JPH01132891A - Screening apparatus - Google Patents

Abstract

PURPOSE: To regulate the flow rate to a proper reject flow rate according to a change in operating conditions such as the composition, concentration, temperature and feed flow rate of a paper stock by detecting a value of pressure loss of a screen cylinder and regulating the reject flow rate while controlling the change in the outlet flow rate to the minimum. CONSTITUTION: Signals from a pressure sensor 13 in an inlet part for a paper stock and a pressure sensor 14 in an outlet part are converted into signals corresponding to the pressure loss of a screen cylinder 5 with a converter 15, stored in a memory with an arithmetic and control unit 16 and evaluated. The reject flow rate is regulated while controlling a change in outlet flow rate from the value of the pressure loss and the tendency of the change to the minimum based on a control algorithsm.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a pressure-type screen zero-contamination chamber applied to the process of 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 a paper stock inlet 1 at the top, as shown in FIG. Selected stock outlet 2 and resect outlet 3 at the bottom
A casing 4 having a casing 4, a screen cylinder 5 having a round hole or an elongated slit-like hole (hereinafter referred to as an aperture) inside the casing 4, and a screen cylinder 5 that rotates at a small distance from the surface of the screen cylinder 5. The screen cylinder 5 is comprised of a cleaning device 6 which serves to remove foreign matter captured by the screen cylinder 5 and keep the surface of the screen cylinder 5 clean.

The cleaning device 6 has a main shaft 71 and a pulley 8 on the main body side. V-belt9. It is connected to a motor 11 via a motor side pulley 10.

The purpose of using such a pressure screen for paper stock is to capture and remove foreign substances such as plastics, bound fibers, and undisintegrated pieces in the paper stock on the surface of the screen cylinder 5, and at the same time to remove high-quality fibers efficiently. It is often passed through an aperture in a screen cylinder. Therefore, in order to prevent clogging of the screen cylinder openings due to foreign matter or fiber aggregates (flocs) in the paper stock, it is necessary to continuously remove foreign matter and flocs captured on the surface of the screen cylinder 5 from the resect outlet 3. 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 is changed by the opening degree of the reject valve 12, but since changing the reject flow rate also changes the outlet flow rate accordingly, which is unfavorable for operation, data on operation using similar stock and operation using a test machine are used. Based on this, in order to ensure long-term stable operation, a slightly higher reject flow rate is set, taking into consideration 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 (valve opening) for the conventional pressure screen mentioned above is set based on the most severe operating conditions expected for the pressure screen during the operation period. Add another 10-
The reject flow rate is selected with a margin of 20%. The reject flow rate selected in this manner is generally not changed unless there is a major change in operating conditions or a malfunction of the pressure screen such as clogging of the screen cylinder occurs.

This type of operation often results in operating at a retract flow rate that is higher than the required flow rate to accommodate the operating conditions of the pressure screen. The problem is that the amount of good quality fibers escaping from the resect outlet increases, greatly reducing efficiency. On the other hand, if the operating conditions of the pressure screen become more severe than expected, the screen cylinder openings will be blocked by foreign matter or flocs in the paper stock due to insufficient retract flow, and the pressure screen will become inoperable. Not only that, but it also has the extremely serious problem of interrupting the operation of the entire subsequent system such as the paper machine.

[Means for solving problems]

The present invention provides a means for solving the above-mentioned problems, and includes a pressure sensor provided at the inlet and outlet of the paper stock of the pressure screen;
A conversion means converts and transmits the pressure measurement value signal of the pressure sensor into a pressure loss value of the screen cylinder, and a control algorithm set in advance based on the output signal from the conversion means is used to control the change in the outlet flow rate to a minimum while reducing the reject flow rate. It is an object of the present invention to provide a sieving device characterized in that it is equipped with arithmetic control means for adjusting the sieving device.

