Flexible ammonia synthesis process adapted to renewable energy fluctuations

Abstract

The application is a flexible synthetic ammonia process suitable for renewable energy fluctuation. The process steps are: a nitrogen buffer tank is arranged between the air separation system and the synthetic ammonia unit, the N2 feed for the synthetic ammonia unit comes from the nitrogen supplied to the nitrogen buffer tank after nitrogen production by the air separation system, and the H2 feed comes from the hydrogen production system configured with partial renewable energy hydrogen production. The H2 feed and the N2 feed are uniformly mixed with the recycle gas from the recycle compressor in the buffer tank to form the reaction gas, and the reaction gas is heated by the heating system to synthesize ammonia and the like. Since the hydrogen production system is configured with partial renewable energy hydrogen production, when the renewable energy fluctuates, the hydrogen production will fluctuate, the feedforward flow signal from the raw material H2 flow meter and the feedback flow signal from the reaction gas flow meter are collected to the feed N2 flow controller, and after system analysis, the N2 flow regulating valve is controlled to adjust the N2 feed amount to keep the system material amount, pressure, treatment load and other parameters stable.

Description

[0001] Technical Field This invention belongs to the field of renewable energy green hydrogen ammonia synthesis technology, specifically a flexible ammonia synthesis process that adapts to the fluctuations of renewable energy.

[0002] Background Technology The synthesis of ammonia from renewable energy-based green hydrogen is one of the most promising hydrogen storage routes. However, due to the volatility of hydrogen production from renewable energy sources, this route faces poor operational stability issues not encountered under the stable feed conditions of traditional ammonia synthesis processes. The volatility of renewable energy-based hydrogen production leads to fluctuations in the feed hydrogen flow rate. These fluctuations not only make it difficult to stably control the pressure in the ammonia synthesis system but also cause mechanical shocks to the process equipment, jeopardizing the normal operation of the system. Therefore, the industry has proposed the concept of flexible ammonia synthesis to address the adaptability of the process under the volatility of renewable energy-based hydrogen production.

[0003] Currently, there are few flexible ammonia synthesis solutions to address fluctuations in hydrogen production from renewable energy sources. Conventional flexible solutions (such as patents CN116081644A and CN118988177A) typically involve installing large-capacity, high-pressure hydrogen storage containers after the hydrogen production system to store surplus hydrogen obtained during peak renewable energy production periods. This ensures a sufficient and stable hydrogen supply even during off-peak periods, maintaining stable material flow rates in key equipment of the ammonia synthesis process. However, this solution requires expensive, highly sealed hydrogen storage containers and pressurization power equipment, and must consider hydrogen storage safety and leakage risks. Therefore, the investment cost of this solution is relatively high.

[0004] The impact of renewable energy hydrogen production fluctuations on the ammonia synthesis process is mainly as follows: (1) Affecting the stability of the air separation system: Cryogenic air separation units and pressure swing adsorption air separation units are generally not suitable for operation under variable load. Fluctuations in hydrogen feed will cause fluctuations in the nitrogen demand that matches the ratio, affecting the load stability of the cryogenic unit or pressure swing adsorption unit, which is not conducive to the stable control of the air separation nitrogen production system. (2) Affecting the control stability of the ammonia synthesis reaction system: Fluctuations in renewable energy hydrogen production will cause repeated fluctuations in the amount of syngas entering the ammonia synthesis reactor, making it difficult to maintain a stable reaction pressure. (3) Damaging the catalyst: Repeated fluctuations in the reactor feed will also cause mechanical impact on the catalyst, resulting in an annual pulverization rate of 10-12% for the ammonia synthesis catalyst. In severe cases, this can lead to rapid deactivation of the catalyst, endangering the normal operation of the system. (4) Increasing the risk of process equipment failure: Frequent fluctuations in the process gas volume in the ammonia synthesis system may cause equipment fatigue, failure of seals due to frequent operation of equipment, and increased risk of hydrogen leakage. Especially under the existing scheme of using high-pressure hydrogen storage containers to smooth out hydrogen supply fluctuations, the hydrogen storage tanks are in a state of frequent and repeated charging and discharging of hydrogen, which greatly increases the risk of hydrogen leakage. Summary of the Invention

[0005] The purpose of this invention is to overcome the adverse effects of the volatility of hydrogen production from renewable energy sources on the ammonia synthesis process and reduce the overall investment cost of the process. This invention proposes a flexible ammonia synthesis process that adapts to the fluctuations in hydrogen production from renewable energy sources. This process can maintain the stability of material flow in key equipment under the condition of hydrogen feed fluctuations by supplementing N2 feed to make up for the reduction in hydrogen supply, setting up nitrogen buffer tanks to replace hydrogen storage tanks, and adopting a combined feedforward and feedback control strategy. This ensures the stable operation of the ammonia synthesis process under the fluctuations in hydrogen production from renewable energy sources.

