U.S. patent application number 12/669609 was filed with the patent office on 2010-09-16 for cryogenic deep-freezing device for products using a porous conveyor belt.
Invention is credited to Beny Bruggeman, Friedhelm Meyer, Cemal Oztas, Didier Pathier, Robert Taylor, Jochen Weidlich.
Application Number | 20100229591 12/669609 |
Document ID | / |
Family ID | 42729580 |
Filed Date | 2010-09-16 |
United States Patent
Application |
20100229591 |
Kind Code |
A1 |
Pathier; Didier ; et
al. |
September 16, 2010 |
CRYOGENIC DEEP-FREEZING DEVICE FOR PRODUCTS USING A POROUS CONVEYOR
BELT
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.
Inventors: |
Pathier; Didier; (Voisins Le
Bretonneux, FR) ; Bruggeman; Beny; (Gent-Wondelgem,
BE) ; Oztas; Cemal; (Voisins Le Bretonneux, FR)
; Taylor; Robert; (Wavre, BE) ; Meyer;
Friedhelm; (Achim, DE) ; Weidlich; Jochen;
(Rastatt, DE) |
Correspondence
Address: |
AIR LIQUIDE USA LLC;Intellectual Property
2700 POST OAK BOULEVARD, SUITE 1800
HOUSTON
TX
77056
US
|
Family ID: |
42729580 |
Appl. No.: |
12/669609 |
Filed: |
July 7, 2008 |
PCT Filed: |
July 7, 2008 |
PCT NO: |
PCT/FR08/51255 |
371 Date: |
May 12, 2010 |
Current U.S.
Class: |
62/381 |
Current CPC
Class: |
F25D 3/11 20130101 |
Class at
Publication: |
62/381 |
International
Class: |
F25D 25/02 20060101
F25D025/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 30, 2007 |
FR |
0736805 |
Claims
1-5. (canceled)
6. A device for the deep-freezing of articles, the device
comprising a porous conveyor belt held in place in the device by
drums, means for pressing the belt onto one of said drums, and a
bath of cryogenic liquid for entirely or partly immersing the belt
to impregnate the belt with cryogenic liquid.
7. The device as claimed in claim 6, characterized in that said
pressing means comprises a system of rollers fastened to a free
wheel capable of pressing the belt onto the drum and of following
the movement of the drum.
8. The device as claimed in claim 7, further comprising a space
between the belt and a bottom of a tank containing the bath, the
space being suitable for enabling gas bubbles that form beneath the
belt within the bath to completely or partly escape via "entry" and
"exit" sides of the belt, thus preventing an overpressure from
being created beneath the belt.
9. The device as claimed in claim 8, characterized in that said
space has a height lying in the 1 cm-10 cm range.
10. The device as claimed in claim 6, characterized in that said
porous conveyor belt is made of a fabric made of synthetic or
natural polymer.
11. The device as claimed in claim 10, characterized in that said
pressing means comprises a system of rollers fastened to a free
wheel capable of pressing the belt onto the drum and of following
the movement of the drum.
12. The device as claimed in claim 11, further comprising a space
between the belt and a bottom of a tank containing the bath, the
space being suitable for enabling gas bubbles that form beneath the
belt within the bath to completely or partly escape via "entry" and
"exit" sides of the belt, thus preventing an overpressure from
being created beneath the belt.
13. The device as claimed in claim 12, characterized in that said
space has a height lying in the 1 cm-10 cm range.
14. The device as claimed in claim 10, characterized in that the
fabric is polyester.
15. The device as claimed in claim 14, characterized in that said
pressing means comprises a system of rollers fastened to a free
wheel capable of pressing the belt onto the drum and of following
the movement of the drum.
16. The device as claimed in claim 15, further comprising a space
between the belt and a bottom of a tank containing the bath, the
space being suitable for enabling gas bubbles that form beneath the
belt within the bath to completely or partly escape via "entry" and
"exit" sides of the belt, thus preventing an overpressure from
being created beneath the belt.
17. The device as claimed in claim 16, characterized in that said
space has a height lying in the 1 cm-10 cm range.
Description
[0001] The present invention relates to a cryogenic product
deep-freezing process and device.
