System and process for synthesis gas production

Abstract

A hydrogen production system including a steam reformer unit, a steam addition line arranged to add steam upstream the steam reformer unit, a hydrogen membrane unit comprising a hydrogen permeable membrane and being arranged to allow at least a part of a reformed stream and a hydrocarbon feed stream to pass on different sides of a hydrogen permeable membrane, so that hydrogen passes from the reformed stream into the hydrocarbon feed stream, thereby forming said hydrogen enriched hydrocarbon stream, and a separation unit downstream the first side of the hydrogen membrane unit, where the separation unit is arranged to separating the reformed stream exiting the first side of the hydrogen membrane unit into a hydrogen product gas and an off-gas.

Claims

1. A hydrogen production system comprising: optionally, one or more gas conditioning stages chosen between the following stages: a hydrogenation stage, a desulfurization stage and a prereforming stage, where the most upstream stage of the one or more gas conditioning stages is arranged to receive a hydrogen enriched hydrocarbon stream and to process said hydrocarbon feed stream into a conditioned hydrocarbon stream, a steam reformer unit downstream the one or more optional gas conditioning units, a steam addition line arranged to add steam upstream the steam reformer unit, and said steam reformer unit being arranged to process the hydrogen enriched hydrocarbon stream or the conditioned hydrocarbon stream together with added steam into a reformed stream, a hydrogen membrane unit downstream said steam reformer unit, said hydrogen membrane unit comprising a hydrogen permeable membrane and being arranged to allow at least a part of the reformed stream to pass on a first side of said hydrogen permeable membrane and a hydrocarbon feed stream to pass on a second side of said hydrogen permeable membrane, so that during operation of the system hydrogen passes from the reformed stream on the first side into the hydrocarbon feed stream on the second side, thereby forming said hydrogen enriched hydrocarbon stream, and a separation unit downstream the first side of said hydrogen membrane unit, said separation unit being arranged for separating the reformed stream exiting the first side of the hydrogen membrane unit into a hydrogen product gas and an off-gas.

2. The hydrogen production system according to claim 1, wherein said separation unit is a pressure swing adsorption unit, a temperature swing adsorption unit, or a combination of a carbon dioxide separation unit and a cold box.

3. The hydrogen production system according to claim 1, wherein the hydrogen membrane unit comprises a polymeric membrane or a ceramic membrane.

4. The hydrogen production system according to claim 1, wherein the reformed stream and the hydrocarbon feed stream are arranged to pass in counter-current or co-currently in the hydrogen membrane unit.

5. The hydrogen production system according to claim 1, wherein said membrane unit comprises an outer tube and a plurality of hollow hydrogen permeable membranes.

6. The hydrogen production system according to claim 1, further comprising a water gas shift unit downstream said steam reformer unit and upstream said hydrogen membrane unit, said water gas shift unit being arranged to convert steam and carbon monoxide in the reformed stream to hydrogen and carbon dioxide.

7. A process for hydrogen gas production, said process comprising the steps of: optionally, passing a hydrogen enriched hydrocarbon stream through one or more gas conditioning stages chosen between the following stages: a hydrogenation stage, a desulfurization stage and a prereforming stage, where the one or more gas conditioning stages is/are arranged to receive the hydrogen enriched hydrocarbon stream and to process said hydrocarbon feed stream into a conditioned hydrocarbon stream, adding steam to the hydrogen enriched hydrocarbon stream or to the conditioned hydrocarbon stream, reforming said hydrogen enriched hydrocarbon stream or the conditioned hydrocarbon stream together with the added steam in a steam reformer unit downstream the one or more gas conditioning units, to a reformed stream, directing at least a part of said reformed stream into a hydrogen membrane unit downstream said steam reformer unit, said hydrogen membrane unit comprising a hydrogen permeable membrane and being arranged to allow at least a part of the reformed stream to pass on a first side of said hydrogen permeable membrane and a hydrocarbon feed stream to pass on a second side of said hydrogen permeable membrane, so that hydrogen passes from the reformed stream on the first side into the hydrocarbon feed stream on the second side, thereby forming said hydrogen enriched hydrocarbon stream; and separating the reformed stream exiting the first side of the hydrogen membrane unit into a hydrogen product gas and an off-gas in a separation unit downstream the first side of said hydrogen membrane unit.

