A method and apparatus for dosing hydrogen in a centrifugal compression system

Abstract

A method for supplying hydrogen for consumption in at least one downstream process, the method comprising: electrolyzing water to provide hydrogen; compressing the hydrogen in a multi-stage compression system to provide compressed hydrogen; and feeding at least a portion of the compressed hydrogen to the downstream process, wherein the multi-stage compression system comprises at least one centrifugal compression stage; wherein the hydrogen is metered with nitrogen upstream of the centrifugal compression stage; and wherein the nitrogen is present in the compressed hydrogen when fed to the downstream process.

Description

Technical Field

[0001] The present invention relates to the supply of hydrogen for consumption in at least one downstream process. In particular, the present invention relates to a method for minimizing the effect of reduced apparent molecular weight on discharge pressure in a centrifugal compression stage of a multi-stage compression system. Background Art

[0002] Positive displacement compressors, such as reciprocating compressors, are commonly used in industrial processes to compress hydrogen. This type of compressor works by confining a continuous volume of gas within an enclosed space, such as by using a piston driven by a crankshaft to deliver gas at high pressure.

[0003] Positive displacement compressors (such as reciprocating compressors) generally offer uniform performance for both very low and high molecular weight gaseous media. Therefore, this type of compressor is suitable for a range of gases, and is particularly well-suited for compressing hydrogen. However, these types of compressors are not ideal for processing large quantities of gas. To achieve this, due to their design, a large number of compressors must be used in parallel. This results in significant capital expenditure and operating costs.

[0004] In contrast, a centrifugal compressor is a dynamic compressor in which gas is compressed by the mechanical action of rotating blades or impellers, which impart velocity to the gas. Gas typically enters at the center of the impeller and is pushed out to the radial edges by the rotational motion, delivering the gas at high velocity, where it strikes the casing. The gas's velocity is converted into static pressure, delivering high-pressure gas. These types of compressors are generally better suited for processing large volumes of gas at a lower cost.

[0005] However, these compressors are generally not suitable for compressing low molecular weight gases such as hydrogen because it is more difficult to build up sufficient centrifugal force due to the lower gas density, making high pressure compression more difficult.

[0006] Therefore, for centrifugal compression, the pressure ratio (discharge pressure divided by inlet pressure for a particular compression stage) is highly sensitive to and dependent on the molecular weight of the gas being compressed. That is, centrifugal compression of a gas with a low molecular weight may result in a discharge pressure at the outlet that is lower than the specified pressure unless additional impellers are used.

[0007] Typically, 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 significantly increases the cost of the compression system and is undesirable due to the inherent mechanical constraints of the system.

[0008] Therefore, it would be desirable in the art to provide a solution that would allow current centrifugal compression systems to maintain pressure ratios in an efficient manner when used with low molecular weight gases, without significantly increasing costs.

[0009] Currently, the inventors are not aware of any prior art that addresses this problem in the context of compressing wet hydrogen in a centrifugal compressor in a downstream process that consumes nitrogen. Summary of the Invention

[0010] According to a first aspect of the present invention, there is provided a method for supplying hydrogen for consumption in at least one downstream process, the method comprising:

[0011] Electrolysis of water to provide hydrogen;

[0012] compressing the hydrogen in a multi-stage compression system to provide compressed hydrogen; and

[0013] feeding at least a portion of the compressed hydrogen to a downstream process,

[0014] wherein the multi-stage compression system includes at least one centrifugal compression stage;

[0015] wherein said hydrogen is metered with nitrogen upstream of said centrifugal compression stage; and

[0016] wherein the nitrogen is present in the compressed hydrogen when fed to the downstream process.

[0017] According to a second aspect of the present invention, there is provided a method for compressing hydrogen using a centrifugal compressor, the method comprising quantitatively supplying nitrogen to the hydrogen upstream of the centrifugal compressor to provide nitrogen-blended hydrogen, and compressing the nitrogen-blended hydrogen in the centrifugal compressor.

[0018] According to a third aspect of the present invention, there is provided an apparatus for supplying hydrogen for consumption in at least one downstream process, the apparatus comprising:

[0019] a plurality of electrolyzers arranged in parallel for electrolyzing water to provide hydrogen;

[0020] a power generation system for generating electricity to power the plurality of electrolytic cells, the power generation system being in conductive communication with the plurality of electrolytic cells;

[0021] a multi-stage compression system for compressing the hydrogen to provide compressed hydrogen, the multi-stage compression system comprising a feed end, an outlet end, and at least one centrifugal compression stage, the feed end being in fluid flow communication with the plurality of electrolyzers;

[0022] a nitrogen source for supplying nitrogen, wherein the source is arranged to meter nitrogen to the hydrogen upstream of the centrifugal compression stage in the multi-stage compression system; and

[0023] At least one downstream processing unit is arranged to receive at least a portion of the compressed hydrogen metered with nitrogen, the downstream processing unit being in fluid flow communication with the outlet end of the multi-stage compression system. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0025] Figure 1 is a simplified flow diagram of a first embodiment of the present invention, wherein hydrogen is produced by electrolysis of water, is metered with nitrogen, is compressed and fed to a downstream ammonia plant, and wherein excess hydrogen is stored under high pressure;

[0026] Figure 2 is a simplified flow diagram of a second embodiment of the present invention in which the multi-stage compression system has a single section and in which a purification unit is shown;

[0027] Figure 3 is a simplified flow diagram of a third embodiment of the present invention, wherein the multi-stage compression system has a low pressure (LP) section and a medium pressure (MP) section;

[0028] Figure 4 The present invention is provided for the first embodiment of the present invention and Figure 1 A further simplified flow chart showing additional details of one option for process integration;

[0029] Figure 5 The second embodiment of the present invention is provided for Figure 1 another simplified flow diagram with additional details of one option for process integration; and

[0030] Figure 6 The second embodiment of the present invention is provided for Figure 1 Another simplified flow chart with additional details of another option for process integration. DETAILED DESCRIPTION

[0031] According to a first aspect of the present invention, there is provided a method for supplying hydrogen for consumption in at least one downstream process.

[0032] The method of the present invention comprises dosing nitrogen with hydrogen to increase the apparent molecular weight of the hydrogen.

[0033] In the context of the present invention, the term "dosing" is intended to mean that nitrogen is fed into hydrogen in small amounts to provide nitrogen-blended hydrogen, wherein the majority of the blended gas is hydrogen.

[0034] The term "hydrogen" may be used to refer to hydrogen before and / or after it has been dosed with nitrogen. The terms "blended hydrogen" or "nitrogen-blended hydrogen" specifically refer to hydrogen after it has been dosed with nitrogen. The term "unblended hydrogen" specifically refers to hydrogen that has not yet been dosed with nitrogen.

[0035] The term "apparent molecular weight" in the context of the present invention is intended to mean the molecular weight of a gaseous medium having a mixture of low molecular weight components and high molecular weight components. The apparent molecular weight of a gas mixture can be measured or, alternatively, estimated by calculating the sum of the products of the mole fraction of each component multiplied by the molecular weight of that component, i.e., for a mixture of gases A+B+...,

[0036] M app =∑(M A ×y A +M B ×y B +…)

[0037] Among them, M X is the molecular weight of component gas X, and y X is the mole fraction of component gas X.

[0038] The term "appropriate" in the context of reduced pressure is intended to mean that the pressure of the nitrogen (or hydrogen blended with nitrogen) is reduced to an appropriate level taking into account the inlet pressures of the stages of the multi-stage compression system to which the reduced pressure nitrogen (or hydrogen blended with nitrogen) is fed.

[0039] In the following discussion of embodiments of the present invention, pressures are given as absolute pressures unless otherwise indicated.

[0040] electrolysis

[0041] The method according to the invention comprises producing hydrogen by electrolysis of water to provide hydrogen.Any suitable form of water electrolysis may be used, including alkaline water electrolysis and polymer electrolyte membrane (PEM) water electrolysis.

[0042] The water used for the electrolysis may be seawater, which may be desalinated and demineralized by reverse osmosis.

[0043] The electricity required for electrolysis may be generated from one or more suitable energy sources including, but not limited to, renewable energy, on-site gasoline, diesel or hydrogen powered generators, fuel cells, or from the local or national grid, or a combination of these sources.

[0044] Preferably, at least some of the electricity required for electrolysis is generated from renewable energy sources, including wind, solar, tidal and hydroelectric energy, or a combination of these sources, particularly wind and solar. The electricity generated from these sources is used to power the electrolyser.

[0045] Preferably, the process is self-contained in terms of electricity generation for the electrolysis.Thus, preferably, the entire electricity requirement for the electrolysis is met using renewable energy sources.

[0046] However, it is contemplated that electricity generated by one or more renewable energy sources may be supplemented by other sources during periods of particularly high demand for products from downstream processes and / or during periods when renewable energy sources are only available below a threshold required to meet demand or are not available at all. In these cases, the additional electricity may be drawn from on-site battery storage and / or generated from one or more on-site gasoline, diesel, or hydrogen-powered generators (including fuel cells) and / or drawn from the local or national power grid.

[0047] The electrolysis can be performed at any suitable scale. However, in some embodiments, the electrolysis can have a total capacity of at least 1 gigawatt (GW). The maximum total capacity of the electrolysis is limited only by practical considerations, such as generating sufficient electricity from renewable energy sources to power multiple electrolysis cells. Thus, the electrolysis can have a maximum total capacity of about 10 GW or greater. The total capacity of the electrolysis can range from 1 GW to about 5 GW, for example, from about 1.5 GW to about 3 GW.

[0048] Hydrogen is typically produced by electrolysis at a pressure slightly above atmospheric pressure, for example about 1.3 bar. However, in some embodiments, electrolysis produces hydrogen at a slightly higher pressure, for example up to about 3 bar.

[0049] Therefore, hydrogen is typically fed to the multi-stage compression system at a pressure in the range from atmospheric pressure to about 3 bar, preferably at a pressure in the range from atmospheric pressure to about 1.5 bar, for example at about 1.1 bar.

[0050] purification

[0051] It will be understood that hydrogen produced by the electrolysis of water will contain impurities. Accordingly, when used in the context of the present invention, the term "hydrogen" is intended to refer to hydrogen with such impurities unless and until the hydrogen is purified.

[0052] In particular, the term encompasses hydrogen produced by electrolysis, which is typically saturated with water at 40° C. and typically contains some residual oxygen, typically about 500 ppm to about 1000 ppm (v). Depending on the tolerances of the downstream processes, these impurities will typically have to be removed.

[0053] In this regard, oxygen is a poison to conventional catalysts used in the Haber process. Thus, in embodiments where the downstream process is ammonia synthesis, the catalyst feed 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 (O), water (HO), carbon monoxide (CO), and / or carbon dioxide (CO). Consequently, the feed will also be dry, i.e., not exceeding 1 ppm of water.

[0054] Processes using conventional “grey” hydrogen (i.e., hydrogen derived from hydrocarbon or carbon-containing feed streams without carbon dioxide capture, such as through downstream processes such as reforming natural gas) or “blue” hydrogen (i.e., hydrogen obtained in the same manner as “grey” hydrogen, but with some or all of the carbon dioxide associated with its production captured), such as refineries, have similar tolerances for oxygen and water.

[0055] The compressed hydrogen is preferably purified upstream before being fed to downstream processes.

