Energy transformation and storage plant

Abstract

An energy transformation and storage plant comprises a main circuit for a working fluid other than atmospheric air. The main circuit connects a storage device (205), a compression unit, a thermal accumulator (100, 210), a reservoir (209) and an expansion unit and is configured to operate the plant in an energy storage configuration or in an energy discharge and generation configuration by a displacement of the working fluid between the storage device (205) and the reservoir (209) through the main circuit and via a cyclic thermodynamic transformation of the working fluid. The plant further comprises an auxiliary circuit (1) which connects the main circuit and / or the storage device (205) and / or the compression volume of the compressor (203) and / or the expansion volume of the expander (202) with at least one portion of the compression unit and / or of the expansion unit, so as to control a temperature and / or a pressure of this portion through the same working fluid.

Description

[0001] “Energy transformation and storage plant”

[0002] DESCRIPTION

[0003] Field of the invention

[0004] The present invention has as its object an energy transformation and storage plant of the type configured to implement a closed cyclic thermodynamic transformation with a working fluid between two mass accumulations, where with management is intended the generation, transformation, absorption and storage of energy.

[0005] More in detail, the present invention refers to an optimized plant configuration capable of exploiting the same working fluid used in the closed cyclic thermodynamic transformation to perform important auxiliary functions, such as isolating the plant from the external environment and / or thermally isolating parts of the plant from others and / or cooling particular areas or elements of the plant.

[0006] Definitions

[0007] In the present description and in the attached claims reference will be made to the following definitions.

[0008] • Cyclic Thermodynamic Transformation (TTC): thermodynamic transformation from a point A to a point B and from a point B to a point A, without necessarily passing through the same intermediate points; the TTC works between two mass storages / accumulations, one initial and the other final, of a working fluid.

[0009] • Thermodynamic Cycle (CT): thermodynamic transformation from a point X to a point Y, wherein X coincides with Y; the thermodynamic cycle (CT) unlike the Cyclic Thermodynamic Transformation (TTC) referred to above has no mass accumulations / storages (of the working fluid), within the cycle, significant for energy purposes.

[0010] • Closed CT and / or TTC: without mass exchange (significant for energy purposes) with the atmosphere.

[0011] • Open CT and / or TTC: with mass exchange (significant for energy purposes) with the atmosphere. i • Auxiliary circuit: a circuit that does not serve directly for the production, transformation and storage of energy, but for internal and accessory services of the system itself (lubrication, temperature and / or pressure control, etc.); the auxiliary circuit performs functions other than the transformations that take place in the main circuit, in the compression volume of the compressor and in the expansion volume of the expander.

[0012] Background of the finding

[0013] The public document W02020 / 039416, on behalf of the same Applicant, shows a process and a plant for energy storage. The plant comprises a variable-volume casing (e.g., a single- or double-membrane gasometer) for the storage of a working fluid other than atmospheric air, in gaseous phase and in pressure eguilibrium with the atmosphere; a reservoir for the storage of this working fluid in liguid or supercritical phase with a temperature close to the critical temperature, wherein the critical temperature is close to the environmental temperature. The plant is configured to implement a closed cyclic thermodynamic transformation, first in one direction in a storage configuration and then in an opposite direction in a discharge configuration, between the casing and the reservoir. In the storage configuration the plant stores heat and pressure and in the discharge configuration it generates energy.

[0014] Also documents WO2021 / 165809, WO2021 / 191786 and WO2022 / 101727, all on behalf of the same Applicant, show plants based on the same principle shown in W02020 / 039416 (closed cyclic thermodynamic transformation between two mass accumulations).

[0015] Summary

[0016] The Applicant has noted that the fluid machines used in the above-described plants are provided with seals. Seals are reguired in all fluid machines wherein the mechanical power, from and to the working fluid (driving or operating machine), passes through a mechanical organ (rotating shaft of a turbomachine or rod in case of an alternative machine) that is typically located in the atmosphere. Seals perform the task of separating the process environment inside the machine from the atmosphere to prevent the working fluid from leaving the machine (if the pressure inside the machine is greater than the atmospheric pressure) or to prevent the working fluid from being contaminated by air of the external environment (if the pressure inside the machine is less than the atmospheric pressure). Seals, however, must work in temperature ranges, with relative speed ranges (e.g., peripheral speed of the shaft relative to the seal) and with predetermined pressure jumps in order to properly function and effectively prevent the passage of fluids. For this purpose, several systems are known to control temperatures, speeds and pressures in proximity of the seals, but they are complex and expensive or, at times, poorly effective.

[0017] The Applicant has also noted that the fluid machines used in the above-described plants, like all the fluid machines, require supports for the moving organ or organs, whether it / they move with rotary motion or with reciprocating motion, that is, components whose task is to interpose themselves between the moving organ or organs and the fixed part of the machine. For example, in case of rotating shafts of turbomachines, the supports are bearings. In case of rods for alternative machines, supports are bushings. Supports (bearings or bushings) often require lubrication to limit friction and thus wear of the components and normally said bearings or bushings work in direct or indirect contact with the atmosphere. For example, in case of turbomachines operating at overpressure with respect to the atmosphere, solutions are known wherein the bearings operating within the turbomachine (e.g., a turbo-expander) operate at significantly higher pressure than the atmospheric one. The lubrication oil is extracted from the bearing area with a level adjustment, is depressurized, and is sent to a lubrication unit that typically operates at a pressure very close to the atmospheric one. Subsequently, the oil is pumped back within the case of bearings. However, this solution has a drawback, namely, the pressurized oil within the bearing case tends to “adsorb” the working fluid which then, due to depressurization, is released into the oil case and then exits the process.

[0018] In this field, the Applicant first aimed at overcom ing the above-mentioned drawbacks to ensure the correct functioning of seals and supports in fluid machines operating in an energy transformation and storage plant of the above-described type.

[0019] In particular, the Applicant aimed at overcoming the problem of working fluid leakage or environmental air inlet through seals, in particular of rotating shaft seals, of fluid machines that are part of an energy transformation and storage plant of the abovedescribed type without having to rely on complex and expensive solutions. The Applicant also aimed at putting the supports of the above-mentioned fluid machines in the conditions suitable for ensuring their correct functioning without having to rely on complex and expensive solutions.

[0020] More generally, the Applicant aimed at controlling temperatures and pressures of determined areas or portions of the fluid machines, and eventually of other machines or devices (motors, generators, speed reducers, etc.) connected to them, being part of an energy transformation and storage plant of the above-described type in a relatively simple and cost-effective way.

[0021] The Applicant also aimed at isolating the plant from the external environment and / or thermally isolate parts of the plant from others and / or to cool particular areas or elements of the plant in a relatively simple and cost-effective way.

[0022] The Applicant has found that the above indicated objectives and others can be achieved exploiting the working fluid used to implement the closed cyclic thermodynamic transformation of the energy transformation and storage plant.

[0023] The Applicant has in particular found that the above indicated objectives and others can be achieved through an energy transformation and storage plant according to the attached claims and / or according to one or more of the following aspects.

