WO2020038538A1

WO2020038538A1 - A cryogenic storage system with a drive system

Info

Publication number: WO2020038538A1
Application number: PCT/DK2019/050244
Authority: WO
Inventors: Hans-Christoph Paul; Kim Andersen; Kim Due JACOBSEN; Torben STEFFENSEN
Original assignee: Hcp Innovation Aps
Priority date: 2018-08-21
Filing date: 2019-08-20
Publication date: 2020-02-27
Also published as: EP3841339C0; DK201870544A1; EP3841339A1; DK180072B1; EP3841339B1

Abstract

A cryogenic storage system comprises a thermally insulated housing with a door (2a), a cryogenic area extending inside the thermally insulated housing, a conveyor system (3) inside the housing and the cryogenic area, said conveyor system comprising an endless chain of storage boxes (4), the endless chain being passed over a driven (19) chain wheel to be driven thereby, and said cryogenic storage system comprising a cooling system. The door (2a) is positioned at an end of the conveyor system (3) comprising the driven (19) chain wheel.

Description

A cryogenic storage system with a drive system

The present invention relates to an ultra-low freeze to cryogenic stor- age system for organic material, especially a large ultra-low freeze to cryogenic storage system for organic material, such as a blood bank, and a method of operating such cryogenic storage system.

In order to successfully preserve biomolecules, cells, and biological tissue for extended periods of time, storage at or below -80°C is generally re- quired. However, both shelf life and the ability to recover living cells are dra- matically improved at even lower temperatures down to about -196°C, which is the boiling point of liquid nitrogen. Therefore, liquid nitrogen is often used as a cooling agent for preservation of organic material, although due care must be taken when handling it in order to avoid frost-bites, also from the nitrogen that vaporizes due to the large temperature difference between the liquid gas and the surrounding air.

Freezers operating at such low temperatures are generally known as cryogenic freezers, and the organic material stored therein is said to be cryo- preserved. There are different opinions on the upper temperature limit below which the term cryogenics should be applied to temperatures. The American National Institute of Standards and Technology has suggested an upper limit of -150°C, while some scientists regard the boiling point of oxygen (-183°C) as the upper limit. However, it is generally agreed, that a freezer refers to a storage device that operates from about -5°C to -20°C, an ultra-low freezer operates from about -50°C to -90°C, and a cryogenic freezer operates from about -140°C to -196°C.

As used herein an ultra-low freeze to cryogenic storage is regarded as a storage operated at temperatures from about -80°C to -200°C and for ease of explanation ultra-low freeze to cryogenic storages are herein referred to as cryogenic storages and correspondingly, ultra-low freeze temperatures to cry- ogenic temperatures are herein commonly referred to as cryogenic tempera- tures, unless otherwise is specifically indicated. Further herein, an area main- tained during operation at cryogenic temperature, as defined herein, is referred to as a cryogenic area. Correspondingly, herein the term cryogenic fluid, gas, liquid is used to designate a fluid, gas, or liquid at cryogenic temperature, as defined herein.

Hospitals, laboratories, and other research institutes all over the world experience an ever increasing need to be able to cryo-preserve, store and han- dle different types of organic material, and many hospitals have storage sys- tems for frozen and cryo-preserved material spread around in many different departments. Such use of a number of relatively small storage systems is not very effective, neither when it comes to the space occupied by the many sys- tems, nor when regarding the energy consumed to keep the stored materials at sufficiently low temperatures.

Especially, when storage systems are arranged as ordinary laboratory freezer compartments, where containers are normally stored in front of and on top of each other in order to maximize the use of the available space within the freezer, the freezer door often is required to be kept open for an extended pe- riod of time while the desired sample container is found, and the interior tem- perature of the storage system increases temporarily. Not only is it energy con- suming to bring back the interior temperature to a desired level, but the samples of material housed near the door of the storage system may degrade rapidly due to repeated thawing and refreezing as the temperature raises and de- creases again every time the door is opened.

W02008/083685A2 discloses a cryogenic storage for portions of or- ganic material such as bags containing blood. The cryogenic storage corn- prises a chain of boxes linked together at a narrow face into an endless chain, which is passed over chain wheels to be driven thereby. Chain wheels are mounted on two horizontal shafts having a mutual horizontal distance. The nar- row faces of the boxes have a short side extending in the traveling direction of the chain and a long side extending in a longitudinal direction parallel to the shafts. Each shaft carries two chain wheels, one at either end of the boxes relative to the long sides thereof. One of the shafts and its chain wheels are driven by a motor through a transmission, especially a self-breaking worm gear, and the other shaft is idling. The shafts, chain wheels and the chain of boxes thus provide a conveyor system, referred to as a paternoster-conveyor.

The boxes are extending from the narrow faces in a direction perpen- dicular to a direction of travel of the conveyor and have open ends opposite the narrow faces through which open ends storage cassettes may be inserted into the boxes. The boxes are adapted to receive a number of storage cassettes side-by-side along the longitudinal direction. The storage cassettes per se are adapted to accommodate a number of containers for storage of e.g. bags con- taining a portion of blood.

The conveyor system is housed in an insulated housing with a door next to the chain of boxes at the idling shaft for withdrawal and insertion of storage cassettes from and into the boxes.

