Hydrogen purification

Abstract

The invention provides an apparatus and method for hydrogen purification comprising a swing adsorption (SA) stage and recycling of purged gaseous impurities.

Description

Technical Field

[0001] The present invention relates to an apparatus and method for hydrogen purification, comprising a variable adsorption (SA) stage and a recirculation of purged gaseous impurities. Background Technology

[0002] Hydrogen production during steam reforming requires a purification step. In steam reforming, this is done via pressure swing absorption (PSA). However, PSA also retains some hydrogen, which is why this technology typically provides 80-90% hydrogen yield. The remaining hydrogen is lost in a low-pressure tail gas, which is best suited for heating in other parts of the plant.

[0003] A more efficient hydrogen separation technology than PSA is needed, which can avoid the over-design of steam reforming equipment. Summary of the Invention

[0004] An apparatus is provided for providing an H2-rich gas stream from a hydrocarbon feedstock, the apparatus comprising:

[0005] - A reforming section, which is arranged to receive the hydrocarbon feed and reform it in at least one reforming step at a first pressure to provide a synthesis gas stream;

[0006] - The CO2 removal stage is arranged to receive the synthesis gas flow from the reforming section and separate CO2 from the synthesis gas flow to provide a CO2-rich stream and a CO2-lean stream.

[0007] - A variable adsorption (SA) stage, the SA stage comprising an adsorbent material and a first purge stream at a pressure equal to or higher than a first pressure; and the SA stage is arranged to receive a lean CO2 stream from a CO2 removal stage;

[0008] -The SA phase includes a first state (A) and a second state (B), wherein:

[0009] In the first state (A), the lean CO2 stream is arranged to contact the adsorbent material, such that...

[0010] ■ At least a portion of the gaseous impurities from the lean CO2 stream, and

[0011] ■ A portion of the hydrogen gas from the aforementioned lean CO2 stream,

[0012] It is adsorbed onto the adsorbent material, thereby providing an H2-rich flow;

[0013] In the second state (B), the first purge stream is arranged to contact the adsorbent material such that at least a portion of the adsorbed gaseous impurities and at least a portion of the adsorbed hydrogen are released from the adsorbent material and enter the first purge stream; thereby providing a first recirculation stream comprising the first purge stream, hydrogen, and gaseous impurities;

[0014] -The device (100) is arranged to recycle the first recirculated stream as feed to the reforming section for the reforming step.

[0015] The present invention also provides a method for providing an H2-rich gas stream from a hydrocarbon feed. This method includes the following general steps:

[0016] i. Provide the equipment described herein;

[0017] ii. The hydrocarbon feed is fed into the reforming section and reformed in at least one reforming step at a first pressure to provide a synthesis gas stream;

[0018] iii. The syngas stream from the reforming section is fed to the CO2 removal stage, and CO2 is separated from the syngas stream to provide a CO2-rich stream and a CO2-lean stream;

[0019] iv. Feed the lean CO2 stream from the CO2 removal stage to the variable adsorption (SA) stage, the SA stage comprising an adsorbent and a first purge stream at a pressure equal to or higher than a first pressure, wherein the SA stage comprises a first state (A) and a second state (B), wherein:

[0020] In the first state (A), the lean CO2 stream comes into contact with the adsorbent material, making...

[0021] ■ At least a portion of the gaseous impurities from the lean CO2 stream, and

[0022] ■ A portion of the hydrogen gas from the aforementioned lean CO2 stream,

[0023] It is adsorbed onto the adsorbent material, thereby providing an H2-rich flow;

[0024] In the second state (B), the first purge stream contacts the adsorbent material, causing at least a portion of the adsorbed gaseous impurities and at least a portion of the adsorbed hydrogen to be released from the adsorbent material and enter the first purge stream; thereby providing a first recirculation stream comprising the first purge stream, hydrogen, and gaseous impurities; and

[0025] v. Recycle the first recirculated stream as feed to the reforming section for the reforming step.

[0026] Further details of the technology of this invention are set forth in the following detailed description, drawings and appended claims.

