FI83240B - Method for controlling a refiner - Google Patents

Description

83240

The present invention relates to a method for adjusting a trowel according to the preamble of claim 1.

In previous solutions, wood chips have been fed to a grinder at a constant speed. Because the density and piece size of the introduced chips vary, it is not possible to achieve a uniform grind in this method.

Adjustable systems are also known in which the chips are fed by an adjustable motor. In one such solution, the feed rate is adjusted so that the power taken by the grinder from the network is kept constant. Although the power taken by the grinder ..... from the mains is constant, the grinder ... becomes uneven due to variations in chip density and moisture. In another adjustable solution, the chips are fed to the grinder at a constant speed set so that the outlet flow and its consistency of the grinder are measured, a product of the measured values is generated, from which the mass flow value is obtained, and the obtained mass flow value is used as a feed rate control variable. Because the generation of the mass flow value is technically difficult and slow, the method used is: Y: the control rate is quite slow. In this case, the quality of the pulp is naturally unsatisfactory.

It is an object of the present invention to obviate the disadvantages of the above-described technique and to provide a completely new type of method for adjusting a grinder.

The invention is based on the fact that the power of the feed screw feeding the grinder is measured and kept constant by adjusting the feed of the chips to the grinder.

More specifically, the method according to the invention is characterized by what is set forth in the characterizing part of claim 1.

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The invention provides considerable advantages.

When measuring the power of the feed motor to measure the density of the chips to be ground, the density of the chips to be ground in the refiner slot can be better stabilized than before, because the control variable is immediately available.

The invention will now be examined in more detail by means of an application example according to the accompanying drawings.

Figure 1 schematically shows one control system according to the invention.

Figure 2 schematically shows another control system according to the invention.

According to Figure 1, the wood chips to be ground are introduced into the grinder: by conveyor 1. The chips are fed and dispensed by means of a feeder 9 rotated by the metering motor 10 into the pre-chamber 2 of the refiner, from where the feed screw 3 rotated by the feed motor 7 In the pre-chamber 2 or in the feed screw 3 or in the blade gap 5, the amount controlled by the regulator 4 is added. Between the blades 5, the chips are ground into a pulp mass and the generated steam drives forward through the mass control valve 6. The purpose of the control valve 6 is to keep the vapor pressure constant. In addition to the idle losses, the feed motor 7 is also loaded by the forces exerted by the chips on the feed screw 3. Since the variation in the density of the chips to be ground causes a variation in the quality of the chips, the power of the feed motor 7 is measured in a manner known per se by a measuring device 8 connected to the feed device 7 of the feed motor 7. 10 speeds are increased and vice versa.

A typical adjustment event is described below by way of example.

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Prior to the density disturbance, the signal proportional to the feed power measured by the measuring device 8 was 2.6 A. When the density disturbance occurred, the signal proportional to the feed power had decreased to 2.3 A. Due to the control operation of the controller 11 known per se, This can be considered as a satisfactory accuracy under the experimental conditions. The freeness level of the resulting pulp before disturbance ranged from 342 to 350 CSF based on a few measured samples. In the event of a density disturbance, the freeness level dropped to 320 CSF, but the adjustment soon corrected to 338 to 348 CSF, which were obtained from a few measured samples. The values mentioned are an indication that the method works. Of course, with better trimmed equipment, even better results can be achieved.

According to Figure 2, there may be two or more grinders; connected in series.

Claims (4)

1. A method for controlling the feed to a refiner, according to which method - by means of metering means (9, 10), chips are metered to a refiner for refining, - by means of feeding means (3, 7) arranged adjacent to the refiner, the chip is measured. refining between refiner blades (5), and - - water is added to the chip before being measured between *: * ·: refiner blades (5), characterized in that - the power absorbed by the feeding means (3, 7) is measured, and - on the base of the measured effect is regulated by: and known per se by the dosing means (10, 9) the amount of chips dosed into the feeding means (3, 7), so that the effect taken by the feeding means (3, 7) remains to the size constant. *: ··: 2. A method according to claim 1, characterized in that the feed of the wood is increased by the dosing means (10, 9) when the effect of the feeding means seeks to decrease. 3. A method according to claim 1, characterized in that the dosage of the chip quantity is controlled continuously on the basis of continuous power measurement. 4. A method according to claim 1, characterized in that the dosage of the chip quantity is controlled for short periods on the basis of short-term power measurement.