8. The process according to claim 7, wherein said separation unit is a pressure swing adsorption unit, a temperature swing adsorption unit, or a combination of a carbon dioxide separation unit and a cold box.

9. The process according to claim 7, wherein the partial pressure of hydrogen in the reformed stream is between 5 and 25 barg.

10. The process according to claim 7, wherein the hydrogen membrane unit comprises a polymeric membrane, or a ceramic membrane.

11. The process according to claim 7, wherein the reformed stream and the hydrocarbon feed stream pass in counter-current or co-currently in the hydrogen membrane unit.

12. The process according to claim 7, further comprising the step of dividing off a first part of the reformed stream and passing only said first part on to said first side of said hydrogen membrane unit.

13. The process according to claim 7, wherein said membrane unit comprises an outer tube and a plurality of hollow hydrogen permeable membranes.

14. The process according to claim 7, further comprising the step of: converting steam and carbon monoxide in the reformed stream to hydrogen and carbon dioxide in a water gas shift unit downstream said steam reformer unit and upstream said hydrogen membrane unit.

15. The process according to claim 7, further separating off water from the stream exiting a retentate side of the hydrogen membrane unit.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 illustrates an embodiment of the hydrogen production system according to the invention.

DETAILED DESCRIPTION OF THE DRAWING

(2) FIG. 1 illustrates an exemplary embodiment of a hydrogen production system 100 according to the invention. The system 100 is arranged to produce a hydrogen stream 15.

(3) The system 100 comprises two gas conditioning units 22, 24. For example, the most upstream gas conditioning unit 22 comprises two gas conditioning stages, viz. a hydrogenation stage and a desulfurization stage. The gas conditioning unit 24 downstream the gas conditioning unit 22 contains a prereforming stage 24, e.g. in the form of an adiabatic prereformer with one or more prereforming catalyst bed(s) (not shown in FIG. 1). Downstream the two gas conditioning units 22, 24 is a steam reformer unit 26 which during operation is heated by a heating unit 28, e.g. one or more rows of burners. The steam reformer unit 26 is arranged to process a hydrogen enriched hydrocarbon stream 2 or a conditioned hydrocarbon stream 6 together with added steam 5 into a reformed stream 8.

(4) A membrane unit 34 is positioned downstream the steam reformer unit 26 and receives a reformed stream 11 which is hydrogen rich.

(5) The reformed stream 8 exiting the steam reformer unit 26 undergoes water gas shift in a shift unit 30, thus becoming a water gas shifted reformed stream 9. The water gas shifted reformed stream 9 is optionally dried by condensing water in a separator unit 32. Typically, the separator unit 32 is positioned upstream the hydrogen membrane unit 34 as shown in FIG. 1, and the stream exiting the separator unit is a dried, water gas shifted and reformed stream 11. Water is outlet from the separator unit in stream 10.

(6) The dotted lines of the units 32, 22 and 24 in FIG. 1 indicate that these units are optional.

(7) During operation of the system 100 a hydrocarbon feed stream 1 is fed to both the heating unit 28 as fuel and as a feed stream 1 to the optional gas conditioning units 22, 24 or to the steam reformer unit 26, via the hydrogen membrane unit 34. The heating unit 28 comprises e.g. a number of burners arranged to burn off the hydrocarbon feed stream 1 as fuel in order to create external heating 7 of tubes (not shown) of the reformer unit 26. The steam reformer unit 26 may be top fired, bottom fired, side fired, or in any other appropriate configuration. Depending on the configuration of burners of the heating unit 28, the heat transfer may take place as convection heating, radiation heating or a combination of both. This is indicated by the arrow 7 in FIG. 1.

(8) The hydrogen membrane unit 34 comprises a hydrogen permeable membrane and is arranged to allow the reformed stream 11 to pass on a first side 34a of the hydrogen permeable membrane and the hydrocarbon feed stream 1 to pass on a second side 34b of the hydrogen permeable membrane, so that during operation of the system 100, hydrogen passes from the reformed stream 11 on the first side 34a into the hydrocarbon feed stream 1 on the second side 34b, thereby forming the hydrogen enriched hydrocarbon stream 2.

