DE10130872A1 - Exhaust gas purification process - Google Patents

Abstract

The invention describes a method for cleaning exhaust gases which contain particulate contaminants or nitrogen oxides. The exhaust gases are cleaned by a filtering matrix at the same time as the regeneration of the filtering matrix. The filtering matrix is regenerated by a small gas or air flow in relation to the exhaust gas flow. The regeneration gas is advantageously preheated. The different functional areas are run through one after the other. The apparatus can be implemented, for example, by rotating elements. The different functional areas are rotated one after the other.

Description

State of the art Removal of soot particles from the exhaust gas

The cleaning of the exhaust gas flow from diesel exhaust gases poses in view of the increasing Tightening the limit values is a current problem. In addition to the removal of nitrogen oxides as well as smaller amounts of CO and hydrocarbons come mainly from Removal of the soot particles is of great importance.

Exhaust gas from diesel engines is characterized by a large exhaust gas flow (based on the Performance) and a low exhaust gas temperature. The large exhaust gas flow (based on the Power) results from the large displacement of diesel engines (in relation to the power) in Combination with a very high compression and a high excess of air in the Combustion.

A mid-range truck engine with a capacity of 6.8 l and an output of 280 hp leads to an exhaust gas flow of approx. 1000 Nm ³ / h. Even a medium-sized car with an output of around 100 hp leads to an exhaust gas flow of over 300 Nm ³ / h at full load.

As a result, there are very high flow velocities in the exhaust system. Already In the case of car gasoline engines, speeds up to in the full load range in the catalyst monolith reached to 40 m / sec. These values are of the same order of magnitude for diesel engines. In Given the high speeds, the exhaust system must be as low as possible Pressure loss can be designed.

Different concepts have become known for removing the soot particles, from which, however, have not yet been successfully implemented on an industrial scale. Soot filters are often used, mainly in the form of parallel square channels where the exhaust gas flows through the porous ceramic wall so that the particles on the Deposit wall. These soot filters have to be regenerated at certain intervals. Doing so the soot filter is heated to a high temperature so that the deposited soot particles burn and thus the soot filter is available for a new filtering process.

Other concepts see metallic filters made of wire mesh, metallic fleece, sintered metallic fleece or sintered metallic forms. These soot filters are also used regenerated at high temperature.

The regeneration process of the filter is problematic. First, for this process Temperatures required that are significantly higher than the mostly existing exhaust gas temperature. Therefore, concepts have become known in which the regeneration by igniting a Brenners is initiated. However, these concepts usually allow regeneration not while driving. On the one hand, the large exhaust gas flow would mean that required power input for the burner too large. The second reason is the big one released heat when burning the soot particles. If the combustion takes place in an uncontrolled manner, very high temperatures can occur which lead to the destruction of the material can. Therefore, with these concepts, regeneration must take place in the stand. In this case can affect the combustion by controlling the amount of air added and thus the Temperature can be limited. However, this results in the serious disadvantage that the Regeneration can only be carried out in the state.

In the meantime, concepts have also become known in which the regeneration during operation is carried out. For this purpose, the exhaust gas is passed through a burner or through a electric heating heated to the temperature required for regeneration. at Given the large amounts of exhaust gas present, this solution requires a large one additional energy input. This is with a significant increase in fuel consumption connected.

Another concept investigated by companies uses a soot filter upstream oxidation catalyst the hydrocarbons contained in the exhaust gas implemented, behind it the soot filtering. For regeneration is now in certain Intervals through the engine control a particularly hydrocarbon-rich exhaust gas generated (enriched mixture). When this exhaust gas is oxidized in the oxidation catalytic converter high exhaust gas temperatures result from the higher concentrations. By a suitable one Engine control increases the exhaust gas temperature so that the Ignition temperature for the soot particles in the downstream soot filter is reached. This will the regeneration of the soot filter is initiated. A disadvantage of this method is that Temperature of the soot filter before the start of the regeneration from the present one Load condition of the engine depends on the driving style can depend. Another disadvantage is that after igniting the regeneration the reaction proceeds automatically due to the heat of reaction released during the combustion of soot and the temperature in the soot filter continues to increase. Because this regeneration in operation takes place, the amount of exhaust gas present is undetermined and of the instantaneous Driving style dependent. This means that the temperature in the soot filter is accidental subject and therefore difficult to control.

In a further concept, an oxidation catalyst is proposed for the soot filter upstream. In this the NO (nitrogen monoxide) also contained in the exhaust gas becomes NO2 (nitrogen dioxide) oxidizes. This NO2 acts as a soot filter in the downstream Oxidizing agent, so that the oxidation of the accumulated soot is already at a lower level Temperatures should expire. In practice, however, this arrangement is also sufficient Exhaust gas temperatures for regeneration of the filter, so that in this case, too Exhaust gas temperature must be increased by additional energy input.

An additional problem is the uniformity of the soot combustion on the soot filter. This is determined by the uniformity of the soot layer on the soot filter and by the Uniformity of the flow through the soot filter is determined. A normally present uneven soot loading on the surface of the soot filter leads to an uneven Flow, to an uneven soot burn-off and thus to uneven Temperatures on the soot filter. If the soot is burned at the same time uncontrolled amount of exhaust gas, so local temperature peaks can occur, the soot filter can destroy.

Another patent (Ceryx) proposed that the exhaust gas flow through a to conduct additional heat exchanger. In this then heat from the cleaned exhaust gas should be transferred to the unpurified exhaust gas. There is also an additional energy input provided by adding fuel. The additional energy input is through the Heat exchanger only slightly reduced. A disadvantage of this concept is that the exhaust gas flow must flow twice through the heat exchanger. This is a significant additional one Pressure loss associated with the high existing exhaust gas flows to a considerable Loss of performance leads. This concept is a driving force for heat transfer Differences in temperature required, partly due to the heat of reaction released is applied. The difference between the heat discharged via the exhaust gas flow and The heat of reaction released by the pollutants contained must be replaced by additional Combustion of fuel can be supplied. The additional heat supply is all the more the better the heat exchange, the lower. The reduction in driving Temperature difference z. B. by a longer heat transfer surface or by internals with a higher heat transfer inevitably lead to a higher one Pressure loss and thus an additional loss of engine power.

