"STABILIZATION PROCESS FOR THE ELECTRICAL NETWORK, THE GAS NETWORK AND/OR THE HYDROGEN NETWORK AND FOR PRODUCING AMMONIA" 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, pos sibly, of the combust ible 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 .

Background art Although it is known how to produce , store and consume hydrogen, there is no unitary proces s 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 Such a proces s must be ef ficient , therefore it must have a high return coef ficient of the energy withdrawn from the network, as well as practical , thus requiring limited storage spaces not linked to particular subsoil conformations , such as exhausted wells in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 amount s of energy such as to exceed the seasonality/unpredictability limit s typically found in the availability of renewable energie s .

It is known that the storage of large amount s of hydrogen and/or oxygen requires the liquefaction of said gases at temperatures compatible with storage at atmospheric pres sure , and that said proces s is energetic, to the point of consuming up to one third of the calorific power of hydrogen, with the ef fect of limiting the production thereof per unit of available electricity .

Furthermore , while hydrogen liquefaction requires a lot of energy (the plant s 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 ef ficiency around 85% , no more than 3 kWh/kg can be obtained, when the vaporization is carried out at ambient pres sure , and no more than 2 kWh/kg when the hydrogen is heated to the network introduction pres sure .

The liquid hydrogen liquefaction and storage systems proposed so far use liquid nitrogen, but such a fluid is generated and imported from the out side , 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 reagent s 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 document s US 2021 / 300759 and US 4 , 107 , 277 describe proces ses 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 20000027 90 describes a nuclear plant which produces electricity stored in the form of liquid nitrogen and liquid oxygen by air separation, and hydrogen by electrolysis.

Summary of the invention

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.

Object of the invention

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.

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 (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 stepof 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 (H2I) and/or gaseous (H ₂ g) 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 (N ₂ I) 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 les s available .

For the purposes of the present invention, step

A) comprises using the liquid and/or cryo-compres sed nitrogen produced and stored in step B ) .

For the purposes of the present invention, step

B ) comprises using the liquid and/or cryo-compres sed hydrogen produced and stored in step A) .

The proces s 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 .

Step A)

For the purposes of the present invention, step A) comprises the sub-steps of :

Al ) sub j ecting a water flow _a l to electrolysis by using electricity, thus obtaining the production of an oxygen flow _a 2 and a hydrogen flow _a 3 ,

A2 ) sub jecting 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 40 of said preliminarily cooled hydrogen flow _a 4 and sending it to an Ammonia Synthesis Unit _a NH ₃ SU,

A4 ) separating a second portion _a 5 of said preliminarily cooled hydrogen flow _a 4 and obtaining a cooled gaseous hydrogen flow _a 8 , which is stored in a gaseous hydrogen tank _a TH ₂ g,

A5 ) separating a third portion _a 9 of said preliminarily cooled hydrogen flow _a 4 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, in sub-step Al ) the electrolytic cell _a EC uses electricity, preferably available in exces s (therefore in circumstances where abundant electricity is available ) .

The term " exces s 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.

In an aspect of the present invention, prior to the preliminary cooling sub-step A2) , the hydrogen flow _a 3 obtained from sub-step Al) can be compressed in a first compressor _a Cl; 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, substep A3) comprises the steps of:

A3a) subjecting said first portion _a 40 of the preliminarily cooled hydrogen flow to compression in a second compressor _a C2, thus obtaining a first portion of compressed hydrogen _a 41.

In the Ammonia Synthesis Unit _a NH ₃ SU, the first portion of compressed hydrogen _a 41 is converted to ammonia NH ₃ 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 _a NH ₃ SU 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, substep A4 ) comprises the sub-steps of :

A4a ) pre-cooling,

A4b ) first cooling,

A4 c ) possible 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 a second heat exchanger _a TE2 for heat exchange with a liquid and/or cryo-compressed nitrogen flow _a 32 at a first heating level , thus obtaining a second portion of the pre-cooled hydrogen flow _a 6 .

