JPH0754643A - Exhaust emission control device and structural body thereof - Google Patents

Abstract

PURPOSE:To enable regenerative efficiency and durability to be improved and also to facilitate the temperature control in regeneration by raising temperature without temperature nonuniformity in a short period. CONSTITUTION:One exhaust emission control device 10 is constituted by combining and arranging twelve pieces of filters 3, 4 formed into a honeycomb shape by a porous silicon carbide sintered body. Heaters 5 as a heating element are provided on the outer peripheral part of the filters 3, 4. A seal member 8 serving as a heat resistant filling material is interposed between the filters 3, 4 adjacent to each other, and its periphery is covered by a heat insulating member 9.

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 purifying exhaust gas of an internal combustion engine and a component thereof.
In particular, the present invention relates to an exhaust gas purifying device of the type in which fine particles in the collected exhaust gas are burned by the heat of an electric heater, and a component thereof.

[0002]

2. Description of the Related Art Conventionally, a filter using a ceramic material has been proposed as a filter used in a so-called electric heater regeneration type exhaust gas purifying apparatus. As such a ceramic material, cordierite (2MgO.2Al ₂ O ₃ .5SiO ₂ ) or the like is generally well known. Then, by using such a material, for example, a filter having a honeycomb structure is formed.

Usually, an electric heater is provided on one end face of this type of filter as a heating element for heating the filter to a predetermined temperature (600 ° C. to 800 ° C.) during regeneration. Then, when electricity is applied to the electric heater, the fine particles collected on one end surface of the filter are ignited and finally burned.

However, in the case of the filter having the above-mentioned structure, the filter is heated only from one surface side by the radiant heat of the heater, so that there is a drawback that a temperature difference is likely to occur between the heating surface and the non-heating surface. In addition, if regeneration is continued in this state, the temperature inside the filter will rise further locally due to abnormal combustion of fine particles, and eventually cracking or melting will occur in a short period of time. was there. For this reason, conventionally, measures have been taken such as controlling various conditions at the time of regeneration (collection amount, heater temperature, energization time, combustion air supply amount, engine operating conditions, etc.).

[0005]

However, since the factors that influence the reproduction state are plural and complicated as described above, it is not easy to strictly control these factors. Further, since it is a method of heating by radiant heat, there is a disadvantage that the temperature of the heater does not always reach the temperature of the filter. Even if the computer is strictly controlled, it is extremely difficult to extend the life of the filter to 2000 hours or more.

Therefore, as a measure for eliminating the drawback of the heater end face arrangement type, for example, winding an electric heater around the outer peripheral surface of the filter can be considered. That is, in this method, the temperature difference in the filter during regeneration is minimized by heating the entire filter from the outer peripheral surface side.

However, even with the above-mentioned heater outer peripheral surface arrangement type filter, it is expected that it will be difficult to sufficiently eliminate the temperature difference in the filter when the filter itself becomes large. Was done. Moreover, in this case, it was expected that the time for raising the temperature of the filter to the regeneration temperature would be long.

The present invention has been made in view of the above circumstances. An object of the present invention is to raise the temperature without temperature unevenness in a short time, so that the regeneration efficiency and durability can be improved. Moreover, it is an object of the present invention to provide an exhaust gas purifying apparatus and its constituent body that can facilitate temperature control during regeneration.

[0009]

In order to solve the above-mentioned problems, in the invention described in claim 1, a plurality of filters made of ceramics sintered bodies having a porous structure are arranged adjacent to each other, and The gist is an exhaust gas purifying device characterized in that a heating element is interposed between adjacent filters.

In this case, a heat resistant filling material may be interposed between adjacent filters, or a heating element may be arranged between the filter and the heat resistant filling material. Further, the composition of the heat resistant filling material may be ceramic fiber, silicon carbide powder and an inorganic binder, or the heat resistant filling material may be extruded into a paper form. Further, a heat-expandable heat insulating material made of ceramic fibers may be arranged at the outermost peripheral portion.

