Process and apparatus for compressing hydrogen in a hybrid compression system

Abstract

A stable discharge pressure of compressed hydrogen produced by electrolysis of water is obtained and maintained at the outlet of a "hybrid" multi-stage compression system, the "hybrid" multi-stage compression system comprising at least a first section and another section downstream of the first section, the first section comprising at least one centrifugal compressor, the at least one centrifugal compressor being at least partially powered by electricity generated from at least one renewable energy source, wherein the other section comprises at least one reciprocating compressor.

Description

Technical Field

[0001] The present invention relates to the compression of hydrogen produced by electrolysis in the context of renewable energy (i.e. "green" hydrogen). In particular, the invention relates to a method of achieving and maintaining a stable discharge pressure at the outlet of a multi-stage compression system, whereby the system is at least partially powered by electricity generated from at least one renewable energy source. Background Art

[0002] Typically, downstream processes that consume compressed hydrogen are powered entirely by electricity generated from conventional energy sources (e.g., on-site gasoline, diesel, or hydrogen-powered generators, fuel cells), or electricity taken from the local or national grid, or a combination of these sources. In this case, the downstream processes are run at maximum capacity to produce the highest possible yield of product.

[0003] However, downstream processes powered by electricity generated by one or more renewable energy sources may involve equipment that is ramped up or down to accommodate changes in the availability of power from the renewable energy sources.

[0004] In this way, the downstream process can be simplified by configuring it in such a way that there is a tight tolerance for variations in the feed pressure of the hydrogen fed to the downstream process. It is also generally preferred to supply the hydrogen at a stable feed pressure to simplify the operation of the downstream process. Therefore, the inventors have recognized that it is desirable to have a multi-stage compression system that generates compressed hydrogen with a stable discharge pressure to be fed to the downstream process, the multi-stage compression system can also be powered by electricity generated by renewable energy, and can compress large amounts of hydrogen generated by electrolysis in a cost-effective and space-efficient manner.

[0005] Furthermore, in this context, it is envisaged that other steps of the overall process, such as those associated with hydrogen generation (e.g. electrolysis) may also be powered by renewable energy sources and therefore a multi-stage compression system is desired that operates efficiently with a system designed to accommodate varying levels of generated hydrogen.

[0006] CN211040479U is a document about dry hydrogen compression in oil refineries. This document discloses a combination of various types of compression, including centrifugal and positive displacement compressors arranged in series and / or in parallel.

[0007] Currently, the inventors are not aware of any prior art that addresses the above mentioned problems in the context of compression of wet hydrogen generated by electrolysis and in the context of renewable energy sources. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention will now be described by way of example only and with reference to the accompanying drawings, in which:

[0009] Figure 1 is a simplified flow chart of an example of the present invention. DETAILED DESCRIPTION

[0010] Technology

[0011] According to a first aspect of the present invention, there is provided a process for supplying hydrogen for consumption in at least one downstream process, the process comprising:

[0012] Producing hydrogen by electrolysis of water;

[0013] compressing the hydrogen gas in a multi-stage compression system including a first section and another section downstream of the first section to generate compressed hydrogen gas; and

[0014] feeding the compressed hydrogen to the downstream process,

[0015] wherein the first section of the multi-stage compression system comprises at least one centrifugal compressor, the at least one centrifugal compressor being powered at least in part by electricity generated from at least one renewable energy source, the or each centrifugal compressor being driven by a dedicated variable frequency drive, and

[0016] Wherein the other section of the multi-stage compression system includes at least one reciprocating compressor.

[0017] In the following discussion of embodiments of the present invention, pressures given are absolute pressures unless otherwise stated.

[0018] Positive displacement compressors (e.g., reciprocating compressors) are commonly used to compress hydrogen in industrial processes. This type of compressor works by confining a continuous volume of gas within an enclosed space, for example by using a piston driven by a crankshaft to deliver the gas at high pressure.

[0019] The performance of a positive displacement compressor (e.g., a reciprocating compressor) is generally the same for very low molecular weight and high molecular weight gaseous media. Therefore, this type of compressor is suitable for a variety of gases, and is particularly suitable for the compression of hydrogen. Therefore, positive displacement compressors (e.g., reciprocating compressors) are ubiquitous in existing industrial processes for compressing hydrogen.

[0020] However, these types of compressors are not the first choice for handling large quantities of gas. For this, due to the structure of these types of compressors, a large number of compressors must be used in parallel. This results in considerable capital expenditure and operating costs.

[0021] An alternative to positive displacement compression is centrifugal compression. A centrifugal compressor is a type of dynamic compressor in which the gas is compressed by the mechanical action of rotating blades or impellers that impart velocity to the gas. The gas typically enters at the center of the impeller and is pushed out to the radial edges under the rotational motion, thereby delivering the gas at high velocity, impacting the casing. The velocity of the gas is converted into static pressure to deliver high-pressure gas. These types of compressors are generally better suited to handling large volumes of gas at a lower cost.

[0022] However, these compressors are generally not suitable for compressing low molecular weight gases (e.g., hydrogen). This is because it is more difficult to establish sufficient centrifugal force due to the lower density of the gas, making high pressure compression more difficult. Typically, in order to compress low molecular weight gases in a centrifugal compression system, the system must be designed with more impellers in series to accommodate the reduced gas density. This design greatly increases the cost of the compression system and is undesirable due to the inherent mechanical limitations of the system.

[0023] Furthermore, for centrifugal compression, the pressure ratio (discharge pressure divided by intake pressure for a particular compression stage) is highly sensitive to and dependent on the molecular weight of the gas being compressed. Therefore, changes in gas molecular weight may result in lower discharge pressure than expected.

[0024] This is particularly a problem when compressing "wet", i.e., water vapor-containing gases, such as hydrogen that has been produced by electrolysis of water. The apparent molecular weight of wet hydrogen is initially higher than that of dry hydrogen, and this molecular weight will decrease as the water vapor is removed, for example by cooling or purification.

[0025] Therefore, the removal of water vapor from the hydrogen generated by electrolysis in turn results in a reduction in the discharge pressure. The inventors have found that this problem is particularly prevalent in systems in which compressed hydrogen is cooled and circulated around a compression stage, or is cooled and / or purified, and then fed to the compression stage from storage.

[0026] The performance of a centrifugal compressor is also susceptible to changes in electrical frequency. In particular, the electrical output from a renewable energy source will operate at a set electrical frequency, which may be inherently variable, for example the electrical frequency may be 60 Hz, but vary from approximately 57.0 Hz to 62.5 Hz during operation. This frequency variation will be reflected in the motor speed of the impeller of the centrifugal compressor, and in turn in the discharge pressure, which is proportional to the square of the rate of change of the motor speed.

[0027] For example, in a multi-stage compression system with only centrifugal compression, a drop in electrical frequency from 60 Hz to 58 Hz will reduce the compressor flow to approximately 96.7% and reduce the discharge pressure from 30 bar to approximately 28 bar. Therefore, a change in electrical frequency may result in a discharge pressure that is lower than the feed pressure desired by the downstream process. This is not ideal in situations where the downstream process requires a stable feed pressure.

[0028] It can therefore be seen that centrifugal compression is unlikely to be used for compression of hydrogen generated by electrolysis and powered by electricity produced by renewable energy sources.

[0029] However, the inventors herein have devised a multi-stage compression system that exploits the respective advantages of both types of compression while mitigating their respective disadvantages, as will be explained in more detail below.

[0030] The invention relates to a process for supplying hydrogen for consumption in at least one downstream process.

[0031] electrolysis

[0032] In the present invention, hydrogen is generated by electrolyzing water. Any suitable form of water electrolysis may be used, including alkaline water electrolysis and polymer electrolyte membrane (PEM) water electrolysis.

