EP2185873B1 - Method for cryogenic cooling a fluid such as helium for supplying a fluid consumer and corresponding equipment - Google Patents

Description

The invention relates to a cryogenic refrigeration process of a fluid, for example helium, for supplying a fluid consumer, as well as a corresponding installation.

In a conventional method, the fluid cyclically circulates successively through a compression stage, a pre-cooling stage and / or fluid cooling stage, and an interface for supplying the consumer with fluid. and collect fluid from the consumer.

This type of process is particularly suitable when the consumer needs a substantially constant heat load, that is to say when the thermal power to be supplied by the refrigeration process is almost constant over time.

Such a method remains unsuitable, however, in the event of a variable thermal load over time.

A reactor used in the field of controlled fusion comprises superconducting elements cooled with liquid helium. In the case of this type of reactor, a pulsed thermal load, varying substantially sinusoidal in time, is necessary in order not to damage the aforementioned superconducting elements.

It therefore appears that, in this particular application, the aforementioned conventional method can not be used without significant over-sizing of the various components of the installation to implement it.

The document FR 1540391 discloses a method for maintaining very low temperature electrical appliances using a fluid subjected to a compression stage, an expansion and cooling stage to be partially liquefied in a reservoir for maintaining a phase equilibrium of the fluid to a target temperature.

The tank supplies electrical appliances for cooling. This system is unsuited to applications undergoing thermal load variations required by the consumer since the flow rates are subject to significant variations (to the compression stage and the expansion and cooling stage).

The invention aims to overcome this drawback by proposing a method of refrigerating a fluid to adapt to thermally variable loads over time.

For this purpose, the invention relates to a refrigeration method according to claim 1.

In this way, it is possible to adjust the amount of cold fluid supplied to the interface, and therefore the thermal load available to the consumer.

In addition, the accumulator can store cold fluid when the thermal load to be supplied is low, that is to say to store in the accumulation means a specific thermal load and to deliver, by heat exchange, at least a portion of this charge stored in fluid for the interface.

Such a method therefore makes it possible to use an installation for its implementation which is simply dimensioned according to the average power to be delivered, the method making it possible to adapt to the peaks of thermal load to be supplied to the consumer.

According to one characteristic of the invention, the amount of fluid returned to the pre-cooling and / or cooling stage is adjusted by at least one controlled bypass valve, for example by means of a pressure sensor.

The amount of cold fluid supplied to the interface is therefore adjusted dynamically by the bypass valve according to the needs of the user.

The documents JP9170834 A and JP61005586 A describe cryogenic refrigeration processes and installations that do not adapt sufficiently satisfactorily to variable heat loads. Advantageously, the fluid from the pre-cooling and / or cooling stage circulates through an expansion turbine.

According to a possibility of the invention, the first part of the fluid from the pre-cooling and / or cooling stage exchanges heat energy with the fluid delivered by the accumulator.

Preferably, the fluid from the pre-cooling and / or cooling stage exchanges the heat energy with the fluid coming from the interface and / or with the second fluid part coming from the pre-cooling stage and / or cooling.

Advantageously, the second and / or third portion of the fluid from the pre-cooling and / or cooling stage exchanges heat energy with the fluid coming from the interface.

According to a possibility of the invention, the second fluid portion from the pre-cooling stage and / or cooling is expanded through an expansion valve.

Preferably, the first portion of the fluid from the pre-cooling and / or cooling stage exchanges heat energy with a first fraction of the fluid from the expansion valve.

According to a feature of the invention, a second fraction of the fluid from the expansion valve is intended to supply the accumulator.

Advantageously, the fluid delivered by the accumulator is returned to the pre-cooling and / or cooling stage.

The invention furthermore relates to a refrigeration installation of a fluid, for example helium, for implementing the method according to the invention, comprising an interface equipped with fluid inlet and outlet members intended respectively for supplying a consumer with fluid and collecting fluid from the consumer, a fluid compression stage coming from the interface, at least one pre-cooling stage and / or cooling the fluid coming from the interface and / or fluid from the compression stage, characterized in that it comprises a damping stage comprising a supply pipe connecting the pre-cooling and / or cooling stage to the fluid inlet members of the interface, a delivery pipe connecting the fluid outlet members of the interface to the pre-cooling stage and / or cooling, and a first branch line connecting upstream of the interface the supply line to the discharge pipe via at least one bypass, the damping stage further comprising a second bypass pipe, connecting upstream of the interface the supply pipe to the discharge pipe, and equipped with accumulator, a first heat exchanger being arranged so as to exchanging heat energy between the fluid from the accumulator and the fluid flowing in the supply pipe.

