BACKGROUND OF THE INVENTION

Field of the Invention (Technical Field) :

An Absorption Vapor Pressure Enhancement Process of the present invention is used to take in a mass of solvent vapor under a first pressure P _1f having an equilibrium condensing temperature T absorb the vapor into an absorbing solution at an elevated temperature higher than T_,, utilize the heat of absorption to generate a substantially equivalent mass of second vapor under a second pressure P ₂ that is substantially higher than the first pressure. The pressure enhancement is accomplished by dilution of the absorbing solution. Therefore, a system of the present invention is equivalent to a compressor that compresses a vapor from the first pressure to the second pressure. The process is particularly useful in pressure enhancement of low pressure vapor, say lower than 10 torr, for which conventional compressors either do not work well or are expensive. The process is therefore useful in processes wherein low pressure vapors are involved; such as in high level refrigeration processes and separation processes including freeze drying processes and multiple phase transformation processes.

The processes and apparatuses of the present invention can be used in absorption refrigeration systems, each using a volatile solvent such as water and a non-volatile solute such as lithium bromide, lithium chloride, calcium chloride, magnesium chloride, ethylene glycol and propylene glycol. A system of the present invention can be used for more than one step of vapor absorption and therefore can attain a high degree of temperature lifting.

The processes and apparatuses of the invention can be used for conducting solid-liquid-vapor (S/L/V) multiple phase transformation processes such as vacuum freezing processes, primary refrigerant eutectic freezing processes and distillative freezing processes. An S/L/V multiple phase transformation refers to simultaneous vaporization and solidification operations by which a mass of liquid is simultaneously partially vaporized and partially solidified to thereby form a first vapor and a mass of solvent solid, the processes of the present invention are to be used in chemical purification, desalination, pollution abatement, and concentration of industrial solutions.

The processes and apparatuses can also be used in the following systems:

(1) Systems for conducting two phase fractional crystallization processes such as in dewaxing of lubrication oil and column crystal¬ lization.

(2) Chemical processing systems such as in recovery of condensable components out of gas streams, e.g. recovery of condensable hydrocarbon from natural gas.

(3) Systems for conducting freezing drying.

(4) Systems for making ice and ice cream.

(5) Systems for cool storage (thermal storage) .

(6) Systems for product cooling such as in meat packing.

(7) Systems for cooling liquids such as fruit juices, beer and wine.

Background Art:

Since an absorption vapor pressure enhancing unit is to be used in handling low pressure vapors, a review of

conventional low pressure handling equipment is presented; since a system of the present invention is used to attain a high level refrigeration involving vapor absorption steps, a review of conventional absorption refrigeration is presented; since systems of the present invention are to be used in various separation processes which generate low pressure vapors, a review of relevant separation processes is presented.

Equipment Used for Handling Low Pressure Vapors: Conventional equipment used for handling low pressure vapors are described in books on (a) Vacuum Technology, and (b) Unit operations in chemical engineering. Examples of these books are:

(1) James L. Ryans, et al "Process Vacuum System Design and Operation," McGraw Hill, 1986 and

(2) Perry's "Chemical Engineers' Handbook" Sixth Edition, McGraw Hill.

Conventional equipment used to handle low pressure vapors are (A) steam jet ejectors, (B) liquid ring vacuum pumps, (C) rotary piston pump, (D) rotary vane pump, and (E) rotary lobe blower. These type of equipment are not suitable for the types of applications the absorption vapor pressure enhancers are intended to be used. This is because this conventional equipment can only handle relatively small volume rates of flow and are very expensive.

Absorption Refrigeration:

A commercial absorption refrigeration unit has (a) an evaporator section, (b) an absorber section, (c) a generator section, and (d) a condenser section.

An absorption refrigeration unit uses water as the refrigerant under a deep vacuum. The unit operates on the

simple principle that under low absolute pressure (Vacuum) , water takes up heat and vaporizes at a low temperature. For example: at 0.25 inches of mercury absolute pressure, water boils at 40 degrees Fahrenheit. To obtain the energy required, it takes heat from and chills another liquid (usually water) . The chilled liquid can than be used for cooling purposes. These operations are conducted in the evaporator section of the unit.

To make the cooling process continuous, the vaporized refrigerant water is absorbed by an absorbing solution, usually lithium bromide water solution. The removal of refrigerant vapor by absorption keeps pressure in the evaporator section low enough for vaporization to continue. Heat of absorption is released and is removed through heat transfer coils by a stream of cooling water. The absorbing solution becomes a diluted absorbing solution. These operations are conducted in the absorber section of the unit.

The diluted absorbing solution is pumped to the generator section where water is vaporized from it at pressure considerable higher than that in the evaporator section described. A stream of high pressure vapor and concentrated absorbing solution are formed. These operations are conducted in the generator section of the unit. The concentrated absorbing solution is heat exchanged with the diluted absorbing solution and is then returned to the absorber section.

The high pressure water vapor is condensed by heat exchange with a stream of cooling water to from a condensate. The condensate is returned to the evaporator section.

The chilled water produced by a conventional single effect absorption refrigeration is generally limited to

about 5 degrees Centigrade (40 degrees Fahrenheit) . The temperature limit attainable by a single effect operation is set by the need of using cooling water near or above ambient temperature and by a limitation of formation of lithium bromide hydrate crystals and anhydrous lithium bromide crystals.

Separation Processes Involving Low Pressure Vapors:

The methods and apparatuses of the present invention are to be used in upgrading heat in separation processes in which low pressure vapors are generated. These processes include (a) freeze drying processes, and (b) various types of solid-liquid-vapor (S/L/V) multiple phase transformation processes. An S/L/V transformation refers to simultaneous vaporization and solidification operations of a mass of liquid to thereby form a first vapor and form a mass of solid which may be a mass of solvent crystals or a mixed mass of solvent and solute crystals. The S/L/V multiple phase transformation processes include (a) Vacuum Freezing Processes, (b) Primary Refrigerant Eutectic Freezing Process, and (c) Distillative Freezing Processes. The methods and apparatuses of the present invention can be adapted to improve these processes by improving handling the low pressure vapors generated, upgrading heat, and melting masses of crystals produced.

Vacuum Freezing Processes:

Several vacuum freezing processes have been introduced by workers in the desalination field. These processes are (1) Vacuum-Freezing Vapor-Compression (VFVC) Process, developed by Colt Industries, (2) Vacuum-Freezing Vapor- Absorption (VFVA) Process, developed by Carrier Corporation, (3) Vacuum-Freezing Ejector-Absorption (VFEA) Process, developed by Colt Industries, (4) Vacuum-Freezing Solid Condensation (VFSC) Process developed in the Catholic

University of America, (5) Absorption Freezing Vapor compression (AFVC) Process, introduced by Concentration Specialists, Inc., (6) Vacuum Freezing High Pressure Ice Melting (VFPIM) , introduced by Chen-Yen Cheng and Sing-Wang Cheng, and (7) Vacuum Freezing Multiple Phase Transformation Process, also introduced by Chen-Yen Cheng and Sing-Wang Cheng.

