Hydrogen compression device, system comprising same and method

Abstract

A compression device includes a hydrogen compressor and a return circuit having an inlet fluidly coupled with a discharge side of a centrifugal compressor and an outlet fluidly coupled with a suction side of the centrifugal compressor. A head loss control valve is positioned in the return circuit. The head loss control valve is adapted to generate a controlled head loss in the return circuit when the compressor operates at a lower flow rate than the surge control line.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to hydrogen compression systems and methods. BACKGROUND

[0002] Many human activities are believed to cause climate change. In particular, energy production through combustion of fossil fuels and subsequent carbon dioxide generation is the source of the increase in concentration of greenhouse gases in the atmosphere, leading to global temperature rise.

[0003] The environmental impact of traditional energy production processes based on thermal cycles fueled by fossil fuels and the resulting climate change consequences triggered the search for alternative energy sources.

[0004] Hydrogen is widely used in several industrial chemical fields, for example for the synthesis of ammonia and its derivatives for agricultural purposes, or for oil refining operations, such as desulfurization of distillates intended for fuel applications.

[0005] In recent years, hydrogen has been considered as a possible alternative to fossil fuels, since its combustion generates water vapor (steam) and does not produce carbon dioxide.

[0006] However, hydrogen does not exist in large quantities in its natural state, so it should be produced starting from raw materials. Depending on the starting material used, hydrogen can be produced by various processes. Some of these processes are not free from environmental impact, among which the process of generating hydrogen is particularly energy-intensive.

[0007] Some hydrogen production processes are based on natural gas or other hydrocarbons. The conversion of these raw materials into hydrogen requires energy, which is currently mainly derived from fossil fuels. In particular, the production of hydrogen from natural gas is usually based on steam reforming (also known as steam methane reforming), which involves the reaction of methane in the presence of water vapor at high pressure and high temperature, in the presence of a catalyst. The method needs to be operated at high temperature (up to 1000°C), which requires a large amount of thermal energy, usually generated by combustion of fossil fuels and subsequent carbon dioxide generation.

[0008] Hydrogen produced by processes that release carbon dioxide into the environment is usually referred to as "gray hydrogen".

[0009] In order to reduce the environmental impact of hydrogen production, carbon capture and storage (CCS) systems are usually used to capture the carbon dioxide generated by the combustion of fossil fuels used to produce hydrogen, thus reducing the amount of carbon dioxide released into the environment. Hydrogen produced with systems with carbon capture and storage is usually referred to as "blue hydrogen". The use of CCS systems is not free from drawbacks, since carbon capture involves a reduction in the overall energy efficiency of the processes involved.

[0010] Hydrogen can also be generated by electrolysis of water powered by electric current. Water is split in an electrolyzer into oxygen (O2) and H2, the oxygen is returned to the atmosphere and the hydrogen produced is called "green hydrogen" if the electricity used to power the electrolyzer is 100% generated by renewable sources such as photovoltaic panels, wind turbines, etc.

[0011] Green hydrogen has no environmental impact in terms of carbon dioxide emissions, as the entire production process is carbon-free. However, handling green hydrogen, and in particular compressing the hydrogen gas for transport or conversion purposes, can become challenging.

[0012] In fact, due to the nature of the renewable energy sources used to power the electrolyzer, green hydrogen production can be discontinuous and the flow can fluctuate and sharply decrease at certain times of the day. When no hydrogen is available, the centrifugal compressor used to compress the hydrogen cannot be turned off, as this generates a fatigue phenomenon which in turn can cause the compressor to fail. In case of low flow of hydrogen stream from the electrolyzer or when production is at idle, the usual practice is to run the compressor at a reduced speed to reduce the power absorbed by the driver, usually an electric motor. If necessary, an anti-surge control valve is opened, the suction and delivery valves are closed and the compressor is run at a reduced speed until hydrogen production is resumed.

[0013] This requires the use of a variable speed electric motor as a driver, which is expensive. Moreover, the rotational speed cannot be reduced below about 60% of the rated speed to avoid crossing the critical speed of the compressor.

[0014] A new system and method aimed at overcoming the above-mentioned drawbacks would be welcome in the art. SUMMARY

[0015] According to one aspect, disclosed herein is a hydrogen compression device that at least partially mitigates or solves the above-mentioned drawbacks.

