Cryogenic Absorption Cycles

Abstract

For the development of power and/or the production of cryogenic fluids, e.g., oxygen, absorption refrigeration cycles are employed. For example, one process comprises the steps of absorbing a refrigerant vapor in a liquid absorbent, increasing the pressure on resultant mixture of said refrigerant and said absorbent, distilling and rectifying the mixture into substantially pure refrigerant vapor and pure absorbent, reducing the pressure on resultant pure liquid absorbent and returning the latter to the absorbing step, cooling and condensing the refrigerant vapor to the liquid state, reducing the pressure upon the liquid refrigerant to below the triple point of the refrigerant to produce solid refrigerant, sublimating the solid refrigerant to the vapor state, and passing resultant refrigerant vapor to the absorbing step at a rate that maintains the pressure below the triple point.

Description

This invention relates to improvements in industrial processes for the development of power and the production of useful industrial products, such as liquid air, liquid oxygen, liquid nitrogen and the development of cryogenic temperatures and is based upon new arrangements and cycles of absorption refrigeration.

BACKGROUND OF THE INVENTION

Since the development of the steam engine in the Seventeenth Century, the common source of energy for man's use has been the combustion of fossils fuels at high temperatures. This burning of fossils fuel in either a furnace or in an internal combustion engine has resulted in the pollution of the atmosphere with both the products of combustion and with heat, and the removal of heat in the development of power has resulted in the thermal pollution of large bodies of water. In a high temperature energy system, such as the steam turbine, the working fluid water is first evaporated at high pressure and then expanded in the turbine and finally condensed to liquid at temperatures above the ambient temperature. The heat rejected is usually discharged into a river or lake. The use of water as the working fluid introduces the exceedingly high heat of vaporization of water. This heat of vaporization is energy of which a large part is lost in the system. Because the prior processes can utilize only a small fraction of the heat supplied by the burning of fuel, the net result is that our environment is subjected to a serious thermal pollution.

SUMMARY OF THE INVENTION

The present invention offers techniques which permit the reduction of polluting effect of the prior process for converting heat into power, as these techniques utilize heat which has been wasted. One embodiment of the present invention begins with air at ambient temperature and pressure and liquifies the air at subatmospheric pressure and temperature and recovers the energy from the air. As a feature of this process the air can be heated during the process by what is now considered to be waste heat, and the energy of this waste heat recovered. The present invention teaches the recovery of useful work from waste heat and from solar energy.

This invention is based upon the employment of one or more absorption refrigeration cycles, so arranged that energy may be recovered from the cycle and allows the production of cryogenic temperatures and the production of useful products. This invention is directed to utilization primarily of cycles in which the refrigerant is highly or completely soluble in the absorbent, such as, but not limited to the use of a hydrocarbon, such as methane, in solution of a higher boiling hydrocarbon, such as ethane or propane. Other combinations such as ethane in solution in propane or propane in butane are illustrative. Further examples of useful combinations are solutions of nitrogen in methane, or ethane, or hydrogen in methane. Any hydrocarbon whose saturation pressure and temperature relationships are between that of methane and butane is acceptable. It is apparent that substituted hydrocarbons such as the halogenated hydrocarbons can be used. In order to secure the maximum differences in temperatures, this invention contemplates the employment of a cascade operation having a series of absorption refrigeration cycles using different refrigerants, such as the use of ethane or propane in the first cycle, ethane or methane in the second cycle, and methane or nitrogen in final cycle. If even lower temperatures are desired, additional cycles using neon, hydrogen or helium as the refrigerants may be employed in lower temperature cycles.

It is thus an object of this invention to provide a system in which very low cryogenic temperatures can be obtained with the energy for the system being derived from waste heat.

It is a further object of the invention to recover the latent energy from low temperature heat sources such as waste heat from power plants or from solar energy.

It is a further object of this invention to recover pure gases from air using low grade heat as the source of the energy needed to separate the pure gas from air.

It is a further object of this invention to recover pure water from saline and impure waters using an absorption refrigeration cycle to supply the energy to separate the pure water from the brine.

It is a further object of this invention to recover energy from fluids which are being liquified.

It is a further object of this invention to produce a low temperature process in which the refrigerant is sublimed.

It is still a further object of this invention to provide an evaporator-sublimator which has a porous partition.

It is a further object of the invention to provide a power system which can be utilized for the propulsion of vehicles in which the amount of heat discharged is substantially reduced and in which the efficiency is materially increased.

Further objects and advantages of the present invention will become apparent upon further study of the specification and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The more specific objects and advantages of this invention will be more readily apparent from the ensuing description wherein reference is made to the accompanying drawings illustrating the preferred embodiments of the invention.

In the drawings,

FIGS. I to X and XV to XVII are schematic flow sheets illustrating the principal features of the various embodiments.

FIG. I shows the basic absorption refrigeration cycle in a simplified form in which an evaporator-sublimator is used.

FIG. II shows an embodiment of the absorption refrigeration cycle of the basic system in which energy is recovered by the cycle.

FIG. III shows another embodiment of the basic system in which energy is recovered.

FIG. IV is another embodiment of the absorption refrigeration cycle which permits the recovery of thermal energy from the system.

FIG. V shows an embodiment of the invention in which two absorption refrigeration cycles are connected in a cascade manner and in which mechanical energy is recovered in each cycle.

FIG. VI shows an embodiment of the invention in which air is liquified and energy is recovered.

FIG. VII shows a further embodiment in which a gas is liquified and in which energy is recovered.

FIG. VIII shows a system for recovering energy from low temperature source by the use of air as a pressure medium.

FIG. IX shows a system similar to FIG. VII in which two turbines are employed.

FIG. X illustrates an embodiment of the invention in which the refrigeration cycle is combined with a saline water distillation system.

FIG. XI is cross-sectional view through an evaporator-sublimator of this invention.

FIG. XII is a cross-sectional view of another embodiment of an evaporator-sublimator of this invention.

