Thermal energy storage system comprising encapsulated phase change material

Abstract

Systems for storing and retrieving thermal energy in encapsulated phase change material are disclosed. Thermal energy is substantially stored and/or retrieved in the form of latent heat. The capsules comprise an outer shell which is impervious to both the heat transfer fluid within which they are submerged and the phase change material encapsulated therewithin. Methods for encapsulating the phase change material are also disclosed.

1 . An apparatus for storing and retrieving thermal energy, said apparatus comprising:
 a tank containing
 a heat transfer fluid; and 
 a plurality of capsules submerged in said heat transfer fluid, wherein each one of said plurality of capsules encapsulates a phase change material; 
   a first heat exchanger in fluid communication with said tank, said first heat exchanger configured for heating said heat transfer fluid; and   a second heat exchanger in fluid communication with said tank, said second heat exchanger configured for cooling said heat transfer fluid.   
     
     
         2 . The apparatus of  claim 1 , wherein
 at least a portion of thermal energy in said heat transfer fluid contained in said tank is transferred to one or more of said plurality of capsules; and   at least a portion of said encapsulated phase change material in said one or more of said plurality of capsules changes from solid to liquid.   
     
     
         3 . The apparatus of  claim 1 , wherein
 at least a portion of said encapsulated phase change material in one or more of said plurality of capsules changes from liquid to solid and releases thermal energy; and   at least a portion of said thermal energy released by said encapsulated phase change material is transferred from said one or more of said plurality of capsules to said heat transfer fluid contained in said tank.   
     
     
         4 . The apparatus of  claim 1 , wherein said heat transfer fluid contained in said tank is of sufficient quantity to substantially fill a substantial number of voids between said plurality of capsules. 
     
     
         5 . The apparatus of  claim 1 , wherein each one of said plurality of capsules comprises an outer shell with a hollow interior, wherein said hollow is at least partially filled with said phase change material. 
     
     
         6 . The apparatus of  claim 5 , wherein said outer shell is impervious to said heat transfer fluid and said phase change material. 
     
     
         7 . The apparatus of  claim 5 , wherein a phase change temperature of said phase change material is less than a phase change temperature of said outer shell. 
     
     
         8 . The apparatus of  claim 5 , wherein said hollow includes a void of sufficient size to accommodate a change in a volume of said phase change material when said phase change material changes from solid to liquid. 
     
     
         9 . The apparatus of  claim 5 , wherein said outer shell is formed with a material selected from the group consisting of sodium chloride, bonded metal particles, sintered metal particles, clay, and mixture of clay and metal. 
     
     
         10 . The apparatus of  claim 5 , wherein each one of said plurality of capsules further comprises a coating encasing said outer shell, wherein said coating substantially fills a substantial number of defects in said outer shell, said defects including cracks, crevices, holes and voids. 
     
     
         11 . The apparatus of  claim 10 , wherein said coating renders said outer shell impervious to said heat transfer fluid and said phase change material. 
     
     
         12 . The apparatus of  claim 1 , wherein said phase change material is selected from the group consisting of sodium nitrate, potassium nitrate, mixture of sodium nitrate and potassium nitrate, inorganic salts and mixtures of salts. 
     
     
         13 . The apparatus of  claim 1 , wherein said plurality of capsules are shaped substantially like a sphere having a diameter in the range of 2 mm to 15 mm. 
     
     
         14 . The apparatus of  claim 1 , wherein said heat transfer fluid heated in said first heat exchanger is
 extracted from said tank at a first location proximate a bottom of said tank; and   returned to said tank at a first location proximate a top of said tank.   
     
     
         15 . The apparatus of  claim 14 , wherein said first heat exchanger is a solar receiver. 
     
     
         16 . The apparatus of  claim 14 , further comprising a control module configured for optimizing heating of said heat transfer fluid in said first heat exchanger. 
     
     
         17 . The apparatus of  claim 16 , wherein said control module optimizes said heating by changing one or more of
 said first location from whereat said heat transfer fluid is extracted from said tank; and   a flow rate of said heat transfer fluid through said first heat exchanger.   
     
     
         18 . The apparatus of  claim 17 , wherein said heat transfer fluid is returned to said tank at a location along a height of said tank whereat a temperature of said fluid within said tank is approximately equal to a temperature of said heat transfer fluid exiting said first heat exchanger. 
     
     
         19 . The apparatus of  claim 16 , wherein said control module is further configured for optimizing a thermocline within said heat transfer fluid within said tank. 
     
     
         20 . The apparatus of  claim 1 , wherein said second heat exchanger comprises
 a third heat exchanger configured for generating superheated steam; and   a fourth heat exchanger configured for generating steam.   
     
     
         21 . The apparatus of  claim 20 , further comprising a control module configured for optimizing
 generation of said superheated steam in said third heat exchanger; and   generation of said steam in said fourth heat exchanger.   
     
