DE102023118576A1 - Start-up of a plant for the catalytic decomposition of ammonia - Google Patents

Abstract

The invention relates to a plant for producing H ₂ by catalytic decomposition of NH ₃ . The plant according to the invention can be operated in a start-up mode in order to heat devices of the plant to an increased operating temperature using a heat transfer medium, eg after an interruption of continuous operation of the plant due to maintenance work. After heating to operating temperature, the plant according to the invention can be operated in a production mode for the continuous production of H ₂ . The invention further relates to a method for starting up a plant for producing H ₂ by catalytic decomposition of NH ₃ .

Description

The invention relates to a plant for producing H ₂ by catalytic decomposition of NH ₃ to H ₂ and N ₂ . The plant according to the invention can be operated in a start-up mode in order to heat devices of the plant to an increased operating temperature using a heat transfer medium, eg after an interruption of continuous operation of the plant due to maintenance work. After heating to operating temperature, the plant according to the invention can be operated in a production mode for the continuous production of H ₂ . The invention further relates to a method for starting up a plant for producing H ₂ by catalytic decomposition of NH ₃ .

H ₂ can be obtained from H ₂ O using renewable energy and then converted into NH ₃ with N ₂ . NH ₃ can be stored and transported much more safely than H ₂ . NH ₃ can then be broken down into H ₂ and N ₂ . After N ₂ has been separated, H ₂ can be used in a wide variety of industrial applications.

The decomposition of NH ₃ to N ₂ and H ₂ is an endothermic reaction (ΔH° = 45.9 kJ mol ^-1 ) in which the amount of substance doubles (2 NH ₃ → N ₂ + 3 H ₂ ), so that the reaction is generally favored by high temperatures and low pressures. The higher the pressure, the higher the temperature must be in order to achieve satisfactory reaction yields. On an industrial scale, the catalytic decomposition of NH ₃ to N ₂ and H ₂ takes place at high temperatures and medium pressure in the gas phase.

Stored NH ₃ is in liquid form in cooled tanks at atmospheric pressure and -32.8°C. NH ₃ is fed into the system at system pressure using a pump. The increased system pressure causes the boiling point of NH ₃ to rise, e.g. at 27.8 bar a to about 62.2°C. In order to convert NH ₃ into the gas phase, heat must be added to evaporate the NH _3. The evaporated NH ₃ is then heated further until it has reached a sufficiently high temperature at which it can be decomposed on an NH ₃ decomposition catalyst.

The known processes for the catalytic decomposition of NH ₃ into N ₂ and H ₂ require the supply of considerable amounts of heat. On the one hand, heat is required to bring the process gas and the NH ₃ decomposition catalyst to a sufficiently high temperature at which satisfactory conversions are achieved. On the other hand, heat is required to maintain the endothermic decomposition reaction.

In large-scale processes, this heat is usually provided by the combustion of an energy source (see e.g. US 4 704 267 A ; FR 1 469 045 A ; CN 111 957 270 A ; CN 113 896 168 A ; WO 2001/087770 A1 ; WO 2011/107279 A1 ; WO 2017/160154 A1 ; WO 2019/038251 A1 ; WO 2012/039183 A1 ; WO 2012/090739 A1 ; WO 2020/095467 A ; WO 2021/257944 A1 ; WO 2022/096529 A1 ; WO 2022/243410 A1 ; WO 2022/265647 A1 ; WO 2022/265648 A1 ; WO 2022/265649 A1; WO 2022/265650 A1 ; WO 2022/265651 A1 In principle, all energy sources can be considered, e.g. natural gas or mixtures of NH ₃ and H ₂ .

Plants for producing H ₂ from NH ₃ are usually operated continuously for long periods without interruption, for example over several weeks or months. Nevertheless, it is occasionally necessary to shut down such plants into a standby mode, for example to carry out safety checks, replace catalyst material or carry out other maintenance work. In the standby mode, the plants cool down to ambient temperature, depending on the duration of the interruption in operation.

In order to bring such a system back into continuous operation from idle mode, it must first be warmed up to operating temperature; NH ₃ cannot be decomposed at room temperature. Different parts of the system usually have different operating temperatures and therefore require warming up to different degrees. Warming up can basically be achieved by passing a heat transfer medium through the process side of the system, e.g. N ₂ , steam, natural gas or mixtures thereof, and starting to burn the energy carrier to provide the heat for the heating process. Depending on its properties, the heat transfer medium can either be circulated in the circuit or burned off via a flare.

In order to reduce the use of fossil fuels or even to avoid them completely, part of the NH ₃ is burned instead of fossil fuels during normal operation of the plant and the resulting combustion heat is used for the heating process. NH ₃ is then both a reactant for the decomposition process and an energy source for generating the necessary heat. However, NH ₃ only burns incompletely when mixed with air, which is why the sole combustion of pure NH ₃ together with combustion air is disadvantageous. The result would be emissions of unburned NH ₃ , which would be unacceptable. In order to avoid the combustion of NH ₃ together with combustion In order to improve the quality of the combustion air, a certain amount of generated H ₂ is added to the NH ₃ to be burned during normal operation of the plant.

However, a major problem when starting up the plant is that no H ₂ is yet available as a decomposition product.

• (i) Erzeugung der Wärme durch Verbrennung von Erdgas oder Propan; dazu wäre kein H₂ erforderlich, es würden jedoch CO₂-Emission anfallen; oder
• (ii) Bereitstellung von H₂ im Kleinmaßstab und anschließende Verbrennung des H₂ im Gemisch mit NH₃, z.B. durch
  • - Erzeugung von H₂ mit Hilfe einer elektrisch beheizten Vorrichtung zur katalytischen Zersetzung von NH₃;
  • - Erzeugung von H₂ durch Elektrolyse von Wasser; oder
  • - Nutzung von gespeichertem H₂, welches aus früherer Herstellung zurückgehalten wurde.

This problem could in principle be solved for the duration of the start-up of the plant by temporary measures, which would be terminated as soon as normal operation is achieved:

• (i) generating heat by combustion of natural gas or propane; this would not require H ₂ but would result in CO ₂ emissions; or
• (ii) Provision of H ₂ on a small scale and subsequent combustion of the H ₂ in a mixture with NH ₃ , e.g. by
  • - Production of H ₂ by means of an electrically heated device for the catalytic decomposition of NH ₃ ;
  • - Production of H ₂ by electrolysis of water; or
  • - Use of stored H ₂ retained from previous production.

However, these solutions have several disadvantages.

The alternative combustion of natural gas or propane would not only lead to undesirable emissions of CO ₂ , but would also require dual operation when burning the energy source. Since the configuration of the burners typically has to be adapted to the energy source, changes to the configuration would have to be made when switching from natural gas/propane to NH ₃ /H ₂ , or a second, separate combustion facility would have to be provided.

The temporary production of H ₂ on a small scale using separate catalytic decomposition devices or electrolysis cells would require considerable additional equipment. This also applies to the storage of H ₂ , which would also be associated with significant safety problems.

WO 2011/150370 A2 relates to the decomposition of NH ₃ into an H ₂ gas mixture, wherein an NH ₃ rich gas mixture of NH ₃ and air is passed into a line in which combustion and decomposition of a portion of the mixture is initiated, releasing heat and H _2. H ₂ mixes with the majority of the gas mixture and the released heat drives the combustion reaction. When starting the NH ₃ flamesplitter, the catalyst can be heated electrically, inductively, by briefly burning chemicals on the catalyst and/or surrounding structure, or by an electric arc. Heating of the catalyst can be used to initiate the combustion and decomposition reactions of the NH ₃ and to supply afterheat to the burning gases as needed until the NH ₃ flamesplitter is fully warmed up. After starting the NH ₃ flame splitter, the power supply can be turned off or turned down so that the energy required to decompose the NH ₃ is essentially provided by the combustion of a portion of the NH ₃ and the combustion of NH ₃ is essentially sufficient to keep the catalyst hot.

WO 2013/119281 A1 relates to the decomposition of NH ₃ into a gas mixture containing H ₂ , whereby an NH ₃ -rich gas mixture of NH ₃ and air enters a heat exchanger. Part of the NH ₃ is burned, the rest is decomposed, producing the gas mixture containing H _2. NH ₃ flame splitters can be brought to operating temperature by burning a starting mixture and then flowing the burned starting mixture through the NH ₃ flame splitters, so that the burned starting mixture thermally contacts the heat exchangers and/or burners of the NH ₃ flame splitters during a starting phase. Since the surface temperatures rise during the warm-up phase, one or more of the following measures can be taken: increasing the total flow of the starting mixture, reducing the oxygen content of the oxidant component, or increasing the total content of the starting mixture. This allows the NH ₃ flame splitters to be started quickly even with a comparatively low flow of purified oxygen. The flow of purified oxygen is turned off at or near the end of the start-up phase.

The state-of-the-art plants and processes for the extraction of H ₂ from NH ₃ are not satisfactory in every respect, particularly with regard to interruptions to normal operation and the subsequent start-up of the plants. There is therefore a need for improved plants and processes that can be carried out economically on a large-scale.

It is an object of the invention to provide an advantageous plant and an advantageous process for producing H ₂ from NH ₃ , which overcome the disadvantages mentioned above. The plant should be able to be started up without additional, costly measures and equipment, and should not rely on any fossil fuels. do not entail any additional safety risks and be economically viable and possible on a large technical scale.

This problem is solved by the subject matter of the patent claims.

It was surprisingly discovered that certain devices that serve other purposes during normal plant operation can be converted and connected differently for the duration of the start-up. In this way, it is possible to obtain sufficient amounts of H ₂ from NH ₃ by decomposition during the start-up of the plant, so that the combustion of NH ₃ in a mixture with H ₂ can be started and the plant can be slowly warmed up to operating temperature. The additional equipment required for starting up the plant is thus minimized.

• - ein Heizelement zum Erwärmen von NH₃;
• - in Strömungsrichtung des NH₃ stromabwärts des Heizelements eine erste NH₃-Zersetzungseinrichtung (Vorreaktor) zum partiellen katalytischen Zersetzen des erwärmten NH₃ unter Erzeugung eines Verbrennungsgases umfassend H₂, N₂ und restliches NH₃;
• - optional, in Strömungsrichtung des Verbrennungsgases stromabwärts der ersten NH₃-Zersetzungseinrichtung (Vorreaktor) eine Vorrichtung zum Zudosieren von Verbrennungsluft in das Verbrennungsgas;
• - in Strömungsrichtung des Verbrennungsgases stromabwärts der ersten NH₃-Zersetzungseinrichtung eine Verbrennungseinrichtung zum Verbrennen des Verbrennungsgases unter Erzeugung von Verbrennungswärme und Rauchgas;
• - einen Verdichter zum Verdichten eines Wärmeträgermediums; und
• - in Strömungsrichtung des Rauchgases stromabwärts der Verbrennungseinrichtung und in Strömungsrichtung des Wärmeträgermediums stromabwärts des Verdichters
  • - einen ersten Wärmetauscher [bevorzugt Rauchgas/Wärmeträgermedium-Wärmetauscher für den Anfahrmodus] und/oder
  • - einen zweiten Wärmetauscher [bevorzugt Rauchgas/Wärmeträgermedium-Wärmetauscher für den Anfahrmodus]
  • zum Erwärmen des Wärmeträgermediums durch Aufnahme von Wärme aus dem Rauchgas; und wobei die wenigstens eine Vorrichtung der Anlage in Strömungsrichtung des Wärmeträgermediums stromabwärts des ersten Wärmetauschers und/oder des zweiten Wärmetauschers angeordnet ist und mit dem Wärmeträgermedium zur Aufnahme von Wärme aus dem Wärmeträgermedium in fluider Verbindung steht.

