MEMBRANE PERMEATE RECYCLING PROCESS FOR USE WITH PRESSURE OSCILLATION ADSORPTION PROCESSES.

Abstract

A process for treating a net gas stream is described. The process includes sending the net gas stream to a compressor to produce a compressed gas stream. The compressed gas stream is then sent to a pressure swing adsorption unit to produce a hydrogen product stream and a tail gas stream. The tail gas stream from the pressure swing adsorption unit is sent to a first membrane unit to produce a first permeate stream and a first non-permeate stream. A portion of the tail gas stream is sent to a second membrane unit to produce a second permeate stream and a second non-permeate stream.

Description

MEMBRANE PIERCING RECYCLING PROCESS FOR USE WITH PRESSURE OSCILLATION ADSORPTION PROCESSES Field of Invention The present description relates to a membrane permeation recycling process that uses hydrogen recovery units and pressure swing adsorption units. Background of the Invention Typically, a membrane separation process includes a feed conditioning section that conditions the membrane feed gas by removing unwanted liquids, solids, and contaminants, and then establishing the desired membrane operating temperature. Gas separation in the membrane separation process is achieved due to the difference in the relative permeation rates of hydrogen and other hydrocarbon components when a pressure differential is present or imposed between a feed side and a permeate side of a semipermeable membrane barrier. Typically, the membrane elements contain the semipermeable membrane barrier. Typically, membrane separation units contain at least two banks of membrane modules. The membrane module banks in the membrane separation section are arranged in parallel and connected by piping. Ref. 322356 common systems that typically distribute the membrane feed gas and collect the membrane-permeated and non-permeated gas streams. The non-permeated conditioning section contains an automatic control valve that maintains pressure on the membrane side and may contain additional equipment such as heat exchangers and inactivated drums to cool the gas and remove any condensate produced after cooling. For this reason, at least two membrane module banks are installed in each membrane unit so that a 25-100% reduction control of the nominal flow rate can be achieved by isolating the individual membrane module banks when the feed flow capacity is reduced and at the same time the stage cutoff control in the membrane module banks is in service. Consequently, an improved process is preferred, which would enhance the existing hydrogen recovery flow scheme associated with a catalytic reformer. There is a need to improve the membrane separation process to enhance permeate recycling from the gases, thereby reducing the operating and capital costs of the unit and the membrane separation process overall. Therefore, an improved pressure swing adsorption unit is required for refinery waste gas separation where high hydrogen and LPG recovery is desirable, and downstream consumers use the high-pressure product hydrogen in processing reactors such as hydroprocessing. Furthermore, a dynamic and robust separation process is required. Furthermore, other desirable features of the present material will become evident from the following detailed description of the material and the claims, taken in conjunction with the accompanying figures and this background information on the material. Brief Description of the Invention Several embodiments described herein relate to an enhanced permeate recycling process that includes a pressure swing adsorption unit and a membrane unit to which a membrane permeate stream is recycled to achieve maximum hydrogen recovery. According to one illustrative embodiment, a process is provided for treating a net gas stream comprising sending the net gas stream to a compressor to produce a compressed gas stream. The compressed net gas stream is then sent to a pressure swing adsorption unit to produce a hydrogen product stream and a tail gas stream. The tail gas stream is then sent to a first membrane unit to produce a first permeate stream and a first waste stream.A portion of the tail gas stream is also sent to a second membrane unit to produce a second permeate stream and a second waste stream. According to another illustrative embodiment, a process is provided for treating a net gas stream comprising sending the net gas stream to a compressor to produce a compressed gas stream, which is further passed to a pressure swing adsorption unit to recover hydrogen as a product stream along with a tail gas stream. The process further includes sending the recovered tail gas stream to a first membrane unit to produce a first permeate stream and a first non-permeate stream. The tail gas stream is then sent to a second membrane unit to produce a second permeate stream and a second non-permeate stream, and the flow of the tail gas stream to the first and second membrane units is then controlled. Accordingly, the present description outlines an improved permeate recycling process that reduces operating and capital expenditures, including control system requirements, to make the system fully flexible and adaptable to changes in system operation. The applicants have discovered that the present solution is achieved by adding a second membrane unit that operates at a lower pressure compared to the first membrane unit, thus reducing the overall size of the membrane unit required for the current flow scheme. Furthermore, the recycling of permeate gas from the second membrane unit to the pressure swing adsorption (PSA) unit is maintained at low pressure, thereby reducing the operating and capital costs of the