A device for maintaining a desired liquid level between interconnected tanks

Abstract

The device for maintaining the liquid level of complementary electrolytes in the flow battery tank has a first and a second interconnected tank 2, 3. The first tank 2 contains the positive electrolyte 2b and the second tank contains the negative electrolyte 3b. The two tanks have a space 2a and 3a respectively for storing air or other inert gas. The tanks themselves are connected by the following pipes: a lower tank connecting pipe 4, an upper tank connecting pipe 5 and an intermediate pipe connecting pipe 6. The apex of the lower tank connecting pipe 4a is designed to remain below the normal liquid level 7 of the two tanks, while the upper tank connecting pipe 5 remains above the desired liquid level 7.

Description

Technical Field

[0001] The present invention relates to an apparatus for maintaining a desired fluid level between a pair of tanks, particularly but not limited to the level of electrolyte in electrolyte tanks used in vanadium redox flow batteries. Background Art

[0002] A vanadium redox cell typically consists of a pair of tanks, one filled with a positive electrolyte and the other filled with a negative electrolyte. Between the tanks is a stack into which the electrolyte in each tank is pumped. A partially permeable membrane separates the two electrolytes in the stack. In the process of transferring charge through the cell, most of the current is in the form of a net transfer of hydrogen ions across the membrane. Water, vanadium ions, sulfate and bisulfate ions may also cross the membrane. This net diffusion causes the electrolyte level in one tank to rise and the electrolyte level in the other tank to fall.

[0003] This problem is known, and there are existing methods to address it. For example, it is common practice to pump excess electrolyte from a relatively full electrolyte tank into another relatively empty electrolyte tank. This is an active means of addressing the problem, and there are other more passive means, including:

[0004] 1. Use a connecting pipe between the electrolyte tanks and set a valve between the electrolyte tanks. The valve is opened regularly under the control of the battery management system.

[0005] 2. Use of overflow pipes connecting electrolyte tanks - although this necessarily requires a level difference between the electrolyte tank levels to work (and can be understood to work with the electrolyte volumes not balanced within a given range). This is also disclosed as a vanadium redox flow battery with "anti-siphon balance pipes in the tanks to allow any solution exceeding the fill limit of one tank to flow back to its original place in the adjacent tank".

[0006] 3. Use a single open tube to maintain fluid communication between the electrolyte in the positive and negative tanks. This tube keeps the two tanks at essentially the same liquid level, which is simple and inexpensive.

[0007] The first method listed above is not a truly passive method because it requires a sensor to determine the appropriate time to open the valve.

[0008] The second case usually requires a capacity loss because there is an inherent imbalance in the liquid level. This is caused by the uncertainty in the amount of electrolyte pumped into the tank and the amount initially displaced by air in the stack.

[0009] Among the methods discussed above, the third method is the most preferred because it is a truly passive method and maintains the volume of the fluid almost exactly. However, there are two major disadvantages:

[0010] If one of the tanks ruptures, it will draw electrolyte from the other tank through the connecting pipe until the level is below the connecting pipe, increasing the volume to be spilled and the heat generated by the mixing of the electrolytes, and

[0011] Tubes are susceptible to air locking, particularly during initial filling and during operation when dissolved gases are released. Summary of the invention

[0012] It is an object of the present invention to provide an improved arrangement for maintaining a desired liquid level between interconnected tanks.

[0013] According to the present invention, there is a device for maintaining the liquid level of complementary electrolytes in a pair of flow battery cells, the device comprising:

[0014] The first slot, and

[0015] The second slot, wherein the first slot and the second slot are connected by:

[0016] The lower tank connecting pipe, and

[0017] Upper tank connecting pipe, wherein:

[0018] The lower tank connecting pipe and the upper tank connecting pipe are connected through the inter-pipe connecting pipe.

