JPH01156588A - Screening apparatus - Google Patents

Abstract

PURPOSE: To provide a screening device capable of preventing the generation of a trouble and carrying out a safe operation by controlling a reject flow rate so as to give a preset screen transmission rate or a reject concentration rate corresponding to the formation, structure and use of a pressure type screen. CONSTITUTION: This screen device is used by detecting fiber concentrations at the paper material inlet 1 and exit 2 or reject exit 3 of a pressure type screen, converting the detected concentration signals into a fiber transmission rate or a reject concentration rate, controlling the change in flow rate at the exit to the minimum value according to a preliminarily set control algorithm on the basis of the output signals outputted from the conversion means, and simultaneously adjusting the opening of the reject valve 18 to control a reject flow rate to a value suitable for an operation condition at the time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pressure screen umbrella applied to a process for removing foreign matter from papermaking raw materials.

[Conventional technology]

A pressure-type screen, which is conventionally well known as a paper pulp sieving device, has an upper fIs as shown in FIG.
A casing 4 having an inlet 1 for K paper stock, an outlet 2 for selected stock and a resect outlet 3 at the bottom, and a screen cylinder 5 provided with round holes or elongated slit-shaped holes (hereinafter referred to as openings) inside the casing 4. , as well as screen cylinder 5
The cleaning device 6 rotates at a small distance from the surface of the screen cylinder 5 and serves to remove foreign matter trapped on the surface of the screen cylinder 5 and keep the surface of the screen cylinder 5 clean. The cleaning device 6 includes a main shaft 7, a pulley 8 on the main body side, and a belt 9. It is connected to a motor 11 via a motor side pulley 10.

The purpose of using such a pressure-type screen for paper stock is 1. Foreign matter such as plastics, bound fibers, and undisintegrated pieces in the paper stock is captured on the surface of the screen cylinder 50 and removed, and at the same time, high-quality fibers are efficiently screened. The purpose is to pass through the opening in the cylinder. For this reason, in order to prevent clogging of the screen cylinder openings due to foreign matter or fiber lumps (flocs) in the paper stock, the foreign matter and flocs captured on the surface of the screen cylinder 5 are continuously removed from the resect outlet 3. If necessary, the paper stock descends along the screen cylinder 5 and is discharged from the resect outlet 3 in the form of concentrated stock containing a large amount of foreign matter.

This reject flow rate changes depending on the opening degree of the reject valve 12, but if the reject flow rate is changed, the outlet If also changes accordingly, which is not favorable for operation. Based on this, in order to ensure stable operation over a long period of time, a slightly higher reject flow rate is set, taking into account the expected fluctuations in operating conditions during the operation period.

[Problem that the invention seeks to solve]

In order to ensure long-term stable operation, the reject flow rate setting (pulp opening degree) in the conventional pressure screen described above is
In addition to the resect flow lid, which assumes the most severe operating conditions of a pressure screen during the operation period, one additional
Rizek) [The amount is selected with a margin of 0-20%. The resect weight thus selected is generally not changed unless there is a significant change in operating conditions or a malfunction of the pressure screen such as clogging of the screen cylinder occurs.

In many cases, such operation results in operation at a reject flow rate that is excessive compared to the required reject flow rate that can correspond to the operating conditions of the pressure pump IJ.

For example, just before supplying to a paper machine, the amount of good fibers in the paper stock that escapes from the resect outlet increases.

There was a problem that efficiency was greatly reduced. Also.

On the other hand, if the operating conditions of the pressure screen become more severe than expected, the openings in the screen cylinder will be blocked by foreign matter or flocs in the paper stock due to a shortage of 61 tons of retract, resulting in the pressure screen not being able to operate. There was an extremely serious problem in that it not only caused problems, but also disrupted the operation of the entire subsequent system such as the paper machine.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention provides concentration sensors provided at the inlet and outlet of the paper stock or the resect outlet of the pressure screen; A conversion means for converting and transmitting a resect g reduction ratio; and an arithmetic control means for adjusting the reject flow rate while minimizing changes in the outlet flow rate using a control algorithm set in advance based on an output signal from the conversion means. This paper proposes a sieving device featuring the following characteristics.

