JPH06307228A - Exhaust gas purification trap - Google Patents

Abstract

(57) [Summary] [Purpose] To remove harmful components in exhaust gas emitted from diesel engines with a high trapping efficiency, a pressure drop that does not rise in a short time, and a renewable trap with low output. . [Structure] A plurality of cylindrical filter elements 11 and heater elements 12 are provided in a trap container 10.
The filter element 11 is composed of a cylindrical molded body obtained by compression molding a three-dimensional steel-like porous body, and the heater element 12
Is placed on the inner peripheral surface thereof, and the heater element 12 includes a plurality of sheath heaters 13.

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 trap for collecting and removing particulates (particles) such as carbon in exhaust gas of a diesel engine.

[0002]

2. Description of the Related Art Exhaust gas from an automobile is one of the major causes of air pollution, and a technique for removing harmful components contained in the exhaust gas is extremely important. Particularly in diesel engine vehicles, the removal of particulates (particulates) mainly composed of NOx and carbon is an important issue.

In order to remove these harmful components, EG
Improvements have been made on the engine side, such as turning R, improving the fuel injection system, and improving the shape of the combustion chamber, but there is no fundamental deciding factor, and the exhaust gas is disclosed in JP-A-58-51235. It has been proposed to remove particulates by a filter installed in the passage, and this post-treatment method is considered to be the most practical at present. By the way, as a trap for collecting the particulates contained in the exhaust gas of a diesel engine, it is necessary to satisfy the following performance from the conditions of use.

First, regarding the collection performance, it is necessary that the collection efficiency of particulates is sufficient to satisfy the cleanliness of passing exhaust gas. The particulate emission amount changes depending on the exhaust amount and load of the diesel engine, but generally it is necessary to be able to collect an average of 60% or more of the emission amount from the diesel engine.

Secondly, it is necessary that the pressure loss with respect to the exhaust gas is small. As the particulates are collected, the pressure loss when the engine exhaust passes through the trap increases, and back pressure is exerted on the engine, which causes an adverse effect. For this reason, it is said that it is usually necessary to suppress the pressure loss after collection to 30 KPa or less. Therefore, if a certain amount of particulates are trapped in the trap,
It is necessary to periodically remove and regenerate the collected matter to recover the initial pressure loss state. If the rate of increase in pressure loss with respect to the amount of collected particulates is large, the frequency of this removal and regeneration operation becomes large, which is not practical. Therefore, it is necessary for the trap not only to have a small initial pressure loss, but also to be hard to increase the pressure loss even when the exhaust gas is passed and the particulates are collected.

Thirdly, it is necessary that the above-mentioned repeated removal / regeneration process can be completed easily with low energy. As a particulate removal and regeneration method, a method using a light oil burner is also being considered, but considering safety and ease of control and installation in a car, the method using an electric heater is the most preferable. It is said to be promising. However, in the case of electric heater regeneration,
It is necessary to be able to reproduce with as low a power as possible so as not to place an excessive burden on the battery and alternator installed in the car.

Conventionally, as a filter element satisfying the above requirements, a wall-flow type honeycomb porous body of cordierite ceramics has been considered to be most practical. In this method, particulates tend to accumulate locally, and because cordierite ceramics have a low thermal conductivity, heat spots are easily formed during regeneration, which may cause the filter to melt or crack due to thermal stress. , Reliability could not be secured. Therefore, at present, a filter element made of a highly reliable metal filter element and a ceramic fiber having a candle-like shape, which is free from cracks and the like at the time of regeneration and has a high reliability, is drawing attention.

[0008]

However, the metal filter element and the ceramic fiber filter element described above cannot have a larger exhaust gas inflow surface area than the wall flow filter made of cordierite ceramics due to its structure. Therefore, when a filter is designed to obtain high collection efficiency, particulates are collected only on the filter surface and cause clogging, resulting in a rapid increase in pressure loss and a short filter regeneration interval. .

Further, in the wall flow filter made of cordierite ceramics, while the regeneration can be efficiently performed with a small amount of electric power by the combustion propagation utilizing the self-heating at the time of burning the particulates, the metal filter element is used. And ceramic fiber filter elements cannot collect as much particulate as the cordierite ceramic wall flow filter,
Since the heat of combustion of particulates is small, regeneration must be performed only with the heat generated by the electric heater. As a result, there is a problem that the amount of regenerated electric power becomes too large.

