Patent Application
20250026650
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.
The present invention is further applicable to the production of ammonia.
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Such a process must be efficient, therefore it must have a high return coefficient of the energy withdrawn from the network, as well as practical, thus requiring limited storage spaces not linked to particular subsoil conformations, such as exhausted wells in which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.
In addition, the electrolytically produced hydrogen can be converted to ammonia, however using the nitrogen produced by an Air Separation Unit (ASU); the presence of oxygen in the reagents fed to the ammonia synthesis reactor, in addition to consuming hydrogen, produces water, which should then be separated, for example by distillation, from the produced ammonia.
Prior art document US 2021/340017 describes the electrolytic production of hydrogen and the subsequent sending thereof partly to ammonia synthesis reactors and partly stored after cooling, while the nitrogen, produced by cryogenic separation, is partly used for the synthesis of ammonia and partly stored for subsequent use.
Prior art documents US 2021/300759 and U.S. Pat. No. 4,107,277 describe processes for the synthesis of ammonia using a hydrogen flow obtained from water electrolysis and a nitrogen flow obtained from an Air Separation Unit (ASU).
Prior art document JP 2000002790 describes a nuclear plant which produces electricity stored in the form of liquid nitrogen and liquid oxygen by air separation, and hydrogen by electrolysis.
The inventors of the present patent application have surprisingly found that it is possible to integrate electrolytic hydrogen production technologies with hydrogen storage technologies, both in liquid and cryo-compressed form, with the use of liquid and/or cryo-compressed nitrogen systems.
Furthermore, the capacity of ammonia to act as a storage and transport medium for hydrogen is conveniently utilized.
In a first object, the present invention describes a process for producing and storing hydrogen, and producing electricity, and for producing and storing liquid and/or cryo-compressed nitrogen, and for producing ammonia.
According to an aspect, the process of the invention comprises a first step of producing and storing hydrogen and ammonia using electricity, preferably in excess, and liquid and/or cryo-compressed nitrogen.
According to another aspect, the process of the invention comprises a second step of generating electricity, producing and storing liquid and/or cryo-compressed nitrogen and for producing ammonia.
According to a further object, a plant for carrying out the process of the invention is described.
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 (step 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 process of the present invention comprises two steps: a first step of producing and storing liquid and/or cryo-compressed hydrogen (step A) and a second step of generating electricity and producing and storing liquid and/or cryo-compressed nitrogen (step B).
More in particular, said step A) is a step of producing and storing hydrogen and for producing ammonia.
In particular, in step A) the hydrogen is produced in liquid (H2l) and/or gaseous (H2g) form, in particular in cryo-compressed gaseous form.
More in particular, step A) is an energy-intensive step, as it uses electricity and, therefore, includes the consumption of electricity; therefore, it is carried out in circumstances where electricity is abundantly available.
As for step B), it is a step of producing and storing liquid and/or cryo-compressed nitrogen and producing ammonia.
In particular, in step B) nitrogen is produced in liquid (N2l) and/or cryo-compressed form.
More in particular, in step B) the nitrogen is produced from a combusted gas flow, which, for example, can be obtained from the combustion of an air flow.
For the purposes of the present invention, step B) is further a step of producing electricity; therefore, it is carried out in circumstances where there is an increased demand for electricity or it is less available.
For the purposes of the present invention, step A) comprises using the liquid and/or cryo-compressed nitrogen produced and stored in step B).
For the purposes of the present invention, step B) comprises using the liquid and/or cryo-compressed hydrogen produced and stored in step A).
The process is described as a whole as comprising step A) and step B); said steps are alternatives to each other.
Each step will be described in greater detail below.
For the purposes of the present invention, step A) comprises the sub-steps of:
In an aspect of the present invention, sub-step A1) is carried out in an electrolytic cell aEC and can use sea water; in this case, the electrolytic cell aEC can be provided with a purge system for the brine B.
According to a preferred aspect of the present invention, in sub-step A1) the electrolytic cell aEC uses electricity, preferably available in excess (therefore in circumstances where abundant electricity is available).
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 a2 obtained from sub-step A1) is intended for export, as a valuable by-product.
In an aspect of the present invention, prior to the preliminary cooling sub-step A2), the hydrogen flow a3 obtained from sub-step A1) can be compressed in a first compressor aC1; therefore, sub-step A2) can be carried out on a hydrogen flow a3 or on a compressed hydrogen flow a3′.