FIG. XIII is a chart showing the conditions during a power recovery cycle of this invention.

FIG. XIV is a cross-sectional view of flash distillation vessel of this invention.

FIGS. XV and XVI are illustrations of this invention in which the power generated is used as a propulsive force.

FIG. XVII shows the invention as applied to liquefaction of gases.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates the basic refrigeration cycle employed by this invention. In this Figure and throughout the description of this specification only the basic elements of the system are described. Auxiliary equipment common to refrigeration systems is omitted from the drawing and from the description to facilitate the understanding of the principles of the invention.

The present invention employs a basic absorption system which includes the step of evaporating the refrigerant in a heat sink by the removal of heat from another body, followed by the absorption of the refrigerant in an absorbent to form a liquid solution. The solution is transferred to another place and heated to separate the refrigerant from the absorbent followed by the condensation and return of the refrigerant to the evaporator. The system preferably is operated with the separator and condenser at a higher pressure than the absorber. While it is possible to introduce a third fluid to the refrigerant and absorbent solution to produce transfer of the fluids by diffusion without the requirements for mechanical energy inputs, this invention contemplates a continuous system in which mechanical energy is used to transfer the solution of refrigerant in absorbent from the zones of lower pressure to the zones of higher pressure. This energy can be recovered, at least in part from the absorbent and the refrigerant as they move from the zones of higher pressure to the zones of lower pressure. In order that substantial refrigerating effects are obtained and that there be available substantial recovery of energy, it is contemplated to have substantial difference in pressure between these zones.

In FIG. I, the evaporator-sublimator 1 is connected by a conduit with the absorber 2. This conduit may be provided with means to produce a lower pressure in the evaporator-sublimator 1 than in the absorber 2. The provision of such means is particularly desirable when the refrigerant is present as a solid in the evaporator-sublimator and the pressure is below the triple point, and when it is desirable to increase the solubility of the refrigerant in the absorbent.

The absorber 2 receives the vapor from the evaporator-sublimator and also receives absorbent from the regenerator 3. The absorber 2 can be provided with known means for effecting contact between the vapor and the liquid. The pressure in the absorber will be maintained below the saturation pressure for the refrigerant in the absorbent. The solution which is a mixture of the refrigerant and absorbent is transferred by the pump 4 to the regenerator 3.

As the refrigerant and absorbent used in the preferred embodiments of this invention may have close boiling points, it is generally necessary to have a distillation process embodying a rectification system to separate the substantially pure refrigerant from the relatively pure absorbent. While it is generally contemplated to employ a rectification column, there are some combinations of refrigerant and absorbent which can be separated by simple distillation.

The regenerator or separator 3 includes a rectification column 8 having a cooling coil 10 to provide the necessary reflux for separation. This column can be of any well-known construction and can be either a plate column or a packed column. The regenerator will also be provided with a heating coil 9. This coil will ordinarily supply the major part of the heat used in the process and will generally reach the highest temperature in the cycle.

In accordance with good distillation practice, the solution of refrigerant and absorbent will be introduced into the column at an optimized point. The composition of the mixture introduced at the point will approximate the composition of the mixture in the column at the point of introduction. The preferred mode of heating the mixture of the refrigerant and absorbent before it is introduced into the column will be described later.

The column 8 will produce a vapor stream of substantially separated refrigerant at the top of the column and a stream of liquid absorbent relatively free from refrigerant from the bottom of the regenerator 3. The absorbent which is hot and under high pressure is returned to the absorber prior to which it must be reduced in temperature and pressure to substantially the temperature and pressure in the absorber. The pressure may be reduced by passing the liquid through the turbine 7 which will recover part of the energy imparted by the pump 4. The liquid absorbent may be cooled, at least in part, by heat exchange with the solution which is being fed to the column 8. The heat exchanger 6 is shown provided with coils or the like for effecting this exchange of heat. When the amount of heat in the liquid absorbent is greater than that which can be absorbed by the solution, the absorbent can be cooled by other means.

The substantially pure vapor discharged from the top of the column is passed through the line 11 to the condenser 12. As the vapor in condenser 12 is under substantially higher pressure than exists in the evaporator, it can be condensed to a liquid at a higher temperature than exists in the evaporator-sublimator 1 or the absorber 2. The condenser 12 will cool the refrigerant to a temperature below its condensation point at the pressure existing in the condenser. This will discharge a portion of the heat from the system.

The condensed refrigerant is passed as a liquid through the pressure reducing means 13. This can be a simple pressure reducing valve or orifice. However, it is preferred to use a device which will recover at least some of the energy available upon the release of pressure. This device will normally take the form of a turbine of known construction, but any other form of device which will recover the energy can be used. It is to be understood that whenever the term "turbine" is used to described a means for recovering energy by pressure reduction, any similar expansion engine is included.

The evaporator-sublimator 1 is provided with a heat exchange means 14, which supplies the heat necessary to vaporize the refrigerant and is cooled to approach the lowest point in the cycle. The evaporator-sublimator 1 is preferably of the construction shown in more detail in FIGS. XI and XII, and will be described later. This evaporator-sublimator is designed to permit the conversion of the refrigerant to vapors by either sublimation or evaporation. The liquid refrigerant from the pressure reduction means 13 is fed into the first compartment 15 of the evaporator-sublimator 1. This compartment is separated from the vapor section 17 by a porous plate 18 through which passes the heat exchange means 14. The liquid in compartment 15 is at a slightly higher pressure than exists in the vapor section 17, and thereby oozes through the porous partition.

When the pressure in the compartment 17 is below the triple point, the refrigerant will freeze as it is passed through the porous partition. The frozen refrigerant will thus block the pores in the plate and prevent further flow. The heat exchange means 14 will then supply the heat necessary to sublime the refrigerant. At this stage the heat exchanger 14 constitutes the heat sink of the process. This manner of operation requires that the pressure in the vapor section be below the triple point for the refrigerant. To maintain this pressure may require the positive removal of vapor from the section 17 by mechanical means.