The chain of boxes is, when driven, traveling through an upper run, around the chain wheels on one of the shafts, through a lower run, and around the chain wheels on the other shaft back to the upper run. Between the upper run and the lower run a space is provided in which a cooling tank is placed. The cooling tank is supplied with liquid nitrogen which by boiling keeps the storage room, i.e. the inside of the housing and the conveyor system cooled to cryo- genic temperatures.

However, a number of problems has arisen in connection with opera- tion of a cryogenic storage of the above art.

It is an object of the present invention to avoid or reduce such prob- lems.

In a first aspect a cryogenic storage system according to the present invention comprises a thermally insulated housing with a door, a cryogenic area extending inside the thermally insulated housing, a conveyor system inside the housing and the cryogenic area, said conveyor system comprising an endless chain of storage boxes, each storage box having a narrow face with two mutu- ally opposite short sides and two mutually opposite long sides, the storage boxes being linked together at the narrow faces for the long sides of neighbour- ing boxes to be positioned in a side-by-side relationship and to extend perpen- dicular to a chain direction and for the short sides to extend in the chain direc- tion, the endless chain being passed over a driven chain wheel to be driven thereby, and said cryogenic storage system comprising a cooling system, the storage boxes extending from the narrow face to an opening opposite the nar- row face and being configured for accommodating a number of storage cas- settes insertable through the opening into the storage box in a longitudinal di- rection of the respective storage cassette,

whereby said cooling system is configured to introduce a dry gas corn- prising a combination of approx. 78% - 85% nitrogen and approx. 15% - 21 % oxygen and maintain/circulate said dry gas at cryogenic temperature in the in- sulated housing.

Hereby is obtained that any gas leaking form the cryogenic area will not represent a hazard to persons present in the vicinity of the cryogenic stor- age due to risk of suffocation. Further, by using dry gas formation of ice inside the cryogenic storage is avoided. It is noted that atmospheric air contains ap- prox. 78% nitrogen, approx. 21 % oxygen and approx. 1 % argon.

In an embodiment the cooling system comprises at least one heat ex- changer configured to exchange heat between the dry gas circulated in the thermally insulated housing and a cryogenic fluid, the heat exchanger compris- ing a heat exchange wall, and the heat exchanger being configured for the cry- ogenic fluid to sweep a first side of the heat exchange wall and the dry gas circulated in the thermally insulated housing to sweep a second side of the heat exchange wall.

In one further embodiment the heat exchanger is configured to let the cryogenic fluid into the cryogenic area for mixing with the dry gas in the ther- mally insulated housing. Hereby is obtained that a cryogenic fluid used to cool the cryogenic storage system may subsequently to heat exchange with the dry gas circulated in the thermally insulated housing be mixed with and supplement the dry gas circulated in the thermally insulated housing with thereby introduc- ing local excess temperature differenced in the cryogenic area.

In another further embodiment the cryogenic fluid is contained in a closed cooling circuit. Hereby is obtained more freedom of choice for the cryo- genic fluid.

In a practical, further embodiment, the closed cooling circuit comprises a storage tank connected in a first semi-circuit to the heat exchanger through a first conduit connection including a controllable valve and a second conduit connection including a compressor, and said storage tank connected to a cry- ogenic gas cooler and liquefier in a second semi-circuit.

In a further practical embodiment, the cryogenic storage system corn- prises a refilling line comprising at least an atmospheric air inlet, an air com- pressor, and an air dryer. Hereby is obtained that replenishment of the dry gas circulated in the thermally insulated housing may be accomplished without risk of formation of ice inside the cryogenic storage.

In another embodiment the cryogenic storage system comprises a storage of liquid nitrogen, a storage of liquid oxygen and control means for controlled dosing of the nitrogen and oxygen to an evaporator for introduction of cryogenic nitrogen gas and cryogenic oxygen gas into the thermally insulated housing. Hereby it is possible to control the amounts of nitrogen and oxygen in composition of the dry gas circulated in the thermally insulated housing.

In another embodiment the cooling system comprises a cryogenic air cooling device adapted to generate cryogenic fluid in the form of dry, cryogenic, atmospheric air, said cryogenic cooling device comprising an air compressor, an air dryer, and a cryogenic air cooler. Hereby the need for storage of liquid nitrogen and liquid oxygen is avoided.

In one further practical embodiment the cryogenic air cooling device is configured to generate dry, liquid, cryogenic, atmospheric air to be evaporated into dry, cryogenic gas in the thermally insulated housing. Hereby is obtained that the cryogenic fluid may relatively easily be temporarily stored, thus gener- ally facilitating operation of the cryogenic storage system and especially of the cooling system.

In another practical embodiment the cryogenic air cooling device is adapted to generate dry, gaseous, cryogenic, atmospheric air to be entered into the thermally insulated housing. Hereby a saving of energy is possible when the atmospheric air is not processed into liquid state.

In an embodiment the cryogenic storage system comprises a fan in the thermally insulated housing. Hereby is provided for forced circulation the dry gas inside the thermally insulated housing.

In an embodiment the cryogenic storage system comprises a fan in the thermally insulated housing said fan being configured to provide for flowing the dry gas circulated inside the thermally insulated housing past the heat ex- change wall of the heat exchanger to provide heat exchange by forced convec- tion. Hereby an effective heat exchange is provided for, and also circulation of the dry gas inside the thermally insulated housing may be assisted.

