FI69707B - DIRECTIVE PROCESSING OF FIBER GLASS MECHANICAL MASSOR - Google Patents

Description

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(51) Kv.lk.4 / lnt.CI. * G 01 N 15/06 (21) Patent application - Patentansöknlng 801 * 177 (22) Application date - Ansökningsdag 07.05.80 (EN) (23) Starting date - Giltighetsdag 07-05.80 (41) Made public - Blivit offentiig 09-11 .80

Patent * and National Board of Registration Date of display and publication— 29-11.85

Patent- och registerstyrelsen '' Ansökan utlagd ooh utl.skrlften publicerad (32) (33) (31) Requested privilege — Begärd prloritet 08-05-79

Canada (CA) 3271 ^ + 6 Proven-Styrkt (71) Domtar Inc., P.O. Box 7210, Montreal, Quebec, Canada (CA) (72) Alkibiadia Karnis, Dollard des Ormeaux, Quebec,

This invention relates to a method and apparatus for the direct control of the physical properties of mechanical pulp. (7 * 0 Berggren Oy Ab (5 * 0 Direct control of the fiber length of mechanical pulps) More particularly, the invention relates to a method and apparatus for directly determining the weight distribution and / or center fiber length of a mechanical pulp fiber length, and to a method and apparatus for directly determining the consistency of a pulp slurry substantially without other fiber properties.

Mechanical pulps means pulps produced primarily by mechanical treatment, with or without chemical or physical auxiliary steps. These masses are e.g. conventional grinding wheels or grinding fibers and pulps obtained by various chemimechanical and thermomechanical processes.

For example, U.S. Patent 3,802,964 discloses that fiber properties such as the center surface area, and in particular the center fiber length, are important in determining the properties of paper made from the pulp. Medium fiber length is very important in predicting 2 69707 tensile, puncture, tear, and wet web strengths. It also affects the scattered reflection coefficient (opacity). The fiber length distribution, on the other hand, is important for tear strength, because in general, for a given average fiber length, it is true that the wider the distribution, the greater the tear strength. However, there are no direct methods available for determining the mean fiber length and fiber length distribution, and such determinations have only been possible in the laboratory.

In U.S. Patent 3,873,416, it has been proposed to determine the L-factor (defined as the total amount of pulp remaining on the 48-mesh screen of the Bauer-McNett fiber length classifier, expressed as weight percent of the feed) or weight-average fiber length by weight ratio of fraction passed or residue to feed. However, as noted above, there are no methods available to directly determine the weight distribution of the fiber length of a mechanical pulp.

Today, consistency meters used in the pulp and paper industry measure consistency indirectly, i.e., they measure other properties of the pulp, such as flow resistance, dielectric properties of the pulp slurry, etc. These properties are related to the consistency as well as other properties of the fiber.

It has been proposed to measure the consistency mainly independently of other pulp properties using the Sperry Gravity Master (see Management & Control, No. 1, 11.11.1968, pp. T179-T186), which guarantees the accuracy of the consistency in the range of 0.4-1.5% of the measured in the range of consistency 12-3%. The operation of this instrument is based on a method of continuously measuring the weight of a stock flowing through a pipe of a given volume.

Thiessen and Dagg (Pulp & Paper Magazine of Canada, September 1959) have also proposed measuring consistency by recording vibrations resulting from unbalanced rotor rotation, whereby the degree of imbalance is determined by the weight difference between a given amount of water and the same amount of pulp slurry.

Neither of the above devices has proven to be commercially satisfactory. Today, no instrument is known by which the consistency of the pulp 3 69707 could be measured directly, essentially independently of the other properties of the pulp.

It is an object of the present invention to provide a method and apparatus for directly determining the weight distribution of the average fiber length and / or fiber length of a mechanical pulp.

Another object of the invention is to provide a method and apparatus for directly determining the absolute value of consistency.

