METHOD AND APPARATUS FOR GENERATING A GAS STREAM WITH A DEFINED AMOUNT OF NITROGEN OXIDES

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of DE 102024128595.8, filed on October 2, 2024, the disclosure of which is incorporated herein by reference.

FIELD

The present disclosure relates to a method and apparatus for generating a gas stream with a defined amount of nitrogen oxides. The invention also relates to an exhaust gas purification test facility.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

DE 10 2021 001 464 A1 discloses a method for establishing an operating strategy for a catalyst and a test bench for carrying out the method.

SUMMARY

This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all of its features.

The method for generating a gas stream with a defined amount of nitrogen oxides according to the present disclosure includes: providing an initial gas stream; introducing a defined amount of ammonia into the initial gas stream; and generating the gas stream by converting the ammonia into nitrogen oxides.

By generating the nitrogen oxides in the initial gas stream by converting the introduced ammonia, the amount of nitrogen oxides in the gas stream can be adjusted very precisely.

The generation of nitrogen oxides from ammonia in the initial gas stream is also very resource-efficient and cost-effective compared to supplying and adding gaseous nitrogen oxides to the initial gas stream. There is no need to use gas containers to enrich the initial gas stream with nitrogen oxides.

The defined amount of nitrogen oxides in the gas stream can be specified or set in the form of a concentration, for example. Put simply, the method according to the invention can be used to generate a gas stream with a specific mass concentration, volume concentration, and/or, preferably, molar concentration of nitrogen oxides.

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

In one variant of the method, the ammonia is introduced into the initial gas stream by introducing urea into the initial gas stream and converting it into ammonia in the initial gas stream. Urea is available in large quantities and, compared to gaseous substances, is particularly easy to handle as a solid or when dissolved in a liquid.

Preferably, the urea is introduced into the initial gas stream by injecting an aqueous urea solution into the initial gas stream. This means that, in addition to urea, water can also be introduced into the feed gas stream. The water can then be converted into ammonia and carbon dioxide, e.g. in a reaction with the urea.

In principle, however, the process can also be carried out without the additional introduction of water, for example by converting water already present in the initial gas stream with the urea to ammonia and carbon dioxide.

In another variant of the process, converting of the urea to ammonia and/or converting of ammonia to nitrogen oxides is supported by a catalyst. This makes the process particularly efficient and undesirable reaction by-products, such as nitrous oxide, are avoided or at least reduced.

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 to a temperature above 500°C, preferably between 600°C and 700°C. It has been shown that this further increases the efficiency of the method and thus a gas stream with a particularly low amount of undesirable by-products can be provided.

Furthermore, it may be provided that an introduction quantity is controlled when introducing the ammonia into the initial gas stream. For example, a nitrogen oxide concentration in the gas stream can be measured and, based on the measurement result, a quantity of ammonia and/or urea fed to the initial gas stream can be adjusted based on the measurement result. This allows the amount of nitrogen oxide in the gas stream to be adjusted with particular precision and/or maintained at a desired value.

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.

The apparatus for generating a gas stream with a defined amount of nitrogen oxides according to the present disclosure includes a gas stream generator for generating an initial gas stream, a nozzle designed to introduce ammonia or urea into the initial gas stream, a metering unit for adjusting the introduction rate of the nozzle, and a reaction section designed to support a chemical reaction in the initial gas flow, whereby nitrogen oxides are generated from the introduced ammonia.

The advantages mentioned for the method according to the present disclosure apply equally to the apparatus according to the present disclosure.

Preferably, the apparatus is designed and set up to carry out the method for generating a gas stream with a defined amount of nitrogen oxides according to the present disclosure.

In one embodiment, the apparatus comprises at least one catalyst that is exposed to the initial gas stream and is designed to support a chemical reaction in which urea is converted to ammonia and/or ammonia is converted to nitrogen oxides.

The catalyst is arranged, for example, in the reaction section of the apparatus.

Two or more catalysts may also be provided, for example, one that supports a chemical reaction that converts urea to ammonia and another that supports a chemical reaction in which nitrogen oxides are produced from ammonia.

The 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 to be particularly effective in supporting the chemical reactions relevant to the method.

The exhaust gas purification test facility according to the invention comprises an apparatus for generating a gas stream with a defined amount of nitrogen oxides according to the invention and a holder for holding an exhaust gas purification system to be tested.

The exhaust gas purification test facility allows exhaust gas purification systems to be tested in a particularly resource-efficient manner. The gas stream required for testing can be provided by the apparatus and fed to the exhaust gas purification system to be tested. This eliminates the need to use gas containers containing gaseous nitrogen oxides to generate the gas stream for testing the exhaust gas purification system.

Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which:

FIG. 1 shows a schematic representation of an exemplary embodiment of an exhaust gas purification test facility according to the invention; and

FIG. 2 shows a schematic representation of a temporal trajectory of a nitrogen oxide concentration of a gas stream, which was generated using an exemplary embodiment of the method according to the invention.

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

The exhaust gas purification test facility 1 shown in FIG. 1 comprises an apparatus 2 for generating a gas flow 3 with a defined amount of nitrogen oxides and a holder 4 for holding an exhaust gas purification system 5 to be tested.

