Elements, apparatus and methods for compression of low temperature compressed gases

Abstract

An element for compressing a gas to be compressed at a low temperature below 40°C, characterized in that the element (1) comprises a housing (2) having at least one rotor (3) rotatably mounted relative to the housing about a shaft (5), an inlet (6) for the gas to be compressed, and an outlet (7) for the compressed gas, the element (1) comprising heating means for the end (9a) of the shaft (5) of the rotor (3) closest to the inlet (6).

Description

[Technical field]

[0001] The present invention relates to an element, an apparatus and a method for compressing a low temperature compressed gas. [Background technology]

[0002] In the following, "low temperature" refers to temperatures below -40° C. The present invention is therefore intended for use at cryogenic temperatures.

[0003] One possible example is the compression of liquefied natural gas (LNG) boil-off gas, although the invention is not limited thereto.

[0004] It is known to use reciprocating or piston compressors for such applications.

[0005] A drawback of such reciprocating or piston compressors is that their operation produces pulsations in the compressed gas supply, in other words the compressed gas supply is not continuous.

[0006] However, some applications require a continuous supply of compressed gas.

[0007] For example, screw compressor elements having a screw rotor are known to provide continuous operation without pulsations in the compressed gas supply, and in addition, the energy consumption of screw compressor elements is low.

[0008] However, screw compressors are not suitable for use in compressing gases below -40°C.

[0009] The screw compressor element includes a cast iron housing and a forged steel screw rotor.

[0010] At such low temperatures, significant thermal distortion occurs.

[0011] A screw rotor typically comprises a rotor body and a shaft as a single unit, which results in the inlet side of the screw compressor element being cooler than the outlet side.

[0012] This causes a temperature gradient from the inlet side to the outlet side of the screw rotor.

[0013] This affects the tolerances and clearances of the screw compressor elements, which will increase due to thermal distortion, resulting in reduced efficiency and performance of the screw compressor elements.

[0014] Thus, gas to be compressed below -40°C is warmed before entering the screw compressor element. Summary of the Invention [Problem to be solved by the invention]

[0015] This solves the thermal deformation problem, but causes significant energy losses since the compressed gas needs to be cooled again after compression. [Means for solving the problem]

[0016] The present invention aims to provide a solution to at least one of the above and / or other drawbacks by providing an element capable of compressing a gas to be compressed at a temperature below -40°C.

[0017] The present invention relates to an element for the compression of a gas to be compressed at low temperatures below -40°C, the element comprising a housing having at least one rotor rotatably mounted about a shaft relative to the housing, an inlet for the gas to be compressed and an outlet for the compressed gas, the element (1) comprising heating means for the end of the shaft of the rotor closest to the inlet (6).

[0018] The advantage is that in this way said end of the shaft can be heated.

[0019] The inlet of the element will be the coldest location since the gas being compressed enters it at a low temperature, resulting in the end of the shaft closest to the inlet being cooled the most.

[0020] This location provides the highest temperature difference with the heating means and therefore optimal heat transfer between the heating means and the rotor.

[0021] Due to the thermal conductivity of the shaft, heat transferred to the shaft will be spread throughout the shaft and into the rotor body of the rotor.

[0022] As a result, the temperature gradient on the rotor from the inlet side to the outlet side of the element that occurs with known elements is eliminated, and the entire rotor is at approximately the same temperature.

[0023] As a result, thermal deformation of the rotor is limited, tolerances and clearances between the rotor and the housing are maintained within acceptable limits, and thermal stresses are limited.

[0024] In a preferred embodiment of the element according to the invention, the heating means comprises a first injection circuit for injecting a heating medium at a temperature higher than the low temperature at the end of the shaft of the rotor closest to the inlet.

[0025] The heating means reaching this end of the rotor shaft are in direct contact with this end, which promotes heat exchange between this heating means and said end.

[0026] In a more preferred embodiment of the element according to the invention, the first injection circuit comprises a nozzle at said end of the shaft, which nozzle injects the heating means directly onto said end.

