Ammonia synthesis process using green hydrogen

Abstract

The process for ammonia synthesis, wherein ammonia synthesis is carried out in a high-pressure synthesis loop (101), part of which is supplied with green hydrogen (26) produced from renewable energy, and hydrogen recovered from the purified stream (21) of the loop is stored in a hydrogen storage tank (103) to compensate for the temporary shortage of green hydrogen when renewable energy is not fully available.

Description

Technical Field

[0001] This invention relates to the field of ammonia synthesis. Background Technology

[0002] Industrially, ammonia is produced by reacting a makeup gas containing hydrogen and nitrogen in an appropriate molar ratio. The makeup gas is typically produced through reforming a hydrocarbon source, such as natural gas.

[0003] The production of supplementary gases typically involves reforming processes and the purification of the reformed gases. Purification usually includes the conversion of CO to CO2, CO2 removal, and methanation. The purified gas thus obtained is supplied to the high-pressure ammonia synthesis circuit via the main syngas compressor.

[0004] In the ammonia synthesis loop, the makeup gas reacts in a suitable ammonia converter to form ammonia. The hot ammonia-containing effluent from the converter undergoes cooling and separation steps to obtain liquid ammonia and a side stream containing unreacted hydrogen and impurities. Typically, a portion of this side stream undergoes a hydrogen recovery process, and the recovered hydrogen is then fed to the suction inlet of the main syngas compressor. Another portion of the side stream is typically reintroduced into the ammonia converter via a recirculator, thus forming the ammonia synthesis loop described above.

[0005] Ammonia synthesis is carried out under high pressure, while the makeup gas is typically produced at a lower pressure. For example, ammonia synthesis may be carried out at approximately 140 bar, while the makeup gas may be produced at approximately 40 bar or lower. Therefore, a main syngas compressor is essential. In most embodiments, the suction side pressure of the main syngas compressor is 15 to 35 bar.

[0006] Nitrogen required for ammonia synthesis can be introduced in the reforming process, typically in a secondary reforming process involving air combustion. In some cases, nitrogen can be added separately (e.g., in the presence of an air separator).

[0007] In summary, the industrial production of ammonia relies on the reforming of hydrocarbons to produce the required hydrogen. Reforming is a typical fuel combustion process that emits large amounts of CO2.

[0008] There is growing interest in reducing the carbon footprint of ammonia production. Applicable regulations and rules could introduce additional taxes related to CO2 emissions, such as taking into account the amount of CO2 produced per tonne of ammonia. CO2 contained in combustion flue gas can be captured, but the related technologies are costly. Producing hydrogen using renewable energy sources is a feasible approach to achieving this goal.

[0009] Hydrogen produced using renewable energy sources is called "green" hydrogen because it does not produce CO2 emissions compared to conventional production through the combustion of reformed fuels. Hydrogen produced by burning fossil fuels is sometimes called "grey" hydrogen. The advantage of using green hydrogen is that it does not form CO2, thus eliminating the need for expensive capture and storage processes.

[0010] A practical example of a process for producing green hydrogen is the electrolysis of water. Water electrolysis requires electricity, which can be produced using renewable energy sources such as solar power, thus producing green hydrogen without releasing CO2 into the atmosphere.

[0011] In addition to "grey" hydrogen, the hydrogen produced in this way can also be injected into existing equipment, typically into the inlet of a syngas compressor or directly into the synthesis loop, to increase equipment output, reduce specific energy consumption, and decrease the associated carbon dioxide footprint.

[0012] However, hydrogen production using renewable energy sources is typically subject to fluctuations. For example, hydrogen production using solar energy is obviously dependent on the availability of sunlight. To compensate for these fluctuations, green hydrogen storage should be provided. When energy is completely or partially unavailable, storage can fully or partially replace green hydrogen production to maintain its significant contribution to ammonia production.

