Kinetic Model-Based State Estimation and Inferential Control of the Causticizing Process, 2011 PEERS Conference

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In this paper we present a new causticizing control system that combines liquor composition measurements and model-based inferencing of lime quality to achieve lime dosage control. Lime addition to the slaker is determined by a stoichiometric calculation where the clarified green liquor flow and chemical composition, the inferred lime quality and the white liquor causticity target value are inputs. A lime quality estimator, based on a high fidelity kinetic-dynamic model of the causticizing process, is used to predict the downstream liquor temperature and composition measurements from the process inputs and the current state estimates, and then the difference between the model predictions and the actual measurements is used to correct the states. The system is extremely flexible as it is able to integrate conventional measurements such as temperature and conductivity, as well as liquor composition measurements from an online analyzer, manual ABC titrations, or a combination of these. Two mill case studies, one involving conventional measurements and one based on an online analyzer, are presented and discussed.