JPH06288225A - Exhaust emission control device - Google Patents

Abstract

PURPOSE:To provide an exhaust emission control device capable of efficiently regenerating a filter as well as capturing environmentally harmful particulates contained in exhaust gas by the filter and especially having a function to efficiently burn the particulates contained in the exhaust gas of a diesel engine and others. CONSTITUTION:This is an exhaust emission control device having a plural number of filter units 3 connected to an exhaust gas pipe 1 through a directional control valve 2, each of the filter units has one or a plural number of filters 4 coated with a porous inorganic oxide and an electric heater 5, the particulates scavenged on the filters 4 are burnt by heating of the electric heater 5, and accordingly, the filters 4 are regenerated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for trapping fine particles in exhaust gas, which is an environmental problem. More specifically, it traps particulate carbonaceous material (particulates) in the exhaust gas of a diesel engine and efficiently The present invention relates to an exhaust gas purifying device for burning.

[0002]

2. Description of the Related Art An attempt has already been made to purify exhaust gas by collecting and burning particulates in exhaust gas from a diesel engine. For example, the actual exploitation Sho 61-551
No. 15 shows an example. The device disclosed in the publication is
A heat radiating member extending in the axial direction is provided in the honeycomb filter, and an electric heater is arranged in front of the honeycomb filter. In this known example, the exhaust gas entering from the inlet side of the honeycomb filter passes between the cells forming the honeycomb filter and flows to the outlet side. During such exhaust gas flow, particulates in the exhaust gas are collected by the filter.

As the amount of collected particulates increases, the pressure loss due to the filter increases, and when the pressure loss exceeds a predetermined value, the electric heater is energized to burn the particulates. However, when the particulates are forcibly combusted in a part of the exhaust pipe in use, it is not preferable to do so while the vehicle is running, and the engine is stopped.

Since the combustion of particulates requires a high temperature of 600 ° C. or higher, energization of the electric heater is
The battery installed in the vehicle with the engine stopped does not make it in time and requires a separate power supply.

Therefore, an attempt has been made to connect a generator directly connected to a diesel engine to an electric heater so as to secure a necessary amount of electricity. This attempt is quite useful.
However, the increase in exhaust gas pressure loss due to particulates trapped in the filter has already put a heavy burden on the diesel engine, and in addition, it is not the best way to impose the burden on the diesel engine on the generator. Absent.

An improvement to this attempt was to connect a pair of filter traps to the exhaust pipe and stop the flow of exhaust gas from the switching valve to the other filter trap while passing the exhaust gas to one filter trap and collect it. The particulates are burned with an electric heater.

According to this improvement plan, before the pressure loss due to the collected particulates is significantly increased, the exhaust gas is caused to flow to another filter trap by the switching valve, and the particulates can be burned. The burden is small.

In this improvement plan, the heat of the electric heater is hard to be transmitted to the filter, and the influence of the outside temperature causes
It has the drawback that the temperature rise in the filter cannot be expected quickly and the particulate combustion efficiency is poor.

Therefore, an object of the present invention is to capture environmentally harmful fine particles contained in exhaust gas with a filter, and
It is an object of the present invention to provide an exhaust gas purifying apparatus capable of efficiently regenerating a filter, and particularly having a function of efficiently burning particulates contained in exhaust gas of a diesel engine or the like.

[0010]

As a result of earnest research in view of the above problems, the present inventor has found that a plurality of foam-type filter units coated with a porous inorganic oxide are connected to each other through a switching valve and trapped in a filter. The present invention has been completed by discovering that when the collected particulates are burned by an electric heater, a part of the exhaust gas is caused to flow through a switching valve, whereby the particulates can be effectively burned and removed.

That is, the exhaust gas purifying apparatus of the present invention has a plurality of filter units connected to the exhaust gas pipe via a switching valve, and each filter unit is one or more coated with a porous inorganic oxide. It has a filter and an electric heater, and the particulates collected on the filter are burned by the heating of the electric heater, so that the filter is regenerated.

[0012]

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

FIG. 1 is a sectional view of an exhaust gas purifying apparatus according to an embodiment of the present invention. In the exhaust gas purifying apparatus of the present invention, a plurality of filter units 3 are connected in the middle of the exhaust gas pipe 1 via the switching valve 2. Each filter unit has one or more filters 4 and the same number of electric heaters 5 as the filters.

The filter 4 has a hollow cylindrical shape. The electric heater 5 is installed in the hollow portion of the cylindrical filter 4. The exhaust gas first enters the hollow portion of the filter 4, passes through the filter 4, and exits the outer peripheral portion of the cylinder.

