JPH0418157B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to centrifugal compressors for raw air compressors, factory air source compressors, and gas compressors for chemical plants used in oxygen production plants and various other plants. This relates to devices for controlling volume and pressure.

[Conventional technology]

Generally, centrifugal compressors in oxygen production plants and various other plants have a multi-stage configuration. In such a multistage centrifugal compressor,
As shown in FIG. 9, the centrifugal compressor 1 has a drive unit 2.
A first stage compressor 4, a second stage compressor 5, which are driven by a power transmission gear 3 that accelerates the rotation from
A third stage compressor 6 and a fourth stage compressor 7 are provided, and 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 10 is provided between the compressors 6 and 7. In addition, compressors 4 and 5 and compressors 6 and 7
are overhanging the same axial end.

In such a centrifugal compressor 1, the air sucked into the first stage compressor 4 is transferred to each compressor 5 to
7 and intercoolers 8 to 10, and is sequentially compressed and cooled, and then sent to the process from the fourth stage compressor 7.

On the inlet side of each stage of compressors 4 to 7, angle-variable inlet guide vanes (GV) 11 to 14 are installed.
are provided, and these inlet guide vanes 11-1
By adjusting the angle of 4, each compressor 4-7
It is possible to adjust the amount of air flowing into the tank. In addition, differential user vanes (DV) 15 to 18 are provided on the outlet side of the compressors 4 to 7 in each stage, and these differential user vanes 15 to 18
By adjusting the angle of each compressor 4-7
It is possible to adjust the amount of air flowing out of the

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

Further, the operating state of the entire centrifugal compressor 1 or the compressors 4 to 7 in each stage, for example, operating state quantities such as air flow rate, temperature, and pressure, are determined by a flow rate sensor 20, a temperature sensor 21, a pressure sensor 22, etc., respectively. is detected by the detection means. A control device 23 is provided between each of the sensors 20 to 22 and the drive device 19.

Conventionally, a control means as shown in FIG. 10 has been disclosed in order to control the above-mentioned multistage centrifugal compressor so that a predetermined air capacity (flow rate) can always be obtained with optimum operating efficiency according to various operating conditions. (Tokukaisho
55-60692). In this control means, the operation amount is controlled to achieve the optimum operating state for various operating states expressed by air flow rate, temperature, pressure, etc. in the entire centrifugal compressor 1 or the compressors 4 to 7 in each stage. As, each stage inlet guide vane 11~
14 and the angles of the diffuser vanes 15 to 18 are programmed and stored in advance in the storage section of the control device 23 (step
S0).

Then, as shown in FIG. 10, the control device 23
When the system receives the state detection values from the sensors 20 to 22, it calculates and monitors the current operating state of the multistage centrifugal compressor from the detected values (step S1), and also performs predetermined operations corresponding to the operating state. The set operation program (combined value of vane angle) is compared to find the amount of operation that can achieve the optimum operating efficiency, and this amount of operation is output to the drive device 19 (step
S2).

Thereafter, it is determined whether the operating state calculated based on the state detection values from the sensors 20 to 22 is the optimal operating efficiency state determined in advance (step
S3). When it is determined that the optimum operating efficiency state is reached,
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 angle) according to the selected operation program is corrected. The output is re-outputted (step S4), and it is determined from the state detection value whether the efficiency has improved (step S5).

In this way, the operating status of each stage is fed back, and the angle combination of the inlet guide vanes 11 to 14 and diffuser vanes 15 to 18 of each stage programmed in advance is monitored to see if it is optimal or not. 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 changes in performance and performance (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 and the diffuser vanes 15 to 18 are used as described above. In addition to the means for controlling the angle of , a control means as shown in FIG. 11 has also been disclosed (Japanese Patent Laid-Open No. 56-66490). This control means controls the angle of the inlet guide vane 11 (see FIG. 9) and the driving machine 2 (see FIG. 9) instead of controlling the angle of the inlet guide vanes 11 to 14 and the differential user vanes 15 to 18. A drive device 19A that controls the rotation speed and adjusts the angle of only the inlet guide vane 11, as shown in FIG.
A rotation speed sensor 24 for detecting the rotation speed of the drive machine 2 and a drive machine control device 25 for controlling the rotation speed of the drive machine 2 are provided. and,
The amount of operation of the inlet guide vane 11 is determined as a manipulated variable for realizing the optimum operating state for various operating states expressed by air flow rate, temperature, pressure, etc. in the entire centrifugal compressor or the compressors 4 to 7 of each stage. Operation table for optimal combination values of angle and rotation speed of drive machine 2 (corresponding to the suction flow rate, the angle of the inlet guide vane 11 and the rotation speed of the drive machine 2 are given to obtain the optimum operating efficiency) control device 23A in advance.
It is programmed and stored in the storage unit 26 inside.