Referring to the processing of aqueous solution by any vacuum freezing process, the aqueous solution is introduced into a chamber which is maintained at a pressure that is somewhat lower than the vapor pressure of the solution at the freezing temperature of the solution to thereby simultaneously flash vaporize water and form ice crystals. This operation is referred to as the S/L/V transformation in a vacuum freezing process. As the result of this operation, a low pressure water vapor, referred to as a first vapor, and an ice-mother liquor slurry, referred to as a first condensed mass, are formed. In the case of sea water desalination, this pressure is around 3.5 Torr. The low pressure water vapor formed has to be removed and transformed into a condensed state; the ice crystals have to be separated from the mother liquor and the resulting purified ice has to be melted to yield fresh water. Furthermore, the heat released in transforming the vapor into a condensed state has to be utilized in supplying the heat needed in melting the ice. The processes described utilize different ways of handling the low pressure vapors generated and different ways of accomplishing the heat reuse.

The Vacuum Freezing Vapor Compression Process is described in the Office of Saline Water, Research and Development Report No. 295. In the process, the low pressure water vapor is compressed to a pressure higher than the triple point pressure of water (4.58 Toor) and is then brought in direct contact with purified ice to thereby

simultaneously condense the water vapor and melt the . e. The main disadvantages of this process are that the special compressor designed to compress the low pressure water vapor cannot be operated reliably, and the compressor efficiency is low.

The Vacuum Freezing Vapor Absorption Process was developed by Carrier Corporation up to 1964, but has been discontinued. The process is described in the Office of Saline Water, Research and Development Report No. 113. In the process, the low pressure water vapor is absorbed by a concentrated lithium bromide solution. The diluted solution is reconcentrated by evaporation and the water vapor so formed is condensed to become fresh water. Heat of absorption is removed by a recysling water stream through a heat transfer surface; the recycling water stream is then used to melt the ice crystals.

The Vacuum Freezing Ejector Absorption Process was also developed by Colt Industries, and is described in Office of Saline Water, Research and Development Report No. 744. In the process, the low pressure water vapor obtained in the freezing step is compressed by a combination of steam ejector and absorber loop. A concentrated sodium hydroxide solution is used to absorb a part of the low pressure vapor; the diluted sodium hydroxide solution is boiled to form water vapor at 300 Torr, and is used to compress the remaining low pressure water vapor.

The Vacuum-Freezing Solid-Condensation Process was developed by Professor H.M. Currand and C.P. Howard of the Catholic University of America and is described in Office of Saline Water, Research and Development Report No. 511. In the process, Freon-12 is used to remove the latent heat released in transforming the low pressure vapor into ice and supply the latent heat needed in the melting of both the ice formed in the freezing step and ice transformed from the low

pressure water vapor.

The Absorption Freezing Vapor Compression (AFVC) Process was introduced by Concentration Specialists, Inc., Andover, Mass., and a 25,000 gdp pilot plant has been built in OWRT (Office of Water Research and Technology) Wrightsville Beach Test Station. The absorption freezing vapor compression (AFVC) Process is a vacuum freezing process in which the freezing is accomplished in a stirred tank crystallizer due to the evaporation of water vapor which in turn is absorbed in an adjacent chamber by a concentrated solution of sodium chloride (NaCl) . The NaCl solution, diluted by the water vapor, is pumped to a generator where it is concentrated to its original strength by a vapor compression cycle using a closed circuit refrigerant as the working fluid. The vapor compression cycle operated between the absorber and generator, taking the heat that is associated with absorption and pumping it up to a level such that it can be used to evaporate the absorbate in the generator. The vapor liberated in the generator is used to melt the ice in direct contact. It is noted that the first vapor is absorbed in the absorbing solution near the freezing temperature, and the heat of absorption is removed by vaporizing a refrigerant.

In the improved Vacuum-Freezing High Pressure Ice Melting Process of U.S. Patent No. 4,236,382, an aqueous solution is flash vaporized under a reduced pressure to simultaneously form a low pressure water vapor and ice crystals. The ice formed is first purified in a counter- washer and then melted inside of heat conductive conduits under a high pressure (e.g. 600 atm.), and the low pressure water vapor is desublimed to form desublimate (ice) on the outside of the conduits. The latent heat of desublimation released is utilized in supplying the heat needed in the ice-melting operation. The desublimate is removed intermittently by an insitu dissolution operation utilizing an aqueous solution such as the feed solution or the

concentrate; about an equivalent amount of ice is formed inside of the conduits by an exchange freezing operation. The ice so formed is also melted by the high pressure ice melting operation described.

The Vacuum Freezing Multiple Phase Transformation Process has also been introduced by Chen-Yen Cheng and Sing- Wang Cheng and is described in U.S. Paten No. 4,505,728. In the process, the first vapor is liquefied by desublimation followed by desublimate melting operations.

The Primary Refrigerant Eutectic Freezing Processes:

The Primary Refrigerant Eutectic Freezing (PREUF) Process has been introduced by Chen-Yen Cheng, Wu-Ching Cheng and Wu-Cheh Cheng and is described in U.S. Paten 4,654,064. The process is used to separate mixtures containing at least one volatile component and two or more crystal-forming components. Heat is removed from a eutectic mixture at near its eutectic temperature by inducing vaporization of a portion of the eutectic mixture at its eutectic temperature. The vapor is liquefied by a two-step process: (a) desublimation, and (b) desublimate-melting. Co-crystallization of different components in the same zone of the freezer, or selective crystallization in different sub-zone of the freezer are possible.

Wet and Dry Distillative Freezing Process:

Wet and Dry Distillative Freezing (DF) Process has been introduced by Chen-Yen Cheng and Sing-Wang Cheng and is described in U.S. Patent No. 4,578,093. A wet and dry distillative freezing process comprises: (a) a first step of transforming a liquid feed mixture into a first solid-liquid mixture, denoted as K, mixture, and an impure liquid L _j , and (b) a second step of subjecting K ₂ mixture, derived from K, mixture, to a dry distillative freezing operation to

thereby form a mass of refined solid phase, denoted as S ₃ , and a low pressure vapor V_,. The low pressure vapor is liquefied by first condensing it into a solid-liquid mixture and then melting the solid so formed.

Freeze Drying Processes:

Freeze drying is used extensively in processing pharmaceuticals, biologicals used in medical research, and foods and concentrated beverages, vegetables, beef, seafood, coffee, and orange juice. The product of freeze drying is a stable solid that can be stored indefinitely at room temperature and that can be reconstituted by simple addition of water. The process is inherently expensive. Therefore, it is limited to applications for which significant improvements in product quality can be demonstrated, and to applications involving expensive products.

The objective of freeze drying is the removal of water from a solid. The process involves three distinct steps: freezing, sublimation, and desorption. Product materials are frequently introduced into the dryer as a frozen solid. If freezing is the initial step of the operation, it is normally accomplished by placing the product in trays on refrigerated shelves inside the vacuum chamber. Sublimation, the second step in the process, is subject to both mass-transfer and heat-transfer limitations, and both chamber pressure and shelf temperature are important process variables. Lower pressures increase drying rates at the expense of increased costs for refrigeration and the vacuum pumping system. Economics will normally dictate pressures in the range 20 to 100 microns for the production of pharmaceuticals and biologicals used in medical research. Freeze dryers used for food preservation normally operate in the range 250 to 750 microns. Production of freeze-dried coffee and freeze-dried orange juice requires pressures in the range 100 to 200 microns.

Freeze dryers operate in the range 20 to 750 microns. This requirement dictates the design of the vacuum pumping system. Four- and five-stage steam jets have been used for freeze-drying applications, particularly those that require high capacity at low operating pressures, but rotary-piston oil-sealed pumps and rotary-blower-rotary-piston oil-sealed pump systems dominate process applications. The vacuum pump evacuates the vacuum chamber.

