Process for ammonia synthesis using green hydrogen and method for modifying ammonia plants

Abstract

A process for the synthesis of ammonia is provided, wherein an ammonia makeup gas (7) containing hydrogen and nitrogen is reacted in an ammonia converter (15) under ammonia formation conditions to obtain an ammonia-containing effluent (8), a first hydrogen portion contained in the ammonia makeup gas (7) is produced by reforming a hydrocarbon source (1) in a reforming process (100), a second hydrogen portion (19) contained in the ammonia makeup gas (7) is produced separately from the reforming process (100) by using at least renewable energy sources (SE, WE), a portion of the hydrogen (19) produced in step (c) is stored in a hydrogen storage facility (103), and if the renewable energy sources (SE, WE) are not fully or partially available, hydrogen (20) from the hydrogen storage facility (103) is used to completely or partially replace the second hydrogen portion (19). The above process includes: evaluating the predicted flow rate of hydrogen (19) produced in step (c); adjusting the flow rate of the hydrocarbon source (1) so that the flow rate of the first hydrogen portion in the ammonia makeup gas (7) is in a desired ratio to the predicted flow rate; detecting the actual amount of hydrogen in the hydrogen storage (103), for example, the fill level; detecting the actual flow rate of hydrogen produced using renewable energy sources (SE, WE); and adjusting the flow rate of hydrogen (20) from the hydrogen storage (103) according to the actual amount and actual flow rate detected in the hydrogen storage (103).

Description

Technical Field

[0001] The present invention relates to the field of ammonia synthesis.

Background Art

[0002] Ammonia is industrially produced by reacting makeup gas containing hydrogen and nitrogen in an appropriate molar ratio. The makeup gas has conventionally been produced by reforming a hydrocarbon source such as natural gas.

[0003] The production of MUG typically involves a reforming process and purification of the reformed gas. Purification typically includes shift conversion of CO to CO2, CO2 removal, and methanation. The purified gas thus obtained is fed into a high-pressure ammonia synthesis loop via a main compressor.

[0004] In the ammonia synthesis loop, the makeup gas is reacted in an appropriate ammonia converter to form ammonia. The hot ammonia-containing effluent of the ammonia converter is subjected to a cooling and separation step, and liquid ammonia and a sidestream containing unreacted hydrogen and impurities are obtained. Typically, a portion of the sidestream is subjected to a hydrogen recovery process, and the recovered hydrogen thus obtained is sent to the suction port of the main compressor. Another portion of the sidestream is typically reintroduced into the ammonia converter using a circulator, thus forming the ammonia synthesis loop described above.

[0005] The nitrogen required for ammonia synthesis can typically be introduced during the reforming process by air combustion secondary reforming. In some cases, nitrogen can be added separately, for example, when an air separation unit (ASU) is used.

[0006] In summary, the industrial production of ammonia depends on hydrocarbon reforming to produce the required hydrogen. Reforming is typically a fuel combustion process that involves a significant amount of CO2 emissions.

[0007] There is rapidly growing interest in reducing the carbon footprint of ammonia production. Applicable standards and regulations could introduce additional taxes related to CO2 emissions, for example, by considering the amount of CO2 per ton of ammonia produced. While CO2 contained in combustion smoke can be captured, the associated technologies are expensive, and most importantly, carbon dioxide capture does not prevent CO2 emissions in process gases and is only a post-hoc remedy. A promising method to achieve this goal is the production of hydrogen using renewable energy sources.

[0008] Hydrogen produced using renewable energy is called "green" hydrogen because, in contrast to conventional fuel combustion production through reforming, it does not produce CO2 emissions. Hydrogen produced by burning fossil fuels is often called "gray" hydrogen. The advantage of using green hydrogen is that no CO2 is formed, and therefore, expensive carbon dioxide capture and sequestration are unnecessary.

[0009] One practically interesting example of a process for producing green hydrogen is the electrolysis of water. While the electrolysis of water requires electricity, this can be produced using renewable resources, leading to the production of green hydrogen without the release of CO2 into the atmosphere.

[0010] The green hydrogen produced in this way can be injected into existing plants, typically during the draw of the synthesis gas compressor, or directly into the synthesis loop in addition to gray hydrogen, thereby increasing plant production, reducing the plant's consumption of specific hydrocarbons, and decreasing the associated CO2 footprint.

[0011] However, the production of green hydrogen from renewable energy sources is typically subject to fluctuations. For example, hydrogen production from solar power clearly depends on the availability of sunlight. To compensate for such fluctuations, green hydrogen storage facilities can be provided. If energy sources are not fully or partially available, storage facilities can completely or partially replace green hydrogen production to maintain a constant minimum flow rate of green hydrogen for ammonia production. Hydrogen storage facilities are implemented in the form of fixed-volume reservoirs, where hydrogen stocks are often controlled by gas pressure. This form of hydrogen storage is characterized by a certain rigidity, and therefore requires constant minimum and maximum hydrogen stocks, resulting in capital and operating costs.

[0012] The drawback of the rigid storage type described above is that its capacity must be sufficiently high to ensure the aforementioned contribution of green hydrogen as required by the process. However, providing large-capacity storage is usually cost-effective, especially when green hydrogen fluctuations are wide-ranging and frequent.

[0013] Fluctuations in green hydrogen production are undesirable because they cause abrupt changes in the load on the ammonia converter. These load changes are potentially harmful to the converter itself and other equipment in the high-pressure synthesis loop if the fluctuations exceed the mechanical and process limits of controlled, safe operation. For example, rapid load changes can cause high gas velocities, potentially damaging the inside of the converter or other components of the loop. Sudden pressure drops can result in impacts ("hammering"), damaging equipment. Furthermore, frequent and sufficiently large pressure changes can lead to equipment wear through fatigue cycles. Similar phenomena can occur with significant fluctuations in operating temperature.

[0014] European Patent Application Publication No. 4 148 020 discloses a prior art method for controlling an ammonia plant. [Overview of the Initiative]

[0015] The present invention aims to overcome the aforementioned drawbacks of the prior art. In particular, the present invention aims to provide a process for the synthesis of ammonia, in which so-called green hydrogen, i.e., hydrogen produced from at least renewable energy sources, is more attractive compared to the current prior art.

