Renewable Energy Process and Method Using a Carbon Dioxide Cycle to Produce Work

Abstract

A renewable energy process and method to capture heat from low temperature sources with a refrigeration cycle to produce electricity using the heat content of sources normally unavailable because of their low temperature. This disclosure uses carbon dioxide (CO 2 ) refrigerate, but other refrigerates may be used as well. Heat is transferred from a low temperature source through an indirect heat exchanger (evaporator) to a refrigerating agent that enters the evaporator as a low temperature sub-cooled liquid or saturated mixture and exits as a vapor. The vapor is then superheated by a pollution free method and directed to a turbine for expansion to produce work. The expanded vapor is converted back to liquid without a condenser for return to the evaporator, resulting in a highly efficient system that does not reject heat into the environment.

What is claimed is: 
     
         1 . A method of producing electric power, the method comprising the steps of:
 extracting a heat content from a low temperature heat source, the low temperature heat source comprising one of water, steam, a gas, or a solid;   indirectly transferring said heat content to a process refrigerate within an evaporator, the process refrigerate comprised of carbon dioxide; and   evaporating the process refrigerate within the evaporator with said heat content, wherein the process refrigerate enters the evaporator as a sub-cooled liquid or saturated mixture and exits the evaporator as a vapor; and   facilitating transfer of said heat content to the process refrigerate by supplying the process refrigerate to the evaporator through an expansion valve, wherein pressure is controlled to maintain the process refrigerate saturation temperature at least 5° F. less than the temperature of the low temperature heat source;   directing the process refrigerate vapor from the evaporator to a first path as a first path vapor, a second path as a second pass vapor, and a third path as a third path vapor;   superheating the first path vapor in at least one indirect heat exchanger;   directing the superheated first path vapor to at least one turbine for expansion and producing work;   directing the expanded first path vapor into at least one gas turbo-expander for further expansion and producing work, thereby producing a cooler first path vapor;   directing the cooler first path vapor into at least one venturi nozzle (convergent-divergent nozzle) for further expansion and further cooling to less than the dry ice deposition temperature of −109.3° F.; and   directing a nitrogen gas spray at a temperature of less than −150° F. into the throat of the at least one venturi nozzle to merge with the said cooler first path vapor, thereby producing a mixture of at least 25° F. less than the carbon dioxide dry ice deposition temperature; and   directing the mixture from the at least one venturi nozzle into a deposition-transition vessel, wherein the deposition-vessel is operating in a nitrogen gas atmosphere at a temperature of at least −150° F. and at a pressure so that the partial pressure of the said cooler first path vapor is of least 14.7 psia and a temperature of at least −125° F., thereby facilitating deposition of a first path dry ice;   collecting a full measure of the first path dry ice in the deposition-transition vessel and then venting said nitrogen gas atmosphere to a storage tank; and   directing a portion of said third path vapor to the deposition-transition vessel, thereby elevating the pressure of the deposition-vessel above the triple point pressure and preventing sublimation of said first path dry ice to a vapor and to cause melting of said first path dry ice to a sub-cooled liquid; and   elevating the pressure of said deposition-transition vessel to at least 900 psia with the remaining portion of said third path vapor, thereby completing the transitioning of the first path dry ice to a first path sub-cooled liquid and heating the sub-cooled liquid to a higher temperature;   elevating said second path vapor to a supercritical pressure and superheated temperature in at least one compressor, thereby forming a supercritical second path vapor;   directing the supercritical second path vapor to the at least one indirect heat exchanger, such that heat from the supercritical second path vapor is transferred to the first path vapor and the supercritical second path vapor exits the at least one heat exchanger as supercritical second path liquid; and   directing said supercritical second path liquid to at least one liquid turbo-generator to produce work, thereby producing a second pass sub-cooled liquid at a pressure of at least 1250 psia;   directing the second pass sub-cooled liquid to a mixing manifold;   directing a volume of nitrogen gas at a pressure of at least 1250 psia and temperature of at least 50° F. to the deposition-transition vessel, thereby elevating the pressure of the deposition-vessel to at least 1200 psia to facilitate draining of the sub-cooled liquid;   directing said sub-cooled liquid contents in the deposition-transition vessel to the mixing manifold, wherein said sub-cooled liquid is merged with said second path sub-cooled liquid, thereby regenerating the process refrigerate at a temperature of at least 5° F. above the freezing point temperature of water; and   directing the process refrigerate from the mixing manifold to at least one expansion valve, wherein pressure is controlled to maintain the process refrigerate saturation temperature in the evaporator at least 5° F. below the temperature of the entering low temperature heat source;   directing said process refrigerate from the at least one expansion valve to the evaporator, thereby completing the first, second, and third path cycles.   
     
