WO2009033911A1

WO2009033911A1 - Exhaust-gas aftertreatment arrangement with reducing agent reservoir, and method for the aftertreatment of exhaust gases

Info

Publication number: WO2009033911A1
Application number: PCT/EP2008/060657
Authority: WO
Inventors: Thomas Wahl; Florian Wahl; Michael Koehler
Original assignee: Robert Bosch Gmbh
Priority date: 2007-09-06
Filing date: 2008-08-14
Publication date: 2009-03-19
Also published as: US20100236225A1; DE102007042409A1; EP2185797A1

Abstract

Proposed are an exhaust-gas aftertreatment arrangement and a method for the reduction of pollutants, in particular for the selective catalytic reduction of nitrogen oxides. The arrangement comprises an exhaust line (7) for conducting the exhaust gas of an internal combustion engine to a treatment unit (3) for the reduction of the pollutants, and at least one reservoir (18) for storing a reducing agent for use in the treatment unit, wherein the reservoir (18) is arranged in the region of the exhaust line and wherein the reservoir (18) extends parallel to the exhaust line and is in heat-conducting contact with the exhaust line and/or with the exhaust gas in the exhaust line.

Description

description

title

Exhaust after-treatment arrangement with reducing agent storage and method for aftertreatment of exhaust gases

State of the art

The invention relates to an exhaust aftertreatment arrangement for the reduction of pollutants or a method for exhaust aftertreatment according to the preamble of the independent claims.

In order to meet the requirements for the exhaust gas quality of vehicles, the so-called SCR process C.SCR "= Selective Catalytic Reduction" is used in diesel vehicles, in particular in commercial vehicles, for the reduction of nitrogen oxides.

This method has been used for some time in cogeneration plants to reduce nitrogen oxide emissions. There, the raw exhaust gas of the heating stage ammonia is added. The exhaust gas laden with ammonia is passed over a catalyst which selectively catalyzes the reaction of ammonia with nitric oxide in the presence of oxygen. The temperatures of the

Catalysts are in a range of 250 degrees Celsius to 500 degrees Celsius. In this case, as a rule, a catalyst is used which has a catalytically active coating of vanadium pentoxide on tungsten oxide-stabilized titanium dioxide (so-called anatase phase). Ammonia and nitrogen monoxide react on the catalyst to harmless substances, water and nitrogen from.

In vehicles, urea is used as a reducing agent instead of ammonia. The catalyzed reduction of nitrogen oxides is a catalyzed Hydrolysis of the urea upstream of ammonia and carbon dioxide. Subsequently, ammonia reacts with the nitrogen oxides further according to the above reaction. In particular, other suitable catalyst materials can also be used in motor vehicles, for example gamma-aluminum oxide-applied transition metal compounds, such as

Iron-doped gamma-alumina. Also, transition metal ion exchanged or impregnated zeolites can be used.

In a direct dosing of gaseous ammonia in the exhaust tract exist over a solution on an aqueous urea solution with trade name

"AdBlue" based exhaust gas denitrification benefits, such as avoiding the use of a corrosive and freeze-capable fluid, Furthermore, the reductant delivery is independent of the exhaust gas temperature.

From WO 99/01205 it is known to store ammonia by incorporation in salts and to initiate thermal desorption as needed. It is also known from this point to use for heating a solid storage medium, the waste heat of the engine coolant and / or the exhaust gas and, if necessary, a buffer volume for already dissolved out of the ammonia storage

Provide ammonia.

From EP 1561 017 it is known to provide at opposite ends of an ammonia storage exhaust gas lines to a coming from a reactor, cached in the ammonia storage

Release auxiliaries for exhaust aftertreatment and to be able to transfer in a further step in the exhaust system.

