Method for storing electrical energy in solid matter

Abstract

The method includes two technological segments (i) a reduction segment and (ii) an oxidation segment that are interconnected by various support technological processes for the regeneration of solutions and gases and heat recuperation. The reduction segment includes an electrolysis that is performed from a solution of chloride salts of an energy carrier. During the electrolysis, these elements reduce to a lower oxidation state, solidify on the electrodes or precipitate to a solid state. The solid substance thus obtained is the energy carrier that can be stored outside of the electrolyser until a need for additional energy emerges. During the electrolysis, chlorine gas develops that is collected and dissolved in water. An HCl solution is regenerated, which is used in the oxidation segment. Oxygen is released in this process. The energy that has thus been stored in the oxidation potential of the energy carrier is released during a spontaneous chemical reaction between the energy carrier and the HCl solution in the oxidation segment. In this chemical reaction, the oxidation state of the chemical elements which constitute the energy carrier is increased to an oxidation state identical to that from before the beginning of the electrolysis. The reaction product hydrogen is formed that represents a high calorific fuel. This fuel can be immediately converted to heat or electrical energy, without a need for intermediate storage, by known methods. Only water enters the entire method, oxygen and hydrogen leave, while the cycle is closed/cyclic for the remaining substances.

Claims

1. A method for storing electrical energy in a solid matter, characterised by comprising: (i) carrying out an electrolysis with an electrical energy source (1) in a reduction segment comprising of an electrolyser (2) with a cathode (3) and an anode (4), wherein from an electrolyte solution, which is a solution of an energy carrier chloride salt, a reduction of the energy carrier ions is carried out until a solid energy carrier is produced, which has a very high volume energy density and is chemically stable, wherein a chlorine gas is produced, and (ii) performing a chemical reaction in an oxidation segment that includes a reaction vessel (5) with an HCI solution, wherein the chemical reaction occurs in the reaction vessel between the solid energy carrier obtained in the reduction segment and the HCI solution, wherein heat, a chloride salt solution of the energy carrier, and hydrogen are produced.

2. Method according to claim 1, characterised in that the hydrogen produced in the oxidation segment is used in fuel cells for generating electrical energy or as fuel for producing heat energy.

3. Method according to claim 1, characterised in that the electrolysis is carried out at room temperature or at a slightly elevated temperature that is below the boiling point of the electrolyte solution.

4. Method according to claim 1, characterised in that the solid energy carrier is stored in a storage (6) for subsequent release of an energy in the oxidation segment.

5. Method according to claim 1, characterised in that an energy in the reaction carried out in the oxidation segment is produced in the form of released heat that is recuperated in a heat recuperator (7) and supplied to a regeneration process of the HCI solution in an electrolyte regenerator (8) and optionally to the electrolysis in the electrolyser (2).

6. Method according to claim 1, characterised in that the reaction chloride salt solution of the energy carrier is optionally stored in acid-resistant tanks (9) or is immediately introduced into a new electrolytic cycle.

7. Method according to claim 1, characterised in that the chlorine gas that develops on the anode (4) during the electrolysis is conducted to an electrolyte regenerator (8), wherein an HCI solution is produced again during a reaction with water, and the regenerated HCI solution is introduced in the oxidation segment, more precisely into the reaction vessel (5) for the reaction with the energy carrier.

8. Method according to claim 1, characterised in that only water enters the method, oxygen and hydrogen leave, while the method is a cycle that is closed/cyclic for the remaining substances.

9. Method according to claim 1, characterised in that the energy carriers is one or more metals selected from Fe, Pb, Zn, Cr, Sn, Co, Ni, the alloys thereof or the intermetallic compounds thereof which have a negative reduction potential, yet a less negative reduction potential than the reduction potential of the water.

10. Method according to claim 1, characterised in that the energy carrier is Fe or Zn.

11. Method according to claim 1, characterised in that in the reduction segment, a FeCl.sub.2 solution is electrolysed in the electrolyser (2), in which the cathode part is separated from the anode part by an ion-permeable membrane, wherein the iron ions Fe.sup.2+ on the cathode (3) are reduced to ametallic iron Fe, while gaseous chlorine 012 is produced on the anode side; when the electrolysis is over, the metallic iron Fe is the energy carrier and can be stored in the storage (6) under an atmosphere of nitrogen; the leaving gaseous chlorine is collected in a process of electrolyte regeneration in the electrolyte regenerator (8) and dissolved in water which is supplied to the method, wherein the HCI solution, which is returned to the reaction vessel (5) of the oxidation segment, and the gaseous O.sub.2 are produced; when a need for energy emerges, the stored metallic iron Fe in the oxidation segment of the method is subject to the reaction with the HCI solution, wherein FeCl.sub.2 and hydrogen are produced, which hydrogen is subsequently used as fuel and the obtained FeCl.sub.2 solution is stored and re-used for the electrolysis in the reduction segment.