[0027] The heating medium is sprayed directly and targetedly by a nozzle onto said end of the shaft so that as large a portion of the heating medium as possible effectively reaches said end of the shaft, thus promoting heat exchange between the sprayed heat medium and said end.

[0028] In a further preferred embodiment of the element according to the invention, the rotor is rotatably mounted relative to the housing by means of bearings, and the element comprises a second injection circuit for injecting the heating medium.

[0029] As a result, the bearings can also be heated to prevent them from cooling too much and freezing up, which could jeopardize their proper operation due to increased friction in the bearings.

[0030] Preferably, a first duct of the second injection circuit having a first supply point for the heating medium to the element is arranged in a first part of the housing, which is located on the side of the housing on which the inlet is located, according to the axial direction of the shaft.

[0031] Alternatively or additionally, a second duct of a second injection circuit having a second supply point for the heating medium to the element is arranged in a second part of the housing which is arranged, according to the axial direction of the shaft, on the side of the housing on which the outlet is arranged.

[0032] This has the advantage that by feeding the heating medium into the element on the inlet side and / or on the outlet side, feeding points can be provided at one and / or two ends of the rotor.

[0033] In other words, the bearing on the inlet side of the element and / or the bearing on the outlet side of the element have respective injection points so that the heating medium is injected as close as possible to the bearings and there is no need to transport the heating medium from the inlet side of the element through the housing to the outlet side of the element or vice versa.

[0034] This will prevent the heating medium from freezing or cooling too much while passing through the housing, which could cause blockage of the heating medium in the element and / or deteriorate the lubricating properties of the heating medium.

[0035] Because the heating medium must travel a limited distance from the supply point through the housing to each bearing, the heating medium cools slightly to maximize the transfer of needed heat to the bearings.

[0036] The first supply point and the second supply point are interconnected by a connecting duct for the heating medium in the housing.

[0037] This connecting duct allows heat exchange between the heating medium injected through the first and second feed points.

[0038] This heat exchange occurs from the hot outlet side of the element to the cold inlet side via the heating medium in the connecting ducts.

[0039] This results in a uniform temperature throughout the heating medium, the housing, and the bearings.

[0040] There is therefore less risk of the heating medium slowing down too much locally within the element.

[0041] According to the invention, it is not excluded that the second injection circuit is connected to, is part of, is integrated in or forms a single unit with the first injection circuit.

[0042] This element is therefore less complex in terms of its construction in terms of the required number of flow passages in the housing for the first and second injection circuits.

[0043] In a preferred embodiment of the element according to the invention, the nozzle, if present, is also configured so that the heating medium can be sprayed onto the bearing.

[0044] In this way, both the end of the rotor shaft closest to the inlet and the inlet-side bearing of the element are sprayed with the heating medium directly and in a targeted manner, so that a significant portion of the heating medium effectively ends up both on said end of the shaft and on the bearing, thus promoting heat exchange between the injected heating medium, on the one hand, and said end and the bearing, on the other hand.

[0045] Preferably, the nozzle comprises at least two nozzle openings.

[0046] In this way, one of the at least two nozzle openings can be targeted at the end of the rotor shaft and another of the at least two nozzle openings can be directed towards the bearing on the inlet side of the element, so that as large a portion of the heating medium as possible effectively reaches both the end of the shaft and the bearing, thus promoting heat exchange between the injected heating medium, on the one hand, and the end and the bearing, on the other hand.

[0047] The invention also relates to an apparatus for compression of a gas to be compressed at low temperatures below -40°C, characterized in that it comprises at least one element according to the invention.

[0048] Of course, such a device has the same advantages as the embodiment of the element according to the invention described above.

[0049] The invention also relates to a method for compressing a gas to be compressed at a low temperature, below -40°C, by means of an element comprising a housing having at least one rotor rotatably mounted around a shaft relative to said housing, an inlet for the gas to be compressed, and an outlet for the compressed gas, the end of the shaft of the rotor closest to the inlet being heated.

[0050] Preferably the cold compressed gas has a temperature of at most -60°C, preferably at most -100°C.