[0024] In a first independent aspect, the present invention relates to an energy transformation and storage plant, comprising: a working fluid other than atmospheric air; a storage device internally bounding a variable volume and configured to store the working fluid in gaseous phase and with a storage pressure Ps in pressure equilibrium with the atmosphere Patm, with low or no overpressure, at each operational phase implemented by the plant; at least one reservoir configured to store the working fluid in liquid or supercritical phase; a compression unit comprising at least one compressor and at least one motor mechanically connected to each other; an expansion unit comprising at least one expander and at least one generator mechanically connected to each other; at least one thermal accumulator, optionally wherein said at least one thermal accumulator comprises at least one heat exchanger combined with at least one thermal mass; a main circuit connecting the variable volume of the storage device, a compression volume of the compressor, said at least one thermal accumulator, said at least one reservoir and one expansion volume of the expander; devices configured to operate the plant in an energy storage configuration or in an energy discharge and generation configuration via a displacement of the working fluid between the storage device and said at least one reservoir through the main circuit and via a cyclic thermodynamic transformation of said working fluid; wherein the plant comprises further an auxiliary circuit. The auxiliary circuit connects at least one portion of the compression unit and / or of the expansion unit with at least one between the main circuit, the variable volume of the storage device, the compression volume of the compressor, the expansion volume of the expander. The auxiliary circuit is configured to control a temperature and / or a pressure of said at least one portion exploiting the same working fluid taken from the cyclic thermodynamic transformation.

[0025] In a second aspect, the present invention relates to a method for controlling a temperature and / or a pressure of said at least one portion of the compression unit and / or of the expansion unit of the plant of the first aspect or of one of the following aspects, comprising: connecting, via the auxiliary circuit, the main circuit and / or the variable volume of the storage device and / or the compression volume of the compressor and / or the expansion volume of the expander with said at least one portion of the compression unit and / or of the expansion unit.

[0026] The auxiliary circuit may comprise lines / pipelines external to the machines (compressor and expander with reducers etc.) but may also be obtained within the machines.

[0027] The Applicant has first of all verified that the plant and the method according to the invention allow to achieve the above listed objects.

[0028] In particular, the Applicant has verified that the invention allows to obtain the following technical effects exploiting the working fluid and through connections with the main circuit and / or with the variable volume of the storage device and / or with the compression volume of the compressor and / or with the expansion volume of the expander:

[0029] - creating a thermal barrier in areas or portions of the fluid machines where necessary (e.g., create a barrier of working fluid colder with respect to the warmer working fluid located in the compression volume of the compressor or in the expansion volume of the expander);

[0030] - keeping the supports and / or seals at a correct temperature for their functioning (e.g., at a temperature lower than the one of the working fluid within the compression volume of the compressor or of the expansion volume of the expander);

[0031] - preventing or at least drastically limiting leakages (losses) of the working fluid from the plant and dispersion into the environment or environmental air inlets into the main circuit and thus contamination of the working fluid, even in presence of lubrication circuits working at atmospheric pressure Patm.

[0032] Further aspects of the invention and additional technical effects are described below.

[0033] In a third aspect, said at least one compressor and said at least one expander comprise each one: a case; at least one moving mechanical organ movable with respect to the case and configured to exchange energy with the working fluid in the respective compression volume of the compressor or in the respective expansion volume of the expander; at least one transmission organ connecting the moving mechanical organ with the respective motor or generator.

[0034] In a fourth aspect, said at least one portion comprises at least one chamber bounded between the case and said at least one transmission organ wherein said at least one chamber is located near the compression volume of the compressor or of the expansion volume of the expander. In this way it is possible to exploit the working fluid, taken via the auxiliary circuit, as a barrier (both thermal and suitable for preventing the passage of fluids) to be interposed between compression volume or the expansion volume and the external environment or supports or seals.

[0035] In a fifth aspect, said at least one compressor and / or said at least one expander comprises / e at least one sealing element operatively coupled to the case and to the transmission organ and separating an environment within case from an external environment.

[0036] In a sixth aspect, said at least one chamber is in fluid communication with said at least one sealing element, optionally via a restriction. In a seventh aspect, said at least one compressor and / or said at least one expander comprises / e supports operatively interposed between the respective transmission organ and the respective case.

[0037] In an eight aspect, said at least one chamber is in fluid communication with said supports, optionally via a restriction.

[0038] In a ninth aspect, the auxiliary circuit comprises: at least one discharge conduit extending from the main circuit and / or from the variable volume of the storage device to said at least one portion of the compression unit and / or of the expansion unit and configured to feed the working fluid in said at least one portion of the compression unit and / or of the expansion unit with a discharge pressure P1 greater than the storage pressure Ps (P1 >Ps).

[0039] In a tenth aspect, the auxiliary circuit comprises: at least one discharge conduit extending from the main circuit and / or from the variable volume of the storage device to said at least one chamber and configured to feed the working fluid in said at least one chamber with a discharge pressure P1 greater than the storage pressure Ps (P1 >Ps).

[0040] In an eleventh aspect, the auxiliary circuit comprises: at least one return conduit extending from said compression unit and / or from said expansion unit until the variable volume at the storage pressure Ps or to a point of the main circuit at a pressure less than discharge pressure P1 .

[0041] In a twelfth aspect, said at least one discharge conduit connects a withdrawal point of the main circuit, which is at the discharge pressure P1 , to said at least one chamber or to said at least one portion of the compression unit and / or of the expansion unit and / or wherein said at least one discharge conduit connects the variable volume to said at least one chamber or to said at least one portion of the compression unit and / or of the expansion unit and comprises a fan or an auxiliary compressor configured to increase the storage pressure Ps of the working fluid coming from the variable volume to the discharge pressure P1 .

[0042] In a thirteenth aspect, the main circuit comprises: first pipelines connecting the storage device with the compression unit and with the expansion unit and second pipelines and optionally third pipelines connecting said at least one reservoir with the compression unit and with the expansion unit, said at least one thermal accumulator being operatively coupled to the second pipelines and / or to said at least one reservoir.

[0043] In a fourteenth aspect, the withdrawal point is located on the second pipelines and / or on the third pipelines, between said at least one reservoir and said at least one thermal accumulator and / or between said at least one thermal accumulator and the compression unit or the expansion unit. Optionally, the withdrawal point is an intermediate withdrawal from the compression volume of the compressor and / or from the expansion volume of the expander, i.e. at an intermediate pressure of the compressor and / or of the expander.

[0044] In a fifteenth aspect, said at least one return conduit extends from at least one auxiliary chamber of said compression unit and / or of said expansion unit; optionally said at least one auxiliary chamber is at a return pressure PO less than discharge pressure P1 (P0<P1 ); optionally the return pressure PO is greater (e.g. by a few millibar) than or equal to the storage pressure Ps (PO >= Ps); optionally the return pressure PO is lower than a working pressure PL within the compression volume of the compressor or of the expansion volume of the expander (PO < PL).