[0027] Brief description of the attached figures

[0028] Figure 1 A schematic layout of a hydrogen production apparatus according to the present invention is shown. Invention Details

[0030] When a segment, unit, or stage is "arranged to receive" a specific gas from another segment, unit, or stage, it is typically arranged to receive it directly. However, in some cases, there are intermediate segments, units, or stages through which the specific gas can pass. Detailed Implementation

[0031] In the following text, the abbreviation %vol will be used to represent the volume percentage of a gas.

[0032] A hydrogen production device is provided, namely a device that provides an H2-rich gas stream from a hydrocarbon feed. The term "H2-rich" should be understood as approximately 95% vol or more.

[0033] Hydrocarbon feedstock is typically selected from natural gas, city gas, naphtha, or biogas, with natural gas being preferred. The hydrocarbon feedstock is characterized by containing a large amount (i.e., more than 50%) of hydrocarbons, such as methane, ethane, propane, butane, etc. Additionally, nitrogen, argon, and carbon dioxide may be present. Note that within the reforming section, the hydrocarbon feedstock will be mixed with a stream containing hydrogen, steam, carbon dioxide, or oxygen to promote the reforming reaction.

[0034] Typically, the device includes:

[0035] -Reorganization segment;

[0036] -CO2 removal stage; and

[0037] - Variable adsorption (SA) stage.

[0038] The reforming section is arranged to receive the hydrocarbon feed and reform it in at least one reforming step to provide a syngas stream. Reforming hydrocarbons into syngas is a known procedure and will not be discussed in detail here.

[0039] Usually, such as Figure 1 As shown, the reforming section includes one or more primary reformer units and optionally one or more pre-reforming units arranged upstream of the reformer units in the hydrocarbon feed. If no pre-reforming unit is present, the hydrocarbon feed is received by the primary reformer unit. If a pre-reforming unit is present, the hydrocarbon feed is received by the pre-reforming unit. The one or more primary reformer units can be selected from an autothermal reactor (ATR), a steam methane reformer (SMR), a convection reformer, and / or a catalytic oxidation (CATOX) type reformer.

[0040] The carbon dioxide removal stage is arranged to receive the syngas from the reforming stage and separate carbon dioxide from the syngas stream to provide a CO2-rich stream and a CO2-lean stream. The CO2 content in the lean CO2 vapor is typically less than 2%, while the CO2-rich stream may contain more than 90% CO2. The CO2 removal stage refers to the unit that removes CO2 from process gases using processes such as chemical absorption. In chemical absorption, CO2-containing gas is passed through a solvent that reacts with and binds the CO2 to it. Most chemical solvents are amines, classified as primary amines such as monoethanolamine (MEA) and diethylene glycolamine (DGA), secondary amines such as diethanolamine (DEA) and diisopropanolamine (DIPA), or tertiary amines such as triethanolamine (TEA) and methyldiethanolamine (MDEA), but ammonia and liquid alkali metal carbonates such as K2CO3 and NaCO3 can also be used.

[0041] The variable adsorption (SA) stage comprises the adsorbent material and a first purge stream. The adsorbent material can be selected from zeolites, activated carbon, or metal-organic frameworks, or mixtures thereof. The adsorbent material is typically in the form of an adsorption bed within the SA stage. Variable adsorption refers to a unit used to adsorb selected compounds. In this type of device, a dynamic equilibrium is established between the adsorption and desorption of gas molecules on the adsorbent material. The adsorption of gas molecules can be caused by spatial, kinetic, or equilibrium effects. The exact mechanism will be determined by the adsorbent used, and the equilibrium saturation will depend on temperature and pressure. Typically, the adsorbent material is processed in a mixed gas until the heaviest compound approaches saturation, after which regeneration is required. Regeneration can be accomplished by changing the pressure or temperature, or by purging with another stream. In practice, this means using a process with at least two units, first saturating the adsorbent in one unit at high pressure or low temperature, then switching units where molecules adsorbed in the same unit are desorbed by decreasing the pressure or increasing the temperature, or by purging with another stream.

