Field of the invention

The invention relates to a method, a system and a device for refrigeration control of horizontal plate freezers. More specifically, the present invention relates to providing a solution for an even distribution of heat exchange medium in plate freezers.

Background

In the continuously growing field of food processing, the demand for better quality and delivery frozen food to the market, the use of plate freezer for freezing packed food items is well known. In horizontal plate freezers, the plates are arranged in a horizontal manner, where the food product are placed on top of cold plate where they can also have contact to the plate above the product. The food items are usually packed in boxes or bags where the food items are subjected to a heat exchange conditions with the cooling media running through the cooling plates. In industrial refrigeration, plate freezers of this type are therefore used to freeze large quantities of packaged products resulting in demand for greater capacity and automation requiring larger horizontal plate freezers.

The heat exchange between the plate and product is generated by a cold refrigerant which flows through piping or conduit in the plate, where the refrigerant used is pumped or injected and circulated through the core of plates at a temperature close to, or at its boiling point. The flow capacity of plates needs to be high enough to transfer a sufficient amount of refrigerant through the plate for a given capacity. In order to have good heat distribution within each plate, a portion of the refrigerant flow will exit the plate as a liquid and the rest of the refrigerant flow will exit the plate in a saturated gas form, where the liquid refrigerant is traditionally circulated with a circulation ratio (mass flow ratio) of gas to liquid at about 1 : 1-10 exiting the plate. The speed of freezing is an important factor which requires the plates are to be at a temperature ranging between - 38°C to -50°C with the common type refrigerants.

A traditional horizontal plate freezer, commonly combined with a pump circulated freezing system, is arranged with a distribution header extending along the whole stack of plates and having a plurality of outlets for dividing a flow of refrigerant into an inlet for each plate. When a liquid refrigerant is circulated in a plate freezer system, the pressure is increased above the boiling point of the liquid refrigerant, when it travels through pipes-system to each user of the system. Thermal energy transfer of a cooling media is higher when the refrigerant is at its boiling point, so an ideal refrigerant is fed into the plate at a pressure close to its boiling point. Therefore, cooling media operating at its boiling point, such as ammonia or CO ₂ , has more efficient heat transfer than non-boiling media, such as Brine, or Glycol.

The freezing time of a batch of products in a plate freezer is determined by the freezing time of the plates with the least or lowest freezing capacity, which are the plates positioned in the top vertical position of the freezer. This problem can be explained by gas bubbles in the liquid travels at the top of the header resulting in a higher percentage of gas phase entering the highest plates. This gas formation is formed by boiling of the liquid phase refrigerant due to heat-transfer through pipe system, and boiling in the vertical distribution header is normally not insulated. In some cases, plate freezers are not in a cabinet at all, with whole plate freezer and distribution header exposed to ambient temperature. This problem can also be explained by static pressure difference due to height difference of the plates, were the highest plates have the lowest pressure upstream of the plate and the lowest plates have the highest inlet pressure, but with higher machines, static pressure from the height difference, becomes more notable, and effects the boiling point refrigerant, in a way that refrigerant high up in the liquid header is closer to is boiling point than in the bottom of liquid header, and therefore more prone to boil due to heat transfer from the surrounding.

Summary of the Invention

The present invention provides a device, a system and method for even distribution cooling media for freezing of items in a plate freezer systems, where the even distribution of refrigerant to all the plates in the freezer refers to even cooling/freezing effect of all the plates. As some of the refrigerant exists in gas phase having reduced cooling effect, the even distribution cooling effect is obtained by separating the gas phase from the liquid phase before feeding the refrigerant into the plates. The distribution and in-feed pipe (liquid header) is designed to extend higher than the inlet to the highest freezing plate in the chamber for collecting gas phase of the cooling media for separation before the refrigerant flows out of distribution liquid header towards each and into each plates. This solution will increase the freezing capacity of the highest plates in a horizontal plate freezer as this secures that plates connected to the highest outlets of a distribution (liquid) header will be fed with refrigerant in liquid phase, and not a blend of liquid and gas which decreases the freezing capacity of the plates. When the refrigerant, in liquid phase enters the liquid header, the flow velocity decreases due to larger diameter of the liquid header, which makes it easier for the gas to separate from the liquid. rior art devices are normally set up to direct the flow of refrigerant to enter the distribution header from the top of header as is shown in Fig. 1, where the outgoing cooling media is either exited through a wet suction line (A) or a combination of a wet suction line and liquid drain (B). In order not to increase diameter of the header beyond what would be practical diameter and due to space and cost constrains.

