JP2010535323A - Product cryogenic quick freezing device using porous conveyor belt - Google Patents

Abstract

The invention relates to a device for freezing articles, that comprises a conveyor with a porous belt maintained in position inside the device by drums, and a means for impregnating the belt of said conveyor with a cryogenic liquid, wherein the impregnation of the belt is carried out by partially or totally immersing the belt in a bath of cryogenic liquid, characterised in that it comprises a means for pressing the belt of the conveyor onto one of said drums.

Description

  The present invention relates to processes and devices for rapidly freezing products at cryogenic temperatures.

It is well known that some foods are very difficult to fast freeze, and therefore it is necessary to use a quick freezing facility that meets the following main requirements:
-Rapid quick freezing with machines that occupy as little floor space as possible (machines that are as small as possible),
-Quick freezing, which must be effective on the lower surface as well as on the upper surface of the product,
-This process must not mark the bottom of the product,
-The product must not stick to the surface on which it is placed; and, if necessary, this equipment must only freeze the surface of the product, not the center of the product (and thereby It needs to give rise to what is called "surface refrigeration" in this industry).

  Examples include the following products: fish fillets covered with marinades; pasty products (eg vegetable puree); meat fillets with sauces.

  At present, such a very difficult product is treated in a cryogenic tunnel by being immersed in liquid nitrogen on a narrow conveyor, and if necessary, an orifice It is provided on the conveyor belt to remove the generated gas and to prevent phenomena such as swelling / deformation of the conveyor belt which could possibly cause productivity problems.

  These immersion tunnels are known for providing high heat transfer over short distances and very small size (if the transfer is not done by immersion, they are very long to process similar products. It is necessary to use equipment).

  Also, the use of a cryogenic quick freezer using a polymer (eg, polyester) belt that is impregnated with liquid nitrogen or passed through a liquid nitrogen bath is particularly suitable when the product is very difficult to process. It has been shown. Such an installation is described in document EP-576665.

  According to this prior art, the size of the conveyor belt hole allows the article to be completely or partially frozen by heat transfer between the article and the cryogenic liquid held on the porous support. As ensured, the cryogenic liquid can be held there.

  To carry out this task successfully, the polyester belt carrying the products to be surface-frozen must carry these products correctly through the quick freezer, in particular, it can be used with a quick freezer and a liquid nitrogen bath. It is fundamental to ensure a uniform passage time inside. The expression “uniform transit time” is understood to mean a constant (ie substantially constant) transit time throughout the manufacturing phase or throughout the day, whatever the product being processed, the batch being processed, etc. Is done.

  A second condition for the success of this operation is uniform immersion in a liquid nitrogen bath, where all products are immersed in liquid nitrogen of a substantially constant depth.

  For the reasons set forth below, Applicants have shown the fact that such quick freezers that immerse the polymer belt in a cryogenic bath under certain circumstances require design improvements.

  These obstacles are attributed to the nature of the conveyor polymer (as is known, which has considerable advantages), and these specific disadvantages are observed with metal belts. Note also that there is no. This is because the drive of the metal belt is "positive" (formed by a gear system that cannot slip), while in the case of polymer belts it is necessary to use a smooth drum that drives the smooth belt Because.

  Furthermore, while metal belts are entirely rigid, polymer belts are inevitably subjected to deformation as they pass through the bath.

Once the above has been understood, the reason why the accuracy and effectiveness of this process is in particular controlling the following two points will be clearer:
The regularity of the transit time through the quick freezer, and the regularity of the depth of the liquid nitrogen bath that the product suffers.

  In order to satisfy the first condition, the speed of the belt must be constantly and sufficiently controlled.

  To satisfy the second condition, the liquid nitrogen bath must have a substantially constant depth throughout the manufacturing period (eg, throughout the day) and the conveyor is substantially from the surface of the bath. At a certain distance, it must pass through this bath in a completely flat state. By doing so, the products are immersed in liquid nitrogen in substantially the same way, so that they always undergo a similar heat treatment at any moment of the day and regardless of the location of the product.

  As an example, if the conveyor is not considered to be perfectly flat, for example if there is a “kump” in the middle of the belt, the product immersed in liquid nitrogen at this location will be As with the product passing along the section, that is, where the conveyor sinks deeper into the bath, it will not be snap frozen.

