FR2521402A1 - Perishable food preservation - in cooling chamber with closed circuit through gas sepn. membrane appts. - Google Patents

Abstract

THE INVENTION CONCERNS THE REFRIGERATION TECHNIQUE. THE INSTALLATION WHICH IS THE SUBJECT OF THE INVENTION IS CHARACTERIZED IN THAT IT IS PROVIDED WITH AT LEAST ONE AUXILIARY MEMBRANE GAS SEPARATOR 3, ANALOGUE TO THE MAIN SEPARATOR 2 AND OF WHICH CAVITY 8 LOCATED ABOVE ITS MEMBRANE COMMUNICATES, ON THE ONE HAND, WITH CAVITY 6 LOCATED ABOVE THE MEMBRANE OF MAIN GAS SEPARATOR 2, AND ON THE OTHER HAND, WITH THE ATMOSPHERE THROUGH TUBING 10, WHILE CAVITY 9 OF SEPARATOR 3 LOCATED AT - BELOW ITS MEMBRANE IS CONNECTED TO VACUUM PUMP 4, MAIN GAS SEPARATOR 2 COMMUNICATES WITH THE ATMOSPHERE THROUGH CAVITY 8 LOCATED ABOVE THE MEMBRANE OF THE AUXILIARY MEMBRANE GAS SEPARATOR 3. L THE INSTALLATION IN QUESTION CAN BE USED FOR EXAMPLE FOR THE PRESERVATION OF PERISABLE FOODS, SUCH AS: FRUIT, VEGETABLES, BERRIES, MEAT, FRESH FISH, ETC.

Description

 The present invention relates to refrigeration equipment and in particular relates to an installation for the conservation of perishable goods, such as fruit, vegetables, berries, meat, fresh fish, etc. in an adjustable gaseous medium with reduced oxygen content.

 We know an installation for the preservation of food products in a gaseous medium with reduced oxygen content (cf. French patent NO 1590579, cl.A23B 5/00, 1970), which includes refrigeration chambers filled with a gaseous mixture, a selective membrane gas exchanger communicating via pipes with said chambers and fans for circulating said mixture. The gas exchanger is in the form of a set of sleeves made of silicone polymer film joined by manifolds. The collectors are connected to the chambers by pipes. The gaseous mixture, under the action of fans, passes from the refrigerating chambers into the sleeves and then returns to the chambers.

The sleeves are blown externally with atmospheric air.

 Under the action of the difference in partial pressures in the chambers and in the air of the atmosphere, carbon dioxide (C02), nitrogen (N2) and oxygen (02) diffuse through the film: the carbon dioxide (released by the fruit when they breathe) and nitrogen diffuse from the room into the atmosphere air, while oxygen from atmospheric air diffuses into the rooms, where it is partially consumed by the fruits when they breathe.

 However, with a gas exchanger thus designed, the required composition of the gaseous medium in the refrigerating chamber is created very slowly (during one month), since the oxygen concentration decreases only as a result of their absorption in the chamber. (fruit breathing). The absorption takes place very slowly, since the oxygen concentration varies at most by 0.5 O per day and that with the decrease in the oxygen concentration in the chamber the speed of its reduction decreases more, this which ultimately reduces the effectiveness of fruit storage.

 Since the gas exchanger does not create a gaseous medium of the required composition and the medium is created by the absorption of oxygen by the fruits in the chamber and by the exchange of gases through the membrane, a such an installation must meet high requirements as to the tightness of the chamber.

 In addition, a gas exchanger thus designed does not make it possible to adjust the composition of the gaseous medium in the chamber. This is essentially linked to the fact that the composition of the gaseous medium in the chamber is determined by the values of the rates of evacuation of the constituents of the mixture through the membrane, as well as by their ratio. These factors depend, on the one hand, on the diffusion characteristics of the membrane, and on the other hand, on the difference of the partial pressures above and below the membrane. As above the membrane the air is always at atmospheric pressure, the motive force of atmospheric oxygen through the membrane towards the chamber is always very high. In this case, a balanced composition of the medium is created in the chamber, depending only on the diffusion characteristics of the membrane. For this reason, to change the composition of the gaseous medium, it is necessary to replace the membrane.

 There is also an installation for the storage of perishable foodstuffs (cf. the review "Kholodilnaya tekhnika", NO 6, p. 7, 1980), which includes a sealed refrigeration chamber, a gas separator communicating with the atmosphere and having a membrane dividing it into two cavities. The cavity located above the membrane of the gas separator communicates with the refrigeration chamber by means of fans ensuring the circulation of the gaseous medium, while the cavity located below the membrane communicates with a vacuum pump.

