Starting up a plant for catalytically decomposing ammonia

Abstract

The invention relates to a plant for preparing H2 by catalytically decomposing NH3. The plant according to the invention can be operated in a start-up mode in order to heat apparatuses of the plant to an increased operating temperature using a heat-transfer medium, e.g. following interruption of a continuous operation of the plant due to maintenance work. After heating to the operating temperature, the plant according to the invention can be operated in a production mode for continuous production of H2. The invention also relates to a method for starting up a plant for preparing H2 by catalytically decomposing NH3.

Description

Start-up of a plant for the catalytic decomposition of ammonia

[0001] The invention relates to a plant for producing H2 by catalytic decomposition of NH3 to H2 and N2. The plant according to the invention can be operated in a start-up mode to heat plant devices to elevated operating temperature using a heat transfer medium, e.g., 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 H2. The invention further relates to a method for starting up a plant for producing H2 by catalytic decomposition of NH3.

[0002] H2 can be extracted from H2O using renewable energy and then converted into NH3 with N2. NH3 can be stored and transported much more safely than H2. NH3 can then be decomposed back into H2 and N2. After N2 is separated, H2 finds a wide variety of industrial applications.

[0003] The decomposition of NH3 to N2 and H2 is an endothermic reaction (AH° = 45.9 kJ-mol 1 ), in which the amount of substance doubles (2 NH3 N2 + 3 H2), so the reaction is generally favored by high temperatures and low pressures. The higher the pressure, the higher the temperature must be to achieve satisfactory reaction yields. On an industrial scale, the catalytic decomposition of NH3 into N2 and H2 takes place at high temperature and medium pressure in the gas phase.

[0004] Stored NH3 is in liquid form in cooled tanks at atmospheric pressure and -32.8°C. NH3 is pumped into the plant at system pressure. Due to the increased system pressure, the boiling point of the NH3 rises, for example, to approximately 62.2°C at 27.8 bar a. To convert NH3 into the gas phase, heat is required to evaporate the NH3. The vaporized NH3 is then further heated until it reaches a sufficiently high temperature at which it can be decomposed on an NH3 decomposition catalyst.

[0005] The known processes for the catalytic decomposition of NH3 into N2 and H2 require the input of significant amounts of heat. On the one hand, heat is required to bring the process gas and the NH3 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.

[0006] In large-scale processes, this heat is usually provided by the combustion of an energy source (cf. 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 Al; WO 2011 / 107279 Al; WO 2017 / 160154 Al; WO 2019 / 038251 Al; WO 2012 / 039183 Al; WO 2012 / 090739 Al; WO 2020 / 095467 A; WO 2021 / 257944 Al; WO 2022 / 096529 Al; WO 2022 / 243410 Al; WO 2022 / 265647 Al; WO 2022 / 265648 Al; WO 2022 / 265649 Al; WO 2022 / 265650 Al; WO 2022 / 265651 Al). In principle, all energy sources are considered, e.g., natural gas or mixtures of NFF and IE.

[0007] Plants for producing H2 from NH3 typically operate continuously for extended periods without interruption, for example, several weeks or months. However, it is occasionally necessary to shut down such plants into a standby mode, for example, to conduct safety checks, replace catalyst material, or perform other maintenance work. During standby mode, the plants cool down to ambient temperature, depending on the duration of the interruption.

[0008] To bring such a plant back into continuous operation from idle mode, it must first be warmed up to operating temperature; NH3 cannot be decomposed at room temperature. Different parts of the plant typically have different operating temperatures and therefore require warming up to varying degrees. Warming up can generally be achieved by passing a heat transfer medium, e.g. N2, steam, natural gas, or mixtures thereof, through the process side of the plant and starting the combustion of the energy carrier to provide the heat for the heating process. Depending on its properties, the heat transfer medium can either be circulated in a circuit or burned off via a flare.

[0009] To reduce or even completely avoid the use of fossil fuels, part of the NH3 is burned instead of fossil fuels during normal operation of the plant, and the resulting combustion heat is used for the heating process. NH3 then serves as a reactant for the decomposition process and as an energy carrier for generating the necessary heat. However, when mixed with air, NH3 only burns incompletely, which is why the sole combustion of pure NH3 together with combustion air is disadvantageous. This would result in emissions of unburned NH3, which is unacceptable. To improve the combustion of NH3 together with combustion air, a certain amount of generated H2 is added to the portion of NH3 to be burned during normal operation of the plant.

[0010] However, a major problem when starting up the plant is that no H2 is yet available as a decomposition product.

[0011] This problem could be solved for the duration of the plant start-up 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 H2 but would result in CCE emissions; or (ii) Provision of H2 on a small scale and subsequent combustion of the H2 in a mixture with NH3, e.g. through - Production of H2 using an electrically heated device for the catalytic decomposition of NH3; - Production of H2 by electrolysis of water; or - Use of stored H2 retained from previous production.

[0012] However, these solutions have several disadvantages.

[0013] The alternative combustion of natural gas or propane would not only lead to undesirable CO2 emissions, but would also require dual operation for the combustion of the fuel. Since the burner configuration typically needs to be adapted to the fuel, switching from natural gas / propane to NH3 / H2 would require configuration changes, or a second, separate combustion system would have to be installed.

[0014] The temporary production of H2 on a small scale using separate catalytic decomposition devices or electrolysis cells would require considerable additional equipment. This also applies to H2 storage, which would also be fraught with significant safety issues.

[0015] WO 2011 / 150370 A2 relates to the decomposition of NH3 into an H2 gas mixture. A NH3-rich gas mixture of NH3 and air enters a line where the combustion and decomposition of a portion of the mixture is initiated, releasing heat and H2. H2 mixes with the majority of the gas mixture, and the released heat drives the combustion reaction. Upon starting the NH3 flame splitter, the catalyst can be heated electrically, inductively, by briefly burning chemicals on the catalyst and / or the surrounding structure, or by an electric arc. Heating the catalyst can be used to initiate the combustion and decomposition reactions of the NH3 and, if necessary, supply residual heat to the burning gases until the NH3 flame splitter is fully heated.After starting the NH3 flame splitter, the power supply can be switched off or reduced so that the energy required to decompose the NH3 is essentially provided by the combustion of a portion of the NH3 and the combustion of NH3 is essentially sufficient to keep the catalyst hot.

[0016] WO 2013 / 119281 A1 relates to the decomposition of NH3 into an H2-containing gas mixture, wherein an NH3-rich gas mixture of NH3 and air enters a heat exchanger. Part of the NH3 is burned, the remainder is decomposed, forming the H2-containing gas mixture. NH3 flame splitters can be heated to operating temperature by burning a starting mixture and subsequently flowing the burned starting mixture through the NH3 flame splitters, so that the burned starting mixture thermally contacts the heat exchangers and / or burners of the NH3 flame splitters during a starting phase. Since the surface temperatures during the warm-up phase increase, one or more of the following measures can be taken: increasing the total flow of the starting mixture, reducing the oxygen content of the oxidizer component, or increasing the total content of the starting mixture. This allows the NH3 flame splitters to be started quickly even with a comparatively low flow of purified oxygen. The flow of purified oxygen is shut off at or near the end of the starting phase.

[0017] The state-of-the-art plants and processes for extracting H2 from NH3 are not entirely satisfactory, particularly with regard to interruptions to normal operation and subsequent plant start-up. Therefore, there is a need for improved plants and processes that can be economically implemented on a large-scale.

[0018] It is an object of the invention to provide an advantageous plant and process for producing H2 from NH3 that overcome the aforementioned disadvantages. Startup of the plant should be possible without additional, costly measures and equipment, should not rely on fossil fuels, should not entail any additional safety risks, and should be economically feasible and feasible on a large-scale.

[0019] This problem is solved by the subject matter of the patent claims.

[0020] It was surprisingly discovered that certain devices that serve other purposes during normal plant operation can be re-functionalized and re-wired for the duration of the start-up. This makes it possible to extract sufficient amounts of H2 from NH3 through decomposition during plant start-up, allowing the combustion of NH3 in a mixture with H2 to begin, and the plant to slowly warm up to operating temperature. The additional equipment required for plant start-up is thus minimized.

[0021] A first aspect of the invention relates to a plant for producing H2 from NH3; wherein the plant is operable in a production mode (normal operation) at operating temperatures; wherein the plant is operable in a start-up mode (start-up operation) 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 for heating NH3; downstream of the heating element in the flow direction of the NH3, a first NFF decomposition device (pre-reactor) for partially catalytically decomposing the heated NH3 to produce a combustion gas comprising H2, N2 and residual NH3; optionally, in the flow direction of the combustion gas downstream of the first NPh reduction 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 NHs 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 a flue gas / heat transfer medium heat exchanger for the 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 downstream of the first heat exchanger and / or the second heat exchanger 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.

[0022] A second aspect of the invention relates to the use of a plant according to the invention for producing H2.

