Heat pump freeze drying system

• US 4,016,657 A
• Filed: 10/04/1973
• Issued: 04/12/1977
• Est. Priority Date: 07/14/1971
• Status: Expired due to Term

• Current Assignee: Now By Change Of Name Chand Arjun Passey, Arjun Dev Passey
• Original Assignee: Now By Change Of Name Chand Arjun Passey, Arjun Dev Passey
• Inventors: Passey, now by change of name Chand Arjun Passey, Arjun Dev
• Primary Examiner(s): Myhre, Charles J.
• Assistant Examiner(s): Anderson, William C.
• Application Number:
  US05/403,437
• Time in Patent Office: 1,286 Days
• Field of Search: 34/5, 34/92, 62/513, 62/324
• US Class Current: 34/92
• CPC Class Codes: F25B 25/02 Compression-sorption machines, plants, or systems
• CPC Class Codes: F25B 29/00 Combined heating and refrigeration systems, e.g. operating alternately or simultaneously
• CPC Class Codes: F25B 49/00 Arrangement or mounting of control or safety devices
• CPC Class Codes: F26B 23/005 using a closed cycle heat pump system with recycling of drying medium F26B21/086; using a heat pipe system
• CPC Class Codes: F26B 5/065 the product to be freeze-dried being sprayed, dispersed or pulverised
• CPC Class Codes: Y02B 30/52 Heat recovery pumps, i.e. heat pump based systems or units able to transfer the thermal energy from one area of the premises or part of the facilities to a different one, improving the overall efficiency
• CPC Class Codes: Y02P 70/10 Greenhouse gas [GHG] capture, material saving, heat recovery or other energy efficient measures, e.g. motor control, characterised by manufacturing processes, e.g. for rolling metal or metal working

Abstract

The invention provides a "COORDINATED HEAT PUMP SYSTEM" which simultaneously satisfies the thermal needs of both the heat source and the heat sink. The heat pump system of the present invention is adapted to continuously withdraw heat from a heat source and continuously deliver heat at a required rate to a heat sink such that the ratio of heat delivered to heat withdrawn may be controlled by a cooling means, said heat pump system comprising a compressor adapted to compress at least a portion of refrigerant vapor from an evaporator thereof wherein a refrigerant withdraws heat from said heat source, a condenser in which refrigerant vapor so compressed is condensed and delivers heat at the required rate, cooling means for balancing the rates of heat delivery and heat withdrawal, and an expansion valve for expanding liquid refrigerant from said condenser into said evaporator. The invention also provides an evacuation system for use in vacuum drying having particular application to freeze-drying which comprises a system of absorber-regenerator-condenser units interlinked by coordinated heat pump systems whereby to provide for stable operation of the aforesaid freeze-drying operation and require a minimum of processing energy and power in the freeze-drying or vacuum drying process.

Claims

1. A freeze-drying system for freeze-drying a material, said material comprising a substance to be removed to effect freeze-drying of said material, which system substantially eliminates need to supply heat from an external heat source for freeze-drying said material;

said system comprising in combination;

a. a drying chamber wherein is maintained a vapor pressure below the triple point pressure of substance to be removed to effect freeze-drying of said material;

b. a means for passing the said material through said drying chamber for freeze-drying thereof during said passage;

c. an evacuation means for continuously removing vapor from said drying chamber as it is generated in said chamber in the freeze-drying of said material, said evacuation means comprising an absorber through which a liquid absorbent medium is continuously passed, said absorbent medium being at a sufficiently low temperature to provide in said absorber a vapor pressure lower than in said chamber whereby to cause the vapor to pass from said drying chamber to said absorber where it is absorbed in said absorbent medium;

an evaporator in which absorbed substance is continuously evaporated from the absorbent medium passing therethrough from said absorber at a rate similar to that at which said vapor is absorbed in said absorbent medium in said absorber, by heat exchange with condensing first refrigerant;

a condenser in which vapor from said evaporator is condensed by heat exchange with evaporating first refrigerant;

