Process and plant for energy storage and release

Abstract

Process for energy storage and release, comprising: implementing a closed cyclic thermodynamic transformation (TTC), first in a forward path in a storage phase and then in a return path 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 the 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. During the storage phase and / or the release phase, internal heat is also intended to be moved among different portions of the working fluid flowing in a first part of a forward path and in a second part of the forward path, respectively, and / or among different portions of the working fluid flowing respectively in a first part of a return path and in a second part of a return path.

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 the plants and processes described above can be improved in several aspects.

[0018] In particular, the Applicant noted that the cyclic thermodynamic transformation (TTC) of the above-mentioned plants and processes can be made more efficient in such a way as to increase the energy released in the discharge phase being equal the energy stored in the charge phase or, conversely, to reduce the energy to be stored in the charge phase being equal the energy released in the discharge phase. The Applicant also noted that the above-mentioned plants can be simplified structurally in such a way as to make them simpler, less bulky, and also more economical.

[0019] The Applicant, therefore, aimed at designing and realizing a plant and a process of the type described above that allow to increase the efficiency thereof and at the same time to reduce the production and installation costs of the plant, being equal the size or the capacity to store and release energy.

[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 amounts of heat are exchanged internally in the cyclic thermodynamic transformation (TTC) i.e., among different portions of the working fluid in the energy release phase and / or the energy storage phase.

[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 a forward path in a storage phase and then in a return path in a release phase, between an enclosure for storing a working fluid other than atmospheric air in the gaseous 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. A critical temperature of the working fluid, intended as the temperature of the respective critical point, is between 0°C and 100°C.

[0023] The storage phase comprises: compressing the working fluid from the enclosure using external energy to be stored; removing an amount of heat (Q) from the working fluid to cool it and storing said amount of heat (Q); removing an additional amount of heat (Qu) from the working fluid to increase a density of the working fluid, storing the additional amount of heat (Qu) and storing the working fluid in the reservoir in liquid or super-critical phase.

[0024] The additional amount of heat (Qu) comprises sensible heat (causes a temperature change) and / or latent heat (causes a state transformation) of the working fluid.

[0025] The release phase also comprises: extracting the working fluid from the reservoir and bringing it into the gas phase by giving to the working fluid the additional amount of heat (Qu) previously stored; giving to the working fluid the amount of heat (Q) previously stored to heat it; making the working fluid expand to release energy; returning the working fluid to the enclosure in the gas phase and in pressure equilibrium with the atmosphere.

[0026] The storage phase comprises also: moving internal heat (QE1) among different portions of the working fluid flowing respectively in a first part of the forward path, downstream of the enclosure and before compressing the working fluid, and in a second part of the forward path, after removing the amount of heat (Q) and before accumulating the working fluid in the reservoir in the liquid or super-critical phase; optionally before removing the additional amount of heat (Qu); and / or the release phase also comprises: moving internal heat (Q2) among different portions of the working fluid flowing respectively in a first part of the return path, between the working fluid storage in the reservoir in the liquid or super-critical phase, optionally after giving to the working fluid the additional amount of heat (Qu), and before giving the amount of heat (Q) to the working fluid, and in a second part of the return path, after making the working fluid expand and before the enclosure.

[0027] 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, intended as temperature of the respective critical point, between 0°C and 100°C; an enclosure configured to contain the working fluid in the gas phase and in pressure equilibrium with the atmosphere; a reservoir configured to contain the working fluid in liquid or super-critical phase; a compressor operatively interposed between the enclosure and the reservoir; an expander operatively interposed between the enclosure and the reservoir, wherein the compressor is placed in parallel with respect to the expander; a high-temperature thermal accumulator in fluid connection, on one side, with the compressor and the expander and, on an opposite side, with the reservoir, wherein the high-temperature thermal accumulator is configured to exchange a quantity of heat (Q) with the working fluid and store or release said quantity of heat (Q); a low-temperature accumulator interposed between the high-temperature thermal accumulator and the reservoir, wherein the low-temperature thermal accumulator is configured to exchange an additional amount of heat (Qu) with the working fluid and store or release said additional amount of heat (Qu); connecting ducts defining a forward path from the enclosure, through the compressor, the high-temperature accumulator, the low-temperature accumulator and until the reservoir and a return path from the reservoir, through the low-temperature thermal accumulator, the high- temperature thermal accumulator, the expander and until the enclosure.

[0028] The plant operates in an energy storage configuration and / or in an energy release configuration.

[0029] In the energy storage configuration, the working fluid transits in the forward path, from the enclosure to the reservoir and is stored in the reservoir.

[0030] In the energy storage configuration, the working fluid transits in the return path, from the reservoir to the enclosure and is stored again in the enclosure. In the storage configuration, the plant stores heat and potential energy in the form of pressure and in the release configuration the plant generates energy.

