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Alexander KALINA

Steam Cycle ( I )

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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.

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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.

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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.

---

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.

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 simplif