JP2001024243A - Cryostat and method for operating the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the increase of a refrigerant liquid collected in a common container with less energy and, in addition, to improve the liquefying rate of a refrigerant. SOLUTION: In a method for operating cryostat, a cryostat in which a refrigerant liquid, such as the liquid helium 18, etc., is housed in individual containers 14 respectively housing objects 16 to be cooled is operated by collectively housing the containers 14 in a common container 10. The evaporative gas of the refrigerating liquid is taken in a liquefying refrigerating device 30 for liquefication and the liquefied gas is recycled to the containers 14. On the other hand, the refrigerant liquid collected in the common container 10 is evaporated by using a heater 40, etc., and the evaporated liquid is recycled to the liquefying refrigerating device 30.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for operating a cryostat for cooling a superconducting magnet or other object to be cooled, which is used for nuclear fusion, superconducting energy storage, accelerators, NMR, linear motor cars, etc., with a coolant such as liquid helium and the like. It is about a cryostat.

[0002]

2. Description of the Related Art Conventionally, as a cryostat for accommodating a cooled object such as a superconducting magnet, a single liquid helium container (refrigerant container) is accommodated in a vacuum container, and liquid helium contained in the liquid helium container. It is known that the object to be cooled is immersed therein.

In such a cryostat, if a plurality of cooling objects are accommodated in a common liquid helium container, if any of the cooling objects is quenched, the liquid helium is As the liquid helium in the container evaporates rapidly, another object to be cooled is exposed from the liquid surface of the liquid helium, and the other object to be cooled is also quenched in a chain. Therefore,
In such a configuration, there is a disadvantage that a large amount of liquid helium is lost when a quench occurs, and a long time is required for restart.

Therefore, as a means for preventing the above-mentioned quench chain from occurring, a cryostat provided with an individual container for individually accommodating a plurality of objects to be cooled has been proposed (for example, JP-A-9-171921). Reference).

FIG. 5 shows an example of the structure. The cryostat shown is a common container 90 having a vacuum heat insulating layer 92 on the outer periphery.
And a plurality of individual containers 9 inside the common container 90.
3 are accommodated. In each individual container 93, a cooling liquid helium 94 is accommodated, and a cooled object (a superconducting magnet 96 in the illustrated example) is individually immersed in the liquid helium 94. In the common container 90, a helium liquefaction refrigeration unit 98 is connected, and the evaporating gas of the liquid helium 94 is collected by the helium liquefaction refrigeration unit 98, and the liquid helium 9 liquefied by the liquefaction refrigeration unit 98.
4 is returned to each individual container 93.

According to such a cryostat, even if a quench occurs in any of the superconducting magnets 96, the rapid evaporation directly attributable to this causes the superconducting magnet 96 in which the quench has occurred to be accommodated. Only the liquid helium 94 in the individual container 93 can prevent the other superconducting magnets 96 from quenching in a chain.

[0007]

In the cryostat, a superconducting magnet 96 is immersed in liquid helium 94 in each individual container 93, and it is completely assumed that the liquid helium 94 will accumulate at the bottom of the common container 90. Absent. Even if the liquid helium 94 overflows or leaks from the individual container 93, if it is very small, it evaporates to helium gas.
Liquid helium should not collect at the bottom of the.

However, when an experiment was conducted using a cryostat of the type described above, it was confirmed that liquid helium 94 actually accumulated at the bottom of the common container 90 as shown in the figure. This phenomenon is caused by a temperature gradient caused by uneven distribution of low-temperature helium gas at the bottom of the common container 90 due to convection of the helium gas in the common container 90 and a pressure gradient caused by the weight of the helium gas. It is considered that the helium gas at the bottom has a relatively lower temperature and a higher pressure than the helium gas at the top, and the pressure of the helium gas at the bottom condenses above the saturation pressure at that temperature.