A first aspect of the invention relates to a plant for producing H ₂ from NH ₃ ;
wherein the plant is operable in a manufacturing mode (normal operation) at operating temperatures;
wherein the system is operable in a start-up mode (start-up operation) to heat at least one device of the system from an initial temperature to an operating temperature;
wherein the start-up mode system comprises at least the following means for heating the at least one device to the operating temperature:

• - a heating element for heating NH ₃ ;
• - in the flow direction of the NH ₃ downstream of the heating element, a first NH ₃ decomposition device (pre-reactor) for partially catalytically decomposing the heated NH ₃ to produce a combustion gas comprising H ₂ , N ₂ and residual NH ₃ ;
• - optionally, in the flow direction of the combustion gas downstream of the first NH ₃ decomposition device (pre-reactor), a device for metering combustion air into the combustion gas;
• - in the flow direction of the combustion gas downstream of the first NH ₃ decomposition device, a combustion device for burning the combustion gas to produce combustion heat and flue gas;
• - a compressor for compressing a heat transfer medium; and
• - in the flow direction of the flue gas downstream of the combustion device and in the flow direction of the heat transfer medium downstream of the compressor
  • - a first heat exchanger [preferably flue gas/heat transfer medium heat exchanger for start-up mode] and/or
  • - a second heat exchanger [preferably flue gas/heat transfer medium heat exchanger for start-up mode]
  • for heating the heat transfer medium by absorbing heat from the flue gas; and wherein the at least one device of the system is arranged in the flow direction of the heat transfer medium downstream of the first heat exchanger and/or the second heat exchanger and is in fluid communication with the heat transfer medium for absorbing heat from the heat transfer medium.

A second aspect of the invention relates to the use of a plant according to the invention for the production of H ₂ .

1. (a) optional, Verdampfen von Wasser unter Erzeugung von Wasserdampf;
2. (b) optional, Verdampfen von flüssigem NH₃ durch Aufnahme von Wärme aus dem Wasserdampf;
3. (c) Erwärmen von NH₃;
4. (d) partielles katalytisches Zersetzen des erwärmten NH₃ in einer ersten NH₃-Zersetzungseinrichtung unter Erzeugung eines Verbrennungsgases umfassend H₂, N₂ und restliches NH₃;
5. (e) optional, Zudosieren von Verbrennungsluft in das Verbrennungsgas;
6. (f) Verbrennen des Verbrennungsgases in einer Verbrennungseinrichtung unter Erzeugung von Verbrennungswärme und Rauchgas;
7. (g) Verdichten eines Wärmeträgermediums;
8. (h) Erwärmen des Wärmeträgermediums durch Aufnahme von Wärme aus dem Rauchgas; und
9. (i) Erwärmen wenigstens einer Vorrichtung der Anlage durch Aufnahme von Wärme aus dem Wärmeträgermedium.

A third aspect of the invention relates to a method for starting up a plant for producing H ₂ from NH ₃ comprising the following steps:

1. (a) optionally, evaporating water to produce water vapor;
2. (b) optionally, evaporation of liquid NH ₃ by absorption of heat from the water vapor;
3. (c) heating of NH ₃ ;
4. (d) partially catalytically decomposing the heated NH ₃ in a first NH ₃ decomposition device to produce a combustion gas comprising H ₂ , N ₂ and residual NH ₃ ;
5. (e) optionally, dosing of combustion air into the combustion gas;
6. (f) burning the combustion gas in a combustion device to produce heat of combustion and flue gas;
7. (g) compressing a heat transfer medium;
8. (h) heating the heat transfer medium by absorbing heat from the flue gas; and
9. (i) Heating at least one device of the system by absorbing heat from the heat transfer medium.

Steps (a), (b) and (e) of the method according to the invention are optional, independently of one another. Preferably, steps (a) to (i), if implemented, are carried out in alphabetical order.

According to the invention, a distinction is made between the production mode (normal operation) and the start-up mode (start-up operation). While H ₂ is already produced from NH ₃ to a certain extent in the start-up mode, the amount and yield of the H ₂ produced preferably differ considerably.

In the start-up mode, both the amount and the yield of H ₂ produced are preferably comparatively low; preferably only the first NH ₃ decomposition device is used for the partial catalytic decomposition of NH ₃ and the intermediate gas produced is burned as combustion gas to generate the required heat.

In the production mode, both the amount and the yield of H ₂ produced are preferably comparatively high; preferably both the first NH ₃ decomposition device (pre-reactor) and the downstream second NH ₃ decomposition device (main reactor) are used for the most complete catalytic decomposition of NH _3. The intermediate product gas produced in the first NH ₃ decomposition device is not burned as combustion gas, but is preferably fed after heating to the downstream second NH ₃ decomposition device, where the most complete decomposition of the NH ₃ takes place. H ₂ is then separated from the product gas produced in the second NH ₃ decomposition device, preferably by pressure swing adsorption, and the resulting residual gas mixture is burned as combustion gas to generate the required heat. Since in practice the decomposition of NH ₃ in the second NH ₃ decomposition device is not absolutely complete (100.0%), a residual amount of NH ₃ remains, which is burned as combustion gas after addition of additional, fresh NH ₃ .

The heat exchangers according to the invention serve to transfer heat from one medium to another medium without the media being mixed together. For the purpose of description, in relation to an "A/B heat exchanger", the medium A that releases the heat is mentioned first, followed by the medium B that absorbs the heat. Accordingly, for example, a "flue gas/NH ₃ heat exchanger" serves to release heat contained in the flue gas to NH _3. The flue gas/NH ₃ heat exchanger is connected accordingly for this purpose, ie flue gas flows through its warmer side, whereas NH ₃ flows through its cooler side.

For the purpose of description, the heat exchangers are numbered. This numbering is merely for linguistic differentiation, but should not be understood to mean that the presence of a heat exchanger with a higher number, e.g. "fourth heat exchanger", always necessarily requires the presence of all heat exchangers with a lower number ("first heat exchanger", "second heat exchanger", "third heat exchanger"). It is thus possible, for example, for the system according to the invention to comprise a second heat exchanger according to the invention and a fourth heat exchanger according to the invention, but neither a first heat exchanger according to the invention nor a third heat exchanger according to the invention.

According to the invention, it is possible and also preferred that one and the same heat exchanger serves a different function in the production mode than in the start-up mode, in particular that other media flow through it at least in part or on one side (warm side vs. cold side). In such cases, for the purposes of description, a distinction is made in individual cases in square brackets between the two operating modes and the respective preferred forms of heat exchange. For example, “first heat exchanger [preferably flue gas/NH ₃ heat exchanger for the production mode; flue gas/heat transfer medium heat exchanger for the start-up mode]” means that the first heat exchanger preferably takes on two different functions: in the production mode, heat from the flue gas is preferably transferred to NH ₃ in the first heat exchanger, and in the start-up mode, heat from the flue gas is preferably transferred to the heat transfer medium in the first heat exchanger. If the heat transfer medium in the start-up mode is NH ₃ , it is ultimately also a flue gas/NH ₃ heat exchanger in the start-up mode. If such a heat exchanger is described in the context of a specific mode (either manufacturing mode or start-up mode), the square brackets following the description may only refer to the corresponding preferred form of heat exchange.

For the purpose of description, unless expressly stated otherwise, the term "water" is used for all its states of aggregation, whereby, depending on temperature and pressure, this water can be liquid or gaseous or exist as a two-phase system, ie possibly also as water vapor. This also applies analogously to "NH ₃ ".

The plant according to the invention comprises a first NH ₃ decomposition device and a second NH ₃ decomposition device, both of which contain NH ₃ decomposition catalyst. The first NH ₃ decomposition device is preferably a fixed bed reactor. In the first NH ₃ decomposition device, the decomposition of NH ₃ preferably takes place adiabatically. The downstream second NH ₃ decomposition device is preferably connected together with a The combustion device is designed analogously to a primary reformer, as used in conventional steam reforming to produce H ₂ , O ₂ and CO/CO ₂ from H ₂ O and CH ₄ .

In production mode, the catalytic decomposition of the NH ₃ takes place in two stages in the first NH ₃ decomposition device and the downstream second NH ₃ decomposition device. The second heat exchanger [preferably flue gas/intermediate product gas heat exchanger for the production mode] is preferably arranged in the flow direction of the NH ₃ downstream of the first NH ₃ decomposition device and preferably upstream of the downstream second NH ₃ decomposition device. In production mode, the second heat exchanger is preferably used to heat the intermediate product gas after it leaves the first NH ₃ decomposition device and before it enters the downstream second NH ₃ decomposition device (main reactor, together with combustion device analogous to primary reformer). In production mode, intermediate product gas in the second heat exchanger preferably absorbs heat from flue gas (cf. , second heat exchanger 67).

In production mode, preheated NH ₃ enters the first NH ₃ decomposition device, in which a partial catalytic decomposition of NH ₃ to N ₂ and H ₂ takes place to a certain extent. An intermediate product gas is formed which still contains considerable residual amounts of non-decomposed NH ₃ , but also already formed N ₂ and H _2. As a result of the endothermic decomposition of NH ₃ , the intermediate product gas preferably cools down. Preferably, the conversion of decomposed NH ₃ in the first NH ₃ decomposition device is at most 25%, more preferably at most 20% of the total conversion achieved overall. Preferably, the conversion of decomposed NH ₃ in the first NH ₃ decomposition device is at least 5%, more preferably at least 10%, even more preferably at least 15% of the total conversion achieved overall. After leaving the first NH ₃ decomposition device, the intermediate product gas is preferably heated again in the second heat exchanger [preferably flue gas/intermediate product gas heat exchanger for the production mode] before it enters the downstream, second NH ₃ decomposition device. The remaining decomposition of NH ₃ then takes place in the second NH ₃ decomposition device until the total conversion is achieved.

In contrast, in start-up mode, the catalytic decomposition of NH ₃ preferably only takes place in one stage, and only in the first NH ₃ decomposition device. In start-up mode, the second NH ₃ decomposition device preferably does not yet contribute to the decomposition of NH ₃ , at least during early phases of the start-up mode.

In start-up mode, preheated NH ₃ enters the first NH ₃ decomposition device, in which a partial catalytic decomposition of NH ₃ to N ₂ and H ₂ takes place to a certain extent. An intermediate product gas is also formed which still contains considerable residual amounts of non-decomposed NH ₃ , but also N ₂ and H ₂ which have already been formed. Preferably, the conversion of decomposed NH ₃ in the first NH ₃ decomposition device is at most 25%, more preferably at most 20%, based on the amount of NH _3. Preferably, the conversion of decomposed NH ₃ in the first NH ₃ decomposition device is at least 5%, more preferably at least 10%, even more preferably at least 15%, based on the amount of NH ₃ .

In contrast to the production mode, in the start-up mode the intermediate product gas formed in the first NH ₃ decomposition device is preferably not fed into the second NH ₃ decomposition device, but instead into the combustion device. The amount of H ₂ formed in the intermediate product gas is sufficient for satisfactory combustion of the NH ₃ , so that the combustion of the intermediate product gas generates sufficient combustion heat to gradually warm up the system to operating temperature.

In preferred embodiments, in start-up mode the NH ₃ stream is divided into a first NH ₃ partial stream and a second NH ₃ partial stream. Only the first NH ₃ partial stream is fed to the first decomposition device. The second NH ₃ partial stream flows through the second NH ₃ decomposition device instead, whereby the second NH ₃ decomposition device absorbs heat from the second NH ₃ partial stream. The second NH ₃ partial stream therefore initially only functions as a heat transfer medium. In this way, the second NH ₃ decomposition device is gradually heated until the start-up temperature (activation temperature) for the catalytic decomposition of NH ₃ is reached, so that from this point on additional H ₂ is produced in the second NH ₃ decomposition device by catalytic decomposition of NH ₃ (cf. ).

In preferred embodiments, the amount of H ₂ in the combustion gas is increased in start-up mode compared to production mode. The larger ratio of H ₂ to NH ₃ promotes combustion, which allows the operating temperature to be reached more quickly.

It is a significant advantage of the invention that the first NH ₃ decomposition device can be used for two different purposes, namely in start-up mode for the production of the combustion gas and in production mode for the first stage a total of two-stage decomposition of NH ₃ for the production of the product gas. The plant according to the invention preferably does not comprise any further separate NH ₃ decomposition device, which is used exclusively in the start-up mode, but not in the production mode. Such separate NH ₃ decomposition devices are commercially available, possibly already equipped with an electric heater, but such additional equipment expenditure can also be dispensed with according to the invention.

