EP1357338B1 - Low temperature freezing system, in particular for freezing, deep freezing and storing of food products - Google Patents

Abstract

In a first phase a classic circuit which has a axial compressor, closed economizer and matched evaporator is used to freeze a fresh product to -18 degrees C. When the temperature has been attained the evaporator is automatically connected to the low pressure circuit of a booster - 65/- 20 degrees C and the compressor and economizer serve as a high pressure booster stage

Description

The present invention relates to a low-temperature refrigeration plant in particular for freezing, freezing and storage of products, such as food products according to the preamble of claim 1. Such an installation is known from EP-A-0 718 568.

Low temperatures, especially between -20 ° C and -60 ° C are particularly interesting in the field of food. Indeed, it has long been observed that maintaining products at such temperatures allows better preservation of the organoleptic qualities of these products. Such low temperatures are also useful, particularly in the field of chemistry or metallurgy. Although their use is still limited, it is due to the fact that refrigeration plants, which cover wide temperature ranges, that is to say ambient temperature at -60 ° C, remain expensive, complex and generally particularly bulky.

Two families of refrigeration plants are today used to cover wide temperature ranges as illustrated in particular by the article by OM Magnussen "Superfreezing low temperature technology" scanref, Volume 21, No. 4, September 1992, pages 34 -41.

The first family of refrigeration plants consists of double-stage installations with an intermediate bottle. These installations, also called "booster", consist of a low-pressure single-stage compressor and a single-stage high pressure compressor separate or double-stage compressors called "compound" screw or piston. In the partial injection cycle, the fluid mass flow rate displaced by the low pressure compressor is sub-cooled under the condensation pressure in an exchanger immersed in the liquid of the intermediate bottle. It is only the difference between the high pressure and low pressure masses which undergoes the relaxation of the high pressure at the intermediate pressure, hence its partial injection name. As the system operates at low suction pressures, the result is the use of a large volume of gas that requires particularly large compressors.

Another family of refrigeration plants has therefore supplanted this first family of installations. This is refrigeration installations called "cascade". The cascade system has two or more different refrigerants flowing in individual circuits. These individual circuits are arranged side by side so that the condenser installed in the low temperature circuit is cooled by the evaporative refrigerant of the other circuit where the temperature is higher. Such an installation is more particularly described in US-A-2,434,221. Thus, in this document, in particular in FIG. 1, it clearly appears a first circuit consisting of a compressor, represented in FIGS. 1, of a condenser, of a pressure reducer 6 and of an evaporator represented at 7. Another refrigerant circuit, said second circuit, completely independent is represented by the references 9 to 20 in which the reference 9 represents the compressor, the reference 16 an expander and the reference 17 the evaporator used for the production of cold in the cold room. It can then be seen in such a circuit that the condenser of the second circuit is constituted by the evaporator of the first circuit. Thus, the fluids of these two circuits circulate in independent individual circuits even if the evaporator of one of the circuits serves as a condenser of the fluid of the other circuit. Such installations therefore remain complex because of the presence of two refrigerants and an expansion tank.

An object of the present invention is therefore to provide a refrigeration plant whose design allows to cover a wide range of temperatures while allowing the use of a single refrigerant inside a compact installation compared to the double-decker or cascade installations known to date.

Another object of the present invention is to provide a refrigeration plant whose design allows to obtain a reliable installation, high performance, small footprint with attractive yields.

For this purpose, the subject of the invention is a low temperature refrigeration plant, in particular for freezing, freezing and storage of products, in particular food products, according to claim 1.

Thanks to the design of such an installation, commissioning of the second circuit is carried out under ideal conditions since the refrigeration plant is already in operation. regime at the temperature of the refrigerant, in particular at the temperature of the economizer bottle and the evaporation temperature allowing the cold room to reach already a temperature of the order of -30 ° C. Thus, the evaporator passes successively and automatically from a fluid supply by means of a first so-called conventional freezing or cooling circuit to a supply by means of a so-called deep freezing or low temperature subcooling circuit. Since the cooling capacity of phase 2 is lower than the cooling capacity of phase 1, the delta T, the temperature difference between the evaporation temperature and the air temperature at the inlet of the evaporator, is lowered. therefore clearly in phase 2, which ensures excellent performance of the installation. Moreover, such an installation is versatile since it can operate permanently in the form of a conventional cooling installation if the second circuit is never activated.