[0033] The water used for electrolysis is typically seawater that has been desalinated (possibly by reverse osmosis) and softened.

[0034] The electricity required for electrolysis can be generated by any suitable energy source. However, in some preferred embodiments, at least some of the electricity required for electrolysis is generated by renewable energy sources, including wind energy, solar energy, tidal energy and hydroelectric energy, or a combination of these energy sources, particularly wind energy and solar energy. The electricity generated from these sources can be used to power the electrolyzer.

[0035] Preferably, the process is independent in terms of power generation for the electrolysis. Thus, preferably all electricity requirements for the electrolysis are met using renewable energy sources.

[0036] However, it is contemplated that during periods when demand for products from downstream processes is particularly high and / or during periods when renewable energy sources are only available below the threshold required to meet demand or not available at all, the electricity generated by one or more renewable energy sources may be supplemented by other sources. In these cases, the additional electricity may be drawn from on-site battery storage and / or generated by one or more on-site gasoline, diesel or hydrogen powered generators (including fuel cells), and / or drawn from the local or national grid.

[0037] The electrolysis can be performed at any suitable scale, in some cases with a total capacity of 1 gigawatt (GW). However, in a preferred embodiment, the electrolysis has a total capacity of at least 1 gigawatt (GW). In some embodiments, the electrolysis has a capacity of at least 300 MW per centrifugal compressor, such as at least 400 MW. The maximum total capacity of the electrolysis is limited only by practical considerations, such as generating enough power from renewable energy sources to power multiple electrolyzers. Thus, the electrolysis can have a maximum total capacity of about 10 GW or more. The total capacity of the electrolysis can be, for example, from 1 GW to about 5 GW, such as from about 1.5 GW to about 3 GW.

[0038] Hydrogen is typically produced by electrolysis at a pressure slightly above atmospheric pressure (e.g., about 1.3 bar). However, in some embodiments, electrolysis produces hydrogen at a slightly higher pressure (e.g., up to about 3 bar).

[0039] Therefore, hydrogen is often fed to the multi-stage compression system at a pressure of from atmospheric pressure to about 3 bar, preferably from atmospheric pressure to about 1.5 bar, for example about 1.1 bar.

[0040] In some embodiments, the amount of hydrogen generated by the electrolyzer is variable, and thus during periods where insufficient hydrogen is generated by electrolysis, hydrogen may be fed to the multi-stage compression system from another source (eg, a hydrogen storage system), as explained below.

[0041] purification

[0042] It will be appreciated that hydrogen produced by electrolysis of water will contain impurities. Therefore, the term "hydrogen" when used in the context of the present invention refers to hydrogen with such impurities unless and until the hydrogen is purified.

[0043] Specifically, the term includes hydrogen produced by electrolysis, which is typically saturated with water at 40°C and often contains some residual oxygen, typically about 500 ppm(v) to about 1000 ppm(v). These impurities will often have to be removed, depending on the tolerances of any downstream processes.

[0044] For example, oxygen is a poison for conventional catalysts used in the Haber process. Therefore, if compressed hydrogen is to be used in a downstream process for ammonia synthesis, the feed to the catalyst will contain less than about 10 ppm, typically less than about 5 ppm, of total oxygen, i.e., oxygen atoms from any impurity source such as oxygen (O2), water (H2O), carbon monoxide (CO) and / or carbon dioxide (CO2). Therefore, the feed will also be dry, i.e., not more than 1 ppm of water.

[0045] Downstream processes, such as refineries, that use conventional "grey" hydrogen (i.e., hydrogen derived from hydrocarbon or carbon-containing feed streams without carbon dioxide capture, such as by reforming natural gas) or "blue" hydrogen (i.e., hydrogen obtained in the same manner as grey hydrogen, but in which some or all of the carbon dioxide associated with its generation is captured) have similar tolerances to oxygen and water.

[0046] In some embodiments, the compressed hydrogen may be purified upstream of being fed to downstream processes.

[0047] For example, residual oxygen in the compressed hydrogen can be converted into water by catalytic combustion of some of the hydrogen in the hydrogen to produce oxygen-depleted compressed hydrogen (containing no more than 1 ppm O2), which can then be dried to produce dry compressed hydrogen (containing no more than 1 ppm water) for use in downstream processes.

[0048] Hybrid Compression System

[0049] The process of the present invention comprises the step of compressing hydrogen gas in a multi-stage compression system to generate compressed hydrogen gas, the multi-stage compression system comprising a first section and another section downstream of the first section.

[0050] Multistage compression systems are hybrid systems responsible for compressing hydrogen from the pressure of the hydrogen produced by electrolysis to a higher pressure that is generally at least slightly higher than the feed pressure of the downstream process.

[0051] The term "hybrid system" as used herein means a system that uses a combination of centrifugal compression in a first section and reciprocating compression in another section downstream of the first section.

[0052] It is readily understood that a "multi-stage" compression system has a plurality of compression stages that may be split between compressors in parallel and / or in series. The overall pressure ratio of each stage is typically in the range of about 1.5 to about 2.5, such as about 2 to about 2.5, in order to limit the increase in the temperature of the compressed gas. In some embodiments, the multi-stage compression system comprises one to eight stages, preferably one to three stages, such as two stages of compression.

[0053] In a multi-stage compression system, coolers are typically required between adjacent stages ("intercoolers"), and a cooler is typically required after the final stage ("aftercooler") to remove the heat of compression from the compressed gas. Thus, in the context of this invention, a "stage" of compression refers to the portion of the compression system between the coolers.

[0054] The multistage compression system comprises at least two compression sections, a first section and another section downstream of the first section. A compression "section" in this context refers to the portion of the compression system between the feed and the product. Each section may include one or more compression stages, and an associated cooler.

[0055] Hydrogen is compressed in at least two sections of a multi-stage compression system. In a first section, hydrogen is compressed to a first high pressure. Then, in another section, the compressed hydrogen is compressed to a final high pressure.

[0056] In some preferred embodiments, the multi-stage compression system has two sections, and in a first section, the hydrogen is compressed to a first high pressure, and in a second section, the compressed hydrogen is further compressed to a final high pressure.

[0057] The final high pressure is preferably not less than 5%, more preferably not less than 2% of the feed pressure desired for the downstream process. The final high pressure may sometimes be higher than the desired feed pressure.

[0058] Any suitable number of compressors may be used in the context of the present invention. It will be appreciated that the total number of compressors depends on the design of the overall system, and in particular the total capacity of the electrolyzers. For example, for a process with a total electrolyzer capacity of 1 GW, the multi-stage compression system may have 2 compressors to 4 compressors. The skilled person will appreciate that processes with higher total capacities will require a greater number of compressors, i.e., for a process with a total electrolyzer capacity of 2 GW, 8 compressors are required in the multi-stage compression system.

[0059] In some examples below, a first section may be referred to as a “low pressure” or “LP” section, and another section may be referred to as a “medium pressure” or “MP” section.

[0060] The compressor in the first section can be appropriately enlarged, for example by 10%, to accommodate the loss of the machine. Additionally or alternatively, the multi-stage compression system can include a spare compressor in the first section or another section, which will be switched in to replace another machine that has failed in the relevant section.

[0061] In the context of the present invention, at least some of the electricity used for said compression of hydrogen in a multi-stage compression system is generated by at least one renewable energy source.

[0062] Suitable renewable energy sources include wind, solar, tidal and hydroelectric energy, or a combination of these sources, particularly wind and solar energy.