If such a liquid helium reservoir is left undisturbed, its level gradually rises, and eventually the individual container 9
3, the meaning of providing the individual container 93 is completely lost. As a means for avoiding such inconvenience, it is conceivable to pump the liquid helium 94 accumulated in the common container 90 out of the container using a pump or the like. However, when such a means is used, energy loss including pump power is required. It becomes remarkably large.

Further, the accumulation of liquid helium 94 at the bottom of the common container as described above indicates that the refrigeration capacity of the liquid helium liquefaction refrigeration system 98 is wasted, and it is desirable to take measures to improve it. It is.

In view of such circumstances, the present invention provides a cryostat operating method and a cryostat capable of preventing an increase in refrigerant liquid accumulated in a common container with a small amount of energy and improving a liquefaction rate of the refrigerant. The purpose is to provide.

[0012]

As means for solving the above problems, the present invention provides a plurality of individual containers for individually accommodating a plurality of objects to be cooled and a common container for accommodating these individual containers collectively. And a method for operating a cryostat in which a refrigerant liquid for cooling the object to be cooled in each individual container is provided, wherein the vaporization gas of the refrigerant liquid is taken into a liquefaction refrigeration apparatus and liquefied. While this is returned to each individual container, the refrigerant liquid accumulated in the common container is evaporated and returned to the liquefaction refrigeration apparatus.

According to this method, it is possible to prevent an increase in the amount of the refrigerant liquid accumulated in the bottom portion of the common container by evaporating the refrigerant liquid without pumping it with a pump or the like. Then, by reducing the evaporated gas to the liquefaction refrigeration apparatus, the liquefaction refrigeration capacity can be fully utilized and the liquefaction rate can be increased.

In order to cause the refrigerant liquid to evaporate, the refrigerant liquid accumulated at the bottom of the common container may be heated, or the refrigerant liquid in the common container may be heated more than the liquid surface of each individual container. The refrigerant located below may be sucked to the compressor inlet side of the liquefaction refrigeration apparatus while heating and exchanging heat with the outside of the cryostat. The former method has an advantage that the degree of improvement in the liquefaction rate is higher than the latter method. In the latter case, there is an advantage that the refrigerant liquid at the bottom of the outer container can be evaporated without using a special heat source.

The amount of heat input for evaporating the refrigerant liquid and the amount of suction to the inlet of the compressor are preferably adjusted in consideration of the balance between the capacity and the operating conditions of the liquefaction refrigeration system. Specifically, a method of adjusting the evaporation amount of the refrigerant liquid so as to maintain a constant liquid level of the refrigerant liquid accumulated in the common container, or a method of adjusting the pressure near the refrigerant liquid accumulated in the common container A method of adjusting the evaporation amount of the refrigerant liquid so as to maintain the predetermined target pressure is preferable.

As described above, in the present invention, since the refrigerant liquid accumulated in the common container is evaporated and returned to the liquefaction refrigeration system, for example, the refrigerant liquid is intentionally overflown from each of the individual containers and the bottom of the common container is removed. It is also possible to flow down the liquid, which makes it unnecessary to manage the liquid level in each individual container, and the operation is further facilitated.

Further, the present invention comprises a plurality of individual containers for individually accommodating a plurality of objects to be cooled, and a common container for accommodating these individual containers collectively. In a cryostat containing a refrigerant liquid for cooling the liquid refrigerant, a liquefied refrigeration apparatus for taking in and liquefying the evaporating gas of the refrigerant liquid and reducing it to each individual container, and a refrigerant collected in the common container Heating means for heating and evaporating the liquid to reduce the liquid to the liquefaction refrigeration apparatus.

In this cryostat, it is more preferable that the heating means is provided at the lowermost part of the common container. This can prevent a large amount of refrigerant liquid from remaining at the bottom of the common container.

