Prediction of metals distribution in mill processes: part 2: fiber line metals profiles.

APPLICATION: Mills can use the information for identifying and preempting scaling problems in kraft mills are closed more and more tightly.

This paper--part 2 of a three-part series--provides the basic equilibrium models for metals profile prediction in kraft pulp mills. The study 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 calculated and controlled in kraft mill chemical recovery systems.

This free-energy minimization method has been successfully applied to metals equilibrium calculations for pulp slurries. Pulp-bound metals, including calcium, magnesium, manganese, sodium, and potassium, can be calculated by free-energy minimization from the proposed equilibrium models for pulp slurries, i.e. species and their formation constants. The effects of pH and DTPA on pulp-bound metals are also predicted from the model.

Temperature and ionic strength affect formation constants. For metals profile prediction in mill processes, 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=28650

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].