BRUNO LORENZO (IT)
| US10634425B2 | 2020-04-28 | |||
| JP2020024064A | 2020-02-13 | |||
| US20120100062A1 | 2012-04-26 | |||
| GB2470062A | 2010-11-10 | |||
| FR3099234A1 | 2021-01-29 |
GROSS R ET AL: "FLUESSIGWASSERSTOFF FUER EUROPA - DIE LINDE-ANLAGE IN INGOLSTADT", BERICHTE AUS TECHNIK UND WISSENSCHAFT, LINDE AG. WIESBADEN, DE, no. 71, 1 January 1994 (1994-01-01), pages 36 - 42, XP000447171, ISSN: 0942-332X
| CLAIMS 1. A process for producing and storing hydrogen in liquid form and in gaseous form in a step A) and for producing electricity and for producing and storing liquid and/or cryo-compressed nitrogen from a combustion gas flow g3 in a step B), wherein said step A) comprises the use of liquid and/or cryo-compressed nitrogen produced and stored in step B) from a combustion gas flow g3 and wherein said step B) comprises the use of hydrogen in liquid form and in gaseous form produced and stored in step A). 2. A process according to the preceding claim, wherein in said step A) and in said step B) a heat exchange step is carried out between a flow of said hydrogen and a flow of said nitrogen. 3. A process according to claim 1 or 2, wherein said electricity is at least partially produced in a fuel cell g'FC. 4. A process according to any one of the preceding claims, wherein said step A) comprises the sub-steps of: Al) subjecting a water flow al to electrolysis by using electricity, thus obtaining the production of an oxygen flow a2 and a hydrogen flow a3, A2) subjecting said hydrogen flow a3 to a preliminary cooling step, thus obtaining a preliminarily cooled hydrogen flow a4, A3) separating a first portion of said preliminarily cooled hydrogen flow a5 and obtaining a cooled gaseous hydrogen flow a8, A4) separating a second portion of said preliminarily cooled hydrogen flow a9 and obtaining a liquid hydrogen flowa17''', which is stored in a liquid hydrogen tank aTH2I. 5. A process according to claim 4, wherein said sub-step Al) is carried out in an electrolytic cell aEC. 6. A process according to the preceding claim, wherein in said sub-step Al) the electrolytic cell aEC uses electricity available in excess. 7. A process according to any one of the preceding claims 4 to 6, wherein said sub-step A3) comprises the sub-steps of: A3a) pre-cooling, A3b) first cooling, A3c) possible stabilization, A3d) one or more further cooling operations. 8. A process according to any one of the preceding claims 4 to 7, wherein said sub-step A4) comprises the sub-steps of: A4a) pre-cooling, A4b) first cooling, A4c) stabilization, A4d) one or more further cooling operations. 9. A process according to the preceding claim, wherein said step A3a) and said step A4a) are carried out by heat exchange with a liquid and/or cryo- compressed nitrogen flow a32 at a first heating level and possibly also with an expanded nitrogen flow a34, thus obtaining a first portion of the pre-cooled hydrogen flow a6 and a second portion of the pre-cooled hydrogen flow a10. 10. A process according to the preceding claim, wherein said pre-cooling step A3a) and/or said step a4a) are also carried out by heat exchange with a refrigerant fluid. 11. A process according to any one of the preceding claims 8 to 10, wherein said sub-step A3b) and said step A4b) are carried out by heat exchange with a pumped liquid and/or cryo-compressed nitrogen flow a31, thus obtaining a first portion of the cooled hydrogen flow a7 and a second portion of the cooled hydrogen flow all. 12. A process according to any one of the preceding claims 8 to 11, wherein said first cooling sub-step A3b) and/or said first cooling sub-step A4b) are also carried out by heat exchange with a refrigerant fluid. 13. A process according to any one of the preceding claims 8 to 12, wherein said stabilization sub-step A4c) converts the hydrogen from the ortho to the para form, thus obtaining a second portion of the cooled and stabilized hydrogen flow a14. 14. A process according to any one of the preceding claims 7 to 13, wherein said sub-step of one or more further cooling operations A3d) and/or A4d) is carried out by heat exchange with a refrigerant fluid. 15. A process according to any one of the preceding claims 8 to 14, wherein the liquid and/or cryo-compressed nitrogen used in sub-steps A3a), A3b), A4a) and A4b) is the liquid or cryo-compressed nitrogen produced and stored in step B). 16. A process according to any one of the preceding claims, wherein said step B) comprises the sub-steps of: Bl) subjecting an air flow gl to combustion in the presence of an overall vaporized hydrogen flow g33, and possibly a compressed recirculating nitrogen flow gR2, and obtaining a combustion gas flow g3, B2) expanding said combustion gas flow g3, thus obtaining an expanded combustion gas flow g4, B3) cooling said expanded combustion gas flow g4 and obtaining a cooled expanded combustion gas flow g6, B4) subjecting said cooled expanded combustion gas flow g6 to a water separation step gwl, thus obtaining a dehydrated combustion gas flow g7, B5) optionally separating a first portion g8 from said dehydrated combustion gas flow g7, which is joined to the air flow gl of sub-step Bl), B6) subjecting a second portion g9 to compression, thus obtaining a compressed dehydrated combustion gas flow g10, B7) subjecting said compressed dehydrated combustion gas flow g10 to cooling and at least one water separation step gw2, thus obtaining a nitrogen flow g13, B8) subjecting said nitrogen flow g13 to condensation, thus obtaining a liquid nitrogen flow g14 stored in a liquid nitrogen tank gTN2l. 17. A process according to the preceding claim wherein said expansion sub-step B2) is carried out in a gas turbine gGT with the production of mechanical energy and possibly electricity by a generator gE. 18. A process according to the preceding claim 16 or 17, wherein a recirculating nitrogen flow gRl is obtained from said liquid nitrogen tank gTN2l, sent to a second compressor gC2, thus obtaining a compressed recirculating nitrogen flow gR2 which is recirculated to the combustor gCOMB for sub-step Bl). 19. A process according to any one of claims 16 to 18, wherein said condensation step B8) uses the gaseous and/or cryo-compressed hydrogen and the liquid hydrogen produced and stored in step A). 