Patent Publication Number: US-2019170025-A1

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

Description:
RELATED APPLICATION 
     This application claims priority as a continuation-in-part of U.S. Provisional Patent Application No. 62/627,251 entitled “Renewable Energy Process and Method Using Carbon Dioxide Cycle to Produce Work”, filed Feb. 7, 2018. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Specifically, the present invention is a process for a refrigeration cycle to produce work from heat sources, heretofore not commercially available because of their low temperatures. Heat may be extracted from any available low temperature source, including solar heated ponds, solar mirror focused heat, geothermal sources, power plant condenser and stack rejected heat, waste heat, solids, molten salt, or vacuum type desalination plants as referenced herein. 
     Heat is transferred from a low temperature source to the cycle 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. This disclosure uses carbon dioxide (CO 2 ) refrigerate, but other refrigerates may be used as well. The vapor is then superheated by a pollution free method to produce work and then regenerated to a liquid without use of a condenser for returning to the evaporator. 
     This process can serve as a stand-alone plant using input from a renewable energy source and not requiring input from fossil or nuclear fuel. It may be integrated with a power plant to recover rejected heat from the plant&#39;s condenser and stack gas to significantly improve combined plant thermal efficiency and increase output. A conventional steam power plant using the Rankine Cycle rejects approximately 55% of its fuel heat input in the condenser and 10% from the stack, resulting in a plant thermal efficiency of 35-40%. This combined CO 2  process and conventional plant can increase plant thermal efficiency up to 70%, generating more power without additional pollutant discharges to the environment. This disclosed cycle may be integrated with a Brayton Cycle or other waste heat sources. 
     Another feature of this process includes its capability to produce both electrical power and desalinated water, by combining this disclosure with a unique steam flash tower as the low temperature heat source as disclosed in U.S. Pat. No. 9,816,400 B1 entitled “Process and Method Using Low Temperature Sources to Produce Electric Power and Desalinate Water”, which patent is by the inventor of this application and is incorporated herein by reference. The combined plant can generate revenues from electricity and desalinated water products, or the plant owner may choose to market the heat content of condenser cooling water to another party. 
     This invention allows power shifting from less efficient plants to retrofitted or new plants with a corresponding credit for reductions in emission of pollutants and CO 2 , and without requiring the addition of high cost pollution collecting equipment. This invention can eliminate cooling towers or the need to locate a plant near a large cooling water source. Water discharge temperature violations, water intake or condenser fouling problems, environmental bio-equilibrium impacts, and forced load reductions during peak summer demand seasons would no longer be issues. Power plant efficiency can improve by returning the cooling water to the condenser at a lower temperature than it received through existing cooling equipment, producing more power output with the resulting reduction in condenser vacuum. 
     2. Prior Art Description 
     Various prior art is available for high temperature supercritical pressure CO 2  power cycles fueled by waste heat gas in the temperature range of 400° F., fossil fuels, or nuclear fuel. This disclosure uses a low temperature sub-critical pressure CO 2  power cycle fueled by low temperature sources at a minimum temperature of at least 60° F., and for which equipment is currently available and by which pollutants are not produced. 
     Prior art is taught by the referenced US Patent to use a CO 2  cycle to produce desalinated water and electricity from power plant cooling water as a low temperature heat source. This disclosure produces electricity from low temperature heat sources but is unique with other equipment selections, with the process refrigerate flow paths through the equipment, and in the method to transition vapor back to liquid without a condenser. 
     Prior art has not disclosed this type of CO 2  cycle to produce work. Existing fossil fueled power plants have environmental issues and also issues with dissipation of rejected heat, ash disposal, and low efficiency operation wasting up to 60% of the fuel input. 
     Geothermal power plants currently operate at efficiencies of up to 20%. This disclosed process can be applied to geothermal power plants to achieve efficiencies of more than 50%. 
     Prior art exists for high temperature solar thermal power plants. This disclosure provides a method to produce low temperature solar thermal power plants, which eliminates the need for large mirror fields to concentrate high temperature solar heat that is harmful to flying birds and creates more expensive plant equipment. The low temperature heat source for this disclosure requires smaller mirror fields and also provides for more effective use of solar heat storage. 
     Other than hydropower and geothermal, prior art has not disclosed an economical system to produce large amounts of renewable, clean electricity with a high capacity factor. This disclosure includes these attributes, besides removing CO 2  and other pollutants from the environment. 