[0063] Preferably, the process is independent in terms of electricity generation for the compressors.Thus, the entire electricity demand for the compressors in a multi-stage compression system can ideally be met using renewable energy sources.

[0064] However, it is contemplated that during periods when demand for products from downstream processes is particularly high and / or during periods when renewable energy sources are only available below the threshold required to meet demand or are not available at all, electricity generated by one or more renewable energy sources may be supplemented by other sources. In these cases, additional electricity may be drawn from on-site battery storage and / or generated by one or more on-site gasoline, diesel or hydrogen powered generators (including fuel cells) and / or drawn from a local or national grid. However, it should be understood that supplementing electricity from non-renewable energy sources is minimized or avoided entirely if possible.

[0065] Electricity generated from the renewable energy source is used to power compressors in a first section of the multi-stage compression system, and preferably also compressors in another section.

[0066] The first compressed section

[0067] In the context of the present invention, "first section" may refer to an initial section or an intermediate section, as long as it is upstream of and in flow communication with another section located downstream thereof. However, in a preferred embodiment, the first section is the initial section of a multi-stage compression system.

[0068] In some embodiments, after compression in the first section, the first high pressure of hydrogen may be in the range of about 2 bar to about 3 bar, such as 2.5 bar. In other embodiments, the first high pressure may be in the range of about 4 bar to about 6 bar, such as 5 bar.

[0069] The first section of the multi-stage compression system according to the invention comprises at least one centrifugal compressor.In a preferred embodiment, all compressors in the first section are centrifugal compressors.

[0070] In some embodiments, the first section includes a plurality of centrifugal compressors arranged in parallel. Those skilled in the art will appreciate that the number of compressors will depend on the scale of the process. For example, the first section may include 2 to 10, or 4 to 6 centrifugal compressors arranged in parallel.

[0071] By using a centrifugal compressor in the first section of a multi-stage compression system, the inventors have found that larger volumes of hydrogen can be compressed at reduced cost compared to prior art arrangements using reciprocating compression. Therefore, the use of a centrifugal compressor in the first section, where the volume of hydrogen is much greater than in later sections, is particularly beneficial. Centrifugal compressors are also less expensive to install and maintain and require a simpler foundation.

[0072] As mentioned above, centrifugal compression is generally not suitable for compressing low molecular weight gases, such as hydrogen (molecular weight of about 2.016 g / mol). However, in the context of the present invention, centrifugal compressors are used to compress hydrogen generated by electrolysis. The hydrogen obtained from electrolysis will be saturated with water vapor and therefore have a much higher apparent molecular weight than dry hydrogen, for example from about 2.45 g / mol to 3.05 g / mol.

[0073] The inventors have also realised that this hydrogen will have a higher apparent molecular weight in the first section of the compression system compared to the other sections. This is because as the hydrogen passes through the compression system, more and more water vapour is removed due to the intercooling between the stages.

[0074] Thus, the inventors have discovered that centrifugal compression is particularly suitable for compressing hydrogen gas generated by electrolysis in the first section of the multi-stage compression system described herein, where the apparent molecular weight of the hydrogen gas is relatively high. This allows for more efficient centrifugal compression because the higher density of the gas creates sufficient centrifugal force to provide compression.

[0075] Furthermore, the use of centrifugal compression requires less space and a smaller number of compressors than reciprocating compression. This also simplifies manufacturing, as fewer stages are required to achieve the same pressure increase than with a reciprocating compressor.

[0076] The or each centrifugal compressor is powered at least in part by electricity from at least one renewable energy source. Preferably, the entire power requirement of the compressors in the first section of the multi-stage compression system is met using renewable energy sources. Suitable types of renewable energy sources are the same as described above.

[0077] As mentioned above, the impeller speed (and therefore the discharge pressure ratio) of the centrifugal compressor is susceptible to small changes in the electrical frequency from the renewable energy source. Therefore, the centrifugal compressor or each centrifugal compressor is also driven by a dedicated variable frequency drive (VFD). Any variable frequency drive suitable for modulating an AC signal can be used, for example by converting it into a DC signal and then regenerating the AC signal to provide a stable frequency. This can be achieved by using a transistor as a switch. The use of a switch allows the VFD to adjust the frequency of the motor supplied by the VFD to the centrifugal compressor, which in turn controls the rotor speed. Suitable types of VFD include, but are not limited to, voltage source inverters (VSI), load commutated inverters (LCI), current source inverters (CSI) or pulse width modulators-voltage source inverters (PWM-VSI).

[0078] By adopting a variable frequency drive, the inventors have found that the effect of changes in electrical frequency on the impeller speed of the centrifugal compressor is mitigated. This prevents the hydrogen discharge pressure at the outlet of the first section from dropping. In addition, the use of a variable frequency drive saves power and is more energy efficient because it allows the same level of motor performance but with lower power consumption.

[0079] Another compressed section

[0080] The further section is located downstream of the first section and is in fluid flow communication with the first section, ie compressed hydrogen product from the outlet of the first section is fed to the inlet of the further section downstream.

[0081] The final high pressure of the compressed hydrogen generated by another section of the multi-stage compression system will typically be at least slightly higher than or equal to the desired feed pressure of the downstream process, for example typically about 10 bar to about 50 bar. Preferably, the final high pressure of the compressed hydrogen is about 25 bar to about 35 bar, more preferably about 30 bar. In embodiments where the downstream process includes the synthesis of ammonia (e.g., by the Haber (or Haber-Bosch) process), then the final high pressure is about 30 bar.

[0082] The further section may have one or more compression stages which may be split between compressors in parallel and / or in series. Depending on the required pressure ratio, the further section may comprise from 1 to 7, for example 2 to 4, compression stages.

[0083] Another section includes at least one reciprocating compressor. A reciprocating compressor can be defined based on the "stroke" of a crankshaft or the number of piston operations. In some embodiments, the reciprocating compressor of another section or each reciprocating compressor includes 4 to 12, preferably 6 to 10 strokes.

[0084] The inventors have determined that by using one or more reciprocating compressors in another section rather than centrifugal compression, a more energy efficient and cost effective way of compressing cooled and / or purified hydrogen gas having a low molecular weight is provided. The space required to implement the reciprocating compressors of the another section is also less than that of a system implementing a centrifugal compressor, as explained above. Reciprocating compressors are also more suitable for compressing smaller volumes of gas, and are therefore particularly suitable for another section of a multi-stage compression system, the other section comprising a later stage of compression of a gas having a smaller volume.

[0085] The use of a reciprocating compressor in another section is additionally advantageous because it is less susceptible to discharge pressure drops due to changes in the apparent molecular weight of hydrogen as the hydrogen is further cooled (or purified). Therefore, there is no effect on discharge pressure when dry hydrogen is fed or circulated from storage.

[0086] Furthermore, compared to centrifugal compression, reciprocating compressors do not experience a drop in discharge pressure due to changes in electrical frequency. Ideally, therefore, the or each reciprocating compressor in the other section is not driven by a variable frequency drive (VFD), thereby saving costs. This is possible because the discharge pressure of a reciprocating compressor is independent of or not dependent on the electrical frequency of the energy source used to power it. In the presence of changes in electrical frequency, the discharge flow rate of the output gas (usually measured as gas volume per unit time, e.g. m 3 / h) changes, rather than discharge pressure changes. Therefore, another advantage of using a reciprocating compressor in another section is that this additionally maintains the discharge pressure during electrical frequency changes. This is particularly useful when the downstream process requires a stable feed pressure.

[0087] Hydrogen compressed using centrifugal compression in a first section is fed to the inlet of a reciprocating compressor in another section downstream.