20. A process according to any one of the preceding claims 3 to 15, wherein said step B) is a step B') comprising the sub-steps of: B'1) combusting an air flow g'l in a combustor g'COMB and obtaining a combustion gas flow g'12, B'2) expanding said combustion gas flow g'12, thus obtaining an expanded combustion gas flow g'13, B'3) cooling said expanded combustion gas flow g'13, thus obtaining a cooled expanded combustion gas flow g' 15, B'4) separating the water and obtaining a nitrogen flow g'20, B'5) subjecting said nitrogen flow g'2O to cooling in an eighth heat exchanger g'TE8, thus obtaining a liquid nitrogen flow g'21, wherein before said step B'1), said air flow g'l is subjected to a treatment comprising the oxygen reduction sub-step in said fuel cell g'FC. 21. A process according to the preceding claim, wherein in step B'l) a flow to be sent to the combustor g'35 is also subjected to combustion and, before being sent to the combustor g'COMB, is subjected to the steps of: b'1) heating, obtaining a heated flow g'50 to be oxidized, b'2) oxidizing the hydrogen contained in said flow g'50 to be oxidized, thus obtaining an oxidized flow g'51, b'3) further cooling, thus obtaining a cooled oxidized flow g'52. 22. A process according to claim 20 or 21, wherein said sub-step B'3) comprises the further sub-steps of: B'3a) cooling said expanded combustion gas flow g'13 in the second heat exchanger g'TE2 by heat exchange with the flow to be sent to the combustor, thus obtaining a first cooled flow g'14, and B'3b) cooling said first cooled flow g'14 in a sixth heat exchanger g'TE6, thus obtaining said expanded and further cooled combustion gas flowg'15. 23. A process according to any one of claims 20 to 22, wherein said sub-step B'4) comprises the further sub-steps of: B'4a) subjecting said expanded and further cooled combustion gas flow g'15 to a first water separation g'wl in a first separator g'Sl, thus obtaining a dehydrated combustion gas flow g'16, B'4b) compressing said dehydrated combustion gas flow g' 16 in a third compressor g'C3 obtaining a compressed dehydrated combustion gas flow g'17, B'4c) cooling said compressed dehydrated combustion gas flow g'17 in a seventh heat exchanger g'TE7, thus obtaining a compressed and cooled dehydrated combustion gas flow g'18; B'4d) subjecting said compressed and cooled dehydrated combustion gas flow g'18 to a second water separation g'w2 in a second separator g'S2, thus obtaining a further dehydrated combustion gas flow g' 19, B'4e) subjecting the further dehydrated combustion gas flow g'19 thus obtained to a further dehydration in a dehydration unit g'DU, thus obtaining the nitrogen flow g'20. 24. A process according to any one of claims 20 to 23, wherein said step B'5) is carried out using the gaseous and/or cryo-compressed hydrogen and the liquid hydrogen produced and stored in step A). 25. A process according to any one of claims 20 to 24, wherein said step B'5) is carried out using the gaseous hydrogen and/or the liquid hydrogen produced and stored in step A) according to any one of claims 1 to 15. 26. A process according to any one of the preceding claims 8 to 25, wherein the liquid and/or cryo-compressed nitrogen used in sub-steps A3a), A3b), A4a) and A4b) is the liquid and/or cryo-compressed nitrogen produced and stored in step B) or B') according to any one of claims 14 to 24. 27. A plant comprising a liquid and/or cryo- compressed nitrogen tank aTN2l, gTN2l, g'TN2l, a liquid hydrogen tank aTH2l, gTH2l, g'TH2l, a gaseous hydrogen tank aTH2g, gTH2g, g'TH2g, an air compressor gTC, g'TCl, g'TC2, a combustor gCOMB, g'COMB, a gas turbine gGT with a generator gE or an expander g'EX and heat exchangers aTE2, aTE3, gTE4, g'TE8 for the heat exchange between a liquid nitrogen flow and a liquid or gaseous and/or cryo-compressed hydrogen flow. 28. A plant according to the preceding claim, wherein the process according to any one of claims 1 to 26 is carried out. 29. A process for producing and storing hydrogen in liquid form and in gaseous form in a step A) and for producing electricity and for producing and storing liquid and/or cryo-compressed nitrogen from a combustion gas flow g3 in a step B), wherein said step A) comprises the use of liquid and/or cryo-compressed nitrogen produced and stored in step B) from a combustion gas flow g3 and wherein said step B) comprises the use of hydrogen in liquid form and in gaseous form produced and stored in step A), wherein said step B) comprises the sub-steps of: Bl) subjecting an air flow gl to combustion in the presence of an overall vaporized hydrogen flow g33, and possibly a compressed recirculating nitrogen flow gR2, and obtaining a combustion gas flow g3, B2) expanding said combustion gas flow g3, thus obtaining an expanded combustion gas flow g4, B3) cooling said expanded combustion gas flow g4 and obtaining a cooled expanded combustion gas flow g6, B4) subjecting said cooled expanded combustion gas flow g6 to a water separation step gwl, thus obtaining a dehydrated combustion gas flow g7, B5) optionally separating a first portion g8 from said dehydrated combustion gas flow g7, which is joined to the air flow gl of sub-step Bl), B6) subjecting a second portion g9 to compression, thus obtaining a compressed dehydrated combustion gas flow g10, B7) subjecting said compressed dehydrated combustion gas flow g10 to cooling and at least one water separation step gw2, thus obtaining a nitrogen flow g13, B8) subjecting said nitrogen flow g13 to condensation, thus obtaining a liquid nitrogen flow g14 stored in a liquid nitrogen tank gTN2l. 30. A process for producing and storing hydrogen in liquid form and in gaseous form in a step A) and for producing electricity and for producing and storing liquid and/or cryo-compressed nitrogen from a combustion gas flow g3 in a step B), wherein said step A) comprises the use of liquid and/or cryo-compressed nitrogen produced and stored in step B) from a combustion gas flow g3 and wherein said step B) comprises the use of hydrogen in liquid form and in gaseous form produced and stored in step A), wherein said step B) is a step B') comprising the steps of: B'1) combusting an air flow g'l in a combustor g'COMB and obtaining a combustion gas flow g'12, B'2) expanding said combustion gas flow g'12, thus obtaining an expanded combustion gas flow g'13, B'3) cooling said expanded combustion gas flow g'13, thus obtaining a cooled expanded combustion gas flow g' 15, B'4) separating the water and obtaining a nitrogen flow g'20, B'5) subjecting said nitrogen flow g'2O to cooling in an eighth heat exchanger g'TE8, thus obtaining a liquid nitrogen flow g'21, wherein before said step B'1), said air flow g'l is subjected to a treatment comprising the oxygen reduction sub-step in said fuel cell g'FC. |
THE GAS NETWORK AND/OR THE HYDROGEN NETWORK" DESCRIPTION
Technical field of the invention
The present invention is applicable to the energy field, and in particular, for the stabilization of the electrical network and, possibly, of the combustible gas network, as well as of the hydrogen network, normally present in a refinery.
