CH714932A1 - Method for charging and discharging electrochemically stored energy. - Google Patents

Abstract

The invention relates to a method for charging and discharging electrochemically stored energy, comprising the following method steps: Charging a first reactor cell (13) by applying a DC electrical voltage, by electrolysis of dewatered (calcined) molten alkalis, in particular alkali-metal alkalis in a location where there is an excess of electrical current, the first reactor cell (13) comprising a first anode space (32) and a first cathode space (30), removing the solid or liquid formed in the electrolysis, metallic product, transport of the solid or liquid metallic product produced during electrolysis to a location where electrical power is needed and where there is a second reactor cell comprising a second anode space and a second cathode space, filling the second anode space with the product, Discharging the second reactor cell e, by bringing the product into contact with a liquid, aqueous electrolyte through a membrane to re-generate liquor and electric current, and stripping off the hydrogen produced at the cathode.

Description

description

FIELD OF THE INVENTION The invention relates to a method for charging and discharging electrochemically stored energy according to the preamble of claim 1.

PRIOR ART The vanadium redox accumulator (vanadium redox flow battery, VRFB) is known from the prior art. Like all rechargeable batteries, it belongs to the rechargeable energy store. It is a type of flow accumulator that uses vanadium compounds in aqueous solutions in both electrolytes. This prevents the problem of mutual contamination due to the diffusion of ions through the membrane.

As with all flow batteries, a main advantage of the vanadium redox battery (vanadium redox flow battery, VRFB) is that, unlike ordinary secondary cells, power and energy are independent of each other. The modular design enables the construction of a battery of any power and capacity. adjustable by the electrode area and the storage capacity by the amount of electrolyte. Deep discharge is also easy. For example, the VRFB accumulator can be completely discharged for a long time without causing any notable aging effects.However, it has a comparatively low energy density of approx. 15 Wh / I to 25 Wh / I electrolyte liquid and the metal vanadium is only available to a limited extent.

The currently available commercial VRFB are used exclusively stationary, especially in the areas of regenerative energy sources for covering peak loads and as load balancing, and also in the area of uninterruptible power supplies.

OBJECT OF THE INVENTION The disadvantages of the prior art described result in the object initiating the present invention in developing a generic charging and discharging method in which charging and discharging is possible at different locations and is carried out with metals which are large Amounts are available.

Description The method for charging the electrochemically stored energy takes place in the following step; Charging a first reactor cell by applying a DC voltage by electrolysis of dehydrated (calcined) molten liquors, especially alkali metal liquors, in a place where there is an excess of electrical current, the first reactor cell comprises a first anode space and a first cathode space.

The problem is solved in the method by the following process steps:

Removal of the solid or liquid metallic product formed during the electrolysis,

- Transport of the solid or liquid metallic product formed during the electrolysis to a place where electrical current is required and where a second reactor cell is present, comprising a second anode space and a second cathode space.

- Filling the second anode compartment with the product.

- Unloading the second reactor cell by passing the product through a. Membrane is brought into contact with a liquid aqueous electrolyte in order to generate alkali and electric current again.

- Removing the hydrogen generated at the cathode.

The ability to store electrochemical energy in a metallic product enables the discharge location to be separate from the charging location and allows the metallic product, preferably sodium, to be transferred from the charging location to the. Unloading site is transported, This allows direct current through electrolysis to be used to manufacture the metallic product directly at a location where the direct electrical current is generated. The metal produced can be transported with little effort to a place where electrical direct current is required. The electrochemically stored energy in the metal can also be stored well and easily until it is discharged. Compared to rechargeable batteries, storage in the metal is much cheaper and takes up much less space.

The lye for electrolysis of the product in the first anode compartment is advantageously anhydrous and melted. As a result, the metal in which the electrochemical energy is stored can be produced by electrolysis. Na ⁺ and OH ions are completely dissociated in the molten liquor and this enables a high yield of metallic sodium to be achieved.

The invention is preferably characterized in that the product formed floats in the first reactor cell on the calcined alkali. As a result, the resulting alkali metal is particularly easy to remove or harvest from the first reactor cell.

CH 714 932 A1 It is preferred if the product in the liquid state is transferred to a transport device when it is hot above 100 ° C. and solidifies in the transport device below 1 ° C. Due to its low melting point, the metal can be pumped liquid into the transport device and can be transported relatively safely in the solidified state. The properties of the selected metal therefore enable simple and safe transport to the place where direct electrical current is required.

