JP2937530B2 - Discharge pressure control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge pressure control device capable of controlling a source pipe pressure of secondary cooling water in a continuous casting facility.

[0002]

2. Description of the Related Art In a continuous casting facility, a plurality of flow control loops are branched from a main pipe through which secondary cooling water circulates, and each flow control loop is supplied with a cooling water flow rate corresponding to a source pipe pressure. You. Generally, the cooling water flow rate fluctuates greatly,
Even if the cooling water flow rate fluctuates greatly, it is necessary to maintain a source pipe pressure that can secure the flow rate required in each flow control loop.

Conventionally, as shown in FIG. 3, a pressure gauge 3 detects a main pipe pressure of a main pipe 2 in which a pipe pressure is maintained by a fluid discharged from a pump 1, and detects the detection result with a pressure controller. 4 to generate a pressure control signal from the deviation between the actual source pipe pressure and the set value. This pressure control signal is transmitted to the pressure regulating valve 5.
To adjust the opening degree, and control the flow rate taken into the pump 1 from the main pipe 2 through the pressure regulating valve 5 to control the main pipe pressure.

On the other hand, in a plurality of flow control loops connected to the main pipe 2, the supplied flow is detected by a flow meter 6, and the detection result is input to a flow controller 7, where the detected flow value and A flow rate adjustment signal is generated from the deviation from the set value. The flow control signal is input to the flow control valve 8 to control the flow in each loop.

As described above, the pressure control and the flow rate control are generally performed independently, and the set value of the pressure control of the main pipe 2 is determined independently of the flow rate of the flow control loop. Was. When the total flow rate of the flow control loop changes greatly, the original pipe pressure also changes greatly.
Has been adjusted based on a set value determined independently of such a change in the flow rate.

[0006]

However, since the valve opening of the pressure control valve 5 is determined by the valve itself, when the flow rate of the flow control loop fluctuates greatly, it greatly fluctuates only with a predetermined set value. If it is attempted to keep the source pipe pressure constant, it is highly likely that the valve opening will be deviated from the valve opening controllable by the pressure regulating valve 5. For example, in the case of continuous casting equipment, the circulation of the secondary cooling water is greatly impeded. And other problems.

The present invention has been made in view of the above circumstances, and can sufficiently cope with a large variation in the total flow rate on the flow control side, and greatly reduces restrictions caused by the controllable opening of the pressure control valve. It is an object of the present invention to provide a discharge pressure control device capable of reducing the pressure.

[0008]

To achieve the above object, a discharge pressure control device according to the present invention discharges a fluid from a pump at a predetermined discharge pressure to a main pipe and is connected to the main pipe. Supplying the fluid to at least one flow control loop,
And a part of the fluid discharged to the main pipe is taken into the pump through a pressure control valve, and the opening of the pressure control valve is adjusted to control the discharge pressure. Pump discharge amount calculating means for obtaining a pump discharge amount based on a discharge flow rate characteristic; total flow calculating means for obtaining a total flow value of the fluid supplied to the flow control loop; and a pump calculated by the pump discharge amount calculating means. A pump discharge pressure calculating means for calculating a discharge pressure of the pump from a discharge amount and a total flow value calculated by the total flow calculating means,
The discharge pressure calculated by this pump discharge pressure calculating means and the discharge pressure
And and a pressure regulating valve control means for controlling the opening of the pressure regulating valve based on the Kan圧discharge pressure setpoint and before <br/> Kimotokan obtained from opening information of the pressure regulating valve It became.

[0009]

According to the present invention, the pump discharge amount calculated by the pump discharge amount calculating means based on the discharge pressure-discharge flow rate characteristic of the pump and the total flow rate of the flow control loop obtained by the total flow rate calculating means are determined. Is calculated by the pump discharge pressure calculating means. Then, the calculated discharge pressure and pressure control valve
The opening degree of the pressure regulating valve is regulated have groups Dzu <br/> to the discharge pressure setpoint and Motokan圧obtained from opening information. As a result, the discharge pressure set value is determined according to the total flow rate on the flow rate control side, and the restriction due to the controllable opening of the pressure control valve is greatly reduced.

[0010]

Embodiments will be described below with reference to the drawings.

FIG. 1 shows functional blocks of a discharge pressure control device according to an embodiment of the present invention. In this control device, the fluid discharged from the pump 10 to the main pipe 11 is supplied to a flow control loop including a plurality of zones. A part of the fluid flowing through the main pipe 11 is returned to the pump 10 through the pressure control valve 12. The main pipe 11 is provided with a pressure gauge 13,
The original pipe pressure measured by the pressure gauge 13 is equal to the pressure of the pressure controller 14.
And input to the pump discharge amount calculation unit 15. The pressure controller 14 generates a control signal for adjusting the opening of the pressure control valve 12 based on a deviation between a measurement pipe pressure input from the pressure gauge 13 and a discharge pressure set value described later. The pump discharge amount calculation unit 15
The discharge flow rate is calculated from the measured pipe pressure based on the discharge pressure-discharge flow rate characteristic of the pump 10 (hereinafter, referred to as “HQ characteristic”), and the calculation result is input to the pressure calculator 16.