Background art
Although it is known how to produce, store and consume hydrogen, there is no unitary process capable of stabilizing both the electrical network and the natural gas network or the hydrogen network (for example in a refinery) or both gas networks.
Such a process must be efficient, therefore it must have a high return coefficient of the energy withdrawn from the network, as well as practical, thus requiring limited storage spaces not linked to particular subsoil conformations, such as exhausted wells in which to store gas; moreover, it must allow the storage of amounts of energy such as to exceed the seasonality/unpredictability limits typically found in the availability of renewable energies. It is known that the storage of large amounts of hydrogen and/or oxygen requires the liquefaction of said gases at temperatures compatible with storage at atmospheric pressure, and that said process is energetic, to the point of consuming up to one third of the calorific power of hydrogen, with the effect of limiting the production thereof per unit of available electricity.
Furthermore, while hydrogen liquefaction requires a lot of energy (the plants currently in use require an average of 11 kWh/kg), the quantity which can be returned during vaporization is much lower. In fact, considering a theoretical energy cost of 3.8 kWh/kg and a machine efficiency around 85%, no more than 3 kWh/kg can be obtained, when the vaporization is carried out at ambient pressure, and no more than 2 kWh/kg when the hydrogen is heated to the network introduction pressure.
The liquid hydrogen liquefaction and storage systems proposed so far use liquid nitrogen, but such a fluid is generated and imported from the outside, while the systems using hydrogen in the generation of electricity simply consider such a gas as available, without taking care of the recovery of the frigories if it is liquid. Prior art document JP2020024064 describes a plant for producing liquid hydrogen for continuously liquefying gaseous hydrogen even if the supply thereof is fluctuating; for example, such a system can be used when producing gaseous hydrogen from renewable energy sources.
US 10,634,425 describes a method for liquefying gaseous hydrogen within a hydrogen liquefaction unit using a high pressure nitrogen flow as the first source of refrigeration; in particular, the high pressure nitrogen flow comes from a nitrogen pipeline. The use of high pressure nitrogen is described as an alternative to a natural gas flow from a high pressure pipeline or an air flow from an air separation unit.
Summary of the invention
The inventors of the present patent application have surprisingly found that it is possible to integrate the electrolytic hydrogen production technologies with the hydrogen storage technologies, both in liquid and cryo-compressed form, with the use of liquid and/or cryo-compressed nitrogen systems.
Object of the invention
In a first object, the present invention describes a process for producing and storing hydrogen, and for producing electricity, and for producing and storing liquid and/or cryo-compressed nitrogen.
According to an aspect, the process of the invention comprises a first step of producing and storing hydrogen using electricity and liquid and/or cryo-compressed nitrogen.
According to another aspect, the process of the invention comprises a second step of generating electricity and liquid and/or cryo-compressed nitrogen.
According to a further object, a plant for carrying out the process of the invention is described.
Brief description of the drawings
Figure 1 depicts the diagram of the storage step according to the process of the present invention.
Figure 2 depicts the diagram of a first embodiment of the generation step according to the process of the present invention.
Figure 3 depicts the diagram of an alternative embodiment of the generation step according to the process of the present invention.
Detailed description of the invention
In the following description, the subscript indication "a" intends to refer to storage step A), while "g" intends to refer to generation step B); the indication " g' " refers to the alternative embodiment of the generation step (phase B ' ) .
In the following description, when referring to a nitrogen or oxygen or hydrogen flow, it is understood that such a flow has a main composition of such an element ; alternatively, the indication can be in the functional sense , if the indicated element is functional to the next step or steps .
The proces s of the present invention comprises two steps : a first step of producing liquid or cryo- compres sed hydrogen ( step A) and a second step of generating electricity and producing and storing liquid and/or cryo-compres sed nitrogen ( step B) .
More in particular, said step A) is a step of producing and storing hydrogen .
In particular, hydrogen is produced in liquid (H 2 I) and/or gaseous (H 2 g) form, pos sibly in cryo- compres sed gaseous form .
As for step B ) , said step is a step of producing electricity and liquid and/or cryo-compres sed nitrogen (where not indicated, liquid and/or cryo-compres sed nitrogen is always intended) .
More in particular, the liquid nitrogen i s produced from a combustion gas f low obtained in step B ) . For the purposes of the present invention, step
A) of producing liquid and gaseous and/or cryo- compressed hydrogen comprises using the liquid and/or cryo-compressed nitrogen produced and stored in step
B).
Each step will be described in more detail below. Step A)
For the purposes of the present invention, step A) comprises the sub-steps of:
Al) subjecting a water flow a 1 to electrolysis by using electricity, thus obtaining the production of an oxygen flow a 2 and a hydrogen flow a 3,
A2) subjecting said hydrogen flow a 3 to a preliminary cooling step, thus obtaining a preliminarily cooled hydrogen flow a 4,
A3) separating a first portion a 5 of said preliminarily cooled hydrogen flow and obtaining a cooled gaseous hydrogen flow a 8, which is stored in a gaseous hydrogen tank a TH 2 g,
A4) separating a second portion a 9 of said preliminarily cooled hydrogen flow and obtaining a liquid hydrogen flow a 17''', which is stored in a liquid hydrogen tank a TH 2 l.