According to a characteristic of the invention, the supply pipe is equipped with an expansion turbine, arranged upstream of the first bypass pipe.

Advantageously, the supply pipe is equipped with a second heat exchanger disposed upstream of the expansion turbine, so as to exchange heat energy between the discharge pipe and the supply pipe.

According to a possibility of the invention, the supply pipe is equipped with a third heat exchanger disposed downstream of the expansion turbine, so as to exchange heat energy between the discharge pipe and the supply pipe. .

Preferably, the first bypass line connects the supply line, at a point between the expansion turbine and the third heat exchanger, to the discharge pipe at a point between the third heat exchanger and the second heat exchanger.

According to an alternative embodiment of the invention, the first bypass pipe connects the supply pipe, at a point between the expansion turbine and the third heat exchanger, to the discharge pipe at a point between the second heat exchanger and the pre-cooling stage and / or cooling, the first bypass line passing through the second heat exchanger, the bypass valve being disposed downstream of the second heat exchanger.

According to another variant embodiment of the invention, the first branch pipe connects the supply pipe, at a point situated downstream of the third heat exchanger, to the discharge pipe at a point situated between the second heat exchanger and the pre-cooling and / or cooling stage, the first bypass pipe successively passing through the third heat exchanger and the second heat exchanger and being equipped with a first bypass valve located upstream of the third heat exchanger and a second bypass valve located downstream of the second heat exchanger.

According to a possibility of the invention, the second bypass pipe is equipped with an expansion valve disposed between the third exchanger and the accumulator.

Preferably, the damping stage comprises a third bypass pipe designed to deflect a portion of the fluid from the expansion valve, the third pipe passing through the first heat exchanger and being connected to the discharge pipe.

According to one characteristic of the invention, the accumulator inside which the first heat exchanger is arranged so as to exchange heat energy between the fluid passing through the first exchanger and the fluid contained in the accumulator.

Advantageously, the interface comprises an enclosure equipped with fluid inlet and outlet means, the supply pipe being equipped with a controlled valve arranged upstream of the fluid inlet members, the valve being controlled, for example via a fluid level sensor inside the enclosure.

In any case, the invention will be better understood from the description which follows with reference to the attached schematic drawing showing, by way of example, three embodiments of this method and this refrigeration system of a fluid.

The first, second and third portions of fluid from the pre-cooling and / or cooling stage are obtained by selective branching of at least a portion of the fluid assembly from the pre-cooling stage. and / or cooling.

The second part of the fluid coming from the pre-cooling and / or cooling stage is obtained by a selective bypass of a part of fluid coming from the pre-cooling and / or cooling stage intended for selectively supplying the interface (first part of the fluid) and / or the accumulator (third part of the fluid) (that is to say that the second fluid part is removed from all the fluid coming from the stage compression).

The third part of the fluid coming from the pre-cooling and / or cooling stage is obtained by a selective bypass of a part of the fluid coming from the pre-cooling stage and / or cooling for selectively directly supplying the interface (1) (that is, the third portion of the fluid is withdrawn from the first fluid portion).

• Figure 1 est une vue schématique d'ensemble de l'installation ;
• Figure 2 est une vue schématique de l'étage d'amortissement de l'installation ;
• Figures 3 et 4 sont des vues correspondant à la figure 1, de deux variantes de réalisation.

The accumulator comprises for example a vacuum insulated cryogenic tank, for example housed in the pre-cooling and / or cooling stage.

• Figure 1 is a schematic overview of the installation;
• Figure 2 is a schematic view of the damping stage of the installation;
• Figures 3 and 4 are views corresponding to the figure 1 , two embodiments.

A helium refrigeration plant according to the invention is described in figure 1 .

As shown more particularly in figure 2 this installation comprises an interface 1 in the form of a cold box or an enclosure equipped with an inlet and a fluid outlet 2, 3 intended respectively to supply a consumer with fluid and to collect fluid from the consumer.