[0006] To achieve the objectives of this invention, the specific technical solution adopted is as follows: A flexible ammonia synthesis process adaptable to fluctuations in renewable energy sources includes the following steps: In the ammonia synthesis process, a nitrogen buffer tank is installed between the air separation system and the ammonia synthesis unit. The N2 feed for the ammonia synthesis unit comes from the nitrogen supplied to the nitrogen buffer tank after nitrogen production in the air separation system, and the H2 feed comes from the hydrogen production system equipped with some renewable energy hydrogen production. The H2 and N2 feeds are then uniformly mixed with the circulating gas from the circulating compressor in the buffer tank to form the reaction synthesis gas, referred to as the reaction gas. After being heated by the heating system, the reaction gas enters the ammonia synthesis reaction system, where ammonia is synthesized under certain reaction conditions. The high-pressure mixed gas obtained after the reaction is cooled to liquid ammonia by the condensation system, and then separated from the unreacted gas by the ammonia separation system. The separated liquid ammonia is sent to the liquid ammonia storage system for low-temperature and high-pressure storage, while most of the separated gas is returned to the buffer tank through the circulating compression system, and a small portion of the gas is sent to the tail gas treatment system as purge gas and then discharged from the system as tail gas.

[0007] Furthermore, in the aforementioned flexible ammonia synthesis process adapted to fluctuations in renewable energy, the reaction conditions in the ammonia synthesis reaction system are: reaction temperature 400~500℃ and reaction pressure 5~15MPa.

[0008] Furthermore, in the aforementioned flexible ammonia synthesis process adapted to renewable energy fluctuations, an H2 flow meter is installed between the hydrogen production system and the buffer tank.

[0009] Furthermore, in the aforementioned flexible ammonia synthesis process adapted to renewable energy fluctuations, a reaction gas flow meter is installed between the buffer tank and the heating system.

[0010] Furthermore, in the aforementioned flexible ammonia synthesis process adapted to renewable energy fluctuations, an N2 flow regulating valve and a feed N2 flow controller are sequentially installed between the nitrogen buffer tanks.

[0011] Furthermore, in the aforementioned flexible ammonia synthesis process adapted to renewable energy fluctuations, since the hydrogen production system is configured to produce hydrogen from a portion of renewable energy sources, fluctuations in renewable energy levels will lead to fluctuations in hydrogen production. In this case, the feedforward flow signal from the raw material H2 flow meter and the feedback flow signal from the reactant gas flow meter converge to the feed N2 flow controller. After system analysis, the N2 flow regulating valve is controlled to adjust the N2 feed rate to maintain the stability of parameters such as material quantity, pressure, and processing load within the system.

[0012] The following content: Original operating condition: refers to the operating condition in which no flexible measures are taken, and the nitrogen supply is reduced by the same amount to maintain the hydrogen-nitrogen feed ratio of the feed gas. Existing conventional flexible solutions: installing hydrogen storage containers after the hydrogen production system.

[0013] Under normal operating conditions, when the amount of hydrogen produced from renewable energy fluctuates, the N2 feed rate and H2 feed rate are adjusted by the same magnitude. This fluctuation in gas volume has an adverse impact on the normal operation of the ammonia synthesis process. Although existing conventional flexible solutions can maintain the stability of the process when hydrogen production from renewable energy fluctuates by setting up hydrogen storage containers, there are problems with the high cost of hydrogen storage equipment and the safety of hydrogen storage.

[0014] To adapt to the volatility of hydrogen production from renewable energy sources, and to reduce the equipment costs and safety risks of existing conventional flexible solutions, the improved process of this invention adopts the following measures: (1) Strategy of supplementing nitrogen feed to compensate for reduced hydrogen supply With reduced hydrogen production from renewable energy sources, the decrease in hydrogen feed will lead to a reduction in syngas volume and gas pressure within the process system. This process employs a strategy of supplementing nitrogen feed to compensate for the reduced hydrogen supply. Specifically, when the hydrogen feed decreases, a certain amount of nitrogen is added at a ratio exceeding the conventional fresh feed gas nitrogen-to-hydrogen ratio (N2 feed rate: H2 feed rate = 1:3) to compensate for the reduced gas volume caused by the decreased hydrogen supply, thus maintaining stable gas volume and pressure. Under the same cycle conditions, to maintain a constant feed rate to the ammonia synthesis reaction system, the hydrogen-to-nitrogen ratio in the fresh feed gas after nitrogen supplementation is controlled between 1.4:1 and 3:1 for different hydrogen feed reduction ratios.

[0015] (2) Install a nitrogen buffer tank to replace the hydrogen storage tank. Under the original operating conditions, when hydrogen production decreases, the nitrogen supply from the air separation unit (ASU) needs to decrease synchronously with the H2 feed rate, which is detrimental to the operational stability of the ASU system. Existing conventional flexible solutions, to maintain downstream hydrogen supply stability during periods of low hydrogen production, typically involve installing a large-capacity, high-pressure hydrogen storage container before the hydrogen feed inlet. This storage container also allows the ASU nitrogen production rate and operating load to remain constant, further promoting stable operation. However, this solution carries higher hydrogen storage costs and safety risks. This improved solution incorporates a nitrogen buffer tank with high pressure resistance. The ASU nitrogen production rate and operating load remain constant. The nitrogen storage pressure in the buffer tank and the N2 feed rate after exiting the buffer tank are adjusted according to process requirements and H2 feed rate. This replaces the hydrogen storage process with a nitrogen buffering process. Combined with a strategy of supplementing nitrogen feed to compensate for reduced hydrogen supply, this approach can maintain stable operation of the ammonia synthesis process even under fluctuations in renewable energy hydrogen production.

