JPH0823289B2 - Diesel exhaust gas purification equipment - Google Patents

Description

TECHNICAL FIELD The present invention relates to a diesel exhaust gas purifying apparatus for removing particulates (soot) contained in the exhaust gas of a diesel engine.

2. Description of the Related Art In recent years, the influence of particulates contained in the exhaust gas of diesel engines on the environment has been feared and regulation has begun. In response to this, in order to purify the exhaust gas of a diesel engine, it has been attempted to attach a filter made of a heat-resistant ceramic honeycomb structure in the middle of an exhaust pipe to filter particulates. The particulates that have been filtered and deposited inside the filter are generally burned by heating with a light oil burner to regenerate and repeatedly use the ceramic filter. The incineration work of this particulate is called regeneration. In this regeneration, Japanese Patent Application Laid-Open No. 61-16221 adjusts the combustion amount of the burner to moderate the heating temperature rise of the ceramic filter. As a result, the peak temperature generated by the combustion of particulates is kept low. However, until now, no one tried to control the internal temperature of the ceramic filter at the time of cooling after the regeneration was completed.

[Problems to be Solved by the Invention] Immediately after regeneration is completed, the temperature inside the ceramic filter is as high as 600 ° C to 700 ° C. At this time, when a large amount of exhaust gas from the engine flows into the ceramic filter at a relatively low temperature of around 200 ° C, the front part of the filter cools and contracts. However, from the middle part to the rear part of the ceramic filter, the temperature remains high for a while. Therefore, the cylindrical ceramic filter is deformed into a spinning shape, and a large tensile stress is generated in the axial direction on the outer peripheral portion of the filter. And the ceramic could not endure and could be damaged. Japanese Patent Laid-Open No. 61-16221 attempts to control the peak temperature generated inside the ceramic filter. However, the thermal stress generated during cooling cannot be avoided.

Therefore, the present invention controls the internal temperature of the ceramic filter at the time of cooling after the regeneration is finished to prevent the ceramic filter from being damaged by thermal stress.

Means for Solving the Problems And the technical means of the present invention for solving the above problems is to gradually reduce the temperature of the gas flowing through the ceramic filter by adjusting the output of the heating means at the time of cooling after the regeneration is completed. Or reduce the amount of gas flowing,
The temperature inside the filter is controlled.

Action The action of the technical means of the present invention is as follows.

That is, generally, by controlling either or both of the temperature and the amount of gas flowing inside the ceramic filter, the temperature distribution inside the filter can be set to an arbitrary state. When the temperature of gas flowing into the filter is gradually lowered or the amount of gas is reduced at the end of regeneration, the temperature difference between before and after and inside and outside the ceramic filter becomes small. Therefore, the thermal stress generated inside the ceramic filter is small, and the filter is protected from destruction.

Embodiment An embodiment of the diesel exhaust gas purifying apparatus of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a vertical cross section of a diesel exhaust gas purifying apparatus, in which 1 is a cylindrical ceramic filter. The ceramic filter 1 is constructed by using a ceramic honeycomb having rectangular cells 2a and 2b, which form a large number of flow passages, as a matrix, and alternately closing one end of each of the cells 2a and 2b with a plug 3. The ceramic filter 1 is housed in a container 5 made of heat-resistant stainless steel after the cushioning material 4 is wound around the outer periphery thereof. The front and rear of the container 5 are tapered in a cone shape and squeezed, one of which is a processing gas connection port 6 and the other of which is a muffler connection port 7. A light oil burner 8 is provided in front of the processing gas connection port 6 toward the front surface of the ceramic filter 1, and the muffler connection port 7 is connected to a muffler (not shown). Light oil burner 8
Has a structure in which the atomizing nozzle 9 is placed at the center, and the air flows from the periphery of the atomizing nozzle 9 through the combustion air port 10 toward the tip of the atomizing nozzle 9. Further, in front of the atomizing nozzle 9, a spark plug 11 for igniting the atomized fuel with a high-pressure discharge arc.
Is installed. An engine exhaust gas introducing pipe 12 is connected between the ceramic filter 1 and the light oil burner 8. The exhaust gas introduction pipe 12 is one of branches of the engine exhaust pipe 13 and an exhaust gas bypass pipe 14. Exhaust gas bypass pipe 14
And the muffler connection port 7 merge on the way. A three-way valve 15 is provided at a branch point between the exhaust gas introduction pipe 12 and the exhaust gas bypass pipe 14 to switch the exhaust gas from the engine to the exhaust gas introduction pipe 12 or the exhaust gas bypass pipe 14 by rotating the exhaust gas introduction pipe 12 and the exhaust gas bypass pipe 14 in the direction of the arrow.

