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Alexander KALINA

Steam Cycle ( I )






( I )

Robert Frenay: "Power Surge"
Claudia Chandler: "Kalina Cycle Goes Commercial"
Alexander Kalina: US Patent # 4,346,561 ~Generation of Energy by Means of a Working Fluid...
Alexander Kalina: US Patent # 4,489,563 ~ Generation of Energy
Alexander Kalina: US Patent # 4,548,043 ~ Method of Generating Energy
Alexander Kalina: US Patent # 4,586,340 ~ Implementing a Thermodynamic Cycle using a Fluid of Changing Concentration

( II )
A. Kalina: USP # 4,604,867 ~ Implementing a Thermodynamic Cycle with Intercooling
A. Kalina: USP # 4,732,005 ~ Direct Fired Power Cycle
A. Kalina: USP # 4,763,480 ~ Implementing a Thermodynamic Cycle with Recuperative Preheating
A. Kalina: USP # 4,899,545 ~ Thermodynamic Cycle
A. Kalina: USP # 4,982,568 ~ Converting Heat from Geothermal Fluid to Electric Power
A. Kalina: USP # 5,029,444 ~ Converting Low Temperature Heat to Electric Power
A. Kalina: USP # 5,095,708 ~ Converting Thermal Energy into Electric Power
A. Kalina: USP # 5,440,882 ~ Converting Heat from Geothermal Liquid and Geothermal Steam to Electric Power
A. Kalina: USP # 5,450,821 ~ Multi-Stage Combustion System for Externally Fired Power Plants
A. Kalina: USP # 5,572,871 ~ Conversion of Thermal Energy into Mechanical and Electrical Power
A. Kalina: USP # 5,588,298 ~ Supplying Heat to an Externally Fired Power System
A. Kalina & Richard Pelletier: USP # 5,649,426 ~ Implementing a Thermodynamic Cycle
A. Kalina & Lawrence Rhodes:USP # 5,822,990 ~ Converting Heat into Useful Energy Using Separate Closed Loops
A. Kalina: USP # 5,950,443 ~ Method and System of Converting Thermal Energy into a Useful Form
A. Kalina & R. Pelletier ~ USP # 5,953,918 ~ Method and Apparatus of Converting Heat to Useful Energy
 


Power Surge

by Robert Frenay

Seventeen years ago, Russian èmigrè Alexander Kalina arrived in Houston, Texas, with $5.36 in his pocket and a plan. That plan has now borne fruit in a process that will considerably reduce global fuel consumption by improving the efficiency of steam-driven power plants, which produce more than two-thirds of the world's energy. If U.S. plants had the new technology, they could save $6 billion a year, according to a Department of Energy (DOE) study.

Kalina's invention has drawn the attention of prominent investors and is now licensed to such major manufacturers of power-plant equipment as General Electric, ABB, Europe's Ansaldo Energia, and Japan's Ebara Corporation.

The steam power plant now used to make electricity was invented 150 years ago by Scottish engineer William Rankine. It uses a heat source-coal, oil, natural gas, geothermal heat-to produce high-pressure steam that drives a turbine. The excess steam is condensed into water, which is then pumped back to a boiler. In a Rankine cycle only about 35 to 40 percent of the heat energy released ever becomes electricity. That means that of the $40 billion spent each year in the United States to fuel steam power plants, nearly $25 billion is lost. And that figure is matched in excess pollution and excess depletion of resources.

Mixing the water with ammonia --- which evaporates at lower temperatures --- can raise efficiency at the heat stage of the cycle. But ammonia also condenses less readily, forcing engineers to use smaller turbines and lowering efficiency. Kalinas' invention solves that problem, using sophisticated thermodynamics to draw off most of the ammonia before the condensation stage. Engineers traditionally strain for productivity gains of 1 percent; a Kalina cycle can boost efficiency by as much as 40 percent.

In 1991 the first Kalina power plan went online at an experimental site run by the DOE in Canoga Park, California. Built with funds from Australian scientist and inventor Ronald Wise, it can supply enough power for more than 1,000 houses. Stephan Schmidheiny, a principal of the Swatch watch company, and well-known speculator George Soros have each purchased 20 percent shares in Kalina's Exergy Corporation. In 1994 the DOE awarded Exergy a $7 million grant for a geothermal plant in Steamboat, Nevada, on which construction will begin later this year. Once it's operational, the DOE will compare its performance with that of two Rankine geothermal plants now in operation there.


http://www.energy.ca.gov/releases/1997_releases/97-06-05_kalina.html

Kalina Cycle Goes Commercial; Energy Commission Accepts First Royalty Payment

Claudia Chandler

The Kalina Cycle, a Russian emigre's dream of making thermal power plants up to 50 percent more efficient, is on the road to commercial reality. And the company that developed the technology, has begun paying back the California Energy Commission royalties on the state's investment. Exergy Inc. of Hayward has made the first royalty payment of $250,000 to the Commission for funding the innovation during its infancy.

"Technologies such as this offer win-win opportunities for California energy producers, consumers and taxpayers," said Governor Pete Wilson. "Not only has the state supported advances in energy efficiency, but California is reaping a share of its commercial success."

The technology is the creation of Dr. Alexander Kalina, who left a high position in the Soviet Union 18 years ago to come to the United States to develop this advanced thermodynamic cycle. He formed Exergy Inc. to commercialize the technology.

The technology uses a mix of water and ammonia rather than water alone to supply the heat recovery system for electricity generation in a power plant. Because ammonia has a much lower boiling point than water, the Kalina cycle is able to begin spinning the steam turbine at much lower temperatures than typically associated with the conventional steam boiler/turbine systems. Similarly, the lower boiling point of ammonia allows additional energy to be obtained on the condenser side of the steam turbine.

Under its Energy Technologies Advancement Program (ETAP) the Energy Commission awarded the project $2.25 million to co-fund a pilot plant in Canoga Park. Under the terms of a royalty agreement, Exergy will pay back total royalties of $6.75 million over a period of time based on its gross revenues. The Energy Commission plows back the royalty funds into ETAP to fund future projects, thus providing a mechanism for a successful project to fund other ETAP projects.

The Canoga Park plant at the U.S. Department of Energy's Engineering Center, has a capacity of six megawatts. It has sold power to the Rocketdyne Division of Rockwell International and Southern California Edison since 1992.

In 1993, General Electric signed an agreement with Exergy for a worldwide exclusive licensing rights to use the technology for combined-cycle systems in the 50 to 150 megawatt range. GE and Exergy are proposing a 110 megawatt combined-cycle project in Livingston, California that will operate at 55 percent efficiency. In addition, GE and Exergy currently have on the drawing board a combined-cycle plant that will operate on an overall efficiency above 62 percent.

Exergy has also signed agreements with Ansaldo Energia of Italy, ABB and Ebara Corporation of Japan for use of the Kalina cycle technology in geotheral, waste incineration and direct-fired coal applications.

The Governor, noting the company's successful ventures abroad said: "Exports of environmentally-friendly energy technology sharpen California's competitive edge in global markets, harnessing the international trade and investment that have been so critical to the California comeback."

The Kalina cycle can be used with any fuel, geotheral source or excess energy. Exergy predicts that with the Kalina technology, geotheral plants can post an efficiency gain of up to 50 percent while coal-fired plants will operate 20 percent more efficiently with the technology.

Through ETAP, the Energy Commission assists California energy research and development companies make energy technologies more efficient or cost-effective, and to help develop alternative sources of energy.

ETAP leverages funds from private companies toward each project. Since its establishment by the Rosenthal-Naylor Act in 1984, the program has funded 68 projects totalling more than $23.4 million, with project sponsors providing more than $175 million in matching funds. The projects provide research, development and manufacturing jobs and tax revenues to state and local governments.

The Kalina cycle was one of the first projects funded by ETAP, the first to sign a royalty agreement and the first to pay royalties to the Commission.


US Patent  # 4,346,561
( August 31, 1982 )

Generation of Energy by Means of a Working Fluid, and Regeneration of a Working Fluid

Alexander Kalina
Abstract --- A method of optimizing, within limits imposed by a heating medium from the surface of an ocean and a cooling medium from an ocean depth, the energy supply capability of a gaseous working fluid which is expanded from a charged high pressure level to a spent low pressure level to provide available energy, the method comprising expanding the gaseous working fluid to a spent low pressure level where the condensation temperature of the working fluid is below the minimum temperature of the cold water, and regenerating the spent working fluid by, in at least one regeneration stage, absorbing the working fluid being regenerated in an absorption stage by dissolving it in a solvent solution while cooling with the cold water, the solvent solution comprising a solvent having an initial working fluid concentration which is sufficient to provide a solution having a boiling point, after dissolving the working fluid being regenerated, which is above the minimum temperature of the cold water to permit effective absorption of the working fluid being regenerated, increasing the pressure and then evaporating the working fluid being regenerated by heating in an evaporation stage with the available hot water, feeding the evaporated working fluid and the solvent solution to a separator stage for separating the evaporated working fluid and the solvent solution, recovering the evaporated, separated working fluid, and recycling the balance of the solvent solution from the separator stage to constitute the solvent solution for the absorption stage; and an apparatus for carrying out the method.
Current U.S. Class: 60/673; 95/179; 95/232; 95/237
Intern'l Class:  F01K 025/10
Field of Search:  60/641.6,641.7,649,673 55/70,89,93

References Cited
U.S. Patent Documents
# 427,401 ~ May., 1890 ~ Campbell 60/673.
# 3,783,613 ~ Jan., 1974 ~ Billings et al. 60/38.
# 4,009,575 ~ Mar., 1977 ~ Hartman, Jr. 60/673.
# 4,037,415 ~ Jul., 1977 ~ Christopher 60/673.
# 4,101,297 ~ Jul., 1978 ~ Uda 55/89.
# 4,297,332 ~ Oct., 1981 ~ Tatani 55/89.
Foreign Patent Documents
# 294,882 ~ Sep., 1929 ~ GB.
# 352,492 ~ Jul., 1931 ~ GB.
# 786,011 ~ Nov., 1957 ~ GB.
# 872,874 ~ Jul., 1961 ~ GB.
# 1,085,116 ~ Sep., 1967 ~ GB.

Description
This invention relates to the generation of energy by means of a working fluid, and to the regeneration of a working fluid. More particularly, this invention relates to a method of and to apparatus for generating energy by means of a working fluid and for regenerating such a working fluid. In the generation of energy by expansion of a working fluid, the energy which can be produced by expansion of the working fluid is limited by the temperatures at which heating and cooling mediums can economically be provided for regeneration of the working fluid. The result is, therefore, that such a working fluid is expanded from a high pressure charged level to a low pressure spent level, with the high pressure charged level being governed by the maximum pressure at which the working fluid can be evaporated with the available heating medium, and with the spent low pressure level being governed by the minimum pressure at which the working fluid can be condensed with the available cooling medium. In practice, therefore, expansion of the working fluid is controlled to provide a spent low pressure level at which the condensation temperature of the working fluid is greater than the temperature of the cooling medium, to permit condensation of the working fluid. In addition, in practice, regeneration is based on condensation of working fluid in a condenser wherein the working fluid is arranged to flow in heat exchange relationship with an available cooling medium. Because of the desire to achieve maximum expansion of the working fluid, regeneration of working fluid is often effected where the temperature difference between the condensation temperature of the spent working fluid at the spent level and the temperature of the available cooling medium is marginal --- often as low as 1.degree. C. This of necessity imposes a requirement for a large condenser with an extensive heat exchange surface, and for a large supply of cooling medium, thereby substantially adding to the operating costs. This is particularly significant where severe restraints are imposed by the temperatures of available heating and cooling mediums as in the case of ocean thermal energy conversion systems. In accordance with one aspect of this invention, there is provided a method of generating energy, which comprises expanding a gaseous working fluid from a charged high pressure level to a spent low pressure level to release energy, and regenerating the spent working fluid by, in a plurality of successive regeneration stages: (a) condensing the working fluid in an absorption stage by dissolving it in a solvent solution while cooling with a cooling medium, the solvent solution comprising a solvent having an initial working fluid concentration which is sufficient to provide a solvent solution boiling range suitable for absorption of the working fluid;

(b) increasing the pressure of the solvent solution containing the dissolved working fluid, and evaporating the working fluid being regenerated by heating in an evaporation stage;

(c) feeding the evaporated working fluid to a succeeding regeneration stage;

(d) recycling the balance of the solvent solution remaining after evaporation of the working fluid, to constitute the solvent solution for the absorption stage of that regeneration stage; and

(e) withdrawing regenerated charged working fluid from a final regeneration stage for re-expansion to release energy;

The working fluid may be expanded to a spent low pressure level where the condensation temperature of the gaseous working fluid is below the minimum temperature of the cooling medium in the absorption stage.

In accordance with another aspect of the invention, there is provided a method of optimizing, within limits imposed by available sources of cooling and heating mediums, the energy supply capability of a gaseous working fluid which is expanded from a charged high pressure level to a spent low pressure level to provide available energy, the method comprising expanding the gaseous working fluid to a spent low pressure level where the condensation temperature of the working fluid is below the minimum temperature of the available cooling medium, and regenerating the spent working fluid by, in a plurality of successive incremental regeneration stages:

(a) condensing the working fluid being regenerated in an absorption stage by dissolving it in a solvent solution while cooling with the cooling medium, the solvent solution comprising a solvent having an initial working fluid concentration which is sufficient to provide a solvent solution boiling range suitable for absorption of the working fluid;

(b) increasing the pressure of the solvent solution containing the dissolved working fluid, and evaporating the working fluid being regenerated by heating in an evaporation stage with the available heating medium;

(c) feeding the evaporated working fluid to a succeeding regeneration stage for condensation;

(d) recycling the balance of the solvent solution remaining after evaporation of the working fluid being regenerated, to constitute the solvent solution for the absorption stage of that regeneration stage; and

(e) withdrawing regenerated working fluid from a final regeneration stage.

Further in accordance with the invention, there is provided a method of optimizing, within limits imposed by available sources of cooling and heating mediums, the energy supply capability of a gaseous working fluid which is expanded from a charged high pressure level to a spent low pressure level to provide available energy, the method comprising expanding the gaseous working fluid to a spent low pressure level, and regenerating the spent working fluid by, in a plurality of successive regeneration stages, condensing the working fluid and then evaporating the working fluid at an increased pressure, the working fluid being condensed in each regeneration stage by absorbing or dissolving it in a solvent solution while cooling with the cooling medium, the solvent solution comprising a solvent having, in each stage, an initial working fluid concentration which is sufficient to provide a solvent solution boiling range suitable for absorption of the working fluid, and the working fluid being evaporated in each stage by increasing the pressure to a level where the working fluid being regenerated can be evaporated with the available heating medium, and then evaporating the working fluid.

The invention further extends to apparatus for generating energy, the apparatus comprising expansion means for expanding a gaseous working fluid from a charged high pressure level to a spent low pressure level to release energy, and a plurality of successive regeneration stages for regenerating such a spent working fluid, each regeneration stage comprising:

(a) an absorber for receiving both a spent working fluid and a solvent solution for dissolving or absorbing the spent working fluid, the absorber having circulation means for circulating a cooling medium through it to cool it;

(b) a pump for pumping a resultant solvent solution from the absorber to increase its pressure;

(c) an evaporator for receiving a resultant solvent solution from the pump, the evaporator having circulation means for circulating a heating medium through it to heat it to evaporate such a working fluid to be regenerated;

(d) a separator for separating such an evaporated working fluid being regenerated, from such a solvent solution;

(e) feed means to feed such an evaporated working fluid to the absorber of a succeeding regeneration stage;

(f) recycle means for recycling a solvent solution from the separator to the condenser;

and a feed conduit for feeding a regenerated working fluid from the separator of a final regeneration stage to the expansion means.

Since the solvent solution in each regeneration stage is recycled, the solvent solution constitutes a closed loop in that stage, and is separate from the solvent solution in each other regeneration stage. Furthermore, in each regeneration stage, the quantity of working fluid being regenerated is dissolved in the solvent solution of that stage, and the equivalent quantity of working fluid being regenerated is evaporated from the solvent solution in the evaporation stage of each regeneration stage.

It will be appreciated that the quantity of solvent solution, and the initial concentration of working fluid in the solvent solution in each regeneration stage will be separately adjusted as may be required for specific operating conditions, and as may be required for variations in the minimum temperature level of an available cooling medium.

The solvent of the solvent solution may be any suitable solvent which is a solvent for the working fluid, which has a boiling point above the maximum temperature which will be attained in any evaporation stage, and which will provide a solvent solution when working fluid is dissolved therein, which has a boiling point which decreases as the concentration of working fluid increases.

While the solvent solution is preferably a binary solution, it will be appreciated that it may be a solution of a plurality of liquids.

A number of working fluids which would be suitable, are known to those skilled in the art. Any of such working fluids may be employed in this invention.

In one embodiment of the invention, the working fluid and solvent may be in the form of hydrocarbons having appropriate boiling points. Thus, for example, the solvent may be in the form of butane or pentane while the working fluid may be in the form of propane. In an alternative example, the working fluid may be an appropriate freon compound, with the solvent being an appropriate solvent for that compound.

In a preferred embodiment of the invention, the working fluid is in the form of ammonia and the solvent is in the form of water. In this embodiment of the invention, at a pressure of one atmosphere the boiling point of water is 100.degree. C. whereas the boiling point of pure ammonia is -33.degree. C. As the concentration of ammonia in water increases, the boiling point of the aqueous ammonia solution will decrease. From binary phase diagrams of water and ammonia solutions, the appropriate initial concentration of ammonia in the solvent solution for each regeneration stage, can readily be determined for this invention from the pressure and temperature which will prevail in each condensation stage.

In a preferred embodiment of the invention, the initial concentration of working fluid in the solvent solution in each regeneration stage, and the proportion of solvent solution to working fluid to be regenerated will be selected so that after complete absorption of the working fluid being regenerated in the absorption stage of that regeneration stage, the solvent solution will have a boiling point marginally above the minimum temperature attained in that absorption stage during use.

In practice, therefore, the minimum quantity of solvent solution will be employed which will satisfy this requirement thereby reducing cooling medium requirements to the minimum, and thereby further reducing heating medium requirements to the minimum.

It will be appreciated that since the pressure is increased between the absorption stage and evaporation stage of each regeneration stage, there will be a step-wise or incremental increase in pressure between each preceeding regeneration stage and each succeeding regeneration stage. It follows, therefore, that the initial concentration of working fluid in the solvent solution for each successive regeneration stage will be correspondingly higher to provide a boiling range for the solvent solution in each stage which is suitable for dissolving or absorbing the working fluid at the pressure prevailing in that stage.

In a preferred embodiment of the invention, the pressure is increased between the absorption and evaporation stages of each regeneration stage, to the maximum pressure at which the working fluid being regenerated can be evaporated effectively in the evaporation stage by the, or by a heating medium, available for heating the evaporation stage.

The pressure is, therefore, preferably increased in each regeneration stage to the maximum level where the solvent solution in each evaporation stage will, after evaporation of the working fluid in that stage, have a boiling point marginally below the maximum temperature attainable in that evaporation stage.

By appropriate control of the pressure, evaporation of the required quantity of working fluid being regenerated can be readily effected in each evaporation stage. Control valve means may, however, be provided to control the quantity of evaporated working fluid which is fed from each regeneration stage to each succeeding regeneration stage. Thus, if a greater quantity of working fluid than that required for regeneration has been evaporated in an evaporator stage, only the required quantity will pass to the succeeding regeneration stage. The balance will be recycled with the solvent solution.

The method of this invention may preferably include the step of, in each regeneration stage, feeding the solvent solution and evaporated working fluid from the evaporation stage to a separation stage for separating the working fluid being regenerated.

The separator stage may be provided by a separator of any conventional suitable type known to those skilled in the art.

The solvent solution which is recycled to the absorption stage in each regeneration stage, is conveniently expanded to reduce its pressure to a pressure corresponding with or approaching that of the pressure of the working fluid being regenerated in that absorption stage.

In a preferred embodiment of the invention, in each regeneration stage, the solvent solution which is recycled, is recycled in heat exchange relationship with the evaporation stage to thereby reduce the heating medium requirements for the evaporation stage.

The solvent solution which is recycled in each regeneration stage, may be recycled at least partially in heat exchange relationship with the absorption stage.

Where the recycled solvent solution is recycled in heat exchange relationship with an absorption stage, the cooling medium requirement will decrease because the quantity of heat to be removed will remain constant, but the capacity of the absorption stage will have to be increased. Conversely, if the recycled solvent solution is not recycled in heat exchange relationship with the absorption stage, the capacity of the absorption stage will decrease while the requirement of cooling medium will increase.

In practice, therefore, depending upon the source and availability of the cooling medium, on the basis of economic considerations, the reduced cost of supplying lesser quantities of cooling medium can be balanced against the capital costs of increasing the capacity of the absorption stages to determine whether the recycled solvent solution should be recycled in heat exchange relationship, or at least partially in heat exchange relationship with the absorption stages, or not at all.

In an embodiment of the invention, all of the absorption stages of the regeneration stages may be carried out separately in a single composite absorption stage which is cooled by means of cooling medium from a common source. Furthermore, all of the evaporation stages may be carried out separately in a single composite evaporation stage which is heated by means of a heating medium from a common source.