It can therefore be seen that the machines available according to the prior art cannot easily meet these two requirements and very often the following two drawbacks are observed:
-Slipping of the belt on its drive drum, resulting in indefinite and poorly controlled transit time;
-Deformation of the conveyor belt in a nitrogen immersion tank: Nitrogen bubbles form under the belt, causing the belt to swell at its center, while the edge remains at the bottom of the tank, so this belt is not used in the bath It no longer remains completely flat. In addition, the tension on the belt also tends to lift the belt in its center, while the edge remains at the bottom of the bath.

  Among the existing solutions to the problems mentioned above, the following proposals in the prior art can be mentioned.

-Regularity of transit time / regular belt speed:
In an attempt to provide a regular belt speed, some manufacturers apply large forces to tension the belt. By doing so, it is believed that the phenomenon of the belt slipping on the drive drum is reduced.

  However, it should be pointed out that the higher the tension, the more the phenomenon of deformation of the belt in the bath. Thus, in practice, a compromise must be sought between belt slip and belt distortion, which results in poorly controlled transit time and bath depth.

-Problems with the regularity of the depth of the liquid nitrogen bath:
In order to avoid belt deformation problems caused by high tension and to provide a bath that is as regular as possible, some manufacturers have reduced the width of the belt and bath or divided the bath into several channels. . Between these channels, what is described as a “ski” applies pressure to the belt in order to keep the belt in place at the bottom of the tank.

  With respect to reducing the width of the belt, users of this type of machine often require high production capacity that would mean a wide (1000 mm wide) machine, so baths and belts The solution to reduce the breadth of is actually not satisfactory.

  The use of a “ski” to try to suppress belt deformation divides the processing area into several channels. For this reason, the user of this machine has to divide its production into many lines and in addition it is impossible to process products wider than the channel (maximum width: approx. 600 mm).

  In addition, this system will certainly divide production into several channels without nitrogen, but if the tank is filled with liquid nitrogen, nitrogen bubbles will form under the belt, which will deform the belt. And create a high enough pressure to form two small bumps, one on each side of the “ski”.

-Nitrogen bubble formation problems To address belt swelling due to nitrogen bubbles trapped under the belt, some manufacturers have developed pressures under the belt by drilling holes in the belt. Has been released. By doing so, gas can escape and the belt returns to some extent depending on the number of orifices and their size.

  However, by doing so, the belt no longer has a smooth surface and the product may occasionally be marked by the belt. In addition, this technique cannot be applied to products that are smaller than the size of the orifice (about 10 mm).

  Therefore, all the solutions described above, in any case, prevent the machine from being used at the optimum conditions for its capacity, and keep the product's quick freezing quality and regularity at a high level. I found it impossible.

  As will be described in detail below, the present invention provides a technical solution to the above-mentioned problem, and by adopting a strategy that is completely different from that used in the prior art, it is consistent. Aims to achieve a belt speed and regular nitrogen bath on the belt at each position of the tank. The strategy is as follows.

Regularity of transit time / regular belt speed Unlike the prior art solutions, to provide a constant belt speed, the belt tension is set to the lowest possible value to eliminate problems in the bath. Do not create. As a result, the belt will slip on its drive drum (usually considered a disadvantage). To prevent this phenomenon, the roller presses the belt against the drum, thereby increasing the angle and contact force between the drum and the belt. By doing so, the local adhesion on the drum is considerably increased, but the belt tension remains low in the rest of the machine, so that the belt does not deform accordingly in the bath. Therefore, the transit time is completely controlled and steady.

  Thus, unlike prior art solutions that recommend very high belt tensions, the present invention employs moderate tensions, but uses a roller to locally press the belt against the drum. The desired tension across the belt is obtained by separating the drums from one another.

  In other words, in order to explain the preceding phenomenon more clearly below, the greater the tension on the polymer belt, the stronger it will come into contact with the drum, so that it will have greater difficulty in passing through the bath. Proceed with it. Conversely, the lower the tension, the more “soft” the system is, so it does not wrap easily and it “slides like a skate” on the drive drum.

  Since the present invention applies a small tension to the conveyor, the system is relatively “soft”, so that it passes through the bath without difficulty, which is belted by a roller (eg, a freewheel that presses and follows its motion). Is pressed against one drum (equipped with a motor).

-Regularity of the depth of the liquid nitrogen bath:
Thanks to the system described above, the belt naturally remains flat in the bath. This situation remains the same in high throughput machines with very wide belts (typically 1200 mm wide).

