Off-line and on-line approach for optimal maintenance management of continuous parallel processes with decreasing performance

The efficiency of equipment units in chemical process plants decreases with time because of fouling, byproduct formation, catalyst deactivation, etc. Therefore, periodic equipment maintenance and/or cleaning are required to restore original operating conditions that allow the desired high productivity rates to be maintained. Maintenance imposes a tradeoff decision between the cost associated with equipment shutdown and the resulting benefit of improvements in productivity. When parallel processing lines are considered in a production facility, the problem becomes more complex because of the presence of material interrelationships. In this work, the solution to this complex maintenance problem is addressed by introducing a simple formulation (NLP) for the planning problem and a procedure for the subsequent implementation of the discrete decisions involved (clean or not, feed assignments) in a real-time environment. This methodology can be considered an extension of the real-time evolution (RTE) approach for continuous processes (Sequeira, S. E.; Graells, M.; Puigjaner, L. Ind. Eng. Chem. Res. 2002, 41 (7), 1815). The main advantage of the proposed methodology is the robustness resulting from the use of on-line information, which reduces the model dependency and, thus, the undesirable effects of variability and plant-model mismatch. The proposed off-line and on-line approaches are tested with benchmark case studies, their performance is evaluated using dynamic simulations, and their long-term behavior is monitored via Monte Carlo simulations.