NO344568B1

NO344568B1 - Method for exhaust-gas aftertreatment

Info

Publication number: NO344568B1
Application number: NO20181466A
Authority: NO
Inventors: Christian Poensgen; Andreas Döring
Original assignee: Man Energy Solutions Se
Priority date: 2018-11-16
Filing date: 2018-11-16
Publication date: 2020-02-03
Also published as: NO20181466A1

Description

The invention relates to a method for exhaust-gas aftertreatment.

From practice, methods are known for exhaust-gas aftertreatment of the exhaust gas from internal combustion engines, which use a particle filter and at least one exhaustgas aftertreatment assembly arranged upstream of the particle filter when viewed in the flow direction of the exhaust gas. The term particle filter is understood to include conventional particle filters, which have a filter medium through which the exhaust gas flows, as well as particle separators, in which the exhaust gas flows around a filter medium functioning as a separation structure.

With regard to an exhaust-gas aftertreatment assembly positioned upstream of the particle filter when viewed in the flow direction of the exhaust gas, this is, in particular, an oxidation catalytic converter for oxidizing nitrogen monoxide (NO) into nitrogen dioxide (NO2).

Thus, when an oxidation catalytic converter for oxidizing NO into NO2is positioned upstream of the particle filter when viewed in the flow direction of the exhaust gas flow, NO is oxidized to NO2with the aid of the residual oxygen O2contained in the exhaust gas flow, according to the following equation:

2 NO O2→ 2 NO2

During the oxidation from nitrogen monoxide to nitrogen dioxide, the equilibrium of the oxidation reaction is on the side of nitrogen monoxide at high temperatures. This results in that the achievable proportion of nitrogen dioxide is strongly limited at high temperatures.

The nitrogen dioxide obtained in the oxidation catalytic converter is converted in the particle filter to carbon monoxide (CO), carbon dioxide (CO2), nitrogen (N2), and nitrogen monoxide (NO) using carbon-containing particles, so-called soot, which collect in the particle filter. A continuous removal of the carbon-containing particulates or the soot accumulated in the particle filter is hereby carried out, in terms of a passive regeneration of the particle filter, wherein this conversion is carried out according to the following equations:

2 NO2+ C → 2 NO CO2

NO2+ C → NO CO

2 C 2 NO2→ N2+ 2 CO2

Thus, when a complete conversion of the carbon-containing particulates or the soot accumulated in the particle filter may not be carried out using such a passive regeneration of the particle filter, then the carbon proportion or soot proportion increases in the particle filter, wherein a particle filter with a filter medium through which the exhaust gas flows tends towards clogging, due to which a so-called exhaust gas back pressure ultimately increases at an internal combustion engine upstream of the exhaust gas treatment system. An increasing exhaust gas backpressure at the internal combustion engine reduces the output of the internal combustion engine and causes an increased fuel consumption. To prevent an increase in the carbon-containing particulates or the soot in the particle filter, it is known from practice to provide the filter medium of a particle filter, through which the exhaust gas flows, with a catalytic coating. Preferably, platinum-containing coatings are thereby used. The use of such particle filters with catalytic coatings may, however, insufficiently prevent the loading of the particle filter with carbon-containing particulates, thus with soot.

It is further known from practice to reduce the loading of soot on a filter medium of a particle filter, through which exhaust gas flows, by using active regeneration of the filter medium. In such an active regeneration, the exhaust gas temperature is actively increased in order to burn off carbon-containing particulates or soot particles, which have accumulated in the filter medium, via an exothermic reaction or oxidation of the hydrocarbons. Burning off the carbon with the aid of oxygen in a particle filter is thereby carried out according to the following equation:

C O2→ CO2

In an active regeneration by burning off the soot particles, a strong temperature increases of up to 1000ºC may form in the particle filter. At this type of strong temperature increase, damage to the particle filter may occur.

US 5,357,755 disclose a trap muffin apparatus with bypass around a trap core. A bypass arrangement utilizing a tubular shutter valve system is described. Forward or reverse regeneration are possible. Bypass to atmosphere without filtration is avoided dual in-line traps or with the segmented trap and control of exhaust gases to traps not being regenerated.

WO 03/004134 relates to a method for purifying exhaust gases containing particulate impurities or nitrogen oxides. The exhaust gases are purified by a filtering matrix which is simultaneously regenerated. The filtering matrix is regenerated by a gas flow or air flow which is weak in relation to the exhaust gas flow. Preferably, the regeneration gas is preheated. The different functional regions are successively crossed. The method can be carried out with rotating elements, where the different functional areas are successively crossed by means of rotation.