In an aspect of the present invention, sub-step Al) is carried out in an electrolytic cell a EC and can use sea water; in this case, the electrolytic cell a EC can be provided with a purge system for the brine B.
According to a preferred aspect of the present invention, the process uses excess electricity; therefore, according to a preferred aspect, in sub- step Al) the electrolytic cell a EC uses excess available electricity.
The term "excess electricity" means electricity produced and available in the electrical network, but which is not used.
In an aspect of the present invention, the oxygen flow a 2 obtained from sub-step Al) is intended for export, as a valuable by-product, or can be released into the atmosphere.
In an aspect of the present invention, prior to the preliminary cooling sub-step A2), the hydrogen flow a 3 obtained from sub-step A1) can be compressed in a first compressor a C1; therefore, sub-step A2) can be carried out on a hydrogen flow a 3 or on a compressed hydrogen flow a 3'.
For the purposes of the present invention, step A2) is carried out in a first heat exchanger a TE1 for heat exchange with an external refrigerant fluid. Such an external refrigerant fluid can be represented by water or air at ambient temperature and is preferably represented by water.
For the purposes of the present invention, sub- step A3) comprises the sub-steps of:
A3a) pre-cooling,
A3b) first cooling,
A3c) possible stabilization (not depicted in the figure),
A3d) one or more further cooling operations.
For the purposes of the present invention, the pre-cooling sub-step A3a) is carried out in a second heat exchanger a TE2 for heat exchange with a liquid and/or cryo-compressed nitrogen flow at a first heating level a 32 and possibly also with an expanded nitrogen flow a 34, as it will be described below, obtaining a first portion of the pre-cooled hydrogen flow a 6.
For the purposes of the present invention, the first cooling sub-step A3b) is carried out in a third heat exchanger a TE3 for heat exchange with a pumped liquid and/or cryo-compressed nitrogen flow a 31, as it will be described below, obtaining a first portion of the cooled hydrogen flow a 7.
For the purposes of the present invention, the pre-cooling sub-step A3a) and/or the first cooling sub- step A3b) are also carried out by heat exchange with a refrigerant fluid flow circulating in a refrigerant fluid circuit, as will be described below.
For the purposes of the present invention, one and any further cooling sub-steps A3d) are carried out by heat exchange in a fourth heat exchanger a TE4 with a refrigerant fluid flow, circulating in a refrigerant fluid circuit, as it will be described below.
From sub-step A3), a cooled gaseous hydrogen flow a 8 is thus obtained, which is stored in a gaseous hydrogen tank a TH 2 g.
For the purposes of the present invention, sub- step A4) comprises the sub-steps of:
A4a) pre-cooling,
A4b) first cooling,
A4c) stabilization.
A4d) one or more further cooling operations.
For the purposes of the present invention, the pre-cooling sub-step A4a) is carried out in the second heat exchanger a TE2 for heat exchange with a liquid and/or cryo-compressed nitrogen flow at a first heating level a 32 and possibly also with an expanded nitrogen flow a 34, as described above, obtaining a second portion of the pre-cooled hydrogen flow a 10. For the purposes of the present invention, the first cooling step A4b) is carried out in the third heat exchanger a TE3 for heat exchange with a pumped liquid and/or cryo-compressed nitrogen flow a 31, as described above, obtaining a second portion of the cooled hydrogen flow a ll.
According to an aspect of the present invention, the second portion of the cooled hydrogen flow a ll can be subjected to the stabilization sub-step A4c) for the catalytic conversion of the hydrogen from the ortho form to the para form, obtaining a second portion of the cooled and stabilized hydrogen flow a 14.
Possibly, the second portion of the cooled hydrogen flow a ll can be divided into a first a 12' and a second a 12'' portion, each of which is subjected to the stabilization step in a respective converter a CONVl, a CONV2, obtaining a first portion of converted hydrogen a 13' and a second portion of converted hydrogen a 13'', which can be joined in the second portion of the cooled and stabilized hydrogen flow a 14.
According to an aspect of the present invention, the cooled and stabilized hydrogen flow a 14 can be subjected to a further first ortho/para cooling and stabilization step A4b), obtaining a further cooled and stabilized hydrogen flow a 15. The cooled hydrogen flow a ll or the further cooled and stabilized hydrogen flow a 15, obtained as described above, are subjected to at least one further ortho/para cooling and stabilization step A4d) in a fourth heat exchanger a TE4 (as described for step A4c)), obtaining an even further cooled and stabilized hydrogen flow a 16.
For the purposes of the present invention, such at least one and possible further cooling and stabilization steps (ortho/para A4d) are carried out by heat exchange (in the presence of an ortho/para conversion catalyst) with a refrigerant fluid, circulating in a refrigerant fluid circuit, as will be described below.
According to an aspect of the present invention, by means of such at least one and possible further ortho/para cooling and stabilization steps carried out in a fifth heat exchanger a TE5 (or in one or further heat exchangers a TE5', a TE5''), hydrogen flows are obtained which are gradually further cooled and stabilized a 17, a 17', a 17''' until obtaining a liquid hydrogen flow a 17''', which is stored in a liquid hydrogen tank a TH 2 I at a temperature of about -195°C.
A recirculating liquid hydrogen flow a H 2 r, which can be subjected to one of the further cooling steps A4d) and ortho/para stabilization (as diagrammatically shown in figure 1), can be obtained from the liquid hydrogen tank a TH 2 I.
For the purposes of the present invention, the liquid nitrogen flow used in the above-described heat exchange steps (sub-steps A3a), A3b), A4a) and A4b)) is a liquid nitrogen flow withdrawn from liquid nitrogen tank a TN 2 l (the embodiment using cryo- compressed nitrogen is contemplated by the present invention even if not depicted in the figures).
In particular, a first liquid nitrogen flow a 30 is obtained from said liquid nitrogen tank a TN 2 l, which is withdrawn and pumped in a pump a PN 2 l.
