JPS62126218A - Exhaust gas filter - Google Patents

Abstract

PURPOSE:To burn out the soot inside the filter throughly even though it is a small accumulation, and prevent the dissolution of the filter, by furnishing a porous film housing a heater and holding a catalyst, in front of the exhaust gas filter. CONSTITUTION:At the exhaust gas flow side of an exhaust gas filter 1, which is composed of a honey comb composition of a porous ceramic with the ends of cells 2 closed alternatively, is furnished a porous film 12 consisting of a glass or ceramic filter including a catalyst therein. The film 12 also has an ignition heater 13 built-in. Therefore, after the soot is trapped partially at the porous film 12 forming some accumulation, it is burned by lighting the ignition heater 13, and it is continued to burn even in a low oxygen density ambiance or at a low temperature because of the existence of the catalyst. In such a reason, since the soot within the ceramic filter is burnt even though the accumulation is small, and never accumulated there too much, the filter will not be dissolved.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention collects carbonaceous particulates (so-called soot) emitted from diesel engines, for example, and burns the collected soot. This invention relates to an exhaust gas filter that aims to reduce soot emissions.

Conventional technology Diesel exhaust gas filters for collecting soot emitted from diesel engines include filters using metal wire mesh coated with alumina, ceramic foam filters with porous tanks made of foaming agents, ceramic fiber mats, Also, honeycomb-shaped ceramic monolith filters and the like have been devised. Among them, a honeycomb-shaped ceramic monolith filter, which has a soot collection efficiency of 90% or more and has a small pressure loss in exhaust gas through the filter, is considered to be a promising filter for removing soot from exhaust gas.

A diesel exhaust gas filter made of a ceramic monolith filter has a honeycomb structure made of a large number of cells made of cell walls formed by an extrusion method using cordierite as a main component. The upstream and downstream cell ends of the structure are made of cement-like, very low porosity, 10ff long
They are alternately occluded with ll11 materials. Due to these upstream and downstream blockages, the cell causes a large pressure loss of exhaust gas in the diesel exhaust gas filter in both the inlet and outlet exhaust gas passages, resulting in a reduction in engine performance.

Therefore, in order to maintain good engine performance, a method is used to regenerate the diesel exhaust gas filter 1 by burning the soot once a certain amount of soot has accumulated. A diesel exhaust gas filter having a honeycomb structure that allows for smooth soot combustion and facilitates repeated filter regeneration is desired.

Problems to be Solved by the Invention - Soot deposited on the cell exhaust gas filter is ignited by sparks in the exhaust gas or the ignition heater at the inlet end, combustion spreads at the inlet end9, and at the same time, the inside of the cell is ignited. Burns downstream.

At this time, some of the soot in the exhaust gas accumulates at the inlet end,
Most of it is deposited within the cells. However, the inlet end of the diesel exhaust gas filter has no effect as a filter, and there is little soot in the blocked area.

For this reason, sufficient combustion heat is not generated in the closed portion, and combustion does not spread downstream of the cell.

In addition, when a certain amount of soot has accumulated and an ignition heater is used to ignite the soot to burn it, the oxygen concentration will be low while the engine is running (usually 1
2 to 16%) and the grain boundary ambient temperature is also low (usually 13%).
o'C to 280°C), so unless the capacity of the ignition heater was increased or a large number of ignition heaters were installed, the ignition would not occur and the combustion would not spread over the entire surface. Therefore, if this phenomenon is reversed, the amount of soot deposited within the cell will increase.

Then, once the soot in the cell is ignited after the cell internal pressure soot has accumulated to a certain level, combustion occurs rapidly, the temperature of the diesel exhaust gas filter rises, and the diesel exhaust gas filter melts.

A solution to the problem: By incorporating a heater in the front of the exhaust gas filter and creating a porous membrane made of glass fiber or ceramic fiber that carries a catalyst, even a small amount of soot buildup can be completely eliminated. The soot in the filter can be burned off.

Function: By providing a porous structure with a built-in heater and a catalyst supported on the front surface of the exhaust gas filter, some of the soot is trapped within the porosity. After a certain amount of soot has accumulated, if the ignition heater is used to ignite the soot, combustion will begin from the soot accumulated on the heater's rotor.

At this time, if a catalyst is present, combustion continues even in a low oxygen concentration atmosphere or at a low temperature, and the flame spreads over the entire surface of the porous body supporting the catalyst. They then become an ignition source and spread to the soot inside the ceramic filter. Therefore, even if the amount of soot deposited inside the ceramic filter is small, it will burn, and there will be no excessive accumulation of soot inside the ceramic filter, as was the case in the past. This does not occur and playback can be repeated smoothly.

Embodiment An embodiment of the present invention is shown in FIG. 1 and will be described. 1 Honey easel exhaust gas filter, 2 is a cell, 3 is a cell wall, 4 is an upstream cell end, 5 is a downstream cell end, 6 is an exhaust gas passage, 7 is an outlet exhaust gas passage, 8 is an inlet closing part, 9 is an outlet closing part , 10
11 is exhaust gas, 12 is a porous thin film carrying a catalyst, 13 is an ignition heater, and 14 is soot accumulated on the surface of the porous body carrying a catalyst. Exhaust gas filter 1
For example, it is manufactured by the following method. 30 parts by weight of alumina fibers cut to 20 mm or less and 16 parts by weight of ceramic raw material powder are suspended in 3000 parts by weight of water, and after adding an organic binder such as polyvinyl acetate to this mixed slurry, it is mixed with a coagulant such as polyacrylamide. It was agglomerated and made into a sheet using a fourdrinier paper machine. A corrugated sheet is created by gluing the corrugated sort and flat sheet together in the same manner as corrugated pole manufacturing, and then this is glued and wrapped around the core to form a no-nikum shape. 1 in 9 people
The same amount of the material described below is applied to each cell at the inlet and outlet cells of the honeycomb alternately so that the exhaust gas that has entered one honeycomb cell passes through the cell wall, transfers to another cell, and is then discharged. The group was closed by injection. This molded product was fired at 1250'C in air to transform the ceramic fibers and ceramic raw material powder into ceramics, thereby obtaining the desired exhaust gas filter with a honeycomb structure. Here, the clogging material is made into a paste by adding 2 parts by weight of a calcined and pulverized inorganic material, 0.1 part by weight of starch, and 2 parts by weight of water. Then, 0.1 part by weight of an organic powder was added in powder form and mixed by stirring. By injecting such a material, the porosity of the material in the blocked portion became 50%.

