Background of the Invention When liquid products, such as liquid foods (e. g. milk) and different types of medicine, are sterilised the product may be heated to a sufficient temperature during a required period of time for killing micro- organisms.

In a continuous process, this can be achieved by continuously supplying the product to a heating tank, from which the product is then continuously passed on.

In this context the product is supplied to and discharged from the tank through an inlet and an outlet respec- tively, which are normally arranged at opposite ends of the tank. Accordingly, the flow through the tank will be random to some extent and, therefore, a situation might occur where the discharged product has not been in the tank long enough for adequate killing to take place.

Moreover, the microorganisms have the ability to travel in the product in a way that differs from the flow pat- tern of the product. Thus even if the product remains in the tank during the required period of time this does not mean that the microorganisms will do so. Consequently, satisfactory killing of undesired microorganisms is not assured.

Admittedly, it is possible to make sure that a suf- ficient temperature is maintained in the product as it is discharged from the tank by insulating the discharge of the tank. In this way, it is possible to extend the time during which the product is heated. Again though, there is a chance that the microorganisms spread in the

product contained in the conduit at a speed that is higher than the flow speed of the product. Thus the risk of contaminaticn of an already sterilised product remains.

A way of achieving reliable killing of micro- organisms would be, in principle, to heat the flow of products over an extremely long distance. However, such a device would require quite a large space.

Summary of the Invention The object of the present invention is thus to provide an improved device for reliable killing of micro- organisms in a fluid flow of products and an improved corresponding method.

Above and in the following description killing of microorganisms means killing of such microorganisms that, for different reasons, are not desirable in the flow of products once sterilisation has been completed. Thus other microorganisms, which, for example, are not in- jurious to the health or do not affect the product durability and which require a higher temperature and/or a longer period of time to be killed, may be allowed to survive the sterilisation of the flow of products.

In order to achieve the object a device according to claim 1 and claim 11 as well as a method according to claim 12 and claim 16 are provided. Preferred embodiments of the device and the method are apparent from claims 2- 10, which are dependent on claim 1, and claims 13-15, which are dependent on claim 12. The invention also relates to use of a device according to the invention according to claim 17.

More specifically, according to the present inven- tion, a device is provided for killing microorganisms in a fluid flow of products, the device being characterised by a duct means made of a flexible material for conveying a flow of products heated to a predetermined temperature and a delimiting means comprising, for the purpose of de- limiting non-intercommunicating subvolumes of the duct

means and of transporting through the duct means a sub- quantity of the flow of products contained in each sub- volume, pressing means that, alternately and in a start- ing position along the duct means, are adapted to engage with the duct means for compression thereof and, while maintaining said engagement, to move along a portion of the duct means, two succeding pressing means thus de- limiting between them a subvolume that does not commu- nicate with the rest of the volume of the duct means.

Thus a device is provided that ensures that a flow of products supplied to it and heated to a predetermined temperature is divided into separate subquantities, which during transport through the duct means are kept apart from each other. It is therefore not possible for the microorganisms to travel from one subquantity to another.

Accordingly, once the subquantities are finally dis- charged from the device it is possible to ensure that they are sterile, which makes it possible to achieve a reliable sterilisation of the entire flow of products.

According to a preferred embodiment of the present invention, the device comprises a means for maintaining a relevant temperature in the heated flow of products.

This means may, for example, ensure that an amount of steam is introduced into the subvolume with each sub- quantity of the flow of products, said steam maintaining the required temperature. Alternatively, said means may serve to insulate the device.

Preferably, the delimiting means is adapted to transport each subquantity during a period of time re- quired for killing the microorganisms in each subquantity at the temperature concerned. Thus it becomes possible to ensure that each subquantity is retained at the relevant temperature during the time required for killing the microorganisms, whereby most reliable killing of the microorganisms is achieved.

Preferably, the subvolumes delimited by the de- limiting means are constant in terms of volume. It will

be appreciated, however, that the subquantities of the flow of products contained in the respective subvolumes need not be constant in terms of volume.