A multiple effect vapor enhancing unit of the present invention can be used to handle the very low pressure water vapor generated in a freeze drying process.

SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION)

Referring to processing of an aqueous mixture, in a process of the present invention, a first water vapor at a first pressure is absorbed into a absorbing solution containing water and a non-volatile solute such as lithium bromide, lithium chloride, calcium chloride, magnesium chloride, ethylene glycol or propylene glycol at substantially the same pressure but at a temperature that is higher than the pure water saturation temperature corresponding to the absorption pressure. The heat released in the absorption operation is transmitted to a mass of pure water to generate a second water vapor at a second pressure that is substantially higher than that of the first vapor, the absorbing solution is diluted in this absorption operation, the absorption of the first vapor, the generation of the second vapor and the dilution of the absorbing solution are collectively referred to as a vapor pressure enhancement operation activated by dilution of the absorbing solution. Two types of vapor pressure enhancement units are introduced: Type A units and Type B units. The methods and apparatuses of the present invention may also be used in enhancing vapor pressure of a non-aqueous solvent.

In a Type A system, the vapor pressure enhancement is accomplished across a vertical heat transfer wall provided with two falling liquid films. The film on one side (Zone 1) is a liquid film of an absorbing solution; the film on the other side (Zone 2) is a liquid film of pure water. When a first vapor at a first pressure is brought in contact with the absorbing solution in Zone 1, the first vapor is absorbed at substantially the same pressure but at a temperature higher than the pure water saturation temperature corresponding to the absorption pressure. The heat released in this absorption operation is transmitted through the vertical heat transfer wall to the falling pure water film to vaporize water and generate second vapor at a second pressure that is higher than that of the first vapor. Therefore, the pure water saturation temperature of the second vapor is higher than that of the first vapor. The effects of this operation are that the first vapor is absorbed into the absorbing solution, the second vapor at a pressure higher than that of the first vapor is generated and the absorbing solution is diluted. A Type A unit may be referred to as a double liquid film unit.

A Type B system also has a first processing zone (Zone 1) and a second processing zone (Zone 2) . A heat exchange coil is placed in zone 1 and another heat exchange coil is place in Zone 2. A first vapor is absorbed into an absorbing solution in zone 1 and a stream of second vapor is generated from water in Zone 2. The two heat exchange coils are connected to form a loop, and a circulating pump is used to circulate a heat transfer medium through the two coils. Heat of absorption is removed by the circulating medium which released heat to vaporize water. A Type B unit may be referred to as a looped coil unit.

In a multiple stage absorption refrigeration system of the present invention, there are more than one vapor pressure enhancement units. A first vapor at a first pressure is pressure enhanced in a first enhancement unit by

a first absorbing solution to become a second vapor at a second pressure; the second vapor is pressure enhanced in a second enhancement unit to become a third vapor at a third pressure by a second absorbing solution, and so on. A high degree temperature lifting is made possible. Therefore, it is possible to reach a low temperature that has not been attainable by a conventional single stage absorption refrigeration. It is also possible to avoid formation of solute crystals from the absorbing solution. It is therefore possible to provide refrigeration needed in such low temperature operations as vacuum freezing operations, distillative freezing operations, ice formation operations, column crystallization, eutectic freezing, and low temperature condensation operations. It is noted that low grade heat may be used to activate a multi-stage absorption refrigeration operations of the present invention.

The absorption vapor pressure enhancement process of the present invention may be used to handle the low pressure first vapor generated in a solid-liquid-vapor multiple phase transformation process to generate a second vapor, which is then used to melt purified solid. The resulting process is referred to as a Multiple Phase Transformation Absorption Melting (MPTAM) Process.

A Multiple Phase Transformation Absorption Melting (MPTAM) Process comprises a multiple phase transformation step in which a feed solution is subjected to simultaneous vaporization and solvent crystallization operation to thereby form a first vapor, V ₁₂ , and a solid-liquid mixture, K ₁₈ (denoted as a first condensed mass) , and is characterized in coupling a temperature elevating first vapor absorption operation with a solvent solid melting operation. The absorbing solution used contains the solvent and a properly selected solute in a properly selected concentration range so that while the absorption pressure is

near or slightly lower than that of the freezing operation, the absorbing temperature is somewhat higher than the melting temperature of the solvent solid.

In one way of conducting the MPTAM Process, the heat released in the absorption step is first used to generate a mass of second vapor and the second vapor is brought in contact with the solvent solid to simultaneously condense the vapor and melt the solid. An integrated system to conduct a MPTAM Process is introduced. In this system, the absorption and second vapor generation operations are conducted around two liquid films formed on the two sides of a heat conduction wall so that the heat of absorption on one side is transmitted through the wall and utilized in supplying the latent heat of vaporization of generating the second vapor.

In another way of conducting the MPTAM Process, the first vapor may also be absorbed into an absorbing solution on the outer surface of a heat exchange conduit that contin a slurry of solvent solid. The heat released in the absorption step is transmitted through the conduit wall to melt the solvent solid.

The absorbing solution is diluted in the absorption operation and the diluted solution is concentrated back to the original concentration. Low grade heat sources, such as low pressure steam in power generation plant, particularly in co-generation plant, or various other sources, may be used to accomplish this operation.

In a freeze drying process, a low pressure water vapor in a range of 20 to 750 microns is generated. A multiple stage absorption vapor pressure enhancing process may be used to transform the low pressure vapor into a liquid state, upgrade the heat and ultimately reject the heat to a convenient heat sink near ambient temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention introduces a new way of enhancing vapor pressure by coupling the pressure enhancing operation with an operation of diluting an absorbing solution. There are Type A enhancement units and Type B enhancement units. An operation conducted in a Type A enhancement unit is referred to as a Type A enhancement operation; an operation conducted in a Type B enhancement unit is referred to as a Type B enhancement operation.

Figure 1 illustrates a Type A unit for conducting the vapor pressure enhancement operation. It shows that a falling film of an absorbing solution and a falling film of a mass of solvent liquid are formed on the two surfaces of a vertical heat conductive wall. A first vapor is absorbed into the film of absorbing solution; a mass of second vapor is generated from the film of solvent liquid. Figure 2 illustrates a equilibrium phase diagram of lithium bromide- water system. The operating conditions of the vapor pressure enhancement operation described are illustrated on Figure 2.

Figure 3 illustrates a Type B system for conducting the vapor pressure enhancement operation. The system comprises a first processing zone, Z-l, in which a first vapor is absorbed into a first absorbing solution to become a second absorbing solution and a second processing zone, Z-2, in which a mass of solvent liquid is vaporized to become a second vapor. A circulating heat transfer medium is circulated between the two processing zones to remove the heat released in the absorption operation and supply the heat needed in the vaporization operation. The operating conditions of the Type B operation are illustrated in Figure 4.

Figure 5 illustrates a conventional absorption refrigeration system using an absorbing solution comprising water and a non-volatile solute, usually lithium bromide. The operating conditions of the system are illustrated in Figure 6. These figures are used to illustrate the performance limitations of a conventional system.

