JP2018053767A - Fluid machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluid machine capable of enlarging an operation range.SOLUTION: In a fluid machine 100, an open type impeller 3 covered with a shroud wall surface 17 and a rotating shaft 6 for rotating the impeller 3 are supported by a radial magnetic bearing 11 and a thrust magnetic bearing 12. The fluid machine has shaft center position detection means 21 for detecting a whirling distance which is the distance between an axial center serving as a reference of a rotation object including the impeller 3 and the shaft center of the rotation shaft, and axial support position control means 22 for exerting control of increasing the clearance between the shroud wall surface 17 and the impeller 3 when the whirling distance is equal to or larger than a first threshold. Further, the axial support position control means 22 exerts control of reducing the clearance between the shroud wall surface 17 and the impeller 3 when the whirling distance is equal to or smaller than a second threshold which is smaller than the first threshold.SELECTED DRAWING: Figure 2

Description

  TECHNICAL FIELD The present invention relates to a fluid machine such as a turbo type blower or a compressor that pumps fluid, and in particular, a fluid having a single-stage centrifugal or mixed flow impeller whose rotating shaft is held by a magnetic bearing. This relates to the expansion of the operating range of the low flow rate operation region and the suppression of surge in the machine.

  In centrifugal and mixed flow turbo-type fluid machines that give energy to working fluids such as gas and liquid by an impeller rotated by a drive machine, in general, the stable operation range is expanded to meet various operating conditions. Is required. As a technique for expanding the stable operation range, a technique for controlling the blade tip clearance between the impeller and the casing wall surface has been proposed.

  For example, in Patent Document 1, by changing the gap between the impeller and the casing wall surface during the transient operation and during the steady operation, contact between the impeller and the casing wall surface due to unstable fluid force generated during the transient operation is prevented. Techniques for achieving improved efficiency during operation are disclosed.

  Moreover, in patent document 2, the axial load which acts on a thrust bearing is calculated from the pressure and temperature obtained from various sensors at the time of operation of a compressor, and the clearance gap between an impeller and a shroud wall surface is changed based on the load. A technique is disclosed.

JP 2014-231826 A JP 2014-231827 A

  The technology for expanding the stable operation range by controlling the tip clearance of the fluid machine is important for ensuring stability during fluid machine operation and preventing damage to the core parts in the fluid machine product such as the impeller. It can be said that it is technology. However, from the viewpoint of expanding the operating range of the fluid machine and suppressing surges, the technique described in Patent Document 1 controls mainly using the axial thrust load, but there is a problem that it cannot be adequately addressed.

  Moreover, considering the load acting on the thrust bearing as in the technique described in Patent Document 2, the thrust force that is increased especially when adjusting the inlet guide vane opening degree is erroneously detected, and the operation is still stable. There is a concern that control is performed to widen the gap between the impeller and the casing wall surface. Therefore, in adjusting the clearance between the impeller and the casing wall surface, it has been desired to control with an appropriate parameter instead of the axial thrust force.

  The present invention is an invention for solving the above-described problems, and an object thereof is to provide a fluid machine capable of expanding an operation range.

  In order to achieve the above object, a fluid machine according to the present invention is an fluid machine in which an open type impeller covered with a shroud wall surface and a rotating shaft for rotating the impeller are supported by a radial magnetic bearing and a thrust magnetic bearing. In the case where the center position detecting means for detecting the swing distance, which is the distance between the center of the rotation target including the impeller and the center of the rotation shaft, and the swing distance is not less than the first threshold value And an axial support position control means for performing control to widen a gap (for example, the blade tip gap 13) between the shroud wall surface and the impeller. Other aspects of the present invention will be described in the embodiments described later.

  According to the present invention, the operating range of a fluid machine can be expanded.

It is sectional drawing which shows the upper half of the fluid machine to which the flow control method concerning this invention is applied. It is a mimetic diagram showing a control system of a fluid machine to which a flow control method concerning a 1st embodiment of the present invention is applied. It is explanatory drawing which shows an example of the clearance control determination which concerns on 1st Embodiment of this invention, (a) is the relationship between the air volume of each state, and discharge pressure, (b) is the axial center position locus in the radial bearing of each state. It is. It is a flowchart which shows the clearance gap control process which concerns on 1st Embodiment of this invention. It is a schematic diagram which shows the control system of the fluid machine to which the flow control method concerning 2nd Embodiment of this invention is applied. It is explanatory drawing which shows an example of the clearance control determination which concerns on 2nd Embodiment of this invention, (a) is the relationship between the air volume of each state, and an impeller inlet part temperature, (b) is the calf surface cross-section flow of each state Is a line.

