Element, device and method for compressing cryogenic gas to be compressed

Abstract

The present application relates to an element, a device and a method for compressing cryogenic gas to be compressed. An element for compressing cryogenic gas to be compressed at a temperature below ‑40°C, the element (1) having a housing (2) accommodating at least one rotor (3), the rotor being mounted to be rotatable about a rotor axis (5) relative to the housing (2), the housing having an inlet (6) for the gas to be compressed and an outlet (7) for the compressed gas, characterized in that the element (1) has a heating device for heating the rotor shaft end (9a) closest to the inlet (6).

Description

Technical Field

[0001] The present invention relates to an element, a device and a method for compressing a cryogenic gas to be compressed.

[0002] In the following, "cryogenic" refers to temperatures below -40° C. Therefore, the present invention is intended for cryogenic applications.

[0003] One usable example is boil-off gas of compressed liquefied natural gas (LNG), but the present invention is not limited thereto. Background Art

[0004] As is known, reciprocating compressors or piston compressors are used for such applications.

[0005] A disadvantage of such reciprocating or piston compressors is that their action causes pulsations in the compressed gas supply. In other words, the compressed gas supply is not continuous.

[0006] However, some applications require an uninterrupted supply of compressed gas.

[0007] For example, it is known that screw compressor elements with screw rotors produce continuous action without pulsation in the compressed gas supply. In addition, the energy consumption of screw compressor elements is also low.

[0008] However, screw compressors are not suitable for compressing gases with a temperature below -40°C.

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

[0010] Significant thermal deformation can occur at such low temperatures.

[0011] The screw rotors are provided with a shaft which usually forms a separate unit from the rotor body, which is cooled more on the screw compressor element inlet side than on the screw compressor element outlet side.

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

[0013] This affects tolerances and clearances in the screw compressor elements, which increase due to thermal deformation, thereby reducing the efficiency and performance of the screw compressor elements.

[0014] Therefore, the gas to be compressed at a temperature below -40°C must be preheated before entering the screw compressor element.

[0015] While this solves the thermal deformation problem, it still results in a significant energy loss since the compressed gas must be cooled again after compression. Summary of the invention

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

[0017] The present invention relates to an element for compressing low-temperature gas to be compressed below -40°C, the element having a housing which accommodates at least one rotor, the rotor being mounted so as to be rotatable about a rotor axis relative to the housing, the housing having an inlet for the gas to be compressed and an outlet for the compressed gas, and characterized in that the element has a heating device for heating the end of the rotor shaft closest to the inlet.

[0018] An advantage is that the rotor shaft end can be heated in this way.

[0019] The inlet of the element will be the coolest part, since this is where the cold gas to be compressed enters. Therefore, the end of the rotor shaft closest to the inlet will be cooled most strongly.

[0020] At this point there will be a maximum temperature difference relative to the heating device, so that the heat transfer between the heating device and the rotor can be optimized.

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

[0022] Thus, the temperature gradient on the rotor from the inlet side to the outlet side of the element which would occur in known elements can be eliminated and the entire rotor will be at nearly the same temperature.

[0023] As a result, thermal deformations of the rotor will be limited, so that tolerances and clearances between the rotor and the housing remain within acceptable limits and thermal stresses remain limited.

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

[0025] The heating medium that ends at the rotor shaft end is in direct contact with the rotor shaft end, which facilitates heat exchange between the heating medium and the rotor shaft end.

[0026] In a further preferred embodiment of the element according to the invention, the first injection circuit is equipped with a nozzle at the rotor shaft end which injects the heating medium directly onto the rotor shaft end.

[0027] The heating medium is injected directly and precisely to the rotor shaft end through the nozzle so that as much heating medium as possible effectively ends up at the rotor shaft end, thereby promoting heat exchange between the injected heating medium and the rotor shaft 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 is equipped with a second injection circuit for injecting a heating medium having a temperature higher than said low temperature into the bearings.

