Plant and process for energy management

Abstract

A plant and a process for energy management which carry out a closed thermodynamic cyclic transformation (TTC), first in one direction in a charging phase and then in an opposite direction in a discharging phase, between a gasometer (2) for storing carbon dioxide in the gaseous phase and at a first storage pressure (PAG') in equilibrium with atmospheric pressure and a mass accumulator (11) for storing carbon dioxide in the liquid phase at a second storage pressure (PA'H). In the charging phase, it is provided for removing heat from the mass accumulator (11) to condense part of the vapor phase of the carbon dioxide contained in it and keep the second storage pressure (PA'H) constant or substantially constant. In the discharging phase, it is provided for transferring heat to the mass accumulator (11) to evaporate part of the liquid phase of the carbon dioxide contained in it and keep the second storage pressure (PA'H) constant or substantially constant.

Description

[0001] Plant and process for energy management

[0002] DESCRIPTION

[0003] Field of the finding

[0004] The present invention has as object a plant and a process for energy management, where with management is intended the absorption, the storage, the transformation and the generation of energy.

[0005] More precisely, the present invention has as object a system capable of absorbing / using energy, of keeping over the time the stored energy and capable of transforming it back into available energy, for example electric, thermal, mechanical energy.

[0006] The present invention can be placed for example in the context of systems for generation from various sources and energy storage of medium and large scale, for both terrestrial and marine applications, typically with powers of hundreds of kW up to tens of MW (for example 20-25MW), but also hundreds of MW, and with storage capacities from a few hundred kWh, up to hundreds of MWh and also up to several GWh. The present invention can also be placed in the field of systems for generation from various sources and energy storage of small scale, for domestic and commercial applications, both terrestrial and marine, typically with powers from a few kW up to a few hundred kW and with storage capacities from a few kWh, up to hundreds of kWh.

[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 inside the cycle significant for energy purposes.

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

[0012] • Open CT and / or TTC: with mass exchange (significant for energy purposes) with the atmosphere.

[0013] • Light overpressure: pressure higher than the atmospheric pressure with a pressure difference with respect to the atmospheric pressure of a few millibars up to a few tens of millibars, for example from 3 - 4 mbar to 70 - 80 mbar.

[0014] Background of the finding

[0015] The public document W02020 / 039416, on behalf of the same Applicant, shows a process and a plant for energy storage. The plant comprises a casing for the storage of a working fluid other than atmospheric air, in the gaseous phase and in pressure eguilibrium with the atmosphere; a reservoir for the storage of this working fluid in the 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 carry out a closed cyclic thermodynamic transformation, first in one direction in a storage configuration and then in an opposite direction in a discharge configuration, between the casing and the reservoir. In the storage configuration the plant accumulates heat and pressure and in the discharge configuration it generates energy.

[0016] Also documents WO2021 / 165809, WO2021 / 191786 and WO2022 / 101727, all on behalf of the same Applicant, show plants based on the same principle shown in W02020 / 039416 (closed cyclic thermodynamic transformation between two mass accumulations).

[0017] Summary

[0018] The Applicant has noted that the above-described processes and plants in documents WO / 2020 / 039416, WO2021 / 165809, WO2021 / 191786 and WO2022 / 101727 can be further improved, in particular with reference to the optimization of the processes and the simplicity of plant construction.

[0019] The Applicant has in particular noted that plants and processes such as the abovedescribed ones that work specifically in the supercritical field, i.e., that are configured to operate a super-critical transformation of the working fluid and accumulate said working fluid in the reservoir at high pressure in the super-critical phase, present criticalities in terms of complexity and cost of the storage systems. Indeed, for example, WO / 2020 / 039416 shows the use of variable volume chambers and compensation circuits to be able to store the working fluid in the super-critical phase and keep a substantially constant pressure in the working fluid in the supercritical phase.

[0020] The Applicant has therefore aimed at conceiving and realizing a system operating by means of cyclic and supercritical thermodynamic transformations (TTC) of a working fluid, similar to those shown in WO / 2020 / 039416, that allows to store more easily and efficiently the working fluid in the high-pressure storage.

[0021] The Applicant has also more generally aimed at realizing a system (plant and process) for absorption, storage (Energy Storage), transformation and generation of energy of the super-critical TTC type such as to allow to manage (absorb, store, transform, generate, sort) the energy coming from various sources (nonrenewable sources and fuels, such as fossil fuels, and renewable and also synthetic sources and fuels) in a flexible, efficient and effective way.

[0022] The Applicant has found that the above indicated objectives can be reached by adopting technical solutions that allow to operate under super-critical conditions but to store the working fluid under sub-critical conditions in high-pressure storage.

[0023] In particular, the indicated objectives and others are substantially achieved by a plant and by a process for the management (absorption, storage, transformation, generation) of energy of the type claimed in the attached claims and / or described in the following aspects.

[0024] In a first independent aspect, the present invention refers to a plant for energy management, comprising: a working fluid other than atmospheric air; a gasometer internally bounding a variable volume containing or configured to contain the working fluid in the gaseous phase and at a first storage pressure (PAG’) constant and equal to the atmospheric pressure or slightly over-pressurized relative to the atmospheric pressure; a compressor in fluid connection with the gasometer; an expander in fluid connection with the gasometer; a thermal accumulator in fluid connection with the compressor and with the expander and configured to exchange heat with the working fluid; a mass accumulator internally bounding a constant volume containing or configured to contain the working fluid in the liquid phase at a second storage pressure (PA’H), the mass accumulator being in fluid connection with the thermal accumulator; a pressure reducing device operatively active between the thermal accumulator and the mass accumulator; a pump operatively active between the thermal accumulator and the mass accumulator; a heat exchange apparatus operatively coupled to the mass accumulator and configured to exchange heat with the working fluid present in the mass accumulator; pipelines and control devices configured to operate the plant in a charging configuration and in a discharging configuration.

[0025] In the charging configuration the working fluid transits from the gasometer to the mass accumulator through the compressor, the thermal accumulator and the pressure reducing device and is accumulated in the mass accumulator; the compressor compresses the working fluid to an end compression pressure (PC; PC2) higher than a critical pressure (Per) of the working fluid, the thermal accumulator absorbs heat from the working fluid and cools said working fluid to an end-cooling temperature (TE) close to the critical temperature (Ter) of the working fluid, preferably lower or a bit higher than the critical temperature (Ter) of the working fluid; the pressure reducing device reduces a pressure of the working fluid to a reduced pressure (PG) lower than the critical pressure (Per) of said working fluid; the working fluid is accumulated in the mass accumulator at the second storage pressure (PA’H) lower than the critical pressure (Per) of the working fluid and in equilibrium with its own vapor phase. In the charging configuration, the heat exchange apparatus removes heat from the mass accumulator to condense part of the vapor phase of the working fluid contained in the mass accumulator and keep the second storage pressure (PA’H) constant or substantially constant in said mass accumulator.

[0026] In the discharging configuration the working fluid transits from the mass accumulator to the gasometer through the pump, the thermal accumulator and the expander and is accumulated in the gasometer; the pump pumps the working fluid with a discharge pressure (PC’) higher than the critical pressure (Per) of the working fluid, the thermal accumulator transfers heat, previously accumulated, to the working fluid and heats said working fluid, the expander expands the working fluid and the working fluid is accumulated in the gasometer at the first storage pressure (PAG’). In the discharging configuration, the heat exchange apparatus transfers heat to the mass accumulator to evaporate part of the liquid phase of the working fluid contained in the mass accumulator and keep the second storage pressure (PA’H) constant or substantially constant in said mass accumulator.

[0027] In a second independent aspect, the present invention refers to a process for energy management, comprising: carrying out a closed cyclic thermodynamic transformation (TTC), first in one direction in a charging phase and then in an opposite direction in a discharging phase, between a gasometer for the storage of a working fluid other than atmospheric air, in the gaseous phase and at a first storage pressure (PAG’) in equilibrium with the atmospheric pressure, and a mass accumulator for the storage of said working fluid in the liquid phase at a second storage pressure (PA’H); wherein in the charging phase the process stores heat and pressure and in the discharging phase generates energy using previously stored heat and pressure.

[0028] In the charging phase, the process comprises: compressing the working fluid to an end compression pressure (PC; PC2) higher than a critical pressure (Per) of the working fluid, cooling said working fluid to an end-cooling temperature (TE) close to the critical temperature (Ter) of the working fluid by storing the heat removed from the working fluid, reducing the pressure of the working fluid to a reduced pressure (PG) lower than the critical pressure (Per) of said working fluid, storing the working fluid in the mass accumulator at the second storage pressure (PA’H) lower than the critical pressure (Per) of the working fluid and in equilibrium with its own vapor phase; wherein in the charging phase the process comprises also: removing heat from the mass accumulator to condense part of the vapor phase of the working fluid contained in the mass accumulator and to keep the second storage pressure (PA’H) constant or substantially constant in said mass accumulator. Preferably, the endcooling temperature (TE) is lower or a bit higher than the critical temperature (Ter) of the working fluid. In the discharging phase, the process comprises: pumping the working fluid with a discharge pressure (PC’) higher than the critical pressure (Per) of the working fluid, transferring heat, previously accumulated, to the working fluid and heating said working fluid, expanding the working fluid and storing it in the gasometer at the first storage pressure (PAG’); wherein, in the discharging phase, the process comprises also: transferring heat to the mass accumulator to evaporate part of the liquid phase of the working fluid contained in the mass accumulator and to keep the second storage pressure (PA’H) constant or substantially constant in said mass accumulator.