[0016] In the embodiments disclosed herein, the hydrogen compression device comprises a hydrogen compressor having a suction side and a delivery side. The compression device further comprises a return circuit having an inlet fluidically coupled to the delivery side of the hydrogen compressor and an outlet fluidically coupled to the suction side of the hydrogen compressor. The compression device can further comprise an anti-surge control valve positioned in reverse parallel to the compressor or to each compressor if more than one compressor is foreseen. A head loss control valve is positioned in the return circuit and is adapted to respond to a drop in compressor flow below a threshold value by generating a controlled head loss in the return circuit in order to maintain the compressor in a stable operating condition at a reduced flow, while recycling hydrogen from the delivery side to the suction side of the compressor through the return circuit.

[0017] If the compression device comprises two compressors in parallel, the head loss control valve can be provided anti-parallel to each of the compressors. Both head loss control valves can be controlled to react to a flow drop by partially opening and recirculating flow from the output side of each compressor to the suction side.

[0018] The or each head loss control valve can be adapted to respond to a drop in compressor flow rate by reducing flow to 50% or less, preferably 30% or less, even more preferably 5% or less of the design flow value.

[0019] According to another aspect, disclosed herein is a system for producing hydrogen gas. The system comprises a hydrogen gas production unit powered by a renewable energy source and a hydrogen gas compression device as described above.

[0020] According to yet another aspect, disclosed herein is a method for operating a hydrogen gas compression device comprising: a hydrogen gas compressor having a suction side and an output side; a return circuit having an inlet fluidically coupled to the discharge side of the hydrogen gas compressor and an outlet fluidically coupled to the suction side of the hydrogen gas compressor; an anti-surge control valve; and a head loss control valve along the return circuit. According to the embodiments disclosed herein, the method comprises the steps of:

[0021] outputting a hydrogen gas stream from a hydrogen gas source to the hydrogen gas compression device;

[0022] compressing the hydrogen gas stream in the hydrogen gas compressor; and

[0023] in response to a drop in hydrogen gas flow below a flow threshold, partially closing the head loss control valve and recirculating hydrogen gas from the output side of the hydrogen gas compressor to the suction side of the hydrogen gas compressor through the return circuit and the partially closed head loss control valve; the partially closed head loss control valve generating a concentrated head loss in the return circuit while recirculating hydrogen gas through the return circuit, such that the compressor is maintained in a stable operating state at a reduced flow.

[0024] Further features and embodiments of the compression device, system and method according to the present disclosure are described below and shown in the appended claims. BRIEF DESCRIPTION OF DRAWINGS

[0025] Reference will now be made in brief to the drawings in which:

[0026] Figure 1 A system for producing hydrogen gas according to the present disclosure is shown in a first embodiment of a green hydrogen production system, the system comprising a compression device;

[0027] Figure 2 A system for producing hydrogen gas according to the present disclosure is shown in a first embodiment of a green hydrogen production system, the system comprising a compression device; Figure 1a graph of pressure ratio versus flow rate of the hydrogen compression device of the system of Figure 1 ;

[0028] Figure 3 a graph showing power savings at reduced hydrogen flow rates;

[0029] Figure 4 a system according to the present disclosure in a second embodiment is shown;

[0030] Figure 5 a system according to the present disclosure in a third embodiment is shown;

[0031] Figure 6 a system according to the present disclosure in a fourth embodiment is shown; and

[0032] Figure 7 a system according to the present disclosure in a fourth embodiment is shown. DETAILED DESCRIPTION

[0033] To at least partially overcome the drawbacks of the prior art hydrogen compression devices, a compression device is disclosed herein that includes novel features adapted to operate a hydrogen compressor at reduced flow rates and constant rotational speed, thereby minimizing the power required to run the compressor. In green hydrogen production and compression facilities, the new compression unit allows for reduced facility costs since a simple, constant speed compressor driver can be used. The need to completely shut down the compressor when hydrogen production becomes zero or too low is also avoided. These advantages are achieved by providing a return circuit in reverse parallel to the compressor. A head loss control valve is positioned in the return circuit. When the hydrogen flow rate is equal to or higher than a threshold value defined by the intersection of the compressor's characteristic curve with the anti-surge control line, the head loss control valve is closed, the return circuit is not active, and the compressor operates at design speed in steady state.