The apparatus of this invention may, therefore, include a single composite absorption unit and a single composite evaporation unit, with all the absorbers of the various regeneration stages being incorporated in the absorption unit, and all the evaporators of the various regeneration stages being incorporated in the evaporated unit.

While this invention may have various applications, and while various types of cooling and heating means known to those skilled in the art, may be employed, this invention can have particular application in regard to the utilization of readily and economically available cooling and heating mediums for the generation of energy.

The invention can, therefore, have specific application where low temperature differential heating and cooling mediums are employed.

A preferred application of the invention would, therefore, be in the field of thermal energy conversion using cool water withdrawn from a sufficient depth from a body of water as the cooling medium, and using, as heating medium, surface water from a body of water, solar heating, surface water heated additionally by solar heating means, or water or heating fluid in the form of waste heat fluids from industrial plants.

A preferred application of the invention would, therefore, be in the field of ocean thermal energy conversion [OTEC] where ocean surface water is used as the heating medium and ocean water withdrawn from a sufficient depth from an ocean is used as the cooling medium, thereby resulting in a low temperature differential between the heating and cooling mediums.

Normally, ocean water would be withdrawn from a depth of about 200 feet to provide the most economical cooling medium at the lowest temperature. The temperature does not tend to decrease significantly beyond a depth of about 200 feet.

The invention further extends to a method of increasing the pressure of a gaseous working fluid from an initial low pressure level to a high pressure level utilizing an available heating medium and utilizing an available cooling medium, which comprises incrementally increasing the pressure of the working fluid by, in a plurality of successive incremental regeneration stages:

(a) absorbing the working fluid being regenerated in an absorption stage by dissolving it in a solvent solution while cooling with such an available cooling medium; the solvent solution comprising a solvent having an initial working fluid concentration which is sufficient to provide a solvent solution boiling range suitable for absorption of the working fluid;

(b) increasing the pressure of the solvent solution containing the dissolved working fluid, and evaporating the working fluid being regenerated in an evaporation stage by heating with such an available heating medium;

(c) feeding the evaporated working fluid which is at an increased pressure level, to a succeeding regeneration stage for absorption;

(d) recycling the balance of the solvent solution remaining after evaporation of the working fluid being regenerated, to constitute the solvent solution for the absorption stage of that regeneration stage; and

(e) withdrawing regenerated working fluid from a final regeneration stage.

In accordance with a further aspect of the invention, there is provided a method of generating energy, which comprises expanding a gaseous working fluid from a charged high pressure level to a spent low pressure level to release energy, and regenerating the spent working fluid by, in at least one regeneration stage:

(a) condensing the working fluid in an absorption stage by dissolving it in a solvent solution while cooling with a cooling medium, the solvent solution comprising a solvent having an initial working fluid concentration which is sufficient to provide a solvent solution boiling range suitable for absorption of the working fluid;

(b) increasing the pressure of the solvent solution containing the dissolved working fluid and evaporating the working fluid being regenerated by heating in an evaporation stage;

(c) withdrawing the evaporated working fluid for re-expansion to release energy; and

(d) recycling the balance of the solvent solution remaining after evaporation of the working fluid, to constitute the solvent solution for the absorption stage of that regeneration stage.

In accordance with a further aspect of the invention there is provided a method of optimizing, within limits imposed by available sources of cooling and heating mediums, the energy supply capability of a gaseous working fluid which is expanded from a charged high pressure level to a spent low pressure level to provide available energy, the method comprising expanding the gaseous working fluid to a spent low pressure level, and regenerating the spent working fluid by, in at least one regeneration stage:

(a) condensing the working fluid being regenerated in an absorption stage by dissolving it in a solvent solution while cooling with the cooling medium, the solvent solution comprising a solvent having an initial working fluid concentration which is sufficient to provide a solvent solution boiling range suitable for absorption of the working fluid;

(b) increasing the pressure of the solvent solution containing the dissolved working fluid, and evaporating the working fluid being regenerated by heating in an evaporation stage with the available heating medium;

(c) withdrawing the evaporated working fluid to constitute a charged working fluid; and

(d) recycling the balance of the solvent solution remaining after evaporation of the working fluid being regenerated, to constitute the solvent solution for the absorption stage of that regeneration stage.

The invention further extends to a method of optimizing, within limits imposed by available sources of cooling and heating mediums, the energy supply capability of a gaseous working fluid which is expanded from a charged high pressure level to a spent low pressure level to provide available energy, the method comprising expanding the gaseous working fluid to a spent low pressure level where the condensation temperature of the working fluid is below the minimum temperature of the available cooling medium, and regenerating the spent working fluid by absorbing the working fluid and then evaporating the working fluid at an increased pressure, the working fluid being absorbed in an absorption stage by dissolving it in a solvent solution while cooling with the cooling medium, the solvent solution comprising a solvent having an initial working fluid concentration which is sufficient to provide a solvent solution boiling range suitable for absorption of the working fluid, and the working fluid being evaporated in an evaporator stage by increasing the pressure and then evaporating the working fluid being regenerated with the available heating medium.

The invention further extends to a method of increasing the pressure of a gaseous working fluid from an initial low pressure level to a high pressure level utilizing an available heating medium and utilizing an available cooling medium having a temperature which need not be below the condensation temperature of the low pressure working fluid, which comprises:

(a) condensing the working fluid being regenerated in an absorption stage by dissolving it in a solvent solution while cooling with such an available cooling medium; the solvent solution comprising a solvent having an initial working fluid concentration which is sufficient to provide a solvent solution boiling range suitable for absorption of the working fluid;

(b) increasing the pressure of the solvent solution containing the dissolved working fluid, and evaporating the working fluid being regenerated in an evaporation stage by heating with such an available heating medium;

(c) recovering the evaporated working fluid which is at the increased pressure level; and

(d) recycling the balance of the solvent solution remaining after evaporation of the working fluid being regenerated, to constitute the solvent solution for the absorption stage.

The expansion of the working fluid from a charged high pressure level to a spent low pressure level to release energy may be effected by any suitable conventional means known to those skilled in the art, and the energy so released may be stored or utilized in accordance with any of a number of conventional methods known to those skilled in the art.

In a preferred embodiment of the invention, the working fluid may be expanded to drive a turbine of conventional type.

In an embodiment of the invention, where the mass ratio between the solvent solution being recycled through an absorption stage and the working fluid being regenerated is sufficient, the pressure of the solvent solution leaving the evaporation stage may be utilized to increase the pressure of the working fluid being regenerated which is introduced into the absorption stage with the recycled solvent solution.

In this embodiment of the invention, instead of expanding the solvent solution which is recycled to reduce its pressure to a pressure corresponding with or approaching that of the pressure of the working fluid being regenerated in an absorption stage, the solvent solution may be injected into the absorption stage in such a manner as to entrain the working fluid and draw the working fluid into the absorption stage.

Various injection systems are known to those skilled in the art which could be used for this purpose. As an example, an injection system such as an injection nozzle having a restricted zone to create a zone of low pressure may be used. With such an injection nozzle, the working fluid will be introduced into the proximity of the restricted zone so that the reduced pressure created will permit the working fluid to be introduced into the absorption stage.

It will be appreciated that, depending upon relative flow rates and pressures, it may still be necessary to control the pressure of the recycled solvent solution by expanding it to provide an appropriate pressure.

By utilizing the pressure, or at least part of the pressure, of the solvent solution which is recycled, this will contribute to an increase in pressure in the absorption stage. This can provide the advantage of improving absorption in the absorption stage, or can be utilized to permit expansion of the working fluid to an even lower spent level. In this event, the initial increase in pressure provided by the solvent solution may be utilized to increase the pressure in the absorption stage, to a level where absorption can be effectively achieved in accordance with this invention.

Applicant believes that this application of the pressure of the solvent solution will tend to be valuable in the first stage, and probably the first and second stages of a multi-stage regeneration system while, in a single stage system or a system employing only two stages it will tend to be less valuable. This will primarily be due to the fact that the mass ratio between the recycled solvent solution and the working fluid will not be sufficient.

Preferred embodiments of the invention are now described by way of example with reference to the accompany drawings.

In the drawings:

FIG. 1 shows a schematic representation of one embodiment of the method and apparatus of this invention;

FIG. 2 shows a fragmentary schematic representation of the method and apparatus of FIG. 1 incorporating a modification to the expansion stage;

FIG. 3 shows a fragmentary schematic representation of a further embodiment of the invention in which injection means is utilized to inject the working fluid being regenerated;

FIG. 4 shows a schematic representation of a further embodiment of the method and apparatus of this invention.

With reference to FIG. 1 of the drawings, numeral 50 refers generally to apparatus for use in generating energy by the expansion of a gaseous working fluid from a charged high pressure level to a spent low pressure level to release energy, and for regenerating the spent working fluid.

The apparatus 50 includes expansion means in the form of a turbine 52 in which a gaseous working fluid is expanded from a charged high pressure level to a spent low pressure level to released energy to drive the turbine 52. The gaseous working fluid at the high pressure level is fed to the turbine 52 along charged line 54 and is discharged from the turbine 52 along spent line 56.

The apparatus 50 further includes regeneration means for regenerating the spent gaseous fluid. The regeneration means comprises four successive incremental regeneration stages.

For ease of reference the components of each regeneration stage have been identified by a letter followed by a suffix in arabic numerals indicating the particular regeneration stage. In addition, the flow lines for each regeneration stage have been identified by reference numerals having a prefix corresponding to that of the particular regeneration stage.

The first regeneration stage comprises an absorber A1 for condensing the gaseous working fluid by dissolving it in a solvent solution, a pump P1 for pumping the solvent solution containing the dissolved working fluid to increase the pressure, evaporator E1 for evaporating the working fluid, and a separator S1 for separating the evaporated working fluid from the solvent solution.

The first regeneration stage includes an influent line 1-1 into which the spent gaseous working fluid from the spent line 56 and solvent solution from a solvent solution recycle line 1-13 are fed into the first stage and through the absorber A1.

The resultant solvent solution from the absorber A1 is fed along line 1-2 to the inlet of the pump P1. The solution is discharged from the pump P1 at an increased pressure along line 1-3 and through the evaporator E1. The solvent solution and evaporated working fluid are fed from the evaporator E1 along line 1-4 to the separator S1. The separated evaporated working fluid is fed from the separator S1 along line 1-5 to the influent line 2-1 of the second stage. The solvent solution from the separator S1 is recycled along solvent solution recycle line 1-13 to the influent line 1-1.

The second, third and fourth regeneration stages correspond exactly with the first regeneration stage except that the evaporated, separated working fluid from the separator S4 is withdrawn along line 4-5 and fed into the charged line 54 to repeat the cycle.

In the preferred embodiment of the invention, the gaseous working fluid is ammonia, whereas the solvent is water. In addition, in the preferred embodiment of the invention, the apparatus 50 is an apparatus for use in producing energy by ocean thermal energy conversion.

The apparatus 50 is, therefore, conveniently installed on the seashore or on a floating platform. In addition, the apparatus 50 includes pump means [not shown] for pumping surface water from the surface of an ocean to the evaporators of the apparatus to constitute the heating medium for the apparatus, and includes pump means [not shown] for pumping cold water from a sufficient depth of such an ocean for constituting the cooling medium for cooling the absorbers of the apparatus 50.

Thus, the absorber A1 includes circulation means having an inlet 1-9 and an outlet 1-10 for circulating deep ocean water through the absorber A1. Similarly, the evaporator E1 includes an inlet 1-11 and an outlet 1-12 for circulating ocean surface water through the evaporator for heating the evaporator E1.

Further, in each regeneration stage, the recycle line 1-13, 2-13, 3-13 and 4-13 has an evaporator heat exchange line 1-15, 2-15, 3-15 and 4-15, respectively, passing in heat exchange relationship through the evaporator E.

In addition, in each of the regeneration stages, the solvent solution recycle line -13 may have a condenser heat exchange line 1-16, 2-16, 3-16 and 4-16, respectively, extending in heat exchange relationship through the absorber A or, alternatively, may completely bypass the absorber A as indicated by chain-dotted lines 1-18, 2-18, 3-18 and 4-18.

Where the recycled solvent solution passes in heat exchange relationship through the absorber of each regeneration stage, it will assist in cooling the absorber and will thus reduce the quantity of cooling water required to effect the required cooling in that absorber since the quantity of heat to be transferred will remain constant. It will, however, necessitate an increase in the absorber capacity and thus, in the absorber size.

In practice, therefore, the capital cost of an increase in absorber size can be balanced against the cost of the additional quantity of cooling medium to decide, on the basis of pure economics, as to whether the recycle line should pass through the absorbers, should completely bypass the absorbers, or should pass partially through the absorbers.

In the preferred embodiment of the invention, the recycle lines will bypass the absorbers.

In the preferred embodiment of the invention, the gaseous working fluid is ammonia, whereas the solvent solution is a solution of ammonia in water.

The use of the apparatus 50, and thus the process of this invention, is now described with reference to a preferred ocean thermal energy conversion system typically employing, as heating medium, surface water at a temperature of 27° C., and employing as cooling medium, deep ocean water [typically at a depth of not less than about 200 feet] having a temperature of about 4° C.

Since the boiling point of pure ammonia is -33° C. at a pressure of one atmosphere, and since the minimum temperature of the cold water cooling medium is 4° C., it would normally not be possible to regenerate ammonia at a pressure of one atmosphere by using such a cooling medium. In other words, regeneration would only be possible if the ammonia working fluid were at a pressure where the boiling point of ammonia is above 4° C.

In other words, regeneration of the gaseous working fluid would only be possible if the working fluid is expanded across the turbine 52 to a pressure at which it is capable of regeneration with the available cooling medium. This imposes a direct and severe limitation on the energy which can be generated since the maximum pressure to which the ammonia working fluid can be regenerated is also limited by the evaporation capacity of the hot water heating medium at 27° C.

In practice, utilizing surface water at a temperature of about 27° C., evaporation of ammonia in the final evaporator E4 can only be achieved in an effective manner at a maximum pressure of about nine atmospheres.

It will be appreciated, therefore, that if the working fluid can be expanded from a charged level of nine atmospheres to a spent level pressure of one atmosphere, as opposed to a spent level pressure of say only four atmospheres, the quantity of energy released will be increased substantially.

In the preferred process as illustrated in FIG. 1, the gaseous ammonia working fluid is indeed allowed to expand across the turbine 52 from a pressure of about nine atmospheres to a pressure of about one atmosphere.

A specific quantity of gaseous working fluid to be regenerated, at a spent pressure level of one atmosphere is, therefore fed to the first stage along influent line 1-1.

This quantity of gaseous working fluid is condensed in the absorber A1 by dissolving it in a solvent solution which is fed along solvent solution recycle line 1-13 into the influent line 1-1 at the same pressure of one atmosphere.

In the preferred embodiment of the invention, the solvent solutions will not be passed in heat exchange relationship through the absorbers. Thus, the spent gaseous ammonia, which may contain about 10% by weight of liquid ammonia, will be at a temperature of about -33° C., whereas the corresponding solvent solution will be at a temperature of about 8° C.

The solvent solution comprises water having an initial ammonia concentration which is sufficient to provide a binary solution which at the pressure of one atmosphere, has a boiling point within the temperature range which will prevail in the absorber A1. Further, the proportion of solvent solution to the quantity of working fluid to be regenerated is such that after the solvent solution has dissolved the quantity of working fluid to be regenerated in the absorber A1, the resultant binary solution will have a concentration which will provide, at the pressure of one atmosphere, a boiling point marginally above the minimum temperature of the cooling medium. The boiling point of the solvent solution will thus be in the region of about 6° C. where the minimum temperature of the cold water is about 4° C.

In this way it will be insured that the total quantity of working fluid to be regenerated will dissolve in the solvent solution, and that the minimum quantity of solvent solution to dissolve that quantity of gaseous ammonia will be employed thereby reducing the cold water requirements and the capacity of the absorber A1 to the practical minimum.

The solvent solution containing the dissolved working fluid being regenerated, will leave the absorber A1 at a temperature of about 6° C. and at a pressure of one atmosphere, and is pumped by the pump P1 to the evaporator E1.

The pump P1 is controlled to increase the pressure of the solvent solution to the maximum pressure at which the dissolved ammonia working fluid can be effectively evaporated in the evaporator E1 by means of the surface water heating medium at a maximum temperature of 27° C.

Preferably, the pressure increase is controlled so that after evaporation of the quantity of working fluid being regenerated, the solvent solution in the evaporator E1 will have a boiling point marginally below 27° C., such as about 25° C.

This pressure can readily be determined from a binary water/ammonia phase diagram in relation to the prevailing ammonia concentration and temperature range in the evaporator E1.

It will naturally be appreciated that the initial concentration of ammonia in water for the solvent solution, as also the required quantity of solvent solution; which is fed to the absorber A1, can also readily be determined from such a phase diagram on the basis of the known pressure and temperature range.

The evaporated working fluid and solvent solution are fed along line 1-4 to the separator S1, where they are allowed to separate.

From the separator S1, the solvent solution, at a temperature of about 25° C. will be recycled along the solvent solution recycle line 1-13 to constitute the solvent solution for the first stage. The separated, evaporated ammonia working fluid at about 25° C. is fed from the separator S1 to the second regeneration stage along influent line 2-1. As in the case of the first regeneration stage, the quantity of working fluid being regenerated, is mixed with a solvent solution recycled from a separator S2 of the second regeneration stage along the solvent solution recycle line 2-13 for dissolving the working fluid in the absorber A2.

Since the pressure in the absorber A2 will be greater than the pressure in the absorber A1, it follows that the initial concetration of ammonia in the solvent solution for the second stage will be correspondingly higher to insure that an appropriate boiling point is again provided for effectively dissolving or absorbing the working fluid being regenerated in the absorber A2.

It will be appreciated that the solvent solution which is recycled from the separator S to the absorber A in each stage leaves the separator S at a higher pressure than the pressure of the influent working fluid. Each solvent solution recycle line 1-13, 2-13, 3-13 and 4-13, therefore, includes a pressure-reducing valve V1, V2, V3 and V4, respectively, for reducing the pressure of the recycled solvent solution to the same pressure as that of the influent working fluid being regenerated.

For each successive regeneration stage, therefore, the initial concentration of ammonia in the solvent solution will increase step-wise in correspondence with the step-wise increase in pressure provided by the pump means in each stage.

It will be appreciated that the apparatus will include an appropriate number of regeneration stages until the quantity of working fluid being regenerated, has been regenerated to the appropriate charged high pressure level in a final regeneration stage such as the fourth regeneration stage shown in the drawing. It will further be appreciated that the spent pressure level to which the working fluid is expanded, will likewise determine the number of regeneration stages required. Thus if the working fluid is expanded to only say 3 atmospheres, only two or three regeneration stages may be required.

In the embodiment illustrated in the drawing, the pump means P4 will increase the pressure of the solvent solution to about nine atmospheres thereby yielding a charged regenerated working fluid at a pressure of about nine atmospheres which is withdrawn from the separator S4 and fed along the charged line 54 to the turbine 52.

It will be appreciated that in the preferred embodiment of the invention, the process will be carried out as a continuous process in which a constant quantity of working fluid by unit time is continuously being expanded across the turbine 52 and is then continuously being regenerated in the regeneration means.

To further illustrate the use of the invention in the preferred embodiment as illustrated in FIG. 1, typical parameters of the process are now indicated with reference to specific theoretical calculations performed on the basis of 1 kilogram of gaseous ammonia working fluid, and on the basis of deep ocean water at a minimum temperature of 4° C. as cooling medium, and surface ocean water at a maximum temperature of 27° C. as heating medium.

These parameters as calculated are set out in Tables I, II, III and IV below for the first, second, third and fourth regeneration stages, respectively.

In each table, the particular point at which the parameter has been calculated, is indicated by the appropriate reference numeral in the drawing. These points are listed in the first column of each table.

The columns in the tables are as follows:

(a) First column--reference numerals (RN);

(b) Second column--temperature (t) in° C.;

(c) Third column--pressure (p) in atmospheres;

(d) Fourth column--ratio by weight of total ammonia (dissolved and undissolved) to water plus total ammonia (RATIO);

(e) Fifth column--weight (w) in kilograms; and

(f) Sixth column--Enthalpy (E) in kcal/g.
 

