Patent Application
20110011097
The present invention relates to industrial devices and methods for chilling or deep-freezing food products.
The chilling of food products generally takes place by convective exchange between a cold gas and the products. The use of cryogenic fluids and fans is already known from manufacturers who wish to deep-freeze foodstuffs.
Deep-freezing or chilling technology is based on the fact that the products are chilled more quickly if they are subjected to impacting jets of a cryogenic fluid.
These impacting jets are created by pressurizing the area above a perforated plate, causing an increase in the speed of the fluid at the holes of the plate. On the industrial scale, these devices take the form of tunnels in which the pressurization above a perforated plate is created by a means for circulating the gas, for example a centrifugal fan, located above the belt on which the food products to be chilled are arranged.
However, the presence of humidity in the enclosed space in which the chilling takes place leads to the formation of frost and to snow deposits when the temperature of the cold gas is below 0° C. In cryogenic tunnels, the temperature can reach −130° C.
The humidity arises from the products which can become partially dehydrated by the presence of humid air mixing with the cold gas, in particular in the case of open-ended machinery such as tunnels.
When the method of convection is based on the speeding up of the cold gas when it passes through holes (which may be circular, oblong, rectangular, etc.), the deposits of snow or ice crystals tend to occur on the edges of these holes. Obstruction of the holes to a greater or lesser degree results therefrom, and they can even become completely blocked. Reducing the flow cross-section of the holes modifies the flow-rate characteristics of the cold gas, which adversely affects the chilling process and can even cause malfunctions.
Patent application EP-1 621 830 discloses a means for overcoming the frosting phenomenon by using mechanical vibrations with the aid of a vibrator mounted on the plate that has the holes. Other patent authors use heating systems to periodically defrost frosted surfaces.
However, these means consume a lot of energy and are difficult to implement.
The object of the present invention is a device and a method for chilling food products, equipped with means for preventing the clogging-up with frost of the holes forming the impacting jets, without the use of mechanical vibration or heating.
To this end, the invention proposes a device for chilling food products by impacting jets which consists of a tunnel comprising
The cold fluid can be cold air obtained by mechanical refrigeration or alternatively a cryogenic fluid.
The cold fluid is preferably a cryogenic fluid chosen from the group including, in particular, nitrogen, carbon dioxide, oxygen, or air, and mixtures thereof.
The chilling device according to the invention is preferably a device for deep-freezing food products. Deep-freezing is a means of freezing food very quickly. This is the technique of choice on the industrial scale when the foodstuffs are flat or small in size, such as, for example, beefburgers, pizzas or diced bacon. The heat-exchange surface area of these foodstuffs is large, and the thickness small, which favors rapid freezing.
In the device according to the invention, the plate or plates provided with through-holes are advantageously made from food-grade stainless steel. These plates can be inclined and disassembled to make it easier to clean them after operation.
Purely by way of example, the through-holes of the plate can have different shapes and, in particular, can take the form of cylinders, circles, elongated holes, trefoils or even cones with beveled or rounded edges. The plates can be flat, V-shaped or even corrugated.
In a conventional but non-restrictive manner, the means for circulating the fluid is a centrifugal fan driven by a motor.
The means for varying the pressure in the zone under pressure P1 and/or the means for cooling the plate or plates down to a temperature below −80° C. and for maintaining that temperature make it possible to prevent the clogging-up with frost of the holes in the plate without making the system more expensive in terms of energy.
According to a particular embodiment of the invention, this device is characterized in that the means for cooling the plate or plates down to a temperature below −80° C. and for maintaining that temperature are chosen from the group including a heat-exchange circuit attached to the plate, a plate that serves as a heat exchanger (also referred to as a plate/heat exchanger), a cold fluid bath on top of the plate or plates, and combinations thereof.
Surprisingly and paradoxically, the inventors have found that when the temperature of the plate is lowered to a temperature below −80° C., the ice crystals do not adhere to the edges of the holes, thus preventing the holes from becoming clogged up.
