Optimal cleaning policies in heat exchanger networks under rapid fouling

This paper addresses the problem of short-term cleaning scheduling in a spe cial class of heat-exchanger networks (HENs). A salient characteristic of t his problem is that the performance of each heat exchanger decreases with t ime and can then be restored to its initial state by performing cleaning op erations. Because of its practical importance, a specific problem has been considered here involving decaying equipment performance due to milk foulin g. A mixed-integer nonlinear-programming (MINLP) model is first presented i ncorporating general fouling profiles. This model is then linearized to a t ight mixed-integer linear-programming (MILP) model which can be solved to g lobal optimality. A detailed objective function is used to account for clea ning cost and energy requirements. The formulations can model serial and pa rallel HENs as well as network arrangements arising from the combination of these basic cases. The optimization algorithm determines simultaneously: ( i) the number of cleaning operation tasks required along with their corresp onding timings and (ii) the optimal utility utilization profile over time. A number of complex heat-exchanger networks examples are presented to illus trate the applicability of the proposed models together with comparative pe rformance results between the MINLP and MILP models.