                  TABLE I
    ______________________________________
    RN     t        p     RATIO    w     E
    ______________________________________
    1-0    -32.0    1.0   .9920     1.0000
                                         354.45
    1-1    +9.0     1.0   .4266    22.2556
                                         -642
    1-2    +6.0     1.0   .4266    22.2556
                                         -20.0
    1-3    +6       1.8   .4266    22.2556
                                         -20.0
    1-4    +25.0    1.8   .4266    22.2556
                                         17.9730
    1-5    +25.0    1.8   .9920     1.0000
                                         400.0
    1-6    +25.0    1.8  .4000    21.2556
                                         0.0
    1-7    +8.0     1.8   .4000    21.2556
                                         -23.4
    1-8    +8.0     1.0   .4000    21.2556
                                         -23.4
    ______________________________________
              TABLE II
    ______________________________________
    RN   t          p     RATIO     w     E
    ______________________________________
    2-1  +10.0      1.8   .5160     17.2457
                                          9.4125
    2-2  +6.0       1.8   .5160     17.2457
                                          -10.80
    2-3  +6.0       3.0   .5160     17.2457
                                          -10.80
    2-4  +25.0      3.0   .5160     17.2457
                                          28.6905
    2-5  +25.0      3.0   .9920      1.0000
                                          403.0
    2-6  +25.0      3.0   .4867     16.2457
                                          5.65
    2-7  +8.0       3.0   .4867     16.2457
                                          -14.63
    2-8  +8.0       1.8   .4867     16.2457
                                          -14.63
    ______________________________________
              TABLE III
    ______________________________________
    RN     t          p     RATIO    w     E
    ______________________________________
    3-1    +10.0      3.0   .6490    8.0000
                                           48.625
    3-2    +6.0       3.0   .6490    8.0000
                                           10.00
    3-3    +6.0       5.0   .6490    8.0000
                                           10.00
    3-4    +25.0      5.0   .6490    8.0000
                                           68.688
    3-5    +25.0      5.0   .9920    1.0000
                                           409.5
    3-6    +25.0      5.0   .6000    7.0000
                                           20.00
    3-7    +8.0       5.0   .6000    7.0000
                                           -2.00
    3-8    +8.0       3.0   .6000    7.0000
                                           -2.00
    ______________________________________
              TABLE IV
    ______________________________________
    RN     t          p     RATIO    w     E
    ______________________________________
    4-1    +10.0      5.0   0.9000   5.4231
                                           124.45
    4-2    +6.0       5.0   0.9000   5.4231
                                           80.0
    4-3    +6.0       9.0   .9000    5.4231
                                           80.0
    4-4    +25.0      9.0   .9000    5.4321
                                           139.59
    4-5    +25.0      9.0   .9920    1.0000
                                           412.0
    4-6    +25.0      9.0   .8792    4.4231
                                           78.0
    4-7    +8.0       9.0   .8792    4.4231
                                           60.0
    4-8    +8.0       9.0   .8792    4.4231
                                           60.0
    4-9    +8.0       5.0   .8792    4.4231
                                          60.0
    ______________________________________

From the above theoretical calculations, the total heat supplied to the four evaporator stages amounted to 1258.35 kcals, while the total heat removed from the four absorption stages mounted to 1200.8 kcals.

The difference of 57.55 is the work put in per kilogram of working fluid regenerated and thus the theoretical amount of work which is available.

The energy required to operate the pumps was calculated to be 2.08 kcals/kg of working fluid regenerated.

The theoretical amount of work available is therefore 55.47 kcal/kg of working fluid.

If it is assumed that the efficiency of the turbine is 85%, the theoretical thermal efficiency will be 4.408%.

The theoretical thermal efficiency of an ideal Carnot cycle system operating with a cooling medium at a constant temperature of 4° C. and with a heating medium at a constant temperature of 27° C., would be 7.04%. However, considering that the temperature of the heating and cooling mediums must change in such a process, the efficiency of the theoretical ideal thermodynamical cycle will be only about 4.9%.

Therefore, the ratio of the efficiency of a system in accordance with this invention on the basis of the theoretical calculations, would be:

(a) 62.55% in relation to an ideal Carnot cycle system;

(b) about 82% in relation to an ideal thermodynamical cycle under corresponding conditions.

It is an advantage of the embodiment of the invention as illustrated with reference to the drawing, that an effective system can be provided for generating energy by using the relatively low temperature differential between surface ocean water as heating medium and deep ocean water as cooling medium.

It is a further advantage of this embodiment that a system can be provided for regeneration of spent gaseous ammonia at a relatively low level of about one atmosphere or less.

It is a further advantage of the embodiment of the invention as illustrated, that because the regeneration range of the gaseous working fluid has been increased, the gaseous working fluid can be expanded from a high pressure level of about nine atmospheres, to a low pressure level of about one atmosphere or less. Thus, the quantity of energy available for release is substantially greater than would be the case if the working fluid were expanded from a pressure of about nine atmospheres to a pressure of only about four or five atmospheres.

The embodiment of the invention as illustrated in the drawing can provide a further advantage arising from the fact that the cold water requirements need only be sufficient to provide a final temperature in each absorber of about 6° C. The temperature of the cold water cooling medium can thus increase across each absorber as indicated in the above tables. Thus, the cooling medium requirements will be substantially less than would be the case if it were necessary to supply a sufficient quantity of cooling water at a sufficient rate to approach the Carnot cycle ideal where the cooling medium would remain at the constant minimum temperature. The same considerations apply to the heating medium, where the hot water is allowed to cool from about 27° C. to the temperature indicated in the above tables across each evaporator stage thereby again providing a substantially reduced heating water requirement over that required by the ideal Carnot cycle operation.

It will be appreciated that since, in each absorber, the cooling range for the solvent solution and working fluid is substantially the same, and the temperature range for the cooling medium is substantially the same, the absorbers of the four regeneration stages can conveniently be combined into a single composite absorber through which the lines 1-1, 2-1, 3-1 and 4-1 pass separately for cooling by means of a single circulating supply of cold water. In the same way, all the evaporators can be combined in a single composite evaporator heated by means of the circulating hot water from a single source.

It will further be appreciated that, theoretically, the quantity of solvent solution in each regeneration stage should remain constant, and that the initial concentration of ammonia in water to constitute the solvent solution, should also remain constant for constant minimum cooling water temperatures and constant maximum heating water temperatures.

In practice, however, the quantity of solvent solution will have to be adjusted during use to compensate for varying conditions and for losses. In addition, the concentration of ammonia in water in each regeneration stage, will have to be adjusted periodically in relation to seasonal variations in the minimum temperature of cold water and maximum temperature of hot water.

It will also be appreciated that where heating of the hot water can economically be achieved, such as by solar heating or the like, the effectiveness of the process of this invention can be improved. Such supplemental heating will, therefore, be employed under appropriate conditions if dictated by economic considerations.

With reference to FIG. 2 of the drawings, numeral 150 refers generally to an alternative embodiment of the method and apparatus of this invention to the embodiment illustrated in FIG. 1.

The apparatus 150 corresponds substantially with the apparatus 50 and corresponding parts are indicated by corresponding reference numerals.

In the apparatus 150, in place of the single turbine 52 of the apparatus 50, a two-stage turbine system is employed comprising a first turbine 152 and a second turbine 153.

The charged working fluid is partially expanded across the first turbine 152 into a heat exchange vessel 170.

From the heat exchange vessel 170 the partially expanded working fluid is led along separate conduits 171 and 172 through the absorber A2 and through the absorber A1 respectively in heat exchange relationship with the cooling water.

Thereafter the partially spent working fluid is further expanded across the second turbine 153 to its final spent level. It is then fed, as before, along the spent line 56 to the influent line 1-1.

Applicant believes that by utilizing a two-stage turbine system with heat exchange of the partially expanded working fluid, the effectiveness of the system can be improved particularly where the system includes a number of regeneration stages. Applicant believes that it will tend to be less significant where fewer stages are employed.

With reference to FIG. 3 of the drawings, the drawing shows, to an enlarged scale, the apparatus of FIG. 1 which has been adapted in the first and second regeneration stages for the pressure of the recycled solvent solution to be utilized in increasing the pressure of the influent spent working fluid into the absorption stage A1 and the absorption stage A2 respectively.

As indicated in FIG. 3, the absorption stage A1 incorporates an injection system for injecting the recycled solvent solution at a pressure substantially higher than the pressure of the spent working fluid into the absorber A1.

The injection system is in the form of an injection nozzle 180 having an intermediate restricted zone to generate a zone of low pressure.

The spent line 56 joins the nozzle 180 at the restricted zone and, as is known those skilled in the art, in an attitude where the reduced pressure generated at the restricted zone by the solvent solution being injected through the nozzle 180 into the absorber A1, will draw the spent working fluid into the nozzle 180 and thus into the absorber A1.

It will be appreciated that the effectiveness of this system will depend upon the mass ratio between the solvent solution being recycled and the working fluid being regenerated.

If the ratio is to low, it will not be possible to introduce the total quantity of working fluid being regenerated by means of the flow of the solvent solution being recycled.

In practice therefore, depending upon conditions, it may be necessary to partially reduce the pressure of the solvent solution being recycled before entry into the nozzle 180, or it may be necessary to introduce some of the working fluid being regenerated through the nozzle 180, and the remainder directly into the absorber A1.

While the absorber A2 has not been illustrated in FIG. 3, it will be appreciated that the working fluid being regenerated in the second regeneration stage will be introduced into the absorber A2 by means of an injection system corresponding to that of the absorber A1.

The embodiment of the invention as illustrated in FIG. 3 of the drawings, can provide the advantage that the pressure of the solvent solution being recycled in the first and second stages respectively can be at least partially utilized to introduce the working fluid being regenerated, and to increase the pressure in the first and second absorbers A1 and A2.

This affect can be utilized to improve the effectiveness of absorption in the first and second absorbers A1 and A2. Alternatively, or in addition, this feature can be utilized to permit expansion of the charged working fluid to a yet lower pressure across the turbine 52, with reliance being placed on the pressure contribution of the solvent solution being recycled to raise the pressure in the absorber A1 to a level where effective absorption of the working fluid being regenerated can be effected. Similarly, if employed in relation to the second regeneration stage, the same considerations will apply where the working fluid introduced into the absorber A2 can be at a lower pressure, and reliance is placed on the pressure of the solvent solution being recycled into the absorber A2, to increase the pressure to a level for effective absorption in the absorber A2.

Applicant believes that the injection system can be advantageous in the apparatus 50 particularly in the first and second stages, but would tend to have lesser value in subsequent stages.

With reference to FIG. 4 of the drawings, reference numeral 450 refers generally to yet a further alternative embodiment of the method and apparatus of this invention.

The system 450 as illustrated in FIG. 4, is designed for use where the charged working fluid is expanded to a relatively higher level than the level described with reference to FIGS. 1 to 3, but regeneration of the spent working fluid is effected in accordance with this invention to provide an economical system with high efficiency.

The apparatus 450 includes a turbine 452, and absorber A, a pump P, a regenerator R, an evaporator E and a separator S.

The spent working fluid expanded across the turbine 452 is fed along spent line 456 to influent line 464. Solvent solution which is recycled from the separator S along solvent solution recycle line 465 is fed through a pressure reducing valve V to reduce the pressure of the solvent solution to that of the spent working fluid, and then into the absorber A through the influent line 464.

As described with reference to FIG. 1, cooling medium in the form of cold deep ocean water is circulated in heat exchange relationship through the absorber A by means of conduit 461, while heating surface water is circulated through evaporator E in heat exchange relationship therewith, along conduit 463.

The spent working fluid is absorbed by the solvent solution in the absorber A whereafter the solvent solution containing the absorbed working fluid has its pressure increased by the pump P.

The solvent solution containing the absorbed working fluid is fed from the pump P along line 466 through the regenerator R and then to the evaporator E for evaporation of the dissolved working fluid being regenerated.

The solvent solution being recycled along the line 465, is passed in heat exchange relationship with the solvent solution passes through the regenerator R to effect heat exchange.

From the evaporator E, the evaporated fluid being regenerated and the solvent solution passes to the separator S for separation, whereafter the separated charged working fluid is fed along charged line 454 to the turbine 452.

To illustrate this embodiment of the invention, typical parameters of the process of the system of FIG. 4, are now indicated with reference to specific theoretical calculations performed on the basis of 1 kilogram of gaseous ammonia working fluid, and on the basis of deep ocean water at a minimum temperature of 4° C. as cooling medium, and surface ocean water at a maximum temperature of 27° C. as heating medium.

These parameters as calculated are set out in Table V below. The particular point at which the parameter has been calculated, has been indicated by the appropriate reference numeral in FIG. 4. These points are listed in the first column of Table V.

                  TABLE V
    ______________________________________
           TEM-             CONCEN-
           PER-     PRES-   TRATION        EN-
           ATURE    SURE    Kg NH.sub.4 /Kg
                                     MASS  THALPY
    POINTS° C.
                    atm.    Solution Kg    K Cal/Kg
    ______________________________________
    0      +25      5.5     0.9920   1.00  388.0
    1      +12      5.5     0.9368   1.75  248.78
    2      +8       5.5     0.9368   1.75  75.00
    3      +8       9.0     0.9368   1.75  75.00
    4      +12      9.0     0.9368   1.75  80.64
    5      +25      9.0     0.9368   1.75  265.45
    6      +25      9.0     0.9920   1.00  407.30
    7      +25      9.0     0.8632   0.75  76.32
    8      +13      9.0     0.8632   0.75  63.16
    9      +10      9.5     0.8632   0.75  63.16
    ______________________________________

It will be noted from Table V that the working fluid is expanded from a charged level of 9 atmospheres to a spent level of 5.5 atmospheres. It will further be noted that the spent working fluid and solvent solution enter the absorber A at a temperature of 12° C., and that the solvent solution containing the absorbed working fluid being regenerated, leaves the absorber A at a temperature of about 8° C.

By using an absorber A for absorbing the spent ammonia working fluid, and by having an appropriate initial concentration of ammonia in water for the solvent solution being recycled, absorption of the ammonia working fluid can commence in the absorber A at a temperature of 12° C. or slightly higher, and complete absorption will have occurred by the time the temperature has been reduced to about 8° C. by the cooling medium at 4° C.

There is therefore a significant temperature difference between the temperature of the cooling medium and the minimum temperatures required for complete absorption of the working fluid being regenerated.

In contrast with a system employing a conventional condensation stage for the condensation of a working fluid such as ammonia, condensation of gaseous ammonia at 5.5 atmospheres would only commence at a temperature of about 5° C. resulting in a marginal difference of 1° C. between the temperature of condensation and the temperature of the available cooling medium, which is at 4° C.

Thus, before condensation can occur in a condensation stage, the temperature of the working fluid would have to be reduced to about 5° C. by the cooling medium at 4° C. It will be appreciated that because of the marginal temperature difference, the requirements of cooling water will be substantial and a substantial heat transfer surface will be required.

In contrast therewith, by utilizing an absorber in accordance with this invention, while both the working fluid being regenerated and the solvent solution being recycled will have to be cooled, because absorption of working fluid can commence at a temperature substantially above the temperature of the cooling medium, and can be completed at a temperature substantially above the temperature of the cooling medium, the amount of cooling water required can be reduced substantially and/or the heat transfer surface requirement can be reduced substantially.

In practice, on the basis of economics, the cooling water requirements, the heat transfer surface area, and the temperature difference between the temperature of the cooling water and the temperature required for complete absorption of the spent working fluid, can be balanced to achieve the most economical system in the light of the operating parameters and capital costs.

Because the solvent solution containing the working fluid being regenerated would leave the absorber A at a temperature higher than the temperature of a condensed working fluid leaving a condenser, evaporation in the evaporator E will be facilitated. By additionally circulating the solvent solution being recycled and the solvent solution containing the absorbed working fluid in heat exchange relationship through the regenerator R, both absorption in the absorber A and evaporation in the evaporator E will be improved.

The system 450 therefore provides the advantage of an increased enthalpy drop across the turbine 452 and provides a system of increased efficiency and economy.

To illustrate the advantages of the system in accordance with this invention, calculations have been performed to compare the system illustrated in FIG. 4 with a conventional OTEC system utilizing a conventional Rankine cycle under the same operating parameters imposed by the temperatures of the heating and cooling mediums. The parameters for the Rankine cycle system were obtained from the publication entitled "OTEC Pilot Plan Heat Engine" by D. Richards and L. L. Perini, John Hopkins University, OTC 3592, 1979.

This comparison is set out in Table VI below.

                  TABLE VI
    ______________________________________

COMPARISON OF OFF-DESIGN OPERATING CHARACTERISTICS OF OTEC PLANTS WITH AMMONIA CLOSED RANKINE CYCLE-[1] AND WATER-AMMONIA ABSORBTION CYCLE OF FIG. 4 IN ACCORDANCE WITH THIS INVENTION-[2] RANKINE- FIG. 4 [1]  CYCLE-[2]
    ______________________________________
    Warm water temperature° C.
                           +27.89     +27.89
    Cold water temperature° C.
                           +4.00      +4.00
    Pressure of evaporation
                   atm.    8.8516     9.00
    Pressure of condensation
                   atm.    6.2784     5.5
    Inlet turbine temperature° C.
                           +20.389    +25.00
    Outlet turbine temperature° C.
                           +10.00     +7.00
    Expansion ratio        1.41       1.636
    Enthalpy drop through
                   kcal    8.524      16.984
    turbine        kg
    Turbine efficiency     0.88       0.88
    Turbine-generator power
                   MW      13.76      12.452
    Sea water pumps power
                   MW      2.856      1.832
    Ammonia pump power
                   MW      0.408      0.124
    Aux power      MW      0.0151     0.0151
    Net electrical power
                   MW      10.345     10.345
    Evaporator water flow
                   kg/h    158.76 .times. 10.sup.6
                                      107.87 .times. 10.sup.6
    Condenser water flow
                   kg/h    158.76 .times. 10.sup.6
                                      95.86 .times. 10.sup.6
    Ammonia flow through
    turbine        kg/h    1.388 .times. 10.sup.6
                                      0.6304 .times. 10.sup.6
    Sea water
    temperature drop
    evaporator° C.
                           2.580      1.89
    condenser/absorber° C.
                           2.505      2.0
    Heat flow through
    evaporator     kcal/h  409.583 .times. 10.sup.6
                                      203.880 .times. 10.sup.6
    condenser/absorber
                   kcal/h  397.752 .times. 10.sup.6
                                      191.715 .times. 10.sup.6
    regenerator    kcal/h  0.0        6.222 .times. 10.sup.6
    Average
    temperature difference
    in evaporator° C.
                           6.12       4.056
    in condenser/absorber° C.
                           4.635      4.933
    in regenerator° C.
                           --         9.87
    Heat
    exchangers surface area
    evaporator     m.sup.2 78,272.5   59,136.79
    condenser/absorber
                   m.sup.2 100,953.65 45,722.09
    regenerator    m.sup.2 0.0        990.87
    Total                  179,681.15 105,849.75
    Net thermal efficiency
                   %       2.1716     4.3627
    ______________________________________
     Thermal efficiency ratio between [2] & [1] = 2.009
     Cold water flow decrese in [2] % = 39.62
     Heat exchangers area decrase in [2] % = 41.09

The significant advantages of the system of FIG. 4 in relation to the conventional Rankine cycle system are clearly apparent from Table VI above. It is clear that the system in accordance with this invention can provide significant imporvements in efficiency and economy. This is particularly significant in OTEC systems and related systems where the severe restraints imposed by the temperatures of the available heating and cooling mediums have heretofore presented a serious barrier to commercial utilization of OTEC systems.


US Patent # 4,489,563
( December 25, 1984 )

Generation of Energy

Alexander Kalina

Abstract ~

A method of generating energy which comprises utilizing relatively lower temperature available heat to effect partial distillation of at least portion of a multicomponent working fluid stream at an intermediate pressure to generate working fluid fractions of differing compositions. The fractions are used to produce at least one main rich solution which is relatively enriched with respect to the lower boiling component, and to produce at least one lean solution which is relatively improverished with respect to the lower boiling component. The pressure of the main rich solution is increased whereafter it is evaporated to produce a charged gaseous main working fluid. The main working fluid is expanded to a low pressure level to release energy. The spent low pressure level working fluid is condensed in a main absorption stage by dissolving with cooling in the lean solution to regenerate an initial working fluid for reuse.

Current U.S. Class: 60/673
Intern'l Class:  F01K 025/06; F01K 025/10
Field of Search:  60/673,649

References Cited
U.S. Patent Documents
427,401 ~ May., 1890 ~ Campbell 60/673.
3,783,613 ~ Jan., 1974 ~ Billings et al. 60/38.
4,009,575 ~ Mar., 1977 ~ Hartman, Jr. 60/648.
4,037,415 ~ Jul., 1977 ~ Christopher 60/673.
4,101,297 ~ Jul., 1978 ~ Uda 55/43.
4,183,218 ~ Jan., 1980 ~ Eberly, Jr. 60/673.
4,195,485 ~ Apr., 1980 ~ Brinkerhoff 60/673.
4,297,332 ~ Oct., 1981 ~ Tatani 423/240.
4,333,313 ~ Jun., 1982 ~ Cardone, et al. 60/673.
4,346,561 ~ Aug., 1982 ~ Kalina 60/673.
Foreign Patent Documents
2,481,362 ~ Oct., 1981 ~ FR 60/673.
48,110 ~ Oct., 1981 ~ JP 60/673.
294,882 ~ Sep., 1929 ~ GB.
352,492 ~ Jul., 1931 ~ GB.
786,011 ~ Nov., 1957 ~ GB.
872,874 ~ Jul., 1961 ~ GB.
1,085,116 ~ Sep., 1967 ~ GB.

Other References
OTEC Pilot Plant Heat Engine--D. Richards and L. L. Perini, John Hopkins University, 1979.
OTEC--A Comprehensive Energy Analysis--T. C. Carlson et al.

Description

This invention relates to the generation of energy. More particularly, this invention relates to a method of generating energy in the form of useful energy from a heat source. The invention further relates to a method of improving the heat utilization efficiency in a thermodynamic cycle and thus to a new thermodynamic cycle utilizing the method.

