A system for steam drying extruded fish feed

Abstract

The present invention relates to a system suitable for steam drying extruded fish feed. The system comprises a drying chamber, a carrier and a steam heating device configured to provide heated steam by increasing the temperature of cooled steam, and a steam distribution device. Cooled steam from the steam drying may be recycled and may be used in the extruder.

Description

[0001] 83514PC01 1 A SYSTEM FOR STEAM DRYING EXTRUDED FISH FEED FIELD OF THE INVENTION The present invention relates to a system for steam drying extruded fish feed. The system comprising, a steam heating device, a drying chamber comprising a fish feed inlet and a dried fish feed outlet. Preferred embodiments also comprise an extruder. BACKGROUND OF THE INVENTION Fish feed production today is often done in extruders or pelletisers with moisture content enough to have chemical reactions such as gelatinisation, protein denaturing and pasteurisation occurring. This excess moisture is then subsequently removed in various models of hot air driers and moisture is led away with this hot air into the environment. I may be tempting to reclaiming heat from the air which has been used to dry the fish feed. However, the heat capacity and thereby the heat energy per volume unit of the air used for drying has been found to be too low to allow for an efficient reclaiming e.g. by heat exchangers. A factor rendering reclaiming inefficient is that that the water evaporated from the fish feed is diluted into large amounts of air. Hence, an more energy efficient drying of fish feed would be advantageous. OBJECT OF THE INVENTION It is an object of the present invention to provide an energy efficient drying of fish feed. It is a further object of the present invention to provide an alternative to the prior art. SUMMARY OF THE INVENTION Thus, the above described object and several other objects are intended to be obtained in a first aspect of the invention by providing a system for steam drying extruded or pelletized fish feed, wherein said fish feed, during use of the system, 83514PC01 2 is exposed to a heated steam whereby said fish feed is dried and said heated steam is cooled to a cooled steam, said system comprising^ preferably, an extruder for extruding fish feed;^ a drying chamber comprising a fish feed inlet configured to receive moist fishfeed to be dried, preferably from said extruder, and a dried fish feed outlet configured for outlet dried fish feed;^ a carrier located inside said drying chamber configured to support said moistfish feed while being exposed to said heated steam;^ a steam heating device configured to provide said heated steam by increasinga temperature of said cooled steam, said steam heating device comprises a compressor configured to increase a temperature of a medium by compression, and a heat exchanger configured to transport heat from said medium to said cooled steam;^ a steam distribution device configured to distribute said heated steam towardsat least a fraction of said fish feed supported by said carrier. Steam heating device preferably refers to a device configured to increase the temperature of steam. In preferred embodiments, the steam heating device may comprise compressor which compresses steam to increase the temperature of the steam. In other preferred embodiments, the steam heating device may comprise a heat pump. Steam as used herein referred to a substance containing water in gas phase. Steam referred to herein is typically at a super heated state where the temperature is higher than its boiling point at the pressure of the steam, which typically is atmospheric pressure. Cooled steam typically refers to a steam that has been used for drying of fish feed and thereby being cooled. Heated steam typically refers cooled steam being heated.Moist fish feed typically refers to a fish feed having a water content, wherein atleast a fraction of the water content is removable by steam. 83514PC01 3 In a second aspect, the invention relates to a method of drying fish feed, the method utilizes a system according to the first aspect, and comprises:^ feeding fish feed into said drying chamber,^ operating said system to provide heated steam, and^ contacting said fish feed with said heated steam.The inventors have realized that by using super heated steam as a drying medium, the heat content per volume medium is surprisingly high enough to allow for reclaiming of the heat by use of a steam heating device. A factor in this is that steam has a relatively high heat capacity compared to air used for drying. BRIEF DESCRIPTION OF THE FIGURES The present invention and preferred embodiments thereof will now be described in more details with regard to the accompanying figures. The figures show ways of implementing the present invention and are not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set. Fig. 1 schematically illustrates a first preferred embodiment of a system for steam drying extruded fish feed. Fig. 2 schematically illustrates a second preferred embodiment of a system for steam drying extruded fish feed. Lower part of Fig. 2 illustrates the heat exchanger arranged inside the drying chamber. Fig. 3 schematically illustrates a third preferred embodiment of a system for steam drying extruded fish feed. Fig. 4 schematically illustrates an embodiment of a system for steam drying extruded fish for which energy calculations are presented in Example 1. Fig. 5 schematically illustrates an embodiment of a system for steam drying extruded fish for which energy calculations are presented in Example 2. Fig. 6 schematically illustrates a fourth preferred embodiment of a system for steam drying extruded fish feed. 83514PC01 4 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Reference is made to the accompanying figures schematically illustrating preferred embodiments of a system for steam drying fish feed. 1. The illustrated systems have an extruder 2 for extruding fish feed. The extruder is typically a screw extruder having a die at the exit of the extruder, which die provides a form to pellets exiting the extruder. In Figs. 1 and 3 the extruder is shown as having two infeeds, namely raw materials 15 and liquid 21 and / or steam. The raw materials are materials from which the fish feed is to be made. The liquid may be condensed steam being mostly water. Mostly water refers to that the liquid may have other components than water in case the steam has such other components, e.g. residues from fish feed pellets. Although Figs. 1 and 3 each illustrates two infeeds, the raw materials and the liquid may be pre-mixed and fed as a mix into the extruder. It is further noted that the raw material may also contain liquid such as water and other liquid components and the liquid being condensed water may constitute an addition of water. It is noted that although the preferred embodiments disclosed herein refers to a system having an extruder for providing an extruded fish feed, drying according to the present invention may be used in general to dry e.g. pelletized fish feed, not necessarily being provided by an extruder. Preferred embodiments of a drying system have a drying chamber 3. The drying chamber is typically a thermal insulated chamber where inflow and outflow of matter is controlled. In the illustrated embodiment, the pellets 16 (fish feed) leaving the extruder is fed into the drying chamber 3 via a fish feed inlet 8. The pellets 16 are typically warm when they enter into the drying chamber 3 due to inter alia the viscous action in the extruder 3, and in some cases also due to applying heat to the extruder 3. In addition, the water content of the pellets entering the drying chamber 3 is higher than desired and the pellets 16 are therefore dried. Drying of the pellets 16 is provided by exposing the pellets to a flow of heated steam such as super heated steam. That the steam is super heated, means that is 83514PC01 5 has a temperature higher than the boiling point of water at the pressure prevailing inside the drying chamber 3, which pressure is typically atmospheric pressure. When the pellets 16 is heated by the flow of super heated steam, at least a fraction of the water content in the pellets 16 evaporates and is “absorbed” into the flow of steam. The temperature of the steam will accordingly decrease and becomes a cooled steam. In the embodiment of Fig. 3, the super heated steam is indicated to have a temperature of 150OC and the steam after having been exposed to the pellets 16 is indicated to have a temperature of 100OC. These temperatures are examples only and other embodiments of the invention may operate at other temperatures. However, it is generally preferred that the steam before being exposed to the pellets 16 is super heated and that the steam after having been exposed to the pellets 16 is still steam, that is having a temperature above the boiling point of water at the prevailing pressure. Reference is made to Fig. 1 schematically illustrating a preferred embodiment of a system 1 for steam drying extruded fish feed. In the illustrated embodiment, the fish feed (pellets 16) is exposed to a heated steam whereby the fish feed is dried and the steam is cooled to a cooled steam. The illustrated embodiment comprises as also detailed above an extruder 2 for extruding fish feed, a drying chamber 3 having a fish feed inlet 8 configured to receive moist fish feed to be dried from the extruder 2 and a dried fish feed outlet 10 configured for outlet dried fish feed. A carrier 14 is located inside the drying chamber 3 and the carried is configured to support the moist fish feed while being exposed to said heated steam. In preferred embodiments, the carrier comprising a grate carrying the fish feed and heated steam flow from a position below the grate and in-between the pellet 16. As the heated steam used for drying of the fish feed is cooled to a cooled steam, there is a need for increasing the temperature of the steam to provide a heated steam if the cooled steam is to be used for drying purposes. To this, preferred embodiments comprise a steam heating device configured to provide the heated 83514PC01 6 steam by increasing a temperature of the cooled steam. It is noted that the steam heating device may be a unitary device, although in many embodiments the steam heating device is made of several individual components pieced together. For example, such a steam heating device typically comprises a compressor 7 configured to increase a temperature of a medium by compression, and a heat exchanger 19 configured to transport heat from said medium to the cooled steam. The operation and configuration of inter alia the compressor are selected so that the compressed medium reaches a temperature above the temperature of the cooled steam in order to allow for an increased temperature of the cooled steam. In order to bring the heated steam in contact with the fish feed, the system typically comprises a steam distribution device. Such a steam distribution device is typically configured to distribute the heated steam towards at least a fraction of said fish feed supported by said carrier 16. In the embodiments illustrated in Figs. 1 and 2 the stream distribution device may typically comprise a manifold arranged below the carrier 16 and configured to distribute heated steam, preferably evenly, along at least a section of the carrier 16. In preferred embodiments, the medium which is compressed by the compressor 7 is cooled steam. Fig. 1 illustrates one such embodiment wherein the steam heating device forms part of a recirculation connection 28 configured to receive the cooled steam, and feed heated steam to the steam distribution device. As illustrated in Fig. 1, the cooled steam being produced during drying of the fish fed exit the drying chamber 3 and flows in external pipe work including the compressor 7 and heat exchanger 19. However, the steam heating device and correspond pipe work may be arranged partly or fully within the drying chamber. In the embodiment of Fig. 1, the recirculation connection 28 receives cooled steam via the cooled steam outlet 9 of the drying chamber 3 and the cooled steam flows towards a first fluidic bifurcation 23 of the recirculation connection 28. The first fluidic bifurcation 23 is located upstream of the heat exchanger 19 and upstream of compressor 7. 83514PC01 7 The first fluidic bifurcation splits the cooled steam into two fractions of cooled steam where one fraction of the cooled steam flows to a cooled steam inlet 24a of the heat exchanger 19, and a second fraction of the cooled steam flows to a low temperature steam inlet 25a of the compressor 7. The quantities of the first and second fractions are typically selected based on a desired increase in temperature of the cooled and a desired amount of heated steam as will be detailed below. The quantities of the first and the second fraction may be set inter alia by utilizing a settable three-way valve for providing the first fluidic bifurcation 23. The compressor 7 is configured to receive the second fraction of cooled steam and compress it, whereby the temperature and pressure of the second fraction of cooled steam are increased. The temperature is increased to a temperature being higher than the temperature of the cooled steam. The heated and pressurised second fraction exits the compressor through a high temperature steam outlet 25b which outlet 25b is fluidicly connected to a high temperature steam inlet 26a of the heat exchanger 19. Accordingly, the first fraction of cooled steam flows through the heat exchanger 19, whereby the first fraction is heated by the steam heated and pressurised by the compressor 7, whereby the first fraction becomes heated steam. The heated steam flows into the drying chamber 3 via the recirculation connection 28 being fluidic connected with a heated steam outlet 24b of the heat exchanger 19. As illustrated, the heated steam outlet 24b is fluidic connected with the recirculation connection 28 upstream of the steam distribution device. An expansion valve (not illustrated) may be arranged to lower the pressure of the heated and pressurised second fraction. Such an expansion valve may be arranged between the compressor and the high temperature inlet 26a, withing the compressor 7 and / or downstream of an outlet of the heat exchanger 19. The actual amounts of steam in the first and second fraction is typically determined based on a number of process parameters. Such process parameters typically include the temperature of the cooled steam, Tcs, a desired temperature of the heated steam, Ths, and the total amount of cooled steam available. 