For the purposes of the present invention, sub-step A3) comprises the steps of: A3a) subjecting said first portion a40 of the preliminarily cooled hydrogen flow to compression in a second compressor aC2, thus obtaining a first portion of compressed hydrogen a41.
In the Ammonia Synthesis Unit aNH3SU, the first portion of compressed hydrogen a41 is converted to ammonia NH3 also using a nitrogen flow as will be described below.
For the purposes of the present invention, the synthesis of ammonia within the Ammonia Synthesis Unit aNH3SU produces heat, which can be recovered by using a first working fluid circulating in a first working fluid circuit, as will be described below.
For the purposes of the present invention, sub-step A4) comprises the sub-steps of:
For the purposes of the present invention, the pre-cooling sub-step A4a) is carried out in a second heat exchanger aTE2 for heat exchange with a liquid and/or cryo-compressed nitrogen flow a32 at a first heating level, thus obtaining a second portion of the pre-cooled hydrogen flow a6.
Possibly, such a step A4a) can also involve an additional heated refrigerant fluid a51, which circulates within a circuit of an additional refrigerant fluid a200, as will be described below.
For the purposes of the present invention, the first cooling sub-step A4b) is carried out in a third heat exchanger aTE3 for heat exchange with a pumped liquid and/or cryo-compressed nitrogen flow a31, as it will be described below, obtaining a second portion of the cooled hydrogen flow a7.
Possibly, such a step A4b) can also involve an additional refrigerant fluid flow a50 circulating in a circuit of an additional refrigerant fluid a200, as will be described below.
For the purposes of the present invention, the pre-cooling sub-step A4a) and/or the first cooling sub-step A4b) can also be carried out by heat exchange with a refrigerant fluid flow circulating in a refrigerant fluid circuit a100, as will be described below.
For the purposes of the present invention, the stabilization step A4c) (as described below with reference to step A5c)) is optional (and not depicted in the figures).
For the purposes of the present invention, one and any further cooling sub-steps A4d) are carried out in a fourth aTE4 heat exchanger for heat exchange with a refrigerant fluid flow circulating in a refrigerant fluid circuit, as it will be described below.
From sub-step A4), a cooled gaseous hydrogen flow a8 is thus obtained, which is stored in a gaseous hydrogen tank aTH2g.
For the purposes of the present invention, sub-step A5) comprises the sub-steps of:
For the purposes of the present invention, the pre-cooling sub-step A5a) is carried out in a second heat exchanger aTE2 for heat exchange with a liquid and/or cryo-compressed nitrogen flow a32 at a first heating level as will be described below, thus obtaining a third portion of the pre-cooled hydrogen flow a10.
Possibly, such a step A5a) can also involve an additional heated refrigerant fluid a51, which circulates within a circuit of an additional refrigerant fluid a200, as will be described below.
For the purposes of the present invention, the first cooling step A5b) is carried out in a third heat exchanger aTE3 for heat exchange with a pumped liquid and/or cryo-compressed nitrogen flow a31, as it will be described below, thus obtaining a third portion of the cooled hydrogen flow a11.
Possibly, such a step A5b) can also involve an additional refrigerant fluid flow a50 circulating in a circuit of an additional refrigerant fluid a200, as will be described below.
According to an aspect of the present invention, the third portion of the cooled hydrogen flow a11 can be subjected to the stabilization sub-step A5c) for the catalytic conversion of the hydrogen from the ortho form to the para form, thus obtaining a third portion of the cooled and stabilized hydrogen flow a14.
Possibly, the flow of the third portion of the cooled hydrogen flow a11 can be divided into a first portion to be stabilized a12′ and a second portion to be stabilized a12″, each of which is subjected to the stabilization step in a respective converter aCONV1, aCONV2 obtaining a first portion of stabilized hydrogen a13′ and a second portion of stabilized hydrogen a13″, which can be joined in the third portion of the cooled and stabilized hydrogen flow a14.
According to an aspect of the present invention, the cooled and stabilized hydrogen flow a14 can be subjected to a further first cooling step A5b) in the third heat exchanger aTE3, thus obtaining a further cooled and stabilized hydrogen flow a15.
The cooled hydrogen flow a11 or the further cooled and stabilized hydrogen flow a15 obtained as described above are subjected to at least one further cooling step A5d) in a fourth heat exchanger aTE4 and any further cooling in a fifth heat exchanger aTE5 and any further fifth heat exchangers aTE5′, aTE5″, aTE5′″, thus obtaining an even further cooled hydrogen flow a16.
