JPS5810593B2 - Turbine phenomenon prevention control device for centrifugal compressors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a turbine phenomenon prevention control device for a centrifugal compressor that prevents a turbine phenomenon occurring in a rotor blade near the final stage of a centrifugal compressor when the discharge side pressure of the centrifugal compressor decreases.

Generally, centrifugal compressors are used to obtain high pressure oxygen in steel mills and the like.

High-pressure oxygen is used in oxygen blowing to accelerate the reaction of molten iron in converters.

In this case, gaseous oxygen delivered from the compressor is once stored in a pressure tank and then supplied to a plurality of converters.

By the way, in a centrifugal compressor, when the discharge side pressure suddenly decreases from the actual discharge pressure due to a sudden change in load, a so-called turbine phenomenon occurs in which the rotor blades near the final stage are subjected to rotational force.

Here, the discharge side pressure under normal conditions is equal to the actual discharge pressure of the compressor if piping losses are ignored, but in this specification, from the perspective of explaining the turbine phenomenon, the pressure on the compressor side of the control valve is expressed as the pressure on the compressor side. It is called side pressure and will be explained separately from the actual discharge pressure of the compressor.

When a turbine phenomenon occurs, the compressor may generate abnormal vibrations and be damaged.

Furthermore, especially in oxygen compressors, abnormal vibrations cause scales to peel off and fall, and when they collide with the rotor blades, the sparks generated cause oxygen to explode, causing a serious accident.

Conventionally, in order to prevent such a turbine phenomenon, the opening degree of a control valve is controlled so that the pressure on the discharge side of the compressor becomes a predetermined value.

This conventional device will be explained with reference to FIG.

In FIG. 1, gaseous oxygen (usually a constant amount) generated from an oxygen plant 1 flows into a compressor 3 via an intake valve 2. In FIG.

Gaseous oxygen flowing into the compressor 3 is pressurized and sent to the pressure tank 6 via the check valve 4 and the control valve 5.

Gaseous oxygen is temporarily stored in a pressure tank 6 and supplied to each load.

The compressor 3 is driven by an AC motor (induction machine or synchronous machine) connected to an AC power supply 11 via a breaker 10.

In this case, the rotation speed of the compressor 3 is generally not controlled for reasons such as large fluctuations in discharge pressure.

Therefore, the AC motor 9 is operated at a rated speed (constant speed) determined by the number of poles and the power supply frequency.

Now, in order to prevent the above-mentioned turbine phenomenon, the opening degree of the control valve 5 is controlled.

That is, the pressure on the discharge side of the compressor 3 is detected by the pressure transmitter 7 and input to the PI controller 8 .

The controller 8 compares the measured value of the discharge side pressure with a set value and controls the opening degree of the control valve 5.

For example, when the pressure on the discharge side becomes smaller than a set value, the opening degree of the control valve 5 is reduced.

Here, the suction valve 2 restricts the flow rate of oxygen flowing into the compressor 3, and by keeping the pressure of the oxygen flowing into the compressor 3 constant, prevents the purity of oxygen from decreasing.

Further, the check valve 4 prevents backflow from the pressure tank 6 when the compressor 3 is stopped.

The check valve 4 may be provided on the pressure tank 6 side of the control valve 5.

Note that the compressor 3 is also provided with a bypass valve that bypasses the valve when the discharge side pressure rises above a set value, but this valve is not shown.

Now, as described above, the turbine phenomenon is prevented by controlling the opening degree of the control valve so that the pressure on the discharge side of the compressor becomes a set value.

However, since the discharge side pressure is controlled to be a set value, the following problems occur when the rotational speed of the compressor changes.

As mentioned above, the AC motor is operated at a speed determined by the power supply frequency.

Therefore, when the power supply frequency changes, the rotational speed of the AC motor, that is, the compressor, changes accordingly.

When the power supply frequency decreases, the rotation speed also decreases.

By the way, the relationship between the discharge pressure and the flow rate of the compressor is as shown in FIG. 2 when the rotation speed is taken as a parameter.

In FIG. 2, the curve C2 is the characteristic at a predetermined rated speed, the curve C1 is the characteristic at the maximum speed due to rotation speed fluctuation, and the curve C3 is the characteristic at the lowest speed.

In addition, in FIG. 2, QN is the rated flow rate.

On the other hand, to explain the cause of the turbine phenomenon in FIG. 3, for example, there are nine blades B on the compressor rotating shaft 3S.
1 to B9 are attached and compress oxygen by rotation.

The suction pressure of the compressor is blade B1. The pressure is increased through each stage from B9 to B9, and reaches the rated pressure PN when passing through the final stage blade B9.

In this state, if the pressure on the discharge side of the compressor drops to, for example, P2, blade B8. Near B9, compressed gas flows out to the discharge side.

Therefore, a turbine phenomenon will be exhibited.

