WO2020170125A2 - Safety apparatus for millibaric pressure control in inert atmosphere for high reactivity liquid solution, and tank and flow battery comprising such safety apparatus - Google Patents

Abstract

A safety apparatus (12; 12') for millibaric pressure control in an inert atmosphere for liquid solutions (14; 14') with high reactivity contained inside a tank (16; 16') comprises: a differential U-shaped pressure gauge (18; 18') suitable for use with a non-reactive liquid, having a first end (20; 20') and a second end (22; 22'). The first end (20; 20') is in fluid connection with an environment having a known pressure; and the second end (22; 22') is in fluid connection with said tank (16; 16'), and with an output line (24; 24') for said inert gas contained inside said tank (16; 16').

Description

"SAFETY APPARATUS FOR MILLIBARIC PRESSURE CONTROL IN INERT ATMOSPHERE FOR HIGH REACTIVITY LIQUID SOLUTION, AND TANK AND FLOW BATTERY COMPRISING SUCH SAFETY APPARATUS"

DESCRIPTION FIELD OF APPLICATION

[0001] The present invention relates to an apparatus for millibaric pressure control in inert atmosphere for high reactivity liquid solution, and a tank and a flow battery comprising such safety apparatus.

PRIOR ART

[0002] As is known, the management of a tank containing a liquid in which the residual volume is filled with an inert gas is particularly complex.

[0003] In particular, it is necessary to provide several devices connected to the tank itself, such as:

- overpressure valves for inert gas;

- means adapted to control the pressure of the inert gas when filling the residual volume;

- means for expelling and possibly sampling any secondary gases that form in the tank.

[0004] The complexity of this type of structure is particularly felt in energy accumulators.

[0005] As is known, the demand for energy is continuously increasing, a requirement that affects the production plants, both at the construction level and in their management .

[0006] Furthermore, the sensitivity towards the environment and the known drawbacks in the use of fossil-type fuels are shifting attention towards renewable energy sources, which as known have the feature of not providing stable and continuous but intermittent power supply.

[0007] Existing electricity grids are designed to provide the power required by users by adapting production in real time. However, this type of operation is incompatible with renewable sources.

[0008] To cope with this type of problem, energy storage systems are used, which must essentially meet two needs: power quality and energy management.

[0009] Regarding the quality of the power, it is meant the ability of the energy storage system to supply energy in short intervals of time, in the presence of a stabilized network, constant power and the possibility of regulating the frequency.

[0010] On the other hand, as regards energy management, it is meant the accumulation and supply in long time intervals, from a few minutes or even hours, in the presence of a leveling of the voltage peaks and of the phase difference between production and supply.

[0011] In addition to these main features, the storage system must also be scalable, that is, modular and therefore adaptable to different conditions of use, versatile and simple to use.

[0012] Furthermore, it must have a low cost in order to be used in a large electricity network.

[0013] Electrochemical storage systems offer features that make them suitable for this type of requirement, to act as intermediaries between intermittent energy sources and traditional electrical networks. They allow excellent scalability thanks to their modularity, combined with a static structure that makes them suitable for use on any site .

[0014] Among the electrochemical systems, the most suitable for large-scale stationary storage are redox flow batteries, which will also be referred to below as RFB batteries (Redox Flow Battery) .

[0015] In fact, RFB batteries show remarkable scalability, flexibility of use, overall efficiency, response speed and duration (in terms of charge and discharge cycles) . Furthermore, they offer an additional advantage given by the independence between the energy that can be stored and the deliverable power.

[0016] The RFB (Redox Flow Battery, in Italian "Flow Batteries") comprise electrochemical cells composed of two electronic conductors (or electrodes), which constitute the terminals of the positive pole and negative pole, separated by an ionic conductor, for example an ion-conducting polymeric membrane (or polymeric electrolyte) .

[0017] In the two compartments formed by the electrodes the liquid electrolytes flow, consisting of two solutions containing the chemical species that produce the energy charge and discharge reactions.

[0018] The positive electrolyte flows to the positive pole, while the negative electrolyte flows to the negative pole.

[0019] In the discharge step, the negative pole acts as an anode and on the surface of its electrode the chemical species contained in the negative electrolyte give an oxidation reaction, freeing electrons; since the polymeric membrane does not allow the electrons to pass, they are forced to flow in the external user circuit until they reach the positive electrode, which acts as a cathode. On the cathode surface there is therefore a reduction reaction of the chemical species contained in the positive electrolyte.

