling at a low speed, is low, the temperature in the filter is such that the particulate matter is sufficiently combusted. The unburned particulate matter remains in the filter, and in particular, a large amount of unburned particulate matter remains at the filter inlet end where the temperature is low, and the pressure loss of the filter increases due to the blockage of the flow path. There was also a problem. On the other hand, in the exhaust gas purifying apparatus of the present invention, at least one inflow side plugging portion 50 is disposed away from the inflow side end face of the ceramic honeycomb filter 11 inside the filter, so that the exhaust gas flows in. Since the temperature is raised by the catalytic reaction by the catalytic material supported on the partition wall 31 arranged on the inflow side from the side plugging portion 50, the temperature inside the filter can be easily maintained at the activation lower limit temperature or more. . For this reason, the exhaust gas purification apparatus of the present invention can efficiently burn particulate matter in the exhaust gas, and in particular, prevents an increase in pressure loss due to accumulation of unburned particulate matter at the inflow side plugged portion. It also has the effect of being able to

Further, as described above, at least one exhaust gas inflow side of the present invention as compared with the exhaust gas purification device constituted by the combination of the oxidation catalyst, the filter, the reducing agent supply source, and the SCR catalyst device, which is a conventional technique Exhaust gas composed of a combination of a filter and an SCR catalyst in which the plugging portion is arranged away from the end face on the exhaust gas inflow side and the catalytic material is supported on at least a part of the partition wall and / or the plugging portion. The reason why the pressure loss of the gas purification device can be reduced is considered as follows.
In general, the pressure loss of a ceramic honeycomb structure used in an exhaust gas purification device is as follows: (1) Pressure loss caused by compression or expansion of exhaust gas at the inlet and outlet of the exhaust gas flow path; (2) Exhaust gas flow It is expressed as the total pressure loss due to flow path resistance in the channel. In the ceramic honeycomb filter, (3) pressure loss when exhaust gas passes through the partition walls is further added to the above. Therefore, at least one exhaust gas inflow side plugging as in the present invention is made of an exhaust gas apparatus composed of a honeycomb structure supporting a conventional oxidation catalyst, a ceramic honeycomb filter, and a honeycomb structure supporting an SCR catalyst. A honeycomb structure in which a stop portion is disposed away from an end surface on the exhaust gas inflow side and a catalytic substance is supported on at least a part of partition walls and / or plugging portions and a honeycomb structure on which an SCR catalyst is supported The exhaust gas purifying device comprising the exhaust gas purifying device as described above is free from pressure loss due to pressure loss at the inflow side and the outlet side of the exhaust gas flow channel and the flow channel resistance in the prior art oxidation catalyst. It is possible to reduce the pressure loss. Further, in the exhaust gas purification apparatus of the present invention shown in FIG. 1, the length of the exhaust gas passage 2 itself can be shortened as compared with the conventional exhaust gas purification apparatus shown in FIG. The overall pressure loss can be reduced, and the exhaust gas purification device can be reduced in size.

The exhaust gas purification method of the present invention includes plugging at least one exhaust gas on the exhaust gas inlet side of a ceramic honeycomb filter disposed in a device for purifying exhaust gas containing nitrogen oxides and particulate matter discharged from a diesel engine. And the catalyst material is supported on at least a part of the partition wall and / or the plugging portion, and the particulate matter in the exhaust gas is contained in the ceramic honeycomb filter. It is characterized in that the NO / NO ₂ molar ratio in the exhaust gas introduced into the SCR catalyst disposed on the exhaust gas discharge side of the filter is set to 1/2 to 2/1. Therefore, conversion to _{N 2} is increased from NO and NO ₂ or the like of the NO _x in the SCR catalyst, the effect also has the purification efficiency of the NO _x can be improved. This is because a ceramic in which at least one exhaust gas inflow side plugging portion is arranged away from the exhaust gas inflow side end face and a catalytic substance is supported on at least a part of the partition wall and / or the plugging portion. In the honeycomb filter, the particulate matter is combusted by the catalytic action of the supported catalyst material. Therefore, NO and NO ₂ are contained in the exhaust gas after the particulate matter discharged from the filter is burnt and purified. It included, and the molar ratio of NO and NO ₂ in the _{NO / NO 2 1 / 2~2 /} 1 and the exhaust gas is easily obtained that, to this, ammonia or a nitrogen-based reducing agent, adding urea When a gas mixture is formed and this gas mixture is introduced onto the SCR catalyst, the conversion rate from NO _x to N ₂ increases, and the NO _x purification efficiency in the exhaust gas purification device is improved. so That.

