Fundamental thermal-hydraulic continuous pulp digester model with grade transition
Résumé
This paper presents a detailed fundamental model of a continuous pulp digester developed for simulation and control. Most modeling efforts in the past have either emphasized reaction kinetics and energy transfer assuming a prescribed flow behavior, or modeled digester hydraulics with simplified reaction kinetics. In this work, we augment the well-known extended Purdue model (Wisnewski et al., 1997) by incorporating axial momentum transport, an immediate consequence of which is ability to simulate chip level and its impact on the Kappa number profile. An essential contribution is the ability to model chip compaction. Interaction between digester hydraulics and kinetics is illustrated via simulation examples. Examples include scenarios that show incipient plugging of the digester vessel. The current work also explores and illustrates the use of higher order finite-difference methods to reduce numerical dissipation and dispersion. Ability to describe chip velocities enables rigorous tracking of transition front within the digester during feedstock grade transitions. Operational difficulties encountered during hardwood to softwood transition are explained using the model.
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