Production of ammonia make-up syngas with cryogenic purification

Abstract

A method and apparatus (1) for producing high purity hydrogen (10). This process comprises the steps of: (I) reforming (2) a desulfurized hydrocarbon feedstock (3) in the presence of steam (4) to obtain a crude synthesis gas (5); (II) subjecting the crude synthesis gas (5) to CO shift (6), carbon dioxide removal (7), methanation (8) and steam condensation (9, 11) to obtain a modified synthesis gas (12); (III) treating the modified synthesis gas (12) in a cryogenic purification section (13) to obtain the high purity hydrogen (10) and a methane-containing tail gas stream (14); wherein the net cold of the cryogenic purification section (13) is provided at least in part by the expansion (19) of the compressed nitrogen-rich gas (15) produced by the air separation unit (16).

Description

Technical Field

[0001] This invention relates to the preparation of high-purity hydrogen using cryogenic purification. More specifically, this invention relates to the preparation of high-purity hydrogen through steam reforming of hydrocarbon feedstocks (e.g., natural gas), and to the modification of syngas through cryogenic purification. Background Technology

[0002] Traditionally, hydrogen is produced from fossil fuels through steam reforming in a process with high temperature (>1000°C) and relatively high pressure, depending on the method parameters.

[0003] In the so-called reforming front end, fossil fuels, water, and oxygen react to produce syngas, which mainly consists of hydrogen, carbon monoxide, and some carbon dioxide. This syngas is then processed and purified to increase the hydrogen content to up to 98 mol%, with the remainder being unreacted fossil fuels, carbon monoxide, and non-condensable gases such as argon, nitrogen, and carbon dioxide.

[0004] The purity of the purified syngas obtained in this way is affected by different method parameters, such as the temperature of the reforming reactor, the steam / carbon (S / C) ratio at the reactor inlet, and the relative oxygen rate.

[0005] The desired purity of hydrogen depends on the intended use of the gas.

[0006] Fuel-grade hydrogen does not require particularly high purity; its purity typically depends on permissible emissions. In contrast, fuel cell (FC) applications require high-purity hydrogen of 4N or 5N grade (where N stands for "high-purity"). Nine (A logarithmic representation). Furthermore, the synthesis loop of an ammonia production unit is highly sensitive to hydrogen impurities (typically oxygen-containing molecules), therefore, the synthesis gas must be purified as effectively as possible.

[0007] Common methods for obtaining high-purity hydrogen gas flow include pressure swing adsorption (PSA), chemisorption, membrane separation, and cryogenic partial condensation.

[0008] PSA has the advantage of accepting large volumes of gases with variable composition. However, the main drawback is that its purification method includes a regeneration step that uses the generated hydrogen as a purge gas, resulting in the loss of approximately 10%-15% of the total hydrogen production, or in any case, requiring recirculation for further processing at the reforming front end.

[0009] Chemisorption and membrane separation have similar drawbacks to PSA, and additionally require very specific concentration and impurity import specifications.

[0010] Cryogenic partial condensation is a well-defined and widely used commercial route for the production of carbon monoxide (CO), sometimes used in hydrogen separation units in the oil and gas industry, and for hydrogen recovery in refining processes. This condensation utilizes the different boiling points of two or more gases separated from a gas mixture.

[0011] While the simplicity of cryogenic partial condensation makes it attractive, the refrigeration requirements involved are high. Among other factors, the refrigerant is expensive or not always readily available.

[0012] US 3,361,534 A, US 2020 / 141637 A1, WO 2008 / 113494 A2, US 2018 / 298292 A1 and GB 1025104 A are known techniques used in this invention. Summary of the Invention

[0013] The present invention aims to overcome the above-mentioned shortcomings of the prior art.

[0014] Specifically, this invention aims to provide a simple and cost-effective method for producing high-purity hydrogen, for example, to meet carbon emission targets or chemical requirements. This method utilizes a traditionally unused gas stream (i.e., nitrogen-rich gas from an air separation unit) to provide at least part of the cooling energy (refrigeration) for the hydrogen cryogenic purification section.

[0015] The problem this invention aims to solve is to overcome the limitations listed above in a cost-effective manner. This problem is solved by the methods, apparatus, and improved methods disclosed below.

[0016] A method for preparing high-purity hydrogen gas includes the following steps:

[0017] (I) Reforming desulfurized hydrocarbon feedstock in the presence of steam to obtain crude syngas;

[0018] (II) The crude syngas is subjected to CO conversion, carbon dioxide removal, methanation and steam condensation (or water removal) to obtain modified syngas;

[0019] (III) The modified syngas is treated in a cryogenic purification section to obtain the high-purity hydrogen and methane-containing tail gas flow. Optionally, preferably after heat exchange, the methane-containing tail gas flow is recycled as the feed for step (I).

[0020] The net cooling of the cryogenic purification section is provided at least in part by the expansion of compressed nitrogen-rich gas generated by the air separation unit (ASU).

[0021] Another object of the present invention is an apparatus for preparing high-purity hydrogen gas, comprising:

[0022] - Reforming section, which is configured to reform desulfurized hydrocarbon feedstock in the presence of steam to obtain crude syngas;

[0023] A CO conversion unit, a carbon dioxide removal unit, a methanation unit, and at least one steam condensation (or water removal) unit are configured to process the crude syngas to obtain modified syngas.

[0024] - A cryogenic purification section for modified syngas to obtain the high-purity hydrogen and methane-containing tail gas stream;

[0025] -Optionally, preferably, after heat exchange, the methane-containing tail gas stream is recirculated as the feed for the reforming section;

[0026] - An air separation unit (ASU) that provides nitrogen-enriched gas and, optionally, an oxygen-enriched stream;

[0027] - An expansion unit for the nitrogen-rich gas in a compressed state to provide a heat exchange medium for cooling the cryogenic purification section.

