Tail Gas Recycle Combined Cycle Power Plant

Abstract

A process is provided for recycling Hydrogen enrichment tail gas to a combined cycle power system.

Claims

1. A process comprising: a. feeding a separator feedstream comprising syngas from converted natural gas to membrane separator means, b. separating the separator feedstream in the separator means to form a first, CO-rich stream and a second, H.sub.2-rich stream, c. feeding the first, CO-rich stream as an oxyfuel combustor feedstream to oxyfuel combustor means for forming sub-critical CO.sub.2 gas turbine working fluid, and d. feeding the sub-critical CO.sub.2 gas turbine working fluid to gas turbine means for producing power, e. wherein the sub-critical CO.sub.2 gas turbine working fluid exits the gas turbine means as gas turbine exhaust which is fed to heat recovery steam generator means for generating steam, and wherein steam from the heat recovery steam generator means is fed as first steam working fluid to first steam turbine means for generating power, f. wherein a first portion of exhaust from the gas turbine means is recycled to the oxyfuel combustor means together with high purity oxygen and the CO-rich stream, g. wherein the second, H.sub.2-rich stream is fed as a H.sub.2 feedstream to pressure swing adsorption hydrogen enrichment means to form an enriched H.sub.2 stream and a tail gas stream, h. wherein the tail gas stream is fed as tail gas recycle to the oxyfuel combustor feedstream, i. wherein the remaining portion of the exhaust from the gas turbine means is captured, and j. wherein a H.sub.2 product of at least about 98% H.sub.2 purity is recovered from the pressure swing adsorption hydrogen enrichment means.

2. The process of claim 1, wherein steam from the heat recovery steam generator means is fed as second steam working fluid to second steam turbine means for generating power.

3. The process of claim 1, wherein the first, CO-rich stream is a retentate stream from the membrane separator means, and wherein the tail gas recycle stream is fed to the retentate stream.

4. The process of claim 1, wherein the H.sub.2-rich stream comprises at least 40% H.sub.2, and the tail gas comprises at least about 5% CO.sub.2.

5. The process of claim 4, wherein the H.sub.2-rich stream comprises at least 50% H.sub.2, the enriched H.sub.2 stream comprises at least about 99% H.sub.2, and the tail gas comprises at least about 8% CO.sub.2.

6. The process of claim 5, wherein the H.sub.2-rich stream comprises at least 60% H.sub.2, the enriched H.sub.2 stream comprises at least about 99.9% H.sub.2, and the tail gas comprises at least about 12% CO.sub.2.

7. The process of claim 6, wherein the H.sub.2-rich stream comprises at least 85% Hz, the enriched H.sub.2 stream comprises at least 99.995% Hz, and the tail gas comprises at least about 16% CO.sub.2.

8. The process of claim 1, wherein the syngas is unshifted.

9. The process of claim 2, wherein the syngas is unshifted.

10. The process of claim 3, wherein the syngas is unshifted.

11. The process of claim 1, wherein the first, CO-rich stream is fed directly from the membrane separator means to the oxyfuel combustor means.

12. (canceled)

13. The process of claim 1, wherein the H.sub.2-rich stream is subjected to a water gas shift reaction before being fed to the hydrogen enrichment means.

14. The process of claim 3, wherein the H.sub.2-rich stream is subjected to a water gas shift reaction before being fed to the pressure swing adsorption means.

15. A process comprising: a. feeding a separator feedstream comprising syngas from converted natural gas to separator means, b. separating the separator feedstream in the separator means to form a first, CO-rich stream and a second, H.sub.2 rich stream, c. feeding the first, CO-rich stream as an oxyfuel combustor feedstream to oxyfuel combustor means for forming sub-critical CO.sub.2 gas turbine working fluid, d. feeding the sub-critical CO.sub.2 gas turbine working fluid to sub-critical CO.sub.2 gas turbine means, the sub-critical CO.sub.2 gas turbine means having a sub-critical CO.sub.2 gas turbine expansion section and a sub-critical CO.sub.2 gas turbine compression section, the subcritical CO.sub.2 gas turbine working fluid being fed to the sub-critical CO.sub.2 gas turbine expansion section for producing power, e. recycling at least a first portion of exhaust from the sub-critical CO.sub.2 gas turbine expansion section to the sub-critical CO.sub.2 gas turbine compression section of the sub-critical CO.sub.2 gas turbine means, wherein the power produced in step (d) is used to power the sub-critical CO.sub.2 gas turbine compression section to compress the recycled sub-critical CO.sub.2 gas turbine exhaust, f. capturing the remaining portion of sub-critical CO.sub.2 gas turbine exhaust, g. feeding the compressed sub-critical CO.sub.2 gas turbine exhaust to the oxyfuel combustor means, h. reacting the first, CO-rich stream with high purity oxygen in the oxyfuel combustor means under sub-critical CO.sub.2 conditions, i. wherein the second, H.sub.2-rich stream is fed as a H.sub.2 feedstream to pressure swing adsorption hydrogen enrichment means to form an enriched H.sub.2 stream and a tail gas stream, j. wherein a H.sub.2 product of at least about 98% H.sub.2 purity is recovered from the pressure swing adsorption hydrogen enrichment means and k. wherein the tail gas stream is fed as tail gas recycle to the oxyfuel combustor feedstream.

16. A process comprising: a. feeding a separator feedstream comprising syngas from converted natural gas to a membrane separator, b. separating the separator feedstream in the separator to form a first, CO-rich stream and a second, H.sub.2-rich stream, c. feeding the first, CO-rich stream as an oxyfuel combustor feedstream to an oxyfuel combustor for forming sub-critical CO.sub.2 gas turbine working fluid, and d. feeding the sub-critical CO.sub.2 gas turbine working fluid to a gas turbine for producing power, e. wherein the sub-critical CO.sub.2 gas turbine working fluid exits the gas turbine as gas turbine exhaust which is fed to a heat recovery steam generator for generating steam, and wherein steam from the heat recovery steam generator is fed as first steam working fluid to a first steam turbine for generating power, f. wherein a first portion of exhaust from the gas turbine is recycled to the oxyfuel combustor together with high purity oxygen and the CO-rich stream, g. wherein the remaining portion of exhaust from the gas turbine is captured, h. wherein the second, H.sub.2-rich stream is fed as a H.sub.2 feedstream to pressure swing adsorption hydrogen enrichment to form an enriched Hz stream and a tail gas stream, i. wherein a H.sub.2 product of at least about 98% H.sub.2 purity is recovered from the pressure swing adsorption hydrogen enrichment means and j. wherein the tail gas stream is fed as tail gas recycle to the oxyfuel combustor feedstream.