WO 2012/073068 is concerned with an engine arrangement comprising an exhaust gases aftertreatment system. The engine arrangement comprises: an internal combustion engine and an exhaust pipe capable of collecting exhaust gases from said engine; an injection device designed to inject an exhaust treatment fluid inside the exhaust pipe, and an aftertreatment device located downstream from the injection device, for at least partially removing undesired components from the exhaust gases; a bypass line branching from the exhaust pipe upstream from the injection device, and capable of carrying a sub-flow of the exhaust gases towards a supply device which is arranged at the aftertreatment device inlet and which is designed to direct said sub-flow towards a sector of the aftertreatment device, while the exhaust gases flowing in the exhaust pipe towards the aftertreatment device pass through the complementary portion of the aftertreatment device; a heater designed to heat the exhaust gases sub- flow; and an additional injection device designed to inject an exhaust treatment fluid inside the bypass line.

DE 102008064540 discloses an emission control device having a particle filter and an inlet for the exhaust gas stream of the particle filter. A flushing system is provided with the particle filter, where the flushing system is stationary in an operative connection. The particle filter is arranged within a flushing area of the flushing system.

US 5,013,340 relates to a rotating particulate trap, which may find application in diesel engines, air conditioning systems, industrial air-filters and the like. The trap includes a disk or cylinder which is formed from material suitable for filtering particulates which are present in the exhaust gases of diesel engines, gas turbines, industrial air or other particulate laden gases. The disk is mounted transversely in the exhaust duct of a diesel engine and in a fresh air duct which is disposed parallel to the exhaust duct. As the disk rotates within the exhaust duct, it filters particulates from the exhaust gases of the diesel engine. The filtered particulates are expelled from the disk by fresh air blowing in the air duct as the disk rotates within the air duct. The fresh air is blown in the air duct in a direction opposite to the flow of exhaust gases within the exhaust duct by a fan or compressor or compressed air jets. The counter flow arrangement of fresh air and combustion gases enhances the effectiveness of particulate removal as the disk rotates between the exhaust duct and the fresh air duct. Particulates expelled from the disk are blown into a filter bag which is attached to the end of the fresh air duct.

US 5,212,948 discloses a trap muffler apparatus with bypass to a common reactive acoustic element. Bypass structure varies from external bypass to a common acoustic element to annular bypass of the ceramic filter to axial bypass through the middle of an annular ceramic filter. Forward or reverse regeneration are possible. Bypass to atmosphere without filtration is avoided with dual in-line traps or with the segmented trap and control of exhaust gases to traps not being regenerated.

US 2010/0269488 concerns a particulate trap system for an exhaust system of an internal combustion engine including a monolithic wall-flow particulate trap having a plurality of contiguous porous walls, and a remotely actuated relief valve downstream of said trap for periodically creating a reverse pressure throughout the exhaust system upstream of the relief valve and including said trap. A reversing apparatus periodically creates a reverse pressure drop across a portion of the contiguous porous walls of said trap to dislodge accumulated particulate and cause a portion of the filtered exhaust gas to flow back through said portion of the contiguous porous walls to remove particulate therefrom. A control system actuates the relief valve and the reversing apparatus. The system is utilized on a vehicle and the reversing apparatus includes a relief valve that is also operative as an exhaust break. Regeneration includes the steps of: creating a backpressure in the entire exhaust system from a location downstream of the trap; creating a reverse pressure drop across only a portion of the porous walls to dislodge accumulated particulate therefrom; and causing a portion of filtered exhaust gas to flow back through said portion of the porous walls to carry the dislodged particulate out of the trap.

US 2005/0160723 relates to a centrifuge suitable for separating soot from an exhaust gas stream of an internal combustion engine; the centrifuge being disposed between, and arranged coaxially in relation to, a raw gas inlet pipe and a clean gas outlet pipe; the centrifuge including a rotating body which is open on both axial end faces, drive vanes arranged adjacent the inlet for driving the centrifuge, and at least one device provided inside said rotating body for reversing or deflecting the exhaust gas flow direction.

From US 5,013,340, a method for exhaust-gas aftertreatment of exhaust gas leaving an internal combustion engine is known using a rotating particle filter, wherein a part or section of the filter medium of the rotating particle filter is rotated into the exhaust gas flow and exhaust gas flows through it, and wherein a part or section of the filter medium of the rotating particle filter is rotated out of the exhaust gas flow and compressed air flows through the filter medium instead of exhaust gas to clean it.

Arising from this, the underlying object of the present invention is to provide a novel method for exhaust-gas aftertreatment.

This problem is solved according to methods for exhaust-gas aftertreatment as disclosed herein.

According to a first aspect of a described method, while exhaust gas flows through the part or section of the filter medium rotated into the exhaust gas flow, a part or section of the filter medium, which is rotated out of the exhaust gas flow, is initially regenerated inside of the rotating particle filter in a first subchamber of the rotating particle filter located outside of the exhaust flow by oxidizing the soot in the filter medium, wherein subsequent to this regeneration, ash is removed from the respective part or section of the filter medium rotated out of the exhaust flow in a second subchamber of the rotating particle filter located outside of the exhaust gas flow, and wherein, subsequent to the regeneration and ash removal, the respective part or section of the filter medium, rotated out of the exhaust gas flow, is rotated into the exhaust gas flow.

