EP3980703A1

EP3980703A1 - A natural gas liquefaction system using renewable energy to produce hydrogen

Info

Publication number: EP3980703A1
Application number: EP20732487.2A
Authority: EP
Inventors: Paolo NOCCIONI; Oriano ZUCCHI; Andrea ALFANI
Original assignee: Nuovo Pignone Technologie SRL
Current assignee: Nuovo Pignone Technologie SRL
Priority date: 2019-06-07
Filing date: 2020-06-03
Publication date: 2022-04-13
Also published as: EP3980704A1; IT201900008367A1; WO2020244808A1; WO2020244809A1

Abstract

An integrated natural gas liquefaction system is disclosed. The system comprises a refrigerant circuit adapted to circulate at least one refrigerant therein, wherein the refrigerant circuit includes at least one refrigerant compressor. An energy collector collects energy from at least one renewable energy resource and uses the collected energy to produce hydrogen. A mechanical power generator, drivingly coupled to the refrigerant compressor, uses hydrogen as a fuel to generate mechanical power.

Description

A NATURAL GAS LIQUEFACTION SYSTEM USING RENEWABLE ENERGY

TO PRODUCE HYDROGEN

DESCRIPTION

TECHNICAL FIELD [0001] The present disclosure relates to natural gas liquefaction technology. More specifically, disclosed herein are novel systems and methods for efficiently liquefying a hydrocarbon feed stream, such as a natural gas feed stream.

BACKGROUND ART

[0002] Natural gas is a mixture of hydrocarbons in a gaseous state. Natural gas com- prises predominantly methane and can contain a portion of other, heavier gaseous com ponents. It is useful to liquefy natural gas for a number of reasons and mainly for storage and transportation purposes. Liquefied natural gas (also referred to with the acronym LNG) occupies a much smaller volume and can thus be transported for in stance with LNG vessels. Liquefied natural gas is not only easier to transport because of the smaller volume occupied, but also safer.

[0003] Several natural gas liquefaction methods have been developed over the last decades. Basically, after a purification pre-treatment, the natural gas is processed through a plurality of cooling stages using heat exchangers to progressively reduce the temperature of the gas until liquefaction. Irrespective of the kind of liquefaction tech- nology used, the refrigeration and liquefaction process is relatively energy consuming. Compressors or compressor trains are required to process cryogenic fluids, i.e. refrig erant fluids, which are used to remove heat from the natural gas stream until liquefac tion.

[0004] Refrigerant compressors are usually driven by gas turbine engines, steam tur- bines or electric motors and they require large quantities of power. A part of the same natural gas which is to be cooled and liquefied is generally used as the main source of energy to run the refrigerant compressors, for instance to generate steam to run a steam turbine, or combustion gas to run a gas turbine engine, which in turn directly drive one or more refrigerant compressors or compressor trains, or else are used to drive electric generators. The electric energy thus generated is used to power electric motors, which drive the refrigerant compressors or compressor trains. Using electric generators to produce electric energy from mechanical energy and electric motors to convert electric energy into mechanical energy to drive the refrigerant compressors avoids the need to run steam or gas turbines at variable speed to adapt the rotational speed to variable flowrate requests from the refrigerant compressors. The driver of the electric generator can rotate at constant speed thus maximizing the efficiency of the driver, while a var iable speed electric motor can in turn drive the refrigerant compressor at variable speed, according to the refrigerant flowrate requirements.

[0005] Electric power for the electric motor driving an LNG compressor train is gen erated by one or more electric generators, as usually no suitable electric distribution grid is available at the site where the LNG plant is located.

[0006] Possible configurations of LNG systems and relevant compressor trains are disclosed in WO2018/206102.

[0007] A common feature of the above described LNG systems is that an important share of natural gas is used to generate the mechanical power required to drive the compressor trains and to increase the volumetric enthalpic content of the natural gas stream through liquefaction. This has a negative impact on the gas liquefaction rate, since part of the gas is used to generate mechanical power to drive the compressors. In addition, fossil fuel consumption for running the liquefaction process also has a nega tive environmental impact, as it generates carbon dioxide.

[0008] It would therefore be desirable to provide an LNG system which reduces the energy consumption and the negative environmental impact. The environmental effect can also lead to an increase in costs or due fees based on applicable regulations or standards requirements.

SUMMARY

[0009] Disclosed herein is a method for liquefying natural gas in an integrated natural gas liquefaction system. The system includes a refrigeration circuit including at least one refrigerant compressor and an energy collector adapted to collect energy from a renewable energy resource. According to embodiments disclosed herein, the method comprises generating power from energy collected by the energy collector and producing hydrogen therewith. The hydrogen is used as a source of energy for driving the refrigerant compressor. The refrigerant compressor is adapted to process a refrig erant and to remove heat from a flow of natural gas.

[0010] According to some embodiments, the step of driving the refrigerant compres- sor with energy from the hydrogen may include fueling a gas turbine engine with said hydrogen and driving the refrigerant compressor with mechanical power generated by the gas turbine engine.

[0011] The method is particularly advantageous in that, in case of hydrogen shortage, the gas turbine can be fueled with natural gas from the natural gas line. A single me- chanical power generator can thus be provided, for driving the compressor of the LNG system when energy (hydrogen) generated from the renewable energy resource is available, and when said energy is absent or insufficient.

[0012] In some embodiments, the step of driving the refrigerant compressor includes the steps of: generating electric energy through fuel cells fueled with the hydrogen; powering an electric motor with the electric energy generated by the fuel cells; and driving the refrigerant compressor with the electric motor. A eco-friendly, low-pollu tion plant is thus obtained.

[0013] According to a further aspect, an integrated natural gas liquefaction system is disclosed herein. The system includes an energy collector adapted to collect energy from a renewable energy resource. The system further includes a hydrogen production facility, adapted to produce hydrogen using energy collected by the energy collector from said renewable energy resource. A power generator is further provided, adapted to be fueled with hydrogen produced by said hydrogen production facility. The system also includes at least one refrigerant circuit adapted to circulate at least one refrigerant therein, for removing heat from the natural gas. The refrigerant circuit includes at least one refrigerant compressor (directly or indirectly) driven by power from the power generator. The refrigerant compressor is adapted to circulate a refrigerant in heat ex change relationship with a flow of natural gas to remove heat therefrom.

[0014] The system may further comprise an energy converter, adapted to convert energy collected by the energy collector into electric energy. The hydrogen production facility can be adapted to produce hydrogen using electric power generated by the energy converter.

[0015] In some embodiments, the mechanical power generator includes a thermal engine adapted to generate mechanical power and drivingly coupled to the refrigerant compressor. The thermal engine is adapted to be fueled with said hydrogen and can be further adapted to be fueled with natural gas, such that in case of hydrogen shortage, mechanical power can still be generated using natural gas from the natural gas feeding line of the LNG system.

[0016] In other embodiments the power generator includes fuel cells, electrically coupled to an electric motor. The fuel cells are powered by hydrogen and generate electric energy. This latter is converted into mechanical power by the electric motor, which in turn drives the refrigerant compressor. An auxiliary mechanical generator can further be provided, adapted to be drivingly coupled to the refrigerant compressor and adapted to be fueled with natural gas. The auxiliary mechanical generator provides supplemental mechanical power in case of hydrogen shortage.

