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.sub.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.

Claims

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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 schematically illustrates this disclosure to capture heat from low temperature sources to produce pollution-free work and to convert the expanded first path vapor back to sub-cooled liquid without a condenser.

[0022] FIG. 1A schematically illustrates the disclosure for applications in which higher temperature heat sources are available to superheat and reheat path A; thereby, eliminating the path B circuit.

[0023] FIG. 2 is a marked CO.sub.2 pressure-enthalpy (P-H) diagram to illustrate an approximate example of the disclosed cycle.

[0024] FIG. 3 depicts a phase diagram showing the physical states of CO.sub.2 under different pressure and temperatures.

DETAILED DESCRIPTION

[0025] FIG. 1 schematically illustrates process 1 of this disclosure. During startup, a sub-cooled liquid process refrigerate at a temperature of at least 5 F. above the freezing point temperature of water (32 F.) is directed from storage tank area 50 by a pump to expansion valve 34, which controls pressure to evaporator 30 and to provide a saturation temperature of at least 5 F. below the entering temperature of the low temperature source 51. A heat content is transferred from low temperature source 51 to the process refrigerate in evaporator 30, after which the process refrigerate exits evaporator 30 as a saturated or slightly superheated vapor. Remaining heat content in low temperature source 51 is returned to the source through 51R if applicable.

[0026] The process refrigerate vapor leaving evaporator 30 is then divided into three separate flow paths (A, B, and C). Path A is directed to first stage indirect heater 30-1 for superheating. Path B is directed to the inlet of compressor 31 wherein it is compressed into a supercritical pressure vapor and superheated by the heat of compression. Compressor 31 is driven by electric motor M during startup and low loads and then switched to turbine 32-2 drive by hydraulic coupling 53 during higher loads. Path B exiting compressor 31 is split into two paths (B1 and B2). Path B1 is directed to first stage indirect heater 30-1, wherein path A is superheated for supplying turbine 32-1 for isentropic expansion to produce work through electric generator G1. Path A exiting turbine 32-1 flows to second stage indirect heater 30-2 for reheating to a higher superheat temperature by path B2. Path A exiting indirect heater 30-2 flows to reheat turbine 32-2 for isentropic expansion and to produce work through electric generator G2.

[0027] Path B1 and path B2 exit indirect heaters 30-1 and 30-2 and recombine to form path B supercritical pressure liquid for directing to liquid turbo-expander 32-3 to produce work through electric generator G3; thereby lowering path B pressure and forming a sub-cooled liquid to merge in mixing manifold 41 with the sub-cooled liquid leaving D-T vessel 33-1.

[0028] Path A superheated vapor leaving final reheat turbine 32-2 is converted back to a sub-cooled liquid in D-T vessel 33-1. All D-T vessels (33-1, 33-2, and 33-3) and associated equipment are duplicates as are the deposition and transition details. Path A leaving reheat turbine 32-2 is directed to gas turbo-expander 32-4, wherein the superheated vapor is isentropically expanded and cooled to a temperature of 80 F. at a pressure of 25 psia; thereby, producing a cooler path A vapor and producing work through electric generator G4. The cooler path A vapor is then directed to manifold header 38 for distribution to parallel trains of D-T vessels 33. In this disclosure, D-T vessels 33-1, 33-2 and 33-3 are referred to collectively as D-T vessels 33. This portion of the cycle is a batch process with the parallel trains operated sequentially to provide a continuous overall process in vapor deposition to dry ice and then dry ice transition to sub-cooled liquid for cycling back to evaporator 30 as the process refrigerate.

[0029] The cooler path A vapor leaving manifold 38 is directed through a selected shut-off valve 35 to venturi nozzle 36 at the inlet to D-T vessel 33-1, wherein path A vapor is isentropically expanded to a pressure just above atmospheric pressure, resulting in a path A vapor temperature near the dry ice deposition of 109.3 F. as may be referenced on FIGS. 3 and 4. Those skilled in the arts may reference a CO.sub.2 T-S (Temperature-Entropy) diagram, which may better demonstrate low pressure and temperature isentropic expansion. To ensure a total phase change to dry ice, a much cooler nitrogen gas spray S.sub.N2 is introduced through control valve 46 to the throat of venturi nozzle 36 to cool the mixture to less than 125 F. To further facilitate deposition, D-T vessel 33-1 is controlled in a nitrogen gas atmosphere, by valve 43 in connection V.sub.N2 and valve 49 in vent V.sub.33, to a temperature of at least 150 F. and at a pressure so that the entering CO.sub.2 vapor partial pressure is at least 14.7 psia. Also, D-T vessel jacket 33J is operated in a nitrogen gas atmosphere at less than 150 F. through control valve 45 in connection J.sub.N2 and control valve 48 in vent connection JV. After the selected D-T vessel 33-1 has achieved its full measure of dry ice of snow-like consistency, shut-off valve 35 is closed and nitrogen gas in D-T vessel 33-1 is vented back to storage tank area 52 through control valve 49 in vent connection V.sub.33.