[0016] The objective is achieved by a process for the synthesis of ammonia, where, (a) Ammonia makeup gas containing hydrogen and nitrogen is reacted in an ammonia converter under ammonia formation conditions to obtain an ammonia-containing effluent. (b) By reforming the hydrocarbon source in the reforming process, the first hydrogen portion contained in the ammonia makeup gas is produced. (c) By using at least a renewable energy source, preferably a variable renewable energy source, a second hydrogen portion contained in the ammonia makeup gas is produced separately from the reforming process described above. (d) A portion of the hydrogen produced (i.e., produced or produced) in step (c) is stored in a hydrogen storage facility. (e) If the renewable energy sources described above are not available in whole or in part, hydrogen from the hydrogen storage facility is used to replace, in whole or in part, the hydrogen produced in process (c). The above process is (f) A step to evaluate the predicted flow rate of hydrogen produced in step (c), (g) A step of adjusting the flow rate of the hydrocarbon source in step (b) such that the flow rate of the first hydrogen portion in the ammonia makeup gas is in a desired ratio to the predicted flow rate in step (f), (h) A step of detecting the actual amount of hydrogen in the hydrogen storage facility, for example, the filling level, (i) A step to detect the actual flow rate of hydrogen produced in step (c), (j) A step of adjusting the flow rate of hydrogen from the hydrogen storage facility according to the actual amount detected in step (h) and the actual flow rate detected in step (i).

[0017] The present invention stems from the discovery that flexible operation of the process allows for remarkable advantages, particularly in reducing storage space in the hydrogen storage facility and reducing mechanical stress in the plant equipment, by adjusting the flow rate of the hydrocarbon source and the flow rate of hydrogen from the hydrogen storage facility based on selected criteria.

[0018] For conventional hydrogen storage facilities, which need to operate under stringent parameters and be designed to store substantial amounts of hydrogen, reducing storage capacity incurs only minimal capital costs.

[0019] On the other hand, infrequent fluctuations in front-end parameters protect the installed equipment from being forced to operate in a periodic mode that affects its mechanical reliability. For example, the process of the present invention can reduce overall mechanical stress without introducing significant changes in temperature and pressure, flow rate through the air or gas compressor, and pressure in the ammonia synthesis loop during the reforming process, thus achieving safe and long-term operation of the equipment.

[0020] These advantages are achievable despite the wide and frequent fluctuations in the flow rate of green hydrogen, which are unavoidable in the production of hydrogen using renewable energy sources, particularly variable renewable energy sources. In this specification, “variable” means that one or more renewable energy sources provide an amount of energy that is subject to change over time.

[0021] Another object of the present invention is a method for retrofitting a plant for ammonia synthesis. The plant to be retrofitted comprises a reforming front end for producing ammonia makeup gas by reforming a hydrocarbon source, and an ammonia synthesis loop including an ammonia converter. The method for retrofitting the plant comprises (I) providing a green hydrogen production device such as a water electrolysis cell that uses a renewable energy source, and a line arranged to supply green hydrogen from the green hydrogen production device to the ammonia converter under pressure; (II) providing a hydrogen storage and an input line arranged to supply green hydrogen to the hydrogen storage, and an output line arranged to supply hydrogen from the hydrogen storage to the ammonia converter; (III) updating the process management system of the plant to implement the above process.

[0022] [Description of Preferred Embodiments of the Present Invention] The hydrocarbon source 1 can be natural gas.

[0023] According to one embodiment, the reforming process 100 includes a step of desulfurizing the hydrocarbon source 1, followed by a step of primary reforming 3 in a combustion furnace and a step of secondary reforming 4 using air in the presence of steam.

[0024] According to another embodiment, the reforming process 100 includes a step of desulfurizing the hydrocarbon source 1, followed by a step of autothermal reforming (ATR) in an adiabatic reactor, optionally without prior reforming. A typical steam-to-carbon ratio in ATR can be less than 2, preferably 1.4 to 1.95. According to yet another embodiment, the steam-to-carbon ratio in ATR can be 2 or more, for example, 2 to 3.5.

[0025] In the autothermal reforming process, preferably oxygen or oxygen-enriched air is supplied. For such purposes, the stream of oxygen (O2) obtained together with hydrogen 19 by electrolysis of water W in step (c) can be used. An additional oxygen source for autothermal reforming, such as an air separation unit (ASU; 31), may be used in the process of the present invention.

[0026] Preferably, the purification 6 of the reformed gas includes a CO shift, CO2 removal, and methanation.

[0027] A particularly preferred process for producing hydrogen 19 in step (c) is the electrolysis of water W. Preferably, the electrolysis of water W, more preferably pressurized alkaline electrolysis, is operated by solar energy SE and / or wind energy WE. In particular, such energy is produced via a solar power plant 104 and / or a wind turbine power plant 105 connected to the electrolyzer, respectively. The solar power plant 104 and / or the wind turbine power plant 105 may be stand-alone plants or may be connected to the power grid.

[0028] According to a preferred embodiment, the above process (k) storing a part of the electrical energy produced by the above renewable energy sources (SE, WE) in a storage battery 46; (l) producing the second hydrogen portion 19 using the electricity stored in the storage battery 46 when the above renewable energy sources SE, WE are not fully or partially available.

[0029] According to another embodiment, the flow of oxygen (O2) obtained together with hydrogen 19 by the electrolysis of water W in step (c) can be supplied to the ATR32 or secondary reformer 4 of the reforming front end 100 via the oxygen supply line 42. Preferably, the flow of oxygen (O2) is compressed by an oxygen compressor 44 and supplied to an oxygen storage 106. The oxygen from the oxygen storage 106 is preferably supplied to the ATR32 or secondary reformer 4 in an amount that does not exceed the design temperature of the ATR32 or secondary reformer, or the design temperature of one or more heat recovery exchangers of the cooling stage 5 located downstream of the ATR32 or secondary reformer 4.

[0030] According to one embodiment, the renewable energy source is biomass or contains biomass. Preferably, the hydrogen 19 is produced in step (c) by a step of converting the biomass into a hydrogen-containing gas, followed by a step of purifying the hydrogen-containing gas.

[0031] Biomass is widely considered a form of renewable energy because it is energy derived from the sun. Biomass can be converted into hydrogen using thermochemical processes or biological processes such as fermentation. Preferred thermochemical processes include gasification, partial oxidation, and steam reforming. The biomass source is preferably plant-based biomass, and more preferably lignocellulosic biomass. In a preferred embodiment, the process for producing hydrogen from biomass includes gasification of such biomass, preferably plant-based biomass.

[0032] A gasification process using oxygen converts biomass into a hydrogen-containing gas, which is then purified in hydrogen to separate the CO2. Although the H2 derived from the biomass causes CO2 emissions, these emissions are within acceptable limits because they are carbon neutral. This is because the amount of CO2 captured by the plant material used as a biomass source through photosynthesis during growth is approximately the same as the amount of CO2 released when the biomass is burned.

[0033] Biomass gasification involves logistics, specifically the collection of biomass, the raw material for gasification, from one or more locations and its transportation to the gasification site. Furthermore, because biomass storage requires significant storage space (land), only a limited amount of biomass can be stored at the gasification site. As a result of these logistical and space constraints, the availability of raw materials for gasification may be affected, and gasification may suffer from fluctuations in the biomass flow rate to the gasifier over time. Consequently, the flow rate of hydrogen produced may also fluctuate over time.

