(193a) Rapid 1st-Pass Design of Dividing-Wall Columns Via Acyclic Simulation Method

The “acyclic” method was proposed by Navarro et al in 2012 to simulate thermally coupled distillation sequences such as side-strippers. This approach allows coupled columns to be simulated once-through without recycle streams, by emulating the pre-fractionator overheads as a refluxed section with superheated vapor, and the pre-fractionator bottoms as a reboiled section with sub-cooled bottoms. The superheated vapor and subcooled liquid, in turn, are replaced by saturated vapor and liquid streams and parallel heat streams transferring the pre-fractionator condenser and reboiler duties to the main column.

The acyclic methodology was implemented as a process simulation procedure that can be used to easily develop 1^st-pass designs for dividing wall columns (DWC). The acyclic simulation runs much more easily than conventional coupled column simulations with recycle streams between the pre-fractionator and main column, facilitating sensitivity studies and preliminary optimization of the number of stages in each section of the DWC, as well as the liquid split ratios.

An optimized acyclic simulation is readily converted to and initialize the corresponding fully-coupled (“cyclic”) column simulations with recycle streams between the pre-fractionator and main column. The reboiler duties vs. product purity calculated by the acyclic method agree within a few percent of the rigorous cyclic simulations. Final simulations using the cyclic simulations are recommended, to allow for final optimization, dynamic simulation to evaluate control strategies, and calculation of hydraulics which can then be turned over to DWC column internals vendors.

An example is shown of a DWC modeled using Aspen Plus first using the acyclic mode and afterwards converted to a rigorous fully-coupled 2-column model (cyclic mode), and the results are compared.