83514PC01 8 The actual amounts of steam in the first and second fraction may be estimated based on the following heat balance equation: Here: ^^^ℎ^^ is the heat of the heated steam^ ^̇^1 is the mass flow of the first fraction^ ^̇^2 is the mass flow of the second fraction^ ^^^^ is the specific heat capacity of the fraction in question^ ^^ℎ^^ is the temperature of the heated steam which is to be obtained^ ^^^^^^ is the temperature of the cooled steam, which temperature often ismeasured and is often a target value ^^^^^^^^^^^ is the temperature of the steam after having heat exchanged with thecooled steam in the heat exchanger 19 ^^^^^^^is the temperature at the outlet 25b of the compressor.As the desired temperature of the heated temperature is known, typically selected by a user, and ^^^^^^^^^^and ^^^^^^can be estimated, ^̇^1and ^̇^2can be determined. As it may be desired to only feed a fraction of the second fraction into the heat exchanger 19, the high temperature steam outlet 25b of the compressor 7 may fluidic connected to the high temperature steam inlet 26a through a second fluidic bifurcation 27, as illustrated in Fig. 1. The second fluidic bifurcation 27 is controllable to divide the high temperature steam from the high temperature steam outlet 25b into two settable fractions, one of which is fed into the high temperature steam inlet 26a of the heat exchanger 19. Settable typically refers to that the amounts of the two fractions are controllable e.g. by a controllable (settable) three-way valve. With regards to the above heat balance equation, ^̇^2is to be amended into the actual amount flowing into the heat exchanger 19. The remaining fraction of the high temperature steam (the fraction which is not fed into the heat exchanger 19) may be used as process water, and in preferred embodiments, the remaining fraction is fed into the extruder 2, by the second fluidic bifurcation which is further fluidic connected with the extruder 2. 83514PC01 9 In preferred embodiments, a low temperature outlet 26b of the heat exchanger 19 is fluidic connected with a receptacle 20 to received steam condensed within said heat exchanger 19. One such embodiment is illustrated in Fig. 1, wherein the steam heated by compressor 7 after having passed through the heat exchanger 19 is fed into the receptacle 20. In preferred embodiments, the steam condenses within the heat exchanger 19 and exit the heat exchanger 19 in liquid form, however, the invention is not limited to such condensing. The recirculation connection 28 may also comprise a pump 18, preferably acting as a circulation pump to pump the first stream of cooled steam towards the heat exchanger and further into the drying chamber 3 via the recirculation connection 28. Such a pump 18 is preferably arranged fluidicly in-between the first bifurcation and the cooled steam inlet 24a of the heat exchanger 19. As illustrated in Fig. 1, the drying chamber 3 may comprise a cooled steam outlet 9 and a heated steam inlet 22, wherein the recirculation connection 28 fluidicly connects the cooled steam outlet 9 with the heated steam inlet 22. Reference is made to Fig. 2 illustrating an embodiment of the invention in which the medium is water being steam and / or condensed steam and said steam heating device comprises a recirculation connection 28 configured to receive a stream of steam from the heat exchanger 19, feed the stream of steam to a low temperature steam inlet 25a of the compressor 7. The compressor 7 increases the pressure and temperature of the steam to provide an increased temperature steam 30 available at a high temperature steam outlet 25b of the compressor 7. This high temperature steam outlet 25b of the compressor is fluidicly connected with the heat exchanger 19 to feed increased temperature steam 30 to the heat exchanger (19). The heat exchanger 19 in Fig. 2 (and in the other illustrated embodiments) is typically of a type where only heat can be exchanged between the increase temperature steam 30 and the cooled steam, that is there is typically no mass exchange between the increased temperature steam and the cooled steam. Depending on the mode of operation, the water in the recirculation connection 28 may be steam, or water exiting the heat exchanger 19 may comprised or be condensed steam. 83514PC01 10 In the embodiment of Fig. 2, the steam heating device further comprises a reboiler 17. The reboiler 17 may comprise a condensing chamber 17a for cooling steam, preferably to liquid water, and a reboiling chamber 17b for heating and / or boiling a medium. In the embodiment of Fig. 2, the medium is preferably steam As illustrated in Fig. 2, the condensing chamber 17a is fluidically connected to the drying chamber 3 and configured to receive a stream of steam from the drying chamber, the steam of stream typically being steam being a mixture of steam that has been used for drying of the fish feed and steam originating from water evaporating from the fish feed. The steam entering the condensing chamber 17a therefore typically contains impurities, such as particles from the fish feed. As illustrated in Fig. 2, the reboiling chamber 17b is fluidically connected to and forms part of said recirculation connection 28. Preferably, an inlet of the reboiling chamber 17b is fluidically connected to an outlet of the heat exchanger 19, and an outlet of the reboiling chamber 17b is fluidically connected to an inlet of the compressor 7 such that a medium, being either steam and / or condensed steam, may be circulated in a closed loop between the heat exchanger 19, the reboiling chamber 17b and the compressor 7. The compressor 7 increases the temperature and pressure of the medium to provide an increased temperature steam 30. The reboiling chamber 17b is in thermal communication with the condensing chamber 17a allowing for transfer of heat energy from the steam in the condensing chamber 17a to the medium steam in the reboiling chamber 17b by condensing of the steam in the condensing chamber 17a. The condensing chamber 17a and reboiling chamber 17b are typically configured to prevent exchange of mass between the two chambers. If the amount of heat energy that can be extracted from the steam in the condensing chamber 17a is in excess of the amount of heat needed to evaporate the medium water in the reboiling chamber 17b, additional water may be added to the reboiling chamber 17b to utilize the excess heat energy. Preferably, the additional water is added to the medium water after leaving the heat exchanger 19 and before entering the reboiling chamber 17b. In Fig. 2, addition of water is shown by the added water infeed 33. Alternatively, if the amount of heat energy that can be extracted from the steam in the condensing chamber 17a is less than 83514PC01 11 needed to fully evaporate the medium water in the reboiling chamber 17b, the reboiling chamber 17b may be supplied with a heating element for providing extra heat energy. In Fig. 2, steam is contained within the drying chamber 3 and is used to dry the fish feed. By drying the fish feed, the steam is cooled to cooled steam. In the illustrated embodiment, the cooled steam may be present above the fish feed typically at an upper section of the drying chamber, and the drying chamber 3 may have a cooled steam outlet 9 at the upper section which outlet 9 is in fluidic connection with the reboiler 17 through a flow connection 36. Control of the amount of the stream of cooled steam going into the reboiler 17 can be obtained in various ways and may include one or more settable valves (not illustrated) arranged in the flow connection 36. An actual amount of cooled steam may be determined based on maintaining the pressure in the drying chamber 3 at substantially atmospheric pressure. Comparing the embodiment of Fig. 2 with the embodiment of Fig. 1, the heat exchanger 19 is in Fig. 2 arranged inside the drying chamber 3. The heat exchanger 19 is configured supply heat from the increased temperature steam 30 to the steam inside the drying chamber which may be considered to be cooled steam. By supplying heat from the increased temperature medium steam 30 to the steam in the drying chamber 3, heated steam is provided for drying the fish feed. The temperature of the increased temperature steam 30 will have a higher temperature than the temperature of the heated steam to allow for heating of the steam in the drying chamber 3 by use of the heat exchanger 19. In the preferred embodiment of Fig. 2, the system is configured for cooling the increased temperature medium steam 30 in the heat exchanger 19 to provide a cooled medium steam 32. This cooled medium steam 32 is provided at an outlet of the heat exchanger 19 and is typically cooled steam or steam condensed within the heat exchanger 19. The system comprises a cooled medium steam connection 38 forming part of the recirculation connection 28 and is configured for transporting the cooled or 83514PC01 12 condensed steam from an outlet of the heat exchanger 19 and out of the drying chamber 3. This has an advantage in the sense that as the medium steam never contacts the steam in the drying chamber, the medium steam is a substantially impurity-free steam, and can be reused in the heating system and / or as a steam feed in other parts of the system which require clean steam. In the embodiment of Fig. 2, the flow connection 36 comprises a low temperature compressor 31. The low temperature compressor 31 is illustrated as a turbo machine, but other types of compressors may be used. The low temperature compressor 31 is typically configured to increase the pressure of the steam by a factor of 2.0, but the invention is not limited to this factor. The compressor is named low temperature as it is arranged to increase the temperature of the cooled steam flowing in the flow connection 36 to the low temperature compressor 31. Accordingly, the low temperature compressor 31 is arranged to receive the stream of steam from the drying chamber 3. The low temperature compressor increases the pressure in the stream of steam and at the same time increases the temperature of the stream of steam. By this, heated and pressurized steam 34 is provided to the reboiler 17. In the embodiment of Fig. 2, the heated and pressurized steam is fed into the condensing chamber 17a of the reboiler 17 which is arranged downstream of the low temperature compressor 31. The reboiler 17 is in some embodiments configured to increase a temperature of said heated and pressurized steam 34. Such an increase of temperature may be provided by at least one heating element arranged e.g. arranged inside the boiler volume to apply heat to the steam in the condensing chamber 17a of the reboiler 17. The heating element made by an electrical element, or heat exchanger received a hot fluid from e.g. a natural gas burner. As illustrated in Fig. 2, the cooled medium steam connection 38 is fluidicly connected to the reboiling chamber 17b of the reboiler 17 and thereby being configured to transport the cooled condensed medium steam to the reboiler 17. In some embodiments, the cooled medium steam is a steam condensate, and such a condensate typically has a temperature lower that the heated and pressurized steam 34. In such embodiments, the system is configured for boiling the steam 83514PC01 13 condensate by the heated and pressurized steam 34. Boiling here refers to that the temperature of the steam condensate is raised to a temperature where the steam condensate becomes steam. As can be realized from Fig. 2, the steam condensate (cooled medium steam 32 in Fig. 2) is a condensate of steam, whereby the boiler 7 in such embodiments may be referred to as a reboiler. As illustrated in Fig. 2 the reboiler 17 comprises a water outlet connection 35 configured to outlet liquid water from the reboiler 17. Water outlet from the reboiler 17 is typically water condensed from steam in the condensing chamber 17a, the steam stemming from the drying chamber 3. The water from the water outlet connection 35 therefore typically contains impurities stemming from the fish feed. The compressor 7 is arranged to receive and compress said heated medium steam after the temperature increase in the reboiler chamber 17b of the reboiler 17 to provide the increased temperature steam 30. In preferred embodiments, the compressor is configured to increase the pressure by a factor 2.7 but the invention is not limited to this factor. In some embodiments, the compressor 7 is of a type which requires the use of liquid water in order to provide a steam-tight seal between moving parts. In this kind of compressor, some of the liquid water evaporates and is mixed into the stream of medium steam. Hence, a steady stream of liquid water may be added to the compressor, which results in a net surplus of medium steam. The increased temperature steam 30 exits the compressor 7 by a high temperature steam outlet 25b of the compressor 7. The outlet 25b is fluidic connected to a high temperature steam inlet 26a of the heat exchanger 19. By this, the heat exchanger 19 is supplied with the increased temperature steam 30 for heating of the steam in the drying chamber 3. As the steam in the steam heating recirculation connection 28 including steam in the heat exchanger 19, in the compressor 7, and in the reboiling chamber (17b) is essentially a clean steam, it has been found advantageous to take out some of the steam and feed it e.g. to the conveyer. To this and further other purposes, the steam heating device has a first fluidic bifurcation 23 arranged downstream of the 83514PC01 14 compressor 7 and upstream of the heat exchanger 19. The first bifurcation 23 is configured for feeding a first fraction of the increased temperature steam 30 to the heat exchanger 19, and a second fraction of the increased temperature steam 30 to a steam consuming device, such as to supply steam to said drying chamber 3 and / or to said extruder 2. As illustrated in Fig. 2, the first bifurcation 23 is arranged in the recirculation connection 28. Preferably, the amount of steam that exits the steam heating device in the first fluidic bifurcation 23 is equal to the surplus of medium steam in the steam heating device stemming from the addition of water in the reboiler 17 and / or compressor 7. Alternatively, the amount of steam that exits the steam heating device in the first fluidic bifurcation 23 may be controlled in order to control the amount of steam which is led to the heat exchanger 19 and consequently control the temperature of the steam in the drying chamber 3. Using clean steam from the steam heating device extracted in the first fluidic bifurcation 23 as a supply steam for the production and / or drying of fish feed has the beneficial effect that excess heat energy from the feed drying system is effectively utilized for a process that would otherwise require a separate stream of heated steam. Additionally, at least the medium steam stemming from feeding water to the compressor 7 which would