Element, device and method for compressing a low-temperature compressed gas

Abstract

Apparatus and method for compressing a gas to be compressed at a low temperature. An element (1) for compressing a gas at a low temperature of -40°C or lower, said element (1) comprising a housing (2) including at least one rotor (3) rotatably arranged relative to said housing (2), said element (1) being configured for compressing the gas by providing a heating duct (8) passing through said housing (2), said heating duct (8) comprising an inlet (9) through which a first heat transfer medium is introduced into the housing (2) at a temperature higher than said low temperature, and an outlet (10) through which the first heat transfer medium is discharged from the housing (2).

Description

Technical Field

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

Background Art

[0002] Hereinafter, "low temperature" means a temperature of -40°C or lower. Therefore, the present invention is intended for cryogenic applications.

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

[0004] It is known that a reciprocating compressor or a piston compressor is used for such applications.

[0005] The disadvantage of such a reciprocating compressor or piston compressor is that pulsation occurs in the supply of the compressed gas due to its operation. In other words, the supply of the compressed gas is interrupted.

[0006] However, in some applications, a continuous supply of compressed gas is required.

[0007] For example, a screw compressor element having a screw rotor is known to operate continuously without generating pulsation in the supply of the compressed gas. In addition, the energy consumption of the screw compressor element is low.

[0008] However, the screw compressor element is not suitable for use in compressing a gas at -40°C or lower.

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

[0010] The thermal deformations of these materials occurring at such low temperatures are various. This affects the tolerances and clearances of the screw compressor elements, which increase due to such thermal deformations, resulting in a decrease in the efficiency and performance of the screw compressor elements.

[0011] Therefore, the gas to be compressed at -40°C or lower is first heated before entering the screw compressor element.

[0012] This solves the problem of thermal deformation, but since it is necessary to cool the compressed gas again after compression, it is accompanied by a large energy loss. Summary of the Invention Problems to be Solved by the Invention

[0013] An object of the present invention is to provide a solution to at least one of the above-mentioned drawbacks and / or other drawbacks by providing an element capable of compressing a gas to be compressed at a temperature of -40°C or lower. Means for Solving the Problems

[0014] The present invention relates to an element for compressing a gas to be compressed at a low temperature of -40°C or lower. This element includes at least one rotor rotatably arranged with respect to a housing, and is provided with a housing having an inlet for the gas to be compressed and an outlet for the compressed gas. The element is configured to compress the low-temperature gas to be compressed by providing a heating duct penetrating the housing in the element. The heating duct is characterized by including an inlet through which a first heat medium is introduced into the housing at a temperature higher than the above-mentioned low temperature, and an outlet through which the first heat medium is discharged from the housing.

[0015] The advantage is that by providing the first heat medium in the heating duct, heat can be supplied to the housing, which can prevent a sharp temperature drop of the housing and / or the rotor due to the low temperature of the gas to be compressed.

[0016] As a result, thermal deformation of the housing and / or the rotor can be restricted, so that the tolerances and clearances between the rotor and the housing are kept within a reasonable range, and thermal stress is restricted.

[0017] The inlet of the heating duct is preferably arranged such that heat is exchanged between the inlet of the housing and the inlet of the heating duct.

[0018] Alternatively or additionally, the outlet of the heating duct is arranged such that heat is exchanged between the outlet of the housing and the outlet of the heating duct.

[0019] Since the temperature of the gas will increase during compression, the inlet temperature will be lower than the outlet temperature. By enabling the first heat medium to first pass through the inlet, which is the coldest position of the element, and finally pass through the outlet, which is the warmest position of the element, it is possible to ensure that the thermal energy of the first heat medium is distributed proportionally or uniformly as heat throughout the housing, and to limit the temperature gradient from the inlet side to the outlet side of the element.

[0020] In a practical embodiment of the element according to the invention, the heating duct comprises branches which are arranged such that heat is exchanged between these branches and the inlet.