The first aspect of the described method initially proposes, using a rotating particle filter, to subject the part or section of the filter medium rotated out of the exhaust gas flow to a regeneration through oxidation of soot and subsequently to an ash removal, in parallel to the exhaust gas purification using the part or section of the filter medium rotated into the exhaust gas flow. The regeneration of the part or section of the filter medium rotated out of the exhaust gas flow is thereby carried out using oxidation in a first subchamber of the rotating particle filter located outside of the exhaust flow, wherein the ash removal is carried out in a second subchamber of the rotating particle filter located outside of the exhaust flow.

Accordingly, at least three subchambers of the rotating particle filter are used in parallel, namely one subchamber of the rotating particle filter located in the exhaust flow for exhaust gas purification, and two subchambers of the rotating particle filter located outside of the exhaust flow for regeneration and ash removal. Accordingly, in parallel to the exhaust gas purification, the filter medium of the rotating particle filter is regenerated or freed from ash in parts or in sections. This enables a particularly advantageous exhaust-gas aftertreatment.

According to an advantageous refinement of the first aspect of the described method, the part or section of the filter medium rotated out of the exhaust gas flow is, subsequent to the regeneration and the ash removal and prior to the rotation into the exhaust gas flow, heated in a third subchamber of the rotating particle filter located outside of the exhaust flow to compensate for the temperature drop in the filter medium occurring during the ash removal.

Using this advantageous refinement may prevent a temperature drop from forming on the exhaust gas side, as a result of the temperature drop of the filter medium occurring during the ash removal, when exhaust gas flows through the corresponding part or section of the filter medium again, which impairs the effectiveness of the exhaust-gas aftertreatment in the exhaust-gas aftertreatment assembly arranged downstream of the rotating particle filter, for example, in catalytic converters.

According to another advantageous refinement of the described method, a part or section of the filter medium, rotated into the exhaust gas flow, is rotated out of the exhaust gas flow for regeneration and into the first subchamber of the rotating particle filter located outside of the exhaust flow, wherein subsequent to the regeneration, this section or part of the filter medium is rotated out of the first subchamber of the rotating particle filter located outside of the exhaust flow and into the second subchamber of the rotating particle filter located outside of the exhaust flow for ash removal, said second chamber is separated on the inflow side from the first subchamber of the rotating particle filter located outside of the exhaust flow, and wherein, subsequent to the ash removal, this section or part of the filter medium is rotated out of the second subchamber of the rotating particle filter located outside of the exhaust flow and is rotated either directly into the exhaust flow or indirectly via the third subchamber of the rotating particle filter located outside of the exhaust flow, said third subchamber is separated on the inflow side from the second subchamber of the rotating particle filter located outside of the exhaust flow. By this means, the filter medium of the rotating particle filter may be subjected, through oxidation of soot, to a regeneration and ash removal in a particularly advantageous way.

According to another advantageous refinement of the described method, the regeneration is implemented as active regeneration under application of heat at the part or section of the filter medium rotated out of the exhaust gas flow, wherein, to heat the part or section of the filter medium of the rotating particle filter to be actively regenerated in the first subchamber located outside of the exhaust flow, heated air is flowed through the same. Preferably, the oxygen content downstream of the rotating particle filter is hereby measured using a sensor positioned downstream of the rotating particle filter and, if necessary, the oxygen content upstream of the rotating particle filter is measured using a sensor positioned upstream of the rotating particle filter, wherein, on the basis of the oxygen content measured by the one or each sensor, a loading of the rotating particle filter with soot and/or a temperature increase of the rotating particle filter as a result of the regeneration and/or a speed of the regeneration is determined, and wherein, on the basis of the oxygen content measured by the one or each sensor, the active regeneration is controlled. By this means, the active regeneration in the rotating particle filter may be realized particularly advantageously, specifically, a control of the active regeneration while preventing temperatures which are too high and thus risk of damage to the rotating particle filter.

According to the present invention, this problem is solved by a method for the exhaustgas aftertreatment system according to Claim 1.

According to the invention, exhaust gas leaving an internal combustion engine is guided across a rotating particle filter in such a way that the exhaust gas flows around a part or section of the filter of the filter medium rotated into the exhaust gas flow, and the exhaust gas does not flow around a part or section of the filter medium rotated out of the exhaust gas flow, wherein the part or section of the filter medium rotated out of the exhaust gas flow is removed from a subchamber of the rotating particle filter located outside of the exhaust flow wherein the filter medium is separated from soot and ash particles and/or from reaction products of the soot and ash particles with the filter medium vi a a separating devise outside of the rotating particle filter, cleaned filter medium is subsequently guided back into the subchamber of the rotating particle filter located outside of the exhaust flow, and is rotated back into the exhaust gas flow.