For example, up to 150 bar g can be pumped.
The pumped liquid nitrogen flow a 31 thus obtained is then used in the first cooling steps A3b) and A4b) obtaining a nitrogen flow at a first heating level a 32.
The nitrogen flow at a first heating level a 32 thus obtained is used in the pre-cooling steps A3a) and A4a), obtaining a gaseous nitrogen flow at a second heating level a 33.
The gaseous nitrogen flow at a second heating level a 33 can then be expanded in an expander a EXN 2 l, obtaining an expanded nitrogen flow a 34, which is further heated by a further possible pre-cooling step A3a) and A4a) until a gaseous nitrogen flow a 35 is obtained, which can be released into the atmosphere or used in the regeneration of molecular sieves.
For the purposes of the present invention, the liquid nitrogen used in the storage step described above is obtained from a generation step B) or B') as described below.
Refrigerant fluid circuit
For the purposes of the present invention, the fluid circulating in the refrigerant fluid circuit a 100 can be represented by hydrogen or helium and is preferably represented by hydrogen.
The refrigerant fluid circuit does not represent a limiting element of the present invention, as it is sufficient that it allows cooling the first a 5 and the second a 9 portions of the preliminarily cooled hydrogen flow a 4 until obtaining liquid and gaseous hydrogen as described above.
According to an embodiment of the present invention, for example depicted in figure 1, such a circuit a 100 can operate according to the Claude cycle.
Such a cycle includes at least two compression steps of the refrigerant fluid contained in a tank a Tfr, and at least three expansion steps, two of which are obtained by expander machines a EXlfr, a EX2fr and the third by a valve a Vfr.
After being withdrawn from the tank a Tfr, the refrigerant fluid flow therefore carries out the heat exchange steps:
- A4c) and A4d) of at least one and any further cooling operations,
- A3b) and A4b) of first cooling, and
- A3a) and A4a) of pre-cooling.
The above steps can be carried out in countercurrent or in co-current and can possibly be repeated, in the same direction or not.
As for the expansion steps, each expansion follows a possible further heat exchange step with the hydrogen flow of steps A4c) and A4d).
Step B)
For the purposes of the present invention, step B) comprises the sub-steps of:
Bl) subjecting an air flow g l to combustion in the presence of an overall vaporized hydrogen flow g 33, and obtaining a combustion gas flow g 3,
B2) expanding said combustion gas flow g 3, thus obtaining an expanded combustion gas flow g 4,
B3) cooling said expanded combustion gas flow g 4 and obtaining a cooled expanded combustion gas flow g 6, B4) subjecting said cooled expanded combustion gas flow g 6 to a water separation step g wl, thus obtaining a dehydrated combustion gas flow g 7,
B5) possibly separating a first recirculation portion g 8 from said dehydrated combustion gas flow g 7, which is joined to the air flow g l of sub-step Bl),
B6) subjecting a second portion g 9 separated from said dehydrated combustion gas flow g 7 to compression, obtaining a compressed dehydrated combustion gas flow glO,
B7) subjecting said compressed dehydrated combustion gas flow g 10 to cooling and at least one water separation step g w2, thus obtaining a nitrogen flow g 13,
B8) subjecting said nitrogen flow g 13 to condensation, thus obtaining a liquid nitrogen flow g 14.
With reference to sub-step Bl), this is carried out in a combustor g COMB.
For the purposes of the present invention, sub- step Bl) can be carried out on an air flow g l preliminarily subjected to filtration by means of a filter g F, thus obtaining a filtered air flow g l'.
In another aspect of the present invention, the air flow g l or the filtered air flow g l' is compressed in a compressor g TC, thus obtaining a compressed air flow g 2.
Therefore, the combustion of sub-step Bl) can be carried out on an air flow g l or filtered air flow g l' or on a compressed air flow g 2.
For the purposes of the present invention, sub- step Bl) can be carried out in the combustor g COMB even in the presence of a compressed recirculating nitrogen flow g R2 as described below.
In a particular aspect of the invention, the air flow g l, possibly filtered g l' and/or compressed g 2, is joined to the first recirculating portion g 8 according to sub-step B5) described above.
Advantageously, such a first recirculating portion g 8 has the effect of moderating the combustion temperature of sub-step Bl), which is normally between 900-1,800°C and preferably is around l,500°C, avoiding the use of complex cooling systems; furthermore, it allows achieving an optimal volumetric flow for the use of a compressor and the gas turbine of the next step .
In an alternative aspect of the present invention, if linked to technical needs of the process or of the combustor, a part of the recirculating portion g 8' can be sent, instead of being suctioned to the compressor g TC, in whole or partially, directly to the combustor gCOMB, as a dilution gas, after compression in a compressor of the recirculating flow g C01
.or the purposes of the present invention, the combustion of sub-step Bl) is carried out in the presence of an overall vaporized hydrogen flow g 33 as it will be described below.
Water and heated combustion gases are obtained with the combustion of sub-step Bl), which are generally referred to with a combustion gas flow g 3.
In an aspect of the present invention, the expansion sub-step B2) is carried out in a gas turbine g GT which, by virtue of the connection with a generator g E, produces electricity.
In an aspect of the present invention, the cooling sub-step B3) of the combustion gases g 4 comprises the sub-steps of:
B3a) cooling in a first heat exchanger g TE1 by a working fluid, circulating in a working fluid circuit, as described below, and
B3b) cooling in a second heat exchanger g TE2 by an external refrigerant fluid.
Such an external refrigerant fluid can be represented by water or air at ambient temperature and is preferably represented by water. In a preferred aspect, after the cooling sub-step
B3a), a portion of the flow g fl can be released into the atmosphere.
For the purposes of the present invention, the external refrigerant fluid used in sub-step B3b) can be represented by ambient temperature air or water.
As for sub-step B4), this comprises the separation of the condensed water g wl by a first separator g Sl.
A first portion g 8, representing the recirculating flow, and a second portion g 9, which is sent to the compressor g C1 for sub-step B6), is thus separated from the dehydrated combustion gas flow g 7 obtained.
