Minimax algebra is used as a tool for modelling Discrete Event Dynamic Systems with different process configurations, including Pipeless Batch Chemical Plants and Flexible Manufacturing Systems. Based on minimax algebra models, a novel technique for routing, scheduling and product mix optimisation is developed by means of Simulated Annealing algorithm. Typical results are presented which demonstrate the usefulness of the representation and the quality of the schedules obtained. In particular, results indicate that the more efficient routes and those which can be operated simultaneously are usually selected, giving high plant utilisation and productivity.