DE102006043101A1 - Apparatus and method for producing ammonia - Google Patents

Abstract

The invention relates to a device for generating ammonia as a reducing agent for the selective catalytic reduction (SCR) of nitrogen oxides in the exhaust gas of a combustion source, in particular an internal combustion engine, wherein the ammonia is admixed in the flow direction upstream of an SCR catalyst to the exhaust gas. In this case, a separate from the combustion source and its exhaust gas management nitrogen oxide generating unit and a separate from the combustion source and its exhaust gas hydrogen generating unit is provided and nitric oxide of the nitrogen oxide generating unit and the hydrogen of the hydrogen generating unit is at least one storage catalyst or a nitrogen oxide storage and a subsequent catalyst for storing the nitrogen oxide and for the formation of the ammonia supplied. DOLLAR A The invention further relates to a process for the production of ammonia as a reducing agent for the selective catalytic reduction (SCR) of nitrogen oxides in the exhaust gas of a combustion source, in particular an internal combustion engine, wherein the ammonia is admixed in the flow direction upstream of an SCR catalyst to the exhaust gas. In this case, nitrogen oxide is generated in a separate from the combustion source and its exhaust gas management nitrogen oxide generating unit and stored in at least one storage catalyst or a nitrogen oxide storage and a subsequent catalyst. Furthermore, hydrogen and / or a hydrogen-carbon monoxide mixture in one of the combustion source ...

Description

State of technology

The The invention relates to a device z or a nitrogen oxide storage and a subsequent catalyst ur production of ammonia as Reducing agent for the selective catalytic reduction (SCR) of nitrogen oxides in the exhaust gas a combustion source, in particular an internal combustion engine, the ammonia in the flow direction is added to the exhaust gas before an SCR catalyst.

The The invention further relates to a process for the production of ammonia as a reducing agent for the selective catalytic reduction (SCR) of nitrogen oxides in the exhaust gas a combustion source, in particular an internal combustion engine, the ammonia in the flow direction in front of an SCR catalyst is added to the exhaust gas.

In connection with future legal requirements regarding the nitrogen oxide emission of motor vehicles, a corresponding exhaust aftertreatment is required. The selective catalytic reduction can be used to reduce the NO _x emission (denitrification) of internal combustion engines, in particular of diesel engines, with temporally predominantly lean, ie oxygen-rich exhaust gas. In this case, a defined amount of a selectively acting reducing agent is added to the exhaust gas. This can be, for example, in the form of ammonia, which is metered in directly in gaseous form, or else obtained from a precursor substance in the form of urea or from a urea-water solution (HWL).

In the DE 10139142 A1 is described an exhaust gas purification system of an internal combustion engine, in which an SCR catalyst is used to reduce the NO _x emission, which reduces the nitrogen oxides contained in the exhaust gas with the reagent ammonia to nitrogen. The ammonia is recovered from a urea-water solution (HWL) in a hydrolysis catalyst upstream of the SCR catalyst. The hydrolysis catalyst converts the urea contained in the HWL to ammonia and carbon dioxide. In a second step, the ammonia reduces the nitrogen oxides to nitrogen, with water being produced as a by-product. The exact procedure has been adequately described in the specialist literature (see WEISSWELLER in CIT (72), pages 441-449, 2000). The HWL is provided in a reagent tank.

adversely in this method is that HWL in the operation of the internal combustion engine is consumed. The consumption is about 4% of fuel consumption. The supply of urea-water solution should correspondingly large area, for Example at gas stations, be assured. Another disadvantage of the method is in the necessary operating temperature range. The thermolysis reaction of the urea-water solution takes place only from temperatures around 130 ° C instead of and the hydrolysis reaction for the conversion of hydrogen and Nitrogen oxide on the hydrolysis catalyst to ammonia only in the range of 200 ° C to 220 ° C. These Temperatures in the exhaust gas, for example, in diesel engines only after a long time Operating time reached. Because of deposits, it can be at temperatures below 200 ° C come to blockages on the dosing unit, which the supply the urea-water solution at least hinder in the exhaust tract. Furthermore, a metered addition the urea-water solution at temperatures below 200 ° C due to a polymerization to inhibit the necessary catalytic Properties on hydrolysis or SCR catalyst lead.