According to a seventh aspect of the present invention, there is provided an exhaust gas purifying apparatus comprising a filter made of a ceramics sintered body having a porous structure and a heating element provided on an outer peripheral portion of the filter. The summary is. In this case, the filter may be formed of a porous silicon carbide sintered body in a honeycomb shape, or the average pore diameter may be 1 μm to 50 μm and the porosity may be 30% to 70%.

[0012]

According to the invention described in claim 1, since each heater heats the filter around it,
The exhaust gas purifying apparatus is heated uniformly from the inside. Therefore, the temperature of the exhaust gas purification device rises evenly within a short time.

According to the seventh aspect of the present invention, since the heating element is provided in advance on the outer peripheral portion of the filter, it becomes extremely convenient as a structural body when constructing the exhaust gas purifying apparatus as described above. . Further, with this configuration, since the filter and the heating element are in contact with each other, the heating efficiency is excellent and the temperature followability is good.

Hereinafter, the exhaust gas purifying apparatus and its constituents of the present invention will be described in detail. In the present invention, it is desirable to interpose a heat resistant filling material between adjacent filters. The reason for this is to prevent a reduction in purification efficiency due to air leakage by filling a void formed when a plurality of filters are combined. In addition, the heat-resistant filling material also serves as an adhesive for bonding the filters together.

The heat-resistant filling material preferably has elasticity, thermal conductivity, insulation and the like in addition to heat resistance. This is because if the elasticity is excellent, the thermal stress can be reliably released even when the filter is subjected to thermal stress due to heating. Further, if the heat conductivity is excellent, the heat of the heating element is quickly and evenly conducted to the filters, and the temperature difference inside the exhaust gas purifying device is also reduced. Furthermore, if the insulating material is excellent, it is possible to prevent a short circuit between the heating elements provided adjacent to each other.

The composition of the heat resistant filling material is preferably ceramic fiber, silicon carbide powder and inorganic binder. This is because the filling material having such a composition has the heat resistance, elasticity, thermal conductivity, insulating property and the like which are desired for the above heat resistant filling material. In this case, suitable ceramic fibers include, for example, alumina-silicate ceramic fiber, alumina fiber, zirconia fiber, silicon carbide fiber and silica fiber.

It is desirable to use a paper-like extruded material as the heat-resistant filling material. With such a shape, it suffices to wind the filter around the outer peripheral surface of the filter, which facilitates the work for disposing the heat-resistant filling material.

In the present invention, it is desirable to place the heating element between the filter and the heat resistant filling material. That is, it is possible to prevent a short circuit between adjacent heat generating elements by using the structure in which the heat generating elements are covered with the heat resistant filling material. Also, with such an arrangement method, heat conductivity from the heating element to the filter is improved.

In the present invention, it is desirable to dispose a thermally expansive heat insulating material made of ceramic fiber at the outermost peripheral portion. The thermally expandable heat insulating material here means a heat insulating material having an elastic structure and having a function of releasing thermal stress.

The reason for this is to prevent heat from escaping from the outermost peripheral portion of the exhaust gas purifying device, thereby minimizing energy loss during regeneration. Further, it is to prevent the displacement of the filter due to the pressure of the exhaust gas, vibration due to traveling, etc., by expanding the ceramic fiber by the heat during regeneration. Regarding the heat insulating material, the various ceramic fibers (excluding silicon carbide fiber) listed above for heat resistant filling substances
Good to use.

Further, in the present invention, it is preferable that the filter is formed of a porous silicon carbide sintered body in a honeycomb shape. This is because the porous silicon carbide sintered body has excellent heat resistance and thermal conductivity. This is because the honeycomb filter has a small pressure loss even when the amount of collected fine particles is increased. Further, it is desirable that the average pore diameter is 1 μm to 50 μm and the porosity is 30% to 70%.
When the average pore diameter is less than 1 μm, the filter is significantly clogged due to the accumulation of fine particles. On the other hand, if the average pore diameter exceeds 50 μm, it becomes impossible to collect fine particles, and the collection efficiency decreases.