In a filter having an electric heater regenerator, the heater element is generally embedded and integrated in the filter element. In that case, when a current is passed through the heater to heat it during regeneration, the filter element is heated accordingly and is then transferred to the particulates trapped in the holes. Therefore, heating the particulates to be regenerated causes a time lag than heating the filter. Further, before the particulates are heated to the regeneration temperature, the filter portion where the particulates are hardly deposited is also heated and heated. Heat is radiated from the heated filter portion due to heat transfer and heat radiation to the atmosphere gas and the trap container, which is wasteful energy consumption from the viewpoint of combustion regeneration of particulates.

In the present invention, while keeping in mind various problems of the above-mentioned conventional exhaust gas purifying trap, high trapping efficiency is maintained while high trapping efficiency is maintained and pressure drop does not sharply rise in a short time. It is an object of the present invention to provide an exhaust gas purifying trap for a diesel engine, which is composed of a metal filter element and a ceramic fiber filter element incorporating a heater, which can be regenerated efficiently, that is, at a low output in a short time. .

[0012]

According to the present invention, as a means for solving the above problems, a cylindrical filter element having a heater element incorporated therein is mounted in a trap container provided in an exhaust system, and the heater element is a gas. The exhaust gas purifying trap is formed as a permeable sheet-like heating element and is installed on the inner diameter side of the filter element.

In this case, in order to reduce the heat radiation of the filter element, it is preferable to cover the inner diameter side of the heater element with a material having a lower thermal conductivity than the planar heating element.

In order to effectively carry out heat transfer and heat radiation from the heater element, the filter element is constructed by combining cylindrical filters having different diameters in a concentric manner with a gap, and the heater element is arranged in the gap of each tubular filter. It is good to choose one.

In any of the above cases, the planar heating element may be one in which an electric heater having an insulating coating is integrally fixed by a gas permeable metallic porous body.

In that case, it is preferable that the metal porous body for integrally fixing the electric heater is a three-dimensional network structure porous body made of a heat-resistant metal.

In any of the above cases, it is preferable that the filter element is a three-dimensional network structure porous body made of a heat-resistant metal.

[0018]

In the filter element provided in the trap of the first aspect of the invention having the above-mentioned structure, the exhaust gas passes through the planar heating element and the particulates are collected by the filter during the collection. Most of the particulates are collected on the surface facing the planar heating element, and the collection density decreases as the distance from this surface increases. On the other hand, during regeneration, the heated sheet heating body first heats the particulates collected on the surface facing the sheet heating body by heat conduction and heat radiation.

In the filter of the present invention, unlike the case where the heater is embedded, the particulates deposited on the heater element are first heated, and then the filter portion is heated. In the meantime, the temperature rise in the filter section is reduced, and as a result, the energy used for waste during regeneration can be reduced.

In the second aspect of the present invention, by covering the side of the above-mentioned gas-permeable sheet-like heating element that does not face the filter element with a material having a lower thermal conductivity than that of the sheet-like heating element, a filter element of the sheet-like heating element is provided. It is possible to reduce the temperature of the surface that is not totally covered, and as a result, it is possible to reduce heat radiation from this surface to the atmosphere gas and the trap container.

According to the third aspect of the invention, the heat transfer and heat radiation from the heater element can be transferred to the particulates trapped in the filter element by disposing the filter element on both surfaces of the heater element facing each other. . That is, the filter element has a structure in which cylindrical filters having different diameters are combined concentrically with a gap, and a structure in which the heater element is arranged in the gap between the cylindrical filters is also an effective form of the present invention.

As the sheet heating body used in the fourth invention,
It is conceivable that an electric heater having an insulating coating is integrally fixed with a gas-permeable metal porous body.

In the fifth invention, as a concrete method, it is effective to fix the electric heater having an insulating coating by sandwiching it with a three-dimensional network structure porous body made of a heat-resistant metal. The three-dimensional network structure porous body has high gas permeability and does not block the passage of exhaust gas. Further, by sandwiching and integrating the heater element with the three-dimensional network structure porous body, a surface having a small thermal resistance can be formed at the interface between the heater element and the three-dimensional network structure porous body by plastic deformation.

As the metal porous body used in the sixth invention,
It is preferable that the particulate collection efficiency be high and the increase in pressure loss due to the collection be small. From this point of view, the three-dimensional network structure porous body made of a heat-resistant metal having continuous ventilation holes has excellent properties. As shown in FIG. 6, an example of the three-dimensional network structure porous body is a porous body having a structure in which a pocket-shaped continuous ventilation hole 1 is surrounded by a skeleton 2. Another example of the three-dimensional network structure porous body is, as shown in FIG. 7, a porous body in which fibrous skeletons 3 are three-dimensionally intertwined to form continuous ventilation holes 4.