Then, as shown in FIG. 11, the control device 23
Upon receiving the state detection values from the sensors 20 to 22, 24, A calculates and monitors the current operating state (operating conditions, suction flow rate, etc.) of the multistage centrifugal compressor from the detected values (step T1). Corresponding to the operating state, especially when the suction flow rate changes due to a change in operating conditions, the operating amount that can realize the optimum operating efficiency is determined based on the operating table in the storage unit 26, and the operating amount is It is output to the drive device 19A and the drive machine control device 25.

That is, the operating states of the drive machine 2 and the inlet guide vane 11 at the present time are compared with the operating table in the storage section 26 (step T2), and it is determined from the comparison result whether or not the operating efficiency is optimal (step T2). T3).

At this time, if it is determined that the operating efficiency is optimal, the control is terminated at that point and the operating state (vane angle and rotation speed) is maintained; however, if it is determined that the operating efficiency is not optimal, the inlet guide After the angle of the vane 11 and the rotational speed of the drive machine 2 are corrected based on the operation table, the obtained operation amount is output to the drive device 19A and the drive machine control device 25 (step T4).

[Problem that the invention seeks to solve]

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 combination of the angle of the inlet guide vanes 11 and the driver 2 In combination with the rotational speed of There is a problem in that it is not possible to perform high-level control (see FIG. 8).

Therefore, the angle of the entrance guide vanes 11 to 14,
Although it is conceivable to simultaneously control the angles of the diffuser vanes 15 to 18 and the rotation speed of the drive machine 2, in this case, the number of control elements becomes too large and it is difficult to actually realize the control.

The present invention aims to solve these problems, and by appropriately selecting and controlling the rotational speed of the drive machine and the angle control of the inlet guide vane and the diffuser vane, a wide flow range can be achieved. It is an object of the present invention to provide a control device for a centrifugal compressor that can control flow rate with extremely high operating efficiency over the entire range.

[Means for solving problems]

Therefore, the centrifugal compressor control device of the present invention
Compressor detection means for detecting a compressor rotation speed; operating state detection means for detecting operating conditions such as flow rate and efficiency in the centrifugal compressor; and compressor control means for controlling the rotation speed of the centrifugal compressor; vane angle control means for controlling the angles of the inlet guide vane and the diffuser vane, respectively;
In order to set the flow rate and efficiency of the centrifugal compressor to the target flow rate and optimum efficiency point, respectively, in the flow rate control, the rotation speed control means and the vane angle are adjusted based on the detection signals from the rotation speed detection means and the operating state detection means. A selection control means for appropriately selecting the control means is provided.

[Effect]

In the centrifugal compressor control device of the present invention described above, the selection control means appropriately selects the rotation speed control means and the vane angle control means based on the detection signals from the rotation speed detection means and the operating state detection means to set the control mode. By switching, in flow rate control, the flow rate in the centrifugal compressor is controlled to be the target flow rate while optimizing efficiency.

[Embodiments of the invention]

Hereinafter, a control device for a centrifugal compressor as an embodiment of the present invention will be explained with reference to the drawings. FIG. 1 is a block diagram thereof, and in this FIG.
The same reference numerals as in FIGS. 9 and 11 indicate substantially the same parts, so the explanation thereof will be omitted. However, in the multistage centrifugal compressor to which the control device of the present embodiment shown in FIG. 1 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 it is different from the multistage centrifugal compressor shown in FIG. 9, the present device can also be applied to the multistage centrifugal compressor shown in FIG.

As shown in FIG. 1, in this embodiment, inlet guide vanes (GV) 11 to 14 are driven by inlet guide vane drive devices 19a to 19d, respectively, and diffuser vanes (DV) 15 to
18 are respective differential user vane drive devices 19
e to 19h.
In addition to the flow rate sensor 20, temperature sensor 21, and pressure sensor 22 as operating state detection means, the sensors include a rotation speed sensor 24 as rotation speed detection means for detecting the compressor rotation speed, and a humidity sensor 27. is 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 unit 29 as rotation speed control means 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 vane angle control calculation unit 30 as a vane angle control means for calculating and outputting control signals to each of the drive devices 19a to 19h to control the angles of the vanes 4 and the differential user vanes 15 to 18, respectively; and a two-stage control means , a central control calculation unit 31 as a selection control means having the functions of a control mode switching means for reducing the flow rate and a control mode switching means for increasing the flow rate;
It is comprised of 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, 24, and 27, calculates the operating state of the multistage centrifugal compressor from these detection signals, and sends these detection signals and operating state signals to a rotation speed control calculation unit 29 and a vane angle control calculation unit 30.
It also 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, the control command input section 3 is input to the central control calculation section 31.
If a flow rate change request is input from 2, the two-step control function of the central control calculation unit 31 causes the rotation speed control calculation to be performed when the compressor rotation speed from the rotation speed sensor 24 is larger than the set value. After the rotation speed control (primary control) of the drive machine 2 is performed by the section 29, the vane angle control calculation section 30 controls the inlet guide vanes 11 to 14 and the differential user vane 15.
-18 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. According to
While maintaining this compressor rotation speed, the vane angle control calculation unit 3 changes from the control mode to the two-step control function.
The angle control mode of the inlet guide vanes 11 to 14 and the diffuser vanes 15 to 18 can be switched by 0. Here, the set value of the compressor rotation speed is given as the minimum rotation speed at which high efficiency can be obtained through rotation speed control without causing surging.

