JPH0579717A - Helium refrigerator - Google Patents

Abstract

PURPOSE:To facilitate the regulation of the volume of generated coldness by operation mode and make possible the back-up for a trouble in a turbine by providing the method of coldness generation that is higher than the temperature level of liquid nitrogen by means of two kinds, namely liquid nitrogen and a high temperature expansion turbine. CONSTITUTION:In operation modes which require much of coldness generation such as in pre-cooling operation, liquefaction operation, etc., valves 32 and 34 are closed to keep the condition that the helium does not flow to a high temperature expansion turbine 16, and a valve 42 is closed and a valve 43 is opened to make the coldness recovery line of the expansion turbine an open system. A valve 41 is opened and liquid nitrogen is supplied from a liquid nitrogen supply line 21. And, the ordinary operation of the expansion turbine 16 stops due to a trouble, helium is switched to liquid nitrogen as a back-up in the same way. Further, a helium refining device 61 is added to make minimum the helium that is consumed for removing the residual nitrogen that stays in the system and, at the same time, make the time for switching short.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryogenic helium refrigerator used for cooling superconducting equipment.

[0002]

2. Description of the Related Art A conventional device will be described with reference to FIG.

The helium gas compressed by the low-stage compressor 1 and the high-stage compressor 2 is separated into oil by the oil separation unit 3, enters the cold box 5, and returns by the heat exchanger 6 to the helium gas and heat. Replaced and cooled. Part of the helium gas expands in two stages in the high-temperature expansion turbine 16 to generate cold, the heat exchanger 6 recovers the cold, and returns to the suction side of the high-stage compressor 2. The other helium gas is further cooled in the heat exchanger 7, and a part of the helium gas is expanded in two stages in the expansion turbine 17 to generate cold, and joins with the returned helium gas. The other helium gas is further cooled by the heat exchanger 7, expanded by the JT valve 39, sent to the cryostat 12 through the low temperature transfer pipe 10, and part of it becomes liquid helium and collects in the liquid helium tank 14. The cooled body 13 is cooled. One gas helium becomes return gas helium, returns to the cold box 5 through the low temperature transfer pipe 11, passes through the heat exchangers 7 and 6, and returns to the suction side of the low-stage compressor 1.

The discharge and suction pressures of these compressors 1 and 2 are
By exchanging gas with the intermediate pressure tank 4 via the pressure adjusting valves 31 and 32, the pressure is adjusted to be constant.

Regarding such a helium refrigerator, for example, Advances in Cryogenic Engineering, Vol. 31, (1986), pages 693 to 698 (Advances in Cryogen).
ic Engineering, Vol. 31 , (19
86) pp693-698).

[0006]

In the above-mentioned prior art, the only method of producing cold on the higher temperature side than the liquid nitrogen temperature level is by using a high temperature expansion turbine. Adjustment of the amount of cold produced by changing the operation mode and turbine failure. There was a problem with the backup at the time.

[0007] The present invention is directed to a more complete change in the operation mode regarding the method of generating cold above the liquid nitrogen temperature level of the helium refrigerator.

[0008]

In order to achieve the above object, there are two types of cold generation methods on the high temperature side of the liquid nitrogen temperature level of a helium refrigerator, one is liquid nitrogen and the other is high temperature expansion turbine. In addition to minimizing the helium gas consumed to remove the nitrogen remaining in the system when switching from liquid nitrogen to a high temperature expansion turbine,
A helium purifier was added to make the switching time shorter.

[0009]

The helium gas at the outlet of the high temperature expansion turbine is introduced so that the liquid nitrogen can be switched and supplied to the high temperature expansion turbine cold recovery line for heat recovery of the cold between the liquid nitrogen temperature level and the room temperature level.

In operation modes such as precooling operation and liquefaction operation which require a large amount of cold generation, liquid nitrogen is used as a cold generation source at a temperature higher than the liquid nitrogen temperature level to increase the amount of cold generation. ..