[0088] As described above, there are various factors that may affect the discharge pressure of the first section including one or more centrifugal compressors, such as gas molecular weight and electrical frequency. Therefore, the discharge pressure of hydrogen at the outlet of the first section may be lower than the expected first high pressure (feed pressure) of another section.

[0089] The present inventors have additionally recognized that these slight drops in the discharge pressure of the centrifugal compressor in the first section can be accommodated without affecting the final high pressure of the multi-stage compression system by using one or more reciprocating compressors in another section.

[0090] A drop in the feed pressure of a reciprocating compressor does not result in a drop in the discharge pressure, since the latter is independent of the feed pressure of the gas. On the contrary, when the feed pressure drops, this results in a drop in the discharge gas flow of the reciprocating compressor. This is in contrast to a centrifugal compressor, the discharge pressure of which depends on the inlet pressure. Therefore, the inventors have surprisingly found that by performing a reciprocating compression after the centrifugal compression, this compensates for the drop in discharge pressure during the centrifugal compression. Therefore, it has been found that this arrangement is particularly suitable for downstream processes that require a stable feed pressure.

[0091] Downstream Process

[0092] The compressed hydrogen may be consumed in a downstream process, or in more than one downstream process arranged in parallel.

[0093] A particular advantage of the present invention is that compressed hydrogen is fed to downstream processes at a stable feed pressure.

[0094] In the context of the present invention, the expression "stable feed pressure" in relation to hydrogen supplied to a downstream process is used herein to refer to a pressure within about 5%, preferably about 2%, of the desired feed pressure of the downstream process.

[0095] For example, where the downstream process involves the generation of ammonia (eg, by Haber (or Haber-Bosch)), the desired feed pressure may be 30 bar, and the stable feed pressure may be anywhere from about 29.4 to about 30.6 bar.

[0096] Downstream processes can include any process that currently uses “grey” hydrogen or “blue” hydrogen. These processes include oil refining and steel making.

[0097] In a preferred embodiment, at least some, such as all, of the compressed hydrogen is used to produce ammonia by the Haber (or Haber-Bosch) process, in which ammonia is produced by reacting a mixture of hydrogen and nitrogen over an iron-based catalyst at high temperature (typically about 400° C. to about 500° C.) and high pressure (typically in the pressure range of about 100 bar to 200 bar).

[0098] In other embodiments, at least some, such as all, of the compressed hydrogen is liquefied by cryogenic cooling. In still further embodiments, at least some, such as all, of the compressed hydrogen is used to generate methanol.

[0099] In a further embodiment, a first portion of the compressed hydrogen is used to generate ammonia and a second portion of the compressed hydrogen is liquefied.

[0100] The electricity required by the downstream process can be generated from any suitable energy source. However, in some preferred embodiments, at least some of the electricity required by the downstream process is generated by renewable energy sources (including wind energy, solar energy, tidal energy and hydroelectric energy, or a combination of these sources, particularly wind energy and solar energy). The electricity generated from these sources can be used to power the downstream process.

[0101] Return of stored hydrogen

[0102] One disadvantage of using electricity generated from renewable energy sources is the inherent fluctuations in energy availability. In some embodiments, in the present invention, this problem can be addressed by providing a system for collecting and storing at least some, preferably all, excess hydrogen generated during periods when production exceeds demand for downstream processes, and distributing the stored hydrogen to the downstream processes during periods when demand exceeds production.

[0103] In some embodiments, the compressed hydrogen may be stored without further compression. In these embodiments, the gas is stored at a maximum pressure of up to the pressure to which the hydrogen is compressed in the multi-stage compression system, for example, up to about the feed pressure of the downstream process (of which there is only one) or about the feed pressure of one of the downstream processes (if there is more than one). In such embodiments, the compressed hydrogen may be stored at a maximum pressure in the region of up to about 25 bar to about 30 bar.

[0104] However, the compressed hydrogen may be further compressed before storage. In these embodiments, the compressed hydrogen may be stored at a pressure of up to about 200 bar, or up to about 150 bar, or up to about 100 bar, or up to about 90 bar, or up to about 80 bar, or up to about 70 bar, or up to about 60 bar, or up to about 50 bar.

[0105] During periods when the level of demand for hydrogen exceeds the level of production, compressed hydrogen is withdrawn from storage and depressurized to produce depressurized hydrogen gas.The pressure may be reduced in any conventional manner, particularly by passing the gas through a valve.

[0106] The pressure of the depressurized hydrogen will depend on the pressure at the point in the multi-stage compression system to which the depressurized hydrogen will be added.

[0107] In some embodiments, the decompressed hydrogen may be fed to the final stage in another section of the multi-stage compression system. In these embodiments, the decompressed hydrogen will be at the inlet pressure of the feed to the final stage.

[0108] In other embodiments, the decompressed hydrogen may be fed to an intermediate stage of a multi-stage compression system. In these embodiments, the decompressed hydrogen will be at an inlet pressure for feeding to the intermediate stage.

[0109] The intermediate stage may be an intermediate stage within the first section, or may be an initial stage within another section downstream of the first section. If there are more than two sections, the intermediate stage may be an initial stage within any additional section downstream of the other section. In these embodiments, the depressurized hydrogen will be at the inlet pressure of the feed to the relevant section, i.e., the "inter-section" pressure.

[0110] In further embodiments, the decompressed hydrogen can be fed to the feed end of the multi-stage compression system, i.e., the initial stage. In these embodiments, the decompressed hydrogen will be the feed pressure of the multi-stage compression system, for example, about 1.1 bar.

[0111] During periods when demand exceeds production, approaches may include:

[0112] reducing the pressure of compressed hydrogen gas extracted from the storage to generate decompressed hydrogen gas at an inlet pressure (first intermediate pressure) of a first stage of a multi-stage compression system; and

[0113] Depressurized hydrogen is fed to the first stage.

[0114] In such an embodiment, once the pressure of the compressed hydrogen in the storage drops to about the inlet pressure of the first stage, the method may include:

[0115] further reducing the pressure of the compressed hydrogen gas extracted from the storage to generate decompressed hydrogen gas at an inlet pressure (a second intermediate pressure) of a second stage upstream of the first stage of the multi-stage compression system; and

[0116] The depressurized hydrogen is fed to the second stage.

[0117] It should be understood that in this context, the terms "first stage" and "second stage" do not refer to the relative positions of the stages in the multi-stage compression system in the downstream direction during normal operation. Instead, the terms are intended only to reflect the order in which the decompressed hydrogen is fed to the stages of the multi-stage compression system during periods when demand exceeds production. The terms "first intermediate pressure" and "second intermediate pressure" should be interpreted accordingly, with the first intermediate pressure being higher than the second intermediate pressure.

[0118] These embodiments may further include feeding the depressurized hydrogen to other stages of the multi-stage compression system upstream of the first and second stages. In these further embodiments, the pressure of the compressed hydrogen extracted from the storage is reduced to the inlet pressure of each stage.

[0119] In some preferred embodiments, the second stage is the initial stage of a multi-stage compression system.

[0120] It should be understood that in embodiments where the decompressed hydrogen is fed to the second stage after the first stage, the gas flow to the first stage stops when the gas flow to the second stage begins. Generally speaking, the decompressed hydrogen flow to a given compression stage stops when the decompressed hydrogen begins to flow to another compression stage.

[0121] In some preferred embodiments, wherein during feeding of said depressurized hydrogen to a stage, the or each centrifugal compressor upstream of said stage is operated such that no net compressed hydrogen is produced.

[0122] Since hydrogen can be returned from storage to the first section and / or an intermediate and / or initial stage of another section of the multi-stage compression system, the compressed hydrogen can be stored at a pressure as low as a minimum of about 5 bar, and possibly even as low as a minimum of about 1.3 bar.