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. When the flow rate increased by the 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. , rotational speed control (primary control) and vane angle control (secondary control). Here, the upper limit value of the flow rate is given as the maximum flow rate obtained in 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 can approach the target flow rate based on the operating state signal from the central control calculation section 31, and a control amount calculation section 29a that calculates an optimal rotational speed control amount that can approach the target flow rate. A manipulated variable calculation unit 2 that calculates the manipulated variable of the drive machine 2 to actually control the compressor rotation speed based on the rotation speed control amount.
9b. Similarly, the vane angle control calculation section 30 includes a control amount calculation section 30a that calculates an optimal vane angle control amount that can approach the target flow rate while maintaining the optimum efficiency state based on the operating state signal from the central control calculation section 31; The drive devices 19a to 19h actually control each vane angle based on the vane angle control amount from the control amount calculating section 30a.
and a manipulated variable calculating section 30b that calculates each manipulated variable.

Next, the operation of the centrifugal compressor control device according to this embodiment will be explained using FIGS. 2 to 8.

First, when changing and controlling the flow rate in the centrifugal compressor 1 of this embodiment, 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 used as a control signal for central control calculation. The information is input to the section 31. If the input target flow rate Q _P is smaller than the current flow rate Q, the central control calculation unit 31 determines that a flow rate reduction request signal has been input, and operates the two-step control function or the flow rate reduction control mode switching function. On the other hand, if the input target flow rate Q _P 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. It is determined whether the compressor rotation speed detected by the sensor 24 is larger than a preset minimum rotation speed (step A2).

When the compressor rotation speed is higher than the minimum rotation speed, the rotation speed of the drive machine 2 is controlled to decrease by the rotation speed control calculation section 29 based on the operating state signal from the central control calculation section 31 ( Step A3), the central control calculation unit 31 determines whether the difference between the flow rate Q changed by this rotation speed control and the target flow rate Q _P is smaller than the flow rate tolerance ΔQ _RPM 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.
If the flow rate is smaller than the allowable flow rate ΔQ _RPM , the rotational speed of the drive machine 2 at that point, that is, the compressor rotational speed is fixed (Step A5: end of primary control by the two-step control function). Then, the control mode is switched from rotation speed control to angle control of the inlet guide vanes 11 to 14 and differential user vanes 15 to 18 (secondary control using a two-step control function), and this vane angle control is finer than rotation speed control. Adjust the flow rate and search for the optimum efficiency operating point (Step A6).

After this, it is determined whether the difference between the flow rate Q changed by the vane angle control and the target flow rate Q _P is smaller than the allowable flow rate ΔQ _V under the vane angle control, and whether the operating state has reached the optimum efficiency. The central control calculation unit 31 determines whether the
A7).

If these conditions are not met, the process returns to the vane angle control in step A6, while
When the above conditions are met, it is determined that the target flow rate Q _P has been reached, and the control mode in the central control calculation unit 31 is controlled to maintain the flow rate Q in the centrifugal compressor 1 at a constant target flow rate Q _P The state is switched to the control mode (described later with reference to FIG. 3) (step A8).

By the way, if it is determined in step A2 that the compressor rotational speed is the preset minimum rotational speed (including the case where the rotational speed becomes the minimum rotational speed state by performing the rotational speed reduction control in step A3), The control mode switching function at the time of flow reduction switches to a control mode in which the flow rate is controlled by base angle control in step A6 while maintaining the compressor rotation speed at the minimum rotation speed without performing rotation speed control. Thereafter, steps A7 and A8 are executed in the same manner as described above.

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

When the compressor rotation speed is higher than the minimum rotation speed, the two-step control function causes the rotation speed control calculation section 29 to control the driving machine 2 based on the operating state signal from the central control calculation section 31. (step B3), and determine whether the difference between the flow rate Q changed by this rotation speed control and the target flow rate Q _P is smaller than the allowable flow rate ΔQ _RPM in the rotation speed control. Judgment is made in the control calculation unit 31 (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 driver 2 at that point, that is, the compressor rotation. The number is fixed (Step B5: end of primary control by two-step control function). Then, the control mode is switched from rotation speed control to angle control of the inlet guide vanes 11 to 14 and the differential user vanes 15 to 18,
Steps B6 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 the 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 maintains 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 the diffuser vanes 15 to 18, and the flow rate is increased at the optimum efficiency operating point by controlling the vane angles (step
B9).