The cold box 1 makes it possible to exchange a heat load with a fluid intended for a consumer constituted, for example, by a cooling circuit for superconducting elements of a controlled fusion reactor.

The installation comprises a compression stage 4 of the fluid coming from the interface 1, a pre-cooling stage 5 and a cooling stage 6 of the fluid.

These stages are known from the prior art and will therefore be briefly described below.

The compression stage 4 compresses the helium from the lower stage, namely the pre-cooling stage 5 and bring the helium to a room temperature.

Helium at high pressure, that is to say at a pressure of between 15 and 20 bar is fed to the precooling stage 5 where it is cooled, in brazed aluminum plate exchangers 7, 8, by the cold helium from the lower stage, that is to say the cooling stage 6.

Pre-cooling is supplemented by heat exchange with liquid nitrogen.

The cooling of the helium continues in the cooling stage 6, via a plurality of exchangers of the aforementioned type and by cryogenic expansion turbines 9 arranged in parallel. For each expansion turbine 9, part of the high-pressure helium flow is withdrawn and relaxed at the average pressure of the cycle. According to a possibility of the invention, the number of expansion turbines 9 varies between 2 or 4 for a refrigerator of high power. The pre-cooling stage brings the helium to the lower stage, that is to say to a damping stage 10, at a temperature of about 20 Kelvin.

The damping stage 10 will now be described in more detail, with reference to Figures 2 to 4 .

This stage 10 includes a supply pipe 11 in which the cold fluid flows from the cooling stage 6 to the interface 1, and a discharge pipe 12 for bringing the hot fluid from the interface 1 to the cooling stage 6.

The helium flowing in the feed pipe 11 passes successively, in the direction of flow, a second heat exchanger 13, a control valve 14, an expansion turbine 15, a third heat exchanger 16, a first heat exchanger 17 and a valve 18 controlled, for example by means of a sensor 19 of the helium level within the chamber 1.

The helium flowing in the discharge pipe 12 passes successively in the direction of flow, the third heat exchanger 16 and the second heat exchanger 13, and is then returned to the cooling stage 6.

The damping stage 10 further comprises a first bypass pipe 21 for directing the fluid from the expansion turbine 15 to the discharge pipe 12, between the second and third heat exchangers 13, 16. The first pipe branch 21 is equipped with a bypass valve 22 controlled, for example by means of a pressure sensor 23. The pressure measurement is performed by this sensor 23 at a point in the supply line 11, downstream of the expansion turbine 15 and upstream of the third heat exchanger 16.

A second bypass pipe 24 makes it possible to deflect a part of the fluid coming from the third heat exchanger 16. The helium circulating in the second channel passes through an expansion valve 25, part of the helium stream coming from this valve 25 then being directed into an accumulator 26, another part passing through the first heat exchanger 17 and then being brought back into the discharge pipe 12, into a point located between the valve 20 and the third heat exchanger 16.

The fluid stored in the accumulator 26 is also directed towards the first heat exchanger 17 and then directed towards the discharge pipe 12, at a point situated between the valve 20 and the third heat exchanger 16.

The accumulator 26 is likely to contain helium both in liquid form but also in gaseous form. An exhaust pipe 27 makes it possible to evacuate the gases towards the discharge pipe 12, at a point thereof located upstream of the third heat exchanger 16.

The heat exchangers 13, 16, 17 make it possible to cool or heat the fluids passing through them, the hot fluids and the cold fluids being arranged to flow countercurrently relative to each other in each of the exchangers. Thus, the helium flowing in the supply line 11 is cooled successively as it passes through the second, third and first exchangers 13, 16, 17. Similarly, the temperature of the helium flowing in the discharge pipe 12 increases as it passes through the second and third heat exchangers 13, 16, and that of the helium from the second bypass pipe 24 or the other. accumulator 26 increases as it passes through the first exchanger 17.

The operation of the damping stage 10 is as follows.

When the heat load absorbed by the consumer is low, the controlled bypass valve 22 is mainly open so that a large part of the fluid coming from the expansion turbine 15 is sent back to the cooling stage 6.

A small portion of the cold helium flow is supplied to the interface 1 by the supply line 11. A certain amount of helium from the part of the aforementioned flow is stored in the accumulator 26, the rest being directed to the discharge pipe 12.

