THERMOCHEMICAL ENERGY STORAGE DEVICE

Abstract

Process for the reversible thermochemical storage of energy and release of energy, wherein, for the storage of energy, orthoboric acid is converted into boric oxide, metaboric acid or boric oxide and metaboric acid by loss of water, wherein, for the release of energy, boric oxide or metaboric acid or boric oxide and metaboric acid are converted into orthoboric acid by reaction with water, wherein the reactions take place in a suspension medium, wherein for the reversible storage of energy, orthoboric acid is present suspended in the suspension medium, and wherein the suspension medium containing orthoboric acid is brought to a temperature at which water loss occurs via an energy source, wherein for the reversible thermochemical release of energy boric oxide and/or metaboric acid are present suspended in a suspension medium, wherein water is added to the suspension medium containing boric oxide or metaboric acid or boric oxide and metaboric acid so that the reaction proceeds to orthoboric acid, wherein the heat generated in this process is dissipated to a heat consumer.

Claims

1. A process for the reversible thermochemical storage of energy and release of energy, wherein, for the storage of energy, orthoboric acid (H.sub.3BO.sub.3) is converted into boric oxide (B.sub.2O.sub.3), metaboric acid (HBO.sub.2, H.sub.2B.sub.4O.sub.7) or boric oxide (B.sub.2O.sub.3), and metaboric acid (HBO.sub.2, H.sub.2B.sub.4O.sub.7) by loss of water, wherein, for the release of energy, boric oxide (B.sub.2O.sub.3) or metaboric acid (HBO.sub.2, H.sub.2B.sub.4O.sub.7) or boric oxide (B.sub.2O.sub.3) and metaboric acid (HBO.sub.2, H.sub.2B.sub.4O.sub.7) are converted into orthoboric acid (H.sub.3BO.sub.3) by reaction with water, characterized in that the reactions take place in a suspension medium, wherein for the reversible storage of energy, orthoboric acid (H.sub.3BO.sub.3) is present suspended in the suspension medium, and wherein the suspension medium containing orthoboric acid (H.sub.3BO.sub.3) is brought to a temperature at which water loss occurs via an energy source, wherein for the reversible thermochemical release of energy boric oxide (B.sub.2O.sub.3) and/or metaboric acid (HBO.sub.2, H.sub.2B.sub.4O.sub.7) are present suspended in a suspension medium, wherein water is added to the suspension medium containing boric oxide (B.sub.2O.sub.3) or metaboric acid (HBO.sub.2, H.sub.2B.sub.4O.sub.7) or boric oxide (B.sub.2O.sub.3) and metaboric acid (HBO.sub.2, H.sub.2B.sub.4O.sub.7) so that the reaction proceeds to orthoboric acid (H.sub.3BO.sub.3), wherein the heat generated in this process is dissipated to a heat consumer.

2. A process for the reversible thermochemical storage of energy, comprising a reaction system in which orthoboric acid (H.sub.3BO.sub.3) is converted into boric oxide (B.sub.2O.sub.3), metaboric acid (HBO.sub.2, H.sub.2B.sub.4O.sub.7) or boric oxide (B.sub.2O.sub.3), and metaboric acid (HBO.sub.2, H.sub.2B.sub.4O.sub.7) by loss of water, characterized in that the orthoboric acid (H.sub.3BO.sub.3) is present suspended in a suspension medium, wherein the suspension medium containing orthoboric acid (H.sub.3BO.sub.3) is brought to a temperature at which water loss occurs via an energy source.

3. A process for the reversible thermochemical release of energy, comprising a reaction system in which boric oxide (B.sub.2O.sub.3) or metaboric acid (HBO.sub.2, H.sub.2B.sub.4O.sub.7) or boric oxide (B.sub.2O.sub.3) and metaboric acid (HBO.sub.2, H.sub.2B.sub.4O.sub.7) are converted into orthoboric acid (H.sub.3BO.sub.3) by reaction with water, characterized in that boric oxide (B.sub.2O.sub.3) or metaboric acid or boric oxide (B.sub.2O.sub.3) and metaboric acid (HBO.sub.2, H.sub.2B.sub.4O.sub.7) are present suspended in a suspension medium, wherein water is added to the suspension medium, wherein water is added to the suspension medium containing boric oxide (B.sub.2O.sub.3) or metaboric acid (HBO.sub.2, H.sub.2B.sub.4O.sub.7) or boric oxide (B.sub.2O.sub.3) and metaboric acid (HBO.sub.2, H.sub.2B.sub.4O.sub.7) so that the reaction to orthoboric acid (H.sub.3BO.sub.3) proceeds.

4. The process according to claim 1, characterized in that the metaboric acid is present as a powder which is suspended in the suspension medium.

5. The process according to claim 1, wherein additives, emulsifiers and/or foam inhibitors are additionally added to the suspension medium.

6. The process according to claim 1, wherein the suspension medium is refined rapeseed oil, mineral oil-based thermal oil or silicone-based thermal oil.

7. The process according to claim 1, wherein the suspension medium is stirred during the reaction.

8. The process according to claim 1, wherein, during thermochemical storage of energy, the water formed is removed from the suspension during the course of the reaction.