Figures 7 and 9 illustrate integrated systems utilizing Type A vapor pressure enhancement operations. In each of these systems, a first vapor formed from any process is subjected to a Type A vapor pressure enhancement operation to become a second vapor and the second vapor is absorbed into another absorbing solution with the heat released in the second absorption operation removed by a stream of cooling medium at a readily available temperature, such as cooling water at ambient temperature. The diluted absorbing solutions are regenerated, heat exchanged and recycled. The two absorbing solutions used may be used in series, in parallel, or be used independently. The system of Figure 7 uses a series approach; the system of Figure 9 uses a parallel arrangement. Figures 8 and 10 illustrate phase diagrams of lithium bromide-water systems. The operating conditions of the systems of Figures 7 and 9 are respectively illustrates in Figures 8 and 10.

Figure 11 illustrates yet another system in which Type A vapor pressure enhancement operations are used twice and the diluted absorbing solutions are regenerated independently. In the system, a first vapor is subjected to a first Type A operation to produce a second vapor and the second vapor is subjected to a second Type A operation to reproduce a third vapor. The third vapor is at such an elevated pressure that it is condensed by a readily available cooling medium. The operating conditions of this system are illustrated by Figure 12.

Figure 13 illustrates integrated systems in which first vapors are subjected to Type B vapor pressure enhancement operations using first absorbing solutions to produce second vapors and the second vapors at elevated pressures are absorbed into second absorbing solutions at elevated temperatures so that heat released in the absorption operations are removed by cooling mediums at temperatures that are readily available. The diluted absorbing solutions are regenerated and recycled.

Figure 14 illustrates a Type A multiple phase transformation process (MPTAM Process) with coupled vapor absorption and crystal melting operations. In this system, the first vapor formed in a solid-liquid-vapor multiple phase transformation operation is subjected to a vapor pressure enhancement operation using a first absorbing solution to thereby produce a second vapor whose pressure is higher than the triple point pressure of the solvent crystals. The second vapor is brought in contact with a mass of solvent crystals to thereby simultaneously condense the second vapor and melt the solvent crystals. The system requires an auxiliary refrigeration system to maintain the system under a properly balanced state. The needed auxiliary refrigeration is accomplished by absorbing a fraction of the second vapor into a second absorbing solution and removing the heat of absorption by a cooling medium at a readily available temperature. The first absorbing solution and the second absorbing solution may be the same solution and be regenerated together.

Figure 15 illustrates a block diagram of the MPTAM System illustrated in Figure 14. It illustrates the functions of the processing zones and also illustrates the material flows among the zones. Figure 16 illustrates the processing steps of the MPTAM system. In this system, the heat of absorbing first vapor is utilized to generate second vapor and the second vapor is used to melt the solvent

solid.

Figure 17 illustrates a Type B Multiple Phase Transformation Process (MTPFM Process) with coupled vapor absorption and crystal melting operations. Figure 18 illustrates a block diagram of a Type B MPTAM System showing the functions of various processing zones; Figure 19 illustrates the processing steps of the process. In this system the first vapor is absorbed into an absorbing solution on the outer surface of a heat exchange conduit that contains a slurry of solvent solid. The heat released in the absorbing step is transmitted through the condiut wall to melt the solvent solid.

DESCRIPTION OF THE PREFERRED EMBODIMENTS (BEST MODES FOR CARRYING OUT THE INVENTION)

A new method of absorbing a first and low pressure vapor into an absorbing solution and generating an equivalent amount of second vapor at an elevated pressure is introduced. These operations are accomplished by diluting an absorbing solution. Two types of units for accomplishing the vapor pressure enhancement are introduced: viz. Type A units and Type B units. A Type A unit may be referred to as a double falling liquid film unit; a Type B unit may be referred to as a looped coil unit. An operation conducted in a Type A unit is referred to as a Type A enhancement operation; an operation conducted in a Type B unit is referred to as a Type B enhancement operation.

Figure 1 illustrates a Type A unit and is used to illustrate a Type A enhancement operation. The unit comprises a vacuum enclosure 1, a partitioner 2 having a multitude of vertical heat transfer walls separating the unit into a first processing zone 3 (Zone 1) and a second processing zone 4 (zone 2) . The unit has a first set of sprayers 5 for spraying an absorbing solution on one side of

the vertical walls to form vertical liquid films 6 of the absorbing solution in Zone 1; the unit has a second set of sprayers 7 for spraying a mass of water on the other side of the vertical walls to form vertical water films 8 in Zone 2. The absorbing solution J ₀₁ enters the sprayer 5, absorbs the first vapor at about the pressure P ₁ of the first vapor but at a temperature substantially higher than the pure water saturation temperature at the first vapor pressure. The absorbing solution is diluted and the diluted solution is discharged as the J ₁₀ stream. The water stream L_„ ₂ is applied to the vertical walls. The heat of absorption is transmitted through the vertical walls and to the falling water film to generate a second vapor V ₂₀ at a second pressure P ₂ . The excess water L^ is recycled to the unit with a make up water to form the 1^ ₂ stream. The pressure P ₂ of the second vapor is substantially higher than P., of the first vapor. Therefore, the operation is referred to as a Type A vapor pressure enhancement operation.

Figure 2 shows the relation between the vapor pressure in Torrs of an aqueous lithium bromide solution and the solution concentration and the solution temperature. Pure water saturation temperatures corresponding to various pressures are also shown along a separate y-axis. The figure also shows the saturation line of anhydrous lithium bromide and the saturation line of hydrated lithium bromide.

The operating conditions of the Type A vapor pressure enhancement operation are also illustrated in Figure 2. It shows that the first vapor enters the unit under a first pressure P ₁ illustrated by the horizontal line 9. The concentration of the initial absorbing solution J ₀₁ and the initial absorbing temperature are represented by point 10. As the absorption operation progresses, the concentrate of the absorbing solution and the absorbing temperature decrease. The concentration of the final solution J ₁₀ and the final absorbing temperature are represented by point 11.

There is a temperature differential between the two liquid films needed for heat transfer. Therefore, the temperature of the falling water film is illustrated by point 12. The condition of the second vapor is illustrated by point 13. It is seen that the pressure P ₂ of second vapor at point 13 is substantially higher than the pressure of the first vapor at point 9. This pressure increase if referred to as the pressure enhancement of the vapor streams. It is seen that this pressure enhancement is accomplished by coupling the pressure enhancement with dilution of the absorbing solution.

Figure 3 illustrates a Type B pressure enhancement unit. It comprises a vacuum enclosure 14, a vertical partitioner 15 separating the unit into a first processing zone 16 (Zone 1) and a second processing zone 17 (Zone 2) , a first spraying device 18 for spraying an absorbing solution J ₀₁ , a second spraying device 19 for spraying water L^. There are heat exchange coils in the two zones connected together with a circulating pump 20. A heat transfer medium is circulated in the loop by the circulation pump. The medium M ₂₁ enters the first zone and absorbs the heat of absorption and leaves the zone as M ₁₂ . The medium enters the second zone and releases heat to the water in Zone 2 to generate second vapor V ₂₀ at a second pressure P ₂ . The medium is cooled to become the M ₂₁ stream. A part of the water introduced in the second zone vaporizes and becomes the second vapor; the rest is discharged as the L^ stream. Make up water is added to the L^ stream to form the Itø stream.