In a further aspect the invention relates to a method of operating a cryogenic storage system comprising a thermally insulated housing with a door, a cryogenic area extending inside the thermally insulated housing, a conveyor system inside the housing and the cryogenic area, said conveyor system corn- prising an endless chain of storage boxes, each storage box having a narrow face with two mutually opposite short sides and two mutually opposite long sides, the storage boxes being linked together at the narrow faces for the long sides of neighbouring boxes to be positioned in a side-by-side relationship and to extend perpendicular to a chain direction and for the short sides to extend in the chain direction, the endless chain being passed over a driven chain wheel to be driven thereby, and said cryogenic storage system comprising a cooling system, the storage boxes extending from the narrow face to an opening op- posite the narrow face and being configured for accommodating a number of storage cassettes insertable through the opening into the storage box in a lon- gitudinal direction of the respective storage cassette, said method being char- acterised by introducing a dry gas comprising a combination of approx. 78% - 85% nitrogen and approx. 15% - 21 % oxygen and circulating said dry gas at cryogenic temperature in the thermally insulated housing. Hereby is obtained that any gas leaking form the cryogenic area will not represent a hazard to persons present in the vicinity of the cryogenic storage due to risk of suffoca- tion.

In a second aspect a cryogenic storage system according to the pre- sent invention comprises a thermally insulated housing with a door, a cryogenic area extending inside the thermally insulated housing, a conveyor system in- side the housing and the cryogenic area, said conveyor system comprising an endless chain of storage boxes, each storage box having a narrow face with two mutually opposite short sides and two mutually opposite long sides, the storage boxes being linked together at the narrow faces for the long sides of neighbouring boxes to be positioned in a side-by-side relationship and to ex- tend perpendicular to a chain direction and for the short sides to extend in the chain direction, the endless chain being passed over a driven chain wheel to be driven thereby, and said cryogenic storage system comprising a cooling system, the storage boxes respectively extending from the narrow face to an opening opposite the narrow face. Items to be stored, may be inserted through the opening into the storage box. In an embodiment the storage boxes are con- figured for accommodating a number of storage cassettes insertable through the opening into the storage box in a longitudinal direction of the respective storage cassette,

In this second aspect, according to the invention the door is positioned at an end of the conveyor system comprising the driven chain wheel.

Hereby a precise drive of the storage boxes in the area at the door is obtained, facilitating accurate positioning of a storage box at the door for inser- tion and/or extraction of a storage cassette from the storage box.

Thus the endless chain is passed around the driven chain wheel through an angle and the door is preferably positioned vis-a-vis the chain wheel on an opposite side relative to the endless chain. Preferably the angle is 45°- 200°, more preferably 90°-180°.

In a further embodiment the driven chain wheel is mounted on a shaft coupled directly to a motor, preferably a torque motor, for the shaft and motor to rotate at a common speed.

Hereby an even more precise drive of the storage boxes in the area at the door is obtained, facilitating accurate positioning of a storage box at the door for insertion and/or extraction of a storage cassette from the storage box.

In a third aspect a cryogenic storage system according to the present invention comprises a thermally insulated housing with a door, a cryogenic area extending inside the thermally insulated housing, a conveyor system inside the housing and the cryogenic area, said conveyor system comprising an endless chain of storage boxes, each storage box having a narrow face with two mutu- ally opposite short sides and two mutually opposite long sides, the storage boxes being linked together at the narrow faces for the long sides of neighbour- ing boxes to be positioned in a side-by-side relationship and to extend perpen- dicular to a chain direction and for the short sides to extend in the chain direc- tion, the endless chain being passed over a driven chain wheel to be driven thereby, and said cryogenic storage system comprising a cooling system, the storage boxes extending from the narrow face to an opening opposite the nar- row face and being configured for accommodating a number of storage cas- settes insertable through the opening into the storage box in a longitudinal di- rection of the respective storage cassette,

and said cryogenic storage system further comprising a position sen- sor configured to sense the presence of a storage box in a sensing position at the door, i.e. in the vicinity of the door.

In an embodiment the position sensor is an optical sensor, whereby the storage boxes may be configured to intersect to cut off or reflect a beam of light when present in the sensing position.

This facilitates accurate positioning of a storage box at the door for insertion and/or extraction of a storage cassette from the storage box.

In a further embodiment each storage box is provided with a machine detectable identification unique to the respective storage box. This facilitates recognition of which storage box is present in the sensing position.

In a forth aspect a cryogenic storage system according to the present invention comprises a thermally insulated housing with a door, a cryogenic area extending inside the thermally insulated housing, a conveyor system inside the housing and the cryogenic area, said conveyor system comprising an endless chain of storage boxes, each storage box having a narrow face with two mutu- ally opposite short sides and two mutually opposite long sides, the storage boxes being linked together at the narrow faces for the long sides of neighbour- ing boxes to be positioned in a side-by-side relationship and to extend perpen- dicular to a chain direction and for the short sides to extend in the chain direc- tion, the endless chain being passed over a driven chain wheel to be driven thereby, and said cryogenic storage system comprising a cooling system, the storage boxes extending from the narrow face to an opening opposite the nar- row face and being configured for accommodating a number of storage cas- settes insertable through the opening into the storage box in a longitudinal di- rection of the respective storage cassette,

wherein the driven chain wheel is positioned centrally relative to a width of the conveyor system defined by the longitudinal ends of the storage boxes. This feature has surprisingly proved to provide for steady operation over a large range of varying temperature.