[0029] In the charging phase / configuration, to keep constant or substantially constant the pressure in the mass accumulator, the increase of the volume occupied by the working fluid that is stored in the liquid phase (i.e. the reduction of the volume occupied by the working fluid vapor) is compensated by condensing all or part of the vapor of the working fluid already contained in the mass accumulator and the one possibly generated during the pressure reduction, if the expansion ends inside the Andrews bell.

[0030] In the discharging phase / configuration, to keep constant or substantially constant the pressure in the mass accumulator, the decrease of the volume of the working fluid in the liquid phase (i.e. the increase of the volume occupied by the working fluid vapor) is compensated by evaporating part of the liquid of the working fluid, otherwise the system depressurizes and cools.

[0031] The plant of the first aspect is configured to carry out the process of the second aspect and / or the process as defined in one or more of the aspects that will follow. The process of the second aspect can be carried out via the apparatus of the first aspect and / or via the plant defined in one or more of the aspects that will follow.

[0032] The Applicant has verified that the plant and the process according to the invention allow to obtain the predetermined objectives.

[0033] The Applicant has verified that the plant and the process according to the invention allow to perform super-critical transformations and at the same time to store the working fluid in the mass accumulator under sub-critical conditions and in the liquid phase in equilibrium with an its own limited vapor phase (two-phase mass accumulator under sub-critical conditions). In the internal volume of the mass accumulator is in fact not present any separator septum between the liquid phase and the vapor phase of the working fluid.

[0034] In particular, the Applicant has verified that the heat exchange apparatus allows to remove heat from the mass accumulator in an amount equal to the latent heat of condensation of part of the vapor initially contained in the mass accumulator that must condense to allow the accumulation of liquid without pressure increase or with a controlled pressure increase. The heat exchange apparatus allows then to keep the second storage pressure constant or substantially constant in the mass accumulator.

[0035] Further aspects of the invention are listed below.

[0036] In an aspect, the expander is coupled to an electrical generator.

[0037] In an aspect, the compressor is coupled to an electrical motor.

[0038] In an aspect, the working fluid is carbon dioxide (CO2) or comprises carbon dioxide (CO2) or is a mixture comprising carbon dioxide as main component. Alternatively, the working fluid is chosen from the group comprising: mixtures of carbon dioxide (CO2) and further substances (in order to correct the critical temperature of the working fluid), SFe, N2O or mixtures of them.

[0039] In an aspect, a ratio between the second storage pressure (PA’H) and the critical pressure (Per) of the working fluid is between 0.2 and 0.99 preferably between 0.4 and 0.95.

[0040] In an aspect, a ratio between the end compression pressure (PC; PC2) and the critical pressure (Per) of the working fluid is between 1.01 and 10.0, preferably between 1.05 and 2.5.

[0041] In an aspect, a ratio between an end-cooling pressure (PE) and the critical pressure (Per) of the working fluid is between 1.01 and 10.0, preferably between 1.05 and 2.5.

[0042] In an aspect, a ratio between the reduced pressure (PG) and the critical pressure (Per) of the working fluid is between 0.01 and 0.99, preferably between 0.4 and 0.9. The reduced pressure (PG) corresponds to the second storage pressure (PA’H) or is only lightly different, for example by a few bars (for example from 1 bar to 5 bar), from the second storage pressure (PA’H). In an aspect, a ratio between the end-cooling temperature (TE) in degrees Kelvin and the critical temperature (Ter) in degrees Kelvin is between 0.4 and 1.1 preferably between 0.75 and 0.95.

[0043] In an aspect, if the working fluid is carbon dioxide (CO2), the second storage pressure (PA’H) is between 20 bar and 70 bar, optionally between 40 bar and 60 bar.

[0044] In an aspect, a liquid / vapor separator is operatively arranged between the pressure reducing device and the mass accumulator.

[0045] In an aspect, a chiller is operatively arranged between the thermal accumulator and the pressure reducing device. In the charging configuration of the plant, the chiller is configured to remove heat from the working fluid entering the pressure reducing device in order to reduce and / or cancel a vapor title of said working fluid at an outlet of the pressure reducing device.

[0046] In an aspect, after cooling the working fluid to the end-cooling temperature (TE) close to the critical temperature (Ter) and before reducing the pressure of the working fluid to the reduced pressure (PG), it is provided for removing heat from the working fluid in order to reduce and / or cancel a vapor title of said working fluid at the end of the pressure reduction, optionally via the chiller of the previous aspect.

[0047] In an aspect, the pressure reducing device comprises a lamination valve.

[0048] In an aspect, in the charging phase, reducing the pressure of the working fluid comprises: laminating the working fluid, optionally via the lamination valve of the previous aspect.

[0049] In an aspect, the chiller is configured to remove heat from the working fluid entering the pressure reducing device, i.e. in the lamination valve, so that an end pressure reduction temperature (TG) of the working fluid exiting said pressure reducing device, i.e. from the lamination valve, is less than a saturated temperature of said working fluid at the reduced pressure (PG) that corresponds to the second storage pressure (PA’H) or is slightly different from the second storage pressure (PA’H).

[0050] In an aspect, removing heat from the working fluid in order to reduce and / or cancel the vapor title of said working fluid at the end of the pressure reduction comprises: bringing the working fluid at the end of the pressure reduction to an end pressure reduction temperature (TG) less than a saturated temperature of said working fluid at the reduced pressure (PG) that corresponds to the second storage pressure (PA’H) or is slightly different from the second storage pressure (PA’H).

[0051] The end pressure reduction temperature (TG) is such that the working fluid at the discharge of the pressure reducing device results sub-cooled with the advantage of not adding vapor to be condensed in the mass accumulator. By subcooling it is possible to condense partly or in toto the vapor of the working fluid contained in the mass accumulator at the beginning of the charging phase, ensuring that the pressure in the mass accumulator is constant or changes a little during the charging phase and reducing or eliminating in toto the heat to be subtracted from the system in the charging phase.

[0052] In an alternative aspect, the pressure reducing device comprises an auxiliary expander, for example an auxiliary turbine.

[0053] In an aspect, the auxiliary expander is capable of extracting energy and transforming it in mechanical and / or electrical energy.

[0054] In an aspect, the auxiliary expander is coupled to an auxiliary electric power generator.

[0055] In an aspect, the auxiliary expander is of action type and in particular is a Pelton turbine.

[0056] In an aspect, in the charging phase, reducing the pressure of the working fluid comprises: subjecting the working fluid to an auxiliary expansion, optionally via the auxiliary expander of the previous aspect.

[0057] In an aspect, the chiller is configured to remove heat from the working fluid entering the auxiliary expander so that the working fluid remains in subcooled liquid status at an outlet of said auxiliary expander.

[0058] In an aspect, removing heat from the working fluid in order to reduce and / or cancel the vapor title of said working fluid at the end of the pressure reduction comprises: removing heat from the working fluid before the auxiliary expansion so that during and at the end of the auxiliary expansion the working fluid remains in subcooled liquid status.

[0059] The Applicant has verified that the chiller allows to obtain an expansion efficiency much higher than a possible two-phase expansion, resulting in the additional advantage of not adding vapor to be condensed in the successive mass accumulator. Also in this case, by subcooling it is possible to condense partly or in toto the vapor of the working fluid contained at the beginning of the charging, ensuring that the pressure in the mass accumulator is constant or changes a little during the charging phase and reducing or eliminating in toto the heat to be subtracted from the system in the charging phase.

[0060] In an aspect, an auxiliary chiller is operatively arranged between the mass accumulator and the pump. In the discharging configuration of the plant, the auxiliary chiller is configured to remove heat from the working fluid entering the pump and reduce risks of a possible cavitation of said pump.

[0061] In an aspect, before pumping the working fluid, in the discharging phase it is provided for removing heat from the working fluid to reduce risks of a possible cavitation in the subsequent pumping, optionally via the auxiliary chiller of the previous aspect.

[0062] The Applicant has verified that by increasing the sub-cooling in inlet pump reduces the risk of cavitation and increases the available net positive suction height (Net Positive Suction Head - NPSH).

[0063] This is an alternative to the configuration wherein the pump is put several meters below the minimum level of the liquid to be pumped (to give NPSH). With the auxiliary chiller in suction, it subcools by reducing the temperature of the fluid while the pressure remains constant.

[0064] In an aspect, the heat exchange apparatus is configured to exchange heat with the external environment.

[0065] In an aspect, the heat exchange apparatus comprises: a heat accumulator configured to exchange heat with the working fluid in the charging configuration and in the discharging configuration, a heat exchanger operatively coupled to the heat accumulator and to the external environment.

[0066] The heat accumulator is configured to store heat (latent) of the working fluid in charging phase and transfer it during the discharging phase.

[0067] In an aspect, the heat exchanger is a cooler / chiller, air directed, or in indirect contact with the atmosphere, for example through a refrigerating fluid storage system and / or a cooling tower and / or air cooler and / or water cooler with river or sea water and / or a chiller.

[0068] In an aspect, the chiller is operatively connected to the heat exchange apparatus. In an aspect, removing heat from the mass accumulator and / or transferring heat to the mass accumulator comprises / e: exchanging heat with the external environment, directly or indirectly, optionally via the heat exchange apparatus according to one or more of the preceding aspects.

[0069] In an aspect, the thermal accumulator comprises a first thermal accumulator at high temperature and a second thermal accumulator at low temperature.

[0070] In an aspect, in the charging configuration the first thermal accumulator at high temperature cools the working fluid to an intermediate temperature (TD; TD1 ) higher than the critical temperature (Ter) and the second thermal accumulator at low temperature cools the working fluid from the intermediate temperature (TD1 ) to the end-cooling temperature (TE) close to critical temperature (Ter).