recycling operation. Additionally, the low-pressure recycling of permeate from the second membrane unit provides purge gas that is sent to the PSA unit, resulting in increased hydrogen recovery from the PSA unit. Consequently, the current permeate recycling process provides a 10% reduction in operating expenses and a 7% reduction in capital costs. These and other features, aspects and advantages of the present invention will be better understood after considering the following detailed description, figures and accompanying claims. Brief Description of the Figures The various modalities will be described from now on in conjunction with the following figures, where similar numbers denote similar elements. Figure 1 is a schematic process flow diagram illustrating the membrane separation process of the prior art. Figure 2 is a schematic flow diagram of the process described herein, illustrating the improvement in the membrane permeate recycling process. Figure 3 illustrates a reduction in the power required to run the system described herein. Figure 4 illustrates the significant reduction in membrane area as required in the present description. Figure 5 is a schematic illustrating the details of the pipe arrangement as used in the present description where the two membrane units are integrated into a single membrane system. Detailed Description of the Invention Those skilled in the art will appreciate that the elements described in Figures 1-5 are illustrated for simplicity and clarity and are not necessarily drawn to scale. For example, the dimensions of some elements in Figures 1-5 may be exaggerated relative to other elements to aid in understanding the various embodiments of this description. Furthermore, common and well-understood elements that are useful or necessary in a commercially feasible embodiment may not be depicted to facilitate a less obstructed view of these various embodiments. Definitions As used in this description, the term current may include various hydrocarbon molecules and other substances. As used in the present description, the term rich may mean an amount of generally at least 50% or at least 70%, preferably 90%, and optimally 95%, in mol, of a compound or class of compounds in a stream. As used in the present description, the term fluid communication means that the material flowing between the listed components is in a fluid state and connects the two components. As used in the present description, the term permeate stream may mean the stream of product that is allowed to pass through the membranes. As used in the present description, the term non-permeate stream can mean the retentive stream that is not allowed to pass through the membranes and remains in the membrane. As used in the present description, the term membrane can mean a selective barrier, which allows some things to pass through it or permeate it, but stops others that remain as a retainer. As used in the present description, the term Cxen where x is an integer means a hydrocarbon stream with hydrocarbons having x carbon atoms. As used in the present description, the term Cx_ where x is an integer means a hydrocarbon stream with hydrocarbons having xy / or fewer carbon atoms and preferably xy fewer carbon atoms. As used in the present description, the term Cx+ where x is an integer means a hydrocarbon stream with hydrocarbons having xy / or more carbon atoms and preferably xy plus carbon atoms. As used in the present description, the term stage cut-off can be defined as the ratio of the permeate flow rate to the membrane feed gas flow rate to a specified value. As used in the present description, the term bank may refer to an array of each parallel membrane module that can be completely isolated from the rest of the process. As used in the present description, the term separator means a vessel having an inlet and at least one overflow vapor outlet and a bottom liquid outlet and may also have an aqueous stream outlet from a box. As used in this description, the term "portion" means an amount or part taken or separated from a main stream without any change in composition compared to the main stream. It also includes dividing the taken or separated portion into multiple portions, where each portion retains the same composition compared to the main stream. The following detailed description is merely illustrative in nature and is not intended to limit the various embodiments or their applications and uses. Furthermore, there is no intention to be restricted by any theory presented in the preceding background or in the following detailed description. The figures have been simplified by the removal of many apparatus commonly used in a process of this nature, such as internal vessel components, temperature and pressure control systems, flow control valves, recirculation pumps, etc., which are not specifically required to illustrate the performance of the invention. Moreover, the illustration of the process of this invention in a specific embodiment is not intended to limit the invention to the specific embodiments set forth herein. As depicted, the process flow lines in the figures may be referred to interchangeably as, e.g., lines, pipes, branches, distributors, streams, effluents, feeds, products, portions, catalysts, withdrawals, recycles, suctions, discharges, and caustics. This description provides an efficient method for recycling hydrogen within the process, achieved by operating some of the tail gas membrane cartridges at a lower permeate pressure and using this permeate as external purge gas in the PSA unit. This results in a significant reduction in the total installed membrane area and a significant reduction in compression power. One mode of membrane permeate