The dynamic modelling of a solvent extraction process.

This thesis is concerned with a project on mixer-settler extraction systems, as a particular example of many liquid- liquid mass transfer processes. The project was aimed at a better practical understanding of the working of such systems and to develop theoretical models, which could then be used for both design and control. The construction of a system of mixer-settler tanks is described, together with the appropriate facilities for pumping and analysis of the process chemicals. The working pilot plant has been extensively tested to discover its characteristics, when subjected to changes in both flow and boundary concentration. Mass balance principles are applied to each contactor stage to develop equations, which include in their description, the flows in each stage. These flow dynamic relationships are extended to include the settler. Laplace transform analysis is used to produce a simplified model of the flow dynamics. An alternative approach, using sensitivity functions, yields a simplified transfer function model that includes a time delay term. This model can adjust to the process dynamics, in real time. A digital process model, based on the mass balance equations has been developed to work on-line using a standard process control computer, under the constraints normal to such equipment. Both modelling approaches are compared against experimental results. The importance of the time varying nature of the process parameters is recognised, and possible adaptive modelling schemes examined. A new parameter adjustment method is developed using correlation techniques. Finally, modelling is considered in the context of automatic control.