If the pressure of the refrigerant in the section 17 is not below the triple point of the refrigerant, the liquid refrigerant will ooze through the porous plate and be evaporated by the heat from the heat exchange 14.

The evaporator-sublimator 1, the absorber 2, the regenerator 3, the column 8, and the condenser 12, are provided with suitable heat exchange means 14, 5, 9, 10 and 16, respectively. The heat exchanger 14 will supply the heat necessary to vaporize the liquid refrigerant and will cool the fluid circulating therein to the lowest temperature in the system. The heat exchangers 5, 10 and 16 will abstract heat from the system.

As this invention prefers the use of refrigerants of the class of methane, ethane, nitrogen, neon, hydrogen and helium with absorbents selected from the lower boiling hydrocarbons and lower boiling point inorganic fluids, the heat of solution in absorber 2 will be relatively small and the amount of heat removed by heat exchanger 5 will be a minimum and in some instances the heat exchanger 5 may be omitted.

Since the refrigerants employed in the present invention have relatively low boiling points, the highest temperature necessary in the regenerator 3 can be relatively low and can be supplied with waste heat or by solar heat. The temperature of condensation selected in the highest temperature cycle can be selected according to the needs of the process and the cooling medium available. In some instances, water at ambient temperature can be used, and in others the heat can be rejected through a suitable heat exchanger directly to the ambient atmosphere.

FIG. II shows another embodiment of the cycle shown in FIG. I which permits the conversion of some of the thermal energy within the absorption refrigeration system to mechanical energy. In this modification, the gaseous refrigerant discharging from the column 208 of the regenerator 203, is first compressed then heated and expanded to recover part of the energy. The gas leaving the column 208 is fed to a compressor 226 through the conduit 211 of a suitable type. The compressed vapor is passed through the heat exchanger 219 where the vapors are heated. All or part of this heat may be supplied by passing the relatively pure absorbent from the regenerator 203 through the heat exchange elements of the exchanger 219. The exchanger may also supply heat from external sources.

The heated and compressed gaseous refrigerant is then expanded through the turbine 220 to convert the thermal energy to mechanical energy. The cooled refrigerant at lower pressure is then passed to the condenser 212 where it is cooled to condensation point. The liquid is then passed through the pressure reduction means 213 and fed into the evaporator-sublimator 201. The vapors from the evaporator-sublimator 201 are passed by mechanical inducement in pump 205 to the absorber 202 and mixed with absorbent which has passed through the heat exchangers 219 and 206 and turbine 207. The solution from the absorber 202 is pumped by pump means 204 through the heat exchanger 206 to the column 208.

Referring to the embodiment illustrated in FIG. III, the pure absorbent from the regenerator 303 is passed through the heat exchange means 319 and supplies part of the heat to the refrigerant which has been compressed by pump 326. The partially cooled absorbent then is passed to the heat exchanger 306 and then through the turbine 307 to the absorber 302. As the absorbent has been partially cooled before arriving at the heat exchanger 306, it supplies only a part of the heat necessary for conditioning the mixture or solution of refrigerant and absorbent to be fed into the column. Additional heat can be supplied to the mixture by cooling the vapors in the heat exchange means 327.

The heat for the separation of the mixture is supplied by the heat exchange means 309, and the refrigerant is vaporized by the heat supplied in the evaporator-sublimator 301 by the heat exchange means 314. Heat is removed from the condenser by the heat exchange means 316, and the absorber by heat exchange means 305. It is to be understood that the area of heat exchange surfaces in the regenerator 303, the condenser 312, the heater 306, the cooler 323, the absorber 302, and the heater 319, will be selected to give the transfer appropriate to steady operation.

The features which are specifically shown in FIGS. I, II and III can be combined or modified by the features of each other and can be used in connection with auxiliary equipment as is well-known in the art.

FIG. IV illustrates a cycle which is an embodiment of the basic cycle and which is designed to produce very low temperatures in single cycle. This arrangement materially reduces the amount of energy required to generate a given refrigerating effect. In this example the values are given for a cycle using methane as the refrigerant and propane as the absorbent.

In a specific operation of FIG. IV, the evaporator-sublimator 401 is supplied with about 0.45 pounds of methane per second at a temperature of about 163.degree. R. and discharges the vapors at about 135.degree. R. at a pressure of 0.1354 psia. The vapors are passed to the absorber 402 and are mixed with about 1.1 pounds per second of propane having a temperature of about 154.5.degree. R. The pressure in the absorber 402 is about 0.0967 psia. The solution of methane in propane is discharged from the absorber at the rate of about 1.6 pounds per second and at a temperature of about 153.degree. R. The solution passes to a heat exchanger corresponding to the heat exchanger 6 of FIG. I. In FIG. IV this heat exchanger has two sections 406 and 406'. The solution enters the section 406' and is heated by indirect heat exchanges with two separate sources of heat. One source of heat is the stream of propane returning from the regenerator 403 to the absorber. This stream is supplied at the rate of about 1.14 pounds per second at a temperature of about 159.degree. R. The other source of heat is the condensed methane from condenser 412 which has a temperature of about 229.degree. R. and is passed through the heat exchanger at the rate of 0.45 pounds per second. Simultaneously, a minor stream of the condensed methane from condenser 412 is introduced into the solution of methane and propane in the heat exchanger section 406' by turbine 425. This stream is supplied at the rate of 0.19 pounds per second. The solution is discharged from the heat exchanger 406' at the rate of 1.79 pounds per second at a temperature of 155.degree. R. The solution is then heated in heat exchanger section 406 to about 374.degree. R, by the stream of propane returning to the absorber. The solution is pressurized by the pumps 404 and 404' to a pressure of about 600 psia and is introduced into column 408 of the regenerator or separator 403. The regenerator 403 is heated by the coil 409 which received a heating medium at 658.degree. R. The separated propane leaves the regenerator at a weight of 1.144 pounds per second at a temperature of 653.degree. R. Before entering the heat exchanger 406, the stream of propane is cooled by passing through heat exchangers 427 and 428. The stream of propane is cooled by fluid passing through coils 421 and 422 to a temperature of about 449.degree. R. The methane leaves the top of the column 408 at the rate of about 5.47 pounds per second and is transferred to heat exchanger 419 where the methane is cooled by fluid in the coil 420. The methane leaving the column 408 is at about 340.degree. R. and is cooled to 336.degree. R. in the heat exchanger 419. A major amount of the methane amounting to about 4.82 pounds per second is returned to the column 408 where it serves as reflux. The minor portion of the methane amounting to about 0.64 pounds per second is transferred to the condenser 412. In condenser 412, the methane is cooled and liquified to a temperature about 229.degree. R. and the stream is passed to the heat exchanger 406'. The major portion of the condensate amounting to 0.45 pounds per second passes through the coil 426 and is passed through the pressure reducing means 413 into the absorber 401. A minor portion of the condensed methane is passed through turbine 425 into contact with the solution in the heat exchanger 406' and mixed therewith.