[0042] The SA stage is configured to receive a lean CO2 stream from the CO2 scavenging stage. The SA stage comprises a first state (A) and a second state (B), and these states are interchangeable. Changes between states may involve opening or closing the stream entering the SA stage. On one hand, changes between states involve temperature changes in the SA stage; that is, the SA stage is a thermotropic adsorption (TSA) stage. Therefore, in this respect, the temperature of the SA stage in the second state (B) is higher than the temperature in the first state (A).

[0043] Appropriately, the SA phase is arranged to alternate between the first state (A) and the second state (B). To improve efficiency and reduce output fluctuations, the SA phase may involve several parallel adsorption reactions in different phases (A, B) at a given time.

[0044] In the first state (A), the lean CO2 stream is arranged to contact the adsorbent material, thereby:

[0045] ■ At least a portion (preferably all) of the gaseous impurities from the lean CO2 stream, and

[0046] ■ A portion of the hydrogen from the lean CO2 stream (304),

[0047] The hydrogen is adsorbed onto the adsorbent material. Because only a portion of the hydrogen from the lean CO2 stream is adsorbed, the remaining unadsorbed H2 continues through the SA stage, thus providing a rich H2 stream.

[0048] Gaseous impurities are typically one or more of the following gases: CO2, CO, Ar, H2O, N2, and CH4.

[0049] The second state (B) is a purging state, in which impurities on the adsorbent material are replaced by purging. In the second state (B) of the SA stage, a first purging stream is arranged to contact the adsorbent material such that at least a portion (and preferably all) of the adsorbed gaseous impurities and at least a portion (preferably all) of the adsorbed hydrogen are released from the adsorbent material and enter the first purging stream. In this way, a first recirculation stream is provided, which comprises a mixture of the first purging stream, hydrogen, and the gaseous impurities. Figure 1 As shown, the device is arranged to feed a first recirculated stream to the reforming section. The device may also be arranged to feed the first recirculated stream upstream of one or more pre-reformer units (if present).

[0050] The SA stage may include a second purge stream and a third state (C). In this third state, the second purge stream is arranged to purge the adsorbent material after the first purge recirculation stream, such that at least a portion of the gaseous impurities are released from the adsorbent material; thereby providing a second recirculation stream, which is recirculated upstream of the reforming step in the reforming section. In this way, the adsorbent material is flushed with a preferred gas phase before returning to state A, thus avoiding contamination of the H2-rich stream by the first purge stream used in state B. The second purge stream may advantageously be hydrogen. In a particular embodiment, the second purge stream has a pressure equal to or higher than the first pressure.

[0051] In a preferred aspect, the first purge stream is a superheated steam stream. Steam is a particularly attractive purge stream because it needs to be a co-feed of the hydrocarbon feed to the reforming section; therefore, the first purge stream, mixed with hydrogen and gaseous impurities, can be centrally recovered. Figure 1As shown, additional steam may be added to the recirculation to precisely match the amount of steam required for the reforming stage. Another advantage of using steam is that it can be easily removed from the H2-rich stream by condensation. The superheated steam stream can be arranged to provide at least a portion of the temperature rise from the first state (A) to the second state (B) in the SA stage. The superheated steam can be obtained from other parts of the equipment, such as other units, like the steam superheater in the waste heat boiler and / or flame heater / waste heat section.

[0052] In terms of alternatives, the first purge stream is part of the hydrocarbon feed in the form of natural gas. This allows the combined stream of the first purge stream with hydrogen and gaseous impurities to be centrally recycled to the reforming section.

[0053] On the other hand, the first and / or second purge stream is a hydrogen stream. This avoids contamination of the H2-rich stream by the first purge stream.

[0054] A preferred configuration is to use steam as the first purge stream instead of the second purge stream. Another preferred configuration is to use natural gas as the first purge stream and hydrogen as the second purge stream.

[0055] The apparatus may also include a shift section arranged in the syngas stream between the reforming section and the CO2 removal stage. The shift section is designed to adjust the contents of the syngas stream; in particular the H / CO ratio, depending on the desired outcome of the apparatus and / or the type of hydrocarbon feed.

[0056] It is important to note that appropriate heat exchanger / temperature control stages and water removal stages should be applied as needed to facilitate the process. These details are not described because those skilled in the art of chemical process design believe they are easily adaptable.