recycling process is discussed and illustrated in Figure 1. The flow diagram in Figure 1 shows a net gas compression and hydrocarbon recovery system 20 to which a net gas stream 10, containing primarily hydrogen-rich gas, is fed. The liquids produced after compression and recovery are collected as a heavy hydrocarbon stream in line 24, and the compressed gas in line 22, containing hydrogen and light hydrocarbons, is fed to a high-pressure PSA unit 30. The PSA unit 30 supplies the hydrogen-rich gas stream in line 32 to a first-stage compressor 40 for further compression, and the hydrogen-rich gas stream is recovered in line 42. The first-stage compressor 40 compresses the hydrogen-rich gas stream from a pressure typically between 250 and 400 psia to 600 and 900 psia. The first-stage compressor unit 40 supplies the recovered hydrogen 42 at high purity (>99.9 mol%) which requires further compression. Unrecovered hydrocarbon and hydrogen impurities are recovered as PSA tail gas in line 34, which is compressed in a PSA tail gas compressor 50. The compressed tail gas stream in line 52 is sent to a first membrane unit 60 to produce a first permeate stream in line 62, which is sent to a dryer 70. The dry gas in line 72 is recycled and blended with the net gas feed stream in line 10. The dryer 70 may include adsorbents to remove moisture (H2O) from the PSA tail gas stream in line 62. The first permeate-free stream in line 64 of the first membrane unit 60 can be combined with other streams from a catalytic reforming unit. The reactor effluent in line 110 (from the reactor, not shown) is injected into a separator unit 80 to produce a separator liquid in line 82. The separator effluent stream in line 82 is mixed with a waste gas stream from the hydroprocessing extractor (supplied from an external source) via line 120, and the first permeate-free stream in line 64 forms a mixed effluent stream in line 84. The mixed effluent stream in line 84 is then fully supplied to an absorber unit 90 installed downstream of the first membrane unit.Absorber 90 produces a fuel gas stream taken from the top of the absorber in line 92 and a heavy hydrocarbon stream in the lower line 94. The heavy hydrocarbon stream in line 94 can be further treated in a depentanizer or debutanizer of the catalytic reforming unit, to separate the pentanes and butanes, respectively. The lower heavy hydrocarbon stream can be further combined with another heavier hydrocarbon stream supplied in line 24 and recovered as an effluent from the net gas compressor and hydrocarbon recovery system 20, forming a mixed stream of heavy hydrocarbon products in line 96. The reactor effluent stream in line 110 is recovered as a catalytic reforming effluent stream comprising materials in the range of hydrogen, light hydrocarbons (C1 to C4), light naphtha (C5 to C6), and heavy naphtha (C6 to C11). Accordingly, the reforming effluent stream in line 110 can be passed to separator 80. In separator 80, the vapors can be separated to provide a reforming vapor stream (not shown) and a reforming liquid stream in line 82. With reference now to Figure 2, a modality for improved and efficient hydrogen recovery from the membrane permeate recycling process is shown. The flow scheme as shown in Figure 2 provides the benefit of recycling a portion of the pressure swing adsorption (PSA) tail gas at low pressure, thereby avoiding costly recompression and reducing the size of the recycling compressor. Figure 2 shows the flow scheme of the present invention with a net gas stream 10 containing primarily hydrogen-rich gas (main hydrogen and remaining hydrocarbons) from a catalytic reforming unit sent to a net gas compressor and hydrocarbon recovery system 20. The liquids produced after compression and recovery are collected as a heavy hydrocarbon stream in line 24. The compressed gas in line 22, containing hydrogen and light hydrocarbons, then passes to a first-stage compressor 30, with an additional compressed stream in line 32 sent to a high-pressure PSA unit 40. However, an alternative flow scheme (not shown here) could utilize a lower-pressure PSA 40 unit that would directly pass the compressed gas in line 22 to the PSA 40 unit without requiring a first-stage compressor 30. Furthermore, the compression system 30 compresses the gas in line 22 to a pressure typically ranging from 250–400 psia to 600–900 psia. The PSA 40 unit supplies the recovered hydrogen 42 at high purity (>99.9 mol%) to the consumer. Unrecovered hydrogen and hydrocarbon impurities collectively form the PSA tail gas stream in line 44, which is further compressed using a PSA tail gas compressor 50, and a recovered compressed tail gas stream in line 52 is further passed to a dryer unit 60. Compressor 50 compresses the PSA tail gas in line 44 to a pressure that typically ranges from 15-25 psia to 250-350 psia. A first portion of the dry gas in line 62 is taken in line 66 and directed to a first membrane unit 70 to produce a first permeate stream in line 72, which is recycled and mixed with the net gas feed stream injected in line 10. A second portion of the dry gas in line 62 is taken in line 64 and sent as a feed gas to a second membrane unit 80 to produce a second permeate stream in line 82, which is recycled to the PSA unit 40. In one aspect of the present description, the dryer unit 60 may also include a separator filled with adsorbents to remove moisture (H2O) from the PSA tail gas stream. The first non-permeate stream recovered as effluent in line 74 of the first membrane unit 70 and the second non-permeate stream recovered as effluent in line 84 of the second membrane unit 80 are combined and mixed with other streams from the catalytic reforming unit (not shown here). The