Hydrogen separation from natural gas

Abstract

Disclosed herein are methods and systems for measuring the concentration of light gases in a main flow stream. The method includes calculating a control parameter as a function of the concentration of light gases in the main flow stream, splitting a portion of the main flow stream to produce a feed stream, and separating the feed stream by selective permeation across a semipermeable membrane to produce a permeate stream enriched in light gases and a retentate depleted in light gases. The ratio of the flow rate of the feed stream to the flow rate of the main flow stream can be increased or decreased depending on the control parameter. Additionally, the area of ​​the semipermeable membrane can be increased or decreased depending on the control parameter.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Non-Provisional Application No. 18 / 499,382, filed November 1, 2023, and U.S. Provisional Application No. 63 / 423,875, filed November 9, 2022. [Background technology]

[0002] As the hydrogen economy continues to expand, dedicated H2 transportation networks are being developed, while at the same time, as an interim solution, fusing hydrogen (H2) into existing natural gas transportation networks has been proposed to decarbonize end users. In some instances, H2-depleted natural gas is needed by end users (such as petrochemical / polymer industries and natural gas liquefaction plants), necessitating technological solutions to remove H2 from natural gas fusion. Furthermore, natural gas transportation networks can also be used to transport hydrogen long distances, where it can be extracted as high-purity hydrogen for clean combustion and / or fuel cell applications. Because the majority of hydrogen is expected to be produced using renewable energy sources that are expected to provide varying amounts of energy to hydrogen production units (e.g., using electrolyzers) over a period of time, hydrogen production is also expected to fluctuate over a period of time. When such fluctuating hydrogen is fused into natural gas, this can result in large fluctuations in the hydrogen concentration of the fused natural gas stream. For applications that can accept variable flow rates of hydrogen product, such as when storage is available, a separation process is needed to "deblend" the hydrogen from natural gas that can compensate for feeds of varying hydrogen concentration. Summary of the Invention

[0003] This disclosure relates to methods and systems for separating hydrogen from natural gas feeds containing varying hydrogen concentrations using techniques such as permselective membranes and adsorption. Adaptive design and dynamic operation can accommodate fluctuations in hydrogen concentration to achieve maximum hydrogen separation during the day when more hydrogen can be produced and integrated into the natural gas feed.

[0004] In some embodiments disclosed herein, the separation process may include a first membrane stage, an interstage compressor, a second membrane stage, and a refinement stage. In some embodiments, the refinement stage may include a pressure swing adsorption (PSA) unit.

[0005] Depending on the hydrogen concentration in the natural gas, the total feed flow rate to the first membrane stage can be controlled based on the number of installed membrane modules, the interstage compressor capacity, and / or the number of rotary valve PSA units (or PSA capacity).

[0006] In addition to controlling the feed flow to the membranes, the total number of membrane modules can be controlled by opening or closing on-off valves upstream of the membrane modules or groups of membrane modules in the first membrane stage. Controlling the total number of membrane modules or total membrane area used to separate hydrogen from natural gas can reduce the amount of methane that permeates into the hydrogen-enriched permeate stream.

[0007] The controlled membrane module in the first membrane stage can maximize the hydrogen content in the permeate stream, which can be compressed with the exhaust gas from the PSA unit in a permeate compressor that can be designed to operate over a wide range of inlet flow rates and composition values.

[0008] The total number of modules online in the second membrane stage can be controlled by opening and closing on-off valves upstream of membrane modules or groups of modules in the second membrane stage in response to changes in flow rate and hydrogen content or the stream exiting the interstage compressor. By controlling the total number of membrane modules online in the second membrane stage, the concentration of hydrogen in the second permeate stream exiting the second membrane stage can be maximized.

[0009] The second permeate stream can then be purified in a PSA unit. The PSA unit can include one or more rotary valve PSA units for low flow rates or one or more switching valve PSA units for high flow rates. Depending on the feed of the PSA unit and the impurities therein, the capacity of the PSA unit can be controlled. In the case of rotary valve PSAs, the number of rotary valve PSAs in operation can be controlled. Depending on the flow rate and concentration of impurities in the second permeate stream and the operating adsorption capacity, the cycle time can be optimized to maximize hydrogen recovery. [Brief explanation of the drawings]

[0010] The present invention is described below in conjunction with the accompanying drawings, in which like numerals refer to like elements and in which:

[0011] [Figure 1] FIG. 1 is a process flow diagram depicting a process for extracting hydrogen from a natural gas stream.

