Process and plant for energy storage and release

Abstract

A process comprises: implementing a closed thermodynamic cyclic transformation (TTC), first in one direction in a storage phase and then in an opposite direction in a release phase, between an enclosure (2) for storing a working fluid other than atmospheric air in the gaseous phase and in pressure equilibrium with the atmosphere, and a reservoir (6) for storing said working fluid in liquid or super-critical phase. The storage phase comprises: A-B preheating the working fluid coming from the enclosure (2); B-C compressing the working fluid a first time using external energy to be stored; C-D removing a first amount of heat (Q1) from the working fluid to cool it a first time and storing the first amount of heat (Q1); D-E further cooling the working fluid by removing excess heat (QE) from the working fluid; E-F compressing the working fluid a second time using additional external energy to be stored; F-G removing a second amount of heat (Q2) from the working fluid to cool it a second time and storing the second amount of heat (Q2); G-H removing a third amount of heat Q3 from the working fluid to increase a density of the working fluid, storing the third amount of heat Q3, and storing the working fluid in the reservoir (6) in liquid or super-critical phase. At least part of the excess heat QE removed in the sub-phase D-E is recovered and used in the sub-phase A-B to preheat the working fluid from the enclosure (2).

Description

[0001] “Process and plant for energy storage and release”

[0002] DESCRIPTION

[0003] Field of the finding

[0004] The present invention has as its object a process and a plant for energy storage and release.

[0005] By energy storage and release plants and processes are intended plants and processes capable of absorbing, storing, transforming, and generating energy, i.e., plants and processes capable of absorbing / using energy, maintaining the stored energy over time and capable of transforming it back into available energy, for example, electrical, thermal, and mechanical energy.

[0006] In particular, the present invention relates to a process and plant for energy storage and release capable of containing the costs of implementing the plant while maintaining or increasing the efficiency of the process compared to known plants / processes.

[0007] Definitions

[0008] In the present description and in the attached claims reference will be made to the following definitions.

[0009] • 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.

[0010] • 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 storages / accumulations of the working fluid, within the cycle, significant for energy purposes.

[0011] • Closed CT and / or TTC: without mass exchange (significant for energy purposes) with the atmosphere. • Open CT and / or TTC: with mass exchange (significant for energy purposes) with the atmosphere.

[0012] • Light over-pressure: pressure above atmospheric pressure with a pressure difference with respect to atmospheric pressure of a few millibars up to a few tens of millibars, for example from 3 to 4 mbar up to 70 to 80 mbar.

[0013] Background of the finding

[0014] The public document W02020 / 039416A1 , on behalf of the same Applicant, shows a process and a plant for energy storage. The plant comprises an enclosure 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 super-critical 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 enclosure and the reservoir. In the storage configuration the plant stores heat and pressure and in the discharge configuration it generates energy.

[0015] The public document WO2021191786A1 , on behalf of the same Applicant, shows a process and a plant similar to the ones described in the preceding document. This plant is also configured to define a closed circuit and implement a closed thermodynamic cycle in the closed circuit with at least part of the working fluid. This document also shows the multi-phase compression with subseguent cooling of the working fluid and heat accumulations in respective accumulators and the multiphase expansion preceded by respective reheatings of the working fluid by means of the previously accumulated heat.

[0016] Summary

[0017] The Applicant noted that compression performed in a single phase, as for example described in W02020 / 039416A1 , reguires reaching very high maximum pressures and thus storing the working fluid in the liguid or supercritical phase at such high pressures, minus the loading pressure drops. The reservoir(s) dedicated to the storage of the working fluid under such conditions must be sized accordingly to withstand such pressures and therefore the costs for its manufacturing, in particular material costs, and also for transportation to the installation site are significant.

[0018] The Applicant noted also that dividing the compression into multi-phases followed by respective heat accumulations allows to reduce the maximum pressures at the end of each compression and thus the storage pressures in the reservoir, with consequent reduction in the costs of making and transporting it. However, this also leads to a reduction in the efficiency of the process.

[0019] The Applicant, therefore, aimed at designing and implementing a plant and process of the type described above that allow to reduce the production and installation costs of the plant, with the same size i.e. , the capacity to store and release energy, and at the same time to ensure a high efficiency, at least equal to the one obtained with a single compressor and a single compression phase.

[0020] The Applicant has found that the above mentioned objectives can be achieved by adopting a process and plant for energy storage and release in which, in the energy storage configuration, the working fluid is compressed and cooled several times and, during the cooling, some of the heat is recovered to preheat the working fluid exiting the enclosure in which it is contained in pressure equilibrium with the atmosphere.

[0021] In particular, the indicated objectives and others are substantially reached by a process and a plant for energy storage and release of the type claimed in the attached claims and / or described in the following aspects.

[0022] In a first independent aspect, the present invention refers to a process for energy storage and release, comprising: implementing a closed thermodynamic cyclic transformation (TTC), first in one direction in a storage phase and then in an opposite direction in a release phase, between an enclosure for storing a working fluid other than atmospheric air in gas phase and in pressure equilibrium with the atmosphere, and a reservoir for storing said working fluid in liquid or super-critical phase; wherein in the storage phase the process accumulates heat and potential energy in the form of pressure and in the release phase the process generates energy. The working fluid has a critical temperature, intended as temperature of the relative critical point, between 0°C and 100°C. The storage phase comprises the following sub-phases: (A-B) preheating the working fluid coming from the enclosure (2); (B-C) compressing the working fluid a first time using external energy to be stored; (C-D) removing a first amount of heat from the working fluid to cool it a first time and storing said first amount of heat; (D-E) further cooling the working fluid by removing excess heat from the working fluid; (E-F) compressing the working fluid a second time using additional external energy to be stored; (F-G) removing a second amount of heat from the working fluid to cool it a second time and storing said second amount of heat; (G-H) removing a third amount of heat from the working fluid to increase a density of the working fluid, storing the third amount of heat and storing the working fluid in the reservoir in liquid or super-critical phase. At least part of said excess heat removed in (D-E) is recovered and used in (A-B) to preheat the working fluid from the enclosure.

