ENERGY STORAGE/WITHDRAWAL SYSTEM FOR A FACILITY

Abstract

The invention relates to a system (100) for storing/withdrawing thermal energy.

The main characteristic of a system according to the invention is that it comprises: a monolithic cementitious material (1) comprising a mass fraction of ettringite of greater than 20%, said material being surrounded by a thermal insulation material (12) and a water insulation material (11), a source (2) of a heat transfer fluid, a device (3) for wetting said fluid in order to carry out a withdrawal phase of the system (100), a device (4) for heating said fluid in order to carry out a storage phase of said system (100), an outlet (6) of the heat transfer fluid from said material (1).

Claims

1. System for storing/withdrawing thermal energy, comprising a monolithic cementitious material comprising a mass fraction of ettringite of greater than 20%, said material being surrounded by a thermal insulation material and a water insulation material, a source of a heat transfer fluid, a device for wetting said fluid in order to carry out a withdrawal phase of the system, a device for heating said fluid in order to carry out a storage phase of said system, an outlet of the heat transfer fluid from said material, wherein said system comprises at least one heat transfer fluid circulation circuit that passes through the heating device and through the wetting device, said circuit being supplied by the source of said fluid and leading to the cementitious material.

2. System according to claim 1, wherein the heat transfer fluid is formed by an inert gas.

3. System according to claim 1, wherein the source of the heat transfer fluid is placed upstream of the wetting device, which is itself placed upstream of the heating device, and in that said heating device is placed upstream of the cementitious material.

4. System according to claim 1, wherein the wetting device and the heating device each operate to order, and can be activated independently of one another depending on the use of said system, either in storage phase, or in withdrawal phase.

5. System according to claim 1, wherein the mass fraction of ettringite in the cementitious material is between 20% and 90%.

6. System according to claim 1, wherein the cementitious material has a porosity of between 10% and 90%.

7. System according to claim 1, wherein the cementitious material (1) has a permeability of between 10.sup.17 m.sup.2 and 10.sup.11 m.sup.2.

8. System according to claim 1, wherein the cementitious material (1) has a compressive mechanical strength of between 0.1 MPa and 70 MPa.

9. System according to claim 1, wherein the water insulation material is formed by an impermeable wall intended to prevent water vapour from coming into contact with the cementitious material.

10. System according to claim 1, wherein the thermal insulation material is formed by at least one material to be chosen from glass wool and polystyrene and in that said at least one impermeable material is placed around the water insulation material.

11. System according to claim 1, wherein the wetting device comprises at least one humidifier suitable for charging said fluid with water.

12. Process for storing/withdrawing thermal energy using a storage/withdrawal system in accordance with claim 1, wherein, in the heat storage phase, it comprises the following steps: a step of heating the heat transfer fluid by means of the heating device in order to obtain a hot gas, the temperature of which is above 30 C., a step of directly passing said hot gas through the cementitious material comprising ettringite, giving rise to an endothermic dehydration of said material and constituting a heat storage phase.

13. Process according to claim 12, wherein the heat storage phase extends over a period of several days, said period being dictated by the amount of cementitious material and the flow rate of fluid used in said process.

14. Process according to claim 12, wherein, in the heat withdrawal phase, it comprises the following steps: a step of wetting the heat transfer fluid by means of the wetting device in order to obtain a wetted gas, a step of directly passing said wetted gas through the cementitious material comprising ettringite and which adsorbs water vapour then is hydrated, a step of exothermic reaction which generates heat transported by the heat transfer fluid, converting the initially cold and wet gas into a hot and dry gas.

15. Process according to claim 12, wherein said process comprises a step of removing the carbon dioxide in the heat transfer fluid before it passes through the cementitious material comprising ettringite in order to prevent a carbonation reaction of said material.

16. Material comprising ettringite for creating a system in accordance with claim 1.

17. Material according to claim 16, wherein said material comprises an ettringitic binder, the porosity and the permeability of which are increased by chemical foaming and/or by mechanical foaming.