The most commonly employed thermodynamic cycle for producing useful energy from a heat source, is the Rankine cycle. In the Rankine cycle a working fluid such as ammonia or a freon is evaporated in an evaporator utilizing an available heat source. The evaporated gaseous working fluid is then expanded across a turbine to release energy. The spent gaseous working fluid is then condensed in a condenser using an available cooling medium. The pressure of the condensed working medium is then increased by pumping it to an increased pressure whereafter the working liquid at high pressure is again evaporated, and so on to continue with the cycle. While the Rankine cycle works effectively, it has a relatively low efficiency. The efficiency of the typical Rankine cycle is such that currently the cost of installation is in the region of about $1,700 to about $2,200 per Kw.
A thermodynamic cycle with an increased efficiency over that of the Rankine cycle, would reduce the installation costs per Kw. At current fuel prices, such an improved cycle would be commercially viable for utilizing various waste heat sources. Applicants prior patent application Ser. No. 143,524 filed Apr. 24, 1980 relates to a system for generating energy which utilizes a binary or multicomponent working fluid. This system, termed the Exergy system, operates generally on the principle that a binary working fluid is pumped as a liquid to a high working pressure. It is heated to partially vaporize the working fluid, it is flashed to separate high and low boiling working fluids, the low boiling component is expanded through a turbine to drive the turbine, while the high boiling component has heat recovered therefrom for use in heating the binary working fluid prior to evaporation, and is then mixed with the spent low boiling working fluid to absorb the spent working fluid in a condenser in the presence of a cooling medium. Applicant's Exergy cycle is compared theoretically with the Rankine cycle in applicant's prior patent application to demonstrate the improved efficiency and advantages of applicant's Exergy cycle. This theoretical comparison has demonstrated the improved effectiveness of applicant's Exergy cycle over the Rankine cycle when an available relatively low temperature heat source such as surface ocean water, for example, is employed. Applicant found, however, that applicant's Exergy cycle provided less theoretical advantages over the conventional Rankine cycle when higher temperature available heat sources were employed. It is accordingly an object of this invention to provide an energy generating system which would provide an improved efficiency not only when lower temperature available heat sources are utilized, but also when higher temperature waste or available heat sources are utilized. In accordance with one aspect of this invention, a method of generating energy comprises: (a) subjecting at least a portion of an initial multicomponent working fluid stream having an initial composition of lower and higher boiling components, to partial distillation at an intermediate pressure in a distillation system by means of relatively lower temperature heat to generate working fluid fractions of differing compositions;

(b) using the generated fractions to produce at least one main rich solution which is relatively enriched with respect to a lower temperature boiling component, and to produce at least one lean solution which is relatively impoverished with respect to a lower temperature boiling component;

(c) increasing the pressure of the main rich solution to a charged high pressure level and evaporating the main rich solution by means of a relatively higher temperature heat to produce a charged gaseous main working fluid;

(d) expanding the gaseous main working fluid to a spent low pressure level to release energy; and

(e) condensing the spent gaseous working fluid in a main absorption stage by dissolving it with cooling in the lean solution at a pressure lower than the intermediate pressure to regenerate the initial working fluid.

In an embodiment of the invention, the relatively lower temperature heat may be selected from one or more members of the group comprising:

(a) a lower temperature portion of the relatively higher temperature heat;

(b) a portion of the relatively higher temperature heat which is not utilized for evaporating the main rich solution;

(c) heat from a relatively lower temperature heat source;

(d) heat recovered from the spent gaseous working fluid; and

(e) heat recovered from the main absorption stage.

The relatively lower temperature heat may conveniently be distributed between the distillation system and a lower temperature portion of a main evaporation stage to preheat the main rich solution prior to evaporation thereof in a main evaporation stage.

The method may conveniently include the steps of:

(a) increasing the pressure of the initial working fluid stream to a first intermediate pressure;

(b) dividing the initial working fluid stream into a first neutral stream and a first distillation stream;

(c) subjecting the first distillation stream to partial distillation in the distillation system to produce a first lower boiling fraction and a first higher boiling fraction;

(d) removing the first higher boiling fraction from the distillation system to constitute the lean solution; and

(e) absorbing the first lower boiling fraction in the first neutral stream to enrich that stream to produce a first rich solution.

In one preferred embodiment of the invention, the method may including the step of withdrawing the first rich solution from the distillation system to constitute the main rich solution.

This embodiment of the invention would be employed in appropriate circumstances where the heating and cooling mediums which are available and are employed, are such that enrichment of the working fluid can be effected sufficiently in a single distillation stage to produce a main rich solution which can be evaporated effectively with the available relatively higher temperature heat source.

In an alternative embodiment of the invention, where justified by the heating and cooling mediums utilized in practicing the invention, the method may include two, three or more distillation stages in the distillation system with a view to producing a main rich solution which is enriched to a greater extent than in a single stage distillation system.

Thus, for example, where the method includes two distillation steps in the distillation stage, the method may include the step of subjecting the first rich solution to at least one second distillation step by:

(a) mixing with the first rich solution a second higher boiling fraction recycled from a succeeding distillation stage of the distillation system to produce a second working fluid stream;

(b) increasing the pressure of the second working fluid stream to a second higher intermediate pressure;

(c) dividing the second working fluid stream into a second neutral stream and a second distillation stream;

(d) subjecting the second distillation stream to partial distillation in the distillation system to produce a second lower boiling fraction, and to produce the second higher boiling fraction which is recycled and mixed with the first rich solution; and

(e) absorbing the second lower boiling fraction in the second neutral stream to produce a second rich solution which has a greater enrichment than the first rich solution.

It will be appreciated that the distillation system can be adjusted and altered in various ways to accommodate the heat sources which are available and to provide the most effective production of rich and lean solution streams for use in the method of this invention.

While the main rich solution may be evaporated partially in the evaporation stage, it is preferred that the main rich solution be evaporated substantially or preferably completely in the main evaporation stage. In this way all heat utilized in evaporating the main rich solution will be effective in providing the charged high pressure working fluid which is available to be expanded and thereby release or generate energy.

If the main rich solution is evaporated only partially, some of the main rich solution which is not evaporated, will have been heated to a relatively high temperature, but will not be available to generate energy. This will therefore reduce the efficiency of the process.

Even if the portion of the main rich solution which is not evaporated is utilized for heat exchange purposes to supply heat to the main rich solution prior to evaporation and/or to supply heat for utilization in the distillation stage, substantial energy losses will occur in the heat exchange system because of the relatively high temperature heat which is involved.

By evaporating the main rich solution substantially completely in a main evaporation state using a relatively high temperature heat, and utilizing all or substantially all of the evaporated main rich solution as the charged gaseous working fluid for releasing energy, applicant believes high temperature energy utilization will be the most efficient.

By using relatively low temperature heat for partial distillation in the distillation system heat losses will be substantially less. Heat losses will naturally still occur in the heat exchanger systems of the distillation system. However, because relatively low temperature heat is being utilized, the quantity of heat loss will be substantially less.

Relatively lower temperature heat for the distillation system of this invention may be obtained in the form of spent relatively high temperature heat, in the form of the lower temperature part of relatively higher temperature heat from a heat source, in the form of relatively lower temperature waste or other heat which is available from the or a heat source, and/or in the form of relatively lower temperature heat which is generated in the method and cannot be utilized efficiently or more efficiently or at all for evaporation of the main rich solution.

In practice, any available heat, particularly lower temperature heat which cannot be used or cannot be used effectively for evaporating the main rich solution, may be utilized as the relatively lower temperature heat for the distillation system. In the same way such relatively lower temperature heat may be used for preheating the main rich solution in a preheater or in a lower temperature part of the main absorption stage.

In one embodiment of the invention, at least part of the lean solution may be used as a second working fluid by having its pressure increased, by being evaporated in a second main evaporator stage, by being expanded to release energy, and by then being condensed with the other spent main working fluid and with any remaining part of the lean solution in an absorption stage.

In this embodiment of the invention, the second working fluid and the main working fluid may be expanded independently, for example, through separate turbines or the like, to release energy.

This embodiment of the invention may be utilized where the higher temperature heat source which is available for use in carrying out the process of this invention, is such that the pressure of the main rich solution could be increased above the capacity of the main evaporator and the turbine or other expansion/energy release means, and yet still be capable of effective evaporation in the main evaporator. In this event the second working fluid which is relatively impoverished with regard to the low boiling components, could be heated first by the high temperature heat source so that it will be evaporated effectively at a lower pressure which is compatible with the pressure capacities of the main evaporator and the turbine. The spent very high temperature heat from such evaporation can then be used in series for evaporating the main rich solution at a convenient pressure. Thereafter, the remaining spent lower temperature heat can be utilized in the distillation system of the invention.

In a similar embodiment of the invention, the initial working fluid stream may be treated in the distillation system to produce in addition to the lean solution, a plurality of rich solution streams having differing compositions. In this embodiment, the rich solution streams may be separately treated to increase their pressures, to evaporate them and to expand them, with the evaporation of each rich solution stream being effected with a heat source temperature range appropriate for the specific composition range of the rich solution stream.

In one preferred application of the method of this invention, the enrichment of portion of the working fluid stream may, in each distillation stage of the distillation system, be increased to the maximum extent possible consistent with effective distillation of the distillation stream in that stage with the available lower temperature heat source, and consistent with effective condensation of the lower boiling fraction in the neutral stream with an available cooling medium in each distillation stage to produce a main rich solution which may be pumped to high pressure prior to effective evaporation.

Various types of heat sources may be used to drive the cycle of this invention. Thus, for example, applicant anticipates that heat sources may be used from sources as high as say 1,000.degree. F. or more, down to heat sources such as those obtained from ocean thermal gradients. Heat sources such as, for example, low grade primary fuel, waste heat, geothermal heat, solar heat and ocean thermal energy conversion systems are believed to all be capable of development for use in applicant's invention.

The working fluid for use in this invention may be any multicomponent working fluid which comprises a mixture of two or more low and high boiling fluids. The fluids may be mixtures of any of a number of compounds with favorable thermodynamic characteristics and having a wide range of solubility. Thus, for example, the working fluid may comprise a binary fluid such as an ammonia-water mixture, two or more hydrocarbons, two or more freons, or mixtures of hydrocarbons and freons.

Enthalpy-concentration diagrams for ammonia-water are readily available and are generally accepted. Ammonia-water provides a wide range of boiling temperatures and favorable thermodynamic characteristics. Ammonia-water is therefore a practical and potentially useful working fluid in most applications of this invention. Applicant believes, however, that when equipment economics and turbine design become paramount considerations in developing commercial embodiments of the invention, mixtures of freon-22 with toluene and other hydrocarbon or freon combinations will become more important for consideration.

The invention further extends to a method of improving the heat utilization efficiency in a thermodynamic cycle using a multicomponent working fluid having components of lower and higher boiling point, which method comprises:

(a) utilizing relatively lower temperature heat to effect partial distillation of at least portion of the working fluid for producing working fluid fractions which have differing compositions; and

(b) utilizing relatively higher temperature heat to completely evaporate at least an enriched portion of the working fluid which has been enriched with respect to a lower boiling component, to produce a gaseous working fluid.

The invention furhter extends to a method of generating useful energy from an available heat source, which comprises:

(a) subjecting a multicomponent working fluid having components of differing boiling points, to partial distillation in a distillation stage to produce an enriched working fluid liquid stream which is enriched with respect to a lower boiling point component;

(b) evaporating the stream substantially completely to produce a vaporized charged working fluid; and

(c) expanding the charged working fluid to release energy.

Still further in accordance with the invention there is provided a method of generating energy, which comprises:

(a) feeding an initial multicomponent working fluid stream to a partial distillation system;

(b) increasing the pressure of the stream to an intermediate pressure;

(c) separating the stream into a neutral stream and a distillation stream;

(d) subjecting the first distillation stream to partial distillation to produce working fluid fractions of differing compositions;

(e) withdrawing the fraction comprising a lean liquid solution which is impoverished with respect to a lower boiling component, from the distillation stage;

(f) mixing the fraction comprising an enriched vapor which is enriched with respect to a lower boiling component, with the neutral stream and condensing it therein by means of a cooling medium to form an enriched liquid stream;

(g) increasing the pressure of the enriched liquid stream;

(h) substantially evaporating the enriched liquid stream in an evaporation stage to produce a charged working fluid vapor;

(i) expanding the charged working fluid vapor to release energy and produce a spent working fluid vapor; and

(j) mixing the spent vapor with the lean liquid solution and condensing it therein in an absorption stage to regenerate the initial working fluid stream.

In general, standard equipment may be utilized in carrying out the method of this invention. Thus, equipment such as heat exchangers, tanks, pumps, turbines, valves and fittings of the type used in a typical Rankine cycles, may be employed in carrying out the method of this invention. Applicant believes that the constraints upon materials of construction would be the same for this invention as for conventional Rankine cycle power or refrigeration systems. Applicant believes, however, that higher thermodynamic efficiency of this invention will result in lower capital costs per unit of useful energy recovered, primarily saving in the cost of heat exchange and boiler equipment. In applications such as geothermal and solar sources, where heat conversion equipment would tend to be a small part of the total investment required to produce or collect heat, the high efficiency of the invention would produce a greater energy output. Therefore, it would reduce the total cost per unit of energy produced.

The expansion of the working fluid from a charged high pressure level to a spent low pressure level to release energy may be effected by any suitable conventional means known to those skilled in the art. The energy so released may be stored or utilized in accordance with any of a number of conventional methods known to those skilled in the art.

In a preferred embodiment of the invention, the working fluid may be expanded to drive a turbine of conventional type.

Preferred embodiments of the invention are now described by way of example with the reference to the accompanying drawings.

In the drawings:

FIG. 1 shows a simplified schematic representation of one system for carry out the method of this invention;

FIG. 2 shows a more detailed schematic representation of one embodiment in accordance with the system of FIG. 1;

FIG. 3 shows a more detailed schematic representation of an alternative embodiment in accordance with the system of FIG. 1;

FIG. 4 shows a simplified schematic representation of an alternative system for carrying out the method of this invention;

FIG. 5 shows a more complete schematic representation of one embodiment in accordance with the system of FIG. 4;

FIG. 6 shows a schematic representation of yet a further alternative system in accordance with this invention for utilizing heat in the form of geothermal heat.

With reference to FIG. 1 of the drawings, reference numeral 10.1 refers generally to one embodiment of a thermodynamic system or cycle in accordance with this invention.

The system or cycle 10.1 comprises a main evaporation stage 12.1, a turbine 16.1, a main absorption stage 20.1, a distillation system 24.1, and a main rich solution pump 28.1.

In use, using an ammonia-water working solution as the binary working fluid, an initial working fluid stream at an initial low pressure will flow from the main absorption stage 20.1 to the distillation system 24.1 along line 22.1. In the distillation system 24.1, the initial working fluid stream would have its pressure increased to an intermediate pressure and would be split into a neutral stream and a distillation stream (not shown in FIG. 1). The distillation stream would be subjected to partial distillation using a low temperature heat source to generate working fluid fractions of differing composition. The fraction which is enriched with respect to the low boiling component, namely enriched with respect to ammonia, would then be added to the first neutral stream and would be condensed in a condenser within the distillation system 24.1 to produce a main rich solution stream leaving the distillation system along line 26.1 and flowing to the main rich solution pump 28.1.

The main rich solution would then be pumped by means of the pump 28.1 to a higher pressure, and then flows along the line 30.1 to the main evaporation stage 12.1 where it is evaporated completely with a relatively higher temperature heat source to form a charged high pressure gaseous working fluid.

The charged gaseous working fluid is then conveyed along line 14.1 to the turbine 16.1 where it is expanded to release energy. The spent gaseous working fluid is then discharged from the turbine 16.1 along the line 18.1 to the main absorption stage 20.1. The working fluid is conveniently expanded to the initial low pressure level.

The fraction of working fluid which is produced in the distillation system 24.1 which is impoverished with respect to the lower boiling component, namely the ammonia, constitutes a high temperature boiling or lean solution stream which leaves the distillation system 24.1 along line 32.1. The lean solution has its pressure reduced across a pressure reducing valve 34.1, and the reduced pressure lean solution flows along line 36.1 to the main absorption stage 20.1.

In the main absorption stage 20.1 the spent gaseous working fluid is condensed by being absorbed into the lean solution while heat is extracted therefrom in the main absorption stage 20.1 by utilizing a suitable available cooling medium.

The relatively higher temperature heat from the waste or other heat source utilized in carrying out the system or cycle of this invention is indicated by reference numeral 40.1. The relatively higher temperature heat 40.1 is fed to the main evaporation stage 12.1 for evaporating the main rich solution completely.

The spent relatively higher temperature heat from the main evaporation stage 12.1 which, because of the conventional pinch point, cannot be utilized efficiently in the main evaporation stage 12.1, now becomes relatively lower temperature heat. This spent heat may therefore be fed along dotted line 42.1 to constitute relatively lower temperature heat 44.1 which is fed to the distillation system 24.1 for effecting partial distillation of the portion of the working fluid in the distillation system.

In addition to the spent relatively higher temperature heat which is fed to the distillation system as the relatively lower temperature heat 44.1, relatively lower temperature heat may also be obtained from another relatively lower temperature available heat source and/or from the heat extracted from the main absorption stage 20.1 as indicated by dotted line 46.1 and/or from heat recovered from the spent gaseous working fluid between the turbine 16.1 and the main absorption stage 20.1 as indicated by dotted line 48.1.

The available heat can be used in a large number of combinations to provide for effective utilization thereof. The way in which the heat will be utilized both for evaporation of the working fluid and for partial distillation in the distillation system 24.1, will therefore vary depending upon the apparatus employed, the capacity of the turbine 16.1, the working fluid employed, the type of heat utilized as the heat source, and the availability of relatively low temperature heat and relatively high temperature heat.

Thus, for example, in the embodiment of FIG. 1, the main evaporation stage 12.1 may include a preheater stage or a low temperature stage 13.1. Relatively lower temperature heat may be fed to the stage 13.1 to preheat the main rich solution prior to evaporation.

Such relatively lower temperature heat may be:

(a) at least portion of the relatively low temperature heat 44.1 which is diverted from dotted line 42.1 and fed to the stage 13.1 along line 43.1;

(b) at least portion of the heat extracted from the higher temperature portion of the main absorption stage 20.1 and fed to the stage 13.1 along line 45.1;

(c) at least portion of the heat recovered from the spent gaseous working fluid downstream of the turbine 16.1 and fed to the stage 13.1 along line 47.1; and/or

(d) relatively lower temperature heat from an available heat source and fed to the stage 13.1 along line 49.1.

With reference to FIG. 2 of the drawings, reference number 10.2 refers to a more detailed schematic representation of a first embodiment of the system of FIG. 1.

The system or cycle 10.2 corresponds essentially with the system 10.1. Corresponding parts are therefore indicated by corresponding reference numerals except that the suffix "0.1" has been replaced by the suffice "0.2."

In the system 10.2, the distillation system 24.2 has been enclosed in a chain dotted line to identify the portions of the system forming the distillation system 24.2.

The initial working fluid stream at an initial low pressure flows along the line 22.2 from the main absorption stage 20.2 into the distillation system 24.2. The initial working fluid stream flows to an intial pump 50.2 where the pressure of the stream is increased to an intermediate pressure.

On the downstream side of the initial pump 50.2, the initial working fluid stream is separated into a first neutral stream which flows along line 52.2, and a first distillation stream which flows along line 54.2.

The distillation system 24.2 includes a first distillation stage D1 which is in the form of a heat exchanger to place the first distillation stream flowing along the line 54.2 in heat exchange relationship with spent gaseous working fluid flowing along the line 18.2.

Relatively lower temperature heat from the spent gaseous working fluid causes partial distillation of the first distillation stream in the first distillation stage D1 to generate working fluid fractions of differing compositions which flow along the line 56.2 to a first separator stage S1.

The first separator stage S1 may be provided by a separator stage of any conventional suitable type known to those skilled in the art.

In the separator stage S1 the working fluid fractions become separated into a lower boiling fraction and a higher boiling fraction. The higher boiling fraction which is impoverished with respect to the ammonia, flows out of the distillation system 24.2 along line 32.2 through the pressure release valve 34.2 and then through the line 36.2 to the main absorption stage 20.2.

The lower boiling fraction which is enriched with respect to the ammonia flows along line 58.2 and is mixed with the first neutral stream flowing along line 52.2 to enrich the first neutral stream. The lower boiling fraction is therefore absorbed in the first neutral stream in a first condensation stage C1 to form a first rich solution stream which leaves the first condensation stage C1.

In the system 10.2, the distillation system 24.2 comprises only a single distillation unit. The first rich solution stream which leaves the first condensation stage C1 therefore constitutes the main rich solution stream which leaves this distillation system 24.2 along the line 26.2 and flows to the main rich solution pump 28.2 where its pressure is increased prior to evaporation in the main evaporation stage 12.2.

In the cycle 10.2, cooling water at ambient temperature is employed both in the main absorption stage 20.2 and in the first condensation stage C1 to effect absorption of gaseous fractions into liquid fractions in these two stages. For the relatively higher temperature heat to effect evaporation of the main rich solution in the main evaporation stage 12.2, exhaust gases from a De Laval diesel engine is utilized to flow along the line 40.2.

A case study was prepared to illustrate the recovery of waste heat from a De Laval diesel engine. Waste heat is available from such an engine in the form of exhaust gas, jacket water and lubrication oil. In the embodiment illustrated in FIG. 2 of the drawings, only the heat available from the exhaust gas was utilized as a heat source since the lower temperature heat was not required.

In the embodiment illustrated in FIG. 3, however, heat available in the form of exhaust gas as well as heat available in the form of jacket water was utilized as the heat source.

The De Laval engine was a model DSRV-12-4 of Transamerica De Laval, Inc. "Enterprise". It had a gross bhp rating of 7,390 and a net bhp rating of 7,313.

