Device and method for thermal-electrochemical energy storage and energy provision

Abstract

The invention proposes a method and a device (10) for thermal-electrochemical energy storage and energy provision. The device (110) comprises: at least one thermal energy store (118), wherein the thermal energy store (118) comprises at least one heat transport medium (121) and at least one storage medium (119) selected from the group consisting of an electromagnetic storage medium, a thermal storage medium; at least one heating device (134), wherein the heating device (134) is designed to receive the heat transport medium (121) from the thermal energy store (118), to heat this medium and return it to the thermal energy store (118); at least one electrochemical cell (146), wherein the electrochemical cell (146) comprises at least one gas chamber (148), wherein the electrochemical cell (146) further comprises at least one first electrode (150) and at least one second electrode (152): wherein the second electrode (152) is designed as a 3-phase electrode (154), wherein the 3-phase electrode (154) has at least one first phase boundary (156) to the gas chamber (148) and at least one second phase boundary (158) to the electrochemical storage medium (119); wherein the electrochemical cell (146) is designed to electrochemically react the electrochemical storage medium (119); and at east one container (160), wherein the container (160) is designed to receive a supply on the heat transport medium (119), wherein the container (160) is further designed to receive the thermal storage medium (119) from the thermal energy store (118).

Claims

1. A device (110) for thermal-electrochemical energy storage and energy provision, comprising at least one thermal energy storage device (118), the thermal energy storage device (118) comprising at least one heat transport medium (121) and at least one storage medium (119) selected from the group consisting of: an electrochemical storage medium, a thermal storage medium; at least one heating device (134), wherein the heating device (134) is adapted to receive the heat transport medium (121) from the thermal energy storage device (118), heat it, and return it to the thermal energy storage device (118); at least one electrochemical cell (146), the electrochemical cell (146) comprising at least one gas compartment (148), the electrochemical cell (146) further comprising at least one first electrode (150) and at least one second electrode (152); wherein the second electrode (152) is formed as a 3-phase electrode (154), the 3-phase electrode (154) having at least a first phase boundary (156) to the gas compartment (148) and at least a second phase boundary (158) to the electrochemical storage medium (119); wherein the electrochemical cell (146) is adapted to electrochemically convert the electrochemical storage medium (119); and at least one container (160), wherein the container (160) is adapted to receive a supply of the heat transport medium (119), wherein the container (160) is further adapted to receive the thermal storage medium (119) from the thermal energy storage device (118).

2. The device (110) according to the preceding claim, wherein the thermal storage medium (119) comprises sodium chloride and calcium chloride in solid form, wherein the electrochemical storage medium (119) comprises sodium cations and chloride anions in liquid form, and wherein the heat transport medium (121) comprises sodium.

3. The device (110) according to any one of the preceding claims, wherein the thermal storage medium (119) is adapted to form a fixed bed (122).

4. The device (110) according to any one of the preceding claims, wherein the heating device (134) is arranged to receive solar energy from an environment of the heating device (134).

5. A method for thermal-electrochemical energy storage and energy provision, comprising the method steps: a) providing a device (110) according to any one of the preceding claims; b) thermally charging the thermal energy storage device (118), wherein the heat transport medium (121) is heated to a temperature of 500° C. to 850° C. by means of the heating device (134), wherein the heat transport medium (121) at least partially changing to a liquid phase; c) electrochemical conversion of the electrochemical storage medium (119) by means of the electrochemical cell; d) electrochemical back reaction by means of the electrochemical cell (146), whereby the electrochemical storage medium (121) re-forms; and e) flowing the electrochemical storage medium (119) into the container (160), whereby the electrochemical storage medium (121) changes into a thermal storage medium (119), whereby thermal energy is released.

6. The method according to the preceding claim, wherein step b) comprises the following substeps: b1) transporting the heat transport medium (121) into the heating device (134); b2) heating the heat transport medium (121) to a temperature between 500° C. to 850° C.; b3) transporting the heat transport medium (121) into the thermal energy storage device (118).

7. The method according to the preceding claim, wherein the heat transport medium (121) releases thermal energy to the thermal energy storage device (119) after heating.

8. The method according to any one of the preceding claims relating to the method, wherein step e) comprises the following substeps: e1) solidifying the thermal storage medium (119) into particles (124); e2) releasing heat of crystallization; e3) absorption of the heat of crystallization by the heat transport medium (121) of the container (160); and e4) transporting the heat of crystallization to a heat power process.

