ARRANGEMENT IN A REGENERATIVE HEAT EXCHANGER

Abstract: An arrangement in a regenerative heat exchanger for heat treatment of liquid food products comprises a holding cell (9) arranged between a final heating step (6) and a regenerative section (4) in the heat exchanger. In the holding cell (9) food product is heat treated during a predetermined time and temperature. A three-way valve (11) is arranged at the outlet from the holding cell (9) which three-way valve is reversible between a stable resting position in which the food product is returned to the inlet of the heat exchanger and an operation position in which the food product is led further to the regenerative section (4), at which the valve body (21) in the three-way valve (11) is arranged to be moved manually to the operation position and be maintained in this position by the pressure of the food product at its passage of the valve.

Description: Arrangement in a regenerative heat exchanger The present invention relates to an arrangement in a regenerative heat exchanger for heat treatment of liquid food products, at which the food product is heated during a predetermined time and temperature in a holding cell between a final heating step and a regenerative section in the heat exchanger. When heat treating liquid food products one desires to achieve as good heat economy as possible. This is especially the case when heat treating at higher temperatures. The heat energy in already heat treated product is used to preheat product which has not been treated. This is usually attained in that untreated food product in a first section of a heat exchanger, the regenerative section, is heated by already treated product which is cooled simultaneously. In a second section in the heat exchanger, the final heating step, the food product is heated by a heat transferring medium to a desired temperature. If the intention of the heat treatment is a pasteurization of the food product, that is a killing of dangerous micro- organisms, the food product must be kept under a pre¬ determined time at a prescribed temperature. Usual combinations are pasteurization 72-75° C during at least 15 seconds or pasteurization 80° C during 3-5 seconds. The necessary holding time is achieved in that the food product is brought to pass a holding cell for example in the shape of a tube coil, the length of which corre¬ sponds to the holding time when the arrangement is used at its maximum capacity. The heat treated product is as mentioned above cooled by- incoming product. If the product shall be kept cool after the heat treatment a separate cooling step is connected to the heat exchanger where the treated product is cooled with a cooling medium for example cold water or ice water. The handling of food products is in a high degree con- ' trolled by rules and regulations from the authorities. As regards milk dairy organizations have also compiled rules. These rules mainly aim at securing that the food product cannot leave the heat exchanger without being sufficiently heat treated. In order to prevent this the heat exchanger is provided with a three-way valve which returns the food product to the inlet of the heat exchanger if the temperature of the food product is too low at the outlet from the holding cell. The function of the three-way valve is controlled with a temperature recorder which also registers the position of the valve. In dairy plants compressed air is used to control the valves which gives a rapid and distinct switchover. When pasteurizing in a small scale a regenerative heat treatment is more advantageous than for example heating in batches of the same amount of product from many points of view. To use the same kind of control arrange¬ ment as in large dairy plants may however be unpropor- tionally expensive. Compressed air control demands both use of a compressor and maintenance of the same, which in a small scale plant is expensive and constitutes a complicating factor. Other solutions to the problem of finding a suitable valve may involve different disadvan- tages. Valves which are actuated by way of a magnet cannot take care of the large amounts of flow which are handled during the heat treatment. Valves driven by motors react too slowly to be used in these connections where the time from sensing an incorrect temperature to adjustment of the valve shall be kept as short as possible. According to the invention there is proposed a simple arrangement in a regenerative heat exchanger which with a high degree of functional security secures that product which has been heat treated in an unsufficient degree cannot leave through the outlet of the heat exchanger. The invention is mainly characterized in that a three- way valve is arranged at the outlet from the holding cell which three-way valve is reversible between a stable rest position in which the food product is returned to the inlet of the heat exchanger and an operation position in which the food product is led further to the regenerative section. The valve body in the three-way valve is arranged to be moved manually to the operation position and to be kept in this position by the pressure of the food product when the product passes the valve. The arrangement according to the invention is advan¬ tageously arranged in such a way that the pressure of the food product is maintained by way of a pump arranged in front of the inlet to the final heating step. In some connections the pressure which is obtained by the pump which transports the food product to the inlet of the heat exchanger may be sufficient to achieve a suffi¬ ciently high pressure at the outlet of the holding cell. Suitably a booster pump is arranged between the regene¬ rative section and the final heating step. A temperature sensing means is usually arranged at the outlet from the holding cell, which means senses the temperature of the food product and if it is too low actuates the pump in such a way that it stops. The pressure of the food product then falls and the valve body automatically returns to its rest position and the food product is instead led back to the inlet of the heat exchanger. With such an arrangement it is prevented that insufficiently heat treated milk may flow through the outlet section of the regenerative part and contami¬ nate the same. The