JPH0576322B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Industrial Application Field The present invention relates to a method for controlling the concentration of sludge in a separation/sedimentation tank for slurry containing sedimentable substances.

This control method can be applied to white liquor settling tanks, green liquor settling tanks, lime mud washers, lime mud tanks, etc. in the causticizing process in kraft pulp production.

(B) Conventional technology and problems Figure 4 shows a conventionally known method for controlling the concentration of sludge in a sedimentation tank.

By detecting the torque of the rake 402 of the sedimentation tank with the torque detector 403, the inverter 40
The sludge concentration is controlled by adjusting the amount of sludge removed by controlling the rotation speed of the lime mud sludge pump 404 having a pump 404. It was difficult to control the sludge concentration stably by controlling the sludge concentration by detecting the overall torque.

(B) Means for Solving the Problems That is, the present invention provides a unit equipped with a DP cell that can perform fresh water purging by making a hole in the detector mounting part in order to detect the concentration of sludge in the sedimentation tank. A concentration detector consisting of a pipe is installed in the sludge drainage piping, and the output of the concentration detector is input to the control controller, and the inverter, which is the operating end, is used to control the rotation speed of the pump and adjust the flow rate of the sludge. to control the sludge concentration, while
In order to remove blockages caused by sediment in the DP cell, there is a periodic automatic cleansing program with clean water, and if the detected value is out of the set range, such as when the concentration detector is abnormal, or the sedimentation tank rake torque abnormal increase control is interrupted. The sludge concentration is controlled stably and inexpensively by an automatic sedimentation tank sludge concentration control method that has the function of maintaining the sludge flow rate at a constant value.

The DP cell used in the present invention can be a general-purpose type used as instrumentation equipment.

The DP cell installation piping may be a single pipe with wear resistance that takes into consideration the flow rate of waste mud.

It is desirable that the attachment part of the DP cell and piping be short, as waste materials tend to accumulate there and the concentration detection value is likely to be distorted. By making a hole from the outside of the DP cell mounting part and penetrating the flange into the inside and attaching fresh water piping to the DP cell for automatic cleaning on a regular basis,
It is possible to easily remove the accumulated sludge material.
It is preferable that the hole be oriented in a tangential direction rather than penetrating toward the center of the attachment part, as this will have a better effect of removing deposits of sludge material.

This periodic cleaning uses an automatic cleaning method in which a timer opens and closes an automatic valve to purge clean water, and the control operation output value is held during cleaning. Cleaning can also be performed manually.

To control the flow rate of sludge, an inverter device is used that controls the pump rotation speed by varying the motor's primary voltage and frequency. It is desirable to install a lower limiter to control the rotation speed so that the pump discharge pressure does not fall below the actual head of the equipment.

Diaphragm valves are used as sludge flow rate control devices.
Although a control valve such as a ball valve can be used, maintenance is problematic due to wear of the valve, so an inverter device that can control the flow rate without using a valve is preferable.

In addition, in order to avoid fluctuations in the amount of sludge discharged when the concentration detector shows an abnormal value due to a process problem, etc., the control device will prevent the indicated value of the concentration detector from falling outside the set range under control. If this happens, use a control device that incorporates a control device that stops control and holds the output, or sets it to a predetermined value and issues an alarm. This control device can be implemented with a digital one-loop controller incorporating a microprocessor.

(D) Example Next, according to the drawings, an example of a method for automatically controlling the sludge concentration in a lime mud sedimentation tank of white liquor in the causticizing process in the kraft pulp manufacturing process will be described.

FIG. 1 is a flow diagram of an embodiment of the invention.
Sludge from the lime mud sedimentation tank 101 is removed by the lime mud drainage pump 1.
08, the sludge is branched into a waste sludge sampling box 112 and a single pipe 103, each of which sends liquid to a lime washer.

The lime mud concentration from the lime mud concentration detector consisting of the DP cell 102 and the single pipe 103 and the torque from the rake torque detector 109 are input to the control controller 111, and the operation output value is given as the output reference of the inverter 107. , the rotation speed of the lime mud sludge pump 108 is controlled to adjust the flow rate of the sludge to control the sludge concentration.

