METHOD AND APPARATUS FOR THE PASTEURIZATION OF LIQUID PRODUCTS IN A CONTINUOUS FLOW

Abstract: According to the invention, the object of the method and the appartus associated herewith is to avoid the disadvantages which arise in a plate pasteurizing apparatus for the pasteurizing of a liquid product in a continuous flow during and after a stop in production. When pasteurizing with known plate pasteurizing apparatus, the product is led through a holding pipe, which has the disadvantage that the temperature in this holding pipe cannot be controlled during a possible stop in production. Therefore, in existing apparatus it is necessary to have a large buffer tank which can contain 1/2 - 1 hour's production, which is very space-demanding. Production in excess of this interval is wasted. According to the invention, this problem is solved by providing each individual zone (6) in the pasteurizing area with a connection (16) for heating (19) and/or cooling (20) of the product, so that in the event of a stop in production it is possible to hold the temperature below the pasteurizing temperature, and upon re-starting to heat the product again to a temperature close to the pasteurizing temperature.

Description: METHOD AND APPARATUS FOR THE PASTEURIZATION OF LIQUID PRODUCTS IN A CONTINUOUS FLOW Description of the invention The invention concerns a method for the pasteurization of a liquid product in a continuous flow in an apparatus which has a heating area, a pasteurizing area and a cooling area, and pump elements for feeding the product in a given flow from the admission opening in the apparatus to its discharge opening through these areas in the order in which they are mentioned, whereby the heating, the pasteurization and the cooling is effected by the transfer of heat between the product in cold and hot state and a liquid, preferably water, which flows through one or more heat exchangers and a holding pipe without temperature regulation in said areas, in that the areas are divided into zones which extend in the product's direction of flow, and the temperature of the water is adjusted in accordance with the course of the heat transfer aimed at in the zone, where one of the part-pasteurization zones is connected to hot and cold water. The invention also concerns an apparatus for the execution of the above method, said apparatus having a heating area, a pasteurization area and a cooling area, and pump elements for feeding the product in a given flow through the areas in the given sequence from the admission opening in the apparatus to its discharge opening, whereby the heating, the pasteurization and the cooling is effected by the transfer of heat between the product in cold and hot state and a liquid, preferably water, which flows through one or more heat exchangers and a holding pipe without temperature regulation in said areas, in that the areas are divided into zones which extend in the product's direction of flow, and the temperature of the water is adjusted in accordance with the course of the heat transfer aimed at in the zone, where one of the part-pasteurization zones is connected to hot and cold water. In the manufacture of products which can be spoiled by bacteria, especially within the foodstuffs industry, it is commonly-known to destroy the bacterial flora by pasteurization, which is a heat treatment which kills the harmful bacteria by exposing them to higher temperatures than they can tolerate. The effect of the pasteurization is measured in PU and depends on the temperature which is used, and on the time for which the product is exposed to this temperature. However, the product is also damaged by intense heating, and demands are therefore placed on the heat treatment with regard to time and temperature. Such a pasteurization of a continuous flow of a liquid product is known e.g. from the brewing industry, in the form of beer or similar products which must later be containerised, for example in bottles. The product to be pasteurised can either be pasteurized before it is transferred to smaller containers, or after the containers have been filled. The following description deals only with a pasteurization process which takes place before the product is transferred to smaller containers, a so- called plate pasteurization. The product flow through a plate pasteurization apparatus will normally take place in the following manner: The product flows into a plate heat exchanger's regenerative part, where energy is exchanged between the cold product on the way in and the hot already-pasteurized product on its way out. The product is thus first heated in the regenerative section, after which it is pumped into the next section of the heat exchanger where it is heated to the pasteurization temperature. The product is now led out into a "holding pipe", the length and flow rate through which is determinative of the pasteurization time. Out of regard for space, the holding pipe is often configured as en elongated spiral. When the product has passed through and reaches the end of the holding pipe, the product has been pasteurized and it is led into the second chamber in the regenerative part of the heat exchanger, where it is cooled down to the discharge temperature by the cold product flowing into the heat exchanger. The pasteurized product can now be filled into a container. In order to adjust the capacity between the filling plant and the pasteurization apparatus, there is often introduced a flow-control valve and a buffer tank. Moreover, use can be made of a cooler if it is desired to further reduce the discharge temperature. A stop in production can occur if other machines, such as e.g. the filling plant or the bottling machine are stopped. A stop in the production line is a problem for a plate pasteurization apparatus, which is dependent on a continuous process in order to achieve the correct processing. During a stoppage, the product in the holding pipe, which has the pasteurization temperature, will not have the possibility of being cooled down. Consequently, the product becomes over-pasteurized and will normally be discarded before