Pos sibly, such a step A4a ) can also involve an additional heated refrigerant fluid _a 51 , which circulates within a circuit of an addit ional refrigerant fluid _a 200 , 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 _a TE3 for heat exchange with a pumped liquid and/or cryo-compres sed nitrogen flow _a 31 , as it will be described below, obtaining a second portion of the cooled hydrogen flow _a 7 .

Pos sibly, such a step A4b ) can also involve an additional refrigerant fluid flow _a 50 circulating in a circuit of an additional refrigerant fluid _a 200, as will be described below.

For the purposes of the present invention, the pre-cooling sub-step A4a) and/or the first cooling substep A4b) can also be carried out by heat exchange with a refrigerant fluid flow circulating in a refrigerant fluid circuit _a 100, 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 _a TE4 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 _a 8 is thus obtained, which is stored in a gaseous hydrogen tank _a TH ₂ g.

For the purposes of the present invention, substep A5) comprises the sub-steps of:

A5a) pre-cooling,

A5b) first cooling,

A5c) stabilization,

A5d) one or more further cooling operations. For the purposes of the present invention, the pre-cooling sub-step A5a ) is carried out in a second heat exchanger _a TE2 for heat exchange with a liquid and/or cryo-compressed nitrogen flow _a 32 at a first heating level as will be described below, thus obtaining a third portion of the pre-cooled hydrogen flow _a 10 .

Pos sibly, such a step A5a ) can also involve an additional heated refrigerant fluid _a 51 , which circulates within a circuit of an addit ional refrigerant fluid _a 200 , 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 _a TE3 for heat exchange with a pumped liquid and/or cryo-compres sed nitrogen flow _a 31 , as it will be described below, thus obtaining a third portion of the cooled hydrogen flow _a l l .

Pos sibly, such a step A5b ) can also involve an additional refrigerant fluid flow _a 50 circulating in a circuit of an additional refrigerant fluid _a 200 , as will be described below .

According to an aspect of the present invention, the third portion of the cooled hydrogen flow _a l l can be sub j ected 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 _a 14.

Possibly, the flow of the third portion of the cooled hydrogen flow _a ll can be divided into a first portion to be stabilized _a 12' and a second portion to be stabilized _a 12' ' , each of which is subjected to the stabilization step in a respective converter _a CONVl, _a CONV2 obtaining a first portion of stabilized hydrogen _a 13' and a second portion of stabilized hydrogen _a 13' ' , which can be joined in the third 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 cooling step A5b) in the third heat exchanger _a TE3, thus 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 cooling step A5d) in a fourth heat exchanger _a TE4 and any further cooling in a fifth heat exchanger _a TE5 and any further fifth heat exchangers _a TE5 ' , _a TE5 ' ' , _a TE5 ^{, ,} ' , thus obtaining an even further cooled hydrogen flow _a 16. 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 _a 17 , _a 17 ' , _a 17" are obtained until a liquid hydrogen flow _a 17 ' ' ' is obtained, which is stored in a liquid hydrogen tank _a TH ₂ l (normally at a temperature below -195 ° C) .

From such a tank a recirculation flow _a H2r can be withdrawn, which can be sub j ected to one of the further cooling steps A5d) ( as it is diagrammatically shown in figure 1 ) .

For the purposes of the present invention, the liquid nitrogen flow used in the above-des cribed heat exchange steps ( sub-steps A4a) , A4b) , A5a ) and A5b ) ) is a liquid nitrogen flow withdrawn from liquid nitrogen tank _a TN ₂ l (the embodiment using cryo- compres sed nitrogen is contemplated by the present invention even if not depicted in the figures ) .

In particular, a first liquid nitrogen flow _a 30 i s 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 A4b ) and A5b ) 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 A4a ) and A5a ) , obtaining a liquid nit rogen flow _a 33 at a second heating level .

For the purposes of the present invention, and as described above , the liquid nitrogen flow _a 33 at a second heating level is sent to an Ammonia Synthesis Unit _a NH ₃ SU .

According to a particular aspect , prior to this , the liquid nitrogen flow _a 33 at a second heating level can actuate a heat exchange step with the refrigerant fluid .

