JPH0512557B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is applicable to a slide valve type screw compressor that is used in a gas turbine or the like where the consumption flow rate fluctuates rapidly. This invention relates to a method for controlling the capacity of an operation.

(Prior art) The gas confinement capacity for trapping, compressing and discharging gas between the male and female rotors meshing with each other is transferred to a slide valve forming a part of the rotor peripheral wall at a predetermined position between fully open and fully closed. A slide valve type screw compressor that is controlled by adjusting the compressor is known. The capacity of the compressor is controlled by the discharge pressure.

A conventional control method for a slide valve type screw compressor will be explained with reference to the block diagram shown in FIG. 5a.

In the figure, 1 is the main body of a slide valve type screw compressor with built-in male and female rotors and a slide valve;
2 is a hydraulic cylinder that controls the position movement of the slide valve;
3 is a four-way switching valve, 4 is a slide resistor for detecting the position of the slide valve, 5 is a surge tank, 6 is a pressure transmitter, 7 is a pressure regulator, 8 is an electrical/electrical positioner, and 9 is a safety valve. Note that 10 is a rotational drive source for the male and female rotors.

The compressor main body 1 compresses gas taken in from a gas supply path indicated by an arrow Gin, and discharges it from a discharge path indicated by an arrow Gout. The discharged compressed gas flows into the surge tank 5 and is pressure regulated before being consumed. Discharge pressure control in this case is performed as follows.

The pressure inside the surge tank 5 . The pressure regulator 7 outputs a signal to the electric/electric positioner 8 when the pressure fluctuation that can be obtained from the input signal shows a deviation larger than a predetermined deviation allowed from the predetermined pressure setting value Pset.
The electrical/electronic positioner 8 combines the input signal from the pressure regulator 7 with the slide valve position detection signal input from the slide resistor 4, and controls the four-way switching valve 3 so as to force the slide valve to a predetermined position. A control command for the switching operation is output, and the hydraulic cylinder 2 is driven and the slide valve is fully opened.
→The gas entrapment capacity of the compressor main body 1 is controlled by making the compressor take a predetermined position between fully closed.

(Problems in the Prior Art) As described above, in the conventional capacity control method of controlling the trapped gas capacity by the discharge pressure, when the consumed flow rate flowing out from the discharge pressure section fluctuates gently,
The control system can follow this sufficiently and will not cause any trouble.

However, when the consumption flow rate fluctuates in steps...for example, when supplying compressed gas to a gas turbine, etc., the control system of the compressor is as shown in Figure 5b.
The pressure drop in the discharge pressure section = surge tank 5 is to be recovered by operating in accordance with the consumption flow characteristic line V shown on the chart with the consumption flow rate v on the vertical axis and the time t on the horizontal axis. There are physical and mechanical limits to the movement speed of the slide valve (for example, load,
It takes about 60 seconds to unload)
The discharge pressure p in the surge tank 5 becomes a pressure characteristic curve P drawn on the chart of FIG. 5c, in which the vertical axis is the discharge pressure p and the horizontal axis is the time t. That is, the pressure characteristic curve P is initially set to a predetermined discharge pressure setting value Pset.
However, when the consumption flow rate increases stepwise as shown in the figure and the pressure in the discharge pressure section 5 suddenly fluctuates downward, the control system responds by moving the slide valve from its normal position toward the load side. I tried to recover the pressure fluctuation by moving it wide, but the discharge pressure remained at the set value.
In recovering to Pset and detecting this and returning the slide valve from the moving position to the normal position,
Since there is a limit to the movement speed, during the time required from the start to the end of movement, the pressure rises beyond the set value Pset indicated by the arrow, and the surge tank 5
The discharge pressure within may deviate significantly from the set value Pset. When such a situation occurs, the safety valve 9 is activated or a trip circuit (not shown) is sometimes rendered conductive.

Activation of the safety valve 9 and conduction of the trip circuit are accompanied by a shutdown of the compressor itself, which causes great damage to equipment that uses compressed gas supplied from the screw compressor.

Originally, the safety valve 9 and the trip circuit were provided as a countermeasure in case of an abnormality, but they cannot be controlled and operated normally.
Since it is undesirable for the emergency countermeasure device to operate due to the slow movement speed of the slide valve even though the slide valve is in operation, a solution for dealing with such a situation has been desired.

(Object of the Invention) The present invention was made in order to solve the above-mentioned problems in the conventional control method of a slide valve type screw compressor that supplies compressed gas to a device whose consumption flow rate fluctuates in steps. It is an object of the present invention to provide a capacity control method for a slide valve type screw compressor that does not cause a situation in which an abnormality countermeasure device is activated during normal control and operation.