     
         22 . The apparatus of  claim 21 , wherein said control module is further configured for optimizing a thermocline within said heat transfer fluid within said tank. 
     
     
         23 . The apparatus of  claim 21 , wherein
 a first stream of said heat transfer fluid is
 extracted from said tank at a second location proximate said top of said tank; and 
 cooled in said third heat exchanger; 
   a second stream of said heat transfer fluid is
 extracted from said tank at a first location between said top and said bottom of said tank; and 
 mixed with said cooled first stream exiting said third heat exchanger to form a stream of mixed fluid; and 
   said stream of mixed fluid is
 cooled in said fourth heat exchanger; and 
 returned to said tank at a second location proximate said bottom of said tank. 
   
     
     
         24 . The apparatus of  claim 23 , wherein said control module optimizes said generation of said superheated steam by changing one or more of
 said second location from whereat said heat transfer fluid is extracted from said tank; and   a flow rate of said first stream of said heat transfer fluid through said third heat exchanger.   
     
     
         25 . The apparatus of  claim 23 , wherein said control module optimizes said generation of said steam by changing one or more of
 said first location between said top and said bottom of said tank from whereat said second stream of heat transfer fluid is extracted from said tank;   a flow rate of said second stream of heat transfer fluid; and   a flow rate of said stream of mixed fluid through said fourth heat exchanger.   
     
     
         26 . The apparatus of  claim 23 , wherein said control module is further configured for extracting said second stream of said heat transfer fluid from a location along a height of said tank whereat a temperature of said heat transfer fluid within said tank is approximately equal to a temperature of said first stream of said heat transfer fluid exiting said third heat exchanger. 
     
     
         27 . The apparatus of  claim 23 , wherein said control module is further configured for returning said stream of mixed fluid to said tank at a location along a height of said tank whereat a temperature of said heat transfer fluid within said tank is approximately equal to a temperature of said stream of mixed fluid exiting said fourth heat exchanger. 
     
     
         28 . The apparatus of  claim 1 , further comprising a control module configured for optimizing a thermocline within said heat transfer fluid within said tank. 
     
     
         29 . The apparatus of  claim 28 , wherein
 heat transfer fluid exiting said first heat exchanger is returned to said tank at a location along a height of said tank whereat a temperature of said heat transfer fluid within said tank is approximately equal to a temperature of said heat transfer fluid exiting said first heat exchanger; and   heat transfer fluid exiting said second heat exchanger is returned to said tank at a location along a height of said tank whereat a temperature of said heat transfer fluid within said tank is approximately equal to a temperature of said heat transfer fluid exiting said second heat exchanger.   
     
     
         30 . The apparatus of  claim 28 , wherein said control module is further configured for
 heating said heat transfer fluid in said first heat exchanger; and   cooling said heat transfer fluid in said second heat exchanger.   
     
     
         31 . The apparatus of  claim 1 , wherein said heat transfer fluid cooled in said second heat exchanger is
 extracted from said tank at a first location proximate a top of said tank; and   returned to said tank at a first location proximate a bottom of said tank.   
     
     
         32 . The apparatus of  claim 31 , further comprising a control module configured for optimizing cooling of said heat transfer fluid in said second heat exchanger. 
     
     
         33 . The apparatus of  claim 32 , wherein said control module optimizes said cooling by changing one or more of
 said first location from whereat said heat transfer fluid is extracted from said tank; and   a flow rate of said heat transfer fluid through said second heat exchanger.   
     
     
         34 . The apparatus of  claim 33 , wherein said heat transfer fluid is returned to said tank at a location along a height of said tank whereat a temperature of said fluid within said tank is approximately equal to a temperature of said heat transfer fluid exiting said second heat exchanger. 
     
     
         35 . The apparatus of  claim 32 , wherein said control module is further configured for optimizing a thermocline within said heat transfer fluid within said tank. 
     
     
         36 . The apparatus of  claim 1 , wherein a phase change temperature of said phase change material encapsulated in said plurality of capsules in a top portion of said tank is greater than a phase change temperature of said phase change material encapsulated in said plurality of capsules in a bottom portion of said tank. 
     
     
         37 . A method of encapsulating a phase change material in a capsule, said method comprising suspending a particle of said phase change material in an air stream;
 coating an entire surface of said suspended particle with at least one layer of a first material, said step of coating comprising
 atomizing a solution of said first material; 
 depositing said atomized first material onto said surface of said suspended particle; and 
 drying said first material deposited on said suspended particle; 
   coating an entire surface of said layer of said first material with at least one layer of a second material; and   encapsulating said phase change material within a shell formed by said second material, said step of encapsulating comprising
 heating said particle coated with said first material and said second material; 
 decomposing said first material; and 
 vaporizing said first material. 
   