[0034] Preferably, the adjustment frequency of step (g) is less than the adjustment frequency of step (j). More preferably, the adjustment frequency of step (g) may be at least 10 times, more preferably at least 50 times, and even more preferably at least 100 times less than the adjustment frequency of step (j).

[0035] More preferably, process (g) is a long-term adjustment and process (j) is a short-term adjustment.

[0036] Long-term adjustments may be carried out at time intervals of 4 days to 7 weeks, preferably 5 days to 6 weeks, and more preferably 6 days to 4 weeks (for example, 1 week, 2 weeks, or 3 weeks).

[0037] Short-term adjustments can be performed at time intervals of 1 minute to 28 hours, preferably 10 minutes to 26 hours, and more preferably 20 minutes to 24 hours (for example, 30 minutes, 1 hour, 12 hours, or 18 hours).

[0038] In step (g), the above adjustment is preferably carried out with a gradual gradient, i.e., over a period of at least 3 hours, for example, 3 to 24 hours, preferably 4 to 18 hours, more preferably 5 to 12 hours, and even more preferably 6 to 10 hours, for example 7 to 9 hours. The flow rate of air to the optional secondary reforming and the flow rate of fuel to the optional primary reforming may also be changed with the same gradual gradient to maintain the required operating parameters.

[0039] The desired ratio in step (g) is preferably such that the flow rate of the first hydrogen portion in the ammonia makeup gas is inversely proportional to the predicted flow rate in step (f).

[0040] According to one embodiment, step (f) is or includes calculating the predicted flow rate of the hydrogen 19 produced in step (c) in past executions of the process. The calculation is or includes the average, weighted average, or rolling average (or mean moving average) of the detected flow rate over a predetermined time period. A rolling average is particularly preferred. The predetermined time period may cover the same time interval as previously defined long-term adjustments.

[0041] According to a possible embodiment, the rolling average may be calculated using weighted detected flow rates. For example, the detected flow rate for the most recent past run of the process (e.g., the previous day or the past two days) may have a higher weight than the detected flow rate for a less recent past run of the process (e.g., one week ago or two weeks ago).

[0042] According to another embodiment, step (f) includes a forecast based on estimated electrical energy 21 generated by renewable energy sources SE,WE in a given geographical area, in particular the geographical area in which the process is carried out. As an example, such an estimate of the generated electrical energy 21 may be based on past or historical use of renewable energy sources SE,WE and / or past or historical meteorological data (solar radiation, wind speed, etc.) in a given geographical area. In fact, meteorological data have a direct impact on the generation of electrical energy.

[0043] In yet another embodiment, step (f) includes a forecast based on electricity costs relating to production costs. Preferably, step (f) is a trigger / signal based on the market price of available electricity using a forecasting mechanism (e.g., short term, such as 1 to 3 days, or long term, such as 1 to 3 weeks).

[0044] Preferably, additional nitrogen 22 may be mixed into the ammonia makeup gas 7 upstream of the ammonia converter 15 to adjust the hydrogen-to-nitrogen molar ratio (H / N) for ammonia synthesis. Preferably, the additional nitrogen 22 is mixed with the hydrogen produced in step (c) at a mixing point or region 30 along the green hydrogen supply line 25, where the green hydrogen supply line 25 connects the electrolytic cell 102 and / or hydrogen storage 103 to the reforming front end 100, the main compressor 11, or the ammonia synthesis loop 101. The H / N molar ratio is preferably 2.9 to 3.1. At least a portion (e.g., all) of the additional nitrogen 22 may be obtained by a dedicated air separation unit (N2 PSA unit) based on cryogenic air separation, pressure swing adsorption (PSA), or selective adsorption, and then residual oxygen is removed by a purification step.

[0045] According to a preferred embodiment, the additional nitrogen 22 is mixed into the airflow 9 supplied to the reforming front end 100 upstream of the air compressor 10 to adjust the hydrogen-to-nitrogen molar ratio for ammonia synthesis. The H / N molar ratio is preferably 2.9 to 3.1. The hydrogen 19 produced in step (c) can be supplied to the ammonia converter 15 via the main compressor 11 or via a dedicated compressor 29. More preferably, at least a portion (e.g., all) of the additional nitrogen 22 is or is the exhaust gas of the nitric acid production process.

[0046] Preferably, the additional nitrogen 22 or exhaust gas is compressed by the air compressor 10. According to another embodiment, the additional nitrogen 22 or exhaust gas is compressed by a dedicated compressor 23.

[0047] According to one embodiment, the electrolytic cell 102 and / or hydrogen storage cell 103 may be connected to the inlet line (suction side) of the main compressor 11 via the green hydrogen supply line 25.

[0048] In other possible embodiments, the electrolytic cell 102 and / or hydrogen storage 103 may be connected via the green hydrogen supply line 25 to the reforming front end 100 (preferably downstream of one or more reforming stages and upstream of the purification of the reformed gas 6), the output line (discharge side) of the main compressor 11, or the ammonia synthesis loop 101. In the latter cases, additional compression may be required to pressurize the green hydrogen supplied by the green hydrogen supply line 25 to the ammonia synthesis pressure.

[0049] According to another embodiment, the electrolytic cell 102 is connected to the hydrogen storage 103 via an input line 24 arranged to supply green hydrogen under pressure to the hydrogen storage 103 by a hydrogen compressor 29. The hydrogen storage 103 has an output line 20 connected to the suction side of the hydrogen compressor 29.

[0050] This loop connection between the hydrogen compressor 29 and the hydrogen storage 103 makes it possible to maintain a desired pressure value in the hydrogen storage 103 (which may vary over time, in particular depending on the actual or current amount of hydrogen stored in the hydrogen storage) and to supply green hydrogen along the green hydrogen supply line 25 using the same hydrogen compressor 29 without the need for additional compressors.

[0051] In further possible embodiments, the electrolytic cell 102 and hydrogen storage cell 103 may be connected to a suitable location in the reforming front end, preferably upstream of the reformed gas purification 6, more preferably upstream of the methanator, upstream of the CO2 removal section, or upstream of the CO shift converter, in order to supply green hydrogen.

[0052] In another embodiment, the hydrogen obtained in step (c) is supplied directly to the ammonia synthesis loop 101 under pressure without going through a compression step carried out by the hydrogen compressor 29. In this embodiment, the hydrogen compressor 29 may be located on a dedicated sideline to supply hydrogen to the hydrogen storage 103.

[0053] In a further embodiment, the nitrogen required to adjust the hydrogen-to-nitrogen molar ratio (H / N) for ammonia synthesis can be obtained by adjusting the flow rate of air 9 to the air compressor 10 supplying the reforming front end 100. In this embodiment, excess nitrogen is introduced into the reforming process 100 for the hydrogen-to-nitrogen (H / N) ratio required by the stoichiometric ammonia synthesis. The flow rate of air 9 is selected such that, when the hydrogen produced in step (c) is mixed with the ammonia makeup gas 7, this excess nitrogen results in a stoichiometric H / N molar ratio for ammonia synthesis.