9. The method according to any one of the preceding claims relating to the method, wherein the storage medium (119) comprises sodium chloride, wherein step c) comprises the following substeps: c1) applying an electric current to the electrochemical cell (146); c2) converting sodium cations of the sodium chloride to sodium at the first electrode (142), wherein the first electrode (142) is connected as a cathode; c3) converting chloride anions of the sodium chloride into chlorine at the second electrode (144), said second electrode (144) being connected as an anode.

10. The method according to the preceding claim, wherein step d) comprises the following substeps: d1) tapping an electric current from the electrochemical cell (146); d2) converting the sodium to the sodium cations at the first electrode (142), the first electrode (142) being connected as an anode; d3) converting the chlorine to the chlorine anions at the second electrode (144), the second electrode (144) being connected as a cathode.

11. Use of a device (110) according to any of the preceding claims relating to the device (110) for storing and providing thermal energy from solar thermal power plants and/or for storing and providing electrical energy from wind power plants.

Description

[0100] In detail show:

[0101] FIG. 1 a schematic representation of an embodiment of a device according to the invention;

[0102] FIG. 2A to FIG. 2D a schematic representation of step b) of the process according to the inventive method

[0103] FIG. 3A and FIG. 3B a schematic representation of an electrochemical cell of a device according to the invention (FIG. 3A) and a schematic representation of a thermal storage container after carrying out step c) (FIG. 3B);

[0104] FIG. 4 a schematic representation of the process steps d) and e) according to the present invention; and

[0105] FIG. 5 an illustration of operations in a thermal energy storage device system according to an embodiment of a concentrating solar thermal power plant with an electric power of 2 MW and a storage for 6 hours.

DESCRIPTION OF THE EMBODIMENTS

[0106] FIG. 1 shows a schematic diagram of an embodiment of a device 110 according to the invention. The device 110 may be attached to a tower top 112 of a tower 114 of a solar thermal power plant. The device 110 may be irradiated with concentrated sunlight, as shown schematically with arrows 116. For further details regarding a structure and an operation of the device 110, please refer to the discussion of FIGS. 2-5.

[0107] FIGS. 2A to 2D show a schematic representation of step b) of the method according to the invention.

[0108] To begin with, a thermal energy storage device 118 is provided. The thermal energy storage device 118 may in particular be formed as a container 120. The thermal energy storage device comprises at least one heat transport medium 121 and at least one storage medium 119 selected from the group consisting of: an electrochemical storage medium, a thermal storage medium. In particular, the thermal energy storage device 118 may comprise sodium chloride, calcium chloride, and sodium.

[0109] Initially, as shown in FIG. 2A, the thermal energy storage device 118 may comprise a fixed bed 122 of particles 124. The particles 124 may include sodium chloride and calcium chloride. In particular, the calcium chloride may be admixed with the sodium chloride to provide a melting point of a mixture of calcium chloride and sodium chloride of 560° C. Channels 126 may be located between the particles 124, particularly free channels 128. A fluid may flow through the channels 126. The fluid 130 may comprise sodium. The vessel may initially have a temperature of 150° C. At the temperature of 150° C., the sodium may be present in liquid form and may be used as a fluid filling the free channels of the packed bed. The sodium can be transported by a pump into a heating device 134 (shown here schematically with arrow 134). In the heating device 134, the sodium can be heated to a temperature of 560° C. Subsequently, the sodium can be transported back to the thermal energy storage device 118 (schematically shown here with arrow 136). In particular, the sodium can re-enter at the bottom 138 of the thermal energy storage device 118.

[0110] The sodium can flow through the free channels 128 between the particles 124 and deliver its thermal energy to the particles 124. Upon further energy input, the particles 124 become liquid, as shown in FIGS. 2B through 2D. Due to a lower density of sodium compared to sodium chloride and calcium chloride, the molten salt may sink to a ground 140 of the container 120.

[0111] As shown in FIG. 2D, the sodium chloride and calcium chloride may at least nearly completely transition to a liquid aggregate state. A first phase 142 may be formed, comprising sodium chloride and calcium chloride. Floating on top of the first phase 142 may be a second phase 144 comprising sodium.