The available heat sources which could be utilized from the waste heat of the De Laval diesel engine are as follows:

    ______________________________________
    EXHAUST GAS
    ______________________________________
    T1          750.degree. F. 319.9.degree. C.
    T2          200.degree.     93.3.degree. C.
    H (heat in  12,566,600 BTU/hr.
                               3,166,472 Kcal/hr.
    exhaust gas
    above 200.degree. F.)
    ______________________________________
______________________________________
    JACKET WATER
    ______________________________________
    T1       175.degree. F.  79.44.degree. C.
    T2       163.degree. F.  72.78.degree. C.
    H        8,440,300 BTU/hr.
                             2,027,130 Kcal/hr.
    ______________________________________
______________________________________
    LUBRICATING OIL
    ______________________________________
    T1       175.degree. F.  79.44.degree. C.
    T2       153.degree. F.  67.22.degree. C.
    H        2,413,290 BTU/hr.
                             608,139 Kcal/hr.
    ______________________________________
 

EXERGY IN AVAILABLE HEAT SOURCE

Exergy is defined at the initial cooling water temperature of 85° F. and final temperature of 105° F. Exergy in heat sources having an initial temperature less than 160° F. is considered de minimus and has been ignored. The exergy in available heat sources is:

(a) exhaust gas--1,431.4 Kw or 1,230,607 Kw/hr;

(b) jacket water--277.9 Kw or 238,190 Kcal/hr;

(c) lubrication oil--78.3 Kw or 67,329 Kcal/hr;

(d) total--1,787.5 Kw or 1,536.846 Kcal/hr.

In the case study which was performed, the temperatures, pressures and concentrations were ascertained from water-ammonia enthalpy/concentration diagrams which are available in the literature.

The case study which was calculated on the basis of the system 10.2 as illustrated in FIG. 2, had the parameters as set out below in Table 1.
 

                                      TABLE 1
    __________________________________________________________________________
    Point
       Temperature
               Pressure
                       Enthalpy   Concentration
                                          Weight
    No.
       °F.
           °C.
               psia
                   kg/cm.sup.2
                       BTU/lb
                             kcal/kg
                                  lb/lb or kg/kg
                                          lb/hr kg/hr
    __________________________________________________________________________
    1  95.0
           35.0
               42.67
                   3.0 21.6  12.0 0.262   42,719.8
                                                19,377.4
    2  95.0
           35.0
               42.67
                   3.0 21.6  12.0 0.262   35,122.7
                                                15,931.4
    3  95.0
           35.0
               42.67
                   3.0 21.6  12.0 0.262    7,597.1
                                                 3,446.0
    4  145.4
           63.0
               42.67
                   3.0 228.4 126.9
                                  0.426   10,282.4
                                                 4,664.0
    5  167.0
           75.0
               42.67
                   3.0 158.4 88.0 0.262   35,122.7
                                                15,931.4
    6  167.0
           75.0
               42.67
                   3.0 813.6 452.0
                                  0.890    2,685.2
                                                 1,218.0
    7  167.0
           75.0
               42.67
                   3.0 104.4 58.0 0.210   32,437.5
                                                14,713.4
    8  95.0
           35.0
               42.67
                   3.0 19.4  10.8 0.426   10,282.4
                                                 4,664.0
    9  95.0
           35.0
               711.16
                   50.0
                       19.4  10.8 0.426   10,282.4
                                                 4,664.0
    10 662.0
           350.0
               711.16
                   50.0
                       1,212.5
                             673.6
                                  0.426   10,282.4
                                                 4,664.0
    11 183.2
           84.0
               14.22
                   1.0 956.9 531.6
                                  0.426   10,282.4
                                                 4,664.0
    12 150.8
           66.0
               14.22
                   1.0 489.6 272.0
                                  0.426   10,282.4
                                                 4,664.0
    13 136.4
           58.0
               14.22
                   1.0 197.1 109.5
                                  0.262   42,719.8
                                                19,377.4
    14 116.6
           47.0
               14.22
                   1.0 104.4 58.0 0.210   32,437.5
                                                14,713.4
    15 95.0
           35.0
               14.22
                   1.0 21.6  12.0 0.262   42,719.8
                                                19,377.4
    16 750.0
           399.0
               --  --  --    --   gas     91,386.0
                                                41,452.0
    17 213.3
           100.7
               --  --  --    --   gas     91,386.0
                                                41,452.0
    18 85.0
           29.4
               --  --  --    --   water   107,936.1
                                                48,959.0
    19 105.0
           40.5
               --  --  --    --   "       107,936.1
                                                48,959.0
    20 85.0
           29.4
               --  --  --    --   "       376,598.0
                                                170,822.0
    21 105.0
           40.5
               --  --  --    --   "       376,598.0
                                                170,822.0
    __________________________________________________________________________

The parameters identified by point numbers 1 through 21 in the first column of Table 1 are those specifically identified by the corresponding numbers in FIG. 2.

This case study generated the following data:

(1) turbine output (at 75% efficiency) --- 774.7 Kw;

(2) total pump work --- 11.3 Kw;

(3) net output --- 763.4 Kw or 656.400 Kcal/hr;

(4) thermal efficiency --- 21.2%;

(5) second law efficiency --- 53.9%;

(6) exergy utilization efficiency --- 42.7%;

(7) internal cycle efficiency 71.9%; and

(8) name plate energy recovery ratio --- 14.6%.

As compared to a conventional Rankine cycle, the second law efficiency was calculated to be 53.9% for the system 10.2 as opposed to 42.8% for a conventional Rankine cycle. Similarly, the exergy utilization efficiency was calculated to be 42.7% for the system 10.2 of FIG. 2, as opposed to 34.2% for the conventional Rankine cycle. This improvement in efficiency would therefore allow for a reduction of installed cost per Kw of between about 40 and 60%.

In calculating the parameters for the system 10.2 of FIG. 2, the starting point was taken as point 11, namely the pressure of the spent gaseous working fluid. This was taken to be one atmosphere which is the lowest pressure which can conveniently handled without being concerned about subatmospheric sealing problems, etc.

Utilizing this pressure as the starting point, the temperature at point 15 would be 35° C. based on the temperature of the cooling water utilized. The concentration of the initial working fluid stream at point 15 would therefore be fixed from the water-ammonia enthalpy/concentration diagrams.

The pressure of the initial working fluid stream would therefore be increase by the initial pump 50.2 to a high pressure at which the first distillation stream may be evaporated effectively in the first distillation stage D1, thereby insuring that the pressure is high enough for effective condensation in the first condensation stage C1.

The design studies which were performed, were not optimized either from the thermodynamic or from an economic point of view.

The parameters would, in practice, be varied to balance the effective utilization of high temperature and low temperature heat sources while balancing equipment and installation costs.

The theoretical calculations which were prepared for the case study, have demonstrated the embodiment of the invention as illustrated in FIG. 2, can provide substantial advantages over the conventional Rankine type cycle even where extremely high temperature waste heat sources are employed as the heating medium. Without wishing to be bound by theory, applicant believes that these advantages are provided by the effective utilization of high temperature heat in the evaporation stage, and low temperature heat in the distillation system thereby effectively utilizing the heat and limiting the magnitude of heat losses.

With reference to FIG. 3 of the drawings, reference numeral 10.3 refers to an alternative embodiment of a cycle or system in accordance with this invention.

The system 10.3 corresponds substantially with the systems 10.1 and 10.2. Corresponding parts are therefore indicated by corresponding reference numeral except that the suffix "0.3" has been employed in place of the suffix "0.2".

The system 10.3 again has a distillation system 24.3 which has been encircled in chain dotted lines to highlight the portions which constitute the distillation system 24.3.

The distillation system 24.3 includes two distillation units with the first distillation unit having a distillation stage D1, a separation stage S1 and a condensation stage C1, while the second distillation unit has a distillation stage D2, a separator stage S2 and a condensation stage C2.

In the system 10.3, cooling jacket water from the De Laval diesel engine would be utilized as the lower temperature heat source to cause partial distillation of the first distillation stream flowing along the line 54.3 into the distillation stage D1.

The partially distilled distillation stream flowing from the distillation stage D1, flows along the line 56.3 to the first separator stage S1. As before, the higher boiling fraction flows along the line 32.3 through the pressure reducing valve 34.3 and then through the line 36.3 to the main absorption stage 20.3. The first lower boiling fraction mixes with the first neutral stream flowing along the line 52.3 and is absorbed in the first neutral stream in the condensation stage C1.

A second high boiling fraction from the second distillation unit flows along line 63.3 through a pressure reducing valve 65.3 to the first condensation stage C1.

The first condensation stage C1 is cooled by means of cooling water at ambient temperature to ensure absorption of the first lower boiling fraction which is enriched with ammonia.

A second working fluid stream is therefore produced in the first condensation stage C1 and flows along the line 67.3 to a second pump 69.3. The second pump 69.3 increases the pressure of the second working fluid stream whereafter the stream is separated into a second neutral stream flowing along the line 71.3, and a second distillation stream flowing along the line 73.3.

The second distillation stream flows through the second distillation stage D2 in heat exchange relationship with the spent gaseous working fluid flowing along the line 18.3. Partial distillation occurs in the stage D2 so that the partially distilled second distillation stream flows along the line 75.3 to a second separator stage S2. The higher boiling fraction from the separator stage S2 constitutes the second higher boiling fraction which flows along line 63.3 to the first condensation stage C1. The second lower boiling fraction flows along line 77.3 and is absorbed into the second neutral stream in the second condensation stage C2. The second condensation stage C2 is again cooled with cooling water at ambient temperature.

The resultant main rich solution emerges from the distillation system 24.3 along line 26.3 and enters the pump 28.3 where it is pumped to an appropriate pressure for complete or substantially complete evaporation in the main evaporation stage 12.3 where it is evaporated with exhaust gases from the DeLeval engine.

As in the case of the system 10.2, a design study was performed on the system 10.3 utilizing not only the exhaust gases from the De Laval engine as the high temperature heat source, but also utilizing the jacket water from the DeLaval engine as the low temperature heat source for use in the distillation system 24.3.

The parameters for the theoretical calculations which were performed again utilizing standard ammonia-water enthalpy/concentration diagrams, are set out in Table 2 below.

In Table 2 below, points 1 through 35 in the first column correspond with the specifically marked points in FIG. 3.

                                      TABLE 2
    __________________________________________________________________________
    Point
       Temperature
               Pressure
                       Enthalpy   Concentration
                                          Weight
    No °F.
           °C.
               psia
                   kg/cm.sup.2
                       BTU/lb
                             kcal/kg
                                  lb/lb or kg/kg
                                          lb/hr kg/hr
    __________________________________________________________________________
    1  95.0
           35.0
               995.60
                   70.0
                       34.2  19.0 0.50    12,015.2
                                                 5,450.0
    2  608.0
           320.0
               995.60
                   70.0
                       1,080.0
                             600.0
                                  0.50    12,015.2
                                                 5,450.0
    3  174.2
           79.0
               14.22
                   1.0 831.4 461.9
                                  0.50    12,015.2
                                                 5,450.0
    4  200.0
           93.3
               --  --  --    --   exhaust gas
                                          91,386.0
                                                41,452.0
    5  750.0
           399.0
               --  --  --    --   exhaust gas
                                          91,386.0
                                                41,452.0
    6  138.2
           59.0
               14.22
                   1.0 492.3 273.8
                                  0.50    12,015.2
                                                 5,450.0
    7  140.0
           60.0
               14.22
                   1.0 229.5 127.5
                                  0.26    38,228.2
                                                17,340.9
    8  95.0
           35.0
               14.22
                   1.0 21.2  11.8 0.26    38,228.2
                                                17,340.9
    9  95.0
           35.0
               28.45
                   2.0 21.2  11.8 0.26    38,228.2
                                                17,340.9
    10 95.0
           35.0
               28.45
                   2.0 21.2  11.8 0.26     6,676.2
                                                 3,027.8
    11 95.0
           35.0
               28.45
                   2.0 21.2  11.8 0.26    31,555.0
                                                14,313.1
    12 167.0
           75.0
               28.45
                   2.0 234.0 130.0
                                  0.26    31,555.0
                                                14,313.1
    13 167.0
           75.0
               28.45
                   2.0 847.8 471.0
                                  0.80     5,340.0
                                                 2,422.2
    14 167.0
           75.0
               28.45
                   2.0 108.9 60.5 0.15    26,214.9
                                                11,890.9
    15 140.0
           60.0
               14.22
                   1.0 108.9 60.5 0.15    26,214.9
                                                11,890.9
    16 122.0
           50.0
               28.45
                   2.0 388.6 215.9
                                  0.50    12,015.2
                                                 5,450.0
    17 129.2
           54.0
               28.45
                   2.0 204.3 113.5
                                  0.36    33,041.8
                                                14,987.5
    18 95.0
           35.0
               28.45
                   2.0 16.6  9.2  0.36    33,041.8
                                                14,987.5
    19 95.0
           35.0
               64.00
                   4.5 16.6  9.2  0.36    33,041.8
                                                14,987.5
    20 95.0
           35.0
               64.00
                   4.5 16.6  9.2  0.36    24,003.7
                                                10,887.9
    21 95.0
           35.0
               64.00
                   4.5 16.6  9.2  0.36     9,038.1
                                                 4,099.6
    22 136.4
           58.0
               64.00
                   4.5 211.0 117.2
                                  0.50    12,015.2
                                                 5,450.0
    23 95.0
           35.0
               64.00
                   4.5 34.2  19.0 0.50    12,015.2
                                                 5,450.0
    24 167.0
           75.0
               64.00
                   4.5 186.1 103.4
                                  0.36    24,003.7
                                                10,887.9
    25 167.0
           75.0
               64.00
                   4.5 801.0 445.0
                                  0.92     2,977.1
                                                 1,350.4
    26 167.0
           75.0
               64.00
                   4.5 99.0  55.0 0.28    21,026.6
                                                 9,537.5
    27 132.8
           56.0
               28.45
                   2.0 99.0  55.0 0.28    21,026.6
                                                 9,537.5
    28 175.0
           79.4
               --  --  --    --   jacket water
                                          559,924.0
                                                253,977.3
    29 163.0
           72.8
               --  --  --    --   jacket water
                                          559,924.0
                                                253,977.3
    30 85.0
           29.4
               --  --  --    --   cooling water
                                          381,156.0
                                                172,889.5
    31 105.0
           40.5
               --  --  --    --   "       381,156.0
                                                172,889.5
    32 85.0
           29.4
               --  --  --    --   "       399,908.0
                                                181,395.9
    33 105.0
           40.5
               --  --  --    --   "       399,908.0
                                                181,395.9
    34 85.0
           29.4
               --  --  --    --   "       106,775.6
                                                48,433.5
    35 105.0
           40.5
               --  --  --    --   "       106,775.6
                                                48,433.5
    __________________________________________________________________________
 

In relation to this case study, the following data was calculated:

1. Turbine output (at 75% efficiency)--875.4 Kw.

2. Total pump work--14.5 Kw.

3. Net output--860.9 Kw or 740,159 Kcal/hr.

4. Thermal efficiency--15.2%.

5. Second law efficiency--51.9%.

6. Exergy utilization efficiency--48.2%.

7. Internal cycle efficiency--69.2%.

8. Name plate energy recovery ratio--16.5%.

In comparing the theoretical calculation for the cycle of system 10.3 with that of a conventional Rankine cycle, it was found that the second law efficiency of the cycle 10.3 was 51.9% as opposed to 42.8% for the conventional Rankine cycle. It was further calculated that the exergy utilization efficiency for the cycle 10.3 was 48.2% as opposed to 34.2% for the conventional Rankine cycle. This improvement over the cycle 10.2 is believed to be as a result of the more effective utilization of the lower temperature waste heat generated by the DeLaval diesel engine during use.

The embodiment of the cycle illustrated in FIG. 3 would therefore again provide the advantage that the cost per installed kilowatt would be reduced by about 50 to 60% in relation to a typical conventional Rankine cycle. It must be appreciated that this is based essentially on theoretical calculations and that the actual installed cost per kilowatt will vary depending upon, design, location and size of plant.

The design studies performed on the cycles 10.2 and 10.3, nevertheless indicate that waste heat from internal combustion engines could be converted economically to useful energy output in a quantity ranging from about 15 to 20% of nameplate capacity of the primary engine using conventionally available component equipment, but using applicant's improved heat utilization in applicant's thermodynamic cycles or systems.

With reference to FIG. 4 of the drawings, reference numeral 10.4 refers generally to yet a further alternative embodiment in accordance with this invention.

The system 10.4 corresponds generally with the system 10.1. Corresponding parts are therefore indicated by corresponding reference numerals except that the suffix "0.4" has been employed in place of the suffix "0.1".

The cycle or system 10.4 would be utilized where the waste heat source available for use, is available at such a high temperature that it could evaporate the main rich solution even where the pressure of that solution has been increased to a pressure far in excess of that which can conveniently be handled by the main evaporator 12 or by the turbine 16.

The cycle 10.4 is therefore designed to utilize such heat in an effective manner without providing pressure which cannot conveniently be handled by the evaporator and turbine.

In the system 10.4, the distillation system 24.4 produces, as before, a lean solution which emerges from the distillation system 24.4 and flows along line 32.4, through pressure reducing valve 34.4, along line 36.4 and into the main absorption stage 20.4.

In addition, however, the distillation system 24.4 produces two rich solution streams having differing compositions. The one rich solution liquid stream which is the least enriched with the low boiling ammonia, and is therefore a higher boiling solution than the remaining rich solution, is fed along line 26.4 to the pump 28.4 and is evaporated in the main evaporation stage 12.4 using the very high temperature available heat source. The evaporated charged gaseous working medium produced in the main evaporation stage 12.4 is fed through a first turbine 16.4 to release energy therein.

The second rich solution liquid stream which is produced in the distillation system 24.4, and which is more enriched with the low boiling ammonia and is therefore a lower boiling fluid than the other rich solution stream, flows along line 27.4 to a pump 29.4 where its pressure is increased. From there it flows along line 80.4 through a preheater 82.4 where it flows in heat exchange relationship with the spent working fluid from the turbine 16.4. Thereafter it flows along line 84.4 into a second main evaporation stage 13.4 where it is evaporated with slightly lower temperature high temperature heat which is recovered from the main evaporation stage 12.4, to evaporate it. Since it is more enriched with low boiling ammonia than the remaining rich solution stream, it can be evaporated effectively utilizing a lower temperature heat source than utilized in the main evaporation stage 12.4.

The evaporation stage 13.4 therefore produces a second charged working fluid which is fed to a second turbine 17.4 to release energy. This spent working fluid flows with the spent working fluid from the turbine 16.4 to the main absorption stage 20.4 for absorption in the lean solution.

The one rich solution stream which flows along the line 26.4 may, in an embodiment of the invention, have the same composition as the stream which leaves the absorption stage 20.4 depending upon the available heat source and the operating conditions.

The system 10.4 is set out in more detail in FIG. 5 and is identified therein by reference numeral 10.5.

The distillation system 24.5 is again identified by being encircled with chain dotted lines. The distillation system 24.5 includes a plurality of distillation units comprising main distillation stages D1 and D2, main condensation stages C1 and C2, and a plurality of separation stages S1, S2 and S3.

A design calculation was performed upon the system 10.5 utilizing exhaust gas, jacket water and lubricating oil from a DeLaval diesel engine as available heat sources. This design calculation provided a calculated second law efficiency of 52.6% as opposed to a second law efficiency for a conventional rankine cycle of 42.8%. It further provided a calculated exergy utilization efficiency of about 51.8% as opposed to a conventional rankine cycle exergy utilization efficiency of 34.2%.

The embodiment of FIG. 5 illustrates how the parameters of the system of this invention may be varied to effectively utilize a large range of available heat sources ranging from very high temperature available heat to low temperature available heat.

For each application of the invention, available heat sources will have to be balanced against specific equipment costs, to arrive at the most appropriate parameters for each application utilizing appropriate multicomponent diagrams for the particular working fluid employed.

The embodiments of the invention as illustrated in the drawings, indicate that the invention can effectively utilize a plurality of different temperature heat sources to produce energy thereby providing for effective heat utilization and reduced heat loss.

Further calculations have been done with the system in accordance with applicant's invention as compared to a conventional rankine system. With a typical system in accordance with this invention, applicant found a second law efficiency of 59.7% as opposed to a second law efficiency of 29.7% for a typical rankine cycle when utilizing surface ocean water and deep ocean water as the heating and cooling mediums for a typical ocean thermal energy conversion system.

In further calculations performed on a heat source in the form of a solar pond, applicant calculated a second law efficiency for applicant's invention of about 80% and an exergy utilization efficiency of about 80% as compared to a second law efficiency and an exergy utilization efficiency of a typical Rankine cycle of about 56%.

With reference to FIG. 6 of the drawings, FIG. 6 indicates a typical cycle in accordance with applicant's invention employed for utilizing waste heat in the form of geothermal heat.

The embodiment of FIG. 6 corresponds essentially with the embodiment of FIG. 2. Corresponding parts have therefore been indicated by corresponding reference numerals except that the suffix "0.6" has been used in place of the suffix "0.2".

The system or cycle 10.6 was designed on a theoretical basis for utilization of a heat source in the form of geothermal heat from a site in the United States known as the East Mesa geothermal site.