[0031] The plant comprises further a heat transfer device operatively coupled to a first part of the forward path between the enclosure and the compressor and to a second part of the forward path between the high-temperature thermal accumulator and the reservoir, optionally between the high-temperature thermal accumulator and the low-temperature thermal accumulator, and / or operationally coupled to a first part of the return path between the reservoir and the high-temperature thermal accumulator, optionally between the low-temperature thermal accumulator and the high-temperature thermal accumulator, and to a second part of the return path between the expander and the enclosure.

[0032] In the energy storage configuration, the heat transfer device is configured to move internal heat between the second part of the forward path and the first part of the forward path; and / or in the energy release configuration, the heat transfer device is configured to move internal heat between the second part of the return path and the first part of the return path. In an aspect, the process of the first aspect is implemented through the plant of the second aspect and / or the plant of the second aspect is configured to carry out the process of the first aspect.

[0033] The Applicant has verified that the process and plant according to the invention allow to achieve the predetermined objectives and more.

[0034] The Applicant has first verified that the process and the plant according to the invention allow to increase the specific work of the system in both the energy storage and the release phase, thus improving the efficiency of the process.

[0035] The Applicant has also verified that the internal heat exchange of the process and of the plant according to the invention allows to reduce the size of heat accumulations and thus to reduce plant footprint and cost.

[0036] 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, in the storage phase, the internal heat is moved from the second part of the forward path to the first part of the forward path, to heat the working fluid before compression.

[0037] In an aspect, in the storage phase, the internal heat moved from the second part of the forward path to the first part of the forward path is used to cool the working fluid after the working fluid has given the amount of heat (Q).

[0038] In an aspect, in the storage phase, the internal heat moved from the second part of the forward path to the first part of the forward path is partially (excess heat) disposed to the external environment.

[0039] In an aspect, in the release phase, the internal heat is moved from the second part of the return path to the first part of the return path, to cool the working fluid after the expansion.

[0040] In an aspect, in the release phase, the internal heat moved from the second part of the return path to the first part of the return path is used to heat the working fluid before giving to the working fluid the amount of heat (Q).

[0041] In an aspect, in the release phase, the internal heat moved from the second part of the return path to the first part of the return path is partially (excess heat) disposed to the external environment. The Applicant has verified that this allows to reduce the size and the complexity of the high-temperature thermal accumulator.

[0042] In an aspect, the transfer of the internal heat is implemented by a heat transport fluid operating in at least one closed circuit.

[0043] In an aspect, said heat transport fluid is chosen from the group comprising: water, water and glycol, oil.

[0044] In an aspect, it is provided to cool the heat transport fluid disposing excess heat to the external environment.

[0045] In an aspect, it is provided to cool the heat transport fluid giving it to an auxiliary accumulator.

[0046] In an aspect, it is provided to heat the heat transport fluid absorbing auxiliary heat from an external heat source.

[0047] In an aspect, it is provided to heat the heat transport fluid absorbing auxiliary heat from the auxiliary accumulator.

[0048] In an aspect, the transfer of internal heat is implemented by a direct exchange of said internal heat between the second part of the forward path and the first part of the forward path.

[0049] In an aspect, the transfer of internal heat is implemented by a direct exchange of said internal heat between the second part of the return path and the first part of the return path.

[0050] In an aspect, compressing the working fluid comprises: compressing the working fluid a first time and compressing the working fluid a second time.

[0051] In an aspect, the amount of heat (Q) is removed after compressing the working fluid the first time and before compressing the working fluid the second time.

[0052] In an aspect, removing the amount of heat (Q) comprises: removing a first amount of heat (Q1) after compressing the working fluid the first time and removing a second amount of heat (Q2) after compressing the working fluid the second time.

[0053] In an aspect, making the working fluid expand comprises: making the working fluid expand a first time and making the working fluid expand a second time.

[0054] In an aspect, the amount of heat (Q) is given after expanding the working fluid the first time and before making the working fluid expanding the second time.

[0055] In an aspect, giving the amount of heat (Q) comprises: giving the first amount of heat (Q1) to the working fluid before making the working fluid expand the first time and giving the second amount of heat (Q2) before making the working fluid expand the second time.

[0056] In an aspect, the second part of the forward path is after compressing the working fluid the second time or after removing the second amount of heat (Q2).

[0057] In an aspect, the first part of the return path is either before the second amount of heat (Q2) is given to the working fluid or before making the working fluid expand the first time.

[0058] In an aspect, the heat transfer device comprises: a first heat exchanger placed on the first part of the forward path and on the second part of the return path.

[0059] In an aspect, the heat transfer device comprises: a second heat exchanger placed on the second part of the forward path and on the first part of the return path.

[0060] In an aspect, the heat transfer device comprises: at least a closed circuit extending between the first heat exchanger and the second heat exchanger.

[0061] In an aspect, the heat transfer device comprises: a heat transport fluid circulating in the closed circuit.

[0062] In an aspect, the closed circuit comprises a first branch extended between the first heat exchanger and the second heat exchanger and a second branch extended between the second heat exchanger and the first heat exchanger.

