DE19845944A1 - Process for the reduction of nitrogen oxides in exhaust gases containing oxygen, in particular exhaust gases from internal combustion engines - Google Patents

Abstract

The invention relates to a method for reducing nitrogen oxides in an exhaust gas flow, especially exhaust gases from internal combustion engines that are subjected to aftertreatment in a catalytic converter. The inventive method is characterised in that a solid reducing agent is transformed into a gas under the effect of heat and the gas is thermally and/or catalytically broken down in a reaction chamber into reductive products which are then mixed with the exhaust gases which are to undergo reduction.

Description

The invention relates to a method for reducing Nitrogen oxides in an oxygen-containing exhaust gas stream, esp especially in exhaust gases from internal combustion engines that a ka talytic exhaust gas aftertreatment in a catalytic converter be drawn.

The catalytic aftertreatment of oxygen containing ABGA sen from internal combustion engines to reduce _NOx emissions requires a so-called selective catalytic reduction, which allows the exhaust gas with the nitrogen oxides, NO and NO ie ₂ molecular nitrogen (N _2), carbon dioxide (CO ₂₎ and to form water, specifically in diesel engines, but also in gasoline engines with direct fuel injection. This is done by supplying reducing agents, which is difficult, however, with regard to the metering in the required small amounts in highly dynamically operated internal combustion engines in mobile use with fluctuating nitrogen emissions.

According to DE-A-44 23 003, a method is proposed for ammonia in one embodiment as a reducing agent, Hydrazine or tricyanoic acid in liquid form the fuel or the combustion air is metered in on the inlet side, so that its components only after the combustion process has ended leave the cylinders and get into the exhaust system. On due to the thermodynamic conditions during combustion process, the reducing agents lose theirs reductive properties.

In another embodiment according to this document proposed the reducing agent in powder form on the Ab gas side of the internal combustion engine. The feed of the powdered reducing agent is made by gravity  and is using a mechanical distribution device with blower air support inserted into the exhaust pipe brings. A dosage of the smallest amounts of reducing agent This technique is very difficult. The usage of hygroscopic reducing agents in this case causes considerable problems because the flowability is a prerequisite for a is the proper functioning of such a system.

According to DE-A-44 36 415 is proposed for a diesel engine gene, part of the diesel fuel directly into the Ab insert gas line. The introduction takes place with Help a porous chamber provided with a glow pencil is so that the diesel fuel introduced into the chamber supplied to the exhaust gas in gaseous form through the porous walls can be. This procedure does not meet today's requirements claims of emission reduction.

Furthermore, a liquid dosage was tried to make eutectic urea-water solution to the exhaust gas. The dosage of such a liquid urea-water Solution even in small quantities is with great accuracy possible. The disadvantage, however, is that for one reducing agent to be injected water must be carried, wel ches not directly in the reduction process for the nitrogen oxide is divided. So it doesn't just have to be a multiple of weight and volume - based on the reducing agent - tanked and be transported, but care must also be taken conditions that the system is generally suitable for winter. A Another disadvantage is that turned into the exhaust gas liquid initially obtained reductive components Need to become. However, are there for proper operation required for certain minimum exhaust gas temperatures, which ins overall a reduction in the overall efficiency of the system for Consequence. The expenditure on equipment is high and prone to failure, since a pump-nozzle system must be used here.  

In order to avoid these disadvantages, according to DE-A-43 08 542 suggested solid urea instead of an aqueous one Urea solution as a reducing agent in the exhaust system respectively. Since urea is hygroscopic and cakes, it is necessary to pre-test the urea in microprills Give up the hopper from which the prills on a grinder deducted and then with the help of compressed air in the exhaust system be blown in through a pressure atomizing nozzle. The Zudo Smallest quantities can be adjusted to adapt to different Exhaust gas quantities are very difficult with this system.

According to DE-A-34 22 175 such nitrogen has been proposed containing reducing agents, which Ammo Release niak to apply thermal. The so won The amount of ammonia can then be supplied directly to the exhaust gas the. The required amount of ammonia can be used Heating power can be controlled. Such a pure thermal system is too slow to dose Ammonia with a highly dynamic, changing Nitrogen oxide emissions from internal combustion engines. The danger of one so-called ammonia breakthrough, d. H. remaining ammo niak concentrations behind a catalyst arrangement given.