[0023] A third aspect of the invention relates to a method for starting up a plant for producing H2 from NH3 comprising the following steps: (a) optionally, evaporating water to produce water vapor; (b) optionally, evaporation of liquid NH3 by absorption of heat from the water vapor; (c) heating of NH3; (d) partially catalytically decomposing the heated NH3 in a first NPh decomposition device to produce a combustion gas comprising H2, N2 and residual NH3; (e) optionally, adding combustion air to the combustion gas; (f) burning the combustion gas in a combustion device to produce heat of combustion 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.

[0024] Steps (a), (b), and (e) of the process according to the invention are optional, independently of one another. Preferably, steps (a) to (i), if implemented, are carried out in alphabetical order.

[0025] According to the invention, a distinction is made between the production mode (normal operation) and the start-up mode (start-up operation). While H2 is already produced from NH3 to a certain extent in the start-up mode, the quantity and yield of the H2 produced preferably differ considerably.

[0026] In start-up mode, both the amount and yield of produced H2 are preferably comparatively low; preferably, only the first NH3 decomposition unit is used for the partial catalytic decomposition of NH3, and the produced intermediate gas is burned as combustion gas to generate the required heat.

[0027] In production mode, both the quantity and yield of H2 produced are preferably comparatively high; preferably, both the first NtE conversion device (pre-reactor) and the downstream second NtE conversion device (main reactor) are used for the most complete catalytic decomposition of NH3 possible. The intermediate gas produced in the first Nkh conversion device is not burned as combustion gas, but is preferably fed after heating to the downstream second Nkh conversion device, where the most complete decomposition of the NH3 possible occurs. H2 is then separated from the product gas produced in the second Nkh conversion 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 NH3 in the second NPh decomposition device is not absolutely complete (100.0%), a residual amount of NH3 remains, which is burned as combustion gas after addition of additional, fresh NH3.

[0028] The heat exchangers according to the invention serve to transfer heat from one medium to another without mixing the media. For the purposes of description, with reference to an "A / B heat exchanger," the heat-emitting medium A is mentioned first, followed by the heat-absorbing medium B. Accordingly, for example, a "flue gas, NH3 heat exchanger" serves to transfer heat contained in the flue gas to NH3. For this purpose, the flue gas / NH3 heat exchanger is wired accordingly, i.e., its warmer side is flowed through by flue gas, whereas its cooler side is flowed through by NH3.

[0029] For the purpose of description, the heat exchangers are numbered. This numbering is merely for linguistic differentiation, but should not be understood as meaning 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 lower numbers ("first heat exchanger", "second heat exchanger", "third heat exchanger"). For example, it is possible 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.

[0030] According to the invention, it is possible and also preferred for one and the same heat exchanger to serve a different function in production mode than in start-up mode, in particular for it to be flowed through by different media at least partially or on one side (warm side vs. cold side). In such cases, for the purposes of description, a distinction is made in individual cases between the two operating modes and the respective preferred forms of heat exchange in square brackets. For example, "first heat exchanger [preferably flue gas / NHi heat exchanger for production mode; flue gas / heat transfer medium heat exchanger for start-up mode]" means that the first heat exchanger preferably performs two different functions: In production mode, heat from the flue gas is preferably transferred to NH3 in the first heat exchanger; in 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 is NH3 in start-up mode, it is ultimately a flue gas / NH3 heat exchanger in start-up mode. If such a heat exchanger is described in the context of a specific mode (either production mode or start-up mode), the corresponding preferred form of heat exchange is referred to in the square brackets.

[0031] For the purpose of this description, unless explicitly stated otherwise, the term "water" is used for all its states of matter. Depending on temperature and pressure, this water can exist in liquid or gaseous form, or as a two-phase system, i.e., possibly also as water vapor. This also applies analogously to "NHf."

[0032] The plant according to the invention comprises a first NFF decomposition device and a second NH3 decomposition device, both of which contain NFh decomposition catalysts. The first NFF decomposition device is preferably a fixed-bed reactor. In the first NH3 decomposition device, the decomposition of NH3 preferably takes place adiabatically. The downstream second NH3 decomposition device is preferably designed together with a combustion device analogous to a primary reformer, as used in conventional steam reforming to produce H2, O2, and CO / CO2 from H2O and CH4.

[0033] In production mode, the catalytic decomposition of the NH3 takes place in two stages in the first NH3 decomposition device and the downstream second NFF conversion device. Preferably, the second heat exchanger [preferably flue gas / intermediate product gas heat exchanger for the production mode] is arranged in the flow direction of the NH3 downstream of the first NFF conversion device and preferably upstream of the downstream second NFF conversion device. In production mode, the second heat exchanger preferably serves to heat the intermediate product gas after Leaving the first NH3 decomposition unit and before entering the downstream second NH3 decomposition unit (main reactor, together with the combustion unit analogous to the primary reformer). In production mode, intermediate gas preferentially absorbs heat from flue gas in the second heat exchanger (see Figure 2, second heat exchanger 67).

[0034] In production mode, preheated NH3 enters the first NH3 decomposition device, where a partial catalytic decomposition of NH3 to N2 and H2 occurs to a certain extent. An intermediate product gas is formed which still contains considerable residual amounts of undecomposed NH3, but also already formed N2 and H2. As a result of the endothermic decomposition of NH3, the intermediate product gas preferentially cools. Preferably, the conversion of decomposed NH3 in the first NH3 decomposition device is at most 25%, more preferably at most 20% of the total conversion achieved. Preferably, the conversion of decomposed NH3 in the first NH3 decomposition device is at least 5%, more preferably at least 10%, even more preferably at least 15% of the total conversion achieved.After leaving the first NH3 decomposition unit, the intermediate gas is preferably reheated in the second heat exchanger (preferably a flue gas / intermediate gas heat exchanger for the production mode) before entering the downstream, second NH3 decomposition unit. The remaining decomposition of NH3 then takes place in the second NH3 decomposition unit until the total conversion is achieved.

[0035] In contrast, in start-up mode, the catalytic decomposition of NH3 preferably occurs in a single stage, specifically only in the first NH3 decomposition device. The second NH3 decomposition device preferably does not yet contribute to the decomposition of NH3 in start-up mode, at least during the early phases of the start-up mode.

[0036] In start-up mode, preheated NH3 enters the first NH3 decomposition device, where a partial catalytic decomposition of NH3 into N2 and H2 occurs to a certain extent. An intermediate gas is also formed, which still contains significant residual amounts of undecomposed NH3, but also already formed N2 and H2. Preferably, the conversion of decomposed NH3 in the first NH3 decomposition device is at most 25%, more preferably at most 20%, based on the amount of NH3. Preferably, the conversion of decomposed NH3 in the first NH3 decomposition device is at least 5%, more preferably at least 10%, and even more preferably at least 15%, based on the amount of NH3.

[0037] In contrast to the production mode, in start-up mode, the intermediate gas formed in the first NH3 decomposition unit is preferably not fed into the second NH3 decomposition unit, but instead into the combustion unit. The amount of H2 formed in the intermediate gas is sufficient for satisfactory combustion of the NH3, so that the combustion of the intermediate gas generates sufficient combustion heat to gradually warm the plant to operating temperature.

[0038] In preferred embodiments, in start-up mode, the NH3 stream is split into a first NH3 substream and a second NH3 substream. Only the first NH3 substream is fed to the first decomposition device. The second NH3 substream flows instead through the second NH3 decomposition device, whereby the second NFF decomposition device absorbs heat from the second NH3 substream. The second NFF substream therefore initially functions only as a heat transfer medium. In this way, the second NH3 decomposition device is gradually heated until the light-off temperature (activation temperature) for the catalytic decomposition of NH3 is reached, so that from this point on, additional H2 is produced in the second NH3 decomposition device by catalytic decomposition of NH3 (see Figure 3).

[0039] In preferred embodiments, the amount of H2 in the combustion gas is increased in start-up mode compared to production mode. The higher ratio of H2 to NH3 promotes combustion, allowing operating temperature to be reached more quickly.

[0040] A significant advantage of the invention is that the first NH3 decomposition device can be used for two different purposes, namely in start-up mode for generating the combustion gas and in production mode for the first stage of a total two-stage decomposition of NH3 to generate the product gas. The plant according to the invention preferably does not comprise any further separate NH3 decomposition device, which is used exclusively in start-up mode, but not in production mode. While such separate NH3 decomposition devices are commercially available, possibly already equipped with an electric heater, such additional equipment expenditure can be dispensed with according to the invention.

[0041] 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 H2O steam generator.

[0042] To ensure that the NH3 is at a sufficiently high temperature for catalytic decomposition in the first NF3 conversion device, the system according to the invention has a heating element for heating NH3 in the start-up mode. The heating element is preferably electrically operated. Thus, the heating of NH3 in step (c) of the process according to the invention preferably takes place using electrical energy.

[0043] Preferably, the heating element is only intended 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 NH3 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, the The entire bypass, including the heating element, is no longer flowing with NH3. To enable such a reaction, suitable valves are preferably provided that allow the targeted flow of NH3 through the bypass or not through the bypass.

[0044] The NH3 is typically provided in liquid form as a starting material and must therefore first be vaporized. This applies not only to the production mode, but also to the start-up mode. According to the invention, the NH3 is preferably vaporized by absorbing heat from water vapor.