[0045] In a sixteenth aspect, the ninth and the fifteenth aspect, the supports are connected to said at least one chamber through a restriction and are at a support pressure P2 less than discharge pressure P1 (P2<P1 ); wherein said support pressure P2 is greater than return pressure PO (P2>P0).

[0046] In a seventeenth aspect, the compression unit and / or the expansion unit comprises / e a lubrication circuit operatively connected to the supports and containing a lubrication oil, wherein the lubrication circuit is at the support pressure P2 and is connected to said at least one return conduit.

[0047] In an eighteenth aspect, the lubrication circuit comprises a pump, configured to pump the lubrication oil to the supports, and a closed vessel for collecting the lubrication oil; wherein a portion of the closed vessel located above a free surface of the lubrication oil is connected to said at least one return conduit.

[0048] In a nineteenth aspect, a separator is located on said at least one return conduit connected to the closed vessel, wherein the separator is configured to separate the lubrication oil adsorbed by the working fluid.

[0049] In a twentieth aspect, said compression unit and / or said expansion unit comprises / e at least one speed reducer mechanically interposed between the transmission organ of the compressor and / or of the expander and the respective motor or generator; wherein said at least one speed reducer comprises: a box, moving organs mounted in the box and supports interposed between said moving organs and the box; wherein the box is in fluid communication with said at least one chamber.

[0050] In a twenty-first aspect, the box is mounted on the case, said at least one chamber is in fluid communication with the box through a restriction and the box is at said support pressure P2.

[0051] In a twenty-second aspect, the box is connected to the lubrication circuit.

[0052] In a twenty-third aspect, said compression unit and / or said expansion unit comprises / e a joint, rigid or flexible, connecting the respective speed reducer with the respective transmission organ.

[0053] In a twenty-fourth aspect, the joint is closed in a respective casing, wherein the casing is in fluid communication with the case and with the box, wherein the casing is in fluid communication with the auxiliary circuit.

[0054] In a twenty-fifth aspect, the casing is connected to the discharge conduit and said casing is at the discharge pressure P1 .

[0055] In a twenty-sixth aspect, at least one between the motor and the generator comprises supports and said supports are at said support pressure P2.

[0056] In a twenty-seventh aspect, the supports of at least one between the motor and the generator are operatively connected to the lubrication circuit.

[0057] In a twenty-eighth aspect, said compression unit and / or said expansion unit comprises / e a container containing the respective motor or generator; wherein the container is in fluid communication with the case and wherein case and the container are isolated from the external environment.

[0058] In a twenty-ninth aspect, the container is in fluid communication with the auxiliary circuit.

[0059] In a thirtieth aspect, the container is connected to the discharge conduit and said container is at the discharge pressure P1 .

[0060] In a thirtieth aspect, the container is connected to the return conduit and said container is at the return pressure PO.

[0061] In a thirty-first aspect, the container is in fluid communication with the box and the box is in fluid communication with the case. In a thirty-second aspect, the case, the box and the container are isolated from the external environment.

[0062] In a thirty-third aspect, said compression unit and / or said expansion unit comprises / e an auxiliary joint connecting the respective speed reducer with the respective motor or generator.

[0063] In a thirty-fourth aspect, the auxiliary joint is closed in a respective auxiliary casing. In a thirty-fifth aspect, the auxiliary casing is in fluid communication with the container and with the box.

[0064] In a thirty-sixth aspect, the auxiliary casing is in fluid communication with the auxiliary circuit.

[0065] In a thirty-seventh aspect, the auxiliary casing is connected to the discharge conduit and said auxiliary casing is at the discharge pressure P1 .

[0066] In a thirty-eighth aspect, said at least one chamber is separated by a single wall from the compression volume of the compressor or from the expansion volume of the expander and the discharge pressure P1 in said at least one chamber is greater than a working pressure PL within the compression volume of the compressor or the expansion volume of the expander (P1 >PL); optionally a ratio between the discharge pressure P1 and the working pressure PL is between 1 .01 and 2.

[0067] In a thirty-ninth aspect, said at least one auxiliary chamber is interposed between said at least one chamber and the compression volume of the compressor or the expansion volume of the expander.

[0068] In a fortieth aspect, at least one between the compressor and the expander is a turbomachine, the transmission organ is a rotating shaft, the moving mechanical organ is an impeller and said at least one chamber is bounded around the rotating shaft by walls of the case.

[0069] In a forty-first aspect, a ratio between the storage pressure Ps and the atmospheric pressure Patm is between 1 and 1.1.

[0070] In a forty-second aspect, a ratio between the discharge pressure P1 and the storage pressure Ps is between 1.01 and 2.

[0071] In a forty-third aspect, a ratio between the return pressure P0 and the storage pressure Ps is between 0.9 and 1 .5.

[0072] In a forty-fourth aspect, a ratio between the support pressure P2 the storage pressure Ps is between 0.9 and 1 .5. The above-indicated pressure ratios are all among absolute pressures.

[0073] As it can be noticed, all the organs of the machines (turbines, compressor, motor, generator, reducers, etc.) of the plant work at pressures close to the atmospheric / environmental one.

[0074] In a forty-fifth or aspect, the working fluid is chosen in the group comprising: CO2, SF6, N2O or a mixture thereof.

[0075] In a forty-sixth aspect, a temperature of the working fluid corresponding to the storage pressure Ps, i.e. of the working fluid in the variable volume of the storage device, is close to the or in equilibrium with the environmental temperature; optionally said temperature of the working fluid corresponding to the storage pressure Ps is between -40 °C and +70 °C, optionally between -10°C and + 45°C.

[0076] In a forty-seventh aspect, a temperature of the working fluid corresponding to the working pressure PL of the compressor, i.e. in the compression volume of the compressor is between 60 °C and 500 °C.

[0077] In a forty-eighth aspect, a temperature of the working fluid corresponding to the working pressure PL of the expander, i.e. in the expansion volume of the expander is between 60 °C and 500 °C.

[0078] In a forty-ninth aspect, a temperature of the working fluid corresponding to the return pressure P0 is between 20 °C and 150 °C.

[0079] In a fiftieth aspect, the storage device internally bounding the variable volume is e.g. a single- or double-membrane gasometer. The double-membrane gasometer comprises an internal membrane bounding the variable volume and containing the working fluid and an external membrane in contact with the environment; the external membrane keeps its own shape, excepting for small variations, with the purpose of protecting the internal membrane from the external environment and from the atmospheric agents.

[0080] In a fifty-first aspect, the working fluid is stored in the reservoir in liquid or supercritical phase with a temperature close to the critical temperature; wherein said critical temperature is close to the environmental temperature, preferably between 0°C and 100°C.

[0081] In a fifty-second aspect, the energy transformation and storage plant according to at least one of the preceding aspects performs or is configured to perform the following energy transformation and storage process: implementing the closed cyclic thermodynamic transformation (TTC), firstly in a direction in a storage configuration / phase and then in an opposite direction in a discharge configuration / phase, between the storage device internally bounding the variable volume and the reservoir, wherein in the storage phase the process accumulates heat and pressure and in the discharge phase it generates energy.

