JP3414445B2 - Particulate filter and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas filter which can be easily regenerated by backwashing and a method for producing the same.

[0002]

2. Description of the Related Art Particulates containing carbon as a main component are contained in the exhaust gas of a diesel engine, and a particulate trap incorporating a ceramic filter has been developed for the purpose of removing the particulates. The ceramic filter has a honeycomb filter having a dust-containing gas passage and a clean gas passage extending in directions parallel to each other, and an intersection extending in a direction in which the dust-containing gas passage and the clean gas passage intersect with each other. There are two types of flow filters.

Two methods are aimed at removing or treating the particulates trapped in the ceramic filter, one of which is to burn the particulates trapped in the filter, and the other is the method of burning the particulates. This is a method of backwashing the particulates collected by the filter, moving them to another place, and then burning them. Both a honeycomb filter and a cross flow filter can be used for these particulate traps.

However, the particulates contain a small amount of non-burnable ash, and when the particulates are incinerated in the filter, the non-burnable ash clogs the filter and the ventilation pressure loss increases, so that the air pressure loss for a long time is increased. The latter method is considered superior because it requires continuous operation.

Since the ceramic filter has heat resistance, it can withstand the heat of combustion of particulates to some extent, but the particulate matter is trapped in the ceramic filter in a large amount, or when backwashing is insufficient. When rapid combustion allowed to curated, problems have a melting point above 1400 ° C., yet even ceramic filter coefficient of thermal expansion is smaller Cody E light quality, thermally damaged by large temperature gradients that occur during melting or filter I tend to get up.

In a particulate trap for backwashing, if the filter is always sufficiently regenerated by backwashing, basically no melting or heat damage to the filter should occur. However, heat damage to the filter occurs under certain operating conditions of the diesel engine, and there is insufficient regeneration of the filter by backwashing, and there is a part where the collected particulates are not separated from the filter wall during backwashing. It turns out that it happens if it remains.

In order to sufficiently regenerate the filter by backwashing, methods such as increasing the pressure of the backwashing gas or rounding the cross-sectional shape of the dust-containing gas passage to eliminate the corner portion where backwashing is difficult to perform are carried out. However, if the backwashing pressure is raised too much, the sealing of the filter becomes a problem, and the method of eliminating the corner part of the dust-containing gas flow path is also used when there are some sticky components in the particulates. Not enough backwash regeneration.

[0008] Such a phenomenon also occurs in a filter of a large dust removing device for removing ash in coal combustion exhaust gas, for example, for removing combustion exhaust gas of a pressurized fluidized bed combustor. For example, unburned components, mainly soot, which are intermittently discharged remain on the surface of a part of the filter without being backwashed and regenerated, and when they are somehow ignited and burned, heat damage to the filter occurs.

[0009]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and has a large processing capacity due to sufficient regeneration of the filter by backwashing, and a gas filter for avoiding heat damage to the filter. Is to provide.

[0010]

The present invention has been made to achieve the above-mentioned object, and the particulates of the present invention are provided.
The filter has an average particle thickness of 4 μm or less, and the surface of the aggregate particles forming the filter surface of the filter has no irregularities on the surface.
A smooth film with a difference of 0.2 μm or less does not block most of the pore openings on the filter surface of the filter.
Ku is reversed to be, characterized in that there use to play back washing.

To remove dust from high-temperature gas, a relatively coarse particle called an aggregate is mixed with fine particles forming a bonding portion (also referred to as a matrix), and the mixed raw material is molded by extrusion molding or press molding and fired. A ceramic filter is used as it is, or on a surface of a filter substrate mainly made of coarse aggregate, a filter layer mainly made of fine aggregate particles is integrally formed.

In either case, the filter surface of the filter has aggregate particles and pore openings between the aggregate particles adjacent to each other, and the aggregate particle surface is originally finer than a micron order. In addition to the unevenness, the fine particles forming the joint are burned on the surface of the aggregate, and the unevenness smaller than the micron order is formed. The trapping particles such as particulates is easily aggregated to each other, the trapping particles phenomenon occurs that the regeneration by backwashing when caught by the fine irregularities than the micron order hardly been made sufficiently.

[0013] In the gas filter of the present invention, the surface of the particle with fine irregularities than those micron order, smooth thin film on the front surface below the average <br/> thickness 4 [mu] m is, the pores of the filter surface without closing the opening almost (but, the average thickness of 4μm membrane following pores about Upon coating 7μm the most
Minutes are blocked. ) Have been formed, the particle surface with fine irregularities than those micron order is as if become as glaze is applied slip Laka.

