WO2011070283A1 - Method and apparatus for cooling and/or deep-freezing materials implementing the injection of two cryogenic liquids - Google Patents

Abstract

The invention relates to a method for cooling materials, in particular food, in a cooling apparatus, the cooling being completely or partially carried out by contacting the materials with a cryogenic liquid. Said method is characterized in that the contacting is carried out by means of the injection of two cryogenic liquids, nitrogen and CO₂. The liquid nitrogen and the liquid CO₂ are injected either separately, into at least two injection points of the apparatus, or by mixing both cryogenic fluids at the injection point. The invention is of use if the apparatus being utilized is a mixing, batch mixing, or grinding chamber, with the injection being carried out into the body of the material in the bottom portion of the chamber.

Description

 The present invention relates to the field of processes for cooling and / or freezing the contents of an enclosure by means of a method for cooling and / or freezing products, particularly foodstuffs, using two a cryogenic liquid. It relates, in particular, the cooling of food products in devices such as tunnels, mixers, kneaders, grinders or kneaders, churns, drums ("tumblers" in the literature) etc ..., the contents of the device can be then solid or pasty as is the case of meat, or liquid.

 If in the following it is more particularly the case of food products, the invention should in no way be restricted to their case, it relates much more generally many other products, including chemical, biological, stem cells etc. ... undergoing such cryogenic cooling operations.

 The following is described in greater detail in the case of grinding mixers, in order to better fix the ideas of the problems that arise.

In such applications for using cryogenic liquids for cooling food products in grinding mixers, the use of C0 ₂ is preferred for its ability to transfer many frigories to the change of state.

Considering the example of meat mixers, it is known that there is a very abundant literature concerning the use of liquid C0 ₂ , especially by injection into the lower part of the mixer, in order to improve the heat exchange conditions. between the cryogenic liquid and the meat. Reference is made, for example, to documents U. S. -4, 476, 686 and EP-744,578. The application to the field of meat is indeed quite massive and emblematic (the products concerned are very varied, ground beef (beef, veal), ground meat, minced pork (sausages ..) _/ chopped poultry (cordon blue, nuggets etc ....)), an area where the temperature control in the mixer must be very efficient:

 it is necessary to compensate for the mechanical heating associated with mixing and chopping;

 it is desirable to obtain a compatible texture for the subsequent forming.

But it should be noted that for several reasons, the demand of this industrial sector for the temperature control of grinding mills is moving towards the use of liquid nitrogen. However, it is known that for liquid nitrogen the value of frigories at the change of state is twice as low as for C0 ₂ . It then summarizes in the following the main characteristics of high or low injection processes, C0 ₂ or nitrogen, in such kneaders.

The high injection C0 ₂ :

- We value the only solid phase of C0 ₂ but the cooling efficiency is interesting at 64 kcal / kg at 20 bar.

 The technique requires an optimum level of loading and requires to adapt the number of blunderbusses (injectors) so as to deposit the dry ice on the whole surface of the meats without creating a pile of snow, but it is necessary to recognize that the setting implemented in high injection is easy.

It is characterized by a great ease of mixing solid meat / solid snow phases, the dry ice is generated in the heart of the product. - The technique always has the risk of extracting dry ice, so it is better to focus on overflow extraction.

 - This technique is traditionally limited to small mixers and small production volumes

(typically less than 100 tonnes per year).

The C0 _{2 also} has a bacteriostatic effect, it limits the development of ^micro¬ organisms.

High nitrogen injection:

 As mentioned above, this technique is limited by a low refrigeration efficiency, close to 36 kcal / kg at 1.5 bar.

 - It is also characterized by the fact that it presents risks of cold spots and therefore by a difficult distribution.

 - High nitrogen injection therefore requires control and control low injection pressure.

 For all these reasons, it should be noted that the high nitrogen injection is very little used.

The low C0 ₂ and nitrogen injection: it makes it possible to valorize the latent heat of the change of state of the cryogenic fluids as well as a part of the specific heat of the gases. This valuation of gases depends on the contact time with the product.

