JP2008002412A - Multiple stage centrifugal compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a quantity of seal gas for shaft sealing while keeping thrust balance in a multiple stage centrifugal compressor. <P>SOLUTION: In the multiple stage centrifugal compressor 80, many centrifugal impellers 1 to 7 are mounted to a rotary shaft 11 and the centrifugal impellers are stored in a casing. Cylindrical balance drums 21, 22 are provided at the suction side of the first stage impeller 1 mounted to the rotary shaft and at the delivery side of the final stage impeller 7 mounted to the rotary shaft, respectively, and balance spaces 31, 32 are formed at the shaft end side of each balance drum. Means 91, 92 communicating with delivery sides of the impellers 3, 5 of intermediate stages excluding a first stage and a final stage in the impellers formed in multiple stages are connected to the balance spaces. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a multistage centrifugal compressor, and more particularly to a multistage centrifugal compressor in which a number of centrifugal impellers are attached to the same shaft.

  An example of a conventional single-shaft multistage centrifugal compressor is described in Patent Document 1. In the centrifugal compressor described in this publication, a thrust balance ring is provided outside the suction side of the first group of impellers, which are low pressure stages, so that there is no internal gas leakage and the axial thrust is balanced. A balance chamber is provided outside the thrust balance ring, and the first group of discharge gases are guided to the balance chamber via a balance line. Accordingly, the discharge pressure and the suction pressure act on both surfaces of the thrust balance ring, and this differential pressure becomes a thrust toward the impeller, and the thrust is balanced. Further, a labyrinth is provided on the partition plate to prevent the second group of suction gas from leaking to the first group impeller side.

JP-A-9-72292

  By the way, in the multistage centrifugal compressor described in the above-mentioned Patent Document 1, although it is considered to equalize the balance chamber and reduce the thrust force, the intermediate nozzle pressure becomes negative pressure at the time of startup and the dry gas seal is used. It is not considered enough to avoid the situation where back pressure is applied.

  The present invention has been made in view of the above-mentioned problems of the prior art, and an object thereof is to reduce the amount of seal gas in a multistage centrifugal compressor while maintaining thrust balance. Another object of the present invention is to improve the reliability of a multi-stage centrifugal compressor even in a transient state such as at startup.

  In the multistage centrifugal compressor in which a number of centrifugal impellers are attached to the same rotating shaft and the centrifugal impeller is accommodated in a casing, the suction side position of the first stage impeller attached to the rotating shaft and the final stage impeller Cylindrical balance drums are provided at the discharge side positions, a balance space is formed on the shaft end side of each balance drum, and the first stage and the last stage of the multistage impellers are formed in the balance space. This is achieved by connecting means for communicating with the discharge side of the intermediate stage impeller except for. In this feature, the means for guiding the discharge gas may be a pipe connecting an intermediate nozzle provided in the downstream of the intermediate stage impeller and the balance space.

  In the above feature, it is preferable that a labyrinth seal is provided in an inner peripheral portion of the casing and opposed to the outer periphery of each balance drum, and a dry gas seal device is provided on the shaft end side from the balance space. A second labyrinth seal may be provided between the sealing device and the balance space, and a means for communicating the second labyrinth seals may be provided.

  According to the present invention, the balance drum is provided at the shaft end, and a part of the discharge gas from the intermediate stage impeller is guided to the balance chamber formed further on the shaft end side than the balance drum. The amount of sealing gas can be reduced while maintaining the above. In addition, the reliability of the multistage centrifugal compressor can be improved even in a transient state such as at startup.

  An embodiment of a multistage centrifugal compressor 80 according to the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram of a multistage centrifugal compressor 80. A plurality of centrifugal impellers 1 to 7 are fixedly attached to a rotating shaft 11 driven by a driving machine (not shown). The rotor composed of the rotating shaft 11 and the centrifugal impellers 1 to 7 is held in a casing 15 that is a stationary part. A bearing device (not shown) is attached to both ends of the rotating shaft 11 and supports the rotating shaft 11 in a radial direction and a thrust direction so as to be rotatable.