[0030] With D-T vessel 33-1 isolated, a portion of path C pressurizes D-T vessel 33-1 above 100 psia through connection PC and control valve 44 to prevent sublimation of dry ice to vapor and facilitate transition to a sub-cooled liquid. Then, D-T vessel 33-1 is heated and pressurized to 900 psia by the remaining portion of path C vapor through connection PC and valve 44, thereby completing the transitioning of dry ice to sub-cooled liquid. Nitrogen gas was previously introduced to jacket 33J at a temperature of at least 50 F. with control valve 45 in connection J.sub.N2 to support the transition phase. Introducing path C vapor near the bottom of D-T vessel 33-1 and bubbling it through the sub-cooled liquid will provide more effective heating.

[0031] Draining of D-T vessel 33-1 is facilitated by reintroducing nitrogen gas at a pressure of at least 1250 psia and temperature of at least 50 F. through connection V.sub.N2 and valve 43, thereby increasing the pressure of D-T vessel 33-1 to at least 1200 psia and replacing the sub-cooled liquid with nitrogen as it drains. Then, drain control valve 37 is opened to direct D-T vessel 33-1 sub-cooled liquid to drain manifold 39 and mixing manifold 41 for merging with the sub-cooled liquid from path B. Drain control valve 37 is closed when D-T vessel 33-1 is drained of sub-cooled liquid.

[0032] D-T vessel 33-1 is prepared for its next deposition batch by placing valve 43 in connection V.sub.N2 into service along with valve 49 in vent connection V.sub.33 to control operating pressure and temperature using nitrogen gas at a temperature of at least 150 F. Jacket 33J is prepared for the next batch by placing valve 45 in connection J.sub.N2 into service along with valve 48 in vent connection JV to control jacket temperature to at least 150 F. by returning warmer nitrogen to storage tank area 52.

[0033] D-T vessels 33-2 and 33-3 were previously prepared for the deposition phase, and as an example, D-T vessel 33-2 is selected to be placed into service next following the same procedures as outlined for vessel 33-1, followed by selection of D-T vessel 33-3 and then back to selection of D-T vessel 33-1, thereby making a continuous process.

[0034] The recombined paths A, B, and C in mixing manifold 41 form the regenerated process refrigerate at a temperature of at least 5 F. above the freezing point temperature of water (32 F.). The process refrigerate then flows through expansion valve 34 for pressure control and control of the saturation temperature of evaporator 30 to at least 5 F. below the temperature of the entering temperature of the low temperature heat source 51, thereby completing path A, B, and C cycles.

[0035] Nitrogen gas is supplied to D-T vessels 33 and jacket 33J from storage tank area 52, which also receives vented nitrogen gas, wherein required conditions are maintained for the cycle. Jacket 33J is equipped with drain JD for off-line maintenance purposes.

[0036] Turbine by-passes are depicted as BP-1 and BP-2 for use during startup and low load operation to ensure that D-T vessels 33 receive the correct pressure and temperature vapor to facilitate deposition.

[0037] FIG. 1-A illustrates an alternate process 1A to using compressor 31 heat of compression in path B to superheat and reheat path A vapor since other heat sources may be available in a conventional plant such as spent or extracted steam, extracted flue gas, or waste heat as shown with Q.sub.SH with Q.sub.RH. Excess heat Q.sub.RTN remaining in these higher temperature heat sources is returned to their respective sources as applicable. Separately fired fossil fuel heaters may be used as well for Q.sub.SH and Q.sub.RH. Alternate process 1A eliminates path B circuit used in process 1, including compressor 31, hydraulic coupling 52, motor M, liquid expander 32-3, generator G3, and mixing manifold 41, resulting in a more economical and efficient plant. All other details are the same as outlined for process 1. The additional fuel input and resulting pollutants required to provide heating steam or extracted flue gas for path A vapor superheating may be offset with less fuel heat input resulting from improved overall plant efficiency. Using low temperature sources 51, such as solar mirror focused heat and geothermal heat, to transfer heat to evaporator 30 would also have heating capabilities to superheat path A vapor.

