Thermal energy storage systems and methods

Abstract

Thermal energy storage systems and methods are provided including a bed, a blend of aggregates packed in the bed, and a high-density heat transfer fluid flowing through the blend of aggregates. The blend of aggregates includes rock materials and may also include non-rock materials. The heat transfer fluid flows through the blend of aggregates such that heat is transferred between the heat transfer fluid and the blend of aggregates. The porosity of the aggregates increases heat transfer and the high density of the heat transfer fluid reduces the pressure gradient of the heat transfer fluid. In exemplary embodiments, the heat transfer fluid is a liquid comprised of carbon-based molecules. Methods of safely storing and releasing energy are provided in which axial thermal conductivity of the bed is minimized and inadvertent pressure release failures are mitigated.

What is claimed is: 
     
         1 . A thermal energy storage system comprising:
 a bed;   a blend of aggregates packed in the bed, the blend including rock materials; and   a high-density heat transfer fluid flowing through the blend of aggregates such that heat is transferred between the heat transfer fluid and the blend of aggregates;   wherein porosity of the aggregates increases heat transfer and the high density of the heat transfer fluid reduces the axial pressure gradient of the heat transfer fluid.   
     
     
         2 . The system of  claim 1  wherein the heat transfer fluid is a liquid with a fluid density of at least 0.4 g/cc at at least one location in the packed bed 
     
     
         3 . The system of  claim 1  wherein the blend of aggregates further includes non-rock materials. 
     
     
         4 . The system of  claim 1  wherein the porosity is less than about 30%. 
     
     
         5 . The system of  claim 4  wherein the porosity is about 10%. 
     
     
         6 . The system of  claim 1  wherein the blend of aggregates comprises one or more of: sand, pebbles, washed rock, quartz, and magnetite. 
     
     
         7 . The system of  claim 1  wherein the packed bed stores energy at temperatures less than about 325° C. 
     
     
         8 . The system of  claim 7  wherein the packed bed stores energy at temperatures less than about 250° C. 
     
     
         9 . The system of  claim 8  wherein the packed bed stores energy at temperatures less than about 150° C. 
     
     
         10 . The system of  claim 1  wherein the packed bed stores energy at temperatures less than about 425° C. 
     
     
         11 . The system of  claim 1  wherein the bed is a vertical cylinder. 
     
     
         12 . The system of  claim 1  further comprising filtering media at a base or top of the bed. 
     
     
         13 . The system of  claim 1  wherein the bed comprises means to facilitate the management of rock particulate contamination. 
     
     
         14 . The system of  claim 1  wherein the surface area of aggregate per unit volume is about 215 m −1 . 
     
     
         15 . The system of  claim 1  wherein the heat transfer fluid has a thermal conductivity of less than about 10% of the aggregates. 
     
     
         16 . A thermal energy storage system comprising:
 a bed including a fluid inlet and a fluid outlet;   a blend of aggregates packed in the bed, the blend including rock materials and non-rock materials; and   a heat transfer fluid flowing through the blend of aggregates such that heat is transferred between the heat transfer fluid and the blend of aggregates, the heat transfer fluid being a liquid comprised of carbon-based molecules.   
     
     
         17 . The system of  claim 16  wherein the heat transfer fluid does not freeze at temperatures above 100° C. 
     
     
         18 . The system of  claim 16  wherein the fluid viscosity of the heat transfer fluid ensures fluid pressure drop from the fluid inlet to the fluid outlet is less than about 5 psid under nominal conditions and less than about 100 psid under cold start-up conditions. 
     
     
         19 . The system of  claim 16  wherein the vapor pressure of the heat transfer fluid is less than twice atmospheric pressure at the highest design temperature of any portion of the bed in direct contact with the heat transfer fluid. 
     
     
         20 . The system of  claim 16  wherein the vapor pressure of the heat transfer fluid is less than about 300 psia at the highest design temperature of any portion of the bed in direct contact with the heat transfer fluid. 
     
     
         21 . A method of storing and releasing energy, comprising:
 packing a blend of aggregates in a bed to minimize axial thermal conductivity of the bed, the blend including rock materials and non-rock materials;   providing a liquid organic heat transfer fluid having a thermal conductivity of less than about 10% of the thermal conductivity of the blend of aggregates; and   directing the heat transfer fluid through the blend of aggregates such that heat is transferred between the heat transfer fluid and the blend of aggregates;   wherein over 85% of stored energy can be extracted in a charge/discharge cycle in less than eighteen hours.   
     
     
         22 . The method of  claim 21  wherein over 85% of stored energy can be extracted in a charge/discharge cycle in less than six hours. 
     
     
         23 . The method of  claim 21  further comprising slowing the rate of release of stored energy by at least one order of magnitude.