The degree of smoothness of the surface of the coating film is 0.2 μm or less, more preferably 0.1 μm or less for the unevenness of the unevenness. There is no hindrance. The degree of smoothness of the coating film surface,
By transmission electron microscopy observation and scanning electron microscope replica image by, or samples from the stereoscopic photograph by scanning electron microscope photographs taken from two angles by inclining the can be estimated.

The filter surface of the ceramic filter is
This smooth surface of the aggregate particles weakens the adhesion of the collected particles to the filter surface of the filter, and backwashing for a long period of time reduces the initial low ventilation pressure loss of the filter. It can be recovered repeatedly and good backwashing property is secured. That is, even if the backwash gas pressure is not increased, the trapped particles remaining on the filter surface of the filter after the backwash are significantly reduced, and the ventilation pressure loss of the filter is significantly reduced on average during the period of use. can Ru.

The fact that the ventilation pressure loss can be reduced is equivalent to the increase in the throughput of the filter, and the retained particles trapped on the filter surface of the ceramic filter are remarkably reduced to be trapped on the filter. It becomes difficult for the trapped particles to ignite, and even if they ignite and burn, the amount of flammable trapped particles collected on the filter is small, so the heat of the ceramic filter Less likely to be damaged.

The thickness of the coating film is preferably as thin as possible to smooth the irregularities so as not to block the opening of the pores on the filter surface of the filter or to narrow the opening, and it depends on the use of the filter. The average thickness of the coating film having a smooth surface is preferably 0.1 μm or more and 2 μm or less.

In the case of a gas filter, fine dust particles, which are trapped particles, are often aggregated particles, so the size of the openings of the pores on the filter surface of the filter should be adjusted. It is not necessary to make it extremely small, and since the dust particles collected by the filter form a filtration layer, it may be considerably large, and the opening diameter of the pores is 0.5 to 20 of the collected particles on average. It should be doubled.

If the average opening diameter of the pores is small, the ventilation pressure loss of the filter itself is large, and the processing capacity of the filter is reduced. If it is too large, the trapped particles enter the pores of the filter and the trapped particles that enter the pores. Collected particles are not removed by backwashing, gradually increasing the ventilation pressure loss of the filter. Therefore, it is preferable to increase the average opening diameter of the pores within a range in which dust particles do not enter the openings of the pores and can be removed by regeneration.

[0020] is coated on the surface of the aggregate particles in the filter surface of the filter, as a smooth film on the surface and choosing those based on silica, easily available raw materials, there are acid resistance, The adhesion strength of the filter to the filtration surface is high,
It is preferable because it has a small coefficient of thermal expansion, is thin, is dense, and can easily form a film having a smooth surface.

The gas filter having excellent backwashability according to the present invention is suitable for a particulate trap for removing particulates in the exhaust gas of a diesel engine, and the adhesion of the particulate to the filter surface of the filter is small. , Backwashing is good and a large filter capacity can be secured, and the particulates are less likely to remain on the filter, so it is difficult for the particulates to ignite on the filter, even if the particulates ignite on the filter. However, since the amount of burned particulates is small, heat damage to the filter hardly occurs.

The gas filter of the present invention can be obtained, for example, by coating or impregnating a filter made of cordierite ceramic with a sol solution obtained by hydrolyzing a metal alkoxide such as ethyl silicate or aluminum alkoxide. However, if a commercially available silica sol is used, the pores on the filter surface of the filter are likely to be clogged, probably because the silica component is less for the viscosity, and the coating film cracks during drying, resulting in a smooth coating. Since it is difficult to form a film, it is preferable to use a sol solution obtained by hydrolyzing a metal alkoxide.

For the coating film, in addition to SiO ₂ and Al ₂ O ₃ ,
ZrO ₂ , TiO ₂ , In ₂ O ₃ , LiAlO ₂ , SnO ₂ ,
Inorganic materials such as Li ₂ O.SiO ₂ , B ₂ O ₃ .SiO ₂ and mixtures thereof can be preferably adopted, and the raw material liquid of these coating films easily wets the filter, that is, the interface energy with the filter material is small. It is necessary. A sol solution obtained by hydrolyzing a metal alkoxide is particularly preferable also in this respect, and a smooth coating film is formed on the surface of aggregate particles on the filter surface of a filter by applying or impregnating a sol solution obtained by hydrolyzing a metal alkoxide. It is easy to do.

