AN EXHAUST GAS TREATMENT SYSTEM

Abstract

The invention provides an exhaust gas treatment system (8) arranged to receive exhaust gases from an internal combustion engine (6), the system comprising an exhaust conduit (10) and a selective catalytic reduction (SCR) catalyst (12) provided in the exhaust conduit (10), characterized in that the system comprises a nitrogen dioxide reducing unit (701) provided in the exhaust conduit (10) upstream of the SCR catalyst (12), wherein the nitrogen dioxide reducing unit (701) is adapted to reduce, at a low temperature, nitrogen dioxide (NO2) in exhaust gases received by the nitrogen dioxide reducing unit (701).

Claims

1. An exhaust gas treatment system (8) arranged to receive exhaust gases from an internal combustion engine (6), the system comprising an exhaust conduit (10) and a selective catalytic reduction (SCR) catalyst (12) provided in the exhaust conduit (10), characterized in that the system comprises a nitrogen dioxide reducing unit (701) provided in the exhaust conduit (10) upstream of the SCR catalyst (12), wherein the nitrogen dioxide reducing unit (701) is adapted to reduce, at a low temperature, nitrogen dioxide (NO2) in exhaust gases received by the nitrogen dioxide reducing unit (701).

2. A system according to claim 1, characterized in that the nitrogen dioxide reducing unit (701) is adapted to reduce nitrogen dioxide in the exhaust gases at a cold start event of the engine (6).

3. A system according to claim 1, characterized in that the nitrogen dioxide reducing unit (701) is adapted to not reduce nitrogen dioxide in the exhaust gases at a high temperature.

4. A system according to claim 1, characterized in that the system comprises means (711) for supplying ammonia (NH3) to the exhaust gases when the temperature of exhaust gases are low.

5. A system according to claim 1, characterized in that the system comprises means (711) for supplying ammonia (NH3) to the exhaust gases, upstream of the SCR catalyst (12), at exhaust gas temperatures below 200 C.

6. A system according to claim 5, characterized in that the means (711) for supplying ammonia comprises means to inject a precursor into the exhaust conduit (10), and an ammonia production catalyst (715) adapted to produce ammonia from the injected precursor at exhaust gas temperatures below 200 C.

7. A system according to claim 6, characterized in that the exhaust conduit (10) comprises a main conduit (102) and a bypass conduit (101), the bypass conduit being branched from the main conduit and arranged to reintroduce exhaust gases into main conduit upstream of the SCR catalyst (12), the ammonia production catalyst (715) being located in the bypass conduit.

8. A system according to claim 5, characterized in that the means (711) for supplying ammonia comprises means for receiving ammonia in solid form.

9. A system according to claim 1, characterized in that the nitrogen dioxide reducing unit (701) is arranged to reduce nitrogen dioxide in the exhaust gases by deposition in the nitrogen dioxide reducing unit (701) of ammonium nitrate provided by a reaction of the nitrogen dioxide in the exhaust gases with ammonia in the exhaust gases to produce the ammonium nitrate.

10. A system according to claim 1, characterized in that the system further comprises means (711) for supplying ammonia upstream of the nitrogen dioxide reducing unit (701), the nitrogen dioxide reducing unit (701) and the SCR catalyst (12) being adapted so that in the nitrogen dioxide reducing unit (701) ammonium nitrate (NH4NO3) is formed from ammonia and nitrogen dioxide faster than ammonium nitrate is formed from ammonia and nitrogen dioxide in the SCR catalyst (12).

11. A system according to claim 10, characterized in that the nitrogen dioxide reducing unit (701) is arranged to store the ammonium nitrate formed in the nitrogen dioxide reducing unit (701).

12. A system according to claim 11, characterized in that the nitrogen dioxide reducing unit (701) presents a length and/or a site density so as for the nitrogen dioxide reducing unit (701) to form the ammonium nitrate from the ammonia and substantially all nitrogen dioxide reaching the nitrogen dioxide reducing unit (701), and to store substantially all the formed ammonium nitrate.

13. A system according to claim 11, characterized in that the nitrogen dioxide reducing unit (701) and the SCR catalyst (12) are arranged so that the ammonium nitrate stored in the nitrogen dioxide reducing unit (701) is not released from the nitrogen dioxide reducing unit (701) below a temperature in the SCR catalyst (12) at which at least one product formed by a decomposition of the ammonium nitrate stored in the nitrogen dioxide reducing unit is converted in the SCR catalyst (12).

14. A system according to claim 11, characterized in that the nitrogen dioxide reducing unit (701) is arranged so that the ammonium nitrate stored in the nitrogen dioxide reducing unit (701) is not released from the nitrogen dioxide reducing unit (701) at temperatures below 200 C.

