Reversible heat exchangers in compressed air energy storage systems

Abstract

A method of processing a stream of compressed air travelling between a gas compressor/expander subsystem and an underground accumulator in a compressed air energy storage system may include directing a thermal storage liquid through the first liquid flow path in a liquid charging flow direction from a thermal source reservoir toward a thermal storage reservoir whereby at least a portion of the thermal energy in the compressed air is transferred from the compressed air into the thermal storage liquid within the first reversible heat exchanger; including redirecting the compressed air through the first gas flow path in a gas discharging flow direction that is opposite the gas charging flow direction and redirecting the thermal storage liquid through the first liquid flow path in a liquid discharging flow direction whereby at least a portion of the thermal energy in the thermal storage liquid is returned into the compressed air.

1 . A method of processing a stream of compressed air travelling between a gas compressor/expander subsystem and an underground accumulator in a compressed air energy storage system operable in at least a charging mode and a discharging mode using at least a first reversible heat exchanger having a first gas flow path and a first liquid flow path, the method comprising:
 a) directing the stream of compressed air from the gas compressor/expander subsystem toward the accumulator when in the charging mode, including directing the compressed air through the first gas flow path in a gas charging flow direction, and directing a thermal storage liquid through the first liquid flow path in a liquid charging flow direction from a thermal source reservoir toward a thermal storage reservoir whereby at least a portion of the thermal energy in the compressed air is transferred from the compressed air into the thermal storage liquid within the first reversible heat exchanger; and   b) directing the stream of compressed air from the accumulator toward the gas compressor/expander subsystem when in the discharging mode, including redirecting the compressed air through the first gas flow path in a gas discharging flow direction that is opposite the gas charging flow direction and redirecting the thermal storage liquid through the first liquid flow path in a liquid discharging flow direction that is opposite the liquid charging flow direction from the thermal storage reservoir toward the thermal source reservoir whereby at least a portion of the thermal energy in the thermal storage liquid is returned into the compressed air within the first reversible heat exchanger.   
     
     
         2 . The method of  claim 1 , wherein the first gas flow path and the first liquid flow path are configured so that when in the charging mode an inlet temperature of the compressed air entering the first reversible heat exchanger is within about 5-25° C. of an outlet temperature of the thermal storage liquid exiting the first reversible heat exchanger. 
     
     
         3 - 13 . (canceled) 
     
     
         14 . The method of  claim 1 , wherein the first gas flow path and the first liquid flow path are configured so that when in the charging mode the gas charging flow direction is opposite the liquid charging flow direction, and so that when in the discharging mode the gas discharging flow direction is opposite the liquid discharging flow direction. 
     
     
         15 - 18 . (canceled) 
     
     
         19 . The method of  claim 1 , wherein the first reversible heat exchanger comprises at least first and second exchanger modules arranged in fluid communication in parallel with each other and step a) includes directing the flow of compressed air through the first and second exchanger modules in parallel. 
     
     
         20 . (canceled) 
     
     
         21 . The method of  claim 1 , wherein the first reversible heat exchanger comprises at least one of a shell-and-tube exchanger, coil wound exchanger (CWHE), plate-and-frame exchanger and braised plate exchanger. 
     
     
         22 . The method of  claim 21 , wherein the first reversible heat exchanger comprises a single tube pass, single shell pass shell-and-tube heat exchanger comprising a plurality of tubes providing a portion of the first gas flow path surrounded by a shell flow path providing a portion of the first liquid flow path, and wherein the compressed air flows through the tubes and the thermal storage liquid flows through the shell flow path. 
     
     
         23 . The system of any  claim 1 , wherein the accumulator comprises a hydrostatically compensated accumulator and further comprising:
 a) when in the charging mode, displacing a corresponding amount of compensation liquid from the layer of compensation liquid out of the accumulator toward a compensation liquid reservoir via a compensation liquid flow path thereby maintaining the layer of compressed air at substantially the storage pressure during the charging mode; and   b) when in the discharging mode, providing a return flow of the compensation liquid into the accumulator as the compressed air is removed thereby maintaining the layer of compressed air at substantially the storage pressure during the discharging mode.   
     
     
         24 . A compressed air energy storage system alternately operable in at least a charging mode and a discharging mode, the system comprising:
 a) an accumulator comprising an underground chamber having an accumulator interior for containing compressed air at a storage pressure;   b) a gas compressor/expander subsystem in fluid communication with the accumulator interior via an air flow path and configured to convey a flow of compressed air into the accumulator when in the charging mode and out of the accumulator when in the discharging mode;   c) a thermal storage subsystem comprising at least a first reversible heat exchanger having a first liquid flow path forming part of a thermal liquid flow path between a thermal source reservoir and a thermal storage reservoir and a first gas flow path forming part of the air flow path between the gas compressor/expander subsystem and the accumulator;   wherein the system is operable in at least:
 a charging mode in which gas from the gas compressor/expander subsystem is conveyed through the air flow path toward the accumulator, including conveying the compressed air through the first gas flow path in a gas charging flow direction, and directing the thermal storage liquid through the first liquid flow path in a liquid charging flow direction from the thermal source reservoir toward the thermal storage reservoir whereby thermal energy is transferred from the compressed air into the thermal storage liquid within the first reversible heat exchanger, and wherein the compressed air enters the accumulator at a storage pressure; and 
 a discharging mode in which air exits the accumulator and is conveyed through the air flow path toward the gas compressor/expander subsystem, including conveying the compressed air through the first gas flow path in a gas discharging flow direction opposite the gas charging flow direction, and redirecting the thermal storage liquid through the first liquid flow path in a liquid discharging flow direction that is opposite the liquid charging flow direction from the thermal storage reservoir toward the thermal source reservoir whereby thermal energy is reintroduced into the compressed air from the thermal storage liquid within the first reversible heat exchanger. 
   
