Method and apparatus for operating a compression system

Abstract

The operation of a multi-stage compression system for compressing a gas feedstock with a variable flow rate is improved by operating the centrifugal compressor or at least one centrifugal compressor in a low-power mode. The multi-stage compression system includes at least one centrifugal compressor with dry gas seals having opposing sealing surfaces. In low-power mode, during periods when the gas flow through the centrifugal compressor is insufficient for normal operation, the opposing surfaces of the dry gas seals do not contact. This operation not only reduces damage to the dry gas seals, thus improving reliability, but also reduces the overall power requirement of the compression system.

Description

Technical Field

[0001] This invention relates to a multi-stage compression system for compressing a gas supply having a wide range of airflow, the multi-stage compression system comprising at least one centrifugal compressor. Specifically, the invention relates to a process for operating such a system and the associated equipment, with the aim of improving reliability and reducing overall power requirements. Background Technology

[0002] Centrifugal compressors are a type of dynamic compressor in which gas is compressed by the mechanical action of rotating blades or impellers (which transmit velocity to the gas). Gas typically enters from the center of the impeller and is propelled to the radial edges by rotational motion, thus delivering the gas at high speed and impacting the casing. The gas velocity is converted into static pressure to deliver high-pressure gas. These types of compressors are particularly suitable for handling large volumes of gas at a relatively low cost.

[0003] To properly compress process gases in a centrifugal compressor, dry gas seals (or "DGS") are typically used to minimize any gas leakage. These dry gas seals contain two opposing sealing surfaces or sealing rings that are separated during normal operation of the centrifugal compressor to compress the gas.

[0004] Typically, the gas used for compression is generated entirely from electricity produced from conventional energy sources (such as on-site gasoline, diesel, or hydrogen-powered generators, fuel cells) or from electricity taken from the local or national grid. In this case, the centrifugal compressor operates at maximum capacity to produce the highest possible yield of net compressed product gas. The motor driving the impeller of the centrifugal compressor therefore typically operates at a fixed speed (e.g., maximum speed).

[0005] Centrifugal compressors may have dry gas seals to prevent or reduce gas leakage. When the compressor motor speed is maintained at a high level, the opposing sealing surfaces of the dry gas seals quickly separate and remain separated. Centrifugal compressors typically operate at full power and are rarely shut down to maximize the output of net compressed gas.

[0006] The present invention addresses problems arising from the operation of centrifugal compressors that receive gas at variable flow rates, for example, using gas generated at least partially from electricity produced by one or more renewable energy sources. Attached Figure Description

[0007] The invention will now be described by way of example only and with reference to the figures, in which:

[0008] Figure 1 This is a simplified flowchart of the first embodiment of the present invention.

[0009] Figure 2 This is a simplified flowchart of the second embodiment of the present invention.

[0010] Figure 3 This is a simplified flowchart of the third embodiment of the present invention.

[0011] Figure 4 The bar graphs and tables provide examples of the process of the invention in the context of four centrifugal compressors arranged in parallel and powered by renewable energy.

[0012] Figure 5 It is a bar graph showing simulated data on the amount of electricity required to power four centrifugal compressors arranged in parallel, according to an example of the invention. Detailed Implementation

[0013] According to a first aspect of the invention, a process is provided for operating a multi-stage compression system for compressing a gas supplied to a compression system at a variable flow rate, the multi-stage compression system comprising at least one centrifugal compressor, the at least one centrifugal compressor including a dry gas seal having opposing sealing surfaces, the process comprising:

[0014] (a) During periods when the gas flow rate through the centrifugal compressor is sufficient for normal operation of the multi-stage compression system, the centrifugal compressor is operated in normal power mode; and

[0015] (b) During periods when the gas flow through the centrifugal compressor is insufficient for normal operation of the multi-stage compression system, the centrifugal compressor, or at least one centrifugal compressor, is operated in a low-power mode sufficient to prevent contact between the opposing sealing surfaces of the dry gas seals in the centrifugal compressor.

[0016] This invention is particularly applicable to processes in which the variable flow rate of gas supplied to a multi-stage compression system is due to the gas being generated using electricity generated at least partially from at least one renewable energy source. This gas may be hydrogen produced by the electrolysis of water.

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

[0018] As described above, the gas used for compression can be generated using electricity, at least partially from at least one renewable energy source. A disadvantage of using renewable energy to generate the gas for compression in the centrifugal compressor is the inherent variability in energy availability, which can swing from full power to no power throughout the day. Although other energy sources (such as battery power or non-renewable energy) can be used to supplement power when availability is low, this may still be insufficient to generate the maximum flow rate of gas required for full operation of the at least one centrifugal compressor.

[0019] For example, the flow rate of the gas used for compression can vary from a maximum flow rate to a very low flow rate, or even no flow rate at all, throughout the day.

[0020] Centrifugal compressors can tolerate some variation in the flow rate of the gas used for compression, but these variations will not reach the required level if they are not periodically shut off. When a centrifugal compressor is shut down or stopped, the speed of the rotor or impeller decreases until the relative sealing surfaces of the DGS no longer separate and come into contact with each other.

[0021] Therefore, frequently turning the centrifugal compressor on and off will accelerate the wear of the DGS. This shortens the lifespan of the centrifugal compressor, thus requiring more frequent replacement or repair, which increases costs. DGS wear also occurs when the centrifugal compressor is restarted or powered on.

[0022] The above-mentioned problems do not apply to centrifugal compressors that compress gases generated entirely from energy from non-renewable power grids, because these compressors are rarely shut down due to their essentially constant maximum gas flow rate for compression.

[0023] Therefore, the inventors have recognized that it is desirable in the art to provide a way of operating a centrifugal compressor that compresses a gas supplied at a wide range of flow rates (e.g., gas generated using electricity at least partially from renewable energy sources) such that the compressor's lifespan is not reduced. Furthermore, or alternatively, in the context of renewable energy, it is also desirable that the operation of the centrifugal compressor conserves as much power as possible.

[0024] The inventors are unaware of any prior art that addresses the aforementioned problems in the context of centrifugal compressors that compress gases generated using electricity at least partially produced from one or more renewable energy sources.

[0025] In the context of this invention, the at least one centrifugal compressor includes within it at least one dry gas seal having opposing sealing surfaces. Any dry gas seal suitable for centrifugal compressors can be used, and these are known in the art, including but not limited to single seals, tandem seals, and double opposing seals.

[0026] As mentioned above, in order to properly compress process gases in a centrifugal compressor, DGS can be used to minimize any gas leakage. These dry gas seals contain two opposing sealing surfaces or sealing rings, one typically a rotating surface (sometimes called the "rotor") and the other a stationary surface (sometimes called the "stator").

[0027] The rotating surface has a lifting geometry designed in it such that when the rotating surface reaches a certain speed, it is lifted away from the stationary surface, thereby forming a tiny gap so that the surfaces do not contact each other, which is used to minimize gas leakage.

[0028] Centrifugal compressors powered by standard non-renewable power grids operate at a fixed speed (typically maximum speed to deliver the maximum amount of product gas). In these cases, during gas compression, as the compressor motor speed remains constant, the opposing sealing surfaces of the dry gas seals rapidly separate and remain unchanged. Due to the continuous power supply from the grid, centrifugal compressors rarely need to be stopped, shut down, or restarted.

[0029] When a centrifugal compressor with a dry gas seal is shut down, the motor speed drops to zero, and the relative sealing surfaces begin to contact. The more frequently this occurs, the more the relative sealing surfaces of the dry gas seal wear over time. This shortens the lifespan of the dry gas seal, meaning the compressor requires more frequent maintenance, increasing overall costs. More frequent maintenance of the compressor in the system also leads to interruptions in the entire process of performing these maintenance, further complicating the operation of the process and increasing costs.

[0030] DGS is often used when compressing high-pressure, low-molecular-weight, flammable, toxic, and / or expensive gases. As DGS ages, more leakage typically occurs at the seals, leading to increased wear and tear, which also has economic consequences.

[0031] In the context of this invention, centrifugal compressors typically compress gases generated using electricity produced at least partially from at least one renewable energy source.

[0032] Suitable renewable energy sources include wind, solar, tidal, and hydropower, or combinations thereof, particularly wind and solar. Preferably, the gas used for compression is generated through a process independent of electricity generation. Ideally, the centrifugal compressor is also powered at least partially by electricity generated from at least one renewable energy source, or entirely by renewable energy. Therefore, renewable energy is preferably used to ideally meet the total electricity demand for generating the gas used for compression and, optionally, for the compressor in a multi-stage compression system.

[0033] In some alternative embodiments, electricity generated by one or more renewable energy sources may be supplemented by other sources during periods of particularly high demand, such as for products from any downstream process, and / or during periods when renewable energy is only available below the threshold required to meet demand or is not available at all. However, these additional energy sources may also be limited, and therefore even with supplemental power from these sources, there may still not be enough electricity for the normal operation of the multi-stage compression system.

[0034] As mentioned above, a disadvantage of using renewable energy sources is the variable availability of the electricity generated from them. When at least partially renewable energy sources are used to generate gas, centrifugal compressors may need to be shut down or restarted more frequently than usual when electricity availability is low. As mentioned above, this reduces the lifespan of dry gas seals and increases maintenance and costs. Furthermore, the frequent starts and stops of centrifugal compressors increase operational risks.

[0035] Centrifugal compressors are at risk of damage every time they are started or stopped. In fact, the chances of a compressor having problems during startup are higher than during shutdown. There are generally critical speeds that should be avoided in this regard. Furthermore, if compressors are shut down for extended periods, they may be more susceptible to pitting and other types of corrosion, which can lead to stress corrosion cracking and ultimately impeller / compressor failure.

[0036] The inventors have devised a process for operating a multi-stage compression system, as described herein, which reduces the number of downtimes of the centrifugal compressor and thus increases the lifespan of dry gas seals. This improves the reliability of the centrifugal compressor.

[0037] In addition, the inventors have devised a process that can save electricity, for example, by allowing the electricity to be used in other parts of the process, such as for generating gas supplies and / or as part of a downstream process that consumes compressed gas.

[0038] Multistage compression systems are used to compress gases, preferably in preparation for consumption in at least one downstream process.

[0039] The gas used for compression is typically generated using electricity, at least partially from at least one renewable energy source, and can be any suitable gas. However, the process has particular applications when the gas used for compression is hydrogen (e.g., hydrogen generated by electrolysis of water). This can be carried out using multiple electrolyzers.

