ENERGY CAPTURE

CROSS-REFERENCE TO RELATED APPLICATIONS

10001] The instant nonprovisionai patent application claims priority to U.S. Provisional Patent Application No. 61 /6Ί 2 J 96 tiled March 16, 201.2 and incorporated by reference in its entirety herein for all purposes. The instant nonprovisional patent application also claims priority to U.S. Provisional Patent Application No. 61/623,491 filed April 12, 2012 and incorporated by reference in its entirety herein for all purposes.

BACKGROUND

| ^' O002] Compressed air s capable of storing energy at densities comparable to lead-acid batteries. Moreover, compressed gas does not. involve issues associated with a battery such as limited lifetime, materials availability, or environmental friendliness.. Thus, there is a need in th art for apparatuses and raethods allowin the storage of energy in in the form of compressed gas, and the recovery of energy by the expansion of that compressed gas.

SUMMARY

[0003] Various techniques may be employed alone or in combination to allow efficient storage and recovery of energy from compressed gas. in certain embodiments, a hydraulic motor may capture energy released by depressuri ation of a separated heat-exchange liquid that was pressurized during gas compression. Particular embodiments may be employed in conjunction with a heat engine. According to some embodiments, a compressed gas storage unit may include a gas-liquid interface between a liquid portion and a gas portion, with a hydraulic pump/motor capturing energy of liquid displaced by an inflow of compressed gas.

BRIEF DESCRIPTION OF THE DRAWINGS

|0O04J Figure I is a simplified schematic view illustrating one embodiment of a compressed gas energy storage system.

(0005] Figure 2 is a simplified schematic view illustrating an embodiment of a compressed gas energy storage system. [00061 Figure 3 is a simplified, schematic view illustrating an embodiment of a compressed gas energy storage system.

[0007j Figure 4 is a simplified schematic view illustrating an embodiment of a compressed gas energy storage system.

(0008] Figure 5 A. is a simplified schematic view illustrating a multi-stage embodiment of a compressed gas energy storage system in compression mode.

[0009} Figure 5B is a simplified schematic view illustrating a .mul ti-stage embodiment of a. compressed gas energy storage:. system in expansion mode.

[0010} Figure 6 is a simplified schematic view illustrating an embodiment of a compressed gas energy storage system.

[0011} Figure 7 is a simplified schematic view illustrating an embodiment of a heat engine.

[0012} Figure 8 shows a simplified vie w of an embodiment of an energy handling system employing foam.

10013] Figures 9A-D show simplified cross-sectional views of a cylinder in an energy delivery mode.

[0014J Figure 9E is a highly simplified plot of gas pressure versus crank angle for an expansion stroke.

[001.5] Figure 10 plots piston position versos crank angle,

[00161 Figure 1 .1 shows one possible configuration of a cam driven piston according to an embodiment.

[0017} Figure 12 shows embodiments of a multistage near-isothermal compressor/expander which can be used for energy storage.

[0018] Figure .12 A shows a .multistage near-isothermal compressor/expander featuring interstage heat exchangers.

[0019 j Figures 13A-D show a pumping scheme according to an embodiment.

[0020} Figure 14 shows an embodiment of a mechanism varying the flow rate of a cam operated hydraulic pump.

(00211 Figures 1 SA-E show various embodiments of multi-stage compressed, gas energy storage systems constructed from only one or two types of cylinders. DESCRIPTION

f 0022 J U.S. Patent Publication No. 2011/0115223 ("the '223 Publication") describing an energy storage and recovery system employing compressed gas as an energy storage medium, is incorporated by reference in its entirety herein for all purposes. Certain apparatuses and methods described i the '223 Publication may employ a reversible mechanism comprising a member moveable within a chamber to compress gas and in turn recover energy from expanding gas. |0023j The '223 Publication describes a number of gas compression and expansion techniques, some of which occur in the presence of a liquid in order to achieve heat transfer across a gas- liquid interface. As employed herein, the term "wet" refers to a gas compression and/or expansion process which takes place in the presence of liquid tor heat exchange.

|0024| Figure 1 is a schematic view of a compressed gas energy storage system 100 illustrating the relationship between a reversible compressor/expander apparatus 102 and various other system elements. In particular, the reversible compressor/expander apparatus 102 comprises walls 104 enclosing a chamber 105 in which a moveable .member 106 is received.

|0025] Flows of fluid into and out of the chamber 105 occur through valves 120 and 122. In particular, in a compression, mode gas is drawn into the chamber through, valve 120 from inlet 124. Gas compressed by the moveable member is then flowed to compressed gas storage unit 130 through valve 122 and. first gas-liquid separator 132.

jO026J In an expansion mode of operation, compressed gas flows into the chamber through valve 122 from the compressed gas storage unit 130. Gas that has expanded within the chambe to drive the moveable member, is then flowed out. of the chamber through valve 120 and second gas-liquid separator 134.

[ ^' 0027] In the particular embodiment illustrated in Figure 1, the moveable member comprises a piston configured to reciprocate within the chamber. However; this is not required, and according to alternative embodiments the moveable member could be configured to experience other forms of motion, including hut not limited to rotation (e.g. a turbine).

[0028] The particular embodiment illustrated in Figure 1 also shows the use of a mechanical linkage 108 comprising a rotating shaft for transfer of power into the chamber to drive the moveable member in gas compression mode, for transfer of power out of the chamber by the moveable member driven in gas expansion mode. However this is also not required and in various embodiments other forms of linkages could be employed, including but not limited to hydraulic linkages, pneumatic linkages, magnetic linkages, and electromagnetic linkages. [0029] Moreover while the particular embodiment illustrated in Figure 1 shows the use of a mechanical linkage in the form of a piston rod and a crankshaft, this is also not required.

Alternative embodiments could employ other forms of mechanical linkages, including but not limited, to chains, belts, driver-follower linkages, pivot linkages, Peaucellier-Lipkin linkages. Sarins linkages, Scott Russel linkages, Chebysliev linkages, Hoekins linkages, swashpJate or wobble plate linkages, bent axis linkages. Watts linkages, track follower linkages, and earn linkages. Cam linkages may employ cams of different shapes, including but not limited to sinusoidal and other shapes. Various types of mechanical linkages are described in Jones in "Ingenious Mechanisms for Designers and Inventors, Vols. I and IF, The Industrial Press (New York 1 35), which is hereby incorporated by reference in its entirety herein for all purposes. (0030] As discussed extensively in the '223 Publication, for efficiency of energy storage and recovery, thermodynamic considerations may favor gas compression and expansion taking place within a narrow temperature range. This can be accomplished by introducing a liquid for heat exchange with ga undergoing compression or expansion. Moreover, such gas-liquid heat exchange can be promoted where a large surface area of a gas-liquid interface is present.

|0031] Accordingly, Figure I shows introduction of a mist of liquid droplets into chamber 105 through pump 140 and sprayer 142, In the compression mode of operation for energy storage, liquid from cold liquid storage unit 154 is flowed by the pump through, multi-way valve 170 for heat exchange with gas being compressed within the chamber. In the expansion mode of operation, liquid from the hot liquid storage unit 15.2 is pumped through multi-way valve 170 for heat exchange with gas expanding within the chamber.

|O032] Following heat exchange, the gas liquid mixture within the chamber is flowed through a separator to recover the introduced liquid for reuse. Accordingly in the expansion mode of operation, an expanded gas-liquid mixture at reduced pressure is flowed through the second gas- liquid separator 134. Tire cooled liquid separated therefrom is then flowed to the cold liquid storage 154.

|O033] The arrow on the separators in the Figure 1 indicate the direction of flow when a gas/liquid mixture is being introduced for separation. During other modes of operation, gas may flow in a direction opposite to the arrow, but little or no separation occurs."