     SUMMARY OF THE INVENTION 
     This invention consists of a CO 2  cycle that uses a refrigerating agent with inherent capabilities of vaporizing at low temperature in three concurrent cycles to produce work. Heat input to the evaporator can be taken from various sources, including rejected heat from a water-steam cycle, waste heat, or a renewable energy heat source. Since organic refrigerates are costly and environmentally unfriendly, CO 2  agent is the preferred refrigerate in this disclosure. CO 2  is safely removed from the environment and provides a non-toxic workplace environment. 
     The evaporator refrigerate operates at sub-critical pressure to which a startup pump located in the storage tank area initially supplies a CO 2  sub-cooled liquid to an expansion valve which controls evaporator pressure and the corresponding saturation temperature. Heat input to the evaporator is supplied from a low temperature heat source, which is at a higher temperature than the refrigerate saturation temperature. 
     The refrigerate absorbs heat in the evaporator and exits as a saturated or slightly superheated vapor. The CO 2  vapor is then split into three paths (A, B, and C). Path A is directed to a first stage indirect heater and path B is directed to a compressor. Path B is compressed to a supercritical pressure vapor and superheated by the heat of compression, and is then split into two paths (B 1  and B 2 ) when exiting the compressor. Path B 1  supplies the first stage indirect heater, wherein path A is superheated and then directed to a turbine for isentropic expansion to produce electricity with a shaft-connected generator before exhausting the turbine as a lower pressure superheated vapor. Path A is then directed from the turbine to a second stage indirect heater for reheating by path B 2 . Path A is then directed to a reheat turbine for expansion and to produce additional work. Paths B 1  and B 2  recombine into path B when exiting the two stages of indirect heat exchangers, which is then directed to a liquid turbo-expander with a generator to produce power and conserve energy. 
     Path A exits the final reheat turbine as a low pressure superheated vapor and isentropically expands through a gas turbo-expander to produce a cooler vapor and additional power with a shaft-connected generator. The cooler vapor is then directed to a manifold header for batch distribution to multiple trains of duplicate deposition-transition (D-T) vessels arranged in parallel flow circuits, which are sequentially operated to provide a continuous process. The D-T vessels are equipped with inlet venturi nozzles to isentropically expand the cooler vapor for further cooling to a temperature of −109.3° F. to affect snow-like dry ice deposition at 14.7 psia pressure. To ensure a total vapor phase change to dry ice, nitrogen gas at a temperature of less than −150° F. is directed into the throat of the venturi nozzle so that the mixture temperature is at least 25° F. below the CO 2  deposition temperature. To further ensure deposition, the atmosphere inside the D-T vessel consists of nitrogen gas at a temperature of less than −150° F. and a pressure so that the CO 2  vapor partial pressure is at least 14.7 psia. The D-T vessel jacket enclosure atmosphere also consists of nitrogen gas at a temperature of less than −150° F. 
     After the D-T vessel receives its full measure of dry ice and nitrogen gas is vented back to the storage tank area, the D-T vessel is isolated by valving and pressurized by a portion of path C vapor to 100 psia (above the triple point pressure) to prevent sublimation to a vapor and facilitate transition to a sub-cooled liquid. Then, the D-T vessel is heated and pressurized to 900 psia by the remaining portion of path C vapor; thereby, completing the transitioning of any remaining dry ice to a sub-cooled liquid. Higher pressure nitrogen gas is reintroduced to the D-T vessel to facilitate draining and replacing of the sub-cooled liquid as it is drained to a mixing manifold for merging with path B sub-cooled liquid leaving the turbo-generator. 
     The mixture in the mixing manifold is a regeneration of the sub-cooled process refrigerate at a temperature of at least 5° F. above the freezing point temperature of water. The process refrigerate is then returned to the evaporator through an expansion valve; wherein the pressure is controlled so that the saturation temperature of the process refrigerate in the evaporator is at least 5° F. below the temperature of the entering temperature of the low temperature heat source; thereby, completing paths A, B, and C cycles. 
     The jacket enclosing the D-T vessel is provided a cold nitrogen gas during the deposition process and a warmer nitrogen gas during the transition process as insulation against heat loss. 
     During operation of the D-T vessels and their jackets, vents and drains to the storage tanks may be controlled with ejectors or vacuum pumps to enable evacuation and control of operating pressure and temperature. Vents may be heat traced to prevent dry ice blockage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         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. 
         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. 
         FIG. 2  is a marked CO 2  pressure-enthalpy (P-H) diagram to illustrate an approximate example of the disclosed cycle. 
         FIG. 3  depicts a phase diagram showing the physical states of CO 2  under different pressure and temperatures. 
     
