JP4963507B2 - Capacity control method of multistage centrifugal compressor - Google Patents

Description

  The present invention relates to a capacity control method for a multistage centrifugal compressor having an inlet guide vane provided in each stage suction section of the multistage centrifugal compressor, and more specifically, avoids surging by simple control of the inlet guide vane. The present invention relates to a capacity control method for a multistage centrifugal compressor capable of extending the operating range.

  In various plants such as chemical plants, multistage centrifugal compressors are used for producing large amounts of high-pressure gas such as raw material air compression, factory air sources or various high-pressure gas sources. In a multi-stage centrifugal compressor equipped with a suction pipe that sucks gas on the suction side of the compressor body, an inlet guide is provided at the inlet of the suction pipe as a capacity control means that changes the flow rate and pressure without changing the rotation speed of the impeller. A vane is provided.

  However, a centrifugal compressor usually has a surging phenomenon, and therefore the capacity adjustment range is limited. Therefore, it is desired to have a wider capacity adjustment range. On the other hand, it is necessary to devise so that the efficiency at the partial load is improved as much as possible. First, the capacity control method of the centrifugal compressor according to the related art 1 for the former demand will be described below.

  In the capacity control method of the centrifugal compressor according to the related art 1, on the vane angle plane determined by the angles of the inlet guide vane and the diffuser vane, a surging line that defines the surging area is set and stored in advance. When the current angles of the inlet guide vane and the diffuser vane are measured and these current angles are within the surging area defined by the surging line, the normal direction vector of the surging line is A value obtained by adjusting the amount of operation of the inlet guide vane and diffuser vane angle necessary for exiting from the surging region and going out of the surging region is obtained as a surging elimination vane angle operation amount vector.

  On the other hand, if the measured current angle is in the vicinity of the surging line outside the surging area, and the vane angle manipulated variable vector determined to go to the target flow rate goes into the surging area, the surging line Based on the vane angle manipulated variable vector, the normal direction component of the surging line is removed to obtain a surging avoiding vane angle manipulated variable vector in the direction along the surging line, and the surging elimination vane angle manipulated variable vector is obtained. Alternatively, the flow rate of the centrifugal compressor is controlled based on the angles of the inlet guide vane and the diffuser vane determined by the surging avoiding vane angle manipulated variable vector (see Patent Document 1).

  However, in order to perform the control as described above, a high-level arithmetic device and a large number of measuring instruments for measuring various measurement values as input values of the arithmetic device are required, which is very expensive. Further, since trial and error operations are included in the control, it takes time to shift to a stable state.

  Next, the capacity control method of the multistage centrifugal compressor according to the prior art 2 for the latter demand described above will be described below with reference to FIG. FIG. 9 is a cross-sectional view showing an example of the structure of a multistage compressor for a refrigerator according to Prior Art 2.

  The capacity control device in the multistage compressor for a refrigerator according to the prior art 2 is a multistage compressor for a refrigerator that can perform a wide capacity control while having high energy savings without attaching a hot gas bypass device whose efficiency is significantly reduced. The following functions are provided in order to provide a capacity control apparatus. That is, this multistage compressor for a refrigerator has a low-stage compression unit 20 and a high-stage compression unit 30 each having one or more impellers 22, 23, 32 at both ends of the electric motor 18. In addition, the rotating shafts of the impellers of the compression units 20 and 30 have a structure directly connected to the rotating shaft 19 of the electric motor 18.

  And the capacity control apparatus in the multistage compressor for refrigerators which concerns on the prior art 2 attaches the suction vanes 24 and 33 to the suction inlet 21a of the low stage compression unit 20, and the suction inlet 31a of the high stage compression unit 30, respectively. The opening and closing of the suction vanes 24 and 33 are controlled by control signals from the control panel 44 via the control motors 27 and 36. The temperature controller provided in the control panel 44 outputs an open / close signal to the control motor 27 on the lower stage side according to the detected temperature from the temperature detecting end. Further, the potentiometer in the low-stage control motor 27 outputs an opening degree signal to the balance adjustment mechanism provided in the control panel 44. The balance adjusting mechanism outputs an open / close signal to the high-stage control motor 36 so that the opening degree is the same as the low-stage side opening signal (see Patent Document 2).

  The capacity control device in the multistage compressor for a refrigerator according to the above-described prior art 2 controls the suction vanes 24 and 33 of the low pressure stage and the high pressure stage so as to have the same opening degree when adjusting the flow rate of the compressor. However, in this method, there is a problem that when the control for reducing the flow rate is performed, only one stage enters the surging region first, and the reduction amount of the flow rate becomes narrow.