In general, since the amount of cold of liquid nitrogen is almost equal to the latent heat and the sensible heat, when the cold is recovered by a heat exchanger, the sensible heat such as helium gas is only recovered. Compared to, the heat transfer area of the heat exchanger is about half. Further, since the liquid nitrogen is stored in the liquid nitrogen storage tank, it is possible to easily increase the supply flow rate. As described above, the amount of cold generation can be significantly increased as compared with the case of using the high temperature expansion turbine.
In normal operation, when the high temperature expansion turbine stops due to a failure or the like, liquid nitrogen is used as a backup. Further, in the initial precooling operation, when a gas having a liquid nitrogen temperature level or higher is used, it is possible to stop all the expansion turbines that are rotating bodies and perform the initial precooling using only liquid nitrogen as a cold generation source.

When switching from the use of liquid nitrogen to the use of the high temperature expansion turbine, it is necessary to remove the nitrogen remaining in the high temperature expansion turbine cold recovery line to the outside of the system, and a nitrogen removing means is provided for this purpose.

At the time of switching the cold-generating means (high-temperature expansion turbine, liquid nitrogen) above the liquid nitrogen temperature level, since the cold-generating source above the liquid nitrogen temperature is eliminated, the capacity of the helium refrigerator is significantly reduced. In addition, the helium gas consumed to remove the residual nitrogen is expensive, so it must be minimized. A helium purifier is added to minimize the consumption of helium gas and to shorten the switching time.

By providing the control device, it is possible to smoothly switch the cold generating means (high temperature expansion turbine, liquid nitrogen) on the higher temperature side than the liquid nitrogen temperature level.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

The helium gas compressed by the low-stage compressor 1 and the high-stage compressor 2 is separated into oil by the oil separation unit 3, enters the cold box 5, and returns by the heat exchanger 6 to the helium gas and heat. It is replaced and cooled. Some of the helium gas is expanded in two stages in the high temperature expansion turbine 16 to generate cold, the heat exchanger 6 recovers the cold, and returns to the suction side of the high-stage compressor 2. The other helium gas is further cooled in the heat exchanger 7, and a part of the helium gas is expanded in two stages in the expansion turbine 17 to generate cold, and joins with the returned helium gas. The other helium gas is further cooled by the heat exchanger 7, expanded by the JT valve 39, sent to the cryostat 12 through the low temperature transfer pipe 10, and part of it becomes liquid helium and collects in the liquid helium tank 14. The cooled body 13 is cooled. One gas helium becomes return gas helium, returns to the cold box 5 via the low temperature transfer pipe 11, passes through the heat exchangers 7 and 6, and returns to the suction side of the low-stage compressor 1.

The discharge and suction pressures of the compressor are controlled by the pressure adjusting valve 3.
The gas is exchanged with the medium pressure tank 4 via 1, 32, so that the pressure is constantly adjusted.

In an operation mode such as a precooling operation or a liquefaction operation that requires a large amount of cold generation, the high temperature expansion turbine 16 is stopped and liquid nitrogen is used as a cold generation source to increase the amount of cold generation. That is, the valves 32 and 34 are closed so that there is no flow of helium gas to the high temperature expansion turbine 16, the valve 42 is closed, and the valve 43 is opened to open the high temperature expansion turbine cold recovery line. afterwards,
The valve 41 is opened, and liquid nitrogen is supplied from the liquid nitrogen supply line 21.

In normal operation, when the high temperature expansion turbine 16 is stopped due to a failure or the like, it is similarly switched to liquid nitrogen as a backup. In this case, since only the cold generated in the high temperature expansion turbine 16 is supplemented, the high temperature expansion turbine 16 can be backed up by supplying a relatively small amount of liquid nitrogen.

In the initial pre-cooling operation of the system, when a gas having a liquid nitrogen temperature level or higher is used, all the expansion turbines 16 and 17, which are rotating bodies, are stopped and only liquid nitrogen is used as a cold generation source. It becomes possible to precool.

