ATR-BASED HYDROGEN PROCESS AND PLANT

Abstract

A plant and process for producing a hydrogen rich gas are provided, said process comprising the steps of: reforming a hydrocarbon feed in a reforming step thereby obtaining a synthesis gas comprising CH.sub.4, CO, CO.sub.2, H.sub.2 and H.sub.2O; shifting said synthesis gas in a shift configuration including a high temperature shift step; removal of CO.sub.2 upstream hydrogen purification unit, such as a pressure swing adsorption unit (PSA), and recycling off-gas from hydrogen purification unit and mix it with natural gas upstream prereformer feed preheater, prereformer, reformer feed preheater or ATR or shift as feed for the process.

Claims

1. A plant for producing a H.sub.2-rich stream from a hydrocarbon feed, said plant comprising: an autothermal reformer (ATR), said ATR being arranged to receive a hydrocarbon feed and convert it to a stream of syngas; a shift section, said shift section comprising a high temperature shift unit, said high temperature shift unit being arranged receive a stream of syngas from the ATR and shift it in a high temperature shift step, thereby providing a shifted syngas stream; a CO.sub.2 removal section, arranged to receive the shifted syngas stream from said shift section and separate a CO.sub.2-rich stream from said shifted syngas stream, thereby providing a CO.sub.2-depleted shifted syngas stream, a hydrogen purification unit, arranged to receive said CO.sub.2-depleted shifted syngas stream, from said CO.sub.2 removal section, and separate it into a high-purity H2 stream and an off-gas stream; wherein said plant is arranged to feed at least a part of the off-gas stream from said hydrogen purification unit as an off-gas recycle stream to the feed side of the ATR, and/or wherein said plant is arranged to feed at least a part of the off-gas stream from said hydrogen purification unit as an off-gas recycle stream to the feed side of the shift section, and/or wherein said plant further comprises at least one prereformer unit arranged upstream the ATR, said prereformer unit being arranged to pre-reform said hydrocarbon feed prior to it being fed to the ATR and wherein said plant (100) is arranged to feed at least a part of the off-gas stream from said hydrogen purification unit as an off-gas recycle stream to the feed side of the prereformer unit.

2. The plant according to claim 1, wherein said off-gas recycle stream is mixed with hydrocarbon feed before being fed to the feed side of the ATR.

3. The plant (100) according to claim 1, wherein said off-gas recycle stream is mixed with hydrocarbon feed before being fed to the feed side of the prereformer unit.

4. The plant according to claim 1, wherein the high temperature shift (HTS) unit comprises a promoted zinc-aluminium oxide based high temperature shift catalyst.

5. The plant according to claim 1, wherein said reforming section further comprises at least one fired heater, arranged to pre-heat said hydrocarbon feed prior to it being fed to the ATR.

6. The plant according to claim 5, wherein said plant is arranged to feed at least a part of the off-gas stream from said hydrogen purification unit as fuel for said fired heater.

7. The plant according to claim 1, wherein the hydrogen purification unit is selected from a pressure swing adsorption (PSA) unit, a hydrogen membrane or a cryogenic separation unit.

8. The plant according to claim 1, wherein the CO.sub.2 removal section is selected from an amine wash unit, or a CO.sub.2 membrane, or a cryogenic separation unit.

9. The plant according to claim 1, wherein the shift section comprises one or more additional high temperature shift units in series.

10. The plant according to claim 1, wherein said shift section further comprises one or more additional shift units downstream the high temperature shift unit.

11. The plant according to claim 10, wherein the one or more additional shift units are one or more medium temperature shift units and/or one or more low temperature shift units.

12. The plant according to claim 1, further comprising a methanol removal section arranged between the shift section and said CO.sub.2 removal section, said methanol removal section being arranged to separate a methanol-rich stream from said shifted syngas stream.