In another embodiment, rollers are provided at the longitudinal ends of the storage boxes for supporting the ends of the storage boxes.

In a fifth aspect a cryogenic storage system according to the present invention comprises a thermally insulated housing with a door, a cryogenic area extending inside the thermally insulated housing, a conveyor system inside the housing and the cryogenic area, said conveyor system comprising an endless chain of storage boxes, each storage box having a narrow face with two mutu- ally opposite short sides and two mutually opposite long sides, the storage boxes being linked together at the narrow faces for the long sides of neighbour- ing boxes to be positioned in a side-by-side relationship and to extend perpen- dicular to a chain direction and for the short sides to extend in the chain direc- tion, the endless chain being passed over a driven chain wheel to be driven thereby, and said cryogenic storage system comprising a cooling system, the storage boxes extending from the narrow face to an opening opposite the nar- row face and being configured for accommodating a number of storage cas- settes insertable through the opening into the storage box in a longitudinal di- rection of the respective storage cassette,

said storage cassettes being configured to receive a plurality of stor- age containers for accommodating e.g. bags containing a portion of blood, wherein each storage cassette is longitudinal and configured to be inserted in the storage box in a longitudinal direction of the storage cassette, the storage cassette having a first longitudinal end and an opposite second longitudinal end, a longitudinal bottom extending between the two longitudinal ends and an open longitudinal top opposite the longitudinal bottom.

In a further embodiment the longitudinal bottom comprises an opening for receiving a pushing element to push a storage container towards the open longitudinal top.

In a further embodiment said opening extends longitudinally in the lon- gitudinal bottom between the two longitudinal ends.

Two or more of the different aspects may advantageously be used to- gether. Especially the second, the third and the forth aspect has surprisingly proved to provide synergetic effects, when two or more of these three aspects are used together, improving greatly the reliability of the operation of the cryo- genic storage system over a large range of temperature variation from installa- tion conditions at e.g. normal surrounding temperature at e.g. 15°C to 40°C to cryogenic storage operating temperatures at -80° to -200°C.

In the following the invention will be explained in further detail by way of examples of embodiments having reference to the accompanying drawings, in which

Fig. 1 shows an embodiment of a cryogenic storage according to the invention;

Fig. 2 shows the cryogenic storage of Fig. 1 omitting a thermally insu- lating housing thereof;

Fig. 3 shows a detail of a longitudinal section of the cryogenic storage of Fig. 1 ,

Fig. 4 is a perspective view of a storage box of the cryogenic storage seen in a first direction;

Fig. 5 is a perspective view showing three storage boxes linked to- gether and seen in a second direction;

Fig. 6 is a perspective view of a cassette;

Fig. 7 is a schematic representation of a cooling system of the cryo- genic storage system of the invention;

Fig. 8 is a schematic representation illustrating another embodiment of a cooling system of the cryogenic storage system of the invention; and

Fig. 9 is a schematic representation of a third embodiment of a cooling system of the cryogenic storage system of the invention.

A cryogenic storage system according to the present invention corn- prises a cryogenic storage having a thermally insulated housing 1 with a door 2, and a conveyor system 3 inside the housing. The door 2 may be provided by a door module 2a configured as disclosed in the applicant’s published inter- national patent application, publication No. WO 2013/034156 A2, which is in- corporated herein by reference. In general, some embodiments of the cryo- genic storage of the invention involve a great deal of similarity with the appli- cant’s older“Device for deep-freezing potions of organic material” disclosed in published international patent application, publication No. WO 2008/083685 A2, which is incorporated herein by reference. However, the present invention differs from the older device by a number of new and inventive features ex- plained herein.

The conveyor system 3 comprises an endless chain of storage boxes

4. Each storage box 4 has a narrow face 5 with two mutually opposite short sides 6 and two mutually opposite long sides 7. The storage boxes 4 are linked together at the narrow faces 5 for the long sides 7 of neighbouring boxes 4 to be positioned in a side-by-side relationship and to extend perpendicular to a chain direction 8 and for the short sides 6 to extend in the chain direction 8 (Fig.

5.

The endless chain is passed over a driven chain wheel 9 (Fig. 3) to be driven thereby. Thus the endless chain is passed around the driven chain wheel 9 through an angle which in the present embodiment is approximately 180°.

The cryogenic storage system comprises a cooling system to be ex- plained further below. The insulated housing 1 comprises openings 10 for con- duits of external parts of the cooling system to communicate with the interior of the insulated housing 1 . Further the thermally insulated housing 1 is shown in Fig. 1 to comprise an inspection door 1 a.

The insulated housing is preferably insulated by means of vacuum in- sulation panels (VIP).

The storage boxes 4 are respectively extending from the narrow face 5 to an opening 1 1 opposite the narrow face 5. The storage boxes 4 are each configured for accommodating a number of storage cassettes 60 (Fig. 6) in- sertable through the opening 1 1 into the storage box 4 in a longitudinal direction of the respective storage cassette 60.