[Effect]

Since the present invention is configured as described above, it has the following effects. Generally, the pressure loss value of the screen cylinder of a pressure screen is an important index for determining the operating state of the pressure screen. In other words, if the pressure loss value is relatively low and there is little fluctuation, there is no risk of blockage during operation, and if the pressure loss value is relatively high and the fluctuation is large, there is a tendency to gradually increase. If this is the case, there is a high possibility that the screen cylinder is becoming increasingly clogged, and if the pressure loss value shows an abnormally high value, it is possible to detect an operating condition such as a hole in the screen cylinder being blocked.

Therefore, the present invention is configured to detect the pressure loss value of this screen cylinder, and adjust the inlet flow rate based on the control algorithm based on the pressure loss value and the tendency of change so that the outlet flow rate does not change. By changing the opening degree of the reject valve and adjusting the reject flow rate to a value suitable for the operating conditions at that time, it is possible to operate a pressure screen with improved stock yield υ, and This prevents interruptions in the operation of subsequent systems such as the most important paper machine, making it possible to achieve long-term stable operation.

〔Example〕

A sieving device according to an embodiment of the present invention will be explained with reference to FIG. Note that the reference numerals 1 to 12 in the figure are the same as in FIG. 4, and the explanation thereof will be omitted. In the figure, 13 is a pressure sensor at the inlet of the stock, 14 is a pressure sensor at the outlet, and 15 is a pressure sensor 13. A conversion device for generating a signal corresponding to the pressure loss value due to passage of the paper stock through the screen cylinder 50 using the signal from the same 14; 16 corresponds to the signal corresponding to the pressure loss value and the outlet flow rate from the flow rate detector 17; an arithmetic and control device that simultaneously receives a signal to set the amount of change in the reject flow rate and the corresponding amount of change in the inlet flow rate;
8 is a reject control valve for changing the reject flow rate;
19 is an inlet control valve for changing the inlet flow rate.

Next, the operation of the above configuration will be explained. Pressure sensor 13
．． The signal from the same 14 is corrected by the converter 15 for the pressure loss occurring in the flow path from the pressure detection part to the screen cylinder 5, the difference in position head between the pressure detection parts, etc., and is a signal corresponding to the pressure loss of the screen cylinder 5. is converted to For example, the pressure measured by the pressure sensor 13 is Pat, the pressure measured by the pressure sensor 14 is the outlet flow rate of Tori 1 paper stock, QA is
-If the proportionality constant is C,, C, then the pressure loss of screen cylinder 5: △P is △P"' (Po Pt) Cs Cz・QA"
−・−−・・(1). Here, the proportionality constant C1 corresponds to a correction term that does not depend on the outlet flow rate QA, such as the position head difference of the detection part, and q corresponds to the outlet flow rate QA, such as the friction loss of the flow path.
This corresponds to a correction term proportional to . In the case of a normal pressure screen, the third term on the right side of equation (1) is the first term. Since it is sufficiently small compared to the second term, △P” (Po Pt) CI・・・−・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・(2
), there is no problem in practical use. Of course, if the third term on the right side of equation (1) cannot be ignored due to the structure of the pressure screen, etc., a flow rate detector 17 such as an electromagnetic flowmeter is used as shown in FIG.
It is necessary to input a signal corresponding to the outlet flow rate of the paper stock into the converter 15 to obtain a signal proportional to the pressure loss value of the screen cylinder 5 using equation (1). The signal corresponding to the pressure loss value from the conversion device 15 is taken into the arithmetic and control device 16 and simultaneously stored in a memory at regular time intervals. A reference level is preset in the arithmetic and control unit 16 to be compared with an input signal corresponding to a pressure loss value, and the magnitude (level) of the input signal is evaluated. for example,
If the input signal is larger 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, while referring to the flow rate signal from the flow rate detector 17, a change in the outlet flow rate is minimized. A setting signal for the inlet control valve 19 is output using the following control algorithm. In this state, when the input signal from the conversion device 15 becomes lower than the reference level corresponding to an abnormality, the setting signal that has been used to increase the reject flow rate is canceled.

