The present invention relates to a method for heating a flow of liquid food product in a food processing line. More particularly, the present invention related to a method for recovering energy used for heating the flow of liquid food product in said food processing line.

Background

A food processing line, such as a dairy system, includes a plurality of food processing equipments arranged to provide a specific treatment of the food. For example, a dairy system may include a separating section, a filtering section, a homogenisation section, and a pasteurisation section etc. Such food processing system typically also includes a number of heaters for providing the necessary treatment of the food product.

The heaters of such food processing system may be provided as indirect heaters or direct heaters. Indirect heaters typically include a heat exchanger, wherein heat is transferred from a high temperature medium to the liquid food product. Direct heaters are e.g. commonly used in ultra heat treatment processing systems, wherein the liquid food product is heated e.g. by providing steam into direct contact with the liquid food product.

Independently of the heating principle such heaters are known to consume vast amount of energy, especially when they are included in large processing system capable of treating large quantities of liquid food product and operating continuously during the day and night.

Hence, there is always a need for reducing the amount of energy needed to run the processing system, since the cost of ownership for the food processing system owner is highly dependent on the overall operating cost of the system. Summary

It is, therefore, an object of the present invention to overcome or alleviate the above described problems.

The basic idea is to provide a method for recovering heat in a liquid food processing line by means of a heat pump.

A further idea is to use the recovered heat for a heater of said processing line arranged upstream of the location of the heat recovering. According to a first aspect, a method for improving energy efficiency in a food processing line by heating a flow of liquid food product flowing through said food processing line is provided. The method comprises the steps of transferring heat from a first flow of said food processing line to an energy transfer medium, increasing the temperature of said energy transfer medium by means of a heat pump, and

transferring heat from said energy transfer medium to a flow of food product entering a heater arranged upstream of the first flow in the food processing line.

Said energy transfer medium may be an intermediate heat transfer medium, such as a refrigerant.

Said first flow of said food processing line may comprise condensed steam being discharged from a flash cooler, and the method may further comprise the steps of: injecting or infusing steam into a flow of liquid food product at a position

downstream of the heater, and subjecting the mix of liquid food product and steam to a flash cooling.

Said first flow of said food processing line may comprise liquid food product entering a cooler.

The step of transferring heat to the flow of liquid food product may be provided for increasing the temperature of the flow of liquid food product by 2 to 50 °C, and preferably by 5 to 15 °C.

The step of transferring heat to the flow of liquid food product may be provided for increasing the temperature of the flow of liquid food product from approximately 75°C to 81 °C.

The step of transferring heat from said energy transfer medium to a flow of liquid food product entering a heater may be provided by means of a heat exchanger.

The step of transferring heat from said energy transfer medium to a flow of food product entering a heater may further comprise transferring heat from said energy transfer medium to an intermediate heat medium, and transferring heat from said intermediate heat medium to said flow of food product entering a heater.

The step of transferring heat from a first flow of said food processing line to an energy transfer medium may further comprise transferring heat from a first flow of said food processing line to an intermediate heat medium, and transferring heat from said intermediate heat medium to said energy transfer medium.

Further, the step of transferring heat from a first flow of said food processing line to an energy transfer medium may comprise capturing heat from said first flow using a heat exchanger, and transferring said heat to said heat pump using a heat transfer medium. According to a second aspect, a food processing system for treating a flow of liquid food product flowing through a food processing line is provided. The system comprises a heater configured to increase the temperature of said liquid food product, and a heat pump capable of increasing the temperature of an energy transfer medium being subject to heat transfer from a first flow arranged downstream of said heater of said food processing line, wherein the energy transfer medium is directed such that heat is transferred from said energy transfer medium to said liquid food product flowing through said heater.

Said first flow of said food processing line may comprises condensed steam being discharged from a flash cooler.

The food processing system may further comprise a further heater configured to inject steam directly into the liquid food product or infuse liquid food product directly into steam, wherein said further heater is arranged downstream of the heater.

Said first flow of said food processing line may comprise liquid food product entering a cooler.

Said heater may further be configured to heat said liquid food product from approximately 75°C to 81 °C.

The food processing system may further comprise a heat exchanger configured to capture heat from said first flow using and via a heat transfer medium transfer said heat to said heat pump.

