| Title of Invention | "METHOD AND DEVICE FOR PROVIDING A GASEOUS MIXTURE" |
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| Abstract | The device (1) according to the invention for providing a gaseous substance mixture comprising at least one of the following substances: a) at least one reducing agent and b) at least one reducing agent precursor, with a reservoir (20) for an aqueous solution (45) comprising at least one reducing agent precursor being formed, from which reservoir (20) aqueous solution (45) can be delivered into at least one metering line (2) with a dispensing opening (3) by a delivery means (19), is characterized in that means (4) for heating the metering line (2) are formed, by means of which the at least one metering line (2) can be heated above a critical temperature which is greater than the boiling temperature of water. The device (1) according to the invention and the method according to the invention advantageously permit the complete evaporation of an aqueous solution comprising urea, and subsequent hydrolysis to form a substance mixture comprising ammonia. Said substance mixture is advantageously metered as a reducing agent into an SCR catalytic converter (18). The fact that the evaporation is carried out outside the exhaust system permits the formation of considerably smaller hydrolysis catalytic converters (17), so. that the device according to the invention is space-saving and cost-saving in comparison with conventional devices for providing a reducing agent for the selective catalytic reduction of nitrogen oxides. (Figure 9) |
| Full Text | Method and device for providing a gaseous substance mixture The subject matter of the present invention is a method and a device unit for providing a gaseous substance mixture which comprises a reducing agent and/or a reducing agent precursor. The method according to the invention and the device according to the invention can advantageously be used in particular for metering in reducing agents for the reduction of nitrogen oxides in the exhaust gas of internal combustion engines. The exhaust gas from internal combustion engines has substances whose emission into the environment is undesirable. In many countries, for example, nitrogen oxides (N0X) may only be contained in the exhaust gas of internal combustion engine up to a certain limit value. In addition to engine-internal measures, by means of which the emissions of nitrogen oxides can be reduced by means of a selection of a suitable operating point of the internal combustion engine, aftertreatment methods have been established which make a further reduction of the nitrogen oxide emissions possible. One option for further reducing the nitrogen oxide emissions is so called selective catalytic reduction (SCR) . Here, a selective reduction of the nitrogen oxides to molecular nitrogen (N2) takes place using a reducing agent. One possible reducing agent is ammonia (NH3). Here, ammonia is often stored not in the form of ammonia but instead, an ammonia precursor is stored, which is converted to ammonia when required. Possible ammonia precursors are for example urea ((NH2)2CO), ammonium carbamate, isocyanic acid (HCNO), cyanuric acid and the like. Urea in particular has proven to be simple to store. Urea is preferably stored in the form of a urea/water solution. Urea and in particular urea/water solution is hygienically harmless, simple to distribute and to store. A urea/water solution of said type is already marketed under the name "AdBlue". DE 199 13 462 Al discloses a method in which a urea/water solution is dosed, upstream of a hydrolysis catalytic converter, into a partial flow of the exhaust gas of an internal combustion engine. During operation, as it impinges on the hydrolysis catalytic converter, the urea is hydrolyzed and thermolyzed to form ammonia, which is used as a reducing agent in an SCR catalytic converter situated downstream. The method described here has the disadvantage that the hydrolysis catalytic converter is cooled by the evaporation of the urea/water solution. In particular where large quantities of ammonia are required, it is possible at least in regions of the hydrolysis catalytic converter for such intense cooling to take place that, here, the hydrolysis reaction no longer takes place or no longer takes place completely. Proceeding from here, it is the object of the present invention to propose a method and a device with which the disadvantages known from the prior art can be at least alleviated. Said object is achieved by means of a device and a method having the features of the independent claims. Advantageous refinements are the subject matter of the respective dependent claims. The device according to the invention serves to provide a gaseous substance mixture comprising at least one of the following substances: a) at least one reducing agent, and b) at least one reducing agent precursor. A reservoir for an aqueous solution comprising at least one reducing agent precursor is formed, from which reservoir aqueous solution can be delivered into at least one metering line with a dispensing opening by a delivery means. Means for heating the metering line are formed, by means of which the metering line can be heated above a critical temperature which is greater than the boiling temperature of water. Here, a reducing agent is to be understood to be a reducing agent which can be used within the context of the selective catalytic reduction of nitrogen oxides. A reducing agent is in particular ammonia. A reducing agent precursor is to be understood to mean a substance which cleaves to a reducing agent or reacts with other substances while giving off a reducing agent. An ammonia precursor such as for example urea can for example cleave to ammonia or react while giving off ammonia. An aqueous solution is to be understood to mean the solution of the reducing agent precursor in water, with it being possible for the aqueous solution to comprise further substances. The dispensing opening is to be understood to mean the opening out of which the gaseous substance mixture is dispensed. The critical temperature is in particular the temperature from which complete evaporation of the aqueous solution takes place. Completely means here in particular that at least 90% by weight of the aqueous solution is evaporated, preferably at least 95% by weight, particularly preferably at least 98% by weight. The critical temperature is in particular above 300°C, preferably above 350°C or even above 400°C, in particular at approximately 420°C or 450°C. It is preferably possible, where relatively large quantities of vapour are required, for a plurality of metering lines to be formed, for example in exhaust systems of utility vehicles. A metering line is to be understood to mean a traversable volume which is delimited by walls. Said metering line can in particular be a type of tube or else a duct which is delimited by walls. Here, the duct can also be formed in a larger component. The device according to the invention advantageously permits the evaporation of an aqueous solution of a reducing agent precursor, for example of a urea/water solution. During the evaporation, both an evaporation of the reducing agent precursor and, depending on the selected temperature, thermolysis at least of parts of the reducing agent precursor to form reducing agent, take place. In particular a hydrolysis catalytic converter is formed downstream of the metering line which promotes the conversion of the reducing agent precursor to the reducing agent. The hydrolysis catalytic converter is in particular disposed in a body common with the metering line. This facilitates to maintain the temperature of the metering line and/or the hydrolysis catalytic converter as thermal conduction takes place from the metering line to the hydrolysis catalytic converter and vice versa. In particular this common body and thus the metering line and the hydrolysis catalytic converter are heatable by one or more heating elements comprising at least one electric heating resistor. The device according to the invention can particularly advantageously be part of an SCR catalytic converter system which serves to reduce the nitrogen oxide component in the exhaust gas of internal combustion engines. The device according to the invention is particularly preferably used in the exhaust systems of motor vehicles such as for example automobiles, motorized two-wheeled vehicles, water vehicles and aircraft. A delivery line can be formed between the reservoir and the heatable metering line, which delivery line is unheated or whose temperature is controlled to a temperature below the critical temperature. It has proven to be particularly advantageous for a delivery line of said type to be heated up to 80 °C. The regulation of the temperature of the delivery line and of the metering line and if appropriate of the hydrolysis catalytic converter formed downstream can dvantageously be carried out separately or in a common regulating loop. According to one advantageous embodiment of the device according to the invention, the delivery means comprises a pump. The pump in particular also serves to dose the aqueous solution, that is to say to proportionally meter the aqueous solution into the metering line. A dosing pump is preferably formed here as the delivery means. Here, a dosing pump is to be understood as a pump allowing the metering of a defined volume per time unit or per stroke. The dosing pump has in particular a maximum dosing capacity of up to 125 ml/min, in particular up to 30 ml/min. The dosing pump allows a continuous flow rate fluctuating about up to 5% around a nominal value of the flow. The dosing pump in particular allows the back-conveying towards the reservoir, in particular with flow rates similar to the usual conveying flow rate. The dosing pump allows in particular a conveying presusure up to 6 bar absolute, in particular up to 2 bar absolute. According to a further advantageous embodiment of the device according to the invention, a valve for dosing the quantity of aqueous solution is formed between the delivery means and the metering line. In an embodiment of said type, a 2 pump can permanently keep the aqueous solution under a predetermined or predefinable pressure, with it being possible for the dosing to take place by opening and closing the valve. According to an advantageous embodiment of the device according to the invention, the means for heating also advantageously comprise at least one of the following elements: a) an electrical resistance heater; b) heat transfer means for utilizing the waste heat of at least one other component; c) at least one Peltier element and d) a means for burning a fuel. Another component is to be understood here to mean a component which is for example part of a motor vehicle and which preferably has a temperature above the critical temperature. These can for example be parts of the exhaust line or of the exhaust system, in particular catalytic converter support bodies. These can also be components which are traversed by a heat-exchanging medium such as oil, or the like. An electrical resistance heater is to be understood to mean a conventional heater which is based on the generation of ohmic heat. In particular it is to be understood that an electrical resistance heater can comprise at least one heating element made of a material having a positive temperature coefficient (PTC) . It is to be understood that a material having a positive temperature coefficient, a so-called PTC-resistor, is in particular an electroconductive material the electric resistance of which increases with increasing temperature. These are in use in particular as so called self-regulating heating elements and are in particular made of a ceramic material, in particular a barium titanate ceramic. Alternatively, PTC resistors made of a polymeric material in particular being doped with soot particles can be used. A Peltier element is to be understood in particular as an electrical component which, when a current is passed through it, generates a temperature difference based on the so-called Peltier effect. A Peltier element preferably comprises one or more elements made from p-doped and n-doped semiconductor material which are connected to one another alternately by means of electrically conductive material. The sign of the temperature difference is dependent on