Device and method for cooling and/or low-temperature liquefaction

Abstract

The invention relates to a device for cooling and/or liquefying, at a low-temperature, a working fluid containing helium or consisting of pure helium. The device includes a working circuit provided with a compressor station and a cold box. The compressor station includes one or more compression stages, each using one or more compressors that include a compressor wheel rigidly connected to an axle that is rotatably mounted on bearings. The axle of each compressor is rotated by an output shaft of a motor via a gear mechanism placed in a mechanical housing including lubricating oil. Said device is characterized in that the inner space of the mechanical housing contains a gaseous atmosphere consisting of a gaseous mixture having a mean molar mass that smaller than the molar mass of the air.

Claims

1. A method for low-temperature liquefaction and/or cooling of a working fluid comprising helium, by using a refrigerator or a liquefier comprising a working circuit provided with a compression station and with a cold box, the refrigerator or the liquefier subjecting a working gas in the working circuit to a cycle comprising, in series, the steps of: compressing the working fluid in the compression station; cooling the compressed working fluid in the cold box; heating of the cooled, compressed working fluid in order to return the cooled, compressed working fluid to the compression station, the compression station comprising one or more compression stages each using one or more compressors comprising a compressor impeller secured to a spindle mounted so that the compressor impeller can rotate on bearings, the spindle of each compressor being rotationally driven by an output shaft of a motor via a gear mechanism housed in a mechanical gearbox containing lubricating oil; controlling a gaseous atmosphere inside an internal volume of the mechanical gearbox so as to contain a gaseous mixture having a mean molar mass that is lower than a molar mass of air, the gaseous atmosphere of inside the mechanical gearbox comprising a molar proportion of helium that is greater than the molar proportion of helium in the air; injecting a buffer gas to at least at one bearing of the compressor or compressors to form a gas barrier; and guiding leaks of working fluid from the working circuit toward a collection zone, wherein at least part of the collection zone comprises the mechanical gearbox, such that a mixture of the buffer gas and the guided leaks of working fluid are fed into an internal volume of the mechanical gearbox.

2. The method of claim 1, wherein the internal atmosphere of the gear box includes a mixture of oil and the working gas and said method further comprising a step of purifying the internal atmosphere of the gearbox in order to separate the working gas and the oil and reinject the purified oil into the gearbox.

3. The method of claim 2, further comprising a step of compressing the mixture of gas and oil of the atmosphere prior to the purification step.

4. The method of claim 1, wherein the working fluid consists of pure helium.

5. The method of claim 1, wherein the working fluid consists of pure helium.

6. The method of claim 1, further comprising the step of purifying the internal atmosphere of the motor gearbox connected to said motor gearbox via a first pipe for tapping a mixture of gas and oil from the gearbox and a second pipe for returning purified oil.

7. The method of claim 6, further comprising the step of compressing the mixture tapped off by the first pipe so as to supply a purification member with a mixture compressed to a determined pressure.

8. The method of claim 1, wherein the molar proportion of helium in the gaseous atmosphere inside the mechanical gearbox is between 5% and 100%.

9. The method of claim 1, wherein the gaseous atmosphere inside the mechanical gearbox is comprised of a predominant molar proportion of helium.

10. The method of claim 1, wherein the gaseous atmosphere inside the mechanical gearbox comprises helium and at least one gas selected from the group consisting of nitrogen, argon, and one or more components of the working fluid.

11. The method of claim 1, wherein at least some of the compressors of the compression station are compressors of a centrifugal type.

12. The method of claim 1, wherein the buffer gas comprises at least one of helium, nitrogen, and one or more components of the working fluid.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 depicts a schematic and partial view illustrating the structure and operation of one exemplary embodiment of a refrigeration and/or liquefaction device according to the invention,

(2) FIG. 2 depicts a schematic and partial view in longitudinal section illustrating one example of a compressor impeller mounted on bearings comprising a drive mechanism according to the invention,

(3) FIG. 3 depicts a schematic and partial front view of one end of the mechanism of FIG. 3, illustrating how a plurality of compressor spindles is driven by the motor,

(4) FIG. 4 depicts a schematic and partial view illustrating the structure and operation of details of another exemplary embodiment of a refrigeration and/or liquefaction device according to the invention, illustrating purification of gas of the device containing lubricating oil.

DETAILED DESCRIPTION OF THE INVENTION

(5) The cooling and/or liquefaction device depicted partially and schematically in FIG. 1 operates at cryogenic temperatures, for example of between 4K and 80K. This device preferably contains a working gas containing helium or consisting of pure helium. The device 1 conventionally comprises a working circuit provided with a compression station 2 and a cold box 3.

(6) The working circuit 18 subjects the working gas to a cycle comprising, in series: a compression of the working fluid in the compression station 2, a cooling (and possibly an expansion) of the working fluid in the cold box 3 and a heating of the working fluid so that it can be returned to the compression station 2.

(7) The compression station 2 comprises one or more compression stages, each one using one or more compressors 12.

(8) As illustrated schematically in FIG. 2, each compressor impeller 12 is secured to a spindle 25 mounted to rotate on bearings 5. A seal 17 is positioned notably at one end of the spindle 25.

(9) The spindle 25 of each compressor 12 is conventionally driven in rotation by an output shaft 6 of a motor 4 via a gear mechanism 7 (notably a speed multiplier system) housed in a mechanical gearbox 8.

(10) As can be seen in FIG. 3, the output shaft 6 of the motor can drive several compressor 12 spindles 25 off at least one gear wheel 7.

(11) The mechanical gearbox 8 is enclosed and contains an oily atmosphere and, for example, a lubricating oil bath 9 set in motion by the mechanical moving parts.