[0023] In a second independent aspect, the present invention refers to a plant for energy storage and release, comprising: a working fluid other than atmospheric air and having a critical temperature between 0°C and 100°C; an enclosure configured to contain the working fluid in gas phase and in pressure equilibrium with the atmosphere; a reservoir configured to contain the working fluid in liquid or supercritical phase; a first compressor and a second compressor in fluid connection with each other in series and operatively interposed between the enclosure and the reservoir; a first expander and a second expander in fluid connection with each other in series and operatively interposed between the enclosure and the reservoir, wherein the first compressor and the second compressor are placed in parallel with respect to the first expander and the second expander; a first thermal accumulator in fluid connection, on one side, with the first compressor and the second expander and, on an opposite side, with the first expander and the second compressor, wherein the first thermal accumulator is configured to exchange a first amount of heat with the working fluid and store or release said first amount of heat; a second thermal accumulator in fluid connection, on one side, with the first expander and the second compressor, wherein the second thermal accumulator is configured to exchange a second amount of heat with the working fluid and store or release said second amount of heat; a third thermal accumulator in fluid connection, on one side, with the second thermal accumulator and, on an opposite side, with the reservoir, wherein the third thermal accumulator is configured to exchange a third quantity of heat with the working fluid and store or release said third quantity of heat; connecting ducts between the enclosure, the reservoir, the first compressor, the second compressor, the first expander, the second expander, the first thermal accumulator, the second thermal accumulator, the third thermal accumulator. The plant operates in an energy storage configuration and / or in an energy release configuration. In the energy storage configuration, the working fluid transits from the enclosure to the reservoir through the first compressor, the first thermal accumulator, the second compressor, the second thermal accumulator, the third thermal accumulator and is stored in the reservoir. In the energy release configuration, the working fluid transits from the reservoir to the enclosure through the third thermal accumulator, the second thermal accumulator, the first expander, the first thermal accumulator, the second expander and is again stored in the enclosure, wherein in the storage configuration the plant accumulates heat and potential energy in the form of pressure and in the release configuration the plant generates energy. The plant also comprises a heat transfer device operatively coupled to the connecting ducts located upstream of the first compressor and upstream of the second compressor. The heat transfer device is configured to remove excess heat from the working fluid entering the second compressor and to transfer at least part of said excess heat to the working fluid entering the first compressor.

[0024] In an aspect, the process of the second aspect is implemented through the plant of the first aspect and / or the plant of the first aspect is configured to carry out the process of the second aspect.

[0025] The Applicant has verified that the process and plant according to the invention allow to achieve the predetermined objectives and more.

[0026] The Applicant has first of all verified that the process and plant according to the invention allow to contain the costs of manufacturing the reservoir(s) in which the working fluid is stored in liquid or super-critical phase, because the compression performed in several phases, followed by respective cooling, allows to reduce the internal pressure of the reservoir(s) and thus to reduce the wall thickness and / or the cost of the material needed to withstand this pressure.

[0027] The Applicant has also verified that this allows to reduce the production and installation costs of the plant as a whole (with the same capacity to store and release energy). The Applicant has also verified that the process and plant according to the invention, thanks to at least partial recovery of excess heat, ensure a high efficiency and an overall high enthalpy jump.

[0028] Further aspects of the process and plant of the invention are listed below. These aspects can be combined with each other and with the process and / or plant of the first and second aspect and / or with the process and / or plant of the attached claims. In an aspect, the recovery of excess heat and preheating of the working fluid from the enclosure are implemented by means of a heat transport fluid operating in a closed circuit. The heat transport fluid absorbs the excess heat from the working fluid in (D-E) and gives said at least part to the working fluid in (A-B).

[0029] The Applicant has verified that the heat exchange described herein is implementable through a relatively simple circuit.

[0030] In an aspect, the heat transfer device comprises: a first heat exchanger placed between the enclosure and the first compressor. In an aspect, the heat transfer device comprises: a second heat exchanger placed between the first heat accumulator and the second compressor. In an aspect, the heat transfer device comprises: a closed circuit extending between the first heat exchanger and the second heat exchanger. In an aspect, the heat transfer device comprises: a heat transport fluid circulating in the closed circuit.

[0031] In an aspect, the heat transport fluid is chosen from the group including: water, water and glycol, oil.

[0032] In an aspect, it is expected to cool and / or heat the heat transport fluid after that said heat transport fluid has absorbed the excess heat from the working fluid in (D-E) and before giving the excess heat to the working fluid in (A-B).

[0033] In an aspect, it is expected to cool and / or heat the heat transport fluid after that said heat transport fluid has given the excess heat to the working fluid in (A-B) and before absorbing the excess heat from the working fluid in (D-E).

[0034] In an aspect, the heat transport fluid absorbs the excess heat from the working fluid through a second heat exchanger operating on the closed circuit.

[0035] In an aspect, the heat transport fluid gives said at least part of the excess heat to the working fluid through a first heat exchanger operating on the closed circuit. In an aspect, the heat transfer device comprises also a cooler and / or a heater operatively active on a first branch of the closed circuit, in said first branch the heat transport fluid flowing from the second heat exchanger to the first heat exchanger.

[0036] In an aspect, the heat transfer device comprises also a cooler and / or a heater operatively active on a second branch of the closed circuit, in said second branch the heat transport fluid flowing from the first heat exchanger to the second heat exchanger.

[0037] In an aspect, cooling the heat transport fluid comprises: disposing excess heat to the external environment.

[0038] In an aspect, heating the heat transport fluid comprises: absorbing auxiliary heat from an external heat source.

[0039] In an aspect, the cooler comprises a first auxiliary heat exchanger interfaced with the external environment.

[0040] In an aspect, the heater comprises a second auxiliary heat exchanger interfaced with an external heat source.

[0041] In an aspect, the cooler comprises a fan coupled to the first auxiliary heat exchanger. In an aspect, the external heat source comprises a cooling circuit configured to remove heat generated by at least one of the first compressor, the second compressor, the first expander, and the second expander due to mechanical and / or electrical inefficiencies.

[0042] The Applicant has verified that the cooling and / or heating operated on the closed circuit allow to adjust accurately the temperature of the working fluid at the inlet of the first and second compressor, i.e., before the first compression and before the second compression.

[0043] In an alternative aspect, the recovery of said at least part of the excess heat and the preheating of the working fluid from the enclosure are implemented by means of a direct exchange of said at least part of the excess heat between the working fluid in (D-E) and the working fluid (A-B), i.e. without any intermediate heat transport fluid.

[0044] In an aspect, said at least part of the excess heat is exchanged through a heat exchanger.

[0045] In an aspect, the heat transfer device comprises a heat exchanger coupled to connecting ducts of the working fluid entering the first compressor and to connecting ducts of the working fluid exiting the first thermal accumulator. The Applicant has verified that this solution, which adopts a single exchanger without any intermediate fluid and circuit, allows to contain the plant's footprint and possibly also costs.

[0046] In an aspect, a temperature of the working fluid in the enclosure (A) is equal to an ambient temperature, for example, 20 °C.

[0047] In an aspect, a pressure of the working fluid in the enclosure (A), in pressure equilibrium with the atmosphere, is approximately equal to an ambient pressure, for example, 1 bar.

[0048] In an aspect, a temperature of the working fluid in the storage phase and after preheating it (B) is between 40°C and 60°C, optionally between 45°C and 55°C. The pressure is still approximately equal to the ambient pressure.

