WO2006125516A1

WO2006125516A1 - Highly effective non-clogging filter unit

Info

Publication number: WO2006125516A1
Application number: PCT/EP2006/004253
Authority: WO
Inventors: Martin Votsmeier; Jürgen GIESHOFF; Thomas Kreuzer
Original assignee: Umicore Ag & Co. Kg
Priority date: 2005-05-21
Filing date: 2006-05-06
Publication date: 2006-11-30
Also published as: DE102005023518B4; JP2008540933A; EP1902202A1; DE102005023518A1

Abstract

According to the invention, the exhaust gas of a diesel engine is directed via at least two serially arranged filter units (I, II) in order to eliminate soot from the exhaust gas. Each filter unit comprises a filter element with a parallel connection (4) which the exhaust gas can penetrate without being filtered. The parallel connections (4, 5) of two successive filter elements are joined to each other by means of a direct, non-clogging flow path. The parallel connections (4, 5) of the successive filter elements (2, 3) are flowingly disposed relative to each other such that the exhaust gas is largely prevented from penetrating directly from one parallel connection into the parallel connection of the successive filter unit, thus ensuring a great total filter efficiency while the counterpressure of the exhaust gas is comparable to conventional filter systems in spite of the parallel connections (4, 5) in the individual filter units. The parallel connections in the filter units ensure emergency operation at a still admissible counterpressure of the exhaust gas in case active or passive filter regeneration fails.

Description

Blockage-free filter unit with high efficiency

description

The invention relates to a blockage-free filter unit for removing soot from the exhaust gas of diesel engines.

Exhaust systems with a particle filter are known. A problem with the operation of particle filters is the increase of the exhaust gas backpressure due to the soot already deposited in the filter. In the worst case, the back pressure can rise so high that it comes to a standstill of the engine. Conventional soot filters must therefore be regenerated from time to time, that is, the soot deposited on them must be burned. With a high soot loading, the combustion heat of the soot can destroy the filter. Regular regeneration prevents this.

Soot burns only at temperatures of about 600 ° C. Although the ignition temperature of the soot can be reduced by the use of catalytically active fuel additives or by catalytic coating of the filter to about 400 ⁰ C, but even with catalytic activation, the ignition temperature of the soot is achieved only in certain operating conditions of the engine. To exclude a blockage of the filter, the soot load of the filter must be monitored consuming by the engine control and, if necessary, a filter regeneration can be initiated by an active increase in the exhaust gas temperature. This active filter regeneration inevitably requires increased fuel consumption. The amount of fuel to be expended for the regeneration measures is additionally increased by the uncertainty in the calculation of the filter load and the necessary safety reserves.

The exhaust systems of older diesel vehicles are often retrofitted with a particulate filter. Since these vehicles are unable to actively regenerate the retrofitted filter, only passive regeneration remains under high load, high exhaust gas temperature operating conditions. Since these operating conditions only from

Case after case occur and partly even over longer periods can completely fail, the retrofit filter must ensure a clog-free operation even with long time passive regeneration passive.

The risk of filter clogging can be avoided by a so-called open filter system. Here is next to the flow path through the filter medium another flow path provided (shunt), which bypasses the filter medium. With increasing soot loading of the filter, the back pressure of the filter increases in comparison to the shunt; a greater portion of the total flow shifts to the shunt and the further increase in filter loading is slowed. In this way, excessive loading of the filter and thus destruction of the filter due to excessive temperatures during regeneration is prevented. Even with complete blockage of the filter material, the exhaust gas can still flow through the shunt, a blockage of the entire system is not possible.

From the literature, a large number of different embodiments of open filter systems is known. An example of an open filter is the German one

Laid-open specification DE 100 44 893 A1. This document describes a particle filter for

Exhaust gas purification of a diesel internal combustion engine with an inside of the filter in

Longitudinally arranged shunt. In this case, the opening of the shunt is arranged at a location of the front end face of the particle filter, which is not or only slightly flowed through by the particle-laden exhaust gas. A similar arrangement is also described in European published patent application EP 0 879 938 A2.

Another example of an open filter system is the European patent application EP 1 219 794 Al. It describes a Wandflußfilter with mutually closed flow channels. To ensure clog-free operation, some of the shutters are partially open so that the affected flow channels allow free passage of the exhaust gas. The use of individual open channels as a shunt in an open filter system is also described in US Pat. No. 4,464,185.