• la figure 1 représente une vue schématique d'une installation frigorifique conforme à l'invention ;
• les figures 2A à 2E représentent de manière schématique le détail d'une installation frigorifique conforme à l'invention, ces figures devant être lues en les disposant côte à côte en vue de reconstituer les circuits complets.

The invention will be better understood on reading the following description of exemplary embodiments, with reference to the appended drawings in which:

• Figure 1 shows a schematic view of a refrigeration plant according to the invention;
• FIGS. 2A to 2E schematically represent the detail of a refrigeration installation according to the invention, these figures to be read by placing them side by side in order to reconstitute the complete circuits.

As mentioned above, the refrigeration system, which is the subject of the invention, is more particularly intended for freezing, freezing and storing products, in particular food products. This installation comprises at least two refrigerant circulation circuits. These circuits are represented in FIG. 1, one in solid line, the other in solid lines and a dashed line consisting of a line and a point. The first circuit is used more particularly for a first cooling phase which constitutes for example a freezing phase of the product up to a temperature of about -18 ° C in the core. This first phase is followed by a second phase where the product is sub-cooled from a temperature of -18 ° C to a temperature of -45 ° C. The second circuit therefore makes it possible to reach negative temperatures that are greater in absolute value than the temperatures of the first circuit. When the core temperature of the product or evaporation temperature of the installation reaches -18 ° C, the installation is automatically connected to the second circuit.

The two refrigerant circulation circuits, which, in the examples shown, are compression-type circuits, each comprise, arranged in series, at least one compressor 2, a condenser 3, a pressure reducer 6 and an evaporator 1. Obviously, the pressure reducer 6, serving to supply the evaporator 1, could have been equivalently replaced by a pump or a thermosiphon system (flood).

As illustrated in the figures, these circuits are common over part of their length and are powered by the same refrigerant capable of supplying the first circuit and / or the second circuit. These first and second circuits comprise, on their common section extending between the letters X and Z, taken in the flow direction of the fluid in Figure 1, at least the evaporator 1 for the production of cold. This evaporator 1 common to both circuits is thus able to be supplied with fluid by one or the other of the circuits as a function of the desired reference temperature.

In the examples shown, these first and second refrigerant circuits are of the compression type and comprise at least one evaporator 1, a compressor 2, a condenser 3 and a pressure reducer 6 common to both circuits. The second circuit is constituted between evaporator 1 and compressor 2, taken in the fluid flow direction, by a bypass of the first circuit. The XZ section common to the two circuits implies that the fluid of the first and second circuits flows at the outlet of compressor 2 through a condenser 3 associated with a tank 4 and then through an economizer 5 or intermediate bottle before reaching the regulator 6 and then at the evaporator 1 for the production of cold. At the level of the economiser 5 or intermediate bottle 5, there is provided a connection reducing a portion of the fluid to the compressor for the two circuits. However, the design of this connection differs from one circuit to another.