According to the present invention a position sensor 12, 13 is config- ured to sense the presence of a storage box 4 in a sensing position in the vicinity of the door 2 as schematically indicated in Fig. 3. The position sensor may be in accordance with a concept known per se and it may e.g. comprise an optical sensor 12 including a light emitter mounted on a frame part 14 of the conveyor system while a protrusion 13 with a reflector is positioned on each storage box 4 to pass the optical sensor 12 closely when the conveyor system is operating moving the storage boxes around in a loop provided by the endless chain. Other embodiments of the position sensor are possible and conceivable to the skilled person.

Further each storage box 4 may be provided with a machine detecta- ble identification label 16 unique to the respective storage box 4 and a reader or sensor 15 configured to identify the label 16 may be provided, e.g. mounted on the frame part 14. Such identification label 16 may be a RFID label and the reader 15 may correspondingly be a RFID reader.

According to the present invention the door is positioned at an end of the conveyor system comprising the driven chain wheel 9 as indicated in Fig. 3, in which however, only the position 17 of the door is indicated, while the door per se together with one of the storage boxes in the endless chain of storage boxes 4 next to the door has been omitted from Fig. 3 to reveal other details. Thus the door 2 is positioned vis-a-vis the driven chain wheel 9 on an opposite side relative to the endless chain of storage boxes 4. The driven chain wheel 9 is mounted on a shaft 18 coupled directly to a motor 19, which in the present embodiment is a torque motor. The motor 19 is seen in Figs. 1 and 2 that are showing the apparatus from the opposite side relative to Fig. 3. As seen in Fig. 1 , the motor 19 is positioned outside the thermally insulating housing 1 to avoid a need to drain heat from the motor away from the inside of the thermally insu- lated housing 1 . Further according to the invention the driven chain wheel 9 is posi- tioned centrally relative to a width of the conveyor system defined by the longi- tudinal ends of the storage boxes 4.

Like disclosed in the above mentioned WO 2008/083685 A2, at the longitudinal ends of the storage boxes 4, rollers 20 are provided for supporting the ends of the storage boxes.

According to the present invention a chain roller 21 is provided cen- trally at the narrow face 5 to rotate around an axis extending in the longitudinal direction of the storage box perpendicular to the chain direction 8 for cooperat- ing with the driven chain wheel 9 in engagement therewith during operation, as schematically indicated in Fig. 3.

The storage cassettes 60 (cf. Fig. 6) are configured to receive a plu- rality of storage containers for accommodating e.g. bags containing a portion of blood. The storage cassettes are longitudinal and configured to be inserted in one of the storage boxes 4 in a longitudinal direction 61 of the storage cas- sette 60. The storage cassettes each has a first longitudinal end 62 and an opposite second longitudinal end 63, a longitudinal bottom 64 extending be- tween the two longitudinal ends 62, 63 and according to the present invention the storage cassette 60 has an open longitudinal top 65 opposite the longitudi- nal bottom 64. Further the longitudinal bottom 64 comprises an opening 66 for receiving a pushing element (not shown) to push a storage container towards the open longitudinal top 65 and said opening 66 extends longitudinally in, and substantially throughout, the longitudinal bottom 64 between the two longitudi- nal ends 62, 63. The storage cassettes 60 are, like the storage cassettes dis- closed in the above mentioned WO 2008/083685 A2, provided with a locking mechanism for locking the storage cassettes 60 to the storage boxes 4 when inserted therein.

The present inventors have realized that, whereas the storage cas- settes of WO 2008/083685 A2 are provided with lockable and openable lids, the storage boxes 4 per se actually fulfils the function of a lid, once the storage cassette have been inserted in a storage box and accordingly the lids can be dispensed with.

Corresponding to the safety tracks for cassettes disclosed in WO 2008/083685 A2, Fig. 14, the apparatus of the present invention comprises guide rails 22 extending below the chain of storage boxes and at either end of the conveyor system as seen in Figs. 2 and 3 to secure that the storage cas- settes do not unintentionally slip out of the storage cassettes in case a locking mechanism of a storage cassette should fail.

Whereas the apparatus according to WO 2008/083685 A2 is cooled by liquid nitrogen which is contained in a cooling tank positioned within the chassis of the apparatus, the cryogenic storage system of the present invention comprises a cooling system which is configured to introduce a dry gas corn- prising a combination of approx. 78% - 85% nitrogen and approx. 15% - 21 % oxygen and to maintain and/or circulate said dry gas at cryogenic temperature in the insulated housing.

Flereby is obtained that any gas leaking form the thermally insulated housing will not represent a hazard to persons present in the vicinity of the cryogenic storage due to risk of suffocation. Further, by using dry gas formation of ice inside the cryogenic storage is avoided. It is noted that atmospheric air contains approx. 78% nitrogen, approx. 21 % oxygen and approx. 1 % argon.

Fig. 7 illustrates schematically a first embodiment of the cooling sys- tem of the cryogenic storage system. The embodiment in Fig. 7 comprises a storage of liquid nitrogen 130 and a storage of liquid oxygen 131 , e.g. pressur- ized tanks as it is known per se, and control means for controlled dosing of the nitrogen and oxygen to respective evaporators 132a and 132b for introduction of cryogenic nitrogen gas and cryogenic oxygen gas into the cryogenic area. The evaporators 132a and 132b are heat exchangers and by allowing the liquid gas, respectively nitrogen gas and oxygen gas, to evaporate on one side of a heat exchange wall 132a’, 132b’ (schematically indicated in Fig. 7) of the re- spective heat exchanger 132a, 132b and flowing air from the inside of the in- sulated housing 1 past the other side of the heat exchange wall 132a’, 132b’ as indicated by a schematically shown propeller or fan 134, it is obtained that the air inside the cryogenic area is cooled while the liquid nitrogen gas and oxygen gas is evaporated and heated, before the latter is led out of the heat exchanger 132a, 132b to be mixed with the air inside the cryogenic area. In this manner a good distribution of the cryogenic gas inside the thermally insulated housing 1 is obtained and thereby an even distribution of the temperature inside the thermally insulated housing 1 is likewise obtained.