The mode of operation as described for FIG. IV presents a specific manner in which the present invention may be applied. While relative quantities and temperatures given are considered as merely illustrative of a single operation, it should be noted that this operation requires only the addition of mechanical energy to operate the pumps 404 and 404'. In this example, the heat supplied was at 658.degree. R. or 199.degree. F. which would be normally considered as waste heat. In this example, the heat supplied is such that Q= about 229 in the regenerator and the heat supplied to the evaporator is such that Q=100. Also in the example, the heat is removed in the exchangers 427 and 428 amounts to such that Q=164 and the amount removed by exchanger 419 amounts to such that Q= about 50 and the heat removed in the condenser is such that Q=124. From these values, it will be appreciated that in the cycle a cooling effect of about one half of the heat supplied is obtained at a temperature of 135.degree. R. or -324.degree. F. with the use of waste heat and minor amount of mechanical energy.

The quantities of refrigerant, absorbent and temperatures may be varied to suit specific problems without departing from the invention.

FIG. V illustrated one manner in which it contemplated to arrange two absorption refrigerating cycles of this invention, in a cascade manner so as to utilize maximum percentage of the energy supplied to the system. The Figure also illustrates how energy can be recovered in a cascade system. In each of the cycles shown in this Figure, the vapors of refrigerant are passed from the respective evaporator-sublimators 501 and 501' to the corresponding absorbers 502 and 502' and are there mixed with the returning absorbent. The separate solutions of refrigerant and absorbent are pumped by pumps 504 and 504' through the respective heat exchangers 506 and 506'. In each of the cycles of this Figure a further refinement of the utilization of energy is shown in that, instead of passing directly from the heat exchangers 506 and 506' to the midpoints of the columns 508 and 508' of the regenerators 503 and 503', the solutions are passed through the heat exchange coils in condensers 512 and 512' and then lead into the columns 508 and 508'. The vapors from the columns 508 and 508' are passed through their respective heat exchangers 520 and 520'. The vapors are heated in these exchangers by heating fluid supplied to coils 524 and 524'. While the connection is not shown on the drawing for passing the returning absorbent from the regenerators 503 and 503'to the heat exchangers 520 and 520', it is to be understood that a portion, at least of the heat supplied to the vapors, may be derived from these sources as shown in FIG. III. The separate streams of vapors heated in exchangers 520 and 520' are expanded by passing them through the corresponding turbines 523 and 523'. The vapors from the turbines are then fed to the condensers 512 and 512' respectively and the energy in the liquid refrigerant recovered in the pressure reducing means 513 and 513' and the liquids passed to the evaporator-sublimators 501 and 501'.

In FIG. V the two cycles are shown as being in heat exchange relation by having a heat transfer means 530 removing heat from condenser 512 and supplying the same heat to the regenerator 503'. Another heat transfer means 531 is shown for removing heat from the condenser 512' and absorber 502' and supplying this heat to the evaporator 501.

The turbines 507 and 507' perform the same functions as the corresponding parts in FIG. I, as do the heat exchangers 505, 509, 510 and 510'.

While the cascade arrangement is illustrated with only two cycles, three, four or more cycles can be constructed and connected in the manner shown. The first cycle of a series could employ ethane as the refrigerant, the second could use methane, and subsequent cycles could employ nitrogen, neon, hydrogen and helium as refrigerants. The number of cycles and the refrigerant will be selected according to the needs of the system.

As shown by the several Figures of the drawing, the available heat in one portion of the system can be transferred to another location in the same cycle where the difference in temperature is sufficient to effect a worthwhile heat exchange. The area of the heat exchange surfaces will be selected to give the desired transfer of heat. The individual features may be combined whenever a significant saving of heat or energy will be effected.

FIG. VI illustrates a generic arrangement for the liquification of a gas such as air, using the heat sink of an individual cycle or a plurality of cycles to remove the heat from the air. In this Figure, the details of the refrigeration cycles have been omitted and are indicated merely by the cooling coils in the heat exchangers 642 and 644.

Atmospheric air enters through a conduit 640 and is passed through the turbine 641 into a region of lower pressure and is passed through the heat exhangers 642 and 644 of the absorption refrigeration cycle. The cooling of the air is provided by substantially isentropic expansion in the turbine and by heat exchange with the heat sinks of the refrigeration evaporators in the heat exchangers 642 and 644, where the air is condensed to liquid. The system may be provided with known means to remove water vapor and carbon dioxide, to avoid fouling of the heat exchanger surfaces.

The liquid air is discharged from the heat exchanger 644 into conduit 645 and may be drawn off as a product by conduit 646. Alternatively, the liquid air may be fed to separator 647, which may be of known construction, e.g., a rectification column which will separate the liquid air into its components. Frequently, only nitrogen and oxygen will be separated, but the invention contemplates the recovery of the minor constituent gases of the atmosphere, e.g., argon, neon, helium, krypton, hydrogen xenon, ozone and radon, if desirable. The carbon dioxide in the air may also be recovered in the process.

