JPH08189337A - Filter for scavenging fine particle in exhaust gas and method for processing exhaust gas - Google Patents

Abstract

PURPOSE: To provide a filter for scavenging the particulates in exhaust gas of a diesel vehicle, which can be recycled in scavenging the particulates, and which can stabilize scavenging efficiency high, and which can be regenerated by a small power. CONSTITUTION: Plural filtering material 1 respectively provided with an opening part 9, through which at least a part of the exhaust gas can be flowed, are arranged along a low passage of the exhaust gas so as to form a filter for scavenging the fine particles in the exhaust gas. Each filtering material 1 has a heat insulating air-permeable material 2, a heater 3 and a scavenging air-permeable material 4. The air-permeable material 4 is positioned in the downstream of the heat insulating air-permeable material 2, and a clearance part 6 at 50mm or less of width is provided between the scavenging air-permeable material 4 and the heat insulating air-permeable material 2, and the heater 3 is positioned in this clearance part 6. Desirably, width of the clearance part 6 is formed at 1-20mm, and a shielding material 5 for cutting the flow of the exhaust gas is provided in a boundary of the clearance part 6 and the opening part, and the heat insulating air-permeable material 2 and the scavenging air-permeable material 4 are made of the non-conductive material.

Description

Detailed Description of the Invention

[0001]

[Industrial application] Gas emitted from diesel vehicles, etc., contains soot-like carbonaceous fine particles, also called particulates (hereinafter abbreviated as "fine particles"). It is one of the causes. Reducing the emission amount of fine particles is one of the important issues to be solved at an early stage in global environmental problems. The present invention relates to a filter for removing fine particles contained in exhaust gas discharged from an internal combustion engine such as a diesel engine and a method for treating exhaust gas.

[0002]

2. Description of the Related Art Heretofore, a ceramic honeycomb structure has been mainly studied as a filter for collecting fine particles in exhaust gas discharged from a diesel engine vehicle (eg, Japanese Patent Laid-Open No. 57-7216). Here, the honeycomb structure is a structure that is divided by partition walls, has a large number of cells whose one end is closed in an alternating positional relationship, and can have a large filtration area per unit volume. For collecting fine particles of exhaust gas from diesel passenger cars, the cell density is 10 to 15 cells / cm ² , and the total number of cells is 1.
500 to 2500, a partition wall thickness of 0.3 to 0.5 mm, and a filtration area of about 1.5 m ² are exemplified.

In order to regenerate the honeycomb structure in which the fine particles are collected, a method of applying a high temperature of 600 ° C. or higher to the whole or a part of the honeycomb structure to ignite the fine particles and remove them by burning has been mainly studied. The exhaust gas is continuously treated by repeating collection and regeneration. In this method, the honeycomb structure having an extremely thin partition wall and a large number of cells as described above may have the property of withstanding a high temperature when fine particles burn and the property of withstanding repeated temperature fluctuations. is necessary.

However, it is extremely difficult to manufacture a honeycomb structure having a large number of cells and a thin partition wall as described above, without containing defects such as pinholes. There are major problems in productivity and reliability as a filter, such that the honeycomb structure is cracked or broken during the process of fluctuation and the collection efficiency is significantly reduced. Moreover, even if the method of regenerating the filter while regenerating the exhaust gas while collecting the fine particles is adopted, the temperature of the exhaust gas flowing through the partition walls of the honeycomb structure is about 150 to 350.
Since the temperature is ℃, which is considerably lower than the combustible temperature range of fine particles, even if a large amount of heat is applied and ignited, it blows off and there is a problem that combustion cannot be continued until the fine particles have sufficiently disappeared. . For this reason, there is a problem in that there is no choice but to adopt a method of alternately collecting and reproducing, such as providing two series of filters and regenerating the other filter while collecting with one filter.
There is a big problem that the particulate collection device is heavy and expensive as a whole.

Furthermore, it is necessary to prepare in the equipment a countermeasure against an emergency situation in which fine particles are abnormally accumulated and the filters are blocked in two series, and the exhaust gas flow path is blocked. In order to solve such problems,
As a completely different type of filter from the conventional one, Japanese Patent Application No. 4-158004 of the present applicant has been proposed. The present invention, in the exhaust gas filter of this earlier application, stability of the collection efficiency in the method of regenerating the filter while electrically heating to burn and remove fine particles, reproducibility is insufficient,
It is difficult to obtain a high collection efficiency of fine particles for a long period of time, and overcoming unsolved problems such as a large amount of electric power required for energizing and heating, resulting in a stable collection efficiency of fine particles and a reduction in regeneration power. Is what gave the progress of.

[0006]

That is, the present invention aims to solve the above-mentioned drawbacks of the prior art, while collecting fine particles in exhaust gas while burning and removing the collected fine particles. It is a filter that can treat exhaust gas in one line, such as, and has a simple structure, high durability, stable collection efficiency, and stable regeneration of the filter by electric heating with low power. The present invention provides a filter for collecting fine particles, and further provides a method for treating exhaust gas using the filter.