[0082] In a fifty-third aspect: in the storage phase, the working fluid, stored in the storage device internally bounding the variable volume, is: compressed, cooled down, storing sensible heat, condensed by making it transit through a saturated vapour area until reaching a liquid phase, storing latent heat in a secondary fluid, and stored in liquid phase in the reservoir with a temperature close to and lower than a critical temperature; in the discharge phase, said working fluid, stored in the reservoir in the liquid phase and at a temperature that is in equilibrium with a temperature of the secondary fluid, is: vaporized by making it transiting through the saturated vapor area until reaching the gaseous phase, receiving the latent heat through the cooling of the secondary fluid, heated by using the sensible heat stored during the storage phase, expanded, and stored in gaseous phase in the storage device internally bounding the variable volume.

[0083] In a fifty-fourth aspect, in each operating condition during the closed cyclic thermodynamic transformation (TTC), the working fluid is in pressure equilibrium with the atmosphere, with low or no overpressure, and the temperature of the secondary fluid is close to the environmental temperature.

[0084] In a fifty-fifth aspect, the energy transformation and storage plant is further configured to define / bound a closed circuit and implement a closed thermodynamic cycle (CT) in said closed circuit with at least one part of said working fluid, optionally while said plant is in the storage configuration or in the discharge configuration, as described in the document WO2021 / 191786. In a fifty-sixth aspect, the energy transformation and storage plant is of the type described in one of the public documents W02020 / 039416, WO2021 / 165809, WO2021 / 191786, WO2022 / 101727, in the name of the same Applicant.

[0085] Further features and advantages will be clearer from the detailed description of preferred, but not exclusive embodiments of an energy transformation and storage plant according to the present invention.

[0086] Description of drawings

[0087] This description will be shown below with reference to the attached drawings, provided for illustrative purposes only and, therefore, not limiting thereto, in which:

[0088] ■ Figure 1 shows an example of an energy transformation and storage plant according to the present invention;

[0089] ■ Figure 2 shows a schematization of the plant of figure 1 ;

[0090] ■ Figure 3 shows a portion of the plant of the preceding figures;

[0091] ■ Figure 4 shows a variant embodiment of the portion of the plant of figure 3;

[0092] ■ Figure 5 shows a further variant of the portion of figures 3 and 4.

[0093] Detailed description

[0094] With reference to the attached figures, with the reference number 200 it has been overall indicated an energy transformation and storage plant according to the present invention. This plant 200 may be realized according to one of the embodiments described in the public documents W02020 / 039416, WO2021 / 165809, WO2021 / 191786, WO2022 / 101727 in the name of the same Applicant.

[0095] The shown plant 200 operates with a working fluid other than atmospheric air, e.g. chosen in the group comprising: carbon dioxide CO2, sulphur hexafluoride SFe, nitrogen oxide N2O or a mixture thereof. The plant 200 is configured to implement a closed cyclic thermodynamic transformation (TTC), first in one direction in a storage configuration / phase and then in an opposite direction in a discharge configuration / phase, wherein in the storage configuration the plant 200 accumulates heat and pressure and in the discharge configuration it generates mechanical and / or electric energy. With reference to figure 1 , the plant 200 comprises an expander, e.g. a turbine 202, and a compressor 203 mechanically connected to a shaft of a moto-generator 204. The turbine 202 together with the moto-generator 204 when it operates in the function of generator form an expansion unit. The compressor 203 together with the moto-generator 204 when it operates in the function of motor form a compression unit. In embodiment variants, the turbine 202 is mechanically connected to a respective generator and the compressor 203 is mechanically connected to a respective motor, wherein motor and generator are two different machines.

[0096] The plant 200 comprises a storage device 205 that internally bounds a variable volume. In the shown and not limiting embodiment, this storage device 205 is defined by a double-membrane gasometer comprising an internal membrane 302 bounding the variable volume and containing the working fluid and an external membrane 301 in contact with the environment. The gasometer is arranged on the ground and is externally in contact with the atmospheric air. The internal membrane 302 of the gasometer internally bounds the above-mentioned variable volume that is configured to contain the working fluid at a storage pressure “Ps” equal to the atmospheric pressure or at a substantially atmospheric pressure. The working fluid contained in the variable volume is in pressure equilibrium with the atmosphere at each operational phase implemented by the plant. The external membrane 301 constantly keeps its own shape excepting for small variations, with the purpose of protecting the internal membrane from the external environment and from the atmospheric agents, such as sun, rain, wind, snow, etc. In the not limiting shown embodiment, the bounded gap between the internal membrane 302 and the external one 301 is filled with environmental air by means of a ventilator 303, schematically shown in figure 2, and a constant overpressure (with respect to the atmospheric pressure) of few millibar is kept. The storage pressure “Ps” is in this case equal to the atmospheric pressure plus the pressure of the air in the gap that serves to support the external membrane 301. The pressure in the gap is kept constant or substantially constant, so that the working fluid contained in the variable volume is in pressure equilibrium with the atmosphere at each operational phase implemented by the plant. The storage device 205 may also be realized as any other storage system of gas at low or no overpressure, wherein as the volume of the working fluid varies, the pressure is kept constant or substantially constant. First pipelines 206 develop between the storage device 205 and an inlet 203a of the compressor 203 and between the storage device 205 and an outlet 202b of the turbine 202 to put in fluid communication the internal volume of the storage device 205 with said compressor 203 and turbine 202. A valve or a valve system, not shown, may be operatively placed on the first pipelines 206 to alternatively put in fluid communication the storage device 205 with the inlet 203a of the compressor 203 or the outlet 202b of the turbine 202 with the storage device 205.

[0097] The plant 200 comprises a thermal accumulator 100 (Thermal Energy Storage - TES) which can be selectively put into fluid communication with an outlet 203b of the compressor 203 or with an inlet 202a of the turbine 202. For this purpose, second pipelines 208 develop between the inlet 202a of the turbine 202 and the thermal accumulator 100 and between the outlet 203b of the compressor 203 and the thermal accumulator 100.

[0098] The thermal accumulator 100 may comprise a primary heat exchanger and a thermal mass, e.g. solid or liquid, and allows to accumulate heat in said thermal mass.

[0099] A valve, or a valve system, not shown, is operatively located on the second pipelines

[0100] 208 to alternatively put in fluid communication the thermal accumulator 100 with the inlet 202a of the turbine 202 or the outlet 203b of the compressor 203 with the thermal accumulator 100.

[0101] A reservoir 209 is in fluid communication with the thermal accumulator 100 and is configured to accumulate the working fluid in liquid or supercritical phase at a temperature close to the critical temperature. The critical temperature of the working fluid is close to the environmental temperature and is preferably between 0°C and 100°C.

[0102] A secondary heat exchanger 210 is operatively active upwards of the reservoir 209 and is configured to operate on the working fluid in the storage phase in the reservoir 209.

[0103] Third pipelines 212 develop between the thermal accumulator 100 and the reservoir

[0104] 209 to put in fluid communication said thermal accumulator 100 with said reservoir 209 and with said secondary heat exchanger 210. Possibly, an upper portion of the reservoir 209 is connected, via connecting lines and a valve not shown, with the secondary heat exchanger 210 in order to recirculate the vapor to make room for the liquid.