[0063] In an aspect, in the storage phase, the first branch is a forward branch of the heat transport fluid from the first heat exchanger to the second heat exchanger and the second branch is a return branch of the heat transport fluid from the second heat exchanger to the first heat exchanger.

[0064] In an aspect, in the release phase, the first branch is a return branch of the heat transport fluid from the second heat exchanger to the first heat exchanger and the second branch is a forward branch of the heat transport fluid from the first exchanger to the second heat exchanger.

[0065] In an aspect, said heat transport fluid is chosen from the group comprising: water, water and glycol, oil.

[0066] In an aspect, the heat transfer device comprises also a cooler operatively active on the closed circuit.

[0067] In an aspect, the cooler is operatively active on the second branch of the closed circuit or on the first branch of the closed circuit. In an aspect, the cooler is also coupled to the low-temperature thermal accumulator and / or to the reservoir.

[0068] In an aspect, the cooler comprises a first auxiliary heat exchanger interfaced with the external environment.

[0069] In an aspect, the heat transfer device comprises also a heater operatively active on the closed circuit.

[0070] In an aspect, the heater is operatively active on the second branch of the closed circuit or on the first branch of the closed circuit.

[0071] In an aspect, the heater is also coupled to the low-temperature thermal accumulator and / or to the reservoir.

[0072] In an aspect, the heater comprises a respective auxiliary heat exchanger interfaced with an external heat source.

[0073] In an aspect, a medium-temperature thermal accumulator is coupled to the closed circuit.

[0074] In an aspect, the medium-temperature thermal accumulator is configured to absorb and store heat from the heat transport fluid or to give previously stored heat to the heat transport fluid.

[0075] In an aspect, the medium-temperature thermal accumulator is placed on a connecting branch of the closed circuit which connects the first branch to the second branch of said closed circuit.

[0076] In an aspect, the heat transfer device comprises: a forward heat exchanger placed on the first part of the forward path and on the second part of the forward path to directly and thermally couple said first part of the forward path and second part of the forward path.

[0077] In an aspect, the heat transfer device comprises: a return heat exchanger placed on the first part of the return path and on the second part of the return path to directly and thermally couple said first part of the return path and second part of the return path.

[0078] In an aspect, the compressor comprises a first compressor and a second compressor in series.

[0079] In an aspect, the high-temperature thermal accumulator is placed between the first compressor and the second compressor. In an aspect, the second part of the forward path is placed downstream of the second compressor.

[0080] In an aspect, the compressor comprises a first expander and a second expander placed in series.

[0081] In an aspect, the high-temperature thermal accumulator is placed between the first expander and the second expander.

[0082] In an aspect, the second part of the return path is placed downstream of the second expander.

[0083] In an aspect, the high-temperature thermal accumulator comprises a first high- temperature thermal accumulator placed between the first compressor and the second compressor and between the first expander and the second expander.

[0084] In an aspect, the high-temperature thermal accumulator comprises a second high- temperature thermal accumulator operatively placed downward of the second compressor in the storage phase and upwards of the first expander in the release phase.

[0085] In an aspect, the second part of the forward path is placed downstream of the second high-temperature thermal accumulator.

[0086] In an aspect, the first part of the return path is placed upstream of the second high- temperature thermal accumulator.

[0087] 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.

[0088] 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.

[0089] In an aspect, the enclosure is of the single- or double-membrane type.

[0090] 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. 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 weather conditions; 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.

[0091] 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.

[0092] In an aspect, the plant comprises a plurality of reservoirs configured to contain the working fluid in liquid or super-critical phase.

[0093] In an aspect, the reservoir or each reservoir is made of metal, optionally steel, optionally carbon steel.

[0094] In an aspect, the high-temperature 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.

[0095] In an aspect, the high-temperature thermal accumulator is a “pressurized packed bed thermal store”.

[0096] In an aspect, the low-temperature thermal accumulator comprises a container containing water.

[0097] In an aspect, the water in the container containing water is at atmospheric pressure. In an aspect, the compressor is mechanically connected to a motor.

[0098] In an aspect, the compressor is of the centripetal or centrifugal or axial type.

[0099] In an aspect, the expander is mechanically connected to a generator.

[0100] In an aspect, the expander is a turbine.

[0101] In an aspect, the turbine is of the centripetal or centrifugal or axial type.

[0102] In an aspect, a storage pressure of the working fluid in the reservoir is between 15 bar and 120 bar, preferably between 40 bar and 75 bar.

[0103] In an aspect, a temperature of the working fluid in the reservoir is between 0 °C and 90 °C, preferably between 10 °C and 50 °C. 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.

