Ross Broadfoot, Darryn Rackemann and Gabriel Fraga
Queensland University of Technology, Brisbane, Australia; r.broadfoot@qut.edu.au; d.rackemann@qut.edu.au; gabriel.fraga@qut.edu.au
Australian pan stages have been using massecuite conductivity since the 1960s as the process variable related to massecuite composition. The signal is used for simple feedback control of the feed rate of syrup, molasses or balance water to the pan. Measurement of massecuite dry substance is currently being considered as an alternative method for pan control. Using a batch pan model, massecuite conductivity and dry substance profiles have been determined for the run-up from footing to pan-full for A and B massecuites for a wide range of process variables. The profiles provide information on the suitability and application of the two measurement systems for automatic control of the feeding of syrup and A molasses to the pan. Conductivity was found to be a function of both crystal content and supersaturation, whereas massecuite dry substance is a function of crystal content but only weakly affected by supersaturation. It is, therefore, expected that a more advanced control methodology will be required for a robust control system using massecuite dry substance. More advanced control arrangements using the profiles could be developed whereby pre-determined set point values from the footing to pan-full could be installed into the DCS with the aim to reduce the operator involvement and provide a more robust production system.