• - das bevorzugt elektrisch betriebene Heizelement und
• - den bevorzugt elektrisch betriebenen H₂O-Dampferzeuger.

Preferably, the system according to the invention essentially comprises only two devices, which are used exclusively in the start-up mode, but not in the production mode, namely

• - the preferably electrically operated heating element and
• - the preferably electrically operated H ₂ O steam generator.

In order that the NH ₃ has a sufficiently high temperature for the catalytic decomposition in the first NH ₃ decomposition device, the system according to the invention has a heating element for heating NH ₃ in the start-up mode. The heating element is preferably electrically operated. The heating of NH ₃ in step (c) of the method according to the invention is therefore preferably carried out using electrical energy.

Preferably, the heating element is only provided for the start-up mode and is switched off in the production mode. In preferred embodiments, the heating element is connected via a line system in a bypass so that the NH ₃ can be passed through the heating element via the bypass in the start-up mode to be heated there. Once the production mode is reached, NH ₃ preferably no longer flows through the entire bypass including the heating element. In order to enable such a reaction to be carried out, suitable valves are preferably provided which enable the targeted flow of the NH ₃ through the bypass or not through the bypass.

The NH ₃ is typically provided in liquid form as a starting material and must therefore first be evaporated. This applies not only to the production mode, but also to the start-up mode. According to the invention, the evaporation of the NH ₃ preferably takes place by absorbing heat from water vapor.

In the production mode, the water vapor is preferably provided by process heat, whereby water as a heat transfer medium absorbs heat from the product gas and/or the flue gas and the thus heated water vapor releases heat to liquid NH ₃ .

In start-up mode, however, there is initially no process heat present, so that the system according to the invention preferably comprises an H ₂ O evaporation device for evaporating water to generate water vapor. The H ₂ O evaporation device is preferably arranged upstream of the heating element in the direction of flow of the NH _3. The H ₂ O evaporation device is preferably heated electrically. The method according to the invention therefore preferably comprises the two optional steps (a) and (b), with the generation of water vapor in step (a) of the method according to the invention preferably taking place using electrical energy.

Preferably, the preferably electrically heated H ₂ O evaporation device is only intended for the start-up mode and is switched off in the production mode. In preferred embodiments, the H ₂ O evaporation device is connected via a line system in a bypass, so that in the start-up mode the water can be passed through the bypass through the H ₂ O evaporation device to be heated and evaporated there. Once the production mode is reached, preferably the entire bypass including the H ₂ O evaporation device is no longer flowed through by water. In order to enable such a reaction to be carried out, suitable valves are preferably provided which enable the targeted flow of the water through the bypass or not through the bypass.

Furthermore, the plant according to the invention preferably comprises an NH ₃ evaporation device for evaporating liquid NH ₃ by absorbing heat from the water vapor.

In this way, in start-up mode, the liquid NH ₃ can first be evaporated by absorbing heat from the water vapor, which in turn is generated in the preferably electrically heated H ₂ O evaporation device. The evaporated NH ₃ is then passed through the preferably electrically heated heating element and heated therein to a temperature which is sufficient for the subsequent partial catalytic decomposition of the NH ₃ in the first NH ₃ decomposition device. The intermediate product gas thus generated is then burned in the combustion device, generating a flue gas and combustion heat.

According to the invention, the heat generated by the combustion of the combustion gases is used not only in the production mode, but also in the start-up mode. The combustion gases can typically have different origins and compositions.

In production mode, the heat of combustion is essentially used to heat the NH ₃ to the necessary reaction temperature so that the reaction heat of the endothermic reaction is provided in the first NH ₃ decomposition device and the downstream second NH ₃ decomposition device and the conversion takes place via both NH ₃ decomposition devices with a high conversion. For this purpose, water vapor is preferably used as a heat transfer medium, especially for the evaporation of the NH ₃ .

• - der erste Wärmetauscher [bevorzugt Rauchgas/Wärmeträgermedium-Wärmetauscher für den Anfahrmodus] und/oder
• - der zweite Wärmetauscher [bevorzugt Rauchgas/Wärmeträgermedium-Wärmetauscher für den Anfahrmodus]

angeordnet zum Erwärmen des Wärmeträgermediums durch Aufnahme von Wärme aus dem Rauchgas.In start-up mode, the combustion heat is essentially used to heat a heat transfer medium, which is preferably compressed in a compressor and then passed through parts of the system. To do this, the heat transfer medium preferably absorbs heat directly from the combustion heat and/or indirectly from the flue gas. To do this, the heat transfer medium is preferably located downstream of the combustion device in the flow direction of the flue gas and downstream of the compressor in the flow direction of the heat transfer medium.

• - the first heat exchanger [preferably flue gas/heat transfer medium heat exchanger for start-up mode] and/or
• - the second heat exchanger [preferably flue gas/heat transfer medium heat exchanger for start-up mode]

arranged to heat the heat transfer medium by absorbing heat from the flue gas.

In preferred embodiments, the heat transfer medium comprises N ₂ or consists essentially of it. N ₂ is preferably circulated through at least part of the system until the desired operating temperatures of the parts of the system are reached. Once this state has been reached, N ₂ is preferably discharged from the system and switched to production mode. For this change, NH ₃ is preferably continuously mixed with the N ₂ and the mixture of N ₂ and NH ₃ is optionally burned via a flare. If the content of NH ₃ in the mixture with N ₂ is large enough, production mode can be started.

In other preferred embodiments, the heat transfer medium comprises NH ₃ or consists essentially thereof. NH ₃ is preferably circulated through at least part of the system until the desired operating temperatures of the parts of the system are reached. Once this state is reached, the production mode is started.

In preferred embodiments, in the start-up mode, the NH ₃ stream is divided into a first NH ₃ partial stream and a second NH ₃ partial stream. Only the first NH _{3 partial stream is fed to the first decomposition device. The second NH 3 partial} stream flows through the second NH ₃ decomposition device instead, whereby the second NH ₃ decomposition device absorbs heat from the second NH ₃ partial stream. The second NH ₃ partial stream therefore initially only functions as a heat transfer medium. In this way, the second NH ₃ decomposition device is gradually heated until the start-up temperature (activation temperature) for the catalytic decomposition of NH ₃ is reached, so that from this point onwards additional H ₂ is produced in the second NH ₃ decomposition device by catalytic decomposition of NH ₃ .

In preferred embodiments, the amount of H ₂ in the combustion gas is increased in start-up mode compared to production mode. The larger ratio of H ₂ to NH ₃ promotes combustion, which allows the operating temperature to be reached more quickly.

In start-up mode, at least one device of the system is arranged in the flow direction of the heat transfer medium downstream of the first heat exchanger and/or the second heat exchanger and is in fluid communication with the heat transfer medium for absorbing heat from the heat transfer medium. This at least one device of the system is heated in start-up mode by absorbing heat from the heat transfer medium.

In preferred embodiments, the at least one device which is heated in the start-up mode by absorbing heat from the heat transfer medium is the second NH ₃ decomposition device (cf. , second NH3 decomposition device 24). In the production mode, the second NH ₃ decomposition device is preferably connected downstream of the first NH ₃ decomposition device and preferably serves for the catalytic decomposition of vaporized NH ₃ to produce a product gas comprising H ₂ and N ₂ . For the change from start-up mode to production mode, the system according to the invention preferably comprises corresponding lines and valves which enable a changed connection (cf. ).

In preferred embodiments, the at least one device which is heated in the start-up mode by absorbing heat from the heat transfer medium is a third heat exchanger [preferably heat transfer medium/water heat exchanger for the start-up mode] (cf. , third heat exchanger 26). In production mode, the third heat exchanger [preferably product gas/ Water heat exchanger for the production mode] preferably for heating water, preferably for heating or generating water vapor, by absorbing heat from the product gas. For the change from start-up mode to production mode, the system according to the invention preferably comprises corresponding lines and valves which enable a changed connection (cf. ).

In preferred embodiments, the at least one device which is heated in the start-up mode by absorbing heat from the heat transfer medium is a fourth heat exchanger [preferably heat transfer medium/heat transfer medium heat exchanger for the start-up mode] (cf. , fourth heat exchanger 20). In the production mode, the fourth heat exchanger [preferably product gas/NH ₃ heat exchanger for the production mode] is used to heat NH ₃ by absorbing heat from the product gas. For the change from start-up mode to production mode, the system according to the invention preferably comprises corresponding lines and valves which enable a changed connection (cf. ).

In preferred embodiments, the at least one device which is heated in the start-up mode by absorbing heat from the heat transfer medium is a fifth heat exchanger [preferably heat transfer medium/water heat exchanger for the start-up mode] (cf. , fifth heat exchanger 28). In the production mode, the fifth heat exchanger [preferably product gas/water heat exchanger for the production mode] is preferably used to heat water by absorbing heat from the product gas. For the change from start-up mode to production mode, the system according to the invention preferably comprises corresponding lines and valves which enable a changed connection (cf. ).

In preferred embodiments, the at least one device which is heated in the start-up mode by absorbing heat from the heat transfer medium is a sixth heat exchanger [preferably heat transfer medium/water heat exchanger for the start-up mode] (cf. , sixth heat exchanger 29). In the production mode, the sixth heat exchanger [preferably product gas/water heat exchanger for the production mode] is preferably used to heat water by absorbing heat from the product gas. For the change from start-up mode to production mode, the system according to the invention preferably comprises corresponding lines and valves which enable a changed connection (cf. ).

In addition, in start-up mode, the flue gas generated during combustion of the combustion gas can also release heat to at least one device in the system. This at least one device is typically arranged in the flue gas duct. This at least one device is preferably arranged downstream of the first heat exchanger and/or the second heat exchanger in the flow direction of the flue gas.

In preferred embodiments, the at least one device which is heated in the start-up mode by absorbing heat from the flue gas is a first flue gas/combustion air heat exchanger (cf. , first flue gas/combustion air heat exchanger 45), which preferably serves in start-up mode and/or in production mode to heat combustion air by absorbing heat from the flue gas.

In preferred embodiments, the at least one device which is heated in the start-up mode by absorbing heat from the flue gas is a flue gas denitrification unit (cf. , flue gas denitrification unit 50), which preferably serves in start-up mode and/or in production mode to clean the flue gas of nitrogen oxides (NOx).

In preferred embodiments, the at least one device which is heated in the start-up mode by absorbing heat from the flue gas is a flue gas/water heat exchanger (cf. , flue gas/water heat exchanger 52), which preferably serves in the start-up mode and/or in the production mode for heating water, preferably for heating or generating water vapor, by absorbing heat from the flue gas.

In preferred embodiments, the at least one device which is heated in the start-up mode by absorbing heat from the flue gas is a second flue gas/combustion air heat exchanger (cf. , second flue gas/combustion air heat exchanger 43), which preferably serves in start-up mode and/or in production mode to heat combustion air by absorbing heat from the flue gas.

Preferably, the combustion device and the second NH ₃ decomposition device are in heat exchange with one another and are configured for a heat flow from the combustion device into the second NH ₃ decomposition device. For this purpose, they are preferably designed analogously to a primary reformer, as is used in conventional steam reforming to produce H ₂ , O ₂ and CO/CO ₂ from H ₂ O and CH ₄ .

In preferred embodiments of the plant according to the invention, the plant in production mode (ie during normal operation) is designed for a throughput based on H ₂ of at least 500 moŀh ^-1 , preferably at least 1000 moŀh ^-1 , more preferably at least 5000 moŀh ^-1 , even more preferably at least 10,000 moŀh ^-1 , most preferably at least 50,000 moŀh ^-1 , and in particular at least 100,000 moŀh ^-1 .

In preferred embodiments of the plant according to the invention, the plant comprises a tank for liquid NH ₃ which has a volume of at least 50 m ³ , preferably at least 100 m ³ , more preferably at least 500 m ³ , even more preferably at least 1000 m ³ , most preferably at least 5000 m ³ , and in particular at least 10,000 m ³ .

