JP2019117869A - Cooling device for superconducting cable and cooling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily set optimum operating conditions of individual refrigerators when cooling a liquefied refrigerant stored in a heat storage tank with a plurality of refrigerators. A cooling device for a superconducting cable according to one embodiment is a refrigeration unit that uses a heat storage tank for storing a liquefied first refrigerant and a second refrigerant having a lower liquefaction temperature than the first refrigerant. A plurality of refrigerating units including a first heat exchanger provided inside the heat storage tank and capable of cooling the first refrigerant with the second refrigerant, and a second heat exchanger provided inside the heat storage tank. A third refrigerant circulation line connected to the second heat exchanger and the superconducting cable for circulating a third refrigerant, and provided at each outlet of the second heat exchanger and the first heat exchanger. A temperature sensor for detecting the temperature of the second refrigerant, and the detection values of the temperature sensors are input, and each of the plurality of refrigeration units is controlled so that the detection value of the temperature sensor becomes a target value. And a control unit for controlling. [Selection diagram] Figure 1

Description

  The present disclosure relates to a cooling device and a cooling method of a superconducting cable.

In order to cool a superconducting power device such as a superconducting cable to a cryogenic temperature equal to or lower than the superconducting critical temperature, a liquefied refrigerant having a cryogenic temperature such as liquid nitrogen is used as a refrigerant. The liquefied refrigerant is generated by a refrigerator and supplied to a superconducting power device such as a superconducting cable.
Among the cooling devices for supplying liquefied refrigerant to the superconducting cable, in the cooling device provided with the heat storage tank, the liquefied refrigerant stored in the heat storage tank is cooled by the refrigerator and supplied to the superconducting cable, or the liquefied refrigerant cooled by the refrigerator May be temporarily stored in a heat storage tank and then supplied to a superconducting cable.

  In Patent Document 1, one heat exchange unit (heat storage tank) having a cooling space for storing the liquefied refrigerant, one refrigerator for cooling the liquefied refrigerant, and the cooling space are provided. A cooling system is disclosed that includes a plurality of heat exchangers and supplies liquefied refrigerant to a plurality of superconducting cables connected to each of the plurality of heat exchangers via a refrigerant supply line. In this cooling system, the temperature of the liquefied refrigerant stored in the cooling space is detected, and the temperature of the liquefied refrigerant supplied to the superconducting cable is an appropriate temperature by controlling the refrigerator so that the temperature becomes a target value. It is supposed to be

Patent No. 5665963 gazette

In order to increase the cooling capacity, a cooling device is required to cool the liquefied refrigerant stored in the heat storage tank with a plurality of refrigerators. In this case, as in Patent Document 1, it is necessary to control the cooling amounts of the plurality of refrigerators so that the temperature of the liquefied refrigerant stored in the heat storage tank becomes a target value.
However, the temperature of the liquefied refrigerant in the heat storage tank indicates the result of the sum of the cooling amounts of the plurality of refrigerators, and whether the cooling amount of each refrigerator is increased or decreased uniformly is the temperature of the liquefied refrigerant in the heat storage tank I can not know from you. Since it is difficult to make the response of the change in the amount of cooling of each refrigerator exactly the same, a large difference may occur in the amount of cooling of each refrigerator during long-term operation. When there is a difference in the amount of cooling between the refrigerators, an unpredictable temperature distribution occurs in the liquefied refrigerant in the heat storage tank, and the temperature measurement of the liquefied refrigerant becomes inaccurate. Then, in order to equalize the amount of cooling of each refrigerator, a means to detect the amount of cooling difference of each refrigerator is needed, and while operation becomes complicated, there is a problem that equipment cost becomes high cost.

  In an embodiment, in view of the above-mentioned subject, when cooling a liquefied refrigerant stored in a heat storage tank with a plurality of refrigerators, individual refrigeration can be operated by equally operating cooling amount of each refrigerator The purpose is to make it possible to easily set the optimum operating conditions of the unit.

(1) A cooling device for a superconducting cable according to an embodiment,
A heat storage tank for storing the first refrigerant in a liquefied state;
A refrigeration unit using a second refrigerant having a liquefying temperature lower than that of the first refrigerant, comprising a plurality of first heat exchangers provided inside the heat storage tank and capable of cooling the first refrigerant with the second refrigerant. A refrigeration unit,
A second heat exchanger provided inside the heat storage tank;
A third refrigerant circulation line connected to the second heat exchanger and the superconducting cable for circulating a third refrigerant;
A temperature sensor provided at the outlet of each of the first heat exchangers for detecting the temperature of the second refrigerant;
A control unit for controlling each of the plurality of refrigeration units so that the detection value of each of the temperature sensors is input, and the detection value of the temperature sensor becomes a target value;
Equipped with

The temperature of the second refrigerant at the outlet of the first heat exchanger after cooling the first refrigerant is determined by the temperature of the first refrigerant and the amount of cooling of the first refrigerant. For example, when the amount of cooling is large, the temperature of the second refrigerant at the inlet and outlet of the first heat exchanger also decreases. On the other hand, when the amount of cooling is small, the temperatures of the inlet and the outlet also become high. At this time, since the temperature of the first refrigerant is the same for each refrigerator, each refrigerator is controlled to have the same amount of cooling. There is also a correlation between the temperature of the second refrigerant and the temperature of the first refrigerant at the outlet of the first heat exchanger.
Therefore, the first refrigerant stored in the heat storage tank can be made to have a desired temperature by controlling each refrigeration unit so that the temperature of the second refrigerant at the outlet of the first heat exchanger becomes a target value. . By thus controlling the temperature of the first refrigerant in the heat storage tank, the temperature of the third refrigerant supplied to the superconducting cable can also be controlled to a desired temperature.
Thus, the temperature of the third refrigerant can be controlled to a desired temperature while equalizing the amount of cooling of each refrigerator.