[0105] The first, second and third pipelines 206, 208, 212 form a main circuit of the plant 200 which connects the variable volume of the storage device 205, a compression volume of the compressor 203, the thermal accumulator 100, the secondary heat exchanger 220, the reservoir 209 and an expansion volume of the turbine 202.

[0106] In the representation of figure 1 , the plant 200 comprises further an additional heat exchanger 213 operatively interposed between the storage device 205 and the compressor 202 and between the storage device 205e and the turbine 202. In alternative not shown embodiments, one additional heat exchanger is dedicated to the compressor 202 and one to the turbine 202.

[0107] A basin 2000 with a liquid, typically water, is connected with the secondary heat exchanger 210 and with the additional heat exchanger 213 and is coupled to a radiator 223 provided with fan 224.

[0108] The heat exchangers are configured to store thermal energy released by the working fluid in the thermal mass of the TES and in the liquid of the basin or to release thermal energy, previously stored, to the working fluid.

[0109] Appropriate devices (e.g. the above-mentioned valves controlled by a control unit) are configured to operate the plant 200 in the energy storage configuration / phase or in the energy discharge and generation configuration / phase via a displacement of the working fluid between the storage device 205 and the reservoir 209 through the main circuit and via a cyclic thermodynamic transformation of the working fluid. The plant is e.g. configured to implement the above-mentioned closed cyclic thermodynamic transformation according to what is described in the public documents W02020 / 039416, WO202 1 / 165809, WO2021 / 191786 and WO2022 / 101727.

[0110] In the storage configuration / phase, the working fluid coming from the storage device 205 is compressed in the compressor 203 and heats. The working fluid then flows through the thermal accumulator 100 that works as a cooler to remove heat from the compressed working fluid, cool it and accumulate the thermal energy (sensible heat) removed from said working fluid as heat in the thermal mass of the TES. The working fluid transfers heat to the liquid (secondary fluid) of the basin 2000 at the secondary heat exchanger 210, condenses and is accumulated in the reservoir 209. In the discharge configuration / phase, the working fluid coming from the reservoir 209 and already warmed by the secondary heat exchanger 210 passes through the primary heat exchanger of the thermal accumulator 100 that now works as a heater and transfers additional heat, previously accumulated in the incoherent material 19, to the working fluid and heats it. The working fluid vaporizes to then be introduced in the turbine 202. The working fluid determines the rotation of the impeller of the turbine 202 and the energy generation via the moto-generator 204 and then it is again stored in gaseous form in the variable volume of the device 205.

[0111] Figure 2 shows more schematically the plant of figure 1 wherein are visible: the storage device 205, a machine block 400 that comprises the compression unit and the expansion unit, a heat accumulation block 500 that comprises the thermal accumulator 100 (Thermal Energy Storage - TES), a working fluid accumulation block 600 that comprises the reservoir 209 and the secondary heat exchanger 210. In this figure 2 are also represented the first, second and third pipelines 206, 208, 212 of the main circuit.

[0112] The energy transformation and storage plant 200 can also be configured to define / bound a closed circuit and implement a closed thermodynamic cycle (CT) in said closed circuit with at least one part of the working fluid, as described in the document WO2021 / 191786. For this purpose, in figure 1 are represented: a supplementary heat exchanger 700 that receives heat from an additional heat source 705. The supplementary heat exchanger 700 is located between the inlet 202a of the turbine 202 and the thermal accumulator 100. The additional heat source 705 is, e.g., a solar source, industrial waste heat recovery (Waste Heat Recovery), exhaust heat from gas turbines.

[0113] A first bypass conduit 310 is configured to connect the outlet 203b of the compressor 203 with the supplementary heat exchanger 700 and bypass the thermal accumulator 100. The first bypass conduit is provided with a respective first valve 311 . A second bypass conduit 320 is configured to connect the outlet 202b of the turbine 202 with the inlet 203a of the compressor 203 and bypass the storage device 205. The second bypass conduit 320 is provided with a respective second valve 321. The first and the second bypass conduit 310, 320 are capable of bounding the closed circuit that comprises the compressor 203, the turbine 202, the additional heat exchanger 213 and the supplementary heat exchanger 700.

[0114] According to the present invention, the plant 200 comprises further an auxiliary circuit 1 which connects the main circuit and / or the variable volume of the storage device 205 and / or the compression volume of the compressor 203 and / or the expansion volume of the turbine 202 with at least one portion of the compression unit and / or of the expansion unit, so as to control a temperature and / or a pressure of said at least one portion through the same working fluid that circulates in the main circuit and that is used to implement the closed cyclic thermodynamic transformation (TTC). The plant 200 according to the invention therefore allows to perform a control method. This control method, which is also part of the invention, allows to control the temperature and / or the pressure of said at least one portion of the compression unit and / or of the expansion unit of the plant 200, and comprises: connecting, via the auxiliary circuit 1 , the main circuit and / or the variable volume of the storage device 205 and / or the compression volume of the compressor 203 and / or the expansion volume of the turbine 202 with said at least one portion of the compression unit and / or of the expansion unit. In the attached figures, the auxiliary circuit 1 is represented for simplicity with lines outside the machines but can also be obtained inside the machines themselves.

[0115] In figure 1 the auxiliary circuit 1 connects the compression unit and the expansion unit only with the variable volume of the storage device 205. In figure 2 is shown a more complex auxiliary circuit 1 that comprises discharge lines that extend from the main circuit and from the variable volume of the storage device 205 until the compression unit and the expansion unit.

[0116] In particular, the auxiliary circuit 1 of figure 2 comprises a first discharge conduit 2 which connects the variable volume of the storage device 205 with the machine block 400, a second discharge conduit 3 and a third discharge conduit 4 that connect the second pipelines 208 with the machine block 400, a fourth discharge conduit 5 which connects the third pipelines 212 with the machine block 400. Furthermore, a return conduit 6 connects the machine block 400 with the variable volume of the storage device 205 and an additional return conduit 7 connects the machine block 400 with the first pipelines 206. On the first discharge conduit 2 is operatively active a fan 8 (but can also be an auxiliary compressor) that has the function to increase the storage pressure “Ps” of the working fluid coming from the storage device 205 to a discharge pressure “P1”. Instead, the working fluid taken from the second discharge conduit 3, from the third discharge conduit 4 and from the fourth discharge conduit 5 is already at a pressure higher than the storage pressure “Ps”, so that it is not necessary the use of a fan or of an auxiliary compressor.

[0117] The discharge 2, 3, 4, 5 and return 6, 7 lines can be rigid or flexible, metallic or of other material, also composite, such as textile joints.

[0118] Figure 3 shows more in detail a turbomachine (that can be part of the expansion unit with the turbine 202 or of the compression unit with the compressor 203 of the plant of figure 1 or of the group machine 400 of figure 2) with the connections to the above-mentioned auxiliary circuit 1. For simplicity, it will be made reference below to the turbine 202, but the same description substantially applies to the compressor 203.

