JPH05280816A - Cryogenic refrigerating machine - Google Patents

Abstract

PURPOSE:To obtain a cryogenic refrigerating machine which exhibits high oil-separating performance, dispenses with complicated piping, and is compact and has high reliability of performance by using an oil-separating device comprising a mist separator and filters in multistages all arranged in a concentric, cylindrical structure. CONSTITUTION:An inlet for gas is formed in a circular direction in the middle of a pressure container 30. Partition walls 32 are provided on the inner side of the pressure container 30 and oil filters 33 are provided in two stages and in a concentric, cylindrical structure on the inner side of the partition walls 32. Two outlets for oil are formed in the bottom of the pressure container 30 and an oil return pipe is connected to each of them. These oil return pipes are connected to the suction side of a compressor. An outlet 35 for helium gas is provided at the top between the outer circumference of the filters and the partition walls 32 and connected to an adsorber. This structure makes it possible for a cryogenic refrigerating machine to exhibit high oil-separating performance, dispense with complicated piping, and be compact and have high reliability of performance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small cryogenic refrigerator using helium or the like as a refrigerant.

[0002]

2. Description of the Related Art As a small refrigerator for refrigerating to an extremely low temperature of about 10 to 20 [K] in absolute temperature, a cold head utilizing the principle of Gifford McMahon (GM) cycle, reverse Stirling cycle, etc. And a helium compressor are combined and widely used for cooling superconducting magnets such as MRI and for cryopumps which are high vacuum pumps. As an example, the basic configuration of a cryogenic refrigerator using the GM cycle will be described with reference to FIG.

Equipment such as a gas cooler (2), an oil separator (3) and an adsorber (4) are provided on the discharge side of the compressor (1), and an intake valve (6) and a GM are connected via a pipe (5).
Connected to a cold head (7). The GM cold head (7) includes a cylinder (8), a first stage regenerator (9), a first stage gas seal (10), and a second stage regenerator (1).
1), 2nd stage gas seal (12), regenerator drive mechanism (13)
Composed of. The first-stage regenerator (9) is connected in series with the second-stage regenerator (11) by a pin (14), both of which are driven by the regenerator drive mechanism (13) to the top dead center of the cylinder (8), It reciprocates at the same time in a fixed cycle between bottom dead centers. 1st stage, 2nd
Gas seals (10) and regenerators (9) and (11) on both stages
(12) is provided to prevent the flow of the refrigerant helium gas in the gaps between the regenerators (9) and (11) and the cylinder (8), respectively. The refrigerant helium gas is stored in the regenerators (9) and (11).
The structure is such that it flows through the cold storage materials (15) and (16) placed inside. An exhaust valve (17), a surge tank (18) and the like are provided between the GM cold head (7) and the gas suction side of the compressor (1) and are connected by a pipe (5).

The refrigerant whose pressure has been raised by the compressor (1) is cooled by the gas cooler (2), and impurities such as oil mist mixed in the refrigerant are removed by the oil separator (3). After the impurities are adsorbed by the adsorber (4), they flow from the intake valve (6) into the GM type cold head (7). Helium gas that is not liquefied even at extremely low temperatures is generally used as the refrigerant. Opening / closing timing of intake valve (6) and exhaust valve (17) and cylinder (8) of regenerator (9), (11)
The positional relationship within is as shown in FIG. That is, when the regenerators (9) and (11) are at the bottom dead center, the intake valve (5) opens and high-pressure helium gas at room temperature flows into the upper space of the cylinder (8). At this time, the exhaust valve (17) remains closed. The regenerators (9) and (11) move to the top dead center with the intake valve (5) open, and the refrigerant helium gas and the regenerator material (15) and heat of the first-stage regenerator (9) storing cold. It flows into the first-stage expansion chamber (19) while being exchanged and cooled, and then exchanges heat with the regenerator material (16) of the second-stage regenerator (11) to be cooled to a lower temperature and then the second-stage expansion chamber. It flows into (20).
At the same time when the regenerators (9) and (11) reach the top dead center, the intake valve (6) is closed and the exhaust valve (17) is opened. Then the exhaust valve (1
Since 7) is connected to the suction side of the low pressure compressor (1), the helium gas undergoes adiabatic expansion and the first and second stages
Cold occurs in the expansion chambers (19) and (20) of the stage. And the exhaust valves (17) until the regenerators (9), (11) reach bottom dead center.
Is open, the cold helium gas in the second-stage expansion chamber (20) exchanges heat with the regenerator material (16) of the second-stage regenerator (11) to store cold in the regenerator material (16), and the refrigerant is The temperature rises and flows into the first expansion chamber (19). Similarly, the first stage regenerator (9)
The heat regenerator material (15) and helium gas exchange heat to raise the temperature to room temperature, flow through the exhaust valve (17) to the outside of the GM cold head (7), and then to the suction side of the compressor (1). Going back. By repeating the above cycle, the expansion chambers (19) and (20) of the first and second stages are cooled to an extremely low temperature. The first stage expansion chamber (19) cools the liquid nitrogen temperature level of about 80 [K], and the second stage expansion chamber (20) cools less than 20 [K] below the cryopump or superconducting magnet. It is a method of using an ordinary cryogenic refrigerator when used for cooling.

