Exhaust gas after-treatment system and method for the exhaust gas after-treatment

Abstract

An exhaust gas after-treatment system for an internal combustion engine, with a particle filter arranged downstream of an internal combustion engine for filtering soot out of the exhaust gas, and with an oxidation catalytic converter arranged upstream of the particle filter and downstream of the internal combustion engine for the oxidation of SO.sub.2 into SO.sub.3. The SO.sub.3 and/or precipitated H2SO.sub.4 serves for the oxidation of soot in the particle filter and thus for the regeneration of the particle filter.

Claims

1. An exhaust gas after-treatment system arranged in an exhaust gas flow of an internal combustion engine, comprising: a particle filter arranged downstream of the internal combustion engine configured to filter soot out of the exhaust gas; and an oxidation catalytic converter arranged upstream of the particle filter and downstream of the internal combustion engine configured to oxidize SO.sub.2 into SO.sub.3, wherein at least one of the SO.sub.3 and precipitated H.sub.2SO.sub.4 serves for oxidation of soot in the particle filter for regeneration of the particle filter based at least in part on a temperature of the exhaust gas.

2. The exhaust gas after-treatment system according to claim 1, wherein the oxidation catalytic converter comprises at least one of vanadium, sodium, iron, cerium, cesium, and oxides of these elements as active component for oxidation of SO.sub.2 into SO.sub.3, wherein the oxidation catalytic converter utilizes at least one of titanium oxide and silicon oxide as a base material.

3. The exhaust gas after-treatment system according to claim 1, wherein the oxidation catalytic converter active component comprises at least 5% vanadium.

4. The exhaust gas after-treatment system according to claim 1, wherein a mass ratio between SO.sub.3 and soot is at least 7:1 downstream of the oxidation catalytic converter, proximate to the particle filter.

5. The exhaust gas after-treatment system according to claim 1, further comprising: a turbine for an exhaust gas turbocharger, wherein the oxidation catalytic converter is arranged upstream of the turbine of the exhaust gas turbocharger and the particle filter is positioned downstream of the turbine.

6. The exhaust gas after-treatment system according to claim 1, further comprising: an oxidation catalytic converter for oxidation of NO into NO.sub.2 arranged upstream of the particle filter and downstream of the internal combustion engine, wherein the NO.sub.2 serves for the oxidation of soot in the particle filter and the regeneration of the particle filter.

7. The exhaust gas after-treatment system according to claim 6, wherein the oxidation catalytic converter for oxidation of NO into NO.sub.2 is connected parallel to the oxidation catalytic converter for oxidation of SO.sub.2 into SO.sub.3.

8. The exhaust gas after-treatment system according to claim 7, further comprising: shut-off valves configured to shut off at least one of the oxidation catalytic converter for the oxidation of NO into NO.sub.2 and the oxidation catalytic converter for oxidation of SO.sub.2 into SO.sub.3 from the exhaust gas flow based at least in part on the Sulphur content of a fuel provided to the internal combustion engine.

9. The exhaust gas after-treatment system according to claim 2, wherein the base material is stabilized by tungsten oxide.

10. The exhaust gas after-treatment system according to claim 3, wherein the oxidation catalytic converter active component comprises at least 9% vanadium.

11. The exhaust gas after-treatment system according to any one of the claim 4, wherein the mass ratio between SO.sub.3 and soot is at least 16:1.

12. A method for exhaust gas after-treatment of exhaust gas leaving an internal combustion engine, comprising: providing the exhaust gas to an oxidation catalytic converter for oxidation of SO.sub.2 into SO.sub.3; providing the exhaust gas, after oxidation by the oxidation catalytic converter, to a particle filter configured to filter soot out of the exhaust gas; and regenerating the particle filter by oxidation of soot in the particle filter with at least one of the SO.sub.3 formed in the oxidation catalytic converter and precipitated H.sub.2SO.sub.4 based at least in part on a temperature of the exhaust gas.