1 _. 0034] In the compression mode of operation, a compressed gas-liquid mixture at elevated pressure i flowed, through the first gas-liquid separator 132. The warm liquid separated therefrom is then flowed to the hot liquid storage 152, [0035] la the energy storage (gas compression) and recovery (gas expansion) scheme just described, the energy consumed in elevating the pressure of the liquid introduced tor heat exchange with the compressed gas, can represent a loss to the system. Accordingly, certain embodiments may seek to recover that energy through the expansion of the pressurized liquid o ce it has been separated.

[0036] Thus, Figure 1 shows the positioning of a hydraulic motor 160 between the first gas liquid separator and the hot liquid storage. Upon separation, the compressed liquid i allowed to flow through the hydraulic motor. This drives the hydraulic motor, whose energy can be harnessed to improve the overall efficiency of the system.

[ ^' 0037] For example, a hydraulic motor may be in communication with the linkage (e.g. a mechanical linkage such as a crankshaft) that drives or is driven by the piston. In this manner, any work extracted by the hydraulic motor can reduce work required to drive the system as a compressor, or add to the work generated by the system operating as an expander. Alternatively, the hydraulic motor may be connected to an electric generator to recover energy in the form of electricity.

[0038] Alternatively or in. combination with placing the hydraulic motor in communication with the linkage,, in certain embodiments energy from, the hydraulic motor driven by expansion of the compressed liquid, can be used to drive a pump that flows liquid into the chamber for heat exchange with gas being compressed therein.

[0039] In this particular embodiment, it is noted that liquid separated by separator 1.34 in expansion mode is at ambient pressure. Accordingly, no energy can be recovered by utilizing a hydraulic motor.

f!M O] Where expansio is performed in multiple stages, however, the pressurized liquid may still be above ambient pressure in intermediate stages. Hence, some amount of energy may remain for recovery. Such an approach is described, in detail below in connection with Figure 5B. |0O41 J Returning to Figure L it is noted that an exchange of thermal energy can further enhance the efficiency of the system. For example, in the compression mode of operation, removal of thermal energy via a heat sink at locations A and/or B may reduce the temperature change experienced, by the gas being compressed, thereby improving efficiency. Additionally, cooling the gas at location A increases the density of the gas, and thus increases the energy density of storage tank 130. Conversely, in the expansion mode of operation, application of thermal energy fro a heat source to locations A and/or B may enhance the amount of energy avaiiabie to be output by the system-. Such exchanges of thermal energy with heat sinks/sources may be accomplished through the use of heat exchanger structures.

[0042] Figure 2 shows another embodiment in which energy from a storage system utilizing compressed gas as a storage medium, may be recovered by a hydraulic motor. Specifically, in this embodiment of a energy storage system 200, the compressed gas storage unit 202 comprises a -gas portion 202a and a liquid portion 202b, with a gas-liquid interface 20.1 present therebetween.

|0O43] The particular embodiment of Figure 2 shows the gas portion and the liquid portion as being in contact along a ree gas-liquid interface. However this is not required, and alternative embodiments could provide moveab!e partition between the gas and liquid portions,

|0O44| The gas portio is in fluid ^' communication with the compression expansion chamber 203 as previously described in connection with the embodiment of Figure 1. The liquid portion is in fluid communication with a liquid reservoir 204 through a hydraulic motor/pump 206. 'O045] In particular,, the selective introduction and withdra wal of liquid to the liquid portion can stabilize the pressure within the gas portion, allowing the compressed gas storage unit to intake and output gas within a narrow pressure range, simplifying operation.. Moreover the energy resulting from .movement of liquid out of the storage unit, can be captured by the hydraulic motor/pump.

1 046 j For example, in operation in th gas expansion mode, compressed gas flows from the gas portion of the compressed gas storage unit. In order to maintain pressure within the gas portion of the compressed gas storage unit, the hydraulic motor/pump is operated as a pump, flowing liquid from the liquid reservoir into the liquid portion.

[ ^' 0047 j In operation in the gas compression mode, however, compressed gas flows into the compressed gas storage unit, This in turn causes the gas pressure within the gas portion to rise, displacing the liquid from the liquid portion. The displaced liquid moves through the hydraulic motor/pump acting as a motor, reducing the gas pressure and returning it to a nominal value. The energ output by the hydraulic motor/pump can be harnessed for other purposes {for example to drive the liquid pump fo the sprayer 209 and/or to dri e a linkage to a moveable member).

|008| The basic approaches illustrated in the embodiments of Figures 1 and 2 can be combined in a multitude of ways. These are now il lustrated in connection with Figures 3-5B.

[0049] Specifically, Figure 3 is a simplified view showing an embodiment of an energy storage and recovery system 300 thai includes two hydraulic motors for energy capture. Hydraulic motor 302 is configured to be driven by depressitrizafion of liquid separated from a compressed gas-liquid mixture as described above in connection with Figure 1 , Hydraulic motor/pump 304 is configured to be driven as a motor by liquid displaced by pressurizatio.il of a liquid -portion of the compressed gas storage unit in response to storage of compressed gas, as described above in connection with. Figure 2. Energy output by one or both of these hydraulic motors can be harnessed to perform useful work.

[0050} Figure 4 is a simplified view showing yet another embodiment of an energy storage and recovery' system 400 that includes two hydraulic motors for energy capture. This embodiment is similar to that of Figure 3, except that a single cold liquid storage 402 functions to receive liquid separated on expansion by gas-liquid separator 404, and to act as a reservoir for liquid from the liquid portion 406 of the compressed gas storage unit 408.

[0051 { ^' The particular embodiments depicted and described so far, have employed gas compression and expansion in a single stage. As described in detail in the '223 Publication, however., compression and/or expansion could occur over multiple stages. The approaches just described are also applicable embodiments where compression and/or expansio occur over multiple stages.

[0652} For example. Figures 5A-B show an embodiment of a multi-stage energy storage and recovery system 500. This system is similar to the embodiment of Figure 4, except that it comprises three stages employed in both the compression and expansion of gas.

f 0053 j In particular, the low pressure stage 502 comprises two separate chambers 504a and 504b, each having a member (here pistons 570) moveable therein to compress gas or be driven by expanding gas. An intermediate stage 506 comprises a single chamber 508 having a moveable member (again a piston 572) disposed therein. A .final, high pressure stage 510 comprising single chamber 51 1 lies between the intermediate stage and a compressed gas storage unit 512, and also includes a piston 574 moveable therein.

