FI67587B - SAETT OCH ANORDNING FOER ATT KONTINUERLIGT AOSTADKOMMA MAETNING AV L-FAKTORN HOS EN PAPPERSMASSASUSPENSION - Google Patents

Description

'- ». L'JI Γα1 M4. Public notice of publication

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Canada (CA) 99380 (71) Domtar Limited, 395 de Maisonneuve Blvd. West, Montreal 101,

Quebec, Canada (CA) (72) Otto L. Forgacs, Baie D'Urfe, Quebec, Alkibiadis Karnis, Dollard des Ormeaux, Quebec, Canada (CA) (74) Berggren Oy Ab (54) Method and apparatus for pulp suspension L-factor to achieve continuous measurement - Sätt och anordning för att kontinuerligt ästad-komma mätning av L-faktorn hos en pappersmassasuspension (62) Divided by application 3391/71 (patent 55091) -Avdelad frän ansökan 3391/71 (patent 55091)

The invention is directed to a method for providing a continuous measurement of the L-factor of a pulp suspension. The invention further relates to a device for applying this method.

The length factor, also referred to as the L-factor, means the sum of the percentages of fibers in the mechanical pulp that remain in the 14, 28, and 48 mesh screens of the Bauer-McNett splitter, essentially as defined in: O.L. Forgacs, Pulp & Paper Magazine of Canada, 64C 1963, page 189.

The method according to the invention is characterized in that the flow and consistency of the pulp suspension are measured and the pulp suspension is fed to a raw material separation screen, where the pulp is divided into a fraction remaining in the sieve and a fraction passed thereafter, after which the flow and consistency of at least one fraction are measured. the ratio of the weight to the weight of the solids in either fraction or to the weight of the solids remaining in the sieve, which value is a measure of the L-factor of the mass.

67587

The device according to the invention is characterized by a raw material distribution screening device comprising a self-cleaning screen cloth, a device supplying a pulp suspension to the self-cleaning screen cloth to divide the pulp into the fraction remaining in the screen and the fraction passing through it, and a calculating device for calculating the L-factor.

A known laboratory method for measuring the weight-average fiber length of a mechanical pulp is the use of a Bauer-McNett splitter screening device. Based on the fiber length sorting results obtained with this device, such as sieves with certain mesh values, namely a 28 mesh sieve, between 28-48 mesh and percentages between 48-100 mesh, approximate complete fiber length distribution curves can be generated for any mechanical pulp. (OL Forgacs, The Characterization of Mechanical I-ul.ps, PPRIC, 1963, Appendix B.) It has been found that the fiber length distribution curve associated with any given weight-average fiber length is more or less constant for pulps made with by any particular method of making mechanical pulps. This meant that the fiber length could be described quite accurately by one figure, and on this basis a simplified method for determining the weight-average fiber length was developed. This method determines the total weight of the mass remaining in the 48 mesh screen, the so-called length factor, i.e. L, which is sufficient to measure the weight-average fiber length of the pulp with sufficient accuracy. For the present invention, a practical method for continuously measuring the L-factor has now been developed in which a stream of fibrous slurry of known exact consistency (preferably of the order of 0.4-1.5%) is directed against a screen with a suitable mesh value in a vertical position, thus dividing the pulp into two fractions. , with the long fiber fraction remaining in the sieve and the short fiber fraction passing through the sieve. The fraction remaining in the sieve is collected and its weight is determined. Under constant conditions, e.g., at a given νϊ ^ 3μ3ηορθηάθ1ΐ3, at a given temperature, etc., the ratio of the weight of fibers remaining in the screen to the weight of fibers fed (or, alternatively, the weight of fibers passed through the screen to the weight of fibers fed) is a function of weight-average fiber length; and thus this ratio can be used to determine the value of the corresponding L-factor, or if desired, the ratio can be used instead of the L-factor as a numerical value representing 3,67587 weight-average fiber length. In any case, it is obvious that the amount of fibers remaining in the screen and consequently said ratio are also affected by other pulp slurry properties and process conditions such as the consistency and flow rate of the fed pulp slurry.

The device is described in more detail in the accompanying drawing, in which reference numeral 60 denotes a self-cleaning screen made of nylon and placed inside the box in a self-cleaning windy preferred position, preferably vertically. The pulp suspension or slurry is fed through a line 61 where its flow can be controlled by a valve 62 and measured by a flow meter 64, and the slurry is sprayed against a screen by a nozzle 63 or the like. An example of a screen set that has been found suitable for this purpose is the Celleco screen set, which is equipped with a screen having a screen size such that it divides the feed mass into substantially equal fractions. A 50 mesh screen provides, in the case of mechanical pulps of softwoods from eastern Canada and Scandinavia, a sufficient fiber distribution for accurate measurement, but other screen sizes may be used depending on the estimated fiber length distribution, provided each fraction represents a substantial proportion of the original pulp. Generally, the screen is subjected to a rapid oscillating motion and is self-cleaning, so that no fibrous mat or cake is formed on its surface.

The fraction remaining in the sieve (or, if desired, the passed fraction) is collected (and diluted if necessary by adding dilution water) and passed through line 65 with temperature measuring device 66 and flow meter 67 to consistency measuring device 68. The fraction passed through the screen is led out of line 69 through. The weight of the mass remaining in the sieve is determined from these flow and consistency measurements. Since the consistency and flow values of the fed slurry are also known, the ratio of the weight of the fraction remaining in the screen (or, if desired, the fraction passed) to the weight of the fed pulp can be easily determined. Based on this ratio, the value of the L-factor is determined, e.g., using a pre-fabricated calibration curve flock or the like, and further, the weight-average fiber length, if desired.

4,67587

Continuous readings are thus obtained for quantities which may be referred to as apparent consistency, degree of grinding, and L-factor (or weight-average fiber length). At the same time, readings are obtained on the flow rate of the pulp slurry fed to the separation screening device, as well as on the flow rate and consistency of the fraction remaining on the screen, as well as on the temperature at different points in the system. The readings thus obtained are parameter values for a group of simultaneous equations in which the actual values of the mass variables, namely the actual values of fiber specific surface area, weight-average fiber length and consistency, are unknown and the number of unknowns is the same as the number of equations.

A calculator for solving a set of equations for calculating weight-average fiber length is described in Patent Publication No. 55091.

Claims (4)

67587 A method for obtaining a continuous measurement of the L-factor of a pulp suspension, characterized in that the flow and consistency of the pulp suspension are measured and the pulp suspension is fed to a raw material distribution screening device, where the pulp is divided into a fraction and a fraction, , in which way the ratio of the weight of the solids in the suspension to the weight of the solids of either fraction or to the weight of the solids of the fraction remaining on the sieve, which is a measure of the L-factor of the mass, can be calculated. Apparatus for measuring the L-kinet of a pulp suspension for applying the method of claim 1, characterized by a raw material distribution screening device comprising a self-cleaning screen fabric (60), a device for feeding a pulp suspension to a self-cleaning screen fabric (60) , an apparatus for measuring the flow (64) and the consistency of the suspension, an apparatus for measuring the flow (67) and the consistency (68) of at least the second fraction, and a calculating device for calculating the L-factor. Device according to Claim 2, characterized in that the calculating device has a device for predetermining the solids of the suspension relative to the solids of one of the fractions or the solids of the fractions remaining in the sieve in relation to the solids of the fraction passing the sieve. Device according to claim 3, characterized in that the self-cleaning screen cloth (60) is mounted substantially perpendicularly, in addition there is a device for causing the screen cloth to vibrate.