[0005]

In such a cryogenic refrigerator, the oil separator (3) plays a very important role. Since the compressor (1) is oil-lubricated and the oil injection method is usually used as a cooling method for the helium compressor, a large amount of refrigeration is contained in the helium gas discharged from the compressor (1). Machine oil is mixed. If this oil flows into the GM type cold head (7), the helium gas flows from the normal temperature part to the cryogenic part, so that the oil is frozen in the process, and the frozen oil is cooled by the regenerator (9),
It accumulates in the (11) and in the cylinder (8) to impede the gas flow and deteriorate the refrigerating capacity, and in extreme cases, it causes galling and destroys the GM cold head (7). When it is used for cooling a magnetic resonance diagnostic apparatus using a superconducting magnet, the small refrigerator is used continuously for a long period of time such as operating continuously for about one year.
Even in such a long period of time, the oil content flowing into the GM cold head (7) must be kept to a very small amount. Therefore, an oil treatment system such as an oil separator (3) and an adsorber (4) is usually provided. This oil treatment system will be described in more detail.

FIG. 6 shows details of the oil separation system of the conventional apparatus. The oil separator (3) is a mist separator (2
It consists of 1) and a multi-stage filter (22). These are connected by a pressure pipe (23). In addition, the mist separator (2
1), the filter (22) is provided with an oil return pipe (24) for collecting the separated oil. Filter (2
The helium gas exiting 2) passes through the adsorber (4) and G
It flows into the M type cold head (7).

A large amount of oil droplets are mixed in the helium gas discharged from the compressor (1). For example, the mist separator (21) separates the oil droplets by a cyclone method. FIG. 7 shows an example of the mist separator (21). The gas that has flowed in from the gas inlet (25) in the circumferential direction is separated into oil by centrifugal force, the mist-like oil is separated by the wire mesh (26), and is discharged from the upper gas outlet (27).
The separated oil flows downward by gravity and is discharged from the oil outlet (28). The oil separated here is recovered from the suction side of the compressor (1) to the compressor (1) through an oil return pipe (24) attached to the lower portion of the mist separator container. At this stage, the oil concentration in helium gas is still several thousand p
pm order and resin filter (2
9) Perform oil separation. FIG. 8 shows an example of the oil filter. The helium gas flowing in from the upper part of the container is separated from the oil by the resin filter (29) and discharged from the upper part of the container. Oil is discharged from the oil outlet (28) at the bottom of the container.
This kind of oil filter is usually a multi-stage combination,
It is possible to separate the impurity concentration at the outlet of the final stage to the ppb order. However, the resin filter (29) alone has a limit in how many stages there are. Therefore, the activated carbon filled in the adsorber (4) is finally adsorbed to remove oil.

Since the adsorber (4) adsorbs oil to the activated carbon, if the oil is adsorbed to the saturated amount, the operation of the refrigerator must be stopped and the adsorber must be replaced with a new one. Therefore, if the performance of the oil separator (3) is poor, the adsorber (4) must be replaced frequently. To improve the performance of the oil separator (3), use a cyclone-type mist separator (21) or a large filter (29), and use a multi-stage filter (29). This is good, but there is a problem in that it causes the device to become large.

Further, since the multi-stage filter (29) must be connected to each other by the pressure pipe (23), complicated pipes are inevitably required, and the flow path of helium gas is enlarged and reduced by the pipe (23). However, there is a problem in that the pressure loss increases due to the discontinuous flow path such as, and the efficiency of the refrigerator decreases. Further, since the pipe (23) is complicated, it is difficult to assemble, and there is a high possibility that gas leakage will occur due to vibration or the like during long-term operation, and long-term reliability is also lacking.

In view of these points, the present invention has a high oil separation performance, is compact, and is equipped with an oil separator having no complicated piping, which enables long-term continuous operation and is excellent in long-term reliability. It is intended to provide a cryogenic refrigerator.

[0011]

In order to achieve the above object, the oil separator of the cryogenic refrigerator according to the present invention is arranged in a concentric cylindrical shape with a mist separator and a multistage filter, and the oil separator is housed in one pressure vessel. It has a different configuration.

[0012]

In the cryogenic refrigerator of the present invention, since a cyclone type mist separator and a multi-stage filter are arranged concentrically in a single pressure vessel, a high oil separation with the same size as the conventional one is achieved. Can demonstrate performance,
Further, since there is no complicated piping, there is no risk of leakage and the like, and high reliability is achieved.