[0051] In a preferred embodiment of the method according to the invention, a heating medium is injected into said end, so that the heating medium has a higher temperature than the gas to be compressed.

[0052] In a more preferred embodiment of the method according to the invention, the rotor is rotatably mounted relative to the housing by means of bearings, and the heating medium is also injected into the bearings.

[0053] Of course, the advantages of such a method overlap with the advantages of the corresponding embodiments of the element according to the invention described above.

[0054] Preferably, the heating medium is a lubricating liquid, more preferably an oil.

[0055] The heating medium is therefore usefully applied not only for heating but also for lubricating the components of the element, this being primarily intended for the bearings.

[0056] Finally, the invention also relates to the use of an element or a device according to the invention for the compression of a gas to be compressed at low temperatures below -40°C.

[0057] In order to better illustrate the characteristics of the present invention, by way of non-limiting examples, several preferred embodiments of an element for compressing a low-temperature gas to be compressed according to the invention and of an apparatus comprising such an element will now be described with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0058] [Figure 1] 1 shows diagrammatically and in perspective an element according to the invention for use in a device according to the invention; [Diagram 2] 1. FIG. [Diagram 3] 3 shows a cross section taken along line III-III in FIG. [Figure 4] 2 shows a schematic and perspective view according to the arrow F4 of FIG. 1, but with part of the housing cut away. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0059] The element 1 according to the invention shown in the figures for use in an apparatus according to the invention is, in this case, a screw compressor element.

[0060] The element 1 comprises a housing 2 which houses inside at least one rotor 3, in this case two helical rotors.

[0061] In this case, the screw compressor element is an oil-free screw compressor element, i.e. no oil is injected into the compression chamber in the housing 2 of the element 1 for lubrication and / or sealing of the helical rotor.

[0062] The helical rotor is disposed rotatably together with a shaft 5 relative to the housing 2 via bearings 4 .

[0063] The housing 2 also comprises an inlet 6 for the cold gas to be compressed and an outlet 7 for the compressed gas.

[0064] According to the invention, the temperature of the gas to be compressed at low temperature is below -40°C, preferably, although not essential to the invention, below -60°C, more preferably below -100°C.

[0065] Obviously, as a result of compression, the compressed gas will have a higher temperature than the gas being compressed prior to compression. Depending on the process, this temperature may be greater than -100°C, -60°C or -40°C.

[0066] According to the invention, the element 1 comprises a first injection circuit 8 for injecting a heating medium at a temperature higher than the low temperature at the end 9a of the shaft 5 of the rotor 3 located closest to the inlet 6. This is shown in figure 3.

[0067] It is important to note that this first injection circuit 8 is used to inject the heating medium into the end 9a of the shaft 5 of the rotor 3 that is closest to the inlet 6. In other words, the first injection circuit 8 is not used to inject oil into the compression chambers.

[0068] This first injection circuit 8 comprises a first duct 10 having a first feed point 11 for the heating medium in the element 1. Through this first feed point 11 the heating medium is conveyed from a heating medium reservoir into the housing 2.

[0069] In addition, the first injection circuit 8 comprises a nozzle 12 located at said end 9a of the shaft 5, which injects the heating medium directly onto said end 9a.

[0070] The nozzle 12 shown in Figures 3 and 4 is provided with a nozzle opening 13a for this purpose.

[0071] In the example shown, the element 1 comprises a second injection circuit 14 .

[0072] It should be noted that this second injection circuit 14 is used to enable injection of the heating medium into the bearing 4. In other words, the second injection circuit 14 is not used to inject oil into the compression chamber.

[0073] As shown in FIG. 3, the second injection circuit 14 comprises two feed points 11 , 15 for the heating medium into the element 1 at two different positions in the housing 2 .

[0074] As shown, the housing 2 has feed points 11, 15 at each end 9a, 9b of the helical rotor 3.

[0075] As a result, the heating medium can be injected as close as possible into the housing 2 , near the bearings 4 at the ends 9 a , 9 b of the shaft 5 of the rotor 3 .

[0076] Ducts 10 , 16 extend from supply points 11 , 15 through the housing 2 to the bearings 4 and supply the heating medium to the bearings 4 .

