Freeze drying system and method

Abstract

To cool a freeze drying chamber and a freeze dryer condenser by using a turbo compressor cooling system and a cold heat storage system.SOLUTION: A freeze-drying system (700) comprising a freeze-drying chamber (710) provided with shelves on which products are placed, a freeze-dryer condenser (720) receiving exhaust gas from the freeze-drying chamber, a first heat-exchange fluid circuit (791) thermally coupled to the freeze-dryer condenser for circulating a first heat-exchange fluid to remove heat from the freeze-dryer condenser, a turbo-compressor refrigeration system (740) thermally coupled to the first heat-exchange fluid circuit, a second heat-exchange fluid circuit (790) thermally coupled to the shelves of the freeze-drying chamber for circulating a second heat-exchange fluid, a heat exchanger (750) for exchanging heat energy between the first heat-exchange fluid circuit and the second heat-exchange fluid circuit, and a phase-change material for storing cold energy; A cold thermal storage system (760) thermally coupled to the first heat exchange fluid circuit.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates generally to freeze-drying processes and apparatus for removing water from products by sublimation. More specifically, the present invention relates to a system and method for cooling freeze-drying chambers and freeze-dryer condensers using a cold heat exchanger (CTES) system. [Background technology]

[0002] Freeze-drying is a process for removing a solvent or suspending agent (typically water) from a product. It is a low-pressure, low-temperature condensation pump process widely used in pharmaceutical manufacturing. The freeze-drying process for removing water involves freezing the water in the product to form ice, sublimating the ice under vacuum, and then passing the resulting water vapor through a condenser. The water vapor condenses as ice in the condenser, where it is then removed from the condenser. Freeze-drying is particularly useful in the pharmaceutical industry because product integrity is maintained during the freeze-drying process, ensuring product stability over relatively long periods of time. Freeze-dried products are usually, but not always, biological materials.

[0003] A typical freeze-drying process used in the pharmaceutical industry can process either bulk product or vial-filled product. In the example bulk freeze-drying system 100 shown in FIG. 1, batches of bulk product 112 are placed on freeze-drying trays 121 within the freeze-drying chamber 110. Freeze-drying shelves 123 are used to support the trays 121. Alternatively, product-filled vials may be placed on the shelves. The freeze-drying shelves function as heat exchangers to transfer heat to and from the trays or vials as required by the process. A heat-transfer fluid flowing through conduits within the shelves 123 is used to remove or add heat.

[0004] The suspended or melted product is frozen by removing heat with a heat transfer fluid. Under vacuum, the frozen product 112 is heated by the heat transfer fluid, causing the ice within the product to sublimate. The vapor resulting from the sublimation of the ice flows through passageway 115 into a condensing chamber 120 containing a condensing coil or other surface 122 maintained below the condensation temperature of the vapor. The heat exchange fluid passes through the coil 122, removing heat and causing the vapor to condense as ice on the coil.

[0005] Both the freeze-drying chamber 110 and the condensation chamber 120 are maintained at a vacuum during the process by a vacuum pump 150 connected to the exhaust of the condensation chamber 120. Non-condensable gases contained within the chambers 110, 120 are removed by the vacuum pump 150 and discharged through an outlet 152 on the higher pressure side.

[0006] The heat exchange fluid circulating through the condenser 220 and the shelves 223 of the freeze-drying chamber 210 may be cooled by the same or different cooling systems. Summary of the Invention

[0007] The present disclosure addresses the above-mentioned needs by providing a freeze-drying system that includes a freeze-drying chamber including a chamber heat exchanger for cooling and heating a product within the freeze-drying chamber. The system further includes a freeze-drying condenser connected to the freeze-drying chamber for receiving exhaust gases from the freeze-drying chamber. A condensing surface of the freeze-drying condenser is provided for condensing the exhaust gases.

[0008] A first heat exchange fluid circuit is selectively connected to the condensing surface for circulating a first heat exchange fluid to the condensing surface, and a turbocompressor refrigeration system is connected to cool the first heat exchange fluid.