[0029] Therefore, it is now also possible to heat the bearings in order to prevent them from cooling down too much and freezing, which would otherwise jeopardize their proper functioning due to increased friction in the bearings.

[0030] Preferably, the first conduit of the second injection circuit has a first feed point for feeding the heating medium into the element, the first conduit being located in a first part of the housing, the first part being located in the axial direction of the rotor shaft on the housing side where the inlet is located.

[0031] Alternatively or additionally, a second conduit of the second injection circuit has a second feed point for feeding the heating medium into the element, the second conduit being located in a second part of the housing, the second part being located axially of the rotor shaft on the housing side where the outlet is located.

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

[0033] In other words, the bearing on the element inlet side and / or the bearing on the element outlet side has its own injection point, so that the heating medium is injected as close to the bearing as possible without the need to transport the heating medium from the element inlet side via the housing to the element outlet side and vice versa.

[0034] This will prevent the heating medium from freezing or cooling too much during its passage through the housing, which could cause the heating medium to become clogged in the element and / or possibly degrade the lubricating properties of the heating medium.

[0035] Since the heating medium only has to travel a limited distance through the housing from the feed point to the respective bearing, the heating medium cools down only slightly, thus allowing the necessary heat to be transferred to the bearing to the greatest extent possible.

[0036] The first feed point and the second feed point are connected to one another via a connecting line for the heating medium in the housing.

[0037] By means of the connecting pipe, heat transfer can take place between the heating medium injected via the first feed point and the second feed point.

[0038] This heat exchange takes place from the higher temperature outlet side to the cold inlet side of the element via the heating medium in the connecting pipes.

[0039] This will even out the temperature throughout the heating medium, throughout the housing and bearings.

[0040] There is therefore less risk of excessive local deceleration of the heating medium in the element.

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

[0042] The structure of the element is therefore less complex in terms of the number of channels in the housing required for the first injection circuit and the second injection circuit.

[0043] In a preferred embodiment of the element according to the invention, the nozzles, if present, are configured to also be able to spray the heating medium onto the bearing.

[0044] In this way, the rotor shaft end closest to the inlet and the bearing on the inlet side of the element can be directly and accurately sprayed with heating medium, so that most of the heating medium effectively ends up on the rotor shaft end and the bearing, thereby promoting heat exchange between the injected heating medium on the one hand and the rotor shaft end and the bearing on the other hand.

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

[0046] In this way, one of the at least two nozzle openings can be aligned with the rotor shaft end and the other of the at least two nozzle openings can be aligned with the bearing on the inlet side of the element, so that as much of the heating medium as possible effectively ends up at the rotor shaft end and the bearing, thereby promoting heat exchange between the injected heating medium on the one hand and the rotor shaft end and the bearing on the other hand.

[0047] The present invention also relates to a device for compressing a gas to be compressed at a low temperature below -40°C, characterized in that the device is equipped with at least one element according to the present invention.

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

[0049] The present invention also relates to a method for compressing a low-temperature gas to be compressed below -40°C by means of an element, the element having a housing accommodating at least one rotor, the rotor being mounted to be rotatable about a rotor axis relative to the housing, and the housing having an inlet for the gas to be compressed and an outlet for the compressed gas, characterized in that the end of the rotor shaft closest to the inlet is heated.

[0050] Preferably, the temperature of the cryogenic gas to be compressed is at most -60°C, and preferably at most -100°C.

[0051] In a preferred embodiment of the method according to the invention, a heating medium is injected into the rotor shaft end, the heating medium having a temperature higher than the temperature of the gas to be compressed.

[0052] In a further 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 this approach overlap with the advantages of the corresponding embodiments of the element according to the invention as described above.

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

[0055] The heating medium is therefore suitable not only for heating, but also for lubrication of components of the element (which are primarily of interest to the bearings).