[0002] It is well known that certain food products are very
difficult to deep-freeze and it is then necessary to use
deep-freezing equipment with the following main requisites: [0003]
rapid deep-freezing with a machine occupying as small a floor area
as possible (smallest machine possible); [0004] deep-freezing that
has to be just as effective for the lower surface of the product as
for its upper surface; [0005] the process must not mark the lower
face of the products; [0006] the products must not stick to the
surface on which they have been placed; and [0007] where necessary,
the equipment must allow only the surface of the product to be
deep-frozen, not the core thereof (and thus it must produce what is
called in the industry "crust freezing").
[0008] The following products may be mentioned as examples: fish
fillets covered with a marinade; pasty products (such as vegetable
purees); meat portions covered with sauce.
[0009] At the present time, such very difficult products are
treated in cryogenic tunnels by being immersed in liquid nitrogen,
on narrow conveyors, if necessary providing orifices in the
conveyor belt, to remove the gas formed and thus prevent the
phenomenon of conveyor belt swelling/distortion, which would, as
may be understood, cause productivity problems.
[0010] These immersion tunnels are well known for providing a high
heat transfer over a short distance, and for being very compact (if
transfer were not to take place by immersion, it would be necessary
to have very long equipment for treating the same products).
[0011] In such cases of products that are very difficult to treat,
it has also been demonstrated that the use of a cryogenic
deep-freezer using a polymer (for example polyester) belt imbibed
with liquid nitrogen or passing through a liquid nitrogen bath is
particularly suitable. Such equipment is described in the document
EP-576 665.
[0012] According to this prior technique, the size of the conveyor
belt pores is such that cryogenic liquid can be retained therein,
so as to ensure that the article is completely or partially frozen
by heat transfer between the article and the cryogenic liquid
retained in the porous support.
[0013] To carry out this operation successfully, the polyester belt
on which the products to be crust-frozen are deposited must convey
the products correctly through the deep-freezer, and in particular
it is essential that it ensure a uniform transit time in the
deep-freezer and in the liquid nitrogen bath. The expression
"uniform transit time" is understood to mean a constant (i.e.
substantially constant) transit time during a production phase, or
over the course of a day, whatever the product treated, the batch
treated, etc.
[0014] The second condition for the success of the operation is a
uniform immersion in the liquid nitrogen bath, all the products
being immersed in a substantially constant depth of liquid
nitrogen.
[0015] For the reasons developed hereinbelow, the Applicant has
demonstrated the fact that in certain situations, such a
deep-freezer with immersion of a polymer belt in a cryogenic bath
requires design improvements.
[0016] It should also be noted that some of these difficulties
arise from the polymer nature of the conveyor (though this does
have considerable advantages, as is known), these specific
drawbacks not being observed with a metal belt. This is because a
metal belt drive is "positive" (formed by systems of gearwheels
that cannot slip) whereas in the case of a polymer belt it is
necessary to use a smooth drum that drives a smooth belt.
[0017] Moreover, whereas a metal belt is perfectly rigid, a polymer
belt will necessarily be subjected to deformations as it passes
through the bath.
[0018] Having read the foregoing, it will now be clearer why the
precision and the effectiveness of the process therefore lie in
particular in controlling two points: [0019] regularity of the
transit time through the deep-freezer; and [0020] regularity in the
depth of the liquid nitrogen power encountered by the product.
[0021] To meet the first condition, the belt speed must be steady
and well controlled.
[0022] To meet the second condition, throughout the production
period (for example throughout the day), the liquid nitrogen bath
must have a substantially constant depth and the conveyor must pass
completely flat through this bath, at a substantially constant
distance from the surface of the bath. Thus, whatever the moment
during the day, and irrespective of the position of the products,
they always receive the same heat treatment since they are immersed
in a substantially identical manner in the liquid nitrogen.
[0023] To give an example, if the conveyor is not considered to be
completely flat, for example having a "bump" in the middle of the
belt, the products that are immersed in the liquid nitrogen at this
point will not be deep-frozen comparably to products passing
through the bath along the edges of the conveyor belt, where this
conveyor descends more deeply into the bath.
[0024] It will therefore be appreciated that the available machines
according to the prior art cannot easily meet these two
requirements and that very often the following two defects are
observed: [0025] slippage of the belt on its drive drum, hence a
variable and insufficiently controlled transit time; [0026]
distortion of the conveyor belt in the nitrogen immersion tank--the
belt no longer remains perfectly flat in the bath since nitrogen
gas bubbles form beneath the belt and swell it in the central part
thereof, whereas the edges remain in place at the bottom of the
tank. In addition, the tension in the belt also has a tendency to
raise the belt at its center, whereas the edges remain in place in
the bottom of the bath.