[0071] In an aspect, each of the operations of cooling the working fluid, in the charging phase, and of heating the working fluid, in the discharging phase, is performed in two stages, optionally via the first thermal accumulator at high temperature and the second thermal accumulator at low temperature of the preceding aspects.

[0072] In an aspect, in the charging phase, in a first phase, the working fluid is cooled to an intermediate temperature (TD) higher than the critical temperature (Ter) and, in a second phase, the working fluid is cooled from the intermediate temperature (TD) to the end-cooling temperature (TE) close to critical temperature (Ter).

[0073] In an aspect, a ratio between the intermediate temperature (TD) in degrees Kelvin and the critical temperature (Ter) in degrees Kelvin is between 1.01 and 2.0, preferably between 1.1 and 1.3.

[0074] The purpose of dividing into the mentioned two phases is to not to have a hot thermal accumulator that is affected by the effects of the actual gas near the critical point, in particular to not to be affected by the variation of the specific heat as the temperature changes.

[0075] In an aspect, the second thermal accumulator at low temperature comprises: a first heat exchanger and a second heat exchanger configured to exchange heat with the working fluid.

[0076] In an aspect, the second thermal accumulator at low temperature comprises: a first reservoir at low temperature, a second reservoir at intermediate temperature and a third reservoir at high temperature containing water, optionally at environmental pressure, and in fluid connection with the first heat exchanger and with the second heat exchanger.

[0077] In an aspect, the first heat exchanger and the second heat exchanger are arranged in series on a working fluid pipeline.

[0078] In an aspect, water flow rates in the first heat exchanger and in the second heat exchanger are different from each other.

[0079] The Applicant has verified that the above shown structure is capable of increasing the efficiency of the second thermal accumulator at low temperature by minimizing the differences in heat exchange temperature (around the critical point wherein the specific heat varies as the temperature varies).

[0080] In an aspect, the end-cooling temperature (TE) in the charging configuration is greater than a pump discharge temperature (TC’) in the discharging configuration.

[0081] The Applicant has verified that this allows to obtain, for the “colder” part of the thermal accumulator (second thermal accumulator at low temperature) a zeroenergy system, i.e. , such that, during the discharging phase, all the heat stored in the charging phase is used.

[0082] In an aspect, a heat transfer device is operatively coupled to working fluid pipelines located downstream of the expander and to working fluid pipelines located downstream of the pump.

[0083] In an aspect, in the discharging configuration, the heat transfer device is configured to transfer part of the discharge heat of the expander to the working fluid in the supercritical state downstream of the pump.

[0084] In an aspect, the heat transfer device is connected to the second thermal accumulator at low temperature.

[0085] In an aspect, the heat transfer device is in fluid connection with the first heat exchanger and with the second heat exchanger.

[0086] In an alternative aspect, the heat transfer device is in fluid connection with an additional heat exchanger placed in parallel with the first heat exchanger and with second heat exchanger.

[0087] In an aspect, the heat transfer device is also operatively coupled to the heat exchange apparatus to remove surplus heat. In an aspect, in the discharging phase, it is provided for transferring to the external environment, optionally via the heat exchange apparatus, surplus heat of the part of the transferred heat.

[0088] In an aspect, the heat transfer device is operatively coupled to the heat exchange apparatus via the second thermal accumulator at low temperature.

[0089] In an aspect, a thermal exchange circuit, connected to the heat exchange apparatus, is coupled to the second thermal accumulator at low temperature to exchange heat with water exiting from the first heat exchanger and / or from the second heat exchanger in the discharging phase / configuration.

[0090] In an aspect, in the discharging phase, it is provided for transferring part of the heat of the expanded working fluid to the working fluid in the supercritical state before heating it or during its heating, optionally via the heat transfer device according to one or more of the preceding aspects.

[0091] The Applicant has verified that this allows to perform the discharging phase at a pressure higher with respect to the charging pressure, increasing the cycle efficiency.

[0092] In an aspect, a first additional heat exchanger is placed between the gasometer and an inlet of the compressor and is configured to regulate a compressor inlet temperature (TB; TB1 ).

[0093] In an aspect, the first additional heat exchanger is configured to perform a preheating (pre-heating), for example with the heat generated by mechanical and electrical inefficiency of the compressor.

[0094] In an aspect, the first additional heat exchanger is configured to perform a precooling (pre-cooling), for example transferring heat to the environment by means of dry coolers, towers, seawater, river water, chillers.

[0095] In an aspect, the first additional heat exchanger is operatively connected to the heat exchange apparatus.

[0096] In an aspect, in the charging phase, it is provided for regulating a temperature (TA) of the working fluid coming from the gasometer before compression, optionally via the first additional heat exchanger according to one or more of the preceding aspects. In an aspect, a second additional heat exchanger is placed between an outlet of the expander and the gasometer and is configured to regulate a gasometer inlet temperature (TG’).

[0097] In an aspect, the second additional heat exchanger is operatively connected to the heat exchange apparatus.

[0098] In an aspect, in the discharging phase, it is provided for regulating a temperature (TF’) of the expanded working fluid before entering in the gasometer, optionally via the second heat exchanger according to one or more of the preceding aspects.

[0099] In an aspect, the first and the second additional heat exchanger are defined by a same exchanger.

[0100] In an aspect, a recuperator is operatively active between both the gasometer and the compressor and between the gasometer and the expander.

[0101] In an aspect, the recuperator is also operatively coupled to the thermal accumulator. In an aspect, the recuperator is configured to exchange heat between the working fluid flowing through the thermal accumulator and the working fluid entering the compressor, in the charging configuration, or exiting the expander, in the discharging configuration.

[0102] In an aspect, in the charging phase, it is provided for using part of the heat removed from the working fluid during cooling to the end-cooling temperature (TE) to heat the working fluid before the compression. This allows, in the charging phase, to increase the specific work of the cycle, optionally via the recuperator according to one or more of the preceding aspects.

[0103] In an aspect, in the discharging phase, it is provided for using part of the heat recovered from the expanded working fluid to heat further the working fluid after pumping and before expansion, optionally via the recuperator according to one or more of the preceding aspects. This allows, in the discharging phase, to increase the cycle efficiency.

[0104] In an aspect, the recuperator is operatively interposed between the first thermal accumulator at high temperature and the second thermal accumulator at low temperature.

[0105] In an aspect, the recuperator is configured to exchange heat between the working fluid flowing between the first thermal accumulator at high temperature and the second thermal accumulator at low temperature and the working fluid entering the compressor, in the charging configuration, or exiting the expander, in the discharging configuration.

[0106] In an aspect, a second compressor is connected in series with the compressor and a second expander is connected in series with the expander.

[0107] In an aspect, the first thermal accumulator at high temperature, in the charging configuration, is operatively active between the compressor and the second compressor and also downstream of the second compressor.

[0108] In an aspect, the first thermal accumulator at high temperature, in the discharging configuration, is operatively active upstream of the second expander and also between the second expander and the expander.

[0109] In an aspect, in the charging phase, compressing and cooling the working fluid comprises: performing a first compression followed by a first cooling and then performing a second compression followed by a second cooling, optionally via the compressor, the first thermal accumulator at high temperature and the second compressor according to one or more of the preceding aspects.

[0110] In an aspect, at the end of the first compression the working fluid is at a subcritical pressure (PC1 ) and at the end of the second compression the working fluid is at the pressure (PC2) higher than the critical pressure (Per).

[0111] In an aspect, temperatures of the working fluid (TC1 , TC2) at the end of the first compression and of the second compression are similar or equal.

[0112] In an aspect, in the discharging phase, heating and expanding the working fluid comprises: performing a first heating followed by a first expansion and then performing a second heating followed by a second expansion, optionally via the expander, the first thermal accumulator at high temperature and the second expander according to one or more of the preceding aspects.

[0113] Further features and advantages will be clearer from the detailed description of preferred, but not exclusive embodiments of a plant and of a process according to the present invention.

[0114] Description of figures

[0115] This description will be shown below with reference to the attached drawings, provided for illustrative purposes only and, therefore, not limiting thereto, in which: ■ figure 1 schematically shows an embodiment of a plant for energy management according to the present invention;

[0116] ■ figure 2 is a T-S diagram relative to the plant of figure 1 ;

[0117] ■ figure 3 shows schematically a first variant of the plant according to the present invention;

[0118] ■ figure 4 is a T-S diagram relative to the plant of figure 3;

[0119] ■ figure 5 is a schematic showing of one of the elements of the plants referred to in the preceding or following figures;

[0120] ■ figure 6 shows schematically a second variant of the plant according to the present invention;

[0121] ■ figure 7 is a T-S diagram relative to the plant of figure 6;

[0122] ■ figure 8 is a schematic showing of a different element of the plants referred to in the preceding or following figures;

[0123] ■ figure 9 is a portion of T-S diagram relative to the element of figure 8;

[0124] ■ figure 10 shows schematically a third variant of the plant according to the present invention;

[0125] ■ figure 10A is a magnification of a part of figure 10;

[0126] ■ figure 11 is a portion of T-S diagram relative to the plant of figure 10;

[0127] ■ figure 12 shows schematically a fourth variant of the plant according to the present invention;

[0128] ■ figure 13 is a T-S diagram relative to the plant of figure 12;

[0129] ■ figure 14 shows schematically a fifth variant of the plant according to the present invention;

[0130] ■ figure 15 is a T-S diagram relative to the plant of figure 14;

[0131] ■ figure 16 shows schematically a sixth variant of the plant according to the present invention;

[0132] ■ figure 17 is a T-S diagram relative to the plant of figure 16.