Figure 4 is the phase diagram of lithium bromide-water mixtures. The operating conditions of the Type B pressure enhancement operation described above are illustrated in the figure. The first vapor V ₀₁ enters at a first pressure illustrated by the horizontal line 21. The initial absorption condition is illustrated by point 22. The

absorbing solution is diluted and the absorbing temperature is lowered. So, the final absorbing condition is illustrated by point 23. Since the temperature of the heat transfer medium is raised in Zone 1 and lowered in Zone 2, the temperature 24 at which the second vapor is generated is substantially lower than that of the final absorbing condition 23. It is noted that this temperature differential between points 23 and 24 in the Type B system is greater than that between points 11 and 12 in the Type A system. Therefore, the pressure 25 of the second vapor generated is lower than 13 in the Type A unit when both are operated under equivalent inlet conditions. It is noted that the component parts needed in assembling a Type B unit are commercially available from suppliers of conventional absorption refrigeration systems.

Figure 5 illustrates a conventional single stage absorption refrigeration system and Figure 6 illustrates the operating conditions. The system comprises a first vessel 26 and a second vessel 27. The first vessel contains a separating wall 28 which separates the vessel into a first processing zone 29 (Zone 1) and a second processing zone 30 (Zone 2) . There are heat exchange coils 31 and 32 in the two zones and there are two spraying devices 33 and 34 in the two zones. There is a partitioner 35 that separates the second vessel into a third processing zone 37 and a fourth processing zone 36. There are heat exchange coils 39 and 38 in the two zones. The two coils 32 and 38 in the second zone and the fourth zone are connected to form a loop.

Zone 1 is an evaporator section in which water L _n and L ₄₁ are sprayed and flash vaporized to form a first vapor stream V ₁₂ and cool the coil 31. In a typical application, a heat transfer medium M ₁₀ enters at a temperature of say 15.5 degrees C (60 degrees F) and is cooled in the coil to become a chilled water stream at a temperature of say 4.44 degrees C (40 degrees F) . Zone 2 is an absorber section.

The first vapor is absorbed into an absorbing solution J ₃₂ that is sprayed into the zone by the sprayer. The heat released in the absorption operation is released to a heat exchange medium M ₀₂ . The heated medium exits as the M ₂₄ stream. The diluted absorbing solution _Ώ is pumped by a pump 40 to Zone 3, which is a generator section. The diluted absorbing solution is heated by a heating medium H ₀₃ which is cooled and exits as H ₃₀ stream. A vapor stream V^ is generated and the absorbing solution is concentrated to the original strength. The concentrated solution is heat exchanged with the dilute absorbing solution ( the heat exchanger is not shown in the figure) and is pumped by a pump 40A and returned to Zone 2 as the J ₃₂ stream. The vapor stream V ₃₄ is condensed by a cooling medium. The condensate L ₄₁ is pumped by a pump 41A to Zone 1. The cooling medium M ₀₂ is used to remove the heat of absorption in zone 2 to become the M ₂₄ stream, which is further used to absorb the heat of condensation in Zone 4 and then discharged from the system as the M ₄₀ stream. A part of the water sprayed in Zone 1 is vaporized. The remainder, L , is pumped by a pump 41 as recycle to Zone 1. The pressure of the first vapor V ₁₂ is illustrated by the horizontal line 42 in Figure 6. The initial absorbing condition and the final absorbing condition in zone 2 are illustrated by points 43 and 44 respectively. The diluted absorbing solution is heat exchanged and sent into the generator (Zone 3) . The initial condition and the final condition in the generator are respectively illustrated by points 45 and 46.

The degree of temperature lifting that can be accomplished in a single stage absorption refrigeration is rather limited, because of the presence of saturation curves of lithium bromide as lithium bromide hydrate and because of the need of rejecting heat to readily available cooling water. In order to reject heat to cooling water at 32 degrees C (90 degrees F) , the absorbing temperature has to be around 43 degrees C (110 degrees F) . However, in order

to absorb water vapor at 1.81 Torrs, for example, the absorbing temperature has to be at less than 15.5 degrees C (60 degrees F) in order not to form crystals of lithium bromide hydrate crystals. It will be shown that by using a multiple steage absorption refrigeration system of the present invention, the problem described can be avoided. The process can circumvent the saturation region.

Figure 7 illustrates a double stage absorption refrigeration system with a Type A pressure enhancer. By referring to Figures 1, 5, and 7, one can recognize that the system of Figure 7 can be obtained by inserting a Type A pressure enhancer of Figure 1 into a conventional absorption refrigeration system of Figure 5. The system comprises a first vessel 47 and a second vessel 48. In the first vessel, there are two main vertical partitioners 49 and 50 and a multitude of vertical partitioners 51. There are a first processing zone 52, a second processing zone 53, a third processing zone 54 and a fourth processing zone 55. Zone 1 is a first vapor generation zone; zone 2 is a first vapor absorption zone for absorbing the first vapor; Zone 3 is a second vapor generation zone; and zone 4 is a second absorption zone absorbing the second vapor. In the second vessel, there is a main partitioner 56 that separates the vessel into a fifth processing zone 57 (Zone 5) and a sixth processing zone 58 (Zone 6) . Zone 5 is a generator section; Zone 6 is a condenser section. There is a first spraying device 59 in Zone 2; there is a second spraying device 60 in Zone 3; there is a third spraying device 61 in Zone 4. There are heat transfer coils 62, 63, and 64 respectively in Zone 4, Zone 5, and Zone 6. There are pumps 65, 66, 67, 68, 69, and 70 for circulating various liquid streams. There are narrow vertical compartments 71 in Zone 2 and there are narrow vertical compartments 72 in Zone 3.

There are two absorption operations taking place in Zone 2 and Zone 4. Therefore, the degree of temperature

lifting that can be accomplished in this system is much greater than that of a conventional single stage system. In operation, a feed L _g ., is introduced into Zone 1 and is subjected to a solid-liquid-vapor multiple phase transformation operation to form a first vapor V ₁₂ and a solid-liquid mixture K ₁₀ under a first pressure P.,. The first vapor is absorbed in an absorbing solution J ₄₂ and the heat is used to generate a second water vapor under a second pressure P ₂ from a water stream L ₆₃ + L^. This pressure- enhancement is accomplished by a Type A enhancement operation. The second vapor V ₃₄ is absorbed by an absorbing solution J ₅₄ and the heat released in this absorption operation is removed by a heat transfer medium M ₀₄ . The diluted absorbing solution 73 (J ₂₅ stream) is sent to the generator (Zone 5) by the pump 65. The solution is subjected to an evaporation operation by the heating medium H ₀₅ to produce a concentrated absorbing solution 77 (J ₅₄ stream) , which is heat exchanged with the cold solution J ₂₅ and pumped by the pump 66 to Zone 4. The diluted absorbing solution 76 (J ₄₂ stream) is pumped by the pump 67 and is introduced into Zone 2. A part of the water L ₆₃ + L _j3 is vaporized to become the second vapor V^. The remaining liquid _j3 is pumped by the pump 68 and recycled to Zone 3. The vapor formed in the generator V ₅₆ is condensed; a part of the condensate L ₆₀ is discharged from the system by the pump 69. The remaining condensate L^ is pumped by the pump 70 and returned to Zone 3.

There are two absorption operations taking place in the system and the solutions are diluted by the absorption operations and concentrated by the generator section. A series arrangement is illustrated in the system of Figure 7. The concentrated absorption solution J ₅₄ enters Zone 4 and is diluted by absorbing the second vapor V ₃₄ to form a diluted absorbing solution J ₄₂ which becomes the absorbing solution in Zone 2. This solution is further diluted by absorbing the first vapor V ₁₂ to become a twice diluted absorbing solution J ₂₅ , which is regenerated in the

generator.