[0020] In the charging step, the reactions are reversed thanks to the energy that the cell receives from the outside, therefore at the positive pole, now anode, there occurs the oxidation of the positive electrolyte, while at the negative pole, now cathode, there occurs the reduction of the negative electrolyte. This qualifies the RFBs as completely reversible, capable both of converting chemical energy into electrical energy and of carrying out the reverse transformation.

[0021] However, RFBs have some drawbacks, among which the low energy density compared to other technologies, which implies the construction of batteries with large surfaces that can give problems of non-uniformity of the flow. In addition, the large surface area reduces the current density. The conductivity of electrolytes makes the batteries subject to shunt current and their thermal instability requires careful control of the temperature.

[0022] The low energy and current densities do not give problems for stationary storage applications based on RFBs, but limit their use in the automotive field, even if some studies do not exclude this possibility by suggesting a mechanical recharge, or simply by replacing the uncharged electrolytes with charged electrolytes.

[0023] Particularly appreciated are vanadium flow redox batteries (VRFB) , which comprise a set of electrochemical cells where the two electrolytes are separated by a proton exchange membrane. Both electrolytes use vanadium: the electrolyte in the positive half-cell contains ions V0₂ ⁺ and V0²⁺, while the electrolyte in the negative half- cell contains ions V³⁺ and V²⁺. Electrolytes can be prepared in various ways, for example by electrolytic dissolution of vanadium pentoxide (V2O5) in sulfuric acid (H2SO4) · Hence, the solution used remains highly acidic.

[0024] In vanadium flow batteries, the two half-cells are also connected to reserve tanks containing a very large volume of electrolyte, which is circulated through the cell with special pumps.

[0025] The limitations mentioned above with reference to the tanks are particularly felt in this type of application.

DISCLOSURE OF THE INVENTION

[0026] The need of solving the drawbacks and limitations mentioned with reference to the prior art is therefore felt .

[0027] Therefore, the need is felt to provide a system which simplifies the management and control of a tank containing a liquid in which the residual volume must be filled with an inert gas.

[0028] In particular, the need is felt for a safety system for millibaric pressure control in inert atmosphere for high reactivity liquid solutions.

[0029] This requirement is met by a safety apparatus for millibaric pressure control in inert atmosphere for high reactivity liquid solutions according to claim 1, by a tank comprising such apparatus according to claim 7 and by a flow battery according to claim 10.

DESCRIPTION OF THE DRAWINGS

[0030] Further features and advantages of the present invention will appear more clearly from the following description of preferred non-limiting embodiments thereof, in which:

figure 1 schematically shows a safety apparatus for millibaric pressure control in inert atmosphere for high reactivity liquid solutions according to the present invention;

figure 2 schematically shows an energy accumulator according to the present invention;

figure 3 schematically shows a portion of the accumulator of figure 2.

[0031] Elements or parts of elements in common to the embodiments described below are referred to with the same reference numerals.

DETAILED DESCRIPTION

[0032] In figure 1, a safety apparatus for millibaric pressure control in inert atmosphere for high reactivity liquid solutions contained in a tank is schematically shown and indicated with reference numeral 12.

[0033] The safety apparatus 12 comprises a U-shaped differential pressure gauge 18 adapted to be used with a non-reactive liquid, having a first end 20 and a second end 22.

[0034] The first end 20 is in fluid connection with an environment having a known pressure, while the second end 22 is adapted to be placed in fluid connection with the tank 16, and with an output line 24 for the inert gas contained inside the tank 16.

[0035] According to a possible embodiment, the

[0036] non-reactive liquid is distilled water. However, it is also possible to use other types of liquid such as: GALDEN^®, diiodomethane, dibromomethane .

[0037] With reference to the example of figure 1, the first end 20 can be in fluid connection with an atmospheric pressure environment.

[0038] According to alternative embodiments, in which the inert gas inside the tank 16 is at very different pressures with respect to the atmospheric pressure, the first end 20 can be connected with an environment with a pressure higher or lower than the atmospheric pressure.