The liquid nitrogen flow _a 34 at a third heating level thus obtained or the liquid nitrogen flow _a 33 at a second heating level are then sent to the Ammonia Synthesis Unit aNH ₃ SU, from which an ammonia flow (NH ₃ ) is obtained .

A purge flow _a 35 released into the atmosphere is also obtained from the Ammonia Synthe sis Unit aNH ₃ SU . Refrigerant fl uid circui t

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 it is preferably represented by hydrogen .

The refrigerant fluid circuit does not represent a limiting element of the present invention, as it is suf ficient that it allows cooling the first _a 5 and the third _a 9 portions of the preliminarily cooled hydrogen flow as described above .

According to an embodiment of the present invention, for example depicted in figure 1 , such a circuit a100 can operate according to the Claude cycle .

Such a cycle includes at least three expansion steps of the refrigerant fluid contained in a tank _a Tfr, of which two expansion steps are obtained by means of a first and a second expander _a EX1 _fr , _a EX2 _fr and the third expansion step by means of a valve _a V _fr .

After being withdrawn from the tank _a T _fr , the refrigerant fluid flow therefore carries out the heat exchange steps : A4d) and A5d) of at least one and optionally further cooling steps,

- A4b) and A5b) of first cooling, and

- A4a) and A5a) 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 A4d) and A5d) .

Additional refrigerant fluid circuit

For the purposes of the present invention and as described above, an additional refrigerant fluid circuit _a 200 can be included.

Such a fluid circulates in a circuit from which an additional refrigerant fluid flow _a 50 originates, which can be involved in step A4b) and/or A5b) (described above) , thus obtaining a heated additional refrigerant fluid flow _a 51.

In turn, such a heated additional refrigerant fluid flow _a 51 can also be involved in step A4a) and/or A5a) (described above) , thus obtaining a further heated additional refrigerant fluid flow _a 52, which recirculates in the circuit _a 200. For the purposes of the present invention, the additional refrigerant fluid can be represented, for example , by nitrogen, ammonia, propane , ethylene . First working fl uid circui t (fll)

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 _a fll l i s first condensed in a heat exchanger of the first working fluid _a TEflI by an external refrigerant fluid, thus obtaining a cooled flow _a fll2 , which is pumped by a pump of the first working fluid _a PflI , thus obtaining a pumped first working fluid flow _a fll 3 .

Said pumped flow _a fll 3 acquires heat from the Ammonia Synthesis Unit _a NH ₃ SU by vaporizing, thus obtaining a heated flow _a flI 4 , which is expanded in a steam turbine _a STflI , which, by virtue of a generator _a EflI , produces electricity .

The expanded flow thus obtained is the first flow of the first working fluid _a fll l which is sent to the exchanger _a TEflI .

For the purposes of the present invention, the first working fluid _a fll 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 . Step B)

For the purposes of the present invention, step B ) comprises the sub-steps of :

Bl ) sub j ecting an air flow _g l to combustion in the presence of a hydrogen flow _g 33 , thus obtaining a combusted gas flow _g 3 ,

B2 ) expanding said combusted gas flow _g 3 , thus obtaining an expanded combusted gas f low _g 4 ,

B3 ) sub j ecting said expanded combusted gas flow _g 4 to a first cooling, thus obtaining an expanded combusted gas flow _g 5 at a first cooling level ,

B4 ) separating a portion _g 40 from said expanded combusted gas flow _g 5 at a first cooling level and sending it to an Ammonia Synthesis Unit gNH ₃ SU for the synthesis of ammonia NH ₃ ,

B5 ) sub j ecting said expanded combusted gas flow _g 5 at a first cooling level to a second cooling step, thus obtaining an expanded gas flow _g 6 at a second cooling level B6) subjecting said expanded gas flow _g 6 at a second cooling level to a water separation step, thus obtaining a dehydrated combusted gas flow _g 7,

B7) possibly separating a first recirculation portion _g 8 from said dehydrated combusted gas flow _g 7, which is joined to the air flow _g l of sub-step Bl) ,

B8) subjecting a second portion _g 9 separated from said dehydrated combusted gas flow _g 7 to compression, obtaining a compressed dehydrated combusted gas flow g10,

B9) subjecting said compressed dehydrated combusted gas flow _g 10 to cooling and at least one water separation step, obtaining a nitrogen flow _g 13,

B10) subjecting said nitrogen flow _g 13 to condensation, thus obtaining a liquid nitrogen flow _g 14, which is sent to a liquid nitrogen tank _g TN ₂ l.