For the purposes of the present invention, the compression sub-step B6) is carried out in a first compressor g Cl, thus obtaining a compressed dehydrated gas flow g 10.
In an aspect of the present invention, the cooling of sub-step B7) is carried out in a third heat exchanger g TE3 and is obtained by heat exchange with a heated gaseous hydrogen flow g 31 and with a heated vaporized hydrogen flow g 22 as described below.
The at least one water separation step is carried out in a second separator g S2, thus obtaining a second water flow g w2. A further dehydration step can be carried out out in a dehydration unit g DU by molecular sieves, thus obtaining a nitrogen flow g 13.
In a preferred aspect, such a dehydration is carried out until reducing the water content below 500 ppm and preferably below 50 ppm.
For the purposes of the present invention, the cooling sub-step B8) is carried out in a fourth exchanger g TE4 for heat exchange with a gaseous hydrogen flow g 30 and with a pumped liquid hydrogen flow g 21.
In particular, such a pumped liquid hydrogen flow g 21 is obtained from a liquid hydrogen flow g 20 pumped by a liquid hydrogen pump g PH 2 I.
The liquid nitrogen flow g 14 thus obtained is stored in a liquid nitrogen tank g TN 2 l.
Non-condensables originate from such a tank g TN 2 l, which form a recirculating nitrogen flow g Rl which can be sent to a second compressor g C2, thus obtaining a compressed recirculating nitrogen flow g R2 consisting mainly of hydrogen, oxygen and nitrogen, which, as described above, can be recirculated to the combustor g COMB for sub-step Bl). For the purposes of the present invention, the liquid nitrogen flow obtained in sub-step B8) is used to carry out the pre-cooling of sub-step A3a).
According to an aspect of the present invention, the liquid nitrogen flow obtained in sub-step B8) is also used to carry out the pre-cooling sub-step A4a).
For the purposes of the present invention, the gaseous hydrogen stored in the gaseous hydrogen tank g TH 2 g and the liquid hydrogen stored in the liquid hydrogen tank g TH 2 l are obtained by steps A3) and A4) of the storage step described above, respectively; therefore, the tanks a TH 2 g and g TH 2 g coincide with each other, as well as the tanks a TH 2 l and g TH 2 l.
For the purposes of the present invention, after sub-step B8) the heated gaseous hydrogen flow g 31 and the heated vaporized hydrogen flow g 22 are both sent to the cooling sub-step B7) in the third exchanger g TE3, thus obtaining a further heated gaseous hydrogen flow g 32 and a further heated vaporized hydrogen flow g 23, which are joined in an overall vaporized hydrogen flow g 33.
Such an overall vaporized hydrogen flow g 33 is sent to the combustor g COMB for sub-step Bl), possibly after having drained a portion g 34, which can be sent to the natural gas network or to the hydrogen network of a refinery.
Working fluid circuit
For the purposes of the present invention, the cooling of sub-step B3a) is obtained with a working fluid which is selected from the group comprising air and water and it is preferably represented by water.
After the heat exchange step B3a) in a first exchanger g TE1, a second heated working fluid flow g fl2 thus obtained is expanded in a steam turbine g STl providing an expanded flow g fl3, which, connected to a first generator g El, can generate electricity.
The thus obtained expanded flow g fl3 is further heated in a second heat exchange in the heat exchanger g TE1 giving a heated flow g fl4, which is subjected to a second expansion in a second expansion turbine g ST2, which, connected to a second generator g E2, can generate electricity.
The thus obtained further expanded flow g fl5 is cooled in a fifth exchanger g TE5 by the use of an external refrigerant fluid and sent, possibly after having been pumped in a working fluid pump g Pfl, thus obtaining a pumped fluid g fll, to the heat exchange step B3a). Such an external refrigerant fluid can be represented by water or air at ambient temperature and is preferably represented by water.
In accordance with an alternative embodiment, the generation step B) according to the present invention is a step B') comprising the use of a fuel cell for producing electricity.
According to such an embodiment, in step B'1) the air flow 1 to be subjected to combustion in the combustor g' COMB is preliminarily subjected to a treatment comprising the following sub-steps: b0) if necessary, filtering by means of a filter g’F, thus obtaining a filtered air flow g' 1', b1) compressing and obtaining a compressed air flow g' 4, b2) heating, thus obtaining a compressed and heated air flow g' 8, b3) reducing the oxygen contained in said compressed and heated air flow g' 8, thus obtaining a reduced flow g' 9, b4) cooling said reduced flow g' 9, thus obtaining a cooled flow g' 10 and joining to an integration flow g' 6. For the purposes of the present invention, the compression sub-step bl) can subject the air flow g' 1 or filtered air flow g' 1' to the sub-steps of: bla) first compression in a first compressor g' C1, thus obtaining a flow at a first compression level g' 2, bib) cooling in a first heat exchanger g' TE1, thus obtaining a flow at a first cooled compression level g' 3, and b1c) second compression in a second compressor g' C2, thus obtaining the compressed flow g' 4.
In particular, sub-step bib) is obtained by heat exchange with an external refrigerant fluid.
Such an external refrigerant fluid can be represented by water or air at ambient temperature and is preferably represented by water.
As for sub-step b2), this comprises three heating steps, in which:
- sub-step b2a) is obtained by heat exchange in a second exchanger g' TE2 with an expanded combustion gas flow g' 13 as described below, thus obtaining a first heating flow g' 5,
- sub-step b2b) is obtained by heat exchange in a third exchanger g' TE3 with a first inert fluid flow g' fil, for example represented by nitrogen, thus obtaining a flow at a second heating level g' 7, and sub-step b2c) is obtained by heat exchange in a fourth exchanger g' TE4 with the reduced flow g' 9, thus obtaining a compressed and heated air flow g' 8.
For the purposes of the present invention, after sub-step b2a) an integration flow g' 6 is separated from the first heating flow g' 5, which is sent to the combustor g' COMB for sub-step B'l) after joining the cooled flow g' 10, giving a joined flow g' 1l.