The control means for controlled dosing of the nitrogen and oxygen to the evaporators 132a, 132b comprise, respectively, in a manner known per se by the skilled person, a pressure regulator 135a, 135b, a flow gauge 136a, 136b, and, in series, a stop valve 137a, 137b and a controllable throttle valve 138a, 138b arranged in parallel a proportional valve 139a, 139b.

Inside the thermally insulated housing 1 a temperature sensor 140 is provided.

Further the cooling system comprises a controller 141 , such as a com- puter, receiving input from the flow gauges 136a, 136b and the temperature sensor 140, and providing output to at least the proportional valves 139a, 139b and possibly also to the other adjustable valves such as the pressure regulators 135a, 135b, the stop valves 137a, 137b and controllable throttle valves 138a, 138b.

Based on the measurements of the flow gauges 135a, 135b and the temperature sensor 140 the flows of nitrogen and oxygen, respectively, are regulated, by control action of the controller 141 , to keep the temperature inside the thermally insulated housing within a pre-set range and keep the rate of the flows of nitrogen and oxygen within a pre-set range providing a mixture of ap- prox. 78% - 85% nitrogen and approx. 15% - 22% oxygen.

The system may also comprise an air sensor 142, such as an oxygen gauge, for sensing the percentage of e.g. oxygen in the air inside the thermally insulated housing. The values measured by the air sensor 142 may be used for feed back to the controller 141 for regulating the ratio between nitrogen and oxygen fed to the system.

Thus in operation, the pressure regulators 135a, 135b reduce the pres- sure of the liquid gas to a preset value and the flow gauges 136a, 136b measures the amount of liquid gas flowing trough the system. In a start-up phase, when much cooling is needed, the stop valves 137a, 137b are open and liquid gas flow to the evaoprators 132a, 132b through the controllable throttle valves 138a, 138b as well as through the proportional valves 139a, 139b. When a desired operation temperature has been reached, the stop valves 137a, 137b are closed and the temperature in the thermally insulated housing 1 is kept constant by regulating the proportional valves 139a, 139b.

Since a certain amount of heat energy flows into the cryogenic area over time due to the thermally insulation being not perfect, though good, and due to items being inserted into and removed from the interior of the thermally insulated housing, liquid nitrogen gas and liquid oxygen gas is correspondingly introduced into the evaporators or heat exchanges 132a, 132b to compensate for said heat flow into the cryogenic area and thereby keep the temperature within the pre-set range. Thereby, however, nitrogen and oxygen gas is added to the contents of gas of the thermally insulated housing or the cryogenic area. A slight overpressure relative to the surroundings may accordingly be present inside the thermally insulated housing that prevents surrounding air penetrating into the cryogenic area through any leaks such as the door, but apart from that, surplus gas inside the cryogenic area is vented through a vent (not shown), preferably to an area (not shown) next to the thermally insulated housing 1 , in which area the temperature is about -20°C, and from which area surplus air is vented to surroundings at e.g. room or outside temperature.

Fig. 8 illustrates schematically how a second embodiment of the cool- ing system of the cryogenic storage system comprises a cryogenic air cooling device configured to generate dry, liquid, cryogenic, atmospheric air to be evap- orated into dry, cryogenic gas in the thermally insulated housing, said cryogenic cooling device comprising an air compressor, an air dryer, and a cryogenic air cooler. Thus Fig. 8 shows an inlet 241 for atmospheric air, an air compressor 242, an air filter 243, an air dryer 244, a cryogenic air cooler 245, a storage tank 246 for storing temporarily dry, liquid, cryogenic, atmospheric air, and a controllable valve 247. The storage tank 246 is in a manner known per se pro- vided with a safety valve 246a. A cryogenic air cooling device generally of this kind is commercially available e.g. from DH Industries under the brand“Stirling Cryogenics”.

In use, atmospheric air is sucked in through the inlet 241 by the com- pressor 242 and is led through the air filter 243 and the air dryer 244 to the cryogenic air cooler 245 whereby the air is transformed into a cryogenic, liquid state before it is led into the storage tank 246. Via the controllable valve 247 cryogenic fluid, i.e. the dry, liquid, cryogenic atmospheric air from the storage tank 246, is led into a heat exchanger 232 inside the thermally insulated hous- ing 1 or the cryogenic area to sweep over a first side of a heat exchange wall 232’ (schematically indicated in Fig. 8) of the heat exchanger 232. Similar to the embodiment in Fig. 7 a schematically indicated propeller or fan 234 flows air from the inside of the thermally insulated housing 1 past a second side of the heat exchange wall 232’. By allowing the dry, liquid, cryogenic atmospheric air to evaporate on the first side of the heat exchange wall 232’ of the heat exchanger and flowing air from the inside of the cryogenic area 1 past the other side of the heat exchange wall 232’ as indicated by the schematically shown fan 234, it is obtained that the air inside the thermally insulated housing 1 is cooled while the dry, liquid, cryogenic atmospheric air is evaporated and heated, before the latter is led out of the heat exchanger 232 to be mixed with the air inside the cryogenic area. In this manner a good distribution of the cry- ogenic gas inside the thermally insulated housing 1 is obtained and thereby an even distribution of the temperature inside the thermally insulated housing 1 is likewise obtained.

