JPH06346894A - Capacity control device for centrifugal compressor - Google Patents

Abstract

PURPOSE:To enable the prevention of surging even without a flow detecting device and make discharge piping or suction piping around a centrifugal compressor compact so as to allow the compressor to be packaged easily. CONSTITUTION:A capacity control device for a centrifugal compressor is provided with a divider for detecting the power (or current) of a motor 42 for driving the centrifugal compressor 1 and dividing the detection value by the discharge absolute pressure of the centrifugal compressor l, and a control part 14 for closing a flow regulating means 3 and opening a pressure regulating changeover valve 9 when the output of the divider 48 becomes the set value or less and opening a flow regulating valve when the pressure detected by a pressure controller 7 reaches the lower limit set value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacity control device for a centrifugal compressor which is applied to, for example, gas pressure feeding to a gas holder.

[0002]

2. Description of the Related Art Conventionally, a gas pressure feeding device shown in FIG. 6 has been known (related invention: Japanese Patent Publication No. 1-252020). This apparatus uses a centrifugal compressor 1, and a suction flow path 2 of the centrifugal compressor 1 is provided with a flow rate adjusting means such as a suction throttle valve (hereinafter, P).
CV) 3 is provided, and the check valve 5 is provided in the discharge flow path 4.
Is provided. Further, in the portion of the discharge flow path 4 on the inlet side of the check valve 5, a flow rate detection switch (hereinafter, referred to as F
A pressure controller (hereinafter, referred to as P) 6 is provided at a portion of the discharge passage 4 on the outlet side, that is, a portion of the discharge passage 4a so that pressure can be detected.
7) is provided. The FS 6 has a flow rate lower limit setter, and the PIC 7 has a pressure lower limit setter. The discharge flow path 4a extending to the right in FIG. 6 reaches, for example, a gas holder (not shown). Further, from the portion of the discharge flow path 4 between the centrifugal compressor 1 and the check valve 5, the gas in the discharge flow path is released to the atmosphere or communicated with the suction flow path 2, and the suction flow A branch flow path 8 for returning to the path 2 is provided,
A pressure adjusting on-off valve (hereinafter referred to as FCV) 9 for adjusting the pressure in the discharge channel 4 is provided in the branch channel 8.

A first instrument air passage 11 extending from the PIC 7 to a drive unit of the PCV 3 via a first three-way solenoid valve 10 having a, b, and c ports extends to the drive unit of the FCV 9 by d. A second instrumentation air flow path 13 having a second three-way solenoid valve 12 having ports e, f is connected. Furthermore, F
Signals indicating the flow rate detected by S6 and the pressure detected by the PIC 7 are input to the control unit 14, and based on these signals, flow path switching control of the first and second three-way solenoid valves 10 and 12 is performed as described later. It has become.

Next, the capacity control that is performed when the gas is pressure-fed by the above-mentioned device will be described with reference to FIG. FIG. 7 shows various pressure-flow rate relationships on the same plane. Curve I shows FCV9 when FCV9 is fully open.
9 shows the resistance curve of 9 and the lower end is on this curve I
I is the discharge gas pressure and discharge gas flow rate of the centrifugal compressor 1 at each opening when the opening θ of the PCV 3 is changed to θ ₁ , ..., θmin, and the straight line III (surge line) is the surge pressure and discharge gas. The relationship with the flow rate, the straight line IV is the lower limit set flow rate (FSL) which is the allowable limit for surge prevention at the discharge gas pressure PS.
Is shown. Further, PS on the vertical axis indicates the pressure set value for constant air pressure control in the PIC 7, and PSL indicates the pressure lower limit set value in the discharge flow path 4a.