In some embodiments the liquid refrigerant is to be introduced into the lower part of the distribution header so that gas bubbles forming in the refrigerant will travel in the same direction of the flow, thereby increasing the separation effect of gas and liquid. The gas phase accumulating in the uppermost portion of the liquid header can be removed in different ways such as by implementing a floating valve, a direct bypass with restriction, electronic valve, manual regulating valve or a solenoid valve.

In some embodiments a refrigeration system according to the present invention is provided in a plate freezer, where the circulation ratio is lower than 1:2. Such embodiments are used in direct expansion systems or semi-flooded systems, where liquid refrigerant is normally circulated towards plate freezer at its boiling point or sub cooled, but no or limited amount of liquid is entering the outlet pipe.

The apparatus and method are designed to facilitate an even distribution of cooling/freezing effect in a plate freezer, ensuring similar or same cooling/freezing time for all the plates in the freezer, and to reduce start-up time of a warm plate freezer after cleaning and defrosting. The combination of one or more of the following embodiments provide the solutions presented herein: a) an in-feeding distribution header or piping with an increased diameter and means for separating gas phase refrigerant from the liquid refrigerant, and b) means for evacuating or exiting gas phase from the top of the distribution header, to avoid it from reducing cooling capacity of the highest plates before feeding the refrigerant into the plates, which provides the improved device and method of the present invention resulting in increased effect of the present plate freezer.

It is an object of the present invention to overcome and/or ameliorate the aforementioned drawbacks of the prior art and to provide an improved and/or alternative and/or additional method or device for facilitating freezing food items in plate freezer systems with plurality of horizontally arranged freezing plates with even freezing capacity of all the freezing plates in a stack of plates. It is one preferred object of the present invention to provide an apparatus having a feeding system for even distribution cooling media to plates in a plate horizontal plate freezer for separation and evacuation of the gas phase of the cooling media. Moreover, it is a preferred object of the present invention to provide an energy efficient method, a system and device, preferably designed for even distribution cooling media to plates in a plate horizontal plate freezer and optimal use of cooling media used in the system. Another preferred object of the present invention is to provide a device having a design for collection, separation and evacuation or exiting of the gas phase of cooing media prior to feeding the cooling media into freezer plates in a horizontal plate freezing system.

The object(s) underlying the present invention is (are) particularly solved by the features defined in the independent claims. The dependent claims relate to preferred embodiments of the present invention. Further additional and/or alternative aspects are discussed below.

Thus, at least one of the preferred objects of the present invention is solved by an apparatus for freezing food items, where the apparatus comprises i) a plurality of freezing plates arranged horizontally, wherein each plate has a hollow space within the plate for cooling medium to flow through, an inlet and an outlet for the cooling medium to enter and exit the plate, ii) a liquid header, and iii) a suction header to transfer the cooling medium to and from each cooling plate. The liquid header extends higher than the inlet of the top freezing plate in the chamber for collecting gas phase of the cooling media, and the apparatus further comprises means for evacuating gas phase or a blend of gas and liquid phase of the cooling media from the top of the liquid header.

Another preferred object of the present invention is solved by a method for operating a flow of cooling media in a plate freezing systems, said method comprising the steps of: a) starting a flow of cooling medium into a liquid header of a freezer apparatus of claims 1-24, said liquid header extending higher than the inlet of the top freezing plate in the chamber, and b) feeding cooling media from the liquid header into and through each plate of the plate freezer, c) receiving cooling media from each plate of the plate freezer into a suction header, and d) re-directing the cooling media into a collecting pipe system through means for adjusting the temperature and the pressure of the cooling media prior to distributing cooling media back into the freezer apparatus.

The method further comprises removing the gas phase from the liquid phase of the cooling medium by: e) collecting the gas phase in the portion of the liquid header extending higher than the inlet of the top freezing plate, and f) evacuating the gas phase or a blend of gas and liquid phase of the cooling media from the top of the liquid header to a suction line.