For the purposes of the present invention, such at least one and any further cooling steps A5d) are carried out by heat exchange with a refrigerant fluid circulating in a refrigerant fluid circuit, as it will be described below.
For the purposes of the present invention, the cooling steps can preferably be carried out in the presence of a catalyst for catalyzing the conversion of hydrogen from the ortho to the para form.
According to an aspect of the present invention, by means of such at least one and any further cooling steps, more and more cooled hydrogen flows a17, a17′, a17″ are obtained until a liquid hydrogen flow a17′″ is obtained, which is stored in a liquid hydrogen tank aTH2l (normally at a temperature below −195° C.).
From such a tank a recirculation flow aH2r can be withdrawn, which can be subjected to one of the further cooling steps A5d) (as it is diagrammatically shown in
For the purposes of the present invention, the liquid nitrogen flow used in the above-described heat exchange steps (sub-steps A4a), A4b), A5a) and A5b)) is a liquid nitrogen flow withdrawn from liquid nitrogen tank aTN2l (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 a30 is obtained from said liquid nitrogen tank aTN2l, which is withdrawn and pumped in a pump aPN2l.
For example, up to 150 bar g can be pumped.
The pumped liquid nitrogen flow a31 thus obtained is then used in the first cooling steps A4b) and A5b) obtaining a nitrogen flow at a first heating level a32.
The nitrogen flow at a first heating level a32 thus obtained is used in the pre-cooling steps A4a) and A5a), obtaining a liquid nitrogen flow a33 at a second heating level.
For the purposes of the present invention, and as described above, the liquid nitrogen flow a33 at a second heating level is sent to an Ammonia Synthesis Unit aNH3SU.
According to a particular aspect, prior to this, the liquid nitrogen flow a33 at a second heating level can actuate a heat exchange step with the refrigerant fluid.
The liquid nitrogen flow a34 at a third heating level thus obtained or the liquid nitrogen flow a33 at a second heating level are then sent to the Ammonia Synthesis Unit aNH3SU, from which an ammonia flow (NH3) is obtained.
A purge flow a35 released into the atmosphere is also obtained from the Ammonia Synthesis Unit aNH3SU.
Refrigerant fluid circuit For the purposes of the present invention, the fluid circulating in the refrigerant fluid circuit a100 can be represented by hydrogen or helium and it 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 a5 and the third a9 portions of the preliminarily cooled hydrogen flow as described above.
According to an embodiment of the present invention, for example depicted in
Such a cycle includes at least three expansion steps of the refrigerant fluid contained in a tank aTfr, of which two expansion steps are obtained by means of a first and a second expander aEX1fr, aEX2fr and the third expansion step by means of a valve aVfr.
After being withdrawn from the tank aTfr, the refrigerant fluid flow therefore carries out the heat exchange steps:
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 A4d) and A5d).
Additional refrigerant fluid circuit For the purposes of the present invention and as described above, an additional refrigerant fluid circuit a200 can be included.
Such a fluid circulates in a circuit from which an additional refrigerant fluid flow a50 originates, which can be involved in step A4b) and/or A5b) (described above), thus obtaining a heated additional refrigerant fluid flow a51.
In turn, such a heated additional refrigerant fluid flow a51 can also be involved in step A4a) and/or A5a) (described above), thus obtaining a further heated additional refrigerant fluid flow a52, which recirculates in the circuit a200.
For the purposes of the present invention, the additional refrigerant fluid can be represented, for example, by nitrogen, ammonia, propane, ethylene.
First Working Fluid Circuit (flI)
As described above, the heat produced by the synthesis of ammonia is recovered by using a first working fluid.
A first flow of the first working fluid aflI1 is first condensed in a heat exchanger of the first working fluid aTEflI by an external refrigerant fluid, thus obtaining a cooled flow aflI2, which is pumped by a pump of the first working fluid aPflI, thus obtaining a pumped first working fluid flow aflI3.
Said pumped flow aflI3 acquires heat from the Ammonia Synthesis Unit aNH3SU by vaporizing, thus obtaining a heated flow aflI4, which is expanded in a steam turbine aSTflI, which, by virtue of a generator aEflI, produces electricity.
The expanded flow thus obtained is the first flow of the first working fluid aflI1 which is sent to the exchanger aTEflI.
