Methods and systems for efficient hydrogen compression

Abstract

The hydrogen compression system comprises a gaseous hydrogen source at a first pressure and a mixing unit adapted to mix hydrogen with an additional gaseous component at the first pressure, the additional gaseous component having an average molecular weight higher than that of hydrogen. A compression unit is adapted to compress a gas mixture comprising hydrogen and the additional gaseous component to a second pressure. A separation unit is fluidly coupled to the compression unit and is adapted to separate compressed hydrogen from the compressed additional gaseous component. An energy recovery device is further provided to recover energy from the expansion of the compressed additional gaseous component from the second pressure to a third pressure. A method for efficient hydrogen compression is also disclosed.

Description

Technical Field

[0001] The present disclosure relates to hydrogen processing. Embodiments disclosed herein relate particularly to systems and methods for improving the efficiency of hydrogen compression.

Background Art

[0002] Hydrogen is used in many industrial applications. In recent years, there has been growing interest in hydrogen, particularly considering its potential use as a fuel instead of natural gas in thermodynamic cycles and as a fuel in fuel cells.

[0003] In many applications, it is necessary to compress hydrogen to a high pressure value of approximately 200 bar or more. In fact, handling hydrogen at room pressure is not convenient because of the very low molecular weight of this gas. Particularly for transport purposes, high pressure values must be achieved in order to increase the specific gravity of the gas and thus reduce its volumetric flow rate.

[0004] However, the compression of low molecular weight gases such as hydrogen is technically difficult. Reaching a pressure value of up to 200 bar in a gas with a low molecular weight requires a large amount of power and has conventionally been achieved by reciprocating compressors. These latter are characterized by a relatively low flow rate and are thus not convenient for handling large gas flows.

[0005] A large compression capacity requires the use of dynamic compressors, particularly centrifugal compressors, which have a large diameter impeller, a high rotational speed leading to a tip speed, and a large number of impeller stages arranged in series. These requirements make hydrogen dynamic compressors expensive and difficult to handle.

[0006] In an attempt to facilitate the compression of hydrogen, it has been proposed to mix hydrogen with an additional gaseous component having a higher molecular weight than hydrogen. The resulting gas mixture has an average molecular weight higher than that of hydrogen and is thus easier to compress even with a smaller centrifugal compressor operating at a lower rotational speed. Next, the additional gaseous component is separated from the compressed hydrogen. A system for enhancing hydrogen compression based on the use of a heavier gaseous component mixed into the hydrogen stream is disclosed in European Patent No. 3789616.

[0007] The compression of the heavier gas mixture and the subsequent separation of the gaseous components require process complexity, which may lead to a decrease in the efficiency of the overall result. Therefore, there remains a need to optimize a hydrogen compression system that provides better performance than conventional devices. SUMMARY OF THE INVENTION

[0008] To improve the efficiency of hydrogen compression, a hydrogen compression system is disclosed herein, the hydrogen compression system including a mixing unit adapted to mix hydrogen and an additional gaseous component at a first pressure, the additional gaseous component having an average molecular weight higher than that of hydrogen. The system further includes a compression unit adapted to compress a gas mixture including hydrogen and the additional gaseous component to a second pressure. A separation unit fluidly coupled to the compression unit is adapted to separate compressed hydrogen from the compressed additional gaseous component. An energy recovery device is further provided that includes an expansion unit fluidly coupled to the separation unit and adapted to depressurize the compressed additional gaseous component from the second pressure to a third pressure lower than the second pressure. The energy recovery device is adapted to recover energy from the expansion of the compressed additional gaseous component from the second pressure to the third pressure.

[0009] The recovered energy can be in the form of thermal energy or mechanical energy. The mechanical energy can be converted to electrical energy or used as is to drive the compressor unit.

[0010] Thermal energy can be recovered in the form of a cooled or chilled fluid and can provide cooling capacity to processes external to the compression system and / or processes internal to the compression system. For example, an additional gaseous component recovered by separation from a mixture of hydrogen and an additional gaseous component and cooled by expansion can be used to remove heat in an intercooler of a compression unit to enhance compression efficiency. For example, when an ultra-low temperature separation process is used, alternatively or in combination, an additional gaseous component expanded at low temperature can be used to assist the separation process in a separation unit. Utilization of the cooling capacity of the expanded additional gaseous component in a heat exchanger external to the hydrogen compression system can also be envisioned as an alternative or additional way to recover energy from the expansion of the additional gaseous component.