17. (canceled)

18. The process of claim 16, wherein the first, CO-rich stream is a retentate stream from the membrane separator, and wherein the tail gas recycle stream is fed to the retentate stream.

19. The process of claim 16, wherein the first, CO-rich stream is fed directly from the separator to the oxyfuel combustor.

20. (canceled)

21. The process of claim 15, wherein the syngas is unshifted.

22. The process of claim 16, wherein the syngas is unshifted.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG. 1 is a schematic diagram of a conventional al NGCC power plant using natural gas as the combustor fuel.

[0037] FIG. 2 is a schematic diagram of a NGCC power plant using separated syngas as fuel for a combined cycle power plant according to an embodiment.

[0038] FIG. 3 is a block diagram according to an embodiment for material balance purposes.

[0039] FIG. 4 is a block diagram according to a further embodiment for material balance purposes.

DETAILED DESCRIPTION OF THE INVENTION

[0040] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein.

[0041] All publications, patents and patent applications cited herein, whether supra or infra, are hereby incorporated herein by reference in their entirety to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. Further, when an amount, concentration, or other value or parameter is given as either a range, preferred range, or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, as well as, any range formed within a specified range, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. For example, recitation of 1-5 is intended to include all integers including and between 1 and 5 and all fractions and decimals between 1 and 5, e.g., 1, 1.1, 1.2, 1.3 etc. It is not intended that the scope of the invention be limited to the specific values recited when defining a specific range. Similarly, recitation of at least about or up to about a number is intended to include that number and all integers, fractions and decimals greater than or up to that number as indicated. For example, at least 5 is intended to include 5 and all fractions and decimals above 5, e.g., 5.1, 5.2, 5.3 etc.

[0042] It is noted that, as used in this specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the content clearly dictates otherwise. Unless otherwise expressly indicated herein, all amounts are based on volume.

[0043] With reference to illustrative FIG. 2 of the drawings, 1a is a process for converting natural gas to syngas, for example, by steam methane reforming (SMR), partial oxidation, or autothermal reforming (ATR). See, for example, U.S. Pat. Nos. 3,479,298, 5,653,774, 6,340,437, 7,481,856, 4,415,484, 7,592,290 and 5,628,931. Steam reforming of natural gas can proceed in tubular reactors that are heated externally. The process uses nickel catalyst on a special support that is resistant against the harsh process conditions. Waste heat from the heating section is used to preheat gases and to produce steam. Partial oxidation of methane is a non-catalytic, large-scale process to make syngas. A catalytic version of partial oxidation (CPO), based on short-contact time conversion of methane, on e.g. rhodium catalysts, is suitable for small-scale applications. Autothermal reforming (ATR) is a hybrid, which combines methane steam reforming and oxidation in one process. Since steam reforming is endothermic the heat needed for reforming is generated inside the reactor by oxidation of a portion of the feed gas as fuel. In accordance with an embodiment, the syngas is not subjected to a water gas shift reaction, that is the syngas feed 1b is unshifted (water gas shifted free).

[0044] There are two advantages with membrane separation of carbon as carbon monoxide from unshifted syngas. When feeding unshifted syngas 1b from 1a to membrane separator means 2, membrane selectivity for H.sub.2/CO is substantially higher than H.sub.2/CO.sub.2. In simulations conducted on commercial membranes provided by commercial membrane manufacturers Generon and Ube Industries, Ltd., the Generon membrane, showed a H.sub.2/CO selectivity of 38.7 and H.sub.2/CO.sub.2 selectivity of 2.5 while an Ube membrane, showed a H.sub.2/CO selectivity of 27.7 and a H.sub.2/CO.sub.2 selectivity of 3.2.

[0045] Second, in simulations the Generon membrane optimized for H.sub.2 production captured 90.42% of the CO in the retentate along with 8.20% of the H.sub.2 and recovered 91.80% of the H.sub.2 in the permeate along with 9.58% of the CO. According to an embodiment, the captured CO in the retentate is directed to the oxyfuel combined cycle wherein it is captured as high purity CO.sub.2 in the exhaust stream. According to simulations, permeate which is directed to H.sub.2 production contains 9.58% of the CO and needs substantially less steam (energy penalty) and capital equipment (cost penalty) in a WGSR to convert the CO to CO.sub.2. Thus, the WGSR energy and capital cost penalties can be reduced by over 90% by separating CO and H.sub.2 in unshifted syngas.

[0046] Syngas feed compositions are well known in the art and can vary depending on the source. By way of nonlimiting example, it is believed that syngas feed 1b can comprise H.sub.2, CO.sub.2, CO, CH.sub.4 and H.sub.2O in the following amounts. The H.sub.2 content can be about 20-80. The CO.sub.2 content can be about 2-25%. The CO content can be about 20-60%. The H.sub.2O content can be up to 20%. The CH.sub.4 content can typically be about 0.1%-2.0%. It is understood that the syngas feed 1b may contain minor amounts of contaminants, e.g., H.sub.2S, NH.sub.3, HCl, COS, and Hg, depending on whether the syngas is from gasified coal or reformed natural gas, and can be removed by known treatments. By way of example, contaminants could comprise less than about 0.5% of syngas feed 1b.

[0047] Separator means 2 can be any known separator means suitable for the purpose of separating the syngas feed stream into a first, CO-rich stream 3 and a second, H.sub.2-rich stream 27. For example, separator means can be membrane separator means or pressure swing adsorption means. Membrane separation is preferred.

