Compressed air energy storage and recovery

Abstract

A compressed air system energy storage and recovery system has a compressed air tank structured to store compressed air above 200 bars, a heat storage unit containing a heat transfer fluid and having a latent heat storage material, and a heat exchanger. The heat exchanger extracts heat from compressed ambient air above 200 bars for storage and to heat compressed air from the tank above 200 bars prior to expansion and use to recover energy in the air motor. Efficiency of energy storage and heat exchange is improved using pressures above 200 bars.

What is claimed is: 
     
         1 . A compressed air system energy storage and recovery system comprising:
 a compressed air tank structured to store compressed air above 225 bars;   a heat storage unit containing a heat transfer fluid and having a latent heat storage material;   a heat exchanger connected on one side to the compressed air tank and connectable to an air compressor and an air motor, and on another side receiving said heat transfer fluid to a cold conduit of the heat storage unit and to a hot conduit of the heat storage unit, the heat exchanger configured to extract heat from compressed ambient air above 200 bars for storage and to heat compressed air from said tank above 200 bars prior to expansion and use to recover energy in the air motor.   
     
     
         2 . The system as defined in  claim 1 , wherein said compressed air tank is structured to store compressed air above 275 bars. 
     
     
         3 . The system as defined in  claim 1 , wherein said heat transfer fluid contains a mixture comprising a liquid and particles of said latent heat storage material. 
     
     
         4 . The system as defined in  claim 3 , wherein said mixture comprises oil and salt particles. 
     
     
         5 . The system as defined in  claim 4 , wherein said mixture further comprises metal particles. 
     
     
         6 . The system as defined in  claim 1 , wherein said heat storage unit comprises a first reservoir of cool heat transfer fluid, a second reservoir of hot heat transfer fluid, and at least one circulation pump. 
     
     
         7 . The system as defined in  claim 1 , further comprising an external heating element for providing heat to said heat storage unit. 
     
     
         8 . The system as defined in  claim 7 , wherein said heating element is an electrical resistive heating element. 
     
     
         9 . The system as defined in  claim 1 , further comprising at least one air compressor configured to compress ambient air to a pressure for storage in said air tank. 
     
     
         10 . The system as defined in  claim 9 , wherein said at least one compressor comprise at least two stages of compression, said heat exchanger comprising separate heat exchanger components for compressed air from each said stage of compression. 
     
     
         11 . The system as defined in  claim 9 , wherein said at least one compressor comprise a single stage of compression. 
     
     
         12 . The system as defined in  claim 10 , wherein said heat exchanger comprises separate heat exchanger components for said stage of compressors and for compressed air from said stage of compression. 
     
     
         13 . The system as defined in  claim 9 , wherein said heat exchanger and said heat storage unit with said heat transfer fluid are configured to have a reverse flow and to absorb and to return more than 80% of the heat energy originally present in compressed air from said at least one air compressor. 
     
     
         14 . The system as defined in  claim 1 , wherein said heat exchanger comprises a number of small bore tubes arranged to conduct said compressed air in parallel. 
     
     
         15 . The system as defined in  claim 14 , wherein said small bore tubes are made of stainless steel and have an inner diameter from 2.5 to 4.5 mm, and a thickness from 0.7 to 2 mm. 
     
     
         16 . The system as defined in  claim 1 , further comprising:
 a working pressure reservoir;   a pressure regulator connecting said heat exchanger to said working pressure reservoir and configured to maintain a predetermined pressure in said working pressure reservoir; and   an air turbine connected to an electric generator, connected to said working pressure reservoir.   
     
     
         17 . The system as defined in  claim 1 , further comprising an air dehumidification unit configured to remove moisture from said compressed air. 
     
     
         18 . A power transmission network comprising:
 at least one compressed air system energy storage and recovery system as defined in  claim 1  and connected to a node of said network for absorbing and releasing electric power in response to a remote control signal;   a remote controller connected to said compressed air system energy storage and recovery system via a communications system and configured to provide said remote control signal.   
     
     
         19 . A method of compressed air energy storage and regeneration comprising:
 using a first energy source to compress air to a pressure above 200 bar;   using a heat exchanger to absorb heat from said air above 200 bar;   storing said absorbed heat in a latent heat storage medium;   storing said compressed air in at least one storage vessel;   expanding said compressed air from said storage vessel to provide expanded air for regeneration of energy;   using a heat exchanger to provide heat to said expanded air from said heat storage medium; and   generating power from said expanded and heated air.   
     
     
         20 . The method as claimed in  claim 19 , wherein said air is compressed above 250 bar.