Dynamic modelling and scheduling of an industrial batch system

This paper addresses the optimal schedule of a resource constrained four-batch digester system of an industrial acid sulphite pulp mill. This involves the development of two different models, one to model the scheduling operational problem and the other the batch digester operation-process model. The first model uses a discrete-time Resource Task Network (RTN) based representation leading to a Mixed Integer Linear Program (MILP) formulation. In this, the main operational limitation, steam availability, is modelled through the definition of a superstructure including the most relevant heating alternatives. The duration of the generated heating tasks was estimated through the use of the process model-a distributed heterogeneous dynamic model in gPROMS, with a heat-transfer resistance at the solid-fluid-interface-validated with experimental plant data. The optimal schedules obtained showed that an increase in the total available steam from the boiler is vital to allow a higher level of productivity and that not much can be done regarding steam sharing improvements. (C) 2002 Elsevier Science Ltd. All rights reserved.