[0011] Further features of the system are outlined below and defined in the appended claims.

[0012] According to a further aspect, a method of compressing hydrogen is disclosed herein, the method comprising: mixing gaseous hydrogen and an additional gaseous component at a first pressure to form a gaseous mixture, wherein the additional gaseous component has a higher average molecular weight than hydrogen; compressing the gaseous mixture in a compression unit at a second pressure higher than the first pressure; separating the compressed hydrogen and the compressed additional gaseous component from each other; expanding the compressed additional gaseous component at a third pressure lower than the second pressure to recover energy from the expansion of the compressed additional gaseous component.

[0013] Further embodiments and advantageous features of the method according to the present disclosure are outlined below and described in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Reference is now made briefly to the accompanying drawings.

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Mode for Carrying Out the Invention

[0015] FIG. 1 shows a schematic diagram of a hydrogen compression system 1. In this embodiment, the hydrogen compression system 1 includes a gaseous hydrogen source 3. As an example, the hydrogen source 3 in FIG. 1 includes a green hydrogen production unit, and hydrogen is produced using energy from a renewable energy source. In the schematic diagram of FIG. 1, the gaseous hydrogen source 3 includes an electrolyzer 5, and the electrolyzer 5 uses electrical energy generated by a photovoltaic power field 7, a wind power plant, a hydro turbine, a combination thereof, or any other energy generator that uses energy from a renewable energy source to produce hydrogen and oxygen by electrolysis.

[0016] Actually, in other embodiments, different gaseous hydrogen sources can be used, for example, by using steam reforming of natural gas or other light hydrocarbons, coal gasification, biomass gasification, methane pyrolysis, etc.

[0017] System 1 further includes a mixing unit 9, where the gaseous hydrogen delivered by the gaseous hydrogen source 3 is mixed with an additional gaseous component. The additional gaseous component can be carbon dioxide (CO2). The additional gaseous component flows into the mixing unit 9 from a delivery line 11 that can be part of a closed circuit, as described in more detail below.

[0018] In the following description, carbon dioxide is often referred to as the additional gaseous component (also called the "hydrogen dopant"), but more generally, in some embodiments, the additional gaseous component can be any gas or gas mixture having an average molecular weight sufficiently higher than that of hydrogen. In some embodiments, the hydrogen compression system is combined with a carbon dioxide capture system or any other CO2 generation process, in which case the additional gaseous component is (at least mainly) carbon dioxide.

[0019] However, in other embodiments, particularly when the system includes a closed circuit for the additional gaseous component, a gaseous component different from carbon dioxide can be used. For example, the additional gaseous component can include hydrocarbons or mixtures of hydrocarbons (CxHy), optionally in combination with carbon dioxide. In some embodiments, a mixture of carbon dioxide and propane can be used. In some embodiments, a fluid commonly used in a refrigerant circuit can be used as the additional gaseous component to be mixed with hydrogen. For example, a mixed refrigerant can be used as the dopant added to the hydrogen stream.

[0020] The average molecular weight (Mw) of the additional gaseous component forming the hydrogen dopant can depend on the chemical nature of the component. For example, for natural gas containing hydrocarbons (CxHy), an average of 16 - 20 may be suitable, but in some cases, when using a refrigerant fluid in combination with carbon dioxide, molecular weights of 30 - 40 and above 40 can be selected.

[0021] The proportion of the additional gas component in the mixture delivered from the mixing unit 9 can vary, for example, from 30 wt% to 70 wt%, depending on the nature and average molecular weight (Mw) of the additional gas component. Typically, when the hydrogen dopant is pure carbon dioxide, a proportion in the range of 30% to 50% thereof may be appropriate. A significant reduction in the power required to compress hydrogen can already be achieved at a carbon dioxide proportion of 30 wt%.

[0022] The mixing unit 9 is fluidly coupled to the compression unit 13 via line 12. The gas mixture in line 12 has a first pressure P1. When the hydrogen source 3 provides hydrogen at ambient pressure, P1 is about 1 bar. However, in some embodiments, the hydrogen source 3 may deliver hydrogen at a higher pressure, for example, approximately 20 bar or more. This can be the case, for example, when the electrolyzer is a high-pressure electrolyzer.

[0023] In the schematic diagram of FIG. 1, the compression unit 13 is shown as a single compressor 15 and driver 17, for example an electric motor. In actual embodiments, the compression unit 13 can include a plurality of sequentially arranged compressors forming one or more compressor trains that can be driven by a single driver or one or more drivers.

