JP4655603B2 - Centrifugal compressor - Google Patents

Description

  The present invention relates to a centrifugal compressor provided with an impeller (impeller).

A centrifugal compressor is known as one of compressors for compressing gas.
For example, as shown in FIG. 6, the conventional centrifugal compressor includes a rotating shaft 12 and a housing 13 to which an impeller 21 (impeller) is attached.
The housing 13 includes a housing body 14 that supports the rotating shaft 12 and a shroud housing 15.
The impeller 21 is disposed between the housing body 14 and the shroud housing 15.
As shown in FIG. 7, the impeller 21 includes two types of rotary blades (long blade 23 and short blade 25) attached in a radial pattern.
The housing body 14 accommodates drive means (not shown) connected to the rotating shaft 12.
The shroud housing 15 forms a suction port 16 communicating with the impeller 21 and a volute 17 (vortex chamber).
The housing body 14 and the shroud housing 15 form a diffuser 18 on the outer periphery of the impeller 21.
Specifically, the diffuser 18 is mainly formed by the housing wall portion 14 a of the housing body 14 and the shroud wall portion 15 d of the shroud housing 15.
The inlet of the diffuser 18 faces the outer periphery of the impeller 21, and the outlet communicates with a volute 17 that leads to a discharge port (not shown).

This centrifugal compressor sucks gas into the housing 13 by the rotation of the impeller 21.
The sucked gas is sent to the diffuser 18 through the impeller 21 and is compressed by at least centrifugal force.
As shown in FIG. 7, the gas compressed by the impeller 21 is a swirl flow including velocity components X and Y in the radial direction and the circumferential direction.
The gas in the diffuser 18 is pumped to the volute 17.
FIG. 8 is a view taken along the line AA in FIG. 7 and shows a velocity distribution vg of the radial flow between the housing wall portion 14a and the shroud wall portion 15d.
Since the gas to be compressed is a viscous fluid, the velocity distribution vg of the gas flow is the largest in the vicinity of the center and becomes smaller as it approaches both wall portions 14a and 15d.

Velocity component V of the flow of gas delivered from the impeller 21 can be divided into radial velocity component X and the circumferential Direction velocity component Y of the impeller 21.
When the amount of gas to be sucked is small (during low flow operation), the radial velocity component X is smaller than the circumferential velocity component Y.
During low flow operation, part of the flow cannot counter the pressure gradient, and part of the gas flows backward along the walls 14a and 15d (the white arrows in FIG. 8 indicate the main gas flow, and solid arrows) Indicates a flow corresponding to the velocity distribution.) A phenomenon occurs, and this phenomenon is called "diffuser stall".

As a related technique, Patent Document 1 discloses a first slit provided concentrically with an impeller on the diffuser wall at the diffuser inlet, and a first slit provided concentrically with the diffuser wall in the middle of the diffuser. A centrifugal compressor in which the second slit is communicated by a bypass channel is disclosed.
Japanese Utility Model Publication No. 6-76697

The conventional centrifugal compressor has a problem that a diffuser stall occurs during low flow operation. When such a diffuser stall occurs, the centrifugal compressor cannot be stably operated.
The technique of Patent Document 1 is applied to a centrifugal compressor including a vane diffuser having blades.
In other words, this technique is a technique for eliminating surging in the vane diffuser blade, and the above-described diffuser stall cannot be solved.
The present invention has been made in view of the above problems, and an object of the present invention is to provide a centrifugal compressor capable of preventing or suppressing a diffuser stall even when the gas flow rate is low. .

In order to achieve the above object, the present invention includes an impeller that is pivotally supported on a housing, a diffuser disposed downstream of the impeller, and a volute that communicates with an outlet of the diffuser. A centrifugal compressor that compresses the sucked gas by at least centrifugal force, the diffuser and the volute being communicated, and a reflux passage for returning a part of the gas of the volute to the diffuser is provided in the housing, The reflux passage is formed in a circular arc groove shape in the circumferential direction of the diffuser .
According to the present invention, during low flow operation, the gas in the diffuser is added with the velocity component of the gas from the reflux passage in addition to the radial velocity component of the gas from the impeller.
The added velocity component provides a momentum that can counter the radial pressure gradient. The added velocity component reduces the low-speed region near the wall and delays the occurrence of backflow. Therefore, even if the gas flow rate is low, the diffuser stall can be prevented or suppressed.

