JPS63235696A - Control method for multistage centrifugal compressor - Google Patents

Abstract

PURPOSE:To easily control a multistage centrifugal compressor by representing the angle of each vane in each stage as the dimensionless vane angle with which the operation flow rate of the centrifugal compressor in each stage becomes the symmetrical operation quantity in the equal ratio for a designed flow rate. CONSTITUTION:The detection signals supplied from a variety of sensors 20-22, 24, and 27 for detecting the operation states of a centrifugal compressor 1 are input into a controller 28. In the controller 28, the control signal supplied into a driving machine 2 so as to control the number of revolution of the centrifugal compressor 1 is calculated in a part 29 and outputted, and the control signals supplied into the driving devices 19a-19h used exclusively for controlling each angle of a plurality of inlet guide vanes 11-14 and diffuser guide vanes 15-18 are calculated in a part 30 and outputted. In this case, the angle of each guide vane 11-18 in each stage is represented as each dimensionless vane angle with which the operation flow rate of the centrifugal compressor 1 in each stage becomes the symmetrical operation quantity in the equal ratio for a designed flow rate.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is applied to multi-stage centrifugal compressors such as raw air compressors used in oxygen production plants and various plants, factory air source compressors, and gas compressors for chemical plants. It concerns a method for controlling the capacity and pressure of a machine.

[Prior Art] Generally, a centrifugal compressor having a multi-stage configuration is used in an oxygen production plant or various plants. In such a multistage centrifugal compressor, as shown in Fig. 8,
The centrifugal compressor 1 includes a first stage compressor 4, which is driven by a power transmission gear 3 that speeds up rotation from a drive machine 2. 2nd stage compressor 5° 3rd stage compressor 6 and 4th stage compressor 7
In addition, an intercooler 8 is provided between the compressors 4 and 5, an intercooler 9 is provided between the compressors 5 and 6, and an intercooler 9 is provided between the compressors 6 and 7.
An intercooler 10 is provided in between.

Note that the compressors 4 and 5 and the compressors 6 and 7 are respectively overhanged on the same shaft end.

In such centrifugal compression Ja1, the air sucked into the first stage compressor 4 is sequentially compressed and cooled by each compressor 5 to 7 and intercooler 8 to 10, and then
It is designed to be sent to the process from the compressor 7 in the first stage.

Variable angle inlet guide vanes (GV) 11 to 14 are provided on the inlet side of the compressors 4 to 7 in each stage, and by adjusting the angles of these inlet guide vanes 11 to 14, each The air capacity flowing into the compressors 4 to 7 can be adjusted.

Further, diffuser vanes (DV) 15 to 18 are provided on the outlet side of the compressors 4 to 7 in each stage.

Adjust the angle of these diffuser vanes 15 to 18.
By doing so, the air capacity flowing out from each compressor 4 to 7 can be adjusted.

The angles of these inlet guide vanes 11 to 14 and diffuser vanes 15 to 18 are each adjusted to arbitrary values by a drive device 19.

Furthermore, this centrifugal compressor 1 as a whole or each stage compressor 4
Operating state quantities 1 to 7, for example, air flow rate, temperature, pressure, etc., are determined by the flow rate sensor 20. Temperature sensor 2
1. It is detected by a detection means such as the pressure sensor 22. A control device 23 is provided between each of the sensors 20 to 22 and the driving device @19.

Conventionally, a control means as shown in FIG. 9 has been disclosed in order to control the multi-stage centrifugal compressor as described above so that a predetermined air capacity (flow rate) can always be obtained with optimum operating efficiency according to various operating conditions. (Japanese Unexamined Patent Publication No. 55-60692).

In this control means, as a manipulated variable for realizing an optimal operating state for various operating states expressed by air flow rate, temperature, pressure, etc. in the entire centrifugal compressor 1 or each stage of compressors 4 to 7, Entrance guide vane 11 for each stage
14 and the angles of the diffuser vanes 15 to 18 are programmed and stored in advance in the storage section in the control device 23 (step SO).

As shown in FIG. 9, upon receiving the state detection values from the sensors 20 to 22, the control device 23 calculates and monitors the current operating state of the multistage centrifugal compressor from the detected values.
At the same time as step SL), the operation program (vane angle combination value) that has been determined in advance is compared with the operating state, and the operation amount that can realize the optimum operation efficiency is determined. Dress up! 119 Li output (XTera/S2).

Thereafter, it is determined whether the operating state calculated based on the state detection values from the sensors 20 to 22 is the optimum operating efficiency state determined in advance (step S3). When it is determined that the system is in the optimum operating efficiency state.

At that point, the control is terminated and the vane angle according to the selected operation program is maintained; however, if it is determined that the operating condition is not optimal, the control output (vane waste degree) according to the selected operation program is corrected. Then, it is determined whether the efficiency has improved based on the detected state value (step S5).

In this way, the operating state of each stage is fed back, and the inlet guide vanes 11 of each stage programmed in advance are fed back.
14 and diffuser vanes 15 to 18 is optimal.

Control is performed to correct the combination of vane angles in the operating program so that optimal operating efficiency can be obtained at all times in response to changes in operating conditions such as aging and performance changes (step S6).

By the way, in order to control the multistage centrifugal compressor so that a predetermined air capacity can always be obtained with optimum operating efficiency according to various operating conditions, the inlet guide vanes 11 to 14 are used as described above.
In addition to the means for controlling the angles of the diffuser vanes 15 to 18, there is also a conventional control means as disclosed in Japanese Patent Laid-Open No. 55-60695. In the control means described above, all angle combinations of the inlet guide vanes 11 to 14 and diffuser vanes 15 to 18 are programmed and stored in accordance with the operating state.
This control means presets a predetermined functional relationship between the operation amounts of the inlet guide vanes 11 to 14 and the diffuser vanes 15 to 18, and controls the inlet guide vanes 11 to 14 and the diffuser vanes 15 according to the operating state based on this functional relationship. ~18 angles can be controlled with one voice.