[0054] Preferably, the first hydrogen portion is introduced into the ammonia synthesis loop 101 together with at least one of the hydrogen 19 produced in step (c) and the hydrogen 20 from the hydrogen storage 103.

[0055] According to a preferred embodiment, the reforming process includes the steps of reforming a hydrocarbon source 1 and purifying the reformed gas thus obtained, thereby obtaining an ammonia makeup gas; supplying the ammonia makeup gas to the ammonia converter 15 via a main compressor 11; and supplying the second hydrogen portion 19 to the ammonia converter 15 via the same main compressor 11 or via a dedicated compressor 29. The additional nitrogen 22 (optional) may be supplied to the ammonia converter 15 via one or more dedicated compressors 23, or first via an air compressor 10 and then via the main compressor 11.

[0056] Preferably, the hydrogen storage chamber 103 is maintained at a pressure of at least 50 bar, preferably 50 to 250 bar, and more preferably 60 to 200 bar. Hydrogen can be stored under pressure in one or more suitable hydrogen storage containers. Therefore, the hydrogen compressor 29 can be expected to raise the hydrogen pressure from electrolysis above the minimum storage pressure.

[0057] According to a preferred embodiment, a portion of the hydrogen produced in step (c) is sent to the hydrogen storage 103 by a hydrogen compressor 29. The hydrogen stored in the hydrogen storage 103 is supplied to the suction side of the hydrogen compressor 29, thereby allowing such a compressor to maintain a desired pressure value in the hydrogen storage 103 and supply the hydrogen 19 contained in the ammonia makeup gas 7.

[0058] In another preferred embodiment, the hydrogen compressor 29 is located downstream of the electrolytic cell 102 and upstream of the hydrogen storage cell 103. Preferably, a green hydrogen output line 20 supplies hydrogen stored in the hydrogen storage cell 103 to the suction side of the hydrogen compressor 29. Thus, a desired pressure value is maintained within the hydrogen storage cell 103. As a result, hydrogen is stored in a cost-effective and space-efficient manner and delivered at a pressure higher than the operating pressure of the front end.

[0059] According to one embodiment, the hydrogen storage facility 103 has a maximum capacity equal to the average weekly production amount of the hydrogen 19 produced in step (c), preferably the average 2-day production amount, and more preferably the average 1-day production amount.

[0060] In a typical embodiment, the second hydrogen portion 19 produced by renewable energy accounts for up to 50%, preferably 1% to 50%, more preferably 2% to 35%, even more preferably 3% to 25%, and even more preferably 5% to 15%, of the hydrogen contained in the ammonia makeup gas 7. However, in some embodiments, green hydrogen may account for the majority (more than 50%) of the total hydrogen.

[0061] In possible embodiments, the ammonia converter 15 is part of the ammonia synthesis loop 101. The ammonia synthesis loop 101 may include the ammonia converter 15, a makeup gas preheater, a cooling and separation stage 16, and a circulator 13. Preferably, the green hydrogen supply line 25 is connected to the ammonia synthesis loop 101 between the circulator 13 and the converter 15, more preferably to the outlet of the circulator 13.

[0062] In other embodiments, the green hydrogen supply line 25 is supplied downstream of the ammonia converter 15, for example, between the ammonia converter 15 and the cooling-separation stage 16, or between the cooling-separation stage 16 and the circulator 13.

[0063] Preferably, in a method for modification, step (III) includes uploading a computer program to the internal memory of the process management system 26 of the plant, the computer program including a software code portion suitable for performing the process, wherein the software code portion is executed by the process management system 26.

[0064] According to another embodiment of the method for modification, the green hydrogen production device is a water electrolytic cell, and the method includes the step of providing a line 42 arranged to supply a flow of oxygen (O2) obtained by the water electrolytic cell from the water electrolytic cell to a reforming front end 100, preferably an ATR 32 or secondary reforming device 4 of the reforming front end 100.

[0065] [Advantages of the product] In an advantageous embodiment, the process of the present invention makes it possible to reduce the size of hydrogen storage facilities and avoid the waste or release of a large portion of fluctuating green hydrogen.

[0066] Advantageously, the dimensions of the hydrogen storage facility used in the process of the present invention can be up to 10 times, preferably up to 20 times, and more preferably up to 30 times smaller than the dimensions of a rigid plant hydrogen storage facility.

[0067] Advantageously, the method of modification according to the present invention maintains the use of the existing front end. Possible hardware changes to the ammonia synthesis section have little impact and cost.

[0068] Furthermore, the modification method of the present invention advantageously allows the operation of existing equipment in the ammonia plant within the constraints of the original design, even though it is necessary to accommodate a significant additional amount of fluctuating green hydrogen, thereby avoiding periodic operation and thus avoiding the problem of mechanical fatigue.

[0069] Advantageously, the nitrogen required to obtain the stoichiometric hydrogen-to-nitrogen (H / N) ratio for ammonia synthesis can be obtained by changing the airflow rate to the air compressor, thereby providing an excess of nitrogen in the ammonia makeup gas relative to the H / N ratio required for ammonia synthesis stoichiometry. The airflow rate is selected such that this nitrogen surplus results in the stoichiometric H / N ratio once green hydrogen is mixed with the ammonia makeup gas through the supply line. In this way, the costs associated with an additional nitrogen source are reduced or eliminated.

[0070] Advantageously, supplying green hydrogen, and optionally additional nitrogen, during the main compressor intake can reduce the investment cost of newly installed compressors.

[0071] Advantageously, the presence of a hydrogen compressor allows for the storage of hydrogen in a cost-effective and space-efficient manner, and enables the delivery of hydrogen at a pressure higher than the operating pressure of the front end. In some embodiments, the hydrogen compressor may be configured to deliver green hydrogen at or above the pressure of the ammonia synthesis loop.

[0072] Advantageously, if an additional nitrogen source is present, such additional nitrogen will not pass through the reforming front end 100, and therefore fluctuations in the reformer outlet temperature are avoided. This is because the airflow rate to the air compressor must not change in order to maintain the desired H / N ratio in accordance with the fluctuations in the amount of hydrogen produced in process (c).

[0073] Advantageously, directly supplying green hydrogen and optional additional nitrogen to the ammonia synthesis loop results in less variation in operating conditions due to fluctuations in green hydrogen (since the mass flow rate of gas circulating in the loop is typically 2-4 times the mass flow rate delivered by the front end), reduces the energy consumption of the main compressor, and therefore reduces CO2 emissions (when the synthesis gas compressor is driven by steam produced at the front end using fossil fuels).

[0074] Advantageously, supplying green hydrogen and optional additional nitrogen to the circulator outlet avoids placing an additional cooling load on the refrigeration section of the ammonia synthesis loop. It also allows for maintaining temperature levels within the loop while limiting the area of ​​heat exchange installed in the loop's gas-gas heat exchangers, and thus limiting their costs.