[0048] Gas separation membranes and the operation thereof for separating gas mixtures are well known. See for example, U.S. Pat. Nos. 5,482,539. 4,990,168, 4,639,257, 2,966,235, 4,130,403, 4,264,338, and 5,102,432. Any known membrane that is operable under the conditions of operation to meet the noted product compositions can be used. For example, Ube membranes and Generon® membranes advertised for H.sub.2 separations would be suitable, as would a polybenzimidazole (PBI) membrane. Reference is made, respectively, to Haruhiko Ohya et al, “Polyimide Membranes: Applications, Fabrications and Properties” by H. Ohya, V. V. Kudryavtsev and S. I, Semenova (Jan. 30, 1997) co-published by Kodansha LYD., 12-21 Otowa 2-Chome Bunkyo-Ku, Tokyo 112, Japan and Gordan and Breach Science Publishers S. A. Emmaplein 5, 1075 AW Amsterdam, The Netherlands, for the Ube membranes and to Jayaweera, Indira S. “Development of Pre-Combustion CO.sub.2 Capture Process Using High-Temperature Polybenzimidazole (PBI) Hollow-Fiber Membranes (HFMs)”, 2017 NETL CO.sub.2 Capture Technology Project Review Meeting, Aug. 21-25, 2017, [online] [retrieved Jan. 17, 2019], [https://www.net1.doe.gov/sites/default/files/2017-12/2I-S-Jayaweera2-SRI-PBIHollow-Fiber-Membranes.pdf], and “Celazole® PBI”, [online] [retrieved Jan. 17, 2019], [https://pbipolymer.com/markets/membrane/].

[0049] As illustrated in FIG. 2, separator means 2 comprises membrane means 2a disposed therewithin. The syngas feedstream is fed to separator means on one side of the membrane means and is separated into separate streams by selective permeation of syngas components therethrough. As shown, the membrane is more permeable to the H.sub.2 contained in the syngas feed stream than it is to CO. The membrane being more selective for H.sub.2 permeation, permeate stream 27 is enriched in H.sub.2 as compared to syngas feed stream 1b, and retentate stream 3 is enriched in CO as compared to the syngas feed stream 1b. Accordingly, stream 27 comprises a H.sub.2-rich stream and stream 3 comprises a CO-rich stream. The CO-rich stream is then sent to a sub-critical CO.sub.2 power plant 33.

[0050] Concepts of mixed-gas separation, gas permeability and selectivity are discussed in a number of publications, including “Materials Science of Membranes for Gas and Vapor Separation”, Edited by Yampolski et al, 2006 John Wiley & Sons; “Pure and mixed gas CH.sub.4 and n-C.sub.4H.sub.10 permeability and diffusivity in poly(l-trimethylsilyl-1-propyne)” Roy D. Raharjo et al, Polymer 48 (2007) 7329-7344, 2006 Elsevier Ltd., “Carbon Dioxide Separation through Polymeric Membrane Systems for Flue Gas Applications”, Colin A. Scholes et al, Cooperative Research Centre for Greenhouse Gas Technologies, Department of Chemical and Biomolecular Engineering, The University of Melbourne, VIC, 3010, Australia; and “Recent Patents on Chemical Engineering”, 2008, 1 52-66, 2008 Bentham Science Publishers Ltd.

[0051] The CO-rich stream 3 comprises primarily CO, with minor amounts of carbon dioxide and hydrogen.

[0052] After optional contaminant removal (not shown), stream 3 should comprise primarily CO and hydrogen. Stream 3 can also comprise a small amount of CO.sub.2 and traces of remaining contaminants. For example, stream 3 can comprise at least about 35%, or at least about 50%, or at least about 65%, or at least about 80% CO. Having the benefit of the disclosure of the present invention, it is seen that the H.sub.2 content of stream 3 depends on operational and plant design objectives. On that basis, it is believed that the stream 3 should comprise less than about 55%, or less than about 40%, or less than about 25%, or less than about 10% H.sub.2. Stream 3 can also comprise a small amount of CO.sub.2 and traces of remaining contaminants. Stream 3 should comprise less than about 0.01%, or less than about 0.001%, or less than about 0.0001%, or less than about 0.00001% of contaminants; and CO.sub.2 should comprise less than about 25%, or less than about 15%, or less than about 10%, or less than about 5% of stream 3. Any upper limit for the CO content of stream 3 is considered to be limited only by the ability of technology to economically enrich stream 3 in CO. It is believed that using present technology, stream 3 can comprise up to 90-95% CO.

[0053] Stream 3 is then fed as oxyfuel combustor feed stream 4 to oxyfuel combustor means 5, wherein it is combined and reacted with high purity oxygen stream 8 of at least about 95% purity from air separation unit means 6 for separating oxygen from air and recycled CO.sub.2 stream 34. Following compression in gas turbine compressor section 11 the oxygen CO.sub.2 gas mixture as shown at 34a is fed to oxyfuel combustor means 5. As shown in FIG. 2, stream 4 is fed directly (other than any optional contaminant removal) to oxyfuel combustor means 5. For example, stream 4 is fed to the oxyfuel combustor means 5 in FIG. 2 in the absence of any intervening process step, e.g., expansion to lower pressure in an expander or compression in a compressor to increase pressure. The oxygen content of stream 8 comprises at least about 95%, at least about 97%, at least about 99%, or at least about 99.5% purity. As discussed in detail below, sub-critical CO.sub.2 exhaust stream 34 after compression in turbine compressor 11 is also fed to combustor means 5. Oxygen stream 8 can be premixed with sub-critical CO.sub.2 exhaust stream 34 either upstream of compression section 11 or in situ within combustor means 5 (shown at 62 in FIG. 2). Means for premixing in situ are known in the art. For example, see Delimont, Jacob et al, “Direct Fired Oxy-Fuel Combustor for sCO2 Power Cycles, February 2018 Oxy-fuel Working Group presentation, [online] [retrieved Aug. 13, 2019], [https://www.net1.doe.gov/sites/default/files/net1-file/sCO2-WorkingGroup-Feb2018_1MWOxyCombustor.pdf].