Exhaust gas from modern engines, e.g. T. already reaches the EURO-3 limit values, only contains still small amounts of soot, so that the heat of reaction released is also low. The guesswork for a modern truck engine shows that due to the soot particles it contains an adiabatic temperature increase of at most a few degrees can be achieved. Even considering additional pollutants such as hydrocarbons and CO (their Proportion due to the high excess air in diesel engines is low) from one adiabatic temperature increase of approx. 10 degrees can be assumed.

From this it can be seen that the additional heat input is especially with large exhaust gas flows can become significant. Another disadvantage of this method is that the Heat transfer is determined by the amount of exhaust gas. This in turn - just like the Exhaust gas temperature - determined by the respective load state of the engine and is therefore random, subject to unpredictable fluctuations caused by the driving style.

Removal of nitrogen oxides from the exhaust gas

As already mentioned, the combustion processes in the diesel engine are characterized by a high excess of air. As a result, fewer pollutants result from incomplete ones Combustion (e.g. CO, hydrocarbons), however, the nitrogen oxide formation is clear at the same time pronounced.

The removal of nitrogen oxides is therefore not yet satisfactory in diesel engines solved problem. The problem arises primarily from the high excess of oxygen in the exhaust gas. In contrast to the 3-way catalytic converter in Otto engines, the oxygen-rich ones can be used in the Atmosphere of diesel exhaust gases does not easily reduce nitrogen oxides to nitrogen.

A similar problem will arise with Otto engines in the future Lean engines, which also have a higher excess air in the engine Work combustion, result

To date, two methods have become known for removing nitrogen oxides from diesel exhaust gas, that are currently still in the experimental phase. One is the selective catalytic Reduction using a reducing agent that uses other methods so-called storage catalysts.

The selective catalytic reduction (SCR) process is based on the denitrification of Smoke gases known from large combustion plants. In these applications it is called The reducing agent ammonia uses nitrogen oxides on a catalyst be reduced The transfer of this process to diesel engines, especially truck Motors is currently in the test phase. For mobile applications from Diesel engines typically use a urea solution as a reducing agent. Besides are other processes with ammonia-releasing substances (e.g. ammonium Carbamate). The disadvantage of this method is that an additional Reducing agent is required, which is carried in a tank in the vehicle and consequently in refueling at regular intervals. Additional problems exist in the required uniform addition of the reducing agent. With an uneven A so-called slip can occur in the unused Reducing agent is emitted. For this reason, in particular for the applications in Cars worked on another process.

In this second method, so-called storage catalysts are used, which in the Nitrogen oxides are temporarily able to be bound sorptively. So that during normal Operating in oxygen-rich exhaust gas, the nitrogen oxides from the exhaust gas to the storage catalytic converter adsorbed and chemically bound. Regeneration must take place after a certain time. For this purpose, a low-oxygen exhaust gas is briefly generated by the engine control. By the Oxygen-poor exhaust gas and the hydrocarbons it contains are those on the Storage catalyst bound nitrogen oxides reduced. After completing this short Regeneration phase regulates the engine control back to normal operation oxygen-rich exhaust gas. The working temperature of the process is around 350 ° C Magnitude of the diesel exhaust gas temperature. The advantage of the method is that no additional reducing agent must be carried in the vehicle. However, there are some Disadvantages compared. Firstly, this is the periodic regeneration required with the required mixture enrichment. This leads in particular to a transient behavior of Engine and exhaust gas cleaning. During the short regeneration cycle, everyone must be in one Catalytic converter-emitting cylinders are operated in an unfavorable operating point. The The resulting change in power and torque of the engine must be replaced by additional Engine control measures are balanced to keep the vehicle moving To provide performance. Other disadvantages of operating with a greased mixture consist in the short-term higher hydrocarbon emissions, in the short-term higher consumption and possible short-term emission peaks.

In the English language literature, these storage catalysts are also called NOx adsorbers or NOx traps. The loading and regeneration on Reactions occurring in the storage catalytic converter can be found in the prior art become.

Task according to the invention

The invention has as its object a system for continuous soot filtering and to develop a regeneration that takes place during exhaust gas cleaning. The Regeneration operation should be largely autothermal, so that additional heating largely can be avoided. The process is also said to be insensitive to changes in the load Engine, which is known to cause considerable fluctuations in the amount of exhaust gas, Lead pollutant loading and exhaust gas temperature. In a further embodiment of the Invention is to be integrated a denitrification of the exhaust gases.

Solution according to the invention

Cause of the problems of local temperature peaks in the regeneration of soot filters are on the one hand in the relatively large regeneration intervals, which are at relatively high local Soot loads can lead. Continuous oxidation of the soot particles could do this Avoid problem; buys with a high ongoing additional energy requirement. The reason for this high additional energy requirement is the heat discharge through the Exhaust gas flow.

According to the invention, both problems can be avoided as follows. In a first area a device suitable for the method according to the invention, which is equipped with a suitable soot-filtering medium specified later, the soot particles are made the exhaust gas stream removed and deposited on the filtering medium. In a second The filtering medium is regenerated in the area of the device. It is crucial that the regeneration takes place only with a smaller partial flow of air or exhaust gas. Through the The following advantages can be achieved by using a partial flow. On the one hand lower heat output due to the fact that only a small partial flow with a higher one Temperature is discharged. Secondly, the amount of the partial flow can be regulated, thus influencing the soot burn-off by regulating the amount of oxygen supplied can be that no too high temperatures arise. This process in the second area the device takes place independently of that in the first area of the device at the same time ongoing exhaust gas cleaning. In a third area, the Device preheating the regeneration gas over that heated during the regeneration filtering medium. Exhaust gas cleaning, regeneration cycle and heat recovery are carried out cyclically in the individual areas of the device.

