FI79759B - FOERFARANDE FOER ANALYZING AV TRAEMASSA. - Google Patents

Description

, 79759

METHOD FOR THE ANALYSIS OF WOOD PULP - FÖRFARANDE FÖR ANALYZERING AV TRKMASSA

The invention relates to a method for analyzing wood pulp 5, in particular for determining its fines content and / or degree of grinding.

Measurement of wood pulp properties based on ultrasonic beam attenuation is previously known from U.S. Pat. No. 2,755,662, U.S. Pat. No. 3,710,615, U.S. Pat. No. 3,914,984 and GB 1302,731. In these known methods, the analysis is based on the determination of ultrasonic attenuation

In measurements based on ultrasonic attenuation, problems are caused by the air in the substance to be measured, such as the pulp stock, especially the microbubbles bound to the particles. Namely, the attenuation of the ultrasound is very much dependent on the amount of air, whereby the variation in the measurand is easily covered under the attenuation caused by the air 20 and the air bubbles.

The purpose of the method according to the invention is to eliminate the interfering effect of air in the measurement of the properties of wood pulp based on the measurement of ultrasonic attenuation.

The method according to the invention is based on the utilization of air concentration measurement of pulp by ultrasonic technology, which method is described in Finnish patent application 851380.

With respect to the features of the method according to the invention, reference is made to the claims.

The method according to the invention is characterized in that it utilizes the property of air bubbles bound to different particles of wood pulp, and in particular microbubbles, to effectively suppress ultrasound, whereby in the previously known methods the measurement problems caused by air bubbles have been completely eliminated.

2 79759

In the method according to the invention, the mass to be examined is aerated by feeding a gas in such a way that the gas binds to the mass, preferably in very small so-called as microbubbles and when the aeration is saturated, i.e. the pulp is no longer able to bind more gas to itself, the aeration is stopped and the saturation ultrasonic attenuation and ultrasound of the pulp are measured to change the attenuation change time constant.

Preferably, in the aeration of wood pulp, when the gas is fed into the wood pulp, the pulp is mechanically processed, e.g. by means of suitable pumps, so that the gas decomposes, i.e. disperses into small bubbles and binds to the wood pulp as small microbubbles as possible.

Preferably, the measurements are performed at a constant consistency of wood pulp, the consistency being, for example, on the order of about e.g. about 1-10 g / l, such as about 6 g / l.

Preferably, the time constant τ of the ultrasonic attenuation change. the wood pulp is determined by measuring the ultrasonic 20 attenuation after aeration, i.e. when as much gas as possible has been bound to the pulp, and then by measuring the time τ during which the attenuation has fallen from its initial saturation value Ao to a certain preset value Ατ. 25 This preset value can be, for example, 1/10 (20dB) of the original saturation value.

The attenuation is measured using an air concentration measurement based on ultrasonic technology, where the air concentration is measured using the ultrasonic attenuation in the wood pulp, i.e. the ultrasonic intensity is sent to the pulp and the attenuated ultrasonic intensity is measured from a certain distance. Then the air concentration is obtained from the formula τ 35 Gc = K · lOLog

ATR

where Xrec = transmitted ultrasonic intensity 40 Itr = received ultrasonic intensity 3 79759 K = calibration factor.

The above values can be used to determine the fines content C * of the pulp. calculate from the formula Cf · = fx (Ao) + fa (χ) / 5 where fx and f2 are mass-specific and experimentally determined functions.

Similarly, from the above values, the degree of grinding BR of the mass can be calculated from the formula BR - fs (Ao) + f * (x), 10 where f3 and are mass - specific and experimentally determined functions.

The method is described in the article "Ultrasonic Measurement of Gaseous Air in Pulp Suspension".

Claims (7)

A method for analyzing wood pulp to determine its particle content and / or grinding rate, characterized in that the pulp, which is to be examined, is aerated by feeding gas into the pulp in such a way that the gas is bonded to the pulp and when the aeration is saturated or the mass no longer binds more gas per se, the aeration and saturation attenuation (Ao) of ultrasound in the pulp is terminated and the time constant (τ) for the change of the attenuation of the ultrasound is measured to determine the pulp content and / or the degree of grinding. 2. A method according to claim 1, characterized in that the pulp is fed mechanically in the pulp at the aeration in such a way that the gas is decomposed or dispersed in small bubbles and bonded to the pulp. Method according to claim 1 or 2, characterized in that the measurement is carried out at a constant thickness of the pulp. 30 Method according to any of claims 1-3, characterized in that the attenuation is measured using an ultrasonic technique based measurement of the air content, wherein the air content is measured by using the attenuation of the ultrasound in the mass 35 as a measuring quantity. Method according to any of claims 1-4, characterized in that the time constant 6 79759 (τ) of the attenuation change is determined by rooting the ultrasonic attenuation after the aeration and by measuring the time (τ), during which the attenuation, when air settles from the pulp, has dropped from the original saturation value (A0) to a predetermined value). 6. A process according to any one of claims 1-5, characterized in that the fine content Cr in the mass is determined on the basis of an experimental function Cr · Cr · = f a. (Ao) + fa (t), where fa. and f2 is to the mass itself relational and experimentally determined functions. Process according to any of claims 15 to 6, characterized in that the grinding degree BR of the pulp is determined on the basis of an experimental function BR BR - fa (Ao) + f * (τ), where fs and f * are til pulp itself and experimentally determined functions.