SYSTEM FOR STORING AND PRODUCING ENERGY TO STABILIZE THE POWER NETWORK

Abstract

A system for storing or producing electricity, which allows stabilization of a power network under conditions of excess availability of electricity or lack thereof and for producing liquefied natural gas is provided.

Claims

1-17. (canceled)

18. A process for producing liquid oxygen and liquid oxygen-depleted air, and possibly natural gas, said process using electricity said process comprising subjecting an air flow withdrawn from a source to the steps of: I) pre-treatment, II) treatment, III) heat exchange, IV) separation, wherein a preliminary step IVa) is carried out, in which a purified and cooled air flow is subjected to cooling inside a reboiler of a distillation column, obtaining a partially condensed flow from which, in a step IVb), a second condensed liquid air flow is separated within a second separator, from the bottom, and laminated by a first lamination valve, obtaining a partially vaporized current that is fed to the distillation column, and a gaseous flow is separated from a head of said second separator and expanded in a turbine with power generation, obtaining an expanded flow that is fed to the distillation column, obtaining an oxygen flow from the reboiler, a second portion of which is sent to a tank, and an oxygen-depleted air flow is obtained from a head of said distillation column, Va) obtaining a liquid oxygen flow and a gaseous oxygen flow from said oxygen flow, Vb) obtaining a liquid oxygen-depleted air flow from said oxygen-depleted air flow, wherein in step Vb), the oxygen-depleted air flow is subjected to a heat exchange step, obtaining a heated oxygen-depleted air flow, which is subjected to one or more steps of: compression, obtaining a compressed flow, cooling, obtaining a compressed and cooled flow, to which a heated recycled gas flow is added, obtaining a second flow, which is compressed, obtaining a second compressed flow, which is cooled, obtaining a further compressed and further cooled flow, which is subjected to a heat exchange step in a heat exchanger with which it is cooled, obtaining an at least partially condensed flow, which is expanded in an expander, obtaining a further condensed flow and with power generation, from which inside a separator, a gaseous head flow which, after being heated in a heat exchange step within the heat exchanger, provides the heated recycled gas flow and, from the bottom of said separator, the liquid oxygen-depleted air flow which is sent to a tank of liquid oxygen-depleted air, are separated, wherein the heat exchange steps in the heat exchanger are carried out using frigories of a refrigeration cycle that uses liquefied natural gas, and wherein in pre-treatment step I) the air flow is subjected to the steps of: Ia) compression in a compressor, obtaining a compressed air flow, Ib) cooling of said compressed air flow in a cooler, obtaining a compressed and cooled air flow, Ic) separation in a first separator of a condensed vapor flow from the bottom of said separator and of a compressed and cooled gaseous flow from a head of said separator.

19. The process of claim 18, wherein in step II), the compressed and cooled gaseous flow is subjected to purification in a treatment unit for removal of impurities, thus obtaining a purified air flow.

20. The process of claim 19, wherein in step III) the purified air flow is subjected to a heat exchange step with which the purified air flow is cooled, thus obtaining a purified and cooled air flow.

21. The process of claim 18, wherein the heat exchange step in the heat exchanger is carried out by further using frigories of a liquefied natural gas flow.

22. A method for stabilizing a power network, comprising carrying out a process according to claim 18, wherein available electricity from the power network is used.

23. A process for producing electricity and liquid carbon dioxide and possibly liquid natural gas, comprising the steps of: A) combusting a fuel flow in presence of a CO.sub.2-rich recirculation flow and a gaseous oxygen flow, obtaining a flow mainly consisting of CO.sub.2 and water at high pressure and temperature, which is expanded in an expander with power production, B) subjecting to heat exchange the expanded flow thus obtained, obtaining an expanded and cooled flow, C) separating, in a first separator, a first bottom portion of condensed water vapor and a first gaseous flow, which is then compressed in a first compressor, from which said CO.sub.2-rich recirculation flow is obtained, which is recirculated to a combustor, and a compressed flow which is cooled, thus obtaining a cooled compressed flow, D) optionally further cooling the cooled compressed flow in a cooler by a refrigerant fluid, obtaining a further cooled flow, separating in a second separator said cooled compressed flow or the further cooled flow, from the bottom of which a second portion of condensed water vapor is obtained, and from a head of which a flow mainly consisting of CO.sub.2 is obtained, E) subjecting said flow mainly consisting of CO.sub.2 to dehydration, obtaining a dehydrated flow, F) cooling said dehydrated flow, thus obtaining a cooled dehydrated flow, to which a second flow mainly consisting of CO.sub.2 is added, thus obtaining a combined flow mainly consisting of CO.sub.2, from which in a third separator a liquid CO.sub.2 flow is separated from the bottom, and a gaseous release flow from the head, G) compressing and cooling said gaseous release flow, obtaining a partially condensed release flow, and H) separating, in a fourth separator, from said partially condensed release flow, a final gaseous release flow from the head and the second flow mainly consisting of CO.sub.2 from the bottom, wherein step B) is carried out by frigories supplied by a liquid oxygen-depleted air flow, and wherein step F) is carried out by frigories supplied by the refrigerant fluid which is cooled by a liquid oxygen flow, thus obtaining said gaseous oxygen flow.