The relatively high temperature heat is fed to the main evaporation stage 12.6 as indicated by reference numeral 40.6 in the form of a hot geothermal brine solution which cools from 335° F. (168.3° C.) to 134.8° F. (56.0° C.).

The cycle 10.6 includes a single distillation unit which includes two partial distillation stages D1 and D2.

The relatively lower temperature heat for the distillation system is provided by the spent gaseous working fluid which flows along line 18.6 and passes through the distillation stage D2. Thereafter, the higher boiling fraction from the separator S1 joins this flow where line 36.6 joins the line 18.6. This combined flow thereafter flows in heat exchange relationship with the first distillation stream through the partial distillation heat exchanger D1.

As in the prior systems, the expansion of the charged working fluid across the turbine 16.6 is controlled to achieve a reduced pressure corresponding to the pressure to which the pressure of the lean solution is reduced by the pressure reducing valve 34.6.

As in the case of the other systems, a design study was performed on the system or cycle 10.6 utilizing geothermal heat as the relatively high temperature heat source and utilizing ambient air as the cooling medium in the main absorption stage 20.6 and in the condensation stage C1.

The parameters for the theoretical calculations which were performed again utilizing standard ammonia-water enthalpy/concentration diagrams are set out in Table 3 below.
 

                                      TABLE 3
    __________________________________________________________________________
    Point
       Temperature
               Pressure
                       Enthalpy  Concentration
                                         Weight
    No.
       °F.
           °C.
               psia
                   kg/cm.sup.2
                       BTU/lb
                            kcal/kg
                                 lb/lb or kg/kg
                                         lb/hr
                                              kg/hr
    __________________________________________________________________________
    1  81.0
           27.2
               113.8
                   8.0 16.6 9.2  0.521   90,358.1
                                              40,985.6
    2  81.0
           27.2
               113.8
                   8.0 16.6 9.2  0.521   78,491.2
                                              35,602.9
    3  81.0
           27.2
               113.8
                   8.0 16.6 9.2  0.521   11,866.9
                                               5,382.7
    4  95.0
           35.0
               113.8
                   8.0 379.6
                            210.9
                                 0.750   23,592.2
                                              10,701.2
    5  149.0
           65.0
               113.8
                   8.0 174.6
                            97.0 0.521   78,491.2
                                              35,602.9
     5a
       107.6
           42.0
               113.8
                   8.0 64.1 35.6 0.521   78,491.2
                                              35,602.9
    6  149.0
           65.0
               113.8
                   8.0 747.0
                            415.0
                                 0.982   11,725.3
                                               5,318.5
    7  149.0
           65.0
               113.8
                   8.0 75.24
                            41.8 0.440   66,765.9
                                              30,284.4
    8  81.0
           27.2
               113.8
                   8.0 97.2 54.0 0.750   23,582.2
                                              10,701.2
    9  81.0
           27.2
               284.5
                   20.0
                       97.2 54.0 0.750   23,592.2
                                              10,701.2
    10 307.4
           153.0
               284.5
                   20.0
                       928.8
                            516.0
                                 0.750   23,592.2
                                              10,701.2
    11 201.2
           94.0
              49.8
                   3.5 837.7
                            465.4
                                 0.750   23,592.2
                                              10,701.2
    12 116.6
           47.0
               49.8
                   3.5 469.8
                            261.0
                                 0.750   23,592.2
                                              10,701.2
    13 116.6
           47.0
               49.8
                   3.5 178.2
                            99.0 0.521   90,358.1
                                              40,985.6
    13a
       104.0
           40.0
               49.8
                   3.5 138.1
                            76.7 0.521   90,358.1
                                              40,985.6
    14 116.6
           47.0
               49.8
                   3.5 75.2 41.8 0.440   66,765.9
                                              30,284.4
    15 81.0
           27.2
               49.8
                   3.5 16.6 9.2  0.521   90,358.1
                                              40,985.6
    16 335.0
           168.3
               118.0
                   8.3 --   --   Brine   97,200.0
                                              44,089.0
    17 134.8
           56.0
               --  --  --   --   Brine   97,200.0
                                              44,089.0
    __________________________________________________________________________
 

The points 1 through 17 in the first column of Table 3 correspond with the specifically marked points in FIG. 6.

In relation to this case study, the following data was calculated:

    ______________________________________
                         Rankine
                                Cycle
                         Cycle  10.6
    ______________________________________
    1   turbine output (at 72% efficiency)
                               530Kw    630Kw
    2   total pump work         75Kw     15Kw
    3   net output             455Kw    615Kw
    4   thermal efficiency      8.6%    10.7%
    5   second law efficiency  35.5%    46.1%
    6   exergy utilization efficiency
                               33.3%    44.5%
    7   internal cycle efficiency
                               49.2%    64.0%
    8   ratio of net output (Rankine Cycle = 1)
                               1.0      1.35
    ______________________________________

This embodiment indicates a substantial theoretical improvement over the conventional Rankine cycle. It further illustrates the effective utilization of geothermal heat as a relatively higher temperature heat source for effecting complete evaporation of a high pressure liquid working fluid which has been enriched, and utilizing relatively lower temperature heat from spent gaseous working fluid as the low temperature heat source for causing partial distillation of portion of the initial working fluid stream to achieve effective enrichment thereof.

Applicant believes that by having working fluids of markedly different composition in the evaporation stage and in the main absorption stage, effective evaporation and heat utilization can be achieved in the evaporation stage for effective and complete evaporation of an enriched portion of a working fluid. Thereafter by utilizing a substantially impoverished fluid in the main absorption stage, the spent working fluid can be effectively condensed and thus regenerated for reuse.

It will be appreciated that heat sources can be obtained from various points in the system and from various heat and waste heat sources to provide for effective evaporation utilizing relatively higher temperature heat, and then utilizing spare relatively higher temperature heat and relatively lower temperature heat from other sources to effect partial distillation and thus enrichment of portion of the working fluid for effective evaporation.


US Patent # 4,548,043
( October 22, 1985 )

Method of Generating Energy

Alexander Kalina

 
Abstract --- A method of generating energy in which working fluid fractions of differing compositions are generated, are subjected to heating in a first evaporator stage, are combined, the combined stream is then evaporated and is expanded to convert its energy into usable form. Thereafter the combined stream is processed to regenerate the differing working fluid fractions for reuse.
US Cl 60/673
 

Intl. Cl. F01K 025/06

References Cited
U.S. Patent Documents
4,346,561 ~ Aug., 1982 ~ Kalina ~ 60/673<>
4,489,563 ~ Dec., 1984 ~ Kalina ~ 60/673

Description

This invention relates to the generation of energy. More particularly, this invention relates to a method of transforming the energy of a heat source into usable form by using a working fluid which is expanded and regenerated. The invention further relates to a method of improving the heat utilization efficiency in a thermodynamic cycle and thus to a new thermodynamic cycle utilizing the method.

The most commonly employed thermodynamic cycle for producing useful energy from a heat source, is the Rankine cycle. In the Rankine cycle a working fluid such as water, ammonia or a freon is evaporated in an evaporator utilizing an available heat source. The evaporated gaseous working fluid is then expanded across a turbine to transform its energy into usable form. The spent gaseous working fluid is then condensed in a condenser using an available cooling medium. The pressure of the condensed working medium is then increased by pumping it to an increased pressure whereafter the working liquid at high pressure is again evaporated, and so on to continue with the cycle. While the Rankine cycle works effectively, it has a relatively low efficiency.

A thermdynamic cycle with an increased efficiency over that of the Rankine cycle, would reduce the installation costs per Kw. At current fuel prices, such an improved cycle would be commercially viable for utilizing various waste heat sources.

Applicants prior U.S. Pat. No. 4,346,561 filed Apr. 24, 1980 relates to a system for generating energy which utilizes a binary or multicomponent working fluid. This system, termed the Exergy system, operates generally on the principle that a binary working fluid is pumped as a liquid to a high working pressure. It is heated to partially vaporize the working fluid, it is flashed to separate high and low boiling working fluids, the low boiling component is expanded through a turbine to drive the turbine, while the high boiling component has heat recovered therefrom for use in heating the binary working fluid prior to evaporation, and is then mixed with the spent low boiling working fluid to absorb the spent working fluid in a condenser in the presence of a cooling medium. Applicant's Exergy cycle is compared theoretically with the Rankine cycle in Applicant's prior patent to demonstrate the improved efficiency and advantages of Applicant's Exergy cycle. This theoretical comparison has demonstrated the improved effectiveness of Applicant's Exergy cycle over the Rankine cycle when an available relatively low temperature heat source such as surface ocean water, for example, is employed. Applicant found, however, that Applicant's Exergy cycle provided less theoretical advantages over the conventional Rankine cycle when higher temperature available heat sources were employed. Applicant then devised a further invention to provide an improved thermodynamic cycle for such applications. This invention utilizes a distillation system in which part of a working fluid is distilled to thereby assist in regeneration of the working fluid component. This invention is the subject matter of Applicant's prior patent application Ser. No. 405,942 which was filed on Aug. 6, 1982, now U.S. Pat. No. 4,489,563. Applicant believes that a thermodynamic cycle can be improved if effective steps can be taken to reduce the effect of the pinch point problem when a working fluid is evaporated with a heating source. It is accordingly one of the objects of this invention to provide a thermodynamic cycle in which the effect of the pinch point problem can be reduced.
 

In accordance with one aspect of this invention, a method of generating energy comprises:

(a) subjecting at least a portion of an initial composite stream having an initial composition of higher and lower boiling components, to distillation at an intermediate pressure in a distillation system to distill or evaporate part of the stream and thus generate an enriched vapor fraction which is enriched with a lower boiling component relatively to both a rich working fluid fraction and a lean working fluid fraction;

(b) mixing the enriched vaor fraction with part of the composite stream and absorbing it therein to produce at least one rich working fluid fraction which is enriched relatively to a composite working fluid with a lower boiling component;

(c) generating at least one lean working fluid fraction from part of the composite stream, the lean working fluid fraction being impoverished relatively to such a composite working fluid with a lower boiling component;

(d) using a remaining part of the initial composite stream as a condensation stream;

(e) condensing vapor contained in the rich and lean working fluid fractions to the extent that it is present in either;

(f) increasing the pressures of the rich and lean working fluid fractions in liquid form to a charged high pressure level;

(g) feeding the rich working fluid fraction and the lean working fluid fraction separately to a first evaporator stage to heat the lean working fluid fraction towards its boiling point, and to evaporate at least part of the rich working fluid fraction;

(h) mixing the lean and rich working fluid fractions to generate a composite working fluid;

(i) evaporating the composite working fluid in a second evaporator stage to produce a charged composite working fluid;

(j) expanding the charged composite working fluid to a spent low pressure level to transform its energy into usable form; and

(k) condensing the spent composite working fluid in an absorption stage by cooling and absorbing it in the condensation stream at a pressure lower than the intermediate pressure to regenerate the initial composite stream.

The lean and rich working fluid fractions, to the extent that they are not generated in liquid form, are cooled to condense them, preferably completely or substantially completely, into liquid form before their pressures are increased to the charged high pressure level.

The rich and lean working fluid fractions will usually both require condensation to generate them in liquid form before they are pumped to the charged high pressure level.

In one embodiment of the invention the entire initial composite stream may be subjected to distillation in the distillation system to produce the enriched vapor fraction, and to produce a stripped liquid fraction from which the enriched vapor fraction has been stripped.

In one example of this embodiment of the invention the enriched vapor fraction may be divided into first and second enriched vapor fraction streams, and the stripped liquid fraction may be divided into first, second and third stripped liquid fraction streams. The first enriched vapor fraction stream may then be mixed with the first stripped liquid fraction stream to produce the rich working fluid fraction, the second enriched vapor fraction stream may be mixed with the second stripped liquid fraction stream to generate the lean working fluid fraction, and the third stripped liquid fraction stream may comprise the remaining part of the initial composite stream which is used as the condensation stream.

In an alternative example of this embodiment of the invention, the stripped liquid fraction may be divided into first, second and third stripped liquid fraction streams, the enriched vapor fraction may be mixed with the first stripped liquid fraction stream to produce the rich working fluid fraction, the second stripped liquid fraction stream may be used as the part of the initial composite stream comprising the lean working fluid fraction, and the third stripped liquid fraction stream may be used as the remaining part of the initial composite stream to constitute the condensation stream.

In an alternative embodiment of the invention, only portion of the initial composite stream may be subjected to distillation in the distillation system to produce the enriched vapor fraction, and to produce a stripped liquid fraction from which the enriched vapor fraction has been stripped.

In this embodiment of the invention the enriched vapor fraction may, for example, be divided into first and second enriched vapor fraction streams and the stripped liquid fraction may be used to constitute or comprise the condensation stream. In this example of the invention, the remaining part of the initial composite stream which is not subjected to distillation may be divided, for example, into first and second composite streams. The first and second enriched vapor fraction streams may be mixed with the first and second composite streams respectively to produce the rich working fluid fraction and the lean working fluid fraction.

It will readily be appreciated that depending upon conditions and circumstances including available heating and cooling sources, the rich and lean working fluid fractions may be generated by mixing varying proportions of the enriched vapor fraction with varying proportions of one or more stripped liquid fractions, one or more initial composite stream fractions which are not subjected to distillation, or by making any combination which will achieve the desired rich and lean working fluid fractions for reducing the pinch point problem in accordance with this invention.

It will further be appreciated that by making appropriate selections from the enriched vapor fraction, from the stripped liquid fraction and from the initial composite stream two, three or more working fluid fractions may be produced which have a range of low boiling component concentrations and which are of appropriate quantities to allow effective separate heating in a first evaporator stage, followed by combining two or more of the streams, followed by separate heating in a subsequent evaporator stage, again followed by mixing of the fluid streams to reduce the number of streams, again followed by evaporation in a subsequent evaporator stage, and so on until a single composite working fluid has been produced which can then be evaporated and expanded to convert its energy into usable form.

In a preferred embodiment of the invention, the condensation stream will be throttled down to the pressure of the spent composite working fluid for absorbing the spent composite working fluid therein in the absorption stage.

The condensation stream and the spent composite working fluid may be cooled in the absorption stage utilizing any appropriate and available cooling medium.
The initial composite stream generated in the absorption stage, or the portion thereof which is to be subjected to distillation, may be subjected to distillation by heating in one or more heat exchangers using any suitable and available heating medium.

Applicant's presently preferred method of subjecting the initial composite stream, or portion thereof, to distillation is by means of relatively low temperature heat. This provides the advantage that the quantity of heat loss in the heat exchanger system will be substantially less, and that low temperature heat may be used for this purpose which cannot conveniently be utilized in other aspects of the cycle.

In a presently preferred embodiment of the invention, distillation may be effected by passing the initial composite stream, or portion thereof, in heat exchange relationship with one or more of the following heating sources:

(a) the spent composite working fluid;

(b) the condensation stream;

(c) the lean working fluid fraction;

(d) the rich working fluid fraction; and

(e) an auxiliary heating source.

Applicant believes that in many applications of the cycle of this invention, no auxiliary heating source will be required. Applicant thus believes that sufficient heat can be extracted from the spent composite working fluid, from the condensation stream, and from the lean and rich working fluid fractions to provide for effective distillation or evaporation of part of the initial composite stream to produce the enriched vapor fraction which is enriched with respect to the lower boiling component or components of the composite stream.

When the initial composite stream is subjected to such distillation, the lower boiling component or components will naturally evaporate or distill first thereby producing the enriched vapor fraction.

The compositions of the rich working fluid and lean working fluid fractions are preferably selected so that they can be heated most effectively in the first evaporator stage with the available heating medium. The first evaporator stage will generally be the low temperature stage of the evaporator.

Thus, for example, the composition should be selected, and the relative quantities should be selected, such that the lean working fluid fraction will be heated towards its boiling point in the first evaporator stage, while the rich working fluid fraction will be heated towards its saturated vapor stage.

Preferably the rich working fluid fraction should be enriched as much as possible with the lower boiling component or components, consistent with the use of a lean working fluid fraction which can have a boiling point at the dew point of the rich working fluid fraction.

In a presently preferred embodiment, the compositions and quantities will be selected so that the lean working fluid will be heated to its boiling point or to substantially its boiling point in the first evaporator stage, while the rich working fluid fraction will be evaporated substantially or completely to be in the form of a saturated vapor in the first evaporator stage.

While both the lean working fluid fraction and the rich working fluid fraction may be heated to a higher temperature in the first evaporator stage, Applicant believes that this will not provide any real thermodynamic advantage in the cycle of this invention.

The rich and lean working fluid fractions are thus selected so that after they have passed through the first evaporator stage, they are substantially or at least generally in equilibrium both in temperature and pressure to reduce any thermodynamic losses which may occur during mixing.

When lean and rich working fluid fractions are first generated in accordance with this invention, they will usually both contain vapor and must therefore be cooled to condense them completely. They are then pumped separately to the charged high pressure level before being fed to the first evaporator stage. While the lean working fluid fraction may sometimes contain no vapor and will therefore not have to be cooled, the rich working fluid fraction will usually contain vapor and will have to be cooled to condense the vapor and provide the fraction in liquid form for effective pressure increase.

They may be cooled utilizing any available cooling medium. In accordance with Applicant's presently preferred embodiment of the invention, the lean working fluid fraction will be cooled by passing it in heat exchange relationship with the initial composite stream which is being subjected to distillation.

Similarly, in accordance with Applicant's presently preferred embodiment, the rich working fluid fraction will be cooled by passing it in heat exchange relationship with an auxiliary cooling source. A preheater system may also be employed between the cooled rich working fluid fraction and the rich working fluid fraction which has not yet been cooled with the cooling medium of the auxiliary cooling source.

In the preferred application of the invention, the rich and lean working fluid fractions will be cooled so that their temperatures will be generally equal or close before they are fed to the first evaporator stage.

After the lean and rich working fluid fractions have passed through the first evaporator stage, and have been mixed to constitute the composite working fluid, they may be heated in the second evaporator stage to evaporate the composite working fluid completely or at least substantially completely.

Applicant believes that the best thermodynamical advantages will be provided if the composite working fluid is evaporated completely in the second evaporator stage. Applicant believes that it will be less advantageous if the composite working fluid is not evaporated completely.

If the composite working fluid is evaporated only partially, some of that fluid, which will have been heated to a relatively high temperature, will not be available to generate energy. This will therefore reduce the efficiency of the process. By evaporating the composite working fluid completely in the second evaporation stage using a relatively high temperature heat, and utilizing all or substantially all of the evaporated composite working fluid as the charged composite working fluid, Applicant believes that high temperature energy utilization will be the most efficient and effective.

In a presently preferred embodiment of the invention, the composite working fluid from the second evaporator stage, will be superheated in a superheater stage.

The charged composite working fluid may be expanded to a spent low pressure level to transform its energy into usable form, utilizing any suitable and available device for this purpose. Devices of this nature are generally in the form of turbines and will generically be referred to in the specification as turbines.

Various single and multi-stage turbines are available and can be selected to provide the appropriate pressure and temperature ranges for effective utilization of this invention.

In an embodiment of the invention a multi-stage turbine system may be used, and at least part of the composite working fluid may be recycled to the superheater stage after passing through a high pressure stage of the turbine, and before entering a low pressure stage of the turbine.

It will readily be appreciated by those skilled in the art that relatively low temperature heat for the distillation system of this invention may be obtained from various sources depending upon circumstances. It may be obtained in the form of spent relatively high temperature heat, in the form of the lower temperature part of relatively higher temperature heat from a heat source, in the form of relatively lower temperature waste or other heat which is available from the or from a heat source, and/or in the form of relatively lower temperature heat which is generated in the method of this invention and cannot be utilized efficiently or more effectively or at all for evaporation of the composite working fluid.

Various types of heat sources may be used in the evaporator stage of the cycle of this invention to evaporate the composite working fluid. In each instance, depending upon available heat sources, the cycle can be adjusted to utilize such heat sources in the most effective manner. For example, Applicant anticipates that heat sources may be used from sources as high as 1,000° F. or more, down to heat sources such as those obtained from ocean thermal gradients. Heat sources such as, for example, low grade primary fuel, waste heat, geothermal heat, solar heat and ocean thermal energy conversion systems are believed all to be capable of development for use in this invention.

The working fluid for use in this invention may be any multi-component working fluid which comprises a mixture of two or more low and high boiling fluids. The fluids may be mixtures of any of a number of compounds with favorable thermodynamic characteristics and having an appropriate or wide range of solubility. Thus, for example, the working fluid may comprise a binary fluid such as an ammonia-water mixture, two or more hydrocarbons, two or more freons, mixtures of hydrocarbons and freons, or the like.

Applicant's presently preferred working fluid is a water-ammonia mixture.

Enthalpy-concentration diagrams for ammonia-water are readily available and are generally accepted. The National Bureau of Standards will supply upon request an article published in the National Bureau of Standards list as Project 758-80. This paper was prepared by Wiltec Research Company, Inc., 488 South 500 West, Provo, Utah, 84601 in 1983 and deals with the experimental study of water-ammonia mixtures and their properties in a wide range of temperatures and pressures. A copy of this paper is attached to this specification and is incorporated herein by reference.

Ammonia-water provides a wide range of boiling temperatures and favorable thermodynamic characteristics. Ammonia-water is therefore a practical and potentially useful working fluid in many applications of this invention. Applicant believes, however, that when equipment economics and turbine design become paramount considerations in developing commercial embodiments of the invention, mixtures of freon-22 with toluene or other hydrocarbon or freon combinations will become more important for consideration.