[0049] In an aspect, a pressure of the working fluid in the storage phase and after compressing it the first time (C) is between 15 bar and 35 bar, optionally between 20 bar and 30 bar.

[0050] In an aspect, a temperature of the working fluid in the storage phase and after compressing it the first time (C) is between 300 °C and 500 °C, optionally between 350 °C and 450 °C.

[0051] In an aspect, a temperature of the working fluid in the storage phase and after cooling it the first time (D) is between 50°C and 70°C, optionally between 55°C and 65°C. The pressure in (D), unless pressure drops, is the same as the pressure in (C).

[0052] In an aspect, a temperature of the working fluid in the storage phase and after further cooling it (E) is between 35°C and 55°C, optionally between 40°C and 50°C. The pressure in (D), unless pressure drops, is the same as the pressure in (C).

[0053] In an aspect, a pressure of the working fluid in the storage phase and after compressing it the second time (F) is less than a critical pressure of said working fluid and removing the third amount of heat from the working fluid comprises: condensing the working fluid (G-H).

[0054] In an aspect, if a pressure of the working fluid exiting the second compressor is less than a critical pressure of said working fluid, the third thermal accumulator works as a condenser in the energy storage configuration and as an evaporator in the energy release configuration. In an aspect, the pressure of the working fluid in the storage phase and after compressing it the second time (F) is less than said critical pressure and between 25 bar and 70 bar, optionally between 40 bar and 55 bar.

[0055] In an aspect, a temperature of the working fluid in the storage phase and after having compressed it the second time (F) is between 90 °C and 110 °C, optionally between 95 °C and 105 °C.

[0056] In an aspect, the temperature of the working fluid in the storage phase and after cooling it the second time (G) is between 5°C and 30°C, optionally between 10°C and 20°C. The pressure in (G), unless pressure drops, is the same as the pressure in (F).

[0057] In an aspect, a temperature and a pressure of the working fluid after the condensation (H) are the same as in (G).

[0058] In an aspect, a pressure of the working fluid in the storage phase and after compressing it the second time (F) is greater than or equal to a critical pressure of said working fluid and removing the third amount of heat from the working fluid comprises: cooling the working fluid (G-H).

[0059] In an aspect, after the cooling it is expected to liquefy the working fluid (H-H’).

[0060] In an aspect, if a pressure of the working fluid exiting the second compressor is greater than or equal to a critical pressure of said working fluid, the third thermal accumulator works as a cooler in the energy storage configuration and as a heater in the energy release configuration.

[0061] In an aspect, a lamination valve or a two-phase expansion turbine is interposed between the third thermal accumulator and the reservoir.

[0062] In an aspect, a pump is operatively interposed between the reservoir and the third thermal accumulator.

[0063] In an aspect, the pressure of the working fluid in the storage phase and after compressing it the second time (F) is greater than or equal to said critical pressure and between 75 bar and 140 bar, optionally between 90 bar and 110 bar.

[0064] In an aspect, a temperature of the working fluid in the storage phase and after compressing it the second time (F) is between 160 °C and 190 °C, optionally between 170 °C and 180 °C.

[0065] In an aspect, the temperature of the working fluid in the storage phase and after cooling it the second time (G) is between 30°C and 50°C, optionally between 35°C and 45°C. The pressure in (G), unless pressure drops, is the same as the pressure in (F).

[0066] In an aspect, a temperature of the working fluid in the storage phase and after removing the third amount of heat (H) is between 20°C and 40°C, optionally between 25°C and 35°C. The pressure in (H), unless pressure drops, is the same as the pressure in (F).

[0067] In an aspect, a temperature of the working fluid in the storage phase and after the liquefaction (H’) is between 15 °C and 35 °C, optionally between 20 °C and 30 °C.

[0068] In an aspect, a pressure of the working fluid in the storage phase and after the liquefaction (H’) is between 70 bar and 130 bar, optionally between 80 bar and 100 bar.

[0069] In an aspect, the release phase comprises: (l-L) extracting the working fluid from the reservoir and bringing it into the gas phase by giving to the working fluid the third amount of heat previously stored.

[0070] In an aspect, the release phase comprises: (L-M) giving to the working fluid the second amount of heat previously stored, to heat it a first time.

[0071] In an aspect, the release phase comprises: (M-N) making the working fluid expand a first time to release energy.

[0072] In an aspect, the release phase comprises: (N-O) giving to the working fluid the first amount of heat previously stored, to heat it a second time.

[0073] In an aspect, the release phase comprises: (O-P) making the working fluid expand a second time to release additional energy.

[0074] In an aspect, the release phase comprises: (P-Q) removing an additional amount of heat from the working fluid.

[0075] In an aspect, the release phase comprises: returning the working fluid to the enclosure in the gas phase and in pressure equilibrium with the atmosphere.

[0076] At the end of the release phase, the working fluid is returned to the initial conditions inside the enclosure.

[0077] In an aspect, a third heat exchanger is operatively interposed between the second expander and the enclosure. In the energy release configuration, the third heat exchanger is configured to remove an additional amount of heat from the working fluid. In an aspect, a temperature of the working fluid in the release phase and after expanding it the first time (N) is greater than a temperature of the working fluid in the storage phase and after compressing it the first time (E) and close to or equal to a temperature of the working fluid in the storage phase and after cooling it the first time (D).

[0078] In an aspect, a temperature of the working fluid in the release phase and after that the second amount of heat has been given to the working fluid (M) is close to or equal to a temperature of the working fluid in the storage phase and after pressing it the second time (F).

[0079] In an aspect, a temperature of the working fluid in the release phase and after that the first amount of heat has been given to the working fluid (O) is close or equal to a temperature of the working fluid in the storage phase and after pressing it the first time (C).

[0080] In an aspect, a temperature of the working fluid in the release phase and after expanding it the first time (N) is between 55 °C and 75 °C, optionally between 60 °C and 70 °C.

[0081] In an aspect, a pressure of the working fluid in the release phase and after expanding it the first time (N) is between 15 bar and 35 bar, optionally between 20 bar and 30 bar.

[0082] In an aspect, a temperature of the working fluid in the release phase and after that the first amount of heat has been given to the working fluid (O) is between 300°C and 500°C, optionally between 350°C and 450°C. The pressure in (O), unless pressure drops, is the same as the pressure in (N).

[0083] In an aspect, a temperature of the working fluid in the release phase and after expanding it the second time (P) is between 80 °C and 120 °C, optionally between 90 °C and 110 °C.

[0084] In an aspect, a pressure of the working fluid in the release phase and after expanding it the second time (P) is equal to the ambient pressure, for example 1 bar.