[0075] Advantageously, the change in Green hydrogen input to the ammonia synthesis loop is selected so that the ammonia production rate is kept within the range of the maximum deviation from the required total average production.

[0076] Advantageously, pressurized alkaline electrolysis has lower investment costs compared to other electrolysis technologies, and reduces power consumption and investment costs by avoiding the compression of green hydrogen starting from atmospheric pressure.

[0077] Advantageously, pressure swing adsorption units (PSAs) are more flexible, cost-intensive, and have lower power consumption and investment costs than alternative air separation technologies.

[0078] The advantages of a single-train cryogenic air separation unit are that it produces ammonia at a higher rate and has a lower investment cost compared to other air separation units with higher production rates as mentioned above.

[0079] Advantageously, using rolling averages makes it possible to obtain useful setpoints for front-end production rates, avoiding ammonia production losses when the storage is empty or power reductions when the storage is completely full. Furthermore, these values ​​as setpoints only require information available to the plant operator.

[0080] Advantageously, a portion of the green hydrogen can be used as fuel in the reforming process. Fluctuations in the availability of green hydrogen can be addressed by the reformer by adjusting the relative amount of green hydrogen fuel to natural gas fuel while keeping the reforming temperature constant. As a result, despite using fluctuating green hydrogen as fuel, there are no fluctuations in the process gas due to steam reforming.

[0081] Advantageously, the hybrid process according to the present invention replaces at least a portion of gray hydrogen with green hydrogen, thereby reducing CO2 emissions. Such reductions occur in two ways: on the one hand, trace amounts of CO2 are generated in the flue gas of the reforming front end; on the other hand, the process gas of the entire reforming unit (process synthesis gas) and the CO2 contained therein are also reduced.

[0082] It is worth mentioning that another known technological strategy for reducing CO2 emissions is electroreforming, in which the fuel used to generate reforming heat at the reforming front end is replaced with electrical energy, and thus no carbon dioxide is produced, including in flue gas. However, if the productivity of the reforming front end is the same, the amount of CO2 in the process synthesis gas remains unchanged (for the most part). This is because the process synthesis gas contains the same amount of CO2, since green hydrogen is not used to partially replace gray hydrogen produced using electrical energy.

[0083] Advantageously, the process of the present invention makes it possible to decouple the green hydrogen supply from the hydrogen storage and ammonia synthesis processes. This is because ammonia synthesis does not depend solely on the flow rate of hydrogen supplied to the storage, and therefore the synthesis takes place independently of the hydrogen storage filling process.

[0084] Advantageously, supplying additional nitrogen to the air compressor results in more stable operation in terms of flow rate compared to a dedicated compressor.

[0085] More precisely, if green hydrogen is available and added, additional nitrogen is typically required and supplied to the air compressor along with the air required for the reforming front-end load. However, if green hydrogen is not available, no additional nitrogen is required, and only the air required for the reforming front-end is supplied to the suction side of the compressor. In either condition, the air compressor is supplied with air and / or additional nitrogen at a gas flow rate exceeding 50% of the air flow rate required for the reforming front-end operating at 100% load.

[0086] This leads to a preferred embodiment in which the gas flow rate supplied to the air compressor may consist of 50% to 115%, preferably 70% to 110%, more preferably 85% to 105%, and even more preferably 97.5% to 102.5%.

[0087] According to another embodiment, if green hydrogen is available, additional nitrogen 22 may be required and supplied to the dedicated compressor 23 at a flow rate up to 100% of the maximum nitrogen flow rate. If green hydrogen is not available, no additional nitrogen is required, and there may be no gas flow to the dedicated compressor (flow rate: 0%). Thus, the dedicated compressor 23 can experience flow rate fluctuations from 0% to 100%. [Brief explanation of the drawing]

[0088] [Figure 1] A simplified diagram of the first embodiment of the present invention. [Figure 2] A simplified diagram of a second embodiment of the present invention. [Figure 3] A simplified diagram of a third embodiment of the present invention. [Figure 4] The power availability from a solar power plant over a period of approximately 200 hours, as illustrated in the example. [Figure 5] The mean-moving average of the power profile shown in Figure 4, calculated over a predetermined period of two weeks. [Figure 6] Rigid hydrogen storage capacity of the plant based on advanced technology. [Figure 7] The required annual adjustment amount for front-end load by the process of the present invention. [Figure 8] A filling profile obtained as a result of a hydrogen storage facility used in the process of the present invention. [Figure 9] Expansion of the dashed area shown in Figure 8 during the time period between 3000 hours and 4000 hours. [Figure 10] A simplified diagram of a fourth embodiment of the present invention. [Figure 11] A simplified diagram of a fifth embodiment of the present invention. [Modes for carrying out the invention]

[0089] [Detailed description of the invention] Figure 1 is a simplified diagram of a preferred embodiment of the present invention, where the main components are represented according to the following list of reference numerals. 1. Hydrocarbon sources such as natural gas 7. Ammonia Makeup Gas 8. Ammonia-containing spills 9. Air supply materials for the modification process 11. Main compressor for ammonia makeup gas 7 12 Recycled gas 13. Circulator 15 Ammonia Converter 16 Cooling Separation Stage 18 Makeup gas from the reforming process (reformed makeup gas) 19 Hydrogen produced in step (c) or the second hydrogen portion or green hydrogen 20 Green hydrogen output lines from hydrogen storage facilities 21 Electrical Energy 22 Additional nitrogen (optional) 23. Dedicated compressor (optional) 24. Green hydrogen input lines in hydrogen storage facilities 25 Green Hydrogen Supply Lines 26 Process Management Systems 27. Part 1 (Purge Gas) 28 Part 2 29 Hydrogen compressor 30 mixing points or areas 35 Valve means 36 Management Lines 37 Management Line 38 Management Line 39 Management Line 40 Management Lines 41 Management Line 42. Electrolytic cell oxygen supply line (optional) 44. Oxygen compressor 45 Oxygen output line 100 Modification process or modification front end 101 Ammonia synthesis loop 102 Electrolytic cell for hydrogen production 103 Hydrogen Storage 104 Solar Power Plants 105 Wind Turbine Power Plant 106 Oxygen storage (optional) SE Renewable energy sources, especially solar energy WE Renewable energy sources, especially wind energy W water O2 (Oxygen)

[0090] Referring to Figure 1, the hydrocarbon source 1 is desulfurized and steam reformed at the reforming front end 100. The desulfurized reformed gas thus obtained is purified to obtain purified synthesis gas.

[0091] The required amount of nitrogen can be introduced in the air supply material 9, which is sent to the reforming front end 100 via the air compressor 10, to obtain an ammonia makeup gas 7 containing purified synthesis gas.

[0092] Ammonia makeup gas 7 is supplied to the ammonia synthesis loop 101 by the main compressor 11. After being preheated in a heat exchanger, the preheated ammonia makeup gas is reacted in the ammonia converter 15.