24. The process of claim 23, wherein a pumped oxygen-depleted air flow is heated by a purified natural gas flow obtained by purifying a natural gas flow, obtaining a liquefied natural gas flow and a pumped heated oxygen-depleted air flow.

25. A method for stabilizing a power network, comprising carrying out a process according to claim 23, wherein an amount of electricity is produced, which the power network is lacking.

26. The method of claim 25, wherein said process is carried out using liquid oxygen-depleted air obtained by a process for producing liquid oxygen and liquid oxygen-depleted air, and possibly natural gas, said process using electricity said process comprising subjecting an air flow withdrawn from a source to the steps of: I) pre-treatment, II) treatment, III) heat exchange, IV) separation, wherein a preliminary step IVa) is carried out, in which a purified and cooled air flow is subjected to cooling inside a reboiler of a distillation column, obtaining a partially condensed flow from which, in a step IVb), a second condensed liquid air flow is separated within a second separator, from the bottom, and laminated by a first lamination valve, obtaining a partially vaporized current that is fed to the distillation column, and a gaseous flow is separated from a head of said second separator and expanded in a turbine with power generation, obtaining an expanded flow that is fed to the distillation column, obtaining an oxygen flow from the reboiler, a second portion of which is sent to a tank, and an oxygen-depleted air flow is obtained from a head of said distillation column, Va) obtaining a liquid oxygen flow and a gaseous oxygen flow from said oxygen flow, Vb) obtaining a liquid oxygen-depleted air flow from said oxygen-depleted air flow, wherein in step Vb), the oxygen-depleted air flow is subjected to a heat exchange step, obtaining a heated oxygen-depleted air flow, which is subjected to one or more steps of: compression, obtaining a compressed flow, cooling, obtaining a compressed and cooled flow, to which a heated recycled gas flow is added, obtaining a second flow, which is compressed, obtaining a second compressed flow, which is cooled, obtaining a further compressed and further cooled flow, which is subjected to a heat exchange step in a heat exchanger with which it is cooled, obtaining an at least partially condensed flow, which is expanded in an expander, obtaining a further condensed flow and with power generation, from which inside a separator, a gaseous head flow which, after being heated in a heat exchange step within the heat exchanger, provides the heated recycled gas flow and, from the bottom of said separator, the liquid oxygen-depleted air flow which is sent to a tank of liquid oxygen-depleted air, are separated, wherein the heat exchange steps in the heat exchanger are carried out using frigories of a refrigeration cycle that uses liquefied natural gas, and wherein in pre-treatment step I) the air flow is subjected to the steps of: Ia) compression in a compressor, obtaining a compressed air flow, Ib) cooling of said compressed air flow in a cooler, obtaining a compressed and cooled air flow, Ic) separation in a first separator of a condensed vapor flow from the bottom of said separator and of a compressed and cooled gaseous flow from a head of said separator.

27. The method of claim 25, wherein for cooling a compressed refrigerant fluid in step F) of said process a liquid oxygen is used, the liquid oxygen being obtained according to a process for producing liquid oxygen and liquid oxygen-depleted air, and possibly natural gas, said process using electricity said process comprising subjecting an air flow withdrawn from a source to the steps of: I) pre-treatment, II) treatment, III) heat exchange, IV) separation, wherein a preliminary step IVa) is carried out, in which a purified and cooled air flow is subjected to cooling inside a reboiler of a distillation column, obtaining a partially condensed flow from which, in a step IVb), a second condensed liquid air flow is separated within a second separator, from the bottom, and laminated by a first lamination valve, obtaining a partially vaporized current that is fed to the distillation column, and a gaseous flow is separated from a head of said second separator and expanded in a turbine with power generation, obtaining an expanded flow that is fed to the distillation column, obtaining an oxygen flow from the reboiler, a second portion of which is sent to a tank, and an oxygen-depleted air flow is obtained from a head of said distillation column, Va) obtaining a liquid oxygen flow and a gaseous oxygen flow from said oxygen flow, Vb) obtaining a liquid oxygen-depleted air flow from said oxygen-depleted air flow, wherein in step Vb), the oxygen-depleted air flow is subjected to a heat exchange step, obtaining a heated oxygen-depleted air flow, which is subjected to one or more steps of: compression, obtaining a compressed flow, cooling, obtaining a compressed and cooled flow, to which a heated recycled gas flow is added, obtaining a second flow, which is compressed, obtaining a second compressed flow, which is cooled, obtaining a further compressed and further cooled flow, which is subjected to a heat exchange step in a heat exchanger with which it is cooled, obtaining an at least partially condensed flow, which is expanded in an expander, obtaining a further condensed flow and with power generation, from which inside a separator, a gaseous head flow which, after being heated in a heat exchange step within the heat exchanger, provides the heated recycled gas flow and, from the bottom of said separator, the liquid oxygen-depleted air flow which is sent to a tank of liquid oxygen-depleted air, are separated, wherein the heat exchange steps in the heat exchanger are carried out using frigories of a refrigeration cycle that uses liquefied natural gas, and wherein in pre-treatment step I) the air flow is subjected to the steps of: Ia) compression in a compressor, obtaining a compressed air flow, Ib) cooling of said compressed air flow in a cooler, obtaining a compressed and cooled air flow, Ic) separation in a first separator of a condensed vapor flow from the bottom of said separator and of a compressed and cooled gaseous flow from a head of said separator.