In the prior art exhaust gas purification device, an oxidation catalyst, a filter, a reducing agent supply source, and an SCR catalyst are arranged in this order so that the oxidation catalyst raises the temperature of the exhaust gas and converts NO _x into NO _2. The filter disposed after the oxidation catalyst combusts the particulate matter using NO ₂ and further purifies NO _x in the SCR catalyst, whereas the exhaust gas purification device and the exhaust gas purification method of the present invention According to the present invention, the particulate matter in the exhaust gas is efficiently burned by the filter 11 and the NO / NO ₂ ratio in the exhaust gas is appropriately adjusted so that the exhaust gas discharged from the filter is passed through the SCR catalyst. Since NO _x can be efficiently reduced, the pressure loss of the entire exhaust gas purification device can be reduced and the purification performance can be improved as compared with the exhaust gas purification device of the prior art.

  The exhaust gas inflow side plugging portion end face of the ceramic honeycomb filter disposed in the exhaust gas purification apparatus of the present invention has a length of 0.7 times or less of the entire length of the ceramic honeycomb filter from the inflow side end face of the ceramic honeycomb filter. It is preferable that the ceramic honeycomb filter is disposed in the section. If the section is disposed beyond the section of 0.7 times the total length of the ceramic honeycomb filter from the inflow side end face 12, the entire length of the ceramic honeycomb filter is restricted. For this reason, the area of the partition wall 32 on the outlet side from the plugging portion on the exhaust gas inflow side is smaller than that of the partition wall 31, and the pressure loss of the entire honeycomb filter may increase. Further, a more preferable arrangement section of the inflow side plugging end face 51 is a section having a length of 0.1 to 0.4 times the entire length of the ceramic honeycomb filter from the end face 12 of the ceramic honeycomb filter inflow side.

  Next, the catalyst material supported on the ceramic honeycomb filter disposed in the exhaust gas purification apparatus of the present invention preferably contains a platinum group metal. The catalyst material containing a platinum group metal mainly This is because the oxidation reaction of the exhaust gas is promoted and the temperature of the exhaust gas is increased, so that the internal temperature of the filter can be more reliably maintained at the activation lower limit temperature or higher. For this reason, the particulate matter in the exhaust gas can be burned efficiently, and an increase in pressure loss due to the accumulation of unburned particulate matter at the inflow side plugged portion can be prevented. The catalyst material containing a platinum group metal includes, for example, Pt, Pd, Ru, Rh or a combination thereof, a platinum group metal oxide, and the like, but may include an alkaline earth metal oxide, a rare earth oxide, and the like. . Further, if the catalyst material containing platinum group metal contains a high specific surface area material made of active alumina such as known γ alumina, the contact area between the platinum group metal etc. and the exhaust gas can be increased, This is preferable because the gas purification efficiency can be increased.

In addition, the activity of the catalyst material supported on the partition wall on the exhaust gas inflow side of the ceramic honeycomb filter disposed in the exhaust gas purification apparatus of the present invention is the activity of the catalyst material supported on the partition wall on the exhaust gas outflow side. It is preferable that the exhaust gas catalytic reaction of the exhaust gas is promoted on the catalytic material carried on the partition wall 31 arranged on the inflow side from the inflow side plugging portion 50 and the reaction heat is increased. This is because it is possible to more reliably maintain the internal temperature of the filter at the activation lower limit temperature or more of the catalyst substance. For this reason, the particulate matter in the exhaust gas can be burned efficiently, and an increase in pressure loss due to the accumulation of unburned particulate matter at the inflow side plugged portion can be prevented. Here, the activity of the catalyst material supported on the partition wall on the exhaust gas inflow side is higher than the activity of the catalyst material supported on the partition wall on the exhaust gas outflow side. The content of the catalytic material containing platinum group metal in the catalytic material supported on the partition wall on the exhaust gas inflow side, the inclusion of alkaline earth metal oxide, rare earth oxide, or base metal catalyst as the promoter material This means that the catalyst performance is high when the catalyst is supported in a larger amount than the catalyst material supported on the partition wall on the exhaust gas outflow side and viewed as the entire supported catalyst.
For example, in the exhaust gas purification apparatus of the present invention, the platinum group metal content in the catalyst material supported on the partition wall on the exhaust gas inflow side from the inflow side plugging portion of the ceramic honeycomb filter is stored in the partition wall on the exhaust gas outflow side. By increasing the content of the platinum group metal in the supported catalyst material, it is possible to prevent an increase in pressure loss over a long period of time.