When the operation of the centrifugal compressor 1 is started, before the discharge gas flow rate reaches the lower limit set value FSL at the detected pressure, based on the signal from FS6, the load operation command signal from the control unit 14 is issued. , A- of the first three-way solenoid valve 10
b port communicates with each other, and the following constant wind pressure control is performed, while the de-e port of the second three-way solenoid valve 12 communicates with the second port.
The FCV 9 is closed by being pressurized by the instrument air having a predetermined pressure from the instrument air flow path 13. The constant air pressure control is performed by adjusting the opening degree of the PCV 3 between the points A and B at the set pressure PS, and the pressure indicated by the points A and B indicates the pressure in the discharge passage 4a at the time of this control. , If the deviation (detected pressure minus the set value) in the PIC 7 is +, the opening θ of the PCV 3 is decreased, and if the deviation is −, the opening θ is increased to increase the discharge flow path 4a.
The pressure at is kept almost constant. When the deviation continues in the negative state, the opening degree θ of the PCV 3 increases and reaches the point A which is the maximum compressor capacity.

On the other hand, if the pressure in the discharge passage 4a tends to increase and the deviation continues to be +, the opening degree θ of the PCV 3 becomes smaller (actuates toward the θmin side). Eventually, the discharge gas flow rate reaches a state of a point B that intersects the straight line IV indicating the lower limit set flow rate (FSL) of the FS 6 for surge prevention. As a result, the FS6 operates to output the no-load operation command signal from the control unit 14, the ef port of the second three-way solenoid valve 12 is communicated, and the instrumentation of a predetermined pressure that pressurizes the drive unit of the FCV 9 is performed. The air is released and released into the atmosphere, and FCV9 is fully opened. At the same time, the a-c ports of the first three-way solenoid valve 10 are communicated with each other to bring the opening degree θ of the PCV 3 to the minimum value θmin (transition from point B to point D in FIG. 7).

Then, the discharge gas pressure and flow rate are in the state of point D, which is the minimum load state of the centrifugal compressor 1.
Power consumption is minimal. Further, in this state, the discharge flow path 4
There is no gas pressure feeding to the a side, and the check valve 3 blocks the backflow of gas. In FIG. 7, the pressure-fed gas in the portion of the discharge flow passage 4a on the right side of the check valve 5 is accumulated. Yes,
A pressure drop gradually occurs with the consumption. Discharge channel 4
When the pressure of a falls to the lower limit set value PSL, that is, PI
When a pressure value equal to the value of PSL is detected by C7,
The ab port of the first three-way solenoid valve 10 is communicated with the PIC
The control state by 7. That is, PCV3 is connected to PIC7, and PCV3 is fully opened. At the same time, the de-e ports of the second three-way solenoid valve 12 are communicated with each other to fully close the FCV 9. As a result, the discharge pressure and flow rate shift from point D to point A '.

Further, when the discharge pressure rises and exceeds point A ', pumping of discharge gas to the discharge channel 4a starts, and the pressure in the discharge channel 4a gradually rises to reach the level of point A. ,
The load / no-load control from the point B to the point A to the point A is shifted to the constant wind pressure control on the line AB, and the same control is repeated thereafter. In FIG. 7, a solid line curve V shows the change in the state of the discharged gas under the above control. That is, in this known technique, by providing the FS6, as soon as the discharge gas flow rate of the centrifugal compressor 1 reaches a predetermined flow rate lower limit value close to the surging region or less, the intake valve PCV3 is shut off and the exhaust valve (release valve) is released. FCV which is a wind valve)
This is a technology based on the premise that surging is prevented by opening 9 to perform no-load operation.

In addition, instead of providing the above-mentioned FS6, as shown in FIG. 8, the input current or power of the electric motor 21 for driving the centrifugal compressor 1 is detected, and the detected value and the reference value are adjusted by the controller 22. When the detected value becomes equal to or less than the reference value, the blow-off valve (surging prevention valve) 23 is opened and
A gas pressure feeding device adapted to perform a blow-off operation is known (Japanese Utility Model Laid-Open No. 63-31292, Related Invention: Japanese Patent Laid-Open No. 52-).
17203). It should be noted that in FIG. 8, a portion indicated by a chain double-dashed line is a known technique, and the discharge pressure control (constant wind pressure control) by the suction throttle valve 24 of the centrifugal compressor 1 and the motor 21
3 shows a loop for overload prevention control of the above. 9 shows the relationship between the discharge pressure of the centrifugal compressor 1 and the air volume,
It also shows the relationship between the input power (or current) and the air volume, I is the surge line, II is the characteristic curve of the compressor, III is the input power (or current) curve, and MAX-W is the overload prevention maximum motor. Power (or current) value, MIN-W indicates the minimum motor power (or current) value for preventing surging, and the reference power (or current) value for preventing surging is A
Set to the point.