[0040] In some embodiments, the process includes generating hydrogen by electrolyzing water. Alternatively or additionally, the process may include supplying compressed hydrogen to at least one downstream process for consumption in that downstream process.

[0041] Therefore, in some preferred embodiments, the process includes:

[0042] Hydrogen gas is produced by electrolyzing water.

[0043] The hydrogen gas is compressed in a multi-stage compression system operating according to the present invention; and

[0044] The compressed hydrogen is supplied to at least one downstream process for consumption in that downstream process.

[0045] Preferably, at least some of the compressed hydrogen is used in the downstream process to generate ammonia and / or methanol, most preferably ammonia.

[0046] As described above, centrifugal compression is particularly suitable for compressing large quantities of hydrogen at a lower cost, and therefore hydrogen compression is particularly preferred and advantageous for the process of the present invention. Furthermore, hydrogen generated by electrolysis is even more suitable for centrifugal compression because it is "wet" and has a higher density, making centrifugal compression of the gas more efficient than compression of hydrogen not generated by electrolysis.

[0047] renewable energy

[0048] The process of the present invention includes compressing a gas supply with a variable flow rate (e.g., using gas generated from electricity produced at least partially from at least one renewable energy source).

[0049] The operation of a compression system is typically directed by a gas generated using electricity produced from renewable energy sources (such as hydrogen from an electrolyzer). Typically, the power required to generate the gas for compression (e.g., using an electrolyzer) is much greater than the power required to operate the compressor. When the gas supply is insufficient or nonexistent, gas is usually injected from a storage tank (see below).

[0050] To minimize environmental impact, it is preferable that the process is independent in generating the power for the gas production and optionally powering the centrifugal compressor. Therefore, it is preferable to use renewable energy sources to meet all the electricity needs for generating the gas for compression and optionally powering the centrifugal compressor, without supplementing the source with non-renewable energy sources.

[0051] It should be understood that when the available electricity generated from renewable energy sources is insufficient for the normal operation of a multi-stage compression system, placing the centrifugal compressor, or at least one of the centrifugal compressors, in a low-power mode risks reducing the net amount of compressed gas generated by the system. In such cases, before considering the use of any non-renewable energy sources to generate more gas (or power the centrifugal compressors), it is preferable to meet the demand for compressed gas by supplying gas from a suitable gas storage system.

[0052] Nevertheless, there may be situations where the demand for compressed gas cannot be met by the gas used for compression (e.g., hydrogen from the electrolyzer) or by the gas storage system. Therefore, it is conceivable that in some embodiments, electricity generated from one or more renewable energy sources may be supplemented by other sources during periods of particularly high demand for products, such as those from downstream processes, and / or during periods when renewable energy is only available below the threshold required to meet said process demand, or is not available at all, and the gas supply from the gas storage system is insufficient to meet said demand.

[0053] Therefore, in some embodiments, at least some of the additional power may be derived from an on-site battery storage device and / or generated by one or more on-site gasoline, diesel, or hydrogen-powered generators (including fuel cells) and / or derived from the local or national grid.

[0054] However, there may be situations where the electricity generated from renewable energy sources and the additional electricity may still be insufficient for the normal operation of the multi-stage compression system.

[0055] In these embodiments, the gas used for compression is generated using a centrifugal compressor, and the centrifugal compressor is optionally powered by...

[0056] (i) Electricity generated at least partially from at least one renewable energy source, and

[0057] (ii) Power from an on-site battery storage system and / or power generated by one or more on-site gasoline, diesel, or hydrogen-powered generators, and

[0058] Its features

[0059] (a) The centrifugal compressor is operated in normal power mode during periods when (i) electricity generated from renewable energy sources and (ii) electricity from a battery storage device and / or electricity generated by one or more on-site gasoline, diesel, or hydrogen-powered generators, and therefore the gas flow through the centrifugal compressor is sufficient for the normal operation of the multi-stage compression system; and

[0060] (b) During periods when (i) electricity generated from renewable energy sources and (ii) electricity from battery storage and / or electricity generated by one or more on-site gasoline, diesel, or hydrogen-powered generators, and therefore the gas flow through the centrifugal compressor is insufficient to enable the multi-stage compression system to operate normally, the centrifugal compressor is operated in a low-power mode, at least sufficient to prevent contact between the relative sealing surfaces of the dry gas seals in the centrifugal compressor, or if more than one, at least one centrifugal compressor.

[0061] Normal power mode

[0062] When the gas flow rate through the centrifugal compressor is sufficient for the normal operation of the multi-stage compression system, the centrifugal compressor of the present invention will operate in normal power mode.

[0063] In the context of this invention, the term "normal power mode" is used herein to refer to the following operating method of a centrifugal compressor, typically in which net compressed hydrogen is generated. The expression "net compressed hydrogen" means the total amount of compressed gas generated minus the total amount of gas circulated.

[0064] The normal power mode includes at least three different operating modes.

[0065] First, the at least one centrifugal compressor is considered to be in normal power mode, in which the at least one centrifugal compressor operates at full power (hereinafter referred to as "maximum" operating power) to provide as much net compressed gas as possible. In this case, the at least one centrifugal compressor operates at substantially 100% of its total power, with a substantially maximum total flow rate of net compressed gas at the product end, i.e., no gas recirculation.

[0066] Second, the at least one centrifugal compressor is considered to be in normal power mode, in which the at least one centrifugal compressor operates at a slightly reduced capacity (hereinafter referred to as "low-down" operation), wherein the power is less than 100% of the maximum power (100%), but at approximately 60% or more, preferably approximately 70% or more, for example from 70% to 80%. This reduction in compressor power results in a reduction in rotor speed, and therefore a corresponding reduction in the net flow rate of compressed gas at the product end of the compressor. To reduce the gas flow rate to the multistage compression system (at a constant discharge pressure), this typically requires a proportional reduction in compressor power. When the centrifugal compressor is in its "maximum" low-down state, the associated flow rate is reduced to the point that compressor surge is not achieved or any anti-surge controller is activated.

[0067] Third, the at least one centrifugal compressor is considered to be in normal power mode, in which the at least one centrifugal compressor operates in maximum low mode, but at least a portion of the compressed gas at the product end is circulated from the product end to the supply end of the centrifugal compressor (hereinafter referred to as "circulation" operation).

[0068] In other words, in this cyclic operation, the power is reduced as much as possible using the lowering operation, and the associated compressed gas flow rate at the product end is reduced proportionally to the gas flow rate entering the multistage compression system. However, if a further reduction in the net compressed gas flow rate is needed due to the decreased gas flow rate entering the multistage compression system, this can be achieved by introducing an increased amount of recirculated gas from the product end of the centrifugal compressor to the supply end. This reduces the total net compressed gas flow rate without further reducing the power supplied to the centrifugal compressor. Therefore, it is preferable that the amount of time spent by the centrifugal compressor in the cyclic operation is minimized, because, although possible, this will not lead to a reduction in energy use. Preferably, if the centrifugal compressor cannot operate at its maximum capacity, it is placed in the lowering operation state under the normal power mode. It should be understood that the cyclic operation is only used when the power of the centrifugal compressor has been reduced as much as possible during the lowering operation.

[0069] Therefore, the normal power mode may include maximum, low, or cyclic operation as described herein, but preferably, the normal power mode includes maximum and low operation.

[0070] In the context of this invention, the phrase "sufficient for normal operation" is intended to mean that there is sufficient gas flow through the centrifugal compressor to generate net compressed gas, allowing the centrifugal compressor to operate at or above maximum low setting. Therefore, "sufficient for normal operation" generally means that there is sufficient electrical power to provide the gas flow to operate the centrifugal compressor in normal power modes, including maximum, low, or cyclic operation as described herein.

[0071] Optionally, if the centrifugal compressor is also powered by renewable energy, this statement is intended to mean that the generated electricity is sufficient to power the centrifugal compressor at the maximum reduced required power or higher. However, as mentioned above, the power required to generate the gas for compression may typically be much higher than the power required to operate the centrifugal compressor. Therefore, for example, in the case of using renewable energy to generate hydrogen for compression via electrolysis, the limiting factor for whether sufficient electricity can be generated for normal operation is the flow rate of the gas generated by the electrolyzer.

[0072] As described above, in some embodiments, electricity generated from one or more renewable energy sources can be supplemented by other sources during periods of particularly high demand, such as for products from any downstream process, and / or during periods when renewable energy is available only below the threshold required to meet demand or is not available at all. In these cases, the additional electricity may be derived from an on-site battery storage system and / or generated by one or more on-site gasoline, diesel, or hydrogen-powered generators (including fuel cells) and / or drawn from the local or national grid. In these embodiments, the gas used for compression in the centrifugal compressor is generated using (i) electricity at least partially generated from at least one renewable energy source, and (ii) electricity from the on-site battery storage system and / or electricity generated from one or more on-site gasoline, diesel, or hydrogen-powered generators.

[0073] Therefore, in these embodiments, the process includes: (b) operating the centrifugal compressor in normal power mode during periods when (i) electricity generated from renewable energy sources and (ii) electricity from on-site battery storage and / or electricity generated from one or more on-site gasoline, diesel, or hydrogen-powered generators, and thus the gas flow through the centrifugal compressor is sufficient for normal operation of the multi-stage compression system.

[0074] During the period of operation in the normal power mode, the centrifugal compressor has a dry gas seal that does not contact (i.e., is separated) from the relative sealing surfaces because the compressor motor speed provides sufficient lift.

[0075] Low power mode

[0076] Based on existing technology, centrifugal compressors are typically shut down or switched off in response to a significant reduction in gas flow to the compression system, so that they can be restarted once the gas flow increases sufficiently. However, the inventors have devised a process by which the centrifugal compressor can instead operate in a "low-power" mode (LP mode).

[0077] Therefore, during periods when the gas flow through the centrifugal compressor is insufficient for normal operation of the multi-stage compression system, the invention includes operating the centrifugal compressor, or at least one centrifugal compressor, in a low-power mode sufficient to prevent contact between the opposing sealing surfaces of the dry gas seals in the centrifugal compressor.

[0078] As described above, in some embodiments, the electricity generated by one or more renewable energy sources can be supplemented by other sources during periods of particularly high demand for products, such as those from downstream processes, and / or during periods when renewable energy is only available below a threshold required to meet the process demand, or is not available at all. In these embodiments, the gas used for compression in the centrifugal compressor is generated using (i) electricity at least partially generated from at least one renewable energy source, and (ii) electricity from an on-site battery storage device and / or electricity generated from one or more on-site gasoline, diesel, or hydrogen-powered generators.