(Structure of the Invention) The structure of the present invention is as follows. (2) When the consumption flow rate of the compressor, which is controlled by controlling the slide valve that forms part of the rotor peripheral wall to take a predetermined position between fully open and fully closed, is to A bypass in which a normally closed valve is inserted is provided between the supply path for supplying the water and the discharge pressure section, and (3) the pressure rise speed of the discharge pressure section is calculated and measured, and (4) When a predetermined pressure exceeding the set value set in the discharge pressure section is reached, the normally closed valve is opened with a step-like opening of large or small depending on the speed of pressure rise mentioned above to create a bypass. (5) A slide valve type characterized in that the normally closed valve is set to close at a slow speed at which the slide valve can control the pressure. A method for controlling the capacity of a screw compressor.

(Function of the Invention) The present invention provides a set value of the discharge pressure part pressure caused by the time required for the unavoidable movement of the slide valve when the consumption flow rate of a slide valve type screw compressor fluctuates in steps. This function prevents the pump from rising by a large amount and enables capacity control using the discharge pressure.

(Embodiment) The control method of the present invention will be described in detail below with reference to the embodiment block diagram shown in FIG.

In the figure, 1 is the main body of a slide valve type screw compressor with built-in male and female rotors and a slide valve;
2 is a hydraulic cylinder that controls the position movement of the slide valve;
3 is a four-way switching valve, 4 is a slide resistor for detecting the position of the slide valve, 5 is a surge tank, 6 is a pressure transmitter, 8 is an electric/electrical positioner, 10 is a rotational drive source for the male and female rotors, and the above The equipment is no different from conventional equipment.

However, the present invention arranges a computing unit 11 in place of the conventional pressure regulator 7 in the circuit in which the above-mentioned various devices are arranged, and also connects the supply path Gin that supplies gas to the compressor body 1 and the surge tank 5. A bypass BP is disposed between them, and a normally closed valve 12 is inserted in the bypass BP.

In the above configuration, the compressor main body 1 is connected to the supply path G
The compressed gas taken in is compressed and discharged from the discharge path indicated by the arrow Gout, and the discharged compressed gas flows into the surge tank 5, is pressure regulated, and is consumed. The pressure fluctuation is detected by the pressure transmitter 6 and a signal is output as in the conventional case.

In the present invention, the signal output of the pressure transmitter 6 is
1, and in the same way as the conventional pressure setting device 7, the calculation unit 11 outputs an output to the electric/electric positioner 8 to control the position of the slide valve when the deviation of the discharge pressure fluctuation exceeds a predetermined allowable deviation. It is set to perform the following actions.

First, the computing unit 11 measures the speed of increase in discharge pressure from the input signal.

In other words, when the consumption flow rate decreases in steps,
The control system operates to restore the reduced pressure in the surge tank 5 to the predetermined set value Pset, but as mentioned above, it takes time from the start to the end of the movement of the slide valve, and the volume of gas taken in during that time is reduced by the slide valve. Since it changes according to the opening degree of the valve, the pressure increase speed in the surge tank 5 changes depending on the reduction range of the consumption flow rate. This relationship is shown in Figures 2a and b. Setting value Pset of the pressure characteristic line P on chart a with the pressure p inside the surge tank 5 on the vertical axis and the time t on the horizontal axis
For example, an increase exceeding the consumption flow rate characteristic line V with a small change in the consumption flow rate is determined according to the consumption flow rate characteristic line V on the chart b in which the consumption rate v is plotted on the vertical axis and the time t is plotted on the horizontal axis.
The behavior is shown as Pb for A, Pb for the medium consumption flow characteristic line VB, and Pc for the large consumption flow characteristic line VC.

Therefore, either the calculating unit 11 calculates and measures the amount of increase in pressure change △ _p per unit time T as shown in the chart of FIG. The predetermined pressure value is as shown in the diagram of Fig. 3b with pressure p on the vertical axis and time t on the horizontal axis.
Calculate the time T1 required to rise from P1 to P2.
It can be set to determine the ejection force increase speed ΔP by measuring it.

Furthermore, the computing unit 11 is caused to calculate the consumption flow rate v from the above-mentioned discharge pressure increase speed ΔP, and the flow rate change amount ΔV is determined from the consumption flow rate v, and in relation to the closing operation speed of the normally open valve 12, which will be described later. , the opening degree % of the normally open valve 12 can be set to be calculated and determined.

Therefore, in the present invention, when the internal pressure p of the surge tank 5 reaches a predetermined pressure P3 exceeding the set value Pset,
Discharge pressure increase speed ΔP obtained by the calculator 11
A signal corresponding to the determined opening degree % of the normally closed valve 12 is set to be output from the computing unit 11 to the electric/electrical positioner 8, and the electric/electrical positioner 8 to which the signal is input is a normally closed valve. 12 to output a valve opening operation command according to the input signal.

