PLANT AND PROCESS FOR PRODUCING HYDROGEN WITH IMPROVED OPERATION OF A LOW TEMPERATURE CO2 REMOVAL UNIT

Abstract

A plant and process for producing a hydrogen rich gas are provided, said process including the steps of: steam reforming a hydrocarbon feed into a synthesis gas; shifting the synthesis gas and conducting the shifted gas to a hydrogen purification unit, subjecting CO.sub.2-rich off-gas from the hydrogen purification unit to a carbon dioxide removal in a low temperature CO.sub.2-removal section and recycling CO.sub.2-depleted off-gas rich in hydrogen to the process. A drying unit upstream the CO.sub.2-removal section is provided, under the addition of regeneration gas produced in the plant and process.

Claims

1. A plant for producing a hydrogen product from a hydrocarbon feed, said plant comprising: a reforming unit, said reforming unit being arranged to receive a hydrocarbon feed and convert it to a syngas stream; a shift section being arranged to receive syngas stream from the steam reforming unit and shift it into a shifted syngas stream; a hydrogen purification unit, arranged to receive said shifted syngas stream and separate it into a high-purity H.sub.2 stream as said hydrogen product, and a CO.sub.2-rich off-gas stream; a steam header arranged to receive steam produced by the cooling of: said syngas stream and/or said shifted syngas stream; a CO.sub.2-rich off-gas compressor, arranged to receive and compress said CO.sub.2-rich off-gas stream into a compressed CO.sub.2-rich off-gas stream; a drying unit arranged to receive the compressed CO.sub.2-rich off-gas stream and provide a dried compressed CO.sub.2-rich off-gas stream; said drying unit further being arranged to receive an inlet regeneration gas stream and to withdraw an exit regeneration gas stream; said drying unit further comprising: a heat exchanging unit arranged to preheat the inlet regeneration gas stream; low temperature CO.sub.2-removal section arranged to receive said dried compressed CO.sub.2-rich off-gas stream for removal of CO.sub.2 from the CO.sub.2-rich off-gas stream or from said dried compressed CO.sub.2-rich off-gas stream, and provide at least: a CO.sub.2-product stream and a CO.sub.2-depleted off-gas stream.

2. The plant according to claim 1, wherein said steam header is a low pressure (LP) steam header or a high pressure (HP) saturated steam header.

3. The plant according to claim 2, wherein said low pressure (LP) steam header or said high pressure (HP) saturated steam header is arranged to receive steam produced by the cooling of said flue gas stream.

4. The plant according to claim 3, wherein said heat exchanging unit of said drying unit is arranged to preheat the inlet regeneration gas stream by indirect cooling of said a flue gas stream generated in said reforming unit as a heat exchanging medium.

5. The plant according to claim 1, wherein said low temperature CO.sub.2-removal section also provides a CO.sub.2-recycling stream; and the plant is further arranged to feed at least a portion of said CO.sub.2-recycling stream to a location upstream said CO.sub.2-rich off-gas compressor and downstream said hydrogen purification unit; or to combine at least a portion of said CO.sub.2-recycling stream with said shifted syngas stream upstream said hydrogen purification unit.

6. The plant according to claim 1, wherein said plant is further arranged for recycling said CO.sub.2-depleted off-gas stream or a portion thereof, at least to the feed side of the reforming unit.

7. The plant according to claim 1, further comprising at least one fired heater arranged to pre-heat said hydrocarbon feed prior to it being fed to the reforming unit, and wherein said plant is arranged to feed at least a part of the CO.sub.2-rich off-gas stream from said hydrogen purification unit, or at least part of said CO.sub.2-depleted off-gas stream as fuel for said fired heater.

8. The plant according to claim 1, wherein said plant further comprises at least one prereformer unit arranged upstream the reforming unit, said prereformer unit being arranged to pre-reform said hydrocarbon feed prior to it being fed to the reforming unit.

9. The plant according to claim 1, wherein said reforming unit comprises an autothermal reformer (ATR), and the plant further comprises an Air Separation Unit (ASU) which is arranged to receive an air stream and produce a N.sub.2-rich stream and an O.sub.2-rich stream; and the inlet regeneration gas stream is at least a portion of said N.sub.2-rich stream.

