WO2009088971A1

WO2009088971A1 - Steam reforming with separation of psa tail gases

Info

Publication number: WO2009088971A1
Application number: PCT/US2009/000022
Authority: WO
Inventors: Jonathan Jay Feinstein; Michael P. Ralston
Original assignee: Tribute Creations LLC
Current assignee: Tribute Creations LLC
Priority date: 2008-01-04
Filing date: 2009-01-05
Publication date: 2009-07-16
Anticipated expiration: 2010-07-04

Abstract

Steam and a hydrocarbon feedstock are reformed in a combustion heated reformer in a manner in which the energy content of the PSA tail gas downstream exceeds the heating requirements of the reformer. The syngas is separated in one or more PSA units into at least a high purity hydrogen stream, at least one process gas recycle stream containing tail gas energy units exceeding the energy units required for heating the reformer, and a burner stream containing the balance of the PSA inlet gases and preferably containing no more energy units than are required for heating the reformer. The recycle streams are recycled as process gas to the reformer, the PSA or both, and the burner stream is used for heating the reformer.

Description

STEAM REFORMING WITH SEPARATION OF PSA TAIL GASES

Cross-Reference to Related Application

This application claims the benefit under 35 USC 1 19 of U.S. Provisional Patent Application Serial No. 61/009,983 filed January 4, 2008, the entire disclosure of which is incorporated herein by reference.

Field of Invention

The present invention relates generally to the field of gas separation.

Background Information

A "PSA unit" as used herein shall mean a pressure swing adsorption bed or group of beds working in parallel such that high and low pressure effluent flows from each of the parallel beds in the PSA unit to the next process unit or use point. Process gases may flow symmetrically back and fourth between multiple beds of a PSA unit without exiting the PSA unit. Multiple PSA units or the like shall describe the use of more than one bed or groups of beds such that a given high or low pressure effluent stream from one bed or group of beds subsequently passes unilaterally to a second bed or group of beds.

All references to percentages of gas content herein refer to volume percentages.

A steam-to-carbon ratio or S/C ratio is defined herein as the ratio of water molecules in the steam to the carbon atoms in the hydrocarbon feedstock of the steam and hydrocarbon mixture that are reformed in a reformer.

Unrecovered H₂ is defined herein as all H₂ exiting a PSA unit not contained in the product or high purity H₂ stream.

High purity H₂ is defined herein as gas containing at least 90% H₂ and preferably at least 99% H₂.

Steam methane reforming (SMR) processes are used to produce hydrogen, or a mixture of at least H₂ and CO, referred to herein as syngas, by combining steam and a hydrocarbon such as methane at temperatures of up to about 860° C and pressures generally in excess of 10 bar to form hydrogen and syngas according to the reactions

1) CH₄ + H₂O = 3H₂ + CO and 2) CH₄ + 2H₂O = 4H₂ + CO₂.

Although no more than 2 moles of steam per mole of carbon (S/C) in the hydrocarbon are required stoichiometrically, S/C ratios in excess of stoichiometric steam requirements are typically used in this process, consuming additional energy to generate steam. Energy cannot be recovered effectively from the unreacted steam because the steam exits the reformer in dilute form mixed with other gas species, substantially lowering the temperature at which it condenses to a temperature below the range for useful heat sources for the SMR process. It would be desirable to operate the SMR process at a lower S/C ratio in such a way that the energy to generate steam could be economically reduced.

Conventional SMR operation is typically at S/C ratios of about 2.2 to 1 or higher because of limitations of the reforming catalyst. At high heat fluxes into the reforming tubes and at lower S/C ratios the catalyst tends to form coke, fouling the process. The use of new catalytic reactor designs, however, makes it possible to operate the reformer at S/C ratios of less than 2.8 to 1 without coking. This in turn creates a new need for a way of utilizing significantly higher PSA tail gas energy content so that the energy savings associated with reducing the amount of steam supplied to the reforming process can be monetized.

At lower ratios of S/C the amount of unreacted steam, referred to herein as steam slip, in the gas exiting the reformer decreases, but the amount of unreacted methane, referred to herein as methane slip, increases. Gases exiting the reformer are typically cooled and passed through a water gas shift reactor to further promote the reaction

3) H₂O + CO = H₂ + CO₂ at temperatures of 200° to 400° C. A large portion of the unreacted steam is then removed by cooling the syngas and passing it through a liquid phase water separator. The resulting syngas is often next separated by a PSA unit into a high purity hydrogen stream and a tail gas stream of the remaining species of CO₂, CH₄, CO, unrecovered H₂, some H₂O, and contaminants such as N₂ or Ar.