[0027] Among the existing solutions to the above-mentioned
problems, mention may be made of the following arrangements in the
prior art:
[0028] Regularity of the Transit Time/Regular Belt Speed:
[0029] In an attempt to provide a regular belt speed, certain
manufacturers tension the belt by applying high forces. Thus, the
phenomenon of the belt slipping on the drive drum is reputed to be
less.
[0030] However, it should be pointed out that the higher the
tension, the greater the phenomenon of belt distortion in the bath.
In practice, a compromise must therefore be found between belt
slippage and belt distortion, which means that the transit time and
the bath depth are not sufficiently well controlled.
[0031] Liquid Nitrogen Bath Depth Regularity Problem:
[0032] To avoid the problem of belt distortion created by the high
tension and to provide as regular a bath as possible, certain
manufacturers reduce the width of the belt and the bath, or else
divide the bath into several channels. Between the channels, what
may be described as "skis" exert pressure on the belt in order for
it to remain in position on the bottom of the tank.
[0033] As regards reducing the width of the belt, users of this
type of machine, since they often require a high production
capacity, which would mean wide machines (1000 mm in width), the
solution consisting in reducing the width of the bath and of the
belt is therefore not really satisfactory.
[0034] The use of "skis" for trying to limit the distortions of the
belt divides the treatment zone into several channels. The user of
the machine must then divide its production into as many lines
with, in addition, the impossibility of treating products wider
than the channels (maximum width: about 600 mm).
[0035] Moreover, in the absence of nitrogen, this system does
admittedly divide the production into several channels; but when
the tank is filled with liquid nitrogen, nitrogen gas bubbles form
beneath the belt and create a pressure high enough to distort the
belt and form two small bumps, one on each side of the "ski".
[0036] Problem of Nitrogen Gas Bubble Formation:
[0037] To remedy belt swelling due to nitrogen gas bubbles trapped
beneath the belt, certain manufacturers release the pressure
created beneath the belt by perforating the latter. Thus, the gas
can escape and the belt comes back down to a greater or lesser
extent depending on the number and the size of the orifices.
[0038] However, the belt then no longer has a smooth surface and
the products may sometimes be marked by the belt. In addition, this
technique is not applicable to products smaller in size than that
of the orifices (about 10 mm).
[0039] In every case, it has therefore been found that all the
above solutions prevent the machine from being used to the optimum
of its capabilities, while the quality and regularity of the
deep-freezing of the product cannot be maintained at a high
level.
[0040] As will be seen in greater detail below, the present
invention provides a technical solution to the above problems,
whereby it aims to establish a constant belt speed and a regular
nitrogen bath above the belt at each point in the tank, by adopting
a completely different strategy from those employed in the prior
art, namely:
[0041] Transit Time Regularity/Regular Belt Speed:
[0042] To provide a constant belt speed, unlike the solutions of
the prior art, the belt tension is set at as low a value as
possible so as not to create a problem in the bath. The belt will
therefore slip on its drive drum (the situation conventionally
considered to be a draw-back). To obviate this phenomenon, rollers
press the belt against the drum, thereby increasing the angle and
the contact force between the drum and the belt. Locally, on the
drum, the adhesion force is thus considerably increased without
correspondingly distorting the belt in the bath, since the belt
tension remains low in the rest of the machine. Thus, the transit
time is perfectly controlled and is steady.
[0043] Thus, unlike the solutions of the prior art that recommend
very high belt tensions, the present invention adopts a moderate
tension, but locally presses the belt onto the drum by means of
rollers, and the desired overall tension in the belt is obtained by
moving the drums apart.
[0044] In other words, in order to try and better explain the
phenomena below, the higher the tension in the polymer belt the
firmer its attachment on the drum, but it then progresses with
greater difficulty through the bath; conversely, the lower the
tension, the "softer" the system, but it then does not turn
easily--it "skates" over its drive drum.
[0045] The present invention applies a low tension to the
conveyor--the system is therefore relatively "soft"; it therefore
passes without any difficulty through the bath and this is
compensated for by pressing the belt onto a single drum (which is
equipped with the motor) via rollers (for example a free wheel that
presses and follows the movement).
