DEVICE AND METHOD FOR THE PARTIAL CONVERSION OF AMMONIA INTO A HYDROGEN-CONTAINING GAS MIXTURE

Description

FIELD OF APPLICATION AND STATE OF THE ART

[0001] The invention relates to a device for the partial conversion of ammonia into a combustible, hydrogen-containing gas mixture.

[0002] In the long term, at least a portion of the fossil fuels currently used will be replaced by so-called green hydrogen. The production and consumption of green hydrogen will be separated both locally and spatially. Since handling, transporting, and storing ammonia, consisting of hydrogen and nitrogen, is significantly easier than handling hydrogen, ammonia is increasingly being used as a carbon-free energy source for transporting green hydrogen. For this purpose, ammonia can be transported cost-effectively over long distances by ship or pipeline.

[0003] However, due to its poor ignitability, ammonia cannot be used directly as a fuel for thermal processes, engines, gas turbines, or other consumers. Therefore, a known use is its reconversion to hydrogen.

[0004] For the reconversion to hydrogen, devices for splitting ammonia (commonly referred to as ammonia crackers) are known. These split ammonia at approximately 850°C into 75% H2 and 25% N2. Ammonia crackers, for example, use a catalyst for this purpose. The resulting cracked gas can either be directly converted into electricity in fuel cells or processed into hydrogen, for example, for fueling bus fleets, trucks, and ships. However, the energy required to completely convert the ammonia into hydrogen and nitrogen is generally too high to use the resulting hydrogen as a fuel.

[0005] EP 3 878 806 A1 discloses a process for the partial conversion of ammonia into a combustible, hydrogen-containing gas mixture, which can be used as a fuel for heat generation or in a heat engine. For this purpose, an ammonia-air mixture is reacted in a catalytic reactor in such a way that part of the ammonia is oxidized to water and nitrogen, while the majority of the ammonia is split into hydrogen and nitrogen. The energy required for the ammonia splitting is obtained from the oxidation reaction. The oxidation takes place on an oxidation catalyst, and the subsequent splitting of the ammonia takes place on a suitable splitting catalyst. The process is said to make it possible to produce a product gas with a volume fraction of up to approximately 50% hydrogen and—with additional separation of water vapor and the use of oxygen instead of air—up to 70% hydrogen.

[0006] CN 217 458 828 U discloses an apparatus and method for fissioning ammonia. Ammonia is vaporized in an evaporator and fed into a fission reactor. The fission gas, containing hydrogen, is fed primarily to a hydrogen consumer. A portion of the hydrogen is fed to a burner via a regulating valve and combusted with air. The regulating valve is controlled by a control unit. The burner exhaust outlet is connected to a heat supply inlet of the fission reactor. The fission reactor further comprises an electric heater for start-up operation. TASK AND SOLUTION

[0007] It is an object of the invention to provide a compact device and a method for the partial conversion of ammonia into a combustible, hydrogen-containing gas mixture which can be used as a fuel for heat generation or in a heat engine, which has a high degree of efficiency.

[0008] According to a first aspect, a device for the partial conversion of ammonia into a combustible, hydrogen-containing gas mixture with an ammonia content is provided, comprising a reactor and a combustion chamber with a supply connection for air or oxygen, wherein the reactor is designed to partially convert ammonia supplied as starting material at a reaction temperature of approximately 500°C to approximately900°C into hydrogen and nitrogen to produce the gas mixture, wherein the combustion chamber is connected to an outlet of the reactor in such a way that a part of the gas mixture flowing out of the reactor can be fed to the combustion chamber, and wherein the combustion chamber is designed to oxidize the part of the fed gas mixture in the combustion chamber, and wherein an outlet of the combustion chamber opens into a feed to the reactor for an ammonia fed as a starting material, so that hot exhaust gas from the combustion chamber upstream of the reactor can be mixed with the ammonia fed as a starting material to form a hot mixture and the hot mixture can be fed to the reactor.

[0009] In other words, a portion of the gas mixture produced by the reactor (also referred to as fission gas) is combusted to use the resulting hot exhaust gas as an energy source for the endothermic reaction taking place in the reactor to split the ammonia supplied as the starting material. The hot exhaust gas produced during combustion is not vented to the environment but is also fed into the reactor and serves as an energy source for the partial splitting of the ammonia taking place in the reactor, thereby cooling the hot mixture supplied. Due to the partial splitting of the ammonia taking place in the reactor, for example, the hot mixture supplied is cooled by approximately 160 K.

