JPH0674582A - Low temperature helium compressor and cooling method therefor - Google Patents

Abstract

PURPOSE:To provide a low temperature helium compressor and a method for cooling the same in which the facility cost of a nitrogen liquefying unit, connecting tubes, etc., can be reduced by decreasing a necessary amount of liquefied nitrogen, a control is simply, and there is no fear of a local strain due to pull-down. CONSTITUTION:The low temperature helium compressor is used for a nitrogen.helium two-stage cascade refrigerating cycle, and comprises a motor 12 for driving a helium compressor 11. The motor has a guide cylinder 14 surrounding the outer periphery of the motor at an interval, cooling fins 16 axially aligned between the cylinder and the outer periphery of the motor, and a helium. nitrogen heat exchanger 18. The fins are cooled with evaporated nitrogen gas, and further helium gas passed through the motor is indirectly cooled with nitrogen gas passed through the fins by the exchanger.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low temperature helium compressor and a cooling method thereof, and more particularly to an electric motor for driving a low temperature helium compressor used in a liquefaction apparatus for producing liquefied helium and a cooling method thereof.

[0002]

2. Description of the Related Art Liquid helium has the lowest boiling point among existing gases, and is used for superconducting power application equipment such as superconducting generators. In order to produce such liquefied helium, a binary refrigeration cycle as shown in FIG. 4 has been conventionally considered. That is, the liquefied helium production apparatus includes a helium refrigeration cycle including a compressor unit 52 containing a plurality of low temperature helium compressors 51 connected in series, and a helium liquefaction unit 53 that adiabatically expands and compresses the compressed helium. , A nitrogen cooling cycle consisting of a nitrogen liquefaction unit 54 for producing liquefied nitrogen and supplying it to the compressor unit 52, compressing helium gas in the compressor unit 52, and cooling the compressed helium gas with liquefied nitrogen, Next, the helium gas is further cooled in the helium liquefaction unit 53, adiabatically expanded to liquefy a part of the helium gas, and the produced liquefied helium is used in the superconducting power generator 55 and the like.

In the above-mentioned liquid helium production apparatus,
An electric motor 57 is used to drive the low temperature helium compressor 51, and it is necessary to cool the heat generated by the electric motor 57 in the compressor unit 52. Conventionally, the cooling of the electric motor 57 is performed by providing a jacket on the casing of the outer periphery of the stator of the electric motor, and introducing liquefied nitrogen into the jacket to cool the stator, the casing, etc., and at the same time, helium gas compressed by the compressor inside the electric motor. The inside of the electric motor was cooled by flowing a part of it. In this case, the liquefied nitrogen that passed through the jacket was supplied to the liquefied nitrogen 58 below the compressor unit, and the helium gas that passed through the inside of the motor was returned to the heat exchanger on the upstream side of the compressor.

[0004]

However, in the above-described cooling of the electric motor, in addition to the amount of liquefied nitrogen required for cooling helium, there is a problem that a considerable amount of liquefied nitrogen is needed for cooling the electric motor. . As a result, the nitrogen liquefaction unit 5
4 and the capacity of the connecting pipe with the compressor unit 52 are increased, and there is a problem that the equipment cost is increased. In addition, the temperature of the nitrogen returning to the nitrogen liquefaction unit 54 is considerably low (about 8
0K). Therefore, it is necessary to provide a connecting portion for a return pipe in a low temperature portion in the nitrogen liquefaction unit, which causes a problem that the nitrogen liquefaction unit becomes complicated and the equipment cost further increases.

Further, it is necessary to supply the liquefied nitrogen in two parts for cooling helium and for cooling the electric motor. Especially, since the electric motors have different loads, a flow control valve 59 for the liquefied nitrogen is provided for each electric motor. It was necessary to control this according to the operating conditions. Therefore, there is a problem in that independent control devices are required. Furthermore, when pre-cooling the compressor unit prior to the start of operation, the electric motor is rapidly cooled by liquefied nitrogen at a very low temperature (about 77K, -196 ° C), which may cause local distortion and prevent the electric motor from rapidly starting. was there.

The present invention was created to solve the above problems. That is, the object of the present invention is to reduce the required amount of liquefied nitrogen to reduce the equipment cost of the nitrogen liquefaction unit, the connecting pipe, etc., the control is simple, and there is no risk of local strain due to precooling. , To provide a low temperature helium compressor and its cooling method.