In the DE 199 22 961 C2 is an exhaust gas purification system for purifying the exhaust gas of a combustion source, in particular an automotive internal combustion engine, at least nitrogen oxides contained therein with an ammonia generation catalyst for generating ammonia using components of at least a portion of the exhaust gas emitted from the combustion source during ammonia generation operating phases and downstream of the ammonia generation catalyst Nitrogen oxide reduction catalyst for the reduction of nitrogen oxides contained in the emitted exhaust gas of the combustion source using the generated ammonia described as a reducing agent. In this case, a combustion-source-external nitrogen oxide generation unit is provided for enriching the exhaust gas supplied to the ammonia generation catalyst with nitrogen oxide produced by it during the ammonia generation operating phases. As a nitrogen oxide generating unit, for example, a plasma generator for plasma-technical oxidation of nitrogen contained in a gas stream supplied in nitrogen oxide is proposed. The hydrogen needed for ammonia production is generated during the ammonia generation operating phases by the operation of the combustion source with a rich, ie fuel-rich, air ratio.

A disadvantage of this method is the relatively high fuel consumption during the necessary rich operating phases. Furthermore, a high energy requirement for the external emission of the nitrogen oxide is required, in particular, since nitrogen oxide must be prepared in a high concentration during the shortest possible ammonia production operating phases and the remaining residual oxygen to generate ammonia energieaufwen dig must be removed. If the hydrogen is generated via a POx catalyst by a partial oxidation reforming (POx), another disadvantage lies in the still insufficient dynamics of hydrogen production.

One Plasmachemisches process for producing a hydrogen-rich Gas mixture is described in WO 01/14702 A1. It will be in an arc a rich fuel-air mixture, preferably under POx conditions.

It Object of the invention, a device of the type described above To provide type, which the production of ammonia with low energy consumption made possible from the resources of the combustion source.

It is further object of the invention, this a suitable method provide.

Advantages of invention

The The object of the invention relating to the device is achieved in that a separate from the combustion source and the exhaust system nitrogen oxide generating unit and a hydrogen generating unit separate from the combustion source and its exhaust passage is provided and that the nitrogen oxide of the nitrogen oxide generating unit and the hydrogen of the hydrogen generation unit at least one storage catalyst or a nitrogen oxide storage and a subsequent catalyst for storing the nitrogen oxide and is fed to form the ammonia. The ammonia production thus finds outside the exhaust line without an interference with the operating state of the combustion source instead of. In an internal combustion engine, therefore, no fuel-consuming Fat operating phases to generate the required for ammonia synthesis hydrogen be provided, the internal combustion engine can be in a consumption-optimized Condition to be operated. The storage of the generated nitrogen oxide in a nitrogen oxide storage compared to the prior art reduces the Energy expenditure for ammonia production. Furthermore omitted by storing the energy-intensive burning of the residual oxygen, which remains in the formation of nitrogen oxide.

In An advantageous embodiment of the invention is the nitrogen oxide storage and the catalyst as a storage catalyst to a structural unit summarized. As a result, the design can be selected particularly compact.

Thereby, that the hydrogen generating unit is fuel and / or a fuel-air mixture and / or a fuel-air-off-gas mixture and the nitrogen oxide generation unit Supplied air and / or exhaust gas is the ammonia from already existing resources of the Won combustion source. Other resources, such as a urea-water solution, do not need to be carried. As another oxidant to atmospheric oxygen can be used for hydrogen production Water are used. This can be achieved, for example, by a fuel-exhaust gas mixture, which has this water content can be realized.

In a cost-effective Embodiment of the invention with a small number of required components and a particularly space-saving construction is a combined hydrogen-nitrogen oxide generating unit provided for alternately generating hydrogen and nitrogen oxide. The production of ammonia with alternating provision of Hydrogen and nitric oxide are made possible by the storage catalyst, in which during the Nitric Oxide Production The nitric oxide is stored and used during the Hydrogen production is the conversion to ammonia.

A Continuous ammonia production is achieved by the fact that the Hydrogen generating unit and the nitrogen oxide generating unit as executed separate units are and that at least two storage catalysts for storing the Nitrous oxide and are provided for the formation of ammonia, wherein the hydrogen generating unit and the nitrogen oxide generating unit via switchable Gas paths alternately verbun with the storage catalysts are the. The nitrogen oxide generation unit and the hydrogen generation unit can for your Task to be optimized. The per unit time produced Amount of hydrogen and nitric oxide can be used during continuous operation be selected smaller with separate generating units than in the respective Operating phase (hydrogen or nitric oxide production) in reciprocal Operation with a generating unit, resulting in an overall lower Energy expenditure leads.

In a preferred embodiment The invention is the at least one storage catalyst as a nitrogen oxide storage with an additional Precious metal loading carried out. It can the nitrogen oxide storage and the precious metal similar to a known nitrogen Storage catalyser (NSC) may be applied to a monolith. The Precious metal causes the catalytic conversion of the stored Nitrous oxide and the supplied Hydrogen to ammonia.