[0016] (3) Adopt a combined feedforward and feedback control strategy Because there is a certain pipeline distance between the material inlet and the inlet of the ammonia synthesis reaction system, the impact of fluctuations in syngas flow and gas pressure caused by a reduction in hydrogen supply at the inlet takes a certain amount of time to be transmitted to the ammonia synthesis reaction system. If only the feedback signal of the inlet flow rate of the ammonia synthesis reaction system is used as the control parameter, it will cause a response delay. The improved scheme of this patent uses the syngas flow rate at the inlet of the ammonia synthesis reaction system obtained by the syngas flow meter as the feedback input signal (end-point control target), and at the same time uses the feed hydrogen flow rate obtained by the raw material H2 flow meter as the feedforward input signal (source early response). The appropriate N2 feed rate is determined by the coordination of the two signals, overcoming the N2 feed matching delay caused by the time it takes for the material to flow in the process pipeline, making the response of the feed N2 regulating valve more accurate, and the material flow in the system more stable and easier to control.

[0017] Furthermore, the aforementioned flexible ammonia synthesis process adaptable to renewable energy fluctuations is applicable to ammonia synthesis processes where the proportion of hydrogen produced from renewable energy is 0-70%.

[0018] Furthermore, in the aforementioned flexible ammonia synthesis process adapted to renewable energy fluctuations, the nitrogen buffer tank is designed to withstand pressure ranging from 0.1 MPa to 35 MPa.

[0019] In the ammonia synthesis process, when hydrogen production from renewable energy fluctuates, the system employs a supplementary N2 feed to compensate for the reduced hydrogen supply and maintain stable material flow rates for key equipment. The hydrogen-to-nitrogen ratio in the fresh feed gas after N2 supplementation is controlled between 1.4:1 and 3:1. The system's N2 feed flow controller uses a "feedforward + feedback" coupled control scheme, combining the "feed hydrogen flow signal" and the "ammonia synthesis reaction system inlet flow signal." A nitrogen buffer tank is installed between the air separation unit and the ammonia synthesis system feed line, allowing the nitrogen buffer tank to actively adjust its internal pressure to temporarily store nitrogen. This overcomes the impact of renewable energy hydrogen production fluctuations on the control stability of the air separation system, the ammonia synthesis reaction system, catalyst performance stability, and process equipment safety in existing technologies, making this process suitable for ammonia synthesis processes where renewable energy hydrogen production accounts for 0-70%.

[0020] It is important to note that the biggest difference between this invention and existing technologies lies in the adoption of a "strategy of supplementing nitrogen feed to compensate for reduced hydrogen supply" and supporting solutions for this strategy. Therefore, during fluctuations in hydrogen production from renewable energy sources, the hydrogen-to-nitrogen ratio of the system's fresh feed gas will be less than 3:1 (responsibility coefficient ratio). This approach is not a conventional solution from a chemical production perspective. Conventional chemical production generally does not employ operating conditions with a hydrogen-to-nitrogen ratio below 3:1, as a low hydrogen feed percentage would lead to reduced equilibrium ammonia yield, decreased ammonia production, and reduced catalyst efficiency. The primary objective of chemical production is to obtain ammonia with the highest space-time yield, emphasizing production profits. However, the main future application of green ammonia synthesis technology is not in chemical production, but rather as a hydrogen and energy storage medium for the consumption and storage of renewable electricity from wind and solar power. Therefore, efficiency is no longer the primary concern.

[0021] Furthermore, the use and purpose of the gas buffer tank in this invention are opposite to those of existing solutions: conventional solutions typically use hydrogen buffer tanks to collect unstable incoming flows and output them at a constant flow rate; this invention does the opposite, by setting up a nitrogen buffer tank to output the constant upstream air separation nitrogen production as a non-constant nitrogen feed rate into the ammonia synthesis system, thereby matching the non-constant fluctuations in hydrogen production from renewable energy sources.

[0022] Therefore, the improved solution has the following characteristics: (1) Compared to conventional and stable chemical processes, the high-frequency fluctuations caused by the volatility of hydrogen production from renewable energy sources cause significant damage to catalysts, and long-term stable operation remains a problem. Compared to the losses from frequent shutdowns due to catalyst damage, a certain degree of reduction in reaction rate under the volatility of hydrogen production from renewable energy sources is an acceptable cost. (2) New ammonia synthesis catalysts are more adaptable to low-hydrogen conditions, and their catalytic activity can be improved and the reaction rate increased by using suitable catalysts. In summary, although low hydrogen-nitrogen ratio operation does not conform to the conventional chemical production objectives, this scheme can achieve continuous operation of the process, which can meet the current application scenario requirements for adapting to the volatility of hydrogen production from renewable energy sources.

