GAS COMPRESSOR

Abstract: A gas compressor (10) comprising an hermetically sealed casing (11) within which is disposed a compressor (12) for compressing gas within the casing (11); conduit means (26,21,22) for supplying a gas to be compressed to the interior of the casing (11) and for discharging compressed gas from the interior of the casing (11); and cooling means (15) for cooling the compressor (12) characterised in that the cooling means (15) effects cooling of at least a part of the gas flowing through the conduit means (26,21,22).

Description: This invention relates to a gas compressor and, although the invention is not so restricted, it relates more particularly to a compressor for compressing a refrigerant gas, such as helium, employed in a refrigeration system. In a compressor for compressing helium gas, considerable heat is generated by the compressor during its operation because the adiabatic coefficient of the helium gas has the large value of K = 1.66. Cooling means have therefore previously been provided for cooling the compressor but these cooling means have not been particularly effective since they have effected direct cooling only of an hermetically sealed casing within which the compressor is disposed and have therefore relied on the inadequate heat conducting properties of the gas within the casing. According, therefore, to the present invention, there is provided a gas compressor comprising an hermetically sealed casing within which is disposed a compressor for compressing gas within the casing; conduit means for supplying a gas to be compressed to the interior of the casing and for discharging compressed gas from the interior of the casing; and cooling means for cooling the compressor characterised in that the cooling means effects cooling of at least a part of the gas flowing through the conduit means. The cooling means are preferably arranged to effect cooling of a by-pass pipe disposed externally of the casing, the by-pass pipe being arranged to communicate with a discharge port through which gas compressed by the compressor is discharged from the casing and with a supply port through through which the said gas is returned to the interior of the casing. The compressor is preferably driven by a motor disposed within the casing. Moreover, there are preferably means disposed within the casing for directing cooled gas from the supply port directly onto both the compressor and the motor. The conduit means preferably comprises a gas discharge pipe which is arranged to receive gas compressed by the compressor and to supply the compressed gas to an expansion unit for expansion therein, the expansion unit being adapted to form part of a refrigeration system, the conduit means also comprising a gas supply pipe for supplying gas which has been expanded in the expansion unit to the interior of the casing for compression therein. The by-pass pipe is preferably arranged to receive a part of the gas flowing through the gas discharge pipe. The invention also comprises a method of compressing a gas comprising employing conduit means to supply a gas to be compressed to the interior of an hermetically sealed casing and for discharging compressed gas from the interior of the casing; employing a compressor disposed within the casing to compress gas within the latter; and employing cooling means to cool the compressor, characterised in that the cooling means effects cooling of at least a part of the gas flowing through the conduit means. The gas is preferably a refrigerant gas such, for example, as helium. The invention is illustrated, merely by way of example, in the accompanying drawings, in which:- Figure 1 is a schematic view of a helium compressor according to the present invention, and Figure 2 is a schematic view of a known helium compressor. As indicated above, in a compressor for compressing helium gas used as a refrigerant gas, considerable heat is generated from the compressor during its operation because the adiabatic coefficient of the helium gas has the large value of K = 1.66. In addition, a motor employed to drive the compressor has also been subjected to a high temperature. A cooling system has therefore been used to cool the compressor and motor, as shown in Figure 2. In Figure 2 there is shown a compressor 2 and a motor 3 which drives the compressor 2, the compressor 2 and motor 3 being disposed in an hermetically sealed casing 1. Low-pressure gas inside the hermetically sealed casing 1 is sucked in and compressed by the compressor 2 and then is discharged from the interior of the casing 1 as high-pressure gas through a discharge port 4. The discharged high-pressure gas passes through an expansion unit 5 of a refrigeration system and thereafter is re-introduced into the hermetically sealed casing 1 through a suction port 6. In order to cool the compressor 2 and the motor 3 disposed in the hermetically sealed casing 1, a cooling pipe 7 is wound round the outer periphery of the casing 1, and cooling water is circulated through the pipe 7 by a mechanical pump or the like, which is not shown in Figure 2, so as to cool the hermetically sealed casing 1 itself and thus indirectly to cool the compressor 2 and the motor 3. However, the kind of cooling system shown in Figure 2 utilizes the heat transfer effect of the gas inside the casing 1, and consequently satisfactory cooling efficiency cannot always be attained. As a result, the life of the compressor 2 and the motor 3 may be shortened. Figure 1 therefore shows a helium compressor 10 of a vertical type according to the present invention. The helium compressor 10 is composed of a compressor 12 and a motor 13 which drives the compressor 12, both the compressor 12 and motor 13 being disposed inside an hermetically sealed casing 11. The helium compressor 10 is provided with an expansion unit 14 which is part of a refrigeration system and in which high pressure gas discharged from the compressor 12 is expanded adiabatically. The helium compressor 10 is also provided with a cooling system 15 which cools down part of the high pressure gas discharged from the compressor 12, the cooled gas being re-introduced into the casing 11. The motor 13 is composed of a stator 16 and a rotor 17, the rotation of the rotor 17 being transmitted to the compressor 12 through a driving shaft 18. High pressure gas which is compressed in the casing 11 by the compressor 12 is sent through a gas discharge pipe 21 by way of a discharge port 19. The gas discharge pipe 21 supplies the compressed gas to the expansion unit 14 where it is expanded adiabatically. The so expanded gas then passes through a gas supply pipe 26 and thus is returned to the hermetically sealed casing 11 through a suction port 20. Part of the high pressure gas from the compressor 12 is introduced into a cooling or by-pass pipe 22 which is disposed externally of the casing 11, the by-pass pipe 22 communicating with the gas discharge pipe 21 through which high pressure gas is supplied to the expansion unit 14. The cooling pipe 22 extends through a cooling water vessel 23 of the cooling system 15 so that the gas passing through the pipe 22 is cooled thereby to a low temperature and is then re-introduced into the hermetically sealed casing 11 through a supply port 24. The cooled gas circulates smoothly through the by-pass pipe 22 under the discharge pressure of the high-pressure gas discharged from the compressor 12. The gas which is thus cooled down to a predetermined temperature by the cooling system 15 is blown directly from the supply port 24 and through a casing 25 onto the compressor 12 and the motor 13 so as to produce a very large cooling effect. Thus the life of the motor 13 and of the compressor 12 can be substantially lengthened, and continuous operation can be effected for a long time, which is an important factor in process control.