[0028] In this specification, the term "compressed" refers to the state or conditions of the nitrogen-rich gas at a pressure higher than 101,325 Pa atm.

[0029] Another object of the present invention is a method for improving an apparatus for producing high-purity hydrogen, said apparatus comprising a reforming section for reforming desulfurized hydrocarbons into crude syngas, and a CO conversion unit, a carbon dioxide removal unit, a methanation unit, and at least one steam condensation (water removal) unit configured to process the crude syngas to obtain modified syngas. The method comprises at least the following steps:

[0030] - If the device to be improved is not already equipped with an air separation unit (ASU), install the air separation unit (ASU) to provide nitrogen-rich gas;

[0031] -If the apparatus to be improved is not yet equipped with a cryogenic purification section for the modified syngas, provide such a cryogenic purification section for the modified syngas.

[0032] -Optionally, a compression unit and a cooling unit for the nitrogen-rich gas are installed;

[0033] -Optionally, install an expansion unit for the compressed and cooled nitrogen-rich stream;

[0034] - Install at least one indirect heat exchanger to feed nitrogen-rich gas or optionally expanded nitrogen-rich gas into the cryogenic purification section to provide a heat exchange medium to cool the pipelines of the cryogenic purification section.

[0035] -Optionally, install a pipeline to recirculate the methane tail gas provided by the cryogenic purification section or the methane tail gas after heat exchange as the feed to the reforming section.

[0036] -Optionally, install a liquid-gas separator to separate high-purity hydrogen and methane-containing tail gas.

[0037] Description of preferred embodiments of the present invention

[0038] Preferably, the high-purity hydrogen gas 10 has a hydrogen content of ≥98.5 mol%, more preferably, from 98.5 mol% to 99.999 mol%, or from 98.5 mol% to 99.5 mol%.

[0039] More preferably, the hydrocarbon feedstock is natural gas or alternative natural gas (SNG), but any suitable reformable hydrocarbon can be used. Natural gas is the most preferred.

[0040] According to one embodiment, before expansion 19, the nitrogen-rich gas 15 is cooled in the cryogenic purification section 13 by heat exchange with the expanded nitrogen-rich gas 37 (preferably: indirect heat exchange, more preferably using a plate-fin heat exchanger, and even more preferably using an aluminum plate-fin heat exchanger).

[0041] According to another embodiment, the nitrogen-rich gas 15 is generated in gaseous form by ASU 16, preferably at room temperature and atmospheric pressure, and then the nitrogen-rich gas 15 is compressed, or compressed at room temperature and above atmospheric pressure, for example at 2 bar to 50 bar, preferably 3 bar to 30 bar, more preferably 5 bar to 15 bar.

[0042] According to another embodiment, the pressure of the modified syngas 12 in the cryogenic purification section 13 is 2 bar gauge pressure (barg) to 100 barg, more preferably 10 barg to 70 barg, even more preferably 20 barg to 50 barg, and even more preferably 30 barg to 40 barg.

[0043] Preferably, step (I) includes reforming the hydrocarbon feedstock 2 in the further presence of an oxygen-enriched stream 22 or oxygen-enriched air as an oxidant, thereby providing the oxygen-enriched stream 22 or oxygen-enriched air by treating the air stream 23 in the ASU 16. The oxygen content of the oxygen-enriched stream 22 or oxygen-enriched air is preferably ≥50 mol%, more preferably ≥70 mol%, and even more preferably ≥90 mol%.

[0044] The oxygen-enriched flow 22 or oxygen-enriched air is preferably provided at a pressure of at least 20 bar, preferably 20 bar to 80 bar, more preferably 30 bar to 70 bar, and even more preferably 45 bar to 60 bar.

[0045] More preferably, the reforming 2 in step (I) includes a partial oxidation (POX) or autothermal reforming (ATR) 40 step. Even more preferably, the POX or ATR step is carried out under conditions of a steam / carbon (S / C) ratio ≤5, preferably ≤3, more preferably ≤2, and even more preferably 1.4 to 1.95.

[0046] According to one implementation scheme, the reorganization 2 in step (I) includes:

[0047] Self-heating reforming (ATR) is arranged to receive the first portion of desulfurized hydrocarbon feedstock and produce the first stream of crude syngas.

[0048] Gas heating reforming includes a first side (e.g., tube side) and a second side (e.g., shell side), wherein the gas heating reforming is arranged to receive a second portion of the desulfurized hydrocarbon feedstock on the first side and to generate a second stream of crude syngas on the same side, and the first stream and the second stream of crude syngas are mixed on the second side to generate the crude syngas.

[0049] According to another embodiment, the modified syngas 12 is treated in the cryogenic purification section 13 at a temperature below -100°C (i.e., minus 100°C), preferably below -130°C, more preferably below -150°C, and even more preferably below -170°C, for example, -180°C to -190°C.

[0050] According to another implementation, the method includes:

[0051] (IV) The nitrogen-rich gas 15 is generated using the ASU 16;

[0052] (V) Compression of the nitrogen-rich gas 15 in step (IV) and cooling of step (IV);

[0053] (VI) Expand the nitrogen-rich gas of step (V) 19 to provide the net cooling to the modified synthesis gas 12 in the cryogenic purification section 13 via indirect heat exchange.

