JPH0784961B2 - Helium liquefier - Google Patents

Description

The present invention relates to a cryogenic helium liquefying refrigerator used for cooling superconducting equipment and the like.

[Conventional technology]

 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 to the heat exchanger 6 to exchange heat with the helium gas. , Cooled. Part 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 by the heat exchanger 7, and a part of the helium gas is expanded in two stages by the expansion turbine 17 to generate cold and join the returned helium gas. The other helium gas is further cooled by the heat exchanger 7 and expanded by the JT valve 39, is sent to the cryostat 12 through the low temperature transfer pipe 10, becomes a part of liquid helium, and is stored in the liquid helium tank 14. The non-cooling body 13 is cooled. One gas helium becomes return gas helium, and returns to the cold box 5 via the low temperature transfer pipe 11 and the heat exchangers 7, 6
To the suction side of the low-stage compressor 1.

The discharge and suction pressures of the compressor are controlled by exchanging gas with the intermediate pressure tank 4 through the pressure adjusting valves 31 and 32.
Adjusted to a constant.

Since a large amount of impure gas exists in the system at the initial stage of operation, the gas helium in the low pressure line is compressed by the recovery compressor 52 via the gas bag 51, purified by the helium purifier 53 and returned to the medium pressure line.

Such a helium liquefier refrigerator is described in, for example, Advances in Cryogenic Engineering Volume 31 (1986), pages 693 to 698 (Advanc
es in Cryogenic Engineering, Vol31, (1986) PP693 ~ 6
98).

[Problems to be Solved by the Invention]

In the above conventional technology, the method of generating cold on the higher temperature side than the liquid nitrogen temperature level is only by the high temperature expansion turbine,
There was a problem in adjusting the amount of cold generation by changing the operation mode and backup in case of turbine failure, and further, there was a problem that purification by an external refiner was necessary at the time of initial purification.

The present invention relates to a method of generating cold on the higher temperature side than the liquid nitrogen temperature level of a helium liquefaction refrigerator, and is aimed at more complete correspondence to a change in the operation mode and ensuring of redundancy, and further, an inexpensive and efficient initial stage. The purpose is to supply a helium liquefier refrigerator that can realize purification.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, there are two types of cold generation method on the high temperature side of the liquid nitrogen temperature level of the helium liquefier refrigerator, one using liquid nitrogen and the other using a high-temperature expansion turbine, and yet another object described above is achieved. To this end, a system for adhering or adsorbing an impure gas is added to the above-described method for generating cold by liquid nitrogen.

[Action]

Medium pressure helium gas, which is the gas discharged from the compressor, is split before entering the cold box, and heat is exchanged with liquid nitrogen in addition to the cold generation above the liquid nitrogen temperature level due to the original heat exchanger and high temperature expansion turbine. Install a liquid nitrogen heat exchanger.

In an operation mode in which a large amount of cold is required, such as a liquefaction operation, liquid nitrogen heat exchanger must be operated in addition to the cold generation by the high temperature expansion turbine to increase the amount of cold generation. Further, in normal operation, when the high temperature expansion turbine stops due to a failure or the like, the liquid nitrogen heat exchanger is operated as a backup. Also, in the initial cooling operation of the system, when using a gas above the liquid nitrogen temperature level, it is possible to stop all the expansion turbines that are rotating bodies and operate the liquid nitrogen heat exchanger to perform initial cooling. Become. At that time, the impure gas in the system is accumulated in the helium line of the liquid nitrogen heat exchanger, but the impure gas can be removed to the outside of the system by heating and emptying the helium line after completion of the initial cooling. .

Further, by detecting the helium gas temperature at the liquid nitrogen temperature level, it becomes clear that the amount of refrigeration above the liquid nitrogen temperature level is excessive or insufficient, and it becomes possible to adjust the gas flow rate flowing to the liquid nitrogen heat exchanger.

〔Example〕

 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 to the heat exchanger 6 to exchange heat with the helium gas. , Cooled. Part 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 by the heat exchanger 7, and a part of the helium gas is expanded in two stages by the expansion turbine 17 to generate cold and join the returned helium gas. The other helium gas is further cooled by the heat exchanger 7 and expanded by the JT valve 39, sent to the cryostat 12 through the low temperature transfer pipe 10, and partly becomes liquid helium and collects in the liquid helium tank 14, The non-cooling 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 the compressor are controlled by exchanging gas with the intermediate pressure tank 4 through the pressure adjusting valves 31 and 32.
Adjusted to a constant.

In an operation mode in which a large amount of cold is required, such as a liquefaction operation, the liquid nitrogen heat exchanger 8 is operated in addition to the cold generation by the high temperature expansion turbine 16 to increase the amount of cold generation. That is, part of the medium pressure gas that enters the cold box 5 is caused to exchange heat with liquid nitrogen in the liquid nitrogen heat exchanger 8, and helium gas at the liquid nitrogen temperature level is passed through the adsorber 9 and the main medium pressure line. Join to. As a result, the amount of cold generation above the liquid nitrogen temperature level will increase.