When the heat load absorbed by the consumer is large, the bypass valve 22 is mainly closed so that the majority of the fluid is directed towards the interface 1. This has the effect to increase the heat load available to the consumer at the interface 1. In addition, the cold fluid stored by the accumulator 26 is delivered and passes through the first heat exchanger 17, so as to cool the fluid of the pipe d supply 11 directed to the interface 1, thereby increasing the heat load supplied to the consumer.

An alternative embodiment of the invention is shown in figure 3 only the positions of the first branch line 21 and the bypass valve 22 having been modified. In this variant, the first bypass pipe 21 connects the supply pipe 11, at a point located between the expansion turbine 15 and the third heat exchanger 16, to the discharge pipe 12 at a point situated between the second heat exchanger 13 and the cooling stage 6, the first bypass pipe 21 passing through the second heat exchanger 13, the bypass valve 22 being disposed downstream of the second heat exchanger 13.

This embodiment avoids a reduction in the efficiency of the second heat exchanger 13. In fact, the efficiency of a heat exchanger may be reduced during the passage of a fluid having a liquid phase and a phase gas. However, the bypass valve 22 generating an expansion and, therefore, a cooling of the fluid passing through it, the fluid disposed behind the bypass valve 22 may be in two-phase form, depending on the operating conditions. The valve 22 thus disposed downstream of the heat exchanger 13 makes it possible not to modify the state of the fluid before passing through this exchanger.

Another variant embodiment is represented in figure 4 . In this case, the first bypass pipe 21 connects the supply pipe 11, at a point situated downstream of the third heat exchanger 16, to the discharge pipe 12, at a point situated between the second heat exchanger 13 and the cooling stage 6, the first bypass pipe 21 passing successively through the third heat exchanger 16 and the second heat exchanger 13 and being equipped with a first bypass valve 28 located upstream of the third heat exchanger 16 and a second bypass valve 29 located downstream of the second heat exchanger 13.

The second and third exchangers 13, 16 are generally grouped together in one and the same heat exchange block. Such a provision bypass valves allows to connect these valves 28, 29 outside the heat exchange block, which is more convenient installation, while ensuring that the fluid passing through each of the exchangers 13, 16 is not two-phase.

It goes without saying that the invention is not limited to the forms of this fluid refrigeration process or this installation, described above as examples, but it encompasses all variants. Thus, in particular, the bypass valve could be controlled by a temperature sensor or by any means making it possible to measure a parameter representative of the consumer's needs.

Claims (14)