13. The method for exhaust gas after-treatment according to claim 12, wherein during operation of the internal combustion engine with a fuel having a high Sulphur content, shutting off the exhaust gas flow by shut-off valves to an oxidation catalytic converter for oxidation of NO into NO.sub.2 so the exhaust gas flow is provided to the oxidation catalytic converter for the oxidation of SO.sub.2 into SO.sub.3, and wherein during operation of the internal combustion engine with a fuel that has a relatively low Sulphur content, shutting off the exhaust gas flow by shut-off valves to the oxidation catalytic converter for the oxidation of SO.sub.2 into SO.sub.3 so the exhaust gas flow is provided to the oxidation catalytic converter for the oxidation of NO into NO.sub.2.

14. The method for exhaust gas after-treatment according to claim 13, wherein the high Sulphur content is a Sulphur content of the fuel above 1,000 ppm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention are explained in more detail with the help of the drawing without being restricted to this. Here it shows:

(2) FIG. 1: is a block diagram of a first exhaust gas after-treatment system;

(3) FIG. 2: is a block diagram of a second exhaust gas after-treatment system; and

(4) FIG. 3: is a block diagram of a third exhaust gas after-treatment system.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

(5) The present invention relates to an exhaust gas after-treatment system for an internal combustion engine, for example for a stationary internal combustion engine in a power plant or for a non-stationary internal combustion engine employed on a ship, which is operated with fuel having a relatively high sulphur content such as heavy fuel oil.

(6) FIG. 1 shows a first exemplary embodiment of an exhaust gas after-treatment system 2 positioned downstream of an internal combustion engine 1, wherein the exhaust gas after-treatment system 2 comprises at least one oxidation catalytic converter 3 for the oxidation of SO.sub.2 into SO.sub.3 and a particle filter 4 arranged downstream of the oxidation catalytic converter 3 for filtering soot out of the exhaust gas of the internal combustion engine 1.

(7) In the oxidation catalytic converter 3, the SO.sub.2 contained in the exhaust gas of the internal combustion engine 1 is oxidised into SO.sub.3, wherein the SO.sub.3 extracted in the process serves for the oxidation of soot in the particle filter 4 and thus for the regeneration of the particle filter 4.

(8) The oxidation of SO.sub.2 into SO.sub.3 in the oxidation catalytic converter 3 takes place according to the following reaction equation:
2SO.sub.2+O.sub.2.fwdarw.2SO.sub.3

(9) The oxidation of the soot in the particle filter 4 with the help of the SO.sub.3 formed in the oxidation catalytic converter 3 in this case takes place according to the following reaction equations:
2SO.sub.3+C.fwdarw.CO.sub.2+2SO.sub.2
SO.sub.3+C.fwdarw.CO+SO.sub.2

(10) Should the exhaust gas cool down below the sulphuric acid dew point, precipitation of H.sub.2SO.sub.4 (sulphuric acid) occurs. H.sub.2SO.sub.4 can likewise be utilised for the oxidation of soot in the particle filter 4 and for the regeneration of the particle filter 4. In the process, sulphuric acid can effectively oxidise soot in particular at exhaust gas temperatures below 250 C. and thus make possible effective regeneration of the particle filter 4.

(11) The oxidation catalytic converter 3 utilises vanadium V and/or potassium K and/or sodium Na and/or iron Fe and/or cerium Ce and/or caesium Cs and/or oxides of these elements as active component for the oxidation of SO.sub.2 into SO.sub.3, wherein the oxidation catalytic converter 3 utilises titanium oxide TiO.sub.2 and/or silicon oxide SiO.sub.2 preferentially stabilised by tungsten oxide WO.sub.3.

(12) The component of vanadium in the oxidation catalytic converter 3, which is present as active component for the oxidation of SO.sub.2 into SO.sub.3, amounts to more than 5%, preferentially more than 7%, particularly preferably more than 9%.

(13) The conversion of SO.sub.2 into SO.sub.3 in the oxidation catalytic converter 3 is effected in such a manner that downstream of the oxidation catalytic converter 3 in the region of the particle filter 4 there is a mass ratio between SO.sub.3 and soot of at least 7:1, preferably of at least 12:1, particularly preferably of at least 16:1.