[0119] The turbomachine of figure 3 comprises a case 9, an impeller 10 connected to a rotating shaft 11 rotating in the case 9 around its own axis of rotation and supported by supports 12, e.g. bearings. The impeller 10 is configured to exchange energy with the working fluid in the respective expansion volume 13 of the turbine 202 that is in fluid communication, as above described, with the main circuit of the plant 200. The turbomachine of the embodiment of figure 3 further comprises a speed reducer 14. The speed reducer 14 can be used because usually the electric machine (motor, generator or moto-generator) to which the turbine or the compressor is connected usually works at 1500 rpm (4poles) or 3000 rpm (2poles), in case of network frequency at 50 Hz, or 1800 rpm or 3600 rpm, in case of network frequency at 60 [Hz] while the turbomachine reaches much higher rotation speeds. The rotating shaft 11 , that carries on its own end the above-mentioned impeller 10, is supported by the bearings that are installed in a box 15 of the speed reducer 14. The speed reducer 14 is mechanically interposed between the turbine 202 and the respective generator (not shown in figure 3). The speed reducer 14 comprises a first toothed wheel 16 keyed on the rotating shaft 11 and geared with a second toothed wheel 17 keyed on an auxiliary shaft 18 also supported in the box 15 by means of bearings. An end of the auxiliary shaft 18 comes out of the box 15 through a seal 19 and is connected to the not shown generator. The sealing element 19 is placed on the slow shaft (auxiliary shaft 18) of the speed reducer 14 and separates the environment inside the box 15 from an external environment.

[0120] The rotating shaft 11 , supported in the box 15 by bearings, develops from the box 15 until inside the case 9. A casing 20 connects the box 15 to the case 9 and surrounds the rotating shaft 11 so that the box 15 and the case 9 are with each other in fluid communication but isolated from the external environment. The impeller 10 is placed at a distal end of the rotating shaft 11 opposite to an end contained in the box 15 and is therefore supported overhanging with respect to the bearings.

[0121] Walls arranged in the case 9 and surrounding the rotating shaft 11 further bound annular chambers. A first wall separates the expansion volume 13 from an adjacent auxiliary chamber 21 that in turn is separated from an adjacent chamber 22 by a second wall. A third wall separates the chamber 22 from the casing 20. The auxiliary chamber 21 is then interposed between the chamber 22 and the expansion volume 13 of the turbine 202. Each of the walls has an its own radially internal edge close to the rotating shaft 11 so as to define an annular passage or restriction that puts adjacent chambers into communication.

[0122] The turbomachine of the embodiment of figure 3 comprises further a lubrication circuit 23 operatively connected to the supports 12 (bearings) in the box 15 and containing a lubrication oil. The lubrication circuit 23 comprises a closed vessel 24 for collecting the lubrication oil. The closed vessel 24 is connected, by means of an oil supply line 25 and an oil return line 26, to the box 15. A pump 27 is operatively arranged along the oil supply line and is configured to pump the lubrication oil to the supports placed in the box 15.

[0123] The first discharge conduit 2 is connected to the chamber 22 and connects it to a withdrawal point of the main circuit which is at the discharge pressure P1 or to the fan 8 and to the variable volume of the storage device 205. The working fluid that flows in the discharge conduit 2 is introduced in the chamber 22 with the above- mentioned discharge pressure “P1” that is greater than storage pressure “Ps” (P1 >Ps).

[0124] One of the return conduits 6 is connected to the auxiliary chamber 21 and connects it to the variable volume of the storage device 205 or to a point of the main circuit at a pressure less than the discharge pressure “P1”. The auxiliary chamber 21 is at a return pressure “P0” less than the discharge pressure “P1” (P0<P1 ) and also less than the working pressure “PL” within the expansion volume 13. The box 15 and the supports / bearings housed thereinto and also the lubrication circuit 23 are at a support pressure “P2” less than the discharge pressure “P1” (P2<P1 ) and greater than the return pressure “PO” (P2>P0). For example, a ratio between the storage pressure “Ps” and the atmospheric pressure “Patm” is between 1 and 1.1 , a ratio between the discharge pressure “P1” and the storage pressure “Ps” is between 1 .01 and 2, a ratio between the discharge pressure “P1” and the working pressure “PL” is between 1.01 and 2, a ratio between the return pressure “PO” and the storage pressure “Ps” is between 0.9 and 1 .5, a ratio between the support pressure “P2” the storage pressure “Ps” is between 0.9 and 1.5. The working fluid present in the expansion volume 13 drains therefore from the above-mentioned expansion volume 13 to the auxiliary chamber 21 and the working fluid in the chamber 22 drains from the chamber 22 to the auxiliary chamber 21. From the auxiliary chamber 21 , the working fluid is brought back in the main circuit and / or in the storage device 205 via the return conduit 6. The auxiliary circuit 1 therefore avoids spills of the working fluid from the expansion volume 13 toward the external environment and performs the function of thermal barrier, i.e. avoids that the heat of the working fluid present in the expansion volume can propagate to other elements of the turbomachine, such as bearings or seals.

[0125] For example, a temperature of the working fluid in the variable volume of the storage device is between 40 °C and 70 °C; a temperature of the working fluid in the compression volume of the compressor is between 60 °C and 500 °C; a temperature of the working fluid in the expansion volume of the expander is between 60 °C and 500 °C; a temperature of the working fluid corresponding to the return pressure P0 is between 20 °C and 150 °C.

[0126] One of the return conduits 6 is connected to a portion of the closed vessel 24 located above a free surface of the lubrication oil. A separator 28 is placed along the return conduit 6 connected to the closed vessel 24 and is configured to separate the lubrication oil adsorbed by the working fluid when the working fluid transits in the box 15. An oil recovery line 29 connects the separator 28 to the closed vessel 24 to reintroduce in the lubrication circuit 23 the oil that, in the separator 28, is separated from the working fluid. From the closed vessel 24, the working fluid that has been adsorbed by the lubrication oil is brought back in the main circuit and / or in the storage device 205 via the respective return conduit 6. The auxiliary circuit 1 therefore avoids spills of the working fluid from the lubrication circuit towards the external environment.

[0127] The embodiment of figure 4 differs from the turbomachine of figure 3 due to the fact that the rotating shaft 11 is not supported overhanging by the supports / bearings 12 of the box 15 but it is supported by supports / bearings 12 placed at opposite ends of the same rotating shaft 11 and located in the case 9 or adjacent to the case 9. The supports / bearings 12 are connected to the lubrication circuit 23. A chamber 22 and an auxiliary chamber 21 are symmetrically located on both sides of the impeller 10 and of the expansion volume 13. Further, the rotating shaft 11 is mechanically connected to a main shaft 30 of the respective speed reducer by means of a joint 31 , rigid or flexible, closed in the casing 20. In this case, the connection of the casing 20 with the discharge conduit 6 can also be useful to cool and remove the heat generated by the ventilation of the joint 31 .