1. Method for the cryogenic cooling of a fluid, for example helium, intended for supplying a fluid consumer, the fluid flowing in a cyclic manner successively through a compression stage (4), a fluid pre-cooling and/or cooling stage (5, 6), and an interface (1) making it possible to supply the fluid to the consumer and collecting the fluid from the consumer, a first portion of the fluid from the pre-cooling and/or cooling stage being directed towards the interface (1), characterised in that a second portion of the fluid from the pre-cooling and/or cooling stage is directed selectively to the pre-cooling and/or cooling stage (5, 6) upstream of the interface (1) based on whether the thermal load required by the consumer is low or high, a third portion of the fluid from the pre-cooling and/or cooling stage upstream of the interface (1) being selectively cooled and directed towards an accumulator (26) designed to selectively store this fluid or to deliver, based on whether the thermal load required by the consumer is low or high, a quantity of fluid already stored in order to cool the first portion of fluid directed towards the interface (1), the first portion of the fluid directly supplying the interface without transiting through the accumulator (26), the second portion of the fluid from the pre-cooling and/or cooling stage being obtained via a selective diverting of a portion of the fluid from the pre-cooling and/or cooling stage intended to selectively supply the interface and/or the accumulator, i.e. the second portion of the fluid is separated from all of the fluid from the compression stage, the third portion of the fluid from the pre-cooling and/or cooling stage being obtained by a selective diverting of a portion of the fluid from the pre-cooling and/or cooling stage intended to selectively directly supply the interface (1), i.e. the third portion of the fluid is separated from the first portion of the fluid.
2. Method according to claim 1, characterised in that the quantity of fluid directed towards the pre-cooling and/or cooling stage (5, 6) is adjusted by at least one diverter valve (22) controlled, for example by way of a pressure sensor (23).
3. Method according to one of claims 1 or 2, characterised in that the fluid from the pre-cooling and/or cooling stage (5, 6) flows through an expansion turbine (15).
4. Method according to one of claims 1 to 3, characterised in that the first portion of the fluid from the pre-cooling and/or cooling stage (5, 6) exchanges heat energy with the fluid delivered by the accumulator (26).
5. Method according to one of claims 1 to 4, characterised in that the second and/or the third portion of the fluid from the pre-cooling and/or cooling stage (5, 6) exchanges heat energy with the fluid from the interface (1).
6. Method according to one of claims 4 or 5, characterised in that the accumulator (26) is selectively supplied with fluid expanded by an expansion valve (25) taking a fraction of the first portion of the fluid, said valve (25) being located downstream of the selective return line of the second portion of the fluid.
7. Method according to claim 1 to 6, characterised in that the fluid delivered by the accumulator (26) can be selectively directed to the pre-cooling and/or cooling stage (5, 6).
8. Method according to any one of claims 1 to 7, characterised in that the thermal load required by the consumer decreases or is relatively low, the first portion of the fluid directed towards the interface is decreased to the benefit on the one hand of the second portion of the fluid directed towards the pre-cooling and/or cooling stage and, on the other hand, of the third portion of the fluid directed towards the accumulator, when the thermal load required by the consumer increases or is relatively high, the second and third portions of the fluid directed respectively towards the pre-cooling and/or cooling stage and towards the accumulator, are decreased to the benefit of the first portion of the fluid directed towards the interface, and in that the first portion of the fluid is selectively increased by fluid delivered via the accumulator (26).
9. Method according to any one of claims 1 to 8, characterised in that the flow rate of the fluid flowing in a cyclic manner is maintained substantially constant in the circuit and in particular in the compression stage.
10. Installation for the cryogenic cooling of a fluid, for example helium, for implementing the method according to one of claims 1 to 9, comprising an interface (1) provided with fluid inlet and outlet members (2, 3) intended respectively to supply a consumer with fluid and to collect fluid from the consumer, a compression stage (4) of the fluid from the interface (1), at least one fluid pre-cooling and/or cooling stage (5, 6) from the interface (1) and/or of the fluid from the compression stage (4), the equipment comprising a damping stage (10) comprising a supply line (11) that connects the pre-cooling and/or cooling stage (5, 6) to the fluid inlet members (2) of the interface (1), a discharge line (12) that connects the fluid outlet members (3) of the interface (1) to the pre-cooling and/or cooling stage (5, 6), and a first diverter line (21) that connects the supply line (11) to the discharge line (12) by way of at least one diverter valve (22), the damping stage (10) comprising a supply line (11) that connects the pre-cooling and/or cooling stage (5, 6) to the fluid inlet members (2) of the interface (1), a discharge line (12) that connects the fluid outlet members (3) of the interface (1) to the pre-cooling and/or cooling stage (5, 6), and a first diverter line (21) that connects upstream of the interface (1) the supply line (11) to the discharge line (12) by way of at least one diverter valve (22), the damping stage (10) further comprises a second diverter line (24), that connects upstream of the interface (1) the supply line (11) to the discharge line (12), and provided with an accumulator (26), a first heat exchanger (17) being arranged so as to exchange heat energy between the fluid from the accumulator (26) and the fluid flowing in the supply line (11).
11. Installation according to claim 10, characterised in that the first diverter line (21) connects the supply line (11), at a point located between an expansion turbine (15) and a third heat exchanger (16), to the discharge line (12), at a point located between a second heat exchanger (13) and the pre-cooling and/or cooling stage (5, 6), the first diverter line (21) passing through a second heat exchanger (13), a diverter valve (22) being arranged downstream of the second heat exchanger (13).
12. Installation according to claim 11, characterised in that the second diverter line (24) is provided with an expansion valve (25) arranged between the third heat exchanger (16) and the accumulator (26).
13. Installation according to claim 12, characterised in that the damping stage (10) comprises a third diverter line designed to divert a portion of the fluid from the expansion valve (25), the third line passing through the first heat exchanger (17) and being connected to the discharge line (12).
14. Installation according to one of claims 10 to 13, characterised in that the interface comprises a chamber (1) provided with fluid inlet and outlet members (2, 3), the supply line (11) being provided with a controlled valve (18) arranged upstream of the fluid inlet members (2), the valve (18) being controlled, for example by way of a fluid level sensor (19) inside the chamber (1).

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