A robust event-based continuous time formulation for tank transfer scheduling

A generalized model is proposed for the continuous time scheduling problem of fluid transfer in tanks. This model generally and more robustly handles the synchronization of time events with material balances than previous proposed models in the literature. A novel method for representing the flow to and from a tank is developed with the potential for significant reduction in the number of necessary time events required for continuous time scheduling formulations. The problem involves the optimal operation of fluid transfer from input sources to tanks, transfer between the tanks, and the transfer from tanks to output destinations. An efficient mixed-integer nonlinear programming formulation is developed based on continuous representation of time domain under the assumption of no simultaneous input and output flow to a tank for fluid streams comprised of multiple components. The new modeling paradigm is applied to examples from the literature for developing refinery crude unit charging schedules.