[0023] Compared with the prior art, the main advantages of the present invention are as follows: (1) The present invention can maintain the stability of parameters such as material quantity, pressure and load in the ammonia synthesis process system under unstable hydrogen production fluctuations, prevent equipment fatigue caused by frequent fluctuations in material quantity, and especially alleviate the mechanical impact of reaction gas flow fluctuations on the catalyst, thus extending the service life of the equipment.

[0024] (2) Compared with the conventional flexible solution of setting up a large-capacity high-pressure hydrogen storage container before the hydrogen feed inlet to maintain the stability of hydrogen supply during the low hydrogen production period, the feed unit of the present invention does not need to set up auxiliary equipment such as high-pressure hydrogen storage tank and hydrogen storage compressor. This avoids the risk of leakage under the frequent repeated filling and discharging of hydrogen in the high-pressure hydrogen storage container, and replaces the high-cost and high-safety hydrogen storage process with a low-cost and safe buffer nitrogen storage process, thereby reducing equipment investment costs.

[0025] (3) The present invention adopts a "feedforward + feedback" joint control strategy with more accurate response and a variety of measures to maintain the stability of system operating parameters, which ensures the stability of process operation and makes the material flow in the system smoother and easier to control. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a flexible ammonia synthesis process adapted to fluctuations in hydrogen production from renewable energy sources, as described in this invention. Figure 2 A graph showing the hydrogen-to-nitrogen ratio of the fresh feed gas to maintain a constant space velocity in the ammonia synthesis reaction system under fluctuations in hydrogen production from renewable energy sources. Figure 3 This is a graph showing the nitrogen production of the air separation system under hydrogen production fluctuations in Example 1, based on renewable energy sources. Figure 4 This is a graph showing the changes in feed rate of the ammonia synthesis reaction system under the fluctuation of hydrogen production from renewable energy in Example 1; Figure 5 This is a comparison of the design volume of the nitrogen buffer tank in this invention and the existing flexible hydrogen storage tank in Example 1; Figure 6This is a graph showing the nitrogen production of the air separation system under hydrogen production fluctuations in Example 2, based on renewable energy sources. Figure 7 This is a graph showing the changes in feed rate of the ammonia synthesis reaction system under the fluctuation of hydrogen production from renewable energy in Example 2; Figure 8 This is a comparison of the design volume of the nitrogen buffer tank in this invention and the existing flexible hydrogen storage tank in Example 2; Figure 9 This is a graph showing the nitrogen production of the air separation system under hydrogen production fluctuations in Example 3, based on renewable energy sources. Figure 10 This is a graph showing the changes in feed rate of the ammonia synthesis reaction system under the fluctuation of hydrogen production from renewable energy in Example 3; Figure 11 This is a comparison of the design volume of the nitrogen buffer tank in this invention and the existing flexible hydrogen storage tank in Example 3. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0029] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this description, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0030] In this invention, some conventional operating equipment, devices and components have been omitted or only briefly described.

[0031] Unless otherwise specified in the examples, the conditions shall be performed according to the standard conditions or the conditions recommended by the manufacturer.

[0032] A flexible ammonia synthesis system adapted to fluctuations in hydrogen production from renewable energy sources also includes an air separation system, a hydrogen production system, a nitrogen buffer tank, a buffer tank, a circulating compression system, a heating system, an ammonia synthesis reaction system, a condensation system, an ammonia separation system, a tail gas treatment system, and a liquid nitrogen storage system. in: An H2 flow meter is installed between the hydrogen production system and the buffer tank; A reaction gas flow meter is installed between the buffer tank and the heating system; An N2 flow regulating valve and a feed N2 flow controller are installed sequentially between the nitrogen buffer tanks.

[0033] The air separation system is connected to the nitrogen buffer tank; the hydrogen production system is connected to both the buffer tank and the N2 flow controller. The buffer tank is connected to both the heating system and the N2 flow controller. A synthetic ammonia reaction system, a condensation system, an ammonia separation system, and a liquid nitrogen storage system are sequentially connected after the heating system. The ammonia reaction system is connected to both the tail gas treatment system and the recirculating compression system. The cyclic compression system is connected to the buffer tank.

[0034] In the above system, the nitrogen buffer tank is designed to withstand pressure ranging from 0.1 MPa to 35 MPa.

[0035] A synthetic ammonia process adapted to renewable energy fluctuations is implemented using the aforementioned system. In this process, a nitrogen buffer tank is installed between the air separation system and the synthetic ammonia unit. The N2 feed for the synthetic ammonia unit comes from the nitrogen supplied to the nitrogen buffer tank after nitrogen production in the air separation system, while the H2 feed comes from a hydrogen production system equipped with some renewable energy-based hydrogen production. The H2 and N2 feeds are then uniformly mixed with circulating gas from the circulating compressor in the buffer tank to form a reaction synthesis gas (reaction gas). After being heated by a heating system, the reaction gas enters the synthetic ammonia reaction system, where ammonia is synthesized at a reaction temperature of 400-500℃ and a reaction pressure of 5-15MPa. The high-pressure mixed gas after the reaction is cooled to liquid ammonia by a condensation system, and then separated from the unreacted gas by an ammonia separation system. The separated liquid ammonia is sent to a liquid ammonia storage system for low-temperature, high-pressure storage, while most of the separated gas is returned to the buffer tank through a circulating compression system, and a small portion of the gas is sent to a tail gas treatment system for treatment and then discharged from the system as tail gas.