[0128] Figure 5 shows another variant in which the turbine 202 and the speed reducer 14 are identical to those of the variant of figure 4. In this variant, the auxiliary shaft 18 of the speed reducer 14 is connected to a shaft 32 of the generator 204 via an auxiliary joint 33 closed in a respective auxiliary casing 34. The generator 204 is supported by respective supports / bearings 12 and housed in a container 35. The auxiliary casing 34, the supports / bearings 12 and the container 35 are in fluid communication with each other through restrictions but are isolated from the external environment. The supports / bearings 12 of the generator 204 are operatively connected to the lubrication circuit 23.

[0129] The first discharge conduit 2 is connected, in addition to the chambers 22, to the casing 20, to the auxiliary casing 34 and to a chamber of the generator 204 interposed between the supports / bearings 12 and the container 35. Therefore, the casing 20, the auxiliary casing 34 and the chamber of the generator 204 interposed between the supports / bearings 12 and the container 35 are at the discharge pressure “P1”. The return conduit 6 is connected, in addition to the auxiliary chambers 21 and to the closed vessel 24 of the lubrication circuit 23, also to the container 35. Therefore, the container 35 is at the return pressure P0 and the supports / bearings 12 are at the support pressure “P2”. In this case, spaces are pressurized between the generator 204 (or motor in case of the compressor) and the supports / bearings 12 at the discharge pressure “P1” and connects the generator storage device 205.

[0130] In other embodiment variants, not shown, the connections with the auxiliary circuit can be different from those of the examples shown above. For example, the container 35 is connected to the discharge conduit 6 and is at the discharge pressure “P1”, i.e. the generator 204 (or motor in case of the compressor, more generally: electric machine) is slightly pressurized at the discharge pressure “P1”.

[0131] In other embodiment variants, not shown in the attached figures, the structure of the turbomachine (compressor or expander) is easier than the one shown in the examples shown above.

[0132] For example, the supports / bearings 12 are placed in the case 9 of the turbomachine instead in the speed reducer 14 (that may also not be present) and / or the sealing element 19 is operatively coupled to the case 9 and to the rotating shaft 11 (in case the relative speeds and the sizes of the rotating shaft allow to mount the sealing element directly on said rotating shaft) and separates an environment within case 9 from an external environment. In this case, e.g., the chamber 22 bounded in the case 9 is in fluid communication with the sealing element 19 and / or with the supports / bearings 12 via a restriction.

[0133] For example, the sealing element is of the type of film liquid or double mechanical seal or wet-face mechanical seal. In case of the adoption of a liquid film mechanical seal, is present a feeding system of a barrier liquid to a barrier chamber that contains part of the mechanical seal and further confines with the chamber 22. This barrier chamber is connected to a separator that operates in a way similar to the separator of the lubrication circuit to separate any adsorbed working fluid from the barrier liquid and this separator can be connected to the auxiliary circuit 1 .

[0134] For example, the auxiliary chamber 21 is not present and the chamber 22 is adjacent to the expansion or compression volume 13 and connected to the discharge conduit 6.

[0135] For example, instead of the sealing element is present only the barrier chamber to create a barrier toward the external environment, with or without separator. The barrier chamber is connected to the feeding system of the barrier liquid, the auxiliary chamber 21 is interposed between the barrier chamber and the chamber 22 and is connected to a recovery system of the barrier fluid. The chamber 22 is at the discharge pressure “P1 ”, the auxiliary chamber 21 is at the pressure “P2”, the barrier chamber is at a barrier pressure “P3”, where P2<P1 , P3<P2 and P3>Patm.

[0136] For example, the supports / bearings are of magnetic or otherwise of a type such as not to request the lubrication circuit and the sealing organs. In this case, the auxiliary circuit can be used only to create a thermal barrier and to fix the pressure close to the pressure PS in the mechanical organs avoiding a pressure design of components that usually are not designed / built to work as pressurized organs (electrical machines, casing of bearings, etc, etc.).

[0137] List of elements

[0138] 1 auxiliary circuit

[0139] 2 first discharge conduit

[0140] 3 second discharge conduit

[0141] 4 third discharge conduit

[0142] 5 fourth discharge conduit

[0143] 6 return conduit

[0144] 7 additional return conduit

[0145] 8 fan

[0146] 9 case

[0147] 10 impeller

[0148] 11 rotating shaft

[0149] 12 supports

[0150] 13 expansion volume

[0151] 14 speed reducer

[0152] 15 box

[0153] 16 first toothed wheel

[0154] 17 second toothed wheel

[0155] 18 auxiliary shaft

[0156] 19 sealing element

[0157] 20 casing

[0158] 21 auxiliary chamber

[0159] 22 chamber

[0160] 23 lubrication circuit 24 closed vessel

[0161] 25 oil discharge line

[0162] 26 oil return line

[0163] 27 pump

[0164] 28 separator

[0165] 29 oil recovery line

[0166] 30 main shaft

[0167] 31 joint

[0168] 32 generator shaft

[0169] 33 auxiliary joint

[0170] 34 auxiliary casing

[0171] 35 container

[0172] 100 thermal accumulator

[0173] 200 plant

[0174] 202 turbine

[0175] 202a inlet of the turbine

[0176] 202b outlet of the turbine

[0177] 203 compressor

[0178] 203a inlet of the compressor

[0179] 203b outlet of the compressor

[0180] 204 moto-generator

[0181] 205 storage device

[0182] 206 first pipelines

[0183] 208 second pipelines

[0184] 209 reservoir

[0185] 210 secondary heat exchanger

[0186] 212 third pipelines

[0187] 213 additional heat exchanger

[0188] 223 radiator

[0189] 224 fan

[0190] 301 external membrane

[0191] 302 internal membrane

[0192] 303 ventilator 310 first bypass conduit

[0193] 311 first valve

[0194] 320 second bypass conduit

[0195] 321 second valve 400 machine block

[0196] 500 heat storage block

[0197] 600 working fluid storage block

[0198] 700 supplementary heat exchanger

[0199] 705 additional heat source 2000 basin

Claims

CLAIMS1 . Energy transformation and storage plant, comprising: a working fluid other than atmospheric air; a storage device (205) internally bounding a variable volume and configured to store the working fluid in gaseous phase and with a storage pressure (Ps) in pressure equilibrium with the atmosphere, with low or no overpressure, at each operational phase implemented by the plant; at least one reservoir (209) configured to store the working fluid in liquid or supercritical phase; a compression unit comprising at least one compressor (203) and at least one motor mechanically connected to each other; an expansion unit comprising at least one expander (202) and at least one generator mechanically connected to each other; at least one thermal accumulator (100, 210); a main circuit connecting the variable volume of the storage device (205), a compression volume of the compressor (203), said at least one thermal accumulator (100, 210), said at least one reservoir (209) and an expansion volume of the expander (202); devices configured to operate the plant in an energy storage configuration or in an energy discharge and generation configuration by a displacement of the working fluid between the storage device (205) and said at least one reservoir (209) through the main circuit and by a cyclic thermodynamic transformation of said working fluid; wherein the plant comprises further an auxiliary circuit (1 ); the auxiliary circuit (1 ) connecting at least one portion of the compression unit and / or of the expansion unit with at least one among the main circuit, the variable volume of the storage device (205), the compression volume of the compressor (203), the expansion volume of the expander (202); the auxiliary circuit (1 ) being configured to control a temperature and / or a pressure of said at least one portion exploiting the same working fluid taken from the cyclic thermodynamic transformation.