In general, standard equipment may be utilized in carrying out the method of this invention. Thus, equipment such as heat exchangers, tanks, pumps, turbines, valves and fittings of the type used in typical thermodynamic cycles such as, for example, Rankine cycles, may be employed in carrying out the method of this invention. Applicant believes that the constraints upon materials of construction would be the same for this invention as for conventional Rankine cycle power or refrigeration systems. Applicant believes, however, that higher thermodynamic efficiency of this invention will result in lower capital cost per unit of useful energy recovered, primarily saving in the cost of heat exchanger and boiler equipment. Applicant believes that this invention will provide a reduction in the total cost per unit of energy produced.

The invention is now described in detail with reference to certain preferred embodiments invention and with reference to the accompanying drawings.

In the drawings:

FIG. 1 shows a schematic representation of one system for carrying out the method of this invention;
 
 

FIG. 2 shows a schematic representation of the system of FIG. 1, but with the superheating stage omitted;

FIG. 3 shows a schematic representation of an alternative embodiment of this invention;

FIG. 4 shows a schematic representation of yet a further alternative embodiment in accordance with this invention; and

FIG. 5 is a graphic representation of a temperature/enthalpy diagram to demonstrate how application of this invention can reduce the pinch point problem.

With reference to FIG. 1 of the drawings, reference numeral 50.1 refers generally to one embodiment of a thermodynamic system or cycle in accordance with this invention.

The system of cycle 50.1 comprises an absorption stage 52, a heat exchanger 54, a recuperator 56, a main heat exchanger 58, a separator stage 60, a preheater 62, pumps 64 and 66, a first evaporator stage 68, a second evaporator stage 70, a superheater section 72, and a multi-stage turbine comprising a high pressure stage 74 and a low pressure stage 76.

The system or cycle of this invention will now be described by way of example by reference to the use of an ammonia-water working solution as the initial composite stream.

This is a continuous system where a charged composite working fluid is expanded to convert its energy into usable form, and is then continually regenerated. A substantially constant and consistent quantity of composite working fluid will therefore be maintained in the system for long term use of the system.

In analyzing the system it is useful to commence with the point in the system identified by reference numeral 1 comprising the initial composite stream having an initial composition of higher and lower boiling components in the form of ammonia and water. At point 1 the initial composite stream is at a spent low pressure level. It is pumped by means of a pump 51 to an intermediate pressure level where its pressure parameters will be as at point 2 following the pump 51.

From point 2 of the flow line, the initial composite stream at an intermediate pressure is heated consecutively in the heat exchanger 54, in the recuperator 56 and in the main heat exchanger 58.

The initial composite stream is heated in the heat exchanger 54, in the recuperator 56 and in the main heat exchanger 58 by heat exchange with the spent composite working fluid from the turbine sections 74 and 76. In addition, in the heat exchanger 54 the initial composite stream is heated by the condensation stream as will be hereinafter described. In the recuperator 56 the initial composite stream is further heated by the condensation stream and by heat exchange with lean and rich working fluid fractions as will be hereinafter described.

The heating in the main heat exchanger 58 is performed only by the heat of the flow from the turbine outlet and, as such, is essentially compensation for under recuperation.

At point 5 between the main heat exchanger 58 and the separator stage 60 the initial composite stream has been subjected to distillation at the intermediate pressure in the distillation system comprising the heat exchangers 54 and 58 and the recuperator 56. If desired, auxiliary heating means from any suitable or available heat source may be employed in any one of the heat exchangers 54 or 58 or in the recuperator 56. This is shown, for example, by dotted line 59 in the heat exchanger 54.

At point 5 the initial composite stream has been partially evaporated in the distillation system and is sent to the gravity separator stage 60. In this stage 60 the enriched vapor fraction which has been generated in the distillation system, and which is enriched with the low boiling component, namely ammonia, is separated from the remainder of the initial composite stream to produce an enriched vapor fraction at point 6 and a stripped liquid fraction at point 7 from which the enriched vapor fraction has been stripped.

In the embodiment illustrated in FIG. 1, the enriched vapor fraction from point 6, is divided into first and second enriched vapor fraction streams as at points 9 and 8 respectively.

Further, in the FIG. 1 embodiment, the stripped liquid fraction from point 7 is divided into first, second and third stripped liquid fraction streams having parameters as at points 11, 10 and 14 respectively.

The enriched vapor fraction at point 6 is enriched with the lower boiling component, namely ammonia, relatively to both a rich working fluid fraction and a lean working fluid fraction as discussed below.

The first enriched vapor fraction stream from point 9 is mixed with the first stripped liquid fraction stream at point 11 to provide a rich working fluid fraction at point 13.

The second enriched vapor fraction stream at point 8 is mixed with the second stripped liquid fraction stream at point 10 to produce a lean working fluid fraction at point 12.

The rich working fluid fraction is enriched relatively to the composite working fluid (as hereinafter discussed) with the lower boiling component comprising ammonia. The lean working fluid fraction, on the other hand, is impoverished relatively to the composite working fluid (as hereinafter discussed) with respect to the lower boiling component.

The third stripped liquid fraction at point 14 comprises the remaining part of the initial composite stream and is used to constitute the condensation stream.
The difference in composition of the lean and rich working fluid fractions at points 12 and 13 is achieved by using difference proportions of vapor to liquid in forming these two fractions.

The lean working fluid fraction is cooled between points 12 and 15 in the recuperator 56 to condense it completely and provide a condensed lean working fluid fraction at point 15.

The rich working fluid fraction at point 13 is partially condensed in the recuperator 56 to point 16. Thereafter the rich working fluid fraction is further cooled and condensed in the preheater 62 (from point 16 to 18), and is finally condensed in the absorption stage 52 by means of heat exchange with a cooling water supply through points 47 to 48.

The lean working fluid fraction at point 15 is then pumped to a charged high pressure level by means of the pump 64 to provide it with parameters as at point 24. Likewise the rich working fluid fraction is pumped to the same or substantially the same charged high pressure level by means of the pump 66. Thereafter it passes through the preheater 62 to arrive at point 25 where it is substantially at the same pressure and temperature as the lean working fluid fraction which is at point 24.

In practice the temperatures at points 24 and 25 should be sufficiently high to prevent water precipitation on the surface of the tubes in the evaporator stage 68.
The flows at points 24 and 25 are then fed separately to the first evaporator stage 68. This is the low temperature stage of the evaporator system where the rich and lean working fluid fractions are heated with the lower temperature portion of a heating source supplied originally from point 43 at high temperature, and leaving the system at point 46.

In the first evaporator stage 68 the rich working fluid fraction is preferably heated from point 25 to point 27 so that it is evaporated entirely and is preferably, at point 27, in the form of a saturated vapor at its dew point. Applicant believes that this will be the most effective heat utilization in the first evaporator stage 68 and that while the rich working fluid fraction could be heated to a lower or higher temperature in this stage, this will provide no advantage and may lead to losses.

The lean working fluid fraction is likewise heated in the first evaporator stage 68 from point 24 to point 26. This is preferably heated such that the lean working fluid fraction is heated to or substantially to its boiling point by the time it reaches point 26. Again Applicant believes that this will be the most effective utilization of heat in relation to the lean working fluid fraction in the first evaporator stage 68, and that heating to a lower or higher temperature will reduce the efficiency of the cycle.

The lean and rich working fluid fractions 26 and 27 are then mixed to form, at point 28, a composite working fluid. When they are mixed they are in thermodynamical equilibrium both in regard to temperature and pressure. Thermodynamical losses on mixing should therefore be very low.
The charged composite working fluid from point 28 is then fed through the second evaporator stage 70 where it is preferably evaporated completely to produce the charged composite working fluid in gaseous form. This is at point 29. From point 29 to point 30 the charged composite working fluid is superheated in the superheater stage 72.

The composite working fluid, with parameters at point 30 is then sent through the high pressure stage 74 of the turbine to transform its energy into usable form.
Both the high pressure stage 74 and the low pressure stage 76 of the turbine are shown to comprise four separate stages. Any appropriate turbine system may, however, be used instead.

After passing through the high pressure stage 74 of the turbine the composite working fluid has parameters as at point 34, with a lower pressure and lower temperature than it had at point 30. From point 34 the composite working fluid is sent back into the superheater section 72 of the evaporator stage, where it is reheated from point 34 to point 35 and is then fed into the low pressure stage 76 of the turbine, where it is fully expanded until it reaches the spent low pressure level at point 39. At point 39 the composite working fluid preferably has such a low pressure that it cannot be condensed at this pressure and at the available ambient temperature. From point 39 the spent composite working fluid flows through the main heat exchanger 58, through the recuperator 56 and through the heat exchanger 54. Here it is partially condensed and the released heat is used to preheat the incoming flow as previously discussed.

The spent composite working fluid at point 42 is then mixed with the condensation stream at point 20. At point 20 the condensation stream has been throttled from point 19 to reduce its pressure to the low pressure level of the spent composite working fluid at point 42. The resultant mixture is then fed from point 21 through the absorption stage 52 where the spent composite working fluid is absorbed in the condensation stream to regenerate the initial composite stream at point 1.

With reference to FIG. 2 of the drawings, reference numeral 50.2 refers generally to an alternative embodiment of an energy system or cycle in accordance with this invention.

The system 50.2 corresponds in all respects with the system 50.1, except that the superheater stage 72 of FIG. 1 has been omitted, and that there is no recycle of the partially expanded composite working fluid through such a superheater stage.

With reference to FIG. 3 of the drawings, reference numeral 50.3 refers to yet a further alternative embodiment of a system or cycle in accordance with this invention.

The system 50.3 corresponds substantially with the system 50.1 of FIG. 1, and corresponding parts are identified with corresponding reference numerals.

In the system 50.3 the stripped liquid fraction at point 7 is divided into first, second and third stripped liquid fractions at points 11, 15 and 10 respectively. Further, in this embodiment, only one enriched vapor fraction is produced at point 6. It is not split into two vapor fraction streams as in the case of the cycles 50.1 and 50.2.

The enriched vapor fraction at point 9 is mixed with the first stripped liquid fraction stream from point 11 to produce the rich working fluid fraction at point 13.

The rich working fluid fraction at point 13 is condensed and cooled in the same way as discussed with reference to FIG. 1 through the recuperator 56, the preheater 62 and the absorption stage 52. It is then pumped to the charged high pressure level by means of the pump 66, passes through the preheater 62 and arrives at point 25.

The second stripped liquid fraction stream is obtained at point 15 after passing, together with the third stripped liquid fraction stream, through the recuperator 56. After point 17, the second and third stripped liquid fraction streams are split with the one being conveyed to point 15 to constitute the lean working fluid fraction. The third stripped liquid fraction stream from point 10 passes through the heat exchanger 54, is throttled from point 19 to point 20 to reach the spent low pressure level, and thus constitutes the condensation stream for absorbing the spent composite working fluid from point 42 in the absorption stage 52.

The lean working fluid fraction at point 15 is pumped to the charged high pressure level by means of the pump 64 and arrives at point 24 where it has substantially the same pressure and temperature parameters as the rich working fluid fraction at point 25.

The remainder of the process is then exactly the same as described with reference to FIG. 1.

With reference to FIG. 4 of the drawings, reference numeral 50.4 refers to yet a further alternative embodiment of a thermodynamic system or cycle in accordance with this invention.

The cycle 50.4 corresponds generally with the cycle 50.2 and thus with the cycle 50.1 as illustrated in FIGS. 2 and 1 of the drawings. Corresponding parts are therefore indicated by corresponding reference numerals.

In the system 50.4, unlike the embodiments of the previous figures, only portion of the initial composite stream which is at the intermediate pressure at point 2 is subjected to distillation in the distillation stage.

In the system 50.4 the enriched vapor fraction at point 6 is again, as in the case of the system 50.1, divided into first and second enriched vapor fraction streams at points 9 and 8 respectively. These streams flow through the recuperator 56 where they are cooled for partial condensation.

The stripped liquid fraction from point 7, comprises the condensation stream. It flows from point 14 through the recuperator 56 to point 17, through the heat exchanger 54 to point 19, and then through the throttle valve to point 20 to absorb therein, in the absorption stage 52, the spent composite working fluid to regenerate the initial composite stream at point 1 as described with reference to FIG. 1.

After point 2 the remaining part of the initial composite stream which is not subjected to distillation in the distillation system, is extracted and divided into first and second composite streams 11 and 10 respectively.

The second enriched vapor fraction stream from point 8, after passing through the recuperator 56, is mixed with the second composite stream from point 10, to constitute the lean working fluid fraction at point 15. This is then again pumped by means of the pump 64 to the charged high pressure level to yield the lean working fluid fraction at point 24.

The first enriched vapor fraction stream from point 9 is fed through the recuperator 56 and through the preheater 62. Thereafter, from point 18, it is mixed with the first composite stream from point 11. This then yields the rich working fluid fraction at point 13 which passes through the absorption stage 52, through the pump 66, and through the preheater 62 to arrive at point 25 with the appropriate temperature and pressure parameters.

As in the case of the embodiment of FIG. 1, these two streams then pass through the first absorption stage, are then mixed at point 28, and are then evaporated in the second absorption stage 70.

The embodiment illustrated in FIG. 4 corresponds with the cycle 50.2. It may also, of course, include a superheater stage 72 and a recycle loop 34 to 35 as illustrated in FIG. 1.

Persons of ordinary skill in this art will appreciate that for appropriate circumstances and conditions, a plurality of lean working fluid fractions or rich working fluid fractions can be generated by selecting quantities of enriched vapor fractions from zero up, and by selecting stripped liquid fractions and/or initial composite stream fractions in appropriate quantities as may be desired.

Applicant will now, without wishing to bound by theory, try to explain the theoretical basis for this invention with reference to the graph of FIG. 5. In this graph temperature is plotted against enthalpy for what Applicant believes would be a typical water-ammonia system in accordance with this invention. The points given in this graph correspond with the points used for the various parameters in the cycle 50.1 of FIG. 1.

The first evaporator stage 68 or the low temperature evaporator stage 68 can be considered as being divided into two portions. In the first portion the rich working fluid fraction and the lean working fluid fraction are heated from points 25 and 24 respectively up to the point designated t.sub.br. Both the rich and the lean working fluid fractions are below their boiling points. In the second part of the first evaporator stage 68, beyond the point t.sub.br the temperatures of both the rich and lean working fluid fractions are above their bubble point temperatures.

If one were to introduce into the first separation stage only the rich working fluid fraction at its given pressure, such a fluid would begin to boil at point t.sub.br. This is a relatively low temperature and will permit the use of the available heat source in full. However, the whole boiling process will take place at a relatively low temperature which would result in increased temperature differences in most parts of the evaporator stage and consequently would result in relatively high thermodynamic losses. This theoretical process is shown in FIG. 5 by the line between point 25 and t.sub.br, by the dotted line from point t.sub.br to point 29a and by the dotted line from point 29a to point 29.

The cooling of the heat source is designated with a chain dotted line from point 43 through to point 46.

If a person were now trying to introduce the composite working fluid, comprising the mixture of the rich working fluid fraction at point 25 and the lean working fluid fraction at point 24, at the same given pressure, while trying to use the available heat source in full, this fluid would only begin to boil at a temperature t.sub.b. This is a temperature which is higher than the temperature of the heat source in the corresponding part of the evaporator stage 68. This would consequently make the process impossible. This impossible process is demonstrated in FIG. 5 by the line 24-t.sub.br -t.sub.b -28-29. Such a process would only be possible if incomplete use is made of the available heat source and the corresponding thermodynamic losses are incurred.

When, however, the rich working fluid fraction and lean working fluid fraction are introduced separately into the first evaporation stage 68 in accordance with this invention, the rich working fluid fraction will start to boil at the relatively low temperature t.sub.br, thereby reducing the "pinch point" problem. At the same time, because the rich working fluid fraction and lean working fluid fraction have been combined at point 28, when they are in thermodynamical equilibrium, the boiling process will take place at a relatively high temperature. The thermodynamic losses are therefore reduced. This, in turn, permits the system to accommodate an increased pressure in the evaporator stage and consequently at the turbine inlet. This combined process is shown in FIG. 5 by the solid line 24-29.

This resultant summary of the enthalpy of the two systems, demonstrates that the curve followed by the system of this invention through the first evaporator stage 68, is further away from the heating medium line in the pinch point zone to thereby reduce the pinch point problem, while it approaches the heating medium line more closely after point 28 to reduce the thermodynamic losses.

Applicant believes that by using more than two working fluid fractions of varying composition which are combined in successive stages as they pass through successive evaporator stages, and by using superheating in an effective number of stages, the heating curve of the working fluid fraction can be smoothened to approach that of the heating fluid more closely and thereby lead to a reduction in thermodynamic losses.

In certain embodiments of the invention where the composite working fluid has been expanded from a very high pressure to a spent low pressure level, the working fluid may, at point 39, have a temperature which is too low. It may also have a significant content of condensed liquid. As a result it can have an adverse effect on the performance of the last stages of the turbine 76. In addition, the quantity and quality of heat remaining in this stream after point 39 may not be sufficient to provide for distillation of the initial composite stream and thus for regeneration of the working fluid fraction. Applicant believes that this potential disadvantage may overcome by the superheater stage 72 and by the recycle loop as employed between points 34 and 35 in FIGS. 1 and 3.


US Patent # 4,586,340
( May 6, 1986 )
Method and Apparatus for Implementing a Thermodynamic Cycle using a Fluid of Changing Concentration
Alexander Kalina
 
Abstract --- A method and apparatus for implementing a thermodynamic cycle involves utilizing partial distillation of a multi-component working fluid stream. At least one main enriched solution is produced which is relatively enriched with respect to the lower boiling temperature component, together with at least one lean solution which is relatively impoverished with the respect of lower boiling temperature component. The main working fluid is expanded to a low pressure level to convert energy to a usable form. This spent low pressure level working fluid is condensed by dissolving with cooling in the lean solution to regenerate an initial working fluid for reuse. A portion of the impoverished fraction may be injected into the charged gaseous main working fluid in order to obtain added work and to increase system efficiency by decreasing the temperature of the output fluid flow when the fluid flow would otherwise have been superheated. A low pressure, low temperature expanded spent fluid may be distilled using low quality heat to create an enriched solution which has a significantly higher concentration of the lower boiling component. For this enriched solution, a reduced temperature and pressure is sufficient to enable distillation. The efficiency of the cycle may be enhanced by charging the spent fluid with the lower boiling temperature component prior to distillation. This may be accomplished by lowering the pressure of the impoverished fraction to separate an additional lower boiling temperature fraction.

Current U.S. Class: 60/673; 60/649; 60/677
Intern'l Class:  F01K 025/06
Field of Search:  60/649,673,677

References Cited

U.S. Patent Documents
USP # 4,534,175 ~ Aug., 1985 ~ Kogan, et al. ~ 60/649.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to methods and apparatus for transforming energy from a heat source into usable form using a working fluid that is expanded and regenerated. This invention further relates to a method and apparatus for improving the heat utilization efficiency of a thermodynamic cycle.

2. Brief Description of the Background Art

In the Rankine cycle, the working fluid such as water, ammonia or a freon is evaporated in an evaporator utilizing an available heat source. The evaporated gaseous working fluid is expanded across a turbine to transform its energy into usable form. The spent gaseous working fluid is then condensed in a condenser using an available cooling medium. The pressure of the condensed working medium is increased by pumping, followed by evaporation, and so on to continue the cycle.

The basic Kalina cycle, described in U.S. Pat. No. 4,346,561, utilizes a binary or multi-component working fluid. This cycle operates generally on the principle that a binary working fluid is pumped as a liquid to a high working pressure and is heated to partially vaporize the working fluid. The fluid is then flashed to separate high and low boiling working fluids and the low boiling component is expanded through a turbine to drive the turbine, while the high boiling component has heat recovered for use in heating the binary working fluid prior to evaporation. The high boiling component is then mixed with the spent low boiling working fluid to absorb the spent working fluid in a condenser in the presence of a cooling medium.

A theoretical comparison of the conventional Rankine cycle and the Kalina cycle demonstrates the improved efficiency of the new cycle over the Rankine cycle when an available, relatively low temperature heat source such as ocean water, geothermal energy or the like is employed.

In applicant's further invention, referred to as the Exergy cycle, the subject of U.S. patent application Ser. No. 405,942, filed Aug. 6, 1982, now U.S. Pat. No. 4,489,563 relatively lower temperature avilable heat is utilized to effect partial distillation of at least a portion of a multicomponent working fluid stream at an intermediate pressure to generate working fluid fractions of differing compositions. The fractions are used to produce at least one main rich solution which is relatively enriched with respect to the lower boiling component, and to produce at least one lean solution which is relatively impoverished with respect to the lower boiling component. The pressure of the main rich solution is increased; thereafter, it is evaporated to produce a charged gaseous main working fluid. The main working fluid is expanded to a low pressure level to convert energy to usable form. The spent low pressure level working fluid is condensed in a main absorption stage by dissolving with cooling in the lean solution to regenerate an initial working fluid for reuse.