According to a second aspect of the invention, it is initially proposed to use a filter medium which exhaust gas flows around in a rotating particle filter, and which is then removed from the rotating particle filter when the filter medium is rotated out of the exhaust gas flow, in order to free the filter medium from soot and ash outside of the rotating particle filter. A particularly effective post treatment is also hereby possible.

According to an advantageous refinement of the invention, it is possible to treat the part or section of the filter medium rotated out of the exhaust gas flow in parallel with the part or section of the filter medium rotated into the exhaust gas flow, in order to thus remove soot from the part or section of the filter medium rotated into the exhaust gas flow within the rotating particle filter in the sense of a regeneration. For this purpose, SO2is preferably oxidized into SO3in an oxidation catalytic converter arranged upstream of the rotating particle filter, wherein the SO3and/or precipitated H2SO4supports the oxidation of soot in the rotating particle filter at the part or section of the filter medium rotated into the exhaust gas flow, and wherein at least vanadium at a proportion of more than 5%, preferably more than 7%, particularly preferably more than 9%, and preferably potassium and/or sodium and/or iron and/or cerium and/or cesium and/or oxides of these elements are used in the oxidation catalytic converter as active components for oxidizing SO2into SO3, wherein titanium oxide and/or silicon oxide, preferably stabilized by tungsten oxide, is used as the base material in the oxidation catalytic converter.

An NO oxidation catalytic converter may be connected in parallel to the SO2oxidation catalytic converter.

Preferred refinements of the invention arise from the dependent claims and the subsequent description. Embodiments of the invention will be explained in greater detail with reference to the drawings, without being limited thereby.

Figure 1 shows a block diagram for clarifying a first variant of a method for exhaust-gas aftertreatment according to a described method;

Figure 2 shows a cross section through the rotating particle filter from Figure 1;

Figure 3 shows a block diagram for clarifying a second variant of the method for exhaust-gas aftertreatment according to the described method;

Figure 4 shows a cross section through the rotating particle filter of Figure 3;

Figure 5 shows a block diagram for clarifying the method according to the invention for exhaust-gas aftertreatment according to the invention; Figure 6 shows a cross section through the rotating particle filter of Figure 5;

Figure 7 shows a block diagram for clarifying a second variant of the method according to the invention for exhaust-gas aftertreatment according to the invention;

Figure 8 shows a block diagram for clarifying a third variant of the method according to the invention for exhaust-gas aftertreatment according to the invention.

The invention relates to a method for exhaust-gas aftertreatment of exhaust gas leaving an internal combustion engine. In particular, the invention is used with regard to internal combustion engines operated using excess air, thus, for example, for maritime diesel internal combustion engines.

With reference to Figures 1 and 2, a method will be subsequently described for the exhaust-gas aftertreatment of exhaust gas 11 leaving an internal combustion engine 10 according to a first aspect of the invention. Thus, Figure 1 shows an internal combustion engine 10, wherein exhaust gas 11 leaving internal combustion engine 10 is guided across a rotating particle filter 12 to the exhaust-gas aftertreatment.

Rotating particle filter 12 comprises a filter medium through which the exhaust gas flows. A first section or a first part of the filter medium is thereby rotated into the exhaust gas flow and the exhaust gas flows through it, wherein a second part or a section of the filter medium is rotated out of the exhaust gas and exhaust gas does not flow through it.

The section or part of the filter medium, through which exhaust gas flows and which is therefore rotated into the exhaust gas flow, is positioned in a subchamber 13 of rotating particle filter 12, through which subchamber exhaust gas flows.

The part or section of the filter medium rotated out of the exhaust gas flow is initially regenerated inside of rotating particle filter 12 in a subchamber 14 of rotating particle filter 12 located outside of the exhaust flow using oxidation of soot in the filter medium, wherein subsequent to this regeneration of the filter medium, this part or section of the filter medium rotated out of the exhaust gas flow is freed from ash in a second subchamber 15 of rotating particle filter 12 located outside of the exhaust flow, in that ash is removed from this part or section of the filter medium.

Subsequent to the regeneration of this part or section of the filter medium in first subchamber 14 and to the ash removal from this part or section of the filter medium in second subchamber 15, this part or section of the filter medium may be subsequently rotated back into the exhaust gas flow. The rotational movement of the filter medium is visualized in Figure 2 by an arrow 16.

The method for exhaust-gas aftertreatment described with reference to Figures 1 and 2 therefore uses at least three subchambers of rotating particle filter 12, specifically one subchamber 13 located in the exhaust flow and two subchambers 14 and 15 located outside of the exhaust flow, wherein the filter medium may be shifted by rotating the same in accordance with arrow 16 by sections or in parts from subchamber 13 into subchamber 14, from subchamber 14 into subchamber 15, and subsequently from subchamber 15 back into subchamber 13, in order to carry out, in parallel to the exhaust-gas aftertreatment in subchamber 13, the regeneration in subchamber 14 and the ash removal in subchamber 15 in series.