The delimiting means of the device is preferably adapted to connect the subvolume, after said transport of a subquantity of the flow of products contained in the respective subvolumes, with a portion of the duct means located downstream of the subvolume and to delimit a new subvolume. This results in a cyclically operating device that feeds the flow of products.

According to another preferred embodiment of the device, each pressing means is adapted to discontinue its engagement after said move and to return to said starting position. Here, the clamping means are preferably each supported by an arm arranged on a common rotatable shaft, and the duct means is preferably concentrically arranged around said shaft in a helical path, the subquantity of the flow of products contained in each subvolume being fed through the duct means by the rotation of the shaft.

The shaft is advantageously arranged in the centre of a cylindrical housing, wherein the clamping means are adapted to compress the duct means against the inner wall of the housing.

The housing may be pressurised to provide a pressure outside the duct means similar to the one inside the duct means. This allows use of a duct means, which certainly is resistant to mechanical pressure, but which is less resistant to pressure differences between the inside and the outside of the duct means.

The duct means may be arranged in one, two or more turns, not necessarily complete ones, around said rotat- able shaft.

The embodiments described above and the variants of the device according to the invention may, of course, be combined in an optional way.

According to the present invention, a device for killing microorganisms in a fluid flow of products is

further provided, which is characterised by a duct means for conveying a flow of products heated to a predeter- mined temperature and a delimiting means adapted to de- limit non-intercommunicating subvolumes of the duct means and to transport a subquantity of the flow of products contained in each subvolume through the duct means, means being arranged for maintaining the relevant temperature during said transport of the subquantities of the flow of products.

According to the present invention, a method for killing microorganisms in a fluid flow of products is further provided, which is characterised by the steps of heating the flow of products to a predetermined tempera- ture, feeding the flow of products to a duct means made of a flexible material, engaging, alternately and in a starting position along the duct means, with the duct means for compression thereof by means of clamping means, two succeeding pressing means thus delimiting between them a subvolume that does not communicate with the rest of the volume of the duct means, and of transporting, by moving the pressing means along a portion of said duct means while maintaining said engagement, a subquantity of the flow of products contained in each subvolume, and thus separated from the rest of the flow of products, through the duct means while maintaining the relevant temperature.

Accordingly, a method is provided, which in a reli- able way allows killing of microorganisms in the flow of products.

Preferably, a subquantity of the flow of products contained in each subvolume is transported through the duct means during the period of time required for killing the microorganisms in the respective subquantities at the temperature concerned.

Preferably, each delimited subvolume is essentially constant in terms of volume.

Preferably, the method further comprises the step of feeding a steam flow to the duct means together with the flow of products, whereby each subvolume is filled on the one hand with a subquantity of the flow of products and, on the other hand, with a subquantity of the steam flow.

In this way, it is easy to ensure that the required tem- perature is maintained in the flow of products.

According to the present invention, a method for killing microorganisms in a fluid flow of products is further provided, which is characterised by the steps of heating the flow of products to a predetermined tempera- ture, feeding the flow of products to a duct means, de- limiting non-intercommunicating subvolumes of the duct means, and transporting a subquantity of the flow of products contained in each subvolume, and thus separated from the rest of the flow of products, through the duct means while maintaining the relevant temperature.

Finally, also use of a device as defined above is provided according to the invention.

The present invention will now be described for exemplifying purposes with reference to the accompanying drawings.

Brief Description of the Drawings Fig. 1 is a side view of an embodiment of the device according to the present invention.

Fig. 2 is a partly sectioned side view of the device shown in Fig. 1.

Fig. 3 is a top plan view of the device in Fig. 1, where a lid of the device has been removed.

Description of Embodiments With reference to Figs 1-3, a device is illustrated for killing microorganisms according to a preferred em- bodiment of the present invention.

The device comprises a cylindrical housing 1, the bottom end of which is sealed by means of a bottom plate 2 and the top end of which is sealed by means of a lid 3.