[0010] The cracked gas produced can be used, for example, to refuel bus fleets, trucks and ships.

[0011] By harnessing the energy from the combustion of a portion of the produced gas mixture, indirect heating of the reactor, which is particularly costly at high power levels in existing plants and / or processes, is no longer necessary for the decomposition of the ammonia supplied as a feedstock. With appropriate process control, efficiencies of at least 90%, and optimally at least 95%, can be achieved in the device.

[0012] In some embodiments, the reactor is a catalytic reactor, for example a reactor with a nickel-based catalyst.

[0013] In one embodiment, the combustion chamber has a volume sufficient to ensure a residence time in the combustion chamber such that supplied oxygen is converted, preferably completely converted, with the residence time preferably being at least 10 ms. In other words, the combustion chamber has a sufficient volume to ensure that a portion of the ammonia in the gas mixture generated by the reactor and supplied to the combustion chamber is also oxidized.

[0014] In one embodiment, a first control device is provided, by means of which a substoichiometric gas mixture / air ratio can be adjusted to the combustion chamber. By controlling the process in the combustion chamber with a substoichiometric gas mixture / air ratio, the formation of pollutants, such as NOx, can be reduced. In one embodiment, for this purpose, at least the oxygen content in the portion of the gas mixture supplied to the combustion chamber is monitored, and the air and / or oxygen supply is adjusted to the oxygen content.

[0015] The terms "first," "first," etc., as well as "second," "second," "third," etc., are used in the context of the application merely to distinguish different components and are not intended to indicate a sequence. Likewise, the use of the term "first," etc., does not require the presence of a separate second component.

[0016] In one embodiment, a second control device is provided as a common structural unit with the first control device or alternatively or in addition to the first control device, which second control device is configured to keep a calorific value of the generated gas mixture at least substantially constant in the event of a change in the demand for the gas mixture. In the event of a change in the demand for the gas mixture, the control device can be used to proportionally adjust an amount of ammonia of the ammonia supplied as a starting material, an amount of gas mixture supplied to the combustion chamber, and / or an amount of air or oxygen supplied to the combustion chamber. The respective amounts can be adjusted depending on the situation, for example, using suitable quantity regulators. This enables rapid adjustment of an amount of a generated gas mixture while maintaining a constant calorific value of the gas mixture.For example, a quantity of the gas mixture produced can be adapted to a changed demand of a consumer who directly uses the gas mixture produced, while at the same time ensuring that the consumer is supplied with a defined calorific value of the supplied gas mixture.

[0017] In one embodiment of the device, a heat exchanger is provided, wherein the ammonia supplied as starting material can be heated in the heat exchanger before mixing with the hot exhaust gas by means of the gas mixture flowing out of the reactor. If the ammonia supplied as starting material is supplied in liquid form, the heat exchanger also serves as an evaporator in certain embodiments. The heat exchanger is designed, for example, as a flat-tube heat exchanger, as is known, for example - but not limited to - from EP 2 584 301 A1. Flat-tube heat exchangers are characterized by their high volumetric surface density. Depending on the design of the device, the entire gas mixture discharged from the reactor or only a portion of the gas mixture discharged from the reactor is passed through the heat exchanger.In one embodiment, a portion of the gas mixture not supplied to the combustion chamber is fed to the heat exchanger, so that this portion is used to heat the ammonia supplied as the starting material. In other embodiments, a portion of the gas mixture supplied to the combustion chamber is fed to the heat exchanger upstream of the combustion chamber to heat the ammonia supplied as the starting material.

[0018] In one embodiment, a third control device is used to control the process in such a way that the part of the gas mixture flowing out of the reactor which is fed to the combustion chamber amounts to a maximum of 10% of the flowing out gas mixture.

[0019] As already explained above, the use of the term "third" does not require the presence of a separate first and / or second component of a similar or identical design. However, in advantageous embodiments, one control device and / or multiple control devices of the device are designed such that, by means of the one or more control devices, the process is controlled in such a way that the portion of the gas mixture flowing out of the reactor that is fed to the combustion chamber amounts to a maximum of 10% of the flowing out gas mixture, regardless of the load of a consumer of the generated gas mixture, with at least one ammonia quantity being adapted to a changed load.