[0133] Detailed description

[0134] With reference to the attached figures, with the reference number 1 it has been overall indicated a plant for energy management according to the present invention.

[0135] Figures 1 and 2 The plant of figure 1 comprises carbon dioxide (CO2) as working fluid. In variants within the scope of the present invention, the working fluid can be a mixture comprising carbon dioxide as main component or SFe, N2O or mixtures of them.

[0136] The carbon dioxide is confined within a closed circuit suitable for carrying out a closed thermodynamic cyclic transformation (TTC), first in a direction in a charging configuration / phase and then in an opposite direction in a discharging configuration / phase, between two mass accumulations of said carbon dioxide (CO2).

[0137] For this purpose, the plant 1 comprises a gasometer 2 that internally bounds a variable volume 3 containing or configured to contain the carbon dioxide in the gaseous phase and at a first storage pressure (PAG’) constant and equal to the atmospheric pressure or slightly over-pressurized relative to the atmospheric pressure.

[0138] In the shown embodiment, the gasometer 2 is of the double membrane type and comprises an internal membrane 201 containing the carbon dioxide and an external membrane 202 in contact with the external environment. The gasometer 2 is arranged on the surface and is externally in contact with the atmospheric air. The internal membrane 201 of the gasometer 2 internally bounds the volume 3 configured to contain the carbon dioxide at atmospheric or substantially atmospheric pressure, i.e. in pressure equilibrium with the atmosphere. The external membrane 202 keeps constantly its own shape excepting for small variations with the purpose of protecting the internal membrane 201 from the external environment and from the atmospheric agents, such as sun, rain, wind, snow, etc. The gap delimited between the internal membrane 201 and the external 202 one is filled with environmental air by means of ventilators and is kept a constant pressure of few millibar. The gasometer 2 can also be realized as any other low or zero overpressure gas storage system, wherein as the volume of the working fluid varies, the pressure is kept constant or substantially constant.

[0139] The plant 1 comprises a compressor 4 in fluid connection with the gasometer 2 and an expander 5 in fluid connection with the gasometer 2. The compressor 4 is for example a centrifugal compressor moved by a respective motor 6. The expander 5 is for example a radial or axial turbine connected to an electrical generator 7. First pipelines 8 connect the gasometer 2 to an inlet 4a of the compressor 4 and, in parallel, to an outlet 5b of the expander 5.

[0140] The plant 1 comprises a thermal accumulator 9 in fluid connection with the compressor 4 and with the expander 5 and configured to exchange heat with the carbon dioxide. The thermal accumulator 9 is a TES (Thermal Energy Storage) that comprises a thermal mass (for example water, oil or melted salts or also solid materials) capable of receiving, absorbing and storing heat transferred from the carbon dioxide that transits in direct or indirect contact (through heat exchangers) with the thermal mass or of transferring heat, previously accumulated, to the carbon dioxide that transits in direct or indirect contact (through heat exchangers) with the thermal mass. Second pipelines 10 connect an outlet 4b of the compressor 4 and, in parallel, an inlet 5a of the expander 5 to the thermal accumulator 9.

[0141] The plant 1 comprises a mass accumulator 11 that internally bounds a constant volume 12 containing or configured to contain the working fluid in the liquid phase at a second storage pressure (PA’H). The mass accumulator 11 is shown schematically in the attached figures and can, for example, comprise one or more reservoirs, for example metallic, suitable for bearing the second storage pressure (PA'H) without substantially deforming, i.e. keeping the volume (or respective volumes) constant 12. Third pipelines 13 connect the thermal accumulator 9 with an inlet 11 a of the mass accumulator 11 and, in parallel, with an outlet 11 b of the mass accumulator 11. A first branch 13a of the third pipelines 13 connects the thermal accumulator 9 with the inlet 11a of the mass accumulator 11 and a second branch 13b of the third pipelines 13 connects the outlet 11 b of the mass accumulator 11 with the thermal accumulator 9.

[0142] Between the thermal accumulator 9 and the mass accumulator 11 is arranged a pressure reducing device 14 configured to reduce the pressure of the carbon dioxide that flows in the first branch 13a of the third pipelines 13, from the thermal accumulator 9 toward the mass accumulator 11 . A pump 15 is instead arranged on the second branch 13b of the third pipelines 13 to pump the carbon dioxide from the mass accumulator 11 toward the thermal accumulator 9, according to the process which will be described in the following. The plant 1 comprises also a heat exchange apparatus 16 operatively coupled to the mass accumulator 11 and configured to exchange heat with the working fluid present in the mass accumulator 11 .

[0143] The mentioned first, second and third pipelines 8, 10, 13, together with electrical or electronic control devices (for example, actuated valves, control units, sensors etc..) are configured to operate the plant 1 in the mentioned charging configuration / phase and in the mentioned discharging configuration / phase, according to the process of the present invention and according to the closed thermodynamic cyclic transformation (TTC).

[0144] The process will be described by referring to figure 1 and the T-S diagram of figure 2.

[0145] In an initial state, the carbon dioxide present in the plant 1 is substantially almost all contained in the internal volume 3 of the gasometer 2 and is in pressure equilibrium with the atmosphere of the external environment (figure 2- point A), i.e. in the gaseous phase and at the first storage pressure (PAG1) constant and substantially equal to the atmospheric one.

[0146] In the charging configuration / phase (figures 1 and 2: points A-C-E-G-H), the carbon dioxide transits from the gasometer 2 to the mass accumulator 11 through the compressor 4, the thermal accumulator 9, the pressure reducing device 14 and is accumulated in the mass accumulator 11 in the liquid phase at a second storage pressure (PA’H).

[0147] In particular, the compressor 4 compresses the carbon dioxide exiting the internal volume 3 of the gasometer 2 to an end compression pressure (PC) higher than a critical pressure (Per) of the working fluid (figures 1 and 2: from point A to point C). For example, a ratio between the end compression pressure (PC) and the critical pressure (Per) of the carbon dioxide is 2. The carbon dioxide heats to an end compression temperature (TC) corresponding to the end compression pressure (PC).

[0148] Then, while the super-critical carbon dioxide passes through the thermal accumulator 9, said thermal accumulator 9 absorbs heat from the carbon dioxide and stores it. The carbon dioxide cools to an end-cooling temperature (TE) close to the critical temperature (Ter) of the carbon dioxide (figures 1 and 2: from point C to point E). In the shown examples, the end-cooling temperature (TE) is lower than the critical temperature (Ter) of the working fluid but, in other embodiments, this endcooling temperature (TE) can be also a bit higher than the critical temperature. For example, a ratio between the end-cooling temperature (TE) in degrees Kelvin and the critical temperature (Ter) in degrees Kelvin of the carbon dioxide is 0.90 or 1 .01 . For example, a ratio between the end cooling pressure (PE) and the critical pressure (Per) of the carbon dioxide is 2.

[0149] The super-critical carbon dioxide at this point passes in the pressure reducing device 14 which reduces its pressure to a reduced pressure (PG) lower than the respective critical pressure (Per). For example, a ratio between the reduced pressure (PG) and the critical pressure (Per) of the carbon dioxide is 0.68.

[0150] The carbon dioxide cools to a reduced temperature (TG) (figures 1 and 2: from point E to point G). In the diagram of figure 2 it is represented the pressure reduction operated by a pressure reducing device 14 defined by a lamination valve (E-G section with G inside the Andrews bell).

[0151] The carbon dioxide exiting the lamination valve is stored in the mass accumulator 11 at the second storage pressure (PA’H) that can correspond to the reduced pressure (PG) or can be slightly different, for example of a few bar (for example, from 1 bar to 5 bar), from the reduced pressure (PG) and lower than the critical pressure (Per). The carbon dioxide is in equilibrium with its own vapor phase (figures 1 and 2: point H). For example, the second storage pressure (PA’H) is equal to 50 bar and a ratio between the second storage pressure (PA’H) and the critical pressure (Per) of the carbon dioxide (73 bar) is equal to 0.68. Between the lamination valve and the mass accumulator 11 can be present a liquid-vapor separator or an area within the mass accumulator 11 can be used to separate the vapor phase from the liquid phase.

[0152] While the carbon dioxide in prevalent liquid phase enters the mass accumulator 11 and fills it, the heat exchange apparatus 16 removes heat from the mass accumulator 11 to condense part of the vapor phase of the carbon dioxide contained in the mass accumulator 11 and keeps the second storage pressure (PA’H) constant or substantially constant.

[0153] In other words, the increase of the volume occupied by the carbon dioxide that is stored in the liquid phase in the mass accumulator 11 (i.e., the reduction of the volume occupied by the working fluid vapor) is compensated by condensing all or part of the vapor of the carbon dioxide already contained in the mass accumulator 11 and the one generated during the pressure reduction.

[0154] In the charging configuration / phase, the plant 1 absorbs electric energy coming from an external grid that feeds the motor 6 of the compressor 4 and stores it in the form of heat and pressure.

[0155] At the end of the charging phase (point H), the carbon dioxide present in the plant 1 is substantially almost all contained in the internal volume 12 of the mass accumulator 11 under sub-critical conditions and in the liquid phase in equilibrium with its own limited vapor phase (two-phase mass accumulator under sub-critical conditions). In the internal volume 12 of the mass accumulator 11 there is no separating septum between the liquid phase and the vapor phase of the carbon dioxide.

[0156] In the discharging configuration / phase (figures 1 and 2: points A’-B’-C’-E’-G’), the carbon dioxide transits from the mass accumulator 11 to the gasometer 2 through the pump 15, the thermal accumulator 9 and the expander 5 and is again stored in the gasometer 2 in the gaseous phase and at the first storage pressure (PAG’) constant in pressure equilibrium with the atmosphere.

