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 .- 47 . (canceled) 
     
     
         48 . A method of energy recovery, the method comprising:
 admitting compressed gas at a first pressure into a first cylinder assembly;   expanding gas within the first cylinder assembly from approximately the first pressure to an intermediate pressure lower than the first pressure;   exhausting gas at the intermediate pressure from the first cylinder assembly into a mid-pressure reservoir;   admitting gas at the intermediate pressure from the mid-pressure reservoir into a second cylinder assembly;   expanding gas within the second cylinder assembly from approximately the intermediate pressure to a second pressure lower than the intermediate pressure; and   exhausting gas at the second pressure from the second cylinder assembly.   
     
     
         49 . The method of  claim 48 , wherein compressed gas is admitted into the first cylinder assembly from a compressed-gas reservoir different from the mid-pressure reservoir. 
     
     
         50 . The method of  claim 49 , wherein the compressed-gas reservoir comprises one or more pressure vessels. 
     
     
         51 . The method of  claim 49 , wherein the compressed-gas reservoir comprises a cavern. 
     
     
         52 . The method of  claim 48 , further comprising exchanging heat between gas and heat-exchange liquid during expansion in the first cylinder assembly. 
     
     
         53 . The method of  claim 48 , further comprising exchanging heat between gas and heat-exchange liquid during expansion in the second cylinder assembly. 
     
     
         54 . The method of  claim 48 , further comprising exchanging heat between gas and heat-exchange liquid during expansion in the first and second cylinder assemblies. 
     
     
         55 . The method of  claim 48 , further comprising mingling heat-exchange liquid with gas within the mid-pressure reservoir. 
     
     
         56 . The method of  claim 55 , wherein mingling heat-exchange liquid with gas comprises spraying heat-exchange liquid into gas. 
     
     
         57 . The method of  claim 48 , wherein gas is exhausted at the second pressure from the second cylinder assembly to a vent to atmosphere. 
     
     
         58 . The method of  claim 48 , wherein expansion of gas within the first cylinder assembly is substantially isothermal. 
     
     
         59 . The method of  claim 48 , wherein expansion of gas within the second cylinder assembly is substantially isothermal. 
     
     
         60 . The method of  claim 48 , wherein the mid-pressure reservoir comprises a pressure-compensated vessel. 
     
     
         61 . The method of  claim 48 , wherein the mid-pressure reservoir has a volume sufficient to supply gas to an interior volume of the second cylinder assembly while maintaining a substantially constant pressure within the mid-pressure reservoir. 
     
     
         62 . The method of  claim 48 , wherein expansion of gas within the first cylinder assembly translates a boundary mechanism within the first cylinder assembly. 
     
     
         63 . The method of  claim 62 , further comprising converting motion of the boundary mechanism into rotary motion. 
     
     
         64 . The method of  claim 63 , wherein the motion of the boundary mechanism is converted into rotary motion via a crankshaft. 
     
     
         65 . The method of  claim 48 , wherein potential energy of gas expanding in at least one of the first or second cylinder assemblies is utilized to produce electricity. 
     
     
         66 . The method of  claim 48 , wherein the mid-pressure reservoir comprises a spray mechanism therewithin for spraying heat-exchange liquid.