JP2003206721A - SiC FILTER AND EXHAUST EMISSION CONTROL DEVICE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device that can effectively remove ash generated at regeneration. <P>SOLUTION: The exhaust emission control device comprises a casing and a porous ceramic filter of honeycomb structure disposed inside. The filter used in the device comprises silicon carbide on which ash containing phosphate and sulfate can deposit, to form the SiC filter. The exhaust emission control device comprises this filter. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a SiC filter and an exhaust gas purifying device, and more particularly to collecting particulates contained in exhaust gas discharged from an internal combustion engine,
Ash (ash) generated when regenerating by combustion
We propose the ones that are excellent in removing effect.

[0002]

2. Description of the Related Art As a device for collecting and removing particulates contained in exhaust gas discharged from an internal combustion engine, for example, a diesel engine, conventionally, a casing and a honeycomb structure arranged inside thereof have been used. An exhaust gas purifying device of a type that is installed in an exhaust system of an internal combustion engine and that includes a cordierite porous ceramic filter has been widely used.

In such a conventional exhaust gas purifying apparatus, as the collection of particulates in the filter attached to the apparatus progresses, the filter layer of the filter is clogged to increase the pressure loss, Deteriorates engine efficiency. For that purpose, a so-called regeneration process is performed in which the collected particulates are burned at appropriate time intervals and removed from the filter. This regeneration process
For example, the filter is attached to the end face on the so-called long axis side along the gas flow direction of the filter, and first, the end face of the filter is heated to a predetermined temperature (600 to 800 ° C) by this heating element to capture the end face of the filter. The collected particulates are ignited and removed by burning, and at the same time, the burning is sequentially propagated in the longitudinal direction which is the gas flow direction.

By the way, when the conventional apparatus is regenerated, due to its structure, the particulate matter in the exhaust gas is not completely removed even if regenerated and burned, and remains as ash (ash) in the filter. There was a problem. Moreover, if this residual ash is left as it is, it will be clogged in the honeycomb-shaped holes, gradually leading to a decrease in the particulate collection efficiency by the filter and an increase in pressure loss, and eventually to the problem of degrading engine efficiency. Caused it.

On the other hand, conventionally, for example, a cordierite filter having a honeycomb structure is supported in a direction in which the exhaust gas flows vertically.
It has been proposed that the ash remaining in the filter when the particulates are collected and regenerated is caused to fall naturally by the vibration of the vehicle or the engine (Patent Document 1: Japanese Utility Model Publication No. 63-1).
1292).

[0006]

[Patent Document 1] (Japanese Utility Model Publication No. 63-11292)

[0007]

However, the conventional technique described in Patent Document 1 has various problems as described below. That is ,. In the cordierite filter, the collection surface of the filter forms an uneven surface due to the pore size distribution of the ceramic. Therefore, the ash deposited on the filter is physically adsorbed by the anchoring action of the uneven surface and cannot be easily removed by vibration of the vehicle or the like.

[0008] When particulates are burned, Ca, Ba, P, Zn, Mg in lubricating oil and fuel additive and S, Fe in fuel are accumulated in the filter as salts such as calcium phosphate and calcium sulfate. Becomes As a result, the ash deposited on the filter is welded to the filter surface that has been melted due to the action of the phosphate, which is its component, that is, the action of lowering the heat resistance of the cordierite ceramic material, and is easily affected by vibration of a vehicle or the like. It cannot be removed. Further, the ash deposited on the filter adheres to the surface of the filter due to the corrosion (chemical reaction) reaction of the cordierite ceramic material due to its component, sulfate, and cannot be easily removed by vibration of the vehicle or the like. ． The filter is installed at a position distant from the engine in order to install a regeneration device such as an afterburner.
Therefore, it is difficult to apply the vibration required to remove the ash due to the running of the vehicle or the change in the frequency of the engine. ． The filter is constantly subject to engine vibration. Therefore, the filter cannot have long-term durability. Further, in some cases, the restraint force of the heat insulating layer provided on the outer periphery of the filter decreases, and the filter cannot be supported in the casing.

Therefore, the main object of the present invention is to remove the ash generated during reproduction effectively.
It is to propose a C filter and an exhaust gas purification device using this filter. Another object of the present invention is to provide a SiC filter and an exhaust gas purifying device which have excellent durability and can effectively remove ash generated during regeneration for a long period of time.