[0009] A second heat exchange fluid circuit is connected to circulate a second heat exchange fluid through the chamber heat exchanger, and an inter-circuit heat exchanger is connected to exchange thermal energy between the first heat exchange fluid and the second heat exchange fluid.

[0010] A cold storage system is connected to cool at least the second heat exchange fluid. The cold storage system includes a phase change material for storing low temperature thermal energy.

[0011] Another embodiment of the invention is a method of freeze-drying a product, the method including sterilizing a freeze-drying chamber using a clean-in-place arrangement, loading the freeze-drying chamber with product, recharging the cold storage system by cooling a phase change material of the cold storage system using a turbo-compressor refrigeration system during at least one of sterilizing and loading the freeze-drying chamber, cooling the interior of the freeze-drying chamber to a process temperature using the turbo-compressor refrigeration system supplemented by the cold storage system after recharging the cold storage system, freezing components of the product in the freeze-drying chamber to form frozen components, sublimating the frozen components in the freeze-drying chamber to form vapor, condensing the vapor in a condenser using the turbo-compressor refrigeration system, and removing the product from the freeze-drying chamber. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of a prior art freeze-drying system. [Figure 2] FIG. 2 is a schematic diagram of a turbocompressor cooling system according to one embodiment of the present disclosure. [Figure 3] FIG. 3 is a graph showing component temperatures at several steps in a freeze-drying cycle according to an embodiment of the present disclosure. [Figure 4] FIG. 4 is a schematic diagram of a freeze-drying system operating during the turnaround portion of a freeze-drying cycle according to an embodiment of the present disclosure. [Figure 5] FIG. 5 is a schematic diagram of a freeze-drying system operating during the freezing portion of a freeze-drying cycle according to an embodiment of the present disclosure. [Figure 6] FIG. 6 is a schematic diagram of a freeze-drying system operating during the freeze-drying portion of a freeze-drying cycle according to an embodiment of the present disclosure. [Figure 7]FIG. 7 is a schematic diagram of a freeze-drying system according to another embodiment of the present disclosure. [Figure 8] FIG. 8 is a flowchart illustrating a method according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] Currently, commercially available freeze dryer cooling systems often use working fluids that are greenhouse gases. Prior to the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer, freeze dryer cooling system working fluids were often based on chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), which are potent ozone-depleting substances. This treaty led to the demise of most of these working fluids. CFCs and HCFCs have been replaced by hydrofluorocarbons (HFCs), such as R-410a and R-507a, which are now widely used. However, HFCs are potent greenhouse gases. Currently, various countries around the world have restricted or banned the use of HFC-based refrigerants. Several companies, including pharmaceutical companies, are actively considering eliminating the use of synthetic refrigerants in their processing equipment, including freeze dryers.

[0014] To address the issue of using a working gas that could potentially be harmful to the environment, the authors utilized a turbocompressor refrigeration system to perform the primary refrigeration function of the freeze-drying system. The turbocompressor refrigeration system utilizes air or nitrogen as the working fluid in a Bell-Coleman cycle (also known as the reverse Brayton cycle), in which the expansion and compression steps approximate isentropic processes and the cooling and heating steps approximate isobaric processes. This system involves a turbocompressor and turboexpander sharing a common shaft with an electric motor. Mechanical energy from the turboexpander complements energy from the motor to drive the turbocompressor, increasing efficiency. The cryogenic working fluid from the expander is used to cool the freeze-drying system's condenser and freeze-drying chamber.

[0015] A schematic diagram of an example turbo-compressor refrigeration system 200 is shown in Figure 2. Energy is extracted from a gaseous working fluid (such as air or nitrogen) compressed by an expander 210 to produce a low-pressure cryogenic gas 221. The extracted energy from the expander 210 is transferred to a compressor unit 214 via a drive shaft 216. The low-pressure cryogenic gas 221 is sent to one or more heat exchangers 295 of a freeze-drying system 290, where it absorbs heat energy from the condenser and shelves in the freeze-drying chamber.