The main disadvantage of the above-described open filter systems lies in the fact that in these systems exhaust gas escapes unfiltered into the environment even during normal operation. With these filter systems, therefore, often the desired filtering effect can not be guaranteed.

Accordingly, there remains a need for a filtration system that allows for clog-free operation without active regeneration and with good filtration efficiency.

The solution of this problem is inventively by the series connection of several filter elements with suitably arranged shunts for the exhaust gas, wherein the shunts form a blockage-free flow path for the exhaust gas in the event of blockage of the filters by soot.

The use of a plurality of cascaded filter elements also in connection with shunts for the individual filter elements is known from the patent literature. Thus, German Patent Application DE 198 55 093 A1 describes a system consisting of two filter elements arranged one behind the other. A partial flow is passed in a shunt on the front filter element and cleaned in the rear element. Another partial stream is cleaned in the front element and passed in a shunt on the rear element. Very similar systems are also described in US Pat. Nos. 6,464,744 B2 and 4,625,511.

US Pat. No. 4,625,511 discloses a system with two filters arranged one behind the other, with only the first filter being shunted. A similar system is also described in German Offenlegungsschrift DE 101 51 698 A1. The advantage of these systems is that a more uniform loading of the two filters is achieved with soot.

The previously described constructions of multiple cascaded filter elements with shunts for one or more filter elements are closed filter systems, that is, they do not meet the requirement for a clog-free filter system. Rather, several filters are connected in series here. The clogging of a filter leads to blockage of the entire system.

The present invention discloses an open, and thus blockage-free, filtration unit with good filter efficiency for the removal of soot from the exhaust of diesel engines. The filter unit consists of at least two filter units which are interlinked at a distance and are flowed through in succession by the exhaust gas. The filter unit is characterized in that each filter unit has one or more shunts, which are laterally offset from each other in two successive filter units and wherein there is a blockage-free flow path between the shunts of the successive filter units.

Each filter unit thus contains a particle filter and one or more shunts through which a portion of the exhaust gas can pass unfiltered through the associated filter unit. The shunts can be arranged both inside the respective particle filter or externally. According to the invention there is a blockage-free flow path between the shunts of two successive filter units, so that even in the case of a complete blockage of the filter, the exhaust gas can flow unhindered through the shunts through the filter unit. The shunts of two successive filter units are laterally offset from each other, so that the exhaust gas fractions, which have flowed through the front particulate filter and cleaned, preferably flow through the shunts of the subsequent filter unit, while the exhaust gas components from the shunts of the front filter unit preferably through the rear particulate filter stream. As a result, despite the shunts in the individual filter units, a high overall filter efficiency at a comparable exhaust back pressure as in conventional filter systems is ensured.

Crucial to the operability of this arrangement is that a direct, clog-free flow connection between the shunts of the filter units arranged one behind the other is possible. Only through this direct flow connection between the shunts of two successive filter units is a free flow path for the exhaust gases through the shunts always ensured in the case of complete blockage of the particulate filter. The shunts in the filter units thus ensure an emergency operation with still permissible exhaust back pressure, if the filter regeneration, be it active or passive, should fail once.

The invention will be explained in more detail with reference to Figures 1 to 3. Show it

Figure 1: Inventive filter unit with external shunts: flow conditions in filters with low soot loading

Figure 2: Inventive filter unit with external shunts: flow conditions in filters with high soot loading

Figure 3: Filter unit of Figure 1 with outlet A of the first shunt in the flow direction of the exhaust gas behind the inlet E of the second shunt

Figure 4: filter unit of Figure 1 with arranged in the shunts Durchfluß- honeycomb bodies

Figure 5: Inventive filter unit of two Wandflußfiltern with internal shunts Figure 6: Monolithic filter unit of individual mutually interlocked cuboid filter elements

The principle underlying the invention can be clearly illustrated by the embodiment shown in Figure 1. FIG. 1 shows a filter unit (1) which contains two filter units (I) and (II). Each filter unit contains a soot filter (2), (3) and associated external shunts (4) and (5). The shunts are laterally offset from one another.

By this arrangement, the exhaust gas entering the filter unit is split into a first partial flow (6) flowing through the filter (2) and into a second partial flow (7) flowing through the secondary port (4). The first partial flow is released by the filter according to its filter efficiency of its soot load, while the second partial flow without filtering through the shunt (4) flows. After flowing through the first filter unit (I), a certain mixing of the first and the second partial flow of the exhaust gas takes place. The mixed exhaust gas is split in the second filter unit into a third (8) and fourth (10) partial flow. The third partial flow flows through soot filter (3) and is released according to its filter efficiency of the remaining soot load (11), while the fourth partial flow unfiltered through the shunt (5) flows.