[0157] In particular, the pump 15 pumps the liquid carbon dioxide with a discharge pressure (PC’) higher than the critical pressure (Per) of the carbon dioxide (figures 1 and 2: points B’-C’). The carbon dioxide heats to a discharge temperature (TC’).

[0158] Then, while the carbon dioxide passes through the thermal accumulator 9, said thermal accumulator 9 transfers the heat previously accumulated to the carbon dioxide. The carbon dioxide heats to an end heating temperature (TE’) (figures 1 and 2: from point C’ to point E’).

[0159] Then, the carbon dioxide expands inside the expander 5 moving mechanical organs of the expander 5, for example turning the impeller or impellers of the turbine, and generating electrical energy via the electrical generator 7 (figures 1 and 2: points E’- G’). In the discharging configuration / phase, the plant 1 generates energy using previously stored heat and pressure. The carbon dioxide exiting the expander 5 is again stored in the gasometer 2 at the first storage pressure (PAG’).

[0160] In the discharging configuration, the heat exchange apparatus 16 transfers heat to the mass accumulator 11 to evaporate part of the liquid phase of the carbon dioxide contained in the mass accumulator 11 and keeps the second storage pressure constant or substantially constant (PA’H).

[0161] In other words, in the discharging phase / configuration, to keep constant or substantially constant the pressure in the mass accumulator 11 , the decrease of the volume of the carbon dioxide in the liquid phase (i.e. the increase of the volume occupied by the carbon dioxide vapor) is compensated evaporating part of the liquid of the carbon dioxide, so that the mass accumulator 11 doesn't depressurize and doesn't cool down.

[0162] Figures 3 and 4 - first variant

[0163] Figures 3 and 4 show schematically a first variant of the plant 1 (and of the respective process) that differs from the above-described plant 1 of figures 1 and 2 because of the further presence of a chiller 17 and of an auxiliary chiller 18. The chiller 17 is arranged on the first branch 13a of the third pipelines 13 and is interposed between the thermal accumulator 9 and the pressure reducing device 14.

[0164] In the charging configuration / phase (figures 3 and 4: points A-C-E-F-G-H), the chiller 17 removes heat from the carbon dioxide entering the lamination valve, so that an end pressure reduction temperature (TG) of the carbon dioxide exiting the lamination valve is less than a saturated temperature of the carbon dioxide at the reduced pressure (PG) that corresponds to the second storage pressure (PA’H) or is slightly different from the second storage pressure (PA’H). Unlike the T-S diagram of figure 2, in figure 4, the carbon dioxide from point E moves to the point F (refrigeration) and then in the point G (lamination) and then rises toward the point H. The removal of heat from the carbon dioxide entering the pressure reducing device 14 operated by the chiller 17 allows to reduce and / or cancel a vapor title of the carbon dioxide at an outlet of the pressure reducing device 14.

[0165] The auxiliary chiller 18 is operatively arranged on the second branch 13b of the third pipelines 13 and is interposed between the mass accumulator 11 and the pump 15. In the discharging configuration / phase, the auxiliary chiller 18 allows to remove heat from the carbon dioxide entering the pump 15 and to reduce risks of a possible cavitation during the pumping in said pump 15. This sub-cooling (sub-cooling) at the inlet of pump 15, in addition to reduce the risk of cavitation, it also increases the available net positive suction height (Net Positive Suction Head - NPSH).

[0166] The pressure reducing device 14 of the plant of figure 3 can also be not a lamination valve but an auxiliary expander, for example an auxiliary turbine, for example of action type, as a Pelton turbine. The auxiliary expander is coupled to an auxiliary electric power generator, not shown, and is capable of extracting energy and transforming it in mechanical and / or electrical energy in the charging phase / configuration.

[0167] In this other variant, the chiller 17 removes heat from the carbon dioxide before entering the auxiliary expander so that the carbon dioxide remains in subcooled liquid status at an outlet of said auxiliary expander. This allows to obtain an expansion efficiency much higher than a possible two-phase expansion.

[0168] The chiller 17 and the auxiliary chiller 18 can also be connected to the heat exchange apparatus 16 to exchange heat with this heat exchange apparatus 16 and with the external environment.

[0169] Figure 5 - heat exchange apparatus

[0170] Figure 5 shows a schematic example of the heat exchange apparatus 16 combined with the mass accumulator 7 and usable in the plants shown here.

[0171] In this example, the heat exchange apparatus 16 is configured to exchange heat, further than with the carbon dioxide contained in the mass accumulator 11 , also with the external environment. Therefore, the heat exchange apparatus 16 allows to remove heat from the mass accumulator 11 and / or transferring heat to the mass accumulator 11 exchanging heat with the external environment.

[0172] The heat exchange apparatus 16 shown comprises a heat accumulator 19 configured to exchange heat with the carbon dioxide and a heat exchanger 20 operatively coupled to the heat accumulator 19 and to the external environment. The heat accumulator 19 stores heat Q (latent) of the carbon dioxide in charging phase / configuration and transfers heat Q to the carbon dioxide in discharging phase / configuration.

[0173] In the example of figure 5, the heat accumulator 19 comprises a respective circuit 21 wherein circulates a thermal carrier. The circuit 21 extends inside the mass accumulator 11 to exchange heat with the carbon dioxide and with a thermal mass of the heat accumulator 19.

[0174] The heat exchanger 20 comprises a respective circuit 22 wherein circulates a thermal carrier. The circuit 22 extends until inside the heat accumulator 19 to exchange heat with the thermal mass of the heat accumulator 19 and with the environment. In embodiment variants, the circuit 22 can be inverted, i.e. the same means used for storing heat in the heat accumulator 19 is used for exchanging heat with the heat exchanger 20.

[0175] The heat exchanger 20 can be an air directed cooler / chiller, or in indirect contact with the atmosphere, for example through a refrigerating fluid storage system and / or a cooling tower and / or air cooler and / or water cooler with river or sea water and / or a chiller.

[0176] A bypass circuit 23 can put into direct fluid communication the circuit 22 of the heat accumulator 19 with the circuit 22 of the heat exchanger 20.

[0177] Figures 6, 7, 8 and 9 - second variant

[0178] Figures 6 and 7 show schematically a second variant of the plant 1 (and of the respective process) that differs from the above-described plant 1 of figures 1 and 2 in that it comprises the chiller 17 shown for the plant of figures 3 and 4 and in that the thermal accumulator 9 comprises a first thermal accumulator 9a at high temperature and a second thermal accumulator 9b at low temperature. The double thermal accumulator 9a, 9b allows to perform each of the operations of cooling the carbon dioxide, in the charging phase, and of heating the carbon dioxide, in the discharging phase in two phases.

[0179] With reference to the T-S diagram of figure 7, in the charging configuration / phase, the first thermal accumulator 9a at high temperature cools the carbon dioxide to an intermediate temperature (TD) higher than the critical temperature (Ter) and the second thermal accumulator 9b at low temperature cools the carbon dioxide from the intermediate temperature (TD) to the end-cooling temperature (TE) close to the critical temperature (Ter). A ratio between the intermediate temperature (TD) and the critical temperature (Ter) is for example equal to 1.3.

[0180] In the discharging configuration / phase, the second thermal accumulator 9b at low temperature heats the carbon dioxide to an intermediate temperature (TD’) higher than the critical temperature (Ter) and the first thermal accumulator 9a at high temperature heats the carbon dioxide from the intermediate temperature (TD’) to the end heating temperature (TE’).

[0181] Figure 8 is a schematic example of the second thermal accumulator 9b at low temperature. In that example, the second thermal accumulator 9b at low temperature comprises a first heat exchanger 24a and a second heat exchanger 24b arranged in series on the second pipelines 10 and configured to exchange heat with the carbon dioxide that flows through the second pipelines 10.

[0182] The second thermal accumulator 9b at low temperature comprises also a first reservoir 25a at low temperature, a second reservoir 25b at intermediate temperature and a third reservoir 25c at high temperature.

[0183] A conduit 26 connects in series the first reservoir 25a with the first heat exchanger 24a, with the second heat exchanger 24b and with the third reservoir 25c. An auxiliary conduit 27 connects the second reservoir 25b with a point of the conduit 26 placed between the first heat exchanger 24a and the second heat exchanger 24b. The conduit 26 exiting the first reservoir 25a is provided with a respective first pump 28a and with a first shut-off and regulation valve 29a arranged in parallel. The conduit 26 exiting the second reservoir 25c is provided with a respective third pump 28c and of a third shut-off and regulation valve 29c arranged in parallel. The auxiliary conduit 27 exiting the second reservoir 25b is provided with a respective second pump 28b and with a second shut-off and regulation valve 29b arranged in parallel. The first reservoir 25a, the second reservoir 25b and the third reservoir 25c contain non-pressurized water, i.e. at environmental pressure. The first pump 28a is configured to pump water from the first reservoir 25a toward the first heat exchanger 24a. The second pump 28b is configured to pump water from the second reservoir 25a towards the connection point of the auxiliary conduit 27 to the conduit 26. The third pump 28c is configured to pump water from the third reservoir 25c toward the second heat exchanger 24b. In this way, water flow rates through the first heat exchanger 24a and through the second heat exchanger 24b are different from each other. In this way, it is possible to minimize the differences of heat exchange temperatures between water and carbon dioxide and thus increase the efficiency of the second thermal accumulator 9b at low temperature. The T-S diagram portion of figure 9 shows the carbon dioxide that cools in charging phase (from point D to point E) and the corresponding water line that heats (a - b - c). The T-S diagram portion of figure 9 shows also the carbon dioxide that heats in discharging phase (from point C’ to point D’) and the corresponding water line that cools (c - b - a). The end-cooling temperature (TE) in the charging configuration is greater than a pump discharge temperature (TO) in the discharging configuration. This allows to obtain, for the “colder” part of the thermal accumulator, i.e. for the second thermal accumulator 9b at low temperature, a zero-energy system, i.e., such that, during the discharging phase, all the heat stored in the charging phase is used.