In general, the present invention relates to a method and apparatus for determining the weight distribution of a mechanical pulp fiber length, wherein the pulp is separated into two streams, the fiber flow rate of each of said streams is measured, each stream is divided by a screen device into a residual fraction and a passed portion. the dividing screen device and the device includes means for measuring the amount of fiber of one selected residual fraction and one selected passed fraction for each split stream, and determining, based on said amounts and the cumulative weight fraction and the cumulative normal distribution ratio of fiber length as a percentage of feed, the cumulative weight of the initial flow.

The present invention also relates generally to a method for measuring the consistency of a pulp slurry, wherein the pulp slurry is continuously passed through a tube, preferably a substantially U-shaped tube, the tube is continuously mechanically vibrated as said slurry flows therethrough, the tube oscillation frequency is continuously measured.

Other features, objects, and advantages of the invention will become apparent from the following detailed description of preferred embodiments of the invention with reference to the accompanying drawings, in which Figure 1 schematically illustrates process control of the invention, Figures 2 and 3 are diagrams showing cumulative residual distribution of various pulps as a percentage of feed probability paper 11a, Fig. 4 is a schematic cross-section of a density cell; 69707 Fig. 5 schematically shows a density cell adapted to indicate consistency; Fig. 6 shows the correlation the consistency of the masses compared to the meter output in millivolts.

As shown in Figure 1, the mechanical pulp sample taken from the process enters the system via line 10 and, depending on the pulp production point from which the sample is taken, passes through the latency removal device 12 and enters the tank 14 via line 16.

A suitable principle for releasing the latent properties of mechanical pulp relatively quickly is used in a laboratory apparatus sold by Noram Quality Control and Research Equipment Ltd. This device releases the latent properties of the mechanical pulp so that the pulp is rapidly circulated through a centrifugal pump (at a pulp temperature of about 90-95 ° C).

The pulp from the tank 14 is pumped through the pump 18 to the consistency meter 20 and returned to the tank 14 via the line 22.

A consistency meter used in a direct monitoring system is required to measure consistency independently of other fiber properties (i.e., fiber length and specific surface area) and to be able to measure absolute consistencies with an accuracy and repeatability of + 5% of the measured consistency. Thus, in the consistency meters used in the present invention, the principle of determining the consistency must be straightforward, i.e., it must be based on the assay consistency.

When measuring consistency using densitometers, it is essential that the sample is substantially airless or free of air and significant amounts of foreign matter, or alternatively that there is no air in the sample and that the contaminants (fillers, etc.) in the fibers are known before the consistency can be determined. define. It is also important that the temperature is precisely controlled or known, because a change in temperature changes the accuracy of the instrument, although the instrument can be calibrated for different temperatures.

Such a consistency meter shown in Figure 4 comprises a density cell 200 with a U-tube 201 through which the pulp sample passes. This U-tube is vibrated by a suitable mechanism, schematically shown at 202, around the nodes marked at 204. Suitable temperature and frequency register devices are provided, as shown at 206 and 208 in Figure 5, respectively, and the output of these devices is fed to a converter 210, which in turn feeds a tape recorder 212 or similar device indicating the consistency of the pulp.

The density cell 200 used to obtain the results presented herein is a "Dynatrol" cell sold under the tradename C1-10H and manufactured by Automation Products, Houston, Texas. This device is used to measure the density of samples. However, when used on a pulp with a consistency range of about 0.1-1.5%, it has been found to give an indication of the absolute consistency of the pulp, which corresponds to the accuracy required to obtain a length distribution of the fibers.

The above-mentioned "Dynatrol" cell was used to measure the consistency and gave the results shown in Fig. 6, i.e., the output of the meter corresponded very reproducibly to the consistency based on five repetitions with the same grind. Figure 7 also shows the accuracies for different types of chemical pulps, abrasives and hot mills.

It is found that the consistency meter of the present invention gives a relatively accurate reading of the absolute consistency.

