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Mill application of a new continuous digester model



A new-generation continuous digester model has been developed based on first principles of fundamental material, energy, and momentum balances. The modeling approach considers all of the important physical and chemical phenomena that are pertinent to digester operations: notably, chip size distribution, dynamics of chip column compaction, diffusion and reaction fluxes between entrapped and free liquor, and relative velocity differences between chip column and liquor flows. The model calculates time-dependent behavior of process conditions including but not limited to chip levels, residual EA (effective alkali) density and Kappa (a measure of the extent of reaction) progression through the digester, temperature and dissolved solids profiles, conversion, and blow consistency. The model emulates real operational conditions as closely as possible so that all process decision variables available to an operator are also similar input variables to the model. The model is fast, nearly 300 times faster than real time on a modern PC, which makes it convenient for a variety of applications. High-fidelity simulations of the model can be used for operating condition optimization, controller design improvements, transition policy development, and training. © 2005 American Institute of Chemical Engineers AIChE J, 2005

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