The regeneration by sections or in parts of the filter medium rotated out of the exhaust gas flow in subchamber 14 of rotating particle filter 12 is preferably carried out as active regeneration and by heating the part or section of the filter medium rotated out of the exhaust gas flow, where in order to heat the part or section of the filter medium to be actively regenerated, heated air 17 flows past the same in subchamber 14 of rotating particle filter 12 located outside of the exhaust flow, said air may be heated, for example, with the aid of a heating device (not shown) to a defined temperature to heat the part or section of the particle filter to be actively regenerated to a defined process temperature for the active regeneration.

Subsequent to the preferably active regeneration of a part or section of the filter medium rotated out of the exhaust gas flow in subchamber 14 of rotating particle filter 12, the regenerated part or section of the filter medium is subjected to an ash removal in subchamber 15 after transferring of the same into subchamber 15 of rotating particle filter 12, in that ash is removed from the previously regenerated part or section of the filter medium, for which purpose preferably a solvent 18 flows through this part or section of the filter medium.

This solvent 18 may, for example, be water or sulfuric acid.

If sulfur-containing ash deposits are to be removed from the filter medium of rotating particle filter 12, then a solution containing sodium carbonate may be guided as a solvent through the part or section of the filter medium which is located in subchamber15 of rotating particle filter 12. Water-soluble sodium sulfate is hereby formed, which may be washed out. The carbonates, if necessary, forming from the ash residues, are water soluble and may be brought into solution with the aid of an acid, for example, with the aid of CaSO4, and washed out. The reaction product CaCl2is highly water-soluble and may be simply washed out of the filter medium using water. For the example of CaSO4, this is carried out as follows:

CaSO4+ Na2CO3→ CaCO3+ Na2SO4

CaCO3+ 2HCl→ CaCl2+ H2O CO2

According to the described method, a rotating particle filter, which has at least three subchambers, is used for exhaust-gas aftertreatment, wherein exhaust gas flows through a first subchamber 13 of rotating particle filter 12 or through a filter medium rotated into this first subchamber 13, and wherein a part or section of the filter medium is rotated out of this subchamber 13 and therefore out of the exhaust flow and into a first subchamber 14 located outside of the exhaust flow and subjected to a regeneration through oxidation of soot, and subsequently to an ash removal in an additional subchamber 15 located outside of the exhaust flow.

Filter medium rotated into the exhaust gas flow is therefore rotated out of the exhaust gas flow and thus out of subchamber 13 for regeneration and rotated initially into first subchamber 14 of particle filter 12 located outside of the exhaust flow, in order to be regenerated in this subchamber 14, wherein, subsequent to the regeneration in subchamber 14 of rotating particle filter 12 located outside of the exhaust gas flow, the corresponding part or section of the filter medium is rotated out of first subchamber 14 of rotating particle filter 12 located outside of the exhaust flow and into second subchamber 15 of the rotating particle filter located outside of the exhaust flow in order to carry out the ash removal in this subchamber 15, which is separated from subchamber 14 on the inflow side.

Advantageous refinements of the method for exhaust-gas aftertreatment described with reference to Figures 1 and 2 are subsequently described with reference to Figures 3 and 4, wherein identical reference numerals are used for identical components in Figures 3 and 4 as were used in Figures 1 and 2. Therefore, to avoid unnecessary repetitions with respect to these identical components in Figures 3 and 4, reference is made regarding this to the embodiments of Figures 1 and 2.

One first difference of Figures 3 and 4 in comparison to Figures 1 and 2 consists in that, in Figures 3 and 4, the rotating particle filter 12 comprises, in addition to two subchambers 14 and 15 located outside of the exhaust flow, an additional subchamber 19 located outside of the exhaust flow, wherein that section or part of the filter medium, which is located in this third subchamber 19 located outside of the exhaust flow, subsequent to the ash removal and therefore prior to the rotation back into the exhaust flow, is heated within subchamber 19 in order to compensate for the temperature drop of the filter medium occurring during the ash removal. This is accomplished in Figure 3 in that heated air 17, which is guided past the filter medium located in first subchamber 14 of particle filter 12, located outside of the exhaust flow, for active regeneration of said filter medium, is recycled and is subsequently guided across subchamber 19 or the filter medium located in subchamber 19 in order to heat the same. By this means, it may be avoided that the exhaust gas is cooled at a filter medium, when a filter medium subjected to a regeneration and ash removal is then subsequently rotated into the exhaust gas flow, by which means it may be guaranteed that, if necessary, additional exhaust-gas aftertreatment assemblies positioned downstream of rotating particle filter 12 may be operated at optimal process temperatures of the exhaust gas.