13. The plant according to claim 1, the CO.sub.2 removal section is a CO.sub.2 membrane, said CO.sub.2 membrane is arranged to produce a hydrogen-rich permeate stream for further enrichment in said hydrogen purification unit and a hydrogen-lean retentate stream, wherein said plant is arranged to feed at least a part of the hydrogen-lean retentate stream from said CO.sub.2 membrane as a hydrogen recycle stream to the feed side of the ATR, and/or wherein said plant is arranged to feed at least a part of the hydrogen-lean retentate stream from said CO.sub.2 membrane as a hydrogen recycle stream to the feed side of the shift section, and/or wherein said plant is arranged to feed at least a part of the hydrogen-lean retentate stream from said CO.sub.2 membrane as a hydrogen recycle stream to the inlet of the CO.sub.2 membrane.

14. The plant according to claim 1, wherein the CO.sub.2 removal section is a cryogenic separation unit, said cryogenic separation unit is arranged to produce a cryogenic unit off-gas stream and said CO.sub.2-depleted shifted syngas stream, wherein said plant is arranged to feed at least a part of the off-gas stream from said cryogenic separation unit as a cryogenic off-gas recycle stream to the feed side of the ATR, and/or wherein said plant is arranged to feed at least a part of the off-gas stream from said cryogenic separation unit as a cryogenic off-gas recycle stream to the feed side of the shift section, and/or wherein said plant is arranged to feed at least a part of the off-gas stream from said cryogenic separation unit as a cryogenic off-gas recycle stream to the feed side.

15. The plant according to claim 1, said plant further comprising a compressor arranged for compressing said off-gas recycle stream, and a membrane separation unit for separating the thus compressed off-gas recycle stream into a permeate membrane stream and a retentate membrane stream, said compressor being adapted upstream said membrane separation unit, said permeate membrane stream being hydrogen rich, and said plant is arranged for recycling said permeate membrane stream, optionally via a compressor, to the feed side of the hydrogen purification unit, and/or said plant is arranged for mixing said permeate membrane stream with said high purity hydrogen stream from the hydrogen purification unit, and for recycling said membrane retentate as fuel for said at least one fired heater.

16. The plant according to claim 1, said plant further comprising a compressor arranged for compressing said off-gas recycle stream, and a CO.sub.2 separation unit for removal of CO.sub.2 from the thus compressed off-gas recycle stream into a CO.sub.2-rich off-gas stream and a CO.sub.2-lean off-gas stream, said compressor being adapted upstream said CO.sub.2 separation unit, and said plant is arranged for recycling said CO.sub.2-lean off-gas stream, optionally via a compressor, to the feed side of the ATR, and/or to the feed side of the shift section, and/or to the feed side of the hydrogen purification unit, and/or as fuel for said at least one fired heater.

17. A process for producing a H.sub.2-rich stream from a hydrocarbon feed, said process comprising the steps of: providing a plant according to claim 1; supplying a hydrocarbon feed to the ATR, and converting it to a stream of syngas; supplying a stream of syngas from the ATR to the shift section, and shifting it in a high temperature shift step, thereby providing a shifted syngas stream; supplying the shifted gas stream from the shift section to the CO.sub.2 removal section, and separating a CO.sub.2-rich stream from said shifted syngas stream, thereby providing a CO.sub.2-depleted shifted syngas stream, supplying said CO.sub.2-depleted shifted syngas stream from said CO.sub.2 removal section to a hydrogen purification unit, and separating it into a high-purity H.sub.2 stream and an off-gas stream; and, feeding at least a part of the off-gas stream from said hydrogen purification unit as an off-gas recycle stream to the feed side of ATR, and/or feeding at least a part of the off-gas stream from said hydrogen purification unit as an off-gas recycle stream to the feed side of the shift section; and/or wherein said plant further comprises at least one prereformer arranged upstream the ATR, being arranged to pre-reform said hydrocarbon feed prior to it being fed to the ATR; feeding at least a part of the off-gas stream from said hydrogen purification unit as an off-gas recycle stream to the feed side of the prereformer unit.

18. The process according to claim 17, wherein the steam/carbon ratio of the synthesis gas supplied from the ATR to the shift section is less than 2.0.

19. The process according to claim 17, wherein the temperature in the high temperature shift step is 300-600° C.

20. The process according to claim 17, wherein the steam/carbon ratio of the synthesis gas from the reforming step, defined as the molar ratio of all steam added upstream the shift section to the carbon of the hydrocarbon feed, is 2.6-0.1.