 This installation makes it possible, by creating a determined rarefaction under the membrane and by choosing the necessary flow rate of atmospheric air in the cavity located below the membrane of the separator, to establish over a wide range the composition of the gaseous medium in the cold room.

 However, the efficiency of the operation of the gas separator in this installation greatly decreases if there is not sufficient uoe tightness of the refrigerating chamber. This is mainly related to the fact that, in the event of insufficient sealing of the chamber, oxygen infiltrates into the chamber. The speed of reduction of the excess pressure or relative pressure of the gas mixture in the chamber can be adopted as a criterion for sealing the chamber; for example, when the relative pressure in the refrigeration chamber goes from 147 Pa to 73.5 Pa in 5 minutes, the concentration of oxygen in the chambers increases to 6 or 7% instead of the 3% necessary. , even in sealed chambers it is not possible to maintain an oxygen concentration below 396, and under these conditions, for an efficient operation of the installation, a gas separator equipped with a membrane is required. large area, because the larger the surface area of the membrane, the greater the amount of concentrated nitrogen that can be obtained, and therefore, the more the percentage of oxygen in the gas mixture can be reduced.

 It was therefore proposed to create an installation for the conservation of perishable foodstuffs in a gaseous medium with reduced oxygen content, in which the separation of atmospheric air would be done so as to allow the range of required concentrations to be widened. 'oxygen and carbon dioxide, and, under conditions of less stringent requirements as to the sealing of the chamber, to ensure the rapid formation of a gaseous medium of required composition and to regulate its composition.

 The solution to this problem consists in that the installation for the conservation of perishable foodstuffs in an adjustable gaseous medium with reduced oxygen content of the type comprising a refrigerating chamber, a gas separator with a membrane communicating with the atmosphere and whose the cavity situated under the membrane is connected to a vacuum pump, while the cavity situated above the membrane communicates with a refrigerating chamber, and a device for forced circulation of said medium, is characterized, according to the invention, in that that it is provided with at least one gas separator with an auxiliary membrane similar to the aforementioned separator, or main separator, and the cavity of which is located above the membrane communicates on the one hand with the cavity situated above the membrane of the separator main gas, and on the other hand, with the atmosphere via a pipe, while the cavity located below the membrane is connected to a vacuum pump, said gas separator to main diaphragm communicating with the atmosphere through the cavity located above the diaphragm of the auxiliary diaphragm gas separator.

 Said auxiliary gas separator makes it possible to very quickly create the required concentration of the gas mixture, since the air, on its path towards the refrigerating chamber, is enriched twice in essential components, Thus, the gas mixture arriving from the gas separator auxiliary gas with reduced oxygen content, is additionally enriched in nitrogen in the main gas separator, so that the gas mixture arriving in the refrigerating chamber is a mixture with high nitrogen content, which makes it possible to rapidly reduce the concentration of oxygen up to 3% and maintain the required concentration in the refrigeration chamber even when the requirements for its tightness are reduced.In addition, the mixture pumped from the cavity of the main gas separator immediately fills with concentrated nitrogen from of the auxiliary gas separator, which prevents possible depletion in the refrigeration chamber and the ingress of atmospheric air into it it through its insufficiently watertight walls.

 It is advantageous to connect the cavity which is located above the membrane of the auxiliary gas separator to the cavity located above the membrane of the main gas separator by means of a device for forced circulation of the medium, which reduces investment costs for maintaining the required concentration and simplifies the design of the installation.

 In addition, the cavity located above the membrane of the auxiliary gas separator can be connected to the refrigeration chamber using a pipe provided with a valve or similar closure member.

 In the installation, the tubing connecting to the atmosphere the cavity located above the membrane of the auxiliary gas separator can be connected to the refrigerating chamber by a pipe provided with a valve or the like, which allows, after loading fruit into the chamber, rapidly lowering the oxygen concentration in the chamber by circulation of the gas mixture through the cavities located above the membrane of the two gas separators connected in series.

The invention will be better understood and other objects, details and advantages thereof will appear more clearly in the light of the explanatory description which will follow of various embodiments given solely by way of example. annexed limitative in which
- Figure 1 shows schematically the installation for the conservation of perishable foodstuffs in an adjustable gaseous medium with reduced oxygen content
- Figure 2 schematically shows the installation for the conservation of perishable foodstuffs, according to the invention, in which the auxiliary gas separator communicates with the main gas separator via a device for forced circulation of the medium5
- Figure 3 shows schematically the installation for the conservation of perishable foodstuffs, according to the invention, in which the tube connecting the auxiliary gas separator to the atmosphere communicates with the refrigeration chamber.

