| Summary: | The recausticizing plant has been recognized as a very important part of the Kraft pulping process. Because of the multiple objectives involved in the operation of the recausticizing plant, different operating conditions, and the complex interdependencies of the various units of the system, the best operating conditions are not obvious. A dynamic model was developed to study the effect of the different operating conditions and the effect of different disturbances and interconnections between the various units on the overall behaviour of a recausticizing plant. Both the thermodynamic and kinetic behaviour of the causticizing reaction have been investigated. A new approach for describing the equilibrium and kinetics of the causticizing reaction was developed, which takes into consideration the nonideality of the green and white liquor. It was found that both the equilibrium and kinetics of the causticizing reaction can be well represented by this approach. A simplified and accurate method was used for describing the lime mud free settling process. Models for all the units in the plant were developed and presented. The models were based on mass balance equations and the pertinent physical properties. The effects of disturbances and different operating conditions were simulated for the entire plant. Simulations showed the complicated dynamic responses of the system and the importance of the control system to achieve better operations. This work has brought to light some previously less known facts about the recausticizing process, and can be used to develop and compare different control strategies before they are implemented in the mills. === Applied Science, Faculty of === Chemical and Biological Engineering, Department of === Graduate
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