In the present invention, the outlet of the reflux passage may be provided near the inlet of the diffuser.
Furthermore, the reflux passage may be linear.
Furthermore, in the present invention, an opening / closing valve may be provided in the reflux passage, and the opening / closing valve is preferably opened during low flow operation of the centrifugal compressor.

  ADVANTAGE OF THE INVENTION According to this invention, even if the flow volume of gas is a low flow volume, the centrifugal compressor which can prevent or suppress a diffuser stall can be provided.

(First embodiment)
Hereinafter, an embodiment of a centrifugal compressor according to the present invention will be described with reference to FIGS.
In addition, about the element which is common or similar to a prior art, the same code | symbol is used and a part of description of a prior art is used.
The centrifugal compressor of this embodiment includes a rotating shaft 12 and a housing 13 to which an impeller 21 (impeller) is attached.
FIG. 1 is a side view showing a schematic outline of a centrifugal compressor. FIG. 2 is a front view showing an outline of the inlet 16 side of the impeller 21 and the diffuser 18. FIG. 3 is an enlarged side view showing the periphery of the reflux passage. FIG. 4 is a view taken along the line BB in FIG. 2 and shows a velocity distribution in the vicinity of the entrance of the diffuser 18.

The centrifugal compressor according to this embodiment and the conventional centrifugal compressor are the same as those of the conventional centrifugal compressor except that the structure of the shroud housing 15 is different.
The impeller 21 shown in FIGS. 1 and 2 includes a disk 22 having a shaft hole 22a for the rotating shaft 12, and two types of rotary blades 23 and 25 formed radially on the disk 22.
The impeller 21 is disposed between the housing body 14 and the shroud housing 15 and is rotatable with respect to the housing 13.
The impeller 21 has a function of sucking gas from the suction port 16 by rotation, compressing the gas by at least centrifugal force, and sending it to the diffuser 18.

[About the impeller]
A known disk 22 can be used for the impeller 21.
As shown in FIG. 1, the disk 22 has two types of rotary blades, a long blade 23 and a short blade 25.
As shown in FIG. 2, there are six long blades 23 and short blades 25, and both 23 and 25 are thin plates.
The long wings 23 and the short wings 25 are alternately arranged on the disk 22 and have a relationship of maintaining the same angle.
For this reason, the short blade 25 is located next to the long blade 23, and the long blade 23 is located next to the short blade 25.
The long blade 23 includes an inducer portion 23 a and a blade portion 23 b, and the short blade 25 includes only a portion substantially corresponding to the blade portion 23 b of the long blade 23.
The long wing 23 reaches the outer peripheral edge 22b of the disk 22 while retreating in the direction opposite to the rotation direction of the disk 22 from the edge of the shaft hole 22a.
The short blades reach the outer peripheral edge 22b of the disk 22 while retreating with a starting point (not shown) at a point away from the shaft hole 22a in the disk 22.

The long blade 23 has an inducer portion 23a on the shaft hole 22a side (upstream side), and the remaining portion (downstream side from the inducer portion 23a) is formed as a blade portion 23b.
The blade width of the inducer portion 23a is set wider than that of the blade portion 23b.
The blade width of the blade portion 23 b is narrower than the blade width of the inducer portion 23 a and further narrows to reach the outer peripheral edge 22 b of the disk 22.
That is, the blade width of the long blade 23 becomes narrower from the upstream side (start point) to the downstream side (end point), and is almost converged at the outer peripheral edge 22 b of the disk 22.
The inducer portion 23a has a function of guiding the blade portion 23b by changing the direction of the gas sucked by the impeller 21.
In this embodiment, although the impeller 21 includes the long blade 23 having the inducer portion 23a and the blade portion 23b and the short blade 25, the impeller 21 having only the long blade 23 may be used.
Alternatively, it may be an impeller having an inducer portion 23a provided independently of the blade portion 23b, or may be an impeller without a clear inducer portion 23a.
Further, the number and type of rotor blades constituting the impeller are not limited, and the number and type of rotor blades according to conditions required for the centrifugal compressor can be set as appropriate.