[0123] In embodiments where the compressed hydrogen is further compressed before storage, another option is to feed the compressed hydrogen extracted from the storage directly to the downstream process after appropriate decompression until the storage pressure drops to the feed pressure of the downstream process. At this point, the pressure of the compressed hydrogen extracted from the storage will be further reduced and the decompressed hydrogen is fed to a stage of the multi-stage compression system according to the present invention. However, these embodiments are not preferred, for example because of the additional capital expenditure of the high pressure storage system.

[0124] In the context of decompression, the term "suitable" means that the pressure of the hydrogen is reduced to an appropriate level taking into account the inlet pressures of the stages of the multi-stage compression system to which the decompressed hydrogen is fed.

[0125] Compared to a high pressure hydrogen storage system that only discharges to the feed pressure of the downstream process, the present invention enables the storage volume of hydrogen to be reduced by using a multi-stage compression system already present in the process to recompress the hydrogen from the storage when the storage pressure drops below the feed pressure. Thus, hydrogen can continue to be withdrawn from the storage until the storage pressure drops to the minimum value of the feed pressure of the multi-stage compression system.

[0126] During periods when hydrogen production is limited due to lack of power for the electrolyser, additional compression power is required, but this can be minimized by supplying hydrogen at the highest possible compressor interstage pressure given the storage pressure at a particular time. It also allows the maximum hydrogen storage pressure to be equal to or lower than the feed pressure of the downstream process, eliminating any additional compression requirements for stored hydrogen.

[0127] It will be appreciated that the same volume of gas is stored in the same storage volume at the same maximum pressure, and that reducing the minimum storage pressure increases the volume of gas that is "releasable" from the storage, ie the available volume of stored gas.

[0128] However, the inventors have recognised that where hydrogen is generated and then compressed in a multi-stage compression system for use in at least one downstream process, the releasable volume of stored hydrogen can be increased by returning hydrogen from storage to a stage in the multi-stage compression system rather than directly to the downstream process, and that this arrangement reduces the total storage vessel volume required for the process.

[0129] For example, for a given mass of releasable hydrogen, storage from a maximum pressure of 200 bar to a minimum pressure of 1.5 bar requires 15% less storage vessel volume than storage from a maximum pressure of 200 bar to a minimum pressure of 30 bar.

[0130] Similarly, for a given mass of releasable hydrogen, storage from a maximum pressure of 100 bar to a minimum pressure of 1.5 bar requires 30% less storage vessel volume than storage from a maximum pressure of 100 bar to a minimum pressure of 30 bar.

[0131] Furthermore, for a given mass of releasable hydrogen, storage from a maximum pressure of 50 bar to a minimum pressure of 1.5 bar requires 60% less storage vessel volume than storage from a maximum pressure of 50 bar to a minimum pressure of 30 bar.

[0132] Furthermore, storage from a maximum pressure of 30 bar to a minimum pressure of 1.5 bar is possible, compared to 30 bar to 30 bar where storage is not permitted.

[0133] Furthermore, although the total storage vessel volume increases as the maximum storage pressure decreases, the lower design pressure allows the vessel walls to be thinner and can reduce the overall capital cost of the storage system. Vessel thickness is often limited to a maximum value for reasons such as manufacturability, and in such cases, a lower design pressure will result in fewer vessels (although each vessel will be larger). Furthermore, the allowable stress of the vessel design can be increased below a specific vessel wall thickness, and if the lower design pressure allows the thickness to be below this threshold, the total vessel metal mass (and therefore the overall cost) can be reduced.

[0134] It should be understood that the compressed hydrogen will undergo intercooling and aftercooling steps (and possibly purification, as appropriate), so that the water vapor content in the decompressed hydrogen is very low, or virtually no water vapor content. Therefore, the decompressed hydrogen will have a lower molecular weight, for example, about 2.016 g / mol.

[0135] As discussed above, centrifugal compression is less efficient when used to compress low molecular weight gases, and therefore this may result in lower than desired discharge pressures when hydrogen entering the compressor is mixed with or replaced by stored hydrogen.

[0136] A particular advantage of the invention is that when decompressed hydrogen from storage is fed to any stage of a multistage compression system, the final high pressure does not drop, since these types of compressors are not affected by the molecular weight drop of the feed gas if it is fed to a reciprocating compression stage in another section.

[0137] Similarly, there is no drop in the final high pressure of a multi-stage compression system where depressurized hydrogen from storage is fed to any stage of a first section comprising one or more centrifugal compressors, because a small drop in the discharge pressure of the first section can be accommodated by the reciprocating compressor of another section. This is not possible in a multi-stage compression system because both the first and second sections in the multi-stage compression utilize centrifugal compression.

[0138] equipment

[0139] According to a second aspect of the present invention, there is provided an apparatus for supplying hydrogen for consumption in at least one downstream process, the apparatus comprising:

[0140] multiple electrolyzers for generating hydrogen;

[0141] an electric power generation system for generating electric power from at least one renewable energy source;

[0142] a multi-stage compression system for compressing hydrogen, the multi-stage compression system comprising a feed end, a first section, another section downstream of the first section, and an outlet end, the feed end being in fluid flow communication with the plurality of electrolyzers;

[0143] at least one downstream processing unit for consuming the compressed hydrogen, the downstream processing unit being in fluid flow communication with the outlet end of the multi-stage compression system;

[0144] wherein the multi-stage compression system is a hybrid system in which the first section comprises at least one centrifugal compressor and the further section comprises at least one reciprocating compressor, and

[0145] Wherein the or each centrifugal compressor is at least partly powered by electricity from the power generation system and driven by a dedicated variable frequency drive.

[0146] Electrolyzer

[0147] The electrolysis of water is provided by a plurality of electrolysis units or "cells". Each unit or cell may be referred to as an "electrolyzer".

[0148] The plurality of electrolyzers typically have a total capacity of at least 1 GW. The maximum total capacity of the electrolyzers is limited only by practical considerations, such as generating sufficient power from renewable energy sources to power the plurality of electrolyzers. Thus, the electrolyzers may have a maximum total capacity of 10 GW or more. The total capacity of the electrolyzers performing electrolysis may be from 1 GW to 5 GW, such as from about 1.5 GW to about 3 GW.

[0149] The plurality of electrolyzers are often composed of a large number (eg, hundreds) of individual cells grouped into "modules" that also include process equipment such as pumps, coolers and / or separators, etc., and these module groups are typically arranged in separate components.

[0150] Each module typically has a maximum capacity of at least 10 MW (eg 20 MW), and each component typically has a total capacity of at least 100 MW (eg 400 MW).

[0151] Any suitable type of electrolyser may be used with the present invention. In this regard, there are three conventional types of electrolyser - alkaline electrolyser, PEM electrolyser and solid oxide electrolyser - and each of these types of electrolyser is theoretically suitable for use with the present invention.

[0152] Alkaline electrolyzers operate by converting hydroxide ions (OH - ) is transported from the cathode to the anode through an electrolyte to produce hydrogen on the cathode side. Electrolyzers using liquid alkaline solutions of sodium hydroxide or potassium hydroxide as electrolytes are commercially available. Commercial alkaline electrolyzers are typically operated in a temperature range of about 100° C. to about 150° C.

[0153] In a PEM electrolyzer, the electrolyte is a solid plastic material. Water reacts at the anode to form oxygen and positively charged hydrogen ions. Electrons flow through an external circuit, and the hydrogen ions selectively pass through the PEM to the cathode. At the cathode, the hydrogen ions combine with electrons from the external circuit to form hydrogen gas. PEM electrolyzers are typically operated in a temperature range of about 70°C to about 90°C.