21. The process according to claim 17, wherein the space velocity in ATR is less than 20000 Nm.sup.3 C/m.sup.3/h.

22. The process according to claim 17, wherein the synthesis gas is washed with water to reduce the methanol content.

23. The process according to claim 17, wherein the CO.sub.2 depleted shifted gas stream comprises less than 500 or 400 ppmv CO.sub.2.

24. The process according to claim 17, wherein the CO.sub.2 removal section is a CO.sub.2-membrane producing i) said CO.sub.2-depleted shifted syngas stream as a hydrogen-rich permeate stream for further enrichment in said hydrogen purification unit and ii) a hydrogen-lean retentate stream; and feeding at least a part of the hydrogen-lean retentate stream as a hydrogen recycle stream to the feed side of the ATR, and/or feeding at least a part of the hydrogen-lean retentate stream as a hydrogen recycle stream to the feed side of the shift section.

25. The process according to claim 17, wherein the CO.sub.2 removal section is a cryogenic separation unit producing a cryogenic unit off-gas stream and said CO.sub.2-depleted shifted syngas stream, and feeding at least a part of the off-gas stream from said cryogenic separation unit as a cryogenic off-gas recycle stream to the feed side of the ATR, and/or feeding at least a part of the off-gas stream from said cryogenic separation unit as a cryogenic off-gas recycle stream to the feed side of the shift section, and/or feeding at least a part of the off-gas stream from said cryogenic separation unit as a cryogenic off-gas recycle stream to the feed side.

26. The process according to claim 17, further comprising a compressor thereby providing a step for compressing said off-gas recycle stream, and a membrane separation unit thereby providing a step for separating the thus compressed off-gas recycle stream into a permeate membrane stream and a retentate membrane stream, said compressing step being conducted prior to said membrane separating step, said permeate membrane stream being hydrogen rich, and recycling said permeate membrane stream, optionally via a compressing step, to the feed side, and/or mixing said permeate membrane stream with said high purity hydrogen stream from the hydrogen purification unit, and recycling said membrane retentate as fuel for said at least one fired heater.

27. The process according to claim 17, further comprising a compressor, thereby providing a step for compressing said off-gas recycle stream, and a CO.sub.2 separation unit thereby providing a step for removing CO.sub.2 from the thus compressed off-gas recycle stream into a CO.sub.2-rich off-gas stream and a CO.sub.2-lean off-gas stream, said compressing step being conducted prior to said CO.sub.2 separation unit, and recycling said CO.sub.2-lean off-gas stream, optionally via a compressing step, to the feed side of the ATR, and/or feed side of the shift section, and/or feed side of the hydrogen purification unit, and/or as fuel for said at least one fired heater.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0130] FIGS. 1 and 2 illustrate layouts of the ATR-based hydrogen process and plant. FIG. 2 comprises the elements of FIG. 1, plus the additional steps of methanol removal and CO.sub.2 removal and different feeding points of an off-gas stream from the hydrogen purification unit.

DETAILED DESCRIPTION

[0131] FIG. 1 shows a plant 100 in which a hydrocarbon feed 1, i.e. main hydrocarbon feed 1, such as natural gas, is passed to a reforming section comprising a pre-reforming unit 140 and autothermal reformer 110. The reforming section may also include a hydrogenator and sulfur absorber unit (not shown) upstream the pre-reforming unit 140. The hydrocarbon steam 1 is mixed with steam 13 and optionally also with a portion of a hydrogen-rich stream 8 from a first hydrogen purification unit 125 located downstream. The resulting hydrocarbon feed 2 is fed to ATR 110, as so is oxygen 15 and steam 13. The oxygen stream 15 is produced by means of an air separation unit (ASU) 145, to which air 14 is fed. In the ATR 110, the hydrocarbon feed 2 is converted to a stream of syngas 3, which is then passed to a shift section. The hydrocarbon feed 2 enters the ATR at 650° C. and the temperature of the oxygen is around 253° C. The steam/carbon ratio of the synthesis gas 3 from the reforming is S/C=0.6. This syngas, i.e. process gas 3 leaves the reforming section at about 1050° C. through a refractory lined outlet section and transfer line to the waste heat boilers in the process gas cooling section.

