Freeze drying device

Abstract

The present invention relates to a freeze-drying apparatus (1) having a drying chamber (10) and a plurality of condenser chambers (30, 40) arranged laterally of the drying chamber (10) and separated therefrom by side walls (32, 42), wherein a plurality of openings (33a-b, 44a-b) are arranged in the side walls (32, 42) within a range of a stack height (HS) of a heating device (50) arranged in the drying chamber (10).

Description

[Technical Field]

[0001] The present invention relates to a freeze-drying apparatus and a method of operating a freeze-drying apparatus. In particular, the present invention relates to a freeze-drying apparatus comprising a drying chamber extending from a first end to a second end of the drying chamber along a longitudinal axis L, from a bottom to a top of the drying chamber along a height axis H, and from a first side to a second side of the drying chamber along a horizontal axis W, a central horizontal plane CP of the drying chamber extending parallel to the longitudinal and horizontal axes and located in the center of the drying chamber relative to the height axis, a door at the first end of the drying chamber, a first condenser chamber disposed on the first side of the drying chamber and having a first wall between the first condenser chamber and the drying chamber, a first condenser chamber including a condenser of the type described above; and a second condenser chamber including a second condenser disposed laterally of the drying chamber on a second side thereof with a second wall between the second condenser chamber and the drying chamber, wherein each of the first and second walls is provided with at least one opening allowing fluid communication between the drying chamber and the respective condenser chamber; and a heating device having a plurality of heating elements spaced apart on a height axis, with a stack height extending between the bottom heating element and the top heating element. [Background technology]

[0002] Freeze drying is a process in which a product is dried by freezing it below the triple point of water and then reducing the pressure to cause the ice to sublimate. A typical application of freeze drying is in drying foods, dietary supplements or pharmaceuticals, where water is the liquid that is removed, but freeze drying can also be used for other products and to remove other liquids.

[0003] A typical level of freeze-drying involves four steps: The freeze-drying process involves freezing the product, loading the frozen product onto appropriate trays (or vice versa) and typically onto a trolley carrying the trays into the freeze-drying machine, drying the product under reduced pressure in the freeze-drying machine, and removing the dried product. The drying process in a freeze-drying machine involves evacuating the drying chamber below the triple point using a vacuum pump and providing heat for the phase transition (heat of sublimation). To handle the water vapor generated in the drying chamber, a condenser (water vapor trap) is placed between the vacuum pump and the drying chamber, where it is cooled to condense / liquefy the water vapor. The condenser plays an important role in the freeze-drying process in terms of capacity and accounts for a significant portion of the operating costs due to the cooling / refrigeration load. The condenser should condense substantially all of the vapor and prevent it from entering the vacuum pump. At the same time, the condenser and its associated components should be able to efficiently remove water vapor from the drying chamber to prevent pressure buildup within the drying chamber, i.e., it should not impose an excessively large pressure drop. Uniform distribution of ice growth on the condenser is also advantageous. A thicker ice layer increases thermal resistance, resulting in a lower refrigerant temperature being required to reach a sufficiently low temperature at the ice surface. At the same time, a thicker ice layer can restrict flow, potentially causing an increase in drying chamber pressure, increasing local gas velocity, reducing local pressure, and again reducing the temperature required to condense the water vapor. In addition to these condenser design objectives, it is also desirable for freeze dryers to be easy to clean, as they are often used for food or other products that have sanitary or hygiene requirements.

[0004] Patent Document 1 discloses a freeze dryer with a condenser located in the drying chamber and condensation tubes positioned for uniform tube temperature and uniform ice growth. While this design can provide limited flow resistance, the condenser cannot de-ice during the drying process and must be sized to condense all vapors during the entire drying process. This can require a large condenser or significant ice accumulation, which can increase refrigeration costs and change condenser capacity during the drying process.

[0005] This can be addressed by using freeze dryers with multiple condensers, each of which can be isolated from the drying chamber for de-icing. During the drying cycle, the condensers are continuously isolated and de-iced, providing a substantially constant condenser capacity and reducing refrigeration costs by preventing excessive temperature drop across the ice layer.

[0006] One such system is the GEA Ray™ for batch freeze drying, which has condensers arranged side-by-side at the bottom of the drying chamber. Patent Document 2 also discloses another freeze dryer with multiple condensers in a separate condenser chamber separated from the drying chamber by a wall, which provides a substantially constant condenser capacity and may reduce ice layer temperature drop by allowing de-icing, but this design may also impede vapor flow, resulting in unnecessary pressure loss, increasing drying chamber pressure, generating excessive gas flow rates, and potentially resulting in uneven ice layer thickness. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] U.S. Patent No. 3,543,411 [Patent Document 2] U.S. Patent No. 3,401,466 Summary of the Invention

[0008] In this context, it is an object of the present invention to provide a freeze-drying apparatus having improved fluid flow characteristics. Further objects may be to reduce operating costs, for example, by reducing refrigeration load, reducing vacuum pump size, increasing product capacity by volume, simplifying freeze-dryer construction, and / or improving cleanability.

[0009] These and further objects are achieved by a freeze-drying apparatus according to the present invention, further characterized in that at least one of the openings in each of the first and second walls extends at least partially within the stack height. At least one opening extending at least partially within the stack height is understood to mean that when the stack height and the height of the opening are projected onto a height axis, there is at least partial overlap between the two projections. Positioning the opening within the stack height can improve the fluid flow characteristics of the freeze-drying apparatus and reduce drying chamber pressure. This can, for example, provide reduced pressure from the drying chamber to the condenser chamber and / or provide a more uniform pressure distribution in the drying chamber and / or condenser chamber. This, in turn, can reduce refrigeration capacity. Improving the fluid flow characteristics of the freeze-drying apparatus can also allow the size of the vacuum pump to be reduced. During operation, trays carrying the product to be dried are positioned between, and possibly above, multiple heating elements. Thus, the stack height is substantially equal to the height of the trays when positioned within the drying chamber. Without being bound by theory, this leveling of the opening with the heating device and therefore with the tray carrying the product creates a less restrictive flow path. The positioning of the condenser, sidewalls, and openings in accordance with the present invention can allow a larger portion of the drying chamber to be used for the trays, increasing the production capacity per unit volume of the freeze-drying device, and the improved fluid flow characteristics of the freeze-drying device can efficiently handle the increased vapor volume generated per unit volume when capacity is increased.

[0010] In an operating state of the freeze-drying apparatus, one or more trolleys are disposed within the drying chamber. The trolleys are configured to support multiple trays in a horizontal position, with the trays extending substantially parallel to a central horizontal plane CP of the drying chamber. When the trolleys are within the drying chamber, the trays are disposed between and typically in contact with multiple heating elements of the heating device. The trolleys are typically secured to a rail device within the drying chamber, allowing the trolleys to be moved within and out of the drying chamber. The trolleys may include multiple support elements for supporting the trays in a horizontal position. The trolleys have a trolley height extending between the bottom and top of the trolley. The bottom of the trolley device may be the bottom support element of the trolley device, and the top of the trolley device may be the top support element. Thus, the height range of the trays may be substantially between the bottom support element and the top support element. The bottom support element is the support element adjacent to the bottom of the drying chamber, and the top support element is the support element adjacent to the top of the drying chamber. Thus, the stack height HS (of the heating apparatus) and the trolley height each substantially correspond to the height range of the trays. The stack height HS is currently considered an appropriate measure of the location of the at least one opening in each of the first and second side walls. However, in an additional or alternative definition of the present invention, the at least one opening in each of the first and second walls extends at least partially within the trolley height and / or within the tray height range. The tray height range is the distance along the height axis between the bottom tray adjacent to the bottom of the drying chamber and the top tray adjacent to the top of the drying chamber, and corresponds to the number of trays that can be accommodated by the heating device in the operating state, i.e., the number of trays corresponding to the size of the freeze-drying operation.

[0011] Unless otherwise specified below, features described for the "condenser chamber" apply to both the first and second condenser chambers, and the freeze-drying apparatus is preferably symmetrical in this respect. Similarly, features for the "side wall" apply to both the first and second side walls unless otherwise specified. The same applies to features relating to the "condenser" or "opening." The freeze-drying apparatus is described with reference to longitudinal, lateral, and height axes, and refers to the orientation of the freeze-drying apparatus when in operation, i.e., with the height axis parallel to gravity. As used herein, the length, width, and height dimensions of elements of the freeze-drying apparatus refer to dimensions measured along the longitudinal, lateral, and height axes, respectively.