[0017] Further additional features and embodiments of the invention are described in more detail here below, reference being made to the attached drawings, and are set forth in the enclosed claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] A more complete appreciation of the disclosed embodiments of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

Fig. l illustrates a simplified schematic representation of a plant according to the present disclosure in one embodiment;

Fig.2 illustrates a simplified schematic representation of a plant according to the present disclosure in a further embodiment;

Fig.3 illustrates a simplified schematic representation of a plant according to the present disclosure in a further embodiment;

Fig.4A, 4B, 4C and 4D summarize several embodiments of energy storage devices suitable for use in an LNG system according to the present disclosure;

Figs.5, 6, 7, 8 and 9 illustrate schematics of integrated LNG systems using concentrated solar energy in one embodiment;

Fig.10 illustrates an LNG system using renewable energy resources to pro duce hydrogen as a fuel for a gas turbine engine; and

Fig.11 illustrates a further LNG system using renewable energy resources to produce hydrogen as a fuel for fuel cells.

DETAILED DESCRIPTION

[0019] A novel and useful integrated natural gas liquefaction system has been devel oped. In order to increase the efficiency of the natural gas liquefaction system, energy from a renewable energy resource at least partly contributes to run one or more refrig- erant compressors. The use of energy from renewable energy resources reduces con sumption of natural gas, or other valuable and non-renewable energy resources to run the drivers of the refrigerant compressors.

[0020] Since renewable energy resources may not be able to provide the full amount of power needed or may deliver more than the power required to drive the refrigerant compressors, according to embodiments disclosed herein measures are adopted to ac cumulate or store surplus of energy delivered by the renewable energy resource for use when insufficient power is delivered by said renewable energy resource. In some em bodiments, surplus electric energy generated by conversion of renewable energy can be exported into an electric distribution grid. [0021] In order to ensure that the LNG system can run also in case of shortage of energy from the renewable energy resource and/or from an energy storage system, auxiliary driving systems can be provided, to run the refrigerant compressors if so required. In some embodiments, the auxiliary driving system may include a gas turbine engine arranged on the same shaftline of the refrigerant compressor train. [0022] Turning now to the drawings, Fig.1 illustrates a schematic of a first embodi ment of an integrated natural gas liquefaction system (herein shortly referred to also as LNG system), labeled 1 as a whole. As mentioned above, a variety of liquefaction technologies and cycles have been developed and can be used to liquefy natural gas. The structure and operation of the liquefaction cycles and systems are not relevant in the context of the present disclosure. What matters is that in general terms a natural gas liquefaction system comprises one or more compressors or compressor trains, which process one or more refrigerant fluids that are subjected to cyclic thermody namic transformations. Mechanical power drives one or more refrigerant compressors. The refrigerant fluid at the delivery side of the compressor(s) is cooled and expanded, to reach low temperatures. The expanded refrigerant removes heat from the flow of natural gas by heat exchange therewith. The heated refrigerant gas is compressed again by the refrigerant compressor(s).

[0023] The present disclosure concerns an efficient way of using renewable energy resources to run one or more refrigerant compressors in an integrated LNG system.

[0024] In the schematic of Fig.1, as well as in the remaining figures, the core of the thermodynamic cycle of the LNG system, which processes the one or more refrigerant fluids, includes at least one refrigerant circuit 3. The refrigerant circuit 3 includes at least one refrigerant compressor. In the schematic ofFig.1, compressor 5 is representa tive of one or more compressors or compressor trains to process one or more refriger ant fluids. The refrigerant circuit further comprises a chiller 7, an expander 9 and a heat exchanger 11. The refrigerant delivered by refrigerant compressor 5 is chilled in chiller 7, e.g. in heat exchange relationship with air, water or a further refrigerant of another refrigerant circuit. The compressed and chilled refrigerant is expanded in ex pander 9 to achieve a sufficiently low temperature, such that heat can be removed therewith from a flow of natural gas (NG) delivered by a pipeline 12 and flowing through the heat exchanger 11. At the exit side of the heat exchanger 11 liquefied natural gas (LNG) is obtained, which is collected in an LNG tank 15.

[0025] Those skilled in the art of LNG systems will understand that the refrigerant circuit 3 is just used as a schematic representation of a generic refrigeration system including one or more refrigerant circuits. The structure and operation of the refriger- ant circuit per se is not particularly relevant. In embodiments disclosed herein, an im portant aspect is that the refrigeration system includes at least one refrigerant compres sor and a mover for the refrigerant compressor, and that at least part of the power to drive the refrigerant compressor is provided by the renewable energy resource.

[0026] In actual practice the refrigerant circuit 3 that is shown only schematically in Fig.1, as well as in the remaining figures, can be configured according to any one of several known refrigeration systems and cycles, or a parts thereof, such as for instance, but without limitation:

- a single mixed refrigerant cycle, marketed under the trademark PRICO®;

- a single mixed refrigerant cycle, marketed by Linde under the trademark LIMUM®;

- a triple cycle mixed refrigerant cascade system, marketed by Linde under the trademark MFC® (Mixed Fluid Cascade);

- a Conoco Phillips CASCADE® system;

- a Shell Double Mixed Refrigerant (DMR) system;

- an APCI® propane/mixed refrigerant system;

- an AP-X® system.

[0027] Construction details and operation of the above mentioned exemplary refrig eration systems are known and will not be described herein.

[0028] The refrigerant compressor 5, which schematically represent one or more compressor trains for one or more refrigerants, is driven by at least one driver. As a matter of fact, in case of more refrigerant compressors, one or more compressors can be grouped to form one or more compressor trains, each driven by at least one respec tive driver. In the embodiment schematically represented in Fig.l, a driver 17 is driv- ingly coupled to refrigerant compressor 5. In general terms, the driver is a mechanical power generator, which generates mechanical power to rotate the refrigerant compres- sor(s) 5.

[0029] By way of example, the driver 17 can include an electric motor. The electric motor is powered by electric energy from an electric energy source, for instance from an electric distribution grid 19 forming part of the LNG system 1.

[0030] Electric energy to the electric distribution grid 19 is provided directly or in- directly by an energy collector 20, which collects energy from a renewable energy resource. In the embodiment ofFig. 1, the renewable energy resource is solar radiation, which is converted into electricity by a photovoltaic field 21 comprised of a plurality of photovoltaic panels 23 electrically coupled to the electric distribution grid 19 via an inverter unit 25. The inverter unit 25 can include a single inverter or a plurality of inverters. Hereon the inverter unit 25 will be referred to simply as“inverter”, but this shall not be construed narrowly. The energy collector 20, therefore, includes photovoltaic panels 23 and the inverter 25. A variable frequency drive 27 can be posi tioned between the inverter 25 and the electric motor 17. In the schematic of Fig.1 the inverter 25 is connected to the variable frequency drive 27 through the electric distri bution grid 19.

[0031] The electric motor 17 can rotate at a rotational speed, which can differ from the frequency of the AC current delivered by the inverter 25, and which can be non constant, to adapt the rotational speed of the refrigerant compressor 5 to the operating conditions of the thermodynamic circuit 3. For instance, if a lower refrigerant flow rate is required, the refrigerant compressor 5 can be driven at lower speed.