[0020] For example, in one embodiment, at least 25% of the ammonia supplied as starting material is to be split, whereby for this purpose the process is carried out in such a way that approximately 7% of the gas mixture produced is burned in the combustion chamber with an air quantity of approximately 0.25 m3 per m3 of the ammonia supplied as starting material.

[0021] To ensure thorough mixing of the ammonia supplied as starting material with the hot exhaust gas, one embodiment provides that the outlet of the combustion chamber has a plurality of outlet nozzles.

[0022] In one embodiment, an electric heater is provided, wherein the electric heater is configured to heat the reactor and / or the ammonia supplied as a starting material upstream of the reactor in a start-up and standby mode and / or for hybrid operation. Hybrid operation refers to an operation in which, based on boundary conditions to be defined, the reaction temperatures required for the cracking are achieved either by combustion of a portion of the generated gas mixture or by means of the electric heater. For example, in one embodiment, heating of the ammonia supplied as a starting material and / or the reactor by means of the electric heater takes place at times when favorable surplus electricity is available.

[0023] In one embodiment, a housing of the combustion chamber is made of a ceramic material and / or has a ceramic coating. Ceramic is characterized by its low susceptibility to corrosion.

[0024] Alternatively or additionally, one embodiment provides that the combustion chamber and / or the reactor are designed for operation at overpressure.

[0025] Alternatively or additionally, in one embodiment, an injector is provided in a supply for the combustion chamber, which injector is designed to suck the gas mixture to the combustion chamber by means of the supplied air or the supplied oxygen.

[0026] According to a second aspect, a process is provided for the partial conversion of ammonia into a combustible, hydrogen-containing gas mixture with an ammonia content, wherein ammonia is partially split into hydrogen and nitrogen by means of a reactor at a reaction temperature of approximately 500°C to approximately 900°C to produce the gas mixture, wherein a portion of the gas mixture flowing out of the reactor is oxidized with air or oxygen in a combustion chamber, wherein a hot exhaust gas from the combustion chamber upstream of the reactor is mixed with the ammonia supplied as starting material to form a hot mixture, and wherein the hot mixture is fed to the reactor.

[0027] In one embodiment, a residence time in the combustion chamber is selected such that oxygen supplied to the combustion chamber is converted, preferably completely converted, wherein a residence time is preferably at least 10 ms.

[0028] In order to reduce the formation of pollutants, such as NOx, particularly when air is used for oxidation in the combustion chamber, in one embodiment a gas mixture / air ratio to the combustion chamber is set substoichiometrically.

[0029] In one embodiment, the calorific value of the generated gas mixture is kept at least substantially constant for use as fuel gas in a consumer. To enable use directly at a consumer with rapid load changes, in one embodiment, the amount of ammonia supplied as a starting material, the amount of gas mixture supplied to the combustion chamber, and / or the amount of air or oxygen supplied to the combustion chamber are adjusted proportionally when the demand for the gas mixture changes.

[0030] In one embodiment, the ammonia supplied as the starting material is heated by the gas mixture flowing out of the reactor before mixing with the hot exhaust gas. In one embodiment, heating occurs indirectly using a flat-tube heat exchanger with a high volumetric surface density.

[0031] For suitable process control, embodiments of the method provide that the portion of the gas mixture flowing out of the reactor which is fed to the combustion chamber amounts to a maximum of 10% of the flowing out gas mixture. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Further advantages and aspects of the invention emerge from the claims and from the description of exemplary embodiments of the invention, which are explained below with reference to the figures. In the figures: Fig. 1 shows a process flow diagram of a process for the partial conversion of ammonia into a combustible, hydrogen-containing gas mixture; Fig. 2 shows a schematic representation of a first embodiment of an apparatus for the partial conversion of ammonia into a combustible, hydrogen-containing gas mixture; and Fig. 3 shows a schematic representation of a second embodiment of an apparatus for the partial conversion of ammonia into a combustible, hydrogen-containing gas mixture. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] Fig. 1 shows a process flow diagram of a process for the partial conversion of ammonia 1 supplied as a starting material into a combustible, hydrogen-containing gas mixture 2. The gas mixture 2 serves, for example, as fuel in a schematically represented consumer 100, for example a heater or an engine, for example on a ship.