2. Plant according to claim 1 , wherein said at least one compressor (203) and said at least one expander (202) comprise each: a case (9); at least one moving mechanical organ movable relative to the case (9) and configured to exchange energy with the working fluid in the respective compression volume of the compressor (203) or in the respective expansion volume of the expander (202); at least one transmission organ connecting the moving mechanical organ with the respective motor or generator; wherein said at least one portion comprises at least one chamber (22) bounded between the case (9) and said at least one transmission organ, wherein said at least one chamber (22) is located near the compression volume of the compressor (203) or the expansion volume of the expander (202).

3. Plant according to claim 2, wherein said at least one compressor (203) and / or said at least one expander (202) comprises / e at least one sealing element (19) operatively coupled to the case (9) and to the transmission organ and separating an environment within case (9) from an external environment; wherein said at least one chamber (22) is in fluid communication with said at least one sealing element (19), optionally via a restriction.

4. Plant according to claim 2 or 3, wherein said at least one compressor (203) and / or said at least one expander (202) comprises / e supports (12) operatively interposed between the respective transmission organ and the respective case (9); wherein said at least one chamber (22) is in fluid communication with said supports (12), optionally via a restriction.

5. Plant according to one of claims 1 to 4, wherein the auxiliary circuit (1 ) comprises: at least one discharge conduit (2, 3, 4, 5) extending from the main circuit and / or from the variable volume of the storage device (205) to said at least one portion of the compression unit and / or of the expansion unit and configured to feed the working fluid into said at least one portion of the compression unit and / or of theexpansion unit with a discharge pressure (P1 ) greater than the storage pressure (Ps); and / or at least one return conduit (6, 7) extending from said compression unit and / or from said expansion unit to the variable volume at the storage pressure (Ps) or to a point of the main circuit at a pressure less than the discharge pressure (P1 ).

6. Plant according to claim 5, wherein said at least one discharge conduit (2, 3, 4, 5) connects a withdrawal point of the main circuit, which is at the discharge pressure (P1 ), to said at least one portion of the compression unit and / or of the expansion unit; and / or wherein said at least one discharge conduit (2, 3, 4, 5) connects the variable volume to said at least one portion of the compression unit and / or of the expansion unit and comprises a fan or an auxiliary compressor (8) configured to increase the storage pressure (Ps) of the working fluid coming from the variable volume to the discharge pressure (P1 ).

7. Plant according to claim 6, wherein the main circuit comprises: first pipelines (206) connecting the storage device (205) with the compression unit and with the expansion unit; and second pipelines (208) connecting said at least one reservoir (209) with the compression unit and with the expansion unit, said at least one thermal accumulator (100, 210) being operatively coupled to the second pipelines (208) and / or to said at least one reservoir (209); wherein the withdrawal point is located on the second pipelines (208), between said at least one reservoir (209) and said at least one thermal accumulator (100, 210) and / or between said at least one thermal accumulator (100, 210) and the compression unit or the expansion unit.

8. Plant according to one of claims 5 to 7, wherein said at least one return conduit (6, 7) extends from at least one auxiliary chamber (21 ) of said compression unit and / or of said expansion unit, wherein said at least one auxiliary chamber (21 ) is at a return pressure (P0) less than the discharge pressure (P1 ).

9. Plant according to one of claims 5 to 8 when claim 5 depends on 4, wherein the supports (12) are connected to said at least one chamber (22) through a restriction and are at a support pressure (P2) less than the discharge pressure (P1 ); wherein said support pressure (P2) is greater than the return pressure (PO); wherein the compression unit and / or the expansion unit comprises / e a lubrication circuit (23) operatively connected to the supports (12) and containing a lubrication oil, wherein the lubrication circuit (23) is at the support pressure (P2) and is connected to said at least one return conduit (6, 7); wherein the lubrication circuit (23) comprises a pump (27), configured to pump the lubrication oil to the supports (12), and a closed vessel (24) for the collection of the lubrication oil; wherein a portion of the closed vessel (24) located above a free surface of the lubrication oil is connected to said at least one return conduit (6, 7).

10. Plant according to claim 9, wherein said compression unit and / or said expansion unit comprises / e at least one speed reducer (14) mechanically interposed between the transmission organ of the compressor (203) and / or of the expander (202) and the respective motor or generator; wherein said at least one speed reducer (14) comprises: a box (15), moving organs mounted in the box (15) and supports (12) interposed between said moving organs and the box (15); wherein the box (15) is in fluid communication with said at least one chamber (22); wherein the box (15) is connected to the lubrication circuit (23).11 . Plant according to one of claims 9 or 10, wherein at least one between the motor and the generator comprises supports (12) and said supports (12) are at said support pressure (P2); wherein the supports (12) of at least one between the motor and the generator are operatively connected to the lubrication circuit (23).

12. Plant according to one of claims 5 to 9 when claim 5 depends on one of claims 2 to 4, wherein said compression unit and / or said expansion unit comprises / e a container (35) containing the respective motor or generator; wherein the container (35) is in fluid communication with the case (9) and wherein the case (9) and the container (35) are isolated from the external environment; wherein the container (35) is in fluid communication with the auxiliary circuit (1 ); wherein the container (35)is connected to the discharge conduit (6, 7) and said container (35) is at the discharge pressure (P1 ).

13. Plant according to one of claims 5 to 12 when claim 5 depends on one of claims 2 to 4, wherein said at least one chamber (22) is separated by a single wall from the compression volume of the compressor (203) or from the expansion volume of the expander (202) and the discharge pressure (P1 ) in said at least one chamber (22) is greater than a working pressure (PL) within the compression volume of the compressor (203) or of the expansion volume of the expander (202); wherein said at least one auxiliary chamber (21 ) is interposed between said at least one chamber (22) and the compression volume of the compressor (203) or the expansion volume of the expander (202).

14. Plant according to one of claims 2 to 4 or according to one of claims 5 to 13 when claim 5 depends on one of claims 2 to 4, wherein: at least one between the compressor (203) and the expander (202) is a turbomachine; the transmission organ is a rotating shaft (11 ); the moving mechanical organ is an impeller (10); said at least one chamber (22) is bounded around the rotating shaft (11 ) by walls of the case (9).

15. Method for controlling a temperature and / or a pressure of said at least one portion of the compression unit and / or of the expansion unit of the plant according to at least one of the preceding claims 1 to 14, comprising: connecting, via the auxiliary circuit (1 ), the main circuit and / or the variable volume of the storage device (205) and / or the compression volume of the compressor (203) and / or the expansion volume of the expander (202) with said at least one portion of the compression unit and / or of the expansion unit.

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