10054} figure 5 A shows operation of the system 500 operating in compression mode. In this mode of operation, pressurized liquid is separated from gas-liquid mixtures received by gas- liquid separators 520, 22, and 524 located on the high pressure sides of the first stage 502, second stage 506, and third stage 51 , respectively.

[0055} Hydraulic motors 530., 532, and 534 are in turn configured to be dri en by

depresstmzation of the pressurized, separated liquid, which is flo wed to hot liquid storage 540, Useful work can be performed by these driven hydraulic motors, including but not limited to operation of one of the liquid pumps 542 used to flow liquid from the cold liquid storage 344 for heat exchange with die gas being compressed.

|0O56 j f igure 5 A also shows the liquid portion 12a of the compressed gas storage unit 512 as being in fluid communication with the cold liquid reservoir 544. As compressed gas enters the storage unit 512, liquid is displaced and drives the .hydraulic purap motor 546. Useful work can be performed by this driven hydraulic pump/motor; including but not limited to operatio of liquid pumps 542 used to flow liquid from the coid liquid storage 544 -for heat ^' exchange with the gas being compressed. It is further noted, that the pressure of the displaced liquid flowing from the storage unit into the cold liquid reservoir, may also serve to reduce the amount of energy consumed by the pumps in the compression mode.

f0057{ In general, hydraulic motors 530, 53.2, 34, and/or 546 may be linked to the crankshaft, that drives or is driven by pistons 570a, 570b, 572, 574. in this manner, any work extracted by the hydraulic motors reduces work required to drive the system 500 as a compressor, or adds to the work generated by the system operating as an expander.

|0058] Figure 5B shows operation of the system 500 operating in expansion mode. In this mode of operation, liquid is separated from gas-liquid mixtures received by gas-liquid separators 522, 520, and 526 located on the lo w pressure sides of the third stage 510, second stage 506, and first stage 502, respectively.

|0059| It is noted that the gas-liquid mixture received by the gas-liquid separator 526 has typically fully expanded, and hence liquid separated therefrom may not exhibit appreciable pressure. Accordingly, that separated liquid is returned to the cold liquid storage without being passed through a hydraulic motor.

[0060] However, the gas-liquid mixtures received by the gas-liquid separators 522 and .520 typicall will not have expanded fully. Accordingly, the liquid separated therefrom may exhibit sufficient pressure to warrant the recovery of energy therefrom. Thus the separated liquid is flowed to the cold liquid storage vi hydraulic motors 532 and 530, respectively.

10061] Again, useful work can be performed by these driven hydraulic motors. In some embodiments, work from the driven hydraulic motors can be used to operate one of the liquid pumps 542 flowing liquid from the hot liquid, storage 540 for heat exchange with the expanding gas. In particular embodiments, work from the driven hydraulic motors may be used to drive a linkage in communication with the moveable member. In certain embodiments, work from the driven hydraulic motors can be used to drive the flow of liquid back into the liquid portion of the compressed gas storage unit to stabilize gas pressure therein, as is now discussed. [0062] Specifically, as compressed gas leaves the storage unit 512 the hydraulic pump/motor 546 is driven to flow liquid from the cok! liquid storage unit back into the liquid portion of the compressed gas storage unit This flowed liquid can stabilize the pressure of the remaining gas in the gas portion 512 b of the storage unit.

f§063] It is further noted that the apparatus 500 of Figures 5A~B includes a liquid circuit driven by pump 580 that is configured to deliver thermal energy to the point A in the system. In compression, cool liquid is delivered to point A by pump 580 for heat exchange. I» expansion, heated liquid is delivered to point. B by pump 580 for heat exchange. This pump 580 represents yet another possible recipient of energy from driven hydraulic motors. Although not explicitly shown, one or more of the other embodiments discussed herein could similarly be configured to also include such a liquid circuit for delivering thermal energy of the appropriate type to point A.

[0064} W hi le the above description has focused upon apparatuses comprising a reversible compressor/expander, this is not required. Alternative embodiments could employ separate structures dedicated to compression or expansion, and which may be in selective mechanical communication with each other through a common linkage - for example a rotating shaft 605 of Figure 6 below.

[0065} Specifically, Figure 6 shows an alternative embodiment of an energy storage and recovery system 600 comprising dedicated, compressor 601 in fluid communication with compressed gas storage unit 608 comprising a liquid portion 606. Compressed gas storage unit 608 is in turn in. fluid communication with dedicated expander 650.

f 0066} Gas-liquid separator 604 is located between the dedicated compressor and the compressed gas storage unit. Depressurization of liquid separated from separator 604 and flowed to hot liquid storage 603, could be harnessed by the hydraulic motor 654 in order to perform useful work. Example of such useful work include driving one of the liquid pumps 656 for spraying liquid, or driving the hydraulic pump/motor 65S to selectively flow liquid into the liquid portion of the compressed gas storage unit so as to mai ntain gas pressure therein.

[0067] While the above description has focused upon apparatuses employing a gas storage unit, mis is not required. Alternative embodiments could take the form of a heat engine lacking an gas storage capability, wherein gas that has been compressed is thereupo expanded to perform useful work . Such an embodiment of a heat engine 700 is shown in Figure 7, wherein prior to compression in chamber 7 1 , gas is flowed through counter-flow heat exchanger 702, There, it is thermally exposed to compressed gas that is flowing for expansion within chamber 750, Application of heat and cooling to respective nodes A and B can drive this process such that useful work is performed by shaft 705,

[0068] As with the previous embodiments, pressurized liquid separated by ^' gas-liquid separator 710 from a compressed gas-liquid mixture received from compressor 701, may be flowed to hydraulic motor 740. Dep.ressurizat.ion. of liquid in the hydraulic motor 740 can be harnessed to perform useful work, for example driving the liquid pumps 742.

[0069} Figure 7 shows an embodiment of a heat engine employing a closed loop for gas flow, allowing gas to be maintained above ambient even at low pressure. Such a closed loop configuration may increase the power density of such an apparatus. However this is not required and alternative embodiments of a heat engine apparatus could receive inlet gas at ambient pressure for compression, and then output gas expanded to substantiall ambient pressure.

[0070} According to still further alternative embodiments, a heat engine function. may be combined with gas storage, for example where compressed gas may enter and leave the compressed gas storage unii via a counterflow heat exchanger. Such a compressed gas storage unit may include a liquid portion, that is in fluid communication with the cold liquid storage through, a hydraulic pump/motor.

[0071 } I . An apparatus comprising:

an element, moveable to compress gas within a chamber;

a sprayer configured to effect gas-liquid heat exchange with gas being compressed within the chamber;

a gas- liquid separator configured to separate a pressurized liquid from a compressed gas- liquid mixture received from the chamber; and

a hydraulic motor configured to be driven by depressmizaiion of the pressurized liquid.

[0072] 2, An apparatus as in claim i further comprising a linkage in communication wit the element, wherein the hydraulic motor is in physical communication with, the linkage.

[0073} 3. An apparatus as in claim 2 wherein the linkage comprises a rotating shaft.

|0074] 4. An apparatus as in claim 1 wherein the hydraulic motor is in physical

communication with a pump in liquid communication with the sprayer.