[0104] Description of figures

[0105] This description will be shown below with reference to the attached drawings, provided for illustrative purposes only and, therefore, not limiting thereto, in which:

[0106] ■ figure 1 shows a plant for energy storage and release according to the present invention in a storage phase;

[0107] ■ figure 2 shows the plant of figure 1 in a release phase;

[0108] ■ figure 3 shows a T-S diagram of a process for energy storage and release according to the present invention and implemented by the plant of figure 1 and 2;

[0109] ■ figure 4 shows a variant of the process of figure 3;

[0110] ■ figure 5 shows a variant of the plant according to the present invention in a storage configuration;

[0111] ■ figure 6 shows the plant of figure 5 in a release configuration;

[0112] ■ figure 7 shows a T-S diagram of a process for energy storage and release according to the present invention and implemented by the plant of figure 5 and 6;

[0113] ■ figures 8 and 9 show respectively the storage and release phase of the process according to the invention.

[0114] Detailed description

[0115] With reference to figures 1 and 2, with the reference number 1 it has been overall indicated a plant for energy storage and release according to the present invention. The plant 1 comprises an enclosure 2 configured to contain a working fluid in the 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 gaseous 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 conditions, 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, by means of valves or dampers, not shown. 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.

[0116] The plant 1 comprises a reservoir 6 of high-pressure-resistant material, for example carbon steel. In variants not shown 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.

[0117] 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.

[0118] Table 1

[0119] The working fluid can also consist of mixtures of the above substances with others as well.

[0120] A compressor 8 of the centripetal or centrifugal or axial type, is operationally 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 compressor 8 and an outlet from the compressor 8 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. The compressor 8 is mechanically connected to a motor 9. The motor 9 is an electric motor and is for example powered by the power grid or by a wind generator or photovoltaic panel system.

[0121] An expander 10, defined by a respective expansion turbine of the centripetal or centrifugal or axial type, is operatively interposed between the reservoir 6 and the enclosure 2. Connecting conduits connect an outlet from the reservoir 6 with an inlet of the expander 10 and an outlet from the expander 10 with an inlet in the variable volume 5 of the enclosure 2. The compressor 8 is then placed in parallel with respect to the expander 10. The compressor 10 is mechanically connected to a generator 11 . The generator 11 is for example connected to the power grid or other electrical power users. The motor 9 and the generator 11 can be also the same electrical machine connected to both the compressor 8 and the turbine 10 by means of clutches or frictions.

[0122] A high-temperature thermal accumulator 12 is in fluid connection, on one side, with the outlet of the compressor 8 and the inlet of the expander 10 and, on the opposite side, with the outlet of the expander 10 and the inlet of the compressor 8. The high- temperature thermal accumulator 12 is for example a 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 compressor 8 or of the working fluid from the expander 10.

[0123] The plant 1 comprises a low-temperature thermal accumulator 13 matched with the reservoir 6 and schematically shown in figures 1 and 2.

[0124] The low-temperature thermal accumulator 13 is configured to store heat in water and release heat from water. For example, the low-temperature thermal accumulator 13 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 low-temperature thermal accumulator 13 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 present in the reservoir 6 (in an energy storage phase / configuration) or coming from the compressor 8 and directed to the reservoir 6 or give heat to the working fluid present in the reservoir 6 or coming from the reservoir 6 and directed to the expander 12 (in an energy release phase / configuration).

[0125] In the embodiment of figures 1 and 2, the connecting conduits are shown as a single tract that from the enclosure 2 connects bifurcating to both the inlet of the compressor 8 and the outlet of the expander 10, and as a single tract that from the reservoir 6 connects bifurcating to both the outlet of the compressor 8 and the inlet of the expander 10. These tracts are then crossed by the working fluid in one direction in the storage phase and in the opposite direction in the release one. The connecting ducts define a forward path from the enclosure 6 through the compressor 8, the high-temperature thermal accumulator 12, the low-temperature thermal accumulator 13 and up to the reservoir 6 and a return path from the reservoir 6, through the low-temperature thermal accumulator 13, the high-temperature thermal accumulator 12, the expander 10 and up to the enclosure 2. In other embodiments, not shown, connecting ducts are divided into storage connecting ducts, configured to carry the working fluid from the enclosure 2 to the reservoir 6 in the storage configuration, and release connecting ducts configured to carry the working fluid from the reservoir 6 to the enclosure 2 in the release configuration.

[0126] The plant further comprises a heat transfer device 14 operatively coupled to a first part of the forward path placed between the enclosure 2 and the compressor 8 and to a second part of the forward path placed between the high-temperature thermal accumulator 12 and the reservoir 6. In the shown embodiment, the mentioned second part is placed between the thermal accumulator 12 and the low-temperature thermal accumulator 13.

[0127] The heat transfer device 14 is further operatively coupled to a first part of the return path placed between the reservoir 6 and the high-temperature thermal accumulator 12 and to a second part of the return path placed between the expander 10 and the reservoir 6. In the shown embodiment, the mentioned first part is placed between the low-temperature thermal accumulator 13 and the high-temperature thermal accumulator 12. In particular, the heat transfer device 14 comprises a first heat exchanger “HE1” placed on the first part of the forward path and on the second part of the return path, which, in the embodiment shown, are defined by the one tract that, starting from enclosure 2, connects by bifurcating to both the inlet of compressor 8 and the outlet of expander 10.