[0032] It shall be noted that the amount of energy provided by the renewable energy resource can be sufficient to drive all compressors of the LNG system 1. However, in some embodiments, the renewable energy resource may be used to provide energy to only one or some refrigerant compressors, or only part of the energy required to drive a compressor or a compressor train. For instance, if two compressors or compressor trains using two separate drivers are provided in the LNG system 1, one of said drivers can be a driver according to the current art, while the other can be a mechanical power generator, directly or indirectly powered by energy from the energy collector. In some embodiments, a share of renewable energy collected by the energy collector 20 can be used also to power other utilities and services in the system, if needed or desirable.

[0033] The energy collector 20 may provide sufficient power to drive the compressor 5, i.e. all compressors of the LNG system 1, or some of them, e.g. if more than one driver is provided and only one or some of them are intended to be powered by energy from the renewable energy resource.

[0034] If the power required by the compressor 5 is lower than the total power gen erated by the inverter 25, the surplus energy can be stored in an energy storage system 29. This latter can be comprised of one or more energy storage facilities, some of which will be described later on. In general, the energy storage system 29 can include one or more storage facilities suitable for this application, selected among the storage facili ties available.

[0035] In case of power shortfall, i.e. if the power provided by the renewable energy resource through the energy collector 20 is insufficient to drive the refrigerant compressor 5, or some of the refrigerant compressors of the system 1, energy stored in the energy storage system 29 can be exploited.

[0036] If insufficient energy is available from the energy storage system 29, or if for whatever reason, it is preferred not to deplete the stored energy, an auxiliary mechan- ical driver can be provided for directly or indirectly driving the refrigerant compres sors). For instance, the auxiliary mechanical driver can be coupled directly to the re frigerant compressor 5 and drive the refrigerant compressor 5 with mechanical power generated by the auxiliary mechanical driver. Hybrid operating conditions can also be foreseen, wherein the compressor or compressor train is driven by power generated by the auxiliary mechanical driver and by power delivered by the energy storage system 29.

[0037] In other embodiments, the auxiliary mechanical driver can drive an electric generator, which converts mechanical power into electric power. The electric power generated by the electric generator driven by the auxiliary mechanical driver can be used to power an electric motor drivingly coupled to the refrigerant compressor 5. Electric power generated by the electric generator driven by the auxiliary mechanical driver can be made available through the electric distribution grid 19 and can be added to electric energy obtained from renewable energy resource through by the energy col lector 20. [0038] In the embodiment of Fig.1 an auxiliary mechanical driver 31 includes a gas turbine engine 31, drivingly coupled to an electric generator 33. The gas turbine engine 31 can comprise a compressor section 31. 1, a combustor section 31.2 and an expander or turbine section 31.3. The gas turbine engine 31 can be fueled with natural gas NG from the pipeline 12. [0039] The LNG system 1 described above and schematically shown in Fig.1 can operate in different modes depending upon the amount of energy available from the renewable energy resource and collected by the energy collector 20, and on the amount of power required to drive the refrigerant compressor 5. As noted above, if energy collector 20 provides more energy than required to drive the refrigerant compressor 5, surplus energy can be stored in the energy storage system 29.

[0040] If insufficient or no power is available from the energy collector 20, energy from the energy storage system 29 can be used to drive the refrigerant compressor 5. For instance, energy from the energy storage system 29 can also be used for short time spans, during which the renewable energy resource provides insufficient energy. If no power or insufficient power is available from the renewable energy resource and the shortage cannot be balanced by energy from the energy storage system 29, the auxil iary mechanical driver 3 1 is used. The gas turbine engine 31 is started and used to generate electric energy via electric generator 33. The electric energy thus generated is converted into mechanical energy by the electric motor 17 to drive the refrigerant compressor 5. [0041] While in Fig. l the energy collector 20 collects solar energy through photo voltaic panels 23, other renewable energy resources can come into play. By way of non-limiting example, Fig.2 illustrates an LNG system, again labeled 1 as a whole, which includes an energy collector 20 comprised of a wind farm, to convert wind en ergy into electric energy. The wind farm is shown at 22. Wind turbines of wind farm 22 are shown at 24. Reference number 25 designates a converter which can convert the electric energy generated by the wind turbines into electric energy suitable for sup ply on the electric distribution grid 19. The remaining components of the integrated LNG system 1 ofFig.2 are the same as in Fig.1 and are labeled with the same reference numbers. These components will not be described again. [0042] One and the same integrated LNG system 1 can exploit different renewable energy resources through various energy collectors. This is pictorially represented by way of example in Fig.3, wherein an integrated LNG system 1 comprises an energy collector 20 including a field 21 of photovoltaic panels 23 and a further energy collec tor 20 including a wind farm 22. Some components of the LNG system 1 in Fig.3 are the same as in Figs. 1 and 2 and are labeled with the same reference numbers used in Figs. 1 and 2 and are not described again.

[0043] Inverters or converters 25 convert the electric energy generated by the wind turbines 24 of the wind farm 22 and by the photovoltaic panels 23 of the photovoltaic field 21 into electric energy at the correct frequency and phase for exportation to the electric distribution grid 19. An energy storage system 29 collects surplus energy which may be available from the energy collector 20. [0044] While the remaining components of the integrated LNG system 1 of Fig.3 could be the same as shown in Figs 1 and 2, in the exemplary embodiment shown in Fig.3 a different way of using mechanical power from the auxiliary mechanical driver is shown. The auxiliary mechanical driver 31 comprises a gas turbine engine which can be drivingly coupled to the refrigerant compressor 5 through a shaft line 40 and a clutch 41. A second clutch 43 is arranged along a shaft line 42, which drivingly con nects the electric motor 17 to the refrigerant compressor 5. When the electric power from the electric distribution grid 19 is insufficient to rotate the electric motor 17, the clutch 43 can be disengaged and the clutch 41 can be engaged, such that mechanical power from the gas turbine engine 31 can be used to directly drive the refrigerant com pressor 5. In some operating conditions, both clutches 43 and 41 can be engaged, and mechanical power from the gas turbine engine 31 and from the electric motor 17 can be used in combination to drive the refrigerant compressor 5.

[0045] The energy storage system 29 can include one or more different storage fa- cilities. With continuing reference to Figs. 1, 2 and 3, Fig.4A summarizes some options for energy storage systems 29 to be used in an LNG system according to the present disclosure.

[0046] An overview of energy storage technologies can be found in Xing Luo et al, “Overview of current development in electrical energy storage technologies and ap- plication potential in power system operation", Applied Energy 137 (2015) 51 1-536, available athttps://www.sciencedirect.com/science/article/pii/S0306261914010290.

[0047] According to some embodiments, the energy storage system 29 can include battery energy storage devices, flow battery energy storage devices, flywheel energy storage devices, supercapacitor energy storage devices, superconducting magnetic en- ergy storage devices, or combinations thereof. In these devices the electric energy is converted and stored in various forms of energy. For instance batteries, including flow batteries, store energy in the form of chemical energy. Flywheel energy storage in volves converting the electric energy in kinetic energy by driving into fast rotation a flywheel, which is arranged in a low-pressure vessel to reduce friction and is supported by low-friction bearings, including a magnetic levitation module, for instance. Super capacitor energy storage systems involve storing electric charges between two con ductive plates separated by a dielectric layer. Superconducting magnetic energy storage involves storing energy in form of an electric current flowing in coils made of superconductive material and maintained at cryogenic temperature to achieve almost zero resistance and thus reduce or substantially eliminate electric losses. In Fig.4A the energy storage system 29 includes a battery 51 and a rectifier 53, which electrically connects the battery to the electric distribution grid 19.