The individual areas of the device can be divided into individual devices or sub-devices be divided, with the respective exhaust gas regeneration gas and hot gas flows in time Change through the dividing heads can be performed. It is particularly advantageous to integrate individual areas into one apparatus. A particularly suitable option this can be done using a rotor. The rotor can filter out soot Contain medium or from such, e.g. B. consist of a soot filter (see below).

By rotating the rotor relative to the exhaust gas inlet and outlet the individual process steps of exhaust gas purification, regeneration and Go through heat exchange. It can prove to be more favorable for the construction of the apparatus if the device is arranged stationary while the exhaust gas supply and Exhaust gas discharge are designed as a rotating exhaust manifold.

In a further advantageous embodiment, the individual areas of the device can be used as separate apparatuses are carried out, to which the exhaust gas is supplied in certain cycles. The switching of the exhaust gas supply and removal in the individual areas can also be carried out via cyclically switched flaps or valves. In this case there is a cyclical one Change of flow in the individual areas or sub-units. This cyclical Change is easier to explain using the example of the rotor.

In the following, the term "rotor" is to be used, including an arrangement should be understood in which the soot filtering medium in a fixed arrangement is housed while the fluid supplies are rotated. Furthermore, the The following functional description also applies to the design with individual, separate devices transfer. For the sake of simplicity, the rotating soot filtering is shown as an example Medium with fixed fluid supplies are described.

The individual areas are changed by rotating the rotor as follows: The Individual areas or segments of the rotor are made by suitable flow feeds flowed with the different fluid flows.

In the first area, the exhaust gas flows through the soot-filtering medium of the rotor and becomes cleaned. This process step is independent of temperature, composition and Amount of exhaust gas flow. By rotating the rotor, the soot-laden material arrives soot filtering medium in the regeneration area. The regeneration of the loaded soot filtering medium with a smaller partial flow of the exhaust gas. Instead of one Partial flow of the exhaust gas can also be air. By the amount of air or Exhaust gas flow (and the amount of oxygen supplied thereby) can burn off the deposited soot. In this way, excess temperatures can be avoided. By the heat of reaction released during soot combustion is heated by the regeneration gas and soot filter. In the sense of low heat loss, this heat can be applied to other areas of the rotor recovered and used to preheat the regeneration gas. If necessary, heat-transferring areas can also be provided in front of or behind the rotor be arranged (see below).

The use of a small partial flow for the regeneration results significantly smaller heat losses, autothermal operation is possible. When using A partial flow of the exhaust gas can be removed from the exhaust gas flow via a regulated flap be branched off. This allows a high degree of independence from Load change behavior of the engine can be achieved.

regeneration gas

A partial flow of the exhaust gas can be used to regenerate the loaded soot-filtering medium be used. This partial flow can be removed from the exhaust gas flow via a regulated flap be branched off.

Alternatively, clean air can also be used for regeneration. Which of the two Possibilities makes more sense depends on the flow guidance - discussed below.

Regeneriergasmenge

The quantity of regeneration gas or quantity of regeneration air results from the required quantity Amount of oxygen required for complete combustion of the deposited soot. To avoid excess temperatures, the amount of regeneration gas or Regenerating air volume can be controlled so that a certain temperature when burning is not exceeded. With a suitable choice of the speed of the rotor and thus the This limitation is not necessary for regeneration cycles. Provided the oxygen limit is too leads to an undesirable formation of CO, this can - if necessary after further air addition - in one downstream catalyst are implemented. Optionally, at least in A catalyst can be arranged in partial areas of the soot-filtering medium. It can too Areas of the soot filtering medium equipped with a catalyst, e.g. B. coated. The amount of regeneration gas must also be matched to the duration of the regeneration cycle. In the rotor, the duration of the regeneration cycle can be easily changed by varying the Speed can be changed. Furthermore, the respective times for Cleaning and regeneration through the division of space between the individual Areas.

Oxidation catalyst

To accelerate the oxidation reactions, at least in some areas of the soot filtering medium a catalyst can be arranged. Areas of the soot filtering medium can be coated with catalyst. Will be for the coating Oxidation catalyst, e.g. B. uses a noble metal-containing catalyst, so this any CO formed are oxidized. Likewise, the oxidation of the deposited soot particles are accelerated.

This method can also be used with storage catalysts to remove nitrogen oxides can be combined from the exhaust gas. This option is described below.

Regenerierintervalle

The regeneration intervals can change the load behavior of the engine and the resulting The amount of soot can be adjusted. With the rotor, this can be done in a simple manner via the speed respectively. When using clocked single devices, this can be done via the cycle time.

Distribution of the rotor segments

The functional areas of the rotor are determined by the arrangement of the fluid inlets and outlets established. This also allows the segmentation for the areas of exhaust gas cleaning, Specify regeneration and heat exchange. For the purposes of this invention, the largest Segment of the rotor for cleaning the exhaust gas flow are available. A smaller one Segment of the rotor should be used for the regeneration of the soot filtering medium. The heat can be exchanged in another segment, which is also smaller.

The required ratio of the segment sizes of the exhaust segment and regeneration segment is determined on the one hand by the soot loading of the engine exhaust gas, on the other hand by the intended maximum soot loading of the filter material and by the intended Duration of regeneration.

Design / design

A particularly suitable option for this can be the use of a rotor. The rotor can contain a soot-filtering medium or from such, e.g. B. one Soot filters exist (see below). The individual fluid inlets and outlets result in the rotor the individual functional areas ("rotor" version).

