Apparatus and Method for Storing Energy

Abstract

In an energy storage and recovery system, working fluid from a first vessel is compressed by power machinery and passes, via a regenerator, into a second vessel, where it is forced to condense, the temperature and pressure of the saturated working liquid/vapour mixture continuously rising during storage. The stored energy is recovered by the vapour returning through the regenerator and power machinery where it expands to produce work before condensing back into the first vessel. The regenerator comprises a gas permeable, solid thermal storage medium which, during storage, stores superheat and some latent heat from the vapour passing through it in respective downstream regions that exhibit continuously increasing temperature profiles during storage and a small temperature difference with the surrounding vapour, thereby minimising irreversible losses during the thermal energy transfers.

1 . An energy storage and recovery system comprising:
 a first vessel configured to store a working fluid as a saturated liquid/vapour mixture L 1  having a temperature T L1 ;   a second vessel configured to store the working fluid as a saturated liquid/vapour mixture L 2  having a temperature T L2 ;   power machinery disposed between the first and second vessels; and   a regenerator disposed between the power machinery and liquid of the working fluid stored in the second vessel,   wherein the system is configured such that:
 (i) in a storage mode, working fluid vapour passes from the first vessel to the power machinery where the working fluid vapour is compressed before passing through the regenerator and condensing in working fluid liquid of the mixture L 2  in the second vessel, so as to produce a progressive increase in the temperature T L2  of the mixture L 2  and in a liquid/vapour equilibrium phase change temperature of the mixture L 2  during the storage mode; and, 
 (ii) in a recovery mode, working fluid vapour passes from the second vessel, through the regenerator to the power machinery where the working fluid vapour is expanded to produce power before condensing in working fluid liquid of the mixture L 1  in the first vessel, so as to produce a progressive decrease in the temperature T L2  of the mixture L 2  and in the liquid/vapour equilibrium phase change temperature of the mixture L 2  during the recovery mode; 
   wherein:   the regenerator comprises a solid thermal storage medium, the solid thermal storage medium being configured such that the working fluid vapour passes through the solid thermal storage medium for direct heat transfer between the working fluid vapour and solid thermal storage medium so as to store and return superheat during the storage and recovery modes, respectively; and,   the system is configured such that some condensation takes place in the regenerator during the storage mode.   
     
     
         2 . A system according to  claim 1 , wherein the solid thermal storage medium is in the form of a porous matrix. 
     
     
         3 . A system according to  claim 1 , wherein the system is configured such that condensation takes place in the regenerator for the full running time of the storage mode. 
     
     
         4 . A system according to  claim 1 , wherein the system is configured to cease operating in the storage mode when condensation is only occurring in a last 5% or less of a downstream length of the regenerator. 
     
     
         5 . A system according to  claim 1 , wherein the system is configured to cease operating in the storage mode when condensation is about to finish in the regenerator such that some of the working fluid vapour is about to start exiting the regenerator as a superheated gas. 
     
     
         6 . A system according to  claim 1 , wherein the system is configured such that there is a progressive decrease in the temperature T L1  of the mixture L 1  and in a liquid/vapour equilibrium phase change temperature of the mixture L 1  during the storage mode, and, a progressive increase in the temperature T L1  of the mixture L 1  and in a liquid/vapour equilibrium phase change temperature of the mixture L 1  during the recovery mode. 
     
     
         7 . A system according to  claim 6 , further comprising a further regenerator configured such that the further regenerator is disposed between the power machinery and the working fluid liquid stored in the first vessel. 
     
     
         8 . A system according to  claim 6 , further comprising additional thermal ballast in the first vessel or a temperature regulating sub-system associated with the first vessel, the additional thermal ballast or the temperature regulating sub-system being configured to reduce respective rates of the progressive decrease and increase in the temperature T L1  of the mixture L 1  during the storage and recovery modes, respectively. 
     
     
         9 . A system according to  claim 1 , wherein the regenerator is configured such that the regenerator is located inside the second vessel above the working fluid liquid of the mixture L 2 . 
     
     
         10 . A system according to  claim 1 , wherein the system is configured to lose waste heat from the first vessel by allowing the working fluid vapour of the mixture L 1  to vent to atmosphere or to a waste heat recapture sub-system, when a vapour pressure of the working fluid vapour of the mixture L 1  exceeds atmospheric pressure or a pressure in the sub-system, respectively. 
     