[0038] An example power cycle is described below to demonstrate process 1 producing electricity, referencing FIG. 2 (CO.sub.2 Pressure-Enthalpy Diagram), and FIG. 3 (CO.sub.2 Phase Diagram).

[0039] FIG. 2 represents process 1 in a P-H diagram. Marked point 1 at the inlet to expansion valve 34 depicts supply of recombined paths A, B, and C sub-cooled liquid process refrigerate at a pressure of 1200 psia and temperature of 40 F. Expansion valve 34 reduces the pressure to 900 psia as shown by the vertical heavy-weighted black line as it supplies evaporator 30. A low temperature source 51 with an entering temperature of 80 F. transfers its heat to the sub-cooled liquid entering evaporator 30, transitioning it into a saturated vapor exiting at a pressure of 900 psia and temperature of 75 F., as marked by the heavy-weighted solid black line arrow (1 to 2).

[0040] The saturated vapor leaving evaporator 30 is split into paths A, B, and C. Path A flows to indirect heater 30-1. Path B flows to the inlet of compressor 31, wherein it is compressed to a superheated supercritical pressure vapor of 3550 psia/250 F. (2 to 3B) as marked by a long-dotted, heavy-weighted black line arrow. Path B then splits into paths B1 and B2 (3B to 4B) for heat transfer to path A as it passes through two stages of heat exchangers (30-1 and 30-2). Path A is superheated to 240 F. in indirect heater 30-1 (2 to 3A) by path B1, followed by isentropic expansion to 280 psia/75 F. through turbine 32-1 (3A to 4A). Path A exhausts turbine 32-1 and flows to second stage indirect exchanger 30-2, wherein it is reheated to 230 F. (4A to 5A) by path B2, followed by isentropic expansion through turbine 32-2 before exhausting as a superheated vapor at 75 psia/80 F. (5A to 6A). Paths B1 and B2 recombine into path B downstream of heat exchangers 30-1 and 30-2 at pressure/temperature conditions of 3540 psia/80 F. and then flows through turbo-expander 32-3 (4B to 4C) to exit as a sub-cooled liquid at pressure/temperature conditions of 1250 psia/50 F., producing power with shaft-connected generator G3.

[0041] The low pressure superheated vapor leaving turbine 32-2 at point 6A is then directed to turbo-expander 32-4 for isentropic expansion to produce work with generator G4 and to reduce its temperature to 80 F. at a pressure of 25 psia (6A to 7A), shown by the heavy-weighted black line arrow. The cooled vapor is then directed to venturi nozzle 36, wherein nitrogen gas spray S.sub.N2 is introduced at the throat at obtain a mixture discharge temperature of at least 125 F. (7A to 8A), shown by the short, double-thin black line arrow. Venturi nozzle 36 directs the mixture into D-T vessel 33-1, which is operating with nitrogen gas at a temperature of at least 150 F. and a pressure so that the partial pressure of the cooled vapor is at least 14.7 psia to facilitate path A dry ice deposition (8A to 9A), shown by the long, double-thin black line arrow.

[0042] After D-T vessel 33-1 receives its full measure of dry ice, this train is taken from service by closing shut-off valve 35 and venting nitrogen gas V.sub.N2 back to storage tank area 52 through valve 49 in connection V.sub.33. During the closing of shut-off valve 35, D-T vessel 33-2 is placed into service to provide a continuous process. D-T vessel 33-1 is then pressurized to 100 psia by a portion of path C vapor through connection PC and valve 44 to prevent dry ice sublimation to vapor and to facilitate transitioning of dry ice to sub-cooled liquid, as shown by the heavy-weighted broken black arrows from point 9A to the large black dot marked on the 100 psia line.

[0043] The sub-cooled liquid in D-T vessel 33-1 is then heated and pressurized to 900 psia by the remaining portion of path C vapor through connection PC and valve 44. During the deposition phase, jacket 33J receives nitrogen at a temperature greater than 50 F. through connection J.sub.N2 and valve 45 while venting cooler nitrogen to storage tank area 52 through valve 48 in connection JV. The pressure in D-T vessel 33-1 is then elevated to 1200 psia with nitrogen gas at a pressure of 1250 psia and a temperature of at least 50 F. through connection V.sub.N2 and valve 43 from storage tank area 52. Drain control valve 37 is then opened to direct D-T vessel 33-1 sub-cooled liquid to drain manifold 39, and then to mixing manifold 41 to merge with path B sub-cooled liquid leaving turbine expander 32-3, forming a recombined process refrigerate.

