Patent Application
20230408189
The invention relates to a plant and a method for producing hydrogen at cryogenic temperature.
The two main ways to produce hydrogen (molecular hydrogen H2) are: electrolysis and chemical production by steam methane reforming (SMR).
In the case of electrolysis, the water molecule is split and this produces hydrogen on the one hand and oxygen (O2) on the other. As regards electrolysis technologies, there are three main families: “PEM” (Proton Exchange Membrane), “Alkaline” and “Solid Oxide”.
These technologies operate optimally at a pressure close to atmospheric pressure for reasons of energy performance and efficiency of the chemical reaction of splitting the water molecule.
PEM technology makes it possible to operate at high pressures without significantly impacting the energy performance of the electrolysis. For example, in the prior art, electrolyzers of several megawatts of power can produce hydrogen and oxygen at 30 bar abs at room temperature.
Although described for example in documents U.S. Pat. No. 4,530,744 or 10,351,962, harnessing the oxygen produced under high pressure is generally not carried out industrially.
These known solutions are however of little interest industrially in hydrogen liquefaction processes because they are not very energy efficient.
One aim of the present invention is to overcome all or some of the drawbacks of the prior art set out above.
To this end, the plant according to certain embodiments of the invention, which moreover complies with the generic definition given in the preamble above, is essentially characterized in that said at least one expansion turbine and said at least one compressor are coupled to the same rotary shaft to transfer work of expanding the hydrogen flow under pressure to the compressor to compress the hydrogen flow upstream of the turbine.
Such a plant makes it possible to efficiently harness the pressure of the hydrogen (in particular at high pressure) produced by an electrolyzer to pre-cool or cool a flow of hydrogen to a cryogenic temperature.
This solution makes it possible to reduce the investment costs for such a plant, in particular by eliminating or reducing the cooling down to 80 to 130 K of the hydrogen to be liquefied. This makes it possible, for example, to reduce or dispense with a liquid nitrogen pre-cooling system with a nitrogen compression station as found in the prior art.
The solution makes it possible to significantly reduce the corresponding operating costs for such a plant (for example 30% less on specific energy, for example kWh/kg of liquefied H2).
In certain embodiments, the invention relates more particularly to a plant for producing hydrogen at cryogenic temperature, in particular liquefied hydrogen, comprising an electrolyzer provided with an oxygen outlet and a hydrogen outlet, a hydrogen circuit to be cooled comprising an upstream end connected to the hydrogen outlet and a downstream end intended to be connected to a member for collecting cooled and/or liquefied hydrogen, the plant comprising a set of heat exchanger(s) exchanging heat with the hydrogen circuit to be cooled, the plant comprising at least one cooling device exchanging heat with at least part of the set of heat exchanger(s), the hydrogen circuit to be cooled comprising a hydrogen flow expansion system and at least one hydrogen compressor upstream of the hydrogen flow expansion system, the hydrogen flow expansion system comprising at least one expansion turbine.
Furthermore, embodiments of the invention may include one or more of the following features:
The invention also relates to a method for producing hydrogen at cryogenic temperature, in particular liquefied hydrogen, using a plant according to any one of the preceding features, the method comprising a step of supplying, by the electrolyzer, a hydrogen flow to the upstream end of the hydrogen circuit, for example at a pressure of between 15 and 150 bar, a step of supplying, by the electrolyzer, an oxygen flow to the upstream end of the oxygen circuit, for example at a pressure of between 15 and 150 bar, the method comprising a step of compression then expansion of the hydrogen flow in which the expansion is carried out by at least one turbine coupled to a shaft, the shaft also being coupled to at least one compressor ensuring the compression of the hydrogen flow before its expansion.
The invention may also relate to any alternative device or method comprising any combination of the features above or below within the scope of the claims.
Further features, advantages and possible applications of the invention are apparent from the following description of working and numerical examples and from the drawings. All described and/or depicted features on their own or in any desired combination form the subject matter of the invention, irrespective of the way in which they are combined in the claims or the way in which said claims refer back to one another.
The hydrogen production plant 1 shown is a device for producing hydrogen at cryogenic temperature, in particular liquefied hydrogen.