Figure 1 shows the flow conditions with low soot loading of the filter (2) and (3): the main mass flow of the exhaust gas passes through both filters and is freed from soot with high efficiency. In contrast, FIG. 2 shows the flow conditions with high soot loading of the filters (2) and (3). Due to the high exhaust gas back pressure of the filter loaded with soot, the main mass flow of the exhaust gas is bypassed by the shunts on the filters. The filter effect is low in this case.

If it is assumed by way of example that the first and second partial flow each make up 50% of the total exhaust gas mass flow and the first partial flow is completely freed of soot in the filter (2), the further assumption is complete mixing of the two partial flows before entering the filter unit (II ) and also halves division of the mass flows on shunt (5) and filter (3) a soot reduction of the exiting the filter unit exhaust gas by 75%.

This value changes constantly during operation of the filtration unit. The more soot deposits in the filters, the more the flow of exhaust gas shifts to the shunts. The ratio of the mass flows of the first to the second partial flow changes dynamically corresponding to the flow resistance formed by the deposition of the soot in the filter (2). The same applies to the ratio of the mass flows of the third to the fourth partial flow. In the extreme case of the blockage of both filters, the entire exhaust gas flows unfiltered over the two shunts. A complete blockage of the filter unit can not occur. The sizing of the shunts is preferably carried out so that in complete blockage of the filter caused by the shunts exhaust back pressure does not exceed a permissible value.

The above-calculated soot reduction can be further improved if it is ensured by fluidic measure that the third partial flow is predominantly formed by the second partial flow and its carbon black is deposited in the second filter unit according to their filter efficiency, while the fourth partial flow predominantly from the first, already Soot-free, partial flow is formed. Such a measure may be, for example, that the outlet (A) of the first shunt (4) is placed in the filter unit in the flow direction of the exhaust gas behind the inlet (E) of the second shunt (5). This arrangement of outlet and inlet is shown in FIG. This ensures that in normal operation at low filter loads, the exhaust gases purified in the front filter preferably flow through the shunt of the second filter element while the exhaust gases from the front shunt are preferably cleaned in the rear filter.

The exhaust back pressure of the two shunts is preferably designed so that just 50% of the exhaust gas flows through the front and rear shunt for a given target loading of the filter unit with soot. At a lower filter load, the proportion of the exhaust gas flowing through the shunts and thus also the soot passage through the filter unit decreases. If the filter load is greater than the target load, a larger part of the exhaust gas flows through the shunts and leaves the system unfiltered: the soot passage through the filter unit increases. With complete blockage of the filter, the exhaust gas leaves the filter unit unfiltered over both shunts.

The overall filtering efficiency of the filtering aggregate depends essentially on the degree of mixing of the individual partial streams in the connecting piece between the inlet (E) of the rear shunt and the outlet (A) of the front shunt. This mixing can be minimized by suitable construction, in the simplest case, for example, by a taper of the connecting piece between the two shunts. The maximum backpressure of the system with fully added filters is determined by the backpressure of the shunts. The dependence of the backpressure of the shunts on the exhaust gas mass flow is determined by the nature of the friction losses in the shunts. Turbulent energy losses lead to a quadratic dependence, while laminar friction losses lead to a linear dependence. Advantageous in the context of the invention, it is when the shunts at low filter loading, ie low flow rate in shunt a maximum proportion of exhaust gases through the filter elements and have clogged filter elements, ie high flow velocity, the lowest possible back pressure. This goal is best met in the case of a mainly laminar friction loss. A laminar friction energy loss can be achieved, for example, by incorporating flow-through honeycomb bodies (13) and (14) into the shunts. An additional advantage of this arrangement is the ability to catalytically coat these additional flow honeycomb body and thus positively influence the regeneration behavior of the system positively.

The filter unit according to the invention is particularly suitable for retrofitting diesel vehicles with a particulate filter. The retrofitted filters must enable trouble-free operation over all operating states of the engine and unlimited operating time even without active regeneration. The filter unit according to the invention meets this requirement. Even with complete blockage of the filter is still a free flow of the exhaust gas through the shunts possible.

