CONSTANT PRESSURE GAS STORAGE IN CONTAINMENTS WITH MITIGATION FOR GAS DISSOLUTION PROBLEMS

Abstract

Disclosed herein is a system for storing gas at almost constant pressure, which involves the injection and withdrawal of a liquid in a process known as hydraulic compensation. This disclosure teaches a way to minimize that dissolution by ensuring that, as the gas containment is charged up, the hydraulic compensation liquid emerges from the containment at the gas storage pressure and the pressure of that liquid is caused to fall in a number of discrete steps with settling volumes present at the nodes between these steps. These settling volumes enable some gas to come out of solution at each node having lost relatively small amounts of pressure. The gas is compressed back up to storage pressure and re-injected into the main storage containment without significant use of energy.

Claims

1. A system for storing a gas at a constant raised pressure, the system comprising: a main gas containment containing the gas at the constant raised pressure and a portion of a hydraulic compensation liquid; an external storage volume at a lower pressure than the constant raised pressure, containing a second portion of the hydraulic compensation liquid; a series of two or more settling volumes, each of the two or more settling volumes containing some gas and a further portion of the hydraulic compensation liquid and being at a different discrete intermediate pressure between the constant raised pressure and the lower pressure of the external storage volume; wherein each of the two or more settling volumes, after a first, highest pressure settling volume, has a lower pressure than an immediately preceding settling volume in the series; two or more gas connections, the two or more gas connections comprising: a first gas connection between an upper portion of the main gas containment and an upper portion of the highest pressure settling volume; and one or more second gas connections, comprising a gas connection between an upper portion of each of the two or more settling volumes, after the first, highest pressure settling volume, and the immediately preceding settling volume in the series; and three or more liquid connections, the three or more liquid connections comprising: a first liquid connection between a lower portion of the main gas containment and a lower portion of the highest pressure settling volume; one or more second liquid connections, comprising a liquid connection between lower portions of each of the two or more settling volumes, after the first, highest pressure settling volume, and the immediately preceding settling volume in the series; and a third liquid connection between a lower portion of a last, lowest pressure settling volume and a lower portion of the external storage volume.

2. The system for storing a gas at a constant raised pressure according to claim 1, further comprising: two or more compressors each associated with one of the two or more gas connections and being configured to transfer gas from the lower pressure side to the higher pressure side of the associated gas connection; and three or more pumps each associated with one of the three or more liquid connections and being configured to drive liquid from the lower pressure side to the higher pressure side of the associated liquid connection.

3. The system for storing a gas at a constant raised pressure according to claim 2, wherein one or more of the three or more pumps are positive displacement pumps configured such that when hydraulic compensation liquid is flowing from the main gas containment towards the external storage volume the positive displacement pumps recover work from the liquid.

4. The system for storing a gas at a constant raised pressure according to claim 2, wherein one or more of the two or more gas connections comprises an associated valve operable to prevent return of gas from the higher pressure side to the lower pressure side of the associated gas connection.

5. The system for storing gas at constant raised pressure according to claim 1, wherein the liquid comprises water.

6. The system for storing gas at constant raised pressure according to claim 5, wherein the liquid consists of water.

7. The system for storing gas at constant raised pressure according to claim 1, wherein the main gas containment is underwater in an open body of water that acts as the external storage volume of liquid.

8. The system for storing gas at constant raised pressure according to claim 1, wherein the gas being stored at constant raised pressure is air.