Further, a gas pressure feeding device shown in FIG. 10 is known (Japanese Patent Laid-Open No. 123232/1990). This device detects the input current (AMP) of the electric motor 31 that drives the centrifugal compressor 1 by the current converter 32 instead of providing the FS 6 described above, and discharge pressure of the centrifugal compressor 1 (from the check valve 33 onward). Pressure) is detected by the pressure converter 34, the combination of these two values is recognized by the controller 35, and the centrifugal compressor 1 is operating in the surge region I on the map shown in FIG. In the above, the centrifugal compressor 1 is operated under no load, and when the centrifugal compressor 1 is operated in the non-surge region II, the centrifugal compressor 1 is controlled to perform constant pressure control operation. Note that f _{1 on} the vertical axis of FIG.
Indicates a fixed constant.

[0011]

Among the above-mentioned known examples,
In the case of the gas pressure feeding device shown in FIG. 6, the FS6 which is a means for detecting the flow rate is generally composed of an orifice, a differential pressure transmitter and a signal setting device. On the other hand, recent gas pressure feeders are often packaged with accessories, and it is not possible to secure the straight pipe length before and after the orifice required for flow rate detection, making accurate flow rate detection difficult. However, there is a problem that the flow rate detection device is generally expensive.

When a sudden load change occurs, PI
Due to the delayed response of C7, the gas holder pressure is
May be higher than the set value (line AB in FIG. 7). In this case, FS6 whose set value is fixed to the value of FLS
Then, surging cannot be prevented. That is, there is a possibility that the path of the alternate long and short dash line VI in FIG. Further, when the setting value of PIC7 is changed, there is a problem that the setting value of FLS also needs to be changed.

In the case of the gas pressure feeding device shown in FIG. 8, when the operating pressure of the centrifugal compressor 1 (the set value of the controller for constant wind pressure control) is changed, it is necessary to change the reference power (or current) value. Further, even if this is automatically performed, there is a problem in that it is necessary to previously obtain the reference power (or current) value for each discharge pressure. Further, when the electric power (or current) approaches the reference electric power (or current) value, the blow-off operation is performed without performing the no-load operation, so that the flow rate is largely changed, such as a factory air source. However, there is a problem that the power loss is large.

When the control system of the gas pressure feeding device shown in FIG. 10 is adopted, a commercially available industrial controller is not possible in terms of function, memory and capacity, and it is either a dedicated controller using a computer or relatively. There is a problem in that an expensive commercially available small or medium-sized process computer is required. Further, in this control method, the blow-off operation of the centrifugal compressor 1 is not performed, but the discharge pressure P is set as the boundary condition of the map.
Is set pressure P _SET × f ₁ or less, or P <current / MIN · A
MP + PM (surge margin) or motor current AMP>
It is decided by three conditions of MIN and AMP. Therefore, if the operation set pressure P _SET of the centrifugal compressor 1 is changed,
Since MIN / AMP also changes, when it is used for an application in which the set pressure P _SET may be changed, it is necessary to obtain the MIN / AMP value for each discharge pressure in advance and change the map.

Further, when the voltage of the electric motor 31 changes, the current value also changes, and there is a problem that the control becomes unstable. The present invention has been made to solve the problems of the prior art, does not require expensive flow rate detection means, the piping around the centrifugal compressor is compact, the surge prevention parameter of the centrifugal compressor can be simply determined, Even if the operating pressure set value of the centrifugal compressor is changed, it is not necessary to change the surge prevention parameter, and it is an object of the present invention to provide a capacity control device for a centrifugal compressor, which is sufficient by using a commercially available general industrial controller.

