Scheduling of industrial distribution manifolds with pre-conditions

The scheduling of two types of manifolds typically found in multipurpose plants is considered. These are, respectively, single and double seat valve manifolds. Although they perform the same general function they are characterised by different operational and structural characteristics. Within the general scheduling problem important aspects such as operational pre-conditions and constraints are considered (e.g. product sequencing and cleaning requirements). These must be guaranteed during operation in order to avoid compromising final product quality, safety and feasibility of operation. The flowpath formulation proposed by Barbosa-Póvoa and Macchietto for the scheduling of distribution manifolds is extended so as to account for operational conditions, modelled through the equipment State Task Network (eSTN) representation and to allow for simultaneous operation of compatible flowpaths with different transfer times. Operating objectives such as due dates, maximal production and production profit are considered. A Mixed Integer Linear Programming formulation is developed and solved using a Branch and Bound standard procedure. Binary variables are used to represent the operational choices that have to be made. An example illustrating the flexibility and applicability of the new formulation to the scheduling of distribution manifolds dealing with operating constraints is presented.