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 first cylinder assembly and a second cylinder assembly in which gas is collectively compressed from an initial pressure to a final pressure, the method comprising:
 pre-expanding gas in the first cylinder assembly to approximately the initial pressure;   following the pre-expansion, admitting gas at the initial pressure into the first cylinder assembly, the pre-expansion reducing coupling loss during the admission of gas;   compressing the gas in the first cylinder assembly to a mid-pressure between the initial pressure and the final pressure, the gas exchanging heat with heat-transfer fluid thereduring;   completing a partial compression cycle by exhausting (i) only a portion of the compressed gas and (ii) at least a portion of the heat-transfer fluid out of the first cylinder assembly into a mid-pressure vessel at the mid-pressure;   mingling compressed gas and heat-transfer fluid within the mid-pressure vessel to form a mid-pressure foam at the mid-pressure;   admitting mid-pressure foam into a second cylinder assembly;   compressing the compressed gas of the mid-pressure foam within the second cylinder assembly to the final pressure;   exhausting gas at the final pressure from the second cylinder assembly; and   repeating the foregoing steps at least once, thereby performing at least one additional compression cycle.   
     
     
         23 . The method of  claim 22 , wherein admitting gas into the first cylinder assembly comprises (i) mixing gas with heat-transfer fluid within a mixing chamber, separate from the first cylinder assembly, to form a foam at the initial pressure, and (ii) admitting the foam into the first cylinder assembly. 
     
     
         24 . The method of  claim 23 , wherein gas mixed with heat-transfer fluid within the mixing chamber is admitted into the mixing chamber from ambient atmosphere. 
     
     
         25 . The method of  claim 23 , wherein mixing gas with heat-transfer fluid within the mixing chamber comprises spraying heat-transfer fluid into the gas within the mixing chamber, the mixing chamber comprising a screen therewithin. 
     
     
         26 . The method of  claim 22 , wherein heat-transfer fluid is sprayed into gas during compression in the first cylinder assembly to the mid-pressure. 
     
     
         27 . The method of  claim 22 , wherein compression of gas in the first cylinder assembly to the mid-pressure is substantially isothermal. 
     
     
         28 . The method of  claim 22 , wherein compression of the compressed gas of the mid-pressure foam within the second cylinder assembly to the final pressure is substantially isothermal. 
     
     
         29 . The method of  claim 22 , wherein, after compression of the compressed gas of the mid-pressure foam, at least a portion of the heat-transfer fluid is exhausted out of the second cylinder assembly. 
     
     
         30 . The method of  claim 22 , wherein gas at the final pressure is exhausted to a compressed-gas storage reservoir. 
     
     
         31 . The method of  claim 30 , wherein the compressed-gas storage reservoir comprises one or more pressure vessels. 
     
     
         32 . The method of  claim 30 , wherein the compressed-gas storage reservoir comprises a cavern. 
     
     
         33 . The method of  claim 30 , further comprising, after compressing the compressed gas of the mid-pressure foam within the second cylinder assembly to the final pressure, exhausting heat-transfer fluid into the compressed-gas storage reservoir. 
     
     
         34 . The method of  claim 22 , wherein admitting gas into the first cylinder assembly comprises actuating a valve to establish a connection between the first cylinder assembly and a source of the gas, the pre-expansion reducing an actuation energy required to actuate the valve. 
     
     
         35 . The method of  claim 22 , wherein at least a portion of the gas that is pre-expanded is within dead volume of the first cylinder assembly. 
     
     
         36 . The method of  claim 22 , wherein exhausting only a portion of the compressed gas out of the first cylinder assembly comprises exhausting substantially all of the compressed gas in the first cylinder assembly that is not within dead volume thereof. 
     
     
         37 . 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 first cylinder assembly. 
     
     
         38 . 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 first cylinder assembly during at least one of gas compression or gas exhaustion, thereby generating control information. 
     
     
         39 . The method of  claim 38 , further comprising utilizing the control information in a subsequent compression cycle to control at least one of the pre-expansion, compression, or exhaustion steps. 
     
     
         40 . The method of  claim 22 , wherein the gas compression in the first cylinder assembly is driven by a load connected to the first cylinder assembly. 
     
     
         41 . The method of  claim 40 , wherein the load is a mechanical crankshaft or a hydraulic pump/motor. 
     
     
         42 . The method of  claim 22 , wherein exhausting only a portion of the compressed gas out of the first cylinder assembly comprises (i) monitoring at least one of a temperature, a pressure, or a position of a boundary mechanism within the first 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 first cylinder assembly. 
     
     
         43 . The method of  claim 42 , wherein the remnant portion of the compressed gas is determined such that a pre-expansion step of a subsequent compression cycle expands the remnant portion to approximately the initial pressure. 
     
     
         44 . The method of  claim 22 , further comprising, before admitting mid-pressure foam into the second cylinder assembly, pre-expanding gas within the second cylinder assembly to approximately the mid-pressure, the pre-expansion reducing coupling loss during the admission of mid-pressure foam. 
     
     
         45 . The method of  claim 44 , wherein admitting mid-pressure foam into the second cylinder assembly comprises actuating a valve to establish a connection between the second cylinder assembly and the mid-pressure vessel, the pre-expansion reducing an actuation energy required to actuate the valve. 
     
     
         46 . The method of  claim 44 , wherein at least a portion of the gas that is pre-expanded in the second cylinder assembly is within dead volume of the second cylinder assembly. 
     
     
         47 . The method of  claim 44 , wherein an amount of the gas that is pre-expanded in the second cylinder assembly is substantially less than an amount of the gas of the mid-pressure foam compressed in the second cylinder assembly. 
     
     
         48 . The method of  claim 22 , wherein exhausting gas at the final pressure from the second cylinder assembly comprises exhausting only a portion of gas at the final pressure from the second cylinder assembly. 
     
     
         49 . The method of  claim 48 , wherein exhausting only a portion of the gas out of the second cylinder assembly comprises exhausting substantially all of the gas in the second cylinder assembly that is not within dead volume thereof. 
     
     
         50 . The method of  claim 22 , wherein exhausting gas at the final pressure from the second cylinder assembly comprises exhausting foam at the final pressure from the second cylinder assembly.