A good storage effect for nitrogen oxide and an efficient catalytic conversion of the stored nitrogen oxide and hydrogen to ammonia can be achieved that the nitrogen oxide storage with carbonates as active Spei cherkomponenten, in particular barium carbonate, barium oxide or sodium carbonate is carried out and / or the noble metal loading is designed as platinum loading. Alternatively, gaseous, liquid or other solid nitrogen oxide are conceivable. The noble metal loading can also be carried out with other materials that cause a reduction of nitrogen oxides by means of hydrogen to ammonia.

A inexpensive Production of hydrogen and nitrogen oxide with low energy expenditure can be achieve that the hydrogen generating unit and / or the nitric oxide generating unit executed as a plasma reactor are. With a plasma reactor, depending on the selected operating mode, Both hydrogen and nitrogen oxide produced at high production rates be, so that an alternating operation as a hydrogen generating unit and performed as a nitrogen oxide generating unit with a plasma reactor can.

Becomes operated the hydrogen generation unit under POx conditions, is therefore the hydrogen generation unit a fuel-air mixture with a lambda less than 1, in particular a lambda between 0.33 and 0.66, supplied, so is hydrogen and Carbon monoxide generated which stores the stored in the storage catalyst Reduce nitric oxide to ammonia.

To A preferred embodiment variant of the invention is intended that the hydrogen generating unit as a thermal evaporator for the fuel with a downstream Refor mierungskatalyator accomplished is. It can stored residual heat, for example from the Operating phase of nitric oxide production, for evaporation of the fuel be used. The reforming of the fuel, so the conversion of the Fuel in a hydrogen-containing gas mixture, takes place at the reforming catalyst.

The residual heat from the operating phase for nitrogen oxide production can be take advantage of the fact that at least one electrode of the plasma reactor as thermal evaporator for run the fuel is. For this purpose, the fuel is partially sprayed sprayed onto the electrode and there further atomized and evaporated. The heat capacity of the electrode is so to choose that the stored amount of heat enough large for the evaporation the required amount Fuel is.

In Another embodiment of the invention is the at least one Electrode of the plasma reactor designed as a hollow electrode, in which the fuel is supplied to the electrode. The fuel will that's all Electrode targeted and fed with low losses.

Suffice the stored Thermal energy of the thermal evaporator not to vaporize the fuel or is the contact time of the fuel with the hot surface of the thermal evaporator for sufficient heat transfer too low, so can a countercurrent heat exchanger for transmission of heat energy from a product gas exiting the reforming catalyst or from a gas stream leaving the plasma reactor supplied to the thermal evaporator Be prepared starting gas from air and fuel. The thermal one Evaporator supplied Fuel or the supplied fuel-air mixture is in the countercurrent heat exchanger advantageously so far heated that the fuel at least partially evaporated. The to the complete Evaporation necessary heat energy can then be transferred to the fuel in the thermal evaporator become.

is while the thermal evaporation of the fuel the plasma reactor off, so will be during This phase of operation necessary for the maintenance of the plasma saved electrical energy. This leads, for example, in motor vehicles with lean-burn engines to a reduction of the exhaust aftertreatment with the ammonia-SCR process related fuel consumption.

In a preferred embodiment of the invention it is provided that during the thermal evaporation of the fuel, the plasma reactor is turned on and that the fuel and / or a fuel-air mixture and / or a fuel-air-exhaust gas mixture a region in the flow direction the plasma zone is supplied. By injecting the fuel into a hot gas with surrounding hot walls, sufficiently rapid vaporization and mixture formation can thus be realized, which ideally results in a nearly rectangular supply of hydrogen and carbon monoxide-containing product gas. Due to the continuous plasma operation, a drop in the temperature during fuel introduction in the fatty phase below the necessary evaporation temperature of the fuel can be avoided. Furthermore, it is prevented by the continuous plasma operation that the temperature of the reforming catalyst drops below its ignition temperature. Another advantage results from the fact that no injection of fuel into the plasma zone takes place, whereby the generation of undesirable products is avoided. An unintentional and uncontrolled conversion of hydrocarbons to substances other than hydrogen and carbon monoxide can be avoided, since only the temperature from the thermalization of the introduced power is used in the plasma for the evaporation and mixture formation and the reforming is completely achieved to hydrogen and carbon monoxide at the subsequent reforming catalyst.

are in an air supply in the flow direction before the thermal evaporator for the fuel and / or before the reforming catalyst Luftleitstege arranged, so the gas flow can be imparted a twist, to a better homogeneity the fuel vapor-air mixture leads. The place where the Fuel is vaporized, this can be in an area with high flow velocity and / or high velocity gradient, which improves mixture formation. The swirl continues to cause the flow of the reforming catalyst improved and an admission of the reforming catalyst with liquid Fuel is avoided.

is the SCR catalyst designed as ammonia storage, so Ammoniakbedarfsspitzen be intercepted by the stock in the SCR catalyst ammonia. The ammonia production rate can be adjusted to a mean ammonia consumption be limited.