[0077] At the location of the bearing 4, appropriate nozzles 12, 17 are provided.

[0078] The nozzles 12 , 17 are provided with a nozzle opening 13 b for spraying the heating medium onto the bearing 4 .

[0079] As shown in FIG. 3, the two supply points 11, 18 are interconnected by a connecting duct 18 for the heating medium in the housing 2.

[0080] This connecting duct 18 will be filled with oil during operation of the device.

[0081] As can be seen from FIG. 3, the first injection circuit 8 and the second injection circuit 14 in this case share the feed point 11 , the duct 10 and the nozzle 12 .

[0082] In this case, the first injection circuit 8 is part of the second injection circuit 14, although this is not essential to the invention.

[0083] It is also possible for the second injection circuit 14 to be connected to, be part of, be integrated into, or form a single unit with the first injection circuit 8 .

[0084] Of course, it is also possible for the first injection circuit 8 and the second injection circuit 14 to be completely separate from each other.

[0085] Further, the nozzle 12 may not only spray oil onto the end 9 a of the shaft 5 , but also onto the bearing 4 .

[0086] In other words, in this case the nozzle 12 has a dual function.

[0087] For this reason, the nozzle 12 comprises two nozzle openings 13a, 13b.

[0088] The screw compressor element operates in a very simple manner as follows.

[0089] During operation of the screw compressor element, the helical rotors work in concert by meshing to draw in gas to be compressed at a low temperature through the inlet 6 of the housing 2 .

[0090] The gas to be compressed is compressed by the helical rotor and leaves the screw compressor element 1 through an outlet 7 in the housing 2 .

[0091] This causes the compressed gas at a low temperature to cool the housing 2 powerfully.

[0092] During the compression process the temperature of the gas will increase, but since the temperature of the gas is still low, the compressed gas will cool the housing 2 after compression.

[0093] During operation of element 1, the heating medium will be fed via feed point 11 and duct 10 to nozzle 12. The heating medium will be sprayed from nozzle opening 13a in end 9a of shaft 5 of rotor 3 closest to inlet 6.

[0094] The end 9 a becomes warm and the heat spreads through the shaft 5 to the entire rotor 3 .

[0095] Since the inlet 6 is the coldest location in the housing 2, it will require the most intense heating.

[0096] The thermal conductivity of the shaft 5 will cause the heat to be directed towards the end 9 b of the shaft 5 furthest from the inlet 6 .

[0097] As a result, the temperature of the entire rotor 3 is kept as high as possible and the temperature becomes uniform.

[0098] As a result of the heating of the rotor 3, the bearing 4 is also indirectly partially heated.

[0099] However, to ensure proper operation of the bearing 4, the second injection circuit 14 will spray a heating medium at a higher temperature than the low temperature onto the bearing 4.

[0100] For the bearings 4 at each end 9a, 9b of the shaft 5 of the rotor 3, special supply points 11, 15 are provided in the housing 2, making it possible to transport the heating medium to the bearings 4 using ducts 10, 16 that are as short as possible.

[0101] The heating medium is sprayed directly onto the bearing 4 through the nozzles 12, 17 and their nozzle openings 13b.

[0102] This will minimise the temperature drop of the heating medium as it passes through the cold housing 2 before reaching the bearings 4 .

[0103] The connecting duct 18 provides a connection between the two feed points 11 , 15 and is intended to allow heat exchange between the heating media injected via both feed points 11 , 15 .

[0104] This connecting duct 18 will be filled with a heating medium which is normally stationary and will not reach the bearing 4, but heat exchange from the hotter outlet 7 to the very cold inlet 6 is still possible via the heating medium in the connecting duct 18.

[0105] This will ensure a uniform temperature throughout the heating medium within the housing 2 , throughout the housing 2 and across the bearings 4 .

[0106] This also eliminates the risk of the heating medium becoming too cold.