[0128] The heat transfer device 14 comprises a second heat exchanger “HE2” placed on the second part of the forward path and on the first part of the return path, which, in the embodiment shown, are defined by the one tract that, starting from enclosure 6, connects by bifurcating to both the outlet of compressor 8 and the inlet of expander 10.

[0129] The heat transfer device 14 comprises a closed circuit 15 that extends between the first heat exchanger “HE1” and the second heat exchanger “HE2”. The closed circuit

[0130] 15 comprises a first branch 16 extended between the first heat exchanger “HE1” and the second heat exchanger “HE2” and a second branch 17 extended between the second heat exchanger “HE2” and the first heat exchanger “HE1”. Inside the closed circuit 15 flows a heat transport fluid defined for example by water, water and glycol, or oil.

[0131] In the non-limiting embodiment of figures 1 and 2, an air cooler 18 is operatively active on the first branch 16 of the closed circuit 15. The air cooler 18 comprises a respective auxiliary heat exchanger interfaced with the external environment and provided with fans to dispose heat outwards.

[0132] A cooler or a heater 19 provided with a respective auxiliary heat exchanger is operatively coupled to the second branch 17 of the closed circuit 15. The cooler 19 is for example coupled to an auxiliary accumulator to store heat removed for cooling. The heater 19 is for example coupled to an external heat source that gives heat to the heat transport fluid.

[0133] A cooler or a heater 20 provided with a respective auxiliary heat exchanger is further operatively active on the first branch 16 of the closed circuit 15 and is operatively thermally coupled to the low-temperature thermal accumulator 13, to the reservoir

[0134] 16 and to the external environment.

[0135] The plant 1 shown comprises further a medium-temperature thermal accumulator 21 placed on a connecting branch 22 belonging to the closed circuit 15. This connecting branch 22 connects the first branch 16 to the second branch 17 of said closed circuit 15. The medium-temperature thermal accumulator 21 is configured to absorb and store heat from the heat transport fluid or to give previously stored heat to the heat transport fluid.

[0136] The plant 1 above described is configured to implement a process for energy storage and release according to the present invention, in accordance with what is shown, for example, in figures 3, 4, 8A and 8B. Figure 4 is a T-S diagram of an example of the process. The plant has an energy storage phase and an energy release phase.

[0137] In the energy storage phase / configuration (figure 1), the working fluid exits the enclosure 2 (by operating special valves not shown), in which it is contained in gaseous phase, in pressure equilibrium with the atmosphere and at the ambient temperature Tamb, and flows sequentially along a forward path and through the first heat exchanger HE1 , the compressor 8, the high-temperature thermal accumulator 12, the second heat exchanger HE2, the low-temperature thermal accumulator 13 and is stored in the reservoir 6 in liquid phase. In the closed circuit 15, the water circulates counterclockwise moving from the first HE1 to the second heat exchanger HE2 through the first branch 16 (forward branch) and from the second heat exchanger HE2 to the first heat exchanger HE1 through the second branch 17 (return branch).

[0138] With reference to figure 4, in the first heat exchanger HE1 , the working fluid is preheated (A-B) by the water circulating in the closed circuit 15. In the compressor 8, the working fluid is compressed (B-C) by using the external electrical energy from for example the power grid to drive the motor 9. In the high-temperature thermal accumulator 12, the working fluid releases an amount of heat Q that is stored in said high-temperature thermal accumulator 12. The working fluid is here cooled (C-D). In the second heat exchanger HE2, the working fluid is cooled further (D-E) by removing internal heat QE1 from the working fluid which is given to the circulating water in the closed circuit 15. In a heat exchanger of the low-temperature thermal accumulator 13, the working fluid is condensed (E-F) by removing an additional amount of heat Qu from the working fluid that is stored in the water of the low- temperature thermal accumulator 13. The working fluid flows into the reservoir 6 and there accumulated in liquid phase (F). As can be seen in figure 4, through the heat transfer device 14 the internal heat QE1 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 15 absorbs the internal heat QE1 from the working fluid in (D-E) and gives it at least partially to the working fluid in (A-B).

[0139] While the working fluid is stored in the reservoir 6, the working fluid properties (temperature and pressure) vary slightly (figure 4: F-G).

[0140] If needed, it is possible to cool and / or heat the water of the closed circuit 15 through the mentioned coolers / heaters 18, 19, 20 to control the temperatures of the working fluid.

[0141] In the energy release phase / configuration (figures 2 and 4), the working fluid exits the reservoir 6 in which it is contained in the liquid phase and flows along a return path and sequentially through the low-temperature thermal accumulator 13, the second heat exchanger HE2, the high-temperature thermal accumulator 12, the first heat exchanger HE1 and is stored back into the enclosure 2 in the gas phase. In the closed circuit 15, the water circulates clockwise moving from the first HE1 to the second heat exchanger HE2 through the second branch 17 (forward branch) and from the second heat exchanger HE2 to the first heat exchanger HE1 through the first branch 16 (return branch).