This plant 1 comprises an electrolyzer 2, preferably of “PEM” (proton exchange membrane) type operating at high pressure, that is to say producing gaseous hydrogen and oxygen at pressures of between 15 and 150 bar, for example equal to 30 bar.
The electrolyzer 2 has an oxygen outlet and a hydrogen outlet.
The plant 1 comprises a hydrogen circuit 3 (or pipe(s)) to be cooled having an upstream end connected to the hydrogen outlet of the electrolyzer 2 and a downstream end intended to be connected to a member 23 for collecting cooled and/or liquefied hydrogen (storage and/or user application for example).
The plant 1 comprises a set of heat exchanger(s) 4, 5, 6, 7, 8 exchanging heat with the hydrogen circuit 3 to be cooled, with the aim of reaching a temperature favorable to the liquefaction of hydrogen.
As shown, at least one separate heat exchanger 25 may be provided at the outlet of the electrolyzer 2 to cool the hydrogen flow (for example by heat exchange with a heat transfer fluid such as water or air for example) to bring the latter to a temperature close to ambient temperature. The electrochemical reaction for the production of hydrogen by electrolysis generally leads to a rise in temperature of a few dozen degrees.
The plant 1 further comprises at least one cooling device 9, 10 exchanging heat with at least part of the set of heat exchanger(s) 4, 5, 6, 7, 8.
Moreover, the plant 1 may comprise an oxygen circuit 190 (at least one pipe) comprising an upstream end connected to the oxygen outlet of the electrolyzer 2 and a downstream end. The downstream end may be connected for example to a device 27 for collecting and/or using oxygen. This collection device may include, for example: an oxygen liquefaction system, an oxygen (pre)-cooling system, a system for compressing oxygen and packaging in cylinders or pressurized storage, a combustion system, a venting system, etc.
As shown, the hydrogen circuit 3 to be cooled comprises a hydrogen flow expansion system 18 and at least one hydrogen compressor 19 upstream of the hydrogen flow expansion system 18. Preferably, all (the entirety) of the hydrogen flow to be cooled/liquefied is expanded in the turbine(s) expansion system 18. In other words, all of the flow to be cooled/liquefied is expanded in the turbine or turbines 18 and this expanded flow is cooled by the cooling device in the set of exchanger(s) so as to be liquefied, for example. The hydrogen flow expansion system 18 comprises at least one hydrogen flow expansion turbine 18 and said expansion turbine 18 and said compressor 19 are coupled to the same rotary shaft 20 to transfer work of expanding the hydrogen flow under pressure to the compressor 19 to compress the hydrogen flow upstream of the turbine 18. The assembly with expansion turbine 18 and compressor 19 coupled to the same rotary shaft 20 is a preferably passive mechanical system, that is to say that it does not include a motor for driving the rotary shaft 20 other than the hydrogen flow.
As shown, the hydrogen circuit 3 preferably comprises several hydrogen compressors 19 arranged in series upstream of the hydrogen flow expansion system 18.
The hydrogen flow expansion system preferably comprises as many expansion turbines 18 arranged in series, each of the compressors 19 being coupled to a rotary shaft 20 to which at least one turbine 18 is also coupled. For example, the compressors 19 and turbines are associated in pairs on separate respective rotary shafts 20 (for example first compressor 19 upstream coupled with first turbine 20 upstream, etc.).
As shown, at the outlet of each turbine 18, the expanded hydrogen flow may optionally pass through separate heat exchangers respectively from upstream to downstream of the first group of heat exchanger(s) 4, 5, 6, 7, to ensure pre-cooling of the hydrogen.
These expansion stages 18 make it possible to harness the pressure of the hydrogen flow (with or without intermediate cooling). This makes it possible to replace or supplement the pre-cooling described above.
This cold provided without any energy consumption makes it possible to reduce the work to be input to cool the hydrogen down to its target temperature (for example via a second cooling device 10 as described in more detail below).
Of course, this way of expanding and harnessing the pressure of the hydrogen flow is not limited to this example. Thus, the expansion of hydrogen from ambient temperature down to a given pre-cooling temperature could be carried out in several stages of radial expansion or in a single stage of expansion, for example via a volumetric expansion valve, in particular to reduce costs.