The The object of the invention relating to the method is solved by Nitrogen oxide in a separate from the combustion source and the exhaust system Nitrogen generating unit generated and stored in at least one storage catalyst is and that hydrogen and / or a hydrogen-carbon monoxide mixture in a separate from the combustion source and the exhaust system Generated hydrogen generating unit and the storage catalyst or a nitrogen oxide storage and a subsequent catalyst supplied and that the hydrogen and the stored nitric oxide in the storage catalyst or the catalyst catalytically to ammonia be implemented. The ammonia production takes place independently of the respective operating state of the combustion source, for example an internal combustion engine, instead, it is not for ammonia synthesis Intervention in the operating state of the combustion source necessary. this makes possible a consumption-optimized operation of the combustion source. The Storage of the generated nitrogen oxide and subsequent catalytic Reaction with the generated hydrogen in the storage catalyst allows an ammonia production with a relatively small amount of energy, in particular, since an otherwise necessary combustion of the residual oxygen, which remains in the formation of nitrogen oxide, is not necessary.

Becomes Hydrogen and / or a hydrogen-carbon monoxide mixture in the Hydrogen generating unit of fuel and / or from a fuel-air mixture and / or from a fuel-air / exhaust gas mixture generates and nitrogen oxide in the nitrogen oxide generation unit Air and / or generated from exhaust gas, so are the production of ammonia only used resources of the internal combustion engine. There is no need additional Resources are provided or carried.

In A preferred embodiment of the invention, which with a small number required Components can be implemented in a combined hydrogen-nitrogen oxide production unit generates nitrogen oxide and hydrogen or a hydrogen-carbon monoxide mixture alternately, wherein the nitric oxide during the nitrogen oxide generation phase stored in the storage catalyst is and in the hydrogen production phase with the hydrogen is converted to ammonia. This discontinuous ammonia production is due to the storage of the nitrogen oxide in the storage catalyst and the reaction with the subsequently generated hydrogen only possible.

In an alternative embodiment hydrogen and nitric oxide are separated from two separate hydrogen and nitric oxide generating units alternately two subsequent ones Storage catalysts for the alternate storage of nitrogen oxide and fed to the production of ammonia, the assignment of the gas flows to the storage catalysts via switchable gas paths takes place. The process allows a continuous Providing ammonia for the reduction of nitrogen oxides in the exhaust gas of the combustion source.

A easy way to provide the needed Starting materials Hydrogen and nitrogen oxide is that the hydrogen or a hydrogen-carbon monoxide mixture and / or the nitrogen oxide Plasmachemisch in at least one plasma reactor by a thermal Plasma are generated. The thermal plasma can, for example, directly by an AC or DC voltage as well as by a Microwave radiation are excited. As in a thermal Plasma can generate both hydrogen and nitric oxide, can the procedure for both separate and combined nitric oxide and hydrogen generating units. Opposite the same potential Nitrogen oxide production by means of burners possesses the plasmachemische Making the advantage of improved dynamic behavior in cold start. Possible Alternatives to the thermal plasma are discharge forms with shorter ones Discharge periods such as spark discharges or nonthermal discharges, as for example by dielectrically impeded discharge arrangements are generated.

A better efficiency in the production of starting materials for ammonia production can be characterized achieve that hydrogen formation or the formation of the hydrogen-carbon monoxide mixture is supported by a partial oxidation (POx) on a POx catalyst.

A alternative method of producing hydrogen is that the production of hydrogen by thermal evaporation of fuel and subsequent Reforming takes place in a reforming catalyst. Prefers For this purpose, the residual heat stored in the system can be used, so that for hydrogen production no additional energy is needed.

A Possibility, stored residual heat for Hydrogen production is the use of fuel by recuperation in a countercurrent heat exchanger and / or by Metering of fuel into a hot zone of the plasma reactor is evaporated. Enough while that taken by the fuel according to one of the methods mentioned Energy only to a partial evaporation of the fuel, is one Combination of the two processes - first warm-up or partial evaporation the fuel by recuperation, then evaporation of the already heated fuel in a hot zone of the plasma reactor - possible.

