Method and apparatus for generating a gas stream with a defined amount of nitrogen oxides

Abstract

The invention relates to a method for generating a gas stream (3) containing a defined amount of nitrogen oxides, comprising the steps of: providing an initial gas stream (7); introducing a defined amount of ammonia into the initial gas stream (7); and generating the gas stream (3) by converting the ammonia to nitrogen oxides. The invention further relates to a device (2) for generating a gas stream (3) containing a defined amount of nitrogen oxides and to an exhaust gas purification test system (1).

Description

[0001] The invention relates to a method and a device for generating a gas stream containing a defined amount of nitrogen oxides. The invention further relates to an exhaust gas purification test system.

[0002] From DE 10 2021 001 464 A1 a method for determining an operating strategy for a catalyst and a test bench for carrying out the method are known.

[0003] The inventive method for generating a gas stream with a defined amount of nitrogen oxides comprises the following steps: - Providing an output gas stream; - Introducing a defined amount of ammonia into the initial gas stream; and - Generating the gas stream by converting the ammonia to nitrogen oxides.

[0004] Because the nitrogen oxides in the initial gas stream are generated by converting the introduced ammonia, the amount of nitrogen oxides in the gas stream can be adjusted very precisely.

[0005] Furthermore, generating nitrogen oxides from ammonia in the initial gas stream is very resource-efficient and cost-effective compared to providing and adding gaseous nitrogen oxides to the initial gas stream. The use of gas cylinders to enrich the initial gas stream with nitrogen oxides is unnecessary.

[0006] The defined quantity of nitrogen oxides in the gas stream can, for example, be specified or adjusted in the form of a concentration. In simplified terms, the method according to the invention can therefore generate a gas stream with a specific mass concentration, volume concentration, and / or preferably molar concentration of nitrogen oxides.

[0007] The gas stream generated by the method according to the invention can, for example, be used to test exhaust gas purification systems and / or exhaust gas aftertreatment systems. Of course, this does not preclude other possible applications.

[0008] In one variation of the process, ammonia is introduced into the initial gas stream by first introducing urea into the stream, where it is converted into ammonia. Urea is available in large quantities and, as a solid or dissolved in a liquid, is particularly easy to handle compared to gaseous substances.

[0009] Preferably, the urea is introduced into the initial gas stream by injecting a urea-water solution into the initial gas stream. In addition to the urea, water can also be introduced into the initial gas stream. The water can then, for example, be converted to ammonia and carbon dioxide in a reaction with the urea.

[0010] In principle, the process can also take place without the additional introduction of water, for example by converting water already present in the initial gas stream into ammonia and carbon dioxide with the urea.

[0011] In another variation of the process, the conversion of urea to ammonia and / or the conversion of ammonia to nitrogen oxides is supported by a catalyst. This makes the process particularly efficient and avoids or at least reduces undesirable reaction byproducts, such as nitrous oxide.

[0012] Alternatively or additionally, the conversion of urea to ammonia and / or the conversion of ammonia to nitrogen oxides can also be achieved by controlling the temperature of the initial gas stream and / or the catalyst(s) to a predetermined temperature, for example, a temperature above 500°C, preferably between 600°C and 700°C. It has been shown that this further increases the efficiency of the process and thus provides a gas stream with a particularly low amount of undesirable byproducts.

[0013] Furthermore, the system can be designed to regulate the amount of ammonia introduced into the initial gas stream. For example, the nitrogen oxide concentration in the gas stream can be measured, and the amount of ammonia and / or urea added to the initial gas stream can be adjusted based on the measurement. This allows the amount of nitrogen oxide in the gas stream to be set with particular precision and / or maintained at a desired value.

[0014] Of course, the amount of nitrogen oxide in the gas stream can also be varied over time, for example by specifically changing the addition of ammonia or urea to the initial gas stream.

[0015] The device according to the invention for generating a gas stream with a defined amount of nitrogen oxides comprises a gas stream generator for generating an initial gas stream, a nozzle configured to introduce ammonia or urea into the initial gas stream, a metering unit for adjusting an introduction rate of the nozzle, and a reaction section configured to support a chemical reaction in the initial gas stream by which nitrogen oxides are generated from the introduced ammonia.

[0016] The advantages mentioned for the method according to the invention apply in the same way to the device according to the invention.

[0017] Preferably, the device is designed and configured to carry out a method according to the invention for generating a gas stream with a defined amount of nitrogen oxides.

[0018] In one embodiment, the device comprises at least one catalyst exposed to the initial gas stream and configured to assist a chemical reaction by which urea is converted to ammonia and / or ammonia to nitrogen oxides.

[0019] The catalyst is, for example, located in the reaction section of the device.