This pre-cooling of the hydrogen may be completed downstream of the circuit 3 by a second cooling device 10 exchanging heat with the hydrogen circuit 3 to be cooled.
As shown, for example, the aforementioned first cooling device 9 (expansion of hydrogen with pre-compression) is placed in heat exchange with a first upstream group of heat exchanger(s) 4, 5, 6, 7 of the set of heat exchanger(s) 4, 5, 6, 7, 8.
The second cooling device 10 may itself be placed in heat exchange with a second downstream group of heat exchangers 8 (represented here by a single heat exchanger but several heat exchangers in series and/or in parallel may be envisaged).
After this pre-cooling of the hydrogen circuit 3 to a temperature of 80 to 100 K for example, the second cooling device 10 provides additional cooling of the hydrogen, for example to a temperature of around 20 K, in order to liquefy same.
As shown schematically, the second cooling device 10 may comprise a cycle gas refrigeration cycle refrigerator (comprising for example hydrogen or helium, or neon, or an optimized combination of the three) to improve the efficiency of the device 10 for final cooling of the hydrogen. Conventionally, this refrigerator of the second cooling device 10 may comprise, arranged in series in a cycle circuit: a mechanism 15 for compressing the second cycle gas (one or more compressors), a member 24 for cooling the second cycle gas (heat exchanger(s) for example), a mechanism 16 for expanding the second cycle gas (turbine(s) and/or expansion valve(s)) and a member 8 for heating the expanded second cycle gas (heat exchangers and in particular heat exchanger(s) in exchange with the hydrogen flow to be cooled).
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The pre-cooling carried out via hydrogen expansion as described above may in particular make it possible to reduce (in particular halve) the consumption of such a cooling fluid (such as liquid nitrogen or with a gas mixing cycle for example).
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As above, the oxygen circuit 190 may comprise at least one oxygen compressor 12 arranged upstream of the oxygen flow expansion system 13. The oxygen flow expansion system 13 comprises at least one expansion turbine 13. Said oxygen expansion turbine 13 and said upstream oxygen compressor 12 are coupled to the same rotary shaft 14 to transfer work of expanding the oxygen flow under pressure to the compressor 12 to compress the oxygen flow upstream of the expansion turbine 13.
The assembly comprising the expansion turbine 13 and the compressor 12 coupled to the same rotary shaft 14 is preferably a passive mechanical system, that is to say that it does not include a motor for driving the rotary shaft 14 other than the oxygen flow. Thus, the expansion turbine 13 is mechanically braked by the compressor 12 coupled to the same shaft 14. Of course, this is not limiting, and it could thus be envisaged to provide a system with a motor with its shaft coupled to the turbine(s) and compressor(s) (to improve the efficiency of the plant where appropriate).
As in the case of hydrogen, this transfer of work for the oxygen flow produces “turboboosting” which therefore consists in integrating one or more cryogenic expansion turbines 13 for which the working fluid is the oxygen previously produced by the electrolyzer 2. The system for braking these turbines is one or more compressors 12 coupled to the same shaft 14. This makes it possible to inject the work of expanding this gas flow as a flow booster upstream at ambient temperature.
As shown, to transfer this cold energy produced to the hydrogen flow, it is possible to integrate in the exchanger or exchangers 4, 5, 6, 7 specific passages, independent of the main hydrogen flow, to allow the cooled oxygen to exchange cold energy/heat energy with the hydrogen to be cooled.
The integration of the expanded oxygen flow in the array of heat exchangers 4, 5, 6, 7 of the hydrogen refrigeration/liquefaction system makes it possible in particular to reduce its volume. Costs are also reduced by sharing the heat exchange lines in one and the same piece of equipment. Furthermore, it is possible to use a typically inert intermediate heat transfer fluid, helium, nitrogen, argon, for example, so as not to risk bringing hydrogen and oxygen into contact in the same piece of equipment.
For example, the hydrogen is cooled down to a target temperature of around 20 K, for example. To this end, the hydrogen flow may be pre-cooled from the temperature at the outlet of the electrolyzer down to a temperature of between 220 and 90 K, and for example of around 100 K.