[0024] In some embodiments, the compression unit 13 includes a centrifugal compressor. Preferably, the compression unit 13 consists of one or more centrifugal compressors arranged in series. In some embodiments not shown, a series of centrifugal compressors and reciprocating compressors can be used, if necessary or preferably.

[0025] The gas mixture delivered on the discharge side of the compression unit 13 is at a pressure P2 that is higher than P1. In some embodiments, the pressure P2 can be approximately 200 bar or more, for example 300 bar or more.

[0026] The delivery side of the compression unit 13 is fluidly coupled to the separation unit 21 via line 19, and the separation unit 21 is adapted to separate hydrogen from additional gas components. The stream of compressed hydrogen separated from the additional gas components is the available product delivered through the compressed hydrogen delivery line 23, while the stream of compressed additional gas components flows through the additional gas component outlet line 25.

[0027] The separation unit 21 can include any separation device adapted to separate hydrogen from additional gas components. The separation technique can be selected from those available in the art based on the chemical nature of the additional gas components, its proportion in the gas mixture, the pressure of the gas mixture delivered by the compression unit 13, the required flow rate, and other technical considerations.

[0028] Exemplary embodiments of possible separation techniques on which the separation unit 21 can be based include, but are not limited to, pressure swing absorption, membrane separation, electrochemical hydrogen separation, cryogenic separation, or combinations thereof. The power absorbed by the operation of the separation unit 21 is schematically shown as Psep in the schematic of FIG. 1 and can be provided by any suitable power source.

[0029] The system 1 further includes an energy recovery device 27. As will become apparent from the following description, the energy recovery device 27 can include means for converting the pressure energy from the compressed additional gas components and generating mechanical energy and possibly electrical energy therewith. However, any device adapted to provide an energy contribution to the system 1 using the stream of compressed additional gas components delivered by the separation unit 21 is understood herein by the energy recovery device 27. For example, the additional gas components can be used to provide cooling capacity by its expansion and are adapted to increase the overall energy efficiency of the system 1.

[0030] The energy recovery device 27 includes an expansion device 28. In some embodiments, the expansion device 28 can include a Joule-Thomson valve or any other static expansion device to generate a flow of expanded cryogenic additional gas components that can be used to provide cooling capacity. In a preferred embodiment, the expansion device 28 includes one or more expanders 29 adapted to convert the pressure energy of the additional gas components into mechanical power available on the shaft 31, such as a turbo expander, for example, a radial turbo expander. In the embodiment of FIG. 1, the shaft 31 is drivingly coupled to a generator 33 adapted to convert mechanical power into electrical power, and this electrical power can be distributed via a power distribution network not shown in FIG. 1 to electrical users including, for example, the driver 17 of the compression unit 13.

[0031] In the exemplary embodiment of FIG. 1, the delivery side of the expander 29 is fluidly coupled to the mixing unit 9 via line 11. The pressure of the additional gas component in line 11 can be P3. In the exemplary embodiment of FIG. 1, P3 = P1, which can be, for example, 1 bar or more, for example, 1 bar to 30 bar, depending on the pressure at which hydrogen is made available from the hydrogen source 3.

[0032] The mixing unit 9, the compression unit 13, the separation unit 21, and the expander 29 form a closed circuit, and the additional gas component circulates, is periodically compressed after mixing with hydrogen, separated from hydrogen, and expanded.

[0033] Continuing to refer to FIG. 1, a further embodiment of the hydrogen compression system 1 according to the present disclosure is shown in FIG. The same reference numerals as those used in FIG. 1 are used to designate the same or equivalent parts in FIG. 2, and they will not be described in detail again.

[0034] The embodiment of FIG. 2 mainly differs from the embodiment of FIG. 1 in that the mechanical power recovered from the expansion of the additional gas components after separation in the separation unit 21 is directly used to drive the compression unit 13. This is pictorially represented by a mechanical connection via a shaft 31 between the expander 29 and the compressor 15. In some embodiments, an electromechanical machine 41 electrically connected to the power grid 45 is also arranged along the shaft line to provide additional mechanical power for driving the compressor 15 when the power recovered from the expansion of the additional gas components in the expander 29 is not sufficient to drive the compressor 15. The surplus power from the expander 29 can be converted into electrical power by the electromechanical machine 41.