One of the preferred objects of the present invention is solved by a system for even distribution cooling media or freezing of items in a plate freezing systems and devices. The system comprises i) providing a plurality of freezing plates arranged with spacing between the plates , for food items to be frozen while resting on said freezing plates, where each plate has a a) hollow space within the plate for cooling medium to flow through, b) an inlet and c) an outlet for the cooling medium to enter and exit the plate, a liquid header and an suction header to transfer the cooling medium to and from each cooling plate, ii) generating a flow of cooling medium at a desired temperature into the liquid header , through each plate of the plate freezer into the suction header, and iii) re directing the cooling media into the liquid header through means for adjusting the temperature and the pressure of the cooling media prior back into the freezer apparatus. The system further comprises iv) separating the gas phase from the liquid phase of the cooling media in a portion of the in-feed pipe extending higher than the inlet of the top freezing plate, v) providing means for exiting or evacuating the gas phase or a blend of gas and liquid phase of the cooling media from the liquid phase of the cooling medium through the top of the liquid header, and vi) providing piping for feeding the gas phase or a blend of gas and liquid phase of the cooling media from the top of the liquid header to a suction line.

Another preferred object of the present invention is solved by a feeding system for even distribution cooling media to plates in a plate horizontal plate freezer. The said feeding system comprises i) in-feed tubing for feeding cooling media into the freezer, ii) a liquid header for transfer the cooling medium to each cooling plate inlet in the plate freezer, and iii) generating a flow of cooling medium at a desired temperature into the liquid header. The feeding system further comprises vi) separating the gas phase from the liquid phase of the cooling media in a portion of the in-feed pipe extending higher than the inlet of the top freezing plate, v) providing means for exiting or evacuating the gas phase or a blend of gas and liquid phase of the cooling media from the liquid phase of the cooling medium through the top of the liquid header, and vi) providing piping for feeding the gas phase or a blend of gas and liquid phase of the cooling media from the top of the liquid header to a suction line. Description of the invention

The following definitions and embodiments relate to the method, the system and the apparatus of the invention.

In the present context the terms "liquid header" or "distribution header" or "distribution and in-feed pipe" are used equally for a pipe which feeds each plate of the freezer through the inlets with heat exchange medium.

In the present context the terms "suction header" or "outlet piping" are used equally for the piping connected to an outlet for heat exchange medium to exit each plate of the freezer.

In the present context the terms "cooling medium" or "heat exchange medium" or "refrigerant" are used equally for the medium directed through the plates in a plate freezer for facilitating heat exchange between items on the plates and the plate itself.

The heat exchange medium is preferably medium such as ammonia or CO2 with a low temperature boiling point.

The apparatus according to claim 1, wherein the apparatus further comprises an isolated chamber and wherein plurality of freezing plates arranged horizontally in the chamber with spacing between the plates for food items to be frozen while resting between said freezing plates.

In an embodiment of the present invention the diameter of the liquid header is increased prior to the inlet or hose to the first/lowest freezing plate.

In an embodiment of the present invention the means for evacuating gas phase or a blend of gas and liquid phase of the cooling media from the top of the liquid header leads to a suction line.

In an embodiment of the present invention the suction line is a wet suction line.

In an embodiment of the present invention the suction line is a dry suction line for super-heated gas.

In an embodiment of the present invention, the apparatus, system or method further comprises means for removing/separating the gas phase from the liquid phase of the cooling media.

In an embodiment of the present invention the means for evacuating gas phase or a blend of gas and liquid phase of the cooling media from the top of the liquid header is a floating valve. In an embodiment of the present invention the means for evacuating gas phase or a blend of gas and liquid phase of the cooling media from the top of the liquid header is a solenoid valve.

In an embodiment of the present invention the means for evacuating gas phase or a blend of gas and liquid phase of the cooling media from the top of the liquid header is a manually regulated valve.

In an embodiment of the present invention the means for evacuating gas phase or a blend of gas and liquid phase of the cooling media from the top of the liquid header is an electronic valve controlled by liquid level switch, or by means of temperature sensor, or by means of a level sensor.

In an embodiment of the present invention the means for evacuating gas phase or a blend of gas and liquid phase of the cooling media from the top of the liquid header is a restriction, such as an orifice, small diameter pipe or nozzle.

In an embodiment of the present invention the apparatus further comprises piping for feeding the gas phase or a blend of gas and liquid phase of the cooling media from the top of the liquid header to a suction line.

In an embodiment of the present invention the means for evacuating gas phase or a blend of gas and liquid phase of the cooling media from the top of the liquid header is positioned in the piping for feeding the gas phase or a blend of gas and liquid phase of the cooling media from the top of the liquid header to a suction line.

In an embodiment of the present invention the liquid header has a flow direction from the bottom to the top of the apparatus.