[0010]

[Means for Solving the Problems] In order to achieve the above object, the inventors first examined the filter material. That is, an experiment was conducted in which ash components such as calcium sulfate and magnesium sulfate were placed on a cordierite plate and a silicon carbide plate and heated at a regeneration temperature. From the results of this experiment, it was found that the cordierite plate reacts with the ash component and melts, but the silicon carbide plate does not react with the ash component and does not melt (see Table 1). On the other hand, it was also found that the cordierite filter has a wide pore size distribution and a large surface anchoring effect, and thus it is difficult to remove the ash that has once strongly adhered. In this respect, it is considered that the filter made of silicon carbide has a narrow pore size distribution, and therefore has a small anchor effect on the surface and is easy to remove the deposit (see FIG. 1).

[0011]

[Table 1]

[0012] Therefore, the inventors have considered the use of SiC as a filter material, and as a result of further earnest research, have conceived an invention having the following contents as the gist configuration.
That is, according to the present invention, the filter used in an exhaust gas purifying apparatus including a casing and a porous ceramic filter having a honeycomb structure disposed inside the casing is used to deposit ash containing a phosphate or a sulfate. It is a SiC filter characterized by being composed of silicon carbide capable of forming.

Further, the present invention proposes an exhaust gas purifying apparatus characterized in that the above-mentioned SiC filter is arranged in a casing.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION
As shown in FIG. 2, it is composed of a tubular metal casing connected to the exhaust pipe of the exhaust system of the internal combustion engine, and a porous ceramic filter arranged in this casing. The filter according to the present invention arranged in this casing is for collecting and removing particulates in the exhaust gas, and particularly, in the present invention, silicon carbide is used as the porous ceramic filter. Characterize.

In the present invention, the reason why silicon carbide is used instead of cordierite as the porous ceramic filter is as follows. ． The ash deposited on the filter is not strongly physically adsorbed by the anchoring action due to the unevenness of the filter surface. The reason for this is that in silicon carbide, since crystals grow uniformly, it is easy to form a sharp pore size distribution, and it is easy to control the pore size. Therefore, the irregularities on the inner wall surface of the filter can be regularly formed, and the ash rarely physically enters the pores. ． As the ash deposited on the filter, salts such as phosphate and sulfate, which are its components, do not contribute to the reaction, so that the ash is deposited in the form of granules or a film on the inner wall surface of the filter with weak adhesion. The reason is that silicon carbide is an extremely chemically stable material and does not react with salts.

In the present invention, this SiC (silicon carbide) filter is arranged so that the flow direction of the gas passing through the inside of the filter is oriented vertically in the vertical portion of the bent casing, as shown in FIG. Install in a proper posture. In the present invention, a vibration oscillating mechanism for vibrating and removing the ash attached to the filter may be attached to the SiC filter having such a structure, if necessary. In this case, it is preferable to provide an ash recovery unit below the vertically placed filter for recovering ash falling off from the filter.

By providing such a function, the following effects can be expected. ． It is possible to apply the vibration necessary for removing the ash to the filter immediately after the reproduction without depending on the running of the vehicle or the change of the vibration frequency of the engine. Further, by controlling the frequency of the vibration oscillation mechanism, the time required to remove the ash can be shortened. Furthermore, the ash that falls as relatively large pieces can be reliably recovered by the ash recovery section such as a hopper provided at the bottom. ． The exhaust gas purification device can be installed in the rear part of the exhaust system that is less susceptible to vibration from the engine. Therefore, the filter has long-term durability.

As is clear from the above description,
According to the filter and the exhaust gas purifying apparatus of the present invention, it is easier to collect and remove the particulates as compared with the conventional type using the cordierite filter. In particular, when the ash removal function is provided, in combination with the adoption of the SiC filter, the ash (ash) generated when the collected particulates are regenerated by burning is effectively and effectively retained for a long period of time. Can be removed.

In the present invention, the vibration oscillating mechanism for vibrating and removing the ash adhering to the filter uses, for example, an electromagnetic vibrator, and is located on the outer surface of the filter casing at a substantially central portion of the filter. It is desirable to be fixed as follows. Moreover, in order to remove ash effectively, frequency 4000-8000Hz, time 5
It is more desirable to attach a vibration oscillation mechanism that can be set to a condition of ~ 30 seconds to the filter.