Disclosure of the invention

The exhaust aftertreatment arrangement according to the invention or the exhaust gas aftertreatment method according to the invention have the characterizing features of the independent claims In contrast, the advantage of providing an energy-efficient temperature control of a reducing agent reservoir, in particular an ammonia storage, and, consequently, an energy-efficient arrangement for reducing, for example, nitrogen oxides contained in the exhaust gas or to ensure energy-efficient exhaust gas aftertreatment. In particular, the additional fuel consumption required by an electrical energy requirement can be reduced. A further advantage is to be considered that the waste heat of the exhaust gas not only optimally utilized for the release of the reducing agent, for example gaseous ammonia, from the storage or a storage substance contained in the storage, but at the same time a space-saving by integrating the storage container in the region of the exhaust line Arrangement provided and otherwise possible problems with the voltage stability of a motor vehicle electrical system can be reduced or even avoided.

Advantageous refinements and improvements of the arrangements and methods specified in the independent claims are possible due to the measures listed in the dependent claims. It is particularly advantageous to provide a direct heat-conducting interaction, for example, by a special shape of the memory, adapted to the

Longitudinal extent of the exhaust tract and in direct arrangement on or within the exhaust gas line, which on the one hand maximizes the heat transfer and the space requirement of the entire arrangement can be minimized.

Further advantages result from further features mentioned in the further dependent claims and in the description.

Brief description of the drawings

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. 1 shows an exhaust aftertreatment arrangement with a voltage applied to the exhaust pipe - A -

FIG. 2 shows an arrangement with a memory arranged within a path of the exhaust gas conduit, FIG. 3 shows an arrangement with a reservoir within a single-path exhaust gas conduit, FIG. 4a shows a reservoir and FIG. 4b shows a reservoir with a cartridge which can be inserted into a container.

Embodiments of the invention

Figure 1 shows an exhaust aftertreatment device 1 with an exhaust pipe 7, in the flow direction 5 of an internal combustion engine, such as a

Diesel engine, incoming exhaust gas to a designed as a catalyst for the selective catalytic reduction of nitrogen oxides treatment unit 3 passes. The exhaust gas line 7 is divided downstream of the SC R catalyst in a first path 9 and in a second path 11, wherein the two paths unite again upstream of the S C R catalyst to a gas-carrying line. Internal combustion engine side performs a first, in particular electrically controllable exhaust valve 13, a so-called partition exhaust valve, the exhaust gas flow either in one of two or taking an intermediate position at the same time in both paths 9 and 11. On the catalyst side can be closed via a second exhaust valve 15 either one of the two paths , In an intermediate position of the second exhaust gas flap, exhaust gas streams from both paths, which combine in front of the catalyst, can also be conducted to the catalyst 3. There is provided a storage 18 for storing ammonia by means of a storage substance 19 of magnesium chloride. The storage tank 17 of the accumulator is arranged parallel to the exhaust pipe, along a wall 8 of the exhaust pipe 7 in the region of the second path 11. The outer side of the storage container and the exhaust pipe touch each other surface and form a heat transfer region 27. Here, the spatial extent 29 of the memory or the storage container is perpendicular to the flow direction 20 of the

Exhaust gas in the second path 11 small compared to its extension along the second path 11 (for example in a ratio in a range of 1:10 to 1:50, in particular in a range of 1:12 to 1:45). An electrically controllable metering valve 21 is mounted on the memory and projecting on its opening side with a front of the SC R catalyst 3 in the exhaust pipe Supply line 23 is connected, wherein between the metering valve and the projecting into the exhaust pipe open end of the supply line, a buffer tank 24 for buffer storage already leaked from the memory ammonia is arranged. This is provided on its side facing the open end of the supply line with a further, not shown closing means, for example, a further electrically controllable valve. The cleaned exhaust gas leaves the catalyst on the side facing away from the reducing agent supply in the flow direction 25 in order to reach the outside via possibly further exhaust-gas treatment arrangements or via the silencer. Furthermore, an electric heating element 31 is on

Memory 18 arranged. An electronic control unit 32 is connected to sensors, not shown, sensor signals 33, such as a nitrogen oxide sensor at the output of the S C R catalyst connected. The closing means on the memory or on the buffer container, in particular the metering valve 21, and the electric heater 31 and the exhaust valves 13 and

15 are supplied via not shown electrical signal lines from the control unit 32 with control signals 34.

