New Thinking in Groundwood Process Control, 1999 International Mechanical Pulping Conference Proceedings

Jouko H.J. Lehto

Kaukas Research Center

Olli Tuovinen

Valmet

Tomas Björkqvist

Tampere University of

Technology

The control of the two-pocket grinders and the groundwood process is a challenging task because the grinder operation is discontinuous in nature and the production rate and pulp quality are dependent on the grinder stones, the condition of which is difficult to keep constant. The objective of this study was to investigate whether the basic grinder control could be improved by means of new control algorithms, and whether the stone condition could be characterized more precisely than at present by using process data, so that grinders could be loaded more efficiently and high, stable production rate and constant quality could be maintained.

The research program described in this paper consisted of three successive studies which were made in the pressure groundwood mill of the UPM-Kymmene Kaukas LWC paper mill in Lappeenranta, Finland. The first study showed that the pulp quality in the grinder pit varied considerably in the short term and that the production resources of the grinders were not fully utilized when running with constant shoe speed. In the second study, two new control modes, the constant SEC control mode and the true constant production rate control mode, were developed. The inter-dependence of SEC and freeness was shown to be valid in stone grinding in the short term as well. Both of the new control modes provided a more stable quality than the constant shoe speed control mode when grinding with one pocket. In normal two-pocket grinding the application of the SEC control mode proved to be difficult because of the unreliable power split between the two pockets. The constant production rate control mode worked better in two-pocket running and in a mill trial it increased production rate by 5 % due to the more efficient use of the grinder's resources. In the third study, an experimental information/decision making system for the monitoring of stone condition was developed. It was noticed that the traditionally calculated sharpness number was not sensitive enough to describe the stone condition when the stone was conditioned by means of high pressure water. The term 'saturation degree' was introduced. It is the time that the hydraulic pressure valve is open more than 90 %. It may be used for automatic triggering of stone conditioning by means of high-pressure water.

With efficient control of grinders and stones, it is possible to carry out the suggested control strategy, the 'optimum operating point strategy', where the idea is simply to maintain all the grinders in an operation point that provides the desired quality and maximum production rate at all times. The means for carrying out the strategy are well controlled stone conditioning and the careful monitoring of the grinders by utilizing the possibilities offered by modern DCSs and up-to-date control algorithms.

Author: Björkqvist, T., Tuovinen, O., Lehto, H.H.J.
New Thinking in Groundwood Process Control, 1999 Internation
New Thinking in Groundwood Process Control, 1999 International Mechanical Pulping Conference Proceedings
32.00

New Releases

TAPPI PRESS Catalog eBook 2024


Experience the Power of Publications in the 2024 TAPPI Press Catalog


Open


 

Kraft Recovery Boilers, Third Edition  


Sponsored by the Recovery Boiler Program R&D Subcommittee of the American Forest & Paper Association (AF&PA) and published by TAPPI Press.


Purchase


 

Handbook For Pulp and Paper Technologists (The SMOOK Book), Fourth Edition

The best-selling text to introduce the entire technology of pulp and paper manufacture.

Purchase

 

Guidelines for Safe Assessment and Operation of Yankee Dryers  


A project of the Yankee Dryer Safety & Reliability Committee.

Purchase

 

Check our newest additions.


TAPPI Press offers some of the most in-depth resources and references for the forest products and related industries. 

See More

   
 

Available for Purchase – Conference Proceedings


TAPPI maintains a record of key conference papers, presentations, and other conference publications, available for purchase in a variety of formats.

See More