[0007]

According to the present invention, nitrogen
A low-temperature helium compressor used for a helium dual refrigeration cycle, comprising an electric motor for driving the helium compressor,
The electric motor has a guide tube surrounding the outer circumference of the electric motor with a gap, a cooling fin and an helium / nitrogen heat exchanger axially aligned with each other between the guide cylinder and the outer peripheral portion of the electric motor. The cooling fins are cooled by the evaporated nitrogen gas, and the helium / nitrogen heat exchanger is configured to indirectly cool the helium gas that has passed through the inside of the electric motor by the nitrogen gas that has passed through the cooling fins. Characterize.

According to a preferred embodiment of the present invention,
The guide cylinder is further provided with a guide plate for guiding the nitrogen gas evaporated by cooling the helium gas to the cooling fins and the helium / nitrogen heat exchanger. Furthermore, according to the present invention, there is provided a cooling method for a low temperature helium compressor used in a nitrogen / helium binary refrigeration cycle, wherein the outer periphery of an electric motor for driving the low temperature helium compressor by nitrogen gas evaporated by cooling the helium gas. And cooling the inside of the electric motor with helium gas, and further cooling the helium gas inside the electric motor with nitrogen gas that has cooled the outer peripheral portion of the electric motor.

[0009]

In the past, the electric motor was cooled by liquefied nitrogen, and the nitrogen evaporated in the compressor unit was returned to the nitrogen liquefaction unit as it is. However, in the present invention, conversely, the electric motor is cooled by liquefied nitrogen gas and liquefied. Nitrogen is only used for its original purpose. That is, according to the present invention described above,
A low-temperature helium compressor having a cooling fin and a helium / nitrogen heat exchanger provided axially aligned with each other between the guide tube and the outer peripheral portion of the electric motor, and using nitrogen gas evaporated by cooling the helium gas. The helium gas that cools the inside of the motor is cooled by the helium gas, and the helium gas that cools the inside of the motor is cooled by the nitrogen gas that cools the outside of the motor. Is considerably higher than in the past (eg, 78K to 117K). Therefore, the amount of liquefied nitrogen required to cool the heat generation of the same electric motor in the compressor unit is reduced, and the equipment cost of the nitrogen liquefaction unit, the connecting pipe, etc. can be reduced.

Further, since the electric motor is cooled by the evaporated nitrogen gas, there is no need for strict control as in the case of using liquefied nitrogen, and a control device is substantially unnecessary.
In addition, there is no possibility that local strain will occur due to pre-cooling.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram of an apparatus for producing liquefied helium using a low temperature helium compressor according to the present invention.
In this figure, the liquefied helium production apparatus is a helium refrigeration unit including a compressor unit 20 containing a plurality of low-temperature helium compressors 10 connected in series, and a helium liquefaction unit 53 that adiabatically expands and compresses the compressed helium. Cycle and compressor unit 20 for producing liquefied nitrogen
And a nitrogen cooling cycle consisting of a nitrogen liquefaction unit 30 supplied to the. That is, the liquefied helium production apparatus is a binary refrigeration cycle including a helium refrigeration cycle and a nitrogen cooling cycle.

In the use of this apparatus, the helium gas is compressed in the compressor unit 20, the compressed helium gas is cooled by the liquefied nitrogen 8, and then the helium gas is further cooled in the helium liquefaction unit 53 and then adiabatically expanded. Then, a part of it is liquefied and the produced liquefied helium is used in the superconducting generator 55 or the like. The helium liquefaction unit 53
It is composed of a heat exchanger, an expander, an expansion valve, and the like. In addition,
The helium liquefaction unit 53 and the superconducting generator 55 are shown in FIG.
Since it is the same as the conventional liquefied helium production apparatus shown in FIG.

Further, as shown in FIG. 1, a plurality of heat exchangers 2, 4, 6 for cooling the helium gas are provided in the compressor unit 20, and heat exchange is provided in the lower part of the compressor unit 20. Liquefied nitrogen 8 for cooling the reactors 2, 4, 6 is supplied to a higher level than the heat exchangers 2, 4, 6. Further, the nitrogen liquefaction unit 30 includes a compressor 32, an expansion valve 34,
It is a nitrogen cooling cycle consisting of a liquefied heat exchanger 36 and a low temperature heat exchanger 38, and another expansion valve 40 is provided in the liquefied nitrogen supply line connecting the upstream side of the expansion valve 34 and the inside of the compressor unit 20. ing. Expansion valve 4 for low temperature and high pressure nitrogen
The pressure is reduced by 0, and most of the liquefied nitrogen is supplied to the compressor unit 20. The pressure inside the compressor unit 20 is normal pressure (1 atm), and about 77 K of liquefied nitrogen and nitrogen gas are supplied, and the liquefied nitrogen mixes with the liquefied nitrogen 8 in the lower part of the compressor unit. Further, a nitrogen gas return line is provided between the upper part of the compressor unit 20 and the connecting portion of the liquefaction heat exchanger 36 and the low temperature heat exchanger 38, and the evaporated nitrogen gas is passed through this line. It is directly returned to the nitrogen liquefaction unit 30.