otherwise create an unwanted surplus of medium steam can be effectively utilized. Therefore, additional energy is saved by the system while reducing waste of water. The first bifurcation is typically embodied as a settable three-way valve as otherwise disclosed herein. In order to distribute heated steam towards the fish feed, the system as illustrated in Fig. 2 comprises one or more fans 12. In Fig. 2, two fans 12 are illustrated and they are arranged to suck steam from the sides of the drying chamber at a lower position of the drying chamber 3. This provides a recirculating of steam as illustrated in Fig. 2 and the fans 2 operate as a steam distribution device. Use of one or more fans 12 as steam distribution device can also be applied to the other embodiments of the invention such as those illustrated in the figures. In Fig. 2, the fans 12 circulates steam inside the drying chamber 3 from 83514PC01 15 an upper position of the drying chamber 3 to a lower position of the drying chamber, and upwards past the fish feed and towards the upper position. The flow of steam and / or condensed steam in the recirculation connection 28 and in the flow connection 36 of the steam heating device in Fig. 2 may require pumping to transport the steam. Such a pumping is typically provided by the low temperature compressor 31 and by the compressor 7 respectively. The curved arrows in Fig. 2 (and in Fig. 6) drawn upward from the pellets 16 indicate steam. In the embodiment of Fig. 3, the medium is a refrigerant 29. At least a fraction of the steam inside the drying chamber 3 recirculates inside the drying chamber 3 and is heated by exchanging heat with a refrigerant to become a heated steam. In the illustrated embodiment, the heat exchanger 19 comprises a condenser 4 and the steam heating device comprises a heat pump. The heat pump comprising the heat exchanger 19 with the condenser 4, a throttle valve 5, an evaporator 6 and the compressor 7 arranged in a closed refrigerant circuit. Heat exchange between the refrigerant and cooled steam to increase the temperature of the cooled stream occurs in a condenser 4 of the heat pump. When the refrigerant passes through the condenser 4, it condenses which results in that the released heat is transported via the heat exchanger 19 to the steam thereby increasing the temperature of the steam. The condenser is typically arranged inside the drying chamber 3. By arranged inside the drying chamber 3 is meant that the steam to be heated does not leave the drying chamber during heating, that is the condenser 4 is arranged to heat at least a fraction of the steam contained inside the drying chamber 3. Accordingly, the part of the condenser in which the refrigerant flows may be placed outside the drying chamber 3. Steam heated by the condenser is typically fed into a steam distribution device composed of pipes where the outflow of the pipes directs the heated steam towards the fish feed. In the embodiment of Fig. 3, the steam distribution device directs heated steam to the underside of the carrier illustrated in as a grate 14. 83514PC01 16 Alternatively or in combination with a steam distribution device, the system may comprise a fan 12, which circulates the steam within the drying chamber 3. Such a fan is illustrated in Fig. 3, where it is located inside the condenser 4, although such a fan or a multitude of fans 12 may be placed inside the drying chamber 3 to circulate the steam. Circulate typically refers to moving steam from an upper part of the drying chamber 3 to a lower part of the drying chamber 3 in a circulating motion. As the heated steam is moved to a lower part of the drying chamber 3, the heated steam may move upwards and through the pellets by gravitational motion. Alternatively to have the condenser 4 arranged inside the drying chamber 3, the condenser may be placed outside the drying chamber 3. In such embodiments, the condenser 4 is fluidicly connected with the interior of the drying chamber 3 by fluid lines to receive steam from the drying chamber and deliver heated steam to the drying chamber. Such fluid lines are typically dimensioned to avoid larger pressure drops through the fluid lines, which typically means reducing number of bends and using fluid lines with a large internal diameter, such as large internal hydraulic diameter. In general, the fluid line to receive steam is typically arranged to receive steam after having dried the fish feed and the fluid line to deliver heated steam is typically arranged to deliver steam to a steam distribution device, e.g. a steam deliver system as disclosed above. The illustrated drying chamber 3 besides having a fish feed inlet 8, also has a steam outlet 9 and a dried fish feed outlet 10, through which the dried pellets 16 leave the drying chamber 3. The steam outlet 9 is connected to a cooled stream connection 11 which fluidicly connects the steam outlet 9 to the extruder 2 through the evaporator 6 of the heat pump. The evaporator involves a heat exchange in which heat of the steam is used to evaporate the refrigerant whereby the steam is cooled. In the embodiment shown in Fig. 3, the steam upstream of the evaporator is indicated to be 100OC and the temperature downstream of the evaporator indicated to be less than 100OC, thus being water being in a liquid phase. These temperatures are examples only and other embodiments of the invention may 83514PC01 17 operate at other temperatures. However, it is generally preferred that the steam upstream of the evaporator is close to the boiling point of water and that water is in liquid phase downstream of the evaporator 6. The cooled stream connection 11 to the extruder 2 is in the illustrated embodiment configured to mix the liquid (the cooled steam after evaporator 6) into a raw material to be processed and / or being processed by extruder 2 to provide the extruded fish feed. Thus, the liquid may be added to the raw materials before entering into the extruder and / or at a position along the extruder 2. There may be a significant steam contribution from the feed entering into the drying chamber 3, as the extruder may deliver superheated material (source of the initial steam) at a temperature of 110°C or even higher. At ambient pressure, a flash off of steam from the feed may be in the order of 3-4% of the moisture content of the feed which together with a boiler 17 may at least contribute in providing the steam for drying. The boiler will be disclosed in detail below. In the embodiment illustrated in Fig. 2, the condenser 4 is arranged inside the drying chamber 3 so that the condenser is fully contained inside the drying chamber 3. In order to increase drying of the pellets, the system for steam drying may have one or more fans 12 arranged to circulate the steam contained inside the drying chamber 3. Such a fan 12 may advantageously be combined with the condenser 4, where the fan 12 is arranged to suck steam through the condenser 4. In the embodiment shown in Fig. 2, the fan is illustrated as being housed within the condenser 4, however the fan may be placed in other positions such as upstream or downstream of the condenser 4. In addition, a multitude of fans 12 may arranged in the drying chamber 3 and / or in the condenser 4. The system for drying typically comprises an electronic processor 13. This processor is typically configured to control the operation the heat pump and, when implemented, the one or more fans 12. The control is carried out so as to raise the temperature of the steam inside the drying chamber by less than 300C, such 83514PC01 18 as by less than 400C, preferably by less than 500C. By “raise the temperature” is typically meant the temperature increase provided by the condenser 4. The processor 13 is typically also configured to control heat pump to decrease the temperature of an outlet steam outlet from said evaporator 6 to a temperature below which the outlet steam condensates into liquid water, such as to a temperature below 1000C, preferably below 950C, such as below 900C and above 850C. By “decrease the temperature” is typically meant the temperature decrease provided by the evaporator. In order to decrease unintended exit of steam from the drying chamber 3, the fish feed inlet 8 may have a lock allowing fish feed to enter into said drying chamber 3 while substantially preventing air to enter into said drying chamber 3 and substantially preventing the steam in the drying chamber 3 to exit the drying chamber 3 through the fish feed inlet 8. In such embodiments, an amount of pellets 16 is introduced into the lock through an entry gate, which subsequently is closed. Thereafter an exit gate providing a passage into the drying chamber 3 is opened and the pellets are brought into the drying chamber. Transport of the pellets into / out from and through the lock is provided e.g. by gravity and / or a conveyer system, e.g. including conveyer belts. Similarly, the dried fish feed outlet 10 may have a lock allowing fish feed to exit the drying chamber 3 while substantially preventing air to enter into the drying chamber 3 and substantially preventing the steam in the drying chamber 3 to exit the drying chamber 3 through the fish feed outlet 10. This lock may be embodied as disclosed above in connection with the lock of the fish feed inlet. As detailed above, the extruder 2 is typically configured to provide the fish feed as pellets. A pellet refers to that the fish feed is in a form of separate pieces. To enhance drying, the drying chamber may be air tight. By providing the drying chamber as an air tight chamber, inflow of air from and outflow of steam to the ambience may be greatly reduced and as the steam is used as heat carrier, containment of the steam inside the drying chamber without being diluted by air entrainment is found advantageous. 83514PC01 19 It has been found to decrease drying time, if the super heated steam passes through a horizontal layer of pellets in a vertical direction. To accomplish this, the drying system has a grate 14 arranged inside the drying chamber 3. The grate 14 is configured to carry the pellets while allowing for a flow of the steam contained in the drying chamber 3 through the grate 14. The grate is made mechanical strong to carry the weight of the pellets 16, and at the same time having openings allowing the steam to pass without the pellets 16 falling through the openings. The one or more fans 12 detailed above may be configured to provide a flow of the steam contained in the drying chamber including a flow upwardly through the grate 14. In the embodiments of Fig. 1, Fig. 2, and Fig. 3, the grate 14 forms part of a conveyer conveying the fish feed from the from the fish feed inlet 8 to the dried fish feed outlet 10. The conveyer comprising a chute leading the fish feed from the fish feed inlet 8 to the surface of a conveyer belt. The conveyer belt is provided as an endless grate belt and is moved by rollers. For the embodiments of Fig. 1 and Fig. 3 and similar embodiments, a fraction of the cooled steam is not re-heated into a heated steam. In the embodiment of Fig. 1 a fraction of the cooled steam ends as a condensate in the receptacle 20, and another fraction 21 may be fed into the extruder 2. In Fig. 3, a fraction of the cooled steam is fed into the extruder 2 after having passed the evaporator 6. Thus, continuously operation may require addition of steam such as heated steam to the system. To accomplish such addition of steam, the system preferably comprises a boiler 17 which is configured for producing steam and is fluidicly connected with e.g. the drying chamber 3 to feed produced steam into the drying chamber 3. While feeding produced steam into the drying chamber 3 may be preferred, produced steam may be introduced into the system in general, and mixed with the heated steam present in the system. The boiler 17 may also be used to initiate drying of fish feed upon a start-up of the system where there is no heated steam in the system. 83514PC01 20 Non-limiting Example 1 – energy calculations for the system schematically illustrated in Fig. 4 In the following, energy calculations are presented in regard to drying of fish feed in a system as disclosed in Fig. 4. The system is specified to operate as presented in the following table: Fish feed input to drying chamber 150 kg / h Relative water content in input fish feed 28% Water flash-off by expansion after extruder in the 4% region around fish feed inlet 8 Relative water content in fish feed after drying – after 7% leaving the dried fish feed outlet 10 Pressure in drying chamber 1.013 bar Saturation temperature in drying chamber 100OC Temperature of steam at cooled steam outlet 9 110OC Temperature of steam inlet to drying chamber at heated stem inlet 22 150OC The relative water content is defined as: where ^^^^is the mass of the fish feed inlet, here 150 kg / h, ^^^^is the mass of the water. Total water content when leaving the extruder 2: ^̇^^^,^^ = 28% ∙ 150^^^^⁄ ℎ = 42^^^^ ⁄ℎIndex ^^ refers to water and index ^^ refers to inlet. Total amount of water flashoff ^̇^^^,^^: ^̇^^^,^^ = 4% ∙ 150^^^^⁄^^^^ ℎ= 6⁄ℎTotal amount of water in dried fish feed ^̇^^^,^^: ^̇^^^,^^ = 7% ∙ 150^^^^⁄^^^^ ℎ= 10.5⁄ℎThus, the total amount of water to be dried actively off (flash drying do not require active drying by steam): 10.5^^^^⁄ℎ= 25.5ℎ 83514PC01 21 Under the assumption that the feed input (pellets) has a temperature around 100OC, the energy ^^ needed to evaporate ^̇^^^,^^can be estimated by: ^^^^ ^̇^^^^^ 25.5⁄ ∙^^ = ,^^=ℎ3.600 15.99 ^^^^3.600 The volume of steam ^^^^^^^^to be transported by the pump 18 (typically being a fan, such as ventilator) can be estimated in the following manner. The heat ^^ needed to evaporate water ^̇^^^,^^is provided by cooling of the steam ^̇^^^from 150OC to 110OC: => ^̇^ = 0.2170.264 =^^3 ^^ 0.36⁄ ^^As the pump 18 transports the steam ^̇^^^in the system (here ^̇^^^is the amount of steam flowing out through cooled steam outlet 9), the pump 18 should be operating and selected so as to provide a pressure increase outbalancing the pressure loss resulting from transporting the steam in the system. A typical value for the pressure loss for a system as in Fig. 4 is in the region of 0.02 bar, thus, the pump increases the pressure of the steam to 1.013 bar + 0.02 bar= 1.033 bar. The pump typically has efficiency of η=0.6. The electrical power ^^^^can be estimated based on (pressure given in kPa): ^^^^^^^^ ∙ ∆^^ 0.36 ∙ 2^^^^= == 1.21 ^^^^^^ 0.6 This electrical power ^^^^goes into the steam and gives rise to a temperature increase in the steam estimated to be in the order of 1.5OC. The compressor 7 has an efficiency of η=0.6 and provides a pressure increase of∆^^ = 5 ^^^^^^. The amount of steam going into the compressor ^̇^^^,^^ is determined inas disclosed below. ^^ = ∆^^ℎ^^^^^^^^^^ ∙ ^^ ∙ ^̇^^^ = (370 ^^^^ − 155^^^^) ∙ 1,84 ∙ ∆^^ℎ^^^^^^^^^^may be defined as per design. The electrical power consumption of the compressor can be estimated by: ^^^^ = ^̇^^^,^^ ∙ ∆ℎ^^ 83514PC01 22 where ^̇^^^,^^is the mass flow of steam through the compressor and ∆ℎ^^,^^^^^^^^is the real change in enthalpy of the mass flow of steam through the compressor. The real change in enthalpy may be determined based on e.g. table look-ups, inthe following referred generic to as “^^^^^^(.. )“and the following relationships (index“c” refers to compressor, “^^^^^^” to output , “^^^^” to inlet): ^^^^,^^^^^^ = ^^^^^^^^^^,^^^^^^ ∙ ∆^^ = 1.033 ∙ 5 = 5.165 barThe saturation temperature at the outlet 25b of the compressor is found by: 155^^^^ Enthalpy ℎ and entropy ^^ are found by: 5.165 ^^^^^^) 5.165 ^^^^^^)The compression in the compressor is assumed to be isentropic: ^^^^,^^^^^^ = ^^^^,^^^^Wherein enthalpy of the steam leaving the compressor can be found by: ℎ^^,^^^^^^ = ^^^^^^(^^^^,^^^^^^;^^^^,^^^^^^) ^^^^^^ ℎ ^^,^^^^ = ^^^^^^(^^^^,^^^^; ^^^^,^^^^^^)wherein ℎ refers to isentropic compression. By this, the change in enthalpy can be calculated as: An estimation of the actual change in enthalpy can be determined by ∆ℎ∆ℎ^^^^= ^^ where ^^ is an efficiency coefficient of the compressor having a numerical value of 0.7. The enthalpy in the steam leaving the compressor can thus be determined as: The power to operate the compressor and the temperature of the steam after the compressor can now be estimated as: ^^^^ = ^̇^^^,^^∆ℎ^^ = 3.2 ^^^^ 83514PC01 23 The compressor 7 raises the temperature of the steam to 370OC and the pressure to 5.165 bar. This heated and compressed stream of steam is fed into the heat exchanger 19. The compressed steam is used for heating the steam to be fed into the drying chamber 3 by use of the heat exchanger 19. The temperature of the steam to be fed into the drying chamber is to be 150OC and the steam after the pump 18 has a temperature of 110O+1.5OC=111.5OC. It is selected that the temperature difference between the compressed steam leaving the heat exchanger is 5OC, that is the temperature of the compressed steam leaving the heat exchanger is 155OC and the heated steam leaving the heat exchanger is 150OC. The heat exchanger is considered to be an ideal heat exchanger. The mass flow of steam out of the compressor ^̇^^^,^^can be estimated based on (∆ refers to the difference between inlet and outlet of the heat exchanger): 15.99 ^^^^ =0.00615 ∆ℎ^^,^^is found by a table look-up for a situation where the pressure of the compressed steam is constant during its passage of the heat exchanger. It noted that a fraction of the compressed steam condensates during passage of the heat exchanger. By lowering the pressure in the compressor steam after passage of the heat exchanger, flash steam can be produced which may e.g. be fed into the drying chamber, or extruder. Alternatively, the pressure may be maintained and the steam with condensate may be used in a high pressure hot water equipment. Thus, based on the above estimations, it can be seen than the estimated electrical power consumption to evaporate 25.5 ^^^^⁄ℎof water from the feed requires^^^^ + ^^^^ = 1.21 ^^^^ + 3.2 ^^^^ = 4.41^^^^As comparison, if hot air was used for drying where reclaiming of energy from the hot air after drying is not feasible, it would have required at least 15.99kW to dry the same amount of feed. No-limiting Example 2 – calculations for the illustrated in Fig. 5 83514PC01 24 In the following, energy calculations are presented in regard to drying of fish feed in a system as disclosed in Fig. 5. The system is specified to operate as presented in the following table. Fish feed input to drying chamber 20,000 kg / h Relative water content in input fish feed 28% Water flash-off by expansion after extruder in the 4% region around fish feed inlet 8 Relative water content in fish feed after drying – after 7% leaving the dried fish feed outlet 10 Pressure in drying chamber 1.013 bar Saturation temperature in drying chamber 100OC Temperature of steam at cooled steam outlet 9 100OC Temperature of heated steam after condenser 4 150OC The relative water content is defined as: where ^^^^is the mass of the fish feed inlet, here 20,000 kg / h, ^^^^is the mass of the water. Total water content when leaving the extruder 2: ^̇^^^,^^ = 28% ∙ 20,000^^^^⁄^^^^ ℎ= 5,600⁄ℎIndex ^^ refers to water and index ^^ refers to inlet. Total amount of water flashoff ^̇^^^,^^: ^̇^^^,^^ = 4% ∙ 20,000^^^^⁄^^^^ ℎ= 800⁄ ℎ Total amount of water in dried fish feed ^̇^^^,^^: ^̇^^^,^^ = 7% ∙ 20,000^^^^⁄^^^^ ℎ= 1,400⁄ ℎ Thus the total amount of water to be dried actively off (flash drying do not require active drying by steam): 800^^^^⁄ ℎ ) − 1,400^^^^⁄ ℎ = 3,400 ℎUnder the assumption that the feed input has a temperature around 100OC, the energy ^^ needed to evaporate ^̇^^^,^^can be estimated by: 83514PC01 25 ^^^^ ^̇^^^,^^^^ 3,400⁄ ∙ 2,257^^^^ / ^^^^ = ℎ 3.6003.600 ^^^^^^ = 2,132 ^^^^⁄ ℎFor the sake of calculations, the condenser 4, the evaporator 6, the throttle valve 5 and the compressor are considered to be a heat pump. It is assumed that the heat pump heats the steam from 100OC to 150OC and that the coefficient of performance ^^^^^^: ^^^^^^ =^^ ^^= 3.4ℎ^^Provides an estimate on the electrical power ^^ℎ^^needed provide a heat ^^ in the amount of 2132 kW: The amount of steam to be circulating inside the drying chamber can be calculated by giving ^̇^^^ = 28.97^^^^⁄28.97 ^^^^⁄^^^^ ^^3 = 48.3⁄^^0.6 ^^^^ ⁄ ^^3The circulation is provided by the fan, and the electrical power consumption of such a fan is typically in the order of 20% of the power consumption of the heat pump. Thus, the electrical power consumption of the fan can be estimated as ^^^^ = 20%627^^^^ = 125.4 ^^^^Accordingly, the total electrical power is: ^^ℎ^^ + ^^^^ = 627^^^^ + 125.4^^^^ = 752.4^^^^As comparison, if hot air was used for drying where reclaiming of energy from the hot air after drying is not feasible, it would have required at least 2.132 kW to dry the same amount of feed. Reference is made to Fig. 6 schematically illustrating a system for drying fish feed in which a number of drying chambers are arranged consecutively to each other. In the illustrated embodiment, four drying chambers are arranged in a row of drying chambers but other numbers than four may be used. Hence, in preferred embodiments, the system comprises at least two consecutive drying chambers 83514PC01 26 3a-d. Consecutive here refers to that fish feed dried in one drying chamber is transported to a subsequent drying chamber. Hence, in preferred embodiments, fish feed is partially dried in an upstream one of the consecutive drying chambers 3a-d and is transported into a downstream one of said consecutive drying chambers (3a-d) for further drying. The drying chambers 3a-d may be equipped with locks at the fish feed inlet 8 and fish feed outlet 10. Alternatively, the consecutive drying chambers 3a-d fish feed inlet and outlet 8, 10 may have an opening area so that an amount of steam flowing from one drying chamber to another through the inlets and outlets 8, 10 may be considered negligible. The embodiment of Fig. 6 is exemplified based on the drying system of Fig. 2, however, the embodiment of for instance Figs. 1-5 may also be used for a system comprising consecutive drying chambers 3a-d. In the illustrated embodiment, an inlet valve 34a-d is provided for each of the consecutive drying chambers. These inlet valves 34a arranged in the recirculation connection 28 of steam heating device in a parallel configuration where each of the inlet valves 34a-d is fluidicly connected with the compressor 7 downstream thereof to receive in parallel increased temperature steam 30 from the compressor 7 and being configured to set a volume flow of increased temperature steam, received from the compressor 7. Each of the inlet valves 34a-d is configured to set a flow of increased temperature steam to a particular value, typically being preselected. The inlet valves are typically settable allowing e.g. a controller or a user to set a flow to a particular value. By this, the amount of temperature increased medium can be set to be individual for each drying chamber 3a-d. The amount of temperature increased medium flowing into a heat exchanger 19 of a drying chamber 3 determines inter alia in combination with the speed at which the fish feed is transported inside the drying chamber 3, the temperature of the steam in the drying chamber and thereby the amount of water dried off from the fish feed in a particular drying chamber. 83514PC01 27 In preferred embodiments, the system is operated so that a selected fraction of the total amount water to be dried off is dried of in a drying chamber. Representative non-limiting examples for a system comprising four drying chambers are Fract1=0.35, Frac2=0.3, Frac3=0.2 and Frac4=0.15. Here e.g. Frac2=0.3 refers to that 30% of the total water to be dried of is dried off in chamber 2. In order to control the amount of steam entering into the flow connection 36 from each of the consecutive drying chambers 3a-d, an outlet valve 35a-d is arranged for each of consecutive drying chambers in parallel in the flow connection 36. These outlet valves 35a-d are arranged upstream of the compressor 31 and are each configured to set a volume flow of cooled steam out of the consecutive drying chambers individually. These outlet valves 35a-d are typically settable valves as otherwise disclosed herein, and the setting of the valves may be carried out by the controller or an operator. In preferred embodiments, an interior volume of the drying chamber 3 during drying is occupied by steam during drying. By this, the amount of e.g. air contained in the drying chamber is, if present, present in negligible amounts. Interior volume a drying herein typically refers to the volume encapsulated by perimeter wall defining a drying chamber. Physical elements, such as fans, fish feed etc do no contribute to the interior volume. A controller as referred to herein is typically an electronic controller, which may have software allowing the controller to perform or instantiate various control functions. In general, preferred embodiments of a drying system is controlled by such as electronic controller to e.g. operate the heat pump, set valves to provide a certain flow and the like. Non-limiting example 4 In the following, energy calculations are indicated in regard to drying of fish feed in a system as disclosed in Fig. 2. The system is specified to operate as presented in the following table. Fish feed input 20,000 kg / h 83514PC01 28 Relative water content in input fish feed 28% Water flash-off by expansion after extruder 4% Relative water content in fish feed after drying 7% Pressure in drying chamber 0.98 bar Saturation temperature in drying chamber 99.7OC The relative water content is defined as: ^^^^ ∙ 100%^^^^where ^^^^is the mass of the fish feed inlet, here 20,000 kg / h, ^^^^is the mass of the water. Total water content when leaving the extruder 2: ^̇^^^,^^ = 28% ∙ 20,000^^^^⁄^^^^ ℎ= 5,600⁄ℎIndex ^^ refers to water and index ^^ refers to inlet. Total amount of water flash-off ^̇^^^,^^: ^̇^^^,^^ = 4% ∙ 20,000^^^^⁄ℎ= 800^^^^⁄ ℎ Total amount of water in dried fish feed ^̇^^^,^^: ^̇^^^,^^ = 7% ∙ 20,000^^^^⁄^^^^ ℎ= 1,400⁄ ℎ Thus, the total amount of water to be dried actively off (flash drying do not require active drying by steam): 800^^^^⁄^^^^ ℎ) − 1,400 ⁄ ℎ = 3,400⁄ℎUnder the assumption that the feed input has a temperature around 100OC, the energy ^^ needed to evaporate ^̇^^^,^^can be estimated by: 3,400 ^^^^⁄ ∙ 2,257^^^^ / ^^^^^^ =^̇^^^,^^^^ = ℎ 3^^^^^^ = 2,132 ^^^^3,600,600 ⁄ ℎWe present the following arrays for the temperature (^^^^), fractions (^^^^), and mass in each chamber. Index i refers to chambers 3a-3d. 83514PC01 29 The temperatures and fractions are typically set according to a specific design, and may have the following values: 0.350.300.20] 0.15To simplify the following calculations, the assumption can be made that when the feed enters a new chamber the temperature of the moisture in the feed is around 100 °C. According, the energy needed to evaporate the moisture of the feed in each chamber is. ^^^^ = ^^^^ ∙ 2,132 ^^^^As the steam in each chamber essentially stems from the feed, there is also some energy needed to heat it further to the set temperature in each chamber. This energy can be calculated by the following equation set. ^^^^ é0.331 ù ê ^^ ú 10 °^^ ê ^^^^ 0 ú ^^ .283 ^^,^^^^^^^^^^ℎ^^^^^^ = (^^^^ − 100 °^^) ∙ ^^^^ ∙ ^̇^^^,^^^^^^^^ = [20 °^^ ê ú 25 °^^] ∙ 2.027^^^^ ∙ ^^∙ ^^ ê ^^^^ú , 30 °^^ ê 0.189 ú ê ^^ ú ê ^^^^ 0. ú ë 142 ^^ û746.8 ^^^^ 6.7 ^^^^ 753.5 ^^^^ ^^^^,^^^^^^^^^^ = ^^^^ + ^^^^,^^^^^^^^^^ℎ^^^^^^ = [640.1 ^^^^ 11.5 ^^^^ 65 426.7 ^^^^] + [9.6 ^^^^] = [1.6 ^^^^ 436.3 ^^^^ ] 320.0 ^^^^ 8.6 ^^^^ 328.6 ^^^^ The energy is provided by condensation of saturated steam at high pressure condensing in the heat exchanger. The amount of steam needed per chamber can be calculated from the following (2113 is a table lookup value). ^^^^ é0.356 ù ê ^^ ú ê ^^^^ 0 ú ê .308 ^^ = ^^ ∙ 2,^^ ú ^^,^^^^^^^^^^ 113 ê ^^^^ú ê 0.206 ú ê ^^ ú ê ^^^^ 0 ú ë .155^^ ûThe flow into each chamber is controlled by valves. Excess water not needed may be removed through bifurcation 23 to avoid overheating in the chambers. The condensed medium water exiting the heat exchanger experiences a pressure drop 83514PC01 30 due to the lowered volume, and the pressure and temperature of the condensate balances out at about 1.56 bar and around 112 °C respectively. The energy available from the condensing chamber 17b can be calculated from the latent heat that can be gained from condensation of the steam from the turbo. The steam enters the turbo at a temperature of around 119 °C, and is compressed to 1.96 bar. This compression lets the steam remain as steam, as the boiling point of water at 1.96 bar is around 119 °C, and the compression increases it slightly. The heat energy from the steam cooling to the boiling point is negligible. Therefore, the total heat energy that can be gained in the condensing chamber 17b can be calculated as the following. ∙2,204^^^^ =2,572 ^^^^ ^^^^ The condensate entering the reboiling chamber is at a slightly lower pressure, and after evaporating is at around 1.76 bar. The amount of water which can be evaporated in the reboiling chamber 17b from the energy in the condensing chamber 17a can therefore be estimated by the following. As the sum of infeed to the heat exchanger (∑^̇^^^,^^^^^^^^^^ = 1.025) is lower than theamount of water which may be heated in the reboiler, extra water can be added to the reboiler in order to utilize all excess heat from the steam. Table used for lookup: https: / / www.engineeringtoolbox.com / saturated-steam-properties-d_457.html