[0039] The second end 22 of the differential pressure gauge 18 can be connected by means of a first duct 26 to the tank 16, and on the first duct 26 a node 28 from which the output line 24 departs can be arranged.

[0040] At least one valve 30 adapted to block a gas flow can be provided on the output line 24. The valve 30 may be : a two-way valve or solenoid valve; or a globe valve or solenoid valve (for linear regulation) . However, it is possible to use other types of valves which are easily conceivable by those skilled in the art.

[0041] Thanks to the output line 24 it is possible to remove any reaction gases that may develop inside the tank .

[0042] According to a possible embodiment, the differential U-shaped pressure gauge 18 comprises two branches having a length between 1.2 and 1.8 metres, and a cross-section having an external diameter between 18 and 22 mm. Advantageously, the differential U-shaped pressure gauge 18 comprises two branches having a length of around 1.5 meters, and a section having an outer diameter of around 20 millimeters.

[0043] As can be seen in figure 1, the filling of inert gas in the tank 16 is controlled by the differential pressure gauge 18 which is adapted to ensure a millibaric control of the overpressure inside the tank by measuring the level difference (indicated with reference numeral 19) of the inert liquid used.

[0044] For example, using distilled water as an inert fluid inside the differential pressure gauge 18, a difference in level equal to 1 cm between the levels of the pipes side by side equals an overpressure of the tank equal to p = 1 mbar in accordance with P = pw g h

wherein p_w represents the density of the distilled water (or other non-reactive liquid with different density) contained in the pressure gauge tubes and g the acceleration of gravity.

[0045] According to a possible embodiment of the present invention, not shown in the accompanying figures, the apparatus 12 may comprise a programmable control unit, adapted to detect the difference in level in the two branches of the differential pressure gauge 18.

[0046] According to a possible embodiment of the present invention, the tank 16 may comprise an input line 32 for the inert gas .

[0047] The input line 32 for the inert gas may comprise, in a per se known manner, a pressure gauge 34 and a valve 36.

[0048] According to a possible embodiment, the pressure gauge 34 may be, for example: a) a Bourdon pressure gauge or b) a piezoelectric pressure gauge.

[0049] According to a possible embodiment, the valve 36 may be, for example: a two-way valve or solenoid valve, or a globe valve or solenoid valve (for linear regulation) .

[0050] However, other types of valve may be used, which can be conceived by the man skilled in the art. [0051] In figure 2, the case in which the apparatus 12 is used in one of the tanks 16 containing the electrolyte for a stack of a flow battery is shown schematically.

[0052] The flow battery 38 comprises at least one discharge line 40 of the electrolyte in fluid communication with a tank 16, containing an electrolyte and a residual volume occupied by an inert gas, on which an apparatus 12 according to the present invention is arranged.

[0053] The flow battery may for example be of the type comprising at least one electrolytic cell, arranged with a first compartment and a second compartment, separated by an ion conductor, and each one arranged with a positive and negative electrode respectively. The compartments are in fluid connection through a duct with respective electrolyte tanks.

[0054] Advantageously, the battery may be an RFB battery.

[0055] Even more advantageously, the battery may be a vanadium flow redox battery. In this case, the electrolyte in the positive half-cell and therefore in a first tank 16 contains ions VC>2⁺ and V0²⁺, while that in the negative half-cell, and therefore in a second tank 16', contains ions V³⁺ and V²⁺.

[0056] Figure 3 schematically shows a flow battery in which both tanks 16, 16' are arranged with a safety apparatus 12, 12’. [0057] In particular, the battery comprises a first tank 16 containing a first electrolyte, for example the positive electrolyte, and a second tank 16' containing a second electrolyte, for example the negative electrolyte.

[0058] The safety apparatuses 12, 12' comprise a U-shaped differential pressure gauge 18, 18' adapted to be used with a non-reactive liquid, having a first end 20, 20' and a second end 22, 22' .

[0059] The first end 20, 20' is in fluid connection with an environment having a known pressure, and the second end 22, 22' is in fluid connection with the tank 16, 16', and with an output line 24, 24' for the inert gas contained inside the tank 16, 16' .

[0060] The other features of the apparatus 12, 12' are those discussed above.

[0061] The flow battery comprises two pumps 42, 42' for conveying the electrolyte through a supply duct 44, 44' to the respective electrodes of the stack cells.

