METHOD OF TRANSPORTING HYDROGEN

Abstract

A method of transporting hydrogen and natural gas by means of a natural gas conduit system is proposed, especially by means of an existing natural gas conduit system. According to the invention, the hydrogen is recovered only downstream of one or preferably multiple natural gas consumers. This resulted in a stepwise increase in the hydrogen content in the natural gas-hydrogen mixture transported, and the subsequent recovery of the pure hydrogen can be affected more easily and efficiently.

Claims

1. A method of transporting hydrogen by means of a natural gas conduit system and of recovering pure hydrogen and on-spec natural gas, comprising the following steps: (a) providing a natural gas conduit system comprising: at least one transport conduit through which a natural gas transport stream flows, a hydrogen introduction site, at least one natural gas withdrawal site downstream of the hydrogen introduction site and a hydrogen withdrawal site downstream of the at least one natural gas withdrawal site, (b) introducing a hydrogen introduction stream into the transport conduit through which the natural gas transport stream flows via the hydrogen introduction site, (c) discharging a first natural gas withdrawal stream comprising at least a portion of the natural gas transport stream from the transport conduit via a first natural gas withdrawal site, (d) feeding the first natural gas withdrawal stream to a first membrane separation apparatus, separating the first natural gas withdrawal stream in the first membrane separation apparatus into a first, hydrogen-depleted retentate stream and a first, hydrogen-enriched permeate stream, (e) discharging the first retentate stream from the first membrane separation apparatus and feeding the first retentate stream to a first natural gas consumer, (f) recycling the first permeate stream into the transport conduit downstream of the first natural gas withdrawal site, which gives a hydrogen-enriched natural gas transport stream that is passed onward, (g) discharging a first hydrogen withdrawal stream comprising at least a portion of the hydrogen-enriched natural gas transport stream from the transport conduit via the hydrogen withdrawal site, (h) feeding the first hydrogen withdrawal stream to a second membrane separation apparatus, separating the first hydrogen withdrawal stream in the second membrane separation apparatus into a second, hydrogen-depleted retentate stream and a second, hydrogen-enriched permeate stream, (i) discharging the second permeate stream from the second membrane separation apparatus as hydrogen discharge stream, and (j) discharging the second, hydrogen-depleted retentate stream from the second membrane separation apparatus and feeding the second retentate stream to a second natural gas consumer or recycling the second retentate stream into the transport conduit.

2. The method according to claim 1, wherein the hydrogen discharge stream is fed to and introduced into a PSA system, and a pure hydrogen stream and at least one PSA offgas stream are discharged from the PSA system.

3. The method according to claim 1, wherein steps (c) to (f), for further natural gas consumers, are repeated at least once, which affords a repeatedly hydrogen-enriched natural gas transport stream that is passed onward.

4. The method according to claim 1, wherein the second natural gas consumer is a steam reforming plant, where the second retentate stream forms part of the steam reforming feed stream.

5. The method according to claim 4, wherein a crude hydrogen stream is produced by means of the steam reforming plant and is introduced into the PSA system for further purification.

6. The method according to claim 1, wherein the first permeate stream and/or the second permeate stream and/or the further permeate streams are compressed.

7. The method according to claim 1, wherein the withdrawal streams, before being fed to a membrane separation apparatus, are heated up.

8. The method according to claim 7, wherein the withdrawal streams, before being fed to the membrane separation apparatus, are heated up by combustion of a heating gas comprising at least a portion of the retentate stream from the membrane separation apparatus or at least a portion of the permeate stream from the membrane separation apparatus or mixtures of the two.

9. The method according to claim 1, wherein the withdrawal streams, before being fed to a membrane separation apparatus, are fed to a particle separator and/or a droplet separator.

10. The method according to claim 1, wherein the first permeate stream and/or the second permeate stream and/or the further permeate streams are fed to an oxygen removal apparatus.

11. The method according to claim 1, wherein the first permeate stream and/or the second permeate stream and/or the further permeate streams are fed to a carbon dioxide removal apparatus.

12. The method according to claim 11, wherein the carbon dioxide removal apparatus comprises at least one apparatus selected from the following group: temperature swing adsorption apparatus (TSA), pressure swing adsorption apparatus (PSA), gas scrubbing apparatus, cryogenic gas fractionation plant.

13. The method according to claim 12, wherein the carbon dioxide removal apparatus comprises a gas scrubbing apparatus and/or a cryogenic gas fractionation apparatus, and the process refrigeration required for operation of these apparatuses is sourced from an air fractionation plant.