In normal operation, when the high temperature expansion turbine 16 is stopped due to a failure or the like, the liquid nitrogen heat exchanger 8 is operated as a backup. That is, the valve 33 is closed, there is no gas flow to the high temperature expansion turbine, and the valve 47
All the helium gas that enters the cold box 5 via the heat exchanger 6 exchanges heat with the return gas helium in the heat exchanger 6, merges with the helium gas that has passed through the liquid nitrogen heat exchanger 8, and proceeds to a lower temperature portion. Since it only compensates for the cold generated in the high temperature expansion turbine 16, the high temperature expansion turbine can be backed up by supplying a relatively small amount of helium gas to the liquid nitrogen heat exchanger 8.

Further, in the initial 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 the liquid nitrogen heat exchanger 8 is operated to perform the initial cooling. It becomes possible. At that time, the impure gas in the system is accumulated in the helium line of the liquid nitrogen heat exchanger, but after the initial cooling is completed, the helium gas line is closed.
By closing 41 and 42, the valve 43 is closed and the supply of liquid nitrogen is stopped.After that, the valves 44 and 45 are opened and heated by nitrogen gas, then the valves 44 and 45 are closed and the valve 46 is closed. Open the vacuum and pull the vacuum with the vacuum device 25 to remove the impure gas from the system.
It can be removed. After the initial cooling is completed, the cooling can be further performed by starting the high temperature expansion turbine 16 even when the liquid nitrogen heat exchanger 8 is heated and evacuated.

Further, by detecting the temperature of the helium gas at the liquid nitrogen temperature level with the temperature detector 63, it is found in the control device 61 that the excess or deficiency of the amount of refrigeration above the target nitrogen temperature level is exceeded and the gas to be passed to the liquid nitrogen heat exchanger 8 By adjusting the flow rate with the valves 41 and 43, optimum valve operation corresponding to the change in the operation mode becomes possible. Also, with the liquid level detector 62,
By knowing the helium level in the liquid helium tank 14,
It goes without saying that a more appropriate operation mode can be grasped.

According to the present embodiment, there are two types of cold generation on the higher temperature side than the liquid nitrogen temperature level, one using liquid nitrogen and one using a high temperature expansion turbine, so it becomes easy to adjust the amount of cold generation depending on the operating mode. It is possible to back up when the high temperature expansion turbine is stopped, and since the impure gas can be adhered or removed by the liquid nitrogen heat exchanger and the adsorber during the initial cooling, the reliability of the helium liquefier refrigerator can be improved. The effect is that stable and efficient operation is possible.

〔The invention's effect〕

According to the present invention, there are two types of cold generation on the higher temperature side than the liquid nitrogen temperature level, one using liquid nitrogen and the other using a high temperature expansion turbine. It is possible to back up when the expansion turbine is stopped, and further, during the initial cooling, the impure gas can be coagulated or adsorbed and removed by the liquid nitrogen heat exchanger and the adsorber. There is an effect that stable and efficient operation can be performed.

[Brief description of drawings]

FIG. 1 is a flow chart of a helium liquefying refrigerator according to an embodiment of the present invention, and FIG. 2 is a flow chart of a conventional helium liquefying refrigerator. 1 ... Low-stage compressor, 2 ... High-stage compressor, 3 ... Oil separation unit, 5 ... Cold box, 6,7 ... Heat exchanger,
8 …… Liquid nitrogen heat exchanger, 9 …… Adsorber, 10,11 …… Low-stage transfer piping, 14 …… Liquid helium tank, 16 …… High temperature expansion turbine, 17 …… Expansion turbine, 25 …… Vacuum suction Equipment, 51 ...
… Gas bag, 52 …… Recovery compressor, 53 …… Refiner, 61…
… Control device, 62 …… Liquid level detector, 63 …… Temperature detector

Claims (4)

[Claims] 1. A normal temperature level having a liquid nitrogen heat exchanger for exchanging heat between liquid nitrogen and helium gas between a normal temperature level and a liquid nitrogen temperature level, and a high temperature expansion turbine whose outlet temperature is the liquid nitrogen temperature level. And a helium gas heat exchanger for exchanging heat between helium gas and helium gas between the liquid nitrogen temperature level and the liquid nitrogen temperature level, and the medium pressure gas as the compressor discharge gas is used as the liquid nitrogen heat exchanger. A helium liquefaction refrigerator capable of producing helium gas at a liquid nitrogen temperature level in a medium pressure line by introducing it to an exchanger or a high temperature expansion turbine or both. 2. The helium line of the liquid nitrogen heat exchanger is heated by flowing a warming gas to the impure gas adhering to the helium line when the heat exchanger with the liquid nitrogen is operating, and the helium line is heated. The helium liquefier refrigerator according to claim 1, wherein the impure gas can be discharged and removed to the outside of the system by drawing a vacuum. 3. The liquefied helium refrigeration according to claim 1 or 2, wherein an adsorber is provided on the low temperature side of the helium line of the liquid nitrogen heat exchanger to add an impure gas adsorption capacity at low temperatures. Machine. 4. The liquid nitrogen heat exchanger alone or at the high temperature expansion by detecting the helium gas temperature at the liquid nitrogen temperature level and adjusting the flow rates of the liquid nitrogen and helium gas flowing through the liquid nitrogen heat exchanger. The helium liquefier refrigerator according to claim 1, comprising a control device that enables optimization of parallel operation of the turbine and the liquid nitrogen heat exchanger.