[0034] The ammonia 1 supplied as starting material is partially split into hydrogen and nitrogen in a reactor 3 at a reaction temperature of approximately 500°C to approximately 900°C to produce the gas mixture 2.

[0035] The heat required for the partial conversion of the ammonia 1 is generated by means of a combustion chamber 4, wherein a part 20 of the gas mixture 2 flowing out of the reactor as well as air or oxygen 5 are fed to the combustion chamber 4 and the gas mixture is oxidized in the combustion chamber 4.

[0036] A hot exhaust gas from the combustion chamber 4 is mixed upstream of the reactor 3 with the ammonia 1 supplied as starting material to form a hot mixture 12 and the hot mixture 12 is fed to the reactor 3.

[0037] The energy required for the splitting of the ammonia present in the hot mixture 12 in the reactor 3 is provided by cooling the gases of the mixture 12, so that indirect heating of the reactor 3 can be dispensed with during operation.

[0038] In the Fig. 1 In the process shown, the ammonia 1 supplied as starting material is also heated by means of the gas mixture 2 in a heat exchanger 6 before being mixed with the exhaust gas from the combustion chamber 4.

[0039] The consumer's demand for the gas mixture 2 varies depending on the type and application of the consumer 100. In the illustrated embodiment, a quantity regulator 11 is provided in a supply of the ammonia 1 supplied as a starting material, whereby the quantity of ammonia supplied as a starting material can be adjusted if the consumer's demand 100 changes. In order to keep the calorific value of the generated gas mixture 2 at least substantially constant even if the consumer's demand 100 changes and the ammonia quantity changes accordingly, the quantity of air or oxygen supplied to the combustion chamber 4 is adjusted proportionally to the quantity of ammonia by means of a quantity regulator 50.

[0040] A measuring device 200 is provided in a supply line of the part 20 of the generated gas mixture 2 to the combustion chamber 4, wherein, depending on the design, a supplied gas mixture quantity and / or a quality of the supplied gas mixture can be monitored by means of the measuring device 200.

[0041] Likewise, a measuring device 210 is provided in a line of the part 21 of the generated gas mixture 2 which is not supplied to the combustion chamber 4, wherein, depending on the design, a supplied gas mixture quantity and / or a quality of the supplied gas mixture can be monitored by means of the measuring device 210.

[0042] Fig. 2 shows a schematic representation of a first embodiment of a device 10 for the partial conversion of ammonia 1 supplied as a starting material into a combustible, hydrogen-containing gas mixture 2 with an ammonia content. The device 10 comprises a reactor 3 and a combustion chamber 4.

[0043] Using reactor 3, the ammonia 1 supplied as starting material can be partially split into hydrogen and nitrogen at a reaction temperature of approximately 500°C to approximately 900°C to produce the gas mixture 2. The reactor 3 shown is a catalytic reactor, but reactors without a catalyst are also conceivable.

[0044] The combustion chamber 4 is connected to an outlet of the reactor 3 such that a portion 20 of the gas mixture 2 flowing out of the reactor 3 is fed to the combustion chamber 4. The combustion chamber 4 has a supply connection 40 for air or oxygen, wherein the supply connection 40 is designed as an injector so that the gas mixture is sucked in by means of the supplied air or the supplied oxygen and fed to the combustion chamber 4. The supplied gas mixture 2 is combusted in the combustion chamber 4. The combustion chamber 4 is dimensioned such that a residence time in the combustion chamber 4 is sufficient to ensure complete conversion of the supplied oxygen.

[0045] In the illustrated embodiment, the combustion chamber 4 is arranged in a feed channel 14 for the ammonia 1 supplied as starting material to the reactor 3, wherein the feed channel 14 surrounds the combustion chamber 4. The combustion chamber 4 has a plurality of outlet nozzles 41 through which an exhaust gas from the combustion is directed into the feed channel 14, so that hot exhaust gas from the combustion chamber 4 upstream of the reactor 3 is mixed with the ammonia 1 supplied as starting material to form a hot mixture, and the hot mixture is fed to the reactor 3.

[0046] The energy required for the splitting of the ammonia 1 supplied to the reactor 3 can be obtained by cooling the hot mixture in the reactor 3.