[0142] With reference to figure 4, in the heat exchanger of the low- temperature thermal accumulator 13, the working fluid is evaporated (G-H) by supplying to it the additional amount of heat Qu previously stored in the water of said low-temperature thermal accumulator 13. In the second heat exchanger HE2, the working fluid receives heat from the water of the closed circuit 15 and heats up (H-l). In the high- temperature thermal accumulator 12, the amount of heat Q previously stored is given to the working fluid; the working fluid is then further heated (l-L). In the expander 10, the working fluid expands and cools (L-M), setting movable organs of the first expander 10 in motion (such as the impeller of a turbine) and then generates electrical energy through the first generator 11. In the first heat exchanger HE1 , the working fluid is cooled (M-O) from the water circulating in the closed circuit 15, before returning in the enclosure 2. The internal heat QE2 is given to the water circulating in the closed circuit 15. As can be seen in figure 4, through the heat transfer device 14 the internal heat removed in (M-O) is recovered at least partially QE2 and used in (H-l) to preheat the working fluid from the reservoir 6. The water that circulates in the closed circuit 15 absorbs the internal heat from the working fluid in (M-O) and gives it at least partially QE2 to the working fluid in (H-l) and partially Qout gives it to the external environment in (N-O).

[0143] The following Table 2 shows example temperatures and pressures of points A, B, C, D, E, F (storage) and G, H, I, L, M, N, O (release) of the T-S diagram of figure 4 that shows the above-described process with carbon dioxide (CO2).

[0144] Table 2

[0145] In the storage configuration, the plant stores heat and potential energy in the form of pressure and in the release phase the process generates electrical energy.

[0146] Figure 3 shows a variant of the process of the invention wherein, unlike what is shown in figure 4, in the storage phase, the working fluid is not pre-heated in the first heat exchanger HE1 but the heat Qout removed in the second heat exchanger HE2 is given to the external environment.

[0147] Figures 5 and 6 show a variant of the plant 1 that comprises a first compressor 8A and a second compressor 8B placed between them in series and a first expander 10A and a second expander 10B placed between them in series. The high- temperature thermal accumulator 12 is placed between an outlet of the first compressor 8A and an inlet of the second compressor 8B. The high-temperature thermal accumulator 12 is further placed between an outlet of the first expander 10A and an inlet of the second expander 10B. The second part of the forward path, where it is placed the second heat exchanger “HE2”, is then placed downstream of the second compressor 8B and the second part of the return path, where it is placed the first heat exchanger “HE1”, is placed downstream of the second expander 10B. Furthermore, an auxiliary cooler 23 is arranged just upstream of the inlet of the second compressor.

[0148] With reference to figure 7, in the storage configuration (figure 5), after the preheating (A-B) implemented through the first heat exchanger (HE1), the working fluid is compressed a first time (B-C) in the first compressor 8A, cooled by giving the mentioned amount of heat (Q) in the high-temperature thermal accumulator 12 (C- D), further cooled by the auxiliary cooler 23 (D-D’), compressed a second time in the second compressor 8B (D’-C’), cooled (C’-E’) in the second heat exchanger (HE2), again cooled (E’-E) and condensed (E-F) through the low-temperature thermal accumulator 13. The heat transfer device 14 removes heat (QE1) in (C’-E’) and transfers it in (A-B).

[0149] With reference to figure 7, in the release phase (figure 6), the working fluid is evaporated (G-H) and heated (H-H’) through the low-temperature thermal accumulator 13. The working fluid is then heated (H’-l) in the second heat exchanger (HE2), made expanded a first time in the first expander 10A (l-L’), heated (L’-L) in the high-temperature thermal accumulator 12 through the amount of heat previously stored, made expanded a second time in the second expander 10A (L-M), cooled again (M-N-O) through the first heat exchanger (HE1). The heat transfer device 14 removes heat in (M-N) and transfers it in (H’-l).

[0150] In embodiment variants, the working fluid in the storage phase is brought in supercritical conditions and at the end of the compression or of the compressions and is stored in the reservoir 6 in liquid or super-critical phase. Also in the release phase, the working fluid can be brought in super-critical conditions before expanding in the expander or in the expanders.

[0151] In embodiment variants, the displacement of internal heat in the storage phase is implemented by a direct exchange of said internal heat between the second part of the forward path and the first part of the forward path and, in the release phase, between the second part of the return path and the first part of the return path. It is then not present the closed circuit 15 with the heat transport fluid but the heat transfer device 14 comprises: a forward heat exchanger placed on the first part of the forward path and on the second part of the forward path to directly and thermally couple said first part of the forward path and second part of the forward path and a return heat exchanger placed on the first part of the return path and on the second part of the return path to directly and thermally couple said first part of the return path and second part of the return path.