[0016]

In order to solve the above problems, the present invention provides a flow rate adjusting means provided in a suction passage of a centrifugal compressor and an upstream side of a check valve provided in a discharge passage. , A branch flow passage branched from the discharge flow passage and provided with an on-off valve communicating with the atmosphere or the suction flow passage, and provided on the downstream side of the check valve so that pressure can be detected, and a detection pressure signal is output and the detected pressure is ,
In addition to the built-in pressure lower limit setting device that outputs the first ON signal when the pressure is below the set pressure and the first OFF signal in other cases,
The higher the detected pressure, the smaller the opening of the flow rate adjusting means, the pressure controller that outputs an opening adjustment signal, the converting means that converts the pressure detected by the pressure controller into an absolute pressure, and the centrifugal compressor. Power detecting means for detecting the electric power supplied to the driving section, calculating means for dividing the value of the detected power by the power detecting means by the absolute pressure value obtained by the converting means, and the output value from the calculating means is set. When the value is less than or equal to the value, the second lower signal is output, and in other cases, the second lower signal is output. The on-off valve is closed and the flow rate adjusting means is opened to perform the load operation, and the flow rate adjusting means based on the opening degree adjusting signal from the pressure controller while the first ON signal and the second ON signal are being output. Constant air pressure control by adjusting the opening of Causes, and the first off signal, the on-off valve by the output of the second off-signal to open, a configuration in which a said flow rate control means controlling device to perform the no-load operation is closed.

[0017]

By configuring as in the above invention, it becomes unnecessary to use the flow rate detecting means for controlling the capacity of the centrifugal compressor, and the value obtained by dividing the shaft power of the compressor by the absolute discharge pressure is constant on the surge line. Paying attention to the fact that it becomes a value, if this value becomes less than or equal to the set value, no-load operation is performed, so it becomes possible to easily perform non-surge control without running in blowout pressure. In the vicinity, the power lower limit setting line is almost parallel to the surge line.
Due to the response delay of IC), the surge can be prevented even if the actual pressure rises or falls below the set pressure.

[0018]

An embodiment of the present invention will be described below with reference to the drawings. Figure 1 shows a gas pumping device to which the capacity control device I ₁ of the centrifugal compressor 1 according to the first embodiment of the present invention, portions which are common with the gas pumping device shown in FIG. 6, the same numbers together The description is omitted. In this device, the electric motor 4 that drives the centrifugal compressor 1 from the power line 41
The power supplied to 2 is formed so as to be detected by the power converter 45 via the instrument current transformer 43 and the instrument transformer 44. Note that the instrument current transformer 43 and the instrument transformer 44 are generally provided on the power line 41 together with the circuit breaker 46 for protection of the electric motor 42 and the like, regardless of the present invention.

On the other hand, a PI for detecting the pressure in the discharge channel 4a
The pressure signal from C7 is led to the adder 47, where the constant is added to the input signal and the absolute pressure is calculated from this signal,
The absolute pressure signal is input to the divider 48, and the power signal from the power converter 45 is input to the divider 48. Then, the electric power signal is output from the divider 48 by the divider 48.
A signal indicating a value divided by the absolute pressure signal of a is input to the power lower limit setter 49. The power lower limit setter 49 compares the above signal from the divider 48 with the power lower limit set value (WSL), and if this signal is less than or equal to the set value, it turns on if the off contact signal is greater than the set value. The contact signal is generated and input to the control unit 14.
In this device, the electropneumatic converter 50 is interposed between the PIC 7 and the first three-way solenoid valve 10.