a first heat pump means adapted to compress at least a portion of first refrigerant vapor from said condenser, pass first refrigerant vapor so compressed to said evaporator and pass condensed first refrigerant from said evaporator through an expansion valve to said condenser, said first heat pump means including a cooling means for removing excess heat from said first refrigerant to maintain heat balance in said evaporator and in said condenser;

a chiller in which the absorbent medium from said evaporator is cooled to restore the absorbent medium to the proper temperature for said absorber for passage to said absorber, by heat exchange with evaporating second refrigerant; and

a means to maintain the absorbent medium in circulation between said absorber, evaporator, and chiller; and

a means to purge the noncondensible gases from the system;

d. a second heat pump means adapted to compress at least a portion of second refrigerant vapor from said chiller, pass the second refrigerant vapor so compressed to a heat exchange means for supplying heat to effect freeze-drying of said material in said drying chamber and pass condensed second refrigerant from heat exchange means through an expansion valve to said chiller, said second heat pump means including a cooling means for removing excess heat from said second refrigerant to maintain heat balance in said heat exchange means and in said chiller.

2. A system as claimed in claim 1 in which said heat exchange means comprises:

a. a cascade heat exchanger in which compressed vapor of second refrigerant is heat exchanged with an evaporating third refrigerant;

b. a heat exchanger means in which compressed third refrigerant vapor is condensed to supply heat for effecting freeze-drying of said material;

c. a third heat pump means adapted to compress at least a portion of third refrigerant vapor from said cascade heat exchanger, pass the third refrigerant vapor so compressed to said heat exchanger means and pass condensed third refrigerant from said heat exchanger means through an expansion valve to said cascade heat exchanger, said third heat pump means including a cooling means for removing excess heat from said third refrigerant to maintain heat balance in said heat exchanger means and in said cascade heat exchanger.

3. A system as claimed in claim 1 for use in freeze-drying a material in which said substance is water, said vapor is substantially water vapor, and in which the absorbent is an aqueous solution of a water vapor pressure depressant.

4. A system as claimed in claim 1 in which said means for passing said material through said drying chamber comprises a means for introducing said material into said drying chamber, a means for retaining said material in said drying chamber for a period sufficient to effect drying of said material to the desired moisture content, and a means for removing the dried material from said drying chamber.

5. A system as claimed in claim 4 in which said material is particulate and frozen.

6. A system as claimed in claim 4 in which said material is atomizable and in which the means for introducing said material into said drying chamber comprises a means for atomizing said material in said drying chamber wherein said atomized material freezes due to prevailing low vapor pressure, said chamber being of a sufficient size and said material being atomized at a location to cause the frozen material to be substantially dried while suspended in said drying chamber.

24. A system as claimed in claim 1 in which the cooling means comprises a heat exchanger between said condenser and said expansion valve adapted to remove excess heat from condensed refrigerant to an external heat sink for the purpose of subcooling control.

25. A system as claimed in claim 1 in which the cooling means comprises means for condensing a portion of the low pressure refrigerant vapor by heat exchange with a heat sink and a means for recycling the so condensed refrigerant to said evaporator.

7. A vacuum drying system for vacuum drying a material, said material comprising a substance to be removed to effect vacuum drying of said material, which system substantially eliminates need to supply heat from an external heat source for vacuum drying said material;

said system comprising in combination;

a. a drying chamber wherein is maintained a subatmospheric pressure to effect vacuum drying of said material;

b. a means for passing the said material through said drying chamber for vacuum drying thereof during said passage;

c. an evacuation means for continuously removing vapor from said drying chamber as it is generated in said chamber in the vacuum drying of said material, said evacuation means comprising an absorber through which a liquid absorbent medium is continuously passed, said absorbent medium being at a sufficiently low temperature to provide in said absorber a vapor pressure lower than in said chamber whereby to cause the vapor to pass from said drying chamber to said absorber where it is absorbed in said absorbent medium;

an evaporator in which absorbed substance is continuously evaporated from the absorbent medium passing therethrough from said absorber at a rate similar to that at which said vapor is absorbed in said absorbent medium in said absorber, by heat exchange with condensing first refrigerant;

a condenser in which vapor from said evaporator is condensed by heat exchange with evaporating first refrigerant;

