Finding Better Limit Cycles in Semicontinuous Distillation. 2. Extended Back-Stepping Design Methodology

In Part 1 [Madabhushi and Adams Ind. Eng. Chem. Res. 2019, 10.1021/acs.iecr.9b02639 ] of this work, we introduced a new design procedure, called the back-stepping design methodology, for the design of zeotropic ternary semicontinuous distillation systems using the aspenONE Engineering suite. The objective of this paper (Part 2) is to present an extended back-stepping design methodology for certain cases whose design space contains a large number of designs that result in an undesirable steady-state behavior compared to a relatively small number of desirable periodic steady states. The extended methodology uses the principal component analysis technique to identify and constrain the domain of the design space to a much smaller region. This domain restriction helps in optimization by greatly reducing that amount of time spent exploring undesirable regions and is particularly useful for high dimensional spaces. The extended design methodology was applied to design the semicontinuous distillation of dimethyl ether, methanol, and water, as a case study. Results indicate that the new design procedure outperforms the status quo by finding a limit cycle that is 57% lower in separating cost.