The second circuit is constituted between evaporator 1 and compressor 2 by a derivation of the first circuit, this branch corresponding to the ZY section. This second circuit is equipped, on its bypass, with a piston compressor 7 connected at the output to an intermediate bottle 5, itself closably connected to the inlet of the suction channel of the compressor 2 common to the first and second circuits. The compressor 2 common to the first and second circuits is constituted of a screw compressor and economizer 5. In the examples shown, the economizer 5 serving the first circuit and the intermediate bottle of the second circuit are preferably constituted by one and the same capacity. The screw compressor 2 is also equipped with a medium pressure low pressure suction suction channel 10 'to which is connected the first economizer output circuit 5 (section WY'). This suction channel WY 'is connected to the economizer 5 so as to form in the first circuit a recirculation loop of at least a portion of the fluid from the condenser 3 towards the compressor 2. Of course, these circuits are selectively activatable depending on the desired cooling temperature. The activation is preferably obtained by actuating at least one shutter member 8, 9 positioned on at least one of the circuits. Thus, the operation of such a refrigerating plant can be described generally as follows. The refrigerant flows at the first circuit between the compressor 2, the condenser 3, the tank 4, the economizer 5, the expander 6 and the evaporator 1. At the evaporator outlet 1, the fluid returns directly to the inlet of the compressor 2 by borrowing the section ZY in Figure 1. Part of the vapors contained in the economizer 5 is reintroduced into the circuit and feeds the channel 10 ' suction medium pressure compressor. Thus, a part of the fluid of this first circuit is brought to recirculate in the compressor part 2, condenser 3, tank 4, economizer 5 thanks to the connection WY 'between economizer 5 and compressor 2. This connection is of the shutter type and is equipped of a closure member 8. This first circuit therefore corresponds to the circuit portions equipped with valves 8 of white color which are represented in the open position. When the evaporation temperature of the installation reaches a predetermined value or corresponds to a predetermined operating time, the second circuit is activated. The compressor part 2 screw and bottle saver 5 serves high pressure booster stage whose low pressure part is no longer calculated for the entire deep freeze but only to ensure the subcooling products. Upon activation of this second circuit, the valves 8, shown in white in Figure 1, are closed while the black valves 9 are open. The fluid then follows a path in accordance with that shown with a solid train and a dotted line and a point in FIG. 1. The fluid at the evaporator outlet 1 is passed through a piston compressor 7 after having passed through a valve 9 closed when the first circuit is activated and open when the second circuit is activated. The fluid at the outlet of this piston compressor 7 is fed into an intermediate bottle. This fluid, at the outlet of the intermediate bottle, is returned to the inlet of the compressor 2 to screw. This portion WY between the bottle 5 and the inlet of the compressor 2 is also equipped with a shutter member 9 to prevent a reflux of the first circuit in the second circuit when the first circuit is activated. At the outlet of the screw compressor 2, the fluid follows the same path as in the case of the first circuit, namely, it passes through the condenser 3 and then the tank 4 before to reach the intermediate or economizer bottle 5 then pass through the expander 6 and supply the evaporator 1.

Thus, at the outlet of the economizer 5 or the intermediate bottle, a circuit portion WY, in the case of the second circuit, brings the refrigerant back to the inlet of the screw compressor 2 at the level of the suction channel, while in the In the case of the first circuit, this same outlet of the bottle 5 or of the economiser 5 brings the fluid entering the compressor 2 via a so-called medium pressure suction channel 10 'which also equips the compressor 2 with a screw. This circuit portion is represented in WY '. The portion WY of the second circuit allows the screw compressor 2 to operate without economizer by becoming the high pressure compressor of a double-stage installation, the first stage is constituted by the compressor 7. The portion WY 'of the first circuit allows a suction of gas contained in the economizer 5 and their injection into the compressor 2 at the channel 10 'suction medium pressure.

In the examples shown, the refrigerant used common to the first and second circuits is R 404 A. The physical properties of this fluid are described in particular in the book "Ashrae fundamentals Handbook" of 1997. This fluid allows operation with moderate pressures (18.5 bar absolute for a condensing temperature of -40 ° C), which is compatible with all refrigeration equipment standards.

It should be noted that the switching of the first circuit to the second circuit and vice versa takes place beyond a predetermined temperature measured and / or calculated. In this In the second case, the operating time of the first circuit may be taken into account, the activation of the second circuit occurring beyond a predetermined duration which is assumed to have attained an evaporation temperature of within a predetermined range.