In preferred embodiments of the plant according to the invention, the plant comprises, in addition to the first NH ₃ decomposition device, a second NH ₃ decomposition device with at least three, preferably at least four, more preferably at least five, even more preferably at least six, most preferably at least seven and in particular at least eight catalyst beds, each of which comprises NH ₃ decomposition catalyst; each catalyst bed is preferably present in a tube; the catalyst beds are preferably connected in parallel. Each catalyst bed preferably contains the same NH ₃ decomposition catalyst.

In preferred embodiments of the plant according to the invention, the plant comprises, in addition to the first NH ₃ decomposition device, a second NH ₃ decomposition device with at least one catalyst bed which comprises NH ₃ decomposition catalyst, wherein the length of the catalyst bed in the flow direction for NH ₃ is at least 1.0 m, preferably at least 1.5 m, more preferably at least 2.0 m, even more preferably at least 2.5 m, most preferably at least 3.0 m and in particular at least 3.5 m; wherein the catalyst bed is preferably present in a tube.

In preferred embodiments of the plant according to the invention, the plant comprises a combustion device with at least three, preferably at least four, more preferably at least five, even more preferably at least six, most preferably at least seven and in particular at least eight burners for burning the combustion gas.

In preferred embodiments of the system according to the invention, the system comprises a first heat exchanger and/or a second heat exchanger, which are designed independently of one another as tube heat exchangers or tube bundle heat exchangers.

In preferred embodiments of the process according to the invention, in the production mode (ie during normal operation) a throughput based on H ₂ of at least 500 mol·h ^-1 is achieved, preferably at least 1000 moŀh ^-1 , more preferably at least 5000 moŀh ^-1 , even more preferably at least 10,000 moŀh ^-1 , most preferably at least 50,000 moŀh ^-1 , and in particular at least 100,000 mol·h ^-1 .

In preferred embodiments of the process according to the invention, in the production mode (ie during normal operation), the liquid NH ₃ is taken from a tank having a volume of at least 50 m ³ , preferably at least 100 m ³ , more preferably at least 500 m ³ , even more preferably at least 1000 m ³ , most preferably at least 5000 m ³ , and in particular at least 10,000 m ³ .

In preferred embodiments of the process according to the invention, in the production mode (ie during normal operation), the catalytic decomposition of NH ₃ takes place on at least three, preferably at least four, more preferably at least five, even more preferably at least six, most preferably at least seven and in particular at least eight catalyst beds, each of which comprises NH ₃ decomposition catalyst; each catalyst bed is preferably present in a tube; the catalyst beds are preferably flowed through in parallel by NH ₃ .

In preferred embodiments of the process according to the invention, in the production mode (ie during normal operation), the catalytic decomposition takes place on at least one catalyst bed which comprises NH ₃ decomposition catalyst, the length of the catalyst bed in the flow direction for NH ₃ being at least 1.0 m, preferably at least 1.5 m, more preferably at least 2.0 m, even more preferably at least 2.5 m, most preferably at least 3.0 m and in particular at least 3.5 m; the catalyst bed is preferably present in a tube

In preferred embodiments of the process according to the invention, in the production mode (i.e. during normal operation), the combustion of the combustion gas takes place with the aid of at least three, preferably at least four, more preferably at least five, even more preferably at least six, most preferably at least seven and in particular at least eight burners.

According to the invention, the catalytic decomposition of NH ₃ means the formation of N ₂ and H ₂ , in State of the art sometimes also referred to as “splitting” or “cracking” of NH ₃ .

According to the invention, the catalytic decomposition of NH ₃ preferably takes place in the absence of O ₂ .

• (i) Verdampfung von NH₃;
• (ii) katalytische Zersetzung von NH₃ unter Zufuhr von Wärme unter Erhalt eines Produktgases umfassend N₂, H₂ und ggf. nicht zersetztes NH₃;
• (iii) Rückgewinnung von Wärme;
• (iv) ggf. Rückgewinnung von nicht zersetztem NH₃;
• (v) Reinigung von H₂.

Preferably, the invention comprises the following measures in the manufacturing mode:

• (i) evaporation of NH ₃ ;
• (ii) catalytic decomposition of NH ₃ with the addition of heat to obtain a product gas comprising N ₂ , H ₂ and optionally undecomposed NH ₃ ;
• (iii) heat recovery;
• (iv) recovery of non-decomposed NH ₃ , if necessary;
• (v) Purification of H ₂ .

H ₂ O is not a product of the reaction and can be present in very small amounts, since H ₂ O is often present in liquid NH ₃ , in concentrations of maximum 0.5 wt.%, typically < 0.3 wt.%. Due to the evaporation of NH _3, it is to be expected that H ₂ O is present in lower concentrations.

NH ₃ - from storage to catalytic decomposition

According to the invention, the NH ₃ is preferably stored as starting material.

Preferably, the stored NH ₃ is in liquid form in a cooled tank, at atmospheric pressure and a temperature below its boiling point of -33.5°C. NH ₃ is fed into the system using a pump, preferably at system pressure.

Before the NH ₃ can be catalytically decomposed, it is preferably heated successively to several temperature levels according to the invention.

Starting from liquid NH _3, NH ₃ is preferably heated and then evaporated to a medium temperature level (<300°C) by absorbing heat from water or water vapor. In production mode, the water vapor is preferably generated by absorbing heat from flue gas and/or product gas. In start-up mode, the water vapor is preferably generated by an electrically operated H ₂ O evaporation device.

Preferably, a preheater is arranged in the flow direction of the NH ₃ downstream of the tank and upstream of the NH ₃ evaporation device, which is preferably used to heat the NH ₃ to the desired temperature at the inlet to the NH ₃ evaporation device and in which NH ₃ absorbs heat from water which in turn has previously left the NH ₃ evaporation device as water vapor condensate. Preferably, water vapor and water vapor condensate are passed in countercurrent through the preheater and the NH ₃ evaporation device.

Subsequently, the NH ₃ is preferably further heated to a high temperature level (>300°C).

In production mode, the further heating of NH ₃ is preferably carried out by absorbing heat directly from flue gas and/or product gas, i.e. without water as a heat transfer medium.

• - bevorzugt ein vierter Wärmetauscher [bevorzugt Produktgas/NH₃-Wärmetauscher für den Herstellmodus];
• - bevorzugt ein erster Wärmetauscher [bevorzugt Rauchgas/NH₃-Wärmetauscher für den Herstellmodus]; und/oder
• - bevorzugt ein zweiter Wärmetauscher [bevorzugt Rauchgas/Zwischenproduktgas-Wärmetauscher für den Herstellmodus].

For this purpose, appropriate heat exchangers are provided for the manufacturing mode:

• - preferably a fourth heat exchanger [preferably product gas/NH ₃ heat exchanger for the production mode];
• - preferably a first heat exchanger [preferably flue gas/NH ₃ heat exchanger for the production mode]; and/or
• - preferably a second heat exchanger [preferably flue gas/intermediate gas heat exchanger for the manufacturing mode].

In start-up mode, further heating of NH ₃ occurs preferably by absorption of heat from an electrical heating element.

In order for the vaporized NH ₃ to be catalytically decomposed in start-up mode, it must be heated to the activation temperature of the NH ₃ decomposition catalyst.

In preferred embodiments, the NH ₃ decomposition catalyst is nickel-based and the vaporized NH ₃ is heated to a temperature in the range of preferably 600 to 650°C.

In other preferred embodiments, the NH ₃ decomposition catalyst is ruthenium-based and the vaporized NH ₃ is heated to a temperature in the range of preferably 350 to 400°C.

In all of these embodiments, NH ₃ (part or all of it) is passed through the electrical heating element and heated therein above the activation temperature of the NH ₃ decomposition catalyst in the first NH ₃ decomposition device. The heated NH ₃ then flows into the first NH ₃ decomposition device, where the NH ₃ is at least partially decomposed. In the preferably adiabatic In this reaction, a conversion of 18% can be achieved, depending on the preheating temperature.

NH ₃ - catalytic decomposition

The catalytic decomposition of NH ₃ according to the invention is the actual reaction for the formation of H ₂ , which basically takes place thermally, but is accelerated by the use of an NH ₃ decomposition catalyst. The catalytic decomposition of NH ₃ can be carried out according to the invention under various conditions using various NH ₃ decomposition catalysts and with various connections with different reactor types.

According to the invention, the catalytic decomposition of NH ₃ is preferably carried out by supplying heat in the presence of an NH ₃ decomposition catalyst. Important parameters for the catalytic decomposition of NH ₃ are the type of NH ₃ decomposition catalyst, the reaction temperature and the reaction pressure.

According to the invention, various materials can be used as NH ₃ decomposition catalysts. The reaction temperature at which the catalytic decomposition of NH ₃ takes place is determined in particular by the choice of the NH ₃ decomposition catalyst.

In preferred embodiments of the invention, a nickel-based NH ₃ decomposition catalyst is used. The reaction temperature and the reaction pressure determine the equilibrium conversion. At 900°C and 20 bar pressure, the decomposition of NH ₃ is almost quantitative. At 650°C, the conversion of NH ₃ is about 98.5%, at 500°C only about 95%. According to the invention, reaction temperatures are preferably set in the range from about 600°C to about 900°C, preferably about 600°C to about 700°C, so that a high conversion is achieved. With regard to energy balance and conversion, optimal reaction temperatures are in the range from about 630°C to 640°C. Nickel-based NH ₃ decomposition catalysts are advantageous despite the comparatively high reaction temperature. Due to the high conversion, the remaining content of non-decomposed NH ₃ in the product gas is comparatively low, so that separate separation of non-decomposed NH ₃ for its recovery is preferably avoided. Instead, the joint separation of N ₂ and non-decomposed NH ₃ from the product gas by pressure swing adsorption is combined during the purification of H ₂ .

Preferably, the NH ₃ decomposition catalyst comprises supported nickel. Preferred carrier materials are selected from the group consisting of Al ₂ O ₃ , MgO, SiO ₂ , mesoporous SiO ₂ (e.g. MCF-17, MCM-41, SBA-15), zeolite (e.g. HY, H-ZSM-5), BaMnO ₃ , BaTiO ₃ , BaZrO ₃ , CaMnO ₃ , Ca-TiO ₃ , CaZrO _{3 , CeO2 , Gd2O3 , GdAlO3} , _KNbO3 , _{La2O3 ,} LaAlO3, _MnO2 , NaNbO3, _{Nb2O5 , Sm2O3} , _SmAlO3 , _SrMnO3 , _{SrTiO3 , SrZrO3} , _TiO2 , _Y2 O ₃ , ZrO ₂ , carbon (e.g. CNTs, SWCNTs, AX-21, MSC-30, MESO-C, GNP, activated carbon, graphene, graphene oxide), attapulgite, hydrocalumite, sepiolite, and mixtures thereof.

In other preferred embodiments of the invention, a ruthenium-based NH ₃ decomposition catalyst is used. For this purpose, reaction temperatures in the range from about 450°C to about 500°C are preferably set according to the invention, although somewhat lower conversions of, for example, about 95% can be achieved, so that the remaining residual content of undecomposed NH ₃ in the product gas is greater.

Alternatively, other NH ₃ decomposition catalysts can be used at even lower reaction temperatures. The lower the reaction temperature, the lower the conversion and the more non-decomposed NH ₃ must be separated from the product gas and recycled.

In preferred embodiments, the first NH ₃ decomposition device comprises two catalyst beds connected in series, of which one catalyst bed contains an NH ₃ decomposition catalyst with a comparatively high activation temperature (preferably a first nickel-based NH ₃ decomposition catalyst) and the other catalyst bed contains an NH ₃ decomposition catalyst with a comparatively low activation temperature (preferably a second nickel-based NH ₃ decomposition catalyst). NH ₃ decomposition catalysts with different activation temperatures are known to a person skilled in the art (see, for example, I. Lucentini et al., Ind. Eng. Chem. Res. 2021, 60, 51, 18560-18611 ). According to the invention, NH ₃ decomposition catalysts based on iron, ruthenium, nickel, cerium, cobalt, chromium, iridium, copper, platinum, molybdenum, palladium, zirconium, tungsten and/or vanadium are preferably used; more preferably based on nickel, iron and/or cerium.