[0056] Finally, the invention also relates to the use of the element or device according to the invention for compressing a gas to be compressed at a low temperature below -40°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In order to better illustrate the features of the present invention, several preferred embodiments of an element for compressing cryogenic gas to be compressed and an apparatus equipped with the element according to the present invention will be described below as non-limiting examples with reference to the accompanying drawings, in which:

[0058] Figure 1 Schematically, in a perspective view, an element according to the invention is shown for use in a device according to the invention;

[0059] Figure 2 Shows along Figure 1 The view indicated by the arrow F2;

[0060] Figure 3 Shows along Figure 1 Cross-sectional view along line III-III;

[0061] Figure 4 The schematic diagram shows the perspective view along Figure 1 The view indicated by arrow F4, but with the housing partially cut away. DETAILED DESCRIPTION

[0062] The element 1 according to the invention shown in the drawing for use in the device according to the invention is in this case a screw compressor element.

[0063] The element 1 comprises a housing 2 in which at least one rotor 3, in this case two helical rotors, is housed.

[0064] The screw compressor element is in this case an oil-free screw compressor element, ie no oil is injected into the compression chamber in the housing 2 of the element 1 for lubricating and / or sealing the screw rotor.

[0065] The screw rotor is arranged rotatably relative to the housing 2 via its axis 5 by means of a bearing 4 .

[0066] The housing 2 also comprises an inlet 6 for the cryogenic gas to be compressed and an outlet 7 for the compressed gas.

[0067] According to the present invention, the temperature of the cryogenic gas to be compressed is below -40°C, preferably but not necessarily below -60°C, and more preferably below -100°C.

[0068] Obviously, as a result of the compression, the temperature of the compressed gas will be higher than the temperature of the gas to be compressed before compression. Depending on the process, the temperature may be higher than -100°C, -60°C or -40°C.

[0069] According to the invention, the element 1 is equipped with a first injection circuit 8 for injecting a heating medium having a temperature higher than said low temperature into the end 9a of the shaft 5 of the rotor 3 which is situated closest to the inlet 6. Figure 3 Shown in.

[0070] It is important to note that the first injection circuit 8 is used to inject the heating medium into the end 9a of the rotor 3 shaft 5 closest to the inlet 6. In other words, the first injection circuit 8 is not used to inject oil into the compression chambers.

[0071] The first injection circuit 8 comprises a first conduit 10 having a first feed point 11 for feeding a heating medium into the element 1. Through the first feed point 11, the heating medium enters the housing 2 from a heating medium reservoir.

[0072] Furthermore, the first injection circuit 8 comprises a nozzle 12 at the aforementioned end 9a of the shaft 5, which injects the heating medium directly onto the aforementioned end 9a.

[0073] Figure 3 and Figure 4 The nozzle 12 shown is equipped with a nozzle opening 13a for the above-mentioned purpose.

[0074] In the example shown, the element 1 is equipped with a second injection circuit 14 .

[0075] It should be noted that the second injection circuit 14 is used to allow the injection of a heating medium into the bearing 4. In other words, the second injection circuit 14 is not used to inject oil into the compression chamber.

[0076] like Figure 3 As shown, the second injection circuit 14 is equipped with two feed points 11 , 15 for feeding the heating medium into the element 1 at two different locations of the housing 2 .

[0077] As shown, the screw rotor 3 has a feed point 11, 15 in the housing 2 at each end 9a, 9b.

[0078] Therefore, the heating medium can be injected into the housing 2 as close as possible to the bearings 4 at the ends 9a, 9b of the shaft 5 of the rotor 3.

[0079] From the feed points 11 , 15 , the pipes 10 , 16 pass through the housing 2 to the bearing 4 , thereby supplying the heating medium to the bearing 4 .

[0080] At the location of the bearing 4, suitable nozzles 12 and 17 are provided.

[0081] The nozzles 12 and 17 have nozzle openings 13 b to spray the heating medium onto the bearing 4 .

[0082] like Figure 3 As shown, the two feed points 11 , 18 are connected to one another via a connecting line 18 in the housing 2 for the heating medium.

