JP2006102636A - Diesel exhaust emission treatment apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diesel exhaust emission treatment apparatus using a diesel particulate filter of high temporal durability. <P>SOLUTION: The diesel exhaust emission treatment apparatus comprises a molded body which makes the base unit of a pair of a porous flat plate and a porous corrugated plate carrying an oxidation catalyst, and is laminated so that corrugated plate ridgelines of the porous corrugated plate may cross alternately with a side surface perpendicular to the corrugated plate ridgeline of the molded body sealed, and an inflow path and an outflow path of the exhaust gas respectively defined between the porous corrugated plates via the porous flat plate, and is characterized in that an average value of gas circulation resistance in the exhaust gas inflow path is to be lower than that in the exhaust gas outflow path. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a diesel exhaust gas treatment device, and more particularly to a diesel exhaust gas treatment device that removes dust, PM (Particulate Matter, particulate matter), and NOx (nitrogen oxide) in exhaust gas discharged from a diesel engine. .

As a conventional diesel exhaust gas treatment method, as shown in Patent Document 1, particles present in exhaust gas of a diesel engine are filtered, and the particles are trapped on the porous wall surface from the gas flowing through the element. A filter having a high temperature resistant filter element having a porous wall to collect and having a catalyst comprising a mixture of a platinum group metal and an alkaline earth metal oxide on the surface of the wall to reduce the temperature at which particle combustion begins. The equipment used is described. This apparatus using a so-called combustion catalyst uses porous ceramics for the filter, so that the dust in the exhaust gas is collected on the porous wall surface, and the exhaust gas is collected while passing through the porous wall surface. Soot is combusted on the porous wall in the presence of a combustion catalyst. Soot is composed mainly of organic compounds such as carbon.
Normally, the oxidation reaction of carbon proceeds as shown in the formula (1) in a high temperature region of 500 ° C. or higher, but the exhaust gas of a diesel engine is at most about 500 ° C., usually around 400 ° C. Without the heat source, the temperature required for the reaction is not reached.

C + O ₂ → CO ₂ (1)
Therefore, by supporting the catalyst using the platinum group metal or the like on a filter, the reaction temperature can be suppressed to about 350 ° C., and a continuous regeneration operation can be performed while collecting and burning dust without an additional heat source.

Further, Patent Document 2 discloses that a gas containing nitrogen dioxide NO ₂ is first passed through a diesel exhaust gas containing nitrogen monoxide NO over a catalyst to convert NO into NO ₂ , and then the nitrogen dioxide NO ₂ is filtered. A diesel exhaust particulate removal method is described in which the particulates removed above are reacted to burn and remove the particulates.

That is, in this method, an oxidation catalyst is placed upstream of the filter to convert NO in the exhaust gas into NO ₂ in advance, and let this burn and react with the dust collected by the filter to remove the dust and NO ₂ . It is what.
However, the above conventional method has the following problems.
First, in the method of Patent Document 1, the dust in the exhaust gas is collected by a filter, and the filter carries an oxidation catalyst. With this oxidation catalyst, the NO in the exhaust gas is expressed by the equation (2). It is oxidized to NO _2.

NO + 1 / 2O ₂ → NO ₂ (2)
This NO ₂ reacts with the dust (main component: carbon) collected by the filter as shown in the formulas (3) and (4) to oxidize and burn the dust.

C (dust) + 2NO ₂ → CO ₂ + 2NO (3)
C (dust) + NO ₂ → CO + NO… (4)
However, normal engine oil contains about 1 to 2 wt% of ash due to the metal additive, and reacts with sulfur in the fuel to form ash mainly composed of CaSO ₄ . This ash coats the surface of the oxidation catalyst to reduce the catalytic activity. For this reason, the ceramic filter carrying the oxidation catalyst shown in Patent Document 1 has a reduced catalytic activity after a certain period of time and dust is burned. However, there was a problem that it was blocked.

Also in the method of Patent Document 2, since the oxidation catalyst is arranged on the upstream side with much dust, it is considered that ash accumulates on the surface of the oxidation catalyst and clogs with time, and the oxidation performance is lowered. Also, ash accumulates on the filter, which eventually increases the filter pressure loss.
Japanese Examined Patent Publication No. 7-106290 Japanese Patent No. 3012249

  An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a diesel exhaust gas treatment apparatus using a diesel particulate filter having high durability over time.