The oxygen and nitrogen may be drawn off at 648 and 649, if desired, to use the separated element as such and may be supplied to other processes. The liquid air from conduit 645 may be passed to pump 661 where the fluid is pressurized and then passed to coil 651. Similarly, the oxygen passes to pump 662 and coil 652, and the nitrogen to pump 663 and coil 653 of heat exchanger 650. The respective streams can then be passed, if desired, to turbines 657, 658 or 659 respectively. The product may be recovered by vessel 660. In the event that oxygen is being passed through the turbine 658, it may be desirable to mix the oxygen with a fuel which is introduced through conduit 656 and to ignite the mixture before the combustion gas is passed through the turbine 658.

This Figure illustrates the many ways in which the absorption refrigeration system can be used commercially to recover energy and to supply liquid, air, oxygen, nitrogen, or the rare gases to industrial processes. Since the process of refrigeration as described in this specification does not require the consumption of large amounts of energy, it provides these materials in an economical manner.

In FIG. VI, the heat exchanger 650 may also serve to transfer heat between two or more of the streams. As for instance the coil 651 which receives liquid air may serve to further cool other streams, or may be further cooled by the other streams. The coil 654 is indicated as a separate heat exchange means for an independent heat transfer medium to supply heat to or to remove heat from the exchanger 650, and may serve to transfer heat between the liquid air, the nitrogen or oxygen and the absorption refrigeration cycle. There may be a plurality of these means as desired. The vessel 660 into which the gases are individually collected may serve as a heat sink for the absorption refrigeration system or as an independent cooling means.

FIG. VII illustrates the basic system for recovering energy using a low temperature in the cycle with air as the energy transfer medium with liquifaction of the air. In this cycle the lowest temperature will be substantially the temperature of liquid air, and the highest temperature normally contemplated is that available from waste heat. While it is preferred to use waste heat as the source of the highest temperature in the cycle, it is clear that if the conditions are feasible the air can be heated to a higher temperature by the combustion of fuel. In the preferred form the cascade absorption refrigeration system is used to produce the low temperatures in the cycle. A cascade refrigeration system as illustrated in FIG. V is indicated by the block 770 in the drawing. This system is provided with heat transfer means 771 to remove heat from the energy producing system. While only a single means 771 is indicated in the drawing it is to be understood that this means may be composed of a plurality of separate connections for transferring heat at different temperatures between the systems.

The heat exchanger, which is shown diagrammatically, is supplied with a gas, usually air, which is condensed by the cooling effect of the transfer means to a liquid. While air is usually the gas employed, nitrogen or other gases can be used to avoid the risk of combustion and oxidation. The liquid air from the heat exchanger 772 is passed to the pump 773 which increases the pressure on the liquid. The change in pressure is usual quite significant. The liquid at the higher pressure is circulated through the heat exchangers 774 and 775 and converted to gas at high pressure and temperature and then is expanded through the turbine 776. The air leaving the turbine is cooled in heat exchanger 774 by heat exchange with the liquid air from the pump 773. The cooled air is then fed to the condenser or heat exchanger 772 completing the cycle.

This Figure shows a simplified energy recovery system, in which energy in the form of heat is supplied to the system by the heat exchanger 775, which roughly corresponds to the boiler of a conventional steam power system, and which converts the liquid air to hot gas at high pressure. The hot compressed air is expanded through the turbine and cooled by the liquid air from the condenser, which corresponds to the condenser of a steam system. The pump 773 corresponds to the injector on a steam boiler system. Since the lowest temperature in the proposed system is near absolute zero the efficiency of the system is high. The maximum efficienty of a steam system is low since the temperature of condensation is high. As pointed out above, while the invention contemplates the use of waste heat, the air may be heated in heater 775 by heat from any source.

FIG. VIII illustrates a more developed system for recovering energy. This Figure employs the basic energy system set forth in FIG. VII. In this Figure, the absorption refrigeration system is indicated by the block 870. This absorption refrigeration system can be like the one shown in FIG. V but the details of the system have been omitted for the purpose of clarity. The refrigeration system is shown as removing heat from the energy recovery system by the heat transfer means 871 associated with the condenser or heat exchanger 872. The liquid gas which will be, hence forth referred for convenience as liquid air, is passed from the condenser 872 to the first pump 873 which increases the pressure of liquid air to about 50 psia. The pressurized liquid air is passed through the heat exchangers 874 and 874' and is heated by the air leaving the turbines. The liquid air is then pressurized by the pump 873' to a very high pressure such as 3500 psia., and is fed to the heat exchanger 874". In this heater, the liquid air is vaporized and converted into gas at high pressure and much higher temperature. The hot gas is further heated in heat exchanger 875 and introduced into the turbine 876. The air as discharged from turbine 876 is reheated to about the original high temperature by the reheater 875' and is expanded through a second turbine 876'. The gas at lower pressure and temperature is reheated to about the original high temperature in reheater 875" and is expanded through the third turbine 876". The air is then passed through the heat exchanger 874" and to the condenser 872 after passing through the cooler 890 and the heat exchangers 874 and 874'.

As an example, this system can be arranged to circulate air at the rate of one pound per second through the cycle. If the pressure in the condenser is maintained at atmospheric pressure, the temperature in the condenser will be about 142.degree. R. The liquid air is pressurized to about 50 psia. and passed through heat exchangers 874' and 874 and the temperature raised to about 165.degree. R. The pump 873 raises the pressure to about 3,500 psia. and the temperature is raised to about 202.degree. R. The liquid air is passed through the heaters 874 and 875 and is converted to gas at 700.degree. R. (240.degree. F.). The hot air is cooled in passing through the turbine 876 to 437.degree. R. and the pressure is reduced to about 565 psia. In the heater 875', the air is returned to the temperature of 700.degree. R. In turbine 876', the temperature is dropped to 473.degree. R. and the pressure to about 91 psia. In the heater 875', the air is reheated to about 700.degree. R. The expansion in turbine 876" drops the temperature of the air to 473.degree. R. and the pressure to atmospheric. The air is cooled in the heat exchangers 890, 874, 874' and 874" before being condensed to liquid at 142.degree. R.