[0035] Continuing to refer to FIGS. 1 and 2, FIG. 3 shows a further embodiment of the hydrogen compression system 1 of the present disclosure. The same reference numerals used in FIGS. 1 and 2 designate the same or equivalent parts in FIG. 3, and they will not be described in detail again.

[0036] In the schematic view of FIG. 3, the compression unit 13 is shown as including a first compressor or compressor stage 15.1 and a second compressor or compressor stage 15.2 arranged in series. For the sake of brevity, in the following description, only the first compressor and the second compressor will be referred to. The delivery side of the first compressor 15.1 is fluidly coupled to the suction side of the second compressor 15.2. An intercooler 15.3 is arranged between the delivery side of the first compressor 15.1 and the suction side of the second compressor 15.2. The gas mixture containing hydrogen and additional gas components is partially compressed by the first compressor 15.1 and cooled before being further compressed by the second compressor 15.2. The number of compressors arranged in series can be more than two, and each intercooler can be arranged between some or all of the pairs of continuously arranged compressors.

[0037] In some embodiments, as shown in FIG. 3, the partially compressed gas mixture containing hydrogen and additional gas components is cooled by heat exchange with a side stream of the expanded additional gas components branched from the discharge side of expander 29. For this purpose, branch line 43 connects the discharge side of expander 29 to the low temperature side of intermediate cooler 15.3. After flowing through intermediate cooler 15.3, the branched stream of the expanded additional gas components flows back to mixing unit 9.

[0038] Optionally, the entire flow rate of the expanded additional gas components delivered by expander 29 can be used as a cooling medium in intermediate cooler 15.3 or any additional plant or process requiring cooling capacity.

[0039] Thus, in the embodiment of FIG. 3, the expanding additional gas components separated from the compressed hydrogen in separation unit 21 are used to increase the energy efficiency of hydrogen compression system 1 in two ways. On the one hand, the pressure energy of the compressed additional gas components is converted into mechanical power and then into electrical power via expander 29 and generator 33. On the other hand, the cold expanded additional gas components provide cooling capacity to remove heat from the partially compressed gas mixture, thus improving the efficiency of compression unit 13 and reducing the power required to compress the gas mixture from pressure P1 to pressure P2.

[0040] Continuing to refer to FIGS. 1, 2, and 3, a further embodiment of hydrogen compression system 1 according to the present disclosure is shown in FIG. 4. The same reference numerals used in FIGS. 1, 2, and 3 designate the same or equivalent parts in FIG. 4, and they will not be described in detail again.

[0041] The hydrogen compression system 1 of FIG. 4, similar to the embodiment of FIG. 3, includes, by way of example, an intercooled compression unit 13 including a first compressor 15.1, a second compressor 15.2, and an intercooler 15.3. Further, the expander 29 of FIG. 4 is drivingly coupled to the compression unit 13 via a shaft 31 such that the mechanical power generated by the expansion of additional gas components within the expander 29 is directly used to drive the compression unit 13. An electromechanical machine 41 electrically connected to the power grid can be disposed on the same shaft line to provide additional power for driving the compression unit or to convert excess mechanical power from the expander 29 into electrical power.

[0042] In the embodiments disclosed so far, the additional gas components circulate within a closed loop and undergo periodic thermodynamic conversions. In practice, the additional gas components are added to hydrogen at pressure P1 in the mixing unit 9, the gas mixture is compressed at pressure P2 in the compression unit 13, the compressed additional gas components are separated from the compressed hydrogen in the separation unit 21, the additional gas components are expanded back to pressure P1 in the expansion device 28, and finally returned to the mixing unit 9 in a closed loop.

[0043] However, this is not the only possible layout for the hydrogen compression system 1.

[0044] In some embodiments, the additional gas components can be processed through an open circuit or through such a closed circuit that does not directly connect the expansion device 28 to the mixing unit 9.

[0045] For example, a continuous flow of additional gas components is added to hydrogen, compressed together with hydrogen, and separated from hydrogen. The separated and compressed additional gas components are at least partially expanded for energy recovery purposes and then removed as a by-product from the hydrogen compression system 1.

[0046] An embodiment including an open circuit for an additional gas component is shown in FIG. 5. In this embodiment, the additional gas component is carbon dioxide. Carbon dioxide can be delivered by a carbon dioxide capture system, which can be provided to treat flue gas from an industrial process or a gas turbine and remove carbon dioxide from the flue gas before discharging the flue gas into the atmosphere. More generally, carbon dioxide can be derived from any industrial process that generates carbon dioxide.

