JPH05331790A - Device for controlling level of white water-recovering pit - Google Patents

Abstract

PURPOSE:To effectively stabilize the white water level of a white water- recovering pit. CONSTITUTION:When the rotation speed-operating amount of a polydisk filter outputted from a rotation speed controller is not contained within a prescribed mid-range, a mid-range calculating section adds a correction value for recovering the white water level of the white water-recovering pit to the target flow control value of a flow controller, and the new value is added to the flow controller as a new flow control target value to control the flow rate of the white water in the white water recovering pit level controller. Thus, two independent control systems are combined by the introduction of the mid-range calculation section to control the level of the white water-recovering pit as a control section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white water recovery pit level control device in a paper pulp manufacturing plant.

[0002]

2. Description of the Related Art Generally, in a white water recovery pit in a paper pulp manufacturing plant, it is necessary to maintain a constant white water level in the pit in order to stabilize the pulp concentration.
A control device for controlling the level of the white water recovery pit has been conventionally provided. This white water recovery pit level control device is a rotation speed control unit for the poly disc filter, a flow control valve for fresh water flowing into the white water recovery pit, and a flow control for white water flowing out from the white water recovery pit and supplied to the poly disc filter. The valve and the flow rate control unit that simultaneously controls the flow rate characteristic are used, but conventionally, the rotation speed control unit and the flow rate control unit are individually controlled. That is, in order to achieve the same purpose of keeping the level of the white water recovery pit constant, the two control systems output independent results without being influenced by the states of the control systems of the other party.

[0003]

However, in such a conventional white water recovery pit level control device as described above, when determining control parameters such as a rotational speed target value and a flow rate target value,
The effect of two control systems on the plant must be taken into consideration, and there is a problem that the parameter settings are complicated, and when one control system exceeds its capability, the other control system must be operated manually. For example, there was a problem that the plant could not be stabilized and the operator was burdened.

The present invention has been made in view of the above-mentioned conventional problems, and with the mutual help of the control systems, the operator's intervention operation can be reduced, and the stability of the plant can be automatically achieved in a wide range. An object is to provide a pit level control device.

[0005]

The white water recovery pit level control device according to the present invention comprises a rotation speed control section for controlling the rotation speed of a poly disc filter which regulates the flow rate of white water flowing into the white water recovery pit, and the white water recovery pit. The flow rate control section for controlling the flow rate control valve for fresh water and the flow rate control valve for white water flowing out from the white water recovery pit and supplied to the poly disc filter at the same time by using the polygonal line characteristic, and the rotation speed control section output. When the rotational speed manipulated variable is outside the predetermined mid-range, the flow rate control target value of the flow rate control unit is added with the correction amount in the direction in which the white water level in the white water recovery pit is recovered, and the flow rate is set as a new flow rate control target value. It is provided with a mid-range computing section to be given to the control section.

[0006]

In the white water recovery pit level control device of the present invention, the rotation speed of the poly disk filter is controlled by the rotation speed control unit to regulate the flow rate of white water flowing into the white water recovery pit so that the white water level in the white water recovery pit is constant. In parallel with this, the flow rate control valve of fresh water flowing into the white water recovery pit and the flow rate control valve of white water flowing out of the white water recovery pit and supplied to the poly disc filter are broken line characteristics. The amount of fresh water that flows into the white water recovery pit and the amount of white water that flows out into the poly disc filter are controlled by the flow rate control unit that controls the white water level in the white water recovery pit at a constant level.

When the rotational speed operation amount of the poly disc filter output from the rotational speed control unit is out of a predetermined midrange, the midrange computing unit sets the white water in the white water recovery pit as the flow control target value of the flow control unit. A correction amount in the direction in which the level recovers is added and given to the flow rate control unit as a new flow rate control target value to control the inflow and outflow amount of white water.

