ESTIMATION OF SHUTDOWN MAINTENANCE COST F OR EVALUATION OF PROCESS DESIGN IN EARLY PLANNING PHASE

The maintenance cost should be considered in the early planning phase of process design for reducing it, and a cost estimation method is ess ential to evaluate alternative design. The shutdown maintenance of con dition basis maintainable equipment modules is concerned here, then th at maintenance plan through the plant life should be optimized on the basis of expected degradation curves of these equipment modules for an accurate process evaluation. The shutdown timing and grouping of equi pment modules, which are maintained at each shutdown period, become de cision variables, and these variables should be optimized simultaneous ly under the constraint of the degradation curves. In this study, the relation between these variables through the degradation curves is con sidered, and a sub-model for sequential two shutdown periods for any e quipment module is provided by introducing 0/1 integer variables, and it is expanded for overall equipment modules and whole plant life. Thi s model is linearized from the consideration of required accuracy in p rocess evaluation, and an integer programming model for the shutdown m aintenance planning is developed.