[0079] In these embodiments, the process includes: (b) operating the centrifugal compressor, or at least one centrifugal compressor, in a low-power mode, at least sufficiently to prevent contact between the opposing sealing surfaces of the dry gas seals in the centrifugal compressor, during periods when (i) electricity generated from renewable energy and (ii) electricity from an on-site battery storage and / or electricity generated from one or more on-site gasoline, diesel, or hydrogen-powered generators, and therefore the gas flow through the centrifugal compressor is insufficient for normal operation of the multi-stage compression system.

[0080] Therefore, in other words, a lack of electricity from renewable energy sources (and a lack of gas flow from storage) could lead to a significant reduction in the flow of gas used for compression, preventing the centrifugal compressor from operating in its normal power mode.

[0081] Therefore, in the event of insufficient power, the rotor speed of the centrifugal compressor, or if there is more than one, will decrease but not completely to zero (i.e., the compressor is not shut down or stopped).

[0082] In the low-power mode, the centrifugal compressor or the at least one centrifugal compressor operates at a low power level sufficient to prevent the opposing sealing surfaces of the dry gas seals in the centrifugal compressor from contacting, and preferably without generating net compressed gas.

[0083] During the low-power mode, the opposing sealing surfaces (sometimes referred to in the art as "rings") are separated and do not contact each other. That is, compared to the normal power mode, the motor speed of the centrifugal compressor or the at least one centrifugal compressor is reduced, but the motor speed is high enough to exceed the so-called "lift-off" speed of the DGS, so that these opposing sealing surfaces remain separated from each other.

[0084] The sealing surfaces typically have a rotating surface and a stationary surface. The rotating surface has a lifting geometry designed therein, such that when the rotating surface reaches a certain speed, it is lifted away from the stationary surface. This creates a tiny gap with the non-contact surface, resulting in minimal gas leakage. Therefore, in the context of this invention, "preventing contact" refers to the presence of said tiny gap with the non-contact surface.

[0085] It should be understood that, due to the non-zero rotor speed during the low-power mode, the centrifugal compressor will operate in a manner that still generates compressed gas. However, this gas will circulate (preferably completely circulate) from the compressor's product end to the supply end. In other words, during the low-power mode, no net compressed gas is generated because only the recirculated gas is compressed.

[0086] The amount of compressor power required to prevent contact between the opposing sealing surfaces depends not only on the design of the centrifugal compressor but also on the design of the dry gas seals. However, centrifugal compressors in low-power mode typically operate above this minimum power threshold to ensure contact is prevented. In low-power mode, the centrifugal compressor power is typically about 5% to about 20% of the compressor's maximum power, for example, about 8% to about 15%, for example, about 10%. The "lift-off" speed is the rotor speed (in rpm) required before the sealing surfaces of the DGS are removed from contact and depends at least in part on the design of the DGS and the manufacturer. In this regard, the manufacturer of a given DGS will indicate the lift-off speed. However, it should be noted that the lift-off speed of a DGS from one manufacturer may differ from that of another, even for DGS with similar designs. Furthermore, the lift-off speed may also change over time as the DGS ages and / or becomes contaminated. With this in mind, the rotor speed during low-power mode is typically at least two or even three times greater than, for example, the lift-off speed indicated by the manufacturer, to ensure that the sealing surfaces in the DGS do not contact. For example, if the lift-off speed of a given DGS is 300 rpm, then the rotor speed of a compressor using this DGS during low-power mode can be approximately 600 rpm or even 900 rpm.

[0087] Technicians are capable of determining the appropriate rotor speed for the DGS in a centrifugal compressor operating in low-power mode through experimentation. However, for illustrative purposes, the rotor speed during low-power mode will be lower than the speed during normal power mode (e.g., about 3000 rpm to about 3500 rpm), and can be in the range of about 100 rpm to about 1500 rpm, for example, from about 200 rpm to about 1000 rpm, or from about 400 rpm to 900 rpm.

[0088] The rotor speed of the centrifugal compressor (or the power supplied to the centrifugal compressor), for example, used to switch between the normal power mode and the low power mode, can be manipulated using suitable means known to those skilled in the art, including but not limited to variable frequency drives (VFDs) and mechanical drives. Other mechanical devices, such as dual-speed motors, can also be used.

[0089] It should be understood that the control system can also be used to monitor and control the rotor speed or power of a centrifugal compressor.

[0090] Multiple centrifugal compressors

[0091] The operation of a multi-stage compression system depends on the flow rate of gas supplied to the compressors, which in turn depends on the available power of the generated gas. Ideally, renewable energy sources would generate enough power to provide the gas flow for compression, allowing all compressors to operate at full power. However, this ideal situation cannot be maintained indefinitely using renewable energy sources.

[0092] As power generated from renewable energy decreases, the flow rate of gas used for compression in the multi-stage compression system also decreases (and if the compressor is powered by renewable energy, the available power to power the compressor decreases), so centrifugal compressors are typically switched to low power to reduce power consumption. As available power continues to decrease, the gas flow through the compressor stages is typically circulated and / or the compressor will sequentially switch to LP mode as available power decreases. Available power will circulate daily, requiring entry into LP mode.

[0093] In some embodiments, the multi-stage compression system includes a plurality (X) of centrifugal compressors arranged in parallel and / or in series.

[0094] In some preferred embodiments, the multi-stage compression system includes multiple (X) centrifugal compressors arranged in parallel, and during periods when the electricity generated from renewable energy sources (and optionally on-site battery storage and / or generators powered by one or more on-site gasoline, diesel, or hydrogen) is insufficient for normal operation of the multi-stage compression system:

[0095] The first number (Y) centrifugal compressors are in the normal power mode, and

[0096] The second number (Z) of centrifugal compressors are in the low-power mode.

[0097] The first and second numbers (Y, Z) are determined based on the gas flow rates to the multi-stage compression system. In this document, X, Y, and Z are integers, where X is 2 or greater; Y and Z can range from 0 to X, and X = Y + Z.

[0098] It should be understood that the control system is typically used to determine and control the number of centrifugal compressors in the low-power mode or normal-power mode.

[0099] This allows none, some, or all of the centrifugal compressors to be placed in the low-power mode as required. One advantage of this is that the multi-stage compression system can continue to generate net compressed gas by keeping one or more centrifugal compressors in the normal power mode, despite the lack of a gas supply stream to operate all centrifugal compressors in the normal power mode.

[0100] Therefore, this embodiment allows for the most efficient use of available electricity, as placing some centrifugal compressors in low-power mode "releases" the available power, which can then be supplied to other parts of the process, such as generating gases (e.g., an electrolyzer for generating hydrogen), compressing gases (e.g., supplying power in normal power mode for operating one or more centrifugal compressors), or providing energy for downstream processes.

[0101] For example, a multi-stage compression system may include four centrifugal compressors arranged in parallel, and:

[0102] (i) During the period in which 80% to 100% of the maximum gas flow rate is directed to the compression system, all four centrifugal compressors are in the normal power mode.

[0103] (ii) During the period in which 60% to 80% of the maximum gas flow rate is directed to the compression system, three centrifugal compressors are in the normal power mode and one centrifugal compressor is in the low power mode;

[0104] (iii) During the period in which 40% to 60% of the maximum gas flow rate is directed to the compression system, both centrifugal compressors are in the normal power mode and both centrifugal compressors are in the low power mode.

[0105] (iv) During the period in which 20% to 40% of the maximum gas flow rate is directed to the compression system, one centrifugal compressor operates in the normal power mode, and three centrifugal compressors operate in the low power mode; and

[0106] (v) During the period in which less than 20% of the maximum gas flow is directed to the compression system, all four centrifugal compressors are in the low normal power mode.

[0107] Those skilled in the art will readily understand that the above examples are applicable to multi-stage compression systems having more or fewer centrifugal compressors arranged in parallel without excessive load.

[0108] In this respect, the above example can also be represented by a general formula. Therefore, in some embodiments, the multi-stage compression system includes multiple (X) centrifugal compressors arranged in parallel, and

[0109] During the period in which the flow rate of the gas heading to the compression system is P% of the maximum flow rate of the gas heading to the compression system,

[0110] The number of centrifugal compressors operating in normal power mode is Y, where Y = x × P%, and Y is rounded to the nearest integer.

[0111] The number of centrifugal compressors operating in the low-power mode is Z, where Z = X – Y, and X, Y, and Z are integers.

[0112] X is the number of centrifugal compressors arranged in parallel, and therefore is not zero. X is typically in the range of 2 to 10. Y and Z are each in the range of 0 to 10, and the sum of Y and Z must equal X, i.e., X = Y + Z.

[0113] Therefore, the present invention allows the number of centrifugal compressors in the low-power mode or the normal-power mode to conserve the available electrical power for the centrifugal compressors as much as possible without excessively shutting down the centrifugal compressors or at least one of them. This reduces wear on dry gas seals and extends the life of the centrifugal compressors. Optionally or additionally, this allows for the conservation of as much electricity as possible, which “frees up” electricity for use elsewhere in the process and is particularly important in the case of renewable energy sources.

[0114] Other compressors

[0115] It should be understood that when one or more centrifugal compressors are switched to low-power mode, this may result in a lower net compressed gas flow rate.

[0116] In some cases, there may not be enough power for the normal operation of any of the centrifugal compressors in the multi-stage compression system, so that the gas for compression can only be supplied at a significantly reduced flow rate, and if so, all the centrifugal compressors can operate in the low-power mode, i.e., the centrifugal compressors do not generate net compressed gas.

[0117] Therefore, in some embodiments, the multi-stage compression system includes at least one additional compressor, and the process includes compressing the gas in the additional compressor during periods when the centrifugal compressor is in a low-power mode.

[0118] The advantage of this embodiment is that the gas continues to be compressed in the multi-stage compression system even when all centrifugal compressors are in low-power mode.

[0119] The additional compressor may be a centrifugal compressor or a reciprocating compressor, preferably a reciprocating compressor. In some preferred embodiments, in the low-power mode, the additional compressor is located downstream of the centrifugal compressor.

[0120] In some embodiments, in the low-power mode, the additional compressor may be part of an additional compression stage downstream of the centrifugal compressor. In a particularly preferred embodiment, the centrifugal compressor in the low-power mode is in a first section, and the additional compressor is a reciprocating compressor that is part of a compression stage in a second section downstream of the first section.

