CA2007715A1

CA2007715A1 - Method for controlling a chip refiner

Info

Publication number: CA2007715A1
Application number: CA 2007715
Authority: CA
Inventors: Aslak Savonjousi
Original assignee: ABB Stromberg Teollisuus Oy
Current assignee: ABB Stromberg Teollisuus Oy
Priority date: 1990-01-12
Filing date: 1990-01-12
Publication date: 1991-07-12

Abstract

(57) ABSTRACT OF THE DISCLOSURE

This publication discloses a method for controlling a chip refiner. According to the method, chips are metered into a chip refiner with the help of metering means (10, 9), feeder means (3, 7) adapted to the chip refiner are used for feeding chips between refiner disks (5) for refining, and water is added to the chips prior to feeding them between the refiner disks (5). In accordance with the invention, input power to the feeder means (3, 7) is measured, and using conventional methods, the volume of chip stock metered to the feeder means (3, 7) is controlled with the help of metering means (10, 9) so as to regulate the input power to the feeder means (3, 7) to constant level.

(Figure 1)

Description

s Method for controlling a chip refiner The presen-t invention relates to a method for controlling a chip refiner in accordance with the preamble of claim 1.

In prior-art implementations, chip stock has been fed into the chip refiner at a constant rate. secause of the variations in the chip stock consistency and chip size, this method is incapable of producing refined stock at a constant quality.

Known in the art are also controlled systems in which chip stock is fed using a variable-speed motor~ In one of these methods, feed rate is controlled by regulating the input power to the chip refiner from the power source to a constant level. Even if a constant load by- the refiner on the power source is maintainedj uneven quality of the refined stock will result, due to variations in chip stock consistency and moisture content. In another method using control means, chip stock is fed lnto the chip refiner at controllable set rate by measuring the output rate and refined stock consistency from the chip refiner, computing the product of these measure-ment variables which is relative to mass flow rate, and the obtained mass flow rate is used as the input variable for the control loop of the input feed rate. Because of the technical difficulties in deriving the value of the mass flow rate, the control response of the method is rather slow. Consequently, an unsatisfactory quality of refined stock results therefrom~

The aim of this invention is to overcome the disadvantages of prior-art methods described above and to achieve a novel method for the control of a chip refiner.

The invention is based on measuring the drive power level of the auger feeding the chip refiner and controlling this power to a constant level by regulating the chip stock feed rate to the chip refiner~

More specifically, the system in accordance with the invention , . :, . :.:
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is characterized by what is stated ln the characterizing part of claim 1.

The invention provides outstanding benefits.

By way of measuring the input power to the dxive motor of the feeder auger in order to obtain a measureme.nt value for the density of the chip stock to be refined, a control method for the regulation of chip stock consistency in the refiner gap to a constant value is achieved that is superior to those used in prior-art methods, because the control variable is immediately available.

The invention is next examined in detail with the help of an exemplifying embodiment illustrated in the attached drawings~

Figure 1 shows in a diagrammatic form a control system in accordance with the invention, Figure 2 shows in a diagrammatlc form another control system in accordance with the inventionO

According to Fig. 1, the chip stock to be refined is brought to the refining plant with the help of a conveyor 1. The chips are fed and metered by means of a metering feeder 9 driven by a metering motor 10 into a feeder bin 2 of the refiner, from where they are further fed by means of a feeder auger 3 driven by a feeder motor 7 into the, gap between the refiner disks 5. Either in the feeder bin 2, i.n the feeder auger 3 or between the gap of the disks 5, water is added to the chips by a volume controlled by a controller 4. Between the disks 5 the chips are ground into refined stock and the developed steam propels the re~ined stock forward via a control valve 6 of the refined stock flow. The purpose of the control valve 6 is to maintain a constant steam pressure level in the refiner. In addltion to internal losses, the eeder motor 7 is loaded by forces imposed by the chips on the feeder auger 3.
Because density variations in fed chip stock tend to cause changes in produced refined stock quali ty, the input power to .

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the feeder motor 7 is measured in a conventlonal manner by means of a measurement equipment 8, whlch is connected to the power input of the feeder motor 7 and whose measurement signal is entered to a control unit 11 of -the metering motor 10. The control unit 11 controls the speed of the metering motor 10 so that a decrease in the input power of the feeder motor 7 produces an increase in the speed of the metering motor 10, and vice versa.

The following example clarifies a typical case of control performance.

Prior to a disturbance in chip stock consistency, the signal level of motor current, which is proportional to the input power, was measured with the measurement equipment 8 to be ?.6 A. At the onset of a density disturbance, the input power representing signal had attained a level of 2.3 A. With the help of control measures performed in the conventional manner by the controller 11, the feed rate of the eeder means was elevated so much that the input power representing signal attained a value of ~.57 A. In the prevailing test conditions, this corrective action can be considered to have an acceptable accuracy. The freeness of the produced refined stock was measured from a few samples prior to the onset of the distur-bance to be 342...350 CSF. At the onset o~ the disturbance, a drop to 320 CSF in freeness was detected, which through the control measures was quickly corrected to a level of 338...348 CSF as measured again from a few samples. The referred values proof the validity of method in function. Using a better trimmed system, even more accurate results are possible.

As shown in Fig. 2, two or more refiners can be connected in tandem.

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Claims

1. A method for controlling the feed rate of a chip refiner, in which method - chip stock is metered by chip stock metering means (9, 10) for refining in a refiner, - chip feeder means (3, 7) arranged to the refiner (5) are used for feeding chips for refining between the refiner disks (5), and - water is added to the chips prior to feeding between the refiner disks (5), c h a r a c t e r i z e d in that - the power input to the feeder means (3, 7) is measured and - on the basis of the measured input power, the quantity of chip stock to be metered to the feeder means (3, 7) is controlled with the help of metering means (10, 9) in a conventional manner so that the input power to the feeder means 13, 7) is regulated to a constant level.

2. A method in accordance with claim 1, c h a r a c t e r-i z e d in that at a decreasing tendency of input power to the feeder means (3, 7) is compensated by increasing the metered chip stock volume with the help of the metering means (10, 9).

3. A method in accordance with claim 1, c h a r a c t e r-i z e d in that the metering of chip stock feed is continu-ously controlled with the help of a continuous power measure-ment.

4. A method in accordance with claim 1, c h a r a c t e r-i z e d in that the metering of chip stock feed is controlled in a short-term cyclic manner with the help of repetitive power measurement performed at short intervals.