Exhaust Gas Post Treatment System And Method For Exhaust Gas Post-Treatment

Abstract

An exhaust gas post treatment system for an internal combustion engine, in particular a heavy fuel oil-powered engine, including an SCR catalyst, using ammonia as a reducing agent for the denitration of the exhaust gas, and a device positioned upstream of the SCR catalyst by which ammonia or an ammonia precursor substance, which is converted to ammonia, introduced upstream of the SCR catalyst. Downstream of the SCR catalyst an exhaust gas scrubber is positioned, by which excess ammonia, contained in the exhaust gas leaving the SCR catalyst, together with sulfur oxides, can be scrubbed out of the exhaust gas forming ammonium salts while maintaining a pH value of approximately 6. For the control thereof, a bypass around the SCR catalyst can be provided as a westgate, or comprising an additional SCR catalyst.

Claims

1.-13. (canceled)

14. An exhaust gas after-treatment system for an internal combustion engine, comprising: an SCR catalytic converter configured for denitrification of exhaust gas that utilizes ammonia as a reduction agent; a device arranged upstream of the SCR catalytic converter in flow direction of the exhaust gas, and configured to introduce the ammonia and/or an ammonia precursor substance into the exhaust gas upstream of the SCR catalytic converter, which is converted in the exhaust gas to form the ammonia; and an exhaust gas scrubber is positioned downstream of the SCR catalytic converter and, via which the ammonia, which is contained in the exhaust gas leaving the SCR catalytic converter, together with sulphur oxides, which are contained in the exhaust gas leaving the SCR catalytic converter, are scrubbed out of the exhaust gas subject by forming ammonia salts.

15. The exhaust gas according to claim 14, wherein the device is configured to introduce the ammonia and/or the ammonia precursor substance into the exhaust gas in a quantity that is greater than an ammonia quantity that is convertible in the SCR catalytic converter, and wherein downstream of the SCR catalytic converter, ammonia is present in a quantity so that a ph value of waste water of the exhaust gas scrubber is between 4 and 8.

16. The exhaust gas according to claim 15, wherein the device introduces the ammonia and/or the ammonia precursor substance into the exhaust gas in a quantity so that the ph value of the waste water lies between one of: 5 and 7, and 5.5 and 6.5.

17. The exhaust gas after-treatment system according to claim 14, further comprising: a bypass via which an exhaust gas part flow is branched off the exhaust gas having an inlet downstream of the device and upstream of the SCR catalytic converter and an outlet downstream of the SCR catalytic converter and upstream of the exhaust gas scrubber.

18. The exhaust gas after-treatment system according to claim 14, further comprising: a bypass having an inlet upstream of the SCR catalytic converter, a first outlet upstream of the SCR catalytic converter, and an outlet downstream of the SCR catalytic converter, wherein the device is arranged to introduce the ammonia and/or the ammonia precursor substance into the bypass upstream of the first outlet, and wherein a first part of the exhaust gas part flow upstream of the SCR catalytic converter can be fed to the exhaust gas main flow and a second part of the exhaust gas part flow downstream of the SCR catalytic converter and upstream of the exhaust gas scrubber can be fed to the exhaust gas conducted via the SCR catalytic converter.

19. The exhaust gas after-treatment system according to claim 17, further comprising an additional SCR catalytic converter is arranged in the bypass.

20. The exhaust gas after-treatment system according to claim 14, further comprising: a turbine of an exhaust gas turbocharger, wherein the device for introducing the ammonia and/or the ammonia precursor substance into the exhaust gas is positioned upstream of the turbine of the exhaust gas turbocharger and the exhaust gas scrubber is arranged downstream of the turbine of the exhaust gas turbocharger.

21. The exhaust gas after-treatment system according to claim 20, wherein a bypass simultaneously serves as turbocharger waste gate.

22. A method for the exhaust gas after-treatment of exhaust gas leaving an internal combustion engine, comprising: denitrification of the exhaust gas via an SCR catalytic converter that utilizes ammonia as reduction agent; introducing the ammonia and/or an ammonia precursor substance, which is converted in the exhaust gas to form the ammonia, into the exhaust gas upstream of the SCR catalytic converter; and scrubbing via an exhaust gas scrubber the exhaust gas downstream of the SCR catalytic converter, via which the ammonia and sulphur oxides contained in the exhaust gas leaving the SCR catalytic converter are scrubbed out of the exhaust gas by forming ammonia salts.