[0054] According to another implementation, the method further includes:

[0055] (II.A) Before treating this modified synthesis gas 12 in step (III), the modified synthesis gas 12 of step (II) is dried with molecular sieve drying unit 20;

[0056] (II.B) After providing the net cooling, the molecular sieve of the molecular sieve drying unit 20 is regenerated with at least a portion of the expanded nitrogen-rich gas;

[0057] (II.C) Optionally, after step (VI) and / or after step (II.B), the nitrogen-rich gas 21, 21' is exhausted.

[0058] The method preferably includes indirect heat exchange of the methane-containing tail gas stream 14 in the cryogenic purification section 13; the heat-exchanged methane-containing tail gas stream 24 is then recycled as the feed for step (I). More preferably, the heat-exchanged methane-containing tail gas stream 24 is mixed with the desulfurized hydrocarbon feedstock 3 upstream of the reforming 2, or fed separately from the desulfurized hydrocarbon feedstock 3 for reforming.

[0059] Preferably, the methane content of the methane-containing tail gas stream 24 is ≥90 mol%, more preferably ≥93 mol%, and even more preferably ≥95 mol%. The balance may be argon and trace amounts of hydrogen and nitrogen.

[0060] According to a preferred embodiment, the method further includes:

[0061] (VII) In the second cryogenic purification section 25, at least a portion 26 of the high-purity hydrogen 10 obtained in step (III) is processed to obtain ultra-high purity hydrogen 27 with a hydrogen content of >99.5 mol%, preferably >99.7 mol%, more preferably ≥99.9 mol%, or even more preferably ≥99.99 mol%, such as 99.999 mol%.

[0062] The step (VII) preferably includes:

[0063] (VII.A) The portion 26 of high-purity hydrogen 10 is washed with liquid nitrogen solution 38 in contact unit 28 (e.g., absorption tower) to obtain washed high-purity hydrogen 29 and impurity solution 30.

[0064] (VII.B) The washed high-purity hydrogen 29 from step (VII.A) is processed in an indirect heat exchange to obtain the ultra-high-purity hydrogen 27 and a tail stream 35 containing liquid nitrogen and impurities, wherein the indirect heat exchange is carried out in one of the following:

[0065] (i) A cryogenic expander or a cryogenic turboexpander 31 fed with compressed ultra-high purity hydrogen 32; or

[0066] (ii) A cryogenic refrigeration unit 33 including a helium or hydrogen refrigerant cycle 34; and

[0067] (VII.C) Recycle the tail fluid flow 35 to the contact unit 28 in step (VII.A).

[0068] According to a preferred embodiment, the liquid nitrogen solution 38 used in step (VII.A) of the portion 26 for washing the high-purity hydrogen 10 in the contact unit 28 is generated by an air separation unit (ASU), preferably by the same ASU that provides net cooling to the cryogenic purification section in step (III).

[0069] Preferably, the cryogenic purification section is cooled by a heat exchange medium through at least one indirect heat exchanger 60.

[0070] More preferably, the device further includes:

[0071] - Compression unit 17 and cooling unit 18 of the nitrogen-rich gas 15 provided by ASU 16;

[0072] - The expansion unit 19 of the compressed and cooled nitrogen-rich stream 36 provides a heat exchange medium to cool the cryogenic purification section 13;

[0073] The cryogenic purification section 13 includes at least one indirect heat exchanger 60 between the modified synthesis gas 12 and the expanded nitrogen-rich gas 37.

[0074] More preferably, the cooling unit 18 and the indirect heat exchanger 60 are integrated in the same device.

[0075] Even more preferably, the compression unit 17 includes a water-cooled compressor to obtain a compressed nitrogen-rich stream 62 at room temperature.

[0076] According to a preferred embodiment, the device further includes:

[0077] - Molecular sieve drying unit 20 for modified syngas 12 upstream of the cryogenic purification section 13;

[0078] - Pipeline 39, which is used to feed at least a portion of the expanded nitrogen-rich gas 37 to the molecular sieve drying unit 20 after passing through the indirect heat exchanger 60, for the purpose of regenerating the molecular sieve of the molecular sieve drying unit 20.

[0079] According to another embodiment, the apparatus further includes a pipeline for feeding the methane-containing tail gas stream 14 into the indirect heat exchanger 60 of the cryogenic purification section 13, and a pipeline for recirculating the heat-exchanged methane-containing tail gas stream 24 as feed into the reforming section 2.

[0080] According to another embodiment, the apparatus further includes a second cryogenic purification section 25 for at least a portion 26 of high-purity hydrogen 10 to obtain ultra-high-purity hydrogen 27.

[0081] The second cryogenic purification section 25 preferably includes:

[0082] - Contact unit 28, such as an absorption tower, is used to wash the portion 26 of high-purity hydrogen 10 with liquid nitrogen solution 38 to obtain washed high-purity hydrogen 29 and impurity solution 30.

[0083] - One of the following: a cryogenic expander or turboexpander 31 fed with compressed ultra-high purity hydrogen 32, or a cryogenic refrigeration unit 33 including a helium or hydrogen refrigerant cycle 34, to obtain the ultra-high purity hydrogen 27 and a tail stream 35 containing liquid nitrogen and impurities; and

[0084] -A pipeline for recirculating the tail flow 35 to the contact unit 28.

[0085] Advantages of the present invention

[0086] Advantageously, the method and apparatus of the present invention ensure the required purity as well as low energy consumption.

[0087] Advantageously, the method and apparatus of the present invention require standard building materials and equipment to ensure robustness and stability.

[0088] Advantageously, the method and apparatus of the present invention are designed to operate under a wide range of process parameters.

[0089] Advantageously, the method and apparatus of the present invention utilize unused nitrogen gas (which is typically available in large quantities) to condense hydrogen gas of a desired fixed concentration or purity.