15. A system according to claim 10, characterized in that the SCR catalyst (12) is a second SCR catalyst (12), and the nitrogen dioxide reducing unit (701) is a first SCR catalyst (12).

16. A system according to claim 1, characterized in that the nitrogen dioxide reducing unit (701) and the SCR catalyst (12) form an integrated element.

17. A system according to claim 16, characterized in that the nitrogen dioxide reducing unit (701) is formed by zone coating of the integrated element.

18. A system according to claim 1, characterized in that the nitrogen dioxide reducing unit (701) and the SCR catalyst (12) are formed by two separate bricks.

19. A system according to claim 1, characterized in that the nitrogen dioxide reducing unit (701) and the SCR catalyst (12) present different active catalytic materials.

20. A system according to claim 1, characterized in that the nitrogen dioxide reducing unit (701) comprises a copper (Cu) zeolite and/or an iron (Fe) zeolite.

21. A system according to claim 1, characterized in that the SCR catalyst (12) comprises an oxide of vanadium.

22. A system according to claim 1, characterized in that the nitrogen dioxide reducing unit (701) is adapted to reduce nitrogen dioxide in the exhaust gases at temperatures below 200 C.

23. A system according to claim 1, characterized in that the nitrogen dioxide reducing unit (701) is adapted to not reduce nitrogen dioxide in the exhaust gases at temperatures above 200 C.

24. A system according to claim 1, characterized in that the nitrogen dioxide reducing unit (701) is adapted to reduce nitrogen dioxide in the exhaust gases by storing nitrogen dioxide in the exhaust gases.

25. A system according to claim 24, characterized in that the nitrogen dioxide reducing unit (701) is adapted to not store nitrogen dioxide in the exhaust gases at temperatures above 250 C.

26. A system according to claim 1, characterized in that the nitrogen dioxide reducing unit (701) is adapted to reduce the nitrogen dioxide by adsorption of the nitrogen dioxide.

27. A system according to claim 26, characterized in that the nitrogen dioxide reducing unit (701) is adapted to release adsorbed nitrogen dioxide at temperatures above 200 C.

28. A system according to claim 1, characterized in that the nitrogen dioxide reducing unit (701) is adapted to reduce the nitrogen dioxide by converting the nitrogen dioxide to nitrogen oxide (NO).

29. A system according to claim 1, characterized in that the nitrogen dioxide reducing unit (701) comprises barium oxide, cerium oxide, and/or aluminum oxide.

30. A system according to claim 24, characterized in that the system comprises means (711) for supplying ammonia to the exhaust gases, upstream of the SCR catalyst (12) and downstream of the nitrogen dioxide reducing unit (701).

31. A system according to claim 24, characterized in that the nitrogen dioxide reducing unit (701) comprises an alkaline metal or an alkaline earth metal.

32. A system according to claim 1, characterized in that the system comprises in addition to the nitrogen dioxide reducing unit (701) an oxidation catalyst (34) provided in the exhaust conduit (10).

33. A vehicle comprising an exhaust gas treatment system according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

[0044] In the drawings:

[0045] FIG. 1 is a side view of a truck comprising an internal combustion engine with an exhaust gas treatment system.

[0046] FIG. 2 shows an embodiment of an internal combustion engine system comprising an internal combustion engine and an exhaust gas treatment system.

[0047] FIG. 3 and FIG. 4 show further embodiments of internal combustion engine systems.

[0048] FIG. 5 shows two graphs depicting the result of a process in a nitrogen dioxide reducing unit in the internal combustion engine system in FIG. 4.

[0049] FIG. 6 shows yet another embodiment of an internal combustion engine system.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

[0050] FIG. 1 shows a vehicle 2 in the form of a truck in a partly cut side view. The vehicle 2 has an internal combustion engine system 4 for the propulsion of the vehicle 2. The internal combustion engine system 4 comprises an internal combustion engine 6 in the form of a diesel engine.

[0051] FIG. 2 shows a first embodiment of an internal combustion engine system comprising the internal combustion engine 6 and an exhaust gas treatment system 8 for treating exhaust gases from the engine 6. The exhaust gas treatment system 8 comprises an exhaust passage 10, or herein also referred to as an exhaust conduit 10 or an exhaust gas line, in the form of a tube for conveying exhaust gases, see arrow 9, discharged from the engine 6.

[0052] The exhaust gas treatment system 8 further comprises a selective catalytic reduction (SCR) catalyst 12 provided in the exhaust passage 10 for selectively reducing NOx contained in the exhaust gas. The SCR catalyst 12 forms a body with an external shape and size matched to an internal shape and size of the exhaust passage so that no, or at least very small amount of, exhaust gases may pass the SCR catalyst 12 without being treated. The SCR catalyst 12 may be formed by a brick of a porous construction. The porosity is what gives the catalyst the high surface area essential for reduction of NOx. Further, the selective catalytic reduction catalyst may be coated on a flow-through monolith.