the direction of the current flow, so that both cooling and heating can be provided by a Peltier element. The use of the electrical resistance heater if appropriate in combination with the utilization of the waste heat of other components has proven to be particularly advantageous. The electrical resistance heater makes it particularly advantageously possible to construct a highly dynamic regulating circuit in which the quantity of gaseous substance which is to be dispensed can be regulated highly dynamically, that is to say in a very quickly-reacting fashion. In particular, the means for heating, for example the resistance heater, are designed such that they have, in addition to the evaporation enthalpy of the aqueous solution, a capacity buffer for equalizing any heat losses of the device. The resistance heater can for example be formed in the manner of at least one heat conductor and/or in the manner of a bar-shaped heating element. Fuel is to be understood in particular to mean hydrocarbons and/or hydrogen. The combustion can also take place flamelessly. According to a further advantageous embodiment of the device according to the invention, the device is designed such that, in operation, the temperature across the length of the metering line is at most 25°C above and below a mean temperature. This is achieved in particular by means of the structural design of the metering line. The metering line is in particular connected to a heat conductor of an electrical resistance heater in such a way that the latter is in contact with the metering line in such a way that the required constancy of the temperature profile can be obtained. This can for example be provided in that the metering line is surrounded by closely-wound windings of a heat conductor, or in that the metering line and the heat conductor are wound together, for example to form a spiral. A materially-joined connection is also preferred between the heat conductor and the metering line. This can also be ensured in that the metering line is connected to the delivery line by means of a connecting unit which minimizes heat losses from the metering line to the delivery line or keeps such heat losses in such a small range as can be compensated by the resistance heater. It is particularly advantageously possible here for a second resistance heater circuit to be formed in the region of the connecting unit between the delivery line and the metering line, in order to be capable of locally compensating the heat losses which occur depending on the operating state. It is possible here in particular for a heat conductor with a varying diameter to be used, so that a higher dissipation of heat takes place in the region adjacent to the connecting unit than in further remote regions of the metering line. It is also particularly advantageously possible for basic heating to be obtained by means of contact for example with the exhaust line. Said contact is composed in particular of a heat-conducting contact by means of a heat conductor or else in that the corresponding device is connected to, or is attached on, to or in, the exhaust line. According to a further advantageous embodiment of the device according to the invention, the metering line has a traversable cross section of at most 20 mm2. The traversable cross section is preferably constant across the length of the metering line. Alternatively the metering line can comprise a diameter of 1 to 3 mm when having a circular cross section. These traversable cross sections advantageously permit as complete an evaporation as possible with a relatively low energy input when simultaneously the possibility of blocking the cross section with byproducts is small. The maximum cross section proposed here additionally advantageously permits highly dynamic control of the dispensed vapor quantity, so that a device of said type is particularly advantageously suitable for use in exhaust systems of internal combustion engines. The traversable cross section is alternatively or additionally greater than 0.2 mm2. If the cross section is less than said minimum cross section, then the line can become blocked by depositions, which are generated during operation, on the edge of the metering line; urea can for example be deposited there. Said blockage of the metering line can for example be dissolved again by means of intensified heating. Depending on the dynamic situation, such intense heating is either not possible, or the reducing agent quantity which is to be dispensed, which results from the then-possible quantity to be dispensed, is too low. According to a further advantageous embodiment of the device according to the invention, the metering line is formed from a material comprising at least one of the following materials: a) copper; b) aluminium; c) a nickel-based material; d) chrome-nickel steel and e) noble steel. Materials in particular which permit good heat conduction have proven to be advantageous. Here, the use of noble steel, chrome-nickel steel and/or nickel-based materials or corresponding alloys has proven to be particularly advantageous, since these materials are largely corrosion-resistant with respect to the solutions composed of reducing agent precursors (for example urea) and also with respect to formic acid. The materials 1.4401, 1.4301, 1.4828, 2.4646, 2.4816 and/or 2.4 633 as per the German industry standard are particularly preferable, with 2.4816 being particularly preferable. Particularly advantageous is the use of aluminium or materials comprising aluminium for forming at least the inner surface of the metering line. Aluminium oxides formed on the surface promote thermolysis and/or hydrolysis of urea to ammonia thos the conversion rate of the reducing agent precursor to reducing agent advantageously is increased compared to other materials even without a coating being catalytically active for hydrolysis. The delivery means according to the invention is particularly preferably a correspondingly designed pump. The quantity of the aqueous solution which can be evaporated in the metering line can be influenced by means of the pump. When switching off the device according to the invention, the delivery device can preferably be utilized for a return delivery for example when the system is switched off, with the rest of the aqueous solution in the metering line which has not been evaporated being delivered back into the reservoir. This particularly advantageously has the result that a dissipation of the reducing agent precursor to the atmosphere is effectively prevented. The generated quantity of reducing agent is preferably regulated by means of the regulation of the capacity of the delivery means. Further regulating mechanisms, such as for example the heating power which is to be introduced, the clocking of a valve with which the metering of aqueous solution to the metering line is controlled, and the like, are possible and in accordance with the invention. It is particularly possible in a particularly advantageous way for the regulation of the capacity of the delivery device to be coupled to the regulation of the heating power, in particular in such a way that the heating power is increased for an increased delivery capacity. According to a further advantageous embodiment of the device according to the invention, the metering line has a length of from 0.1 to 5 m. The length of the metering line is defined on the basis of the maximum expected delivery capacity, that is to say as a function of the maximum nitrogen oxide concentration in the exhaust gas of the internal combustion engine. With rising maximum nitrogen oxide concentration, the length of the metering line also increases. Preferable is a length of the delivery line of 0.2 to 0.8 m, particularly preferably of 0.5 m. According to a further advantageous embodiment of the device according to the invention, the metering line has a wall thickness of 0.1 to 0.5 mm. Said wall thicknesses have been proven to be particularly advantageous since they permit good heating and at the same time have a sufficiently great heat capacity that, in the event of an intense rise in the quantity of aqueous solution which is to be evaporated, evaporation initially takes place on account of the high heat capacity, until the means for heating the metering line can output a sufficiently high heating power. According to a further advantageous embodiment of the device according to the invention, the metering line preferably has a heat capacity of at least 150 J/K. Said heat capacities can advantageously serve to compensate an inertia of the means for heating the metering line in the event of large transients in the heating power. An embodiment is even preferable in which the heat capacity is at least 200 J/K. In particular the metering line changes direction at least once in particular direction changes in particular for at leastis 90°. By this drops of liquid being accelerated by an expaning volume of gas are disintegrated by striking the wall of the metering line and are further evaporated. Furthermore preferred are at least two of such changes in direction. The surface roughness Rz of the metering line is in particular in the range of 8 to 12 microns. Here, the term surface roughness Rz is to be understood in particular as an averaged surface roughness which is collected by the measurement of the distance of the surface to be measured from a reference surface wherein on five measuring tracks the respective maximum and minimum value of the distance is measured and the differences of these respective values are gathered. The averaged surface roughness is the mean value of these five differences. Thes surface values of the surface roughness have been found to be in particular advantageous as they promote the heat transfer and, consequently, the effectivity of evaporation increases. The thermal conductivity of the material froj which the meterning line is made is in particular at least 200 W / (m K) (Watt per meter and Kelvin) at 0°C. At least portions of the surface of the metering line comprise oxides of aluminium, titanium and/or vanadium for promoting the hydrolyses of reducing agent precursor to reducing agent, in particular of urea to ammonia. According to a further advantageous embodiment of the device according to the invention, the metering line and the means for heating the metering line have, at least in at least one partial region, at least one of the following arrangements relative to one another: a) the metering line and the means for heating the metering line are formed coaxially with respect to one another at least in a partial region; b) the metering line and the means for heating the metering line are formed concentrically with respect to one another at least in a partial region; c) the metering line and the means for heating the metering line are formed adjacent to one another at least in a partial region; d) the metering line is formed at least in a partial region so as to be wound around the means for heating the metering line; e) the means for heating the metering line constitutes, at least in partial regions, a bar-shaped heating element, with the metering line being formed to be wound around said bar-shaped heating element; and f) the metering line forms a duct in a bar-shaped heating element. According to a further advantageous embodiment of the device according to the invention, the metering line and the means for heating the metering line are connected to one another in a materially joined fashion at least in partial regions. The metering line and the means for heating the metering line are in particular brazed and/or welded to one another. According to a further advantageous embodiment of the device according to the invention, the metering line is at least partially provided with a coating which catalyses the hydrolysis of a reducing agent precursor to form a reducing agent. It is thus possible for already a part or the entire metering line to be used for the hydrolysis of the reducing agent precursor. According to a further advantageous embodiment of the device according to the invention, said device comprises at least one measuring sensor for determining the temperature of the metering line. The means for heating the metering line, if they comprise an electrical resistance heater, can in particular be used for temperature measurement by measuring the resistance. At least one measuring