After this, it is determined whether the difference between the flow rate Q changed by the vane angle control and the target flow rate Q _P is smaller than the allowable flow rate ΔQ _V under the vane angle control, and whether the operating state has reached the optimal efficiency. The central control calculation unit 31 determines whether the
B10). If these conditions are not met,
It is determined whether the flow rate Q at that point has reached a predetermined upper limit value (step B11). If the flow rate Q is not at the predetermined upper limit, the step is repeated.
While returning to the vane angle control using B9, if 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.

Furthermore, if the conditions in step B10 are met, it is determined that the target flow rate Q _P has been reached, and
The control mode in the central control calculation unit 31 is switched to a control mode (described later with reference to FIG. 3) in which the flow rate Q in the centrifugal compressor 1 is maintained at a constant target flow rate _QP and an optimum efficiency operating state (step B8). ).

After the flow rate Q in the centrifugal compressor 1 reaches the target flow rate _QP as described above, the control mode in the central control calculation unit 31 becomes the constant flow rate control mode (steps A8 and B8). The control flow using this constant flow rate control mode is explained in the third section.
This will be explained using figures.

As shown in FIG. 3, when a constant flow rate control request is received in steps A8 and B8 or by a control signal from the control command input unit 32 to set the constant flow rate control mode (step C11, the central control calculation unit 31 constantly monitors the detection signal from the flow rate sensor 20, 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 (=Q _P -Q) is determined, and it is determined whether the magnitude of the flow rate variation ΔQ is smaller than the flow rate allowable value ΔQ _V in vane angle control (step C2). If the magnitude of this flow rate variation ΔQ is smaller than the flow rate allowable value ΔQ _V , the state returns to the flow rate fluctuation monitoring state again, while if it is less than the flow rate allowable value ΔQ _V , the inlet guide vanes 11 to 14 and the diffuser vanes 15 to 18 angle control (step
C3), correct the flow fluctuation ΔQ to maintain the flow rate Q at a constant target flow rate Q _P and the optimal efficient operating state.

At this time, the central control calculation unit 31 constantly integrates and stores the flow rate fluctuation amount ΔQ corrected by vane angle control, and the magnitude of the integrated value ΣΔQ is larger than the flow rate allowable value ΔQ _RPM by rotation speed control. It is determined whether or not is also small (step C4). This integrated value ΣΔQ
If the magnitude of is smaller than the allowable flow rate value ΔQ _RPM , the state returns to the flow rate fluctuation monitoring state in step C2 again, while if it is greater than the allowable flow rate value ΔQ _RPM , the current compressor rotation speed detected by the rotation speed sensor 24 It is determined whether or not the rotation speed is larger than a preset minimum rotation speed (step C5).

If the compressor rotational speed is larger than the minimum rotational speed, the rotational speed of the drive unit 2 is controlled by the rotational speed control calculation unit 29, and the compressor rotational speed is increased by one step corresponding to the flow rate allowable value ΔQ _RPM . Control. At the same time, the angles of the inlet guide vanes 11 to 14 and the diffuser vanes 15 to 18 are controlled to bring the flow rate Q to the target flow rate _QP and the optimum efficiency 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, then , 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 to be greater than the minimum rotation speed, so the rotation speed in step C6 Perform numerical control.
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 at an optimally efficient operating state even if it fluctuates due to environmental changes.However, constant flow rate maintenance control based on the flow shown in Fig. It is effective when using gas turbines or steam turbines that cannot control the rotation speed, and interpolates the flow rate value obtained stepwise by stepwise rotation speed control using finer vane angle control and controls the operating state to the optimum efficiency. considered to be a thing.

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 of this embodiment. The detailed parts used in the realization, especially the method for determining the control amount of the vane angle (steps A6, B6, B9,
C3) will be explained using FIGS. 4 to 7.

In this embodiment, a multi-stage centrifugal compressor equipped with four stages of centrifugal compressors 4 to 7 is controlled. When controlling the vane angle, inlet guide vanes 11 to 14 and diffuser vanes 15 to 15 in each stage are controlled. 18 separately and independently, the control operation would be extremely complicated and complicated, and the convergence would also be unstable. Therefore, the angles of the inlet guide vanes 11 to 14 and the diffuser vanes 15 to 18 are made dimensionless, and a set of dimensionless inlets is created. The control operation is simplified by representing the guide vane angle α and the dimensionless diffuser vane β.

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. 5a and 5b. Generally, as a characteristic of a centrifugal compressor, there is a flow rate-discharge pressure (Q-P) curve as shown in FIG. 5a. If the centrifugal compressor is single, there is naturally only one characteristic curve, so there is no need to make the angles of the inlet guide vane and the diffuser vane dimensionless, but in the case of a multi-stage centrifugal compressor, there is only one characteristic curve. As shown in Figure b, the characteristic curves are different for each stage of centrifugal compressor.

