Prediction of metals distribution in mill processes, Part 3 of 3: NPE management in kraft chemical recovery.

APPLICATION: This study will help mills manage nonprocess element (NPE) on a mill-wide basis. In particular, better dregs removal achieves significantly drier lime mud to the kiln.

This series of papers provide the basic equilibrium models for metals profile prediction in kraft pulp mills. Part 2 of this series demonstrates that metals profiles in fiber lines can be predicted by combining an equilibrium engine with existing process simulators. Part 3 of this series shows how nonprocess metals can be controlled and calculated in kraft mill chemical recovery systems.

Free energy minimization has been successfully applied to metals equilibrium calculations for kraft mill liquors and slurries. Calcium, magnesium, manganese, sodium, and potassium can be calculated by free-energy minimization, from the proposed species and their formation constants.

Temperature and ionic strength affect formation constants. For metals profile prediction in mill fiber lines (Part 2), dissolved organics from kraft cooking have a significant role in keeping metals in the liquor. Unfortunately, the composition of dissolved organics from kraft cooking is very complicated and further study is needed to define species formed from metals and dissolved organics. In the current model, dissolved organics are represented by an equivalent univalent component. View this paper online at http://www.tappi.org/index.asp?pid=28862

Yongxiang Gu is with the Department of Food Science, Zhejiang University, China, Lou Edwards is with the Department of Chemical Engineering, University of Idaho, Moscow, Idaho, USA. Email Edwards at [e-mail].