[For production]

The present invention has the following effects by taking the above measures. In general, the fiber passage rate, which is expressed as the ratio between the outlet concentration and the population concentration of the pressure screen, and the resect concentration rate, which is expressed as the ratio between the resect concentration and the inlet 8 degrees, are both important indicators for determining the operating condition of the pressure screen. becomes. In other words, if the fiber passage rate is relatively high and there is little variation, or if the resect concentration rate is relatively low and there is little variation, then the operating state is safe from clogging, and the fiber passage rate is relatively low and there is little variation. If the width tends to increase or gradually decrease, or if the resect concentration rate is relatively high and the fluctuation width increases or gradually increases, the screen cylinder is becoming clogged. There is a high possibility that you have. Also, I#1. When the fiber passage rate shows an abnormally low value or when the resect concentration ratio shows an abnormally high value, it is possible to detect an operating condition such as a blockage of the openings of the screen cylinder.

Therefore, by detecting the fiber concentration at the inlet and outlet or resect outlet, and based on the value and change tendency of the fiber passage rate or resect concentration rate obtained by conversion, the outlet flow rate can be determined based on the control algorithm. By adjusting the inlet a amount so that it does not change, it is possible to operate the pressure screen with improved paper stock yield, and most importantly, to prevent interruptions in the operation of subsequent systems such as the paper machine, and to avoid long-term problems. Stable operation can be achieved.

〔Example〕

An embodiment of the present invention will be explained with reference to FIG. Reference numerals 1 to 11 in the figure are the same as those in FIG. 7, so their explanation will be omitted. Reference numeral 13 denotes a concentration sensor at the inlet of the stock, 14a a concentration sensor at the outlet, 15a a conversion device for generating a signal corresponding to the fiber passage rate using the signals from the concentration sensors 13 and 14a, and 16a a fiber an arithmetic and control device that receives and receives a signal corresponding to the passage rate and a signal corresponding to the outlet flow rate from the IT detector 17, and simultaneously outputs a setting signal for the amount of change in the reject flow rate and the amount of change in the population IT accompanying it; Reference numeral 18 is a resect control valve for changing the resect flow rate, and 19 is an inlet control valve for changing the population flow rate. The concentration sensors 13 and 14a output concentration signals proportional to the fiber concentration, and various concentration sensors such as optical type, ultrasonic type, radiation type, and fluid friction loss type have been put into practical use. It is selected depending on the characteristics such as the fiber in the material and the amount added, as well as the concentration range.

Next, the operation of the above configuration will be explained.

The signals from the concentration sensors 13, 14 & are sent to the converter 15.
It is converted into a signal proportional to the fiber passage rate at a. In other words, the concentration at the inlet measured by the concentration sensor 13 is expressed as CI%.
If the concentration at the outlet measured by the concentration sensor 14a is OA, then the fiber passage rate has the following relationship: KA=CA/Cr (1). Signal conversion is performed using equation (1).

In addition, when there is almost no change in the concentration of the supplied paper stock during the operation period, the fiber passage rate KA is proportional to the concentration Oh K at the outlet, so the concentration sensor 13 at the inlet is
can be omitted. In this case, the conversion device 15a
Then, the arithmetic and control unit 16aK fits 5! Converts 11 signals.

A signal corresponding to the fiber passage rate from the conversion device 15a is taken into the arithmetic and control device 16a and simultaneously stored in a memory at regular time intervals. The arithmetic and control device 16a has a reference level preset for comparison with an input signal corresponding to the fiber passage rate, and evaluates the magnitude (rail) of the human power signal from the conversion device fff15a.

For example, if the input signal is smaller than a reference level corresponding to an abnormality, a setting signal for the reject control valve 18 that rapidly increases the reject flow rate is output, and at the same time the flow rate detector 17 is output.
With a control algorithm that minimizes the change in the outlet flow rate while referring to the cliff signal from.

A setting signal for the inlet control valve 19 is output. From this state,
When the input signal from the conversion device fli 15a becomes equal to or higher than the reference level corresponding to an abnormality, the setting signal for increasing the reject Rfk up to that point is canceled.