[0121] It is conceivable that the additional compressor will receive gas for compression at a suitable pressure (i.e., approximately at the inlet pressure of the additional compressor). In this case, the term "suitable" is intended to mean that, taking into account the inlet pressure of the gas supplied to the additional compressor, the pressure of the gas is reduced to an appropriate level.

[0122] The gas used for compression in the additional compressor can be supplied from various sources. However, it is particularly preferred that the gas be supplied from a storage system, as described below.

[0123] Return of stored gas

[0124] One drawback of using electricity generated from renewable energy sources (e.g., for gas production) is the inherent volatility of energy availability, which in turn leads to fluctuations in the flow rate of gas supplies to the system. In some embodiments, this problem can be addressed in the present invention by providing a system for collecting and storing at least some, preferably all, of excess gas generated during periods when production exceeds the needs of downstream processes, and distributing the stored gas to the downstream processes during periods when demand exceeds production.

[0125] In the context of this invention, the storage system can also be used to distribute the stored gas to the additional compressor for compression, wherein the centrifugal compressor, or if more than one, at least one centrifugal compressor is operating in the low-power mode.

[0126] Therefore, in a further embodiment, the gas is supplied to the additional compressor by extracting compressed hydrogen from a storage device and, after appropriate depressurization, supplying the depressurized hydrogen to the additional compressor, which is located downstream of the centrifugal compressor in the low-power mode.

[0127] In some embodiments, the compressed gas can be stored without further compression. In these embodiments, the gas is stored at a maximum pressure equal to the pressure to which the gas is compressed in a multi-stage compression system, for example, at most about the supply pressure of one of the downstream processes (if there are more than one). In such embodiments, the compressed gas may be stored at a maximum pressure in the range of about 25 bar to about 30 bar.

[0128] However, the compressed gas can be further compressed before storage. In these embodiments, the compressed gas can be stored at a pressure of up to about 200 bar, or up to about 150 bar, or up to about 100 bar, or up to about 90 bar, or up to about 80 bar, or up to about 70 bar, or up to about 60 bar, or up to about 50 bar.

[0129] During periods when gas demand exceeds production levels, compressed gas is drawn from storage and depressurized to produce depressurized gas. The pressure can be reduced using any conventional method, particularly by passing the gas through a valve.

[0130] The pressure of the depressurized gas will depend on the pressure at the point in the multi-stage compression system where the depressurized gas will be introduced.

[0131] In some embodiments, depressurized gas may be supplied to the final stage of a multi-stage compression system. In these embodiments, the depressurized gas will be at the inlet pressure of the feed to the final stage.

[0132] In other embodiments, the depressurized gas may be supplied to an intermediate stage of the multi-stage compression system. In these embodiments, the depressurized gas will be at the inlet pressure of the feed to the intermediate stage.

[0133] The intermediate stage can be an intermediate stage within a compression section, or, in the case of two or more sections in a multi-stage compression system, an initial stage within another compression section downstream of the first compression section. In these embodiments, the depressurized gas from the storage chamber will be at the inlet pressure of the feed to the further compression sections, i.e., the "inter-section" pressure.

[0134] In a further embodiment, depressurized gas may be supplied to the supply end of the multi-stage compression system, i.e., the initial stage. In these embodiments, the depressurized gas will be the supply pressure of the multi-stage compression system, for example, about 1.1 bar.

[0135] However, in a particularly preferred embodiment, depressurized gas may be supplied to a downstream stage of the centrifugal compressor operating in the low-power mode. Therefore, the term "intermediate" or "final" stage as used herein may refer to the downstream stage of the centrifugal compressor operating in the low-power mode.

[0136] As described above, this allows for the continuous compression of at least some gas in the multi-stage compression system during the period in which the centrifugal compressor, or if more than one, operates in the low-power mode. Therefore, although one or more of the centrifugal compressors operate in the low-power mode and do not generate net compressed gas, the use of additional compressors and storage systems allows for the maintenance of a net compressed gas flow rate at the outlet of the multi-stage compression system.

[0137] In embodiments where the compression system includes a low-pressure (LP) section of a centrifugal compressor and a medium-pressure (MP) section of a reciprocating compressor, a stored gas may be injected upstream of the MP section, for example, between the LP and MP sections. The stored gas may also be injected between the housings of the LP centrifugal compressor.

[0138] During periods when demand exceeds production, methods may include:

[0139] The pressure of the compressed gas extracted from the memory is reduced to generate depressurized gas at the inlet pressure (first intermediate pressure) of the first stage of the multi-stage compression system; and

[0140] The depressurized gas is supplied to the first stage.

[0141] In such an embodiment, once the pressure of the compressed gas in the storage chamber drops to approximately the inlet pressure of the first stage, the method may include:

[0142] Further reduce the pressure of the compressed gas extracted from the memory to generate depressurized gas at the inlet pressure (second intermediate pressure) of the second stage upstream of the first stage of the multi-stage compression system; and

[0143] The depressurized gas is then supplied to the second stage.

[0144] It should be understood that, in this context, the terms "first stage" and "second stage" do not refer to the relative downstream positions of stages in a multi-stage compression system during normal operation. Rather, the terms are intended only to reflect the order in which depressurized gas is supplied 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 as the first intermediate pressure being higher than the second intermediate pressure.

[0145] These embodiments may further include supplying depressurized gas to other stages of a multi-stage compression system upstream of the first and second stages. In these further embodiments, the pressure of the compressed gas drawn from the memory is reduced to the inlet pressure of each stage.

[0146] In some preferred embodiments, the second stage is the initial stage of a multi-stage compression system.

[0147] It should be understood that in embodiments where depressurized gas is supplied to the second stage after the first stage, the gas flow to the first stage stops when the gas flow to the second stage begins. Generally, the depressurized gas flow to a given compression stage stops when the depressurized gas begins to flow to another compression stage.

[0148] In some preferred embodiments, during the supply of the depressurized gas to the first stage, a centrifugal compressor upstream of the stage, or at least one centrifugal compressor if more than one, operates in the low-power mode.

[0149] Because the gas can be returned from the storage to the intermediate and / or initial stages of the multi-stage compression system, the compressed gas can be stored at a minimum pressure of about 5 bar, or even possibly as low as about 1.3 bar.

[0150] In embodiments where the compressed gas is further compressed before storage, another option is to supply the compressed gas extracted from storage directly to the downstream process after appropriate depressurization until the storage pressure drops to the supply pressure of the downstream process. At this point, the pressure of the compressed gas extracted from the storage is further reduced, and the reduced-pressure gas is supplied to the first stage of the multi-stage compression system according to the invention. However, these embodiments are not preferred, for example, due to the additional capital expenditure of the high-pressure storage system.

[0151] In the context of depressurization, the term "appropriate" is intended to mean, taking into account the inlet pressure of a stage in a multi-stage compression system, that the pressure of the gas is reduced to an appropriate level, and the depressurized gas is supplied to the multi-stage compression system.

[0152] Compared to high-pressure storage systems that only release gas at the supply pressure to downstream processes, these embodiments of the present invention, by using a multi-stage compression system already present in the process, recompress the gas from the storage unit when the storage pressure drops below the supply pressure, thereby reducing the gas storage volume. Therefore, gas can continue to be extracted from the storage unit until the storage pressure drops to the minimum supply pressure of the multi-stage compression system.

[0153] During periods when gas production is constrained due to factors such as a lack of power in the electrolyzer, additional compression power is required. However, given a storage pressure at a specific time, this additional compression power can be minimized by supplying gas at the highest possible interstage pressure of the compressor. It also allows the maximum gas storage pressure to be equal to or lower than the supply pressure of any downstream process, thus eliminating any additional compression requirements on the stored gas.

[0154] It should be understood that the same volume of gas is stored in the same storage volume at the same maximum pressure, and reducing the minimum storage pressure increases the volume of gas that can be "released" from the storage, i.e., the usable volume of the stored gas.

[0155] However, the inventors have recognized that, in the case of generating gas and then compressing the gas in a multi-stage compression system for use in at least one downstream process, the releasable volume of the stored gas can be increased by returning the gas from the storage to one stage of the multi-stage compression system instead of directly returning it to the downstream process, and this arrangement reduces the total storage container volume required by the process.

[0156] For example, for a given mass of releasable gas, storing from a maximum pressure of 200 bar to a minimum pressure of 1.5 bar requires 15% less storage container volume compared to storing from a maximum pressure of 200 bar to a minimum pressure of 30 bar.

[0157] Similarly, for a given mass of releasable gas, storage from a maximum pressure of 100 bar to a minimum pressure of 1.5 bar requires 30% less storage container volume than storage from a maximum pressure of 100 bar to a minimum pressure of 30 bar.

[0158] Furthermore, for a given mass of releasable gas, storage from a maximum pressure of 50 bar to a minimum pressure of 1.5 bar requires 60% less storage container volume compared to storage from a maximum pressure of 50 bar to a minimum pressure of 30 bar.

[0159] Furthermore, storage is feasible at a maximum pressure of 30 bar to a minimum pressure of 1.5 bar, compared to the 30 bar range where storage is not permitted.

[0160] Furthermore, although the total storage container volume increases with decreasing maximum storage pressure, lower design pressure allows for thinner container walls and can reduce the total capital cost of the storage system. Container thickness is often limited to a maximum value for reasons such as manufacturability, and in this case, lower design pressure will result in fewer containers (although each container will be larger). Additionally, the allowable stress in the container design can be increased below a certain container wall thickness, and if lower design pressure allows thicknesses below this threshold, the total container metal mass (and therefore the total cost) can be reduced.

[0161] Gas used for compression

[0162] The gas used for compression in a multi-stage compression system can be any gas suitable for compression in a centrifugal compressor, having a variable flow rate. The gas is preferably generated using electricity produced at least partially from at least one renewable energy source. However, hydrogen (preferably generated by the electrolysis of water) is particularly preferred for compression.

[0163] Any suitable form of water electrolysis can be used, including alkaline water electrolysis and polymer electrolyte membrane (PEM) water electrolysis.

[0164] The water used for electrolysis is usually desalinated seawater (possibly desalinated via reverse osmosis) and softened water.

[0165] The electricity required for electrolysis can be generated at least partially from any suitable renewable energy source. However, in some preferred embodiments, at least some of the electricity required for electrolysis is generated from renewable energy sources, including wind, solar, tidal, and hydropower, or combinations of these energy sources, particularly wind and solar. The electricity generated from these sources can be used to power the electrolyzer.