[0045] In production mode, the steam is preferably provided by process heat, with water as a heat transfer medium absorbing heat from the product gas and / or the flue gas and the thus heated steam transferring heat to liquid NH3.

[0046] In start-up mode, however, no process heat is initially present, so the system according to the invention preferably comprises an H2O evaporator for evaporating water to generate steam. The H2O evaporator is preferably arranged upstream of the heating element in the direction of flow of the NH3. The H2O evaporator is preferably electrically heated. Therefore, the process according to the invention preferably comprises the two optional steps (a) and (b), with the generation of steam in step (a) of the process according to the invention preferably taking place using electrical energy.

[0047] Preferably, the preferably electrically heated H2O evaporation device is provided only for the start-up mode and is switched off in the production mode. In preferred embodiments, the H2O evaporation device is connected to a bypass via a line system, so that in the start-up mode, the water can be passed through the bypass through the H2O evaporation device to be heated and evaporated there. Once the production mode is reached, water preferably no longer flows through the entire bypass, including the H2O evaporation device. To enable such a reaction, suitable valves are preferably provided which allow the targeted flow of water through the bypass or not through the bypass.

[0048] In addition, the system according to the invention preferably comprises an NFF evaporation device for evaporating liquid NH3 by absorbing heat from the water vapor.

[0049] In this way, in start-up mode, the liquid NH3 can first be evaporated by absorbing heat from the water vapor, which in turn is generated in the preferably electrically heated H2O evaporation device. The evaporated NH3 is then passed through the preferably electrically heated heating element, where it is heated to a temperature sufficient for the subsequent partial catalytic decomposition of the NH3 in the first NFF combustion device. The intermediate gas thus produced is then combusted in the combustion device, generating flue gas and combustion heat.

[0050] 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.

[0051] In production mode, the heat of combustion essentially serves to heat the NH; to the required reaction temperature, so that the reaction heat of the endothermic reaction is provided in the first NH; decomposition unit and the downstream second NH; decomposition unit, and the conversion takes place via both NH; decomposition units with high conversion. For this purpose, steam is preferably used as the heat transfer medium, especially for the evaporation of the NH;.

[0052] 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. For this purpose, the heat transfer medium preferably absorbs heat directly from the combustion heat and / or indirectly from the flue gas. For this purpose, the flue gas flow direction is preferably downstream of the combustion device and the heat transfer medium flow direction is preferably downstream of the compressor. - 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.

[0053] In preferred embodiments, the heat transfer medium comprises or consists essentially of N2. N2 is preferably circulated through at least part of the system until the desired operating temperatures of the system components are reached. Once this state is reached, N2 is preferably discharged from the system and switched to production mode. For this change, NH3 is preferably continuously added to the N2, and the mixture of N2 and NH3 is optionally combusted via a flare. Once the NH3 content in the mixture with N2 is sufficiently high, production mode can be started.

[0054] In other preferred embodiments, the heat transfer medium comprises or consists essentially of NH3. NH3 is preferably circulated through at least part of the system until the desired operating temperatures of the system components are reached. Once this state is reached, the production mode is initiated.

[0055] In preferred embodiments, in start-up mode, the NH3 stream is split into a first NH3 substream and a second NH3 substream. Only the first NH3 substream is fed to the first decomposition device. The second NH3 substream flows instead through the second NH3 decomposition device, whereby the second NH3 decomposition device absorbs heat from the second The second NH3 partial stream initially functions only as a heat transfer medium. In this way, the second NH3 decomposition device is gradually heated until the light-off temperature (activation temperature) for the catalytic decomposition of NH3 is reached, so that from this point on, additional H2 is produced in the second NH3 decomposition device through catalytic decomposition of NH3.

[0056] In preferred embodiments, the amount of H2 in the combustion gas is increased in start-up mode compared to production mode. The higher ratio of H2 to NH3 promotes combustion, allowing operating temperature to be reached more quickly.

[0057] In start-up mode, at least one device of the system is arranged downstream of the first heat exchanger and / or the second heat exchanger 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. This at least one device of the system is heated in start-up mode by absorbing heat from the heat transfer medium.

[0058] In preferred embodiments, the at least one device heated in start-up mode by absorbing heat from the heat transfer medium is the second NFF decomposition device (see Figure 2, second NH3 decomposition device 24). In production mode, the second NH3 decomposition device is preferably connected downstream of the first NH3 decomposition device and preferably serves for the catalytic decomposition of vaporized NH3 to produce a product gas comprising H2 and N2. For the transition from start-up mode to production mode, the system according to the invention preferably comprises corresponding lines and valves that enable a modified connection (see Figure 2).

[0059] In preferred embodiments, the at least one device that is heated in start-up mode by absorbing heat from the heat transfer medium is a third heat exchanger [preferably a heat transfer medium / water heat exchanger for the start-up mode] (see Figure 2, third heat exchanger 26). In production mode, the third heat exchanger [preferably a product gas / water heat exchanger for the production mode] preferably serves to heat water, preferably to heat or generate steam, by absorbing heat from the product gas. For the transition from start-up mode to production mode, the system according to the invention preferably comprises corresponding lines and valves that enable a modified wiring (see Figure 2).

[0060] 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 a heat transfer medium / heat transfer medium heat exchanger for the start-up mode] (see Figure 2, fourth heat exchanger 20). In the production mode, the fourth heat exchanger [preferably a product gas / NH3 heat exchanger for the production mode] serves to heat NH3 by absorbing of heat from the product gas. For the transition from start-up mode to production mode, the system according to the invention preferably includes appropriate lines and valves that allow for a modified connection (see Figure 2).

[0061] In preferred embodiments, the at least one device that is heated in start-up mode by absorbing heat from the heat transfer medium is a fifth heat exchanger [preferably a heat transfer medium / water heat exchanger for the start-up mode] (see Figure 2, fifth heat exchanger 28). In production mode, the fifth heat exchanger [preferably a product gas / water heat exchanger for the production mode] preferably serves to heat water by absorbing heat from the product gas. For the transition from start-up mode to production mode, the system according to the invention preferably comprises corresponding lines and valves that enable a modified wiring (see Figure 2).

[0062] In preferred embodiments, the at least one device that is heated in start-up mode by absorbing heat from the heat transfer medium is a sixth heat exchanger [preferably a heat transfer medium / water heat exchanger for the start-up mode] (see Figure 2, sixth heat exchanger 29). In production mode, the sixth heat exchanger [preferably a product gas / water heat exchanger for the production mode] preferably serves to heat water by absorbing heat from the product gas. For the transition from start-up mode to production mode, the system according to the invention preferably comprises corresponding lines and valves that enable a modified wiring (see Figure 2).

[0063] Furthermore, in start-up mode, the flue gas generated during combustion of the combustion gas can also transfer heat to at least one device in the system. This at least one device is typically located in the flue gas duct. This at least one device is preferably located downstream of the first heat exchanger and / or the second heat exchanger in the flow direction of the flue gas.

[0064] 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. Figure 2, first flue gas / combustion air heat exchanger 45), which preferably serves in the start-up mode and / or in the production mode to heat combustion air by absorbing heat from the flue gas.

[0065] 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. Figure 2, flue gas denitrification unit 50), which preferably serves in the start-up mode and / or in the production mode to clean the flue gas of nitrogen oxides (NOx).

[0066] 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. Figure 2, 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.

[0067] 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. Figure 2, second flue gas / combustion air heat exchanger 43), which preferably serves in the start-up mode and / or in the production mode to heat combustion air by absorbing heat from the flue gas.

[0068] Preferably, the combustion device and the second NH3 decomposition device are in heat exchange with each other and are configured for a heat flow from the combustion device to the second NH3 decomposition device. For this purpose, they are preferably designed analogously to a primary reformer, as used in conventional steam reforming to produce H2, O2, and CO / CO2 from H2O and CEE.

[0069] In preferred embodiments of the plant according to the invention, the plant is designed in production mode (ie during normal operation) for a throughput based on H2 of at least 500 mol-h 1 designed, preferably at least 1000 mol-h 1 , preferably at least 5000 mol-h 1 , more preferably at least 10,000 mol-h 1 , most preferably at least 50,000 mol-h 1 , and in particular at least 100,000 mol-h 1 .

[0070] In preferred embodiments of the plant according to the invention, the plant comprises a tank for liquid NH3, which has a volume of at least 50 m 3 has, preferably at least 100 m 3 , preferably at least 500 m 3 , more preferably at least 1000 m 3 , preferably at least 5000 m 3 , and in particular at least 10,000 m 3 .

[0071] In preferred embodiments of the plant according to the invention, the plant comprises, in addition to the first NH3 decomposition device, a second NH3 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 comprising NH3 decomposition catalyst; wherein each catalyst bed is preferably present in a tube; wherein the catalyst beds are preferably connected in parallel. Preferably, each catalyst bed contains the same NH3 decomposition catalyst.

[0072] In preferred embodiments of the plant according to the invention, the plant comprises, in addition to the first NH3 decomposition device, a second NH3 decomposition device with at least one catalyst bed which comprises NH3 decomposition catalyst, wherein the length of the catalyst bed in the flow direction for NH3 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 especially at least 3.5 m; wherein the catalyst bed is preferably present in a tube.