[0016] The freeze dryer return line 220 from the freeze drying system 290 passes through a recuperative heat exchanger 225 where additional thermal energy is exchanged between the freeze dryer return line 220 and the compressor output 215, increasing system efficiency. The resulting low temperature and pressure working fluid in the freeze dryer return line 220 is sent to the inlet of the compressor 214.

[0017] Using mechanical energy from the motor 212 and from the expander 210, the compressor 214 compresses the working fluid, producing a high-pressure, high-temperature working fluid in the compressor output 215. Heat is rejected from the working fluid to the atmosphere by an air cooler 230 or a water cooler or other similar device. As mentioned above, additional heat energy is transferred from the compressor output 215 to the freeze dryer return line 220 by the recuperative heat exchanger 225. The resulting high-pressure, low-temperature working fluid is sent to the expander 210 to complete the cycle.

[0018] A typical temperature cycle 300 of a commercial freeze-drying system is shown schematically in Figure 3. In the schematic, freeze-drying chamber shelf temperature 305 and condenser coil temperature 310 are shown as a function of successive steps 315 of the freeze-drying cycle, including loading 316, freezing 317, freeze-drying 318, unloading 319, and turning over 320.

[0019] During the loading portion 316 of the cycle, shelf and condenser coil temperatures are maintained near ambient temperature as vials or bulk materials are loaded into the chamber, or alternatively, the shelves may be cooled as required by the product's operating instructions. During the turnover portion 320 of the cycle, the system is unloaded, thawed, cleaned, sterilized, dried, and leak-checked. Ice on the condenser coil is melted and drained. High-temperature detergents can be used to clean or sterilize the freeze-drying components, including the freeze-drying chamber and condenser. Clean-in-place (CIP) and sterilization-in-place arrangements that do not require disassembly of the freeze-drying equipment may also be used. For example, permanently installed steam nozzles or sterilizing sprayers can be used to clean the interior of the equipment. The freeze-dryer cooling system can be used to warm the condenser during defrosting and to cool the shelves during loading during the turnover portion of the cycle. The shelf loading temperature is between ambient and -50°C, depending on process conditions. The freeze-dryer cooling system can also be used to cool the system after drying. During a leak test, the freeze dryer cooling system is operated to evaluate for refrigerant leaks.

[0020] During the freezing portion 317 of the cycle, the temperature of the product in the freezing chamber must be reduced from ambient conditions to below -40°C. The rate of temperature change during the freezing portion 317 of the cycle directly affects the overall cycle time of the freeze-drying system, as other steps in the cycle may not be performed during that time. Therefore, the cooling capacity of the freeze-drying system directly affects the cycle time. Furthermore, the freezing rate must be carefully controlled to control important product quality attributes within the frozen product. Therefore, a freeze-drying system with sufficient capacity to maintain the desired cooling rate is critical.

[0021] During the freeze-drying portion 318 of the cycle, the freeze-drying chamber is maintained at a low process temperature. The freeze-drying chamber cooling system must absorb heat from condensation in the condenser to maintain the freeze-drying chamber at the process temperature. Additionally, heat must be introduced into the system (shelf) to drive the sublimation process. Sublimation of the ice within the product removes energy from the product, causing the product to cool until sublimation stops. A significant amount of heat must be added through the shelf to keep the sublimation process going.

[0022] During the primary drying phase 318a, the crystalline water ice is slowly sublimated to avoid the formation of liquid water, which could degrade the product. During the secondary drying phase 318b, the phase change from ice to water is no longer a concern, so the remaining individual water molecules are removed at higher temperatures. For example, typical shelf temperatures in primary drying can be -10°C to +10°C or even 20°C, while secondary drying can be 20°C to 40°C. In the secondary phase, the shelf requires little or no cooling. In other cases, the product requires a very slow process with a shelf temperature of -30°C. In such cases, a bleed may be required during cooling for control purposes, as pumping energy tends to heat the system.