[0047] In the illustrated embodiment, a heat exchanger 6 is also provided. In the exemplary embodiment, the ammonia 1 supplied as the starting material is heated by a portion 21 of the generated gas mixture 2 that is not supplied to the combustion chamber 4.

[0048] In the illustrated embodiment, an electric heater 7 is also provided, by means of which the reactor 3 can be heated during start-up or standby operation.

[0049] A pressure-resistant vessel 9 with insulation 90 is provided around the reactor 3 and the combustion chamber 4. With appropriate design of the insulation 90, wall losses can be kept well below 1%.

[0050] In the illustrated embodiment, a flow regulator 24 is provided in a line for the portion 21 of the generated gas mixture 2 that is not fed to the combustion chamber 4. The flow regulator 24 can be used to adjust the percentage of the outflowing gas mixture 2 that is to be fed to the combustion chamber 4. For suitable process control, the adjustment is made in embodiments such that the portion 20 of the gas mixture 2 flowing out of the reactor that is fed to the combustion chamber 4 amounts to a maximum of 10% of the outflowing gas mixture 2.

[0051] In order to vary the volume of the generated gas mixture 2, a flow regulator 11 is provided in a supply line for the ammonia 1 supplied as the starting material. Furthermore, a flow regulator 50 is provided in a supply line for air or oxygen 5.

[0052] In order to keep a calorific value of the gas mixture 2 produced by means of the reactor 3 at least substantially constant when a demand for the gas mixture 2 changes, an amount of ammonia 1 supplied as starting material, an amount of gas mixture supplied to the combustion chamber 4 and an amount of air or oxygen supplied to the combustion chamber 4 are adjusted proportionally to one another.

[0053] A measuring device 200 is provided in a supply line of the part 20 of the generated gas mixture 2 to the combustion chamber 4, wherein, depending on the design, a supplied gas mixture quantity and / or a quality of the supplied gas mixture can be monitored by means of the measuring device 200.

[0054] In some embodiments, process control can be monitored and / or controlled by means of a schematically illustrated control device 102. In one embodiment, additional temperature sensors 31, 32 are provided for monitoring. Temperatures at the inlet and outlet of reactor 3 can be measured using the temperature sensors 31, 32.

[0055] The construction volume for the combustion chamber 4 and the reactor 3 can be kept very compact.

[0056] Fig. 3 shows a schematic representation of a second embodiment of a device 10 for the partial conversion of ammonia 1 supplied as a starting material into a combustible, hydrogen-containing gas mixture 2 with an ammonia content. The device 10 according to Fig. 3 largely corresponds to the device 10 according to Fig. 2 and the same reference numerals are used for identical components. For a description of these components, see above.

[0057] In contrast to the design according to Fig. 2 comprises the device according to Fig. 3 Additionally, an electric heater 8 is arranged around the combustion chamber 4 in the feed channel 14 of the ammonia 1 supplied as the starting material, which is designed, for example, as a heating coil. By means of the additional electric heater 8, the ammonia 1 supplied as the starting material can be heated before being fed to the reactor 3. The additional electric heater 8 thus allows hybrid operation of the device 10, with the ammonia 1 supplied as the starting material being heated either by combustion or by means of the electric heater 8.

Claims

1. Device for partial conversion of ammonia into a combustible, hydrogen-containing gas mixture (2) with an ammonia fraction, comprising a reactor (3), wherein the reactor is configured to partially crack ammonia (1), supplied as a starting material, at a reaction temperature of 500°C to 900°C into hydrogen and nitrogen in order to generate the gas mixture (2), characterized in that the device (10) further comprises a combustion chamber (4) with a supply connection (40) for air or oxygen, wherein the combustion chamber (4) is connected to an outlet of the reactor (3) in such a way that part (20) of the gas mixture (2) flowing out of the reactor (3) can be supplied to the combustion chamber (4), wherein the combustion chamber (4) is configured to oxidize the part (20) of the supplied gas mixture (2) in the combustion chamber (4), and wherein an outlet of the combustion chamber (4) opens out in a supply to the reactor (3) for the ammonia (1) supplied as a starting material, so that hot exhaust gas of the combustion chamber (4) upstream of the reactor (3) can be mixed with the ammonia (1) supplied as the starting material to form a hot mixture (12) and the hot mixture (12) can be supplied to the reactor (3).

