DE19821869A1 - Filter unit for removal of soot from diesel exhaust gases - Google Patents

Abstract

Exhaust gases pass through a filling of fibrous crystalline aluminum oxide, entering a first soot filtration zone (4). A second zone (5) is a separator. A third zone (6) contains catalyst and is followed by an outlet (3). Preferred Features: Fibers are directed parallel to gas flow in the first zone, and perpendicular to it in the second. Zones are formed by appropriately stacked and orientated mats. The casing is hollow and cylindrical with a passage (7) bordered by a cylindrical, perforated wall made gas-tight with the end walls (8, 9). The mats fill the entire volume between end walls. The zones are cylindrical. Catalyst is finely divided in the third zone. The assembly forms a prefabricated filter cartridge. The first end wall (8) is a detachable cover. End wall projections reach into the filling. Inlet and outlet walls are perforated sheet or woven wire. An integral unit (22) in the passage, regenerates the filter. The unit may be the internal wall, acting as an electrical resistance heater.

Description

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

Filter devices of this type are known in numerous embodiments (DE 40 33 019 A1, DE 42 44 511 A1, DE 44 47 314 A1, DE 195 05 211 A1). They are based on the knowledge that fibrous filter material, which contains approximately 65 to 95% by weight Al ₂ O ₃ with silicon dioxide (SiO ₂ ) and possibly small amounts of zirconium dioxide (ZrO ₂ ) as the remainder, is an excellent filter medium for soot-containing exhaust gases. Such a filtering material has the additional advantage that it has a high Temperaturfe stability and therefore not only for the filtration of hot exhaust gases from internal combustion engines, but also for regeneration, ie for periodic removal of the soot layers deposited on the filtering material with the help of electrical heating devices, Burners or the like is suitable.

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 simultaneously use the filter material as a carrier of oxidation and / or reduction catalysts in order to remove pollutants present in the gases, such as hydrocarbons ( HC), carbon monoxides (CO) and nitrogen oxides (NO _x ) to be oxidized or reduced by catalytic reactions and thus largely rendered harmless.

The results achieved with the known filter devices are not yet over sufficiently satisfactory. In particular, the catalytic effect leaves something to be desired. In addition, an insufficient filter effect is achieved in many cases. In particular Experiments have shown that the filter material is not sufficiently stable to the vibrations and vibrations that occur during operation (e.g. in a motor vehicle) gene is and after a relatively short period of operation to an almost dusty The mass disintegrates, as a result of which the filtering properties are practically lost.

The invention is therefore based on the object of the filter device at the beginning designated genus so that they permanently good filtering properties and has improved catalytic properties. In addition, the filter device should be better Obtain controllable filtering properties.

The characteristic features of claim 1 serve to solve this problem.

Further advantageous features of the invention emerge from the subclaims.

The invention is described below in conjunction with the accompanying drawing Embodiment explained in more detail. Show it:

Fig. 1 shows a rough schematic, partially broken open in the upper part of a longitudinal section through a filter device according to the invention and

FIG. 2 is a top view of the filter device according to FIG. 1.

According to Fig. 1, a filter device according to the invention contains a housing 1 , each having an inlet 2 and outlet 3 for the gas formed by a gas-permeable wall and including a space arranged between these two, in which there is a filling which is essentially made of crystalline There is alumina 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 separate zones 4 , 5 and 6 , which are arranged one behind the other in the direction of flow of the gas (arrow v = inflow direction, arrows w = throughflow and outflow direction) and through which the gas flows in succession. The first zone 4 in the flow direction is oriented exclusively as a soot filter. The third zone 6 is preferably used exclusively for catalyzing. The second zone 5 serves as a separation zone which prevents the third zone 6 from being loaded with soot.

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 v 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 forms the outlet 3 as a whole. 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 closes the space between the cylinder walls in a gastight manner. As a result, the space occupied by the crystalline aluminum oxide filling is hermetically sealed except for the area occupied by the entrance 2 and exit 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, is along the Whole th, formed by the entrance 2 , cylindrical inlet surface can flow radially into the housing 1 . The inlet 2 , the outlet 3 and the passage 7 preferably extend over the entire length of the housing 1 measured in the direction of the arrow v .

To achieve a good filter effect, it has proven to be advantageous to form the filling at least in the region of the first and second zones 4 and 5 from crystalline aluminum oxide with a directed fiber shape. In particular, the first zone 4 consists of a schematically indicated fiber shape 10 , which is oriented in the direction of flow of the gas (arrows w ), while the second zone 5 is made of crystalline aluminum oxide with a schematically indicated fiber shape 11 , which is essentially perpendicular to the direction of flow of the gas is arranged. This fiber orientation 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 directed predominantly parallel to the flow direction, whereas when using the same filter material but with an orientation perpendicular to the flow direction, none or only a low depth effect can be achieved, ie soot particles contained in the gas predominantly accumulate on the flow surface. As a result, good filter properties are achieved in the area of the first zone 4 , while the second zone 5 acts as a separation zone which already largely collects soot particles penetrating the first zone 4 in the area of an interface 12 between the first and second zones 4 and 5 and accordingly dimensioned thickness does not let particles through to the third zone 6 .