(2) In one embodiment, in the configuration of (1),
It has a pressure adjusting unit capable of adjusting the pressure of the gas phase part in the heat storage tank.
According to the structure of said (2), the melting point of the 1st refrigerant | coolant stored in the thermal storage tank can be adjusted by adjusting the pressure of the gaseous-phase part in a thermal storage tank by the said pressure adjustment part. By adjusting the melting point of the first refrigerant, as described later, it becomes possible to generate the solid phase portion of the first refrigerant. By generating the solid phase portion, heat can be stored using heat of fusion larger than sensible heat, so the amount of heat storage can be increased.

(3) In one embodiment, in the configuration of (2),
The pressure adjustment unit is
A pressure vessel provided at a lower position than the heat storage tank, in which the first refrigerant in a liquefied state is stored, and a gas phase part is formed above the liquid surface of the first refrigerant;
A decompression line in communication with the gas phase portion and the heat storage tank;
A pressure control valve provided in the pressure reducing line and capable of adjusting the opening degree;
A refrigerant inflow line communicating with a liquid phase portion of the pressure tank and the heat storage tank;
Equipped with
According to the structure of said (3), the inside of a thermal storage tank can be pressurized by transmitting the pressure of the pressurization tank pressurized by natural heat input into the thermal storage tank through a refrigerant | coolant inflow line. This facilitates the generation of the solid phase portion of the first refrigerant in the heat storage tank. In addition, by adjusting the opening degree of the pressure control valve, the first refrigerant in the gas phase part in the pressure tank can be discharged into the heat storage tank through the pressure reduction line, and the pressure tank can be depressurized. The pressure in the heat storage tank can be adjusted to a desired pressure.

(4) In one embodiment, in the configuration of (3),
A pressure sensor is provided to detect the pressure of the gas phase part.
According to the configuration of the above (4), the pressure in the gas phase portion of the pressure tank is detected by the pressure sensor, and the opening degree of the pressure adjusting valve is controlled based on the detected value. The pressure can be controlled to the desired pressure.

(5) In one embodiment, in any one of the configurations (1) to (4),
The first heat exchanger is configured to flow the second refrigerant from the top to the bottom,
The second heat exchanger is configured to flow the third refrigerant from the bottom to the top.
According to the configuration of (5), since the refrigerant whose temperature is higher in the lower region than in the upper region flows in both the first heat exchanger and the second heat exchanger, the first refrigerant around the heat transfer tube is lower than the upper region The temperature is higher in the region. Therefore, since the first refrigerant in the upper region is heavier, convection of the first refrigerant in the heat storage tank is promoted, and the temperature difference of the first refrigerant in the heat storage tank can be reduced.

(6) In one embodiment, in any one of the configurations (1) to (5),
At least a portion of the second heat exchanger is disposed below the first heat exchanger.
According to the configuration of (6), since the temperature of the third refrigerant returning from the superconducting cable is higher than that of the second refrigerant, the ambient temperature of the second heat exchanger through which the third refrigerant flows is the first refrigerant through which the second refrigerant flows It is higher than the ambient temperature of the heat exchanger. Since the second heat exchanger is disposed at the lower side, the temperature distribution of the first refrigerant in the heat storage tank is such that the lower side is warm and the upper side is cold. Therefore, convection is promoted in the vertical direction, and the temperature difference in the heat storage tank is reduced.

(7) In one embodiment, in any one of the configurations (1) to (6),
And a plurality of superconducting cable cooling units that include the third refrigerant circulation line and the second heat exchanger, and supply the third refrigerant in a liquefied state to each of the plurality of superconducting cables;
Third heat for exchanging heat among the third refrigerants flowing through a return line for returning the third refrigerant to the second heat exchanger among the third refrigerant circulation lines of the plurality of superconducting cable cooling units It has a switchboard.

  When there is a difference in cable length or heat load between the plurality of superconducting cables, the temperature of the return refrigerant after cooling the plurality of superconducting cables may be different. However, even in this case, since the third refrigerant flowing through the return line is subjected to heat exchange by the third heat exchanger, the temperature difference between the third refrigerants returning to the plurality of second heat exchangers can be reduced. Therefore, since the difference in the amount of heat exchange in the second heat exchanger can also be reduced, the temperature difference of the third refrigerant supplied to the superconducting cable can be reduced.

(8) A method of cooling a superconducting cable according to an embodiment,
A heat storage tank for storing the first refrigerant in a liquefied state;
A refrigeration unit using a second refrigerant having a liquefying temperature lower than that of the first refrigerant, comprising a plurality of first heat exchangers provided inside the heat storage tank and capable of cooling the first refrigerant with the second refrigerant. A refrigeration unit,
A second heat exchanger provided inside the heat storage tank;
A third refrigerant circulation line connected to the second heat exchanger and the superconducting cable for circulating the third refrigerant;
A cooling device for a superconducting cable comprising
The temperature control step of controlling the plurality of refrigeration units so that the temperature of the first refrigerant flowing through the outlet of each of the first heat exchangers becomes a target value.

  According to the method of (8), in the temperature control step, the heat storage tank is controlled by controlling the plurality of refrigeration units such that the temperature of the second refrigerant at the outlet of the first heat exchanger becomes a target value. The stored first refrigerant can be brought to a desired temperature. By thus controlling the temperature of the first refrigerant in the heat storage tank, the temperature of the third refrigerant supplied to the superconducting cable can also be controlled to a desired temperature.

(9) In one embodiment, in the method of (8),
In the temperature control step, the plurality of refrigeration units are controlled such that the temperature of the first refrigerant flowing through the outlet of each of the first heat exchangers becomes the same.
As described above, the amount of cooling of each refrigeration unit has a unique correlation with the temperature of the second refrigerant at the outlet of the first heat exchanger. Therefore, by controlling the plurality of refrigeration units so that the temperature of the first refrigerant at the outlet of each first heat exchanger is the same, it is possible to evenly distribute the cooling amount to each refrigeration unit. Thus, the operation control of each refrigeration unit can be optimized.