For the purposes of the present invention, the first working fluid afll can be represented by water or air and is preferably represented by water.
For the purposes of the present invention, the above condensation is obtained by heat exchange with an external refrigerant fluid.
Such an external refrigerant fluid can be represented by water or air and is preferably represented by water.
For the purposes of the present invention, step B) comprises the sub-steps of:
For the purposes of the present invention, the pre-cooling of sub-step A4a) and the pre-cooling of sub-step A5a) are carried out using the liquid nitrogen flow obtained and stored in sub-step B10).
According to an aspect of the present invention, the cooling of sub-step A4b) and the cooling of sub-step A5b) are also carried out using the liquid nitrogen flow obtained and stored in sub-step B10).
With reference to sub-step B1), this is carried out in a combustor gCOMB.
For the purposes of the present invention, sub-step B1) can be carried out on an air flow g1 preliminarily subjected to filtration by means of a filter gF, thus obtaining a filtered air flow g1′.
In another aspect of the present invention, the air flow g1 or the filtered air flow g1′ is compressed in a compressor gTC, thus obtaining a compressed air flow g2.
Therefore, the combustion of sub-step B1) can be carried out on an air flow g1 or filtered air flow g1′ or on a compressed air flow g2.
For the purposes of the present invention, sub-step B1) can be carried out in the combustor gCOMB even in the presence of a compressed flow of non-condensables gR2 as described below.
In a particular aspect of the invention, the air flow g1, possibly filtered g1′ and/or compressed g2, is joined to the recirculating flow g8 according to sub-step B7) described above.
In an alternative aspect of the present invention as shown in
Advantageously, such a recirculating flow g8 and such a further recirculating flow g8″ have the effect of moderating the combustion temperature of sub-step B1), which is normally between 900-1,800° C. and preferably is around 1,500° 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.
For the purposes of the present invention, the combustion of sub-step B1) is carried out in the presence of an overall vaporized hydrogen flow g33 obtained as will be described below.
Water and heated combusted gases are obtained with the combustion of sub-step B1), which are generally referred to with a combusted gas flow g3.
In an aspect of the present invention, the expansion sub-step B2) is carried out in a gas turbine gGT with mechanical energy production which, by virtue of a generator gE, produces electricity.
In an aspect of the present invention, the first cooling sub-step B3) of the combusted gases g4 is carried out in a first heat exchanger gTE1 by a third working fluid gflIII, circulating in a third working fluid circuit, as described below.
In a preferred aspect, after the cooling sub-step B3), a portion of the flow gf1 can be released into the atmosphere.
In an aspect of the present invention, the second cooling sub-step B5) is carried out in a second heat exchanger gTE2 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.
As for sub-step B6), this comprises separating a first portion of condensed water gw1 from the bottom of a first separator gS1.
The first dehydrated flow obtained g7 is then divided into a first portion g8, representing the recirculating flow to the compressor gTC and into a second portion g9, which is sent to the compressor gC1 for sub-step B8).
For the purposes of the present invention, the compression sub-step B8) is carried out in a first compressor gC1, thus obtaining a compressed dehydrated gas flow g10.
In an aspect of the present invention, the cooling of sub-step B9) is carried out in a third heat exchanger gTE3 and is obtained by heat exchange with a heated gaseous hydrogen flow g31 and/or with a heated vaporized hydrogen flow g22 as described below, thus obtaining a dehydrated and compressed gas flow g11.
The at least one water separation step is carried out on said dehydrated and compressed gas flow g11 in a second separator gS2, thus obtaining a second portion of condensed water gw2 and a further dehydrated and compressed gas flow g12.
A further dehydration step can be carried out on said further dehydrated and compressed gas flow g12 in a first dehydration unit gDU1 by molecular sieves, thus obtaining a nitrogen flow g13.
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 B10) is a condensing step carried out in a fourth exchanger gTE4 for heat exchange with a gaseous hydrogen flow g30 and with a pumped liquid hydrogen flow g21.
In particular, such a gaseous hydrogen flow g30 is obtained from a gaseous hydrogen tank gTH2g.
In particular, such a pumped liquid hydrogen flow g21 is obtained from a liquid hydrogen flow g20 obtained from a liquid hydrogen tank gTH2l pumped by a liquid hydrogen pump gPH2l.