[0085] In an aspect, a temperature of the working fluid in the reservoir and at the beginning of the release phase (I) is between 5 °C and 30 °C, optionally between 10 °C and 20 °C. In an aspect, a pressure of the working fluid in the reservoir and at the beginning of the release phase (I) is between 25 bar and 70 bar, optionally between 40 bar and 55 bar.

[0086] In an aspect, bringing the working fluid into the gas phase comprises: evaporating the working fluid (l-L).

[0087] In an aspect, a temperature and a pressure of the working fluid after the evaporation (L) are the same as in (I).

[0088] In an aspect, a temperature of the working fluid in the release phase and after that the second amount of heat (M) has been given to the working fluid is between 90°C and 110°C, optionally between 95°C and 105°C. The pressure in (M), unless pressure drops, is the same as the pressure in (L).

[0089] In an aspect, extracting the working fluid from the reservoir comprises: pumping the working fluid to increase pressure and temperature and returning it in the supercritical phase (I’-l).

[0090] In an aspect, a temperature of the working fluid in the release phase and after the pumping (I) is between 20 °C and 40 °C, optionally between 25 °C and 35 °C.

[0091] In an aspect, a pressure of the working fluid in the release phase and after the pumping (I) is between 75 bar and 140 bar, optionally between 90 bar and 110 bar. In an aspect, a temperature of the working fluid in the release phase and after that the third amount of heat (L) has been given to the working fluid is between 30°C and 50°C, optionally between 35°C and 40°C. The pressure in (L), unless pressure drops, is the same as the pressure in (I).

[0092] In an aspect, a temperature of the working fluid in the release phase and after that the second amount of heat has been given to the working fluid (M) is between 160°C and 190°C, optionally between 170°C and 180°C. The pressure in (M), unless pressure drops, is the same as the pressure in (L).

[0093] In an aspect, the compressions with subsequent coolings by removal and accumulation of amounts of heat can be more than two.

[0094] In a aspect, the expansions with subsequent heatings by giving the amounts of heat previously stored can be more than two.

[0095] In an aspect, the working fluid is carbon dioxide (CO2) or comprises carbon dioxide (CO2) or is a mixture comprising carbon dioxide as the main component. Alternatively, the working fluid is chosen from the group comprising: mixtures of carbon dioxide (CO2) and other substances (for the purpose of correcting the critical temperature of the working fluid), SFe, N2O or their mixtures.

[0096] In an aspect, the enclosure has the structure of a gasometer internally delimiting a variable volume containing the working fluid in pressure equilibrium with the atmosphere.

[0097] In an aspect, the enclosure is of the single- or double-membrane type.

[0098] In an aspect, the single-membrane enclosure comprises a membrane externally in contact with the environment and internally delimiting a variable volume containing the working fluid; the membrane deforms in accordance with the amount of working fluid contained in the variable volume in such a way as to maintain constant a pressure of the working fluid contained in said variable volume.

[0099] In an aspect, the double-membrane enclosure comprises an inner membrane internally delimiting a variable volume containing the working fluid and an outer membrane in contact with the environment; the outer membrane maintains its shape, unless small variations, with the purpose of protecting the inner membrane from the external environment and weathering; the inner membrane deforms in accordance with the amount of working fluid contained in the variable volume in such a way as to maintain a constant pressure of the working fluid contained in said variable volume.

[0100] In an aspect, a cavity delimited between the inner membrane and the outer membrane is filled with ambient air by fans and a constant pressure of a few millibars is maintained, optionally from 2 mbar to 50 mbar.

[0101] In an aspect, the plant comprises a plurality of reservoirs configured to contain the working fluid in liquid or super-critical phase.

[0102] In an aspect, the reservoir or each reservoir is made of metal, optionally steel, optionally carbon steel.

[0103] In an aspect, the first thermal accumulator comprises a container containing inert solid material configured to retain heat given by the working fluid or to give up heat to the working fluid.

[0104] In an aspect, the first thermal accumulator is a “pressurized packed bed thermal store”. In an aspect, the second thermal accumulator comprises a container containing water, optionally at a pressure of less than 10 bar, optionally less than 5 bar, optionally at atmospheric pressure.

[0105] In an aspect, the third thermal accumulator comprises a container containing water, optionally at atmospheric pressure.

[0106] In an aspect, the first compressor and the second compressor are mechanically connected to at least one motor.

[0107] In an aspect, the first compressor and the second compressor are of the centripetal or centrifugal or axial type.

[0108] In an aspect, the first expander and the second expander are mechanically connected to at least one generator.

[0109] In an aspect, the first expander and the second expander are turbines, optionally of the centripetal or centrifugal or axial type.

[0110] Further features and advantages will appear more from the detailed description of preferred, but not exclusive, embodiments of a process and of a plant for energy storage and release, according to the present invention.

[0111] Description of figures

[0112] This description will be shown below with reference to the attached drawings, provided for illustrative purposes only and, therefore, not limiting thereto, in which:

[0113] ■ figure 1 shows a plant for energy storage and release according to the present invention;

[0114] ■ figure 2 shows a variant of the plant of figure 1 ;

[0115] ■ figure 3 shows a T-S diagram of a process for energy storage and release according to the present invention and operated by the plant in figure 1 or figure 2;

[0116] ■ figure 4 shows an additional variant of the plant of figure 1 ;

[0117] ■ figure 5 shows a T-S diagram of a variant of the process for energy storage and release according to the present invention and operated by the plant in figure 1 or figure 4.

[0118] Detailed description With reference to the attached figures, with the reference number 1 it has been overall indicated a plant for energy storage and release according to the present invention.

[0119] The plant 1 comprises an enclosure 2 configured to contain a working fluid in gas phase and in pressure equilibrium with the atmosphere. In the exemplary embodiment shown, the enclosure 2 is a double-membrane gasometer comprising an inner membrane 3 containing the working fluid and an outer membrane 4 in contact with the environment. The gasometer is arranged on the surface and is externally in contact with atmospheric air. The inner membrane 3 of the gasometer delimits within it a variable volume 5 configured to contain the working fluid in the gas phase and at atmospheric or substantially atmospheric pressure, that is, in pressure equilibrium with the atmosphere. The inner membrane 3 deforms in accordance with the amount of working fluid contained in the variable volume in such a way as to maintain constant a pressure of the working fluid contained in said variable volume. The outer membrane 4 constantly maintains its shape unless small variations with the purpose of protecting the inner membrane from the external environment and weather, such as sun, rain, wind, snow, etc. The cavity delimited between the inner membrane 3 and the outer membrane 4 is filled with ambient air by fans, not shown, and a constant pressure of a few millibars is maintained, for example from 2 mbar to 50 mbar. The enclosure 2 can also be made with a single membrane or as any other low or zero overpressure gas storage system, in which as the volume of working fluid changes, the pressure is kept constant or substantially constant.