[0007]

DISCLOSURE OF THE INVENTION The present invention provides an exhaust gas in which a plurality of filter media having an opening through which at least a part of the exhaust gas can flow are arranged along a flow path of the exhaust gas. A filter for collecting particulates, wherein each filter material has a heat insulating ventilation material, a heating element, and a collection ventilation material, and the collection ventilation material is located downstream of the heat insulating ventilation material. A gap portion having a width of 50 mm or less is provided between the collecting ventilation member and the heat insulating ventilation member, and the heating element is a filter located in the gap portion, preferably, the width of the gap portion is 1 to 20 mm,
A shielding material that blocks the flow of exhaust gas is provided at the boundary between the gap and the opening, and the heat insulating ventilation material and the collection ventilation material are made of a non-conductive material. It is a filter in which the size of the opening provided is gradually reduced to the downstream side of the exhaust gas. An example of the structure of the filter medium is shown schematically in FIGS. A filter constructed by disposing a plurality of filter media inside an outer cylinder (exhaust gas duct) is schematically shown in FIG.

Further, according to the present invention, a filter having an opening and having a heat-insulating ventilation material, a heating element, and a collection ventilation material and arranged along the exhaust gas passage is used. A method for treating exhaust gas in which fine particles are collected and, in parallel, heated fine particles collected by a heating element are burned and removed, in which at least a part of the exhaust gas containing fine particles has an opening in each filter medium. The other exhaust gas passes through the heat-insulating ventilation material, and the exhaust gas that has passed through the heat-insulating ventilation material is filtered by the collection ventilation material to collect fine particles, and the heating elements of each filtration material are sequentially intermittently And heat the collected ventilation fine particles present in the gap of 50 mm or less in width between the collection ventilation material and the heat insulation ventilation material by adhering to the collection ventilation material to insulate the collection ventilation material from the collection ventilation material. Use the heat insulation of the ventilation material to heat above the combustion temperature, Oxygen required for combustion of particles is a method of treating exhaust gas using oxygen contained in the exhaust gas, and preferably the flow path of the exhaust gas flowing to the opening along the surface of the trapping ventilation material is substantially in the gap portion. In the absence of heat, the heat generated by the heating element and the heat insulating properties of the collection ventilation material and the heat insulation ventilation material are used to heat and remove the particulates present in the gap to a temperature above the combustion temperature for combustion removal. In addition, the differential pressure before and after the filter is detected, and the frequency per unit time for intermittently energizing and heating the heating elements of each filter medium is changed accordingly, and the differential pressure is lower when the differential pressure is higher. This is a method of increasing the frequency per unit time more than the time.

Each of the plurality of filtration media constituting the filter of the present invention includes a heat insulating ventilation material, a heating element, and a collection ventilation material. Here, the adiabatic ventilation material refers to a constituent material that has an appropriately low thermal conductivity necessary for suppressing the dissipation of heat generated by the heating element, and also has a ventilation property through which exhaust gas can pass. The heat insulating vent material needs to have a property of withstanding the temperature at which the collected fine particles are burned, and it is desirable that at least the portion of the heat insulating vent material facing the heating element has a heat resistance of 500 ° C. or higher. The material and structure of this insulating vent material can be selected in a wide range.

For example, there are low density porous materials having appropriately low thermal conductivity of various heat resistant materials, and specifically, alumina, silica, various silicate glasses, aluminum nitride, boron nitride, Low density sintered bodies and foams of various heat-resistant inorganic materials such as boron carbide and silicon carbide,
Alternatively, a preferable example is a molded body of ceramic fiber such as alumina fiber, silica fiber, alumina silicate fiber, potassium titanate fiber, aluminum nitride fiber and the like.
In addition, a material that has an appropriately low thermal conductivity, but the material itself does not have sufficient air permeability, for example, has a material that has one or more holes with a diameter of several mm for providing air permeability. It can also be used as a ventilation material. As a typical example, it is also possible to open only one ventilation hole in a highly heat insulating material and use it as a heat insulating ventilation material as shown in FIGS. Furthermore, for example, a metal plate is joined to a molded body having a high heat insulating property such as a low-density sintered body of the above-mentioned inorganic material or a ceramic fiber molded body to improve strength and shape retention, and a suitable penetrating therethrough. Also suitable are composite materials which are perforated in size and number for ventilation.

The collecting ventilation material is a constituent material capable of filtering exhaust gas and collecting fine particles contained therein, and is made of a material having appropriate ventilation and heat resistance like the heat insulating ventilation material. However, in order to collect the fine particles, it is also necessary to have an appropriate pore size. Further, since most of the collected fine particles are in contact with the collecting ventilation material, the temperature to be heated when burning the fine particles is higher than that of the heat insulating ventilation material, preferably 800 ° C. or higher, and more preferably 900. Has heat resistance of ℃ or above. Further, it is also necessary to have mechanical strength to withstand a pressure difference between the front and back surfaces of the collecting ventilation material during filtration.

Materials suitable for such conditions include, as described above, low density sintered bodies or foams of various inorganic materials which are porous bodies, and molded bodies of ceramic fibers, which have an appropriate pore size. However, from the viewpoint of heat resistance and mechanical strength, a molded body of ceramic fiber such as alumina fiber, silica fiber, alumina silicate fiber, aluminum nitride fiber, silicon carbide fiber is more suitable. is there. In general, the molded body of these ceramic fibers has a high heat insulating property.
The size of the average pore diameter of the collecting ventilation material is appropriately 1 to 100 μm, and more preferably 10 to 50 μm.