These cooling means are economical. Indeed, when the cooling of the plates is effected by a heat exchanger, and according to a preferred embodiment of the invention, the cryogenic fluid passing through the heat exchanger is taken from the circuit for supplying the chilling machinery. The cryogenic fluid contributes directly or indirectly to the cooling of the fluid that is in contact with the products.
These cooling means are easy to implement: the heat exchanger attached to the plate can be a tube fixed to one or both faces of the plate and within which a cold fluid circulates. The heat exchangers preferably have a form that allows them to pass as closely as possible to as many holes as possible, and thus to favor the cooling of the plate around as many holes as possible.
According to a particular embodiment of the invention, the heat exchanger attached to the plate has one or more passes required for cooling as many through-holes as possible. Another embodiment consists in using a material which is a good conductor of heat for the plate, or which would be in contact with the plate in order to cool the edge of the holes. This material would be cooled locally by a cooling circuit.
Furthermore, this heat exchanger attached to the plate has a form and a connection to the plate such that heat exchange is favored. By way of example, the use may be envisaged either of a weld of a form and made from materials that a person skilled in the art will be capable of defining and/or of a thermal compound.
It is preferable that the plate is cooled optimally at the through-holes and for as many holes as possible. The plate/heat exchanger can thus be formed by two plates that may or may not have baffles, for better distribution of the cold fluid. The use of baffles makes it possible to prevent the fluid following preferred channels, and thus promotes the cooling of as many holes as possible.
According to an embodiment of the device according to the invention where a bath of cold fluid is used as the means for cooling the plate down to a temperature below −80° C. and for maintaining that temperature, the plate is equipped with edges that are sufficiently high, with tubular holes and with a means for regulating the level of the bath. Such a device can make it possible to prevent the cold fluid from overflowing through the through-holes and over the edges of the plate.
According to a particular embodiment, and with the aim of further reducing the energy costs, the device can be designed in such a way that the fluid which is stirred within the zone under pressure P1 is cooled only in contact with the cold plate. In this embodiment, the fluid arrives in the zone under pressure P1 at an ambient temperature T1 and cools to a temperature T2 when it passes through the through-holes of the plate which is at a temperature T3 below −80° C., T2 lying between T1 and T3. The means for cooling the fluid can thus be the means for cooling the plate.
The means for cooling the plate down to a temperature below −80° C. and for maintaining that temperature have the advantage that they are easy to implement, in particular on existing and inexpensive cooling devices, as a person skilled in the art can simply swap conventional perforated plates with perforated plates provided with heat exchangers.
According to another aspect of the invention, the device is characterized in that the means for varying the pressure are chosen from the group including frequency inverters and pressurized storage tanks.
Varying the pressure in the zone under pressure P1 can be effected, in a particular embodiment of the invention, by varying the circulation rate of the centrifugal fan. If the circulation rate of the centrifugal fan increases, the pressure in the zone under pressure P1 increases. In this case, to obtain a variation in the pressure in the zone under pressure P1, the speed of the motor driving the centrifugal fan is varied according to controlled proportions.
Another way of generating a variation in the pressure in the zone under pressure P1 is to intermittently supply an additional quantity of pressurized fluid to the zone under pressure P1. This fluid can come from a pressurized tank connected to the zone under pressure P1 by means for releasing the pressure of the tank which are, for example, valves. The opening and closing of these releasing means are activated so as to generate the desired variation in pressure in the zone under pressure P1.
These two means for varying the pressure in the zone under pressure have the advantage of being able to be used on existing machinery for chilling foodstuffs.
The present invention also proposes a method for chilling food products by impacting jets, in which
According to a preferred embodiment of this method, the cold fluid is a cryogenic fluid chosen from the group including, in particular, nitrogen, carbon dioxide, oxygen, air, and mixtures thereof.