The inventor of the present invention has appreciated that it would be highly desirable to enable the efficient use of a very low pressure and temperature fluid at the turbine outlet, in the Exergy cycle. Regardless of the temperature of the cooling water in the condenser, the higher the pressure of condensation in the Exergy cycle, the higher is the concentration of the lower boiling component in the basic solution. However, the higher the pressure of condensation, the higher the pressure at the turbine outlet and the higher the concentration of the lower boiling component at the turbine outlet. This higher concentration basic solution requires for distillation, heat of a lower temperature. Thus, by reducing the pressure, and consequently the temperature at the turbine outlet, the concentration of the lower boiling component of the basic solution may be lowered and a higher temperature may be required at the turbine outlet to provide for distillation.

This contradiction might be addressed by balancing the pressure at the turbine outlet with the cooling water temperature. However, to achieve the maximum power output, the turbine outlet pressure must be as low as possible. When the turbine outlet pressure and temperature are reduced, as described above, the concentration of the lower boiling component of the basic solution decreases. This results in a cycle requiring exactly the opposite action to increase the turbine outlet pressure and temperature. The situation worsens with higher available cooling water temperature.

The inventor of the present invention has also appreciated the desirability of controlling the outlet temperature of the fluid exiting the turbine in the Exergy cycle. The efficiency of a thermodynamic cycle such as the Exergy cycle may be improved by heating the fluid in the boiler to the highest possible temperature with the available heat source. However, it is still desirable that the fluid exiting from the turbine be at a temperature and pressure close to that of a saturated vapor. To the extent that the exiting vapor is superheated, exergy is wasted.

It is particularly desirable in the Exergy cycle to obtain only slightly superheated vapor or saturated vapor from the turbine while inputting fluid at the highest possible temperature to the turbine. This is because in the Exergy cycle the output from the turbine is not simply condensed, but instead is used for distillation. The superheating of the fluid outletted from the turbine may cause unnecessary exergy losses in the cycle as a whole. For example, since the spent fluid from the turbine may be used to pre-heat the condensed fluid in a heat exchanger prior to regeneration, as described in the aforementioned patent application, an inefficiently high temperature difference may exist in the heat exchanger.

If one attempts to overcome this problem by further fluid expansion in the turbine, one obtains a lower temperature at the turbine outlet but a lower pressure as well. This lower pressure fluid is more troublesome to distill because more heat is required and this lower pressure fluid requires a larger quantity of lean solution to absorb it. Thus, this approach to the solution of the problem of exergy losses arising from the high temperature of the fluid exiting the turbine is not desirable.

SUMMARY OF THE INVENTION

It is a primary object of one aspect of the present invention to provide a method and apparatus for increasing the efficiency of the Exergy cycle by enabling the selection of a low pressure and temperature basic solution at the turbine outlet through enrichment of the basic solution from the turbine prior to its regeneration by partial distillation.

It is a further object of the present invention to provide such a method and apparatus that lessens the heat loading on the condenser.

It is a primary object of another aspect of the present invention, to decrease the exergy losses arising from the superheating of the fluid exiting from the turbine without unduly lowering the pressure of the fluid.

It is another object of the present invention to provide a method and apparatus that efficiently regulates the temperature of the fluid exiting from a turbine in the Exergy cycle and uses any extra heat to obtain extra energy in the turbine.

These and other objects of the present invention may be achieved by a method of generating usable energy including the step of vaporizing at an upper intermediate pressure, only part of an initial multi-component working fluid stream having lower and higher temperature boiling components to form a first vapor fraction. The first vapor fraction is therefore enriched with the lower boiling temperature component. The vapor fraction is mixed with part of the initial working fluid stream and absorbed therein to produce a rich solution, enriched relatively to the initial working fluid stream with respect to the lower temperature boiling component. The remaining part of the initial working fluid stream is used as a lean solution which is impoverished relatively to the main solution with respect to the lower temperature boiling component. The pressure of the rich solution is increased to a charged high pressure level. The rich solution is evaporated to produce a charged gaseous main working fluid that is expanded to a spent low pressure level to transform its energy into usable form. The spent main working fluid is cooled and condensed by absorbing it in a part of the lean solution. An enriched fraction is separated from a part of the lean solution. The enriched fraction is enriched relatively to the lean solution with respect to the lower boiling temperature component. The enriched fraction is mixed with the condensed main working fluid to form an initial multi-component working fluid stream.

In accordance with another preferred embodiment of the present invention a method of generating usable energy includes the step of generating a vapor fraction by vaporizing only part of an initial multi-component working fluid stream having lower and higher temperature boiling components. The vapor fraction is enriched with the lower boiling temperature component. The vapor fraction is mixed with part of the initial working fluid stream and absorbed therein to produce a rich solution enriched relatively to the working fluid stream with respect to the lower temperature component. The remaining part of the initial working fluid stream is used as a lean solution impoverished relatively to the rich solution with respect to lower temperature boiling component. The pressure of the rich solution is increased to a charged high pressure level. The rich solution is evaporated to produce a charged, superheated gaseous main working fluid and expanded to a spent low pressure level to convert energy into a usable form. The spent main working fluid is cooled and condensed by dissolving it in a portion of the lean solution. A portion of the lean solution is also injected into the charged gaseous working fluid to lower the temperature of the gaseous working fluid. This injection may be made into the charged gaseous working fluid while the main working fluid is continuing to expand or it may be made into the gaseous main working fluid after the fluid has been completely expanded.

In accordance with still another preferred embodiment of the present invention an apparatus for generating usable energy with a multi-component working fluid includes a turbine with a gas inlet and a gas outlet. A distilling device is in fluid communication with the turbine gas outlet. This device is adapted to separate a lower boiling temperature component from a higher boiling temperature component of the multi-component working fluid using the heat of the outlet gas from the turbine. The distilling device includes a mixing section arranged to mix separated lower boiling temperature fraction with the working fluid to form a rich solution. A condenser is arranged to condense the rich solution and an evaporator communicates with the condenser and the inlet to the turbine. The injector is arranged to inject lean solution from the distilling device into the superheated fluid near the outlet of the turbine.

In accordance with yet another preferred embodiment of the present invention, an apparatus for generating usable energy with a multi-component working fluid includes a turbine having a gas inlet and a gas outlet and a condenser connected to condense the spent fluid from the turbine. A first distilling device is in fluid communication with the turbine gas outlet. This device is adapted to separate a lower boiling temperature component from a higher boiling temperature component and the multi-component working fluid. The distilling device includes a mixing section arranged to mix a separated lower boiling temperature fraction with the working fluid to form a rich solution. The second distilling device is arranged to separate a lower boiling temperature fraction from the fluid remaining after the lower boiling temperature component has been separated in the first distilling device. The second distilling device includes a mixer section adapted to mix a lower boiling temperature fraction separated by the second distilling device into the spent fluid from the condenser. An evaporator communicates with the condenser and the inlet to the turbine.

In accordance with another preferred embodiment of the present invention a regenerator for spent multi-component working fluid having a temperature and pressure too low for condensation by conventional means with an available cooling medium includes a first pump for increasing the pressure of the spent fluid. A concentrator increases the concentration of the lower boiling temperature component of the working fluid. A second pump increases the pressure of the concentrated fluid. A heat exchanger, communicating with the concentrator, is arranged to transfer heat from the unconcentrated spent fluid and to transfer heat to the concentrated spent fluid. A first separator communicates with the heat exchanger for separating a portion of the lower boiling temperature component from the concentrated fluid and for recombining the separated portion of the lower boiling temperature component with a portion of the remainder of the concentrated fluid so as to form a regenerated working fluid that may be condensed by the available cooling system. A second separator for extracting a lower boiling temperature component from a portion of the remainder of the concentrated fluid is arranged to supply lower boiling temperature component to the concentrator. The second separator may include a fluid pressure lowering device for extracting the lower boiling temperature component.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic representation of one system for carrying out one embodiment of the method and apparatus of the present invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

Referring to the drawing wherein like reference characters are utilized for like parts throughout the several views, a system 10, shown in FIG. 1, implements a thermodynamic cycle, in accordance with one embodiment of the present invention, using a boiler 102, a turbine 104, a condenser 106, a pump 108, and a distilling subsystem 126. The subsystem 126 includes a recuperator 110, a distilling gravity separator 112, a heater 114, a preheater 116, a deconcentrating separator 118, and a concentrator 120.

Various types of heat sources may be used to drive the cycle of this invention. Thus, for example, heat sources with temperatures as high as, say 500° C. or more, down to low heat sources such as those obtained from ocean thermal gradients may be utilized. Heat sources such as, for example, low grade primary fuel, waste heat, geothermal heat, solar heat or ocean thermal energy conversion systems may be implemented with the present invention.

A variety of working fluids may be used in conjunction with this system including any multi-component working fluid that comprises a lower boiling point fluid and a relatively higher boiling point fluid. Thus, for example, the working fluid may be an ammonia-water mixture, two or more hydrocarbons, two or more freons, mixtures of hydrocarbons and freons or the like. In general the fluid may be mixtures of any number of compounds with favorable thermodynamic characteristics and solubility. The system or cycle of this invention may be described by way of example by reference to the use of an ammonia-water working solution.

In an ammonia/water working solution, the ammonia constitutes the lower boiling component with a boiling point of -33° C., while water is the higher boiling component with a boiling point of 100° C. Then the higher the concentration of ammonia, the lower the boiling point of the water/ammonia composite.

The charged composite working fluid implements a continuous system wherein the fluid is expanded to convert energy into an usable form followed by continuous regeneration. A substantially constant and consistent quantity of the composite working fluid may therefore by maintained in the system for long term use.

The Exergy cycle utilized herein is generally described in pending U.S. patent application Ser. No. 405,942, filed on Aug. 6, 1982 in the name of the inventor of the present invention, and in ASME paper 84-GT-173 entitled "Combined Cycle System With Novel Bottoming Cycle" by A. I. Kalina. The pending application and ASME paper are hereby expressly incorporated herein by reference.

The basic spent working fluid in a condensed state, termed the distillation fluid herein, at point 1 has its pressure increased by the pump 122 to point 2 where the fluid exists as a subcooled liquid at a lower intermediate pressure, which is intermediate which respect to the pressure at the turbine inlet 30 and outlet 38. From point 2 the subcooled liquid is directed through the top of the concentrator 120 where it is mixed, for example by spraying, with the flow of saturated vapor having a higher concentration of the lower boiling point component arriving from point 28. The pressure at point 28 is made essentially the same as the pressure at point 2. Because of the increase in the pressure provided by the pump 122 the distillation fluid more easily absorbs the saturated vapor arriving from the point 28.

As a result of mixing in the concentrator 120, a saturated liquid passes outwardly from the concentrator 120 through the point 41. This saturated liquid has a higher concentration of the lower boiling component than the liquid existing at the point 2 so that the liquid at point 41 may be termed an "enriched" liquid. This enriched liquid is pumped by the pump 124 to an upper intermediate pressure at point 42. The liquid is then successively heated in preheater 116, heater 114, and recuperator 110. The heating processes in the preheater 116 and heater 114 are performed by recuperation of the heat of counterflowing outlet fluid from the turbine 104 as well as the heat from other fluids utilized in the system. However, the heating in the recuperator 110 is performed only by the heat of the flow from the turbine 104 outlet 38 and, as such, is compensation for under recuperation.

The enriched flow at point 5, for example, is partially evaporated and passes into the distilling gravity separator 112. Vapor, strongly enriched by the lower boiling point component is separated and passes through point 6. A lean stripped liquid, impoverished with respect to the lower boiling component which is substantially removed, exits from the separator 112 through point 7.

The lean liquid flow from the separator 112 is divided into three flow paths, identified by the points 8, 10, and 40. The flow of liquid passing through point 8 is proportionately mixed with the vapor from point 6. As a result, the generated mixture, passing point 9, has the necessary concentration of lower boiling and higher boiling components, to be used as the working fluid for the remainder of the cycle. The proportion of lower and higher boiling components forming the working fluid is selected to minimize the energy losses during operation. Generally, the fluid at point 9 is enriched with the lower boiling component with respect to the fluid at point 5.

In order to achieve the greatest possible efficiency it is also advantageous to choose the working composition concentration to get the minimum exergy losses in the boiler 102. As a practical matter, the applicable optimal range lies between 50 to 70 percent by weight of the low boiling component in most, but not necessarily all cases. Generally, it is advantageous to include at least 20 to 25% by weight of the higher boiling component.

This enriched working fluid is cooled in the heater 114, thereby providing the heat for the heating of the fluid passing from the point 3 to the point 4, as described above. In the boiler preheater 130, the flow is further cooled so that the fluid is completely condensed in the condenser 106, by cooling water flowing along the line 24 to 23.

The condensed working fluid is pumped by the pump 108 from the point 14 to the point 21 so that it moves counterflow through the preheater 116. The working fluid then flows through the boiler 102 where it is heated and preferably substantially evaporated. Most preferably the working fluid is completely evaporated, and superheated at point 30. The flow of boiler heating fluid is indicated by the line 25 to 26.

The superheated vapor is then expanded in the turbine 104 outputting the desired mechanical power. If the working fluid at point 38 is still superheated vapor, lean liquid from the distilling gravity separator 112 may be injected into the expanding working fluid in the turbine 104. This injection is most practical into the inlet to the last or the next to the last turbine stage. However, this result may also be accomplished by injection into fluid stream following exit from the turbine 104, for example at the point 38, as indicated in a dashed line in FIG. 1. As a result of this injection near the turbine outlet, the working fluid from the previous stage of the turbine 104 has its concentration changed in travelling from the point 36 to the point 39.

When the saturated liquid injection is accomplished before the last turbine stage it must be done in such proportions that the state of the working fluid in the following stage of the turbine 104 is still a superheated vapor. However, the temperature of the mixed gas at the point 39 is lower than the temperature of the gas in the turbine preceeding injection. Also, the concentration of the lower boiling point component at the point 39 is lower than the concentration at the point preceeding injection. The enthalpy at the point 39 is also lower than the enthalpy at the point preceding injection. Similarly the enthalpy, temperature and lower boiling component concentration at the outlet of the turbine 104 are lower than they would have been without injection. In addition, the weight flow rate at the turbine outlet is higher than at the point preceeding injection, since this flow rate is equal to the sum of the flow rates into the juncture 132.

The injection is most advantageously proportioned so that the outlet of the last stage of the turbine 104 has the characteristics of a saturated or wet vapor instead of superheated vapor. Alternatively, where injection is performed into the gas that has already exited from the turbine, the gas becomes a saturated vapor upon mixing with the injected fluid.

The pressure of the inlet fluid in the line 136 is made substantially equal to the pressure in the line 137 preceeding injection. To achieve this result, a pressure equalizing device 138 is utilized. The pressure equalizing device 138 may take the form of a throttle valve, when it is necessary to decrease the pressure of the incoming fluid to match that of the turbine. The device 138 may be totally omitted when the pressure of the inlet flow happens to equal that of the flow within the turbine 104. The pressure equalizing device 138 may take the form of a pump when it is necessary to increase the pressure in the line 136 to equal that in the line 137.

The turbine outlet flow passes from the point 38 consecutively through the recuperator 110, heater 114, and preheater 116 so that the flow is cooled and partially condensed. However, the pressure at the turbine outlet and consequently, at the recuperator 110 outlet, the heater 114 outlet, and the preheater 116 outlet may be so low that it may not be possible to condense the fluid at that pressure with the available cooling water temperature. While this result may appear to be unfortunate at first glance, in fact, this means that the energy of the fluid has been fully utilized in the turbine 104.

To overcome this problem, a portion of the stripped liquid flow removed from the distilling separator 112 is cooled in the heater 114 as it flows from the point 10 to the point 12. This process provides the heat necessary for the heating process of the fluid moving from point 3 to point 4. The stripped liquid flow is throttled by the throttle valve 140 to the lower intermediate pressure, at the point 27 (so that pressure at point 27 equals pressure at point 2). This fluid, at the lower intermediate pressure, is directed into the de-concentrating separator 118 where it is separated into two streams due to the lowering of the fluid pressure by the valve 140. The first stream is a saturated vapor which extends through the point 28, and is relatively enriched with respect to the lower boiling component. The second stream is an absorbing, lean solution passing through point 29, that is relatively impoverished with respect to the lower boiling component and therefore tends to readily absorb the low boiling component. The vapor passing through the point 28 is directed into the concentrator 120 where it is mixed with subcooled liquid flow from point 2 to increase the lower boiling component concentration of the fluid.

The absorbing lean solution passes the point 29 with the same pressure as the enriched flow at point 42 (upper intermediate pressure), but the lean solution has a much lower concentration of the lower boiling component than the flow at point 42. As a result, the temperature at the point 29 is always higher than the temperature at the point 42. Therefore the absorbing, lean flow at point 29 is sent through the preheater 116 where it is cooled, providing part of the heat necessary for heating the fluid flowing from the concentrator 120 through the preheater 116.

The cooled, absorbing, lean solution is throttled by the throttle valve 142 to a low pressure substantially equal to the pressure at the turbine outlet with parameters similar to those at the point 17. The turbine outlet flow at point 17 and the absorbing, lean solution flow at point 19 are mixed, generating a flow of a basic solution at point 18. The concentration of the higher boiling component in the flow at the point 18 is such that the fluid can be completely condensed at the available cooling water temperature. Therefore, this flow is fully condensed in the condenser 106 to reach the parameters of the fluid at point 1, after which the above-described process is repeated.

Those skilled in the art will appreciate that it is desirable in terms of thermal efficiency to have the highest possible fluid temperature at the inlet to the turbine. This is because it always beneficial to have the working fluid and the heating fluid at relatively close temperatures. By maximizing the temperature at the inlet to the turbine 104, a greater power output may be obtained from the turbine 104 with a consequently greater enthalpy drop than would be obtained if a lower temperature were utilized.

Nevertheless, the temperature at the turbine outlet must increase corresponding to the increased temperature at the turbine inlet. This may mean that the working fluid flow leaving the turbine 104 may still be in a superheated vapor state. However, this extra energy existing in the form of superheated vapor is essentially useless in the distillation process and is generally useless in the cycle as a whole. This means that there is an incomplete use of the energy potential of the working fluid.

To achieve the highest possible cycle efficiency, a relatively high concentration of the lower boiling point component in the working fluid passing through the boiler 102 and the turbine 104 is desirable. However, at the same time, it is preferable to have a lower concentration of the lower boiling component in the turbine output flow passing through the distillation subsystem 126.

Thus the injection of liquid into the turbine 104 through the injector 139, immediately reduces the lower boiling component concentration of the flow passing through the last stages of the turbine 104, causing thermodynamic losses. Those losses are compensated for by the higher weight flow rate of the flow through the last stages of the turbine 104. Absent this accommodation, the potential energy in the fluid flow through the turbine would be unused and would be essentially wasted in the heat exchange processes of the distillation subsystem 126.

It should be understood that the present cycle may be operable without the use of injection of liquids from the separator 112 into the turbine 104. Specifically if the fluid exiting from the outlet of the turbine 104 is not superheated, injection may be wasteful and is generally unnecessary.

When injection of liquid into the turbine 104 is appropriate, the point of injection is determined by the point where the smallest possible exergy losses result in the cycle. One of ordinary skill in the art will be capable of determining this point. It generally will lie somewhere in the latter stages of the turbine or after exit from the turbine.

Through the use of the liquid injection system, additional power may be gained from the turbine 104. This arises primarily from the higher flow rate through the turbine 104. However, it can be appreciated that the available energy is utilized in a more efficient manner to increase the output from the turbine 104.

The concentrator 120 and related components enable the concentration of the basic solution to be chosen to accommodate a relatively low pressure and temperature at the turbine outlet. Thus, even where the pressure and temperature at the turbine outlet are seemingly insufficient to enable distillation of the basic solution, the operation of the system is not adversely affected. This is because an enriched solution, having a significantly higher concentration of the lower boiling component, is the one that is subjected to the distillation process. For this enriched solution a lower turbine outlet temperature is sufficient to enable distillation to proceed on an efficient basis.

However, it should also be appreciated that this result is achieved while decreasing the heat loading on the condenser 106. This is because part of the hot liquid from the separator 112 is diverted to other processes, without condensation, and therefore less condensation is necessary. In other words, the fluid outletted from the turbine 104 is mixed, before condensation, with absorbing, lean flow which is even leaner than the liquid flow coming from the distilling separator 112. Therefore, after absorption, the leaner portion of the flow which is coming into the condenser 106 is in the form of liquid, and thus a lower quantity of heat has to be removed to produce condensation. This presumably lowers condenser surface requirements and increases the efficiency of the system.

Overall, with present invention using the injector 139, the average temperature of the fluid flow from the point 38 to the point 17 is effectively increased. At the same time the average temperature of the required heat from the point 42 to the point 5 is decreased by injecting the enriched vapor in the concentrator 120. Thus, separately and in combination, these effects serve to increase overall system efficiency.

Relatively lower temperature heat for the distillation subsystem 126 of this invention may be obtained in the form of spent relatively high temperature heat, the lower temperature part of relatively higher temperature heat from a heat source, the relatively lower temperature waste or other heat which is available from a heat source, and/or the relatively lower temperature heat that cannot be utilized efficiently for evaporation in the boiler. In practice, any available heat, particularly lower temperature heat which cannot be used effectively for evaporation, may be utilized as the relatively lower temperature heat for the distillation subsystem 126. In the same way such relatively lower temperature heat may be used for preheating.

While the present invention has been described with respect to a single preferred embodiment, those skilled in the art will appreciate a number of variations and modifications therefrom and it is intended within the appended claims to cover all such variations and modifications as come within the true spirit and scope of the present invention.




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