Therefore, when the pressure (discharge pressure P) is almost constant due to the resistance on the device side, each inlet guide vane 11 to 1
4 is one dimensionless inlet guide vane angle such that the operating flow rates Q1 to Q4 of centrifugal compressors 4 to 7 in each stage have similar operating flow rates at the same ratio to the design flow rate Q _D (=Q1). In addition to expressing it as α, each differential user vane 15 to 18 also has a design flow rate Q _D (=Q
1) is expressed as one dimensionless diff user vane angle α that provides a similar operating flow rate with the same ratio.

That is, in FIG. 5b, if the angles of the diffuser vanes 15 to 18 are constant at the design value, the pressure ratio distribution at each stage is unchanged, and the design discharge pressure P _D at a certain stage is constant, each inlet guide vane 11 Flow rates Q1 to Q4 are determined for angles of ~14. The ratio Q2/ _Q1 (Q3/
The angles (GV 1 to GV 4 ) of the inlet guide vanes 11 to 14 of each stage such that Q1, _Q4 / _Q1 ) are the same
is expressed as a dimensionless inlet guide vane angle α as shown in the following equation (1).

α=K _o α・(α _o /α _op −1) …(1) Here, α _o is the angle of the n-th stage inlet guide vane,
α _op is the reference angle of the nth stage inlet guide vane, K _o α
is the coefficient of the n-th stage inlet guide vane angle determined so that the n-th stage operating flow rate is similar to the design flow rate Q _D for each stage.

Also, in exactly the same way as this dimensionless entrance guide vane angle α, the differential user vanes 15 to 15 of each stage are
The angle of 18 is also expressed as a dimensionless diff user vane angle β as shown in the following equation (2).

β=K _o β・(β _o /β _op −1) …(2) Here, β _o is the angle of the n-th stage differential user vane, β _op is the reference angle of the n-th stage differential user vane,
K _o β is a coefficient of the diff user vane angle of the nth stage determined so that the operating flow rate of the nth stage is similar to the design flow rate Q _D of each stage.

Then, in the control amount calculation unit 30a of the vane control calculation unit 30, the inlet guide vanes 11 to
14 and the differential user vanes 15 to 18 are represented as a set of dimensionless entrance guide vane angle α and dimensionless differential user vane β, respectively, which are defined as described above. Following the flow shown below, the dimensionless vane angle plane αβ is determined by these dimensionless vane angles α and β.
The vane angle control amount is determined above (the method for determining the vane angle control amount described here is called an extrapolation method).

As mentioned above, when the vane angle control mode is entered in steps A6, B6, B9, and 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, Fig. 6a
As shown in the figure, three points A, B, and C that include the same point in the vicinity of the current vane position A are selected (step D1). Then, for the selected three points A, B, and C, the operation amount calculating section 30b and the driving device 19a
By ~19h, the entrance guide vane 11~
14 and the diffuser vanes 15 to 18, and the flow rate Q and efficiency η at each point A, B, and C are
(Step D2). Here, the flow rate Q is
Detected by the flow rate sensor 20 and sent to the central control calculation unit 3
1 to the control amount calculation unit 30a, while the efficiency η is calculated in the central control calculation unit 31 based on the detection signals from the sensors 20 to 22 and then input to the control amount calculation unit 30a. .

In step D3, a plurality of first extrapolation points (nine in this example) are expanded and set on the non-dimensional vane angle plane αβ so as to surround the first actual measurement points A to C. do. Then, the flow rate and efficiency at each extrapolation point ~ are calculated from the actual measurement point A ~
The prediction is made from the actual flow rate and actual efficiency at C (step D4).

In other words, as mentioned above, the flow rate Q and the efficiency η
has a characteristic curved surface (Q ₀ > Q ₁ > Q ₂ > Q ₃ > for flow rate, η ₀ > η ₁ > η ₂ > η ₃ for efficiency) as shown in Figure 7 for each rotational speed. , three actual measurement points A
From the actual flow rate and actual efficiency at points C to C, a flow rate characteristic curved surface and an efficiency characteristic curved surface corresponding to the characteristic curved surface shown in FIG. 7, respectively, are estimated by plane approximation or curved surface approximation. Then, based on this estimated characteristic curved surface, the flow rate and efficiency at each extrapolation point 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 ₀ ,
Q ₁ , Q ₂ , Q ₃ have constant flow lines, and η ₀ , η ₁ , η ₂ , η ₃ have constant efficiency lines). In particular, in the figure, there is a relationship between Q ₀ > Q ₁ > Q ₂ > Q ₃ regarding the flow rate, and there is a relationship between the vane angle and the increase/decrease in flow rate such that the flow rate will necessarily increase if the vane angles α and β are large. , this relationship is set and stored in the control amount calculation unit 30 in advance, and the reliability of the flow rate value actually measured in step D2 is verified in steps D5 and D6.