23. The method according to claim 22, wherein different ammonia concentrations are adjusted via an inlet cross section of the SCR catalytic converter.

24. The method according to claim 23, wherein an equipartition index of the ammonia upstream of the SCR catalytic converter lies below 0.8.

25. The method according to claim 24, wherein the equipartition index of the ammonia downstream of the SCR catalytic converter lies below 0.7 and/or 0.6.

26. The exhaust gas according to claim 14, wherein the internal combustion engine is a marine diesel engine operated with heavy fuel oil.

27. The exhaust gas after-treatment system according to claim 18, further comprising an additional SCR catalytic converter is arranged in the bypass.

28. The exhaust gas after-treatment system according to claim 20, wherein the turbine of an exhaust gas turbocharger, wherein the SCR catalytic converter is arranged upstream of the turbine of the exhaust gas turbocharger.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Preferred further developments of the invention are obtained from the subclaims and the following description. Exemplary embodiments of the invention are explained in more detail by way of the drawing without being restricted to this. There it shows:

[0019] FIG. 1 is a schematic representation of an exhaust gas after-treatment system for an internal combustion engine according to the invention;

[0020] FIG. 2 is a schematic representation of an exhaust gas after-treatment system for an internal combustion engine according to the invention;

[0021] FIG. 3 is a schematic representation of an exhaust gas after-treatment system for an internal combustion engine according to the invention;

[0022] FIG. 4 is a schematic representation of an exhaust gas after-treatment system for an internal combustion engine according to the invention;

[0023] FIG. 5 is a schematic representation of an exhaust gas after-treatment system for an internal combustion engine according to the invention;

[0024] FIG. 6 is a schematic representation of an exhaust gas after-treatment system for an internal combustion engine according to the invention;

[0025] FIG. 7 is a schematic representation of an exhaust gas after-treatment system for an internal combustion engine according to the invention;

[0026] FIG. 8 is a schematic representation of an exhaust gas after-treatment system for an internal combustion engine according to the invention; and

[0027] FIG. 9 is a schematic representation of an exhaust gas after-treatment system for an internal combustion engine according to the invention.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

[0028] The present invention relates to an exhaust gas after-treatment system for an internal combustion engine, in particular for a marine diesel engine operated with heavy fuel oil. Furthermore, the invention relates to a method for the exhaust gas after-treatment on such an internal combustion engine.

[0029] FIG. 1 shows, in a highly schematic manner, an internal combustion engine 10 with multiple cylinders 11. Exhaust gas 12, which leaves the internal combustion engine 10, is conducted via an exhaust gas after-treatment system located downstream of the internal combustion engine 10, which comprises an SCR catalytic converter 13. Accordingly, the exhaust gas 12 leaving the internal combustion engine 10 is fed to the SCR catalytic converter 13 as untreated exhaust gas 12 and leaves the SCR catalytic converter 13 as at least partially treated exhaust gas 14. In the SCR catalytic converter 13, a reduction agent is required for the exhaust gas emission control, namely for denitrifying the exhaust gas 12, wherein as reduction agent ammonia is utilised. The NH.sub.3 precursor substance urea, carbamide, guanidium-formiate can also be employed.

[0030] The ammonia needed for the exhaust gas emission control in the SCR catalytic converter 13 can be added in metered quantity to the untreated exhaust gas 12 upstream of the SCR catalytic converter 13 with the help of a device 15, namely either directly as ammonia or as ammonia precursor substance, which is then converted into ammonia in the exhaust gas.

[0031] In particular when ammonia is added to the exhaust gas 12 leaving the internal combustion engine 10 is the device 15 an ammonia generator.

[0032] In particular when an ammonia precursor substance is added in metered quantity to the exhaust gas 12, the device 15 preferentially has a nozzle with the help of which the ammonia precursor substance, in particular urea, is injected into the exhaust gas 12. The urea is then evaporated in the exhaust gas upstream of the SCR catalytic converter 13 to form steam, carbon dioxide, and ammonia.

[0033] In the SCR catalytic converter 13, the exhaust gas 12 leaving the internal combustion engine 10 is denitrified subject to using the ammonia so that accordingly in the exhaust gas 14, nitrogen oxides are removed from the exhaust gas downstream of the SCR catalytic converter 13.

