Year 2003
Hannu Seppälä

Numerical simulation for evaluation of the usability of secondary treated effluent as process water at mechanical pulp mill.

This thesis studied the effects of different supply flow waters at the groundwood mill. The studied supply waters were sand filtrated effluent, ozone treated effluent and white water from the paper machine. Two simulation models were made. The first was the model of the Wet End Simulator at KCL, the second model of the wire press section at the pulp mill. The dynamic simulation program that was used in the thesis was Propose.

The aim in the thesis was using the Wet End Simulator model to find right distribution ratios for four different detrimental substances and to use these distribution ratios in the groundwood mill model. The purpose of the wire press model was to compare the effect of wash waters on detrimental substances in pulp and circulating waters at the pulp mill. The aim was to see how the different supply waters and the ratios between wash water and filtrate affect the contents of the detrimental substances. The wire press model also examined the fluctuation of the process.

The theoretical part consists of two parts. The first part concentrates on the manufacture of mechanical pulp and the detrimental substances in it. The second part concentrates on the simulation programs used in the pulp and paper industry.

There were one trial run with the Wet End Simulator during this thesis and one measurement day at the groundwood mill. These results were used as references with the ones got from the simulation models.

The results showed that the most significant effect on the washing of the detrimental substances was the amount of wash water. The more wash water is used the less detrimental substances are carried to the paper machine. With dissolved substances (TOC) the improvement would be better than with substances, which have some retention into pulp web. The treated effluent was quite equivalent with paper machine white water. The fluctuation range, too, decreases with increasing amount of wash water used.

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