[0013] Hydrogen storage must be carried out under high pressure to be economically viable. For example, cost-effective hydrogen storage should be carried out at least 50 bar, typically between 50 and 300 bar. Unfortunately, existing green hydrogen production technologies on the market provide hydrogen at low or moderate pressures, insufficient for storage. For instance, existing technologies for water electrolysis can typically produce hydrogen at pressures of around 20 to 30 bar.

[0014] Therefore, storing green hydrogen requires compression. The necessary hydrogen compressors are expensive and consume a lot of electricity, making the transition to green hydrogen less economically attractive. Another problem is that commercially available hydrogen compressors are typically positive displacement compressors, which are inherently less reliable than turbine compressors such as centrifugal compressors. To ensure acceptable system reliability, backup units must be installed, further increasing costs. Summary of the Invention

[0015] The present invention aims to overcome the aforementioned drawbacks of the prior art. In particular, the present invention aims to provide a process and apparatus for ammonia synthesis that is more attractive than the prior art due to the use of so-called green hydrogen (i.e., hydrogen produced using renewable energy).

[0016] This objective is achieved through the process described in this invention. In this invention, ammonia is produced using hydrogen conventionally produced via a reforming process and hydrogen produced from renewable energy sources (green hydrogen). A hydrogen storage device is provided, and the hydrogen in the storage device is used to compensate for some or all of the unavailability of the renewable energy source.

[0017] Hydrogen is supplied to the hydrogen storage tank, the hydrogen being recovered from the side stream separated after the cooling and separation process of the converter effluent.

[0018] This invention discovers that recovered hydrogen can be considered as a portion of green hydrogen recovered from an ammonia synthesis circuit, which is supplied with both conventional and green hydrogen. Therefore, in situations where relevant energy sources are unavailable, using the recovered hydrogen to replace green hydrogen can maintain a positive effect of reducing total CO2 emissions while ensuring a certain ammonia production capacity.

[0019] On the other hand, hydrogen recovered from the aforementioned sidestream (also known as loop purification) can typically be obtained at high pressure (far exceeding the pressure required to produce green hydrogen). The recovered hydrogen can be stored directly without compression. Eliminating the compressor used for hydrogen storage reduces costs and consumption, and removes a potential source of failure. In some embodiments, the recovered hydrogen may still require compression, for example, storage at very high pressures such as 200 bar, but in any case, the compression cost of the hydrogen used for storage will be significantly reduced due to this invention. Detailed Implementation

[0020] A particularly preferred process for producing green hydrogen is water electrolysis. Water electrolysis can be driven by electricity generated from one or more renewable energy sources, such as solar energy.

[0021] In other embodiments, green hydrogen can be produced from biomass. Biomass is widely considered a renewable energy source because its energy originates from the sun and can be increased rapidly. Biomass can be converted into hydrogen through thermochemical processes or biological processes such as fermentation. Preferred thermochemical processes include gasification, partial oxidation, and steam reforming. The biomass source is preferably lignocellulosic biomass. In a preferred embodiment, the biomass hydrogen production process includes the gasification of such lignocellulosic biomass.

[0022] Hydrogen storage is preferably carried out at a pressure of at least 50 bar, more preferably at a pressure of 50 bar to 200 bar. Hydrogen can be stored under pressure in one or more suitable storage containers.

[0023] The pressure of the recovered hydrogen is at least 50 bar, preferably 50 to 100 bar, and particularly preferably 50 to 90 bar. Therefore, as long as the pressure of the recovered hydrogen is equal to or greater than the storage pressure, the recovered hydrogen can be sent to the storage device without compression.

[0024] In embodiments with higher storage pressures, compression is still required. However, the present invention still has advantages because the pressure of the obtained hydrogen is relatively high, i.e., because the compression ratio for storage is lower compared to the prior art.

[0025] In this invention, ammonia is produced partly using hydrogen conventionally produced from reforming and partly using green hydrogen. Green hydrogen can not only reduce the carbon footprint but also increase production capacity. Due to the mixed production of hydrogen, this process can be considered a hybrid process. In a typical embodiment, hydrogen produced from renewable energy sources may account for up to 50% of the total hydrogen in the supplementary gas, preferably 20% to 50%. However, in some embodiments, green hydrogen may account for a larger portion (more than 50%) of the total hydrogen.