Description

[0065] FIG. 1 is a general schematic view of a storage/withdrawal system according to the invention,

[0066] FIG. 2 is a schematic view of the part of the system from FIG. 1 required for the heat storage phase,

[0067] FIG. 3 is a schematic view of the part of the system from FIG. 1 required for the heat withdrawal phase,

[0068] FIG. 4 is a schematic view of a thermochemical reactor of a storage/withdrawal system according to the invention,

[0069] FIG. 5 is a diagram illustrating an example of the variation of the temperature in a cementitious material of a storage/withdrawal system according to the invention, during a heat withdrawal phase,

[0070] FIG. 6 is a diagram illustrating an example of the variation of the temperature in a cementitious material of a storage/withdrawal system according to the invention, during two heat withdrawal cycles.

[0071] In order to facilitate the reading of the detailed description, a storage/withdrawal system will be denoted under the simple designation system. Similarly, a storage/withdrawal process will be denoted under the simple designation process.

[0072] A cementitious material 1 of a system according to the invention is intended to form the constituent material of the walls and/or various partitions of an industrial facility or of a domestic dwelling. In order to describe the operating principle of such a system and the various steps of the associated process, the detailed description will focus on a system comprising a thermochemical reactor, the structure and the physicochemical properties of which are representative of those of the walls or partitions that would be formed by this cementitious material.

[0073] By referring to FIG. 1, a system 100 according to the invention comprises a circuit 8 for circulation of a heat transfer fluid, comprising a source 2 of said fluid, a wetting device 3, a heating device 4, the thermochemical reactor 5 comprising the cementitious material 1, and an outlet 6 of this heat transfer fluid. In the example considered, the source 2 of heat transfer fluid is a nitrogen cylinder. The wetting device 3 comprises at least one bubbler 7 suitable for charging the nitrogen with water, it being possible for said water to be present in the form of a liquid or vapour. The circuit 8 has at least one flowmeter 9 that makes it possible to measure the nitrogen flow rate and therefore to control it. The heating device 4 comprises at least one solar collector or another source of preferentially renewable energy able to recover heat over a temperature range between 30 C. and 100 C. The heating device 4 and the wetting device 3 may be activated independently of one another and may therefore operate alternately. The circuit 8 passes firstly through the wetting device 3, then through the heating device before passing through the thermochemical reactor 5, the fluid resulting from the passage through said reactor 5 then being discharged to the atmosphere in order to heat a room or a premises.

[0074] By referring to FIG. 4, the thermochemical reactor 5 comprises a shell 10 consisting of a cylindrical wall enclosing a monolithic cementitious material 1 comprising a large mass fraction of ettringite, of between 20% and 90%. This material 1 constitutes a cylindrical block having the following characteristics: [0075] a high porosity of between 10% and 90%, [0076] a permeability of between 10.sup.17 m.sup.2 and 10.sup.11 m.sup.2, [0077] a mechanical strength of between 0.1 MPa and 70 MPa.

[0078] The shell 10 is split into an inner shell 11 formed by a layer of PVC (polyvinyl chloride) that comes into contact with the outer lateral surface of the cementitious block 1 and an outer shell 12 formed by a layer of glass wool surrounding the PVC layer 11 and being in contact therewith. The PVC layer 11 acts as a water insulation material and the glass wool layer 12 acts as a thermal insulation material. This thermochemical reactor 5 has an inlet 13 for nitrogen originating from the heating device 4 or from the wetting device 3, and a nitrogen outlet 14 after this nitrogen has passed through the monolithic cementitious block 1. Thermal sensors, such as for example thermocouples, and water sensors may be inserted into the cementitious block 1 in order to enable the control of the temperature of said block 1 and of the water vapour pressure in the reactor 5, over time.

[0079] All the measurement elements present in the system 100 make it possible to acquire the operating parameters of said system 100, which may then be recorded and processed by a computer 15.