Next, the procedure for switching from using liquid nitrogen to using the high temperature expansion turbine 16 will be described. First, the valve 41 is closed to stop the supply of liquid nitrogen. By stopping the supply of liquid nitrogen, the generation of cold on the higher temperature side than the liquid nitrogen temperature level disappears, and the medium pressure outlet temperature of the heat exchanger 6 rises, so that the liquid nitrogen held in the heat exchanger 6 evaporates. After the liquid nitrogen held in the heat exchanger 6 is evaporated, the valve 43 is closed, the valve 44 is opened, and the vacuum evacuation device 60 evacuates via the evacuation line 23 to form a high temperature expansion turbine cold recovery line. Most of the remaining nitrogen is removed outside the system. After that, the valves 33, 34, and 45 are opened to start the high-temperature expansion turbine 16, and a small amount of residual nitrogen is adsorbed and removed by the helium purifier 61 via the purification line 24 and returned to the high-stage compressor 2. When there is no nitrogen remaining in the high temperature expansion turbine cold recovery line, the valve 42 is opened and the valve 45 is closed.

The valves 46, 47, 48, 49, 50,
Reference numeral 51 is provided so that when the high-temperature expansion turbine 16 fails, only the high-temperature expansion turbine 16 is heated so that it can be removed and repaired, and the helium gas after replacement can be replaced. Further, the valves 52, 53 and 54 are provided so that the helium purifier 61 can also be used for the initial refining operation of the entire system.

As described above, since a complicated procedure is required to switch the cold generation source (high-temperature expansion turbine, liquid nitrogen) on the higher temperature side than the liquid nitrogen temperature level, a control device is provided to smoothly switch the temperature. It goes without saying that is effective.

According to this embodiment, since there are two types of cold generation on the higher temperature side than the liquid nitrogen temperature level, that is, liquid nitrogen and high temperature expansion turbine, it is easy to adjust the amount of cold generation depending on the operation mode. As a result, it is possible to back up when the high temperature expansion turbine stops, and in addition, it is possible to switch the cold generation source on the higher temperature side than the liquid nitrogen temperature level in a short time and minimize the helium gas consumed. This has the effect of improving reliability and enabling stable and efficient operation.

[0025]

According to the present invention, there are two types of cold generation on the higher temperature side than the liquid nitrogen temperature level: liquid nitrogen and high temperature expansion turbine. Therefore, the amount of cold generation can be adjusted by the operation mode. This makes it easier to back up when the high-temperature expansion turbine is stopped, and can switch the cold generation source on the higher temperature side than the liquid nitrogen temperature level in a short time, and the helium gas consumed can be minimized. This has the effect of improving reliability and enabling stable and efficient operation.

[Brief description of drawings]

FIG. 1 is a flow chart of an embodiment of the present invention.

FIG. 2 is a flow chart of a conventional example.

[Explanation of symbols]

1 ... Low-stage compressor, 2 ... High-stage compressor, 3 ... Oil separation unit, 5 ... Cold box, 6, 7 ... Heat exchanger, 10,
11 ... Low temperature transfer pipe, 14 ... Liquid helium tank, 16 ... High temperature expansion turbine, 17 ... Expansion turbine, 60 ... Vacuum drawing device, 61 ... Helium refiner.

Claims (4)

[Claims] 1. A cryogenic helium refrigerator comprising a compressor for compressing helium gas, a heat exchanger, an expansion turbine, a deep cooling pipe, a cold box having a deep cooling valve, etc., and an outlet temperature of the liquid nitrogen temperature level. It has a high temperature expansion turbine and a high temperature expansion turbine cold recovery line that introduces the outlet helium gas of the high temperature expansion turbine and exchanges and recovers the cold between the liquid nitrogen temperature level and the room temperature level. It is characterized by having a switching means so that liquid nitrogen can be switched and introduced into the line, and having a helium purifier for removing residual nitrogen in the high temperature expansion turbine cold recovery line when switching from using liquid nitrogen to using the high temperature expansion turbine. And a helium refrigerator. 2. A vacuum evacuation means for discharging residual nitrogen in the cold recovery line of the high temperature expansion turbine to the outside of the system when switching from using liquid nitrogen to using the high temperature expansion turbine. Helium refrigerator. 3. The helium refrigerator according to claim 1, further comprising a control device for smoothly switching between use of the high temperature expansion turbine and use of liquid nitrogen. 4. The helium refrigerating machine according to claim 1, wherein the helium purifier for removing residual nitrogen in the high temperature expansion turbine cold recovery line can also be used for the initial refining operation of the entire system. ..