The air permeability of the heat insulating ventilation material and the collection ventilation material is
For example, using the method of JIS-L1096, the differential pressure is 12.
Area of ventilation material 1c in 7 mm (0.5 inch) water column
It can be represented by the amount of air permeation per m ² . The air permeability value of the collecting ventilation material is 1 to 100 cm ³ / (cm ² · sec) in the state where fine particles are not adhered, and more practically, it is about ^{3 to} 30 cm ^3. / (Cm ² ·
Seconds). This value of the heat insulating ventilation material preferably has at least twice the air permeability of the heat insulating ventilation material in order to prevent the pressure loss of the filter from unnecessarily increasing, and more preferably 5 to 500 times. Have sex.

This air permeability can be adjusted by the size of the pore size and the thickness of each air permeable material. In the case of a heat insulating air permeable material, as described above, if necessary, for example, a diameter of several mm or less is used. It is also possible to adjust the air permeability to a high level by opening an appropriate number of holes.

A gap having a width of 50 mm or less is provided between the heat insulating ventilation material and the collection ventilation material. That is, the two ventilation materials are arranged at a distance of 50 mm or less, preferably the width of the gap is 1 to 20 mm, and the heat insulating ventilation material is arranged on the upstream side of the exhaust gas. At the boundary between the gap and the opening,
As shown in FIGS. 1 to 4, it is desirable to provide a shielding material for blocking the passage of the exhaust gas from the gap to the opening. The shield can be made of any material that is substantially gas impermeable. Preferably, it is made relatively thin with a width of several mm or less having the same width as the gap between the heat insulating ventilation material and the collection ventilation material, and fixed to the heat insulation ventilation material and the collection ventilation material.

The heating element is mainly located in this gap,
Nickel-chromium alloy, iron-chromium-aluminum alloy (kanthal), silicon carbide, molybdenum disilicide,
It is possible to use a heating element obtained by processing a material such as lanthanum chromite into a linear shape or a band shape. The heating element is, for example, as shown in FIG. 1 or FIG. 3 when viewed from the flow direction of the exhaust gas so that all the fine particles collected on the collecting ventilation material are efficiently heated to the combustion temperature as uniformly as possible. It is formed into a shape and arranged so as to be mainly located in the gap portion in the vicinity of the fine particles to be collected. One guideline is to make the shape such that the space between adjacent heating elements is 3 cm or less. In addition, 1
It is not always necessary to heat one filter element with one heating element, and two or more heating elements may be attached to one filtering element to heat the filtering element in a divided manner.

In order to prevent the heating element to be electrically heated from coming into contact with the heat-insulating ventilation material or the collection ventilation material and causing an electric current to flow through the ventilation material to prevent the temperature of the heating element from rising or becoming unstable, The material is preferably non-conductive in nature. That is, as a material constituting the filter medium of the present invention, the heat insulating ventilation material is a low density of ceramic materials such as alumina, silica, various silicate glasses, aluminum nitride, and boron nitride, which have non-conductivity and heat resistance. Of sinter or foam,
Or, a molded article of ceramic fiber is a preferable example, and the ventilation material for collection has a non-conductive property and heat resistance, and has a relatively high mechanical strength such as alumina fiber, silica fiber, alumina silicate fiber, aluminum nitride fiber. A preferable example is a molded body of ceramic fiber such as. In order to improve the strength of these ventilation materials, metal materials such as wire mesh, perforated metal plate, punching metal, etc., which have relatively high strength and high air permeability, are placed on the opposite side of the side facing the heating element to ventilate. Reinforcing the permeable material is also an example of a preferred embodiment of the present invention.

The shape of the filter material including the heat insulating vent material, the heating element, and the collecting vent material is not particularly limited, and the shape of the entire filter material viewed from the flow direction of the exhaust gas is shown in FIG.
Such as a circle, a rectangle as shown in Fig. 3, a square as well,
It may have any shape such as an ellipse or a triangle. Although it is not necessary to limit the shape of the filter material as viewed from the direction perpendicular to the flow of the exhaust gas, the trapping ventilation material and the heat insulating ventilation material have substantially the same thickness, and their gaps have the same width, A shape having the same thickness as the entire filter medium is one preferable embodiment. It is a guideline that the thickness of the heat insulating ventilation material is 1 to 20 mm and the thickness of the collection ventilation material is 0.5 to 10 mm.

The area of the filter medium should be designed according to the amount of exhaust gas, the concentration of fine particles, the number of filter media, etc.
5 with an exhaust gas filter of a large diesel vehicle of 000 cc
A diesel vehicle having an exhaust capacity of 00 to 1500 cm ² and a displacement of 3000 cc is 100 to 400 cm ^{2 as} a rough guideline for the area of the filter medium as seen from the flow direction of the exhaust gas.

The fine particles adhering to the collecting air-permeable material may fall off together when they reach a thickness of, for example, 1 mm due to vibration or the like, and accumulate below the gap. For this reason, when the area of the filter medium becomes large, for example, 1000 cm ² , the distance that it falls and moves becomes long, and the heat from the heating element to the fine particles and the supply of oxygen in the exhaust gas may become non-uniform. To make the supply of heat and oxygen non-uniform, for example, a partition wall is provided in the gap between the heating elements as shown in FIG. 3, and the gap is divided to shorten the distance that the fine particles can move. Can be reduced by The partition wall has a thickness of, for example, about 1 mm, a width that is the same as that of the gap portion, and is arranged so as to extend horizontally between two parallel heating elements as shown in FIG. This is a preferred example. The material of the partition wall may be any material as long as it has no or little gas permeability and has heat resistance of about 600 ° C. or higher.