Tail gas containing a limited amount of methane slip can be utilized as fuel for the burners in the reformer. SMR operation at S/C ratios of less than 2.8, referred to herein as steam lean reforming, causes greater methane slip to exit the reformer and water gas shift reactor than at higher S/C ratios in which the methane slip can be fully utilized as a fuel for the burners in the reformer. At S/C ratios less than about 2.8 to 1 and particularly below 2 to 1 , the increased methane slip causes the combustion energy content of the tail gas to exceed the heating requirements of the burners in the reformer.

Other methods, collectively referred to herein as parallel reforming, consist of a first stream of a hydrocarbon and steam being heated and reformed in a combustion heated first reformer and a second stream of a hydrocarbon and steam being heated and reformed with heat from the outlet reformed gas or from the flue gas from the first reformer. Because parallel reforming reforms more hydrocarbon and steam for a given amount of combustion heat compared to practices in which all of the hydrocarbon and steam are heated and reformed in a combustion heated reformer, the energy content of the resulting downstream PSA tail gas for parallel reforming is increased and may be in excess of the heat required by the combustion heated reformer.

The gas energy content of the PSA tail gas downstream of parallel reforming or steam lean reforming which is in excess of the combustion heated reformer requirements could be used to generate steam export from the SMR plant, but in many situations the steam may not be needed. If used in a gas turbine for driving compressors, the excess energy units may or may not be competitive to the alternative use of an electric motor. Further, the tail gas may contain sufficient quantities of CO, CO₂, and/or H₂ as to prohibit its use as an export fuel, gas turbine fuel or in other applications. It may therefore be necessary to consume all of the tail gas energy within the SMR plant to monetize the energy savings that result from lowering the amount of fuel needed for combustion heating of the reformer in lean steam or parallel reforming practices.

Wet scrubbing by physical or chemical absorption OfCO₂ into an amine or carbonate solution to extract CO₂ from syngas is known. Use of wet scrubbing in combination with PSA is known to enable co-production of H₂ and CO₂.

US Patent 5,669,960, incorporated herein by reference in its entirety, teaches the use of a single PSA unit to separate syngas from an SMR reformer and water gas shift unit into a high purity hydrogen stream, a combustible-rich tail gas stream, and a third stream that is combustible-lean and carbon dioxide-rich. The purpose is to concentrate the energy content of the tail gas into a smaller volume of gas. This in turn permits the use of this tail gas as a burner fuel which produces a stable flame or as a recycled feedstock to the reformer. With regard to using the tail gas as fuel for the burners in the reformer, the prior art solves a problem related to conventional SMR reforming in which the tail gas may have insufficient combustion energy content to support a stable flame. It does not anticipate the existence of a PSA tail gas that has energy concentration suitable for stable flames and energy content in excess of that required for burner fuel, its need for treatment, or a method for its treatment. With regard to using the combustible-rich stream as recycled feedstock to the reformer, known techniques do provide a method for expelling carbon units, but is significantly ineffective in providing feedstock for further reforming reaction. As taught, the combustible-rich stream contains CH₄ and the unrecovered H₂ in the PSA unit. Because reforming reactions 1 and 2 are thermodynamically reversed in accordance with the third and fourth powers of the H₂ partial pressure, respectively, use of gas containing the proportions of H₂ taught or implied in the prior art is relatively ineffective for the promotion of reactions I and 2 in the forward direction. The H₂ units recycled to the reformer along with the recycled CH₄ would prevent the CH₄ from effectively reacting, while burdening the reformer with additional pressure drop and heating requirements. To separate the CH₄ from the unrecovered H₂ requires methods not disclosed or implied in prior art, for the purpose of reacting the recycled CH₄ more completely. Neither the concept nor the advantage of recirculating CH₄ to the feed gas stream to the reformer while selectively preventing the recirculation of product H₂ to the reformer of a plant producing and recovering H₂ are disclosed, taught or suggested in prior art.