When controlling a multi-stage centrifugal compressor, the number of inlet guide vanes and diffuser vanes to be controlled increases.
Although it is necessary to determine a large number of manipulated variables for each operating state, the control means for multistage centrifugal compressors described above are all designed to easily and reliably determine the manipulated variables in response to various operating states. It is proposed as.

[Problems to be Solved by the Invention] However, in the conventional centrifugal compressor control means as described above, the combination of the angles of the inlet guide vanes 11 to 14 and the angles of the diffuser vanes 15 to 18, or the inlet guide Angle of vanes 11 to 14 and diffuser vane 1
The functional relationship between angles 5 to 18 and operating conditions, etc. must be set in advance, and in order to set such various data, a considerable amount of time is required before the multistage centrifugal compressor actually operates or at the beginning of its operation. There is a problem in that a test run period of 100 yen is required, and in particular, a huge amount of data is required to preset the optimal combination for one year's operating conditions.

In addition, especially in the latter control means, since the angles of the inlet guide vanes 11 to 14 and the angles of the diffuser vanes 15 to 18 are uniquely determined as control variables for the operating condition, the optimum combination is selected at the initial stage of operation. Even if it is,
It is impossible to always maintain the optimal combination in response to environmental changes and secular changes, and even if the functional relationship is corrected every time an environmental change or secular change occurs, in order to obtain a new functional relationship, it is necessary to repeat the above method again. There are also problems in that it requires a trial run period and a huge amount of data.

Furthermore, as mentioned above, since the vane angles in each stage are uniquely given by the combination or functional relationship, it is not possible to achieve a good matching state for the operation of each stage.
There are also problems such as a narrower driving range and inability to drive efficiently.

The present invention aims to solve these problems, and it is possible to solve this problem by providing a large number of inlet guide vanes and diffusers for each stage, without requiring a test run period or a huge amount of data as described above. Provides a control method for a multi-stage centrifugal compressor that allows the angle of the vanes to be easily handled as a control variable and achieves a good matching condition for each stage to achieve a wide operating range and high efficiency operation. The purpose is to

[Means for Solving the Problems] For this reason, 1) the method for controlling a multistage centrifugal compressor of the present invention is such that the angles of the inlet guide vanes and diffuser vanes at each stage are adjusted so that the operating flow rate of the centrifugal compressor at each stage is the design flow rate. , respectively, as a set of dimensionless inlet guide vane angle and dimensionless diffuser vane angle that have similar operating flow rates at the same ratio. Next, the operating amounts of the above inlet guide vane and diffuser vane at each stage are expressed as The set of dimensionless inlet guide vane angles and dimensionless diffuser vane angles are determined as the set of dimensionless inlet guide vane angles and dimensionless diffuser vane angles, and the set of dimensionless inlet guide vane angles and dimensionless diffuser vane angles thus determined are determined as the set of dimensionless inlet guide vane angles and dimensionless diffuser vane angles at each stage. After the angles of the guide vane and the diffuser vane are converted, the multistage centrifugal compressor is controlled based on the angles of the inlet guide vane and the diffuser vane.

[Function] In the method for controlling a multistage centrifugal compressor of the present invention described above, the angles of the inlet guide vane and diffuser vane at each stage are expressed as a set of dimensionless inlet guide vane angle and dimensionless diffuser vane angle. , a set of dimensionless inlet guide vane angles and a dimensionless diffuser vane angle in the same way as controlling a single stage centrifugal compressor, and a set of determined dimensionless inlet guide vane angles and a dimensionless diffuser vane angle. A multi-stage centrifugal compressor is controlled based on the angles of the inlet guide vanes and diffuser vanes obtained by converting the vane angles.

[Embodiments of the Invention] A method of controlling a multi-stage centrifugal compressor as an embodiment of the present invention will be explained below with reference to the drawings. Fig. 1 is a flowchart thereof. First, the method according to the present embodiment will be explained. First, the configuration of a multistage centrifugal compressor to which the method of this embodiment is applied, a control device for the multistage centrifugal compressor, and its basic functions will be explained with reference to FIGS. 2 to 4. Incidentally, in FIG. 2, the same reference numerals as in FIG. 8 indicate substantially the same parts, so a description thereof will be omitted.

However, in the multi-stage centrifugal compressor to which the control device of the present embodiment shown in FIG. 2 is applied, the compressors 4 to 7 are all arranged on the same axis and the power transmission gear 3 is omitted, as shown in FIG. Although different from the multi-stage centrifugal compressor in FIG. 8, the method of the invention also applies to the multi-stage centrifugal compressor in FIG.

As shown in FIG. 2, in the multistage centrifugal compressor in this embodiment, inlet guide vanes (GV) 11 to 14 are driven by inlet guide vane drive devices 19 a to 19 d, respectively, and diffuser vane (DV) 15 ~1
8 are diffuser vane drive devices 19a to 19, respectively.
It is designed to be driven by h. Further, as a sensor, a flow rate sensor 20. Temperature sensor 21. In addition to the pressure sensor 22, there is a rotation speed sensor 2 that detects the compressor rotation speed.
4 and a humidity sensor 27 are provided.