According to a third aspect, a dairy system is provided comprising a food processing system according to the second aspect.

In this context, a heat pump should be interpreted broadly as a device capable of transferring heat from a heat source to a heat sink, wherein the temperature of the heat source is lower than the temperature of the heat sink. Preferably, the heat pump may be implemented as a commercially available heat pump operating on the physical principles of phase transitions of a refrigerant.

Further, liquid food product is defined as a food product being possible to pump through a food processing line. Hence, liquid food product includes food products having different viscosities as well as arbitrary amount of solid content. Liquid food product is thus defined as a common term for drinks, milk, juice, soups, puree, baby food, etc.

Brief Description of Drawings

The above, as well as additional objects, features, and advantages of the present invention, will be better understood through the following illustrative and non- limiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, wherein:

Fig. 1 is a process scheme for a liquid food processing system utilizing a method according to prior art;

Fig. 2a is a process scheme of a liquid food processing system utilizing a method according to an embodiment;

Fig. 2b is a process scheme of a liquid food processing system utilizing a method according to another embodiment; and

Fig. 3 is a process scheme of a liquid food processing system utilizing a method according to a further embodiment.

Detailed Description

With reference to Fig. 1 a known liquid food processing system 100 is shown. The food processing system 100 is configured to provide an ultra heat treatment process for producing aseptic products ranging from white milk to viscous ice cream mix.

Food product, such as raw milk, is introduced at the left end of the figure, denoted by the reference "A". A first heater 1 10 is arranged to increase the

temperature of the raw milk from approximately 4°C to 75°C. Downstream of the first heater 1 10 a second heater 120 is provided for increasing the temperature of the food product even further, preferably from 75°C to 81 °C. For this purpose the second heater 120 utilizes steam, wherein the heat of the steam is transferred indirectly to the food product via a heat exchanger. A further heating means 130 is provided downstream of the second heater 120 by which steam is directly injected into the food product for forming a mix of food product and steam. The temperature rapidly increases to approximately 140°C, whereby the mix of food product and steam is kept at this temperature for a certain time in order to provide sufficient sterilization of the food product.

In order to separate the steam from the food product a flash cooler 140 is provided downstream of the steam injector 130. The flash cooler 140 is a vacuum chamber in which the steam boils off and is separated from the food product. The food product, now having returned to the temperature of approximately 80°C, is then further processed by various food processing equipment (not shown) whereafter it is cooled down to approximately 4°C before exiting the food processing system at the output "B". The cooling is preferably provided in two steps, wherein the first step includes the first heater 1 10 which utilizes the heat of the food product to increase the temperature of the incoming food product to 75°C. At the same time the return food product is cooled down to approximately 12°C. A final cooler 150 is further provided in order to further decrease the temperature of the food product to the desired discharge temperature of 4°C.

So far, a known processing system has been described. Now referring to Fig. 2a , a processing system 200 according to an embodiment is shown.

Similarly to the previously described system, the processing system 200 includes a first heater 210 for heating incoming liquid food product, such as milk or any other food product being subject to the treatment, from approximately 4°C to 75°C. A second heater 220 provides additional heating to approximately 81°C, whereafter the food product is exposed to a direct injection of steam at heater 230. The preheating up to 81 °C is preferred since burning of the steam injection outlet may in such case be avoided.

The heater 230 may also be an infusion heater, in which liquid food product is directly infused in steam for providing the necessary heating.

The liquid food product, at this stage being mixed with steam, is kept at an elevated temperature of approximately 140°C during some time before it is subject to a rapid cooling by means of a flash cooler 240. The flash cooler 240 includes two discharge outlets 242, 244 of which the first one 242 discharges food product at a temperature of approximately 80°C, i.e. the same temperature as prior to the steam injection. In the embodiment illustrated in fig 2a, steam is discharged from the second outlet 244. The exact temperatures of the discharged water and food product, respectively, are set such that no dilution of the food product occur during the heating and cooling steps.