14. The method according to claim 1, wherein the first membrane separation apparatus and/or the second membrane separation apparatus and/or a further membrane separation apparatus are configured with multiple separation stages.

15. The method according to claim 1, wherein the withdrawal streams and/or the permeate streams obtained between the multiple separation stages are compressed to pressures between 20 and 100 bara before being introduced into a downstream separation stage.

16. The method according to claim 1, wherein the hydrogen content of the natural gas transport stream after step (b) is between 5 mol % and 50 mol %, and in that the hydrogen content of the gas streams released to the natural gas consumer is less than mol %.

17. The method according to claim 1, wherein the hydrogen content of the hydrogen discharge stream that is introduced into the PSA system is at least greater than 35 mol %.

18. The method according to claim 1, wherein the second retentate stream is recycled into the transport conduit downstream of the first hydrogen withdrawal site, which gives a hydrogen-depleted natural gas transport stream that is passed onward.

19. The method according to claim 1, wherein the at least one PSA offgas stream is recycled into the transport conduit or fed to a further natural gas consumer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Developments, advantages and possible applications of the invention are also apparent from the following description of working and numerical examples and the drawings. All features described and/or depicted form, either in themselves or in any combination, the invention, regardless of the way they are combined in the claims or the back-references therein.

[0053] FIG. 1 illustrates a first example of a method or plant for co-transportation of hydrogen in an existing natural gas conduit and for recovering on-spec natural gas and pure hydrogen according to the invention,

[0054] FIG. 2 illustrates a second example of a method or plant for co-transportation of hydrogen in an existing natural gas conduit and for recovering on-spec natural gas and pure hydrogen according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0055] FIG. 1 shows a first example of a method or plant for co-transportation of hydrogen in an existing natural gas conduit 10 and for recovering on-spec natural gas and pure hydrogen according to a first configuration of the invention.

[0056] Natural gas flows through the transport conduit 10 with a temperature in this example of, for example, 15° C. (depending on the ambient conditions) and a pressure of around 60 barn. Via conduit 20, a hydrogen stream is introduced into conduit 10, so as to give a hydrogen content of about 10 mol % downstream of the hydrogen introduction site.

[0057] At the site of the first hydrogen consumer is a first hydrogen withdrawal site at which, via conduit 30, 31 and a dosage valve disposed in the conduit pathway, a substream of the natural gas-hydrogen mixture is discharged from conduit 10. Then the discharged substream is heated up by means of a heater or heat exchanger (not shown) to a temperature of 30 to 100° C., preferably to a temperature of 50 to 90° C., in one example to a temperature of 70 to 80° C., and then conducted onward to and introduced into a first membrane separation apparatus 32. This is preferably followed by a particle separator (likewise not shown) and/or a droplet separator which, by mechanical means, keep particles and liquid droplets away from the downstream membrane separation apparatus, such that the latter is not impaired. In an alternative preferred configuration (not shown), the discharged substream is first guided through a particle separator and/or a droplet separator and subsequently heated before entry into the first membrane separation apparatus 32. This has the advantage that solid particles and/or droplets do not get into the membrane separation apparatus, where they can lead to soiling or to blockages. In addition, the subsequent heating evaporates any entrained and undeposited droplets from the discharged substream, which offers additional protection of the membranes.

[0058] The membrane separation apparatus can be operated in a single-stage or preferably multistage manner; in a multistage execution, on account of the pressure drop that occurs over each membrane separation stage, compression between the stages is advantageous.

[0059] In the first membrane separation apparatus 32, a first, hydrogen-depleted and methane-enriched, retentate stream is obtained, which is released to the first natural gas consumer as on-spec natural gas via conduit 33 after optional further workup. In an example which is not shown, the gas stream discharged via conduit 33 is cooled by means of a cooler or a heat exchanger before being released to the first natural gas consumer. The same applies, in a further example, to further or preferably all retentate streams released to natural gas consumers. This is important since natural gas consumers are usually set up to process cool natural gas streams, but not to process hot natural gas streams.

[0060] In addition, a first, hydrogen-enriched and methane-depleted, permeate stream from the membrane separation apparatus 32 is discharged via conduit 34, having a pressure of typically less than 20 bara, for example 10 bara. Since impurities such as oxygen and/or carbon dioxide that are present in the natural gas have a tendency to leave the membrane separation apparatus via the permeate stream, in one example, the latter is sent to a deoxygenation and/or carbon dioxide removal apparatus 35 in which, by means of purification methods known to those skilled in the art, for example absorption of oxygen-binding adsorbents and/or carbon dioxide removal by means of gas scrubbing, for example with amine-containing scrubbing agents, oxygen and/or carbon dioxide are removed.