[0021] Alternatively or additionally, in a practical embodiment of the element according to the invention, the heating duct comprises a plurality of bends and / or curves which are arranged such that heat is exchanged between these bends and / or curves on the one hand and the inlet on the other hand.

[0022] As a result, the first heat medium will be in closer contact with the inlet for a longer period of time or over a longer distance than if the heating duct were not provided with branches, bends and / or curves.

[0023] "Close contact" means that heat transfer is possible between the first heat medium and a part of the housing around the inlet.

[0024] This will contribute to the proper heating of the housing around the inlet and will make it possible to avoid excessive temperature drops there.

[0025] In a preferred embodiment of the element according to the invention, the heating duct is designed such that a first heat medium can flow from an inlet portion of the housing (this inlet portion is arranged axially along the shaft of the rotor on the side where the inlet of the housing is located) to an outlet portion of the housing (this outlet portion is arranged axially along the shaft on the side where the outlet of the housing is located), and / or vice versa.

[0026] As a result, the entire housing or at least the main part of the housing can be heated by heat exchange with the first heat medium in the heating duct.

[0027] In the next preferred embodiment of the element according to the invention, the rotor is rotatably arranged with respect to the housing by bearings, and the element comprises an injection circuit for injecting a second heat medium into the bearings at a temperature higher than a low temperature.

[0028] As a result, the bearings can also be heated to prevent the bearings from getting too cold and freezing, which could endanger the normal operation of the bearings due to increased friction of the bearings.

[0029] The first duct of the injection circuit having a first supply point for the second heat medium is preferably arranged in a first part of the housing that is arranged axially along the shaft of the rotor on the side where the inlet of the housing is located.

[0030] Alternatively or additionally, the second duct of the injection circuit having a second supply point for the second heat medium is arranged in a second part of the housing that is arranged axially along the shaft of the rotor on the side where the outlet of the housing is located.

[0031] The advantage is that the supply points can be arranged at one and / or both ends of the rotor by supplying a second heat medium to the inlet side and / or the outlet side of the element.

[0032] In other words, the bearing on the inlet side of the element and / or the bearing on the outlet side of the element have unique injection points such that the second heat medium is injected as close as possible to the bearing, and there is no need to carry the second heat medium from the inlet side of the element to the outlet side of the element, or vice versa, through the housing.

[0033] In this way, it is possible to prevent the second heat medium from freezing or becoming overly cold when passing through the housing, which could otherwise cause clogging of the second heat medium and / or deterioration of the lubricating properties of the second heat medium within the element.

[0034] The second heat medium only needs to travel a limited distance through the housing from the supply point to the associated bearing, so the second heat medium will cool minimally, and as a result, the second heat medium can dissipate maximum heat to the bearing.

[0035] The first supply point and the second supply point can be interconnected by a connection duct for the second heat medium within the housing.

[0036] This connection duct enables heat exchange between the second heat medium injected through the first supply point and the second supply point.

[0037] This heat exchange occurs from the high-temperature outlet side of the element towards the low-temperature inlet side through the second heat medium within the connection duct.

[0038] This will ensure a uniform temperature throughout the second heat medium, the entire housing, and the bearings.

[0039] As a result, there is also a low risk that the second heat medium will be locally over-cooled within the element.

[0040] At least a part of the heating duct is preferably arranged such that heat is exchanged between the heating duct and the first duct, the second duct and / or the connecting duct, respectively.

[0041] As a result, there is a low risk that the second heat medium will be overcooled in the injection circuit.

[0042] In a preferred embodiment of the element according to the invention, the element comprises heating means for the end of the rotor shaft that is closest to the inlet.

[0043] The advantage is that in this way the above-mentioned end of the shaft can be heated.

[0044] At this position, there will be the largest temperature difference with the heating means, enabling the maximum possible heat transfer between the heating means and the rotor.

[0045] Due to the thermal conductivity of the shaft, the heat transferred to the shaft will be distributed throughout the shaft and the rotor body of the rotor.

