Simple continuous-time formulation for short-term scheduling of batch and continuous processes

A new and simple general mathematical formulation for scheduling multipurpose plants involving batch and/or continuous processes, based on the resource-task network (RTN) representation, is presented. The formulation uses a uniform-time-grid continuous-time representation and results in a very efficient mixed integer linear programming model that can be solved to optimality for a given number of event points. The performance of the formulation is illustrated through the solution of two case studies that have been thoroughly examined in the literature: the first involves a continuous plant and is solved for three different storage policies, and the second concerns a batch plant. The formulation is shown to compare favorably to existing continuous-time formulations. More specifically, a new optimal solution is obtained for the finite intermediate storage scenario of the first case that is also a global optimal solution.