Alternatively, a version can be used in which the soot filtering medium is fixedly arranged while the fluid inlets and outlets are rotated ("stator" - Execution). The version with a fixed soot filter and rotating fluid distributors can make more sense with sensitive ceramic filter media. It can make sense to use the not to arrange rotating fluid distributor directly on the filter material. Rather, one can Transition area can be arranged. Then the seal from the ceramic matrix In this case, this transition area must also be decoupled Segment segmentation to mix between the individual segments prevention.

Instead of the rotor or stator version, the device can also consist of individual ones There are sub-devices which are flowed through alternately by the respective fluid flows. In this case the fluid flows are switched between the individual sub-units through suitable flaps or valves.

Operation of the rotor / stator

In the rotor version and in the stator version, the rotation can either continuously, or there can be a clocked rotary movement in which the rotating unit is rotated by a certain segment.

Type of soot filtering material

Different materials and different materials can be used as the soot filtering matrix in the apparatus Comments are used. On the one hand, this can be a ceramic honeycomb monolith soot filter in which the individual Channels are alternately closed at the entrance or at the exit. (So-called wall flow Filter). Alternatively, a ceramic fiber filter, a metallic fiber filter or a metallic fleece filter can be arranged in the apparatus. Furthermore, sintered metal filters or sintered ceramic filter can be used.

The metallic designs offer the advantage of higher strength Thermal stresses and a higher resistance to temperature changes.

Form of the soot filtering material

The soot-filtering material can have a honeycomb structure shape such as that of existing ones Soot filtering is known. This shape offers the due to the parallel channels Advantage that the flow is conducted in the direction of flow without transverse components. Thereby can cross-mix between the individual areas without additional measures be avoided.

Alternatively, the soot-filtering material can be arranged in the form of fleece or fiber mats become. To avoid cross flow, the rotor cross section should be in individual segments are divided between which cross-mixing is avoided can be.

It is also possible to arrange the filter material in the form of parallel walls. For the formation of Segments these walls can also be arranged in a star shape in such a way that they Form segments.

In a further design, a continuous soot-filtering material can be used in that of air filters Known design zigzag folded can be arranged. With suitable folding segments are also formed.

Shape of the rotor / stator

The simplest form of rotor or stator can consist of a cylindrical monolith. This design offers z. B. on when ceramic honeycomb monoliths are used.

It is also possible to arrange the rotor or stator in the form of a hollow cylinder. This can e.g. B. useful when using zigzag folded soot filtering elements.

In the cylindrical arrangement, the individual fluid streams flow through sensibly in the axial direction. With the hollow cylinder arrangement, the Flow guidance can be carried out both axially and radially.

Upstream or downstream heat exchanger areas

In a further embodiment, heat-exchanging areas can precede the rotor downstream. These can e.g. B. run as a heat exchanger. Thereby a further improvement in heat exchange can be achieved.

More use cases

In addition to the use for exhaust gas purification in diesel engines, this invention can also be used other engine concepts (e.g. Otto engines with direct injection) are used for which emit substances or particles that accumulate on a filter attached to it must then be cleaned in a regeneration step.

Further applications can also arise in stationary exhaust air purification, if z. B. aerosol-containing exhaust air flows or particle-laden exhaust air flows must be cleaned.

Combination with a denitrification process with storage catalytic converters

The process according to the invention can be particularly advantageously carried out with denitrification combine with storage catalytic converters.

For this purpose, the soot-filtering medium can be provided with a storage catalytic converter, at least in some areas equipped, preferably coated. In a first area, one for the The device suitable for the method according to the invention is always cleaned Exhaust gas from normal engine operation. The nitrogen oxides on the storage catalytic converter bound. The regeneration of the Storage catalyst. It is crucial that the regeneration only with a smaller one Partial flow of the exhaust gas takes place. By using a partial flow, the Achieve the following advantages: On the one hand, the partial flow can be independent of the respective Control the load state of the engine. This means that regeneration can always be carried out with a constant or optionally with an adapted current. Another advantage consists in the fact that only a small partial flow with an oxygen-poor and possibly hydrocarbon-containing exhaust gas must be generated.

There are decisive advantages such. B. in that the engine is always in normal Operating mode is running; a change to the regeneration mode with enriched mixture is not required.

In a particularly advantageous embodiment of the method, in a first area the device continuously and simultaneously the soot particles on the filtering medium attached and the nitrogen oxides bound to the storage catalyst. This will make the exhaust gas at the same time cleaned of soot particles and nitrogen oxides. When using a suitable the oxidation accelerating catalyst can also in the same range Hydrocarbons and carbon monoxide are removed from the exhaust gas. In others Areas of the device are then the soot-filtering medium and the storage catalyst continuously regenerated.

In the regeneration segment, the soot filtering medium can be regenerated by regulation of the partial stream, a low-oxygen and possibly carbon-containing gas is generated. With Such a low-oxygen and possibly carbon monoxide-containing gas can then be used in one Regeneration segment of the storage catalyst to be regenerated.

The term storage catalytic converter designates a composition that is capable of To bind nitrogen oxides from the oxygen-containing exhaust gas and the under oxygen and possibly oxidative conditions can be regenerated again (e.g. BaO). typical Storage catalytic converters consist of three active components: one Oxidation catalyst (e.g. platinum), an adsorbent (e.g. barium oxide) and one Reduction catalyst (e.g. rhodium). The adsorbent can be elements from the groups contain the alkaline earths, the alkali metals or the rare earths.

As already described for the pure soot filter process, the individual areas of the Device can be divided into individual devices or sub-devices, the respective Exhaust gas, regeneration gas and hot gas flows alternate through the dividing heads can be performed. It is particularly advantageous to separate the individual areas into one apparatus integrate. A particularly suitable option for this can be the use of a rotor consist.