[0057] The present invention also provides a method for providing an H2-rich gas stream from a hydrocarbon feed. This method includes the following general steps:

[0058] i. Provide the equipment described herein;

[0059] ii. The hydrocarbon feed is fed into the reforming section and reformed in at least one reforming step at a first pressure to provide a synthesis gas stream;

[0060] iii. The syngas stream from the reforming section is fed to the CO2 removal stage, and CO2 is separated from the syngas stream to provide a CO2-rich stream and a CO2-lean stream;

[0061] iv. Feed the lean CO2 stream from the CO2 removal stage to the variable adsorption (SA) stage, the SA stage comprising an adsorbent and a first purge stream at a pressure equal to or higher than a first pressure, wherein the SA stage comprises a first state (A) and a second state (B), wherein:

[0062] In the first state (A), the lean CO2 stream comes into contact with the adsorbent material, making...

[0063] ■ At least a portion of the gaseous impurities from the lean CO2 stream, and

[0064] ■ A portion of the hydrogen gas from the aforementioned lean CO2 stream,

[0065] It is adsorbed onto the adsorbent material, thereby providing an H2-rich flow;

[0066] In the second state (B), the first purge stream contacts the adsorbent material, causing at least a portion of the adsorbed gaseous impurities and at least a portion of the adsorbed hydrogen to be released from the adsorbent material and enter the first purge stream; thereby providing a first recirculation stream comprising the first purge stream, hydrogen, and gaseous impurities; and

[0067] v. Recycle the first recirculated stream as feed to the reforming section for the reforming step.

[0068] Suitablely, in the method, the SA phase is initially in the first state (A), and then alternates between the first state (A) and the second state (B). As described above, preferably, the temperature of the SA phase in the second state (B) is higher than its temperature in the first state (A).

[0069] All details of the above equipment, with appropriate modifications, are relevant to the methods described herein.

[0070] This invention is based on the understanding that a portion of the hydrogen produced in the variable adsorption stage can be recycled and used as feed for the reforming step, with the aim of improving the overall hydrogen yield of the equipment. This invention is also based on the understanding that it is feasible to provide the first purge stream of the variable adsorption stage at a pressure equal to or higher than that of the reforming reaction, thus allowing the recirculation of the hydrogen-rich gas from the variable adsorption stage to the reforming step to be carried out without the need for a compressor.

[0071] Specifically, the first purge stream can be a portion of the hydrocarbon feed to the reforming step, or a portion of the superheated steam feed to the reforming step, both of which can be used at pressures equal to or higher than those of the reforming step. Alternatively, the first purge stream can be a hydrogen stream, for example, a high-pressure stream from a separate process or a portion of a hydrogen-rich first recycle stream from the SA stage, which can be used at pressures equal to or higher than those of the reforming step, or slightly lower, in which case minimal compression is required.

[0072] Current technology allows for high H2 yields, exceeding PSA's 85% and potentially reaching levels on the order of +95%. Therefore, current technology offers a more efficient pathway for hydrogen production. Based on overall plant layout, this technology will enable the construction of more contact reformers, as the increased yield means less gas needs to be processed to produce a given amount of H2. This also translates to lower natural gas consumption and CO2 emissions compared to modern standards.

[0073] Higher H2 yields can be achieved compared to using a pressure shift absorption PSA stage. This will allow for the construction of more compact steam reformers, as overproduction will no longer be an issue.

[0074] Example 1

[0075] Table 1 summarizes one embodiment of the invention. A given amount of hydrocarbon feed (101) is reformed in a reforming section (200) to obtain a synthesis gas stream (201). In a CO2 removal stage (300), CO2 is removed from this stream to produce a lean CO2 stream (304) and a rich CO2 stream (303). The lean CO2 stream (304) is then separated in an SA stage (400) to produce a rich H2 stream (409). The SA is purged with steam (405), and 50% of this stream is recycled back to the reformer, while the other half is condensed as tail gas. Additionally, steam and some hydrogen are added to the reforming section to promote pre-reforming and reforming in this section. Note that the total feed to the reformer is a mixture of the pre-reformed hydrocarbon feed (101), steam, and hydrogen.