DESCRIPTION OF EMBODIMENTS Embodiments for carrying out the present invention will be described in detail with reference to the drawings as appropriate.
<< first embodiment >>
FIG. 1 is a sectional view showing an upper half of a fluid machine 100 to which a flow control method according to the present invention is applied. In addition, the white arrow in FIG. 1 shows the flow of the fluid (same in FIG. 2). Here, as an example of the single-stage fluid machine 100, a centrifugal turbo blower will be described as an example. However, the present invention may be applied to other mixed flow fluid machines. In the present embodiment, the fluid machine 100 is an aeration blower used in, for example, an aeration facility in a sewage treatment plant.

  The fluid machine 100 includes inlet guide vanes 2 (IGVs, guide vanes) that are blade rows provided radially with respect to the rotating shaft 6. The fluid machine 100 is mounted on a rotary shaft 6 (drive shaft) that is rotated by a motor 10, and an impeller 3 that boosts the fluid, a fluid that is downstream of the impeller 3 and flows from the outlet of the impeller 3. A circular blade row diffuser 4 for converting the dynamic pressure of the gas into a static pressure, and a discharge scroll 5. The circular blade row diffuser 4 may be a vaneless diffuser without blades. Further, the discharge scroll 5 may be another form of discharge flow path similar to the scroll. Each component of the fluid machine 100 is stored in the casing 7 and constitutes an internal flow path. In addition, the inlet guide vane 2 is rotated by the guide blade driving machine 1.

  In such a fluid machine 100, the fluid is sucked from the suction flow path 8 of the fluid machine 100 and flows into the impeller 3 in a state where an arbitrary turning angle is given by the variable inlet guide vane 2. The fluid flowing into the impeller 3 is pressurized by the impeller 3, decelerated by the circular blade cascade diffuser 4, and then guided to the discharge passage 9 by the discharge scroll 5. In the fluid machine 100, the blade tip gap 13 is provided between the shroud wall surface 17 of the casing 7 and the impeller 3.

  Next, a control method for realizing the expansion of the operation range in the fluid machine 100 configured as described above will be described with reference to FIGS.

  FIG. 2 is a schematic diagram showing a control system of the fluid machine 100 to which the flow rate control method according to the first embodiment of the present invention is applied. A rotating shaft 6 for driving the impeller 3 of the fluid machine 100 is directly connected to the motor 10. The rotary shaft 6 is supported by a radial magnetic bearing 11 in the radial direction and a thrust magnetic bearing 12 in the axial direction.

  The controller 20 includes a shaft center position detecting unit 21 that detects a swinging distance that is a distance between an axis center that is a reference of the rotation target including the impeller 3 and the axis center of the rotating shaft 6, and the swinging distance is the first. When it is equal to or greater than the threshold value, control is performed to widen the blade tip gap 13 between the shroud wall surface 17 and the impeller 3, and the shroud wall surface 17 and the blades when the swing distance is equal to or less than a second threshold value that is smaller than the first threshold value. And an axial support position control means 22 that performs control for narrowing the gap with the vehicle 3.

  The shaft center position detection means 21 monitors the shaft center position of the rotating shaft 6 supported by the radial magnetic bearing 11 based on the displacement information of the gap sensor 25 (radial direction displacement sensor). That is, the shaft center position detecting means 21 monitors the locus of the shaft center position as the shaft position at all times during the operation of the fluid machine 100. The gap sensors 25 are preferably provided at four locations on the stator side of the motor 10 at a pitch of 90 degrees in the circumferential direction.