Analogous to the pure soot filtering process, the term "rotor" are used, including including an arrangement in which the soot filtering medium is housed in a fixed arrangement, while the Fluid feeds are rotated. Furthermore, the following functional description can be also transferred to the version with individual separate devices. The simplicity For the sake of example, the rotating soot-filtering medium with fixed should in the following Fluid supplies are described.

With this arrangement, the simultaneous removal of soot by the soot-filtering material and the removal of the nitrogen oxides by the storage catalytic converter take place in the largest area of the rotor. Areas loaded with soot and nitrogen oxides enter the regeneration area by rotating the rotor. In the regeneration area, on the one hand, the deposited soot particles are oxidized in the manner already described using a small regeneration gas stream. The following effects can be achieved by regulating the amount of regeneration gas:
First, the temperature can be limited. On the other hand, a low oxygen gas can be generated with a small amount of regeneration gas. Thirdly, the amount of regeneration gas can be reduced to such an extent that the oxygen contained therein is completely consumed and a gas containing carbon monoxide is also generated. Such a gas containing carbon monoxide can be used in a particularly advantageous manner for the regeneration of the storage catalytic converter. The oxygen content measured via a lambda probe can be used for regulation.

With the gas thus generated by the particle oxidation, the regeneration of the Storage catalyst are performed. The regeneration of soot filters and Storage catalytic converter can also be carried out in successive segments. Especially However, it is advantageous to regenerate both in the same segment.

In principle, the regeneration gas can also be used to regenerate the storage catalytic converter additional fuel can be added. Regeneration with gas containing carbon monoxide has the advantage, however, that no additional fuel is required.

regeneration gas

A partial flow of the exhaust gas can be used to regenerate the loaded soot-filtering medium be used. This partial flow can be removed from the exhaust gas flow via a regulated flap be branched off. This allows a high degree of independence from Load change behavior of the engine can be achieved. In addition, through this independent Partial gas flow, the conditions for regeneration are optimized.

In combination with the soot filter with partial flow regeneration can also be used for regeneration clean air can be used. Which of the two options makes more sense depends on the - discussed below - flow control.

Regeneriergasmenge

The amount of regeneration gas or the amount of regeneration air can be controlled independently by a flap the respective load state of the engine can be regulated.

The amount of regeneration gas must also be matched to the duration of the regeneration cycle. In the rotor, the duration of the regeneration cycle can be easily changed by varying the Speed can be changed.

Regenerierintervalle

The regeneration intervals can change the load behavior of the engine and the resulting Amount of nitrogen oxides can be adjusted. With the rotor, this can be done in a simple manner Speed. When using single clocked devices, this can be done via the cycle time respectively.

Distribution of the rotor segments

The functional areas of the rotor are determined by the arrangement of the fluid inlets and outlets established. This also allows the segmentation for the areas of exhaust gas cleaning and Specify regeneration. For the purposes of this invention, the largest segment of the rotor for Cleaning the exhaust gas flow are available. A smaller segment of the rotor is said to be for the regeneration of the storage catalyst can be used. When combining this The method with the soot filter can also be used in a further segment that is also smaller Heat exchange takes place.

The required ratio of the segment sizes of the exhaust segment and regeneration segment is determined on the one hand by the NOx concentrations of the engine exhaust gas, on the other hand by the intended maximum loading of the storage catalytic converter and by the time required for regeneration.

Design / design

A particularly suitable option for this can be the use of a rotor. The rotor can be coated with storage catalytic converter at least in areas or entirely consist of this. The individual fluid inlets and outlets result in the rotor individual functional areas ("rotor" version).

Alternatively, an embodiment can also be used in which the storage catalytic converter is fixedly arranged while the fluid inlets and outlets are rotated ("stator" - Execution). The version with fixed storage catalytic converter and rotating Fluid distributors can make more sense with sensitive ceramic carrier media.

Instead of the rotor or stator version, the apparatus can also consist of individual ones There are sub-devices which are flowed through alternately by the respective fluid flows. In this case the fluid flows are switched between the individual sub-units through suitable flaps or valves.

In all arrangements it can be useful to include part of the carrier matrix Coating storage catalytic converter, while other, uncoated areas for the Heat exchange is available. This makes it z. B. possible an optimal Set the operating temperature range for the storage catalytic converter.

In addition, it can e.g. B. be advantageous by the arrangement and size of heat exchangers Areas in the segments and by arranging the aforementioned heat exchangers Segments to set a high temperature profile of approx. 700 ° C, at which a Sulfur poisoning of the storage catalytic converter can be reversed.

Type of carrier matrix for the storage catalytic converter

Different materials and different materials can be used as the carrier matrix in the apparatus Comments are used. In principle, all carrier materials can be used, including those for conventional storage catalysts are used. The same applies to the type of storage catalysts used. All materials can also be used here come, which are also used in conventional storage catalytic converters. So it can ceramic matrix z. B. be a ceramic honeycomb monolith, which acts as a carrier matrix for the Storage catalytic converter is used.

In combination with the process with the soot filter with partial flow regeneration, the carrier can for the storage catalyst can also be a ceramic honeycomb monolith soot filter, in which the individual channels are alternately closed at the inlet or outlet. Alternatively, a ceramic fiber filter or a metallic fiber filter can also be used in the apparatus arranged and coated with storage catalyst. Sintered metal filters or sintered ceramic filters can also be used may also have a coating with storage catalyst in some areas.

It is also possible to arrange the soot-filtering matrix and the storage catalytic converter in series to arrange.

It is also possible to channel the soot-filtering matrix onto the storage catalytic converter to bring in additional carriers. In this case, it is particularly advantageous if the channels of the soot filter on the side facing away from the engine with the storage catalyst on one additional carriers.