incoming reactor effluent in line 110 is injected into a separator unit 90, thereby producing a separator liquid stream in line 92. The separator liquid stream 92 is further mixed with the hydroprocessing exhaust gas stream injected by an external source in line 120 and combined with the first non-permeate stream 74 and the second non-permeate streams in line 84 to form a combined effluent stream 94 that goes to the absorber unit 100.Absorber unit 100 produces a fuel gas stream recovered from the top of the absorber in line 102 and a heavier hydrocarbon stream recovered from the bottom of the absorber through line 104. The lower heavy hydrocarbon stream 104 can be further treated in a depentanizer or debutanizer unit of a catalytic reforming unit. Additionally, the lower heavy hydrocarbon stream recovered in line 104 can be blended with the heavier hydrocarbon stream flowing in line 24 and recovered as effluent from the net gas compressor and hydrocarbon recovery system 20. The resulting blended stream flows in line 106.The reactor effluent stream in line 110 is recovered as a catalytic reforming effluent stream comprising materials in the range of hydrogen, light hydrocarbons (from C4 to C4), light naphtha (C5 to Cg) and heavy naphtha (Cg to Cu). As an alternative feature, part or all of the fuel gas stream in line 102 can also be recycled to the net gas compressor and hydrocarbon recovery system 20 to recover hydrogen from the fuel gas stream (C2-). In one aspect of the present invention, the net gas compressor and hydrocarbon recovery system 20 may include a separator in fluid communication with the compressor to separate any liquid present and to pass the vapor or gas portion of the stream to the next process stage or compression stage. Additionally, coolers may also be included for cooling. Furthermore, the compressor may have a maximum of two stages. The membrane feed pretreatment section commonly comprises a feed dryer, a feed filter, or a feed coalescer or drum separator and feed flow meter with pressure and temperature compensation.A feed heater is installed in the membrane pretreatment section to condition the temperature of the membrane feed gas to a constant value. Furthermore, gas separation in the membrane separation unit occurs due to differences in the relative permeation rates of hydrogen and other hydrocarbon components when a pressure differential is imposed between the feed and permeate sides of a semipermeable membrane barrier. This semipermeable membrane barrier is contained within the membrane elements. It performs the separation and is typically, though not exclusively, made of a material selected from the cellulose acetate, polyimide, or polysulfone group, etc., which exhibits selectivity between permeable molecules such as hydrogen and less permeable molecules such as hydrocarbons. In the improved flow scheme, as shown in Figure 2, the PSA tail gas portion is sent to a separate membrane unit instead of the single membrane unit used in the schemes shown in Figure 1. This membrane unit operates with a lower permeate flow extraction rate and a lower permeate pressure (20 psig) compared to the primary tail gas membrane (85 psig permeate pressure). Due to the lower permeate pressure, the driving force for permeation is greater. The reduced permeate pressure increases the membrane feed-to-permeate-pressure ratio. Reducing the permeate pressure from 85 psig (100 psia) to 20 psig (35 psia) increases this ratio by a factor of nearly 3 and reduces the required membrane area by a factor of 3. Because the cost of membrane systems is proportional to the installed membrane area, this results in a significant cost reduction. A further reduction in the required membrane area comes from the removal of the permafluorescence flow. The permafluorescence from the smaller membrane is recycled directly to the PSA unit instead of through the PSA feed recontact and pressure compression sections and is no longer used as PSA feed gas, but rather as PSA blowdown gas. The hydrogen purity of this blowdown gas is high (97 mol% or higher), whereas the recycled permafluorescence from the main tail gas membrane has a lower hydrogen purity (67 mol%). Using the recycled hydrogen as blowdown gas in the PSA unit allows for greater hydrogen recovery in the PSA process, since the amount of blowdown gas normally used for internal purging can now be used for pressure equalization during concurrent depressurization through further optimization of the PSA cycle equalization stages.Reducing the recycle flow rate slightly improves the quality of the PSA feed gas, which also has a beneficial effect on the PSA unit's recovery and the required absorber bed volume, and in turn, both of these have a positive impact on the cost of the PSA unit. The flow scheme in Figure 2 with two membrane units can be made highly flexible, as the allocation of PSA tail gas flow rates to each of the two membranes can be optimized for any given case and is determined by the process operating conditions (pressure) and the desired total hydrogen recovery. In this refinery example, 77% of the PSA tail gas passes to the smaller membrane, which generates the recycle blowdown gas. In an illustrative manner, the relative energy requirements of the two systems are shown. Figure 3 illustrates the relative difference in power required by the prior art system and the system described herein. The readings shown by the upper line represent the power required to operate the process as illustrated in Figure 1 of the prior art, and the readings shown by the lower line represent the power required to carry out the process described herein by the applicants. Furthermore, a comparison of the improved scheme with