[0053] The exhaust gas treatment system 8 further comprises ammonia supply means 711, or means 711 for supplying ammonia into the exhaust passage 10 upstream of the SCR catalyst 12, for the NOx reduction process in the SCR catalyst. The ammonia supply means 711 comprises means 712 for receiving ammonia in solid form. For example, the ammonia may be provided as a product marketed under the name of AdAmmine by the company Amminex Emissions Technology A/S. The ammonia supply means 711 is arranged to convert the solid ammonia to liquid ammonia. The ammonia supply means 711 is further arranged to spray by means of an injector 713 the ammonia into the exhaust gas passage 10.

[0054] Thus, the system does not provide for injecting urea into the exhaust passage 10 for the SCR catalyst process, since this requires thermolysis of the urea, which in turn requires a relatively high exhaust gas temperature. Supplying ammonia to the exhaust gases allows supplying a reductant for the SCR catalyst process also when the temperature of exhaust gases are low, e.g. below 200 C.

[0055] The exhaust gas treatment system 8 further comprises upstream of the SCR catalyst 12 and upstream of the injector 713 an oxidation catalyst (DOC) 34 having the function of oxidizing carbon monoxide (CO), hydrocarbons (HC) and nitrogen monoxide (NO) contained in the exhaust gases. The DOC 34 may use precious metals such as platinum and/or palladium.

[0056] The exhaust gas treatment system 8 further comprises a diesel particulate filter (DPF) 36 disposed downstream of the DOC 34 and upstream of the injector 713 for capturing and collecting particulate matter contained in exhaust gas. The DPF may also have catalytic functions for oxidizing.

[0057] The exhaust gas treatment system 8 also comprises a nitrogen dioxide reducing unit 701 provided in the exhaust conduit 10 upstream of the SCR catalyst 12 and downstream of the injector 713. The nitrogen dioxide reducing unit 701 forms a body with an external shape and size matched to an internal shape and size of the exhaust passage 10 so that no, or at least very small amount of, exhaust gases may pass the nitrogen dioxide reducing unit 701 without being manipulated as described below.

[0058] The nitrogen dioxide reducing unit 701 is adapted to reduce nitrogen dioxide (NO2) in exhaust gases received by the nitrogen dioxide reducing unit 701 at a low temperature, more specifically below 200 C., e.g. at a cold start event of the engine 6 or at a low load operation of the engine.

[0059] The nitrogen dioxide reducing unit 701 is arranged to reduce NO2 in the exhaust gases by deposition in the nitrogen dioxide reducing unit 701 of ammonium nitrate (NH4NO3) provided by a reaction of the NO2 in the exhaust gases with ammonia injected by the ammonia supply means 711. Further, the nitrogen dioxide reducing unit 701 and the SCR catalyst 12 are adapted so that in the nitrogen dioxide reducing unit 701 ammonium nitrate is formed from ammonia and NO2 faster than ammonium nitrate is formed from ammonia and NO2 in the SCR catalyst 12.

[0060] The nitrogen dioxide reducing unit 701 presents a length and a site density so as for the nitrogen dioxide reducing unit 701 to form the ammonium nitrate from the ammonia and substantially all NO2 reaching the nitrogen dioxide reducing unit 701, and to store substantially all the formed ammonium nitrate.

[0061] Thereby, the nitrogen dioxide reducing unit 701 provides a sacrifice function whereby nitrogen dioxide reducing unit 701 during low temperature operations gets poisoned by ammonium nitrate and the SCR catalyst 12 is avoids such poisoning due to the fact that the NO2 in the exhaust gases have been consumed by the ammonium nitrate forming process in the nitrogen dioxide reducing unit 701. Enough ammonia is injected by the ammonia supply means 711 to support the NOx reduction process of the SCR catalyst 12 as well as the ammonium nitrate forming process in the nitrogen dioxide reducing unit 701.

[0062] The nitrogen dioxide reducing unit 701 and the SCR catalyst 12 are arranged so that the ammonium nitrate stored in the nitrogen dioxide reducing unit 701 is not released from the nitrogen dioxide reducing unit 701 below a temperature in the SCR catalyst 12, e.g. 200 C., at which products, exemplified above as N2O, NO2 and NH3, formed by a decomposition of the ammonium nitrate stored in the nitrogen dioxide reducing unit is converted in the SCR catalyst 12. Further, the nitrogen dioxide reducing unit 701 is adapted to not reduce nitrogen dioxide in the exhaust gases at temperatures above 200 C.

