Optimal scheduling of heat-integrated multipurpose plants under fouling conditions

This work presents a systematic mathematical framework for scheduling the o peration of multipurpose plants involving heat-integrated unit operations u nder fouling considerations. A salient characteristic of this problem is th at 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 ite rative procedure is proposed for the solution of the resulting non-convex M INLP model, involving the solution of a series of mixed integer linear prog ramming 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 f low rate profiles over time. An example problem is presented to illustrate the applicability of the proposed approach. It is proved that fouling consi derations can significantly affect the production schedule as well as heat integration opportunities. (C) 2001 Elsevier Science Ltd. All rights reserv ed.