Thermal Storage System

Abstract

An apparatus for storing and retrieving thermal energy from a phase change material including a plurality of heat exchangers. Each one of the plurality of heat exchangers provides the means for transferring energy between the phase change material on a primary side of the heat exchanger and a fluid on a secondary side of the heat exchanger. The phase change material is a mixture of two or more inorganic salts.

1 . An apparatus for storing and retrieving thermal energy, the apparatus comprising:
 a tank containing a phase change material;   a first heat exchanger fluidly connected in series with a second heat exchanger, wherein
 the phase change material from the tank enters a primary side of the second heat exchanger; 
 the phase change material flows through and exits the second heat exchanger and enters a primary side of the first heat exchanger; 
 the phase change material flows through and exits the first heat exchanger and enters the tank; 
 a first fluid enters and flows through a secondary side of the first heat exchanger wherein energy is transferred between the phase change material and the first fluid; and 
 the first fluid exits the first heat exchanger and enters and flows through a secondary side of the second heat exchanger wherein energy is transferred between the phase change material and the first fluid; and 
   a third heat exchanger fluidly connected in series with a fourth heat exchanger, wherein
 the fourth heat exchanger is embedded within the phase change material within the tank; 
 a second fluid from an energy source enters and flows through a secondary side of the third heat exchanger; 
 the second fluid exits the third heat exchanger and enters and flows through a secondary side of the fourth heat exchanger wherein energy is transferred between the second fluid and the phase change material surrounding the secondary side of the fourth heat exchanger; 
 the second fluid exits the fourth heat exchanger and returns to the energy source; 
 the phase change material from the tank enters and flows through a primary side of the third heat exchanger wherein energy is transferred between the phase change material and the second fluid; and 
 the phase change material exits the third heat exchanger and enters the tank. 
   
     
     
         2 . The apparatus of  claim 1 , wherein the phase change material comprises a composition in a thermodynamic equilibrium state of liquid and solid. 
     
     
         3 . The apparatus of  claim 1 , wherein
 each of the first, the second and the third heat exchangers comprise shell and tube heat exchangers;   the primary side of each of the first, the second and the third heat exchangers comprises a shell; and   the secondary side of each of the first, the second and the third heat exchangers comprises a plurality of tubes.   
     
     
         4 . The apparatus of  claim 1 , wherein
 the first fluid entering the first heat exchanger includes feed water;   the first fluid exiting the first heat exchanger and entering the second heat exchanger comprises saturated steam; and   the first fluid exiting the second heat exchanger comprises superheated steam.   
     
     
         5 . The apparatus of  claim 4 , wherein the superheated steam is used for generating electricity. 
     
     
         6 . The apparatus of  claim 1 , wherein
 the secondary side of the fourth heat exchanger comprises a plurality of tubes embedded within the phase change material; and   the second fluid flows through the plurality of tubes.   
     
     
         7 . The apparatus of  claim 6 , wherein
 the phase change material comprises a mixture of at least two or more inorganic salts.   
     
     
         8 . The apparatus of  claim 7 , wherein the mixture comprises 83.2 percent by weight sodium nitrate and 16.8 percent by weight sodium hydroxide. 
     
     
         9 . The apparatus of  claim 1 , wherein the phase change material comprises a dilute eutectic composition. 
     
     
         10 . The apparatus of  claim 9 , wherein the dilute eutectic composition comprises a mixture of at least two or more inorganic salts. 
     
     
         11 . The apparatus of  claim 10 , wherein the dilute eutectic composition comprises a dilute eutectic composition in sodium nitrate including sodium nitrate in the range of 98 to 99 percent by weight and sodium hydroxide in the corresponding range of 2 to 1 percent by weight. 
     
     
         12 . The apparatus of  claim 10 , wherein
 the inside surface of the shell for each one of the first, the second and the third heat exchanger comprises a coating of a salt phobic compound; and   the outside surfaces of the plurality of tubes in each one of the first, the second, the third and the fourth heat exchanger comprise a coating of the salt phobic compound.   
     
     
         13 . The apparatus of  claim 1 , wherein the phase change material within the tank is thermally stratified. 
     
     
         14 . The apparatus of  claim 13 , wherein
 the phase change material entering the second heat exchanger comprises the phase change material extracted from near a top of the tank; and   the phase change material exiting the first heat exchanger enters the tank near a bottom of the tank.   
     