    
    
     DETAILED DESCRIPTION 
       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  51 R if applicable. 
     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 (B 1  and B 2 ). Path B 1  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 G 1 . Path A exiting turbine  32 - 1  flows to second stage indirect heater  30 - 2  for reheating to a higher superheat temperature by path B 2 . Path A exiting indirect heater  30 - 2  flows to reheat turbine  32 - 2  for isentropic expansion and to produce work through electric generator G 2 . 
     Path B 1  and path B 2  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 G 3 ; 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 . 
     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 G 4 . 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. 
     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 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 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 N2  and valve  49  in vent V 33 , to a temperature of at least −150° F. and at a pressure so that the entering CO 2  vapor partial pressure is at least 14.7 psia. Also, D-T vessel jacket  33 J is operated in a nitrogen gas atmosphere at less than −150° F. through control valve  45  in connection J 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 33 . 
     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  33 J at a temperature of at least 50° F. with control valve  45  in connection J 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. 
     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 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. 
     D-T vessel  33 - 1  is prepared for its next deposition batch by placing valve  43  in connection V N2  into service along with valve  49  in vent connection V 33  to control operating pressure and temperature using nitrogen gas at a temperature of at least −150° F. Jacket  33 J is prepared for the next batch by placing valve  45  in connection J 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 . 
     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. 
     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. 
     Nitrogen gas is supplied to D-T vessels  33  and jacket  33 J from storage tank area  52 , which also receives vented nitrogen gas, wherein required conditions are maintained for the cycle. Jacket  33 J is equipped with drain JD for off-line maintenance purposes. 
     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. 
       FIG. 1 -A illustrates an alternate process  1 A 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 SH  with Q RH . Excess heat Q 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 SH  and Q RH . Alternate process  1 A eliminates path B circuit used in process  1 , including compressor  31 , hydraulic coupling  52 , motor M, liquid expander  32 - 3 , generator G 3 , 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. 
     An example power cycle is described below to demonstrate process  1  producing electricity, referencing  FIG. 2  (CO 2  Pressure-Enthalpy Diagram), and  FIG. 3  (CO 2  Phase Diagram). 
       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 ). 
     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  3 B) as marked by a long-dotted, heavy-weighted black line arrow. Path B then splits into paths B 1  and B 2  ( 3 B to  4 B) 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  3 A) by path B 1 , followed by isentropic expansion to 280 psia/75° F. through turbine  32 - 1  ( 3 A to  4 A). Path A exhausts turbine  32 - 1  and flows to second stage indirect exchanger  30 - 2 , wherein it is reheated to 230° F. ( 4 A to  5 A) by path B 2 , followed by isentropic expansion through turbine  32 - 2  before exhausting as a superheated vapor at 75 psia/80° F. ( 5 A to  6 A). Paths B 1  and B 2  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  ( 4 B to  4 C) to exit as a sub-cooled liquid at pressure/temperature conditions of 1250 psia/50° F., producing power with shaft-connected generator G 3 . 
     The low pressure superheated vapor leaving turbine  32 - 2  at point  6 A is then directed to turbo-expander  32 - 4  for isentropic expansion to produce work with generator G 4  and to reduce its temperature to −80° F. at a pressure of 25 psia ( 6 A to  7 A), shown by the heavy-weighted black line arrow. The cooled vapor is then directed to venturi nozzle  36 , wherein nitrogen gas spray S N2  is introduced at the throat at obtain a mixture discharge temperature of at least −125° F. ( 7 A to  8 A), 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 ( 8 A to  9 A), shown by the long, double-thin black line arrow. 
     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 N2  back to storage tank area  52  through valve  49  in connection V 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  9 A to the large black dot marked on the 100 psia line. 
     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  33 J receives nitrogen at a temperature greater than 50° F. through connection J 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 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. 
     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 . 
     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. 
     In storage tank area  50 , shown enclosed in heavy-weighted dotted-black lines, CO 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. 
     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 
     *Condenser Cooling Water as Low Temperature Source  51 :
         Water Mass Flow=51,382,500 lb/hr   Water Temperature In/Out of Evaporator 30  =80° F./50° F.   Differential Enthalpy=30 BTU/lb   Heat Content Available=1,541.5×10 6  BTU/hr       

     CO 2  Process Refrigerate in Evaporator:
         Temperature/Enthalpy Entering Evaporator=40° F./40 BTU/lb   Saturation Pressure/Temperature=900 psig/75° F.   Vapor Saturation Enthalpy=125 BTU/lb   Differential Enthalpy=85 BTU/lb   Mass Flow to Evaporator=1,541.5×10 6 /85=18,135,000 lb/hr   Path A, B, and C Mass Flow=6,045,000 lb/hr each       

     Turbine and Compressor Isentropic Efficiencies, η j =90% 
     Generator Efficiency, η g =98% 
     Net Enthalpy Differential, ΔH N , BTU/lb=93−29=64 BTU/lb ( FIG. 2 ) 
     Pump and Refrigeration Auxiliary Power Losses Not Considered 
     Heat Loss to the Environment=0 
     Net Work in Megawatts, MWn: 
         MWn =Mass Flow, lb/hr×Δ H   N , BTU/lb×η g ×η j /(3412×1000)
         Where, 3412=BTU per kilowatt hour       

         MWn= 6,045,000×64×0.98×0.90/(3412×1000)=100
 
     In summary, approximately 100 MW N  is produced from the heat content of the cooling water of a conventional 200 MW N  power plant, which is currently rejected into the atmosphere by a cooling tower or to a nearby cooling water source. 
     *Note: When heat content is extracted from power plant condenser cooling water, special care should be exercised to detect and prevent CO 2  contamination of the cooling water returning from evaporator  30  to the condenser. CO 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 2  can be taken off-line to isolate it for repairs, while its load is smoothly transferred to the other evaporator  30 .