The liquid nitrogen flow g14 thus obtained is stored in a liquid nitrogen tank gTN2l.
A flow of non-condensables gR1 can develop from such a tank gTN2l, and can be sent to a second compressor gC2, thus obtaining a compressed flow of non-condensables gR2 consisting mainly of hydrogen, oxygen and nitrogen, which, as described above, can be recirculated to the combustor gCOMB for sub-step B1).
For the purposes of the present invention, the pre-cooling of sub-step A4a) is carried out by using the liquid nitrogen flow obtained in sub-step B10).
According to an aspect of the present invention, the pre-cooling sub-step A5a) can also be carried out by using the liquid nitrogen flow obtained in sub-step B10).
For the purposes of the present invention, the gaseous hydrogen stored in the gaseous hydrogen tank gTH2g and the liquid hydrogen stored in the liquid hydrogen tank gTH2l are obtained by steps A4) and A5) of the storage step A) described above, respectively; therefore, the tanks aTH2g and gTH2g coincide with each other, as well as the tanks aTH2l and gTH2l.
For the purposes of the present invention, after sub-step B10) the heated gaseous hydrogen flow g31 and/or the heated vaporized hydrogen flow g22 are both sent to the cooling sub-step B9) in the third exchanger gTE3, thus obtaining a vaporized heated hydrogen flow g32 and a further vaporized heated hydrogen flow g23, which are joined in an overall vaporized hydrogen flow g33.
Such an overall vaporized hydrogen flow g33 is sent to the combustor gCOMB for sub-step B1), possibly after having drained a portion g34, which can be sent to the natural gas network or to the hydrogen network of a refinery.
As described above, in step B4) a portion of the expanded combusted gases g40 at a first cooling level is separated, which is sent to an Ammonia Synthesis Unit gNH3SU.
Before being involved in the synthesis of ammonia NH3, such a portion g40 is subjected to one or more compression and cooling cycles for the separation of the condensed water and is subjected to compression.
Therefore, for this purpose, such a portion g40 is subjected to the steps:
For the purposes of the present invention, each of steps B4a) to B4c) are repeated one or more times until the desired dehydration level is obtained.
For the purposes of the present invention, a portion of synthesis hydrogen g35 is separated from the overall vaporized hydrogen flow g33 and sent to the Ammonia Synthesis Unit gNH3SU for the synthesis of ammonia NH3.
The synthesis nitrogen flow g45 and the portion of synthesis hydrogen g35 are then sent to the Ammonia Synthesis Unit.
A purge flow a36 released into the atmosphere is also obtained from the Ammonia Synthesis Unit gNH3SU.
For the purposes of the present invention, the synthesis of ammonia within the Ammonia Synthesis Unit gNH3SU produces heat, which can be recovered by using a second working fluid circulating in a second working fluid circuit, as will be described below.
Third Working Fluid Circuit (flIII)
For the purposes of the present invention, the first cooling of sub-step B3) is obtained with a third working fluid which is selected from the group comprising air and water and is preferably represented by water.
After the first-cooling heat exchange step B3) in a first exchanger gTE1, the third flow of the third heated working fluid gflIII3 thus obtained is expanded in a steam turbine gST1flIII, thus obtaining an expanded flow gflIII4; since such a turbine is connected to a first generator gE1, electricity can be produced.
The thus obtained expanded flow gflIII4 is further heated in the first heat exchanger gTE1, giving a heated flow of the third working fluid gflIII5, which is subjected to a second expansion in a second expansion turbine gST2flIII; since this is connected to a second generator gE2, electricity can be produced.
The further expanded flow of the second working fluid gflIII6 thus obtained is cooled in the exchanger of the third working fluid gTEflIII by using an external refrigerant fluid, thus obtaining a cooled flow gflIII1, which is pumped in a pump of the third working fluid gPflIII, thus obtaining a pumped flow gflIII2, which is used in the heat exchange step B3).
Such an external refrigerant fluid can be represented by water or air and is preferably represented by water.
Second Working Fluid Circuit (flII)
As described above, the heat produced by the synthesis of ammonia is recovered by using a second working fluid.
A first flow of the second working fluid gflII1 is first condensed in a heat exchanger of the second working fluid gTEflII by an external refrigerant fluid, thus obtaining a cooled flow gflII2, which is pumped by a pump of the second working fluid gPflII, thus obtaining a pumped second working fluid flow gflII3.