Further, the present invention comprises a plurality of individual containers for individually accommodating a plurality of objects to be cooled, and a common container for collectively accommodating these individual containers. In a cryostat in which a refrigerant liquid for cooling is stored, a liquefied refrigeration apparatus for taking in and liquefying the evaporative gas of the refrigerant liquid and reducing it to each individual container, and each individual container in the common container And a heating passage through which the refrigerant located below the liquid surface of the refrigerant liquid in Step 1 is heated by exchanging heat with the outside of the cryostat and then guided to the compressor inlet of the liquefaction refrigeration apparatus.

This heating passage can be utilized in combination with the heating means.

If a flow control valve for controlling the flow rate of the refrigerant is provided in the heating passage, the flow rate can be controlled by
The liquid level management or pressure management of the refrigerant liquid in the lower part of the common container becomes possible.

[0022]

FIG. 1 shows a first embodiment of the present invention.
A description will be given based on FIG.

The cryostat shown has a common container 10 as a common container, and a vacuum heat insulating layer 12 is formed on the outer periphery of the common container 10. A plurality of individual containers 14 are accommodated in the common container 10, a liquid helium 18 as a refrigerant liquid is accommodated in each individual container 14, and a superconducting magnet 16 is immersed as a cooled object. In the illustrated example, a support shaft 22 hangs down from the top flange 20 that closes the upper opening of the common container 10 into the container, and the support shaft 22
Two individual containers 14 are arranged radially.

In the present invention, the specific number and layout of the individual containers 14 can be appropriately set. Further, the specific individual containers 14 may be connected to each other by a communication pipe or the like to share the liquid helium. For example, three individual containers 14 may be communicated with each other to divide all six individual containers 14 into two groups. In this case, even if the quench occurs in the superconducting magnets 16 in one group, it is possible to prevent the quench from occurring in the superconducting magnets 16 in the other group due to this. In addition, Japanese Patent Application Laid-Open No.
As shown in Japanese Patent Application Publication No. 1-2005, the present invention can be applied to an apparatus of a type in which only the upper part of the individual container (that is, the part above the superconducting magnet housing part) is shared.

A liquefaction refrigeration unit 30 for helium is connected to the common container 10. This liquefaction refrigerator 30
The helium gas evaporated from each individual container 14 is collected by a collection pipe 26, liquefied, and liquid helium is distributed to each individual container 14 through a distribution pipe 28.

When the individual containers 14 are grouped as described above, the liquid helium may be supplied to one of the individual containers 14 belonging to each group.

As shown in FIG.
Comprises a compressor 31 and a cool box 32, and the main heat exchangers 33A, 33B, 33C, 33D, 33
E, heat exchanger 34 for pre-cooling, expander 35A for generating cold,
35B and a JT valve 36.

The helium gas discharged from the compressor 31 is supplied to the main heat exchangers 33A to 33A along the high pressure line.
After being cooled sequentially through E and liquefied by adiabatic expansion by the JT valve 36, it is distributed to each individual container 14 through the distribution pipe 28, while the low-temperature helium gas evaporated from each individual vessel 14 is collected through the collection pipe 26. The helium gas is recovered, sequentially passes through the main heat exchangers 33E to 33A along the low pressure line, cools the helium gas on the high pressure line side, and is then sucked into the inlet side of the compressor 31. By the operation of the liquefaction refrigeration apparatus 30, the liquid helium 18 necessary for keeping the superconducting magnet 16 cool in the cryostat is supplied at any time.

Further, as a feature of this cryostat, a bottom portion (the lowest portion in the illustrated example) of the common container 10
A heater 40 as heating means is provided.

Next, the operation procedure of the cryostat will be described.

1) The inside of the outer periphery of the common container 10 is evacuated to form a vacuum heat insulating layer 12.

2) Pre-cool the inside of the cryostat. This pre-cooling is performed by supplying liquid nitrogen into the cryostat through a pre-cooling line (not shown) and gradually supplying liquid helium, but the procedure is general and will not be described here.