12. Method according to claim 11, characterised in that the energy density by volume in the iron as the energy carrier is higher than that of currently used energy carriers intended for storing electrical energy and amounts to 11.20 kWh/l.

Description

(1) The method of the invention will be described hereinbelow and is illustrated in the figures which show:

(2) FIG. 1: General diagram of the method of the inventiona technological process of oxidation/reduction electrical energy storage in a solid substance

(3) FIG. 2: Diagram of the method of the inventiona technological process of electrical energy storage, wherein metallic iron is an energy carrier.

(4) The first key segment, i. e. the reduction segment, is represented by the electrolytic reduction formation of a solid matter, i. e. energy carrier. In the reduction segment, from an electrolyte solution consisting of a chloride salt solution and an energy carrier, a reduction of energy carrier ions is performed at room temperature or at a slightly elevated temperature that is below the boiling point of this solution, until a solid energy carrier is formed. The preferred energy carriers are metals M (e. g. Fe, Pb, Zn, Cr, Sn, Co, Ni) or the alloys thereof (e. g. ZnFe alloys) or the intermetallic compounds thereof (e. g. Fe.sub.3Zn.sub.10, FeZn.sub.7, Fe.sub.5Sn.sub.3, FeSn) which have a negative reduction potential, yet a less negative one than the reduction potential of the water. The most preferred energy carrier is Fe or Zn.

(5) The reduction segment consists of an electrolyser 2 with a cathode 3 and an anode 4, where electrolysis is carried out with an electrical energy source 1. During the electrolysis, the energy carriers are reduced to a lower oxidation state, solidify on the electrodes or precipitate into a solid state. On the cathode 3, the ions of the energy carriers, e. g. the metallic ions M.sup.2+ are reduced to a metal M, the gaseous chlorine (Cl.sub.2) is produced on the anode side. These electrochemical reactions are given by the following chemical equations:
M.sup.2+.sub.(aq)+2e.sup..fwdarw.M.sub.(s)at the cathode:
2e.sup.+2Cl.sup..sub.(aq).fwdarw.Cl.sub.2(g)at the anode:

(6) During the electrolysis, the metals M (e. g. Fe, Pb, Zn, Cr, Sn, Co, Ni) or the alloys thereof (e. g. ZnFe alloys) or the intermetallic compounds thereof (e. g. Fe.sub.3Zn.sub.10, FeZn.sub.7, Fe.sub.5Sn.sub.3, FeSn) are formed which represent an energy carrier having a very high volume density and chemical stability.

(7) The working parameters, the types of electrodes, electrolytic cells and electrolytes, and other electrolytic conditions are specific for individual electrolytic systems. The electrolytic conditions for the systems that are relevant for this invention have mainly already been researched and described. An example of such electrolysis is the electrolysis of nickel and iron chloride solutions, which was described by Tanimura et al..sup.iv The energy efficiencies of these electrolytic methods reach 95% and more.

(8) The obtained energy carrier, i. e. the reduced energy carrier, is stored in a storage 6 for subsequent energy release in the oxidation segment of the method of the invention. The energy carriers thus obtained are normally not very reactive and environmentally harmful, yet may slowly corrode. The energy carrier is preferably stored under an inert atmosphere of nitrogen independent on the corrosion properties of the energy carrier. Oxidation or any other surface reaction (e. g. with CO.sub.2, H.sub.2O etc.) is herewith prevented. The reacted material will not subsequently react with HCl, which will result in material and consequently energy losses. The storage under an inert atmosphere of nitrogen prevents the loss of material and allows that the entire energy carrier is used for the release of energy and then returned to the cycle.

(9) The second key segment of the method of the invention is the oxidation segment, wherein a chemical reaction occurs in a reaction vessel 5, in which the oxidation potential of the energy carrier is released and hydrogen is formed as fuel. The chemical reaction occurs between the HCl solution and the energy carrier (e. g. a metal having a general designation M) according to the reaction
M.sub.(s)+xHCl.sub.(g).fwdarw.MCl.sub.x(aq)+x/2H.sub.2(g)

(10) To achieve a good efficiency of the method of the invention, it is important for the reaction to be thermodynamically spontaneous, which means that the Gibbs free energy gets reduced during the reaction. No additional energy needs to be supplied for the reaction to take place. In the reaction, energy is produced in the form of released heat that can be recuperated in a heat recuperator 7 and delivered to the regeneration process of the HCl solution to an electrolyte regenerator 8 and, if needed, also to the electrolysis, particularly to the electrolyser 2. The reactions relevant for this technological process have already been described and assessed in terms of thermodynamics, yet have never been used in the method that is the object of this patent protection.

(11) Once the reaction is over, the metallic chloride reaction solution is optionally stored in acid-resistant tanks 9 or immediately introduced to a new electrolytic cycle.