[0012] In some embodiments, at least one opening in each of the first and second walls extends completely within the stack height HS.

[0013] In some embodiments, a first one of the openings in each sidewall extends above the central horizontal plane of the drying chamber, and a second one of the openings in each sidewall extends below the central horizontal plane. In this manner, steam has at least two entry points into each condenser chamber, allowing steam emanating from trays above and below the central horizontal plane to flow toward the first and second openings, respectively. This can reduce drying chamber pressure and / or increase pressure uniformity within the drying chamber and / or condenser chamber, providing more uniform drying conditions for the product across the drying chamber and more uniform condensation conditions across the condenser chamber, and / or more efficiently utilizing the condenser surface area. When the height of a first opening extending above the central horizontal plane is projected onto a height axis, it is understood that at least a portion of the projection, and possibly all of the projection, is above the projection of the central horizontal plane on the height axis. Correspondingly, when a second opening extending below the central horizontal plane projects the height of the second opening onto the height axis, it is understood that at least a portion of the projection, and possibly all of the projection, is below the projection of the central horizontal plane on the height axis.

[0014] Additionally or alternatively, a first one of the openings in each side wall extends above a central horizontal heater plane of the drying chamber, and a second one of the openings in each side wall extends below the central horizontal heater plane, which extends parallel to the longitudinal and transverse axes and is centrally disposed with respect to the stack height HS.

[0015] The first opening and the second opening may have the same dimensions, i.e. the same length and height. They typically have the same longitudinal position.

[0016] Typically, openings are provided in the sidewall along substantially the entire length of the drying chamber, the length of the drying chamber extending from the first end to the second end of the drying chamber. The openings typically have the same dimensions.

[0017] In some embodiments, the first opening is disposed at least partially above each condenser, and the second opening is disposed at least partially below each condenser. This can further improve the flow characteristics of the freeze dryer, for example, reducing pressure drop and / or increasing pressure uniformity. In a further development, the first and second openings extend completely above and below each condenser. By an opening disposed at least partially above a condenser, it is understood that when the height of the opening and the height of the condenser are projected on a height axis, at least a portion of the projection of the opening is above the projection of the condenser. Correspondingly, by "extending completely above" the projection of the condenser, the projection of the opening is located completely above the projection of the condenser. Thus, the first opening may be disposed to the side and above each condenser, and the second opening may be disposed to the side and below each condenser. Furthermore, by disposing the openings above and below each condenser, respectively, it is possible to use a closing mechanism (valve) that moves into the condenser chamber when opening, as will be described in more detail below.

[0018] In some embodiments, the first and / or second openings extend at least partially within the range of the stack height HS. Thus, at least one opening that extends at least partially within the range of the stack height HS may be the first opening and / or the second opening. Similarly, the first and / or second openings may extend at least partially along the range of the trolley height and / or the tray height.

[0019] In some embodiments, the first and second openings extend partially with the stack height HS and partially above and below the stack height HS, respectively. This can further improve fluid flow characteristics by providing an open flow path for both vapor flowing laterally from the trays toward the openings and vapor flowing around (above and below) the heating device, which can be a significant portion of the vapor, especially when the opposite condenser is deicing.

[0020] In some embodiments, an intermediate portion of each of the first and second walls extends between the respective first and second walls. By "solid" it is understood that no openings are provided between the condenser chamber and the drying chamber, i.e., the intermediate portion is uninterrupted. Having a solid intermediate portion between the first and second openings can provide a simpler and / or more cost-effective structure, as openings add cost and complexity to the side walls. Thus, while increasing the number of openings may further improve flow characteristics, they also increase manufacturing costs. Having the first and second openings arranged as described above in each side wall, along with a solid intermediate portion, provides a structure that advantageously balances improved flow characteristics and cost efficiency.

[0021] In an alternative embodiment, further openings are located in the intermediate portion, and the first opening, the second opening and possibly further openings in the intermediate portion may be distributed substantially equidistantly across the height of each wall.

[0022] In some embodiments, at least one of the openings in each side wall extends across the central horizontal plane CP of the drying chamber. This provides a centrally located opening within the drying chamber, which can also improve flow characteristics. The centrally located opening may be located between the first opening and the second opening. In some embodiments, all of the openings in the side walls are such centrally located openings, i.e., the portions of the first and second side walls above and above the centrally located opening are solid.

[0023] In some embodiments, the openings in the first and second walls are each symmetrically positioned about the central horizontal plane CP of the drying chamber. Having symmetrically positioned openings in the drying chamber can improve flow characteristics and distribution of steam inflow to the condenser, thereby improving the uniformity of condenser loading and ice accumulation. Additionally or alternatively, the openings may be symmetrically positioned about the central horizontal heater plane. Using the central horizontal heater plane as a reference plane for symmetrical placement of openings can be advantageous when the heaters, and therefore the trolleys and trays, are offset from the central horizontal plane of the drying chamber.

[0024] In some embodiments, the openings in each side wall are symmetrically disposed about the horizontal midplane of the associated condenser, the horizontal midplane of the associated condenser being centered relative to the height of the respective condenser.

[0025] In some embodiments, the first and second openings in each side wall are symmetrically arranged around a central horizontal plane of the drying chamber, and / or around a central heating horizontal device plane, and / or around a central horizontal plane of an associated condenser.

[0026] In some embodiments, the plurality of openings are provided as a plurality of sets of openings, each set including at least two openings arranged consecutively along the longitudinal axis. As previously mentioned, the openings are typically arranged along substantially the entire length of the drying chamber. However, having long openings involves equally long sealing elements for closing the deicing openings, which may be prone to warping and therefore require more reinforcement. Therefore, having a series of continuous openings can provide a more robust and / or simpler structure.

[0027] All of the specific opening embodiments described herein may be provided as multiple sets of openings, i.e., longitudinal arrays of openings. Thus, a set of first openings may be provided together with a set of second openings in each of the side walls. Correspondingly, a centrally arranged set of openings may also be considered. As used herein, a set of openings is two or more openings arranged consecutively along the longitudinal axis and having the same height position. A set of openings may also be referred to as a row of openings. Conversely, multiple openings having the same longitudinal position but different height positions may be referred to as a row of openings. Thus, the first and second openings in the side walls may be considered a row of openings.

[0028] Multiple openings in a set of openings may allow fluid communication between the drying chamber and different condenser chambers when more than one condenser chamber is disposed along the longitudinal axis or between the drying chamber and the condenser chamber.

[0029] In some embodiments, the first and second condenser chambers are each provided with a vacuum outlet, the vacuum outlets being located distally relative to the first and second walls, respectively, as viewed in the lateral direction W. The distal location of the outlets can also improve flow characteristics within the condenser chambers, improving water vapor distribution and contact between the water vapor and the condenser. The vacuum outlets are connected to one or more vacuum pumps for evacuating the drying chambers.

[0030] Each condenser chamber can have a condenser chamber width WC, as measured along the horizontal axis W, from a respective side wall to an opposing wall of the respective condenser chamber. The condenser chamber width can be measured centrally relative to the height of the respective side wall. The distally located vacuum outlets can be positioned at a distance from the respective side wall equal to at least 50%, e.g., at least 60%, 70%, 80%, or even 90% of the condenser chamber width WC, as measured, for example, to an outlet opening in a vacuum manifold.

[0031] The vacuum outlet may be substantially centrally located relative to the height of each of the first and second condensers and / or relative to the height of each of the first and second condenser chambers.

[0032] In some embodiments, the first condenser and the second condenser comprise parallel-extending tube segments, with the tube segments at the vacuum outlet spaced closer to each other than the tube segments distal to the vacuum outlet. In this manner, the tubes adjacent to the vacuum outlet can function as a filter with improved mass transfer to capture remaining condensable vapors, if any, at the vacuum outlet. The inventors have found that closer spacing of the tube segments at the vacuum outlet improves the amount of condensable vapor captured while only slightly increasing flow resistance.

[0033] The tube segments at the vacuum outlet are more closely spaced, and may refer to the first one, two, three, four, or five layers of the tube segments, counting from the vacuum outlet in a direction perpendicular to the opening of the vacuum outlet. The spacing between the tube segments refers to the gap distance between the tube segments. The closer spacing may be in one or two dimensions, for example, the tube segments may be more closely spaced with respect to the height axis and / or the horizontal axis.

[0034] The term "parallel tube sections" may refer to tubes in a shell-and-tube condenser, where the tubes are typically bent so that a single tube can form multiple parallel tube sections.