[0034] When the hydrogen flow rate from the hydrogen source drops below a minimum threshold value or becomes zero, the compressor continues to rotate at design speed, but part or all of the hydrogen flow is recirculated from the output side to the suction side of the compressor through the return circuit and through the head loss control valve. The partially open head loss control valve generates a head loss in the return circuit. The valve is opened to a certain percentage of its full bore such that the characteristic curve of the return circuit intersects the operating characteristic curve of the compressor at a steady operating point. By reducing the flow rate to a minimum value by partially closing the head control valve, the power absorbed by the motor driving the compressor is minimized. In some embodiments, the head control valve can be closed so as to reach a total flow rate lower than 50% of the design flow rate value, preferably lower than 30%, even more preferably equal to or lower than 5%.

[0035] Thus, stable operation of the hydrogen compressor at small or zero hydrogen flow from the green hydrogen source is achieved, while operating the compressor at constant speed, thereby avoiding expensive variable speed motors, and minimizing power consumption, while avoiding the need to stop the compressor.

[0036] Figure 1 A first embodiment of a hydrogen production system comprising a novel hydrogen compression arrangement according to the present disclosure is shown in the schematic diagram. The hydrogen production system 1 comprises a hydrogen source 3 and a hydrogen compression arrangement 5. The hydrogen source 3 is a green hydrogen source. In some embodiments, the hydrogen source 3 comprises one or more electrolyzers powered by electricity from an electricity distribution grid 7. In Figure 1 In the schematic diagram, a single electrolyzer 9 is shown, but it will be appreciated that the hydrogen source can comprise multiple electrolyzers.

[0037] The electricity can be generated by one or more renewable energy resources, globally indicated at 10. For example, the electricity can be generated by a photovoltaic field, schematically shown at 11, a wind farm, schematically shown at 13, a solar concentrator power plant, a hydroelectric power plant, a tidal power plant, or a combination thereof.

[0038] The hydrogen generated by the electrolyzer 3 can be at ambient pressure or higher, for example if a high-pressure electrolyzer is used. Generally, further compression of the hydrogen from the electrolyzer 9 is required. To this end, the system comprises a hydrogen compression arrangement 5. The hydrogen compression arrangement 5 comprises a hydrogen compressor 17, which is driven in rotation by a mechanical power source 18, typically an electric motor. In advantageous embodiments, the motor 18 is a constant speed electric motor.

[0039] The hydrogen compressor 17 can be a multi-stage compressor. In some embodiments, the hydrogen compressor 17 is a multi-stage centrifugal compressor.

[0040] The compressor 17 comprises a suction side 17.1 fluidically coupled with the hydrogen source 3. The compressor 17 further comprises an output side 17.2 fluidically coupled with a pressurized hydrogen output conduit 19. An intake valve 21 is arranged upstream of the suction side 17.1, and an output valve 23 is arranged downstream of the output side 17.2.

[0041] The hydrogen compression arrangement 5 further comprises a return circuit 25. The return circuit 25 comprises an inlet 25.1 fluidically coupled with the discharge side 17.2 of the compressor 17, and an outlet 25.2 fluidically coupled with the suction side 17.1 of the compressor 17. When the return circuit 25 is open, hydrogen is circulated in the return circuit 25 from the discharge side 17.2 of the compressor 17 to the suction side 17.1 of the compressor 17 in counter-parallel with the compressor 17.

[0042] The return circuit 25 can be used as an anti-surge line. An anti-surge control valve 27 can be positioned along the return circuit 25 and can operate as known in the art. In particular, the anti-surge control valve 27 can be a fast opening valve adapted to fully open in a short time when the operating point of the compressor 17 approaches the surge control line, thus preventing the surge phenomenon to occur.

[0043] In Figure 1 Embodiments, the return circuit 25 further comprises a head loss control valve 29 positioned in the return circuit 25 in parallel to the anti-surge control valve 27. The head loss control valve 29 is adapted to generate a controlled head loss in the return circuit 25 to stabilize the compressor operation at low or zero hydrogen flow rates, as will be described in more detail below.

[0044] The hydrogen compression device further comprises a cooler 31, in Figure 1 Embodiments, the cooler is arranged along the return circuit 25 downstream of the head loss control valve 29 and the anti-surge control valve 27 and upstream of the outlet 25.2 of the return circuit 25.

[0045] Figure 2 A characteristic curve diagram of the compressor 17 is shown. The volumetric flow through the compressor is plotted on the horizontal axis and the pressure ratio is plotted on the vertical axis. The operating curve of the compressor 17 in a normal operating state is shown at CI. SC2 is the surge control line. Stable operation of the compressor requires the operating point to remain to the right of SC2. Since the operating point will move along the increasing curve C2, a flow below Fth at constant rotational speed of the compressor will cause the compressor to become unstable. Typically, when the operating point on curve C2 becomes unstable, the compressor is prevented from operating at a flow to the left of SC2.