  Between the leftmost impeller used as the first stage impeller 1 and the bearing device and between the rightmost impeller used as the final stage impeller 7 and the bearing device, the process gas which is the working gas of the centrifugal compressor 80 However, in order to prevent leakage to the outside of the centrifugal compressor 80, dry gas seal type shaft seal devices 61 and 62 are provided. The shaft seal devices 61 and 62 are dry gas seal rotary rings 61A and 62A attached to the rotary shaft 11, and dry gas seal stationary rings 61B and 62B attached to the casing 15 so as to face the dry gas seal rotary rings 61A and 62A. And have.

  A cylindrical balance drum 21 is attached to the rotary shaft 11 on the shaft end side of the first stage impeller 1 and adjacent to the first stage impeller 1. Similarly, a cylindrical balance drum 22 is attached to the rotary shaft 11 on the shaft end side of the final stage impeller 7 and adjacent to the final stage impeller 7. Balance labyrinths 26 and 27 are attached to the wall surface of the casing 15 facing the balance drums 21 and 22. Balance spaces 31 and 32 partitioned by seal labyrinths 33 and 34 and balance labyrinths 26 and 27 are formed on the shaft end side which is the back side of the balance drums 21 and 22.

  The seal labyrinths 33 and 34 act as non-contact seals with the rotary shaft 11, and are formed of two-stage seals 33a and 33b; 34a and 34b, respectively. The above-mentioned dry gas seals 61 and 62 are disposed adjacent to the seal labyrinths 33 and 34. Seal gas spaces 51 and 52 and dry gas seal leak spaces 71 and 72 are formed on the front and rear sides of the dry gas seals 61 and 62 in the axial direction.

  A suction line 41 is connected to the suction portion of the first stage impeller 1, and the process gas is sucked at the pressure Ps. From the first stage impeller 1 to the sixth stage impeller 6, stationary flow paths 42 to 47 are formed downstream of each stage, which are discharge flow paths of that stage and serve as suction flow paths to the next stage. The stationary flow paths 42 to 47 are provided with a vaned diffuser, a vaneless diffuser, a return vane, or the like as necessary. A discharge channel 48 is connected to the downstream side of the final stage impeller 7, and the process gas pressurized by the final stage impeller 7 is collected and supplied to a demand source outside the compressor 80.

Here, the left and right seal gas spaces 51 and 52 are connected to each other by a seal gas line (pipe) 94, and the dry gas 49 for sealing passes through the seal gas line 94 to the seal gas spaces 51 and 52. Infused with Pg. The left and right dry gas seal leak spaces 71 and 72 are connected by a dry gas leak line (pipe) 95. The gas used for sealing at the dry gas seals 61 and 62 and flowing into the dry gas seal leak spaces 71 and 72 is sent from the dry gas leak line 95 to the flare as the leak gas 50 at the pressure Pf. Further, in the seal labyrinths 33 and 34 formed in two stages, seal gas blowing spaces 33c and 34c are formed in the middle of each, and the seal gas blowing spaces 33c and 34c are connected to each other with a seal labyrinth pressure equalization line (pipe). 93 is connected.

The most characteristic configuration in this embodiment is that the discharge side of the intermediate stage impeller is connected to the left and right balance spaces 31 and 32. Specifically, the balance space 31 adjacent to the balance drum 21 provided on the first stage impeller 1 side and the discharge flow path 44 of the third stage impeller 3 are connected by the first balance pipe 91. On the other hand, the balance space 32 adjacent to the balance drum 21 provided on the final stage impeller 7 side and the discharge flow path 46 of the fifth stage impeller are connected by a second balance pipe 92.

  The operation of the multistage centrifugal compressor 80 of the present embodiment configured as described above will be described below. When the rotating shaft 11 is driven to rotate, the impellers 1 to 7 of each stage compress the process gas sucked from the suction line 41 or the discharge lines 42 to 46 of the previous stage, and increase the pressure to the next stage impellers 2 to 7. Or it sends to the discharge line 48.

At this time, the differential pressure between the suction pressure Ps of the compressor 80 and the discharge pressure P _3d of the third stage impeller 3 acts on the balance drum 21 on the suction side. As a result, a thrust force in the right direction indicated by a white arrow in the figure is generated on the balance drum 21. A differential pressure between the discharge pressure Pd of the final stage impeller 7 and the discharge pressure P _5d of the fifth stage impeller 5 acts on the discharge-side balance drum 22. As a result, a rightward thrust force indicated by a white arrow in the figure is generated on the balance drum 22. On the other hand, in each impeller 1-7, due to the difference between the gas pressure acting on the back surface of the core plate and the gas pressure acting on the back surface of the side plate, the thrust force in the left direction indicated by the black arrow in the figure is generated. To do. Therefore, the diameters of the two balance drums 21 and 22 are adjusted to oppose the thrust force acting on the impellers 1 to 7.