[0035] In some embodiments, at least one guide fin element extends from the vacuum outlet toward the sidewall. Multiple guide fin elements may be provided at each vacuum outlet, spaced apart to form an inlet flow path for the vacuum outlet. A guide fin element may be provided at the top of the vacuum outlet and another guide fin element may be provided at the bottom of the vacuum outlet to form an inlet flow path between the guide fins. The guide fin elements may extend at an angle to the horizontal. The guide fin elements may extend inside the condenser, for example, between the parallel tube sections of a shell-and-tube condenser. Having such guide fin elements guides the vapor flow inside the condenser, preventing the vapor from bypassing the condenser and thus improving contact between the vapor and the condenser.

[0036] If the outlet is located proximal to the side wall, the guide fin element may extend from the vacuum outlet into the condenser, away from the side wall.

[0037] The vacuum outlet is typically a manifold extending along the longitudinal axis with multiple outlet openings disposed along the manifold. Guide fin elements may be disposed above and below the outlet openings and extend along the longitudinal direction. The outlet openings may face toward the respective condensers, e.g., in a direction parallel to the transverse axis.

[0038] In a further development, at least some of the tube sections arranged between the guide fin elements of the vacuum outlet are closer together than the tube sections arranged distally.

[0039] The arrangement of the vacuum outlet as described above, independent of the arrangement of the openings in the side wall, can be considered a further aspect of the present invention. Accordingly, also disclosed herein is a freeze-drying apparatus, wherein the vacuum outlet is as described above.

[0040] In some embodiments, at least one of the first and second condensers comprises a plurality of tube segments having a diameter and extending parallel to one another, the plurality of tube segments being arranged such that, when viewed in a cross section extending perpendicular to the longitudinal axis of the drying chamber, the plurality of tube segments form a plurality of spaced-apart linear rows extending parallel to the height axis of the drying chamber, the linear rows being spaced apart by a lateral distance at least equal to the diameter of the plurality of tube segments. The lateral distance is measured along a lateral axis from the surface of the plurality of tube segments in one linear row to the surface of the plurality of tube segments in an adjacent linear row. The lateral distance may be 1-5 times the diameter of the plurality of tube segments, e.g., 1-3 times, 1.5-3 times, or 1.5-2.5 times the diameter of the plurality of tube segments. While it has previously been thought to be advantageous to stagger the tube sections and cause the vapor to follow a winding (zigzag) path between the tube sections, it has been discovered that spacing the linear rows of tube sections and providing open flow paths therebetween improves the flow of water vapor within the condenser, improves water vapor capture, and / or reduces the pressure drop across the condenser.

[0041] The tube segments may further be arranged to form spaced apart linear rows extending parallel to a transverse axis of the drying chamber, the linear rows being spaced apart by a height distance at least equal to half the diameter of the tube segments, which height distance may be less than the transverse distance, such as 0.5-3, or 0.5-2, 0.5-1.5, or 0.8-1.2 times the diameter of the tube segments.

[0042] The condenser chamber may further include guide fin elements, other than those associated with the vacuum outlets, arranged above and / or below the condensers in the direction of extension of each linear row of the condensers. In this manner, the guide fin elements guide water vapor into the flow paths formed between the linear rows. Such guide fin elements may include curved portions, which angle the guide fin elements toward the respective openings in the respective side walls.

[0043] In some embodiments, the cylindrical housing of the freeze-drying device defines an internal chamber, and the first and second walls each extend as a chord into the internal chamber, thereby providing a drying chamber, a first condenser chamber, and a second condenser chamber. This can provide both a simple structure in which the cylindrical housing is provided and the sidewalls, heating device, rails, and condensation are arranged as modules within it. A tubular shape is generally advantageous for pressure vessels and can also provide better flow characteristics compared to more angular cross-sections. The sidewalls extending as a chord refer to a circular cross-section of the cylindrical housing perpendicular to the longitudinal axis. The sidewalls are typically parallel to the height axis.

[0044] In another embodiment, a housing, such as a cylindrical housing of a freeze-drying device, defines a drying chamber, and first and second condenser chambers are attached to the exterior of the housing on either side. Thus, the first and second sidewalls are respective portions of the housing, which may be curved in embodiments where the housing is cylindrical. Such embodiments may be referred to as having an "external condenser." An attached condenser chamber refers to a condenser housing attached to the housing. The condenser chamber may be directly attached to the housing, i.e., there is no additional piping between the drying chamber and the condenser chamber, and the housing forms the walls of the condenser chamber.

[0045] In some embodiments, the freeze-drying apparatus further comprises at least two first condenser chambers on a first side of the drying chamber, arranged sequentially along the longitudinal axis, and at least two second condenser chambers on a second side of the drying chamber, arranged sequentially along the longitudinal axis. In this way, by dividing the total condensation surface area into, for example, four condenser chambers, it becomes possible to de-ice, for example, one condenser at a time, thereby enabling 75% of the total condenser surface to be treated for drying the product. The feasibility of this depends on the duration of the de-icing process, which is affected by the pressure in the condenser chamber during de-icing and the uniformity of the ice layer distribution over the condenser surface area. The improved flow characteristics of the present invention may contribute to more uniform flow within the condenser chamber, and therefore a more uniform ice layer, making it possible to de-ice one out of four condensers at a time.

[0046] In a further aspect of the present invention, there is provided a method of operating a freeze-drying apparatus as disclosed herein, having at least two first condenser chambers arranged sequentially along a longitudinal axis and at least two second condenser chambers arranged sequentially along the longitudinal axis. This method is having three of the plurality of condenser chambers in an open position in fluid communication with the drying chamber; further comprising: the condenser chamber being in a closed position without fluid communication with the drying chamber; Condensing / condensing water vapor onto the three condensers while deicing the further condenser chambers.

[0047] The method may further include sequentially closing one condenser chamber at a time for de-icing while the other condenser chambers condense water vapor.

[0048] In some embodiments of the freeze-drying apparatus, each opening has an associated valve, and each valve is movable between an open position and a closed position that seals the drying chamber from the associated condenser chamber. The valve allows the condenser chamber to be sealed for de-icing.

[0049] In some embodiments, each valve includes a sealing element movable between an open position and a closed position, the sealing element being configured to move from the sidewall into the respective condenser chamber when moving from the closed position to the open position. Moving the sealing element into the condenser chamber when in the open position means that when closed for de-icing, the pressure difference between the drying chamber and the condenser chamber contributes to maintaining a seal because the pressure is greatest in the condenser chamber. This can increase the pressure in the condenser chamber, thereby shortening de-icing times, and / or can simplify the design of the valve, as it does not have to withstand a counter-acting pressure difference.

[0050] In a further development, a proximal portion of each sealing element relative to a respective condenser is configured to move further along the transverse axis W than a distal end of the respective sealing element when the valve moves from the closed position to the open position. This is preferable for openings located above and below the condenser so that the sealing elements direct the vapor flow to the condenser. This may also reduce pressure drop.

[0051] In some embodiments, the first and second openings extend above and below the respective condensers, respectively, and each sealing element of the valve is connected to a valve actuator by a valve member. The valve actuator is positioned outside the condenser chamber, and the valve member has an extended position in which the valve is closed and a retracted position in which the valve is open. The valve member is housed in a pressure-resistant housing so that it can be extended between the extended and retracted positions. In this way, the valve actuator can be located outside the condenser chamber, outside the cylindrical housing, which, for example, provides greater access for maintenance or replacement while reducing the amount of components housed in the condenser chamber that may be detrimental to the flow characteristics within the condenser chamber and / or allows for more condenser surface within the condenser chamber, or reduces the size of the condenser chamber and increases the size of the drying chamber to allow for more product. The pressure-resistant housing may be attached to the end of the valve member and the inner condenser chamber wall, and the end of the valve member is movable between the extended and retracted positions. The pressure-resistant housing may be a bellows-like housing. A valve actuator is understood to be a drive means, e.g., a motor, that moves the valve member and the sealing element. The valve actuator may be located outside the cylindrical housing of the freeze-drying device. The valve member extends into the associated condenser chamber.

[0052] In some embodiments, the opening in at least one of the first and second side walls is a laterally extending opening extending downwardly relative to the height axis.

[0053] In the freeze-drying apparatus, the height of the drying chamber extends along a height axis between the bottom and top of the drying chamber, and each of the at least one opening in each of the first and second side walls has an opening height along the height axis H. The height of the opening may be evaluated as the height of the projection of the opening onto the height axis.