In the start-up mode, the catalytic decomposition of the NH ₃ preferably takes place, in particular on the NH ₃ decomposition catalyst with the comparatively low activation temperature (preferably a second nickel-based NH ₃ decomposition catalyst). In the production mode, however, the catalytic decomposition of the NH ₃ preferably takes place first, in particular on the NH ₃ decomposition catalyst with the comparatively high activation temperature (preferably a first nickel-based NH ₃ - decomposition catalyst), and optionally additionally or subsequently on the NH ₃ decomposition catalyst with the comparatively low activation temperature (preferably a second nickel-based NH ₃ decomposition catalyst).

According to the invention, the reaction pressure is preferably about 15 bar a to about 25 bar a. The stoichiometry of the reaction (2 NH ₃ → N ₂ + 3 H ₂ ) increases the volume, which is why an increased reaction pressure generally has a negative effect on the conversion. On the other hand, it is sensible to operate the entire process at higher pressures in order to limit the container volume and thus the investment costs. With a reaction pressure of just 1 bar, conversions of more than 99% could be achieved at reaction temperatures from 400°C. However, since a reaction pressure of 1 bar is only useful for very small systems, the system according to the invention is preferably operated at a higher reaction pressure, even if this means that a certain loss in conversion has to be accepted.

The reaction pressure is particularly predetermined by the way in which the H ₂ is purified. The pressure swing absorption (PSA) preferred according to the invention for purifying H ₂ can preferably be operated effectively at a pressure in the range from about 15 bar to about 25 bar. The pressure of the product gas when leaving the second NH ₃ decomposition device is preferably in the range from about 15 to about 25 bar a, more preferably about 18 bar a to about 22 bar a, even more preferably about 19 bar a to about 21 bar a. In this way, a good balance is found between the requirements of pressure swing adsorption on the one hand and the conversion achieved on the other.

The decomposition of NH ₃ can basically take place in different reactor types.

In adiabatic reaction, the internal heat of the reaction gas is used as an energy source for the reaction. Suitable reactors for this are autothermal reformers and secondary reformers, which work with internal energy generation. Combustion air is added to the process gas and part of the reaction gas is burned to increase the temperature so that the desired temperature prevails at the reactor outlet. The disadvantage is the presence of water in the process gas that is produced during combustion and must be removed by condensation. Part of the non-decomposed NH ₃ then dissolves in the condensed water and is lost or must be recycled. In addition, the high temperatures lead to the formation of significant amounts of nitrogen oxides.

According to the invention, these disadvantages are avoided by physically separating the product gas from the combustion gas and the flue gas formed therefrom.

In the production mode, the decomposition of NH ₃ according to the invention preferably takes place in two stages in two NH ₃ decomposition devices through which the gas flows one after the other. In the first NH ₃ decomposition device, only a portion of the NH ₃ is initially partially decomposed. The remaining decomposition of NH ₃ up to the maximum conversion achieved then takes place in the second NH ₃ decomposition device. For this purpose, the second NH ₃ decomposition device together with the combustion device according to the invention preferably forms a reactor as described in more detail above and designed analogously to a primary reformer.

In the start-up mode, the decomposition of NH ₃ according to the invention preferably takes place in one stage, namely only in the first NH ₃ decomposition device, which may optionally comprise several catalyst beds connected in series.

In both operating modes, the preheated NH ₃ enters the first NH ₃ decomposition device, which contains NH ₃ decomposition catalyst and in which a partial catalytic decomposition of NH ₃ to N ₂ and H ₂ takes place to a certain extent. An intermediate product gas is formed which still contains considerable residual amounts of non-decomposed NH ₃ , but also already formed N ₂ and H _2. As a result of the endothermic decomposition of NH ₃ , the intermediate product gas preferably cools down. Preferably, the conversion of decomposed NH ₃ in the first NH ₃ decomposition device is at most 25%, more preferably at most 20% of the total conversion achieved overall. Preferably, the conversion of decomposed NH ₃ in the first NH ₃ decomposition device is at least 5%, more preferably at least 10%, even more preferably at least 15% of the total conversion achieved overall.

After leaving the first NH ₃ decomposition device, the intermediate gas is used differently depending on the operating mode.

In start-up mode, the intermediate gas is mixed with NH ₃ if necessary and then burned in the combustion device with the supply of combustion air.

As already mentioned, in preferred embodiments in the start-up mode the NH ₃ stream is divided into a first NH ₃ partial stream and a second NH ₃ partial stream. Only the first NH ₃ partial stream is fed to the first decomposition device. The second NH ₃ partial stream flows instead through the second NH ₃ decomposition device. whereby the second NH ₃ decomposition device absorbs heat from the second NH ₃ partial flow. The second NH ₃ partial flow therefore initially only functions as a heat transfer medium. In this way, the second NH ₃ decomposition device is gradually heated until the start-up temperature for the catalytic decomposition of NH ₃ is reached, so that from this point on additional H ₂ is produced in the second NH ₃ decomposition device by catalytic decomposition of NH _3. For example, it is possible for the first NH ₃ partial flow to be fed to the first NH ₃ decomposition device and for all of the intermediate product gas produced thereby (e.g. at 20% conversion: 20 mol% H ₂ + N ₂ and 80 mol% undecomposed NH ₃ ) to be completely burned in the combustion device. The second NH ₃ partial stream is neither fed to the first NH 3 decomposition device nor burned, but is preferably used as a heat transfer medium, preferably circulated for this purpose, and preferably serves, among other things, to heat the second NH ₃ decomposition device.

In the production mode, the intermediate product gas is preferably heated again before it enters the downstream, second NH ₃ decomposition device. The remaining decomposition of NH ₃ then takes place in the second NH ₃ decomposition device until the total conversion is achieved.

In production mode, the product gas is formed in the second NH ₃ decomposition device according to the invention by decomposition of NH ₃ and leaves the second NH ₃ decomposition device via its own outlet. The combustion gas is burned together with combustion air in the combustion device and the flue gas formed in the process also leaves the combustion device via its own outlet, preferably into a flue gas channel. Product gas and flue gas are not mixed with one another, but remain physically separated from one another. Combustion heat formed during the combustion of the combustion gas flows as a heat flow into the second NH ₃ decomposition device and thus supplies the heat required to maintain the endothermic decomposition of NH ₃ .

In preferred embodiments of the invention, the catalytic decomposition of NH ₃ in the production mode in the second NH ₃ decomposition device takes place analogously to a primary reformer. For this purpose, the analog primary reformer comprises both the second NH ₃ decomposition device according to the invention and the combustion device according to the invention. For this purpose, the NH ₃ decomposition catalyst is preferably arranged in the second NH ₃ decomposition device according to the invention in at least one tube through which NH ₃ flows, more preferably at least two tubes, even more preferably at least three tubes. The at least one tube contains the NH ₃ decomposition catalyst. The at least one tube is preferably flowed through with NH ₃ from top to bottom. In a physically separate combustion chamber, a mixture of NH ₃ and H ₂ is preferably burned together with combustion air as combustion gas (combustion device). The N ₂ formed in addition to H ₂ during the catalytic decomposition of NH ₃ is inert and serves as an additional heat carrier. The combustion heat generated by the combustion process in the combustion chamber of the combustion device is used to heat the second NH ₃ decomposition device, preferably the pipe or pipes through which the NH ₃ to be decomposed is passed. For this purpose, a heat flow is passed from the combustion device into the second NH ₃ decomposition device.

The NH ₃ decomposition catalyst in the first NH ₃ decomposition device is preferably the same as in the second NH ₃ decomposition device. If the first NH ₃ decomposition device comprises several catalyst beds connected in series, preferably at least one of these catalyst beds connected in series contains the same NH ₃ decomposition catalyst as the second NH ₃ decomposition device.

combustion gas

According to the invention, heat is provided by combustion of a combustion gas in a combustion device. For this purpose, the combustion device preferably has one or more burners, preferably at least two burners, more preferably at least three burners.

The combustion gas preferably contains NH ₃ . This applies in particular to the start-up mode. The combustion device according to the invention is therefore preferably an NH ₃ combustion device.

The combustion gas preferably contains a mixture of H ₂ and NH ₃ , since this mixture produces a medium flame temperature and has better combustion properties than pure NH ₃ . A suitable mixing ratio of H ₂ and NH ₃ also results in less nitrogen oxide being formed than in the absence of H ₂ .

In the production mode, the residual gas mixture that remains after the separation of H ₂ from the product gas, preferably by pressure swing adsorption, is preferably used as the combustion gas. Fresh NH ₃ is preferably added to this residual gas mixture. Since pressure swing adsorption typically does not separate the complete amount of H ₂ from the product gas, the remaining amount of H ₂ in the residual gas mixture preferably acts as a combustion improver for the NH ₃ .

The intermediate product gas formed in the first NH ₃ decomposition device in the start-up mode contains H ₂ and is mixed with additional NH ₃ if necessary and burned in the combustion device in the start-up mode to form flue gas. Due to the at least partial decomposition of NH _3, a sufficient amount of H ₂ is available to ensure or improve the combustion of the NH ₃ .

In start-up mode, the preferably electrically operated H ₂ O evaporation device and the electrical heating element require electrical energy to evaporate and further heat the NH ₃ for the catalytic decomposition; the subsequent combustion of NH ₃ together with the H ₂ formed by the catalytic decomposition then provides the heat to heat the heat transfer medium.

As already mentioned, in preferred embodiments, the amount of H ₂ in the combustion gas is increased in start-up mode compared to production mode. The higher proportion of H ₂ in the combustion gas promotes the combustion of the mixture of NH ₃ and H ₂ , as a result of which the operating temperature can be reached more quickly. Accordingly, the process according to the invention is preferably operated in production mode with an H ₂ proportion A ₁ and in start-up mode with an H ₂ proportion A ₂ , where A ₂ > A ₁ . In preferred embodiments, the relative difference between A ₂ and A ₁ is at least 1 vol.%, more preferably at least 2 vol.%, even more preferably at least 3 vol.%, most preferably at least 4 vol.%, and in particular at least 5 vol.%.

The person skilled in the art will recognize that the state during the start-up mode does not have to be statically constant, but can change dynamically, particularly in view of the continuous heating of the system or parts thereof. It is therefore preferred according to the invention that for at least part of the total duration of the start-up mode, the proportion A ₂ is increased in comparison to the proportion A _1. For example, the start-up mode can be divided in time into a first section and an immediately subsequent second section of the total duration, with A ₂ > A ₁ during the first section and A ₂ = A ₁ during the second section.

combustion air

Preferably, the combustion device (combustion chamber of the reactor) is supplied with combustion air, which is preferably preheated beforehand in a first flue gas/combustion air heat exchanger and/or a second flue gas/combustion air heat exchanger. Preferably, the first flue gas/combustion air heat exchanger and/or the second flue gas/combustion air heat exchanger are arranged in the flue gas channel, wherein the combustion air absorbs heat from the flue gas.

Preferably, the combustion air is cleaned by a filter before being fed into the system, compressed to the required pressure using a compressor and then passed through the first flue gas/combustion air heat exchanger and/or the second flue gas/combustion air heat exchanger in the flue gas duct and heated. From there, the heated combustion air flows into the combustion device. Shortly before entering the combustion device or within the combustion device, the combustion air is mixed with the combustion gas (preferably NH ₃ mixed with H ₂ ).

Product gas - after catalytic decomposition until purification of H ₂

• - bevorzugt ein dritter Wärmetauscher [bevorzugt Produktgas/Wasser-Wärmetauscher für den Herstellmodus];
• - bevorzugt ein vierter Wärmetauscher [bevorzugt Produktgas/NH₃-Wärmetauscher für den Herstellmodus];
• - bevorzugt ein fünfter Wärmetauscher [bevorzugt Produktgas/Wasser-Wärmetauscher für den Herstellmodus]; und/oder
• - bevorzugt ein sechster Wärmetauscher [bevorzugt Produktgas/Wasser-Wärmetauscher für den Herstellmodus]).