[0046] The hydrogen flow that can be obtained from the hydrogen source 3 depends on the availability of electricity on the power grid 7. Since the electricity is generated from renewable resources, the hydrogen flow can drop below Fth or become zero if reduced electricity can be obtained from the renewable resources or no electricity can be obtained therefrom.

[0047] To prevent the compressor from becoming unstable when the hydrogen production is at idle, a common practice according to the prior art is to reduce the rotational speed of the compressor and thus move on a different operating curve that intersects SC2 at a lower flow. However, this approach requires the use of a variable speed motor for the compressor 17, which increases the cost of the system. Moreover, it should be avoided to reduce the speed below 60% of the rated speed to prevent the compressor from operating near the critical speed. Therefore, a further reduction of the hydrogen flow would require stopping the compressor. Repeatedly switching off and restarting the compressor would cause fatigue stresses on the turbomachinery and should therefore be avoided.

[0048] To overcome the drawbacks of the prior art, the hydrogen compression system 5 of the present disclosure uses a head loss control valve 29, possibly in combination with the suction valve 21 or the discharge valve 23 or both, to cause the reduced hydrogen flow to be partially or fully recirculated through the return circuit 25 and introduce a controlled head loss in the return circuit 25 or the main hydrogen circuit, such that the compressor continues to operate at a stable operating point despite the reduced flow.

[0049] More specifically, when green hydrogen production is at idle and the hydrogen flow becomes zero, e.g., because power is not available or insufficient power is available, the suction valve 21 and the discharge valve 23 are closed, the anti-surge control valve 27 is maintained closed, and the head loss control valve 29 is partially opened, such that a reduced hydrogen flow is maintained in the return circuit 25. The head loss control valve 29 introduces a concentrated pressure drop in the return circuit 25, such that the operating point of the compressor 17 is stable even if it is on the left side of the surge control line SC2, i.e., the flow is below Fth. As mentioned, the flow of the partially closed head loss control valve can be equal to or less than 50% of the design flow value, in some embodiments equal to or less than 30%, in other embodiments equal to or less than 5%.

[0050] In Figure 2 particular, the curves C20, C50, and C90 are characteristic curves of the return circuit 25 at variable opening values of the head loss control valve 29. For example, the curve C90 shows the characteristic curve of the return circuit 25 with the head loss control valve 29 opened 90%, the curve C50 shows the characteristic curve of the return circuit 25 with the head loss control valve 29 opened 50%, and the curve C20 shows the characteristic curve with the head loss control valve 29 opened 20%.

[0051] As Figure 2 shown, the characteristic curve is a sharply rising curve. If the head loss control valve 29 is opened 50%, the operating point P50 of the compressor 17 is defined by the intersection of the compressor characteristic curve C2 with the characteristic curve C50 of the return circuit 25, i.e., the external circuit into which the compressor 17 is inserted. Since the change in flow will be balanced by the change in head loss introduced in the return circuit 25 by the partially closed head loss control valve 29, the operating point P50 is a stable operating point of the compressor 17. Specifically, if the flow through the compressor 17 drops, the external return circuit 25 will react with a reduction in head loss, which offsets the drop in flow and causes the compressor 17 to return to the operating point P50, thus becoming stable.

[0052] Thus, due to the partial closing of the head loss control valve 29, the increased head loss in the closed return circuit 25 by the head loss control valve 29 stabilizes the operating point of the compressor 17 at a reduced flow rate value without the need to modify the rotational speed of the compressor 17. While multiple stable operating points can be identified along the curve C2 by keeping the head loss control valve 29 in a partially open state, in some embodiments, the head loss control valve 29 is maintained in the most localized (partially closed) state in which the compressor operation is stable. Thus, the recirculation flow rate, and therefore the related power required for recirculation, is minimized. In Figure 2 In the exemplary embodiment shown, for example, the operating point P20 is preferred over the operating point P50 because the compressor is operating in a stable state in both P20 and P50, but the power absorbed by the compressor is lower in point P20 because the flow rate handled by the compressor 17 is smaller.

[0053] The benefits of this approach are twofold. On the one hand, the compressor 17 can operate at a constant speed in the region to the left of SC2 even in the condition in which the H2 from the hydrogen source 3 is at zero flow rate. This avoids the need for a variable speed motor and a variable frequency drive (VFD). VFDs are expensive components and can be prone to wear, failure and require maintenance, thus leading to reduced availability of the system.