The values set forth in this cycle are illustrated by the chart shown in FIG. XIV. The points on the diagram are identified as follows: 1, indicates the condition of the liquid air leaving the condenser 872; 2, the condition of the liquid air leaving the pump 873; 3, 4 and 5, the condition of the liquid air leaving the heat exchanger 874, 874' and 875'; 6, the condition of the air leaving the pump 873'; 7, the condition of the air leaving the heater 875 and entering the turbine 876; 8, the condition of the air discharged from the first turbine 876; 9, the condition of the air leaving the reheater 875' and entering the second turbine 876'; 10, the condition of the gas as discharged from the second turbine; 11, the condition of the air leaving the second reheater 875" and entering the third turbine 876"; 12, the condition of the air as discharged from the third turbine; 13, 14, 15 and 16, the condition of the air as it is cooled and returned to the condenser at point 1.

The liquid air flowing from the condenser 872 is pressurized by the pump 873 (point 2 on the chart) and is returned in indirect heat exchange in heater 874 to absorb part of the latent heat of the condensing air. This transfer of energy is possible with air, as air is essentially a binary mixture of oxygen and nitrogen, and the dew point temperature is approximately 5.5.degree. F. higher than its bubble point. The heat exchanger 874 warms the liquid air to slightly below its saturation point (point 4 on the chart). The liquid is pressurized by pump 873' to the pressure at turbine inlet (point 8 on the chart). The liquid at high pressure is vaporized in the heat exchanger 875. In this heat exchanger, the highest temperature in the cycle is reached. The temperature shown can readily be reached by employing low quality thermal energy, such as waste heat. Nothing in this disclosure should be construed as preventing the use of higher temperatures which can be obtained from other heat sources.

The system shown, when supplied with air at the rate of one pound per second, would produce about two hundred horsepower in excess of that required to operate the pumps 873 and 873', subject to the limitation of the efficiencies of the turbines and losses in the system.

FIG. IX illustrates another embodiment of the invention for the recovery of energy, preferably using the absorption refrigeration system as a means for establishing the necessary temperature differential. In this Figure 970 indicates an absorption refrigeration system and 971 indicates a heat transfer means for transfering heat from the power recovery system to the heat sink of the refrigeration cycle. This system includes a condenser 972 for liquifying a gas such as air. The liquid air is pressurized by the pump 973 and is heated by the heat exchanger 974. The heating medium is the air being cooled and condensed. The pressurized and heated liquid air is vaporized in the heat exchanger 975 and is introduced into the turbine 976 and then reheated in reheater 975' and passed into turbine 976'. This turbine discharges the air at the pressure of the condenser.

This Figure shows an arrangement generally corresponding to the system of FIG. VIII, but in which the construction has been simplified. This Figure shows an arrangement which will allow a substantial recovery of power with a lower plant investment. The actual selection of the number of turbines and the number of reheaters will depend upon an economic balance between the cost of equipment and the value of the power drived.

FIG. X illustrates the recovery of pure water by the use of a low grade heat source. In the production of water from saline water or impure water, one of the major problems has been the cost of the power required to vaporize the water. Another problem has been the scaling of the water in the heating vessels. The utilization of the absorption refrigeration systems of this invention will overcome some of these previous difficulities.

In FIG. X the evaporator of the absorption refrigeration system is indicated as 1001, the refrigerant absorber as 1002, the pump for the solution of refrigerant and absorbent as 1004, the regenerator as 1003 and the column as 1008. The vapors of the refrigerant are passed to the heater 1019 and are heated by indirect heat exchange with the absorbent from the regenerator 1003. The heated vapors are then expanded through the turbine 1020, to recover energy and to cool the vapors. The vapors are condensed in condenser 1012 and the liquid refrigerant is passed through the pressure reduction means 1013 to the evaporator 1001. The refrigeration system thus far disclosed is similar to that shown in FIG. IV.

The condenser 1012 includes a heat exchanger element 1021 through which is passed the water to be distilled. The refrigerant and the pressure of condensation are selected so that the heat of the condensing vapors heats the water to be distilled. The warmed water is then passed to the heat exchange element 1006' in the heat exchanger 1006, and the water is further heated by the absorbent returning to the absorber 1002 from the regenerator 1003.

The hot water is then fed into the distillation system. The distillation system comprises a series of flash chambers which utilize the latent heat in the water to vaporize a portion of the water. The hot water is introduced in the first flash chamber 1080, and a portion of the water flashed into steam. The steam is fed through the heat exchange means 1082 in the second flash chamber 1081 and is condensed. The water from the first flash chamber is fed to the second chamber 1081 which is at a lower pressure. A second quantity of water flashes into steam. While only two flash chambers are shown, it is to be understood that the number of flash chambers may be selected according to the design criteria of such distillation systems.

The vapors from the final flash chamber and the condensate from the heat exchanger 1082 are fed into the condensing chamber 1083. This chamber is cooled by heat exchange element 1084 through which is circulated a heat exchanger medium which also is passed through the element 1014 of the evaporator 1001. The non-condensible gases in the saline water are removed from the distillation system by the ejector 1086. The evaporator 1001 which is heated by the condensing water vapor in the condenser 1083, will maintain a minimum pressure and temperature in the water vapor condenser. The unevaporated water or waste brine from the final distillation stage is discharged through the heat exchange means 1087 in the refrigerant condenser 1012 or through the heat exchange means 1088 in the refrigerant absorber 1002, to remove the heat of these elements. In a like manner, the distilled water is passed through the heat exchanger means 1089 in the refrigerant condenser 1012 or through the heat exchange means 1091 in the absorber 1002 or through both.

