Optimal scheduling of heat-integrated multipurpose plants under fouling conditions

This work presents a systematic mathematical framework for scheduling the operation of multipurpose plants involving heat-integrated unit operations under fouling considerations. A salient characteristic of this problem is that the performance of each heat-integrated unit, which decreases with time due to fouling, can be restored to its initial state by performing cleaning operations. Based on a uniform time discretization, the overall problem is formulated as a mixed integer non-linear programming (MINLP) model. An iterative procedure is proposed for the solution of the resulting non-convex MINLP model, involving the solution of a series of mixed integer linear programming and non-linear programming subproblems. The optimization algorithm determines simultaneously: (i) the production schedule, (ii) the number of cleaning operations required along with their corresponding timings, (iii) the optimal utility utilization profile and (iv) the heat transfer medium flow rate profiles over time. An example problem is presented to illustrate the applicability of the proposed approach. It is proved that fouling considerations can significantly affect the production schedule as well as heat integration opportunities. (C) 2001 Elsevier Science Ltd. All rights reserved.