In DE-A-42 00 514 the reducing agent is ge into the exhaust gas pumps. The reducing agent is outside the exhaust gas troms into reductive components, so-called fission products, disassembled. The aim of this procedure is to react ons speed of the actual reduction step in Re reducing nitrogen oxide system and a height To bring about efficiency in the overall catalytic system. The egg common problems regarding the dosage at highly dynamic Nitrogen oxide generation remains unexplained here too. The sy stem can only with stationary or nearly stationary Nitric oxide generation is used because of the risk of Breakthrough of ammonia is given.  

According to DE-U-297 08 591 the solid, nitrogenous Re detergent in a pressure-resistant converter to ammonia converted. An intermediate storage for ammonia becomes temporary clocked filled and emptied. In this invention, the Adaptation of the reducing agent flow to a highly dynamic one Exhaust gas volume provided. This system requires one Pressure-resistant pressure vessel arrangement for temporarily storing the Ammonia is a problem substance.

The invention has for its object a method of to create the type described above, which he above Disadvantages discussed does not have.

This object is achieved according to the invention in that a reducing agent present as a solid under heat action transformed into gas and the gas in a reaction chamber thermally and / or catalytically in reductive products is disassembled, which is then the exhaust gas to be reduced in front of the Ka Talysator are added. The term "gas" or "Ver gas "in the sense of the present invention includes both Conversion "solid liquid gas" as well as the subima tion, d. H. the immediate transition from "solid gas". Of the each transition from solid to gas that occurs depends on the type of reducing agent used.

The method according to the invention has in particular for vehicles the advantage that the reducing agent to be used in solid Shape, d. H. with the least amount of inventory can be performed. The other advantage is that the generated and for the catalytic reaction in the exhaust gas data lysator needed gas much easier to reduce that the exhaust gas can be mixed in, with corresponding Regular interventions in the context of gasification of the solid also the smallest quantities can be added.

Another advantage of this invention is that reducing agents can also be used in the liquid or gaseous phase which do not disintegrate into fission products in a storage container and / or in a metering chamber. Problem substances, such as ammonia, are then not stored, but only created when they are converted into reductive products. When it is stored, the reducing agent also does not disintegrate into fission products which are ineffective for NO _x reduction.

The decomposition of the reducing agent converted into gas in reductive products can now either according to the invention a pyrolysis reaction with further heat or by the supply of water, in particular water vapor, by a catalytically supported hydrolysis reaction. The hydrolysis reaction has the advantage that the Ab gas temperatures are sufficient or at least only low Temperature increase is necessary. On the other hand, there is Advantage that the water vapor content in combustion sufficient exhaust gases, so that little or no additional Liche amounts of water are to be fed to the hydrolysis reaction to be able to perform.

In a further advantageous embodiment of the invention provided that the required amount of gas by changing the heating power acting on the solid is regulated. The change in the gas flow can, for example, about a controllable dosing valve.

In a further embodiment of the invention it is provided that the amount of gas required by changing the solids supply is regulated. A combination is particularly advantageous both measures, so that for a gassing of the feast required minimum heating power is applied and then about an increase in heating power and / or an increase the amount of gas required for the solids supply can be increased and vice versa, so depending on the respective accrued, operational exhaust gas volume imported the reductive products in gaseous form apply.  

In a particularly expedient embodiment of the invention, it is further provided that the amount of exhaust gas components, in particular NO _x and / or reductive products of the reducing agent, in particular amide ions and / or isocyanic acid and / or ammonia, is recorded behind the catalyst. This measure can be ensured with the help of a corresponding Steuerein device that the reducing agent is only introduced into the exhaust gas in the amount required. The amount of reductive products behind the catalyst should be "zero" if possible. If increased values are determined, the supply of reducing agent must be reduced. If the proportions of NO _{x are recorded} , regulation of the supply of reducing agent is also possible. In an embodiment, it is expedient for the reducing agent to be metered in via a control device as a function of the NO _x values detected.

In an advantageous embodiment, it is also provided that the metering of the reducing agent via a control unit as a function of engine-specific maps on the NO _x contents and / or the HC contents in the exhaust gas follows. If such empirically determined maps are "stored" in the engine control system, it is possible to perform the metering depending on the operation even without complex exhaust gas sensors, since these maps are "read" during operation in the control device and "stored" for the respective operating point in the map "The amount of reducing agent is added.