[0002] 83514PC01 31 ITEMIZED LIST OF PREFERRED EMBODIMENTS Item 1. A system (1) for steam drying extruded fish feed, wherein said fish feed, during use of the system, is exposed to a heated steam whereby said fish feed is dried and said heated steam is cooled to a cooled steam, said system comprising^ an extruder (2) for extruding fish feed;^ a drying chamber (3) comprising a fish feed inlet (8) configured to receivemoist fish feed to be dried from said extruder (2) and a dried fish feed outlet (10) configured for outlet dried fish feed;^ a carrier located inside said drying chamber (3) configured to support saidmoist fish feed while being exposed to said heated steam;^ a steam heating device configured to provide said heated steam by increasinga temperature of said cooled steam, said steam heating device comprises a compressor (7) configured to increase a temperature of a medium by compression, and a heat exchanger (19) configured to transport heat from said medium to said cooled steam;^ a steam distribution device configured to distribute said heated steam towardsat least a fraction of said fish feed supported by said carrier (14). Item 2. A system according to item 1, wherein said medium is said cooled steam, and said steam heating device forms part of a recirculation connection (28) configured to receive said cooled steam, and feed heated steam to said steam distribution device, said recirculation connection (28) comprises:^ a first fluidic bifurcation (23) upstream of said heat exchanger (19) andupstream of said compressor (7), wherein^ said first fluidic bifurcation (23) is configured for feedingo a first fraction of said cooled steam to cooled steam inlet (24a) of saidheat exchanger (19), and oa second fraction of said cooled steam to a low temperature steam inlet(25a) of said compressor (7),^ a high temperature steam outlet (25b) of said compressor (7) is fluidicconnected to a high temperature steam inlet (26a) of said heat exchanger (19), 83514PC01 32^ a heated steam outlet (24b) of said heat exchanger (19) is fluidic connectedwith said recirculation connection (28) upstream of said steam distribution device. Item 3. A system according to item 2, wherein said high temperature steam outlet (25b) is fluidic to said high temperature steam inlet (26a) through a second fluidic bifurcation (27), said second fluidic bifurcation (27) being controllable to divide said high temperature steam from said high temperature steam outlet (25b) into two settable fractions, one of which is fed into said high temperature steam inlet (26a) of said heat exchanger (19). Item 4. A system according to item 3, wherein said second fluidic bifurcation is further fluidic connected with said extruder (2) to feed another of said two settable fractions to said extruder (2) Item 5. A system according to any one of the preceding items 2-4, wherein a low temperature outlet (26b) of said heat exchanger (19) is fluidic connected with a receptacle (20) to received steam condensed within said heat exchanger (19). Item 6. A system according to any one of the preceding items 2-5, comprising a pump (18) arranged fluidicly in-between said first bifurcation and said cooled steam inlet (24a). Item 7. A system according to any one of the preceding items, wherein said drying chamber comprises a cooled steam outlet (9) and a heated steam inlet (22), wherein said recirculation connection (28) fluidicly connects said cooled steam outlet (9) with said heated steam inlet (22). Item 8. A system (1) for steam drying extruded fish feed according to item 1, wherein^ said medium is a refrigerant^ said heat exchanger (19) comprises a condenser (4) and said steam heatingdevice comprises a heat pump comprising said condenser (4), a throttle valve (5), an evaporator (6) and said compressor (7) arranged in a closed refrigerant circuit; 83514PC01 33^ said condenser (4) is arranged to heat at least a fraction of said cooled steam,and^ said evaporator is arranged to cool at least a fraction of said cooled steam.Item 9. A system according to item 8, wherein said drying chamber (3) comprises a cooled steam outlet (9) fluidic connected to a cooled stream connection (11) of said system, said cooled stream connection (11) is fluidic connected to said extruder through said evaporator (6) to provide a further cooled steam to said extruder. Item 10. A system according to item 9, wherein said cooled stream connection (11) comprising a fluid buffer arranged downstream of said evaporator (6) and upstream of said extruder (2) Item 11. A system according to any one of the preceding items 8-11, wherein said condenser (4) is arranged inside said drying chamber (3). Item 12. A system according to any one of the preceding items, further comprising one or more fans (12) arranged to circulate said cooled steam and said heated steam inside the drying chamber (3). Item 13. A system according to any one of the preceding items, when dependant on claim 8, comprising a processor (13) configured to control the operation of said heat pump and said one or more fans (12) to raise the temperature of said cooled steam inside said drying chamber by less than 300C, such as by less than 400C, preferably by less than 500C. Item 14. A system according to item 13, wherein said processor (13) is configured to control said heat pump to decrease the temperature of an outlet steam from said evaporator (6) to a temperature below which said outlet steam condensates into liquid water, such as to a temperature below 1000C, preferably below 950C, such as below 900C and above 850C. Item 15. A system according to any one of the preceding items, wherein said fish feed inlet (8) comprising a lock allowing fish feed to enter into said drying 83514PC01 34 chamber (3) while substantially preventing air to enter into said drying chamber (3) and substantially preventing said steam in the drying chamber (3) to exit said drying chamber (3) through said lock. Item 16. A system according to any one of the preceding items, wherein said dried fish feed outlet (10) comprising a lock allowing fish feed to exit said drying chamber (3) while substantially preventing air to enter into said drying chamber (3) and substantially preventing said steam in the drying chamber (3) to exit said drying chamber (3) through said lock. Item 17. A system according to any one of the preceding items, wherein the extruder (2) is configured to provide the fish feed as pellets. Item 18. A system according to any one of the preceding items, wherein the drying chamber is air tight. Item 19. A system according to any one of the preceding items, wherein said carrier comprising a grate (14) arranged inside said drying chamber, said grate (14) is configured to carry said fish feed and allow flow of said steam contained in the drying chamber (3) through said grate (14). Item 20. A system according to item 12 and 19, wherein said one or more fans (12) are configured to provide a flow of said steam contained in the drying chamber including a flow upwardly through said grate (14). Item 21. A system according to item 19 or 20, wherein said grate forms part of a conveyer conveying the fish feed from the from the fish feed inlet (8) to the dried fish feed outlet (10). Item 22. A system according to any one of the preceding claims, comprising a boiler (17) configured for producing steam and fluidicly connected with said system, preferably fluidicly connected with said drying chamber (3) to feed produced steam into said system. 83514PC01 35 Item 23. A method of drying fish feed, the method utilizes a system according to any one of the preceding claims, and comprises:^ feeding fish feed into said drying chamber,^ operating said system to provide heated steam, and^ contacting said fish feed with said heated steam.Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms “comprising” or “comprises” do not exclude other possible elements or steps. Also, the mentioning of references such as “a” or “an” etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