  In addition, the partition on the exhaust gas inflow side from the inflow side plugging portion 50 of the ceramic honeycomb filter disposed in the exhaust gas purification device of the present invention has an oxidation catalyst such as Pt, Pd, Ru, Rh, etc. A large amount of catalyst material containing a platinum group metal is supported, and the partition wall 32 on the exhaust gas outflow side has a base metal catalyst as a promoter, typically a catalyst material made of lanthanum oxide, cesium oxide, or vanadium oxides. Since a large amount of catalyst material containing platinum group metal is supported, fine particles are burned efficiently, so that an increase in pressure loss can be prevented over a long period of time.

In the exhaust gas purifying apparatus of the present invention, at least one exhaust gas inflow side plugged portion of the ceramic honeycomb filter in which a desired flow path of the porous ceramic honeycomb structure is plugged from the end surface of the exhaust gas inflow side. A filter which is arranged apart from each other and in which a catalytic substance is supported on at least a part of the partition walls and / or plugging portions and an SCR catalyst which purifies nitrogen oxide (NO _x ) are arranged in this order. Te, although purifies NO _x and particulate matter discharged from a diesel engine, upstream of the SCR catalyst is provided a source of reducing agent, after the addition of the reducing agent to the exhaust gas, the exhaust gas Supply to SCR catalyst. Further, when ammonia is generated unreacted or as a double product downstream of the SCR catalyst, an ammonia purification catalyst may be disposed on the downstream side of the SCR catalyst.

  The honeycomb structure filter provided in the exhaust gas purification apparatus of the present invention preferably has a partition wall porosity of 50% to 80% and an average partition wall pore size of 10 to 40 μm. When the porosity of the partition walls of the honeycomb filter is less than 50%, the ventilation resistance when the exhaust gas passes through the partition walls increases, so the pressure loss of the filter increases and the pressure loss of the entire exhaust gas purification device also increases. Because. On the other hand, if the porosity exceeds 80%, the strength of the filter is lowered, and there is a risk of damage due to mechanical stress or vibration when used as an exhaust gas purification device. The porosity of the honeycomb filter is preferably 60 to 75%.

  If the average pore diameter of the partition walls of the honeycomb filter is less than 10 μm, the ventilation resistance when exhaust gas passes through the partition walls increases, so the pressure loss of the filter increases and the pressure loss of the exhaust gas purification device as a whole also increases. Because. On the other hand, if the average pore diameter exceeds 40 μm, the strength of the filter is lowered, and there is a risk of damage due to mechanical stress or vibration when used as an exhaust gas purification device. A more preferable range of the average pore diameter of the honeycomb filter is 15 to 25 μm.

  The partition wall thickness of the honeycomb filter provided in the exhaust gas purification apparatus of the present invention is preferably 0.1 to 0.5 mm, and the partition wall pitch is preferably 1.2 mm or more. When the partition wall thickness is less than 0.1 mm, the strength of the honeycomb filter decreases, which is not preferable. On the other hand, when the partition wall thickness exceeds 0.5 mm, the ventilation resistance of the partition wall to the exhaust gas increases, so that the pressure loss of the honeycomb filter increases. A more preferable partition wall thickness is 0.2 to 0.4 mm. Further, when the partition wall pitch is less than 1.2 mm, the opening area of the inlet of the honeycomb filter becomes small, and the pressure loss at the inlet of the honeycomb filter becomes large.

  As the material constituting the partition wall of the honeycomb filter provided in the exhaust gas purification device, since the present invention is mainly used for purifying exhaust gas of a diesel engine, a material having excellent heat resistance should be used. It is preferable to use a ceramic material whose main crystal is at least one selected from the group consisting of cordierite, alumina, mullite, silicon nitride, silicon carbide and LAS. Among these, a honeycomb structure having cordierite as a main crystal is most preferable because it is inexpensive, excellent in heat resistance and corrosion resistance, and has low thermal expansion.

