Supplementary Information files for "Single and multi-objective shutdown optimization of a multistage continuous crystallizer"

Supplementary files for article "Single and multi-objective shutdown optimization of a multistage continuous crystallizer"This study presents the first model-based optimal shutdown procedure of a multistage continuous crystallization process which aims at the maximization of on-spec production and minimization of the shutdown time. The cooling antisolvent crystallization of Aspirin (acetylsalicylic acid) in a three-stage continuous crystallizer was used as a case study. To address the optimal shutdown problem, several single optimization scenarios were considered to assess the impact of the degrees of freedom, discretiza-tion schemes, and optimization settings such as the constraints. The proposed optimal shutdown procedures showed that significant amounts of on spec crystals can be produced both at fixed and variable shutdown times. Most importantly, the optimal shutdown procedures can match the steady state productivity, based on the shutdown to steady state productivity ratio (STSPR) which can easily reach 100%. Moreover, the residual shutdown material, considered as waste, can be dramatically reduced by >80% compared to the current standard shutdown procedures. Given the conflicting nature of the maximization of on spec production and minimization of the shutdown time, a multi-objective optimization of the shutdown operation was also addressed to identify the set of Pareto optimal solutions. Finally, a multicriteria decision aiding method, based of multi-attribute utility theory, was proposed to rank the Pareto optimal solutions to support the decision making and help identify a suitable and feasible single optimal shutdown solution.© The Authors, CC BY 4.0论文《多级连续结晶器单目标与多目标停机优化》补充材料。本研究首次提出了基于模型的多级连续结晶过程最优停机流程，该流程旨在最大化合格产品产量并最小化停机时长。本研究以阿司匹林（Aspirin，化学名乙酰水杨酸（acetylsalicylic acid））在三级连续结晶器中的冷却反溶剂结晶过程为案例展开研究。为解决最优停机问题，本研究设计了多组单目标优化场景，用以评估自由度、离散化方案以及约束条件等优化设置的影响。所提出的最优停机流程表明，无论停机时长固定与否，均可产出大量合格晶体产品。最为关键的是，基于停机至稳态产率比（shutdown to steady state productivity ratio, STSPR），最优停机流程可实现与稳态生产等同的产能，该比值可轻松达到100%。此外，相较于当前标准停机流程，被视作废弃物的停机残留物料可大幅减少80%以上。鉴于合格产品产量最大化与停机时长最小化的目标属性相互冲突，本研究同时开展了停机操作的多目标优化，以求解帕累托最优解集（Pareto optimal solutions）。最后，本研究提出了一种基于多属性效用理论（multi-attribute utility theory）的多准则决策辅助方法，用于对帕累托最优解集进行排序，以辅助决策并筛选出合适且可行的单目标最优停机方案。© 作者，CC BY 4.0