The operating conditions of the two absorption operations and the regeneration operation are illustrated in Figure 8. The pressure of the first vapor V ₁₂ is illustrated by the horizontal line 81. The initial and final absorbing conditions in Zone 2 are respectively illustrated by point 82 and 83. The second vapor is formed at a temperature illustrated by 83A and the condition of the second vapor is illustrated by point 84. The second vapor is absorbed in the second absorption operation. The initial and final absorbing conditions in the second absorption operation are illustrated by points 85 and 86. The twice diluted absorbing solution 83 is heat exchanged and regenerated in the generator section. The initial and final conditions in the generator are illustrated by point 87 and 88. The conditions of the absorbing solutions follow the loop with a first step from 87 and 88 in the generator, a second step from 85 to 86 in the absorption operation in Zone 4 and a third step, from 82 and 83 in the absorption operation in Zone 2.

The system illustrated in Figure 9 is similar to the system illustrated by Figure 7. It also contains two vessels 47 and 48. Equivalent parts in the two figures are referred to by the same number. Therefore, the descriptions and operational procedures described in connection with the system of Figure 7 can be used to describe the system and operating procedures of the system of Figure 9. The only difference between the two systems are the flow arrangements of the absorbing solutions. In the system of Figure 9, a parallel flow arrangement is shown. The absorbing solution after being concentrated in the generator section is divided into two streams, J ₅₄ and J ₅₂ , which are respectively used as absorbing solutions in Zone 4 and Zone 2. The diluted absorbing solutions J ₄₅ and J ₂₅ are heat exchanged and returned to the generator to be reconcentrated.

The conditions of the two absorbing operations and the reconcentration operation in the system of Figure 9 are illustrated by various points in Figure 10. The pressure of the first vapor is shown by the horizontal line 89. The initial condition and the final condition of the absorption operation in Zone 2 are illustrated by points 90 and 91. The second vapor is generated at the temperature of point 91A. The condition of the second vapor is illustrated by point 92. The initial and final absorption conditions in Zone 4 are illustrated by points 93 and 94. The two diluted absorbing solutions 91 and 94 are both returned to the generator. The initial and final conditions of the solution in the generator are illustrated by points 95 and 96.

It is noted that the absorbing solutions returned to the generator in the parallel arrangement are of lower concentration than that of a series arrangement. Therefore, the operation condition of the generator in the parallel arrangement are milder than those in the series arrangement. One may use a multiple effect evaporator in reconcentrating the absorbing solutions.

Figure 11 illustrates a system with two Type A pressure enhancing units. It also has two absorbers. The two diluted absorbing solutions are shown to be regenerated in two separate generators. The system comprises a first vessel 97, a second vessel 98, and a third vessel 99. The first vessel has a first processing zone 100 (Z-l) that contains a first vapor generator, a second processing zone 101 (Z-2) that contains an absorber for the first vapor, a third processing zone 102 (Z-3) that contains a second vapor generator, a fourth processing zone 103 (Z-4) that contains an absorber for the second vapor, a fifth processing zone 104 (Z-5) that contains a third vapor generator, and a sixth processing zone 105 (Z-6) that contains a condenser for the third vapor. The second vessel contains a seventh zone 106

(Z-7) which contains a first generator and an eighth zone 107 (Z-8) which contains a first condenser. The third vessel contains a ninth zone 108 (Z-9) that contains a second generator and a tenth zone (Z-10) that contains a second condenser.

In operation, a first vapor V ₁₂ is generated in Zone 1; the first vapor is subjected to a first Type A pressure enhancement to generate a second vapor V^; the second vapor is subjected to a second Type A pressure enhancement to generate a third vapor V ₅₆ ; the third vapor is condensed in Zone 6 by a cooling water available. The first diluted absorbing solution J ₂₇ is regenerated in zone 7 and is returned as J _n ; the second diluted absorbing solution J ₄₉ is regenerated in Zone 9 and is returned as J ₉₄ . The vapor streams V ₇₈ and V ₉₁₀ that are generated in the generators are condensed in the condensers in Zone 8 and Zone 10 respectively.

The conditions prevailing in the vapor generation operations, the vapor absorption operations and absorption solution regeneration operations are illustrated by various points in Figure 12. The pressure of the first vapor V ₁₂ is illustrated by the horizontal line 110; the initial and final conditions of the absorption operation in zone 2 are illustrated by points 111 and 112; the temperature of generating the second vapor is shown by point 113; the conditions of the second vapor V^ is shown by point 114; the initial and final conditions of the absorption operation in zone 4 are shown by points 115 and 116; the temperature at which the third vapor is generated is shown by point 117; the condition of the third vapor is shown by point 118. The initial and final conditions in the regeneration of the first diluted absorbing solutions are illustrated by points 119 and 120; the initial and final conditions in the regeneration of the second absorbing solution are illustrated by points 121 and 122.

The system illustrated by Figure 13 has a Type B pressure enhancer. This system is similar to the system of Figure 7 and can be obtained by replacing the Type A pressure enhancer by the Type B pressure enhancer. The operations of the two systems are similar.

The system has a first vessel 123 and a second vessel 124. The first vessel contains a first zone 125 (Z-l) that contains a first vapor generator, a second zone 126 (Z-2) that contains an absorber for the first vapor, a third zone

127 that contains a second vapor generator and a fourth zone

128 that contains an absorber for the second vapor. The second vessel has a fifth zone 130 that contains a generator and a sixth zone 129 that contains a condenser. There are sprayers 131, 132, and 133 in Zone 2, Zone 3 and Zone 4 respectively; there are heat transfer coils 134, 135, 136, 137, and 138 in the zones. There are pumps 139, 140, 141, 142, and 143 for circulating various liquid streams. Since the system description and system operation are similar to those of the system of Figure 7 detailed descriptions are omitted.

Figure 14 illustrates a Type A multiple phase transformation process with coupled vapor absorption and crystal melting (MPTAM) operations. In this system, the first vapor formed in a solid-liquid-vapor multiple phase transformation operation is subjected to a Type A vapor pressure enhancement operation using a first absorbing solution to thereby produce a second vapor whose pressure is higher than the triple point pressure of the solvent crystals. The second vapor is brought in contact with a mass of solvent crystals to thereby simultaneously condense the second vapor and melt the solvent crystals. The system requires an auxiliary refrigeration system to maintain the system under a properly balanced state. The needed auxiliary refrigeration is accomplished by absorbing a fraction of the second vapor into a second absorbing

solution and removing the heat of absorption by a cooling medium at a readily available temperature. The first absorbing solution and the second absorbing solution may be the same solution and be regenerated together.

The system comprises a first vessel 145, a second vessel 146 and a third vessel 147. There is a type A pressure enhancer in the first vessel. The first vessel contains a first zone 148 (Z-l) that contains a first vapor generator, a vertical wall partition 149, a second processing zone 150 (Z-2) that contains an absorber for the first vapor, a third processing zone 151 (Z-3) that contains a second vapor generator, a fourth processing zone 152 (Z-4) that contains a crystal elter, a fifth processing Zone 153 that contains an absorber for an excess second vapor. The second vessel contains a sixth processing zone 154 that contains a generator for regenerating the absorbing solution and a seventh processing zone 155 that contains a vapor condenser. The third vessel contains an eighth processing zone (Z-8) that contains a crystal washer.