[0020] It is also possible to provide two or more catalysts, for example one that supports a chemical reaction that converts urea to ammonia and another that supports a chemical reaction that produces nitrogen oxides from ammonia.

[0021] At least one catalyst contains, for example, platinum and / or copper zeolite and / or iron zeolite and / or vanadium pentoxide and / or cerium and / or barium. These materials have proven particularly effective in supporting the chemical reactions relevant to the process.

[0022] The exhaust gas purification test system according to the invention comprises a device according to the invention for generating a gas flow with a defined amount of nitrogen oxides and a holder for holding an exhaust gas purification system to be tested.

[0023] The exhaust gas purification test system allows for particularly resource-efficient testing of exhaust gas purification systems. The gas flow required for testing can be supplied by the device and fed to the exhaust gas purification system under test. This eliminates the need for gas cylinders containing gaseous nitrogen oxides to generate the gas flow for testing the exhaust gas purification system.

[0024] Preferred embodiments are explained in more detail with reference to the following figures. These show - Fig. 1 a schematic representation of an embodiment of an exhaust gas purification test system according to the invention; and - Fig. 2 a schematic representation of a time course of a nitrogen oxide concentration of a gas stream which was generated with an embodiment of a method according to the invention.

[0025] The in Fig. The exhaust gas purification test system 1 shown comprises a device 2 according to the invention for generating a gas flow 3 with a defined quantity of nitrogen oxides and a holder 4 for holding an exhaust gas purification system 5 to be tested.

[0026] In Fig. In 1, an exhaust gas purification system 5 to be tested is inserted into the holder 4. The exhaust gas purification system 5 to be tested is arranged such that it is exposed to gas flows 3 generated by the device 2.

[0027] The device 2 comprises a gas generator 6 for generating an output gas stream 7. For example, the gas generator 6 is a burner that burns natural gas to generate the output gas stream 7.

[0028] Furthermore, the device 2 comprises a nozzle 8 designed to introduce ammonia or urea into the output gas stream 7, and a metering unit 9 for adjusting the injection rate of the nozzle 8.

[0029] The device 2 also includes a reaction section 10 which is configured to assist a chemical reaction in the initial gas stream 7, by which nitrogen oxides are produced from ammonia.

[0030] In the exemplary embodiment, the reaction section 10 of the device 2 comprises a first catalyst 11 which is exposed to the initial gas stream 7 and which is configured to assist a chemical reaction by which urea is converted to ammonia.

[0031] The device 2 further comprises a second catalyst 12, which is exposed to the output gas stream 7 downstream of the first catalyst 11 and which is configured to assist a chemical reaction by which ammonia is converted to nitrogen oxides.

[0032] At least one of the catalysts 11, 12 may contain platinum and / or copper zeolite and / or iron zeolite and / or vanadium pentoxide and / or cerium and / or barium and / or mixtures of the aforementioned materials.

[0033] In the exemplary embodiment, the device 2 further comprises a temperature controller 13 for setting a temperature of the catalysts 11, 12 and a sensor 14 for measuring a nitrogen oxide concentration in the gas stream 3.

[0034] Furthermore, the device 2 includes a cooling unit 15 for cooling the gas stream 3, which is arranged downstream of the catalysts 11, 12.

[0035] The in Fig. The device 2 shown in Figure 1 is designed and configured to carry out a method according to the invention for generating a gas stream 3 with a defined amount of nitrogen oxides.

[0036] In a first step of the process, the gas generator 6 provides an initial gas stream 7 by burning natural gas.

[0037] In the exemplary embodiment, the mass and / or volume flow rate of the output gas stream 7 can be adapted to the exhaust gas purification system 5 under test. For example, if an exhaust gas purification system 5 of a truck is to be examined, an output gas stream 7 with a higher mass and / or volume flow rate can be provided by means of the gas flow generator 6 than for testing a passenger car exhaust gas purification system 5.

[0038] In a second step of the process, a defined amount of ammonia is introduced into the initial gas stream 7.

[0039] For this purpose, a urea-water solution is injected into the output gas stream 7 via nozzle 8. Thus, both urea and water in liquid form are supplied to the output gas stream 7. The urea is then converted into ammonia in the output gas stream 7, for example by reacting with the supplied water, producing ammonia and carbon dioxide.

[0040] Dies ist selbstverständlich nicht einschränkend zu verstehen. Es ist auch denkbar, dass mittels der Düse 8 Harnstoffpulver in den Ausgangsgasstrom 7 eingebracht wird, das dann mit im Ausgangsgasstrom 7 bereits vorhandenem Wasser zu Ammoniak reagiert.