3) Connect the helium liquefaction refrigeration system 30 to the cryostat and start up. Thereby, the liquid helium 18 necessary for immersing the superconducting magnet 16 is supplied to each individual container 14. At this time, as the liquid level adjustment of the liquid helium 18 in the individual containers 14, it is also possible to control the operation of the liquid helium 30 so that the liquid level is maintained at a constant level, and the bottom of each individual container 14 Heater (a heater different from the heater at the bottom of the common container 10)
May be provided so that the excess liquid helium 18 is appropriately evaporated.

4) Since a vertical temperature gradient and a pressure gradient are generated in the common container 10 for the above-described reason, the low-temperature helium gas at the bottom of the common container starts to condense, and the liquid helium 18 Begin to accumulate (Fig. 1 (b)
reference). Therefore, the heater 40 is operated at an appropriate timing to evaporate the liquid helium 18 at the bottom of the common container.
Since the evaporated helium gas 18 is recovered in the liquefaction refrigeration apparatus 30 through the recovery pipe 26, the liquefaction rate of the entire system is improved accordingly.

However, if the amount of heat input by the heater 40 is too large, the balance between the liquefaction refrigeration apparatus 30 and the liquefaction refrigeration capacity will be lost, resulting in excessive heat input. It is preferable to determine in consideration of operating conditions. Specifically, the liquid level of the liquid helium 18 at the bottom of the common container is maintained substantially constant, or the pressure near the liquid level is maintained at a target pressure (for example, a saturation pressure of helium gas corresponding to the target temperature). Thus, a method of adjusting the heat input is preferable.

According to the above-described cryostat and operation method, the heater 40 is provided at the bottom of the common container 10 without using a device requiring a special power source such as a pump.
Simple and low cost of adding a little heat input,
With a low-energy configuration, the effect of preventing an increase in the liquid helium 18 accumulated at the bottom of the common container 10 and improving the liquefaction rate is obtained.

According to this method, each individual container 14
Intentionally overflow liquid helium 18 from
It is also possible to perform an operation of evaporating the liquid helium 18 accumulated at the bottom of the common container 10 by the heat input by the heater 40 due to the overflow, thereby eliminating a heater for controlling the liquid level in each individual container 14 and the like. Benefits are also obtained.

Next, a second embodiment will be described with reference to FIGS.

In this embodiment, instead of the heater 40 shown in FIG. 1B, a heating pipe 42 for connecting the inside of the common container 10 and the liquefaction refrigeration unit 30 is introduced. As shown in FIG. 3, one end (lower end) 42a of the heating pipe 42 is
The lower portion of the common container 10, specifically, a portion below the liquid level of the liquid helium 18 in each individual container 14, and the other end is the inlet side of the compressor 31 in the liquefaction refrigeration apparatus 30 as shown in FIG. It is connected to the.

In the middle of the heating pipe 42, the heating pipe 4
2 is provided with a heat exchanger 44 for exchanging (that is, heating) the helium gas flowing through the air with the atmosphere outside the cryostat, and a flow control valve 46 for adjusting the flow rate of the helium gas in the heating pipe 42 is provided. Have been.

In this cryostat, when the flow control valve 46 is opened during the operation, the helium gas in the lower part of the common container 10 is led out of the container by the power of the compressor 31, and is heated by the heat exchanger 44. It is sucked into the compressor 31. In this way, the low-temperature helium gas at the lower portion of the common container is extracted and the pressure is reduced, so that the evaporation of the liquid helium 18 collected at the bottom of the common container is promoted, the increase is prevented, and the evaporated helium gas is removed. The liquefaction rate is improved by being collected in the liquefaction refrigeration apparatus 30 through the collection pipe 26.

In this cryostat and its operation method, since a part of the helium gas is heated and then introduced into the liquefaction refrigeration unit 30, the degree of improvement in the liquefaction rate is higher than that in the first embodiment. Although lowered, there is an advantage that the liquid helium 18 at the bottom of the common container can be evaporated without using a heat source such as the heater 40. Also in this method, the liquid level of the liquid helium 18 collected at the bottom and the pressure near the liquid surface are monitored, and the flow control valve 46 is operated so as to maintain the liquid level or the pressure near the liquid surface constant. It is more preferable to adjust the gas flow rate.