All detection signals from the sensors 20 to 22, 24, and 27 are input to the control device 28. This control device 28 includes a rotation speed control calculation section 29 that calculates and outputs a control signal to the drive machine 2 in order to control the rotation speed of the centrifugal compressor 1, and a rotation speed control calculation section 29 that calculates and outputs a control signal to the drive machine 2 to control the rotation speed of the centrifugal compressor 1. a vane angle control calculation unit 30 that calculates and outputs control signals to each of the drive devices 19a to 19h in order to control the angles of the vane angles, and a central control calculation unit 3.
1, and a control command input section 32 for inputting control command signals to the central control calculation section 31.

Here, the central control calculation unit 31 controls the sensors 20 to 22.2.
4. Receives the detection signals from 27, calculates the operating state of the multistage centrifugal compressor from these detection signals, and outputs these detection signals and operating state signals to the rotation speed control calculation section 29 and the vane angle control calculation section 30. In addition, it has a two-stage control function, a control mode switching function when the flow rate is reduced, a control mode switching function when the flow rate is increasing, and a constant flow rate maintenance control function, which will be described later.

That is, when a flow rate change request is input to the central control calculation section 31 from the control command input section 32, the two-step control function of the central control calculation section 31 changes the compressor rotation speed from the rotation speed sensor 24. When it is larger than the set value, the rotation speed of the drive machine 2 is controlled by the rotation speed control calculation unit 29 (primary control).
After performing this, the inlet guide vanes 11 to 14 and the diffuser vanes 15 to 15 are controlled by the vane angle control calculation unit 30.
Eighteen angle controls (secondary controls) are performed.

In particular, when the flow rate change request is a reduction request, when the compressor rotation speed reaches the set value by the rotation speed control of the primary control, the central control calculation unit 31 functions to switch the flow reduction control mode. This makes it possible to switch from the control mode using the two-step control function to the angle control mode of the inlet guide vanes 11 to 14 and the diffuser vanes 15 to 18 using the vane angle control calculation unit 30 while maintaining the compressor rotation speed. There is. Here, the set value of the compressor rotation speed is given as the minimum rotation speed at which high efficiency can be obtained without causing surging through rotation speed control.

In particular, when the flow rate change request is an increase request, the control mode switching function for flow rate increase of the central control calculation unit 31 causes the compressor rotation speed to change when the compressor rotation speed is at the set value. If the flow rate is not maintained, the vane angle control mode is set by the vane angle control calculation unit 3o, and when the flow rate increased by this vane angle control mode reaches a predetermined upper limit value, the control mode is switched to the control mode using the two-step control function, Rotation speed control (primary control) and vane angle control (secondary control) are performed.

Here, the upper limit value of the flow rate is given as the maximum flow rate obtained by the vane angle control mode at the minimum rotation speed.

Note that the rotational speed control calculation section 29 includes a control amount calculation section 29a that calculates an optimal rotational speed control amount that approaches the target flow rate based on the operating state signal from the central control calculation section 31, and The operating amount calculating section 29b calculates the operating amount of the drive machine 2 to actually control the compressor rotational speed based on the rotational speed control amount. Similarly, the vane angle control calculation section 30 includes a control amount calculation section 30a that calculates an optimal vane angle control amount that approaches the target flow rate while maintaining the optimum efficiency state based on the operating state signal from the central control calculation section 31; The vane angle calculation section 30b calculates the operation amounts of the drive devices 19a to 19h to actually control each vane angle based on the vane angle control amount from the control amount calculation section 30a.

Next, the basic operation of the above-mentioned centrifugal compressor control device to which the method of this embodiment is applied will be explained using FIGS. 3 and 4.

First, when changing and controlling the flow rate in the centrifugal compressor 1, a target flow rate Qp is set in the control command input section 32 of the control device 28, and this target flow rate Qp is inputted as a control signal to the central control calculation section 31. Ru. In this central control calculation unit 31, if the input target flow rate Qp is smaller than the current flow rate Q, it is determined that a flow rate reduction request signal has been input, and the two-step control function or the control mode switching function at flow rate reduction operates. If the input target flow rate Qp is larger than the current flow rate Q, it is determined that a flow rate increase request signal has been input, and the two-step control function or the control mode switching function when increasing the flow rate is operated.

When changing the flow rate to decrease, as shown in FIG. 3(a), the central control calculation unit 31 determines that the request is to decrease the flow rate based on the target flow rate Q as described above (step A1). It is determined whether the compressor rotation speed detected by the rotation speed sensor 24 is larger than a preset minimum rotation speed (step A2).

When the compressor rotation speed is larger than the minimum rotation speed, the rotation speed control calculation section 29 takes steps to reduce the rotation speed of the drive machine 2 based on the operating state signal from the central control calculation section 31. A3) The central control calculation unit 31 determines whether the difference between the flow rate Q changed by the rotation speed control and the target flow rate Qp is smaller than the flow rate tolerance ΔQRPM under the rotation speed control (step A4). .

If the above flow rate difference is greater than or equal to the flow rate allowable value ΔQ RPM, the process returns to step A2 to determine the rotation speed, while if it is smaller than the flow rate allowable value ΔQ RPM, the rotation speed of the drive unit 2 at that time, that is, the compressor rotation speed. (Step A5: End of primary control by two-step control function). and,
Change the control mode from rotation speed control to inlet guide vane 11-1
4 and the angle control of diffuser vanes 15 to 18 (2
This vane angle control is used to adjust the flow rate more finely than the rotational speed control and search for the optimum efficiency operating point (step A6).

After this, the difference between the flow rate Q changed by the vane angle control and the target flow rate Qp is the allowable flow rate ΔQ in the vane angle control.
The central control calculation unit 31 determines whether or not it is smaller than v and whether or not the operating state is at the optimum efficiency (step A7).

