(391h) Heat Pumps for Electrification of Multicomponent Distillation Trains: An MINLP Formulation

Thermal separations are crucial to chemical and petrochemical sectors, but they significantly contribute to fossil fuel consumption and greenhouse gas emissions. Distillation is the primary separation technology, accounting for 90-95% of all liquid phase separations¹ and around 2.5% of total energy consumption in the USA². To address this sustainability challenge, it is critical to enhance the energy efficiency of distillation.

One potential solution is to electrify the process using heat pumps. This will reduce greenhouse gas emissions by utilizing energy from renewable sources while increasing the exergy efficiency of distillation, ultimately reducing the energy required for the given separation³. However, feasibility and efficiency of heat pumping for multi-component separation depends on the operating conditions and sequencing of splits. A sequential optimization approach that involves selecting configuration before integrating heat may produce sub-optimal designs and leave valuable opportunities untapped. Therefore, an approach that models and globally optimizes distillation train sequencing is needed.

In this study, we present a new shortcut model, that relies on a simple algebraic equation which accurately predicts the work requirement of a mechanical vapor recompression type heat pump for any number of components without using cumbersome thermodynamics. We integrate this equation into a superstructure based Mixed Integer Non-Linear Programming (MINLP) formulation which embeds the complete search space of configurations, thereby creating the first comprehensive approach to finding globally optimum Heat Pump Assisted Distillation (HPAD) designs for general `n' component zeotropic separations. Using a few case studies, we demonstrate the potential savings and greenhouse gas reductions that can be achieved by exploring the use of heat pumps.

In summary, this study highlights the significant role of heat pumps in improving energy efficiency of distillation while reducing greenhouse gas emissions. The proposed approach offers a promising pathway towards a more sustainable future for chemical and petrochemical industry.

(1) Humphrey, J. L.; Keller II, G. E. Separation Process Technology: Performance, Selection, Scaleup. McGraw Hill 1997.

(2) Chapas, R. B.; Colwell, J. A. Industrial Technologies Program Research Plan for Energy-Intensive Process Industries. 2007. https://doi.org/10.2172/1218715.

(3) Tumbalam Gooty, R.; Chavez Velasco, J. A.; Agrawal, R. Methods to Assess Numerous Distillation Schemes for Binary Mixtures. Chemical Engineering Research and Design 2021, 172, 1–20. https://doi.org/10.1016/J.CHERD.2021.05.022.