Japanese Patent Publication No. 8-14279 JP 2000-291597 A

  Accordingly, an object of the present invention is to provide a surging by simply and effectively controlling the inlet guide vane in a capacity control method for a multi-stage centrifugal compressor having an inlet guide vane provided in each stage suction section of the multi-stage centrifugal compressor. It is an object of the present invention to provide a capacity control method for a multi-stage centrifugal compressor that can expand the operating range by expanding the throttle area of the capacity.

In order to achieve the above object, the means adopted by the capacity control method of the multistage centrifugal compressor according to claim 1 of the present invention is a multistage centrifugal system having inlet guide vanes provided in each stage suction section of the multistage centrifugal compressor. In the compressor capacity control method, the relative ratio of each stage of the inlet guide vane angle is controlled to be a constant ratio , and the ratio is set to become smaller toward the downstream downstream stage. It is characterized by doing.

According to the capacity control method of a multistage centrifugal compressor according to claim 1 of the present invention, the relative ratio of the angle of the inlet guide vane for each stage is controlled to be a constant ratio , and the ratio is set downstream. Since it is set to become smaller as it goes to the rear stage on the side , each stage can be operated with the same level of margin from the surging line, and only a specific stage can be prevented from approaching the surging line first. It is possible to increase the aperture area of the capacity. In addition, when setting the capacity control of the compressor, the adjustment can be performed effectively and reliably.

It is a typical structure figure showing typically the structure of the 4-stage centrifugal compressor concerning Embodiment 1 or 3 of the present invention. It is a performance curve figure which shows the change of a flow-pressure characteristic by using the angle of a guide vane as a parameter in the general multistage centrifugal compressor in the Example of this invention. It is a figure which shows an example of the flow volume-pressure characteristic of the compressed gas in the plant which the multistage centrifugal compressor shown in FIG. 2 supplies. FIG. 2 shows operating points of each stage when capacity control is performed in a multistage centrifugal compressor having the performance of FIG. 2 according to a comparative example of the present invention. FIG. b) shows the operating point of the second stage compressor, respectively. In the comparative example of the present invention, the operating point of each stage when capacity control is performed in the multistage centrifugal compressor having the performance of FIG. 2 is shown. FIG. (C) is the operating point of the third stage compressor, FIG. d) shows the operating point of the fourth stage compressor, respectively. FIG. 2 shows operating points of each stage when capacity control is performed in the multistage centrifugal compressor having the performance of FIG. 2 according to the embodiment of the present invention. FIG. b) shows the operating point of the second stage compressor, respectively. FIG. 2C shows operating points of each stage when capacity control is performed in the multistage centrifugal compressor having the performance of FIG. 2 according to the embodiment of the present invention. FIG. d) shows the operating point of the fourth stage compressor, respectively. It is a typical structure figure showing typically the structure of the 4-stage centrifugal compressor concerning Embodiment 2 of the present invention. It is sectional drawing which shows the structural example of the multistage compressor for refrigerators which concerns on the prior art 2. FIG.

  First, an example in which the capacity control method for a multistage centrifugal compressor according to Embodiment 1 of the present invention is applied to a four-stage centrifugal compressor with a built-in speed increaser will be described below with reference to FIG. FIG. 1 is a schematic structural diagram schematically showing the structure of a four-stage centrifugal compressor according to Embodiment 1 of the present invention.

  In the four-stage centrifugal compressor according to the first embodiment of the present invention, the input shaft 5 is driven by the electric motor 6 and the power is transmitted through the speed increaser 16, and the first-stage compressor 1 and the second-stage compressor. 2, the third stage compressor 3 and the fourth stage compressor 4 are increased in speed. Inlet ports of the first to fourth stage compressors 1 to 4 are respectively provided with inlet guide vanes 7 to 10 and guide vane operating devices 11 to 14 for operating them.

  The gas sucked through the inlet guide vane 7 provided in the suction portion of the first stage compressor 1 is compressed by the first stage compressor 1 and then discharged to a first stage discharge passage (not shown). Then, it is introduced into the second stage compressor 2 through the inlet guide vane 8 provided in the suction portion of the second stage compressor 2. Then, the gas sucked through the inlet guide vane 8 is further compressed by the second stage compressor 2 and then discharged into a second stage discharge passage (not shown), and the first stage vane 9 through the inlet guide vane 9. Introduced into the three-stage compressor 3.