  Next, at least one exhaust gas inflow side plugged portion of the ceramic honeycomb filter used in the exhaust gas purifying apparatus of the present invention plugged with a desired flow path of the porous ceramic honeycomb structure is exhaust gas inflow An example of a method for forming a plugged portion of the ceramic honeycomb filter 11 arranged away from the side end face will be described with reference to FIG. A resin mask 80 having a resin slurry introduction passage 81 provided in a checkered pattern is attached to the exhaust gas inflow side end face of the honeycomb structure as shown in FIG. The slurry-like plugging material 53 is introduced through the slurry introduction passage 81 and filled in a part of the flow path of the honeycomb structure. After that, the water contained in the slurry-like plugging material 53 is absorbed into the partition walls of the honeycomb structure, and the plugging material is deposited on the partition walls to obtain the shape retention. After discharging the slurry and removing the resin mask, the solidified plugging material is dried. At this time, the slurry-like plugging material present in the resin slurry introduction passage 81 does not solidify because there is no water absorption from the partition wall. Therefore, by adjusting the length of the slurry introduction passage, the exhaust gas inflow side opening can be adjusted. The formation position of the sealing portion from the end face on the inflow side of the honeycomb structure can be determined. On the other hand, the end face on the outflow side forms a plugging portion at the end, and then the plugging material is fired to integrate the partition wall and the plugging material.

As another method, after inserting a needle-like tube from the end of the honeycomb structure to a predetermined position of the flow path, and introducing a predetermined amount of paste-like plugging material into the predetermined position through this tube, A method of drying and firing, a method of embedding ceramic chips in the honeycomb structure and firing, etc. can be employed.
Furthermore, a ceramic honeycomb structure that is not plugged is disposed on the exhaust gas inflow side end face of a ceramic honeycomb filter having a conventional structure that is plugged at both ends, and the two are integrated to manufacture the filter. Is also possible.

The SCR catalyst provided in the exhaust gas purifying apparatus of the present invention has an SCR catalyst material on the partition wall surface of a ceramic honeycomb structure having a plurality of flow holes axially partitioned by a porous partition wall inside the outer peripheral wall and the outer peripheral wall. It is good to form by carrying. In particular, the exhaust gas purification device of the present invention is
At least one exhaust gas inflow side plugging portion of the ceramic honeycomb filter plugged in a desired flow path of the porous ceramic honeycomb structure is disposed away from the end surface of the exhaust gas inflow side, and the partition wall and / or Alternatively, the filter and the SCR catalyst in which the catalyst material is supported on at least a part of the plugged portion are arranged in this order, and the particulate matter is efficiently burned by the ceramic honeycomb filter. the exhaust gas discharged, since the effectively reduce NO _x in the SCR catalyst, used in the SCR catalyst, the geometric surface area of the ceramic honeycomb structure is larger is preferable. For this reason, the partition wall thickness of the honeycomb structure is preferably 0.05 to 0.25 mm, and the partition wall pitch is preferably 0.8 to 1.6 mm. When the partition wall thickness is less than 0.05 mm, the strength of the honeycomb filter decreases, which is not preferable. When the partition wall thickness exceeds 0.25 mm, the ventilation resistance to the exhaust gas increases, so the pressure loss of the honeycomb structure increases. It is. A more preferable partition wall thickness is 0.08 to 0.15 mm. In addition, if the partition wall pitch is less than 0.8 mm, the opening area at the inlet of the honeycomb structure becomes small, and thus the pressure loss of the honeycomb structure increases, and the partition wall pitch exceeds 1.6 mm. This is because the geometric surface area is reduced and the purification performance of the SCR catalyst is lowered. A more preferable partition pitch is 0.9 to 1.3 mm.

  Further, when the ceramic honeycomb structure used for the SCR catalyst provided in the exhaust gas purification apparatus of the present invention has the partition wall thickness and partition wall pitch as described above, the porosity of the partition walls of the honeycomb structure is as follows. Is preferably 25% to 45%, and the average pore diameter of the partition walls is preferably 1 to 10 μm. This is because when the porosity of the partition walls of the honeycomb structure is less than 25%, the SCR catalyst substance is hardly supported and the purification performance may be deteriorated. When the porosity exceeds 45%, the thickness of the partition walls This is because the strength of the honeycomb structure is lowered and may be damaged due to mechanical stress or vibration when used as an exhaust gas purification device.

  Further, when the average pore diameter of the ceramic honeycomb structure used for the SCR catalyst provided in the exhaust gas purification apparatus of the present invention is less than 1 μm, the SCR catalyst substance is hardly supported and the purification performance may be deteriorated. When the average pore diameter exceeds 10 μm, the partition wall thickness is as thin as 0.05 to 0.25 mm, so that the strength of the honeycomb structure is lowered and the machine is used as an exhaust gas purification device. This is because it may be damaged by mechanical stress or vibration.