When using the device, it is important that the stock is diluted with substantially impurity-free water to the measurement consistency, otherwise the final reading of the consistency meter may be affected by impurities in the dilution water. Thus, when the present invention is applied to e.g. hot milling, the pulp is diluted from the relatively high consistency it has when leaving the refiner to a consistency within the operating range of the density cell by adding substantially impurity-free water rather than circulating water, etc. , that when significant amounts of substantially free of dilution water are used, the consistency measurement will be very accurate.

The operation of the consistency meter is relatively simple because the stock diluted to the consistency required by the density cell, thus having a consistency of 0.1-1.5%, is continuously fed through the U-tube 201, the U-tube is vibrated by device 202, and the frequency of vibrations is determined by sensor 208. This information is fed to a converter 210, which in turn uses a recorder 212 or other suitable detector. Although the instrument used has a U-tube, the shape of the tube could possibly be changed with other suitable modifications to the equipment.

R2, the coefficient of determination for the consistency diagram and for the meter output diagram in Figures 6 and 7, respectively, is equal to about 0.99, which clearly shows a very accurate correlation between the consistency and the meter reading.

If it is desired to determine the density of the pulp slurry above said 1.5%, at least a portion of the slurry must obviously be diluted to said range using fresh water, the amount of fresh water added being noted and used to calculate the consistency of the pulp based on the measured consistency.

In any case, the consistency meter 20 measures the consistency of the stock in the tank 14 and preferably controls the addition of water through the line 24 via the control valve 26 so that the consistency of the stock in the tank 14 remains substantially constant. The consistency meter 20 is connected to the valve 26 by a control line 30 and to the main controller 28 by a line 32. If the consistency in the tank 14 is always kept constant, the control line 32 can be omitted because it is not variable in the system.

The stock in the tank 14 is recycled through the pump 34 and line 44 to fiber length monitoring means 48 including a distributor 50 with two strainers with different aperture sizes (mesh sizes), as shown at 52 and 54.

69707

The screen 52 is fed from line 44 via line 56 at a constant feed rate controlled by a flow meter 58 which, as shown, controls valve 62 via line 60. Processing of this flow meter 58 may also be directed to main controller 28 via line 64. However, if the flow of line 56 is kept constant, apparently the supply to main controller 28 via line 64 can be omitted.

Likewise, the pulp flows into the screen 54 through line 66, preferably at a constant rate controlled by a flow meter 68 connected to valve 72 by control line 70. Flow meter 68 is also connected by line 74 to main controller 28, but this control line 74 may be omitted if flow in line 66 occurs at a fixed rate.

In the arrangement shown, the filters passed through the two screens 62 and 64 are connected and fed through line 76 to line 78, which returns the pulp to the system. The fractions remaining on the screens 52 and 54 are measured by a consistency meter 80 and a flow meter and a consistency meter 84 and a flow meter 86, respectively, and then fed through lines 88 and 90, respectively, to line 78. 86 is connected to the main controller 28 by lines 96 and 98, respectively.

In the mediators shown, two residual fractions of the screens are measured. If desired, the two passed fractions can be kept separate and these fractions can be measured instead, or a combination of passed and residual fractions can be measured (i.e., the fraction passed through one sieve and the residual fraction from the other sieve).

For example, the screen sizes of the screens 52 and 54 may be 41 mesh and 35 mesh. Other combinations and sieve sizes may also be used, but care must be taken in selecting the size of the sieve, because if too large a mesh size is used, the fibers may tend to wrap around the sieve and give unacceptable results. If, on the other hand, too small a screen size is used, the sensitivity of the instrument is considerably reduced. In general, the screen size should be selected from 30 to 50 mesh, preferably from 35 to 45 mesh.

The amount of pulp remaining in the 41707 mesh screen can be related to the R-48 fraction of the Bauer-NcNett sorter, which determines the L-factor of the pulp. This has been found to be a useful measurement in determining the properties of a given mass. The mass remaining on the 35-mesh screen can be related to the R-28 fraction of the Bauer-McNett sorter.