[0046] As a result, it is possible to eliminate the temperature gradient across the rotor from the inlet side to the outlet side of the element, such as occurs in known elements, and the entire rotor will be at approximately the same temperature.

[0047] As a result, the thermal deformation of the rotor is limited, the tolerances and clearances between the rotor and the housing are maintained within a reasonable range, and the thermal stress is limited.

[0048] The invention also relates to an apparatus for compressing a low-temperature compressed gas of -40°C or lower, the apparatus comprising at least one element according to the invention.

[0049] It goes without saying that such an apparatus has the same advantages as the above-described embodiments of the element according to the invention.

[0050] The present invention also relates to a method for compressing a compressed gas at a low temperature of -40°C or lower using an element, the element comprising a housing, the housing comprising at least one rotor rotatably arranged with respect to the housing, and having an inlet for the compressed gas to be compressed and an outlet for the compressed gas, the element comprising a heating duct passing through the housing, a first heat medium being introduced into the housing at the inlet of the heating duct and the first heat medium being discharged from the housing at the outlet of the heating duct, characterized in that.

[0051] The temperature of the compressed gas at low temperature is preferably at most -60°C, more preferably at most -100°C.

[0052] The first heat medium is preferably a mixture of water and glycol having at least 40% glycol. In this way, the first heat medium has a freezing temperature lower than -40°C.

[0053] The temperature of the first heat medium at the inlet of the heating duct is preferably at least 60°C.

[0054] The greater the temperature difference between the first heat medium and the compressed gas to be compressed, the greater the driving force for heat exchange between the first heat medium and the compressed gas to be compressed.

[0055] In a preferred embodiment of the method according to the present invention, the rotor is rotatably arranged with respect to the housing by means of a bearing, and a second heat medium is injected into the bearing.

[0056] The advantages of such a method needless to say overlap with the advantages of the corresponding embodiment of the element according to the present invention described above.

[0057] Preferably, the second heat medium is a lubricating fluid, preferably oil.

[0058] In this way, the second heat medium is useful not only for heating the bearing but also for lubricating the bearing.

[0059] Finally, the invention also relates to the use of an element or device according to the invention for compressing a low-temperature compressed gas of -40 °C or lower.

[0060] To better illustrate the features of the invention, some preferred embodiments of an element according to the invention for compressing a low-temperature compressed gas and a device comprising such an element are described below by way of non-limiting examples with reference to the accompanying drawings.

Brief Description of the Drawings

[0061]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

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

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

[0064] The screw compressor element is, in this case, an oil-free screw compressor element, meaning that no oil is injected for lubrication and / or sealing of the helical rotors in the compression chamber within the housing 2 of the element 1.

[0065] The helical rotors are arranged such that the shaft 5 is rotatably mounted with respect to the housing 2 by bearings 4.

[0066] Furthermore, the housing 2 comprises an inlet 6 for the low-temperature compressed gas and an outlet 7 for the compressed gas.

[0067] According to the present invention, the temperature of the low-temperature gas to be compressed is -40°C or lower, preferably, although not essential in the present invention, -60°C or lower, and more preferably -100°C or lower.

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

[0069] According to the present invention, the housing 2 is provided with a heating duct 8 passing through the housing 2. The heating duct 8 is shown in FIG. 2.

[0070] The heating duct 8 has an inlet 9 for introducing a first heat medium into the housing 2 and an outlet 10 for discharging this first heat medium from the housing 2.

[0071] The inlet 9 and the outlet 10 of the heating duct 8 are shown in FIGS. 1 and 3.

[0072] In this case, although not essential according to the present invention, the first heat medium is a mixture of water and a glycol also called 1,2-ethanediol or ethylene glycol.

[0073] The first heat medium preferably contains at least 40% glycol. As a result, the first heat medium has a freezing temperature lower than -40°C.

[0074] The first heat medium itself will have a temperature of, for example, 60°C.

[0075] As shown in FIG. 3, the inlet 9 of the heating duct 8 is located near the inlet 6 of the housing 2, and the outlet 10 of the heating duct 8 is located near the outlet 7 of the housing 2.