(14) FIG. 2 shows a further development of the exhaust gas after-treatment system 2 of FIG. 1, wherein the internal combustion engine of FIG. 2 is an exhaust gas supercharged internal combustion engine, in which exhaust gas is expanded in a turbine 5 of an exhaust gas turbocharger to extract mechanical energy, which serves for driving a compressor of the exhaust gas turbocharger to compress charge air to be fed to the internal combustion engine 1 in the compressor of the exhaust gas turbocharger.

(15) In particular when, as shown in FIG. 2, the exhaust gas after-treatment system 2 accordingly comprises a turbine 5 of an exhaust gas turbocharger is the oxidation catalytic converter 3 positioned upstream of the turbine 5 and the particle filter 4 downstream of the turbine 5. The high pressures and temperatures upstream of the turbine 5 of an exhaust gas turbocharger favour the oxidation of SO.sub.2 into SO.sub.3 in the oxidation catalytic converter 3.

(16) A further advantageous further development of the exhaust gas after-treatment system 2 of FIG. 1 is shown by FIG. 3, wherein the version of FIG. 3 is used in particular in internal combustion engines 1 operated both with fuel having a relatively high sulphur content and also with fuel having a relatively low sulphur content.

(17) Accordingly, FIG. 3 shows an exhaust gas after-treatment system 2 which in turn comprises an oxidation catalytic converter 3 arranged downstream of the internal combustion engine 1 for the oxidation of SO.sub.2 into SO.sub.3 and a particle filter 4 arranged downstream of said oxidation catalytic converter 3 for filtering soot out of the exhaust gas, wherein however the exhaust gas after-treatment system 2 of FIG. 3 additionally comprises an oxidation catalytic converter 6 for the oxidation of NO into NO.sub.2. The NO.sub.2 extracted in the oxidation catalytic converter 6 likewise serves for the oxidation of soot in the particle filter 4 and thus the regeneration of the same.

(18) In FIG. 3, the oxidation catalytic converter 6 for the oxidation of NO into NO.sub.2 is connected parallel to the oxidation catalytic converter 3 for the oxidation of SO.sub.2 into SO.sub.3, wherein the exhaust gas of the internal combustion engine is conducted, dependent on the opening position of shut-valves 7, 8, either via the oxidation catalytic converter 3 or via the oxidation catalytic converter 6.

(19) In particular when the internal combustion engine 1 is operated with a fuel that has a relatively high sulphur content, the shut-off valves 8 open and the shut-off valves 7 closed, so that the exhaust gas flow of the internal combustion engine 1 is then conducted via the oxidation catalytic converter 3 for the oxidation of SO.sub.2 into SO.sub.3 and the oxidation catalytic converter 6 for the oxidation of NO into NO.sub.2 is separated from the exhaust gas flow. If by contrast the internal combustion engine 1 of FIG. 3 is operated with fuel that has a relatively low sulphur content, the shut-off valves 7 are opened and the shut-off valves 8 closed, so that the exhaust gas is conducted via the oxidation catalytic converter 6 for the oxidation of NO into NO.sub.2, wherein the oxidation catalytic converter 3 for the oxidation of SO.sub.2 into SO.sub.3 is separated or shut off from the exhaust gas flow. The version of FIG. 3 is suitable in particular for use in marine engines, which on the one hand are operated with fuel having a relatively high sulphur content and on the other hand with fuel having a relatively low sulphur content. Here, dependent on the type of fuel used, suitably adapted passive regeneration of the particle filter 4 optionally via NO.sub.2 or SO.sub.3 can then be ensured.

(20) During operation of the internal combustion engine 1 with fuel having a relatively high sulphur content the shut-off valves 7 are closed is the oxidation catalytic converter 6, which serves for the oxidation of NO into NO.sub.2, kept free of sulphur. An alternative to this consists in omitting the shut-off valves and rendering the oxidation catalytic converter 6 operationally following operation with fuel having a relatively high sulphur content in that the exhaust gas temperature is raised and sulphur thus desorbed in the oxidation catalytic converter 6. The version with the shut-off valves 7, 8 however is preferred since following operation of the internal combustion engine 1 with sulphur-containing fuel the oxidation catalytic converter 6 is then ready for operation immediately following this.

(21) In particular, the exhaust gas after-treatment system is employed in internal combustion engines which are operated with fuel the sulphur content of which amounts to at least 1,000 ppm.

(22) 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.