Transfer of oxidative rotor partial flow regeneration to other processes

The invention can also be applied to other processes that require periodic regeneration need to transfer. This can e.g. B. the combination of adsorptive exhaust air purification and subsequent oxidative regeneration of the adsorbent. The adsorbed Components are regenerated directly on the adsorbent Using the rotor with Partial flow regeneration also offers the decisive factor in this process combination The advantage of continuous operation.

Examples of circuit variants

The following descriptions show exemplary circuit variants. The shown Variants are only examples and do not show all of the above Arrangements.

The following diagrams show the circuit type using the example of a rotor version. The same circuits are also possible with stator versions or with separate sub-units with a switchover by means of flaps or valves (clocked units). In all of the figures, the rotor with the segments was represented by a replacement diagram, as shown in Fig. 8.

Fig. 1 illustrates the exemplary arrangement shows a rotor at its example, the method for cleaning the exhaust gases will be demonstrated in the following models. The rotor ( 1 ) consists of a matrix ( 2 ). This can consist of a soot-filtering material or at least partially contain such a soot-filtering material. An inflow region ( 3 ) is arranged in front of the rotor and an outflow region ( 4 ) is arranged downstream of the rotor. In the inflow and outflow areas, the flow through the rotor is divided into several segments ( 5 ). The rotor itself can have a completely homogeneous structure. Different gas flows can flow through the individual segments. By rotating the rotor ( 1 ), the rotor matrix passes through different segments one after the other and can be flowed through differently as described below.

In the following, a substitute diagram is to be used for a simpler, clearer illustration. This replacement diagram is shown in Fig. 2. The rotary movement of the rotor is represented in a linear movement. The flow through the rotor matrix in the individual segments is to be represented by the individual areas ( 6 ).

Fig. 3 shows the exemplary embodiment of a stator design. This contains a fixed matrix ( 7 ). A rotating inflow area ( 8 ) is arranged in front of the matrix and a rotating outflow area ( 9 ) is arranged after the matrix. The inflow and outflow area can be divided into several segments ( 10 ). By synchronous rotation of the inflow and outflow area, the fixed matrix can be acted upon with different gas flows at different times and locations. The stator version is also to be explained using a replacement diagram. Fig. 4 shows the equivalent diagram of the stator design. The rotary movement of the inflow and outflow areas is represented by a linear movement of the matrix. The flow through the matrix in the individual segments is to be represented by the individual areas ( 6 ). The comparison with Fig. 2 shows that the rotor and stator design can be described with the same replacement diagram.

Fig. 5 shows an exemplary embodiment with several sub-sets ( 11 ). In the example shown here, the dividing devices are separated, but they can also be arranged in a common housing. The dividing heads can switch elements ( 12 ), for. B. flaps or valves are alternately acted upon with different gas flows ( 13 ), ( 14 ). As a result, different gas flows can flow through the matrix in the sub-sets in alternation. In Fig. 5, an embodiment with three part apparatus and two different gas streams is exemplified. Arrangements according to the invention can also include several sub-sets and further gas flows. The inflow can also take place with different gas flows from different sides.

Fig. 6 shows an equivalent diagram of an embodiment with separate dividing heads. Here too, the dividing heads are represented by different areas ( 6 ) in the replacement diagram. The alternating flow through the matrix in the individual sub-units is symbolized in the replacement diagram by a linear movement of the matrix through the individual areas ( 6 ) of the replacement diagram. The comparison with Fig. 2 and Fig. 4 shows that this version can also be described with this replacement diagram.

In addition, other designs are also conceivable, which also deal with such Have a replacement diagram displayed.

The process sequence of the exhaust gas purification according to the invention is therefore to be described below such replacement graphs are shown.

Is Fig. 7 shows an example of a process variant, the exhaust gas purification part with power regeneration in the air as a regeneration medium is used. In the case of trucks, the small air flow required for regeneration can optionally be taken from the existing compressed air system, so that an additional blower can be omitted. The exhaust gas ( 15 ) coming from the engine is cleaned in the matrix ( 16 ) in the largest area of the arrangement. The matrix can consist of or contain a soot filtering material to remove the soot particles from the exhaust air. In this case, the soot is separated from the exhaust air on the soot filtering material. In many engine load conditions, the temperature of the exhaust gases is so low that there is no or only slow oxidation of the soot particles in this area. The cleaned exhaust gas ( 29 ) leaves the apparatus. Through a continuous or cyclical transport of the matrix between the individual areas, which is shown in the diagram by the horizontal arrow, the areas of the matrix loaded with soot and nitrogen oxides reach the regeneration segment ( 17 ). The matrix is regenerated there. The air ( 19 ) used for regeneration first flows through the matrix in the heat exchange segment ( 18 ). The air is heated by the hot matrix. If necessary, the regeneration air after the flow through the heat exchange segment z. B. additionally heated by a heater ( 20 ). The regeneration air preheated to the oxidation temperature now flows through the regeneration segment ( 17 ). The soot particles deposited on the matrix are oxidized to carbon dioxide by the hot regeneration air. The released heat of reaction also heats the matrix in the regeneration segment. The exhaust gas from the regeneration segment can be fed to the exhaust with the cleaned engine exhaust gas. Through a continuous or cyclical transport of the matrix between the individual areas, which is shown in the diagram by the horizontal arrow, the part of the matrix heated in the regeneration segment subsequently reaches the heat exchange segment ( 18 ). There, at least part of the heat of the matrix is absorbed by the incoming regeneration air ( 19 ), which in turn heats up the regeneration air ( 19 ).

The heater ( 20 ) can be designed as an electric heater or as a burner. The heater can be used as a start heater when starting from a cold state. The oxidation can be controlled by regulating the amount of regeneration air, so that the temperature of the matrix which arises can be limited.

