Multi-phase thermodynamic modelling of pulp suspensions: Review of the methodology

Thermodynamic models have been increasingly applied to describe the multi-component chemistry of pulp suspensions. Their advantage is the inclusion of a great number of phases and chemical species in fibre line and paper-making furnish. The equilibrium models may consider both non-selective ion-exchange (Donnan equilibrium) and ion-specific complex formation in order to predict the distribution of ions between the fibre and aqueous phases. In this work, an extended Gibbs free energy method, also combined with reaction kinetics, was used. The Pitzer formalism was introduced to describe the activities of the solution phases. The constructed model was then applied to paper-making applications. Additionally, the multi-phase model was used in creating a neural network-based meta-model of pulp suspension pH. The Gibbsian method appears to be the best option for the calculation of chemical equilibrium in the multi-phase pulp suspension. The meta-models can be further used for ad-hoc applications, such as soft sensors.