In the present invention, the SiC filter may be either an integral type or a complex type, but one or a combination of filter units having a triangular, square, rectangular or regular hexagonal sectional shape may be used. It is desirable to use them by collecting them in a columnar shape. Because
By setting the cross-sectional shape of the filter unit in this way, there are no restrictions on manufacturing, and by appropriately combining these, it is possible to select a filter that suits the capacity of the internal combustion engine, and to make it any casing shape. This is because it is possible to reduce restrictions on mounting the exhaust gas purification device. Further, it is desirable that the filter unit is formed of a porous ceramic sintered body into a honeycomb shape. This is because the porous ceramic sintered body has excellent heat resistance and thermal conductivity, and the honeycomb filter has a small pressure loss even when the amount of collected fine particles is increased.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the exhaust gas purifying apparatus of the present invention is applied to an exhaust gas purifying system for diesel vehicles will be described below with reference to the drawings. FIG. 2 is a schematic diagram of a diesel engine 1 equipped with an exhaust gas purification device. In this figure, the exhaust gas after combustion in the engine cylinder passes from the exhaust manifold 2 through the exhaust pipe 3 as shown by the arrow a, and the tubular metal casing 4 connected in the middle of the exhaust pipe 3 It is discharged through the silicon carbide filter 5 arranged in the casing 4. The casing 4 is connected to the exhaust pipe 3 via a vibration absorbing flexible pipe. The silicon carbide filter 5 is provided with the inlet portion 51 on the lower side and the outlet portion 52 on the upper side, and the electromagnetic vibrator 6a constituting the vibration oscillation mechanism 6 is arranged.
6b is an outer surface of the casing 4, and is attached so as to be located substantially in the center of the filter. Further, the casing 4 and the exhaust pipe 3 are connected so that the exhaust gas is bent at a substantially right angle and flows, and further, an ash receiving hopper 7 is arranged below the silicon carbide filter inlet portion 51. Further, a drain plug 8 is attached to the lower side of the ash receiving hopper 7.
The hopper 7 of this embodiment constitutes the ash recovery unit of the present invention. A fuel injection nozzle 9 is attached upstream of the exhaust gas to the silicon carbide filter inlet 51, and an ignition plug 10 is attached downstream thereof.

Now, the exhaust gas discharged from the exhaust manifold 2 as described above is changed to a substantially right angle by flowing through the exhaust pipe 3 and the casing 4, and the silicon carbide filter 5
By passing through, the particulates are collected and purified. Then, when the pressure sensor 11 attached to the exhaust pipe 3 on the upstream side of the silicon carbide filter 5 detects a pressure loss of a set value or more, the fuel injection nozzle 9 and the spark plug 10 are activated in the filter 5, and the filter 5 is activated. A so-called regeneration process is performed to burn and remove the particulates collected in. However, the collected particulates are not completely removed even when regenerated, and remain as ash (ash) in the filter 5, and if the residual ash is left as it is, it is clogged in the honeycomb-shaped holes and pressure The loss will increase. Therefore, in the present invention, a temperature detector (thermocouple) attached to the exhaust gas outflow side of the filter
When the temperature of 12 or more is detected, the regeneration is completed and the electromagnetic vibrators 6a and 6b are activated to vibrate the filter 5 to remove the ash. The ash thus removed from the filter 5 is stored in the ash receiving hopper 7 located below the silicon carbide filter inlet portion 51. Further, the ash accumulated in the ash receiving hopper 7 is periodically taken out by the drain plug 8 and discarded.

As described above, the pressure sensor 11 and the temperature detector
The vibration oscillation mechanism 6 is configured by a control system that operates the electromagnetic vibrators 6a and 6b by the detection output of 12 and the like.

[0024]

As described above, according to the present invention, it is possible to provide an exhaust gas purifying apparatus which is capable of effectively removing ash generated during regeneration for a long period of time and which is excellent in durability.

[Brief description of drawings]

FIG. 1 is a graph showing a pore size distribution according to a filter material.

FIG. 2 is a schematic view of a diesel engine equipped with the exhaust gas purification device of the present invention.

[Explanation of symbols]

1 diesel engine 2 exhaust manifold 3 exhaust pipe 4 casing 5 Silicon carbide filter 51 Filter inlet 52 Filter outlet 6 Vibration oscillation mechanism 6a, 6b Electromagnetic vibrator 7 Ash receiving hopper 8 drain plug 9 Fuel injection nozzle 10 Spark plug 11 Pressure sensor 12 Temperature detection

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Claims (2)

[Claims] 1. A filter for use in an exhaust gas purifying apparatus comprising a casing and a porous ceramic filter having a honeycomb structure arranged therein, wherein ash containing phosphate or sulfate is deposited. A SiC filter characterized in that it is made of silicon carbide. 2. An exhaust gas purifying apparatus comprising the SiC filter according to claim 1 arranged in a casing.