Flexibility Assessment of Heat Exchanger Networks: From a Thorough Data Extraction to Robustness Evaluation
Résumé
Due to process variabilities and operational modifications, operating parameters of Heat Exchanger Network (HEN) may alter its output temperatures. Nevertheless, the impact of these disturbances depends largely on the topology of the HEN. As a consequence, it can be relevant to evaluate the flexibility of a HEN after its synthesis. Flexibility of a HEN refers to the ability of a system to operate at a finite number of set points. In this framework, the implementation of this property is broken down into several aspects. In this contribution, the first level of flexibility concerning the robustness (ability of the system to absorb disturbances without changing utility flowrates) is addressed and compared to other contribution, this criterion is not formulated as a generic one but as a criterion that strongly depends on the studied process. As a consequence, to evaluate its value, the first step is to perform an enhanced data collection by identifying the most frequent disturbances and by pointing out the critical streams i.e. the streams whose output temperature absolutely needs to be kept into a strict interval; then, given this information, a robustness criterion can be formulated for a given HEN. In this paper, a methodology relying on several models is developed to address this issue: a Mass Equilibrium Summation enthalpy non-linear model (MESH) dedicated to the enhanced data collection, a Mixed Integer Linear Programming (MILP) model used for the HEN synthesis and finally a linear model developed for the modeling of the HEN response to disturbances. This methodology is first illustrated through a basic academic example and finally applied to an industrial case study.
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