 The installation for storing perishable foodstuffs in an adjustable gaseous medium with reduced oxygen content comprises a sealed refrigeration chamber 1 (FIGS. 1 to 3), gas separators with main and auxiliary membranes, respectively 2 and 3, a pump vacuum 4 and devices 5 for forced circulation of the medium, the latter can be of any known type, for example fans. The perishable goods are placed in the refrigerating chamber 1 filled with gaseous medium with reduced oxygen content.

 The main 2 and auxiliary 3 gas separators are of the same type and arranged in series. it should also be noted that the installation, as a function of the volume of the refrigerating chamber 1, may comprise several gas separators with auxiliary membranes 3.

 As main and auxiliary membrane gas separators 2 and 3, gas separators of known types are used, for example, made up of a set of membrane elements, selective with respect to nitrogen and carbon dioxide and sharing each gas separator 2 and 3 in a cavity located above the membrane 6 and below the membrane 7 (for the main separator 2) and above the membrane 8 and below the membrane R (for auxiliary separator 3).

 The cavity 8 located above the membrane of the auxiliary separator 3 communicates, on the one hand, with the atmosphere by a tube 10, and on the other hand, by a pipe II with the cavity 6 located above the membrane of the main separator 2, so that the main gas separator 2 communicates with the atmosphere through the cavity 8 located above the membrane of the auxiliary gas separator 3.

 The cavity 6 located above the membrane of the main membrane gas separator 2 (FIG. 1) communicates with the refrigeration chamber 1 by means of lines 12 and 13. In the lines 12 and 13 are mounted the devices 5 forced circulation of the gaseous medium.

 The cavities 7 and 9 located below the membrane (Figures 1 to 3) of the separators communicating by the iSermediary of lines 14, 15 and 16 with the vacuum pump 4, and in the lines 14 and 15 are mounted valves or the like 17 and 18 making it possible to close the lines 14 and 15 and, if necessary, to cut off any of the cavities from the vacuum pump 4.

 The cavity 7 located below the membrane of the main separator 2 can have a tube 19 fitted with a valve or the like 20 intended, if necessary, to make this cavity 7 communicate with the atmosphere.

 In the installation for the conservation of perishable foodstuffs represented in FIG. 2, unlike that of FIG. 1, the cavity 8 located above the membrane of the auxiliary gas separator 3 communicates with the cavity 6 situated above of the membrane of the main gas separator 2 by means of the device 5 for forced circulation of the medium. The cavity 8 located above the membrane of the auxiliary gas separator 3 communicates with the refrigerating chamber 1 by means of a pipe 21 fitted with a valve or the like 22, while the cavity 6 located above the membrane of the main separator 2 is connected to the refrigerating chamber 1 by means of a pipe 23 equipped with a valve or the like 24, which makes it possible, if necessary, to cut from the chamber 1 the cavity 6 situated above separator membrane 2.

In the installation for the conservation of perishable foodstuffs shown in Figure 3, unlike that of Figure 2, the tubing 10 connecting to the atmosphere the cavity 8 located above the membrane of the auxiliary gas separator 3 communicates with the refrigerating chamber 1 by means of a pipe 25 equipped with a valve or the like 26, which makes it possible to carry out in two ways the circulation of the gaseous mixture of the chamber 7; either via the two separators 2 and 3 connected in series, or only using the main separator 2 with make-up supply of concentrated nitrogen via the separator 3
In the refrigeration chamber 1 (FIGS. 1 to 3) is placed a sensor 27 (gas analyzer or time relay) forming part of the control system for automatic regulation of the gas mixture currents and ensuring the operation of all the valves. As a sensor 27 and as a control system for automatic regulation of said currents, devices widely known in the field can be used.

 The installation according to Figure 1 works as follows. After activation of the vacuum pump 4 and the fans 5, the gaseous medium begins to circulate between the refrigerating chamber 1 and the membrane gas separator 2, the pressure inside the membrane elements then decreases an absolute pressure 20 kPa.

there is a difference in the partial pressures of carbon dioxide, oxygen and nitrogen on the membranes, determining the diffusion of these components of the gas mixture through the membranes. The part of the gas mixture which is sucked in using the pump of the refrigerating chamber 1 is completed by k stream of concentrated nitrogen arriving from the cavity 8, situated above the membrane of the auxiliary separator 3, at the cavity 6 located above the membrane of the main separator 2, and from there to the refrigeration chamber.

 This excludes a possible rarefaction in the refrigerating chamber 1 and a possible infiltration of oxygen from the air in the chamber 1.