Further, the heating pipe 42 shown in the second embodiment and the heater 40 shown in the first embodiment are combined, and the liquid helium 1 is heated by the heater 40.
The rise in pressure due to evaporation of 8 may be suppressed by deriving helium gas through heating tube 42.

In the above embodiment, the liquid helium liquefied by the liquefaction refrigeration apparatus 30 is directly reduced to the individual containers 14, but the reduction may be indirect. For example, the liquid helium liquefied by the liquefaction refrigeration apparatus 30 may be stored in a liquid helium container separate from the cryostat, and the liquid helium may be appropriately supplied from the liquid helium container to each individual container 14 in the cryostat. .

[0045]

In the cryostat shown in FIGS. 1 and 2, when the heat input by the heater 40 was not performed at all and when the heat input was 0.5 W, the obtained liquefaction rate was expressed by the following equation (1). Calculated based on As a result, it was found that the liquefaction rate in the former case was 60%, whereas the liquefaction rate in the latter case was 63.3%, and the liquefaction rate was improved by 3.3%.

[0046]

(Liquefaction rate) = (H1−H2 + Q1) / (H1−H3) where H1 is the evaporating helium gas (1.2 atm, 4.4K, 29.92 J /
g) specific enthalpy (J / G), H2 is specific enthalpy (J / G) of helium gas (1.6 atm, 4.8K, 18.35 J / g) introduced into the JT valve 36, H3 is liquid helium in the cryostat (1.2atm, 4.4K, 10.66J / g) specific enthalpy (J /
G) and Q1 are values (J / G) obtained by dividing the heat input by the JT valve flow rate (1 g / s).

The heat input (0.5 W) is an upper limit value determined by the balance with the operation conditions of the liquefaction refrigeration unit 30. However, the liquefaction refrigeration unit 30 is increased in liquefaction refrigeration capacity (for example, helium in the JT valve 36). By increasing the flow rate), the amount of heat input can be further increased, and the liquid separation rate can be further increased.

[0048]

As described above, according to the present invention, the evaporative gas of the refrigerant in the cryostat is taken into the liquefaction refrigeration apparatus and liquefied, and the liquefied gas is returned to the individual vessels provided in the cryostat. Since the refrigerant liquid accumulated in the common container accommodated collectively is evaporated and returned to the liquefaction refrigeration apparatus, an increase in the refrigerant liquid accumulated in the common container is prevented with a small energy, and the refrigerant is liquefied. It has the effect of improving the rate.

[Brief description of the drawings]

FIG. 1A is a sectional view taken along line AA of FIG. 1B, and FIG. 1B is a sectional front view showing an internal structure of a cryostat according to a first embodiment of the present invention.

FIG. 2 is a flow sheet of the liquefaction refrigeration apparatus used in the first embodiment of the present invention.

FIG. 3 is a sectional front view of a cryostat according to a second embodiment of the present invention.

FIG. 4 is a flow sheet of a liquefaction refrigeration apparatus used in a second embodiment of the present invention.

FIG. 5 is a cross-sectional front view showing the internal structure of a conventional cryostat.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Common container (common container) 14 Individual container 16 Superconducting magnet (cooled body) 18 Liquid helium 26 Recovery pipe 28 minute pipe 30 Liquefaction refrigeration equipment 31 Compressor 40 Heater (heating means) 42 Heating pipe 44 Heat exchanger 46 Flow rate Control valve