[0003] 83514PC01 36 LIST OF REFERENCE SYMBOLS USED 1 System for steam drying extruded fish feed 2 Extruder 3 Drying chamber 4 Condenser 5 Throttle valve 6 Evaporator 7 Compressor 8 Fish feed inlet 9 Cooled steam outlet 10 Dried fish feed outlet 11 Cooled stream connection 12 Fan 13 Processor 14 Grate 15 Raw material 16 Pellet (fish feed pellet) 17 Boiler, such as reboiler 17a Condensing chamber 17b Reboiling chamber 18 Pump 19 Heat exchanger 20 Receptacle 21 process water connection, e.g. input to extruder 2 22 Heated steam inlet 23 First fluidic bifurcation 24a Cooled steam inlet of heat exchanger 24b Heated steam outlet of heat exchanger 25a Low temperature steam inlet of compressor 25b High temperature steam outlet of compressor 26a High temperature steam inlet of heat exchanger 26b Low temperature steam outlet of heat exchanger 27 Second fluidic bifurcation 28 Recirculation connection 29 Refrigerant 83514PC01 37 30 Increased temperature steam 31 low temperature compressor 32 Cooled medium steam 33 Added water infeed 34 Heated and pressurized steam 35 Water outlet connection 34a-d Inlet valves 35a-d Outlet valves 36 Flow connection 38 Cooled medium steam connection

