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 . A method of increasing efficiency of an energy-recovery process performed in a cylinder assembly in which gas is expanded, the cylinder assembly being selectively fluidly connected to a high-side component by a high-side valve and selectively fluidly connected to a low-side component by a low-side valve, the method comprising:
 performing a first valve transition by opening the high-side valve to allow compressed gas to enter the cylinder assembly from the high-side component, the cylinder assembly containing gas at a first pressure prior to the first valve transition;   performing a second valve transition by closing the high-side valve, the gas within the cylinder assembly expanding thereafter;   performing a third valve transition by opening the low-side valve to allow a portion of the expanded gas to enter the low-side component from the cylinder assembly, wherein (i) a remnant portion of the gas remains in the cylinder assembly after the third valve transition and (ii) the expanded gas is at a second pressure prior to the third valve transition;   performing a fourth valve transition by closing the low-side valve, the remnant portion of the gas within the cylinder assembly being compressed thereafter to approximately the first pressure; and   enforcing a transition restriction comprising at least one of (i) performing the first valve transition only when the first pressure is approximately equal to a pressure of the high-side component or (ii) performing the third valve transition only when the second pressure is approximately equal to a pressure of the low-side component.   
     
     
         2 . The method of  claim 1 , wherein the high-side component comprises a compressed-gas storage reservoir. 
     
     
         3 . The method of  claim 1 , wherein the high-side component comprises a second cylinder assembly for at least one of compressing gas or expanding gas within a pressure range higher than a pressure range of operation of the cylinder assembly. 
     
     
         4 . The method of  claim 1 , wherein the high-side component comprises a mid-pressure vessel for containing gas at a pressure within both of or between pressure ranges of operation of the cylinder assembly and a second cylinder assembly for at least one of compressing gas or expanding gas within a pressure range higher than a pressure range of operation of the cylinder assembly. 
     
     
         5 . The method of  claim 1 , wherein the low-side component comprises a vent to atmosphere. 
     
     
         6 . The method of  claim 1 , wherein the low-side component comprises a second cylinder assembly for at least one of compressing gas or expanding gas within a pressure range lower than a pressure range of operation of the cylinder assembly. 
     
     
         7 . The method of  claim 1 , wherein the low-side component comprises a mid-pressure vessel for containing gas at a pressure within both of or between pressure ranges of operation of the cylinder assembly and a second cylinder assembly for at least one of compressing gas or expanding gas within a pressure range lower than a pressure range of operation of the cylinder assembly. 
     
     
         8 . The method of  claim 1 , wherein the high-side valve and the low-side valve are actuated valves. 
     
     
         9 . The method of  claim 8 , wherein each of the high-side valve and the low-side valve is a hydraulically actuated valve, a variable cam actuated valve, an electromagnetically actuated valve, a mechanically actuated valve, or a pneumatically actuated valve. 
     
     
         10 . The method of  claim 1 , wherein the second valve transition is timed to admit an amount of gas into a volume of the cylinder assembly that is expandable to the second pressure therein. 
     
     
         11 . The method of  claim 1 , further comprising monitoring at least one of a temperature within the cylinder assembly, a pressure within the cylinder assembly, a position of a boundary mechanism within the cylinder assembly, the pressure of the high-side component, or the pressure of the low-side component during an expansion cycle comprising the first, second, third, and fourth valve transitions, thereby generating control information. 
     
     
         12 . The method of  claim 11 , further comprising utilizing the control information in a subsequent expansion cycle to control timing of at least one of the first, second, third, or fourth valve transitions of the subsequent expansion cycle. 
     
     
         13 . The method of  claim 12 , wherein the timing is controlled to maximize efficiency of the subsequent expansion cycle. 
     
     
         14 . The method of  claim 1 , further comprising thermally conditioning gas with heat-transfer fluid during at least a portion of an expansion cycle comprising the first, second, third, and fourth valve transitions. 
     
     
         15 . The method of  claim 14 , wherein the thermal conditioning renders the gas expansion substantially isothermal. 
     
     
         16 . A method of increasing efficiency of an energy-recovery process performed in a cylinder assembly in which gas is expanded, the cylinder assembly being selectively fluidly connected to a high-side component by a high-side valve and selectively fluidly connected to a low-side component by a low-side valve, the method comprising:
 performing, within the cylinder assembly, a plurality of expansion cycles each comprising:
 performing a first valve transition by opening the high-side valve to allow compressed gas to enter the cylinder assembly from the high-side component, 
 performing a second valve transition by closing the high-side valve, the gas within the cylinder assembly expanding thereafter, 
 performing a third valve transition by opening the low-side valve to allow a portion of the expanded gas to enter the low-side component from the cylinder assembly, a remnant portion of the gas remaining in the cylinder assembly after the third valve transition, and 
 performing a fourth valve transition by closing the low-side valve, the remnant portion of the gas within the cylinder assembly being compressed thereafter; and 
   during each expansion cycle, altering a timing of at least one of the first, second, third, or fourth valve transitions to maximize efficiency of the expansion cycle.   
     
     
         17 . The method of  claim 16 , wherein the timing is altered based at least in part on control information generated during a previous expansion cycle. 
     
     
         18 . The method of  claim 17 , wherein the control information comprises at least one of a temperature within the cylinder assembly, a pressure within the cylinder assembly, a position of a boundary mechanism within the cylinder assembly, the pressure of the high-side component, or the pressure of the low-side component.