Systems and methods for integrating concentrated solar thermal and geothermal power plants using multistage thermal energy storage

Abstract

Systems and methods are described for removing thermal energy from power plant heat engines, storing, and then recovering the stored energy. The removed or stored thermal energy can raise the enthalpy of lower temperature heat sources for utilization in electric power generating plants. Included also are systems and methods for integrating and cascading multistage thermal energy storage to supply multiple heat users at different temperatures. The methods apply to power plants utilizing thermal energy from concentrated solar thermal energy collectors, fuel-fired heaters, or gas turbine-generator heat recovery units. Several embodiments use the stored energy to extend solar thermal power plant operation, particularly the bottom power cycle. Other embodiments extract thermal energy from a solar thermal power plant, storing a portion of the energy extracted, and recovering this thermal energy to continuously heat geothermal fluids utilized in a geothermal power plant, and heat geothermal power plant working fluids.

1 - 108 . (canceled) 
     
     
         109 . A method for storing thermal energy comprising heating a thermal storage media using thermal energy contained within hot partially expanded working fluids extracted from a heat engine expansion step in either a Rankine cycle or a Kalina cycle thermal power plant. 
     
     
         110 . The method of  claim 109 , wherein the hot working fluids exchange thermal energy into the storage media. 
     
     
         111 . The method of  claim 109 , wherein the Rankine cycle working fluids comprise water and steam, and the hot working fluids extracted are predominantly steam flows at multiple pressures and temperatures. 
     
     
         112 . The method of  claim 111 , wherein the heat engine is a steam expansion turbine that drives an electricity generator in the power plant. 
     
     
         113 . The method of  claim 110 , further comprising the step of using thermal energy to charge multiple stages of thermal energy storage; charging storage modules at each stage using either the extracted working fluids or the heat transfer fluid in a temperature range chosen for that stage; such that at the end of the charge period, the storage media in the storage modules in each stage has been heated to a different temperature range. 
     
     
         114 . The method of  claim 113 , wherein at least one flow of extracted working fluid exchanges thermal energy into the storage media in the temperature range chosen for that stage. 
     
     
         115 . The method of  claim 113 , wherein the heat engine is an expansion turbine and further comprising the step of extracting flows of hot working fluids from the selected stages of the turbine; then using the flows to heat the heat transfer fluid sequentially in series of heat exchangers; selecting each extracted fluid flow to provide the heat duty required by each heat exchanger to achieve the desired temperature change. 
     
     
         116 . The method of  claim 115 , further comprising the step of heating the heat transfer fluid using working fluids with temperatures in the range of the lowest temperature stage; then using a portion of the heat transfer fluid flow to heat the lowest temperature storage stage; followed by heating the remainder of the heat transfer fluid flow using working fluids with temperatures in the next higher temperature range; then using a portion of the heat transfer fluid flow to heat the next higher temperature storage stage; and so forth with additional sequential heat exchange using higher temperature working fluids to increase the temperature of the heat transfer fluid coupled with using a portion of the heat transfer fluid flow to charge sequentially higher temperature stages of the thermal energy storage; until the remaining heat transfer fluid flow is heated to highest temperature range that can be reached using thermal energy from the highest temperature working fluids in thermal power plant; then using at least a portion of the remaining heat transfer fluid to heat a storage stage to that temperature range. 
     
     
         117 . The method of  claim 113 , further comprising the step of using thermal energy contained in hot vaporized working fluid from the boiler in the thermal power plant to charge at least one of the thermal energy storage modules in a storage stage such that the storage stage temperature range approaches the boiler temperature. 
     
     
         118 . Method of  claim 113 , further comprising the step of using thermal energy from heat source at a higher temperature than the boiler temperature to charge at least one of the thermal energy storage modules in a storage stage such that the storage stage temperature range approaches the heat source temperature. 
     
     
         119 . Method of  claim 118 , wherein the thermal energy charges the storage stage using the heat transfer fluid, and further comprising the step of using a separate high temperature circulation loop wherein: heat transfer fluid from a surge vessel is pumped to a heat exchanger train; and the heat transfer fluid is heated in a heat exchanger train having of at least one heat exchanger using hot working fluids extracted from the thermal power plant; and the heat transfer fluid is heated further by a higher temperature heat source exchanging thermal energy into the heat transfer fluid; and the fully heated heat transfer fluid is circulated through at least two thermal energy storage modules in series, exchanging heat into the storage modules and recharging each module through the temperature range of at least one storage stage. 
     
     
         120 . The method of  claim 118 , wherein the thermal energy is transferred to storage using molten salt and the thermal energy storage consists of molten salt storage. 
     
     
         121 . The method of  claim 113 , further comprising the step of charging the different stages of thermal energy storage in a cascade charge method with at least two cascade steps; with a discharged or partially discharged storage module heated and charged at a lower temperature stage in one step; then switched into a different position in the cascade, then heated and charged at a higher temperature stage in a second step. 
     
     
         122 . The method of  claim 121 , wherein the fluid transferring thermal energy into the storage media flows through at least two storage modules; and further comprising the step of charging the first module in a higher temperature cascade step; then charging the following module in a sequentially lower temperature cascade charge step. 
     
     
         123 . The method of  claim 122 , further comprising the step of adding more cascade steps at higher temperature ranges; wherein the thermal energy storage is charged in at least one of the additional cascade steps using heat transfer fluid heated by one of the heat sources for the thermal power plant. 
     
     
         124 . The method of  claim 123 , wherein at least one of the heat sources is one of the following:
 concentrated solar thermal energy collectors that concentrate solar energy and converts the solar energy to thermal energy, which then heats a heat transfer fluid that feeds thermal energy to the thermal power plant;   a fired heater;   a heat recovery unit that recovers heat from flue gas of a fired heater;   a heat recovery unit recovering thermal energy from the exhaust working fluid from a Brayton cycle or Ericsson cycle heat engine.   
     
     
         125 . The method of  claim 123 , wherein the thermal energy storage has a mixture of storage modules using different energy storage media, including at least one of the following:
 the storage module uses sensible heat storage material as the storage media;   the storage module uses a phase change material as the storage media;   the module uses phase change material and stores thermal energy at a high enough temperature to heat the boiler in the thermal power plant.   
     
     
         126 . The method of  claim 109 , further comprising the step of recovering thermal energy from the storage media using power plant working fluids or a heat transfer fluid. 
     
     
         127 . The method of  claim 126 , further comprising the step of using the heated fluids and using additional extracted hot working fluids to provide a continuous supply of thermal energy to users; wherein the thermal energy is supplied by utilizing either the heated working fluids directly; or using either the heated working fluids or the heated heat transfer fluid in a heat exchanger to provide thermal energy. 
     
     
         128 . The method of  claim 127 , further comprising the step of recovering thermal energy from storage media in stages, with each stage recovering thermal energy in a different temperature range. 
     
     
         129 . The method of  claim 128 , further comprising the step of using a cascade discharge method that recovers the thermal energy with at least two cascade steps; such that a charged storage module discharges thermal energy at a higher temperature stage in one step; then the storage module is switched into a different position in the cascade and discharges thermal energy at a lower temperature stage in a second step. 
     
     
         130 . The method of  claim 129 , wherein fluid recovering thermal energy from the storage media flows through at least two storage modules; and further comprising the step of recovering thermal energy from the first module in a lower temperature cascade discharge step; then recovering thermal energy from the following modules in sequentially higher temperature cascade discharge steps.