DE29808664U1 - Filter device for removing soot from soot-containing gases, in particular from exhaust gases from diesel engines - Google Patents

Description

DE 7519 ·.."..'·«·'-Patent Attorney

Graduate Physicist

Reinfried Frhr. &ngr;. Schorlemer

Karthäuserstr. 5A 34117 Kassel Germany

Telephone (0561) 15335

(0561)780031

Fax/Telecopter (0561)780032

Company Ing. Wolfgang Mertner Inn. Ing. Kurt Kirscht, 37318 Wahlhausen

Filter device for removing soot from soot-containing gases, especially from exhaust gases from diesel combustion engines

The invention relates to a filter device of the type specified in the preamble of claim 1.

Filter devices of this type are known in numerous designs (DE 40 33 019 Al, DE 42 44 511 Al, DE 44 47 314 Al, DE 195 05 211 Al). They are based on the knowledge that fibrous filter material containing approx. 65 to 95 wt. % Al ₂ O ₃ with silicon dioxide (SiO ₂ ) and possibly small amounts of zirconium dioxide (ZrO ₂ ) as the remainder is ideally suited as a filter medium for exhaust gases containing soot. Such a filter material has the additional advantage that it is highly temperature resistant and is therefore suitable not only for filtering hot exhaust gases from internal combustion engines, but also for regeneration, i.e. for periodically removing the soot layers deposited on the filter material with the aid of electrical heating devices, burners or the like.

In order to improve the quality of the largely soot-free gases emitted by such a filter device, it is also known from the publications cited above to use the filter material simultaneously as a carrier of oxidation and/or reduction catalysts in order to oxidize or reduce pollutants present in the gases, such as hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO _x ), by catalytic reactions and thus render them largely harmless.

The results achieved with the known filter devices are not yet sufficiently satisfactory. In particular, the catalytic effect leaves much to be desired. In addition, in many cases the filtering effect is inadequate. In particular, tests have shown that the filtering material is not sufficiently stable against the vibrations and oscillations that occur during operation (e.g. in a motor vehicle) and after a relatively short period of operation it disintegrates into an almost dust-like mass, whereby the filtering properties are practically lost.

The invention is therefore based on the object of designing the filter device of the type described at the outset in such a way that it has permanently good filtering properties and improved catalytic properties. In addition, the filter device should have better controllable filtering properties.

The characterizing features of claim 1 serve to solve this problem. 15

Further advantageous features of the invention emerge from the subclaims.

The invention is explained in more detail below in conjunction with the accompanying drawings using an exemplary embodiment. They show:
20

Fig. 1 is a roughly schematic longitudinal section, partially broken away in the upper part, through a filter device according to the invention and

Fig. 2 is a plan view of the filter device according to Fig. 1.

According to Fig. 1, a filter device according to the invention contains a housing 1, which has an inlet 2 and an outlet 3 for the gas, each formed by a gas-permeable wall, and encloses a space arranged between these two, in which there is a filling which consists essentially of crystalline aluminum oxide in fiber form. This filling serves on the one hand as a soot filter, and on the other hand as a catalyst. For this purpose, the filling contains three spatially separated zones 4, 5 and 6, which are arranged one behind the other in the flow direction of the gas (arrow γ = inflow direction, arrows w_ = flow and outflow direction) and are successively filtered by the gas.

The first zone 4 in the flow direction is designed exclusively as a soot filter. The third zone 6 is preferably used exclusively for catalysis. The second zone 5 serves as a separation zone, which prevents the third zone 6 from being loaded with soot.
5

According to a particularly preferred embodiment of the invention, the housing 1 is designed as a hollow cylinder which has a central passage 7, the axis of which runs parallel to the direction of the arrow γ and is delimited by an inner cylinder wall which as a whole forms the inlet 2 into the housing. The cylinder wall forming the inlet 2 is surrounded at a radial distance by an outer cylinder wall which as a whole forms the outlet 3. At a lower end in Fig. 1, the housing 1 is closed with a first end wall 8 which seals both the space between the two cylinder walls and the passage 7 in a gas-tight manner. At the opposite end, the housing 1 has a second, annular end wall 9. This preferably leaves the passage 7 free over its entire cross-sectional area, but seals the space between the cylinder walls in a gas-tight manner. As a result, the space occupied by the crystalline aluminum oxide filling is hermetically sealed except for the area occupied by the inlet 2 and outlet 3, whereas the passage 7 is free from the end wall 9 to the end wall 8, so that the gas supplied by means of a line (not shown) can flow radially into the housing 1 along the entire cylindrical inlet surface formed by the inlet 2. Preferably, the inlet 2, the outlet 3 and the passage 7 extend over the entire length of the housing measured in the direction of the arrow v.