That is, the first actual measurement points A to C shown in FIG. 6a
Regarding actual measurement points A and B, it is clear from the above relationship that the flow rate at point B is always larger than the flow rate at point A. , actual measurement point A
and B are compared with a pre-stored flow rate increase/decrease relationship (step D5), and if the increase/decrease relationship is reversed, it is determined that the comparison result causes a logical pre-emption (step D6). , it is determined that the measurement error by the flow rate sensor 20 is large, the data acquisition based on this actual measured flow rate is canceled, and the process returns to step D2 to obtain the actual measured flow rate again. Also,
If it is determined that the above comparison result does not cause a logical safeguard (step D6), the process moves to the next step D7. In this way, by verifying the reliability of the actual measured flow rate, vane angle control can be performed without losing sight of the target flow rate due to fluctuations in the flow rate measured during control execution or measurement errors. It becomes like this.

If it is determined in step D6 that the above comparison result does not cause a logical pre-emption, then in step D7, the predicted flow rate is determined from the first extrapolation points ~ to the target flow rate.
Select an extrapolation point that is close to Q _P and has a high predicted efficiency.

Next, in step D8, it is determined whether the extrapolation point selected in step D7 falls within the surging region. The surging area is the seventh
As shown in the figure, the surging prevention line is placed on the dimensionless vane angle plane αβ at each compressor rotation speed.
It can be specified by SL (shaded side of surging prevention line SL). Therefore, in the control amount calculating section 30a, the surging prevention line SL that defines the surging area is set and stored in advance as a function of the dimensionless vane angles α and β for each compressor rotational speed, and the surging prevention line SL is set and stored in advance in step D7. Each time an extrapolation point is selected, it is checked whether the extrapolation point crosses the surging prevention line SL and enters the surging region.

If the selected extrapolation point is within the surging region, select from among the extrapolation points other than the currently selected extrapolation point that the predicted flow rate is close to the target flow rate Q _P and the predicted efficiency is After selecting the higher value (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 rate Q _P 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 highly efficient 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 the extrapolation point in Fig. 6a has been selected], the coordinates of this extrapolation point are A certain set of dimensionless inlet guide vane angle α and dimensionless differential user vane angle β is defined as the actual inlet guide vanes 11 to 14 and differential user vane 15 at each stage.
Convert to an angle of ~18 (step D10).

In other words, from the above-mentioned equations (1) and (2), the vane angles α _o and β _o (in this example, n = 1 to 4) to be actually operated are determined.
We seek.

In step D10, which calculates the actual vane angles α _{o and} β _o from the dimensionless vane angles α and β, if a disturbance causing variation in the operating point is detected in any of the centrifugal compressors 4 to 7, the following procedure is performed. hand,
The deviation of the operating flow rate from the similar operating flow rate in the centrifugal compressor of the stage in which the disturbance occurred can be corrected.

Operating characteristics of each stage (head H, suction flow rate of the next stage)
Q ₂₀ ) is generally expressed as the following equation.

H=x・R・T ₁・{(P ₂ /P ₁ ) ^k-1/k −1}/(x-1)
...(3) Q ₂₀ ∝1/P ₂ ...(4) Here, x is the specific heat ratio, R is the gas constant, T ₁ is the suction temperature, P ₁ is the suction pressure, and P ₂ is the discharge pressure.

The angles of the inlet guide vanes 11 to 14 and the diffuser vanes 15 to 18 of each stage are set from the dimensionless vane angles α and β to (1), ( Even if it is determined by equation 2) 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) H of the centrifugal compressor that caused the disturbance will change. Therefore, from equation (3), the discharge pressure
_P2 becomes larger. As a result, according to equation (4), the suction flow rate Q ₂₀ of the next stage decreases, and the similar operation flow rate changes.

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

Therefore, as shown in equations (5) and (6), based on the detected disturbance, the dimensionless correction amount [K _o α・A ₁・(a _o t/α _o0 ), etc.] and add each dimensionless correction amount to the dimensionless entrance guide vane α and the dimensionless differential user vane β (5),
From equation (6), the angles of the inlet guide vane and diffuser vane at the stage where the disturbance occurred are determined.

α=K _o α・{α _o /α _o0 +A ₁・(α _o t/α _o0 ) +A ₂・(α _oRH /α _o0 )+…−1}…(5) β=K _o β・{β _o /β _o0 +B ₁・(β _o t/β ₀ ) +B ₂・(β _oRH /β _o0 )+…−1}…(6) Here, α _o t is the disturbance correction due to the suction temperature of the nth stage amount, α _oRH is the disturbance correction amount due to the nth stage humidity, β _o
t is the amount of disturbance correction due to the suction temperature of the nth stage, β _oRH is the amount of disturbance correction due to the humidity of the nth stage, A ₁ , A ₂ , B ₁ ,
B ₂ is a coefficient.