[0152] In embodiment variants, the plant 1 , in addition to all the elements shown in figures 5 and 6, comprises an additional high-temperature thermal accumulator placed downstream of the second compressor 8B in the storage phase and upstream of the first expander 10a in the release phase. In other words, there is a first high- temperature thermal accumulator placed between the first compressor 8A and the second compressor 8B and between the first expander 10A and the second expander 10B and a second high-temperature thermal accumulator placed between the second compressor 8B and the second heat exchanger HE2 and then between said second heat exchanger HE2 and the first expander 10A. The second part of the forward path, upon which it is placed the second heat exchanger HE2 is then placed downstream of the second high-temperature thermal accumulator and the first part of the return path, upon which it is equally placed the second heat exchanger HE2 is placed upstream of the second high-temperature thermal accumulator. It follows that the storage phase of the process provides for removing a first amount of heat (Q1) after compressing the working fluid the first time and removing a second amount of heat (Q2) after compressing the working fluid the second time and the release phase of the same process provides for giving the first amount of heat (Q1) to the working fluid before making the working fluid expand the first time and giving the second amount of heat (Q2) to the working fluid before making the working fluid expand the second time.

[0153] List of elements

[0154] 1 plant

[0155] 2 enclosure

[0156] 3 inner membrane

[0157] 4 outer membrane

[0158] 5 variable volume 6 reservoir

[0159] 7 inner volume

[0160] 8 compressor

[0161] 9 motor

[0162] 10 expander

[0163] 11 generator

[0164] 12 high-temperature thermal accumulator

[0165] 13 low-temperature thermal accumulator

[0166] 14 heat transfer device

[0167] 15 closed circuit

[0168] 16 first branch

[0169] 17 second branch

[0170] 18 air cooler

[0171] 19 cooler or a heater

[0172] 20 cooler or a heater

[0173] 21 medium-temperature thermal accumulator

[0174] 22 connection branch

[0175] 23 auxiliary cooler

[0176] HE1 first heat exchanger

[0177] HE2 second heat exchanger

Claims

CLAIMS1. Process for energy storage and release, comprising: implementing a closed cyclic thermodynamic transformation (TTC), first in a forward path in a storage phase and then in a return path 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; 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: compressing the working fluid from the enclosure (2) using external energy to be stored; removing an amount of heat (Q) from the working fluid to cool it and storing said amount of heat (Q); removing an additional amount of heat (Qu) from the working fluid to increase a density of the working fluid, storing the additional amount of heat (Qu), and storing the working fluid in the reservoir (6) in liquid or super-critical phase; wherein the release phase comprises: extracting the working fluid from the reservoir (6) and bringing it into the gas phase by giving to the working fluid the additional amount of heat (Qu) previously stored; giving to the working fluid the amount of heat (Q) previously stored to heat it; making the working fluid expand to release energy; feeding the working fluid back into the enclosure (2) in the gas phase and in pressure equilibrium with the atmosphere; wherein the storage phase also comprises: moving internal heat between different portions of the working fluid flowing respectively in a first part of the forward path, downstream of the enclosure (2) and before compressing the working fluid, and in a second part of the forward path, after removing the amount of heat (Q) and before accumulating the working fluid in the reservoir (6) in the liquid or super-critical phase; and / orwherein the release phase also comprises: moving internal heat between different portions of the working fluid flowing respectively in a first part of the return path, between the working fluid storage in the reservoir (6) in the liquid or super-critical phase and before giving the amount of heat (Q) to the working fluid, and in a second part of the return path, after expanding the working fluid and before the enclosure (2).

2. Process according to claim 1 , wherein, in the storage phase, the second part of the forward path is before removing the additional amount of heat (Qu).

3. Process according to claim 1 or 2, wherein, in the release phase, the first part of the return path is after giving to the working fluid the additional amount of heat (Qu).

4. Process according to any one of claims 1 to 3, wherein in the release phase, the internal heat is moved from the second part of the return path to the first part of the return path, to cool the working fluid after expansion and optionally to heat the working fluid before giving the amount of heat (Q) to the working fluid.

5. Process according to any one of claims 1 to 4, wherein, in the storage phase, the internal heat is moved from the second part of the forward path to the first part of the forward path, to heat the working fluid before compression and optionally to cool the working fluid before removing the additional amount of heat (Qu).

6. Process according to any one of claims 1 or 5, wherein the transfer of the internal heat is implemented by a heat transport fluid operating in at least one closed circuit (15); wherein said heat transport fluid is selected from the group comprising: water, water and glycol, oil.

7. Process according to claim 6, further comprising: cooling the heat transport fluid by disposing of excess heat to the external environment or by transferring it to an auxiliary storage and / or heating the heat transport fluid by absorbing auxiliary heat from an external heat source or from the auxiliary storage.

8. Process according to any one of claims 1 to 5, wherein the displacement of internal heat is implemented by a direct exchange of said internal heat between the second part of the forward path and the first part of the forward path and / or between the first part of the return path and the second part of the return path.