(10) In one embodiment, in the method of (8) or (9),
In the temperature control step,
When the temperature of the first refrigerant flowing through the outlet of each of the first heat exchangers is higher than the target value, the amount of cooling of the refrigeration unit is increased;
The cooling amount of the refrigeration unit is reduced when the temperature of the first refrigerant flowing through the outlet of each of the first heat exchangers is lower than the target value.
According to the above method (10), the temperature of the first refrigerant at the outlet of the first heat exchanger can be set to a desired temperature, whereby the temperature of the first refrigerant supplied to the superconducting cable is also desired Can be controlled to

(11) In one embodiment, in the method according to any one of (8) to (10),
And a solid phase generation step of controlling the refrigeration unit such that at least a part of the first refrigerant stored in the heat storage tank generates a solid phase.
According to the method of (11), at least a part of the first refrigerant stored in the heat storage tank in the solid phase generation step generates the solid phase, so heat can be stored using heat of fusion larger than sensible heat , Heat storage can be increased.

(12) In one embodiment, in the method of (11),
In the solid phase generation step,
The pressure of the first refrigerant in the heat storage tank is made higher than the pressure of the third refrigerant in the second heat exchanger.
According to the method of (12), by generating the solid phase portion in at least a part of the first refrigerant stored in the heat storage tank, heat can be stored using heat of fusion larger than sensible heat, and the amount of heat storage can be increased . Further, since the pressure of the third refrigerant is lower than the pressure of the first refrigerant, the temperature of the first refrigerant is higher than the melting point of the third refrigerant. For this reason, the third refrigerant flowing through the third refrigerant circulation line does not freeze, and the supply of the third refrigerant to the superconducting cable can be maintained.

  According to one embodiment, when the liquefied refrigerant stored in the heat storage tank is cooled by the plurality of refrigeration units and cooled to a desired temperature, the optimal operating conditions of the individual refrigeration units can be easily set.

It is a block diagram showing a cooling device concerning one embodiment. It is a block diagram showing a cooling device concerning one embodiment. It is a block diagram showing a cooling device concerning one embodiment. It is a block diagram showing a cooling device concerning one embodiment. It is a block diagram showing a control system of a cooling device concerning one embodiment. It is a diagram which shows the relationship of the temperature and pressure which determine the phase change of a refrigerant | coolant. It is process drawing which shows the cooling method which concerns on one Embodiment.

Hereinafter, some embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements and the like of the components described as the embodiments or shown in the drawings are not intended to limit the scope of the present invention to these, but are merely illustrative examples.
For example, a representation representing a relative or absolute arrangement such as “in a direction”, “along a direction”, “parallel”, “orthogonal”, “center”, “concentric” or “coaxial” is strictly Not only does it represent such an arrangement, but also represents a state of relative displacement with an angle or distance that allows the same function to be obtained.
For example, expressions that indicate that things such as "identical", "equal" and "homogeneous" are equal states not only represent strictly equal states, but also have tolerances or differences with which the same function can be obtained. It also represents the existing state.
For example, expressions representing shapes such as quadrilateral shapes and cylindrical shapes not only represent shapes such as rectangular shapes and cylindrical shapes in a geometrically strict sense, but also uneven portions and chamfers within the range where the same effect can be obtained. The shape including a part etc. shall also be expressed.
On the other hand, the expressions "comprising", "having", "having", "including" or "having" one component are not exclusive expressions excluding the presence of other components.

  1 to 4 show a superconducting cable cooling apparatus 10 (10A, 10B, 10C, 10D) according to some embodiments. In these drawings, the hollowed out valve indicates the open state, and the black-painted valve indicates the closed state.

In Figures 1-4, the cooling apparatus 10 (10A to 10D) includes a storage tank 12 for storing the first refrigerant LR ₁ liquefied state, the second refrigerant liquefaction temperature than the first refrigerant LR ₁ is low _{R 2} And a plurality of refrigeration units 14a and 14b using The plurality of refrigeration units 14a and 14b include first heat exchangers 16a and 16b provided inside the heat storage tank 12 and capable of cooling the first refrigerant with the second refrigerant.
Superconducting cable 18 (18a, 18b) to the third refrigerant _{R 3} refrigerant supply supplying portion 20 (20a, 20b) of the liquefied state of the superconducting critical temperature below the temperature, the second heat provided within the heat storage tank 12 the exchanger 22 (22a, 22b), connected to the second heat exchanger 22 and the superconducting cable 18, first to circulate between the third refrigerant _{R 3} second heat exchanger 22 and superconducting cable 18 And 3 refrigerant circulation lines 23 (23a, 23b).

  At the outlet of each of the first heat exchangers 16a, 16b, temperature sensors 26a, 26b for detecting the temperature of the second refrigerant are provided. As shown in FIG. 5, the detection values of the temperature sensors 26a and 26b are input to the control unit 40, and the control unit 40 sets the plurality of refrigeration units 14a and 14b such that the detection values of the temperature sensors 26a and 26b become target values. Control.

Second refrigerant R ₂ are used those having a lower liquidus temperature than the first refrigerant LR ₁ which is stored in the thermal storage tank 12. When liquefied nitrogen is used as the first refrigerant, for example, He gas, Ne gas, or a mixed gas thereof is used as the second refrigerant.
In one embodiment, nitrogen is used as the first refrigerant R ₁ and the third refrigerant R _3.