[0075] 5. An apparatus as in claim 1 wherein the chamber is in fluid communication with a next compression stage through the gas-liquid separator.

[0076} 6, An apparatus as in claim 1 wherein the chamber is in fluid communication with a counterflow heat exchanger through the gas-Hquid separator. 100771 7, An apparatus as in claim 1 wherein the chamber is in fluid communication with a compressed gas storage unit through the gas-liquid separator.

[0O78j 8. An apparatus as in claim 7 wherein the chamber is in fluid communi cation with a gas portion of the compressed gas storage unit, the compressed gas storage un it further comprising a liquid portion.

10079] 9. An apparatus as in claim 8 further comprising a gas-Hqiiid interface between the gas portion and the liquid portion.

[0080} 10. An apparatus a in claim 6 further comprising a hydraulic pump/motor configured to be dr ven by liquid flowed from the liquid portion.

[008.1] 1 1. An apparatus as in claim 10 wherein the hydraulic pump/motor is in physical communication with a pump in liquid communication with the sprayer.

[0082} 12. An apparatus, as in claim 8 further comprising a moveable partition between the liquid portion and the gas portion.

[0083] 13 A apparatus as in claim I wherein the element moveable within the chamber comprises a dedicated compressor.

[0084] 14. An apparatus as in claim 1 wherei the element moveable within the chamber comprises a reversible compressor/expander.

[0085] I S. An apparatus as m claim 14 further comprising:

a second gas-liquid separator configured to separate a second pressurized liquid from an expanded gas-liquid mixture received from the chamber; and

a second hydraulic motor configured to be dri ven by depressurization of the second pressurized liquid.

[0086] 16, An. apparatus comprising:

a compressed, gas storage unit comprising a gas portion in fluid communication with a chamber receiving an element moveable to compress gas, a liquid portion in liquid

communication wit a liquid reservoir through a hydraulic pump/motor, and a gas-liquid interface between the gas portion and the liquid portion,

[0087] 17. An apparatus as in claim 16 further comprising:

a gas-liquid separator configured to separate a pressurized liquid from a compressed gas- liquid mixture received from the chamber; and

a Iiydraulic motor configured to be driven by depressurization of the pressurized liquid.

[0088] 18, A apparatus as in claim 1.6 wherein the element moveable within the chamber comprises a dedicated compressor. |00S9| 19. An apparatus as n claim 16 wherein the element moveable within the chamber comprises a reversible compressor/expander.

[0890] The selec tive use of a hydraulic motor driven by expansion of pressurized liquid, can also serve to enhance the thermodynamic performance of the apparatus. Figure 12 shows embodiments of a multistage near-isothermal, compressor/expander which can he used for energy storage.

[0091 { in this architecture,, a liquid is introduced into the compression chambers in the form of spray droplets or bulk liquid. During compression, the high heat capacity of the liquid removes the heat of compression from the gas as it is being compressed.

f O092J Liquid droplets provide a large surface area, for rapid heat exchange with the gas. The gas will have a limited temperature rise doe to the presence of liquid.. Relatively low

temperature operation will make it economical to store hot liquid and pressurized gas.

[0893] The pressurized, gas can run in the reverse cycle through the expanders to generate power. Introducing liquid spray in the expansion process wil l prevent significant, temperature drop, and wil l therefore increase the power output of the process.

[0894] The particular configuration shown i the Figure 12 has three stages. However, the energy storage system may comprise any number of stages.

[0095] In the architecture of Figure 12, the gas and liquid from one stage are fed to the next stage without heat exchange. If the introduced liquid spray is at the same temperature as the intake gas, the discharge gas-liquid mixture will be at slightly higher temperature due to the heat of compression. Therefore, the heat of compression will accumulate ^' in the gas and in the liquid in all of the stages.

f!1096] The gas discharged from the last compressor stage will be at moderately high temperature. The discharged gas is cooled by the cold liquid source in a counter-flow heat exchanger before entering the storage tank.

[0097] The discharged liquid is at high temperature and high pressure. Part of the energy of the discharged liquid is reclaimed by passing it through a. hydraulic motor that lowers the liquid pressure to atmospheric.

f 0098 j The resultant hot liquid is stored in an insulated tank at atmospheric pressure, insulated low-pressure liquid reservoirs are less expensive than insulated high-pressure liquid reservoirs.

[0099] Since the gas temperature is lowered before entering the gas tank, the energy density of the storage gas tank can remain substantially the same as the case with interstage heat exchangers. I 0100] Embodiments conform ng to the general architecture- of Figure 12, may eliminate the need for interstage hydraulic pumps that otherwise lower the discharged liquid pressure to atmospheric. An example of a con figuration utilizing such interstage hydraulic pumps is shown in Figure 12 A.

1 ^' ΟΙ.ΘΙ] By contrast, according to the architecture of Figure 12, since the liquid discharged from one stage is at its high pressure, the liquid pump of the next stage will spend less power to pump liquid into the (next stage) compression chamber. This will decrease the losses, and will therefore increase the efficiency.

|0i62| An architecture as in Figure 12 may eliminate the need for interstage heat exchangers that otherwise operate at relatively lo temperature deltas. By contrast, the only heat exchanger in the architecture of Figure 12 will operate at moderately high temperature delta. Beat

exchangers are typically more effective and more efficient at high temperature deltas between the heat exchange media,

£0103.] The quality of the heat stored in the moderately high temperature liquid reservoir is higher than the case with interstage heat exchangers. This will result in higher thermal efficiency of the system.

[0104} The temperature of the hot liquid reservoir can be optimized to yield maximize efficiency at low cost. Liquid temperature may be high enough to yield high thermal efficiency, but wot too high to make the insulated liquid tank overly expensive.

£0105] i . An apparatus comprising;

a low pressure wet compression stage;

a ilrst gas liquid separator configured to separate a first heated pressurized liquid received from the low pressure wet compression stage;

a high pressure wet compression stage configured to receive the first heated pressurized liquid;

a second gas liquid separato configured to separate a second pressurized liquid received from the high pressure wet compression stage, the second pressurized liquid comprising accumulated heat transferred from the low pressure wet compression stage and from the high pressure wet compression stage; and

a heat exchanger configured to communicate the accumulated heat from the second pressurized liquid to a liquid flow for a wet expansion process,

[OI.06J 2. An apparatus as in claim 1. wherein the high pressure wet compression stage is reversible to perform the wet expansion process, [01071 3. An apparatus as in claim i wherein the heat exchanger comprises a counterflow heat exchanger.

|0108 j 4. An apparatus as in claim 1 wherein at least one of the first wet compression stage and the second wet compression stage are configured to undergo reciprocating motion.

[0109] 5. An. apparatus as in claim 4 wherein at least one of the first wet compression stage and the second wet compression stage comprise a piston n communication with a. crankshaft, fOl Oj 6. An apparatus as in claim ί wherein at least one of the first wet compression stage and the second wet compression stage are configured to undergo rotary motion.

|0J 111 7, An apparatus as in claim 6 wherein at least one of the first wet compression stage and the second wet compression stage comprise a turbine.