  As a material constituting the partition walls of the ceramic honeycomb structure used for the SCR catalyst provided in the exhaust gas purification apparatus of the present invention, the present invention is mainly used for purifying exhaust gas of a diesel engine. It is preferable to use a ceramic material having at least one main crystal selected from the group consisting of cordierite, alumina, mullite, silicon nitride, silicon carbide and LAS. Among these, a honeycomb structure having cordierite as a main crystal is most preferable because it is inexpensive, excellent in heat resistance and corrosion resistance, and has low thermal expansion.

V ₂ O ₅ , WO ₃ , TiO ₂ are suitable as the catalyst material used for the SCR catalyst provided in the exhaust gas purification apparatus of the present invention. In addition to these, Pt, Fe ₂ O ₃ , CuO, Mn ₂ O ₃ , Cr ₂ O ₃ , MoO ₃ or the like may be used.

As described above, according to the exhaust gas purification apparatus of the present invention, particulate matter and NO _x harmful components in the exhaust gas can be effectively reduced, and the number of parts required for the exhaust gas purification apparatus is reduced. be able to. In addition, since the number of components that cause pressure loss is small, it is possible to reduce the pressure loss of the exhaust gas purification device as a whole, and it is possible to reduce the size as compared with the exhaust gas purification device of the prior art.

(Example)
A method for manufacturing the filter 11 in the exhaust gas purification apparatus according to the embodiment of the exhaust gas purification apparatus for a diesel engine according to the present invention will be described with reference to FIG.
Add a molding aid and a pore-forming agent to a cordierite-forming raw material powder such as kaolin, talc, silica, aluminum hydroxide, alumina, etc., inject a specified amount of water, mix thoroughly, and extrude into a honeycomb structure. The moldable clay was adjusted. Then, extrusion molding using a known extrusion mold, to produce a honeycomb structure molded body having a square-shaped passage surrounded by a partition wall on the outer peripheral wall and the inner peripheral side of the outer peripheral wall, A ceramic honeycomb structure having a partition wall structure with a diameter of 267 mm, a total length of L305 mm, a partition wall pitch of 1.50 mm, a partition wall thickness of 0.3 mm, a partition wall porosity of 65%, and an average pore diameter of 20 μm is fired after drying. A body 10 was produced.

  Next, as shown in FIG. 3, a mask 80 made of resin having a slurry introduction passage 81 provided in a checkered pattern on the exhaust gas inflow side end face of the honeycomb structure is attached, and a slurry-like plugging material is passed through the slurry introduction passage. Introduced, a part of the flow path of the honeycomb structure was filled. Then, after the plugging material was attached to the partition walls and shape retention was obtained, the resin mask was removed and the plugging material 53 was dried. On the other hand, the plugging portion on the exhaust gas outflow side end face of the honeycomb structure has a masking film attached to the end face with an adhesive and then perforated so as to have a checkered pattern, followed by a slurry-like plugging material. Was introduced from the end face to form a plugged portion. Next, the plugging material was fired while controlling the temperature using a batch-type firing furnace, whereby a honeycomb filter 11 was obtained. At this time, the distance X between the exhaust gas inflow side end surface 51 of the exhaust gas inflow side plugging portion and the honeycomb filter end surface 12 was set to 100 mm.

For the honeycomb filter, a catalyst material made of platinum (Pt), cerium oxide, and activated alumina is applied to the partition wall surface and inside the pores in the partition wall, and further to the plugging portion surface and the pores in the plugging portion. It was carried inside. The supported amount was 2 g / L in terms of Pt amount (meaning 2 g supported per 1 L of honeycomb filter volume).
As shown in FIG. 2, the filter 11 created as described above is disposed in the exhaust passage 2 of the engine 1 with a filter 11, a reducing agent supply device 6 that can eject ammonia and the like, and an SCR catalyst 5. Here, the SCR catalyst 5 has a partition structure having a diameter of 267 mm, a total length of L 200 mm, a partition pitch of 1.06 mm, and a partition wall thickness of 0.11 mm, a partition wall porosity of 30%, and an average pore diameter of 5 μm. A cordierite ceramic honeycomb structure was formed by supporting V ₂ O ₅ , WO ₃ and TiO ₂ . The reducing agent supply device 6 is formed with a reducing agent injection valve 6b that can spray ammonia water, liquid ammonia, or aqueous urea solution into the exhaust passage 2 from the reducing agent tank 6a.