The organic powder used here may be a synthetic polymer such as polyester, a natural polymer such as starch, or a combustible inorganic powder such as carbon particles. By increasing the mixing proportion of organic powder to 100 parts by weight, the porosity of the material can be increased to t-95%.

Next, the porous body supporting the catalyst is, for example, a silica glass fiber or a mullite ceramic porous body used in the above-mentioned filter, which is wash-coated with alumina or the like to increase the surface area. In this case, a silica glass fiber was used. Oxidation catalysts include platinum, metals such as sodium, V2O6, MoO2, FJ.
203. Although there are O metal oxides such as N iO, and organic acid salts such as manganese, cobalt, and copper, a platinum catalyst was used in this example.

In this supporting method, the above-mentioned silica fiber was impregnated in a methanol solution containing 1 weight of chloroplatinic acid, and then heat-treated at SOO°C. The point heater used a nichrome wire, and the surface of the nichrome wire was thermally sprayed with ceramic mainly composed of alumina.

The silica fibers carrying this catalyst were placed on the front surface of the exhaust gas filter in such a way that they were in close contact with each other. These devices were installed at the exhaust port of a diesel engine to collect the emitted soot into a filter. Similarly, a comparative experiment was conducted using a type of trap in which silica fibers carrying a catalyst were not attached to the front surface, and the results are shown in FIG. At this point, the ignition heater was installed so that it was in contact with the trap surface. An example of the implemented configuration is shown in FIG. Note that the numbers shown in the figure are the same as in FIG. The example was carried out on a test bench using a diesel engine with a displacement of 4.31 mm, and the differential pressure before and after the trap, temperature,
Additionally, a video camera was installed in front of the engine to monitor combustion conditions. As shown in Figure 3, the differential pressure before and after the trap is approximately 10K.
I turned on the ignition heater when the temperature reached PA, that is, 3.5 hours after I started driving.

At this time, in the trap configured according to the present invention, combustion occurred from around the ignition heater, and then slow combustion continued over the entire surface of the trap. The flame then spread to the inside of the trap, and it burned out almost completely in about 3 minutes. Therefore,
The differential pressure before and after the trap returned to its original level. Further, the maximum temperature inside the trap at that time was 1100°C. on the other hand,
In the conventional trap, the ignition heater's turn caused a little combustion, but the flame did not spread, and the differential pressure across the trap did not drop significantly. When the ignition heater was fired at an additional 7 hours, the trap of the present invention showed almost the same results as when fired at 3.5 hours. However, the conventional
As expected, only the soot around the ignition heater burned, but the soot inside the trap did not burn at all. Next 1
When ignited after 1 hour, the trap of the present invention has 3.6
After 7 hours, the results were almost the same, but when the conventional trap was ignited, it began to burn, and the combustion was almost complete in about 5 minutes. At this time, the maximum temperature inside the trap was 135
It showed σC・. After this, some soot leakage was observed in the center. After that, it was operated continuously, but the one of the present invention was
If you ignite when the pressure difference before and after the trap is around 10Kpa,
It burned almost completely, and the maximum temperature during combustion was around 1000°C. Conventional traps do not spread when the amount of soot shows a differential pressure of about 10 Kpa, and the
The fire only spread when the pressure reached 0Kpa or higher. However, with the amount of soot at this time, the temperature inside the filter rose too much and sooting of the ceramic began to occur, resulting in soot leaking.

Effects of the invention An oxidation catalyst is supported on the exhaust gas inflow side of an exhaust gas filter formed by alternately closing the cell ends of a honeycomb structure made of porous ceramic, and a porous body with a built-in heater is placed adjacent to the filter. When a suitable amount of soot has accumulated, by igniting the heater, most of the accumulated soot is combusted, providing an exhaust gas filter that does not melt and can be easily regenerated, unlike conventional filters.

[Brief explanation of drawings]

FIG. 1 is a partial sectional view of an exhaust gas filter according to an embodiment of the present invention, FIG. 2 is a characteristic comparison diagram of the same exhaust gas filter and a conventional example, and FIG. 3 is a partial sectional view of a conventional diesel exhaust gas filter. 1...Diesel exhaust gas filter, 2...
... Cell, 3 ... Cell wall, 10 ... Soot, 11 ... Exhaust gas, 12 ... Catalyst-supported porous body, 13 ...・Ignition heater. Name of agent: Patent attorney Toshio Nakao and one other person
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Claims (1)

[Claims] (1) An oxidation catalyst is supported on the front part of a structure made of porous ceramic having a plurality of cells with alternately closed parts provided at the ends thereof, independently of the ceramic porous body, and a part thereof An exhaust gas filter characterized by having a porous thin film made of glass or ceramic fibers with a built-in heater.