The exhaust system is designed so that the exhaust gas flow can be controlled via flaps in two lines can be removed (so-called twin-flow system). The

Ammonia storage substance is accommodated in a storage container, which is arranged on a one of the two exhaust gas lines, that a good heat transfer from the exhaust gas takes place to the storage substance. The good heat transfer can be supported by a suitable choice of materials made of materials with high thermal conductivity and a suitable structural design, for example by using a mutually intermeshing rib structure of the exhaust pipe and storage tank. The heat input of the passing exhaust gas into the ammonia storage substance ammonia is released. Due to the liberated, gaseous ammonia (and any by-products when using alternative storage materials) creates an overpressure in the designed as a pressure vessel storage tank. The gaseous ammonia is metered into the exhaust gas line via the metering valve 21 or the closing means attached to the buffer container. The exhaust gas flow for heating the ammonia storage substance can be adjusted via the division exhaust valve 13 become. The amount of heat that is introduced into the ammonia storage substance is dependent on the temperature and the mass flow of the exhaust gas flowing through the path 11. The control of the flap position and thus also the ammonia release can be done by means of a mass flow meter, a temperature sensor or an exhaust pressure sensor. The measured value is detected in the control unit 32 and controlled according to the position of the distribution exhaust valve 13 via control signals 34. The exhaust gas flow in the path 11 is adjusted at each operating point of the internal combustion engine so that the respectively required amount of ammonia is available for the reduction of nitrogen oxides. If the exhaust heat in certain operating points for the

Supply of reducing agent for nitrogen oxide reduction is insufficient, the electric heating element 31 can additionally heat the storage or the storage substance for the ammonia release. The electric heater can also be used for an early onset dosing during cold start of the engine, where otherwise would still be expected with the motor vehicle exempt polluted exhaust gas, because the exhaust gas temperatures for the dissolution of the ammonia from the storage substance is not enough. The heating element increases in cooperation with the exhaust valve control and the dynamic range of the possible dosage of the reducing agent, both in terms of time, that is, with respect to the response time of the dosing to an electronically controlled requirement of increased amounts of reducing agent, as well as in terms of quantity, ie in terms of per unit time maximum possible delivery amount of reducing agent. Also, the buffer tank 24 may help to shorten the response time of the dosing by this one within a very short time, especially during cold start of the engine, retrievable amount of gaseous ammonia. A buffer volume also serves the provision of gaseous ammonia for higher dynamic requirements in general, that is also in terms of quantity, as already carried out in connection with the electric heating element.

In alternative embodiments, the arrangement can also be provided without electric heating or without buffer container. In a further alternative embodiment, the exhaust flaps can be omitted. Furthermore, a buffer volume can not be used as a separate container but as a partial volume be provided within the storage container. The storage substance can also be accommodated instead of in a container in a replaceable cartridge, which in turn can be introduced into the container. In a further variant, the storage container itself may also be designed as an exchangeable cartridge, whereby the heat transfer from the exhaust gas to

Improved storage substance, because then instead of three intermediate walls (exhaust pipe, wall of the storage container, wall of the cartridge) separate only two intermediate walls, the exhaust gas from the storage substance, namely the wall of the exhaust pipe and the wall of serving as a cartridge storage container. The introduction of the ammonia storage substance

Magnesium chloride ensures easy refilling of the exhaust aftertreatment system with new ammonia via standard cartridge replacement. The arrangement is also suitable for a variety of ammonia storage materials from which ammonia is obtained by thermal desorption or thermolysis, i. Temperature effect, is released.

Suitable storage substances may, for example, besides magnesium chloride, be many other salts, in particular other chlorides and / or sulfates of one or more alkaline earth elements (such as CaCb) and / or one or more 3d subgroup elements such as manganese, iron, cobalt, nickel, copper and / or zinc , Furthermore, organic adsorbents and ammonium salts such as e.g.