As the filter 4 installed in the exhaust gas purifying device, a porous one having excellent heat resistance, thermal shock resistance and the like is used, but a porous material made of ceramic or metal which has been proposed as an exhaust gas converter up to now. Quality filters can be used. Further, it may be a filter in which a casing is filled with a porous pellet or granular material, or a filter in which a casing is filled with a heat-resistant fibrous material. Considering durability and the like, a ceramic filter is preferably used, and a foam-type or honeycomb-type filter can be preferably used. Considering the ease of manufacturing and the like, it is preferable to use a foam filter made of ceramic.

As the ceramics forming the filter, alumina, silica, zirconia, titania and their composite inorganic oxides, and mullite, cordierite and other composite inorganic oxides can be used. Preferred ceramic materials include cordierite, mullite, alumina and composites thereof.

The porosity of the filter is 40 in order to keep the pressure loss when the exhaust gas passes through the filter within an allowable range.
~ 90%. If the porosity is less than 40%, it becomes difficult for exhaust gas to pass through the filter, and if it exceeds 90%, the strength of the filter decreases. The density is determined by the material of the filter and the porosity, but for a diesel engine, it is generally preferably 0.3 to 0.7 g / ml. If the density is less than 0.3 g / ml, the strength is too low to be practical, and the collection efficiency of carbon fine particles becomes low. On the other hand, when it exceeds 0.7 g / ml, the flow of the exhaust gas is not smooth and the pressure loss is high.

In the purifying apparatus of the present invention, it is particularly preferable to use a foam type filter. In this case, it is preferable that the porosity of the filter is 60 to 90% and the density is 0.3 to 0.6 g / ml. The pore diameter is preferably 250 to 900 μm. If the pore size exceeds 900 μm, the contact area with the exhaust gas becomes too small and the collection rate decreases. The arithmetic mean of the preferable pore sizes is 250 to 500 μm.

In the purifying apparatus of the present invention, a high-density thin layer can be provided on the outlet side of the filter (the outer peripheral surface of the cylindrical filter) to enhance the trapping function. The thickness of this thin layer is 5 to 2000 μm. Preferred thickness is 10-50μ
m. The thin layer preferably has a porosity of 40 to 70% and a density of 0.4 to 0.8 g / ml. The pore size is 3 ~
The thickness is preferably 80 μm. The preferred arithmetic mean of pore size is 2
It is set to 0 to 30 μm. The material of this thin layer has the same selection range as the filter body, but it is preferable to use the same material as the filter body.

In the present invention, the inner and outer surfaces of the ceramic filter made of the above-mentioned material are coated with a porous inorganic oxide to promote the burning and removal of particulates.
When a thin layer is provided on the outlet side of the filter, the surface of the thin layer can be coated with a porous inorganic oxide.
Examples of the porous inorganic oxide include silica, alumina, titania, zirconia, titania-alumina, silica-alumina, zirconia-alumina, silica-titania, silica-zirconia, titania-zirconia and the like. Among these, it is preferable to use an alumina-based ceramic (alumina or a composite ceramic of alumina and another oxide) or a ceramic material such as zirconia, titania, or titania-zirconia.

When a porous inorganic oxide layer such as titania is formed on the surface of the filter, the porous inorganic oxide layer is
It is preferably 1 to 20% by weight of the filter. It is more preferably 5 to 15% by weight.

The porous inorganic oxide layer can be formed on the filter by a wash coat method, a sol-gel method or the like. The wash coating method is a method of forming an inorganic oxide layer on the filter by immersing the filter in the above-mentioned porous inorganic oxide slurry and drying it.

Further, the sol-gel method is a supporting method in which an organic salt (for example, an alkoxide) of a metal forming an inorganic oxide is hydrolyzed, the obtained sol is coated on a filter, and a colloid is obtained by contact with water vapor or the like. This is a method of forming an inorganic oxide layer on a filter by forming a film of particles, followed by drying and baking.

Electric heater 5 used in the purification apparatus of the present invention
Should be one that is not easily oxidized at high temperature. Specific examples include a corrosion-resistant nichrome wire, a Fe-Cr-Al alloy-based high-temperature heating element, and a kanthal wire. The arrangement shape of the heater is not particularly limited as long as the filter can be uniformly and efficiently heated.

Next, the operation will be described. As shown in FIG. 1, when a gas containing particulates or the like flows from the upstream side 1 to the downstream side of the exhaust passage, the gas passes through the switching valve 2 and passes through the filter 4 from the inner peripheral side to the outer peripheral side. During that time, the particles are captured by the filter 4. The pressure loss increases as the particles gradually accumulate. When the back pressure of the exhaust gas reaches a predetermined value, the switching valve 2 is switched to reduce the flow rate of the exhaust gas, the filter 4 is uniformly heated by the electric heater 5, and the particulates collected in the filter 4 are burned. Is done. The back pressure of the exhaust gas at which the regeneration process starts is 500 to 1500 mmAq. The exhaust gas flow rate during the regeneration process depends on the size of the purification device, but it is 2
It is preferably from 0 to 150 liters / minute. The operating time of the electric heater is preferably 2 to 20 minutes. At this time, the temperature of the filter 4 is preferably 300 to 600 ° C, and more preferably 400 to 500 ° C.