(12) According to one advantageous feature, the internal volume of the mechanical gearbox 8 contains a gaseous atmosphere consisting of a gaseous mixture having a mean molar mass that is lower than the molar mass of air. What that means to say is that, instead of providing an atmosphere of air or of nitrogen in this gearbox 8, provision is made for the internal gas atmosphere to have a molar mass that is lower than air or nitrogen. For example, the inside of the gearbox contains a determined proportion of helium.

(13) For preference, the gaseous environment inside the mechanical gearbox 8 contains helium and possibly at least one of the following gases: nitrogen, argon, one or more component of the working fluid. The gaseous atmosphere inside the mechanical gearbox 8 for example comprises a molar proportion of helium that is higher than the proportion of helium in air. For preference, the gaseous atmosphere of the inside of the mechanical gearbox 8 comprises a predominant molar proportion of helium, possibly supplemented by at least one of the following: nitrogen, argon, air, one or more component of the working fluid.

(14) This gaseous atmosphere makes it possible to greatly reduce the contribution of the mechanical losses of the compressor and thus improve the efficiency of the device. Specifically, friction between moving parts (spindles, gears, gear sets, etc.) is reduced in an atmosphere of gas having a relatively lower molar mass. The higher the speed at which the mechanical moving parts are moving, the greater this reduction in friction is.

(15) A source of low molar mass gas can be provided in order to sustain this atmosphere within the gearbox 8. One or more sensors may be provided to monitor this atmosphere and regulate its composition if need be.

(16) For preference, the mechanical gearbox 8 is therefore sealed.

(17) As illustrated in FIGS. 1 and 2, the device 1 may optionally comprise a member 10 for injecting a buffer gas at least at one bearing 5 of the compressor or compressors 12 in order to form a gas barrier guiding leaks of working fluid coming from the working circuit toward a collection zone.

(18) In addition, advantageously and although this is not necessary, the mixture of buffer gas and of working gas recovered can be used to feed the inside of the mechanical gearbox 8 (in order to form the atmosphere of low molar mass).

(19) Indeed, in such a case, if helium is already present in the working gas, it is advantageous to use this same helium gas as buffer gas and/or to allow the helium or the working gas to leak into the gearbox 8 (as has been illustrated schematically using arrows in FIG. 2).

(20) By contrast, the other sealing systems on the spindle 25 can be simpler than the solutions proposed in the prior art. The overall cost of manufacture of the compressor may thus be reduced.

(21) For preference, the helium thus sent into the mechanical gearbox 8 needs to be recuperated because losing it would reduce the economic benefit of the solution.

(22) In order to achieve that, this helium transferred into the mechanical gearbox 8 is preferably recuperated and treated. Thus, a first oil separation system may be installed so as to limit the quantity of oil that will leave the gearbox 8 of the compressor 12. The recovered helium may contain impurities of air if the mechanical gearbox 8 is not perfectly sealed against the outside.

(23) It is therefore necessary to make the mechanical gearbox 8 (notably containing the speed multiplication mechanism) as sealed as possible against the external environment in order to avoid excessive losses of helium to the outside.

(24) As illustrated schematically in FIG. 1, it is therefore also preferable to provide a purification system 11 for purifying the recovered helium (line 16) so as to separate the residual oil and also purify this helium of the other contaminants (for example: air, water, etc.) so that it can be recuperated and possibly reinject (line 14) this helium into the working cycle.

(25) Usually, the oil 9 of this mechanical gearbox is also managed by a system external to it with a tank, a pump, and injection and regulating valves.

(26) The oil circuit in contact with the helium will also need to limit losses of helium to the outside.

(27) The purification system 11 will preferably contain a conventional element of the mechanical filtration, coalescer, and/or adsorption type, allowing the removal of oil vapors and droplets present in the helium.

(28) As illustrated in the example of FIG. 3, a first tapping pipe 16 recovers the mixture of gas and oil from the gearbox 8 to a purification member 111. The purification member 111 in FIG. 3 may comprise or consist of a coalescer making it possible to limit the amount of oil that leaves the gearbox in liquid form with direct return via a line 13. Another outlet 14 of the purification member 111 may comprise a stream that still needs to be treated for vapors and/or other impurities.

(29) If this member 111 performs all of the purification task, the purified oil can be returned to the mechanical gearbox 8 via a second, return, pipe 13. The helium recovered during the purification is sent, for example, into the working circuit.

(30) As illustrated in FIG. 4, it may be necessary to compress this helium mixed with oil recovered by the tapping pipe 16 prior to treatment (purification). A recuperation compressor 15 may be provided for this purpose upstream of the purification member 11.

(31) According to one advantageous particular feature, if this recuperation compressor 15 is of the oil compressor type, the same oil (or a chemically compatible oil) is used for the mechanical gearboxes 8 of the compressors 12 of the compression station 2 and for the recuperation compressor 15. If this recuperation compressor 15 is a lubricated-screw type compressor, a determined oil is needed to allow better final separation of the oil and of the helium. For example, a synthetic-type oil with a low saturation vapor pressure can be used.

(32) The purification member 11 may thus be common to the two compression systems (the compressors 12 of the station 2 and the recuperation compressor 15).

(33) This allows standardization and a reduction in the overall cost of the device.

(34) The device and the method thus make it possible to simplify the structure of the bearings 5. The cost of the device 1 and of the operation of same are lower. The performance of the compressor drive mechanism in the mechanical gearbox 8 is notably improved.

(35) While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

(36) The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

(37) Comprising in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing i.e. anything else may be additionally included and remain within the scope of comprising. Comprising is defined herein as necessarily encompassing the more limited transitional terms consisting essentially of and consisting of; comprising may therefore be replaced by consisting essentially of or consisting of and remain within the expressly defined scope of comprising.

(38) Providing in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

(39) Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

(40) Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

(41) All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.