As for sub-step b3), this is obtained in the anode of a fuel cell, thus obtaining the reduction of oxygen and the formation of a reduced flow g' 9.
The thus obtained reduced flow g' 9 is cooled in sub-step b4) by the heat exchange described above with reference to sub-step b2c).
According to the alternative embodiment of the present invention, an overall vaporized hydrogen flow g' 33 is sent to the combustor g' COMB for the combustion of sub-step B'l).
In particular, such an overall vaporized hydrogen flow g' 33 is obtained by joining a heated gaseous hydrogen flow g' 41 and a pumped and heated vaporized hydrogen flow g' 32, as described below.
Furthermore, for the purposes of the present invention, a compressed recirculating nitrogen flow g' R2 consisting mainly of hydrogen, oxygen and nitrogen, obtained as described below, can be joined with such an overall vaporized hydrogen flow g' 33, giving a flow to be subjected to combustion g' 35.
From the same overall vaporized hydrogen flow g' 33 a portion g' 34 can be drawn, which can be sent to the natural gas network or to the hydrogen network of a refinery.
For the purposes of the present invention, such heated gaseous hydrogen g' 41 and pumped and heated vaporized hydrogen g' 32 flows are obtained from the respective tanks g' TH 2 g and g' TH 2 I.
For the purposes of the present invention, before being sent to the combustor g' COMB for sub-step B'1), such a flow to be sent to the combustor g' 35 is subjected to the steps of: b'1) heating, obtaining a heated flow g' 50 to be oxidized, b'2) oxidizing the hydrogen contained in the heated flow g' 50 to be oxidized, thus obtaining an oxidized flow g' 51, b'3) further cooling, thus obtaining a cooled oxidized flow g' 52.
In particular, sub-step b'1) is obtained in the first heat exchanger g' TE2 for heat exchange with the expanded combustion gas flow g' 13. For the purposes of the present invention, the heating step b'1) is carried out in the same exchanger as sub-step b2a).
As for sub-step b'2), this is obtained in the cathode of a fuel cell g' FC and, in particular, in the same fuel cell of sub-step b3).
The further cooling sub-step b'3) is carried out in a fifth heat exchanger g' TE5 for heat exchange with a third inert fluid flow g' fi3, for example represented by nitrogen, as described below.
In particular, a first inert fluid flow g' fi1 carries out the heat exchange in the third heat exchanger g' TE3, thus obtaining a second inert fluid flow g' fi2, which is pumped by an inert fluid pump g' Pfi, thus obtaining the third inert fluid flow g' fi3 referred to above.
After heat exchange in the fifth heat exchanger g' TE5, the first inert fluid flow g' fil of step b2b) is obtained.
According to the alternative embodiment described above, a combustion gas flow g' 12 is obtained from the combustion step B'1), which is subjected to the further steps of: B'2) expanding said combustion gas flow g' 12 in an expander g' EX, thus obtaining an expanded combustion flue gas flow g' 13,
B3) cooling said expanded combustion gas flow g' 13 and obtaining an expanded and further cooled combustion gas flow g' 15,
B'4) separating the water and obtaining a nitrogen flow g' 20,
B'5) subjecting said nitrogen flow g' 20 to cooling and condensation in an eighth heat exchanger g' TE8, thus obtaining a liquid nitrogen flow g' 21.
Such a liquid nitrogen flow g' 21 is then stored in a liquid nitrogen tank g' TN 2 l.
The non-condensables originate from the liquid nitrogen tank g' TN 2 l; in fact, a recirculating flow g' Rl is obtained from the tank, which is compressed in a fourth compressor g' C4, giving the compressed recirculating nitrogen flow g' R2 described above.
For the purposes of the present invention, the liquid nitrogen flow obtained in sub-step B'5) is used to carry out the pre-cooling sub-step A3a).
According to an aspect of the present invention, the liquid nitrogen flow obtained in sub-step B'5) is also used to carry out the pre-cooling sub-step A4a). For the purposes of the present invention, sub- step B'3) comprises the further sub-steps of:
B'3a) cooling said expanded combustion gas flow g' 13 in the second heat exchanger g' TE2, thus obtaining a first cooled flow g' 14, and
B'3b) cooling said first cooled flow g' 14 in a sixth heat exchanger g' TE6, thus obtaining said expanded and further cooled combustion gas flow g' 15.
Step B'3b) is carried out by heat exchange with an external refrigerant fluid.
Such an external refrigerant fluid can be represented by water or air at ambient temperature and is preferably represented by water.
For the purposes of the present invention, said sub-step B'4) comprises the further sub-steps of:
B'4a) subjecting said expanded and further cooled combustion gas flow g' 15 to a first water separation g' wl in a first separator g' Sl, thus obtaining a dehydrated combustion gas flow g' 16,
B'4b) compressing said dehydrated combustion gas flow g' 16 in a third compressor g' C3 obtaining a compressed dehydrated combustion gas flow g' 17,
B'4c) cooling said compressed dehydrated combustion gas flow g' 17 in a seventh heat exchanger g' TE7, thus obtaining a compressed and cooled dehydrated combustion gas flow g' 18,
B'4d) subjecting said compressed and cooled dehydrated combustion gas flow g' 18 to a second water separation g' w2 in a second separator g' S2, thus obtaining a further dehydrated combustion gas flow g' 19,
B'4e) subjecting the flow thus obtained to further dehydration in a Dehydration Unit g' DU, thus obtaining the nitrogen flow g' 20.
For the purposes of the present invention, step B'4c) is carried out in the seventh heat exchanger g' TE7 for heat exchange with an external refrigerant fluid.
Such an external refrigerant fluid can be represented by water or air at ambient temperature and is preferably represented by water.
For the purposes of the present invention, step B'4e) in the Dehydration Unit g' DU is carried out until the water content is reduced below 500 ppm and preferably below 50 ppm.
According to the alternative embodiment of the present invention, sub-step B'5) is carried out by heat exchange with the gaseous hydrogen flow g' 40 and with the pumped liquid hydrogen flow g' 31.