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Katsuya Tsutsumi 2-1-1, Shiobara, Minami-ku, Fukuoka City Kyushu Electric Power Co., Inc. (72) Hidemi Hayashi 2-47, Shiobara, Minami-ku, Fukuoka City Kyushu Electric Power Co., Inc. (72) Hidemasa Yamamura 1-6-14 Edobori, Nishi-ku, Osaka-shi Inside Kobe Steel Works, Ltd. (72) Yukio Watanabe 1-6-16-1 Edobori, Nishi-ku, Osaka Co., Ltd. Inside Kobe Steel (72) Inventor Satoshi Hanai 2-4 Suehirocho, Tsurumi-ku, Yokohama-shi F-term (reference) 3L044 BA07 CA16 DB03 EA02 FA04 GA02 HA03 JA03 JA05 KA04 KA05 4M114 AA05 AA14 AA19 AA31 BB03 BB03 BB03 BB09 CC03 CC16 DA02 DA05 DA08 DA09 DA26 DA33

Claims (11)

[Claims] 1. A cooling apparatus comprising: a plurality of individual containers accommodating a plurality of objects to be cooled individually; and a common container accommodating the individual containers collectively, and each individual container cools the object to be cooled therein. For operating a cryostat in which a refrigerant liquid is stored, wherein the vaporized gas of the refrigerant liquid is taken into a liquefaction refrigeration apparatus to be liquefied and reduced in each individual container, while being accumulated in the common container. A method for operating a cryostat, comprising evaporating a refrigerant liquid and returning it to the liquefaction refrigeration apparatus. 2. The method for operating a cryostat according to claim 1, wherein the refrigerant liquid accumulated at the bottom of the common container is heated and evaporated. 3. The method for operating a cryostat according to claim 1, wherein the refrigerant located below the liquid surface of the refrigerant liquid in each of the individual containers in the common container is heated and exchanged with the outside of the cryostat. A method for operating the cryostat, wherein the suction is performed at the compressor inlet side of the liquefaction refrigeration apparatus. 4. The method for operating a cryostat according to claim 1, wherein an evaporation amount of the refrigerant liquid is adjusted so as to maintain a constant liquid level of the refrigerant liquid stored in the common container. A method for operating a cryostat, comprising: 5. The method for operating a cryostat according to claim 1, wherein the amount of evaporation of the refrigerant liquid is maintained such that a pressure near the refrigerant liquid accumulated in the common container is maintained at a predetermined target pressure. A method for operating a cryostat, characterized by adjusting the pressure. 6. The cryostat operating method according to claim 1, wherein the refrigerant liquid overflows from each of the individual containers and flows down to the bottom of a common container. 7. A plurality of individual containers for individually accommodating a plurality of objects to be cooled, and a common container for collectively accommodating these individual containers, wherein each individual container cools the object to be cooled therein. And a liquefaction refrigeration system for taking in and liquefying the evaporative gas of the refrigerant liquid and reducing the same to each individual container, and heating the refrigerant liquid stored in the common container. And a heating means for evaporating and evaporating the liquefied refrigeration equipment to return to the liquefaction refrigeration apparatus. 8. The cryostat according to claim 7, wherein said heating means is provided at a lowermost portion of said common container. 9. A cooling apparatus comprising: a plurality of individual containers for individually accommodating a plurality of objects to be cooled; and a common container for accommodating the individual containers collectively, and each individual container cools the object to be cooled therein. And a liquefaction refrigeration system for taking in and liquefying the evaporative gas of the refrigerant liquid and reducing it to each individual container, and a refrigerant liquid in each individual container within the common container. A heating passage for heating the refrigerant located below the liquid level with the outside of the cryostat by exchanging heat with the outside of the cryostat and then leading the refrigerant to the compressor inlet of the liquefaction refrigeration apparatus. 10. The cryostat according to claim 7, wherein the refrigerant located below the liquid surface of the refrigerant liquid in each individual container in the common container is heated by exchanging heat with the outside of the cryostat and then heated. A cryostat comprising a heating passage leading to a compressor inlet of a liquefaction refrigeration apparatus. 11. The cryostat according to claim 9, wherein a flow control valve for adjusting a flow rate of the refrigerant is provided in the heating passage.