sensor for example in the form of a thermoresistor can alternatively or additionally be formed. According to a further advantageous embodiment of the device according to the invention, the measuring sensor can be connected to a power source. The measuring sensor can thereby also be used as a resistance heater, for example in the form of an emergency program if the metering line has become blocked. Within the context of said emergency program, the metering line can preferably be heated to a temperature higher than the critical temperature, preferably considerably higher than the critical temperature. Here, temperatures are preferable of 550°C and more, in particular 600°C and more. According to a further aspect of the present invention, a method is proposed for providing a gaseous substance mixture comprising at least one of the following substances: a) at least one reducing agent and b) at least one reducing agent precursor. An aqueous solution of at least one reducing agent precursor is delivered from a reservoir into at least one metering line. The at least one metering line is heated in such a way that the aqueous solution is completely evaporated to form the gaseous substance mixture. Complete evaporation is to be understood in particular to mean that the aqueous solution or water leaves the metering line predominantly not in the form of droplets. Complete evaporation is to be understood in particular to mean that 90% by weight and more, preferably 95% by weight and more, particularly preferably 98% by weight and more of the aqueous solution is evaporated. The reducing agent particularly preferably comprises ammonia, and a preferred reducing agent precursor is urea. It is preferably possible, where relatively large quantities of vapour are required, for a plurality of metering lines to be formed, for example in exhaust systems of utility vehicles. Also particularly preferable is a method for the selective catalytic reduction of nitrogen oxides in the exhaust gas of an internal combustion engine, in which method urea is present in an aqueous solution and is delivered from a reservoir into a metering line, with the metering line being heated in such a way that the aqueous solution is substantially completely evaporated to form a gaseous substance mixture comprising at least one of the following substances: a) a reducing agent such as in particular ammonia and b) at least one reducing agent precursor such as in particular urea, with the gaseous substance mixture being introduced into the exhaust system upstream of an SCR catalytic converter. A hydrolysis catalytic converter is particularly preferably formed between the metering of the gaseous substance mixture and the SCR catalytic converter. Within the context of this invention, a catalytic converter is to be understood as a support body which has a corresponding catalytic coating. The support body is particularly preferably a honeycomb body made from ceramic or metallic material, a correspondingly coated tube, a wire-mesh support or the like. A hydrolysis catalytic converter thereby constitutes a catalytic converter support body which catalyzes the hydrolysis of at least one reducing agent precursor and in particular of urea, in particular has a correspondingly designed coating. An SCR catalytic converter thereby constitutes a catalytic converter support body which has a coating which catalyzes the selective catalytic reduction of nitrogen oxides. Here, it is particularly advantageous if the reducing agent precursor is metered into an aqueous solution which comprises further constituents, in particular for reducing the freezing point. The aqueous urea solution can in particular comprise ammonium formate, that is to say the corresponding salt of the formic acid, and/or formic acid. A corresponding solution can be obtained under the trade name "Denoxium". Depending on the embodiment of the exhaust system in which the method according to the invention is used, and in particular depending on the embodiment of the metering line, of the aqueous solution and in particular also depending on the selection of the reducing agent precursor(s) and of the reducing agent (s), it can be necessary for the metering line to be heated to other temperatures. When using an aqueous urea solution which is marketed for example also as "AdBlue" or as "Denoxium", temperatures of 350°C or more and even in particular 400 to 450°C, in particular of approximately 420 °C, have been proven to be particularly advantageous. According to a further advantageous embodiment of the method according to the invention, at least one of the reducing agent precursors a) urea and b) ammonium formate is comprised in at least one of the following components: A) the substance mixture and B) the aqueous solution. It is thus possible in particular for the method according to the invention to lead to the formation of a substance mixture which comprises urea and if appropriate also already ammonia. The substance mixture is particularly preferably supplied to a hydrolysis catalytic converter situated downstream for further hydrolysis and therefore for the formation of ammonia. It is preferable for substantially complete conversion to the reducing agent to be obtained in this way, in particular of 90% by weight and more, preferably of 95% by weight and more, particularly preferably of 98% by weight and more. According to a further advantageous embodiment of the method according to the invention, the temperatures in the metering line are between 380 and 450°C. Said temperatures have proven to be particularly advantageous, since they on the one hand lead to substantially complete evaporation of the aqueous solution, and on the other hand effectively prevent the excessive formation of depositions in the interior of the metering line. The temperature in the metering line is preferably approximately 380°C. According to a further advantageous embodiment of the method according to the invention, the temperature along a length of the metering line is at most 25 °C above and below a mean temperature. This temperature constancy particularly advantageously results in the formation of depositions being effectively prevented. Corresponding trials have surprisingly shown that it is by no means necessary for a point with a temperature below the condensation temperature of one of the substances to be present for a deposition to be formed. It was in fact shown that even relatively slight temperature fluctuations of the metering line had the result that precipitation, in particular of urea, took place at the relatively cold points, which led to blockage of the metering line or to a reduction in the delivery capacity on account of a reduction in the traversable cross section of the metering line. It was shown that a method in which as constant a temperature as possible is present across the length of the metering line is advantageous, since substantially no depositions are formed here. The method is to be selected in particular such that a fluctuation range of approximately 50°C, that is to say a temperature of at most 25 °C above and below a mean temperature, is not exceeded across the length of the metering line. According to a further advantageous embodiment of the method according to the invention, a heating power which varies by up to 500 W/s is used during the heating process. A heating power of said type advantageously makes it possible to form a particularly dynamic system in which the quantity of the gaseous substance mixture which is supplied can particularly advantageously be very quickly adapted to the requirements of the corresponding system. According to a further advantageous embodiment of the method according to the invention, a quantity of 0.5 ml/s of the aqueous solution is delivered into the metering line. This quantity has proven to be sufficient in order to cover even high demand peaks of the gaseous substance mixture or for example of a reducing agent which is contained in the gaseous substance mixture. According to a further advantageous embodiment of the method according to the invention, the metering line has a traversable cross section of at most 20 square millimetres. A maximum cross section of said type on the one hand permits a highly dynamic method, so that large quantities of the gaseous substance mixture can be provided in a very short period of time, and on the other hand permits the design of a small and compact system which can be used with only a small spatial requirement even in mobile applications, for example in exhaust systems of motor vehicles. According to a further advantageous embodiment of the method according to the invention, the metering line is heated to a second temperature which is higher than the critical temperature at which complete evaporation of the aqueous solution takes place. This can be carried out in particular if the metering line is blocked, in order to dissolve depositions in the metering line and/or allow said depositions to react. Here, the second temperature is up to 600°C, preferably up to 800°C. particularly preferably up to 900 °C. If the metering line is made of aluminum the second temperature is preferably 500°C. According to a further advantageous embodiment of the method according to the invention, before the start of the evaporation, the temperature of the metering line is determined and aligned with other known temperatures. It is possible here in particular to use the measurement values of measuring sensors which determine the temperature of other components, for example of an external thermometer, of a thermometer for determining the cooling water temperature, or the like. According to a further advantageous embodiment of the method according to the invention, the heating of the metering line is carried out by means of an electrical resistance heater, preferably by means of a heat conductor, with the resistance of said resistance heater being determined before the start of heating, and the heating of the metering line taking place as a function of the determined resistance. It is thereby possible in particular to warn the user of damage in the resistance heater, or the like. According to a further advantageous embodiment of the method according to the invention, the heating power is monitored during the heating of the metering line. Here, the heating is preferably interrupted if, over a predefinable timespan, the heating power remains below a value which is dependent on the quantity of aqueous solution to be evaporated. In the ongoing regulation, this indicates that there is a blockage or a reduced freely traversable cross section of the metering line. In this case, it is possible to initiate emergency measures, for example an operation of the means for heating the metering line to a second, higher temperature stage, in order to thereby clean the depositions in the metering line by means of dissolution and/or reaction. In an automobile, it is then possible, if the means for heating the metering line comprise an electrical resistance heater, for a power supply to be taken from a generator of the automobile, for example an alternator, with the power preferably being tapped off before the regulation of the voltage of the alternator, since higher voltages are usually present here. The details and advantages disclosed for the device according to the invention can also be transferred and applied to the method according to the invention. The details and advantages disclosed for the method according to the invention can also be transferred and applied to the device according to the invention. The invention is explained in more detail below on the basis of the appended figures, without the invention being restricted to the exemplary embodiments shown therein. In the figures, in each case schematically: Figure 1 shows a device for providing a gaseous substance mixture in a first embodiment as a perspective view; Figure 2 shows the first embodiment of the device for providing a gaseous substance mixture in a sectioned view; Figure 3 shows a delivery line for delivering the aqueous solution from a reservoir to the metering line; Figure 4 shows a view of a device for the selective catalytic reduction of nitrogen oxide in the exhaust gas of an internal combustion engine; Figure 5 schematically shows a second exemplary embodiment of an evaporator unit; Figure 6 shows a device for providing a reducing