Instead of or in addition to the mo it is advisable to use the tax-specific characteristic maps establish the metering of the reducing agent in depend of catalyst-specific maps with regard to the Degree of turnover and / or the storage capacity of the aftertreatment perform catalyst.  

Also a time-varying clock frequency or a vari The opening cross section of a metering valve can be as Map are determined and never in the control device be put down.

Likewise, the specific gasification rate of the reduction mit depending on the heating output and / or heating temperature set up as a map and in the control device stored and for the metering of the gasified reduction mit means are also used.

By a combined tap of the maps or by an overlay of two or more maps, for example way of the engine-specific, the catalyst-specific and the map of the specific gasification rate can be in the control device a control signal for metering he testify to an optimal supply of the reduction mit leads to an optimal exhaust gas aftertreatment is achieved.

In a further advantageous embodiment of the invention The method provides that the gas in a carrier gas in Form of exhaust gas and / or air premixed and the premix is added to the exhaust gas flow. This measure is a more even distribution of small amounts of reducing agents possible in the exhaust gas flow, since "streaks" are avoided here and a reduction in the total exhaust flow in the desired Dimension is guaranteed.

The effect of heat from the solid Gas generated from the reducing agent is thermodynamically incorporated in this way represents that this is a slight overpressure compared to the Ab has gas pressure, so that here in the simplest way "natural", from the given heat output and / or given NEN supply amount of solids-dependent pressure drop generated becomes. This pressure drop generated by the heating power enables exact gas dosing. This can can be caused, for example, by the reduction mit  tel in at least one pressure-tight container or card ink is stored, which only in the direction of the reduced rende exhaust gas is openable. The result of heating Gas volume builds a correspondingly small one in the container Overpressure, for example 0.5 bar above the exhaust gas counter pressure, which then lets the gas flow out. The effect of heating can via a heat supply via the container wall and / or but at least one heating element on the inside of the container Reducing agents are applied. For exact dosing of the reducing agent can be, for example, the differential pressure between the heating chamber in which the gasification takes place and Exhaust pipe measured and regulated via the heating output. Via the metering valve, which clocks in an advantageous manner works, it is then possible to get precisely dosed amounts of Re measuring agents.

In order here however flow resistances in the required To overcome flow channels, it is in another form device of the invention useful if the admixture to the exhaust gas with the help of a pressure gradient between the gasification area and the exhaust gas flow takes place. This can be done easily by making sure that the exhaust duct at the admixing point is designed in the manner of a Venturi tube, so that the due to the speed increase in the exhaust gas flow Lowering the static pressure the corresponding Druckge cases against the gasification device and the Ab flow of the generated gas is favored. In addition or instead of using the pressure drop in the exhaust gas flow the admixture of the reducing agent gas using a Partial flow of exhaust gas or air take place via an ent talking blower is generated.

If there is a pressure gradient between the gasification area and the Mixing area, in particular an overpressure can be generated can, it is appropriate if the supply amount of gasified Reducing agent via a controllable metering device, ins In particular, a metering valve is made, which is via the control unit  direction is controlled. The dosage can be, for example by opening the metering valve in cycles.

The container can be used as a refill container or especially in front may be provided as a replacement cartridge. There with results in a manageable unit that only is to be attached, the closure being opened and closed a tight connection to the treatment direction is created.

Depending on the design of the facility, when plugging in also appropriate fittings in the tank filling are brought, such as level sensors, mecha African discharge devices, heating devices, given if in connection with gas extraction devices. Exchange Cartridges can also be used as a cartridge battery in order to cover the longest possible operating periods.

In a further embodiment of the invention it is provided that the solid reducing agent cyanuric acid and / or melamine and / or urea and / or biuret and / or trioret and / or other nitrogenous reducing agents individually or in Mi that are used after the phase change has been completed from solid to gaseous with further energy supply in right have ductile products disassembled or several of these compos components are used. Has been particularly useful here proven using cyanuric acid.

The solid reducing agent can be in a free-flowing state be set. Here, the free-flowing reduction mit tel from a storage container directly via mechanical Systems are promoted in a heating device and / or are in the heater as a whole.

In another embodiment of the invention, that the solid reducing agent in the form of a compact is set. Such compacts can, for example, as Tablets stack or packaged as rods or the like  be then against the heater accordingly be pushed and / or total in the heater tion.