Other coating films include polycarbosilane,
Organosilicon resins such as polysilazane, polysilazastyrene, and silicone, and fluororesins soluble in organic solvents can be used depending on the application, but a sol solution obtained by hydrolyzing a metal alkoxide forms a more heat-resistant film. it can. Alternatively, an aqueous solution such as an aqueous solution of metal acetylacetonate, an aqueous solution of metal silicate, an aqueous solution of metal carboxylate, etc. can be used, but it is difficult to form a coating film having a smooth surface due to the large surface tension.

Materials for the gas filter of the present invention include mullite, cordierite, alumina and β-sposite.
Interview main emission substance, silicon nitride, ceramics such as silicon carbide, glass, inorganic material or a metal material having a self-supporting or rigid, such as metal can be used. The shape of the filter may be a cross flow type, a honeycomb type, or a tube.

As the material of the filter, it is preferable to select ceramics from the viewpoint of corrosion resistance, heat resistance, and easy control of pore size. Furthermore, since it is excellent in thermal shock resistance and heat resistance, it is made of cordierite, β- and more preferably, that of Supoji Interview main emission protein or silicon carbide.

Preferred gas filter of the present invention, a filter base having a larger average pore diameter filter consists predominantly coarse aggregate particles, Ri smaller Do mainly fine aggregate particles formed on the surface of the filter base And a filter layer having an average pore diameter. By adopting such a configuration, wear gas <br/> scan filter of small large dimension of ventilation pressure loss in production.

The fine aggregate particles of the filter layer formed on the surface of the filter substrate are preferably made of the same material as that of the filter substrate, but silicon carbide-based aggregate particles are chemically stable regardless of the material of the filter substrate. It is preferable in terms of heat resistance and thermal conductivity.

To manufacture the gas filter of the present invention,
For example, a ceramic powder mainly composed of a cordierite aggregate with a controlled particle size, a fine powder of clay or the like that forms a joint, and a pore-giving material with a controlled particle size (those that are burnt to form pores during firing). ) in kneading an organic binder and water mixture was added, such as methyl cellulose, filter with the required pore size distribution can be obtained by firing the dried extruded.

As the pore-imparting material, pitch coke powder having a small iron content, for example, classified one having an average particle size in the range of 20 to 100 μm is used. The filter is
A filter base having a large average pore diameter mainly composed of coarse aggregate particles, and a filter layer having an average pore diameter of a size suitable for the particle size distribution of the trapped particles formed on the surface of the filter substrate. preferable. As the fine aggregate forming the filter layer, for example, aggregate particles having an average particle size of 1 to 100 μm are selected, and the average thickness of the filter layer is 10 μ depending on the purpose.
m to 500 μm.

When the average thickness of the filter layer is less than 10 μm, it becomes difficult to cover the large pores existing near the surface of the filter substrate with the filter layer, and the thickness is 50.
If it exceeds 0 μm, the ventilation pressure loss of the filter becomes large and the processing capacity of the filter becomes small. The formation of the filter layer is
For example, a slurry of fine aggregate powder mixed with a pore-forming material and a binder is applied to or sprayed onto the surface of the core die of the isostatic press press, and the filter base material is mainly used around the core die. It is performed by filling powder raw material composed of coarse particles, isostatically press-molding, and firing.

In addition, the filter layer is formed by coating the surface of the fired filter substrate with a slurry in which fine aggregate particles of 1 to 100 μm are dispersed by brush or spraying, or by immersing the filter substrate in the slurry. It is also possible to deposit the filter layer and then fire it.

Further, a fine aggregate powder containing no binder is rubbed against the surface of a filter base (sintered body) mainly composed of coarse aggregate and having a large average pore diameter to hydrolyze a solution of metal alkoxide. To form a filter layer by spraying on the surface, or to disperse the fine aggregate particles to be the filter layer in a solution obtained by hydrolyzing a metal alkoxide, dip the filter substrate in this solution, There is also a method of simultaneously adhering to form a filter layer on the surface of the substrate of the filter and forming a thin and smooth film on the surface of fine aggregate particles.

In order to form a smooth thin liquid film on the surface of aggregate particles in the vicinity of the filter surface of the filter, when the coating liquid is an inorganic salt solution, the thin liquid filter is treated with ammonia gas. Then, it is preferable to gelate and heat to solidify. Also, a film having a smooth surface can be formed by deposition from the gas phase.