agent; Figure 7 schematically shows an alternative embodiment of the evaporator unit in cross section; Figure 8 shows a detail of an opening-out point of a dosing line into an exhaust line; Figure 9 shows an exemplary embodiment of a device for providing a gaseous substance mixture, in section; Figure 10 schematically shows a device for providing a gaseous substance mixture; Figure 11 shows an example of a possible metering unit for metering the reducing agent substance mixture to the exhaust gas; Figure 12 shows a further example of a possible metering unit for metering the reducing agent substance mixture to the exhaust gas; Figure 13 shows an exemplary embodiment of a device for treating the exhaust gas of an internal combustion engine; Figure 14 shows a means for depositing droplets; Figures 15 to 18 show exemplary embodiments of evaporator units; Figures 19 and 2 0 show a further exemplary embodiment of a device for providing a gaseous substance mixture; Figure 21 shows a further exemplary embodiment of a device for treating exhaust gas; Figure 22 shows a detail of an opening-out region of a metering unit into the exhaust line and Figures 23 and 24 show examples for honeycomb bodies as catalytic converter support bodies. Figure 1 schematically shows a device 1 for providing a gaseous substance mixture comprising at least one of the following substances: a) at least one reducing agent, and b) at least one reducing agent precursor. These are in particular the reducing agent ammonia and the reducing agent precursor urea. The device 1 comprises a metering line 2 with a dispensing opening 3. Furthermore, means 4 for heating the metering line 2 are formed, with which means 4 the metering line 2 can be heated above a first critical temperature which is higher than the boiling temperature of water. The device 1 also comprises a reservoir (not yet shown here) which can be flow-connected to the metering line 2. That is to say in particular that a fluid stored in the reservoir, such as for example an aqueous solution comprising at least one reducing agent precursor, can, during operation, flow through the metering line 2 to the dispensing opening 3. By means of said device 1, a gaseous substance mixture can be provided which contains at least one reducing agent and/or at least one reducing agent precursor. In the present exemplary embodiment, the means 4 for heating the metering line 2 are wound in spiral fashion together with said metering line 2. In this way, a fluid flowing through the metering line 2 is heated and ultimately evaporated. As a result, a gaseous substance mixture which contains at least one reducing agent precursor is dispensed through the dispensing opening 3. Depending on the selection of the temperature, the means 4 for heating the metering line 2, at least partial thermolysis of the reducing agent precursor can even already take place in the metering line 2, so that the gaseous substance mixture dispensed through the dispensing opening also already contains reducing agent, such as for example ammonia, in addition to a reducing agent precursor such as for example urea. Furthermore, the device 1 for providing a gaseous substance mixture also comprises a measuring sensor 5, by means of which the temperature at at least one point of the metering line 2 can be measured. The measuring sensor 5 can for example be a conventional thermal element or a conventional thermoresistor. The device 1 and/or the individual components which require an electrical terminal preferably comprise a cable length for realizing the electrical terminals. A cable length is to be understood in particular to mean a cable connection which is at least half of a metre, preferably at least one metre long. This allows plug-type contacts to be formed in regions which, in particular in automobiles, are exposed to only a small extent to environmental influences such as spray water, stone impacts or the like. Figure 2 shows the device 1 from figure 1 in section. It is possible to clearly see the metering line 2, through which the aqueous solution comprising at least one reducing agent precursor can flow during operation, and the means 4 for heating the metering line 2. The metering line 2 can have a constant cross section, though this can also be variable, as in the present example. Here, however, the traversable cross section of the metering line 2 is preferably between 0.75 mm2 and 20 mm2; the traversable cross section is preferably in the region of approximately 3 mm2. Said traversable cross sections have been proven to be advantageous since, on the one hand, fast and substantially complete evaporation of the aqueous solution is possible with a cross section of said type, and on the other hand, the cross section is large enough that the formation of depositions in the interior of the metering line 2 is substantially avoided. Figure 2 also shows the measuring sensor 5 for determining the temperature of the metering line 2. Here, the means 4 for heating the metering line 2 are operated in such a way that, in operation, the temperature across the length of the metering line 2 is at most 5°C above and below a mean temperature. The mean temperature substantially corresponds here to the first critical temperature. The metering line 2 is formed in particular from a copper alloy. Figure 3 schematically shows the delivery line 6, via which the metering line 2 can, in operation, be connected to a reservoir (not yet shown here) . The delivery line 6 has means 7 for temperature control. In this exemplary embodiment, the means 7 for temperature control comprise in each case a plurality of Peltier elements 8 and a cooling body 9. The Peltier elements 8 are in each case provided with electrical terminals 10, by means of which they can be supplied with current. Here, depending on the polarity of the current, the Peltier elements 8 are used for heating or for cooling, so that basic temperature control of the delivery line 6 can be obtained with said Peltier elements 8. The cooling body 9 serves in particular to radiate heat energy if the delivery line 6 is cooled by the Peltier element(s) 8. The delivery line 6 can be connected to a further component by means of a connecting unit 11. Depending on the design of the device, said component can be the metering line 2 as already referred to above, or generally an evaporator unit 12. The metering line 2 can then be part of the evaporator unit 12. In general, the connecting unit 11 is formed at least partially from a material with a thermal conductivity of less than 10 W/m K (Watt per metre and Kelvin). The connecting unit 11 is formed in particular from a ceramic material and/or polytetrafluoroethylene (PTFE). The connecting unit 11 is in particular designed such that a temperature gradient of 4 0 K/mm (Kelvin per millimeter) and greater can be maintained over a length 57 of the connecting unit 11. This permits a method in which the evaporator unit 12 and/or the metering line 2 has a considerably higher temperature than the delivery line 6. The evaporator unit can for example have a temperature of 300°C or more, 400°C or more or of 420°C or more, and thereby lead to substantially complete evaporation of the aqueous solution within the evaporator unit 12, while the delivery line 6 has a temperature level of only 70°C or more, 80'C or more or 90°C or more in order to ensure that the aqueous solution is not yet evaporated in the delivery line 6. Figure 4 schematically shows a device 15 for treating the exhaust gas 13 of an internal combustion engine (not shown). The exhaust gas 13 of the internal combustion engine flows through an exhaust line 14. The device 15 for treating the gases 13 of an internal combustion engine comprises a reducing agent solution evaporator 16, a hydrolysis catalytic converter 17 and an SCR catalytic converter 18. In the reducing agent solution evaporator 16, an aqueous solution comprising a reducing agent precursor is evaporated. Urea in particular is used as a reducing agent precursor. The reducing agent solution evaporator 16 comprises, in this exemplary embodiment, an evaporator unit 12 comprising a metering line 2 which is heated by a means 4 for heating the metering line 2. Said metering line 2 is connected by means of a connecting unit 11 to a delivery line 6. The delivery line 6 is surrounded by means 7 for controlling the temperature of the delivery line 6, which means 7 can for example comprise one or more Peltier elements 8 and/or a cooling body 9, as shown above. The aqueous solution of at least one reducing agent precursor can be delivered by delivery means 19 from a corresponding reservoir 20 into the delivery line 6. In the evaporator unit 12, a gas is provided which comprises at least one reducing agent precursor such as for example urea and if appropriate also ammonia which has already been generated from the thermolysis of urea. Said gaseous substance mixture is introduced into the hydrolysis catalytic converter 17 formed downstream of the reducing agent solution evaporator 16. The hydrolysis catalytic converter 17 is designed such that in particular urea is hydrolyzed to form ammonia by means of a corresponding catalytically active coating which is applied to said hydrolysis catalytic converter 17. In general, the hydrolysis catalytic converter 17 serves for the hydrolysis of a reducing agent precursor to form a reducing agent. The gas which leaves the hydrolysis catalytic converter 17, which gas contains a reducing agent and is referred to as a reducing agent substance mixture, is metered into the exhaust line 14 via a dosing line 21. The dosing line 21 opens out into the exhaust line 14 at a dosing opening which is situated upstream of the SCR catalytic converter 18. Formed downstream of the dosing opening 22 and upstream of the SCR catalytic converter 18 are mixing means 23 in the form of a guide plate which cause a mixture of the reducing agent substance mixture with the exhaust gas 13. The SCR catalytic converter 18 therefore attains a mixture of reducing agent and exhaust gas which leads to a reduction of the nitrogen oxides contained in the exhaust gas 13 in the SCR catalytic converter 18. Here, a quantity of reducing agent substance mixture is preferably provided which is such that as complete a conversion of the nitrogen oxides in the exhaust gas 13 as possible can take place in the SCR catalytic converter 18. Figure 5 schematically shows a further exemplary embodiment of an evaporator unit 12. This illustration shows the evaporator unit 12 in section. The evaporator unit 12 comprises an evaporator chamber 24 which encompasses a substantially closed volume. In this exemplary embodiment, the evaporator chamber 2 4 has merely a first opening 25 for connecting a delivery line 6 (not shown here) for delivering the aqueous solution, and a second opening 26 for connecting a metering line 2 (not shown here) for discharging the gaseous substance mixture. Formed in the first opening 25 is a nozzle 62 as a means for dosing the aqueous solution 45 into the evaporator chamber 24. Said nozzle 62 serves to dose the aqueous solution 45 into the evaporator chamber 24. The evaporator unit 12 additionally has means for heating the evaporator chamber 24. In the present exemplary embodiment, said means are formed by corresponding heat conductors 27 which are in contact with the evaporator chamber 24. As shown here, said heat conductor 27 can be of asymmetric design, that is to say a higher density of heat conductors per unit area is formed in the regions which are situated substantially opposite the first opening 25 than in the regions which are not situated substantially opposite the first opening 25. Furthermore, said means cumulatively comprise a means 63 for burning hydrocarbons, such as for example a burner. A burner of said type can also be suitable for carrying out a flameless combustion of hydrocarbons. The evaporator chamber 24 is preferably formed from a material comprising at least one of the following materials: a) copper; b) aluminium; c) noble steel; d) a nickel-based material and e) chrome-nickel steel. The volume of the evaporator chamber 24 is preferably 1.5 to 10 cm3. In operation, the heat conductor 27 is preferably operated with a heating power of up to approximately one kilowatt per second, with the maximum heating power being fixed as a function of the application. In passenger