Air separation units are well known, for example, as illustrated in U.S. Pat. Nos. 2,548,377, 4,531,371 and 4,382,366. See also, Rong Jiang, Analysis and Optimization of ASU for Oxyfuel Combustion [online] [retrieved Feb. 19, 2019] [http://ieaghg.org/docs/General_Docs/5oxy%20presentations/Session%207B/7B-05%20-%20R.%20Jiang%20(SASPG%20Ltd.).pdf], and “History and progress in the course of time, [online] [retrieved Feb. 19, 2019] [https://www.linde-engineering.com/en/images/Air_separation_plants_History_and_progress_in_the_course_of time_tcm19-457349.pdf]. Before the use of a separator means to separate hydrogen from the syngas feed stream 1b in accordance with the present invention, a considerable portion of the oxygen produced in prior air separation units was consumed by reaction with H.sub.2 contained in the combustor fuel stream 4. Combustion in accordance with an embodiment of the present invention, results in stream 9 comprised primarily of CO.sub.2 working fluid with a substantially reduced amount of steam. The CO.sub.2 content of the oxyfuel combustion exhaust in stream 9 will, of course, vary, depending on the amount of H.sub.2 recovery in the membrane permeate and the amount of CO.sub.2 in the membrane feed stream both of which affects the CO.sub.2 content in the CO.sub.2 oxyfuel combustion exhaust. In any event, it can comprise at least about 50%, at least about 60% at least about 70%, at least about 80% or at least about 90% CO.sub.2, with the balance comprising H.sub.2O, and contaminants such as N.sub.2+Ar.

[0054] Sub-critical CO.sub.2 stream 9 formed in combustor means 5 is then fed to the expansion section 10 of sub-critical CO.sub.2 turbine means wherein power is produced to power compression section 11 and electricity generator 12. Expanded sub-critical CO.sub.2 exhaust 13 is then fed to known heat recovery steam generator means (HRSG) 14, wherein exhaust 13 indirectly heats a water stream (not shown) to produce working fluid steam stream 13b. The working fluid steam stream 13b is fed to a first, known steam turbine means 15 that powers electricity generator 15a. Condensed steam stream 13a is recycled back to the HRSG 14.

[0055] Sub-critical CO.sub.2 exhaust 25 from HRSG 14 is then fed to heat exchanger cooling means 16 for indirect cooling with cooling fluid 24. Cooled sub-critical CO.sub.2 stream 26 is sent to condensed water separator means 17 for removing condensed water 18 from cooled sub-critical CO.sub.2 stream 26. Since stream 26 comprises less water due to the separation of hydrogen from stream 1b by separator means 2, cooling means 23 energy and equipment size requirements can be significantly reduced. Cooling fluid 24 for heat exchangers 16 and 20 is provided by known cooling fluid cooling means 23. The sub-critical CO.sub.2 working fluid leaving the water separator 17, is compressed in CO.sub.2 compressor means 19, and then cooled in aftercooler heat exchanger means 20 to remove heat of compression. Compressed and cooled sub-critical CO.sub.2 stream 21 is then circulated for at least partial capture in stream 22 and recirculation in stream 34 and then forwarded back to oxyfuel combustor means 5. As shown in FIG. 2, at least a first portion 34 of recycle stream 21 is recycled to oxyfuel combustor means 5. The remaining portion 22 of the recycle stream is captured for storage or further use, for example, in enhanced oil recovery. Recycle stream 34 is a working fluid for the optimum performance of the sub-critical CO.sub.2 oxyfuel combustor 5 and the sub-critical CO.sub.2 combustion turbine shown at 10 and 11. Recycling the sub-critical CO.sub.2 to oxyfuel combustor means 5 enables the sub-critical CO.sub.2 power cycle to operate with sub-critical CO.sub.2 as the working fluid in the gas turbine. The cycle is operated below the critical point of CO.sub.2.

[0056] Stream 27 comprises primarily H.sub.2 with small quantities of CO.sub.2, CO and trace quantities of H.sub.2O. Stream 27 can comprise at least about 40%, or at least about 50% H.sub.2 or at least about 60%, or at least about 85% H.sub.2. Having the benefit of the disclosure of the present invention, it is seen that the CO content of stream 27 depends on operational and plant design objectives. On that basis, it is believed that stream 27 should comprise less than about 10% CO, or less than about 5% CO, or less than about 3% CO, or less than about 1% CO with the balance comprising other components such as CO.sub.2 and H.sub.2O. Any upper limit for the H.sub.2 content of stream 27 is limited only by the ability of technology to economically enrich stream 27 in H.sub.2. It is believed that using present technology, stream 27 can comprise up to about 90-95% H.sub.2.

[0057] H.sub.2-rich gas stream 27 is fed to any known process, for example, pressure swing adsorption or palladium proton membrane treatment, for further enrichment to high purity H.sub.2 and further use. Any H.sub.2 enrichment process that produces at least an enriched H.sub.2 product stream, and a byproduct/tail gas stream would be suitable. Pressure swing adsorption (PSA) is preferred. By way of non-limiting example, the high purity H.sub.2 can be used for [0058] 1. Zero emission transportation fuel in an internal combustion engine or in a fuel cell to power an electric motor, [0059] 2. Gas welding, [0060] 3. Hydrotreating to remove sulfur in petroleum refining, [0061] 4. Chemicals production, [0062] 5. Generation of electricity, [0063] 6. As a reducing agent, [0064] 7. Potentiometry and Chemical analysis, [0065] 8. In gas chromatography, or [0066] 9. Rocket fuel for space programs
As shown in FIG. 2, permeate H.sub.2-rich stream 27 is fed as a H.sub.2 feed stream to hydrogen enrichment means 141 wherein an enriched H.sub.2 stream 261 and a tail gas recycle stream 260 are formed. The tail gas stream 260 typically comprises CO, CO.sub.2, H.sub.2 and possibly a minor amount of CH.sub.4. Stream 260 can comprise less than about 25%, less than about, 20%, less than about 10% or less than about 5% CO.sub.2. Tail gas recycle stream 260 is fed to the retentate CO-rich stream 3 from separator 2. If necessary to increase the pressure of tail gas recycle stream 260, optional compressor 63 is provided. PSA processes typically feed tail gas as fuel, for example, to a steam methane reformer when used, or make use of an additional process to treat the tail gas with an adsorbent in an additional PSA unit or an absorbent such as dimethylethanolamine to remove CO.sub.2 therefrom. By combining the tail gas recycle stream 260 with the retentate CO-rich stream 3 in accordance with the present invention, it is possible to form an oxyfuel gas turbine fuel 4 that can accomplish minimal or even near zero carbon emission hydrogen. This result is enabled without the need to add an additional process.

