An approach for optimising the cleaning schedule in heat exchanger networks (HENs) subject to fouling is presented. This work focuses on HEN applications in crude oil preheat trains located in refineries. Previous approaches have focused on using mixed-integer nonlinear programming (MINLP) methods involving binary decision variables describing when and which unit to clean in a multi-period formulation. This work is based on the discovery that the HEN cleaning scheduling problem is in actuality a multistage optimal control problem (OCP), and further that cleaning actions are the controls which appear linearly in the system equations. The key feature is that these problems exhibit bang-bang behaviour, obviating the need for combinatorial optimisation methods. Several case studies are considered; ranging from a single unit up to 25 units. Results show that the feasible path approach adopted is stable and efficient in comparison to classical methods which sometimes suffer from failure in convergence.

提出了一种在结垢的热交换器网络（HENs）中优化清洁时间表的方法。这项工作的重点是HEN在炼油厂的原油预热机组中的应用。先前的方法集中于使用混合整数非线性规划（MINLP）方法，该方法涉及描述多周期配方中何时以及清洁哪个单元的二进制决策变量。这项工作基于以下发现：HEN清洁计划问题实际上是一个多阶段最优控制问题（OCP），并且清洁行为是线性出现在系统方程式中的控件。关键特征是这些问题表现出爆炸式的行为，从而消除了对组合优化方法的需求。考虑了几个案例研究；从单个单元到25个单元不等。