  The axial support position control means 22 monitors the axial position of the rotary shaft 6 supported by the thrust magnetic bearing 12 based on the displacement information of the axial sensor 26 (axial displacement sensor). Then, the axial support position control means 22 moves the floating position of the rotary shaft 6 in the axial direction according to the swing distance according to predetermined threshold values (for example, the first threshold value and the second threshold value). Control is performed to widen / narrow the distance of the blade tip gap 13 between the shroud wall surface 17 and the impeller 3. Specifically, the current value flowing in the electromagnet coil of the thrust magnetic bearing 12 is controlled. By this control, it is possible to suppress the stall caused by the impeller 3 and to enlarge the operating range.

  FIG. 3 is an explanatory view showing an example of clearance control determination according to the first embodiment of the present invention, where (a) shows the relationship between the air volume and the discharge pressure in each state, and (b) shows in the radial bearing in each state. It is an axial center position locus. FIG. 3B shows the locus of the shaft levitation position in the radial bearing that is assumed when the actual fluid machine 100 is operated. For example, if the point I in FIG. 3A is the design point of the fluid performance of the impeller 3, separation or backflow has occurred on the blade surface in the impeller 3 on the large wind flow rate side of the design point. Therefore, the locus of the shaft levitation position is located substantially at the reference center portion of the bearing, as shown in the upper left diagram of FIG.

  However, when the operating point of the fluid machine 100 in FIG. 3A is moved to the point II on the low air flow side, the change in the relative inflow angle to the impeller 3 due to the flow rate phenomenon causes the change in the impeller 3. Separation or backflow occurs on the blade surface. For this reason, as shown in the upper right diagram of FIG. 3B, the locus of the shaft levitation position in the bearing greatly fluctuates. At this time, when the location indicated by the dotted line in the figure is provided as the first threshold value 31, when the locus of the axial center position crosses the first threshold value 31, the axial support position control means 22 of the controller 20 is The floating position in the axial direction of the rotary shaft 6 is shifted to the motor 10 side. As a result, the blade tip gap 13 is widened, and separation and backflow can be suppressed. When the blade tip gap 13 is widened, the point III in FIG. 3A moves. This is because when the blade tip gap 13 is widened, the discharge pressure P also slightly decreases. In the case of III, the locus of the axial center position converges within the first threshold 31 as shown in the lower left diagram of FIG.

  Generally, when the blade tip gap 13 is narrowed, the leakage flow passing through the blade tip gap 13 is reduced, so that the fluid efficiency of the fluid machine 100 is improved. On the other hand, the load acting on the blade surface of the impeller 3 increases. For this reason, peeling (stall) is likely to occur on the blade surface. The load on the blade surface of the impeller 3 is the largest at the blade end on the shroud wall surface 17 side, and the operating range of the low flow rate side of the fluid machine 100 is determined by the presence or absence of separation at that portion. It's not too much to say. Therefore, by widening the blade tip gap 13 and reducing the load at the blade tip of the impeller 3, it is possible to suppress the separation and expand the operating range.

  Magnetic levitation type bearings such as the radial magnetic bearing 11 and the thrust magnetic bearing 12 used in this configuration often include a sensor that monitors the levitation position of the rotary shaft 6 in advance. By inputting the sensor information of this sensor to the controller 20, the controller 20 always detects the axial center position. Based on a predetermined threshold (for example, the first threshold and the second threshold), the locus of the axial center position is controlled to widen / narrow the blade tip gap 13.

  When separation occurs on the blade surface of the impeller 3, an unstable fluid force is generated in the radial direction and the axial direction. This unstable fluid force causes a swing of the floating position of the magnetic bearing. In order to suppress this whirling, it is important to suppress the peeling that occurs in the vicinity of the impeller 3, and the whirling can be suppressed by controlling the blade tip gap 13.

  In the present embodiment, the locus of the shaft levitation position is detected for the rotating shaft 6 in the radial magnetic bearing 11 and the blade tip gap 13 is controlled. When the radial magnetic bearing 11 swings around, the thrust magnetic bearing 12 similarly tends to increase the load. However, the load acting on the thrust magnetic bearing 12 is not caused by the separation that occurs in the impeller 3, but rather tends to depend on the flow rate change flowing into the impeller 3. That is, as the flow rate decreases, the load acting on the thrust magnetic bearing 12 tends to increase relatively linearly. At this time, in the fluid machine 100 including the inlet guide vane 2, the operation is stably realized even in a low flow rate range by giving a pre-swivel to the inlet of the impeller 3. Even so, the load on the thrust magnetic bearing 12 increases. Therefore, an increase in the load on the thrust magnetic bearing 12 does not necessarily give a signal for stalling or surge. Therefore, there is a problem that it is impossible to perform control using the load on the thrust magnetic bearing 12 as a threshold value. This embodiment is created in order to solve the said subject.