As described above, by combining the electric heater and the filter with the porous inorganic oxide, there is no rapid temperature rise during regeneration, and stable particulate combustion removal can be performed. At the same time, combustion of fine particles is promoted by the inorganic oxide with which the filter 4 is coated, and hydrocarbons, nitrogen oxides, and carbon monoxide are also purified.

In FIG. 1, the exhaust passage may be arranged in the opposite direction to that of the above embodiment. In that case, the gas passes through the filter 4 from the outer peripheral side to the inner peripheral side, but the effects are the same as those described above. In this case, the electric heater 5 is arranged only on the inner peripheral surface and the outer peripheral surface of the cylindrical filter or on the outer peripheral surface thereof.

Although the exhaust gas purifying apparatus of the present invention has been described with reference to FIG. 1 as an example, the present invention is not limited to this and can take various forms without departing from the gist of the present invention. For example, as shown in FIG. 2, the filter unit 3 may be composed of two filters.

The present invention will be described in more detail by the following examples. Example 1 A slurry of powdery γ-alumina was prepared, and a cylindrical foam type cordierite filter (volume: 1300c) was prepared.
m ³ , density 0.42 g / ml, porosity 80%), dried, and fired stepwise to 700 ° C., and a filter having a γ-alumina layer on the inner and outer peripheral surfaces of the cylindrical filter. It was created. The coating amount of γ-alumina is 10% by weight based on the weight of the filter.

Next, as shown in FIG. 2, two filters are set as a set in the filter unit, and 2200c is set.
It was connected via a switching valve in the middle of the exhaust pipe of the diesel engine of c. When the engine speed is 2000 rpm, the particulates are collected and the pressure loss is 1000 mmA.
When it becomes q, the regeneration process starts. The amount of exhaust gas entering the filter during regeneration was 30 liters / minute (200 ° C.). The amount of electricity supplied to the electric heater during the regeneration step was 700W.
The regeneration step time was 5 minutes. In this way, the purification device was able to perform stable collection and regeneration.

Example 2 In the same manner as in Example 1, using a slurry of titania instead of γ-alumina, a cylindrical foam type cordierite filter (volume: 1300 cm ³ , density: 0.42).
g / ml, porosity 80%) was coated with 10% by weight of titania. Particulates were collected under the same conditions as in Example 1, and stable collection and regeneration could be performed.

[0032]

As described above, the exhaust gas purifying apparatus of the present invention uses in combination an electric heater and a filter with an inorganic oxide to incinerate and remove combustible fine particles such as particulates captured by the filter, The filter can be efficiently regenerated without clogging.

The purifying apparatus of the present invention can be mainly used for exhaust gas treatment of diesel engines.

[Brief description of drawings]

FIG. 1 is a sectional view showing an exhaust gas purifying apparatus according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing an example of a filter and an electric heater used in the exhaust gas purifying apparatus of the present invention.

[Explanation of symbols]

 1 ... Exhaust gas pipe 2 ... Switching valve 3 ... Filter unit 4 ... Filter 5 ... Electrothermal heater

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Claims (5)

[Claims] 1. An exhaust gas purifying apparatus for collecting and combusting and removing particulates contained in exhaust gas discharged from a diesel engine, comprising a plurality of filter units connected to an exhaust gas pipe via a switching valve, Each filter unit has one or more filters coated with a porous inorganic oxide, and an electric heater, the particulates collected on the filter is burned by the heating of the electric heater, thus An exhaust gas purification device characterized in that a filter is regenerated. 2. The exhaust gas purifying apparatus according to claim 1, wherein the filter is a cylindrical body, and a flow direction of the exhaust gas in the filter is a direction from an inner peripheral surface of the cylindrical body toward an outer peripheral surface thereof. An exhaust gas purification device characterized by: 3. The exhaust gas purifying apparatus according to claim 1 or 2, wherein exhaust gas is caused to flow at a flow rate of 20 to 150 liters / minute by controlling the switching valve when the filter is regenerated. . 4. The exhaust gas purifying apparatus according to claim 1, wherein the filter is a porous foam-type ceramic material. 5. The exhaust gas purifying apparatus according to any one of claims 1 to 4, wherein the outer peripheral surface on the outlet side of the filter has a fine structure of a thin layer.