The first heat exchanger 16a, in 16b, and first refrigerant R ₁ which is stored in the thermal storage tank 12 is cooled by the second refrigerant R ₂ is cooled to the superconducting critical temperature or lower. First refrigerant stored in the thermal storage tank 12, the third refrigerant of the third refrigerant R ₃ circulating the third refrigerant circulation line 23 in the second heat exchanger 22 is cooled to the superconducting critical temperature below the temperature was cooled Is supplied to the superconducting cable 18.
For example, using nitrogen as the first refrigerant and the third refrigerant, when using a Ne gas as the second coolant, the temperature of the third refrigerant R ₃ to be supplied to the superconducting cable 18 is controlled so as to 69～70K, heat storage The first refrigerant LR ₁ in the liquefied state stored in the tank 12 is controlled to be 68 to 69 K, and the temperature of the second refrigerant at the outlet of the first heat exchangers 16 a and 16 b is 67 to 68 K It is controlled.

The second temperature of the refrigerant R ₂ at the outlet of the first heat exchanger 16a, 16b after cooling the first refrigerant is determined by the temperature and the cooling amount of the first refrigerant in the first heat exchanger of the first refrigerant Be For example, when the amount of cooling of the first refrigerant is large, the temperature difference between the second refrigerant and the first refrigerant at the outlet of the first heat exchanger becomes large. On the other hand, when the amount of cooling of the first refrigerant is small, the temperature difference between the second refrigerant and the first refrigerant at the outlet of the first heat exchanger decreases. At this time, since the temperature of the first refrigerant is the same for each refrigerator, each refrigerator is controlled to have the same amount of cooling. There is also a correlation between the temperature of the second refrigerant and the temperature of the first refrigerant at the outlet of the first heat exchangers 16a and 16b.

  Therefore, the first stored in the heat storage tank 12 is controlled by controlling each of the plurality of refrigeration units 14a and 14b such that the temperature of the second refrigerant at the outlet of the first heat exchangers 16a and 16b becomes the target value. The refrigerant can be brought to a desired temperature. By controlling the temperature of the first refrigerant in the heat storage tank 12 in this manner, the temperature of the third refrigerant supplied to the superconducting cable 18 can also be controlled to a desired temperature.

For example, as described above, the amount of cooling of each refrigerator, the temperature of the first refrigerant, and the temperature of the second refrigerant at the outlet of the first heat exchanger are mutually correlated. The temperature of the first refrigerant can be regarded as uniform in each first heat exchanger, and the target value of the temperature of the second refrigerant at the outlet of the first heat exchanger is made identical in each first heat exchanger. For example, the amount of cooling of each refrigerator can be equally distributed.
Thus, the temperature of the third refrigerant can be controlled to a desired temperature while equalizing the amount of cooling of each refrigerator.

In one embodiment, the heat storage tank 12 has a heat insulating structure using a vacuum double structure or a heat insulating material in order to make it difficult to vaporize the first refrigerant LR ₁ in a liquefied state stored by preventing the intrusion of the outside air temperature. Do.
In one embodiment, as the third refrigerant, a material that can be liquefied in a critical temperature region capable of maintaining the superconducting state of the superconducting cable 18 is preferable, and a material having high insulating properties is preferable. From such conditions of use, liquefied nitrogen can be used. Also, in view of safety and cost, nitrogen can be used.
Since it is desirable that the first refrigerant has large specific heat and can transfer heat, a substance that can be liquefied in the temperature range of the third refrigerant is preferable, and liquefied nitrogen can be used.

  In one embodiment, the refrigeration units 14a and 14b include the second refrigerant gas circulation lines 24a and 24b, the compressors 28a and 28b provided in the second refrigerant gas circulation lines 24a and 24b, the water coolers 30a and 30b, and the cold heat recovery heat Exchanger 32a, 32b and expansion turbine 34a, 34b are provided, and a reverse Brayton cycle is comprised as a thermal cycle. The rotating shafts of the compressors 28a and 28b and the expansion turbines 34a and 24b are integrally formed with the rotating shafts of the motors 36a and 36b, and the compressors 28a and 28b and the expansion turbines 34a and 34b are driven by the motors 36a and 36b.

The refrigerant gas adiabatically compressed by the compressors 28a and 28b is cooled by the cooling water w in the water cooling units 30a and 30b, and then the refrigerant returned from the first heat exchangers 16a and 16b in the cold heat recovery heat exchangers 32a and 32b. It is further cooled by exchanging heat with the gas. Thereafter, the refrigerant gas expansion turbine 34a, after being further cooled by being depressurized by 34b, the first heat exchanger 16a, to cool the first refrigerant LR ₁ with 16b.

In one embodiment, the constituent units of the refrigeration units 14a and 14b excluding the compressors 28a and 28b, the motors 36a and 36b, and the water cooling units 30a and 30b are vacuum containers (cold boxes) 38a, in order to suppress heat intrusion from the outside. It is housed in 38b.
The refrigeration units 14a and 14b illustrated in FIG. 1 are single-stage compression using one compressor, but may be a multi-stage compression system in which a plurality of compressors are arranged in series.

In one embodiment, the refrigerant supply unit 20 (20a, 20b) is a heat storage tank 42 (42a, 42a, 42b) for temporarily storing the third refrigerant after cooling the superconducting cable 18 in the third refrigerant circulation line 23 (23a, 23b). And a liquid pump 44 (44a, 44b) for circulating the third refrigerant stored in the heat storage tank 42 to the third refrigerant circulation line 23. The third refrigerant circulation line 23 (23a, 23b), the temperature sensor 46 (46a, 46b) for detecting the third temperature of the refrigerant _{R 3} circulating the third refrigerant circulation line 23 and the flow rate of the third refrigerant Flow rate sensors 48 (48a, 48b) for detecting are provided.

  In one embodiment, in order to control the amount of cooling of the first refrigerant in the first heat exchangers 16a, 16b, as shown in FIG. 5, the control unit 40 controls the number of rotations of the motors 36a, 36b. The amount of cooling of the first refrigerant can be increased by increasing the number of revolutions of the motors 36a and 36b. In addition, the amount of cooling of the first refrigerant can be reduced by reducing the number of revolutions of the motors 36a and 36b.