Conversely, when the input signal from the conversion device 15 is smaller than the reference level corresponding to normality (when the reject flow rate has increased more than necessary), a setting signal for the reject control valve 18 that slowly decreases the reject flow rate; Outputs a setting signal for the outlet control valve that minimizes the change in the outlet flow rate. When the input signal from the conversion device 15 returns to the reference level corresponding to normality from this state, the setting signal for reducing the reject flow rate up to that point is canceled. As for the input signal from the conversion device 15, 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.

Reference levels are determined based on operational experience and operating data from test machines, but in practice, the number of reference levels is not limited to two, normal and abnormal, but can be any number depending on the characteristics of the pressure screen and operating conditions. That's fine.

Next, the evaluation of the trend in the pressure loss value of the screen cylinder 5 can be basically achieved by mutually 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 by processing these amounts of change using an appropriate averaging method, the trend of the pressure loss value can be determined. A value is required.

If this trend value is positive, it indicates that the pressure loss value is increasing, and if it is larger than the preset reference level of the trend value corresponding to an abnormality, a setting signal to slowly increase the resect flow rate and an outlet Outputs a setting signal that minimizes the change in flow rate. When the trend value becomes less than the reference level from this state, the setting signal that has been used to increase the reject flow rate is canceled.

Conversely, if the trend value is negative and greater than the reference level, a setting signal that slowly decreases the reject flow rate and a setting signal that minimizes the change in the outlet flow rate are output, and when the trend value becomes less than the reference level, the setting signal is released. do.

The above are the basic functions of the arithmetic and control unit 16, 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 a pump drive device 21 having a variable speed function such as a DC motor is used to rotate the stock supply pump as an adjustment means to minimize changes in the outlet flow rate. It changes the number.

〔Effect of the invention〕

Since the present invention is configured as described above, it has the following effects. i.e. in the form of a pressure screen.

The reject flow rate is adjusted according to the operating conditions at that time so that the pressure loss value of the screen cylinder falls within a preset range according to the structure and application.

As a result, it achieves long-term stable operation, and at the same time adjusts the reject flow rate to an appropriate amount in response to changes in operating conditions such as stock composition, concentration, temperature, and supply flow rate, which solves the problem of conventional pressure screens. Point (1): If there is a significant change in operating conditions, the screen cylinder openings will become clogged, making it impossible to operate, and the operation of subsequent systems such as the paper machine will be interrupted. (2) Solving problems such as a large amount of high-quality fibers in the paper stock escaping from the J-Sekt outlet.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical cross-sectional view of a sieving device according to an embodiment of the present invention, FIG. 2 is a schematic vertical cross-sectional view of another embodiment of the present invention, and FIG. 3 is a schematic vertical cross-sectional view of another embodiment of the present invention. A schematic longitudinal cross-sectional view of
Figure 4 is a schematic diagram of the conventional example, (a) is its longitudinal cross-sectional view, (b)
) is its plan view. l...Entrance, 2...Exit, 3...Resect exit,
4...Casing, 5...Screen cylinder, 6
... Purifier, 12... Reject valve, 13... Pressure sensor (inlet part), 14... Pressure sensor (outlet part)
, 15... Conversion device, 16... Arithmetic control device, 17
...Flow rate detector, 18...Reject control valve, 19.
...Inlet control valve, addition...supply pump, 21...pump drive device. Agent Patent Attorney Akatsuki Sakama 2 famous birds 1 Figure 2m Figure 3

Claims (1)

[Claims] a pressure sensor provided at the inlet and outlet of the paper stock of the pressure screen; a conversion means for converting and transmitting a pressure measurement value signal of the pressure sensor into a pressure loss value of the screen cylinder;
1. A sieving device comprising: arithmetic control means for adjusting a retract 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.