[0166] Preferably, the process is independent in terms of power generation for electrolysis. Therefore, it is preferable to use renewable energy to meet all the electricity requirements of electrolysis.

[0167] However, it is conceivable that during periods of particularly high demand for products from downstream processes and / or during periods when renewable energy is only available below the threshold required to meet demand or is not available at all, electricity generated by one or more renewable energy sources can be supplemented by other sources. In these cases, the supplemental electricity may be taken from on-site battery storage and / or generated by one or more on-site gasoline, diesel, or hydrogen-powered generators (including fuel cells), and / or taken from the local or national grid.

[0168] Electrolysis can be carried out at any suitable scale, with some cases having a total capacity of less than 1 GW. However, in preferred embodiments, electrolysis has a total capacity of at least 1 gigawatt (GW). The maximum total capacity of electrolysis is limited only by practical considerations, such as generating enough power from renewable energy to power multiple electrolyzers. Thus, electrolysis can have a maximum total capacity of about 10 GW or greater. The total capacity of electrolysis can be, for example, from 1 GW to about 5 GW, or from about 1.5 GW to about 3 GW.

[0169] Hydrogen is typically produced by electrolysis at pressures slightly above atmospheric pressure (e.g., about 1.3 bar). However, in some embodiments, electrolysis produces hydrogen at slightly higher pressures (e.g., up to about 3 bar).

[0170] Therefore, hydrogen is often supplied to multi-stage compression systems at pressures ranging from atmospheric pressure to about 5 bar, for example from atmospheric pressure to about 3 bar, preferably from atmospheric pressure to about 1.5 bar, for example about 1.1 bar.

[0171] In some embodiments, the amount of hydrogen generated by the electrolyzer is variable, and therefore during periods when the hydrogen generated by electrolysis is insufficient, hydrogen can be supplied from another source (e.g., a hydrogen storage system) to the multi-stage compression system, as explained below.

[0172] purification

[0173] In a preferred embodiment where the gas used for compression is hydrogen generated by electrolysis, it will be noted that the hydrogen generated by electrolysis is typically saturated with water at 40°C. Therefore, this hydrogen often contains some residual oxygen, typically from about 500 to about 1000 ppm(v). These impurities often must be removed, depending on the tolerances of any downstream processes.

[0174] In this respect, oxygen is a poison for conventional catalysts used in the Haber process. Therefore, 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 (O2), water (H2O), carbon monoxide (CO), and / or carbon dioxide (CO2). Consequently, the feed will also be dry, i.e., no more than 1 ppm of water.

[0175] Downstream processes using conventional "grey" hydrogen (i.e., hydrogen derived from hydrocarbon or carbon-containing feedstocks without capturing carbon dioxide, such as through reformed natural gas) or "blue" hydrogen (i.e., hydrogen obtained in the same manner as gray hydrogen, but with some or all of the carbon dioxide associated with its formation captured) have similar tolerance to oxygen and water. However, hydrogen liquefaction often has more stringent specifications and requires no more than 10 ppb of water and 1 ppm of oxygen in the feedstock.

[0176] The compressed hydrogen produced by electrolysis is preferably purified before being supplied to downstream processes. In this regard, the residual oxygen in the compressed hydrogen can be converted into water by the catalytic combustion of some of the hydrogen to produce oxygen-deficient 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.

[0177] Multi-stage compression system

[0178] A multi-stage compression system is responsible for compressing gas from the pressure at which it is generated to a high pressure. For example, in cases where at least some of the compressed gas is supplied to at least one downstream process, the high pressure is generally a pressure at least slightly higher than the supply pressure of said downstream process.

[0179] It is readily understood that a "multi-stage" compression system has multiple compression stages, which may be separated between compressors connected in parallel and / or in series. The total pressure ratio of each stage is generally 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.

[0180] In multi-stage compression systems, coolers (“intercoolers”) are typically required between adjacent stages, and a cooler (“aftercooler”) is typically required after the final stage to remove the heat generated during compression from the compressed gas. Therefore, in the context of this invention, a “stage” of compression refers to a portion of the compression system between coolers.

[0181] Compressed hydrogen generated by a 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 is about 25 bar to about 35 bar, preferably about 30 bar. In other embodiments, the pressure of the compressed hydrogen is about 10 bar to about 12 bar, preferably about 11 bar.

[0182] In some embodiments, the multi-stage compression system has only a single section to compress hydrogen to the desired high pressure. In other embodiments, the multi-stage compression system includes a first section and at least one additional section downstream of the first section.

[0183] In a particular embodiment, the multi-stage compression system has two sections: a first (low pressure or "LP") section compresses hydrogen from the supply pressure of the multi-stage compression system to a first high pressure ranging from about 2 bar to about 6 bar, and a second (medium pressure or "MP") section compresses hydrogen from the first high pressure to the final high pressure desired by downstream processes.

[0184] In some embodiments, after compression in the first section, the first high pressure of the hydrogen can be in the range of about 2 bar to about 3 bar, for example, 2.5 bar. In other embodiments, the first high pressure can be in the range of about 4 bar to about 6 bar, for example, 5 bar.

[0185] In a preferred embodiment, the multi-stage compression system includes a phase separator upstream of each compression stage to remove liquid water. For low-pressure centrifugal compressors, the phase separator is often incorporated as a separate unit into the intercooler to potentially realize capital and electricity benefits and simplify the system.

[0186] Downstream processes

[0187] In some embodiments, the compressed gas may be consumed in a downstream process or in more than one downstream process arranged in parallel.

[0188] In a preferred embodiment where the gas used for compression is hydrogen, downstream processes may include any processes currently using "grey" or "blue" hydrogen. These processes include oil refining and steel manufacturing.

[0189] In a more preferred embodiment, at least some, for example all, of the compressed gases are hydrogen used to generate ammonia via the Haber (or Haber-Bosch) process. In this process, ammonia is generated by reacting a mixture of hydrogen and nitrogen over an iron-based catalyst at high temperatures (typically from about 400°C to about 500°C) and high pressures (typically in the pressure range of about 100 bar to 200 bar).

[0190] In other preferred embodiments, at least some, for example all, of the compressed gas is hydrogen used to generate methanol, for example by CO2 hydrogenation.

[0191] In some embodiments, at least some, such as all, of the compressed gas is hydrogen used to generate ammonia and / or methanol.

[0192] In other embodiments, at least some, such as all, of the compressed hydrogen is liquefied by cryogenic cooling.

[0193] In a further embodiment, a first portion of the compressed hydrogen is used to generate ammonia, and a second portion of the compressed hydrogen is liquefied.

[0194] equipment

[0195] According to a second aspect of the invention, an apparatus is provided for operating a multi-stage compression system for compressing a gas using the process of the invention as described herein, the apparatus comprising:

[0196] A multi-stage compression system for compressing gas, the multi-stage compression system including a supply end, at least one centrifugal compressor and an outlet end, the at least one centrifugal compressor including at least one dry gas seal having opposing sealing surfaces;

[0197] A control system is used to switch the centrifugal compressor or each centrifugal compressor between a normal power mode and a low power mode based on the flow rate of the gas supply to the multi-stage compression system as required.

[0198] Power generation system

[0199] In some preferred embodiments, the device includes a power generation system for generating electricity from at least one renewable energy source, and wherein the gas used for compression is generated at least partially using the electricity generated from the power generation system.

[0200] Electricity is generated from at least one renewable energy source, such as wind and / or solar energy, to produce compressed gas (and possibly to power the centrifugal compressors of a multi-stage compression system or each centrifugal compressor).

[0201] To minimize environmental impact, it is preferable that the process is independent in terms of generating electricity to produce the gas for compression (and optionally power the centrifugal compressor). Therefore, it is preferable to meet all electricity needs using renewable energy sources without supplementing the energy supply with non-renewable energy sources. In this case, before considering the use of any non-renewable energy sources, it is preferable to meet the demand for compressed gas by supplying the gas from a suitable storage system.

[0202] However, for example, there may not be enough gas available to supply from the storage system. Therefore, in some embodiments, the power generation system includes an on-site battery storage system and / or one or more on-site gasoline, diesel, or hydrogen-powered generators. Power from the battery storage system and / or one or more on-site gasoline, diesel, or hydrogen-powered generators can be used to supplement additional power, or during periods of particularly high demand for products, such as those from downstream processes, and / or during periods when renewable energy is only available below the threshold required to meet the process demands, or is not available at all.

[0203] In embodiments where wind energy is used to generate electricity, the power generation system will include multiple wind turbines. In embodiments where solar energy is used to generate electricity, the power generation system will include multiple photovoltaic cells or "solar cells".

[0204] Some embodiments will include multiple wind turbines and multiple photovoltaic cells.

[0205] The term “conductive communication” will be understood to mean that the power generation system will be connected to the compressor or each compressor in a safe and efficient manner using appropriate wires and / or cables, along with any other relevant equipment.

[0206] In the context of this invention, the centrifugal compressor or each centrifugal compressor may also be driven by a dedicated variable frequency drive, mechanical drive or dual-speed motor.

[0207] In some preferred embodiments, the power generation system also generates electricity to power the centrifugal compressor of the multi-stage compression system and / or any downstream processes.

[0208] Multi-stage compression system

[0209] As mentioned above, a multi-stage compression system comprises multiple stages, each typically having a compression ratio in the range of about 2 to about 2.5. Intercoolers are usually located between adjacent stages, and an aftercooler may be required after the final stage.

[0210] The stages of a multi-stage compression system can be arranged in at least two compression sections, a first section and another section downstream of the first section.

[0211] Each section may include one or more compression stages and an associated cooler. A phase separator may also be included upstream of each compression stage to remove liquid from the hydrogen to be compressed.

[0212] In a specific embodiment, the multi-stage compression system has two sections: a first (low pressure or "LP") section compresses hydrogen from the supply pressure of the multi-stage compression system to a first high pressure, and another (medium pressure or "MP") section compresses hydrogen from the first high pressure to the final high pressure desired by the downstream process.

[0213] An LP segment can have one or more compression levels, such as two, and an MP segment can have two or more compression levels, such as three or four.

[0214] The number of compressors used will depend on the total capacity of the process. For example, for a process with a total electrolyzer capacity of 2.2 GW (for hydrogen production), a multi-stage compression system could have 8 to 10 compressors. Technicians will understand that processes with higher total capacities will require a greater number of compressors.