[0061] The oxygen- and/or carbon dioxide-depleted permeate stream is discharged from the deoxygenation and/or carbon dioxide removal apparatus 35 by means of conduit 36, recompressed to the transport conduit pressure of around 60 bara by means of a compressor 37. and recycled to and introduced into the transport conduit 10 via conduit 38. The introduction is effected downstream of the first natural gas withdrawal site, which gives a hydrogen-enriched natural gas transport stream that is passed onward. Depending on the nature of the apparatus 35, the compressor 37 may also be connected upstream of the apparatus 35.

[0062] The withdrawal of further substreams of the transported natural gas-hydrogen mixture via a further natural gas withdrawal site downstream of the first natural gas withdrawal site and downstream of one another can be effected once or preferably more than once at the site of further natural gas consumers. This is indicated in FIGS. 1 and 2 in that the function block with reference numerals between 30 and 38 is put between dotted square brackets and provided with a multiplier n that symbolizes the number of substream withdrawals and may assume integer values of 1 or greater. Downstream of each functional block n, the hydrogen content in the further-transported natural gas-hydrogen mixture increases, as illustrated in the numerical example that follows. Preference is given to withdrawal of at least two substreams, in one example a withdrawal of at least three substreams, of the transported natural gas-hydrogen mixture upstream of the first hydrogen withdrawal site.

[0063] At the site of the first hydrogen consumer, a substream of the natural gas-hydrogen mixture that has been enriched with hydrogen once or preferably more than once, most preferably at least twice, is discharged from the transport conduit 10 as the first hydrogen withdrawal stream via a conduit 40 and a metering valve disposed in the conduit pathway, which forms a first hydrogen withdrawal point. Then the discharged substream is heated up by means of a heater or heat exchanger (not shown) to a temperature of 30 to 100° C., preferably to a temperature of 50 to 90° C. This is preferably followed by a particle separator (likewise not shown) and/or a droplet separator which keep particles and liquid droplets away from the downstream membrane separation apparatus, such that the latter is not impaired. In an alternative preferred configuration (not shown), the hydrogen withdrawal stream is first guided through a particle separator and/or a droplet separator and subsequently heated before entry into a second membrane separation apparatus 42. This has the advantage that solid particles and/or droplets do not get into the membrane separation apparatus, where they can lead to soiling or to blockages. In addition, the subsequent heating evaporates any entrained and undeposited droplets from the discharged substream, which offers additional protection of the membranes.

[0064] Then the heated gas stream that has been freed of particles/droplets is guided onward to and introduced into a second membrane separation apparatus 42. The membrane separation apparatus can be operated in a single-stage or preferably multistage manner; in a multistage execution, on account of the pressure drop that occurs over each membrane separation stage, compression between the stages is advantageous.

[0065] In the second membrane separation apparatus, the first hydrogen withdrawal stream is separated into a second, hydrogen-depleted retentate stream and a second, hydrogen-enriched permeate stream. The second, hydrogen-depleted and methane-enriched, retentate stream is discharged via conduit 46 from the second membrane separation apparatus, optionally recompressed by means of a compressor 47 and wholly or partly returned to the transport conduit 10 via conduit 48. Alternatively (not shown), the second retentate stream may also be fed wholly or partly to a further natural gas consumer; this would be the second natural gas consumer when n=1.

[0066] The second, hydrogen-enriched permeate stream is discharged via conduit 43 from the second membrane separation apparatus as hydrogen discharge stream and, in the working example shown, introduced into a PSA system 44 for generation of pure hydrogen. In the PSA system 44, the hydrogen stream is purified further by multistage pressure swing adsorption under conditions known per se to the person skilled in the art. Via conduit 45, it is then possible to discharge a pure hydrogen stream having a water content of, for example, 99.9 mol % from the PSA system. It is particularly preferable here when the hydrogen content of the hydrogen discharge stream that is introduced into the PSA system is already at least greater than 35 mol %, preferably at least 40 mol %, more preferably at least 50 mol %, most preferably at least 60 mol %. Through the combination of an optionally multistage membrane pre-separation and a PSA post-separation, it is possible to recover a particularly pure hydrogen stream in a particularly efficient manner. Studies show that this is true especially when the minimum values given above for the hydrogen content in the hydrogen discharge stream are observed. It is particularly favourable here when there are at least two enrichment steps in the membrane pre-separation, and the hydrogen discharge stream enriched in this way is introduced into the PSA system.

