Automation of white pans at the Tongaat Hulett refinery

Pan boiling relies substantially on "art" rather than "science", thus requiring skilled and experienced operators to optimise crystal sugar production. This puts heavy demands on staffing, training and skills transfer. Particularly in this context, automated pan boiling has the potential to provide substantial benefits in terms of plant capacity, process performance and product quality. Successful pan automation relies largely on the following aspects: instrumentation that reliably measures appropriate process parameters, a suitable control strategy that relies both on crystallisation fundamentals (science) and practical considerations (art), and control hardware that implements the strategy in a manner that is easy to understand, operate, configure, modify and maintain. Building on past experience with pan automation, an updated control system was installed on a fourth boiling batch pan at the Tongaat Hulett refinery. Existing measurements were supplemented with a pan stirrer power measurement, an online refractometer and an online microscope. New control hardware, a Yokogawa Distributed Control System (DCS), was installed. Pan boiling control strategies, using the expanded range of measurements available, have been developed. The control strategies have been implemented on the DCS, tested and then operated in production mode for an extended period. The new control strategy has changed the previous manual shock seeding to automated seeding with ball milled slurry in an attempt to approach the ideal of "full seeding". Work is continuing to replicate the success of this automation to the other four refined sugar batch pans. This paper describes details of the instrumentation installed, the control strategies implemented and the preliminary results that have been obtained.