{0112] 8. An apparatus as in. claim J further comprising a thermally insulated liquid storage tank configured to receive the second pressurized liquid prior to exposure to the heat exchanger. |0113] 9, An apparatus as in claim 1 further comprising a hydraulic motor configured to recover energy from, depressurtzaiion of the second pressurized liquid.

1 114] Energy handling systems may store and recover energy utilizing a compressible liquid foam. In certain embodiments, energy is stored by compr essing the gas component, of the foam, with the foam's liquid component absorbing heat across an extensive gas-liquid interface to enhance a thermodynamic efficiency of compression. The compressed foam may be stored in a pressure vessel The stored energy may be released by allowing the foam, to expand and drive moveable member. Heat exchange between the gas and liquid components of the foam may serve to enhance a thermodynamic efficiency of the. gas phase during expansion,

f 0115] Compression and expansion of air under conditions of relatively small temperature change (e.g. substantiall isothermal), can result in substantial thermodynamic efficiencies. One way of achievi ng such condi tions is by way of beat exchange between the air and a liquid medium having a high heat capacity. One possible liquid medium is water.

101161 ^' U.S. Patent Publication No. 201 1/01 15223 is hereby incorporated by reference in its entirety for all purposes. The ^* 223 Publication describes in detail, methods and apparatuses that may be employed to perform the compression and/or expansion of a gas in conjunction with heat exchange with a liquid. It should be appreciated that embodiments discussed herein include one or more concepts discussed in the '223 Publication,

|0117] Liquid, foams comprise a mixture of a gas component in bubble form, separated by a hquid component as a membrane. Liquid foams can vary in bubble density, but in general exhibit an extremely large surface area between gas and liquid. 1 _. 0118] This large surface area between gas and liquid allows for high rates of heat exchange across the interface. And where the liquid exhibits a high heat capacity, a foam can serve as a useful medium tor the compression and expansion of gas under memiodynamically favorable conditions.

I ^' OJ.1.9] Figure 8 shows a simplified view of an embodiment of an. apparatus configured to utilize foam for energy handling. In particular, system 800 comprises a chamber 802 having a moveable member 804 present therein.

|0120] While Figure 8 shows a moveable member in the form of a reciprocating solid piston, a variet of di fferent types of moveable members could possibly be employed. Some types of moveable members may be configured to experience reciprocating motion within the chamber. Examples of such reciprocating members include but are not limited to solid pistons (including free pistons), liquid pistons, combinations of liquid and solid pistons, and flexible diaphragms. |0121 J Certain types of mo veable members may be configured to experience rotational motion within the chamber. Examples of such rotating members include but are not limited to turbines, quasi-totbines, rotors, gerotors, scrolls, vanes, lobes, screws, and gears.

|0122| The moveable member is in selective communication with a linkage 806. While Figure 8 shows a mechanical linkage in the form of piston rod, this is not required. The linkage may comprise one or several forms, including but not limited to linkages that are mechanical, hydraulic, pneumatic, electro-magnetic, or electrostatic in nature.

.0123] A wide variety of mechanical linkages may possibly be used. Exa mples include but are not limited to multi-node gearing systems such as planetary gear systems. Examples of mechanical linkages include shafts such as crankshafts, chains, belts, driver- follower linkages, pivot linkages, Peaucellier-Lipkin linkages. Sarins linkages, Scott ussel linkages, Chebyshev linkages, Hoekins linkages, swashplate or wobble plate linkages, bent axis linkages. Watts linkages, track follower linkages, and cam linkages. Cam. linkages may employ cams of different shapes, including but not limited to sinusoidal and other shapes. Various types of mechanical linkages are described in Jones in "Ingenious Mechanisms for Designers and Inventors, Vols. I and IF, The Industrial Press (New York 1 35), which is hereby incorporated by reference in its entirety herein for all purposes.

|0124| The linkage may be selectively driven by an energy source 808 to compress a fluid present within the chamber. Examples of such energy sources include but are not limited to turbines (e.g. steam, wind, combustion), motors (e.g. diesel), motor/generators, and others. [0125] The linkage may also be selectively driven by a fluid expanding within the chamber. This linkage may be configured to drive an electrical generator, which may be a motor/generator as shown. In certain embodiments, the generator may be shared with another device, for ex ample a generator of a turbine such as a wind, steam, or combustion turbine. Linkages such as .multi-node gearing systems (e.g. planetary gears) may be useful in this regard according to certain embodiments.

|0126| The chamber is configured to receive a compressible fluid in the form of a liquid foam 820. Many types of liquid foams are known. Some types of liquid foams are used for agricultural applications, for example marking of crop borders in fields,

j 0127] Other foams which may be suitable for energy handling are fire-fighting foams. One type of such loam is a protein foam . Protein foams are produced by the hydrolysis of grartulized keratin protein (protein hydrolysate) such as feathers and hoof and horn meal. Stabilizing additives and inhibitors may be included for purposes of corrosion prevention, viscosity control, and bacterial decomposition resistance.

|0128] Fluoroprotein foams (including film forming fhioroprotein foams) have fluorochemical surfactants in addition to other com ponents of protein foams. These surfactant .may increase foam viscosity and/or change other properties of the foam such as bubble density.

[01 9] Aqueous film forming foams used in i reflghting, may also be employed in energy handling according to various embodiments. Such aqueous film forming foams may be formed from a. combination of fluorochemical surfactants and synthetic foaming agents. The aqueous ^• film may be produced by the action of the fluorochemical surfactant reducing the surface tension of the foam solution to where the solution can be supported on the surface of a hydrocarbon.

[0130] Alcohol resistant aqueous film, forming foams are also used in ftrefighting. Sach foams may be produced from a combination of synthetic detergents, fluorocheniicals, and

polysaccharide polymer. The polysaccharide polymer component forms a membrane which prevents degradation of the foam by elements such as polar solvents,

10131] Synthetic detergent foams exhibiting mid- and high- expansion characteristics are also available. Such synthetic foams are a mixture of synthetic foaming agents and stabilizers. As used herein, high-expansion foams may exhibit an expansion ratio above 200: 1. Mid-expansion foams may exhibit an expansion ratio from about 20: 1 to 200; 3. Low expansion foams may exhibit an expansion ratio of up to about 20:1 ,

{01.32] Foams ma be created by the use of a fbamer S22 receiving a flow from a pump 823. Such foaming device may typically involve the introduction of materials in a concentrated form. (such as surfactants, detergents, foaming agents, etc.) into a flow of gas and liquid from respective sources 824, 826, followed by mixing,

10133} Examples of materials that may be introduced to a liquid to promote foam formation, include but are not limited to carrageenan, sodium lauryl ether sulfate, sodium lauryl sulfate, and ammonium lauryl sulfate.

|0134] Such introduction may be accomplished in passive manner (e.g. by venturi structures), actively by pumping, or by some combination of both approaches. Foams can be created from liquids and gases by techniques such as agitation or aeration.

f 0135] Once created, the foam may be flowed, into the chamber for compression.

Displacement of the moveable member within the chamber, reduces an available volume to hold the gas component of the foam. Heat resulting from the resulting gas compression is transferred across the ex tensi ve s urface area of the gas-liquid in terface, reducing a temperature change experienced by the gas where the liquid component exhibits a high heat capacity.