[0046] Regularity of the Liquid Nitrogen Bath Depth:
[0047] Thanks to the system described above, the belt naturally
remains flat in the bath. This situation remains valid in the case
of high-capacity machines with very wide belts (typically 1200 mm
in width).
[0048] This is because the presence of the rollers allows the belt
to be less tensioned in its entirety, and therefore the belt
remains flat more easily (any tension creates distortion
somewhere); to summarize, the presence of the rollers enables two
technical problems to be solved at the same time.
[0049] The Question of Nitrogen Gas Bubbles:
[0050] As mentioned, when the bath is filled with liquid nitrogen,
the nitrogen gas bubbles that form beneath the belt have a tendency
to raise it and distort it.
[0051] The bubbles that form must therefore be removed without
stoppage during production. To do this, according to the present
invention, a space is provided between the belt and the bottom of
the tank. This space allows the gas bubbles to escape via the entry
and exit sides of the belt in the system, without creating an
over-pressure beneath the belt and therefore without raising it.
Thus, the belt remains in place, completely flat at a fixed
distance from the surface of the liquid nitrogen bath.
[0052] In other words, the belt does not pass over the bottom of
the tank, rather it passes at a certain "height" of a few mm or cm
above the bottom of the tank (typically an order of magnitude of 1
to 10 cm is suitable for implementing the invention), but of course
below the cryogenic liquid level, thereby providing a belt/bottom
space. It is then conceivable, without at any time being tied to
such an explanation, that the observed nondistortion is due to the
fact that although the bubbles are directed toward the underside of
the belt, they do not accumulate here--they naturally are
discharged toward the entry/exit ends of the bath and the swashing
observed by the Applicant at the entries/exits during its
experiments confirm this hypothesis.
[0053] In conclusion, by applying this combination of techniques it
is possible for the key points of the process to be completely
controlled in those cases that are the hardest to treat: [0054] the
transit time through the apparatus and through the nitrogen bath is
completely controlled and constant; [0055] the depth of the bath
and the intensity of the cryogenic treatment are completely
controlled: the depth of the bath is constant for all products--it
can be easily adjusted depending on the requirements.
[0056] It should also be noted that the proposed solution according
to the present invention operates effectively, including with a
wide belt, for example 1200 mm in width or more, thereby making it
possible to achieve high production capacities. This also makes it
possible to treat very wide products. However, of course it is also
very suitable for smaller widths (300, 400, 600, 800 or 1000
mm).
[0057] Although an advantageous implementation has been described
in which the two techniques--presence of rollers and space provided
between the belt and the bottom of the tank--have been combined, it
should be noted that, without departing from the scope of the
present invention, it is conceivable that, for certain easier
widths to treat, and also for certain products, only one of the
technical features may be employed, in the presence of pressing
rollers, while still obtaining the desired results.
[0058] In any case, thanks to the control provided by the process,
the size of this type of machine may be increased and the
production capacity is no longer limited by technical problems.
[0059] Moreover, the quality of the deep-freezing is constant and
the process parameters may be adjusted to the best advantage, so as
to optimize the process and reduce its cost.
[0060] Overall, it is the effectiveness and the efficiency of the
process that benefit from the improvements proposed by the
invention.
[0061] The present invention relates to a device for the
deep-freezing of articles, comprising a porous belt conveyor held
in place in the device by drums, and means for impregnating said
belt of the conveyor with cryogenic liquid, the impregnation of the
belt taking place entirely or partly by immersing the belt in a
bath of cryogenic liquid, characterized in that it includes means
for pressing the belt onto one of said drums.
[0062] According to one of the embodiments of the invention, said
pressing means consist of a system of rollers fastened to a free
wheel capable of pressing the belt onto said drum and of following
the movement of this drum.
[0063] According to one of the preferred embodiments of the
invention, a space is left between the conveyor and the bottom of
the tank containing said bath, this space being suitable for
enabling gas bubbles that form beneath the conveyor within the bath
to completely or partly escape via the "entry" and "exit" sides of
the conveyor of the device, without creating an overpressure
beneath the conveyor.
[0064] Advantageously, said conveyor is made of a porous material,
this being a fabric made of synthetic or natural polymer, whether
woven or nonwoven, and preferably made of polyester.