Claims

83514PC01 38 CLAIMS 1. A system (1) for steam drying extruded or pelletized fish feed, wherein said fish feed, during use of the system, is exposed to a heated steam whereby said fish feed is dried and said heated steam is cooled to a cooled steam, said system comprising^ preferably an extruder (2) for extruding fish feed;^ a drying chamber (3) comprising a fish feed inlet (8) configured to receivemoist fish feed to be dried, preferably from said extruder (2), and a dried fish feed outlet (10) configured for outlet dried fish feed;^ a carrier located inside said drying chamber (3) configured to support saidmoist fish feed while being exposed to said heated steam;^ a steam heating device configured to provide said heated steam by increasinga temperature of said cooled steam, said steam heating device comprises a compressor (7) configured to increase a temperature of a medium by compression, and a heat exchanger (19) configured to transport heat from said medium to said cooled steam;^ a steam distribution device configured to distribute said heated steam towardsat least a fraction of said fish feed supported by said carrier (14).

2. A system according to claim 1, wherein said medium is said cooled steam, and said steam heating device forms part of a recirculation connection (28) configured to receive said cooled steam, and feed heated steam to said steam distribution device, said recirculation connection (28) comprises:^ a first fluidic bifurcation (23) upstream of said heat exchanger (19) andupstream of said compressor (7), wherein^ said first fluidic bifurcation (23) is configured for feedingo a first fraction of said cooled steam to cooled steam inlet (24a) of saidheat exchanger (19), and oa second fraction of said cooled steam to a low temperature steam inlet(25a) of said compressor (7),^ a high temperature steam outlet (25b) of said compressor (7) is fluidicconnected to a high temperature steam inlet (26a) of said heat exchanger83514PC01 39^ a heated steam outlet (24b) of said heat exchanger (19) is fluidic connectedwith said recirculation connection (28) upstream of said steam distribution device.