FIG. 2 is an overall configuration diagram of the low temperature helium compressor according to the present invention. As shown in FIG. 2, the low temperature helium compressor 10 includes an electric motor 12 that drives a helium compressor 11.
The motor 12 includes a guide tube 14 surrounding the motor outer periphery with a gap, and cooling fins 16 and helium / nitrogen heat provided axially aligned with each other between the guide tube 14 and the outer peripheral portion of the motor 12. And a exchanger 18. The electric motor 12 is
The rotor 12a, the bearing 12b, the stator 12c, etc. are provided, and the helium compressor 11 is driven by the rotation of the rotor 12a. The compressed helium gas can be introduced into the electric motor 12. The cooling fins 16 are preferably aluminum fins fitted around the casing of the electric motor. The helium / nitrogen heat exchanger 18 indirectly cools the helium gas that has passed through the inside of the electric motor by the nitrogen gas that has passed through the cooling fins 16. The helium / nitrogen heat exchanger 18 is a fin-tube heat exchanger, and nitrogen gas flows around the fins and helium gas flows inside the tubes. Further, the guide cylinder 14 is provided with a guide plate 19 for guiding the nitrogen gas evaporated by cooling the helium gas to the cooling fin 16 and the helium / nitrogen heat exchanger 18. The guide plate 19 preferably partitions the interior of the compressor unit 20 and guides the entire amount of evaporated nitrogen gas to the guide cylinder 14.

According to the cooling method of the low temperature helium compressor of the present invention, the electric motor 12 for driving the helium compressor 11 by the nitrogen gas evaporated by cooling the helium gas.
The outer peripheral portion is cooled, the inside of the electric motor 12 is cooled with helium gas, and the helium gas that has cooled the inside of the electric motor is further cooled with nitrogen gas that has cooled the outer peripheral portion of the electric motor. That is, in FIG. 1, all of the nitrogen gas that has undergone heat exchange in the heat exchangers 2, 4, and 6 and has evaporated is the cooling fin 16 and the guide cylinder 14.
After taking the heat generated by the electric motor 12 through the space between them, it enters the helium / nitrogen heat exchanger 18 provided at the upper part of the electric motor 12, and exchanges heat with the helium gas after cooling the inside of the electric motor flowing inside the tube, and the compressor unit. It goes out of 20 and is returned to the nitrogen liquefaction unit 30. On the other hand, helium / nitrogen heat exchanger 18
The helium gas cooled in (1) is returned to the outlet side of the compressor at the previous stage, and is again sucked into the compressor via the heat exchanger. Further, in the example of FIG. 1, in the case of the one-stage compressor, the cooled helium gas merges with the inlet gas and enters the heat exchanger 2.

According to the present invention, the cooling fin 16 and the helium / nitrogen heat exchanger 18 are provided between the guide cylinder 14 and the outer peripheral portion of the electric motor 12 so as to be axially aligned with each other. The nitrogen gas evaporated by the cooling of the gas cools the outer peripheral portion of the electric motor 12 that drives the helium compressor 11, and the helium gas cools the inside of the electric motor.
Further, since the helium gas that has cooled the inside of the electric motor is cooled by the nitrogen gas that has cooled the outer peripheral portion of the electric motor, the temperature of the nitrogen gas that exits the compressor unit becomes higher than in the conventional case (for example, 78K to 117K). That is, by heat exchange, the entire amount of heat generated by the electric motor is absorbed by the nitrogen gas, and the amount of liquefied nitrogen consumed is reduced. Therefore, the amount of liquefied nitrogen required to cool the heat generated by the same electric motor in the compressor unit 20 is reduced. As a result, the equipment cost of the nitrogen liquefaction unit, the connecting pipe, etc. can be reduced.

Further, since the electric motor load and the amount of evaporated nitrogen gas are almost proportional to each other, and the electric motor and the compressor are directly connected and are operated in the same temperature range, the flow rate control of the nitrogen gas in the electric motor cooling system is performed. Not particularly necessary. That is, since the electric motor is cooled by the evaporated nitrogen gas, there is no need for strict control as in the case of cooling by liquefied nitrogen, and a control device is substantially unnecessary. Further, since the pre-cooling uses the gas after cooling the heat exchanger, it is not rapidly cooled, and there is no possibility of causing local distortion in the electric motor.