  Further, in the third-stage compressor 3 and the fourth-stage compressor 4, the gas compressed to a high pressure by continuously repeating the same compression process is discharged from a fourth-stage compressor 4 (not shown). It is discharged to the flow path, and finally supplied to a customer (plant or the like) communicated with this fourth stage discharge flow path.

  On the other hand, the four-stage centrifugal compressor is provided with a controller 15, and the controller 15 is pre-calculated with a plurality of program patterns capable of calculating the angles of the inlet guide vanes 7 to 10 based on a command signal. And a control means capable of outputting a control signal to each of the guide vane operation devices 11 to 14 based on the calculation result of the calculation means.

  Then, when a command signal that “a gas of a certain amount of pressure and a flow rate of some amount” is input to the controller 15 from the plant side, the angle of the inlet guide vanes 7 to 10 is calculated by the calculation means based on this command signal. As long as the command signal is not changed, a program pattern in which the relative ratio of each stage is always a constant ratio is selected, and calculation is performed by this program. Next, the calculation result is input to the control means, and the control means outputs a control signal to each of the guide vane operation devices 11 to 14 for control.

  That is, in the capacity control method for the multistage centrifugal compressor according to the first embodiment of the present invention, the calculation means stored in the controller 15 calculates the angles of the inlet guide vanes 7 to 10, and Based on the calculation results, control signals are output from the control means to the guide vane operation devices 11 to 14, respectively, and the guide vane operation devices 11 to 14 are operated by the control signals.

  Then, the operation of the guide vane operation devices 11 to 14 controls the inlet guide vanes 7 to 10 to adjust the capacity of each stage of the compressor. As a result, each stage can be operated with the same level of margin from the surging line, and only a specific stage can be prevented from approaching the surging line first, and the capacity restriction area can be increased. Become.

  In the capacity control method for the multi-stage centrifugal compressor according to the first embodiment of the present invention, the case of the 4-stage centrifugal compressor has been described. However, the multi-stage centrifugal compressor having two or more stages may be used. In any case, the present invention is applicable. Moreover, although the example in which the guide vane and the guide vane manipulator are provided in all stages of the multistage centrifugal compressor has been described, the guide vane and the guide vane manipulator need not necessarily be provided in all stages.

  Next, in a general multi-stage centrifugal compressor having an inlet guide vane and having compressor characteristics as shown in FIGS. 2 and 3, a comparative example to which the above-described conventional technique 2 is applied and an embodiment to which the present invention is applied. Is described below. FIG. 2 relates to an embodiment of the present invention, and FIG. 3 is a performance curve diagram showing changes in flow rate-pressure characteristics using a guide vane angle as a parameter in a general multistage centrifugal compressor, and FIG. 3 is a diagram of the multistage centrifugal compressor shown in FIG. It is a figure which shows an example of the flow volume-pressure characteristic of the compressed gas in the plant to supply.

As shown in FIG. 2, the performance of this multistage centrifugal compressor decreases both the discharge flow rate and the discharge pressure as the guide vane angle increases from -30 degrees to 60 degrees. Further, if the discharge flow rate is reduced at each guide vane angle, the surging line shown by the alternate long and short dash line in the figure is reached and a surging phenomenon occurs. In general, when the flow rate of the compressed gas used in the plant decreases, the required compressor discharge pressure tends to slightly decrease as shown in FIG. Further, there are cases where operation is performed under partial load operation conditions Q ₁ and Q ₂ with respect to the discharge flow rate Q _d of the rated operation condition.

<Comparative example>
First, a comparative example in which the prior art 2 is applied to the multistage centrifugal compressor will be described with reference to FIGS. 4 and 5 relate to a comparative example of the present invention, and show operating points of each stage when capacity control is performed in the multistage centrifugal compressor having the performance of FIG. 2, and FIG. 4 (a) is the first stage compressor. 4 (b) shows the operating point of the second stage compressor, FIG. 5 (c) shows the operating point of the third stage compressor, and FIG. 5 (d) shows the operating point of the fourth stage compressor. Show.

  That is, FIGS. 4 and 5 show a case where the guide vane angle is controlled to be 30 degrees in all stages in the multistage centrifugal compressor having the above characteristics. As shown in FIG. 4A, the operating point of the first stage compressor is located in the vicinity of the surge line indicated by the alternate long and short dash line, and the flow rate margin sm1 to the surge line is very small. That is, surging occurs at a discharge flow rate smaller than the flow rate Q1, and operation is impossible.

  On the other hand, in the second to fourth stage compressors, each of the flow margins sm2 to sm4 up to the surge line is larger than the flow margin sm1 of the first stage compressor, and is still likely to operate with a smaller flow rate. I understand that there is. That is, the flow rate margin to the surge line tends to increase as the latter stage is reached, and the flow rate margin sm4 of the fourth stage compressor still has sufficient margin even at the discharge flow rate at which the first stage compressor reaches the surge line. It is shown that.