[0184] Figures 10, IQA and 11 - third variant

[0185] Figures 10, 10A and 11 schematically show a third variant of the plant 1 (and of the respective process) that differs from the plant 1 of the above-described second variant (figures 6, 7, 8 and 9) in that it comprises also a heat transfer device 30 operatively coupled to the first pipelines 8 of the working fluid located downstream of the outlet 5b of the expander 5 and to the third pipelines 13 of the working fluid located downstream of the pump 15. In the discharging configuration / phase, this heat transfer device 30 is configured to transfer part of the discharge heat of the expander 5 to the working fluid in the supercritical state downstream of the pump 15.

[0186] Also, the second thermal accumulator 9b at low temperature (figure 10A) is similar but not identical to the one shown in figure 8 for the second variant. Unlike the one of figure 8, the third pump 28c of the third reservoir 25c is placed on a circuit part 31 that extends to a heat exchanger 32 arranged on the first pipelines 8 and downstream of the outlet 5b of the expander 5. In the discharging configuration / phase, the third pump 28c is configured to pump the water from the third reservoir 25c towards the heat exchanger 32 and, back, toward the second heat exchanger 24b.

[0187] The heat transfer device 30 comprises therefore this circuit part 31 with the respective heat exchanger 32. Therefore, the part of the discharge heat of the expander 5 is transferred to the working fluid in the supercritical state downstream of the pump 15 via the water of the second thermal accumulator 9b at low temperature. In the charging configuration / phase, the third pump 28c is not operative, the third shut-off and regulation valve 29c is open and in regulation, and the first and the second pump 28a, 28b work. In the discharging configuration / phase, the closed third shut-off and regulation valve 29c and the third pump 28c is operative.

[0188] Figure 11 is a portion of the T-S diagram that shows the effect of the transfer of part of the discharge heat of the expander 5 to the working fluid in the supercritical state downstream of the pump 15 performed via the heat transfer device 30. In the charging phase / configuration, the carbon dioxide cools (D- E) while the water heats (a - b - c). In the discharging phase / configuration, by effect of the heat transfer device 30, the water cools along the line placed higher (c’ - b’ - a’) and the carbon dioxide heats from C’ to D’.

[0189] In a not shown variant, the heat transfer device 30 is in fluid connection with an additional heat exchanger placed in parallel with the first heat exchanger 24a and with the second heat exchanger 24b.

[0190] As shown in figures 10 and 10A, the heat transfer device 30 is also operatively coupled to the heat exchange apparatus 16 which has the purpose of removing any surplus heat and transferring it to the external environment. The heat transfer device 30 is operatively and indirectly coupled to the heat exchange apparatus 16 via the second thermal accumulator 9b at low temperature. For this purpose, a thermal exchange circuit 33 comprises a respective heat exchanger 34 operatively coupled to the conduit 26 of the second thermal accumulator 9b at low temperature in a point placed between the first heat exchanger 24a and the second heat exchanger 24b to exchange heat with water exiting the first heat exchanger 24a in the discharging phase / configuration. A respective circuit 35 connects this respective heat exchanger 34 with the heat exchange apparatus 16, for example with the heat accumulator circuit 21 of the heat accumulator 19 of figure 5.

[0191] Figures 12 and 13 - fourth variant

[0192] Figures 12 and 13 schematically show a fourth variant of the plant 1 (and of the respective process) that differs from the above-described plant 1 of figures 1 and 2 in that it comprises the chiller 17, shown for the plant of figures 3 and 4, and in that it comprises a first additional heat exchanger 36 placed between the gasometer 2 and the inlet 4a of the compressor 4 and a second additional heat exchanger 37 placed between an outlet 5b of the expander 5 and the gasometer 2.

[0193] The first additional heat exchanger 36 is configured to regulate a compressor inlet temperature (TB), i.e. to modify a temperature (TA) of the carbon dioxide coming from the gasometer 2 before compression. The first additional heat exchanger 36 can be configured to perform a pre-heating (pre-heating A - B in figure 13), for example with heat generated by mechanical and electrical inefficiency of the compressor 4, or to perform a pre-cooling (pre-cooling), for example by transferring heat to the environment by means of dry coolers, towers, seawater, river water, chiller.

[0194] In the shown and example embodiment, the first additional heat exchanger 36 comprises a respective circuit 38 connected with the heat exchange apparatus 16, for example with the heat accumulator circuit 21 of the heat accumulator 19 of figure 5.

[0195] The second additional heat exchanger 37 is configured to regulate an inlet temperature (TG’) to the gasometer 2, i.e. to modify a temperature (TF’) of the expanded carbon dioxide before entering the gasometer 2. Figure 13 shows the cooling F’ - G’ after the expansion E’ - F’ in the discharging phase / configuration.

[0196] In the shown and example embodiment, the second additional heat exchanger 37 comprises a respective circuit 39 connected with the heat exchange apparatus 16, for example with the heat accumulator circuit 21 of the heat accumulator 19 of figure 5. The respective circuit 39 of the second additional heat exchanger 37 can be connected or partly coincident with the respective circuit 38 of the first additional heat exchanger 36. In embodiment variants, the first additional heat exchanger 36 and the second additional heat exchanger 37 can also be defined by a unique exchanger.

[0197] Figures 14 and 15 - fifth variant

[0198] Figures 14 and 15 schematically show a fifth variant of the plant 1 (and of the respective process) that differs from the above-described plant 1 of the second variant of figures 6 and 7 in that it comprises the second additional heat exchanger 37 of the fourth variant and comprises also a recuperator 40. This recuperator 40 is operatively active between both the gasometer 2 and the compressor 4 and between the gasometer 2 and the expander 5 and is operatively coupled to the thermal accumulator 9, in particular it is operatively interposed between the first thermal accumulator 9a at high temperature and the second thermal accumulator 9b at low temperature.

[0199] Pipelines of the carbon dioxide that connect the first thermal accumulator 9a at high temperature with the second thermal accumulator 9b at low temperature are thermally coupled to the first pipelines 8 at the recuperator 40 and the second additional heat exchanger 37 results operatively interposed between the gasometer 2 and this recuperator 40.

[0200] In the charging configuration / phase, the recuperator 40 allows the heat exchange between the carbon dioxide flowing from the first thermal accumulator 9a at high temperature toward the second thermal accumulator 9b at low temperature and the carbon dioxide entering the compressor 2. In the charging configuration / phase, part of the heat removed from the carbon dioxide during cooling to the end-cooling temperature (TE) is used for heating the carbon dioxide before compression (figure 15, D1 - D2, A - B).

[0201] In the discharging configuration / phase, the recuperator 40 allows the heat exchange between the carbon dioxide flowing from the second thermal accumulator 9b at low temperature towards the first thermal accumulator 9a at high temperature and the carbon dioxide exiting the expander 5. In the discharging configuration / phase, part of the heat recovered from the expanded carbon dioxide is used for heating further the carbon dioxide after pumping and before expansion (figure 15, F’1 - F’3, D’1 - D’2).

[0202] Figures 16 and 17 - sixth variant

[0203] Figures 16 and 17 schematically show a sixth variant of the plant 1 (and of the respective process) that differs from the above described plant 1 of the fifth variant of figures 14 and 15 in that it comprises two compressors 4, 41 and two expanders 5, 43. A second compressor 41 mechanically connected to the motor 6 or, as shown, provided with a respective second motor 42 is in fact connected in series with the compressor 4 and a second expander 42 mechanically connected to the generator 7 or, as shown, provided with a respective second generator 44 is connected in series with the expander 5.

[0204] In particular, the outlet 4b of the compressor 4 is connected to an inlet 41 a of the second compressor 41 . An outlet 41 b of the second compressor 41 is connected to the recuperator 40. An inlet 43a of the second expander 43 is connected to the recuperator 40 and an outlet 43b of the second expander 43 is connected to the inlet 5a of the expander 5.

[0205] The first thermal accumulator 9a at high temperature, in the charging configuration / phase, is operatively active between the compressor 4 and the second compressor 41 and also between the second compressor 41 and the recuperator 40. Therefore, in the charging configuration / phase, is performed a first compression (figure 17, B1 - C1 ) followed by a first cooling (figure 17, C1 - B2) and then a second compression (figure 17, B2 - C2) followed by a second cooling (figure 17, C2 - D1 ). At the end of the first compression (C1 ), the carbon dioxide is at a subcritical pressure (PC1 ) and at the end of the second compression the carbon dioxide is at the pressure (PC2) higher than the critical pressure (Per). Temperatures of the carbon dioxide (TC1 , TC2) at the end of the first compression and of the second compression are similar or equal and also the temperatures (TB2, TD1 ) of the carbon dioxide at the end of the first cooling and of the second cooling are similar or equal.

[0206] The first thermal accumulator 9a at high temperature, in the discharging configuration / phase, is operatively active between the recuperator 40 and the second expander 43 and also between the second expander 43 and the expander 5. Therefore, in the discharging configuration / phase, is performed a first heating (figure 17, D’2 - E’1 ) followed by a first expansion (figure 17, E’1 - F’1 ) and then performing a second heating (figure 17, FT - E2’) followed by a second expansion (figure 17, E’2 - F’2).

