A systematic methodology is presented for the synthesis, optimal planning and scheduling of plant utility systems. The methodology first addresses long-term synthesis and planning problems and continues with short-term maintenance scheduling applications. The synthesis approach determines new units, their layout, their number and capacities, as well as the operating strategies appropriate in view ... [Show full abstract] of process variations. The scheduling problem methodology determines maintenance, along with shut-down and start-up schedules for uncertain operational scenarios. The optimisation technology is applied in the form of natural decomposition schemes.