Before expansion (downstream of the compressors 12), the oxygen may for example be brought to a pressure of between 15 and 150 and to a temperature close to ambient temperature, thanks to exchangers for cooling between compression stages (then at the end) which have a cold source such as industrial water. All or some of this pre-cooling may be carried out via expanded oxygen as described above.
The inventors have determined in particular that this harnessing of the oxygen and/or hydrogen pressure with overpressure allows a saving of approximately 45% on the consumption of liquid nitrogen (saving on electrical energy consumed to produce liquid nitrogen) for a plant with a daily production of 25 tons of hydrogen to be cooled from 300 K to 85 K.
Naturally, this advantage still stands in the event of use of another pre-cooling device (nitrogen cycle cooler, for example).
In the case where the pressure of the oxygen flow at the outlet of the electrolyzer 2 is around 70 bar, it is possible to achieve a saving on operating costs of around 50 to 70% for the function of pre-cooling of the hydrogen flow.
As shown, the oxygen circuit 190 may comprise several oxygen compressors 12 arranged in series upstream of the oxygen flow expansion system 13. The oxygen flow expansion system for its part comprises a plurality of expansion turbines 13 and each of the compressors 12 is coupled to a rotary shaft 14 to which at least one turbine 13 is also coupled.
For example, all or some of these elements could be integrated into a (for example single) turbomachine having n turbines and n compressors mounted on either side of the same shaft.
In the non-limiting example shown, the oxygen circuit 190 comprises as many compressors 12 arranged in series upstream as expansion turbines 13 arranged in series downstream, the compressors and turbines 13 are coupled in pairs to respective rotary shafts 14. For example, the first turbine (upstream) is coupled with the first compressor (upstream), the second turbine with the second compressor, etc.
Of course, the invention is not limited to this configuration comprising only turboboosters, and it is possible to provide turboboosters of this type and, additionally, one or more conventional turbines (the same goes for the aforementioned hydrogen flow compression/expansion system).
Preferably, an oxygen cooling system 21 is provided at the outlet of at least some of the compressors 12. For example, a cooler (cooling exchanger in exchange with a fluid such as air or water) may be interposed at the outlet of each compressor in order to improve the isothermal efficiency of each compression stage.
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Furthermore, preferably, after the outlet of the turbines 13 in series, the oxygen flow respectively passes through the heat exchangers 4, 5, 6, 7 in series from upstream to downstream. This passage through the exchangers thus produces cooling or heating of the oxygen flow after each expansion stage (cooling or heating depending on the pressure conditions of the oxygen flow and the temperature of the exchanger 4, 5, 6, 7 concerned). To be specific, when the fall in pressure of the oxygen flow at the terminals of the turbine is relatively large, the exchange of heat with the heat exchanger 4, 5, 6, 7 located at the outlet will tend to heat the flow (for the purpose of thermodynamic optimization of the hydrogen flow refrigeration cycle) whereas, on the contrary, in the event of a relatively lower fall in pressure, the passage through the heat exchanger 4, 5, 6, 7 located at the outlet will tend to cool the flow (as shown in
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The turbines are preferably of the centripetal and radial technology type. This allows pooling of the expansion technologies throughout the liquefaction plant.
The compressors are preferably of the centrifugal type.
In a variant not shown in detail, the oxygen circuit 190 produces liquefied oxygen downstream, which is recovered. To this end, all or part of the oxygen flow may pass through heat exchangers separate from the exchangers 4, 5, 6, 7, 8 in exchange with the hydrogen flow.
Of course, some compressors or turbines may not be coupled to a shaft to which another wheel of a turbine (or respectively of a compressor) is also coupled. In other words, not all of the turbines (or compressors) are necessarily coupled to the same shaft as a compressor and vice versa. Likewise, more than two wheels (compressors and/or turbines) may be coupled to the same shaft.
While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.
The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.
“Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms “consisting essentially of” and “consisting of” unless otherwise indicated herein.
“Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.
Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.
Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.
All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.
| Number | Date | Country | Kind |
|---|---|---|---|
| FR2011491 | Nov 2020 | FR | national |
This application is a § 371 of International PCT Application PCT/EP2021/079034, filed Oct. 20, 2021, which claims the benefit of FR2011491, filed Nov. 9, 2020, both of which are herein incorporated by reference in their entireties.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/079034 | 10/20/2021 | WO |