As the heat of the food product is used as a heat source for the first heater 210 in the same manner as previously described with reference to Fig. 1 , the discharged steam coming from the flash cooler 240 is used as a cold side input of a heat pump 260. The heat pump 260 may be a conventional heat pump operating by means of phase transitions of a refrigerant, or may be an electrical or chemical heat pump operating according to its respective principles. The refrigerant of the heat pump 260, indicated by the closed loop 262, acts as a heat transfer medium and pumps heat from the cold side or source, i.e. the discharged condensed steam having a

temperature of approximately 78°C such that the condensed steam reduces its temperature to approximately 70°C after passing through the heat pump 260. Hence, the temperature difference of the source is approximately 8°C.

The hot side, or heat sink, of the heat pump 260, indicated by the closed loop denoted as 264, comprises an intermediate heat medium, such as water, and is heated to a temperature of approximately 85°C and delivers at least some of the transferred heat to the second heater 220 for indirect heating of the incoming food product before the steam injection 230.

The food product exits the food processing system at "B" after passing a final cooler 250 reducing the temperature of the food product from approximately 12°C to 4°C.

By the provision of the heat pump 260 the overall energy consumption is significantly reduced, which is particularly advantageous in that the cost-of-ownership for a processing system according to the described embodiment is reduced. As an example, theoretical calculations show that the overall steam consumption can be reduced by 15%. Further, as the temperature of the water condensate is decreased by the heat pump the amount of water needed to cool down the water condensate is also decreased.

Instead of directly transferring the steam to the heat pump 260 as illustrated in fig 2a, a heat exchanger 264 may be added as illustrated in fig 2b. In this set up the steam from the flash cooler 240 is fed into the heat exchanger 264 in which the steam is condensated into hot water and then fed via a heat transfer medium 266 to the heat pump 262. By using the heat exchanger 264 in this way, problems associated with feeding steam directly into the heat pump can be overcome.

Further, instead of having a closed loop between the heat exchanger 264 and the heat pump 260, non-closed loop solutions may be used as well.

Now referring to Fig. 3 another embodiment of a liquid food processing system 300 is shown. The food processing system 300, including equipment to form a pasteurizer, has a first heater 310, a second heater 320, a first cooler 330 and a final cooler 340.

The food product enters the system 300 at "A", i.e. at the left end of the figure.

Typically, the temperature of the introduced food product is approximately 4°C. The food product passes through a first heater 310 which is capable of heating the food product up to approximately 60°C. The second heater 320, arranged downstream the first heater 310, is provided for heating the food product up to approximately 70°C or slightly above. The downstream cooler 330 is provided for decreasing the temperature of the food product to approximately 12°C after the food product is kept at its elevated temperature during some time. Before the food product exits the pasteurizer 300 at "B" a final cooler 340 decreases the temperature further down to approximately 4°C.

The first cooler 330 forms part of the first heater 310, such that heat from the heated food product is transferred indirectly to the incoming food product for providing the necessary heating. Hence, the first cooler 330 and the first heater 310 may be constructed as a regenerative heat exchanger. The final cooler 340 is formed as a part of a heat pump 350, wherein the heat pump 350 is provided for connecting the second heater 320 with the final cooler 340. The food product entering the final cooler 340 at the temperature of 12°C forms the heat source for increasing the temperature of the intermediate heat transfer medium, i.e. the refrigerant 344 of the heat pump. Hence, the heat of the food product entering the cooler 340 is pumped to the refrigerant 344 which is circulated in a closed loop. The refrigerant 344 transfers heat to the food product entering the second heater 320 via an intermediate heat medium 342 such that the heat recovered from the cooler 340 may heat the food product entering the second heater 320 to its desired temperature of 70°C.

The use of a heat pump 350 as the final cooler 340 enables efficient recovery of the heat of the food product such that the overall energy consumption of the food processing system 300 may be reduced.

Although an intermediate heat medium 264, 342 has been described with reference to Figs. 2 and 3, other embodiments omitting such intermediate heat medium are also possible. Further to this, an intermediate heat medium could also be arranged between the first flow of the food processing line acting as the cold side of the heat pump and the refrigerant, i.e. the heat transfer medium. Combinations of intermediate heat medium, on the cold side and on the hot side, respectively, are also possible.

The invention has mainly been described with reference to a few

embodiments. However, as is readily understood by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended claims.