Another difference of the embodiment of Figures 3 and 4 over the embodiment of Figures 1 and 2 consists in that, in Figures 3 and 4, a sensor 20 or 21 is present both upstream of rotating particle filter 12 and also downstream of the same, with the aid of which the oxygen content in the air supplied for the active regeneration via first subchamber 14 may be measured upstream and downstream of rotating particle filter 12, specifically upstream and downstream of first subchamber 14 of rotating particle filter 12 located outside of the exhaust flow.

On the basis of the oxygen content detected by sensors 20, 21, a loading of the respective part or section of the filter medium of rotating particle filter 12 to be regenerated using soot is determined prior to the regeneration and/or a temperature increase as a result of the regeneration is determined and/or a speed of the regeneration is determined, in order to, for example, thus control the active regeneration if a temperature increase which is too high, as a result of the regeneration, is detected, in particular, by influencing the heating device which functions for heating the air used for active regeneration.

From the oxygen content downstream of rotating particle filter 12, which is measured by sensor 21, and additionally from the oxygen content upstream of rotating particle filter 12, which is detected by sensor 20, the burned off soot amount may be determined according to the following equation:

C O2→ CO2

Each burned off oxygen molecule hereby corresponds to a carbon molecule. By using an integration over time, the loading of the part or section of the filter medium of rotating particle filter 12 to be regenerated with soot may be determined prior to the soot burn off.

The temperature increases as a result of the soot burn off may be determined according to the following equation:

ΔT = mC* HuC/Δt * d/dt(m) * α

where ΔT corresponds to the temperature increase as a result of the soot burn off, mCcorresponds to the loading of the respective part or section of the filter medium to be regenerated using soot prior to the soot burn off, HuCcorresponds to the heating value of the soot, Δt corresponds to the duration of the soot burn off, d/dt(m) corresponds to the air mass flow, and α corresponds to the heat capacity.

Upstream of rotating particle filter 12, an oxidation catalytic converter (not shown) for oxidizing NO into NO2may be positioned in order to provide NO2for passive regeneration of the part or section of the filter medium located in subchamber 13 and therefore in the exhaust gas flow. The NO2proportion of the total NOxproportion is hereby preferably adjusted such that the NO2proportion is more than 10%, preferably more than 20%, particularly preferably more than 50% of the total NOxproportion in order to guarantee an optimal passive regeneration of the filter medium within subchamber 13 and use of NO2. The desired NO2proportion to the total NOxproportion may be adjusted using the NO oxidation catalytic converter, if necessary, supported by a reduction of the combustion temperature in the internal combustion engine.

In the embodiment of Figures 3 and 4, an oxidation catalytic converter 22 for oxidizing SO2into SO3is positioned upstream of rotating particle filter 12, wherein the SO3generated and/or H2SO4precipitated may be used in oxidation catalytic converter 22 in order to oxidize soot in the filter medium within subchamber 13 of rotating particle filter 12, through which exhaust gas flows.

SO3+ O → CO SO2

2 SO3+ O → CO2+ 2SO2

As an active component for the oxidation of SO2into SO3, at least vanadium is used in oxidation catalytic converter 22 with a proportion of more than 5%, preferably more than 7%, particularly preferably more than 9%, wherein as additional active components for the oxidation of SO2into SO3, if necessary, potassium and/or sodium and/or iron and/or cerium and/or cesium and/or oxides of these elements may be used. Titanium oxide and/or silicon oxide, preferably stabilized by tungsten oxide, is used as the base material in the oxidation catalytic converter 22 in order to oxidize SO2into SO3.

Thus, if an oxidation catalytic converter 22 for oxidizing SO2into SO3is present upstream of rotating particle filter 12, then a mass ratio between SO3and soot is preferably adjusted to at least 7:1, preferably at least 12:1, particularly preferably at least 16:1 in the region of rotating particle filter 12.

In the embodiments of Figures 1 through 4, the flow directions of subchambers 13 through 15, 19 are preferably all in the same direction or identical, thus not in the opposite direction. This may be gathered, in Figures 1, 3, from the orientation of the arrows representing a flow direction of exhaust gas, air, and solvent.

An embodiment of a method according to the present invention is subsequently described with reference to Figures 5 and 6, wherein an internal combustion engine 30 is shown in Figure 5, the exhaust gas 31 of which is supplied to the exhaust-gas aftertreatment via a rotating particle filter 32. Rotating particle filter 32 thereby accommodates a filter medium through which, in contrast to the embodiments from Figures 1 through 4, exhaust gas does not flow, instead, exhaust gas flows around said filter medium. This filter medium is preferably a granulate, wherein soot and ash or reaction products of soot and ash deposit on the granulate during the exhaust-gas aftertreatment.