Inside the housing, a shaft 4 is arranged extending along the longitudinal centre axis of the housing 1. The shaft 4 is rotatably mounted in the lid 3 of the housing 1. The shaft 4 supports a delimiting means 5, which com- prises four holding means 6 evenly distributed around the circumference. In each holding means 6 an arm 7 is mounted, which extends towards the inner wall 8 of the housing 1. Each arm 7 supports, in turn, a pressing means in the form of a roller 9 extending parallel to the inner wall 8. As shown in Fig. 2, the rollers 9 have a length that essentially corresponds to the height of the cylin- drical housing 1. Each arm 7 comprises a fixing means 10 allowing adjustment of the bearing pressure of the roller 9 against the inner wall 8. The shaft 4 is rotatable with the aid of a driving means (not shown), whereby the rollers 9 are rotatable within the housing 1 along its inner wall 8.

Furthermore, a duct means in the form of a tube 11 is concentrically arranged around the shaft 4, thus ex- tending along the inner wall 8 of the housing 1, between said wall 8 and the rollers 9. The tube 11 is made of a flexible material and extends one and a half turns in a helical/spiralling path around the shaft 4 between an in- let 12 and an outlet 13, which is indicated in Fig. 2 by a dash-dotted line between the inlet 12 and the out- let 13. Naturally, the number of turns by which the tube 11 extends around said shaft 4 is not limited to the number shown. Consequently, both a greater and a smaller number of turns, not necessarily complete ones, are con- ceivable. The inlet 12 and the outlet 13 connect tangen- tially, on opposite sides, to the housing 1 and are ori- ented the same way and vertically offset.

Connecting conduits 14,15 are connected to the inlet 12 and the outlet 13.

When using the device according to the invention a heated and pressurised fluid flow of products is supplied to the device through one of the connecting conduits 14.

Said heating may, for example, be effected by supplying the flow of products in the form of drops and/or film to a volume filled with steam. More specifically, the heated flow of products is fed to the tube 11 of the device through the inlet 12. The shaft 4 is rotated in the di- rection indicated by the arrow in Fig. 3.

During the rotation of the shaft 4, the rollers 9 will be moved along the tube 11. Furthermore, the engage- ment of each roller 9 with the tube 11 will result in a compression of the tube 11. Consequently, two subsequent rollers 9 will delimit between them a subvolume dV sepa- rated from the remaining volume of the tube 11. Thus the subvolumes dV delimited by the engagement of the rol- lers 9 with the tube 11 cannot communicate with each other.

The subvolumes dV formed by the engagement of the rollers 9 with the tube 11 are essentially constant in terms of volume. It will be appreciated, however, that the subquantities of the flow of products need not be constant in terms of volume.

The device may further comprise a means for main- taining the relevant temperature in the subquantities during their transport through the duct means. Such a means may, for example, be adapted to introduce steam into the respective subvolumes. Thus each subquantity of the flow of products need not fill up its subvolume dV. Accordingly, it is conceivable-as well as prefer- red-that each subquantity only fills up part of its subvolume dV and that steam, preferably at the same positive pressure as the flow of products, fills up the rest of the subvolume dV. The pressure and temperature of the steam ensure that the required temperature can be maintained in each subquantity of the flow of products while being fed through the device. In the above de- scribed case, where the flow of products is heated by introducing it in the form of drops and/or a film to a volume filled with steam, the required temperature can

thereby be ensured by letting a part of the heating medium, i. e. the steam, accompany the flow of products to the device according to the invention at maintained pressure and temperature.

The flow of products that enters through the inlet 12 will thus be continuously supplied to the non-inter- communicating subvolumes dV of the tube 11 and thereby divided into separate subquantities. These subquantities will then be passed on by the rotation of the shaft 4, while being kept apart from each other. A product film may indeed form on the inside of the tube 11 and get in contact with the different subquantities. However, any product film formed will remain in the device for such a long time that the film will become sterile, and there- fore there is no risk of contamination of the different subquantities.

Each subvolume dV and the subquantity of the flow of products contained therein will be passed on through the action of two subsequent rollers 9 so that they, after one and a half turns, may be supplied to the tube segment or part 16 of the tube 11 that leads to the outlet 13 of the device. The front one of the two rollers 9, in the direction of rotation, will by its rotation first connect the subvolume dV with the tube segment 16 downstream of the subvolume dV, whereupon the rear roller 9, during its continued rotation, will press out the subquantity of the flow of products concerned through the tube segment 16 concerned. The same procedure will then be repeated for the following subvolumes dV and the subquantities of the flow of products contained therein during the continued rotation of the shaft 4.