(9) This first side 34a of the hydrogen permeable membrane is also denoted the retentate side, and the second side 34b of the hydrogen permeable membrane is also denoted the permeate side, since the main permeation of gasses across the hydrogen permeable membrane is the permeation of hydrogen from the reformed stream 11 into the hydrocarbon feed stream 1. The streams 1 and 11 pass in countercurrent in the system 100; however, the invention is not limited to this configuration and the streams 1 and 11 could alternatively pass the hydrogen membrane unit co-currently.

(10) The reformed stream 11 entering the first side of the hydrogen membrane unit 34 is a gas comprising both hydrogen and carbon monoxide. After passage of the hydrogen membrane unit 34 the components of the gas have changed slightly, thus providing a reformed stream 12. The hydrogen content of the reformed stream 12 after passage of the membrane unit 34, is thus lowered slightly compared to the hydrogen amount in the reformed stream 11, while the permeate gas, viz. the hydrogen enriched hydrocarbon stream 2, is a gas with an increased amount of hydrogen compared to the hydrocarbon feed stream 1. By choosing the right parameters of the hydrogen membrane unit 34, the hydrogen enriched hydrocarbon stream 2 may be saturated with a desired amount of hydrogen.

(11) Steam 5 is added to the system upstream of the reformer unit. In the case, where the system 10 comprises a prereformer unit 24, the steam 5 is added upstream the prereformer unit 24. In the case where the system 10 does not include a prereformer unit 24 or a prereformer stage, steam 5 is to be added upstream the steam reformer unit 26. Alternatively, steam 5 may be added both upstream the prereformer unit 24 and between the prereformer unit 24 and the steam reformer unit 26. In the case where the system 100 comprises both the preconditioning unit 22, e.g. including a hydrogenation stage and a desulfurization stage, the steam 5 is added to the stream 3 exiting the preconditioning unit 22, resulting in the stream 4. The stream 4 is subsequently fed into the second preconditioning unit 24, e.g. an adiabatic prereformer, resulting in the preconditioned stream 6 with added steam (from the steam input 5). The preconditioned stream 6 is fed to the reformer unit 26.

(12) If the system 100 comprises more than one gas conditioning stage, the order of the gas conditioning stages is typically such that a hydrogenation stage, if present, is the most upstream of the gas conditioning stages, followed by a desulfurization stage, if present, whilst the prereforming stage typically is the most downstream of the gas conditioning stages.

(13) The system 100 typically moreover includes a separation unit. This separation unit is a separation unit 32 between the shift unit 30 and the hydrogen membrane unit 34, arranged to separate off water 10 from the reformed and water gas shifted stream 9.

(14) Downstream of the hydrogen membrane unit 34 is a separation unit 36 in the form of an adsorption unit. The adsorption unit 36 is a temperature swing adsorption unit (TSA) or a pressure swing adsorption unit (PSA). The adsorption unit 36 is arranged to separate off undesired parts of the reformed stream 12 as an off gas 16. The off gas 16 typically includes hydrocarbons and may be used as further fuel to the burners of the heating unit 28. The remaining gas 15 from the adsorption unit is the product gas in the form of a hydrogen gas of substantial purity.

(15) As an alternative to an adsorption unit, the separation unit 36 could be a combination of a carbon dioxide separation unit, also denoted a CO.sub.2 stripper, and a cold box downstream the CO.sub.2 stripper. In this alternative, carbon dioxide in the reformed stream 12 exiting the first side of the hydrogen membrane unit 34 is removed and the resulting gas enters a cold box. A hydrogen product gas of substantial purity, a carbon monoxide gas as well as an off-gas exits the cold box. The off-gas may be used as further fuel to the burners of the heating unit 28.

(16) The streams 11 and 1 pass in countercurrent in the system 100; however, the invention is not limited to this configuration and the streams 1 and 11 could alternatively pass the hydrogen membrane unit co-currently.