Ammonium carbamate suitable ammonia storage substances that can be used.

FIG. 2 shows a further exhaust aftertreatment arrangement 40, in which the same or similar components as in the arrangement shown in FIG. 1 are provided with the same reference number and will not be described again. In contrast to the arrangement according to FIG. 1, in which a storage tank is integrated in the area of the exhaust gas line but is arranged outside the exhaust gas flow, the arrangement 40 has a storage tank 41 arranged within the exhaust gas pipe 7 in the region of the path 11. Of the

Storage tank is in this case locked by means of releasable struts 43, so that the exhaust gas can flow past at least on one side between the storage wall and the wall of the exhaust pipe. In the present introduction of the storage container for the ammonia storage substance in the exhaust pipe of the container is directly exposed to the exhaust gas full flow in the path 11, whereby the heat transfer region in comparison to the arrangement of Figure 1 ensures an improved heat-conducting contact between the exhaust gas and storage substance. A

Refilling the storage container can be done by connecting an ammonia gas storage in a workshop via a connection device, not shown. Alternatively it can be provided to provide a screw / flange connection, which makes it possible to replace the memory together with the exhaust pipe (path 11) against a filled storage.

Figure 3 shows an exhaust aftertreatment arrangement 46, in which, similar to the arrangement of Figure 2, the storage vessel 41 is exposed to the exhaust gas full flow, but not the exhaust full flow of a sub-path, but, dispensing with a division of the exhaust gas flow, the entire of the

Internal combustion engine derived exhaust gas flow. In the case of a too high exhaust gas temperature, which leads to an excessive desorption of ammonia, can be caused by a designed as an air supply line for cooling air cooling device 47, a cooling of the exhaust gas. Again, the storage substance can be heated via a non-illustrated electric heater in the event that the base heat of the exhaust gas is insufficient.

FIG. 4 a shows once again, diagrammatically, a detail of the preceding exhaust aftertreatment arrangements, namely a memory 18 whose storage substance 19 is located in a storage tank 17. to

Removal of reducing agent, the metering valve 21 is disposed on one side of the memory. This storage container 17, as stated above, be designed as an exchangeable and standardizable cartridge. FIG. 4b shows an alternative embodiment of a reducing agent reservoir which can be used in one of the described arrangements or methods, into whose storage container 17 not directly the ammonia storage substance but a cartridge 51 is inserted, which in turn contains the ammonia storage substance. In this case, the storage container forms, so to speak, a heat-transferring sleeve, in the interior of which replaceable cartridges can be inserted as needed.

Claims

claims

1. exhaust aftertreatment arrangement for reducing pollutants contained in an exhaust gas of an internal combustion engine, in particular for the selective catalytic reduction of nitrogen oxides, with an exhaust pipe (7) for conducting the exhaust gas to a treatment unit (3) for the reduction of

Contaminants and having at least one memory (18) for storing a reducing agent for use in the treatment unit, wherein the memory (18) is arranged in the region of the exhaust pipe, characterized in that the memory (18) extends parallel to the exhaust pipe and with the exhaust pipe and / or the exhaust gas contained in the exhaust pipe is in heat-conducting contact.

2. exhaust aftertreatment device according to claim 1, characterized in that the memory (18) and the exhaust pipe (7) are arranged such that the memory with the exhaust pipe and / or the exhaust gas interacts directly thermally conductive.

3. exhaust aftertreatment arrangement according to claim 1 or 2, characterized in that the heat-conducting contact is adapted for thermal dissolution of the reducing agent from a storage substance (19) of the memory (18), in particular for exciting a thermal desorption of the reducing agent from the storage substance and / or Exciting at least partial thermolytic decomposition of the storage substance (19) to form the reducing agent.

4. exhaust aftertreatment device according to claim 3, characterized in that the storage substance is in solid phase at room temperature.