[0090] Advantageously, the method and apparatus of the present invention allow carbon emissions to be reduced to below a specific level in fuel-grade production, for example, 40 g. CO2 / kg H2 Or higher, for example, 100 g CO2 / kg H2 (The latter is equivalent to 36.4 g) CH4 / kg H2 Or the concentration of CH4 in H2 is 4.55 mmol. CH4 / mol H2 ).

[0091] Advantageously, the use of a methanation step or unit prior to cryogenic purification allows for the removal (through chemical conversion) of trace amounts of CO and CO2, which would cause problems in the cryogenic purification section or step and ultimately in the downstream use of high-purity hydrogen.

[0092] First, CO has a much lower boiling point than methane, so it will end up in the product stream.

[0093] Second, CO2 has a much higher boiling point, and it will freeze at the operating temperature of the cryogenic purification section.

[0094] Third, cryogenic purification of gas mixtures with two or more gas components (“multi-gas mixtures”) involves a much more complex separation process compared to binary mixtures. In contrast, this invention allows for simple single-stage two-phase separation.

[0095] Advantageously, the nitrogen-rich gas used for molecular sieve regeneration does not need to be ultrapure; trace amounts of oxygen and argon are acceptable. This is extremely important because using this nitrogen does not increase the high power consumption of oxygen production in the ASU. This is because it is not synthetic nitrogen, but only used for refrigeration purposes and the regeneration step, as it is readily available and dry.

[0096] Advantageously, the method and apparatus of the present invention are technically robust and can be applied to the separation of different methods, even in the presence of variable method parameters.

[0097] Advantageously, the methane converter combined with the drying section ensures that the final H2-rich stream is free from oxygen poisoning, thus allowing the unpoisoned stream to be used for optional ammonia synthesis.

[0098] Advantageously, the fact that the liquefied methane tail gas stream can be recycled as feed to the reforming section or step increases the overall conversion rate of the method.

[0099] Advantageously, using nitrogen-rich gas as the refrigerant allows methane to be recirculated under pressure without having to reduce its temperature through expansion of the lamination valve, which is advantageous compared to the PSA method of feeding low-pressure tail gas into the recirculation.

[0100] It has been found that using a nitrogen-rich stream as the cooling medium for the cryogenic section is an effective measure to improve plant capacity and substantially maintain the overall LHV efficiency of the method. A first advantage is that this invention utilizes a nitrogen-rich stream as the cooling medium to provide net cooling for the cryogenic section, rather than performing energy-consuming expansion of the crude syngas as suggested in the prior art.

[0101] Another advantage is that the nitrogen-rich stream is used efficiently, primarily as the refrigerant in the cryogenic separation section, avoiding the feeding of large amounts of inert nitrogen through the downstream purification equipment of the reformer. Therefore, significant advantages are achieved without the disadvantage of a significant increase in volumetric flow rate processed in the reformer, CO conversion unit, and CO2 removal unit.

[0102] Furthermore, due to the treatment in the cryogenic purification section with nitrogen refrigeration, the present invention is particularly effective in removing methane and other impurities from modified syngas.

[0103] Integration with the air separation unit is particularly effective, enabling the availability of an oxygen-enriched stream that can be advantageously injected into the reforming section or step (e.g., ATR or POX), thus enhancing the upstream section's capacity for crude syngas production.

[0104] Advantageously, if the ASU provides a nitrogen-containing flow under pressure, the method or apparatus can eliminate one or more compressors.

[0105] These advantages will become more apparent from the following detailed description of the preferred embodiments. Attached Figure Description

[0106] Figure 1 A simplified block diagram of the method or apparatus according to a first embodiment of the present invention;

[0107] Figure 1A A simplified block diagram of a method or apparatus according to a second possible embodiment of the present invention;

[0108] Figure 2 and Figure 3 A simplified block diagram of a method or apparatus, which shows in more detail the second cryogenic purification section according to different embodiments;

[0109] Figure 4 Vapor-liquid equilibrium (VLE) diagram of a binary system of ammonia and water at atmospheric pressure. Detailed Implementation

[0110] Figure 1 This is a simplified embodiment of a preferred embodiment of the present invention. The hydrocarbon feedstock 50 is preheated in the feedstock preheater 41, fed into the hydrodesulfurization (HDS) unit 42, and then further preheated through indirect heat exchange with the hot flue gas from the gas turbine 43.

[0111] The preheated desulfurized hydrocarbon feedstock 3 is then fed together with the steam stream 4 into the pre-reforming unit 44 to obtain the pre-reformed effluent 45 after indirect heat exchange with the hot flue gas from the gas turbine 43.

[0112] The pre-reformed effluent 45 is then fed into an autothermal reforming (ATR) unit 40, where it is converted into crude syngas 5, which contains water vapor (H2O), hydrogen (H2), a certain amount of carbon monoxide (CO), carbon dioxide (CO2), unreacted desulfurized hydrocarbon feedstock, other impurities, and optional nitrogen. The hot crude syngas 5 is cooled in a downstream heat exchanger 46.

[0113] The steam 4 fed into the pre-reform unit 44 is obtained by a steam generator 47 with a feed water flow 48. Heat is transferred to the steam generator 47 via an indirect heat exchanger 68 that is in thermal contact with the hot flue gas from the gas turbine 43 and via the hot effluent crude syngas from the ATR in the downstream heat exchanger 46.