[0120] The plant 1 comprises a reservoir 6 of high-pressure-resistant material, for example carbon steel. In variants not shown the reservoirs 6 may be more than one. The reservoir 6 defines an inner volume 7 and is configured to contain the working fluid in liquid or super-critical phase.

[0121] The working fluid is different from atmospheric air and has a critical temperature, intended as the temperature of the respective critical point, close to the ambient temperature, preferably between 0°C and 100°C. Examples of possible working fluids are listed in the following table 1.

[0122] Table 1

[0123] The working fluid can also consist of mixtures of the above substances with others as well.

[0124] A first compressor 8 and a second compressor 9, of the centripetal or centrifugal or axial type, are in fluid connection with each other in series and are operatively interposed between the enclosure 2 and the reservoir 6. Connecting conduits connect an outlet from the variable volume 5 of the enclosure 2 to an inlet of the first compressor 8, an outlet from the first compressor 8 to an inlet of the second compressor 9, and an outlet from the second compressor 9 to an inlet in the reservoir 6. By the term connecting conduits is generically intended one or more elements that delimit one or more conduits suitable to be passed through by a fluid and thus to convey and transport the fluid.

[0125] The first compressor 8 is mechanically connected to a first motor 10. The second compressor 9 is mechanically connected to a second motor 11 . The first and second motors 10, 11 are electric motors and are for example powered by the power grid or by a wind generator or photovoltaic panel system.

[0126] A first expander 12 and a second expander 13, defined by respective expansion turbines of the centripetal or centrifugal or axial type, are in fluid connection with each other in series and are operatively interposed between the reservoir 6 and the enclosure 2. Connecting conduits connect an outlet from the reservoir 6 with an inlet of the first expander 12, an outlet of the first expander 12 to an inlet of the second expander 13, an outlet of the second expander 13 to an inlet in the variable volume 5 of the enclosure 2. The first compressor 8 and the second compressor 9 are therefore placed in parallel with respect to the first expander 12 and the second expander 13.

[0127] The first expander 12 is mechanically connected to a first generator 14. The second expander 13 is mechanically connected to a second generator 15. The first and second generator 14, 15 are for example connected to the power grid or other electrical power users. A first thermal accumulator 16 is in fluid connection, on one side, with the outlet of the first compressor 8 and the inlet of the second expander 13 and, on the opposite side, with the outlet of the first expander 12 and the inlet of the second compressor 9. The first thermal accumulator 16 is a pressurized packed bed thermal store (pressurized packed bed thermal store) and comprises a container inside which is contained inert solid material configured to either retain heat given by the working fluid or to give heat to the working fluid. Valves, compartments, and internal conduits, not shown, allow the alternate passage through the inert solid material of the working fluid from the first compressor 8 and directed to the second compressor 9 or of the working fluid from the first expander 12 and directed to the second expander 13.

[0128] A second thermal accumulator 17 is in fluid connection, on one side, with the inlet of the first expander 12 and the outlet of the second expander 9 and, on an opposite side, with a third thermal accumulator 18. The third thermal accumulator 18 is in fluid connection, on one side, with the second thermal accumulator 17 and, on an opposite side, with the reservoir 6.

[0129] The second thermal accumulator 17, shown only schematically in figure 1 , is configured to store heat in water and release heat from water. For example, the second thermal accumulator 17 comprises a container containing water at low pressure, for example at a pressure of less than 10 bar or less than 5 bar or at atmospheric pressure and a circuit with a heat exchanger in which the water circulates. The heat exchanger of the second thermal accumulator 17 is thermally coupled to the connecting conduits of the working fluid, so that the water can both absorb and retain heat from the working fluid coming from the second compressor 9 and directed to the third thermal accumulator 18 or give heat to the working fluid coming from the third thermal accumulator 18 and directed to the first expander 12. Also the third thermal accumulator 18, schematically shown in figure 1 , is configured to store heat in water and release heat from water. As shown, the third thermal accumulator 18 comprises a container 19 containing water at atmospheric pressure and a circuit 20 with a heat exchanger 21. The heat exchanger 21 of the third thermal accumulator 18 is thermally coupled to the connecting conduits of the working fluid, so that the water can both absorb and retain heat from the working fluid coming from the second thermal accumulator 17 and directed to the reservoir 6 or give heat to the working fluid coming from the reservoir 6 and directed to the second thermal accumulator 17.

[0130] A pump 22 is operatively active between the reservoir 6 and the third thermal accumulator 18 to pump the working fluid in liquid phase from the reservoir 6 to the third thermal accumulator 18.

[0131] In the embodiment of figure 1 , connecting ducts are divided into storage connecting ducts 100 (solid line in figures), configured to carry the working fluid from the enclosure 2 to the reservoir 6 in the storage configuration, and release connecting ducts 200 (dashed line in figures), configured to carry the working fluid from the reservoir 6 to the enclosure 2 in the release configuration.

[0132] The plant 1 also comprises a heat transfer device 23 operatively coupled to the connecting ducts located upstream of the first compressor 8 and upstream of the second compressor 9. The heat transfer device 23 comprises: a first heat exchanger HE1 , a second heat exchanger HE2, a closed circuit 24 extending between the first heat exchanger HE1 and the second heat exchanger HE2. An auxiliary pump 25 is operative on the closed circuit 24 to circulate water in said closed circuit 24.

[0133] The first heat exchanger HE1 is placed on a connecting duct between the outlet from the enclosure 2 and the inlet into the first compressor 8 and thermally couples this connecting duct to the closed circuit 24. The second heat exchanger HE2 is placed on a connecting duct between the first thermal accumulator 16 and the inlet into the second compressor 9 and thermally couples this connecting duct to the closed circuit 24.

[0134] In the exemplary embodiment shown, the heat transfer device 23 further comprises a cooler 26 operatively active on a first branch of the closed circuit 24, in which the water flows from the second heat exchanger HE2 to the first heat exchanger HE1 , and a heater 27 operatively active on a said second branch of the closed circuit 24 in which the water flows from the first heat exchanger HE1 to the second heat exchanger HE2. The cooler 26 comprises a first auxiliary heat exchanger interfaced with the external environment and a fan coupled to the first auxiliary heat exchanger. The heater 27 comprises a second auxiliary heat exchanger interfaced with an external heat source that, in the shown example, is a cooling circuit configured to remove heat generated by the second motor 11 due to mechanical and / or electrical inefficiencies. In variants not shown, the positions of the cooler 26 and heater 27 can be different. For example, the cooler 26 is operatively active on the second branch of the closed circuit 24 and the heater 27 is operatively active on the first branch of the closed circuit 24.