[0154] Solid oxide electrolyzers use solid ceramic materials as electrolytes that selectively conduct negatively charged oxygen ions (O 2- ). Water at the cathode combines with electrons from the external circuit to form hydrogen gas and negatively charged oxygen ions. The oxygen ions pass through the solid ceramic membrane and react at the anode to form oxygen gas and produce electrons for the external circuit. Solid oxide electrolyzers must be operated at a sufficiently high temperature for the solid oxide membrane to function properly, for example, at about 700°C to about 800°C.

[0155] Due to the lower operating temperatures, the use of alkaline electrolyzers and / or PEM electrolyzers is generally preferred.

[0156] The plurality of electrolytic cells may be arranged in at least two parallel groups. In these embodiments, the apparatus comprises:

[0157] a first header to collect hydrogen from each electrolyzer in each group; and

[0158] a second header that collects hydrogen from the first header and feeds the hydrogen to a feed end of the multi-stage compression system;

[0159] In some embodiments, wherein the apparatus further comprises a storage system for storing compressed hydrogen, the apparatus further comprises a conduit for feeding the compressed hydrogen from the storage system to the second header after suitable decompression.

[0160] Power generation systems for compression

[0161] The electricity used for compression is generated by at least one renewable energy source, such as wind and / or solar energy.

[0162] In embodiments where wind energy is used to generate electricity, the power generation system will include a plurality of wind turbines. In embodiments where solar energy is used to generate electricity, the power generation system will include a plurality of photovoltaic cells or "solar cells."

[0163] Some embodiments will include multiple wind turbines and multiple photovoltaic cells.

[0164] The expression "in conductive communication" will be understood to mean that appropriate wires and / or cables will be used, together with any other relevant equipment, to connect the power generation system to the or each compressor in a safe and efficient manner.

[0165] In the context of the present invention, the or each centrifugal compressor is also driven by a dedicated variable frequency drive. Any variable frequency drive already mentioned herein as being suitable for modulating an AC electrical signal, for example by converting it to a DC signal before regenerating it, to provide a stable electrical frequency may be used.

[0166] In some preferred embodiments, the power generation system also generates electricity for electrolysis.

[0167] Multi-stage compression system

[0168] As described above, a multi-stage compression system includes a plurality of stages with a compression ratio typically in the range of about 2 to about 2.5. Intercoolers are typically provided between adjacent stages, and an aftercooler may be required after the final stage.

[0169] The stages of the multi-stage compression system are also arranged in at least two compression sections, a first section and another section downstream of the first section.

[0170] The first section comprises at least one centrifugal compressor driven at least in part by electricity generated from at least one renewable energy source, the or each centrifugal compressor being driven by a dedicated variable frequency drive. The other section comprises at least one reciprocating compressor, preferably also powered at least in part by electricity generated from at least one renewable energy source.

[0171] Each section may include one or more compression stages, and associated coolers. A phase separator may also be included upstream of each compression stage to remove liquid from the hydrogen being compressed. For LP centrifugal compressors, the phase separator is often incorporated into the intercooler as a separate unit to potentially realize capital and power benefits and simplify the system.

[0172] In a specific embodiment, the multi-stage compression system has two sections, a first (low pressure or "LP") section compresses hydrogen from a feed pressure to the multi-stage compression system to a first high pressure, and another (medium pressure or "MP") section compresses hydrogen from the first high pressure to a final high pressure desired by the downstream process.

[0173] The LP section may have one or more, for example two, compression stages, and the MP section may have one or more, for example 2 or 3, compression stages.

[0174] For example, for a process with a total electrolyser capacity of 1 GW, the multistage compression system may have 5 to 15 compressors, such as 7 to 13 compressors or 9 to 11 compressors, as required. Those skilled in the art will appreciate that processes with a higher total capacity will require a greater number of compressors.

[0175] The compressor in the LP section may be appropriately oversized, for example by 10%, to accommodate the loss of the machine. Additionally or alternatively, the multi-stage compression system may include a spare compressor in the LP or MP section, which will be switched in to replace another machine that has failed in the relevant section.

[0176] Purification system

[0177] In some embodiments, where there are downstream processes that cannot tolerate the levels of water and oxygen inherently present in the compressed hydrogen generated by electrolyzing water, the apparatus may include a purification system in which the compressed hydrogen is purified.

[0178] The purification system typically includes a "deoxygenation" unit in which oxygen is removed by catalytic combustion of the hydrogen to produce water and oxygen-depleted compressed hydrogen.

[0179] The oxygen-depleted gas may then be dried in a dryer, such as an adsorption unit, such as a temperature swing adsorption (TSA) unit, to generate dry compressed hydrogen for use in downstream processes.

[0180] Downstream processing unit

[0181] In some embodiments, there may be a downstream processing unit, which may be any unit that utilizes hydrogen as a feedstock.

[0182] Examples of suitable downstream processing units include oil refineries, steel manufacturing facilities, ammonia synthesis facilities, or hydrogen liquefaction facilities. In some embodiments, the ammonia synthesis facility is arranged in parallel with the hydrogen liquefaction facility.

[0183] In particularly preferred embodiments, the downstream processing unit comprises an ammonia synthesis plant (eg using the Haber-Bosch process) and / or a methanol synthesis plant (eg using CO 2 hydrogenation).

[0184] Control System

[0185] In some embodiments, the apparatus includes a control system that controls not only the pressure and flow of compressed hydrogen from the multi-stage compression system to the storage system, such as during periods when hydrogen production exceeds demand, but also controls the pressure and flow of compressed hydrogen to the multi-stage storage system, such as during periods when hydrogen demand exceeds production.

[0186] In some embodiments, the control system will simply seek to maintain the pressure of the hydrogen in the downstream header of the downstream process. Thus, in order to continuously provide a fixed amount of hydrogen to the downstream process, a pressure controller will be maintained on the exhaust header feeding the downstream process.

[0187] If the pressure in the discharge header exceeds the required feed pressure (eg, because more hydrogen is available than gas is consumed by downstream processes), the pressure can be relieved by opening a valve in the feed line to storage.

[0188] Once the pressure in the discharge header drops to the required feed pressure, the valve in the feed line to the reservoir will close.

[0189] If the pressure in the discharge header drops below the required feed pressure (eg because less hydrogen is available than gas is consumed by downstream processes), the pressure is increased by opening a valve in the first return line from storage to the first stage in the multi-stage compression system.

[0190] The valve in the first return line will remain open until the pressure in the discharge header exceeds the required feed pressure, indicating that the hydrogen production level has returned to the required level, at which time the valve will close, or until the pressure in the storage vessel drops to approximately the inlet pressure of the first stage of the multi-stage compression system fed by the first return line.

[0191] In the latter case, not only is the valve in the first return line closed, but also the valve in the second return line from the storage to the second stage (upstream of the first stage) in the multi-stage compression system is opened to continue feeding hydrogen from the storage back to the downstream process.

[0192] This type of control system may be referred to as a "split range" control system.

[0193] Storage System

[0194] In some embodiments, the apparatus includes a storage system for storing compressed hydrogen. In such embodiments, the storage system is in fluid flow communication with the outlet end of the multi-stage compression system and at least one compression stage of the multi-stage compression system.

[0195] Storage systems typically include multiple pressure vessels and / or piping segments connected to a common inlet / outlet header.

[0196] The pressure vessel may be spherical, e.g. up to about 25 m in diameter, or "bullet-shaped", i.e. a horizontal vessel up to about 12 m in diameter with a large L / D ratio (typically up to about 12:1).

[0197] Salt domes can also be used if the geological conditions of the site allow.