  This is because the presence of the rollers does not place a very strong tension on the entire belt, and as a result, the belt is more easily kept flat (any tension will cause distortion somewhere). In summary, the presence of a roller makes it possible to solve two technical problems simultaneously.

-Nitrogen bubble problems As mentioned above, when the bath is filled with liquid nitrogen, the nitrogen bubbles that form under the belt tend to lift and deform it. Therefore, the generated foam must be removed without stopping the production. To do this, according to the invention, a space is provided between the belt and the bottom of the tank. This space allows air bubbles to escape through the inlet and outlet of the belt in this system without creating excessive pressure under the belt and thereby lifting the belt. In doing so, the belt remains perfectly flat at a fixed distance from the surface of the liquid nitrogen bath.

  In other words, the belt does not pass over the bottom of the tank, but rather a certain “height” (typically on the order of 1 to 10 cm) several millimeters or centimeters above the bottom of the tank. Suitable for practicing the invention), of course, providing a belt / bottom space by passing under the surface of the cryogenic liquid. Therefore, the observed deformation does not occur due to the fact that the bubbles are directed to the lower surface of the belt but do not accumulate there without any explanation. Bubbles spontaneously release towards the bath inlet / outlet, and the intense flow observed by the applicant during the experiment at the inlet / outlet confirms this hypothesis.

In conclusion, by applying this combination of techniques, it is possible to completely control the key points of this process in cases where it is most difficult to handle:
The transit time through the device and through the nitrogen bath is completely controlled and constant;
-The bath depth and the strength of the cryogenic treatment are completely controlled. The bath depth is constant for all products. It can be easily adjusted on demand.

  It should also be noted that the solution proposed by the present invention using a wide belt, for example a belt with a width of 1200 mm or more, is effective and makes it possible to achieve a high production capacity. . This also makes it possible to process very wide products. However, of course, it is also very suitable for smaller widths (300, 400, 600, 800 or 1000 mm).

  Having described an advantageous embodiment using a combination of two technologies: the presence of a roller and the space provided between the belt and the bottom of the tank, a width and a product that are easier to handle It should also be noted that it is conceivable that only one of the previous technical features can be adopted in the presence of the presser roller while obtaining the desired result.

  In any case, the control provided by this process can increase the size of this type of machine and the production capacity is no longer limited by technical problems.

  Moreover, the quality of the quick freeze is constant and the process parameters can be adjusted most effectively to make the most of this process and reduce its cost.

  Overall, it is the effectiveness and efficiency of this process that benefits from the improvements proposed by the present invention.

  The present invention is a device for rapidly freezing articles, comprising a porous belt conveyor held by a plurality of drums at a predetermined position in the device, and means for impregnating the belt of the conveyor with a cryogenic liquid. A device wherein the impregnation of the belt is performed in whole or in part by immersing the belt in a bath of cryogenic liquid, and means for pressing the belt against one of the plurality of drums It is related with the device characterized by including.

  According to one aspect of the invention, the means for pressing comprises a system of rollers fixed to a freewheel capable of pressing a belt against the drum and following the movement of the drum.

  According to one of the preferred embodiments of the present invention, a space is left between the conveyor and the bottom of the tank containing the bath, and this space allows air bubbles generated under the belt in the bath to be removed from the conveyor. Is suitable for allowing full or partial escape through the conveyor "inlet" and "outlet" in the device without creating excessive pressure underneath.

  The conveyor is advantageously made of a porous material, which is a synthetic or natural polymer woven or non-woven fabric, preferably made of polyester.

  The present invention will be more fully understood by describing the description of non-limiting embodiments, which are given by way of example only, and with reference to the accompanying FIGS.

FIG. 1a is a longitudinal view of the structure of a conventional quick freezer having a polyester belt and a nitrogen bath. FIG. 1b is a side view of the structure of a prior art quick freezer having a polyester belt and a nitrogen bath. FIG. 2a shows the structure of a quick freezer according to the invention with a polyester belt and a nitrogen bath (utilizing a system consisting of several rollers and the space left between the belt and the bottom of the liquid nitrogen tank). It is the figure seen from the direction. FIG. 2b shows the structure of a quick freezer having a polyester belt and a nitrogen bath according to the present invention (utilizing a system consisting of a plurality of rollers and the space left between the belt and the bottom of the liquid nitrogen tank). It is the figure seen from the direction.