     
     
         25 - 27 . (canceled) 
     
     
         28 . The system of  claim 24 , wherein during the charging mode an inlet temperature of the compressed air entering the first gas flow path is within about 5-25° C. of an outlet temperature of the thermal storage liquid exiting the first liquid flow path. 
     
     
         29 - 32 . (canceled) 
     
     
         33 . The system of  claim 24 , wherein during the discharging mode an outlet temperature of the air exiting the first gas flow path is within about 5-25° C. of an inlet temperature of the thermal storage liquid entering the first liquid flow path. 
     
     
         34 - 35 . (canceled) 
     
     
         36 . The system of  claim 24 , wherein the thermal storage subsystem further comprises at least a second reversible heat exchanger having a second liquid flow path forming part of a thermal liquid flow path between the thermal source reservoir and the thermal storage reservoir and a second gas flow path forming part of the air flow path between the compressor/expander subsystem and the accumulator. 
     
     
         37 . The system of  claim 36 , wherein the second liquid flow path is fluidly connected in parallel with the first liquid flow path. 
     
     
         38 - 39 . (canceled) 
     
     
         40 . The system of  claim 24 , wherein the first reversible heat exchanger comprises at least one of a shell-and-tube exchanger, coil wound exchanger (CWHE), plate-and-frame exchanger and braised plate exchanger. 
     
     
         41 . The system of  claim 40 , wherein the first reversible heat exchanger comprises a single tube pass, single shell pass shell-and-tube heat exchanger comprising a plurality of tubes providing a portion of the first gas flow path surrounded by a shell flow path providing a portion of the first liquid flow path, and wherein the compressed air flows through the tubes and the thermal storage liquid flows through the shell flow path. 
     
     
         42 . (canceled) 
     
     
         43 . The system of  claim 41 , wherein the first reversible heat exchanger is vertically oriented, and when in the charging mode the compressed air enters at an upper end of the first reversible heat exchanger, flows in a generally downwardly direction through the first gas flow path and exits at a lower end of the first reversible heat exchanger. 
     
     
         44 - 52 . (canceled) 
     
     
         53 . The system of  claim 24 , wherein the first reversible heat exchanger is configured as a counterflow heat exchanger in which the gas charging flow direction is generally opposite the liquid charging flow direction and the gas discharging flow direction is generally opposite the liquid discharging flow direction. 
     
     
         54 . (canceled) 
     
     
         55 . The system of  claim 24 , wherein the thermal source reservoir is configured for containing the thermal storage liquid at a low storage temperature and the thermal storage reservoir is in communication with the thermal source reservoir via the thermal liquid flow path and is configured to contain the thermal storage liquid at a high storage temperature. 
     
     
         56 . The system of  claim 24 , wherein when in the charging mode the thermal storage liquid exiting the first liquid flow path is at a temperature that is greater than a boiling temperature of the thermal storage liquid when at atmospheric pressure. 
     
     
         57 . (canceled) 
     
     
         58 . The system of  claim 24 , wherein the thermal storage liquid comprises at least one of water, mineral oil and synthetic oil. 
     
     
         59 . The system of  claim 24 , wherein the first reversible heat exchanger includes a first end at which the compressed air enters the first gas flow path during the charging mode and exits the first gas flow path during the discharging mode, and an opposing second end at which the compressed air exits the first gas flow path during the charging mode and enters the first gas flow path during the charging mode, and wherein the first end is at a higher temperature than the second end during both the charging and discharging modes. 
     
     
         60 . The system of  claim 59 , wherein the first end is at a higher elevation than the second end. 
     
     
         61 - 62 . (canceled) 
     
     
         63 . The system of  claim 24 , wherein during the discharging mode the air exits the first gas flow path at between about 180 and 250° C. 
     
     
         64 . (canceled) 
     
     
         65 . The system of  claim 24 , where the compressed air energy storage system comprises an underground hydrostatically compensated accumulator configured to contain a layer of compensation liquid beneath a layer of the compressed air at the storage pressure. 
     
     
         66 - 69 . (canceled) 
     
     
         70 . The system of  claim 21 , where the compressor/expander subsystem has at least two stages, and where there are at least two reversible heat exchangers, one for each stage of compression/expansion. 
     
     
         71 . The system of  claim 70 , where the compressed air flows alternatively through the at least two stages compressor/expander subsystem and the at least two reversible heat exchangers during the charging and discharging modes. 
     
     
         72 . (canceled)