PROCESS AND APPARATUS FOR COMPRESSING HYDROGEN GAS IN A HYBRID COMPRESSION SYSTEM

Abstract

A stable discharge pressure of compressed hydrogen gas generated from the electrolysis of water is achieved and maintained at the outlet of a “hybrid” multistage compression system comprising at least a first section comprising at least one centrifugal compressor powered at least in part by electricity generated from at least one renewable energy source and a further section downstream of the first section, wherein the further section comprises at least one reciprocating compressor.

Claims

1. A process for supplying hydrogen for consumption in at least one downstream process, said process comprising: producing hydrogen gas by electrolysis of water; compressing said hydrogen gas in a multistage compression system comprising a first section and a further section downstream of said first section to produce compressed hydrogen gas; and feeding said compressed hydrogen gas to said downstream process(es), wherein said first section of said multistage compression system comprises at least one centrifugal compressor powered by electricity generated at least in part from at least one renewable energy source, the or each centrifugal compressor being driven by a dedicated variable frequency drive, and wherein said further section of said multistage compression system comprises at least one reciprocating compressor.

2. The process according to claim 1, wherein at least some of the compressed hydrogen gas is used to produce ammonia in the downstream process(es).

3. The process according to claim 1, wherein within said first section hydrogen gas is compressed to a first elevated pressure, and wherein within said further section compressed hydrogen gas is further compressed to a further elevated pressure.

4. The process according to claim 1, wherein the multistage compression system has two sections, and in the first section hydrogen gas is compressed to a first elevated pressure, and within the second section compressed hydrogen gas is further compressed to a final elevated pressure.

5. The process according to claim 1, wherein said hydrogen gas is fed to said multistage compression system at a feed pressure from atmospheric pressure to 3 bar, preferably from atmospheric pressure to 1.5 bar.

6. The process according to claim 1, wherein said compressed hydrogen gas produced by said multistage compression system has a pressure from 10 bar to 50 bar.

7. The process according to claim 1, wherein said first section comprises from 1 to 4 stages of centrifugal compression, and said further section comprises from 1 to 7 stages of reciprocating compression.

8. The process according to claim 1, wherein said first section comprises from 1 to 7 centrifugal compressors arranged in parallel, and said further section comprises from 1 to 5 reciprocating compressors arranged in parallel.

9. The process according to claim 1, wherein during periods when more hydrogen gas is produced by said electrolysis than is required for said downstream process(es), said method comprises feeding excess compressed hydrogen gas to storage, optionally after further compression; and wherein during periods when more hydrogen gas is required for said downstream process(es) than is produced by said electrolysis, said method comprises withdrawing compressed hydrogen gas from storage and, after suitable pressure reduction, feeding said reduced pressure hydrogen gas to an inter-stage of said first section or an initial stage of said further section of said multistage compression system.

10. The process according to claim 9, wherein during said periods when more hydrogen gas is required for said downstream process than is produced by said electrolysis, said method comprises: reducing the pressure of said compressed hydrogen gas withdrawn from storage to produce reduced pressure hydrogen gas at the inlet pressure to a stage in the first or further section of said multistage compression system; and feeding said reduced pressure hydrogen gas to said stage.

11. The process according to claim 10, wherein during feeding of said reduced pressure hydrogen gas to said stage, each centrifugal compressor upstream of said stage is operating such that no net compressed hydrogen gas is being produced.

12. The process according to claim 1, wherein said electrolysis has a total capacity of at least 300 MW.

13. An apparatus for supplying hydrogen gas for consumption in at least one downstream process, said apparatus comprising: a plurality of electrolysers for producing hydrogen gas; an electricity generation system for generating electricity from at least one renewable energy source; a multistage compression system for compressing hydrogen gas, said multistage compression system comprising a feed end, a first section, a further section downstream of said first section and an outlet end, said feed end being in fluid flow communication with said plurality of electrolysers; at least one downstream processing unit for consuming compressed hydrogen gas, said downstream processing unit(s) being in fluid flow communication with said outlet end of said multistage compression system; wherein said multistage compression system is a hybrid system in which said first section comprises at least one centrifugal compressor and said further section comprises at least one reciprocating compressor, and wherein the or each centrifugal compressor is powered at least in part by electricity from said electricity generation system and driven by a dedicated variable frequency drive.