[0048] With continuing reference to Figs. 1, 2 and 3, a different energy storage sys tem 29 is shown in Fig.4B. This exemplary embodiment includes a cryogenic energy storage system, for instance a liquefied air storage system, also known as LAES sys tem. The energy storage system, again labeled 29 as a whole, can include an air com- pressor 55 driven by an electric motor 57, which is electrically coupled to the electric distribution grid 19. Surplus of electric energy made available by the energy collector 20 is used to power the electric motor 57. The compressed air delivered by the air compressor 55 is chilled and liquefied and finally collected in a liquid air storage tank 59. More specifically, air liquefaction is achieved by compressing an air flow by means of air compressor 55, chilling the compressed air flow in heat exchangers 58 A, 58B and expanding the chilled air flow in an expander or in a Joul e-Thomson valve 60.

[0049] The liquid air is maintained at low temperature in the liquid air storage tank 59. When energy is to be recovered from the cryogenic energy storage system 29, a cryogenic pump 62 delivers a flow of liquefied air through a heater 64 and the pres- surized and heated air flow is expanded in an expander 66, for instance a turbo-ex- pander. Mechanical power generated by the expander 66 drives an electric generator 68 and the electric power thus generated is delivered to the electric distribution grid 19 for driving the refrigerant compressor 5 of the integrated LNG system 1.

[0050] With continuing reference to Figs. 1, 2 and 3, a hydro energy storage system 29 is shown in Fig.4C. The hydro energy storage system can comprise a lower water reservoir 70A and an upper water reservoir 70B. A pipeline 72 connects the lower water reservoir 70 A and the upper water reservoir 70B. A reversible pump-turbine 74 arranged in the pipeline 72 is adapted to pump water from the lower reservoir 70 A to the upper reservoir 70B and to be driven into rotation by water flowing in the opposite direction, from the upper reservoir 70B to the lower reservoir 70A. An electric ma chine 76 is drivingly coupled to the reversible pump-turbine 74. When the reversible pump-turbine 74 operates in the pumping mode, the electric machine 76 operates in a motor mode and is powered by electric energy from the electric distribution grid 19. The electric energy is thus converted into mechanical energy by the electric machine 76 and in potential hydro energy by the pump-turbine 74. When the reversible pump- turbine 74 operates in the turbine mode, the potential hydro energy is converted into mechanical energy by the pump-turbine 74 and in electric energy by the electric ma chine 76 operating in a generator mode.

[0051] In other embodiments, the hydro energy storage system may include separate pump and turbine, arranged in separate ducts, one for pumping water from the lower reservoir 70 A to the upper reservoir 70B and the other for flowing water from the upper reservoir 70B to the lower reservoir 70A. A single electric machine, adapted to operate in a motor mode and in a generator mode can be provided, and selectively coupled to the pump and to the turbine. Alternatively, separate electric motor and elec tric generator can be drivingly coupled to the pump and to the turbine, respectively.

[0052] Compressed air energy storage systems (CAES systems) can be used as an alternative energy storage system 29. With continuing reference to Figs. 1, 2 and 3, an exemplary CAES system is shown in Fig.4D and labeled again 29. The CAES system includes an air compressor 80, a cavern 82 and/or a pressurized air tank 83 and a tur bine 84. In the exemplary embodiment of Fig.4D the air compressor 80 and the turbine 84 are arranged on the same shaftline 86. An electric machine 87 arranged along the shaftline 86 can be connected selectively to the air compressor 80 through a first clutch 88 A and to the turbine 84 through a second clutch 88B.

[0053] In an energy accumulation mode the electric machine 87 operates in an elec tric motor mode and converts electric energy available from the electric distribution grid 19 into mechanical energy, to drive the air compressor 80. Compressed air deliv- ered by the air compressor 80 can be cooled in a heat exchanger 89 and accumulated in the cavern 82 and/or in the pressurized air tank 83. The turbine 84 is inoperative and the clutch 88B can be disengaged.

[0054] In an energy delivery mode the clutch 88A can be disengaged and the clutch 88B can be engaged to connect the electric machine 87 to the turbine 84. The electric machine 87 operates in the generator mode. Compressed air previously stored in cav ern 82 and/or in pressurized air tank 83 is delivered to a combustor 92 where compressed air can be mixed with a fuel, for instance natural gas form pipeline 12. Combustion gas from the combustor 92 is expanded in turbine 84 to generate mechan ical power which is converted into electric power by the electric machine 87 operating in the generator mode. Exhaust gas from the turbine 84 can be used to preheat the compressed air in a pre-heater 94 arranged upstream of the combustor 92. A variable frequency drive 90 can be connected between the electric machine 87 and the electric distribution grid 19.

[0055] The energy storage systems 29 illustrated in Figs. 4 A, 4B, 4C, 4D are shown by way of example only. Those skilled in the art of energy storage will understand that other energy storage systems can be used, either alone or in various combinations, in order to store energy surplus generated by the renewable energy resource. The selec tion of the energy storage technology may depend upon several factors, among which environmental conditions, availability of natural or artificial water reservoirs, air tanks or caverns, etc.. [0056] Energy from the energy storage system 29 can be used either to provide sup plemental energy to cover peak power demand by the refrigerant circuit 3, or to pro vide energy when energy from the renewable energy resource is unavailable, for in stance at night in case of a solar photovoltaic plant, or when no wind blows, in case of a wind farm. [0057] According to some embodiments, solar energy can be exploited by means of a concentrated solar power plant and converted into thermal energy. Exemplary em bodiments using concentrated solar power plant are shown in Figs 5, 6, 7, 8, 9.

[0058] In embodiments using concentrated solar power plants, an integrated natural gas liquefaction system may include at least one refrigerant circuit adapted to circulate at least one refrigerant therein, wherein the refrigerant circuit includes at least one re frigerant compressor; and wherein the refrigerant circuit is adapted to remove heat from a flow of natural gas. The integrated natural gas liquefaction system further in cludes a concentrated solar power plant, comprised of at least one solar concentrator adapted to concentrate solar radiation. Thermal energy from the solar concentrator is transferred to a thermodynamic cycle, wherein heat from the concentrator is converted into mechanical power by the thermodynamic cycle through a mechanical power generator and possibly further converted into electric power. The thermodynamic cy cle is therefore an energy converter which may convert energy from the renewable energy resource into another useful form of energy, such as mechanical or electric energy, as disclosed here below. [0059] The system may further include a heat storage facility, to store heat from the concentrated solar power plant

[0060] The system may further include an energy storage system adapted to store electric energy, suitably converted into another form of storageable energy prior to storage. [0061] Heat can be transferred directly from the solar concentrator to a working fluid of the thermodynamic cycle. In embodiments heat is transferred from the solar con centrator to the thermodynamic cycle through an intermediate heat transfer circuit.