FIG. 4 is a flowchart showing the gap control processing according to the first embodiment of the present invention. An example of the gap control process of the controller 20 will be described.
In the xy coordinates shown in FIG. 3B, if the origin of the xy coordinates is the reference origin of the rotation target,
(X, Y): Coordinates from the reference origin in the radial direction of the rotating shaft 6 RL: Distance from the reference origin of the rotating shaft 6 (swinging distance)
RL1: first threshold 31 (threshold for widening the blade tip gap 13)
RL2: second threshold 32 (threshold for narrowing the blade tip gap 13)
0 <RL2 <RL1
And

  The axial center position detecting means 21 detects (X, Y) based on the sensor information of the gap sensor 25 (step S1) and calculates RL (step S2). The axial support position control means 22 determines whether or not RL ≧ RL1 (step S3). If RL ≧ RL1 (step S3, Yes), the blade tip is based on the sensor information of the axial sensor 26. Control to widen the gap 13 is performed (step S4). On the other hand, if RL ≧ RL1 is not satisfied (step S3, No), the process returns to step S1.

  The axial center position detecting means 21 detects (X, Y) based on the sensor information of the gap sensor 25 (step S5) and calculates RL (step S6). The axial support position control means 22 determines whether or not RL ≦ RL2 (step S7). If RL ≦ RL2 (step S7, Yes), the blade tip is based on the sensor information of the axial sensor 26. Control to narrow the gap 13 is performed (step S8), and the process returns to step S1. On the other hand, if RL ≦ RL2 is not satisfied (step S7, No), the process returns to step S5.

  In the configuration described above, the first threshold value 31 is set and the blade tip gap 13 is widened at the swinging distance that is the distance between the reference axis center and the axis center of the rotating shaft 6. It is not limited. In other words, the blade tip gap 13 may be controlled so that the swirl distance, which is the distance between the reference axis center and the axis center of the rotating shaft 6, is always the minimum value. Specifically, the axial support position control means 22 may adjust the clearance between the shroud wall surface 17 and the impeller 3 so that the swing distance is equal to or smaller than the first threshold value (this book). Called composition).

  By combining the above-described configuration with the present configuration, stable operation and high efficiency can be performed at all times, so that better operating conditions can be maintained in terms of performance.

  Further, according to the first embodiment, the load acting on the radial magnetic bearing 11 can always be minimized. The fact that the load acting on the radial magnetic bearing 11 is always the minimum is synonymous with the value of the current flowing through the electromagnet coil of the radial magnetic bearing 11 being the minimum. When the current value is small, the amount of heat generated by the radial magnetic bearing 11 is also reduced, which is advantageous from the viewpoint of bearing cooling. Since the bearing temperature can be kept low, the amount of cooling air can be reduced, which is also effective for energy saving.

  With respect to the gap between the shroud wall surface 17 and the impeller 3 of the fluid machine 100 described above, the operation range on the low flow rate side can be expanded without having to install many sensors by the gap control method of the present embodiment.

<< Second Embodiment >>
In the first embodiment, the axial center position detection means 21 is used, but in the second embodiment, a case will be described in which the backflow detection means 23 that detects the backflow from the impeller 3 toward the upstream side is used.

  FIG. 5 is a schematic diagram showing a control system of the fluid machine 100 to which the flow rate control method according to the second embodiment of the present invention is applied. The controller 20 includes a backflow detection means 23 for detecting a backflow of fluid upstream of the leading edge of the impeller 3 based on sensor information of the backflow detection sensor 14, and the axial support position control means 22 is a backflow detection means 23. When a reverse flow is detected, control is performed to widen the gap between the shroud wall surface 17 and the impeller 3. The reason why the blade tip gap 13 is widened is that, as in the first embodiment described above, the blade tip gap 13 is widened to reduce the blade surface load of the impeller 3, thereby causing peeling or This is to suppress backflow. In FIG. 5, the backflow detection means 23 detects backflow, but the backflow detection sensor 14 itself may detect backflow and input it to the controller 20.