[0073] 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 combustion of the combustion gas.

[0074] 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.

[0075] In preferred embodiments of the process according to the invention, in the production mode (ie during normal operation) a throughput based on H2 of at least 500 mol-h 1 achieved, preferably at least 1000 mol-h 1 , preferably at least 5000 mol-h 1 , more preferably at least 10,000 mol-h 1 , most preferably at least 50,000 mol-h 1 , and in particular at least 100,000 mol-h 1 .

[0076] In preferred embodiments of the process according to the invention, in the production mode (ie during normal operation), the liquid NH3 is taken from a tank with a volume of at least 50 m 3 taken, preferably at least 100 m 3, preferably at least 500 m 3 , more preferably at least 1000 m 3 , preferably at least 5000 m 3 , and in particular at least 10,000 m 3 .

[0077] In preferred embodiments of the process according to the invention, in the production mode (ie during normal operation), the catalytic decomposition of NH3 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 comprising NH3 decomposition catalyst; wherein each catalyst bed is preferably present in a tube; wherein the catalyst beds are preferably flowed through in parallel by NH3.

[0078] 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 NH3 decomposition catalyst, wherein the length of the catalyst bed in the flow direction for NH3 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

[0079] In preferred embodiments of the process according to the invention, in the production mode (ie 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.

[0080] According to the invention, the catalytic decomposition of NH3 means the formation of N2 and H2, occasionally referred to in the prior art as "cleavage" or "cracking" of NH3.

[0081] According to the invention, the catalytic decomposition of NH3 preferably takes place in the absence of O2.

[0082] Preferably, the invention comprises the following measures in the manufacturing mode: (i) evaporation of NH3; (ii) catalytic decomposition of NH3 with the addition of heat to obtain a product gas comprising N2, H2 and optionally undecomposed NH3; (iii) heat recovery; (iv) recovery of non-decomposed NH3, if necessary; (v) Purification of H2.

[0083] H2O is not a product of the reaction and can be present in very small amounts, as H2O is often present in liquid NH3, at concentrations of a maximum of 0.5 wt%, typically < 0.3 wt%. Due to the evaporation of NH3, H2O is expected to be present in lower concentrations. NH3 - from storage to catalytic decomposition

[0084] According to the invention, the NH3 is preferably stored as starting material.

[0085] The stored NH3 is preferably in liquid form in a cooled tank, at atmospheric pressure and a temperature below its boiling point of -33.5 °C. NH3 is fed into the plant using a pump, preferably at plant pressure.

[0086] Before the NH3 can be catalytically decomposed, it is preferably heated successively to several temperature levels according to the invention.

[0087] Starting with liquid NH3, the NH3 is preferably heated and subsequently evaporated to a medium temperature level (<300°C) by absorbing heat from water or steam. In production mode, the steam is preferably generated by absorbing heat from flue gas and / or product gas. In start-up mode, the steam is preferably generated by an electrically operated H2O evaporation device.

[0088] Preferably, a preheater is arranged in the flow direction of the NH3 downstream of the tank and upstream of the NH3 evaporation device. This preheater preferably serves to heat the NH3 to the desired temperature at the inlet to the NH3 evaporation device and in which NH3 absorbs heat from water, which in turn has previously left the NH3 evaporation device as steam condensate. Steam and steam condensate are preferably passed in countercurrent through the preheater and the NH3 evaporation device.

[0089] Subsequently, the NH3 is preferably further heated to a high temperature level (>300°C).

[0090] In production mode, the further heating of NH3 is preferably carried out by absorbing heat directly from flue gas and / or product gas, i.e. without water as a heat transfer medium.

[0091] For this purpose, appropriate heat exchangers are provided for the manufacturing mode: - preferably a fourth heat exchanger [preferably product gas / NHs heat exchanger for the manufacturing mode]; - preferably a first heat exchanger [preferably flue gas / NHs heat exchanger for the manufacturing mode]; and / or - preferably a second heat exchanger [preferably flue gas / intermediate gas heat exchanger for the manufacturing mode].

[0092] In start-up mode, further heating of NH3 occurs preferentially by absorbing heat from an electrical heating element.

[0093] In order for the vaporized NH3 to be catalytically decomposed in start-up mode, it must be heated to the activation temperature of the NPh decomposition catalyst.

[0094] In preferred embodiments, the NH3 decomposition catalyst is nickel-based and the vaporized NH3 is heated to a temperature in the range of preferably 600 to 650°C.

[0095] In other preferred embodiments, the NPh decomposition catalyst is ruthenium-based and the vaporized NH3 is heated to a temperature in the range of preferably 350 to 400°C.

[0096] In all of these embodiments, NH3 (part or all of it) is passed through the electric heating element and heated therein above the activation temperature of the NH3 decomposition catalyst in the first NTE decomposition device. The heated NH3 then flows into the first NTE decomposition device, where the NH3 is at least partially decomposed. In the preferably adiabatic reaction, a conversion of, for example, 18% can be achieved, depending on the preheating temperature. NH3 - catalytic decomposition

[0097] The catalytic decomposition of NH3 according to the invention is the actual reaction for the formation of H2, which basically proceeds thermally but is accelerated by the use of an NPh decomposition catalyst. The catalytic decomposition of NH3 can be carried out according to the invention under various conditions using different NIE decomposition catalysts and with various configurations with different reactor types.

[0098] According to the invention, the catalytic decomposition of NH3 is preferably carried out by supplying heat in the presence of an NH3 decomposition catalyst. Important parameters for the catalytic decomposition of NH3 are the type of NfE decomposition catalyst, the reaction temperature, and the reaction pressure.

[0099] Various materials can be considered as the NH3 decomposition catalyst according to the invention. The reaction temperature at which the catalytic decomposition of NH3 occurs is determined in particular by the choice of the NH3 decomposition catalyst.

[0100] In preferred embodiments of the invention, a nickel-based NfE decomposition catalyst is used. The reaction temperature and reaction pressure determine the equilibrium conversion. At 900°C and 20 bar pressure, the decomposition of NH3 is almost quantitative. At 650°C, the NH3 conversion is approximately 98.5%, and at 500°C, only approximately 95%. According to the invention, reaction temperatures are preferably set in the range of approximately 600°C to approximately 900°C, preferably approximately 600°C to approximately 700°C, so that a high conversion is achieved. With regard to energy balance and conversion, optimal reaction temperatures are in the range of approximately 630°C to 640°C. Nickel-based NH3 decomposition catalysts are advantageous despite the comparatively high reaction temperature.Due to the high conversion, the remaining content of undecomposed NH3 in the product gas is comparatively low, so separate separation of undecomposed NH3 for its recovery is preferable. Instead, N2 and undecomposed NH3 are separated together from the product gas by pressure swing adsorption during the purification of H2.

[0101] Preferably, the NH3 decomposition catalyst comprises supported nickel. Preferred support materials are selected from the group consisting of Al2O3, MgO, SiCE, mesoporous SiCE (e.g. MCF-17, MCM-41, SBA-15), zeolite (e.g. HY, H-ZSM-5), BaMnO3, BaTiO3, BaZrO3, CaMnO3, CaTiO3, CaZrO3, CeO2, Gd2O3, GdAlO3, KNbO3, La2O3, LaAlO3, MnO2, NaNbO3, Nb2O5, Sm2O3, SmAlCh, SrMnO3, SrTiO3, SrZrO3, TiO2, Y2O3, ZrO2, carbon (e.g. CNTs, SWCNTs, AX-2I, MSC-30, MESO-C, GNP, activated carbon, graphene, graphene oxide), Attapulgite, hydrocalumite, sepiolite, and mixtures thereof.

[0102] In other preferred embodiments of the invention, a ruthenium-based NH3 decomposition catalyst is used. For this purpose, reaction temperatures in the range of approximately 450°C to approximately 500°C are preferably set according to the invention, although somewhat lower conversions of, for example, approximately 95% can be achieved, so that the remaining residual content of undecomposed NH3 in the product gas is higher.

[0103] Alternatively, other NH3 decomposition catalysts can be used at even lower reaction temperatures. The lower the reaction temperature, the lower the conversion, and the more undecomposed NH3 must be separated from the product gas and recycled.

[0104] In preferred embodiments, the first NH3 decomposition device comprises two catalyst beds arranged in series, one of which contains an NH3 decomposition catalyst with a comparatively high activation temperature (preferably a first nickel-based NH3 decomposition catalyst) and the other catalyst bed contains an NFh decomposition catalyst with a comparatively low activation temperature (preferably a second nickel-based NFh decomposition catalyst). NFh decomposition catalysts with different activation temperatures are known to those skilled in the art (see, for example, I. Lucentini et al., Ind. Eng. Chem. Res. 2021, 60, 51, 18560-18611). According to the invention, NFF reduction 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.

[0105] In start-up mode, the catalytic decomposition of the NH3 preferably takes place, in particular, on the NFE decomposition catalyst with the comparatively low activation temperature (preferably a second nickel-based NFF decomposition catalyst). In production mode, however, the catalytic decomposition of the NH3 preferably takes place first, in particular, on the NFF decomposition catalyst with the comparatively high activation temperature (preferably a first nickel-based NH3 decomposition catalyst), and optionally additionally or subsequently on the NH3 decomposition catalyst with the comparatively low activation temperature (preferably a second nickel-based NH3 decomposition catalyst).