     
         2 . The method according to  claim 1 , wherein said low temperature heat source comprises one of a cooling water or cooling air of a power plant condenser, a concentrated solar heat from a mirror farm, a geothermal source, a solar heated pond, and a solar storage heat source. 
     
     
         3 . The method according to  claim 1 , further comprising implementing the method with an alternate process; wherein an alternate heat source is used to superheat the first path vapor, thereby, eliminating the second path. 
     
     
         4 . The method according to  claims 1 ,  2 , and  3 , further comprising implementing the method, wherein the alternate heat source to superheat the first path vapor comprises one of a concentrated solar heat from a mirror farm, a geothermal source, an exhaust gas from a boiler, gas turbine, or separately fired heater, flue gas or steam extracted from a power plant boiler, and spent or auxiliary steam extracted from a power plant cycle. 
     
     
         5 . The method according to  claim 1 , wherein said process refrigerate is carbon dioxide or any refrigerate with similar properties. 
     
     
         6 . The method according to  claim 1 , wherein the deposition-transition vessel comprises a plurality of deposition-transition vessels arranged in parallel paths and operated sequentially to provide a continuous first path cycling process by timing of the parallel paths in alternation. 
     
     
         7 . The method according to  claim 1 , the method further comprising: splitting the second path at an outlet of the at least one compressor, wherein a portion of the supercritical second path vapor is supplied to each of the plurality of heat exchangers, such that heat from the supercritical second path vapor is transferred to the first path and the supercritical second path vapor exits each of the plurality of heat exchangers as supercritical second path liquid; and recombining the supercritical second path liquid from said plurality of heat exchangers before entering the at least one turbo-expander. 
     
     
         8 . The method according to  claims 1  and  6 , wherein the plurality of deposition-transition vessels are each enclosed with a jacket, wherein a nitrogen gas atmosphere is maintained at a temperature of less than −150° F. to insulate against heat loss during the first path vapor deposition phase to dry ice and a nitrogen gas atmosphere is maintained at a temperature of at least 50° F. to insulate against heat loss during the first path dry ice transition phase to sub-cooled liquid. 
     
     
         9 . The method according to  claims 1  and  8 , wherein nitrogen gas pressure and temperature conditions in the deposition-transition vessel and jacket are maintained by one or more of a vacuum pump, an ejector device, and a compressor. 
     
     
         10 . The method according to  claims 1  and  3 , further comprising implementing the method as a retrofit in combination with an existing power plant, in combination with a new power plant, or as a stand-alone power plant. 
     
     
         11 . The method according to  claims 1  and  3 , further comprising implementing the method as a retrofit in combination with an existing plant or in combination with a new plant, wherein a cooling water tower is not required when the condenser cooling water is recirculated from the carbon dioxide evaporator back to the condenser. 
     
     
         12 . The method according to  claims 1  and  3 , further comprising implementing the method as a retrofit in combination with an existing plant or in combination with a new plant, wherein a continuous flow of cooling water to the condenser from a nearby water source and a continuous return from the condenser to the nearby water source is not required when the condenser cooling water is recirculated from the carbon dioxide evaporator back to the condenser.