[0215] The compressor in the LP section can be appropriately enlarged, for example, by 10%, to accommodate machine wear. Additionally or optionally, the multi-stage compression system can include a backup compressor in the LP or MP section, which will be connected to replace another machine in the relevant section that has failed.

[0216] control system

[0217] The device includes a control system for switching between a centrifugal compressor or each centrifugal compressor in a normal power mode and a low power mode based on the flow rate of the gas supply to the multi-stage compression system as required.

[0218] In embodiments where an electricity generation system indicating the flow rate of the gas supply is present, the electricity generation system generates electricity from at least one renewable energy source. However, as described above, in some embodiments, the electricity generation system further includes an on-site battery storage device and / or electricity generated by one or more on-site gasoline, diesel, or hydrogen-powered generators. In such embodiments, the device includes a control system for switching the centrifugal compressor, or each centrifugal compressor, between a normal power mode and a low power mode based on the level of electricity generated by the at least one renewable energy source of the electricity generation system and the on-site battery storage device and / or by one or more on-site gasoline, diesel, or hydrogen-powered generators, according to requirements.

[0219] It should be understood that the control system is electrically connected to the centrifugal compressor or each centrifugal compressor in the multi-stage compression system.

[0220] The control system implements the process of the present invention. When describing the control system, the two modes, "low power mode" and "normal power mode," may have the same characteristics as described herein regarding the process of the present invention.

[0221] Therefore, the control system is configured as follows:

[0222] (a) During periods when the gas flow rate through the centrifugal compressor is sufficient for normal operation of the multi-stage compression system, instruct the centrifugal compressor to operate in normal power mode; and

[0223] (b) During periods when the gas flow to the centrifugal compressor is insufficient for normal operation of the multi-stage compression system, instruct the centrifugal compressor, or if more than one, at least one centrifugal compressor, to operate in a low-power mode sufficient to prevent contact between the opposing sealing surfaces of the dry gas seal in the centrifugal compressor.

[0224] In some embodiments, the control system simply calculates how many centrifugal compressors will operate in low-power or normal-power mode based on the gas flow rate to the multi-stage compression system (and optionally to power the centrifugal compression), and then sends a signal to each compressor to operate in this manner.

[0225] Therefore, the control system governs the most efficient way to operate a centrifugal compressor in a multi-stage compression system without excessively shutting it down. This increases compressor life by reducing wear on dry gas seals and minimizing maintenance frequency and costs. It also allows more electricity to be "released" to other parts of the process, such as gas generation or any downstream processes.

[0226] Electrolytic cell

[0227] In some preferred embodiments, the gas used for compression is hydrogen, preferably generated by the electrolysis of water. Therefore, in this embodiment, the apparatus includes multiple electrolyzers for generating hydrogen, wherein the supply end of the multi-stage compression system is in fluid flow communication with the multiple electrolyzers. The electrolyzers are at least partially powered by electricity generated from the power generation system.

[0228] The electrolysis of water can be provided by multiple electrolysis units or "cells". Each unit or cell can be called an "electrolytic cell".

[0229] The multiple electrolyzers typically have a total capacity of at least 1 GW, but in some cases, the capacity may be less than 1 GW. The maximum total capacity of the electrolyzers is limited only by practical considerations, such as generating sufficient power from renewable energy sources to power the multiple electrolyzers. Therefore, the electrolyzers can have a maximum total capacity of 10 GW or greater. The total capacity of the electrolyzers performing electrolysis can range from 1 GW to 5 GW, for example from approximately 1.5 GW to approximately 3 GW.

[0230] The multiple electrolytic cells are often composed of a large number (e.g., hundreds) of individual cells grouped into “modules”, which also include process equipment such as pumps, coolers and / or separators, and these module groups are typically arranged in separate components.

[0231] Each module typically has a maximum capacity of at least 10MW (e.g., 20MW), and each component typically has a total capacity of at least 100MW (e.g., 400MW).

[0232] This invention can use any suitable type of electrolytic cell. In this regard, there are three conventional types of electrolytic cells—alkaline electrolytic cells, PEM electrolytic cells, and solid oxide electrolytic cells—and each of these types of electrolytic cells is theoretically applicable to this invention.

[0233] Alkaline electrolyzers are operated by introducing hydroxide ions (OH-) into the electrolyte. - Electrolytes are transported from the cathode to the anode via an electrolyte to generate hydrogen on the cathode side. Electrolyzers using a liquid alkaline solution of sodium hydroxide or potassium hydroxide as the electrolyte are commercially available. Commercial alkaline electrolyzers typically operate in a temperature range between approximately 100°C and approximately 150°C.

[0234] 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 hydrogen ions selectively pass through the PEM to the cathode. At the cathode, the hydrogen ions combine with electrons from the external circuit to form hydrogen gas. PEM electrolyzers typically operate in a temperature range of approximately 70°C to approximately 90°C.

[0235] Solid oxide electrolyzers use solid ceramic materials as the electrolyte to selectively conduct negatively charged oxygen ions (O2) at high temperatures. 2- At the cathode, water combines with electrons from an external circuit to form hydrogen gas and negatively charged oxygen ions. The oxygen ions pass through the solid ceramic membrane and react at the anode to form oxygen gas and generate electrons for the external circuit. The solid oxide electrolyzer must be operated at a sufficiently high temperature for the solid oxide membrane to function properly, for example, at approximately 700°C to approximately 800°C.

[0236] Due to the lower operating temperature, alkaline electrolyzers and / or PEM electrolyzers are generally preferred.

[0237] The plurality of electrolytic cells may be arranged in at least two parallel groups. In these embodiments, the apparatus includes:

[0238] The first manifold collects hydrogen from each electrolyzer in each group; and

[0239] The second manifold collects hydrogen from the first manifold and supplies the hydrogen to the supply end of the multi-stage compression system.

[0240] In some embodiments, the apparatus further includes a storage system for storing compressed hydrogen, and a conduit for supplying compressed hydrogen from the storage system to a second manifold after appropriate depressurization.

[0241] These embodiments of the invention can use any suitable water source. However, in embodiments where seawater is used to generate water for electrolysis, the apparatus will further include at least one unit (or appliance) for seawater desalination and softening.

[0242] Purification system

[0243] In some embodiments, where there are downstream processes where the levels of water and oxygen inherent in compressed hydrogen generated by electrolysis of water are intolerable, the apparatus may include a purification system in which the compressed hydrogen is purified.

[0244] Purification systems typically include a "deoxygenation" unit, in which oxygen is removed by the catalytic combustion of hydrogen to produce water and oxygen-depleted compressed hydrogen.

[0245] The oxygen-deficient gas can then be dried in a dryer (e.g., an adsorption unit, such as a temperature-switched adsorption (TSA) unit) to produce dried, compressed hydrogen for downstream processes.

[0246] Downstream processing unit

[0247] In some embodiments, the device includes at least one downstream processing unit for consuming compressed gas, the downstream processing unit being in fluid flow communication with the outlet end of the multi-stage compression system.

[0248] The downstream processing unit can be any unit that uses gas (e.g., hydrogen) as a feed.

[0249] Examples of suitable downstream processing units include oil refining equipment, steelmaking equipment, ammonia synthesis equipment, or hydrogen liquefaction equipment. In some embodiments, the ammonia synthesis equipment and the hydrogen liquefaction equipment are arranged in parallel.

[0250] In a particularly preferred embodiment, the downstream processing unit includes an ammonia synthesis apparatus (e.g., using the Haper (Haper-Bosch) process) and / or a methanol synthesis apparatus (e.g., using CO2 hydrogenation).

[0251] Storage System

[0252] In some embodiments, the device includes a storage system for storing compressed gas, the storage system being in fluid flow communication with the outlet end of the multi-stage compression system and at least one compressor of the multi-stage compression system.

[0253] Storage systems typically consist of multiple pressure vessels and / or piping segments connected to a common inlet / outlet manifold.

[0254] Pressure vessels can be spherical, for example, up to about 25m in diameter, or “bullet-shaped,” that is, horizontal vessels with a large L / D ratio (typically up to about 12:1) up to about 12m in diameter.

[0255] Salt domes may also be used if the geological conditions of the site permit.

[0256] In some embodiments, the device includes a second control system that controls not only the pressure and flow rate of compressed gas from the multi-stage compression system to the storage system, for example during periods when gas production exceeds demand, but also the pressure and flow rate of compressed gas destined for the multi-stage storage system, for example during periods when gas demand exceeds production.

[0257] It should be understood that the second control system may be integrated with or separate from the control system for the power mode of the centrifugal compressor described above.

[0258] In some embodiments, the second control system will simply seek to maintain the pressure of the gas in the downstream manifold of the downstream process. Therefore, in order to continuously supply a fixed amount of gas to the downstream process, the pressure controller will be maintained on the discharge manifold supplying the downstream process.

[0259] If the pressure in the discharge manifold exceeds the required supply pressure (e.g., because there is more gas available than is consumed by downstream processes), the pressure can be released by opening a valve in the supply line leading to the storage unit.

[0260] Once the pressure in the discharge manifold drops to the required supply pressure, the valve in the supply line to the storage unit will close.

[0261] If the pressure in the discharge manifold drops below the required supply pressure (e.g., because less gas is available than is consumed by downstream processes), the pressure is increased by opening a valve in the first return line from storage to the first stage of the multi-stage compression system.

[0262] The valve in the first return line will remain open until the pressure in the discharge manifold exceeds the required supply pressure, indicating that the gas production level has returned to the required level. At this point, the valve will close, or until the pressure in the storage container drops to approximately the inlet pressure of the first stage of the multi-stage compression system supplied by the first return line.

[0263] In the latter case, not only are the valves in the first return line closed, but the valves in the second return line from the storage to the second stage (upstream of the first stage) of the multi-stage compression system are also opened to continue supplying gas from the storage back to the downstream process.

[0264] This type of control system can be called a "split-range" control system.

[0265] Aspects of the present invention include:

[0266] #1. A process for operating a multi-stage compression system for compressing a gas feedstock having a variable flow rate, the multi-stage compression system comprising at least one centrifugal compressor, the at least one centrifugal compressor including a dry gas seal having opposing sealing surfaces, the process comprising:

[0267] (a) During periods when the flow rate of the gas passing through the centrifugal compressor is sufficient for normal operation of the multi-stage compression system, the centrifugal compressor is operated in normal power mode; and

[0268] (b) During periods when the flow rate of the gas passing through the centrifugal compressor is insufficient for normal operation of the multi-stage compression system, the centrifugal compressor, or at least one centrifugal compressor, is operated in a low-power mode sufficient to prevent contact between the opposing sealing surfaces of the dry gas seals in the centrifugal compressor.