[0067] There are certain instances in which the industry specifications for hydrogen products require very low amounts of CO. For example, the U.S. Department of Energy issued the following Hydrogen Fuel Quality Specifications for Polymer Electrolyte Fuel Cells in Road Vehicles:

Hydrogen Fuel Quality Specifications for Polymer Electrolyte Fuel Cells in Road Vehicles (energy.gov)

TABLE-US-00001 TABLE 1-1 Directory of limiting characteristics (maximum allowable limits of contaminants) from ISO FDIS 14687-2 Characteristics (assay) Type I, Type II Grade D Hydrogen fuel index 99.97% (minimum mole fraction) .sup.a Total non-hydrogen gases 300 μmol/mol Maximum concentration of individual contaminants Water (H.sub.2O) 5 μmol/mol (5.0 ppm) Total hydrocarbons b (Methane basis) 2 μmol/mol (2.0 ppm) Oxygen (O.sub.2) 5 μmol/mol (5.0 ppm) Helium (He) 300 μmol/mol (300 ppm) Total Nitrogen (N.sub.2) and Argon (Ar) .sup.b 100 μmol/mol (100 ppm) Carbon dioxide (CO.sub.2) 2 μmol/mol (2.0 ppm) Carbon monoxide (CO) 0.2 μmol/mol (0.2 ppm) Total sulfur compounds .sup.c (H.sub.2S basis) 0.004 μmol/mol Formaldehyde (HCHO) 0.01 μmol/mol Formic acid (HCOOH) 0.2 μmol/mol Ammonia (NH.sub.3) 0.1 μmol/mol Total halogenated compounds .sup.d 0.05 μmol/mol (Halogenate ion basis) Maximum particulates concentration 1 mg/kg NOTE: For the constituents that are additive, such as total hydrocarbons and total sulfur compounds, the sum of the constituents are to be less than or equal to the acceptable limit. The tolerances in the applicable gas testing method are to be the tolerance of the acceptable limit. .sup.a The hydrogen fuel index is determined by subtracting the “total non-hydrogen gases” in this table, expressed in mole percent, from 100 mole percent. .sup.b Total hydrocarbons include oxygenated organic species. Total hydrocarbons are measured on a carbon basis (μmolC/mol). Total hydrocarbons may exceed 2 μmol/mol due only to the presence of methane, in which case the summation of methane, nitrogen, and argon is not to exceed 100 ppm. .sup.c As a minimum, includes H2S, COS, CS2 and mercaptans, which are typically found in natural gas. .sup.d Includes, for example, hydrogen bromide (HBr), hydrogen chloride (HCl), chlorine (Cl2), and organic halides (R-X)
Other examples of high hydrogen purity specifications are

TABLE-US-00002 H.sub.2 Purity Grades H.sub.2, % non-H.sub.2, ppm Combustion Engine.sup.1 98.000 20,000 Fuel Cell.sup.2 99.970 300 Rocket fuel & Electronic.sup.3 99.999 10 .sup.1International Organization for Standardization (ISO)14687: 2019 .sup.2Hydrogen Fuel Quality Specifications for Polymer Electrolyte Fuel Cells in Road Vehicles, Department of Energy, Energy Efficiency & Renewable Energy, Fuel Cells Technologies Office, Nov. 2, 2016 .sup.3Hydrogen Diverse supply offers for many industries and applications, Air Liquide, 2022
When necessary to meet those specifications, the H.sub.2-rich stream from membrane separator means 2 can be subjected to an additional process step to remove or convert the CO therein to CO.sub.2. An additional advantage of using this additional process step is that less CO and higher hydrogen concentration is fed to the hydrogen enrichment step, e.g., the pressure swing adsorption unit which allows for a significant size reduction of the pressure swing adsorption unit.

[0068] A preferred additional process step is the well-known water gas shift reaction as follows:

CO+H.sub.2OCO.sub.2+H.sub.2

Using this additional process step, it is believed that CO levels in the hydrogen product 261 can be less than about 6 ppm, or less than about 3 ppm, or less than 1 ppm, or less than about 0.210 ppm, or less than about 0.205 ppm, or less than 0.200 ppm, or even 0.153 ppm or less.

[0069] As shown in FIG. 2, permeate H.sub.2-rich stream 27 is fed as a H.sub.2 feed stream to a water gas shift reactor (WGSR) 262 to convert residual permeate CO to CO.sub.2 and generate additional hydrogen in shifted stream 264. Steam generated in Boiler 263 is fed to the WGSR to effect the reaction. Hydrogen enrichment means 141 forms an enriched H.sub.2 stream 261 and a tail gas recycle stream 260. The tail gas stream 260 typically comprises H.sub.2, CO.sub.2, and CO and possibly a trace amounts of CH.sub.4, N.sub.2 and H.sub.2O. Stream 261 can comprise at least about 98.0%, at least about 99.0%, at least about 99.90%, at least about 99.95%, at least about 99.995% or at least about 99.999% H.sub.2. Recycle H.sub.2 enrichment tail gas stream 260 is fed to the retentate CO-rich stream 3 from separator 2. PSA processes typically feed tail gas as fuel, for example, to a steam methane reformer, or make use of an additional process to treat the tail gas with an adsorbent in an additional PSA unit or solvent absorbent such as dimethylethanolamine to remove CO.sub.2 therefrom. By combining the tail gas recycle stream 260 with the retentate CO-rich stream 3 in accordance with the present invention, it is possible to form an oxyfuel gas turbine fuel stream 4 that can accomplish minimal or even very near zero carbon emission hydrogen production. By way of non-limiting illustrative example, this can enable at least about 90%, or at least about 95%, or at least about 99% CO.sub.2 capture in the combusted oxyfuel after water knockout and a virtual zero CO.sub.2 emission concentration of less than about 30 ppmv (parts per million volume), less than about 20 ppmv, less than about 15 ppmv, or less than about 10 ppmv in the high purity hydrogen product stream 261.