the line is re-started. A second problem is to achieve the correct temperatures when the line is re-started. The regenerative section will have the average temperature between the cold and the hot product, while at the same time the supply of heat to the heating section is closed down. Therefore, the "new" product must be discarded until the temperature is correct, or it must be replaced by water which is also discarded. These circumstances result in a loss of resources and not least in a delay in the re-starting of the production. Therefore, the above-mentioned buffer tank will often be introduced after the plate pasteurization apparatus. This buffer tank will normally be capable of containing up to half an hour's production, and can hereby reduce the number of stoppages of the plate pasteurization apparatus. Another way in which this problem can be solved is to provide the plate pasteurization apparatus with a by-pass. Compared with the simple plate pasteurization apparatus, here there is introduced an extra valve which can open for the circulation, so that the pasteurized product can again be used as input to the plate pasteurization apparatus. The function of the cooler during the by-pass is to cool the pasteurized product down to the normal input temperature, so that the temperature balance is maintained through the whole of the plate pasteurization apparatus. The result is that the same product is pasteurized again and again and therefore becomes over-pasteurized. For this reason, the plate pasteurization apparatus will often be filled with water just before it goes into by-pass. Before re-starting, the water must again be replaced by the product. This procedure takes time and results in a great consumption of water and a certain product wastage, which means that a large buffer tank after the plate pasteurization apparatus is necessary in order to reduce the number of times the production line is stopped. The use of a by-pass also has the result that during a stoppage, continuous use is made of the same energy for heating as during operation. Moreover, a corresponding energy is used for the cooling of the product or the water which is circulated. It is therefore the object of the invention to provide a method for avoiding the disadvantages of space-demanding equipment and resource- demanding procedures and to avoid product wastage by over- pasteurization. This object is achieved by a method of the kind disclosed in the introduction, said method according to the invention being characterized in that the pasteurization area is divided into a number of individual pasteurization zones with connections for both heating and cooling, or for the cooling of the product in the event of a stop in production in order to be able to hold the temperature below the pasteurization temperature, and upon re-starting to heat the product to a temperature which is close to the pasteurization temperature. By this method it is ensured that pasteurization can take place without a great waste of the product and of substitution water and a high consumption of energy during an operational stoppage, in that during the stoppage it is not necessary to replace the product with water. At the same time, it is also ensured that no under-pasteurization of the product occurs, and that over-pasteurization is limited to the greatest possible extent. The method also ensures that it is possible for production to take place without a buffer tank between the pasteurization apparatus and the filling machine, or with a possible buffer tank with very small volume. The invention also concerns an apparatus for execution of the method and of the kind disclosed in the introduction, said apparatus according to the invention being characterised in that between the cold and the hot part of the regenerative heat exchanger it contains a pasteurizing part which consists only of heat exchangers, e.g. plate heat exchangers, said heat exchangers being divided into zones, each having a connection for both a heating medium and a cooling medium, or solely for a cooling medium in one or more of the zones. This apparatus results in a considerable saving in space, in that despite the introduction of a further heat exchanger, space is saved for both holding pipe and for the buffer tank. Moreover, since there is no continuous consumption of energy for heating and cooling during a stop in production, a saving in energy is achieved. Furthermore, a more simple cleaning of the apparatus is achieved, i.e. Central Inplace Cleaning, in that the construction does not include extra pipe loops or pipe ends without flow. Moreover, the buffer tank is very small or can be omitted completely, which all-in-all will save large amounts of CIP liquids and CIP installations. Description of the figures in the drawing Fig. 1 shows a schematic example of a general embodiment of a pasteurizing apparatus for the pasteurization of liquid products in a continuous flow, fig. 2 shows a schematic example of a pasteurizing apparatus as shown in fig. 1 , but with two regenerative zones and three pasteurizing zones, and fig. 3 shows a schematic example of a pasteurizing apparatus as shown in fig. 2, but with re-circulation in the regenerative part. Description of an example embodiment Generally seen, an apparatus for the pasteurizing of liquid products in a continuous flow, as for example fluid foodstuffs and beverages, consists of a regenerative part 2 into which the product is fed by a supply pump 1. After the regenerative part 2, the product is led further to the pasteurizing part 6 which cannot only heat the product to the pasteurization temperature, but also cool the product down in the event of a stop in production. Both the regenerative part 2 and the pasteurizing part 6 consist of heat exchangers. Heating or cooling takes place by supplying hot or cold water via a mixing valve 16 to the pasteurizing part 6. Temperature sensors 5, 11 are placed before and after the pasteurizing part 6, so that the pasteurization process can be controlled. Between the regenerative part 2 and the pasteurizing part 6 there are also