US Patent 6,500,241 , incorporated herein by reference in its entirety, teaches co- production of H₂ and CO₂ from syngas evolved from a reformer or partial oxidation unit followed by a water gas shift reactor. In one embodiment taught in US Patent 6,500,241 (see column 3, lines 19-42 thereof) a wet scrubbing unit is used in combination with a H₂ PSA unit and a liquefaction unit. In another embodiment (see column 5, lines 39-51 thereof) the patent teaches the use of a CO₂ PSA unit, a H₂ PSA unit, and a liquefaction unit. The recycling of an intermediate stream to the H₂ PSA for increased H₂ yield is taught. Use of either of the disclosed combinations of three separation process units requires substantially more capital equipment investment.

Summary of the Invention

It is an object of the present invention to provide a SMR process wherein the fuel requirements for reforming are less than the energy content of the downstream PSA tail gas and wherein the energy contained in the PSA tail gas is effectively and economically utilized.

It is another object of the present invention to produce more hydrogen product from a given molar volume of steam and methane reactants entering an SMR reactor.

It is still another object of the present invention to reduce the amount of separation equipment used to separate CO₂ for export into a useful product, or for sequestration from the atmosphere.

It is yet a further object of the present claimed invention to reduce the thermal mass of flue gas from the reformer.

Other benefits will become apparent from the disclosure to one of ordinary skill in the art.

Steam and a hydrocarbon feedstock are reformed in a combustion heated reformer in such a way that the fuel requirements for reforming are less than the energy content of the downstream PSA tail gas, preferably by employing at least one of reformer at a S/C ratio of less than 2.8 and more prefereably less than 2 to 1 or by employing parallel reforming. The syngas is separated in one or more PSA units into at least a stream containing high purity hydrogen, at least one process gas recycle stream containing tail gas energy units which together with the burner stream exceed the energy units required for heating the reformer, and a burner stream containing the balance of the PSA inlet gases and preferably containing no more energy units than are required for heating the reformer. The recycle streams are recycled as process gas to the reformer, the PSA, or both, and the burner stream is used for heating the reformer.

Brief Description of Drawings

FIG. 1 is a schematic representation of the present invention according to a first embodiment.

FIG. 2 is a schematic representation of the present invention according to a second embodiment. FIG. 3 is a schematic representation of the present invention according to a third embodiment.

FIG. 4 is a schematic representation of the present invention according to a preferred fourth embodiment.

FIG. 5 is a schematic representation of the present invention according to a fifth embodiment.

FIG. 6 is a schematic representation of the present invention according to a sixth embodiment.

Detailed Description

The following detailed description discloses various exemplary embodiments and features of the invention. These exemplary embodiments and features are not meant to be limiting of the claimed invention.

Referring now to Figure 1 , a hydrocarbon feedstock such as methane is combined with steam at a S/C ratio of less than 2.8 and preferably less than 2, or steam and a hydrocarbon are parallel reformed. Reforming preferably takes place at a pressure in excess of 10 bar and the mixture is introduced together via line 1 into one or more reformers 2 wherein the reactants are heated and reacted to form a syngas in the presence of a suitable catalyst. While one reformer 2 is shown in Fig. 1 , it is foreseen that more than one reformer may be employed. Use of a reforming catalytic reactor with high effective catalyst loading and high axial heat transfer enables reforming to take place at low S/C ratios without forming coke deposits in the reforming catalytic reactor. US patent application 2006/0008399A 1 and WIPO patent application WO2006/058060A2, which are incorporated herein by reference in their entirety, teach examples of suitable reforming catalytic reactors.

The outlet syngas from the reformers is conveyed by line 3 to heat exchanger 4 in which the syngas is cooled to a temperature of around 200⁰ C. The syngas is preferably conveyed by line 5 to optional water gas shift reactor 6 in which the H₂O and CO contents of the syngas are reduced and the H₂ and CO₂ contents are increased. The syngas is preferably conveyed by line 7 to optional heat exchanger 8 in which the syngas is further cooled. The syngas is preferably then conveyed by line 9 to optional water separation unit 10 in which water condensate is removed.

