Residence Time of Fiber in a Single Disc Refiner, 1999 International Mechanical Pulping Conference Proceedings

Esko Härkönen

UPM-Kymmene

Erkki Huusari

Sunds Defibrator

Pekka Ravila

Indmeas Oy

One of the most important factors in the control of the refining phenomenon is the residence time of the fiber in the refiner. Despite its great importance, knowledge of this is still fairly diffuse.

UPM-Kymmene and Sunds Defibrator have made residence time measurements in connection with the JAMA-project, in which the basics of fiber refining in the TMP refiner plate gap are studied. In the JAMA-project SD-65 refiners were equipped with a front plate and stator segment with radially spaced holes for sample-taking from the plate gap. The same holes were used for the feeding of radioactive tracer into the plate gap and for observing the passage of the tracer material through the refiner.

The residence time was measured by means of a radioactive tracer material with a short half-life. All measurements were made during normal pulp production. Residence time measurements were made for the 1st and 2nd stage refiners and for two reject refiners. In this article the testing methodology and the results of the tests are described. Measurements show that there is an intensive mixing zone at the beginning of the plate gap. After the fiber has passed the steam turning point it passes the plate gap rapidly.

The total residence time of fiber in different refiners and with different segments varies between 2.1 and 7.5 seconds, while the radial velocity of fiber at the outer periphery is about 0.5 m/s in cases measured.