     
         15 . The apparatus of  claim 14 , wherein
 the phase change material entering the second heat exchanger comprises a liquid state of the phase change material; and   the phase change material entering the tank near the bottom of the tank comprises thermodynamic equilibrium state of liquid and solid.   
     
     
         16 . The apparatus of  claim 13 , wherein
 the phase change material entering the third heat exchanger comprises the phase change material extracted from near the bottom of the tank; and   the phase change material exiting the third heat exchanger enters the tank near the top of the tank.   
     
     
         17 . The apparatus of  claim 16 , wherein
 the phase change material entering the third heat exchanger comprises thermodynamic equilibrium state of liquid and solid; and   the phase change material exiting the third heat exchanger comprises the phase change material in the liquid state.   
     
     
         18 . The apparatus of  claim 13 , wherein
 the phase change material entering the third heat exchanger comprises the phase change material in the liquid state; and   the phase change material exiting the third heat exchanger comprises the phase change material in a saturated state.   
     
     
         19 . The apparatus of  claim 18 , wherein the saturated state is a thermodynamic equilibrium state of liquid and vapor. 
     
     
         20 . The apparatus of  claim 18 , wherein the saturated state is vapor. 
     
     
         21 . The apparatus of  claim 13 , wherein
 the phase change material entering the third heat exchanger comprises the phase change material in the liquid state; and   the phase change material exiting the third heat exchanger comprises the phase change material in a superheated vapor state.   
     
     
         22 . The apparatus of  claim 13 , wherein the fourth heat exchanger is positioned near the bottom of the tank. 
     
     
         23 . The apparatus of  claim 22 , wherein the phase change material near the bottom of the tank comprises thermodynamic equilibrium state of liquid and solid. 
     
     
         24 . The apparatus of  claim 1 , wherein the energy source includes a heating source. 
     
     
         25 . The apparatus of  claim 1 , wherein the energy source includes a cooling source. 
     
     
         26 . A method for storing and retrieving thermal energy from a phase change material within a tank, the method comprising the steps of:
 transferring energy from the phase change material to a first fluid; and   transferring energy from a second fluid to the phase change material.   
     
     
         27 . The method of  claim 26 , further comprising the steps of:
 flowing the first fluid through a secondary side of a first heat exchanger;   flowing the first fluid exiting the first heat exchanger through a secondary side of the second heat exchanger;   extracting the phase change material from the tank;   flowing the phase change material through a primary side of the second exchanger;   transferring energy from the phase change material flowing through the second heat exchanger to the first fluid flowing through the second heat exchanger;   flowing the phase change material exiting the second heat exchanger through a primary side of the first heat exchanger;   transferring energy from the phase change material flowing through the first heat exchanger to the first fluid flowing through the first heat exchanger; and   returning the phase change material exiting the first heat exchanger to the tank.   
     
     
         28 . The method of  claim 27 , further comprising the steps of:
 extracting the phase change material from the tank;   flowing the phase change material through a primary side of a third heat exchanger;   returning the phase change material from the third heat exchanger to the tank;   extracting the second fluid from an energy source and flowing the second fluid through a secondary side of the third heat exchanger;   transferring energy from the second fluid flowing through the third heat exchanger to the phase change material flowing through the third heat exchanger;   flowing the second fluid exiting the third heat exchanger through a secondary side of a fourth heat exchanger, wherein the secondary side of the fourth heat exchanger is embedded within the phase change material in the tank;   transferring energy from the second fluid flowing through the fourth heat exchanger to the phase change material surrounding the secondary side of the fourth heat exchanger; and   returning the second fluid exiting the fourth heat exchanger to the energy source.   
     
     
         29 . The method of  claim 28 , further comprising the step of maintaining the phase change material in a thermodynamic equilibrium state of liquid and solid. 
     
     
         30 . The method of  claim 29 , further comprising the step of maintaining the phase change material in a thermally stratified state. 
     
     
         31 . The method of  claim 30 , wherein
 the step of flowing the phase change material through the second heat exchanger further comprises the step of extracting the phase change material from near a top of the tank; and   the step of returning the phase change material exiting the first heat exchanger to the tank further comprises the step of returning the phase change material near a bottom of the tank.   
     
     
         32 . The method of  claim 31 , wherein
 the step of flowing the phase change material through the third heat exchanger further comprises the step of extracting the phase change material from near the bottom of the tank; and   the step of returning the phase change material exiting the third heat exchanger to the tank further comprises the step of returning the phase change material near the top of the tank.