In this way, even when searching for a highly efficient extrapolation point that is close to the target flow rate Q _P , 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 that has caused a disturbance, then equations (5) and (6) are used, and for a stage that has not caused a disturbance, equations (1) and (2) are used to create a set of non-disturbances. The actual entrance guide vanes 11 to 1 are calculated from the dimensional entrance guide vane angle α and the dimensionless differential user vane angle β.
4 and the angles of the differential user vanes 15 to 18 are determined, and the operation amount calculation section 30b of the vane angle control calculation section 30 determines the driving device 19a according to the obtained angle.
-19h to output a control signal to the inlet guide vanes 11-14 and the differential user vanes 15-1.
8 (step D11).

After this, it is determined whether the difference between the flow rate Q changed by the above vane drive control and the target flow rate Q is smaller than the flow rate allowable value ΔQ _V in the vane angle control (step D12), and the flow rate difference is determined. If the flow rate difference is smaller than the flow rate tolerance ΔQ _V , vane angle control is ended at that point, while if the above flow rate difference is greater than the flow rate tolerance ΔQ _V , the process returns to step D3 and three new basic points are selected. Then, steps D3 to D12 are executed in the same manner as described above for these second base points and second extrapolation points expanded to surround the second base points.

Here, the basic point selected for the second time is the 6th
As shown in Figure a, one of the first measurement points
Point A, the extrapolation point selected at the first time and where the flow rate and efficiency were actually measured by operating the inlet guide vanes 11 to 14 and the diffuser vanes 15 to 18 in step D12, and the first extrapolation point. Three points are selected from the remaining extrapolation points, and around these base points, the second extrapolation points,...
The flow rates and efficiencies at the nine points corresponding to the actual measurement points B and C and the new extrapolation points P ₁ to _{P 4} are predicted based on the values of the actual measurement points A and the extrapolation points.

In this way, until the conditions in step D12 are met, the operating points are selected and the inlet guide vanes 11-14 and the diffuser vanes 15-1
8 to actually measure the flow rate and efficiency, and then expand the extrapolation points to find an extrapolation point that is close to the target flow rate _QP and has high efficiency, and then controls the vane angle.

In the above implementation sequence, the expansion of extrapolation points around the basic point is limited to nine linear extrapolation points, as shown in Figure 6a, but as shown in Figure 6b, Fifteen additional secondary extrapolation points may be selected around the nine primary extrapolation points to predict flow rate and efficiency for these extrapolation points as well. However, although the number of actual measurement points is three in this example, it is not limited to this, and is four.
There may be more than one. Further, the method of developing the extrapolation points is not limited to that shown in FIGS. 6a and 6b, and the range of the extrapolation points may be changed arbitrarily.

As described above, according to the apparatus of this embodiment, for example, as the simplest example, the compressor rotation speed RPM1
Then, (α, β) = (α ₁ ,
When reducing the flow rate from the operating state where the flow rate is Q ₀ at point a of β ₁ ) to the target flow rate Q ₂ ,
According to the flow, first, the compressor rotation speed is decreased to the minimum rotation speed RPM2 preset by the rotation speed control mode (primary control in the two-step control function), and the flow rate is adjusted to αβ as shown in Fig. 7. After setting (α ₁ , α ₁ ) on the plane, the vane angle control mode (following the flow in Figure 4) moves from point a to point b (a, β ₂ ) which is close to the target flow rate Q ₂ and has high efficiency η ₁ . ) is searched for and the flow rate is reduced.

Further, FIG. 8 shows that the control mode selection performed by the device of the present invention, that is, the rotation speed control is
A method of appropriately selecting a control mode using a two-stage control function included as the next control and a vane angle control mode based on the upper limit value of the set rotation speed or flow rate was compared with other conventional methods. The effect on efficiency and flow range is explained.
FIG. 8 is a graph showing flow rate-efficiency characteristics under each control method assuming a constant discharge pressure. As shown in FIG. 8, only rotational speed control provides good efficiency, but the flow rate range is small. If only the angle of the inlet guide vane is controlled, as shown by curve _L1 , the flow rate range increases compared to the case where only rotational speed control is used, but the efficiency decreases on the small flow rate side. If only the angle of the diffuser vane is controlled, the flow rate range is wide, but the efficiency is significantly reduced, as shown by curve _L2 .

Furthermore, in cases where the angle control of the inlet guide vane and the differential user vane is combined, or where the rotation speed control and the angle control of the inlet guide vane are combined, as shown by curves L ₃ and L ₄ respectively,
Both have a wide flow rate range, but they still suffer from a drop in efficiency on the small flow rate side.

However, according to the device of the present invention, as shown by curve _L5 , it is possible to obtain extremely high efficiency even on the small flow rate side while maintaining a wide flow rate range.