The invention is illustrated schematically with reference to drawings poses. Show it:

Fig. 1 shows schematically the implementation of a reduction by means of reductive in a pyrolysis reaction to produce products,

Fig. 2 is a flow chart for a first embodiment of a process for the production and supply of gaseous reductive products according to the process flow according to. Fig. 1

Fig. 3 schematically shows the implementation of a reduction by means of reductive in a hydrolysis reaction to produce products,

Fig. 4 shows a modification of the embodiment of Fig. 2,

Fig. 5 shows a practical arrangement for installation on a vehicle to carry out the method acc. Fig. 4.

In Fig. 1, the basic reaction of the implementation of a solid reducing agent, here cyanuric acid, in the gas form and then the decomposition into a reductive product and its admixture to the reducing exhaust gas and the subsequent exhaust gas aftertreatment is shown in a catalyst. With (HNCO) ₃ , cyanuric acid, heat with a temperature level of 300 to 450 ° C is required for the conversion from a solid form into the gas form. A further supply of heat converts the gaseous cyanuric acid into 3 (HNCO), isocyanic acid. A further heat supply with a temperature level of more than 400 ° C is required here. Isocyanic acid is then in turn reacted with heat at a temperature level of 450 to 750 ° C in a possibly catalytically supported pyrolysis reaction in the required reductive products, which is essentially formed by the NH (amide ion) in the reaction of isocyanic acid, which then the exhaust gas is mixed. The subsequent catalytically supported reaction between NH and NO _x in the exhaust gas catalyst requires a temperature level of the exhaust gas of more than 400 ° C. Such a temperature level is given, for example, in stationary systems, in particular internal combustion engines operated stationary in the full-load range.

The flow diagram according to FIG. 2 shows an exhaust pipe 1 of an internal combustion engine, for example a diesel engine, which is provided with a catalytic converter device 2 which has a selective reduction catalytic converter. Exhaust gas flows through exhaust gas line 1 in the direction of arrow 3 .

The exhaust pipe 1 is assigned a device 4 for the supply of egg nes present as a solid reducing agent. The device 4 consists essentially of a storage container 5 for a present as a solid reducing agent 6. The reducing agent 6 can be in free-flowing form or as a solid. The storage container 5 can be provided with egg ner conveyor 7 , with which the solid 6 is conveyed in the direction of an outlet opening 8 . In the embodiment shown here, the Förderein device 7 is shown schematically by a press plate 7.1 with a loading spring 7.2. The pressure plate 7.1 can also be provided with a seal, so that pressurization can take place via the backward space, for example via a branch duct with exhaust gas. The reservoir 5 must be in its transition area to the outlet opening 8 so that no "bridges" can form. In the area of the outlet opening 8 , a mechanical metering device 8.1 can be provided which, in the case of free-flowing reducing agent, metered in volumetrically, for example, or scrapes off corresponding particle quantities in the case of a solid body via a drive. The reducing agent itself must not tend to stick or bake, but must keep its flowability even under changing external conditions, such as changing seasons. If the arrangement is not connected to the motor and vibrations are thereby introduced into the container 5 , the arrangement of a corresponding vibrator can be expedient, which is controlled periodically and prevents bridging.

The dosing device 8.1 opens into a chamber-shaped heating device 9 which has a porous heatable wall which comes in direct contact with the supplied solid reducing agent, here only represented by a schematic heating coil 9.1 , so that the gasification process can take place here. When using compacts in the form of bars or tablets, the mechanical dosing device is omitted. The allocation of the storage container and the heating device must then be designed in such a way that the reducing agent is pressed onto the heating device via a corresponding conveying device. By heating the container walls, which are then thermally insulated from the outside, or by means of heating elements immersed in the container filling, the gasification of the reducing agent can be effected or supported, as indicated in FIG. 4 with the heating coil 12.1 .

The gaseous reducing agent now enters from the heating device 9 into a metering chamber 10 , the walls of which are provided with thermal insulation 11 and which is provided in the wall area with a further heating device 12 , so that a condensation of the gaseous reducing agent on the walls is avoided.