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 substep A5b) are also carried out using the liquid nitrogen flow obtained and stored in sub-step B10) . With reference to sub-step Bl) , this is carried out in a combustor gCOMB.

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 gl or filtered air flow _g l' or on a compressed air flow _g 2.

For the purposes of the present invention, substep Bl) can be carried out in the combustor gCOMB even in the presence of a compressed flow of noncondensables _g R2 as described below.

In a particular aspect of the invention, the air flow gl, possibly filtered _g l' and/or compressed _g 2, is joined to the recirculating flow _g 8 according to substep B7) described above.

In an alternative aspect of the present invention as shown in figure 2, if linked to technical needs of the process or of the combustor, a portion _g 8' of the recirculating flow _g 8 can be sent, instead of being suctioned to the compressor _g TC, in whole or partially directly to the combustor _g COMB, as a dilution gas, after compression in a compressor _g C0, obtaining a compressed recirculating flow _g 8 ^, ' .

Advantageously, such a recirculating flow _g 8 and such a further recirculating flow _g 8' ' have 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.

For 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 obtained as will be described below.

Water and heated combusted gases are obtained with the combustion of sub-step Bl) , which are generally referred to with a combusted 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 with mechanical energy production which, by virtue of a generator _g E, produces electricity.

In an aspect of the present invention, the first cooling sub-step B3) of the combusted gases _g 4 is carried out in a first heat exchanger _g TEl by a third working fluid _g flIII, 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 _g fl 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 _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.

As for sub-step B6) , this comprises separating a first portion of condensed water _g wl from the bottom of a first separator _g Sl .

The first dehydrated flow obtained _g 7 is then divided into a first portion _g 8, representing the recirculating flow to the compressor _g TC and into a second portion _g 9, which is sent to the compressor _g Cl for sub-step B8) .

For the purposes of the present invention, the compression sub-step B8) 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 B 9 ) 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/or with a heated vaporized hydrogen flow _g 22 as described below, thus obtaining a dehydrated and compres sed gas flow _g l l .

The at least one water separation step is carried out on said dehydrated and compres sed gas flow _g l l in a second separator _g S2 , thus obtaining a second portion of condensed water _g w2 and a further dehydrated and compres sed gas flow _g 12 .

A further dehydration step can be carried out on said further dehydrated and compres sed gas flow _g 12 in a first dehydration unit _g DUl 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 B10 ) is a condensing step 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 gaseous hydrogen flow _g 30 i s obtained from a gaseous hydrogen tank _g TH ₂ g . In particular, such a pumped liquid hydrogen flow _g 21 is obtained from a liquid hydrogen flow _g 20 obtained from a liquid hydrogen tank _g TH ₂ l pumped by a liquid hydrogen pump _g PH ₂ l. .

The liquid nitrogen flow _g 14 thus obtained is stored in a liquid nitrogen tank _g TN ₂ l .

A flow of non-condensable s _g Rl can develop from such a tank _g TN ₂ l , and can be sent to a second compres sor _g C2 , thus obtaining a compres sed 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 sub-step Bl ) .

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 BI O ) .

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 BI O ) .

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 A4 ) and A5 ) of the storage step A) described above , respectively; therefore, the tanks _a TH ₃ g and _g TH ₃ 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 B10) the heated gaseous hydrogen flow _g 31 and/or the heated vaporized hydrogen flow _g 22 are both sent to the cooling sub-step B9) in the third exchanger _g TE3, thus obtaining a vaporized heated hydrogen flow _g 32 and a further vaporized heated hydrogen flow _g 23, which are joined in an overall vaporized hydrogen flow _g 33.

Such an overall vaporized hydrogen flow g33 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.