[0106] According to the invention, the reaction pressure is preferably between about 15 bar a and about 25 bar a. The stoichiometry of the reaction (2 NH3 N2 + 3 H2) increases the volume, which is why an increased reaction pressure generally has a negative effect on the conversion. On the other hand, it is advisable to operate the entire process at higher pressures in order to limit the vessel volume and thus the investment costs. With a reaction pressure of only 1 bar, conversions of more than 99% could be achieved at reaction temperatures above 400°C. However, since a reaction pressure of 1 bar is only appropriate for very small plants, the plant according to the invention is preferably operated at a higher reaction pressure, even if this entails a certain loss in conversion.

[0107] The reaction pressure is particularly determined by the design of the H2 purification. The pressure swing absorption (PSA) for purifying H2, which is preferred according to the invention, can preferably be effectively operated at a pressure in the range of about 15 bar to about 25 bar. The pressure of the product gas upon leaving the second NFF reduction device is preferably in the range of 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 achieved conversion on the other.

[0108] The decomposition of NH3 can basically take place in different reactor types.

[0109] In adiabatic reaction conditions, the internal heat of the reaction gas is used as the energy source for the reaction. Suitable reactors for this purpose are autothermal reformers and secondary reformers, which operate with internal energy generation. Combustion air is added to the process gas, and a portion of the reaction gas is combusted to raise the temperature to the desired temperature at the reactor outlet. A disadvantage is the presence of water in the process gas produced during combustion, which must be removed by condensation. Some of the undecomposed NH3 then dissolves in the condensed water and is lost or must be recycled. Furthermore, the high temperatures lead to the formation of significant amounts of nitrogen oxides.

[0110] According to the invention, these disadvantages are avoided by physically separating the product gas from the combustion gas and the flue gas formed therefrom.

[0111] In production mode, the decomposition of NH3 according to the invention preferably takes place in two stages in two NPh conversion devices through which the gas flows one after the other. In the first NPh conversion device, only a portion of the NH3 is initially partially decomposed. The remaining decomposition of NH3 up to the maximum conversion achieved then takes place in the second NH3 conversion device. For this purpose, the second NPh conversion device, together with the combustion device according to the invention, preferably forms a reactor, as described in more detail above, designed analogously to a primary reformer.

[0112] In start-up mode, the decomposition of NH3 according to the invention preferably takes place in one stage, namely only in the first NPh decomposition device, which may optionally comprise several catalyst beds arranged in series.

[0113] In both operating modes, the preheated NH3 enters the first NPh conversion device, which contains an NH3 conversion catalyst and in which a partial catalytic decomposition of NH3 to N2 and H2 occurs to a certain extent. An intermediate product gas is formed which still contains significant residual amounts of undecomposed NH3, but also already formed N2 and H2. As a result of the endothermic decomposition of NH3, the intermediate product gas preferentially cools. Preferably, the conversion of decomposed NH3 in the first NH3 conversion device is at most 25%, more preferably at most 20% of the total conversion achieved. Preferably, the conversion of decomposed NH3 in the first NPh conversion device is at least 5%, more preferably at least 10%, even more preferably at least 15% of the total conversion achieved.

[0114] After leaving the first NPh reduction device, the intermediate gas is used differently depending on the operating mode.

[0115] In start-up mode, the intermediate product gas is mixed with NH3 if necessary and then burned in the combustion device with the supply of combustion air.

[0116] As already mentioned, in preferred embodiments, in start-up mode, the NFF stream is split into a first NH3 substream and a second NH3 substream. Only the first NH3 substream is fed to the first decomposition device. The second NH3 substream instead flows through the second NH3 decomposition device, whereby the second NH3 decomposition device absorbs heat from the second NH3 substream. The second NH3 substream therefore initially functions only as a heat transfer medium. In this way, the second NH3 decomposition device is gradually heated until the start-up temperature for the catalytic decomposition of NH3 is reached, so that from this point on, additional H2 is produced in the second NH3 decomposition device by catalytic decomposition of NH3. For example, it is possible that the first NFF fraction stream is fed to the first NFh decomposition device and all the intermediate gas produced (e.g.at 20% conversion: 20 mol% H2 + N2 and 80 mol% undecomposed NH3) is completely combusted in the combustion device. The second NFF part stream is neither fed to the first NH3 decomposition device nor combusted, but is preferably used as a heat transfer medium, preferably circulated for this purpose, and preferably serves, among other things, to heat the second NFF decomposition device.

[0117] In production mode, the intermediate gas is preferably reheated before entering the downstream, second NH3 decomposition device. The remaining decomposition of NH3 then takes place in the second NFh decomposition device until the total conversion is achieved.

[0118] In production mode, the product gas is formed in the second NFF decomposition device according to the invention by the decomposition of NH3 and exits the second NIE decomposition device via its own outlet. The combustion gas is combusted together with combustion air in the combustion device, and the flue gas thus formed also exits the combustion device via its own outlet, preferably into a flue gas duct. Product gas and flue gas are not mixed with each other but remain physically separated. Combustion heat generated during the combustion of the combustion gas flows as a heat flow into the second NH3 decomposition device, thus providing the heat required to maintain the endothermic decomposition of NH3.

[0119] In preferred embodiments of the invention, the catalytic decomposition of NH3 in the production mode in the second NH3 decomposition device takes place analogously to a primary reformer. For this purpose, the analog primary reformer comprises both the second NFF decomposition device according to the invention and the combustion device according to the invention. For this purpose, the NH3 decomposition catalyst is preferably arranged in the second NFF decomposition device according to the invention in at least one tube through which NH3 flows, more preferably at least two tubes, even more preferably at least three tubes. The at least one tube contains the NFF decomposition catalyst. The at least one NH3 preferably flows through the tube from top to bottom. In a physically separate combustion chamber, a mixture of NH3 and H2 is preferably burned as the combustion gas together with combustion air (combustion device). The N2 formed alongside H2 during the catalytic decomposition of NH3 is inert and serves as an additional heat transfer medium. The combustion heat generated by the combustion process in the combustion chamber of the combustion device is used to heat the second NIA decomposition device, preferably the tube(s) through which the NH3 to be decomposed is passed. For this purpose, a heat flow is directed from the combustion device into the second NFh decomposition device.

[0120] The NH3 decomposition catalyst in the first NIA decomposition device is preferably the same as in the second NH3 decomposition device. If the first NIA decomposition device comprises several catalyst beds arranged in series, preferably at least one of these catalyst beds arranged in series contains the same NFF decomposition catalyst as the second NH3 decomposition device. combustion gas

[0121] 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.

[0122] The combustion gas preferably contains NH3. This applies particularly to the start-up mode. The combustion device according to the invention is therefore preferably an NH3 combustion device.

[0123] The combustion gas preferably contains a mixture of H2 and NH3, as this mixture produces a medium flame temperature and exhibits better combustion properties than pure NH3. A suitable mixing ratio of H2 and NH3 also results in less nitrogen oxide formation than in the absence of H2.

[0124] In production mode, the residual gas mixture remaining after the separation of H2 from the product gas, preferably by pressure swing adsorption, is preferably used as the combustion gas. Fresh NH3 is preferably added to this residual gas mixture. Since pressure swing adsorption typically does not completely separate the H2 from the product gas, the remaining amount of H2 in the residual gas mixture preferably serves as a combustion improver for the NH3.

[0125] The intermediate gas formed in the first NH3 combustion device during start-up mode contains H2 and is optionally mixed with additional NH3 and combusted in the combustion device during start-up mode to form flue gas. Due to the at least partial decomposition of NH3, a sufficient amount of H2 is available to ensure or improve the combustion of the NH3.

[0126] In start-up mode, the preferably electrically operated H2O evaporation device and the electrical heating element require electrical energy to evaporate and further heat the NH3; for the catalytic decomposition; the subsequent combustion of NH3; together with the H2 formed by the catalytic decomposition then provides the heat to heat the heat transfer medium.

[0127] As already mentioned, in preferred embodiments, the amount of H2 in the combustion gas is increased in start-up mode compared to production mode. The higher proportion of H2 in the combustion gas promotes the combustion of the mixture of NH3 and H2, whereby the operating temperature can be reached more quickly. Accordingly, the process according to the invention is preferably operated in production mode at an H2 proportion Ai and in start-up mode at an H2 proportion A2, where A2 > Ai applies. In preferred embodiments, the relative difference between A2 and Ai 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.%.

[0128] Those 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 light of the continuous heating of the system or parts thereof. Thus, according to the invention, it is preferred that for at least part of the total duration of the start-up mode, the proportion A2 is increased compared to the proportion Ai. For example, the start-up mode can be divided into a first section and an immediately subsequent second section of the total duration, with A2 > Ai during the first section and A2 = Ai during the second section. Combustion air

[0129] Preferably, combustion air is supplied to the combustion device (combustion chamber of the reactor), which air 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 duct, with the combustion air absorbing heat from the flue gas.