The exhaust gas purification apparatus of the present invention having the above-described configuration is provided with at least one exhaust gas inflow side plugging of a ceramic honeycomb filter in which a desired flow path of a porous ceramic honeycomb structure having an outer diameter of 267 mm and a total length of 305 mm is plugged. The ceramic honeycomb filter 11 in which the stop portion is arranged away from the end surface on the exhaust gas inflow side and the catalytic substance is supported on at least a part of the partition wall and / or the plugging portion, and the ceramic having an outer diameter of 267 mm and a total length of 200 mm the SCR catalyst 5 in the honeycomb structure catalyst material is supported and arranged in this order, each of the volume, the ceramic honeycomb filter is 17077Cm ^3, the SCR catalyst is 11198Cm ^3, required the entire exhaust system The ceramic honeycomb structure has a length of 505 mm and a volume of 28275 cm ³ Become.

The exhaust gas purifying apparatus having the above-described configuration includes at least one ceramic honeycomb filter in which a desired flow path of the porous ceramic honeycomb structure is plugged in the exhaust passage 2 on the downstream side of the engine 1 in order from the upstream side. The exhaust gas inflow side plugging portion is disposed away from the exhaust gas inflow side end face, and the filter 11 in which the catalyst substance is supported on at least a part of the partition wall and / or the plugging portion, and ammonia are ejected. Since the reducing agent supply device 6 and the SCR catalyst 5 that can be produced are provided, purification is performed as follows. When the amount of particulate matter collected on the filter 11 increases, in order to avoid an increase in pressure loss due to clogging of the filter, in accordance with the operating state of the diesel engine 1, fine particles on the filter carrying the catalyst material are collected. After estimating the amount of deposition, fuel is injected unburned upstream of the filter to promote the oxidation reaction of the fuel on the catalyst material, and the heat of reaction causes the internal temperature of the filter to be the activity of the catalyst material. Maintain above the minimum temperature and burn the deposited particulates. At this time, since the exhaust gas inflow side plugging portion of the ceramic honeycomb filter 11 is arranged away from the end surface of the exhaust gas inflow side, the temperature of the plugging portion is maintained to be equal to or higher than the activation temperature of the catalyst substance, It is possible to reduce an increase in pressure loss of the filter 11 due to flow path blockage due to particulate accumulation on the inflow side end face of the gas inflow side plugging portion. Further, the exhaust gas discharged from such configuration of the filter, include NO and NO _2, and, the molar ratio of NO and NO ₂ was at 1 / 2~2 / 1 NO / NO 2 Since it is easy to obtain exhaust gas, ammonia, which is a reducing agent, is added to the exhaust gas from the reducing agent supply device to form a gas mixture, and when this gas mixture is introduced onto the SCR catalyst, NO _x is converted to N ₂ . The conversion rate increases and NO _x is converted to N ₂ with high efficiency and purified.

(Conventional example)
A conventional example will be described with reference to FIG.
A cordierite-forming raw material powder such as kaolin, talc, silica, aluminum hydroxide, and alumina can be extruded into a honeycomb structure by adding a molding aid, injecting a specified amount of water, and further mixing. Adjusted the soil. Then, extrusion molding using a known extrusion mold, to produce a honeycomb structure molded body having a square-shaped passage surrounded by a partition wall on the outer peripheral wall and the inner peripheral side of the outer peripheral wall, A ceramic honeycomb having a partition wall structure having an outer diameter of 267 mm, a total length of 152 mm, a partition wall pitch of 1.46 mm, a partition wall thickness of 0.2 mm, a partition wall porosity of 35%, and an average pore diameter of 5 μm. A structure was produced.
A catalyst substance composed of platinum (Pt), cerium oxide, and activated alumina was supported on the ceramic honeycomb structure on the partition wall surface and inside the pores in the partition wall. The supported amount was 2 g / L in terms of Pt, and an oxidation catalyst 3 containing a catalyst material composed of Pt, cerium oxide, and activated alumina in the honeycomb structure was prepared.
On the other hand, according to the same method as in the example, it has a partition structure with an outer diameter of 267 mm, an overall length of 305 mm, a partition pitch of 1.5 mm, and a partition wall thickness of 0.3 mm, a partition wall porosity of 65%, and an average pore diameter of 20 μm. A ceramic honeycomb structure was prepared. Next, a masking film is attached to the exhaust gas inflow side end face of the honeycomb structure with an adhesive, and a hole is formed so as to have a checkered pattern, and a slurry-like plugging material is introduced from this hole. Filled. Then, after the plugging material was attached to the partition walls and shape retention was obtained, the masking film was removed and the plugging material was dried. Similarly, after forming a plugging portion on the exhaust gas outflow side end surface of the honeycomb structure, the plugging material is fired while controlling the temperature using a batch-type firing furnace, and a desired honeycomb honeycomb structure is obtained. The channel was plugged at the end. Further, a ceramic honeycomb filter 4 in which a catalyst material composed of Pt, cerium oxide, and activated alumina is supported on the partition wall surface and inside the pores in the partition wall, and further on the plugging portion surface and inside the pores in the plugging portion. Got. The supported amount was 2 g / L in terms of Pt amount.
Further, in the same manner as in the example, it has a partition structure with a diameter of 267 mm, an overall length of L 200 mm, a partition pitch of 1.06 mm, and a partition wall thickness of 0.11 mm, a partition wall porosity of 30%, and an average pore diameter of 5 μm. This cordierite ceramic honeycomb structure was formed by supporting V ₂ O ₅ , WO ₃ and TiO ₂ .
As shown in FIG. 4, the filter 4 created as described above is disposed in the exhaust passage 2 of the engine 1 by providing an oxidation catalyst 3, a filter 4, a reducing agent supply device 6 that can eject ammonia and the like, and an SCR catalyst 5. To do. The reducing agent supply device 6 includes a reducing agent injection valve 6b that can spray ammonia water, liquid ammonia, or an aqueous urea solution into the exhaust passage 2 from the base agent tank 6a.