28. The method of claim 22, wherein the liquid oxygen-depleted air flow is pumped by an oxygen-depleted air pump, obtaining a pumped oxygen-depleted air flow, which is heated by heat exchange with a natural gas flow obtained according to a process for producing liquid oxygen and liquid oxygen-depleted air, and possibly natural gas, said process using electricity said process comprising subjecting an air flow withdrawn from a source to the steps of: I) pre-treatment, II) treatment, III) heat exchange, IV) separation, wherein a preliminary step IVa) is carried out, in which a purified and cooled air flow is subjected to cooling inside a reboiler of a distillation column, obtaining a partially condensed flow from which, in a step IVb), a second condensed liquid air flow is separated within a second separator, from the bottom, and laminated by a first lamination valve, obtaining a partially vaporized current that is fed to the distillation column, and a gaseous flow is separated from a head of said second separator and expanded in a turbine with power generation, obtaining an expanded flow that is fed to the distillation column, obtaining an oxygen flow from the reboiler, a second portion of which is sent to a tank, and an oxygen-depleted air flow is obtained from a head of said distillation column, Va) obtaining a liquid oxygen flow and a gaseous oxygen flow from said oxygen flow, Vb) obtaining a liquid oxygen-depleted air flow from said oxygen-depleted air flow, wherein in step Vb), the oxygen-depleted air flow is subjected to a heat exchange step, obtaining a heated oxygen-depleted air flow, which is subjected to one or more steps of: compression, obtaining a compressed flow, cooling, obtaining a compressed and cooled flow, to which a heated recycled gas flow is added, obtaining a second flow, which is compressed, obtaining a second compressed flow, which is cooled, obtaining a further compressed and further cooled flow, which is subjected to a heat exchange step in a heat exchanger with which it is cooled, obtaining an at least partially condensed flow, which is expanded in an expander, obtaining a further condensed flow and with power generation, from which inside a separator, a gaseous head flow which, after being heated in a heat exchange step within the heat exchanger, provides the heated recycled gas flow and, from the bottom of said separator, the liquid oxygen-depleted air flow which is sent to a tank of liquid oxygen-depleted air, are separated, wherein the heat exchange steps in the heat exchanger are carried out using frigories of a refrigeration cycle that uses liquefied natural gas, and wherein in pre-treatment step I) the air flow is subjected to the steps of: Ia) compression in a compressor, obtaining a compressed air flow, Ib) cooling of said compressed air flow in a cooler, obtaining a compressed and cooled air flow, Ic) separation in a first separator of a condensed vapor flow from the bottom of said separator and of a compressed and cooled gaseous flow from a head of said separator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] FIG. 1 shows the process of the invention according to a first aspect thereof in which electricity is stored (peak shaving) through the storage of liquid oxygen and liquid (oxygen) depleted air.

[0057] FIG. 2 shows the process of the invention in a second aspect thereof, in which the generation of electricity and possibly of liquefied natural gas is actuated.

DETAILED DESCRIPTION OF THE INVENTION

[0058] In a first object, the present invention describes a process for producing natural gas and for producing liquid oxygen and liquid oxygen-depleted air.

[0059] Such a process comprises steps which involve: [0060] an air cycle, [0061] a refrigeration cycle,
and possibly a natural gas cycle.

[0062] For the purposes of the present invention, the aforementioned cycles are connected to one another by means of one or more heat exchange steps.

[0063] In a first aspect, the process of the invention achieves the storage step mentioned above (references to this aspect are preceded for convenience by .sub.a).

[0064] In particular, such a process comprises subjecting an air flow .sub.a1 withdrawn from a source .sub.aIN.sub.air to the steps of: [0065] I) pre-treatment, [0066] II) treatment, [0067] III) heat exchange, [0068] IV) separation, obtaining a flow of oxygen .sub.a40 and an oxygen-depleted air flow .sub.a13, [0069] Va) obtaining a liquid oxygen flow .sub.a44 and a gaseous oxygen flow .sub.a43 from said oxygen flow .sub.a40, [0070] Vb) obtaining a liquid oxygen-depleted air flow .sub.a13 from said oxygen-depleted air flow .sub.a23.

[0071] More in detail, in such a pre-treatment step I) the air flow .sub.a1 is subjected to the steps of: [0072] Ia) compression in a compressor .sub.aC.sub.air, thus obtaining a compressed air flow .sub.a2, [0073] Ib) cooling said compressed air flow .sub.a2 in a cooler .sub.aHE.sub.air, thus obtaining a compressed and cooled air flow .sub.a3, [0074] Ic) separation in a first separator S1.sub.air of a condensed vapor flow .sub.a4 from the bottom of said separator S1.sub.air and of a compressed and cooled gaseous flow .sub.a5 from the head of said separator .sub.aS1.sub.air.

[0075] In particular, in step Ib) the cooling is obtained by heat exchange with a cooling fluid, for example represented by air or water.

[0076] For the purposes of the present invention, steps Ia), Ib) and Ic) can be repeated several times, until a compressed and cooled gaseous air flow .sub.a5 is obtained at the appropriate pressure for the subsequent operations.