Each filter medium has an opening. here,
The opening can be located at an arbitrary position where a part of the heat insulating ventilation material and the collection ventilation material is hollowed out as shown in FIG. 1, or the heat insulation ventilation material and the collection ventilation material as shown in FIG. It can also be at any position between the outer cylinder and the outer cylinder (exhaust gas duct). The opening can be located at such an arbitrary position, but it is preferable that the plurality of filter media do not overlap with each other in the flow direction of the exhaust gas, and the position of the opening is located offset from the center of the filter media. This is an example of a preferred mode in which the openings are rotated 180 degrees and the openings are alternately positioned when viewed from the flow direction of the exhaust gas. Further, each filter medium may have a plurality of openings.

In the filter medium, about 60 to 95% of the exhaust gas passes through the opening and about 5 to 40% of the exhaust gas passes through the opening in the state where the fine particles are not attached to the collecting ventilation member. It is preferably designed to penetrate. Specifically, it is designed in consideration of the pressure loss of the filter and the desired values of the particulate collection rate. The relationship between the area of the collection ventilation material and the size of the opening corresponding to the relationship between the flow rate of these openings and the flow rate of the collection ventilation material varies depending on the characteristics of the collection ventilation material. 1/10 of the area of the collecting ventilation material when viewed from the flow direction
Is the magnitude opening tentative standard of 1/40, a large diesel exhaust gas filter exhaust amount 10000cc 50~200cm ^2, in diesel cars exhaust amount 3000cc 10 to 40 cm ² is the opening size of the It is a guide.

The filter of the present invention is a system in which the concentration of fine particles in the exhaust gas is gradually reduced by each filter medium, and the concentration of fine particles in the exhaust gas becomes lower in the downstream filter medium. Therefore, if the relationship between the area of the filter media and the size of the opening is the same for all the filter media of the same number, the downstream filter media will accumulate less fine particles than the upstream filter media, By gradually reducing the size of the filter downstream, the pressure difference between the front and back surfaces of the filter can be increased further downstream, and the amount of exhaust gas passing through the filter downstream can be increased. Is. As a result, it is possible to reduce the difference in particle deposition rate between the upstream side and the downstream side. The size of the most downstream filter medium is not limited, but is preferably 20 to 80% of the size of the opening of the most upstream filter medium.

The number of the filtering materials varies depending on the target collection rate of the fine particles, but is preferably 5 to 100, more preferably 10 to 40. Further, the gap between the front and rear of the plurality of filter media is appropriately 5 to 50 mm.

To regenerate the filter, the collected fine particles are
It is carried out by heating with a heating element located in the gap to remove by combustion. The fine particles are heated mainly in a state where they adhere to the collecting ventilation material and are present in a gap portion having a width of 50 mm or less between the collecting ventilation material and the heat insulating ventilation material. As described above, the heat insulating ventilation material is made of a porous material having low thermal conductivity and low density, and the ventilation material for collection is also a kind of porous material having low thermal conductivity, for example, ceramic. It can be a shaped body of fibers. Therefore, the fine particles can be heated in a narrow space sandwiched by materials having low thermal conductivity.

Oxygen in exhaust gas can be used as oxygen required for combustion of fine particles. Oxygen in the exhaust gas of a diesel engine mounted on a vehicle is generally 5% by volume or more and about 10% by volume on a time average, although it varies depending on the load and running condition of the engine. Here, in the case of burning the fine particles, it is preferable to heat the fine particles in a state where there is substantially no flow path of the exhaust gas flowing to the opening along the surface of the collecting ventilation material. The reason for this is to suppress heat deprivation by the flow of exhaust gas as much as possible, and to make the particles reach the combustion temperature with a small amount of electric power. As one of the measures for blocking the flow path, there is a method of providing a shielding material for blocking the flow path of the exhaust gas at the boundary between the gap and the opening as described above.

It should be noted that the present invention does not exclude the method of introducing air or oxygen for combustion of fine particles into the exhaust gas, and in order to prevent a considerable increase in the flow rate of the exhaust gas and thus a significant increase in the differential pressure of the filter, A method of introducing air only during the period when the heating element is energized or a method of introducing a small amount of air directly into the gaps where the fine particles are present can be implemented in the filter of the present invention.

The amount of exhaust gas passing through the openings of the filter medium and the amount of exhaust gas passing through the heat insulating ventilation material and the collection ventilation material are
It depends on the resistance of each flow. For example, if the opening is made small, the resistance of the flow of the exhaust gas flowing through the opening is high, the proportion of the exhaust gas passing through the collection ventilation material is relatively large, and the pressure loss as the filtering material is large, and vice versa. The opposite is true. That is, the differential pressure before and after the filter in the state where no fine particles adhere can be adjusted by the size of the opening, and can be easily measured by measuring the differential pressure before and after the filter in the state where no fine particles adhere. You can ask.

When fine particles are accumulated in the collecting ventilation material, the passage resistance is increased and the ratio of the particles flowing through the collecting ventilation material is reduced, the collection rate of the fine particles is lowered, and the fine particles are entirely accumulated in the filtering material. The differential pressure before and after the filter becomes high. As described above, the differential pressure before and after the filter during operation has a positive relationship with the accumulated amount of fine particles, and the accumulated amount can be determined by the differential pressure before and after the filter. When the accumulated amount is large and the collection rate of fine particles is low, it is desirable to reduce the accumulated amount early. Therefore, during the period when the differential pressure is large, the regeneration cycle is shortened, the frequency per unit time for heating the heating element by energization is increased, and when the differential pressure returns to a low level, the frequency may be reduced. It is convenient in terms of both efficiency.