[0036] Since the hydrogen production system is equipped with some renewable energy sources, fluctuations in renewable energy sources will cause fluctuations in the hydrogen production rate. At this time, the feedforward flow signal from the raw material H2 flow meter and the feedback flow signal from the reaction gas flow meter are converged to the feed N2 flow controller. After system analysis, the N2 flow regulating valve is controlled to adjust the N2 feed rate to maintain the stability of parameters such as material quantity, pressure, and processing load in the system.

[0037] Under normal operating conditions, when the amount of hydrogen produced from renewable energy fluctuates, the N2 feed rate and H2 feed rate adjust to the same magnitude. This fluctuation in gas volume negatively impacts the normal operation of the ammonia synthesis process. To adapt to the volatility of hydrogen production from renewable energy, the improved process of this invention adopts the following measures: (1) Strategy of supplementing nitrogen feed to compensate for reduced hydrogen supply With the reduction in hydrogen production from renewable energy sources, the decrease in hydrogen feed will lead to a decrease in the syngas volume and gas pressure within the process system. This patent's improved solution employs a strategy of supplementing nitrogen feed to compensate for the reduced hydrogen supply. Specifically, when the hydrogen feed decreases, a certain amount of nitrogen is supplemented at a ratio exceeding the conventional fresh feed gas nitrogen-to-hydrogen ratio (N2 feed rate: H2 feed rate = 1:3) to compensate for the reduced gas volume in the process system caused by the reduced hydrogen supply, thus maintaining stable gas volume and pressure. Under the same cycle conditions, to maintain a constant feed rate in the ammonia synthesis reaction system, the hydrogen-to-nitrogen ratio in the fresh feed gas after nitrogen supplementation is controlled between 1.4:1 and 3:1 for different hydrogen feed reduction ratios. The relationship between the hydrogen-to-nitrogen ratios in the fresh feed gas corresponding to each hydrogen feed reduction ratio is as follows: Figure 2 As shown.

[0038] (2) Install a nitrogen buffer tank to replace the hydrogen storage tank. Under the original operating conditions, when hydrogen production decreases, the nitrogen supply from the air separation unit (ASU) needs to decrease synchronously with the H2 feed rate, which is detrimental to the operational stability of the ASU system. Existing conventional flexible solutions, to maintain downstream hydrogen supply stability during periods of low hydrogen production, typically involve installing a large-capacity, high-pressure hydrogen storage container before the hydrogen feed inlet. After installing the storage container, the ASU nitrogen production rate and operating load can remain constant, further promoting stable operation of the ASU system. However, this solution carries higher hydrogen storage costs and safety risks. The improved solution in this patent incorporates a nitrogen buffer tank with high pressure resistance. The ASU nitrogen production rate and operating load remain constant. The nitrogen storage pressure in the buffer tank and the N2 feed rate after exiting the buffer tank are adjusted according to process requirements and H2 feed rate. This replaces the hydrogen storage process with a nitrogen buffering process. Combined with a strategy of "supplementing nitrogen feed to compensate for reduced hydrogen supply," the stable operation of the ammonia synthesis process can be maintained even under fluctuations in renewable energy hydrogen production.

[0039] (3) Adopt a combined feedforward and feedback control strategy Because there is a certain pipeline distance between the material inlet and the inlet of the ammonia synthesis reaction system, the impact of fluctuations in syngas flow and gas pressure caused by a reduction in hydrogen supply at the inlet takes a certain amount of time to be transmitted to the ammonia synthesis reaction system. If only the feedback signal of the inlet flow rate of the ammonia synthesis reaction system is used as the control parameter, it will cause a response delay. The improved scheme of this patent uses the syngas flow rate at the inlet of the ammonia synthesis reaction system obtained by the syngas flow meter as the feedback input signal (end-point control target), and at the same time uses the feed hydrogen flow rate obtained by the raw material H2 flow meter as the feedforward input signal (source early response). The appropriate N2 feed rate is determined by the coordination of the two signals, overcoming the N2 feed matching delay caused by the time it takes for the material to flow in the process pipeline, making the response of the feed N2 regulating valve more accurate, and the material flow in the system more stable and easier to control.

[0040] Example: The ammonia synthesis reaction is carried out based on a flexible ammonia synthesis system and process adapted to fluctuations in hydrogen production from renewable energy sources, as described in the specific embodiment. A schematic diagram of the specific process flow is shown below. Figure 1 As shown.