a first heat pump means adapted to compress at least a portion of first refrigerant vapor from said condenser, pass first refrigerant vapor so compressed to said evaporator and pass condensed first refrigerant from said evaporator through an expansion valve to said condenser, said first heat pump means including a cooling means for removing excess heat from said first refrigerant to maintain heat balance in said evaporator and in said condenser;

a chiller in which the absorbent medium from said evaporator is cooled to restore the absorbent medium to the proper temperature for said absorber for passage to said absorber, by heat exchange with evaporating second refrigerant;

a means for maintaining the absorbent medium in circulation between said absorber, evaporator, and chiller; and

a means to purge the noncondensible gases from the system;

d. a second heat pump means adapted to compress at least a portion of second refrigerant vapor from said chiller, pass the second refrigerant vapor so compressed to a heat exchange means for supplying heat to effect vacuum drying of said material in said drying chamber and pass condensed second refrigerant from said heat exchange means through an expansion valve to said chiller, said second heat pump means including a cooling means for removing excess heat from said second refrigerant to maintain heat balance in said heat exchange means and in said chiller.

8. A system as claimed in claim 7 in which said heat exchange means comprises:

a. a cascade heat exchanger in which compressed vapor of second refrigerant is heat exchanged with an evaporating third refrigerant;

b. a heat exchanger means in which compressed third refrigerant vapor is condensed to supply heat for effecting vacuum drying of said material;

c. a third heat pump means adapted to compress at least a portion of third refrigerant vapor from said cascade heat exchanger, pass the third refrigerant vapor so compressed to said heat exchanger means and pass condensed third refrigerant from said heat exchanger means through an expansion valve to said cascade heat exchanger, said third heat pump means including a cooling means for removing excess heat from said third refrigerant to maintain heat balance in said heat exchanger means and in said cascade heat exchanger.

9. A system as claimed in claim 8 including a subcooling means between the said heat exchanger means and the said expansion valve through which said condensed third refrigerant passes from said heat exchanger means to said cascade heat exchanger, said subcooling means supplying heat to a heat sink external to the said third heat pump means for the purpose of subcooling control.

10. A system as claimed in claim 8 in which the cooling means in said third heat pump means comprises a means for condensing a portion of the low pressure refrigerant vapor by heat exchange with a heat sink and a means for recycling the so condensed refrigerant to said cascade heat exchanger.

11. A system as claimed in claim 7 in which a vapor pressure below the triple point pressure of said substance to be removed is maintained in said drying chamber to effect freeze-drying of said material.

12. A system as claimed in claim 7 in which the cooling means in said first heat pump means comprises a means for condensing a portion of the low pressure refrigerant vapor by heat exchange with a heat sink and a means for recycling the so condensed refrigerant to said condenser.

13. A system as claimed in claim 7 in which the cooling means in said second heat pump means comprises a means for condensing a portion of the low pressure refrigerant vapor by heat exchange with a heat sink and a means for recycling the so condensed refrigerant to said chiller.

14. A system as claimed in claim 7 including a subcooling means between the said evaporator and the said expansion valve through which said condensed first refrigerant passes from said evaporator to said condenser, said subcooling means supplying heat to a heat sink external to the said first heat pump means for the purpose of subcooling control.

15. A system as claimed in claim 7 including a subcooling means between the said heat exchange means and the said expansion valve through which said condensed second refrigerant passes from said heat exchange means to said chiller, said subcooling means supplying heat to a heat sink external to the said second heat pump means for the purpose of subcooling control.

16. A system as claimed in claim 7 for use in vacuum drying a material in which said substance is water, said vapor is substantially water vapor, and in which the absorbent is an aqueous solution of a water vapor pressure depressant.

17. A system as claimed in claim 7 including a separator between said drying chamber and said evacuation means, said separator being adapted to remove partially dried particulate material entrained in vapor passing therethrough and a means for supplying heat to said separator to effect drying of said particulate material, said heat being supplied by one of the heat pump means of said drying system.