As described above, according to the device of this embodiment, the control by the two-stage flow rate control function including the rotation speed control of the drive machine 2 as the primary control, and the control by the inlet guide vane 11 to
14 and the angle control of the diffuser vanes 15 to 18 as appropriate, it becomes possible to control the flow rate in extremely high operating conditions over a wide flow rate range as described above.

That is, according to the device of this embodiment, when controlling the flow rate, when the rotation speed is larger than the set value, the flow rate control (primary control) is performed efficiently in large steps by controlling the rotation speed, and the flow rate is controlled. After approaching the target flow rate, vane angle control (secondary control) can search for the target flow rate and high efficiency point, 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 and the differential user vanes 15 to 18
When controlling the angle of the vane, the appropriate operating point is directly searched and determined by the extrapolation method shown in Fig. 4, so there is no need to program combinations of vane angles, etc. in advance, unlike conventional means. Another advantage is that it can always perform highly efficient control with a minimum number of operations while responding quickly to environmental changes and changes over time.

Furthermore, in this example, for the multi-stage centrifugal compressor, by using the dimensionless inlet guide vane angle α and the dimensionless differential user vane angle β,
Inlet guide vane 11 as a control element among many
14 and the angles of the differential 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. .

Although the above embodiment describes the case where the device of the present invention is applied to a multi-stage centrifugal compressor, the device of the present invention can also be applied to a single centrifugal compressor, and in this case, the above-mentioned The same effect as the above embodiment can be obtained without using the dimensional vane angle.

〔Effect of the invention〕

As described above, according to the present invention, the selection control means appropriately selects the rotation speed control means and the vane angle control means based on the detection signals from the rotation speed detection means and the operating state detection means to switch the control mode. With this configuration, flow rate control can be performed with extremely high operating efficiency over a wide flow rate range.

[Brief explanation of drawings]

Figures 1 to 8 show a control device for a centrifugal compressor as an embodiment of the present invention. Figure 1 is a block diagram thereof, and Figure 2a is for explaining the control procedure when a flow rate reduction request is made. 2b is a flowchart for explaining the control procedure when the flow rate is increased. FIG. 3 is a flowchart for explaining the control procedure in the constant flow rate control mode. A flowchart for explaining in detail the angle control procedure of the entrance guide vane and the diffuser vane, FIGS. Graphs showing the flow rate-discharge pressure characteristics, Figures 6a and 6b are both dimensionless vane angle planes for explaining the extrapolation method in the angle control procedure of the inlet guide vane and diffuser vane, and Figure 7 is a graph showing the non-dimensional vane angle plane. A graph showing a flow rate characteristic curve, an efficiency characteristic curve, and a surging area on a dimensional vane angle plane, FIG. 8 is a graph showing a flow rate-efficiency characteristic for explaining the effect of the device of the present invention, and FIG. 9 is a graph showing a general FIG. 10 is a flowchart for explaining the control means of a conventional centrifugal compressor, and FIG. 11 is a flowchart for explaining the control means of another conventional centrifugal compressor. It is a flowchart. In the figure, 1... centrifugal compressor, 11-14... inlet guide vane, 15-18... diffuser vane, 20... flow rate sensor as operating state detection means, 21... temperature sensor as operating state detection means, 22... Pressure sensor as operating state detection means, 24... Rotation speed sensor as rotation speed detection means, 29... Rotation speed control calculation section as rotation speed control means, 30... Vane angle control calculation section as vane angle control means, 31 ...a central control calculation section serving as a selection control means having the functions of a two-stage control means, a control mode switching means for reducing the flow rate, and a control mode switching means for increasing the flow rate;

Claims (1)

[Scope of Claims] 1. A centrifugal compressor having angle-variable inlet guide vanes and diffuser vanes on the inlet side and the outlet side, respectively, comprising: rotational speed detection means for detecting the compressor rotational speed; an operating state detection means for detecting operating states such as flow rate and efficiency in the centrifugal compressor; and a vane angle control means for controlling the centrifugal compressor, and in order to control the flow rate and efficiency of the centrifugal compressor to a target flow rate and an optimum efficiency point, respectively, based on detection signals from the rotation speed detection means and the operating state detection means. A control device for a centrifugal compressor, characterized in that a selection control means is provided for appropriately selecting the rotation speed control means and the vane angle control means. 2. Two-stage control means, wherein the selection control means performs primary control by the rotation speed control means and then secondary control by the vane angle control means;
When the compressor rotational speed detected by the rotational speed detection means reaches a set value during the flow rate reduction control by the primary control of the two-stage control means, the compressor rotational speed is maintained and the two-stage control means control mode switching means for switching from a control mode to a control mode using the vane angle control means; and a flow rate increase control mode switching means for switching the control mode to the control mode using the angle control means and switching to the control mode using the two-step control means when the flow rate detected by the operating state detection means reaches a predetermined upper limit value. A control device for a centrifugal compressor according to claim 1.