2. Device according to Claim 1, characterized in that the combustion chamber (4) has a volume to ensure a dwell time in the combustion chamber (4) such that supplied oxygen is converted, wherein the dwell time is preferably at least 10 ms.

3. Device according to Claim 1 or 2, characterized in that a first control device is provided, by means of which a gas-mixture / air ratio to the combustion chamber (4) can be set to be substoichiometric.

4. Device according to Claim 1, 2 or 3, characterized in that a second control device is provided, which is configured to keep a calorific value of the gas mixture (2) generated by means of the reactor (3) at least substantially constant when there is a change in a demand for the gas mixture (2), wherein an amount of ammonia of the ammonia (1) supplied as the starting material, an amount of gas mixture supplied to the combustion chamber (4) and / or an amount of air or oxygen supplied to the combustion chamber (4) can be set proportionally by means of the control device when there is a change in a demand for the gas mixture (2).

5. Device according to one of Claims 1 to 4, characterized in that a heat exchanger (6) is provided, wherein the ammonia (1) supplied as a starting material can be heated in the heat exchanger (6) before mixing with the hot exhaust gas by means of the gas mixture (2) flowing out of the reactor (3).

6. Device according to one of Claims 1 to 5, characterized in that process management is performed by means of a third control device, so that the part (20) of the gas mixture (2) flowing out of the reactor that is supplied to the combustion chamber (4) is a maximum of 10% of the gas mixture (2) flowing out.

7. Device according to one of Claims 1 to 6, characterized in that the outlet of the combustion chamber (4) has a multiplicity of outlet nozzles (41).

8. Device according to one of Claims 1 to 7, characterized in that an electric heater (7, 8) is provided, wherein the electric heater (7, 8) is configured to heat the reactor (3) and / or the ammonia (1) supplied as a starting material upstream of the reactor (3) in a starting and standby mode and / or for a hybrid mode.

9. Device according to one of Claims 1 to 8, characterized in that the housing (42) of the combustion chamber (4) consists of a ceramic material and / or the housing (42) of the combustion chamber (4) has a ceramic coating and / or in that the combustion chamber (4) and / or the reactor (3) is configured for operation at positive pressure and / or in that an injector which is configured to aspirate the gas mixture to the combustion chamber by means of the supplied air or the supplied oxygen is provided in a supply for the combustion chamber.

10. Method for partially converting ammonia into a combustible, hydrogen-containing gas mixture (2) with an ammonia fraction, wherein an ammonia (1), supplied as a starting material, is partially cracked at a reaction temperature of 500°C to 900°C into hydrogen and nitrogen by means of a reactor (3) in order to generate the gas mixture (2), characterized in that, in a combustion chamber (4), a part (20) of the gas mixture (2) flowing out of the reactor (3) is oxidized with air or oxygen, a hot exhaust gas of the combustion chamber (4) upstream of the reactor (3) is mixed with the ammonia (1) supplied as a starting material to form a hot mixture and the hot mixture is supplied to the reactor (3).

11. Method according to Claim 10, characterized in that a dwell time in the combustion chamber (4) is chosen such that an oxygen supplied to the combustion chamber (4) is converted, preferably completely converted, wherein a dwell time is preferably at least 10 ms.

12. Method according to Claim 10 or 11, characterized in that a gas-mixture / air ratio to the combustion chamber is set to be substoichiometric.

13. Method according to Claim 10, 11 or 12, characterized in that a calorific value of the gas mixture (2) generated is kept at least substantially constant, wherein an amount of ammonia of the ammonia (1) supplied as the starting material, an amount of gas mixture supplied to the combustion chamber (4) and / or an amount of air or oxygen supplied to the combustion chamber (4) are set proportionally when there is a change in a demand for the gas mixture (2).

14. Method according to one of Claims 10 to 13, characterized in that the ammonia (1) supplied as a starting material is heated before mixing with the hot exhaust gas by means of the gas mixture (2) flowing out of the reactor (3).

15. Method according to one of Claims 10 to 14, characterized in that the part (20) of the gas mixture (2) flowing out of the reactor (3) that is supplied to the combustion chamber (4) is a maximum of 10% of the gas mixture flowing out.