[0023] Most commercially available pharmaceutical freeze dryer applications have maximum floor space requirements for installation in a laboratory or manufacturing facility, and new freeze dryer cooling systems must occupy an area comparable to that occupied by traditional HFC-based systems.

[0024] The authors found that a reasonably sized turbo-compressor cooling system did not have the peak capacity required to maintain the cooling / freezing cycle of a commercial freeze dryer within acceptable cycle times. To take advantage of the environmental benefits of a turbo-compressor cooling system in a commercial freeze drying system, while meeting the system's peak cooling requirements and maximum floor space specifications, the authors supplemented the turbo-compressor cooling system with a cold energy storage (CTES) system.

[0025] CTES systems store and recover cold energy for low-temperature applications. CTES utilizes the latent heat storage properties of materials. This technology can store heat at different temperatures or in different phases, storing the energy for later use.

[0026] Two approaches / types of energy storage materials can be used: sensible and latent. The sensible approach uses a large amount of cold fluid and relies on the latent heat storage of that fluid. Thermal energy is gradually transferred to the fluid as its temperature increases.

[0027] Latent heat systems use the phase change energy of phase change materials (PCMs) to provide a near-constant temperature energy sink. Latent heat systems use a smaller volume for greater energy storage.

[0028] Examples of PCMs for low temperature applications include paraffin (organic) (~-37°C), petroleum-derived materials, plant-derived materials, eutectic salts (~-65°C), and alcohol / glycols (~-100°C). In one embodiment of the system described herein, a eutectic salt-based PCM is used to complement the turbocompressor cooling system of a freeze dryer.

[0029] A freeze-dryer cooling system 400 according to one embodiment of the present disclosure is shown schematically in Figures 4-6. Bold flow paths indicate the flow of heat transfer fluid during specific steps of the freeze-drying cycle. In particular, Figure 4 shows the flow paths during the turnaround portion of the cycle, Figure 5 shows the freezing portion of the cycle, and Figure 6 shows the freeze-drying portion of the cycle.

[0030] The freeze-drying components of the system include a freeze-drying chamber 410 with a cooling shelf 423 and a condenser 420, each of which is cooled during the freeze-drying cycle. The cooling system 400 includes two separate circuits, each containing a heat-transfer fluid: a first circuit 491 containing the condenser 420 and a second circuit 490 containing the freeze-drying chamber 410. Both circuits 490, 491 pass through an inter-circuit heat exchanger 450, such as a brazed plate heat exchanger, to transfer thermal energy between the two circuits. Preferably, heat exchange between the fluids in the two circuits occurs without an intervening or intermediate heat-transfer fluid. The heat-transfer fluid in each of the first and second circuits 491, 490 may be a liquid heat-transfer oil.

[0031] The first circuit 491 includes a turbo-compressor cooling system 440 connected to cool the heat transfer fluid in the first circuit, which is circulated by a circulation pump 430. Adjustable valves 441, 442 control the proportion of heat transfer fluid circulated from the turbo-compressor cooling system 440 through the condenser 420 and the proportion of heat transfer fluid circulated through the inter-circuit heat exchanger 450.

[0032] The turbo-compressor cooling system includes a heat exchanger for transferring thermal energy between a working fluid of the turbo-compressor and a heat transfer fluid of a first circuit, preferably without an intervening or intermediate heat transfer fluid.

[0033] The second circuit 490 of the freeze dryer cooling system 400 cools the shelves 423 or other heat transfer elements of the freeze drying chamber 410. Heat is removed from the heat transfer fluid of the second circuit 490 by the inter-circuit heat exchanger 450 and transferred to the heat transfer fluid of the first circuit 491. The heat transfer fluid of the second circuit 490 is circulated by the shelf / CTES circulation pump 470.