[0056] In this regard, residual oxygen in the compressed hydrogen can be converted to water by catalytic combustion of some of 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.

[0057] In the context of the present invention, the purification process does not remove any, or at least any significant amount, of nitrogen from the hydrogen.

[0058] compression

[0059] The method according to the present invention comprises the step of compressing hydrogen in a multi-stage compression system to produce compressed hydrogen. The multi-stage compression system is responsible for compressing hydrogen from the pressure at which it is generated by electrolysis to a high pressure which is usually at least slightly higher than the feed pressure of the downstream process.

[0060] As explained in more detail below, at some point before or during the various stages of compression, the hydrogen will be metered with nitrogen. Thus, in this section, "hydrogen" may refer to either unadulterated hydrogen or nitrogen-adulterated hydrogen, depending on at which stage upstream in the multi-stage compression system the hydrogen is metered.

[0061] It will be readily understood that a "multi-stage" compression system has multiple compression stages that can be split between compressors connected 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 (e.g., about 2 to about 2.5) to limit the temperature rise of the compressed gas.

[0062] In multi-stage compression systems, 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. Therefore, in the context of this invention, a compression "stage" refers to the portion of the compression system between the coolers.

[0063] A multi-stage compression system comprises one or more compression sections. In this context, a compression "section" refers to the portion of the compression system between the feed and the product. Each section may comprise one or more compression stages and associated coolers.

[0064] In the present invention, a multi-stage compression system includes at least one centrifugal compression stage. That is, the compressors used in one, some, or all stages are centrifugal compressors. The multi-stage compression system may include multiple centrifugal compressors. Preferably, at least the first or initial compression stage in the multi-stage compression system includes a centrifugal compressor.

[0065] It should be understood that in some embodiments, a multi-stage compression system may have at least one centrifugal compression stage combined with at least one reciprocating compression stage, ie, a stage including a reciprocating compressor.

[0066] It is contemplated that in some preferred embodiments, all stages of the multi-stage compression system are centrifugal compression stages.

[0067] The compressed hydrogen leaving the outlet end of the multi-stage compression system will have been dosed with nitrogen (at some point upstream of the centrifugal compression stages) and therefore contains nitrogen.

[0068] The compressed hydrogen blended with nitrogen produced by the multi-stage compression system typically has a pressure of about 10 bar to about 50 bar. In some embodiments, the pressure of the compressed hydrogen blended with nitrogen is about 25 bar to about 35 bar, preferably about 30 bar. In other embodiments, the pressure of the compressed hydrogen blended with nitrogen is about 10 bar to about 12 bar, preferably about 11 bar.

[0069] In some embodiments, the multi-stage compression system has only a single section to compress the hydrogen to the desired high pressure. In other embodiments, the multi-stage compression system includes a first section and at least one further section downstream of the first section.

[0070] In a particular embodiment, the multi-stage compression system has two sections, a first (low pressure or "LP") section in which the hydrogen is compressed from the feed pressure to the multi-stage compression system to a first high pressure in the range of about 2 bar to about 6 bar; and a second (medium pressure or "MP") section in which the hydrogen is compressed from the first high pressure to a final high pressure required for downstream processes.

[0071] In some embodiments, the first high pressure after hydrogen is compressed in the first section 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.

[0072] Downstream Process

[0073] The compressed hydrogen is consumed in a downstream process, or in more than one downstream process arranged in parallel.

[0074] Downstream processes can include any process that currently uses “grey” or “blue” hydrogen. Such processes include oil refining and steelmaking.

[0075] In the present invention, the downstream process consumes hydrogen. In some preferred embodiments, at least some, such as all, of the compressed hydrogen blended with nitrogen is used in a downstream process that consumes nitrogen, or in which nitrogen is a reactant.

[0076] More preferably, at least some, for example 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 at high pressure, typically in the range of about 100 bar to 200 bar.

[0077] Quantitative supply of nitrogen to hydrogen

[0078] In order to improve the performance of a centrifugal compression stage in which hydrogen is to be compressed, the present invention consists in dosing nitrogen with the hydrogen to increase the apparent molecular weight of the gas feed entering the centrifugal compression stage.

[0079] Pure hydrogen has a molecular weight of 2.016. However, as described above, wet hydrogen generated by the electrolysis of water will typically be saturated with water, which has a molecular weight of 18.015, which is significantly higher than the molecular weight of hydrogen. Thus, "wet" hydrogen has a higher "apparent" molecular weight than pure hydrogen, typically about 3, but must be between the molecular weights of pure hydrogen and pure water (2.016 and 18.015, respectively), depending on the water content. Thus, in some embodiments, hydrogen generated by the electrolysis of water will have an apparent molecular weight of about 2.5 to about 4, or about 2.5 to about 3.5.

[0080] As the water-saturated hydrogen passes through the intercoolers and aftercoolers of the multi-stage compression system, water is removed from the hydrogen through condensation of gaseous water and phase separation of liquid water. This removal of water from the hydrogen also results in a decrease in the apparent molecular weight of the hydrogen as heavier water molecules are extracted and the hydrogen is dried. With the water removed, the apparent molecular weight of the hydrogen approaches approximately 2.

[0081] As mentioned above, in a centrifugal compressor, the pressure ratio (discharge pressure divided by the inlet pressure of the compression stage) is highly sensitive to and dependent on the molecular weight of the gas being compressed.

[0082] This change in apparent molecular weight due to drying of the wet hydrogen between stages in a multi-stage compression system is detrimental to the performance of the centrifugal compressor of each subsequent stage, resulting in discharge pressures below the specified pressure.

[0083] This effect is shown in Table 1 below. In particular, it can be seen that the amount of water removed between stages and hence the reduction in apparent molecular weight results in a reduction in the pressure ratio on recycle.

[0084] For example, hydrogen is compressed in stage 1 to a specified discharge pressure of 2.5 bar. Between stages, the gas loses water (0.067 to 0.030 water mole fraction) and therefore has a reduced apparent molecular weight (3.089 mol.wt. to 2.488 mol.wt.). The gas is then recycled back through stage 1 having these characteristics, and the discharge pressure of the recycled gas from stage 1 is 2.167 bar, which is much lower than the specified pressure.

[0085]

[0086]

[0087] In the present invention, this problem is solved by metering a typically small amount of nitrogen into the hydrogen gas before or during compression of the gas. Specifically, the method of the present invention comprises metering nitrogen into the hydrogen gas upstream of at least one centrifugal compression stage of a multi-stage compression system, thereby providing nitrogen-blended hydrogen.

[0088] The hydrogen is metered with nitrogen upstream of any centrifugal compression stage of the multi-stage compression system. However, it is particularly preferred that the hydrogen is metered with nitrogen upstream of or before the initial stage of the multi-stage compression system being the centrifugal compression stage, i.e. before any compression of the hydrogen occurs.

[0089] If the method includes metering nitrogen to the hydrogen between stages of a multi-stage compression system, the method also includes compressing the nitrogen (or reducing the pressure of the nitrogen, as the case may be) to a pressure that is substantially the same as the pressure of the hydrogen stream to which the nitrogen is to be fed, or to a pressure that is substantially the same as the inlet pressure between the stages of the multi-stage compression system.

[0090] By dosing nitrogen with the hydrogen upstream of at least one stage in a multi-stage compression system, thereby increasing the nitrogen content of the hydrogen, the apparent molecular weight of the compressed gas increases. This enables the centrifugal compressor in that stage to generate sufficient centrifugal force to provide a specified pressure ratio (discharge pressure divided by the inlet pressure of the compression stage). This, in turn, allows the hydrogen to be compressed in a smaller, more cost-effective centrifugal compression system with fewer stages.

[0091] Once the nitrogen-blended hydrogen undergoes compression and passes through the intercooler and aftercooler, the apparent molecular weight of the nitrogen-blended hydrogen will only decrease if the water is removed. This means that even if the water content changes and the apparent molecular weight decreases, the apparent molecular weight is still at a level at which the centrifugal compressor operates more efficiently. This will occur even if all the water is removed to provide completely "dry" hydrogen (e.g., after a purification process).

[0092] As a result, the apparent molecular weight does not drop to a level where the performance of the centrifugal compressor is negatively impacted. This eliminates the need to resort to conventional methods for mitigating pressure ratio drops. For example, conventional methods for increasing pressure ratio typically involve increasing impeller speed during operation, which requires increased power and is limited by the impeller's maximum speed. Alternatively, another approach is to design a multi-stage compression system with more stages. Once the present invention has been implemented, neither of these methods is necessary.

[0093] The amount of nitrogen fed into the hydrogen to dose it can be selected based on the amount of water present in the hydrogen generated by electrolysis. For example, where the water saturation level is lower, the amount of nitrogen added can be higher to compensate, and vice versa.

[0094] It may also depend on the point at which the nitrogen is fed to the hydrogen. This is because the hydrogen may be less saturated with water before being fed to an intermediate stage of compression than before being fed to the initial stage of compression in a multi-stage compression system.

[0095] In some embodiments, after dosing, the nitrogen-blend hydrogen has at most about 24 mol %, or at most about 20 mol %, or at most about 15 mol %, or at most about 10 mol %, or at most about 5 mol % nitrogen.

[0096] In some embodiments, after dosing, the nitrogen-doped hydrogen has at least about 0.05 mol %, or at least about 0.1 mol %, or at least about 0.5 mol %, or at least about 1 mol %, such as at least about 2 mol % nitrogen.

[0097] In some embodiments, after dosing, the nitrogen-doped hydrogen has about 0.5 mol% to about 10 mol%, such as about 1 mol% to about 5 mol% or about 2 mol% to about 4 mol%, preferably about 3 mol% nitrogen.

[0098] Alternatively, the amount of nitrogen to be added can be determined based on the desired apparent molecular weight, as this can be measured. In some embodiments, hydrogen is metered in an amount of nitrogen such that the resulting nitrogen-doped hydrogen has an apparent molecular weight (in g / mol) of about 2.05 to about 7, such as about 2.1 to about 5, or about 2.5 to about 4, or preferably about 2.5 to about 3.5.

[0099] In some embodiments, hydrogen is metered with an amount of nitrogen such that the apparent molecular weight of the nitrogen-blended hydrogen is greater than the apparent molecular weight of unblended nitrogen hydrogen (i.e., hydrogen obtained from the electrolysis of water or from a storage system) by an amount in the range of about 0.1 to about 3.0, e.g., about 0.5 to about 2.0, or preferably about 0.7 to about 1.5.

[0100] The method may include metering nitrogen to hydrogen upstream of any centrifugal compression stage in a multi-stage compression system to target a particular compression stage with poor performance, such as a stage from which a certain amount of water has already been removed. Here, "upstream" of a stage means that the gas is fed into the gas stream before being fed into the inlet of the stage, i.e., before it is compressed. Hydrogen is metered with nitrogen upstream of a stage in the multi-stage compression system so that the particular stage in question experiences better performance due to the higher apparent molecular weight of the hydrogen blended with nitrogen.

[0101] In some embodiments, the method comprises metering nitrogen to the hydrogen upstream of an intermediate stage of a multi-stage compression system. However, in a preferred embodiment, the method comprises metering nitrogen to the hydrogen upstream of an initial stage of the multi-stage compression system (which is a centrifugal compression stage, i.e., before any compression of the hydrogen occurs). This is because the increased apparent molecular weight of the hydrogen will improve the performance of the centrifugal compressors of all subsequent stages of the multi-stage compression system.