In order to achieve the above object, the invention claimed in the present application is as follows.
(1) having a molded body in which a pair of a porous corrugated plate and a porous flat plate carrying an oxidation catalyst is a basic unit, and the corrugated ridgelines of the porous corrugated plate are alternately crossed, An exhaust gas treatment apparatus in which a side surface orthogonal to the corrugated plate ridge line of the formed body is sealed, and an exhaust gas inflow path and an outflow path are formed between the porous corrugated plate and the porous corrugated plate, respectively. A diesel exhaust gas treatment apparatus, wherein an average value of gas flow resistance in the exhaust gas inflow path is set lower than an average value of gas flow resistance in the exhaust gas outflow path.
(2) The apparatus according to (1), wherein an opening size of the corrugated plate in the exhaust gas inflow path is larger than that in the exhaust gas outflow path.

(3) The exhaust gas inflow path is formed by stacking two or more corrugated plates having different opening sizes so that an opening ratio of the exhaust gas inflow path entrance is as large as possible ( The apparatus according to 1) or (2).
(4) The apparatus according to any one of (1) to (3), wherein the length of the corrugated plate in the exhaust gas inflow path is shorter than that in the exhaust gas outflow path.

(5) The device according to any one of (1) to (4), wherein the porosity of the flat plate on the gas upstream side is smaller than the porosity on the gas downstream side.
(6) The apparatus according to any one of (1) to (5), wherein a rectifier is provided in the vicinity of the upstream side of the corrugated plate orthogonal to the gas inlet path of the intersecting honeycomb body.
(7) Increase the amount of catalyst supported on the corrugated plate opened in the gas inlet path of the intersecting honeycomb body, and decrease the amount of catalyst supported on the corrugated plate and / or flat plate orthogonal thereto, or avoid supporting it. The device according to any one of (1) to (6), wherein

(1) According to the invention, when the unburned dust is accumulated under low temperature conditions, and the ash such as CaSO ₄ generated by combustion is accumulated, the other end of the corrugated plate having a large mesh size is opened. Thus, accumulated dust and ash such as CaSO ₄ generated by combustion can be removed, and stable operation can be performed without increasing the filter differential pressure. Further, when a corrugated plate with a large opening is used on the gas inlet side, the time for clogging with accumulated dust is extended, and it becomes easy to remove the dust and ash, thereby improving the life.
(2) If the corrugated plates of the exhaust gas inflow path are stacked by combining two or more corrugated plates and flat plates with different mesh sizes, and the combination of corrugated plates is selected so that the opening ratio of the inlet of the exhaust gas inflow path becomes large In addition to the above-described effects, dust collision and accumulation in the exhaust gas inflow path can be reduced.

(3) By combining corrugated sheets with small openings, the strength of the crossed honeycomb body can be improved and deformation can be prevented. Further, the strength of the crossed honeycomb body can be further improved by using a corrugated plate, a flat plate, a porous plate, or a porous plate in which pores of the porous plate are closed at the end.
(4) By distributing the porosity of the flat plate sandwiched between the corrugated plates, reducing the porosity of the gas upstream portion and increasing the porosity in the downstream portion, the exhaust gas circulated from the center to the downstream portion of the filter. After that, it becomes filtered and the burning rate of soot and dust is improved.
(5) If a rectifying plate is placed in the gas inflow portion, it is possible to prevent dust from adhering and accumulating on the cross-sectional portions of the corrugated plates arranged orthogonally.

  The molded body on which the oxidation catalyst is supported in the present invention is a product in which a pair of porous corrugated plate and porous flat plate is a basic unit and is laminated so that corrugated ridge lines of the porous corrugated plate alternately intersect, The exhaust gas treatment apparatus of the present invention seals the side surface orthogonal to the corrugated ridge line of such a shape, and provides an exhaust gas inflow path and an outflow path between the porous flat plate and the porous corrugated sheet, respectively. It forms and processes exhaust gas. As the corrugated plate and flat plate material, a thin filter material such as porous ceramic paper is preferably used.

Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is an explanatory view of a crossed honeycomb body carrying a catalyst used in the exhaust gas treatment apparatus of the present invention. This filter is formed by laminating the flat plate 3, the corrugated plate 1, the flat plate 3, the corrugated plate 2, the flat plate 3, and the corrugated plate 1 in this order, and the dust in the exhaust gas emitted from the diesel engine is collected by the filter. An oxidation catalyst is supported on at least a part of these flat plate and corrugated plate, and NO in the exhaust gas is oxidized into NO ₂ as represented by the equation (2) by the action of the oxidation catalyst.

NO + 1 / 2O ₂ → NO ₂ (2)
This NO ₂ reacts with the dust (main component: carbon) collected by the filter 2 as shown in the formula (3) to burn the dust.

C (dust) + 2NO ₂ → CO ₂ + 2NO (3)
At this time, the opening surface of the corrugated plate 2 is laminated so as to be orthogonal to the opening surface of the corrugated plate 1, and the exhaust gas containing the dust flows from the opening surface A of the corrugated plate 2, but the facing surface (crossing) If the side surface A ′ of the honeycomb body is closed by a valve or the like (not shown) so that no gas flows, the exhaust gas passes through the porous flat plate 3 joined to the corrugated plate 2 as indicated by the dotted line, and the corrugated plate 1 Are discharged from the opening surfaces B and B ′ between the flat plate 3 and the flat plate 3 and the opposite surfaces (other side surfaces of the intersecting honeycomb body) (not shown). When the exhaust gas passes through the flat plate 3, the dust collected on the surface of the flat plate 3 is combusted according to the above equation (3).

  An oxidation catalyst is supported on the cross honeycomb body used in the present invention. In particular, the catalyst is required for the corrugated plate 2 and the flat plate 3 corresponding to the upstream side, and it is necessary to support a large amount of catalyst on the flat plate 1 corresponding to the outlet side. Absent. When the corrugated plate 2 and the flat plate 3 are produced, an oxidation catalyst is supported on the corrugated plate 2 and a flat plate 1 (low oxidation catalyst supported or non-supported) is laminated to produce a honeycomb body. An intersecting honeycomb body carrying a catalyst component can be produced. By this method, the amount of catalyst supported on the corrugated plate opened in the gas inlet path of the intersecting honeycomb body is increased, and the amount of catalyst supported on the corrugated plate and / or flat plate orthogonal thereto is relatively decreased or not supported. It is possible to manufacture the exhaust gas treatment device.

  In the embodiment shown in FIG. 1, the opening size of the corrugated plate 2 forming the surface A on the inlet side of the exhaust gas (the bottom side a2 of the corrugated mountain shown in FIG. 1-b, the height b2 of the mountain), and the corrugated plate 1 Are arranged such that there is a relationship of a1 ≦ a2 and b1 ≦ b2 between the sizes (a1, b1 shown in FIG. 1-a). For example, a1 = 3.3mm, b1 = 1.9mm, a2 = 3.7mm, b2 = 2.5mm, etc. can be shown, but a1 <a2 and b1 = b2, or a1 = a2 and b1 <b2 . After all, in order to make the opening size of the corrugated plate 2 on the gas inlet side large and the opening size of the corrugated plate 1 on the outlet side small, (a1 × b1) <(a2 × b2) do it. If the mesh size is excessively increased, the strength of the honeycomb body is lowered. Therefore, it is desirable to select appropriately according to the back pressure of the exhaust gas.

  By using the cross honeycomb body as shown in FIG. 1, even if unburned dust is deposited on the corrugated sheet 2 at a low load or low temperature, the opening time is large, so the time until the plug is closed can be lengthened and the durability can be increased. improves. This is the same effect even if the size of the openings of the corrugated plates 1 and 2 is equal to a certain value or more, but it is more effective to increase only the opening size of the path on the inflow side of the exhaust gas. . The accumulated dust is burned away when the temperature is raised, and the differential pressure returns to a steady value. Since the flow resistance to the gas flowing from the A plane to the A ′ plane in FIG. 1 is smaller than the flow resistance to the gas in the direction penetrating from the A plane to the B and B ′ planes, accumulated dust and ash are discharged. In this case, it is not necessary to close the B and B ′ surfaces (and the opposing surfaces), and by opening only the A ′ surface, the gas flow in the AA ′ direction becomes dominant. 'A means (such as a closing valve) for closing the gas flow path to the surface becomes unnecessary. Therefore, not only the accumulated ash can be easily discharged, but also quick performance recovery can be achieved.