[0047] More specifically, referring to the embodiment of FIG. 5, the hydrogen compression system 1 includes a hydrogen source 3 and a mixing unit 9 where the gaseous hydrogen delivered by the hydrogen source 3 is mixed with an additional gas component. In the embodiment of FIG. 5, the additional gas component is carbon dioxide (CO2) delivered by a carbon capture system (abbreviated as CCS) labeled 51. The carbon capture system 51 can be an amine-based carbon dioxide reduction system, a mixed salt process, a cooled ammonia process, or any other process adapted to remove carbon dioxide from flue gas generated by an industrial plant 53.

[0048] As a non-limiting example, in FIG. 5, the plant 53 is a power generation plant including a gas turbine engine 55 driven by fossil fuel. The gas turbine engine 55 can be drivingly coupled to a generator 57 to convert mechanical power into electrical power. The generator 57 is connected to a power distribution network 45. In other embodiments, the gas turbine engine 55 can be used as a driver for another machine, such as a compressor train or any other load.

[0049] The flue gas from the gas turbine engine 55 is treated in a gas purification facility 59 and then treated in a carbon capture system 51, where the carbon dioxide contained in the flue gas is captured and the flue gas with less carbon dioxide is discharged into the atmosphere (chimney 61).

[0050] The carbon dioxide capture system 51 is fluidly coupled to the mixing unit 9 through line 11 such that carbon dioxide from the carbon capture system 51 is mixed with hydrogen from the hydrogen source 3. In some embodiments, only a portion of the carbon dioxide delivered by the carbon dioxide capture system 51 (or other CO2-producing industrial process) will be delivered to the mixing unit 9.

[0051] The mixing unit 9 is then fluidly coupled to the compression unit 13 through line 12. The gas mixture in line 12 has a first pressure P1, and the compression unit 13 compresses the gas mixture at a second pressure P2. In some embodiments, the pressure P2 can be approximately 200 bar or more, for example, 300 bar or more.

[0052] In the schematic of FIG. 5, the compression unit 13 includes a compressor train comprising a first compressor 15.1 and a second compressor 15.2 and an intercooler 15.3 therebetween. Different numbers of compressors can be envisioned on the same or different shaft lines of one or more compressor trains. In the exemplary embodiment of FIG. 5, a driver 17, such as an electric motor, rotationally drives the compressor trains 15.1, 15.2 and is electrically connected to the power grid 45.

[0053] The delivery side of the compression unit 13 is fluidly coupled to the separation unit 21 through line 19, and the separation unit 21 is adapted to separate hydrogen from carbon dioxide. The stream of compressed hydrogen separated from carbon dioxide is delivered through the compressed hydrogen delivery line 23, while the stream of compressed carbon dioxide flows through the carbon dioxide outlet line 25.

[0054] As already described with respect to the foregoing embodiments, the separation unit 21 can include any separation device adapted to separate hydrogen from additional gaseous components. The separation technique can be selected from among those available in the art based on the chemical nature of the additional gaseous components and their proportion in the gas mixture, the pressure of the gas mixture delivered by the compression unit 13, the required flow rate, and other technical considerations.

[0055] The hydrogen compression system 1 further includes an energy recovery device or section 27. In the embodiment of FIG. 5, the energy recovery device or section 27 includes an expander 29, such as a radial turbo expander, and a cooling circuit fluidly coupled to the intercooler 15.3. The expander 29 converts the pressure energy of the compressed carbon dioxide into mechanical power. The cooling circuit provides a cooling capacity to enhance the efficiency of the compression unit 13 as described above.

[0056] The mechanical power generated by the expander 29 is available on the shaft 31. In the embodiment of FIG. 5, the shaft 31 is drivingly coupled to a generator 33 adapted to convert the mechanical power into electrical power, and this electrical power can be delivered via the power distribution network 45 to one or more electrical loads, including, for example, the driver 17 of the compression unit 13.

[0057] Similar to the embodiments of FIGS. 3 and 4, in the hydrogen compression system 1 of FIG. 5, a branch line 43 connects the discharge side of the expander 29 to the low temperature side of the intercooler 15.3 to provide cooling capacity to the intercooler and improve the efficiency of the compression unit 13. After flowing through the intercooler 15.3, the branched flow of the additional gaseous components that have expanded flows back to the main carbon dioxide discharge line 44. In other embodiments, the entire flow of the expanded carbon dioxide from the expander 19 can be used as a cooling medium in one or more intercoolers of the compression unit 13, or in different processes or devices where cooling capacity is required.