As mentioned previously, the flow of products has been heated when it is fed to the device. In order to achieve the desired killing of microorganisms, each subquantity must be maintained at a predetermined tem- perature for a specific period of time. Accordingly, the killing is a function of time and temperature. This func-

tion means, for example, that a subquantity with a lower temperature must be kept at this temperature for a longer period of time.

For this purpose, the shaft 4 of the device is adapted to rotate at a speed that is adjusted to the temperature of the incoming flow of products as well as to the distance that each subvolume dV and the subquan- tity contained therein is moved. This makes it possible to ensure that each subquantity of the flow of products is maintained at the required temperature during the re- quired period of time. In particular, it is possible to ensure that each subquantity is maintained at an abso- lute, controlled temperature during a required period of time without the risk of local overheating or the risk of too long holding times locally.

In this context, it should be mentioned that the temperature and time need not be set so that all micro- organisms present in the respective subquantities are killed. It may, for example, be enough to ensure that all health-impairing and product-damaging microorganisms are killed. It is also possible that there may be harmless microorganisms, which survive the processing. Conse- quently, what is important is that time and temperature are adjusted so that a number of pre-selected types of microorganisms are killed.

As mentioned previously, the duct means is prefer- ably composed of a tube 11 made of a flexible material, preferably a plastic material. Such a tube 11 presents several advantages.

The tube 11 is particularly easy to clean. This is done by the introduction of a cleaning agent into the device, which is operated as usual. The lack of corners, gaps and the like in the tube 11 ensures an excellent cleaning result.

Furthermore, the tube 11 is easily replaced. This can be done when the tube 11 is worn-out or as an alter- native to cleaning the tube 11.

The tube 11 being made of a plastic material it does not have the same burning effect as, for example, a stain- less steel pipe that is heated to the same temperature.

Thus, if the flow of products consists of milk, the prob- lem associated with steel pipes, i. e. the milk being burnt when it makes contact with the hot inner wall of the pipe, is avoided.

Certain flexible plastic materials resist mechanical pressure well, whereas their resistibility to pressure differences is limited. There is therefore a risk that a tube 11 made of such a material will be exposed to great stress, since the flow of products is normally introduced into the tube 11 at a pressure of 2-5 bars and the pres- sure inside the device, on the outside of the tube 11, is either atmospheric or slightly negative. To solve this problem the housing 1 of the device is preferably pres- surised in order to obtain a similar pressure on the in- side and outside of the tube 11. By ensuring that the pressure on the outside of the tube 11 is constant, alterations of the shape of the tube 11 caused by pres- sure differences are avoided, which in turn ensures that the subvolumes dV formed by the engagement of the rollers 9 with the tube 11 remain essentially constant in terms of volume.

As mentioned above the flow of products fed to the device is preferably pressurised. This allows the flow of products to be kept at a sufficiently high temperature without boiling. Moreover, the device works advantage- ously against an atmospheric pressure or a slightly negative pressure, which, for example, may mean that the outlet 13 is connected to a tank (not shown) with atmos- pheric pressure. Once a connection is established between a subvolume dV and the tube segment 16, which in turn is connected with the outlet 13, the subquantity of the flow of products contained in the subvolume dV will be sucked out of the subvolume dV, through the outlet 13 and into

the tank. Accordingly, a fast and reliable evacuation of the subvolumes dV is achieved.

According to the invention, a device is thus pro- vided that allows reliable killing of microorganisms.

More specifically, this is achieved by dividing the flow of products into separate subquantities, which are then kept apart during a period of time that, depending on the temperature of the flow of products, is sufficient to en- sure that the desired microorganisms are killed. The risk of the microorganisms spreading in the flow of products and contaminating an already sterilised product is there- by eliminated.

It will be appreciated that the invention is not limited to the embodiment shown. Several modifications and variations can be achieved within the scope of the invention. Thus the scope of the invention is defined solely by the appended claims.