9. The process according to claim 8, wherein the water formed is removed by pumping and/or gassing, in particular with nitrogen.

10. The process according to claim 1, wherein the temperature during storage of energy is set to 110 to 200 C., preferably between 135-165 C.

11. The process according to claim 1, wherein the pressure during storage of energy is set to below 200 mbar, preferably below 100 mbar.

12. The process according to claim 1, wherein the pressure is set to at least 5 bar, preferably at least 8 bar, during the release of energy.

13. A system for the thermochemical storage of energy and release of energy, with at least one suspension reactor, wherein an energy source is associated with the suspension reactor, wherein an agitation device is provided in the suspension reactor, wherein an outlet for water vapor from the suspension reactor and a water reservoir connected to the outlet is present, wherein a feed line is provided into the suspension reactor which is connected to the water reservoir, wherein a heat exchanger is provided at the suspension reactor, wherein the heat exchanger is connectable to a consumer.

14. The system according to claim 13, wherein a control device is provided which is designed in such a way that the amount of energy delivered to the heat exchanger at the suspension reactor can be controlled.

15. The system according to claim 13, wherein a gas supply line is provided for the suspension reactor.

16. The system according to claim 15, wherein a heat exchanger is associated with the gas supply line.

17. The system according to claim 13, wherein a heat exchanger is assigned to the outlet.

18. The system according to claim 13, wherein the feed line has a device for controlling the flow rate.

19. The system according to claim 18, wherein the control device is designed in such a way that the amount of energy delivered to the heat exchanger at the suspension reactor can be controlled via the device for controlling the flow rate.

20. The system according to claim 13, wherein two suspension reactors are provided which are connected via at least one bypass line, wherein means for transporting the contents of one suspension reactor into the other suspension reactor are provided.

21. The system according to claim 13, wherein an energy source and a consumer are provided.

22. The system according to claim 13, wherein a device for preheating and/or evaporating the water is provided in the supply line.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0049] The invention is explained in more detail with the aid of the figures and figure descriptions.

[0050] FIG. 1 schematically shows the reversible reaction equilibrium of the orthoboric acid/metaboric acid/boric oxide system for the charging process (FIG. 1a) and the discharging process (FIG. 1b) of a reactor and for the process according to the invention, respectively.

[0051] FIG. 2 schematically shows a system of one embodiment of a thermochemical energy storage system according to the invention or the process according to the invention.

[0052] FIG. 3 schematically shows a system for carrying out a process for reversible thermochemical energy storage.

[0053] FIG. 3 schematically shows a system for carrying out a process for reversible thermochemical energy storage.

[0054] FIG. 4 schematically shows a system for carrying out a process for reversible thermochemical energy release.

[0055] FIG. 5 schematically shows a system for carrying out a process for reversible thermochemical energy storage and release.

[0056] FIG. 6 schematically shows a system for carrying out a process for reversible thermochemical energy storage and release.

[0057] FIG. 1a shows the charging process and FIG. 1b the discharging process for a thermochemical reactor based on an orthoboric acid/metaboric acid/boron oxide system. The reactor contains powdered orthoboric acid suspended in a suspension medium (e.g. thermal oil). To charge the thermochemical energy store, the reaction enthalpy (H.sub.R) is supplied to the suspended orthoboric acid in the form of heat, so that reaction (I)) 2H.sub.3BO.sub.3.fwdarw.B.sub.2O.sub.3+3H.sub.2O takes place. This reaction can also proceed in multiple steps via metaboric acid according to reactions (II) and (III) or (IV), (V) and (VI). The formation of boron oxide from orthoboric acid can be reduced or prevented by shorter reaction times and/or slightly lower temperatures (e.g., up to 150 C.). The reverse reaction (Ia) B.sub.2O.sub.3+3H.sub.2O.fwdarw.2H.sub.3BO.sub.3 is used for discharge, releasing the reaction enthalpy. Again, the reaction process can be multistep according to reactions (Ha) and (IIIa) or (IVa), (Va) and (VIa). During the charging process, the water produced is removed.

[0058] This can be done, for example, by pumping, by applying a vacuum, via nitrogen gassing or the like. In order for these schematically illustrated reactions to take place in the processes according to the invention, they can take place in thermochemical reactors, as shown in the following figures.

[0059] FIG. 2 shows a schematic diagram of a thermochemical energy storage system according to the invention. A reactor 1 is provided in which there is a suspension of orthoboric acid in a suspension medium such as thermal oil, to which heat Q is supplied via an energy source not shown when the energy store is charged. Water, metaboric acid (not shown) and B.sub.2O.sub.3 are formed in the suspension. During the reaction, it is envisaged that the suspension is agitated, for example by stirring. The water is discharged from reactor 1 and can be stored if necessary. The suspension medium with metaboric acid and/or B.sub.2O.sub.3 remains in reactor 1. In the embodiment shown, the suspension medium with the boron oxide (and/or metaboric acid) in reactor 1 may be contacted with water for heat release. The reactor 1 may be a stand-alone reactor 1 or the same reactor 1 as for energy storage. Water is added to reactor 1 so that the reverse reaction B.sub.2O.sub.3+3H.sub.2O.fwdarw.2H.sub.3BO.sub.3 occurs. Heat is released in the process, which is used for a consumer.