The metering chamber 10 is a reaction chamber 13 nachgeschal tet, which is provided with a further heating device 14 and makes it possible to divide the incoming from the metering chamber 10 in the re action chamber 13 reducing agent gas thermally into its reductive components. When using cyanuric acid, ie (HNCO) ₃ in the reaction chamber 13 according to the diagram acc. Fig. 1 with the help of the additional heat supply by the heating device 14 via the decomposition into HNCO and into the faster reducing NH generated the reductive product. The supply of the gas to the reaction chamber 13 can be regulated via a metering valve 10.1 ( FIG. 2), which operates in an analog or clocked manner.

The gas can be discharged directly from the reaction chamber 13 via a mixing pipe 15 . The mouth of the admixing tube 15 can in this case be provided with a mechanical distribution device 16 in order to bring about as uniform a distribution as possible over the entire flow cross-section before entering the catalyst 2 . The distribution device can, for example, be formed by a baffle plate at the outlet opening. It is appropriate for a swirl body 16.1 to be arranged in the exhaust pipe 1 at least in front of the mouth of the admixing pipe.

In order to improve the mixture in the exhaust pipe, a premixing chamber 17 is assigned to the reaction chamber 13 in the exemplary embodiment shown here, which is connected via a feed pipe 18 for a carrier gas. Hot air and a partial exhaust gas stream can be used as carrier gases, which are provided via appropriate sources and with the appropriate pre-pressure. Exhaust gas as a carrier gas can be removed upstream from the exhaust pipe 1 . At the premixing chamber 17 , part of the oxygen-containing carrier gas can thus be premixed with the gaseous reducing agent flowing in from the reaction chamber 13, and the premixing then into the exhaust pipe as described above due to the pressure drop between the mouth 16 of the supply pipe 15 and the (higher) pressure in the premixing chamber 17 are introduced. An controllable valve 19 in front of the premixing chamber 17 can prevent an uncontrolled outflow of the reducing agent, for example in the event of a vehicle fire. Appropriately, all "hot" chambers and the Verbindungska channels are surrounded with the insulating jacket 11 .

The overall arrangement is connected to a control device 20 , which in turn can be connected to the engine control. On the one hand, the heating power of the heating device 9 is controlled via the control device 20 , the supply of heating energy being controlled via a corresponding temperature sensor 21 . In Fig. 2, the heating energy can be optimally controlled by a pressure sensor 26. In the control system, engine-specific and / or specific characteristics of the aftertreatment device, NO _x characteristics and / or HC characteristics can be "stored" for all operating states, so that the Supply of reducing agent can be regulated according to the specifications of the maps.

Via the control device 20 , both the heating power of the heating device 12 of the metering chamber 10 and the heating power of the heating device 14 of the reaction chamber 13 are in each case controlled and regulated accordingly via temperature sensors 22 and 23 and the valve 19 is controlled. Between rule the metering chamber 10 and the reaction chamber 13 , a further metering valve 10.1 can be arranged that can also be designed as a check valve that opens only when needed, so that the heating of the reaction chamber 13 is also switched on only when needed, while via the heater in the heating chamber 9 a basic temperature level is maintained. A basic pressure level can be maintained via a pressure sensor 26 .

Via an adjustable drive mechanism (not shown here), it is also possible to regulate the quantities supplied to the heating device 9 with the aid of the control device 20 also via the feed of the conveying device 7 and / or the mechanical metering device 8.1 . The regulation of the supply quantities of solid reducing agent from the storage container 5 is always useful when a lower and an upper limit temperature is sufficient for the heating device 9 and a change in the quantity of gas to be generated is only possible by changing the solids supply. Another way of reducing the heating power to be applied is to subdivide the storage container into individual segments filled with reducing agent, which can be charged separately with heating power, so that not all of the reducing agent in the supply ratio has to be brought to a higher temperature level.

Via a sensor 24 , which is arranged in the exhaust duct 1 behind the catalyst device 2 , there is also the possibility of ensuring that not too much reducing agent is supplied. With this sensor 24 , the decomposition products of the reducing agent used in the exhaust gas stream can be detected, in particular amide ions and / or isocyanic acid and / or ammonia or also nitrogen oxides and then, via the control device 20, regulation of the heating power of the heating device 9 and / or regulation the supply of reducing agent from the storage container 5 can be influenced and / or dosing by means of the dosing valve 10.1.

The fill level in the storage container 5 can be checked via a sensor 25 , so that when a minimum quantity is reached a corresponding signal is generated which indicates to the operator the need for refilling. Alternatively, the heating output can also be monitored, for example via the duration or frequency of activation of the metering valve. If the output rises above a limit value, a signal to replace the cartridge can be given.