In order to achieve a good filter effect, it has proven advantageous to form the filling, at least in the area of the first and second zones 4 and 5, from crystalline aluminum oxide with an aligned fiber shape. In particular, the first zone 4 consists of a schematically indicated fiber shape 10 which is aligned in the direction of flow of the gas (arrows sO), while the second zone 5 is made of crystalline aluminum oxide with a schematically indicated fiber shape 11 which is arranged essentially perpendicular to the direction of flow of the gas. This fiber alignment is based on the surprising finding that a good depth effect can be achieved in the first zone 4, especially when using a filter material which is aligned predominantly parallel to the flow direction, whereas when using

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the same filtering material, but with an alignment perpendicular to the flow direction, no or only a small depth effect can be achieved, i.e. soot particles contained in the gas mainly collect on the surface against which the flow occurs. This results in good filter properties in the area of the first zone 4, while the second zone 5 acts as a separation zone that largely collects soot particles penetrating the first zone 4 in the area of a boundary surface 12 between the first and second zones 4 and 5, and with a correspondingly dimensioned thickness does not allow any particles to pass through to the third zone.

The filling of the filter device in the area of the first zone 4 is preferably composed of ring-shaped disks 14 stacked on top of one another, which are obtained from aluminum oxide mats or plates by cutting, punching or the like, whereby the fiber orientation in the mats or plates is selected to be essentially parallel to their broad sides and therefore, according to Fig. 2, also runs essentially parallel to the separation planes 15 located between the individual disks 14. In contrast, the filling in the area of the second zone 5 can consist, for example, of at least one square or rectangular cutout obtained from the same mat or plate, which is placed at least once in the circumferential direction around the stack of disks 14 and forms an enclosure enclosing it.

The third zone 6 can be designed and manufactured like the second zone 5, although the orientation is less important and a completely random orientation could also be chosen. In addition, the zone 6 of the filling is obtained from an aluminum oxide in fiber form, which, in contrast to the material of zones 4 and 5, was previously additionally coated with catalytically active material in finely distributed form by coating it at least on its surface, but preferably also in its entire depth, with catalyst materials in the form of platinum, palladium, rhodium or the like. The third zone 6 preferably borders directly on the zone 5 along an interface 16 running parallel to the interface 12 and to the direction of the arrow v.

The panes 14 and, appropriately, also the zones 5 and 6 completely fill the space between the end walls 8 and 9. The first zone 4 preferably borders

directly to the cylinder wall forming the inlet 2, while the third zone 6 directly borders on the cylinder wall forming the outlet 3. In order to avoid creepage paths for the gas to be cleaned in the area of the separation planes 15, in which no or only a slight filtering effect is achieved, the stack of disks 14 is preferably arranged between the end walls 8 and 9 with a certain prestress acting in the direction of the arrow v. A corresponding prestress is also expedient for the casings arranged in zones 5 and 6, since otherwise undesirable creepage paths could arise in the area of interfaces 17 and 18, respectively, with which the disks 14 and zones 5 and 6 border on the end walls 8 and 9. In order to make such leaks largely impossible, the end walls 8 and 9 are provided with preferably annular webs 20 protruding into the filling, according to a particularly preferred embodiment of the invention, which keep the gas flowing in through the inlet 2 away from the boundary surfaces 17, 18. For the same reason, at the end of the passage 7 where the gas flows in, a collar 21 extending over the boundary surface 18 and covering it is formed on the end wall 9. A corresponding collar 21a is formed on the end wall 8.

The gas-permeable cylinder walls forming the inlet 2 and the outlet 3 are preferably designed as wire mesh, perforated sheets or the like, which on the one hand do not cause an increase in the flow resistance, and on the other hand hold the filling firmly within the housing 1. At least one of the end walls 8, 9 is preferably designed as a cover that is detachably connected to the housing 1 so that the filter device can be opened at any time for inspection, warning and control purposes. In addition, the filter device described is expediently designed as a completely prefabricated filter cartridge that can be handled and transported as a whole. This filter cartridge can, for example, be designed so that it can be easily attached to a vehicle (car, forklift, motorboat or the like) with a diesel engine and connected to its exhaust pipe, whereby installation in a conventional silencer pot can also be provided if required. However, it was surprisingly found that the filter device described also has such good sound-insulating properties that a separate silencer is no longer necessary.