[0077] The repetition of such steps shall be compatible with the necessary plant complexity and the consequent constructional and operating costs.

[0078] According to the treatment step II), the compressed and cooled gaseous flow .sub.a5 is subjected to a purification in a Treatment Unit .sub.aTU.sub.air for the removal of impurities, thus obtaining a purified air flow .sub.a6.

[0079] For the purposes of the present invention, such impurities are represented by residual humidity, carbon dioxide, hydrocarbons, among which, in particular, acetylene.

[0080] In the subsequent heat exchange step III), the purified air flow .sub.a6 is subjected to a step in which it is cooled to a temperature close to the condensation point thereof, with possible partial condensation, obtaining a purified and cooled air flow .sub.a7.

[0081] Such a cooling is carried out in particular in the exchanger .sub.aMHE.

[0082] In separation step IV) a preliminary step IVa) is carried out, in which the purified and cooled air flow .sub.a7 is subjected to a further cooling inside the reboiler .sub.aRa of a distillation column .sub.aDa obtaining a partially condensed flow .sub.a8.

[0083] From said partially condensed flow .sub.a8 inside a second separator .sub.aS2.sub.air in a step IVb), a second condensed liquid air flow .sub.a10 is separated from the bottom, which is laminated by a first lamination valve .sub.aV1, thus obtaining a laminated current .sub.a12 then fed to the same distillation column .sub.aDa.

[0084] From the head of the second separator .sub.aS2.sub.air, a gaseous flow .sub.a9 is instead separated, which is expanded in a turbine .sub.aTEX.sub.air generating power and obtaining an expanded flow .sub.a11 which is fed to the distillation column .sub.aDa.

[0085] A flow of oxygen-depleted air .sub.a13 is obtained from the head of the distillation column .sub.aDa.

[0086] In a preferred aspect of the present invention, said oxygen-depleted air flow .sub.a13 has an oxygen content of less than 12% v/v.

[0087] Advantageously, thereby, the oxygen content is less than the flammability limit of the liquefied natural gas, contributing to a greater safety of the process and of the plant in which it is carried out.

[0088] According to a possible embodiment, a column bottom current .sub.aR1 is obtained from the bottom of the distillation column .sub.aDa which is sent to the reboiler .sub.aRa of the column .sub.aDa for step IV) to then be recirculated to the bottom of the column as flow .sub.aR2; equivalent variants of such an embodiment can be implemented by those skilled in the art based on contingent needs.

[0089] In step Va), from the reboiler .sub.aRa a it is further obtained a liquid oxygen flow .sub.a40, of which a first portion .sub.a41 is pumped into a first oxygen pump .sub.aP1O.sub.2 thus obtaining a pumped flow .sub.a42, which is subjected to a heat exchange step in the exchanger .sub.aMHE wherein it is heated, obtaining a vaporized (gaseous) oxygen flow .sub.a43.

[0090] A second portion .sub.a44 of the liquid oxygen flow is sent to a liquid oxygen reservoir .sub.aTO.sub.21, in which it is stored and from which a use flow .sub.aF1O.sub.2 can be withdrawn, which can be pumped into a second oxygen pump .sub.aP2O.sub.2, thus obtaining a pumped use flow .sub.aF2O.sub.2.

[0091] In step Vb), the oxygen-depleted air flow .sub.a13 is subjected to a heat exchange step in the exchanger a MHE, thus obtaining a heated oxygen-depleted air flow .sub.a14.

[0092] Such a heated oxygen-depleted air flow .sub.a14 is then subjected to the steps of: [0093] compression, in a first compressor .sub.aC1.sub.wa, thus obtaining a compressed flow .sub.a15, [0094] cooling, in a first cooler .sub.aHE1.sub.wa, thus obtaining a compressed and cooled flow .sub.a16.

[0095] In particular, the cooling in the first cooler .sub.aHE1.sub.wa is carried out using a refrigerant fluid represented for example by air or water.

[0096] The compression and cooling steps can be repeated one or more times depending on needs and taking into account the complexity of the plant and the operating and construction costs.

[0097] For example, the compressed and cooled flow .sub.a16 can be compressed in a further first compressor .sub.aC1.sub.wa, thus obtaining a further compressed flow .sub.a15 to be cooled in a further first cooler .sub.aHE1.sub.wa, thus obtaining a further first compressed and cooled flow .sub.a16.

[0098] In accordance with an embodiment of the present invention, said first compressed and cooled flow .sub.a16 or said further first compressed and cooled flow .sub.a16 can be rejoined with a heated recycled gas flow a 26, obtained as described below, generating a second flow .sub.a17.

[0099] Said second flow .sub.a17 is compressed in a second compressor .sub.aC2.sub.wa to obtain a second compressed flow .sub.a18 which is cooled in a second cooler .sub.aHE2.sub.wa, thus obtaining a second compressed and cooled flow .sub.a19.

[0100] The compression and cooling steps can be repeated one or more times depending on needs and taking into account the complexity of the plant and the operating and construction costs.

[0101] For example, the second compressed and cooled flow .sub.a19 can be compressed in a further second compressor .sub.aC2.sub.wa, thus obtaining a further second compressed flow .sub.a18, which can be cooled in a further second cooler .sub.aHE2.sub.wa, thus obtaining a further second compressed and cooled flow .sub.a19.