[0207] List of elements

[0208] 1 plant

[0209] 2 gasometer

[0210] 201 internal membrane

[0211] 202 external membrane 3 internal gasometer volume

[0212] 4 compressor

[0213] 4a compressor inlet

[0214] 4b compressor outlet

[0215] 5 expander

[0216] 5a expander inlet

[0217] 5b expander outlet

[0218] 6 motor

[0219] 7 electrical generator

[0220] 8 first pipelines

[0221] 9 thermal accumulator

[0222] 9a first thermal accumulator

[0223] 9b second thermal accumulator

[0224] 10 second pipelines

[0225] 11 mass accumulator

[0226] 11a mass accumulator inlet

[0227] 11 b mass accumulator outlet

[0228] 12 internal mass accumulator volume

[0229] 13 third pipelines

[0230] 13a first branch of the third pipelines

[0231] 13b second branch of the third pipelines

[0232] 14 pressure reducing device

[0233] 15 pump

[0234] 16 heat exchange apparatus

[0235] 17 chiller

[0236] 18 auxiliary chiller

[0237] 19 heat accumulator

[0238] 20 heat exchanger

[0239] 21 heat accumulator circuit

[0240] 22 heat exchanger circuit

[0241] 23 bypass circuit

[0242] 24a first heat exchanger

[0243] 24b second heat exchanger 25a first reservoir

[0244] 25b second reservoir

[0245] 25c third reservoir

[0246] 26 conduit

[0247] 27 auxiliary conduit

[0248] 28a first pump

[0249] 28b second pump

[0250] 28c third pump

[0251] 29a first shut-off and regulation valve

[0252] 29b second shut-off and regulation valve

[0253] 29c third shut-off and regulation valve

[0254] 30 heat transfer device

[0255] 31 circuit part

[0256] 32 heat exchanger

[0257] 33 thermal exchange circuit

[0258] 34 heat exchanger

[0259] 35 circuit

[0260] 36 first additional heat exchanger

[0261] 37 second additional heat exchanger

[0262] 38 first additional heat exchanger circuit

[0263] 39 second additional heat exchanger circuit

[0264] 40 recuperator

[0265] 41 second compressor

[0266] 41a second compressor inlet

[0267] 41 b second compressor outlet

[0268] 42 second motor

[0269] 43 second expander

[0270] 43a second expander inlet

[0271] 43b second expander outlet

[0272] 44 second generator

Claims

CLAIMS1 . Plant for energy management, comprising: a working fluid other than atmospheric air; a gasometer (2) internally bounding a variable volume (3) containing or configured to contain the working fluid in the gaseous phase and at a constant first storage pressure (PAG1) equal to atmospheric pressure or slightly over-pressurized relative to the atmospheric pressure; a compressor (4; 4, 41 ) in fluid connection with the gasometer (2); an expander (5; 5, 43) in fluid connection with the gasometer (2); a thermal accumulator (9; 9a, 9b) in fluid connection with the compressor (4; 4, 41 ) and the expander (5; 5, 43) and configured to exchange heat with the working fluid; a mass accumulator (11 ) internally bounding a constant volume (12) containing or configured to contain the working fluid in the liquid phase at a second storage pressure (PA'H), the mass accumulator (11 ) being in fluid connection with the thermal accumulator (9; 9a, 9b); a pressure reducing device (14) operatively active between the thermal accumulator (9; 9a, 9b) and the mass accumulator (11 ); a pump (15) operatively active between the thermal accumulator (9; 9a, 9b) and the mass accumulator (11 ); a heat exchange apparatus (16) operatively coupled to the mass accumulator (11 ) and configured to exchange heat with the working fluid in the mass accumulator (11 ); pipelines and control devices configured to operate the plant (1 ) in a charging configuration and in a discharging configuration; wherein in the charging configuration the working fluid transits from the gasometer (2) to the mass accumulator (11 ) through the compressor (4; 4, 41 ), the thermal accumulator (9; 9a, 9b) and the pressure reducing device (14) and is accumulated in the mass accumulator (11 ); the compressor (4; 4, 41 ) compresses the working fluid to an end compression pressure (PC; PC2) above a critical pressure (Per) of the working fluid; the thermal accumulator (9; 9a, 9b) absorbs heat from the working fluid and cools said working fluid to an end-cooling temperature (TE) close to the critical temperature (Ter) of the working fluid; the pressure reducing device (14) reduces a pressure of the working fluid to a reduced pressure (PG) lower than thecritical pressure (Per) of said working fluid; the working fluid is stored in the mass accumulator (11 ) at the second storage pressure (PA'H) lower than the critical pressure (Per) of the working fluid and in equilibrium with its own vapor phase; wherein, in said charging configuration, the heat exchange apparatus (16) removes heat from the mass accumulator (11 ) to condense part of the vapor phase of the working fluid contained in the mass accumulator (11 ) and keep the second storage pressure (PA'H) in said mass accumulator (11 ) constant or substantially constant; wherein in the discharging configuration the working fluid transits from the mass accumulator (11 ) to the gasometer (2) through the pump (15), the thermal accumulator (9; 9a, 9b) and the expander (5; 5, 43) and is accumulated in the gasometer (2); the pump (15) pumps the working fluid with a discharge pressure (PC) higher than the critical pressure (Per) of the working fluid, the thermal accumulator (9; 9a, 9b) transfers heat, previously stored, to the working fluid and heats said working fluid, the expander (5; 5, 43) expands the working fluid and the working fluid is stored in the gasometer (2) at the first storage pressure (PAG1); wherein, in said discharging configuration, the heat exchange apparatus (16) gives up heat to the mass accumulator (11 ) to evaporate part of the liquid phase of the working fluid contained in the mass accumulator (11 ) and keep the second storage pressure (PA'H) in said mass accumulator (11 ) constant or substantially constant.

2. Plant according to claim 1 , comprising a chiller (17) operatively disposed between the thermal accumulator (9; 9a, 9b) and the pressure reducing device (14); in the charging configuration of the plant (1 ), the chiller (17) being configured to remove heat from the working fluid entering the pressure reducing device (14) in order to reduce and / or cancel a vapor title of said working fluid at an outlet of the pressure reducing device (14).

3. Plant according to claim 1 or 2, comprising an auxiliary chiller (18) operatively arranged between the mass accumulator (11 ) and the pump (15); in the discharging configuration of plant (1 ), the auxiliary chiller (18) being configured to remove heat from the working fluid entering the pump (15) and reduce risks of possible cavitation of said pump (15).

4. Plant according to any of claims 1 to 3, wherein the pressure reducing device (14) comprises a lamination valve.

5. Plant according to claim 4 when dependent on 2, wherein the chiller (17) is configured to remove heat from the working fluid entering the lamination valve so that an end pressure reduction temperature (TG) of the working fluid exiting said a lamination valve is less than a saturated temperature of said working fluid at the reduced pressure (PG).

6. Plant according to any of claims 1 to 3, wherein the pressure reducing device (14) comprises an auxiliary expander.

7. Plant according to claim 6 when dependent on 2, wherein the chiller (17) is configured to remove heat from the working fluid entering the auxiliary expander so that the working fluid remains in the liquid subcooled state to an outlet of said auxiliary expander.

8. Plant according to any of claims 1 to 7, comprising a liquid-vapor separator operatively located between the pressure reducing device (14) and the mass accumulator (11 ).

9. Plant according to one of claims 1 to 8, wherein the heat exchange apparatus (16) is configured to exchange heat with the external environment; optionally wherein the heat exchange apparatus (16) comprises: a heat accumulator (19) configured to exchange heat with the working fluid in the charging configuration and the discharging configuration, a heat exchanger (20) operatively coupled to the heat accumulator (19) and to the external environment.

10. Plant according to claim 9 when depending on one of claims 2, 5, 7, wherein the chiller (17) is operatively connected to the heat exchange apparatus (16).11 . Plant according to any one of claims 1 to 10, wherein the thermal accumulator (9; 9a, 9b) comprises a first thermal accumulator (9a) at high temperature and asecond thermal accumulator (9b) at low temperature; wherein in the charging configuration the first thermal accumulator (9a) at high temperature cools the working fluid to an intermediate temperature (TD; TD1 ) higher than the critical temperature (Ter) and the second thermal accumulator (9b) at low temperature cools the working fluid from the intermediate temperature (TD1 ) to the end-cooling temperature (TE) close to the critical temperature (Ter).

12. Plant according to claim 11 , wherein a ratio of the intermediate temperature(TD) in degrees Kelvin to the critical temperature (Ter) in degrees Kelvin is between 1 .01 and 2.0, wherein a ratio of the end-cooling temperature (TE) in degrees Kelvin to the critical temperature (Ter) in degrees Kelvin is between 0.4 and 1.1.

13. Plant according to claim 11 or 12, wherein the second thermal accumulator (9b) at low temperature comprises: a first heat exchanger (24a) and a second heat exchanger (24b) configured to exchange heat with the working fluid; a first reservoir (25a) at low temperature, a second reservoir (25b) at intermediate temperature and a third reservoir (25c) at high temperature containing water at ambient pressure and in fluid connection with the first heat exchanger (24a) and the second heat exchanger (24b); wherein the first heat exchanger (24a) and the second heat exchanger (24b) are arranged in series on a working fluid pipeline; wherein water flow rates in the first heat exchanger (24a) and in the second heat exchanger (24b) are different from each other.

