Dead-volume management in compressed-gas energy storage and recovery systems

Abstract

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.

What is claimed is: 
     
         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.