[0198] Water Source

[0199] These embodiments of the invention may use any suitable water source. However, in embodiments where seawater is used to generate water for electrolysis, the apparatus will further comprise at least one unit (or apparatus) for desalination and softening of seawater.

[0200] aspect

[0201] Aspects of the invention include:

[0202] #1. A process for supplying hydrogen for consumption in at least one downstream process, the process comprising:

[0203] Producing hydrogen by electrolysis of water;

[0204] compressing the hydrogen gas in a multi-stage compression system including a first section and another section downstream of the first section to generate compressed hydrogen gas; and

[0205] feeding the compressed hydrogen to the downstream process,

[0206] wherein the first section of the multi-stage compression system comprises at least one centrifugal compressor, the at least one centrifugal compressor being powered at least in part by electricity generated from at least one renewable energy source, the or each centrifugal compressor being driven by a dedicated variable frequency drive, and

[0207] Wherein the other section of the multi-stage compression system includes at least one reciprocating compressor.

[0208] 2. A process according to #1, wherein at least some of the compressed hydrogen is used to generate ammonia in the downstream process.

[0209] 3. The process according to #1, wherein the hydrogen is compressed to a first high pressure in the first section, and wherein the compressed hydrogen is further compressed to another high pressure in the another section.

[0210] 4. A process according to #1, wherein the multi-stage compression system has two sections, and in the first section hydrogen is compressed to a first high pressure, and in the second section the compressed hydrogen is further compressed to a final high pressure.

[0211] 5. The process according to #1, wherein the hydrogen is fed to the multi-stage compression system at a feed pressure from atmospheric pressure to 3 bar, preferably from atmospheric pressure to 1.5 bar.

[0212] 7. The process according to #1, wherein the compressed hydrogen generated by the multi-stage compression system has a pressure of from 10 bar to 50 bar.

[0213] 8. A process according to #1, wherein the first section includes 1 to 4 stages of centrifugal compression and the other section includes 1 to 7 stages of reciprocating compression.

[0214] 9. The process according to #1, wherein the first section comprises from 1 to 7 centrifugal compressors arranged in parallel, and the other section comprises from 1 to 5 reciprocating compressors arranged in parallel.

[0215] 10. A process according to #1, wherein during periods when the electrolysis generates more hydrogen than required by the downstream process, the method includes feeding excess compressed hydrogen to storage, optionally after further compression; and

[0216] During periods when the downstream process requires more hydrogen than is produced by the electrolysis, the method comprises extracting compressed hydrogen from storage and, after appropriate decompression, feeding the decompressed hydrogen to an intermediate stage of the first section or an initial stage of the other section of the multi-stage compression system.

[0217] 11. The process of #10, wherein during the period when the downstream process requires more hydrogen than is produced by the electrolysis, the method comprises:

[0218] reducing the pressure of the compressed hydrogen gas extracted from storage to generate depressurized hydrogen gas at an inlet pressure of a stage in the first section or the other section of the multi-stage compression system; and

[0219] The depressurized hydrogen is fed to the stage.

[0220] 12. A process according to #11, wherein during feeding of the depressurized hydrogen to the stage, each centrifugal compressor upstream of the stage is operated so that no net compressed hydrogen is produced.

[0221] 13. A process according to #1, wherein the electrolysis has a total capacity of at least 300 MW.

[0222] 14. An apparatus for supplying hydrogen for consumption in at least one downstream process, the apparatus comprising:

[0223] multiple electrolyzers for generating hydrogen;

[0224] an electric power generation system for generating electric power from at least one renewable energy source;

[0225] a multi-stage compression system for compressing hydrogen, the multi-stage compression system comprising a feed end, a first section, another section downstream of the first section, and an outlet end, the feed end being in fluid flow communication with the plurality of electrolyzers;

[0226] at least one downstream processing unit for consuming the compressed hydrogen, the downstream processing unit being in fluid flow communication with the outlet end of the multi-stage compression system;

[0227] wherein the multi-stage compression system is a hybrid system in which the first section comprises at least one centrifugal compressor and the further section comprises at least one reciprocating compressor, and

[0228] Wherein the or each centrifugal compressor is at least partly powered by electricity from the power generation system and driven by a dedicated variable frequency drive.

[0229] 15. The process according to #14, comprising:

[0230] a storage system for storing compressed hydrogen gas, the storage system being in fluid flow communication with the outlet end of the multi-stage compression system and with at least one compressor of the multi-stage compression system; and

[0231] A control system for controlling the pressure and flow of compressed hydrogen from the multi-stage compression system to the storage system, and for controlling the pressure and flow of compressed hydrogen from the storage system to the multi-stage compression system based on the hydrogen production level of the electrolyzer and / or the needs of downstream processes.

[0232] Figure 1 A multi-stage compression system is shown having a first section with two LP centrifugal compression stages 12 and 15 , and another section with two MP reciprocating compression stages 19 and 22 .

[0233] Feed 1 comprises hydrogen supplied by an electrolyser, which is fed through a phase separator 11 to remove liquid water, thereby generating feed 2. Feed 2 is then fed to the centrifugal compression stage 12 of the first (LP) section for compression. After compression, the hot compressed hydrogen is cooled in an intercooler 13 using a cooling water stream, and then fed through a phase separator 14 to generate feed 3. Although in Figure 1 , but for LP centrifugal compressors, the phase separator will often be incorporated into the intercooler as a single unit to potentially achieve capital and power benefits and simplify the system.

[0234] At this point, feed 3 may optionally be mixed with stream 9 containing dry hydrogen from storage, or completely replaced by stream 9 as the case may be. The mixed hydrogen feed 4 is then fed to the second centrifugal compression stage 15 in the first (LP) section. After compression, the hot compressed hydrogen is cooled in an intercooler 16 before passing through a phase separator 17 to generate feed 5.

[0235] Feed 5 is then optionally mixed with a stream 10 containing dry hydrogen from storage, or completely replaced by stream 10 , as the case may be, to generate a mixed feed 6 .

[0236] Feed 6 is then fed to a reciprocating compression stage 19 in another (MP) section. After compression, the hot compressed hydrogen is cooled in an intercooler 20 before passing through a phase separator 21 and then fed to a reciprocating compression stage 22 in another (MP) section to generate a feed 8 containing compressed hydrogen at a final high pressure (which is the feed pressure desired for downstream processes). Feed 8 will then be optionally purified and fed to at least one downstream process for consumption.

[0237] Streams 24, 26, 28, 30 and 32 feed gas into and out of a compressor (not shown) in parallel.

[0238] The following examples will now be explained in more detail. Figure 1 The system shown, the example contains data generated by computer simulation (Aspen+, version 10). The following example is used to illustrate the manner in which the hybrid multi-stage compression system of the present invention resists molecular weight variations in the hydrogen feed.

[0239] Example 1

[0240] Example 1 1 2 5 6 7 8 10 Wet mass flow rate kg / h 49341.5 9868.3 7029.6 35148.1 11716.0 10749.0 0.0 Wet volume flow rate <![CDATA[m 3 / h]]> 348176.0 71407.6 16316.8 84059.9 28337.3 5323.5 0.3 Wet molar flow <![CDATA[Nm 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

[0241] Example 1 shown in the table above describes the properties of feed / stream 1 to feed / stream 10 at different points in a multi-stage compression system that compresses hydrogen generated by electrolysis to feed a downstream process having a desired feed pressure of 30 bar.

[0242] In this example, the multi-stage compression system is operated at full flow using feed 1 (wet hydrogen from the electrolyzer). This is likely because there is sufficient electricity from renewable energy sources to power all compressors in the electrolysis and / or compression system. Therefore, under these conditions, there is no requirement to feed depressurized hydrogen from storage to the system via stream 9 or stream 10.

