An MINLP formulation to identify thermodynamically-efficient distillation configurations

Designing configurations for separation of multicomponent mixtures by distillation is challenging because of (i) combinatorial explosion of the choice set, and (ii) nonconvex nature of the governing equations. This work proposes a novel Mixed Integer Nonlinear Program (MINLP) that is formulated to identify configurations that minimize the total exergy loss/maximize thermodynamic efficiency of the separation process. The formulation in its default form has several nonlinear nonconvex equations. We propose a model reformulation via a simple variable elimination technique to reduce the system of nonlinear equations to a single equation, which we refer to as the exergy constraint. We describe the properties of exergy constraints and exploit them in deriving additional valid cuts for the problem. Finally, we use the model for a case study concerning the recovery of Natural Gas Liquids (NGLs) from shale gas.