The filling of the filter device in the region of the first zone 4 is preferably composed of annular discs 14 stacked one above the other, which are obtained from aluminum oxide mats or plates by cutting, punching or the like, the fiber orientation in the mats or plates being substantially parallel is selected on the broad sides thereof and therefore, according to FIG. 2, also runs essentially parallel to parting planes 15 located between the individual disks 14 . In contrast, the filling in the area of the second zone 5 z. B. consist of at least one obtained from the same mat or plate, square or rectangular cutout, which is placed around the outside of the stack of disks 14 at least once in the circumferential direction and forms an envelope enclosing this.

The third zone 6 can be designed and manufactured like the second zone 5 , although the alignment is less important and a completely random direction could also be selected. In addition, 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 in finely divided form with catalytically active material, by at least on its surface, but preferably also in its catalyst material 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 which runs parallel to the interface 12 and the direction of the arrow v .

The disks 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 on the cylinder wall forming the inlet 2 , while the third zone 6 borders directly on the cylinder wall forming the outlet 3 . In order to avoid that there are 15 creepage paths for the gas to be cleaned in the region of the separating planes, in which no or only a slight filter effect is achieved, the stack of disks 14 is preferably interposed with a certain tension acting in the direction of the arrow v the end walls 8 and 9 arranged. A corresponding pre-tensioning is also expedient for the envelopes arranged in zones 5 and 6 , since otherwise undesirable creepage paths could result in the area of interfaces 17 and 18 with which the disks 14 and zones 5 and 6 on the end walls 8 and 9 limit. In order to make such leaks largely impossible, the end walls 8 and 9 according to a particularly preferred embodiment of the invention are preferably provided with annular, protruding into the filling webs 20 which keep the gas flowing in through the inlet 2 from the interfaces 17 , 18 . For the same reason, at the end of the passage 7 , at which the gas flows in, a collar 21 which extends over and covers the interface 18 is formed on the end wall 9 . A corresponding collar 21 a 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 plates or the like, which on the one hand do not increase 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 detachably connected to the housing 1 , so that the filter device can be opened at any time for inspection, maintenance 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 e.g. B. be designed so that it can be easily attached to a vehicle (car, fork lift, motor boat or the like) with a diesel engine and connected to its exhaust pipe, and if necessary an installation in a conventional silencer pot can be provided. However, it was surprisingly found that the filter device described also has such good sound-absorbing properties that a separate silencer can be omitted.

When operating the filter device described, the gas to be cleaned, for. B. the exhaust gas of a diesel engine, the open end of the passage 7 in the direction of arrow v . From there, the gas is distributed radially or perpendicular to the direction of arrow v through the perforated wall forming the entrance 2 or the like to the individual disks 14 of the first zone 4 , in which particles contained in the gas, in particular soot particles, are retained. If the gas reaches the interface 12 , the soot filtering is practically complete, which is shown in the experiment that zone 5 is only very slightly covered with soot particles and practically no soot particles also reach the interface 16 . Within zone 6 , the gas freed from interfering particles can therefore be treated catalytically. Because of the use of crystalline aluminum oxide in fiber form, a very large catalyst surface interacting with the gas is made available with simple means. Because of the separation 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 is gradually enriched with soot and thereby rendered 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 . It is also advantageous that, despite the use of a fiber-shaped filling, a mechanically stable, easy-to-manufacture filter cartridge can be created.

The regeneration of the filter device, ie the removal of the soot particles collected in zone 4 , can expediently be carried out using an ignition source 22 , for. B. a burning or heating device, which is also indicated in Fig. 1. This is preferably an electric heating coil which extends essentially over the entire position of the passage 7 , but in comparison to this has such a small cross-section that it does not hinder 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 addition, in this case the end wall 8 has an opening 23 opening into the passage 7 , through which compressed air can be introduced into the passage 7 by means of a line 24 , which enables the soot particles to be burned.

Alternatively, a separate regeneration device can be provided for the regeneration. This consists e.g. B. from a closed housing, the operating opening for inserting the complete filter device according to FIGS. 1 and 2, a compressed air inlet and outlet and the necessary monitoring elements and electrical controls. While the ignition source 22 or the combustion or heating device enables regeneration from time to time when the internal combustion engine or the like is stopped, but without disassembly, a separate regeneration device has the advantage that the filter cartridge described is completely from the vehicle having the internal combustion engine or the like. Can be removed and regenerated, while at the same time an exchangeable filter cartridge is installed in the vehicle or the like, so that it only needs to be stopped for the short time of the conversion. In addition, suitable sensors in the form of pressure gauges or the like are appropriately assigned to the filter device described, in order to be able to determine when the soot filter section of the filter device has to be regenerated, although it is alternatively also possible to carry out the regeneration periodically after a preselected period of time.

