Method for the exploitation of natural gas deposits rich in co 2 with synthetic gas production

Abstract

The present patent application relates to a method for exploiting natural gas deposits that are rich in carbon dioxide by converting the carbon dioxide into methane and water by hydrogenation.

Description

[0001] " Method for the exploitation of natural gas deposits rich in CO₂ with synthetic gas production"

[0002] DESCRIPTION

[0003] As far as the exploitation of natural gas (NG) reserves is concerned, it is typical to remove pollutants, such as hydrogen sulphide and carbon dioxide, by means of purification technologies, such as amines, membranes or combinations of these.

[0004] Purification plants are often equipped with units for transforming hydrogen sulfide into sulfur, while carbon dioxide is released into the atmosphere or re-injected into the wells.

[0005] While the first solution poses environmental problems, the reinjection can, however, dilute the hydrocarbons constituting the natural gas, making the exploitation of the wells increasingly difficult and less convenient.

[0006] One strategy for using carbon dioxide is therefore to transform it into methane through methanation with the addition of hydrogen.

[0007] The transformation of carbon dioxide into methane with hydrogen is typically carried out in a methanation plant, usually consisting of several reactors placed in series, where the Sabatier reaction is conducted, which transforms carbon dioxide and hydrogen into methane and water (in the working conditions of the reactors, albeit to a very limited extent, heavier hydrocarbons are also obtained).

[0008] The Lurgi plant is shown schematically in Figure 1.

[0009] In this plant, a stream of reactants, consisting mainly of carbon dioxide and hydrogen, is combined with a stream of compressed recirculation gas. The resulting stream is heated and then fed to a first methanation reactor (R1), where it undergoes the Sabatier reaction until it reaches equilibrium conditions.

[0010] A gas stream containing mainly carbon dioxide, hydrogen, methane and water emerges from the R1 reactor, at a higher temperature than the incoming stream due to the heat developed in the reactor under almost adiabatic conditions.

[0011] The stream emerging from R1 is partially cooled by heat exchange with a gas stream, of the same chemical composition, which continues the Sabatier reaction in a second reactor R2.

[0012] The partially cooled stream emerging from R1 is further cooled by heat exchange in a boiler, where the heat transferred from it produces high-pressure water vapor, thus obtaining the cooled stream emerging from R1.

[0013] The cooled stream emerging from R1 is divided into two streams: a stream called the recirculation stream and the aforementioned stream emerging from R1 continuing the reaction, which exchanges heat and is heated by the energy transferred by the stream emerging from R1, becoming the stream emerging from R1 that continues the reaction in the second reactor R2.

[0014] The recirculation stream is compressed by means of a compressor, obtaining the compressed recirculation gas stream mentioned above.

[0015] The stream emerging from R1 that continues the heated reaction is fed to the reactor R2, where the Sabatier reaction continues.

[0016] The reacted gas stream emerges from R2, composed mainly of methane, water, hydrogen, and carbon dioxide, and possibly heavier hydrocarbons belonging to the C2+ class. The reacted gas stream emerging from R2 is cooled in a boiler, in which high-pressure water vapor and a cooled reacted gas stream emerging from R2 are produced.

[0017] The cooling of the reacted gas stream emerging from cooled R2 is separated, by means of a separator, into its liquid components, mainly consisting of water, and gaseous, consisting almost entirely of methane, hydrogen and carbon dioxide; the liquid phase (condensates) is removed from the system, while the gaseous phase, called SNG, is sent to purification from carbon dioxide and water to achieve the specifications required for the product.

[0018] The possibility of creating a methanation reactor that can be switched on and off daily, in order to follow the trend of electrolytic hydrogen availability, has been investigated.

[0019] Methanation reactors require an almost continuous supply; in fact, frequent switching on and off reduces the life of the catalyst and the heat exchange trains, as well as requiring rather long times to develop the thermal profiles that guarantee the correct conversion of the reagents.

[0020] This problem is solved by producing and consuming hydrogen, in methanation, even in periods of energy scarcity, trying to decrease the hydrogen needs of the reactors by bringing them to the Turndown.

[0021] Alternatively, it is possible to accumulate the hydrogen that is not to be produced, in the form of compressed gas (possibly at low temperature to increase its density), or in liquid form, much more suitable for large accumulations.

[0022] However, to date, the state of the art of (non-magnetic) hydrogen liquefaction requires 10 to 13 KWh / kg (DOE source), where the lowest values are obtained by using low-speed volumetric compressors (90% efficiency), as reported in " Large scale hydrogen liquefaction under the aspect of economic viability".

[0023] Again, since the Sabatier reaction is very exothermic, the control of the temperature in the methanation reactors is problematic, and generally requires the recycling of large quantities of reaction products entering the first reactor, using a recirculation compressor, working at high temperature, therefore in technologically challenging conditions, or the injection of steam, which however degrades the quality of the recoverable heat, because the condensation of the water vapor produces heat exchange curves that are poorly adapted to the production of low pressure steam.

[0024] Also for the production of hydrogen, it should be noted that SOEC-type electrolyzers cannot be switched on and off cyclically, except at the cost of long waiting times, which follow the heating curves of the equipment, in order to limit its degradation.

[0025] To solve these problems, it is typical to burn fuel when renewable energies are not available (at night, for example, with regard to a solar field) to keep both the SOEC and the methanation reactors running with the hydrogen it generates, albeit under Turndown conditions.

[0026] Since the use of a fuel implies both the production of a nonrenewable resource and the production of carbon dioxide, it is clear that this is to the detriment of the benefits provided by the use of renewable energy.

[0027] To date, various types of electrolytic cells have been developed, but the most promising for large-scale use are the Solid Oxydes Electrolytic Cells (SOEC), which hydrolyze water vapor at high temperature, with high efficiencies and large conversion factors.

[0028] Hydrogen and oxygen are obtained from the hydrolyzed steam; the latter is often considered a waste product, to the point that the electrode at which it is generated is flushed with air, in order to lower its partial pressure and reduce the voltage of the electrolytic cell, with consequent savings in electrical energy.

[0029] Alternatively, the flushing can be carried out with steam which, being easily condensable, allows at least the recovery of oxygen at a high degree of purity.

[0030] Summary of the invention

[0031] The inventors of the present patent application have developed a method that surprisingly allows a carbon dioxide methanation plant to be kept in continuous operation by using electrolytic hydrogen.

[0032] This method involves the use of an oxy-combustion system that feeds the electrolysis process in the Turndown phases, where said oxy-combustion system uses a synthetic fuel produced in the Full Run phase.

[0033] Since the fuel used in the oxy-combustion system is cyclically consumed and regenerated by means of renewable energies, it constitutes an energy vector and a system for accumulating said energies.

[0034] Obj ect of the invention

[0035] In accordance with a first obj ect of the present invention, a method for the production of a synthetic gas is described. In particular, this method is carried out under conditions of abundant electricity availability.

[0036] In accordance with a second obj ect of the present invention, a method for producing a synthetic gas is described.

[0037] In particular, this method is carried out in conditions of scarce electricity.

[0038] The first and second methods described, in the context of the present invention, can be considered as a first and a second phase, respectively, of a method for maintaining the continuous operation of the methanation reactors in conditions of low energy availability.

[0039] A third obj ect describes a plant for implementing the methods of the invention.

[0040] Detailed description of the invention

[0041] In accordance with a first obj ect, a method for producing a synthetic gas is described.

[0042] These conditions can be referred to as Full Run conditions of a methanation plant.

[0043] For the purposes of the present invention, this method is carried out starting from a natural gas flow, preferably obtained from natural natural gas wells.

[0044] In the remainder of the description, this natural gas flow will be referred to as the "initial natural gas flow ".

[0045] For the purposes of the present invention, this initial natural gas stream comprises CO₂ in an amount of about 1-70% (v / v).

[0046] For the purposes of the present invention, this natural gas stream also comprises C₁₋₅ light hydrocarbons. According to an aspect of the present invention, this natural gas flow also comprises hydrogen sulphide and possibly other sulphur compounds.

[0047] The term "synthetic gas" means a synthetic gas rich in methane obtained from a methanation process; that is, with a methane content of at least 40%.

[0048] In the present description and in the present invention, the term "natural gas" refers to methane-rich gas obtained from a natural well, while the term "synthetic gas" means a methane-rich gas obtained as a product of methanation and which can be considered as a synthetic natural gas, as it is produced, and not extracted, from a well.

[0049] This synthetic gas can be produced from a natural gas, extracted from a well, and subjected to methane enrichment phases so as to increase its concentration, for example through the methanation of the carbon dioxide contained therein, until a synthetic natural gas is obtained, with a methane concentration similar to that of the natural gas to be fed into the network.

[0050] In an aspect of the invention, the natural gas is in fact represented by the initial natural gas flow, obtained from a well.

[0051] The method of the invention according to the first obj ect described is carried out in conditions of abundance of electrical energy, that is, in the presence of an availability of electrical energy greater than the needs of the other utilities.

[0052] According to a preferred aspect of the invention, this electrical energy is produced from renewable (discontinuous) energy sources and is, for example, represented by solar, wind, or nuclear electrical energy.

[0053] The above method is schematically shown in Figure 2.

