(449f) Modeling and Experimental Studies on the Start-up of a Divided Wall Column for High-Purity Separation of Aromatic Reformate

The increasing application of divided wall columns in chemical industry is driven by the fact that it can save up to 30% energy and capital cost than conventional separation sequence. Only few works have been reported on the start-up of divided wall columns, which is inherently a strongly nonlinear process. Here, for the first time the start-up of a divided wall column pilot plant is explored for separating an aromatic reformate, which contains trace water, eight aromatic components and two paraffins. Very high product purities above 99.95wt.% are specified. A four step start-up method is proposed and testified in Aspen Dynamics simulation and real operation of the pilot plant. The proposed start-up method is consisted of pre-feeding stage, benzene withdrawing stage, toluene withdrawing stage and continuous feeding stage. In the first three stages, the column pressure drop is selected as the key parameter for control the reboiler duty. In the last stage, the reboiler temperature is the key control parameter for the divided wall column. Besides, controlling the temperature on sensitive plate (Set point equals to steady-state value) by withdraw flowrate in the same section can reduce up to 40% start-up time than withdrawing at a constant flowrate in the second and third stages. The four-loop temperature control structure has been testified effectively on the pilot plant when facing 10% feed flow rate and composition fluctuations. The energy cost is calibrated by a steam vortex flowmeter, and results showed that the energy consumption of the divided wall column can reduce up to 30% than that of the conventional separation sequence, which is also consistent with the simulation results.