Further, as another means of controlling the cooling amount of the first refrigerant, and controls the second circulation amount of the refrigerant R ₂ circulating second coolant gas circulation line 24a, the 24b. The amount of cooling of the first refrigerant can be increased by increasing the amount of circulation of the second refrigerant. Moreover, the amount of cooling of the first refrigerant can be reduced by reducing the amount of circulation of the second refrigerant.

  In order to realize this control, for example, as shown in FIGS. 1 to 4, the second refrigerant gas circulation lines 24a and 24b on the downstream side of the water cooling unit 30 using the cooling water w as a cooling medium, and the compressor 28a, Branch lines 50a and 50b connecting the second refrigerant gas circulation lines 24a and 24b upstream of 28b are provided, and buffer tanks 52a and 52b are provided in the branch lines 50a and 50b. On-off valves 54a, 54b and 56a, 56b are provided on the upstream and downstream branch lines 50a, 50b of the buffer tanks 52a, 52b. As shown in FIG. 5, the control unit 40 opens and closes the on-off valves 54a, 54b and 56a, 56b to increase or decrease the storage amount of the second refrigerant stored in the buffer tanks 52a, 52b, thereby the second refrigerant The circulation amount of the second refrigerant circulating in the gas circulation lines 24a and 24b can be controlled.

  Since the second refrigerant gas circulation lines 24a and 24b on the downstream side of the compressors 28a and 28b have high pressure, by opening the on-off valves 54a and 54b, one of the second refrigerant flowing in the second refrigerant gas circulation lines 24a and 24b Can be accommodated in the buffer tanks 52a and 52b. Further, since the second refrigerant gas circulation lines 24a and 24b on the upstream side of the compressors 28a and 28b have a low pressure, opening the on-off valves 56a and 56b allows a part of the second refrigerant in the buffer tanks 52a and 52b to It can be returned to the second refrigerant gas circulation line 24a, 24b.

  In one embodiment, when the pressure in the gas phase portion of the heat storage tank 12 exceeds the allowable value, a relief valve 58 capable of releasing the gas in the gas phase portion to the outside is provided.

  In one embodiment, the cooling device 10 (10B) shown in FIG. As shown in FIG. 6, the pressure adjustment unit 60 adjusts the pressure of the gas phase portion in the heat storage tank 12 to a pressure higher than the boundary A between the gas phase and the solid phase, whereby the liquefied state stored in the heat storage tank 12 is stored. In the first refrigerant, the solid phase can be generated. As a result, since the first refrigerant can be stored in the heat storage tank 12 using heat of fusion larger than the sensible heat in the liquefied state, the heat storage amount of the heat storage tank 12 can be increased.

  FIG. 6 shows the relationship between temperature and pressure that determines the phase change of nitrogen as an example of the refrigerant. In the figure, line A shows the boundary between the liquid phase and the solid phase. For example, at a point X above the line A, a solid phase is obtained, and at a point Y below the line A, a liquid phase is obtained. Here, assuming that the pressure of the third refrigerant in the second heat exchanger 22 (22a, 22b) is point Y and the pressure of the first refrigerant in the heat storage tank 12 is point X, the first refrigerant is in the solid phase portion. Even when the temperature is reached, the third refrigerant can be in a state where no solid phase part is created.

  When nitrogen is used as the first refrigerant, the amount of cooling of each of the refrigeration units 14a and 14b is controlled so that the detection value of the temperature sensors 26a and 26b becomes equal to or lower than the melting point (about 63 K) of nitrogen. By this, at least a part of the liquefied nitrogen in the heat storage tank 12 can be made into a solid phase. At this time, when a portion of the liquefied nitrogen circulating in the third refrigerant circulation line 23 is frozen, the circulation amount of the liquefied nitrogen decreases, and the cooling amount of the superconducting cable 18 decreases. At this time, the temperature of the first refrigerant is maintained at the melting point as long as the first refrigerant is controlled to be constant at the pressure of point X in FIG. 6 and the first refrigerant is in the gas-liquid two-phase state. For this reason, when the third refrigerant is controlled to be constant at the pressure at point Y, the third refrigerant does not freeze. However, when the entire first refrigerant freezes, the temperature of the first refrigerant can fall below the melting point, so it is important to control so that the amount of the solid phase of the first refrigerant does not become excessive.

  In one embodiment, a solid phase portion of the first refrigerant is generated to adhere to the surfaces of the first heat exchangers 16a, 16b. When the first refrigerant is nitrogen, the thermal conductivity of solid nitrogen is significantly smaller than the metal material constituting the piping of the first heat exchangers 16a, 16b, so solid nitrogen adhering to the surface of the first heat exchangers 16a, 16b As the thickness of the layer increases, the amount of heat transfer between the solid nitrogen and the second refrigerant decreases, and the temperature of the second refrigerant at the first heat exchanger outlet decreases. When the temperature of the second refrigerant decreases, the control unit 40 controls the amount of cooling of the refrigeration units 14a and 14b to decrease. This can prevent the generation of excess solid nitrogen.

On the other hand, as a comparative example, when the first temperature of the refrigerant LR ₁ liquefied state stored in the thermal storage tank 12 and the control target, the first refrigerant LR ₁ because of the gas-liquid two-phase state, there is no change in melting point. Therefore, even if the amount of production of solid nitrogen increases or decreases, the temperature of the first refrigerant does not change, so the amount of production of solid nitrogen can not be properly controlled.