[0062] In some embodiments, the mechanical power generator is drivingly connected to the refrigerant compressor. [0063] The integrated natural gas liquefaction system further comprises a first elec tric machine adapted to be drivingly coupled to the mechanical generator and electri cally coupled to an electric distribution grid. This latter is functionally coupled to an energy storage system, adapted to store surplus energy generated by the mechanical power generator and suitably converted into a storageable form of energy. [0064] In some embodiments, the integrated natural gas liquefaction system further comprises an auxiliary mechanical driver, such as a combustion engine, for instance, a gas turbine engine, drivingly coupled to a second electric machine, adapted to con vert mechanical power generated by the auxiliary mechanical driver into electric power. [0065] The second electric machine is electrically coupled to the electric distribution grid to supply electric power to the first electric machine, for driving the refrigerant compressor, when insufficient power is provided by the mechanical power generator.

[0066] The auxiliary mechanical driver can include a combustion engine fueled with natural gas, or with hydrogen, or with a combination thereof. Hydrogen can be produced electrically, exploiting electric power generated by the first electric machine, for instance.

[0067] The thermodynamic cycle can include a steam or vapor cycle, such as a Ran- kine cycle, or a closed or open gas cycle, such as a Bray ton cycle. [0068] In embodiments, a heat generator fueled with a suitable fuel, such as natural gas, can be associated to the thermodynamic cycle, for providing additional thermal power to the working fluid, for instance in case insufficient thermal power is provided by the concentrated solar power plant. A heat generator can be used in combination with an open or with a closed thermodynamic cycle. The heat generator can be used, e.g., as a boiler or a re-heater to heat or re-heat a steam or vapor flow in a Rankine cycle, for instance. In embodiments, the heat generator can be used to heat a flow of compressed gas, e.g., in an open or closed Brayton cycle.

[0069] Figs. 5 to 9 illustrate embodiments of integrated natural gas liquefaction sys tems using concentrated solar power plants. [0070] More in detail, Fig. 5 illustrates an integrated LNG system 1 including a re frigerant circuit 3 adapted to circulate a refrigerant fluid therein. The refrigerant circuit 3 includes a refrigerant compressor 5, a chiller 7, an expander 9 and a heat exchanger 11. The refrigerant delivered by refrigerant compressor 5 is chilled in chiller 7 and expanded in expander 9 to achieve a sufficiently low temperature, such that heat can be removed therewith from natural gas (NG) flowing in pipeline 12. At the exit side of the heat exchanger 11, liquefied natural gas (LNG) is obtained, which is collected in an LNG tank 15. As mentioned above in connection with Fig.1, the refrigerant circuit 3 and relevant refrigerant compressor 5 are used as simple pictorial representa tion for any kind of refrigerant facility, which may include one or more compressor trains and one or more refrigerant circuits, according to any available LNG technology.

[0071] In the embodiment of Fig.5 an energy collector, again labeled 20, is provided to collect solar energy. The energy collector 20 includes a concentrated solar power plant 101. Concentrated solar power plants are known in the art and do not require a detailed description. Only the main components thereof will be mentioned herein. In some embodiments, the concentrated solar power plant 101 can include a closed circuit adapted to circulate a heat carrier fluid, which transfers heat from solar concentrators to a thermodynamic circuit, where heat is partly converted into mechanical power. In the exemplary embodiment of Fig. 5 the concentrated solar power plant 101 includes a solar concentrator 103. Several kinds of solar concentrators are known in the art and may be used in the concentrated solar power plant 101. By way of example only, in Fig.5 the concentrator 103 includes a plurality of heliostats, such as parabolic mirrors 103 A, for instance. A closed heat carrier fluid circuit 105 transfers heat from the solar concentrator 103 to a thermodynamic circuit 107.

[0072] In the exemplary embodiment of Fig.5 the thermodynamic circuit is adapted to perform a regenerative Rankine cycle and includes a steam or vapor turbine 109, which may include a high pressure turbine 109 A and a low pressure turbine 109B. In this embodiment, therefore, the steam or vapor turbine 109 is a mechanical power gen erator, which generates mechanical power to drive the refrigerant compressor 5 of the refrigerant circuit 3 exploiting renewable energy. In some embodiments, the process fluid processed through the steam or vapor turbine 109 can be water. In other embod- iments, the process fluid can be an organic working fluid.

[0073] The process fluid circulating in the thermodynamic circuit 107 is heated, va porized and superheated using heat from the closed heat carrier fluid circuit 105, through a heater 111, a vaporizer 113 and a superheater 115. Superheated steam or vapor is partly expanded in the high-pressure turbine 109 A, re-heated in a re-heater 117 and further expanded in the low-pressure turbine 109B. Expanded steam or vapor is condensed in a condenser 119 and pumped by a pump 121 again through the heating section of the circuit, including heater 111, vaporizer 113 and superheater 115.

[0074] In some embodiments the thermodynamic circuit 107 can include an auxiliary boiler, wherein heat is generated e.g. by burning natural gas, when insufficient solar power is available, for instance. The boiler can be arranged to supplement thermal energy to one or more of the sections of the closed steam or vapor circuit. In the sche matic of Fig.5 the boiler is shown at 123 and is configured to supply regeneration heat. More in general, the boiler can be used to provide supplemental thermal energy to the heater, vaporizer and/or superheater of the steam and/or vapor circuit, whenever no heat or insufficient heat is provided by the concentrator 103.

[0075] In some embodiments the steam or vapor turbine 109 and the refrigerant compressor 5 can be arranged on a common shaftline. A clutch 131 can be arranged along the shaftline between the steam or vapor turbine 109 and the refrigerant com pressor 5.

[0076] In some embodiments, an electric machine, e.g. an electric motor/generator 133 can be drivingly coupled to the steam or vapor turbine 109 and/or to the refrigerant compressor 5. In the schematic of Fig. 5 an electric motor/generator 133 is arranged on the same shaftline as the refrigerant compressor 5 and the steam or vapor turbine 109 is drivingly coupled thereto through a clutch 135. The electric motor/generator 133 is electrically coupled to the electric distribution grid 19.

[0077] The electric distribution grid 19 can be functionally coupled to an energy stor age system 29, as shown in Figs. 1, 2 and 3, not shown in Fig.5. In some embodiments, if the mechanical power generated by the steam or vapor turbine 109 exceeds the needs from refrigerant compressor 5, surplus power can be converted into electric power by electric motor/generator 133, which is operated in the generator mode, and stored in the energy storage system 29. Conversely, energy from the energy storage system 29 can be used if insufficient heat is available from the concentrated solar power plant 101 and/or from the boiler 123.

[0078] In some embodiments, the integrated LNG system 1 of Fig.5 can further in clude a gas turbine engine 31, similar to the gas turbine engine 31 ofFigs. 1 and 2. The gas turbine engine 31 can be operated to drive an electric generator 33 connected to the electric distribution grid 19, if energy from the concentrated solar power plant 101 and/or from the energy storage system 29 is insufficient and if no boiler 123 is pro vided or if said boiler 123 provides insufficient heat or is temporarily unavailable, for instance. Mechanical power generated by the gas turbine engine 31 is converted into electric energy by the electric generator 33. The electric energy is made available through electric distribution grid 19 to drive the electric motor/generator 133 in the motor mode and drive the refrigerant compressor 5 therewith, either alone or in com bination with the steam or vapor turbine 109.

[0079] In some embodiments, the concentrated solar power plant 101 may also in clude a heat accumulator 102.

[0080] While in Fig.5 the concentrated solar power plant 101 uses linear solar concentrators, in other embodiments, heliostats concentrating solar energy on a re ceiver placed on top of a tower can be used. The receiver can be part of a closed circuit, wherein a heat transfer fluid circulates. The heat transfer fluid can transfer heat to a working fluid, which converts thermal energy into mechanical energy through a Ran- kine cycle, for instance.