The exhaust gas purifying apparatus according to the conventional example having the above-described configuration plugs the oxidation catalyst 3 in which the oxidation catalyst material is supported on the ceramic honeycomb structure, the desired flow path of the porous ceramic honeycomb structure at both ends, and The ceramic honeycomb filter 4 in which the catalyst material is supported on at least a part of the partition walls and / or the plugged portions, and the SCR catalyst 5 in which the catalyst material is supported on the ceramic honeycomb structure are arranged in this order, The outer diameter, total length, and volume of each of the oxidation catalyst 3 are 267 mm in outer diameter, 152 mm in total length, 8510 cm ³ in volume, the ceramic honeycomb filter 4 is 267 mm in outer diameter, 305 mm in total length, 17077 cm ³ in volume, and SCR catalyst 5 is 267 mm in outer diameter. 200 mm, a volume 11198cm ^3, the length of the ceramic honeycomb structure required entire exhaust gas system Is 657mm, the volume becomes a 36785cm ^3.

In the conventional exhaust gas purifying apparatus having the above configuration, the oxidation catalyst 3 and the desired flow path of the porous ceramic honeycomb structure are sealed at both ends in the exhaust passage 2 on the downstream side of the engine 1 in order from the upstream side. And a filter 4 in which a catalytic substance is supported on at least a part of the partition walls and / or plugging portions, a reducing agent supply device 6 that can eject ammonia and the like, and an SCR catalyst 5 are provided. It is purified as follows. When the amount of particulate matter trapped in the filter 4 increases, in order to avoid an increase in pressure loss due to clogging of the filter, in accordance with the operating state of the diesel engine 1, fine particles on the filter carrying the catalyst material are collected. After estimating the amount of deposition, fuel is injected unburned upstream of the oxidation catalyst 3 to promote an oxidation reaction of the fuel on the oxidation catalyst material, and NO in the exhaust gas is effective for NO ₂ The internal temperature of the filter 4 is increased by the reaction heat, and at least a part of the particulate matter in the exhaust gas is burned and removed at a relatively low temperature in the presence of NO ₂ by the ceramic honeycomb filter 4. Further, a nitrogen-based reducing agent is added to the exhaust gas having a high NO ₂ content to form a gas mixture, and this gas mixture is passed over the SCR catalyst, so that nitrogen oxides (NO _x ). Is converted to N ₂ and purified. However, in the exhaust gas purifying apparatus of this conventional example, since the oxidation catalyst 3 and the ceramic honeycomb filter 4 are arranged in series by the exhaust passage, the exhaust gas that has become a high temperature due to the catalytic reaction in the oxidation catalyst is converted into the oxidation catalyst. When passing through the exhaust passage between the filter and the filter, the temperature drops and flows into the filter. Especially when the exhaust gas temperature itself flowing into the purification device is low, such as during low speed running, the temperature inside the filter The temperature at which the substance is sufficiently combusted may not be reached, and unburned particulate matter remains on the end face of the filter inflow side plugging portion where the temperature is the lowest among the filters, blocking the flow path, There was a problem of increasing the pressure loss of the filter. Further, since the exhaust gas having a wide range of molar ratio of NO / NO ₂ in the exhaust gas exhausted from the filter having such a configuration is obtained in the range of 1/3 to 4/1, the reducing agent is added to the exhaust gas. When ammonia, which is a reducing agent, is added from a supply device to form a gas mixture and this gas mixture is introduced onto the SCR catalyst, the conversion rate from NO _x to N ₂ may decrease depending on the molar ratio.

