JP2007177737A - Centrifugal compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a centrifugal compressor having a wide flow range, which stably operates without rotating stall. <P>SOLUTION: In the centrifugal compressor using a closed impeller 2 and provided with a vane-less diffuser 3, provided is a communication hole 10 connecting: an inlet hole 11 provided on a circumference direction side wall 3a in an impeller shroud 5 side of the vane-less diffuser 3; and an outlet hole 12 provided right behind a labyrinth seal 4 arranged in a disk inlet part of the impeller shroud 5, and an opening center position Dh of the inlet hole 11 is established in a range of 1.1-1.3 times of an outer diameter Di of the closed impeller 2 (Dh=1.1Di-1.3Di). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a centrifugal compressor provided with a vaneless diffuser used in a petrochemical or natural gas plant, and more particularly to a technique for preventing a rotating stall in the centrifugal compressor.

Conventionally, an impeller is rotatably supported in a housing, and when the impeller rotates, a fluid such as air or gas is sucked from a fluid inlet of the housing to give a centrifugal force, and the kinetic energy is applied to the diffuser and the scroll unit. Centrifugal compressors are known that are configured to be converted into pressure energy and sent out.
Examples of the above-described centrifugal compressor include a high-pressure industrial centrifugal compressor used in, for example, petrochemical and natural gas plants. In such a centrifugal compressor, a closed impeller is used and a vaneless diffuser is adopted as a standard component. FIG. 5 is a cross-sectional view showing a conventional vaneless diffuser section. In FIG. 5, reference numeral 1 denotes a rotary shaft of a centrifugal compressor, 2 denotes a closed impeller that rotates integrally with the rotary shaft 1, and 3 denotes a centrifugal force. A vaneless diffuser serving as a fluid flow path, 4 is a labyrinth seal, and 5 is an impeller shroud.

In addition, in order to improve the flow characteristics without changing the vane shape and mounting structure of the vaned diffuser, a bypass hole is formed in the throat portion of the diffuser, and this bypass hole and the impeller that is the low pressure portion on the compressor suction side are formed. It has been proposed to provide a bypass passage that communicates with an inlet facing the outer periphery. The proposed bypass hole is applicable not only to a centrifugal compressor provided with a variable diffuser with blades but also to a diffuser with fixed blades or a diffuser without blades. (For example, see Patent Document 1)
JP-A-9-119396 (see FIG. 1)

By the way, the high-pressure industrial centrifugal compressor described above has a problem of rotational stall in the vaneless diffuser section. For example, as shown in FIG. 6, this rotating stall is known to occur when the centrifugal compressor is operated in a low flow rate region of q1 or less. In this case, the flow rate q1 is a turning stall generation point in the centrifugal compressor, and a flow rate range W1 in a low flow rate region is a turning stall generation region.
Such a rotating stall is not preferable because it causes the shaft vibration of the rotary shaft 1 and the vibration of the discharge pipe (not shown) connected to the compressed fluid outlet of the centrifugal compressor to increase.

Therefore, the flow rate q1 at the turning stall point is moved to the lower flow rate side by narrowing the low flow rate region (W1) where the turning stall occurs to a minimum, and thus stable without causing the turning stall. It is desirable to develop a centrifugal compressor with an expanded flow range that allows operation.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a centrifugal compressor having a wide flow rate range capable of stable operation without causing a rotating stall. .

In order to solve the above problems, the present invention employs the following means.
A centrifugal compressor according to the present invention uses a closed impeller and includes a vaneless diffuser.
A communication hole is provided to connect between an inlet hole provided in a circumferential side wall on the impeller shroud side of the vaneless diffuser and an outlet hole provided immediately after a labyrinth seal provided in a disk inlet portion of the impeller shroud, The opening center position Dh of the inlet hole is set to a range of 1.1 to 1.3 times (Dh = 1.1 Di to 1.3 Di) with reference to the outer diameter Di of the closed impeller. It is a feature.

  According to such a centrifugal compressor, the inlet hole provided in the circumferential side wall on the impeller shroud side of the vaneless diffuser and the outlet hole provided immediately after the labyrinth seal provided in the disk inlet portion of the impeller shroud. A range of 1.1 to 1.3 times in which a communication hole is provided to connect the openings, and the opening center position Dh of the inlet hole is a radial position at which a turning stall starts to occur on the basis of the outer diameter Di of the closed impeller Therefore, the static pressure around the inlet hole can be reduced to make the circumferential pressure distribution non-uniform. In this case, if there is only one inlet hole, the efficiency of the centrifugal compressor can be minimized.