  FIG. 6 is an explanatory diagram showing an example of the clearance control determination according to the second embodiment of the present invention, where (a) shows the relationship between the air volume in each state and the impeller inlet temperature, and (b) shows the child in each state. It is a cow face section streamline. Fig.6 (a) has shown the driving | running state at the time of applying 2nd Embodiment. I and II in the figure will be described as being the same as the operating points shown in the performance curve of the air volume-discharge pressure correlation described in FIG.

  In the fluid machine 100, when separation occurs on the blade surface of the impeller 3, a reverse flow is generated from the impeller 3 toward the upstream side. That is, it is possible to determine whether or not separation has occurred on the blade surface of the impeller 3 based on the presence or absence of the backflow.

  Backflow can be detected by using various sensors such as a bypass type flow sensor, but the simplest configuration may be temperature detection by a thermocouple. At operating point I, which is an operating point in the vicinity of the design point, as shown in the distribution of streamlines on the meridional plane cross section shown in the left diagram of FIG. 6B, no backflow occurs and the working fluid flows cleanly from suction to discharge. Further, the inlet temperature indicated by the thermocouple used as the backflow detection sensor 14 is kept low.

  On the other hand, at the operating point II, which is the operating point in the vicinity of the surge shown in the right diagram of FIG. 6B, a backflow occurs in the vicinity of the shroud side front edge of the impeller 3 where the backflow detection sensor 14 is installed. When a reverse flow occurs due to the separation generated in the impeller 3, the high-temperature fluid generated when the pressure is increased by the impeller 3 flows back. That is, when backflow occurs, the temperature detected by the thermocouple installed as the backflow detection sensor 14 is rapidly shifted to high temperature. When this shift to a high temperature is detected, the blade tip gap 13 is widened to suppress separation that occurs in the impeller 3, maintain a stable operating state, and realize an expansion of the operating range.

  In the present embodiment, it has been described that the blade tip gap 13 is widened, but the gap between the shroud wall surface 17 and the impeller 3 can be adjusted. Specifically, as described above, when the backflow detection means 23 is a temperature detection means, the axial support position control means 22 determines whether the shroud wall surface 17 and the impeller 3 When the control for widening the gap is performed and the temperature is equal to or lower than the second temperature lower than the first temperature, the control for narrowing the gap between the shroud wall surface 17 and the impeller 3 may be performed.

  In the first and second embodiments, the centrifugal fluid machine has been described as an example. However, the present invention is not limited to the centrifugal type, and is a technique applicable to all rotating machines. In addition, the control method of the fluid machine 100 targeted in the present invention is a single-stage machine, but it is a technique that can be applied even to a multi-stage machine.

  In summary, the fluid machine 100 according to the present embodiment is a fluid machine having a radial bearing controlled by a magnetic bearing, a thrust bearing and an open type centrifugal impeller, and constantly monitoring the shaft levitation position in the radial bearing, When the trajectory of the shaft levitation position change exceeds a certain threshold value (for example, the first threshold value), the shaft levitation position of the thrust bearing is controlled to move to the motor 10 side.

  According to this configuration, when the swing of the shaft floating position in the radial bearing is detected, the blade tip gap 13 formed between the shroud wall surface 17 and the impeller 3 is widened to suppress the swing and stabilize Expansion of operating range can be achieved.

  It is known that when the fluid machine 100 is operated in a low flow rate region from the flow rate assumed at the time of design, the load acting on the radial bearing and the thrust bearing increases. When the operating point of the fluid machine 100 shifts to a lower flow rate side than the design point and the operation becomes unstable, the axial center position cannot be maintained at the center position of the bearing and the load acting on the radial bearing swings in the circumferential direction. Draw a trajectory like this. If this locus falls within a certain threshold, it can be said that the vehicle is operating stably.