[0034] The CTES system 460 is selectively included (or excluded) from the second circuit 490 using a bypass valve 463 and valves 461, 462. As explained in more detail below, heat is transferred from the CTES 460 to the heat transfer fluid in the first circuit 491 (refrozen the CTES), i.e., stored cold energy is transferred from the CTES to the heat transfer fluid (supplementing the turbo-compressor refrigeration system in cooling the shelf). Preferably, the heat exchange between the CTES 460 and the fluid in the second circuit 490 occurs without the use of an intervening or intermediate heat transfer fluid, i.e., without the use of another heat transfer fluid to transfer heat between the CTES 460 and the heat transfer fluid in the first circuit 491.

[0035] A heater circuit 425 is provided to selectively heat the heat transfer fluid flowing to the freeze-drying chamber 410 during the sublimation portion of the freeze-drying cycle. Valve 426, in conjunction with bypass valve 411, controls whether the heat transfer fluid flows through shelf 423 or bypasses the shelf circuit during refreezing of the CTES.

[0036] The bold circuit lines in the exemplary cooling system 400 shown in Figure 4 indicate the flow of heat transfer fluid in the two circuits 490, 491 during the turnaround portion 320 of the freeze-drying cycle (Figure 3) where the CTES system is refrozen for use in the next freeze-drying cycle. During this time, the freeze-drying chamber 410 and condenser 420 are not being used for freeze-drying and no product is being processed in the freeze-drying chamber.

[0037] 4, by closing valve 442 and opening valve 441, the heat transfer fluid in first circuit 491 circulates between turbo-compressor cooling system 440 and inter-circuit heat exchanger 450 without cooling condenser 420. Thus, the entire cooling capacity of turbo-compressor cooling system 440 is directed to cooling the heat transfer fluid in second circuit 490 via inter-circuit heat exchanger 450.

[0038] 4, the heat transfer fluid in second circuit 490 is circulated directly from intercircuit heat exchanger 450 to CTES system 460. Valve 411 is opened and valve 426 is closed, bypassing freeze-drying chamber 410 in second circuit 490.

[0039] 4 allows the CTES system 460 to be refrigerated and prepared for the next freeze-drying cycle during the portion of the turnaround portion 320 of the freeze-drying cycle when either or both of the freeze-drying chamber 410 and the condenser 420 are bypassed by the refrigeration system. The refrigeration system is available to refrigerate the CTES system 460 when these freeze-drying components are bypassed during one or more of the unloading, defrosting, cleaning, sterilizing, drying, and leak-checking operations performed during the turnaround portion of the cycle. It can be seen that such an arrangement allows the CTES system 460 to be used to supplement the turbocompressor refrigeration system 440 with no or minimal increase in overall cycle time caused by the CTES system refreezing.

[0040] 5 illustrates the operation of the system during the freeze portion 318 of the freeze-drying cycle and the flow of heat transfer fluid in the two circuits 490, 491. The heat transfer fluid in the first circuit 491 is distributed to both the condenser 420 and the inter-circuit heat exchanger 450 by opening both valves 441, 442. The flow to the condenser 420 is controlled to bring its components to the process temperature.

[0041] As shown in FIG. 5 , the heat transfer fluid in the second circuit 490 is cooled by the turbo-compressor refrigeration system 440 via the inter-circuit heat exchanger 450. The heat transfer fluid in the second circuit 490 is further cooled by the CTES 460 before circulating through the shelves 423 of the freeze-drying chamber 410. Thus, the combined cooling capacity of the turbo-compressor refrigeration system 440 and the CTES 460 is available to rapidly cool the shelves to process temperatures and maintain them there during the freeze-drying portion 317 of the freeze-drying cycle. The increased cooling capacity of the CTES therefore reduces the cycle time for the freeze-drying portion of the cycle. The CTES can also be used to supplement the turbo-compressor refrigeration system 440, if desired, during the freeze-drying portion 318 of the freeze-drying cycle.

[0042] 6 illustrates the operation of the system and the flow of heat transfer fluid in the two circuits 490, 491 during the freeze-drying portion 318 (FIG. 3) of the freeze-drying cycle. The CTES system 460 can be bypassed during freeze-drying by closing valve 462 and opening bypass valve 463. The CTES does not need to supplement the turbo-compressor cooling system 440 to maintain the process temperature within the freeze-drying chamber 410.

