The objectives of this investigation were to: • Develop a capacitance measuring device that can be used for measuring composition of ethanol-water mixtures. • Implement this measurement technique on a laboratory clistillation column for top product composition measurement and control. • Compare the results obtained in this manner with previously used inferred measurements by temperature. Experiments were conducted to calibrate the capacitance cell ie, to obtain a relation between composition of an ethanol and water mixture and the output of the capacitance cell. Open loop tests were executed on the distillation column to determine if the capacitance device had any negative influence on measurement compared to composition measurements via temperature. Top product composition control using the capacitance cell under dosed loop conditions was also tested, to observe the capacitance cell's performance. The capacitance cell gave repeatable readings during the calibration procedure. In the open loop tests, process models were obtained for control purposes and no negative influence was observed. The capacitance cell's closed loop responses were observed to be satisfactory. It was simple to construct, easy to operate and proved to be a relatively inexpensive device. In the final analysis, the capacitance cell proved to be a useful device in direct measurements of composition of binary mixtures, and offers scope for further development in its application to the control of top product composition in distillation columns of industrial scale.
Dissertation (M Eng (Control Engineering))--University of Pretoria, 2006.