<Example>
Next, an embodiment to which the present invention is applied will be described with reference to FIGS. FIGS. 6 and 7 relate to the embodiment of the present invention, and show operating points of each stage when capacity control is performed in the multistage centrifugal compressor having the performance of FIG. 2, and FIG. 6A shows the first stage compressor. FIG. 6B shows the operating point of the second stage compressor, FIG. 7C shows the operating point of the third stage compressor, and FIG. 7D shows the operating point of the fourth stage compressor. Show.

That is, in the embodiment to which the present invention is applied, in the multistage centrifugal compressor having the above characteristics, the setting angle of the inlet guide vanes 7 to 10 is set so that the relative ratio of each stage is always a constant ratio. Control is performed to the values indicated by the equations (1) to (4).
f (1st) = a × f (base) (1)
f (2nd) = b × f (base) (2)
f (3rd) = c × f (base) (3)
f (4th) = d × f (base) (4)

here,
f (base): guide vane reference setting angle
f (1st): First stage compressor guide vane setting angle
f (2nd): Second stage compressor guide vane setting angle
f (3rd): Third stage compressor guide vane setting angle
f (4th): 4th stage compressor guide vane setting angle
a, b, c, d: proportionality constant

  A command signal from the plant is input to the controller 15, and the above f (base) is calculated by the arithmetic means housed in the controller 15 based on this command signal, and then the above equations (1) to (4) Then, the angle of the guide vane at each stage of the compressor is calculated, and a control signal is output to the guide vane operating units 11 to 14 at each stage by the control means housed in the controller 15.

In the case of the operating point Q ₁ in FIGS. 6 and 7, assuming that a = 1.15, b = 1.05, c = 0.95, and d = 0.85, f (base) = 30 [ Degree]
f (1st) = 34.5 [degree]
f (2nd) = 31.5 [degree]
f (3rd) = 28.5 [degrees]
f (4th) = 25.5 [degrees]
It becomes.

As shown in FIGS. 6 and 7, the flow rate margin sm1~sm4 up surge line at each stage of the operating point Q ₁ is has a same level, there is still a margin to the surge line even in this operating point Q ₁ , and can operated even operating point Q ₂ to which targeted further flow. That is, it can be seen that the flow rate control range of the compressor is increased by the present invention.

In addition, the capacity control method of the multistage centrifugal compressor according to the present invention can perform sufficient flow rate control without using complicated control as shown in the prior art 1 described above. In general, when the flow rate-pressure characteristics as shown in FIG. 2 are required, the flow rate can be controlled more effectively by setting the constants a to d so as to satisfy the following equation (5). Is possible.
a>b>c> d (5)

  In general, in the multistage centrifugal compressor according to the present invention, the inlet pressure of the first stage compressor is often hardly changed even when the discharge flow rate is changed. However, the required discharge pressure decreases as the discharge flow rate decreases, as shown in FIG. Therefore, when the flow rate of the compressed gas used in the plant is reduced, the discharge pressure of the compressor at each stage is also reduced. In this case, the ratio of the volume flow rate on the inlet side of the second stage compressor to the volume flow rate at the time of rating is larger than that of the first stage compressor. The value of the ratio in the rear stage is larger than that in the front stage as well in the compressors in the third and subsequent high pressure stages (downstream downstream stage). In other words, it can be said that the operating point tends to move away from the surging line as the latter stage. In view of the above, it is more effective to set so as to satisfy the above formula (5).

Next, a capacity control method for a multistage centrifugal compressor according to Embodiment 2 of the present invention will be described with reference to FIG.
However, the second embodiment of the present invention differs from the first embodiment in that the first embodiment of the present invention is a multistage centrifugal compressor with a built-in speed increaser, whereas the second embodiment of the present invention is different from the first embodiment. In the single-shaft multistage centrifugal compressor, as described later, the first embodiment has a configuration in which the guide vanes of each stage are all controlled by different independent guide vane operating devices. On the other hand, the second embodiment has a configuration in which a part of the multistage guide vanes is controlled by a common guide vane operating device. Except for these differences, the second embodiment is exactly the same as the first embodiment. Therefore, the same components as those in the first embodiment are denoted by the same reference numerals, and different points will be described below.