[0093] The converter effluent is sent to the cooling and separation stage 16. From here, the ammonia-containing effluent 8 and the recycled gas 12 are separated.

[0094] The recycled gas 12 is divided into a first portion 27 (purge gas) and a second portion 28. The first portion 27 is sent to a hydrogen recovery unit (HRU), where hydrogen is separated from other impurities such as non-condensable gases. The second portion 28 is recirculated in the ammonia synthesis loop 101 via a circulator 13. The circulator 13 compensates for the pressure drop while maintaining circulation in the ammonia synthesis loop 101. The HRU may use a cryogenic system, a membrane-based system, or a PSA.

[0095] The electrolytic cell 102 is powered by at least a renewable energy source, namely solar energy SE and / or wind energy WE, which produces electrical energy 21 for carrying out the electrolysis of water W. The electrical energy 21 is produced via a solar power plant 104 and / or a wind turbine power plant 105. Hydrogen 19 and oxygen O2 are produced by the electrolysis of water W. Such oxygen can be delivered to the reforming front end 100 via the electrolytic cell oxygen supply line 42. The flow of oxygen O2 can be compressed by an oxygen compressor 44 and supplied to an oxygen storage room 106, and then supplied to the reforming front end 100 in appropriate amounts. The oxygen storage room 106 has an oxygen output line 45 connected to the suction side of the oxygen compressor 44.

[0096] The electrolytic cell 102 may be connected to the inlet line of the main compressor 11 via the green hydrogen supply line 25. Alternatively (see dotted arrow), the green hydrogen supply line 25 may connect the electrolytic cell 102 to the reforming front end 100, to the output line of the main compressor 11, or directly to the ammonia synthesis loop 101. In these latter alternatives, an additional compressor (not shown) may be required to pressurize the green hydrogen supplied by the electrolytic cell 102 to the ammonia synthesis pressure, or alternatively, a hydrogen compressor 29 may be used for such a purpose (see below).

[0097] The electrolytic cell 102 is further connected to the hydrogen storage cell 103 via an input line 24, which is configured to supply pressurized green hydrogen to the hydrogen storage cell 103 by the hydrogen compressor 29. The hydrogen storage cell 103 has an output line 20 connected to the suction side of the hydrogen compressor 29. This loop connection between the hydrogen compressor 29 and the hydrogen storage cell 103 makes it possible to maintain a desired pressure value in the hydrogen storage cell 103 and to supply green hydrogen along the green hydrogen supply line 25 using the same hydrogen compressor 29 without the use of an additional compressor.

[0098] Additional nitrogen 22 is supplied to the hydrogen supply line 25 by a dedicated compressor 23, and the molar ratio of hydrogen to nitrogen for ammonia synthesis can be adjusted. Such additional nitrogen 22 can be obtained by an air separation unit 31 (see, for example, Figure 3) or by pressure swing adsorption (PSA).

[0099] The process control system 26 is functionally connected to the reforming front end 100, the electrolytic cell 102, the hydrogen storage 103, optionally the hydrogen compressor 29, the solar power plant 104, and / or the wind turbine power plant 105 via the respective process control lines 36, 37, 38, 39, 40, and 41, and the process for ammonia synthesis is controlled as follows:

[0100] The ammonia synthesis loop 101 receives the ammonia makeup gas 7 conventionally produced at the reforming front end 100, along with the green hydrogen 19 from line 25. For example, hydrogen from the electrolytic cell 102 may account for about 10% of the total hydrogen contained in the ammonia makeup gas 7.

[0101] Based on the availability of renewable energy sources for the electrolytic cell 102 (for example, based on the electricity generated), hydrogen from the storage unit 103 can be used as a partial or complete substitute for the production in the electrolytic cell 102. For example, assuming that the electrolytic cell 102 uses solar energy SE, the stored hydrogen (drawn from the storage unit 103 via line 20) can be used at night and / or on cloudy days when solar energy is reduced.

[0102] The use of hydrogen storage facilities is beneficial in terms of carbon dioxide emissions because they store only green hydrogen.

[0103] According to the process of the present invention, first, the predicted flow rate of green hydrogen produced by the electrolytic cell 102 is evaluated. This evaluation may include calculations (e.g., mathematical averages) from the detected flow rates of the green hydrogen 19 in past implementations of the process, and / or predictions based on estimated electrical energy 21 generated via renewable energy sources in a given geographical area.

[0104] Next, the flow rate of the hydrocarbon source 1 is adjusted (for example, via a valve means 35 functionally connected to the process control system 26) so that the flow rate of the first hydrogen portion in the ammonia makeup gas 7 (and more precisely, in the reformed makeup gas 18) becomes a desired ratio to the predicted flow rate.

[0105] The actual amount of green hydrogen in the hydrogen storage facility 103, for example, the filling level, and the actual flow rate of hydrogen produced in process (c) are also detected, and the flow rate of green hydrogen 20 in the hydrogen storage facility 103 is adjusted according to the actual amount and actual flow rate. The flow rates of air 9 and fuel for the reforming process may change accordingly or may be kept constant instead.

[0106] More precisely, the flow rate of green hydrogen supplied to the ammonia synthesis loop 101 can be set between a minimum and a maximum value, depending on the actual amount in the hydrogen storage 103 (e.g., the fill level). If the actual amount exceeds the upper threshold, the maximum amount of green hydrogen is supplied. If the actual amount is less than the lower threshold, the minimum amount of green hydrogen is supplied. If the fill level is between these thresholds, an intermediate amount of green hydrogen, falling between the minimum and maximum amounts, is supplied to the ammonia synthesis loop 101.

[0107] However, if the amount of green hydrogen supplied to the ammonia synthesis loop 101 is greater than or less than the amount produced in process (c), the difference is either drawn from or sent to the hydrogen storage 103.

[0108] Figure 2 shows another embodiment of the process of the present invention. The same reference numerals as in Figure 1 indicate the same or corresponding technical features. Furthermore, the following reference numerals are used. 2 Desulfurization 3. Primary reforming equipment such as combustion furnaces 4 Secondary reforming device 5 Cooling 6. Purification of reformed gas, preferably with (one or more) shift converters and carbon dioxide removal. 10 Air compressor

[0109] The reforming front end 100 is shown in more detail. The hydrocarbon source 1 passes through the stages of desulfurization 2, primary reformer 3, and secondary reformer 4 in order. The air supply material 9 is compressed in the air compressor 10 and then sent to the secondary reformer 4.

[0110] Subsequently, the effluent from the secondary reformer 4 is subjected to a cooling stage 5, and such cooled effluent passes through (one or more) shift converters and a carbon dioxide removal stage 6. One or more shift converters, for example, a low-temperature shift converter may be provided after a high-temperature shift converter. Carbon dioxide removal can be carried out, for example, by amine or carbonate solution washing, pressure swing adsorption (PSA), or another technique for removing CO2 from the gas. Thus, a reformed makeup gas 18 is obtained.