[0054] In particular, this method for the production of synthetic gas comprises the steps of:

[0055] I ) obtaining a synthetic gas flow 2 and heat from an initial natural gas flow 1 subjected to methanation,

[0056] II ) obtaining a flow of hydrogen gas 4 and a flow of oxygen gas 5 by electrolysis.

[0057] For the purposes of the present invention, step II ) is carried out on a steam flow 3 obtained from a first water flow wl vaporized by the heat developed in the methanation step I ).

[0058] For the purposes of the present invention, the hydrogen gas flow 4 obtained in step II) is sent to the methanation step I ).

[0059] According to an embodiment of the invention, before being subjected to the methanation step I), the hydrogen gas flow 4 may be subjected to a compression step.

[0060] According to an aspect of the present invention, before step I), the initial natural gas flow 1 may be subjected to a purification step 0) in a purifier P.

[0061] In particular, said step 0) is a purification step from sulfur compounds.

[0062] According to a preferred embodiment, the purification step 0) eliminates the sulfur compounds present in the initial natural gas flow 1. In particular, said purification removes these sulfur compounds to a concentration suitable for the production of liquefied synthetic gas and less than 50 ppm.

[0063] According to an embodiment of the invention, desulphurisation can be carried out by means of an absorption column.

[0064] According to an embodiment of the invention, desulfurization can be carried out using an aqueous solution of a tertiary amine.

[0065] According to an aspect of the present invention, the purification step may also comprise a step of removing heavy metals, in order to prevent the so-called poisoning of the methanation catalysts.

[0066] According to an embodiment of the invention, the removal of heavy metals can be carried out by means of activated carbon filters.

[0067] The initial purified natural gas flow 1 ' thus obtained is then sent to the methanation phase I ).

[0068] Therefore, the initial natural gas flow of step I ) can be a purified initial natural gas flow 1 '.

[0069] For the purposes of the present invention, the natural gas flow richer in methane 2 is sent to the natural gas network ("network" in Figure 2 ).

[0070] According to an aspect of the present invention, the methane-richer natural gas flow 2 produced has a CO₂ content of less than 100 ppm.

[0071] According to an embodiment of the invention, before being introduced into the natural gas network, said natural gas flow richer in methane 2 can be subjected to a dehydration phase. In particular, this dehydration reduces the water content below the limits allowed for the production of liquefied natural gas and therefore preferably below 100 ppm.

[0072] For the purposes of the present invention, the natural gas richer in methane 2 has a higher methane content than the initial natural gas flow 1.

[0073] For the purposes of the present invention, the electrolysis step II ) is carried out in an electrolyzer E (or water splitter).

[0074] According to an aspect of the present invention, the electrolysis phase II ) is carried out using a first energy source el.

[0075] According to a preferred aspect of the present invention, said first energy source el is represented by a renewable (discontinuous) energy source, such as, for example, solar energy, wind energy, or nuclear energy.

[0076] For the purposes of the present invention, said first renewable energy source el is used when available, for example under Full Run conditions, as described in the present patent application.

[0077] For the purposes of the present invention, the method may comprise a further step III ) of oxygen liquefaction, which is carried out in an oxygen liquefier OL.

[0078] According to an aspect of the present invention, step III ) of oxygen liquefaction is carried out using a second energy source e2.

[0079] According to a preferred aspect of the present invention, said second energy source e2 is represented by a renewable (discontinuous) energy source, such as, for example, solar energy, wind energy, or nuclear energy. An alternative embodiment of the method described above is schematically represented in Figure 3.

[0080] In particular, this method for producing a synthetic gas comprises the steps of:

[0081] I ) obtaining a synthetic gas flow 2 and heat from an initial natural gas flow 1, 1 ' subjected to methanation,

[0082] II ) obtaining a flow of hydrogen gas 4 and a flow of oxygen gas 5 by electrolysis,

[0083] III ) liquefying said flow into gaseous oxygen 5, obtaining a flow of liquefied oxygen 6.

[0084] IV) obtaining a portion 7 of said synthetic gas flow, and V) subj ecting said portion 7 of synthetic gas to liquefaction, obtaining a flow of liquefied synthetic gas 8.

[0085] For the purposes of the present invention, step II ) is carried out on a steam flow 3 obtained from a first water flow wl vaporized by the heat developed in the methanation step I ).

[0086] For the purposes of the present invention, the hydrogen gas flow 4 obtained in step II) is sent to the methanation step I ).

[0087] According to an embodiment of the invention, before being subjected to the methanation phase I ), the hydrogen gas flow 4 can be subjected to a compression phase.

[0088] According to an aspect of the present invention, before step I ), the initial natural gas flow 1 is subjected to a purification step 0 ).

[0089] In particular, said step 0) is a purification step from sulfur compounds. According to a preferred embodiment, the purification step 0) eliminates the sulfur compounds present in the initial natural gas flow 1.

[0090] In particular, said purification removes these sulfur compounds up to a concentration suitable for the production of liquefied synthetic gas.

[0091] According to an embodiment of the invention, desulfurization can be carried out by means of an absorption column.

[0092] According to an embodiment of the invention, desulfurization can be carried out using an aqueous solution of a tertiary amine.

[0093] According to an aspect of the present invention, the purification phase may also include a phase of removing heavy metals, in order to prevent the so-called poisoning of the methanation catalysts.

[0094] According to an embodiment of the invention, the removal of heavy metals can be carried out by means of activated carbon filters.

[0095] The initial purified natural gas flow 1 ' thus obtained is then sent to the methanation phase I ).

[0096] Therefore, the natural gas flow subjected to step I ) can be an initial natural gas flow 1 or a purified initial natural gas flow 1 ’.

[0097] According to an aspect of the present invention, the methanation step I ) can also be carried out in the presence of a flow of liquefied carbon dioxide 11, possibly pumped by a liquefied carbon dioxide pump PCO2l, obtaining a flow of pumped liquefied carbon dioxide 11 ' (not shown in the Figure). This flow of liquefied carbon dioxide 11 can be obtained from a TCO2l storage tank.

[0098] For the purposes of the present invention, the methane-richer natural gas flow 2 (synthetic gas) obtained from step I ) is sent to the natural gas network ("network" in Figure 3).

[0099] For the purposes of the present invention, the electrolysis step II ) is carried out in an electrolyzer E (or water splitter).

[0100] According to an aspect of the present invention, step II ) of electrolysis is carried out using a first energy source el.

[0101] According to a preferred aspect of the present invention, said first energy source el is represented by a renewable (discontinuous) energy source, such as, for example, solar energy, wind energy, or nuclear energy.

[0102] For the purposes of the present invention, said first renewable energy source el is used when available, for example under Full Run conditions, as described in the present patent application.

[0103] For the purposes of the present invention, step III ) of oxygen liquefaction is carried out in an oxygen liquefier OL.

[0104] According to an aspect of the present invention, step III ) of oxygen liquefaction is carried out using a second energy source e2.

[0105] According to a preferred aspect of the present invention, said second energy source e2 is represented by a renewable (discontinuous) energy source, such as, for example, solar energy, wind energy, or is represented by nuclear energy.

[0106] According to an aspect of the present invention, the liquefaction step V) is carried out in a synthetic gas liquefier LSG. According to an aspect of the present invention, the liquefaction step V) is carried out using a third energy source e3.

[0107] Said third energy source e3 may correspond to the second energy source e2 and / or the fourth energy source e4.

[0108] The liquefied synthetic gas flow obtained from step V) is accumulated in a tank TLSG.

[0109] According to an aspect of the present invention, a first recovery hydrogen flow 9 can also be obtained from step V), which is sent to the methanation step I ).

[0110] According to an aspect of the present invention, a second recovery hydrogen flow 10 can also be obtained from the liquefied synthetic gas tank TLSG, which is sent, independently of the first recovery hydrogen flow 9, to the methanation step I ).

[0111] According to an embodiment of the present invention, the optional step of liquefying an air flow 12 can also be carried out, obtaining a liquefied air flow 13.

[0112] According to an aspect of the present invention, the liquefaction step of the air flow 12 is carried out in an air liquefier AL.

[0113] According to an aspect of the present invention, said step is carried out using a fourth energy source e4.

[0114] Said fourth energy source e4 may correspond to the second energy source e2 and / or the third energy source e3.

[0115] The obtained liquefied air flow 13 is subsequently accumulated in a liquefied air tank TAl.

[0116] For the purposes of the present invention, step III) of liquefying the oxygen flow 5, step V) of liquefying the portion 7 of the synthetic gas flow and, if carried out, the step of liquefying the air flow 12, are carried out in an integrated structure ( ILF, Integrated Liquefaction Facilities'), i. e. in the same liquefaction unit (structure).

[0117] For the purposes of the present invention, this integrated structure can be represented by a nitrogen liquefier, which can comprise one or more heat exchangers in series.

[0118] According to an embodiment of the invention, the heat developed by the methanation phase I ) can be the heat produced by one or more methanators (not shown in the Figures).

[0119] In accordance with a second obj ect of the present invention, a method for the production of a synthetic gas is described, in particular, under conditions of scarcity of electrical energy, i. e. in the presence of a reduced availability of electrical energy, i. e. less than the needs of the other utilities.