  In the seal labyrinths 33 and 34 provided on the shaft end side with respect to the balance spaces 31 and 32, the seal gas blowing spaces 33 c and 34 c are connected to each other by the seal labyrinth pressure equalization line 93. The pressures 33c and 34c are equalized. Further, since the seal gas blowing spaces 33c and 34c are adjacent to the balance spaces 31 and 32 via the labyrinths 33b and 34a, the seal labyrinths 33 and 34 are equalized by a pressure intermediate between the balance spaces 31 and 32. .

That is, the pressure is equalized by the pressure between the discharge pressure P _5d of the fifth stage impeller 5 and the discharge pressure P _3d of the third stage impeller 3. Since the pressure acting on the seal labyrinths 33 and 34 is equalized, the pressure Pg of the seal gas blown into the seal gas spaces 51 and 52 from the seal gas blowing line (pipe) 94 can be made the same pressure. As a result, the shaft sealing devices 61 and 62 on both sides can be made the same.

  By the way, since the multistage centrifugal compressor 80 for process has a relatively simple configuration and high reliability, a lot of dry gas seals are used for the shaft seal devices 61 and 62. Also in this embodiment, the dry gas seals 61 and 62 are disposed at both ends of the rotating shaft 11. In the dry gas seals 61 and 62, supply of seal gas is indispensable. It is easiest to use process gas discharged from the compressor 80 as the seal gas.

  Therefore, a seal gas supply device (not shown) reduces a part of the process gas to the required pressure Pg and blows it into the seal gas spaces 51 and 52. A minute amount of the seal gas passes between the rotary rings 61A and 62A and the stationary rings 61B and 62B of the shaft seal devices 61 and 62 and is discharged as flare. Most of the seal gas returns to the suction side of the compressor 80 through the gap between the seal labyrinths 33 and 34.

In the dry gas seals 61 and 62, it is necessary to keep the seal gas pressure Pg higher than the flare pressure Pf so that a reverse pressure does not occur between the seal gas spaces 51 and 52 and the seal leak spaces 71 and 72 communicating with the flare ( Pg> Pf). When the reverse pressure is applied, the dry gas seals 61 and 62 may be damaged. Therefore, when the flare pressure Pf is high, the seal gas pressure Pg must be increased. Usually, the sealing gas pressure Pg is set higher than the suction pressure of the compressor 80 by about 10 kPa. When the flare pressure Pf is set in this manner, the differential pressure acting on the seal labyrinths 41 and 42 is reduced, and the amount of seal gas can be reduced.

  However, when the present invention is applied to a refrigerator compressor, the flare pressure Pf increases and the suction pressure of the compressor 80 becomes substantially atmospheric pressure. Therefore, it is necessary to supply a seal gas having a pressure higher than the suction pressure Ps of the compressor 80 so that a reverse pressure does not act on the dry gas seals 61 and 62.

  For example, the seal gas pressure Pg of the ethylene refrigeration compressor 80 having a flare pressure Pf of 0.3 MPa needs to be 0.31 MPa or more. If the suction pressure Ps of the compressor 80 at this time is 0.155 MPa, the differential pressure of the seal labyrinth portions 33 and 34 according to the conventional method becomes 0.16 MPa, and the leakage amount of the seal gas increases.

  Here, taking the ethylene refrigeration compressor 80 as an example, the present invention will be described. The compression ratio is 10.5, and the suction pressure is 0.155 MPa as described above. The suction-side balance space 31 communicates with the discharge line 44 of the third stage impeller 3, and the discharge-side balance space 32 communicates with the discharge line 46 of the fifth stage impeller 5. As for these pressures, the discharge pressure of the third stage impeller 3 is 0.535 MPa, and the discharge pressure of the fifth stage impeller 5 is 0.98 MPa.