[0012] In a particularly preferred embodiment, the product is sodium. Sodium is a. very widespread metal and has a particularly low melting point for metals of approx. 97 ° C at atmospheric pressure / which simplifies transport, as described above. It can also be easily produced from sodium hydroxide as described above.

It has proven to be useful if the solidified product in the transport device with an inert gas, in particular nitrogen, is applied. As a result, the solidified metal is shielded from the environment and safe transport can be guaranteed.

In a further particularly preferred embodiment of the invention, the product in the liquid state is transferred to the second reactor cell and in the second reactor line the electrochemical potential is released by metal cations, in particular sodium cations, through a membrane from the second anode space diffuse the second cathode space and an aqueous alkali (electrolyte) in the second cathode space, with which metal cations are enriched. This procedure and the reactants involved make it possible to generate direct electrical current from the energy electrochemically stored in the sodium.

In a further preferred embodiment of the invention arises in the electrochemical reaction in the second reactor cell, an electrical direct current and / or hydrogen, the hydrogen can be used as an energy source for driving motors or in the chemical industry. The direct electrical current can be directly from the second reactor cell. Be taken off where it is needed.

It proves to be advantageous if direct current with a voltage that is as uniform as possible is used for charging the first reactor cell. This allows the power yield to be optimized. However, it is also possible to operate the first reactor cell with a fluctuating DC voltage, as is usually provided by solar cells.

The direct current expediently comes from solar cells and electronic circuits provide the most uniform possible voltage for charging the first reactor cell.

The invention is also preferably characterized in that the second reactor cell is activated when electricity is required at the location where the electrical current is required and the direct current harvested when the second reactor cell is discharged is converted once into alternating current or into batteries is saved. The production of the direct electrical current in the second reactor cell is extremely flexible, since it can be produced at any time if required and there are no lead times until direct current is produced.

In a particularly preferred embodiment of the invention, the membrane is a tubular membrane which floats in the aqueous electrolyte, the second anode space being provided within the tubular membrane. The tubular membrane allows the liquid sodium to be in a closed space with the largest possible. Exchange surface to the electrolyte can be abandoned.

The hose membrane is expediently fiber-reinforced, as a result of which it can be pressurized without bursting.

It proves to be advantageous for the flow of sodium ions in the electrolyte if different pressures are applied in the second anode space and the second cathode space. The higher pressure in the hose membrane can take place, for example, by injecting an inert gas into the hose membrane.

In a further preferred embodiment of the invention, the amount of hydrogen and direct current in the second reactor cell is controlled by the choice of the process parameters pressure and temperature. The temperature control can be realized by cooling the second reactor cell. The pressure control can be done by pressurizing the hose membrane with an inert gas. The choice of process parameters can be used to regulate whether hydrogen production or the production of direct current should be increased.

Further advantages and features emerge from the following description of an embodiment of the invention with reference to the schematic representations. In a representation that is not to scale:

1: a plan view of a tube reactor with a plurality of tubes, which can act as an anode or cathode,

2 shows a sectional illustration of the tubular reactor along the sectional plane II-II;

Fig. 3: Detailed view of the tubular reactor of Fig. 1 when it is used as a first reactor cell and

CH 714 932 A1

Fig. 4: View detail of the tubular reactor when used as a second reactor cell.

The present invention relates to a method for charging and discharging electrochemically stored energy at two different locations. The charging or discharging takes place in a tubular reactor 11. For charging, the tubular reactor is used as a first reactor cell 13, which first reactor cell 13 is adapted to the charging process (FIG. 3). The tubular reactor is used as a second reactor cell 15 for discharging Which second reactor cell 15 is adapted to the discharge process (FIG. 4).

The tubular reactor 11 is an electrochemical reactor which can be filled with different electrolytes. A plurality of tube bundles 17 are immersed in the electrolyte. A tube bundle 17 comprises an inner tube 19 and. an outer tube 21. The inner tubes 19 and the outer tubes 21 are respectively in a first and a third tube plate 23a, 23b or a second tube plate 25a and a fourth tube plate 25b. The inner tubes 19 can be connected as an anode or as a cathode, since they are insulated from one another by the tube sheets 23a, 23b. Between the first tube sheet 23a and the second tube sheet 25a and. The third tube sheet 23b and the fourth tube sheet 25b are arranged with a first and a second wedge seal 27, 29, which have a sealing effect between the corresponding tube sheets 23a, 25a and 23b, 25b by bracing the tube sheets. The flange seals 27, 29 are electrically insulating and gas-tight between the tube sheets.