  Further, since the corrugated plate 1 arranged so as to intersect with the corrugated plate 2 is oriented perpendicularly to the gas flow direction, the exhaust gas containing the dust partly collides with the corrugated plate 1 and the dust on the corrugated plate 1 In this honeycomb body, since the opening size of the corrugated plate 1 is large and the thickness is thin, the aperture ratio of the A surface is high and the collision probability is low. It becomes difficult to deposit.

  FIG. 1-c shows the honeycomb body as viewed from the gas inlet surface A. The honeycomb (a) in which the corrugated plates 1a are alternately stacked and the honeycomb in which the corrugated plates 1b having a larger mesh size are stacked ( In b), the aperture ratio of the gas inlet surface A (the value obtained by dividing the opening area of the corrugated plate 2 by the area of the inlet surface A) is not changed to 0.5, and the dust collision rate does not change greatly. However, the honeycomb (c) laminated with the corrugated sheet 1a with the corrugated sheet 1b with the larger opening size facing the gas inlet surface A side has an aperture ratio of 0.6 and larger than (a) and (b).・ Since accumulation is suppressed, it is more desirable that the differential pressure does not increase easily.

  It has been found that when the size of the openings of the corrugated plates 1 and 2 exceeds a certain value, the strength of the honeycomb body is greatly reduced. This is because when the opening size of the corrugated plate portion is large, the number of contact points with the flat plate 3 is reduced and the strength is lowered, and there is a problem that it is difficult to handle the product. In this embodiment, since the corrugated sheet 1 having a small mesh is sandwiched, the strength of the present honeycomb body is ensured.

  FIG. 2 is an explanatory view of a crossed honeycomb body showing another embodiment of the present invention. The difference from FIG. 1 of this embodiment is that the opening size of the corrugated sheet 2 forming the surface A on the inlet side of the exhaust gas (the corrugated crest peak a2 and the crest height b2 shown in FIG. 2-b) Regardless of the corrugated plate 1 size (a1, b1 shown in FIG. 2-a), the length LA of the corrugated plate 2 in the gas flow direction is made smaller than the length LB in the width direction, This is to reduce the flow resistance of gas in the route.

  According to the embodiment of FIG. 2, the flow resistance to the gas flowing from the A plane to the A ′ plane is smaller than the flow resistance to the gas in the direction penetrating from the A plane to the B and B ′ planes. When discharging soot and ash, it is not necessary to close the B and B 'surfaces (and their opposite surfaces), and only the A' surface is opened, and the gas flow in the AA 'direction is dominant. Therefore, means (such as a closing valve) for closing the gas flow path to the surfaces B and B ′ is not necessary. Further, since the corrugated sheet 1 having a small mesh is stacked between the corrugated sheets 2 having a large mesh, effects such as easy maintenance of the strength of the honeycomb body can be obtained.

  Further, FIG. 3 is an explanatory view of a crossed honeycomb body showing another embodiment of the present invention, in which the opening size of the corrugated sheets 1 and 2 and the length of the corrugated sheets 1 and 2 are changed, and the corrugated sheet 2 The gas flow resistance in the direction of is made smaller than the flow resistance when penetrating the flat plate 3, and the same effect as the embodiment of FIGS. 1 and 2 can be obtained.

FIG. 4 shows a similar embodiment of the present invention, in which the porosity of the flat plate 3 sandwiched between the corrugated plates 1 and 2 is made smaller on the upstream side and larger on the downstream side. For example, it can be produced by supporting a large amount of small particle size powder such as TiO ₂ on the upstream side of the porous flat plate and decreasing the amount of powder supported toward the downstream side. As the loading method, various methods are conceivable, such as applying the powder directly, or applying it in the form of a slurry, suspension, solution, paste or the like with some solvent added.

According to the embodiment of FIG. 4, prevents the dust is closed at the inlet portion, and after the exhaust gas has flowed to the central-downstream portion of the filter, since to be filtered, by the activity of the oxidation catalyst, NO ₂ Is produced in a sufficient amount, so that the combustion of the dust is promoted and the combustion rate of the dust is improved.