If these conditions are not met, repeat step A.
While returning to the vane angle control in step 6, if the above conditions are met, it is determined that the target flow rate Qp has been reached,
The control mode in the central control calculation unit 31 is switched to a control mode (described later with reference to FIG. 4) in which the flow rate Q in the centrifugal compressor 1 is maintained at a constant target flow rate Qp (step A8).

By the way, if it is determined in step A2 that the compressor rotation speed is the preset minimum rotation speed (including the case where the rotation speed is reduced to the minimum rotation speed state by performing the rotation speed reduction control in step A3), By using the control mode switching function when the flow rate is reduced, step A6 is performed while maintaining the compressor rotational speed at the minimum rotational speed without performing rotational speed control thereafter.
Switch to control mode in which flow rate is controlled by vane angle control. Thereafter, in the same manner as described above, step A7. Execute A8.

On the other hand, when changing the flow rate to increase, as shown in FIG. It is determined whether the compressor rotation speed detected by 24 is larger than a preset minimum rotation speed (
Step B2).

When the compressor rotation speed is higher than the minimum rotation speed, the central control calculation unit 31
The rotation speed control calculation unit 29 increases the rotation speed of the drive machine 2 based on the operating state signal from step B3), and calculates the flow rate Q changed by this rotation speed control and the target flow rate QF.
The central control calculation unit 31 determines whether the difference between the
Step B4).

If the above flow rate difference is greater than or equal to the flow rate allowable value ΔQ RPM, the control returns to the rotation speed increase control in step B3 again, while if it is smaller than the flow rate allowable value ΔQ RPM, the rotation speed of the drive machine 2 at that point, that is, the compressor rotation. fix the number (step B5: end of primary control by two-step control function), and change the control mode from rotation speed control to inlet guide vane 11.
to 14 and the angle control of the diffuser vanes 15 to 18, and steps 86 to B8, which are exactly the same as steps A6 to A8 in the flow rate reduction request flow described above, are executed (secondary control using a two-step control function).

By the way, if it is determined in step B2 that the compressor rotation speed is the preset minimum rotation speed, the flow increase control mode switching function is used.

While maintaining the compressor rotation speed at the minimum rotation speed, the control mode is switched to angle control of the inlet guide vanes 11 to 14 and diffuser vanes 15 to 18, and this vane angle control controls the increase in flow rate at optimal efficiency operation. (Step B9).

After this, the difference between the flow rate Q changed by the vane angle control and the target flow rate Qp is the allowable flow rate ΔQ in the vane angle control.
The central control calculation unit 31 determines whether or not it is smaller than v and whether or not the operating state is at the optimum efficiency (step B10). If these conditions are not met, it is determined whether the flow rate Q at that point has reached a predetermined upper limit (step B11). If the flow rate Q is not at the predetermined upper limit value, step B is performed again.
On the other hand, when the flow rate Q reaches a predetermined upper limit value, the control mode in the central control calculation unit 31 is switched to the control mode using the two-step control function, and the process moves to step B3.

In addition, when the conditions in step BIO are satisfied, it is determined that the target flow rate Qp has been reached, and the control mode in the central control calculation unit 31 is changed so that the flow rate Q in the centrifugal compression V11 is set to a constant target flow rate Qp and optimal efficiency. The control mode is switched to a control mode (described later with reference to FIG. 4) in which the operating state is maintained (step B8).

After the flow rate Q in the centrifugal compressor 1 reaches the target flow rate Qp as described above, the central control calculation unit 31
The control mode is constant flow rate control mode (
Step A8. B8). The control flow in this constant flow rate control mode will be explained with reference to FIG.

As shown in FIG. 4, step A8. When receiving a constant flow rate control request to set the constant flow rate control mode by B8 or a control signal from the control command input unit 32 (step C1), the central control calculation unit 31 receives a detection signal from the flow rate sensor 20. is constantly monitored, and when the flow rate Q fluctuates from the target flow rate Qp due to environmental changes such as atmospheric temperature changes, the flow rate variation ΔQ (= Qp - Q) is calculated, and the magnitude of the same flow rate variation ΔQ is calculated. Determine whether the flow rate is smaller than the allowable flow rate ΔQv in vane angle control (step C2)
. If the magnitude of this flow rate variation ΔQ is smaller than the flow rate allowable value ΔQv, the state returns to the flow rate fluctuation monitoring state again, while if it is greater than the flow rate allowable value ΔQv, the inlet guide vanes 11 to 14
Then, the angle control of the diffuser vanes 15 to 18 is performed (step C3) to correct the flow rate fluctuation ΔQ and
is maintained at a constant target flow rate Qp and at an optimally efficient operating state.

At this time, the central control calculation unit 31 always integrates and stores the flow rate fluctuation amount ΔQ corrected by vane angle control, and the magnitude of the integrated value ΣΔQ is determined from the flow rate allowable value ΔQ RPM by rotation speed control. (step C4), the magnitude of this integrated value ΣΔQ is the allowable flow rate Δ
If it is smaller than Q RPM, the flow rate fluctuation monitoring state is returned to step C2 again, while if it is greater than the flow rate allowable value ΔQRP, the current compressor rotation speed detected by the rotation speed sensor 24 is set to the preset minimum rotation speed. It is determined whether the number is greater than the number (step C5).

When the compressor rotation speed is larger than the minimum rotation speed, the rotation speed control calculation unit 29 controls the rotation speed of the drive machine 2 to control the compressor rotation speed by one step corresponding to the flow rate tolerance value ΔQRPM. do. At the same time, the angle control of the inlet guide vanes 11 to 14 and the diffuser vanes 15 to 18 is not performed, the flow rate Q is set to the target flow rate Qp and the optimum operating state, and the integrated value ΣΔQ is also reset to zero (step C6). .