[0120] According to a preferred embodiment of the invention, this electrical energy is scarcely available, as it is produced from renewable energy sources such as solar, wind, or nuclear electricity.

[0121] For the purposes of the present invention, these conditions are the conditions in which a methanation plant is in the Turndown phase.

[0122] According to a preferred aspect, said method is therefore carried out using electricity obtained by oxy-combustion.

[0123] For the purposes of the present invention, this method is carried out starting from a flow of natural gas obtained from natural natural gas wells.

[0124] For the purposes of the present invention, this natural gas flow comprises CO2in an amount of about 1-70% (v / v). For the purposes of the present invention, this natural gas flow also comprises C1-5light hydrocarbons.

[0125] According to an aspect of the present invention, this natural gas flow also comprises hydrogen sulphide and possibly other sulphur compounds.

[0126] The term "synthetic gas" means a synthetic gas rich in methane obtained from a methanation process (a "synthetic natural gas" ).

[0127] Said synthetic gas is in practice a synthetic natural gas, that is, produced by methanation and not extracted.

[0128] The above method is schematically represented in Figure 4 and further in Figures 8 and 9.

[0129] In particular, this method for producing a synthetic gas in conditions of low electricity availability comprises the steps of:

[0130] VI ) conducting an oxy-combustion step obtaining a fifth energy source (e5), a first flow of carbon dioxide from oxy-combustion (28 ) and a second flow of carbon dioxide from oxy-combustion (29) VII ) obtaining a synthetic gas flow (2, 71 ) and heat from an initial natural gas flow ( 1, 51 ) subjected to methanation, VIII ) obtaining a flow of hydrogen gas (4, hl ) and a flow of oxygen gas (5, ol ) by electrolysis.

[0131] For the purposes of the present invention, step VIII ) is carried out on a steam flow 23 obtained from a first water flow wl vaporized by the heat developed in the methanation step VII ).

[0132] For the purposes of the present invention, the hydrogen gas flow 24 obtained in step VIII ) is sent to the methanation step VII ). According to an aspect of the present invention, prior to steps VI ) and VII ), the initial natural gas flow 21 may be subjected to a purification step Ob) in a purifier P.

[0133] In particular, said step Ob) is a purification step from sulfur compounds.

[0134] In particular, said purification removes these sulfur compounds to a concentration suitable for the production of liquefied synthetic gas, and less than 50 ppm.

[0135] According to an embodiment of the invention, desulphurisation can be carried out by means of an absorption column.

[0136] According to an embodiment of the invention, desulfurization can be carried out using an aqueous solution of a tertiary amine.

[0137] According to an aspect of the present invention, the purification step may also comprise a step of removing heavy metals, in order to prevent the so-called poisoning of the methanation catalysts.

[0138] According to an embodiment of the invention, the removal of heavy metals can be carried out by means of activated carbon filters.

[0139] The initial purified natural gas flow 21 ' thus obtained is then sent to the methanation phase VII ).

[0140] Therefore, the natural gas flow subjected to step VII ) can be a purified natural gas flow 21 '.

[0141] According to an aspect of the present invention, the oxycombustion step VI ) is carried out in the presence of a liquefied oxygen flow 26.

[0142] In particular, said liquefied oxygen flow 26 is obtained from a liquefied oxygen storage tank TO2l. For the purposes of the present invention, the oxy-combustion step VI ) can be carried out in the presence of the gaseous oxygen flow 25 obtained from step VIII ).

[0143] For the purposes of the present invention, the oxygen combustion step VI ) can be carried out in the presence of a liquefied synthetic gas flow 27.

[0144] In particular, said liquefied synthetic gas flow 27 is obtained from a liquefied synthetic gas storage tank TLSG.

[0145] According to an aspect of the present invention, the oxy-combustion step VI ) can also be carried out in the presence of a portion of the initial natural gas flow 21 ' ' ' or a portion 21 ' ' of the purified initial natural gas flow obtained from step Ob).

[0146] For the purposes of the present invention, said fifth source of energy e5 obtained from step VI ) is used to conduct the electrolysis step VIII ).

[0147] For the purposes of the present invention, said fifth source of energy e5 is used in the Turndown phase, as described in the present patent application.

[0148] In fact, since a renewable energy source is not available, the electrolysis phase VIII ) is carried out using the fifth energy source e5 obtained by oxy-combustion.

[0149] For the purposes of the present invention, the first flow of carbon dioxide 28 (part in liquid form and part in gaseous form) is obtained by cooling and liquefaction by heat exchange with the flow of liquefied synthetic gas 27 and / or with the flow of liquefied oxygen 26 and accumulated in a tank of liquefied CO2TCO2l. For the purposes of the present invention, said second flow of carbon dioxide 29 is stored in a natural well.

[0150] According to a preferred aspect of the present invention, the liquefied oxygen flow 26 used in the oxy-combustion step VI ) and obtained from a liquefied oxygen storage tank TO2l is obtained according to the method of the present invention described above carried out under conditions of abundance of electrical energy (so-called Full Run).

[0151] According to a preferred embodiment of the present invention, the liquefied synthetic gas flow 27 used in the oxy-combustion step VI ) and obtained from a liquefied synthetic gas storage tank TLSGis obtained according to the method of the present invention described above carried out under conditions of abundance of electrical energy (so-called Full Run).

[0152] An alternative embodiment of the method described above is shown in Figure 5.

[0153] In particular, this method comprises the steps of:

[0154] VI ) conducting an oxy-combustion step obtaining a fifth energy source (e5), a first flow of carbon dioxide from oxy-combustion (28 ) and a second flow of carbon dioxide from oxy-combustion (29), VII ) obtaining a synthetic gas flow 22, and heat, from a natural gas flow 21, 21 ' subjected to methanation in a methanator, VIII ) obtaining a hydrogen gas flow 24 and an oxygen gas flow 25 by electrolysis.

[0155] For the purposes of the present invention, step VIII ) is carried out on a steam flow 23 obtained from a first water flow wl vaporized by the heat developed in the methanation step VII ). For the purposes of the present invention, the hydrogen gas flow 24 obtained in step VIII ) is sent to the methanation step VII ).

[0156] According to an aspect of the present invention, prior to step VII ), the initial natural gas flow 21 may be subjected to a purification step Ob) in a purifier P.

[0157] In particular, said step Ob) is a purification step from sulfur compounds.

[0158] In particular, said purification removes these sulfur compounds to a concentration suitable for the production of liquefied synthetic gas and less than 50 ppm.

[0159] According to an embodiment of the invention, desulphurisation can be carried out by means of an absorption column.

[0160] According to an embodiment of the invention, desulfurization can be carried out using an aqueous solution of a tertiary amine.

[0161] According to an aspect of the present invention, the purification step may also comprise a step of removing heavy metals, in order to prevent the so-called poisoning of the methanation catalysts.

[0162] According to an embodiment of the invention, the removal of heavy metals can be carried out by means of activated carbon filters.

[0163] The initial purified natural gas flow 21 ' thus obtained is then sent to the methanation phase VII ).

[0164] Therefore, the natural gas flow subjected to phase VII ) can be a purified initial natural gas flow 21 '.

[0165] For the purposes of the present invention, the oxy-combustion step VI ) can be carried out in the presence of a liquefied oxygen flow 26. In particular, said liquefied oxygen flow 26 is obtained from a liquefied oxygen storage tank TO2l.

[0166] For the purposes of the present invention, the oxy-combustion step VI ) can be carried out in the presence of the gaseous oxygen flow 25 obtained from step VIII ).

[0167] For the purposes of the present invention, the oxy-combustion step VI ) is carried out in the presence of a liquefied synthetic gas flow 27.

[0168] In particular, said liquefied synthetic gas flow is obtained from a liquefied synthetic gas storage tank TLSG.

[0169] According to an aspect of the present invention, the oxy-combustion step VI ) can also be carried out in the presence of a portion of the initial natural gas flow 21 ' ' ' or a portion 21 ' ' of the purified initial natural gas flow obtained from step Ob).

[0170] For the purposes of the present invention, the oxy-combustion step VI ) can also be carried out in the presence of a liquefied air flow 31, obtaining a gaseous air flow 32.

[0171] In particular, said liquefied air flow 31 is obtained from a liquefied air storage tank TAl.

[0172] For the purposes of the present invention, said fifth source of energy e5 obtained in step VI ) is used to conduct the electrolysis step VIII ).

[0173] For the purposes of the present invention, said fifth source of energy e5 is used in the Turndown phase, as described in the present patent application.

[0174] For the purposes of the present invention, the first flow of carbon dioxide 28 (part in liquid form and part in gaseous form) is cooled and liquefied by heat exchange with the flow of liquefied synthetic gas 27 and / or with the flow of liquefied oxygen 26 and possibly also by the flow of liquefied air 31, and is accumulated in a tank of liquefied CO2Tco2l.

[0175] For the purposes of the present invention, said second flow of carbon dioxide 29 is stored in a natural well.

[0176] For the purposes of the present invention, the flow of liquefied carbon dioxide 11 is obtained from said liquefied carbon dioxide storage tank TCO2l, which can be used in step I ) of methanation (Figure 3).