that of the prior art system is shown in Figure 3 over a range of hydrogen recoveries. The results show a consistent operational benefit of approximately 10% less compression power. An important aspect of this invention relates to the operating pressure of the PSA unit.It was discovered that the benefit of using an external purge gas in the PSA cycle is greater for higher pressure ratios (feed pressure to purge pressure) in the PSA unit. PSA units operating at higher pressures can perform additional pressure equalization stages that increase hydrogen recovery. Furthermore, as indicated in the present invention, a PSA pressure ratio of 37 was used to maximize the efficiency of the external purge. This PSA pressure ratio is determined based on the ratio of feed gas pressure to tail gas pressure, i.e., 815 psia / 22 psia. To achieve this high PSA pressure ratio, the PSA feed gas is compressed, and a high-pressure cycle is used to generate product hydrogen for downstream high-pressure consumers (e.g., hydrocracker). With reference to Figure 4 below, the total membrane area previously required is shown by the upper line and the total membrane area now required by the present description is shown by the lower line, with a reduction of the total membrane area from 1.4X to 5X times in a hydrogen recovery range of 96.5% to 98.5%, respectively. Figure 5 shows the piping details of the permeate section of a system that combines the first membrane unit 70 and the second membrane unit 80 into an integrated membrane unit that meets the requirements of the flow scheme in Figure 2 of this invention. Figure 5 also shows three membrane module banks 220, 230, and 240, each containing individual membrane modules 222, 232, and 242. Each membrane module bank can be isolated from the membrane permeate headers by bank isolation valves 226 and 228, 236 and 238, and 246 and 248. Within the membrane module banks 220, 230, and 240, lines 224, 234, and 244 connect the membrane modules, which are installed in parallel. Segregation valves 252 and 254 are in the open position, connecting banks 230 and 240 to stage 1.Segregation valves 250 and 260 are in the closed position, separating bank 220 from the other banks 230 and 240 and thus constituting stage 2. The first membrane unit, operating at high permeate pressure, is in stage 1, and the second membrane unit, operating at low permeate pressure, is in stage 2. The permeate product 270 from stage 1 and the permeate product 268 from stage 2 are withdrawn at opposite ends of the permeate header. Control valve 256 regulates the pressure in stage 2 in the permeate line 268, while control valve 258 regulates the lower pressure in stage 1 in the permeate line 270. An additional feature of the present invention is the integrated membrane units and the control of the integrated membrane units in a single unit that has two membrane separation sections operating at different permeate pressures. The integrated membrane unit of the present invention has at least two banks of membrane modules for the high permeate pressure section (stage 1) and at least two banks of membrane modules for the low permeate pressure section (stage 2). The banks can be the same size or different sizes, depending on the process requirements. The integrated membrane unit has a common feed section and no common permeate section, while the permeate section is divided into two. The piping of the integrated membrane system has two distinct permeate destinations that are integrated into a common assembly. Since there are two permeate connections at different pressure levels, both permeate streams are drawn from opposite ends of the main permeate manifold. For this purpose, one or more automatic segregation valves are installed in the permeate header. The valve(s) segregate the different membrane banks that make up the Stage 1 and Stage 2 membrane units, while simultaneously allowing each stage to operate at its own permeate pressure level. The invention assumes that each membrane stage has at least two banks, meaning that the smallest configuration of the integrated system would have at least four banks of membrane modules. In such a smaller configuration, at least one segregation valve must be installed to separate the two membrane sections. For larger membrane systems, where stage 1 and / or stage 2 are configured to have more than two banks of modules, additional segregation valves can be installed. This configuration adds flexibility to the system. In the most flexible configuration, with Nh banks belonging to stage 1 and NL banks belonging to stage 2, a total of NH+ NL- 1 segregation valves can be installed. One of these valves would be in a fully closed position, while the others are in an open position. This configuration allows for high system flexibility in changing the flow ratio between the gas used as recycle gas to the PSA feed inlet (from Stage 1 at high permeate pressure) and the gas recycled to the PSA to provide a purge inlet (from Stage 2 at low permeate pressure). Depending on the required split of external PP or recycle gas, the position of the control valves can be modified to change the number of membrane module banks belonging to Stage 1 or Stage 2. One valve will be closed, segregating Stage 1 from Stage 2, while the other valves will be open. The banks connected to the high-pressure side of the closed segregation valve constitute Stage 1, while the banks connected to the low-pressure side of the closed segregation valve constitute Stage 2.To change the ratio of membrane feed gas flowing to stage 1 and stage 2, and therefore the ratio of external PP or recycle gas, the individual stage cutoff controllers of each stage can be used. For larger changes, it