[0012] [Figure 2] 1 is a graphical representation showing an exemplary variation in the concentration of hydrogen in natural gas as a function of time.

[0013] [Figure 3] 3 is a graphical representation showing the rate of hydrogen extraction as a function of time for natural gas streams whose concentrations vary as shown in FIG. 2.

[0014] [Figure 4]3 is a graphical representation of the flow rate of a feed stream as a function of time for a natural gas stream having varying concentrations as shown in FIG. 2.

[0015] [Figure 5] 3 is a graphical representation of the power consumed by an inter-stage compressor as a function of time for a natural gas stream whose concentration varies as shown in FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0016] The following detailed description provides only preferred exemplary embodiments and is not intended to limit the scope, applicability, or configuration of the present invention. Rather, the following detailed description of preferred exemplary embodiments will provide those skilled in the art with an effective description for implementing preferred exemplary embodiments of the present invention. Various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the present invention, as set forth in the appended claims.

[0017] FIG. 1 is a process flow diagram depicting a process for extracting hydrogen from a hydrogen-containing natural gas stream. A portion of the main flow stream 102 may be split to form a feed stream 104. In some embodiments, the main flow stream 102 may be a natural gas pipeline. The feed stream 104 may be optionally heated in a first feed preheater 110 to prevent condensation in the first membrane stage 120 to form a first-stage membrane feed stream 112. The first membrane stage 120 may comprise one or more membrane modules containing membrane materials that selectively permeate light gases, such as hydrogen, over methane. A first hydrogen-enriched permeate stream 122 may exit the first membrane stage 120 and be compressed in an interstage compressor 130 to form a compressed permeate stream 132. A hydrogen-depleted first retentate stream 124 may exit the first membrane stage 120 and be compressed in a blower 125 to form a compressed retentate stream 126, which may be returned to the main flow stream 102. In some embodiments, the compressed residue stream 126 may be returned to the main flow stream 102 downstream from where the feed stream 104 is split. If necessary, a separator 140 may be used to remove liquid condensates 142, such as water. The overhead 144 from the separator 140 may be heated as needed in a second feed preheater 150 to produce a second-stage membrane feed 152, which will prevent condensation in the second membrane stage 160. The second membrane stage 160 may comprise one or more membrane modules containing a membrane material that selectively permeates hydrogen over methane. The second membrane stage 160 may use the same membrane material as the first membrane stage 120, or a different membrane material. The second hydrogen-enriched permeate stream 162 may then be purified in a refinement stage 170, such as a pressure swing adsorption (PSA) system. The second hydrogen-depleted residue stream 164 may be recycled to the first-stage membrane 112. A hydrogen product stream 172 exits the refinement stage 170 at the purity required by downstream customers. A hydrogen-depleted tail gas stream 174 exits the refinement stage 170 and may be compressed in the interstage compressor 130 to improve overall hydrogen recovery.The hydrogen-depleted exhaust gas stream 174 may be combined with the first permeate stream 122 prior to compression. If the pressures of the two streams are different, the hydrogen-depleted exhaust gas stream 174 and the first permeate stream 122 may enter different stages of the inter-stage compressor 130.

[0018] An adaptive design with dynamic control can compensate for fluctuations in hydrogen content in the main flow stream 102 and extract the needed hydrogen at the lowest overall cost. The extracted H2 flow can vary as the H2 concentration in the main flow stream 102 varies. The hydrogen concentration in the main flow stream 102 can vary over a 24-hour period. The hydrogen product stream 172 can be stored as a compressed gas or liquid to ensure a constant product supply to users.