14. The apparatus according to claim 13, comprising: a storage system for storing compressed hydrogen gas, said storage system being in fluid flow communication with said outlet end of said multistage compression system and at least one compressor of said multistage compression system; and a control system for controlling pressure and flow of compressed hydrogen gas from said multistage compression system to said storage system and for controlling pressure and flow of compressed hydrogen gas from said storage system to said multistage compression system based on the level of production of hydrogen gas by said electrolysers and/or the demand of the downstream process(es).

Description

BRIEF DESCRIPTION OF THE FIGURES

[0212] The invention will now be described by example only and with reference to the figures in which:

[0213] FIG. 1 is a simplified flowsheet for an example of the present invention.

[0214] FIG. 1 shows a multistage compression system having a first section with two LP centrifugal compression stages 12 and 15, and a further section with two MP reciprocating compression stages 19 and 22.

[0215] Feed 1 contains hydrogen gas supplied from electrolysers, which is fed through phase separator 11 to remove liquid water to produce feed 2. Feed 2 is then fed to the centrifugal compression stage 12 in the first (LP) section for compression. Following compression, the hot compressed hydrogen gas is cooled in intercooler 13 using a cooling water stream before it is then fed through phase separator 14 to produce feed 3. Although shown separately in FIG. 1, for LP centrifugal compressors, the phase separator will usually be combined into the intercooler as a single unit to potentially enable capital and power benefits and simplify the system.

[0216] At this point, feed 3 may optionally be mixed with, or entirely replaced by (as the case may be), stream 9 which contains dry hydrogen gas from storage. The mixed hydrogen gas feed 4 is then fed to a second centrifugal compression stage 15 in the first (LP) section. Following compression, the hot compressed hydrogen gas is cooling in intercooler 16 before being passed through phase separator 17 to produce feed 5.

[0217] Feed 5 is then optionally mixed with, or entirely replaced by (as the case may be) stream 10 which contains dry hydrogen gas from storage, to produce mixed feed 6.

[0218] Feed 6 is then fed to reciprocating compression stage 19 in a further (MP) section. Following compression, the hot compressed hydrogen gas is cooled in intercooler 20 before being passed through phase separator 21 and subsequently fed to reciprocating compression stage 22 in the further (MP) section to produce feed 8 containing compressed hydrogen at a final elevated pressure (which is the desired feed pressure for the downstream process(es)). Feed 8 will then be optionally purified and fed to at least one downstream process for consumption.

[0219] Streams 24, 26, 28, 30 and 32 feed gas to and from compressors in parallel (not shown).

[0220] The system depicted in FIG. 1 will now be explained in more detail with reference to the following Examples which contain data generated by computer simulation (Aspen Plus, ver. 10). The following Examples serve to illustrate the ways in which the hybrid multistage compression system of the present invention is resistant to changes in molecular weight of the hydrogen gas feed.

Example 1

[0221]

TABLE-US-00001 Example 1 1 2 5 6 7 8 10 Wet Mass Flowrate kg/h 49341.5 9868.3 7029.6 35148.1 11716.0 10749.0 0.0 Wet Volumetric m.sup.3/h 348176.0 71407.6 16316.8 84059.9 28337.3 5323.5 0.3 Flowrate Wet Molar Flow Nm.sup.3/h 362011.6 72402.3 68870.3 344353.2 114784.4 113581.1 0.0 Pressure bara 1.22 1.19 6.32 6.25 6.18 30.20 6.25 Temperature deg C. 42.00 42.00 40.00 40.00 40.00 106.09 40.00 Molecular Weight 3.05 3.05 2.29 2.29 2.29 2.12 2.02

[0222] Example 1 shown in the table above describes the properties of feeds/streams 1 to 10 at various points in a multistage compression system which is compressing hydrogen gas produced by electrolysis to be fed to a downstream process which has a desired feed pressure of 30 bar.