[0060] The reaction in reactor 1 is preferably carried out in such a way that a stoichiometric amount of water is added, i.e., 3 moles of H.sub.2O are added to 1 mole of B.sub.2O.sub.3. In addition, a metering device may be provided to meter the water flow and thus time the water supply so that the heat release is continuous. The water supplied to reactor 1 may be the stored water released in reactor 1. If the stored water is used, a closed system can be used in which no feed is required and a stoichiometrically correct ratio between B.sub.2O.sub.3 and H.sub.2O is automatically present. During the reaction in reactor 1, it is also envisaged that the suspension is agitated, for example by stirring.

[0061] Reactor 1 can be operated with suspended orthoboric acid where large amounts of heat are generated, e.g. in industrial plants or at solar collectors. After reactor 1 is loaded with B.sub.2O.sub.3, the mixture of suspension medium and boron oxide can be removed and transported to a location where the energy in reactor 1 is to be released again (e.g. in a single building heating system or a district heating system).

[0062] FIG. 3 shows a plant with a reactor 1a suspension reactor(filled with a suspension of thermal oil and orthoboric acid) for thermochemical energy storage. Energy in the form of heat for the reaction in reactor 1 is provided via an external energy source through line 2. The heat can come from a heating device or, for example, a solar collector or the like and be transferred to the reactor 1 via a heat exchanger. Furthermore, an agitating device 9 is provided with motor drive M to agitate the suspension. While the reaction is taking place, the resulting water vapor is drawn off from the suspension reactor 1 via the outlet (fume hood) 5, cooled via the heat exchanger 6 and stored in a reservoir 7. Furthermore, an external gas supply 4 with a dry gas such as nitrogen is provided to accelerate the water removal, whereby the gas of the external gas supply 4 can be preheated with a heating device 3.

[0063] FIG. 4 shows a system with a reactor 1 (suspension reactor) filled with a suspension of thermal oil and boron oxide for thermochemical energy release. Analogous to FIG. 3, an agitating device 9 is provided with motor drive M to agitate the suspension. In order for the reaction to proceed, water is fed into reactor 1 from a water reservoir 7 via feed line 8. The heat generated is dissipated via a conduit 2 to a heat exchanger and conducted to a consumer.

[0064] FIG. 5 shows a system for thermochemical energy storage and release, with a single reactor 1a suspension reactor(initially filled with a suspension of thermal oil and orthoboric acid). The system of FIG. 5 has essentially the two systems of FIGS. 3 and 4 and is used for energy storage and release. In the operating state of energy storage, energy for the reaction in reactor 1 is first provided via an external energy source through line 2. The suspension is stirred via an agitating device 9 with motor drive M. The resulting water vapor is drawn off from the suspension reactor 1 via the outlet 5, cooled via the heat exchanger 6 and stored in a reservoir 7. External gassing 4 with nitrogen is provided to accelerate the removal of water, and the nitrogen can be preheated by a heating device 3. When the reaction to B.sub.2O.sub.3 is complete, the system is charged. To release energy, the mode of operation is changed so that the reaction B.sub.2O.sub.3+H.sub.2O proceeds. For this purpose, water is fed into the reactor from the water reservoir 7 via the feed line 8. The heat generated by the reaction is dissipated via a conduit 2 to a heat exchanger and conducted to a consumer.

[0065] The system according to FIG. 6 shows a design variant for thermochemical energy storage and release, with two reactors 1, 1 (suspension reactors). One reactor 1 is initially filled with a suspension of thermo-oil and orthoboric acid and is used for energy storage. In the operating state of energy storage, energy for the reaction in reactor 1 is initially provided via an external energy source through line 2. In the embodiment example shown, the external energy source is a solar collector. Here, too, an agitating device 9 with motor drive M is provided to agitate the suspension. Water vapor produced is extracted from the suspension reactor 1 via the outlet 5, cooled via the heat exchanger 6 and stored in a reservoir 7. An external gassing 4 with nitrogen accelerates the water withdrawal and the heating device 3 can additionally heat the gas. When the reaction to B.sub.2O.sub.3 is complete, the system is charged. The suspension of B.sub.2O.sub.3 can be transferred to the second reactor 1 via the bypass line 13. To release energy and to allow the reaction B.sub.2O.sub.3+H.sub.2O to proceed, the mode of operation is changed. For this purpose, water is fed from the water reservoir 7 into the reactor 1 via the feed line 8. A device for preheating and/or evaporating 14 the water is provided in the feed line. The heat generated by the reaction is conducted via a line 2 to a heat exchanger and fed to a consumer. Conceivable consumers are radiators, hot water consumers, etc. After the reaction to H.sub.3BO.sub.3 has proceeded, the suspension can be returned to the first reactor 1 via the bypass line 12. Then the charging process starts again.