EXAMPLES

Below are Nonlimiting Illustrative Examples

Example 1

[0070]

TABLE-US-00003 TABLE 1 UBE Industries, Ltd., Polyimide Membrane H.sub.2 and CO Permeability and Selectivity vs. Temperature Data Barrer.sup.3 Barrer.sup.3 1000T.sup.−1(K).sup.−1 selectivity GPU.sup.1 GPU.sup.1 GPU.sup.2 GPU.sup.2 H.sub.2 CO ° F x ° C H.sub.2/CO H.sub.2 CO H.sub.2 × 10.sup.−6 CO × 10.sup.−6 (×10.sup.−10) (×10.sup.−10)  77.91 3.35 25.51 134.78 0.31 0.002 4.135 0.031 4.135 0.0307 140.60 3.00 60.33 100.00 0.80 0.008 10.671 0.107 10.671 0.1067 207.27 2.70 97.37 75.95 1.80 0.024 24.010 0.316 24.010 0.3161 260.60 2.50 127.00 65.00 2.60 0.040 34.681 0.534 34.681 0.5336 212.00 2.68 100.00 74.88 UBE membrane maximum operating temperature is 100° C. 1-P/I (mm.sup.3/s/m.sup.2/Pa) Selectivity for 100° C. calculated by equation 2-P/l (cm.sup.3/s/cm.sup.2/cm Hg) 3-P (cm.sup.3-cm)/s/cm.sup.2/cm Hg) when I = 0.0001 cm membrane thickness Source: Polyimide Membranes-Applications, Fabrication, and Properties by Haruhiko Ohya, Vladislav V. Kudryavtsev and Svetlana I. Semenova (Jan. 30, 1997) page 250 Gordan and Breach Science Publishers S.A., Emmaplein 5, 1075AW Amsterdam, The Netherlands Pg. 250, FIG. 6.7, Temperature of pure gas permeation rates through asymmetric polyimide hollow fiber membrane . . . by UBE Industries, Ltd. (From Haraya, K. et al., Gas Separation and Purification, 1, 4 (1987))

TABLE-US-00004 TABLE 2 UBE Industries, Ltd., Polyimide Membrane H.sub.2 and CO.sub.2 Permeability and Selectivity vs. Temperature Data Barrer.sup.3 Barrer.sup.3 1000T.sup.−1(K).sup.−1 selectivity GPU.sup.1 GPU.sup.1 GPU.sup.2 GPU.sup.2 H.sub.2 CO.sub.2 ° F x ° C H.sub.2/CO.sub.2 H.sub.2 CO.sub.2 H.sub.2 × 10.sup.−6 CO.sub.2 × 10.sup.−6 (×10.sup.−10) (×10.sup.−10)  77.91 3.35 25.51 6.89 0.31 0.045 4.135 0.600 4.135 0.6003 140.60 3.00 60.33 8.00 0.80 0.100 10.671 1.334 10.671 1.3339 207.27 2.70 97.37 8.82 1.80 0.204 24.010 2.721 24.010 2.7212 260.60 2.50 127.00 9.29 2.60 0.280 34.681 3.735 34.681 3.7349 212.00 2.68 100.00 9.97 UBE membrane maximum operating temperature is 100° C. .sup.1P/I (mm.sup.3/s/m.sup.2/Pa) Selectivity for 100° C. calculated by equation .sup.2P/I (cm.sup.3/s/cm.sup.2/cm Hg) .sup.3P (cm.sup.3-cm)/s/cm.sup.2/cm Hg) when I = 0.0001 cm membranw thickness Source: Polyimide Membranes-Applications, Fabrication, and Properties by Haruhiko Ohya, Vladislav V. Kudryavtsev and Svetlana I. Semenova (Jan. 30, 1997) page 250 Gordan and Breach Science Publishers S.A., Emmaplein 5, 1075AW Amsterdam, The Netherlands, Pg. 250, FIG. 6.7, Temperature of pure gas permeation rates through asymmetric polyimide hollow fiber membrane . . . by UBE Industries, Ltd. (From Haraya, K. et al., Gas Separation and Purification, 1, 4 (1987))

[0071] In Tables 1 and 2, UBE Industries, Ltd. (UBE) is a Japanese multinational manufacturer of polyimide hydrogen separation membranes and have supplied membranes globally to industry for many years.

[0072] H.sub.2 and CO permeability values versus temperature are presented in Table 1 and H.sub.2 and CO.sub.2 permeability values are presented in Table 2. The GPU unit, also known as permeance, is a pressure normalized steady state flux for a given membrane thickness and is given as volumetric flow per unit area per second per unit differential pressure across the membrane. The Barrer unit, also known as permeability, is a steady state flux normalized for both membrane thickness and pressure differential across the membrane and is given as volumetric flow times membrane thickness, per unit area per second per unit differential pressure across the membrane. Selectivity is the ratio of the respective GPU or Barrer units, e.g., Hz/CO selectivity at 97.37° C. of 75.95 is determined by following ratio:

24.1010 cm.sup.3/cm.sup.2/s/cm Hg divided by 0.316.sup.3/cm.sup.2/s/cm Hg=75.95

It can be seen from the Tables 1 and 2 that Hz/CO selectivity is more sensitive to temperature change than H.sub.2/CO.sub.2 selectivity. The maximum operating temperature for the UBE polyimide membrane is 150° C. Operating an UBE polyimide membrane separator means at the maximum temperature of 150° C. increases overall system thermal efficiency. Further, the trendline equation in Table 3 calculates a H.sub.2/CO selectivity of 63.33 at 150° C., a selectivity reduction of only 2.6% compared with 127° C. Furthermore, based a trendline algorithm for temperature vs. H.sub.2 GPU values in Table 3, H.sub.2 GPU is increased by about 30% at 150° C. compared with 127° C. In general, mixed gas selectivity will be lower than pure gas selectivity.