Rotating particle filter 32 has, according to Figure 6, two subchambers 33, 34, specifically a subchamber 33 located in the exhaust gas flow and a subchamber 34 located outside of the exhaust gas flow. Exhaust gas flows around the filter medium, which is located in subchamber 33, while in contrast exhaust gas does not flow around the filter medium, which is located in subchamber 34. The filter medium can be rotated, in accordance with arrow 35, from first subchamber 33 of rotating filter 32 into second subchamber 34 of rotating particle filter 32 and therefore rotated out of the exhaust flow; likewise, the filter medium may be transferred out of second subchamber 34 of rotating filter particle 32 and into first subchamber 33 of rotating particle filter 32 and therefore rotated into the exhaust flow.

According to the second aspect of the invention, an exhaust gas flows around the filter medium in subchamber 33 of rotating particle filter 32, then, when said filter medium has been shifted into subchamber 34 of rotating particle filter 32 and therefore had been rotated out of the exhaust flow, the filter medium is removed from subchamber 34 of rotating particle filter 32 and supplied to a separating device 36. Arrow 37 in Figure 5 visualizes the removal of the filter medium or granulate from subchamber 34 of rotating particle filter 32 and the transfer of the same into separating device 36.

In separating device 36, soot and ash are removed from the filter medium, which is preferably granulate, in particular by a mechanical peeling process, thus, for example, with the aid of a separating device 36 designed as a drum peeler, in order to subsequently supply cleaned granulate in accordance with arrow 38 to rotating particle filter 32 again, specifically to second subchamber 34 of the same, and subsequently, in the accordance with arrow 35, into subchamber 33 again and thus to rotate into the exhaust flow. Soot and ash particles and/or reaction products of the soot and ash particles with the granulate, which have been separated from the granulate in separating device 36, are discharged from separating device 36 in accordance with arrow 39.

Figure 7 clarifies a refinement of the method described with reference to Figures 5 and 6, wherein in Figure 7, in accordance with Figure 3, an oxidation catalytic converter 22 for oxidizing SO2into SO3is positioned upstream of rotating particle filter 12, wherein the SO3generated by oxidation catalytic converter 22 and/or precipitated H2SO4functions directly to oxidize soot in rotating particle filter 32, thus in that filter medium which is located in subchamber 33 of rotating particle filter 32 through which exhaust gas flows.

In oxidation catalytic converter 22, at least vanadium, preferably potassium and/or sodium and/or iron and/or cerium and/or cesium and/or oxides of these elements are thereby again used as active components for the oxidation of SO2into SO3; titanium oxide and/or silicon oxide, preferably stabilized by tungsten oxide, is used as the base material in oxidation catalytic converter 22.

The vanadium proportion is at least 5%, particularly preferably at least 7%, particularly preferably at least 9%, wherein downstream of oxidation catalytic converter 22, a mass ratio is adjusted between SO3and soot of at least 7:1, preferably at least 12:1, particularly preferably 16:1 in the region of rotating particle filter 32, specifically in the region of subchamber 33 of the same. In the variant of Figure 7, an oxidation of soot in rotating particle filter 32 is therefore carried out, specifically inside of subchamber 33 of the same through which exhaust gas flows, and soot is removed from the filter medium outside of rotating particle filter 32 in separating device 36.

Figure 8 shows a refinement of the method of Figure 7, in which not only oxidation catalytic converter 22, which functions to oxidize SO2into SO3, is arranged upstream of rotating particle filter 32, but also an additional oxidation catalytic converter 40, which functions to oxidize NO into NO2. These two oxidation catalytic converters 22, 40 are connected to one another in parallel, wherein each of oxidation catalytic converters 22, 40 may be blocked or separated from the exhaust gas flow via stop valves 41. If fuel with a large sulfur content is used in internal combustion engine 30, then the exhaust gas flow is guided via oxidation catalytic converter 22 to oxidize SO2into SO3and NO oxidation catalytic converter 40 is separated from the exhaust gas flow by valve 41. By this means, NO oxidation catalytic converter 40, which functions to oxidize NO into NO2, is kept free of sulfur. If, in contrast, a fuel is used with a relatively low sulfur content, then SO2oxidation catalytic converter 22 may be separated from the exhaust gas flow by closing corresponding valve 41 and the exhaust gas is guided via NO oxidation catalytic converter 40 to oxidize NO into NO2. The variant of Figure 8 is particularly suited for use in maritime engines, which are operated with fuels which have large sulfur contents and also with fuels with low sulfur contents.

An alternative to Figure 8 consists in omitting stop valves 41 and making oxidation catalytic converter 40 operational following operation with fuel with high sulfur contents in that the exhaust gas temperature is increased and thus sulfur is desorbed in oxidation catalytic converter 40. The variant with stop valves 41 is, however, preferred, as oxidation catalytic converter 40 is immediately available for use subsequent to an operation of internal combustion engine 1 with sulfur-containing fuel.