[0081] In other embodiments, concentrated solar power can be converted into me chanical power using a Bray ton cycle. Concentrated solar power can heat a flow of compressed air, which is then expanded in a power turbine. The power turbine gener ates mechanical power to drive an electric generator. The power turbine can be driv- ingly coupled to an air compressor, e.g. an axial air compressor, which compresses the air which is then heated by means of concentrated solar power. In other embodiments, the entire mechanical power generated by the power turbine can be converted into electric energy and the air compressor can be driven by an electric motor. An auxiliary combustor can be provided, to provide heat if the solar energy is insufficient.

[0082] Fig.6 illustrates a schematic of an integrated LNG system 1 including a re frigerant circuit, again schematically shown at 3, and an energy collector 20, which includes a concentrated solar power plant 101. The refrigerant circuit 3 can be config ured as described above in connection with Figs. 1 and 2, for instance, and will not be described again.

[0083] In the embodiment of Fig.6 the concentrated solar power plant 101 includes a tower 201, on top of which a receiver 203 is installed. Heliostats 205 focus solar radiation on the receiver 203, where a heat transfer fluid flows, for example a molten salt. The receiver 203 forms part of a closed heat transfer circuit 207.

[0084] In some embodiments, the closed heat transfer circuit 207 can include a hot fluid reservoir 209 and a cold fluid reservoir 21 1. Hot heat transfer fluid from the re ceiver 203 is collected in the hot fluid reservoir 209, where solar energy can be stored as thermal energy. Hot heat transfer fluid can circulate from the hot fluid reservoir 209 through a steam or vapor generation system 213 into the cold fluid reservoir 211, wherefrom the exhausted heat transfer fluid flows back to the receiver 203.

[0085] The steam or vapor generation system 213 can include a superheater 215, an evaporator 217 and pre-heater 219. Hot heat transfer fluid from the hot fluid reservoir flows sequentially through the superheater 215, the evaporator 217 and the pre-heater 219 in heat exchange relationship with a working fluid circulating in a closed circuit 221 where the working fluid undergoes sequential thermodynamic transformations to convert heat into mechanical power. The working fluid circulating in the closed circuit 5 is pre-heated in pre-heater 219, evaporated in evaporator 217 and superheated in su perheater 215. The hot and pressurized working fluid expands sequentially in a high- pressure steam or vapor turbine 223 and in a low-pressure steam or vapor turbine 225. The partly expanded working fluid from the high-pressure steam or vapor turbine 223 can be regenerated in regenerator 221 in heat exchange relationship with the heat trans it) fer fluid, prior to be further expanded in the low-pressure steam or vapor turbine 225.

[0086] The spent working fluid exiting the low-pressure steam or vapor turbine 225 is condensed in a condenser 227 and collected in a tank 229, wherefrom condensed working fluid is pumped by pump 231 in the steam or vapor generator system 213 again.

15 [0087] In the exemplary embodiment of Fig.6, the mechanical power generated by the steam or vapor turbines 223 and 225 drives an electric generator 233, which is electrically connected to an electric distribution grid 19. The electric motor 17 of the refrigerant circuit 3 can be powered by electric energy from the electric distribution grid 19. 0 [0088] In other embodiments, not shown, similarly to the arrangement of Fig.5, the steam or vapor turbines 223 and 225 can directly drive in rotation the compressor 5 of the refrigerant circuit 3.

[0089] In some embodiments, an auxiliary gas turbine engine 31 can be provided to drive an electric generator electrically connected to the electric distribution grid 19, 5 similarly to the embodiment of Fig.2, to generate electric power if no or insufficient power is generated by generator 233.

[0090] In other embodiments, the auxiliary mechanical driver can include a gas tur bine engine, which can be drivingly coupled, through a clutch for instance, to the re frigerant compressor 5, as shown in the embodiment of Fig.3.

30 [0091] While in Figs. 5 and 6 solar energy is used in combination with a Rankine cycle to generate mechanical power to drive the refrigerant compressor 5, in other embodiments a different cycle can be used to convert heat into mechanical power, for instance a Bray ton cycle using a gas turbine engine.

[0092] An embodiment of an integrated natural gas liquefaction system using con centrated solar power and a Brayton cycle is illustrated in Fig. 7.

[0093] In summary, the system of Fig. 7 includes at least one refrigerant circuit adapted to circulate at least one refrigerant therein, wherein the refrigerant circuit in cludes at least one refrigerant compressor; and wherein the refrigerant circuit is adapted to remove heat from a flow of natural gas. The integrated natural gas lique faction system further includes a concentrated solar power plant, comprised of at least one solar concentrator adapted to concentrate solar radiation. Thermal energy from the solar concentrator is transferred to a thermodynamic cycle, wherein heat from the con centrator is converted into mechanical power by a gas turbine engine comprised of a working fluid compressor and a working fluid expander. Working fluid compressed by the working fluid compressor is heated by thermal power collected by solar con centrator and the hot, compressed working fluid is expanded in the working fluid ex pander.

[0094] The thermodynamic cycle can be a closed cycle or an open cycle. In Fig.7 the thermodynamic cycle is an open cycle.

[0095] The thermodynamic cycle is an energy converter which converts energy from the renewable energy resource into another form of useful energy, such as mechanical and/or electric energy.

[0096] The gas turbine engine is drivingly coupled to the compressor of the refriger ant circuit and may be further drivingly coupled to an electric machine, such as an electric generator or an electric motor/generator. The electric machine is electrically coupled to an electric distribution grid, which may transfer electric power to an energy storage system. The thermodynamic cycle may include a combustor, wherein natural gas or another fuel is used to generate additional thermal power to heat the compressed working fluid prior to expansion in the working fluid expander, in case of shortage from the concentrated solar power plant. The system may further include a heat storage facility, to store heat from the concentrated solar power plant. [0097] Turning now to the drawings, more in detail, Fig.7 illustrates an integrated LNG system 1, including a refrigerant circuit 3 which can include the same compo nents as already described above and labeled with the same reference numbers used in the previously mentioned figures. The integrated LNG system 1 further includes an energy collector 20 adapted to collect solar energy. In the embodiment of Fig.7 the energy collector 20 comprises a concentrated solar power plant again labeled 101, which includes a tower 201 with a receiver 203 arranged at the upper end of the tower 201. Heliostats 205 focus solar radiation on the receiver 203, where a heat transfer fluid flows, for example a molten salt. The receiver 203 forms part of a closed heat transfer circuit 207. In the embodiment of Fig.7 the closed heat transfer circuit 207 includes a hot fluid reservoir 209 and a cold fluid reservoir 211. Hot heat transfer fluid from the receiver 203 is collected in the hot fluid reservoir 209, where solar energy can be stored as thermal energy. Hot heat transfer fluid can circulate from the hot fluid reservoir 209 through an air heater 251 into the cold fluid reservoir 211, wherefrom the exhausted heat transfer fluid flows back to the receiver 203.

[0098] In the air heater 251 thermal energy is transferred from the heat transfer fluid circulating in the closed circuit 207 to compressed air, delivered by an air compressor 253. Compressed hot air is expanded in a power turbine 255 and is discharged through a stack 257. The exhaust air can be used to pre-heat the compressed air delivered by the air compressor 253 in a pre-heating heat exchanger 258.