[0269] #2. The process according to #1, wherein during operation in the low-power mode, the centrifugal compressor or the at least one centrifugal compressor operates at a power of about 20% or less relative to the maximum power and does not generate net compressed gas.

[0270] #3. The process according to #1 or #2, wherein during operation in the low-power mode, the centrifugal compressor or the at least one centrifugal compressor operates at a rotor speed in the range of about 100 rpm to about 1500 rpm and does not generate net compressed gas.

[0271] #4. The process according to any of #1 to #3, wherein during operation in the normal power mode, the centrifugal compressor or the at least one centrifugal compressor operates at a power of about 70% or higher relative to the maximum power and optionally generates at least some net compressed gas.

[0272] #5. The process according to any of #1 to #4, wherein the multi-stage compression system includes at least one additional compressor, and during the time period specified in (b), the process includes compressing the gas in the additional compressor.

[0273] #6. The process according to any one of #1 to #5, wherein the gas used for compression is hydrogen.

[0274] #7. According to the process described in #6, the hydrogen is generated by electrolyzing water.

[0275] #8. The process according to #6 or #7, wherein the gas is supplied to the additional compressor by: extracting compressed hydrogen from a storage device and, after appropriate depressurization, supplying the depressurized hydrogen to the additional compressor, the additional compressor being located downstream of the centrifugal compressor in the low-power mode.

[0276] #9. The process according to any one of #5 to #8, comprising supplying the compressed hydrogen to at least one downstream process for consumption in the downstream process.

[0277] #10. The process according to #9, wherein at least some of the compressed hydrogen is used to generate ammonia and / or methanol in the downstream process.

[0278] #11. The process according to #9 or #10, wherein during the time period specified in (b), the process includes extracting compressed hydrogen from a memory and, after appropriate depressurization, supplying the depressurized hydrogen to the downstream process.

[0279] #12. An apparatus for operating a multi-stage compression system for compressing a gas according to #1, the apparatus comprising:

[0280] A multi-stage compression system for compressing gas, the multi-stage compression system including a supply end, at least one centrifugal compressor and an outlet end, the at least one centrifugal compressor including at least one dry gas seal having opposing sealing surfaces;

[0281] A control system is used to switch the centrifugal compressor or each centrifugal compressor between a normal power mode and a low power mode based on the flow rate of the gas supply to the multi-stage compression system as required.

[0282] #13. The device according to #12, comprising:

[0283] An electricity generation system for generating electricity from at least one renewable energy source, wherein the gas used for compression is generated at least in part using electricity generated from the electricity generation system.

[0284] #14. The device according to #12 or #13, including

[0285] Multiple electrolyzers are used to generate hydrogen gas.

[0286] The electrolytic cell is at least partially powered by electricity generated from the power generation system, and

[0287] The supply end of the multi-stage compression system is in fluid flow communication with the plurality of electrolytic cells.

[0288] #15. The apparatus according to any one of #12 to #14, comprising at least one downstream processing unit for consuming compressed gas, the downstream processing unit being in fluid flow communication with the outlet end of the multi-stage compression system.

[0289] #16. The device according to any one of #12 to #15, comprising:

[0290] A storage system for storing compressed gas, the storage system being in fluid communication with the outlet end of the multi-stage compression system and at least one compressor of the multi-stage compression system; and

[0291] The second control system is used to control the pressure and flow rate of compressed gas from the multi-stage compression system to the storage system, and to control the pressure and flow rate of compressed gas from the storage system to the compressor of the multi-stage compression system based on the flow rate of the gas supply to the multi-stage compression system.

[0292] Detailed description of the attached figures

[0293] according to Figure 1 Hydrogen gas is generated at approximately atmospheric pressure by electrolyzing water in multiple electrolytic cells, generally indicated by reference number 2.

[0294] A stream of hydrogen gas, 4, is discharged from the electrolyzer 2 at a pressure slightly above atmospheric pressure (e.g., about 1.1 bar) and supplied to a multi-stage compression system 20 to generate a stream of compressed hydrogen gas, 12. In this example, the multi-stage compression system 20 includes four centrifugal compressors arranged in parallel, generally indicated by reference numeral 6.

[0295] The electricity required to power the electrolyzer 2 is generated at least in part by renewable energy sources such as wind and / or solar (not shown). However, in some embodiments, at least some additional electricity may be derived from an on-site battery storage system and / or from electricity generated by one or more on-site gasoline, diesel, or hydrogen-powered generators (including fuel cells) and / or from a local or national grid (not shown).

[0296] Compressed hydrogen from each of the centrifugal compressors 6 is supplied to manifold 10, forming a combined stream 12 of compressed hydrogen. The combined stream 12 can be supplied to a downstream stage of compression (not shown) or at least one downstream process (not shown).

[0297] Each centrifugal compressor 6 is electrically connected to a control system indicated by reference number 30. The control system 30 monitors the amount of airflow to the multi-stage compression system and instructs one or more of the centrifugal compressors 6 to be in low-power mode or normal-power mode (or to switch between them).

[0298] For example, during periods when the power generated from renewable energy sources (and optionally from non-overlapping battery storage and / or one or more on-site gasoline, diesel, or hydrogen-powered generators) (not shown), and therefore the gas flow through the centrifugal compressors is sufficient for normal operation of the multi-stage compression system 20, the control system 30 instructs the four centrifugal compressors 6 to operate in normal power modes (i.e., at maximum, low, or cyclic operation).

[0299] However, during periods when the electricity generated from renewable energy (and optionally from a non-overlapping battery storage device and / or one or more on-site gasoline, diesel, or hydrogen-powered generators) (not shown), and therefore the gas flow through the centrifugal compressors is insufficient for normal operation of the multi-stage compression system 20, the control system 30 instructs one, two, three, or all four centrifugal compressors 6 to operate in a low-power mode as required. As described herein, in this low-power mode, this low-power mode is at least sufficient to prevent contact between the opposing sealing surfaces of the dry gas seals in the centrifugal compressors 6 or each of the centrifugal compressors 6.

[0300] Although not shown for simplicity, multistage compression systems typically include an intercooler between compression stages and an aftercooler after the final stage. A phase separator may also be present upstream of each compression stage to remove liquid from the flow entering the stage.

[0301] Figure 2 A second embodiment of the invention has been described. The same reference numerals are used to denote... Figure 2 In the flowchart and Figure 1 The flowcharts share common characteristics. The following are the differences. Figure 2 The first embodiment and Figure 1 Discussion of the characteristics of the process shown.

[0302] about Figure 2 The multi-stage compression system 20 has an LP section containing the four centrifugal compressors 6 arranged in parallel, and also includes an MP section containing four reciprocating compressors arranged in parallel, generally indicated by reference numeral 14.

[0303] Hydrogen stream 4 is supplied to the LP section, where it is compressed from about 1.1 bar to about 5 bar and supplied to manifold 10 to generate combined stream 12. Combined stream 12 is then supplied to the MP section using reciprocating compressor 14, where it is further compressed to generate stream 16 at a pressure about 1 bar higher than that of any downstream process (not shown).

[0304] In this diagram, the control system 30 again monitors the gas flow rate (e.g., based on available power) and instructs one or more of the centrifugal compressors 6 to operate in low-power mode or normal-power mode (or switch between them) as required. However, even when the net compressed gas flow rate is reduced due to one or more of the centrifugal compressors 6 operating in low-power mode (e.g., by supplying hydrogen from the storage tank to the compressor 14), the presence of the downstream compression section of the four reciprocating compressors 14 allows the multi-stage compression system to continue compressing hydrogen.

[0305] Figure 3 A second embodiment of the invention is depicted. The same reference numerals are used to denote... Figure 3 In the flowchart and Figure 2 The flowcharts share common characteristics. The following are the differences. Figure 3 The first embodiment and Figure 2 Discussion of the characteristics of the process shown.

[0306] about Figure 3 The device shown includes a storage system 40.

[0307] Dry hydrogen can be stored in storage system 40 up to the maximum pressure required for downstream process supply, such as approximately 26 bar for ammonia appliances. In these embodiments, a stream 38 of compressed hydrogen is taken from the outlet of a multi-stage compression system, the pressure is appropriately adjusted via valve 42, and then supplied to storage system 40.

[0308] Alternatively, hydrogen can be stored at higher pressures, such as up to 50 bar or even 100 bar or higher. In such an embodiment, the hydrogen stream 38 has been removed from the outlet of the multi-stage compression system, compressed in the storage compression system, and its pressure is adjusted as required by valve 42 before being supplied to the storage system 40.

[0309] During periods when hydrogen demand exceeds production, hydrogen from storage system 40 can be supplied directly as stream 48 to the hydrogen supply heading to downstream process (not shown) after appropriate depressurization (e.g., via valve 56). In some embodiments, hydrogen extracted from storage can be supplied as stream 46 to the point between the LP and MP sections of multi-stage compression system 20 after appropriate depressurization (e.g., via valve 54). In a further embodiment, hydrogen extracted from storage can be supplied as stream 44 to the supply heading to the LP section including centrifugal compressor 6 after appropriate depressurization (e.g., via valve 52).

[0310] In some embodiments, hydrogen extracted from the storage system is supplied to a downstream process (not shown) in the form of stream 48 until the pressure in the storage system drops to approximately the supply pressure of the downstream process, at which point valve 56 closes and valve 54 opens. The extracted hydrogen can then be supplied in the form of stream 46 to points between sections of the multistage compression system 20 until the pressure in the storage system drops to approximately the supply pressure of the MP section. At this point, valve 54 closes and valve 52 opens, thereby supplying the hydrogen extracted from stream 44 to the supply of the LP section of the multistage compression system 20.

[0311] Compared to supplying hydrogen from the storage unit solely through line 48, the advantage of this sequential method of supplying hydrogen from the storage unit to the downstream process is that it represents a more energy-efficient way to return hydrogen to the process during periods when demand exceeds production.

[0312] In some preferred embodiments of the invention, during periods when one or more centrifugal compressors 6 are operating in low-power mode, hydrogen extracted from the storage tank can be supplied as a stream 46 to the point between the LP and MP sections of the multi-stage compression system 20 after appropriate depressurization (e.g., via valve 54). A second control system (optionally integrated with the first control system) can control the flow rate of hydrogen extracted via valve 54 such that the compressed hydrogen stream from the centrifugal compressor 6 is supplemented with hydrogen from the storage tank.