The detailed design of such an installation will now be described with reference to FIGS. 2A to 2E. Thus, FIGS. 2A to 2E show the refrigeration scheme for the execution of a refrigeration system of a long liner tuna boat. Such boats go fishing for a period of about 15 days. From the port, the holds C1, C2 in which the fish will be stored are at room temperature. These shims must therefore reach a temperature close to -60 ° C. During fishing periods, each tunnel is loaded with fresh tuna, the fresh tuna being at room temperature. Once the tunnel is filled, the freezing step is started by activating the first circuit of the installation and then the freezing step by activating the second circuit of the installation. Once the freezing and freezing cycles are complete, the tuna is then transported to a storage hold at -60 ° C.

The two tunnels are for example designed to have a freezing capacity of 2 tons per cycle at -45 ° C heart. The shims, represented here in the form of cleat C1 and C2 wedge, have meanwhile volumes of the order of 100 m ³ at -60 ° C. The C3 bait block has a volume of 10 m ³ at -20 ° C. The outside temperature is 35 ° C and the external humidity is 80%. The thermal insulation coefficient of the refrigerated rooms K is equal to 0.2 kcal / hr.

• déperditions : 23876 kcal/21h
• renouvellement d'air : 908 kcal/21h.
• équivalent thermique du travail des moto ventilateurs : 119196kcal/21h.
• 2028kg de thon de +30°C à -18°C : 177855 kcal/21h.
• TOTAL : 321835 kcal/21h
• soit : 15325 kcal/h.

The detailed thermal balance of a tunnel in phase 1, that is to say with a tuna, whose temperature is brought from + 30 ° C to -18 ° C, can be described as follows:
Internal dimensions: 4.1.3,6.h = 1,7m.
External dimensions: 4,7,4,2.h = 2,3m.

• losses: 23876 kcal / 21h
• air change: 908 kcal / 21h.
• thermal equivalent of motorcycle fans work: 119196kcal / 21h.
• 2028kg of tuna from + 30 ° C to -18 ° C: 177855 kcal / 21h.
• TOTAL: 321835 kcal / 21h
• that is: 15325 kcal / h.

• déperditions : 10000kcal/6h
• équivalent thermique du travail des moto ventilateurs : 22704kcal/6h
• 2028 kg de thon de -18°C à -45°C : 22450 kcal/6h
• TOTAL : 55154 kcal/6h
• soit : 9192 kcal/h.

The detailed heat balance of a phase 2 tunnel corresponding to a sub-cooling stage of the tuna from -18 ° C to -45 ° C can be described as follows:

• losses: 10000kcal / 6h
• thermal equivalent of motorcycle fans work: 22704kcal / 6h
• 2028 kg of tuna from -18 ° C to -45 ° C: 22450 kcal / 6h
• TOTAL: 55154 kcal / 6h
• that is: 9192 kcal / h.

• Tunnel N°1 ou N°2 : Phase 1, congélation à -18°C à coeur.
• Durée : 21h ; Puissance nécessaire : 17,8 kW.
• Phase 2 ; sous-refroidissement de - 18°C à - 45°C à coeur.
• Durée : 6h, Puissance nécessaire : 10,7kW.
• Cale de 100m3 : Puissance nécessaire : 8,3kW.
• Cale de 80m3 : Puissance nécessaire : 7,5kW.
• Cale de 10m3 : Puissance nécessaire : 1,6kW.

The summary of the thermal balance of the different items can therefore be established as follows:

• Tunnel No.1 or No.2: Phase 1, freezing at -18 ° C at the core.
• Duration: 21h; Power required: 17.8 kW.
• Phase 2; subcooling from -18 ° C to -45 ° C to the core.
• Duration: 6h, Power required: 10,7kW.
• 100m3 shim: Power required: 8.3kW.
• 80m3 chock: Power required: 7,5kW.
• 10m3 shim: Power required: 1,6kW.

The installation is still equipped with two low-pressure piston-motor compressors (see FIG. 2c), for example of the Mycom brand, type F8WA. The speed of rotation can be of the order of 1450 rpm, the operating speed of -65 ° C / -20 ° C with cooling capacities of 16.7 kW and an absorbed power of 16.5 kW.

The power regulation of such compressors can be 50, 75, 100% and the power of the electric drive motor is 22 kW.