[About shroud housing]
A shroud housing 15 shown in FIG. 1 includes a suction port wall portion 15a that forms a suction port 16, a shroud portion 15b that is formed to follow the impeller 21, a volute wall portion 15c that forms an outer shell of the volute 17, A diffuser 18 and a volute 17 are provided, and a shroud wall portion 15d is provided.
The inlet port wall portion 15 a forms a cylindrical inlet port 16 in front of the impeller 21.
The shroud portion 15 b follows the impeller 21 from the inlet 16 side of the impeller 21 to the vicinity of the inlet of the diffuser 18.
The volute wall 15c forms a volute 17 having a circular cross section, and its end surface is in contact with the housing wall 14a.
The shroud wall portion 15d isolates the diffuser 18 and the volute 17 and forms the diffuser 18 by the opposing housing wall portion 14a.
Accordingly, it can be said that the volute 17 is formed by the shroud portion 15b, the volute wall portion 15c, and the shroud wall portion 15d.

The diffuser 18 has an inlet on the outer peripheral edge 22b side of the impeller 21 and an outlet on the volute 17 side.
The diffuser 18 has a function of converting the velocity energy of the gas fed from the impeller 21 into pressure energy.
The outlet of the diffuser 18 communicates with the volute 17, and the end of the shroud wall 15d faces the outlet.
Thus, the diffuser 18 is disposed downstream of the impeller 21 and is provided over the circumferential direction of the impeller 21.

The shroud wall portion 15 d has a reflux passage 26 that communicates the volute 17 and the diffuser 18.
The reflux passage 26 is a passage for returning a part of the high-pressure gas in the volute 17 to the diffuser 18.
Here, the gas flowing from the volute 17 through the reflux passage 26 to the diffuser 18 is referred to as reflux gas for convenience of explanation.
The reflux passage 26 is a passage for increasing at least the radial velocity component X of the gas in the diffuser 18 by the reflux gas.
The outlet of the reflux passage 26 is connected to the vicinity of the inlet of the diffuser 18, and the inlet is provided at a position where the reflux passage 26 is as short as possible.
For this reason, it can be said that the reflux passage 26 is provided between the shroud portion 15b and the shroud wall portion 15d.
The purpose of shortening the reflux passage 26 is to suppress the pressure loss caused by the reflux gas passing through the reflux passage 26.
The shortened reflux passage 26 can deliver the flow rate required to increase the radial velocity component X of the gas in the diffuser 18.

Here, the reflux passage 26 is formed from a combination of four arc-shaped grooves.
For this reason, the reflux passage 26 is formed over substantially the circumferential direction of the diffuser 18 . In an embodiment of this, since the volute 17 and the diffuser 18 are isolated in the shroud wall portion 15d, but volute 17 and the diffuser 18 is provided so as to be aligned in the axial direction of the rotary shaft 12, the return passage 26 is volute 17 and the diffuser 18 can be provided regardless of the arrangement.
For example, a centrifugal compressor in which a volute 17 is provided on the outer peripheral side of the diffuser 18 may be used. In this case, the reflux passage is preferably formed by a passage forming member such as a pipe.

FIG. 3 shows the state of the centrifugal compressor during low flow operation.
When the centrifugal compressor operates at a low flow rate, the gas (the white arrow in FIG. 3) sent out by the impeller 21 to the diffuser 18 passes through the diffuser 18 and reaches the volute 17 through the outlet of the diffuser 18.
The pressure of the volute 17 is higher than the pressure of the diffuser 18.
For this reason, a part of the gas of the volute 17 passes through the reflux passage 26 as the reflux gas (solid arrow in FIG. 3) and travels toward the diffuser 18.
The reflux gas merges with the gas from the impeller 21 in the vicinity of the inlet of the diffuser 18.
The reflux gas increases the velocity component X in the radial direction in FIG. 2 by merging with the gas from the impeller 21.
That is, the gas in the diffuser 18 includes a radial velocity component possessed by the gas from the impeller 21 and at least a radial velocity component added by the reflux gas.