In one embodiment, as shown in FIG. 2, the pressure adjustment unit 60 is stored the first refrigerant LR ₁ inside the liquefied state, the gas phase portion g is formed on the first liquid level above the coolant LR ₁ A pressure tank 62 is provided. The pressure tank 62 includes a gas phase portion g formed in the upper part in the tank and a pressure reducing line 64 in communication with the inside of the heat storage tank 12, and a pressure adjusting valve 66 capable of adjusting the opening degree is provided in the pressure reducing line 64.
Pressurizing圧槽62 has a vacuum insulation structure, the amount of heat input into the first refrigerant LR ₁ which is liquid storage therein is configured to be less. However, since the temperature of the first refrigerant LR ₁ by a slight heat input (natural heat input) to the first refrigerant LR ₁ gradually increases, a part is vaporized, the pressure of the pressurized圧槽62 gradually The pressure rises as well, and the pressure in the heat storage tank 12 also rises through the refrigerant inflow line 70.

In one embodiment, the pressure tank 62 is provided below the heat storage tank 12. A refrigerant inflow line 70 is connected between the heat storage tank 12 and the pressure tank 62. Although first refrigerant LR ₁ of liquefied in the heat storage tank 12 through the refrigerant inlet line 70 becomes possible flow into the pressurized圧槽62 by its own weight, the pressure regulating valve 66 is in the pressurized圧槽62 when closed pressure overcomes the pressure due to the weight of the first refrigerant LR _1, have prevented from flowing into the pressurizing圧槽62 from the first thermal storage tank 12 of the refrigerant LR _1. At this time, when the pressure control valve 66 is opened, the pressure of the pressurizing tank 62 is larger than that of the heat storage tank 12 by the amount of self weight of the first refrigerant LR ₁ , so the vaporized first refrigerant LR ₁ in the pressurizing tank 62 is a heat storage tank. Flow to 12 Since the heat storage tank 12 is cooled to the melting point, the vaporized first refrigerant LR ₁ flowing into the heat storage tank 12 immediately recondenses, so the pressure of the heat storage tank 12 does not change depending on the flow of the vaporized first refrigerant LR ₁ .

On the other hand, in the pressure tank 62, the vaporized first refrigerant LR ₁ is discharged to the heat storage tank 12, and the inflow of the first refrigerant LR ₁ cooled from the refrigerant inflow line 70 causes the inside of the pressure tank 62 to down first temperature of the refrigerant LR ₁ of, whereby the internal pressure of the圧槽62 decreases. The amount of pressure drop of the pressure tank 62 changes according to the amount of the first refrigerant LR ₁ discharged to the heat storage tank 12 by the pressure control valve 66. Therefore, the pressure regulating valve 66 vaporizes from the pressure tank 62 to the heat storage tank 12 so that the pressure decrease amount is such that the pressure increase of the pressure tank 62 due to the natural heat input to the pressure tank 62 is offset. adjusting the first amount of the refrigerant LR _1. By this, the pressure of the pressurization tank 62 and the thermal storage tank 12 can be controlled uniformly.

  In one embodiment, the pressure sensor 68 for detecting the pressure of the gas phase part g of the pressurization tank 62 is provided. The pressure in the gas phase portion g is detected by the pressure sensor 68, and the pressure in the heat storage tank 12 can be controlled to a desired pressure by controlling the opening degree of the pressure control valve 66 based on the detected value.

  In one embodiment, a relief valve 72 is provided to release the gas of the gas phase part g to the outside when the pressure of the gas phase part g of the pressure tank 62 exceeds the allowable value.

In one embodiment, the cooling device 10 (10A, 10B) shown in FIGS. 1 and 2 is configured such that the first heat exchangers 16a, 16b flow the second refrigerant from the top to the bottom. The second heat exchanger 22 is configured to flow the first refrigerant from the lower portion to the upper portion. The second refrigerant exchanges heat with the first refrigerant in the first heat exchangers 16a and 16b, and the temperature rises. Therefore, the temperature of the upper portion, which is the upstream side of the second refrigerant, is lower than that of the lower portion, which is the downstream side. On the other hand, since the third refrigerant exchanges heat with the first refrigerant in the second heat exchanger 22 and the temperature drops, the lower portion which is the upstream side of the third refrigerant has a higher temperature than the upper portion which is the downstream.
According to this embodiment, since the temperature of the lower region is higher than the upper region in both the first heat exchangers 16a and 16b and the second heat exchanger 22, the first refrigerant around the heat transfer tube is lower than the upper region. The temperature is higher. Therefore, since the first refrigerant in the upper region is heavier, convection in the vertical direction of the first refrigerant in the heat storage tank 12 is promoted, and the temperature difference of the first refrigerant in the heat storage tank 12 can be reduced.

In one embodiment, at least a portion of the second heat exchanger 22 of the cooling device 10 (10C) shown in FIG. 3 is installed below the first heat exchangers 16a and 16b.
According to this embodiment, since the temperature of the first refrigerant returning from the superconducting cable 18 is higher than that of the second refrigerant, the ambient temperature of the second heat exchanger 22 through which the first refrigerant flows is the first heat through which the second refrigerant flows It becomes higher than the ambient temperature of the exchangers 16a, 16b. Since the second heat exchanger 22 is disposed below the first heat exchangers 16a and 16b, the temperature distribution of the first refrigerant in the heat storage tank 12 is warm in the lower part and cold in the upper part. Therefore, the convection in the vertical direction is promoted, and the temperature difference in the heat storage tank 12 is reduced.

In one embodiment, the cooling device 10 includes the third refrigerant circulation line 23 and the second heat exchanger 22, and supplies the third refrigerant R ₃ in a liquefied state to each of the plurality of superconducting cables 18 (18a, 18b). A plurality of refrigerant supply units 20 (20a, 20b) are provided.
In one embodiment, the cooling device 10 (10D) is shown in FIG. 4, among the plurality of third refrigerant circulation line 23, return line for the third refrigerant R ₃ of a superconducting cable 18 back to the second heat exchanger 22 A third heat exchanger 76 is provided for exchanging heat between the third refrigerants flowing through the air flow 74 (74a, 74b).