14. Plant according to one of claims 1 to 13, wherein the end-cooling temperature(TE) in the charging configuration is greater than a pump discharge temperature (TC) in the discharging configuration.

15. Plant according to any one of claims 1 to 14, comprising a heat transfer device (30) operatively coupled to working fluid lines located downstream of the expander (5; 5, 43) and to working fluid lines located downstream of the pump (15); wherein, in the discharging configuration, the heat transfer device (30) is configured to transfer part of the discharge heat from the expander (5; 5, 43) to the working fluid in the supercritical state.

16. Plant according to claim 15 when dependent on one of claims 11 to 13, wherein the heat transfer device (30) is connected to the second thermal accumulator (9b) at low temperature.

17. Plant according to claim 15 when dependent on claim 13, wherein the heat transfer device (30) is in fluid connection with the first heat exchanger (24a) and the second heat exchanger (24b) or wherein the heat transfer device (30) is in fluid connection with an additional heat exchanger placed in parallel with the first heat exchanger (24a) and the second heat exchanger (24b).

18. Plant according to one of claims 15 to 17, wherein the heat transfer device (30) is also operatively coupled to the heat exchange apparatus (16) to remove surplus heat.

19. A plant according to claim 18 when dependent on 16 or 17, wherein the heat transfer device (30) is operatively coupled to the heat exchange apparatus (16) via the second thermal accumulator (9b) at low -temperature.

20. Plant according to one of claims 1 to 19, comprising a first additional heat exchanger (36) placed between the gasometer (2) and an inlet (4a) of the compressor (4) and configured to regulate a compressor inlet temperature (TB; TB1 ); optionally, the first additional heat exchanger (36) being operatively connected to the heat exchange apparatus (16).21 . Plant according to any one of claims 1 to 20, comprising a second additional heat exchanger (37) placed between an outlet (5b) of the expander (5) and the gasometer (2) and configured to regulate a gasometer inlet temperature (TG1); optionally, the second additional heat exchanger (37) being operatively connected to the heat exchange apparatus (16).

22. Plant according to any one of claims 1 to 21 , comprising a recuperator (40) operatively working between both the gasometer (2) and the compressor (4; 4, 41 )and between the gasometer (2) and the expander (5; 5, 43); the recuperator (40) being further operatively coupled to the thermal accumulator (9; 9a, 9b); the recuperator (40) being configured to exchange heat between the working fluid flowing through the thermal accumulator (9; 9a, 9b) and the working fluid entering the compressor (4; 4, 41 ), in the charging configuration, or leaving the expander (5;5, 43), in the discharging configuration.

23. Plant according to claim 22 when dependent on one of claims 11 , 12 or 13, wherein the recuperator (40) is operatively interposed between the first high temperature thermal accumulator (9a) and the second low temperature thermal accumulator (9b); the recuperator (40) being configured to exchange heat between the working fluid flowing between the first high-temperature thermal accumulator (9a) and the second low-temperature thermal accumulator (9b) and the working fluid entering the compressor (4; 4, 41 ), in the charging configuration, or leaving the expander (5; 5, 43), in the discharging configuration.

24. Plant according to any of claims 11 , 12 or 13 or according to claim 23, comprising: a second compressor (41 ) connected in series with the compressor (4) and a second expander (43) connected in series with the expander (5); wherein the first thermal accumulator (9a) at high-temperature, in the charging configuration, is operatively active between the compressor (4) and the second compressor (41 ) and also downstream of the second compressor (41 ); wherein the first thermal accumulator (9a) at high-temperature, in the discharging configuration, is operatively active upstream of the second expander (43) and also between the second expander (43) and the expander (5).

25. Process for energy management, comprising: carrying out a closed thermodynamic cyclic transformation (TTC), first in one direction in a charging phase and then in the opposite direction in a discharging phase, between a gasometer (2) for storing a working fluid other than atmospheric air, in the gaseous phase and at a first storage pressure (PAG1) in equilibrium with atmospheric pressure, and a mass accumulator (11 ) for storing said working fluid, in the liquid phase at a second storage pressure (PA'H); wherein in the chargingphase the process stores heat and pressure and in the discharging phase it generates energy using previously stored heat and pressure; wherein in the charging phase, the process comprises: compressing the working fluid to an end compression pressure (PC; PC2) higher than a critical pressure (Per) of the working fluid, cooling said working fluid to an end-cooling temperature (TE) close to the critical temperature (Ter) of the working fluid by storing the heat removed from the working fluid, reducing the pressure of the working fluid to a reduced pressure (PG) lower than the critical pressure (Per) of said working fluid, storing the working fluid in the mass accumulator (11 ) at the second storage pressure (PA'H) lower than the critical pressure (Per) of the working fluid and in equilibrium with its own vapor phase; wherein in the charging phase the process also comprises: removing heat from the mass accumulator (11 ) to condense part of the vapor phase of the working fluid contained in the mass accumulator (11 ) and keeping the second storage pressure (PA'H) in said mass accumulator (11 ) constant or substantially constant; wherein in the discharging phase, the process comprises: pumping the working fluid with a discharge pressure (PC) higher than the critical pressure (Per) of the working fluid, transferring heat, previously stored, to the working fluid and heating said working fluid, expanding the working fluid and storing it in the gasometer (2) at the first storage pressure (PAG1); wherein, in the discharging phase, the process further comprises: giving up heat to the mass accumulator (11 ) to evaporate part of the liquid phase of the working fluid contained in the mass accumulator (11 ) and keeping the second storage pressure (PA'H) in said mass accumulator (11 ) constant or substantially constant.

26. Process according to claim 25, wherein, after cooling the working fluid to the end-cooling temperature (TE) close to the critical temperature (Ter) and before reducing the pressure of the working fluid to the reduced pressure (PG), said process in the charging phase comprises: removing heat from the working fluid in order to reduce and / or cancel a vapor title of said working fluid at the end of the pressure reduction.

27. Process according to claim 25 or 26, wherein, before pumping the working fluid, said process in the discharge phase comprises: removing heat from the working fluid to reduce risks of possible cavitation in subsequent pumping.

28. Process according to one of claims 25 to 26, wherein, in the charging phase, reducing the pressure of the working fluid comprises: laminating the working fluid.

29. Process according to claim 28 when dependent on 26, wherein removing heat from the working fluid in order to reduce and / or cancel the vapor title of said working fluid at the end of pressure reduction comprises: bringing the working fluid at the end of pressure reduction to an end pressure reduction temperature (TG) less than a saturated temperature of said working fluid at the reduced pressure (PG).

30. Process according to one of claims 25 to 26, wherein, in the charging phase, reducing the pressure of the working fluid comprises: subjecting the working fluid to an auxiliary expansion.31 . Process according to claim 30 when dependent on 26, wherein removing heat from the working fluid in order to reduce and / or cancel the vapor title of said working fluid at the end of pressure reduction comprises: removing heat from the working fluid prior to the auxiliary expansion so that during and at the end of the auxiliary expansion the working fluid remains in the subcooled liquid status.

32. Process according to any of claims 25 to 31 , wherein removing heat from the mass accumulator (11 ) and / or transferring heat to the mass accumulator (11 ) comprise / s: exchanging heat with the external environment, directly or indirectly.

33. Process according to one of claims 25 to 32, wherein each of the operations cooling the working fluid, in the charging phase, and heating the working fluid, in the discharging phase, is performed in two stages; wherein in the charging phase, in a first stage, the working fluid is cooled to an intermediate temperature (TD) above the critical temperature (Ter) and, in a second stage, the working fluid is cooled fromthe intermediate temperature (TD) to the end-cooling temperature (TE) close to the critical temperature (Ter).

34. Process according to claim 33, wherein a ratio of the intermediate temperature (TD) in degrees Kelvin to the critical temperature (Ter) in degrees Kelvin is between 1 .01 and 2.0, wherein a ratio of the end-cooling temperature (TE) in degrees Kelvin to the critical temperature (Ter) in degrees Kelvin is between 0.4 and 1.1.

35. Process according to one of claims 25 to 34, wherein the end-cooling temperature (TE) in the charging phase is greater than a pump discharge temperature (TC) in the discharging phase.

36. Process according to any of claims 25 to 35, comprising: in the discharging phase, transferring part of the heat of the expanded working fluid to the working fluid in the supercritical state before heating it or during its heating.

37. Process according to claim 36, comprising: giving up to the external environment surplus heat from the part of the heat transferred.

38. Process according to one of claims 25 to 37, comprising: in the charging phase, adjusting a temperature (TA) of the working fluid from the gasometer (2) before compression.

39. Process according to one of claims 25 to 38, comprising: in the discharging phase, adjusting a temperature (TF1) of the expanded working fluid before entering the gasometer (2).

40. Process according to any one of claims 25 to 39, comprising: in the charging phase, using part of the heat removed from the working fluid during cooling to the end-cooling temperature (TE) to heat the working fluid before compression; and / or, in the discharging phase, using part of the heat recovered from the expanded working fluid to further heat the working fluid after pumping and before expansion.41 . Process according to any of claims 25 or 40, wherein, in the charging phase, compressing and cooling the working fluid comprises: performing a first compression followed by a first cooling and then performing a second compression followed by a second cooling, wherein at the end of the first compression the working fluid is at a subcritical pressure (PC1 ) and at the end of the second compression the working fluid is at the pressure (PC2) above the critical pressure (Per), wherein temperatures of the working fluid (TC1 , TC2) at the end of the first compression and the second compression are similar or equal.

42. Process according to any one of claims 25 to 41 , wherein, in the discharging phase, heating and expanding the working fluid comprises: performing a first heating followed by a first expansion and then performing a second heating followed by a second expansion.

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