10. The plant according to claim 1, wherein the inlet regeneration gas stream is selected from: at least a portion of any of said: CO.sub.2-product stream, CO.sub.2-depleted off-gas stream, CO.sub.2-recycling stream, and dried compressed CO.sub.2-rich off-gas stream; at least a portion of said hydrogen product.

11. The plant according to claim 1, wherein the plant further comprises: a cooler arranged to receive the exit regeneration gas stream for condensing its water content and to provide a dried exit regeneration gas stream; a recycle regeneration gas compressor arranged to receive and compress the exit regeneration gas stream or the dried exit regeneration gas stream into a compressed exit regeneration gas stream or compressed dried exit regeneration gas stream, and recycle it to: inlet of said drying unit; or inlet of said hydrogen purification unit; or inlet of said CO.sub.2-rich off-gas compressor.

12. The plant according to claim 1, wherein the low temperature CO.sub.2-removal section is a cryogenic separation unit comprising a cryogenic compressor; the plant further comprising a superheated steam header and a steam turbine for providing electricity for said cryogenic compressor, and said steam turbine is arranged to receive a portion of steam from said superheated steam header for providing said electricity.

13. The plant according to claim 1, wherein: the drying unit is a temperature swing adsorption (TSA) unit.

14. The plant according to claim 6, wherein the plant is arranged for said CO.sub.2-depleted off-gas stream or a portion thereof being directly recycled to at least the feed side of the reforming unit.

15. The plant according to claim 1, wherein the plant is arranged to directly feed said shifted syngas stream to said hydrogen purification unit.

16. A process for producing a hydrogen product from a hydrocarbon feed, said process comprising the steps of: providing a plant according claim 1; supplying the hydrocarbon feed to the reforming unit, and converting it to the syngas stream; supplying the stream of syngas from the reforming unit to the shift section, and shifting it in a shift step, thereby providing the shifted syngas stream; supplying the shifted gas stream from the shift section to hydrogen purification unit, and separating it into high-purity H.sub.2 stream as said hydrogen product and CO.sub.2-rich off-gas stream; the process further comprising: compressing said CO.sub.2-rich off-gas stream into the compressed CO.sub.2-rich off-gas stream; drying the compressed CO.sub.2-rich off-gas stream in a drying unit under the addition of an inlet regeneration gas stream, thereby providing the dried compressed CO.sub.2-rich off-gas stream and the exit regeneration gas stream; preheating the inlet regeneration gas stream thereby providing a cooled heat exchanging medium as: a steam condensate, a cooled steam, a cooled synthesis gas, a cooled shifted syngas stream, and/or a cooled flue gas stream; supplying the dry compressed CO.sub.2-rich off-gas stream to a CO.sub.2-removal step in a low temperature CO.sub.2-removal section, thereby providing a CO.sub.2-product stream, a CO.sub.2-depleted off-gas stream, and/or a CO.sub.2-recycling stream.

17. The plant of claim 1, wherein the heat exchanging unit is arranged to preheat the inlet regeneration gas stream by indirect cooling of said shifted syngas stream as a heat exchange medium.

18. The plant of claim 1, wherein the heat exchanging unit is arranged to preheat the inlet regeneration gas stream by indirect cooling of said syngas stream as a heat exchange medium.

19. The plant of claim 1, wherein the heat exchanging unit is arranged to preheat the inlet regeneration gas stream by indirect cooling of said steam from said steam header as a heat exchange medium.

20. The plant of claim 1, wherein the heat exchanging unit is arranged to preheat the inlet regeneration gas stream by indirect cooling of said flue gas stream as a heat exchange medium.

21. The plant of claim 1, wherein the heat exchanging unit is arranged to preheat the inlet regeneration gas stream by indirect cooling of said steam produced by cooling of said flue gas stream as a heat exchange medium.

22. The plant of claim 1, wherein heat from a heat exchange medium is used to heat a drying stream of the drying unit and/or regenerate an adsorption material or bed or of the drying unit.

23. The plant of claim 22, wherein heat drying unit is a temperature swing adsorption (TSA) unit.

24. The plant of claim 1, wherein the reforming unit comprises an autothermal reformer (ATR).

25. The plant of claim 1, wherein the reforming unit is a combination of an autothermal reformer (ATR) and a gas heated reformer (GHR).