placed booster pumps 4, 12 which ensure that the product has constant over-pressure in the apparatus. The product is now led back to the regenerative part 2 where it transfers its heat to the product in the inlet. Hereafter, the product is led to an outlet 18 where, for example, a filling plant (not shown) can be placed. The apparatus can be produced in several configurations, depending on demands regarding temperatures and pasteurizing. The temperatures used in the following are thus only examples, since each product has its own specific temperature requirements. The apparatus taken here as starting point (see fig. 2) is intended for the pasteurizing of beer. The apparatus consists of two main heat exchangers, i.e. a regenerative heat exchanger which is divided into two zones 2, 3, and a pasteurizing heat exchanger which is divided into three zones 6, 8, 10. The product is led into the regenerative zone 2 by means of a supply pump 1 , where the product at 2°C is heated to 33°C. The product is now led further to the second regenerative zone 3 where it is heated to 65°C. A booster pump 4 and 12 ensures that there is an over-pressure, partly in the pasteurizing heat exchanger 6, 8, 10 and partly in the cooling part of the regenerative heat exchanger 2, 3. This over-pressure ensures that in the event of a possible leakage, air or fluid does not come into the pipe system, but only out. In this way it is avoided that bacteria capable of survival are transferred to the pasteurized product. A temperature sensor 5 is provided before the inlet to the pasteurizing heat exchanger. A valve 21 (see fig. 3) is placed as close as possible to the pasteurizing heat exchanger. During normal operation, this valve 21 ensures that the inlet and the outlet from the regenerative heat exchanger 3 on the non- pasteurized side are held separate. During a stop in production, the valve 21 is opened, whereby re-circulation is made possible in this side of the regenerative heat exchanger 3. This valve is optional and is not used in the cases/configurations where the outlet temperature from the heat exchanger 3 is below the temperature limit for the recording of PU. At the inlet to the first zone 6 of the pasteurizing heat exchanger, the product at 65°C is heated on the primary side to 72°C, this temperature being held through the zones 8 and 10. A valve 22 is placed as close as possible after the pasteurizing heat exchanger. Under normal operation, this valve must ensure that the inlet and outlet from the regenerative heat exchanger 3 are held separate on the pasteurized side. During a stop in production, the valve is opened, whereby re-circulation becomes possible in this second side of the regenerative heat exchanger 3. When the product leaves the last pasteurizing zone 10, it is pumped via the booster pump 12 into the cooling part of the regenerative part 3 and is cooled down to approx. 40°C, and further to the last regenerative zone 2 where the product is cooled down to 9°C. A flow-control valve 13 can be placed after the regenerative part. Hereafter, the product flows through a cooler 14 and further to an outlet 18 where a possible buffer tank and/or a bottling or containerising plant is placed. With an embodiment having a minimal buffer tank, the flow-control valve 13 ensures that the buffer tank does not get over-filled, i.e. that the flow is controlled by the level in the buffer tank. In an apparatus without buffer tank, it is the filling plant (not shown) which determines the flow through the apparatus. The cooler 14 is used only if the outlet temperature of the product becomes too high, e.g. as a result of a stop in operations and subsequent re-starting. A temperature sensor 7, 9, 11 is placed after each pasteurizing part 6, 8, 10. A temperature sensor 15 is also placed after the cooler 14. These sensors register whether or not the necessary temperatures have been achieved, so that heating and cooling respectively can be controlled on the secondary side of the pasteurizing heat exchanger 6, 8, 10. The heating/cooling sources in the regenerative part 2, 3 consist of the product itself (hence regenerative), and in the pasteurizing part 6, 8, 10 of hot and cold water 19, 20 respectively, where the amount of heat in the water is determined by signals from the temperature sensors 7, 9, 11 in the individual pasteurizing zones 6, 8, 10. The regulation of the water supply itself is effected in a mixing valve 16 of commonly-known type. The return water from the secondary side of the pasteurizing heat exchanger is led away via a return pipe 17, possibly for heating with a view to re-use in the heat exchanger. The following is a description of the apparatus during a stop in production. The regenerative heat exchanger can be divided into two zones 2 and 3 as shown, or constitute a single zone. In the event of a stop in production, the temperature profile in the first zone will be constant for the first minutes, after which the temperature will slowly approach the average temperature for the heat exchanger. In the second zone, or if there is only one zone, the temperature in the last part of the exchanger and in the pipe connections hereto will be so high that PU is recorded. To avoid this, re-circulation takes place in both the regenerative zones and pipe connections until a constant average temperature is achieved below the temperature limit for the recording of PU (e.g. 53°C). The re-circulation is effected by opening the valves 21 and 22. The pasteurizing zones 6, 8, 10 will be cooled down to e.g. 56°C during a production stop, so that the recording of PU is stopped. The following is a description of the apparatus when re-started after a stop in production. After a stop in production, all of the pasteurizing zones are re-heated to the normal temperatures to ensure that no under-pasteurization occurs, and also that over-pasteurizing is limited as much as possible. When re-starting an apparatus without buffer tank, the process is controlled by raising the temperature on the secondary side of the pasteurizing heat exchanger 6, 8, 10 depending on the speed of flow.