[0067] In a particular configuration of the invention, the entire amount of the natural gas-hydrogen mixture remaining in the transport conduit 10 is discharged as hydrogen discharge stream (not shown). In this configuration, the retentate stream obtained in the membrane separation is recycled into the transport conduit 10 and introduced into the transport conduit 10 upstream of one of the natural gas withdrawal sites, for example the last natural gas withdrawal site before the recovery of hydrogen. In this way, the methane content remaining in the retentate stream can be fed to and utilized by a natural gas consumer, for example the last natural gas consumer.

[0068] FIG. 2 shows a second example of a method or plant for co-transportation of hydrogen in an existing natural gas conduit 10 and for recovering on-spec natural gas and pure hydrogen in a second configuration of the invention, which corresponds to the working example shown in FIG. 1 up to reference numeral 45.

[0069] By contrast with the working example shown in FIG. 1, in FIG. 2 the methane-enriched and hydrogen-depleted retentate stream is discharged from the second membrane separation apparatus via conduit 52 and fed to a steam reforming plant 50. Alternatively, plant 50 may also be configured as a plant for performing a different method of synthesis gas production, for example as a gasifying plant or as a plant for partial hydrocarbon oxidation. In plant 50, the retentate stream as part of the feed stream comprising hydrocarbons is converted in a manner known to the person skilled in the art to synthesis gas, i.e. hydrogen-carbon monoxide mixtures. After any further enrichment of hydrogen by means of CO conversion and removal of the carbon oxides (neither shown in FIG. 2), the crude hydrogen stream obtained is likewise fed to the PSA system 44 via conduit 54 in order to increase the yield of pure hydrogen.

[0070] Numerical Example The table that follows compiles the physical properties and compositions of a natural gas-hydrogen mixture with 10 mol % of hydrogen transported within a transport conduit upstream of, between and downstream of two natural gas withdrawal sites (“stages”).

[0071] After passing the two natural gas withdrawal sites (“stages”), the hydrogen content is already around 60 mol %, and after a total of three natural gas withdrawal sites (not shown) the hydrogen content is actually more than 70 mol %. This facilitates the recovery of pure hydrogen in a downstream PSA system.

[0072] In the numerical example shown in the table, permeate for stage B with n=2 was introduced as feed stream into the PSA system 44. Conduits 36B and 38B therefore correspond to conduit 40 or 43.

TABLE-US-00001 Stage 1 30A 33A permeate/ 36B 33B Natural Stage 1 Natural Stage 2 Stage 2 gas natural 36A gas permeate/ natural Conduit withdrawal gas to Stage 1 withdrawal Feed to gas to Name stage 1 consumer permeate stage 2 PSA consumer Temperature [° C.] 15 72 74 15 76 75 Pressure [bara] 60.0 59.2 10.0 60.0 12.0 59.2 Molar flow rate 38889 27178 11710 11710 6185 5525 [m3(STP)/h] Mass flow rate [kg/h] 27231 20849 6382 6382 2344 4038 H2 [mol %] 10.00 0.46 32.13 32.13 60.39 0.50 CH4 [mol %] 84.60 93.17 64.70 64.70 35.91 96.93 C2 . . . C4+ [mol %] 3.95 5.41 0.57 0.57 0.08 1.12 CO2 + N2 [mol %] 1.45 0.95 2.60 2.60 3.62 1.45 Index A, B relates to values 1, 2 of the multiplier n for number of withdrawal stages

LIST OF REFERENCE SYMBOLS

[0073] 10 Transport conduit

[0074] 20 Conduit

[0075] 30 Conduit

[0076] 31 Conduit

[0077] 32 First membrane separation apparatus

[0078] 33 Conduit

[0079] 34 Conduit

[0080] 35 Deoxygenation and/or carbon dioxide removal apparatus

[0081] 36 Conduit

[0082] 37 Compressor

[0083] 38 Conduit

[0084] 40 Conduit (first hydrogen withdrawal stream)

[0085] 42 Second membrane separation apparatus

[0086] 43 Conduit

[0087] 44 PSA system

[0088] 45 Conduit

[0089] 46 Conduit

[0090] 47 Conduit

[0091] 48 48 Conduit

[0092] 52 Steam reforming plant

[0093] 54 Conduit