When operating the described filter device, the gas to be cleaned, e.g.

Exhaust gas from a diesel internal combustion engine is fed to the open end of the passage 7 in the direction of the arrow v. From there, the gas is distributed radially or perpendicularly to the direction of the arrow v through the perforated wall or the like forming the inlet 2 onto the individual disks 14 of the first zone 4, in which particles contained in the gas, in particular soot particles, are retained. When the gas reaches the interface 12, the soot filtration is practically complete, which is shown in the test by the fact that zone 5 is only very slightly covered with soot particles and practically no soot particles reach the interface 16. Within zone 6, the gas freed of disruptive particles can therefore be treated catalytically. Due to the use of crystalline aluminum oxide in fiber form, a very large catalyst surface that interacts with the gas is made available using simple means. Because of the separating effect brought about by zone 5, despite the spatial series connection of the soot filter section and the catalyst section within the same housing 1, it can be avoided that the catalyst zone gradually becomes enriched with soot and thus becomes unusable. This applies even if the actual filtering zone 4 is composed of the disks 14 and it cannot be ruled out that numerous soot particles also migrate through the interfaces 15 and reach the interface 12. Another advantage is that despite the use of a fiber-form filling, a mechanically stable, easy-to-manufacture filter cartridge can be created.

The regeneration of the filter device, i.e. the removal of the soot particles accumulated in zone 4, can be carried out expediently with an ignition source 22, e.g. a combustion or heating device, which is additionally indicated in Fig. 1. This is preferably an electric heating coil which extends essentially over the entire length of the passage 7, but has such a small cross-section compared to the latter that it does not impede the flow of the supplied gas. According to a particularly preferred embodiment, the inner cylinder wall of the housing 1 could also be designed as a resistance heating element. In this case, the end wall 8 also has an opening 23 leading into the passage 7, through which compressed air can be introduced into the passage 7 by means of a line 24, which enables the combustion of the soot particles.

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Alternatively, a separate regeneration device can be provided for the regeneration. This consists, for example, of a closed housing which has an operating opening for inserting the complete filter device according to Fig. 1 and 2, a compressed air inlet and outlet and the necessary monitoring elements and electrical controls. While the ignition source 22 or combustion or heating device enables regeneration to take place from time to time when the internal combustion engine or the like is shut down, but without dismantling, a separate regeneration device has the advantage that the described filter cartridge can be completely removed from the vehicle or the like containing the internal combustion engine and regenerated, while at the same time a replaceable filter cartridge is installed in the vehicle or the like, so that it only needs to be shut down for the short time of the conversion. Furthermore, suitable sensors in the form of manometers or the like are suitably assigned to the described filter device in order to be able to determine when the soot filter section of the filter device must be regenerated, although it is alternatively also possible to always carry out the regeneration periodically after a preselected period of time has elapsed.

Aluminium oxide fibre mats have proven to be particularly suitable for zones 4, 5 and 6 of the filling. These are offered by Rath GmbH, D-40223 Düsseldorf, under the name "Altra Mat 80" in densities of 60 to 140 kg/m ³ and in thicknesses of approx. 12.5 mm and 25 mm. According to the associated data sheet, this material contains 80 wt. % Al ₂ O ₃ and 20 wt. % SiO ₂ , and the continuous operating temperature of the material is 1600 ⁰ C. Tests have surprisingly shown that this material is also extremely stable mechanically and does not disintegrate or crumble even during continuous operation. In contrast, the housing 1 or the cylinder walls and end walls are preferably made of high-temperature-resistant stainless steel. In addition, high-temperature-resistant adhesives could be used to additionally firmly connect the individual panes 14 to one another in the area of the interfaces 15 or to the end walls 8 and 9 in the area of the interfaces 17 and 18.

The invention is not limited to the described embodiment, which can be modified in many ways. In particular, the housing 1 can also consist of a hollow cylinder with a cross-section other than circular, in particular, for example, with a square or oval cross-section. A circular cross-section brings

However, this has the advantage that the flow paths lying radially to the axis (arrows v) are essentially the same length everywhere. Furthermore, if required, further zones with special properties and additional partition walls made of perforated sheets, wire mesh or similar can be provided within the housing and possibly also between zones 4, 5 and 6, provided that they do not undesirably lead to an excessive reduction in the flow resistance. In addition, the housing does not have to be hollow-cylindrical as a whole, since the individual zones can be composed of aluminum oxide fiber mats stacked parallel and/or transversely to the flow direction with the appropriate orientation, even if they are arranged one behind the other in a manner other than that described. Furthermore, the third zone 6 can be designed as a one-way or multi-way catalyst as required, whereby the entire filter device should be arranged as close as possible to the diesel engine or similar that generates the exhaust gas in order to be able to optimally utilize the heat stored in the exhaust gas for the catalytic effect within zone 6.