3. A system according to claim 2, wherein said high temperature steam outlet (25b) is fluidic to said high temperature steam inlet (26a) through a second fluidic bifurcation (27), said second fluidic bifurcation (27) being controllable to divide said high temperature steam from said high temperature steam outlet (25b) into two settable fractions, one of which is fed into said high temperature steam inlet (26a) of said heat exchanger (19).

4. A system according to claim 3, wherein said second fluidic bifurcation is further fluidic connected with said extruder (2) to feed the other of said two settable fractions to said extruder (2) 5. A system according to any one of the preceding claims 2-4, wherein a low temperature outlet (26b) of said heat exchanger (19) is fluidic connected with a receptacle (20) to received steam condensed within said heat exchanger (19).

6. A system according to any one of the preceding claims 2-5, comprising a pump (18) arranged fluidicly in-between said first bifurcation and said cooled steam inlet (24a).

7. A system according to any one of the preceding claims, wherein said drying chamber comprises a cooled steam outlet (9) and a heated steam inlet (22), wherein said recirculation connection (28) fluidicly connects said cooled steam outlet (9) with said heated steam inlet (22).

8. A system according to claim 1, wherein said medium is water being steam and / or condensed steam, and said steam heating device comprises ^a recirculation connection (28) configured to receive a stream of steamfrom said heat exchanger (19), feed said stream of steam to said compressor (7) providing an increased temperature steam (30), and feed increased temperature steam (30) to said heat exchanger (19).83514PC01 40 9. A system according to 8, wherein said steam heating device comprising a reboiler (17), said reboiler comprising; ^a condensing chamber (17a) arranged in fluid connection with said dryingchamber (3) and configured to receive a stream of said cooled steam from said reaction chamber (3) and cool said cooled steam, ^a reboiling chamber (17b) arranged in fluid connection with saidrecirculation connection (28) and configured to receive a stream of cooled medium steam (32) being medium steam and / or condensed medium steam from said heat exchanger (19), heat said medium, and feed said heated medium to said compressor (7) to compress and increase a temperature of said heated medium to provide an increased temperature steam (30) to said heat exchanger (19), wherein, said condensing chamber (17a) is in thermal communication with said reboiling chamber (17b) such that heat energy from said stream of cooled steam from said reaction chamber (3) is transferred to said medium in said reboiling chamber, and wherein said medium is steam or condensed steam.

10. A system according to claim 9, wherein^ said heat exchanger is arranged inside said drying chamber and configured tosupply heat from said increased temperature heated steam (30) to steam inside said drying chamber (3) to provide said heated steam,^ said system is configured for cooling said increased temperature steam (30) insaid heat exchanger (19) to provide a cooled medium steam (32), being medium steam and / or medium steam condensed with said heat exchanger (19), and^ said system comprising a cooled medium steam connection (38) configured fortransporting said cooled medium steam (32) from said heat exchanger (19) to said reboiler (17).

11. A system according to claim 10, comprising a flow connection (36) between said drying chamber (3) and said condensing chamber of said reboiler (17), said recirculation connection comprising a low temperature compressor (31), wherein^ said low temperature compressor (31) is83514PC01 41 oarranged to receive said stream of steam from said drying chamber (3),and obeing configured to increase a pressure and a temperature of saidstream of steam to provide a heated and pressurized steam (34), and^ said reboiler (17) being arranged downstream of said low temperaturecompressor (31) and being configured to increase a temperature of said cooled medium steam by using energy from said heated and pressurized steam (34).

12. A system according to any one of claims 10 or 11, wherein said reboiler (17) comprises a water outlet connection (35) configured to outlet water such as steam and / or condensed steam from said reboiler (17).

13. A system according to claim 12, wherein said water from said reboiler is condensed from said heated and pressurized steam (34).

14. A system according to any one of the preceding claims 8-13, wherein said steam heating device comprises a first fluidic bifurcation (23) arranged downstream of said compressor (7), said first bifurcation (23) is configured for feeding^ a first fraction of said increased temperature steam (30) to said heatexchanger (19), and^ a second fraction of said increased temperature steam (30) to said dryingchamber (3) and / or to a steam consuming device, such as said extruder (2).

15. A system according to claim 14, wherein said recirculation connection (28) comprises said first fluidic bifurcation (23) arranged downstream of said compressor (7).

16. A system according to any one of the preceding claims, wherein said steam distribution device comprises one or more fans (12) arranged to circulate steam inside said drying chamber (3) from an upper position of said drying chamber (3) to a lower position of said drying chamber, and upwards towards said upper position.83514PC01 42 17. A system (1) for steam drying extruded fish feed according to claim 1, wherein^ said medium is a refrigerant^ said heat exchanger (19) comprises a condenser (4) and said steam heatingdevice comprises a heat pump comprising said condenser (4), a throttle valve (5), an evaporator (6) and said compressor (7) arranged in a closed refrigerant circuit;^ said condenser (4) is arranged to heat at least a fraction of said cooled steam,and^ said evaporator is arranged to cool at least a fraction of said cooled steam.

18. A system according to claim 17, wherein said drying chamber (3) comprises a cooled steam outlet (9) fluidic connected to a cooled stream connection (11) of said system, said cooled stream connection (11) is fluidic connected to said extruder through said evaporator (6) to provide a further cooled steam to said extruder.

19. A system according to claim 18, wherein said cooled stream connection (11) comprising a fluid buffer arranged downstream of said evaporator (6) and upstream of said extruder (2) 20. A system according to any one of the preceding claims 17-19, wherein said condenser (4) is arranged inside said drying chamber (3).

21. A system according to any one of the preceding claims, further comprising one or more fans (12) arranged to circulate said cooled steam and said heated steam inside the drying chamber (3).

22. A system according to any one of the preceding claims, when dependant on claim 17, comprising a processor (13) configured to control the operation of said heat pump and said one or more fans (12) to raise the temperature of said cooled steam inside said drying chamber by less than 500C, such as by less than 400C, preferably by less than 300C.83514PC01 43 23. A system according to claim 22, wherein said processor (13) is configured to control said heat pump to decrease the temperature of an outlet steam from said evaporator (6) to a temperature below which said outlet steam condensates into liquid water, such as to a temperature below 1000C, preferably below 950C, such as below 900C and above 850C.

24. A system according to any one of the preceding claims, wherein said fish feed inlet (8) comprising a lock configure to allowing fish feed to enter into said drying chamber (3) while substantially preventing air to enter into said drying chamber (3) and substantially preventing said steam in the drying chamber (3) to exit said drying chamber (3) through said lock.

25. A system according to any one of the preceding claims, wherein said dried fish feed outlet (10) comprising a lock configured to allowing fish feed to exit said drying chamber (3) while substantially preventing air to enter into said drying chamber (3) and substantially preventing said steam in the drying chamber (3) to exit said drying chamber (3) through said lock.

26. A system according to any one of the preceding claims, wherein the extruder (2) is configured to provide the fish feed as pellets.

27. A system according to any one of the preceding claims, wherein the drying chamber is airtight.

28. A system according to any one of the preceding claims, wherein said carrier comprising a grate (14) arranged inside said drying chamber, said grate (14) is configured to carry said fish feed and allow flow of said steam contained in the drying chamber (3) through said grate (14).

29. A system according to claim 16 or 21, wherein said one or more fans (12) are configured to provide a flow of said steam contained in the drying chamber including a flow upwardly through said grate (14).83514PC01 44 30. A system according to claim 28 or 29, wherein said grate forms part of a conveyer conveying the fish feed from the from the fish feed inlet (8) to the dried fish feed outlet (10).

31. A system according to any one of the preceding claims, comprising a boiler (17) configured for producing steam and fluidicly connected with said system, preferably fluidicly connected with said drying chamber (3) to feed produced steam into said system.

32. A system according to any one of the preceding claims 2-16, when dependant on claim 2 or 8, comprising^ at least two consecutive drying chambers (3a-d), wherein fish feed beingpartially dried in an upstream one of said consecutive drying chambers (3a-d) is transported into a downstream one of said consecutive drying chambers (3a-d) for further drying, and^ an inlet valve (34a-d) for each of said consecutive drying chambers arrangedin said recirculating connection (28), each of said inlet valves (34a-d) is fluidicly connected with said compressor (7) downstream thereof to receive in parallel increased temperature steam (30) from said compressor and being configured to set a volume flow of said increased temperature steam received from said compressor (7) individually.

33. A system according to 32, comprising^ an outlet valve (35a-d) for each of said consecutive drying chambers arrangedin parallel (7) and being configured to set a volume flow of cooled steam out of said consecutive drying chambers individually.

34. A system according to any one of the preceding claims, wherein an interior volume of said drying chamber (3) during use is occupied by steam.

35. A method of drying fish feed, the method utilizes a system according to any one of the preceding claims, and comprises:^ feeding fish feed into said drying chamber,^ operating said system to provide heated steam, and^ contacting said fish feed with said heated steam.

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