9. Process according to any one of claims 1 to 8, wherein compressing the working fluid comprises compressing the working fluid a first time and compressing the working fluid a second time; wherein the amount of heat (Q) is removed after compressing the working fluid the first time and before compressing the working fluid the second time or wherein removing the amount of heat (Q) comprises removing a first amount of heat (Q1) after compressing the working fluid the first time and removing a second amount of heat (Q2) after compressing the working fluid the second time; and wherein making the working fluid expand comprises making the working fluid expand a first time and making the working fluid expand a second time; wherein the amount of heat (Q) is given after making the working fluid expand the first time and before making the working fluid expand the second time or wherein giving the amount of heat (Q) comprises giving the first amount of heat (Q1) to the working fluid before making the working fluid expand the first time and giving the second amount of heat (Q2) to the working fluid before making the working fluid expand the second time; where the second part of the forward path is either after compressing the working fluid the second time or after removing the second amount of heat (Q2); wherein the first part of the return path is either before the second amount of heat (Q2) is given to the working fluid or before the working fluid expands the first time.

10. 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 the 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 compressor (8; 8A, 8B) operationally interposed between the enclosure (2) and the reservoir (6); an expander (10; 10A, 10B) operationally interposed between the enclosure (2) and the reservoir (6), wherein the compressor (8; 8A, 8B) is placed in parallel with respect to the expander (10; 10A, 10B); a high-temperature thermal accumulator (12) in fluid connection, on one side, with the compressor (8; 8A, 8B) and the expander (10; 10A, 10B) and, on an opposite side, with the reservoir (6), wherein the high-temperature thermal accumulator (12) is configured to exchange an amount of heat (Q) with the working fluid and store or release said amount of heat (Q); a low-temperature thermal accumulator (13) interposed between the high- temperature thermal accumulator (12) and the reservoir (6), wherein the low- temperature thermal accumulator (13) is configured to exchange an additional amount of heat (Qu) with the working fluid and to store or release said additional amount of heat (Qu); connecting ducts defining a forward path from the enclosure (2), through the compressor (8; 8A, 8B), the high-temperature thermal accumulator (12), the low- temperature thermal accumulator (13) and up to the reservoir (6) and a return path from the reservoir (6), through the low-temperature thermal accumulator (13), the high-temperature thermal accumulator (12), the expander (10; 10A, 10B) and up to the enclosure (2); 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 in the forward path, from the enclosure (2) to the reservoir (6) and is stored in the reservoir (6); in the energy release configuration, the working fluid transits in the return path, from the reservoir (6) to the enclosure (2) and is again stored in the enclosure (2), wherein in the storage configuration the plant (1) stores heat and potential energy in the form of pressure and in the release configuration the plant (1) generates energy; wherein the plant (1) further comprises a heat transfer device (14) operatively coupled to a first part of the forward path between the enclosure (2) and the compressor (8; 8A, 8B) and to a second part of the forward path between the high- temperature thermal accumulator (12) and the reservoir (6) and / or operationallycoupled to a first part of the return path between the reservoir (6) and the high- temperature thermal accumulator (12) and to a second part of the return path between the expander (10; 10A, 10B) and the enclosure (2); wherein, in the energy storage configuration, the heat transfer device (14) is configured to move internal heat between the second part of the forward path and the first part of the forward path; and / or wherein, in the energy release configuration, the heat transfer device (14) is configured to move internal heat between the second part of the return path and the first part of the return path.

11. Plant according to claim 10, wherein the second part of the forward path is between the high-temperature thermal accumulator (12) and the low-temperature thermal accumulator (13).

12. Plant according to claim 10 or 11 , wherein the first part of the return path is between the low-temperature thermal accumulator (13) and the high-temperature thermal accumulator (12).

13. Plant according to any one of claims 10 to 12, wherein the heat transfer device (14) comprises: a first heat exchanger (HE1) located on the first part of the forward path and on the second part of the return path, a second heat exchanger (HE2) located on the second part of the forward path and on the first part of the return path, at least one closed circuit (15) extending between the first heat exchanger (HE1) and the second heat exchanger (HE2), a heat transport fluid circulating in the closed circuit (15).

14. Plant according to claim 13, wherein said heat transport fluid is chosen from the group including: water, water and glycol, oil.

15. Plant according to claim 13 or 14, wherein the heat transfer device (14) further comprises a cooler and / or heater (18, 19, 20) operatively active on the closed circuit (15); wherein the cooler comprises a respective auxiliary heat exchangerinterfaced with the external environment; and / or wherein the heater comprises a respective auxiliary heat exchanger interfaced with an external heat source.

16. Plant according to claim 10, wherein the heat transfer device (14) comprises: a forward heat exchanger placed on the first part of the forward path and on the second part of the forward path to directly and thermally couple said first part of the forward path and second part of the forward path; a return heat exchanger placed on the first part of the return path and on the second part of the return path to directly and thermally couple said first part of the return path and second part of the return path.

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