The installation is still equipped with three motorcycle compressors 2 high pressure screw, one of them in relief or extra. These motorcycle compressors 2 can be branded Bitzer Type OSN5361-K with a rotation speed of 2900 rpm. When these compressors 2 operate economizer on the first circuit, they have a cooling capacity of 34.7 kW and an absorbed power of 23.5 kW. When operating without economizer in cooperation with the cylinder 5, it has a cooling capacity of 45.3 kW and a power consumption of 23.1 kW, a power control of 75 and 100% and a power of the electric motor. B35 shape drive of 30 kW.

Each of the tunnels, shown in T1, T2, is equipped with a ventilated battery or evaporator 1, supplied with direct expansion and with air defrosting. Electrical valves placed on the liquid and suction lines make it possible to automatically switch from the first conventional freezing or cooling circuit to the second intense subcooling circuit. In order to avoid pressure drops, the electric suction valves are motorized full-flow valves. Each evaporator 1 is equipped with a liquid-vapor exchanger 18, so that the The temperature of the gases sucked by the low-pressure piston compressors shall be not less than -50 ° C.

Each of the shims, shown in C1, C2, C3 in the figures, is equipped with a ventilated battery 1 ', supplied with direct expansion and with electric defrosting. As a result, these batteries are each equipped with a safety thermostat which cuts off the supply of the resistors when the evaporator is at a high temperature. Electrical valves placed on the liquid and suction lines also make it possible to start lowering the temperature of the evaporators. shim at -25 ° C before the fishing trip using the screw compressor 2 with economizer 5, before using the low pressure circuit of the booster to reach the temperature of -60 ° C. As for the tunnels and for the same reasons, each evaporator of the holds C1, C2 is equipped with a liquid-vapor exchanger 18.

The C3 shim is equipped with a ventilated battery 1 'supplied with direct expansion and electric defrosting. This battery is of course only connected to the screw compressor with economizer circuit. Each of these stations is equipped with a thermostameter 12 (thermostat + temperature indication). Shims at -60 ° C are also equipped with a temperature recorder allowing control by the buyer of the cargo.

The engine room comprises a series of low pressure compressors corresponding to the piston compressors 7 of the general scheme. These reciprocating compressors are provided with a liquid-stripping bottle 14 with a liquid subcooler coil and are each equipped with a direct-expansion oil cooler 15, an oil level controller 16 in the crankcase, the possible surplus of oil in the crankcase compressors will be injected at the suction of the priority screw compressor, an oil separator 17.

These compressors 7 operate in cooperation with an economizer intermediate bottle 5. The latter is provided with a cooling pot for the gases discharged by the low-pressure compressors 7, a high-pressure liquid supply with a liquid level controlled by a switch 19. A second float switch 20 ensures the safety of the compressors when the level is too high. This economizer intermediate bottle 5 is again equipped with a constant pressure valve 21 in order to limit the pressure to -20 ° C. in the present case. We also find the classic elements such as safety valve, liquid indicator ...

The installation comprises three motorcycles 2 identical screw compressors that can work both during the conventional freezing regime adopted in the first phase, ie + 40 ° C to -34 ° C with economizer, or single stage without economizer at -20 ° C -40 ° C when operating the high pressure stage of the booster, during phase 2 of tunnels, phase of intense subcooling or when cooling chocks to -60 ° C is necessary. This unit is equipped with a common oil separator 23, which facilitates the automatic oil returns and a single oil cooler 24. The compressors are also equipped with a 25 anti-liquid bottle with coil subcooler liquid. An oil decocenter 26 placed on the general discharge allows an automatic recovery of the oil dissolved in the freon of the intermediate bottle by means of an ejector system 27.

The installation also comprises a condenser 3 of the multitubular condenser type forming a reservoir. Condensation of high pressure discharge gases is provided by this seawater condenser. This condenser acts as a reservoir and also allows the thermosiphon supply of the oil cooler.

The refrigeration system allows the simultaneous operation of all stations in all cases, such as tuna storage chutes at -60 ° C, a bait wedge in service, a tunnel N ° 1 in phase intense subcooling (Phase 2) and tunnel No. 2 in the conventional freezing phase (Phase 1).