  When there is a difference in cable length or heat load among the plurality of superconducting cables 18 (18a, 18b), the temperature of the return refrigerant after cooling the plurality of superconducting cables 18 may be different. However, even in this case, in order to cause the third refrigerant flowing in the return line 74 (74a, 74b) to exchange heat with each other by the third heat exchanger 76, the third refrigerant returns to the plurality of second heat exchangers 22 (22a, 22b) The temperature difference of the refrigerant can be reduced. Therefore, since the difference in the amount of heat exchange in the plurality of second heat exchangers 22 can be reduced, the temperature difference of the third refrigerant supplied to the plurality of superconducting cables 18 can be reduced.

In the cooling device 10 (10D) shown in FIG. 4, the liquid pump 44 (44a, 44b) is provided in the return line 74 (74a, 74b), and the third refrigerant R in the liquefied state is provided in the return line 74 (74a, 74b). ₃ flow in the same direction, ie, in the direction towards the second heat exchanger 22 (22a, 22b).

  In the cooling device 10 (10D), when one superconducting cable 18 (18a) breaks down, the supply of the third refrigerant to the broken superconducting cable 18 is stopped. Then, in the third refrigerant circulation line 23 (23a), the third refrigerant is circulated so as to bypass the failed superconducting cable 18. As a result, the third refrigerant warmed by the third heat exchanger 76 can be circulated to the failed second heat exchanger 22 (22a) on the side of the superconducting cable, so that the surroundings of the second heat exchanger 22 (22a) can be obtained. Overcooling can be suppressed.

In one embodiment, as shown in FIG. 4, a line 78 is provided to connect the inlet and the outlet of the superconducting cable 18 during steady operation, and the third refrigerant circulation line 23 is connected to the line 78. The on-off valves 80 and 82 are provided in the line 78 on the side and the downstream side of the connection of the third refrigerant circulation line 23, respectively.
During normal operation, the on-off valve 80 is closed and the on-off valve 82 is opened to supply the third refrigerant to the superconducting cable 18 (18 a). When the superconducting cable 18 (18a) breaks down, opening the on-off valve 80 and closing the on-off valve 82 circulates the third refrigerant circulation line 23 (23a) while bypassing the superconducting cable 18 (18a). Can be formed. As a result, it is possible to suppress excessive cooling around the second heat exchanger 22 (22a) on the failed side.

In the method of cooling a superconducting cable according to one embodiment, as shown in FIG. 7, the plurality of refrigeration units are set such that the temperature of the first refrigerant flowing through the outlet of each of the first heat exchangers 16a and 16b becomes a target value. 14a and 14b are controlled (temperature control step S10).
According to the above method, in the temperature control step S10, each of the plurality of refrigeration units 14a and 14b is controlled so that the temperature of the second refrigerant at the outlet of the first heat exchangers 16a and 16b becomes the target value. The first refrigerant stored in the heat storage tank 12 can be made to have a desired temperature. Thus, by controlling the temperature of the first refrigerant in the heat storage tank 12, the temperature of the first refrigerant supplied to the superconducting cable 18 can also be controlled to a desired temperature.

  In one embodiment, in the temperature control step S10, the plurality of refrigeration units 14a and 14b are controlled such that the temperature of the first refrigerant flowing through the outlet of each of the first heat exchangers 16a and 16b is the same. The amount of cooling of each of the refrigeration units 14a and 14b has a unique correlation with the temperature of the second refrigerant at the outlet of the first heat exchangers 16a and 16b. Therefore, by controlling the plurality of refrigeration units 14a and 14b so that the temperature of the first refrigerant at the outlet of each first heat exchanger is the same, the amount of cooling can be evenly distributed to each refrigeration unit. Thus, the operation control of each refrigeration unit can be optimized.

In one embodiment, when the temperature of the first refrigerant flowing through the outlet of each of the first heat exchangers 16a and 16b is higher than the target value in the temperature control step S10, the amount of cooling of the refrigeration unit is increased, and the first thermal When the temperature of the first refrigerant flowing through the outlet of each of the exchangers is lower than the target value, the amount of cooling of the refrigeration unit is reduced.
According to this method, the temperature of the first refrigerant flowing through the outlet of each of the first heat exchangers can be set to a desired temperature, whereby the temperature of the first refrigerant supplied to the superconducting cable is also desired. It can control to temperature.

In one embodiment, as shown in FIG. 7, the plurality of refrigeration units 14 a and 14 b are controlled such that at least a portion of the first refrigerant stored in the heat storage tank 12 generates a solid phase portion (solid phase portion generation Step S12).
According to this method, at least a part of the first refrigerant stored in the heat storage tank 12 generates a solid phase portion, so heat can be stored using heat of fusion larger than sensible heat, and the heat storage amount can be increased.

In one embodiment, in the solid phase portion generation step S12, the pressure of the first refrigerant in the heat storage tank 12 is set higher than the pressure of the third refrigerant in the second heat exchanger.
According to this embodiment, at least a part of the first refrigerant stored in the heat storage tank 12 can generate the solid phase portion. As a result, heat can be stored in the heat storage tank 12 using melting heat larger than sensible heat, and the heat storage amount can be increased. In addition, it is possible to prevent the third refrigerant flowing in the third refrigerant circulation line 23 from generating a solid phase portion, whereby the third cable flowing through the third refrigerant circulation line 23 does not freeze, and thus the superconducting cable 18 The supply of the third refrigerant can be maintained.

  In the cooling device 10 (10D), the third heat exchanger 76 is provided when steady operation is performed in the heat storage tank 12 in a state in which the liquid phase and the solid phase cooled to the melting point or less of the first refrigerant are mixed. It is possible to prevent the third refrigerant from freezing in the piping of the second heat exchanger 22 (22a) on the side of the failed superconducting cable 18 (18a).