[0243] It can be seen that the discharge pressure at the outlet of the other (MP) section (i.e. feed port 8) is the required approximately 30 bar. This system resists changes in the electrical frequency of the renewable energy source that powers the compressor. It can also be seen that despite the decrease in molecular weight as the hydrogen is compressed in subsequent stages, the MP reciprocating compressor is still able to output a discharge pressure of approximately 30 bar. This is possible because reciprocating compressors are not affected by the decrease in molecular weight, which would not be the case if a centrifugal compressor was used instead.

[0244] Example 2

[0245]

[0246]

[0247] *=Minimum flow rate (circulation)

[0248] Example 2 shown in the table above also describes the properties of feed / stream 1 to feed / stream 10 at different points in a multi-stage compression system, which compresses hydrogen generated by electrolysis to feed a downstream process having a desired feed pressure of 30 bar.

[0249] In this example, the multi-stage compression system is operated at zero flow using feed 1 (wet hydrogen from the electrolyser). This may be because there is sufficient electricity from renewable energy sources to power all compressors in the electrolysis and / or compression system.

[0250] Therefore, under these conditions, 100% of the hydrogen used for compression in stream 6 is decompressed hydrogen, which is fed from storage to the first stage of another (MP) section via stream 10. Again, the decompressed hydrogen in stream 10 has been cooled and purified, and therefore has a molecular weight of 2.02. It can be seen that, since the dry hydrogen from stream 10 is compressed only in reciprocating compressors 19 and 22, the discharge pressure of the multi-stage compression system does not drop due to the reduction in the molecular weight of the hydrogen. In this way, the multi-stage compression system provides compressed hydrogen with a final high pressure of 30 bar, suitable for feeding to downstream processes.

[0251] The present inventors have found that if an MP centrifugal compressor is used instead of an MP reciprocating compressor, it is not possible to have a stable output pressure under all conditions.

[0252] The foregoing 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 teachings. It should be understood that any feature described with respect to any one example may be used alone or in combination with other features described, and may also be used in combination with any feature of any other example, or in combination with any combination of any other examples.

[0253] In this specification, unless explicitly stated otherwise, the word "or" is used in the sense of an operator that returns a true value when either or both of the conditions are met, rather than the operator "exclusive or" which requires only one of the conditions to be met. The word "comprising" is used in the sense of "including", rather than meaning "consisting of".

[0254] All prior teachings mentioned above are hereby incorporated herein by reference. Acknowledgment of any previously published document in this document is not to be taken as an acknowledgment or representation that its teachings were common general knowledge in Australia or elsewhere at that time.

Claims

1. A process for supplying hydrogen for consumption in at least one downstream process, the process comprising: Producing hydrogen by electrolysis of water; compressing the hydrogen gas in a multi-stage compression system including a first section and another section downstream of the first section to generate compressed hydrogen gas; as well as feeding the compressed hydrogen generated by the multi-stage compression system to the downstream process, wherein the first section of the multi-stage compression system comprises at least one centrifugal compressor powered at least in part by electricity generated from at least one renewable energy source, a cooler for cooling hydrogen compressed by the centrifugal compressor, and a phase separator for removing liquid from the hydrogen compressed by the centrifugal compressor, the or each centrifugal compressor being driven by a dedicated variable frequency drive for adjusting the frequency supplied by the variable frequency drive to the motor of the centrifugal compressor to prevent a reduction in discharge pressure at an outlet of the first section, and wherein the other section of the multi-stage compression system includes at least one reciprocating compressor to maintain a discharge pressure at an outlet of the other section during electrical frequency changes; During periods when the electrolysis generates more hydrogen than required by the downstream process, the process includes feeding excess compressed hydrogen to storage; and During periods when the downstream process requires more hydrogen than is produced by the electrolysis, the process comprises extracting compressed hydrogen from storage and, after appropriate decompression, feeding the decompressed hydrogen to an intermediate stage of the first section or an initial stage of the other section of the multi-stage compression system.

2. The process of claim 1, wherein at least some of the compressed hydrogen is used to generate ammonia in the downstream process.

3. The process of claim 1, wherein in the first section the hydrogen is compressed to a first high pressure, and wherein in the further section the compressed hydrogen is further compressed to another high pressure.

4. The process according to claim 1, wherein the multi-stage compression system has two sections, and in the first section hydrogen is compressed to a first high pressure, and in the second of the two sections the compressed hydrogen is further compressed to a final high pressure.

5. The process of claim 1, wherein the hydrogen is fed to the multi-stage compression system at a feed pressure ranging from atmospheric pressure to 3 bar.

6. The process according to claim 5, wherein the feed pressure is from atmospheric pressure to 1.5 bar.

7. The process of claim 1, wherein the compressed hydrogen generated by the multi-stage compression system has a pressure of from 10 bar to 50 bar.

8. The process of claim 1, wherein the first section comprises 1 to 4 stages of centrifugal compression and the another section comprises 1 to 7 stages of reciprocating compression.

9. The process of claim 1, wherein the first section comprises from 1 to 7 centrifugal compressors arranged in parallel and the another section comprises from 1 to 5 reciprocating compressors arranged in parallel.

10. The process of claim 1, wherein the excess compressed hydrogen is fed to the storage after further compression.

11. The process of claim 1 , wherein during the period when the downstream process requires more hydrogen than is produced by the electrolysis, the process comprises: reducing the pressure of the compressed hydrogen gas extracted from storage to generate depressurized hydrogen gas at an inlet pressure of a stage in the first section or the other section of the multi-stage compression system; as well as The depressurized hydrogen is fed to the stage.

12. The process of claim 11, wherein during feeding of the depressurized hydrogen to the stage, each centrifugal compressor upstream of the stage is operated such that no net compressed hydrogen is produced.

13. The process of claim 1 wherein the electrolysis has a total capacity of at least 300 MW.

14. An apparatus for supplying hydrogen for consumption in at least one downstream process, the apparatus comprising: multiple electrolyzers for generating hydrogen; an electric power generation system for generating electric power from at least one renewable energy source; a multi-stage compression system for compressing hydrogen, the multi-stage compression system comprising a feed end, a first section, another section downstream of the first section, and an outlet end, the feed end being in fluid flow communication with the plurality of electrolyzers; at least one downstream processing unit for consuming compressed hydrogen output from an outlet end of the multi-stage compression system, the downstream processing unit being in fluid flow communication with the outlet end of the multi-stage compression system; wherein the multi-stage compression system is a hybrid system in which the first section includes at least one centrifugal compressor, a cooler for cooling hydrogen compressed by the at least one centrifugal compressor, and a phase separator for removing liquid from the hydrogen compressed by the at least one centrifugal compressor, and the other section includes at least one reciprocating compressor to maintain a discharge pressure at an outlet end of the multi-stage compression system during electrical frequency changes, and wherein the or each centrifugal compressor is at least partly powered by electricity from the power generation system and driven by a dedicated variable frequency drive, the variable frequency drive being configured to adjust the frequency supplied by the variable frequency drive to the motor of the centrifugal compressor to prevent a reduction in discharge pressure at the outlet of the first section; Wherein, the device further comprises: a storage system for storing compressed hydrogen gas, the storage system being in fluid flow communication with the outlet end of the multi-stage compression system and with at least one compressor of the multi-stage compression system; and A control system for controlling the pressure and flow of compressed hydrogen from the multi-stage compression system to the storage system, and for controlling the pressure and flow of compressed hydrogen from the storage system to the multi-stage compression system based on the hydrogen production level of the electrolyzer and / or the needs of downstream processes.

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