[0102] As described above, in some embodiments, the multi-stage compression system may include a first section and at least one additional section downstream of the first section. In these embodiments, the method may include metering nitrogen to the hydrogen at an initial stage of the first section of the multi-stage compression system. In other embodiments, the method may include metering nitrogen to the hydrogen at an initial stage of at least one additional section of the multi-stage compression system.

[0103] In a preferred embodiment, the downstream process of the present invention consumes nitrogen. More preferably, the downstream process comprises ammonia synthesis. Thus, the method may include feeding additional nitrogen to the compressed nitrogen-blended hydrogen feed to prepare for consumption in the downstream process. The amount of additional nitrogen to be added may be based on the amount of nitrogen to be consumed in the downstream process. The amount of additional nitrogen may also be based on the amount of nitrogen already present in the compressed hydrogen.

[0104] Preferably, the method comprises compressing the additional nitrogen before feeding it to the compressed nitrogen-blended hydrogen so that it is at a pressure suitable for feeding to a downstream process.

[0105] In such embodiments, the method includes feeding additional nitrogen to the compressed nitrogen-blended hydrogen to produce a synthesis gas (or "syngas") mixture for consumption in a downstream process. For example, if the downstream process is ammonia synthesis, additional nitrogen is fed to the nitrogen-blended hydrogen such that the ammonia synthesis gas has a molar ratio of about 25 mol% nitrogen and about 75 mol% hydrogen.

[0106] Thus, for example, additional nitrogen need only be added in an amount to "top up" the nitrogen level to the required amount, in preparation for consumption in downstream processes.

[0107] Therefore, in some embodiments, nitrogen can be added at two separate stages in the overall process. First, hydrogen is metered with nitrogen upstream of the centrifugal compression stage in a multi-stage compression system. Second, additional nitrogen is then fed into the compressed hydrogen to prepare it for consumption in downstream processes.

[0108] Therefore, a particular advantage of the present invention is that the process does not require nitrogen removal upstream of the downstream process. That is, nitrogen fed to the hydrogen for dosing does not need to be removed later because it is consumed in the downstream process.

[0109] Thus, an additional advantage of the process is that no expensive additional equipment for gas separation or extraction is required to remove the nitrogen. Furthermore, in embodiments where the downstream process consumes nitrogen and therefore already involves a nitrogen source and feed line, all that is required to implement the present invention is an additional feed line (and possibly a valve) that meters nitrogen to the hydrogen upstream of the centrifugal compression stage.

[0110] In embodiments where a hydrogen storage system is used, a particular advantage of adding a small amount of nitrogen upstream of the compression stage, rather than introducing 25 mol% or more, is that the storage volume required for the storage system is not significantly increased. For example, adding 25 mol% nitrogen would increase the storage requirement by approximately 33% by volume.

[0111] Furthermore, nitrogen is produced more efficiently at high pressure, thus providing a more efficient overall process by adding the majority of the nitrogen for use in downstream processes after compression but upstream of the downstream process.

[0112] In some embodiments, the amount of hydrogen generated by the electrolysis of water may be variable. This may be inherent in systems where some of the electricity generated by the electrolysis comes from a renewable power source or energy source, such as, for example, solar or wind power.

[0113] In an embodiment in which the amount of hydrogen generated by electrolysis of water is variable, the amount of nitrogen fed to the hydrogen is determined based on the amount of hydrogen produced by electrolysis.

[0114] For example, the amount of nitrogen fed to the hydrogen can be fixed relative to the amount of hydrogen. That is, as the amount of hydrogen decreases (due to a lack of renewable power), the amount of nitrogen fed to the hydrogen is reduced by the same amount. This advantageously enables the concentration of nitrogen in the hydrogen to remain constant.

[0115] In some embodiments, the above-described method of controlling the flow rate and / or pressure of nitrogen can be implemented by a suitable control system configured to monitor the amount of hydrogen generated by electrolysis by measurement. For example, the measurement can be performed by direct flow measurement, or alternatively, it can be inferred from measurement of the electrolyzer current.

[0116] In some embodiments, the method may further include a feedback loop that takes into account information about the nitrogen concentration in the nitrogen-doped hydrogen. This can be determined by measuring the gas composition, such as for example by using a mass spectrometer or a density meter.

[0117] By determining the amount of nitrogen to be added based on the amount of hydrogen, this enables careful control of the nitrogen concentration. For example, it advantageously allows the nitrogen concentration to remain constant despite variations in the amount of hydrogen.

[0118] In embodiments where the flow rate of hydrogen from the electrolyzer is variable and a hydrogen storage system is used, it is disadvantageous to add all the nitrogen required for the downstream process (i.e., 25 mol% for ammonia synthesis) to the hydrogen upstream of the compression stage. This is because the flow rate from the nitrogen source would also need to be variable over a wide range. This in turn would require a high-capacity air separation unit (ASU) to cope with this.

[0119] For example, if the flow rate to the electrolyzer varies between 0% and 130% of the ammonia plant demand, and the nitrogen source supplies all of the nitrogen to the downstream processes upstream of the compression stage, the nitrogen source will need to vary its flow rate accordingly, sometimes requiring shutting down or venting nitrogen when the electrolyzer flow is 0% (and hydrogen blended with nitrogen is instead supplied from storage).

[0120] In contrast, by dosing a small amount of nitrogen into the hydrogen and then adding additional nitrogen later, the change in the flow rate of the nitrogen source (e.g., ASU) will be much smaller relative to the capacity of the nitrogen source (e.g., ASU). For example, adding 3 mol% nitrogen to the hydrogen only requires a change in the flow rate of the nitrogen source (e.g., ASU) of about 4%. Advantageously, this means that the nitrogen source does not need to be shut down when the electrolyzer flow reaches 0% (and hydrogen is supplied from storage).

[0121] Hydrogen storage

[0122] Depending on the type of electricity generated for electrolysis, the present invention may include the use of hydrogen storage in the process.

[0123] European Patent Application No. 20188259.4 in the same name as the present applicant describes a method for storing hydrogen for a multi-stage compression system, and this document is incorporated herein by reference in its entirety.

[0124] In some embodiments where the electricity generated for electrolysis can come from renewable energy sources, the availability of energy will inherently fluctuate. This results in less hydrogen being produced by electrolysis. One way this problem can be addressed is by providing a system for collecting and storing at least some, and preferably all, of the excess nitrogen-blended hydrogen produced during periods when production exceeds demand from downstream processes, and distributing the stored nitrogen-blended hydrogen to downstream processes during periods when demand exceeds production.

[0125] In some embodiments, the compressed hydrogen blended with nitrogen can 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 blended with nitrogen is compressed in the multi-stage compression system, such as up to about the feed pressure of the downstream process (if only one is present) or about the maximum feed pressure of one of the downstream processes (if more than one is present). In such embodiments, the compressed hydrogen blended with nitrogen may be stored at a maximum pressure in the range of up to about 25 bar to about 30 bar.

[0126] However, the compressed hydrogen blended with nitrogen may be further compressed prior to storage. In these embodiments, the compressed hydrogen blended with nitrogen may be stored at a pressure of at most about 200 bar maximum, or at most about 150 bar maximum, or at most about 100 bar maximum, or at most about 90 bar maximum, or at most about 80 bar maximum, or at most about 70 bar maximum, or at most about 60 bar maximum, or at most about 50 bar maximum.

[0127] During periods when hydrogen demand levels exceed production levels, compressed nitrogen-blended hydrogen is withdrawn from storage and depressurized to produce depressurized nitrogen-blended hydrogen (hereinafter referred to as "depressurized hydrogen" for simplicity). The pressure can be reduced in any conventional manner, particularly by passing the gas through a valve.

[0128] The pressure of the reduced pressure hydrogen will depend on the pressure at the point in the multi-stage compression system at which the reduced pressure hydrogen is to be added.

[0129] In some embodiments, the decompressed hydrogen can be fed to the final stage 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.

[0130] In other embodiments, the decompressed hydrogen can be fed to the final stage of the multi-stage compression system. In these embodiments, the decompressed hydrogen will be at the inlet pressure of the feed of the intermediate stage.

[0131] The intermediate stage may be an intermediate stage within a compression section, or, in the case of a multi-stage compression system with two or more sections, an initial stage within a further compression section downstream of the first compression section. In these embodiments, the reduced pressure hydrogen will be at the inlet pressure of the feed to the further compression section, i.e., the "inter-section" pressure.

[0132] In further embodiments, the reduced pressure hydrogen can be fed to the feed end, ie, the initial stage of the multi-stage compression system. In these embodiments, the reduced pressure hydrogen will be the feed pressure of the multi-stage compression system, for example, about 1.1 bar.

[0133] During periods when demand exceeds production, methods may include:

[0134] reducing the pressure of the compressed hydrogen gas taken out from the storage to produce reduced-pressure hydrogen gas at the inlet pressure (first intermediate pressure) of the first stage of the multi-stage compression system; and

[0135] Hydrogen under reduced pressure is fed to the first stage.

[0136] In such embodiments, once the pressure of the compressed hydrogen in the storage drops to about the inlet pressure of the first stage, the method may include:

[0137] further reducing the pressure of the compressed hydrogen gas taken out from the storage to produce reduced-pressure 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

[0138] Reduced pressure hydrogen is fed to the second stage.

[0139] It should be understood that the terms "first stage" and "second stage" in this context do not refer to the relative positions of the stages in the downstream direction of the multi-stage compression system during normal operation. Rather, these terms are intended only to reflect the order in which the reduced-pressure 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, meaning that the first intermediate pressure is higher than the second intermediate pressure.

[0140] These embodiments may further include feeding the decompressed hydrogen to other stages upstream of the first and second stages of the multi-stage compression system. In these additional embodiments, the pressure of the compressed hydrogen taken from the storage is reduced to the inlet pressure of the corresponding stage.

[0141] In some preferred embodiments, the second stage is the initial stage of a multi-stage compression system.

[0142] It will be appreciated that in embodiments where the reduced pressure hydrogen is fed to the second stage after the first stage, the flow to the first stage is stopped when the flow to the second stage begins. Generally, the flow of reduced pressure hydrogen to a given compression stage is stopped when the flow to another compression stage begins.

[0143] Since hydrogen can be returned from storage to intermediate and / or initial stages of the multi-stage compression system, the compressed hydrogen can be stored at a pressure down to a minimum of about 5 bar, perhaps even down to a minimum of about 1.3 bar.

[0144] In embodiments where the compressed hydrogen is further compressed before storage, another option is to feed the compressed hydrogen removed from 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 removed from storage is further reduced, and the decompressed hydrogen is fed to one stage of the multi-stage compression system according to the present invention. However, these embodiments are not preferred, for example due to the additional capital cost of the high-pressure storage system.

[0145] Compared to high-pressure hydrogen storage systems that only discharge to the feed pressure of the downstream process, this can reduce the storage volume of hydrogen by using a multi-stage compression system already present in the process to recompress hydrogen from the storage when the storage pressure drops below the feed pressure. Therefore, 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.

[0146] During periods when hydrogen production is limited by a lack of electricity to 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. This also allows the maximum hydrogen storage pressure to be equal to or lower than the feed pressure to the downstream process, eliminating any additional compression requirements for hydrogen storage.