If, in high injection, the liquid nitrogen had a very large refrigeration efficiency disadvantage compared with the CO ₂ , in low injection, the cooling efficiency of the nitrogen is close to that of the CO ₂ (the contact time between the gas and the reactor). product allows to valorize the gases). Nitrogen also has the advantage of offering solubility in fats and water much lower than C0 ₂ . The observed fluid consumption is approximately 20% higher in low nitrogen injection compared to the low C0 ₂ injection. In all of this context, it is conceivable, and it is one of the objectives of the present invention, that it would be advantageous to be able to have a new method for cooling products in such devices, and in particular in kneaders. in low injection of the fluid, a process allowing a better valorization of the gases and in particular to value the part of the gases which it is not currently in the existing processes.

As will be seen in more detail in the following, the method according to the invention, of cooling products in a cooling apparatus, using a cryogenic liquid placed in contact with the products, is remarkable in that we will obtain a better valorization of the gases thanks to the injection not of a single fluid but of two fluids - liquid nitrogen and liquid C0 ₂ - and through exchanges of frigories between the C0 ₂ and the nitrogen , the liquid nitrogen and the liquid CO _{2 that} can be injected according to the invention either separately at at least two injection points of the apparatus, or by mixing at the point (s) of injection itself. same (themselves).

By fixing once again the ideas in the case of the example of the low injection in a kneader, the method according to the invention, of cooling a mass of product contained in an enclosure (of mixer type, kneader, crusher ...), using a cryogenic liquid injected into the mass of material in the lower part of the enclosure, is remarkable in that one will obtain a better valorization of the gases thanks to the injection of two fluids - nitrogen and C0 ₂ - and not a single fluid, and through the exchange of frigories between CO ₂ and nitrogen. The present invention thus relates to a method for cooling products, especially food products, in a cooling apparatus, the apparatus used being a mixer-type chamber, a mixer, or a grinder or kneader, which can contain a mass of product to be cooled, using a cryogenic liquid injected into the mass of material in the lower part of the chamber, characterized in that one injects within the mass of material in the lower part of the enclosure two cryogenic liquids, nitrogen and CO ₂ , the liquid nitrogen and the liquid CO ₂ being injected either separately into at least two injection points of the apparatus or by mixing in situ at at least one injection point .

It will be noted that among the abundant literature dealing with the injection of a cryogenic liquid into a cryogenic cooling apparatus, there is the document EP-1 887 296 which deals with the production of cryogenic mixtures for supplying cryogenic apparatus. cooling of products. This document considers that it is not satisfactory to inject different fluids by separate channels, it recommends the realization of a mixture upstream of the cooling chamber and the injection of this pre-done mixture, it then makes the mixture of cryogens (gaseous and / or liquid and / or solid) in a very conventional manner by using an upstream mixing chamber, etc.

We will show below, in particular by comparative examples, but also by extremely efficient modes of realization of the mixtures at the point of connection on a device of the type kneader, that the analysis that carried out this document is erroneous in the case of kneaders in low injection: the separate injections of liquid nitrogen and C0 ₂ on the one hand, and on the other hand the low injection of mixtures of liquid nitrogen and liquid C0 ₂ by mixing at the point (s) of injection on the mixer gives remarkable results, and allows actually a better valorization of gases through the exchange of frigories between C0 ₂ and nitrogen.

According to one of the implementations of the invention, there is moreover, in the upper part of the enclosure, a forced convection system, making it possible to recycle and use the cooling power of the cold gases resulting from the low injection of cryogenic liquids.

 This forced convection system can be constituted using, for example, fans or by using a turbine, for example by way of illustration, 0.38 KW type fans equipped with 45 ° blades inclined at 45 °.

According to one of the embodiments of the invention, the two cryogenic liquids, nitrogen and CO ₂ , are injected into at least one injection point of the apparatus, by mixing at the injection point, injector used to perform an exchange of frigories between the two liquids at the base of the injection.

According to one of the forms of such an implementation where the mixing is carried out at the injection point, the injector used is a _two- pipe, concentric injector, the liquid C0 ₂ passing preferentially through the outer tube (the the "coldest" temperature inside, the "highest" temperature outside, in contact with the ambient temperature).