The duration of operation of tunnels in phase 1, open white electrical valves, black closed electric valves according to figure 2a can be set by a "coupatan" type clock which, once the displayed time has elapsed, passes the same tunnel in phase 2. The black-colored electric valves are then open, those of white color closed, according to Figure 2a. The power regulation of the low pressure compressors is done through the pressure sensor 28 according to Figure 2b. The power regulation of the high-pressure compressors 2 is done by means of the pressure sensor 29 according to FIG. 2d. The power regulation of compressors operating as economizer is done through the pressure sensor 30 according to Figure 2c. Each of the three screw compressors 2, according to FIG. 2d, can also operate in a high-pressure stage of the booster system, electric valve 31 (corresponding to the member 9 of FIG. 1) open, valves 32 and 33 (corresponding to the members 8 of Figure 1) closed, that in system with economizer (circuit No. 1), electric valves 32 and 33 (corresponding to the members 8 of Figure 1) open, electric valve 31 (corresponding to the member 9 of Figure 1) closed.

Claims (5)

1. Low temperature frigorific plant notably freezing , deep - freezing and the storage of products , particulary food products , the aforementioned plant has at least two frigorific circuits to ensure the refrigerant flow, the first one called first circuit has a first cooling step to reach a temperature in the region of - 18°C , the other one called second circuit used for subcooling preferably from -18°C to -45°C , each frigorific circuit of the compression type containing , connected in series at least one compressor ( 2 ) , one condenser ( 3 ) and one evaporator ( 1 ) through which flow a refrigerant , the evaporator being supplied by an expansion valve , or by a pump or by flooded gravity operation , these frigorific circuits being common on one part ( XZ ) of its length and being supplied by the same refrigerant suitable for alternative circulation in either aforementioned circuits , these circuits containing on their common section ( XZ ) at least one condenser ( 3 ) , preferably one expansion valve ( 6 ) , and the evaporator ( 1 ) used to refrigeration , this evaporator ( 1 ) being supplied by refrigerant by either of the aforementioned circuit according to the required air temperature , characterised by the fact the first and second frigorific circuits contain notably a common compressor ( 2 ) composed of a screw compressor and one economisor ( 5), this screw compressor ( 2 ) being equipped at its entrance with a connection ( WY') designed for intermediate suction pressure which may shut , shut when the second circuit is running , these suction connection ( WY' ) being connected to the economisor ( 5 ) so as to form in the first circuit a constant circulation of at least one part of the refrigerant coming from the condenser ( 3 ) towards the compressor ( 2 ) , and characterised also by the fact that the second circuit is located between the evaporator ( 1 ) and the compressor ( 2 ) , in the way of the refrigerant flow by means of a diversion of the first circuit , the second circuit being equipped on its diversion , with a reciprocating compressor ( 7 ) , connected at its outflow to a intermediate cooler , this cooler being itself connected in such a way that it can be closed up at the entrance of the suction connection ( WY ) of the compressor, common to the first and second circuits .
2. Frigorific plant in accordance with claim 1 , characterised by the fact that the first and second circuits can be alternately activated according to the required cooling temperature , the activation being preferably obtained by the activation of at least one closing valve ( 8 , 9 ) located on at least one of the circuits.
3. Frigorific plant in accordance with claims 1 and 2 , characterised by the fact that the economisor ( 5 ) and the intermediate cooler of the second circuit are performed by the same device.
4. Frigorific plant in accordance with claims 1 to 3 , characterised by the fact that the first circuit is equipped in the area located between the evaporator ( 1 ) and the compressor ( 2 ) , further down the diversion aiming at forming the second circuit , of a closing valve ( 8 ) , such as an automatic valve activated when the predetermined temperature has been reached , measured and / or calculated notably according to the running time of the first circuit.
5. Frigorific plant in accordance with one of the claims 1 to 4 , characterised by the fact that the common refrigerant used for the first and second circuit is R404a

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