FIG. 4 is an arrow view taken along the line BB in FIG. 2 and shows a flow velocity distribution VG between the housing wall 14a and the shroud wall 15d during low flow operation.
In FIG. 4, white arrows indicate the main gas flow, and solid arrows indicate the gas flow corresponding to the velocity.
Further, in FIG. 4, for convenience of explanation, the speed distribution vg in the case of a centrifugal compressor not provided with the reflux passage 26 is indicated by a chain line.
In this embodiment, a part of the low speed region L (broken line hatching in FIG. 4) that develops when there is no return passage 26 is eliminated.
For this reason, the backflow of the gas along both wall parts 14a and 15d is prevented or suppressed.
This is because the merging of the reflux gas and the gas from the impeller 21 increases the velocity component X in the radial direction and fills at least a part of the low speed region L near the wall surface that causes the back flow.
Here, the reflux gas eliminates a part of the low speed region L shown in FIG.
That is, the relative flow rate increase due to the reflux to the diffuser 18 inlet increases the velocity (momentum) of the radial component of the gas and reduces the low speed region L of the wall boundary layer to prevent backflow.

When the centrifugal compressor is operated at a high flow rate, the gas passes through the reflux passage 26 toward the diffuser 18.
The gas in the volute 17 flows to the diffuser 18 through the reflux passage 26 even during high flow operation.
The flow of the reflux gas to the diffuser 18 does not greatly affect the performance of the centrifugal compressor.
Even if it may be affected somewhat, the centrifugal compressor may be designed taking into consideration that the reflux gas flows into the diffuser 18.

Since the centrifugal compressor according to this embodiment has the above-described configuration and operates as described above, the following effects can be obtained.
(1) Since the above centrifugal compressor has a configuration in which the diffuser 18 and the volute 17 are communicated with each other and the reflux passage 26 for returning a part of the gas of the volute 17 to the diffuser 18 is provided, the gas in the diffuser 18 is In addition to the radial velocity component of the gas from the impeller 21, the velocity component of the gas (reflux gas) from the reflux passage 26 is added. The added velocity component reduces the low-speed region near the wall and delays the occurrence of backflow. Therefore, even if the gas flow rate is low, the diffuser stall can be prevented or suppressed.
(2) Since the centrifugal compressor has a configuration in which the outlet of the reflux passage 26 is provided near the inlet of the diffuser 18, the gas in the diffuser 18 is a velocity component (radius) of the gas (reflux gas) from the reflux passage 26. (Direction) can be added early. Therefore, the diffuser stall is less likely to occur in the range from the vicinity of the inlet of the diffuser 18 to the vicinity of the outlet.
(3) Since the centrifugal compressor has a configuration in which the reflux passage 26 is linear, it is easy to suppress the pressure loss of the gas (reflux gas) in the reflux passage 26. Therefore, the gas in the recirculation passage 26 can suppress the waste due to pressure loss and add the velocity component X in the radial direction. (4) The diffuser stall can be prevented or suppressed only by providing the recirculation passage 26 in the diffuser 18. For this reason, by providing the reflux passage 26 in the diffuser 18 of the conventional centrifugal compressor, the centrifugal compressor can be modified to prevent or suppress the diffuser stall.

(Second Embodiment)
Next, a centrifugal compressor according to a second embodiment will be described with reference to FIG.
FIG. 5 is an enlarged view of an essential part showing the periphery of the reflux passage 26 in a cutaway manner.
Here, for convenience of explanation, a part of the reference numerals used in the first embodiment described above is used in common, the description of the common or similar configurations is omitted, and the description of the first embodiment is used. In addition, a configuration different from that of the first embodiment will be described.
The reflux passage 26 shown in FIG.
The on-off valve 27 is a valve that allows gas to pass through or shut off through the reflux passage 26.
The on-off valve 27 in this embodiment is a valve that closes the reflux passage 26 during high flow operation and opens the reflux passage 26 during low flow operation.
That is, it can be said that the valve opens and closes the reflux passage 26 according to the operation state of the centrifugal compressor.
The type and form of the on-off valve 27 are not particularly limited, but a valve that automatically opens and closes according to the operating state of the centrifugal compressor is preferable.
As the means and control for opening and closing the on-off valve itself, known ones may be selected as appropriate.
Furthermore, the opening / closing valve 27 is more preferably a valve that is opened / closed by the pressure difference between the volute 17 and the diffuser 18.
Specifically, for example, a bendable open / close valve or the like can be used.