According to another of the forms of such an implementation where the mixing is carried out at the injection point, the injector used is a tritubes injector concentric, preferentially implementing the fluids as follows: liquid nitrogen passes through the inner tube; liquid C0 ₂ passes into the annular space between the first tube and the second tube which is concentric to it;

 - Liquid nitrogen passes through the annular space between the third tube, the outermost, and the second tube which is concentric to it.

As will be better illustrated below, the experiments carried out by the Applicant clearly demonstrate the positive contribution of an injection of two cryogenic liquids instead of one, on several parameters and performances governing such a cooling process.

Without being in any way limited by the explanations that the Applicant advances below, we can think that the following phenomena occur, very advantageously.

Two cryogenic liquids are injected into the apparatus, and exchanges of frigories are carried out between the CO ₂ and the nitrogen, extremely valuable exchanges, as will be seen.

In particular, we observe the sub-cooling of the formed snow (it is known that, at atmospheric pressure, the injected liquid CO ₂ passes to the state of snow and gas), sub-cooling which increases the transfer capacity of cold to the product.

But also considering such situations of low injections in mixers, kneaders etc ... it is likely here that the liquid nitrogen by releasing its Kcal in the product, generates gas having a very low temperature in the top of the equipment, and then the gaseous C0 ₂ up towards the top of the equipment solidifies in contact with very cold nitrogen present in the gas overhead, snow can again return to contact with the product and transfer his frigories to this product (somehow as in a "high injection" type process).

 And it is conceivable that then the presence of forced convection added in the upper part of such a mixer (for example via the presence of a fan) can further increase these transfers.

The invention may furthermore adopt one or more of the following technical characteristics:

 the two fluids are injected separately into at least two injection points on the apparatus, and the following three steps of control of the process are implemented:

 i) the injection of the two fluids is carried out continuously until a target temperature is reached in the mass of product treated;

 j) stopping the injection during a given stopping time (for example a few tens of seconds, for example 30 seconds);

 k) the temperature in the treated mass is measured: if the measured temperature is substantially equal to the desired target temperature, the mixer is switched off, whereas if the measured temperature is higher than the set temperature, restarts the injection until the set temperature is reached.

 The term "stop mode" means the stop of mixing (and injection), the operator can then empty the mixer when he deems it appropriate.

This embodiment is particularly advantageous for treating lots ("batches") of very different materials (quantity, quality in particular in fat content, etc.) and in particular to adapt to the fact that the present invention allows, as as we will see later, significant reductions in treatment times and therefore greatly improved productivity, thus lowering the cycle time to be done without at any time take the risk of generating different temperatures depending on the volume of product treated.

According to one embodiment of the invention, in order to avoid causing dry ice in the extraction system of the cooling apparatus, it is necessary to promote the absorption of the snow generated in the upper part of the enclosure by the product, it is then proposed to size the extraction system to avoid promoting gas speeds capable of driving snow. If the desired gas velocities will be different according to the configuration of the cooling apparatus, it will be preferred according to the invention to use so-called "overflow" extractions.

 Recall that the person skilled in the art of cooling or freezing equipment knows the principle of these so-called "overflow" extractions (as illustrated very schematically in FIG. 7 below), where either a space is left between the equipment and the extraction pipe, ie the extraction pipe itself is cut in one place.

 The advantages of such a configuration in the context of the present invention include the following:

 -> the "cut" allows the evacuation of condensate resulting from the evacuation of such cold gases, limiting the risk of return of these condensates in the equipment;

-> the "cut" allows to limit the evacuation speeds and in particular to avoid evacuation overspeeds and therefore speeds that would evacuate not only gas but also snow that forms in the top of the kneader (according to the mechanism of exchange of frigories described higher as obtained by the present invention).

According to a preferred mode of implementation of the invention, it is implemented on the liquid nitrogen tank supplying the apparatus, a regulation of the pressure of the liquid phase (foot control tank), this in order to promote conditions in which the amount of liquid nitrogen reaching the apparatus is regulated, irrespective of the level of filling of the nitrogen tank, and therefore the height of the liquid ("liquid column").