(12) The chlorine gas that develops on the anode during the electrolysis is conducted to commercially available gas scrubbers, wherein an HCl solution is formed again during a reaction with water. The reaction occurs in two stages as shown by the chemical equation
2Cl.sub.2+2H.sub.2O.fwdarw.2HCl+2HClO.fwdarw.4HCl+O.sub.2

(13) The HClO that is produced in the first stage dissociates into HCl under the influence of light or heat. Water is introduced into the process; the oxygen gas exits it. The regenerated HCl solution is introduced into the oxidation segment, more precisely into the reaction vessel, for a reaction with the energy carrier.

(14) An embodiment of the method of the invention is described hereinbelow, wherein metallic iron is the energy carrier. An example of the method of the invention, i. e. a chloride cycle for storing surplus electrical energy in a solid substance, is oxidation and reduction of iron and is shown in FIG. 2. In the reduction segment, the FeCl.sub.2 solution is electrolysed in the electrolyser 2, in which the cathode part is separated from the anode part by an ion-permeable membrane. In the cathode part, the iron ions (Fe.sup.2+) on the cathode 3 are reduced to the metallic iron (Fe), while gaseous chlorine (Cl.sub.2) is produced on the anode side. These electrochemical reactions are illustrated by the following chemical equations:
Fe.sup.2+.sub.(aq)+2e.sup..fwdarw.Fe.sub.(s)at the cathode:
2e.sup.+2Cl.sup..sub.(aq).fwdarw.Cl.sub.2(g)at the anode:

(15) When the electrolytic process is over, the iron is the energy carrier and can be stored in the storage 6. The leaving gaseous chlorine is collected in the process of electrolyte regeneration and dissolved in the water which is supplied to the system, in which the HCl solution and the gaseous O.sub.2 are produced. The process is conducted in the electrolyte regenerator 8. The HCl solution is conducted to the oxidation segment. When a need for energy emerges, the stored iron is subject to a reaction with the HCl solution in the reaction vessel 5 in the oxidation segment. In the reaction, Fe.sub.2Cl and hydrogen are produced according to the equation:
Fe.sub.(s)+2HCl.sub.(aq).fwdarw.FeCl.sub.2(aq)+H.sub.2(g)
The energy in the reaction is produced in the form of released heat which can be recuperated in the heat recuperator 7 and supplied to the regeneration process of the HCl solution in the electrolyte regenerator 8 and optionally to electrolysis in the electrolyser 2.

(16) The FeCl.sub.2 solution is stored in acid-resistant tanks 9 and is re-used for the electrolysis of surplus electrical energy. In the oxidation segment one mole of H.sub.2 gas is obtained per each mole of Fe. On this basis, it can be calculated that the volume energy density in the iron as the energy carrier in this chloride oxidation-reduction process is 11.20 kWh/l, which is considerably more than the volume energy density of the currently used energy carriers. The gaseous hydrogen has the volume energy density of 0.0018 kWh/l, hydrogen compressed to 700 bar 1.55 kWh/l, liquefied hydrogen 2.81 kWh/l, hydrogen stored in metallic hydrides 3.18 kWh/l. It also exceeds the values of liquid fossil fuels such as diesel (9.94 kWh/l) or even kerosene (10.38 kWh/l).

(17) This invention is not obvious with respect to the prior art and is innovative because processes have been included in the technological cycle of electrical energy storage in a solid matter that have not been described before: new chemistry on the basis of oxidation-reduction conversion of metallic chlorides performance of electrolysis at low temperatures from a solution production of an energy carrier having a very high volume density that is chemically stable and ecologically unharmful.

(18) This invention is useful since it allows a sustainable storage of huge electrical energy surpluses from the electric grids in a long period of time. The method of the invention has high energy yields and almost zero loss discharge over time. The method is environmentally friendly because the substance cycle of the method is closed, no material deposits or harmful emissions are produced since the entire material circles within the process. Only water enters the process, while hydrogen and oxygen leave the process. A further benefit of the invention is the fact that the energy carriers have very high volume energy densities that even exceed the volume energy density of kerosene. It is herewith allowed that a huge amount of stored energy is stored in a relatively small volume.

REFERENCES

(19) .sup.i E. Schaefer, K. Hemmer, Storage of solar-, wind- or water energy by electrolysis of metal hydroxideby supplying hydroxide of e.g. lithium, sodium, potassium etc. to electrolysis cell and passing current through cell, with additional heat supply, DE19523939 (A1) (1997). .sup.ii V. Lagana, F. Saviano, G Fusco, Process for the storage of electrical energy by electrolysis of alkali metal hydroxides, IL60167 (A) (1983). .sup.iii M. Vogelmann, Combined chemical and physical process useful in the field of storage of electrical energy and carbon dioxide, comprises carrying out melt flow electrolysis of sodium chloride for extracting metallic sodium and gaseous chloride, DE10200900775 (A1) (2010). .sup.iv Y. Tanimura, T. Itoh, M. Kato. Y. Mikami, Electrolytic regeneration of Iron (III) Chloride Etchant II. Continuous Electrolysis, Denki Kagaku vol. 64, pp. 301-306 (1996)