A heating element can be arranged on the fourth tube plate 25b in order to set the electrolyte temperature or to start and control the electrochemical reaction. A circulation device, in particular a circulation pump, can also be provided on the fourth floor 25b in order to. to be able to circulate the electrolyte.

To charge electrochemically stored energy, the tubular reactor described above is used as the first reactor cell 13 (FIG. 3). The inner tubes 19 serve as anodes. The space that surrounds the outer tubes 21 can be regarded as the anode space 30. The first reactor cell 13 is filled with a liquid, calcined, (anhydrous) alkali as the electrolyte. When an electrical DC voltage is applied, the recombination of OH ions results in oxygen and water vapor from the alkali. These gases can escape through the steam dome 31.

The outer tubes 2.1 are preferably made of ceramic material. The outer tube 21 is broken through in the region of the second and fourth tube sheets 25a, 25b. This enables a connection to the outer wall of the first reactor cell 13, which enables the exchange between the first cathode space 30 and the first anode space. 32 ensures. The space within the inner tubes 19 can be regarded as the first anode space 32. Metallic sodium, in the form of drops, forms on the outer wall. The sodium floats on the molten sodium hydroxide solution because it has a lower specific weight than the sodium hydroxide solution. The liquid sodium can be harvested or suctioned off at the first outlet 34, which first outlet 34 is formed between the first tube plate 23a and the second tube plate 25a. The molten sodium has a temperature of approx. 300 ° C. The sodium hydroxide solution is completely dissociated as Na ⁺ and OH ions, since the anhydrous sodium hydroxide solution is a liquid in which the ions inevitably form.

The electrolyte circulation takes place between the inner tube 19 and the outer tube 21 with an overflow to the inside through openings in the inner tube 19 and the outer tube 21 in the region of the second and fourth tube plate 25a, 25b, on the fourth tube plate 25b, the depleted electrolyte pumped out and. with the. Mixed electrolyte, which is located outside the outer tubes 21 in the first reactor cell 13. The electrolyte again releases its sodium excess on the outer wall of the first reactor cell 13.

The electrolyte level 33 is shown in the inner tube 19, in the outer tube 21 and outside the outer tube. The tubular reactor 11 can be cooled with an internal cooling 35 and an external cooling 37 in order to be able to thermally regulate the electrolysis.

The metallic sodium generated in the first reactor cell is transferred in the liquid state at over 100 ° C in a transport device / for example in a tanker truck. The pure sodium cools and solidifies in the transport device. During transport, the sodium is overlaid with an inert gas, for example nitrogen, for safety reasons. The sodium can also be temporarily stored, the electrochemically stored energy in the sodium being temporarily stored until it is discharged in the second reactor cell 15.

[0032] The sodium is transported to a place where. electrical current is required. The second reactor cell 15 is positioned at this location. The electrochemically stored energy contained in the liquid sodium is discharged in the second reactor cell 15.

The second reactor cell 15 is filled with liquid sodium. In the second reactor cell 15 there is also an aqueous sodium hydroxide solution as the electrolyte. The liquid sodium must be kept away from the caustic soda so that the electrical potential can arise. The liquid sodium is therefore filled into a tubular membrane 39 which, however, does not allow the diffusion of sodium ions into the sodium hydroxide solution. metallic sodium. The hose membrane 39 also prevents water from the alkali from entering the hose membrane 39 in which the sodium is located. The sodium ions form in the membrane and diffuse through it. The space in the tube membrane 39 is considered to be the second anode space 40. The second cathode space space 44 is defined outside the tube membrane. The sodium ions react with the H + cations and the OH anions of the aqueous alkali

CH 714 932 A1 on hydrogen and NaOH. At the same time, water-steam must be applied in a steam diffuser 41 in order to provide H ⁺ ions. The steam diffuser 41 is arranged in the inner tube 19. This creates 4OH- + 6H ⁺ -> 4H2O + H2 in the inner tube 19. This reaction takes place in the circulation of the electrolyte along the inner tube 19. The hydrogen produced can be collected between the first tube plate 23a and the second tube plate 25a and can be discharged through the second outlet 42. The inner tube 19 and the outer tube 21 have first and second perforations 43, 45 through which electrolyte can flow. The Na ⁺ ions diffusing through the tubular membrane displace the H ⁺ ions, since sodium is more negative than hydrogen according to the voltage series. This shifts the equilibrium in the above reaction to the product side.