Such aluminum oxide fiber mats, which are available from Rath GmbH, D-40223 Düsseldorf, under the name "Altra Mat 80" in densities of 60 to 140 kg / m have proven to be a particularly well-suited material for zones 4 , 5 and 6 of the filling ³ and in thicknesses of approx. 12.5 mm and 25 mm. According to the corresponding data sheet, this material contains 80% by weight Al ₂ O ₃ and 20% by weight SiO ₂ , and the continuous operating temperature of the material is 1600 ° C. Surprisingly, tests have 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 adhesive could be used to additionally connect the individual disks 14 to one another in the area of the interfaces 15 or to areas 17 and 18 with the end walls 8 and 9 in the area of the interfaces.

The invention is not restricted to the exemplary embodiment described, which can be modified in many ways. In particular, the housing 1 can also consist of a hollow cylinder with a circular, other than z. B. with a square or oval cross section. However, a circular cross section has the advantage that the flow paths lying radially to the axis (arrows v ) are essentially of the same length everywhere. Furthermore, if necessary, further zones with special properties and additional partition walls consisting of perforated plates, wire nets or the like can be provided within the housing and possibly also between zones 4 , 5 and 6 , provided that they do not undesirably result in an excessive reduction the flow resistance is brought about. In addition, the housing does not have to be hollow-cylindrical as a whole, since the individual zones, even if they are arranged one behind the other in a manner other than that described, can be composed of aluminum mats stacked parallel and / or transversely to the direction of flow with a corresponding orientation. Furthermore, the third zone 6 can be designed as a one-way or reusable catalytic converter, the entire filter device should be arranged as close as possible to the diesel engine or the like generating the exhaust gas, in order to optimize the heat stored in the exhaust gas for the catalytic effect within the To be able to use Zone 6 . Finally, it goes without saying that the individual features can also be used in combinations other than those described and illustrated.

Claims (18)

1. Filter device for removing soot from soot-containing gases, in particular exhaust gases from diesel engines, with a housing ( 1 ), each having an inlet ( 2 ) and outlet ( 3 ) formed by a gas-permeable wall for the gas and one Includes the entrance ( 2 ) and the exit ( 3 ) space, 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 against 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 ) set up as a soot filter, a second zone ( 5 ) following this, designed as a separation zone and a subsequent third zone ( 6 ) set up as a catalyst, these three Zones ( 4 , 5 , 6 ) between the inlet ( 2 ) and the outlet ( 3 ) in the direction of flow ( 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 region of the first and second zones ( 4 , 5 ) made of crystalline aluminum oxide with a within the first zone ( 4 ) substantially parallel and in the second zone ( 5 ) in consists essentially of fiber shape ( 10 , 11 ) directed perpendicular to the flow direction ( w ) of the gas. 3. Filter device according to claim 2, characterized in that the three zones of Filling composed of slices stacked one on top of the other or one behind the other are made of mats with a fiber shape oriented essentially parallel to the broad sides are preserved. 4. Filter device according to one of claims 1 to 3, characterized in that the housing ( 1 ) is essentially designed as a hollow cylinder and a central passage serving as a gas feed line ( 7 ), an inner bordering the passage ( 7 ) Inlet ( 2 ) forming a cylinder wall, an outer cylinder wall surrounding the inner cylinder wall, forming the outlet ( 3 ), a first end wall ( 8 ) which closes the entire hollow cylinder in a gas-tight manner and a second annular ring which only closes the hollow cylinder in a gas-tight manner between the two cylinder walls , The passage ( 7 ) leaving the end wall ( 9 ). 5. Filter device according to claim 4, characterized in that the first zone ( 4 ) of the filling is composed of stacked, annular discs ( 14 ) 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 over the entire height of the hollow cylinder, the first zone ( 4 ) cylindrical enclosing envelope. 8. Filter device according to one of claims 5 to 7, characterized in that the third zone ( 6 ) of the filling as a corresponding to the second zone ( 5 ) formed and this cylindrical surrounding envelope and is provided in finely divided form with catalytically active material . 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 detachably connected to the housing ( 1 ) cover. 11. Filter device according to one of claims 4 to 10, characterized in that the first zone ( 4 ) of the filling directly to the inner cylinder wall, the third zone ( 6 ) of the filling directly to the outer cylinder wall and the second zone ( 5 ) Filling immediately adjacent to the first and third zones ( 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 bias 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 ) surrounding the ring, projecting into the filling or covering webs or collars ( 20 , 21 ) are provided . 14. Filter device according to one of claims 1 to 13, characterized in that the wall forming the entrance ( 3 ) and / or exit ( 4 ) consists of a wire mesh or perforated plate. 15. Filter device according to one of claims 1 to 14, characterized in that it is provided with an integrated device ( 22 ) for regeneration of the first and second zones ( 4 , 5 ) of the filling. 16. Filter device according to one of claim 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 supplying 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 ).