[0019] In a preferred embodiment, one tank contains the positive electrolyte and the other electrolyte tank contains the negative electrolyte. A preferred embodiment of the present invention is intended for use in a vanadium redox flow battery, wherein the stack is located between two electrolyte tanks, with electrolyte from each tank being pumped to the stack. It is envisaged that the above arrangement may be used in any situation where a desired fill level is maintained between two tanks connected to each other.

[0020] In a preferred embodiment, the lower tank connection pipe is connected to the first and second tanks below the normal / desired liquid level of each tank, thereby allowing continuous communication between them. It is envisaged that the inlet / outlet of the lower tank / connection pipe may extend into the body of the tank.

[0021] Typically, the lower trough connecting tube is curved so that it has a high point between the first and second troughs. The curve may be gradual, or more pronounced, as contemplated. In one variation, the lower trough connecting tube may be generally "W" shaped, with the saddle of the "W" extending even further upward to ensure a high point relative to the tube opening. Alternatively, the lower trough connecting tube may be straight.

[0022] In one embodiment of the present invention, the lower tank connecting tube is a thin tube. The lower tank connecting tube is adapted to minimize the volume of electrolyte that is relatively stagnant due to being located in the lower tank connecting tube.

[0023] In another embodiment of the invention, the lower tank connecting tube is adjusted to have sufficient volume so that it can accommodate approximately the entire volume of electrolyte moved between tanks during one half cycle of charge or discharge. The lower tank connecting tube may have a constant pore size, or the pore size may be variable.

[0024] In a preferred embodiment, the lower tank connecting pipe is adapted to prevent rapid mixing of the electrolyte, for example by providing it with a length:diameter ratio.

[0025] Typically, the upper tank connecting pipe connects to the first and second tanks above the normal liquid level. Although the upper and lower pipes may have the same diameter, it is preferred to have the upper tank connecting pipe have a larger diameter. It is envisaged that the aperture range is 10mm-80mm, preferably 25mm. However, the aperture required for the redox battery depends on the capacity of the redox battery it is to be used in.

[0026] In a preferred embodiment, the relatively larger diameter of the upper tank connecting pipe is adapted to allow it to act as an overflow pipe in the event that the lower tank connecting pipe becomes blocked, for example, by sediment.

[0027] The inter-tube connecting pipe is usually connected to the upper and lower tank connecting pipes at the same time. This is preferably achieved by connecting the inter-tube connecting pipe to the lower pipe at the highest part of the lower pipe.

[0028] Preferably, the lower tube, the upper tube and the tube-to-tube connection tube are substantially in the same plane, ie substantially perpendicular to the ground. Alternatively, the tubes may not be aligned with each other as long as the tube-to-tube connection tube is generally positioned so that there is an inclination between the lower and upper tubes.

[0029] In a preferred embodiment, the upper tank connecting tube is generally flat, although it may be curved. The same is true for the overflow tube, for example, when the present invention is used as part of a vanadium redox flow battery, the upper tank connecting tube allows the movement of an argon or nitrogen blanket between the two tanks.

[0030] The disclosed prior arrangement means that it is no longer necessary to precisely control the process of filling the tank. This means that different filling levels in the tank can be adjusted by a single system arranged according to the invention.

[0031] In a preferred embodiment, the present invention is intended for use with vanadium redox flow batteries. It is contemplated that any process involving multiple cells where mass transfer between cells is an issue may utilize the invention disclosed herein. Typically, the liquid is an electrolyte. However, it is contemplated that any liquid may be used.

[0032] Refers to Normal Electrolyte Level. Normal Level is used interchangeably with Desired Fill Level. The same device can be set to function within the Normal Electrolyte Level range as long as other conditions are met. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] To aid understanding of the present invention, specific embodiments thereof will now be described by way of example with reference to the accompanying drawings, in which:

[0034] Figure 1 A cross-sectional view showing a vanadium redox flow battery according to the present invention and

[0035] Figure 2 Shows Figure 1 An arrangement in which one of the slots is pierced. DETAILED DESCRIPTION

[0036] refer to Figure 1 , a cross-sectional view of a pair of electrolyte tanks can be seen, which are equipped with a device according to a preferred embodiment of the present invention 1. There is a positive electrolyte tank 2 and a negative electrolyte tank 3. Each electrolyte tank has a portion filled with electrolyte 2b, 3b and a portion that is a gap 2a, 3a. The gap can be filled with argon or other inert gas to form a covering layer.

