engleski

Towards a comprehensive approach to optimal control of non-ideal binary batch distillation

Despite being the most widely applied technology for liquid mixtures separations, distillation separation efficiency is quite low resulting in wasteful energy use, especially in batch mode particularly suitable for flexible small-scale production. Additionally, the flexibility and inherent dynamic nature of batch distillation processes pose challenging design, modelling and operational problems. In this work, start-up and production phases of the batch distillation of non-ideal binary mixture are modelled by a system of differential and algebraic equations, taking into account mixture non-idealities. Product maximization and time minimization problems are solved by two Pontryagin maximum principle-based approaches—Discretized and Parameterized approach. A case study of ethanol-water mixture batch distillation at two levels of separation difficulty and the liquid holdup is conducted. Results show that optimal time and energy savings of up to 26% can be achieved compared to the Conventional constant reflux ratio profile. Total reflux is confirmed as optimal for the start-up phase, albeit in some cases optimal transition to production phase occurs well before the steady- state composition is achieved. Discretized optimal reflux ratio is a basis for parsimonious input parameterization in the Parameterized approach. The performance of optimal parsimonious input parameterization is negligibly suboptimal compared to the Discretized approach for a fraction of computational cost. It is shown that optimal control performance may strongly vary with the change of process parameters. Proposed methods can be used as a framework for a comprehensive analysis of batch distillation optimal control to provide a path towards increased process sustainability.

Batch distillation ; non-ideal mixture ; optimal control ; Pontryagin maximum principle ; Parameterized approach

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