In the flow control loop, the flow supplied to the zone is measured by the flow meter 17, and the measured flow value is input to the flow controller 18. This flow controller 18
A control signal for adjusting the opening degree of the flow control valve 19 is sent from the flow control valve 1 based on the deviation between the preset flow set value and the measured flow rate.
Enter 9

On the other hand, the respective measured flow rates of the flow meters 17 in the respective flow control loops are input to the adder 20, where they are added and then input to the pressure calculator 16. The pressure calculator 16 calculates the discharge pressure P of the pump 10 as P = {1.17 · (Q−F) / CV _min } ²

Calculated by the following calculation. In the above equation, Q is the pump discharge amount calculated by the pump discharge amount calculation unit 15, F is the total flow rate of the flow control loop calculated by the adder 20, and CV _min is the controllable pressure control valve 12. Minimum C
Each V value is shown. The pump discharge pressure calculated by the pressure calculator 16 is input to the function generator 21. The function generator 21 has a function of converting the output of the pressure calculator 16 that changes in an analog manner into a step-like change, and is provided with a hysteresis function to prevent hunting in a step portion. The pump discharge pressure subjected to such processing by the function generator 21 is input to the lower limit circuit 22 in which the maximum value of the required source pressure in the multiple flow control loop is set.

Further, in this embodiment, in each flow control loop, in order to obtain a source pipe pressure (required source pressure) required for securing a flow rate for each zone, each flow rate is set in the flow controller 18. The flow rate set value of the flow rate control loop is input to the required source pressure calculation unit 23. This required source pressure calculator 23
The required source pressure for each zone calculated in step 2 is the maximum value selection circuit 2.
4 is input. The maximum value selection circuit 24 inputs the maximum value from the input required source pressures to the lower limit circuit 22 as the required source pressure. The lower limit circuit 22 applies a limit when the output (the pump discharge pressure) from the function generator 21 is lower than the required base pressure input from the maximum value selection circuit 24, and the set value of the pump discharge pressure is equal to or lower than the required base pressure. Behave as if not. The output of the lower limit circuit 22 is input to the switch circuit 30 directly or via the hold circuit 25. The pump discharge pressure selected by the switch circuit 30 is input to the pressure controller 14 as the discharge pressure set value through the upper and lower limit circuit 26 in which an allowable range for protecting the pump is set.

An opening lower limit circuit 27 is provided between the pressure controller 14 and the pressure control valve 12.
The opening lower limit circuit 27 sets an allowable lower limit for pump protection, and applies a limit when the opening command falls below the lower limit. Further, the valve minimum opening check circuit 28 monitors the opening command value (control signal) MV given to the pressure control valve 12, and the opening command value MV falls below the minimum opening Z _min of the pressure control valve 12. Then, the switch circuit 30 is switched to the hold circuit 25 to hold the discharge pressure set value at the current value. Next, the operation of the present embodiment configured as described above will be described.

The discharge amount Q and discharge pressure P of the pump 10 are shown in FIG.
Are defined by the HQ characteristics shown in FIG. Discharge rate is pump 1
The sum of the flow returned to zero and the total flow in the flow control loop
You. The flow rate returned to the pump 10 is controlled by the pressure control valve 12.
And the pump discharge pressure. Pump 1
The flow rate f returned to 0 depends on the CV value of the pressure control valve 12 and the pressure control.
The pressure difference P between the inlet side and the outlet side of the drain valve 12 is related as follows.
There is a clerk. P = (1.17 · f / CV)^Two  Assuming that the discharge amount of the pump 10 is Q and the total flow rate is F, the pump
The flow rate f returned to is f = Q-F. The controllable minimum CV value of the pressure control valve 12 is CV
_minThen, the pump discharge pressure P becomes P = {1.17 · (Q−F) / CV, as described above._min｝^Two  Becomes

Therefore, in the present embodiment, the actual pump discharge amount Q is calculated by the pump discharge amount calculating section 15 from the original pipe pressure serving as the pump discharge pressure based on the HQ characteristic.
Calculates the total flow rate F of the flow control loop, and inputs the calculation results to the pressure calculator 16 to calculate the pump discharge pressure.

Here, since the pump discharge amount Q and the total flow rate F change over time, the pump discharge pressure P calculated by the pressure calculator 16 also changes. Fluctuation of the pump discharge pressure P (original pipe pressure) becomes a disturbance condition of the flow control loop. Therefore, even if the output of the pressure calculator 16 fluctuates, the output value fluctuates only in steps by the function generator 21.