In the production mode, product gas leaves the second NH ₃ decomposition device at a high temperature. In order to utilize the heat contained in the product gas, at least one heat exchanger is preferably provided in the flow direction of the product gas downstream of the second NH ₃ decomposition device for the production mode, through which the product gas flows before the product gas is fed to a purification of H ₂ :

• - preferably a third heat exchanger [preferably product gas/water heat exchanger for the manufacturing mode];
• - preferably a fourth heat exchanger [preferably product gas/NH ₃ heat exchanger for the production mode];
• - preferably a fifth heat exchanger [preferably product gas/water heat exchanger for the manufacturing mode]; and/or
• - preferably a sixth heat exchanger [preferably product gas/water heat exchanger for the manufacturing mode]).

Product gas - residual amounts of non-decomposed NH ₃

In the production mode, the recovery of NH ₃ preferred according to the invention preferably serves to separate non-decomposed NH ₃ from the product gas and to make it available for further use as combustion gas or recovered reactant. A separate recovery of NH ₃ is preferably dispensed with. Thus, according to the invention, in the production mode, the purification of H ₂ from the product gas is preferably carried out by pressure swing adsorption (PSA). According to the invention, small residual amounts of non-decomposed NH ₃ can preferably be separated during pressure swing adsorption, whereby the recovery of NH ₃ and the purification of H ₂ are combined into a single step.

Product gas - purification of H ₂ and separation of residual gas mixture

In the production mode, H ₂ is particularly preferably purified by pressure swing adsorption (PSA) according to the invention. An adsorptive separation in a pressure swing adsorption device is preferred according to the invention, among other things because it takes place at moderate pressures and also achieves high purity of H ₂ , if required ≥ 99.9%, with a yield of H ₂ in the range of e.g. approx. 80 to 85%. As already mentioned, pressure swing adsorption can also separate residual amounts of NH ₃ and possibly H ₂ O in the same work step. For this purpose, the product gas is preferably cooled to the desired temperature using a sixth heat exchanger [preferably product gas/water heat exchanger for the production mode] before entering the pressure swing adsorption device. The corresponding amount of heat is preferably absorbed by the water in the sixth heat exchanger. The cooling water heated in this way is preferably used according to the invention to preheat NH ₃ in a preheating device in which NH ₃ absorbs heat from the water. The cooled product gas is then preferably fed to a pressure swing adsorption device, where the gas mixture is separated under pressure by adsorption.

H ₂ - after purification until storage

In production mode, the separated H ₂ preferably leaves the pressure swing adsorption device and is preferably brought to an increased pressure, for example to approximately 200 bar, using an H ₂ compressor. However, compression of the separated H ₂ to an increased pressure is not absolutely necessary and pressures of significantly less than 200 bar are also included according to the invention. The compressed H ₂ then preferably flows through a first H ₂ heat exchanger, in which cooling water absorbs heat from the compressed H _2. In preferred embodiments, the separated H ₂ is then brought to a further increased pressure using a second H ₂ compressor. The further compressed H ₂ then preferably flows through a second H ₂ heat exchanger, in which cooling water also absorbs heat from the compressed H _2. The compressed H ₂ is then discharged from the system at a pressure of, for example, approximately 70 bar and, for example, stored in a suitable pressure vessel or fed directly for further use.

residual gas mixture

In production mode, the residual gas mixture remaining after the purification/separation of H ₂ , preferably in the pressure swing adsorption device, typically contains N ₂ , H ₂ O, residual NH ₃ and H ₂ . Preferably, the residual gas mixture is fed to the combustion device so that it can be used to generate combustion heat.

flue gas

• - bevorzugt ein zweiter Wärmetauscher [bevorzugt Rauchgas/Zwischenproduktgas-Wärmetauscher für den Herstellmodus; bevorzugt Rauchgas/Wärmeträgermedium-Wärmetauscher für den Anfahrmodus];
• - bevorzugt ein erster Wärmetauscher [bevorzugt Rauchgas/NH₃-Wärmetauscher für den Herstellmodus; Rauchgas/Wärmeträgermedium-Wärmetauscher für den Anfahrmodus];
• - bevorzugt ein erster Rauchgas/Verbrennungsluft-Wärmetauscher;
• - bevorzugt ein Rauchgas/Wasser-Wärmetauscher; und/oder
• - bevorzugt ein zweiter Rauchgas/Verbrennungsluft-Wärmetauscher.

The flue gas leaves the combustion device at a high temperature and preferably enters a flue gas duct. In order to use the heat contained in the flue gas, heat exchangers are preferably provided in the flow direction of the flue gas downstream of the combustion device, through which the flue gas flows before the flue gas is released into the environment, e.g. via a chimney:

• - preferably a second heat exchanger [preferably flue gas/intermediate gas heat exchanger for the production mode; preferably flue gas/heat transfer medium heat exchanger for the start-up mode];
• - preferably a first heat exchanger [preferably flue gas/NH ₃ heat exchanger for the production mode; flue gas/heat transfer medium heat exchanger for the start-up mode];
• - preferably a first flue gas/combustion air heat exchanger;
• - preferably a flue gas/water heat exchanger; and/or
• - preferably a second flue gas/combustion air heat exchanger.

In start-up mode, the flue gas formed during the combustion of the mixture comprising NH ₃ and H ₂ also flows through the flue gas channel and thereby preferably heats the second heat exchanger [preferably flue gas/heat transfer medium heat exchanger for start-up mode] and then preferably the first heat exchanger [preferably flue gas/heat transfer medium heat exchanger for start-up mode], both of which release heat to the heat transfer medium. The flue gas then preferably flows through the first flue gas/combustion air heat exchanger, preferably the flue gas denitrification unit, preferably the flue gas/water heat exchanger and preferably the second flue gas/combustion air heat exchanger. In this way, Combustion air or water is heated by absorbing heat from the flue gas.

water or water vapor

Demineralized water is preferably fed into the system as the water for generating steam. Air and other gases dissolved in the water are preferably removed in a degasser.

The water is preferably preheated via a fifth heat exchanger. In the production mode, the fifth heat exchanger [preferably product gas/water heat exchanger for the production mode] is preferably flowed through by product gas, so that water absorbs heat from the product gas. In the start-up mode, the fifth heat exchanger [preferably heat transfer medium/water heat exchanger for the start-up mode] is preferably flowed through by heat transfer medium, so that water absorbs heat from the heat transfer medium. In the flow direction of the product gas/heat transfer medium, the fifth heat exchanger is preferably arranged downstream of the third heat exchanger.

Preferably, the water is then passed through a flue gas/water heat exchanger and heated. The flue gas/water heat exchanger cools the flue gases from the combustion device in the flue gas duct, whereby the heat contained in the flue gas is used to heat the water vapor.

The steam is then preferably fed into a steam drum.

From the steam drum, the water is preferably passed through a third heat exchanger and thereby absorbs further heat, in order to then preferably be returned to the steam drum. The third heat exchanger is arranged downstream of the second NH ₃ decomposition device in the flow direction of the product gas/heat transfer medium. In production mode, the third heat exchanger [preferably product gas/water heat exchanger for production mode] is preferably used to cool the product gas after it leaves the second NH ₃ decomposition device, with heat contained in the product gas also being used to heat the water vapor. In start-up mode, the third heat exchanger [preferably heat transfer medium/water heat exchanger for start-up mode] is preferably used to transfer heat from the heat transfer medium to water. In start-up mode, hot water vapor is also generated in an H ₂ O evaporation device and, if necessary, fed to the NH ₃ evaporation device together with the water vapor from the steam drum.

By condensing the water vapor in the NH ₃ evaporator, heat is generated to evaporate the preheated NH _3. After flowing through the NH ₃ evaporator, the steam condensate is preferably fed to the preheater, which serves to preheat the NH ₃ so that the heat contained in the water vapor is used in two stages to heat the NH _3. After flowing through the preheater, the steam condensate can be discharged from the system.

As long as there is not enough heat available in the start-up mode to generate water vapor, the preferably electrically operated H ₂ O evaporation device provides water vapor. The NH ₃ fed from the tank into the system is preferably preheated in the preheater using the electrically generated water vapor, analogous to the production mode, and then evaporated in the NH ₃ evaporation device.

heat transfer medium

In start-up mode, a heat transfer medium, preferably N ₂ or NH ₃ , is passed through at least part of the system in order to absorb combustion heat or heat from the flue gas and to heat one or more devices in the system to operating temperature. The heat transfer medium is preferably circulated and brought to the necessary pressure using a compressor. The system according to the invention preferably comprises several valves at suitable locations in order to close the main process path at several locations in start-up mode and to enable the circulation of the heat transfer medium.

Preferably, in start-up mode, the heat transfer medium circulates from the compressor to a fourth heat exchanger [preferably heat transfer medium/heat transfer medium heat exchanger for start-up mode], where it absorbs heat from cross-flow heat transfer medium.

From there, the heat transfer medium flows preferentially to a first heat exchanger in start-up mode [preferably flue gas/heat transfer medium heat exchanger for start-up mode], where it absorbs heat from the flue gas.

Subsequently, in start-up mode, the heat transfer medium flows preferentially to a second heat exchanger [preferably flue gas/heat transfer medium heat exchanger for start-up mode], where it also absorbs heat from the flue gas.

From there, the heat transfer medium flows preferentially through the second NH ₃ -zero decomposition device, where it absorbs combustion heat, which flows as a heat flow from the combustion device into the second NH ₃ decomposition device.

Afterwards, in start-up mode, the heat transfer medium preferably reaches a third heat exchanger [preferably heat transfer medium/water heat exchanger for start-up mode], where it transfers heat to water.

Subsequently, in start-up mode, the heat transfer medium preferably flows again through the fourth heat exchanger [preferably heat transfer medium/heat transfer medium heat exchanger for start-up mode] (i.e. cross-flow), where it transfers heat to the heat transfer medium flowing in cross-flow.

Afterwards, in start-up mode, the heat transfer medium preferably flows through a fifth heat exchanger [preferably heat transfer medium/water heat exchanger for start-up mode], where it transfers heat to water.

Subsequently, in start-up mode, the heat transfer medium preferably flows through a sixth heat exchanger [preferably heat transfer medium/water heat exchanger for start-up mode], where it also transfers heat to water.

Finally, the heat transfer medium is returned to the compressor.

Description of the figures

The invention is explained in more detail below using preferred embodiments with reference to the figures. each show, by means of flow diagrams, preferred embodiments of systems according to the invention on which preferred embodiments of the method according to the invention can be carried out. The embodiment according to a variant of the embodiment according to and only shown as a section. which is not in the section of Details shown preferably correspond to those of .

In Such a process is illustrated schematically. Part of the total NH ₃ used is burned in a mixture with H ₂ and O ₂ (reaction (A)). Combustion releases heat of combustion Δ. The other part of the NH ₃ is catalytically decomposed to H ₂ and N ₂ with the addition of combustion heat, the mixture formed containing a residual amount of undecomposed NH ₃ in addition to H ₂ and N ₂ (reaction (B)). Reactions A and B are preferably carried out separately from one another in a common reactor which is designed analogously to a primary reformer. The majority of the H ₂ is separated as a product from the mixture formed during the decomposition of NH ₃ , typically by pressure swing adsorption (PSA)), and the remaining mixture of unseparated H ₂ , N ₂ and undecomposed NH ₃ is fed to the combustion (recirculation (C)).

If the amount of unseparated H ₂ contained in the remaining mixture is insufficient for satisfactory combustion of NH ₃ , H ₂ can be diverted from the product H ₂ and also fed to the combustion (recirculation (D)). However, this is not preferred. Pressure swing adsorption typically already achieves an excellent purity of H ₂ , and the residual gas mixture remaining in the pressure swing adsorption device after separation of the H ₂ contains a sufficient amount of H ₂ in addition to N ₂ and residual NH ₃ , which can hardly be avoided for process-related reasons. By returning this H ₂ -containing residual gas mixture to the combustion device, the energy contained in the residual gas mixture can be used to generate combustion heat. Additional enrichment of the residual gas mixture with H ₂ for combustion does not make economic sense, at least not in production mode, and is therefore not preferred. If the total amount of the residual gas mixture is not sufficient to generate the required amount of heat for the catalyzed decomposition of NH ₃ , according to the invention the amount of NH ₃ in the combustion gas is preferably increased, but not the amount of H ₂ from the purified valuable product.

illustrates a preferred system according to the invention. For convenience, the production mode and start-up mode are explained one after the other below.