{ ^' 0136] Once the foam has been compressed., it may be fed upstream, for example to a next compression stage 807. Where the foam has been compressed to reach a desired pressure, the gas component of the foam may be flowed to a pressure vessel 809 for storage.

[0137} In certain embodiments, the compressed foam itsel f may be flo wed directly into the pressure vessel hi such embodiments, care can be taken, to maintai the foam in its compressed state, without excessive draining changing a basic nature of the foam while it is stored.

f 0l38| Under certain circumstances, maintaining the foam at elevated temperatures may serve to reduce foam draining. Thus according to some embodiments heat transferred from the gas component to the liquid component during compression, can be retained in the pressure vessel to aid in maintaining the foam in an undrained state. Heat from various sources (internal and or external) may also be harnessed for this purpose.

[0139] Thus in some embodiments, a temperature of the pressure vessel may be maintained at/near a desired temperature in order to reduce/avoid foam draining. Such temperature control could be accomplished by the use of insulating jackets and/or the circulatio of a temperature control liquid in thermal communication with walls of the vessel

[0140] Under certain circumstances, a bubble membrane exposed to an electric field has been observed to have a significantly longer lifetime. This may be attributable to having the electric field arranged to increase the membrane wall thickness. According to particular embodiments, thi effect may be employed to stabilize the structure of a foam that is used for energy storage of for other purposes. f OMl j Internal coatings of various ^' types within the pressure vessel could also be used to discourage draining of the compressed foam. Vibration and/or pulsation dampeiiers may foe employed between the pressure vessel and surrounding machinery in order to reduce the disruption or coalescence of bubbles present within the compressed foam.

I ^' OJ.42] According to certain embodiments, the compressed foam may be intentionally flowed through a defoaming device (shown as 830 in Figure 8) prior to the compressed gas component of the foam being stored in. the pressure vessel. Such deibammg accelerates the foam draining process, separating the foam into its liquid and gas components.

|0J 3} A variety of detbaming techniques are possible. Examples of such techniques include but are not limited to spraying the f am with liquid droplets, applying sonic energy, performing gravity separation, performing ^' centrifugal separation, and passing the foam through a physical mesh (straining).

|0144} The resulting storage of only the compressed gas component of the foam, can avoid issues arising from draining where foam is attempted to be stored over a period of time. This approach can also reduce the volume and hence cost of the pressure storage vessel, as the incompressible liquid component of the foam does not occupy space therein.

|0145} However, such an approach may involve re-foaming of the compressed gas in order to allow for heat exchange upon expansion. In particular the reco very of energy through gas expansion, may comprise the reverse process of compression.

[©146} Namely, compressed gas is flowed to an expander. Expansion of the compressed gas against a moveable member serves to drive a generator.

|0147{ In certain embodiments, the compressed gas is in the form of a gas component of a foam However, this is not required. In. certain embodiments the compressed gas is in the form of gas separated from a compres sed, foam (e.g. by the defoamer 830 of Figure 8 ), either prior to or following its storage.

10148} According to certain embodiments, gas expansion may take place in the same chamber as that, in which compression of foam has occ urred. Use of such a same reversible apparatus for foam expansion as for roam compression, may reduce a number of system elements and hence a cost of procuring and ma intaining those parts.

10149} Alternatively, expansion of the foam may take place in a separate chamber dedicated for that purpose. Use of such a dedicated expander may be particularly appropriate in embodiments where foam is being expanded concurrent with compression. One example is where a source of thermal energy is available on a continuous basis to power a heat engine configuration featuring foam expansion thai is ongoing with foam compression.

[OiSOj Following expansion, in certain embodiments the foam may he subjected to defoaming, with the gas and liquid components separated. Such a defoamer following expansion is shown as 832 in the particular embodiment of Figure 8.

[0151] Alternative embodiments could employ a closed system, wherein expanded foam is retained and recycled for use as input in a next compression cycle . Such closed approaches may avoid the cost of initial form formation and the consumption of precursors thereto. Examples of foam precursors can include but are not limited to particles, proteins, natural detergents, synthetic detergents, surfactants, wetting agents, foaming agents, and others,

f 0.152] Foams according to particular embodiments may employ various materials as the liquid and or gas components. Some typical foams may comprise bubbles of air within liquid water. However, other gases/gas mixtures can be used in various embodiments, including but not limited to non-flammable gases such as helium, nitrogen, and carbon dioxide. Other possible candidates for gases to be used include hydrocarbons such as pentane. propane, butane, isobutane, hydrogen, nitrous oxide, other noble gasses such as argon, refrigeration, compounds such as CFCs, and/or mixtures thereof.

|0153] And while the above discussion has focused upon the use of aqueous foams comprising water, this is not required. According to alternative embodiments, liquids other than water can be used. Examples of other liquid candidates include but. are not limited to oils or other organic liquids.

|0I54] As noted above, the transfer of heat between liquid and gas components of the foam may serve to enhance the thermodynamic efficiency of compression and/or expansion processes. Efficiency of energy handling may als be enhanced through the exercise of careful control over the timing of the valving responsible for the intake and/or exhaust of gas or foam, during compression and expansion cycles. Such control over valve timing is discussed in detail in the '223 Publication, as well as in U.S. Patent Application No. 13/552,580 filed, on July 18, 201.2 and incorporated by reference in its entirety herein for all purposes.

[0155] As discussed extensively in the "223. Publication, under certain modes of operation, energy stored in th e form of compressed gas may be recovered through expansion under controlled conditions, to drive a moveable member, in certain embodiments, the moveable member may comprise a piston that is driven by gas expanding within a cylinder to undergo reciprocating motion. 10156] As further described in the '223 Publication as well as herein, liquid may be introduced during this energy delivery mode (or expansio mode, or discharge mode) in orde to exchange heat with the expanding gas. Figures 9A-D show simplified cross-sectional views of a cylinder in this energy delivery mode,

l ^' OJ.57] in particular, Figure 9A shows the position of the piston 900 near To Dead Center (TDC) of the cylinder 902 at the beginning of the expansion stroke. At this time, the valve 904 between the cylinder head and the high pressure side, is opened to allow the flow of compressed gas into the cylinder,

|0158] Figure 9B shows the piston 900 moving in a downward direction toward the Bottom Dead Center (BDC) position, driven by the expanding gas. At this time, the valve 904 is still open to continue to admit compressed gas into the cylinder.

[015.9} Figure C shows the piston 900 moving further downward toward BDC position. At this time, the valve 904 is closed, halting the flow of compressed gas such that a volume V is admitted into the cylinder. Continued expansio of this existing volume of compressed gas continues to drive the piston downward,

[0.160} Figure 9D shows the end of the expansion stroke, with piston 900 at the BDC position. Depending upo the particular conditions and operational parameters, at this point the gas volume V may or may not have fully expanded, to a particular pressure (e.g.. near ^' ambient pressure for a final expansion stage, or near an expected intake pressure for an intermediate expansion stage).

[0.161] The expansion stroke shown in Figures A-D, is followed by an exhaust stroke, Therein, the valve between the cylinder and the low pressure side is opened, so that expanded gas is flo wed from the cylinder as the reciprocating piston begins its upward journey toward TDC and to the next expansion stroke.