The chilling method according to the invention is advantageously a deep-freezing method.
The variation in the pressure P1 is preferably short and with a small amplitude, which has the advantage of being inexpensive in terms of energy and not requiring any significant modification to the chilling device.
The variation in pressure is preferably a notched sequence, the amplitude of which is a pressure difference ΔP between a normal operating value and a selected set value that is lower or greater than the normal value, said pressure difference ΔP lies between 10 and 1000 Pa, in particular between 200 and 800 Pa and preferably between 400 and 600 Pa, and the time for which the variation in pressure is applied Δt lies between 1 and 60 s, in particular between 2 and 30 s and preferably between 5 and 15 s.
The method of the invention is preferably implemented with the device described above.
This variation in pressure can be achieved by varying the rate at which the cold fluid is circulated in the zone P1 of the device.
This variation in pressure can thus be caused by the brief and sudden release of pressure coming from a pressurized tank connected to the zone under pressure P1. This release of pressure takes place when a release means such as, for example, a valve is opened. The opening and closing of this pressure release means can be automated.
The method according to the invention has the advantageous feature of being able to be applied to existing chilling or deep-freezing devices.
Other features and advantages of the invention will become apparent on reading the following description. This description is purely illustrative and must be read in conjunction with the attached drawings, in which:
a, 7b, 8, 9a and 9b are drawings of means for cooling the plate according to particular embodiments of the invention.
When the device in
When the above-described device is operated in the presence of humidity supplied by a vapor generator such as that described in Example 1 below, it is observed, as can be seen in
The invention proposes to attach means for preventing such clogging-up to the known device for chilling foodstuffs.
In a first embodiment of the invention, such means can take the form of means for cooling the plate down to a temperature below −80° C. and for maintaining that temperature, as illustrated in
a and 7b show other drawings of heat-exchange devices attached to a plate. The cold fluid is caused to circulate in proximity to the through-holes 4 of the plate 3 in a cold fluid circuit 15. In these figures it can be clearly seen that the pipe is fixed on the plate very closely to the edge of the holes and that its cross-section is such that it allows maximum heat exchange with the plate.
A third embodiment of the means for cooling the plate down to a temperature below −80° C. and for maintaining that temperature is illustrated in
A device such as that described in
The vapor generator runs for about 4 hours from the beginning of the operating cycle.
The temperature of the tunnel is maintained at −80° C. During operation, the pressure in the zone under pressure P1 is measured by means of a manometer or pressure sensor placed in the zone under pressure P1 of the lower plate and variations in the pressure curve are observed, indicating partial blocking of the holes. After 4 hours of operating, the plates are photographed (lower plate seen from below in
The device in Example 1 is used, modified by fixing a heat exchanger to the underside of the lower plate, which makes it possible to maintain the temperature of the latter in the region of −100° C., a few centimeters away from the heat-exchange tube during operation.
This heat exchanger, which is shown in
Liquid nitrogen at approximately −187° C. is passed through the heat exchanger, allowing the plate to be cooled down.
The holes cooled by the heat exchanger are the holes in the rows 4 and 5 and the lines 2 to 6 indicated in
The vapor generator is run throughout the operating cycle, i.e. for 4 hours.
The pressure P1 is maintained at 550 Pa and the temperature in the tunnel at −60° C.
After 4 hours of operating, the top side of the lower plate is photographed. The resulting photograph is shown in
The device in Example 1 is used and the pressure is varied over time in the sequence shown in
PN is chosen to be equal to 550 Pa and PH to be equal to 1330 Pa.
The temperature of the tunnel is maintained at −60° C. The vapor generator is run throughout the trial, i.e. for 4 hours.
After 4 hours of operating, the top side of the upper plate is photographed (
| Number | Date | Country | Kind |
|---|---|---|---|
| 0851590 | Mar 2008 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR09/50384 | 3/10/2009 | WO | 00 | 9/10/2010 |