[0114] In the air separation unit (ASU) 16, the airflow 23 is separated into a nitrogen-enriched flow 15 and an oxygen-enriched flow 22. The oxygen-enriched flow 22 is fed to the ATR 40 on its own, or mixed with air before being fed to the ATR 40 to obtain oxygen-enriched air. The nitrogen-enriched flow 15 (depending on whether it has been compressed) can be fed to the compression unit 17 to obtain a compressed nitrogen-enriched flow 62, and then fed to the cooling unit 18 to obtain a compressed and cooled nitrogen-enriched flow 36.

[0115] The hot effluent crude syngas 5 from ATR 40 is cooled in a downstream heat exchanger 46 and a feedstock preheater 41, and then processed sequentially in a CO conversion unit 6, a first steam condensation unit 9, a carbon dioxide removal unit 7, a methanation unit 8, and a second steam condensation unit 11 to obtain modified syngas 12.

[0116] CO conversion unit 6 (which converts CO and water vapor into CO2 and H2) includes a high-temperature conversion subunit 49 and a low-temperature conversion subunit 51, which generates conversion gas 52.

[0117] In the first steam condensation unit 9, the shift gas 52 is divided into a first condensed fraction 53 fed to the steam generator 47 and a first gaseous fraction 54 fed to the carbon dioxide removal unit 7.

[0118] In the carbon dioxide removal unit 7 (e.g., including an amine scrubbing tower), the first gaseous fraction 54 is separated into a CO2-rich stream 55 and a CO2-lean stream 56. The CO2-rich stream 55 is sent to the compression and storage unit 57, or alternatively, to the urea synthesis unit.

[0119] The lean CO2 stream 56 is fed into the methanation unit 8, where residual CO2 and trace amounts of carbon monoxide react with hydrogen to produce a methanation effluent 58 that mainly contains hydrogen, methane, and vapor, as well as small amounts of impurities.

[0120] In the second steam condensation unit 11, the methanation effluent 58 is separated into a second condensate fraction 59, which is fed into the steam generator 47, and a second gaseous fraction, which is used to produce modified syngas 12. The modified syngas mainly consists of hydrogen and methane, and contains other impurities.

[0121] The modified syngas 12 can undergo heat exchange in a cooling unit 61 (e.g., an ammonia cooling unit) and then pass through a molecular sieve drying unit 20 to obtain dried modified syngas 12'. The molecular sieve drying unit 20 may include at least a first drying subunit 63 and a second drying subunit 64 arranged in parallel. These drying subunits 63, 64 can be controlled such that when the modified syngas 12 is dried through the first drying subunit 63, the second drying subunit 64 is regenerated, and vice versa, so that the molecular sieve drying unit 20 can operate continuously.

[0122] The dried modified syngas 12' is cooled in the indirect heat exchanger 60 of the cryogenic purification section 13 to obtain cooled syngas 65. The temperature of the cooled syngas 65 can be -180°C to -190°C, and the pressure can be 30 barg to 35 barg. The necessary cooling is provided by a compressed nitrogen-rich stream (more precisely, by a compressed and cooled nitrogen-rich stream 36) that is cold-expanded in the expansion unit 19. The expanded nitrogen-rich gas 37 provides a heat exchange medium to cool the cooling unit 18 and / or the cryogenic purification section 13, wherein it indirectly exchanges heat with the compressed nitrogen-rich stream 62 and / or the modified syngas 12.

[0123] The cooled syngas 65 is then fed into the first liquid-gas separator 66, where high-purity hydrogen 10 and a methane-containing tail gas stream 14 are separated.

[0124] use allow Vapor-liquid equilibrium (VLE) diagram of a binary gas mixture (see, for example, [reference]). Figure 4 This separation is possible: from a region of the gas mixture (see point (a)), once the temperature of the mixture decreases until point (c), a two-phase mixture forms. The gas phase will have a higher concentration of the more volatile component (point (d)), and the liquid phase will be more concentrated with the less volatile component (point (e)). The composition of these two phases can be read from the coordinates of point (d) for the gas phase and point (e) for the liquid phase. The mole fraction of the first component at that temperature is represented in the coordinates corresponding to point (d) or (e), and the mole fraction of the second component is 1 minus the mole fraction of the first component.

[0125] The methane tail gas stream 24 is heated in the indirect heat exchanger 60, and then the tail gas stream 24 is injected into the same pipeline as the hydrocarbon feedstock 50 upstream of the feedstock preheater 41 and recycled as the heat-exchanged methane tail gas stream 24 as the feedstock of the reforming section 2.

[0126] High-purity hydrogen 10 is heated in an indirect heat exchanger 60 and then separated into a first portion 26 and a second portion 67. The first portion 26 is processed in a second cryogenic purification section 25 to obtain ultra-high-purity hydrogen 27. The second portion 67 can be fed to provide fuel for the combustor of the gas turbine 43.

[0127] In summary, in the indirect heat exchanger 60, modified syngas 12 (or dry modified syngas 12') and compressed nitrogen-rich stream 62 transfer their heat to another fluid. Methane tail gas 14, high-purity hydrogen 10, and expanded nitrogen-rich gas 37 are heated by the other fluid.

[0128] Optionally, after recovering hydrogen from the expanded nitrogen-rich gas 37, a first portion 21 of the expanded nitrogen-rich gas 37 can be discharged at position 21. After the expanded nitrogen-rich gas 37 has been heated in the indirect heat exchanger 60, at least a second portion 39 of the expanded nitrogen-rich gas 37 can replace the first drying subunit 63 and the second drying subunit 64 for regenerating the molecular sieve. After regeneration, the effluents of the first drying subunit 63 and the second drying subunit 64 can be discharged at position 21'.

[0129] Figure 1A The block diagram illustrates a second embodiment of the method or apparatus of the present invention. Unless otherwise specified, reference numerals are consistent with... Figure 1 The same as in [the previous sentence].