Relationships have been obtained by developing a regression equation based on experimental results for a 41-mesh target (WF) 41 = L + B (R-48) C + AC2 1 and likewise for a 35-mesh target (WF) 35 = 11 + B1 (R-28) C + A1C2 2 where L, B, A and, B "*", AF are constant and C is the consistency of the stock and WF is the weight fraction of the respective sieve.

For a given consistency, Equations 1 and 2 can be written (R-48) = K (WF) 41 + P 3 and (R-28) = K1 (WF) 35 + P1 4 where K, K1, P, P ^ · again signify experimentally defined constants. The weight fractions of the 41- and 35-mesh sieves are measured by calculating the consistency and flow rate of each such residual fraction relative to the flow and consistency of the pulp fed to the sieves.

In addition, it has been found that a cumulative normal probability distribution ratio exists between the cumulative residual fractions as a percentage of feed and fiber length (as determined by Tasman Pin Vol. 55 No. 1 January 1972) obtained from the fiber length classification results of the Bauer-McNett sorter. Four different pulps were dispensed with a conventional Bauer-McNett laboratory dispenser and the results were plotted on cumulative normal probability paper, with Figure 2 showing the cumulative residual fraction as a percentage of feed relative to fiber length. Closed triangles are the points defined for the first ground, open triangles are the points defined for the second ground, closed circles are the points defined for the first hot mill, and open circles are the points defined for the second hot mill.

9 69707

The diagrams are very accurate straight lines, and thus the determination of any two points on either curve accurately determines the fiber length distribution of the pulp over a substantial range, including the average fiber length, which is 50% of the longer fibers and 50% of the shorter fibers.

Although only four pulps are labeled on paper, several pulps have been tested in Figure 2 and all have resulted in similar straight lines. However, if the pulp contains too much fine material (-200 mesh), the straightness ratio may not be maintained at the lower end of the lines.

To test other results, there are mass fractions as defined in "Characterization of Mechanical Pulps".

Pulp & Paper Magazine of Canada, 1963, Forgacs, similarly drawn on normal probability paper, resulting in clearly straight lines (see Figure 3).

The fiber length distribution can therefore be obtained from these results.

The weight fractions (WF) in Equations 1 and 2 can be calculated if the fiber flows to the fractionators are known or kept constant by flow meters 58 and 68 and the consistency and flow of the residual fractions are measured at 80 and 82 for sieves 52 or 84 and 86 for sieves 54 in WF = CF rr

Via CfFf, where WF is equal to the weight fraction C 1 and F 2 is equal to the consistency and flow of the fibers flowing to the screens 52 and 54 and C 1. and Fr are the consistency and flow of the residual fraction of the screen 52 or 54.

Using the above ratios, the input of various meters to the main controller 28 can be used to determine the fiber length characteristics of the pulp, including fiber length distribution, average fiber length, L-factor, etc., which can be shown in appropriate tables on the display panel 100.

The invention may be modified without departing from the spirit of the invention as defined in the appended claims.

Claims (7)

A method for linearizing the weight-based fiber length distribution in a pulp, characterized in that it comprises feeding the pulp in two streams, measuring the amount of the streams, fractionating each of the streams with screen means in a retaining chamber and a transmitted one. screen fraction, wherein the screen means for one of the two flows has a different mesh width than the screen means for the other flow, measuring the amounts of each of either the retained or transmitted screen fraction for each screen member, and determining the fiber length distribution in the pulp on the basis of the quantities of the measured fractions, the mesh widths of the screening means, the two flow rates and the cumulative normal distribution ratio between fiber length and cumulative residual fraction as a percentage of the input flow. 2. A method according to claim 1, characterized in that the two flows are substantially the same. Method according to claim 2, characterized in that the quantities of the selected fractions are measured by measuring the concentration and flow rate of the selected fractions. 4. Device for linear determination of the weight-based fiber length distribution in a pulp, characterized by means (34,62, 72) for feeding the pulp in two flows, means (58,68) for measuring