[0054] In some embodiments, the cross-section of the freeze-drying device is perpendicular to the longitudinal axis, and the sum of the opening heights in the first side wall or the second side wall is equal to at least 10% of the height of the drying chamber, preferably at least 15%, 20%, 25%, 30%, 35%, or 40% of the height of the drying chamber. Thus, the sum of the opening heights can be in the range of 10-60%, 10-50%, 10-40%, 15-60%, 15-55%, 15-50%, 15-45%, 15-40%, 20-60%, 20-55%, 20-50%, 20-45%, 20-40%, 25-60%, 25-55%, 25-50%, 25-45%, 25-40%, 30-60%, 30-55%, 30-50%, 30-45%, or 30-40%. As used herein, the sum of the opening heights in a given sidewall is a means of viewing a cross-section of the freeze-drying apparatus, the cross-section being perpendicular to the longitudinal direction (and thus parallel to the height axis), projecting all openings in a given sidewall as they extend into the cross-section, and summing the resulting projected heights of the openings. Providing such openings advantageously reduces the vapor velocity at the openings. Matching the openings to the height of the drying chamber is useful because the height of the drying chamber scales with the volume and number of trays, and therefore with the product sized for the freeze-drying process; therefore, the height of the drying chamber is related to the vapor generation rate within the drying chamber. In embodiments having a cylindrical housing, the height of the drying chamber corresponds to the diameter of the interior chamber.

[0055] In a further embodiment or further development of the aforementioned embodiment, the height of at least one of the openings in the first side wall or the second side wall is at least 5% of the height of the drying chamber, preferably at least 5%, 7.5%, 10%, 12.5%, 15%, 17.5%, 20%, 22.5%, 25%, 27.5%, or at least 30% of the height of the drying chamber. Therefore, the height of such individual openings should be 5-40%, 5-35%, 5-30%, 5-27.5%, 5-25%, 5-22.5%, 5-20%, 5-17.5%, 5-15%, 7.5-40%, 7.5-35%, 7.5-30%, 7.5-27.5%, 7.5-25%, 7.5-22.5%, 7.5-20%, 7.5-17.5%, 7.5-15%, 10-40%, 10-35%, 10-30%, 10-27.5%, 10-25%, 10-22.5%, 10-20%, 10-17.5%, 10-15%, 10-15% of the height of the drying chamber. The range may be 2.5-40%, 12.5-30%, 12.5-30%, 12.5-27.5%, 12.5-25%, 12.5-25%, 12.5-22.5%, 12.5-20%, 12.5-17.5%, 15-40%, 15-35%, 15-30%, 15-27.5%, 15-25%, 15-22.5%, 17.5-40%, 17.5-35%, 17.5-30%, 17.5-27.5%, 17.5-25%, 17.5-22.5%, 20-40%, 20-35%, 20-30%, 25-40%, or 25-35%. Having such large individual openings can provide a large total opening height in a given sidewall in a cost-effective manner with a small number of openings. For example, an embodiment having first and second openings, each with an opening height in the range of 10-30% of the drying chamber height, provides a total opening height in the sidewall of 20-60% of the drying chamber height.

[0056] In some embodiments, the height of at least one opening in each of the side walls extending within the stack height HS is at least equal to the spacing between adjacent heating elements, preferably at least two or three times the spacing between adjacent heating elements. The height of the opening may be 1 to 10 times the spacing between adjacent heating elements, e.g., 1-8, 2-8, 1-6, 2-6, 2-5, 3-5, 2-4, or 3-4 times the spacing between adjacent heating elements. The spacing between heating elements is measured along the height axis in this disclosure. The heating device comprises multiple heating elements configured to provide heat to the products being dried. Heat can be transferred by direct contact between the heating elements and the tray (or trolley support element), by conduction, and / or by thermal radiation. The heating elements may be in the form of heating plates. The heating device may be positioned so that the heating elements overlap the tray carrying the products, i.e., so that the tray is positioned between two heating elements. The bottom heating element may be the heating element closest to the bottom of the drying chamber, and the top heating element may be the heating element closest to the top surface of the drying chamber.

[0057] The first and second side walls extend along the longitudinal axis. The first and second side walls may extend substantially from the first end to the second end of the drying chamber, for example, when only one condenser is provided on each side of the freeze-drying apparatus. Alternatively, two or more first and two or more second side walls may be provided consecutively along the longitudinal axis, for example, when multiple condenser chambers are provided on each side of the freeze-drying apparatus. A wall separating two condenser chambers both located on the same side of the freeze-drying apparatus is not considered a side wall in this disclosure, but is referred to as an intermediate wall. These intermediate walls extend in a direction along the transverse axis.

[0058] In a preferred embodiment, the first and second side walls each have one or more first openings above the central horizontal plane of the drying chamber and extending at least partially within the stack height, and one or more second openings below the central horizontal plane of the drying chamber and extending at least partially within the stack height, the first and second openings being symmetrically arranged around the central horizontal plane extending between the first and second openings, and each of the first and second openings extending at least partially, preferably above and below the associated condenser.

[0059] In a further aspect of the present invention, there is provided a method for operating a freeze-drying apparatus as disclosed herein, the method comprising: i. placing a plurality of trays carrying products within a drying chamber; ii. opening openings in the first and second side walls; iii. condensing the vapor on first and second condensers; iv. closing an opening in one of the first side wall or the second side wall to de-ice an associated condenser; v. opening the opening in one of the first side wall or the second side wall after deicing; vi. repeating steps 4 and 5 until the product is dry.

[0060] Also disclosed herein is a freeze-drying apparatus in which a first one of the openings in each sidewall extends above a central horizontal plane of the drying chamber, and a second one of the openings in each sidewall extends below the central horizontal plane. While it is currently considered advantageous for the first and second openings to extend within the stack height, freeze-drying apparatuses having first and second openings extending outside the stack height are also contemplated. Such first and second openings can have the characteristics described herein, such as symmetrical placement, dimensions, and / or location above and below the condenser, as disclosed herein.

[0061] Further embodiments and details of the invention will become apparent from the following detailed description of the invention. [Brief explanation of the drawings]

[0062] Hereinafter, an embodiment of the present invention will be described with reference to the schematic diagrams. [Figure 1] FIG. 1 is a cross-sectional view of a first end of a freeze-drying apparatus according to the present invention. [Figure 2] FIG. 2 shows a perspective view of an embodiment of a freeze-drying apparatus. [Figure 3a-3b] 3a-3b show details of the vacuum outlet in the condenser chamber. [Figures 4a-4e] 4a-4e show different configurations of the opening in the second sidewall. [Figure 5] FIG. 5 shows the results of a CFD simulation of the configuration of FIGS. 4a-4e compared to a prior art configuration. [Figure 6] FIG. 6 is a diagram showing the relative drying chamber pressure in the CFD simulation of FIG. [Figure 7a-7b] 7a-7b show ice growth rates on a condenser in an embodiment of the present invention compared to a prior art configuration obtained by CFD simulation. [Figure 8] FIG. 8 shows a further CFD simulation of an embodiment of the present invention. [Figure 9a-9b] 9a-9b show details of an embodiment of a valve positioned in an opening. [Figure 10] FIG. 10 shows a detail of an embodiment of a valve positioned in an opening. [Figure 11a-11b] 11a-11b show details of an embodiment of a valve placed in an opening. [Figure 12] FIG. 12 shows a detail of an embodiment of a valve positioned in the opening. [Figure 13] FIG. 13 shows a CFD simulation of a further embodiment in which one condenser chamber is closed. DETAILED DESCRIPTION OF THE INVENTION

[0063] FIG. 1 shows a freeze-drying apparatus 1 viewed along a longitudinal axis L (see FIG. 2 ) from a first end (not shown) of a drying chamber 10 toward a second end 12 of the drying chamber 10. The freeze-drying apparatus has a door (not shown) at the first end and is closed at the second end 12. Thus, the product to be dried moves in and out of the drying chamber at the first end, or is moved therefrom. The freeze-drying apparatus 1 has a cylindrical housing 2 defining an internal chamber 3, which is a cylindrical space extending from the first end to the second end 12. A first side wall 32 and a second side wall 42 each extend as a chord within the cylindrical housing 2, thereby dividing the internal chamber 3 into the drying chamber 10, a first condenser chamber 30, and a second condenser chamber 40. The first side wall 32 and first condenser chamber 30 are located on a first side 15 of the drying chamber, which is the left side in Figure 1, and the second side wall 42 and second condenser chamber are located on a second side 16 of the drying chamber, which is the right side in Figure 1. Locating the condenser chambers 30, 40 to the side of the drying chamber 10 in this way has the advantage that the product to be dried cannot fall from a tray (not shown) into the condenser chambers 30, 40. The condenser chambers are more difficult to clean than the inside of the drying chamber 10.