may be necessary to change the allocation of a bank of membrane modules from stage 1 to stage 2, or vice versa. To allow such changes without shutting down the membrane system, positioners are installed on the automatic segregation valves to allow slow opening and prevent pressure shock waves between the high and low permeate pressure sides. When reconfiguring a bank from one stage to another, manipulating the segregation valves on each side of the bank will enable the configuration change. To change the bank from stage 1 (high pressure) to stage 2 (low pressure), the open segregation valve connecting the bank to stage 1 is closed first, and then the closed segregation valve connecting to stage 2 is opened incrementally. To change the bank from stage 2 (low pressure) to stage 1 (high pressure), the open segregation valve connecting the bank to stage 2 is closed first, and then the closed segregation valve connecting to stage 1 is opened incrementally.The control system will maintain high feed pressure and non-permeable pressures and will control stage cutoff of both stage 1 and stage 2 by modifying the pressure on their respective permeable sides. Based on the specific properties of the two membrane sections (installed area), the control system can calculate how much gas will go to each bank from a single flow measurement and the amount of membrane area installed in stage 1 and stage 2. It can then use this information to control the stage cutoff from a single feed flow measurement instead of two. This is a benefit of the membrane assembly design, not only because of the reduced cost due to fewer instruments, but also because the assembly requires less straight piping for flow measurements. However, if both membrane sections operate at the same temperature, the feed heater that maintains the membrane's operating temperature can be common, with a common temperature control loop and temperature control valve. If both stages operate at different temperatures, a common feed heater can still be used, but separate membrane feed temperature control loops and corresponding control valves would be required for both separation stages, or an additional (smaller) heat exchanger could be used for the higher of the operating temperatures.In addition, when both stages operate at different temperatures, segregation valves can also be added to the feed headers to direct feed gas of different temperatures to the separation sections of stage 1 and stage 2, when both ends of the feed header receive feed gas at different temperatures. Savings in operating costs are achieved through lower energy requirements, as well as a significant reduction in the size of membrane units while maintaining at least the same or higher hydrogen production. More specifically, the present description achieves the same hydrogen and LPG recovery while reducing operating costs by approximately 10% and capital costs by approximately 7%. The reduction in operating costs is due to the lower net gas compression requirement of the catalytic reforming unit (reduced recycle flow from the larger membrane) and the reduced compression of PSA tail gas (higher PSA recovery and reduced PSA feed gas flow). The lower capital costs result from the smaller total membrane area installed and the lower cost of the compression equipment. It should be appreciated and understood by those skilled in the art that many other components such as valves, pumps, filters, coolers, etc. were not shown in the figures because it is believed that their details are well known to those skilled in the art and a description of them is not necessary to implement or understand the modalities of the present invention. Specific modalities Although the following is described in conjunction with specific modalities, it shall be understood that this description is intended to illustrate and not limit the scope of the foregoing description and appended claims. A first embodiment of the invention is a process for treating a net gas stream comprising sending the net gas stream to a compressor to produce a compressed gas stream; sending the compressed gas stream to a pressure swing adsorption unit to produce a hydrogen product stream and a tail gas stream; sending the tail gas stream to a first membrane unit to produce a first permeate stream and a first non-permeate stream; and sending a portion of the tail gas stream to a second membrane unit to produce a second permeate stream and a second non-permeate stream. An embodiment of the invention is any one or all of the embodiments in this paragraph up to and including the first embodiment in this paragraph, further comprising compressing the tail gas stream before sending the tail gas stream to the first and second membrane units.One embodiment of the invention is any one or all of the embodiments in this paragraph up to and including the first embodiment in this paragraph, wherein the first permeate-free stream and the second permeate-free stream are sent to an absorber unit to produce a fuel gas stream and a 63+ stream. Another embodiment of the invention is any one or all of the embodiments in this paragraph up to and including the first embodiment in this paragraph, further comprising a control system for controlling the flow of the tail gas stream to the first membrane unit and the second membrane unit. Another embodiment of the invention is any one or all of the embodiments in this paragraph up to and including the first embodiment in this paragraph, wherein the second permeate stream from the second membrane unit is recycled to the pressure swing adsorption unit as purge gas.One embodiment of the invention is any one or all of the embodiments in this paragraph up to and including the first