If the porosity is less than 30%, the filter may become too dense and exhaust gas may not be able to flow inside. Therefore, collection of fine particles may be impossible. On the other hand, if the porosity exceeds 70%, there will be too many voids in the filter,
There is a possibility that the strength will be weakened and the collection efficiency of the fine particles will be reduced.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment in which the present invention is embodied in an exhaust gas purification system for a diesel engine will be described in detail below with reference to FIGS.

As shown in FIG. 6, the exhaust gas purification system 1 includes a metal casing 2. The passage 2a of the casing 2 is connected to the exhaust pipe Ea of the diesel engine E as an internal combustion engine. Casing 2
An exhaust gas purifying device 10 is provided therein to remove fine particles in the gas discharged from the diesel engine E.

As shown in FIG. 4, the exhaust gas purifying apparatus 10 of this embodiment is composed of eight prismatic filters 3 and four filters 4 each having a right-angled isosceles triangular cross section.

As shown in FIGS. 1 to 3, a prism (3
3 mm × 33 mm × 150 mm) filter 3 has communication holes 3a having a substantially square cross section formed regularly along the axial direction. Each communication hole 3a has an inner wall 3 with a thickness of 0.3 mm.
They are separated from each other by b. One end on either the exhaust gas inflow side or the outflow side of each communication hole 3a is sealed in a checkered pattern by a sealing piece 3c made of a porous sintered body. As a result, cells C1 and C2 that are open only on either the inflow side or the outflow side of the filter 3 are formed. The inner walls 3b of the cells C1 and C2 carry an oxidation catalyst composed of platinum group elements, other metal elements and oxides thereof. In addition, the filter 4 has the same shape as the filter 3 except that the cross-sectional shape is an isosceles right triangle.
It has the same configuration as. And in the case of the filters 3 and 4 of the present embodiment, the average pore diameter is 14 μm and the pore diameter is 40.
%, The cell wall thickness is 0.3 mm, and the cell pitch is 1.8 mm.

As shown in FIGS. 1 to 5, a heater 5 as a heating element is joined to the outer peripheral surfaces of the filters 3 and 4. In the present embodiment, the heater 5 is a tantalum wire having a diameter of 2 mm and bent in a wavy shape. Further, in this embodiment, the heaters 5 of the filters 3 and 4 are connected in series. As shown in FIG. 6, the end of the heater 5 is connected to the wiring 6
It is electrically connected to the battery (12V) 7 via. In this case, 24 instead of 12V battery 7
A V battery may be used. In addition, a voltage higher than that of the battery 7 (100 V household power source or 200 V
V commercial power supply) may be used.

As shown in FIGS. 4 and 5, the filters 3 and 4 are covered with a paper-like sealing material (thickness: 2.5 mm) 8 as a heat-resistant filling material. Therefore, in the case of this exhaust gas purification device 10, the heating element 5 is in a state of being interposed between the adjacent filters 3 and 4.
In addition, the outermost peripheral portion of the exhaust gas purification device 10 has a thickness of 15
A heat insulating material 9 of mm is provided.

Next, an example of a procedure for manufacturing the exhaust gas purification device 10 will be introduced. After a mixed powder of 70% by weight of α-type silicon carbide powder and 30% by weight of β-type silicon carbide powder is wet-mixed, an organic binder (methyl cellulose) and water are added to the mixture in predetermined amounts and kneaded. Then, a honeycomb-shaped molded body is obtained by extrusion molding this kneaded product. Next, the molded body is dried using a microwave dryer. Further, after sealing the communication hole 3a of the molded body with a paste for forming the sealing piece 3c made of a porous sintered body,
The paste for the sealing pieces 3c is dried again using the dryer. Then, after the dried body is degreased at 600 ° C., it is further baked at 2200 ° C. in an argon atmosphere. As a result, the porous honeycomb filters 3, 4 are obtained.