Further, in order to ensure the minimum flow rate of sludge, a lower limit is provided for the operation output value of the controller 111.

The inverter 107 includes a lime mud drainage pump 1.
Set the minimum rotation speed so that the discharge pressure of 08 does not fall below the actual head of the equipment.

FIG. 2 shows the controller installed in the control controller 111.
It is a concentration adjustment flowchart.

Sludge concentration input 201, rake torque input 202
are compared with respective set values 203, 204 in the control controller.

If the lime mud concentration indication value is out of the upper and lower limits, the control is interrupted and the flow rate of waste mud is kept constant2.
05, and an alarm 206 is issued.

Also, if an abnormality occurs in the condition of the lime mud settling tank 101 and the rake torque rises above the setting, the control is interrupted, the flow rate of the sludge is maintained 205, and the alarm 2 is issued.
Emit 06.

This makes it possible to avoid sudden fluctuations in the flow rate of sludge when an abnormality occurs in the lime mud concentration detector or when an abnormality occurs in the state of the lime mud sedimentation tank 101.

FIG. 3 shows the controller installed in the control controller 111.
It is a DP cell periodic cleaning flow diagram.

To remove deposits on the DP cell mounting flange,
At each time set in the cleaning interval timer 301, switch the sludge flow rate to manual and start fresh water purge cleaning 3
05, the cleaning is continued 306, 307 for the time set in the cleaning timer, and after the time set in the cleaning timer, the cleaning is ended 308, 309, and the control is restarted 310.

The results of implementing this control method are as follows.
In other words, in a white liquor clarifier in the causticizing process of the kraft pulp manufacturing process, if the capacity is 335 m ² and it is a 4-stage type, the white liquor throughput is 51 m ² /H. If this control method is not introduced, the sludge concentration will decrease. The average value was 44.1 Baume and the standard deviation was 1.6 Baume, but as a result of introducing this control method, the average value of Baume for sludge removal was 46.9 Baume.
The standard deviation was 0.5 double Baume. DP
There are almost no cell sensor problems.

Effects of the Invention As a result of implementing the present invention in the white liquor clarifier during the causticizing process of the kraft pulp manufacturing process, the dispersion of the sludge concentration was reduced and the sludge concentration was increased, resulting in an increase in the white liquor recovery rate. This improved the cleaning efficiency of the next step, the lime washer, and contributed to an increase in the causticizing process capacity. In addition, the detection value is stable by adopting a periodic automatic cleaning method for the DP cell.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the implementation of a method for automatically controlling sludge concentration in a lime mud settling tank. Figure 2 is a block diagram showing the implementation of the lime mud sludge concentration adjustment flow. Figure 3 is DP
FIG. 3 is a block diagram showing the implementation of an automatic cell cleaning flow.
FIG. 4 is a diagram showing a conventional settling tank sludge concentration control method. 101...Lime mud sedimentation tank, 102...DP cell,
103...Single pipe, 104...DP cell attachment part, 1
05... Fresh water piping, 106... Automatic opening/closing valve, 10
7... Inverter, 108... Lime mud drainage pump, 109... Rake torque detector, 110...
Rake motor, 111...Control controller, 112...
... Sludge sampling box, 401... Lime mud sedimentation tank, 402... Rake, 403... Rake torque detector, 404... Lime mud drainage pump, 40
5... Inverter, 406... Sludge sampling box, 407... Rake motor.

Claims (1)

[Claims] 1 DP to be cleaned regularly on the sludge drainage piping of the sedimentation tank
A concentration detector using a cell is installed, and the pump rotation speed is controlled by the output of the concentration detector to adjust the flow rate of sludge to control the sludge concentration, and the sludge concentration detector is set within the set range. A settling tank waste sludge concentration control method characterized in that when the sedimentation tank rake torque is out of range, or when settling tank rake torque increases abnormally, the waste sludge flow rate control is interrupted to maintain the waste sludge flow rate at a constant value.