The partially dried syngas is then conveyed by line 1 1 to a PSA unit 12 in which the syngas is separated into various product and tail gas streams. The PSA unit is a conventional H₂ PSA unit as is typically used in an SMR plant. The PSA unit is fitted with valves to separate the inlet gas, which is provided to the PSA unit, into a high purity H₂ stream designated the product stream, and two tail gas streams designated the burner stream and the feedstock stream, respectively. The product stream containing high purity H₂ exits the PSA unit via line 13. A feedstock stream exits the PSA unit via line 14, is subsequently compressed in compressor 15, and is recycled to the process gas inlet line 1 of the reformer via line 16. A burner stream exits the PSA unit via line 17, which conveys the burner stream to the reformer burners (not shown) providing at least part of the burner fuel requirements. Line 17 may contain a blower or compressor (not shown).

The product stream provided in line 13 contains most of the inlet H₂ to the PSA unit in the form of high purity H₂. The product stream exits the product or high pressure outlet end of each bed in the PSA unit. The feedstock stream contains CH₄, most of the H₂O and CO₂, and some of the unrecovered hydrogen. The feedstock stream preferably contains at least all tail gas energy units in excess of the energy units required for the reformer burner fuel requirements, with as much of those excess energy units as possible being in the form Of CH₄ and as few as possible being in the form of H₂. The burner stream contains the balance of the inlet gas to the PSA unit and preferably contains no more energy units than are required for heating the reformer. All tail gas streams of each embodiment exit the opposite end of each bed from the product stream. The method and apparatus for separating the tail gas into multiple streams of different compositions from each other are described below.

Referring now to Fig. 2, a second embodiment is illustrated in which all components corresponding to Figure 1 have the same numbering as in Fig. 1. In the second embodiment all of the components of the first embodiment are employed, and an additional tail gas stream designated the CO₂ stream is conveyed from PSA unit 12 via line 18. In the second embodiment the CO₂ stream contains most of the H₂O and CO₂ from the inlet gas to the PSA unit. The product stream contains high purity hydrogen, and the feedstock stream contains at least some of the energy units exceeding the energy units required for heating the reformer. The burner stream contains the balance of the inlet gas to the PSA unit, including most of the unrecovered H₂ and preferably contains no more energy units than are required for heating the reformer. The CO₂ stream is vented, beneficiated into a useful product, or sequestered from the atmosphere. CO₂ beneficiation may be by means of compression, further purification, or both.

Referring now to Fig. 3, a third embodiment is illustrated in which all components corresponding to Fig. 1 have the same numbering as in Fig. 1. In the third embodiment all of the components of the first embodiment are employed, and an additional tail gas stream designated the PSA recycle stream is conveyed from PSA unit 12 via line 19, which is compressed in compressor 20 and is then returned via line 21 to the inlet line of PSA unit 12 or is equivalently returned to PSA unit 12. In the third embodiment the product and feedstock stream gas contents are as defined above in connection with the first embodiment. The PSA recycle stream contains a substantial portion of the unrecovered H₂. As progressively higher portions of the unrecovered H₂ are included in the PSA recycle stream, they will be increasingly mixed with CO, CH₄ and other tail gas components and the concentration of H₂ in the PSA recycle stream will decline. The PSA recycle stream preferably contains only as much H₂ as is possible consistent with a suitable H₂ concentration so as to make its compression and recovery via PSA unit 12 economically attractive in view of its effect on net capital and energy costs. The burner stream contains the balance of the inlet gas to PSA unit 12 and preferably contains no more energy units than are required for heating the reformer.