  In general, an open-type centrifugal impeller causes separation or backflow from the blade shroud-side front edge of the impeller, resulting in stall. Therefore, if this separation and backflow can be suppressed, it can be said that expansion of the operating range in the low flow rate region can be realized. The occurrence of separation from the blade shroud side front edge end of the impeller 3 results from an increase in the load on the blade end of the impeller 3. The load on the blade tip increases as the blade tip clearance between the impeller and the shroud wall surface decreases, and the load decreases as the blade tip clearance increases. This is because the larger the blade tip gap is, the more the leakage flow from the gap increases, so the loss increases. That is, the efficiency is lowered. On the other hand, since the fluid force acting on the blade is reduced by increasing the leakage flow, the blade load is reduced. As a result, the occurrence of peeling and backflow can be suppressed. The working range is expanded by reducing the impeller load by using this phenomenon and delaying the stall.

  In general, a magnetic bearing is often provided with a sensor for detecting a shaft floating position in advance in the bearing. Therefore, in the first embodiment, the operating range can be expanded without increasing the number of sensors.

  In the second embodiment, the backflow detection sensor 14 is provided at the inlet of the impeller 3, and when this sensor detects backflow, the floating position of the thrust bearing can be moved to the motor 10 side.

  According to this configuration, the reverse flow upstream of the leading edge of the impeller, which is a phenomenon specific to the centrifugal impeller, is detected by the sensor, and the shaft levitation position of the thrust bearing is moved to the motor side. As a result, the gap between the shroud wall surface 17 and the impeller 3 is widened to reduce the blade load, thereby suppressing separation. As a result, the stable operation range can be expanded.

  According to the present embodiment, it is possible to realize the operation range expansion on the low flow rate side of the fluid machine 100 without adding a sensor or with a minimum number of sensors. In addition, as shown in FIGS. 3 and 4, this control method can suppress the whirling in the magnetic bearing, so that the value of the current flowing through the bearing can be reduced. Thereby, since the temperature rise of a bearing can be suppressed, extension of a heat-resistant life is realizable about the insulation kind of a magnetic bearing.

DESCRIPTION OF SYMBOLS 1 Guide vane drive machine 2 Inlet guide vane 3 Impeller 4 Circular blade cascade diffuser 5 Discharge scroll 6 Rotating shaft 7 Casing 8 Suction flow path 9 Discharge flow path 10 Motor 11 Radial magnetic bearing 12 Thrust magnetic bearing 13 Blade end gap 14 Backflow detection Sensor 17 Shroud wall surface 20 Controller 21 Axial center position detection means 22 Axial support position control means 23 Backflow detection means 100 Fluid machine

Claims (6)

An open type impeller covered with a shroud wall surface, and a rotating machine for rotating the impeller is a fluid machine supported by a radial magnetic bearing and a thrust magnetic bearing,
An axial center position detecting means for detecting a swinging distance which is a distance between an axis center serving as a reference of a rotation target including the impeller and an axis center of the rotation axis;
A fluid machine comprising: an axial support position control unit that performs control to widen a gap between the shroud wall surface and the impeller when the swing distance is equal to or greater than a first threshold value. The axial support position control means is
2. The fluid machine according to claim 1, wherein when the swinging distance is equal to or smaller than a second threshold value that is smaller than the first threshold value, control is performed to narrow a gap between the shroud wall surface and the impeller. The axial support position control means is
The fluid machine according to claim 2, wherein a clearance between the shroud wall surface and the impeller is adjusted so that the swing distance is equal to or smaller than the first threshold value. Instead of the axial center position detection means, provided with a backflow detection means for detecting a backflow of fluid upstream of the leading edge of the impeller,
2. The fluid machine according to claim 1, wherein the axial support position control unit performs control to widen a gap between the shroud wall surface and the impeller when the backflow detection unit detects backflow. 3. Instead of the axial center position detection means, provided with a backflow detection means for detecting a backflow of fluid upstream of the leading edge of the impeller,
The fluid machine according to claim 1, wherein the axial support position control unit adjusts a gap between the shroud wall surface and the impeller based on an output value of the backflow detection unit. The backflow detection means is a temperature detection means,
The axial support position control means performs control to widen a gap between the shroud wall surface and the impeller when the temperature detected by the temperature detection means is equal to or higher than the first temperature, and a second lower than the first temperature. The fluid machine according to claim 5, wherein when the temperature is equal to or lower than the temperature, control is performed to narrow a gap between the shroud wall surface and the impeller.

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