[0034] According to the invention, an exhaust gas scrubber 16 is positioned downstream of the SCR catalytic converter 13. By way of the exhaust gas scrubber 16, ammonia, which is contained in the exhaust gas 14 leaving the SCR catalytic converter 13, can be scrubbed out of the exhaust gas together with sulphur oxides, which are likewise contained in the exhaust gas 14 leaving the SCR catalytic converter 13, subject to forming ammonia salts.

[0035] Accordingly, exhaust gas 17, which has been subjected to both denitrification and desulphurisation and from which sulphur oxides and nitrogen oxides have accordingly been removed, is present downstream of the exhaust gas scrubber 16.

[0036] Accordingly, the exhaust gas 14 leaving the SCR catalytic converter 13 and on the other hand as so-called scrubbing agent 18, preferentially water is fed to the exhaust gas scrubber 16, wherein on the one hand the desulphurised exhaust gas 17 and on the other hand waste water 19 enriched with ammonia salts leave the exhaust gas scrubber.

[0037] It is therefore in the interest of the present invention to utilise the device 15 positioned upstream of the SCR catalytic converter 13 in such a manner that via the same, ammonia and/or an ammonia precursor substance is introduced into the exhaust gas in a quantity that is greater than the ammonia quantity that is convertible in the SCR catalytic converter 13. Accordingly, ammonia is present in the exhaust gas 14 downstream of the SCR catalytic converter 13 in a quantity that can be utilised in the exhaust gas scrubber 16 in order to scrub sulphur oxides out of the exhaust gas 14 for the desulphurisation of the same subject to forming ammonia salts.

[0038] Here, the device 15 positioned upstream of the SCR exhaust gas 13 introduces the ammonia and/or the ammonia precursor substance into the exhaust gas 12 in a quantity so that downstream of the SCR catalytic converter 13 ammonia is contained in the exhaust gas 14 in a quantity so that the ph value of the waste water 19 of the exhaust gas scrubber 16 lies between 4 and 8, preferably between 5 and 7, particularly preferably between 5.5 and 6.5. This can be established via a regulating circuit, in which the ph value of the waste water 19 is measured, compared with a set value and independently thereof the device 15 subject to adapting the quantity of ammonia and/or of the ammonia precursor substance introduced into the exhaust gas from the device is activated so that the measured ph value is approximately the set point value.

[0039] With the invention, effective desulphurisation and denitrification of exhaust gas, in particular for a marine diesel engine operated with heavy fuel oil is possible, wherein both for denitrification and also for the desulphurisation ammonia as operating substance is used in each case. Through the increased quantity of the ammonia that is available for the denitrification in the region of the SCR catalytic converter 13 a particularly effective denitrification of the exhaust gas is possible in the region of the SCR catalytic converter 13. The ammonia that is contained in the exhaust gas 14 downstream of the SCR catalytic converter 13 is utilised in the region of the exhaust gas scrubber 16 for the desulphurisation of the exhaust gas.

[0040] FIG. 2 shows a further development of the exemplary embodiment of FIG. 1, wherein the exemplary embodiment of FIG. 2 differs from the exemplary embodiment of FIG. 1 merely in that the exhaust gas after-treatment system of FIG. 2 comprises a bypass 20. By way of the bypass 20, exhaust gas can be branched off from the exhaust gas 12 subject to forming an exhaust gas main flow 12a and an exhaust gas part flow 12b upstream of the SCR catalytic converter 13 and downstream of the device 15, which serves for introducing the ammonia and/or the ammonia precursor substance into the exhaust gas 12, wherein the exhaust gas main flow 12ais conducted via the SCR catalytic converter 14, and wherein the exhaust gas part flow 12b is conducted past the SCR catalytic converter 13 via the bypass 20.

[0041] Downstream of the SCR catalytic converter 13 the exhaust gas part flow 12b conducted past the same can be united with the exhaust gas flow 14 leaving the SCR catalytic converter 13 in order to be then conducted jointly via the exhaust gas scrubber 16. The denitrification in the SCR catalytic converter 13 and the desulphurisation in the exhaust gas scrubber 14 can thereby be adjusted or controlled to a certain degree independently of one another.

[0042] FIG. 3 shows a further development of the exemplary embodiment of FIG. 2, in which in the bypass 20 a further SCR catalytic converter 21 is positioned in order to also conduct the exhaust gas part flow 12b upstream of the exhaust gas scrubber 16 via its own SCR catalytic converter 21 for denitrification. This can further improve the denitrification of the exhaust gas.