The system can be used in conducting a solid-liquid- vapor multiple phase transformation process. A feed L^ is introduced in zone 1 and is subjected to a multiple phase transformation to produce a first vapor V ₁₂ and a solid- liquid mixture K ₁₈ . The first vapor is subjected to a Type A pressure enhancement to produce a second vapor V ₃₄ . The crystals in the solid-liquid mixture K ₁₈ are washed and purified in Zone 8 to produce a concentrate L _gg and a purified solid-liquid mixture K^. The second vapor is brought in contact with K^ in Zone 4, condenses and simultaneously melts the crystals to produce a purified product L ₄₀ . Because of heat leakage into the system and imperfect heat exchange operations, the amount of second vapor produced is greater than the amount that can be condensed by melting the crystals in K^. Therefore, there is some excess second vapor V ₄₅ . The excess second vapor is

absorbed by a second absorption operation and the heat of absorption is removed by a cooling medium entering as M^ and leaving as M _gg . The diluted absorbing solution J ₂₆ from Zone 2 and the diluted absorbing solution J ₅₆ from zone 5 are reconstituted in the generator in Zone 6 by a heating medium that enters as H^ and leaves as H^. The concentrated absorbing solution is divided into two streams J ₆₂ and J ₆₅ and are respectively used in Zone 2 and Zone 5. The vapor V ₆₇ formed in the generator is condensed in Zone 7 by a cooling medium that enters as M, _j7 and leaves as M ₇₀ .

Figure 15 shows a block process diagram of the Type A MPTAM system illustrated by Figure 14 and illustrates the functions of the various zones. The system comprises a multiple phase transformation zone (Zone 1) , a temperature elevating first vapor absorption zone (Zone 2) , a second vapor generation zone (Zone 3) , a simultaneous condensation- melting zone (Zone 4) , an auxiliary heat rejection zone (Zone 5) , absorbing solution regeneration zones (Zones 6 and 7) and a solvent crystal purification zone (Zone 8) . Figure 16 illustrates the processing steps involved.

Referring to Figures 15 and 16, the process comprises:

Step 1: Multiple Phase Transformation - A mass of liquid feed L _g , is introduced into the multiple phase transformation zone 1 that is maintained under a pressure lower than the vapor pressure of the solution in the zone at its freezing temperature to thereby form a first vapor, V ₁₂ , and a first condensed mass, K ₁₈ , containing a first mass of solvent crystals, S ₁₈ , and a mother liquor, M ₁₈ .

Step 2: Temperature Elevating First Vapor Absorption - The first vapor, V ₁₂ , is absorbed into an absorbing solution, J ₆₂ , in Zone 2 to form a diluted or weak absorbing solution, J ₂₆ . The absorbing solution in the zone contains a properly selected solute within a proper concentration

range so hat, while the absorption pressure is near or somewhat jwer than the multiple phase trans ^rmation pressure in Zone 1, the absorption temperature is somewhat higher than the second vapor generation temperature of Step 3 to be described. The absorption solution J ₆₂ is diluted by this absorption operation to become the diluted absorbing solution, J ₂₆ . The diluted absorbing solution is then concentrated back to the original concentration in Step 5 to be described.

Step 3: Second Vapor Generation - A mass of liquid, normally a mass of solvent, is vaporized in Zone 3 to form a mass of second vapor, V ₃₄ , whose condensing temperature is near or somewhat higher than the melting temperature of the second condensed mass in Zone 4. Zone 3 is separated from Zone 2 by heat conducting wall(s). Zone 2 and Zone 3 are in a heat exchange relation, and the heat of vaporization is provided by the heat released in the absorption step. Step 4 is conducted by bringing the second vapor, V ₃₄ , into heat exchange relation with the second condensed mass in Zone 4 to thereby simultaneously condense the second vapor and melt the solvent crystals in the solid-liquid mixture K^. The second vapor may be brought into a direct or indirect contact heat exchange relation to accomplish the desired simultaneous condensation and crystal melting operations. The liquid solvent used for the second vapor generation may either come from Zone 4, L ₄₃ , or from zone 7, L^.

Step 4: Simultaneous Condensation-Melting - A second condensed mass (slush) , K^, containing a second mass of solvent crystals, S^, is placed in Zone 4. A mass of second vapor, V^, is brought into contact with the second condensed mass to melt the solvent crystals. The purified solvent liquid L ₄ is divided into a product, L ₄₀ , and a mass L ₄₈ , that is recycled to Zone 8 for crystal washing. One may also recycle a stream L ₄₃ to Zone 3 for generating second vapor.

Step 5: Regeneration of the Absorbing Solution - The diluted absorbing solution, J ₂₆ and J ₅₆ , are combined and the combined stream is concentrated in Zone 6 to produce a mass of enriched absorbing solution J ₆₂ and J ₆₅ which is returned to zones 2 and 5 and a mass of purified solvent L^. This concentration operation can be accomplished in many ways, such as (a) single effect evaporation, (b) a multiple effect evaporation, (c) a single effect vapor compression evaporation, (d) a multiple effect vapor compression evaporation, (e) a freezing operation, etc. It is noted that low grade heat such as waste heat from various sources may be used to drive this concentration step. A mass of low pressure steam from a co-generation plant is a convenient heat source for this regeneration operation.

Step 6: Crystal Purifications - The first condensed mass, K ₁₈ , obtained in step 1, may be subjected to a crystal purification operation in Zone 8 using some purified solvent L ₄₈ to produce a mass of concentrate L _gg and a second condensed mass, K^, which is subjected to the step 4 operation described.

Step 7: Solvent Recycling - A portion of the purified solvent produced in steps 4 and 5, L ₃ and/or L^, is recycled to zone 3 for generating the second vapor; another portion of the purified solvent, L ₄₈ and/or L^, is recycled to Zone 8 for crystal washing.

Step 8: Auxilary Cooling - Due to heat leakages into the system and temperature differentials needed for heat exchange operations, there is a need for an auxiliary cooling operation. In other words, there is an excess second vapor that cannot be condensed by melting the mass of solvent crystals. The auxiliary cooling can be accomplished by condensing the excess second vapor, or by absorbing it into an absorbing solution J ₆₅ to thereby produce a diluted

absorbing solution J ₅₆ which is regenerated in Zones 6 and 7. The heat of absorption Q ₅₀ is rejected to a cooling water stream.

Figure 17 illustrates an integrated system in which Type B MPTAM Process can be conducted. The system comprises a main unit 157, and a crystal washing unit 158. the main unit comprises a vacuum vessel, 159, that contains a multiple phase transformation Zone 160 (Zone 1) , a temperature elevating first vapor absorption Zone 161 (Zone 2) , a solvent crystal melting Zone 162 (Zone 4) , an absorbing solution regenerating Zone 163 and 164 (Zones 6 and 7), and an auxiliary cooling unit 165. The regeneration zone is divided into an evaporation sub-zone 163 and vapor condensing sub-zone 164. Rotating screws or disks, 165, are used to conduct the multiple phase transformation operation in Zone 1. It is noted that in Type B MPTAM system, there is no second vapor generation operation. The system used is quite similar to a system used in absorption refrigeration that is used to produce chill water manufactured by companies such as Trane Co., in Wisconsin, and Carrier Corp., in Syracuse, N.Y.