[0107] The invention is not limited to the embodiments described by way of example and shown in the drawings, but the element for compressing a low-temperature gas to be compressed according to the invention and the device comprising such an element can be implemented in all forms and dimensions without going beyond the scope of the invention as defined in the claims. [Explanation of symbols]

[0108] 1 element 2. Housing 3 Rotor 5 Shaft 6 entrance 7 Exit 9a end

Claims

1. An element for compressing a gas to be compressed at low temperatures below -40°C, The element (1) comprises a housing (2) comprising at least one rotor (3) rotatably mounted relative to the housing (2) around a shaft (5), an inlet (6) for the gas to be compressed, and an outlet (7) for compressed gas, The element (1) comprises heating means for the end (9a) of the shaft (5) of the rotor (3) which is closest to the inlet (6).

2. 2. The element of claim 1, wherein the temperature of the cold compressed gas is at most -60°C.

3. 3. An element as claimed in claim 1 or 2, wherein the heating means comprises a first injection circuit (8) for injecting a heating medium at a temperature higher than the low temperature onto the end (9a) of the shaft (5) of the rotor (3).

4. 4. An element according to claim 3, wherein the first injection circuit (8) comprises a nozzle (12) arranged at the end (9a) of the shaft (5), the nozzle (12) spraying the heating medium directly onto the end (9a).

5. 5. The element according to claim 4, wherein the rotor (3) is rotatably mounted relative to the housing (2) by means of a bearing (4), and the element (1) comprises a second injection circuit (14) for injecting a heating medium at a temperature higher than the low temperature against the bearing (4).

6. 6. The element according to claim 5, wherein a first duct (10) of the second injection circuit (14) having a first supply point (11) for the heating medium to the element (1) is arranged in a first part of the housing (2) located on the side of the housing (2) on which the inlet (6) is arranged, according to the axial direction of the shaft (5).

7. 7. An element according to claim 6, wherein a second duct (16) of the second injection circuit (14) having a second supply point (15) for the heating medium to the element (1) is arranged in a second part of the housing (2) located on the side of the housing (2) on which the outlet (7) is arranged, according to the axial direction of the shaft (5).

8. 8. An element according to claim 7, wherein the first feed point (11) and the second feed point (15) are interconnected by a connecting duct (18) for a heating medium in the housing (2).

9. 9. An element according to any one of claims 5 to 8, wherein the second injection circuit (14) is connected to the first injection circuit (8), is part of the first injection circuit (8), is integrated into the first injection circuit (8), or forms a single unit with the first injection circuit (8).

10. 10. An element according to any one of claims 5 to 9, wherein the nozzle (12) is configured so as to be able to spray the heating medium also onto the bearing (4).

11. Element according to claim 10, wherein the nozzle (12) comprises at least two nozzle openings (13a, 13b).

12. 12. An element according to any one of claims 1 to 11, wherein the element (1) is a screw compressor element equipped with at least one helical rotor.

13. Element according to claim 12, wherein the element (1) is an oil-free screw compressor element.

14. An apparatus for the compression of a gas to be compressed at low temperatures below -40°C, comprising at least one element (1) according to any one of claims 1 to 13.

15. A method for compressing a gas to be compressed at a low temperature of −40° C. or less by an element, comprising the steps of: The element (1) comprises a housing (2) comprising at least one rotor (3) rotatably mounted relative to the housing (2) around a shaft (5), an inlet (6) for the gas to be compressed, and an outlet (7) for compressed gas, The method, wherein the end (9a) of the shaft (5) of the rotor (3) closest to the inlet (6) is heated.

16. 16. The method of claim 15, wherein the compressed gas at low temperature has a temperature of up to -60°C.

17. 17. The method according to claim 15 or 16, wherein a heating medium is injected into the end (9a), so that the heating medium has a higher temperature than the gas to be compressed.

18. 18. The method according to claim 17, wherein the rotor (3) is rotatably mounted relative to the housing (2) by means of bearings (4), and the heating medium is also injected into the bearings (4).

19. 19. The method of claim 17 or 18, wherein the heating medium is a lubricating liquid.

20. Use of an element according to any one of claims 1 to 13 or a device according to claim 14 for the compression of a gas to be compressed at low temperatures below -40°C.

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