[0313] This has the further advantage of ensuring that the decrease in the flow rate of net compressed hydrogen from stream 16 to the downstream process (not shown) is minimized even though one or more centrifugal compressors 6 are operating in low-power mode.

[0314] Figure 4 A graph illustrating an example of renewable energy output is shown. It should be understood that the renewable energy data is for illustrative purposes only and is not intended to reflect the true value of solar energy output.

[0315] This example uses only solar energy as a renewable energy source; however, it should be understood that this example can be extrapolated to other renewable energy sources, on-site battery storage, or one or more on-site gasoline, diesel, or hydrogen-powered generators, as described herein. Solar energy is used in this example to simplify the exemplary data for ease of interpretation—it is understood that using a combination of renewable and non-renewable energy sources will present more complex energy output diagrams, for example, but the principle is the same as described herein.

[0316] from Figure 4 The graph (top) shows that the electrical power generated from solar energy varies throughout the day (08:00 to 16:00). In this example, the electricity generated by solar energy is used to power the electrolyzer, and is therefore related to the amount of gas produced for compression. This gas is then, for example... Figures 1 to 3 The compression is achieved in four centrifugal compressors arranged in parallel within a multi-stage compression system, as shown in the diagram. The operational data of the centrifugal compressors is... Figure 4 The table shows that each centrifugal compressor is labeled 1 to 4.

[0317] Figure 4 The table shown indicates the number of centrifugal compressors that perform supercharging or switch to low-power or normal-power modes in low-power or normal-power modes, based on the generated gas flow rate, which is based on the electricity generated from solar energy.

[0318] from Figure 4 The table shows that:

[0319] (i) At 08:00, 20% of the total power is generated by solar energy, and therefore there is not enough energy to provide sufficient gas flow for compression in all four centrifugal compressors (1, 2, 3, 4) in normal power mode (NPM), so the four centrifugal compressors are in low power mode (LPM);

[0320] (ii) At 09:00, 40% of the total power is generated by solar energy, and therefore there is enough energy to provide sufficient gas flow for compression in one centrifugal compressor (1) in normal power mode (NPM), and three centrifugal compressors (2, 3, 4) are in low power mode (LPM);

[0321] (iv) At 10:00, 60% of the total power is generated by solar energy, and therefore there is enough energy to provide sufficient gas flow for compression in the two centrifugal compressors (1, 2) in normal power mode (NPM), and the two centrifugal compressors (3, 4) are in low power mode (LPM).

[0322] (v) At 11:00, 80% of the total electricity is generated by solar energy, and therefore there is sufficient energy to provide adequate gas flow for compression in the three centrifugal compressors (1, 2, 3) in normal power mode (NPM), and one centrifugal compressor (4) is in low power mode (LPM); and

[0323] (vi) At 12:00, 100% of the total electricity is generated by renewable energy, and therefore there is enough energy to provide sufficient gas flow for compression in all four centrifugal compressors (1, 2, 3, 4) under normal power mode (NPM).

[0324] It should be understood that Figure 4 The example shown can also be described using the general formula given above.

[0325] exist Figure 4 In the example shown, it can be seen that no centrifugal compressor is completely shut down in response to a lack of available power generated from the solar energy throughout the day. Therefore, this allows for a number of centrifugal compressors operating in either the low-power mode or the normal-power mode that conserve as much available power as possible without excessively shutting down any centrifugal compressor or at least one of the centrifugal compressors. This reduces wear on dry gas seals and extends the lifespan of the centrifugal compressors, thus lowering costs.

[0326] Figure 5This is a bar graph illustrating simulated data over time of the electrical power used to power four centrifugal compressors arranged in parallel, according to an example of the invention. In this simulation example, the electrical power available in the electrolyzer for gas generation determines the electrical power supplied to the centrifugal compressors. The simulated electrical power used to power the electrolyzer to generate hydrogen for compression in the centrifugal compressors is based on renewable energy sources. The maximum power of each centrifugal compressor is 10 MW, and the total maximum power of all four compressors is 40 MW. The x-axis shows the amount of power supplied to all four centrifugal compressors (from 10 MW to 40 MW), and the y-axis roughly shows the amount of time that power levels are supplied. These results were generated using computer simulation software that uses real-world data on available wind and solar power collected over more than 30 years.

[0327] This graph shows that for approximately one-third of the time (60,000 hours; 6.8 years), the centrifugal compressors operate at a total power of approximately 10 MW, with all four compressors operating in low-power mode. For approximately another third of the time (65,000 hours; 7.4 years), the centrifugal compressors operate at a total power of approximately 22 MW, with two compressors likely operating in normal power mode and two in low-power mode. For approximately another third of the time (55,000 hours; 6.3 years), the centrifugal compressors operate at a total power of approximately 40 MW, with all four compressors operating at maximum power in normal power mode. Any peak power less than approximately 35 MW could result in at least one centrifugal compressor operating in low-power mode. At a 26 MW LP CC power level, it is possible that two centrifugal compressors operate at maximum power, one centrifugal compressor operates in low-power mode, and one centrifugal compressor operates in low-power mode.

[0328] therefore, Figure 5 Significant power savings can be achieved by switching a centrifugal compressor to a low-power mode based on the gas flow rate through the centrifugal compressor, depending on the available power.

[0329] The foregoing description has illustrated and described examples of the principles described. This description is not intended to be exhaustive or to limit these principles to any precise form disclosed. Many modifications and variations are possible in accordance with the foregoing teachings. It should be understood that any feature described with respect to any example may be used alone or in combination with other features described, and may also be used in combination with any feature of any other example, or in any combination of any other example.

[0330] In this specification, unless otherwise expressly stated, the word "or" is used in the sense of the operator that returns a truth value when any one or both of the stated conditions are met, not in the sense of the operator "XOR" that requires only one of the conditions to be met. The word "including" is used in the sense of "containing," not in the sense of "consisting of."

[0331] All of the aforementioned prior teachings are hereby incorporated herein by reference. Any acknowledgment of any previously published document herein should not be construed as an acknowledgment or representation that its teachings were common knowledge in Australia or elsewhere at the time.

Claims

1. A process for operating a multi-stage compression system for compressing a gas feedstock having a variable flow rate, the multi-stage compression system comprising a centrifugal compressor including a dry gas seal having opposing sealing surfaces, the process comprising: (a) During periods when the flow rate of the gas passing through the centrifugal compressor is sufficient for normal operation of the multi-stage compression system, the centrifugal compressor is operated in normal power mode. as well as (b) During periods when the available electricity generated from renewable energy is insufficient for the normal operation of the multi-stage compression system, such that the flow rate of gas passing through the centrifugal compressor is insufficient for the normal operation of the multi-stage compression system, at least one centrifugal compressor is operated in a low-power mode sufficient to prevent contact between the relative sealing surfaces of the dry gas seals in the centrifugal compressor. In the low-power mode, the at least one centrifugal compressor does not generate net compressed gas, wherein the compressed gas is completely circulated from the product end of the at least one centrifugal compressor to the supply end of the at least one centrifugal compressor.

2. The process of claim 1, wherein during operation in the low-power mode, the at least one centrifugal compressor operates at 20% or less of its maximum power.

3. The process according to claim 1, wherein during operation in the low-power mode, the at least one centrifugal compressor operates at a rotor speed in the range of 100 rpm to 1500 rpm.

4. The process of claim 1, wherein during operation in the normal power mode, the centrifugal compressor operates at 70% or higher of its maximum power and generates at least some net compressed gas.

5. The process according to claim 1, wherein the gas used for compression is hydrogen.

6. The process according to claim 5, wherein the hydrogen is generated by the electrolysis of water.

7. The process of claim 1, wherein the multistage compression system includes an additional compressor, and wherein during periods when available electricity generated from renewable energy is insufficient for normal operation of the multistage compression system such that the flow rate of gas passing through the centrifugal compressor is insufficient for normal operation of the multistage compression system, the process includes compressing the gas in the additional compressor.

8. The process of claim 7, wherein the gas is supplied to the additional compressor by: extracting compressed hydrogen from a storage device and, after appropriate depressurization, supplying depressurized hydrogen to the additional compressor, the additional compressor being located downstream of the centrifugal compressor in the low-power mode.

9. The process of claim 5, further comprising supplying compressed hydrogen to at least one downstream process for consumption in said downstream process.

10. The process of claim 9, wherein at least some of the compressed hydrogen is used to generate ammonia and / or methanol in the downstream process.

11. The process of claim 9, wherein during a period when the available electricity generated from renewable energy is insufficient for normal operation of the multi-stage compression system, such that the flow rate of gas passing through the centrifugal compressor is insufficient for normal operation of the multi-stage compression system, the process includes extracting compressed hydrogen from a storage device and, after appropriate depressurization, supplying depressurized hydrogen to the downstream process.

12. An apparatus for operating the process according to claim 1, the apparatus comprising: A multi-stage compression system for compressing gas, the multi-stage compression system including a supply end, a centrifugal compressor and an outlet end, the centrifugal compressor including at least one dry gas seal having opposing sealing surfaces; A control system is configured to independently switch each centrifugal compressor between a normal power mode and a low power mode based on the flow rate of the gas supply to the multi-stage compression system as required.

13. The apparatus of claim 12, comprising a power generation system for generating electricity from at least one renewable energy source, wherein the gas for compression is generated at least partially using the electricity generated from the power generation system.

14. The apparatus according to claim 12, comprising a plurality of electrolyzers for generating hydrogen gas. The electrolytic cell is at least partially powered by electricity generated from the power generation system, and The supply end of the multi-stage compression system is in fluid flow communication with the plurality of electrolytic cells.

15. The apparatus of claim 12, further comprising at least one downstream processing unit for consuming compressed gas, the downstream processing unit being in fluid flow communication with the outlet end of the multi-stage compression system.

16. The device according to claim 12, comprising: A storage system for storing compressed gas, the storage system being in fluid flow communication with the outlet end of the multi-stage compression system and at least one compressor of the multi-stage compression system; as well as A second control system is configured to control the pressure and flow rate of compressed gas from the multi-stage compression system to the storage system, and to control the pressure and flow rate of compressed gas from the storage system to the compressor of the multi-stage compression system based on the flow rate of the gas supply to the multi-stage compression system.

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