In operation, feed L ₀₁ is introduced in Zone 1, to form a first vapor, V ₁₂ , and a solid-liquid mixture, K ₁₈ . The first vapor and a recycled enriched absorbing solution, J ₆₂ , are introduced into Zone 2 and a solvent solid-liquid mixture, K^, is introduced into Zone 4. Zone 4 is inside of heat conductive conduits that are placed within Zone 2. The first vapor is absorbed into the absorbing solution to form diluted absorbing solution J ₂₆ , and the heat released in the absorbing operation is utilized to melt the solvent crystals in Zone 4, and thereby form purified solvent L ₄ . A portion of the purified solvent, ^, is recycled to Zone 8 to wash solvent crystals; the rest becomes purified solvent product L ₄₀ .

The need and structure of the auxiliary cooling unit 165 is similar to those described in connection with the Type A MPTAM system. The operation conducted in Zone 1 of a Type B system is also similar to that in a Type A system described. The diluted absorbing solution, J ₂₆ , is subjected to an evaporation operation in Zone 6 using some low grade heat and the vapor so formed is condensed by cooling water in Zone 7.

As has been described, the key features in the MPTAM processes are: (1) temperature elevation of first vapor absorption and (2) heat coupling between the first vapor absorption operation in Zone 2 and the melting operation of the solvent solid in Zone 4. Temperature elevation is defined as the difference between the absorption temperature in Zone 2 and the multiple phase transformation temperature T_, in Zone 1. The absorption pressure P ₂ is near or somewhat lower than the multiple phase transformation pressure P_, in Zone 1. for a given solute used in formulating the absorbing solution, the concentration to be used depends on the amount of temperature elevation needed. For a given solute used, there is a limit to the degree of temperature elevation attainable. This limit may be set by the solubility limit or viscosity limit.

For ease of conducting the first vapor absorption operation and for ease of regenerating the absorbing solution, it is desirable to use as low a concentration absorbing solution as possible. It is therefore important to reduce the degree of temperature elevation needed. Reduction of the temperature differential is needed for heat coupling, i.e. T ₂ -T ₄ . This value may be as high as 10 degrees Centigrade. However, it is desirable to limit this value to less than 5 degrees Centigrade or even less than 3 degrees Centigrade.

Figure 18 shows a schematic illustratioin of a system in which Type B MPTAM Process of figure 17 is conducted. The system comprises a multiple phase transformation zone (Zone 1) , a temperature elevating first vapor absorption zone (Zone 2), a solvent crystal melting zone (Zone 4), an absorbing solution regeneration zone (Zones 6 and 7) , and a solvent crystal purification zone (Zone 8) . Figure 19 illustrates the processing steps. As shown by these two figures, the processing steps in the Type B MPTAM Process are similar to the processing steps in the Type A MPFAM Process, with the following exceptions: (a) Second vapor is not generated, (b) the latent heat of melting a mass of purified solvent crystals (step 4) is supplied by transferring heat from Zone 2 to Zone 4 through heat conducting walls. Therefore, the latent heat released in the first vapor absorption step is utilized in supplying the latent heat needed in melting the solvent crystals.

Freeze dryers operate in the range of 20 to 750 microns. Conventional ways of handling the low pressure vapor in a freeze dryer are to use four and five stage steam jets or to use rotary-piston oil sealed pumps and rotary- blower-rotary-piston oil-sealed pump. It is, however, more economical to use an absorption vapor pressure enhancer system of the present invention to handle the low pressure vapor. Because of pressure is very low, two or more stages of temperature lifting absorption are needed.

A freeze drying process may be conducted in the systems illustrated in Figures 7, 9, and 11. It is noted that in each of these systems, there are two stages of temperature lifting vapor absorption. The operations of a freeze drying system is similar with the MPTAM Process. Therefore, a detail description is omitted.

In conclusion, the following remarks are presented:

(1) A cooling medium is needed to remove heat from an absorption operation or a condensation operation. It is important to distinguish an internal cooling medium from an external cooling medium. An internal cooling medium is one that is regenerated and recycled within the system. For example, L ₆₃ and L _j3 in Figure 7 that are used to remove heat of absorption in Zone 2 and thereby partially vaporized is an internal cooling medium because the water that becomes the second vapor is absorbed in Zone 4 and is recovered and recycled after being vaporized in Zone 5 and condensed in Zone 6. An external cooling medium refers to a cooling medium that is not recycled within the system. Examples are (a) ambient air, (b) well water, lake water, and river water and (c) cooling water recycled from a cooling tower in which heat has been rejected to the ambient air.

(2) An external cooling medium is available at 26.6 to 32.2 degrees Centigrade (80 to 90 degrees F) and can be used until its temperature reaches 43.3 to 49 degrees Centigrade (110 to 120 degrees F) .

(3) A conventional absorption refrigeration system can remove heat at 40 degrees F and is therefore able to produce chilled water at 40 degrees F. It has not been able to produce ice. A system of the present invention can remove heat at a much lower temperature. Therefore, it can be used to produce ice.

(4) The word "stage" will be used to refer both to a vapor absorption operation and a pressure enhancement operation. A unit represented by either Figure 1 and Figure 3 has one stage of pressure enhancement; a system of Figure 7 or Figure 9 has one stage of pressure enhancement and two stages of vapor absorption; a system of Figure 11 has two stages of

pressure enhancements and two stages of vapor absorption; a system of Figure 13 or Figure 14 has one stage of pressure enhancement and two stages of vapor absorption.

(5) Terminology used in the claims to be presented is illustrated as follows: Referring to Figure 11, a feed vapor is subjected to an N-stage (N=2) absorption vapor pressure enhancement operation in a processing system having N processing zones, respectively designated as PE-1, PE-2, , PE-n, , PE-N Zones. In the figure, PE-1 represents Z-2, 101 and Z-3, 102, and PE-2 represents Z-4, 103 and Z-5, 104. Each pressure enhancing zone, PE-n Zone, has a n-th stage first vapor absorbing sub- zone designated as PEA-n sub-zone and an n-th stage second vapor generation sub-zone designated as PEB-n sub-zone. Referring to Figure 11, Z-2 is PEA-1 and Z-3 is PEB-1, Z-4 is PEA-2 and Z-5 is PEB-2. The n-th stage first vapor is designated as (V _A ) _n and the n-th stage second vapor is designated as (V _B ) _n . Therefore, V ₁₂ in Figure 11 is (V _A ) _r V ₃₄ is both (V,,), and (V _A ) ₂ and V ₅₆ is (V _B ) ₂ . The absorbing solution used in the PE-n zone is designated as (J _A ) _n . The absorbing temperature in PE-n zone is designated as (T) _n ; the pure solvent saturation temperature of the n-th stage first vapor is designated as (T _A ) _n . The pressure in the n-th stage first vapor absorption sub-zone is designated as (P _A ) _n ; the pressure in the n-th stage second vapor generation sub-zone is designated as (P _B ) _n . Since the processing zones are located in sequence, (V _B ) _n becomes (V _A ) _n+1 , and (P _A ) _n+1 is somewhate lower than (P _B ) _n . Due to the temperature lifting vapor absorption, (T _j ) _n is substantially higher than (T _A ) _n and is also higher than W _n - ( ^τ β) _n ^{is also} higher than (T _A ) _n .