[0102] Said further compressed and further cooled flow .sub.a19/.sub.a19 is subjected to a heat exchange step in the exchanger .sub.aLHE with which it is cooled, obtaining an at least partially condensed flow .sub.a20.

[0103] Said partially condensed flow .sub.a20 is expanded in an expander .sub.aTEX.sub.wa generating power and obtaining a further condensed flow a 21.

[0104] Inside a separator .sub.aS.sub.wa, a gaseous head flow .sub.a22 is separated from said further condensed flow .sub.a21 which, after being heated in a heat exchange step in the heat exchanger .sub.aLHE, generates the heated recycled gas flow .sub.a26 mentioned above.

[0105] A liquid oxygen-depleted air flow .sub.a23 is obtained from the bottom of the separator .sub.aS.sub.wa, which is sent to a tank .sub.aT.sub.air to be stored.

[0106] A flow .sub.aF1.sub.air is obtained from such a tank .sub.aT.sub.air which, after being pumped by a pump .sub.aP.sub.air, forms a use flow of pumped liquid oxygen-depleted air .sub.aF2.sub.air.

[0107] A portion of the oxygen-depleted air flow .sub.a24 is laminated by a second lamination valve .sub.aV2, thus obtaining a laminated flow .sub.a25 at the head pressure of the distillation column .sub.aDa and fed thereto.

[0108] For the purposes of the present invention, the frigories necessary for the heat exchange steps in the exchanger .sub.aLHE can also be further provided by a refrigeration cycle.

[0109] According to an aspect of the present invention, such a refrigeration cycle is represented by a liquefied natural gas cycle.

[0110] In particular, a cooled and expanded liquefied natural gas flow .sub.a60 obtained from an expansion step, for example in a liquefied natural gas expander .sub.aEX.sub.rc, carries out a heat exchange by releasing the frigories thereof by heat exchange in the exchanger .sub.aLHE to the further compressed and further cooled flow .sub.a19, generating a heated current .sub.a61.

[0111] The heated current .sub.a61 at the outlet of the exchanger LHE is compressed in a compressor of the refrigeration cycle .sub.aC.sub.rc, thus obtaining a compressed flow .sub.a62 which is then cooled in a cooler of the refrigeration cycle .sub.aHE.sub.rc obtaining a compressed and cooled flow .sub.a63.

[0112] According to a particular aspect of the present invention, the compression and cooling in the refrigerant cycle can be repeated several times in a further compressor of the refrigeration cycle .sub.aC.sub.rc, thus obtaining a further compressed flow .sub.a62, possibly cooled in a further cooler .sub.aHEr.sub.c of the refrigeration cycle, until a cryogenic flow .sub.a63 is obtained; the repetition of such steps depends on the needs and complexity of the plant and the construction and operating costs.

[0113] Said cryogenic flow .sub.a63 is then further cooled by heat exchange in the heat exchanger .sub.aLHE, thus obtaining a further cooled flow .sub.a64, which, in a preferred aspect, is then expanded in the refrigeration cycle (or liquefied natural gas) expander .sub.aEX.sub.rc with power production.

[0114] According to a particular aspect of the present invention, a further liquefied natural gas flow a 50 in output from a dedicated tank .sub.aT.sub.LNG can be sent to the heat exchanger .sub.aLHE and pumped by a liquefied natural gas pump P.sub.LNG, thus obtaining a further pumped liquefied natural gas flow .sub.a51.

[0115] The pumped liquefied natural gas flow .sub.a51 heats up and vaporizes in the exchanger .sub.aLHE, creating a further natural gas flow .sub.a52 fed to the network.

[0116] Thus for the purposes of the present invention, heat exchanges are carried out between the purified air flow .sub.a6, which is cooled to a cooled purified air flow .sub.a7 (step III), the oxygen-depleted air flow .sub.a13, which is heated to a heated oxygen-depleted air flow .sub.a14 (step Vb), and the pumped oxygen flow .sub.a42, which is heated and vaporized providing the vaporized oxygen flow .sub.a43.

[0117] In particular, said heat exchanges are carried out in the exchanger .sub.aMHE.

[0118] Thus for the purposes of the present invention, heat exchanges are carried out between the second compressed and cooled flow .sub.a19 (or a further second compressed and cooled flow 19), which is cooled to an at least partially condensed flow .sub.a20, the gaseous head flow .sub.a22, which is heated providing the heated gaseous recycled flow .sub.a26, the cryogenic flow .sub.a63, which is cooled to a further cooled flow .sub.a64, the cooled and expanded natural gas flow .sub.a60 providing the heated flow .sub.a61, and possibly also between the pumped liquefied natural gas flow .sub.a51, which is heated and vaporized giving the further natural gas flow .sub.a52.

[0119] In particular, said heat exchanges are carried out in the exchanger .sub.aLHE.

[0120] For the purposes of the present invention, the steps of the process described above are carried out using electricity.

[0121] In a second object, the present invention describes a process for producing electricity and liquid carbon dioxide; optionally and preferably also liquid natural gas.

[0122] Such a process comprises steps which involve: [0123] an oxygen-depleted air cycle, [0124] a cycle by means of a refrigerant fluid, [0125] an oxygen cycle,
and possibly a liquefied natural gas cycle.