  According to one embodiment, when the liquefied refrigerant stored in the heat storage tank is cooled by a plurality of refrigerators, the optimum operating conditions of the individual refrigerators can be easily set.

DESCRIPTION OF SYMBOLS 10 (10A, 10B, 10C, 10D) Cooling device 12, 42 (42a, 42b) Heat storage tank 14a, 14b Refrigerating unit 16a, 16b 1st heat exchanger 18 (18a, 18b) Superconducting cable 20 (20a, 20b) Refrigerant Supply part 22 (22a, 22b) second heat exchanger 23 (23a, 23b) third refrigerant circulation line 24a, 24b second refrigerant gas circulation line 26 (26a, 26b), 46 (46a, 46b) temperature sensor 28a, 28b compressor 30a, 30b water cooling unit 32a, 32b cold heat recovery heat exchanger 34a, 34b expansion turbine 36a, 36b motor 38 (38a, 38b) vacuum vessel 40 control unit 44 (4a, 44b) liquid pump 48 (48a, 48b) Flow sensor 50a, 50b Branch line 52a, 52b Buffer tank 54 , 54b, 56a, 56b, 80, 82 on-off valve 58, 72 relief valve 60 pressure regulator 62 pressure tank 64 pressure reducing line 66 pressure regulating valve 68 pressure sensor 70 refrigerant inlet line 74a, 74b return line 76 third heat exchanger LR ₁ 1st refrigerant R ₂ 2nd refrigerant R ₃ 3rd refrigerant g Gas phase part w Cooling water

Claims (12)

A heat storage tank for storing the first refrigerant in a liquefied state;
A refrigeration unit using a second refrigerant having a liquefying temperature lower than that of the first refrigerant, comprising a plurality of first heat exchangers provided inside the heat storage tank and capable of cooling the first refrigerant with the second refrigerant. A refrigeration unit,
A second heat exchanger provided inside the heat storage tank;
A third refrigerant circulation line connected to the second heat exchanger and the superconducting cable for circulating a third refrigerant;
A temperature sensor provided at the outlet of each of the first heat exchangers for detecting the temperature of the second refrigerant;
A control unit for controlling each of the plurality of refrigeration units so that the detection value of each of the temperature sensors is input, and the detection value of the temperature sensor becomes a target value;
An apparatus for cooling a superconducting cable, comprising:   The cooling device of a superconducting cable according to claim 1, further comprising a pressure adjusting unit capable of adjusting the pressure in the heat storage tank. The pressure adjustment unit is
A pressure vessel provided at a lower position than the heat storage tank, in which the first refrigerant in a liquefied state is stored, and a gas phase part is formed above the liquid surface of the first refrigerant;
A decompression line in communication with the gas phase portion and the heat storage tank;
A pressure control valve provided in the pressure reducing line and capable of adjusting the opening degree;
A refrigerant inflow line communicating with a liquid phase portion of the pressure tank and the heat storage tank;
The cooling apparatus of the superconducting cable according to claim 2, comprising:   The cooling device for a superconducting cable according to claim 3, further comprising a pressure sensor for detecting the pressure. The first heat exchanger is configured to flow the second refrigerant from the top to the bottom,
The cooling device for a superconducting cable according to any one of claims 1 to 4, wherein the second heat exchanger is configured to flow the first refrigerant from the lower part to the upper part.   The cooling device of a superconducting cable according to any one of claims 1 to 5, wherein at least a part of the second heat exchanger is installed below the first heat exchanger. And a plurality of superconducting cable cooling units that include the third refrigerant circulation line and the second heat exchanger, and supply the third refrigerant in a liquefied state to each of the plurality of superconducting cables;
Third heat for exchanging heat among the third refrigerants flowing through a return line for returning the third refrigerant to the second heat exchanger among the third refrigerant circulation lines of the plurality of superconducting cable cooling units The cooling device for a superconducting cable according to any one of claims 1 to 6, further comprising a exchanger. A heat storage tank for storing the first refrigerant in a liquefied state;
A refrigeration unit using a second refrigerant having a liquefying temperature lower than that of the first refrigerant, comprising a plurality of first heat exchangers provided inside the heat storage tank and capable of cooling the first refrigerant with the second refrigerant. A refrigeration unit,
A second heat exchanger provided inside the heat storage tank;
A third refrigerant circulation line connected to the second heat exchanger and the superconducting cable for circulating the third refrigerant;
A cooling device for a superconducting cable comprising
A method of cooling a superconducting cable, comprising a temperature control step of controlling the plurality of refrigeration units so that the temperature of the first refrigerant flowing through the outlet of each of the first heat exchangers becomes a target value.   9. The system according to claim 8, wherein, in the temperature control step, the plurality of refrigeration units are controlled such that the temperature of the first refrigerant flowing through the outlet of each of the first heat exchangers becomes the same. How to cool superconducting cables. In the temperature control step,
When the temperature of the first refrigerant flowing through the outlet of the first heat exchanger is higher than the target value, the amount of cooling of the refrigeration unit to which the first heat exchanger belongs is increased;
The cooling amount of the refrigeration unit to which the first heat exchanger belongs is reduced when the temperature of the first refrigerant flowing through the outlet of the first heat exchanger is lower than the target value. Or the cooling method of the superconducting cable as described in 9.   11. The method according to claim 8, further comprising: a solid phase generation step of controlling the plurality of refrigeration units such that at least a part of the first refrigerant stored in the heat storage tank generates a solid phase. The method for cooling a superconducting cable according to any one of the preceding claims. In the solid phase generation step,
The method according to claim 11, wherein the pressure of the first refrigerant in the heat storage tank is higher than the pressure of the third refrigerant in the second heat exchanger.

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