[0177] A particular embodiment of the method of the present invention for the production of synthetic gas is shown schematically in Figure 6.

[0178] As described above, these conditions can be referred to as Full Run conditions of a methanation plant.

[0179] For the purposes of the present invention, this method is carried out from a natural gas flow obtained from natural natural gas wells.

[0180] For the purposes of the present invention, this natural gas flow comprisesco2in an amount of about 1-70% (v / v).

[0181] For the purposes of the present invention, this natural gas stream also comprises C₁₋₅ light hydrocarbons.

[0182] flow to an aspect of the present invention, this natural gas flow also comprises hydrogen sulphide and possibly other sulfur compounds. The term "synthetic gas" means a synthetic gas rich in methane obtained from a methanation process, meaning a methane percentage of at least 40%.

[0183] The method of the invention is carried out in conditions of abundance of electrical energy, i. e. in the presence of an availability of electrical energy greater than the needs of other users.

[0184] According to a preferred aspect of the invention, this electrical energy is produced from renewable (discontinuous) energy sources and is, for example, represented by solar, wind, or nuclear energy.

[0185] In particular, an initial natural gas flow 51 is obtained from a natural gas well D, which can be preliminarily compressed by a natural gas compressor KNG.

[0186] In a Purification Unit P, said initial natural gas flow 51 can optionally be purified of sulfur compounds, obtaining the purified initial natural gas flow 52.

[0187] Said initial purified natural gas flow 52 is heated in a first heat recovery unit EX1, obtaining an initial purified and heated natural gas flow 53, which is intended for the methanation phase.

[0188] For the purposes of the present invention, said initial purified natural gas flow 52 can be heated to a temperature such as to guarantee sufficient reaction kinetics and a thermal profile that is not too high in the methanation reactor; typically about 250°C.

[0189] A final methanation product 68 is obtained from the methanation. More specifically, a first methanation flow 54 is obtained from the initial purified and heated natural gas flow 53 and is sent to a first methanator Ml.

[0190] As described below, a second methanation flow 55 is also obtained from the initial purified and heated natural gas flow 53, which is sent to a second methanator M2.

[0191] As described below, a third methanation flow 56 is also obtained from the initial purified and heated natural gas flow 53, which is sent to a third methanator M3.

[0192] As described below, a fourth methanation flow 57 is also obtained from the initial purified and heated natural gas flow 53, which is sent to a fourth methanator M4.

[0193] In particular, said first methanation flow 54 is sent to the first methanator Ml from which a first methanation product 58 is obtained.

[0194] For the purposes of the present invention, said first methanation product 58 is characterized by a temperature of about 450-600°C and preferably of about 500°C.

[0195] In particular, said first methanation product 58 is cooled in the first heat recovery unit EX1 by heat exchange with the initial purified natural gas flow 52, obtaining a first cooled methanation product 59.

[0196] Said first cooled methanation product 59 can be further cooled in a first heat exchanger TE1, obtaining a first further cooled methanation product 60, which is sent to the second methanator M2. For the purposes of the present invention, said first heat exchanger TE1 operates by means of a refrigerant fluid represented by air or water.

[0197] For the purposes of the present invention, said first further cooled methanation product 60 is sent to the second methanator M2 together with the second methanation flow 55.

[0198] A second methanation product 61 is obtained from the second methanator M2.

[0199] For the purposes of the present invention, said second methanation product 61 is characterized by a temperature of approximately 450-600°C and preferably approximately 500°C.

[0200] In particular, said second methanation product 61 is cooled in a second heat recovery unit EX2, obtaining a second cooled methanation product 62.

[0201] Said second cooled methanation product 62 is sent to the third methanator M3.

[0202] For the purposes of the present invention, said cooled second methanation product 62 is sent to the third methanator M3 together with the third methanation flow 56.

[0203] A third methanation product 63 is obtained from the third methanator M3, which is cooled in a Heat Exchange Unit EXU, which manages the heat developed in the methanation phase, obtaining a third cooled methanation product 64.

[0204] For the purposes of the present invention, said cooled third methanation product 64 has a temperature of approximately 250°C.

[0205] Said cooled third methanation product 64 is sent to the fourth methanator M4. For the purposes of the present invention, said cooled third methanation product 64 is sent to the fourth methanator M4 together with the fourth methanation flow 57.

[0206] A fourth methanation product 65 is obtained from the fourth methanator M4.

[0207] For the purposes of the present invention, said fourth methanation product 65 is characterized by a temperature of approximately 450-600°C and preferably approximately 500°C.

[0208] In particular, said fourth methanation product 65 is cooled in the Heat Exchange Unit EXU, obtaining a fourth cooled methanation product 66.

[0209] Said fourth cooled methanation product 66 is conveyed to the fifth methanator M5.

[0210] A fifth methanation product 67 is obtained from the fifth methanator M5, which is cooled in the Heat Exchange Unit EXU, obtaining a fifth cooled methanation product which represents the final methanation product 68.

[0211] For the purposes of the present invention, said fifth cooled methanation product 68 has a temperature of approximately 100°C.

[0212] Preferably, before being sent to the gas network, said final methanation product 68 is dehydrated.

[0213] For this purpose, said final methanation product 68 is cooled in a second heat exchanger TE2, obtaining a cooled final methanation product 69.

[0214] For the purposes of the present invention, said second heat exchanger TE2 operates by means of a refrigerant fluid represented by air or water. For the purposes of the present invention, said cooled final methanation product 69 has a temperature close to room temperature.

[0215] Said cooled final methanation product 69 is treated in a first separator S1, from which a first portion of dehydration water ww1 and a dehydrated methanation product 70 are obtained.

[0216] In a dehydration unit DI, said dehydrated methanation product 70 is further dehydrated, obtaining a synthetic gas flow to be sent to the network 71.

[0217] In particular, said synthetic gas flow to be sent to the network 71 is represented by a flow of methane and hydrogen.

[0218] In particular, hydrogen represents about 10% (v / v).

[0219] The configuration described in this embodiment includes five methanators, but a greater or lesser number of methanators may be provided.

[0220] For the purposes of the present invention, a flow of hydrogen gas is also sent to the methanation phase described above.

[0221] For the purposes of the present invention, said hydrogen gas flow is obtained by electrolysis.

[0222] According to a preferred aspect of the invention, this electrolysis is carried out using energy obtained from renewable (discontinuous) sources, such as, for example: solar energy, wind energy, or nuclear energy.

[0223] For this purpose, a first flow of water w51 represented, for example, by a flow of boiler feed water is vaporized and superheated, obtaining a first flow of superheated steam w52. For the purposes of the present invention, the necessary heat is provided by a plurality of heat exchanges in the Heat Exchange Unit EXU.

[0224] In particular, said heat exchanges can be carried out with one or more of the following flows:

[0225] - the third methanation product 63,

[0226] - the fourth methanation product 65,

[0227] - the fifth methanation product 67.

[0228] Said first flow of superheated steam w52 is further superheated in the second heat exchanger EX2, obtaining a further superheated steam flow w53.

[0229] For the purposes of the present invention, a heat exchange is carried out in the second heat exchanger EX2 with the flow of the second methanation product 61.

[0230] Said further superheated steam flow w53 is further superheated in a third heat exchanger EX3, obtaining a steam flow to be hydrolyzed w54.

[0231] For the purposes of the present invention, said flow of steam to be hydrolyzed has a temperature of approximately 700°C.

[0232] Said flow of steam to be hydrolyzed w54 is sent to an electrolyzer E1 for an electrolysis phase.

[0233] For the purposes of the present invention, the electrolyzer El is represented, for example, by a Solid Oxides Electrolytic Cell (SOEC) type electrolyzer.

[0234] A first flow of hydrogen gas hl and a first flow of oxygen gas ol are obtained from the electrolysis phase. For the purposes of the present invention, said hydrogen gas flow hl comprises a water content of approximately 50% (v / v).

[0235] For the purposes of the present invention, said gaseous oxygen flow ol comprises oxygen in a concentration of approximately 99% (v / v).

[0236] For the purposes of the present invention, said hydrogen gas flow hl is cooled to obtain a first cooled hydrogen gas flow h2.

[0237] In particular, the hydrogen gas flow hl is cooled from about 800°C to about 440°C.

[0238] In particular, said cooling is obtained in the third heat exchanger EX3 by heat exchange with the further superheated steam flow w53.

[0239] The cooled hydrogen gas flow h2 is further cooled in a fourth heat exchanger EX4, obtaining a further cooled hydrogen gas stream h3.

[0240] In particular, the further cooled hydrogen gas flow h3 has a temperature of about 300°C.

[0241] Said further cooled hydrogen gas stream h3 is subjected to one or more compression and cooling steps, obtaining a compressed and further dehydrated hydrogen flow h8.

[0242] In particular, said flow of further cooled hydrogen gas h3 is cooled in a third heat exchanger TE3 obtaining a flow of hydrogen at a first cooling level h4 from which a second portion of dehydration water ww2 is separated in a second separator S2, obtaining a flow of hydrogen gas at a first dehydration level h5. For the purposes of the present invention, said third heat exchanger TE3 operates by means of a refrigerant fluid represented by air or water.