FIG. 2 shows a part of the sequence circuit in the control unit 14, and the contact 46X is closed when the circuit breaker 46 is turned on and the electric motor 42 and the centrifugal compressor 1 are in the starting state or the operating state. To do. When the contact 46X is closed, the timer 46XT starts to operate, and the time is set to elapse after the startup time of the centrifugal compressor 1. When the time is up, the contact 46XT is closed, and the first, second, and third directions are closed. Coil SV1 of solenoid valves 10 and 12
0 and SV12 are energized. Further, the output contact WSL of the power lower limit setting device 49 and the output contact PSL of the pressure lower limit setting device built in the PIC 7 are connected in parallel, and the coils SV10 and SV12 are energized.

Next, the capacity control in the device having the above structure will be described. The pressure in the discharge passage 4a is 0 kgf
When the centrifugal compressor 1 is started in the state of / cm ² G,
Since the pressure in the discharge flow path 4a is equal to or lower than the set value PSL, the output contact PSL is in the ON state, that is, the circuit is closed. Therefore, after the start-up time has elapsed, the timer contact 46XT is closed and the first and first 2 Three-way solenoid valve 10, 12 coil SV1
0, SV12 is energized. When the second three-way solenoid valve 12 is energized, the de port will be in communication. And the second
FCV by instrumentation air of a predetermined pressure from the instrumentation air flow path 13
9 is fully closed.

At the same time, the first three-way solenoid valve 10 is energized,
The ab port is in the communication state, and the pressure signal from the PIC 7 is sent to the drive unit of the PCV 3 via the electropneumatic converter 50. At this time, since the actual detected pressure is lower than the set value of PIC7, the signal from PIC7 is a signal for fully opening PCV3, and PCV3 is in a fully open state. Therefore, the centrifugal compressor 1 sends gas with a flow rate of 100% or more, for example, to a gas holder (not shown).

The pressure of this gas holder reaches the set value PSL of the pressure lower limit setter, and its output contact PSL is in the OFF state, that is, the circuit is opened, but the output contact W of the power lower limit setter 49.
SL is in the ON state, that is, closed, and the energization of the first and second three-way solenoid valves 10 and 12 is continued. Then, if the consumption of the pressure-fed gas is small or not, the PIC7 will eventually be released.
The discharge pressure rises up to the set value PS in, the output from the PIC7 drops, and the PCV3 starts to operate in the closing side,
Since the gas pressure feed to the gas holder continues, the pressure in the discharge passage 4a continues to rise. Both the amount of air discharged from the centrifugal compressor 1 and the shaft power decrease as the pressure increases and the PCV 3 changes as it closes. Then, the value obtained by dividing the input power to the electric motor 42 by the pressure in the discharge flow path 4a becomes equal to or less than the set value WLS in the power lower limit setting unit 49, and the output contact WSL of the power lower limit setting unit 49 is in the OFF state, that is, the circuit is opened.

Already, the output contact PS of the pressure lower limit setter
Since L is in the off state, the output contacts WSL are opened, so that the coils SV10 and SV12 of the first and second three-way solenoid valves 10 and 12 are simultaneously de-energized.
When this energization is cut off, the ef port of the second three-way solenoid valve 12 is brought into communication, the instrumentation air supplied to the drive part of the FCV 9 is released to the atmosphere, and the FCV 9 is fully opened. . At the same time, the energization of the first three-way solenoid valve 10 is cut off, so that the bc port is in the communication state,
The signal pressure air from the PIC7, which was supplied to the drive unit of the PCV3, is also released to the atmosphere, and the opening degree of the PCV3 is closed to the minimum value (θmin).

As a result, the pressure on the upstream side of the check valve 5, that is, the discharge pressure of the centrifugal compressor 1 decreases to near atmospheric pressure, and the centrifugal compressor 1 shifts to a no-load operation state in which the power consumption is minimum. . The transition of the pressure and flow rate states in the capacity control of the centrifugal compressor 1 will be described with reference to FIG. In addition,
This FIG. 3 is a diagram corresponding to FIG. 7, and is expressed in the same way as FIG. 7, and items common to FIG. 7 will be omitted using the same expressions. The curve IV corresponds to the straight line IV indicating the lower limit flow rate setting value for surge prevention in FIG. 7, and is the setting line of the electric power lower limit setter 49, and the centrifugal compressor 1
Since it is close to the straight line III that shows the relationship between the surge pressure and the gas flow rate, and the straight line that intersects near the origin, the centrifugal compressor 1
It becomes almost parallel to the line III near the rated pressure of.