[0058] In some embodiments, carbon dioxide is expanded at pressure P3 in expander 29 of expansion device 28, and pressure P3 is lower than delivery pressure P2 of compression unit 13 but higher than pressure P1 of carbon dioxide at the inlet of mixing unit 9. In some embodiments, expander 29 can be replaced by an expansion valve or a general static expansion device. For example, pressure P1 can be approximately atmospheric pressure (1 bar), or more generally less than 30 bar. Pressure P2 can be 200 bar or more, and the final expansion pressure P3 of carbon dioxide can be 50 bar or more, preferably approximately 70 bar. The partially expanded carbon dioxide is in a state suitable for transportation or storage.

[0059] Similar to the embodiments described above, also in the embodiment of FIG. 5, at least a part of the power used to compress the additional gas component (carbon dioxide) contained in the gas mixture processed by compression unit 13 is recovered by the expansion of carbon dioxide from pressure P2 to pressure P3, and thus the overall energy efficiency of hydrogen compression system 1 is improved. The power required by compression unit 13 is reduced by utilizing the cold expanded carbon dioxide stream as a cooling medium in the intercooler, and thus the overall energy efficiency of hydrogen compression system 1 is further improved.

[0060] Continuing to refer to FIGS. 1, 2, 3, 4, and 5, a further embodiment of hydrogen compression system 1 of the present disclosure is shown in FIG. 6. In FIG. 6, the same reference numerals as in FIG. 5 are used to indicate the same parts, and they will not be described in detail again. The main difference between FIGS. 5 and 6 is that, similar to the embodiment of FIG. 4, expander 29 is drivingly coupled to compression unit 13 via shaft 31, so that the mechanical power generated by the expansion of the compressed carbon dioxide is used to directly drive compression unit 13. Auxiliary electromechanical machine 41 electrically connected to power distribution network 45 can be provided on the same shaft line to generate mechanical power when required to drive compression unit 13, or to convert excess mechanical power from expander 29 into electric power.

[0061] Continuing to refer to FIGS. 1, 2, 3, 4, 5 and 6, FIG. 7 shows a further embodiment of a hydrogen compression system 1 similar to the system of FIG. 5. The same reference numerals designate the same or similar components already described above and will not be described again. The main difference from FIG. 5 is that the cooled and expanded carbon dioxide from the expander 29 is used as a cooling medium to reduce the power required by the separation unit 21. If the latter requires cooling of the gaseous hydrogen and carbon dioxide mixture to effect separation of the hydrogen, at least part of the cooling capacity can be provided by the expanded carbon dioxide delivered through duct 73 to heat exchanger 71 within separation unit 21. A valve can be provided to adjust the expanded carbon dioxide flow rate as required and to appropriately distribute the expanded and cooled carbon dioxide flow through bypass line 75, intercooler 15.3, and separation unit 21.

[0062] The expanded carbon dioxide stream can be used as a cooling medium to reduce the power required by the separation unit 21 even in a closed loop configuration similar to that shown in FIGS. 1-4. An embodiment is schematically shown in FIG. 8, where the same reference numerals used in FIG. 4 designate the same or equivalent elements and will not be described again. Similar to the embodiment of FIG. 7, in FIG. 8 as well, the heat exchanger 71 within the separation unit 21 utilizes the cooled and expanded carbon dioxide delivered through duct 73 from the delivery side of the expander 29. After cooling the gas mixture in the separation unit 21, the warmed carbon dioxide stream is returned to the mixing unit 9.

[0063] Generally speaking, the cooling capacity provided by the flow of carbon dioxide or other additional gaseous components cooled and expanded on the delivery side of the expander 29 can be utilized in any process that requires a flow of cooling medium. This is schematically represented in FIG. 9, where a system similar to that of FIG. 2 is shown using the same reference numbers to designate the same elements. A general heat exchanger 77 can be used to utilize the cooling capacity of the expanded additional gaseous components to cool the fluid flowing within a general circuit 79 for a general process 81. In FIG. 9, the expander is combined with the compressor on a single shaft line, but in other embodiments, as described with respect to some of the foregoing embodiments, the expander can be mechanically separated from the compressor, and independent electromechanics can be provided for the expander on one side and the compressor on the other side.