[0054] Secondly, by reducing the flow rate handled by the compressor 17, it is possible to reduce the power absorbed by the compressor 17. The electrical power required to drive the compressor in the hydrogen idle state is in fact useless from a production point of view and is only intended to avoid shutdowns of the compressor 17, since repeated shutdowns and restarts of the compressor over time can lead to fatigue failures of the turbomachinery.

[0055] Figure 3 The power savings that can be achieved by reducing the flow rate with controlled head loss in the return circuit 25 are shown in the graph in FIG. 3. The first curve A illustrates the power savings in percentage units on the vertical axis as a function of the flow rate percentage plotted on the horizontal axis. The second curve B illustrates the power savings as a function of the speed reduction according to the current state-of-the-art approach, in which the compressor speed is reduced to allow the compressor to operate at a reduced flow rate. In Figure 3 The 100% flow rate plotted on the rightmost point of the horizontal axis in the graph of FIG. 3 is the minimum flow rate that the compressor 17 can handle without entering the unstable operating range. In other words, Figure 3 The 100% flow rate in the graph of FIG. 3 is Figure 2 the flow rate Fth in FIG. 2.

[0056] Figure 3The graph shows that operating the compressor at 8% of flow with the head loss control valve 29 in a partially closed condition will result in a power saving corresponding to that which would be achieved in a standard compression system by running the compressor at 50% of rated speed. As mentioned, it is generally avoided to derate below 60% of rated speed to prevent turbine problems due to vibrations close to the first critical speed. Therefore, the system of the present invention allows for a higher power saving if compared to the current state of the art of variable compressor speed.

[0057] In summary, by rotating the compressor 17 at constant speed and compensating for the lack of hydrogen flow from the hydrogen source 3 by recirculating the flow through the localized head loss control valve 29, the compression system is allowed to operate at very low flow in steady state, allowing for an improved power saving with a simpler and cheaper constant speed motor 18 if compared to the current system using derating.

[0058] When the hydrogen flow is recirculated through the return circuit, the cooler 31 removes the heat generated by compression to prevent the recirculated hydrogen from overheating.

[0059] In some operating conditions, while the hydrogen production can not be completely interrupted, the produced flow can be below a threshold Fth at which the operation of the compressor 17 at nominal rotational speed becomes unstable. This situation can be solved in different ways, all based on the idea of controlling the head loss of the external circuit to which the compressor 17 is connected, i.e. by modifying the characteristic curve of the circuit in which the compressor 17 is located so that the operating point of the compressor 17 is defined by the intersection of the characteristic curve C2 of the compressor 17 with the steep characteristic curve of the external circuit.

[0060] In one embodiment, when the hydrogen flow drops below Fth, the suction valve 21 can be partially closed, the head loss control valve 29 is maintained fully closed, and the output valve 23 is maintained fully open. Due to the concentrated head loss in the suction valve 21, the head loss in the external circuit to which the compressor 17 is connected increases, and the characteristic curve of the circuit increases sharply as a function of flow. The operating point of the compressor 17 becomes stable at low flow without the need to derate.

[0061] According to another embodiment, the suction valve 21 can be maintained fully open, the head loss control valve 29 can be maintained fully closed, and the head loss in the external circuit can be adjusted by reducing the aperture of the output valve 21. The characteristic curve of the circuit becomes sharply increasing, and its intersection with the curve C2 again defines a stable operating point at reduced flow without having to change the rotational speed of the compressor 17.

[0062] According to yet another embodiment, the suction valve 21 can be maintained fully open, while the head loss control valve 29 and the output valve 21 are partially closed. The head loss downstream of the compressor 17 is increased and the characteristic curve of the circuit to which the compressor 17 is connected becomes steep, so that the operating point of the compressor on the characteristic curve C2 becomes stable as described above.

[0063] A combination of the above methods can be used.

[0064] The valves 21, 23, 29 can be controlled so as to modify the degree of localization thereof as a function of the hydrogen flow rate from the hydrogen source 3.

[0065] With continued reference to Figure 1 , Figure 2 and Figure 3 , Figure 4 a schematic view illustrating another embodiment of a system according to the present disclosure is exemplified. Same reference numerals represent same elements shown in Figure 1 , will not be described in detail again.