On the other hand, if it is determined in step C5 that the compressor rotation speed is the preset minimum rotation speed, it is determined whether the integrated value ΣΔQ is positive or negative (step C7), and if the integrated value ΣΔQ is positive, It is sufficient to control the rotation speed in the direction of increasing the flow rate Q, that is, in the direction of increasing the compressor rotation speed, and it is sufficient to control the compressor rotation speed so that it becomes larger than the minimum rotation speed, so the rotation speed in step C6 control. Further, if the integrated value ΣΔQ is negative, the flow rate fluctuation monitoring state in step C2 is returned to again with the vane angle maintained without performing rotational speed control.

In this way, the flow rate Q in the centrifugal compressor 1 is always maintained at a constant target flow rate Qp and an optimally efficient operating state even if it fluctuates due to environmental changes. Holding control is particularly effective when using a gas turbine or steam turbine that cannot control minute rotational speed as the drive unit 2.The holding control is particularly effective when using a gas turbine or steam turbine that cannot control the rotational speed in a minute manner. It is thought that this interpolation is performed and control is performed to achieve the optimum efficiency operating state.

Up to this point, we have explained the three major control functions (flow rate reduction change control, flow rate increase change control, and constant flow rate maintenance control) by the centrifugal compressor control device to which the method of this embodiment is applied. The part directly related to the method of the present invention, that is, the method for determining the control amount of the vane angle when performing these controls (steps A6, B6, B9, and C3) will be explained with reference to FIG. 1 and FIGS. 5 to 7. . and,
In this embodiment, the features of the present invention are that the extrapolation method is performed on a dimensionless vane angle plane, as will be described later, and step 010 in FIG. 1.

In the method of this embodiment, a multistage centrifugal compressor having four stages of centrifugal compressors 4 to 7 is controlled.
When controlling the vane angle, if the inlet guide vanes 11 to 14 and the diffuser vanes 15 to 18 at each stage are controlled separately and independently, the control operation will be extremely complicated and complicated, and the convergence will also be unstable.
14 and the diffuser vanes 15 to 18 are made dimensionless and represented by a set of dimensionless inlet guide vane angle α and dimensionless diffuser vane β, thereby simplifying and simplifying the control operation.

First, the definitions and meanings of the dimensionless inlet guide vane angle α and the dimensionless diffuser vane β will be briefly explained with reference to FIGS. 5(a) and 5(b). In general, the characteristics of a centrifugal compressor are as shown in Figure 5(a): flow rate - discharge pressure (
There is a Q-P) curve. If the centrifugal compressor is single-stage, there is naturally only one characteristic curve, so there is no need to make the angles of the inlet guide vane and diffuser vane dimensionless. As shown in (b), the characteristic curves differ for each stage of centrifugal compressor.

Therefore, when the pressure (discharge pressure P) is almost constant due to the resistance on the device side, the angle of each inlet guide vane 11 to 14 is adjusted so that the operating flow rate Q1 to Q4 of the centrifugal compressors 4 to 7 in each stage is the design flow rate Qo ( = Q1) is expressed as one dimensionless inlet guide vane angle α that has a similar operating flow rate at the same ratio, and each diffuser vane 15 to 18 is also It is expressed as one dimensionless diffuser vane angle β such that the flow rates Q1 to Q4 are similar operating flow rates at the same ratio to the design flow rate Qo (=Ql).

That is, in FIG. 5(b), the diffuser vane 15
.about.18 as a constant design value, the pressure ratio distribution of each stage remains unchanged, and the design discharge pressure Po of a certain stage is constant, the flow rates Q1 to Q4 are determined for the angles of the respective inlet guide vanes 11 to 14. The ratio Q to these design flow rates Qo (=01)
2/Ql (Q3/Ql, Q4/Ql) are the same angles (Gv□
~Gv4) is expressed as a dimensionless inlet guide vane angle α as shown in equation (1) below.

α=Knα・(αn/αn0-1)...(1) Here, αn is the angle of the n-th stage entrance guide vane, αn0 is n
The stage inlet guide vane reference angle Knα is a coefficient of the nth stage inlet guide vane angle determined so that the nth stage operating flow rate becomes a similar operating flow rate for each stage with respect to the design flow rate Qo.

Also, in exactly the same way as this dimensionless inlet guide vane angle α, the angles of the diffuser vanes 15 to 18 at each stage are also
It is expressed as a dimensionless diffuser vane angle β as shown in the following equation (2).

β=Knβ・(βn/βna-1) ''(2) Here, βn is the angle of the n-th stage diffuser vane, βn0
is a reference angle of the n-th stage diffuser vane, and Knβ is a coefficient of the n-th stage diffuser vane angle determined so that the operating flow rate of the n-th stage becomes a similar operating flow rate of each stage with respect to the design flow rate QD.

In the control amount calculating section 30a of the vane control calculating section 30, the angles of the inlet guide vanes 11 to 14 and the diffuser vanes 15 to 18 are defined in advance as a set of dimensionless inlet guides as described above.

The vane angle α and the dimensionless diffuser vane β are respectively expressed as Determine the angle control amount (the method for determining the vane angle control amount described here is called the extrapolation method).

As mentioned above, step A6. B6. B9. When the vane angle control mode is entered at C3, in this embodiment, the control amount calculation unit 30a of the vane angle control calculation unit 30 starts the flow shown in FIG.

On the dimensionless vane angle plane αβ, as shown in FIG. 6(a), select three appropriate points A, B, and C including point A in the vicinity of the current vane position ff1A (step Di).
. Then, with respect to the three selected points A, B, and C, the operation amount calculation unit 30b and the driving devices 19a to 19h actually drive the inlet guide vanes 11 to 14 and the diffuser vanes 15 to 18, and Flow rate Q at C
and the efficiency η are actually measured (step D2). Here, the flow rate Q is detected by the flow rate sensor 20 and input to the control amount calculation unit 30a via the central control calculation unit 31, while the efficiency η is detected by the central control based on the detection signals from the sensors 20 to 22. After being calculated in the calculation unit 31, the control amount calculation unit 3
Input to 0a.