The heat-insulating ventilation material, the heating element, the collection ventilation material, and the optional shielding material, and the filtering material having the partition wall are integrally fixed by any ordinary method such as welding, adhesion, and tightening. This is an example of a preferred embodiment in which one unit is used and a plurality of units are fixed in the outer cylinder. Examples of this fixing method include, for example, directly fixing the filter medium to the outer cylinder by welding or the like, or fixing a support member to which the filter medium is easily attached inside the outer cylinder, and bolting the filter medium to the support member, for example. It may be fixed by welding or the like. Alternatively, a stackable support that fits exactly in the outer cylinder may be prepared, a filter medium may be attached to the support, and the stack may be arranged in the outer cylinder.

[0031]

The function and technical concept of the filter of the present invention, which is suitable as a filter for collecting fine particles contained in the exhaust gas of a diesel engine and enables stable high particle collection efficiency and low regeneration power, will be described.

The fine particle collecting mechanism of the filter of the present invention uses the pressure difference between the front and back surfaces of the filter medium, which is generated in the process of flowing the exhaust gas, by shielding the flow path of the exhaust gas with a plurality of filter media having openings. However, this is a collection method in which the operation of collecting some of the fine particles in the exhaust gas is repeated a plurality of times in succession. That is, in the flow of exhaust gas as shown in FIG. 5, by disposing a plurality of filter media having openings in the flow path of the exhaust gas, the flow is narrowed, the direction of the flow is changed, etc. A differential pressure of the exhaust gas is generated between the back surfaces, and the exhaust gas penetrates the trapping ventilation material of the filter material at a flow rate corresponding to the differential pressure, and the contained fine particles are filtered.

Further, since the heating elements of the respective filter media are structurally distinct, the heating for burning the fine particles can be carried out by energizing the heating elements independently.
That is, it is possible to energize only one of the heating elements, for example, one heating element at a certain moment, and then sequentially energize another heating element.

In the above collection method, for example, 90% of the exhaust gas flows through the opening of one filter medium, 10% of the exhaust gas penetrates the collecting ventilation material, and 10% of one filter medium is used.
In the filter in which n pieces of filter media are arranged along the flow path of the exhaust gas, the uncollected particles are ideally 0.9 power of n, and n is 10 If so, the uncollected fine particles are reduced to 35%, and if n is 20, the fine particles are reduced to 12%.

In order to obtain such an ideal trapping efficiency in this system, it is obvious that it is necessary that the fine particles trapped in the filter medium do not leave the filter medium and accompany again with the flow of the exhaust gas. . Here, the flow of the exhaust gas at a high velocity in the direction parallel to the surface of the filter medium acts to blow the collected fine particles from the filter medium. That is, in the above example, 90% of the exhaust gas flows along the surface of the filter medium without penetrating the filter medium, and exerts a force to separate the collected fine particles from the filter medium.

The flow of the exhaust gas along the surface of the filter medium in the vicinity of the collected fine particles is constituted by two kinds of ventilation materials, and the upstream side has a high heat insulating property and an appropriate ventilation property. There is a heat insulating ventilation material, and a collection ventilation material having a fine average fine pore diameter suitable for collecting fine particles is arranged on the downstream side, and an appropriate width is provided between these two kinds of ventilation materials. It is possible to remarkably reduce the amount by providing the gap portion, and it is possible to further reduce the amount by providing a shielding material for blocking the flow of the exhaust gas at the boundary between the gap portion and the opening portion. As a result, it became clear that the fine particle collection rate close to the ideal state can be achieved.
The reason for this is that by providing a distance between the flow of exhaust gas outside the gap and the collection ventilation material, it is possible to effectively reduce the influence on the surface vicinity of the collection ventilation material from the outside.
Further, it is considered that by substantially blocking the flow path of the exhaust gas from the gap portion to the opening portion, the flow other than in the direction of penetrating the collection ventilation material can be effectively and significantly reduced.

The electric power required to heat the heating element by energization to regenerate the filter material finally affects the fuel efficiency of the diesel vehicle, and therefore it is desirable to be as small as possible. 2 for large trucks
kW or less, and 1 kW or less for passenger cars. It has been clarified that the filter of the present invention can be regenerated with a sufficiently low electric power, which is considered to be due to the following reason.

First, when the filter material of the filter of the present invention is regenerated, the state of fine particles is mainly present in the gap portion formed by two kinds of porous bodies having low thermal conductivity, and has a width of less heat radiation. It is a state where it exists together with a heating element in the space of a narrow gap. Therefore, it is possible to effectively block the dissipation of the heat of the heating element and the combustion heat of the fine particles, and further, the space of the gap provides a heat transfer space by radiation and promotes the uniformization of the temperature of the heated object. As described above, it is considered that the heat is in an ideal state for being efficiently transmitted to the entire particles.