26. The plant of claim 1, wherein the reforming unit comprises a steam methane reformer (SMR).

27. The plant of claim 1, wherein the shift section is a high temperature shift unit, medium temperature shift unit or a combination thereof.

28. The plant of claim 1, wherein the hydrogen purification unit is a pressure swing adsorption (PSA) unit.

29. The plant of claim 1, wherein the low temperature CO2-removal section is a cryogenic separation unit.

30. The plant of claim 1, wherein the low temperature CO2-removal section is a physical absorption unit, an adsorption unit or a combination thereof.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0129] FIG. 1 illustrates a layout of an ATR-based hydrogen process and plant in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

[0130] The appended FIG. 1 (drawing) shows a plant 100 for producing hydrogen 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 a reforming unit 110 here illustrated as an autothermal reformer. The reforming section may also include a hydrogenator and sulfur absorber unit (not shown) upstream the pre-reforming unit 140. The hydrocarbon stream 1 is mixed with steam 13. The resulting hydrocarbon feed 2 is fed to ATR 110, as so is oxygen-rich stream 15 and steam 13. The oxygen-rich stream 15 is produced by means of an air separation unit (ASU) 145 to which air 14 is fed. The ASU 145 produces also a nitrogen-rich stream 19, which in this embodiment of the invention is used as inlet regeneration gas stream in drying unit 190 of the plant 100. In the ATR 110, the hydrocarbon feed 2 is converted to a syngas stream 3, which is then passed to a shift section 115, 150. The shift section comprises for instance 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 (LTS) unit 150 may also be included in the shift section. It would be understood that the shift section may include any of HTS, MTS and LTS, or combinations thereof. Additional or extra steam 13 may also be added downstream the HTS unit 115 but upstream the low temperature shift unit 150. From the shift section, a shifted gas stream 5 is then fed, e.g. directly fed as shown here, to a hydrogen purification unit 125, e.g. a PSA-unit, from which a high-purity H.sub.2 stream as hydrogen product 8 is produced, as well as a CO.sub.2-rich off-gas stream 9.

[0131] A CO.sub.2-rich off-gas recycle compressor 185 is arranged to receive and compress said CO.sub.2-rich off-gas stream 9 into a compressed CO.sub.2-rich off-gas stream 9. A drying unit 190, e.g. a TSA unit, is arranged downstream to receive the compressed CO.sub.2-rich off-gas stream 9 and provide a dried compressed CO.sub.2-rich off-gas stream 9. The drying unit 190 is further arranged to receive inlet regeneration gas stream 19, here illustrated as said nitrogen-rich stream 19, and to withdraw an exit regeneration gas stream 19. Inlet regeneration stream 19 may also be at least a portion of CO.sub.2-product stream 11, or at least a portion of CO.sub.2-depleted off-gas stream 17, 17, 17, or at least a portion of optional CO.sub.2-recycling stream 21; or at least a portion of hydrogen product 8.

[0132] A heat exchanging unit (heater, not shown) is arranged in the drying unit 190 to preheat the inlet regeneration gas stream 19 by indirect cooling of a heat exchanging medium, here illustrated as steam 13 from a steam header, e.g. a low pressure (LP) steam header or HP saturated steam header of the plant 100 (not shown). A cooled heat exchanging medium as a steam condensate 13 is thereby generated and withdrawn. A low temperature CO.sub.2-removal section 180, e.g. a cryogenic unit, is arranged to receive said dried compressed CO.sub.2-rich off-gas stream 9 for removal of CO.sub.2, thereby providing: a CO.sub.2-product stream 11, CO.sub.2-depleted off-gas stream 17, 17, 17, and CO.sub.2-recycling stream 21.

[0133] The plant 100 is further arranged for recycling, e.g. directly recycling, the CO.sub.2-depleted off-gas stream or a portion thereof 17, 17, 17 to the feed side of the prereformer 140, or to the feed side of the reforming unit, here ATR 110, or to the shift section (not shown). The plant 100 may further comprise at least one fired heater (not shown) arranged to pre-heat the hydrocarbon feed 1, 2 prior to it being fed to the reforming unit 110. The CO.sub.2-depleted off-gas stream 17, 17, 17 is thereby provided as fuel for the fired heater.