[0041] The first catalyst 11 supports the chemical reaction by which the urea in the initial gas stream 7 is converted to ammonia.

[0042] Alternatively, ammonia can be introduced directly into the output gas stream 7 via the nozzle 8. In this case, the first catalyst 11 can be omitted.

[0043] In a third step of the process, gas stream 3 containing a defined amount of nitrogen oxides is generated by converting the ammonia in the initial gas stream 7 into nitrogen oxides. For example, this can be achieved through a chemical reaction of the ammonia with oxygen present in the initial gas stream 7. In simplified terms, the initial gas stream 7 is enriched with ammonia as a result of the chemical reactions taking place within it, transforming it into gas stream 3 containing the defined amount of nitrogen oxides.

[0044] Optionally, the temperature of the output gas stream 7 and / or at least one of the catalysts 11 12 can also be controlled by means of the temperature controller 13. For example, the temperature can be set to a value above 500°C, preferably between 600°C and 700°C, to support the chemical reaction of urea to ammonia and / or of ammonia to nitrogen oxides. It has been shown that this increases the efficiency of the process and reduces the amount of undesirable byproducts in the gas stream 3.

[0045] Nach dem Durchlaufen des Reaktionsabschnittes 10 kann der Gasstrom 3 mittels der Kühleinheit 15 gekühlt werden, um eine gewünschte Temperatur einzustellen, bevor der Gasstrom 3 dann dem zu testenden Abgasreinigungssystem 5 zugeführt wird.

[0046] In this embodiment, the amount of ammonia introduced into the outlet gas stream 7 is also controlled. For this purpose, the nitrogen oxide concentration in the gas stream 3 is determined by means of the sensor 14, and the injection rate of the nozzle 8 is adjusted accordingly using the metering unit 9. If the measured nitrogen oxide concentration is too low, the injection rate of urea or ammonia into the outlet gas stream 7 can be increased by means of the nozzle 8 until a corresponding target value for the measured nitrogen oxide concentration is reached. This allows the amount of nitrogen oxide in the gas stream 3 to be set very precisely and changed as needed.

[0047] Fig. Figure 2 shows a schematic representation of a time course 16 of a nitrogen oxide concentration of a gas stream 3 produced by means of the inventive method.

[0048] As can be seen in the figure, the defined quantity of nitrogen oxides in the gas stream 3 can be changed, for example by increasing or decreasing the injection rate of the nozzle 8 using the metering unit 9. In this way, different test conditions for the exhaust gas purification systems 5 under test can be set quickly and easily. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2021 001 464 A1

[0002]

Claims

[1] Method for generating a gas stream (3) containing a defined amount of nitrogen oxides, comprising the steps: - Providing an output gas stream (7); - Introducing a defined amount of ammonia into the initial gas stream (7); - Generating the gas stream (3) by converting the ammonia to nitrogen oxides. [2] Method according to claim 1, wherein the ammonia is introduced into the initial gas stream (7) by introducing urea into the initial gas stream (7) and converting it to ammonia in the initial gas stream (7). [3] Method according to claim 2, wherein the urea is introduced into the initial gas stream (7) by injecting a urea-water solution into the initial gas stream (7). [4] Method according to claim 2 or 3, wherein the conversion of the urea to ammonia and / or the conversion of the ammonia to nitrogen oxides is supported by a catalyst (11, 12). [5] Method according to one of the preceding claims, wherein the quantity introduced is controlled when introducing the ammonia into the initial gas stream (7). [6] Device for generating a gas stream (3) containing a defined amount of nitrogen oxides, comprising - a gas generator (6) for generating an output gas stream (7), - a nozzle (8) designed to introduce ammonia or urea into the output gas stream (7), - a metering unit (9) for adjusting the injection rate of the nozzle (8), and - a reaction section (10) designed to assist a chemical reaction in the initial gas stream (7) by which nitrogen oxides are generated from ammonia. [7] Device according to claim 6, configured and equipped to carry out a method for generating a gas stream (3) with a defined amount of nitrogen oxides according to any one of claims 1 to 5. [8] Device according to claim 6 or 7, further comprising at least one catalyst (11, 12) exposed to an initial gas stream (7) generated by the gas stream generator (6) and configured to assist a chemical reaction by which urea is converted to ammonia and / or ammonia to nitrogen oxides. [9] Device according to claim 8, wherein the catalyst (11, 12) contains platinum and / or copper zeolite and / or iron zeolite and / or vanadium pentoxide and / or cerium and / or barium. [10] Exhaust gas purification test system comprising a device (2) according to one of claims 6 to 9 for generating a gas stream (3) with a defined amount of nitrogen oxides and a holder (4) for holding an exhaust gas purification system (5) to be tested.

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