Systems and methods for reducing dead volume in compressed-gas energy storage systems

Abstract

In various embodiments, dead space and associated coupling losses are reduced in energy storage and recovery systems employing compressed air.

What is claimed is: 
     
         1 .- 27 . (canceled) 
     
     
         28 . A method of energy recovery utilizing a first cylinder assembly comprising therewithin (i) a piston and (ii) dead space when the piston is disposed at a limit of travel within the first cylinder assembly, the method comprising:
 substantially filling the dead space with liquid;   thereafter, admitting compressed gas at a first pressure into the first cylinder assembly, whereby the liquid prevents expansion of gas into the dead space;   expanding the gas within the first cylinder assembly to a second pressure lower than the first pressure, thereby translating the piston within the first cylinder assembly; and   exhausting substantially all of the gas at the second pressure from the first cylinder assembly.   
     
     
         29 . The method of  claim 28 , further comprising, after expanding gas to the second pressure, exhausting at least a portion of the liquid from the first cylinder assembly. 
     
     
         30 . The method of  claim 29 , wherein (i) the at least a portion of the liquid and (ii) the gas at the second pressure are exhausted through a vent to atmosphere. 
     
     
         31 . The method of  claim 29 , wherein (i) the at least a portion of the liquid and (ii) the gas at the second pressure are exhausted to a second cylinder assembly. 
     
     
         32 . The method of  claim 31 , further comprising expanding gas within the second cylinder assembly from approximately the second pressure to a third pressure lower than the second pressure. 
     
     
         33 . The method of  claim 29 , wherein the first cylinder assembly defines a single opening through which (i) compressed gas is admitted into the first cylinder assembly and (ii) gas and liquid are exhausted from the first cylinder assembly. 
     
     
         34 . The method of  claim 29 , further comprising substantially filling dead space within a conduit fluidly connecting the first cylinder assembly and the second cylinder assembly with liquid. 
     
     
         35 . The method of  claim 28 , wherein substantially filling the dead space with liquid comprises (i) introducing liquid into the dead space, thereby displacing gas therefrom, (ii) exhausting the displaced gas and a portion of the liquid from the first cylinder assembly, and (iii) controlling the introduction of the liquid into the dead space to minimize flow of liquid out of the first cylinder assembly. 
     
     
         36 . The method of  claim 28 , wherein substantially filling the dead space with liquid comprises utilizing at least one of a pressure sensor or flow meter to detect when the dead space is substantially filled with liquid. 
     
     
         37 . The method of  claim 28 , wherein (a) a valve controls exhaustion of the gas out of the first cylinder assembly and (b) the dead space comprises (i) space within the first cylinder assembly and (ii) at least one of space within the valve or space within a conduit between the valve and the first cylinder assembly. 
     
     
         38 . The method of  claim 28 , further comprising introducing heat-transfer fluid into the gas such that heat is exchanged between the heat-transfer fluid and the gas during expansion. 
     
     
         39 . The method of  claim 38 , wherein the heat-transfer fluid is introduced into the gas in the form of a spray. 
     
     
         40 . The method of  claim 38 , wherein the heat-transfer fluid is introduced into the gas and the liquid is introduced into the first cylinder assembly to substantially fill the dead space via the same circulation system. 
     
     
         41 . The method of  claim 28 , wherein substantially filling the dead space with liquid comprises introducing the liquid into the first cylinder assembly through (i) a check valve configured to substantially prevent flow of liquid out of the first cylinder assembly and (ii) a flow-control valve in series with the check valve. 
     
     
         42 . The method of  claim 28 , wherein the gas at the second pressure is exhausted through a vent to atmosphere. 
     
     
         43 . The method of  claim 28 , wherein the gas at the second pressure is exhausted to a second cylinder assembly. 
     
     
         44 . The method of  claim 43 , further comprising expanding gas within the second cylinder assembly from approximately the second pressure to a third pressure lower than the second pressure. 
     
     
         45 . The method of  claim 43 , further comprising substantially filling dead space within a conduit fluidly connecting the first cylinder assembly and the second cylinder assembly with liquid. 
     
     
         46 . The method of  claim 28 , wherein the first cylinder assembly defines a single opening through which (i) compressed gas is admitted into the first cylinder assembly and (ii) gas is exhausted from the first cylinder assembly. 
     
     
         47 . The method of  claim 28 , wherein admitting compressed gas into the first cylinder assembly comprises opening a valve, and further comprising closing the valve during the expansion of the gas within the first cylinder assembly.