Curve I'shows the pressure at the gas holder D
From the point, the resistance curve of the discharge flow path system in which the gas is pressure-fed is shown without gas consumption. The curve VI by the one-dot chain line is
The change of the discharge air volume and discharge pressure from the centrifugal compressor 1 at the time of initial charging of the gas holder when there is no gas consumption described above is shown. That is, the centrifugal compressor 1 is operated at the discharge pressure point D after starting, but the timer 46XT (FIG. 2) is used.
Simultaneously with the time up, the PCV3 is fully opened, the FCV9 is fully closed, and the discharge pressure of the centrifugal compressor 1 shifts from point D to point A ″, and when the operation exceeds rated air volume and rated power, points A ′ and A
Fill to the point. When the point A, which is the set value PS of the PIC7, is filled, the PIC7 starts to close the PCV3, but since there is no gas consumption, the discharge gas flow rate and the power consumption of the centrifugal compressor 1 are reduced, but the discharge flow path 4a The pressure rises to point C.

When reaching the point C, the power lower limit setter 49 operates, the first and second three-way solenoid valves 10 and 12 are simultaneously de-energized, the FCV9 is fully opened, and the PCV3 is closed, and centrifugal compression is performed. The discharge gas flow rate and discharge gas pressure of the machine 1 move from the point C to the point D along the curved line VI of the one-dot chain line,
The centrifugal compressor 1 is in the no-load operation state, but the pressure of the gas holder is kept in the charged state indicated by the point C.

Next, when gas consumption starts and the pressure in the gas holder reaches the pressure lower limit set value PSL in the PIC 7, the first and second three-way solenoid valves 10 and 12 are simultaneously energized. As a result, the FCV 9 is fully closed, the PCV 3 is fully open, and the centrifugal compressor 1 is in a load operation state. That is, the discharge gas flow rate and discharge gas pressure of the centrifugal compressor 1 shift from point D to point A'in FIG. Further, when the gas consumption amount is the amount from point A to point B in FIG. 3, after the discharge gas pressure of the centrifugal compressor 1 is increased to point A, the constant air pressure control by the PIC 7 works to discharge gas. The pressure of the passage 4a (≈discharge gas pressure) is maintained at the set value PS of the PIC7.

After that, when the gas consumption decreases and becomes equal to or less than the amount of point B in FIG. 3, the power lower limit setting device 49 operates and the first and second three-way solenoid valves 10 and 12 are simultaneously de-energized. . As a result, the FCV 9 is fully opened, the PCV 3 is closed, and the centrifugal compressor 1 is in a no-load operation state.
Then, the above-mentioned control is repeated according to the gas consumption. As described above, the input power to the electric motor 42 that drives the centrifugal compressor 1 is detected, and this detected value is used as the discharge flow path 4a.
When the value divided by the pressure is less than a certain value, the centrifugal compressor 1 is operated without load, and when the pressure in the discharge passage 4a is less than the certain value, the centrifugal operation is performed with a load, thereby performing the surging of the centrifugal compressor 1. It is possible to perform constant pressure control and load / no-load operation control while preventing the above.

Therefore, according to the above-mentioned capacity control device, surging can be prevented even without the flow rate detecting device, and when the flow rate detecting device is installed in the discharge pipe or the suction pipe around the centrifugal compressor. Such constraints are eliminated and the compressor can be packaged easily. The part within the frame X of the device shown in FIG. 1 can be realized by one programmable single-loop controller using a commercially available microprocessor.
₁ can be realized simply by building a program, and there is no need to add control hardware. Therefore, the cost can be reduced as a whole because a relatively expensive flow rate detecting device is unnecessary.