[0130] exist Figure 1A In this process, the high-purity hydrogen 10 separated in the first liquid-gas separator 66 is divided into a first portion 26 and a second portion 67 upstream of the indirect heat exchanger 60. The first portion 26 is processed in the second cryogenic purification section 25 to obtain ultra-high purity hydrogen 27. Only the second portion 67 is heated in the indirect heat exchanger 60.

[0131] Figure 2 and Figure 3 Two implementation schemes for the second cryogenic purification section 25 are shown.

[0132] In both embodiments, a first portion 26 of high-purity hydrogen is washed with liquid nitrogen solution 38 in contact unit 28 (preferably an absorption tower) to obtain washed high-purity hydrogen 29 and a solution containing impurities 30. Optionally, the solution containing impurities 30 can be discharged after heating in indirect heat exchanger 60. The washed high-purity hydrogen 29 is recovered at the top of contact unit 28 and cooled in second indirect heat exchanger 70 to obtain cooled high-purity hydrogen 71. The cooled high-purity hydrogen 71 is then fed to a second liquid-gas separator 72.

[0133] exist Figure 2In this embodiment, the second liquid-gas separator 72 separates cooled high-purity hydrogen 71 into ultra-high-purity hydrogen 27 and a tail stream 35 containing liquid nitrogen and impurities. The tail stream 35 is recirculated in a liquid nitrogen solution 38 to feed to the contact unit 28. The ultra-high-purity hydrogen 27 can be sent for storage. This storage can be carried out at cryogenic conditions (liquid hydrogen transport) or after compression at room temperature and high pressure.

[0134] exist Figure 2 In one embodiment, the cryogenic refrigeration unit 33 provides net refrigeration to the second cryogenic purification section 25. This cryogenic refrigeration unit 33 includes a helium or hydrogen refrigerant cycle 34. The liquid refrigerant cycle 34 typically includes a compressor 73, a condenser 74 (e.g., a water-cooled condenser), an expander unit 75, and an evaporator connected in a closed loop. In this embodiment, a second indirect heat exchanger 70 constitutes the evaporator of this liquid refrigerant cycle 34. The liquid refrigerant cycle 34 may also include an additional heat exchanger 76 for exchanging heat between the evaporating refrigerant stream 77 and the condensing refrigerant stream 78.

[0135] exist Figure 3 In one embodiment, the second liquid-gas separator 72 separates cooled high-purity hydrogen gas 71 into a tail liquid stream 35 (containing liquid nitrogen and impurities) and a compressed ultra-high-purity hydrogen stream 32. As in the aforementioned embodiments, preferably after heat exchange in the second indirect heat exchanger 70, the tail liquid stream 35 is recirculated in a liquid nitrogen solution 38 to feed to the contact unit 28. The compressed ultra-high-purity hydrogen stream 32 is fed as the working fluid to the cryogenic expander or cryogenic turboexpander 31.

[0136] The cryogenic (turbine) expander 31 includes an expander unit 75 and a third liquid-gas separator 79. An expanded ultra-high purity hydrogen stream 80 obtained downstream of the expander unit 75 is fed into the third liquid-gas separator 79 to separate a third condensate fraction 81 and a third gaseous fraction 82. Both the third condensate fraction 81 and the third gaseous fraction 82 are heated in a second indirect heat exchanger 70 to obtain a heated condensate stream 83 and ultra-high purity hydrogen 27. Optionally, the heated condensate stream 83 and ultra-high purity hydrogen 27 can be further heat-recovered in the indirect heat exchanger 60 of the cryogenic purification section 13.

[0137] The heated condensate stream 83 can be used as fuel for the reforming section 2 or as fuel-grade hydrogen. Ultra-high purity hydrogen 27 can be sent for compression and storage. List of reference numerals

[0138] 1. Apparatus or method for preparing high-purity hydrogen gas

[0139] 2. Reorganization steps or sections

[0140] 3. Desulfurized hydrocarbon feedstock

[0141] 4. Steam

[0142] 5. Crude syngas

[0143] 6 CO conversion steps or units

[0144] 7. Carbon dioxide removal steps or units

[0145] 8. Methanation step or unit

[0146] 9. First steam condensation step or unit, or first water removal step or unit

[0147] 10 High-purity hydrogen gas

[0148] 11. Second steam condensation step or unit, or second water removal step or unit

[0149] 12 Modified Syngas

[0150] 12' Dry modified synthesis gas

[0151] 13 Cryogenic Purification Section

[0152] 14 Methane-containing tail gas flow

[0153] 15. Nitrogen-rich gas

[0154] 16. Air Separation Unit (ASU)

[0155] 17. Compression steps or units

[0156] 18 Cooling steps or units

[0157] 19. Expansion Steps or Units

[0158] 20. Drying step or molecular sieve drying unit

[0159] 21 Exhaust procedure or exhaust port

[0160] 21' Exhaust step or exhaust port

[0161] 22 Oxygen-enriched flow

[0162] 23 Airflow

[0163] 24. Methane tail gas stream after heat exchange

[0164] 25 Second (or ultra-low temperature) cryogenic purification section

[0165] 26. The portion of high-purity hydrogen (preferably the first portion)

[0166] 27 Ultra-high purity hydrogen gas

[0167] 28 contact units, preferably an absorption tower.

