Control of a batch pulp digester using a simplified mechanistic model to predict degree of polymerisation

The availability of substantial computational capability in industrial environments has rendered the traditional S-factor prediction of cook time o control DP inadequate, compared to what can be achieved with more sophisticated predictive models. A fundamental model, in simplified form, ith adjustable parameters, was developed and its accuracy to predict DP based on given operating conditions was tested using available plant ata. This model was built into a control structure for implementation on an operational batch digester. Because the parameters form part of fundamental relationships in the model, realistic bounds can be placed on them during the optimisation rocess, enabling a better understanding of the behaviour of the model. Overall control of the batch digestion process takes place in three interdependent, but distinct time frames, namely continuous control of digester emperature based on a calculated setpoint, using a model-based approach to predict DP on a cook-to-cook basis and lastly while the final DP must e kept on target through a number of cooks (N cooks), taking into account long-term changes in the process. This long-term optimisation takes lace in the third time frame. 2006 Elsevier Ltd. All rights reserved.