[0099] The power turbine 255 and the air compressor 253 are mechanically coupled through a shaft 259, such that mechanical power generated by the expansion of the compressed hot air in the power turbine 255 is used to drive the air compressor 253. The additional power generated by the power turbine 255 and which is not required to drive the air compressor 253 is available on an output shaft 261.

[0100] The power turbine 255, the air compressor 253, the shaft 259 and the air heater 251 form part of a gas turbine engine globally labeled 265, where ambient air performs a Brayton cycle to convert heat, delivered to the air by the heat transfer fluid circulating in the closed circuit 207, into mechanical power available on the output shaft 261.

[0101] In the embodiment of Fig.7 the output shaft 261 is drivingly coupled to the refrigerant compressor 5 of the refrigerant circuit 3, such that mechanical power made available by the gas turbine engine 263 directly drives the refrigerant compressor 5. In other embodiments, not shown, the output shaft 261 can be mechanically coupled to an electric generator, which provides electric power exported on an electric distribu- tion grid 19. Electric energy from the electric energy distribution grid 19 can be used to power an electric motor, which converts the electric power into mechanical power to drive the refrigerant compressor 5, according to an arrangement similar to Fig.1.

[0102] To recover surplus power made available on output shaft 261, an electric gen erator 271 can be drivingly coupled to the outputs shaft 261 and electrically connected to the el ectri c di stributi on grid 19.

[0103] If insufficient power is available from the energy collector 20, a combustor 273 can be provided, through which compressed air flows prior to be expanded in the power turbine 255. A fuel, for instance natural gas diverted from the pipeline 12, can be mixed to compressed air in the combustor 273 and the air/fuel mixture can be ig- nited to generate compressed, high-temperature combustion gas, which is expanded in the power turbine 255.

[0104] In a modified embodiment of the system shown in Fig.7 air can be heated directly in the receiver 203 and the closed circuit 207 can be omitted. A heat storage system can be provided, to store any surplus of thermal energy, for instance using reservoirs of a heat storage medium.

[0105] Several other alternative embodiments of an integrated LNG system 1 includ ing an energy collector 20 comprising a concentrated solar power plant can be envis aged. With continuing reference to Fig. 5, in Fig. 8 a further embodiment of an inte grated LNG system 1 exploiting mechanical power generated by a concentrated solar power plant 101 is illustrated. The same or corresponding elements and components already described with reference to Fig.5 are labeled with the same reference numbers and will not be described again.

[0106] In the embodiment of Fig.8 the boiler 123 is omitted, but in other embodi ments, not shown, also a boiler 123 can be provided.

[0107] In Fig.8 the electric motor/generator 133 can operate in a generator mode if the mechanical power generated by the steam or vapor turbine 109 exceeds the power needed to drive the refrigerant compressor 5. Electric energy generated by the electric generator 133 can be used to produce hydrogen in a water electrolyzer 141, which can be electrically coupled to the electric distribution grid 19 via a rectifier 143. Hydrogen produced by the electrolyzer 141 can be stored in a hydrogen storage tank 145 and can be used, when so required, as a fuel to power a gas turbine engine 31 (see also Fig.1).

[0108] If required, a mixture of hydrogen from the hydrogen storage tank 145 and natural gas from natural gas pipeline 12 can be fed to the combustor 31.2 of the gas turbine engine 31. The gas turbine engine 31 can be operated to drive an electric gen erator 33, which provides electric power to the electric distribution grid 19 to power the electric motor/generator 133 when this latter is operated in the motor mode to drive the refrigerant compressor 5.

[0109] Thus, in the embodiment of Fig.8, solar power can be used to drive the refrig erant compressor 5 and to further generate electric power if sufficient solar power is available. The electric energy is converted into chemical energy by hydrogen produc tion and stored in the hydrogen storage tank 145. The energy stored in chemical form can be used when no solar power is available for continuity of operation of the refrig erant circuit 3.

[0110] Hydrogen can be produced also using a different concentrated solar power plant as described above.

[0111] While in the embodiment of Fig.8 solar energy is primarily used to generate mechanical power and drive the refrigerant compressor 5 therewith, in other embodi ments solar energy, or energy from another renewable energy resources, can be ex ploited fully to produce hydrogen. This latter can fuel a gas turbine engine to drive the refrigerant compressor 5 of the refrigerant circuit 3. In some embodiments, solar en ergy can be converted into chemical energy, stored in the form of hydrogen, by pho- tocatalytic water splitting.

[0112] In other embodiments, hydrogen can be produced by water electrolysis, in which case the solar energy is converted into electric energy either directly in a pho tovoltaic system or using a concentrated solar power plant to generate mechanical power, which is used to drive an electric generator. [0113] In other embodiments, not shown, electric power for the production of hydro gen can be provided by a wind farm.

[0114] With continuing reference to Figs. 5 and 8, in Fig.9 an exemplary embodi ment of an integrated LNG system 1 is illustrated, which includes an energy collector adapted to collect energy from a renewable energy resource, using concentrated solar power to generate hydrogen. The integrated LNG system 1 of Fig.9 includes a concen trated solar power plant 101 as in the embodiments of Figs. 5 or 8. The main compo nents of the concentrated solar power plant 101 are labeled with the same reference numbers as in Figs. 5 and 8 and will not be described again. A different concentrated solar power plant can be used, for instance as disclosed in Figs. 6 and 7.

[0115] In the embodiment ofFig.9 the steam or vapor turbine 109 generates mechan ical power to drive an electric generator 133, which converts the mechanical energy into electric energy delivered to an electrolyzer 141 to produce hydrogen by water electrolysis. The hydrogen thus produced can be stored in a hydrogen storage tank 145 and used to fuel a gas turbine engine 31. The gas turbine engine 31 drives the refrig erant compressor 5 of the refrigerant circuit 3. If needed or desired, natural gas from the pipeline 12 can be used alone or mixed with hydrogen from the hydrogen storage tank 145.

[0116] While in Fig. 9 solar energy is collected by a concentrated solar power plant 101, in other embodiments solar energy can be coll ected in different ways, for instance by means of a field 21 of photovoltaic panels 23 (Fig.1), to produce electric energy which is then used for hydrogen production by electrolysis. Other energy collectors for collecting energy from a renewable energy resources can be used to generate elec tric energy for electrolytic production of hydrogen, for instance wind turbines of a wind farm 22.

[0117] Fig.10 illustrates an integrated LNG system 1, wherein the energy collector 20 for collecting energy from a renewable energy resource (here again solar energy) comprises a field 21 photovoltaic panels 23 and wind turbines 24 of a wind farm 22, to generate electric energy delivered through inverters 25 to an electric distribution grid 19. The electric energy thus generated is used to produce hydrogen in an electro lyzer 141. Hydrogen is collected in a hydrogen storage tank 145 to fuel a gas turbine engine 31. As mentioned above, natural gas can be mixed with hydrogen in the com bustor 31.2 or used alone if insufficient or no hydrogen is available from the tank 145. The gas turbine engine 31 drives the refrigerant compressor 5 of the refrigerant circuit 3. [0118] Hydrogen produced exploiting power from the renewable energy resource can alternatively be used in fuel cells, adapted to generate electric power. The electric power can in turn be used to power an electric motor adapted to drive the refrigerant compressor(s) 5 of the refrigerant circuit 3.