Claims: 1. A gas compressor (10) comprising an hermetically sealed casing (11) within which is disposed a compressor (12) for compressing gas within the casing (11); conduit means (26,21,22) for supplying a gas to be compressed to the interior of the casing (11) and for discharging compressed gas from the interior of the casing (11); and cooling means (15) for cooling the compressor (12) characterised in that the cooling means (15) effects cooling of at least a part of the gas flowing through the conduit means (26,21,22). 2. A gas compressor as claimed in claim 1 characterised in that the cooling means (15) is arranged to effect cooling of a by-pass pipe (22) disposed externally of the casing (11), the by-pass pipe (22) being arranged to communicate with a discharge port (19)through which gas compressed by the compressor (12) is discharged from the casing and with a supply port (24) through which the said gas is returned to the interior of the casing (11). 3. A gas compressor as claimed in claim 1 or 2 characterised in that the compressor (12) is driven by a motor (13) disposed within the casing (11). 4. A gas compressor as claimed in claim 3 when dependent upon claim 2 characterised in that there are means (25) disposed within the casing (11) for directing cooled gas from the supply port (24) directly onto both the compressor (12) and the motor (13). 5. A gas compressor as claimed in any preceding claim characterised in that the conduit means (26,21,22) comprises a gas discharge pipe (21) which is arranged to receive gas compressed by the compressor (12) and to supply the compressed gas to an expansion unit (14) for expansion therein, the expansion unit (14) being adapted to form part of a refrigeration system, the conduit means (26,21,22) also comprising a gas supply pipe (26) for supplying gas which has been expanded in the expansion unit (14) to the interior of the casing (11) for compression therein. 6. A gas compressor as claimed in claim 5 when dependent upon claim 2 in which the by-pass pipe (22) is arranged to receive a part of the gas flowing through a gas discharge pipe (21). 7. A method of compressing a gas comprising employing conduit means (26,21,22) to supply a gas to be compressed to the interior of an hermetically sealed casing (11) and for discharging compressed gas from the interior of the casing (11); employing a compressor (12) disposed within the casing (11) to compress gas within the latter; and employing cooling means (15) to cool the compressor (12) characterised in that the cooling means (15) effects cooling of at least a part of the gas flowing through the conduit means (26,21,22). 8. A method as claimed in claim 7 in which the gas is a refrigerant gas. 9. A method as claimed in claim 8 in which the refrigerant gas is helium. 10. A helium compressor (10) wherein a compressor (12) and a motor (13) driving this compressor (12) are disposed in a hermetically-sealed casing (11) and helium gas is used as a refrigerant, characterised in that the helium compressor comprises a cooling system (15) attached thereto to cool down forcibly part of the high-pressure gas discharged outside the casing (11) from the aforesaid compressor (12) and to introduce same into the casing (11).

Inventors: KAKINUMA, MASAMI
Applicants: SEIKO SEIKI KABUSHIKI KAISHA
Application year: 1987
Main classification: F25B9
IPC codes: F25B31, F04B37, F04B39