[0130] Preferably, the combustion air is cleaned by a filter before being fed into the system, compressed to the required pressure with 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 NH3 mixed with H2). Product gas - after catalytic decomposition until purification of H2

[0131] In production mode, product gas leaves the second NH3 decomposition device at a high temperature. 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 NH3 decomposition device for the production mode, through which the product gas flows before the product gas is fed to a H2 purification stage: - preferably a third heat exchanger [preferably product gas / water heat exchanger for the manufacturing mode]; - preferably a fourth heat exchanger [preferably product gas / NHs heat exchanger for the manufacturing 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 undecomposed NH3

[0132] In production mode, the recovery of NH3 preferred according to the invention preferably serves to separate undecomposed NH3 from the product gas and make it available for further use as combustion gas or recovered reactant. Separate recovery of NH3 is preferably dispensed with. Thus, in production mode, H2 is preferably purified from the product gas by pressure swing adsorption (PSA). Small residual amounts of undecomposed NH3 can preferably be separated during pressure swing adsorption, thereby combining the recovery of NH3 and the purification of H2 into a single step. Product gas - purification of H2 and separation of residual gas mixture

[0133] In the production mode, H2 is particularly preferably purified by pressure swing adsorption (PSA) according to the invention. 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 H2 purity, if required > 99.9%, with an H2 yield in the range of, for example, approximately 80 to 85%. As already mentioned, pressure swing adsorption can also separate residual amounts of NH3 and possibly H2O in the same step. For this purpose, the product gas is cooled to the desired temperature before entering the pressure swing adsorption device, preferably using a sixth heat exchanger [preferably a product gas / water heat exchanger for the production mode]. The corresponding amount of heat is preferably absorbed by the water in the sixth heat exchanger.According to the invention, the cooling water thus heated is preferably used to preheat NH3 in a preheating device, where NH3 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. H2 - after purification until storage

[0134] In production mode, the separated H2 preferably leaves the pressure swing adsorption device and is preferably brought to an elevated pressure, for example to approximately 200 bar, using an H2 compressor. However, compression of the separated H2 to elevated pressure is not absolutely necessary, and pressures of significantly less than 200 bar are also encompassed according to the invention. The compressed H2 preferably then flows through a first H2 heat exchanger, in which cooling water absorbs heat from the compressed H2. In preferred embodiments, the separated H2 is then brought to a further elevated pressure using a second H2 compressor. The further compressed H2 preferably then flows through a second H2 heat exchanger, in which cooling water also absorbs heat from the compressed H2.The compressed H2 is then discharged from the plant at a pressure of, for example, approximately 70 bar and stored, for example, in a suitable pressure vessel or directly used for further purposes. Residual gas mixture

[0135] In production mode, the residual gas mixture remaining after the purification / separation of H2, preferably in the pressure swing adsorption device, typically contains N2, H2O, residual NH3, and H2. The residual gas mixture is preferably fed to the combustion device so that it can be used to generate combustion heat. flue gas

[0136] The flue gas leaves the combustion system at a high temperature and preferably enters a flue gas duct. To utilize the heat contained in the flue gas, heat exchangers are preferably provided downstream of the combustion system in the direction of flue gas flow. The flue gas flows through these heat exchangers 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 / NHs heat exchanger for the production mode; flue gas / heat transfer medium heat exchanger for the start-up mode]; - preferably a first fuel gas / combustion shift heat exchanger: - preferably a flue gas / water heat exchanger; and / or - preferably a second flue gas / combustion air heat exchanger.

[0137] Even in start-up mode, the flue gas formed during the combustion of the mixture comprising NH3 and H2 flows through the flue gas duct and thereby preferentially 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 [the start-up mode], both of which transfer heat to the heat transfer medium. The flue gas then flows preferentially through the first flue gas / combustion air heating element, preferably the flue gas denitrification unit, preferably the flue gas / water heat exchanger, and preferably the second flue gas / combustion air heating element. In this way, the combustion air or water is heated by absorbing heat from the flue gas. Water or water vapor

[0138] Demineralized water is preferably fed into the plant as the water for steam generation. Air and other gases dissolved in the water are preferably removed in a deaerator.

[0139] Preferably, the water is preheated via a fifth heat exchanger. In production mode, the fifth heat exchanger [preferably a 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 start-up mode, the fifth heat exchanger [preferably a 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.

[0140] 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 system in the flue gas duct, using the heat contained in the flue gas to heat the water vapor.

[0141] The steam is then preferably fed into a steam drum.

[0142] From the steam drum, the water is preferably passed through a third heat exchanger, where it absorbs further heat before being preferably returned to the steam drum. The third heat exchanger is arranged downstream of the second NH3 decomposition device in the flow direction of the product gas / heat transfer medium. In production mode, the third heat exchanger [preferably a product gas / water heat exchanger for the production mode] preferably serves to cool the product gas after it leaves the second NH3 decomposition device, with the heat contained in the product gas also being used to heat the steam. In start-up mode, the third heat exchanger [preferably a heat transfer medium / water heat exchanger for the start-up mode] preferably serves to transfer heat from the heat transfer medium to water. In start-up mode, hot steam is also generated in an H2O evaporator and, if necessary,together with the steam from the steam drum of the NHs evaporation device.

[0143] Condensation of the steam in the NH3 evaporator generates heat to evaporate the preheated NH3. After flowing through the NH3 evaporator, the steam condensate is preferentially fed to the preheater, which preheats the NH3. The heat contained in the steam is used in two stages to heat the NH3. After flowing through the preheater, the steam condensate can be discharged from the plant.

[0144] As long as sufficient heat is not available to generate steam in start-up mode, the electrically operated H2O evaporator provides steam. The NH3 fed from the tank into the plant is preheated in the preheater using the electrically generated steam, analogous to the production mode, and then evaporated in the NH3 evaporator. Heat transfer medium

[0145] In start-up mode, a heat transfer medium, preferably N2 or NH3, is passed through at least part of the system to absorb combustion heat or heat from the flue gas and heat one or more system devices to operating temperature. The heat transfer medium is preferably circulated and brought to the required pressure by a compressor. The system according to the invention preferably comprises several valves at suitable locations to close the main process path at several points during start-up mode and enable the circulation of the heat transfer medium.

[0146] In start-up mode, the heat transfer medium preferably 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 the cross-flow heat transfer medium.

[0147] 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.

[0148] 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.

[0149] From there, the heat transfer medium flows preferentially through the second NH3 decomposition device in start-up mode, where it absorbs combustion heat, which flows as a heat flow from the combustion device into the second Nff decomposition device.

[0150] 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. TI

[0151] 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] (ie cross-flow), where it transfers heat to the heat transfer medium flowing in cross-flow.

[0152] 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.

[0153] In start-up mode, the heat transfer medium then flows preferentially through a sixth heat exchanger [preferably heat transfer medium / water heat exchanger for start-up mode], where it also transfers heat to water.

[0154] Finally, the heat transfer medium is returned to the compressor. Description of the illustrations

[0155] The invention is explained in more detail below using preferred embodiments with reference to the figures. Figures 1, 2, and 3 each show, using flow diagrams, preferred embodiments of systems according to the invention, on which preferred embodiments of the process according to the invention can be carried out. The embodiment according to Figure 3 is a variant of the embodiment according to Figure 2 and is shown only as a section; the details not shown in the section of Figure 3 preferably correspond to those of Figure 2.

[0156] Figure 1 schematically illustrates such a process. Part of the total NIE input is combusted in a mixture with FE and O2 (reaction (A)). Combustion releases heat of combustion A. The other part of the NH3 is catalytically decomposed into H2 and N2 with the addition of combustion heat. The resulting mixture contains, in addition to H2 and N2, a residual amount of undecomposed NH3 (reaction (B)). Reactions A and B are preferably carried out separately in a common reactor, which is analogous to a primary reformer. The majority of the H2 is separated as a product from the mixture formed during the decomposition of NH3, typically by pressure swing adsorption (PSA), and the remaining mixture of unseparated H2, N2, and undecomposed NH3 is fed to combustion (recycle (C)).

[0157] If the amount of unseparated H2 contained in the remaining mixture is insufficient for satisfactory combustion of NH3, H2 can be diverted from the product H2 and also fed into the combustion (recirculation (D)). However, this is not preferred. Pressure swing adsorption typically already achieves excellent H2 purity, and the remaining H2 in the pressure swing adsorption device after separation of the H2 In addition to N2 and residual NH3, the residual gas mixture contains a sufficient amount of H2, which can hardly be avoided for process-technical reasons. By returning this H2-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 H2 for combustion is not economically viable, at least not in production mode, and is therefore not preferred. If the total amount of the residual gas mixture is insufficient to generate the required amount of heat for the catalyzed decomposition of NH3, the invention preferably increases the amount of NH3 in the combustion gas, but not the amount of H2 from the purified valuable product.

[0158] Figure 2 illustrates a preferred system according to the invention. For convenience, the manufacturing mode and start-up mode are explained sequentially below.

[0159] Plant / process according to Figure 2 in manufacturing mode'.