Example 2

[0073]

TABLE-US-00005 TABLE 3 SRI International, Polybenzimidazole (PBI) Membrane H.sub.2, CO and CO.sub.2 mixed gas Permeability and Selectivity vs. Temperature Data Barrer.sup.2 Barrer.sup.2 selectivity GPU.sup.1 GPU.sup.1 H.sub.2 CO ° F ° C H.sub.2/CO H.sub.2 × 10.sup.−6 CO.sub.2 × 10.sup.−6 (×10.sup.−10) (×10.sup.−10) 437.00 225.00 103.0 80.0 0.775 80.0 0.775 .sup.1P/I (cm3/s/cm2/cm Hg) .sup.2P (cm.sup.3- cm)/s/cm.sup.2/cm Hg) when I = 0.0001 cm membrane thickness Barrer.sup.2 Barrer.sup.2 selectivity GPU.sup.1 GPU.sup.1 H.sub.2 CO.sub.2 ° F ° C H.sub.2/CO.sub.2 H.sub.2 × 10.sup.−6 CO.sub.2 × 10.sup.−6 (×10.sup.−10) (×10.sup.−10) 437.00 225.00 40.0 80.0 2.00 80.0 2.00 .sup.1P/I (cm3/s/cm2/cm Hg) .sup.2P (cm.sup.3 x cm)/s/cm.sup.2/cm Hg) when I = 0.0001 cm membrane thickness PBI DATA: The PBI data in Table 3 is available at: https://www.netl.doe.gov/sites/default/files/2017-12/21-S-Jayaweera2-SRI-PBI-Hollow-Fiber-Membranes.pdf

Example 3

[0074] Non-limiting examples of mixed gas selectivity concentrations of the first separated CO-rich stream and the second separated H.sub.2-rich stream achieved by the Ube membrane and the Generon® membrane.

TABLE-US-00006 Ube mem- CO.sub.2 CO CH.sub.4 Ar/N.sub.2 H.sub.2 H.sub.2S H.sub.2O brane conc. conc. conc. conc. conc. conc. conc. Cooled 2.88% 23.98% 0.96% 0.20% 71.93% 0.00% 0.05% syngas Feed, 20° C. First 3.82% 56.80% 2.38% 0.48% 36.52% 0.00% 0.00% CO-rich stream, 20° C. Second 2.26%  2.25% 0.02% 0.02% 95.37% 0.00% 0.08% H.sub.2-rich stream, 20° C. Cooled 2.88% 23.97% 0.96% 0.20% 71.90% 0.00% 0.09% syngas Feed, 30° C. First 3.86% 67.06% 2.88% 0.57% 25.63% 0.00% 0.00% CO-rich stream, 30° C. Second 2.41%  3.19% 0.04% 0.02% 94.21% 0.00% 0.13% H.sub.2-rich stream, 30° C. Cooled 2.88% 23.96% 0.96% 0.20% 71.88% 0.00% 0.12% syngas Feed, 40° C. First 3.83% 64.90% 2.84% 0.56% 27.87% 0.00% 0.01% CO-rich stream, 40° C. Second 2.41%  4.09% 0.05% 0.02% 93.25% 0.00% 0.17% H.sub.2-rich stream, 40° C. Cooled 2.87% 23.92% 0.96% 0.20% 71.76% 0.00% 0.29% syngas Feed, 50° C. First 4.04% 70.87% 3.14% 0.61% 21.33% 0.00% 0.01% CO-rich stream, 50° C. Second 2.39%  4.55% 0.06% 0.03% 92.56% 0.00% 0.41% H.sub.2-rich stream, 50° C. Cooled 2.87% 23.99% 0.97% 0.19% 71.97% 0.00% 0.01% syngas Feed, 38° C. First 2.93% 89.53% 3.88% 0.76%  2.90% 0.00% 0.00% CO-rich stream, 38° C. Second 2.85%  5.42% 0.15% 0.03% 91.54% 0.00% 0.01% H.sub.2-rich stream, 38° C. Cooled 2.87% 23.99% 0.97% 0.19% 71.97% 0.00% 0.01% syngas Feed, 38° C. First 3.02% 73.49% 2.93% 0.58% 19.98% 0.00% 0.00% CO-rich stream, 38° C. Second 2.81%  3.26% 0.15% 0.03% 93.74% 0.00% 0.13% H.sub.2-rich stream, 38° C. Cooled 2.87% 23.99% 0.97% 0.19% 71.97% 0.00% 0.01% syngas Feed, 38° C. First 3.28% 67.29% 2.69% 0.53% 26.21% 0.00% 0.00% CO-rich stream, 38 ° C. Second 2.67%  2.83% 0.13% 0.02% 94.34% 0.00% 0.01% H.sub.2-rich stream, 38° C. Cooled 2.87% 23.99% 0.97% 0.19% 71.97% 0.00% 0.01% syngas Feed, 57° C. First 3.74% 59.84% 2.51% 0.49% 33.42% 0.00% 0.00% CO-rich stream, 57° C. Second 2.38%  3.69% 0.10% 0.02% 93.79% 0.00% 0.02% H.sub.2-rich stream, 57° C.

Example 4

[0075] The present inventor initiated a study to compare membrane performance of an Ube commercial membrane (at 40° C.) and a Generon® commercial membrane (at 38° C.) in separating a syngas. The mixed gas selectivity of these membranes was compared for mixed gas H.sub.2/CO.sub.2 (shifted syngas) vs. mixed gas H.sub.2/CO separations (unshifted syngas).

Membrane Performance Comparison on Unshifted and Shifted Syngas:

[0076] H.sub.2/CO mixed gas selectivity in the Ube and Generon® commercial gas separation membranes for separating unshifted syngas is substantially higher than their H.sub.2/CO.sub.2 mixed gas selectivity for separating shifted syngas. The increase in mixed gas selectivity is greater by more than an order of magnitude, enabling higher recoveries and purities in unshifted syngas for the respective separated gases.

[0077] As an example, for a given unshifted syngas feed composition, the Ube membrane recovers 87.3% of the H.sub.2 at 93.3% purity in the permeate and 88.5% of the CO at 64.9% purity in the retentate. In contrast, for a given shifted syngas feed composition, the Ube membrane recovers 89.2% of the H.sub.2 at 82.8% purity in the permeate and 45.1% of the CO.sub.2 at 52.2% purity in the retentate.