A temperature sensor 240 is provided inside the thermally insulated housing, and further a controller 248, such as a computer, is provided for re- ceiving input from the temperature sensor 240, and providing output to the con- trollable valve 247.

In operation, based on the output of the temperature sensor 240, the controllable valve 247 is regulated, by control action of the controller 248, to provide a flow of the cryogenic fluid to keep the temperature inside the cryo- genic area within a pre-set range.

As with the first embodiment, since a certain amount of heat energy flows into the cryogenic area over time due to the thermally insulation being not perfect, though good, and due to items being inserted into and removed from the interior of the thermally insulated housing, dry, liquid, cryogenic, atmos- pheric air is correspondingly introduced into the evaporator or heat exchange 232 to compensate for said heat flow into the cryogenic area and thereby keep the temperature within the pre-set range. Thereby, however, dry, cryogenic, atmospheric air is added to the contents of gas of the thermally insulated hous- ing or the cryogenic area. A slight overpressure relative to the surroundings may accordingly be present inside the cryogenic area that prevents surround- ing air penetrating into the thermally insulated housing through any leaks such as the door, but apart from that, surplus gas inside the thermally insulated hous- ing is vented, as described in relation to Fig. 7.

In a variant of the embodiment shown in Fig 8, the air sucked in through the inlet is cooled and compressed to a cryogenic gaseous state, but not into liquid state, whereby an overall saving of energy may be obtained corn- pared to the embodiment described above with reference to Fig. 8. Intermedi- ate storing of gas however, is more challenging than storing of liquid.

Thus in a third embodiment the cooling system comprises a cryogenic air cooling device configured to generate dry, cryogenic, atmospheric air to be entered into the cryogenic area, said cryogenic cooling device comprising an air compressor 242’, an air dryer 244’ and a cryogenic air cooler 245’, and pref- erably also an air filter 243’ like the cryogenic air cooling device described above with reference to Fig. 8.

In the third embodiment cryogenic fluid, that in this case is dry, gase- ous, cryogenic, atmospheric air, may be led into a heat exchanger like the cry- ogenic fluid is in the second embodiment, in order to heat the cryogenic fluid before it enters into the interior of the thermally insulated housing, but it is also possible to provide for merely mixing, preferably in a separate chamber, the cryogenic fluid with the air already inside the cryogenic area to provide for a good distribution of the cryogenic gas inside the thermally insulated housing 1 and an even distribution of the temperature inside the thermally insulated hous- ing 1 . Referring to Fig. 9, in a forth embodiment of the cryogenic storage sys- tem the cooling system comprises at least one heat exchanger configured to exchange heat between the dry gas circulated in the thermally insulated hous- ing and a cryogenic fluid, the heat exchanger comprising a heat exchange wall, and the heat exchanger being configured for the cryogenic fluid to sweep a first side of the heat exchange wall and the dry gas circulated in the thermally insu- lated housing to sweep a second side of the heat exchange wall, wherein the cryogenic fluid is contained in a closed cooling circuit.

Thus the embodiment shown in Fig. 9 comprises a closed cooling cir- cuit comprising a first storage tank 346 for a cryogenic liquid, an evaporator or heat exchanger 332 positioned inside the cryogenic area of the cryogenic stor- age system, a first conduit connection between the storage tank 346 and the heat exchanger 332 said first conduit connection comprising a controllable valve 347, a second conduit connection between the heat exchanger 332 and the storage tank 346 said second conduit connection comprising a first com- pressor 349, and a cryogenic gas cooler and liquefier 345 connected to the storage tank 346 through an upper gas conduit and a lower liquid conduit. The storage tank 346 comprises a safety valve 346a.

For the cryogenic liquid breathability need not be considered like for the embodiments in which the cryogenic liquid ends up as air inside the ther- mally insulated housing 1 with the prospect of leaking to the surroundings. Ac- cordingly, any liquid having appropriate characteristics, e.g. in respect of evap- oration temperature, may be chosen.

Further, the cryogenic storage system in this forth embodiment corn- prises a refilling line connected to the inside of the cryogenic area, said refilling line comprising an inlet 341 for atmospheric air, an air compressor 342, an air filter 343, an air dryer 344, a second storage tank 350, and a second controlla- ble valve 351.

Also the cryogenic storage system of this forth embodiment comprises a temperature sensor 340 for sensing the temperature inside the thermally in- sulated housing, a pressure gauge 352 for sensing a pressure difference be- tween the inside of the thermally insulated housing 1 and the surroundings, and a fan 334 for providing for a flow of the air inside the cryogenic area to sweep over a second side of heat exchange wall 332’ (schematically indicated in Fig. 9) of the heat exchanger 332 while cryogenic liquid from the first storage tank 346 is introduced to a first side of said heat exchange wall 332’. Further the cryogenic storage system comprises a controller 348, such as a computer.