  That is, in the first embodiment, the guide vanes 7 to 10 at each stage are controlled independently by the guide vane operating devices 11 to 14, whereas in the second embodiment, the guide vanes 7 to 10 are controlled independently. The guide vanes 7 and 9 of the first and third stage compressors 1 and 3 are connected by the link mechanism and the like, and the guide vanes 8 and 10 of the second and fourth stage compressors 2 and 4 are connected by the common guide vane operating unit 50. It is configured to be operated by another common guide vane operating device 51.

And the capacity | capacitance control method of the multistage centrifugal compressor which concerns on Embodiment 2 of this invention is given by following Formula (in order that the angle of the guide vanes 7-10 connected in this way may become the same angle by the said link mechanism. Control to the values shown in 6) and (7).
f (1st) = f (3rd) = a × f (base) (6)
f (2nd) = f (4th) = b × f (base) (7)
Therefore, according to the capacity control method for a multistage centrifugal compressor according to the second embodiment of the present invention, the capacity control method of the present invention can be applied to a wider range of multistage centrifugal compressors than the second embodiment. Become.

Next, a capacity control method for a multistage centrifugal compressor according to Embodiment 3 of the present invention will be described with reference to FIG.
However, the third embodiment of the present invention differs from the first embodiment described above in that the first embodiment of the present invention calculates the set angles of the inlet guide vanes 7 to 10 by the expressions (1) to (4). In the third embodiment, the angle value is converted into a trigonometric function tan as shown in the following formulas (8) to (11), and then multiplied by a constant to obtain the inverse trigonometric function atan. Recalculate and calculate. The trigonometric function may be sin or cos in addition to tan.

f (1st) = atan [a × tan {f (base)}] (8)
f (2nd) = atan [b × tan {f (base)}] (9)
f (3rd) = atan [c × tan {f (base)}] (10)
f (4th) = atan [d × tan {f (base)}] (11)

Although the calculation is slightly complicated, depending on the characteristics of the compressor, the capacity control method according to the third embodiment may expand the flow range of the multistage centrifugal compressor more. Such compressor characteristics will be described below.
First, the head (which is closely related to the discharge pressure) H of the centrifugal compressor is proportional to the right side as shown in the following equation (12).
H∝U2 / Cu2-U1 / Cu1 (12)

  Here, U2 and U1 indicate the peripheral speeds of the impeller inlet and outlet, and are the same regardless of the angle of the guide vanes if the rotational speed is constant. Cu2 is a circumferential component of the absolute velocity of the gas at the exit of the impeller, and there is little change depending on the flow rate condition but not so much. On the other hand, Cu1 is a circumferential component of the absolute velocity of the gas at the impeller inlet, and becomes 0 if the guide vane angle is 0 degrees. The flow rate control by the guide vane is to control the value of Cu1 by this guide vane. When the value of Cu1 increases, the value of H decreases and the discharge pressure decreases as can be seen from the above equation (12). It will be. In this way, guide vane control performs flow rate adjustment by changing the operating point.

  If the inflow velocities are the same, the circumferential component is proportional to tan {f (base)}. However, when the guide vane angle is about 0 to 45 degrees, the angle and tan {f (base)} Although the rate of change is the same, when the angle is about 60 degrees, the increase amount of tan {f (base)} is larger than the increase amount of the angle itself. In the case of a multistage centrifugal compressor having compressor characteristics in which a slight change in angle at such an angle greatly affects the operating point, the embodiment of the present invention using the above equations (8) to (11) 3 may be effective.

  As described above, according to the capacity control method of the multistage centrifugal compressor according to the present invention, the relative ratio of the angle of the inlet guide vane to each stage is controlled to be a constant ratio. Therefore, it is possible to operate from the surging line with a margin of the same level, and it is possible to prevent only a specific stage from approaching the surging line first, and to increase the capacity throttle region. Further, according to the capacity control method of another multistage centrifugal compressor according to the present invention, the relative ratio of each angle of each stage is set so as to become smaller toward the downstream downstream stage. When setting the capacity control of the machine, the adjustment can be performed effectively and reliably.

1: First stage compressor, 2: Second stage compressor,
3: Third stage compressor, 4: Fourth stage compressor,
5: Input shaft, 6: Electric motor,
7-10: Entrance guide vanes,
11-14, 50, 51: Guide vane operating device,
15: Controller,
16: Gearbox

Claims (1)

In the capacity control method of a multistage centrifugal compressor having an inlet guide vane provided in each stage suction portion of the multistage centrifugal compressor, the relative ratio of each stage of the angle of the inlet guide vane is a constant ratio. A capacity control method for a multistage centrifugal compressor, characterized in that the control is performed and the ratio is set so as to decrease as it goes downstream .

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