[0111] Figure 3 shows another embodiment of the process of the present invention. The same reference numerals as in Figures 1 and 2 indicate the same or corresponding technical features. Furthermore, the following reference numerals are used. 31. Air Separation Unit (ASU) 32. Autothermal Reforming (ATR) 33. Oxygen supply line from ASU to ATR 34 Nitrogen supply line from ASU to ATR spillway 43 Nitrogen supply line from ASU to mixing point or area

[0112] An alternative reforming front-end 100 is shown in more detail. The desulfurization hydrocarbon source 1 is reformed in the autothermal reforming stage 32. Subsequently, the ATR effluent goes through the reformed gas purification stage 6 to obtain the reformed makeup gas 18.

[0113] The air supply material 9 is sent to the air separation unit 31, where the air is separated into an oxygen stream and a nitrogen stream. The oxygen stream is supplied to the ATR 32 via line 33, and the nitrogen stream is supplied between the ATR 32 and the reformed gas purification stage 6 via line 34, providing the amount of nitrogen required for ammonia synthesis.

[0114] The oxygen O2 produced in the electrolytic cell 102 can also be supplied to the ATR 32 via the electrolytic cell oxygen supply line 42.

[0115] A portion of the nitrogen stream separated in the air separation unit 31 may be supplied to a mixing point or region 30 in a nitrogen supply line 43, preferably via a dedicated compressor 23, to adjust the hydrogen-to-nitrogen molar ratio (H / N) for ammonia synthesis, providing additional nitrogen 22.

[0116] Figure 10 shows an alternative embodiment of Figure 1, comprising a battery 46 electrically connected to (one or more) renewable energy sources SE, WE, thereby allowing a portion of the electrical energy produced by (one or more) energy sources to be stored in the battery 46. In other words, the battery 46 is charged by (one or more) renewable energy sources SE, WE, for example, when there is an excess of electrical energy produced by (one or more) renewable energy sources SE, WE compared to the energy required to produce the second hydrogen portion 19.

[0117] The battery 46 is further electrically connected to the electrolytic cell 102 so that, for example, when the renewable energy sources SE, WE are not fully or partially available, the second hydrogen portion 19 can be produced using the electricity stored in the battery 46. This means that the battery 46 can supply power to the electrolytic cell 102 when needed.

[0118] Figure 11 shows an alternative embodiment of Figure 2, in which additional nitrogen 22 is mixed into the airflow 9 supplied to the reforming front end 100 at an upstream position of the air compressor 10. At least a portion of such additional nitrogen 22 may be or may include the exhaust gas of the nitric acid production process.

[0119] Figure 11 also shows another flow of additional nitrogen 22, which is compressed in a dedicated compressor 23 and directed to a mixing point or region 30. The dashed lines for the dedicated compressor 23 and connecting pipes indicate that these components are optional and that the additional nitrogen 22 can only be supplied by mixing it with the airflow 9.

[0120] The present invention will be described herein in view of the following non-limiting embodiments. [Examples]

[0121] This example relates to the ammonia plant shown in Figure 1, where a second hydrogen component (green hydrogen) equivalent to 10% of the hydrogen required to produce a total of 1,000 tons of ammonia per day is used.

[0122] Green hydrogen is produced by the electrolysis of water using renewable energy. In this example, such power is delivered solely by the solar power plant 104. However, other tests (not shown) conducted using wind energy, or a combination of solar and wind energy, yielded results consistent with the evidence obtained by using only the solar power plant 104.

[0123] Figure 4 shows a typical example of the availability of electricity from solar power plant 104 for approximately 200 hours (about 8 days).

[0124] The mean moving average (calculated over 337 hours, or two weeks) for this power profile is shown in Figure 5. The resulting curve shows the average availability of green hydrogen throughout the year, and therefore the seasonality of the power profile. As can be seen, power availability, and therefore green hydrogen production, is about 2.5 times higher in summer (around 4000 hours) than in winter (around 0 and 9000 hours).

[0125] As a result, a conventional hybrid plant ("rigid" plant), designed to accommodate the same input of green hydrogen but without the flexible operation of the present invention, would require an impractically large hydrogen storage capacity to accommodate up to 825 tons of hydrogen needed between 6,000 and 7,000 hours of plant operation, in order to operate at a constant ammonia production rate and achieve the same goal of 10% green hydrogen input overall. The H2 storage facility filling profile is shown in Figure 6. Figure 6 demonstrates that a large storage capacity is essential for a "rigid" plant because the availability of green hydrogen is seasonally unbalanced.

[0126] In contrast, a hybrid plant operating according to the process of the present invention can use the same total amount of green hydrogen delivered with the same profile as in the above case, with a hydrogen storage size of only 24 tons of hydrogen, which is equivalent to the average green hydrogen production over 32 hours.

[0127] Figure 7 shows the adjustments required for the front-end load throughout the year in process (g).

[0128] In this case, adjustments are made weekly, where the new setting point is determined to be equal to the rolling average of green hydrogen availability over the past two weeks. The resulting curve reflects the seasonality of the power profile, with the annual average load on the front end being approximately 90%, as predicted.

[0129] Thanks to the variability correction provided by the front end, the ammonia synthesis section only needs to operate flexibly at an ammonia production rate of 5% of the total production, which is within the acceptable range of variability for the existing equipment. The resulting hydrogen storage refueling profiles are shown in Figures 8 and 9. Figure 9 is an enlarged view of Figure 8 for the interval between 3000 and 4000 hours. As can be seen, hydrogen storage in this case only mitigates short-term (hours to days) fluctuations in the availability of green hydrogen, which cannot be absorbed by the relatively small flexibility of the ammonia synthesis loop by adapting its load and ammonia production.

[0130] Overall, when comparing the production costs of ammonia fractions produced with a 10% green hydrogen input, and considering the investment costs of the green hydrogen production section and its operating costs (primarily electricity to power one or more electrolyzers), a hybrid plant managed by the present invention results in production costs that are more than three times lower than a "rigid" hybrid plant. This large difference is actually caused by the very large and expensive hydrogen storage capacity that is installed, mainly in the case of rigid plants.