In FIG. 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 in such a way that it is exposed to gas streams 3 generated by the apparatus 2.

The apparatus 2 comprises a gas stream generator 6 for generating an initial gas stream 7. For example, the gas stream generator 6 is a burner that burns natural gas to generate the initial gas stream 7.

Furthermore, the apparatus 2 comprises a nozzle 8 which is designed to introduce ammonia or urea into the initial gas stream 7, and a metering unit 9 for adjusting an introduction rate of the nozzle 8.

The apparatus 2 also has a reaction section 10 designed to support a chemical reaction in the initial gas stream 7, through which nitrogen oxides are produced from ammonia.

In the embodiment, the reaction section 10 of the apparatus 2 comprises a first catalyst 11 that is exposed to the initial gas stream 7 and is designed to support a chemical reaction that converts urea into ammonia.

The apparatus 2 further comprises a second catalyst 12, which is exposed to the initial gas stream 7 downstream of the first catalyst 11 and which is designed to support a chemical reaction that converts ammonia into nitrogen oxides.

At least one of the catalysts 11,12 may comprise 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.

In the embodiment, the apparatus 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.

Additionally, the apparatus 2 comprises a cooling unit 15 for cooling the gas stream 3, which is arranged downstream of the catalysts 11,12.

The apparatus 2 shown in FIG. 1 is designed and configured to carry out a method for generating a gas stream 3 with a defined amount of nitrogen oxides according to the invention.

In a first step of the method, the gas stream generator 6 provides an initial gas stream 7 by burning natural gas.

In the exemplary embodiment, the mass and/or volume flow rate of the initial gas stream 7 is adaptable to the exhaust gas purification system 5 to be tested. If, for example, an exhaust gas purification system 5 of a truck is to be tested, the gas stream generator 6 can be used to provide an initial gas stream 7 with a higher mass and/or volume flow rate than for testing an exhaust gas purification system 5 of a passenger car.

In a second step of the method, a defined amount of ammonia is introduced into the initial gas stream 7.

For this purpose, an aqueous urea solution is injected into the initial gas stream 7 by means of the nozzle 8. Both urea and water are thus supplied to the initial gas stream 7 in liquid form. The urea is then converted into ammonia in the initial gas stream 7, for example by reacting with the supplied water, thereby producing ammonia and carbon dioxide.

This is not to be understood as restrictive, of course. It is also conceivable that urea powder is introduced into the initial gas stream 7 by means of the nozzle 8, which then reacts with the water already present in the initial gas stream 7 to form ammonia.

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

Alternatively, ammonia can also be introduced directly into the initial gas stream 7 by means of nozzle 8. In this case, the first catalyst 11 is not required.

In a third step of the method, gas stream 3 is produced with a defined amount of nitrogen oxides by converting the ammonia in the initial gas stream 7 into nitrogen oxides. This can occur, for example, by way of a chemical reaction of the ammonia with oxygen present in the initial gas stream 7. In simple terms, the initial gas stream 7 becomes the gas stream 3 with a defined amount of nitrogen oxides by way of being enriched with ammonia and as a result of the following chemical reactions taking place in it.

Optionally, the temperature of the initial gas stream 7 and/or at least one of the catalysts 11,12 can 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, in order to support the chemical reaction from urea to ammonia and/or from ammonia to nitrogen oxides. It has been shown that this increases the efficiency of the method and reduces the amount of undesirable by-products in the gas stream 3.

After passing through the reaction section 10, the gas stream 3 can be cooled by means of the cooling unit 15 to set a desired temperature before the gas stream 3 is then fed to the exhaust gas purification system 5 to be tested.

Furthermore, in the exemplary embodiment, the introduction quantity is controlled when introducing the ammonia into the initial gas stream 7. For this purpose, the nitrogen oxide concentration in gas stream 3 is determined by sensor 14 and, based on this, the introduction rate of nozzle 8 is adjusted by metering unit 9. If the measured nitrogen oxide concentration is too low, the injection rate of urea or ammonia into the initial gas stream 7 can be increased by nozzle 8 until a corresponding setpoint value for the measured nitrogen oxide concentration is reached. This allows the amount of nitrogen oxide in the gas stream 3 to be adjusted very precisely and to be changed as required.

FIG. 2 shows a schematic representation of the temporal trajectory 16 of the nitrogen oxide concentration of a gas stream 3 generated using the method according to the invention.

As can be seen from the figure, the defined amount of nitrogen oxides in the gas stream 3 can be changed, for example by increasing or decreasing the introduction rate of the nozzle 8 by means of the metering unit 9. In this way, various test conditions for exhaust gas purification systems 5 to be tested can be quickly and easily set up.

Unless otherwise expressly indicated herein, all numerical values indicating mechanical/thermal properties, compositional percentages, dimensions and/or tolerances, or other characteristics are to be understood as modified by the word “about” or "approximately" in describing the scope of the present disclosure. This modification is desired for various reasons including industrial practice, material, manufacturing, and assembly tolerances, and testing capability.

As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.”

The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.