Dynamic operations in the planning and scheduling of multi-products batch plants

Abstract: "Execution of tasks in dynamic batch units provides additional operating freedom via transient control profiles. When considered at the design and scheduling stage, this freedom can stretch the limits of profitability under strict market, facility and time constraints. The work in this paper incorporates dynamic processing conditions for products in a multi-product batch plant, as opposed to fixing the process by recipes, in the broader context of equipment design, production planning, scheduling and inventory considerations. The objective is a general function of fixed design costs, operating costs, production revenues etc. Decisions include stage processing times for products, transient stage operating policies, continuous design parameters, production capacity and production schedules. The infinite dimensional optimal control problem for each operation is solved using collocation over finite time elements ([6], [7]). Scheduling, with its combinatorial complexity, is addressed in the scope of flowshop plants for specific transfer policies using the Aggregated Scheduling model in [3] and [4]. Two examples are solved via sequential and simultaneous solution approaches. The smaller first example allows transient control at the reaction stage for problems with relevant objectives in planning and scheduling. The second example allows transient control at the reaction and high purity separation stage for a general objective function. Considerable savings achieved in most situations are reported, along with moderate computational requirements for solving the examples.