In an embodiment of the present invention the liquid header has a flow direction from the top to the bottom of the apparatus.

In an embodiment of the present invention the apparatus further comprises one or more electronic control or expansion valve(s) positioned between the liquid header and the plate inlet for controlling the amount of cooling medium circulating to each plate, depending on required freezing load thereby saving energy).

In an embodiment of the present invention a control valve or regulating valve is positioned between plate outlet and wet suction line for each plate.

In an embodiment of the present invention a control valve or expansion valve is positioned between outlet of the liquid header and a group of plates. In an embodiment of the present invention the gas phase or a blend of gas and liquid phase of the cooling media is bypassed over to suction header or wet suction line from other high position upstream of plates, than the top of header.

In an embodiment of the present invention the liquid header is in a vertical position or a diagonal position. apparatus, system or method further comprises an additional plate at the top of freezer for the purpose of bypassing gas phase or a blend of gas and liquid phase of the cooling media over to the suction header or wet suction line. apparatus, system or method further comprises a liquid separator above or in the upper part of the liquid header.

In an embodiment of the present invention the hollow space in each freezing plate is tubing or flow channels within the plate for cooling medium to flow through.

In an embodiment of the present invention the gas phase or a blend of gas and liquid phase of the cooling media is bypassed over to outlet piping from other high position upstream of plates, than the top of header. This can be obtained by a gas trap, positioned upstream of plates being a small receiver, or vertical pipe, for the purpose of gathering gas.

In an embodiment of the present invention it further comprising separating the liquid phase of the cooling media from the gas phase and feeding gas phase of the cooling media over to a dry suction line or a blend of gas and liquid phase of the cooling media over to a wet suction line.

In an embodiment of the present invention the pump circulated media pressure is reduced to a value just above the boiling pressure of refrigerant by the means of regulating valve(s) upstream of the liquid header.

In an embodiment of the present invention the freezer system is a refrigeration system working as a direct expansion system, comprising expansion valves positioned between liquid header and the plate inlet, wherein a two phase flow of a blend of gas and liquid is present at plate inlet.

In an embodiment of the present invention the plate freezing system is a plate freezer with a plurality of freezing plates arranged horizontally, wherein each plate has a hollow space within the plate for cooling medium to flow through, an inlet and an outlet for the cooling medium to enter and exit the plate, ii) a liquid header, and iii) a suction header to transfer the cooling medium to and from each cooling plate. In an embodiment of the present invention the plate freezing system is arranged in an isolated chamber with means for feeding food items into the freezer and onto the freezer plates, as well as feeding the food items off the freezer plates and out of the isolated chamber.

Description of various embodiments

The present invention will become more fully understood from the detailed description given hereinafter and the accompanying drawings which are given by way of illustration only, and thus, are not limitative of the present invention, and wherein:

FIG. 1 outlines the design of prior art plate freezers

FIG. 2 is a general outline of a freezer of the present invention

FIG. 3 shows different embodiments of removing the gas phase or a blend of gas and liquid phase of the cooling media.

Figure 2 shows a plate freezer system according to the present invention comprising a plurality of freezing plates 2 with spacing 3 between the plates 2 for placing food items to be frozen on while resting on the freezing plates. Each plate has a hollow space, such as piping or conduit (not shown), within the plate for heat exchange medium to flow through the plate. Each plate further comprises an inlet 4 and an outlet 5 for the heat exchange medium to enter and exit the plate 2. Each inlet is connected to a distribution and in-feed pipe (liquid header) 4 and each outlet is connected to an outlet piping (suction header) 5, to transfer the heat exchange medium to and from each plate. The liquid line 10 feeding the heat exchange medium to the chamber brings a flow of heat exchange medium to the lower part of the chamber 1 to generate a flow in distribution and in-feed pipe 6 from the bottom to the top of the apparatus. As is shown here, the distribution and in-feed pipe 6 extends higher than the inlet to the top freezing plate in the chamber for collecting gas phase of the cooling media. Furthermore, the diameter of the distribution and in-feed pipe 6 is increased prior to the inlet 4 to the first/lowest freezing plate 2. The figure also shows means 9 for removing the gas phase or a blend of gas and liquid phase of the cooling media from the top of the distribution and in-feed pipe 6 to the outlet piping 7 or wet suction line 7. The figure also shows liquid drain 11, from the bottom of the suction manifold 5, were liquid refrigerant by the means of a pump, is pumped up to the wet suction line 7, were relevant this drain is used to reduce pressure drop in the suction manifold 5, where height of manifold effects the boiling pressure of the refrigerant. Figure 3 shows several different embodiments for systems of removing the gas phase or a blend of gas and liquid phase of the cooling media from the top of the distribution and in-feed pipe 6 to the suction line 7. In Fig. 3(A), a floating valve 20 is shown as the means for removing the gas phase or a blend of gas and liquid phase of the cooling media, where the gas is bypassed over to a wet suction line 7, whereas in Fig. 3(B) a floating valve 20 is shown as the means for removing the gas phase or a blend of gas and liquid phase of the cooling media, but the gas is bypassed over to suction header 5. The float valve opens when gas is present and closes when liquid is present, providing a simple robust mechanical control. In Fig. 3(C) a solenoid valve 30 is used as the means for removing the gas phase or a blend of gas and liquid phase of the cooling media. The solenoid valve 30 is controlled by simple liquid level switch, without logic controller, to bypass the gas over to outlet piping. Fig 3(D) shows a manual regulating valve 40 as the means for removing the gas phase or a blend of gas and liquid phase of the cooling media and bypass the gas/liquid over to wet suction 7. This solution is less energy effective, as liquid can also go through the regulating valve and for best performance the regulating valve has to be manually operated, for different situation of the freezing process, as there is no automation control present.