[0026] Green hydrogen (possibly replaced by stored hydrogen) can be supplied to the suction side of the main syngas compressor. In a preferred embodiment, the green hydrogen can be produced at the same or substantially the same pressure as the purified make-up gas, which is obtained through reforming and purification.

[0027] The intake line of the main syngas compressor can be connected to the reforming front end, and further connected to a green hydrogen producer (e.g., a water electrolyzer), and further connected to a hydrogen storage tank.

[0028] Reforming processes can be carried out using various techniques known in the art. Reforming processes may include primary reforming in a combustion furnace followed by secondary reforming with a suitable oxidant. The oxidant is typically air, but may also be oxygen-enriched air or pure oxygen if available. Purification of the reformed gas may include CO transfer, carbon dioxide removal, and methanation.

[0029] A preferred embodiment of the invention includes: reforming a hydrocarbon source at the front end to produce ammonia supplement gas; supplying the ammonia supplement gas to an ammonia synthesis loop including an ammonia synthesis converter via a main syngas compressor; removing a hydrogen-containing purge stream from the ammonia loop; treating a portion of the purge stream to separate the hydrogen contained therein and obtain recovered hydrogen; providing an additional hydrogen supply separately obtained from renewable energy (preferably via water electrolysis); supplying the additional hydrogen to the input of the main syngas compressor; providing a hydrogen storage tank to partially or completely replace the additional hydrogen supply when the renewable energy is not fully available; and supplying at least a portion of the recovered hydrogen to the hydrogen storage tank.

[0030] Preferably, a portion of the recovered hydrogen is supplied to the storage tank, and the remainder is supplied to the input of the main syngas compressor to reintroduce it into the ammonia synthesis loop.

[0031] In a typical embodiment, the ammonia converter is part of the ammonia synthesis loop. The ammonia synthesis loop may include an ammonia converter, a supplemental gas preheater, a cooling and separation stage, and a recirculator. Hydrogen produced separately from renewable energy sources or extracted from a hydrogen storage tank may be introduced into the loop at an appropriate location (preferably via the main syngas compressor).

[0032] Another aspect of the present invention is a device according to the present invention. Attached Figure Description

[0033] Figure 1 This is a simplified embodiment of a preferred embodiment of the present invention, wherein the following main items are represented.

[0034] 100 Refactored Front-Ends

[0035] 101 Ammonia Synthesis Circuit

[0036] 102 Solar-powered water electrolyzer for hydrogen production

[0037] 103 Hydrogen Storage

[0038] 1. Hydrocarbon source, such as natural gas

[0039] 2 Desulfurization

[0040] 3. Primary reformers, such as gas furnaces

[0041] 4. Second-stage reformer

[0042] 5. Converters. One or more converters may be provided, such as a high-temperature converter and a subsequent low-temperature converter.

[0043] 6. Carbon dioxide removal, for example by washing with amine or carbonate solutions or by pressure swing adsorption (PSA) or another technique for removing CO2 from a gas.

[0044] 7 Methanation

[0045] 8. Purified replenishment gas

[0046] 9. Air supply for the second stage reformer

[0047] 10 air compressors

[0048] 11 Main Syngas Compressor

[0049] 12 Syngas Dryer

[0050] 13 Circulators

[0051] 14. Heat exchangers, fresh gas preheaters, and reaction effluent coolers

[0052] 15 Ammonia Synthesis Converter

[0053] 16 Cooling-Separation Stage

[0054] 17. Hydrogen recovery unit (HRU) based on membrane system or PSA or other suitable technology

[0055] 18 Fuel delivered to primary reformer 3

[0056] SP solar energy, i.e., the power source for electrolyzer 102.

[0057] The following will discuss Figure 1 To be further described.

[0058] The desulfurized natural gas 1 undergoes steam reforming in the primary reformer 3, and a portion of the reformed gas obtained is further processed in the secondary reformer 4. The effluent from the secondary reformer is purified to obtain makeup gas 8.