[0168] 29. High-purity hydrogen gas after washing

[0169] 30 solutions containing impurities

[0170] 31 Cryogenic expander or cryogenic turbo expander

[0171] 32 Compressed ultra-high purity hydrogen stream

[0172] 33 Cryogenic Refrigeration Unit

[0173] 34. Helium or hydrogen refrigerant cycle

[0174] 35 Tailstream

[0175] 36. Compressed and cooled nitrogen-rich stream

[0176] 37. Expanded nitrogen-rich gas

[0177] 38 Liquid nitrogen solution

[0178] 39. The feed line from the expanded nitrogen-rich gas to the molecular sieve drying unit.

[0179] 40. Autothermal Reforming (ATR) Steps or Units

[0180] 41 Raw material preheater

[0181] 42 Hydrodesulfurization (HDS) step or unit

[0182] 43 Gas turbine

[0183] 44. Pre-restructuring steps or units

[0184] 45 Pre-reformed effluent

[0185] 46 Downstream heat exchangers

[0186] 47 Steam generator

[0187] 48. Water flow

[0188] 49. High-temperature conversion steps or sub-units

[0189] 50 Hydrocarbon Raw Materials

[0190] 51. Low-temperature conversion steps or sub-units

[0191] 52. Shifting Gas

[0192] 53 First condensate fraction

[0193] 54 First gaseous fraction

[0194] 55 CO2-rich stream

[0195] 56. Lean CO2 Stream

[0196] 57 Compression and storage units

[0197] 58 Methanation effluent

[0198] 59 Second condensate fraction

[0199] 60 Indirect heat exchanger

[0200] 61 Cooling unit, such as an ammonia cooling unit

[0201] 62 Compressed nitrogen-rich stream

[0202] 63 First Drying Subunit

[0203] 64 Second Drying Subunit

[0204] 65. Refrigerated synthesis gas

[0205] 66 First Liquid-Gas Separator

[0206] 67. The second part of high-purity hydrogen gas

[0207] 68 Indirect Switch

[0208] 69. Purified liquid nitrogen

[0209] 70 Second Indirect Heat Exchanger

[0210] 71. Cooled high-purity hydrogen gas

[0211] 72 Second Liquid-Gas Separator

[0212] 73 Compressor

[0213] 74. Condenser, preferably a water-cooled condenser.

[0214] 75 Expander Equipment

[0215] 76 Additional heat exchangers

[0216] 77 Evaporating refrigerant flow

[0217] 78. Condensing refrigerant flow

[0218] 79 Third Liquid-Gas Separator

[0219] 80 Expanded ultra-high purity hydrogen gas stream

[0220] 81 Third condensate

[0221] 82 Gaseous fraction

[0222] 83 Heated condensate flow

Claims

1. A process (1) for producing high-purity hydrogen (10), comprising the steps of: (I) reforming (2) a desulfurized hydrocarbon feedstock (3), such as natural gas, in the presence of steam (4) to obtain a raw synthesis gas (5); (II) subjecting the raw synthesis gas (5) to CO shift (6), carbon dioxide removal (7), methanation (8) and steam condensation (9, 11) to obtain a modified synthesis gas (12); (III) treating the modified synthesis gas (12) in a cryogenic purification section (13) to obtain the high-purity hydrogen (10) and a methane-containing tail gas stream (14); optionally, after preferably heat exchange, recycling the methane-containing tail gas stream as feed to step (I); wherein the net refrigeration of the cryogenic purification section (13) is at least partly provided by expansion (19) of compressed nitrogen-rich gas (15) produced by an air separation unit (ASU; 16).

2. The process according to claim 1, wherein prior to expansion (19), the nitrogen-rich gas (15) is cooled in the cryogenic purification section (13) by heat exchange with expanded nitrogen-rich gas (37).

3. The process according to any one of the preceding claims, wherein the nitrogen-rich gas (15) is produced in gaseous form by the ASU (16), preferably at room temperature and atmospheric pressure, followed by compression, or at room temperature and at a pressure higher than atmospheric pressure, such as a pressure of 2 to 50 bar, preferably 3 to 30 bar, more preferably 5 to 15 bar.

4. The process according to any one of the preceding claims, comprising: (IV) producing the nitrogen-rich gas (15) with the ASU (16); (V) compressing (17) and cooling (18) the nitrogen-rich gas (15) of step (IV); (VI) expanding (19) the nitrogen-rich gas of step (V) to provide the net refrigeration to the modified synthesis gas (12) in the cryogenic purification section (13) by indirect heat exchange.

5. The process according to any one of the preceding claims, further comprising: (II.A) drying the modified synthesis gas (12) of step (II) with a molecular sieve drying unit (20) prior to treating the modified synthesis gas (12) in step (III); (II.B) regenerating the molecular sieve of the molecular sieve drying unit (20) with at least part of the expanded nitrogen-rich gas after providing the net refrigeration.

6. The process according to any one of the preceding claims, wherein step (I) comprises reforming (2) the hydrocarbon feedstock in the further presence of an oxygen-rich stream (22) or oxygen-enriched air as oxidizing agent, whereby the oxygen-rich stream (22) or the oxygen-enriched air is provided by treating an air stream (23) in the ASU (16).

7. The method of any of the preceding claims, comprising: indirect heat exchange of the methane-containing tail gas stream (14) in the cryogenic purification section (13); subsequent recycling of the heat-exchanged methane-containing tail gas stream (24) as feed to step (I); optionally, the methane content of the methane-containing tail gas stream (24) is > 90 mol%.

7. The process according to any one of the preceding claims, wherein the methane content of the methane-containing tail gas stream (14) is > 90 mol%, preferably > 95 mol%, more preferably > 99 mol%.

8. The process according to any one of the preceding claims, further comprising: (VII) treating at least a portion (26) of the high-purity hydrogen (10) obtained in step (III) in a second cryogenic purification section (25) to obtain ultra-high purity hydrogen (27) having a hydrogen content > 99.5 mole%, preferably > 99.7 mole%, more preferably > 99.9 mole%, even more preferably > 99.99 mole%, for example 99.999 mole%.