[0078] As another example, for a given unshifted syngas feed composition, the Generon® membrane recovers 91.8% of the H.sub.2 at 93.7% purity in the permeate and 90.4% of the CO at 73.5% purity in the retentate. In contrast, for a given shifted syngas feed composition, the Generon® membrane recovers 91.8% of the H.sub.2 at 79.1% purity in the permeate and 28.1% of the CO.sub.2 at 45.9% purity in the retentate. The above comparisons are presented in the table below:

TABLE-US-00007 Retentate Permeate H.sub.2 rec. H.sub.2 purity CO rec. CO purity Ube unshifted syngas 87.3% 93.3% 88.5% 64.9% Generon ® unshifted 91.8% 93.7% 90.4% 73.5% syngas H.sub.2 rec. H.sub.2 purity CO.sub.2 rec. CO.sub.2 purity Ube shifted syngas 89.2% 82.8% 45.1% 52.2% Generon ® shifted 91.8% 79.1% 28.1% 45.9% syngas
The recoveries and purities of the separated CO.sub.2 from shifted syngas is substantially lower than the recoveries and purities of the separated CO from unshifted syngas.

Example 6

Mass and Energy Balance with Water Gas Shift Reaction

[0079] The following data is based on use of a Generon® membrane operated at 38.7° C. with a H.sub.2/CO selectivity of 34.1.
The numbers on the left refer to the reference numbers in FIG. 3.

TABLE-US-00008 1b Syngas: mole/hr. CO 2399 CO.sub.2 287 H.sub.2 7197 N.sub.2 19 CH.sub.4 97 H.sub.2O 1 10000 27 H.sub.2 rich permeate: mole/hr. CO 230 CO.sub.2 198 H.sub.2 6607 N.sub.2 002 CH.sub.4 010 H.sub.2O 001 7048 264 Shifted H.sub.2 rich permeate: mole/hr. fraction CO 7 0.0005 CO.sub.2 421 0.0305 H.sub.2 13359 0.9680 N.sub.2 2 0.0001 CH.sub.4 100 0.0008 H.sub.2O 1 0.0001 13890 1.0000 261 PSA Product mole/hr. fraction CO 0.00 0.000000153 CO.sub.2 0.00 0.000009543 H.sub.2 10554 0.999990000 N.sub.2 0.00 0.000000045 CH.sub.4 0.00 0.000000236 H.sub.2O 0.00 0.000000023 10554 1.000000000 260 Tail Gas recycle: fraction CO 6.7 0.0021 CO.sub.2 420.7 0.1296 H.sub.2 2805.4 0.8642 N.sub.2 2.0 0.0006 CH.sub.4 10.4 0.0032 H.sub.2O 1.0 0.0003 3246.2 1.0000 4 Combined fuel from, CO-rich retentate stream 3 and tail gas recycle 260 mole/hr. fraction CO 2175.9 0.3510 CO.sub.2 510.0 0.0823 H.sub.2 3395.6 0.5478 N.sub.2 19.0 0.0031 CH.sub.4 97.0 0.0156 H.sub.2O 001.0 0.0002 6198.4 1.0000 22 CO.sub.2 to sequestration or pipeline for use Combusted fuel after water K/O mole/hr. fraction CO 0.000 0.0000 CO.sub.2 2782.9 0.9932 H.sub.2 0.000 0.0000 N.sub.2 19.0 0.0068 CH.sub.4 0.000 0.0000 H.sub.2O 0.000 0.0000 2801.9 1.0000

Example 7

Mass and Energy Balance without Water Gas Shift Reaction

[0080] The following data is based on use of a Generon® membrane operated at 38.7° C. with a H.sub.2/CO selectivity of 34.1.
The numbers on the left refer to the reference numbers in FIG. 4.

TABLE-US-00009 1b Syngas: mole/hr. CO 2399 CO.sub.2 287 H.sub.2 7197 N.sub.2 19 CH.sub.4 97 H.sub.2O 1 10000.00 27 H.sub.2 rich permeate: mole/hr. CO 229.8242 CO.sub.2 197.7430 H.sub.2 6606.8460 N.sub.2 01.9969 CH.sub.4 10.4275 H.sub.2O 0.010000 7047.8376 261 H.sub.2 production: Mole/hr. fraction CO 0.0272 0.000005212 CO.sub.2 0.0234 0.000004484 H.sub.2 5219.4083 0.999990000 N.sub.2 0.0002 0.000000045 CH.sub.4 0.0012 0.000000236 H.sub.2O 0.0001 0.000000023 5219.5605 1.000000000 260 Tail gas recycle: Mole/hr. fraction CO 229.7970 0.125684 CO.sub.2 197.7196 0.108139 H.sub.2 1387.4377 0.758836 N.sub.2 1.9967 0.001092 CH.sub.4 10.4236 0.005702 H.sub.2O 0.9999 0.000547 1828.3771 1.000000 4 Combined fuel from, CO-rich retentate stream 3 and tail gas recycle stream 260: mole/hr. Fraction CO 2398.9728 0.501821 CO.sub.2 286.9766 0.060030 H.sub.2 1977.5917 0.413675 N.sub.2 18.9998 0.003974 CH.sub.4 96.9988 0.020290 H.sub.2O 0.9999 0.000209 4780.5395 1.000000 22 Combusted fuel after water K/O: mole/hr. Fraction CO 0.000000 0.000000 CO.sub.2 2782.9482 0.993219 H.sub.2 0.000000 0.000000 N.sub.2 18.9998 0.006781 CH.sub.4 0.000000 0.000000 H.sub.2O 0.000000 0.000000 2801.9479 1.000000

[0081] PSA gas is typically combusted with air to generate process heat. A syngas feed of 10,000 mole/hr. gives a tail gas recycle of 3,246.3 mole/hr. Directing the tail gas to a vented combustor emits 76,718 (metric) tonne/yr. of uncaptured CO.sub.2 vented to the atmosphere. As illustrated in FIGS. 2 and 3, when the PSA tail gas is combined with the Gas Separation Membrane retentate to form a combined fuel stream of 6,198.4 mole/hr. to the oxyfuel combined cycle. 100% of the carbon in the syngas feed is captured as 487,563.2 tonne/yr. of as CO.sub.2 in the oxyfuel combined cycle exhaust at 99.32% purity. Some PSA systems make use of an additional process to treat the tail gas with an adsorbent in an additional PSA unit or an absorbent such as dimethylethanolamine to remove CO.sub.2 therefrom. In contrast to a system which uses additional PSA or an absorbent process to further remove CO.sub.2 recycling the tail gas to the membrane separator retentate stream allows for the omission of an additional PSA unit or an absorbent process. In addition, because of moving most of the CO in the tail gas to recycle, PSA requirements are substantially reduced.