[0013]

1 and 2 show an embodiment of the present invention.
FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention, and FIG. 2 is a transverse sectional view of the same. For the parts not shown below, the numbers in the figures already explained are used. A gas inlet (31) is provided in the circumferential direction near the center of the pressure vessel (30).
A partition (32) is provided inside the pressure vessel (30), and a two-stage oil filter (33) is concentrically provided inside the partition (31). There are two oil outlets (34) in the lower part of the pressure vessel (30), and the oil return pipes (24) are connected to them respectively. The oil return line is a compressor (1)
Is connected to the suction side of. A helium gas outlet (35) is provided in an upper portion between the outer periphery of the filter (29) and the partition wall (32) and is connected to the adsorber (4).

In such a structure, the helium gas discharged from the compressor (1) and containing a large amount of oil is introduced into the pressure vessel (30) from the oil separator gas inlet (31) in the circumferential direction. .. The oil droplets are separated from helium by centrifugal force, and the separated oil is collected in the lower part of the oil separator by gravity and is collected from the oil outlet (34) through the oil return pipe (24) to the compressor (1). .. On the other hand, helium gas is used at the filter inlet (3
It is introduced from 6) into the center of the oil separator (3). Helium gas flows from the inside to the outside of the filter tube (33), and the oil is collected in the filter tube (33). The separated oil collects in the lower part due to gravity, goes out from the oil outlet (34) in the central lower part, and is collected in the compressor (1) through the oil return pipe (24). The helium gas from which the oil has been separated flows from the upper oil separator gas outlet (35) and flows into the adsorber (4).

In the oil separator of the cryogenic refrigerator of this embodiment, since the pressure vessel is one, centrifugal separation can be effectively performed on the outermost peripheral side of the vessel, so that a compact size and high oil separation can be achieved. It can exert its performance. Further, since complicated pipes are eliminated, there is no reduction in refrigerator efficiency caused by pressure loss due to expansion / contraction of pipes, and there is no fear of gas leakage, so that high long-term reliability can be obtained.

Another embodiment is shown in FIG. In this embodiment, a glass wool (37) filled layer is used as an oil separation layer instead of the resin filter (33). Also in this embodiment, by using one pressure vessel, centrifugal separation is effectively performed on the outermost peripheral side, and since complicated pipes are eliminated, it has high oil separation performance and high long-term reliability.

[0017]

As described above, since the cryogenic refrigerator according to the present invention uses the oil separator in which the mist separator and the multistage filter are concentrically arranged,
It is possible to provide a cryogenic refrigerator that can exhibit high oil separation performance, eliminates complicated piping, and is compact and has high reliability.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an oil separator of a cryogenic refrigerator of the present invention.

2 is a cross-sectional view of FIG.

FIG. 3 is a diagram showing a cryogenic refrigerator according to another embodiment of the present invention.

FIG. 4 is a block diagram of a conventional device

FIG. 5 is a diagram showing an operation of a conventional device.

FIG. 6 is a diagram showing details of an oil separator of a conventional device.

FIG. 7 is a block diagram of a mist separator of an oil separator of a conventional device.

FIG. 8 is a configuration diagram showing a filter of an oil separator of a conventional device.

[Explanation of symbols]

 1 ... Compressor 2 ... Gas cooler 3 ... Oil separator 4 ... Adsorber 5 ... Piping 6 ... Intake valve 7 ... GM type cold head 8 ... Cylinder 9 ... First stage regenerator 10 ... First stage gas seal 11 ... Second Stage regenerator 12 ... Second stage gas seal 13 ... Regenerator drive mechanism 14 ... Pin 15 ... First stage regenerator material 16 ... Second stage regenerator material 17 ... Exhaust valve 18 ... Surge tank 19 ... First stage expansion chamber 20 ... Second stage expansion chamber 21 ... Mist separator 22 ... Filter 23 ... Piping 24 ... Oil return piping 25 ... Gas inlet 26 ... Wire mesh 27 ... Gas outlet 28 ... Oil outlet 29 ... Filter 30 ... Container 31 ... Gas inlet 32 ... Partition 33 ... Filter 34 ... Oil outlet 35 ... Gas outlet 36 ... Filter inlet 37 ... Glass wool

Claims (2)

[Claims] 1. A cryogenic refrigerator having a compressor,
As a separator for removing impurities such as oil contained in the refrigerant discharged from the compressor, a cyclone separator and a filter are concentrically arranged in a cylindrical shape, and these are housed in a single pressure vessel. Cryogenic refrigerator. 2. The cryogenic refrigerator according to claim 1, wherein the cyclone separator is provided on the outermost peripheral portion of the pressure vessel.