[0126] For the purposes of the present invention, the aforementioned cycles are connected to one another by means of one or more heat exchange steps.

[0127] Such a process achieves the generation step mentioned above (references to this aspect are preceded by the .sub.g).

[0128] In particular, the combustion of a fuel .sub.gF in a combustor .sub.gCOMB is obtained in a step A) in the presence of a carbon dioxide-rich recirculation flow .sub.g6 and a gaseous oxygen flow .sub.g47.

[0129] The combustion produces a combusted flow .sub.g1 consisting mainly of CO.sub.2 and water at high pressure and temperature, which is expanded in a power-producing expander .sub.gTEX.

[0130] Preferably, the expansion is carried out up to almost atmospheric pressure, while the temperature is lowered to about 700 C.

[0131] The expanded combusted flow .sub.g2 thus obtained in a step B) is subjected to a heat exchange in a Heat Recovery Unit .sub.gWHRU in which it is cooled, obtaining an expanded and cooled flow .sub.g3.

[0132] For the purposes of the present invention, the cooling is preferably carried out up to about 90 C.

[0133] Inside the Heat Recovery Unit .sub.gWHRU, the heat exchange of step B) is carried out with a pumped oxygen-depleted air flow .sub.g61 or pumped and heated flow .sub.g62 and possibly also with a heated and expanded air flow .sub.g64, which circulate within an air cycle, as it will be described below.

[0134] In a step C) the expanded and cooled flow .sub.g3 is subjected to a separation step in a first separator .sub.gS1 from the bottom of which a first portion .sub.g4 of condensed water vapor is obtained.

[0135] A first gas flow .sub.g5 is obtained from the head of said first separator .sub.gS1, which is then compressed in a first compressor .sub.gC1, from which a CO.sub.2-rich recirculation flow .sub.g6 is obtained, which is recirculated to the combustor .sub.gCOMB in order to decrease the combustion temperature.

[0136] A compressed flow .sub.g8 is also obtained from the first compressor .sub.gC1, which is sent to the Heat Recovery Unit .sub.gWHRU, thus obtaining a cooled compressed flow .sub.g9.

[0137] In a preferred aspect, the compressed flow .sub.g8 is withdrawn from the first compressor .sub.gC1 at a pressure of about 10 barg.

[0138] Inside the Heat Recovery Unit .sub.gWHRU, the heat exchange is carried out with a pumped oxygen-depleted air flow .sub.g61 or pumped and heated flow .sub.g62, which circulates within an air cycle, as it will be described below.

[0139] In the case wherein the cooling inside the Heat Recovery Unit .sub.gWHRU does not reach ambient temperature, it is possible to further cool the cooled compressed flow .sub.g9 in a cooler .sub.gHE.sub.ag, by means of a refrigerant fluid represented for example by air or water, obtaining a further cooled flow .sub.g10.

[0140] The cooled compressed flow .sub.g9 or the further cooled flow .sub.g10 is subjected to a separation step D) in a second separator .sub.gS2 from whose bottom a second portion .sub.g11 of condensed water vapor is obtained.

[0141] A flow .sub.g12 with a main composition of carbon dioxide is obtained from the head of the second separator .sub.gS2, which is subjected to a treatment step E) in a Dehydration Unit .sub.gDHU wherein it is dehydrated by separating a flow from the bottom .sub.g13 mainly consisting of condensed water and a dehydrated flow .sub.g14 from the head.

[0142] For the purposes of the present invention, such a dehydration is carried out up to less than about 500 ppm and preferably up to less than about 50 ppm of water.

[0143] The dehydrated flow .sub.g14 obtained is then subjected to a cooling step F) in a refrigerant bath .sub.gRB, thus obtaining a cooled dehydrated flow .sub.g15.

[0144] A second laminate flow with a main composition of CO.sub.2 g22 obtained as described below is joined to the cooled dehydrated flow .sub.g15, thus obtaining a combined flow with a main composition of CO.sub.2 g16.

[0145] In a third separator .sub.gS3 from such a combined flow with a main composition of CO.sub.2 g16 a flow of liquid CO.sub.2 g17 is separated from the bottom and a gaseous release flow .sub.g18 is separated from the head.

[0146] In particular, such a liquid CO.sub.2 flow .sub.g17 consists of at least 95% CO.sub.2.

[0147] In a step G) such a gaseous release flow .sub.g18 can be compressed in a second compressor .sub.gC2, thus obtaining a compressed gaseous release flow .sub.g18.

[0148] The gaseous release flow .sub.g18 or the compressed gaseous release flow .sub.g18 is sent to the refrigerant bath .sub.gRB wherein it is cooled and partially condensed, obtaining a partially condensed release flow .sub.g19.

[0149] A final gaseous release flow .sub.g20 is separated in a step H) from such a partially condensed release flow .sub.g19 in a fourth separator .sub.gS4 which is released into the atmosphere, possibly after being further treated to reduce the carbon content thereof.

[0150] In particular, such a gaseous release flow .sub.g20 mainly comprises argon, nitrogen, carbon dioxide and oxygen.