Secondly, the flow of the exhaust gas in the gap portion in the direction parallel to the surface of the collecting ventilation material is suppressed by using the shielding material. Further, as described above, the exhaust gas that originally penetrates one filter medium is, for example, only 10% of the whole, and when the filter medium needs to be regenerated, it penetrates the filter medium due to clogging by fine particles. It is considered that the amount of exhaust gas generated is further reduced, and therefore the amount of heat taken by the flow of exhaust gas from the heating element and the fine particles and the ventilation material heated by the heating element is also reduced.

In addition to the effect of realizing the high collection rate and the low regeneration power, the gap seems to play an indispensable basic role for establishing the filter of this system. That is, in order for the filter of this system to be beneficial, only a small part of the filter medium is used for filtration, and the deviation of the adhesion of fine particles is not large, and the entire filter medium is effectively used. It is necessary. However, in the filter structure and the flow of exhaust gas as shown in FIG. 5, the direction and speed of the flow of exhaust gas in the vicinity of the surface of the filter medium are not equal in each part of the filter medium. For example, if the flow velocity near the surface of the filter medium immediately downstream of the opening has a large component in the direction perpendicular to the filter surface, and the flow velocity near the surface of the filter far from the opening has a large component parallel to the filter surface. Conceivable. Such a difference in flow velocity and direction causes a partial difference in the differential pressure of the filter medium and separation of fine particles, and if left as it is, it is possible to result in uneven adhesion of fine particles and a low collection rate. Experienced by the inventors.

However, the condition of the flow of the exhaust gas in the vicinity of the surface of the collecting ventilation material can be largely changed by the gap portion provided upstream of the collecting ventilation material. That is, as described above, since only part of the exhaust gas flows into the gap,
The flow velocity in the gap is much smaller in absolute value than in the outside of the gap, so even if there is a difference in flow velocity at various places near the surface of the collection ventilation material, it will only be a difference within the range of small absolute values. . Further, the action of the shielding material suppresses the flow flowing out of the gap along the surface of the collection ventilation material, and the forced flow along the surface near the surface of the collection ventilation material is extremely small or It can be brought to a substantially nonexistent state.

Thus, the exhaust gas flowing into the gap is
It is used for the differential pressure between the front and back surfaces of the collecting ventilation material in the state where the influence of the outside is small and the flow velocity is small. On the other hand, as a general property of the filter material, when fine particles are deposited on the surface, ventilation resistance increases, and the amount of penetrating gas in that area decreases. This means that even if there is a region where the gas is relatively easily penetrated in the collecting ventilation material due to the non-uniform flow of the exhaust gas, the exhaust gas is preferentially discharged in that region first. Although it is penetrated and filtered, it means that the penetration rate decreases as the accumulation of fine particles progresses, and that the filter material inherently has the property of migrating a relatively easy-to-penetrate region to another part that has not yet accumulated. .

In order for the property of the filter medium to be easily obtained that the deposition amount is originally uniformed, the influence other than the pressure difference between the front surface and the back surface of the filter medium is required to be small, and the exhaust gas is easily discharged to the flowable portion. There should be a space to move around.
It is considered that the space of the gap portion plays this role and provides a space in which the exhaust gas can freely move so that the exhaust gas itself selects a region in which the accumulation of the fine particles of the ventilation material is small. Therefore, irrespective of the positions of the openings, even if the openings are extremely unevenly distributed as shown in FIG. 3, the heating element is not upstream of the collection ventilation material and is uneven with respect to the collection ventilation material. Even if it is located at, it is considered that substantially the entire surface of the collection ventilation material becomes available for filtration.

By these actions, high collection efficiency of fine particles becomes possible, and it becomes possible to heat the fine particles to the combustion temperature with a sufficiently small electric power while flowing the exhaust gas. Therefore, while collecting the fine particles. It is possible to provide a series of filters that can be reproduced.

[0045]

EXAMPLES Example 1 Fifteen filter media were prepared in the following manner. As a heat insulating ventilation material, a commercially available heat insulating material alumina-silica fiber felt-shaped molded product having a thickness of 3 mm (composition: 45% alumina,
Silica 53%, fiber diameter: 3 μm, thermal conductivity: about 0.1
0 W / (m · ° C.), bulk density: 0.15 g / cm ³ )
Perforated plate made of SUS304 with a thickness of about 0.7 mm (diameter 1
mm holes were joined in a grid pattern at intervals of 3 mm between the centers), and the felt-shaped molded product also used a plate-shaped material having holes with a diameter of 1 mm at the same positions as the metal holes.

As a ventilation material for collection, an alumina cloth having a thickness of about 1.0 mm obtained by satin weaving alumina long fibers having a diameter of about 10 μm (display composition: alumina 99.5%, average pore diameter: about 30 μm, pores) Rate: about 65%). JI
The air permeation amount of these ventilation materials at a pressure difference of 12.7 mm water column measured according to S-L1096 is about 160 cm ³ / (cm ² · sec) for the heat insulating ventilation material and about 14 cm ³ for the collection ventilation material. It was / (cm ² · sec). As the heating element, an iron-nickel-chromium alloy linear heating element having a diameter of 1.5 mm was used.

The heat insulating vent material and the trapping vent material were each cut into a circle with a diameter of 200 mm, and the heating element was shaped so as to have a shape as shown in FIG. A filter medium as shown in FIGS. 1 and 2 was prepared. The opening was a circular hole having a diameter of 55 mm, the center of which was located 50 mm from the center of the circular filter medium. Outer diameter of 198 mm and length of 7 m between heat insulating ventilation material and collection ventilation material
m, 1mm thick SUS304 ring is placed,
The spacer provided a gap having a width of about 7 mm. Around the opening, as a shielding material, inner diameter 55 mm, thickness 1 mm,
A 12 mm long SUS304 ring was placed. Reinforce the collection ventilation material by cutting a wire mesh with a 2 mm opening made of SUS304 wire material with a diameter of 0.8 mm into a circle with a diameter of 200 mm and making contact with the downstream surface of the collection ventilation material. did.