[0147] It will be appreciated that the same volume of gas is stored at the same storage volume at the same maximum pressure, and that lowering the minimum storage pressure increases the "releasable" volume of gas from the storage, ie the available volume of stored gas.

[0148] Where hydrogen is produced and subsequently 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 the hydrogen from storage to one stage in the multi-stage compression system rather than directly to the downstream process - such an arrangement reduces the total storage vessel volume required for the process.

[0149] For example, storage from a maximum pressure of 200 bar to a minimum pressure of 1.5 bar requires 15% less storage vessel volume for a given mass of releasable hydrogen compared to storage from a maximum pressure of 200 bar to a minimum pressure of 30 bar.

[0150] Similarly, storage from a maximum pressure of 100 bar to a minimum pressure of 1.5 bar requires 30% less storage vessel volume for a given mass of releasable hydrogen than storage from a maximum pressure of 100 bar to a minimum pressure of 30 bar.

[0151] Furthermore, storage from a maximum pressure of 50 bar to a minimum pressure of 1.5 bar requires 60% less storage vessel volume for a given mass of releasable hydrogen compared to storage from a maximum pressure of 50 bar to a minimum pressure of 30 bar.

[0152] Further, 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.

[0153] Furthermore, while the total storage vessel volume increases with decreasing maximum storage pressure, lower design pressures allow for thinner vessel walls and can reduce the overall capital cost of the storage system. For reasons such as manufacturability, vessel thickness is often limited to a maximum, and in such cases, a lower design pressure will result in fewer vessels (but each vessel will be larger). Furthermore, the allowable stress in the vessel design can be increased below a specific vessel wall thickness, and if the lower design pressure allows for thicknesses below this threshold, the overall vessel metal mass (and therefore overall cost) can be reduced.

[0154] In embodiments where the method includes storing and reusing excess hydrogen, the method preferably includes metering nitrogen to the hydrogen upstream of the point at which any decompressed hydrogen is fed from storage. This enables the concentration of nitrogen in the nitrogen-blended hydrogen to remain constant, as the decompressed hydrogen is not metered with a second amount of nitrogen when it is recycled.

[0155] Method of using a centrifugal compressor

[0156] According to a second aspect of the present invention, there is provided a method for compressing hydrogen using a centrifugal compressor, the method comprising quantitatively supplying nitrogen to the hydrogen upstream of the centrifugal compressor to provide nitrogen-blended hydrogen, and compressing the nitrogen-blended hydrogen in the centrifugal compressor.

[0157] It will be understood that features described above in relation to the first aspect of the present invention are equally applicable to the second aspect, and vice versa, so long as they are compatible.

[0158] The amount of nitrogen that is fed to the hydrogen for dosing may depend on the amount of water present in the hydrogen. It may also depend on the point at which the nitrogen is fed to the multi-stage compression system.

[0159] In some embodiments, after dosing, the nitrogen-blend hydrogen comprises less than 25 mol% or up to about 20 mol% or up to about 15 mol% or up to about 10 mol% or preferably up to about 5 mol% nitrogen.

[0160] In some embodiments, after dosing, the nitrogen-doped hydrogen includes at least about 0.05 mol % or at least about 0.1 mol % or at least about 0.5 mol % or at least about 1 mol % or preferably about 2 mol % or more nitrogen.

[0161] In some embodiments, after dosing, the nitrogen-doped hydrogen comprises about 0.5 mol% to 10 mol% or about 1 mol% to about 5 mol% or about 2 mol% to about 4 mol% or preferably about 3 mol% nitrogen.

[0162] Alternatively, the amount of nitrogen to be added can be determined based on the desired apparent molecular weight, as this can be measured. In some embodiments, hydrogen is metered in an amount of nitrogen such that the resulting nitrogen-doped hydrogen has an apparent molecular weight (in g / mol) of about 2.05 to about 7, such as about 2.1 to about 5, or about 2.5 to about 4, or preferably about 2.5 to about 3.5.

[0163] In some embodiments, hydrogen is metered with an amount of nitrogen such that the apparent molecular weight of the nitrogen-blended hydrogen is greater than the apparent molecular weight of unblended nitrogen hydrogen (i.e., hydrogen obtained from the electrolysis of water or from a storage system) by an amount in the range of about 0.1 to about 3.0, e.g., about 0.5 to about 2.0, or preferably about 0.7 to about 1.5.

[0164] As previously mentioned, by dosing nitrogen with the hydrogen, the apparent molecular weight of the hydrogen fed to the compressor is increased. This enables the centrifugal compressor to generate sufficient centrifugal force to provide a specified pressure ratio (discharge pressure divided by inlet pressure). This, in turn, allows hydrogen to be compressed in a multi-stage compression system with fewer stages.

[0165] Device

[0166] According to a third aspect of the present invention, there is provided an apparatus for supplying hydrogen for consumption in at least one downstream process, the apparatus comprising:

[0167] a plurality of electrolyzers arranged in parallel for electrolyzing water to provide hydrogen;

[0168] a power generation system for generating electricity to supply the plurality of electrolytic cells, the power generation system being in conductive communication with the plurality of electrolytic cells;

[0169] a multi-stage compression system for compressing hydrogen to provide compressed hydrogen, the multi-stage compression system comprising a feed end, an outlet end, and at least one centrifugal compression stage, the feed end being in fluid flow communication with the plurality of electrolyzers;

[0170] a nitrogen source for supplying nitrogen, wherein the source is arranged to meter nitrogen to the hydrogen upstream of a centrifugal compression stage in a multi-stage compression system; and

[0171] At least one downstream processing unit is arranged to receive at least a portion of the compressed hydrogen metered with nitrogen, the downstream processing unit being in fluid flow communication with the outlet end of the multi-stage compression system.

[0172] electrolytic cell

[0173] Electrolysis of water is provided by a plurality of electrolysis units or "cells." Each unit or cell may be referred to as an "electrolyzer."

[0174] 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 electricity 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 range from 1 GW to 5 GW, for example, from about 1.5 GW to about 3 GW.

[0175] Electrolysers typically consist of a large number, eg hundreds, of individual cells grouped into "modules" which also contain process equipment such as pumps, coolers and / or separators etc., and groups of these modules are typically arranged in a single building.

[0176] Each module typically has a maximum capacity of at least 10 MW, such as 20 MW, and each building typically has a total capacity of at least 100 MW, such as 400 MW.

[0177] Any suitable type of electrolyser may be used with the present invention. In this regard, there are three general 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.

[0178] The alkaline electrolyzer converts hydroxide ions (OH - ) is transported from the cathode to the anode, where hydrogen is generated. Electrolyzers using liquid alkaline solutions of sodium hydroxide or potassium hydroxide as the electrolyte are commercially available. Commercial alkaline electrolyzers typically operate at temperatures ranging from about 100°C to about 150°C.

[0179] 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 migrate 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 typically operate at temperatures ranging from approximately 70°C to approximately 90°C.

[0180] Solid oxide electrolyzers use solid ceramic materials as electrolytes, which 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, generating electrons for the external circuit. Solid oxide electrolyzers must operate at sufficiently high temperatures for the solid oxide membrane to function properly, for example, between about 700°C and about 800°C.

[0181] Due to the lower operating temperatures, alkaline electrolyzers and / or PEM electrolyzers are generally preferred.

[0182] The plurality of electrolytic cells may be arranged in at least two parallel groups. In these embodiments, the apparatus comprises:

[0183] a first header to collect hydrogen from each electrolyzer in each group; and

[0184] a second header for collecting hydrogen from the first header and feeding the hydrogen to a feed end of the multi-stage compression system;

[0185] In some embodiments, the nitrogen source is arranged to feed nitrogen to at least one of the first headers, thereby dosing nitrogen with the hydrogen. Preferably, the nitrogen source is arranged to feed nitrogen to each of the first headers.

[0186] In some embodiments, wherein the apparatus further comprises a storage system for excess hydrogen, the apparatus comprises a conduit for feeding compressed hydrogen blended with nitrogen from the storage system to the second header after appropriate decompression.

[0187] Power generation systems for electrolyzers

[0188] The electricity used for electrolysis can be generated by any suitable energy source (including renewable or non-renewable energy sources). Preferably, the electricity can be generated by at least one renewable energy source (such as wind energy and / or solar energy).

[0189] 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."

[0190] Some embodiments will include multiple wind turbines and multiple photovoltaic cells.

[0191] The expression "in electrical communication" will be understood to mean that the power generation system will be connected to the electrolyser in a safe and efficient manner using appropriate wires and / or cables and any other relevant equipment.

[0192] Multi-stage compression system

[0193] In the present invention, the multi-stage compression system includes at least one centrifugal compression stage. As described above, the multi-stage compression system may include a plurality of stages, typically having a compression ratio in the range of about 1.5 to about 2.5 (e.g., about 2 to about 2.5). Intercoolers are typically provided between adjacent stages, and an aftercooler may be required after the final stage.

[0194] The stages of the multi-stage compression system are also arranged in one or more compression sections. Each section may include one or more compression stages and associated coolers.

[0195] In a particular embodiment, the multi-stage compression system has two sections, a first (low pressure or "LP") section in which the hydrogen is compressed from the feed pressure to the multi-stage compression system to a first high pressure; and a second (medium pressure or "MP") section in which the hydrogen is compressed from the first high pressure to a final high pressure desired for downstream processes.

[0196] The LP section may have one or more, for example two, compression stages, and the MP section may have two or more, for example three or four, compression stages. In some embodiments, both the LP section and the MP section may include centrifugal compression stages. In other embodiments, the LP section and / or the MP section may include a combination of centrifugal and reciprocating compressors. In some embodiments, the LP section includes at least one centrifugal compression stage, and the MP section includes at least one reciprocating compression stage. In some embodiments, the LP section includes at least one centrifugal compression stage, and the MP section includes centrifugal and / or reciprocating compression stages. It is contemplated that in some particularly preferred embodiments, all stages of the multi-stage compression system are centrifugal compression stages.

[0197] For example, for a process with a total electrolyzer capacity of 1 GW, the multi-stage compression system may have 2 to 4 compressors. It will be understood by those skilled in the art 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, 5 compressors may be required in the multi-stage compression system.

[0198] The compressors in the LP section may be oversized, for example by 10%, to accommodate the loss of a machine. Additionally or alternatively, a multi-stage compression system may include a spare compressor in the LP or MP section that will be switched in to replace another machine that has failed in the relevant section.

[0199] As will be explained in greater detail below, hydrogen will be metered with nitrogen upstream of at least one centrifugal compression stage in a multi-stage compression system. Thus, in the following discussion, references to "hydrogen" collected from the compressor may also refer to "nitrogen-blended hydrogen" for embodiments in which nitrogen has been added upstream of a particular centrifugal compression stage. In any case, it will be understood that the hydrogen after the final stage of compression will be metered with nitrogen at some point upstream.

[0200] As described above, a multi-stage compression system can include a single section. In these embodiments, the section typically includes a plurality of compressors arranged in parallel, each compressor including at least one centrifugal compression stage. The apparatus can further include a third header to collect compressed hydrogen from each compressor and feed the compressed hydrogen, containing nitrogen, to at least one downstream processing unit, or to a purification system upstream of at least one downstream processing unit.