When name is The fuel evaporation zone can be replaced by a previous one Plasma operation heated electrode of the plasma reactor can be used. For this purpose, the fuel on the hot electrode of the plasma reactor dosed. The fuel can be previously heated by recuperation or be partially evaporated. The warming The electrode takes place, for example, in the phase for plasma-chemical Generation of the nitrogen oxide.

A another possibility stored residual heat to use hydrogen production, is that the evaporation of fuel by metering in fuel and / or a fuel-air mixture and / or a fuel-air-exhaust gas mixture in a hot area in the flow direction takes place after the plasma zone. The plasma can continue to operate be, so by an uninterrupted energy input into the Eduktgas sufficient heating the gas flow is achieved. This ensures, for one thing the temperature in the evaporation zone is sufficiently high and on the other hand, the temperature of the reforming catalyst so high, that is a fast light-off time of the catalyst can be realized. The coupled-in plasma power can be achieve a fast temperature control. Since the fuel the Does not go through the paint area, can negative influences in the reducing agent yield, for example by a reaction avoiding fuel in methane and producing unwanted products become. The reforming of the fuel is not uncontrolled in plasma, but exclusively in the reforming catalyst.

Prefers is the gas flow in front of the evaporation zone of the fuel and / or before the reforming catalyst imparted a twist. there causes a swirl of the gas flow in front of the evaporation zone of the fuel a better homogenization of the fuel vapor-air mixture. The Place where the fuel is evaporated should be in one Area with high flow velocity or high velocity gradients. A twist the gas flow before the reforming catalyst also causes a better homogeneity as well as an ideal influx of the Reformierungskatalysators, an admission of the reforming catalyst with the fuel used can be avoided.

The Reduction of the nitrogen oxides contained in the exhaust of the combustion source is achieved in that the formed in the storage catalyst Ammonia is stored in the SCR catalyst and that nitrogen oxides in the exhaust of the combustion source by the stored ammonia reduced to nitrogen and water. By the storage of ammonia in the SCR catalyst may require ammonia demand be intercepted. Furthermore, one of the operating conditions the combustion source independent Ammonia production and caching possible.

drawings

The Invention will be described below with reference to the figures shown in the figures Embodiments explained in more detail. It demonstrate:

1 a schematic representation of an exhaust aftertreatment system of an internal combustion engine with separate generating units for hydrogen and nitrogen oxide

2 a schematic representation of an exhaust aftertreatment system of an internal combustion engine having a combined generating unit for hydrogen and nitrogen oxide

3 a schematic representation of a generating unit for hydrogen and nitrogen oxide

4 a timing for a pulsed plasma operation

Description of the embodiments

1 schematically shows an exhaust aftertreatment system 1 for an internal combustion engine 22 with an air supply 20 and an SCR catalyst 26 , SCR catalysts operate on the principle of selective catalytic reduction, in which nitrogen oxides (NO _x ) are reduced to nitrogen and water by means of the reducing agent ammonia in oxygen-containing exhaust gases. In the device according to the invention, the ammonia is generated from air or exhaust gas and fuel. These are a hydrogen generating unit 10 and a nitrogen oxide generating unit 11 intended. The hydrogen generation unit 10 is via an air supply 14 with air and via a fuel metering 13 fueled. In another embodiment, the air supply 14 also exhaust or a mixture of air and exhaust gas lead. The hydrogen generation unit 10 is implemented as a plasma reactor in which the fuel is supplied to a plasma, in which hydrogen and carbon monoxide is generated from the hydrocarbons of the fuel.

The nitric oxide generating unit 11 is designed as a plasma reactor in which nitrogen and oxygen from the supply air to nitrogen oxide are converted. The nitrogen oxide is in a first mode via a switchable gas path 16 a storage catalyst 17.1 fed and stored there. Will now in a second mode of hydrogen from the hydrogen generation unit 10 in the storage catalyst 17.1 initiated, the desired ammonia is generated at the noble metal loading from the stored nitrogen oxide and the supplied hydrogen and a gas path 18 the exhaust system 24 fed. During this second mode, the nitrogen oxide from the nitrogen oxide generating unit 11 via the reversible gas path 16 a second storage catalyst 17.2 fed and stored there. If it is switched back to the first operating mode, nitrogen oxide becomes the storage catalytic converter 17.1 supplied and stored there during the second storage catalyst 17.2 Is supplied hydrogen and reacted with the stored nitrogen oxide at the noble metal loading to ammonia.