[0041] The hydrogen feedstock for the ammonia synthesis project comes from two sources: photovoltaic hydrogen production and stable power generation. Under full-load operation of the hydrogen production system, the proportion of hydrogen produced by photovoltaic power generation in the total hydrogen supply for the ammonia synthesis system is [percentage missing]. η H2 (Range range of 30%~70%), the proportion of stable electricity-generated hydrogen to the hydrogen supply from the ammonia synthesis system feedstock is (1- η H2 Hydrogen production fluctuation cycle T The reduction percentage of hydrogen feed is δ When producing hydrogen at full load, assuming the original operating condition (meaning without taking flexible measures, reducing the nitrogen supply by the same amount to maintain the hydrogen-nitrogen feed ratio of the feed gas), the H2 feed rate is... q H2,full N2 feed rate is q N2,full The H2 and N2 feed rates under full-load hydrogen production conditions are the same in this invention. Under fluctuating hydrogen production conditions, the H2 feed rate corresponding to the original operating conditions is... q H2,full-δ N2 feed rate is q N2,full-δ The present invention maintains the same H2 feed rate as the original operating condition under fluctuating hydrogen production conditions, but the N2 feed rate differs from the original operating condition. q N2,full-δ,本发明方案 Furthermore, the existing conventional flexible scheme used for comparison with this scheme smooths out H2 feed fluctuations by incorporating a hydrogen production system followed by a hydrogen storage container. Therefore, the H2 and N2 feed rates of the existing conventional flexible scheme remain constant, respectively. qH2,储氢方案 and q N2,储氢方案 .

[0042] Assume that the full-load photovoltaic hydrogen production time (t1) of a certain ammonia synthesis project is 5 hours during the day; when sunlight begins to decrease in the evening, the photovoltaic hydrogen production will gradually and uniformly decrease to 0 within time t2 = 0.5 hours; when sunlight begins to recover in the morning, the photovoltaic hydrogen production will uniformly increase from 0 to its maximum value within time t3 = 0.5 hours. Clearly, within this fluctuation cycle... T The maximum reduction percentage of hydrogen feed over 24 hours δ max equal η H2 .

[0043] The following three specific embodiments will compare the original working condition, existing conventional flexible solutions, and the solution of this invention to demonstrate the innovation of this invention. Specifically: Original operating condition: refers to the operating condition in which no flexible measures are taken, and the nitrogen supply is reduced by the same amount to maintain the hydrogen-nitrogen feed ratio of the feed gas. Existing conventional flexible solutions: installing hydrogen storage containers after the hydrogen production system.

[0044] Example 1 H2 feed rate when producing hydrogen at full photovoltaic capacity q H2,full =3 kmol / h and N2 feed rate q N2,full Taking 1 kmol / h as an example, let the proportion of photovoltaic hydrogen production to the hydrogen supply of the ammonia synthesis system be... η H2 =70%, assuming the moment when hydrogen production begins at full load is the initial time point 0, the changes in the main parameters within the system are as follows: 1.1 Changes in nitrogen production from the air separation system The existing conventional flexible scheme (hydrogen production system with hydrogen storage container installed after hydrogen production system) air separation nitrogen production capacity q N2,空分,储氢方案 The average hydrogen consumption for ammonia synthesis under this scheme can be used as a basis. q H2,储氢方案 Approximate calculations can be performed using equations (1) and (2): (1) (2) The nitrogen production capacity of the air separation system in this invention q N2,空分,本发明方案 It can be approximated by formula (3): (3) The nitrogen production of the air separation system under the fluctuation of renewable energy hydrogen production within 48 hours is shown in [link to relevant data]. Figure 3 .

[0045] During periods when hydrogen production is not possible using renewable energy sources, the hydrogen-to-nitrogen ratio in the fresh feed gas is 3:1 under the original operating conditions and existing conventional flexible schemes, while the hydrogen-to-nitrogen ratio in the fresh feed gas of this invention is 1.45:1.

[0046] 1.2 Changes in feed rate of the ammonia synthesis reaction system The changes in feed rate of the ammonia synthesis reaction system under the fluctuation of renewable energy hydrogen production over 48 hours are shown in the figure. Figure 4 .

[0047] 1.3 Comparison of design volumes of nitrogen buffer tanks and hydrogen storage tanks The maximum molar hydrogen storage capacity of existing conventional flexible solutions (hydrogen storage containers installed after the hydrogen production system) in hydrogen storage tanks n H2,max,储氢方案 It can be approximated by formula (4): (4) The maximum molar capacity of nitrogen in the nitrogen buffer tank of this invention n N2,max,本发明方案 It can be approximated by formula (5): (5) Photovoltaic hydrogen production ratio in hydrogen production systems η H2 The pressure is set at 70%, and the pressure of the nitrogen buffer tank in this invention and the hydrogen storage tank in the existing flexible solution is 20 MPa. A comparison of the corresponding design volumes is shown below. Figure 5 .

[0048] Example 2 H2 feed rate when producing hydrogen at full photovoltaic capacity q H2,full =3 kmol / h and N2 feed rate q N2,full Taking 1 kmol / h as an example, let the proportion of photovoltaic hydrogen production to the hydrogen supply of the ammonia synthesis system be... η H2 =50%, and assuming the moment when hydrogen production begins at full load is the initial time point 0, the changes in the main parameters within the system are as follows: 2.1 Changes in nitrogen production from the air separation system Existing conventional flexible air separation nitrogen production capacity q N2,空分,储氢方案 The nitrogen production capacity of the air separation system according to the present invention q N2,空分,本发明方案 The calculation method is the same as in Example 1.