vehicles, the maximum heating power is preferably approximately 500 to 700 W/s, and in utility vehicles, preferably approximately 1200 to 1500 W/s. The heat capacity of the evaporator chamber 24 is preferably less than 120 J/K, particularly preferably 100 to 110 J/K. The first opening 25 and the second opening 26 preferably enclose an angle of 30 to 70°. The aqueous solution 45 is preferably delivered at up to 150 ml/min into the evaporator chamber 24, preferably at up to 100 ml/min, particularly preferably at up to 30 ml/min. In the region of the second opening 26, the evaporator chamber 24 preferably has means with which infiltration of droplets into second opening 26 can be avoided. Said means are in particular means with which a gas film situated between the droplet and the wall of the evaporator chamber 24 can be penetrated. Said means are in particular projections of the walls or the like. The structures 28 can likewise be formed in this region. Furthermore, the evaporator chamber 2 4 has, in the interior, one or more structures 28 which serve to produce a larger surface for evaporating the aqueous solution. Said structures 28 are drawn relatively large in the present exemplary embodiment; said structures 28 can however also be a structured surface which is provided for example by applying a corresponding coating to the inner surface of the evaporator chamber 24. Said structures 28 can alternatively or additionally also comprise macroscopic structures which have a structure amplitude of a number of millimetres or even more. In general, said structures 28 are to be understood as means for increasing the wetting capacity of the surface of the evaporator chamber 24. Figure 6 schematically shows the first exemplary embodiment of the evaporator chamber 24 connected to an exhaust line 14. Here, the evaporator chamber 24 is provided with a casing 29. Said casing 29 is preferably formed from a corresponding thermal insulator which reduces heat losses to the environment. The means 27 for heating the evaporator chamber 24 can be connected by means of heat conductor terminals 30 to a current source (not illustrated) . The evaporator unit 12 is connected by means of the second opening 26 to a hydrolysis catalytic converter 17. The hydrolysis catalytic converter 17 has means 31 for controlling the temperature of the hydrolysis catalytic converter 17, which means 31 are composed in the present exemplary embodiment of a corresponding heating wire which is wound around the hydrolysis catalytic converter 17. Formed around the hydrolysis catalytic converter 17 is a corresponding casing 32 which constitutes in particular thermal insulation of the hydrolysis catalytic converter 17 with respect to the environment in order to minimize as far as possible any occurring heat losses. In the present exemplary embodiment, the hydrolysis catalytic converter is connected directly to the exhaust line 14 by virtue of projecting into the latter. Formed in the exhaust line 14 is a corresponding bore, into which the hydrolysis catalytic converter 17 or its casing 32 can be inserted in as sealed a manner as possible. As sealed a connection as possible between the hydrolysis catalytic converter 17 and the exhaust line 14 can be produced by corresponding connecting means 33. Also formed, as passive mixing means, is a guide plate 34, by means of which the reducing agent substance mixture 35 which leaves the hydrolysis catalytic converter 17 is mixed with the exhaust gas flowing in the exhaust line 14. In operation, the evaporator unit 12 serves to produce a gaseous substance mixture from an aqueous solution which contains urea as a reducing agent precursor. The gaseous substance mixture generated in the evaporator unit 12 contains at least urea and if appropriate also already ammonia which has been generated by thermolysis of the corresponding urea. Said substance mixture is conducted via the second opening 2 6 into the hydrolysis catalytic converter 17 in which substantially complete hydrolysis of the urea takes place to form ammonia. Here, a reducing agent substance mixture 35 which comprises ammonia is generated in the hydrolysis catalytic converter. A method is particularly preferred in which 98% and more of the urea is ultimately converted to ammonia. Figure 7 schematically shows an alternative embodiment of the evaporator unit from figures 5 and 6. In contrast to the first exemplary embodiment shown above, this alternative embodiment additionally has a third opening 36. In operation, exhaust gas can be introduced into the evaporator chamber 24 in a continuous or pulsatile fashion through said third opening 36. It is possible in this way to obtain an improved distribution of the urea in the generated gas in comparison to the first exemplary embodiment. Furthermore, an evaporator unit 12 of said type can also be used for evaporating solid urea, since water is introduced into the evaporator chamber 24 by the exhaust gases of the internal combustion engine which are introduced through the third opening 36, which water can later be used in the hydrolysis catalytic converter 17 for the hydrolysis of the urea to form ammonia. Figure 8 schematically shows the opening-out point of a dosing line 21 into the exhaust line 14 as a part of a corresponding metering unit 46. Here, the dosing line 21 is surrounded by a heat conductor 38 which is also formed around the opening-out point of the dosing line 21 into the exhaust line 14. Figure 9 schematically shows, at a first intersection, a further possibility of a device 1 for providing a gaseous substance mixture comprising a reducing agent. The device 1 comprises a metering line 2, around which is wound a corresponding means 4 for heating the metering line 2, or which is wound together with said means 4. The metering line 2 and the means 4 for heating the metering line 2 are formed together in a common casing 29. A first temperature measuring sensor 39 is formed within the winding of the metering line 2. Said first temperature measuring sensor 39 can be connected by means of a first connecting element 40 to a corresponding control unit (not shown here). The evaporator unit 12 is connected by means of the dispensing opening 3 of the metering line 2 to a hydrolysis catalytic converter 17. The hydrolysis catalytic converter 17 has a coating which catalyses the hydrolysis of urea to form ammonia. The hydrolysis catalytic converter 17 is surrounded by means 31 for controlling the temperature of the hydrolysis catalytic converter, which means 31 comprise a correspondingly formed heating wire. Said means 31 for controlling the temperature of the hydrolysis catalytic converter 17 can be connected in an electrically conductive manner to a corresponding power supply by means of corresponding first heat conductor terminals 41. This correspondingly applies to the means 4 for heating the metering line 2, which means 4 can be provided with a corresponding power supply by means of corresponding second heat conductor terminals 42. The hydrolysis catalytic converter 17 has a second temperature measuring sensor 43 which can be connected by means of a corresponding second connecting element- 44 to a control unit (not shown). The temperature within or on the hydrolysis catalytic converter 17 can be determined by means of the second temperature measuring sensor 43. In operation, an aqueous urea solution 45 is delivered into the metering line 2. The means 4 for heating the metering line 2 serve to heat the metering line 2 and thereby evaporate said aqueous urea solution and, if appropriate, depending on the temperature control, an at least partial thermolysis of the contained urea takes place to form ammonia. The corresponding gaseous substance mixture is introduced through the dispensing opening 3 into the hydrolysis catalytic converter 17, in which hydrolysis, preferably substantially complete hydrolysis of the contained urea takes place to form ammonia. A corresponding reducing agent substance mixture 35 leaves the hydrolysis catalytic converter 17, which reducing agent substance mixture 35 can be introduced into an exhaust line 14 of an exhaust system of an internal combustion engine. A method is preferable here in which the temperatures of the evaporator unit 12 and/or of the hydrolysis catalytic converter 17 are monitored by means of the temperature measuring sensors 39, 43, and both components 12, 17 can be heated by the corresponding means 4, 31. Figure 10 schematically shows a device 1 for providing a gaseous substance mixture 35 comprising at least one reducing agent. Said device 1 comprises, sequentially, a delivery line 6, by means of which an aqueous solution is delivered from a reservoir (not shown) into an evaporator unit 12. The evaporator unit 12 is adjoined by a hydrolysis catalytic converter 17, and the latter is adjoined by a dosing line 21 for metering the corresponding substance mixture to an exhaust line 14 (not shown) or by a metering unit 46 for metering the reducing agent substance mixture to the exhaust line 14. The evaporator unit 12 has a third temperature measuring sensor 47. The temperature of or in the delivery line 6 can be measured with said third temperature measuring sensor 47. The dosing line 21 and/or the metering unit 46 optionally has a fourth temperature measuring sensor 48, with which the temperature of the dosing line 21 and/or of the metering unit 4 6 or the temperature in the dosing line 21 and/or in the metering unit 46 can be measured. The evaporator unit 12 has means 4 for heating the metering line 2 and/or means 27 for heating the evaporator chamber 24. The hydrolysis catalytic converter 17 can optionally, alternatively or in addition to the means 4, 27, have means 31 for controlling the temperature of the hydrolysis catalytic converter 17. Optionally, alternatively or in addition, the delivery line 6 has temperature control means 4 9, by means of which the temperature of the delivery line 6 can be controlled. Particularly possible, advantageous and inventive here are one or more Peltier elements. The dosing line 21 and/or the metering unit 4 6 have metering temperature control means 50, by means of which the temperature of the dosing line 21 and/or of the metering unit 46 can be controlled. The use of at least one Peltier element is also advantageous here. All of the formed temperature control means 4, 27, 31, 49, 50 and all of the formed temperature measuring sensors 39, 43, 47, 48 are connected to a control unit 51. Said control unit 51 carries out the regulation of the temperature in a regulating loop which comprises at least one means 4, 27, 31, 49, 50 for temperature control and at least one temperature measuring sensor 39, 43, 47, 48. The number of temperature measuring sensors 39, 43, 47, 48 is preferably greater than the number of means 4, 27, 31, 49, 50 for controlling the temperature of the components 6, 2, 24, 17, 21, 46. The control unit 51 is preferably connected to a controller of the internal combustion engine or is integrated therein. The data of the controller of the internal combustion engine and the operating parameters of the internal combustion engine can advantageously be incorporated in the control of the evaporation and/or of the delivery to the evaporator unit 12. Figure 11 schematically shows a detail of a device for providing a gaseous substance mixture. Formed in an exhaust line 14 upstream of an SCR catalytic converter 18 is a honeycomb body 52 with ducts which can be traversed by a fluid, which honeycomb body 52 is part of a corresponding mixing means 53. The honeycomb body 52 is designed such that it can be traversed by the exhaust gas at least partially at an angle with respect to the main flow direction of the exhaust gas. Here, the main flow direction 54 is indicated by a corresponding arrow in figure 11. In the present exemplary embodiment, the honeycomb body 52 is of conical design. The honeycomb body has in particular a relatively large cutout 55 which is free from ducts. The dosing line 21 as part of the metering unit 46 opens out into said cutout 55, through which dosing line 21 the reducing agent substance mixture 35 is introduced in operation. Figure 12 schematically shows an example of a metering unit 4 6 with a dosing line 21 for metering the reducing agent substance mixture into an exhaust line 14. Here, the dosing line 21 extends through the wall of the