In this way, the two independent control systems are combined by introducing the mid-range computing section, and one control system is used to perform the level control of the white water recovery pit.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a circuit block diagram of an embodiment of the present invention. On the equipment plant 1 side, a white water recovery pit 1 is provided.
1. A poly disk filter 12 for circulating the white water in the white water recovery pit 11, a fresh water inflow control valve 13, a white water outflow control valve 14, and a circulation pump 15 which are controlled to open and close in parallel at the same time by the broken line characteristic are provided. There is. The white water recovery pit 11 is provided with a level sensor 16 for detecting the white water level.

As shown in detail in FIGS. 1 and 2, on the control device 2 side, a rotation speed control device 21 for controlling the rotation speed of the poly disc filter 12, a fresh water inflow control valve 13 and a white water outflow amount. The flow rate control device 22 that controls the valve opening degree with the control valve 14 at the same time using the broken line characteristic, and the rotation speed manipulated variable MV1 output by the rotation speed control device 21 has a predetermined midrange MH to ML (MH> ML). Outside, ie MV
When 1 ≧ MH or MV1 ≦ ML, the flow control device 22 is added as a new flow control target value by adding the correction amount in the direction in which the white water level of the white water recovery pit 11 is recovered to the flow control target value of the flow control device 22. And a signal conversion device 24 that performs digital conversion of signals from the equipment plant 1 side and analog conversion of output signals.

The rotation speed control device 21 uses the level target value SV1 given from a level setter (not shown) as an actual level signal PV from the level sensor 16 of the white water recovery pit 11.
And PID calculation to perform rotation speed control signal MV1
Is provided.

The flow rate control device 22 adds the flow rate target value correction amount ΔSV output from the midrange computing device 23 to the flow rate target value SV2 given from a flow rate setting device (not shown), and an adder 22a. Subsequent flow rate target value (SV
2 + ΔSV) is compared with the actual level signal PV to perform a PID calculation to obtain a control amount, and a PID calculation unit 22b for determining the control amount and a fresh water inflow control valve 1 for the output of the PID calculation unit 22b
3, the control amount MV2, M of each white water outflow control valve 14
The broken line characteristic graphs 22c and 22d for outputting V3 are provided.

Next, the operation of the white water recovery pit level control device having the above configuration will be described.

In the white water recovery pit 11, a circulation pump 15
Causes white water to circulate through the poly disc filter 12,
Here, a part of the white water is filtered according to the number of rotations thereof, transferred to a clear pit (not shown), and the rest is returned to the white water recovery pit 11.

The adjustment of the white water level in the white water recovery pit 11 is performed by controlling the rotation speed of the poly disc filter 12, the fresh water inflow control valve 13 and the white water outflow control valve 1.
It is performed by controlling the valve opening degree of No. 4.

Normally, the level signal PV of the level sensor 16 of the white water recovery pit 11 is fed back to the rotation speed control device 21 and the flow rate control device 22, respectively.

Therefore, on the side of the rotation speed control device 21, PI based on the deviation between the rotation speed target value SV1 and the actual level signal PV.
The D control calculation is performed and the rotational speed increasing / decreasing manipulated variable MV1 is output.

On the side of the flow rate control device 22, PID control calculation is performed based on the deviation between the target flow rate value SV2 and the actual level signal PV to obtain the flow control reserve amount, and based on this, the polygonal line characteristic graphs 22c and 22d are used to control the valve. Open / close operation amount MV
2 and MV3 are obtained, and these are given to the fresh water inflow amount control valve 13 and the white water outflow control valve 14, respectively, and the fresh water supply amount and the white water circulation amount are controlled to control the white water level to a constant amount.

However, when the manipulated variable MV1 by the rotational speed control device 21 exceeds a preset midrange, the midrange computing device 23 obtains a flow rate correction value ΔSV, which is used as a flow rate target of the flow rate control device 22. The value is added to the value SV2 to obtain the final target value, the PID calculation based on this is performed, and the flow rate is controlled.