[0062] Furthermore, temperature sensors 46, 48; 46', 48' adapted to measure the temperature of the electrolyte leaving or entering the electrolyte cell may be provided.

[0063] According to a possible embodiment, the apparatus may comprise a secondary device 50 at the input of the stack .

[0064] The secondary device 50 may comprise an overpressure valve 52 on the input line 54 of the stack, which in case of overpressure is suitable for putting in fluid communication the input line of the stack with the tank 16.

[0065] According to a possible embodiment, the overpressure valve 52 may comprise a shaped piston 56, and an elastic element 58 (for example a spring) adapted to push the shaped piston 56 towards the stack inlet. The secondary device comprises an outlet duct 60, in fluid communication with the tank 16.

[0066] If the pressure on the input line 54 should increase, the shaped piston is adapted to move in opposition to the resistance of the elastic element 58, putting the input line 54 in fluid communication with the outlet duct 60. According to a possible embodiment, the secondary device 50 comprises a drain valve 62 adapted to put the input line 54 of the stack in fluid communication with the outlet duct 58 and therefore with the tank 16.

[0067] According to a possible embodiment, the secondary device may comprise a mixing duct 64 and a mixing valve, adapted to put the two electrolytes in fluid communication, acting simultaneously on the secondary device 50 of both sides of the stack.

[0068] The advantages that can be achieved with a safety apparatus 12 according to the present invention are now apparent .

[0069] The apparatus allows creating an overpressure with millibaric control in tight containers for high reactivity solutions, using inert gases.

[0070] Secondly, the device allows preventing the entry of atmospheric oxygen which could pollute the solution contained in the tank.

[0071] The apparatus can be easily used in any application where there is a tank whose residual volume must be filled with nitrogen or other inert gas through an inert gas input line, with the aim of preventing contamination of the liquid solution contained by the aggression of atmospheric air and therefore by oxygen.

[0072] In fact, the filling of inert gas is controlled by a differential pressure gauge which ensures a millibaric control of the overpressure inside the tank by measuring the difference in level of liquid (for example distilled water) contained therein. In fact, a difference h = 1 cm between the two levels equals an overpressure of the tank equal to p = 1 mbar.

[0073] Furthermore, the device allows protection of the electrolyte or process fluid from atmospheric oxygen

[0074] Furthermore, the apparatus allows the calibrated flow of inert gas to remove any reaction gas that may develop and their collection for subsequent analysis. [0075] In fact, it also allows expelling and sampling any secondary gases formed in the tank, such as hydrogen.

[0076] In addition, the apparatus also acts as an overpressure valve: if the pressure inside the tank increases, the inert gas expels the distilled water contained in the pipes through the drainage line of the tank, preventing overpressure which can lead to the breakage of the tank.

[0077] The present invention allows managing the electrolytic solutions in the tanks avoiding contamination with oxygen, measuring small overpressures, avoiding excessive overpressures and allowing the sampling of the evolving gas.

[0078] A further advantage of the present invention is the possibility of replacing the electrolyte contained inside the cell with the nitrogen present inside the tank in order to empty the cell from the electrolytic solution while preserving the electrodes and membranes from the oxygen contained in the air, in case of long periods of non-use of the battery.

[0079] In addition, if one wants to empty the stack, the drain valve will open which puts the inlet of the stack in communication with the tank (this function is carried out simultaneously in the positive and negative circuits, since the apparatus may comprise a secondary device for each side of the stack) . If there are valves in the output section of the stack, they must be open to allow the electrolyte to escape. At the same time, the outflow valve will be opened to allow the flow of nitrogen (contained in the tank) which replaces the electrolyte in the stack. This prevents the electrolyte from remaining in the stack for long periods in resting conditions. It should be noted that filling the stack with nitrogen prevents the entry of atmospheric oxygen, which could occur with the electrolyte-filled stack in case of leaks of the latter, resulting in oxidation of some internal components .

[0080] Furthermore, there is the possibility of mixing between the two electrolytes which will take place by opening the mixing valve (this function is carried out simultaneously in the positive and negative circuits) .