[0065] The present invention will be better understood on reading
the description of a nonlimiting exemplary embodiment, given solely
for the purpose of illustration, and by reference to the appended
FIGS. 1 and 2 which illustrate, in longitudinal and transverse
views respectively, the structure of a deep-freezer having a
polyester belt and a nitrogen bath according to the prior art and
according to the present invention (employing a system of rollers
and a space left between the belt and the bottom of the liquid
nitrogen tank).
[0066] FIGS. 1a and 1b show schematically the main constituent
components of a deep-freezer having a polyester belt and a nitrogen
bath according to the prior art, as described in the introductory
part of the present application.
[0067] Thus, the features of a preferred embodiment for
implementing the present invention may be readily appreciated in
FIGS. 2a and 2b: [0068] the device comprises rollers for pressing
the conveyor belt onto the drive drum (the drum on the left in the
figure, provided with the motor), the rollers forming part of a
free wheel pressing the conveyor belt onto said drum and capable of
following the movement of this drum.
[0069] Also described below are measures for advantageously
perfecting the implementation of the press rollers, which measures
may prove to be advantageous in certain cases, especially according
to the products treated or according to the type of conveyor belt
of the user site in question. As will be understood, these
improvement measures are not absolutely necessary for the present
invention to be properly implemented--they may simply prove to be
advantageous in certain very particular cases, namely: [0070] i)
When the belt is pinched/compressed between the drive drum and the
press rollers, a problem may sometimes arise at the moment when the
belt join fasteners pass over the drum--in some makes this join is
thicker than the belt (by way of illustration, about 5 mm as
opposed to 2 mm in the case of the belt) and may then remain jammed
at the press rollers, which may result in the conveyor belt being
immobilized.
[0071] It is then possible in this very particular case to fit the
drum with bars that in no way impede its operation and make it
possible to provide a passage for the thicker join. In some ways
with such an arrangement, the following operation is observed:
[0072] the join arrives on the drum in a space between two bars. In
this case, the join may pass without any problem between the drum
and the rollers; [0073] the join arrives on the drum just at a bar
(join on the bar). In this case, it cannot pass and the drum starts
to slip on the belt (the drum continues to rotate but the belt
remains stationary). Once the drum has slipped slightly, the join
now finds itself in a space between two bars and can then pass.
This small slip is very temporary and in no way impedes the correct
operation of the apparatus, and this improvement thus makes it
possible for the belt to continue advancing even when the join
passes between the drum and the rollers. [0074] j) When the
apparatus is operating cold, and according to the features of the
equipment in question, expansion may vary the dimensions and the
geometry of the apparatus very slightly. This is sometimes
sufficient to deflect the belt to one side, which would have the
consequence of rapidly damaging the edges of the belt and therefore
requiring it to be prematurely replaced.
[0075] In this particular case, a system for actively guiding the
belt may therefore be proposed, in which a sensor detects the
position of the belt.
[0076] As an example, when the belt is positioned too much to the
right, the angle of the drive drum at the exit of the machine is
automatically modified via an actuator, this having the consequence
of repositioning the belt more to the left.
[0077] Conversely, when the belt is positioned too much to the
left, the angle of the drive drum at the exit of the machine is
automatically modified via an actuator, this having the consequence
of repositioning the belt more to the right.
[0078] When the belt is thus correctly centered in the machine
frame, the belt lifetime is very substantially increased. In
addition, with the rubbing of the belt on the edges of the machine
eliminated, the regularity of advance of the belt is further
improved and the process may be even more precise.
[0079] Given below is an example of the implementation of the
installation shown in FIG. 2.
[0080] Very good results are thus obtained with an apparatus
measuring 6 meters in length and having a belt 1.2 meters in width,
which deep-freezes a wide range of meat-based products, such as
cooked hamburgers, raw or cooked meatballs, sausages, strips of
meat, or cubes of ham. It will be understood that, for this wide
range of products to be effectively treated, the deep-freezer with
an immersion bath must be capable of being adapted. In certain
cases, the transit time must be short (typically 1 minute) and the
nitrogen bath very shallow (typically 5 mm in depth). For other,
more difficult products, the transit time must be long (typically
10 minutes) and the bath must be relatively deep (typically 50 mm).
Experience has shown that by applying the abovementioned technique,
the entire range of products in question can be correctly treated,
the deep-freezing being constant and regular over the course of
time and during production phases.
* * * * *