  At this time, the pressure of the seal labyrinth parts 33 and 34 is a pressure between 0.535 and 0.980 MPa. Therefore, even if the flare pressure Pf is as high as 0.30 MPa, the seal gas pressure Pg may be set higher by about 10 kPa than the pressure of the seal labyrinth portions 33 and 34. That is, since the differential pressure of the seal labyrinth parts 33 and 34 is about 10 kPa, the differential pressure of the seal gas pressure is reduced as compared with about 160 kPa required in the prior art, and the seal gas blowing amount can be reduced.

Since the balance spaces 31 and 32 communicate with the discharge lines 44 and 46 of the third and fifth stage impellers 3 and 5, respectively, the discharge pressure of each impeller 3 and 5 immediately after the compressor 80 is started. Rises. Therefore, even if the suction pressure Ps becomes a negative pressure and the supply of the seal gas is not in time, the third stage and the seal gas spaces 51 and 52 are passed through the balance spaces 31 and 32 and the seal labyrinth pressure equalization line 93. It is possible to prevent the discharge gas compressed by the fifth stage impellers 3 and 5 from flowing and the seal gas spaces 51 and 52 from becoming negative pressure. Thus, no back pressure is applied to the dry gas seals 61 and 62, and the reliability of the compressor 80 is improved.

  In the present embodiment, the balance space 31 communicates with the discharge line 44 of the third stage impeller 3 and the balance space 32 communicates with the discharge line 46 of the fifth stage impeller 5, but the balance spaces 31 and 32 communicate with each other. The discharge line of an impeller is not restricted to this, It can change to the discharge line of another stage as needed. However, since the pressure of the seal labyrinth parts 33 and 34 is equalized in the pressure range of the stage to be communicated, the discharge line that communicates so as to be higher than the flare pressure Pf is selected.

  Further, the balance spaces 31 and 32 may be connected to an intermediate nozzle (not shown). However, when the intermediate nozzle is a suction nozzle, there is a possibility that the intermediate nozzle pressure may become negative at the time of start-up, and thus it is necessary to provide a protection means so that a reverse pressure is not applied to the dry gas seal.

  According to this embodiment, even when the suction pressure Ps of the compressor 80 is low and the flare pressure Pf is high, the amount of seal gas can be reduced compared to the conventional case. Since the amount of seal gas is reduced, the seal gas supply device that supplies the seal gas to the compressor can be made compact, and the cost of the compressor system can be reduced. Furthermore, even in a transient state such as when starting up, no back pressure is applied to the shaft seal device, and the reliability of the compressor is improved.

It is a schematic diagram of one Example of the multistage centrifugal compressor which concerns on this invention.

Explanation of symbols

1-7 ... impeller, 11 ... rotating shaft, 15 ... casing, 21, 22 ... balance drum,
26, 27 ... balance labyrinth, 31, 32 ... balance space, 33, 34 ... seal labyrinth, 51, 52 ... seal gas space, 61, 62 ... shaft seal device (dry gas seal),
61A, 62A ... dry gas seal rotating ring, 61B, 62B ... dry gas seal stationary ring, 71, 72 ... dry gas seal leak space, 80 ... multistage centrifugal compressor, 91-95 ... piping, Pg ... seal gas pressure, Ps ... Compressor suction pressure, Pd ... Compressor discharge pressure, Pf ... Flare pressure.

Claims (4)

  In a multistage centrifugal compressor in which a number of centrifugal impellers are attached to the same rotating shaft and the centrifugal impellers are housed in a casing, the suction side position of the first stage impeller and the discharge side position of the last stage impeller attached to the rotating shaft In addition, a cylindrical balance drum is provided, a balance space is formed on the shaft end side of each balance drum, and an intermediate except for the first stage and the last stage in the multistage impeller formed in each balance space. A multistage centrifugal compressor, characterized in that a means communicating with the discharge side of the stage impeller is connected.   The multistage centrifugal compressor according to claim 1, wherein the means for guiding the discharge gas is a pipe connecting an intermediate nozzle and a balance space provided downstream of the intermediate stage impeller.   2. A labyrinth seal is provided in an inner peripheral portion of the casing, which is opposed to the outer periphery of each balance drum, and a dry gas seal device is provided closer to the shaft end than the balance space. The multistage centrifugal compressor described in 1. The multi-stage centrifugal compressor according to claim 3, wherein a second labyrinth seal is provided between the dry gas seal device and the balance space, and means for communicating the second labyrinth seals is provided. .

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