[0076]

[0077] Example 2

[0078] Table 2 summarizes a comparative embodiment in which the first recirculated stream 408 from the SA unit is not returned to the reforming section. Similar to Example 1, a given amount of hydrocarbon feed (101) is reformed in the reforming section (200) to produce a synthesis gas stream (201). In the CO2 removal stage (300), CO2 is removed from this stream to produce a CO2-lean stream (304). It is then separated in the SA stage (400) to produce an H2-rich stream (409). In this case, the SA is a more typical PSA, where tail gas is produced directly. Additionally, steam and some hydrogen are added to the reforming section to facilitate pre-reforming and reforming of this section. Note that the total feed to the reformer is a mixture of pre-reformed hydrocarbon feed (101), steam, and hydrogen.

[0079]

[0080] Using the method of the present invention presented in Example 1, it is shown that the magnitude of the H2-rich flow (409) increases from the basic case to 32103 Nm in Example 2.3 / h increased to 39752 Nm in Example 1 3 / h. Therefore, by means of the method of the present invention, the hydrogen yield from a given amount of hydrocarbon feed (101) is increased by 24%. This yield can be further increased by increasing the utilization rate of the purge stream (405) used in Example 1 (50% in Example 1). In contrast, using 70% of the purge stream would result in a 29% increase in the yield of the H2-rich stream (409).

[0081] Other reference numerals in the figure:

[0082] Hydrodesulfurization (HDS) and sulfur adsorption unit 80

[0083] Heat exchanger / waste heat boiler 209

[0084] The transformed synthetic gas flow 201'

[0085] Transformation segment 500

[0086] Although the invention has been described with reference to various aspects, examples and embodiments, those skilled in the art may combine these aspects, examples and embodiments in a manner that still falls within the scope of the invention.

Claims

1. An apparatus for providing an H2-rich gas stream from a hydrocarbon feed, the apparatus (100) comprising: - a reforming section (200) arranged to receive a hydrocarbon feed (101) and to reform it in at least one reforming step to provide a synthesis gas stream (201), the at least one reforming step being carried out at a first pressure; - a CO2 removal stage (300) arranged to receive the synthesis gas stream (201) from the reforming section (200) and to separate CO2 from the synthesis gas stream (201) to provide a CO2-rich stream (303) and a CO2-lean stream (304); - a swing adsorption stage (400), the swing adsorption stage (400) comprising an adsorbent material and a first purge stream (405) at a pressure equal to or higher than the first pressure; and the swing adsorption stage being arranged to receive the CO2-lean stream (304) from the CO2 removal stage (300); - wherein the swing adsorption stage (400) comprises a first state (A) and a second state (B), wherein: in the first state (A), the CO2-lean stream (304) is arranged to contact the adsorbent material, such that at least a portion of gaseous impurities from the CO2-lean stream (304), and a portion of hydrogen from the CO2-lean stream (304), are adsorbed onto the adsorbent material, thereby providing an H2-rich stream (409); in the second state (B), the first purge stream (405) is arranged to contact the adsorbent material, such that at least a portion of the adsorbed gaseous impurities and at least a portion of the adsorbed hydrogen are released from the adsorbent material and into the first purge stream (405); thereby providing a first recycle stream (408) comprising the first purge stream (405), hydrogen and the gaseous impurities; - the apparatus (100) is arranged to recycle the first recycle stream (408) to the reforming section (200) as a feed for the reforming step; wherein the first purge stream (405) is a superheated steam stream; wherein the CO2 removal stage (300) is a unit utilizing chemical absorption; and wherein the swing adsorption stage is a temperature swing adsorption stage.

2. The apparatus according to claim 1, wherein the swing adsorption stage (400) is arranged to alternate between the first state (A) and the second state (B).

3. The apparatus according to any one of the preceding claims, wherein the temperature of the swing adsorption stage in the second state (B) is higher than its temperature in the first state (A).

4. The apparatus according to claim 1 or 2, wherein at a given time, the swing adsorption stage (400) has a plurality of parallel adsorption reactions in different stages.