9. The process according to claim 8, wherein the step (VII) comprises: (VII.A) washing the portion (26) of the high-purity hydrogen (10) with a liquid nitrogen solution (38) in a contact unit (28), for example an absorption column, to obtain a washed high-purity hydrogen (29) and an impurities-containing solution (30); (VII.B) treating the washed high-purity hydrogen (29) of step (VII.A) in indirect heat exchange to obtain the ultra-high purity hydrogen (27) and a tail stream (35) comprising liquid nitrogen and impurities, the indirect heat exchange being carried out in one of: (i) a cryogenic turboexpander (31) fed with a compressed ultra-high purity hydrogen stream (32); or (ii) a cryogenic refrigeration unit (33) comprising a helium or hydrogen refrigerant cycle (34); and (VII.C) recycling the tail stream (35) to the contact unit (28) of step (VII.A).

10. A plant (1) for the production of high-purity hydrogen (10), comprising: - a reforming section (2) configured to reform a desulfurized hydrocarbon feedstock (3) in the presence of steam (4) to obtain a raw synthesis gas (5); - a CO shift unit (6), a carbon dioxide removal unit (7), a methanation unit (8) and at least one steam condensation unit (9, 11) configured to treat the raw synthesis gas (5) to obtain a modified synthesis gas (12); - a cryogenic purification section (13) of the modified synthesis gas (12) to obtain the high-purity hydrogen (10) and a methane-containing tail gas stream (14); - optionally, a line recycling the methane-containing tail gas stream (14) as feed to the reforming section (2), preferably after heat exchange; - an air separation unit (ASU; 16) providing a nitrogen-rich gas (15) and, optionally, an oxygen-rich stream (22); - an expansion unit (19) of the nitrogen-rich gas (15) in a compressed state to provide a heat exchange medium to refrigerate the cryogenic purification section (13).

11. The plant according to claim 10, further comprising: - a compression unit (17) and a cooling unit (18) of the nitrogen-rich gas (15) provided by the ASU (16); - an expansion unit (19) of the compressed and cooled nitrogen-rich stream (36) to provide a heat exchange medium to refrigerate the cryogenic purification section (13); the cryogenic purification section (13) comprises at least one indirect heat exchanger (60) between the modified synthesis gas (12) and the expanded nitrogen-rich gas (37).

12. The apparatus of claim 11, wherein the cooling unit (18) and the indirect heat exchanger (60) are integrated in the same equipment.

13. The apparatus of any one of claims 10 to 12, further comprising: - a molecular sieve drying unit (20) for drying the modified synthesis gas (12) upstream of the cryogenic purification section (13); - a line (39) for feeding at least part of the expanded nitrogen-rich gas (37) to the molecular sieve drying unit (20) for regenerating the molecular sieve of the molecular sieve drying unit (20) after passing through the indirect heat exchanger (60).

14. The apparatus of any one of claims 10 to 13, further comprising a line for feeding the methane-containing tail gas stream (14) to the indirect heat exchanger (60) of the cryogenic purification section (13), and a line for recycling the heat-exchanged methane-containing tail gas stream (24) as a feed to the reforming section (2).

15. The apparatus of any one of claims 10 to 14, further comprising: - a second cryogenic purification section (25) of at least a portion (26) of the high-purity hydrogen (10) to obtain an ultra-high purity hydrogen (27); the second cryogenic purification section (25) comprises: • a contacting unit (28), such as an absorption column, for washing the portion (26) of the high-purity hydrogen (10) with a liquid nitrogen solution (38) to obtain a washed high-purity hydrogen (29) and an impurities-containing solution (30); • one of: a cryogenic expander or turbo-expander (31) fed with a compressed ultra-high purity hydrogen stream (32), or a cryogenic refrigeration unit (33) comprising a helium or hydrogen refrigerant cycle (34) to obtain the ultra-high purity hydrogen (27) and a tail liquid stream (35) comprising liquid nitrogen and impurities; and • a line for recycling the tail liquid stream (35) to the contacting unit (28).

16. A method of retrofitting an apparatus for the production of high-purity hydrogen: the apparatus to be retrofitted comprises a reforming section for reforming desulfurized hydrocarbons into a raw synthesis gas, and a CO shift unit, a carbon dioxide removal unit, a methanation unit and at least one steam condensation unit configured to process the raw synthesis gas to obtain a modified synthesis gas; the method comprises at least the steps of: - installing an air separation unit (ASU; 16) if not already equipped in the apparatus to be retrofitted; 16) providing a nitrogen-rich gas (15); - if the plant to be improved does not already have a cryogenic purification section (13) of the modified synthesis gas (12), providing said cryogenic purification section (13) of the modified synthesis gas (12); - optionally, installing a compression unit (17) and a cooling unit (18) of the nitrogen-rich gas (15); - optionally, installing an expansion unit (19) of the compressed and cooled nitrogen-rich stream (36); - installing at least one indirect heat exchanger (60) to feed the nitrogen-rich gas (15) or optionally the expanded nitrogen-rich gas (37) to the cryogenic purification section (13) to provide a heat exchange medium to refrigerate the lines of the cryogenic purification section (13); - optionally, installing a line to recycle the methane-containing tail gas stream (14) or the heat-exchanged methane-containing tail gas stream (24) provided by the cryogenic purification section (13) as feed to the reforming section (2); - optionally, installing a liquid-gas separator (66) to separate the high-purity hydrogen (10) and the methane-containing tail gas stream (14).

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