In step D3, the first plurality (nine in this example) of extrapolation points ■ to ■ are developed on the dimensionless vane angle plane αβ so as to surround the first base point A-C. Set. Then, the flow rate and efficiency at each extrapolation point ■ to ■ are predicted from the actual flow rate and effective efficiency at basic points A to C (step D6).

In other words, as mentioned above, the flow rate Q and efficiency η are
Characteristic curves as shown in Figure 7 for each rotation speed (Q for flow rate, >Q, >Q, >Q, and η for efficiency.〉η
, 〉η2〉η□), and from the actual flow rate and effective efficiency at the three basic points A-C, the flow rate characteristic curve and the efficiency characteristic curve corresponding to the characteristic curve shown in Fig. 7 are approximated by a plane or a curved surface. Estimated by Then, based on this estimated characteristic curved surface, the flow rate and efficiency at each extrapolation point (■) to (■) are predicted.

By the way, on the dimensionless vane angle plane αβ, the flow rate Q and efficiency η generally have a tendency (characteristic surface: Q oHQ, , Q, , Q) as shown in FIG.
, is the isoflow line, η. , η1. η2. η.

has isoefficiency lines). In particular, in the figure, there is a relationship of Q, >Q, >Q, >Q for the flow rate, and the vane angle α
Since there is a relationship between the vane angle and the increase/decrease in the flow rate such that the flow rate always increases as , β increases, this relationship is set and stored in the control amount calculation section 30a in advance, and step D
Step D5.2 verifies the reliability of the flow rate value actually measured in step D5. Perform by D6.

In other words, for the first group Mokugyo A to C shown in FIG. 6(a), the flow rate at point B will always be larger than the flow rate at point A between basic points A and B from the above relationship. Is it clear that each basic point A according to step D2?
- Of the actual measured flow rate of C, basic points A and B are compared with the pre-stored flow rate increase/decrease relationship (step D5), and if the increase/decrease relationship is reversed, the comparison result is a logical contradiction. In step D6), it is determined that the measurement error by the flow rate sensor 20 is large, and data acquisition based on this actual measured flow rate is canceled.

The process returns to step D2 to obtain the actual measured flow rate again.

Further, if it is determined that the above comparison result does not cause a logical contradiction (step Da), the first step D7
Move to. In this way, by verifying the reliability of the actual measured flow rate, vane angle control can be performed without losing the direction of the target flow rate due to fluctuations in the flow rate measured during control execution or measurement errors. Become so.

If it is determined in step D6 that the comparison result does not cause a logical contradiction, step D
In 7, from among the first extrapolation points ■～■ above,
An extrapolation point is selected where the predicted flow rate is close to the target flow rate Qp and the predicted efficiency is high.

Next, in step D8, it is determined whether the extrapolation point selected in step D7 falls within the surging region. As shown in FIG. 7, the surging region can be defined by the surging prevention line SL on the dimensionless vane angle plane αβ for each compressor rotation speed (shaded side portion of the surging prevention line SL).
In the control amount calculation unit 30a, a surging prevention line SL that defines a surging area is set and stored in advance as a function of dimensionless vane angles α and β for each compressor rotation speed, and an extrapolation point is determined in step D7. Each time it is selected, it is checked whether the extrapolated point crosses the surging prevention line SL and enters the surging area.

If the selected extrapolation point is within the surging region, the predicted flow rate is close to the target flow rate Qp and the predicted efficiency is high among the extrapolation points other than the currently selected extrapolation point. After selecting the object (step D9), it is checked again in step D8 whether or not the extrapolated point falls within the surging region. By repeating this, an extrapolation point that is close to the target flow IQp and has high efficiency is selected from extrapolation points other than the extrapolation points within the surging region.

In this way, it is possible to reliably prevent surging from occurring due to vane angle control.

When a high-efficiency extrapolation point that is close to the target flow rate and does not fall into the surging region is selected [here, it is assumed that extrapolation point ■ in Fig. 6 (a) has been selected], this extrapolation point Convert a set of dimensionless inlet guide vane angle α and dimensionless diffuser vane angle β, which are the coordinates of (2), into the actual angles of the inlet guide vanes 11 to 14 and diffuser vanes 15 to 18 at each stage (step DIO).
.

In other words, from equations (1) and (2) mentioned above, the vane angles αn and βn (in this example, n=1 to 4) that should be actually operated are determined.
).

From the dimensionless vane angles α, β to the actual vane angles αn, β
In step DIO for determining n, centrifugal compressors 4 to
When a disturbance that causes a variation in the operating point is detected in any of the above cases, the deviation of the operating flow rate from the similar operating flow rate in the centrifugal compressor of the stage where the disturbance occurred can be corrected in the first order manner.

The operating characteristics of each stage (suction flow rate Q2° of the next stage of head H9) is generally expressed as in the following equation.

n=ni・R−T1・((P2/P,)” −1) Bani−
1)...(3) Qzo" 1/P 2...
-(4) Here, X is the specific heat ratio, R is the gas constant, T is the suction temperature, P is the suction pressure, and B2 is the discharge pressure.

