(109c) Design of a 4-Product Dividing Wall Column: One Vs Multiple Partition Wall Configurations

Preliminary evaluations using a simple but reliable short-cut method indicated that a 15 component aromatic's mixture can be separated very efficiently into four fractions according to given product specifications employing a complex dividing wall column (DWC). Using predicted vapor and liquid splits as initial guesses facilitated carrying out rigorous simulations which indicated that a three-columns-in-parallel internal configuration, which implies installation of two partition walls in parallel, enables higher energy efficiency than more practical, one partition wall configuration. The later has been implemented in practice (one column in operation at BASF) as a packed column equipped with high performance structured packings provided with efficient and robust wall scrappers, which allow fixing the off-centre partition walls by packed beds. From installation and troubleshooting point of view, un-fixed partition walls that are assembled form detachable elements require minimum installation/dismantling effort and time. In this paper a further step has been made, i.e. available technology used to dimension properly a DWC with multiple partition walls placed in parallel in off-centre positions to accommodate internal flow as required according to outcome of rigorous simulations. The liquid splits can be easily set by mechanical means while the multiple vapor splits are arranged by adjusting the parallel sections pressure drop accordingly. This can be achieved by choosing proper design of structured packing and accompanying internals. Simple and complex design options of the four-product DWC are presented, including related total annualized costs, and relative advantages/disadvantages discussed. Although the energy saving gain is substantial the configuration is that complex that from process and mechanical point of view that increased effort and capital as well as related uncertainties do not justify practical implementation.