The process described with reference to FIG. 1 and FIG. 2 requires relatively high temperatures in the pyrolysis reaction and in the later catalytically supported reaction of the reductive product produced in the exhaust gas, as is the case with an internal combustion engine operated at full load in stationary operation.

In Fig. 3 is another basic reaction of the implementation of a solid reducing agent, here cyanuric acid, in the gas form and then the decomposition into a reductive product and its admixture to the reducing exhaust gas and the subsequent exhaust gas aftertreatment in a catalyst represents schematically. With (HNCO) ₃ , cyanuric acid, heat with a temperature level of 300 to 450 ° C is required for the conversion from a solid form into the gas form. By adding water vapor at 150 to 350 ° C, the gaseous cyanuric acid is converted to NH ₃ (ammonia), which takes place as a catalytically supported hydrolysis reaction. The ammonia obtained as a reductive product is then mixed into the exhaust gas. The subsequent catalytically supported reaction between NH ₃ and NO _x in the exhaust gas catalyst requires a temperature level of the exhaust gas of only more than 120 ° C. Such a temperature level is given, for example, in the case of non-stationary internal combustion engines in vehicles which are also operated in the partial load range.

Fig. 4 shows in the form of a flow chart, the method accordingly the process according to. Fig. 3, as is particularly appropriate for vehicle engines with changing load requirements. The process is based on the use of an exchangeable cartridge 5.1 with a reducing agent filling. It is expedient if the heating and Vergasungsein direction 9 / is brought medium filling in immediate contact with the reduction 10th The closed cartridge 5.1 is connected to the device in a pressure-tight manner, the heating device 12.1 touching the interface or penetrating into the reducing agent filling 6 . The resulting reducing agent gas, which is under a corresponding excess pressure, can then pass into the reaction chamber 13 via a clocked or analog metering valve 10.1 controlled by the control device 20 . Appropriate capitalization for the exact Do the arrangement of a choke point 10.2 is gang in over between the heating and gasification device 9/10 and the reaction chamber 13. Again, all are "hot" chambers and connecting channels including cartridge 5.1 surrounded by an insulating jacket, which here is not shown to simplify the drawing.

In order to be able to realize a NO _x reduction at exhaust gas temperatures of approximately 150 ° C. to 350 ° C., reaction 13 in reaction chamber 13, for example when using cyanuric acid, results in a reaction essentially in ammonia as a reductive product. For this purpose, water-containing exhaust gas is fed via a feed line 18.1 to the reaction chamber 13 , in order to act as a hydrolysis. A hydrolysis catalyst 13.1 can support the decomposition, so that here the degree of conversion, reaction temperature and residence time of the gas during the transformation into reductive components in the reaction chamber 13 can be optimized.

In FIG. 5, a practical arrangement of a device for carrying out the reaction method according to FIG. 3, working in accordance with the flow diagram according to FIG. 4, is shown schematically in its individual components. Here, from the gas line 1, a storage container 5 , preferably in the form of an interchangeable cartridge for a solid form (trickle or solid) present reducing agent angeord net. The designed as a heater 9 porous bottom is in communication with the metering chamber 10 , in which the auxiliary heater 12 is arranged, through which this space is heated so that resublimation of the gas generated is avoided. Via the controlled metering valve 10.1 , a correspondingly dimensioned amount of gas is transferred into a reaction chamber 13.1 designed as a hydrolysis catalyst, which is heated via the heating device 14 in order to bring about the decomposition of the gas here. A partial exhaust gas stream, as indicated in FIG. 4 as partial exhaust gas stream 18.1 , can be introduced in front of the reaction chamber 13 through a discharge pipe 1.1 from the exhaust pipe 1 . The water content in the exhaust gas is usually sufficient for the course of the hydrolysis reaction of the gas with the water to bring about the desired formation of reductive products, as shown in FIG. 3 for cyanuric acid as a reducing agent. If necessary, small amounts of water vapor can be injected. From the reaction chamber 13 , the gaseous reducing agent present in the form of reductive products enters the exhaust gas channel 1 via the feed pipe 15 . By a stationary mixer, for example, wing-shaped swirl body 16.1 in front of and behind the introduction point for the reductive products, the exhaust gas is swirled in the feed area in such a way that a practically uniform distribution over the entire flow cross section in the exhaust gas line 1 is achieved.