In the above centrifugal compressor, it is preferable that the outlet hole is opened by inclining the communication hole in the direction opposite to the impeller rotation direction, thereby reducing the swirling flow of the flow flowing into the labyrinth. it can.
In the above centrifugal compressor, it is preferable to provide a plurality of the inlet holes in the circumferential direction, whereby the circumferential pressure distribution can be made even more uneven.

  According to the present invention described above, the static pressure around the inlet hole is reduced to make the circumferential pressure distribution non-uniform, so that the turning stall is less likely to occur by preventing the turning in the stalled area (stall cell). As a result, the low flow rate value (turning stall occurrence point) that generates the turning stall can be lowered, and the flow range in which stable operation is possible can be expanded. Such an effect of preventing the rotation stall becomes more remarkable by increasing the number of inlet holes in the circumferential direction.

Further, by providing the outlet hole with an inclination opposite to the impeller rotation direction, it is possible to obtain the effect of a swirl canceller that relaxes the swirling flow of the flow flowing into the labyrinth and reduces anxiety and low vibration.
Accordingly, a centrifugal compressor having a wide flow rate range in which a stable operation can be performed without fear of the occurrence of a turning stall is realized by providing a turning stall occurrence point (flow rate value) that generates a turning stall at a lower flow rate side. Effects can be obtained.

Hereinafter, one embodiment of a centrifugal compressor concerning the present invention is described based on a drawing.
FIG. 1 is a cross-sectional view showing a vaneless diffuser portion of a centrifugal compressor. This centrifugal compressor is for high-pressure industrial use used in petrochemical, natural gas plants, etc., and uses a closed impeller 2 with a shroud (not shown) and a vaneless diffuser 3.
The closed impeller 2 is attached so as to protrude in the circumferential direction from the rotating shaft 1 supported by the casing, and rotates integrally with the rotating shaft 1 that obtains a driving force from a driving source (not shown). When the closed impeller 2 rotates, a fluid such as air or gas is sucked from a fluid inlet (not shown) of the housing, and centrifugal force is applied to the fluid to send it to the vaneless diffuser 3.

The vane-less diffuser 3 is a flow path that is connected to a space in which the closed impeller 2 rotates, converts the kinetic energy of the fluid given centrifugal force by the closed impeller 2 to pressure energy, and sends it out. The downstream side of the vaneless diffuser 3 communicates with a fluid outlet (not shown) of the casing.
Reference numeral 4 in the figure denotes a labyrinth seal that is attached for the purpose of preventing fluid from leaking from a gap formed between the closed impeller 2 and the disk inlet 5a (see FIG. 2) of the impeller shroud 5. It has been.

Thus, the centrifugal compressor that uses the closed impeller 2 and includes the vaneless diffuser 3 includes an inlet hole 11 provided in the circumferential side wall 3a on the impeller shroud 5 side of the vaneless diffuser 3, and the impeller shroud. A communication hole 10 is provided to connect the outlet hole 12 provided immediately after the labyrinth seal 4 disposed at the disk inlet portion 5a. In the configuration example shown in FIG. 1, the inlet hole 11 is provided in one place in order to suppress a decrease in efficiency of the centrifugal compressor.
By providing such a communication hole 10, a part of the fluid flows out from the high-pressure side inlet hole 11 to the low-pressure side outlet hole 12, so that the static pressure decreases around the inlet hole 11. As a result, in the circumferential side wall 3a of the vane-less diffuser 3, the circumferential pressure distribution intersecting the rotating shaft 1 becomes non-uniform.

The opening center position Dh of the inlet hole 11 described above is set in a range of 1.1 to 1.3 times (Dh = 1.1 Di to 1.3 Di) with reference to the outer diameter Di of the closed impeller 2. This is because the start position of the rotating stall and the position where the pressure fluctuation is large are in the range of 1.1 to 1.3 times (Dh = 1.1 Di to 1.3 Di) with reference to the outer diameter Di of the closed impeller 2. It is based on having obtained the knowledge.
That is, the inlet hole 11 is provided in the circumferential side wall 3a of the vaneless diffuser 3 that is on the outer side in the circumferential direction from the outer diameter Di, if the diameter of the locus of rotation of the tip of the closed impeller 2 is the outer diameter Di. The center of the opening is located on a virtual circle having a diameter Dh with the rotation axis 1 as the center.

