Single- and multi-objective optimisation of hybrid distillation-pervaporation and dividing wall column structures

The separation of azeotropic mixtures is often energy intensive, thus process intensification (PI) becomes an attractive route to enhance energy efficiency. Two of the most commonly used separation intensifications are dividing wall columns and hybrid distillation-membrane processes. In this work, three typical hybrid distillation structures, distillation followed by pervaporation (D-P), pervaporation followed by distillation (P-D), and distillation followed by pervaporation then by distillation (D-P-D), are considered and compared with a hybrid dividing wall column (H-DWC) structure, which is a highly integrated process combining a dividing wall column and a pervaporation membrane network. The four structures are compared by both single-objective and multi-objective optimisation. It is shown that the D-P-D and H-DWC structures require significantly lower total annualized costs than the other two designs due to requiring smaller membrane area, as these two structures use the membrane only to help the mixture composition cross the azeotropic point

A shortcut design method for complex distillation structures

Distillation is by far the most common fluid separation method in the chemical industry, and its design is routinely conducted using commercial design software, often based on initial shortcut calculations. Whilst simulation and optimisation of simple distillation systems are fairly straightforward, the design of more complex structures, such as dividing wall columns (DWC), can prove problematic due to failure to initialise or to converge, and no adequate shortcut methods exists for these structures. In this work, a novel shortcut method is presented which can solve the shortcut design problem simultaneously also for complex structures using a simple optimisation procedure without the need for iterative manual calculations. The method is illustrated by four case studies. The shortcut design variables obtained using this method can be used to initialise rigorous simulation or optimisation problems, thus greatly reducing the risk of initialisation failure or convergence issues, also for very complex structures