Here, 75 parts by weight of ceramics fiber (alumina silicate ceramics fiber), 10 parts by weight of silicon carbide powder and 15 parts by weight of silicon dioxide as an inorganic binder were mixed and kneaded, and the mixture was extruded into a sheet having a thickness of 3 mm. To do. Then, the structure S formed by joining the heater 5 to the outer peripheral surfaces of the filters 3 and 4 is covered with the sheet-shaped sealing material 8. Next, the construct S covered with the sealing material 8 is combined. Finally, the outermost peripheral portion of the structure S is coated with a ceramic fiber heat insulating material (63% by weight of ceramic fiber, 7% by weight of α-sepiolite, 20% by weight of unexpanded vermiculite and 10% by weight of organic binder) 9. Then, the desired exhaust gas purification device 10 as shown in FIG. 4 is obtained.

Next, the flow of exhaust gas when the above-mentioned exhaust gas purifying apparatus 10 is arranged at a predetermined position and the diesel engine E is started will be described. As shown by arrow A1 in FIG.
Is introduced into the cell C1 having an opening on the inflow side of. Then
The exhaust gas passes through the inner wall 3b and is introduced into the adjacent cell C2, that is, C2 which is open to the outflow side. At this time, movement of fine particles contained in the exhaust gas is blocked by the inner wall 3b. Therefore, only the fine particles are trapped on the inner wall 3b. Then, the purified exhaust gas passes through the cell C2 opened on the outflow side and is finally discharged from the filters 3 and 4.

In the case of the exhaust gas purification system 1 of this embodiment, as shown in FIG. 6, the pressure sensor Ps is provided at a position upstream of the exhaust gas purification device 10 in the exhaust pipe Ea.
Is installed. The pressure sensor Ps is electrically connected to the piezoelectric conversion element Pe. The piezoelectric conversion element Pe outputs a predetermined electric signal to the control device C based on the detection signal output from the pressure sensor Ps. The control device C is adapted to turn on / off the switch Sw provided on the wiring 6 based on the detection signal from the piezoelectric conversion element Pe.

An air supply pipe Ca is arranged at a position downstream of the exhaust gas purification device 10 in the exhaust pipe Ea. The air supply pipe Ca is connected to the compressor Co. Therefore, at the time of regeneration, secondary air for combustion promotion is supplied through the air supply pipe Ca into the exhaust pipe Ea.

Next, a characteristic evaluation test carried out in a state where the exhaust gas purification devices 3 and 4 are incorporated in the exhaust gas purification system 1 as described above will be described. In this characteristic evaluation test, two types of exhaust gas purifying devices made of cordierite were manufactured as Comparative Examples 1 and 2 with respect to the examples. Comparative Example 1
Then, as shown in FIG. 7B, the heater H1 is wound around the outer peripheral portion of the filter F. In Comparative Example 2, as shown in FIG. 7C, the heater H2 was disposed on the downstream end face of the filter F.

Then, the diesel engine E is operated,
First, the exhaust gas purifying apparatus 10 collected fine particles in the exhaust gas. At that time, the control device C was made to monitor the pressure change in the exhaust pipe Ea during the collection operation. Then, the collecting operation was continued until the pressure value reached a constant value.
The amount of fine particles collected during this period was calculated to be 15
It was g / liter. The calculated value is calculated based on the change in weight before and after the collection process, with the volume of the exhaust gas purification device 10 as the total amount of the gas passage portion.

After the completion of the collection operation was detected, the controller C closed the switch Sw to start energizing the heater 5. After a lapse of a predetermined time from the start of energization (after the end of the temperature rising process), the compressor Co is operated and 20 cm of secondary air for combustion promotion is supplied from the air supply pipe Ca.
Supplied at a rate of ³ / min.