[0064] The drying chamber 10 extends from a first side 15 to a second side 16 along a horizontal axis W and from a bottom 13 of the drying chamber 10 to a top 14 of the drying chamber 10 along a height axis H. The longitudinal axis (shown in FIG. 2), the horizontal axis W, and the height axis H are perpendicular to one another. A central horizontal plane CP of the drying chamber extends along the horizontal axis W and the longitudinal axis L at a height midway between the top 14 and the bottom 13 of the drying chamber 10, i.e., in the center of the drying chamber with respect to the height axis.

[0065] A heating device 50 having a plurality of heating elements 51, 52 is disposed within the drying chamber 10. In this embodiment, the heating elements are heating plates extending horizontally within the drying chamber 10 and spaced apart along a height axis H. The heating elements 51, 52 form two stacks of heating elements, disposed on a first side 15 and a second side 16 of the drying chamber 10, respectively. In operation, a tray carrying product to be dried is disposed between the heating elements 51, 52, and the heating elements 51, 52 provide heat to the product to drive the drying process. In each stack of heating elements 51, 52, the top heating element 52 is disposed proximate the top 14 of the drying chamber, and the bottom heating element 51 is disposed proximate the bottom 13 of the drying chamber. A stack height HS of the heating device 50 extends between the top heating element 52 and the bottom heating element 51. It can be seen that the stack height HS substantially corresponds to the height to which a stack of multiple trays (not shown) extends when the freeze dryer is in operation. The central horizontal plane CP of the drying chamber coincides with a central horizontal heater plane HP, which in this embodiment is centrally located relative to the stack height HS. In this embodiment, the heater 50 is heated by a hot fluid, such as steam, circulated through pipes 53 and distributed by manifold 54 to each heating element 51, 52.

[0066] A rail arrangement is provided within the drying chamber and comprises a rail 80 at the top 14 of the drying chamber and a trolley support 81 at the bottom 13 of the drying chamber. The rail arrangement is configured to receive a trolley (not shown) carrying a tray (not shown) carrying the product to be dried.

[0067] The first condenser 31 is disposed within the first condenser chamber 30, and the second condenser 41 is disposed within the second condenser chamber 40. As can be seen, the first and second condenser chambers 30, 40 are symmetrically positioned on opposite sides of the drying chamber 10. The first and second condensers 31, 41 are shell-and-tube condensers, and in this embodiment, the U-shaped ends of the tubes are visible in FIG. 1. Fluid communication between the drying chamber 10 and the condenser chambers 30, 40 is established through openings 33a, 33b in the first sidewall 32 and openings 43a, 43b in the second sidewall 42. Openings 33a, 43a are disposed above the respective condensers 31, 41, and openings 33b, 43b are disposed below the respective condensers 31, 41, distributing the incoming water vapor across the condensers from above and below. In this embodiment, each of the openings 33a-33b, 43a-43b is positioned within the stack height HS. The opening 33a in the first side wall 31 and the opening 43a in the second side wall 41 extend above the central horizontal plane CP and the central horizontal heater plane HP, respectively, and are therefore considered "first openings" according to the present invention. Similarly, the openings 33b in the first side wall 31 and the openings 43b in the second side wall 41 extend below the central horizontal plane CP and the central horizontal heater plane HP, respectively, and are therefore considered "second openings" according to the present invention. As can be seen from the figure, the first opening 33a and the second opening 33b in the first side wall 31 are positioned symmetrically with respect to the central horizontal plane CP and the central horizontal heater plane HP of the drying chamber. In this embodiment, the central horizontal plane CP of the drying chamber coincides with the central horizontal heater plane HP and the central condenser plane, and therefore the first opening and the second opening are symmetric with respect to these planes. By arranging the openings symmetrically around the heating device and / or condenser, steam flow distribution within the drying chamber and / or condenser chamber can be improved.

[0068] Intermediate portions 34, 44 of side walls 31, 41 extend between the respective first and second openings and are solid in this embodiment.

[0069] Reference is now made to FIG. 2, which illustrates an embodiment of a freeze-drying apparatus 1 in a perspective view. The cylindrical housing is not shown to allow for detailed illustration of the drying chamber 10 and condenser chambers 30, 40. The freeze-drying apparatus 1 includes a plurality of reinforcing elements 17 spaced apart along a longitudinal axis L from the first end 11 to the second end 12 of the drying chamber, with the reinforcing elements 17 attached to the housing. The freeze-drying apparatus 1 illustrated in FIG. 2 includes four condenser chambers 30, 40, 60, 70, two on a first side 15 and two on a second side 16 of the drying chamber. The two condenser chambers 30, 60 on the first side 15 are arranged sequentially along the longitudinal axis L and are both designated as the "first condenser chambers" 30, 60. Similarly, the two condenser chambers 40, 70 on the second side 16 are arranged sequentially along the longitudinal axis L and are both designated as the "second condenser chambers." The two second condenser chambers 40, 70 are separated by an intermediate wall 47 and are therefore not in fluid communication. The same applies to the two first condenser chambers 30, 60, although the corresponding intermediate wall is not visible in Figure 2. As can be seen, the two first condenser chambers 30, 60 are identical to the two second condenser chambers 40, 70 except for their longitudinal positions. The condenser 41 is a shell-and-tube condenser with multiple parallel tubes 41a through which water vapor condenses / liquefies during drying. Each condenser chamber 30, 40, 60, 70 has four openings: two openings (first openings) above the condenser and above the central horizontal plane of the drying chamber, and two openings (second openings) below the condenser and below the central horizontal plane of the drying chamber. In the first condenser chamber 30, two first openings are designated by reference numerals 33a and 33c, and in the second condenser chamber 40, two second openings are designated by reference numerals 43b and 43d. Thus, in this embodiment, each condenser chamber has a set of first openings and a set of second openings, each set of openings being arranged sequentially along the longitudinal axis L. All of the openings have the same rectangular shape with rounded corners and the same dimensions. As in FIG. 1, the openings are arranged symmetrically within the stack height with respect to the central horizontal heater plane (not shown) and the central horizontal plane of the drying chamber (not shown), which may be difficult to discern from the perspective view of FIG. 2.

[0070] 2, each opening includes a valve 36 having a sealing element 36a. The sealing element 36a is configured to close the associated opening and, therefore, in this embodiment, is a rectangular plate. For example, if the pair of first openings 33a, 33c were instead provided as a single opening, the corresponding sealing element would be twice as long as the sealing element in FIG. 2. Each valve also includes a valve actuator (not shown, see FIGS. 11-12) attached to the outside of the cylindrical housing (not shown), which is configured to move the sealing element 36a between a closed position, e.g., shown at openings 33c and 43d, where the drying chamber 10 is sealed from the condenser chamber 40, to an open position, shown at openings 33a and 43b, where water vapor can flow between the drying chamber 10 and the condenser chambers 30, 40. Further details of valves that can be used in the freeze-drying apparatus 1 are shown in FIGS. 9 and 11 and are described in more detail below.

[0071] In FIG. 2, a trolley 83 is positioned within the drying chamber 10 and is in the process of moving along rails 80 from the first end 11 to the second end 12 of the drying chamber.

[0072] Reference is now made to Figures 3a-3b, which illustrate further details of the condenser chamber. Figures 3a-3b illustrate a cross-sectional view of a condenser chamber 40 including a second condenser 41 having parallel tube portions 41a and a second sidewall 42, although the details shown may apply to all condenser chambers. The left side of Figure 3a illustrates simulated ice growth rates (in mm / hr) on the condenser tube portions 41a, some of which are not visible due to low ice growth rates, shown in white. On the left side of Figure 3a, the vacuum outlet 45 is centrally located within the condenser chamber 40 relative to the height axis H, here proximal to the second sidewall 42, within 30% of the width WC of the condenser chamber (measured along the horizontal axis and centrally relative to the height axis H) from the second sidewall 42. While this works, it has been found that moving the vacuum outlet 45 to a more distal position relative to the second side wall 42, as shown on the right side of FIG. 3a, improves the flow characteristics of the condenser chamber 40 and potentially increases contact between the water vapor and the condenser, potentially bringing the vapor into contact with a cooler condenser surface area and increasing condensation. On the right side of FIG. 3a, the vacuum outlet 45 is positioned at a distance from the second side wall 42 equal to approximately 55% of the lateral width WC of the condenser chamber. The vacuum outlet 45 on the right side of FIG. 3a further comprises two guide fins 45a extending in a direction toward the second side wall 42, in this case at an angle of approximately 30° relative to the lateral axis W. The guide fins 45a guide the water vapor into the interior of the condenser 41 before passing between the two guide fins 45a, which appear to form an entrance to a flow path leading to a vacuum outlet opening (not shown) facing the second side wall 42. In FIG. 3a, the vacuum outlet 45 is a tubular manifold with an outlet opening (not visible) oriented parallel to the horizontal axis W, on the right side in the left-hand embodiment and on the left side in the right-hand embodiment.