     
     
         38 . The method of  claim 37 , wherein said capsule is shaped substantially like a sphere having a diameter in the range of 2 mm to 15 mm. 
     
     
         39 . The method of  claim 37 , wherein said step of encapsulating renders said second material impervious. 
     
     
         40 . The method of  claim 37 , further comprising rendering said second material impervious by coating an entire surface of said layer of said second material with one or more layers of a third material after said step of encapsulation. 
     
     
         41 . The method of  claim 40 , wherein said second material and said third material are same. 
     
     
         42 . The method of  claim 37 , further comprising substantially filling a substantial number of defects in said layer of said second material by applying one or more layers of a third material after the step of encapsulating, wherein said defects include cracks, crevices, holes and voids. 
     
     
         43 . The method of  claim 42 , wherein said second material and said third material are same. 
     
     
         44 . The method of  claim 37 , wherein said phase change material is selected from the group consisting of sodium nitrate, potassium nitrate, mixture of sodium nitrate and potassium nitrate, and inorganic salts. 
     
     
         45 . The method of  claim 37 , wherein said first material is a sacrificial compound having a decomposition temperature generally less than a phase change temperature of said phase change material and a phase change temperature of said second material, and wherein the step of encapsulating generally comprises thermally decomposing said first material. 
     
     
         46 . The method of  claim 45 , wherein said sacrificial compound is selected from the group consisting of an organic polymer, hydroxy-propyl methyl cellulose, carboxy-methyl cellulose, ethyl cellulose, polyethelene and poly vinyl chloride. 
     
     
         47 . The method of  claim 37 , wherein said second material is selected from the group consisting of sodium chloride, bonded metal particles, sintered metal particles, clay, and mixture of clay and metal. 
     
     
         48 . The method of  claim 37 , further comprising applying one or more additional layers of said first material before coating with said second material. 
     
     
         49 . The method of  claim 48 , further comprising rendering said second material impervious by coating an entire surface of said layer of said second material with one or more layers of a third material after said step of encapsulation. 
     
     
         50 . The method of  claim 48 , further comprising substantially filling a substantial number of defects in said layer of said second material by applying one or more layers of a third material after the step of encapsulating, wherein said defects include cracks, crevices, holes and voids. 
     
     
         51 . The method of  claim 48 , further comprising applying one or more additional layers of said second material before the step of encapsulating. 
     
     
         52 . The method of  claim 51 , wherein said step of encapsulating renders said second material impervious. 
     
     
         53 . The method of  claim 51 , further comprising rendering said second material impervious by coating an entire surface of said layer of said second material with one or more layers of a third material after said step of encapsulation. 
     
     
         54 . The method of  claim 51 , further comprising substantially filling a substantial number of defects in said layer of said second material by applying one or more layers of a third material after the step of encapsulating, wherein said defects include cracks, crevices, holes and voids. 
     
     
         55 . The method of  claim 37 , further comprising applying one or more additional layers of said second material before the step of encapsulating. 
     
     
         56 . The method of  claim 55 , wherein said step of encapsulating renders said second material impervious. 
     
     
         57 . The method of  claim 55 , further comprising rendering said second material impervious by coating an entire surface of said layer of said second material with one or more layers of a third material after said step of encapsulation. 
     
     
         58 . The method of  claim 55 , further comprising substantially filling a substantial number of defects in said layer of said second material by applying one or more layers of a third material after the step of encapsulating, wherein said defects include cracks, crevices, holes and voids. 
     
     
         59 . The method of  claim 37 , further comprising
 submerging a plurality of capsules in a heat transfer fluid, wherein each one of said plurality of capsules encapsulates said phase change material;   transferring at least a portion of thermal energy in said heat transfer fluid to one or more of said plurality of capsules; and   subjecting at least a portion of said phase change material encapsulated in said one or more of said plurality of capsules to change from solid to liquid.   
     
     
         60 . The method of  claim 59 , further comprising transferring thermal energy to said heat transfer fluid from a means other than said phase change material. 
     
     
         61 . The method of  claim 59 , further comprising
 submerging a plurality of capsules in a heat transfer fluid, wherein each one of said plurality of capsules encapsulates said phase change material;   subjecting at least a portion of said phase change material encapsulated in one or more of said plurality of capsules to change from liquid to solid and release thermal energy; and   transferring at least a portion of said thermal energy release by said phase change material form one or more of said plurality of capsules to said heat transfer fluid.   
     
     
         62 . The method of  claim 61 , further comprising
 transferring thermal energy to said heat transfer fluid from a first means other than said phase change material; and   transferring thermal energy from said heat transfer fluid to a second means other than said phase change material.   
     