By arranging a second cartridge 5.3 , which is connected by means of a feed line 28 to the dosing chamber 10 of the first cartridge 5 and in which a check valve 29 is arranged, a correspondingly larger amount of reducing agent can be made available. The second cartridge 5.3 is also equipped with a heating device 9 for generating a reducing agent gas and a metering chamber 10 with an additional heating device 12 .

The arrangement acc. Fig. 5 can also be modified so that in addition to an "active" cartridge 5 for normal operation, a second cartridge for the cold start phase is arranged, which is only switched on in the start phase. The heating capacity of this second cartridge can be designed so that corresponding amounts of reducing agent gas are available very quickly.

Claims (19)

1. A method for reducing nitrogen oxides in an oxygen-containing exhaust gas stream, in particular exhaust gases from combustion engines, which are subjected to a catalytic exhaust gas aftertreatment in a catalyst, characterized in that a reducing agent present as a solid converts into gas under the action of heat and the gas in a reaction chamber is thermally and / or catalytically broken down into reductive products, which are then added to the exhaust gas to be reduced before the catalyst. 2. The method according to claim 1, characterized in that the Gas is decomposed with the addition of heat by pyrolysis. 3. The method according to claim 1, characterized in that the Gas with the supply of water, in particular water vapor Hydrolysis is disassembled. 4. The method according to claim 1 to 3, characterized in that the amount of gas required by changing the on the Solid heating power is regulated. 5. The method according to any one of claims 1 to 4, characterized ge indicates that the amount of gas required by change the solids supply is regulated. 6. The method according to any one of claims 1 to 5, characterized in that behind the catalyst, the amount of individual NEN exhaust components, in particular NO _x and / or of reductive products of the reducing agent, in particular amide ions and / or isocyanic acid and / or ammonia is detected becomes. 7. The method according to any one of claims 1 to 6, characterized in that the metering of the gasified reduction by means of in the exhaust gas flow via a control device in dependence on the amounts of gas components, in particular NO _x and / or reductive Pro, detected behind the catalyst products of the reducing agent. 8. The method according to any one of claims 1 to 7, characterized in that the metering of the gasified reduction is carried out by means of a control device as a function of mo-specific maps on the NO _x content and / or the HC content in the exhaust gas. 9. The method according to any one of claims 1 to 8, characterized ge indicates that the addition of the gasified reduction by means of a control device depending on ka tester-specific maps with regard to the degree of turnover and / or the storage capacity of the catalytic aftertreatment processing facility. 10. The method according to any one of claims 1 to 9, characterized ge indicates that the addition of the gasified reduction by means of a control device depending on characteristic fields in relation to the pressure drop of the gas compared to the Exhaust occurs. 11. The method according to any one of claims 1 to 10, characterized ge indicates that the addition of the gasified reduction by means of a control device depending on characteristic fields related to the heating used for gasification performance takes place. 12. The method according to any one of claims 1 to 11, characterized ge indicates that the gas in a carrier gas in the form of Ab gas and / or air premixed and the premix to the exhaust gas trom is mixed. 13. The method according to any one of claims 1 to 12, characterized ge indicates that the admixture with the help of a pressure drop les between the gasification area and the exhaust gas flow follows.   14. The method according to any one of claims 1 to 13, characterized ge indicates that with a pressure drop between the Verga range and the exhaust gas flow via an admixture controllable metering device, in particular a metering valve, he follows. 15. The method according to any one of claims 1 to 14, characterized ge indicates that the reducing agent in at least one pressure-tight container is stored, which only in the direction of the exhaust gas to be reduced can be opened. 16. The method according to any one of claims 1 to 15, characterized ge indicates that the reducing agent by supplying heat to Container over the wall and / or at least over a heater element is gasified inside the container. 17. The method according to any one of claims 1 to 16, characterized ge indicates that as a solid reducing agent cyanuric acid and / or melamine and / or urea and / or biuret and / or Trioret and / or other nitrogenous reducing agents, used individually or in mixtures, which according to Vollzo phase change from solid to gaseous with another Have the energy supply broken down into reductive products. 18. The method according to any one of claims 1 to 17, characterized ge indicates that the solid reducing agent in free-flowing Condition is used. 19. The method according to any one of claims 1 to 19, characterized ge indicates that the solid reducing agent in the form of Compacts is used.