[0112] FIG. 3A illustrates a schematic diagram of an electrochemical cell 146 of a device 110 according to the invention. The electrochemical cell 146 includes a gas compartment 148, and a first electrode 150 and a second electrode 152. The second electrode 152 is configured as a 3-phase electrode 154. The 3-phase electrode 154 includes at least a first phase boundary 156 to the gas compartment 148 and at least a second phase boundary 158 to the sodium chloride and calcium chloride. The electrochemical cell 146 may be configured to convert sodium cations of the sodium chloride to elemental sodium and to convert chloride anions of the sodium chloride to chlorine, particularly chlorine gas. The chlorine gas may pass into gas compartment 148. Subsequently, the chlorine gas may be directed into gas cylinders (not shown) for storage.

[0113] Referring to FIG. 3, a schematic diagram of a thermal energy storage device 118 is shown after performing step c). After electrochemical conversion of sodium chloride to sodium and chlorine using electrochemical cell 146, a majority of the sodium chloride may have been converted.

[0114] FIG. 4 shows a schematic representation of process steps d) and e) according to the present invention. During step d), an electrochemical back reaction may occur. The sodium may donate an electron and may pass into the liquid sodium chloride as a sodium cation. At the second electrode 152, a Cl.sub.2-molecule may accept two electrons from the gas and pass into the electrolyte as two chloride anions. An electrochemical potential can be formed, which can be used to generate electricity. By a use of the 3-phase electrode 154, the back reaction can take place. During step d), a lower temperature may be targeted in the electrochemical cell 146 than during the charging phase. This may result in a discharge of the electrochemical cell 146 over at least substantially the entire phase of the discharge at a higher power, and thus more electrical energy may be extracted than was required for storage.

[0115] Once the chlorine gas is at least nearly completely converted back into the electrolyte solution, step e) can begin. The sodium, which is present in the thermal energy storage device 118, can release thermal energy to the thermal power process and flow into a container 160 at a lower temperature (shown schematically with arrow 162). Droplets of the sodium chloride and/or calcium chloride may solidify into solid particles 124 in the container 160 due to the comparatively cold sodium, and may release heat of crystallization to the sodium. The sodium may transport this heat to the thermal power process for power generation. In turn, the fixed bed 122 can form. Once the vessel 160 is filled with particles 124, the sodium can continue to dissipate heat until the power-to-heat process can no longer be economically operated.

[0116] FIG. 5 shows an illustration of operations in a thermal energy storage device system in accordance with an embodiment of a concentrating solar thermal power plant having an electrical output of 2 MW and a storage for 6 hours. This is an illustration of the first embodiment example explained in the above description.

[0117] A diagram is shown schematically illustrating a temperature of the thermal energy storage device 118 and a content of the thermal energy storage device 118 during the various process phases. It is assumed here that the thermal energy storage device 118 has a temperature corresponding to an ambient temperature at the beginning (before phase 1 in the diagram). This may be the case, for example, during an initial start-up or after maintenance work. During phase 1 in the diagram, the amount of sodium circulating as a heat transport medium between the thermal energy storage device and the heating device 134 may be liquid. This can be done, particularly electrically, by heating the sodium from 300 K to 372 K, which corresponds to the melting temperature of sodium, and going through the phase change. Likewise, the amount of sodium chloride present as a solid bulk must be heated. Since this energy is stored as thermal energy, which must first be converted back into electrical energy, this process is basically of little significance in terms of electrical storage capacity, since this heat is present at a very low level. A start-up and shut-down process is only occasionally required, and the system is generally maintained at a temperature level above the melting point of sodium. This will result, through sufficient thermal insulation, in basically only a small amount of electrical power being required to maintain this temperature. During shutdown, some of this thermal energy can still be converted into electrical energy. In the process, the temperature drops continuously and the efficiency of the conversion deteriorates, so that the efficiency previously used can no longer be expected. Assuming that the efficiency is only a quarter of that specified in the embodiment examples as ε=0.36, this amount of energy accounts for about 0.1% of the total amount of electrical energy that can be stored (noted as 0.1% in the figure).

[0118] Subsequently, the now liquid sodium and the solid sodium chloride are heated up to a temperature of about 800° C. (phase 2). In combination with a solar thermal power plant, this is done by supplying thermal energy. The amount of energy thermally stored as a result accounts for about 1.1% of the equivalent electrical storage capacity of the reservoir.