[0201] In some embodiments using a storage system, the apparatus may further comprise a conduit for feeding compressed nitrogen-blended hydrogen from the storage system to the second header after appropriate decompression.

[0202] However, a multi-stage compression system may include:

[0203] a first section comprising a plurality of compressors arranged in parallel, each compressor comprising at least one stage; and

[0204] A second section is downstream of the first section, the second section including a plurality of compressors arranged in parallel, each compressor including at least two stages arranged in series.

[0205] In these embodiments, the apparatus may include:

[0206] a third header that collects compressed hydrogen from each compressor in the first section and feeds the compressed hydrogen to the compressors in the second section; and

[0207] The fourth header collects the compressed hydrogen from each compressor in the second section and feeds the compressed hydrogen blended with nitrogen to a downstream processing unit or to a purification system upstream of the downstream processing unit.

[0208] In some embodiments using a storage system, the apparatus may further comprise a conduit for feeding compressed nitrogen-blended hydrogen from the storage system to the third header after appropriate decompression.

[0209] The plurality of electrolytic cells may be arranged in at least two groups. In these embodiments, the multi-stage compression system may include:

[0210] a first section comprising a plurality of compressors arranged in parallel in at least two groups, each compressor comprising at least two stages arranged in series; and

[0211] A second section is downstream of the first section, the second section including a plurality of compressors arranged in parallel, each compressor including at least two stages arranged in series.

[0212] The apparatus may further comprise:

[0213] at least two first headers, each first header collecting hydrogen from each electrolyzer in a group and feeding the hydrogen to a feed end of a corresponding group of compressors in a first section of the multi-stage compression system;

[0214] a second header that collects compressed hydrogen from each set of compressors in the first section and feeds the compressed hydrogen to the compressors in the second section; and

[0215] The third header collects the compressed hydrogen from each compressor in the second section and feeds the compressed hydrogen blended with nitrogen to a downstream processing unit or to a purification system upstream of the downstream processing unit.

[0216] In some embodiments, the nitrogen source is arranged to feed nitrogen to at least one of the first headers, thereby metering nitrogen to the hydrogen. Preferably, the nitrogen source is arranged to feed nitrogen to each of the first headers. In such embodiments, the compressor train in the first stage and / or the compressor of the second stage comprises a centrifugal compressor.

[0217] In other embodiments, the nitrogen source is arranged to feed nitrogen to the second header, thereby metering nitrogen to the compressed hydrogen. In such embodiments, the compressor of the second section comprises a centrifugal compressor.

[0218] In some embodiments using a storage system, the apparatus may further include a conduit for feeding the compressed hydrogen blended with nitrogen from the storage system to at least one of the first headers after appropriate decompression. Additionally or alternatively, the apparatus of these embodiments may include a conduit for feeding the compressed hydrogen blended with nitrogen from the storage system to the second header after appropriate decompression.

[0219] Purification system

[0220] In embodiments where downstream processes cannot tolerate the water and oxygen levels inherent in compressed hydrogen produced by electrolysis of water, the apparatus will include a purification system to purify the compressed hydrogen.

[0221] The purification system will typically include a "deoxygenation" unit in which oxygen is removed by catalytic combustion of the hydrogen, producing water and oxygen-depleted compressed hydrogen. The purification system described in the context of the present invention does not substantially remove any nitrogen from the nitrogen-admixed hydrogen.

[0222] The oxygen-depleted gas may then be dried in a dryer, for example an adsorption unit, such as a temperature swing adsorption (TSA) unit, to produce dry compressed hydrogen for downstream processes.

[0223] Downstream processing units

[0224] The downstream processing unit may be any unit that utilizes hydrogen as a feed.

[0225] Examples of suitable downstream processing units include an oil refinery, a steel manufacturing plant or an ammonia synthesis plant. Preferably, the downstream processing unit is or comprises an ammonia synthesis plant.

[0226] Nitrogen source

[0227] The apparatus includes a nitrogen source. It will be appreciated that the nitrogen can be fed from any suitable nitrogen source. For example, the nitrogen source can be a cryogenic air separation unit (ASU) that produces nitrogen by cryogenic distillation at a pressure at which nitrogen is taken from the ASU (referred to as the discharge pressure, e.g., about 10 bar).

[0228] In some embodiments, nitrogen is drawn from the ASU at a pressure lower than the discharge pressure and then fed to the hydrogen. For example, nitrogen can be drawn from the ASU at a pressure of about 4 bar or about 1.1 bar. This results in the ASU consuming less power overall because less nitrogen is compressed to discharge pressure.

[0229] A nitrogen source will be connected to a feed line that delivers nitrogen to the hydrogen upstream of at least one stage of the multi-stage compression system. The feed line may include a valve for reducing the pressure of the nitrogen accordingly.

[0230] For example, where nitrogen is fed to hydrogen obtained from electrolysis, the valve reduces the pressure of the nitrogen to a pressure just above atmospheric pressure (e.g., about 1.1 bar). In other embodiments, where nitrogen is fed to hydrogen between stages of a multi-stage compression system, the apparatus may include a valve for reducing the pressure to the inlet pressure of the feed for the interstage. Alternatively, the apparatus may include a compressor that increases the pressure of the nitrogen so that it has substantially the same pressure as the inlet pressure of the feed for the interstage.

[0231] In embodiments where nitrogen is consumed by downstream processes, such as when the downstream process comprises ammonia synthesis, the nitrogen source may additionally supply the additional nitrogen required by the downstream process. In such embodiments, the additional nitrogen will typically be compressed to a suitable pressure in a compressor in preparation for the downstream process. Alternatively, the additional nitrogen may first be added to the feed of the downstream process, which is then subsequently compressed in a compressor to a pressure suitable for the downstream process.

[0232] For example, the nitrogen will be at a pressure up to the maximum pressure to which the hydrogen is compressed in a multi-stage compression system, such as up to a pressure of about the feed pressure to the downstream processes (of which there is only one) or about the maximum of the feed pressure to one of the downstream processes (if there is more than one).

[0233] In other embodiments, the nitrogen used for dosing of hydrogen is supplied from a separate nitrogen source.

[0234] Storage System

[0235] In some embodiments, the apparatus includes a hydrogen storage system for storing compressed nitrogen-blended hydrogen. In such embodiments, the storage system is in fluid flow communication with an outlet of the multi-stage compression system and at least one compression stage of the multi-stage compression system.

[0236] Storage systems typically include numerous pressure vessels and / or pipe segments connected to a common inlet / outlet header.

[0237] The pressure vessel may be a sphere, for example up to about 25 m in diameter, or a "bullet", ie a horizontal vessel with a large L / D ratio (typically up to about 12:1) and a diameter of up to about 12 m.

[0238] Salt domes can also be used if the site geology permits.

[0239] Preferably, the nitrogen source is arranged to feed nitrogen to the hydrogen before or upstream of the point at which the storage system is in fluid flow communication with at least one centrifugal compression stage of the multi-stage compression system. This enables the concentration of nitrogen in the nitrogen-blended hydrogen to remain constant because the depressurized hydrogen released from the storage is not metered with a subsequent amount of nitrogen.

[0240] control system

[0241] In some embodiments, the apparatus includes a control system for monitoring and controlling the flow and / or pressure of nitrogen from the nitrogen source to the hydrogen, wherein the flow rate is determined based on the rate at which hydrogen is generated by the electrolyzer (or the amount of hydrogen generated). It will be appreciated that the features described above with respect to the methods of the present invention can be implemented using such a control system.

[0242] In some embodiments, the control system may be configured to monitor the amount of hydrogen generated by electrolysis by measurement. For example, such measurement may be made by direct flow measurement, or alternatively inferred by measurement of the electrolyzer current.

[0243] In some embodiments, the control system may implement a feedback loop that takes into account information about the nitrogen concentration in the hydrogen gas blended with nitrogen. Such information may be determined by measuring the gas composition, for example by using a mass spectrometer or a density meter.

[0244] By determining the amount of nitrogen to be added based on the amount of hydrogen, this enables careful control of the concentration of nitrogen. For example, it advantageously allows the nitrogen concentration to remain constant despite variations in the amount of hydrogen.

[0245] In embodiments in which a storage system is used, the apparatus may include a control system that controls not only the pressure and flow of compressed hydrogen from the multi-stage compression system to the storage system, for example during periods when hydrogen production exceeds demand, but also controls the pressure and flow of compressed hydrogen from the storage system to the multi-stage compression system, for example during periods when hydrogen demand exceeds production.

[0246] In some embodiments, the control system will simply seek to maintain the pressure of the hydrogen in the downstream header leading to the downstream process.Thus, in order to continuously provide a fixed amount of hydrogen to the downstream process, a pressure controller is maintained on the discharge header feeding the downstream process.

[0247] If the pressure in the discharge header exceeds the required feed pressure (for example because more hydrogen is available than is consumed by downstream processes), the pressure will be relieved by opening a valve in the feed line to storage.

[0248] Once the pressure in the discharge header drops to the desired feed pressure, the valve in the feed line to the reservoir is closed.

[0249] If the pressure in the discharge header drops below the required feed pressure (e.g. because less hydrogen is available than consumed by downstream processes), the pressure will be increased by opening a valve in the first return line from storage to the first stage in a multi-stage compression system.

[0250] The valve in the first return line will remain open until the pressure in the discharge header exceeds the desired feed pressure, indicating that the hydrogen production level has returned to the desired 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 through the first return line.

[0251] In the latter case, not only will the valve in the first return line be closed, but 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 will be opened to continue feeding hydrogen from the storage back to the downstream process.

[0252] This type of control system may be referred to as a "split range" control system.

[0253] water source

[0254] The present invention may be used with any suitable water source. However, in embodiments where seawater is used to produce water for electrolysis, the apparatus will further comprise at least one unit (or device) for desalination and demineralisation of the seawater.

[0255] aspect

[0256] #1. A method for supplying hydrogen for consumption in at least one downstream process, the method comprising:

[0257] Electrolysis of water to provide hydrogen;

[0258] compressing the hydrogen in a multi-stage compression system to provide compressed hydrogen; and

[0259] feeding at least a portion of the compressed hydrogen to a downstream process,

[0260] wherein the multi-stage compression system includes at least one centrifugal compression stage;

[0261] wherein the hydrogen is metered with nitrogen upstream of the centrifugal compression stage; and

[0262] Where nitrogen is present in compressed hydrogen when it is fed to downstream processes.

[0263] #2. The method according to #1, wherein after metered supply, the hydrogen gas includes nitrogen in an amount ranging from about 0.5 mol% to about 10 mol%.

[0264] #3. The method according to #1, wherein after quantitative supply, the resulting nitrogen-blended hydrogen has an apparent molecular weight in the range of about 2.05 to about 7.

[0265] #4. A method according to any one of #1 to #3, wherein hydrogen is metered to nitrogen upstream of an initial stage of a multi-stage compression system.

[0266] #5. A method according to any one of #1 to #3, wherein hydrogen is metered to nitrogen downstream of an initial stage of a multi-stage compression system and upstream of an intermediate stage of the multi-stage compression system.

[0267] #6. A method according to any one of #1 to #5, wherein the centrifugal compression stage has a feed end, and the hydrogen is metered into the nitrogen at the feed end of the centrifugal compression stage.

[0268] #7. A method according to any one of #1 to #6, wherein the downstream process consumes nitrogen.