[0119] Fig.1 1 illustrates a schematic of a further integrated LNG system 1 including a refrigerant circuit 3 with one or more compressors schematically represented by com pressor 5. The same reference numbers used in Fig.1 1 are used to designate the same or equivalent parts as already disclosed in connection with Fig.10. In the embodiment of Fig.11 electricity generated by an energy collector 20, adapted to collect energy from a renewable energy resource, is used to produce hydrogen by electrolysis in an electrolyzer 141. The hydrogen thus produced is collected in a hydrogen tank 145, wherefrom hydrogen is fed to a fuel cell system 146. Chemical energy from the hy drogen flow is converted into electrical energy by the fuel cell system 146 and exported to an electric distribution grid 19 via inverter 148 or any other electric energy condi tioning device. The electric distribution grid 19 powers an electric motor 152 drivingly coupled via a clutch 154 to the compressor(s) 5 of the refrigerant circuit 3. A gas tur bine engine 31 can be provided as an auxiliary driver to drive the compressor 5 should no power be available on the electric distribution grid 19.

[0120] In general, disclosed herein is a method for liquefying natural gas in an inte grated natural gas liquefaction system in which at least one refrigerant circuit is inte- grated with an energy collector adapted to collect energy from a renewable energy resource. The method includes the step of generating power with energy collected by the energy collector and producing hydrogen using said power in a hydrogen produc tion facility. The method also includes the further step of generating power (either mechanical or electrical, for instance) by means of a power generator fueled with said hydrogen.

[0121] While in the examples described above solar energy and wind energy are used to provide useful power to drive the refrigerant compressors, other renewable energy resources can be used. For instance, tidal or wave power generation systems may be used, which convert energy from tide or sea waves into other forms of useful power, such as mechanical power or electrical power. The electrical or mechanical power gen- erated by the renewable energy resource can be used to drive compressors 5 of the refrigerant circuit 3 and excess power, if available, can be stored as described above. In some embodiments, electric energy generated by the renewable energy resource can be used for hydrogen production. Several tidal and wave power generation devices and plants are disclosed in“Intermittent wave energy generation system with hydraulic energy storage and pressure control for stable power outpuf , Journal of marine Sci ence and Technology, December 2018, vol. 23, issue 4, pp. 802-813; and T.J. Ham mons,“Tidal Energy Technologies: Currents, Wave and offshore Wind Power in the United Kingdom, Europe and North America” available at http://cdn.inte- chweb.org/pdfs/9342.pdf. These plants and devices may be included in an energy col- lector, adapted to collect energy from the respective renewable energy resource.

[0122] In yet further embodiments, the energy collector 20 of an integrated ENG system 1 may include a geothermal plant, wherein geothermal heat is used to generate mechanical power for mechanical drive or electric generation. In the first instance, the mechanical power is used directly to drive compressor(s) 5 of the refrigeration circuit 3. In the second instance, mechanical power can be converted into electric power, which is then used to drive the refrigerant compressor(s) 5 via an electric motor.

[0123] While the invention has been described in terms of various specific embodi ments, it will be apparent to those of ordinary skill in the art that many modifications, changes, and omissions are possible without departing form the spirit and scope of the claims. In addition, unless specified otherwise herein, the order or sequence of any process or method steps may be varied or re-sequenced according to alternative em bodiments.

[0124] Various embodiments of the invention are contained in one or more of the following clauses, which can be combined in any suitable fashion unless otherwise indicated herein:

Claims

1. A method for liquefying natural gas in an integrated natural gas liq uefaction system comprising a refrigeration circuit including at least one refrigerant compressor and an energy collector adapted to collect energy from a renewable energy resource; the method comprising the following steps:

generating power from energy collected by the energy collector and pro ducing hydrogen therewith; and

driving the refrigerant compressor with power generated from said hydro gen.

2. The method of claim 1, further comprising the steps of converting energy collected by the energy collector into electric energy, and producing hydrogen using electric power generated by the energy converter.

3. The method of claim 1 or 2, wherein the energy collector includes a concentrated solar power plant; and further including the following steps:

converting thermal power from the concentrated solar power plant into me chanical power through a thermodynamic cycle;

converting mechanical power into electric power;

producing hydrogen with the electric power.

4. The method of claim 3, wherein a portion of the mechanical power is used for directly driving the refrigerant compressor.

5. The method of one or more of the preceding claims, further compris ing the step of fueling a thermal engine with said hydrogen and producing mechanical power therewith.

6. The method of claim 5, wherein the thermal engine includes a gas turbine engine.

7. The method of claim 5 or 6, further comprising the steps of:

converting mechanical power generated by the thermal engine into electric power;

converting electric power generated by the thermal engine into mechanical power and driving the refrigerant compressor therewith.

8. The method of claim 5 or 6, wherein the thermal engine is drivingly coupled to the refrigerant compressor, and further comprising the step of driving the refrigerant compressor with said gas turbine engine.

9. The method of one or more of claims 4 to 8, further comprising the step of fueling the thermal engine alternatively with natural gas, hydrogen or a mixture thereof, depending upon availability of said hydrogen.

10. The method of claim 1 or 2, wherein the steps of:

driving the refrigerant compressor includes the steps of: generating electric en ergy through fuel cells fueled with said hydrogen;

powering an electric motor with the electric energy generated by the fuel cells; and driving the refrigerant compressor with said electric motor.

11. An integrated natural gas liquefaction system comprising: an energy collector adapted to collect energy from a renewable energy resource; a hydrogen production facility, adapted to produce hydrogen through energy col- lected by the energy collector from said renewable energy resource;

a power generator, adapted to be fueled with hydrogen produced by said hydro gen production facility; and

at least one refrigerant circuit adapted to circulate at least one refrigerant therein, wherein the refrigerant circuit includes at least one refrigerant compressor driven by power from said power generator.

12. The system of claim 11, further comprising an energy converter, adapted to convert energy collected by the energy collector into electric energy, and wherein the hydrogen production facility is adapted to produce hydrogen using electric power generated by the energy converter.

13. The system of claim 11 or 12, further comprising a hydrogen storage tank.

14. The system of one or more of claims 11 to 13, wherein the power generator includes a thermal engine adapted to be fueled with said hydrogen.

15. The system of claim 14, wherein the thermal engine is adapted to be drivingly coupled to the refrigerant compressor.

16. The system of claim 14 or 15, wherein the thermal engine is further adapted to be fueled by natural gas.

17. The system of claim 14 or 15 or 16, wherein the thermal engine in cludes a gas turbine engine.

18. The system of one or more of claims 11 to 17, wherein the energy collector includes a concentrated solar power plant including a thermodynamic cycle adapted to convert thermal power into mechanical power.

19. The system of claim 18, wherein the concentrated solar power plant comprises a turbine adapted to convert thermal power into mechanical power and to be drivingly coupled to an electric machine.

20. The system of claim 19, wherein the turbine is further adapted to be drivingly coupled to the refrigerant compressor.

21. The system of one or more of claims 11 to 13, wherein said power generator includes fuel cells, electrically coupled to an electric motor, the electric mo- tor being drivingly coupled to the refrigerant compressor.

22. The system of claim 19, further comprising an auxiliary mechanical generator, adapted to be drivingly coupled to the refrigerant compressor and adapted to be fueled with natural gas.