The filters are always thermally regenerated when the engine is operated under high load with high exhaust gas temperatures. To aid regeneration, the filters and shunts may be catalytically coated. The filters are advantageously provided with a coating which lowers the soot ignition temperature and the shunts are provided with an oxidation coating. In addition, an oxidation catalyst can be arranged in front of the filter, which oxidizes the nitrogen monoxide contained in the exhaust gas to nitrogen dioxide. Nitrogen dioxide is a strong oxidizing agent and can burn the soot deposited on the filters even at relatively low exhaust gas temperatures.

The previously described simple embodiment of the invention with externally routed past the filters shunts has the disadvantage that in the case of a once occurred clogging of the filter, the exhaust flow is completely through the shunts and the filter elements in a regeneration therefore heated very slowly from the front side by heat conduction Need to become. More advantageous is a Integration of the shunts directly into the filters, for example in the case of a Wandflußfilters through some open channels. Such an embodiment of the invention is shown in Fig. 3. Numeral (20) denotes an exhaust gas purifying case in which two wall flow filters (21) and (22) are arranged one behind the other. In both filters, some flow channels are formed as flow channels, that is, as shunt channels.

The shunt channels are advantageously distributed over the filter so that a uniform heating of the filter is ensured in the regeneration. The total flow resistance must be set via the number of open channels. For a uniform heating of the filter during regeneration, a higher number of open channels is advantageous. Given the overall flow resistance, the number of open channels can be increased as the flow resistance of the individual open channels is increased. For this purpose, either the diameter of the open channels can be made smaller than the diameter of the regular filter channels or partially blocked channels can be used.

According to the shunt channels are arranged geometrically in two successive filters so that the exhaust gas from the shunt channels of the front filter preferably meet on active filter channels in the rear filter and vice versa. Strörungssimulationsrechnungen the inventor show that such a selective on-flow of the shunt channels can be realized very easily and efficiently by laterally offset from each other shunt channels. The mixing between the individual partial flows amounts to a few percent.

Ceramic Wandflußfilter are usually composed of individual cuboidal elements. A particularly favorable embodiment using such cuboid filter element is shown in FIG 4. The filter units (I) and (II) are located in an exhaust gas cleaning housing (30) and each consist of several cuboid filter elements. Each filter element has some shunt channels, wherein the shunt channels are laterally offset from one another in successive filter elements according to the invention.

Each filter unit consists of short (32), (34) and long (31), (33) filter elements, each arranged in a checkered pattern. The short and long filter elements are arranged in the two successive filter units complementary to each other, so that a toothing of the two filter units (I) and (II) is possible. The toothing of the successive filter increases the mechanical stability of the entire filter unit and leads to a monolithic structure. As a result, the geometrically precise relative arrangement of the open channels is ensured in a simple manner. The overall filter unit can also contain some completely continuous filter cuboids without shunt channels.

In a further embodiment of the invention, the individual filter elements are formed by correspondingly structured metal foils with integrated filter materials. Again, the shunt channels of each front and rear filter element must be geometrically arranged so that a selective flow according to the invention of the shunt channels is ensured. This can for example be achieved in a simple manner when the two filter elements consist of spirally wound corrugated sheet layers and the shunt channels are arranged in the front and rear filter element in radially offset layers. Again, the system need not necessarily consist of two separate filter monoliths, but the respective front and rear filter elements may for example be designed in radially varying length, so that the front and rear filter elements can be interlocked to increase the stability of the system.

The geometric embodiment of the invention is not limited to the relatively simple geometries listed here. In particular, in the embodiment as a metal filter, the individual filter elements can also be arranged in a very complex form. It is important that according to the invention for a large number of filter channels each have a shunt and that these shunt channels are geometrically connected so that in the case of complete blockage of the filter elements a free flow of the exhaust gas through the shunt channels is possible.

Another embodiment of the invention uses catalytically coated filter elements. In this case, a different coating can be selected for the front and rear filter elements. The shunt channels can also be catalytically coated. In this case, the same or a different coating can be selected as for the filter channels. For example, in the case of a fully loaded filter, the flow is largely through the shunt channels. It is therefore helpful to coat the shunt channels with an oxidation catalyst in order to generate as much exotherm as possible during the regeneration. In return, it makes sense to optimize the coating of the filter walls in the direction of a reduced soot ignition temperature. The invention is particularly advantageous when using novel highly porous filter materials. These materials show only a moderate filter efficiency when completely unloaded. The filter efficiency then increases in the loaded state by the formation of a filter cake. A filter system according to the present invention is designed so that for a preselected 'standard load' 50% of the exhaust gas passes through the shunt and 50% through the filter units. The back pressure at standard load is half of the counter pressure occurring at full load. In this design, the unloaded filter more than 80% of the exhaust gases go through both filter elements so that here also almost a complete Rußabschei- fertilg is reached. As the loading of the filter increases, the proportion of the double-filtered gas decreases, but the filter efficiency of the porous filter material increases. In this way, a good degree of separation is achieved over the entire normal operating range.