  FIG. 5 shows still another embodiment of the present invention. In order to increase the strength of the intersecting honeycomb body, a flat plate, a porous plate, and a porous plate in which pores of the porous plate are closed are used. A laminate having a thickness of ˜50 mm, or a laminate having the thickness. The crossed honeycomb body has four opening surfaces through which exhaust gas flows in and out, and the remaining two surfaces hold the present honeycomb body. As shown in FIG. A plate or hard plate 4 is laminated to increase its strength. At this time, when a corrugated plate is used, it is desirable to laminate so that a material with a small mesh is at the end as shown in FIG. In FIG. 7, the thicknesses that are different in thickness by several levels are made smaller toward the end, but only one type of corrugated plate, flat plate, porous plate, or the like having a small opening may be laminated. By reinforcing the cross honeycomb body in this way, the end portion is not deformed by heat in use, contact with dust, etc., and the strength can be increased.

  Further, as shown in FIG. 8, rectifying means such as a flat plate 6 or a triangular rectifying plate 7 is arranged upstream of the non-opening portion of the entrance face of the crossed honeycomb body to deposit dust in the non-opening portion. It is desirable to prevent. The shape of the rectifying means is not limited to a triangle and a flat plate, and any shape can be used as long as dust can be prevented from adhering. By providing the flat plate 6 or the rectifying plate 7, it is possible to prevent dust from adhering to the non-opening particularly during low temperature operation, and to suppress an increase in the differential pressure of the honeycomb body. In addition, it is more desirable to support the oxidation catalyst at a high concentration on the flat plate 6 or the rectifying plate 7 because the oxidation function of the dust is enhanced on the upstream side of the exhaust gas.

Explanatory drawing of the crossing honeycomb body used for the Example of this invention. Explanatory drawing of the crossing honeycomb body used for the other Example of this invention. Explanatory drawing of the crossing honeycomb body used for the other Example of this invention. Explanatory drawing of the crossing honeycomb body used for the other Example of this invention. Explanatory drawing of the crossing honeycomb body used for the other Example of this invention. FIG. 6 is a side view of the cross honeycomb body shown in FIG. 5. Explanatory drawing which shows the example of arrangement | positioning of the flat plate used for reinforcement | strengthening of a cross honeycomb body, a corrugated sheet, or a porous board. Explanatory drawing which has arrange | positioned the baffle plate etc. in the crossing honeycomb body.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Corrugated board, 2 ... Corrugated board, 3 ... Flat plate, 4 ... Corrugated board, porous board or hard board, 5 ... Corrugated board, 6 ... Flat plate, 7 ... Rectification board.

Claims (7)

A molded body having a pair of a porous corrugated sheet and a porous flat sheet carrying an oxidation catalyst as a basic unit, and laminated so that corrugated ridge lines of the porous corrugated sheet alternately intersect, An exhaust gas treatment apparatus in which a side surface orthogonal to the corrugated ridge line is sealed, and an exhaust gas inflow path and an outflow path are formed between the porous flat plate and the porous corrugated sheet, respectively, A diesel exhaust gas treatment apparatus, characterized in that an average value of gas flow resistance in the path is lower than an average value of gas flow resistance in the exhaust gas outflow path. The apparatus according to claim 1, wherein an opening size of the corrugated plate in the exhaust gas inflow path is larger than that in the exhaust gas outflow path. 2. The exhaust gas inflow path is formed by laminating two or more corrugated plates having different mesh sizes so that an opening ratio of the exhaust gas inflow path entrance is as large as possible. 2. The apparatus according to 2. The apparatus according to any one of claims 1 to 3, wherein the length of the corrugated plate in the exhaust gas inflow path is shorter than that in the exhaust gas outflow path. The apparatus according to any one of claims 1 to 4, wherein a porosity of a gas upstream side of the flat plate is made smaller than a porosity of a gas downstream side. The apparatus according to any one of claims 1 to 5, further comprising a rectifying means in the vicinity of the upstream side of the corrugated plate orthogonal to the gas inlet path of the intersecting honeycomb body. The amount of catalyst supported on the corrugated plate opened in the gas inlet path of the crossed honeycomb body is increased, and the amount of catalyst supported on the corrugated plate and / or flat plate perpendicular thereto is reduced or not supported. 7. A device according to claim 1, characterized in that it is characterized in that

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