[0076] The inlet 6 of the housing 2 is the coldest location because the compressed gas enters here at a low temperature. At the inlet 9 of the heating duct 8, the temperature of the first heat medium is the highest because no heat exchange with the housing 2 has occurred yet. When passing through the heating duct 8, the temperature of the first heat medium generally decreases until it reaches the outlet 10 near the outlet 7, which is the location with the highest temperature of the housing 2.

[0077] In this case, although not essential according to the present invention, the heating duct 8 is designed with bends and dendritic or branched portions so that the first heat medium can flow through the entire housing 2.

[0078] In this way, heating of the entire housing 2 is ensured, and it can be guaranteed that the temperature of the housing 2 becomes as uniform as possible.

[0079] In addition, the heating duct 8 has a dendritic portion located near the inlet 6 of the housing 2.

[0080] "Near the inlet 6" means that heat exchange can occur between the heat medium and the inlet 6 of the housing 2.

[0081] This ensures that the housing 2 near the inlet 6 is heated more than other parts of the housing 2 because the first heat medium circulates more in the housing 2 near the inlet 6 and more heat exchange occurs between the first heat medium and the housing 2 near the inlet 6.

[0082] Also, the heating duct 8 can have a plurality of bends or curves near the inlet 6 of the housing 2 instead of or in addition to the dendritic or branched portions. This makes it possible to obtain the same effect as described above for the dendritic portion near the inlet 6 of the housing 2.

[0083] In the illustrated example, the element 1 includes an injection circuit 11.

[0084] It should be noted that this injection circuit 11 is used to enable the injection of the second heat medium into the bearing 4. In other words, the injection circuit 11 is not used for the injection of oil into the compression chamber.

[0085] As shown in FIG. 2, the injection circuit 11 comprises two supply points 12, 13 for the second heat medium into the element 1 at two different positions within the housing 2.

[0086] As shown in the figure, in the housing 2, the supply points 12, 13 are present at each end 14a, 14b of the rotor 3.

[0087] As a result, the second heat medium can be injected into the housing 2 as close as possible to the bearings 4 at the ends 14a, 14b of the shaft 5 of the rotor 3.

[0088] The ducts 15a, 15b will penetrate the housing 2 from the supply points 12, 13 to the bearing 4 in order to supply the second heat medium to the bearing 4.

[0089] The bearing 4 is provided with a suitable nozzle 16.

[0090] As shown in FIG. 2, the two supply points 12, 13 are interconnected by a connection duct 17 for the second heat medium within the housing 2.

[0091] This connection duct 17 will be filled with the second heat medium during the operation of the device.

[0092] In this case, a part of the heating duct 8 will be located near the connection duct 17 and / or the above-mentioned ducts 15a, 15b, enabling heat exchange with the heat medium within these ducts 8, 15a, 15b, 17.

[0093] In other words, the first heat medium can heat the second heat medium.

[0094] The screw compressor element operates in a very simple manner as follows.

[0095] During the operation of the screw compressor element, each helical rotor rotates in cooperation so as to mesh with each other, and sucks in the low-temperature gas to be compressed through the inlet 6 of the housing 2.

[0096] The gas is compressed by the helical rotor 3 and will be discharged from the screw compressor element 1 through the outlet 7 of the housing 2.

[0097] In this case, the low-temperature gas to be compressed will strongly cool the housing 2.

[0098] Although the temperature of the gas rises during the compression process, the temperature of the gas will still be low, and after compression, the compressed gas will still cool the housing 2.

[0099] During the operation of the element 1, the first heat medium will flow through the heating duct 8 and will heat the housing 2.

[0100] The temperature of the first heat medium at the inlet 9 of the heating duct 8 is, for example, 60 °C, but it is obvious that this temperature of the first heat medium will be selected according to the temperature of the low-temperature gas to be compressed.

[0101] The heating will be greater near the inlet 9 where the first heat medium has the highest temperature than near the outlet 10 where the first heat medium will have a low temperature.