Since these porous bodies have a high porosity, the gas flow resistance is extremely small, and since the skeleton forms a three-dimensional network, the particulate collection performance is excellent. This three-dimensional network structure porous body is also advantageous in reducing the regeneration power in that it has a low bulk density and a small heat capacity. Further, since this three-dimensional network structure porous body has excellent moldability, the pore size can be freely controlled by compression processing or the like.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. 1 is an embodiment of an exhaust gas purifying trap for a diesel engine of the present invention. Cylindrical filter element 1
1 and seven heater elements 12 located on the inner surface of each cylindrical filter are mounted in the trap container 10. In the case of this embodiment, the exhaust gas is a cylindrical filter 1.
1 is supplied from the inner surface, the particulates are removed, and then discharged from the outer surface.

FIG. 2A shows a perspective view including a partial cross section of the filter element 11. Filter element 11
Is a NiCrAl three-dimensional network structure porous body (Sumitomo Electric Industries, Ltd., trade name "Celmet", average pore diameter 400 µm) compression molded to 1/3 in the plate thickness direction, outer diameter 48 mm, inner diameter 36
It is composed of a cylindrical molded body having a length of mm and a length of 190 mm. The heater element 12 has a sheath heater 13 having an outer diameter of 4 mm and an effective length of 190 mm, which has a NiV heater of 12 V and 50 W.
The outer diameter is 34 mm, the inner diameter is 24 mm, and the length is 190 m, which is made of a NiCrAl three-dimensional network structure porous body having an average pore diameter of 1 mm.
In the cylindrical molded body of m, four pieces are built in and integrated at equal intervals in the circumferential direction.

The trap having the above construction was mounted on the evaluation apparatus shown in FIG. 3, and the trap was collected for 2 hours under the constant load constant speed operation of 3/4 load and 1600 rpm. Then, with the switching valve flowing most of the exhaust gas to the bypass, the built-in heater was energized for regeneration.

The outline of the illustrated evaluation apparatus is as follows.
A car 20 having a 3400 cc, 4-cylinder direct-injection diesel engine is installed in the chassis dynamometer 21,
A trap 22 was attached to the exhaust pipe. A bypass circuit 23 and a switching valve 24 are provided in the trap portion. Exhaust gas passing through the trap is a dilution tunnel 25.
Be led to. A filter type particulate concentration measuring device 26 is installed in the dilution tunnel to measure the particulate concentration in the exhaust gas.

The following is the result of measuring the purifying action of the trap of Example 1 by the evaluation apparatus as described above.
The initial pressure loss of this filter was 95 mmAq, and the pressure loss increased to 3200 mmAq when collected for 2 hours. Seven minutes after the start of regeneration, the pressure loss recovered to an initial value of 95 mmAq. The amount of exhaust gas passing through the filter portion at the start of regeneration was 2 l / min, and at the end of regeneration was 35 l / min.

FIG. 2B shows the structure of the filter element 111 used for comparison. The filter 112 is formed from a cylindrical molded body having an outer diameter of 48 mm, an inner diameter of 36 mm, and a length of 190 mm, which is obtained by compression-molding a NiCrAl three-dimensional network structure porous body having an average pore diameter of 400 μm similar to that of Example 1 to 1/3 in the plate thickness direction. Become. Heater 113 is 12V, 50W, outer diameter 4m
Four sheath heaters of m were used for each filter. A trap incorporating this filter element was evaluated under the same conditions as in Example 1.

The initial pressure loss of this filter was 98 mmAq, and the pressure loss when collecting for 2 hours was 3350 mmAq. The pressure loss recovers to 2800 mmAq only 7 minutes after the start of regeneration, and finally the pressure loss is 99 mm 12 minutes after the start of regeneration.
It recovered to almost the initial value of Aq.

Embodiment 2 FIG. 4 is a perspective view showing the structure of a filter element and a heater used in another embodiment of the present invention. The filter element 11 ′ has an average pore diameter of 40 as in the first embodiment.
An outer diameter of 48 mm and an inner diameter of 36 m obtained by compression-molding a 0 μm NiCrAl three-dimensional network structure porous body into 1/3 in the plate thickness direction.
It is composed of a cylindrical molded body of m and a length of 190 mm. The heater element 12 'is the same as that in the first embodiment, Ni of 12V, 50W.
A sheath heater 13 'having a Cr heater and having an outer diameter of 4 mm and an effective length of 190 mm is formed of a NiCrAl three-dimensional mesh structure porous body having an average pore diameter of 1 mm, and has an outer diameter of 34 mm and an inner diameter of 24 m.
m, 190 mm long cylindrical molded body with 4 circumferentially equidistantly assembled and integrated, and then the inner surface of the three-dimensional network structure porous body was covered with alumina-zirconia ceramic with a thickness of 0.5 mm. Then, the heat insulating layer 14 'is formed.

