DEAD-VOLUME MANAGEMENT IN COMPRESSED-GAS ENERGY STORAGE AND RECOVERY SYSTEMS
In various embodiments, coupling losses between a cylinder assembly and other components of a gas compression and/or expansion system are reduced or eliminated via valve-timing control.
1 - 21 . (canceled)
22 . A method of increasing efficiency of an energy-storage process performed in a cylinder assembly in which gas is compressed from an initial pressure to a final pressure, the method comprising:
pre-expanding gas in the cylinder assembly to approximately the initial pressure;
following the pre-expansion, admitting gas at the initial pressure into the cylinder assembly, the pre-expansion reducing coupling loss during the admission of gas;
compressing the gas in the cylinder assembly to the final pressure;
completing a compression cycle by exhausting only a portion of the compressed gas out of the cylinder assembly; and
repeating the foregoing steps at least once, thereby performing at least one additional compression cycle.
23 . The method of claim 22 , further comprising thermally conditioning the gas with heat-transfer fluid during compression.
24 . The method of claim 23 , wherein the thermal conditioning renders the compression substantially isothermal.
25 . The method of claim 23 , wherein the heat-transfer fluid is sprayed into the gas.
26 . The method of claim 23 , wherein the heat-transfer fluid forms a foam with the gas.
27 . The method of claim 23 , wherein, after compression of the gas, at least a portion of the heat-transfer fluid is exhausted out of the cylinder assembly.
28 . The method of claim 22 , wherein the gas is admitted into the cylinder assembly from a vent to atmosphere, the initial pressure being approximately atmospheric pressure.
29 . The method of claim 22 , wherein the gas is admitted into the cylinder assembly from a second cylinder assembly in which gas is compressed to the initial pressure from a pressure less than the initial pressure.
30 . The method of claim 22 , wherein the portion of the compressed gas is exhausted to a compressed-gas storage reservoir.
31 . The method of claim 22 , wherein the portion of the expanded gas is exhausted to a second cylinder assembly in which gas is compressed from the final pressure to a pressure higher than the final pressure.
32 . The method of claim 22 , wherein admitting gas into the cylinder assembly comprises actuating a valve to establish a connection between the cylinder assembly and a source of the gas, the pre-expansion reducing an actuation energy required to actuate the valve.
33 . The method of claim 22 , wherein at least a portion of the gas that is pre-expanded is within dead volume of the cylinder assembly.
34 . The method of claim 22 , wherein exhausting only a portion of the compressed gas out of the cylinder assembly comprises exhausting substantially all of the compressed gas in the cylinder assembly that is not within dead volume thereof.
35 . The method of claim 22 , wherein an amount of the gas that is pre-expanded is substantially less than an amount of the gas compressed in the cylinder assembly.
36 . The method of claim 22 , further comprising monitoring at least one of a temperature, a pressure, or a position of a boundary mechanism within the cylinder assembly during at least one of gas compression or gas exhaustion, thereby generating control information.
37 . The method of claim 36 , further comprising utilizing the control information in a subsequent compression cycle to control at least one of the pre-expansion, compression, or exhaustion steps.
38 . The method of claim 22 , wherein the gas compression is driven by a load connected to the cylinder assembly.
39 . The method of claim 38 , wherein the load is a mechanical crankshaft or a hydraulic pump/motor.
40 . The method of claim 22 , wherein exhausting only a portion of the compressed gas out of the cylinder assembly comprises (i) monitoring at least one of a temperature, a pressure, or a position of a boundary mechanism within the cylinder assembly, thereby generating control information, and (ii) based at least in part on the control information, discontinuing the gas exhaustion, thereby trapping a remnant portion of the compressed gas within the cylinder assembly.
41 . The method of claim 40 , wherein the remnant portion of the compressed gas is determined such that a pre-expansion step of a subsequent expansion cycle expands the remnant portion to approximately the initial pressure.