[0162] Figure 9E is a highly simplified plot of gas pressure versus crank angle for the expansion cycle from TDC (crank angle ~ 0°) to BDC (crank angle =.180°). This figure shows thai the bulk of expansion of the gas, and hence the balk of any temperature change to be affected by heat transfer, occurs abruptl during the early stages of the expansion stroke. Thus, it may be difficult to achieve the water-to-air mass ratios desirable for the amount of heat exchange useful for high efficiency operation, over this short, time frame.

[0163] Figure 9A-D also show that the intake high pressure valve 904 is open for a relatively short period of time, during which high pressure air is admitted into the cylinder. This narrow windo for opening/closing the valve may pose challenges to its design, and in particular to actively controlling the valve to admit only selected volumes of compressed gas for expansion. 101641 Accordingly, in some embodiments it may be desirable to use a piston motion profile that spends more time near TDC. Such piston motion profile can increase the amount of water sprayed during the intake process. More ver, it may enhance the mixing of the sprayed droplets with air, and hence the effectiveness of the heat exchange between air and sprayed droplets.

[0165j in addition, a piston motion profile that spends more time at TDC may also relax the brief timing window in which the high press ure side valve is called upon to operate. It can also decrease pumping loss and reverse valve flow.

( ^' 0166] Figure 10 plots piston position versus crank angle. Figure 10 shows that according to various embodiments, the piston motion profile can be configured to be symmetric or asymmetric with respect to I DC.

|0167) According to certain embodiments, one approach to achieving a desired piston motion profile may be through the use of a cam driven piston. One possible configuration 1100 of a cam driven piston is shown in Figure 11.

[0168] In this configuration, two cams 1.1.01 and 1 102 rotate on the same shaft 1 103 along axis A. The follower 1 104 has two rollers 1106, 1. 108 fixed on the follower, that touch the surface of their corresponding cams 1102 and 1 101. One of the cams 1101 provi des the force to push the piston towards the TDC, and the other cam 3 1 2 provides the force towards BDC.

f 0169J Other cam-drive piston configurations are possible. In one alternative configuration, two cams may run on two different shafts and/or one follower roller, with or without springs. |017O1 Embodiments employing cam-driven piston mechanisms may reduce a size of the flywheel. Certain embodiments may eliminate a cross-head assembly, and load reversal and lubrication demands.

[0171] Anothe approach to generating a customized piston motion profile, may be to use a mii i-crosshead/multi-connecting-rod mechanical linkage between crank and piston rod. In such a configuration, the crank shaft rotates at near-constant speed, hut there are multiple linkages between the crankpin and the piston.

[0172] The erossheads may be guided on curves, rather than straight lines. In such an embodiment, the overall motion will be such thai the piston residence time at TDC is more than its time at BDC.

(0173) 1. An apparatus comprising: a cylinder receiving a reciprocating piston configured to be driven from a TDC position to a BDC position by expanding gas admitted to the cylinder from a high pressure side through a valve; and

a mechanical linkage configured to enhance residence time of the piston at the TDC position.

[0174] 2, An apparatus as in claim 1 wherein the mechanical linkage comprises a. cam and a cam follower.

|0!75] 3. An apparatus a in claim 2 wherein the cam follower comprises a roller.

[0176] 4, An apparatus as in claim 2 wherein the cam comprises a first cam responsible for moving the piston to TDC, and the mechanical linkage further comprises a second cam responsible for moving the piston to BDC.

[0177} 5. An apparatus as in claim 1 wherein the mechanical linkage comprises a crank.

10178} 6. An apparatus as in claim 5 wherein the mechanical linkage comprises a crosshead,

[0179] 7 An. apparatus as in claim. 6 wherein the crosshead is guided on. a curve.

[0180] 8. An apparatus as in claim 1. wherein the mechanical linkage is configured to enhance the residence time at the TDC position in a symmetrical manner.

[0181 } 9. An apparatus as in. claim 1 wherein the mechanical, linkage is configured to enhance the residence time at the TDC position in. an asymmetrical manner,

10182] The use of cams imparting variable timing operation is not limited to a reciprocating moveable member. According to other embodiments, a pump component that, is responsible for the introduction of liquid for heat exchange, may also be operated with variable timing utilizing a cam or other structure.

[0183] Cam operated hydraulic pi lingers can generate a profiled pulse of liquid flow as shown in the Figure- 13 A. The cam poshes a moving membrane to displace liquid in a chamber through a one-way discharge valve. The cam then pulls the moving membrane to intake replenishing liquid from a one-way intake valve. There will be no liquid pumping during suction stroke.

[0184] A combination of multiple cam operated hydraulic plungers can be used to generate any liquid pumping profile as shown in the Figure ! 3B, Such an approach allows pumping to occur at all times,

[0185} Efficient operation of an energy storage system may call for a pumping profile that maximizes thermal efficiency of the cycle, while minimizing the parasitic loss of spray. Such an efficient pumping profile can be generated using multiple cam operated hydraulic plungers, with profiles and timing of the individual cams being different from one another. f 01S6] The approach of Figure 13B calls for the hydraulic plungers to be connected together on the discharge end Also, the spray nozzles installed on the compression chamber may be connected together, nd fed by the discharge Ike of the plungers. This is shown in the Figures i 3C-D, respectively.

I ^' OJ.87] Although in the arrangement shown in. Figures 13C-D ail of the plungers feed all of the nozzles, other arrangements are possible. Multiple plungers can feed a subset of nozzles in the chamber.

f0188] Embodiments as shown in Figures 13 B-D ma reduce or eliminate pulsation of liquid into the chamber, A pulsed, liquid accelerates to maximum flow velocity, and then decelerates back to zero velocity.

f0189| By contrast, in the approach shown i the embodiments of Figures 13B~D, liquid accelerates/decelerates from, one velocity to a slightly ^' higher/lower velocity. Therefore, proper timing of the spray pump can be achieved at lower acceleration limits, thereby reducing the probability of cavitation.

$0190] Another issue that may arise in connection with pulsed liquid approaches, is that the discharge Sines are pressurized and then depressurized in each cycle of the plunger motion. Since liquids are slightly compressible, the volume of the liquid in the discharge line acts as a compressible spring that, reduces the volumetric efficiency of the pomp,

f 01.91] Flexibility of the pipes may also reduce volumetric efficiency of the pump. Frequent pressure cycles in the liquid and in the pipe may also generate heat, which reduces mechanical efficienc of the pump.

|0192] The pump profile proposed according to embodiments, may significantly reduce these loss channels. This is because it significantly reduces the -amplitude of the pressure cycles. 1 _. 0193] Another problem thai may arise with a pulsed liquid approach, is that when the plunger is in suction stroke or is stationary, air from the compressio chamber may enter the liquid line and flow backwards towards the liquid pump. This will reduce volumetric efficiency of the pump, and will add to the dead volume of the compression chamber. Again, such issues may be avoided by embodiments as shown in Figures 13B-D,

|0194] i . An apparatus comprising;

a plurality of cam operated hydraulic plungers connected together on a discharge Sine, with profiles and timing of the individual cams being different from one another; and

a plurality of spray nozzles installed in a gas compression chamber and connected together and fed by the discharge line. | 0I9S| 2, The apparatus as in claim i wherein all of the plurality of cam operated hydraulic plungers feed all of the spray nozzles,

[0196] 3. The apparatus as in claim .1 wherein multiple cam operated hydraulic plungers feed a subset of the spray nozzles.