Referring now to Fig. 4, a preferred fourth embodiment is illustrated in which all components corresponding to Fig. 3 have the same numbering as in Fig. 3. In the fourth embodiment all of the components of the third embodiment are employed, and an additional tail gas stream designated the CO₂ stream is conveyed from PSA unit 12 via line 18. In the fourth embodiment the product and PSA recycle stream gas contents are as defined in the third embodiment, the feedstock stream contains at least some of the energy units in excess of the energy requirements for heating the reformer, the CO₂ stream contains most of the H₂O and CO₂ from the inlet gas to the PSA unit, and the burner stream contains the balance of the inlet gas to the PSA unit and preferably contains no more energy units than are required for heating the reformer. Referring now to Fig. 5, a fifth embodiment is illustrated in which all components corresponding to Fig. 1 have the same numbering as in Fig. 1. In the fifth embodiment all of the components of the first embodiment are employed except that items 14, 15, and 16 for conveying a feedstock stream to the reformer inlet line are not included, and an additional tail gas stream designated the PSA recycle stream is conveyed from PSA unit 12 via line 19. is compressed in compressor 20 and returned via line 21 to PSA inlet line 1 1 or is equivalently returned to PSA unit 12. In the fifth embodiment the product stream gas content is high purity H₂. The PSA recycle stream contains a substantial portion of the unrecovered H₂. As progressively higher portions of the unrecovered H₂ are included with the PSA recycle stream, they will be increasingly mixed with CO, CH₄ and other tail gas components and the concentration of H₂ in the PSA recycle stream will decline. The PSA recycle stream preferably contains only as much H₂ as is possible consistent with a suitable H₂ concentration so as to make its compression and recovery via the PSA unit economically attractive in view of its effect on net capital and energy costs. The burner stream contains the balance of the inlet gas to the PSA unit and preferably contains no more energy units than are required for heating the reformer. No tail gas is separated or recirculated as feedstock to the reformer inlet. In this embodiment the energy units in excess of those required for use in the reformer burners is separated from the tail gas in the form of H₂ for recirculation to the PSA unit, as opposed to in all other embodiments in which the excess energy units are at least partly separated in the form of CH₄ for recirculation to the reformer.

The tail gas streams are separated from each other as required in each embodiment by timing the opening and closing of valves at the tail gas outlet end of each PSA bed to allow the gas exiting each bed at particular times to be directed to the respective tail gas outlet lines described in the respective embodiments. While not being held to this explanation or sequence, it is understood that molecular sieves used in PSA units for separating a high purity H₂ product have different adsorptive affinities for H₂O, CO₂, CH₄, CO, and H₂, such that these respective gases exit PSA beds as tail gas in this approximate and overlapping sequence during the collective depressurization and purge portions of a complete PSA process cycle. Where such molecular sieves are used, the CO₂ stream, followed by the feedstock stream followed by the burner stream followed by the PSA recycle stream are diverted from a given bed by opening only valves to lines 18, 17, 14, and 19, respectively, while all other valves to outlet lines are closed, to the extent that each of these respective tail gas streams is employed in the respective embodiments. Any or all outlet lines 18, 17, 14, and 19, respectively, may contain a surge tank. If more than one type of molecular sieve is used in a bed, the various molecular sieves are preferably layered from the gas inlet end to the H₂ product outlet end in such sequence as to accentuate H₂ recovery and separation of the tail gas stream compositions from each other. If multiple PSA units are used, different molecular sieves are preferably used in the sequence of PSA units as to accentuate H₂ recovery and separation of the tail gas stream compositions from each other.

Referring now to Fig. 6, a sixth embodiment is illustrated in which all components corresponding to Fig. 3 have the same numbering as in Fig. 3. In the sixth embodiment syngas is conveyed from water separator 10 via line 22 to PSA unit 23, in which the syngas is separated into a first stream and a CO₂ stream. The first stream is conveyed via line 11 to PSA unit 12, which corresponds to PSA unit 12 in Figure 3. All outlet lines from PSA unit 12 correspond to those of like numbering exiting unit 12 in Figure 3. The CO₂ stream is exported from PSA unit 23 and from the system via line 24. PSA unit 23 contains a molecular sieve for separating H₂O and CO₂ from syngas. The CO₂ stream exported via line 24 contains most of the H₂O and CO₂ entering PSA unit 23, and preferably contains less than 10% CH₄ and yet smaller volume percentages of CO and H₂ The balance of the syngas entering PSA unit 23 is conveyed to PSA unit 12 via line 1 1. A PSA recycle stream exits PSA unit 12 via line 19 and preferably contains only as much H₂ as is possible consistent with a suitable H₂ concentration so as to make its compression and recovery via PSA unit 12 economically attractive in view of its effect on net capital and energy costs. A feedstock stream exits PSA unit 12 via line 14 and contains at least some of the energy units exceeding the energy requirements needed for heating the reformer. A burner stream exits PSA unit 12 via line 14 and contains the balance of the inlet gas to PSA unit 12. The burner stream preferably contains no more energy units than are required for heating in the reformer.