exhaust line 14 in a curved state. The dosing line 21 has perforations 56 in the region which projects into the exhaust line 14. Here, the curvature or the curved entry of the dosing line 21 into the exhaust line 14 is not strictly necessary; the dosing line 21 could equally well enter into the exhaust line 14 perpendicularly or straight. Additionally formed here is a guide plate 23 which leads to a further improved mixture of the reducing agent substance mixture with the exhaust gas 13 in the exhaust line 14. Figure 13 schematically shows an embodiment of the device 1 for treating the exhaust gas of an internal combustion engine (not illustrated). Here, the evaporator unit 12 and the hydrolysis catalytic converter 17 are formed in a first exhaust branch 58. A distribution of the exhaust gas between the first 58 and the second exhaust gas branches 59 is obtained using a means 60 for flow guidance. The SCR catalytic converter 18 is formed downstream of the opening-out point 61 of the first exhaust branch 58 into the second exhaust branch 59. The evaporator unit 12 preferably has means 64 for depositing droplets, which means 64 can for example be formed within the metering line 2 or in or downstream of the second opening 26 of the evaporator chamber 24. Figure 14 shows an exemplary embodiment of a means 64 of said type for depositing droplets. Said means 64 is connected to the metering line 2 or generally to a line 65 through which vapour passes. Should droplets still be present in the vapour, these are deposited in the present example by the action of inertia. Formed in the means 64 are one or more impact plates 66 which force the flow to undergo deflections 67. The impact plate 66 and/or the housing 68 of the means 64 are heated, so that deposited droplets are likewise evaporated. Instead of the means 64 for depositing droplets shown here, it is also possible to alternatively or cumulatively take other measures; for example, the metering line 2 or the line 65 can, in regions, have narrowed cross sections, projections, deflections or the like. Figure 15 schematically shows a further exemplary embodiment of an evaporator unit 12, in which a metering line 2 can be heated by means 4 for heating the metering line 2. Here, the means 4 for heating the metering line 2 comprise a bar-shaped heating element 69 which can be connected by means of electrical terminals 70 to a power source. Formed in the metering line 2 is a means 64 for depositing droplets which can be heated by means of the contact with the rod-shaped heating element 69. Figure 16 schematically shows a further exemplary embodiment of an evaporator unit 12 in which the metering line 2 is wound, in the form of a loop, twice around the bar-shaped heating element 69. Figures 17 and 18 show exemplary embodiments of evaporator units 12 in which the metering line 2 is not wound around the longitudinal axis of the bar-shaped heating element 69 but is fastened in loops to the bar-shaped heating element 69. Fundamentally preferred is a materially-joined connection between the metering line 2 and the bar-shaped heating element 69, in particular a brazed connection. Figures 19 and 20 schematically show a further exemplary embodiment of a device 1 for providing a gaseous substance mixture comprising at least one of the following substances: a) a reducing agent, preferably ammonia, and b) at least one reducing agent precursor, in particular urea, having a hydrolysis catalytic converter 17. The device 1 comprises at least one metering line 2, in the present exemplary embodiment four metering lines 2, which are wound in spiral fashion around a bar-shaped heating element 69. Each of the metering lines 2 has in each case one dispensing opening 3, through which, in operation, a gaseous substance mixture which comprises a reducing agent is dispensed. The dispensing openings 3 are in each case distributed so as to be distributed substantially uniformly on a circle. The metering lines 2 are connected to a reservoir 20 (not shown here) from which an aqueous solution 45 of at least one reducing agent precursor is delivered into the metering line 2 by a delivery means 19. The metering lines 2 and the heating element 69 are part of a corresponding reducing agent solution evaporator 16. Formed downstream of the dispensing openings 3 is a hydrolysis catalytic converter 17 which can likewise be heated by a bar-shaped heating element 69. In one advantageous refinement, only one bar-shaped heating element 69 is formed, which heating element 69 is in thermal contact both with the metering line(s) 2 and with the hydrolysis catalytic converter 17. In the present exemplary embodiment, the hydrolysis catalytic converter 17 is embodied as an annular honeycomb body. The hydrolysis catalytic converter 17 is adjoined downstream by a dosing line 21, via which, in operation, the gas flow comprising at least one reducing agent can be introduced into the exhaust line 14. A mechanical connection to the exhaust line 14 can be produced by the connecting means 71. Also formed is thermal insulation 72, by means of which the hydrolysis catalytic converter 17 is thermally decoupled from the exhaust line 14. Also formed is a heat shield 73, by means of which the hydrolysis catalytic converter 17 is protected from a radiation of heat. Furthermore, air gap insulation 74, which likewise serves as thermal insulation, is provided between an outer housing 75 and an inner housing 76. Figure 20 shows a cross section through that region of the metering lines 2 which can be seen encircling the rod-shaped heating element 69. Figure 21 schematically shows a further exemplary embodiment of a device 15 for treating exhaust gas 13. In contrast to the embodiment in figure 4, a valve 77 is formed in the delivery line 6, which valve 77 serves for dosing the aqueous solution 45 into the evaporator unit 12. The valve 77 can be actuated by means of a control terminal 78. Figure 22 schematically shows an opening-out region 79 of a metering unit 46 into the exhaust line 14. Here, the exhaust line 14 and/or the metering unit has an aperture 80 which, in operation, produces a dead zone or calming zone of the exhaust gas flow, and consequently a region of reduced pressure, in the opening-out region 79, and thereby ensures that no exhaust gas is pressed into the dosing unit 46. The dosing unit 4 6 also has a temperature sensor 81 which comprises an annular thermoresistor. Should depositions form in said region, then the temperature sensor 81 can be connected to a power source (not shown) in order to thereby bring about a temperature increase to a second nominal temperature, for example of 600°C or 800°C, and cause a dissolution of reduction of the depositions. Figure 23 schematically shows a cross section through a honeycomb body 82 which can be used both as a hydrolysis catalytic converter 17 and also as an SCR catalytic converter 18, with it being necessary here for other catalytically active coatings to be applied. The honeycomb body 82 is constructed from smooth metallic layers 83 and corrugated metallic layers 84 which, in this exemplary embodiment, are layered to form three stacks and are then wound with one another. The honeycomb body 82 also comprises a casing tube 85 which closes off the honeycomb body 82 to the outside. Smooth 83 and corrugated layers 84 form ducts 86 which can be traversed by exhaust gas 13. Figure 24 shows a further example of a honeycomb body 87 which is of annular design and can be used both as a hydrolysis catalytic converter 17 and also as an SCR catalytic converter 18, with it being necessary here for other catalytically active coatings to be applied. The honeycomb body 87 is constructed from layers 88 which have smooth 89 and corrugated sections 90 which are folded onto one another and form ducts 8 6 which can be traversed by exhaust gas 13. The honeycomb body 87 is closed off by means of an outer casing tube 91 and an inner casing tube 92. In the case in particular of a metering line 2 which is heated by means 4, 69, it is fundamentally advantageous to provide, heating from the other side in addition to single-sided heating. It is for example possible for further heating elements to be formed which enclose the metering line from the outside. It is fundamentally advantageous if, at a certain cross section of the metering line 2 the temperature over the periphery differs from a mean temperature at most by +25 °C or -25°C in operation. The hydrolysis catalytic converter 17 is fundamentally also a tube which is provided with a coating which catalyses the hydrolysis in particular of urea to form ammonia, or else a casing tube having at least one structured metallic layer which is applied on the inside to the outer periphery and which preferably has a freely traversable cross section radially in its interior which is at least 20% of the entire cross section of the casing tube. Said embodiments are preferably heated from the outside. Before the provision of reducing agent upstream of the SCR catalytic converter 18 commences, the process is fundamentally as follows: it is initially checked as to whether a current supply or fuel supply is ensured for the temperature control and/or heating means 4, 27, 31, 49, 50, 63, 69; if it is determined that the current and/or fuel supply is ensured, then the evaporator unit 12 and if appropriate the hydrolysis catalytic converter 17 are heated in each case to a predetermined nominal temperature, in particular a metering line 2 is heated to approximately 360 to 400°C and/or an evaporator chamber 24 is heated to approximately 250 to 350°C; aqueous solution 45 is delivered in parallel to the evaporator chamber 24, in particular to the connecting unit 11, with it being possible on the one hand for a volume of aqueous solution 45 to be delivered which substantially corresponds to the volume of the delivery line 6, and on the other hand for a corresponding sensor, which operates for example on the basis of conductivity measurement, to be formed at a corresponding point, for example on, in or adjacent to the connecting unit 11; the temperature of the SCR catalytic converter 18 or of the exhaust line 14 is then determined, in particular measured and/or calculated from the data of an engine controller. If the temperature of the SCR catalytic converter 18 is above a predefinable limit value, in particular the "light-off" temperature of the SCR catalytic converter 18, the evaporator unit 12 is supplied with the aqueous solution 45. If the evaporator unit 12, the metering line 2 and/or the evaporator chamber 24 are still substantially at their operating temperature, then the above-specified diagnosis steps can be omitted. In operation, the heating power imparted to the evaporator unit 12 correlates with the delivery quantity of aqueous solution 45. This means in particular that it is checked as to what level of nominal heating power is required for the evaporation of the respective delivery quantity. If the measured actual heating power for a timespan is below the nominal heating power, then a warning is output to the user, since a reduction of the cross section of the metering line 2 and/or of the dosing line 21 could then be present. It is also advantageous, at regular, predefinable time intervals, to heat the evaporator unit 12, the metering line 2, the evaporator chamber 24, the hydrolysis catalytic converter 17, the dosing line 21 and/or the metering unit 4 6 to a temperature which is above the normal operating temperature, in order to thereby dissolve any depositions which may be present. When the evaporation is ended, which occurs for example when the internal combustion engine is switched off, the aqueous solution 45 can be returned from the metering line 2. Before the return delivery from the metering line 2, the delivery of aqueous solution 45 is preferably firstly suspended, with the evaporator unit 12, the metering line 2 and/or the evaporator chamber 24 however still being heated to the usual temperature in order to thereby carry out complete evaporation and to thereby prevent any impurities present in the evaporator unit 12, the metering line 2 and/or the evaporator chamber 24 from passing into the delivery line 6 during the return delivery. After a certain time has elapsed, the return delivery can be initiated by the delivery means. A valve is advantageously formed on or adjacent to the