FIG. X demonstrates the application of absorption refrigeration system of this invention using a low temperature heat source to produce energy and to perform useful chemical engineering unit process operations. While this example shows the application of the process of this invention to the distillation of water, it is apparent that other liquids could be distilled in a similar manner. Furthermore, the temperature differential available from the absorption refrigeration cycles of this invention can be used in other unit processes requiring temperature changes. For example, water could be purified by freezing rather than by distillation. The invention could also be used to dehydrate materials as by freeze drying since the invention can produce both low temperature and low pressure.

FIG. XI shows the construction of a preferred form of the evaporator-sublimator of this invention. The figure is a cross section through the vessel constituting the evaporator-sublimator. The vessel is normally provided with insulation about the walls. The interior of the vessel is divided into a liquid receiving section 1101 and a vapor section 1103 with a porous plate 1102 separating the section from each other. The liquid to be vaporized is introduced into the section 1101 by the pipe 1104. The vapor is removed from section 1103 by the pipe 1105. This pipe is designed to maintain the pressure in the section 1103 at a desired level. The pipe 1105 may include a fan, if necessary, to maintain the desired pressure.

The porous plate 1102 which serves as a partition, is formed of an open cell material such as porous brick or stone or metal which will permit the slow passage of the liquid through the partition. The partition includes a heat exchange means 1114 which will supply the heat necessary to vaporize the liquid. This heat exchange means serves as the heat sink in the refrigeration cycle.

The evaporator-sublimator is operated as a sublimating means by establishing a pressure in the section 1103 which is below the triple point of the refrigerant. Under these conditions, the refrigerant, as it passes through the partition 1102, will freeze in the passages and block further flow of liquid. The heat exchange means 1114 will supply heat to sublimate the refrigerant. As the refrigerant is evaporated, more liquid refrigerants will pass into the plate and be frozen. Thus, the passage for the liquid is automatically limited to the rate at which the frozen material is sublimed by the heat.

When the pressure in the chamber is above the triple point of refrigerant, the liquid will ooze through the plate and be heated by the heat exchange means and will evaporate into the chamber 1102. This will occur before the system has reached the triple point pressure at the time the system is being started up or the system can be operated under these conditions as desired.

FIG. XII is another embodiment of the evaporator-sublimator. In this Figure, the liquid chamber is designated as 1201, the vapor chamber as 1203 and the porous plate as 1202. The liquid is supplied by pipe 1204 and the vapor removed by pipe 1205. This embodiment differs from that shown in FIG. XI by having the feed pipe 1204 pass through the vapor section 1203. This pipe includes the heat exchange means 1207 in the vapor section. This permits the liquid refrigerant to be further cooled before entering the chamber 1201. This construction assures a rapid stabilization of conditions to enable the operation of the evaporator-sublimator as a sublimator. The heat sink is designated by the heat exchange means 1214.

FIG. XIII shows a vapor separator particularly adapted to be used in the flash distillation chambers of the system shown in FIG. X. While particularly adapted for this type of system, the separator can be used in any distillation system benefitted by little or no entrainment of the distilland in the vapor. In this Figure, 1301 indicates the vessel for receiving the liquid to be distilled through the pipe 1302 and discharging the vapor through the pipe 1303. In the vessel above the level of the boiling liquid is a baffle means 1304. This baffle means includes a shaft 1305 which is mounted for rotation about an axis. A series of turbine blades 1307 are secured in an inclined position to the shaft so that the passage of vapor towards the outlet pipe 1303 cause the shaft to rotate. A perforate plate 1306 secured to the shaft above the turbine blades rotates with the shaft. The plate, preferably in the form of a fine mesh screen, engages any droplets of liquid and centrifugally throws them outwardly away from the outlet. While it is preferred to have the vapors rotate the screen, it would be possible to use other means for the purpose.

FIGS. XV and XVI illustrate a more specific embodiment of the cycles shown in FIG. VI. In these Figures, the energy recovery system is used to provide motive power for a vehicle. The vehicle may be any vehicle requiring energy for propulsion, such as aircraft, boats, air-cushioned vehicles as Hovercraft and trains, railroad cars, road vehicles or tube cars. The power derived can be used directly as in the thrust of a jet or indirectly by the use of a driven turbine.

In FIG. XV, the heat sink of an absorption refrigeration system is indicated by the block 1570. The power generating system receives air from the atmosphere at 1560. The entrance may be in the form of a scoop, taking advantage of the vehicles forward motion to increase the flow of air. The entering air is passed to the precooler 1571 and is conveyed from there to the turbocompressor 1572. The compressed air passes through the heat exchange means 1573 in the precooler. The compressed air is fed to the turbine 1574 and there expanded. The cooled air is then passed into the condenser 1577, in which it is further cooled by supplying heat to the refrigeration cycle, and is condensed to a liquid. The liquid air is pressurized by the pump 1575 and passed to the heat exchanger 1576 in the refrigeration cycle. This exchanger heats the air to vaporize it. The hot pressurized air is fed to the nozzle of the thrust means 1578. Fuel may also be supplied to the thrust nozzle through line 1579 and burnt with the air to supply reaction forces to the vehicle.

Heat exchange connection 1580, 1581 and 1582 transfer heat from the refrigeration cycle to the precooler, to the condenser, and to the heater. The precooler will use well-known techniques to free the air from ice, carbon dioxide and the like and to remove the ice from the precooler.

The thrust means 1578 may be a jet engine or a rocket nozzle or a turbojet engine. While it is desirable, in many instances, to use fuel in the engine, wherever the added heat of combustion or the polluting effect of combustion is to be avoided, the engine may be powered solely by the expanding gas.