[0269] #8. A method according to #7, wherein additional nitrogen is added to the compressed hydrogen upstream of the downstream process as needed.

[0270] #9. A method according to any one of #1 to #8, wherein the multi-stage compression system includes a first section and at least one additional section downstream of the first section.

[0271] #10. The method of #9, wherein hydrogen is metered into the nitrogen upstream of the initial stage of the first section of the multi-stage compression system.

[0272] #11. A method according to #9, wherein hydrogen is metered to nitrogen downstream of a first section of a multi-stage compression system and upstream of an initial stage of at least one further section.

[0273] #12. A method according to any one of #1 to #10, wherein during a period when more hydrogen is produced by electrolysis than is required for a downstream process, the method comprises feeding the excess compressed hydrogen to a storage, optionally after additional compression;

[0274] wherein during periods when downstream processes require more hydrogen than is produced by electrolysis, the method comprises withdrawing compressed hydrogen from storage and, after appropriate decompression, feeding the decompressed hydrogen to a stage of the multi-stage compression system, and

[0275] It stores compressed hydrogen containing nitrogen.

[0276] #13. A method according to #12, wherein during periods when more hydrogen is required than is produced by electrolysis, hydrogen is metered with nitrogen upstream of the stages of a multi-stage compression system to which reduced pressure hydrogen is fed.

[0277] #14. The method according to any one of #1 to #13, wherein the amount of hydrogen provided by electrolysis of water is variable, and the hydrogen is metered to the nitrogen in an amount determined based on the amount of hydrogen provided by electrolysis.

[0278] #15. A method for compressing hydrogen using a centrifugal compressor, the method comprising quantitatively supplying nitrogen to the hydrogen upstream of the centrifugal compressor to provide nitrogen-blended hydrogen, and compressing the nitrogen-blended hydrogen in the centrifugal compressor.

[0279] #16. An apparatus for supplying hydrogen for consumption in at least one downstream process, the apparatus comprising:

[0280] a plurality of electrolyzers arranged in parallel for electrolyzing water to provide hydrogen;

[0281] a power generation system for generating electricity to supply the plurality of electrolytic cells, the power generation system being in conductive communication with the plurality of electrolytic cells;

[0282] a multi-stage compression system for compressing hydrogen to provide compressed hydrogen, the multi-stage compression system comprising a feed end, an outlet end, and at least one centrifugal compression stage, the feed end being in fluid flow communication with the plurality of electrolyzers via a feed header;

[0283] a nitrogen source for supplying nitrogen, wherein the source is arranged to meter nitrogen to the hydrogen upstream of a centrifugal compression stage in a multi-stage compression system; and

[0284] At least one downstream processing unit is arranged to receive at least a portion of the compressed hydrogen metered with nitrogen, the downstream processing unit being in fluid flow communication with the outlet end of the multi-stage compression system.

[0285] #17. An apparatus according to #16, wherein the nitrogen source is arranged to feed nitrogen to a feed header to meter nitrogen to the hydrogen, and the multi-stage compression system contains a single section, which includes a plurality of compressors arranged in parallel, each compressor including at least one centrifugal compression stage; the apparatus further includes a header for collecting compressed hydrogen from each compressor and feeding the compressed hydrogen containing nitrogen to a downstream processing unit or to a purification system upstream of the downstream processing unit.

[0286] #18. The apparatus according to #16 or #17, wherein the multi-stage compression system comprises:

[0287] a first section comprising a plurality of compressors arranged in parallel, each compressor comprising at least one centrifugal compression stage; and

[0288] a second section downstream of the first section, the second section comprising a plurality of compressors arranged in parallel, each compressor comprising at least two centrifugal compression stages arranged in series;

[0289] The device includes:

[0290] a first header for collecting compressed hydrogen from each compressor in the first section and feeding the compressed hydrogen to the compressors in the second section; and

[0291] a second header for collecting compressed hydrogen from each compressor in the second section and feeding the compressed hydrogen containing nitrogen to a downstream processing unit, or to a purification system upstream of the downstream processing unit,

[0292] The nitrogen source is arranged to feed nitrogen to the feed header to meter nitrogen into the hydrogen.

[0293] #19. The apparatus according to any one of #16 to #18, wherein the plurality of electrolytic cells are arranged in at least two groups, and the multi-stage compression system comprises:

[0294] a first section comprising a plurality of compressors arranged in parallel in at least two groups, each compressor comprising at least two centrifugal compression stages arranged in series; and

[0295] a second section downstream of the first section, the second section comprising a plurality of compressors arranged in parallel, each compressor comprising at least two centrifugal compression stages arranged in series;

[0296] The device includes:

[0297] at least two first headers, each first header collecting hydrogen from each electrolyzer in a group and feeding the hydrogen to the feed end of a corresponding compressor group in the first section of the multi-stage compression system,

[0298] wherein the nitrogen source is arranged to feed nitrogen to each of the first headers to meter nitrogen to the hydrogen;

[0299] a second header for collecting compressed hydrogen from each set of compressors in the first section and feeding the compressed hydrogen to the compressors in the second section; and

[0300] The third header is used to collect the compressed hydrogen from each compressor in the second section and feed the compressed hydrogen to a downstream processing unit or to a purification system upstream of the downstream processing unit.

[0301] #20. An apparatus according to any one of #16 to #19, comprising a control system for controlling the flow of nitrogen from the nitrogen source to the hydrogen, the flow being determined based on the level of hydrogen produced by the electrolyzer.

[0302] #21. The apparatus according to any one of #16 to #20, comprising a storage system for storing compressed hydrogen containing nitrogen, the storage system being in fluid flow communication with an outlet end of the multi-stage compression system and at least one compression stage of the multi-stage compression system, and

[0303] wherein the nitrogen source is arranged to meter nitrogen to the hydrogen upstream of a point in which the storage system is in fluid flow communication with at least one centrifugal compression stage of the multi-stage compression system.

[0304] In some of the following figures and examples, a hydrogen storage system and, in some cases, a purification unit are shown. However, it should be understood that the present invention can be practiced without the use of a hydrogen storage system or purification unit, which are shown here for completeness purposes only.

[0305] As described above, a multi-stage compression system includes a plurality of stages, typically having a compression ratio in the range of about 1.5 to about 2.5, such as about 2 to about 2.5. Intercoolers are typically provided between adjacent stages, and an aftercooler may be required after the last stage. Figures 1 to 3 In the drawings, for simplicity, multi-stage compression systems are depicted as having one or two compression stages, and an intercooler and / or aftercooler.

[0306] According to the first example showing the present invention Figure 1 , hydrogen is produced at approximately atmospheric pressure by electrolyzing water in a plurality of electrolyzer cells, generally designated by reference numeral 2. The electricity required to power the electrolyzers can be generated, at least in part, by renewable energy sources such as wind (generally designated by cell 4) and / or solar (generally designated by cell 6), or can be generated by diesel, gasoline, or hydrogen-powered generators (generally designated by cell 5) or obtained from a power grid (not shown), or can be generated by a combination of these sources. A stream 7 of hydrogen is removed from the electrolyzer 2 at a pressure just above atmospheric pressure (e.g., approximately 1.1 bar).

[0307] A stream 200 of nitrogen is produced by cryogenic distillation in an air separation unit (ASU; not shown). Stream 200 is at the discharge pressure of the ASU, e.g., about 10 bar, and is reduced in pressure across valve 202 to a pressure just above atmospheric pressure (e.g., about 1.1 bar) to provide a stream 204 of nitrogen. Stream 204 of nitrogen is fed to stream 7 of hydrogen to provide a hydrogen stream 8, which is metered with nitrogen to produce a hydrogen stream 8 containing about 3 mol% nitrogen.

[0308] The nitrogen-blended hydrogen feed 8 is then fed to the initial stage 12 of a multi-stage compression system 10 (schematically shown in the figure as having a first centrifugal compression stage 12, an intercooler 14, a second centrifugal compression stage 16, and an aftercooler 18) to produce a compressed nitrogen-blended hydrogen gas stream 24 at a pressure of 20 to 40 bar. To achieve such high pressures, the multi-stage compression system typically has at least two compression sections.

[0309] As mentioned above, the hydrogen from the electrolyzer is typically wet (saturated at 40° C.) and contains some oxygen (typically 500 ppm to 1000 ppm). Therefore, the hydrogen is purified in a purification unit (not shown) located at an intermediate point in the multi-stage compression system, typically at a pressure in the range of about 20 bar to about 40 bar, for example, about 30 bar. In this regard, oxygen is removed by catalytic combustion of some of the hydrogen to form water in a "deoxygenation" unit (not shown), and the oxygen-depleted hydrogen (containing no more than 1 ppm O2) is dried by adsorption in a dryer unit (not shown). The purified compressed hydrogen stream 17 typically contains no more than 5 ppm total oxygen, including 1 ppm water.

[0310] A stream 26 of nitrogen is produced by cryogenic distillation in an air separation unit (ASU; not shown) and is compressed in a compressor 28 to produce a compressed nitrogen stream 30 having a purity of about 99.99% at a pressure of 20 to 40 bar. Stream 30 is then combined with a compressed nitrogen-blended hydrogen stream 24 to form a combined stream 32 of ammonia synthesis gas containing 25 mol% nitrogen and 75 mol% hydrogen, which is fed to an ammonia synthesis plant 34.

[0311] Optionally, during periods when more hydrogen is produced by electrolysis than is required by the ammonia plant 34, a stream 36 of excess compressed nitrogen-blended hydrogen may be removed and fed to a compressor system 38 where the hydrogen is compressed, for example, to 200 bar before being sent as stream 40 (via control valve 42) to storage 44.

[0312] Optionally, during periods when the ammonia plant 34 requires more hydrogen than is produced by electrolysis, a compressed nitrogen-blended hydrogen stream 46 is removed from the storage 44 , depressurized through a valve 48 to produce a depressurized hydrogen stream 50 at a pressure between 20 and 40 bar, which is fed to stream 24 to supplement the hydrogen feed to the ammonia plant 34 .

[0313] Figure 2 A second embodiment of the present invention is depicted. The same reference numerals are used to denote Figure 2 The characteristics of the flow chart in Figure 1 The following is the same flowchart as Figure 2 The first embodiment of Figure 1Discussion of the distinguishing features of the illustrated processes.

[0314] about Figure 2 , multi-stage compression system 10 has a single section containing all of the compression stages (generally represented as centrifugal compression stage 12 and centrifugal compression stage 16) and associated intercoolers and aftercoolers (generally represented as coolers 14 and 18 that produce condensate streams 15 and 19, respectively), and compresses the hydrogen in stream 8 from about atmospheric pressure to about 30 bar.

[0315] exist Figure 2 Additional details of the purification unit 22 are provided in . In this regard, the compressed nitrogen-blended hydrogen stream 20 is fed to a "deoxygenation" unit 52 where residual oxygen is removed by catalytic conversion to water to produce an oxygen-depleted nitrogen-blended hydrogen stream 54, which is cooled by indirect heat exchange in a cooler 56 to produce a condensate stream 57, which is then dried by adsorption in a unit 58 to produce the compressed nitrogen-blended hydrogen stream 24.