A trap incorporating this filter element was also evaluated under the same conditions as in Example 1. The initial pressure loss of this filter was 96 mmAq, and the pressure loss was 3160 mmAq when collected for 2 hours. 6 minutes after the start of regeneration, the pressure loss is 9
It recovered to almost the initial value of 8 mmAq.

Embodiment 3 FIG. 5 is a perspective view showing the structure of a filter element and a heater element used in another embodiment of the present invention.
The filter 11 ″ is composed of a concentric double cylinder, and the outer cylinder 11
Both A ″ and the inner cylinder 11B ″ are made of the same Ni as in the first embodiment.
CrAl three-dimensional network porous body (average pore size 400μ
m) is formed by compression molding 1/3 in the plate thickness direction, and the shape is 58 mm in outer diameter, 46 mm in inner diameter, 190 mm in length and 32 mm in outer diameter, 20 mm in inner diameter, 1 in length.
It is 90 mm.

The heater element 12 "has an outer diameter of 4 mm with a NiV heater of 12 V and 50 W as in the first embodiment.
A sheath heater 13 ″ with an effective length of 190 mm is used with an average hole diameter of
4 mm outer diameter 44 mm, inner diameter 34 mm, length 190 mm cylindrical molded body made of NiCrAl three-dimensional net-structure porous body and integrated at equal intervals in the circumferential direction. Was incorporated into the gap of the double cylindrical filter so that the gaps were substantially equal.

Four filter elements were mounted in the same trap container as in Example 1 and evaluated under the same conditions as in Example 1. The initial pressure loss of this filter is 92 mmAq,
When collected for 2 hours, the pressure loss was 2850 mmAq. Seven minutes after the start of regeneration, the pressure loss recovered to 95 mmAq.

[0038]

As described in detail above, the trap for purifying exhaust gas of a diesel engine of the present invention has a high heating efficiency by an electric heater and requires a small amount of electric power for combustion regeneration. Therefore, exhaust gas purification treatment is strictly required. However, it can be effectively used for diesel vehicles with limited battery capacity.

[Brief description of drawings]

FIG. 1 is a sectional view of a trap according to an embodiment.

FIG. 2A is a perspective view including a partial cross section of a filter element of a first embodiment, and FIG. 2B is a perspective view including a partial cross section of a filter element of a comparative example.

FIG. 3 is a conceptual diagram of a collection performance evaluation device.

FIG. 4 is a perspective view including a partial cross section of a filter element according to another embodiment.

FIG. 5 is a perspective view including a partial cross section of a filter element according to another embodiment.

FIG. 6 is an enlarged view of a three-dimensional network structure porous body.

FIG. 7 is an enlarged view of a fibrous porous metal body.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Continuous ventilation hole of three-dimensional network structure porous body 2 Framework of three-dimensional network structure porous body 3 Framework of fibrous metal porous body 4 Continuous ventilation hole of fibrous metal porous body 10 Trap container 11, 11 ', 11 "Filter element 12, 12 ', 12 "heater element 13, 13', 13" sheath heater 20 car 21 dynamometer 22 trap 23 bypass circuit 24 switching valve 25 dilution tunnel 26 particulate concentration measuring instrument

Claims (6)

[Claims] 1. A tubular filter element having a heater element incorporated therein is mounted in a trap container provided in an exhaust system, and the heater element is formed as a gas-permeable planar heating element, which is a filter element. An exhaust gas purification trap installed on the inner diameter side of the. 2. The exhaust gas purifying trap according to claim 1, wherein an inner diameter side of the heater element is covered with a material having a lower thermal conductivity than that of the planar heating element. 3. The exhaust gas purifying according to claim 1, wherein the filter element is constructed by concentrically combining with a cylindrical filter having an inner diameter with a gap, and the heater element is arranged in the gap between the cylindrical filters. For trap. 4. The planar heating element is one in which an electric heater having an insulating coating is integrally fixed with a gas-permeable metal porous body, according to any one of claims 1 to 3. Exhaust gas purification trap. 5. The exhaust gas purifying trap according to claim 4, wherein the metal porous body integrally fixing the electric heater is a three-dimensional network structure porous body made of a heat-resistant metal. 6. The filter element is a three-dimensional network structure porous body made of a refractory metal.
6. The exhaust gas purification trap according to any one of 1 to 5.