Optimization of multipurpose process plant operations: A multi-time-scale maintenance and production scheduling approach

- Novel optimization based approach for the integrated maintenance and production scheduling of process plants.
- Introduction of residual useful life and operation modes of plant units as key concepts for the integration.
- Modeling of degradation of unit performance due to aging effects.

Scheduling of production and maintenance plays a fundamental role in the effective operation of process plants. Frequently the two decision processes are independently addressed, overlooking the tight relation existing between the way the plant is operated to produce the required goods and the appearance of maintenance requirements. The presence of degradation phenomena affecting the performance of plant units and limiting the operational choices makes the integration of the two decision processes even more important. In this paper an industrial framework for the integration of maintenance and production scheduling of process plants is presented as well as some considerations on how the presence of plant unit degradation impacts on the scheduling problem. The proposed approach ties industrial key-components such as asset management and production scheduling closer together and represents therefore a contribution to the smart manufacturing revolution. The integrated maintenance and production scheduling problem is formulated as a mixed integer linear program (MILP) and tested on a generic process plant described as a State Task Network (STN).