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Dynamic simulation of brown stock washers and bleach plants

University of British Columbia

Dynamic process simulators of brown stock washers and multistage bleach plants were developed for process control. SIMNON, a dynamic simulation language, was employed as a platform for constructing the simulators. The washing process simulator was used to investigate dynamic behavior of a three-stage countercurrent washing plant and to evaluate process control strategies. Good understanding of interactions of the operating units and the dynamics of the washing system were achieved, and significantly improved washing by better control were shown. For dynamic modelling of the bleach plant, pulp flow patterns in the retention towers were modelled using tracer responses from different towers. A model consisting of a cascade of CSTR's and a PFR showed good correspondence with measurements. A linear relationship was derived to correlate delignification and brightening. Unit operation models for mixing, reactions and washing were formulated using mass balances on liquor, fibres, chromophores, chemicals, pH and dissolved solids. Bleaching kinetic models from the literature were evaluated and incorporated into the bleaching process simulator. Using the simulator and industrial conditions, a dynamic model of a CDEDED bleach plant was built and used to simulate responses of the CE kappa number and brightness to changes in the chemical charge, incoming kappa number and production rate. Dynamic characteristics of nonlinearity and long time delay were identified. This simulator could be applied to other bleaching sequences to study process dynamics and control strategies if the bleaching kinetics used in those sequences were known.

Thesis/Dissertation

application/pdf

2008-08-27

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http://hdl.handle.net/2429/1530

Chemical and Biological Engineering

University of British Columbia

UBCV

DSpace