BEST MODE FOR CARRYING OUT THE INVENTION

  1a and 1b schematically show the main components of a prior art quick freezer having a polyester belt and a nitrogen bath as described in the introductory part of the present application.

For example, the features of the preferred embodiment for practicing the present invention can be easily understood in FIGS. 2a and 2b:
The device comprises a roller for pressing the conveyor belt against the drive drum (the drum on the left side of the figure, equipped with a motor), which presses the conveyor belt against the drum, It forms part of a freewheel that can follow the movement of the drum.

In addition, means for advantageously performing the presser roller will be described below. In particular, it will be appreciated that this measure may be advantageous depending on the product to be processed or on the type of conveyor belt at the point of use. As will be appreciated, this improvement is not absolutely necessary to properly practice the present invention. It can be seen that they are only advantageous in some very limited cases. That is,
i) If the belt is clamped / squeezed between the drive drum and the presser roller, problems can sometimes occur at the moment the fasteners that connect the belt pass over the drum. This connecting portion is thicker than the belt (for example, about 5 mm compared to 2 mm for the belt), so it may be held by the press roller, and as a result, the conveyor belt may not move. .

Therefore, in this very limited case, it is conceivable to attach a bar to the drum that never obstructs its operation and allows a thicker connection to pass through. With such an arrangement, the following effects can be observed at a certain point.
The connection reaches the space between the two bars on the drum. In this case, the connecting portion can pass between the drum and the roller without any problem.

  The connection reaches the position where the bar is on the drum (connection above the bar); In this case, it cannot pass and the drum begins to slide on the belt (the drum continues to rotate but the belt remains stationary). If the drum slides slightly, the connection is in the space between the two bars and can thereby be passed through. This small slip is extremely temporary and will never interfere with the correct operation of the device, so this improvement allows the belt to continue to advance even when the connection passes between the drum and roller. To do.

  j) When the device is operating in the cold state, due to the characteristics of the device, the size and shape of the device may change very slightly due to expansion. This is sometimes sufficient to bias the belt to one side, which results in immediate damage to the belt edge, which requires it to be replaced early.

  Therefore, in this particular case, a system that actively guides the belt and in which a sensor detects the position of the belt can be proposed.

  As an example, if the belt is too far to the right, the angle of the drive drum at the exit of the machine is automatically changed by the actuator, which causes the belt to reposition to the left.

  Conversely, if the belt is too far to the left, the angle of the drive drum at the exit of the machine is automatically changed by the actuator so that the belt is repositioned to the right.

  If the belt is thus accurately moved to the center of the machine frame, the life of the belt is greatly extended. In addition, belt friction on the edge of the machine is eliminated, and the regularity of belt travel is further enhanced, and this process can be even more precise.

  An example of implementation of the facility shown in FIG. 2 is shown below.

  For example, a 6 meter long device with a 1.2 meter wide belt, cooked hamburger, uncooked or cooked meatballs, sausage, minced meat or bowl of ham, etc. Very good results can be obtained with a device that rapidly freezes a wide variety of meat products. As will be appreciated, this quick freezer with an immersion bath should be applicable to efficiently treat this wide variety of products. The transit time must be short (typically 1 minute) and the nitrogen bath may be very shallow (typically 5 mm deep). For other more difficult products, the transit time must be long (typically 10 minutes) and the bath must be relatively deep (typically 50 mm deep). Experiments have shown that by applying the techniques described above, all products in the range can be processed accurately, and that this rapid freezing is constant and regular over time and during the manufacturing stage. It was.

Claims (5)

  A device for rapidly freezing articles comprising a porous belt conveyor held in place in the device by a plurality of drums, and means for impregnating the conveyor belt with cryogenic liquid, The impregnation of the belt is performed in whole or in part by immersing the belt in a bath of cryogenic liquid, and includes means for pressing the belt against one of the plurality of drums; Device characterized by.   2. The pressing means comprises a system of rollers fixed to a freewheel capable of pressing the belt of the conveyor against the drum and following the movement of the drum. The device described.   A space is left between the belt and the bottom of the tank that houses the bath, which space allows air bubbles generated under the belt in the bath to pass through the “inlet” of the belt in the device and Device according to claim 1 or 2, characterized in that it is suitable for allowing full or partial escape through an "exit".   4. The device of claim 3, wherein the space has a height in the range of 1 cm-10 cm.   The porous belt is made of a porous material, which is a synthetic or natural polymer woven or non-woven fabric, preferably made of polyester. A device according to

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