[0081] Furthermore, the secondary device prevents the pressure difference between the two sides of the stack from reaching dangerous values for the integrity of the membranes and for the sealing of the gaskets. This occurrence can occur following various events: accidental obstructions of the pipe section downstream of the stack, obstruction in the hydraulic pipes inside the stack, incorrect closure of a valve of an outlet pipe. If the difference between the pressure (upstream of the stack) with respect to the tank exceeds a safety value, the overpressure valve made by means of the shaped piston keyed for example on a calibrated spring may slide on a guide (for example in Teflon) which guarantees the hydraulic seal. In case of overpressure, the valve will allow direct communication between the stack feed tube and the tank, discharging the overpressure.

[0082] A man skilled in the art may make modifications and/or replacements of elements described with equivalent elements to the embodiments described above in order to meet specific needs, without departing from the scope of the appended claims.

Claims

1. Safety apparatus (12; 12') for millibaric pressure control in inert atmosphere for high reactivity liquid solutions (14; 14') contained inside a tank (16; 16'), comprising:

a U-shaped differential pressure gauge (18; 18') adapted to be used with a non-reactive liquid, having a first end (20; 20') and a second end (22; 22') wherein: said first end (20; 20 ') is in fluid connection with an environment having a known pressure; and

said second end (22; 22') is in fluid connection with said tank (16; 16'), and with an output line (24; 24') for said inert gas contained inside said tank (16; 16') .

2. Safety apparatus (12; 12') according to claim 1, characterized in that said non-reactive liquid is distilled water.

3. Safety apparatus (12; 12') according to any one of the preceding claims, characterized in that said first end (20, 20') is in fluid connection with an atmospheric pressure environment.

4. Safety apparatus (12; 12') according to any one of the preceding claims, characterized in that said second end (22; 22') is connected by a first duct (26; 26') to the tank (16; 16'), on said first duct (26; 26' ) there being present a node (28; 28') from which said output line (24; 24') departs.

5. Safety apparatus (12; 12') according to any one of the preceding claims, characterised in that on said output line (24; 24') at least one valve (30; 30') adapted to block a gas flow is provided.

6. Safety apparatus (12; 12') according to any one of the preceding claims, characterised in that said differential U-shaped pressure gauge (18; 18') comprises two branches having a length between 1.2 and 1.8 metres, and a cross-section having an external diameter between 18 and 22 mm.

7. Tank (16; 16') adapted to contain a liquid solution and a residual volume of inert gas characterized in that it comprises a safety apparatus according to any one of the claims 1-6.

8. Tank (16; 16') according to claim 7, characterized in that it comprises an input line (32; 32') .

9. Tank (16; 16') according to claim 8, characterized in that said input line (32; 32') for the inert gas comprises a pressure gauge (34; 34') and a valve (36; 36' ) .

10. Flow battery (38) comprising at least one electrolytic cell comprising a first compartment and a second compartment, separated by an ionic conductor, and each provided with a positive and negative electrode respectively, said compartments being in fluid connection with respective electrolyte tanks;

said flow battery being characterized in that at least one of said electrolyte tanks is provided with a safety apparatus (12; 12') for millibaric pressure control in inert atmosphere for high reactivity liquid solutions (14; 14') contained inside a tank (16; 16') according to any one of the claims 1 to 6.

11. Flow battery (38) according to the preceding claim, characterized in that said battery is of the vanadium flow type.

12. Flow battery (38) according to any one of claims 10- 11, characterized in that it comprises a secondary device (50) in input to a stack, said secondary device (50) comprising an overpressure valve (52) on an input line (54) to the stack, said overpressure valve being adapted to put the input line (54) in fluid communication with the tank (16, 16') .

13. Flow battery (38) according to the preceding claim, characterized in that said overpressure valve (52) comprises a shaped piston (56), and an elastic element (58) adapted to push the shaped piston (56) towards the inlet of the stack; said secondary device comprising an outlet duct (60) in fluid communication with the tank (16) .

14. Flow battery (38) according to any one of claims 12-

13, characterized in that the secondary device (50) comprises a drain valve (62) adapted to put the input line (54) of the stack in fluid communication with the outlet duct (58) and thus with the tank (16) .

15. Flow battery (38) according to any one of claims 12-

14, characterized in that the secondary device (50) comprises a mixing duct (64) and a mixing valve, suitable for putting the two electrolytes in fluid communication, acting simultaneously on the secondary device (50) of both sides of the stack.