[0019] The controller may be configured to increase or decrease the feed flow rate to the first membrane stage 120 to control the permeate flow rate 122. Any number of process variables, such as the hydrogen content of the natural gas feed, may be monitored to control the feed flow rate. The flow rate of the feed stream 104 may be controlled in response to control parameters calculated as a function of the concentration of hydrogen in the main flow stream 102 and various design parameters of the first membrane stage 120 and the second membrane stage 160. The control parameters may be calculated to provide a constant hydrogen product flow rate when averaged over a time scale of 1 hour to 7 days, or 12 hours to 48 hours.

[0020] The controller may be configured to isolate a number of membrane modules in the first membrane stage 120 from the first stage membrane feed 112 by switching one or more isolation valves. In some embodiments, the first membrane stage may be partially scaled down, such as by reducing the pressure gradient across the membrane. Any number of process variables, such as the hydrogen content of the feed stream 104 and the feed flow rate to the first membrane stage 120, may be monitored to control the number of membrane modules in the first membrane stage 120. Reducing the number of operating membrane modules in the first membrane stage 120 may reduce the flow rate of the first permeate stream 122 and / or increase the hydrogen concentration in the first permeate stream 122. This may reduce the total power required to compress the first permeate stream 122 in the inter-stage compressor 130.

[0021] Similarly, the controller may be configured to isolate a number of membrane modules in the second membrane stage 160 from the second stage membrane feed 152 by switching one or more isolation valves. Any number of process variables, such as the hydrogen content and / or total flow rate of the second stage membrane feed 152, may be monitored to control the number of membrane modules in the second membrane stage. Reducing the number of operating membrane modules in the second membrane stage 160 may reduce the flow rate of the second permeate stream 162 and / or increase the hydrogen concentration in the second permeate stream 162, thereby improving the performance of the refinement stage 170. Using the values ​​of the flow rate and H content of the feed to the second membrane stage 160, the controller estimates the number of membrane modules (or module groups) needed in the second membrane stage 160 to process the first permeate 122 and tail gas 174 from the refinement stage 170 to optimally maximize hydrogen extraction. This may be controlled through one or more on-off valves. Estimating the number of modules helps to effectively utilize the adsorption capacity.

[0022] If refinement stage 170 comprises a PSA, adsorption capacity and cycle time can be optimized using various controls. If multiple rotary valve PSAs are in parallel, such controls determine how many such PSAs are operated to process the PSA feed. In some embodiments, hydrogen applications have lower purity requirements such that the second permeate stream is sufficiently pure that the refinement stage can be eliminated. Applications with lower purity requirements for hydrogen can include refineries and power plants.

[0023] The adaptive control of the hydrogen extraction process uses measurements of hydrogen concentration in the natural gas stream to adjust the feed flow rate to the first membrane stage 120, the number of modules (or module groups) in the first membrane stage 120, the number of modules (or module groups) in the second membrane stage 160, the number of PSAs in the refinement stage 170, and It can be designed to calculate the cycle time of the PSA.

[0024] 1 utilizes a two-stage membrane process in which a second membrane stage is installed on the permeate exiting the first membrane stage, but those skilled in the art will understand that any permutation of membrane stages can be used as determined by basic optimization. For example, more stages can be installed on the successive permeate stream to increase hydrogen purity, or more stages can be installed on the successive retentate stream to increase hydrogen recovery.

[0025] Aspects of the present invention include, but are not limited to, the following.

[0026] Aspect 1: A method comprising: measuring a concentration of a light gas in a main flow stream; calculating a control parameter as a function of the concentration of the light gas in the main flow stream; splitting a portion of the main flow stream to produce a feed stream; separating the feed stream by selective permeation across a semipermeable membrane to produce a permeate stream enriched in the light gas and a retentate depleted in the light gas, wherein the ratio of the flow rate of the feed stream to the flow rate of the main flow stream is increased or decreased in response to the control parameter, and wherein the area of ​​the semipermeable membrane is increased or decreased in response to the control parameter.

[0027] Embodiment 2: The method of embodiment 1, further comprising separating the permeate stream in one or more adsorption units to produce a light gas product, wherein the number of adsorption units is increased or decreased depending on the control parameters.

[0028] Embodiment 3: The method of embodiment 2, wherein the cycle time of the adsorption unit is increased or decreased depending on the control parameter.