18. A system as claimed in claim 7, in which said means for passing said material through said drying chamber comprises a means for introducing said material into said drying chamber, a means for retaining said material in said drying chamber for a period sufficient to effect drying of said material to the desired moisture content, and a means for removing the dried material from said drying chamber.

19. A system as claimed in claim 18 in which said material is particulate.

20. A system as claimed in claim 18 in which said material is atomizable and in which the means for introducing said material into said drying chamber comprises a means for atomizing said material in said drying chamber, said chamber being of a sufficient size and said material being atomized at a location to cause the atomized material to be substantially dried while suspended in said drying chamber.

21. A vacuum drying system for vacuum drying of a material, said material comprising a substance to be removed to effect vacuum drying of said material, which system substantially eliminates need to supply heat from an external heat source for vacuum drying said material;

said system comprising in combination;

a. a drying chamber wherein is maintained a subatmospheric pressure, the vapor pressure in the drying chamber being maintained above the triple point pressure of substance to be removed to effect vacuum drying of said material;

b. a means for passing the said material through said drying chamber for vacuum drying thereof during said passage;

c. an evacuation means for continuously removing vapor from said drying chamber as it is generated in said chamber in the vacuum drying of said material, said evacuation means comprising an absorber through which liquid of said vapor is continuously passed, said liquid being at a sufficiently low temperature to provide in said absorber a vapor pressure substantially lower than in said drying chamber but yet above the said triple point pressure whereby to cause vapor to pass from said drying chamber to said absorber where it is condensed in said liquid;

a chiller adapted to cool the said liquid from said absorber to a proper temperature for said absorber for passage to said absorber, by heat exchange with evaporating second refrigerant;

a means to maintain the said liquid in circulation between said absorber and chiller; and

a means to purge the noncondensible gases from the system;

d. a second heat pump means adapted to compress at least a portion of second refrigerant vapor from said chiller, pass so compressed second refrigerant vapor to a heat exchange means for supplying heat to effect vacuum drying of said material in said drying chamber and pass condensed second refrigerant from said heat exchange means through an expansion valve to said chiller, said second heat pump means including a cooling means for removing excess heat from said second refrigerant to maintain heat balance in said heat exchange means and in said chiller;

e. and a means for continuously removing liquid at a rate corresponding to that at which said vapor is condensed in said absorber to prevent the accumulation of said liquid in said absorber.

22. A system as claimed in claim 21 in which said heat exchange means comprises:

a. a cascade heat exchanger in which compressed vapor of second refrigerant is heat exchanged with an evaporating third refrigerant;

b. a heat exchanger means in which compressed third refrigerant vapor is condensed to supply heat for effecting vacuum drying of said material;

c. a third heat pump means adapted to compress at least a portion of third refrigerant vapor from said cascade heat exchanger, pass the third refrigerant vapor so compressed to said heat exchanger means and pass condensed third refrigerant from said heat exchanger means through an expansion valve to said cascade heat exchanger, said third heat pump means including a cooling means for removing excess heat from said thrid refrigerant to maintain heat balance in said heat exchanger means and in said cascade heat exchanger.

23. A heat pump system adapted to continuously withdraw heat from a heat source and continuously deliver heat at a required rate to a heat sink such that the ratio of heat withdrawn to heat delivered may be controlled by a cooling means, said heat pump system comprising a compressor adapted to compress at least a portion of refrigerant vapor from an evaporator thereof wherein a refrigerant withdraws heat from said heat source, a condenser in which refrigerant vapor so compressed is condensed and delivers heat at the required rate, cooling means for balancing the rates of heat delivery and heat withdrawal, an expansion valve for expanding liquid refrigerant from said condenser into said evaporator, and a liquid-vapor suction line heat exchanger for adequately superheating the portion of refrigerant vapor prior to its compression in the said compressor,.