9. A system for storing a gas at constant raised pressure, the system comprising: a main gas containment configured to receive gas from a pressurized gas manifold and to return gas to the pressurized gas manifold, and containing a hydraulic compensation liquid; a first pump/motor through which the hydraulic compensation liquid can enter and leave the main gas containment, wherein the hydraulic compensation liquid is in communication with a first settling volume on the other side of the pump/motor from the main gas containment; a first gas compressor configured to drive gas from the first settling volume back into the pressurized gas manifold; a second settling volume, wherein the first settling volume is in communication with the second settling volume via a second pump/motor through which the hydraulic compensation liquid can pass between the first and second settling volumes; a second gas compressor configured to drive gas from the second settling volume back into the first settling volume; a third settling volume, wherein the second settling volume is in communication with the third settling volume via a third pump/motor through which the hydraulic compensation liquid can pass between the second and third settling volumes; a third gas compressor configured to drive gas from the third settling volume back into the second settling volume; and an external storage volume, wherein the third settling volume is in communication with the external storage volume via a baseline pump/motor through which the hydraulic compensation liquid can pass between the third settling volume and the external storage volume; wherein the main gas containment is at a higher pressure than the first settling volume, the first settling volume is at a higher pressure than the second settling volume, the second settling volume is at a higher pressure than the third settling volume, and the third settling volume is at a higher pressure than the external storage volume.

10. The system for storing gas at constant raised pressure according to claim 9, wherein the first, second, third, and baseline pump/motors are configured to extract power from the hydraulic compensation liquid as it flows away from the main gas containment when the main gas containment is receiving gas from the pressurized gas manifold.

11. The system for storing gas at constant raised pressure according to claim 9, wherein the first, second, third, and baseline pump/motors are configured to extract power from the hydraulic compensation liquid as it flows away from the main gas containment when the main gas containment is receiving gas from the pressurized gas manifold.

12. The system for storing gas at constant raised pressure according to claim 9, further comprising non-return valves configured to prevent gas flow from higher pressure origins into the first, second, and third settling volumes.

13. The system for storing gas at constant raised pressure according to claim 9, wherein a bottom of the first settling volume is above a bottom of the main gas containment, a bottom of the second settling volume is above the bottom of the first settling volume, a bottom of the third settling volume is above the bottom of the second settling volume, and a bottom of the external storage volume is above the bottom of the third settling volume, wherein the hydraulic compensation liquid must pass first rise and then fall as it passes through each of the first, second, and third settling volumes.

14. The system for storing gas at constant raised pressure according to claim 9, wherein the main gas containment is underwater in a body of water and the body of water is the external storage volume.

15. The system for storing gas at constant raised pressure according to claim 13, wherein the hydraulic compensation liquid is water.

16. The system for storing gas at constant raised pressure according to claim 9, wherein the main gas containment comprises a set of discrete storage volumes.

17. A system for storing a gas at constant raised pressure, the system comprising: a main gas containment configured to receive gas from a pressurized gas manifold and to return gas to the pressurized gas manifold, and containing a hydraulic compensation liquid, wherein the hydraulic compensation liquid is in communication with a first settling volume; a first gas compressor configured to drive gas from the first settling volume back into the pressurized gas manifold; a second settling volume, wherein the first settling volume is in communication with the second settling volume such that the hydraulic compensation liquid can pass between the first and second settling volumes; a second gas compressor configured to drive gas from the second settling volume back into the first settling volume; a third settling volume, wherein the second settling volume is in communication with the third settling volume such that the hydraulic compensation liquid can pass between the second and third settling volumes; a third gas compressor configured to drive gas from the third settling volume back into the second settling volume; and an external storage volume, wherein the third settling volume is in communication with the external storage volume such that the hydraulic compensation liquid can pass between the third settling volume and the external storage volume; wherein the main gas containment is at a higher pressure than the first settling volume, the first settling volume is at a higher pressure than the second settling volume, the second settling volume is at a higher pressure than the third settling volume, and the third settling volume is at a higher pressure than the external storage volume; wherein a bottom of the first settling volume is above a bottom of the main gas containment, a bottom of the second settling volume is above the bottom of the first settling volume, a bottom of the third settling volume is above the bottom of the second settling volume, and a bottom of the external storage volume is above the bottom of the third settling volume, wherein the hydraulic compensation liquid must pass first rise and then fall as it passes through each of the first, second, and third settling volumes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG. 1 illustrates three settling volumes for the hydraulic compensation liquid between the main gas storage containment and the external storage volume for the liquid, according to at least one embodiment of the disclosure.