[0151] Instead, a recovery liquid flow .sub.g21 is obtained from the bottom of the fourth separator S4, which is laminated by a first lamination valve .sub.gV1, thus obtaining a laminated flow with a main composition of CO.sub.2 g22 to the pression of the third separator .sub.gS3 and it is reunited with the cooled dehydrated flow .sub.g15 as described above.

[0152] For the purposes of the present invention, the refrigerant bath .sub.gRB operates on a refrigerant cycle in which a refrigerant fluid RF circulates.

[0153] In particular, such a refrigerant fluid is selected from the group comprising CF4, argon, R32, R41, R125 or another refrigerant fluid known in the field.

[0154] To this purpose, inside the refrigerant bath .sub.gRB, the dehydrated flow .sub.g14, as well as the gaseous release flow .sub.g18 or the compressed gaseous release flow .sub.g18, are cooled by a cooled flow .sub.gRF1 of the refrigerant fluid, which heats up to obtain a heated refrigerant fluid flow .sub.gRF2.

[0155] Such a heated refrigerant fluid flow RF2 is pumped into a refrigerant fluid cycle blower .sub.gCRF providing a pumped refrigerant fluid flow .sub.gRF3, which is then cooled in the heat exchanger by an oxygen cycle .sub.gErb, thus obtaining a cooled refrigerant fluid flow .sub.gRF1.

[0156] In particular, the oxygen cycle originates from a tank .sub.gTO.sub.2 where liquid oxygen is stored.

[0157] In fact, a liquid oxygen flow .sub.g45 originates from the tank .sub.gTO.sub.2 which is pumped by an oxygen pump .sub.gPO.sub.2, thus obtaining a pumped liquid oxygen flow .sub.g46.

[0158] Such a pumped liquid oxygen flow .sub.g46 carries out a heat exchange step in the oxygen cycle exchanger .sub.gErb, transferring the frigories thereof to the pumped refrigerant fluid flow .sub.gRF3, thus obtaining a gaseous oxygen flow .sub.g47.

[0159] The gaseous oxygen flow .sub.g47 thus obtained is sent to the combustor .sub.gCOMB as described above.

[0160] In an aspect of the invention, the oxygen flow sent to the combustor .sub.gCOMB is characterized by high purity >95%.

[0161] Therefore, for the purposes of the present invention, the dehydrated flow .sub.g14 is indirectly cooled by the pumped liquid oxygen flow .sub.g46, through the refrigerant fluid in the refrigerant bath .sub.gRB.

[0162] As reported above, inside the Heat Recovery Unit .sub.gWHRU, heat exchanges are carried out with one or more oxygen-depleted air flows circulating within an oxygen-depleted air circuit.

[0163] In particular, from an oxygen-depleted air tank .sub.gT.sub.air, an oxygen-depleted air flow .sub.g60 is withdrawn which is pumped by a pump .sub.gP.sub.air thus obtaining a pumped oxygen-depleted air flow .sub.g61.

[0164] In a preferred aspect, the pumping is carried out up to a pressure of about 80 barg.

[0165] Such a pumped oxygen-depleted air flow .sub.g61, before being sent to the Heat Recovery Unit .sub.gWHRU, can perform a heat exchange in a natural gas exchanger .sub.gELNG with a purified natural gas flow .sub.g41 obtained as described below, obtaining a pumped heated oxygen-depleted air flow .sub.g62.

[0166] The oxygen-depleted air flow .sub.g61 or the heated oxygen-depleted air flow .sub.g62 is sent to the Heat Recovery Unit .sub.gWHRU in which it performs a heat exchange with the compressed flow .sub.g8 and the expanded combusted flow .sub.g2, thus obtaining a further heated oxygen-depleted air flow .sub.g63.

[0167] In an embodiment of the invention, such a further heated oxygen-depleted air flow .sub.g63 can optionally be expanded in a first expander .sub.gEX.sub.air with power generation, obtaining a further heated expanded oxygen-depleted air flow .sub.g64.

[0168] Such a further heated expanded oxygen-depleted air flow .sub.g64 can be sent again to the Heat Recovery Unit .sub.gWHRU for further heat exchange with the expanded combusted flow .sub.g2, thus obtaining an even further heated oxygen-depleted expanded air flow .sub.g63.

[0169] In a preferred aspect of the present invention, the further heated oxygen-depleted air flow .sub.g63 or the even further heated expanded oxygen-depleted air flow .sub.g63 exits the Heat Recovery Unit .sub.gWHRU with a temperature of about 450-500 C.

[0170] Before being released into the atmosphere, it can possibly be further expanded in a further expander .sub.gEX.sub.air with power generation, achieving an oxygen-depleted release air flow .sub.g64.

[0171] Alternatively, such an oxygen-depleted release air flow .sub.g64 can be used in the regeneration of the Air Treatment Unit (.sub.gTUair) or in the Natural Gas Purification Unit (.sub.gPU) or in the carbon dioxide Dehydration Unit (.sub.gDHU).

[0172] According to an embodiment of the present invention reported above, the pumped oxygen-depleted air flow .sub.g61 can be heated in a liquefied natural gas heat exchanger .sub.gELNG by a purified natural gas flow .sub.g41 obtained from a natural gas Purification Unit .sub.gPU operating on an initial natural gas flow .sub.g40 taken from the network .sub.gNet, normally at a pressure of about 70 barg.