5. The apparatus according to claim 1 or 2, wherein the swing adsorption stage (400) comprises a second purge stream and comprises a third state (C), wherein the second purge stream is arranged to purge the adsorbent material after being purged with the first purge recycle stream (405), such that at least a portion of the gaseous impurities is released from the adsorbent material; thereby providing a second recycle stream that is recycled to the reforming section (200) upstream of the reforming step.

6. The apparatus according to claim 1 or 2, wherein the adsorbent material is selected from a zeolite, activated carbon or a metal organic framework, or a mixture thereof.

7. The apparatus according to claim 1 or 2, wherein the superheated steam stream is arranged to provide at least part of the temperature increase of the swing adsorption stage (400) from the first state to the second state.

8. The apparatus according to claim 1 or 2, wherein the first purge stream (405) is part of the hydrocarbon feed in the form of natural gas.

9. The apparatus according to claim 5, wherein the first and / or second purge stream is a hydrogen stream.

10. The apparatus according to claim 1 or 2, wherein the reforming section (200) comprises one or more primary reformer units (220), and one or more pre-reformer units (221) arranged upstream of the primary reformer units (220) in the hydrocarbon feed (101), and wherein the apparatus (100) is arranged to feed the first recycle stream (408) upstream of the one or more pre-reformer units (221).

11. The apparatus according to claim 1 or 2, wherein the one or more primary reformer units (220) are selected from an autothermal reactor (ATR), a steam methane reforming reactor (SMR), a convection reforming reactor and / or a catalytic oxidation (CATOX) type reforming reactor.

12. The apparatus according to claim 1 or 2, further comprising a shift section (500) arranged in the syngas stream (201) between the reforming section (200) and the CO2 removal stage (300).

13. A method for providing a H2-rich gas stream from a hydrocarbon feed, the method comprising: i. providing an apparatus (100) according to any one of the preceding claims; ii. feeding a hydrocarbon feed (101) to a reforming section (200) and reforming it in at least one reforming step performed at a first pressure to provide a syngas stream (201); iii. feeding the syngas stream (201) from the reforming section (200) to a CO2 removal stage (300) and separating CO2 from the syngas stream (201) thereby providing a CO2-rich stream (303) and a CO2-lean stream (304); iv. feeding the CO2-lean stream (304) from the CO2 removal stage (300) to a swing adsorption stage (400) comprising an adsorbent material and a first purge stream (405) at a pressure equal to or higher than the first pressure, wherein the swing adsorption stage (400) comprises a first state (A) and a second state (B), wherein: in the first state (A), the CO2-lean stream (304) is contacted with the adsorbent material such that ■at least part of the gaseous impurities from the CO2-lean stream (304), and ■part of the hydrogen from the CO2-lean stream (304), are adsorbed onto the adsorbent material thereby providing a H2-rich stream (409); iv. feeding the H2-rich stream (409) to a pressure swing adsorption section (600) comprising a second purge stream (606) at a pressure equal to or higher than the first pressure, wherein the pressure swing adsorption section (600) comprises a first state (C) and a second state (D), wherein: in the first state (C), the H2-rich stream (409) is contacted with the adsorbent material such that ■at least part of the hydrogen from the H2-rich stream (409), is adsorbed onto the adsorbent material thereby providing a H2-enriched stream (607); and in the second state (D), the H2-enriched stream (607) is contacted with the adsorbent material such that ■at least part of the hydrogen from the H2-enriched stream (607), is desorbed from the adsorbent material thereby providing a H2-rich stream (608). In the second state (B), a first purge stream (405) is contacted with the adsorbent material, such that at least a portion of the adsorbed gaseous impurities and at least a portion of the adsorbed hydrogen are released from the adsorbent material and into the first purge stream (405); thereby providing a first recycle stream (408) comprising the first purge stream (405), hydrogen and the gaseous impurities; and v. recycling the first recycle stream as a feed to a reforming step to a reforming section (200).

14. The method according to claim 13, wherein the swing adsorption stage (400) is initially in a first state (A) and then alternates between the first state (A) and a second state (B).

15. The method according to any one of claims 13-14, wherein the temperature of the swing adsorption stage in the second state (B) is higher than the temperature thereof in the first state (A).

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