In Figs 3(E), 3(F) and 3(G) different embodiments of electronic valves 50 are shown, with a level switch and logic controller in Fig. 3(E) and 3(G), for more smooth control of valve, than the solution shown in Fig 3(C), were only a level switch is used to control the electronic valve for keeping a stable liquid level height in top of the liquid header 6. The electronic valve can either be a solenoid valve or a motor valve when a logic controller is uses in combination with a liquid level switch. Electronic valve can also be controlled by using input of temperature and pressure transmitters, which is a preferred embodiment when a freezer is combined with direct expansion refrigerating system as in 3(G) as well as with dry suction 7 (superheated gas), or a wet suction 7. However, in Fig 3(F), a level sensor is used to keep the liquid level height within a certain range by use of the electronic valve where only refrigerant in gas phase is bypassed over to suction line 7. In Fig 3(H) a restriction 60 is used for removing the gas phase or a blend of gas and liquid phase of the cooling media, as a simple, low-cost solution. This solution is not adjustable and less energy efficient than the embodiments described above. The embodiments in Figs. 3 (A), (B), (C), (E), (F) and (G) are suitable for direct expansions refrigeration system with wet suction, as well as pump circulated refrigeration systems. Embodiments in Figs. 3 (A), (B), (E), (F) and (G) are suitable for direct expansions refrigeration system with dry suction, as well as pump circulated refrigeration systems. As used herein, including in the claims, singular forms of terms are to be construed as also including the plural form and vice versa, unless the context indicates otherwise. Thus, it should be noted that as used herein, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise.

Throughout the description and claims, the terms "comprise", "including", "having", and "contain" and their variations should be understood as meaning "including but not limited to", and are not intended to exclude other components.

The present invention also covers the exact terms, features, values and ranges etc. in case these terms, features, values and ranges etc. are used in conjunction with terms such as about, around, generally, substantially, essentially, at least etc. (i.e., "about 3" shall also cover exactly 3 or "substantially constant" shall also cover exactly constant).

The term "at least one" should be understood as meaning "one or more", and therefore includes both embodiments that include one or multiple components. Furthermore, dependent claims that refer to independent claims that describe features with "at least one" have the same meaning, both when the feature is referred to as "the" and "the at least one".

It will be appreciated that variations to the foregoing embodiments of the invention can be made while still falling within the scope of the invention. Features disclosed in the specification, unless stated otherwise, can be replaced by alternative features serving the same, equivalent or similar purpose. Thus, unless stated otherwise, each feature disclosed represents one example of a generic series of equivalent or similar features.

Use of exemplary language, such as "for instance", "such as", "for example" and the like, is merely intended to better illustrate the invention and does not indicate a limitation on the scope of the invention unless so claimed. Any steps described in the specification may be performed in any order or simultaneously, unless the context clearly indicates otherwise.

All of the features and/or steps disclosed in the specification can be combined in any combination, except for combinations where at least some of the features and/or steps are mutually exclusive. In particular, preferred features of the invention are applicable to all aspects of the invention and may be used in any combination.