[0243] Subsequently, said hydrogen gas flow at a first level of dehydration h5 is compressed in a first compressor KI obtaining a hydrogen gas flow at a first level of dehydration and at a first level of compression h6.

[0244] Said hydrogen gas flow at a first level of dehydration and at a first level of compression h6 is further cooled in a fourth heat exchanger TE4 obtaining a hydrogen gas flow at a first level of dehydration and at a first level of cooled compression h7, from which, in a third separator S3, a third portion of dehydration water ww3 is separated, obtaining the compressed and further dehydrated hydrogen flow h8.

[0245] For the purposes of the present invention, the cooling, separation and compression steps can be repeated n times according to operational needs.

[0246] Said compressed and further dehydrated hydrogen flow h8 is compressed in a second compressor K2 obtaining a further dehydrated and further compressed hydrogen flow h9.

[0247] Said further dehydrated and further compressed hydrogen flow h9 is heated in the fourth heat exchanger EX4 by heat exchange with said cooled hydrogen gas flow h2, obtaining a hydrogen flow from methanation h10.

[0248] For the purposes of the present invention, said hydrogen flow from methanation hlO preferably has a temperature of approximately 250°C. The gaseous oxygen flow ol is liquefied in an oxygen liquefier, obtaining a first liquefied oxygen flow o2.

[0249] For the purposes of the present invention, the liquefaction of oxygen can be carried out in an integrated structure ( ILF, Integrated Liquefaction Facilities).

[0250] For the purposes of the present invention, this integrated structure can be represented by a nitrogen liquefier, which can comprise one or more heat exchangers in series.

[0251] For the purposes of the present invention, a flow of air al can be liquefied, obtaining a flow of liquefied air a2.

[0252] For the purposes of the present invention, the liquefaction of air is carried out in an integrated structure ( ILF, Integrated Liquefaction Facilities).

[0253] For the purposes of the present invention, such an integrated structure may be represented by a nitrogen liquefier, which may comprise one or more heat exchangers in series.

[0254] An alternative embodiment of the invention is, for example, represented in Figure 7, which shows a variant of the method of Figure 6.

[0255] In particular, a portion 72 of the synthetic gas flow to be sent to the network (obtained according to the method described above) is subjected to a liquefaction phase.

[0256] In particular, said portion 72 of the synthetic gas flow to be sent to the network is cooled, obtaining a portion of the cooled synthetic gas flow 73, which is subsequently rolled by a first valve VI and sent to a fourth separator S4. From the bottom of said fourth separator S4, a flow of dehydrogenated synthetic gas 74 is obtained, which is laminated through a second lamination valve V2, obtaining a flow of liquefied synthetic gas 75, which is accumulated in a tank of liquefied synthetic gas TLSG.

[0257] For the purposes of the present invention, a first recovery hydrogen flow 76 is collected from the head of said liquefied synthetic gas tank TLSG and is compressed in a third compressor K3, obtaining a first compressed recovery hydrogen flow 77, which is sent to the methanation.

[0258] According to an embodiment of the invention, said first compressed recovery hydrogen flow 77 is sent to one of the methanators, for example, to the fifth methanator M5 or, in any case, it can be sent to the last methanator.

[0259] According to an embodiment of the invention, a purification hydrogen flow 78 is obtained from the head of the fourth separator S4, which is compressed in a fourth compressor K4, obtaining a compressed recovery hydrogen flow 79, which is sent to the methanation.

[0260] According to an embodiment of the invention, said compressed recovery hydrogen flow 79 is sent to one of the methanators, for example, to the fifth methanator M5 or, in any case, it can be sent to the last methanator.

[0261] Furthermore, according to an aspect of the present invention, said compressed recovery hydrogen flow 79 can be sent to the methanation after mixing with the first compressed recovery hydrogen flow 77. For the purposes of the present invention, the cooling of the flow of the portion 72 of the synthetic gas flow to be sent to the network is carried out in an integrated structure ( ILF, Integrated Liquefaction Facilities).

[0262] For the purposes of the present invention, such an integrated structure may be represented by a nitrogen liquefier, which may comprise one or more heat exchangers in series.

[0263] A particular embodiment of the method of the present invention for the production of synthetic gas is shown schematically in Figure 8.

[0264] In particular, said method is carried out in conditions of scarcity of electrical energy, that is, in the presence of a reduced availability of electrical energy, as it is lower than the needs of the other utilities.

[0265] As described above, these conditions can be referred to as the Turndown conditions of a methanation plant.

[0266] According to a preferred embodiment of the invention, this electrical energy is scarcely available, as it is produced from renewable (discontinuous) energy sources such as solar, wind, or nuclear energy.

[0267] According to a preferred aspect, said method is carried out using electrical energy accumulated in accordance with the method for producing a synthetic gas.

[0268] These conditions can be referred to as Full Run conditions of a methanation plant. For the purposes of the present invention, this method is carried out starting from a flow of natural gas obtained from natural wells of natural gas.

[0269] For the purposes of the present invention, this natural gas flow comprises CO2in an amount of about 1-70% (v / v).

[0270] For the purposes of the present invention, this natural gas flow also comprises Cl-5 light hydrocarbons.

[0271] According to an aspect of the present invention, this natural gas flow also comprises hydrogen sulphide and possibly other sulphur compounds.

[0272] The term "synthetic gas" means a synthetic gas rich in methane obtained from a methanation process.

[0273] In particular, an initial natural gas flow 51 is obtained from a natural gas well D, which can be preliminarily compressed by a natural gas compressor KGN.

[0274] In a Purification Unit P, said flow 51 can optionally be purified from sulfur compounds, obtaining the initial purified natural gas flow 52.

[0275] Said initial purified natural gas flow 52 is heated in a first heat recovery unit EX1, obtaining an initial purified and heated natural gas flow 53, which is intended for the methanation phase.

[0276] For the purposes of the present invention, said initial purified natural gas flow 52 can be heated to a temperature such as to guarantee sufficient reaction kinetics and a thermal profile that is not too high in the methanation reactor; typically about 250°C.

[0277] A final methanation product 68 is obtained from the methanation. More specifically, from the initial purified and heated natural gas flow 53, a first methanation flow 54 is sent to a first methanator Ml.

[0278] As described below, a second methanation flow 55 is also obtained from the initial purified and heated natural gas flow 53, which is sent to a second methanator M2.

[0279] As described below, a third methanation flow 56 is also obtained from the initial purified and heated natural gas flow 53, which is sent to a third methanator M3.

[0280] As described below, a fourth methanation flow 57 is also obtained from the initial purified and heated natural gas flow 53, which is sent to a fourth methanator M4.

[0281] In particular, said first methanation flow 54 is sent to the first methanator Ml, from which a first methanation product 58 is obtained.

[0282] For the purposes of the present invention, said first methanation product 58 is characterized by a temperature of about 450-600°C and preferably of about 500°C.

[0283] In particular, said first methanation product 58 is cooled in the first heat recovery unit EX1 by heat exchange with the initial purified natural gas flow 52, obtaining a first cooled methanation product 59.

[0284] Said first cooled methanation product 59 can be further cooled in a first heat exchanger TE1, obtaining a first further cooled methanation product 60, which is sent to the second methanator M2. For the purposes of the present invention, said first heat exchanger TE1 operates by means of a refrigerant fluid represented by air or water.

[0285] For the purposes of the present invention, said first further cooled methanation product is sent to the second methanator M2 together with the second methanation flow 55.

[0286] A second methanation product 61 is obtained from the second methanator M2.

[0287] For the purposes of the present invention, said second methanation product 61 is characterized by a temperature of approximately 450-600°C and preferably approximately 500°C.

[0288] In particular, said second methanation product 61 is cooled in a second heat recovery unit EX2, obtaining a second cooled methanation product 62.

[0289] Said second cooled methanation product 62 is sent to the third methanator M3.

[0290] For the purposes of the present invention, said cooled second methanation product 62 is sent to the third methanator M3 together with the third methanation flow 56.

[0291] A third methanation product 63 is obtained from the third methanator M3, which is cooled in a Heat Exchange Unit EXU, obtaining a third cooled methanation product 64.

[0292] For the purposes of the present invention, said cooled third methanation product 64 has a temperature of about 250°C.

[0293] Said cooled third methanation product 64 is sent to the fourth methanator M4. For the purposes of the present invention, said cooled third methanation product 64 is sent to the fourth methanator M4 together with the fourth methanation flow 57.

[0294] A fourth methanation product 65 is obtained from the fourth methanator M4.

[0295] For the purposes of the present invention, said fourth methanation product 65 is characterized by a temperature of approximately 450-600°C and preferably approximately 500°C.

[0296] In particular, said fourth methanation product 65 is cooled in the Heat Exchange Unit EXU, obtaining a fourth cooled methanation product 66.

[0297] Said fourth cooled methanation product 66 is conveyed to the fifth methanator M5.

[0298] A fifth methanation product 67 is obtained from the fifth methanator M5, which is cooled in the Heat Exchange Unit EXU, obtaining a fifth cooled methanation product which represents the final methanation product 68.

[0299] For the purposes of the present invention, said fifth cooled methanation product 68 has a temperature of approximately 100°C.