Claims

claims

1. Filter unit of at least two spaced-apart filter units, which are flowed through to remove soot from the exhaust gas of diesel engines in succession from the exhaust gas, characterized in that each filter unit has one or more shunts, which are laterally offset from each other in two successive filter units and wherein there is a blockage-free flow path between the shunts of the successive filter units.

2. Filter unit according to claim 1, characterized in that the shunts are dimensioned so that they absorb 10 to 50% of the volume flow of the exhaust gas at fully regenerated filter.

3. Filter unit according to claim 2, characterized in that the filter units connected in series each contain a filter selected from the group consisting Wandflußfilter, ceramic foam filter, metal foam filter, metal filter and bag filter and the shunts are formed by exhaust pipes, the led laterally past the respective filters are.

4. Filter unit according to claim 3, characterized in that the shunts are equipped with laminar friction losses.

5. Filter unit according to claim 4, characterized in that in the shunts monolithic flow honeycomb body are arranged.

6. Filter unit according to claim 5, characterized in that the filter and / or the flow honeycomb body are coated catalytically.

7. Filter unit according to claim 6, characterized in that in that the filters and / or the flow-through honeycomb bodies are coated with an oxidation catalytic converter.

8. Filter unit according to claim 7, characterized in that the concentration of the coating with the oxidation catalyst on the

Durchfluß- honeycomb bodies is greater than on the filters.

9. Filter unit according to claim 1, dadurc h geke nnz e i c hnet that the two filter units connected in series each contain a Wandflußfilter and the shunts are formed by the fact that a part of the flow channels of Wandflußfilter are designed as flow channels.

10. Filter unit according to claim 9, characterized in that the distance between the Wandflußfilter is between 1 and 200 times a channel diameter.

11. Filter unit according to claim 10, characterized in that the wall-flow filters are made up of a plurality of parallelepiped-shaped filter elements of different lengths, each element having a plurality of flow channels, the elements of different lengths being arranged complementary to one another in the successive wall flow filters toothed to form a monolithic filter unit.

12. Filter unit according to claim one of claims 9 to 11, dadurc h gekennze i c hnet that the Wandflußfilter and their flow channels are coated catalytically.

13. A method for removing soot from the exhaust gas of a diesel engine comprising the steps of: a) directing the exhaust gas flow through a first filter unit with shunt, wherein the soot load of a first partial flow of the exhaust gas is deposited in the first filter unit according to their filter efficiency, while a second

Partial flow of the exhaust gas passes through the first filter unit unfiltered via the shunt and thereafter, b) passing the exhaust gas flow through a second filter unit with shunt, wherein the soot load of a third partial stream of the exhaust gas is deposited in the second filter unit according to their filter efficiency, while a fourth partial flow of the exhaust gas passes through the second filter unit unfiltered via the shunt.

14. The method according to claim 13, characterized in that it is ensured by fluidic measures that the third partial flow is predominantly formed by the second partial flow and its soot is deposited in the second filter unit according to their filter efficiency, while the fourth partial flow predominantly from the first , already freed from soot, partial flow is formed.

15. The method according to claim 10, characterized in that the exhaust gas stream is passed after exiting the second filter unit via at least one further filter unit with shunt, wherein the division of the exhaust gas stream and the soot deposition takes place as in the first or second filter unit.

16. The method according to claim 1, characterized in that an active regeneration of the filter units is initiated when the mass flow is increased by the shunts of initially 5 to 30% by the soot load to 40 to 70% of the total exhaust gas mass flow.

17. The method according to any one of claims 10 to 12, characterized in that the shunts of the filter units are guided past each of the filter unit.

18. The method according to claim 16, characterized in that filter units and / or shunts are catalytically coated.

19. The method according to any one of claims 10 to 12, characterized that the shunts of the filter units are each passed through the filter units.

20. The method according to claim 18, characterized in that filter units and / or shunts are catalytically coated