[0083] When the device is running, the connecting pipe 18 will be filled with oil.

[0084] like Figure 3 As shown, the first injection circuit 8 and the second injection circuit 14 share a common feed point 11 , a conduit 10 and a nozzle 12 in this example.

[0085] In the present example, but not necessarily for the invention, the first injection circuit 8 is therefore part of the second injection circuit 14 .

[0086] The second injection circuit 14 may also be connected to the first injection circuit 8 , be part of the first injection circuit 8 , be integrated into the first injection circuit 8 , or form a single unit with the first injection circuit 8 .

[0087] Of course, the first injection circuit 8 and the second injection circuit 14 can also be completely separated from each other.

[0088] It is also possible that the nozzle 12 sprays the oil not only onto the end 9 a of the shaft 5 but also onto the bearing 4 .

[0089] In other words: in this case, the nozzle 12 has a dual function.

[0090] For this purpose, the nozzle 12 is equipped with two nozzle openings 13 a and 13 b .

[0091] The operation of the screw compressor element is very simple and is described below.

[0092] During the operation of the screw compressor element, the spiral rotors will work together by meshing with each other and suck in the low-temperature gas to be compressed through the inlet 6 in the shell 2.

[0093] The gas to be compressed is compressed by the screw rotor and will leave the screw compressor element 1 through the outlet 7 in the housing 2 .

[0094] Therefore, the low-temperature gas to be compressed will strongly cool the housing 2 .

[0095] Although the gas temperature increases during the compression process, the gas temperature is still low enough that the compressed gas will still cool the shell 2 after compression.

[0096] During operation of the element 1, the heating medium will be delivered to the nozzle 12 via the feed point 11 and the conduit 10. The heating medium will be sprayed through the nozzle opening 13a onto the end 9a of the shaft 5 of the rotor 3 closest to the inlet 6.

[0097] The end 9 a will be heated and the heat will be spread through the shaft 5 to the entire rotor 3 .

[0098] Since the inlet 6 is the coldest part of the housing 2, the strongest heating is required here.

[0099] Due to the thermal conductivity of the shaft 5 , the heat will be transferred to the end 9 b of the shaft 5 which is farthest from the inlet 6 .

[0100] Therefore, the temperature in the entire rotor 3 will be kept as high as possible and the temperature will also be uniform.

[0101] Due to the heating of the rotor 3, the bearing 4 will also be partially heated indirectly.

[0102] However, in order to ensure the normal operation of the bearing 4 , the second injection circuit 14 will inject the heating medium having a temperature higher than the low temperature onto the bearing 4 .

[0103] For each bearing 4 on each end 9a, 9b of the shaft 5 of the rotor 3, a dedicated feed point 11, 15 is provided in the housing 2, allowing the heating medium to be delivered to the bearing 4 using the shortest possible conduits 10, 16.

[0104] The heating medium is sprayed directly onto the bearing 4 through the nozzles 12, 17 and their nozzle openings 13b.

[0105] This will minimize the temperature drop of the heating medium as it passes through the cold housing 2 before reaching the bearing 4 .

[0106] The connecting pipe 18 providing a connection between the two feed points 11 , 15 is intended to allow heat exchange between the heating media injected through the two feed points 11 , 15 .

[0107] The connecting pipe 18 will be filled with a heating medium, and although this heating medium is usually stationary and does not reach the bearing 4 , heat can still be exchanged from the higher temperature outlet 7 to the very cold inlet 6 via the heating medium in the connecting pipe 18 .

[0108] This will ensure that the entire heating medium in the housing 2, the entire housing 2 and the bearing 4 are at a uniform temperature.

[0109] Therefore, there is no risk of cooling the heating medium too much.

[0110] The invention is not limited to the embodiments described as examples and shown in the drawings, but the element for compressing cryogenic gas to be compressed and the device equipped with the element according to the invention can be realized in various forms and sizes without exceeding the scope of the invention defined by the claims.