[0059] The required amount of nitrogen can be introduced through air supply 9 and ignited in the secondary reformer 4.

[0060] Makeup gas 8 is supplied to ammonia circuit 101 by main synthesis gas compressor 11. After preheating in exchanger 14, preheated makeup gas 28 is reacted in ammonia converter 15.

[0061] The effluent 19 from the converter is preheated with fresh replenishing gas in exchanger 14, and then enters cooling and separation stage 16. Ammonia 20 and purified gas 21 are separated here.

[0062] The purified gas 21 is divided into a first portion 29 and a second portion 30. The first portion 29 is fed into HRU 17, where hydrogen is separated from other impurities (e.g., non-condensable gases). The second portion 30 is reintroduced into the ammonia circuit 101 via circulator 13. The circulator compensates for pressure drop to maintain circulation in circuit 101.

[0063] The hydrogen recovery device 17 can use a cryogenic system, a membrane-based system, or a PSA. Techniques for removing hydrogen from gas mixtures are well known to those skilled in the art and therefore need not be described in detail.

[0064] The gas flow 22 containing recovered hydrogen can be fed into the inlet of the main compressor 11 via line 23 and / or into the H2 storage tank 103 via line 24. If the storage pressure is greater than the pressure of the gas flow 22, i.e. greater than the delivery pressure of HRU 17, the compressor can be supplied in line 24.

[0065] The residual gas separated in HRU 17 may be combustible, and the residual gas is recycled as fuel for primary reformer 3 via line 25.

[0066] The inlet line of compressor 11 is connected to electrolyzer 102 via green hydrogen supply line 26. H2 storage 103 has an output line 27 connected to the green hydrogen supply line 26.

[0067] During operation, the main syngas compressor 11 receives supplemental gas 8 conventionally produced at the front end 100, as well as green hydrogen from receiving line 26 and recovered hydrogen from line 23. For example, hydrogen from electrolyzer 102 may account for approximately 30% of the hydrogen supplied to compressor 11.

[0068] During normal operation, the recovered hydrogen in line 24 is stored for later use, and line 27 can be shut off (e.g., via a suitable valve). The recovered hydrogen 22 can be partially or completely supplied to the inlet of compressor 11 or to storage tank 103, depending on the situation. For example, when storage tank 103 reaches full capacity, hydrogen 22 can be completely reintroduced into the loop via line 23 at any time.

[0069] Depending on the availability of power to the electrolyzer 102, the hydrogen in the storage tank 103 can be used to partially or completely replace the production of the electrolyzer 102. For example, assuming that the electrolyzer 102 uses solar energy SP, then during nighttime and / or cloudy periods, when solar energy levels are low, the stored hydrogen (extracted from the storage tank 103) can be used.

[0070] It should be noted that the recovered hydrogen 22 and the hydrogen stored in the storage tank 103 can be considered "partially green" hydrogen because they are recovered from the loop that partially supplies green hydrogen. Therefore, from the perspective of carbon dioxide emissions, using the storage tank is beneficial.

[0071] The carbon dioxide 31 separated from the removal unit 6 can be stored or used in other processes (e.g., in the synthesis of urea in an associated urea plant). Utilizing the separated carbon dioxide instead of emitting it is clearly another advantage in reducing environmental impact.

[0072] In a typical embodiment, the pressure of the supplemental gas 8 is approximately 20 to 25 bar. The ammonia converter can operate at approximately 140 bar. The recovered hydrogen 22 can be at a pressure of 50 to 90 bar or higher. Storage can be carried out at the pressure of the gas flow 22, or at even higher pressures using a compressor.