The above ring-shaped spacer is attached to the above SU.
The S304 perforated plate and the SUS304 wire mesh are locally welded to fix the heat insulating ventilation material and the collection ventilation material. Similarly, the shielding material is also welded and fixed to the perforated plate and wire mesh. did. The heating element was made by forming a hole in the above spacer and guiding it to the gap, and sealing the periphery of the hole with an insulating material. The heating element was located in the gap almost in contact with the collecting ventilation material. Fifteen disc-shaped filter media with a diameter of 200 mm and a thickness of about 12 mm were created by rotating the position of the opening by 180 degrees in an outer cylinder with an inner diameter of 203 mm, with a front and rear spacing of 20 m.
m was fixed locally by welding, and the gap between the filter medium and the outer cylinder was sealed with a heat-resistant seal material to prepare the filter of the present invention. The heating element was introduced to the outside by making a hole in the outer cylinder, and was connected to a lead wire at a position several mm from the outer cylinder, and the periphery of the hole was sealed with an insulating material.

As a diesel engine, the displacement is 3300
cc, compression ratio 23, maximum output approx. 45 kW / 2000 rp
A horizontal water-cooled single-cylinder engine of m was operated with a load of 75%, and the exhaust gas was guided to the filter of the present invention for treatment.

Five minutes after the start of filtration, the differential pressure before and after the filter was 5.9 kPa, and the exhaust gas pollution degree (J
Smoke meter DSM-1 according to IS-D8004
(Measured with 0 type) was 44%, and the exhaust gas pollution degree at the filter outlet was 15%. If the exhaust gas is continuously treated while being guided to the filter, the differential pressure before and after the filter and the exhaust gas pollution degree at the filter outlet will gradually increase, and after 2 hours the differential pressure will be 8.8 kPa and the exhaust gas pollution at the filter outlet. The degree reached 22%. The exhaust gas pollution degree at the filter inlet at this time was 44%, which was the same as immediately after the start of filtration. The oxygen concentration in the exhaust gas was 9 to 11% by volume. Two hours and 10 minutes after the start of filtration, intermittent energization was started while introducing exhaust gas into the filter. A voltage of 24 V was applied to both ends of each heating element of the filter medium, the supply power was set to 810 watts, electricity was sequentially applied to each heating element for 3 minutes, and this state was continued for 20 hours. The differential pressure before and after the filter is 6.6-
7.8 kPa, exhaust gas pollution degree at the filter inlet is 41-
45%, exhaust gas pollution degree at the filter outlet is 16-19%
It was stable in each range.

Comparative Example 1 Fifteen filter media including a heating element and a collecting ventilation material were prepared in substantially the same manner as the filtration material prepared in Example 1 except that the heat insulating ventilation material was not used. Then, they were fixed in the outer cylinder to prepare a filter. While introducing exhaust gas of a diesel engine to the filter in the same manner as in Example 1, each heating element is electrically heated in the same manner as in Example 1,
The operation was performed for 10 hours. As a result, the exhaust gas pollution degree at the filter outlet was 37 to 45%, which was not significantly decreased.

Example 2 As a heat insulating air-permeable material, the same alumina-silica fiber molding as used in Example 1 and having a felt-like shape and having a thickness of 3 mm,
A plate-like material having a thickness of about 0.7 mm joined to a non-breathable SUS304 thin plate and provided with only one ventilation hole was used in the state shown in FIGS. 3 and 4. The collecting ventilation material has the same thickness as that used in Example 1, about 1.0 mm.
An alumina cloth was used, and the same heating element as in Example 1 was used as the heating element.

1 heat-insulating ventilation material and 1 collection ventilation material
It was cut into a rectangle of 50 mm × 180 mm and 150 mm × 200 mm, the heating element was formed into the shape shown in FIG. 3, and the parallel lines were bent at intervals of about 15 mm. In the same manner as in Example 1, a wire mesh made of SUS304 wire and having an opening of 2 mm was cut into 150 mm × 200 mm, and the wire was placed in contact with the downstream surface of the collection ventilation material to obtain the collection ventilation material. Reinforced. The outer shape is 148 mm x 198 mm, the length is 10 mm,
Using a square SUS304 ring having a wall thickness of 2 mm as a spacer, the width is obtained by locally welding the thin plate of SUS304 of the above-mentioned heat insulating ventilation material and the wire mesh made of SUS304 to the spacer in the same manner as in Example 1. A filter medium having a gap of about 10 mm was formed.

Fifteen pieces of this filter material were used, and the inside dimension was 152
It is inserted into an outer cylinder of mm × 215 mm, the positions of the openings are alternated, and the front and rear intervals are set to 20 mm, and the filter material is locally welded and fixed to the outer cylinder. The filter of the present invention was prepared by sealing with a sealing material. In this case, the opening corresponds to a gap of 150 mm × 15 mm between the collecting ventilation material, the heat insulating ventilation material and the outer cylinder, and the spacer also serves as the shielding material. The heating element was introduced to the outside by making a hole in the outer cylinder, and was connected to a lead wire at a position several mm from the outer cylinder, and the periphery of the hole was sealed with an insulating material.