 For exemplary embodiments of this footwell regulation, reference may be made to the document WO2004 / 005791A2, for example by acting on the pressure of the gas at the top of the tank, for example by vaporizing liquid taken from the bottom of the tank for forming gas sent to the top of said tank.

Other features and advantages of the present invention will thus become more clearly apparent in the following description, given by way of illustration but in no way limiting, with reference to the accompanying drawings for which:

 FIG. 1 is a schematic representation of a conventional mixer of the prior art (for example of meat) with two troughs, using, on each side of the mixer, a series of liquid nitrogen injection nozzles in the lower part of the mixer;

 FIG. 2 illustrates one embodiment of the invention in a mixer with a trough, with the aid of two separate injections of the two fluids, made on the same side of the trough;

FIG. 3 provides a partial view of the upper part (cover) of a mixing chamber according to one of the implementations of the invention, the part high being provided with a forced convection system consisting of two fan blades 45 degrees inclined at 45 °;

 Figure 4 provides a summary table of implementation tests of the invention and comparative tests;

 Figure 5 provides an example of two-tube injector for mixing at the injection point;

 FIG. 6 provides an example of a three-way injector for mixing at the point of injection.

 Figure 7 provides a very partial diagram illustrating an overflow extraction structure, in relation to the top of a kneader.

FIG. 1 shows the lower part of a conventional mixer of the prior art (for example a meat mixer) with two troughs 2 and 3, for which a series of cryogenic fluid injection nozzles is used. for example, liquid nitrogen on each side of the apparatus.

 It is symbolized by reference numeral 5 in the figure, the injection nozzles cryogenic liquid, connecting to the wall of the mixer, nozzles themselves fed through flexible 6 by a distribution manifold and feeding 7, advantageously positioned as is the case in this figure 1 in the upper position relative to the injection nozzles.

 In order not to unnecessarily load the figure, there is shown, at reference 4, by simple crosses, the shafts of the rotor shafts of the mixer, a shaft per mixer trough as shown in Figure 1.

As can be seen from reading this figure 1, the position of the injection nozzles along the wall of each trough (beta angle), as well as the inclination of each injection nozzle relative to the horizontal (angle alpha), adopt here advantageous values, in order to prevent the cryogenic liquid jet from crossing the shafts and rotors of the mixer (avoid the risk of creating cold spots). by interesting a maximum portion of the mass of product to be cooled contained in the mixer, but also on the other hand to avoid, by the inclination of the injection nozzle relative to the horizontal, that during the subsequent cleaning of the mixing water, this water can not go back into the cryogenic liquid supply line.

 It has thus been possible to consider that a beta angle close to 45 ° with respect to the vertical gives good results, and that an angle alpha of at least 10 ° with respect to the horizontal is a setting that is advantageous. to adopt.

As indicated above, FIG. 3 provides a partial view of the upper part of a mixing chamber (cover), the upper part of which is provided with a forced convection system consisting of two fans of 45 blades inclined at 45.degree. °. The mode shown here is of course only an exemplary embodiment, many other configurations (number of fans, numbers of blades per fan, inclination etc. ..) can be envisaged without departing from the scope of the present invention.

The convection system shown in Figure 3 is the one used for the practical and comparative examples (with and without high convection) reported below.

FIG. 5 provides an example of a two-tube injector making it possible to carry out mixing at the injection point, and thus to achieve an exchange of frigories between the two gases at the base of the injection. As is preferred according to the invention, the liquid C0 ₂ passes through the outer tube, which promotes the cooling of C0 ₂ with nitrogen, limits the heat input, and easily allows to generate venturis effects on nitrogen .

 As will be clear to those skilled in the art, such an injector is to be connected to the apparatus in question, for example a low injection kneader, preferably by means of quick connection, especially for cleanability issues well known to the skilled person.

