ATR-Based Hydrogen Process and Plant

Abstract

A plant and process for producing a hydrogen rich gas and improved carbon capture are provided, said process comprising the steps of: reforming a hydrocarbon feed by optional prereforming, autothermal reforming (ATR), yet no primary reforming, thereby obtaining a synthesis gas; shifting said synthesis gas in a shift section including a high temperature shift step; removal of CO.sub.2 upstream hydrogen purification unit, thereby producing a hydrogen rich stream and an off-gas stream, and where at least part of the off-gas stream is recycled to the process, thus to the ATR and optional prereforming, and/or to the shift section.

Claims

1. A plant (100) 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 the 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 H.sub.2 stream and an off-gas stream-; wherein said plant is absent of a primary reforming unit; 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 as an off-gas recycle stream to the feed side of the shift section; and wherein said plant is arranged to provide an inlet temperature of said hydrocarbon feed to the ATR of below 600° C.

2. The plant according claim 1, 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 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.

3. The plant according to claim 1, wherein said plant is absent of a prereformer unit.

4. The plant according to claim 1 further comprising: a hydrogenator unit and a sulfur absorption unit arranged upstream said at least one pre-reformer unit or said ATR, 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 hydrogenator unit; and wherein the plant is arranged for the outlet temperature of said sulfur absorption unit matching the inlet temperature of the ATR.

5. The plant according to claim 1, wherein said plant is arranged to provide a steam-to-carbon ratio in the ATR of 0.4 or higher, yet said steam-to-carbon ratio being not greater than 2.0, and/or wherein the ATR is arranged to operate at 20-30 barg.

6. The plant of claim 1, wherein said plant further comprises a heater arranged to pre-heat said hydrocarbon feed prior to it being fed to the ATR and/or prior to it being fed to at least one prerefomer unit.

7. The plant according to claim 6, 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, and/or wherein said plant is arranged to feed a portion of the H.sub.2-rich stream as fuel for said fired heater.

8. The plant according to claim 1, wherein said plant is absent of a fired heater arranged to pre-heat said hydrocarbon feed prior to it being fed to the ATR and/or prior to it being fed to at least one prerefomer unit.

9. 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.

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

11. 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; wherein the process is absent of primary reforming; wherein the process comprises 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 ATR; and/or as an off-gas recycle stream to the feed side of the shift section; and wherein the inlet temperature of said hydrocarbon feed to the ATR is below 600° C.

12. The process of claim 11, comprising: prereforming said hydrocarbon feed prior to it being fed to the ATR, 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 the prereformer unit.

13. The process of claim 11, further comprising adding steam to: the ATR, the hydrocarbon feed, and/or the syngas stream prior to entering the shift section.

14. The process of claim 11, wherein the steam-to-carbon ratio in the ATR is 0.4 or higher, yet said steam-to-carbon ratio being not greater than 2.0, and/or wherein the ATR is arranged to operate at 20-30 barg.

15. The process of claim 11, comprising: pre-heating said hydrocarbon feed in a heater, such as an electrical heater or a fired heater, prior to it being fed to the ATR, and/or prior to it being fed to at least one prerefomer unit, and feeding at least a part of the off-gas stream and/or a portion of the H.sub.2-rich stream from said hydrogen purification unit as fuel for said fired heater.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0164] 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

[0165] 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 in the ATR e.g. 0.8, 0.6 or 0.4 and the pressure lower than 30 barg, for instance 24-28 barg. This syngas, here being the process gas 3 exits the ATR at about 1050° C. through a refractory lined outlet section and transfer line to the waste heat boilers in the process gas cooling section.

[0166] 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.

[0167] From the shift section, a shifted gas stream 5 is thus produced, which is then fed to a CO.sub.2-removal section (not shown). The CO.sub.2-removal section separates a CO.sub.2-rich stream from the syngas stream (5), thereby providing a CO.sub.2-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 H.sub.2-rich stream 8 (high-purity H.sub.2 stream) and an off-gas recycle stream 9 is produced. This off-gas recycle stream 9 serves as fuel for an optional fired heater 135 and optionally also as fuel for steam superheaters. A portion of the H.sub.2-rich stream is optionally also used as fuel (not shown) for the fired heater 135. 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).

[0168] 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.

[0169] 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 CO.sub.2-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 CO.sub.2-removal section separates such CO.sub.2-rich stream 10 from the syngas stream 5, thereby providing a CO.sub.2-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 H.sub.2-rich 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). Thereby the carbon capture in the hydrocarbon feed is further increased. 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.