The present invention relates to a centrifugal compressor, particularly a centrifugal compressor suitable for use in gas fields yielding natural gas.
In conjunction with the increase in demand for fossil fuel and the advancement of extracting technologies, development is recently shifting from conventional gas fields to non-conventional gas fields. As a result, it is necessary to install compressors in severe environments, such as under very deep seas and directly below gas fields.
To extract natural gas from under very deep seas, a method is considered in which a compressor (subsea compressor) is installed on the sea bottom several hundred meters deep and natural gas is pressure-fed from an underground reservoir. To extract natural gas from directly below gas fields, a method is proposed in which a compressor is installed in a gas well several thousand meters underground and gas is compressed on the bottom of the well and fed onto the ground. For this purpose, research and development are being conducted on compressors (downhole compressors).
In the initial phase, the underground pressure is high but the internal pressure is reduced as gas is extracted. As long as the underground pressure of a gas field is high, it is possible to let natural gas flow to the ground by itself. When the pressure is reduced to a limit or below, gas cannot flow to the ground by itself any longer. For this reason, a gas well with a reduced pressure is conventionally considered as being exhausted.
However, even after the underground pressure is reduced to a level insufficient to let gas flow by itself, a considerable quantity of natural gas remains in the gas field.
Consequently, it is considered that the production capacity of a gas field can be recovered by using a downhole compressor to boost the pressure directly below the gas field.
Since the above-mentioned subsea compressors and downhole compressors are installed on the bottom of a gas field or directly below a gas field, they are operated in very severe environments.
In general, the working fluids for compressors used in gas fields yielding natural gas include not only natural gas but also liquid containing water and soft liquid hydrocarbons called condensate. These compressors are placed in an operating environment in which the liquid is mixed. Especially, under a very deep sea or directly below a gas field mentioned above, compressors are exposed to an environment with a very high rate of the liquid.
A liquid that entered inside a compressor in such an environment is considered to cause various problems, including degradation in efficiency due to collision with an impeller, the narrowing of an operating range and the production of unstable fluid force due to the block of a flow path caused by fouling, and the reduced thickness of an impeller due to erosion. Therefore, compressors used in gas fields yielding natural gas require a technology to operate the compressor without degrading the performance thereof in an operating environment in which the liquid is prone to mix.
Conventional technologies of compressors that cope with the above problems are disclosed in Documents 1 and 2.
Document 1 discloses that grooves are formed in the surface of a vane of an impeller and the grooves are utilized to flow a fluid outward in the radial direction, the fluid having flowed in from the direction of a rotating shaft.
Document 2 discloses that grooves are extended from an inlet area to an outlet area such that a fluid flows from the inlet area outward in the radial direction with the rotation of an impeller disk.
Document 1: JP 2014-141909
Document 2: JP 2003-511596
In the technologies disclosed in Documents 1 and 2, although the installation of grooves makes the fluid flow easily, the fluid remains inside the compressor and is likely to attach to the impeller and, therefore, the problems have not been solved fundamentally yet.
The present invention has been made in consideration of the foregoing problems. An object of the present invention is to provide a centrifugal compressor that can be operated without degrading the efficiency of the impeller or reducing the operating range thereof even when the centrifugal compressor is operated in an environment in which a liquid likely mixes.
To achieve the above object, a centrifugal compressor of the present invention includes a rotating shaft which rotates rotationally, and an impeller including a hub fixed to the rotating shaft and a plurality of vanes fixed to the hub at a predetermined interval in a circumferential direction, wherein the centrifugal compressor compresses a fluid by rotation of the impeller, and wherein the hub includes a plurality of through holes penetrating the hub from a front side to a rear side of the impeller.
The present invention brings about an effect of providing a centrifugal compressor that can be operated without degrading the efficiency of the impeller or reducing the operating range thereof even when the centrifugal compressor is operated in an environment in which a liquid likely mixes.
Hereafter, a description will be given to a centrifugal compressor according to embodiments of the present invention with reference to the drawings. Through the following description of the embodiments, identical components will be indicated with identical reference characters.