The on-off valve 27 closed at the time of high flow operation reliably eliminates the influence on the performance of the centrifugal compressor caused by the reflux gas flowing into the diffuser 18.
For this reason, the centrifugal compressor can be designed without considering that the reflux gas flows into the diffuser 18.
Since the on-off valve 27 is opened at a low flow rate, the same effect as the first embodiment can be obtained.
Since the centrifugal compressor has a configuration in which the opening / closing valve 27 is provided in the reflux passage 26, the reflux gas flows to or is blocked from the diffuser 18 depending on the operation state of the centrifugal compressor. Therefore, the operation state of the centrifugal compressor can be set so as not to be affected by the reflux gas with respect to the diffuser 18.
Since the on-off valve 27 in the centrifugal compressor is opened when the centrifugal compressor is operated at a low flow rate, the reflux gas flows to the diffuser 18 during the low flow rate operation. Gas does not flow.
Therefore, the centrifugal compressor can prevent or suppress the diffuser stall at the time of low flow operation.
Further, the centrifugal compressor is not affected by the reflux gas during the operation other than the low flow rate operation.

The centrifugal compressor according to the above-described embodiment shows an embodiment of the present invention, and the present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the gist of the invention. Is possible.
Moreover, a well-known component and means can be suitably employ | adopted for the component except the shroud housing 15. FIG.

It is a side view which fractures | ruptures and shows the outline | summary of the centrifugal compressor which concerns on 1st Embodiment. It is a front view which shows the impeller and diffuser of the centrifugal compressor which concern on 1st Embodiment. It is an enlarged side view which fractures | ruptures and shows the periphery of the recirculation | reflux channel | path of the centrifugal compressor which concerns on 1st Embodiment. FIG. 3 is a view taken along the line B-B in FIG. 2 and showing a radial velocity distribution in the vicinity of the diffuser inlet. It is an expanded side view which fractures | ruptures and shows the periphery of the recirculation | reflux channel | path of the centrifugal compressor which concerns on 2nd Embodiment. It is a side view which fractures | ruptures and shows the outline | summary of the centrifugal compressor which concerns on a prior art. Is a front view showing an impeller and diffuser engagement Ru centrifugal compressor in the prior art. FIG. 8 is a view taken along the line AA in FIG. 7 and showing a radial velocity distribution in the vicinity of the diffuser inlet.

Explanation of symbols

21 Impeller 12 Rotating shaft 13 Housing 14 Housing body 14a Housing wall portion 15 Shroud housing 15d Shroud wall portion 16 Suction port 17 Volute 18 Diffuser 22 Disc 22a Shaft hole 22b Outer peripheral edge 23 Long blade 23a Inducer portion 23b Blade portion 25 Short shape Blade 26 Recirculation passage 27 On-off valve

Claims (5)

A centrifugal compressor comprising: an impeller pivotally supported by a housing; a diffuser disposed downstream of the impeller; and a volute communicating with an outlet of the diffuser, and compressing at least centrifugal force a gas sucked into the housing by rotation of the impeller The compressor includes a return passage that communicates the diffuser and the volute and returns a part of the gas of the volute to the diffuser in the housing, and the return passage has an arc groove shape, and the diffuser A centrifugal compressor characterized by being formed over the circumferential direction . The centrifugal compressor according to claim 1, wherein an outlet of the reflux passage is provided in the vicinity of an inlet of the diffuser. The centrifugal compressor according to claim 1 or 2, wherein the reflux passage is linear. The centrifugal compressor according to any one of claims 1 to 3, wherein an opening / closing valve is provided in the reflux passage. 5. The centrifugal compressor according to claim 4, wherein the on-off valve is opened during low flow operation.

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