In order for each stage to have a similar operating flow rate to the design flow rate, the angles of the inlet guide vanes 11 to 14 and diffuser vanes 15 to 18 of each stage are set from the dimensionless vane angles α and β to (1), (2) Even if it is determined by the formula and given as the manipulated variable, if only the suction temperature of a certain stage becomes relatively low due to a disturbance, the head (suction pressure) I (of the centrifugal compressor that caused the disturbance) will not change. Therefore, (3
) According to the equation, the discharge pressure P2 becomes larger. As a result, (4)
From the formula, the suction flow rate of the next stage is Q. decreases, and the similar operation flow rate changes.

Due to this disturbance, the operating flow rate at each stage is similar to the design flow rate, which may result in a decrease in efficiency due to poor matching of operating points, or surging may occur early in a certain stage. As a result, the operating range becomes narrower.

Therefore, as shown in equations (5) and (6), in order to cancel the disturbance based on the detected disturbance, the non-dimensional correction amount [Knα・A・(αnt/αno ) Find Etoko.

From equations (5) and (6) obtained by adding each dimensionless correction amount to the dimensionless inlet guide vane angle α and the dimensionless diffuser vane angle β, it is found that Angle αn, β
We are looking for n.

α=Knα0(αn/αno ” A 11(αnt/
αn(+)+ A 2@(αnRH/αno)÷−@−
-1)...(5) β=Knβ・(βn/βno"B1"(β, 1t/βn
o)+B,・(βnRH/βno)+・・・−1)・・
・(6) Here, αnt is the disturbance correction amount due to the nth stage suction temperature,
αnR11 is the disturbance correction amount due to the nth stage humidity, βnt is the disturbance correction amount due to the nth stage suction temperature, βnRH is the disturbance correction amount due to the nth stage humidity, A□# A,, BLIB2
is the coefficient.

In this way, even when searching for a highly efficient extrapolation point close to the target flow rate Qp, it is possible to correct the deviation of the operating flow rate from the similar operating flow rate in the centrifugal compressor where disturbance has occurred. Furthermore, by this modification, the flow rate at each stage can always be made to be a similar operating flow rate to the design flow rate.

As described above, if there is a stage where a disturbance has occurred (5
), (6), and in the case where there is no stage with disturbance, equations (5) and (6) become equations (1) and (2), and a set of dimensionless inlet guide vane angle α and dimensionless The actual angles of the inlet guide vanes 11 to 14 and the diffuser vanes 15 to 18 are determined from the dimensional diffuser vane angle β, and the operating amount calculation section 30b of the vane angle control calculation section 30 calculates the driving devices 19a to 19a according to the obtained angles. 1
9h to output the control signal to the inlet guide vanes 11 to 1.
4 and diffuser vanes 15 to 18 are driven and controlled (step D11).

After this, the flow rate Q changed by the above vane drive control
and the target flow rate Q is smaller than the allowable flow rate ΔQv in vane angle control (step D12).
If the flow rate difference is smaller than the flow rate tolerance ΔQv, vane angle control is ended at that point, while if the flow rate difference is greater than or equal to the flow rate tolerance ΔQv, the process returns to step D3 and three new basic points are set. Steps D1 to D12 are performed in the same manner as described above for the selected and second base points and the second extrapolation points expanded to surround the base points.

Here, the basic points selected for the second time are shown in Fig. 6(a).
As shown in FIG. Actual measurement point that was the insertion point ■
, and the remaining extrapolation points selected from the first extrapolation points, and around these basic points, the first
Flow rates at positions corresponding to nine points: the second extrapolation points ■, ■, ■, basic points B and C, and new extrapolation points p1 to p4.

Predict the efficiency d1 based on the values of basic point A, actual measurement point ■, and extrapolation point ■
Slurp.

In this way, the flow rate and efficiency are actually measured by operating the inlet guide vanes 11 to 14 and the diffuser vanes 15 to 18 until the conditions in step D12 are satisfied,
Then expand the extrapolated points.

Vane angle control is performed by finding a highly efficient extrapolation point that is close to the target flow rate Qp.

In the above embodiment, the expansion of extrapolation points around the basic point is limited to nine linear extrapolation points as shown in FIG. 6(a), but as shown in FIG. 6(b). As shown, 15 additional secondary extrapolation points may be selected around the 9 primary extrapolation points to predict the flow rate and efficiency for these extrapolation points as well. However, although the number of basic points is three in this example, it is not limited to this and may be four or more. Also, the method of expanding the extrapolation points is also shown in Figure 6 (a). ) and (b), and the range of extrapolation points may be changed arbitrarily.

According to the present embodiment, for example, as the simplest example, the flow rate is Q at point a of (α, β) = (α0.β1) on the dimensionless vane angle plane at the compressor rotation speed RPMI.

When reducing the flow rate from a certain operating state to the target flow rate Q2, follow the flow shown in Fig. 3 (,).

First, the compressor rotation speed is reduced to the minimum rotation speed RPM2 preset in the rotation speed control mode (primary control in the two-step control function), and the flow rate is adjusted to a on the αβ plane as shown in FIG. After setting the point (α1.β1), the vane angle control mode (following the flow shown in Fig. 1) moves from point a to point b (α2.β), which is close to the target flow rate Q2 and has high efficiency η□.
2) is searched for and the flow rate is reduced.

As described above, according to the method of this embodiment, by using a set of dimensionless inlet guide vane angle α and dimensionless diffuser vane angle β for a multistage centrifugal compressor, the inlet guide as a control target, which is a large number, can be controlled. Vane 11-1
4 and the angles of the diffuser vanes 15 to 18 can be handled as one set, so the multi-stage centrifugal compressor can be controlled extremely easily without complicating the control. A good matching condition can be obtained for the stages, and a wide operating range and high efficiency operation in θ can be achieved.