After depositing the thin film on the filter, 100
The film may be dried at ~ 200 ° C to solidify it, but by heating at a higher temperature, for example, 500 ~ 1400 ° C, a film having a stronger and smooth surface can be formed and a backwashing property is further improved. Is obtained. However, if the heating temperature is higher than 1200 ° C., the smooth surface may be roughened , probably because the reaction between the membrane and the aggregate or the crystallization of the membrane occurs depending on the material of the filter.

[0036]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0037] Figures 1 and 2 is a schematic view of a cross section of the enlarged vicinity of the surface of the filter for explaining the gas filter according to the present invention, FIG. 1 is a large average pore diameter, mainly composed of coarse aggregate particles A filter layer 2 made of fine aggregate particles and having a small average pore diameter is formed on the surface of the filter substrate 1, 3 is fine aggregate particles constituting the filter layer, and 4 is fixed to the surface of the aggregate particles. It was is not the thin film. Also,
FIG. 2 is a schematic view of a cross section in which a part of FIG. 1 is further enlarged, and 5 is a trapped particle (for example, particulate).

Test Example 1 Used as a filter substrate for an exhaust gas particulate trap of a diesel engine having an effective filter area of 5 m ^{2 made} of a porous body of cordierite ceramics having an average pore diameter of 20 μm and a porosity of 40%. A cross-flow filter was prepared. On the other hand, 6% by weight of ethyl silicate, 76% by weight of ethyl alcohol, 6% by weight of water, 2% by weight of polyvinyl butyral, and an average particle size of 15.5 μm.
A dispersion solution containing 10% by weight of fine aggregate particles of cordierite (No. 1000) was prepared.

The filter substrate was washed with acetone, and the filter substrate was dipped in the liquid in which the fine aggregate particles of cordierite were dispersed, and pulled up at a speed of 5 cm / sec. This filter is dried and then heated at 1000 ° C. to completely solidify the membrane, and the obtained filter is incorporated into a particulate trap for removing particulates of a diesel engine, and the particulates in the exhaust gas of the diesel engine (aggregated particle size 1 to 10 μm) was removed. The test results are summarized in Table 1.

Test Examples 2 to 19 Under the conditions according to Test Example 1, the concentration of ethyl silicate was changed to change the thickness of the film (Test Examples 2, 3, 4,
14), the thickness of the filter layer was changed by changing the pulling rate (Test Examples 6, 7, 8 and 15), and the average particle size of the fine aggregate particles of the cordierite to be dispersed was changed and the average of the filter layer was changed. Those with different pore sizes (Test Examples 16 and 17),
Further, fine gel particles of about 0.5 μm were added to the film to increase the surface roughness (Test Example 18), and fine aggregate particles of the filter layer were made of silicon carbide and alumina (Test Example). 11, 12), one in which the heating temperature after drying was changed (Test Examples 9, 10, 19), one in which no filter layer was added (Test Example 5), and one in which no coating film was applied (Test Example 13). I made a prototype.

The thickness of the coated membrane and filter layer depends on the ESC
Investigated by A and Auger or SEM, the filter surface
The roughness of the coated particle surface was measured by SEM and TEM observation, and the average pore diameter of the filter layer was measured by a mercury porosimeter.

The backwashing property of the filter was evaluated by connecting a particulate trap equipped with a filter to a diesel engine, operating the diesel engine in a certain mode for about 1 hour, and then backwashing the filter immediately after the backwashing. The weight of the particulates adhering to the filter (the filter is removed after the test and the weight of the filter is measured to determine the difference from the initial weight of the filter) and the ventilation pressure loss before and after the test (at a constant flow rate from the upstream side to room temperature). The ventilation pressure loss of the filter was measured by flowing clean air, and the ventilation pressure loss after the test was measured after the backwashing.), And these results are summarized in Table 1.

[0043] In Table 1, was used having an average particle diameter of 30μm to aggregate particles of Test Example 4, 14 the filter layer.

[0044]

[Table 1]

Of these test examples, test examples 1 to 12 and test examples 15 to 17 are examples of the present invention, and the others are comparative examples. The filters of Test Example 5 and Test Example 17 both have large pores open on the filter surface, and are not suitable for a particulate trap filter. From these test results, the following can be understood.
First, in Test Example 13 in which the film having a smooth surface is not coated and Test Examples 18 and 19 in which the film is not coated and is not smooth, a large amount of particulate remains in the filter even when backwashing is performed. Vent pressure loss was relatively high.