[0037] Connected to both the positive electrolyte tank 2 and the negative electrolyte tank 3 is a lower tank connection tube 4. The lower tank connection tube 4 has a high length: diameter ratio. In addition, the lower tank connection tube 4 is designed to ensure that it has a high point 4a. The entire lower tank connection tube 4 and its apex 4a are designed to be lower than the normal liquid level 7 of the two tanks.

[0038] In addition to the lower tank connecting pipe 4, there is also an upper tank connecting pipe 5. The diameter of the upper tank connecting pipe 5 may be greater than the diameter of the lower tank connecting pipe 4. Figure 1 It can be seen that the upper tank connecting pipe 5 is connected to the positive electrolyte tank 2 and the negative electrolyte tank 3 at a level higher than the normal electrolyte level 7. The upper tank connecting pipe 5 can act as an overflow pipe when the lower tank connecting pipe 4 is blocked.

[0039] In addition to the lower tank connecting tube 4 and the upper tank connecting tube 5, there is also an inter-tube connecting tube 6. The inter-tube connecting tube 6 connects the lower tank connecting tube 4 to the upper tank connecting tube 5. The connection is usually made between the apex 4a of the first tube 4 and the body of the second tube 5, which is located approximately in the middle of the upper and lower tubes 5, 4. The inter-tube connecting tube is connected to the high point 4a of the first tube 4, which allows gas to escape through the inter-tube connecting tube 6 to enter the upper tube 5 and then enter the air gap 2a, 3a. The connecting tube 6 is generally vertical, although it may be in other directions in other embodiments.

[0040] In a variation of the present invention, the lower tank connecting tube 4 and / or the upper tank connecting tube 5 may extend to one or both of the positive electrolyte tank 2 and the negative electrolyte tank 3 .

[0041] Figure 1The arrangement shown is such that if either the positive electrolyte tank 2 or the negative electrolyte tank 3 is punctured, the gas from the second tube 5 can move through the connecting tube 6 into the first tube 4. Moving the gas in this way prevents severe siphoning from occurring. Figure 2 shown.

[0042] Figure 2 and Figure 1 The difference is that the tank 3 has a perforation 8. There are a positive electrolyte tank 2 and a negative electrolyte tank 3. The electrolyte tanks 2 and 3 are connected by a first tube 4 and a second tube 5. The first tube 4 has an apex 4a. A connecting tube 6 connects the first tube 4 and the second tube 5.

[0043] The dotted line 7 indicates the normal filling level of the tank. Due to the perforation 8 in the electrolyte tank 3, the electrolyte leaks from the tank. The liquid level in the tank 3 drops until the filling area 3b of the tank 3 is below the perforation 8. The inter-tube connection 6 allows the air gaps 2a, 3a from the two tanks to enter the lower tank connection 4 and fill the gaps. This prevents the formation of siphons, thereby reducing the total volume of overflow. The tank should only be emptied to the liquid level 9a, which corresponds to the apex 4a of the lower part of the lower tank connection 4. If there were no inter-tube connection 6, a siphon would be generated in the lower tank connection 4 and the electrolyte tank 2 would continue to drain downwards to the boundary line 9b.

[0044] In a variant of the invention, the lower tube and / or the upper tube may extend into the electrolyte tank. If any tank having a first tube 4 extending into the body of the tank is pierced, the electrolyte level of the unpierced tank will be lower because the siphon effect will last longer.

[0045] The lower tank connection pipe 4 is usually curved with a high point 4a. The greater the difference between the lower pipe opening in the tank and the apex 4a, the less the influence of the siphon on the emptying of the tank.

[0046] The invention is not intended to be restricted to the details of the foregoing embodiments.