[0029] Embodiment 4: The method of any one of embodiments 1 to 3, further comprising storing at least a portion of the permeate or a stream resulting from the permeate.

[0030] Embodiment 5: The method of any one of embodiments 1 to 4, wherein the semipermeable membrane comprises a plurality of modules, and the area of ​​the semipermeable membrane is increased by connecting one or more of the plurality of modules to the feed stream and decreased by isolating one or more of the plurality of modules from the feed stream.

[0031] Embodiment 6: The method of any one of embodiments 1 to 5, further comprising combining the retentate stream with the main flow stream.

[0032] Embodiment 7: The method of any one of embodiments 2-6, wherein the control parameters are calculated to produce a light gas product at a constant flow rate when averaged over a period of from 1 hour to 7 days.

[0033] Aspect 8: The method of any one of Aspects 1-7, wherein the concentration of light gases in the main flow stream fluctuates with a frequency of less than 24 hours.

[0034] Aspect 9: A method comprising: measuring a concentration of a light gas in a main flow stream; calculating a control parameter as a function of the concentration of the light gas in the main flow stream; splitting a portion of the main flow stream to produce a feed stream having a feed flow; separating the feed stream by selective permeation across a first semipermeable membrane to produce a first permeate stream enriched in the light gas and a first retentate depleted in the light gas; wherein a ratio of a flow rate of the feed stream to a flow rate of the main flow stream is increased or decreased in response to the control parameter; an area of ​​the first semipermeable membrane is increased or decreased in response to the control parameter; the first semipermeable membrane comprises a plurality of modules; and the area of ​​the first semipermeable membrane is increased by connecting one or more of the plurality of modules to the feed flow and decreased by isolating one or more of the plurality of modules from the feed stream.

[0035] Embodiment 10: The method of embodiment 9, further comprising compressing the first permeate stream to produce a compressed permeate stream.

[0036] Embodiment 11: The method of embodiment 10, further comprising separating the compressed permeate stream by selective permeation across a second semipermeable membrane to produce a second permeate stream enriched in light gases and a second retentate depleted in light gases, and combining the second retentate with the feed stream.

[0037] Embodiment 12: The method of embodiment 11, further combining separating the second permeate stream in a number of adsorption units to produce a light gas product and a light gas-depleted tail gas stream, and combining the tail gas stream with the first permeate stream.

[0038] Embodiment 13: The method of embodiment 11 or 12, wherein the area of ​​the second semi-permeable membrane increases or decreases in response to a control parameter.

[0039] Embodiment 14: The method of embodiment 12 or 13, wherein the number of adsorption units is increased or decreased depending on a control parameter.

[0040] Embodiment 15: The method of any one of embodiments 9 to 14, wherein the control parameters are calculated to produce a light gas product at a constant flow rate when averaged over a period of from 1 hour to 7 days.

[0041] Aspect 16: The method of any one of aspects 9-15, wherein the concentration of light gases in the main flow stream fluctuates with a frequency of less than 24 hours.

[0042] Aspect 17: A system comprising: an analyzer in fluid flow communication with the main flow stream and configured to measure a concentration of light gases; a control valve in fluid flow communication with the main flow stream to produce a feed stream; a semipermeable membrane in fluid flow communication with the feed stream and configured to produce a permeate stream enriched in light gases and a retentate depleted in light gases; and a controller in electrical communication with the analyzer and the semipermeable membrane and configured to increase or decrease the area of ​​the semipermeable membrane as a function of a calculated control parameter.

[0043] Aspect 18: The system of aspect 17, wherein the controller is configured to receive a signal from the analyzer and calculate the control parameter as a function of the concentration of the light gas in the main flow stream.

[0044] Aspect 19: The system of aspect 17 or 18, further comprising one or more adsorption units in fluid flow communication with the semipermeable membrane and configured to separate the permeate stream and produce a light gas product and a tail gas stream.

[0045] Aspect 20: The system of aspect 19, wherein the controller is configured to increase or decrease the number of adsorption units depending on the control parameters.