embodiment in this paragraph, wherein the first membrane unit and the second membrane unit operate at the same temperature. Another embodiment of the invention is any one or all of the embodiments in this paragraph up to and including the first embodiment in this paragraph, wherein the first membrane unit and the second membrane unit operate at different temperatures. A further embodiment of the invention is any one or all of the embodiments in this paragraph up to and including the first embodiment in this paragraph, wherein the control system controls the permeate pressure of the first membrane unit and the second membrane unit by controlling the ratio of the permeate flow rate to the membrane feed flow rate for the first membrane unit and the second membrane unit.One embodiment of the invention is any one or all of the embodiments in this paragraph up to and including the first embodiment in this paragraph, wherein the control system measures a quantity of gas flow to each membrane bank within each of the first and second membrane units. Another embodiment of the invention is any one or all of the embodiments in this paragraph up to and including the first embodiment in this paragraph, wherein the control system is combined with the control system for the pressure swing adsorption unit. A further embodiment of the invention is any one or all of the embodiments in this paragraph up to and including the first embodiment in this paragraph, wherein the control system for the membrane units is separate from a control unit for the pressure swing adsorption unit.One embodiment of the invention is any one or all of the embodiments described in this paragraph up to and including the first embodiment herein, wherein the control system combines the measurement of the gas flow rate to a single valve to control the amount of gas delivered to the second membrane unit. Another embodiment of the invention is any one or all of the embodiments described in this paragraph up to and including the first embodiment herein, which combines the first membrane unit and the second membrane unit, further comprising segregation valves with positioners to allow slow opening of the valves, thus preventing pressure shock waves. A third embodiment of the invention is any one or all of the embodiments described in this paragraph up to and including the first embodiment herein, wherein at least one bank of the membrane units is at a lower pressure than at least one other bank of the membrane units.One embodiment of the invention is any one or all of the embodiments in this paragraph up to and including the first embodiment in this paragraph, wherein the first membrane unit and the second membrane unit each comprise at least two banks. Another embodiment of the invention is any one or all of the embodiments in this paragraph up to and including the first embodiment in this paragraph, wherein the first membrane unit and the second membrane unit each comprise a different membrane polymer. A further embodiment of the invention is any one or all of the embodiments in this paragraph up to and including the first embodiment in this paragraph, wherein the pressure swing adsorption unit comprises a protective adsorbent layer at one end of a hydrogen product adsorbent bed for removing impurities from the second membrane permeate stream.An embodiment of the invention is any one or all of the embodiments in this paragraph up to and including the first embodiment in this paragraph, further comprising at least one of detecting at least one process parameter and generating a signal or data from the detection; generating and transmitting a signal; or generating and transmitting data. A second embodiment of the invention is a process for treating a net gas stream comprising sending the net gas stream to a compressor to produce a compressed gas stream; sending the compressed gas stream to a pressure swing adsorption unit to produce a hydrogen product stream and a tail gas stream; sending the tail gas stream to a first membrane unit to produce a first permeate stream and a first non-permeate stream; sending a portion of the tail gas stream to a second membrane unit to produce a second permeate stream and a second non-permeate stream; and controlling a flow of the tail gas stream to the first membrane unit and the second membrane unit.One embodiment of the invention is any one or all of the embodiments in this paragraph up to and including the second embodiment in this paragraph, further comprising a control system that controls the permeate pressure of the first membrane unit and the second membrane unit by controlling a ratio of the permeate flow to the membrane feed flow for the first membrane unit and the second membrane unit. Without further details, it is believed that, by using the foregoing description, a person skilled in the art can use the present invention to its fullest extent and readily determine its essential features, without departing from its spirit and scope, to make various changes and modifications to the invention and adapt it to various uses and conditions. The specific preferred embodiments mentioned above should therefore be considered merely illustrative and not limiting the remainder of the description in any way, and are intended to encompass various equivalent modifications and arrangements included within the scope of the appended claims. In the above, all temperatures are stated in degrees Celsius and all parts and percentages are by weight, unless otherwise stated. It is hereby stated that, as of this date, the best method known to the applicant for putting the aforementioned invention into practice is the one that is clear from the present description of the invention.