[0066] Figure 1 The main difference between the embodiment of Figure 4 and the embodiment of Figure 4 is that, in , the return circuit 25 comprises the anti-surge control valve 27 and the head loss control valve 29 arranged in series, instead of in parallel. In normal operating conditions, the anti-surge control valve 27 is fully closed and the head loss control valve 29 is fully open, since the return circuit comprises a portion of the output line extending from the output side of the compressor 17 and the valve 23, the head loss control valve 29 being positioned in said portion of the output line.

[0067] When the compressor 17 approaches the surge control line SC2 for any reason, for example because of a sudden drop in flow rate, the anti-surge control valve 27 can be fully open and the head loss control valve 29 can be partially closed. The output valve 23 can be partially or fully closed. This avoids the occurrence of the surge phenomenon and modifies the characteristic curve of the circuit in which the hydrogen compressor 17 is placed, i.e. a concentrated head loss is introduced at the head loss control valve 29.

[0068] Figures 1 to 3 When the hydrogen flow rate drops or stops completely, for example because the hydrogen production is at idle, the head loss control valve 29 can be set in an intermediate partially open condition, so as to introduce a concentrated head loss in the return circuit 25 as described in connection with Figures 1 to 3 , and the compressor 17 can continue to operate at constant speed and reduced flow rate. Unlike the embodiment of Figure 4 , since the anti-surge control valve 27 and the head loss control valve 29 in are in series, instead of in parallel, the anti-surge control valve 27 is maintained fully open.

[0069] As mentioned above, in idle state or at low hydrogen flow from the hydrogen source, compressor shutdown is avoided, thereby preventing fatigue failure of the compressor and significantly reducing the power required to operate the compressor (see Figure 3 ).

[0070] With continued reference to Figure 1 , Figure 2 , Figure 3 and Figure 4 , another embodiment of the system according to the present disclosure is shown in Figure 5 . The same reference numerals denote the same elements shown in Figure 1 , which will not be described in detail again.

[0071] The main difference with respect to the embodiment of Figure 1 is that in Figure 5 the head loss control valve 29 and the anti-surge control valve 27 are positioned along the return circuit 25 downstream of the cooler 31, so that the recirculated hydrogen is cooled before entering the valve arrangement. An alternative position of the cooler 31 along the hydrogen output line 19 is shown in dashed line.

[0072] With continued reference to Figures 1 to 5 , Figure 6 a further embodiment is shown. This embodiment differs from the embodiment of Figure 4 in that the cooler 31 is arranged upstream of the anti-surge control valve 27. Another position of the cooler 31 is shown in dashed line, between the head loss control valve 29 and the output valve 23.

[0073] In the embodiments of Figure 4 and Figure 6 , where the anti-surge control valve 27 and the head loss control valve 29 are positioned in series along the return circuit 25, the return circuit has an inlet 25.1 between the output side 17.2 of the compressor and the head loss control valve 29. This means that, when hydrogen is partially or fully recirculated, the circuit section between the output side 17.2 and the output valve 23 becomes part of the return circuit 25. In normal operating conditions, when the head loss control valve 29 is fully open and the anti-surge control valve 27 is fully closed, the hydrogen flowing through the circuit section between the output side 17.2 of the compressor 17 and the output valve 23 is fed to the output line 19 instead of being recirculated, and thus the entire circuit section between the output side 17.2 of the compressor 17 and the output valve 23 forms part of the output line and does not operate as return circuit.

[0074] In the above embodiments, the operating state of the compressor and associated valve arrangements can be controlled by a control unit (not shown). The control unit may, for example, detect the flow rate, pressure ratio and rotational speed of the compressor, etc. The control unit can be functionally coupled to the compressor, the anti-surge control valve 27 and the head loss control valve 29. The control unit can be adapted to control the anti-surge control valve 27 and the head loss control valve 29 to operate as described above in response to a surge condition or in response to a flow rate falling to equal or below a flow rate threshold value, e.g. set by a surge control line.

[0075] In other embodiments, the system disclosed herein can comprise more than one compressor. Figure 7 Embodiments are exemplified with a compression arrangement comprising two serially connected compressors. In Figure 7 the same reference numerals are used to designate the same or equivalent parts or components as in the previous figures, which will not be described in detail again. Figures 1 to 6

[0076] In Figure 7 embodiments, the compression arrangement 5 comprises a first compressor 17 having a suction side 17.1 and an output side 17.2. The first compressor is fluidly coupled to a suction side 18.1 of a second compressor 18. Reference 18.2 indicates an output side of the second compressor 18.