 Figure 6 illustrates an example of injector tritubes for mixing at the injection site. The mode illustrated here implements the fluids as follows:

liquid nitrogen passes through the inner tube; liquid C0 ₂ passes into the annular space between the first tube and the second tube which is concentric to it;

 - Liquid nitrogen passes through the annular space between the third tube, the outermost, and the second tube which is concentric to it.

Here again it will be understood, this arrangement promotes the contact between the two fluids to cool the liquid C0 ₂ .

As already mentioned above, the two-tube or three-tube injectors according to the invention, making it possible to carry out mixing at the injection point on the mixer, such as those illustrated in the context of FIGS. 5 and 6, can be powered and connected. to the apparatus in question, by very simple means of supplying the injector and quick connection, but it will also be possible to envisage using more complex injection valve of the injector, such as allowing the control automated distribution of fluids between the different channels of the injector (for example a valve controlled by a pneumatic actuator).

The following is a description of the conditions of practical examples of implementation of the invention and, in the case of a mass-meat cooling mixer:

 - Use of a brand blender HOBART, a single trough (as shown schematically in Figure 2, and when the convection is present it is in accordance with Figure 3 attached);

 low injection system: use of two injectors on the same side of the trough, and two solenoid valves controlled at the same time (it will have understood many other configurations of injections, number, on each side, the same side etc are possible and will be chosen according to the operating conditions, including the type of kneader, the size of the kneader etc ...).

 According to the invention, it is possible to use very simple injectors, commercially available such as simple orifices, or even more elaborate injectors such as those which the Applicant has developed as described in documents EP-744 578 or EP-2 041 026. .

 - Cryogenic fluid sources used:

■ use of a liquid C0 ₂ tank stored at 15 bar and -20 ° C, which is placed on a scale to evaluate consumption;

 ■ use of a reserve of liquid nitrogen at a pressure of 3, 6 bar, here again reservoir which is placed on a scale to evaluate consumption;

- the treated product was a fresh beef meat with a fat content of 20% coarse grinding (freezing point -1 ° C, water content 62%, specific heat above freezing point 0.85 kcal / kg, specific heat below freezing point 0.36 kcal / kg, latent heat 55 kcal / kg);

 the initial temperature of the pre-ground meat is in the range of 3.5 to 4 ° C., the reference temperature after grinding is substantially -1 ° C.

the average time of a kneading cycle is usually at this industrial site of 12 minutes, in low injection C0 ₂ .

 - protocol followed:

^■ Temperature measurement of the fresh ore incorporated in the mixer.

^■ Injection of cryogenic liquids continuously, with or without the presence of forced convection (63 Hertz) based on two coupled and monitored factors:

 a temperature of the meat in the mill from -0.6 ° C to -1 ° C .;

 - a motor intensity of 6 amperes.

^■ In parallel:

 o The intensity of the mixer is relieved thanks to an amperometric clamp.

 o The temperatures inside the mixer, outside the mixer (at the opening / closing of the lid) and the temperature of the exhaust gases are recorded.

^■ Temperature measurement of the ore after grinding.

^■ Verification of the visual appearance and texture of the milled ore as well as the steak formed downstream by a production manager, checks completed not a bacteriological analysis of the product formed. The tests are carried out on batches of 150 kg of meat (according to the test considered the test is repeated 3 to 4 times to ensure a good reproducibility and representativeness of the results observed).

In all cases the tests implement injectors of simple type (single pipes connected to the mixer).

- Test No. 1 - Comparative: Injection of liquid nitrogen alone, without additional convection implementation.

Tests No. 2 - according to the invention: tests without implementation of convection, injection of the two cryogenic liquids separately according to Figure 2 (two injectors on the same side of the mixer).

- Tests N ° 3: same tests as the N ° 2 but with here additional implementation of a high convection.

In other words, these tests are characterized by a constant of intensity parameters at the end of treatment (6A), of the freezing stage (the intensity at the end of treatment being always the same), of the ore used and pre-milled. , the batch weight treated, the target temperature after grinding sought (substantially - 1 ° C).