[0316] The adsorption beds in unit 58 are regenerated using a compressed nitrogen-admixed hydrogen stream 60 taken from stream 24. Stream 60 is depressurized to about 14 bar by valve 62 and depressurization stream 64 for regeneration of dryer 58. The spent regeneration gas is returned as recycle stream 66 to the hydrogen stream in the intermediate stage of multi-stage compression system 10 for recompression. As a result, water is removed as condensate stream 19.

[0317] The remaining part 68 of stream 24 is combined with nitrogen stream 30 from an ASU (not shown) (possibly after decompression if necessary) to form synthesis gas stream 32, which is fed to an ammonia plant 34 where it is compressed (not shown) to the pressure required for ammonia synthesis.

[0318] If desired, the compressed nitrogen-blended hydrogen stream 36 can be depressurized through valve 42 and fed to storage unit 44 where it is stored at a pressure of up to 26 bar. When desired, the nitrogen-blended hydrogen stream 46 is removed and depressurized across valve 96 before being returned as stream 98 to feed the initial stage 12 of the multi-stage compression system 10.

[0319] Nitrogen feed 204 is fed to stream 7 to provide nitrogen-blended hydrogen stream 8. Thus, reduced pressure hydrogen feed 98 is fed to nitrogen-blended hydrogen stream 8 before it is fed to initial stage 12 of multi-stage compression system 10.

[0320] Figure 3 A third embodiment of the present invention is depicted. The same reference numerals are used to denote Figure 3 The characteristics of the flow chart in Figure 1 and 2The following is the same as the flowchart in Figure 3 The second embodiment of Figure 1 and 2 Discussion of the features that distinguish the processes shown.

[0321] The multi-stage compression system 10 has an LP section 70 including a centrifugal compressor 12 , an intercooler (not shown), and an aftercooler 14 , and an MP section 72 including a centrifugal compressor 16 , an intercooler (not shown), and an aftercooler 18 .

[0322] Hydrogen stream 7 is metered with nitrogen from stream 204 to provide nitrogen-blended hydrogen stream 8. Stream 8 is then fed to LP section 70 where it is compressed from about 1.1 bar to about 5 bar, and the effluent from LP section 70 is fed to the MP section where it is further compressed to a pressure of about 1 bar above the pressure at the downstream point where stream 68 is mixed with nitrogen stream 30.

[0323] Therefore, when the pressure at the point where the nitrogen-blended hydrogen and nitrogen mix is about 10 bar, the MP section 72 compresses the nitrogen-blended hydrogen to about 11 bar. Alternatively, when the pressure at the point where the nitrogen-blended hydrogen and nitrogen mix is about 26 bar, the MP section 72 compresses the nitrogen-blended hydrogen to about 27 bar.

[0324] The purified nitrogen-laden hydrogen stream 60 used to regenerate the dryer 58 can be fed to a blower 74 and a heater 76 before being fed to the dryer 58 as stream 78. In addition, the spent regeneration gas stream 66 can be recycled to the purification unit 22 at a point between the "deoxygenation" unit 52 and the dryer 58. The water removed in the dryer 58 is thus discharged from the system in the form of a condensate stream 57.

[0325] As described above, the compressed nitrogen-blended hydrogen stream 68 can be mixed with the nitrogen stream 30 from the ASU (not shown) at the discharge pressure of the nitrogen taken from the ASU (e.g., about 10 bar). In these embodiments, the combined gases are compressed in the compressor system 80 to produce the synthesis gas stream 32 at a pressure of about 26 bar, which is then fed to the ammonia plant 34 where it is further compressed in the compression system 82 before being fed to the catalytic reactor (not shown).

[0326] Alternatively, compressed nitrogen-blended hydrogen stream 68 can be mixed with nitrogen stream 30 from an ASU (not shown) at the feed pressure of the ammonia plant (i.e., about 26 bar). In these embodiments, nitrogen stream 26 from the ASU is compressed in compression system 28 to produce compressed nitrogen at about 26 bar, which is then mixed with compressed nitrogen-blended hydrogen to produce synthesis gas stream 32. Stream 32 is then fed to an ammonia plant 34 where it is further compressed in compression system 82 before being fed to a catalytic reactor (not shown).

[0327] The dry nitrogen-blended hydrogen can be stored in a storage system 44 up to the maximum feed pressure of the ammonia plant, i.e., about 26 bar. In these embodiments, compressed nitrogen-blended hydrogen stream 36 is taken from stream 24, appropriately pressure-adjusted across valve 42, and fed to the storage system.

[0328] Alternatively, the nitrogen-blended hydrogen may be stored at higher pressures, for example up to a maximum pressure of 50 bar or even 100 bar or higher. In such embodiments, stream 84 of nitrogen-blended hydrogen is removed from stream 24, compressed in storage compression system 86 to form stream 88, which is pressure-adjusted across valve 90 as needed before being fed to storage system 44.

[0329] During periods when demand for hydrogen exceeds production, nitrogen-blended hydrogen from storage system 44 may be fed, after appropriate decompression (e.g., across valve 48), in the form of stream 50 directly to the compressed nitrogen-blended hydrogen feed in stream 24 of ammonia plant 34. In some embodiments, nitrogen-blended hydrogen withdrawn from storage may be fed, after appropriate decompression (e.g., across valve 92), in the form of stream 94 to a point between LP section 70 and MP section 72 of multi-stage compression system 10. In other embodiments, nitrogen-blended hydrogen withdrawn from storage may be fed, after appropriate decompression (e.g., across valve 96), in the form of stream 98 to the feed of the initial centrifugal compression stage 12 of LP section 70.

[0330] In some embodiments, hydrogen blended with nitrogen withdrawn from storage is fed to ammonia plant 34 in stream 50 until the pressure in the storage system drops to approximately the feed pressure to plant 34, at which point valve 48 will be closed and valve 92 will be opened. The withdrawn gas can then be fed to a point between sections 70, 72 of multi-stage compression system 10 in stream 94 until the pressure in the storage system drops to approximately the feed pressure to MP section 72. At this point, valve 92 is closed and valve 96 is opened, thereby providing the withdrawn gas in stream 98 to the feed to the initial centrifugal stage of multi-stage compression system 10.

[0331] An advantage of this sequential method of feeding hydrogen from storage to the downstream process is that it represents a more energy efficient method of returning hydrogen to the process during periods where demand exceeds production than feeding hydrogen from storage via line 98 alone.

[0332] Figure 4 Shown Figure 2 An arrangement of electrolyzers and multi-stage compression systems is depicted. The same reference numerals are used to denote Figure 4 The following is a discussion of the distinguishing features of this arrangement.

[0333] In this regard, a plurality (two) of electrolyzer units 100 are arranged in parallel in at least two parallel groups (group 2a and group 2b). The hydrogen produced in each unit 100 in group 2a is collected by a first header 102a, and the hydrogen produced in each unit 100 in group 2b is collected by another first header 102b.

[0334] Nitrogen stream 200 is produced by cryogenic distillation in an air separation unit (ASU; not shown). Stream 200 is then split into two streams 200a and 200b.

[0335] Stream 200a is reduced in pressure across valve 202a to just above atmospheric pressure (eg, about 1.1 bar) to provide nitrogen stream 204a. Nitrogen stream 204a is fed to first header 102a to provide a hydrogen stream within header 102a that has been metered with nitrogen.

[0336] Similarly, stream 200b is reduced in pressure across valve 202b to a pressure just above atmospheric pressure (e.g., about 1.1 bar) to provide nitrogen stream 204b. Nitrogen stream 204b is fed to first header 102b to provide a hydrogen stream within header 102b that has been metered with nitrogen.

[0337] The hydrogen mixed with nitrogen is then collected from the first headers 102a, 102b via the second header 104.

[0338] The multi-stage compression system 10 has a plurality of centrifugal compressors 106 arranged in parallel. Hydrogen mixed with nitrogen is distributed to the feed of each compressor through the second header 104.

[0339] The compressed nitrogen-blended hydrogen gas is collected from each compressor 106 via a third header 108, which then feeds the compressed nitrogen-blended hydrogen gas to a purification unit (not shown).

[0340] As shown, the plurality (2) of electrolyzer units 100 may include one or more additional parallel groups 2c, etc. (not shown) of electrolyzer units 100, each additional group producing additional nitrogen-blended hydrogen by metering a nitrogen gas stream 204c, etc. (not shown) for collection by additional first headers 102c, etc. (not shown), which in turn will be collected by an extension of the second header 104 (not shown).

[0341] In such an embodiment, the multi-stage compression system 10 would include additional compressors (not shown) arranged in parallel, and the nitrogen-blended hydrogen would be distributed to the feeds of the additional compressors via an extension of the second header 104. Additionally, compressed nitrogen-blended hydrogen would be collected from the additional compressors via an extension of the third header 108 (not shown).

[0342] During periods when demand for hydrogen exceeds production, hydrogen blended with nitrogen from storage 44 may be fed, after appropriate pressure reduction (valve 96), in the form of stream 98 to a second header 104, which distributes the gas feed to compressor 106. Hydrogen blended with nitrogen from storage 44 may alternatively or subsequently be fed, after appropriate pressure reduction (valve 48), in the form of stream 50 to a third header 108.

[0343] Figure 5 Shown Figure 3 An arrangement of electrolyzers and multi-stage compression systems is depicted. The same reference numerals are used to denote Figure 5 The following is a discussion of the distinguishing features of this arrangement.

[0344] The multi-stage compression system 10 has an LP section 70 including a plurality of centrifugal compressors 106 arranged in parallel. A third header 112 collects compressed hydrogen blended with nitrogen from the compressors 106 in the LP section 70.

[0345] The multi-stage compression system 10 also has an MP section 72 including a plurality of centrifugal compressors 114 arranged in parallel, and the compressed nitrogen-blended hydrogen from the LP section 70 is distributed to the compressors 114 through a third header 112. A fourth header 116 collects the compressed nitrogen-blended hydrogen from the compressors 114 in the MP section 72 and then feeds the compressed nitrogen-blended hydrogen to a purification unit (not shown).

[0346] As shown, the plurality (2) of electrolyser units 100 may include one or more additional parallel groups 2c, etc. (not shown) of electrolyser units 100, each additional group producing additional nitrogen-blended hydrogen that has been metered with nitrogen from nitrogen stream 204c, etc. (not shown) for collection by additional first headers 102c, etc. (not shown), which in turn will be collected by an extension of the second header 104 (not shown).

[0347] In such an embodiment, the LP section 70 of the multi-stage compression system 10 would include additional compressors (not shown) arranged in parallel, and the nitrogen-blended hydrogen would be distributed to the feeds of the additional compressors via an extension of the second header 104. Additionally, the compressed nitrogen-blended hydrogen would be collected from the additional compressors via an extension of the third header 112 (not shown).

[0348] The MP section 72 of the multi-stage compression system 10 will also contain additional compressors (not shown) arranged in parallel.

[0349] During periods when demand for hydrogen exceeds production, hydrogen blended with nitrogen from storage 44 may be fed, after appropriate pressure reduction (valve 92), in the form of stream 94 to third header 112 for distribution to compressor 114. Alternatively, or subsequently, hydrogen blended with nitrogen from storage 44 may be fed, after appropriate pressure reduction (valve 96), in the form of stream 98 to second header 104 for distribution to compressor 106.

[0350] It is also possible that hydrogen admixed with nitrogen from the storage 44 can be fed to the fourth header 116 in the form of a stream 50 after appropriate pressure reduction (valve 48 ).