Claims

1. A process for treating a net gas stream, characterized in that it comprises: sending the net gas stream to a compressor to produce a compressed gas stream; sending the compressed gas stream to a pressure swing adsorption unit to produce a hydrogen product stream and a tail gas stream; sending the tail gas stream to a first membrane unit to produce a first permeate stream and a first non-permeate stream; and sending a portion of the tail gas stream to a second membrane unit to produce a second permeate stream and a second non-permeate stream.

2. The process conforming to claim 1, characterized in that it further comprises compressing the tail gas stream before sending the tail gas stream to the first and second membrane units.

3. The process according to claim 1, characterized in that the first permeate-free stream and the second permeate-free stream are sent to an absorber unit to produce a combustible gas stream and a C3+ stream.

4. The process according to claim 1, characterized in that it further comprises a control system for controlling the flow of the tail gas stream to the first membrane unit and the second membrane unit.

5. The process according to claim 1, characterized in that the second permeate stream from the second membrane unit is recycled to the pressure swing adsorption unit as purge gas.

6. The process according to claim 4, characterized in that the control system controls the permeate pressure of the first membrane unit and the second membrane unit by controlling a ratio of the permeate flow to the membrane feed flow for the first membrane unit and the second membrane unit.

7. The process according to claim 1, characterized in that it combines the first membrane unit and the second membrane unit further comprises segregation valves with positioners to allow slow opening of the valves, avoiding pressure shock waves.

8. The process according to claim 1, characterized in that at least one bank of membrane units is at a lower pressure than at least one bank of membrane units.

9. The process according to claim 1, characterized in that the pressure swing adsorption unit comprises a protective adsorbent layer at one hydrogen product end of an adsorbent bed for removing impurities from the second membrane permeate stream.

10. A process for treating a net gas stream characterized in that it comprises: sending the net gas stream to a compressor to produce a compressed gas stream; sending the compressed gas stream to a pressure swing adsorption unit to produce a hydrogen product stream and a tail gas stream; sending the tail gas stream to a first membrane unit to produce a first permeate stream and a first non-permeate stream; sending a portion of the tail gas stream to a second membrane unit to produce a second permeate stream and a second non-permeate stream; and controlling a flow of the tail gas stream to the first membrane unit and the second membrane unit.