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 using an autothermal reformer (ATR) 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; passing the shifted syngas to a first hydrogen purification unit, e.g. a PSA unit; passing a portion of the off-gas from the first hydrogen purification unit to a second hydrogen purification unit, and using off-gas from the first and second hydrogen purification unit as e.g. fuel for a preheater unit before the ATR.

Claims

1. A plant for producing a H.sub.2-rich stream from a main hydrocarbon feed, said plant comprising: a reforming section, said reforming section 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 (HTS) unit, said high temperature shift unit being arranged to receive a stream of syngas from the ATR and shift it in a high temperature shift step, thereby providing a shifted syngas stream; a water separation section, said water separation section comprising a separator unit, said water separation section arranged to receive the shifted syngas stream from said shift section and separating water from said shifted syngas stream as a process condensate stream in said separator unit thereby providing a water-depleted shifted syngas stream; a first hydrogen purification unit, arranged to receive said water-depleted shifted syngas stream from said separator unit, and separate it into a first high-purity H.sub.2 stream and a first off-gas stream; means for separating said first off-gas stream into a first off-gas fuel stream and a first off-gas feed stream; a second hydrogen purification unit, arranged to receive said first off-gas feed stream and separate it into a second high-purity H.sub.2 stream and a second off-gas fuel stream; and said reforming section further comprises at least one fired heater arranged to pre-heat said main hydrocarbon feed prior to it being fed to said ATR, and said plant is arranged to feed said first off-gas fuel stream and/or said second off-gas fuel stream as fuel for said at least one fired heater.

2. The plant according to claim 1, wherein said plant is without i.e. is absent of a steam methane reformer unit (SMR) upstream the ATR, and/or is without a CO.sub.2-removal section downstream said shift section and upstream said water separation section.

3. The plant according to claim 1, wherein said plant further comprises a compressor arranged for compressing said first off-gas feed stream prior to it being fed to said second hydrogen purification unit.

4. The plant according to claim 1, wherein the first high-purity H.sub.2 stream is mixed with the second high-purity H.sub.2 stream to form a hydrogen-rich stream.

5. The plant according to claim 2, wherein said first off-gas fuel stream and/or said second off-gas fuel stream are mixed to form a combined off-gas fuel stream prior to being fed as fuel for said at least one fired heater.

6. The plant according to claim 1, wherein said reforming section further comprises at least one pre-reforming unit which is arranged upstream the ATR to pre-reform said main hydrocarbon feed and form said hydrocarbon feed prior to it being fed to the ATR.

7. The plant according to claim 7, wherein said reforming section further comprises a hydrogenator unit, a sulfur absorption unit arranged upstream said at least one pre-reformer unit, and a hydrogen-recycling compressor for feeding a portion of said first high-purity H.sub.2 stream into said main hydrocarbon feed prior to it being fed to the feed side of said at least one pre-reformer unit or prior to it being fed to the feed side of said hydrogenator.

8. The plant according to claim 1, wherein said first hydrogen purification unit and said second hydrogen purification unit are selected from a pressure swing adsorption (PSA) unit, a hydrogen membrane, a cryogenic separation unit, or combinations thereof.

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

10. The plant according to claim 1, wherein the shift section comprises one or more additional high temperature shift units in series, and/or one or more additional shift units downstream the high temperature shift unit.

11. A process for producing a H.sub.2-rich stream from a main 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 gas stream; supplying the shifted gas stream from the shift section to a water separation section, and separating water from said shifted syngas stream as a process condensate stream in a separator unit, thereby providing a water-depleted shifted syngas stream; supplying said water-depleted syngas stream to a first hydrogen purification unit, and separating it into a first high-purity H.sub.2 stream and a first off-gas stream, separating said first off-gas stream into a first off-gas fuel stream and a first off-gas feed stream; feeding said first off-gas feed stream into a second hydrogen purification unit and separating it into a second high-purity H.sub.2 stream and a second off-gas fuel stream; and pre-heating said main hydrocarbon feed prior to being fed to said ATR in at least one fired heater, and feeding said first off-gas fuel stream and/or said second off-gas fuel stream as fuel for said at least one fired heater.

12. The process of claim 11, wherein the process further comprises pre-reforming said main hydrocarbon feed in at least one pre-reforming unit to form a hydrocarbon feed prior to it being fed to the ATR, and mixing a portion of said first high-purity H.sub.2 stream with main hydrocarbon feed before being fed to the feed side of said at least one pre-reforming unit.

13. The process according to claim 12, wherein the steam to carbon ratio of the synthesis gas supplied from the ATR to the shift section is less than 2.0.

14. The process according to claim 11, wherein the steam to carbon ratio defined as the molar ratio of all steam added upstream the shift section to the carbon of main hydrocarbon feed and/or hydrocarbon feed, is 2.6-0.1.

15. The process according to claim 11, wherein the process further comprises adding steam (13) to any of: main hydrocarbon feed, hydrocarbon feed, an oxygen stream (15) fed to the ATR, ATR, HTS unit, additional shift units downstream the HTS unit, or combinations thereof.

Description

BRIEF DESCRIPTION OF THE FIGURE

[0081] The sole FIGURE illustrates a layout of the ATR-based hydrogen plant and process according to an embodiment of the invention including two hydrogen purification units (PSA-units).

DETAILED DESCRIPTION OF THE FIGURE

[0082] The FIGURE shows a plant 100 according to an embodiment of the invention in which a main hydrocarbon feed 1, such as natural gas, is passed to a reforming section comprising a pre-reforming unit 140 and autothermal reformer (ATR) 110. The reforming section may also include a hydrogenator and sulfur absorber unit (not shown) upstream the prereforming unit 140. The main hydrocarbon steam is mixed with steam 13 and optionally also with a hydrogen-rich stream 8 from a first hydrogen purification unit 125 located downstream. The resulting hydrocarbon feed 2 is fed to the 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 section 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.

[0083] The shift section comprises a high temperature shift (HTS) unit 115 where steam 13 also may be added upstream. Additional shift units, such as medium and low temperature shift units (not shown) may also be included in the shift section. 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. (T=135 C.); LT shift: Tin/Tout: 195/250 C. (T=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.

[0084] From the shift section, a shifted gas stream 5 is thus produced, which is then cooled and fed to a water separation section comprising a separator unit 120 e.g. a process condensate separator, thereby providing a water-depleted shifted syngas stream 7 and a process condensate stream 6. The syngas stream 7 is then fed to a first hydrogen purification unit 125, e.g. a first PSA-unit, from which a first high purity H.sub.2 stream 8 and a first off-gas stream 9 are produced. This first off-gas stream 9 is divided in a first off-gas fuel stream 9 and a first off-gas feed stream 10. The latter is fed to a second hydrogen purification unit 130, e.g. a second PSA-unit, which produces a second high-purity H.sub.2 stream 8 and a second off-gas fuel stream 11. The first and second off-gas fuel streams 9 and 11 are combined into a common off-gas fuel stream 12, which 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 main hydrocarbon feed 1 and hydrocarbon feed 2. The first and second high-purity hydrogen streams 8, 8 are combined into a final hydrogen-rich stream 8, e.g. the H.sub.2 product stream. By the invention it is now possible to improve recovery of hydrogen and at the same time reduce the consumption of hydrocarbon feed, e.g. natural gas.