As illustrated in
As illustrated in
In the configuration of this embodiment, a working fluid sucked from a suction port (located on the left side of
When a conventional centrifugal compressor 1, shown in
In the above-mentioned configuration in this embodiment, the liquid that flowed into the impeller 10 is about to attach to the hub 14 but almost all the droplets are discharged to the rear side of the impeller 10 through the through holes 15 formed between the position of the outside diameter Rh of the hub 14 and the position of the outside diameter Rsh of the shroud 13. This makes it possible to prevent the liquid from attaching to the vanes 12 and suppress degradation in the efficiency due to increase in the shaft power of the impeller 10. Since attaching of the droplets to the vanes 12 and the hub 14 is suppressed, it is possible to suppress the narrowing of the operating range and the production of unstable fluid force due to the block of the flow path.
Therefore, by forming the plural through holes 15 penetrating the hub 14 from the front side to the rear side of the impeller 10 as in this embodiment, even when the centrifugal compressor 1 is operated in an environment in which the liquid is mixed, droplets that entered the impeller 10 can be efficiently removed and the compressor 1 can be operated without degrading the efficiency of the impeller 10 or narrowing the operating range thereof.
The configuration of the centrifugal compressor 1 according to this embodiment illustrated in
In the configuration of this embodiment, a working fluid sucked from a suction port (located on the left side of
Therefore, by forming the plural through holes 15 penetrating the hub 14 from the front side to the rear side of the impeller 10 and the grooves 17 extended from the rotating shaft 11 side to the through holes 15 as in this embodiment, even when the centrifugal compressor 1 is operated in an environment in which the liquid is mixed, droplets that entered the impeller 10 can be efficiently removed and the compressor 1 can be operated without degrading the efficiency of the impeller 10 or narrowing the operating range thereof.
The configuration of the centrifugal compressor 1 according to this embodiment illustrated in
The above-mentioned leakage reducing member 16 includes a protruded portion 14A protruded in the axial direction from the rear side (right side of
In the configuration in this embodiment, the liquid that entered the impeller 10 is about to attach to the hub 14 but almost all the droplets are discharged to the rear side of the impeller 10 through the through holes 15 located between the position of the outside diameter Rh of the hub 14 and the position of the outside diameter Rsh of the shroud 13. This makes it possible to prevent the liquid from attaching to the vanes 12 and suppress degradation in the efficiency due to increase in the shaft power of the impeller 10. In addition, owing to the leakage reducing member 16 provided on the rear side of the impeller 10, it is possible to reduce a leakage flow flowing back from the outlet of the impeller 10 to the through holes 15. Therefore, it is possible to suppress degradation in the efficiency of the impeller 10.
Therefore, by forming the plural through holes 15 penetrating the hub 14 from the front side to the rear side of the impeller 10 and the leakage reducing member 16 for reducing a leakage flow flowing back from the outlet of the impeller 10 to the through holes 15 as in this embodiment, even when the centrifugal compressor 1 is operated in an environment in which the liquid is mixed, droplets that entered the impeller 10 can be efficiently removed and the compressor 1 can be operated without degrading the efficiency of the impeller 10 or narrowing the operating range thereof.
The present invention is not limited to the above-mentioned embodiments and includes various modifications. For example, the above embodiments are described in detail in order to make the present invention easy to understand and the invention is not necessarily limited to the embodiments provided with all the configuration elements described herein. Some configuration elements of an embodiment may be replaced with or added to configuration elements of another embodiment. In addition, with respect to each embodiment, some configuration elements thereof may be added to, deleted from, or replaced with other configuration elements thereof.
1 . . . Centrifugal compressor
10 . . . Impeller
11 . . . Rotating shaft
12 . . . Vane
13 . . . Shroud
14 . . . Hub
14A . . . Protruded portion
15 . . . Through hole
16 . . . Leakage reducing member
17 . . . Groove
18 . . . Casing
18A . . . Unevenness portion
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/JP2015/064374 | 5/19/2015 | WO | 00 |