As described above, in step B4) a portion of the expanded combusted gases _g 40 at a first cooling level is separated, which is sent to an Ammonia Synthesis Unit _g NH ₃ SU.

Before being involved in the synthesis of ammonia NH ₃ , such a portion _g 40 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 _g 40 is subjected to the steps: B4a) of compression in a first nitrogen compressor _g ClN2, thus obtaining a first compressed portion _g 41,

B4b) of cooling in a fifth heat exchanger _g TE5, thus obtaining a compressed and cooled portion of the nitrogen flow _g 42,

B4c) of separating a third portion of the condensed water _g w3 in a third separator _g S3, thus obtaining a portion of dehydrated nitrogen flow _g 43,

B4d) of further dehydration in a second Dehydration Unit _g DU2 by means of appropriate molecular sieves, thus obtaining a portion of the further dehydrated nitrogen flow _g 44,

B4e) of compressing the portion of the further dehydrated nitrogen flow _g 44 in a second nitrogen compressor _g C2N ₂ , thus obtaining a synthesis nitrogen flow _g 45.

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 _g 35 is separated from the overall vaporized hydrogen flow _g 33 and sent to the Ammonia Synthesis Unit gNH ₃ SU for the synthesis of ammonia NH ₃ . The synthesis nitrogen flow _g 45 and the portion of synthesis hydrogen _g 35 are then sent to the Ammonia Synthesis Unit.

A purge flow _a 36 released into the atmosphere is also obtained from the Ammonia Synthesis Unit gNH ₃ SU.

For the purposes of the present invention, the synthesis of ammonia within the Ammonia Synthesis Unit gNH ₃ SU 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 (fllll)

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 _g TEl, the third flow of the third heated working fluid _g flIIl3 thus obtained is expanded in a steam turbine _g STlflIII, thus obtaining an expanded flow _g flIII4; since such a turbine is connected to a first generator _g El, electricity can be produced .

The thus obtained expanded flow _g flIII4 is further heated in the first heat exchanger _g TEl, giving a heated flow of the third working fluid _g flIII5, which is subjected to a second expansion in a second expansion turbine _g ST2flIII; since this is connected to a second generator _g E2, electricity can be produced.

The further expanded flow of the second working fluid _g flIIl6 thus obtained is cooled in the exchanger of the third working fluid _g TEflIII by using an external refrigerant fluid, thus obtaining a cooled flow gflllll, which is pumped in a pump of the third working fluid gPfllll, thus obtaining a pumped flow _g flIIl2, 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 (fill)

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 gfllll is first condensed in a heat exchanger of the second working fluid gTEflll by an external refrigerant fluid, thus obtaining a cooled flow _g flll2, which is pumped by a pump of the second working fluid _g PflII, thus obtaining a pumped second working fluid flow _g flll3. Said pumped flow _g fllll3 acquires heat from the

Ammonia Synthesis Unit gNH ₃ SU by vaporizing, thus obtaining a heated flow gfllII4, which is expanded in a steam turbine gSTflll, which, by virtue of a generator gEflll, produces electricity.

The expanded flow thus obtained is the first flow of the second working fluid gfllll which is sent to the exchanger _g TEflII.

For the purposes of the present invention, the second working fluid fill 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' l to be subjected to combustion in the combustor _g' COMB according to step B' l) is preliminarily subjected to a treatment comprising the following sub-steps: bO) if necessary, filtering by means of a filter _g' F, thus obtaining a filtered air flow _g' l', bl) compressing, obtaining a compressed air flow g-4, b2) heating and obtaining a compressed and further heated air flow _g' 8, b3) reducing the oxygen contained in said compressed and further heated air flow _g' 8, thus obtaining a reduced flow _g' 9, b4) cooling, thus obtaining a cooled reduced flow _g' 10 and joining to a heated integration flow 6.

For the purposes of the present invention, the compression sub-step bl) can subject the air flow _g' l or filtered air flow _g' l' to the sub-steps of: bla) first compression in a first compressor _g' Cl, thus obtaining a flow at a first compression level _g' 2, bib) cooling in a first heat exchanger _g' TEl, thus obtaining a flow at a first cooled compression level _g' 3, and blc) second compression in a second compressor _g' C2, thus obtaining the compressed flow _g' 4.