I ^' OJ.97] Exercise of precise control over a multistage compressed air energy storage system according to embodiments, can be challenging owing to complexity and the number of components. For example, there may be no direct way of controlling the pressure ratios in each stage during operation,

[0198] Rather, the pressure ratios are settled to conserve the mass flow throughout the system, and also to maintain the top pressure of the storage tank. Typically, when the mass flow in one stage is reduced, the pressure ratio in other stages increases (and the volumetric efficiency drops) to match the reduced mass flow rate.

|0199] As is now described herein, however, one approach to controlling system performance .may ^' be to increase or decrease the dead volume in each stage. According to certain

embodiments, such control over dead volume may be implemented by increasing or decreasing the piston-cylinder head clearance.

[0200} Another technique for changing the dead volume, may be to add a small volume with a movable membrane. This membrane can be positioned to create the desired additional dead volume.

[0201] Such additional dead volume may have a bore-to-stroke ratio that is much smaller than 1 (e.g. slender cylinder) in order to heat exchange with the walls. Or, the additional dead volume may be a bore-to-stroke ratio thai is much larger than 1 (e.g. a disk-shaped cylinder} in order to receive liquid spray droplets and ensure proper heat exchange.

[0202] i . A method comprising:

controlling operation of an energy storage apparatus by varying an amount of dead volume in a wet compression stage,

[0203] Another approach to controlling operation of a compressed air energy storage system according to various embodiments, may be to vary the flow rate of liquid spray. Changing the liquid spray rate can result in higher/lower heat of compression, and higher/lower discharge temperatures.

[0204] To enhance system performance and better control operation, it may be desirable to vary the liquid flow rate white other operating conditions remain fixed. Cam operated hydraulic pumps running on a same shaft as the compressors, may not have the flexibility to vary flow rate. [Θ2Θ5] Specifically, when the ambient temperature is below the freezing point of the liquid spray, may not be feasible to spray liquid into the intake atmospheric air. In such scenario, the spray liquid is eliminated in the lowest pressure stage. The air will go through an adiabatic compression cycle and will, heat up to higher temperatures before being fed to the second and later compression stages (if present).

10206] One approach to varying the liquid flow rate, is to use a bypass line around the pump, in normal operation, the b pass line is closed., and 100% of the pumped water is sprayed into the cylinder. When the bypass line is fully open, 100% of the pumped water will pass through the bypass and 0% will be sprayed into the compression chamber. Rate of liquid flow into the compression chamber can be varied by changing the percentage of the bypass valve between 0.0% and 1.00,0%,

[0207} Another approach to vary ing the flo w rate of the cam operated hydraulic pump, is to employ a mechanism to change the swept di stance of the plungers. Such a mechanism can be .mechanically or electronically actuated.

[02O8| For example, as shown in the specific embodiment of Figure 14, a lever arm can transfer the translation of the cam to the plunger . Varying the position of the pivot can vary the stroke of the plunger pump,

f 0209} 1. A method comprising:

controlling operation of an energy storage apparatus by varying a flow rate of liquid spray into a wet compression stage.

[0210] 2. A method as in claim I wherein the varying of the flow rate is accomplished using a bypass Sine around a liquid pump,

{0211] 3, A method as in claim 1 wherein the varying of the flow rate is accomplished using a mechanism to change a swept distance of plungers of a cam operated hydraulic pump.

[0212] According to certain embodiments, it may be possible to construct, a multistage compressed gas energy storage system with limited number of cylinder types/sizes. Such an approach may conserve resources by reducing development time for the design of new cylinders specific to the stage.

[0213] For example, certain embodiments may construct a two stage machine with only a single type of cylinder. One such arrangement is shown in Figure 15 A. That figure illustrates a 4-1 arrangement, in which four small (S) cyl inders are hooked up in parallel as the first stage of a two stage compressor. The second stage is comprised of only one small cylinder. [0214] The maximum pressure of a system such as in Figure ISA, depends on the maximum pressure rating of the small cylinder type, as well as the maximum pressure ratio capability of the cylinder. Other two stage configurations are possible, e.g. 2- 1 , 3- 1 , 5-1, 5-2, and other combinations.

£§2.15] A. three-stage system -according to an. embodiment may be constructed with one or two types of cylinders. A possible (but complex) configuration is a 16-4-1 arrangement, all made from small cylinders.

|0216] Figure 15B shows an alternative embodiment employing a 1-4-1 arrangement. The lowest pressure stage is a large (L) cylinder, and the rest of the system is made from small (S) cylinders. The middle stage of Figure 15B is a parallel connection of four small cylinders.

Other such combinations of l arge and small cylinders in three stages are also possible, e.g. 1-3-1 , 3-16-5.

|0217) Figure 15C shows another alternative embodiment This system comprises a 4- 1 - 1 arrangement of a three stage machine. In this configuration, the design, pressure of the large cylinder may be higher than the maximum intake pressure of the third stage. Figure 15 D is a pictorial depiction showing the di fference in size between the two types of cy li nders in the system of Figure ! 5€.

[02-3.8] Figure 15E shows a 4-1 -4-1 architecture (four-stage) made out of two types of cylinders. In this arrangement the average pressure ratio per stage is lower, and therefore, the volumetric effici ency of the cylinders increase.

021.9J Different stages of such structures ma spin at different speeds to achieve one or more purposes. For example, operation at different speeds may serve to balance the mass flow, to follow the desired power in/out, or to increase efficiency. Depending on the cost/price of each cylinder type and additional required components, an optimum arrangement for various types of applications may be designed that achieves a desired cost per unit of power.

|022O J Ϊ . An apparatus comprising:

a plurality of compression stages limited to compressors of a first size and compressors of a second size smaller than the first size, at least one stage comprising a plurality of compressors arranged in parallel, in fluid communication with a next stage comprising a single compressor; and

a compressed gas storage unit configured to receive and store compressed gas.

[0221] 2. An apparatus as in claim 1 wherein the at least one stage comprises a wet compression stage. [0222] 3. An apparatus as in claim 1 wherein the at least one stage comprises a plurality of reciprocating compressors.

|0223 j 4. An apparatus as in claim 1 wherein the at least one stage comprises a plurality of rotating compressors .

£0224] 5. An. apparatus as in claim 1. wherein the plurality of compressors are of the first size, and the single compressor is of the second size.

|0225| 6. An apparatus as in claim 1 wherein the plurality of compressors are of the second size, and tlie single compressor is of the first size.

[0226] 7, An apparatus as in claim 1 wherein the at least one stage is reversible to perform wet compression or wet expansion.

{0227] 8. An apparatus as i claim 1 wherein the compressed gas storage unit is configured to receive the compressed gas from the next stage.

97