The results of the tests are summarized in the table presented in figure 4 below, results which make it possible to draw the following conclusions: it is clearly observed by the implementation of the invention a reduction of the treatment time, reduction which is all the higher when an additional high convection is implemented;

- There is clearly also a decrease in fluid consumption implemented. This reduction in consumption is to be related to the subcooling of C0 ₂ carried out thanks to the invention, but also to the limitation of the calefaction phenomenon, thus improving the heat transfer;

 the presence of a forced convection makes it possible to further improve each of these performances (treatment time and consumption);

 in other words, the treatment lasts for a shorter time, the engines are therefore implemented less time, which allows the entry of fewer calories from the outside and less mechanical energy of the motors transferred to the system;

 - the amount of frigories transferred to the mass, compared to the usual conditions of site treatment is the same, the transfer has been improved, whether with convection or without the presence of forced convection high. More precisely, the optimization of the process is to be linked to a synergy of cumulative effects.

 The use of two fluids makes it possible to operate with a

C0 ₂ subcooled, injected into the mass of material, while creating a cold gaseous sky, able to re-solidify the C0 ₂ gaseous escaping to the top of the enclosure.

 And it is conceivable, when forced high convection is implemented, it only reinforces these effects.

With regard to the role of this forced convection, these results unambiguously show that this forced convection introduced into the upper part of the enclosure has an indisputable and positive effect on the overall transfer of frigories achieved on the treated mass.

 This could seem paradoxical given the compact mass treated, or given the time available during treatment, time that may appear too low.

We can try to provide the following explanation: for comparison, in a traditional cryogenic tunnel is installed a fan of 0.20kW / m ² to achieve a convection of 80W / m / ° K. According to the present invention, and this is its merit, one can typically install 7.5 kW on a single m ² , to have a convection that can be estimated at about 200 W / m ² / ° K which is considerable.

 It can be considered that the conditions of the invention then approach part of the convection type "impaction" (also called "impingement" in this medium).

Claims

claims 1. A method of cooling products, especially food, in a cooling apparatus, the apparatus used being a mixer-type chamber, mixer, or mill, which can contain a mass of product to be cooled, using a a cryogenic liquid injected into the mass of material in the lower part of the chamber, characterized in that two cryogenic liquids, nitrogen and C0 are injected into the mass of material in the lower part of the chamber; ₂ , the liquid nitrogen and the liquid C0 ₂ being injected either separately into at least two injection points of the apparatus, or by mixing in situ in at least one injection point. 2. Cooling method according to the claim 2, characterized in that there is moreover, in the upper part of the enclosure, a forced convection system, making it possible to recycle and use the cooling power of the cold gases resulting from the low injection of cryogenic liquids. 3. Cooling method according to one of the preceding claims, characterized in that the two cryogenic liquids, nitrogen and CO ₂ , are injected into at least one injection point of the apparatus, by mixing at said point of injection. injection, the injector used to perform an exchange of frigories between the two liquids at the base of the injection. 4. Cooling method according to the claim 3, characterized in that the injector used is a _two- pipe concentric injector, the liquid C0 ₂ preferably passing through the outer tube. 5. Cooling method according to claim 3, characterized in that the injector used is a tritubes injector, concentric, preferably implementing the fluids as follows: liquid nitrogen passes through the inner tube; liquid C0 ₂ passes into the annular space between the first tube and the second tube which is concentric to it;  - Liquid nitrogen passes through the annular space between the third tube, the outermost, and the second tube which is concentric to it. 6. Cooling method according to one of the preceding claims, characterized in that the two fluids are separately injected into at least two injection points on the apparatus, and in that the following three steps are implemented. Process control:  i) the injection of the two fluids is carried out continuously until a target temperature is reached in the mass of product treated;  j) stopping the injection during a given stopping time;  k) a measurement is made of the temperature in the mass of treated product and if the measured temperature is substantially equal to said set temperature the mixer is switched off mode, while if the measured temperature is greater than the temperature of set point the injection is restarted until the set temperature is reached. 7. Cooling method according to one of the preceding claims, characterized in that the apparatus is provided with gas extraction means, and in that that these means are of type said overflow extraction.