Flow Scanner digester control integration at Frövi – a status report
The kraft mill at Frövi, Sweden, is continuing to work towards a full integration of the Flow Scanner data in their Digester Control System (DCS). So far the Flow Scanner has been used to regulate the amount of black liquor and helps keep a constant wood-to-liquor ratio when the woodchips are dry. The next step is to apply it to the white liquor dosage such that it matches the dry content of the woodchips entering the digester.
The integration must also handle belt stops and wood chip flow changes, intermediate storage buffer levels, and several other atypical process behaviours. A model to take account of these parameters and determine when the necessary change in white liquor dosage occurs has been developed with the help of external consultants. The results of this model have been compared to the existing control strategy over a period of several months. Up to 10% differences between the fixed dry content per unit volume and the dynamic measurements of the Flow Scanner have been observed. There is good reason to believe that this can account for a significant part of the Kappa instability.
The DCS has been programmed with the model parameters and the next phase of the project is ready to begin. Further adjustment of the model and control parameters is anticipated before the optimal settings are determined. Mantex look forward to reporting Frövi’s success in due course!