In particular, sub-step bib) of cooling in a first heat exchanger _g' TEl 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:

- sub-step b2a) is obtained by heat exchange in a second exchanger _g' TE2 with an expanded fluid 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 fifth working fluid, for example represented by nitrogen, thus obtaining a heated compressed air flow _g' 7 , and

- sub-step b2c) is obtained by heat exchange in a fourth exchanger _g' TE4, thus obtaining a compressed and further heated air flow _g' 8, where such a heat exchange is carried out with the reduced flow _g' 9 output from the anode.

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' ll sent to the combustor _g' COMB for sub-step B' l) .

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 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 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' TH ₂ g and _g' TH ₂ l, in which they are stored after the storage sub-steps A4) and A5) described above with reference to step A) ; 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, a portion _g' 70 which is sent to the Ammonia Synthesis Unit _g' NH ₃ SU 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' l) , such a flow to be sent to the combustor _g' 35 is subjected to the steps of: b'l) heating, obtaining a heated flow _g' 5O to be oxidized, b'2) oxidizing the hydrogen, thus obtaining an oxidized flow _g' 51, b'3) further cooling, thus obtaining a cooled oxidized flow _g' 52.

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' l) 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' flvl, 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' l) , which is subjected to the further steps of :

B'2) expanding said combusted gas flow _g' 12 in an expander _g' EX, thus obtaining an expanded combustion flue gas flow _g' 13, B'3) cooling said expanded combusted gas flow g-13, thus obtaining a cooled expanded combusted gas flow _g' 15,

B'4) separating the water and obtaining a nitrogen flow _g' 20 ,

B' 5) separating a first portion of said nitrogen flow _g' 21 and subjecting it to cooling in an eighth heat exchanger _g' TE8, thus obtaining a liquid nitrogen flow _g' 22,

B' 6) sending a second portion of said nitrogen flow _g' 60 to an Ammonia Synthesis Unit _g' NH ₃ SU for the synthesis of ammonia.

The liquid nitrogen flow _g' 22 is then stored in a liquid nitrogen tank _g' TN ₂ l.

A flow of non-condensables _g' Rl can develop from such a tank _g' TN ₂ l, 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, substep B' 3) comprises the further sub-steps of: B'3a) cooling said expanded combusted 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 cooled combusted gas flow _g' 15.

For the purposes of the present invention, said sub-step B' 4) comprises the further sub-steps of:

B'4a) subjecting said expanded and cooled combusted gas flow _g' 15 to a first water separation _g' wl in a first separator _g' Sl, thus obtaining a dehydrated combusted gas flow _g -16,

B' 4b) compressing said dehydrated combusted gas flow _g' 16 in a third compressor _g' C3 obtaining a compressed dehydrated combusted gas flow _g' 17,

B'4c) cooling said compressed dehydrated combusted gas flow _g' 17 in a seventh heat exchanger _g' TE7, thus obtaining a compressed and cooled dehydrated combusted gas flow _g' 18 by heat exchange with an external refrigerant fluid;

B'4d) subjecting said flow to a second water separation _g' w2 in a second separator _g' S2, thus obtaining a further dehydrated combusted 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.

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' PH ₂ l a liquid hydrogen flow _g' 30 obtained from the liquid hydrogen tank _g' TH ₂ l.

As for step B' 6) , before sending to the Ammonia Synthesis Unit _g' NH ₃ SU, the second portion of nitrogen _g' 60 is compressed in a nitrogen compressor _g' CN ₂ , thus obtaining a compressed nitrogen flow _g' 61.

The synthesis of ammonia NH ₃ is thus obtained from the nitrogen flow _g' 61 and the hydrogen flow _g' 70.

Ammonia NH ₃ 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' NH ₃ SU. For the purposes of the present invention, the synthesis of ammonia within the Ammonia Synthesis Unit _g' NH ₃ SU 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 (fllV)

A first flow _g' flIVI is first condensed in a heat exchanger of the fourth working fluid _g' TEfllV by an external refrigerant fluid, thus obtaining a cooled flow _g' flIV2, which is pumped by a pump of the fourth working fluid _g' PfllV, 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' NH ₃ SU by vaporizing, thus obtaining a heated flow of the fourth working fluid _g' flIV4, which is expanded in a steam turbine _g' STfllV, which, by virtue of a generator _g' EfllV, produces electricity .