[0064] In FIGS. 5, 6, and 7, the combination of the carbon dioxide capture system 51 and the mixing unit 9 has been described. However, when the carbon dioxide is derived from a gas turbine engine, as described above, the additional gaseous component can be a different gas or gas mixture containing carbon dioxide or any other suitable gas, can be mixed with hydrogen for compression purposes, and can be separated from hydrogen, having a beneficial effect in terms of compression power savings.

[0065] Figure 10 shows a schematic diagram of the hydrogen compression system 1, where an additional gas component circulates in a separate circuit, and this separate circuit can then be opened or closed (as shown by way of example), and the fluid circulates and is adapted to be mixed with hydrogen for the purpose of reducing the compression power described above. The same reference numerals already used in Figures 1 - 9 designate the same components or elements as described above, and they will not be described in detail again. In Figure 10, the expanded additional gas component is collected in a circuit 91 which may include a general process 93. For example, the additional gas component can be a refrigerant, for example, a mixed refrigerant processed in a refrigeration circuit for natural gas liquefaction or other purposes. Thus, the additional gas component circulates within a closed circuit including an expansion device 28, from which energy is recovered in the form of heat or mechanical power / electricity as described above, making the hydrogen compression process require less electrical power and be more efficient.

[0066] On the delivery side of the expansion device 28, the additional gas component can be in a gaseous state, a liquid state, or a two - phase state, i.e., partially vapor and partially liquid. The state of the expanded additional gas component can depend, inter alia, on the chemical composition of the component, the separation technology used in the separation unit 21, and / or the pressure conditions.

[0067] Generally speaking, when the additional gas component is at least partially in a liquid state on the outlet side of the separation unit 21, the expansion device 28 usually includes an expansion valve instead of, or in addition to, a turboexpander arranged downstream of the expansion valve. When the expansion is carried out by an expansion valve rather than a turboexpander, the energy recovery from the expanded or expanding additional component recovered in the separation unit 21 is mainly, or even exclusively, in the form of cooling capacity.

[0068] In some embodiments, for example, when an open cycle as shown in Figures 5, 6, and 7 is provided, the additional gas component is recovered in a form that is at least partially liquefied on the delivery side of the expansion device 28 and can be usefully utilized as a cooling medium or further condensed to a complete liquid state, for example, for transportation purposes.

[0069] In a closed cycle, as shown in FIGS. 1, 2, 3, 4, and 9, the (partially) liquefied additional gas components on the delivery side of the expansion device 28 can be evaporated in the heat exchanger 71 of the separation unit 21 (see, for example, FIG. 8) and / or the intermediate cooler 15.3 (see, for example, FIGS. 6 and 7) and / or the general cooling heat exchanger 77 (FIG. 9) before being recycled to the mixing unit 9.

[0070] Exemplary embodiments are disclosed above and shown in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions, and additions may be made to what is specifically disclosed herein without departing from the scope of the invention as defined in the following claims.

Claims

1. A hydrogen compression system comprising: a gaseous hydrogen source; a mixing unit fluidly coupled to the gaseous hydrogen source through a hydrogen inlet and further fluidly coupled to an inlet line adapted to supply an additional gaseous component to the mixing unit, the additional gaseous component having an average molecular weight higher than that of hydrogen, the mixing unit being adapted to mix hydrogen from the gaseous hydrogen source with the additional gaseous component at a first pressure to form a gaseous mixture containing hydrogen and the additional gaseous component; a compression unit fluidly coupled to the mixing unit and adapted to compress the gaseous mixture to a second pressure; a separation unit fluidly coupled to the compression unit and adapted to separate the compressed gaseous mixture into a stream of compressed hydrogen and a stream of compressed additional gaseous component; a compressed hydrogen delivery line through which the stream of compressed hydrogen is removed from the system; an energy recovery device including an expansion unit fluidly coupled to the separation unit and adapted to decompress the stream of compressed additional gaseous component from the second pressure to a third pressure lower than the second pressure, the energy recovery device being adapted to recover energy from the expansion of the compressed additional gaseous component from the second pressure to the third pressure.

2. The hydrogen compression system according to claim 1, wherein the energy recovery device is adapted to recover thermal energy, mechanical energy, or a combination thereof.

3. The hydrogen compression system according to claim 1 or 2, wherein the expansion unit includes an expander adapted to generate mechanical power by the expansion of the compressed additional gaseous component.