In a particularly advantageous embodiment, the matrix ( 16 ) is additionally equipped, at least in some areas, with a storage catalytic converter. In this case, the engine exhaust gas ( 15 ) in the matrix ( 16 ) is also cleaned of nitrogen oxides in the largest area of the arrangement. The nitrogen oxides accumulate on the storage catalytic converter and are chemically bound there. In this case, the chemical conversion of the nitrogen oxides bound on the storage catalytic converter also takes place in the regeneration segment. The storage catalytic converter is regenerated at the same time. The chemical reactions in these processes are known from conventional storage catalysts according to the prior art, so that their description can be omitted here. To regenerate the storage catalytic converter, it can be particularly advantageous to regulate the amount of regeneration air in such a way that the oxygen in the regeneration air is at least largely consumed and an at least small amount of carbon monoxide is formed. This carbon monoxide results in a particularly favorable regeneration of the storage catalytic converter. The carbon monoxide on the storage catalytic converter is converted into harmless substances.

Instead of the regeneration of the storage catalytic converter, hydrocarbons such. B. from the fuel to regenerate the storage catalyst. A small amount of hydrocarbons ( 21 ) can be added to the regeneration air before it enters the regeneration segment.

Another advantageous embodiment is shown in FIG. 8. A catalyst ( 22 ) is arranged before entry into the regeneration segment. The added hydrocarbons ( 21 ) are oxidized on this catalyst. As a result, the temperature of the regeneration air entering the regeneration segment can also be increased.

In further advantageous configurations, the matrix ( 16 ) can be at least partially equipped with a catalyst, for example a noble metal catalyst, preferably coated. On the one hand, this catalyst promotes the oxidation of the soot particles, so that this can take place even at lower temperatures. On the other hand, the added hydrocarbons ( 21 ) can also be oxidized on this catalyst. As a result, the temperature of the matrix ( 16 ) can be raised further, so that an improved oxidation of the deposited soot particles takes place. This arrangement of a catalyst on or in the matrix can of course also be used advantageously in the embodiments listed below.

Fig. 9 shows a further embodiment of the method. Instead of air, a small partial flow ( 23 ) from the cleaned exhaust gas of the engine is used for regeneration. This has the following advantages: on the one hand, the exhaust gas is already warmer, which means that overall higher temperatures can be achieved during regeneration. Secondly, the exhaust gas has a lower concentration of oxygen. This is particularly advantageous if a storage catalytic converter is used at the same time. Then, with the oxygen-poorer gas, a favorable regeneration of the storage catalytic converter can take place in the regeneration segment. As a small disadvantage of this arrangement, it must be accepted that the exhaust gas flow must be conveyed with a blower ( 24 ).

Fig. 10 shows a further arrangement with a partial flow regeneration can be performed in the preheating of the regenerating air in a further upstream heat exchanger (25). This heat exchanger can, for. B. be designed as a plate-like heat exchanger or as a heat exchanger with fins. The use of a counterflow heat exchanger is advantageous. By preheating the regeneration air in the upstream heat exchanger, overall higher temperatures can be achieved during regeneration.

Fig. 11 shows a simple embodiment in which a heat exchange segment has been dispensed with. Since in this case the regeneration gas is only at a lower temperature, the regeneration gas probably has to be heated with an additional heater ( 26 ). This heating input can also be done by burning additional fuel. This combustion can optionally take place on an upstream catalytic converter. In this embodiment, a partial flow ( 27 ) of the exhaust gas coming from the engine is used as the regeneration gas. Since this has a somewhat higher pressure level due to the pressure loss of the downstream matrix, no fan is required. In this case, the amount of regeneration gas can be regulated in a simple manner via a flap ( 28 ).

FIG. 12 and FIG. 13 show an embodiment with partial flow regeneration, is used in the unpurified for the regeneration of engine exhaust. The embodiment in FIG. 13 corresponds to the embodiment in FIG. 12 when the direction of rotation of the rotor is reversed in FIG. 12. In these versions, regeneration takes place through uncleaned engine exhaust. A start heater can be provided for starting from the cold state. In the embodiment in Fig. 12, the heat of the heated matrix is used incompletely. In the embodiment of FIG. 13, most of the heat of the hot regeneration gas is carried in the exhaust gas.

This heat can be used in different ways, as shown by way of example in FIG. 14 and in FIG. 15.

In the figures Fig. 11- Fig. 14, the amount of the partial flow can be controlled via a flap. If the mass flow density in the regeneration gas segment is selected to be lower than in the exhaust gas purification segment, the pressure of the exhaust gas can be sufficient to push the partial flow of the regeneration gas through the regeneration segment and heat exchanger segment (especially since the arrangement according to Fig. 14 and Fig. 15 has already cleaned the heat exchanger segment). However, the pressure of the exhaust gas upstream of the soot filter depends on the intended loading of the soot filter and can change during operation. If necessary, a blower may be necessary to supply the regeneration gas.

Fig. 14 shows the embodiment of Fig. 13, but which has been expanded by an additional heat exchanger. The heat generated during the regeneration process can now be transferred to the incoming regeneration gas.

Alternatively, as shown in FIG. 15, this heat can be transferred in a further regeneration segment to that part of the rotor matrix which enters the regeneration segment at the next time step. This variant has the disadvantage that there are three passages through the filter material, which results in a higher pressure loss on the regeneration gas side.

To further improve the use of heat, there are also other circuits with a different arrangement the heat exchange segments and the fluid connections possible. For example, one is further advantageous circuit conceivable, but in which the unpurified exhaust gas from the Back should be fed. These other circuits must also be considered be that on the one hand the expenditure on equipment increases significantly and on the other hand the number the deflections of the fluid and possibly the number of passes through the filtering matrix also increases, resulting in a higher pressure loss of the regeneration gas.