connecting unit 11, by means of which valve air can be sucked in during the return delivery. The return delivery fundamentally takes place until the delivery line 6 is substantially emptied into the reservoir 20. In the event of intense changes in the delivery quantity of the aqueous solution 45 which is to be delivered, which can for example be attributed to a sharply-rising concentration of nitrogen oxides in the exhaust gas of the internal combustion engine, situations can occur in which the evaporator unit 12 is not capable of immediately evaporating a considerably higher quantity of aqueous solution 45, since the correspondingly increased heating cannot take place so quickly. In this case, it is preferable to increase the delivery quantity of aqueous solution 45 only to such an extent that complete evaporation is still possible. The quantity of reducing agent to be dispensed, and consequently also the quantity of aqueous solution 45 which is to be evaporated, can be determined as a function for example of at least one of the following conditions: a) the nitrogen oxide concentration in the exhaust gas; b) a forecast nitrogen oxide generation which preferably occurs when the exhaust gas passes the SCR catalytic converter 18; c) the maximum quantity of reducing agent which can be converted directly by the SCR catalytic converter 18. The reservoir 20, the delivery line 6, the evaporator unit 12, the metering line 2, the evaporator chamber 24 and/or the hydrolysis catalytic converter 17 can be formed to be in thermal contact for example with the fuel tank of the internal combustion engine. For frost protection reasons, said fuel tank usually has a heater, which can then also provide frost protection for the above-specified components. According to a further advantageous present aspect, a device 1 is described for providing a gaseous substance mixture comprising at least one of the following substances: a) at least one reducing agent and b) at least one reducing agent precursor. Here, a reservoir 20 for an aqueous solution 45 comprising at least one reducing agent precursor is formed, which reservoir 20 can be flow-connected to an evaporator chamber 24. Furthermore, a means for dosing the aqueous solution 45 is formed in the evaporator chamber 24, with means 27, 63 for heating the evaporator chamber 24 being formed, with which means 27, 63 the evaporator chamber 24 can be heated to a temperature greater than or equal to a critical temperature at which the aqueous solution is at least partially evaporated. According to one advantageous refinement of said device 1, the means for dosing the aqueous solution 45 comprise at least one nozzle 62. The evaporator chamber 24 advantageously has a substantially closed volume which has only a first opening 25 for connecting a delivery line 6 for the aqueous solution 45, and a second opening 26 for connecting a metering line 2 for discharging the gaseous substance mixture. According to one advantageous refinement of said device 1, the evaporator chamber 24 encompasses a substantially closed volume which has only a first opening 25 for connecting a delivery line 6 for the aqueous solution, a second opening 2 6 for connecting a metering line 2 for discharging the gaseous substance mixture, and a third opening 36 for metering exhaust gas 14. A further advantageous refinement of said device provides that means 27, 63 for heating the evaporator chamber 24 comprise at least one of the following components: a) an electrical resistance heater 27 and b) a means 63 for burning a fuel. It is also advantageous that the evaporator chamber 24 is substantially spherically symmetrical. Here, the evaporator chamber 2 4 preferably has a radius of 2mm to 25mm. It is also advantageous for the evaporator chamber 24 to have a volume of 30 to 4000 mm3. The means 27, 63 for heating the evaporator chamber can impart a heating power of up to 5 kW. A delivery line 6 for delivering the aqueous solution 45 is also advantageously formed, which delivery line 6 connects the evaporator chamber 24 to a reservoir 20 and in which a delivery means 19 is formed, by means of which a fluid can be delivered through the delivery line 6. According to a further advantageous embodiment of said device, the latter is designed such that, in operation, the temperature of the evaporator chamber 24 is at most 25 °C above and below a mean temperature. It is also advantageous for the evaporator chamber 24 to have, at least in partial regions, means 28 for increasing the wetting capacity of the surface. Said means 28 can in particular comprise a structuring of the inner surface (projections or the like) of the evaporator chamber 24. Also described is a method for providing a gaseous substance mixture comprising at least one of the following substances: a) at least one reducing agent and b) at least one reducing agent precursor. An aqueous solution 45 of at least one reducing agent precursor is delivered into an evaporator chamber 24, with the evaporator chamber 2 4 being heated in such a way that the aqueous solution 45 is completely evaporated to form the gaseous substance mixture. Said method can advantageously be further developed in that the evaporator chamber 24 has a substantially closed volume which has only a first opening 25 for connecting a delivery line 6 for the aqueous solution 45, and a second opening 26 for connecting a metering line 2 for discharging the gaseous substance mixture. Alternatively, the evaporator chamber 24 can encompass a substantially closed volume which has only a first opening 25 for connecting a delivery line 6 for the aqueous solution 45, a second opening 26 for connecting a metering line 2 for discharging the gaseous substance mixture, and a third opening 36 for metering exhaust gas 14. Said method can advantageously be further developed in that the heating is regulated. The evaporator chamber 24 is in particular heated to a mean temperature of 250 to 300 °C. It is also advantageous for the evaporator chamber 24 to be heated to a mean temperature in such a way that the temperature does not at any point of the evaporator chamber 2 4 deviate from a mean temperature by more than +25°C or -25'C. Also described is a device 15 for treating the exhaust gas of an internal combustion engine. Said device 15 comprises a reducing agent solution evaporator 16, a hydrolysis catalytic converter 17, which is connected to the reducing agent solution evaporator 16, for the hydrolysis of in particular urea to form ammonia, and an SCR catalytic converter 18 for the selective catalytic reduction of nitrogen oxides (NOx). The reducing agent solution evaporator 16 comprises an evaporator unit 12 for providing a gaseous substance mixture comprising at least one of the following substances: a) at least one reducing agent precursor and b) a reducing agent. An aqueous solution 45 comprising at least one reducing agent precursor can be evaporated by means of the evaporator unit 12. The SCR catalytic converter 18 is formed in the exhaust line 14, with the reducing agent solution evaporator 16 and the hydrolysis catalytic converter 17 being formed outside, and such that they can be connected to, the exhaust line 14. Said device 15 can advantageously be refined in that a delivery line 6 for connecting the evaporator unit 12 is connected to a reservoir 20 for the aqueous solution 45. Here, the delivery line 6 and the evaporator unit 12 are connected to one another by means of a connecting unit 11. Said connecting unit 11 is at least partially made from a material with a thermal conductivity of less than 10 W/m K (Watt per metre and Kelvin) , preferably of less than 2 W/m K, particularly preferably of less than 1 W/m K, in particular of 0.2 W/m K. It is also advantageous for the connecting unit 11 to be constructed from at least one material comprising at least one of the following materials: a) a ceramic material and b) polytetrafluoroethylene (PTFE). It is also advantageous for the connecting unit 11 to be constructed such that that a temperature gradient of 40 K/itim (Kelvin per millimetre) and greater can be maintained over a length of the connecting unit 11. In addition, the hydrolysis catalytic converter 17 has a heat capacity of at most 60 J/K (Joule per Kelvin). The volume of the hydrolysis catalytic converter 17 is 100 ml or less. The hydrolysis catalytic converter preferably comprises a casing tube, with the casing tube not being incorporated in the determination of the above-specified heat capacity. At least one at least partially structured metallic layer is preferably formed in the casing tube. Preferably provided in the inner region is a free region without the formation of any at least partially structured layers, which free region encompasses at least 20 or even 50% by area of the cross-sectional area of the casing tube. The hydrolysis catalytic converter 17 advantageously has a cell density of less than 600 cpsi (cells per square inch) , preferably of 400 cpsi and less, particularly preferably of 300, 200 or 100 cpsi and less. The hydrolysis catalytic converter 17 is preferably mechanically connected to the exhaust line 14. The hydrolysis catalytic converter 17 is preferably thermally decoupled from the exhaust line 14. According to a further advantageous embodiment of said device 15, at least one bar-shaped heating element 69 is formed, by means of which at least one of the following components can be heated: a) the hydrolysis catalytic converter 17 and b) at least parts of the evaporator chamber 24. It is also advantageous that the temperature of at least one of the following components can be controlled: a) at least parts of the delivery line 6; b) the hydrolysis catalytic converter 17; c) at least parts of the evaporator unit 12; d) a dosing line 21 for metering the generated ammonia to the exhaust system; and e) a metering unit 4 6, by means of which the hydrolysis catalytic converter 17 can be connected to the exhaust gas line 14. It is also advantageous that means 4, 7, 27, 31, 49, 50 for temperature control are formed, which means comprise at least one of the following components: a) a heating wire; b) a Peltier element 8; c) a cooling body 9; d) a bar-shaped heating element 69 and e) a means 63 for burning a fuel. It is also advantageous that at least one of the following components has a coating which catalyses the hydrolysis of urea: a) at least parts of the connecting unit 11; b) at least parts of a metering line 2 for metering the gaseous substance mixture to the hydrolysis catalytic converter 17; c) at least parts of the evaporator unit 12; d) at least parts of a dosing line 21 for metering the generated reducing agent to the exhaust system, and e) at least parts of a metering line 46, by means of which the hydrolysis catalytic converter 17 can be connected to the exhaust line 14. It is also advantageous that a metering unit 4 6 is formed, by means of which the hydrolysis catalytic converter 17 can be flow-connected to an exhaust line 14 of the internal combustion engine. The metering unit 46 comprises in particular a passive mixing means, by means of which the introducible substances can be mixed with the exhaust gas. The mixing means preferably comprise at least one of the following components: a) a guide plate 34 and b) a honeycomb body 52 which is designed such that the exhaust gas 13 can flow through it at least partially at an angle with respect to the main flow direction 45 of the exhaust gas. The honeycomb body 52 advantageously has ducts and apertures which can be traversed by a fluid and connect adjacent ducts to one another. In one advantageous refinement of said device 15, at least one of the following components: a) the metering unit 4 6 and b) the exhaust line 14 is designed such that, in operation, the opening-out region of the metering unit 46 into the exhaust line 14 forms a flow calming zone or dead zone. According to a further advantageous embodiment of said device 15, thermal insulation 72 is formed downstream of the hydrolysis catalytic converter 17. Said thermal insulation 72 is preferably formed directly adjacent to the hydrolysis catalytic converter 17. According to a further advantageous embodiment of said device 15, at least one of the following components has at least one temperature sensor: a) the metering unit 46; b) the hydrolysis catalytic converter 17; c) the SCR catalytic converter 18; d) the