The expanded flow thus obtained is the first flow of the fourth working fluid _g' flIVI which is sent to the exchanger _g' TEfllV.

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 cryocompressed hydrogen tanks of the storage step and the generation step coincide.

More generally, in the present description, the following coincide with each other:

- the tanks _a TH ₂ g, _g TH ₂ g and _g' TH ₂ g, and

- the tanks _a TH ₂ l, _g TH ₂₁ and _g' TH ₂ l.

As described above, the liquid or cryo-compressed nitrogen tanks of the storage step and the generation step also coincide; therefore:

- the following tanks coincide: _a TN ₂ l, _g TN ₂ l and g _' TN ₂ l.

Similarly, the Ammonia Synthesis Units of the storage step and the generation step coincide (respectively: aNH ₃ SU, g aNH ₃ SU and _g' NH ₃ SU) , as do the first, second and fourth working fluids and the respective cycles described above ( _a fll, _g flII 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 _a TN ₂ l, _g TN ₂ l, _g' TN ₂ l, a liquid hydrogen tank _a TH ₂ l, _g TH ₂ l, _g' TH ₂ l, a gaseous hydrogen tank _a TH ₂ g, _g TH ₂ g, _g' TH ₂ g, an Ammonia Synthesis Unit _a NH ₃ SU, gNH ₃ SU, _g' NH ₃ SU for the synthesis of ammonia with a working fluid circuit, an air compressor _g TC, _g' TCl, _g' TC2, a combustor for subjecting an air flow to combustion _g COMB, _g' COMB, a gas turbine _g GT with a generator _g E or an expander _g' EX for generating electricity and possibly a further turbine in the working fluid circuit of the Ammonia Synthesis Unit _g STflII, _g' STflIV connected to a generator for further 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 cryocompressed hydrogen flow.

Therefore, for the purposes of the present invention, the liquid nitrogen flow withdrawn from said liquid and/or cryo-compressed nitrogen tank _a TN ₂ l, _g TN ₂ l, _g' TN ₂ l is intended for said Ammonia Synthesis Unit _a NH ₃ SU, _g NH ₃ SU, _g' NH ₃ SU 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 _a TH ₂ l , _g TH ₂ l , _g' TH ₂ l or gaseous hydrogen tank _a TH ₂ g, _g TH ₂ g, _g' TH ₂ g; or the liquid and/or gaseous hydrogen flow obtained from said liquid hydrogen tank _a TH ₂ l , _g TH ₂ l , _g' TH ₂ l or gaseous hydrogen tank _a TH ₃ g, _g TH ₂ g, _g' TH ₂ g is intended for said Ammonia Synthesis Unit _a NH ₃ SU, _g NH ₃ SU, _g' NH ₃ SU after the heat exchange mentioned above , together with a nitrogen flow obtained from a combusted gas flow obtained from said combustor _g COMB, _g' COMB, while the liquid nitrogen flow obtained after said heat exchange is intended for said liquid and/or cryo-compres sed nitrogen tank _a TH ₂ l , _g TH ₂ l , _g' TH ₂ l .

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 proces s as described above .

From the description provided above , the advantages of fered by the present invention will be apparent to those skilled in the art .

The present invention allows integrating electrolytic hydrogen product ion technologies with hydrogen storage technologies , both in gaseous and cryo-compres sed form, with the use of a gas turbine or an electrolytic cell , which can produce electricity and nitrogen, with a hydrogen frigorie s recovery system and an ammonia production system .

Therefore , the proces s described allows :

- stabilizing the electrical network, by virtue of the absorption of exces s 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 proces s can further be used for producing gaseous oxygen, even at high pres sure , to be used for other purposes .

The described proces s 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 proces s is capable of producing liquid ammonia continuously, overcoming the dif ficulties 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. * * *