Next, the operation of the configuration of this embodiment will be described. First, during normal operation of the diesel engine, the three-way valve 15 is at the position shown in the figure, and the exhaust gas from the engine reaches the front surface of the ceramic filter 1 through the exhaust gas introduction pipe 12. From here, the exhaust gas enters the cell 2a that is open to the light oil burner 8 side of the ceramic filter 1, where it passes through the cell wall and enters the cell 2b that is open to the muffler connection port 7 side. At this time, the particulates contained in the exhaust gas cannot pass through the cell wall and remain in the cell 2a that is open to the light oil burner 8 side. Is emitted to the atmosphere through a muffler. The particulates that remain in the ceramic filter 1 and accumulate, clogging the filter,
It becomes the resistance of the exhaust gas flow and raises the engine back pressure. This increases the differential pressure across the ceramic filter 1 according to the amount of particulate accumulation. If the filter differential pressure corresponding to the maximum allowable amount of particulates of the ceramic filter 1 is reached, the next regeneration operation is started.

In the regeneration, first, the three-way valve 15 is rotated clockwise by about 40 degrees as viewed from above in FIG. 1, the exhaust gas flowing in the exhaust gas introduction pipe 12 is blocked, and the flow is switched to the exhaust gas bypass pipe 14. Then, the exhaust gas flowing into the exhaust gas bypass pipe 14 is released to the atmosphere through the muffler muffler.
Simultaneously with the switching of the three-way valve 15, the light oil burner 8 is operated. The high temperature combustion gas generated by the light oil burner 8 rises according to the temperature rise curve (a) as shown in FIG. 2 by controlling the output of the light oil burner, flows into the ceramic filter 1 and is heated. If the temperature of the combustion gas is maintained at about 750 ° C. as shown in (b), the internal temperature of the ceramic filter 1 becomes 600 ° C. or higher, and the deposited particulates start burning. After a few minutes, the particulates are burned out and the ceramic filter 1 returns to its original clean condition. When it is confirmed by the differential pressure before and after the filter that the ceramic filter 1 has returned to the original clean state and the regeneration has been completed, the combustion amount of the light oil burner 8 is gradually reduced and the temperature of the combustion gas flowing into the filter is changed to the first value. As shown in Fig. 2 (c), the descending speed is 60 ℃ /
Gradually lower in minutes. After about 5 minutes, the combustion gas temperature
When the temperature reaches 500 ° C or lower, the light oil burner is stopped, the three-way valve 15 is switched to the original position, and the normal operation state is restored. The curve of the broken line in FIG. 2 (d) shows the temperature of the gas flowing into the ceramic filter 1 when the above operation is not performed. Further, in this embodiment, the combustion amount of the light oil burner 8 is reduced so that the exhaust gas temperature decreases linearly, but this may be reduced stepwise. Further, instead of the light oil burner 8, the same operation can be performed by using an electric heater as the heating means. The rate of combustion gas descent is 200 ° C /
A minute is enough.

Next, the operation of another invention showing the same effect will be described. After the regeneration is completed by the above operation, the light oil burner 8 is stopped and the combustion air of the burner is continuously sent to the ceramic filter 1 as it is. At this time, light oil burner 8
The amount of air is selected to be about 1/10 of the engine exhaust gas amount. Then, the temperature inside the ceramic filter 1 gradually decreases. After about 5 minutes, the air supply to the light oil burner 8 is stopped when the combustion gas temperature reaches 500 ° C. or lower, the three-way valve 15 is switched to the original position, and the normal operation state is restored. Further, in another embodiment of the present invention, the three-way valve 15 is slightly opened immediately after the regeneration is completed, and only one tenth of the exhaust gas amount during normal operation is guided to the ceramic filter 1. After about 5 minutes, the combustion gas temperature becomes 50
When the temperature reaches 0 ° C. or lower, the three-way valve 15 is switched to the original position to return to the normal operating state.

Effect of the Invention The present invention, after the regeneration is completed, gradually reduce the output of the heating means such as a burner, or after sending a part of air or engine exhaust gas to the ceramic filter for a while,
By flowing an ordinary amount of exhaust gas, a large temperature difference is not generated before and after the filter and in the radial direction during cooling. As a result, no large axial thermal stress was generated in the outer peripheral portion of the ceramic filter, and thermal cracking did not occur. Therefore, the diesel exhaust gas purifying apparatus to which the present invention is applied can ensure the durability almost corresponding to the service life of the engine.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a diesel exhaust gas purifying apparatus according to an embodiment of the present invention, and FIG. 2 is a temperature curve diagram of gas flowing into a ceramic filter. 1 ... Ceramic filter, 4 ... Buffer material, 5 ... Container, 8 ... Light oil burner, 9 ... Atomizing nozzle, 14 ... Exhaust gas bypass pipe, 15 ... Three-way valve.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hisanori Shimoda 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. 72) Inventor Hiroki Kusakabe 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References

Claims (1)

[Claims] 1. An exhaust gas purifying apparatus comprising a heat resistant filter, a container accommodating the filter, and a heating means located on the exhaust gas inflow side of the filter, wherein the particulates are incinerated while the exhaust gas flow is blocked from the filter. Diesel exhaust gas purifying apparatus, characterized in that the temperature is reduced while controlling the temperature drop rate of the filter, and when the temperature of the filter is below a predetermined temperature, the entire amount of exhaust gas is introduced into the filter.