The explanation of this figure 3 is for the case of rated speed, curve C2 in figure 2.
In the case of curves C1 and C3, the discharge side pressure that causes the turbine phenomenon is Pl.

It will look like P3.

In this way, the discharge side pressure that causes the turbine phenomenon depending on the rotation speed of the compressor is also Pl.

P2. It fluctuates to P3.

Therefore, if the discharge side pressure setting value set in the controller 8 is set to the discharge side pressure P2 at the rated speed, when the speed decreases, the discharge flow rate of the compressor becomes zero, and although the compressor is rotating, there is no gas in the load. This means that the material will not be pumped.

On the other hand, increasing speed will result in a turbine phenomenon.

This is clear from the fact that the pressure limit value P2 of the curve C1 is smaller than Pl.

To solve this problem, it is possible to set the pressure at the maximum speed of the rotational speed fluctuation, but if this is done, the opening degree of the control valve will be reduced, which will reduce the discharge flow rate and reduce operating efficiency. do.

As described above, if the control valve opening degree is controlled by setting the discharge side pressure at one point, there is a problem that the turbine phenomenon cannot be satisfactorily prevented when the rotational speed of the compressor fluctuates.

The present invention has been made in view of the above-mentioned problems, and its purpose is to provide a turbine phenomenon prevention control device for a centrifugal compressor that can effectively prevent the turbine phenomenon even when the rotational speed fluctuates. be.

The feature of the present invention is that the rotational speed of the compressor and the discharge side pressure set value are changed, and the control valve opening degree is controlled so that the difference between the actual discharge pressure and the discharge side pressure is within a predetermined value. be.

An embodiment of the present invention will be described with reference to FIG.

In Fig. 4, the same symbols as in Fig. 1 indicate equivalents, 12 is a so-called cascade setting type controller whose set value can be varied depending on external conditions, 13 is a transformer, and 14 is the frequency F of the AC power supply 11. A frequency converter 15 outputs a signal V proportional to the frequency F as shown in FIG. 5, and a ratio setter 15 outputs a discharge pressure set value PS proportional to the signal V as shown in FIG.

Note that the set value PS1. PS2. PS3 is the limit value P1. shown in FIG. P2. It is set slightly larger than P3.

In this configuration, if the AC power supply 11 has the rated frequency FN, the discharge pressure set value P82 is given to the controller 12 from the ratio setter 15.

The controller 12 controls the opening degree of the control valve 5 so that the discharge side pressure becomes a set value P82.

The set value PS2 is set slightly larger than the discharge side pressure P2 that causes the turbine phenomenon shown in FIG.

Therefore, no turbine phenomenon occurs.

Now, when the frequency F of the AC power source 11 becomes high, for example FH, the set value PS1 is given to the controller 12.

Therefore, the controller 12 controls the opening degree of the control valve 5 to such an opening degree that the discharge side pressure becomes the set value PS1.

Further, the controller 12 controls the control valve 5 so that the discharge side pressure becomes PS3 when the frequency F becomes FL.

In this way, the set value of the discharge side pressure is changed according to fluctuations in the power supply frequency, that is, the rotational speed of the compressor, so the discharge flow rate can be stabilized without becoming zero or reducing the operating efficiency of the compressor. Turbine phenomenon can be prevented.

In the above-described embodiment, fluctuations in the rotational speed of the compressor are detected using the power supply frequency, but the same effect can be achieved by attaching a speed detector to the compressor or the electric motor and detecting the rotational speed.

As explained above, according to the present invention, the turbine phenomenon can be effectively prevented without reducing the operating efficiency of the compressor.

Although the above description has been made regarding the case where the rotational speed of the compressor fluctuates due to the power supply frequency, it goes without saying that the same method can be used even when the rotational speed fluctuates due to other causes.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an example of a conventional device, Fig. 2 is a pressure-flow characteristic diagram of a compressor, Fig. 3 is a compression process diagram of a centrifugal compressor, and Fig. 4 is an example of an embodiment of the present invention. The configuration diagram shown in FIG. 5 is an input/output characteristic diagram of the frequency detector and ratio setter in FIG. 4. 3... Compressor, 5... Control valve, 6...
...Pressure tank, 7...Pressure transmitter, 9...
...AC motor, 11...AC power supply, 12.
...PI controller, 14...Frequency detector, 15...Ratio setter.

Claims (1)

[Scope of Claims] 1. A centrifugal compressor that compresses and discharges incoming gas; a control valve provided on the discharge side of the compressor; and a valve control device that controls the opening degree of the control valve, detects the rotation speed of the compressor, changes the discharge side pressure set value according to this rotation speed, and adjusts the actual discharge pressure of the compressor and the discharge side pressure. A turbine phenomenon prevention control device for a centrifugal compressor, characterized in that the difference between the pressure and the pressure is within a predetermined value. 2. The turbine phenomenon prevention control device for a centrifugal compressor according to claim 1, wherein the rotational speed of the compressor is detected based on the AC power frequency of an AC motor that drives the compressor.