Claims

1. A device for maintaining the level of complementary electrolytes in a pair of flow electrolyte tanks, the device comprising: The first slot, and The second slot, wherein the first slot and the second slot are connected by: a lower tank connector configured to provide continuous fluid communication between the first tank and the second tank, and Upper tank connecting pipe, wherein the lower tank connecting pipe and the upper tank connecting pipe are connected by an inter-tube connecting pipe, wherein the inter-tube connecting pipe is configured to allow gas to escape from the lower tank connecting pipe into the upper tank connecting pipe via the inter-tube connecting pipe; wherein the lower tank connecting pipe is curved so that it has a high point between the first tank and the second tank, The inter-tube connecting pipe is connected to the lower tank connecting pipe at the high point of the lower tank connecting pipe.

2. The apparatus for maintaining the liquid levels of complementary electrolytes in a pair of liquid flow electrolyte tanks according to claim 1, wherein: One of the first tank and the second tank contains positive electrode electrolyte, the other tank contains negative electrode electrolyte, and the battery stack is located between the two tanks.

3. An apparatus for maintaining liquid levels of complementary electrolytes in a pair of flowing electrolyte tanks according to claim 1 or 2, wherein a lower tank connecting pipe is connected to the first tank and the second tank at a point below the desired liquid level of each tank.

4. The device for maintaining the liquid levels of complementary electrolytes in a pair of liquid flow electrolyte tanks according to claim 1 or 2, wherein: The lower tank connecting pipe is W-shaped.

5. The device for maintaining the liquid levels of complementary electrolytes in a pair of liquid flow electrolyte tanks according to claim 1 or 2, wherein: The lower tank connecting tube has a bore diameter of 10 mm to 80 mm to minimize the volume of electrolyte that is relatively stagnant due to being located in the lower tank connecting tube.

6. The device for maintaining the liquid levels of complementary electrolytes in a pair of liquid flow electrolyte tanks according to claim 1 or 2, wherein: The lower tank connecting pipe is adapted to have sufficient volume so that it can accommodate the entire volume of electrolyte moved between the tanks during one charging or discharging half-cycle.

7. The device for maintaining the liquid levels of complementary electrolytes in a pair of liquid flow electrolyte tanks according to claim 1 or 2, wherein: The lower tank connecting pipe has a constant or variable bore diameter.

8. The device for maintaining the liquid levels of complementary electrolytes in a pair of liquid flow electrolyte tanks according to claim 1 or 2, wherein: The upper tank connecting pipe is connected to the first tank and the second tank at a position above a desired liquid level.

9. The device for maintaining the liquid levels of complementary electrolytes in a pair of liquid flow electrolyte tanks according to claim 1 or 2, wherein: The diameter of the upper tank connecting pipe is greater than the diameter of the lower tank connecting pipe.

10. The device for maintaining the liquid levels of complementary electrolytes in a pair of liquid flow electrolyte tanks according to claim 1 or 2, wherein: The upper tank connecting pipe is adapted to act as an overflow pipe when the lower tank connecting pipe is blocked.

11. The device for maintaining the liquid levels of complementary electrolytes in a pair of liquid flow electrolyte tanks according to claim 1 or 2, wherein: The lower tank connecting pipe, the upper tank connecting pipe and the inter-tube connecting pipe are on the same plane.

12. The device for maintaining the liquid levels of complementary electrolytes in a pair of liquid flow electrolyte tanks according to claim 1 or 2, wherein: The upper tank connecting pipe allows the gas blanket to move between the first tank and the second tank.

13. The device for maintaining the liquid levels of complementary electrolytes in a pair of liquid flow electrolyte tanks according to claim 1 or 2, wherein: The device is used as part of a vanadium redox flow battery.

14. A vanadium redox flow battery having a pair of flowing electrolyte tanks and comprising means for maintaining the levels of complementary electrolytes in the pair of flowing electrolyte tanks according to any one of claims 1 to 13.

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