5. exhaust aftertreatment arrangement according to claim 4, characterized in that the storage substance (19) from at least one salt and / or at least one sulfate of one or more alkaline earth elements and / or one or more 3d-subgroup elements and / or at least one organic adsorber is formed.

6. exhaust aftertreatment device according to claim 5, characterized in that the salt is an ammonium salt.

7. exhaust aftertreatment arrangement according to one of the preceding claims, characterized in that the spatial extent (29) of the memory in a direction perpendicular to the flow direction of the

Exhaust gas is small compared to the spatial extent in the flow direction of the exhaust gas.

8. Exhaust after-treatment arrangement according to one of the preceding claims, characterized in that the memory has a storage container (17) and that the storage container extends along a wall (8) of the exhaust pipe (7).

9. exhaust aftertreatment arrangement according to claim 8, characterized in that the storage container (17) rests against the wall (8) and / or is attached.

10. Aftertreatment arrangement according to one of the preceding

Claims, characterized in that the memory (18) has a replaceable cartridge (51).

11. Aftertreatment device according to claim 8 or 9 and according to claim 10, characterized in that the storage container (17) is adapted to receive the replaceable cartridge (51).

12. Exhaust after-treatment arrangement according to claim 8 or 9 and according to claim 10, characterized in that the replaceable cartridge is formed by the storage container (17).

13. exhaust aftertreatment arrangement according to one of the preceding claims, characterized in that the memory (18) within the

Exhaust pipe (7) is arranged.

14. exhaust aftertreatment arrangement according to one of the preceding claims, characterized in that the exhaust gas line upstream of the processing unit (3) in a first path (9) and in a second path (11) and that the heat-conductive contact via at least one of the two paths ( 9, 11) takes place.

15. exhaust aftertreatment device according to claim 14, characterized in that both paths open into the processing unit.

16. Exhaust after-treatment arrangement according to claim 15, characterized in that a switchable exhaust flap (15) is provided via the two paths upstream of the processing unit are merged.

17. Aftertreatment arrangement according to one of claims 14, 15 or 16, characterized in that a switchable division exhaust valve (13) is arranged for selectively introducing the exhaust gas in the first (9) or in the second path (11).

18. exhaust aftertreatment arrangement according to claim 17, characterized in that the division exhaust valve (13) is adapted to also assume an intermediate position, so that exhaust gas can be introduced into both the first and in the second path.

19. Exhaust after-treatment arrangement according to one of the preceding claims, characterized in that a heating element (31) is provided for heating the accumulator independently of a heat derived from the exhaust gas.

20. Aftertreatment arrangement according to one of the preceding

Claims, characterized in that the memory (18) is arranged downstream of the Aufbereitungseinheit Abgasstromaufwärts.

21. Aftertreatment device according to one of the preceding claims, characterized in that a cooling device (47) is provided for cooling the memory.

22 exhaust gas after treatment arrangement according to one of the preceding claims, characterized in that the memory is arranged an electrically controllable metering valve (21).

23. Aftertreatment arrangement according to claim 22, characterized in that an electrical control unit (32) for controlling the

Metering valve is provided.

24. exhaust aftertreatment arrangement according to one of the preceding claims, characterized in that for buffering already leaked from the memory (18) reducing agent before metering into the exhaust pipe (7), a buffer tank (24) is provided.

25. Exhaust after-treatment arrangement according to one of the preceding claims, characterized in that the treatment unit (3) comprises a catalyst, in particular a catalyst adapted for selective catalytic reduction.

26. A method for exhaust aftertreatment for the reduction of pollutants contained in an exhaust gas of an internal combustion engine, in particular for the selective catalytic reduction of nitrogen oxides, wherein the exhaust gas is passed via an exhaust pipe from the internal combustion engine to a treatment unit (3) for reducing the pollutants and wherein a

Reducing agent for use in the processing unit is stored in a memory, wherein the memory (18) is arranged in the region of the exhaust pipe, characterized in that the memory (18) extends parallel to the exhaust pipe and the exhaust pipe and / or the exhaust gas contacted thermally conductive.