That the exhaust line 24 admixed ammonia is mixed with the exhaust gas of the internal combustion engine 22 the SCR catalyst 26 fed where the NO _x contained in the exhaust gas is reduced by means of the ammonia to nitrogen and water. To control the processes of the internal combustion engine 22 a motor control 23 assigned by means of a Gaswegsteuersignals 25 the switchable gas path 16 switches between the first and second modes, the fuel metering 13 to the hydrogen generation unit 10 controls and via a control line 15 the nitrogen oxide generating unit designed as a plasma reactor 11 controls. Furthermore controls the engine control 23 a fuel metering 21 the internal combustion engine 22 and processes signals from lambda probes, not shown here.

In another embodiment, the hydrogen generating unit 10 be designed as a thermal evaporator. The vaporized fuel is mixed with the supply air to a reforming catalyst, not shown here 32 fed, in which the hydrocarbons are converted from the fuel to hydrogen and carbon monoxide. Furthermore, the nitrogen oxide generating unit 11 be executed as a NO _x burner.

2 schematically shows the exhaust aftertreatment system 1 for the internal combustion engine 22 with a combined hydrogen-nitrogen oxide production unit 12 for hydrogen and nitric oxide. In the combined hydrogen-nitrogen oxide generating unit designed as a plasma reactor 12 Nitrogen oxide and hydrogen are generated in successive operating phases. In a first phase of operation is from the on the air supply 14 supplied nitrogen in the plasma reactor nitrogen oxide and in a storage catalyst 17 saved. The storage catalyst 17 is loaded with precious metal, so that the hydrogen produced in a second phase of operation can be converted with the stored nitrogen oxide to ammonia, via the gas path 18 the exhaust system 24 is supplied. The hydrogen is in the combined hydrogen-nitrogen oxide generating unit 12 generated from fuel, that of the combined hydrogen-nitrogen oxide production unit 12 by means of fuel metering 13 is supplied. In the plasma of the combined hydrogen-nitrogen oxide production unit 12 The hydrocarbons of the fuel are converted to hydrogen and carbon monoxide.

As according to the embodiment according to 1 will be in the execution 2 the internal combustion engine 22 Combustion air via the air supply 20 and fuel over the fuel metering 21 fed. The processes are controlled by the engine control 23 controlled, in particular via the control line 15 the operating phases of the combined hydrogen-nitrogen oxide production unit 12 controls. Again, the generated ammonia in the SCR catalyst reduces 26 the nitrogen oxides contained in the exhaust gas to nitrogen and water.

In one embodiment, one electrode may be the combined hydrogen-nitrogen oxide generating unit embodied as a plasma reactor 12 be designed as a hollow electrode through which the fuel is introduced. The heating of the electrode during plasma operation is then used to vaporize the fuel. The evaporation of the fuel outside of the plasma with anschlie ßender conversion to hydrogen and carbon monoxide in a downstream reformer is advantageous in that a higher proportion of the desired products hydrogen and carbon monoxide is formed than when reacting the fuel in a plasma reactor.

In a further embodiment of the combined hydrogen-nitrogen oxide production unit 12 This can be carried out in the operating phase of hydrogen production as a thermal evaporator, in which the fuel is fed in a string jet to the heated plasma electrodes in the previous operation and evaporated there. To improve the evaporation can be arranged in the gas path before the evaporation point baffles or swirl body.

3 schematically shows the structure of the combined hydrogen-nitrogen oxide generating unit 12 , About the air supply 14 Air and / or exhaust gas is the nitrogen oxide generating unit designed as a plasma reactor 11 fed. The nitrogen oxide produced there in the first phase of operation becomes the storage catalyst 17 fed and stored there. In the second phase of operation becomes on the hot surfaces in the nitrogen oxide production unit 11 a mixture forming zone 30 by adding fuel via the fuel metering 13 generated. Here, the nitrogen oxide generating unit 11 at least temporarily continue to operate, the temperature in the mixture forming zone 30 to obtain. To improve the supply of the mixture to the reforming catalyst 32 are air ducts 31 intended. In one embodiment, to improve evaporation in the mixture forming zone 30 be arranged in the flow direction in front of this Luftleitstege. The in the second phase of operation in the reforming catalyst 32 generated hydrogen is in the storage catalyst 17 reacted with the nitrogen oxide stored there to ammonia and by means of an injection 33 the exhaust system, not shown here 24 fed.

In another embodiment, the mixture formation zone 30 arranged downstream of the plasma zone in the flow direction. The plasma operation can then take place during the metered addition of fuel and serves to heat the gas stream. As a result, the temperature in the evaporation zone can be controlled as well as a rapid heating of the reforming catalyst 32 be achieved. By injecting the fuel outside the plasma zone, the undesirable production of by-products in the plasma, such as the conversion of fuel to methane, can be avoided.