In operation of this forth embodiment of the cryogenic storage system, in order to compensate for a flow of heat energy into the cryogenic area due to the thermally insulation being not perfect, though good, and due to items being inserted into and removed from the interior of the thermally insulated housing, the air inside the cryogenic area is swept over the second surface of the heat exchange wall 332’ of the heat exchanger 332 by means of the fan 334, to be cooled by cryogenic liquid evaporating at the first surface of the heat exchange wall 332’ of the heat exchanger 332. The cryogenic liquid that has evaporated in the heat exchanger 332 is transferred as return gas to the first storage tank 346 by action of the first compressor 349. The return gas is extracted form the first storage tank 346 by the cryogenic gas cooler and liquefier 345, which corn- presses and cools the return gas into a cryogenic liquid state before it is led back into the first storage tank 346 as cryogenic liquid. The cryogenic liquid is led from the first storage tank 346 back into the heat exchanger 332 under control of the controllable valve 347. Thus cryogenic liquid is led into the evap- orator or heat exchanger 332 under the control of the controllable valve 347 which in turn is controlled by the controller 348 based on measurements of the temperature sensor 340, to keep the temperature in the cryogenic area within the pre-set range.

While at the three former embodiments of the cryogenic storage sys- tem, cryogenic gas or air is added to the contents of gas of the thermally insu- lated housing or the cryogenic area in correspondence with the cooling of the cryogenic area, thereby possibly providing a slight overpressure relative to the surroundings that prevents surrounding air penetrating into the thermally insu- lated housing through any leaks such as the door, such effect is not present with the present forth embodiment.

To ensure that air leaking from the thermally insulated housing 1 is not replaced by possibly humid, surrounding air, dry, atmospheric air is fed from the second storage tank 350 of the refilling line to maintain a slight overpres- sure inside the thermally insulated housing 1. Thus dry, atmospheric air is added from the second storage tank 350 under the control of the second con- trollable valve 351 which in turn is controlled by the controller 348 based on measurements of the pressure gauge 352. The contents of the second storage tank 350 is supplemented by action of the air compressor 342 under control of the controller 348 based on measurements of a second pressure gauge (not shown) in the second storage tank 350.

Claims

P A T E N T C L A I M S

1 . A cryogenic storage system comprising a thermally insulated hous- ing (1 ) with a door (2), a cryogenic area extending inside the thermally insulated housing (1 ), a conveyor system (3) inside the housing and the cryogenic area, said conveyor system comprising an endless chain of storage boxes (4), each storage box (4) having a narrow face (5) with two mutually opposite short sides (6) and two mutually opposite long sides (7), the storage boxes being linked together at the narrow faces for the long sides of neighbouring boxes to be positioned in a side-by-side relationship and to extend perpendicular to a chain direction (8) and for the short sides to extend in the chain direction, the endless chain being passed over a driven chain wheel (9) to be driven thereby, and said cryogenic storage system comprising a cooling system, the storage boxes ex- tending from the narrow face to an opening (1 1 ) opposite the narrow face, c h a r a c t e r i z e d in that

the door (2) is positioned at an end of the conveyor system (3) corn- prising the driven chain wheel (9).

2. A cryogenic storage system according to claim 1 , wherein the driven chain wheel (9) is mounted on a shaft (18) coupled directly to a motor (19), preferably a torque motor.

3. A cryogenic storage system according to claim 1 or 2, further corn- prising a position sensor (12) configured to sense the presence of a storage box in a sensing position in the vicinity of the door (2).

4. A cryogenic storage system according to claim 3,

wherein the position sensor is an optical sensor (12), whereby the stor- age boxes may be configured to intersect to cut off or reflect a beam of light when present in the sensing position.

5. A cryogenic storage system according to any one of claims 1 to 4, wherein each storage box (4) is provided with a machine detectable identifica- tion (16) unique to the respective storage box.

6. A cryogenic storage system according to any one of the claims 1 to 5, wherein the driven chain wheel (9) is positioned centrally relative to a width of the conveyor system (3) defined by the longitudinal ends of the storage boxes (4).

7. A cryogenic storage system according to any one of claims 1 to 6, wherein rollers (20) are provided at the longitudinal ends of the storage boxes for supporting the ends of the storage boxes.

8. A cryogenic storage system according to any one of claims 1 to 7, wherein the storage boxes are configured for accommodating a number of stor- age cassettes (60) insertable through the opening into the storage box (4) in a longitudinal direction of the respective storage cassette (60).

9. A cryogenic storage system according to claim 8, wherein said stor- age cassettes (60) are configured to receive a plurality of storage containers for accommodating e.g. bags containing a portion of blood, wherein each stor- age cassette (60) is longitudinal and configured to be inserted in the storage box in a longitudinal direction (61 ) of the storage cassette, the storage cassette having a first longitudinal end (62) and an opposite second longitudinal end (63), a longitudinal bottom (64) extending between the two longitudinal ends and an open longitudinal top (65) opposite the longitudinal bottom.

10. A cryogenic storage system according to claim 9, wherein the Ion- gitudinal bottom (64) comprises an opening (66) for receiving a pushing ele- ment to push a storage container towards the open longitudinal top.

11. A cryogenic storage system according to claim 10, wherein said opening (66) extends longitudinally in the longitudinal bottom (64) between the two longitudinal ends (62, 63).