Another embodiment of the method is shown in FIG. 16. A partial flow from the exhaust gas coming from the engine is also used as the regeneration gas. The amount of this regeneration gas can be regulated via a flap. The regeneration gas flows through a first heat exchanger segment. The regeneration gas is preheated by the hot matrix. If necessary, the regeneration gas can subsequently be heated further by heating. The regeneration gas then flows into the regeneration segment, where the regeneration takes place. The oxidation reactions during regeneration heat both the regeneration gas and the matrix. The regeneration gas heated by the reaction then flows through a second heat exchanger segment. The regeneration gas cools down there and releases its heat to the matrix. This will preheat the matrix. The matrix preheated in this way then into the regeneration segment. The matrix, which is further heated in the regeneration segment by the oxidation reactions, then arrives in the first heat exchanger segment. There the heat of the matrix is absorbed by the incoming regeneration air. This embodiment of the method results in a particularly extensive heat exchange.

The exemplary embodiments listed present only a few examples. Further versions and in particular combinations of the presented versions are possible. 1-6 1 rotor
2 Matrix of the rotor segment
3 inflow area
4 stripping area
5 segments of the rotor
6 areas (in the replacement diagram)
7 fixed matrix of the stator design
8 rotating inflow area (inflow area) of the stator version
9 rotating outflow area of the stator version
10 segments of the inflow and outflow area
11 dividing heads
12 switching elements (in the version with dividing heads)
13 gas stream 1
14 gas stream 2

Claims (29)

1. Process for cleaning exhaust gases characterized by the following features: - that particulate air contaminants and / or nitrogen oxides are separated on a filtering medium, - At the same time, the filtering medium is regenerated by reacting the deposited substances, - to regenerate the filtering medium, a smaller air or gas flow is used compared to the exhaust gas flow, - The regeneration of part of the filtering medium takes place simultaneously while in other areas of the filtering medium the exhaust gas flow is cleaned. 2. The method according to claim 1, characterized in that the resulting during the reaction Heat is at least partially absorbed by a heat storage medium. 3. The method according to claim 1, characterized in that in the heat storage Mass stored heat at least partially for preheating the regeneration gas is being used. 4. The method according to claim 1, characterized in that at least part of the filtering Medium in the areas to be cleaned and at least part of the filtering medium in the regeneration areas are exchanged continuously or cyclically. 5. The method according to claim 1, characterized in that at least part of the filtering Medium continuously or cyclically between cleaning areas, regeneration areas and heat exchanging areas. 6. The method according to claim 1, characterized in that the filtering medium Oxidation of the particulate deposited on the filtering medium Air pollution is regenerated. 7. The method according to claim 1, characterized in that the filtering medium at least is equipped in some areas with a substance that accumulates nitrogen oxides and chemical bond. 8. The method according to claim 7, characterized in that the nitrogen oxide binding substance can be regenerated by reaction. 9. The method according to claim 1, characterized in that in the formation of particles resulting carbon monoxide for the regeneration of the nitrogen oxide binding substance is being used. 10. The method according to claim 1, characterized in that by regulating the Regeneration air amount an at least partially incomplete oxidation to form Carbon monoxide is produced. 11. The method according to claim 1, characterized in that the regulation of The amount of regeneration air is such that temperatures in the regeneration area exceed 450 ° C, preferably temperatures above 550 ° C can be reached. 12. The method according to claim 1, characterized in that the filtering medium at least is equipped in some areas with a catalyst that oxidizes the particles supported. 13. The method according to claim 1, characterized in that the regeneration gas first in is preheated in a heat-exchanging area, subsequently in one Regeneration area undergoes a reaction. 14. The method according to claim 1, characterized in that the regeneration gas first in is preheated in a heat-exchanging area, subsequently in one Regeneration area undergoes a reaction and subsequently its heat to one emits another heat-exchanging area at least partially. 15. The method according to claim 1, characterized in that a small regeneration gas Airflow is used. 16. The method according to claim 1, characterized in that a small regeneration gas Part of the exhaust gas is used. 17. Device for carrying out the method according to claim 1, characterized in that that the device has different functional areas. 18. Device for carrying out the method according to claim 1, characterized in that that the device has different functional areas and a filtering matrix continuously or cyclically runs through these different functional areas. 19. The apparatus according to claim 18, characterized in that the functional areas comprise at least one cleaning area in which the exhaust gas is cleaned. 20. The apparatus according to claim 18, characterized in that the functional areas comprise at least one regeneration area in which the filtering matrix is regenerated. 21. The apparatus according to claim 18, characterized in that the functional areas comprise at least one heat-exchanging area in which heat between the Matrix and the regeneration gas is transferred. 22. The apparatus for performing the method according to claim 1, characterized in that the device includes a rotating element which is different Has functional areas. 23. Device for carrying out the method according to claim 1, characterized in that that the device includes at least one rotating element which has different functional areas and a filtering matrix continuously or cycles through these different functional areas. 24. Device for carrying out the method according to claim 1, characterized in that that the device includes a rotating matrix which is continuous or cyclical goes through different functional areas of cleaning and regeneration. 25. Device for carrying out the method according to claim 1, characterized in that that the device includes a rotating matrix which is continuous or cyclical different functional areas from cleaning, regeneration and heat exchange passes. 26. Device for carrying out the method according to claim 1, characterized in that that the device includes at least one rotating element which different gas flows distributed over different functional areas. 27. Device for carrying out the method according to claim 1, characterized in that that the device includes at least one rotating element which different gas flows in different functional areas and thereby a filtering matrix continuously or cyclically steps from cleaning and regeneration experiences. 28. Device for carrying out the method according to claim 1, characterized in that that the device includes at least one rotating element which different gas flows in different functional areas and thereby a filtering matrix continuously or cyclically steps from cleaning, regeneration and Undergoes heat exchange. 29. Device for carrying out the method according to claim 1, characterized in that that the device contains dividing heads that serve different functions and their respective functions are exchanged cyclically.