 The concentrated nitrogen is obtained in a manner known per se, namely, by separation, on the membranes, of the air supplied by the pipes 10 in the auxiliary separator 3.

By entering the separator 2, the stream of concentrated nitrogen is further enriched in nitrogen in the cavity 6 located above the membrane of the separator 2, thus ensuring a high concentration of oxygen in the refrigerating chamber, even in presence of leaks in the chamber walls. From the auxiliary separator 3 to the main separator 2, always comes a quantity of gas equal to that of the gaseous mixture pumped through the membranes of the main separator, which excludes a possible rarefaction in the refrigerating chamber 1.

 If the oxygen concentration in the refrigerating chamber is lower than the standard, the sensor 27 transmits a signal to the valve 20, which opens in to allow a current of air to arrive in the cavity located below the membrane of the main separator 2. The oxygen, through the membranes, arrives in the cavity 6 situated above the membrane of the separator 2 and then in the refrigerating chamber 1 thereby increasing the concentration of oxygen in the chamber 1.

 If the oxygen concentration in the refrigerating chamber 1 is higher than the standard, the sensor 27 transmits a signal to the valves 20, 17, 18. The valve 20 closes by cutting off the current of atmospheric air towards the cavity 7 located at the - below the membrane of the main separator, while in valves 17 and 18 the passage section increases, and this results in an increase in the rarefaction in the cavities located below the membrane of the separators and a decrease in the concentration of oxygen in the refrigeration chamber as a result of its diffusion diffusion through the membranes of separators 2 and 3.

 The installation represented in FIG. 2 works essentially in the same way as that of FIG. 1, except that the concentrated nitrogen arriving from the cavity situated above the membrane of the auxiliary separator 3 passes through the main separator 2 by mixing beforehand with the gaseous medium arriving from the refrigerating chamber via line 21. In this way, the risk of a rarefaction in chamber 1 decreases even more and the infiltration of atmospheric air into the chamber through its insufficiently tight walls decreases more.

 The installation of FIG. 3 operates in a similar manner to that of FIG. 2, except that the pipe 25 comprising the valve 26 and connected to the cavity situated above the membrane of the auxiliary separator 3 makes it possible to circulate the gaseous mixture through the separators 2 and 3 connected in series, which it is necessary to achieve immediately after the char S ent fruit in the room. This allows the oxygen concentration in the chamber to be reduced more quickly from 20.7% to 10%. When the oxygen cancentration reaches 10%, the valve 26 closes and the installation operates in the conditions described above, that is to say that the circulation of the gaseous mixture is carried out via the main separator 2 and that the auxiliary separator 3 supplies the system with concentrated nitrogen.

 Thus, the creation and regulation of the composition of the gaseous medium are ensured, in the refrigeration chambers of the installations according to the invention, even in the event of less stringent requirements as to the tightness of the refrigeration chambers 1, for example, in chambers in which a variation of 73.5 Pa (difference between 147 and 73.5 Pa) of the excess pressure or relative pressure takes place in 5 minutes. This makes it possible to reduce by 1.5 times, compared with known installations, the losses of products caused by microbiological and physiological alterations.

Claims (3)

R E V E N D I C A T I O N S CLAIMS  1. Installation for the preservation of perishable foodstuffs in an adjustable gaseous medium with reduced oxygen content, of the type comprising a refrigerating chamber (1), a membrane gas separator (2), communicating with the atmosphere and the cavity of which ( 7) located below the membrane is connected to a vacuum pump (4), while the cavity (6) located above the membrane communicates with the refrigeration chamber (1) and a device (5) for forced circulation said gaseous medium, characterized in that it is provided with at least one gas separator with an auxiliary membrane (3), similar to the main separator (2) and the cavity (8) of which is located above its membrane communicates, on the one hand, with the cavity (6) located above the membrane of the main gas separator (2), and on the other hand, with the atmosphere by a tube (10), while the cavity (9 ) of the separator (3) located below its membrane is connected to the vacuum pump (4), the main gas separator (2) commu connecting with the atmosphere through the cavity (8) located above the membrane of the gas separator with auxiliary membrane (3).  2. Installation according to claim 1, characterized in that the cavity (8) located above the membrane of the auxiliary gas separator (3) communicates with the cavity (6) located above the membrane of the gas separator main (2) by means of the device (5) for forced circulation of the gaseous medium, and with the refrigerating chamber (1), using a pipe (21) provided with a valve (22).  3. Installation according to one of claims 1 and 2, characterized in that the tube (10) communicating with the atmosphere the cavity (8) located above the membrane of the auxiliary gas separator (3) communicates with the refrigerating chamber (1) via a pipe (25) provided with a valve (26).