[0135] A third heat exchanger HE3 is operatively interposed between an outlet from the second expander 13 and the inlet in the enclosure 2. In the embodiment of figure 1 , the third heat exchanger HE3 is associated with a circuit 28 in fluid connection with the container 19 of the water of the third thermal accumulator 18.

[0136] The plant 1 of the variant of figure 2, is different from the one of figure 1 because the heat transfer device 23 comprises only one heat exchanger HE coupled to connecting ducts of the working fluid entering the first compressor 8 and to connecting ducts of the working fluid exiting the first thermal accumulator 16. There is no intermediate heat transport fluid and the recovery of said at least part of the excess heat QE and the preheating of the working fluid from the enclosure 2 are implemented by means of a direct exchange between the working fluid in (D-E) and the working fluid in (A-B).

[0137] A cooler 26a similar to the one above described is operatively coupled to connecting ducts of the working fluid placed between the heat exchanger HE and the second compressor 9 and a heater 27a similar to the one above described is operatively coupled to connecting ducts of the working fluid placed between the first heat accumulator 16 and the heat exchanger HE.

[0138] Furthermore, the container 19 of the water of the third thermal accumulator 18 exchanges heat with the external environment through an additional auxiliary heat exchanger 29 interfaced with the external environment and a fan coupled to the additional auxiliary heat exchanger 29.

[0139] The plant 1 above described (of figure 1 and figure 2) is capable of implementing a process for energy storage and release according to the present invention, as described below with reference to figures 1 , 2 and 3. The plant 1 is configured to implement a closed cyclic thermodynamic transformation (TTC), first in one direction in an energy storage phase / configuration and then in an opposite direction in an energy discharge phase / configuration, between the enclosure 2 and the reservoir 6. In the storage phase / configuration, the plant / process stores heat and potential energy in the form of pressure, and in the release phase / configuration, the plant / process generates electrical energy.

[0140] In the energy storage phase / configuration, the working fluid exits the enclosure 2 (by operating suitable valves not shown), in which it is contained in gas phase in pressure equilibrium with the atmosphere and at the ambient temperature Tamb, and flows sequentially through the first heat exchanger HE1 , the first compressor 8, the first thermal accumulator 16, the second heat exchanger HE2, the second compressor 9, the second thermal accumulator 17, the third thermal accumulator 18, and is stored in the reservoir 6 in liquid phase.

[0141] With reference to figure 3, in the first heat exchanger HE1 , the working fluid is preheated (A-B) by the water circulating in the closed circuit 24. In the first compressor 8, the working fluid is compressed (B-C) by using the external electrical energy from for example the power grid to drive the first motor 10. In the first thermal accumulator 16, the working fluid releases a first amount of heat (Q1) that is stored in said first thermal accumulator 16; the working fluid is cooled here a first time (C- D). In the second heat exchanger HE2, the working fluid is cooled further (D-E) by removing excess heat QE from the working fluid which is transferred to the circulating water in the closed circuit 24. In the second compressor 9, the working fluid is compressed (E-F) by using again the external electrical energy from for example the power grid to drive the second motor 11. In the second thermal accumulator 17, the working fluid releases a second amount of heat Q2 that is stored in said second thermal accumulator 17; the working fluid is cooled here a second time (F-G). In the heat exchanger 21 of the third heat accumulator 18, the working fluid is condensed (G-H) by removing a third amount of heat Q3 from the working fluid that is stored in the water of the container 19. The working fluid flows into the reservoir 6 and there accumulated in liquid phase (H).

[0142] As can be seen in figure 3, through the heat transfer device 23, the excess heat QE removed in (D-E) is recovered at least partially and used in the (A-B) to preheat the working fluid from the enclosure 2. The water that circulates in the closed circuit absorbs the excess heat QE from the working fluid in (D-E) and gives it at least partially to the working fluid in (A-B).

[0143] While the working fluid is stored in the reservoir 6, the working fluid properties (temperature and pressure) vary slightly (figure 3: H-l). Eventually, it is possible to cool and / or heat the water of the closed circuit by means of the above-mentioned cooler 26 and heater 27 of figure 1 to control the working fluid temperatures in B and E or to control these temperatures directly by means of the cooler 26a and the heater 27a of figure 2.

[0144] In the energy release phase / configuration, the working fluid exits the reservoir 6 (by operating the pump 22) in which it is contained in the liquid phase and flows sequentially through the third thermal accumulator 18, the second thermal accumulator 17, the first expander 12, the first thermal accumulator 16, the second expander 13, the third heat exchanger HE3 and is accumulated back into the enclosure 2 in the gas phase.

[0145] With reference to figure 3, in the heat exchanger 21 of the third thermal accumulator 18, the working fluid is evaporated (l-L) by supplying to it the third amount of heat Q3 previously stored in the water of the container 19. In the second thermal accumulator 17, the second amount of heat Q2 previously stored is transferred to the working fluid; the working fluid is heated here a first time (L-M). In the first expander 12, the working fluid expands a first time (M-N) and sets movable organs of the first expander 12 in motion (such as the impeller of a turbine) and then generates electrical energy through the first generator 14. In the first thermal accumulator 16, the first amount of heat Q1 previously stored is given to the working fluid; the working fluid is heated here a second time (N-O). In the second expander 13, the working fluid expands a second time (O-P) and sets movable organs of the second expander 13 in motion (such as the impeller of a turbine) and then generates additional electrical energy through the second generator 15. In the third heat exchanger HE3, the working fluid is further cooled (P-Q) by removing an additional amount of heat and until it returns to the ambient temperature Tamb. The working fluid flows back into the enclosure 2 and here accumulated in the gas phase and in pressure equilibrium with the atmosphere (Q = A).

[0146] The following Table 2 shows example temperatures and pressures of points A, B, C, D, E, F, G, H (storage) and I, L, M, N, O, P, Q (release) of the T-S diagram of figure 3 that shows the above-described process with carbon dioxide (CO2). As can be seen, the maximum pressure of the transformation after the second compression (F) is less than the critical pressure of CO2 so that the CO2 remains sub-critical, condenses (G-H) in the storage phase and evaporates (l-L) in the release one. Table 2

[0147] The plant 1 of the variant of figure 4, differs from the one of figure 1 because of the presence of a lamination valve 30 interposed between the third thermal accumulator HE3 and the reservoir 6. Instead of the lamination valve 30 there can be a two- phase expansion turbine, not shown.

[0148] Furthermore, working parameters of the plant are adjusted so that the pressure of the working fluid in the storage phase and after compressing it the second time (F) is greater than or equal to the critical pressure of CO2.

[0149] Therefore, as shown in figure 5, the CO2 is cooled (G-H) in the heat exchanger 21 of the third thermal accumulator 18 but does not condense. Furthermore, after cooling, the lamination valve 29 liquefies the working fluid (H-H') bringing it to a sub- critical condition.