In the present invention, the arithmetic unit 11 is set as described above, and on the other hand, the normally closed valve 12 is set to close at a slow speed. This is because if the valve is closed rapidly, the valve will be closed before the position control operation of the slide valve is completed, and the pressure inside the surge tank 5 will reach the predetermined pressure P3 again, and the calculator 11 will move to the electric/electrical positioner 8. This is because it outputs a signal.

Therefore, according to the valve opening operation command output from the electric/electric positioner 8, the normally closed valve 12 increases the opening degree in % according to the pressure increase speed ΔP as shown in FIG. 3c. If it is small, the valve will be opened with the opening degree % small. By opening the normally closed valve 12, the bypass BP becomes conductive, and the compressed gas in the surge tank 5 flows out through the bypass BP.
The pressure in the surge tank 5 gradually decreases from the predetermined pressure P3 exceeding the set value Pset, and the compressed gas corresponding to the flow rate change amount ΔV is returned to the supply pipe Gin.

The operation of each part of a compressor embodying the present invention is shown in the diagrams of FIGS. 4a to 4d. The control system operates in response to the fluctuation in the step-like consumption flow rate b, and the pressure inside the surge tank 5 increases accordingly, and the pressure rise reaches the set value.
When Pset is exceeded and the predetermined pressure P3 is reached (a), a signal is output from the computing unit 11, and the normally closed valve 12 opens at a predetermined opening degree, and then gradually returns to a substantially closed state (c). During this time, the slide valve is closed to the surge tank 5.
When the internal pressure rises and reaches the set value Pset, movement is started based on the output signal from the calculator 11, and the opening degree of the slide valve changes from the load side close position to the unload side open position as shown in d. The end of the movement and the return of the normally closed valve 12 to the closed state are almost synchronized.

Therefore, the discharge pressure in the surge tank 5 is effectively reduced before the safety valve or trip circuit is activated, and the capacity control based on the discharge pressure of the slide valve can be continued without any hindrance. Become.

(Effects of the Invention) By implementing the present invention, even if the consumption flow rate fluctuates in steps, there is no possibility that the abnormality countermeasure device will operate during normal control operation.
The slide valve type screw compressor can be operated with capacity control based on the discharge pressure in a reliable manner, and the operation of a device using the compressed gas produced by the slide valve type screw compressor is ensured. Also,
Since the setting is to detect the discharge pressure increase speed, it is possible to estimate the range of fluctuation in the consumption flow rate, so it is possible to perform optimal capacity control based on the estimated value. Furthermore, unlike a safety valve that is left open when activated and releases compressed gas to the outside, a normally closed valve closes almost immediately after opening, and capacity is controlled almost constantly by moving the slide valve. from,
The effects brought about are enormous, such as improved shaft power.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the control method of the present invention.
2A and 2B are pressure characteristic diagrams and consumption flow rate characteristic diagrams showing the relationship between the pressure increase behavior exceeding the set value in the surge tank 5 and the consumption flow rate, respectively, and FIGS. 3A and 3B are respectively the arithmetic unit 11 Fig. 3c is a diagram explaining how to determine the opening of a normally closed valve using the calculator 11, and Figs. Fig. 5a is a block diagram illustrating the conventional control method of a slide valve type screw compressor, and Fig. 5b and c are diagrams showing the operation of each part of a slide valve type screw compressor. FIG. 2 is a consumption flow characteristic diagram and a surge tank discharge pressure characteristic diagram when the fuel consumption changes. 1...Compressor body, 5...Discharge pressure section (surge tank), 12...Normally closed valve, BP...Bypass,
Gin...Gas supply path.

Claims (1)

[Claims] 1 The gas confinement capacity, which traps gas between the male and female rotors that mesh with each other, compresses it, and discharges it, is fully opened to the slide valve that forms part of the rotor peripheral wall in accordance with the pressure of the discharge pressure section into which the discharged gas flows. ←――→When the consumption flow rate of a compressor that is controlled by keeping it at a predetermined position between fully closed and fluctuates rapidly,
A bypass in which a normally closed valve is inserted between the supply path for supplying gas to the compressor and the discharge pressure section is provided, and the pressure rise speed of the discharge pressure section is calculated and measured. When a predetermined pressure exceeding the set value set in the pressure section is reached, the normally closed valve is opened at a step-like opening degree depending on the speed of pressure rise mentioned above to open the bypass. A slide valve type screw compressor, characterized in that the compressed gas is returned to the supply pipe by the slide valve, and the closing operation of the normally closed valve is set to a slow speed at which the slide valve can control the pressure. Capacity control method.