evaporator unit 12; e) the metering line 2; f) the evaporator chamber 2 4 and g) a dosing line 21 for metering the generated reducing agent to the exhaust line 14. Said temperature sensor can preferably be connected to a power supply, so that it can also be used for heating the corresponding component a) to g). According to a further advantageous embodiment of said device 15, a delivery means 19 is formed, by means of which the aqueous solution 45 can be delivered from a reservoir to the evaporator unit 12. The delivery means 19 preferably comprises at least one pump, preferably a delivery pump. According to one advantageous embodiment, the pump can build up a delivery pressure which is greater than the highest possible exhaust gas pressure on the metering unit 4 6 and/or on the dosing line 21 during operation of the internal combustion engine. According to a further advantageous embodiment of the device 15, at least one valve for dosing the aqueous solution 4 5 is formed between the delivery means 19 and the evaporator unit 12. Also to be described here is an advantageous method for treating the exhaust gas of an internal combustion engine. The method comprises at least the following steps: a) providing at least one of the following substances: al) reducing agent and a2) gaseous substance mixture comprising at least one reducing agent precursor; b) hydrolysis of the at least one reducing agent precursor, with a reducing agent substance mixture 35 being obtained; c) subjecting an SCR catalytic converter 18 to the reducing agent substance mixture 35 and the exhaust gas 14 for the at least partial selective catalytic reduction of nitrogen oxides (NOx) contained in the exhaust gas. A mixture of the reducing agent substance mixture 35 with at least parts of the exhaust gas 14 takes place after step b). Said method can advantageously be refined in that, in step a), an evaporation of an aqueous solution 45 comprising at least one reducing agent precursor takes place in an evaporator unit 12. It is also preferable that step b) at least partially takes place in a hydrolysis catalytic converter 17. According to a further advantageous embodiment of said method, the temperature of at least one of the following components is regulated: a) at least parts of the evaporator unit 12; b) the hydrolysis catalytic converter 17; c) a delivery line 6 for delivering the aqueous solution 45; d) a metering line 2 for metering the gaseous substance mixture to the hydrolysis catalytic converter 17; e) a dosing line 21 for metering the generated reducing agent to the exhaust system; and f) a metering unit 46, by means of which the hydrolysis catalytic converter 17 can be flow-connected to an exhaust gas line 14 of the internal combustion engine. Here, said connection is formed upstream of the SCR catalytic converter 18. It is also advantageous that the temperature of at least one of the following components is controlled: a) at least parts of the evaporator unit 12; b) the hydrolysis catalytic converter 17; c) a delivery line 6 for delivering the aqueous solution 45 to an evaporator unit 12; d) a metering line 2 for metering the gaseous substance mixture to the hydrolysis catalytic converter 17; e) a dosing line 21 for metering the generated reducing agent to the exhaust system; and f) a metering unit 46, by means of which the hydrolysis catalytic converter 17 can be flow-connected to an exhaust gas line 14 of the internal combustion engine. A further embodiment of said method comprises the delivery of the aqueous solution 45 through a delivery line 6 to the reducing agent solution evaporator 16. It is advantageous here if the aqueous solution 45 can be returned through the delivery line 6. According to a further advantageous embodiment of said method, up to 2.5 ml of aqueous solution 45 are evaporated within one second. According to a further advantageous embodiment of said method, the temperature of at least one of the following components is determined before the start of a temperature control measure: a) the hydrolysis catalytic converter 17; b) the evaporator unit 12; c) a dosing line 21 for metering the generated reducing agent to the exhaust line 14; and d) a metering unit 4 6, by means of which the hydrolysis catalytic converter 17 can be flow-connected to the exhaust line 14 of the internal combustion engine, and is aligned with at least one further temperature of another component. According to a further advantageous embodiment of said method, the evaporation of the aqueous solution 45 takes place only if the temperature alignment yields that the determined temperature level and the temperature of the other component differ at most by a predefinable difference value. The device 1 according to the invention and the method according to the invention advantageously permit the complete evaporation of an aqueous solution comprising urea, and subsequent hydrolysis to form a substance mixture comprising ammonia. Said substance mixture is advantageously metered as a reducing agent into an SCR catalytic converter 18. The fact that the evaporation is carried out outside the exhaust system permits the formation of considerably smaller hydrolysis catalytic converters 17, so that the device according to the invention is space-saving and cost-saving in comparison with conventional devices for providing a reducing agent for the selective catalytic reduction of nitrogen oxides. List of reference symbols 1 Device for providing a gaseous substance mixture 2 Metering line 3 Dispensing opening 4 Means for heating the metering line 5 Measuring sensor 6 Delivery line 7 Means for temperature control 8 Peltier element 9 Cooling body 10 Electrical terminal 11 Connecting unit 12 Evaporator unit 13 Exhaust gas 14 Exhaust line 15 Device for treating the exhaust gas of an internal combustion engine 16 Reducing agent solution evaporator 17 Hydrolysis catalytic converter 18 SCR catalytic converter 19 Delivery means 20 Reservoir 21 Dosing line 22 Dosing opening 23 Mixing means 2 4 Evaporator chamber 25 First opening 2 6 Second opening 2 7 Means for heating the evaporator chamber 28 Structure 29 Casing of the evaporator unit 30 Heat conductor terminal 31 Means for temperature control of the hydrolysis catalytic converter 32 Casing of the hydrolysis catalytic converter 33 Connecting means 34 Conducting plate 35 Reducing agent substance mixture 3 6 Third opening 37 Guide structure 38 Heat conductor 39 First temperature measuring sensor 40 Connecting element 41 First heat conductor terminal 42 Second heat conductor terminal 43 Second temperature measuring sensor 44 Second connecting element 45 Aqueous solution 4 6 Metering unit 47 Third temperature measuring sensor 48 Fourth temperature measuring sensor 4 9 Temperature control means 50 Metering temperature control means 51 Control unit 52 Honeycomb body 53 Mixing means 54 Main flow direction 55 Cutout 56 Perforation 57 Length 58 First exhaust branch 59 Second exhaust branch 60 Means for flow guidance 61 Opening-out point 62 Nozzle 63 Means for burning hydrocarbons 64 Means for depositing droplets 65 Line 66 Impact plate 67 Deflection 68 Housing 69 Bar-shaped heating element 70 Electrical terminal 71 Connecting means 72 Thermal insulation 73 Heat shield 74 Air gap insulation 75 Outer housing 76 Inner housing 77 Valve 78 Control terminal 79 Opening-out region 8 0 Aperture 81 Temperature sensor 82 Honeycomb body 83 Smooth metallic layer 84 Corrugated metallic layer 85 Casing tube 8 6 Duct 87 Annular honeycomb body 88 Layer 8 9 Smooth region 90 Corrugated region 91 Outer casing tube 92 Inner casing tube Claims 1. Device (1) for providing a gaseous substance mixture comprising at least one of the following substances: a) at least one reducing agent and b) at least one reducing agent precursor, with a reservoir (20) for an aqueous solution (45) comprising at least one reducing agent precursor being formed, from which reservoir (20) aqueous solution (45) can be delivered into at least one metering line (2) with a dispensing opening (3) by a delivery means (19), characterized in that means (4) for heating the metering line (2) are formed, by means of which the at least one metering line (2) can be heated above a critical temperature which is greater than the boiling temperature of water. 2. Device according to claim 1, in which the inner surface of the metering line (2) comprises a surface roughness Rz of 8 to 12 microns. 3. Device according to one of the preceding claims, in which the metering line (2) is made of a material with a coefficient of thermal conduction of at least 200 W/m K (Watt per Meter and Kelvin). 4. Device according to one of the preceding claims, in which the metering line (2) has at least one change of direction of at least 90°. 5. Device according to one of the preceding claims, in which the means (4) for heating comprise at least one of the following elements: a) an electrical resistance heater;. b) heat transfer means for utilizing the waste heat of at least one other component; c) at least one Peltier element and d) a means for burning a fuel. 6. Device according to one of the preceding claims, in which the device (1) is designed such that, in operation, the temperature across the length of the metering line (2) is at most 25 degrees Celsius above and below a mean temperature. 7. Device according to one of the preceding claims, in which the metering line (2) is formed from a material comprising aluminium. 8. Device according to one of the preceding claims, in which the metering line has a heat capacity of at least 150 J/K (Joule per Kelvin). 9. Device according to one of the preceding claims, in which the metering line (2) is at least partially provided with a coating which catalyses the hydrolysis of a reducing agent precursor to form a reducing agent. 10. Device according to one of the preceding claims, in which the metering line (2) and a hydrolysis catalytic converter (17) are formed in a common heatable body. 11. Method for providing a gaseous substance mixture comprising at least one of the following substances: a) at least one reducing agent and b) at least one reducing agent precursor, with an aqueous solution (45) of at least one reducing agent precursor being delivered from a reservoir (20) into a metering line (2), characterized in that the metering line (2) is heated in such a way that the aqueous solution (45) is completely evaporated to form the gaseous substance mixture. 12. Method according to Claim 11, in which the temperatures in the metering line (2) are at a mean temperature between 380°C and 450'C. 13. Method according to Claim 11 or 12, in which the temperature along a length of the metering line (2) is at most 25 degrees Celsius above or below a mean temperature. 14 Method according to one of claims 11 to 13, in which the metering line has at least one change of direction of at least 90°. 15. Method according to one of Claims 11 to 14, in which the metering line (2) is heated to a second temperature which is higher than the critical temperature at which complete evaporation of the aqueous solution (45) takes place. 16. Method according to one of Claims 11 to 15, in which the heating of the metering line (2) is carried out by means of an electrical resistance heater, with the resistance of said, resistance heater being determined before the start of heating, and the heating of the metering line (2) taking place as a function of the determined resistance. |
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| Patent Number | 258842 | ||||||||||||||||||
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| Indian Patent Application Number | 8770/DELNP/2008 | ||||||||||||||||||
| PG Journal Number | 07/2014 | ||||||||||||||||||
| Publication Date | 14-Feb-2014 | ||||||||||||||||||
| Grant Date | 10-Feb-2014 | ||||||||||||||||||
| Date of Filing | 17-Oct-2008 | ||||||||||||||||||
| Name of Patentee | EMITEC GESELLSCHAFT FUR EMISSIONSTECHNOLOGIE MBH | ||||||||||||||||||
| Applicant Address | HAUPTSTRASSE 128, 53797 LOHMAR GERMANY | ||||||||||||||||||
Inventors:
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| PCT International Classification Number | B01D 53/94 | ||||||||||||||||||
| PCT International Application Number | PCT/EP2007/004361 | ||||||||||||||||||
| PCT International Filing date | 2007-05-16 | ||||||||||||||||||
PCT Conventions:
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