heat exchange areas in this section have a temperature which is lower than the pasteurizing temperature and if dangerous microorganisms enter this section they are not killed at a later stage when the prescribed pasteurizing temperature is obtained again in the holding cell. With an arrangement according to the invention it is also secured that the valve body of the three-way valve returns to its rest position if there is a failure of power. If a such occurs the pump stops, at which the pressure of the food product diminishes and the valve body returns to its rest position. If the power returns the food product is returned to the inlet of the heat exchanger until the desired temperature has been obtained after the holding cell. The temperature sensing means is advantageously designed such that the sensed temperature also is registered continuously. The demand from the authorities that the effect of the heat treatment shall be documented is then fulfilled. It is also suitable to provide the three-way valve with means which senses the position of the valve body, which means, when the valve body is in its rest position, is arranged to see to that the pump starts to work again. In this way all problems with incrustations in the final heating step are avoided since the food product then again flows through the final heating step and the holding cell. The food product is not allowed to leave the heat exchanger but is led in return to the inlet of the heat exchanger as long as the temperature of the food product is lower than the prescribed value at the outlet from the holding cell. When the desired value has been obtained the valve body is moved manually to its operation position and the food product is brought to pass the regenerative part in order to be cooled in the same. In order to guarantee the reliability of the arrangement the position sensing means may be arranged to stop the pump if the valve body of the three-way valve is moved manually to its operation position before the desired temperature of the food product has been achieved. The mentioned position sensing means are with advantage arranged to indicate the position of the valve body. The position of the valve body is suitably registered when a simultaneous registration of the temperature of the food product at the outlet from the holding cell is done. In order to hinder that insufficiently heat treated product, when returned to the inlet by the valve, shall have the possibility to leak past the valve body, rules in some countries regarding pasteurization demand the presence of means for a special draining of leakage. When such demands are to be met, two three-way valves are connected in series after each other. Correctly heat treated product passes both the valves on the way to the regenerative section. If the heat treatment is insuffi¬ cient the first three-way valve returns the food product to the inlet. Should any product pass the valve body in this first three-way valve due to a leakage, the second three-way valve prevents the food product to pass on to the regenerative section. The two valve bodies may be moved independently of each other. Both return to the rest position when the pump stops and the pressure of the food product falls. The valve bodies may also be connected mechanically in order to secure a simultaneous manoeuvring. In order to prevent that food product which has not been heat treated shall have the possibility to enter and mix with heat treated product if a leakage occurs in the regenerative section, there is a pressure regulating valve at the outlet from the regenerative section of the heat exchanger, which valve ensures a desired high pressure level of the heat treated product. If a leakage then should occur heat treated product enters into and is mixed with untreated product. If the desired high pressure level could not be obtained in the regenerative section, means is arranged to control that the valve body of the three-way valve is not kept in operation position. The arrangement according to the invention is described further with reference to the attached drawing, fig 1 of which shows an arrangement for heat treatment of a food product in a regenerative heat exchanger with a three- way valve according to the invention and fig 2 of which shows an embodiment of a three-way valve according to the invention. In fig 1 there is shown a balance tank 1 provided with an inlet with a float valve for a food product 2. The food product is sucked from the balance tank through a disposable milk filter 3 to a regenerative heat exchanger, a plate heat exchanger 4, by means of a pump 5. In the plate heat exchanger the incoming food product meets heat treated product in counter current, at which the heat treated product is cooled and the incoming product is heated. The pump 5 is a positive pump, pre¬ ferably an impeller pump, with a pump wheel of rubber. The food product is pumped further into a final heating step 6 in the heat exchanger. In this step the food product is heated to a desired high temperature by a heat transfer medium. The final heating step advan¬ tageously consists of a plate heat exchanger, where the food product is heated by means of a hot water. The water circulates in a special circuit 7 and is heated by electricity. From the final heating step the food product is led to a holding cell 9 which consists of a helicoidally wound tube. The holding cell is suitably built up of modules which are connected to the desired length. The food product passes through the holding cell 9 in an undisturbed rising flow. At the outlet of the holding cell the product temperature is sensed by means of a temperature sensor 10. At the outlet of the holding cell there is also a three-way valve 11, which, depen- ding on the temperature which is sensed by the tempera¬ ture sensor 10, alternatively returns the food product to the inlet of the heat exchanger or makes the product pass further on through the regenerative section of the heat exchanger. The valve body in the three-way valve is moved' manually to the operation position, i.e. to a position where the food product which has been heat treated in the desired degree is led further to the regenerative section of the heat exchanger where the product is cooled by incoming untreated product. At