On the other hand, the maximum one of the required pipe pressures for each zone calculated by the required source pressure calculation unit 23 is input to the lower limit circuit 22. As a result, a necessary flow rate is secured in all zones. Then, the pump discharge pressure P output from the function generator 21 is output to the switch circuit 30. When the pump discharge pressure P is smaller than the required pipe pressure selected by the maximum value selection circuit 24, the selected required pipe pressure is output as a discharge pressure set value. Then, the pump discharge pressure P output from the lower limit circuit 22 is input to the pressure controller 14 via the switch circuit 30 and the upper and lower limit circuit 26 as a discharge pressure set value. When the opening command value MV output from the pressure controller 14 falls below the minimum opening Z _min , the switch circuit 30 is switched to the hold circuit 25 side, and the pump discharge pressure before falling below the minimum opening Z _min. Is input to the pressure controller 14. In this way, the discharge pressure set value determined according to the fluctuating flow rate is set in the pressure controller 14 while being sequentially updated.

For example, in the case of a continuous casting facility, the set value of the cooling water flow rate varies greatly from 0 to the maximum flow rate according to the operation state. When the cooling water flow rate is zero, the pressure control valve 12 is fully opened, and the discharge pressure is kept constant. Then, depending on the operating conditions, the opening degree of the pressure control valve 12 decreases as the total flow value of the cooling water increases. Further, when the total flow rate value increases, the pressure control valve 12 falls below the minimum controllable opening and cannot be controlled.

In this embodiment, when the total flow rate F increases, the pump discharge pressure P (pressure setting value) set in the pressure controller 14 decreases, and the state changes from the state A shown in FIG. 2 along the HQ characteristic curve. Transition to state B. As a result, the discharge amount Q increases, the opening of the pressure control valve 12 increases, and does not fall below the minimum controllable opening. In the case where the total flow rate is reduced, the pressure control valve 12 can be prevented from exceeding the controllable maximum opening in the same manner.

As described above, according to the present embodiment, the optimum discharge pressure P is automatically calculated from the HQ characteristics of the pump 10, the total flow rate value, and the minimum controllable opening of the pressure control valve 12, and is set to the discharge pressure. Since the pressure is set in the pressure controller 14 to control the pressure of the main pipe 11, the restriction caused by the controllable opening of the pressure control valve 12 can be greatly relaxed, and the large fluctuation of the total flow value can be achieved. Can be adequately dealt with. Note that the present invention is not limited to the pump discharge pressure control of the cooling water, but can be applied to the air discharge pressure control by a blower.

[0024]

As described above in detail, according to the present invention, it is possible to sufficiently cope with a large fluctuation in the total flow rate on the flow control side, and to greatly reduce restrictions caused by the controllable opening of the pressure control valve. And a discharge pressure control device that can perform the control.

[Brief description of the drawings]

FIG. 1 is a functional block diagram of a discharge pressure control device according to one embodiment of the present invention.

FIG. 2 is a characteristic diagram showing an operation of one embodiment and HQ characteristics of a pump.

FIG. 3 is a functional block diagram of a conventional discharge pressure control device.

[Explanation of symbols]

Reference numeral 10: pump, 11: main pipe, 12: pressure control valve, 13:
Pressure gauge, 14: Pressure controller, 15: Pump discharge amount calculation unit, 16: Pressure calculator, 17: Flow meter, 18: Flow controller, 19: Flow control valve, 20: Adder.

Continuation of the front page (56) References JP-A-53-140486 (JP, A) JP-A-61-74015 (JP, A) JP-A-61-34370 (JP, A) (58) Fields investigated (Int) .Cl. ⁶ , DB name) G05D 16/00-16/20

Claims (1)

(57) [Claims] 1. A pump discharges a fluid to a main pipe at a predetermined discharge pressure, supplies the fluid to at least one flow control loop connected to the main pipe, and discharges the fluid to the main pipe. A discharge pressure control device that controls a discharge pressure by adjusting a degree of opening of the pressure control valve by taking a part of the fluid into the pump through a pressure control valve; Pump discharge amount calculating means for calculating the amount; total flow rate calculating means for calculating the total flow value of the fluid supplied to the flow control loop; pump discharge amount calculated by the pump discharge amount calculating means and the total flow rate calculating means a pump discharge pressure calculating means and a total flow rate value calculated in calculating the discharge pressure of the pump discharge pressure and the calculated in the pump discharge pressure calculation means
Equipped with a, and the pressure regulating valve control means for controlling the opening of the pressure regulating valve based on the Kan圧discharge pressure setpoint and before <br/> Kimotokan obtained from opening information of the pressure regulating valve A discharge pressure control device characterized by the above-mentioned.