[0043] A further version of the invention is shown by FIG. 4, wherein in the exemplary embodiment of FIG. 4 the exhaust gas after-treatment system also comprises a bypass 22. In the exemplary embodiment of FIG. 4, the exhaust gas 12 can be again divided, via the bypass 22, into an exhaust gas main flow 12a and an exhaust gas part flow 12b, wherein the exhaust gas main flow 12a is mandatorily conducted via the SCR catalytic converter 13.

[0044] In contrast with the exemplary embodiments of FIGS. 2 and 3 however it is provided in the exemplary embodiment of FIG. 4 that the device 15, which serves for introducing the ammonia and/or the ammonia precursor substance into the exhaust gas, is assigned to the bypass 22 so that accordingly the bypass 22 divides the exhaust gas upstream of the device 15 into the exhaust gas main flow 12a and the exhaust gas part flow 12b. The device 15 introduces the ammonia and/or the ammonia precursor substance into the exhaust gas part flow 12b, wherein the exhaust gas part flow 12b is divided into two parts 12b1 and 12b2 downstream of the device 15.

[0045] The part 12b1 of the exhaust gas part flow 12b is conducted past the SCR catalytic converter 13 and downstream of the SCR catalytic converter 13 as well as upstream of the exhaust gas scrubber 16 mixed with the exhaust gas 14 that leaves the SCR catalytic converter 13.

[0046] The part 12b2 of the exhaust gas part flow 12b is mixed upstream of the SCR catalytic converter 13 with the exhaust gas main flow 12a and together with the exhaust gas main flow 12a conducted via the SCR catalytic converter 13.

[0047] FIG. 5 shows a further development of the exemplary embodiment of FIG. 4, in which in agreement with the exemplary embodiment of FIG. 3, a further SCR catalytic converter 21 is fed to the bypass 22, via which in the exemplary embodiment of FIG. 5 the part 12b1 of the exhaust gas part flow 12b is conducted.

[0048] FIG. 6 shows a further development of the exemplary embodiment of FIG. 5, in which a hydrolysis catalytic converter 23 is assigned to the bypass 22 downstream of the device 15, which in the exemplary embodiment of FIG. 6 serves for adding a metered quantity of an ammonia precursor substance to the exhaust gas part flow 12b. By way of the hydrolysis catalytic converter 23, the conversion of the ammonia precursor substance into ammonia in the exhaust gas part flow 12b can be improved or promoted. Dividing the exhaust gas part flow 12b into the two parts 12b1 and 12b2 takes place downstream of the hydrolysis catalytic converter 23.

[0049] FIGS. 7 and 8 show two exemplary embodiments of the invention, with which the version of FIG. 1 is employed with an exhaust gas supercharged internal combustion engine. Accordingly, FIG. 7 shows an internal combustion engine 10 with a single-stage exhaust gas supercharging device via a single exhaust gas turbocharger 24, wherein of the exhaust gas turbocharger 24 a turbine 25 and a compressor 26 are shown. In FIG. 7, the SCR catalytic converter 13 including the device 15, which serves for adding the ammonia and/or the ammonia precursor substance in metered quantity to the exhaust gas 12, is arranged upstream of the turbine 25 of the exhaust gas turbocharger 24, but the exhaust gas scrubber 16 is positioned downstream of the turbine of the exhaust gas turbocharger 24. Because of the high pressures and temperatures upstream of the turbine 25, the denitrification of the exhaust gas in the region of the SCR catalytic converter 13 is promoted. Energy extracted in the turbine 25 during the expansion of the denitrified exhaust gas 14 is utilised in order to compress charge air 27 to be fed to the internal combustion engine 10 in the region of the compressor 26 of the exhaust gas turbocharger 24.