[0300] Preferably, before being sent to the natural gas network, said final methanation product 68 is dehydrated.

[0301] For this purpose, said final methanation product 68 is cooled in a second heat exchanger TE2, obtaining a cooled final methanation product 69.

[0302] For the purposes of the present invention, said second heat exchanger TE2 operates by means of a refrigerant fluid represented by air or water. For the purposes of the present invention, said cooled final methanation product 69 has a temperature close to room temperature.

[0303] Said cooled final methanation product 69 is treated in a first separator S1, from which a first portion of dehydration water ww1 and a dehydrated methanation product 70 are obtained.

[0304] In a dehydration unit DI, said dehydrated methanation product 70 is further dehydrated, obtaining a synthetic gas flow to be sent to the network 71.

[0305] In particular, said final flow of synthetic gas to be sent to the network 71 is represented by a flow of methane and hydrogen.

[0306] In particular, hydrogen represents about 10% (v / v).

[0307] The configuration described in this embodiment includes five methanators, but a greater or lesser number of methanators may be provided.

[0308] For the purposes of the present invention, a flow of hydrogen gas is also sent to the methanation phase described above.

[0309] For the purposes of the present invention, said hydrogen gas flow is obtained by electrolysis.

[0310] According to a preferred aspect of the invention, this electrolysis is carried out using energy e5 obtained from an oxycombustion phase.

[0311] With regard to the production of hydrogen gas, a first flow of water w51 represented by a flow of boiler feed water is vaporized and superheated, obtaining a first flow of superheated steam w52.

[0312] For the purposes of the present invention, the necessary heat is provided by a plurality of heat exchanges in the Heat Exchange Unit EXU. In particular, said heat exchanges can be carried out with one or more of the following flows:

[0313] - the third methanation product 63,

[0314] -the fourth methanation product 65,

[0315] - the fifth methanation product 67.

[0316] Said first flow of superheated steam w52 is further superheated in the second heat exchanger EX2, obtaining a further superheated steam flow w53.

[0317] For the purposes of the present invention, a heat exchange is carried out in the second heat exchanger EX2 with the flow of the second methanation product 61.

[0318] Said further superheated steam flow w53 is further superheated in a third heat recovery unit EX3, obtaining a steam flow to be hydrolyzed w54.

[0319] For the purposes of the present invention, said flow of steam to be hydrolyzed has a temperature of approximately 700°C.

[0320] Said flow of steam to be hydrolyzed w54 is sent to an electrolyzer E1 for an electrolysis phase.

[0321] For the purposes of the present invention, the electrolyzer El is represented, for example, by a Solid Oxides Electrolytic Cell (SOEC) type electrolyzer.

[0322] A first flow of hydrogen gas hl and a first flow of oxygen gas ol are obtained from the electrolysis phase.

[0323] For the purposes of the present invention, said hydrogen gas flow hl comprises a water content of approximately 50% (v / v). For the purposes of the present invention, said gaseous oxygen flow ol comprises oxygen in a concentration of approximately 99% (v / v).

[0324] For the purposes of the present invention, said hydrogen gas flow hl is cooled to obtain a first cooled hydrogen gas flow h2.

[0325] In particular, the hydrogen gas flow hl is cooled from about 800°C to about 440°C.

[0326] In particular, said cooling is obtained in the third heat exchanger EX3 by heat exchange with the further superheated steam flow w53.

[0327] The heated hydrogen gas flow h2 is further cooled in a fourth heat exchanger EX4, obtaining a further cooled hydrogen gas flow h3.

[0328] In particular, the further cooled hydrogen gas flow h3 has a temperature of about 300°C.

[0329] Said further cooled hydrogen gas flow h3 is subjected to one or more compression and cooling steps obtaining a further dehydrated hydrogen flow h8.

[0330] In particular, said further cooled hydrogen gas flow h3 is cooled in a third heat exchanger TE3, obtaining a hydrogen stream at a first cooling level h4, from which a second portion of dehydration water ww2 is separated in a second separator S2, obtaining a hydrogen gas flow at a first dehydration level h5.

[0331] For the purposes of the present invention, said third heat exchanger TE3 operates by means of a refrigerant fluid represented by air or water.

[0332] Subsequently, said hydrogen gas flow at a first level of dehydration h5 is compressed in a first compressor K1, obtaining a hydrogen gas flow at a first level of dehydration and at a first level of compression h6.

[0333] Said hydrogen gas flow at a first level of dehydration and at a first level of compression h6 is further cooled in a fourth heat exchanger TE4, obtaining a hydrogen gas flow at a first level of dehydration and at a first level of cooled compression h7, from which, in a third separator S3, a third portion of dehydration water ww3 is separated, obtaining a fully dehydrated hydrogen flow h8.

[0334] For the purposes of the present invention, the cooling, separation and compression steps can be repeated n times according to operational needs.

[0335] Said flow of totally dehydrated hydrogen h8 is compressed in a second compressor K2, obtaining a flow of further dehydrated and compressed hydrogen h9.

[0336] Said further dehydrated and compressed hydrogen flow h9 is heated in the fourth heat exchanger EX4 by heat exchange with said cooled hydrogen gas flow h2, obtaining a hydrogen flow from methanation h10.

[0337] For the purposes of the present invention, said hydrogen flow from methanation preferably has a temperature of approximately 250°C.

[0338] The gaseous oxygen flow ol is sent to an Oxycombustion Power Plant (OPP) for the oxycombustion step.

[0339] For the purposes of the present invention, a flow of liquefied oxygen o3 is pumped by a liquefied oxygen pump PO2l, obtaining a flow of pumped liquefied oxygen o4. Said pumped liquefied oxygen flow o4 is sent to the Oxycombustion Unit (OPP) for the oxycombustion phase.

[0340] In particular, said liquefied oxygen flow o3 is obtained from a liquefied oxygen storage tank TO2l.

[0341] According to a preferred embodiment of the present invention, the liquefied oxygen flow o3 intended for the oxy-combustion step and obtained from a liquefied oxygen storage tank TO2l is obtained according to the method described above of the present invention, carried out under conditions of abundance of electrical energy (Full Run).

[0342] For the purposes of the present invention, the oxycombustion step can be carried out in the presence of a portion of the initial natural gas flow 51 ', possibly compressed by a natural gas compressor KNG, or a portion of the initial purified natural gas flow 52 ', as described above in relation to the method of the present invention carried out under conditions of abundance of electrical energy (Full Run).

[0343] A first flow of carbon dioxide 28 (part in liquid form and part in gaseous form) and a second flow of carbon dioxide 29 are also obtained from the oxy-combustion step.

[0344] For the purposes of the present invention, said first flow of carbon dioxide 28 is obtained by cooling and liquefaction by heat exchange with the flow of liquefied synthetic gas Isgl, or possibly the flow of pumped liquefied synthetic gas lsg2, and / or with the flow of liquefied oxygen o3, or possibly the flow of pumped liquefied oxygen o4, and accumulated in a tank of liquefied CO2TCO2l. For the purposes of the present invention, said second flow of carbon dioxide 29 can be stored in a natural well.

[0345] According to a preferred embodiment of the present invention, the liquefied synthetic gas flow Isgl used in the oxy-combustion step and obtained from a liquefied synthetic gas storage tank TLSG is obtained according to the method described above of the present invention carried out under conditions of abundance of electrical energy (Full Run) and may possibly be a pumped synthetic gas flow lsg2 from a liquefied synthetic gas pump PLSG.

[0346] A fourth portion of dehydration water ww4 is also obtained from the oxy-combustion step.

[0347] An alternative embodiment of the invention is, for example, represented in Figure 9, which shows a variant of the method of Figure 8.

[0348] In particular, an initial natural gas flow 51 is obtained from a natural gas well D, which can be preliminarily compressed by a natural gas compressor KGN.

[0349] In a Purification Unit P, said flow 51 can optionally be purified of sulfur compounds, obtaining the initial purified natural gas flow 52.

[0350] Said initial purified natural gas flow 52 is heated in a first heat recovery unit EX1, obtaining an initial purified and heated natural gas flow 53, which is intended for the methanation step.

[0351] For the purposes of the present invention, said initial purified natural gas flow 52 can be heated to a temperature such as to guarantee sufficient reaction kinetics and a thermal profile of the methanation reactor that is not too high; typically about 250°C. A final methanation product 68 is obtained from the methanation. More specifically, a first methanation flow 54 is sent from the initial purified and heated natural gas flow 53 to a first methanator Ml.

[0352] As described below, a second methanation flow 55 is also obtained from the initial purified and heated natural gas flow 53, which is sent to a second methanator M2.

[0353] As described below, a third methanation flow 56 is also obtained from the initial purified and heated natural gas flow 53, which is sent to a third methanator M3.

[0354] As described below, a fourth methanation flow 57 is also obtained from the initial purified and heated natural gas flow 53, which is sent to a fourth methanator M4.

[0355] In particular, said first methanation flow 54 is sent to the first methanator Ml from which a first methanation product 58 is obtained.

[0356] For the purposes of the present invention, said first methanation product 58 is characterized by a temperature of about 450-600°C and preferably of about 500°C.