     
         63 . The method of  claim 37 , further comprising
 submerging a plurality of capsules in a heat transfer fluid, wherein each one of said plurality of capsules encapsulates said phase change material;   subjecting at least a portion of said phase change material encapsulated in one or more of said plurality of capsules to change from liquid to solid and release thermal energy; and   transferring at least a portion of said thermal energy release by said phase change material form one or more of said plurality of capsules to said heat transfer fluid.   
     
     
         64 . The method of  claim 63 , further comprising transferring thermal energy from said heat transfer fluid to a means other than said phase change material. 
     
     
         65 . A method of encapsulating a phase change material in a capsule, said method comprising
 suspending a particle of said phase change material in an air stream;   coating an entire surface of said suspended particle with at least one layer of a mixture of
 a binder and metal particles, said step of coating comprising 
 depositing said mixture onto said surface of said suspended particle; and 
 drying said mixture deposited on said suspended particle; 
   encapsulating said phase change material within said capsule, said step of encapsulating comprising
 heating said particle coated with said mixture; 
 vaporizing said binder; and 
 sintering said metal particles to form a shell encapsulating said phase change material. 
   
     
     
         66 . The method of  claim 65 , wherein said shell is shaped substantially like a sphere having a diameter in the range of 2 mm to 15 mm. 
     
     
         67 . The method of  claim 65 , wherein said step of encapsulating renders said shell impervious. 
     
     
         68 . The method of  claim 65 , further comprising rendering said shell impervious by coating an entire surface of said shell with a sealant after said step of encapsulating. 
     
     
         69 . The method of  claim 65 , further comprising substantially filling a substantial number of defects in said shell by applying one or more layers of a sealant after the step of encapsulating, wherein said defects include cracks, crevices, holes and voids. 
     
     
         70 . The method of  claim 65 , wherein said phase change material is selected from the group consisting of sodium nitrate, potassium nitrate, mixture of sodium nitrate and potassium nitrate, and inorganic salts. 
     
     
         71 . The method of  claim 65 , wherein said binder is a sacrificial compound having a decomposition temperature generally less than a phase change temperature of said phase change material, and wherein the step of encapsulating generally comprises thermally decomposing said binder. 
     
     
         72 . The method of  claim 71 , wherein said sacrificial compound is selected from the group consisting of an organic polymer, clay, and mixture of clay and metal. 
     
     
         73 . The method of  claim 65 , further comprising applying one or more additional layers of said mixture before said step of encapsulating. 
     
     
         74 . The method of  claim 65 , further comprising sequentially repeating said steps of coating and encapsulating in an alternating manner until a pre-determined number of shells have been formed, wherein encapsulating is a final step. 
     
     
         75 . The method of  claim 74 , further comprising applying a sealant after encapsulating and before coating. 
     
     
         76 . The method of  claim 74 , comprising rendering said capsule impervious by coating an entire surface of said capsule with a sealant after said final step of encapsulating. 
     
     
         77 . The method of  claim 74 , further comprising substantially filling a substantial number of defects in said shell by applying one or more layers of a sealant after the step of encapsulating, wherein said defects include cracks, crevices, holes and voids. 
     
     
         78 . The method of  claim 65 , further comprising
 submerging a plurality of capsules in a heat transfer fluid, wherein each one of said plurality of capsules encapsulates said phase change material;   transferring at least a portion of thermal energy in said heat transfer fluid to one or more of said plurality of capsules; and   subjecting at least a portion of said phase change material encapsulated in said one or more of said plurality of capsules to change from solid to liquid.   
     
     
         79 . The method of  claim 78 , further comprising transferring thermal energy to said heat transfer fluid from a means other than said phase change material. 
     
     
         80 . The method of  claim 78 , further comprising
 submerging a plurality of capsules in a heat transfer fluid, wherein each one of said plurality of capsules encapsulates said phase change material;   subjecting at least a portion of said phase change material encapsulated in one or more of said plurality of capsules to change from liquid to solid and release thermal energy; and   transferring at least a portion of said thermal energy release by said phase change material form one or more of said plurality of capsules to said heat transfer fluid.   
     
     
         81 . The method of  claim 80 , further comprising
 transferring thermal energy to said heat transfer fluid from a first means other than said phase change material; and   transferring thermal energy from said heat transfer fluid to a second means other than said phase change material.   
     
     
         82 . The method of  claim 65 , further comprising
 submerging a plurality of capsules in a heat transfer fluid, wherein each one of said plurality of capsules encapsulates said phase change material;   subjecting at least a portion of said phase change material encapsulated in one or more of said plurality of capsules to change from liquid to solid and release thermal energy; and   transferring at least a portion of said thermal energy release by said phase change material form one or more of said plurality of capsules to said heat transfer fluid.   
     
     
         83 . The method of  claim 82 , further comprising transferring thermal energy from said heat transfer fluid to a means other than said phase change material.