Then, as shown in FIG. 7A, the temperature T at each of the positions P1 to P6 of the exhaust gas purifying apparatus 10 is shown.
1 to T6 were measured with a thermocouple over time. Similarly, in Comparative Examples 1 and 2, the temperatures T1 to T6 at the respective positions P1 to P6 were measured.

In this test, the temperature T
The process until the average value of 1 to T6 reaches 600 ° C is referred to as the "temperature raising process". Further, the process from the start of the temperature rising process and the supply of the secondary air to the end of the combustion of the fine particles is referred to as a "regeneration process". Then, the time (minutes) required for the temperature raising process and the regeneration process is obtained, and the sum of these is calculated as the energizing time (minutes).
And Further, the maximum temperature difference ΔT (° C.) at each of the positions P1 to P6 was determined for each of the temperature raising process and the regeneration process. The results are shown in Table 1.

Also, in this test, the exhaust gas purification device 10
The time (hours) until the cracks of the filters 3 and 4 constituting the above were reached was also investigated. Similarly, the said test was done also about Comparative Examples 1 and 2. The results are shown in Table 2.

[0040]

[Table 1]

[0041]

[Table 2]

As is clear from Table 1, the time required for the temperature raising process and the time required for the regeneration process in Comparative Example 1
It was shorter than 2. Moreover, the maximum temperature difference .DELTA.T (.degree. C.) at each of the positions P1 to P6 was smaller than that of Comparative Examples 1 and 2.

That is, according to the present embodiment, it means that the exhaust gas purifying apparatus 10 can be heated in a short time without temperature unevenness and can be regenerated in a short time. In addition, shortening the time required for the temperature raising process and the regeneration process means that the total energization time is shortened. Therefore, according to the embodiment, efficient regeneration can be performed with a small amount of electric energy. Moreover, in the case of the embodiment, the maximum temperature difference ΔT (° C.) at each of the positions P1 to P6 is also relatively small, so that there is an advantage that the temperature control during reproduction can be facilitated.

Further, as is clear from Table 2, in the embodiment, the filter 3, even after being used for more than 20000 hours.
4 did not reach the crack. On the other hand, in Comparative Example 1, 3000 hours and in Comparative Example 2, 2000 hours.
It was impossible to withstand the use of time. That is, it is understood that the exhaust gas purifying apparatus 10 of the present embodiment has extremely excellent durability as compared with Comparative Examples 1 and 2.

Further, according to the structure of the exhaust gas purifying apparatus 10 of this embodiment, it was confirmed that the regeneration can be surely performed even if the supply amount of the secondary air is small.
Therefore, there is an advantage that the compressor Co can be made small in size.

The present invention is not limited to the above embodiment, but can be modified as follows. For example, (a) the number of combinations of the constituents S is 1 as in the above embodiment.
The number is not limited to two and can be any number. In this case, it is of course possible to appropriately combine and use the structural bodies S having different sizes and shapes. In addition, it is particularly advantageous to manufacture a large-sized exhaust gas purification device by adopting a structure characterized by combining a plurality of constituent bodies S.

(B) Exhaust gas purifying apparatus 10 of the above embodiment
It can be considered that one large filter is divided into a plurality of pieces along the axial direction. Therefore, for example, a modification in which the filter is divided into a donut shape or a state where the filter is divided perpendicularly to the axial direction may be considered.

(C) Not limited to the honeycomb filters 3 and 4 as shown in the above embodiment, it is of course possible to adopt, for example, a three-dimensional mesh structure, a foam shape, a noodle shape, a fiber shape or the like. is there. Further, as the ceramic material for the filters 3 and 4, materials other than silicon carbide may be selected.

(D) The heater 5 is not limited to the metal wire as in the above embodiment. That is, the heater 5
Can also be produced by methods such as metallization, printing of a conductor paste, and sputtering.

(E) Sealing material 8 as heat resistant filling material
Does not necessarily have to be a paper-like one as in the embodiment. For example, a method of directly applying the slurry before being formed into a paper shape to the outer peripheral surfaces of the filters 3 and 4 to form a layer made of a heat resistant filling substance may be used.