[0039] FIG. 2 shows an implementation where a significant source of pressure in the hydraulic compensation liquid arises due to manostatic (hydrostatic) pressure head, according to at least one embodiment of the disclosure.

[0040] FIG. 3 shows an implementation for underwater storage of compressed air, according to at least one embodiment of the disclosure where there is a significant source of pressure in the hydraulic compensation liquid due to manostatic (hydrostatic) pressure head. There may be no specific external storage volume for the hydraulic compensation liquid in this realisation as the entire body of surrounding water may play that role.

DETAILED DESCRIPTION

[0041] A first embodiment of the invention is disclosed here through FIG. 1. A main gas containment (10) receives gas from a pressurised gas manifold (20) and can return gas to that manifold. The lowest part of the containment (10) is filled with hydraulic compensation liquid (30). This liquid (30) can enter/leave the containment (10) only by passing though a first reversible positive-displacement pump/motor (31). On the other side of this first reversible positive-displacement pump/motor (31), the fluid is in communication with a first settling volume (32). Associated with this first settling volume (32) is a first small gas compressor (33) capable of driving gas at the first intermediate pressure back into the pressurised gas manifold (20).

[0042] The first settling volume (32) is in communication with a second settling volume (35) via a second reversible positive-displacement pump/motor (34). The only way that hydraulic compensation liquid can pass between the first and second settling volumes ((32) and (35)) is via that second reversible positive-displacement pump/motor (34). Associated with the second settling volume (35) is a second small gas compressor (36) capable of driving gas at the second intermediate pressure back into the top of the first settling volume (32).

[0043] The second settling volume (35) is in communication with a third settling volume (38) via a third reversible positive-displacement pump/motor (37). The only way that hydraulic compensation liquid can pass between the second and third settling volumes ((35) and (38)) is via that third reversible positive-displacement pump/motor (37). Associated with the third settling volume (38) is a third small gas compressor (39) capable of driving gas at the third intermediate pressure back into the top of the second settling volume (35).

[0044] The third settling volume (38) is in communication with an external storage volume (40) for holding hydraulic compensation liquid via a baseline reversible positive-displacement pump/motor (50). The only way that hydraulic compensation liquid can pass between the third settling volume (38) and the external storage volume (40) is via that baseline reversible positive-displacement pump/motor (50).

[0045] During the process of charging the main gas containment (10), gas enters this containment via the pressurised gas manifold (20) and the hydraulic compensation liquid (30) leaves the containment in order to ensure that the pressure remains constant. The hydraulic compensation liquid passes through the first reversible pump/motor unit (31) and power is extracted from the flowing liquid as the pressure drops. The liquid then enters the first settling volume (32) and some gas escapes from the liquid and floats into the upper part of that settling volume. If the liquid level in that storage volume falls below a certain pre-determined level, gas compressor (33) acts to draw gas out of that storage volume and drive it back into the pressurised gas manifold (20).

[0046] The hydraulic compensation liquid then passes through the second reversible pump/motor unit (34) and more power is extracted from the flowing liquid as the pressure drops further. The liquid then enters the second settling volume (35) and some more gas escapes from the liquid and floats into the upper part of that settling volume. If the liquid level in that storage volume falls below a certain pre-determined level, gas compressor (36) acts to draw gas out of that storage volume and drive it back into the first settling volume (32).

[0047] The hydraulic compensation liquid then passes through the third reversible pump/motor unit (36) and still more power is extracted from the flowing liquid as the pressure drops still further. The liquid then enters the third settling volume (38) and some more gas escapes from the liquid and floats into the upper part of that settling volume. If the liquid level in that storage volume falls below a certain pre-determined level, gas compressor (39) acts to draw gas out of that storage volume and drive it back into the second settling volume (35).

[0048] Finally, hydraulic compensation liquid then passes through the baseline reversible pump/motor (50) surrendering the last of the available power in that liquid before entering the external storage volume (40). It is worth noting that some gas would then escape at ambient pressure.