[0160] In production mode, liquid NH3, which is present at low temperature and elevated pressure, is pumped from tank 10 via line 11 through preheater 13 by means of pump 12 and heated. The NH3 is vaporized in NH3 evaporator 14 and then flows via line 15 to branch 16, where the NPh stream is split into two partial streams. Starting at branch 16, a first partial stream of NH3 is expanded and fed via line 17 to combustion device 18. A second partial stream of NH3 is conducted from branch 16 via line 19 through the fourth heat exchanger [preferably a product gas / NPh heat exchanger for the production mode] 20 and then flows via line 21 through the first heat exchanger [preferably a flue gas / NIL heat exchanger for the production mode] 22, where the NH3 is further heated. The preheated NH3 is fed to the first NH3 decomposition device 65, where partial catalytic decomposition takes place, preferably adiabatically.The intermediate product gas leaving the first NfL decomposition device 65 is fed via line 66 to the second heat exchanger [preferably a flue gas / intermediate product gas heat exchanger for the production mode] 67, which is arranged in the flue gas duct 49 upstream of the first heat exchanger 22 in the flow direction of the flue gas. There, the intermediate product gas is heated and then introduced via line 23 into the second NfL decomposition device 24. The flow through the second NH3 decomposition device 24 is preferably from top to bottom. The heat required to maintain the reaction is generated by heating the second NfL decomposition device 24 by combustion of H2 and NH3 in the combustion device 18.

[0161] In the production mode, after the decomposition of NH3, the product gas formed (comprising N2, H2 and possibly residual NH3) 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 / NIL heat exchanger for the production mode] 20, then line 27 and for further cooling a fifth heat exchanger [preferably a 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 a 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 H2 separated in this way leaves the pressure swing adsorption device 31 via line 32, is brought to an increased pressure via a first H2 compressor 33, flows through a first H2 heat exchanger 34, a second H2 compressor 35 for further pressure increase, a second H2 heat exchanger 36, and is discharged from the plant at a pressure of, for example, approximately 70 bar via line 37.

[0162] The residual gas mixture remaining in the pressure swing adsorption device 31 after separation of the H2 contains N2, residual NH3 and H2 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.

[0163] In production mode, combustion air for the combustion process in the combustion device 18 is cleaned via filter 40, compressed by compressor 41, passed via line 42 through the second combustion gas / combustion air heating element 43, and heated. The combustion air then flows via line 44 and through the first combustion gas / combustion air heating element 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 NH3 supplied via line 17 to burn it and thus generate combustion heat.

[0164] In production mode, the hot flue gas from combustion in combustion device 18 is first cooled via the second heat exchanger [preferably a flue gas / intermediate gas heat exchanger for production mode] 67, whereby heat is obtained for heating the intermediate gas supplied to the second NH3 decomposition device 24 after leaving the first NIL decomposition device 65. The flue gas is then further cooled via the first heat exchanger [preferably a flue gas / intermediate gas heat exchanger for production mode] 22, whereby heat is obtained for heating the NH3 supplied to the first NIL decomposition device 65. The flue gas is then passed further 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 line 51 through flue gas / water heat exchanger 52, where heat is extracted to heat the water. It then flows through the second flue gas / combustion air heating element 43, which also serves to heat the combustion air. The flue gas is then compressed in the end region of flue gas duct 49 by flue gas compressor 53 and exits the system via chimney 54.

[0165] In production mode, water for steam generation is fed via line 55, passed through the fifth heat exchanger [preferably a product gas / water heat exchanger for production mode] 28, and then passed at elevated temperature to deaerator 56, where air and other gases dissolved in the water are removed. By means of pump 57, the water is passed via line 58 through flue gas / water heat exchanger 52 and heated. The flue gas / water heat exchanger 52 serves to cool the flue gases from the combustion device 18 in the flue gas duct 49, whereby the thermal energy contained in the flue gas is used to heat the steam, which, after passing through the flue gas / water heat exchanger 52, is then passed via line 59 into the steam drum 60.Water can be passed from steam drum 60 via line 61 through the third heat exchanger [preferably a product gas / water heat exchanger for the production mode] 26, thereby absorbing further heat energy and then being returned to the steam drum via line 62. The third heat exchanger 26 is arranged in the outlet line 25 downstream of the second NH3 decomposition device 24 in the flow direction of the product gas and serves to cool the product gas after it leaves the second NH3 decomposition device 24. The heat obtained can thus be used to generate additional steam.

[0166] In production mode, the hot steam generated in steam drum 60 is introduced via line 63 into the upper section of the NH3 evaporator 14. Condensation of the steam generates heat to evaporate the preheated NH3. After flowing through the NH3 evaporator 14, the steam condensate is fed via line 64 to the preheater 13, which preheats the NH3 so that the heat contained in the steam is used in two stages to heat the NH3. After flowing through the preheater 13, the steam condensate can be discharged from the plant.

[0167] System / process according to Figure 2 in start-up mode

[0168] In the plant concept according to the invention, a heat transfer medium, preferably N2 or NH3, is passed through at least part of the plant in start-up mode to absorb heat from the combustion device or the flue gas and to heat plant devices to operating temperature. The cold heat transfer medium is preferably circulated and passed through a compressor 77 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 to allow circulation of the heat transfer medium. The first NH3 decomposition device 65 is excluded from the circulation.

[0169] As long as there is insufficient heat available for steam generation during start-up, the preferably electrically operated H2O evaporation device 84 provides steam. The NH3 fed into the plant from tank 10 is preheated with the help of the electrically generated steam in preheater 13, analogous to the production mode, and then subsequently evaporated in the NH3 evaporation device 14. In order for the evaporated NH3 to be catalytically decomposed, it must be heated to the activation temperature of the NH3 decomposition catalyst, preferably to 600 to 650°C in the case of a nickel-based NFh decomposition catalyst, and preferably to 350 to 400°C in the case of a ruthenium-based NFF decomposition catalyst.

[0170] In start-up mode, NH3 (part or all of it) is passed through the electric heating element 74 and heated therein above the activation temperature of the NFF conversion catalyst in the first NIT conversion device 65. The heated NH3 then flows via line 73 into the first NIL conversion device 65, where the NH3 is at least partially decomposed. In the preferably adiabatic reaction, a conversion of, for example, 18% can be achieved, depending on the preheating temperature.

[0171] In start-up mode, the intermediate gas thus formed contains H2 and is optionally mixed with additional NH3 and combusted in the combustion device 18 to form flue gas. Due to the partial decomposition of NH3, a sufficient amount of H2 is available to ensure or improve the combustion of the NH3. The preferably electrically operated H2O evaporation device 84 and the electric heating element 74 require electrical energy to evaporate and further heat the NH3 for the catalytic decomposition; the subsequent combustion of NH3 together with the H2 formed by the catalytic decomposition then provides the heat to heat the heat transfer medium.

[0172] 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 NfL circulating 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 a heat transfer medium / water heat exchanger for start-up mode] 28 and then the sixth heat exchanger [preferably a heat transfer medium / water heat exchanger for start-up mode] 29, which ensures a constant inlet temperature in the downstream nitrogen compressor, which compensates for the pressure loss throughout the system. Alternatively, the downstream compressor can also be an N2 / NH3 compressor, which performs a dual function, i.e., is used to compress both the N2 and the NH3.

[0173] In preferred embodiments, in start-up mode, the NH3 stream is divided into a first NH3 substream and a second NH3 substream. Only the first NH3 substream is added to the first The second NFL partial stream is separated via line 80 after flowing through the first heat exchanger [preferably the flue gas / heat transfer medium heat exchanger for the start-up mode] 22, flows preferably through the second heat exchanger [preferably the flue gas / heat transfer medium heat exchanger for the start-up mode] 67 and then the second NFL decomposition device 24, whereby the second NH3 decomposition device 24 absorbs heat from the second NFL partial stream. The second NFL partial stream therefore initially functions only as a heat transfer medium. In this way, the second NH3 decomposition device 24 is gradually heated until the light-off temperature (activation temperature) for the catalytic decomposition of NFL is reached, so that from this point on, additional FL is produced in the second NFL decomposition device 24 by catalytic decomposition of NFL.

[0174] The heat transfer medium is heated in start-up mode as it flows through the cold side of the fourth heat exchanger [preferably a heat transfer medium / heat transfer medium heat exchanger for start-up mode] 20, where it absorbs heat from the cross-flow heat transfer medium. Furthermore, the heat transfer medium is heated as it flows through the first heat exchanger [preferably a flue gas / heat transfer medium heat exchanger for start-up mode] 22 and the second heat exchanger [preferably a flue gas / heat transfer medium heat exchanger for start-up mode] 67, where it absorbs heat from the flue gas. Furthermore, the heat transfer medium is heated as it flows through the second NFL decomposition device 24, where it absorbs combustion heat, which flows as a heat flow from the combustion device 18 into the second NFL decomposition device 24.