[0046] As used herein, the article "a" or "an," when applied to any feature in the embodiments of the invention described in the specification and claims, means one or more. The use of "a" and "an" does not limit the meaning to a single feature unless such a limitation is specifically stated. The article "the" preceding a singular or plural noun or noun phrase indicates the particular named feature and may have singular or plural connotations depending on the context in which it is used.

[0047] The term "and / or" between a first element and a second element includes any of the following meanings: (1) the first element only, (2) the second element only, or (3) the first element and the second element. The term "and / or" between the last two elements of a list of three or more elements means at least one of the elements in the list, including any specific combination of elements in the list. For example, "A, B, and / or C" has the same meaning as "A, and / or B, and / or C," and includes the following combinations of A, B, and C: (1) A only, (2) B only, (3) C only, (4) A and B but not C, (5) A and C but not B, (6) B and C but not A, and (7) A, B, and C.

[0048] The adjective "any" means one, some, or all in any quantity indiscriminately.

[0049] The phrase "at least a portion" means "partially or entirely." "At least a portion of a stream" has the same composition as the stream from which it originates, with the same concentration of each species.

[0050] As used herein, "first," "second," "third," etc. are used to distinguish between multiple steps and / or features and do not indicate total number or relative position in time and / or space unless expressly stated as such.

[0051] The terms "depleted" or "lean" mean that the indicated component has a smaller mole percent concentration than the original stream from which it was formed. "Depleted" and "lean" do not mean that the stream is completely devoid of the indicated component.

[0052] The terms "rich" or "enriched" mean that the indicated component has a greater mole percent concentration than in the original stream from which it was formed.

[0053] "Downstream" and "upstream" refer to the intended direction of flow of the transferred process fluid. If the intended direction of flow of the process fluid is from a first device to a second device, the second device is downstream of the first device. In the case of recirculation flow, downstream and upstream refer to the first pass of the process fluid.

[0054] Although individual embodiments may be discussed herein, it should be understood that the present disclosure covers all combinations of the disclosed embodiments, including, but not limited to, combinations of different components, combinations of method steps, and system features. [Example]

[0055] An embodiment such as that shown in FIG. 1 was analyzed using commercially available Aspen™ process modeling software to compare the adaptive design with a non-adaptive design. FIG. 2 is a graphical representation of the concentration of hydrogen in the main flow stream 102, varying from 4% to 18% over the course of a day. All percentages are on a volumetric basis. FIG. 3 is a graphical representation of the flow rate of the hydrogen product stream 172 for the adaptive design compared to the non-adaptive design. FIG. 4 is a graphical representation of the flow rate of the feed stream 104 for the adaptive design compared to the non-adaptive design. FIG. 5 is a graphical representation of the power consumed by the inter-stage compressor 130 for the adaptive design compared to the non-adaptive design. In general, the power consumption of the adaptive design may be lower than the non-adaptive design, demonstrating that varying the hydrogen production rate over time minimizes the amount of methane slipping off the membrane and the need for recompression. For adaptive designs, the feed flow 104 can be controlled at 30-100% of maximum flow rate, up to 22% of the membrane modules can be in isolation, the interstage compressor 130 can be turned down to up to 40% capacity, the PSA can be turned down to up to 35% capacity, and the PSA cycle time can be controlled to maintain constant H recovery.

[0056] The adaptive design can also accommodate H2 concentrations in natural gas higher than the designed range if additional H2 production and demand increases H2 fusion. Generally, the existing skid may be capable of extracting the same amount of hydrogen per day. Even more can be extracted if sufficient adsorption capacity is provided to purify more H2. Generally, the number of membrane modules required for higher H2 fusion rates may be lower than the number of modules required for lower H2 fusion. Thus, with several modules sequestered at higher H2 concentrations, the existing skid may extract the same hydrogen per day using the same calculated control parameters at different set points.

[0057] The overall cost to extract H2 using an adaptive design may be reduced by at least 30%, at least 20%, or at least 10% compared to a non-adaptive design. In some embodiments, the total flow rate of first permeate stream 122 may be reduced using an adaptive design, thus reducing the total power required to compress first permeate stream 122. In at least some embodiments, the total number of membrane modules required to remove the same amount of hydrogen may be reduced with an adaptive design compared to a non-adaptive design.