[0049] The process of discharging the main pressurised gas containment is almost exactly the reverse of the process of charging with one key difference. In the charging process, gas continuously released from the hydraulic compensation liquid as it falls in pressure and most of that gas is compressed back up to the storage pressure and fed back into the main gas manifold (20). During discharging, the compressors ((33), (36) and (39)) do not act in reverse as expanders and neither does any gas flow back into the settling volumes from higher-pressure origins. In fact, these compressors could be fitted with non-return valves to prevent such flows. Each one of the settling volumes gradually becomes emptied of the gas present in it until there is no further gas present in the settling volume.

[0050] A second embodiment of the invention is disclosed through the use of FIG. 2.

[0051] Conceptually, this is identical to the first embodiment except that the mechanism by which pressure increases or decreases occur in the hydraulic compensation liquid is via hydrostatic head rather than via pumping (to increase pressure) or the operation of a hydraulic motor (to decrease pressure). Importantly, the settling volumes ((32), (35) and (38)) are located at local maxima of elevation so that the hydraulic compensation liquid must first rise and then fall as it passes through each one of the settling volumes. This provides the essential opportunity for dissolved gas to escape and to accumulate at these points.

[0052] A third embodiment of the invention is disclosed using FIG. 3. Conceptually, this is minor further development over the second embodiment. In this embodiment, the main gas containment (1) is held deep underwater. This has major advantages in that the external hydrostatic pressure of the water obviates the requirement for large amounts of structural material in the gas containment. In this case, the external storage volume for the hydraulic compensation liquid is normally the entire body of water surrounding the containment.

[0053] To implement the present invention in the context of deep underwater storage of gas, it is only necessary to observe that the path taken by the hydraulic compensation liquid should involve it passing back up to the surface of the water so that the pressure in that liquid falls back to ambient pressure. In nearly all practical cases, the hydraulic compensation liquid would be the same water as the water surrounding the gas containment but it does not have to be. When there is a difference, the actual hydraulic compensation liquid can itself be held in a flexible containment either floating atop the main body of water (if it is lighter than the local water) or at the bed of the water body (if it is heavier than the local water).

[0054] The invention has been explained in the above embodiments using three intermediate settling volumes ((32), (35) and (38)) but it will be obvious that fewer or more of these could be used and the principles of the invention are the same irrespective of whether the number is as low as 1 or as high as 10 or more. In most practical implementations

[0055] The main gas containment (10) has been illustrated in FIGS. 1, 2 and 3 as a single containment volume but it is clear that this can be implemented as a set of discrete storage volumes.

[0056] In FIGS. 2 and 3, reversible pump/motor units have been shown in the connection between the main gas containment and the first settling volume (32), in the connections between the settling volumes ((32)-(35) and (35)-(38)) and in the connection between the final settling volume (38) and the external storage volume (40). Obviously, some or all of the pressure differences required in these different connections can be achieved from hydrostatic head and this is especially relevant in contexts such as embodiment #3 where the main gas containment is deep underwater.

[0057] In the descriptions of the three embodiments above, no settling volume has the same pressure as atmospheric pressure. In cases where the gas itself has a value and/or where it has the potential to do environmental harm, some implementations might include a baseline settling volume at atmospheric pressure so that gas that was still dissolved in the hydraulic compensation liquid prior to that liquid passing through the baseline reversible pump/motor unit (50) in the direction of reducing pressure could be captured.

[0058] The text in the above description has implied that all gas emerging from the hydraulic compensation liquid as it becomes de-pressurised in stages should be compressed back using small standalone compressors such that it all ends back up in the main gas containment. There is a distinct option here that potentially avoids the requirement for some of the standalone gas compressors. That separate option is that the main gas compression train will itself have points in it at intermediate pressures between full gas storage pressure and ambient. In some cases, it might be convenient to feed the gas emerged from dissolution back into points in the main compression cycle. This potentially saves some significant capital costs.