Catalytically inactive granulate may be used as the granulate in rotating particle filter 32. In particular, granulate made of cordierite, granite, corundum, aluminum oxide, or from metallic materials is used. Due to a diversion of the soot and ash particles in rotating particle filter 32, the soot and ash particles are deposited on the catalytically inactive granulate due to impaction and/or diffusion and/or interception. Preferably, catalytically active granulate is used. In this case, components of the exhaust gas may react with the granulate in rotating particle filter 32.

Thus, if catalytically active granulate is used, a drum peeler is preferably used as separating device 36. Thus, if catalytically inactive granulate is used, a drum screen, a vibrating sieve, a mill, or a washing device with water as the washing medium, may be used as separating device 36 for cleaning the granulate.

Rotating particle filter 32 may be designed to be multistage. Thus, exhaust gas to be purified initially flows through rotating particle filter 32 into a first stage and subsequent to this into a second stage of rotating particle filter 32. Both stages of rotating particle filter 32 may then be designed as described above and are connected serially one behind the other. In the region of each of the stages, the granulate may be rotated out of the exhaust flow, may be freed from soot and ash in a separating device 36 outside of the stage of rotational particle filter 32, and subsequently may be supplied back to the respective stage of rotating particle filter 32.

Thus, if, as shown in Figure 2, rotating particle filter 32 is designed as multistage, the chemical composition of the granulate and/or the size of the granulate preferably deviates from one another in the individual stages of rotating particle filter 32.

A vanadium-containing fuel may also be used to operate internal combustion engine 30. In this case, vanadium oxide is deposited on the surface of the granulate, by which means soot and SO2may be oxidized in subchamber 33 of rotating particle filter 32.

The above method may also be used for internal combustion engines with turbochargers. An SO2oxidation catalytic converter is thus positioned advantageously upstream of a turbine of the exhaust gas turbocharger in order to support the oxidation of SO2into SO3due to the pressures and temperatures prevailing upstream of the turbine.

List of reference numerals:

10 Internal combustion engine

11 Exhaust gas

12 Rotating particle filter

13 Subchamber

14 Subchamber

15 Subchamber

16 Rotational direction

17 Air

18 Solvent

19 Subchamber

20 Sensor

21 Sensor

22 Oxidation catalytic converter

30 Internal combustion engine

31 Exhaust gas

32 Rotating particle filter

33 Subchamber

34 Subchamber

35 Rotational direction

36 Separating device

37 Granulate

38 Granulate

39 Soot/Ash

40 Oxidation catalytic converter

41 Stop valve

Claims

1. A method for exhaust-gas aftertreatment of an exhaust gas (31) leaving an internal combustion engine (30), characterised in that the exhaust gas (31) is guided across a rotating particle filter (32) in such a way that exhaust gas (31) flows around a part or section of the filter medium rotated into the exhaust gas flow, and exhaust gas (31) does not flow around a part or section of the filter medium rotated out of the exhaust gas flow, wherein the part or section of the filter medium rotated out of the exhaust gas flow is removed from a subchamber (34) of the rotating particle filter (32) located outside of the exhaust flow wherein the filter medium is separated from soot and ash particles and/or from reaction products of the soot and ash particles with the filter medium via a separating device (36) outside of the rotating particle filter (32), cleaned filter medium is subsequently guided back into the subchamber (34) of the rotating particle filter (32) located outside of the exhaust flow, and is rotated back into the exhaust gas flow.

2. The method according to Claim 1, characterized in that a granulate is preferably used for the filter medium around which the exhaust gas flows.

3. The method according to one of Claims 1 through 2, characterized in that upstream of the rotating particle filter (12, 32), SO2is oxidized into SO3in an oxidation catalytic converter (22) wherein the SO3and/or precipitated H2SO4functions to oxidize soot in rotating particle filter (12, 32) at the part or section of the filter medium rotated into the exhaust gas flow, and wherein at least vanadium in a proportion of more than 5%, preferably more than 7%, particularly preferably more than 9%, and preferably additionally potassium and/or sodium and/or iron and/or cerium and/or cesium and/or oxides of these elements are used as active components for the oxidation of SO2into SO3, wherein titanium oxide and/or silicon oxide, preferably stabilized by tungsten oxide, is used as the base material in the oxidation catalytic converter.

4. The method according to Claims 3, characterized in that downstream of the oxidation catalytic converter (22), a mass ratio is adjusted between SO3and soot of at least 7:1, preferably at least 12:1, particularly preferably 16:1 in the region of the rotating particle filter (32).

5. The method according to Claim 3 or 4, characterized in that upstream of the rotating particle filter (12, 32), NO is oxidized into NO2in an oxidation catalytic converter (40), wherein the NO2functions to oxidize soot in the rotating particle filter (12, 32) at the part or section of the filter medium rotated into the exhaust gas flow, and wherein the oxidation catalytic converter (40) for oxidizing NO into NO2is connected in parallel to the oxidation catalytic converter (22) for oxidizing SO2into SO3, wherein both of oxidation catalytic converters (22, 40) may be separated from the exhaust gas flow via stop valves (41).