[0063] The nitrogen dioxide reducing unit 701 may be an SCR catalyst, herein referred to as a first SCR catalyst 12, and the SCR catalyst described above may be referred to as a second SCR catalyst 12. In this embodiment, the nitrogen dioxide reducing unit 701 and the SCR catalyst 12 form an integrated element. Thereby, the nitrogen dioxide reducing unit 701 may be formed by zone coating of the integrated element. In alternative embodiments, the nitrogen dioxide reducing unit 701 and the SCR catalyst 12 may be formed by two separate bricks.

[0064] The nitrogen dioxide reducing unit 701 and the SCR catalyst 12 present different active catalytic materials, whereby said sacrificial function of the nitrogen dioxide reducing unit 701 is provided. The nitrogen dioxide reducing unit 701 may comprise a copper (Cu) zeolite and/or an iron (Fe) zeolite, and the SCR catalyst 12 may comprise an oxide of vanadium. More generally, the SCR catalyst 12 may be made from a ceramic materials used as a carrier, such as titanium oxide, and active catalytic components being oxides of base metals, such as vanadium, molybdenum and tungsten, zeolites, or various precious metals.

[0065] Reference is made to FIG. 3 showing an alternative embodiment of the invention. Herein the exhaust conduit 10 comprises a main conduit 102 and a bypass conduit 101, the bypass conduit 101 being branched from the main conduit 102 and arranged to reintroduce exhaust gases into main conduit upstream of the SCR catalyst 12. The means 711 for supplying ammonia comprises an ammonia production catalyst 715 located in the bypass conduit 101, and means 714 to inject a precursor into the bypass conduit 101, upstream of the ammonia production catalyst 715. The ammonia production catalyst 715 is adapted to produce ammonia from the injected precursor at exhaust gas temperatures below 200 C. The ammonia production catalyst is preferably relatively small in size. In some embodiments, the ammonia production catalyst comprises titanium dioxide (TiO2). The precursor may be urea or of any other type of ammonia carrier, e.g. ammonia carbamate, isocyanate, and guanidinium formate or similar.

[0066] Reference is made to FIG. 4 showing yet another embodiment of the invention. Herein the means 711 for supplying ammonia to the exhaust gases is arranged to supply the ammonia downstream of the nitrogen dioxide reducing unit 701. The nitrogen dioxide reducing unit 701 is adapted to reduce nitrogen dioxide in the exhaust gases, at low temperatures, by storing nitrogen dioxide in the exhaust gases, and by converting the nitrogen dioxide to nitrogen oxide (NO). For this the nitrogen dioxide reducing unit 701 may comprise an alkaline metal or an alkaline earth metal. In some embodiments the nitrogen dioxide reducing unit 701 comprises barium oxide, cerium oxide, and/or aluminum oxide.

[0067] The nitrogen dioxide reduction process of the nitrogen dioxide reducing unit 701 comprises adsorption of the nitrogen dioxide. Thereby, one portion of the adsorbed NO2 is immediately converted to NO and released. Another portion of the adsorbed NO2 is stored and released at a higher temperature, e.g. at 200 C. or above. Further, the nitrogen dioxide reducing unit 701 is adapted to not store nitrogen dioxide in the exhaust gases at temperatures above 250 C.

[0068] It should be noted that the arrangement shown in FIG. 4, where the means 711 for supplying ammonia to the exhaust gases is arranged to supply the ammonia downstream of the nitrogen dioxide reducing unit 701, may be provided, as in FIG. 3, with an ammonia production catalyst 715 located in a bypass conduit 101, and means 714 to inject a precursor into the bypass conduit 101, upstream of the ammonia production catalyst 715.

[0069] The graphs of FIG. 5 show the result of a test conducted by the inventors, with a nitrogen dioxide reducing unit according to an embodiment of the invention. The graphs show the variation of the amounts of NO2 and NO coming out of the nitrogen dioxide reducing unit 701 as the temperature changes. As can be seen the total amount of NO2 and NO coming into the nitrogen dioxide reducing unit is constant. In the upper graph it can be seen that at low temperatures the amount of NO is relatively high, but as the temperature increases the amount of NO is reduced. In the lower graph it can be seen that at low temperatures the amount of NO2 is relatively low, but as the temperature increases the amount of NO2 is increased.

[0070] FIG. 6 shows a further embodiment of the invention. The exhaust gas treatment system 8 comprises an exhaust conduit 10 and an SCR catalyst 12 provided in the exhaust conduit 10. The system further comprises a nitrogen dioxide reducing unit 701 provided in the exhaust conduit 10 upstream of the SCR catalyst 12. The nitrogen dioxide reducing unit 701 is adapted to reduce, at a low temperature, nitrogen dioxide NO2 in exhaust gases received by the nitrogen dioxide reducing unit 701. Advantages thereof have been discussed above.

[0071] It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.