ft is foreseen that other embodiments to separate the syngas into the equivalent of product, burner, and process gas recycle streams as taught in any of the preceding embodiments via the combination of multiple PSA units can be devised by a person of ordinary skill in the art to which the present invention pertains. Although the present invention has been described in terms of certain preferred embodiments, various features of separate embodiments can be combined to form additional embodiments not expressly described. Moreover, other embodiments apparent to those of ordinary skill in the art after reading this disclosure are also within the scope of this invention. Furthermore, not all of the features, aspects and advantages are necessarily required to practice the present invention. Thus, while the above detailed description has shown, described, and pointed out novel features of the invention as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the apparatus or process illustrated may be made by those of ordinary skill in the art without departing from the scope and spirit of the invention. The invention may be embodied in other specific forms not explicitly described herein. The embodiments described above are to be considered in all respects as illustrative only and not restrictive in any manner. Thus, scope of the invention is indicated by the following claims rather than by the foregoing description.

I l

Claims

We claim:

1 . A steam reforming process comprising: reforming steam and a hydrocarbon feedstock to form syngas in a combustion- heated reformer; separating the syngas in at least one PSA unit into at least a high purity hydrogen stream, a feedstock stream containing CH₄ constituting at least some of energy units in excess of those required for combustion in the reformer, and a burner stream containing the balance of the inlet gas to the at least one PSA unit, including unrecovered H₂, and recycling at least a portion of the burner stream to the combustion-treated reformer for combustion therein, and recycling at least a portion of the feedstock stream to a reformer feedstock inlet.

2. The steam reforming process according to claim I wherein the separation of syngas into feedstock and burner streams comprises venting purge gases from respective beds of the at least one PSA unit at different times within respective purge cycles to respective feedstock and burner streams.

3. The steam reforming process according to claim I wherein the separation of tail gases into feedstock and burner streams comprises utilizing multiple PSA units in which purge gas from a first PSA unit is vented to the feedstock stream and purge gas from a second PSA is vented to the burner stream.

4. The steam reforming process according to claim I wherein the tail gases are separated into at least one of a PSA recycle stream which is recycled to at least one PSA unit or a carbon dioxide rich outlet stream.

5. A steam reforming process comprising: reforming steam and a hydrocarbon to form syngas in a combustion-heated reformer; separating the syngas in at least one PSA unit into at least a high purity hydrogen stream, a PSA recycle stream containing some of the recovered H₂ constituting at least some of the energy units in excess of those required for combustion in the combustion- treated reformer, and a burner stream containing the balance of the inlet gas to the at least one PSA unit, compressing and recycling at least a portion of the PSA recycle stream to the at least one PSA unit, and recycling at least a portion of the burner stream to the combustion-treated reformer for combustion therein.

6. The steam reforming process according to claim 5 wherein the separation of tail gases into PSA recycle and burner streams comprises venting purge gases from respective beds of the at least one PSA unit at different times within respective purge cycles to respective PSA recycle and burner streams.

7. The steam reforming process according to claim 5 wherein the separation of tail gases into PSA recycle and burner streams comprises utilizing a plurality of multiple PSA units in which purge gas from a first PSA unit is vented to the burner stream and purge gas from a second PSA of the first PSA is vented to a PSA recycle stream.

8. The steam reforming process according to claim 5 wherein the tail gases are separated into at least one of a feedstock stream which is recycled to the reformer feedstock inlet or a carbon dioxide rich outlet stream.

9. A steam reforming apparatus comprising: a combustion heated reformer for reforming steam and a hydrocarbon feedstock to form syngas, the combustion heated reformer having an inlet and an outlet; at least one PSA unit operatively coupled to the combustion heated reformer to separate the syngas into at least a high purity hydrogen stream, a fuel stream for combustion heating in the combustion heated reformer and a process recycle stream, the at least one PSA unit having an inlet and a plurality of outlets, the fuel stream being provided from the at least one PSA to the combustion heated reformer for combustion heating; means for conveying the high purity hydrogen stream from a respective one of the plurality of outlets of the at least one PSA unit; and means for recycling the process recycle stream from a respective one of the plurality of outlets of the at least one PSA unit to at least one of the inlet of combustion heated reformer or the inlet of the at least one PSA unit.

10. The stream reforming apparatus according to claim 9, wherein the process recycle stream contains at least some of energy units of the fuel stream and process recycle stream in excess of those required for combustion in the combustion heated reformer, and the fuel stream contains a remainder of the inlet gas to the at least one PSA unit not distributed to the high purity hydrogen stream or to the process recycle stream.