the outlet of the heat exchanger there is a counter pressure valve 12, the counter pressure of which is determined by the weight of the valve body. The valve body of the three-way valve is kept in its upper position, the operation position, by the pressure of the food product when this passes the three-way valve. The position of the valve body is sensed with an inductive sensor 13. A temperature sensing means 14 is arranged at the outlet from the final heating step in the heat exchanger. This sensor controls the heating of the hot water which circulates in the circuit 7. A relay 15 is arranged to start and to stop the pump 5. The signals from the temperature sensor 10 and the sensor 13 run to a control means 16 from which the signals run to the relay 15. The control means comprises a recorder and a limit value sensor. In fig 2 there is shown a three-way valve according to the invention. The valve has a cylindrical valve housing 17 with an inlet 18 for incoming food product and two outlets 19 and 20. In the rest position the valve body of the valve 21 tightens the outlet 19 and the product passes out through the outlet 20 and is transported further through a connection 22. The valve body may be moved manually to its upper position, the operating position, by means of a bowl 23 on the outside of the valve which is firmly connected to the valve body. The inductive transmitter 13 gives a signal when the valve body is in its lower position. The valve body is provided with packings 24, 24' in its upper and lower part. When a food product shall be heat treated in the plant which is shown in fig 1 it is transported by the pump 5 into the regenerative section 4 of the heat exchanger and by this to the final heating step 6. The valve body is then manually moved to its upper position by the operator and the food product is brought to pass the regenerative section in the heat exchanger and is cooled by incoming product. When the food product passes the valve, the pressure of the product keeps the valve body in its upper position. If the temperature which is sensed by the temperature sensor 10 is too low, the control means 16 gives a signal to the pump to stop, at which the flow towards the valve 11 stops and the valve body returns to its lower position. When the valve body is in this lower position the position sensor 13 gives a signal to the control means 16 which starts the pump again, the food product is then returned to the balance tank 1. When the temperature of the product rises the flow through the holding cell will have a sufficient high temperature. When this is indicated by the tempera¬ ture sensor 10 the operator lifts the valve body to its upper position and the product is led through the regenerative part and out from the plant. With an arrangement of this kind, a very reliable plant is obtained, which effectively prevents product which is insufficiently heat treated to pass out from the plant.

Claims: Claims 1. An arrangement in a regenerative heat exchanger for heat treatment of liquid food products, at which the food product is heat treated during a predetermined time and temperature in a holding cell (9) between a final heating step (6) and a regenerative section (4) in the heat exchanger, c h a r a c t e r i z e d i n that a three-way valve (11) is arranged at the outlet from the holding cell, which three-way valve is reversible between a stable rest position in which the food product is returned to the inlet of the heat exchanger and the operation position, in which the food product is led further to the regenerative section, at which the valve body (21) in the three-way valve (11) is arranged to be moved manually to the operating position and kept in this by the pressure of the food product at its passage through the valve. 2. An arrangement according to claim 1, c h a r a c ¬ t e r i z e d i n that the pressure of the food product is maintained by way of a pump arranged in front of the inlet to the inal heating step (5). 3. An arrangement according to claims 1-2, c h a ¬ r a c t e r i z e d i n that the temperature sensing means (10) is arranged at the outlet from the holding cell (9), which means (10), at too low a temperature of the food product, influences the pump (5) such that it stops, at which the three-way valve returns to its rest position and food product is returned to the inlet of the heat exchanger. 4. An arrangement according to claims 1-3, c h a - r a c t e r i z e d i n that said temperature sensing means is arranged to register the temperature continuously. 5. An arrangement according to claim 1-3, c h a ¬ r a c t e r i z e d i n that the three-way valve is provided with means (13) which senses the position of the valve body, which means (13) when the valve body is in its rest position, is arranged to make the pump start working again. 6. An arrangement according to claim 5, c h a r a c ¬ t e r i z e d i n that said position sensing means (13) is arranged to stop the pump if the three-way valve is moved to the operation position at too low a tempera- ture of the food product. 7. An arrangement according to claim 6, c h a r a c ¬ t e r i z e d i n that said position sensing means (13) is arranged also to indicate the position of the valve body (21). 8. An arrangement according to claim 7, c h a r a c ¬ t e r i z e d i n that said position sensing means (13) is arranged to continuously register the position of the valve body (21), at which the temperature also is registered by the temperature sensing means. 9. An arrangement according to claim 1-3, c h a ¬ r a c t e r i z e d i n that a pressure regulating valve (12) is arranged at the outlet from the regenera¬ tive section of the heat exchanger in order to secure such a pressure level of the heat treated product that product, which has not yet been treated, cannot contami¬ nate heat treated product if a leakage occurs in the regenerative section. 12 10. An arrangement according to claim 9, c h a ¬ r a c t e r i z e d i n that the valve body (21) in the three-way valve is not kept in.operation position if said pressure level is not achieved.

Inventors: LIDMAN MAGNUS, LIDMAN, MAGNUS
Applicants: ALFA LAVAL AGRI INT, ALFA-LAVAL AGRICULTURE INTERNATIONAL AB
Application year: 1992
Main classification: A23L3
IPC codes: A23C3, A23L3