[0175] In start-up mode, the heat transfer medium is cooled as it flows through the third heat exchanger [preferably a heat transfer medium / water heat exchanger for start-up mode] 26, where it transfers heat to water, and as it flows through the warm side of the fourth heat exchanger [preferably a heat transfer medium / heat transfer medium heat exchanger for start-up mode] 20, where it transfers heat to the cross-flow heat transfer medium. Furthermore, the heat transfer medium is cooled as it flows through the fifth heat exchanger [preferably a heat transfer medium / water heat exchanger for start-up mode] 28 and then the sixth heat exchanger [preferably a heat transfer medium / water heat exchanger for start-up mode] 29, where it transfers heat to water.

[0176] The flue gas formed during the combustion of the mixture comprising NFL and FL flows through the flue gas duct 49 in start-up mode, heating the second heat exchanger [preferably a flue gas / heat transfer medium heat exchanger for start-up mode] 67 and then the first heat exchanger [preferably a flue gas / heat transfer medium heat exchanger for start-up mode] 22, both of which transfer heat to the heat transfer medium. The flue gas then flows through the first flue gas / combustion shift heat exchanger 45, the flue gas denitrification unit 50, the flue gas / water heat exchanger 52, and the second flue gas / combustion shift heat exchanger. In this way, combustion air or water is heated by absorbing heat from the flue gas.

[0177] 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 using valves 68, 75, 79, 81, 82, 83.

[0178] If NH; or another combustible gas is used as the heat transfer medium, it can be discharged via line 76 and valve 68 and subsequently combusted at the flare tower 70. Condensate is preferably separated beforehand in separation device 71. This condensate can comprise water, which is present in small amounts in the NH; (< 0.5 wt%), and / or NH; that was not converted in the second NH; decomposition device 24 during start-up mode.

[0179] Figure 3 illustrates a preferred variant of the system according to the invention according to Figure 2. Since the production mode according to the variant of Figure 3 largely corresponds to that according to Figure 2, only the start-up mode is expediently explained below.

[0180] If N2 is used as the heat transfer medium, NH3 can be added continuously.

[0181] System / process according to Figure 3 in start-up mode

[0182] According to this preferred embodiment, for the start-up mode, the electric heating element 74 is arranged downstream of the valve 82 and upstream of the first NH3 decomposition device 65 in the direction of NH3 flow. The valve 82 regulates which portion of NH3 is fed into the first NH3 decomposition device 65 for partial catalytic decomposition and which portion of NH3 is fed via line 80 into the second NH3 decomposition device 24 as a heat transfer medium.

[0183] Via valve 75, which is installed downstream of branch 16 in the direction of NH3 flow, the supply of fuel -NH3 to the combustion device 18 is temporarily blocked or regulated; this function is performed by the first NH3 decomposition device 65 and valve 82.

[0184] The circulation of the NH3 as a heat transfer medium then occurs according to the invention as follows: With valve 75 closed, the NH3 is passed past branch 16 to the fourth heat exchanger 20 (not shown again in Figure 3) and then to the first heat exchanger 22. From there, it is divided into a first NH3 partial flow and a second TML partial flow.

[0185] The first b L partial stream is fed into the first NH 3 decomposition device 65 via valve 82. 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.

[0186] The second NH3 partial stream is fed via line 80 with valve 81 closed via the second heat exchanger 67 to the second NH3 decomposition device 24, where it initially serves as a heat transfer medium (provided the activation temperature of the NH3 decomposition catalyst in the second NH3 decomposition device has not yet been reached). The second NH3 partial stream leaving the second NH3 decomposition device 24 is passed 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 not shown again in Figure 3). Valve 83 and valve 68 are closed, so that the second NH3 partial stream is passed via line 76 to the compressor 77 (all not shown again in Figure 3). Part of the NH3 is consumed in this way, and intermediate product gas, for example, is passed via line 19. List of reference symbols: 10 Tank 29 sixth heat exchanger [preferably Pro- 11 Duct gas / water heat exchanger line for the 12 Pump manufacturing mode; heat transfer medium 13 Preheater dium / water heat exchanger for the 14 NHs evaporation device start-up mode] 15 Line 30 Line 16 Branch 31 Pressure swing adsorption device 17 Line 32 Line 18 Combustion unit 33 H2 compressor 19 Line 34 first ^-heat exchanger 20 fourth heat exchanger [preferably product gas / NH3 heat exchanger for production mode; 35 H2 compressor 36 second ^ heat exchanger 37 hydrogen outlet line / heat transfer medium heat exchanger for start-up mode] 38 return line 39 branch line 21 Line 40 Filter for combustion air 22 First heat exchanger [preferably flue gas / NHs heat exchanger for the production mode; flue gas / heat transfer medium heat exchanger for the start-up mode] 42 Line 43 Second flue gas / combustion air heat exchanger 23 Line 45 first fuel gas / combustion air heat 24 second NHs decomposition device exchanger 25 Outlet line 46 Line 26 Third heat exchanger [preferably product gas / water heat exchanger for the manufacturing mode; heat transfer medium / water heat exchanger for the start-up mode] 47 Branch line 48 Branch line 50 Flue gas denitrification unit 51 Line Line 52 flue gas / water heat exchanger 28 Fifth heat exchanger [preferably product gas / water heat exchanger for production mode; heat transfer medium / water heat exchanger for start-up mode] 53 Flue gas compressor 54 Chimney 55 Line for water supply 56 Deaerator 57 Pump 58 Line Line 71 condensate separator Steam drum 72 pump Line 73 Line Line 74 electric heating element Line 75 valve Line 76 Line first NHs decomposition unit 77 Compressor Line 78 additional tank second heat exchanger [preferably 79 valve flue gas / intermediate product gas heat exchanger for production mode; 80 line 81 valve flue gas / heat transfer medium heat exchanger for start-up mode] 83 valve Valve 84 H2O evaporation device. Line Torch tower

Claims

Patent claims:

1. A plant for producing H2 from NH3; 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 NH3; - in the flow direction of the NH3 downstream of the heating element (74), a first NH3 reduction device (65) for partially catalytically decomposing the heated NH3 to produce a combustion gas comprising H2, N2 and residual NH3; - optionally, in the flow direction of the combustion gas downstream of the first NFh reduction device (65), a device for metering combustion air into the combustion gas; - in the flow direction of the combustion gas downstream of the first NFh reduction device (65), a combustion device (18) for burning the combustion gas to produce combustion heat and flue gas; - a compressor (77) for compressing a heat transfer medium; and - 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 downstream of the combustion device (18) in the flow direction of the flue gas and downstream of the compressor (77) in the flow direction of the heat transfer medium; 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.

2. The system according to claim 1, wherein the at least one device is selected from: - a second NFh decomposition device (24), preferably in production mode, for the catalytic decomposition of vaporized NH3 to produce a product gas comprising H2 and N2; a third heat exchanger (26); preferably in the production mode for heating water, preferably for heating or generating steam, by absorbing heat from the product gas; - a fourth heat exchanger (20); preferably in production mode for heating NH by absorbing heat from the product gas; - a fifth heat exchanger (28); preferably in the 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.

3. The plant according to claim 1 or 2, wherein the plant 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 steam, 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.

4. The system according to any one of the preceding claims, wherein the heating element (74) is electrically heated.

5. The system according to any one of the preceding claims, comprising in the flow direction of the NH; upstream of the heating element (74) - an H2O evaporation device (84) for evaporating water to produce water vapor; and - an NH evaporation device (14) for evaporating liquid NH by absorbing heat from the water vapor.

6. The system according to claim 5, wherein the H2O evaporation device (84) is electrically heated.

7. The plant according to any one of the preceding claims, wherein the combustion device (18) and the second NHs 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 NHs decomposition device (24).

8. A process for starting up a plant for producing H2 from NH3 comprising the following steps: (c) heating of NH3; (d) partially catalytically decomposing the heated NH3 in a first NFh decomposition device (65) to produce a combustion gas comprising H2, N2 and residual NH3; (e) optionally, adding combustion air to 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.

9. The method of claim 8, wherein the at least one device is selected from: - a second NH3 decomposition device (24), preferably after start-up of the plant, for the catalytic decomposition of vaporized NH3 to produce a product gas comprising H2 and N2; - a third heat exchanger (26); preferably after start-up of the plant for heating water, preferably for heating or generating steam, by absorbing heat from the product gas; - a fourth heat exchanger (20); preferably after start-up of the plant for heating NH3 by absorbing heat from the product gas; - a fifth heat exchanger (28); preferably after start-up of the plant for heating water by absorbing heat from the product gas; and a sixth heat exchanger (29); preferably after start-up of the plant for heating water by absorbing heat from the product gas.

10. The process according to claim 8 or 9, wherein the heating of NH; in step (c) is carried out using electrical energy.

11. The method according to any one of claims 8 to 10, which comprises the additional steps (a) evaporation of water to produce water vapor; and (b) Evaporation of liquid NH by absorption of heat from the water vapor.

12. The method according to claim 11, wherein the generation of steam in step (a) is carried out using electrical energy.

13. The method according to any one of claims 8 to 12, wherein the heat transfer medium is circulated through at least a portion of the plant.

14. The method according to any one of the preceding claims, wherein the heat transfer medium comprises or consists essentially of N2.

15. The method according to any one of the preceding claims, wherein the heat transfer medium comprises or consists essentially of NH3.

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