[0357] In particular, said first methanation product 58 is cooled in the first heat recovery unit EX1 by heat exchange with the initial purified natural gas flow 52, obtaining a first cooled methanation product 59.

[0358] Said first cooled methanation product 59 can be further cooled in a first heat exchanger TE1, obtaining a first further cooled methanation product 60, which is sent to the second methanator M2. For the purposes of the present invention, said first heat exchanger TE1 operates by means of a refrigerant fluid represented by air or water.

[0359] For the purposes of the present invention, said first further cooled methanation product is sent to the second methanator M2 together with the second methanation flow 55.

[0360] A second methanation product 61 is obtained from the second methanator M2.

[0361] For the purposes of the present invention, said second methanation product 61 is characterized by a temperature of approximately 450-600°C and preferably approximately 500°C.

[0362] In particular, said second methanation product 61 is cooled in a second heat recovery unit EX2, obtaining a second cooled methanation product 62.

[0363] Said second cooled methanation product 62 is sent to the third methanator M3.

[0364] For the purposes of the present invention, said cooled second methanation product 62 is sent to the third methanator M3 together with the third methanation flow 56.

[0365] A third methanation product 63 is obtained from the third methanator M3, which is cooled in a Heat Exchange Unit EXU, obtaining a third cooled methanation product 64.

[0366] For the purposes of the present invention, said cooled third methanation product 64 has a temperature of about 250°C.

[0367] Said cooled third methanation product 64 is sent to the fourth methanator M4. For the purposes of the present invention, said cooled third methanation product 64 is sent to the fourth methanator M4 together with the fourth methanation flow 57.

[0368] A fourth methanation product 65 is obtained from the fourth methanator M4.

[0369] For the purposes of the present invention, said fourth methanation product 65 is characterized by a temperature of approximately 450-600°C and preferably approximately 500°C.

[0370] In particular, said fourth methanation product 65 is cooled in the Heat Exchange Unit EXU, obtaining a fourth cooled methanation product 66.

[0371] Said fourth cooled methanation product 66 is conveyed to the fifth methanator M5.

[0372] A fifth methanation product 67 is obtained from the fifth methanator M5, which is cooled in the Heat Exchange Unit EXU, obtaining a fifth cooled methanation product which represents the final methanation product 68.

[0373] For the purposes of the present invention, said fifth cooled methanation product 68 has a temperature of approximately 100°C.

[0374] Preferably, before being sent to the gas network, said final methanation product 68 is dehydrated.

[0375] For this purpose, said final methanation product 68 is cooled in a second heat exchanger TE2, obtaining a cooled final methanation product 69.

[0376] For the purposes of the present invention, said second heat exchanger TE2 operates by means of a refrigerant fluid represented by air or water. For the purposes of the present invention, said cooled final methanation product 69 has a temperature close to room temperature.

[0377] Said cooled final methanation product 69 is treated in a first separator S1, from which a first portion of dehydration water ww1 and a dehydrated methanation product 70 are obtained.

[0378] In a dehydration unit DI, said dehydrated methanation product 70 is further dehydrated, obtaining a synthetic gas flow to be sent to the network 71.

[0379] In particular, said synthetic gas flow to be sent to the network 71 is represented by a flow of methane and hydrogen.

[0380] In particular, hydrogen represents about 10% (v / v).

[0381] The configuration described in this embodiment includes five methanators, but a higher or lower number of methanators may be provided.

[0382] For the purposes of the present invention, a flow of hydrogen gas is also sent to the methanation phase described above.

[0383] For the purposes of the present invention, said hydrogen gas flow is obtained by electrolysis.

[0384] According to a preferred aspect of the invention, this electrolysis is carried out using a fifth energy source e5 obtained from an oxy-combustion phase.

[0385] With regard to the production of hydrogen gas, a first flow of water w51, preferably represented by a flow of boiler feed water, is superheated, obtaining a first flow of superheated steam w52.

[0386] For the purposes of the present invention, the necessary heat is provided by a plurality of heat exchanges in the Heat Exchange Unit EXU. In particular, said heat exchanges can be with one or more of the following flows:

[0387] - the third methanation product 63,

[0388] -the fourth methanation product 65,

[0389] - the fifth methanation product 67.

[0390] Said first flow of superheated steam w52 is further superheated in the second heat exchanger EX2, obtaining a further superheated steam flow w53.

[0391] For the purposes of the present invention, a heat exchange is carried out in the second heat exchanger EX2 with the flow of the second methanation product 61.

[0392] Said further superheated steam flow w53 is further superheated in a third heat recovery unit EX3, obtaining a steam flow to be hydrolyzed w54.

[0393] For the purposes of the present invention, said steam flow to be hydrolyzed has a temperature of approximately 700°C.

[0394] Said flow of steam to be hydrolyzed w54 is sent to an electrolyzer E1 for an electrolysis phase.

[0395] For the purposes of the present invention, the electrolyzer E1 is represented, for example, by a Solid Oxides Electrolytic Cell (SOEC) type electrolyzer E1.

[0396] A first flow of hydrogen gas hl and a first flow of oxygen gas ol are obtained from the electrolysis step.

[0397] For the purposes of the present invention, said hydrogen gas flow hl comprises a water content of approximately 50% (v / v).

[0398] For the purposes of the present invention, said gaseous oxygen flow ol comprises oxygen in a concentration of about 99% (v / v). For the purposes of the present invention, said hydrogen gas flow hl is cooled to obtain a first cooled hydrogen gas flow h2.

[0399] In particular, the hydrogen gas flow hl is cooled from about 800°C to about 440°C.

[0400] In particular, said cooling is obtained in the third heat exchanger EX3 by heat exchange with the further superheated steam flow w53 mentioned above.

[0401] The heated hydrogen gas stream h2 is further cooled in a fourth heat exchanger EX4, obtaining a further cooled hydrogen gas flow h3.

[0402] In particular, the further cooled hydrogen gas flow h3 has a temperature of about 300°C.

[0403] Said further cooled hydrogen gas flow h3 is subjected to one or more compression and cooling steps, obtaining a further dehydrated hydrogen flow h8.

[0404] In particular, said further cooled hydrogen gas flow h3 is cooled in a third heat exchanger TE3 obtaining a hydrogen flow at a first cooling level h4, from which, in a second separator S2, a second portion of dehydration water ww2 is separated, obtaining a hydrogen gas flow at a first dehydration level h5.

[0405] For the purposes of the present invention, said third heat exchanger TE3 operates by means of a refrigerant fluid represented by air or water.

[0406] Subsequently, said hydrogen gas flow at a first level of dehydration h5 is compressed in a first compressor KI obtaining a hydrogen gas flow at a first level of dehydration and at a first level of compression h6. Said hydrogen gas flow at a first level of dehydration and at a first level of compression h6 is further cooled in a fourth heat exchanger TE4 obtaining a hydrogen gas flow at a first level of dehydration and at a first level of cooled compression h7, from which, in a third separator S3, a third portion of dehydration water ww3 is separated, obtaining a fully dehydrated hydrogen flow h8.

[0407] For the purposes of the present invention, the cooling, separation and compression steps can be repeated n times according to operational needs.

[0408] Said further dehydrated hydrogen flow h8 is compressed in a second compressor K2, obtaining a totally dehydrated and compressed hydrogen flow h9.

[0409] Said further dehydrated and compressed hydrogen flow h9 is heated in the fourth heat exchanger EX4 by heat exchange with said cooled hydrogen gas flow h2, obtaining a hydrogen flow from methanation h10.

[0410] For the purposes of the present invention, said hydrogen flow from methanation preferably has a temperature of approximately 250°C.

[0411] The gaseous oxygen flow ol is sent to an Oxy-combustion Unit (OPP) for the oxy-combustion phase.

[0412] For the purposes of the present invention, a flow of liquefied oxygen o3 is pumped by a liquefied oxygen pump PO2I, obtaining a flow of pumped liquefied oxygen o4.

[0413] Said pumped liquefied oxygen flow o4 is sent to the Oxycombustion Unit (OPP) for the oxy-combustion phase. In particular, said liquefied oxygen flow o3 is obtained from a liquefied oxygen storage tank TO2l.

[0414] According to a preferred aspect of the present invention, the liquefied oxygen flow o3 intended for the oxy-combustion step and obtained from a liquefied oxygen storage tank TO2l is obtained according to the method described above of the present invention, carried out under conditions of abundance of electrical energy (Full Run).

[0415] For the purposes of the present invention, the oxy-combustion step can be carried out in the presence of a portion 51 ' of the initial natural gas flow, possibly compressed by a natural gas compressor KNG, or a portion of the initial purified natural gas flow 52 ', as described above in relation to the method of the present invention carried out under conditions of an abundance of electrical energy (Full Run).

[0416] For the purposes of the present invention, the oxy-combustion can also be carried out in the presence of a flow of liquefied synthetic gas Isgl, possibly pumped lsg2 obtained by pumping through a liquefied synthetic gas pump PLSG a flow of liquefied synthetic gas Isgl obtained from a liquefied synthetic gas storage tank TLSG.