Finally, it is understood that the individual features can also be used in combinations other than those described and shown.

Claims (18)

fc · f -9- Claims 1. Filter device for removing soot from soot-containing gases, in particular exhaust gases from diesel internal combustion engines, with a housing (1) which has an inlet (2) and outlet (3) for the gas, each formed by a gas-permeable wall, and encloses a space bordering the inlet (2) and the outlet (3), in which there is a filling of fibers containing aluminum oxide, which is designed on the one hand as a soot filter, on the other hand as a catalyst for hydrocarbons, carbon monoxide and/or nitrogen oxides, characterized in that the filling consists of crystalline aluminum oxide in fiber form and contains a first zone (4) designed as a soot filter, a second zone (5) following this and designed as a separation zone, and a third zone (6) following this and designed as a catalyst, these three zones (4, 5, 6) being located between the inlet (2) and the outlet (3) in the flow direction (w) of the gas are arranged one behind the other. 2. Filter device according to claim 1, characterized in that the filling at least in the area of the first and second zones (4, 5) consists of crystalline aluminum oxide with a fiber shape (10, 11) directed essentially parallel to the flow direction (w) of the gas within the first zone (4) and essentially perpendicular to the flow direction (w) of the gas in the second zone (5). 3. Filter device according to claim 2, characterized in that the three zones of the filling are composed of discs stacked one above the other or one behind the other, which are obtained from mats with a fiber shape directed essentially parallel to the broad sides. 4. Filter device according to one of claims 1 to 3, characterized in that the housing (1) is designed essentially as a hollow cylinder and has a central passage (T) serving as a gas supply line, an inner cylinder wall bordering the passage (T) and forming the inlet (2), an outer cylinder wall surrounding the inner cylinder wall and forming the outlet (3), a first end wall (8) which seals the entire hollow cylinder in a gas-tight manner and a second annular end wall (9) which seals the hollow cylinder in a gas-tight manner only between the two cylinder walls and leaves the passage (T) free. 5. Filter device according to claim 4, characterized in that the first zone (4) of the filling is composed of annular disks (14) stacked one above the other, which are obtained from fiber mats. 6. Filter device according to claim 5, characterized in that the discs (14) fill the entire space between the two end walls (8, 9). 7. Filter device according to one of claims 4 to 6, characterized in that the second zone (5) of the filling consists of at least one casing extending over the entire height of the hollow cylinder and cylindrically enclosing the first zone (4). 8. Filter device according to one of claims 5 to 7, characterized in that the third zone (6) of the filling is designed as a casing corresponding to the second zone (5) and cylindrically enclosing the latter and is provided with catalytically active material in finely distributed form. 9. Filter device according to one of claims 1 to 8, characterized in that it is designed as a completely prefabricated filter cartridge. 10. Filter device according to one of claims 4 to 9, characterized in that the first end wall (8) is designed as a cover detachably connected to the housing (1). 11. Filter device according to one of claims 4 to 10, characterized in that the first zone (4) of the filling directly borders on the inner cylinder wall, the third zone (6) of the filling directly borders on the outer cylinder wall and the second zone (5) of the filling directly borders on the first and the third zone (4, 6). 12. Filter device according to one of claims 5 to 11, characterized in that at least one of the three zones (4, 5, 6) is arranged with a preselected prestress between the two end walls (8, 9). 13. Filter device according to one of claims 4 to 12, characterized in that the end walls (8, 9) with the passage (7) annularly surrounding, projecting into the filling -11-
or are provided with webs or collars (20, 21) covering them. 14. Filter device according to one of claims 1 to 13, characterized in that the wall forming the inlet (3) and/or outlet (4) consists of a wire mesh or perforated sheet. 15. Filter device according to one of claims 1 to 14, characterized in that it is provided with an integrated device (22) for regenerating the first and second zones (4, 5) of the filling. 16. Filter device according to one of claims 15, characterized in that the device (22) is arranged in the passage (7) of the hollow cylinder. 17. Filter device according to one of claims 15 or 16, characterized in that the first end wall (8) has an opening (23) opening into the passage (7) and intended for the supply of compressed air. 18. Filter device according to one of claims 15 to 17, characterized in that the inner cylinder wall is designed as a resistance heating element of the device (22).