Furthermore, according to the method of this embodiment, it is possible to correct the deviation of the operating flow rate from the similar operating flow rate in the centrifugal compressor where disturbance has occurred, and furthermore, by this correction, the flow rate at each stage can be adjusted to the design flow rate. Since the operating flow rates can always be similar, the angles of the inlet guide vanes 11 to 14 and the diffuser vanes 15 to 18 can always be expressed as a set of dimensionless inlet guide vane angle α and dimensionless diffuser vane angle β. Imperial edict 1. Another advantage is that it can prevent inconveniences such as a decrease in efficiency and a decrease in the operating range due to poor matching of operating points due to disturbances.

Further, according to the present embodiment, control by a two-step control function including rotational speed control of the drive machine 2 as the primary control, and control of the inlet guide vanes 11 to 14 and the diffuser vanes 15 to
By appropriately selecting and performing the 18 angle controls, flow rate control can be performed with extremely high operating efficiency over a wide flow rate range.

Furthermore, according to this embodiment, when controlling the flow rate, when the rotation speed is larger than the set value, the flow rate control (primary control) is efficiently performed in large steps by the rotation speed control, and the flow rate is adjusted to the target flow rate. After approaching , a point with a target flow rate and high efficiency can be searched by vane angle control (secondary control), which has the advantage of being able to control the flow rate while maintaining high efficiency.

Further, according to this embodiment, the entrance guide vanes 11 to 14
When controlling the angles of the diffuser vanes 15 to 18, the appropriate operating points are directly searched and determined by the extrapolation method shown in FIG. There is no need to program it at all, and it has the advantage of being able to constantly perform highly efficient control with a minimum number of operations while responding quickly to environmental changes and changes over time.

[Effects of the Invention] As described above, according to the control method for a multistage centrifugal compressor of the present invention, the angles of the inlet guide vanes and diffuser vanes at each stage are adjusted in advance so that the operating flow rate of the centrifugal compressor at each stage is equal to the design flow rate. In contrast, the angles of the inlet guide vanes and diffuser vanes, which are a large number of control objects, can be expressed as a set of dimensionless inlet guide vane angles and diffuser vane angles that have similar operating flow rates at the same ratio. It is now possible to handle a multi-stage centrifugal compressor as a set, and it is possible to control a multi-stage centrifugal compressor extremely easily without complicating the control, and it is also possible to obtain a good matching condition for each stage. This has the effect of realizing a wide operating range and highly efficient operation.

[Brief explanation of the drawing]

1 to 7 show a method for controlling a multi-stage centrifugal compressor as an embodiment of the present invention. A block diagram showing the configuration of the device, FIG. 3(a) is a flow chart for explaining the control procedure when the above-mentioned control device requests a flow reduction, and FIG. 3(b) shows a control procedure when the above-mentioned control device requests a flow increase. Flowchart for explaining the procedure. FIG. 4 is a flowchart for explaining the control procedure in the constant flow rate control mode of the control device. FIGS. 5(a) and 5(b) are both dimensionless inlet guide vane angles. and graphs showing flow rate-discharge pressure characteristics for explaining the dimensionless diffuser vane angle, Figures 6(a) and 6(b) both explain the extrapolation method in the angle control procedure of the inlet guide vane and diffuser vane. Figure 7 is a graph showing the flow rate characteristic curve, efficiency characteristic curve and surging area on the dimensionless vane angle plane, and Figure 8 is a block diagram showing a general multi-stage centrifugal compressor. 9 are flowcharts for explaining control means for a conventional multi-stage centrifugal compressor. In the figure, 1 - centrifugal compressor, 11 - 14 - inlet guide vane, 15 - 18 - diffuser vane, 20 - flow rate sensor, 24 - rotation speed sensor. 29--rotation speed control calculation section, 30--vane angle control calculation section, 31...-central control calculation section.

Claims (2)

[Claims] (1) In a multi-stage centrifugal compressor that has multiple stages of centrifugal compressors and has angle-variable inlet guide vanes and diffuser vanes on the inlet and outlet sides of each centrifugal compressor, the inlet guide vanes and When controlling the multi-stage centrifugal compressor by adjusting the angle of the diffuser vane, the angle of the inlet guide vane and diffuser vane at each stage is determined in advance so that the operating flow rate of the centrifugal compressor at each stage is relative to the design flow rate. Let us express each set of dimensionless inlet guide vane angle and dimensionless diffuser vane angle as a set of dimensionless inlet guide vane angle and dimensionless diffuser vane angle that have similar operating flow rates at the same ratio, and then calculate the operating amount of the above-mentioned inlet guide vane and diffuser vane at each stage as the set of dimensionless inlet guide vane angle and dimensionless diffuser vane angle. 1 above determined as the dimensionless inlet guide vane angle and the dimensionless diffuser vane angle.
Convert the set of dimensionless inlet guide vane angles and dimensionless diffuser vane angles into the above inlet guide vane and diffuser vane angles at each stage, and then perform the above multistage centrifugal compression based on these inlet guide vane and diffuser vane angles. A method for controlling a multi-stage centrifugal compressor, characterized by controlling a compressor. (2) When a disturbance that causes variation in the operating point is detected in any stage of the centrifugal compressor, the method is to correct the deviation of the operating flow rate from the similar operating flow rate in the centrifugal compressor of the stage where the disturbance occurs. , find the non-dimensional correction amounts of the above-mentioned inlet guide vanes and diffuser vanes in all stages based on the detected disturbances, and calculate the non-dimensional correction amounts for the above-mentioned set of non-dimensional inlet guide vane angles and non-dimensional diffuser vane angles. and then converting the set of dimensionless inlet guide vane angles and dimensionless diffuser vane angles into inlet guide vane and diffuser vane angles in all the stages. A method for controlling a multistage centrifugal compressor according to item 1.