In this filter, as in Example 1, 75% of a diesel engine with a displacement of 3301 cc was used.
Led exhaust gas under load. 5 minutes after the start of filtration, the differential pressure before and after the filter was 6.3 kPa, the exhaust gas pollution degree at the filter inlet was 45%, and the exhaust gas pollution degree at the filter outlet was 14%.
%Met. When the exhaust gas is continuously guided to the filter and the differential pressure is 8.3 kPa and the exhaust gas pollution degree at the filter outlet reaches 21% after 2 hours, the heating element is intermittently introduced while introducing the exhaust gas into the filter. Energization started. A voltage of 24 V was applied to both ends of each heating element of the filter medium, the supply power was set to 890 watts, and energization was sequentially performed for each heating element for 2 minutes, and this state was continued for 20 hours. The differential pressure before and after the filter during this period is 6.9-
7.1 kPa, exhaust gas pollution degree at the filter inlet is 41-
46%, exhaust gas pollution degree at the filter outlet is 15-18%
It was stable in each range.

In FIGS. 1 and 3, the linear heating element positioned between the heat insulating ventilation material and the collection ventilation material is shown by a broken line, but both are one heating element. In FIG.
The flow of exhaust gas is indicated by arrows. 1 to 5 are schematic explanatory views, and the dimensions are not in the same ratio. The respective dimensions are described in the examples.

[0057]

EFFECTS OF THE INVENTION In a filter having a structure capable of collecting and regenerating fine particles in exhaust gas of a diesel vehicle with only one series,
It is possible to provide a filter that has a high collection efficiency of fine particles and requires less electric power for electric heating.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of the configuration of a filter medium as seen from the flow direction of exhaust gas.

FIG. 2 is a schematic diagram showing an example of the configuration of a filter medium as seen from the direction perpendicular to the flow of exhaust gas.

FIG. 3 is a schematic view showing another example of the configuration of the filter medium as seen from the flow direction of exhaust gas.

FIG. 4 is a schematic view showing another example of the configuration of the filter medium as seen from the direction perpendicular to the flow of exhaust gas.

FIG. 5 is an explanatory diagram showing a flow of exhaust gas.

[Explanation of Codes] 1 ... Filtering material 2 ... Insulating ventilation material 3 ... Heating element 4 ... Collection ventilation material 5 ... Shielding material 6 ... Gap 7 ... Spacer 8 ... Partition wall 9 ... Opening 10 ... Outer cylinder 11 … Wire mesh 12… Ventilation holes

Claims (9)

[Claims] 1. A filter for collecting fine particles in exhaust gas, comprising a plurality of filter media, each of which has an opening through which at least a part of exhaust gas can flow, and is arranged along a flow path of the exhaust gas. , Each filter material has a heat insulating ventilation material, a heating element, and a collection ventilation material, and the collection ventilation material is located downstream of the heat insulation ventilation material. A filter in which a gap having a width of 50 mm or less is provided between the materials, and the heating element is located in the gap. 2. The filter according to claim 1, wherein the width of the gap is 1 to 20 mm. 3. The filter according to claim 1 or 2, wherein a shielding material that blocks the flow of exhaust gas is provided at the boundary between the gap and the opening. 4. The filter according to claim 1, wherein the heat insulating ventilation material and the collection ventilation material are made of a non-conductive material. 5. A partition wall provided in the gap portion.
The filter according to any one of 1. 6. The filter according to any one of claims 1 to 5, wherein the size of the opening provided in each filter medium is gradually reduced toward the downstream side of the exhaust gas. 7. A heat insulating ventilation material, a heating element, comprising an opening,
And using a filter in which a plurality of filtration materials having a ventilation material for collection are arranged along the flow path of the exhaust gas, the fine particles in the exhaust gas are collected, and in parallel, the fine particles collected by the heating element are heated. A method of treating exhaust gas for combustion removal, wherein in each filter material, at least a part of the exhaust gas containing fine particles passes through the opening, and the other exhaust gas passes through the heat insulating ventilation material and passes through the heat insulating ventilation material. The exhaust gas is filtered with a collection ventilation material to collect fine particles, and the heating elements of each filtration material are heated intermittently by electric current, and adhered mainly onto the collection ventilation material to collect ventilation. The fine particles collected in the gap of 50 mm or less in width between the material and the heat insulating ventilation material are heated to a combustion temperature or higher by utilizing the heat insulating properties of the collection ventilation material and the heat insulating ventilation material to burn the fine particles. The required oxygen is the exhaust gas that uses the oxygen contained in the exhaust gas. Processing method. 8. The heat generated by the heating element and the trapping ventilating material and the heat insulating material in a state where there is substantially no flow of the exhaust gas flowing along the surface of the trapping ventilating material to the opening in the gap. The method according to claim 7, wherein the heat insulating property of the aeration material is used to heat and remove the fine particles existing in the gap to a temperature equal to or higher than the combustion temperature. 9. The differential pressure before and after the filter is detected, and the frequency per unit time of intermittently energizing and heating the heating elements of the respective filter media is changed accordingly, and the differential pressure is higher when the differential pressure is higher. The method according to claim 7, wherein the frequency per unit time is increased more than when the pressure is low.