[0102] Since the inlet 6 is the coldest place in the housing 2, most of the heating will be required here.

[0103] Due to the branch near the inlet 6 of the housing 2, the first heat medium will exchange heat with the part of the housing 2 near the inlet 6 for a longer time than when there is no branch, enabling sufficient heating of the said part of the housing 2.

[0104] Thereafter, the first heat medium flows through the entire housing 2 along the heating duct 8 and heats the housing 2.

[0105] It should be noted that by heating the housing 2, the rotor 3 is also heated indirectly by the first heat medium.

[0106] As a result, the temperature of the entire element 1 is maintained as high as possible and becomes uniform.

[0107] As a result of heating the housing 2, the bearing 4 is also indirectly and partially heated.

[0108] However, in order to ensure the proper function of the bearing 4, the injection circuit 11 injects the second heat medium into the bearing 4 at a temperature higher than the low temperature of the compressed gas.

[0109] Regarding the bearings 4 at both ends 14a, 14b of the shaft 5 of the rotor 3, the housing 2 is provided with special supply points 12, 13, and the second heat medium can be conveyed to the bearings 4 using ducts 15a, 15b as short as possible.

[0110] In this way, before the second heat medium reaches the bearing 4, if it passes through the cold housing 2, the temperature drop of the second heat medium can be limited as much as possible.

[0111] Furthermore, since a part of the heating duct 8 is arranged near the ducts 15a, 15b, this helps to ensure that the temperature of the second heat medium on its way to the bearing 4 does not drop as much as possible, and the bearing 4 can be heated to the maximum extent.

[0112] The purpose of the connection duct 17 that provides a connection between the two supply points 12, 13 is to enable heat exchange regarding the second heat medium injected through the two supply points 12, 13.

[0113] This connection duct 17 will be filled with a second heat transfer medium, which usually remains stationary and does not reach the bearing 4, but heat exchange from the high-temperature outlet 7 to the very low-temperature inlet 6 will be made possible via the second heat transfer medium within the connection duct 17.

[0114] This will ensure a uniform temperature throughout the second heat transfer medium within the housing 2, throughout the entire housing 2, and through the bearing 4.

[0115] In this case, there is also no risk of the second heat transfer medium being overcooled.

[0116] Furthermore, since a part of the heating duct 8 is arranged close to the connection duct 17, this will help ensure that the temperature of the second heat transfer medium does not drop as much as possible within the connection duct 17. In this way, freezing of the second heat transfer medium can be prevented, thereby preventing the connection duct 17 from becoming clogged.

[0117] The present invention is not limited to the embodiments described by way of example or shown in the drawings, and the elements for compressing the low-temperature compressed gas according to the present invention and the apparatus provided with such elements can be realized in various shapes and dimensions without departing from the scope of the present invention defined in the claims.

Claims

1. An element for compressing a low-temperature compressed gas at -40°C or lower, wherein the element (1) comprises a housing (2), the housing (2) includes at least one rotor (3) rotatably arranged with respect to the housing (2), and has an inlet (6) for the compressed gas and an outlet (7) for the compressed gas, the element (1) is configured to compress the low-temperature compressed gas by providing a heating duct (8) passing through the housing (2), the heating duct (8) having an inlet (9) through which a first heat medium is introduced into the housing (2) at a temperature higher than the low temperature, and an outlet (10) through which the first heat medium is discharged from the housing (2), the element (1) is a screw compressor element having at least one helical rotor, and the element (1) is an oil-free screw compressor element. The element is characterized by the above.

2. The temperature of the compressed gas is at most -60°C. The element according to Claim 1.

3. The first heat medium is a water and glycol mixture having at least 40% glycol. The element according to Claim 1 or 2.

4. The inlet (9) of the heating duct (8) is arranged such that heat is exchanged between the inlet (6) of the housing (2) and the inlet (9) of the heating duct (8). The element according to any one of Claims 1 to 3.