Conversely, if the input signal from the converter 1f15a is even higher than the reference level corresponding to normality (if the reject flow rate has increased more than necessary), the reject control valve 18 that slowly decreases the reject i (i) Outputs a setting signal and a setting signal for the outlet control valve that minimizes the change in the outlet flow rate.When the input signal from the converter [15a] returns to the reference level corresponding to normality from this state, the reject flow rate up to that point is output. Cancel the setting signal to be reduced.Conversion device N15
As for the input signal from a, in order to avoid excessive fluctuations in the setting signal, it is desirable to perform averaging processing using the signal value stored in the memory based on the current input signal. The reference level is determined based on operational experience and operational data from test machines, but in practice, the number of reference levels is not limited to two, normal and abnormal, but can be set arbitrarily depending on the characteristics of the pressure screen and operating conditions. The number is sufficient.

Next 1cf; #L Evaluation of the change trend in the fiber passage rate can basically be carried out by mutually comparing signal values stored in the memory at prescribed time intervals. For example, subtract the last memorized signal value from the current human input signal value ~
- The trend value of the fiber passage rate can be obtained by storing the values in the memory as the amount of change and processing these amounts of change using an appropriate averaging method.

If this trend 9 value is negative, it indicates that the fiber passage rate is on the decline, and if this value is smaller than the preset reference level of the trend 9 value, which corresponds to an abnormality, the resect flow rate should be adjusted. Output a setting signal that increases slowly and a setting signal that minimizes the change in the exit it. When the trend 9 value becomes equal to or higher than the reference level from this state, the setting signal for increasing rezek)fil& is canceled.

On the other hand, if the trend 3 value is positive and larger than the reference level, a setting signal that slowly decreases the reject flow rate,
A setting signal that minimizes the change in the outlet flow rate is output, and the setting signal is canceled when the trend 9 value becomes less than the reference level.

The above are the basic functions of the arithmetic and control unit 16a, but in implementation, arbitrary combinations and modifications can be made depending on the characteristics and operating conditions of the pressure screen. Further, various display, recording, and alarm functions will not be explained, but can be incorporated as appropriate. FIG. 3 shows another embodiment in which the feed pump of one stock is controlled by a pump drive 21 with variable speed capability, such as a DC motor, as a regulating means to minimize changes in the outlet flow rate. It changes the rotation speed.

In all of the above embodiments, control was carried out based on the fiber passage rate. Next, an embodiment in which control is carried out based on the resect concentration rate will be described with reference to FIG. 4. The same parts in the figure as in FIG. 1 are given the same symbols and the explanation will be omitted. In FIG. 4, reference numeral 14b is a concentration sensor at the resect outlet, and like the concentration sensors 13 and 14a, various concentration sensors that have been put into practical use are used to determine the characteristics and concentration range of the fibers in the stock, the amount added, etc. You can choose accordingly.

Further, tsb is a conversion device for generating a signal corresponding to the resect concentration rate using the signals from the concentration sensors 13 and 141), and 16b corresponds to the signal corresponding to the resect concentration rate and the outlet am from the flow rate detection 1517. This is an arithmetic and control device that simultaneously outputs a setting signal for the amount of change in i(&) and the amount of change in the inlet flow rate accompanying it.

Next, the operation of the above configuration will be explained.

The signals from the concentration sensors 13 and 14b are sent to the conversion device 15.
In step 1), it is converted into a signal proportional to the resect concentration rate.

That is, if the concentration at the inlet measured by the concentration sensor 13 is CI, and the concentration at the resect outlet measured by the concentration sensor 141 is OR, then the resect concentration rate KR is KR=OR/CI... ... Since the relationship is (2), the conversion device 151) converts the signal according to (2) 2.

In addition, if there is almost no change in the concentration of the supplied paper stock during the operation period, the resect concentration rate KR is equal to the concentration OR
Therefore, the concentration sensor 13 at the inlet can be omitted as illustrated in FIG. In this case as well, the conversion device 15t) converts the concentration signal so as to be compatible with the arithmetic and control device 161).

A signal corresponding to the resect concentration rate from the conversion device 151) is taken into the arithmetic and control device 16b, and simultaneously stored in the memory at prescribed time intervals. A reference reference for comparison with an input signal corresponding to the resect concentration rate is preset in the arithmetic and control unit 161), and the conversion device t5b
Evaluate the size of the human input signal from

For example, if the human input signal is larger than a reference level corresponding to an abnormality, a setting signal for the reject control valve 18 is output that rapidly increases the reject flow rate, and at the same time the flow rate detector 17 is output.
The setting signal for the population control valve 19 is output using a control algorithm that minimizes the change in the outlet it while referring to the fftit signal from the fftit signal. In this state, when the human power signal from the conversion device f15b becomes lower than the reference level corresponding to an abnormality, the setting signal for increasing the reject flow rate up to that point is canceled.