[0223] In this Example the multistage compression system is operating with feed 1 (the wet hydrogen gas from the electrolysers) at full flow. This may be because there is enough electricity available from the renewable energy source used to power electrolysis and/or all of the compressors in the compression system. Thus, under these conditions no reduced pressure hydrogen is required to be fed to the system from storage via streams 9 or 10.

[0224] It can be seen that the discharge pressure at the outlet of the further (MP) section (i.e. feed 8) is the required .Math.30 bar. This system is resistant to changes in the electrical frequency of the renewable energy source that powers the compressors. It can also be seen that despite the reduction in molecular weight as the hydrogen gas is compressed in subsequent stages, the MP reciprocating compressors still manage to output a discharge pressure of .Math.30 bar. This is possible as reciprocating compressors are unaffected by the reduction in molecular weight, this would not the be case if these were replaced with centrifugal compressors.

Example 2

[0225]

TABLE-US-00002 Example 2 Stream 1 2 5 6 7 8 10 Wet Mass Flowrate kg/h 0 Min* Min* 22788.77 7596.281 7596.281 22788.77 Wet Volumetric Flowrate m.sup.3/h 0 Min* Min* 45423.15 15620.3 4304.223 45423.15 Wet Molar Flow Nm.sup.3/h 0 Min* Min* 253367 84455.91 84455.91 253367 Pressure bara 1.2 1.2 6.2 6.5 6.3 30 6.5 Temperature deg C. 42 42 40 40 40 133.96 40 Molecular Weight 3.05 3.05 2.02 2.02 2.02 2.02 2.02 *= minimum flow (recycle)

[0226] Example 2 shown in the table above also describes the properties of feeds/streams 1 to 10 at various points in a multistage compression system which is compressing hydrogen gas produced by electrolysis to be fed to a downstream process which has a desired feed pressure of 30 bar.

[0227] In this Example the multistage compression system is operating with feed 1 (the wet hydrogen gas from the electrolysers) at zero flow. This may be because there is not enough electricity available from the renewable energy source used to power electrolysis and/or all of the compressors in the compression system.

[0228] Thus, under these conditions 100% of the hydrogen gas for compression in stream 6 is reduced pressure hydrogen gas fed from storage via stream 10 to the first stage of the further (MP) section. Again, the reduced pressure hydrogen gas in stream 10 has been cooled and purified and therefore has a molecular weight of 2.02. It can be seen that since said dry hydrogen gas from stream 10 is being compressed only in reciprocating compressors 19 and 22, there is no drop in the discharge pressure of the multistage compression system as a result of the reduced molecular weight of the hydrogen gas. As such, the multistage compression system provides compressed hydrogen gas with a final elevated pressure of 30 bar suitable for feeding to the downstream process.

[0229] The present inventors found that a stable output pressure under all conditions would not be possible if the MP reciprocating compressors were replaced with MP centrifugal compressors.

[0230] The preceding description has been presented to illustrate and describe examples of the principles described. This description is not intended to be exhaustive or to limit these principles to any precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is to be understood that any feature described in relation to any one example may be used alone, or in combination with other features described, and may also be used in combination with any features of any other of the examples, or any combination of any other of the examples.

[0231] In this specification, unless expressly otherwise indicated, the word “or” is used in the sense of an operator that returns a true value when either or both of the stated conditions are met, as opposed to the operator “exclusive or” which requires only that one of the conditions is met. The word “comprising” is used in the sense of “including” rather than to mean “consisting of”.

[0232] All prior teachings above are hereby incorporated herein by reference. No acknowledgement of any prior published document herein should be taken to be an admission or representation that the teaching thereof was common general knowledge in Australia or elsewhere at the date thereof.