Further, generally, in an electric motor driven centrifugal compressor, a control for preventing overload of the electric motor is often added, and FIG. 4 shows a second embodiment of the present invention to which such control is added. 1 shows a gas pressure feeding device to which the capacity control device I _{2 according} to the present invention is applied. The apparatus shown in FIG. 4 is different from the apparatus shown in FIG. 1 only in the portion within a frame Y surrounded by a one-dot chain line, except that a power controller 61 and a selector 62 are newly added. Portions which are substantially the same and correspond to each other are designated by the same reference numerals, and description thereof will be omitted. In the case of the capacity control device according to the present invention, the power lower limit setting line becomes substantially parallel to the straight line III in FIG. 3, that is, the surge line of the compressor. Therefore, even if the setting value PS of the PIC 7 is changed, the power lower limit setting value is changed. There is an advantage that there is no need to change.

The part inside the frame Z shown in FIG. 5 is the third part of the present invention.
FIG. 4 shows a part of the capacity control device according to the embodiment, and in FIG. 4, when PCV3 is used as a guide vane for capacity adjustment,
Instead of the frame Y, it is replaced and a new correction calculator 7 is added.
1 is added. Then, the value of the centrifugal compressor shaft power (kW) / the absolute discharge pressure (P _A ) of the centrifugal compressor is corrected by the signal that determines the guide vane angle from the selector 62. Preferably, the guide vane angle is directly detected and corrected. The reason is that the surge line of the centrifugal compressor 1 does not become a straight line due to the change of the guide vane angle. In the above embodiment, the power supplied from the power line 46 is detected, but the present invention is not limited to this, and when the power supply voltage does not change, the power is used instead of the power. The current flowing through the line 46 may be detected.

[0033]

As is apparent from the above description, according to the present invention, the flow rate adjusting means provided in the suction passage of the centrifugal compressor and the upstream side of the check valve provided in the discharge passage, A branch flow path branched from the discharge flow path and provided with an on-off valve that communicates with the atmosphere or the suction flow path, is provided on the downstream side of the check valve so that pressure can be detected, and a detected pressure signal is output, and the detected pressure is In addition to having a built-in pressure lower limit setting device that outputs a first ON signal when the pressure is equal to or lower than a set pressure and a first OFF signal in other cases, the opening of the flow rate adjusting unit is set to be smaller as the detected pressure is higher. A pressure controller that outputs an opening adjustment signal, a converter that converts the pressure detected by the pressure controller to an absolute pressure, a power detector that detects the power supplied to the drive unit of the centrifugal compressor, The value of the electric power detected by the electric power detection means is obtained by the conversion means. A calculating unit that divides by the pressure value, a power lower limit setting unit that outputs a second OFF signal when the output value from the calculating unit is less than or equal to a set value, and a second ON signal in other cases, and centrifugal compression After the machine is started, the opening / closing valve is closed by the first ON signal from the pressure lower limit setter, the flow rate adjusting means is opened to perform the load operation, and the first ON signal,
While the second ON signal is being output, the constant wind pressure control is performed by adjusting the opening of the flow rate adjusting means based on the opening adjusting signal from the pressure controller, and the first OFF signal and the second OFF signal are controlled. The control unit is configured to open the on-off valve and close the flow rate adjusting unit by output to perform no-load operation.