     
         11 . A system according to  claim 1 , wherein the system is configured such that the working fluid liquids of the mixtures L 1  and L 2  are each initially preheated or precooled to respective selected temperatures before commencement of the storage mode. 
     
     
         12 . A system according to  claim 1 , wherein the working fluid comprises a water/steam mixture. 
     
     
         13 . A system according to  claim 1 , wherein the system is configured such that, during the storage mode, superheat and latent heat are stored along the solid thermal storage medium of the regenerator in a respective upstream superheat transfer region and downstream latent heat transfer region, and wherein a temperature profile of the solid thermal storage medium progressively increases in temperature in both the upstream superheat transfer region and the downstream latent heat transfer region during the storage mode. 
     
     
         14 . A system according to  claim 13 , wherein during the storage mode a temperature difference ΔT between the working fluid vapour and the solid thermal storage medium contacted by the working fluid vapour is generally less than 15° at at least one selected position in the superheat transfer region and/or the latent heat transfer region. 
     
     
         15 . A method of operating an energy storage system using a working fluid that undergoes a phase change, the method comprising:
 storing energy in an energy storage/charging mode comprising:
 evaporating an amount of a saturated liquid L 1  having a temperature T L1  to form a first vapour; 
 doing work by compressing the first vapour to a higher temperature and pressure; and 
 cooling and condensing an amount of the compressed first vapour to a liquid L 2  having a temperature T L2  so that there is a transfer of thermal energy from the first vapour to the liquid L 2 ; and 
   further comprising recovering the energy in an energy recovery/discharging mode comprising:
 evaporating an amount of saturated liquid L 2  at a temperature T L2  to form a second vapour; 
 heating the second vapour to superheat it; 
 expanding the second vapour to a lower pressure and temperature to generate work; and 
 condensing an amount of the expanded second vapour back to the liquid L 1  having the temperature T L1 ; 
   wherein the energy storage system comprises a lower pressure side in which the working fluid is present as a liquid/vapour mixture L 1  at a lower vapour pressure, and a higher pressure side in which the working fluid is present as a liquid/vapour mixture L 2  at a higher vapour pressure, the lower and higher pressure sides being separated by at least one compressor/expander operating so as to transfer vapour between the respective lower and higher pressure sides at the respective lower and higher vapour pressures,   wherein during charging and discharging the temperature TL 2  is greater than the temperature T L1 ,   wherein heating the second vapour uses stored thermal energy, and   wherein the stored thermal energy is stored by direct transfer to thermal media in a regenerator through which gas passes for subsequent return, the regenerator comprising a throughflow regenerator having a solid thermal storage medium so as to allow direct heat transfer between the vapour and solid medium,   wherein all sensible heat transfer upon cooling prior to condensing occurs within the regenerator.   
     
     
         16 . A method of storing and recovering energy comprising:
 in a storage mode, compressing working fluid vapour from a first vessel containing a saturated working liquid/vapour mixture by power machinery;   passing the compressed working fluid, via a regenerator, into a second vessel, where the compressed working fluid condenses into a saturated working liquid/vapour mixture, a temperature and vapour pressure of which increase as more energy is stored therein;   in a recovery mode, recovering stored energy by evaporation of vapour from the saturated working liquid/vapour mixture in the second vessel such that the temperature and vapour pressure of the mixture decrease;   returning the vapour through the regenerator; and   expanding the returned vapour in power machinery so as to produce work before condensing back into the saturated working liquid/vapour mixture of the first vessel,   wherein the regenerator comprises a gas permeable, solid thermal storage medium, and   wherein during the storage mode superheat and latent heat are stored along the solid thermal storage medium in a respective upstream superheat transfer region and downstream latent heat transfer region, and   wherein the temperature profile of the solid thermal storage medium increases in temperature in both the upstream superheat transfer region and the downstream latent heat transfer region during the storage mode.   
     
     
         17 . (canceled) 
     
     
         18 . (canceled) 
     
     
         19 . A system according to  claim 7 , wherein the further regenerator is located inside the first vessel above the working fluid liquid of the mixture L 1 .