FIG. 3 shows an example of calculation comparing the material balance in the nitrogen liquefaction unit between (A) the conventional method and (B) the method of the present invention.
(A) and (B) compare the case where the same amount of heat is recovered from the electric motor by cooling. As is clear from the comparison between (A) and (B), the return temperature of nitrogen gas is 7
It is 117K in (B) compared to 8K, which is considerably higher in the present invention. This is because the vaporized nitrogen gas is not returned as it is as in the conventional case, but is returned after being used for cooling the electric motor in the present invention. Due to this difference in temperature, the total amount of nitrogen gas required is (A) 6,325 kg / h (B) 6,
290 kg / h, and the amount supplied to the compressor unit is (A) 1,398 kg / h to (B) 1,136 kg / h
To about 20%. Furthermore, the return temperature is 117K
Therefore, the returned nitrogen gas can be directly returned to the connection portion between the liquefaction heat exchanger 36 and the low temperature heat exchanger 38. Therefore, it is not necessary to provide a connecting portion for the return pipe in the low temperature portion in the nitrogen liquefaction unit as in the conventional case.

[0019]

As described above, according to the present invention, 1. Since the supply amount of liquefied nitrogen is small and the nitrogen gas return temperature is high, it is easy to connect the nitrogen liquefaction system and the helium liquefaction system and design both equipments. 2. Since the supply amount of liquefied nitrogen is small, the nitrogen liquefaction unit can be small. 3. No need for a controller for cooling the motor Since the pre-cooling uses the gas after cooling the heat exchanger, there is an effect that there is no possibility of causing local distortion due to a sudden change in the temperature of the electric motor.

That is, in summary, conventionally, the electric motor was cooled by liquefied nitrogen, and the liquefied nitrogen vaporized in the compressor unit was returned to the nitrogen liquefaction unit as it is. To cool the motor,
Since liquefied nitrogen is used only for its original purpose, it is possible to reduce the required amount of liquefied nitrogen and reduce the equipment cost of the nitrogen liquefaction unit, connecting pipes, etc., easy control, no controller is required, and pre-cooling is possible. This has the effect of eliminating the possibility of local distortion.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an apparatus for producing liquefied helium using a low temperature helium compressor according to the present invention.

FIG. 2 is an overall configuration diagram of a low temperature helium compressor according to the present invention.

FIG. 3 is a comparative example of material balance in a nitrogen liquefaction unit.

FIG. 4 is an overall configuration diagram of a conventional liquid helium production apparatus.

[Explanation of symbols]

 2, 4, 6 heat exchanger 8 liquefied nitrogen 10 low temperature helium compressor 11 helium compressor 12 electric motor 14 guide cylinder 16 cooling fin 18 helium / nitrogen heat exchanger 19 guide plate 20 compressor unit 30 nitrogen liquefaction unit 32 compressor 34 Expansion valve 36 Liquefied heat exchanger 38 Low temperature heat exchanger 40 Expansion valve 53 Helium liquefaction unit 55 Superconducting generator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kei Asakura 3-2-16 Toyosu, Koto-ku, Tokyo Ishikawajima Harima Heavy Industries, Ltd. Toyosu General Office (72) Inventor Mikiro Mori 3-2 Toyosu, Koto-ku, Tokyo No. 16 Ishikawajima Harima Heavy Industries Co., Ltd.Toyosu General Office

Claims (3)

[Claims] 1. A low-temperature helium compressor used in a nitrogen / helium binary refrigeration cycle, comprising a motor for driving the helium compressor, the motor including a guide cylinder surrounding the motor outer periphery at intervals, and the guide cylinder. It has a cooling fin and a helium / nitrogen heat exchanger provided axially aligned with each other between the cylinder and the outer peripheral portion of the electric motor, the cooling fin being cooled by the evaporated nitrogen gas, and the helium / nitrogen heat exchanger. The low temperature helium compressor is characterized in that the nitrogen heat exchanger indirectly cools the helium gas that has passed through the inside of the electric motor by the nitrogen gas that has passed through the cooling fins. 2. The guide cylinder is further provided with a guide plate for guiding the nitrogen gas evaporated by cooling the helium gas to the cooling fins and the helium / nitrogen heat exchanger. Low temperature helium compressor as described in. 3. A cooling method for a low temperature helium compressor used in a nitrogen / helium binary refrigeration cycle, wherein the nitrogen gas evaporated by cooling the helium gas comprises:
Cooling the outer peripheral portion of the electric motor driving the helium compressor, cooling the inside of the electric motor with helium gas, and further cooling the helium gas cooling the inside of the electric motor with nitrogen gas that has cooled the outer peripheral portion of the electric motor. Cooling method for low temperature helium compressor.