[0073] A further embodiment of the vacuum outlet 45 is shown in FIG. 3b, in which the outlet 45 is positioned at a distance from the second side wall 42 equal to approximately 60% of the width WC of the condenser chamber. In this embodiment, the vacuum outlet 45 has a rectangular cross-section with multiple openings 45b spaced apart along the longitudinal axis L. The location of the vacuum outlet 45 is measured here at the vacuum outlet openings 45b, which face the second side wall 42 and are positioned within the inlet flow passage defined by the guide fins 45a. As can be seen, the first layer of tube segments 41b, counting from the outlet openings 45b, are more closely spaced than the tube segments distal to the vacuum outlet 45, e.g., the tube segments proximal to the second side wall 42. In this manner, the tube segments function as a filter for any remaining condensable gas immediately prior to the outlet openings. In this embodiment, the tube segments are more closely spaced along the height axis H; however, it is also contemplated that multiple layers of tube segments may be more closely spaced along the horizontal axis W. The spacing in the first layer of tube segments is here about 2 / 3 of the diameter of the tube segments, while the spacing distal to the vacuum outlet is approximately equal to the diameter (in the height axis) of the tube segments. Additional guide fins 48 (separate from those at the vacuum outlet) are provided in the second condenser chamber to guide the vapor flow into the condenser 41. In the embodiment of Figure 3a (right-hand), the guide fin elements 48 have curved portions that slope the guide fin elements towards the first and second openings 43a, 43b.

[0074] In FIG. 3a, the tube segments 41a are arranged in a staggered configuration as seen in a cross section perpendicular to the longitudinal axis (corresponding to the views of FIGS. 3a-3b), such that water vapor flowing downward and upward from the first and second openings 43a and 43b, respectively, follows a serpentine path between the tube segments 41a toward the vacuum outlet 45. In FIG. 3b, the tube segments 41a are seen arranged in a plurality of linear rows 41c along the height axis H, with the plurality of linear rows 41c spaced apart by a lateral distance LD between the linear rows 41c of the tube segments 41a. Thus, an open flow path exists along the height axis H. The tube segments 41a are also arranged in a plurality of linear rows 41r spaced apart by a height distance HD. The lateral distance LD and the height distance HD are measured from the surface of the tube segment in the adjacent linear row 41c or linear row 41r, respectively. In FIG. 3b, the lateral distance is approximately twice the diameter of the tube segment 41a, and the height distance HD is approximately equal to the diameter of the tube segment. The lateral distances LD and HD described herein refer to the general spacing of the tube segments 41a within the condenser, and not to the local spacing proximate the vacuum outlet 45, which may be closer to provide a filter section as described above. Guide fin elements 48 within the condenser chamber 40 below the condenser 41 are positioned as extensions of the straight rows 41c of tube segments 41a, whereby the guide fin elements 48 guide water vapor into the open flow paths between the straight rows of tube segments 41a.

[0075] 4a-4f, next, show a second side of the tubular freeze-drying apparatus 1, as viewed along the longitudinal axis. FIG. 4a shows a freeze-drying apparatus in which a second condenser 41 is positioned inside the drying chamber 10, providing a direct flow path for vapor from the trays 82 to the second condenser 41. Thus, FIG. 4a can provide a benchmark for evaluating the performance of other configurations, and FIG. 4a is an "ideal" case for fluid flow characteristics.

[0076] 4b shows a configuration with a second side wall 42 providing a condenser chamber 40, with a centrally located opening 43e extending symmetrically across the central horizontal plane CP (and central heating plane) being provided as the only opening to the condenser chamber 40 (multiple such central openings may be arranged consecutively along the longitudinal axis L). The centrally located opening 43e extends within the rack height HS.

[0077] 4c shows an arrangement in which the opening 43f in the second side wall 42 extends laterally and faces downward relative to the height axis H. This opening also extends within the rack height HS.

[0078] 4d shows an external condenser configuration in which a cylindrical housing 2 defines the drying chamber 10 and a condenser chamber 40 is mounted on the outside of the cylindrical housing 2. A centrally located opening 43e is formed in the portion of the cylindrical housing 2 that forms the wall 42 of the condenser chamber 40, which portion is therefore considered the second side wall 42.

[0079] 1 and 2, the first opening 43a in the second side wall 42 extends above the central horizontal plane CP, HP and above the second condenser 41, and the second opening 43b extends below the central horizontal plane CP, HP and below the second condenser 41. For illustrative purposes, the stack height HS of the heating device is shown along with the height range HT of the trays, it being understood that the trays are slightly shorter than the former.

[0080] Figure 4f shows a prior art configuration with a heating device 50' in the drying chamber 10' of the freeze-drying apparatus 1', in which the condenser chamber 40' with the opening 43' is arranged below the heating device 50' in relation to the heating device 50' in the height axis direction.

[0081] In FIGS. 4 b , 4 d and 4 e the height of each opening is equal to about 17% of the height of the drying chamber, which here is the diameter of the cylindrical housing 2 , for example.

[0082] Reference is now made to FIG. 5, which shows a computational fluid dynamics (CFD) simulation of the configuration shown in FIGS. 4a-4e and a similar configuration of Applicant's prior art system in operation. FIG. 5 shows the pressure profile in freeze-drying apparatus 1. The unit scale for each configuration is the same, so the results can be compared. The simulations reflect the same operating conditions, e.g., the same steam generation rate, the same non-condensable gas inlet rate, and the same condenser temperature in each case. In general, the simulations shown herein are not necessarily optimized configurations or optimized with respect to operating conditions. The simulations were performed using Applicant's proprietary software.

[0083] Referring first to the configuration in the upper left of Figure 5, this shows Applicant's prior art system with a heater stack and a condenser chamber located below the trays. It has been found that the pressure field within the drying chamber is relatively uniform, with a pressure level of approximately 0.01 kPa, with slightly higher pressures within the stack of trays, while in the area immediately below the trays above the condenser chamber the pressure is approximately 0.005 kPa, and within the condenser chamber the pressure ranges from approximately 0.00 to 0.002 kPa. It is desirable to reduce the pressure drop from the drying chamber to the condenser chamber.

[0084] Moving on to a simulation of the "ideal" configuration shown in Figure 4a, the top center configuration in Figure 5, which can serve as a benchmark for performance. As can be seen, the pressure is substantially uniform, at approximately 0.006 kPa in the drying chamber and approximately 0.003 kPa in the condenser region. Thus, the "ideal" configuration reduces the pressure in the drying chamber compared to the prior art. The pressure in the condenser region is also higher, closer to the drying chamber pressure, and more uniform than the prior art, meaning improved water vapor distribution across the condenser and a lower pressure drop from the drying chamber to the condenser region. While the ideal configuration improves flow characteristics, it does not allow for sealing the condenser from the drying chamber for de-icing.

[0085] Turning now to the "top / bottom gate" embodiment at the top right of Figure 5, this embodiment includes a first opening and a second opening in the second sidewall. The pressure profile in Figure 5 shows that the pressure within the drying chamber is comparable to an ideal configuration of about 0.006 kPa, and an improvement over prior art configurations.

[0086] Referring now to the embodiment at the bottom left of Figure 5, which shows an "outer gate" with a centrally located opening within the stack height that leads to a condenser chamber attached to the cylindrical housing, it can be seen that the pressure within the drying chamber is about 0.006 kPa, and the condenser chamber pressure at the opening is about 0.00 kPa at the opening and about 0.003 kPa proximal to the opening.

[0087] Referring now to the bottom center embodiment of Figure 5 showing a "lower gate," the centrally located opening extends laterally and points downward. Comparing the pressure profile to the prior art, the average drying chamber pressure is reduced, but compared to the ideal, the pressure within the drying chamber is less uniform.