This mid-range correction operation will be described with reference to the flowchart of FIG. 3 and the timing chart of FIG. 4. The mid-range given to the mid-range arithmetic unit 23 is MH to ML (MH> ML), and the rotation speed control is performed. When the manipulated variable MV1 from the device 21 exceeds this midrange, a timer is started (steps S1, S
2) If TM1 continues to deviate from the mid range for a certain period of time (step S3), it is determined that the control capability of the rotation speed control device 21 is over, and the flow control device 22 needs assistance, The flow rate correction ΔSV is obtained by the range computing device 23. That is, the departure direction is ML ≧
In the case of MV1, the correction amount ΔSV is set to ΔSV1 (negative value), and when the departure direction is MV1 ≧ MH, the correction amount ΔSV is set to ΔSV2 (positive value), and the correction amount ΔSV1 or Δ
SV2 is sent to the flow rate control device 22, and the flow rate control device 22 adds this correction amount ΔSV1 or ΔSV2 to the normal flow rate control target value SV2 to obtain the final flow rate control target value, and performs PID control calculation based on this to perform flow rate control. Valve 13,1
The valve opening degree 4 is controlled (steps S4 to S7).

Then, a delay of TM2 is given for a fixed time in order to see the effect of changing the white water level by this one-time correction (steps S8 and S9).

Thereafter, the correction amount ΔSV is set to 0, it is again judged whether or not the rotation speed correction amount MV1 is within the midrange, and if there is a deviation, the flow control target value SV2 is set according to the direction.
If it is within the midrange, the mitt range correction function is stopped until the next departure (step S1).
0, S11).

In this way, when the white water level in the white water recovery pit 11 exceeds the control capability of the poly disc filter 12, the white water level control amount is increased by the flow rate control to cover the white water level for artificial operation. By reducing the amount, the white water level is quickly controlled and stabilized to reach the target level.

Incidentally, the range of mid range MH to ML, 1
Size of correction amount ΔSV for each time, timer time TM1, TM
Parameters such as 2 are experimentally determined according to the size and capacity of the plant and are not particularly limited.

[0026]

As described above, according to the present invention, when the rotational speed operation amount of the poly disc filter output by the rotational speed control unit is out of the predetermined midrange, the midrange computing unit operates as the flow control unit. Since the flow rate control target value is added with the correction amount in the direction in which the white water level in the white water recovery pit is recovered and given to the flow rate control unit as a new flow rate control target value, the inflow and outflow amount of white water is controlled. Now, the rotation speed control and the flow rate control are performed independently of each other, but when necessary, the white water level can be controlled by complementing them, and the white water level is quickly stabilized at the target level. Can be controlled.

[Brief description of drawings]

FIG. 1 is a circuit block diagram of an embodiment of the present invention.

FIG. 2 is a detailed circuit block diagram of a control system in the above embodiment.

FIG. 3 is a flowchart showing the operation of the above embodiment.

FIG. 4 is a timing chart illustrating the operation of the above embodiment.

[Explanation of symbols]

 1 Equipment Plant 2 Control Device 11 White Water Recovery Pit 12 Poly Disc Filter 13 Fresh Water Inflow Control Valve 14 White Water Outflow Control Valve 15 Circulation Pump 16 Level Sensor 21 Rotation Speed Control Device 22 Flow Control Device 23 Mid-range Computing Device 24 Signal Converter 22a Adder 22b PID calculator 22c, 22d Broken line characteristic graph PV Actual level signal MV1 Rotation speed control amount MV2 Fresh water flow control amount MV3 White water flow control amount ΔSV Flow control correction amount SV1 Revolution speed target value SV2 Flow control target value

Claims (1)

[Claims] 1. A rotation speed control unit for controlling the rotation speed of a poly disc filter that regulates the flow rate of white water flowing into the white water recovery pit, a flow rate control valve of fresh water flowing into the white water recovery pit, and an outflow flow from the white water recovery pit. And a flow rate control unit for simultaneously controlling the flow rate control valve of white water supplied to the poly disc filter by using a polygonal line characteristic, and the rotation speed operation amount output by the rotation speed control unit is outside a predetermined midrange. In addition, the flow rate control unit is provided with a mid-range calculation unit that adds a correction amount in a direction in which the white water level of the white water recovery pit is restored to the flow rate control target value to give a new flow control target value to the flow rate control unit. White water recovery pit level control device.