[0150] In the release configuration, the pump 22 increases pressure and temperature of the CO2 and brings it back to the super-critical phase (I'-l) and the heat exchanger 21 of the third thermal storage tank 18 works as a heater by heating the CO2 (l-L) but without evaporating it.

[0151] The following Table 3 shows example temperatures and pressures of points A, B, C, D, E, F, G, H, H’ (storage) and I, I’, L, M, N, O, P, Q (release) of the T-S diagram of figure 5 that shows the above-described process with carbon dioxide (CO2). As can be seen, the maximum pressure of the transformation after the second compression (F) is less than the critical pressure of CO2 so that CO2 is super-critical in F-G-H and l-L-M but is stored in the reservoir 6 in sub-critical liquid phase (H1and I').

[0152] In a variant not shown in figures, the super-critical CO2 may be stored in the reservoir, so that the sections (H, H’) and (1-1’) of figure 5 are not present.

[0153] The process between the remaining points A, B, C, D, E (storage) and N, O, P, Q (release) is as described previously with reference to figure 3.

[0154] Table 3

[0155] List of elements

[0156] 1 plant

[0157] 2 enclosure

[0158] 3 inner membrane

[0159] 4 outer membrane

[0160] 5 variable volume

[0161] 6 reservoir

[0162] 7 inner volume

[0163] 8 first compressor

[0164] 9 second compressor 10 first motor

[0165] 11 second motor

[0166] 12 first expander

[0167] 13 second expander

[0168] 14 first generator

[0169] 15 second generator

[0170] 16 first thermal accumulator

[0171] 17 second thermal accumulator

[0172] 18 third thermal accumulator

[0173] 19 container of the third thermal accumulator

[0174] 20 circuit of the third thermal accumulator

[0175] 21 heat exchanger of the third thermal accumulator

[0176] 22 pump

[0177] 23 heat transfer device

[0178] 24 closed circuit

[0179] 25 auxiliary pump

[0180] 26 cooler

[0181] 27 heater

[0182] 28 circuit

[0183] 29 additional heat exchanger

[0184] HE1 first heat exchanger

[0185] HE2 second heat exchanger

[0186] HE3 third heat exchanger

Claims

CLAIMS1. Process for energy storage and release, comprising: implementing a closed thermodynamic cyclic transformation (TTC), first in one direction in a storage phase and then in an opposite direction in a release phase, between an enclosure (2) for storing a working fluid other than atmospheric air in gas phase and in pressure equilibrium with the atmosphere, and a reservoir (6) for storing said working fluid in liquid or super-critical phase; wherein in the storage phase the process accumulates heat and potential energy in the form of pressure, and in the release phase the process generates energy; the working fluid having a critical temperature between 0°C and 100°C; wherein the storage phase comprises the following sub-phases:A-B preheating the working fluid coming from the enclosure (2);B-C compressing the working fluid a first time using external energy to be stored;C-D removing a first amount of heat Q1 from the working fluid to cool it a first time and storing said first amount of heat Q1;D-E further cooling the working fluid by removing excess heat QE from the working fluid;E-F compressing the working fluid a second time using additional external energy to be stored;F-G removing a second amount of heat Q2 from the working fluid to cool it a second time and storing said second amount of heat Q2;G-H removing a third amount of heat Q3 from the working fluid to increase a density of the working fluid, storing the third amount of heat Q3 and storing the working fluid in the reservoir (6) in liquid or super-critical phase; wherein at least part of said excess heat QE removed in the sub-phase D-E is recovered and used in the sub-phase A-B to preheat the working fluid from the enclosure (2).

2. Process according to claim 1 , wherein the recovery of said at least part of the excess heat QE and the preheating of the working fluid from the enclosure (2) are implemented by means of a heat transport fluid operating in a closed circuit (24);wherein said heat transport fluid absorbs the excess heat QE from the working fluid in the sub-phase D-E and gives said at least part to the working fluid in the subphase A-B.

3. Process according to claim 2, wherein said heat transport fluid is chosen from the group including: water, water and glycol, oil.

4. Process according to claim 2 or 3, further comprising: cooling and / or heating the heat transport fluid after said heat transport fluid has absorbed the excess heat QE from the working fluid in the sub-phase D-E and before giving the excess heat QE to the working fluid in the sub-phase A-B and / or after said heat transport fluid has given the excess heat QE to the working fluid in the sub-phase A-B and before absorbing the excess heat QE from the working fluid in the sub-phase D-E, to adjust the temperature of the working fluid before the first compression and / or before the second compression.

5. Process according to claim 4, wherein cooling the heat transport fluid comprises: disposing excess heat to the external environment; and / or heating the heat transport fluid comprises: absorbing auxiliary heat from an external heat source.

6. Process according to any one of claims 2 to 5, wherein, in the sub-phase D- E, the heat transport fluid absorbs the excess heat QE from the working fluid through a second heat exchanger (HE2) operating on the closed circuit (24); wherein, in the sub-phase A-B, the heat transport fluid gives said at least part of the excess heat QE to the working fluid through a first heat exchanger (HE1) operating on the closed circuit (24).

7. Process according to claim 1 , wherein the recovery of said at least part of the excess heat QE and the preheating of the working fluid from the enclosure (2) are implemented by means of a direct exchange of said at least part of the excess heat QE between the working fluid in the sub-phase D-E and the working fluid in the subphase A-B.

8. Process according to claim 7, wherein said at least part of the excess heat QE is exchanged through a heat exchanger (HE).

9. Process according to one of claims 1 to 8, wherein a pressure (Pc) of the working fluid in the storage phase and after compressing it the first time (C) is between 15 bar and 35 bar.

10. Process according to any one of claims 1 to 9, wherein a pressure (PF) of the working fluid in the storage phase and after compressing it the second time (F) is less than a critical pressure (Pent) of said working fluid and wherein removing the third amount of heat from the working fluid comprises: condensing the working fluid; or wherein a pressure (PF) of the working fluid in the storage phase and after compressing it the second time (F) is greater than or equal to a critical pressure (Pent) of said working fluid and wherein removing the third amount of heat from the working fluid comprises: cooling the working fluid.11 . Process according to claim 10, wherein the pressure (PF) of the working fluid in the storage phase and after compressing it the second time (F) is less than said critical pressure (Pent) and between 25 bar and 70 bar, optionally between 40 bar and 55 bar; or wherein the pressure (PF) of the working fluid in the storage phase and after compressing it the second time (F) is greater than or equal to said critical pressure (Pent) and between 75 bar and 140 bar.