[0043] The heater circuit 425, which is not activated during the freezing portion of the cycle, is used to apply heat energy to the shelves for sublimation under vacuum during the freeze-drying portion of the cycle.

[0044] Both the condenser 420 and the shelf 423 are cooled by the turbo-compressor refrigeration system 440, but these two freeze-drying system components have different cooling requirements. The condenser 420 generally has lower temperature requirements than the shelf, but does not require as much cooling capacity to achieve and maintain these lower temperatures. In contrast, the shelf 423 does not need to be cooled to as low a temperature as the condenser, but it does require greater cooling capacity than the condenser 420. In the freeze-drying cooling systems shown in Figures 4, 5, and 6, the condenser 420 is located in a first circuit 491 equipped with the turbo-compressor refrigeration system 440, and the shelf 423 is located in a second circuit 490 equipped with the CTES 460. The turbo-compressor refrigeration system 440 meets the cooling capacity requirements of the condenser 420 without being supplemented by the CTES 460. Supplementing the turbo-compressor with the CTES in the second circuit 490 meets the cooling requirements of the shelf without unnecessarily cooling the heat transfer fluid used in the first circuit 491 to cool the condenser.

[0045] The exemplary cooling system 700 shown in Figure 7 illustrates another embodiment of the system. In the configuration of Figure 7, the CTES 760 is located in the first heat exchange fluid circuit 791, shown in bold, rather than in the second heat exchange fluid circuit as shown in Figures 4-6. In the cooling system 700 of Figure 7, the CTES 760 is located in series with the turbo-compressor cooling system 740.

[0046] By placing the CTES 760 in a separate circuit 791 from the circuit 790 containing the freeze-drying chamber 710, the freeze-drying chamber shelf circuit 723 can be heated and operated simultaneously with the recharging of the CTES. During the freeze-drying process, the heater 725 is typically activated, and the heat transfer fluid in the circuit 790 is at a temperature above the refreezing temperature of the CTES. These conditions preclude the recharging of a CTES located in the same circuit 790 as the shelf 723. In the refrigeration system 700 shown in FIG. 7, the CTES is placed in series with the turbo-compressor expander in the primary refrigeration circuit 791. In this configuration, placing the CTES in circuit 791 allows the CTES to be charged during the freeze-drying process, particularly during primary and secondary drying, because there are portions of the cycle where there is excess energy from the turbo-compressor expander that allows refreezing to begin. In this case, the primary refrigeration circuit is run at a temperature sufficient to allow the refreezing process to occur.

[0047] When the set point of condenser 720 is above the set point of primary circuit 791, valve 742 opens in proportion to the amount of cooling required to maintain the condenser at its set point. Valve 741 may be closed and valve 743 may be opened to bypass inter-circuit heat exchanger 750, second circuit 790, and shelf 723, forming a primary refrigeration circuit. This primary refrigeration circuit is independent of shelf or condenser cooling and includes pump 730, turbocompressor 740, and CTES 760, providing direct and efficient recharge of the CTES.

[0048] A method 800 according to an embodiment of the present disclosure is shown in Figure 8. The freeze-drying chamber is first disinfected, or sterilized (operation 810), after being emptied of the product processed in the previous cycle. In pharmaceutical manufacturing, all equipment parts that come into contact with the product or process are typically cleaned using a clean-in-place (CIP) arrangement and sterilized using steam or chemical fluid cleaners permanently installed on the equipment. No product is present in the freeze-drying chamber during the cleaning and sterilization operations.

[0049] Next, the product is loaded into the freeze-drying chamber by placing the product on a shelf (operation 820). The product may be in bulk form or may be in a vial with a partially open stopper to allow water vapor to escape from the vial during the freeze-drying process. Both the product and the freeze-drying chamber shelves are at ambient temperature or are pre-cooled during the loading process. In one embodiment, a CTES system is used to speed the pre-cooling process. In another embodiment, the CTES system is bypassed during the pre-cooling process, conserving the CTES cooling energy and using it to cool the product loaded on each shelf.