Claims

1. A process used for ammonia synthesis, wherein: a) Under ammonia synthesis pressure, ammonia supplement gas containing hydrogen and nitrogen reacts in an ammonia converter to obtain an ammonia-containing effluent; b) The ammonia-containing effluent is cooled and separated to obtain liquid ammonia and a side stream containing hydrogen and impurities; c) At least a portion of the side stream undergoes a hydrogen recovery process to obtain recovered hydrogen; d) The first part of the hydrogen contained in the ammonia supplement gas is produced in the reforming process by reforming the hydrocarbon source; e) The second portion of the hydrogen contained in the ammonia supplement gas is produced separately from the reforming process using renewable energy; f) Deliver at least a portion of the recovered hydrogen obtained in step c) to a hydrogen storage tank; g) When all or part of the renewable energy source is unavailable, hydrogen from the storage device is used to replace all or part of the second portion of the hydrogen in step e).

2. The process according to claim 1, wherein the second portion of the hydrogen in step e) is produced by the electrolysis of water.

3. The process according to claim 2, wherein the electrolysis of water is driven by solar energy.

4. The process according to claim 1, wherein the hydrogen storage is carried out at a pressure of at least 50 bar.

5. The process according to claim 1, wherein the pressure of the recovered hydrogen obtained in step c) is at least 50 bar.

6. The process according to claim 1, wherein when the recovery pressure of the hydrogen is sufficient for storage, the recovered hydrogen obtained in step c) is delivered to the hydrogen storage tank without compression, or, when the storage pressure is higher than the recovery pressure, the recovered hydrogen obtained in step c) is compressed.

7. The process of claim 1, wherein the second portion of hydrogen produced using renewable energy accounts for at most 50% of the hydrogen in the supplementary gas.

8. The process according to claim 1, wherein the second portion of hydrogen is produced at the same or substantially the same pressure as the purified replenishment gas, which is obtained by reforming and purification.

9. The process of claim 1, wherein the ammonia converter is part of an ammonia synthesis loop and introduces hydrogen produced separately from renewable energy sources or extracted from a hydrogen storage tank into the loop.

10. The process according to claim 1, wherein: The reforming step includes reforming the hydrocarbon source and purifying the obtained reformed gas to obtain reformed and purified gas; the reformed and purified gas, which can be supplemented with nitrogen, is supplied to the ammonia converter through the main syngas compressor; and hydrogen produced separately from renewable energy is supplied to the ammonia converter through the main syngas compressor.

11. The process of claim 10, wherein hydrogen produced separately from renewable energy sources is supplied together with reformed and purified gas to the suction side of the main syngas compressor.

12. The process of claim 1, wherein a first portion of the side stream separated from the converter effluent is fed to hydrogen recovery, while a second portion of the side stream is reintroduced into the ammonia converter.

13. The process according to claim 1, wherein the hydrogen storage is carried out at a pressure of 50 bar to 200 bar.

14. The process according to claim 1, wherein the pressure of the recovered hydrogen obtained in step c) is 50 to 100 bar.

15. The process of claim 1, wherein the second portion of hydrogen produced using renewable energy accounts for 20% to 50% of the hydrogen in the supplementary gas.

16. Equipment for ammonia synthesis, comprising: The reforming front end is used to generate ammonia supplementary gas by reforming the hydrocarbon source; Ammonia synthesis circuit, which includes an ammonia synthesis converter; The main synthesis gas compressor has an input line connected to the front end and a delivery line connected to the synthesis loop, such that the compressor is arranged to supply the supplementary gas produced in the front end to the synthesis loop. A green hydrogen production unit driven by renewable energy, having a line arranged to supply hydrogen from the green hydrogen production unit to a main syngas compressor; A hydrogen storage device having a line connected to the input terminal of the main synthesis gas compressor; A hydrogen recovery unit is arranged to recover unconverted hydrogen from a purified stream separated from the effluent of the ammonia converter. The equipment also includes wiring arranged to supply recovered hydrogen from the recovery unit to the hydrogen storage tank.

17. The apparatus of claim 16, further comprising a control system configured to supply hydrogen from a hydrogen storage tank to a main syngas compressor when the renewable energy source is not fully available, to compensate for a related shortage of hydrogen from the green hydrogen production unit.

18. The device according to claim 16, wherein the green hydrogen production device is a water electrolyzer.

Images