4 shows the timing for a timer 40 for a pulsed plasma operation for successively generating nitrogen oxide and hydrogen in the combined hydrogen-nitrogen oxide generating unit, not shown here 12 , which is designed as a plasma reactor for the production of nitrogen oxide and thermal evaporator for the fuel for the production of hydrogen. A plasma power 41 is over a timeline 45 applied. Furthermore, a lambda value 49 over one to the first timeline 45 same second time axis 46 applied. In a first phase of operation, the plasma power is 41 to a plasma setpoint 42 and the lambda value 49 to a leaner value 47 adjusted, which corresponds to the supply of air substantially. In a second phase of operation is via a synchronization 44 on the one hand the plasma power 41 is reduced to zero and the lambda value remains at a level 48 lowered. The fat value 48 is advantageously set to a lambda of 0.35, since then there is the optimum ratio of hydrogen to carbon monoxide and 1 of oxygen to carbon. The setting of the lambda can take place in that the ratio of supply air to the amount of fuel which is evaporated at the heated electrodes, is selected accordingly. To improve the evaporation of the fuel and or the supply air can be preheated in a heat exchanger. As a heat source, the heat occurring in the reforming catalyst or the SCR catalyst in the exothermic reactions taking place there can be used. An advantage of such an embodiment is that during the second operating phase, the plasma power is reduced to zero and thus a reduced power consumption can be achieved.

Claims (29)