[0132] The shift section comprises a high temperature shift (HTS) unit 115 where additional or extra steam 13′ also may be added upstream. Additional shift units, such as a low temperature shift unit 150 may also be included in the shift section. Additional or extra steam 13′ may also be added downstream the HTS unit 115 but upstream the low temperature shift unit 150. By way of example, in a shift section including high and medium/low temperature shift, the high temperature shift operates under the following conditions: HT shift: Tin/Tout: 330/465° C. (ΔT=135° C.); LT shift: Tin/Tout: 195/250° C. (ΔT=55° C.). After reforming, about 28.3 vol % CO is present in the syngas 3 (dry basis). In the high temperature shift converter, the CO content is reduced to approximately 7.6 vol %, and the temperature increases from 330° C. to 465° C. The heat content of the effluent from the high temperature CO converter is recovered in a waste heat boiler and in a boiler feed water preheater. The process gas from the high shift converter is thereby cooled to 195° C. and passed on to the medium/low temperature shift converter in which the CO content is reduced to approximately 1.0 vol %, while the temperature increases to 250° C.

[0133] From the shift section, a shifted gas stream 5 is thus produced, which is then fed to a CO2-removal section (not shown). The .sub.CO2-removal section separates a .sub.CO2-rich stream from the syngas stream (5), thereby providing a CO2-depleted syngas stream (7). This syngas stream (7) is then fed to a hydrogen purification unit 125, e.g. a PSA-unit, from which a high purity H.sub.2 stream 8 and an off-gas recycle stream 9 is produced. This off-gas recycle stream 9 serves as fuel for a fired heater 135 and optionally also as fuel for steam superheaters. The fired heater 135 provides for the indirect heating of hydrocarbon feed 1 and hydrocarbon feed 2. Preferably, the off-gas recycle stream 9 to the fired heater is the uncompressed portion of the off-gas stream which has been passed through an off-gas recycle compressor (not shown).

[0134] FIG. 2 shows specific embodiments of the invention in addition to the elements of FIG. 1, in the form of a methanol removal and water wash section 160 and CO.sub.2-removal section 170, as well as feeding points of the off-gas 9 from the hydrogen purification unit 125.

[0135] From the shift section, a shifted gas stream 5 is produced, which is fed to the optional methanol removal and water wash section 160, thereby producing a feed syngas stream 6 which is then fed to the CO.sub.2-removal section 170 comprising e.g. a CO.sub.2-absorber and a CO2-stripper. In the CO.sub.2-removal section 170, the CO.sub.2 content in the outlet stream from shift section (shifted gas stream 5) is reduced to 20 ppmv. All methanol in the synthesis gas going to the CO.sub.2 removal section will leave this section with the process condensate and the CO.sub.2 product stream. A water wash on the synthesis gas 5 going to the CO.sub.2 removal section or on the CO.sub.2 product stream can minimize the methanol content in the CO.sub.2 product stream 10. The CO2-removal section separates such CO.sub.2-rich stream 10 from the syngas stream 5, thereby providing a CO2-depleted syngas stream 7. This syngas stream 7 is then fed to a hydrogen purification unit 125, e.g. a PSA-unit, from which a high purity H.sub.2 stream 8 and an off-gas stream 9 are produced. The plant 100 is arranged to feed at least a part of the off-gas stream 9 from said hydrogen purification unit 125 as an off-gas recycle stream 9′ to the feed side of the ATR 110, and/or as an off-gas recycle stream 9″ to the feed side of the shift section, and/or as an off-gas recycle stream 9′″ to the feed side of the prereformer unit 140, e.g. by mixing with natural gas feed 1 upstream a prereformer feed preheater (not shown). Preferably, the off-gas recycle stream 9′, 9″, 9′″ to respectively the ATR (110), shift (HTS unit 115) and pre-reformer unit (140) is the compressed portion of the off-gas stream 9 which has been passed through an off-gas recycle compressor (not shown). The off-gas recycle stream 9 may also serve as fuel for a fired heater 135 and optionally also as fuel for steam superheaters, as described in connection with FIG. 1.