Said pumped flow gfllII3 acquires heat from the Ammonia Synthesis Unit gNH3SU by vaporizing, thus obtaining a heated flow gfllII4, which is expanded in a steam turbine gSTflII, which, by virtue of a generator gEflII, produces electricity.
The expanded flow thus obtained is the first flow of the second working fluid gflII1 which is sent to the exchanger gTEflII.
For the purposes of the present invention, the second working fluid flII can be represented by water or air and is preferably represented by water.
For the purposes of the present invention, the above condensation is obtained by heat exchange with an external refrigerant fluid.
Such an external refrigerant fluid can be represented by water or air 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 g′FC for producing electricity.
According to such an embodiment, the air flow g′1 to be subjected to combustion in the combustor g′COMB according to step B′1) is preliminarily subjected to a treatment comprising the following sub-steps:
For the purposes of the present invention, the compression sub-step b1) can subject the air flow g′1 or filtered air flow g′1′ to the sub-steps of:
In particular, sub-step b1b) of cooling in a first heat exchanger g TE1 is obtained by heat exchange with a fluid selected between air and water.
As for sub-step b2), this comprises three heating steps, in which:
For the purposes of the present invention, after sub-step b2a) of heat exchange in a second exchanger g′TE2, a heated integration flow g′6 is separated, which is joined to the cooled reduced flow g′10, thus obtaining an integrated flow g′11 sent to the combustor g′COMB for sub-step B′1).
As for sub-step b3) of oxygen reduction, this is obtained in the anode of a fuel cell g′FC, 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′1).
In particular, such a hydrogen flow is an overall vaporized hydrogen flow g′33 obtained by joining a heated gaseous hydrogen flow g′41 and/or a pumped and heated gaseous hydrogen flow g′32, as described below.
A release portion g′34 released into the atmosphere can be separated from the overall vaporized hydrogen flow g′33.
Furthermore, for the purposes of the present invention, a non-condensables 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 send to the combustor g′COMB for combustion g′35.
For the purposes of the present invention, such flows of heated gaseous hydrogen g′41 and pumped and heated gaseous hydrogen g′32 are obtained from the respective tanks g′TH2g and g′TH2l, in which they are stored after the storage sub-steps A4) and A5) described above with reference to step A); therefore, the tanks aTH2g and g′TH2g coincide with each other, as well as the tanks aTH2l and g′TH2l.
For the purposes of the present invention, a portion g′70 which is sent to the Ammonia Synthesis Unit g′NH3SU as described below is separated from the overall vaporized hydrogen flow g′33.
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:
In particular, the heating sub-step b′1) is obtained in the first heat exchanger g′TE2 for heat exchange with the expanded combusted 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 second flow of a fifth working fluid g′flv2 for example represented by nitrogen, circulating in a fifth working fluid circuit, as described below.
In particular, a third flow of a fifth working fluid g′flv3 carries out the heat exchange in the third heat exchanger g TE3, thus obtaining a first flow of the fifth working fluid g′flv1, which is pumped by a pump of the fifth working fluid g′Pflv, thus obtaining the second flow of the fifth working fluid g′flv2 above.
In an aspect of the present invention, said third flow of the fifth working fluid g′flv3 is the flow involved in the heat exchange of sub-step b2b).
According to the alternative embodiment described above, a combusted gas flow g′12 is obtained from the combustion step B′1), which is subjected to the further steps of:
The liquid nitrogen flow g′22 is then stored in a liquid nitrogen tank g′TN2l.
A flow of non-condensables g′R1 can develop from such a tank g′TN2l, which can be sent to a fourth compressor g′C4, thus obtaining a compressed flow of non-condensables g′R2 consisting mainly of hydrogen, oxygen and nitrogen, which, as described above, can be recirculated to the combustor g′COMB for the combustion step B′1).
For the purposes of the present invention, sub-step B′3) comprises the further sub-steps of:
For the purposes of the present invention, said sub-step B′4) comprises the further sub-steps of:
In a preferred aspect, such a dehydration is carried out until reducing the water content 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/or 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′PH2l a liquid hydrogen flow g′30 obtained from the liquid hydrogen tank g′TH2l.
As for step B′6), before sending to the Ammonia Synthesis Unit g′NH3SU, the second portion of nitrogen g′60 is compressed in a nitrogen compressor g′CN2, thus obtaining a compressed nitrogen flow g′61.