[0050] The CTES system is recharged (operation 830) during one or more operations of the turnaround portion 320 of the freeze-drying cycle (FIG. 3). The CTES system is recharged by cooling the phase change material in the CTES system using a turbo-compressor refrigeration system. In the embodiment described above with reference to FIG. 4, two separate heat transfer fluid circuits 490, 491 are used to recharge the CTES. The heat transfer fluid in the first circuit 491 is cooled by the turbo-compressor refrigeration system. This heat transfer fluid is used to cool the heat transfer fluid in the second circuit 490, which then passes through the CTES system to refrozen the phase change material.

[0051] Because the refill operation 830 is performed in parallel with the sterilization and loading operations 810, 820, the use of a CTES system to supplement the turbocompressor cooling system does not unduly lengthen the overall freeze-drying cycle time.

[0052] Once the CTES system is recharged, the freeze-drying chamber is cooled (operation 840) and the product is frozen using a turbo-compressor refrigeration system supplemented by the CTES. The length of time required to perform this operation is reduced by supplementing the turbo-compressor refrigeration system with the CTES. In embodiments including a phase-change material-based CTES system, the phase-change material is maintained at a substantially constant temperature because heat is transferred from the freeze-drying chamber shelves by the heat transfer fluid. During this operation, the heat transfer fluid cooled by the turbo-compressor refrigeration system may be used to cool the condenser in preparation for the freeze-drying operation.

[0053] After the product is frozen, it is freeze-dried in a freeze-drying chamber (operation 850). The freeze-drying operation typically involves subjecting the product to vacuum pressure while maintaining the product in a frozen state. A small amount of heat is applied to the product to initiate sublimation of the freezing solvent or suspending medium.

[0054] Finally, the chamber is returned to substantially ambient pressure and temperature, and the freeze-dried product is removed from the chamber (operation 860). Because neither the freeze-drying chamber nor the condenser are cooled during this operation, refill operation 830 may begin during removal in preparation for the next freeze-drying cycle.

[0055] The foregoing detailed description is to be understood in all respects as illustrative and exemplary, but not restrictive, and the scope of the invention disclosed herein is to be determined not from the description of the invention, but from the claims, which are to be interpreted in accordance with the full breadth allowed by patent law. It will be understood that the embodiments shown and described herein are merely illustrative of the principles of the invention, and that various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention. [Explanation of symbols]

[0056] 700···Cooling system 710...Lyophilization chamber 720···Condenser 740···Turbo compressor cooling system 760···CTES 790...Second Circuit 791...First heat exchange fluid circuit

Claims

1. a freeze-drying chamber including a chamber heat exchanger for cooling and heating the product within the freeze-drying chamber; a freeze-drying condenser connected to the freeze-drying chamber for receiving exhaust gas from the freeze-drying chamber; a condensing surface of the freeze dryer condenser for condensing the exhaust gas; a first heat exchange fluid circuit selectively connected to the condensing surface for circulating a first heat exchange fluid to the condensing surface; a turbocompressor refrigeration system connected to cool the first heat exchange fluid; a second heat exchange fluid circuit connected to circulate a second heat exchange fluid through the chamber heat exchanger; an inter-circuit heat exchanger connected to exchange thermal energy between the first heat exchange fluid and the second heat exchange fluid; a cold energy storage system including a phase change material for storing cold energy and connected to cool at least the second heat exchange fluid; A freeze-drying system comprising:

2. 10. The freeze-drying system of claim 1, wherein the cold thermal storage system is connected to cool the second heat exchange fluid without the use of an intermediate heat exchange fluid.

3. 3. The freeze-drying system of claim 2, further comprising a bypass passage in the second heat exchange fluid circuit for selectively bypassing the cold thermal storage system.

4. 4. The freeze-drying system of claim 3, further comprising a bypass passage in the second heat exchange fluid circuit for selectively bypassing the chamber heat exchanger.