Plant/process according to Figure 2 in manufacturing mode:

In the production mode, liquid NH ₃ , which is present at a low temperature and increased pressure, is led from tank 10 via line 11 by means of pump 12 through preheater 13 and heated. In NH ₃ evaporation device 14, the NH ₃ is evaporated and then flows via line 15 to branch 16, where the NH ₃ flow is divided into two partial flows. Starting from branch 16, a first partial flow of NH ₃ is expanded and fed via line 17 to combustion device 18. A second partial flow of NH ₃ is fed from branch 16 via line 19 through the fourth heat exchanger [preferably product gas/NH ₃ - Heat exchanger for the production mode] 20 and then flows via line 21 through the first heat exchanger [preferably flue gas/NH ₃ heat exchanger for the production mode] 22, where the NH ₃ is further heated. The preheated NH ₃ is fed to the first NH ₃ decomposition device 65, where a partial catalytic decomposition takes place, preferably adiabatically. The intermediate product gas leaving the first NH ₃ decomposition device 65 is fed via line 66 to the second heat exchanger [preferably flue gas/intermediate product gas heat exchanger for the production mode] 67, which is arranged in the flue gas duct 49 in the flow direction of the flue gas upstream of the first heat exchanger 22. There the intermediate product gas is heated up and then introduced via line 23 into the second NH ₃ decomposition device 24. The second NH ₃ decomposition device 24 is preferably flowed through from top to bottom. The heat required to maintain the reaction is generated by heating the second NH ₃ decomposition device 24 by combustion of H ₂ and NH ₃ in the combustion device 18.

In the production mode, after the decomposition of NH _3, the product gas formed (comprising N ₂ , H ₂ and possibly remaining NH ₃ ) flows through the third heat exchanger [preferably product gas/water heat exchanger for the production mode] 26, then the fourth heat exchanger [preferably product gas/NH ₃ heat exchanger for the production mode] 20, then line 27 and, for further cooling, a fifth heat exchanger [preferably product gas/water heat exchanger for the production mode] 28, which is preferably operated with water. Finally, the product gas is further cooled by means of a sixth heat exchanger [preferably product gas/water heat exchanger for the production mode] 29 and then fed via line 30 to a pressure swing adsorption device 31, where the gas mixture is separated under pressure by adsorption. The H ₂ separated in this way leaves the pressure swing adsorption device 31 via line 32, is brought to an increased pressure via a first H ₂ compressor 33, flows through a first H ₂ heat exchanger 34, a second H ₂ compressor 35 for further pressure increase, a second H ₂ heat exchanger 36 and is discharged from the system at a pressure of, for example, about 70 bar via line 37.

The residual gas mixture remaining in the pressure swing adsorption device 31 after separation of the H ₂ contains N ₂ , residual NH ₃ and H ₂ and is returned via return line 38 and fed to the combustion device 18 via branching line 39, so that energy contained in the residual gas mixture can be used to generate combustion heat.

In production mode, combustion air for the combustion process in the combustion device 18 is cleaned via filter 40, compressed by means of compressor 41, passed via line 42 through the second flue gas/combustion air heat exchanger 43 and heated. The combustion air then flows via line 44 and through the first flue gas/combustion air heat exchanger 45, is further heated there and then flows via line 46 and the two branching branch lines 47 and 48 into the combustion device 18, where the combustion air is fed to the partial flow of NH ₃ fed via line 17 in order to burn it and thus generate combustion heat.

In the production mode, the hot flue gas from the combustion in the combustion device 18 is first cooled via the second heat exchanger [preferably flue gas/intermediate gas heat exchanger for the production mode] 67, whereby heat is obtained for heating the intermediate gas supplied to the second NH ₃ decomposition device 24 after leaving the first NH ₃ decomposition device 65. The flue gas is then further cooled via the first heat exchanger [preferably flue gas/NH ₃ heat exchanger for the production mode] 22, whereby heat is obtained for heating the NH ₃ supplied to the first NH ₃ decomposition device 65. The flue gas is then passed through flue gas duct 49 via the first flue gas/combustion air heat exchanger 45, by means of which the combustion air is preheated, and then flows through flue gas denitrification unit 50, by means of which the flue gas is cleaned of nitrogen oxides (NOx). The flue gas then flows through flue gas/water heat exchanger 52 via line 51, whereby heat is obtained for heating water, and then flows through the second flue gas/combustion air heat exchanger 43, which also serves to heat the combustion air. The flue gas is then compressed in the end area of the flue gas duct 49 by means of the flue gas compressor 53 and leaves the system via chimney 54.

In the production mode, water for the production of steam is fed in via line 55, passed through the fifth heat exchanger [preferably product gas/water heat exchanger for the production mode] 28 and then passed at an increased temperature into degasser 56, in which air and other gases dissolved in the water are removed. By means of pump 57, the water is passed through flue gas/water heat exchanger 52 via line 58 and heated. The flue gas/water heat exchanger 52 serves to in the flue gas duct 49, the thermal energy contained in the flue gas being used to heat the water vapor, which is then passed through line 59 into the water vapor drum 60 after passing through the flue gas/water heat exchanger 52. Water can be passed from the water vapor drum 60 via line 61 through the third heat exchanger [preferably product gas/water heat exchanger for the production mode] 26 and thereby absorb further thermal energy in order to then be returned to the water vapor drum via line 62. The third heat exchanger 26 is arranged in the outlet line 25 in the flow direction of the product gas downstream of the second NH ₃ decomposition device 24 and serves to cool the product gas after it leaves the second NH ₃ decomposition device 24. The heat gained in this way can thus be used to generate further water vapor.

In production mode, the hot steam generated in the steam drum 60 is introduced via line 63 into the upper area of the NH ₃ evaporator 14. The condensation of the steam generates the heat to evaporate the preheated NH _3. After flowing through the NH ₃ evaporator 14, the steam condensate is fed via line 64 to the preheater 13, which serves to preheat the NH ₃ so that the heat contained in the steam is used in two stages to heat the NH _3. After flowing through the preheater 13, the steam condensate can be discharged from the system.

System/process according to Figure 2 in start-up mode

In the system concept according to the invention, in start-up mode a heat transfer medium, preferably N ₂ or NH ₃ , is passed through at least part of the system in order to absorb heat from the combustion device or the flue gas and to heat the system's devices to operating temperature. The cold heat transfer medium is preferably circulated and passed through a compressor 77 in order to build up the necessary pressure. In start-up mode, the main process path is closed at several points with at least some of the valves 68, 75, 79, 81, 82, 83 in order to enable the circulation of the heat transfer medium. The first NH ₃ decomposition device 65 is excluded from the circulation.

As long as there is not enough heat available to generate water vapor during start-up, the preferably electrically operated H ₂ O evaporation device 84 provides water vapor. The NH ₃ fed from the tank 10 into the system is preheated with the help of the electrically generated water vapor in analogy to the production mode in preheater 13 and then evaporated in the NH ₃ evaporation device 14. In order for the evaporated NH ₃ to be catalytically decomposed, it must be heated to the activation temperature of the NH ₃ decomposition catalyst, in the case of a nickel-based NH ₃ decomposition catalyst preferably to 600 to 650°C, in the case of a ruthenium-based NH ₃ decomposition catalyst preferably to 350 to 400°C.

In the start-up mode, NH ₃ (part or all of it) is passed through the electric heating element 74 and heated therein above the activation temperature of the NH ₃ decomposition catalyst in the first NH ₃ decomposition device 65. The heated NH ₃ then flows via line 73 into the first NH ₃ decomposition device 65, where the NH ₃ is at least partially decomposed. In the preferably adiabatic reaction, a conversion of 18%, for example, can be achieved, depending on the preheating temperature.

In start-up mode, the intermediate product gas thus formed contains H ₂ and is optionally mixed with further NH ₃ and burned in the combustion device 18 to form flue gas. Due to the partial decomposition of NH _3, a sufficient amount of H ₂ is available to ensure or improve the combustion of the NH _3. The preferably electrically operated H ₂ O evaporation device 84 and the electrical heating element 74 require electrical energy to evaporate and further heat the NH ₃ for the catalytic decomposition; the subsequent combustion of NH ₃ together with the H ₂ formed by the catalytic decomposition then provides the heat to heat the heat transfer medium.

In start-up mode, the heat transfer medium circulates from the compressor 77 to the fourth heat exchanger [preferably heat transfer medium/heat transfer medium heat exchanger for start-up mode] 20 on the cold side, from there via line 21 to the first heat exchanger [preferably flue gas/heat transfer medium heat exchanger for start-up mode] 22, and then via line 80 to the second heat exchanger [preferably flue gas/heat transfer medium heat exchanger for start-up mode] 67. From there, the heat transfer medium flows through the second NH ₃ decomposition device 24 and reaches the third heat exchanger [preferably heat transfer medium/water heat exchanger for start-up mode] 26 via line 25 and then the fourth heat exchanger [preferably heat transfer medium/heat transfer medium heat exchanger for start-up mode] 20 on the hot side. From there, the heat transfer medium flows through the fifth Heat exchanger [preferably heat transfer medium/water heat exchanger for the start-up mode] 28 and then the sixth heat exchanger [preferably heat transfer medium/water heat exchanger for the start-up mode] 29, which ensures a constant inlet temperature in the downstream nitrogen compressor, which compensates for the pressure loss across the system. Alternatively, the downstream compressor can also be an N ₂ /NH ₃ compressor, which fulfils a dual function, ie is used to compress both the N ₂ and the NH ₃ .

In preferred embodiments, in the start-up mode, the NH ₃ stream is divided into a first NH ₃ partial stream and a second NH ₃ partial stream. Only the first NH ₃ partial stream is fed to the first decomposition device 65. The second NH ₃ partial stream is separated via line 80 after flowing through the first heat exchanger [preferably flue gas/heat transfer medium heat exchanger for the start-up mode] 22, preferably flows through the second heat exchanger [preferably flue gas/heat transfer medium heat exchanger for the start-up mode] 67 and then the second NH ₃ decomposition device 24, whereby the second NH ₃ decomposition device 24 absorbs heat from the second NH ₃ partial stream. The second NH ₃ partial stream therefore initially only functions as a heat transfer medium. In this way, the second NH ₃ decomposition device 24 is gradually heated until the light-off temperature (activation temperature) for the catalytic decomposition of NH ₃ is reached, so that from this point on additional H ₂ is produced in the second NH ₃ decomposition device 24 by catalytic decomposition of NH ₃ .

The heat transfer medium is heated in the start-up mode when it flows through the cold side of the fourth heat exchanger [preferably heat transfer medium/heat transfer medium heat exchanger for the start-up mode] 20, where it absorbs heat from the heat transfer medium guided in cross-flow. In addition, the heat transfer medium is heated when it flows through the first heat exchanger [preferably flue gas/heat transfer medium heat exchanger for the start-up mode] 22 and the second heat exchanger [preferably flue gas/heat transfer medium heat exchanger for the start-up mode] 67, where it absorbs heat from the flue gas. In addition, the heat transfer medium is heated when it flows through the second NH ₃ decomposition device 24, where it absorbs combustion heat which flows as a heat flow from the combustion device 18 into the second NH ₃ decomposition device 24.

The heat transfer medium is cooled in the start-up mode when it flows through the third heat exchanger [preferably heat transfer medium/water heat exchanger for the start-up mode] 26, where it gives off heat to water, and when it flows through the warm side of the fourth heat exchanger [preferably heat transfer medium/heat transfer medium heat exchanger for the start-up mode] 20, where it gives off heat to the heat transfer medium guided in cross-flow. The heat transfer medium is also cooled when it flows through the fifth heat exchanger [preferably heat transfer medium/water heat exchanger for the start-up mode] 28 and then the sixth heat exchanger [preferably heat transfer medium/water heat exchanger for the start-up mode] 29, where it gives off heat to water.