4. The hydrogen compression unit according to claim 3, wherein the expander is drivingly coupled to the compression unit such that the mechanical power generated by the expander is used to drive the compression unit.

5. The hydrogen compression unit according to claim 3 or 4, wherein the expander is drivingly coupled to a generator adapted to convert the mechanical power generated by the expander into electrical power.

6. The hydrogen compression system according to any one of claims 1 to 5, wherein the energy recovery device includes a heat transfer circuit.

7. The compression unit includes at least a first compressor or compressor stage, a second compressor or compressor stage, and an intercooler therebetween, and the heat transfer circuit provides cooling capacity to the intercooler and is adapted to remove heat from the partially compressed mixture of hydrogen and the additional gaseous component by heat exchange with the flow of the expanded additional gaseous component discharged from the expansion unit. The hydrogen compression system according to claim 6.

8. The delivery side of the expansion unit is fluidly coupled to the mixing unit, and the mixing unit, the compression unit, the separation unit, and the expansion unit form a closed circuit for the additional gaseous component. The hydrogen compression system according to one or more of claims 1 to 7.

9. The mixing unit is fluidly coupled to an open circuit, and the additional gaseous component flows within the open circuit. The hydrogen compression system according to any one of claims 1 to 7.

10. The additional gaseous component includes carbon dioxide recovered from a carbon dioxide generating process. The hydrogen compression system according to claim 9.

11. The third pressure is higher than the first pressure. The hydrogen compression system according to claim 9 or 10.

12. The compression unit includes at least one dynamic compressor, preferably at least one centrifugal compressor. The hydrogen compression system according to one or more of claims 1 to 11.

13. The compression unit further includes at least one reciprocating compressor. The hydrogen compression system according to claim 12.

14. A method of compressing hydrogen, comprising: delivering a flow of gaseous hydrogen from a hydrogen source to a mixing unit; delivering a flow of an additional gaseous component to the mixing unit, the additional gaseous component having an average molecular weight higher than that of hydrogen; mixing the gaseous hydrogen and the additional gaseous component in the mixing unit to form a gaseous mixture at a first pressure; compressing the gaseous mixture in a compression unit at a second pressure higher than the first pressure; delivering the compressed gaseous mixture to a separation unit to separate a flow of compressed hydrogen and a flow of the compressed additional gaseous component from each other; supplying the flow of compressed hydrogen through a compressed hydrogen delivery line; Expanding the compressed additional gas component at a third pressure lower than the second pressure and recovering energy from the expansion of the compressed additional gas component, and a method for compressing hydrogen.

15. The method according to claim 14, wherein the step of expanding the compressed additional gas component includes expanding the compressed additional gas component in an expander, thereby generating mechanical power.

16. The method according to claim 15, further comprising driving at least one of the compression unit and an electromechanical device that converts mechanical power into electric power using the mechanical power.

17. The method according to any one of claims 14 to 16, including recovering thermal energy from the expansion of the additional gas component by using the expanded additional gas component as a cooling fluid in a heat exchanger.

18. During the step of compressing the gas mixture to the second pressure, cooling the partially compressed gas mixture by heat exchange with the expanded additional gas component, and removing heat from a separation unit where the compressed hydrogen and the compressed additional gas component are separated from each other by heat exchange with the expanded additional gas component. The method according to claim 17, including one or more of the above steps.

19. The step of compressing the gas mixture is Compressing the gas mixture at an intermediate pressure in a first compressor; Cooling the partially compressed gas mixture in an intercooler; Further compressing the gas mixture in a second compressor, and The method according to any one of claims 14 to 18, wherein heat is removed from the partially compressed gas mixture by heat exchange with the expanded additional gas component.

20. The method according to any one of claims 14 to 19, including circulating the additional gas component in a closed circuit and mixing the expanded additional gas component with the flow of gaseous hydrogen.

21. The method according to any one of claims 14 to 20, wherein the additional gas component contains carbon dioxide.

22. The method according to claim 21, wherein the flow of carbon dioxide is provided by a carbon dioxide generation process.

23. The method according to claims 21 and 22, wherein the third pressure is higher than the first pressure.

24. The step of compressing the gas mixture is performed in a compression system comprising at least one centrifugal compressor, or a combination of at least one centrifugal compressor and at least one reciprocating compressor, according to one or more of claims 14 to 23.

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