The synthesis of ammonia NH3 is thus obtained from the nitrogen flow g′61 and the hydrogen flow g′70.
Ammonia NH3 and a purge flow g′80 released into the atmosphere, containing nitrogen, argon, hydrogen and oxygen, in varying amounts, is obtained from the Ammonia Synthesis Unit g′NH3SU.
For the purposes of the present invention, the synthesis of ammonia within the Ammonia Synthesis Unit g′NH3SU produces heat, which can be recovered by using a fourth working fluid fllV circulating in a fourth working fluid circuit, as will be described below.
Fourth Working Fluid Circuit (flIV)
A first flow g′flIV1 is first condensed in a heat exchanger of the fourth working fluid g′TEflIV by an external refrigerant fluid, thus obtaining a cooled flow g′flIV2, which is pumped by a pump of the fourth working fluid g′PflIV, thus obtaining a pumped flow of the fourth working fluid g′flIV3.
Said pumped flow g′flIV3 acquires heat from the Ammonia Synthesis Unit g′NH3SU by vaporizing, thus obtaining a heated flow of the fourth working fluid g′flIV4, which is expanded in a steam turbine g′STflIV, which, by virtue of a generator g′EflIV, produces electricity.
The expanded flow thus obtained is the first flow of the fourth working fluid g′fllV1 which is sent to the exchanger g TEflIV.
For the purposes of the present invention, the fourth working fluid can be represented by water or air and is preferably represented by water.
For the purposes of the present invention, the external refrigerant fluids may be represented by water or air at room temperature and are preferably represented by water.
As described above, for the purposes of the present invention, the liquid and gaseous or cryo-compressed hydrogen tanks of the storage step and the generation step coincide.
More generally, in the present description, the following coincide with each other:
As described above, the liquid or cryo-compressed nitrogen tanks of the storage step and the generation step also coincide; therefore:
Similarly, the Ammonia Synthesis Units of the storage step and the generation step coincide (respectively: aNH3SU, gNH3SU and g′NH3SU), as do the first, second and fourth working fluids and the respective cycles described above (aflI, gflII and g′flIV).
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 aTN2l, gTN2l, g′TN2l, a liquid hydrogen tank aTH2l, gTH2l, g′TH2l, a gaseous hydrogen tank aTH2g, gTH2g, g′TH2g, an Ammonia Synthesis Unit aNH3SU, gNH3SU, g′NH3SU for the synthesis of ammonia with a working fluid circuit, an air compressor gTC, g′TC1, g′TC2, a combustor for subjecting an air flow to combustion gCOMB, g′COMB, a gas turbine gGT with a generator gE or an expander g′EX for generating electricity and possibly a further turbine in the working fluid circuit of the Ammonia Synthesis Unit gSTflII, g′STflIV connected to a generator for further generating electricity, and heat exchangers aTE2, aTE3, gTE4, g′TE8 for the heat exchange between a liquid nitrogen flow and a liquid and gaseous and/or cryo-compressed hydrogen flow.
Therefore, for the purposes of the present invention, the liquid nitrogen flow withdrawn from said liquid and/or cryo-compressed nitrogen tank aTN2l, gTN2l, g′TN2l is intended for said Ammonia Synthesis Unit aNH3SU, gNH3SU, g′NH3SU after the heat exchange mentioned above, while after said heat exchange the liquid and/or gaseous hydrogen flow is intended for said liquid hydrogen tank aTH2l, gTH2l, g′TH2l or gaseous hydrogen tank aTH2g, gTH2g, g′TH2g; or the liquid and/or gaseous hydrogen flow obtained from said liquid hydrogen tank aTH2l, gTH2l, g′TH2l or gaseous hydrogen tank aTH2g, gTH2g, gTH2g is intended for said Ammonia Synthesis Unit aNH3SU, gNH3SU, g′NH3SU after the heat exchange mentioned above, together with a nitrogen flow obtained from a combusted gas flow obtained from said combustor gCOMB, g′COMB, while the liquid nitrogen flow obtained after said heat exchange is intended for said liquid and/or cryo-compressed nitrogen tank aTN2l, gTN2l, g′TN2l.
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.
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 and an ammonia production system.
Therefore, the process described allows:
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.
The described process is capable of producing liquid ammonia continuously, overcoming the difficulties related to discontinuous operations of the ammonia reactor.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102021000030677 | Dec 2021 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2022/061702 | 12/2/2022 | WO |