Claims: C L A I M S 1. Method for the pasteurization of a continuous flow of a liquid product in an apparatus which has a heating area, a pasteurizing area and a cooling area, and pump elements for feeding the product in a given flow from the admission opening in the apparatus to its discharge opening, through the above areas in the order in which they are mentioned, whereby the heating, the pasteurizing and the cooling is effected by the transfer of heat between the product itself in cold and in hot condition and a liquid, preferably water, which flows through one or more heat exchangers and a holding pipe without temperature regulation in the said areas, in that the areas are divided into zones which extend in the flow direction of the product, and the temperature of the water is adjusted in accordance with the course of the heat transfer aimed at in the zone, where one of the part pasteurizing zones is connected to hot and cold water, characterized in that the pasteurizing area (6) is divided into a number of individual pasteurizing zones (7,9,11) with connection (16) for both heating and cooling (19,20) or, in the event of a stop in production, for cooling (20) of the product in order to hold the temperature under the pasteurizing temperature, and upon re- starting to heat the product again to a temperature close to the pasteurizing temperature. 2. Method according to claim 1 , characterized in that during a stop in production, the water on the secondary side in the pasteurizing part (6) is held at a temperature between 50 and 60°C. 3. Method according to claim 1 , characterized in that when production is re-started, the water on the secondary side in the pasteurizing part (6) is brought up to a temperature of between 65 and 72°C. 4. Method according to claim 1 , characterized in that the flow is controlled by one or more flow-control valves (13) on the basis of the temperature measured after the individual pasteurizing zone (11). 5. Method according to claim 1 , characterized in that at least one of the sides, the primary and the secondary side of the regenerative part (2) respectively, can be re-circulated via one or more valves (21 ,22). 6. Apparatus for the pasteurizing of a liquid product in a continuous flow, said apparatus being for use in the execution of the method disclosed in claim 1 , and having a heating area, a pasteurizing area and a cooling area, and pump elements for feeding the product in a given flow from the admission opening in the apparatus to its discharge opening, through the above areas in the order in which they are mentioned, whereby the heating, the pasteurizing and the cooling is effected by the transfer of heat between the product itself in cold and in hot condition and a liquid, preferably water, which flows through one or more heat exchangers and a holding pipe without temperature regulation in the said areas, in that the areas are divided into zones which extend in the flow direction of the product, and the temperature of the water is adjusted in accordance with the course of the heat transfer aimed at in the zone, where one of the part pasteurizing zones is connected to hot and cold water, characterized in that the apparatus between the cold and the hot part of the regenerative heat exchanger (2) contains a pasteurizing part (6) consisting of heat exchangers (6), said heat exchangers being divided into zones, each of which has a connection (16) for both a heating medium (19) and a cooling medium (20), or only for a cooling medium in one or more of the zones. 7. Apparatus according to claim 6, characterized in that a temperature sensor (11) is placed after the individual pasteurizing zone. 8. Apparatus according to claims 6-7, characterized in that the pasteurizing part is arranged to hold the temperature of the water between 50 and 60°C in the event of a stop in production. 9. Apparatus according to claims 6-8, characterized in that the pasteurizing part is arranged to bring the water up to a temperature between 65 and 70°C when production is re-started. 10. Apparatus according to claims 6-7, characterized in that a flow-control valve (13) is placed between the regenerative zone and the outlet from the apparatus, said valve (13) regulating the flow in the apparatus on the basis of signals from a meter which measures the level in a buffer tank. 11. Apparatus according to claim 6, characterized in that the pasteurizing part (6) consists of one or more plate heat exchangers.

Inventors: DALUM KIM CHRISTIAN, NIELSEN JOERGEN TAGE, DALUM, KIM, CHRISTIAN, NIELSEN, JOERGEN, TAGE
Applicants: DALUM KIM CHRISTIAN, NIELSEN JOERGEN TAGE, SANDER HANSEN A S, DALUM, KIM, CHRISTIAN, NIELSEN, JOERGEN, TAGE, SANDER HANSEN A/S
Application year: 1999
Main classification: A23L3
IPC codes: A23L3