As described above, an electrical direct current and / or hydrogen is formed in the electrochemical reaction in the second reactor cell 15. By selecting the reaction parameters such as temperature and pressure, you can set how much direct current and hydrogen is generated. The electrochemical reaction can be controlled via the internal cooling 35 and the external cooling 37. The tubular membrane 39 floats in the aqueous electrolyte and. is preferably fiber-reinforced. As a result, the liquid sodium in the tubular membrane can be pressurized in order to improve the diffusion of the sodium ions. It is possible to generate the pressure in the hose membrane by blowing in an inert gas above the sodium level. As already explained in the description of FIG. 2, circulation of the electrolyte is possible with a circulation pump. The sodium-enriched electrolyte from the second reactor cell 15 is made water-free again by boiling. After the calcination, anhydrous sodium hydroxide solution is fed into the first reactor cell 13, which closes the circuit.

Legend:

[0035]

tubular reactor

First reactor cell

Second reactor cell

tube bundle

inner tube

outer tube

23a First tube sheet

23b third tube sheet

25a Second tube sheet

25b fourth tube plate

First flange seal

Second flange seal

First cathode room

steam dome

First anode room

33, electrolyte level

First exit

internal cooling

external cooling

hose membrane

Second anode room

Steam diffuser

Second exit

CH 714 932 A1

First perforations

Second cathode compartment

Second perforations

Claims (15)

claims 1. A method for charging and discharging electrochemically stored energy comprising the following process steps: Charging a first reactor cell (13) by applying an electrical direct voltage by electrolysis of dehydrated (calcined) molten alkalis, in particular of alkali metal alkalis, in a place where there is an excess of electrical current . - Wherein the first reactor line (13) comprises a first anode space (32) and a first cathode space (30), further characterized by Removal of the solid or liquid metallic product formed during the electrolysis, Transporting the solid or liquid metallic product formed during the electrolysis to a place where electrical current is required and where a second reactor cell (15) is present, comprising a second anode space (44) and a second cathode space (44), Filling the second anode compartment (40) with the product, - Discharging the second reactor cell (15) by bringing the product through a membrane (39) into contact with a liquid aqueous electrolyte to generate alkali and electric current again and - Removing the hydrogen generated at the cathode. 2. The method according to claim 1, characterized in that the alkali for the electrolysis of the product in the first anode space (32) is water-free and melted. 3. The method according to claim 1 or 2, characterized in that the product formed in the first reactor cell (13) floats on the calcined alkali. 4. The method according to any one of the preceding claims, characterized in that the product is transferred in the liquid state at over 100 ° C in a transport device and solidifies in the transport device below 100 ° C. 5. The method according to any one of the preceding claims, characterized in that the product is sodium. 6. The method according to any one of the preceding claims, characterized in that the solidified product is acted upon in the transport device with an inert gas, in particular nitrogen. 7. The method according to any one of the preceding claims, characterized in that the product in the liquid state is transferred to the second reactor cell (15) and, in the second reactor cell (15), the electrochemical potential is released by metal cations, in particular sodium Cations, diffuse through a membrane (39) from the second anode space (40) into the second cathode space (44) and an aqueous alkali as electrolyte in the second cathode space (44) is enriched with the metal cations. 8. The method according to any one of the preceding claims, characterized in that in the electrochemical reaction in the second reactor cell (15), an electrical direct current and / or hydrogen is formed. 9. The method according to any one of the preceding claims, characterized in that for charging the first reactor cell (13) direct current with a voltage as uniform as possible is used. 10. The method according to claim 9, characterized in that the direct current comes from solar cells and electronic circuits provide as uniform a voltage as possible for charging the first reactor cell (13). 11. The method according to any one of the preceding claims, characterized in that the second reactor cell (15) is activated when electricity is required at the location at which electrical current is required and the direct current harvested when the second reactor cell is discharged is converted once into alternating current or is stored in batteries. 12. The method according to any one of the preceding claims, characterized in that the membrane is a tubular membrane (39) which floats in the aqueous electrolyte, the second anode space (40) being provided within the tubular membrane (39). 13. The method according to claim 12, characterized in that the tubular membrane. (39) is fiber reinforced. 14. The method according to any one of the preceding claims, characterized in that in the second anode space (40) and. different pressures are applied to the second cathode compartment (44). 15. The method according to any one of the preceding claims, characterized in that the amount of hydrogen and direct current in the second reactor cell (15) is controlled by the choice of the process parameters pressure and temperature. CH 714 932 A1