[0077] Reference 23 indicates an output valve of the first compressor 17, while reference 24 indicates an output valve of the second compressor 18. A first cooler 31 is located between the output side 17.2 of the first compressor 17 and the suction side 18.1 of the second compressor 18, while a second cooler 32 is located between the output side 18.2 of the second compressor 18 and the second output valve 24.

[0078] A first branch 25 or part of the return circuit is arranged in reverse parallel with the first compressor 17. The first branch 25 of the return circuit comprises an inlet 25.1 fluidly coupled to the discharge side 17.2 of the first compressor 17, e.g. between the cooler 31 and the output valve 23, and an outlet 25.2 fluidly coupled to the suction side 17.1 of the first compressor 17 downstream of the suction valve 21. The head loss control valve 29 is positioned between the inlet and the outlet of the branch 25 of the return circuit.

[0079] A second branch or part 26 of the return circuit is arranged in reverse parallel with the second compressor 18. The second branch 26 of the return circuit comprises an inlet 26.1 fluidly coupled to the discharge side 18.2 of the second compressor 18 between the cooler 32 and the output valve 24, and an outlet 26.2 fluidly coupled to the suction side 18.1 of the second compressor 18 downstream of the valve 23. The head loss control valve 30 is positioned between the inlet and the outlet of the second return circuit 26.

[0080] ​In this embodiment, a single anti-surge control valve is positioned along the common branch 28 of the return circuit, in anti-parallel with the first and second compressors 17, 18. The common branch 28 of the return circuit: coincides with the inlet of the second return circuit 26, inlet 26.1; and coincides with the outlet of the first return circuit 25, outlet 25.1.

[0081] In fact, in this embodiment, the return circuit thus comprises the branch 28, which is anti-parallel to the first and second compressors 17, 18 arranged in series and which contains the single anti-surge control valve 27. The return circuit also comprises the branch 25, which is anti-parallel to the first compressor 17 and which comprises the first head loss control valve 29. Finally, the return circuit also comprises the branch 26, which is anti-parallel to the second compressor 18 and which comprises the second head loss control valve 29.

[0082] During normal operation, the anti-surge control valve 27 and the two head loss control valves 29, 30 are closed.

[0083] The anti-surge control valve 27 protects the two compressors 17, 18 from surging, and opens if the operating point approaches the anti-surge line, if necessary.

[0084] When the hydrogen flow drops below a threshold, or if it is not possible to obtain hydrogen from the hydrogen source 3, the two head loss control valves 29 and 30 can be partially opened to provide a return circuit for hydrogen recirculation through the two compressors 17, 18 at low flow in a stable operating condition, as described above with respect to the embodiment of Figures 1 to 6 If no flow originates from the hydrogen source 3, the valves 21, 23 and 24 can be closed, and the head loss control valves 29, 30 can be partially closed, so that the two compressors continue to absorb operation at low flow and low power.

[0085] Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. Those skilled in the art will appreciate that various changes, omissions and additions can be made to the specifics set out above without departing from the scope of the present application as defined by the following claims.

Claims

1. A hydrogen compression device, comprising: A hydrogen compressor, the hydrogen compressor including an intake side and an output side; A return loop having an inlet fluidly coupled to the discharge side of the hydrogen compressor and an outlet fluidly coupled to the suction side of the hydrogen compressor; and Anti-surge control valve; Its features A head loss control valve is positioned in the return loop and adapted to respond to a decrease in compressor flow rate below a threshold by generating a controlled head loss in the return loop, so as to maintain the compressor in a stable operating state at a reduced flow rate, while recirculating hydrogen from the output side of the compressor to the suction side through the return loop.

2. The apparatus according to claim 1, wherein the anti-surge control valve and the pressure head loss control valve are arranged in parallel.

3. The apparatus of claim 2, wherein the anti-surge control valve is controlled such that it closes when the compressor is maintained in a stable operating state with a reduced flow rate.

4. The device according to claim 1, wherein the anti-surge control valve and the pressure head loss control valve are connected in series.

5. The apparatus of claim 4, wherein the anti-surge control valve is controlled such that the anti-surge control valve is fully open when the compressor is maintained in a stable operating state with a reduced flow rate.

6. The apparatus according to any one of the preceding claims, wherein the hydrogen compressor comprises a multi-stage compressor.

7. The apparatus according to any one of the preceding claims, wherein the hydrogen compressor comprises a power compressor.

8. The apparatus according to any one of the preceding claims, wherein the hydrogen compressor comprises a multi-stage centrifugal compressor.