[0088] Referring now to the configuration at the bottom right of Figure 5, which shows a "side gate," the configuration has a centrally located opening in the second side wall that extends as a chord within the cylindrical housing. This configuration exhibits a reduced and more uniform drying chamber pressure of less than 0.009 kPa compared to prior art solutions. Similarly, the condenser chamber pressure is approximately 0.004 kPa and is substantially uniform.

[0089] Thus, each of the embodiments in Figures 4b-4e improves the fluid flow characteristics of the freeze-drying apparatus. This is also reflected in Figure 6, which shows the relative drying chamber pressure for each of the six configurations in Figure 5 evaluated at the same location in each of the six simulations. The prior art solution (baseline) is the reference, with a relative chamber pressure of 100%, approximately 47% for the ideal solution (ideal), approximately 50% for the configuration with first and second openings (top / bottom), approximately 54% for the external condenser chamber configuration (outer gate), approximately 80% for the configuration with downward openings (lower gate), and approximately 82% for the configuration with centrally located openings (side gate).

[0090] Reference is now made to Figures 7a-7b, which show ice growth rates (in mm / hr) on the condenser surface in a CFD simulation of a prior art configuration (Figure 7a) similar to Figure 4f, and an embodiment of the present invention (Figure 7a) similar to the embodiment of Figure 4e, i.e., the "top-down" embodiment. As can be seen, the ice growth rate in the prior art configuration is highest at opening 43' (darker shading), resulting in a thick ice layer that can increase pressure drop, and the ice growth rate may be more uniform across condenser 41'. In the embodiment on the right, the ice growth rate is lower and more uniform throughout the condenser, implying better flow characteristics.

[0091] Reference is now made to FIG. 8 , which shows CFD-simulated velocity profiles for two embodiments of the freeze-drying apparatus 1. In the left-hand configuration, the first and second side walls 31 and 41 have respective first openings 33 a, 43 a that extend partially within the stack height HS, partially above the stack height HS, and above the drying chamber central horizontal plane CP, which appears to substantially coincide with the condenser central horizontal plane and the central horizontal heater plane HP. The first openings 33 a, 43 a also extend completely above their respective condensers 30 and 40, since there is no overlap between the opening height HO and the condenser height HC. In this embodiment, each opening height HO is equal to approximately four times the distance between two adjacent heating elements, or approximately 13% of the drying chamber height measured along the height axis between the bottom 13 and top 14 of the drying chamber. The first and second side walls 31 and 41 are provided with corresponding second openings 33 b, 43 b, respectively. Thus, in a cross section of the freeze-drying device perpendicular to the longitudinal axis (i.e., the cross section shown in FIG. 8 ), the sum of the opening heights (HO) in each of the first and second side walls 32, 42 is approximately 26% of the height of the drying chamber. The middle portions 34, 44 of each side wall 31, 41 appear solid in the left-hand embodiment. Note that the corner portions of the tubular housing 2 at the openings correspond to the sealing elements 46 of the valves (not shown) that open and close the respective openings. The right-hand embodiment corresponds to the left-hand embodiment, except that nine openings 33, 43 are provided in each side wall, and each opening height HO is approximately equal to the distance between adjacent heating elements, which is approximately 2.9% of the height of the drying chamber. In a cross section of the freeze-drying device perpendicular to the longitudinal axis, there are nine openings in each side wall, thus resulting in a total opening height of approximately 26% of the height of the drying chamber. One of the openings extends across the central horizontal plane CP, and four additional openings are provided symmetrically above and below the central horizontal plane CP, four of which are provided within the stack height HS. The location of the vacuum outlet 45 is shown in the second condenser 40 and has a corresponding location in the first condenser chamber in both embodiments shown in Figure 8.By comparing the velocity profiles of the two embodiments, it can be seen that the right-hand embodiment with nine openings provides a slightly more uniform velocity field in the condenser chamber than the left-hand embodiment, but the right-hand embodiment is more cost-effective and has a simpler structure with fewer moving components, thus reducing the risk of error. The embodiment shown in Figure 8 is exemplary; a taller heating device 50 can be used, and it is contemplated to increase the number of trays in the freeze-drying apparatus 1, as shown in Figure 1.

[0092] 9a-9b, a cross-sectional view of an embodiment of the freeze-drying apparatus 1 and details of the valve 36 are shown. The first condenser chamber 30 extends partially within the stack height HS of the heating device 50 and includes first and second openings 33a, 33b in the first side wall 32 that extend above and below the first condenser 31, respectively. The opening height HO of each opening is approximately 9 times the spacing between adjacent heating elements 51 and approximately 22% of the height of the drying chamber 10 (which is the same as the diameter of the interior chamber defined by the cylindrical housing 2).

[0093] The lower left and upper right valves 36 are in an open position, allowing fluid communication between the drying chamber 10 and the first and second condenser chambers 30 and 40, and the upper left and lower right valves are in a closed position. The sealing element 36a moves into the condenser chamber 30 when moving from the closed position to the open position (FIG. 9b). The valves 36 are hinged such that the proximal portion 36ap of the sealing element 36a moves further in the lateral direction W than the distal portion 36ad of the sealing element 36a, where the proximal portion 36ap is the portion of the sealing element 36a proximal to the condensers 31 and 41, and the distal portion 36ad is distal to the respective condensers 31 and 41. In this way, the sealing element 36a assumes a position that directs water vapor toward the condenser 31. A valve actuator (designated 36f, but in a position not shown, see FIG. 12) is located outside the condenser chambers 30 and 40 and outside the cylindrical housing 2. The valve member 36b is connected to the sealing element 36a via a hinge 36e and to a valve actuator (not shown). When the valve is open, the valve member 36b is in the extended position as shown in FIG. 9b. When the valve is closed, the valve member 36b is in the extended position as shown in the upper right valve of FIG. 9a. The valve member 36b is housed within a pressure / vacuum-resistant housing 36d, shown here schematically but also as a collapsible (bellows-like) housing that extends between the closed and open positions of the valve 36. The housing 36d has one end attached to the interior surface of the condenser chamber 30 and the other end attached to the end 36be of the valve member, as shown in more detail in FIG. 12. Here, the end 36be is a plate connected to the sealing element 36a via a hinge 36e. A valve seat 36c is provided in the first side wall 32 against which the sealing element 36a abuts in the closed position. The sealing element 36a is further supported by a hinge arm 36g attached to the side wall. During de-icing, the valve 36 is in a closed position, and the pressure difference between the drying chamber 10 and the condenser chamber 30 contributes to keeping the valve 36 closed. In FIG. 9a, the upper left and lower right valves are the same type having a pressure-tight housing 36d, unlike the lower left and upper right valves, which are alternative embodiments in which the valve member 36b extends and moves through a pressure-tight hollow cylinder. This is for illustrative purposes; in practice, the valves would typically be the same type.

[0094] 10, which shows a perspective view of a first side 15 of the freeze-drying apparatus. A set of first openings 33a, 33c, 33e, 33e are arranged sequentially along the longitudinal axis L, and a set of second openings 33b, 33d, 33e are arranged sequentially along the longitudinal axis.

[0095] Reference is now made to Figures 11a-11b, which illustrate a further embodiment of valve 36 for an opening (shown as second opening 33b in Figure 11a). Valve 36 is shown as a model isolated from the freeze-drying apparatus (not shown), and therefore the illustrated cabinet is not a condenser chamber. Figure 11a is a perspective view showing valve 36 with the valve actuator (motor) 36f outside the cabinet (which would be the condenser chamber if installed in the freeze-drying apparatus (not shown)) and the sealing element open. Figure 11b illustrates valve 36b from another perspective.

[0096] 12, a cross section of an embodiment of valve 36 is shown showing valve actuator 36f outside of condenser chamber 30. Valve actuator 36f is connected to hinge 36e via valve member 36b, which extends into condenser chamber 30 within expandable pressure housing 36d. Pressure housing 36d is shown here schematically. Valve member 36b and pressure housing 36d extend from a frustum-shaped extension of housing 2. Housing 2 and the frustum-shaped extension form the interior surface of condenser chamber 30. Pressure housing 36d is attached to end 36be and interior surface 36i of valve member 36e, thereby forming a space that receives valve member 36e and is sealed from condenser chamber 30.