[0049] The nitrogen production of the air separation system under the fluctuation of renewable energy hydrogen production within 48 hours is shown in [link to relevant data]. Figure 6 .

[0050] During periods of hydrogen production without renewable energy, the hydrogen-to-nitrogen ratio in the fresh feed gas of the original operating conditions and existing conventional flexible schemes is 3:1, while the hydrogen-to-nitrogen ratio in the fresh feed gas of the present invention is 2.09:1.

[0051] 2.2 Changes in the feed rate of the ammonia synthesis reaction system The changes in feed rate of the ammonia synthesis reaction system under the fluctuation of renewable energy hydrogen production over 48 hours are shown in the figure. Figure 7 .

[0052] 2.3 Comparison of design volumes of nitrogen buffer tanks and hydrogen storage tanks The maximum molar hydrogen storage capacity of existing conventional flexible hydrogen storage tanks n H2,max,储氢方案 The maximum nitrogen molar storage capacity of the nitrogen buffer tank of the present invention n N2,max,本发明方案 The calculation method is the same as in Example 1.

[0053] Photovoltaic hydrogen production ratio in hydrogen production systems η H2 The pressure is set at 50%, and the pressure of the nitrogen buffer tank in this invention and the hydrogen storage tank in the existing flexible solution is 20 MPa. A comparison of the corresponding design volumes is shown below. Figure 8 .

[0054] Example 3 H2 feed rate when producing hydrogen at full photovoltaic capacity q H2,full =3 kmol / h and N2 feed rate q N2,full Taking 1 kmol / h as an example, let the proportion of photovoltaic hydrogen production to the hydrogen supply of the ammonia synthesis system be... η H2 =30%, assuming the moment when hydrogen production begins at full load is the initial time point 0, the changes in the main parameters within the system are as follows: 3.1 Changes in nitrogen production from the air separation system Existing conventional flexible air separation nitrogen production capacity q N2,空分,储氢方案 The nitrogen production capacity of the air separation system according to the present invention q N2,空分,本发明方案 The calculation method is the same as in Example 1.

[0055] The nitrogen production of the air separation system under the fluctuation of renewable energy hydrogen production within 48 hours is shown in [link to relevant data]. Figure 9 .

[0056] During periods of hydrogen production without renewable energy, the hydrogen-to-nitrogen ratio in the fresh feed gas of the original operating conditions and existing conventional flexible schemes is 3:1, while the hydrogen-to-nitrogen ratio in the fresh feed gas of the present invention is 2.51:1.

[0057] 3.2 Changes in the feed rate of the ammonia synthesis reaction system The changes in feed rate of the ammonia synthesis reaction system under the fluctuation of renewable energy hydrogen production over 48 hours are shown in the figure. Figure 10 .

[0058] 3.3 Comparison of design volumes of nitrogen buffer tanks and hydrogen storage tanks The maximum molar hydrogen storage capacity of existing conventional flexible hydrogen storage tanks n H2,max,储氢方案 The maximum nitrogen molar storage capacity of the nitrogen buffer tank of the present invention n N2,max,本发明方案 The calculation method is the same as in Example 1.

[0059] Photovoltaic hydrogen production ratio in hydrogen production systems η H2 The pressure is set at 30%, and the pressure of the nitrogen buffer tank in this invention and the hydrogen storage tank in the existing flexible solution is 20 MPa. A comparison of the corresponding design volumes is shown below. Figure 11 .

[0060] Summary of Examples 1-3: Depend on Figure 3 , Figure 6 and Figure 9 It is known that under the fluctuation of hydrogen production from renewable energy sources, the original operating conditions require frequent adjustments to the air separation nitrogen production rate according to the hydrogen production fluctuations; both the existing conventional flexible solutions and the improved solution of this invention can maintain a constant air separation nitrogen production rate. Therefore, the solution of this invention is beneficial for maintaining stable control of the air separation nitrogen production system.

[0061] Depend on Figure 4 , Figure 7 and Figure 10 It is known that under the fluctuation of hydrogen production from renewable energy, the feed rate of the ammonia synthesis reaction system under the original operating conditions fluctuates significantly. However, under both the existing conventional flexible scheme and the improved operating conditions of this invention, the gas flow rate through the ammonia synthesis reaction system remains essentially constant, and the pressure fluctuations at various points in the system are far less than under the original operating conditions, greatly mitigating the mechanical impact of gas flow fluctuations on process equipment, especially the catalyst. Therefore, the solution of this invention provides better protection for the catalyst and process equipment.

[0062] Depend on Figure 5 , Figure 8 and Figure 11It can be seen that, under different renewable energy hydrogen production configuration ratios, the nitrogen buffer tank design volume of the present invention is smaller than the hydrogen storage tank design volume of the existing flexible scheme, resulting in lower equipment costs. Since the requirements for the safety performance of high-pressure containers for hydrogen storage are much higher than those for nitrogen storage, it can be seen that the equipment cost and safety of the present invention are superior to those of the existing conventional flexible schemes.