In Test Example 14, since the average thickness of the membrane was larger than 4 μm, most of the pore openings of the filter layer were closed and the ventilation pressure loss was large. In the coating film having a thickness of about 5 μm, cracks occurred and the surface smoothness was lost, and it is presumed that the amount of residual particulates increased due to this.

Further, if the thickness of the filter layer is large (Test Example 15) or the average pore diameter of the filter layer is small (Test Example 16), the ventilation pressure loss of the filter becomes large , and
Use is restricted depending on the target. In Test Example 5 in which the filter layer is not formed and Test Example 17 in which the pore diameter of the filter layer is large, the amount of residual particulate matter is not so large because the particulates have penetrated into the inside of the filter, but the ventilation pressure loss is large. ing. Also, test example 1
It can be seen that when the heating temperature is higher than necessary as in No. 9, the smoothness of the coating film is lost due to crystallization and the backwashing property is impaired.

Instead of the ethyl silicate used in Test Example 1, an aqueous sodium silicate solution, a polysilastyrene solution,
When a trimethylmethoxysilane solution was used as a coating solution, ethyl silicate was the most excellent, followed by trimethylmethoxysilane, polysilastyrene, and sodium silicate in that order in terms of residual amount of particulates and ventilation pressure loss.

[0049]

In the gas filter of the present invention, the fine irregularities on the surface of the aggregate particles on the filter surface of the filter are smoothed by the thin film covered therewith , so that the collected particles
The force of adhesion of the particles to the filter surface is small, the backwashing of the trapped particles collected in the filter is facilitated, regeneration is sufficiently performed, and the filter can be used in a state of low ventilation pressure loss as a whole.

Therefore, the processing capacity of the filter is increased,
If the collected particles are combustible particles such as particulates emitted from a diesel engine, the amount of particulates remaining in the filter will decrease on average, and the particulates in the filter will The risk of burning is reduced, and even if the particulates may burn in the filter, the risk of thermal damage to the filter is almost eliminated because the combustion heat generated is small. Further, since the backwashing pressure can be lowered, the load on the backwashing device can be reduced, and further, the filter size can be reduced for the same throughput.

When the material of the coated film is mainly composed of silica, the backwashability and the acid resistance of the filter are good, and water repellency and oil repellency are imparted to the film by selecting the material of the film. can also, Ru can impart high backwash resistance even for particles containing particles and oil containing water in the filter.

[Brief description of drawings]

FIG. 1 is an enlarged schematic view of a cross section near a surface of a filter for explaining a configuration of an example of a gas filter according to the present invention.

FIG. 2 is a schematic view in which a part of a cross section near the surface of the filter of FIG. 1 is further enlarged.

[Explanation of symbols]

1: Filter base 2: Filter layer 3: Fine aggregate particles constituting the filter layer 4: Smooth surface film 5: Collected particles

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI F01N 3/02 ZAB F01N 3/02 ZAB

Claims (5)

(57) [Claims] 1. A surface of aggregate particles constituting a filter surface of a filter has an average thickness of 4 .mu.m or less, and a surface unevenness drop.
By There 0.2μm or less smooth film, such ku majority of the pores of the opening in the filter surface of the filter is closed
Patti, characterized in that the overturned, are use to play back washing
Curate filter. 2. A particulate filter according to claim 1 Symbol placing the film is composed mainly of silica. 3. A filter, wherein the filter has a large average pore diameter mainly composed of coarse aggregate particles, and an average thickness 10 mainly composed of fine aggregate particles formed on the surface of the filter base.
The particulate filter according to claim 1 or 2 , wherein the particulate filter is formed of a filter layer having a thickness of about 500 µm. 4. A filter surface of a filter used after backwashing is coated or impregnated with a solution obtained by hydrolyzing a metal alkoxide to dry and solidify, and most of the pores opened in the filter surface of the filter are closed. as no preparation of the particulate filter, which comprises coating the surface of the aggregate particles fall of unevenness of the average thickness of 4μm or less at the surface constitutes the filter surface of the filter by the following smooth film 0.2μm Method. 5. A filter used by backwashing and reclaiming, wherein fine aggregate particles forming a filter layer are dispersed in a liquid obtained by hydrolyzing a metal alkoxide on a filter substrate mainly composed of coarse aggregate particles. The dispersion is applied or impregnated to form a filter layer made of fine aggregate particles on the filter substrate, and the average thickness of the fine aggregate particles is 4
A method for producing a particulate filter, which comprises forming a smooth film having a surface roughness of 0.2 μm or less when the thickness is less than or equal to μm .