[0351] Figure 6 Shown Figure 3 Another arrangement of electrolyzers and multi-stage compression systems is depicted. The same reference numerals are used to denote Figure 6 The following is a discussion of the distinguishing features of this arrangement.

[0352] In this arrangement, the first section of the multi-stage compression system is divided into at least two parallel sub-sections 70a and 70b; the first sub-section 70a contains a first plurality of centrifugal compressors 106a arranged in parallel, and the second sub-section 70b contains a second plurality of centrifugal compressors 106b arranged in parallel.

[0353] The hydrogen gas produced in each unit 100 within the first group 2a is collected by a first header 102a, and the hydrogen gas produced in each unit 100 within the second group 2b is collected by another first header 102b.

[0354] Nitrogen stream 200 is produced by cryogenic distillation in an air separation unit (ASU; not shown) at the pressure at which the nitrogen is taken from the ASU (eg, about 10 bar). Stream 200 is then split into two streams 200a and 200b.

[0355] Stream 200a is reduced in pressure to just above atmospheric pressure (eg, about 1.1 bar) across valve 202a to provide nitrogen stream 204a. Nitrogen stream 204a is fed to first header 102a to provide a nitrogen-blended hydrogen stream within header 102a that has been metered with nitrogen.

[0356] Similarly, stream 200b is reduced in pressure across valve 202b to a pressure just above atmospheric pressure (e.g., about 1.1 bar) to provide nitrogen stream 204b. Nitrogen stream 204b is fed to first header 102b to provide a nitrogen-blended hydrogen stream within header 102b that has been metered with nitrogen.

[0357] The hydrogen gas blended with nitrogen is collected in the first header 102a, which also distributes the gas to the compressor 106a in the first subsection 70a of the multi-stage compression system 10. Similarly, the hydrogen gas blended with nitrogen is collected in the first header 102b, which also distributes the gas to the compressor 106b in the second subsection 70b of the multi-stage compression system 10.

[0358] The compressed hydrogen blended with nitrogen produced by the compressor 106a in the first subsection 70a is collected by the second header 112a, and the compressed hydrogen blended with nitrogen produced by the compressor 106b in the second subsection 70b is collected by the second header 112b.

[0359] The third header 118 collects the compressed nitrogen-blended hydrogen from the second headers 112 a and 112 b and feeds the gas to the centrifugal compressor 114 in the second section 72 of the multi-stage compression system 10 .

[0360] As shown, the plurality (2) of electrolyzer units 100 may include one or more additional parallel groups 2c, etc. (not shown) of electrolyzer units 100, each additional group producing additional nitrogen-blended hydrogen that is metered with nitrogen via a nitrogen feed 204c, etc. (not shown) to provide nitrogen-blended hydrogen for collection by another first header 102c, etc. (not shown).

[0361] In such embodiments, the LP section 70 of the multi-stage compression system 10 would include additional compressors (not shown) arranged in parallel in additional parallel subsections 70 c, etc., and the nitrogen-blended hydrogen would be distributed to the feeds of the additional compressors via additional first headers 102 c, etc. Furthermore, the compressed nitrogen-blended hydrogen would be collected from the additional compressors via an extension (not shown) of the third header 118 .

[0362] The MP section 72 of the multi-stage compression system 10 will also contain additional compressors (not shown) arranged in parallel.

[0363] During periods when demand for hydrogen exceeds production, nitrogen-blended hydrogen from storage 44 can be fed in the form of stream 94 to a third header 118 after appropriate pressure reduction (valve 92) for distribution to compressor 114 in the second section 72 of the multi-stage compression system 10.

[0364] Alternatively or subsequently, the hydrogen blended with nitrogen from the storage 44 may be fed, after appropriate pressure reduction (valve 96), in the form of stream 98 to the one or more first headers 102a, 102b for distribution to the compressors 106a, 106b in the second subsection 70b of the multi-stage compression system 10. Stream 98 is fed to the one or more first headers 102a, 102b downstream of the point at which the one or more nitrogen streams 204a, 204b are fed to the one or more first headers 102a, 102b.

[0365] To keep it simple, Figure 6 Only the first header 102b of the feed is shown. However, it should be understood that stream 98 can be fed into the header 102a.

[0366] The hydrogen blended with nitrogen from the storage 44 can be fed to the fourth header 116 in the form of stream 50 after appropriate pressure reduction (valve 48 ).

[0367] While the invention has been described with reference to the preferred embodiments depicted in the drawings, it will be understood that various modifications are possible within the spirit and scope of the invention as defined in the following claims.

[0368] In this specification, unless expressly stated otherwise, the word "or" is used in the sense of an operator that returns a true value when one or both of the conditions are met, rather than the operator "exclusive or" which requires that only one of the conditions be met. The word "comprising" is used in the sense of "including", rather than meaning "consisting of".

[0369] All of the above prior teachings are incorporated herein by reference. Acknowledgement herein of any previously published 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 method for supplying hydrogen for consumption in at least one downstream process, the method comprising: Electrolysis of water to provide hydrogen; compressing the hydrogen in a multi-stage compression system to provide compressed hydrogen; and feeding at least a portion of the compressed hydrogen to a downstream process, wherein the multi-stage compression system includes at least one centrifugal compression stage; wherein said hydrogen is metered with nitrogen upstream of said centrifugal compression stage; wherein after the metered supply, the resulting nitrogen-admixed hydrogen has an apparent molecular weight in the range of 2.05 to 7; and wherein the nitrogen is present in the compressed hydrogen when fed to the downstream process. 2 . The method according to claim 1 , wherein after metering, the hydrogen gas includes the nitrogen gas in an amount ranging from 0.5 mol % to 10 mol %.

3. The method of claim 1 , wherein the hydrogen is metered with the nitrogen upstream of an initial stage of the multi-stage compression system.

4. The method of claim 1 , wherein the hydrogen is metered with the nitrogen downstream of an initial stage of the multi-stage compression system and upstream of an intermediate stage of the multi-stage compression system.

5. The method of claim 1, wherein the centrifugal compression stage has a feed end, and the hydrogen is metered with the nitrogen at the feed end of the centrifugal compression stage. The method of claim 1 , wherein the downstream process consumes nitrogen.

7. The method of claim 1 wherein additional nitrogen is added as needed to the compressed hydrogen upstream of the downstream process.

8. The method of claim 1, wherein the multi-stage compression system comprises a first section and at least one additional section downstream of the first section.

9. The method of claim 8, wherein the hydrogen is metered with the nitrogen upstream of an initial stage of the first section of the multi-stage compression system.

10. The method of claim 8, wherein the hydrogen is metered with the nitrogen downstream of the first section of the multi-stage compression system and upstream of an initial stage of the at least one further section.

11. The method of claim 1 , wherein during periods when more hydrogen is produced by the electrolysis than is required for downstream processes, the method comprises feeding excess compressed hydrogen to storage, optionally after additional compression; wherein during periods when the downstream process requires more hydrogen than is produced by the electrolysis, the method comprises withdrawing compressed hydrogen from storage and, after appropriate decompression, feeding the decompressed hydrogen to a stage of the multi-stage compression system, and The compressed hydrogen gas containing the nitrogen gas is stored therein.

12. A method according to claim 11, wherein during periods when more hydrogen is required than is produced by the electrolysis, the hydrogen is metered with the nitrogen upstream of the stage of the multi-stage compression system into which the reduced pressure hydrogen is fed. 13 . The method according to claim 1 , wherein an amount of hydrogen provided by the electrolysis of water is variable, and the hydrogen is dosed with an amount of nitrogen determined based on the amount of hydrogen provided by the electrolysis of water.

14. An apparatus for supplying hydrogen for consumption in at least one downstream process according to the method of claim 1, the apparatus comprising: a plurality of electrolyzers arranged in parallel for electrolyzing water to provide hydrogen; a power generation system for generating electricity to power the plurality of electrolytic cells, the power generation system being in conductive communication with the plurality of electrolytic cells; a multi-stage compression system for compressing hydrogen to provide compressed hydrogen, the multi-stage compression system comprising a feed end, an outlet end, and at least one centrifugal compression stage, the feed end being in fluid flow communication with the plurality of electrolyzers via a feed header; a nitrogen source for supplying nitrogen, wherein the source is arranged to meter nitrogen to the hydrogen upstream of the centrifugal compression stage in the multi-stage compression system; and At least one downstream processing unit is arranged to receive at least a portion of the compressed hydrogen metered with nitrogen, the downstream processing unit being in fluid flow communication with the outlet end of the multi-stage compression system.

15. The apparatus according to claim 14, wherein the nitrogen source is arranged to feed nitrogen to the feed header to meter nitrogen to the hydrogen, and the multi-stage compression system contains a single section, the section comprising a plurality of compressors arranged in parallel, each compressor comprising at least one centrifugal compression stage; the apparatus further comprises a header for collecting compressed hydrogen from each compressor and feeding the compressed hydrogen containing nitrogen to the downstream processing unit or to a purification system upstream of the downstream processing unit.

16. The apparatus of claim 14, wherein the multi-stage compression system comprises: a first section comprising a plurality of compressors arranged in parallel, each compressor comprising at least one centrifugal compression stage; and a second section downstream of the first section, the second section comprising a plurality of compressors arranged in parallel, each compressor comprising at least two centrifugal and / or reciprocating compression stages arranged in series; The device comprises: a first header for collecting compressed hydrogen from each compressor in the first section and feeding the compressed hydrogen to the compressors in the second section; and a second header for collecting compressed hydrogen from each compressor in the second section and feeding the compressed hydrogen containing nitrogen to the downstream processing unit, or to a purification system upstream of the downstream processing unit, wherein the nitrogen source is arranged to feed nitrogen to the feed header to meter nitrogen to the hydrogen.

17. The apparatus of claim 14, wherein the plurality of electrolytic cells are arranged in at least two groups, and the multi-stage compression system comprises: a first section comprising a plurality of compressors arranged in parallel in at least two groups, each compressor comprising at least two centrifugal compression stages arranged in series; and a second section downstream of the first section, the second section comprising a plurality of compressors arranged in parallel, each compressor comprising at least two centrifugal and / or reciprocating compression stages arranged in series; The device comprises: at least two first headers, each first header collecting hydrogen from each electrolyzer in a group and feeding the hydrogen to the feed end of a corresponding compressor group in the first section of the multi-stage compression system, wherein the nitrogen source is arranged to feed nitrogen to each of the first headers to meter nitrogen to the hydrogen; a second header for collecting compressed hydrogen from each set of compressors in the first section and feeding the compressed hydrogen to the compressors in the second section; and a third header for collecting compressed hydrogen from each compressor in the second section and feeding the compressed hydrogen to the downstream processing unit or to a purification system upstream of the downstream processing unit; 18. The apparatus of claim 14, comprising a control system for controlling the flow of nitrogen from the nitrogen source to the hydrogen, the flow being determined based on the level of hydrogen produced by the electrolyzer.

19. The apparatus of claim 14, comprising a storage system for storing compressed hydrogen gas containing nitrogen, said storage system being in fluid flow communication with said outlet end of said multi-stage compression system and at least one compression stage of said multi-stage compression system, and wherein the nitrogen source is arranged to meter nitrogen to the hydrogen upstream of a point in which the storage system is in fluid flow communication with the at least one centrifugal compression stage of the multi-stage compression system.

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