Conversely, when the human power signal from the converter 15b is smaller than the reference level corresponding to normality (when the resect flow rate has increased more than necessary), it is set as a setting signal for the resect control valve 18 that slowly decreases the resect flow rate. , outputs a setting signal for the outlet control valve that minimizes the change in the outlet flow rate. When the human power signal from the conversion device 15b returns to a reference level corresponding to normality from this state, the setting signal for reducing the reject weight up to that point is canceled. The input signal from the conversion device tsb is also subjected to averaging processing using the signal value stored in the memory based on the current input signal in order to avoid excessive fluctuations in the setting signal, as in the previous embodiment. is desirable. In this embodiment as well, the reference level is determined from operational experience and operational data from a test machine, but in implementation, the number of reference levels is not limited to two, normal and abnormal.
Any number may be used depending on the characteristics of the pressure screen and operating conditions.

Next, the change tendency (trend 1) of the resect concentration rate can also be evaluated by basically comparing the signal values stored in the memory at prescribed time intervals. for example,
The value obtained by subtracting the signal value stored immediately before from the current input signal value is stored in memory as the amount of change, and these amounts of change are processed using an appropriate averaging method.
The trend of ffl shrinkage rate "l'i (i) is determined.

If this trend value is positive, it indicates that the resect concentration rate is increasing, and if this value is larger than the preset reference level of trend 0 value corresponding to an abnormality, it indicates that the resect concentration rate is increasing. Outputs a setting signal that slowly increases the output flow rate and a setting signal that minimizes the change in the outlet flow rate. When the trend value becomes less than the reference level from this state, the setting signal for increasing the reject flow rate up to that point is canceled.

Conversely, if the trend value is negative and larger than the reference level, a setting signal that slowly decreases the reject flow rate,
A setting signal that minimizes the change in the exit at is output, and the setting signal is canceled when the trend value becomes less than the reference level.

The above are the basic functions of the arithmetic and control unit [16b], but as in the above embodiments, arbitrary combinations and modifications can be made depending on the characteristics and operating conditions of the pressure screen. Similarly, explanations of various display, recording, and alarm functions are omitted, but they can be incorporated as appropriate.

FIG. 6 shows another embodiment in which, like the embodiment of FIG. 3 above, a variable speed function such as a DC electric car is used as a means of adjustment to minimize changes in the outlet flow cover. The pump driving device @B changes the rotation speed of the stock supply pump.

〔Effect of the invention〕

According to the present invention, the resect flow rate is adjusted according to the operating conditions at that time so that the screen fiber passage rate or the resect concentration ratio falls within the preset range of the screen fiber passage rate or resect concentration rate according to the type, structure, and application of the pressure screen. adjusted.

As a result, stable operation can be achieved over a long period of time, and the reject flow rate can be adjusted to an appropriate level in response to changes in operating conditions such as stock composition, concentration, temperature, and supply flow rate, which eliminates the problems of conventional pressure screens. (1) If there is a significant change in the operating conditions, the screen cylinder openings will become clogged, causing the screen cylinder to become inoperable and the operation of subsequent systems such as the paper machine will be interrupted. Problems such as the large number of high-quality fibers will be solved.

[Brief explanation of the drawing]

1 to 6 are schematic cross-sectional views showing mutually different embodiments of the present invention, and FIG. 7 is a schematic view of an example of a conventional sieving device (at is a plan view thereof, (tel is a longitudinal section thereof). 1. Population; 2. Outlet; 3. Reject outlet; 4. Casing; 5. Screen cylinder; 6. Cleaning device; 13, 14a,
14b...Concentration sensor* 15 a + 15 b
・"Conversion device; 16a, 16b... Arithmetic control device; 17... Flow rate detector; 18... Reject control valve; 19... Inlet control valve; Addition... Supply pump; 21.
...Pump drive device.

Claims (1)

[Claims] Concentration sensors provided at the inlet and outlet of the stock or the resect outlet of the pressure screen; conversion means for converting and transmitting the concentration measurement signal of the concentration sensor into a fiber passage rate or resect concentration rate; A sieving device characterized by comprising arithmetic control means that adjusts a retract flow rate while minimizing changes in the outlet flow rate using a preset control algorithm based on an output signal from the conversion means.