Claims

1. A process for the synthesis of ammonia, (a) Ammonia makeup gas (7) containing hydrogen and nitrogen is reacted in an ammonia converter (15) under ammonia formation conditions to obtain an ammonia-containing effluent (8). (b) In the reforming process (100), the hydrocarbon source (1) is reformed to produce the first hydrogen portion contained in the ammonia makeup gas (7), (c) By using at least renewable energy sources (SE, WE), a second hydrogen portion (19) contained in the ammonia makeup gas (7) is produced separately from the reforming process, (d) A portion of the hydrogen produced in step (c) is stored in the hydrogen storage facility (103). (e) If the renewable energy sources (SE, WE) are not available in whole or in part, hydrogen (20) from the hydrogen storage (103) is used to replace in whole or in part the hydrogen produced in step (c). The aforementioned process, (f) A step of evaluating the predicted flow rate of the hydrogen (19) produced in step (c), (g) A step of adjusting the flow rate of the hydrocarbon source (1) in step (b) such that the flow rate of the first hydrogen portion in the ammonia makeup gas (7) is in a desired ratio to the predicted flow rate in step (f), (h) A step of detecting the actual amount of hydrogen in the hydrogen storage facility (103), for example, the filling level, (i) A step to detect the actual flow rate of hydrogen produced in step (c), A process comprising (j) adjusting the flow rate of hydrogen (20) from the hydrogen storage (103) according to the actual amount detected in step (h) and the actual flow rate detected in step (i).

2. The process according to claim 1, wherein the adjustment frequency of step (g) is less than the adjustment frequency of step (j), preferably, the adjustment frequency of step (g) is at least 10 times, more preferably at least 50 times, and even more preferably at least 100 times less than the adjustment frequency of step (j).

3. Process (g) is a long-term adjustment, and process (j) is a short-term adjustment. The aforementioned long-term adjustment is carried out at time intervals of 4 days to 7 weeks, preferably 5 days to 6 weeks, and more preferably 6 days to 4 weeks. The process according to claim 1 or 2, wherein the short-term adjustment is performed at time intervals of 1 minute to 28 hours, preferably 10 minutes to 26 hours, and more preferably 20 minutes to 24 hours.

4. The process according to any one of claims 1 to 3, wherein step (f) is the calculation of the predicted flow rate from the detected flow rate of the hydrogen (19) produced in step (c) in a past execution of the process, or includes the calculation thereof.

5. The process according to claim 4, wherein the calculation is a rolling average of the detected flow rate over a predetermined period of time, or includes the rolling average.

6. The process according to any one of claims 1 to 5, wherein step (f) includes a prediction based on estimated electrical energy (21) generated by the renewable energy sources (SE, WE) in a given geographical area.

7. The process according to any one of claims 1 to 6, wherein additional nitrogen (22) is mixed with the ammonia makeup gas (7) upstream of the ammonia converter (15) to adjust the hydrogen-to-nitrogen molar ratio for ammonia synthesis, the hydrogen (19) produced in step (c) is supplied to the ammonia converter (15) via a main compressor (11) or a dedicated compressor (29), and at least a portion of the additional nitrogen (22) is obtained by cryogenic air separation or pressure swing adsorption (PSA).

8. The process according to any one of claims 1 to 7, wherein additional nitrogen (22) is mixed into the airflow (9) supplied to the reforming front end (100) upstream of the air compressor (10) to adjust the hydrogen-to-nitrogen molar ratio for ammonia synthesis, the hydrogen (19) produced in step (c) is supplied to the ammonia converter (15) via a main compressor (11) or a dedicated compressor (29), and at least a portion of the additional nitrogen (22) is or includes the exhaust gas of the nitrate production process, preferably the exhaust gas is compressed by the air compressor (10).

9. The process according to any one of claims 1 to 8, wherein the hydrogen (19) in step (c) is produced by the electrolysis of water (W), preferably by pressurized alkaline electrolysis.

10. The process according to claim 9, wherein the electrolysis of the water (W), preferably pressurized alkaline electrolysis, is operated by solar energy (SE) and / or wind energy (WE), particularly via a solar power plant (104) and / or a wind turbine power plant (105).

11. (k) A step of storing a portion of the electrical energy produced by the renewable energy source (SE, WE) in a storage battery (46), (l) The process according to any one of claims 1 to 10, further comprising the step of producing the second hydrogen portion (19) using electricity stored in the battery (46) when the renewable energy source (SE, WE) is not available in whole or in part.

12. The process according to any one of claims 1 to 11, wherein the renewable energy source is biomass or includes biomass, and the hydrogen (19) is produced in step (c) by a step of converting the biomass into a hydrogen-containing gas using a thermochemical process, for example gasification, or a biological process, for example fermentation, and a step of purifying the hydrogen-containing gas thereafter.

13. The process according to any one of claims 1 to 12, wherein a portion of the hydrogen (19) produced in step (c) is sent to the hydrogen storage (103) by a hydrogen compressor (29), and the hydrogen stored in the hydrogen storage (103) is supplied to the suction side of the hydrogen compressor (29), thereby causing such a compressor to maintain a desired pressure value in the hydrogen storage (103) and supply hydrogen contained in the ammonia makeup gas (7).

14. The process according to any one of claims 1 to 13, wherein the hydrogen storage facility (103) is maintained at a pressure of at least 50 bar, preferably 50 bar to 250 bar, and preferably 60 bar to 200 bar.

15. The process according to any one of claims 1 to 14, wherein the hydrogen storage facility (103) has a maximum capacity of the average weekly production amount of the hydrogen (19) produced in step (c), preferably the average two-day production amount, and more preferably the average one-day production amount.

16. The process according to any one of claims 1 to 15, wherein the hydrogen (19) produced by renewable energy accounts for a maximum of 50%, preferably 1% to 50%, more preferably 2% to 35%, even more preferably 3% to 25%, and even more preferably 5% to 15% of the hydrogen contained in the ammonia makeup gas (7).

17. The process according to any one of claims 1 to 16, wherein the reforming process (100) is a step of reforming a hydrocarbon source (1) and purifying the reformed gas thus obtained, thereby obtaining the ammonia makeup gas, supplying the ammonia makeup gas to the ammonia converter (15) via a compressor (11), and supplying the hydrogen (19) produced in step (c) to the ammonia converter (15) via the same compressor (11), wherein an optional additional nitrogen (22) is supplied to the ammonia converter (15) via one or more dedicated compressors (23), or via an air compressor (10), and then via a main compressor (11).

18. A method for modifying a plant for ammonia synthesis, wherein the plant is A reforming front end (100) for generating ammonia makeup gas (7) by reforming a hydrocarbon source (1), The system comprises an ammonia synthesis loop (101) including an ammonia converter (15), The method for modifying the plant is (I) A step of providing a green hydrogen production device such as a water electrolytic cell (102) that uses renewable energy sources (SE, WE), and a line (25) arranged to supply green hydrogen under pressure from the green hydrogen production device to the ammonia converter (15), (II) A step of providing a hydrogen storage facility (103), an input line (24) arranged to supply the green hydrogen to the hydrogen storage facility (103), and an output line (20) arranged to supply hydrogen from the hydrogen storage facility (103) to the ammonia converter (15), (III) The step of updating the process control system (26) of the plant in order to carry out the process described in any one of claims 1 to 17, A method comprising step (III) uploading a computer program to the internal memory of the process management system (26) of the plant, wherein the computer program includes a portion of software code suitable for performing the process, and the portion of software code is executed by the process management system (26).

Images