[0044] The recombined process refrigerate in mixing manifold 41, now at a temperature of at least 40 F., is then returned to expansion valve 34 as the process refrigerate, labeled as point 1, completing the cycles of paths A, B, and C. These functions are shown on FIG. 2 by the heavy-weighted solid black line arrow from the dot on the 100 psia line to point 1. Expansion valve 34 controls the saturation temperature of the process refrigerate in evaporator 30 to 75 F. by isenthalpic reduction of the pressure of the process refrigerate to 900 psia as shown by the vertical heavy-weighted black line from point 1.

[0045] The examples shown in this disclosure to demonstrate process 1 may be modified to suit design conditions of manufacturers, including choice of refrigerate, operating pressures and temperatures, design of turbines for other pressure and temperature conditions, or splitting of paths A, B, and C into other mass flow proportions.

[0046] In storage tank area 50, shown enclosed in heavy-weighted dotted-black lines, CO.sub.2 pressure and temperature conditions are maintained for process 1 so that sub-liquid may be supplied during startups or load increases, and sub-liquid may be received during load reductions or shutdowns. In storage tank area 52, shown in enclosed lightly-weighted dotted-black lines, nitrogen gas conditions are maintained by controlling pressure and temperature so that D-T vessels 33 may be supplied nitrogen when required and receive nitrogen when vented.

[0047] As may be noted on FIG. 2, compressor 31 enthalpy of compression (29 BTU/lb) is considerably less than the total enthalpy of expansion (93 BTU/lb) provided by turbines 32-1, 32-2, 32-3, and 32-4. Assuming a 50% split between paths A and B, the net positive power production is 69% of gross output. The example below shows the estimated power producing capabilities of this disclosed cycle.

Assumptions: Combine with Conventional 200 gross megawatt/hour Power Plant

[0048] *Condenser Cooling Water as Low Temperature Source 51: [0049] Water Mass Flow=51,382,500 lb/hr [0050] Water Temperature In/Out of Evaporator30 =80 F./50 F. [0051] Differential Enthalpy=30 BTU/lb [0052] Heat Content Available=1,541.510.sup.6 BTU/hr

[0053] CO.sub.2 Process Refrigerate in Evaporator: [0054] Temperature/Enthalpy Entering Evaporator=40 F./40 BTU/lb [0055] Saturation Pressure/Temperature=900 psig/75 F. [0056] Vapor Saturation Enthalpy=125 BTU/lb [0057] Differential Enthalpy=85 BTU/lb [0058] Mass Flow to Evaporator=1,541.510.sup.6/85=18,135,000 lb/hr [0059] Path A, B, and C Mass Flow=6,045,000 lb/hr each

[0060] Turbine and Compressor Isentropic Efficiencies, .sub.j=90%

[0061] Generator Efficiency, .sub.g=98%

[0062] Net Enthalpy Differential, H.sub.N, BTU/lb=9329=64 BTU/lb (FIG. 2)

[0063] Pump and Refrigeration Auxiliary Power Losses Not Considered

[0064] Heat Loss to the Environment=0

[0065] Net Work in Megawatts, MWn:

MWn=Mass Flow, lb/hrH.sub.N, BTU/lb.sub.g.sub.j/(34121000) [0066] Where, 3412=BTU per kilowatt hour

MWn=6,045,000640.980.90/(34121000)=100

[0067] In summary, approximately 100 MW.sub.N is produced from the heat content of the cooling water of a conventional 200 MW.sub.N power plant, which is currently rejected into the atmosphere by a cooling tower or to a nearby cooling water source.

[0068] *Note: When heat content is extracted from power plant condenser cooling water, special care should be exercised to detect and prevent CO.sub.2 contamination of the cooling water returning from evaporator 30 to the condenser. CO.sub.2 may cause corrosion problems and leaks in the condenser that enter the boiler feedwater condensate, thereby decreasing the pH of the condensate and possibly causing corrosion problems in downstream equipment. The best option to avoid this event is to install two full capacity evaporators 30 that operate in parallel with shared loads so that the evaporator 30 leaking CO.sub.2 can be taken off-line to isolate it for repairs, while its load is smoothly transferred to the other evaporator 30.