26. A heat pump system adapted to continuously withdraw heat from a heat source and to continuously deliver heat at the required rate to a heat sink such that the ratio of heat withdrawn to heat delivered may be controlled by a cooling means, said heat pump system comprising a combination of means through which a refrigerant is circulated, said combination of means including an evaporator wherein the said refrigerant withdraws heat from said heat source, a bleeding means for bleeding a portion of low pressure refrigerant vapor coming from said evaporator, a compressor adapted to compress the remaining unbled portion of refrigerant vapor coming from said evaporator, a condenser in which the refrigerant vapor so compressed is condensed and delivers heat the required rate to said heat sink, a cooling means for balancing the rates of heat delivery and heat withdrawal, an expansion valve for expanding the condensed refrigerant from said condenser into said evaporator, and a liquid-vapor suction line heat exchanger for adequately superheating the unbled portion of refrigerant vapor prior to compression thereof in said compressor

27. A system as claimed in claim 26 including a subcooling means between said condenser and said expansion valve adapted to remove excess heat from said condensed refrigerant to a heat sink external to the said heat pump system for the purpose of subcooling control.

28. A system as claimed in claim 26 in which the said cooling means comprises a means for condensing the said bled portion of low pressure refrigerant vapor by heat exchange with a heat sink external to the said heat pump system, and a means for recycling the so condensed refrigerant to said evaporator.

29. An evacuation system substantially eliminating the need to supply heat from an external heat source for continuously removing vapor from a vacuum drying chamber maintained at a pressure above the triple point of the substance of the vapor as said vapor is generated in said chamber in the vacuum drying of a material, said system comprising an absorber through which liquid of said vapor is continuously passed;

said liquid being at a sufficiently low temperature to provide in said absorber a pressure substantially lower than in said chamber but yet above the said triple point pressure whereby to cause vapor to rapidly pass from said chamber to said absorber where it is condensed in said liquid, a chiller adapted to cool heated liquid from the absorber to the desired temperature for said absorber by heat exchange with evaporating refrigerant for passage to said absorber and a heat pump means adapted to compress at least a portion of low pressure refrigerant vapor from said chiller and pass so compressed refrigerant vapor to a heat exchange means for heating the material in said chamber and passing condensed liquid refrigerant from said heat exchange means through an expansion valve to said chiller;

said heat pump means including a cooling means for removing excess heat from said refrigerant to maintain a heat balance between said chiller and said chamber, and a means for continuously removing said liquid at a rate corresponding to that at which the said liquid is formed by condensing vapor in said absorber in order to maintain a steady state condition.

30. A system as claimed in claim 29 in which the liquid is water.

31. A system as claimed in claim 29, in which said heat exchange means comprises a cascade heat exchanger in which said compressed refrigerant vapor is heat exchanged with an evaporating third refrigerant and a third heat pump means adapted to compress at least a portion of the vapor of the third refrigerant from said cascade heat exchanger and pass compressed third refrigerant vapor to a heat exchanger means in said chamber for heat exchange with material therein and pass condensed liquid third refrigerant from said heat exchanger means in said chamber through an expansion valve to said cascade heat exchanger, said third heat pump means including a cooling means for removing excess heat from said third refrigerant to maintain a heat balance between the said cascade heat exchanger and the said heat exchanger means in the chamber.

32. A system as claimed in claim 31 in which the cooling means of the said heat pump means comprises a means for condensing a portion of the low pressure refrigerant vapor by heat exchange with a heat sink and a means for recycling the so condensed refrigerant to the chiller;

and the cooling means of the third heat pump means comprises a means for condensing a portion of the low pressure third refrigerant vapor by heat exchange with a heat sink and a means for recycling the so condensed refrigerant to the cascade heat exchanger.

33. An evacuation system substantially eliminating the need to supply heat from an external heat source for continuously removing vapor from a vacuum drying chamber as it is generated in said chamber in the vacuum drying of a material, said system comprising an absorber through which a liquid absorbent medium is continuously passed, said absorbent medium being at a suficiently low temperature to provide in said absorber a vapor pressure substantially lower than in said chamber whereby to cause vapor to rapidly pass from said chamber to said absorber where it is absorbed in said absorbent medium, an evaporator in which liquid is continuously evaporated from the absorbent medium passing therethrough from said absorber at a rate similar to that at which said vapor is absorbed in said absorbent medium in said absorber, by heat exchange with condensing first refrigerant, a condenser in which vapor from said evaporator is condensed by heat exchange with evaporating first refrigerant, first heat pump means adapted to compress at least a portion of first refrigerant vapor from said condenser, pass first refrigerant vapor so compressed to said evaporator and pass condensed first refrigerant from said evaporator through an expansion valve to said condenser, said first heat pump means including cooling means for removing excess heat from said first refrigerant to maintain a heat balance between the evaporator and condenser, and a chiller adapted to cool heated absorbent medium from said evaporator to restore the absorbent medium to the desired temperature for said absorber for passage to said absorber.