The flue gas formed during the combustion of the mixture comprising NH ₃ and H ₂ flows through the flue gas channel 49 in the start-up mode and heats the second heat exchanger [preferably flue gas/heat transfer medium heat exchanger for the start-up mode] 67 and then the first heat exchanger [preferably flue gas/heat transfer medium heat exchanger for the start-up mode] 22, both of which release heat to the heat transfer medium. The flue gas then flows through the first flue gas/combustion air heat exchanger 45, the flue gas denitrification unit 50, the flue gas/water heat exchanger 52 and the second flue gas/combustion air heat exchanger. In this way, combustion air or water is heated by absorbing heat from the flue gas.

When the system has warmed up sufficiently to switch from start-up mode to production mode, the circulation of the heat transfer medium is stopped by means of valves 68, 75, 79, 81, 82, 83.

If NH ₃ or another combustible gas is used as the heat transfer medium, it can be discharged via line 76 and valve 68 and then burned at the flare tower 70. Condensate is preferably separated beforehand in the separation device 71. This condensate can comprise water, which is present in small amounts in the NH ₃ (≤ 0.5% by weight), and/or NH ₃ which was not converted in the second NH ₃ decomposition device 24 in the start-up mode.

illustrates a preferred variant of the inventive system according to . Since the manufacturing mode according to the variant of largely in accordance with corresponds, only the start-up mode is explained below.

If N ₂ is used as the heat transfer medium, NH ₃ can be added continuously.

System/process according to Figure 3 in start-up mode

According to this preferred embodiment, for the start-up mode, the electric heating element 74 is arranged in the flow direction of the NH ₃ downstream of the valve 82 and upstream of the first NH ₃ decomposition device 65. The valve 82 regulates which proportion of NH ₃ is passed into the first NH ₃ decomposition device 65 for partial catalytic decomposition and which proportion of NH ₃ is passed via line 80 into the second NH ₃ decomposition device 24 as a heat transfer medium.

The supply of fuel NH ₃ to the combustion device 18 is temporarily blocked or regulated via valve 75, which is installed downstream in the direction of flow of the NH ₃ directly after branch 16; this function is performed by the first NH ₃ decomposition device 65 and the valve 82.

The circulation of the NH3 as a heat transfer medium then takes place according to the invention as follows: The NH ₃ is passed past branch 16 to the fourth heat exchanger 20 (in not shown again) and then passed to the first heat exchanger 22. From there, it is divided into a first NH ₃ partial stream and a second NH ₃ partial stream.

The first NH ₃ partial stream is fed via valve 82 into the first NH ₃ decomposition device 65. Valve 81 is closed so that the intermediate product gas leaving the first NH ₃ decomposition device is fed via branching line 39 to the combustion device 18 and burned therein.

The second NH ₃ partial flow is fed via line 80 with the valve 81 closed via the second heat exchanger 67 to the second NH ₃ decomposition device 24, where it initially serves as a heat transfer medium (provided that the activation temperature of the NH ₃ decomposition catalyst in the second NH ₃ decomposition device has not yet been reached). The second NH ₃ partial flow leaving the second NH ₃ decomposition device 24 is fed via lines 25 and 27 to the fourth heat exchanger 20, then to the fifth heat exchanger 28 and finally to the sixth heat exchanger 29 (all in not shown again). Valve 83 and valve 68 are closed so that the second NH ₃ partial flow is directed via line 76 to the compressor 77 (all in not shown again). A portion of the NH ₃ is consumed in this way and intermediate product gas is passed via line 19.

List of reference symbols:

10

tank

11

Line

12

pump

13

preheater

14

NH ₃ evaporation device

15

Line

16

junction

17

Line

18

incineration facility

19

Line

20

fourth heat exchanger [preferably product gas/NH ₃ heat exchanger for production mode; heat transfer medium/heat transfer medium heat exchanger for start-up mode]

21

Line

22

first heat exchanger [preferably flue gas/NH ₃ heat exchanger for the production mode; flue gas/heat transfer medium heat exchanger for the start-up mode]

23

Line

24

second NH ₃ decomposition device

25

outlet line

26

third heat exchanger [preferably product gas/water heat exchanger for production mode; heat transfer medium/water heat exchanger for start-up mode]

27

Line

28

fifth heat exchanger [preferably product gas/water heat exchanger for production mode; heat transfer medium/water heat exchanger for start-up mode]

29

sixth heat exchanger [preferably product gas/water heat exchanger for production mode; heat transfer medium/water heat exchanger for start-up mode]

30

Line

31

pressure swing adsorption device

32

Line

33

H ₂ compressor

34

first H ₂ heat exchanger

35

H ₂ compressor

36

second H ₂ heat exchanger

37

hydrogen outlet line

38

return line

39

branching line

40

filter for combustion air

41

compressor

42

Line

43

second flue gas/combustion air heat exchanger

44

Line

45

first flue gas/combustion air heat exchanger

46

Line

47

branch management

48

branch management

49

flue gas duct

50

flue gas denitrification unit

51

Line

52

flue gas/water heat exchanger

53

flue gas compressor

54

Chimney

55

pipe for the supply of water

56

degasser

57

pump

58

Line

59

Line

60

steam drum

61

Line

62

Line

63

Line

64

Line

65

first NH ₃ decomposition device

66

Line

67

second heat exchanger [preferably flue gas/intermediate product gas heat exchanger for production mode; flue gas/heat transfer medium heat exchanger for start-up mode]

68

valve

69

Line

70

torch tower

71

condensate separator

72

pump

73

Line

74

electric heating element

75

valve

76

Line

77

compressor

78

additional tank

79

valve

80

Line

81

valve

82

valve

83

valve

84

H ₂ O evaporation device.

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. 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

• US 4 704 267 A [0006]
• FR 1 469 045 A [0006]
• CN 111 957 270 A [0006]
• CN 113 896 168 A [0006]
• WO 2001/087770 A1 [0006]
• WO 2011/107279 A1 [0006]
• WO 2017/160154 A1 [0006]
• WO 2019/038251 A1 [0006]
• WO 2012/039183 A1 [0006]
• WO 2012/090739 A1 [0006]
• WO 2020/095467 A [0006]
• WO 2021/257944 A1 [0006]
• WO 2022/096529 A1 [0006]
• WO 2022/243410 A1 [0006]
• WO 2022/265647 A1 [0006]
• WO 2022/265648 A1 [0006]
• WO 2022/265650 A1 [0006]
• WO 2022/265651 A1 [0006]
• WO 2011/150370 A2 [0015]
• WO 2013/119281 A1 [0016]

Cited non-patent literature

• I. Lucentini et al., Ind. Eng. Chem. Res. 2021, 60, 51, 18560-18611 [0104]

Claims (15)

A plant for producing H ₂ from NH ₃ ; wherein the plant is operable in a production mode at operating temperatures; wherein the plant is operable in a start-up mode to heat at least one device of the plant from an initial temperature to an operating temperature; wherein the plant for the start-up mode comprises at least the following devices for heating the at least one device to the operating temperature: - a heating element (74) for heating NH ₃ ; - downstream of the heating element (74) in the flow direction of the NH ₃ , a first NH ₃ decomposition device (65) for partially catalytically decomposing the heated NH ₃ to produce a combustion gas comprising H ₂ , N ₂ and residual NH ₃ ; - optionally, downstream of the first NH ₃ decomposition device (65) in the flow direction of the combustion gas, a device for metering combustion air into the combustion gas; - in the flow direction of the combustion gas, downstream of the first NH ₃ decomposition device (65), a combustion device (18) for burning the combustion gas to generate combustion heat and flue gas; - a compressor (77) for compressing a heat transfer medium; and - in the flow direction of the flue gas, downstream of the combustion device (18) and in the flow direction of the heat transfer medium, downstream of the compressor (77), a first heat exchanger (22) and/or a second heat exchanger (67) for heating the heat transfer medium by absorbing heat from the flue gas; and wherein the at least one device of the system is arranged downstream of the first heat exchanger (22) and/or the second heat exchanger (67) in the flow direction of the heat transfer medium and is in fluid communication with the heat transfer medium for absorbing heat from the heat transfer medium. The plant according to claim 1 , wherein the at least one device is selected from: - a second NH ₃ decomposition device (24); preferably in production mode for the catalytic decomposition of vaporized NH ₃ to produce a product gas comprising H ₂ and N ₂ ; - a third heat exchanger (26); preferably in production mode for heating water, preferably for heating or generating water vapor, by absorbing heat from the product gas; - a fourth heat exchanger (20); preferably in production mode for heating NH ₃ by absorbing heat from the product gas; - a fifth heat exchanger (28); preferably in production mode for heating water by absorbing heat from the product gas; and - a sixth heat exchanger (29); preferably in production mode for heating water by absorbing heat from the product gas. The plant according to claim 1 or 2 , wherein the system comprises at least one device selected from: - a first flue gas/combustion air heat exchanger (45); preferably in start-up mode and/or in production mode for heating combustion air by absorbing heat from the flue gas; - a flue gas denitrification unit (50); preferably in start-up mode and/or in production mode for cleaning the flue gas of nitrogen oxides (NOx); - a flue gas/water heat exchanger (52); preferably in start-up mode and/or in production mode for heating water, preferably for heating or generating water vapor, by absorbing heat from the flue gas; - a second flue gas/combustion air heat exchanger (43); preferably in start-up mode and/or in production mode for heating combustion air by absorbing heat from the flue gas. The system according to any preceding claim, wherein the heating element (74) is electrically heated. The system according to one of the preceding claims, comprising in the flow direction of the NH ₃ upstream of the heating element (74) - an H ₂ O evaporation device (84) for evaporating water to produce water vapor; and - an NH ₃ evaporation device (14) for evaporating liquid NH ₃ by absorbing heat from the water vapor. The plant according to claim 5 , wherein the H ₂ O evaporation device (84) is electrically heated. The plant according to any one of the preceding claims, wherein the combustion device (18) and the second NH ₃ decomposition device (24) are in heat exchange with each other and are configured for a heat flow from the combustion device (18) into the second NH ₃ decomposition device (24). A method for starting up a plant for producing H ₂ from NH ₃ comprising the following steps: (c) heating NH ₃ ; (d) partial catalytic decomposition of the heated NH ₃ in a first NH ₃ decomposition device (65) to produce a combustion gas comprising H ₂ , N ₂ and residual NH ₃ ; (e) optionally, metering combustion air into the combustion gas; (f) burning the combustion gas in a combustion device (18) to produce combustion heat and flue gas; (g) compressing a heat transfer medium; (h) heating the heat transfer medium by absorbing heat from the flue gas; and (i) heating at least one device of the system by absorbing heat from the heat transfer medium. The procedure according to claim 8 , wherein the at least one device is selected from: - a second NH ₃ decomposition device (24); preferably after starting up the system for the catalytic decomposition of vaporized NH ₃ to produce a product gas comprising H ₂ and N ₂ ; - a third heat exchanger (26); preferably after starting up the system for heating water, preferably for heating or producing water vapor, by absorbing heat from the product gas; - a fourth heat exchanger (20); preferably after starting up the system for heating NH ₃ by absorbing heat from the product gas; - a fifth heat exchanger (28); preferably after starting up the system for heating water by absorbing heat from the product gas; and - a sixth heat exchanger (29); preferably after starting up the system for heating water by absorbing heat from the product gas. The procedure according to claim 8 or 9 , wherein the heating of NH ₃ in step (c) is carried out using electrical energy. The procedure according to one of the Claims 8 until 10 which comprises the additional steps of (a) evaporating water to produce water vapor; and (b) evaporating liquid NH ₃ by absorbing heat from the water vapor. The procedure according to claim 11 , wherein the generation of water vapor in step (a) is carried out using electrical energy. The procedure according to one of the Claims 8 until 12 , wherein the heat transfer medium is circulated through at least part of the system. The method according to any one of the preceding claims, wherein the heat transfer medium comprises or consists essentially of N ₂ . The method according to any one of the preceding claims, wherein the heat transfer medium comprises NH ₃ or consists essentially thereof.

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