In particular, said pumped liquid hydrogen flow g' 31 is obtained by pumping with a liquid hydrogen pump g' PH 2 I a liquid hydrogen flow g' 3O obtained from the liquid hydrogen tank g' TH 2 I.
For the purposes of the present invention, the gaseous hydrogen stored in the gaseous hydrogen tank g' TH 2 g and the liquid hydrogen stored in the liquid hydrogen tank g' TH 2 I are obtained by steps A3) and A4) of the storage step described above, respectively; therefore, the tanks a TH 2 g and g' TH 2 g coincide with each other, as well as the tanks a TH 2 I and g' TH 2 I.
As described above, for the purposes of the present invention, the liquid nitrogen and liquid and gaseous hydrogen tanks of the storage step and the generation step coincide (respectively: a TN 2 l, g TN 2 l, g' TN 2 l; a TH 2 l, g TH 2 l, g' TH 2 l, a TH 2 g, gTH 2 g, g' TH 2 g).
In other words, the liquid nitrogen used in step A) coincides with the liquid nitrogen produced in generation step B) or B'); likewise, the liquid hydrogen and the gaseous hydrogen obtained with the storage step A) are used in the generation step B) or B').
More in particular, the liquid nitrogen used in step A) is produced in step B) or B') from a combustion gas flow. In accordance with a further object, a plant for carrying out the above-described process of the invention is described.
In particular, such a plant comprises: a liquid and/or cryo-compressed nitrogen tank a TN 2 l, g TN 2 l, g' TN 2 l, a liquid hydrogen tank a TH 2 I, g TH 2 I, g' TH 2 I, a gaseous hydrogen tank a TH 2 g,gTH 2 g, g' TH 2 g, an air compressor g TC, g' TCl, g' TC2, a combustor for combusting an air flow gCOMB, g' COMB, a gas turbine g GT with a generator g E or an expander g' EX for generating electricity, and heat exchangers a TE2, a TE3, g TE4, g' TE8 for the heat exchange between a liquid nitrogen flow and a liquid and gaseous and/or cryo-compressed hydrogen flow.
According to an aspect of the present invention, a fuel cell g' FC for the further production of electricity can be further comprised.
According to a particular aspect of the present invention, the plant is that which carries out the process as described above.
Two applications of the process of the present invention will be described below.
Electricity storage and production cycle
Since the alternation of day and night and the different distribution of solar energy during the day brings a misalignment between demand and supply, it is possible to design a solar field to cover the peak demand, thus eliminating the need to resort to other energy sources (fossil) and store the excess energy to be able to use it during the night.
The excess energy can be used to produce hydrogen on site, by electrolysis, and store it both in liquid and cold and compressed gas form (cryo-compression).
The storage in gaseous form, given the low energy density technically obtainable, is limited and, despite having a lower energy cost, it is not economical when enough energy is to be stored to overcome the seasonal variations in electricity production: storage lasting more than a few hours or a few days requires storage in liquid form.
Therefore, the system can accumulate, at each cycle, both energy in the form of cryo-compressed hydrogen, which will be used entirely (or almost) during the night, and energy in the form of liquid hydrogen to be stored during the summer to compensate for the lack of daily production thereof during the winter.
The storage of liquid nitrogen will instead be countercyclical with respect to liquid hydrogen and, therefore, the quantity of nitrogen supplied by the gas turbine can be varied through the purge fl; the effect of the purge on energy generation by the power cycle is inversely proportional to the quantity of nitrogen made available.
Stabilization of the hydrogen network of a "green" refinery
The electricity produced by a solar field must not only supply energy to a refinery, but also directly produce hydrogen, by electrolysis, to be sent to the hydrogen network of the refinery, storing a part thereof both for electricity generation and to compensate for the lack of hydrogen in other hours.
During the generation step, hydrogen must also be vaporized in a quantity greater than that required by the consumption of the power cycle, in order to supply the hydrogen network in the absence of the electrolytic source.
Therefore, the power cycle must limit the purge fl to provide a greater quantity of nitrogen for the recovery of all the hydrogen frigories.
Similarly, the natural gas network can be stabilized, however taking into account the limits of admissibility of hydrogen in methane pipelines, mainly linked to the different calorific value of hydrogen and natural gas; in fact, the greater the quantity of hydrogen, the lower the energy transport capacity of the pipeline.
From the description provided above, the advantages offered by the present invention will be apparent to those skilled in the art.
The present invention allows integrating electrolytic hydrogen production technologies with hydrogen storage technologies, both in gaseous and cryo-compressed form, with the use of a gas turbine or an electrolytic cell, which can produce electricity and nitrogen, with a hydrogen frigories recovery system.
Therefore, the process described allows:
- stabilizing the electrical network, by virtue of the absorption of excess energy or by feeding energy into the network;
- stabilizing the combustible gas network,
- stabilizing the hydrogen network, because it is capable of producing hydrogen to be fed into the natural gas network or the hydrogen network, for example inside a refinery.
The described process can further be used for producing gaseous oxygen, even at high pressure, to be used for other purposes.
The described process advantageously does not release carbon dioxide into the environment. Furthermore, it does not require an air separation unit (ASU) to produce liquid nitrogen to be stored and uses widely available and technologically "mature" technologies such as gas turbines.
In fact, the process of the invention uses "self- produced" hydrogen and nitrogen, i.e., produced within the same process and, therefore, not required from external sources.
In the embodiment which applies sea water electrolysis, the described process can also be used to desalinate water, producing discrete amounts thereof as a by-product.
The use of gaseous hydrogen and liquid hydrogen allows optimally balancing the requirements of not having to bear excessive costs for storing hydrogen as a cryo-compressed gas, avoiding the (economic and logistical) problem of having metal containers suitable for storage.
Furthermore, while storage in gaseous form is normally used for a short period, for example daily, storage in liquid form is ideal in the long term; this allows adapting the process to specific needs, for example seasonal needs.
According to particular applications of the present invention, the electricity used in the storage step can be excess electricity absorbed from the network.
For example, it can be energy from renewable sources, such as photovoltaic energy, which, by its nature, has a daily and seasonal trend.
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