(F) In the case of the manufacturing method of (e), the slurry for forming the filters 3 and 4 and the slurry for forming the heat-resistant filling material layer are used, and one of the extruders simultaneously performs the above-mentioned processes. The slurry may be extruded. That is, the slurry for forming the filters 3 and 4 is extruded from the central portion of the jig of the extrusion molding machine, and at the same time, the slurry for forming the heat resistant filling material layer is extruded from the outer peripheral portion of the jig. According to this method, the structural body S can be efficiently manufactured in a short time.

(G) When constructing the exhaust gas purifying apparatus 10, it is not always necessary to use the structural body S in which the heaters 5 are provided on the filters 3 and 4 as in the above embodiment. For example, after a plurality of filters 3 and 4 are combined, the heater 5 is inserted into the space between the adjacent filters 3 and 4 and the same space is filled with the slurry for forming the heat resistant filling material layer. The gas purification device 10 can also be manufactured.

(H) Instead of the embodiment in which the heaters 5 are connected in series, they may be connected in parallel.

[0054]

As described in detail above, according to the exhaust gas purifying apparatus and its constituents of the present invention, it is possible to raise the temperature without temperature unevenness in a short time, so that the regeneration efficiency and durability are improved. There is an excellent effect that the temperature can be controlled easily at the time of reproduction.

[Brief description of drawings]

FIG. 1 is a perspective view showing a structure of an exhaust gas purification device.

2 is a partially cutaway enlarged cross-sectional view taken along the line AA of FIG.

FIG. 3 is an enlarged cross-sectional view taken along the line BB of FIG.

FIG. 4 is a partially cutaway perspective view showing an exhaust gas purifying apparatus including a plurality of components.

FIG. 5 is a partially enlarged cross-sectional view showing an exhaust gas purification device.

FIG. 6 is a schematic cross-sectional view showing a state in which an exhaust gas purifying device is incorporated.

7 (a) to 7 (c) are schematic views for explaining a method of performing a comparative test of Examples and Comparative Examples 1 and 2. FIG.

[Explanation of symbols]

3, 4 ... Filter, 5 ... Heater as heating element, 8 ... Sealing material as heat resistant filling material, 9 ... Heat insulating material, 10 ... Exhaust gas purifying device, S ... Constituent body.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B01J 35/04 301 8017-4G

Claims (9)

[Claims] 1. A plurality of filters (3, 4) made of a ceramics sintered body having a porous structure are arranged adjacent to each other, and a heating element (5) is provided between the adjacent filters (3, 4).
An exhaust gas purifying device characterized in that an intervening exhaust gas. 2. The exhaust gas purifying apparatus according to claim 1, wherein a heat resistant filling material (8) is interposed between the adjacent filters (3, 4). 3. The heating element (5) is the filter (3,
4. Exhaust gas purification device according to claim 2, characterized in that it is arranged between 4) and the refractory filling material (8). 4. The exhaust gas purifying apparatus according to claim 2, wherein the composition of the heat resistant filling material (8) is ceramic fiber, silicon carbide powder and an inorganic binder. 5. The exhaust gas purifying apparatus according to claim 2, wherein the heat-resistant filling material (8) is extruded into a paper shape. 6. The exhaust gas purifying apparatus according to claim 2, wherein a heat-expandable heat insulating material (9) made of ceramic fiber is arranged at the outermost peripheral portion. 7. Exhaust gas composed of a filter (3, 4) made of a ceramics sintered body having a porous structure and a heating element (5) provided on the outer peripheral part of the filter (3, 4). Purification device structure. 8. The exhaust gas purifying apparatus according to claim 7, wherein the filters (3, 4) are formed in a honeycomb shape by using a porous silicon carbide sintered body. 9. The filter (3, 4) has an average pore diameter of 1
The exhaust gas purifying apparatus according to claim 8, wherein the exhaust gas purifying apparatus has a porosity of 30 to 70%.