[0097] Referring to FIG. 13, a simulated velocity profile of a further embodiment is shown, having first and second openings 43a, 43b extending partially within the stack height HS. In this simulation, the first condenser chamber (not shown) is closed for de-icing, and the second condenser chamber 40 is in operation. In this embodiment, the rack apparatus 50 has two stacks 55, 56 of heating elements offset from the drying chamber 10, in the sense that the central heating device plane HP is offset from the central horizontal plane CP of the drying chamber 10. The first and second openings 43a-43b are symmetrically arranged about the central horizontal plane CP and each have an opening height HO that is approximately seven times the distance between adjacent heating elements in the stacks 55, 56, which is equal to approximately 20% of the height of the drying chamber. Thus, in a cross-section of the freeze-drying apparatus perpendicular to the longitudinal axis, the sum of the opening heights HO in each side wall is approximately 40% of the height of the drying chamber. It can be seen that the condenser tube portions 41a are arranged in linear columns and linear rows in a manner similar to that of FIG. 3b. As can be seen, when the condenser chambers are positioned transversely to the heating device and one condenser chamber is closed for de-icing, the water vapor from stack 55 will essentially flow into the flow pattern from the other stack 56, which is closer to the open condenser chamber, here second condenser chamber 40, rather than distorting the existing water vapor flow, as would be the case in other configurations such as the one shown in the upper left of Figure 5.

Claims

1. Freeze-drying apparatus (1), The freeze-drying apparatus (1) is A drying chamber (10) is provided, the drying chamber (10) extending along a longitudinal axis (L) from a first end (11) to a second end (12) of the drying chamber (10), extending along a height axis (H) from the bottom (13) to the top (14) of the drying chamber (10), and extending along a transverse axis (W) from a first side (15) to a second side (16) of the drying chamber (10), the central horizontal plane (CP) of the drying chamber (10) extending parallel to the longitudinal axis (L) and the transverse axis (W), and positioned in the center of the drying chamber (10) with respect to the height axis (H), A door at the first end (11) of the drying chamber (10), A first condenser chamber (30) including a first condenser (31) positioned laterally with respect to the drying chamber (10) on the first side (15), wherein the first condenser chamber (30) has a first side wall (32) between it and the drying chamber (10), A second condenser chamber (40) comprising a second condenser (41) positioned laterally with respect to the drying chamber (10) on a second side (16), wherein the second condenser chamber (40) has a second side wall (42) between it and the drying chamber (10), Each of the first side wall (32) and the second side wall (42) has at least one opening (33a-33d, 43a-33d) that allows fluid communication between the drying chamber (10) and the first condenser chamber (30) and the second condenser chamber (40), Furthermore, in a freeze-drying apparatus (1) comprising a heating device (50) having a plurality of heating elements (51, 52), wherein the plurality of heating elements (51, 52) are spaced apart along the height axis (H) and have a stack height (HS) extending between the bottom heating element (51) and the upper heating element (52), At least one of the openings (33a-33d, 43a-33d) extends at least partially within the range of the stack height (HS) in each of the first side wall (32) and the second side wall (42), The first openings (33a, 43a) extend above the central horizontal plane (CP) in the respective first side walls (32) and second side walls (42), The second openings (33b, 43b) extend below the central horizontal plane (CP) in the respective first side wall (32) and second side wall (42), A freeze-drying apparatus (1), characterized in that the intermediate portions (34, 44) of the first side wall (32) and the second side wall (42), which extend between the first opening (33a, 43a) and the second opening (33b, 43b), are solid.

2. The freeze-drying apparatus (1) according to claim 1, wherein the first openings (33a, 43a) are at least partially provided above the first condenser (31) and the second condenser (41), and the second openings (33b, 43b) are at least partially provided below the first condenser (31) and the second condenser (41).

3. The freeze-drying apparatus (1) according to any one of claims 1-2, wherein the first openings (33a, 43a) and the second openings (33b, 43b) extend at least partially within the range of the stack height (HT).

4. The freeze-drying apparatus (1) according to claim 1, wherein at least one of the openings (43e) extends across the central horizontal plane (CP) of the drying chamber (10) in each of the first side wall (32) and the second side wall (42).

5. The freeze-drying apparatus (1) according to claim 1, wherein the openings (33a-33d, 43a-33d) are arranged symmetrically in each of the first side wall (32) and the second side wall (42) with respect to the central horizontal plane (CP) of the drying chamber (10), and / or are arranged symmetrically with respect to a central horizontal heating device plane (HP) that is parallel to the longitudinal axis (L) and the transverse axis (W) and extends centrally with respect to the stack height (HS).

6. The freeze-drying apparatus (1) according to claim 1, wherein the openings (33a-33d, 43a-33d) are provided as a plurality of sets of openings (33a, 33c; 33b, 33d; 43a, 43c; 43b, 43d), and each set of openings includes at least two openings arranged continuously along the longitudinal axis (L).

7. The height of the drying chamber (10) extends along the height axis (H) between the bottom (13) and the top (14) of the drying chamber (10), and each of the first side wall (32) and the second side wall (42) has at least one opening, each having an opening height (HO) along the height axis (H). The freeze-drying apparatus (1) according to claim 1, wherein in a cross-section of the freeze-drying apparatus (1) perpendicular to the longitudinal axis (L), the sum of the opening heights (HO) in the first side wall (32) or the second side wall (42) is equal to at least 10%, preferably at least 20% or 30%, of the height of the drying chamber (10).

8. The freeze-drying apparatus (1) according to claim 7, wherein the opening height (HO) of the at least one opening in the first side wall (32) or the second side wall (42) is at least 5% of the height of the drying chamber (10), preferably at least 7.5%, 10%, 12.5%, 15%, or 17.5%.

9. The freeze-drying apparatus (1) according to claim 1, wherein a vacuum outlet (45) is provided in each of the first condenser chamber (30) and the second condenser chamber (40), and the vacuum outlet (45) is positioned distal to the first side wall (32) or the second side wall (42) when viewed on the horizontal axis (W).

10. The freeze-drying apparatus (1) according to claim 9, wherein the first condenser (31) and the second condenser (41) each have a plurality of parallel tubular portions (41a), and the plurality of tubular portions at the vacuum outlet (45) are spaced more closely together than the plurality of tubular portions distal to the vacuum outlet.

11. The freeze-drying apparatus (1) according to claim 9, further comprising at least one guide fin (45a) element extending in a direction toward the first side wall (32) or the second side wall (42) from the vacuum outlet.

12. The freeze-drying apparatus (1) according to claim 1, wherein the cylindrical housing (2) of the freeze-drying apparatus (1) defines an internal chamber (3), and the first side wall (32) and the second side wall (42) each extend as a chord into the internal chamber, thereby providing the drying chamber (10), the first condenser chamber (30), and the second condenser chamber (40).

13. The drying chamber (10) is arranged sequentially along the longitudinal axis (L), and on the first side (15) there are at least two first condenser chambers (30, 60), The freeze-drying apparatus (1) according to claim 1, comprising at least two second condenser chambers (30, 70) on the second side (16) of the drying chamber (10) which is sequentially arranged along the longitudinal axis (L).

14. The freeze-drying apparatus (1) according to claim 1, wherein each of the openings (33a-33d, 43a-33d) has an associated valve (36, 46), and each valve (36, 46) is movable between an open position and a closed position that seals the drying chamber (10) from the first condenser chamber (30) and the second condenser chamber (40).

15. Each valve (36, 46) is provided with a sealing element (36a, 46a) movable between the open position and the closed position, wherein the sealing element (36a, 46a) is configured to move from the first side wall (32) or the second side wall (42) to the first condenser chamber (30) and the second condenser chamber (40), respectively, when moving from the closed position to the open position, and preferably the valve (36, 46) is configured such that the proximal portion of each sealing element (36a, 46a) with respect to the first condenser chamber (30) and the second condenser chamber (40), respectively, moves further along the transverse axis (W) than the distal end of each sealing element (36a, 46a) when moving the valve (36, 46) from the closed position to the open position, the freeze-drying apparatus (1) according to claim 14.

16. The freeze-drying apparatus (1) according to claim 1, wherein at least one of the first condenser (31) and the second condenser (41) has a plurality of tube portions (41a), each of the plurality of tube portions (41a) having a diameter and extending parallel to each other, and when the plurality of tube portions (41a) are viewed in a cross section extending perpendicular to the longitudinal axis (L) of the drying chamber (10), the plurality of tube portions (41a) extend parallel to the height axis (H) of the drying chamber (10) and form a plurality of spaced-apart linear rows (41c), and the plurality of linear rows (41c) are spaced at a lateral distance (LD) at least equal to the diameter of the plurality of tube portions (41a).

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