5. The outlet (10) of the heating duct (8) is arranged such that heat is exchanged between the outlet (7) of the housing (2) and the outlet (10) of the heating duct (8). The element according to any one of Claims 1 to 4.

6. The heating duct (8) comprises a branched portion, and the branched portion is arranged such that heat is exchanged between the branched portion and the inlet (6). The element according to any one of Claims 1 to 5.

7. The heating duct (8) has a plurality of bent portions and / or curved portions, and the bent portions and / or curved portions are arranged such that heat is exchanged between the bent portions and / or curved portions on one hand and the inlet (6) on the other hand. The element according to any one of Claims 1 to 6.

8. The heating duct (8) is designed such that the first heat medium can flow from the inlet portion of the housing (2) to the outlet portion of the housing (2) and / or vice versa. The inlet portion is arranged along the axial direction of the shaft (5) of the rotor (3) on the side where the inlet (6) of the housing (2) is located. The outlet portion is arranged along the axial direction of the shaft (5) on the side where the outlet (7) of the housing (2) is located. The element according to any one of claims 1 to 7.

9. The rotor (3) is rotatably arranged with respect to the housing (2) by a bearing (4). The element (1) comprises an injection circuit (11) for injecting a second heat medium into the bearing (4) at a temperature higher than the low temperature. The element according to any one of claims 1 to 8.

10. The first duct (15a) of the injection circuit (11) having the first supply point (12) for the second heat medium is arranged along the axial direction of the shaft (5) of the rotor (3) on the side where the inlet (6) of the housing (2) is located and is arranged in the first part of the housing (2). The element according to claim 9.

11. The second duct (15b) of the injection circuit (11) having the second supply point (13) for the second heat medium is arranged along the axial direction of the shaft (5) of the rotor (3) on the side where the outlet (7) of the housing (2) is located and is arranged in the second part of the housing (2). The element according to claim 9 or 10.

12. The first supply point (12) and the second supply point (13) are interconnected by a connection duct (17) for the second heat medium within the housing (2). The element according to claim 11, which cites claim 10.

13. At least a part of the heating duct (8) is arranged such that heat is exchanged between the heating duct (8) and the first duct (15a), the second duct (15b) and / or the connection duct (17). The element according to claim 12.

14. The element (1) comprises heating means for the end of the shaft of the rotor (3) that is closest to the inlet (6). The element according to any one of claims 1 to 13.

15. An apparatus for compressing a compressed gas at a low temperature of -40°C or lower, the apparatus comprising at least one element (1) according to any one of claims 1 to 14.

16. A method for compressing a compressed gas at a low temperature of -40°C or lower using the element (1), wherein the element (1) comprises a housing (2), the housing (2) includes at least one rotor (3) rotatably arranged with respect to the housing (2), and has an inlet (6) for the compressed gas and an outlet (7) for the compressed gas, wherein the element (1) comprises a heating duct (8) passing through the housing (2), a first heat medium is introduced into the housing (2) at an inlet (9) of the heating duct (8) at a temperature higher than the low temperature, and the first heat medium is discharged from the housing (2) at an outlet (10) of the heating duct (8), wherein the element (1) is a screw compressor element having at least one helical rotor, and the element (1) is an oil-free screw compressor element. A method characterized by this.

17. The method according to claim 16, wherein the temperature of the compressed gas is at most -60°C.

18. The method according to claim 16 or 17, wherein the first heat medium is a mixture of water and glycol having at least 40% glycol.

19. The method according to any one of claims 16 to 18, wherein the temperature of the first heat medium is at least 60°C at the inlet (9) of the heating duct (8).

20. The method according to any one of claims 16 to 19, wherein the rotor (3) is rotatably arranged with respect to the housing (2) by a bearing (4), and a second heat medium is injected into the bearing (4).

21. The method according to claim 20, wherein the second heat medium is a lubricating fluid.

22. Use of an element according to any one of claims 1 to 14 or the apparatus according to claim 15 for compressing a compressed gas at a low temperature of -40°C or lower.

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