For this reason, it is possible to prevent surging even without a flow rate detecting device, and the discharge pipe around the centrifugal compressor,
Alternatively, the constraint condition as in the case where the flow rate detecting device is installed in the suction pipe is eliminated, and the compressor can be packaged easily. Also, note that the value obtained by dividing the shaft power of the compressor by the absolute discharge pressure is a constant value on the surge line, and if this value is below the set value, no-load operation is performed. As a result, non-surge control can be easily performed without blowing air, and power can be reduced. Further, as for the characteristic data of the compressor for surge prevention, the surge prevention parameter can be determined by obtaining only one surge point in the vicinity of the rated pressure of the compressor, so that the trial run process can be greatly shortened. Furthermore, near the rated pressure of the compressor,
Since the power lower limit setting line is almost parallel to the surge line, it is not necessary to change the surge prevention parameter even if the operating pressure setting value of the compressor is changed. Due to the response delay of the pressure controller (PIC), Even if the actual pressure rises and falls, it will be possible to prevent surges. In addition, a general industrial controller called a programmable single-loop controller can be realized at a relatively low cost.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a gas pressure feeding device to which a capacity control device according to a first embodiment of the present invention is applied.

FIG. 2 is a diagram showing a part of a sequence circuit of a control unit in the device shown in FIG.

3 is a diagram showing the characteristics of the centrifugal compressor in the apparatus shown in FIG. 1 and the relationship between discharge gas flow rate and discharge gas pressure in capacity control.

FIG. 4 is an overall configuration diagram of a gas pressure feeding device to which a capacity control device according to a second embodiment of the present invention is applied.

FIG. 5 is a diagram showing a part of a control unit of a capacity control device according to a third embodiment of the present invention.

FIG. 6 is an overall configuration diagram of a gas pressure feeding device to which a conventional capacity control device is applied.

7 is a diagram showing the characteristics of the centrifugal compressor in the device shown in FIG. 6 and the relationship between discharge gas flow rate and discharge gas pressure in capacity control.

FIG. 8 is an overall configuration diagram of a gas pressure feeding device to which another conventional capacity control device is applied.

9 is a diagram showing the relationship between the air flow rate of the centrifugal compressor shown in FIG. 8, the discharge gas pressure, and the input power (current).

FIG. 10 is an overall configuration diagram of a gas pressure feeding device to which another conventional capacity control device is applied.

11 is a map diagram showing a relationship between a discharge gas flow rate and a discharge gas pressure of the centrifugal compressor shown in FIG.

[Explanation of symbols]

I ₁ , I ₂ Capacity control device 1 Centrifugal compressor 3 Flow rate control means 4, 4a Discharge flow path 5 Check valve 7 Pressure controller 8 Branch flow path 9 Pressure control on-off valve 10 First three-way solenoid valve 12 Second three-way Solenoid valve 14 Control unit 41 Power line 42 Electric motor 43 Current transformer for instrument 44 Transformer for instrument 45 Power converter 47 Adder 48 Divider 49 Power lower limiter 50 Electropneumatic converter

Claims (1)

[Claims] 1. An opening / closing device that branches from the discharge flow path and communicates with the atmosphere or the suction flow path on the upstream side of the flow rate adjusting means provided in the suction flow path of the centrifugal compressor and the check valve provided in the discharge flow path. A branch flow path provided with a valve and a pressure-detectable unit provided on the downstream side of the check valve to output a detection pressure signal, and the detection pressure is
In addition to the built-in pressure lower limit setting device that outputs the first ON signal when the pressure is below the set pressure and the first OFF signal in other cases,
The higher the detected pressure, the smaller the opening of the flow rate adjusting means, the pressure controller that outputs an opening adjustment signal, the converting means that converts the pressure detected by the pressure controller into an absolute pressure, and the centrifugal compressor. Power detecting means for detecting the electric power supplied to the driving section, calculating means for dividing the value of the detected power by the power detecting means by the absolute pressure value obtained by the converting means, and the output value from the calculating means is set. When the value is less than or equal to the value, the second lower signal is output, and in other cases, the second lower signal is output. The on-off valve is closed and the flow rate adjusting means is opened to perform the load operation, and the flow rate adjusting means based on the opening degree adjusting signal from the pressure controller while the first ON signal and the second ON signal are being output. Constant air pressure control by adjusting the opening of And a control section for opening the on-off valve and closing the flow rate adjusting means to perform no-load operation in response to the output of the first off signal and the second off signal. Capacity control device.