[0058] While the principles of the present invention have been described above in connection with a preferred embodiment, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

Claims

1. It is a method, To measure the concentration of light gases in the main flow stream, Calculating the control parameters as a function of the concentration of the light gas in the main flow stream. To divide a portion of the aforementioned main flow stream and generate a feed stream, The feedstream is separated by selective permeation across the semipermeable membrane to generate a permeate stream enriched with the light gas and a residue depleted of the light gas, and This includes separating the aforementioned permeate stream with one or more adsorption units to generate light gas products, The ratio of the flow rate of the feedstream to the flow rate of the main flowstream increases or decreases according to the control parameter. The area of ​​the semipermeable membrane increases or decreases according to the control parameter. A method in which the number of adsorption units increases or decreases according to the control parameter.

2. The method according to claim 1, wherein the cycle time of the adsorption unit is increased or decreased according to the control parameter.

3. The method according to claim 1, further comprising storing at least a portion of the permeate or a stream arising from the permeate.

4. The method according to claim 1, wherein the semipermeable membrane comprises a plurality of modules, and the area of ​​the semipermeable membrane increases by connecting one or more of the plurality of modules to a feedflow and decreases by isolating one or more of the plurality of modules from the feedstream.

5. The method according to claim 1, wherein the control parameters are calculated so that the light gas product is produced at a constant flow rate over a period of 1 hour to 7 days.

6. The method according to claim 1, wherein the concentration of the light gas in the main flow stream fluctuates at a frequency of less than 24 hours.

7. It is a method, To measure the concentration of light gases in the main flow stream, Calculating the control parameters as a function of the concentration of the light gas in the main flow stream. To divide a portion of the main flow stream and generate a feedstream having a feed flow, The feedstream is separated by selective permeation across the first semipermeable membrane to generate a first permeate stream enriched with the light gas and a first residue depleted of the light gas. Compressing the first transparent stream to generate a compressed transparent stream, The compressed permeate stream is separated by selective permeation across the second semipermeable membrane to generate a second permeate stream enriched with the light gas and a second residue depleted of the light gas. Mixing the second residue with the feedstream, The second permeate stream is separated by a certain number of adsorption units to generate light gas products and an exhaust gas stream from which the light gas has been depleted, and This includes mixing the exhaust gas stream with the first permeate stream, The ratio of the flow rate of the feedstream to the flow rate of the main flowstream increases or decreases according to the control parameter. The area of ​​the first semipermeable membrane increases or decreases according to the control parameter. The first semipermeable membrane includes a plurality of modules, and the area of ​​the first semipermeable membrane increases by connecting one or more of the plurality of modules to the feedflow, and decreases by isolating one or more of the plurality of modules from the feedstream. The area of ​​the second semipermeable membrane increases or decreases according to the control parameter. A method in which the number of adsorption units increases or decreases according to the control parameter.

8. The method according to claim 7, wherein the control parameters are calculated so that the light gas product is produced at a constant flow rate over a period of 1 hour to 7 days.

9. The method according to claim 7, wherein the concentration of the light gas in the main flow stream fluctuates at a frequency of less than 24 hours.

10. It is a system, An analyzer, which is connected to the main flow stream and fluid flow, and is configured to measure the concentration of light gases. A control valve, which is in fluid flow communication with the main flow stream to generate a feedstream, A semipermeable membrane, which is in fluid flow communication with the feedstream and is configured to generate a permeate stream enriched with the light gas and a residue after the light gas has been depleted, A controller, which communicates with the analyzer and the semipermeable membrane via electrical signals, is configured to increase or decrease the area of ​​the semipermeable membrane according to control parameters calculated as a function of the concentration of the light gas. The system comprises one or more adsorption units, which are in fluid flow communication with the semipermeable membrane and configured to separate the permeate stream and generate light gas products and exhaust gas streams, A system in which the controller is configured to increase or decrease the number of adsorption units according to the control parameters.

11. The system according to claim 10, wherein the controller is configured to receive a signal from the analyzer and to calculate the control parameters as a function of the concentration of the light gas in the main flow stream.

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