(17) By choosing the right parameters of the hydrogen membrane unit 34, the hydrogen enriched hydrocarbon stream 2 may be saturated with a desired amount of hydrogen.

EXAMPLE

(18) In Table 2 below the result of a simulation using a polymer based membrane is given. As an example, a membrane inspired by a polymer type membrane was used for the simulation. The relative permeances of the used membrane is indicated in Table 1 below:

(19) TABLE-US-00001 TABLE 1 Compound Relative permeance H.sub.2O >400 H.sub.2 90 CO.sub.2 30 O.sub.2 9 CO 1.8 N2 1 CH.sub.4 0.6

(20) Ethane has a relative permeance estimated to 0.06. Thus it is clear that the simulated membrane has a high permeance for hydrogen and a lower permeance for carbon monoxide, nitrogen, methane, and ethane.

(21) In the simulation, a hydrogen rich gas of 0.2% N.sub.2, 5.7% CH.sub.4, 4.4% CO, 15.4% CO.sub.2, and 74.3% H.sub.2 was used as a feed to the first side of the hydrogen permeable membrane and a hydrocarbon feed stream of 1.3% N.sub.2, 97% CH.sub.4, 0.7% CO.sub.2, and 1% C.sub.2H.sub.6 was used as feed to the second side of the hydrogen permeable membrane. The simulation was simplified to an outer tube having the hydrogen rich gas feed separated from the inner tube with the hydrocarbon feed and a membrane integrated in the wall in-between, with the two feeds entering the configuration in countercurrent. The mass transfer coefficients of the species in Table 2 was scaled to achieve an exit concentration of roughly 2% H.sub.2 in the hydrocarbon feed.

(22) The molar flow of the hydrogen rich gas on the first side of the membrane and the hydrocarbon feed stream on the second side of the membrane were identical; however, a gas pressure of 23.5 barg of the hydrogen rich gas was assumed and a hydrocarbon feed stream pressure of 30 barg. It should be noted that any component may travel across the membrane, but that the rate is defined by the relative permeance for the specific membrane and the difference in partial pressure. Thus, H.sub.2, CO.sub.2, and CO will all travel from the hydrogen rich gas on the first side of the hydrogen permeable membrane and into the hydrocarbon feed stream, because of the partial pressure of the specific gas components determines the direction of the driving force. The actual transfer of the gas components from the hydrogen rich gas to the hydrocarbon feed are in the given case 8479 Nm.sup.3/h for H.sub.2, 564 Nm.sup.3/h for CO.sub.2, and 11 Nm.sup.3/h for CO, which is the combined effect of differences in partial pressure and the relative permeance of the species.

(23) TABLE-US-00002 TABLE 2 Flow P N.sub.2 CH.sub.4 CO CO.sub.2 H.sub.2 C.sub.2H.sub.6 [Nm.sup.3/h] [barg] [%] [%] [%] [%] [%] [%] Gas entering the first side of H.sub.2 membrane In 382000 23.5 0.2 5.7 4.4 15.4 74.3 0.0 Out 373038 23.0 0.2 5.9 4.5 15.6 73.8 0.0 Hydrocarbon feed (second side of H.sub.2 membrane) In 382000 30.0 1.3 97.0 0.0 0.7 0.0 1.0 Out 390962 30.0 1.3 94.8 0.0 0.8 2.2 1.0

(24) As the partial pressure of the hydrocarbons in the hydrocarbon feed stream is higher than the partial pressure thereof in the hydrogen rich gas, hydrocarbons will travel opposite the hydrogen and into the hydrogen rich gas. With an estimated low permeance of C.sub.2H.sub.6 and a low partial pressure, the actual flux of these hydrocarbons is very small and almost indifferent from an overall mass balance perspective. However, 91 Nm.sup.3/h of methane was found to be transferred to the hydrogen rich gas from the hydrocarbon feed.

(25) Overall, the results in Table 2 show that the polymer type membrane can facilitate transfer of hydrogen in a single pass membrane with a high selectivity, as 93% of the flux (relative to the total flux in both direction) over the membrane was hydrogen.

(26) While the invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant's general inventive concept.