[0119] As soon as the temperature of 800° C. is reached, an isothermal operating phase begins (=operation at constant temperature, phases 3, 4, 5, 6, 8, 9, 10, 11). The hot, liquid sodium moves upward by releasing its thermal energy through the NaCl bed in thermal energy storage device 118. Once the melting temperature is reached by the salt mixture, drops of molten salt sink to the bottom of vessel 120, where they form a liquid phase on which the sodium floats due to its lower density. The thermal charging process (phases 2, 3) is completed as soon as the salt has changed to the liquid aggregate state. Melting requires an amount of energy that, assuming ε=0.36 equivalent, is slightly less than 4% of the electrical storage capacity of the reservoir. Liquid salt can then be continuously transported during phase 4 to the electrochemical cell 146, where sodium and chlorine are electrochemically generated with the application of an electric current. The sodium can be returned to thermal energy storage device 118 where it becomes part of a floating phase. Once the sodium chloride in the tank is converted to sodium and chlorine, the electrochemical charging process is complete. The thermal energy storage device 118 is at least almost completely charged with electrochemical energy. Now, at most, further thermal energy can be added, which would cause the temperature to rise (not shown in the diagram). The thermal and electrochemical charging processes can run simultaneously. For electrochemical discharging (phase 5), the electrochemical cell is operated with reversed polarity compared to charging and liquid sodium chloride is formed from sodium and chlorine. Thereafter (phase 6 or simultaneously), thermal energy is removed from the liquid sodium in the thermal energy storage device 118 so that the sodium temperature drops below the melting temperature of the sodium chloride-calcium chloride mixture. The salt mixture formed in the electrochemical cell 146 can then be dropped (first half phase 7) into the liquid sodium, where it gives up its thermal and solidification energy to the sodium. The salt crystallizes into particle 124 and rebuilds the bulk. The volume of sodium continuously displaced by the addition of salt is fed to the electrochemical cell. Electrochemical and thermal discharge thus also occur, at least partially, simultaneously. Then a loading phase can begin again.

[0120] As soon as a part of the salt mixture is liquid, electrical energy from the thermal power process of the solar power plant can be stored electrochemically. For this purpose, the solid initial mass of sodium chloride is electrochemically converted to 38% sodium and 62% chlorine gas. The latter requires, for example, a pressure vessel in which the Cl.sub.2 can be stored in liquid form at room temperature and greater than 7.5 bar. By running off the back reaction, this electrical energy is recovered. Once the electrochemical back reaction has started during discharge, sodium chloride is formed. This is dropped into cool liquid sodium in the thermal energy storage device system, forming salt crystals that sink to the bottom. Thus, the solid bulk is renewed. Heat is released during crystallization. As soon as the thermal energy storage device 118 is filled again with the salt bed, the isothermal discharge phase is completed. It is now still possible to thermally discharge the entire thermal energy storage device 118 to just above the melting temperature of the sodium.

[0121] Assuming a recoverable electricity price of 6 ct/kWh, and for a cost assumption for sodium chloride of about 2 ct/kg, the storage facility can store electrical energy for about 1.3 ct/kWh, based on raw material costs. In comparison, energy storage in a storage medium that is currently state of the art in solar thermal, solar salt, based on raw material costs in solar thermal power plants is currently about 25 ϵ/kWh. The investment cost for the amount of salt required in the thermal energy storage device 118 is basically amortized after only one isothermal charging and discharging cycle at this assumed electricity and raw material price.

LIST OF REFERENCE SIGNS

[0122] 110 Device [0123] 112 Tower top [0124] 114 Tower [0125] 116 Arrow [0126] 118 Thermal energy storage device [0127] 119 Storage medium [0128] 120 Container [0129] 121 Heat transport medium [0130] 122 Fixed bed [0131] 124 Particle [0132] 126 Channel [0133] 128 Free channel [0134] 130 Fluid [0135] 132 Arrow [0136] 134 Heating device [0137] 136 Arrow [0138] 138 Bottom [0139] 140 Ground [0140] 142 First phase [0141] 144 Second phase [0142] 146 Electrochemical cell [0143] 148 Gas compartment [0144] 150 First electrode [0145] 152 Second electrode [0146] 154 3-phase electrode [0147] 156 First phase boundary [0148] 158 Second phase boundary [0149] 160 Container [0150] 162 Arrow