9. The apparatus according to any one of the preceding claims further includes an intake valve upstream of the intake side of the hydrogen compressor and an output valve downstream of the output side of the hydrogen compressor.

10. The apparatus of claim 9, wherein the head loss control valve is positioned between the output valve and the suction side of the compressor.

11. The apparatus of claim 9 or 10, wherein at least one of the intake valve and the output valve is controlled to regulate head loss in the circuit to which the hydrogen compressor is fluidly coupled.

12. The apparatus according to any one of the preceding claims, wherein the head loss control valve is adapted to respond to a decrease in flow rate by reducing the flow rate to 50% or less, preferably 30% or less, or even more preferably 5% or less of the design flow rate value.

13. The apparatus according to any one of the preceding claims, wherein the hydrogen compressor comprises a first hydrogen compressor and a second hydrogen compressor connected in series; wherein the anti-surge valve is disposed in the return loop between the output side of the second compressor and the suction side of the first compressor; wherein the head loss control valve is positioned in the return loop between the output side of the first compressor and the suction side of the first compressor; and wherein the second head loss control valve is positioned in the return loop between the output side of the second compressor and the suction side of the second compressor.

14. A system for producing hydrogen gas, the system comprising: A hydrogen production unit, wherein the hydrogen production unit is powered by renewable energy; Hydrogen compression apparatus according to one or more of the preceding claims.

15. The system of claim 14, wherein the hydrogen production unit is an electrolysis production unit powered by electricity generated from at least one renewable energy source.

16. A method for operating a hydrogen compression device, the hydrogen compression device comprising: A hydrogen compressor having an intake side and an output side; A return loop having an inlet fluidly coupled to the discharge side of the hydrogen compressor and an outlet fluidly coupled to the suction side of the hydrogen compressor; an anti-surge control valve; and a head loss control valve along the return loop; the method includes the following steps: A stream of hydrogen gas is output from a hydrogen source to the hydrogen compression device; The hydrogen stream is compressed in the hydrogen compressor; as well as In response to a decrease in hydrogen flow rate below a flow threshold, the head loss control valve is partially closed, and hydrogen is recirculated from the output side of the hydrogen compressor to the suction side of the hydrogen compressor via the return loop and the partially closed head loss control valve. The partially closed head loss control valve generates a concentrated head loss in the return loop while recirculating hydrogen through the return loop, thereby maintaining the compressor in a stable operating state with the reduced flow rate.

17. The method of claim 16, wherein the anti-surge control valve and the head loss control valve are positioned in parallel in the return loop; and wherein the step of recirculating hydrogen includes the step of recirculating hydrogen through the partially closed head loss control valve while the anti-surge control valve is kept closed.

18. The method of claim 16, wherein the anti-surge control valve and the head loss control valve are positioned in series in the return loop; and wherein the step of recirculating hydrogen includes the step of recirculating hydrogen through the partially closed head loss control valve and through the anti-surge control valve which is maintained in an open state.

19. The method of claim 16, wherein the hydrogen compressor comprises a first hydrogen compressor and a second hydrogen compressor connected in series; wherein the anti-surge valve is disposed in the return loop between the output side of the second compressor and the suction side of the first compressor; wherein the head loss control valve is positioned in the return loop between the output side of the first compressor and the suction side of the first compressor; wherein the second head loss control valve is positioned in the return loop between the output side of the second compressor and the suction side of the second compressor; and wherein the step of recirculating hydrogen comprises the step of recirculating hydrogen through a partially closed head loss control valve and a partially closed second head loss control valve while the anti-surge control valve is kept closed.

20. The method according to any one of claims 16 to 19, wherein the hydrogen compressor comprises a multi-stage compressor.

21. The method according to any one of claims 16 to 20, further comprising the step of responding to the decrease in hydrogen flow rate: Close the upstream suction valve of the hydrogen compressor and the downstream output valve of the hydrogen compressor, wherein the inlet of the return loop is located between the output side of the compressor and the output valve, and the outlet of the return loop is located between the suction valve and the suction side of the compressor; and Hydrogen gas is circulated through the return loop at a reduced flow rate.

22. The method of claim 21, wherein the head loss control valve is positioned between the output side of the compressor and the output valve downstream of the compressor.

23. The method according to any one of claims 16 to 22, wherein the step of partially closing the head loss control valve comprises reducing the flow rate of the head loss control valve to 50% or less, preferably 30% or less, or even more preferably 5% or less of the design flow rate value.

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