Device for producing ammonia as a reducing agent for the selective catalytic reduction (SCR) of nitrogen oxides in the exhaust gas of a combustion source, in particular an internal combustion engine ( 22 ), wherein the ammonia in the flow direction in front of an SCR catalyst ( 26 ) is admixed to the exhaust gas, characterized in that a separate from the combustion source and its exhaust gas management nitrogen oxide generating unit ( 11 ) and a separate from the combustion source and its exhaust gas flow hydrogen generating unit ( 10 ) is provided and that the nitrogen oxide of the nitrogen oxide generating unit ( 11 ) and the hydrogen of the hydrogen generation unit ( 10 ) at least one storage catalyst ( 17 ) or a nitrogen oxide storage and a subsequent catalyst for storing the nitrogen oxide and for the formation of the ammonia is supplied. Apparatus according to claim 1, characterized in that the nitrogen oxide storage and the catalyst as a storage catalyst ( 17 ) to a Assembly is summarized. Apparatus according to claim 1 or 2, characterized in that the hydrogen generating unit ( 10 ) Fuel and / or a fuel-air mixture and / or a fuel-air-exhaust mixture and the nitrogen oxide generation unit ( 11 ) Air and / or exhaust gas is supplied. Device according to one of claims 1 to 3, characterized in that a combined hydrogen-nitrogen oxide generating unit ( 12 ) is provided for the alternate production of hydrogen and nitrogen oxide. Device according to one of claims 1 to 3, characterized in that the hydrogen generating unit ( 10 ) and the nitric oxide generating unit ( 11 ) are designed as separate units and that at least two storage catalysts ( 17.1 . 17.2 ) are provided for storing the nitrogen oxide and for forming the ammonia, wherein the hydrogen generating unit ( 10 ) and the nitric oxide generating unit ( 11 ) via a reversible gas path alternately with the storage catalysts ( 17.1 . 17.2 ) are connected. Device according to one of the preceding claims, characterized in that the at least one storage catalyst ( 17 ) is designed as a nitrogen oxide storage with an additional noble metal loading. Apparatus according to claim 6, characterized in that the storage catalyst ( 17 ) is carried out with carbonates as active storage components, in particular barium carbonate, barium oxide or sodium carbonate and / or the noble metal loading is carried out as platinum loading. Device according to one of the preceding claims, characterized in that the hydrogen generating unit ( 10 ) and / or the nitric oxide generating unit ( 11 ) are designed as a plasma reactor. Device according to one of the preceding claims, characterized in that the hydrogen generating unit ( 10 ) A fuel-air mixture with a lambda less than 1, in particular a lambda between 0.33 and 0.66, is supplied. Device according to one of the preceding claims, characterized in that the hydrogen generating unit ( 10 ) as a thermal evaporator for the fuel with a downstream Reformierungskatalyator ( 32 ) is executed. Device according to claim 10, characterized in that that at least one electrode of the plasma reactor as a thermal Evaporator for run the fuel is. Device according to one of claims 10 or 11, characterized that the at least one electrode of the plasma reactor as a hollow electrode accomplished is, in which the fuel is supplied to the electrode. Device according to one of the preceding claims, characterized in that a countercurrent heat exchanger for the transfer of heat energy from one of the reforming catalyst ( 32 ) product gas or from an emerging from the plasma reactor gas stream is provided on a the thermal evaporator supplied educt gas of air and fuel. Device according to one of the preceding claims, characterized characterized in that during the thermal evaporation of the fuel of the plasma reactor off is. Device according to one of the preceding claims, characterized characterized in that during the thermal evaporation of the fuel the plasma reactor is turned on is and that the fuel and / or a fuel-air mixture and / or a fuel-air-exhaust mixture an area in the flow direction fed to the plasma zone is. Device according to one of the preceding claims, characterized characterized in that in an air supply in the flow direction before the thermal evaporator for the fuel and / or before the reforming catalyst Luftleitstege are arranged. Device according to one of the preceding claims, characterized in that the SCR catalyst ( 26 ) is designed as ammonia storage. Process for the production of ammonia as a reducing agent for the selective catalytic reduction (SCR) of nitrogen oxides in the exhaust gas of a combustion source, in particular an internal combustion engine ( 22 ), wherein the ammonia in the flow direction in front of an SCR catalyst ( 26 ) is admixed with the exhaust gas, characterized in that nitrogen oxide in a separate from the combustion source and its exhaust gas management nitrogen oxide generating unit ( 11 ) and in at least one storage catalyst ( 17 ) and that hydrogen and / or a hydrogen-carbon monoxide mixture are in a separate from the combustion source and its exhaust gas hydrogen generation Ness ( 10 ) and the storage catalyst ( 17 ) or a nitrogen oxide storage and a subsequent catalyst is supplied and that the hydrogen and the stored nitrogen oxide in the storage catalyst ( 17 ) or the catalyst are catalytically converted to ammonia. A method according to claim 18, characterized in that hydrogen and / or a hydrogen-carbon monoxide mixture in the hydrogen generating unit ( 10 ) is generated from fuel and / or from a fuel-air mixture and / or from a fuel-air / exhaust gas mixture and that nitrogen oxide in the nitrogen oxide generation unit ( 11 ) is generated from air and / or exhaust gas. A method according to claim 18 or 19, characterized in that in a combined hydrogen-nitrogen oxide generating unit ( 12 ) alternately nitrogen oxide and hydrogen or a hydrogen-carbon monoxide mixture is generated, wherein the nitrogen oxide during the nitrogen oxide production phase in the storage catalyst ( 17 ) is stored and converted in the hydrogen production phase with the hydrogen to ammonia. A method according to claim 18 or 19, characterized in that hydrogen and nitrogen oxide from two separate hydrogen and nitrogen oxide generating units ( 10 . 11 ) alternately two subsequent storage catalysts ( 17.1 . 17.2 ) for alternately storing the nitrogen oxide and for generating the ammonia, the assignment of the gas flows to the storage catalytic converters ( 17.1 . 17.2 ) via switchable gas paths ( 16 ) he follows. Method according to one of Claims 18 to 21, characterized that the hydrogen or a hydrogen-carbon monoxide mixture and / or the nitric oxide plasmachemisch in at least one plasma reactor a thermal plasma are generated. Method according to one of claims 18 to 22, characterized that the hydrogen formation or the formation of the hydrogen-carbon monoxide mixture is supported by a partial oxidation (POx) on a POx catalyst. Method according to one of claims 18 to 23, that the production of hydrogen by thermal evaporation of fuel and subsequent reforming in a reforming catalyst ( 32 ) he follows. Method according to Claim 24, characterized that the fuel by recuperation in a countercurrent heat exchanger and / or by metering fuel into a hot zone the plasma reactor is evaporated. Method according to one of claims 24 or 25, characterized that fuel on the hot Electrode of the plasma reactor is metered. Method according to one of claims 24 or 25, characterized that the evaporation of fuel by metering of fuel and / or a fuel-air mixture and / or a fuel-air-exhaust gas mixture in a hot area in the flow direction takes place after the plasma zone. Method according to one of claims 18 to 27, characterized in that the gas flow before the evaporation zone of the fuel and / or before the reforming catalyst ( 32 ) a swirl is imposed. Method according to one of claims 18 to 28, characterized in that in the storage catalyst ( 17 ) formed in the SCR catalyst ( 26 ) is stored and that nitrogen oxides are reduced in the exhaust gas of the combustion source by the stored ammonia to nitrogen and water.