JPS62785A - Precooling method of cryogenic device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a method for precooling a cryogenic device used in superconducting equipment, etc., and specifically, a method for precooling the device by cooling liquid nitrogen. In particular, the present invention relates to a precooling method for a cryogenic device typified by a helium liquefaction refrigerator.

[Prior Art] A helium liquefier will be described below as an example of a cryogenic device. Figure 2 shows a plurality of heat exchangers 4a, 4b, 5 to 9.
．． 3 cn [Zhang a121.10°11 and expansion valve 12 (
This shows a helium liquefaction machine in which a Joule-Thompson valve and the like are disposed inside the coal topo 7, and a compressed la2 and liquid helium storage tank 15 are disposed outside the cold box 1. The He gas cyclically supplied from the low pressure pipe 16 is
m2 and introduced into the high pressure pipe 3. The introduced He gas is adiabatically expanded by the expansion fi21, 10.11, and is sequentially cooled by the generated cold.Furthermore, it is partially liquefied by the Joule-Thomson effect in the expansion valve 2, and the generated liquid He is stored in the storage tank 15. .

[Problems to be Solved by the Invention] In the He liquefaction machine as shown in FIG. A pre-cooling operation had to be carried out for several hours. Heat exchangers 4a, 4b and an expander 21 are provided in the cold box 1 as auxiliary refrigerators for the purpose of effectively performing precooling operation. However, since the expander 21 is used at low temperatures for long periods of time, it tends to cause defects in operational reliability and a rise in the cost of machinery and equipment.In order to avoid this, in recent years, devices such as the one shown in Fig. It is commonly used. That is, liquid nitrogen (hereinafter simply L) is used as an auxiliary refrigerator installed in the cold box 21.
It is equipped with a supply pipe 13 (denoted as N2) and a heat exchanger 4, and has as few mechanical moving parts as possible.With such a device, LN2 can be supplied directly from a large LN2 tank to the heat exchanger 4. In addition to supplying the Helium, it requires fewer mechanical moving parts and attached equipment, and is superior to the He liquefier shown in FIG. 2 in terms of operational stability and equipment cost.

However, in the precooling method using LN2, the cold used for precooling is mainly the latent heat when LN2 evaporates,
The temperature of the resulting refrigeration is approximately 77.7 mm, which is the boiling point temperature of LN2.
The lower limit is 4''K, and if the heat exchanger 4 is used, the effective cooling temperature will be 80' or more, which is a bottleneck in improving the precooling effect of the liquefier.

Therefore, the present inventors have conducted various studies aimed at improving the precooling effect by keeping the effective utilization temperature of LN2 used in cryogenic equipment as low as 80', and as a result, they have completed the present invention. It's arrived.

[Means for solving the problem] When performing precooling using LN2, in the present invention, liquid nitrogen is supplied to a precooling section formed in a low-pressure atmosphere, and cooling is generated under conditions where the boiling point of the liquid nitrogen is low. The gist lies in the fact that

[Function] In ordinary heat exchangers and heat shields that use LN2, LN2 is supplied under atmospheric pressure, and after cooling each device to near the boiling point temperature of the LN2, it is discharged from the system as N2 gas. . The boiling point temperature of LN2 is approximately 77.4”K at 1 atm.
However, if we focus on the principle that the boiling point decreases in a low-pressure atmosphere (below 1 atm) and supply LN2 under vacuum, for example, at a pressure of about 100↑orr, the boiling point of LN2 will drop to about 65'K. be able to. However, the degree of pressure reduction must be such that the liquid N2 does not solidify.

Therefore, if the heat exchanger and heat shield section to which LN2 is supplied are kept in a low-pressure atmosphere using a vacuum pump or the like, it becomes possible to cool them to a temperature lower than that at normal pressure. However, this requires the addition of a mechanical operating part such as a vacuum pump, but since this device can be installed outside the cold box in a normal temperature area, there is no need to consider troubles during low-temperature operation.

[Example] The first example of a typical He liquefaction machine in which the method of the present invention is utilized is as follows.
As shown in the figure, there are heat exchangers 4 to 9 in the cold box l.
An expander 10.11 and an expansion valve 12 are provided, and an LN2 supply pipe 13, a N2 discharge pipe 14, and a vacuum pump 17 connected to the discharge pipe 14 are provided as pre-cooling devices. Incidentally, the vacuum pump 17 is installed outside the cold box l under a normal temperature atmosphere.

When starting up the He liquefaction machine, LN is supplied by the vacuum pump 17.
2 is depressurized to a pressure that does not solidify, and the LN2 supply pipe 13 to L
Supply N2. At the same time, the pressurizer 2 is operated to pressurize and circulate He gas into the cold box 1, and first the heat exchanger 4
The expansion machine io is cooled by branching a part of the expansion machine io,
In this pre-cooling stage, the LN2 supply is stopped and the He The operation continues for one hour using only gas, and then the expansion valve 12 starts to liquefy the He gas to store LHe in the storage tank 15.

As mentioned above, by lowering the effective utilization temperature of LN2 to 80", the amount of LN2 required for precooling can be reduced, and precooling can be performed more effectively, so H
The flow rate of the compressor 2 in the e-circulation system can now be reduced by about 20%.

The present invention is not only applicable to heat exchangers for pre-cooling, but also to cooling the heat shield part in a cold box or the heat shield plate of a cryo-pen, as shown in Figure 4. Can be applied. FIG. 4 shows an embodiment of a liquid He refrigerator, with cryostat 19
Although this is a refrigerator for keeping a cooled member (such as an a conductive magnet) immersed in LHe at an extremely low temperature, this is not intended to limit the present invention.

[Effects of the Invention] By utilizing the method of the present invention for cooling or pre-cooling a cryogenic device, it becomes possible to lower the effective temperature of LN2 and increase the cooling effect. This has made it possible to reduce the capacity of the compressor and heat exchanger used in cryogenic equipment, making it possible to downsize the cryogenic equipment itself.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing a typical embodiment of a He liquefaction machine used in the method of the present invention, Figs. 2 and 3 are explanatory diagrams showing a liquefaction machine used in a conventional He liquefaction method, and Fig. 4 is an explanatory diagram showing a typical embodiment of a He liquefaction machine used in the method of the present invention. FIG. 2 is an explanatory diagram showing an example of a liquefied He refrigerator used for. 1...Cold box 2...Compression a 3...He high pressure pipe 4.4
a, 4b, 5, 8, 7, 8.9 = heat exchanger 10.
11... Expander 12... Expansion valve 13...
Liquid N2 supply v14...N2 discharge pipe! 5...Liquid H
e storage tank 18... He low pressure pipe 17... vacuum pump 18... heat shield section 18... cryostat 20... object to be cooled

Claims (1)

[Claims] A method of pre-cooling a cryogenic device with liquid nitrogen, characterized in that liquid nitrogen is supplied to a pre-cooling section formed in a low-pressure atmosphere, and cooling is generated under conditions that lower the boiling point of the liquid nitrogen. How to pre-cool the device.