[0063] Comparing the original operating conditions, existing conventional flexible solutions, and the solution of this invention, the analysis of the above three specific embodiments shows that the improved solution proposed in this invention can maintain the stability of parameters such as material quantity, pressure, and processing load in the ammonia synthesis process under the fluctuation of hydrogen production from renewable energy, preventing equipment fatigue caused by frequent fluctuations in material quantity, and especially mitigating the mechanical impact of reaction gas flow fluctuations on the catalyst. Under the original operating conditions where hydrogen production fluctuations frequently impact the catalyst, the annual pulverization rate of ammonia synthesis catalyst with a radial pressure resistance of 400 N / piece can reach 12%; while under the solution of this invention, the annual pulverization rate of the catalyst is ≤3% (normal annual pulverization rate under stable feed), the catalyst life is improved, and the catalyst replacement cost is reduced. At the same time, the solution of this invention avoids the safety risks of the hydrogen storage process, and its equipment cost and safety are superior to existing conventional flexible solutions.

[0064] Finally, it should be noted that the above examples are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and can have many variations. For example, different fluctuation frequencies, fluctuation periods, and fluctuation amplitudes in renewable energy hydrogen production require different optimal nitrogen buffer tank volumes, pressures, and other parameters. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of this invention should be considered within the scope of protection of this invention.

Claims

1. A flexible ammonia synthesis process adaptable to fluctuations in renewable energy, characterized in that... Includes the following steps: A nitrogen buffer tank is installed between the air separation system and the ammonia synthesis unit. The N2 feed for the ammonia synthesis unit comes from the nitrogen supplied to the nitrogen buffer tank after nitrogen production in the air separation system, and the H2 feed comes from the hydrogen production system equipped with some renewable energy hydrogen production. The H2 and N2 feeds are then uniformly mixed with the circulating gas from the circulating compressor in the buffer tank to form reaction synthesis gas, referred to as reaction gas. The reaction gas is heated by the heating system and then enters the ammonia synthesis reaction system to synthesize ammonia under certain reaction conditions. The high-pressure mixed gas obtained after the reaction is cooled to liquid ammonia by the condensation system and then separated from the unreacted gas by the ammonia separation system. The separated liquid ammonia is sent to the liquid ammonia storage system for low-temperature and high-pressure storage. Most of the separated gas is returned to the buffer tank through the circulating compression system, and a small portion of the gas is sent to the tail gas treatment system as purge gas and then discharged from the system as tail gas. An H2 flow meter is installed between the hydrogen production system and the buffer tank; a reaction gas flow meter is installed between the buffer tank and the heating system; an N2 flow regulating valve and a feed N2 flow controller are installed sequentially between the nitrogen buffer tanks. The feedforward flow signal from the raw material H2 flow meter and the feedback flow signal from the reaction gas flow meter are converged to the feed N2 flow controller. After system analysis, the N2 flow regulating valve is controlled to adjust the N2 feed rate to maintain the stability of material quantity, pressure, and processing load parameters within the system. When the hydrogen feed rate decreases, a certain amount of nitrogen is supplemented at a ratio exceeding the conventional fresh feed gas nitrogen-hydrogen ratio to compensate for the reduction in process gas volume caused by the reduced hydrogen supply, thus maintaining the stability of gas volume and pressure. The ratio exceeding the conventional fresh feed gas nitrogen-hydrogen ratio means that the N2 feed rate to H2 feed rate = 1:

3. Under the same circulation conditions, to maintain a constant feed rate in the ammonia synthesis reaction system, the hydrogen-nitrogen ratio in the fresh feed gas after nitrogen supplementation is controlled between 1.4:1 and 3:1 under different hydrogen feed rate reduction ratios.

2. The flexible ammonia synthesis process adaptable to renewable energy fluctuations according to claim 1, characterized in that: The reaction conditions in the ammonia synthesis reaction system are: reaction temperature 400~500℃ and reaction pressure 5~15MPa.

3. A flexible ammonia synthesis process adaptable to renewable energy fluctuations according to claim 1 or 2, characterized in that: The nitrogen production rate of the air separation unit remains constant with the operating load. The nitrogen storage pressure in the buffer tank and the N2 feed after exiting the buffer tank are adjusted according to process requirements and H2 feed rate. The hydrogen storage process is replaced by a nitrogen storage buffer process, which maintains the stable operation of the ammonia synthesis process under the fluctuation of hydrogen production from renewable energy.

4. The flexible ammonia synthesis process adaptable to renewable energy fluctuations according to claim 3, characterized in that: This process is applicable to ammonia synthesis processes where hydrogen production from renewable energy accounts for 0-70%.

5. A flexible ammonia synthesis process adaptable to renewable energy fluctuations according to claim 3, characterized in that: The nitrogen buffer tank is designed to withstand pressure ranging from 0.1 MPa to 35 MPa.

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