[0417] According to a preferred aspect of the present invention, the pumped liquefied synthetic gas flow lsg2 used in the oxy-combustion step and obtained from a liquefied synthetic gas storage tank TLSGis obtained according to the above-described method of the present invention carried out under conditions of abundance of electrical energy (Full Run). For the purposes of the present invention, the oxy-combustion can also be carried out in the presence of a pumped liquefied air flow a4 obtained by pumping a liquefied air flow a3 obtained from a liquefied air storage tank TAI through a liquefied air pump Pl.

[0418] According to a preferred aspect of the present invention, the pumped liquefied air flow a4 used in the oxy-combustion step and obtained from the liquefied air storage tank TAI is obtained according to the above-described method of the present invention carried out under conditions of abundant electrical energy (Full Run).

[0419] A first flow of carbon dioxide 28 and a second flow of carbon dioxide 29 are also obtained from the oxy-combustion step.

[0420] For the purposes of the present invention, said first flow of carbon dioxide 28 is obtained by cooling and liquefaction by heat exchange with the flow of liquefied synthetic gas Isgl, or possibly the flow of pumped liquefied synthetic gas lsg2, with the flow of liquefied o3, or possibly the flow of pumped liquefied oxygen o4, and / or with the flow of liquefied air a3, or possibly the flow of pumped liquefied air a4, and accumulated in a tank of liquefied CO2TCO2l.

[0421] For the purposes of the present invention, said second flow of carbon dioxide 29 can be accumulated in a natural well.

[0422] As described above, the method of the invention for producing a synthetic gas under conditions of abundant electrical energy is integrated with the method of the invention for producing a synthetic gas carried out under conditions of scarce electrical energy.

[0423] In particular, one or more of the following integrations can be identified: - the liquefied oxygen flow for the oxy-combustion step is obtained by liquefying the oxygen flow produced by the electrolysis step;

[0424] - the liquefied synthetic gas flow for the oxy-combustion step is obtained by liquefying the synthetic gas obtained from the methanation;

[0425] the liquefied air flow for the oxy-combustion phase is obtained in the Full Run phase from the liquefaction of an air flow;

[0426] - the carbon dioxide flow obtained from the oxy-combustion phase is intended for the methanation phase;

[0427] - the energy developed by the oxy-combustion step is used to conduct the electrolysis step.

[0428] Furthermore, note that:

[0429] - part of the heat developed in the methanation stage is used for the production of steam for the electrolysis stage.

[0430] In accordance with a third obj ect, a plant for conducting the methods of the invention is described.

[0431] In particular, said plant comprises:

[0432] a methanation unit M for a flow of natural gas rich in carbon dioxide obtained from a well and for the production of heat, an electrolysis unit El,

[0433] an ILF liquefaction unit for the liquefaction of one or more fluids selected from: oxygen, air, synthetic gas,

[0434] an oxy-combustion unit (OPP) for the production of carbon dioxide and energy,

[0435] if necessary, a purification unit for natural gas rich in carbon dioxide, tanks for the storage of one or more liquefied fluids selected from: liquefied oxygen, liquefied air, liquefied synthetic gas, liquefied carbon dioxide.

[0436] From the above, the advantages of the present invention will be apparent to the person skilled in the art.

[0437] In particular, the invention provides a system that makes it possible to exploit natural gas deposits, in which a significant fraction is represented by carbon dioxide, transforming this load into synthetic gas formed mainly of methane and hydrogen having characteristics suitable for transport and marketing.

[0438] Furthermore, the system can operate as a whole without requiring interruptions, with limited load variations within the typical working range of the component technologies (typically 110% - 30%).

[0439] Another advantage is that a system is provided that eliminates the carbon dioxide present in the natural gas well load through the use of an excess availability of energy, possibly and preferably obtained from renewable sources.

[0440] Furthermore, the process of the invention allows for the preparation and possible use of electrolytically produced oxygen, which could also be commercially exploited.

[0441] The present invention also satisfies the prospect of replacing part of the natural gas normally transported in the pipelines with hydrogen generated by electrolysis and, therefore, in principle, generated by means of renewable sources.

[0442] The electrolytic hydrogen, produced by oxidation-reduction in an electrolytic cell, can then be compressed, dehydrated and mixed with natural gas.

Claims

CLAIMS1. A method for producing a synthetic gas ( 2. 71 ) comprising the steps of:I ) obtaining a synthetic gas flow ( 2. 71 ) and heat from an initial natural gas flow ( 1. 51 ) subjected to methanation,I I ) obtaining a flow of hydrogen gas ( 4, hl ) and a flow of oxygen gas ( 5, ol ) by electrolysis,wherein said electrolysis step I I ) is carried out on a vapor flow to be subjected to electrolysis ( 3, w54 ) obtained from a first water flow (wl, w51 ) vapori zed by the heat produced in the methanation phase I ),characteri zed by the fact that said initial natural gas flow ( 1, 51 ) has a carbon dioxide content of about 1 -70% (v / v).

2. The method for producing a synthetic gas ( 2, 71 ) according to the preceding claim, wherein a further flow of liquefied carbon dioxide ( 11 ) is subjected to the methanation step I ).

3. The method for producing a synthetic gas ( 2, 71 ) according to any one of the preceding claims, wherein said electrolysis step I I ) is carried out using a first available energy source ( el ).

4. The method for producing a synthetic gas ( 2, 71 ) according to any one of the preceding claims, wherein said electrolysis step I I ) is carried out using a first available renewable energy source ( el ).

5. The method for producing a synthetic gas ( 2, 71 ) according to any one of the preceding claims, comprising the further step I I I )of liquefying said gaseous oxygen flow ( 5, ol ) obtaining a liquefied oxygen flow ( 6, o2 ).

6. The method for producing a synthetic gas ( 2, 71 ) according to any one of the preceding claims, comprising the further step of:IV) obtaining a portion ( 7, 72 ) of said synthetic gas flow, and V) subj ecting said portion ( 7, 72 ) of synthetic gas to liquefaction, obtaining a flow of liquefied synthetic gas ( 8, 75 ).

7. The method for producing a synthetic gas ( 2, 71 ) with the simultaneous production and storage of electrical energy according to any one of the preceding claims, comprising the further step of subj ecting a flow of air ( 12, al ) to liquefaction, obtaining a flow of liquefied air ( 13, a2 ).

8. The method for producing a synthetic gas ( 2, 71 ) according to any one of the preceding claims, wherein the liquefaction of the gaseous oxygen ( 5, ol ), the liquefaction of the air flow ( 12, al ) and the liquefaction of the portion ( 7, 72 ) of the synthetic gas are carried out in the same liquefaction unit.

9. The method for producing a synthetic gas ( 2, 71 ) according to any one of the preceding claims, wherein a first recovery hydrogen flow ( 9, 78 ) and possibly also a second recovery hydrogen flow ( 10, 76 ) are also obtained from step V), which can be subjected, independently of each other, to the methanation step I ).

10. A method for producing synthetic gas ( 22, 71 ) comprising the steps of:VI ) carrying out an oxy-combustion step obtaining a fi fth energy source ( e5 ), a first flow of carbon dioxide from oxy-combustion ( 28 ) and a second flow of carbon dioxide from oxy-combustion ( 29 ),VI I ) obtaining a synthetic gas flow ( 2, 71 ) and heat from an initial natural gas flow ( 1, 51 ) subjected to methanation,VI I I ) obtaining a flow of hydrogen gas ( 4, hl ) and a flow o f oxygen gas ( 5, ol ) by electrolysis,wherein said electrolysis step VI I I ) is carried out on a steam flow ( 3, w52 ) obtained from a first water flow (wl, w51 ) vapori zed by the heat produced by the methanation step VI I ), by means of said fi fth energy source ( e5 ) obtained in step VI ) and whereinsaid oxy-combustion step VI ) is carried out using liquefied synthetic gas ( 8, 27, lsgl ) obtained from the liquefaction of the portion ( 2, 72 ) of the synthetic gas produced in the methanation step.

11. The method for producing synthetic gas ( 22, 71 ) according to the preceding claim, wherein said oxy-combustion step VI ) can be carried out by also using a portion ( 21 ' ' ', 51 ' ) of the initial natural gas flow.

12. The method for producing synthetic gas ( 22, 71 ) according to claim 10 or 11, wherein the liquefied flow ( 26, o2 ) obtained according to the method of claim 5 or 8 is sent to said oxy-combustion step VI ).

13. The method for producing synthetic gas according to any one of claims 10 to 12, wherein the flow of lique fied air ( 13, a2 ) obtained according to the method of claim 7 or 8 is sent to said oxy-combustion step VI ).

14. A plant for conducting a method according to any one of the preceding claims, comprising:a methanation unit (M) for a flow of natural gas ( 11, 21, 51 ) rich in carbon dioxide obtained from a well ( D) and for the production of heat,an electrolysis unit (El ),a liquefaction unit ( ILF) for the liquefaction of one or more fluids chosen from: oxygen, air, synthetic gas,an oxy-combustion unit ( OPP ) for the production of carbon dioxide and energy,optionally, a puri fication unit ( P ) for the natural gas ( 11, 21, 51 ) rich in carbon dioxide,tanks for the storage of one or more liquefied fluids chosen from: liquefied oxygen, liquefied air, liquefied synthetic gas, liquefied carbon dioxide ( TO2l, TAl, TLSG, TCO2l).

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