FIG. XVI illustrates another embodiment of the invention as used for the propulsion of a vehicle. In this Figure, the air enters the system at 1660 and is passed to the precooler 1671. The dried cooled air is fed to the compressor 1672. The compresser gas then is passed to the heat exchanger 1673 in the precooler and then fed to the turbine 1674 and is there expanded. The air is condensed in condenser 1677. The liquid air is passed through the heat exchange means 1683 in the precooler and is further heated in the heat exchanger 1684 before being introduced into the propulsion means 1678. The heat exchangers 1681 and 1682 transfer heat to the refrigeration cycle.

In this example the precooler is not connected with the refrigeration cycle as shown in the previous figure.

FIG. XVII shows an embodiment of the invention as applied to the use of gases such as nitrogen, hydrogen, neon and helium as refrigerants.

FIG. XVII illustrates one absorption refrigeration cycle of a cascade system. In this Figure, the absorber 1702 feeds the solution of a gas such as hydrogen in a liquid hydrocarbon to the pump 1704 and hence to the heat exchanger 1706 and to the column 1708 of the regenerator or separator 1703. The heat necessary to separate the gas from the absorbent is preferably supplied by the condenser of another cycle in the cascade arrangement by means 1709. The gas is then supplied to a heat exchanger 1712. This exchanger is arranged to remove heat from the gas and supply this heat to an evaporator of another cycle in the cascade system. This heat exchanger also includes another heat exchange element 1721. The cooled gas from the heat exchanger 1712 is passed through the expansion means 1713 into the chamber 1722. This chamber is at lower pressure than 1712 and a portion of the gas is liquified and is passed into the evaporator-sublimator 1701. The vapors from the evaporator-sublimator 1701 and the vapors from the chamber 1722 are combined and are passed through the heat exchanger element 1721 in the chamber 1712 and then passed to the absorber 1702.

The vapors separated from the liquid and the vapors from the evaporator-sublimator thus serve to cool the gas in the chamber 1712.

When hydrogen is the refrigerant, the heat exchanger 1712 may be cooled by the heat sink of an evaporator-sublimator of another cycle of the cascade to 94.degree. R. The hydrogen is further cooled by the heat exchange element 1721 by the hydrogen from the evaporator and the chamber 1722. The hydrogen is cooled to the liquefaction by passage through the expansion means 1713. The liquid hydrogen from chamber 1722 may be passed to the evaporator 1701 in which it may serve as the heat sink in connection with a cooler cycle for liquifying helium. If liquid hydrogen is desired as a product, it is withdrawn from the chamber 1722 and make up hydrogen is supplied to the absorber 1702.

The same cycle is employed to liquify helium with the exception that liquid hydrogen is employed as the cooling fluid in the element of the heat exchanger 1712.

A neon cycle can be substantially the same as for hydrogen, and will include the expansion of neon in the means 1713. It is desirable to include a cycle in the cascade system, and then the neon heat sink will be used to cool the hydrogen before liquefaction.

The several figures of the drawing illustrates preferred embodiments of the invention. The several embodiments show numerous ways in which it is contemplated to apply the invention to recover energy from low temperature heat sources, and to perform chemical processes and recover valuable products.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and can without department from the spirit and scope thereof, make various changes and modifications of the invention to adapt it to various usages and conditions.

Claims

What is claimed is:

1. A refrigeration process comprising the steps of:

absorbing a refrigerant vapor in a liquid absorbent;

increasing the pressure on resultant mixture of said refrigerant and said absorbent;

distilling and rectifying the mixture into substantially pure refrigerant vapor and pure absorbent;

reducing the pressure on resultant pure liquid absorbent and returning the latter to the absorbing step;

cooling and condensing the refrigerant vapor to the liquid state;

reducing the pressure upon the liquid refrigerant to below the triple point of the refrigerant to produce solid refrigerant;

sublimating the solid refrigerant to the vapor state; and

passing resultant refrigerant vapor to the absorbing step at a rate that maintains the pressure below the triple point.

2. A process according to claim 1 wherein prior to the sublimating step the liquid refrigerant is passed through a porous plate and solid refrigerant is formed in said plate.

3. A process according to claim 2 wherein the porous plate is heated to sublimate the refrigerant.

4. A process according to claim 1 wherein the passage of the refrigerant from the sublimation step to the absorbing step is induced by mechanical means.

5. A process according to claim 1 in which the pressure on the liquid absorbent is reduced by passing said liquid absorbent through a turbine, thereby recovering energy therefrom.

6. A process according to claim 1 in which the refrigerant is selected from the group consisting of nitrogen, hydrogen, neon, helium and hydrocarbon having a saturation pressure between that of butane and methane; and the absorbent is a liquid having a freezing point below the temperature of the process and selected from the group consisting of a hydrocarbon liquid and an inorganic liquid.

7. A process according to claim 1 wherein the refrigerant is methane and the absorbent is selected from ethane and propane.

8. A process according to claim 1 wherein the cooling and condensing of the refrigerant is conducted in heat exchange with a separate absorbent refrigeration cycle.

9. A process according to claim 1 wherein the heat for distilling and rectifying the mixture is supplied by heat exchange with a separate absorbent refrigeration cycle.

10. A process for the recovery of energy and refrigeration comprising the steps of:

absorbing a refrigerant vapor in a liquid absorbent;

increasing the pressure on the resultant mixture of refrigerant and absorbent;

distilling and rectifying the mixture into substantially pure refrigerant vapor and pure absorbent;

heating the refrigerant vapor from the distillation step by indirect heat exchange with absorbent from the distillation step, to simultaneously increase the temperature of the vapor refrigerant and reduce the temperature and pressure of the liquid absorbent;

recovering energy from the refrigerant vapor by reducing its temperature and pressure;

condensing the vaporous refrigerant to the liquid state;

recovering the energy of the liquid refrigerant by reducing its pressure and temperature;

evaporating the liquid refrigerant under reduced pressure; and

returning the absorbent and the refrigerant to the absorbing step.