[0080] A system according to the invention makes it possible to become charged with heat, then to store this heat over an unlimited given period of time, before restoring it to order, when the heating requirements take effect.

[0081] A storage/withdrawal process using a system 100 according to the invention comprises the following steps: [0082] AIn the charging phase, illustrated in FIG. 2 (this phase may for example take place in summer where the amount of sunshine is considerable) [0083] A step of heating the heat transfer fluid 2 in order to obtain a hot gas, the temperature of which is between 50 C. and 70 C., and preferentially is equal to 60 C. This heating step is carried out by means of the heating device 4, and in particular by means of the solar collector. [0084] A step of passing said hot gas through the cementitious material 1 comprising ettringite, giving rise to an endothermic dehydration and constituting a heat storage phase. Indeed, the nitrogen is thus heated between 30 C. and 100 C. before passing through the cementitious block 1 housed in the thermochemical reactor 5, the passage through said block 1 being facilitated by the high porosity thereof. The nitrogen then heats the cementitious block 1 of ettringite, which is dehydrated, simulating the heat storage phase. The endothermic desorption of water over the ettringite, which is a physicochemical reaction, makes it possible to store heat. The thermal energy is thus stored and conserved in the cementitious material 1, while said material 1 remains insulated from water. For this charging phase, the device 3 for wetting the nitrogen is not needed and is not therefore activated. A complete charging phase lasts around several days depending on the amount of cementitious material 1 used and on the fluid flow rate. By way of example, on average 3 days are required for several kilograms of material and a nitrogen flow rate of 2 l/min. The chemical part of the heat charging process (endothermic dehydration) is linked to the reversible conversion of ettringite to metaettringite, by loss of 18 water molecules per ettringite molecule:

3CaO.Al.sub.2O.sub.3.3CaSO.sub.4.3H.sub.2O.fwdarw.3CaO.Al.sub.2O.sub.3.3CaSO.sub.4.12H.sub.2O+18H.sub.2O [0085] B In the discharging phase, illustrated in FIG. 3 (this phase may for example take place in winter where the heating requirements are high) [0086] A step of wetting the heat transfer fluid 2 by means of the wetting device 3 in order to obtain a wetted gas. This wetting step is carried out by means of the wetting device 3, and in particular, by means of bubblers. The gas resulting from the wetting device 3 is thus charged with water vapour. The wetted gas can pass through the monolithic cementitious material 1 comprising ettringite since said material 1 is porous and permeable. [0087] A step of passing said wetted gas through the cementitious material 1 comprising ettringite and which adsorbs water vapour then is hydrated. The adsorption is a physical phenomenon and the hydration is a chemical phenomenon. The chemical part of the heat restoring process is linked to the rehydration of metaettringite to ettringite by a gain of 18 water molecules per ettringite molecule:

3CaO. Al.sub.2O.sub.3.3CaSO.sub.4.12H.sub.2O+18H.sub.2O.fwdarw.3CaO. Al.sub.2O.sub.3.3CaSO.sub.4.30H.sub.2O [0088] A step of exothermic reaction at the cementitious material, which generates heat transported by the heat transfer fluid 2, transforming the initially cold and wet gas into a hot and dry gas. During this heat withdrawal phase, the heating device 4 is not needed and is not therefore activated.

[0089] By referring to FIG. 5, the maximum temperature increase in the cementitious material 1 may for example reach 16 C., during a heat withdrawal phase. This temperature increase depends on the amount of material, on the relative humidity and on the flow rate of fluid used. Such a diagram shows that the heat withdrawal phase may last up to 3 days, which remains a long period relative to that of the systems using zeolite type materials, for which this period does not exceed 24 h.

[0090] FIG. 6 illustrates the reversibility of the storage process of a system according to the invention. The reversibility of the heat storage process is linked to that of the chemical reaction for dehydrating and rehydrating ettringite.