34. A system as claimed in claim 33, in which the heated absorbent medium is cooled in the chiller by heat exchange with evaporating second refrigerant and which system includes second heat pump means adapted to compress at least a portion of second refrigerant vapor from said chiller and pass the second refrigerant vapor so compressed to heat exchange means for heating the material in said chamber and passng condensed second refrigerant from said heat exchange means through an expansion valve to said chiller, said second heat pump means including cooling means for removing excess heat from said second refrigerant to maintain a heat balance between said chiller and said chamber.

35. A system as claimed in claim 34 in which said heat exchange means comprises a cascade heat exchanger in which compressed vapor of the second refrigerant is heat exchanged with an evaporating third refrigerant and third heat pump means adapted to compress at least a portion of the vapor of the third refrigerant from said cascade heat exchanger, pass the compressed vapor of the third refrigerant to a heat exchanger means of said chamber for heat exchange therein and pass condensed liquid third refrigerant from said heat exchanger means through an expansion valve to said cascade heat exchanger, said third heat pump means includng a cooling means for removing excess heat from said third refrigerant to maintain heat balance between the said cascade heat exchanger and the said heat exchanger means of the said chamber.

36. A system as claimed in claim 35 in which the cooling means in said third heat pump means comprises a means for condensing a portion of the low pressure refrigerant vapor by heat exchange with a heat sink and a means for recycling the so condensed refrigerant to the said heat exchanger.

37. A system as claimed in claim 34 in which the cooling means in said second heat pump means comprises a means for condensing a portion of the low pressure refrigerant vapor by heat exchange with a heat sink and a means for recycling the so condensed refrigerant to the said chiller.

38. A system as claimed in claim 34, including a heat exchanger between the said chamber and the said expansion valve for supplying heat to an external heat sink for the purpose of subcooling control.

39. A system as claimed in claim 34 for use in freeze-drying a material in which the vapor is water vapor and in which the absorbent is an aqueous solution of a water vapor pressure depressant.

40. A system as claimed in claim 39 in which the absorbent is an aqueous solution of lithium bromide.

41. In combination with a vacuum drying chamber, an evacuation system as claimed in claim 33.

42. The combination as claimed in claim 41 in which the vacuum drying chamber comprises a chamber, a means for passing particulate frozen material through said chamber, a means for maintaining a subatmospheric vapor pressure in said chamber below the triple point pressure of ice whereby to cause sublimation of the ice from said frozen material and a means for introducing heat recovered and delivered by said heat pump means into said chamber, said chamber being of a sufficient size and said particulate material being introduced at a point to cause the frozen material to be substantially dried while suspended in said chamber.

43. The combination as claimed in claim 41 including a means for supplying microwave energy into said chamber to dry particulate material therein while said material is in suspension in said chamber.

44. The combination as claimed in claim 42 in which the chamber includes an atomizer for spraying droplets of an aqueous mixture of said material into said chamber which droplets freeze almost immediately to form said particulate material.

45. The combination as claimed in claim 44 including a separator between said chamber and said evacuation means, said separator being adapted to remove suspended partially dried particulate material entrained in the water vapor passng therethrough and a means for supplying heat recovered and delivered by said heat pump means to said separator to complete drying of said particulate material separated in said separator.

46. A system as claimed in claim 33 in which the cooling means in said first heat pump means comprises a means for condensing a portion of the low pressure refrigerant vapor by heat exchange with a heat sink and a means for recycling the so condensed refrigerant to said condenser.

47. A system as claimed in claim 33 including a heat exchanger between the said evaporator and the said expansion valve for supplying heat to an external heat sink for the purpose of subcooling control.