[0050] FIG. 8 shows a version of an internal combustion engine 10 with a two-stage exhaust gas supercharging device, which accordingly comprises two exhaust gas turbochargers 24a, 24b. The exhaust gas turbocharger 24a is a high-pressure exhaust gas turbocharger and the exhaust gas turbocharger 24b is a low-pressure exhaust gas turbocharger. In FIG. 8, the SCR catalytic converter 13 and the device 15 for introducing the ammonia or the ammonia precursor substance into the exhaust gas 12 are arranged downstream of the high-pressure turbine 25a of the high-pressure turbocharger 24a and upstream of the low-pressure turbine 25b of the low-pressure turbocharger 24b, whereas the exhaust scrubber 16 is arranged downstream of the low-pressure turbine 25b of the low-pressure turbocharger 24b. Energy extracted in the exhaust gas turbochargers 24a, 24b during the expansion of the exhaust gas in the region of the turbines 24a, 25b is utilised in order to compress the charge air 27 to be fed to the internal combustion engine 10 in two stages, namely in the region of the low-pressure compressor 26b and of the high-pressure compressor 26a of low-pressure exhaust gas turbocharger 24b and high-pressure turbocharger 24a.

[0051] It is pointed out here that the versions of FIGS. 2 to 6 can each be utilised also combined with an internal combustion engine 10 that is supercharged in a single stage or in two stages. Then, corresponding to the exemplary embodiments of FIGS. 7 and 8, the SCR catalytic converters 13 and if applicable 21 including the bypasses 20, 22 are positioned upstream of a turbine 25 and 25b respectively of an exhaust gas turbocharger 24 and 24b respectively, whereas the exhaust gas scrubbers 16 are positioned downstream of the respective turbine 25, 25b of the respective exhaust gas turbocharger 24, 24b.

[0052] In the exemplary embodiments of the FIGS. 1 to 8, the ammonia or the ammonia precursor substance is introduced into the exhaust gas via the device 15 in such a manner that, via the inlet cross section of the one or each SCR catalytic converter 13 or 21, a uniform ammonia concentration is adjusted.

[0053] In contrast with this, FIG. 9 shows a further development of the exemplary embodiment of FIG. 1, in which via the inlet cross section of the SCR catalytic converter 13 different ammonia concentrations are adjusted. Accordingly, two devices 15a, 15b are shown in FIG. 9, which in each case serve for introducing ammonia or an ammonia precursor substance into the exhaust gas 12 leaving the internal combustion engine 10 upstream of the SCR catalytic converter 13, namely in such a manner that via the inlet cross section of the SCR catalytic converter a different ammonia concentration is adjusted. This can be ensured for example in that the two devices 15a, 15b introduce the ammonia or the ammonia precursor substance into the exhaust gas 12 with a different mass flow, as shown in FIG. 9, directly in the inlet region of the SCR catalytic converter 13. Here, the adjustment of an ammonia concentration that is different over the inlet cross section of the SCR catalytic converter 13 preferentially in such a manner that downstream of the SCR catalytic converter 13 in the exhaust gas 14 leaving the SCR catalytic converter 13 and accordingly upstream of the exhaust gas scrubber 16 an equipartition index of the ammonia lies below 0.8, preferably below 0.7, particularly preferably below 0.6.

[0054] The equipartition index of ammonia downstream of the SCR catalytic converter can be determined according to the following equations:

[00001]$\gamma =1-0.5*\stackrel{\_}{\omega }$$\stackrel{\_}{\omega }=\frac{1}{n}*\underset{i=1}{\overset{n}{.Math.}}.Math.{\omega }_i$${\omega }_i=\frac{1}{\stackrel{\_}{c}}*\sqrt{{\left(c_i-\stackrel{\_}{c}\right)}^2}$$\stackrel{\_}{c}=\frac{1}{n}*\underset{i=1}{\overset{n}{.Math.}}.Math.c_i.$

[0055] wherein the equipartition index of the ammonia is downstream of the SCR catalytic converter 13, wherein c.sub.i is the ammonia concentration at the i.sup.th measurement point upstream of the SCR catalytic converter 13, and wherein n is the total number of the measurement points downstream of the SCR catalytic converter 13.

[0056] It is therefore in the interest of the present invention for the exhaust gas emission control of an internal combustion engine 10, in particular of an internal combustion engine operated with heavy fuel oil, for the denitrification and desulphurisation to utilise ammonia in each case, wherein the denitrification takes place in an SCR catalytic converter 13 and the desulphurisation in an exhaust gas scrubber 16 downstream thereof. Here, the SCR catalytic converter 13 is operated with excess ammonia so that downstream of the SCR catalytic converter 13 and upstream of the exhaust gas scrubber 16 a defined ammonia quantity is present which can be utilised for the desulphurisation in the exhaust gas scrubber 16.

[0057] Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.