In the centrifugal compressor having such a configuration, the inlet hole 11 is opened in the circumferential region (Dh = 1.1Di to 1.3Di) in the vane diffuser 3 where the rotational stall starts to occur. Since it is possible to prevent the turning in the stalled area (stall cell) by making the pressure distribution in the direction non-uniform, the turning stall is less likely to occur. As a result, as shown in FIG. 3, since the flow rate at the turning stall occurrence point can be reduced to q2 (q2 <q1), the flow rate range (turning stall occurrence region) W2 in the low flow rate region where the turning stall occurs. It becomes narrower than the conventional W1, and the flow rate range enabling stable operation is expanded.
In addition, a plurality of the inlet holes 11 described above are opened in the circumferential direction and connected to the communication hole 10, whereby the effect of preventing the turning stall can be further increased.

  By the way, although the exit hole 12 of embodiment mentioned above is opening from the communicating hole 10 extended straightly in the direction orthogonal to the rotating shaft 1 as shown in FIG. 2, as shown in the modification shown in FIG. It is good also as the exit hole 12A which provided the inclination opposite to a rotation direction. The outlet hole 12A opens from the communication hole 10A provided with the inclined passage 13 inclined in the direction opposite to the impeller rotation direction (counterclockwise in the illustrated example). Will flow out from the outlet hole 12 at the tip of the inclined passage 13 toward the closed impeller 2 rotating toward the outlet hole 12. That is, since the high-pressure fluid that has flowed from the inlet hole 11 is inclined in a direction that cancels the swirling flow that flows into the labyrinth 4, the swirl that relaxes the swirling flow that flows into the labyrinth 4 and reduces anxiety and low vibration. A canceller effect can be obtained.

As described above, according to the centrifugal compressor of the present invention, the turning stall generation point (flow rate value) that generates the turning stall can be moved to the lower flow rate side, so that there is no fear of causing the turning stall. The range of flow rate that can be operated can be widened. Therefore, the cause of increasing the shaft vibration of the rotating shaft 1 caused by the rotation stall and the vibration of the discharge pipe (not shown) connected to the compressed fluid outlet of the centrifugal compressor is eliminated, and the centrifugal compressor and the same are used. The reliability and durability of the device can be improved.
In addition, this invention is not limited to embodiment mentioned above, In the range which does not deviate from the summary of this invention, it can change suitably.

It is a figure which shows one Embodiment of the centrifugal compressor which concerns on this invention, (a) is principal part sectional drawing which shows a vane less diffuser part, (b) is AA sectional drawing of (a). (A) is the B section enlarged view of Fig.1 (a), (b) is CC sectional drawing of (a). It is a performance curve figure of the centrifugal compressor which shows the turning stall generation point of the centrifugal compressor by the present invention. It is a figure which shows the modification of FIG.2 (b). It is principal part sectional drawing which shows the vaneless diffuser part of a centrifugal compressor as a prior art example. It is a performance curve figure of the centrifugal compressor which shows the turning stall generation | occurrence | production point of the prior art example shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rotating shaft 2 Closed impeller 3 Vane-less diffuser 4 Labyrinth seal 10, 10A Communication hole 11 Inlet hole 12, 12A Outlet hole 13 Inclined passage

Claims (3)

In a centrifugal compressor that uses a closed impeller and has a vaneless diffuser,
A communication hole is provided to connect between an inlet hole provided in a circumferential side wall on the impeller shroud side of the vaneless diffuser and an outlet hole provided immediately after a labyrinth seal provided in a disk inlet portion of the impeller shroud,
The opening center position Dh of the inlet hole is set to a range of 1.1 to 1.3 times (Dh = 1.1 Di to 1.3 Di) with reference to the outer diameter Di of the closed impeller. Features centrifugal compressor.   2. The centrifugal compressor according to claim 1, wherein the outlet hole is opened by inclining the communication hole in the direction opposite to the impeller rotation direction.   The centrifugal compressor according to claim 1 or 2, wherein a plurality of the inlet holes are provided in the circumferential direction.

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