[0173] In the Purification Unit .sub.gPU the initial natural gas flow .sub.g40 is treated according to methods known in the field in order to (i) reduce its water content, preferably below 500 ppm of water and even more preferably below 50 ppm and/or (ii) to reduce its sulfur content, preferably below 500 ppm of sulfur and even more preferably below 10 ppm and/or (iii) to reduce its carbon dioxide content, preferably below 500 ppm of carbon dioxide and even more preferably below 50 ppm.

[0174] After the heat exchange step in the exchanger g ELNG, the condensed natural gas flow .sub.g42 obtained is sent to a tank .sub.gTLNG wherein it is properly stored.

[0175] According to the need, a liquefied natural gas flow .sub.g50 can be taken from such a tank .sub.gTLNG, which can be pumped by a liquefied natural gas pump .sub.gP.sub.LNG resulting in a pumped liquefied natural gas flow .sub.g51.

[0176] For the purposes of the present invention, the liquid oxygen-depleted air flow employed in the heat exchange step in the exchanger .sub.gELNG for cooling the purified natural gas flow .sub.g41 and in the heat exchange with the expanded combusted flow .sub.g2 in the Heat Recovery Unit (.sub.gWHRU) is the liquid oxygen-depleted air obtained from the storage step and, in particular, from the separation step Vb) in the separator .sub.aS.sub.wa of the oxygen-depleted air cycle and stored in the tank .sub.aT.sub.air.

[0177] For the purposes of the present invention, the liquid oxygen used in the heat exchange step in the exchanger .sub.gErb of the liquid oxygen cycle for cooling the pumped refrigerant fluid flow .sub.gRF3 is the liquid oxygen .sub.a40 obtained from the generation step and, in particular, output the reboiler .sub.aRa of the distillation column .sub.aDa and (or the portion .sub.a44 thereof) stored in the tank .sub.aTO.sub.2.

[0178] For the purposes of the present invention, the liquefied natural gas obtained after the heat exchange with oxygen-depleted air is stored within an appropriate tank .sub.gILNG, and, after being taken as a flow .sub.g50 and pumped giving the pumped flow .sub.g51, can be used to supply the additional refrigeration units necessary for the heat exchange carried out in the heat exchanger .sub.aLHE of the storage process described above.

[0179] The liquid or gaseous products obtained in accordance with the storage step and with the generation step according to the present invention are stored in appropriate tanks which coincide with each other; in other words, the liquefied natural gas tank (T.sub.LNG), the liquid oxygen-depleted air tank (T.sub.AIR), the liquid oxygen tank (T.sub.O2) of the storage step coincide with the corresponding tanks of the generation (or production) step.

[0180] For the purposes of the present invention, in the above description, the pressure values are preferably to be understood as follows: [0181] LNG: 5-150 barg, approximately, and preferably 70 barg; [0182] oxygen and the recycling current to the combustor: 8-450 barg, approximately, and preferably 35 barg; [0183] oxygen-depleted air: 10-400 barg, approximately, and preferably 150 barg; [0184] dehydrated carbon dioxide: it is between triple point pressures and the critical pressure of CO.sub.2.

[0185] In light of the above, it is apparent that the processes described are integrated and connected to one another.

[0186] In particular, the first process (STORAGE) is preferably carried out in a condition of electricity supply exceeding demand (excess) and allows the preparation and storage of liquefied oxygen-depleted air, of liquefied oxygen; as well as the production of natural gas to be introduced into the network.

[0187] In a particular aspect of the invention, the first process is carried out within a method for stabilizing the power network, in particular in situations of excess of electricity.

[0188] Such a method comprises carrying out the first process using an amount of electricity exceeding the demand.

[0189] Furthermore, the second process (GENERATION) is preferably carried out under conditions of demand for electricity with respect to demands (shortage) and allows the production of electricity in several steps, as well as the preparation and storage of liquefied natural gas.

[0190] In a particular aspect of the invention, the second process is carried out in the context of a method for stabilizing the power network, in particular, in periods of under-supply.

[0191] Such a method comprises carrying out the second process using a storage of liquid (oxygen) depleted air and liquid oxygen stored under conditions of excess electricity or, as described above, by means of a STORAGE process.

[0192] In a third object of the invention, a method for stabilizing the power network is described, comprising implementing the STORAGE process and the GENERATION process according to the conditions and availability of electricity, advantageously further leading to the production and storage of LNG.

[0193] From the description provided above, the several advantages offered by the present invention will be apparent to those skilled in the art.

[0194] The method described by the present invention allows high efficiency; for example, 90% with respect to fuel, 45% overall efficiency (i.e., taking into account all the forms of energy fed into the system).

[0195] Furthermore, the method is capable of stabilizing the power network by absorbing excess energy or by introducing produced energy.

[0196] The method can also conveniently produce liquefied natural gas and gaseous oxygen at high pressure.

[0197] The method described by the present invention allows not releasing carbon dioxide into the environment, allowing the implementation of an environmentally sustainable process.

[0198] Overall, the method comprises processes which are simpler, from a technical point of view, than the sum of the other processes which lead to the same results, such as oxy-combustion and LAES technologies, for example also due to the use of a single distillation column.