12. Process according to any one of claims 1 to 11 , wherein the release phase comprises the sub-phases: l-L extracting the working fluid from the reservoir (6) and bringing it into the gas phase by giving to the working fluid the third amount of heat Q3 previously stored;L-M giving to the working fluid the second amount of heat Q2 previously stored, to heat it a first time;M-N making the working fluid expand a first time to release energy;N-0 giving to the working fluid the first amount of heat Q1 previously stored, to heat it a second time;O-P making the working fluid expand a second time to release additional energy;P-Q removing an optional additional amount of heat from the working fluid and returning the working fluid to the enclosure (2) in the gas phase and in pressure equilibrium with the atmosphere.

13. Process according to claim 12, wherein a temperature (TN) of the working fluid in the release phase and after expanding the first time (N) is greater than a temperature (TE) of the working fluid in the storage phase and after compressing the first time (E) and close to or equal to a temperature (TD) of the working fluid in the storage phase and after cooling the first time (D).

14. Process according to claim 12 or 13, wherein a temperature (TM) of the working fluid in the release phase and after the second amount of heat has been given to the working fluid (M) is close to or equal to a temperature (TF) of the working fluid in the storage phase and after it has been compressed the second time (F).

15. Process according to any one of claims 12 to 14, wherein a temperature (To) of the working fluid in the release phase and after the first amount of heat has been given to the working fluid (O) is close to or equal to a temperature (To) of the working fluid in the storage phase and after it has been compressed the first time (C).

16. Plant for energy storage and release, comprising: a working fluid other than atmospheric air and having a critical temperature between 0°C and 100°C; an enclosure (2) configured to contain the working fluid in gas phase and in pressure equilibrium with the atmosphere; a reservoir (6) configured to contain the working fluid in liquid or super-critical phase;a first compressor (8) and a second compressor (9) in fluid connection with each other in series and operatively interposed between the enclosure (2) and the reservoir (6); a first expander (12) and a second expander (13) in fluid connection with each other in series and operatively interposed between the enclosure (2) and the reservoir (6), wherein the first compressor (8) and the second compressor (9) are placed in parallel with respect to the first expander (12) and the second expander (13); a first thermal accumulator (16) in fluid connection, on one side, with the first compressor (8) and the second expander (13) and, on an opposite side, with the first expander (12) and the second compressor (9), wherein the first thermal accumulator (16) is configured to exchange a first amount of heat Q1 with the working fluid and store or release said first amount of heat Q1 ; a second thermal accumulator (17) in fluid connection, on one side, with the first expander (12) and the second compressor (9), wherein the second thermal accumulator (17) is configured to exchange a second amount of heat Q2 with the working fluid and store or release said second amount of heat Q2; a third thermal accumulator (18) in fluid connection, on one side, with the second thermal accumulator (17) and, on an opposite side, with the reservoir (6), wherein the third thermal accumulator (18) is configured to exchange a third quantity of heat Q3 with the working fluid and store or release said third quantity of heat Q3; connecting ducts (100, 200) between the enclosure (2), the reservoir (6), the first compressor (8), the second compressor (9), the first expander (12), the second expander (13), the first thermal accumulator (16), the second thermal accumulator (17), and the third thermal accumulator (18); wherein the plant (1) operates in an energy storage configuration and / or in an energy release configuration; in the energy storage configuration, the working fluid transits from the enclosure (2) to the reservoir (6) through the first compressor (8), the first thermal accumulator (16), the second compressor (9), the second thermal accumulator (17), the third thermal accumulator (18) and is stored in the reservoir (6); in the energy release configuration, the working fluid transits from the reservoir (6) to the enclosure (2) through the third thermal accumulator (18), the second thermal accumulator (17), the first expander (12), the first thermalaccumulator (16), the second expander (13) and is again stored in the enclosure (2), wherein in the storage configuration the plant (1) accumulates heat and potential energy in the form of pressure and in the release configuration the plant (1) generates energy; wherein the plant (1) also comprises a heat transfer device (23) operatively coupled to the connecting ducts located upstream of the first compressor (8) and upstream of the second compressor (9), wherein the heat transfer device (23) is configured to remove excess heat QE from the working fluid entering the second compressor (9) and to transfer at least part of said excess heat QE to the working fluid entering the first compressor (8).

17. Plant according to claim 16, wherein the heat transfer device (23) comprises: a first heat exchanger (HE1) located between the enclosure (2) and the first compressor (8), a second heat exchanger (HE2) located between the first heat accumulator (16) and the second compressor (9), a closed circuit (24) extending between the first heat exchanger (HE1) and the second heat exchanger (HE2), a heat transport fluid circulating in the closed circuit (24).

18. Plant according to claim 17, wherein said heat transport fluid is chosen from the group including: water, water and glycol, oil.

19. Plant according to claim 17 or 18, wherein the heat transfer device (23) further comprises a cooler (26) and / or a heater (27) operatively active on a first branch of the closed circuit, in said first branch the heat transport fluid flowing from the second heat exchanger (HE2) to the first heat exchanger (HE1) and / or on a second branch of the closed circuit, in said second branch the heat transport fluid flowing from the first heat exchanger (HE1) to the second heat exchanger (HE2).

20. Plant according to claim 19, wherein the cooler (26) comprises a first auxiliary heat exchanger interfaced with the external environment; and / or the heater (27) comprises a second auxiliary heat exchanger interfaced with an external heat source.21 . Plant according to claim 20, wherein the cooler (26) comprises a fan coupled to the first auxiliary heat exchanger; and / or wherein the external heat source comprises a cooling circuit configured to remove heat generated by at least one of the first compressor (8), the second compressor (9), the first expander (12), and the second expander (13) due to mechanical and / or electrical inefficiencies.

22. Plant according to claim 16, wherein the heat transfer device (23) comprises a heat exchanger (HE) coupled to connecting ducts of the working fluid entering the first compressor (8) and to connecting ducts of the working fluid exiting the first thermal accumulator (16).

23. Plant according to any one of claims 16 to 22, wherein, if a pressure of the working fluid exiting the second compressor (9) is less than a critical pressure (Pent) of said working fluid, the third thermal accumulator (18) operates as a condenser in the energy storage configuration and as an evaporator in the energy release configuration; or wherein, if a pressure of the working fluid exiting the second compressor (9) is greater than or equal to a critical pressure (Pent) of said working fluid, the third thermal accumulator (18) works as a cooler in the energy storage configuration and as a heater in the energy release configuration.

24. Plant according to any one of claims 16 to 23, comprising a lamination valve (29) or a two-phase expansion turbine interposed between the third thermal accumulator (18) and the reservoir (6) and / or a pump (22) operatively interposed between the reservoir (6) and the third thermal accumulator (18).

25. Plant according to any one of claims 16 to 24, comprising a third heat exchanger (HE3) operatively interposed between the second expander (13) and the enclosure (2), wherein, in the energy release configuration, the third heat exchanger (HE3) is configured to remove an additional amount of heat from the working fluid.

Images