5. 5. The freeze-drying system of claim 4, further comprising a valve in the first heat exchange fluid circuit for selectively bypassing the freeze-drying condenser.

6. 6. The freeze-drying system of claim 5, further comprising one or more circulation pumps in the first heat exchange fluid circuit for circulating the first heat exchange fluid.

7. 7. The freeze-drying system of claim 6, further comprising one or more circulation pumps in the second heat exchange fluid circuit for circulating the second heat exchange fluid.

8. 8. The freeze-drying system of claim 7, further comprising a heater circuit connected to the second heat exchange fluid circuit for selectively heating the second heat exchange fluid.

9. 10. The freeze-drying system of claim 1, wherein the cold thermal storage system is connected to cool the first heat exchange fluid without the use of an intermediate heat exchange fluid.

10. 10. The freeze-drying system of claim 9, further comprising a bypass passage in the first heat exchange fluid circuit for selectively bypassing the inter-circuit heat exchanger.

11. sterilizing the freeze-drying chamber using a clean-in-place arrangement; loading product into the freeze-drying chamber; recharging the cold thermal storage system by cooling a phase change material of the cold thermal storage system using a turbo-compressor refrigeration system during at least one of the sterilizing and the loading; cooling the interior of the freeze-drying chamber to a process temperature using the turbo-compressor refrigeration system supplemented by the cold storage system after recharging the cold storage system; freezing components of the product in the freeze-drying chamber to form frozen components; sublimating the frozen components in the freeze-drying chamber to form a vapor; condensing the vapor in a condenser using the turbocompressor refrigeration system; removing the product from the freeze-drying chamber; A method for freeze-drying the product comprising:

12. recharging the cold thermal storage system cooling a first heat transfer fluid using the turbocompressor refrigeration system; cooling a second heat transfer fluid with the first heat transfer fluid via an inter-circuit heat exchanger; cooling the phase change material of the cold thermal storage system using the second heat transfer fluid; The method of claim 11 further comprising:

13. circulating the first heat transfer fluid through the turbo-compressor refrigeration system, through the circuit-to-circuit heat exchanger, and through a bypass line bypassing the condenser while cooling the interior of the freeze-drying chamber to the process temperature; circulating the first heat transfer fluid through the turbo-compressor refrigeration system, through the circuit-to-circuit heat exchanger, and through the condenser while sublimating the frozen components and condensing the vapor; The method of claim 12 further comprising:

14. circulating the second heat transfer fluid through the circuit-to-circuit heat exchanger, through the cold thermal storage system, and through the freeze-drying chamber while cooling the interior of the freeze-drying chamber to the process temperature; circulating the second heat transfer fluid through the circuit-to-circuit heat exchanger, through the cold storage system, and through a bypass line bypassing the freeze-drying chamber while the cold storage system is being recharged; The method of claim 13 further comprising:

15. recharging the cold thermal storage system cooling the phase change material of the cold thermal storage system using a first heat transfer fluid that transfers thermal energy between the cold thermal storage system and the turbo-compressor without an intermediate heat transfer fluid; The method of claim 11 further comprising:

16. circulating the first heat transfer fluid through the turbo-compressor cooling system, through the cold heat storage system, through an inter-circuit heat exchanger, and through a bypass line bypassing the condenser while cooling the interior of the freeze-drying chamber to the process temperature; circulating the first heat transfer fluid through the turbo-compressor refrigeration system, through a bypass line bypassing the cold thermal storage system, through the circuit-to-circuit heat exchanger, and through the condenser while sublimating the frozen components and condensing the vapor; The method of claim 15 further comprising:

17. circulating a second heat transfer fluid through the circuit heat exchanger and through the freeze-drying chamber while the interior of the freeze-drying chamber is cooled to the process temperature; circulating the second heat transfer fluid through the circuit-to-circuit heat exchanger and through a bypass line bypassing the freeze-drying chamber while the cold thermal storage system is being recharged; 17. The method of claim 16 further comprising:

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