Claims

1. An oil-free screw compressor element for compressing low-temperature gas to be compressed below -40°C, The oil-free screw compressor element comprises a housing (2) which accommodates at least one rotor (3), the rotor being mounted so as to be rotatable about a rotor axis (5) relative to the housing (2), the housing having an inlet (6) for the gas to be compressed and an outlet (7) for the compressed gas, no oil being injected into the compression chamber in the housing of the oil-free screw compressor element for lubricating and / or sealing the rotor, It is characterized in that The oil-free screw compressor element has a heating device for heating the end (9a) of the rotor shaft closest to the inlet (6); The heating device comprises a first injection circuit (8) for injecting a heating medium having a temperature higher than the low temperature into the rotor shaft end (9a); The first injection circuit (8) is equipped with a nozzle (12) located at the end (9a) of the rotor shaft, and the nozzle (12) directly injects the heating medium onto the end (9a) of the rotor shaft; The rotor (3) is rotatably mounted relative to the housing (2) via a bearing (4), and the oil-free screw compressor element is provided with a second injection circuit (14) for injecting a heating medium having a temperature higher than the cryogenic temperature into the bearing (4); The nozzle (12) has two nozzle openings (13a, 13b), and the two nozzle openings are used to spray the heating medium onto the rotor shaft end (9a) and the bearing (4) respectively; a first duct (10) of the second injection circuit (14) having a first feed point (11) for feeding a heating medium into the oil-free screw compressor element, the first duct being located in a first part of the housing (2), the first part being located in the axial direction of the rotor shaft (5) on the side of the housing where the inlet (6) is located; a second duct (16) of the second injection circuit (14) having a second feed point (15) for feeding a heating medium into the oil-free screw compressor element, the second duct being located in a second part of the housing (2), the second part being located in the axial direction of the rotor shaft (5) on the housing side where the outlet (7) is located; The first feed point (11) and the second feed point (15) are connected to each other via a connecting pipe (18) provided in the housing (2), the connecting pipe being filled with a stationary heating medium to allow heat exchange between the heating medium injected through the first feed point and the second feed point.

2. The oil-free screw compressor element according to claim 1, characterized in that The temperature of the cryogenic gas to be compressed is at most -60°C, or at most -100°C.

3. The oil-free screw compressor element according to claim 1, characterized in that 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).

4. The oil-free screw compressor element according to claim 1 or 2, characterized in that An oil-free screw compressor element has at least one screw rotor.

5. A device for compressing low-temperature gas to be compressed below -40°C, characterized in that: The device is equipped with at least one oil-free screw compressor element according to any one of claims 1 to 4.

6. A method for compressing a cryogenic gas to be compressed at a temperature below -40°C by means of an oil-free screw compressor element according to any one of claims 1 to 4, the oil-free screw compressor element having a housing (2) accommodating at least one rotor (3) mounted to be rotatable about a rotor axis (5) relative to the housing (2), and having an inlet (6) for the gas to be compressed and an outlet (7) for the compressed gas, It is characterized in that The end (9a) of the rotor shaft closest to the inlet (6) is heated.

7. The method according to claim 6, characterized in that The temperature of the cryogenic gas to be compressed is at most -60°C, or at most -100°C.

8. The method according to claim 6 or 7, characterized in that: A heating medium is injected into the rotor shaft end (9a), wherein the temperature of the heating medium is higher than the temperature of the gas to be compressed.

9. The method according to claim 8, characterized in that The rotor (3) is rotatably mounted relative to the housing (2) via bearings (4), and a heating medium is also injected into the bearings (4).

10. The method according to claim 8, characterized in that The heating medium is a lubricating liquid.

11. The method according to claim 8, characterized in that The heating medium is oil.

12. Use of the oil-free screw compressor element according to any one of claims 1 to 4 or the device according to claim 5 for compressing cryogenic gases to be compressed at a temperature below -40°C.

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