As described above, in the exhaust gas purifying apparatus according to the embodiment of the present invention, since the filter 11 has a function of effectively burning and purifying the particulate matter by the action of the catalytic substance, the exhaust gas of the present invention. The purification device includes the filter 11 and the SCR catalyst 5, and the length of the ceramic honeycomb structure necessary for the entire exhaust gas device is 505 mm and the volume is 28275 cm ³ , whereas the exhaust gas purification device of the comparative example Then, the length of the ceramic honeycomb structure required for the entire exhaust gas apparatus is 657 mm, and the volume is 36785 cm ^3. According to the exhaust gas purification apparatus of the present invention, the particulate matter and nitrogen oxide (NO _x ) can be purified. A large effect can be obtained that the rate can be maintained high and the pressure loss of the entire exhaust gas purification device can be reduced. Further, since the honeycomb structure necessary for the exhaust gas purifying apparatus of the present invention is the filter 11 and the SCR catalyst 5, as compared with the exhaust gas purifying apparatus in which the oxidation catalyst, the ceramic honeycomb filter, and the SCR catalyst are disposed as in the prior art. Since the pressure loss is kept low, the entire purification device can be downsized.

It is a block diagram of the exhaust system of the diesel engine which shows the exhaust gas purification apparatus of this invention. It is a schematic cross section of a honeycomb filter in an embodiment of the present invention. FIG. 3 is a schematic cross-sectional view illustrating a situation where a plugging material is introduced into a honeycomb structure. It is a block diagram of the exhaust system of the diesel engine which shows the conventional exhaust gas purification apparatus.

Explanation of symbols

1: Engine 2: Exhaust passage 3: Oxidation catalyst 4: Filter 5: SCR catalyst 6: Reducing agent supply device 7: Exhaust gas 10: Honeycomb structure 11: Honeycomb filter 12: Inlet side end face 13: Outlet side end face 20: Outer periphery Wall 30: partition wall 31: partition wall on the inflow side from the inflow side plugging portion 32: partition wall on the outflow side from the inflow side plugging portion 40: channel 41: channel 42 opened on the end surface of the inflow side: inflow side Flow path 43 opened at the end face: Flow path opened to the exhaust gas outflow side 50: Inflow side plugging section 51: Inflow side plugging section end face 52: Outflow side plugging section 53: Plugging material 60: catalyst material 70: unburned particulates 80: mask 81: slurry introduction passage 90: exhaust gas inflow 91: exhaust gas inflow 92: exhaust gas outflow X: plugging portion formation position

Claims (5)

An apparatus for purifying exhaust gas containing nitrogen oxides and particulate matter discharged from a diesel engine, comprising at least one ceramic honeycomb filter plugging a desired flow path of a porous ceramic honeycomb structure An exhaust gas inflow side plugged portion is disposed away from an end surface of the exhaust gas inflow side, and a filter in which a catalytic material is supported on at least a part of the partition wall and / or the plugged portion, and an SCR catalyst, The exhaust gas purifying device is arranged in this order. The exhaust gas inflow side plugging portion end face of the ceramic honeycomb filter is disposed in a section having a length not more than 0.7 times the total length of the ceramic honeycomb filter from the inflow side end face of the ceramic honeycomb filter. The exhaust gas purification apparatus according to claim 1. The exhaust gas purification device according to any one of claims 1 to 2, wherein the catalyst substance supported on the ceramic honeycomb filter comprises a platinum group metal. 4. The activity of the catalyst material supported on the partition wall on the exhaust gas inflow side of the ceramic honeycomb filter is higher than the activity of the catalyst material supported on the partition wall on the exhaust gas outflow side. The ceramic honeycomb filter according to any one of the above. At least one exhaust gas inflow side plugging portion of the ceramic honeycomb filter disposed in the device for purifying exhaust gas containing nitrogen oxides and particulate matter discharged from the diesel engine is from the exhaust gas inflow side end surface. The catalyst material is supported on at least a part of the partition walls and / or the plugging portions, and the particulate matter in the exhaust gas is burned in the ceramic honeycomb filter, and the exhaust gas of the filter An exhaust gas purification method, wherein the molar ratio of NO / NO ₂ in the exhaust gas introduced into the SCR catalyst arranged on the exhaust side is set to 1/2 to 2/1.

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