Steady-State Behavior and Dynamic Control of Agrawal Divided-Wall Column for Aromatics Separation

An agrawal divided-wall column (ADWC) has two divided walls and is capable of separating four products mixtures with high purity. This work studies the separation of benzene (B), toluene (T), o-xylene (X) and 1, 3, 5-trimethylbenzene (H) in an ADWC. The steady-state of the ADWC was set up in Aspen, and then an economic optimization configuration and the operation parameter of the column was obtained. The new arrangement of ADWC showed that it had some advantages of the energy and capital cost compared with the conventional direct separation configuration(DS), Kaibel divided-wall column (KDWC) and fully extended Petlyuk divided-wall column (PDWC).It could save about 10% energy and capital cost compared with KDWC, while reduced the structure complexity and had less separation areas compared with PDWC configuration. Composition profiles of the tower showed a few features. The prefractionator splits toluene and 1, 3, 5-trimethylbenzene, and then the middle part of the column splits benzene and o-xylene. In the main column, the upper, middle and lower parts split benzene and toluene, toluene and o-xylene, o-xylene and 1, 3, 5-trimethylbenzene, respectively. The intermediate compounds o-xylene and toluene have some remixing in the prefractionator and the bottom of the middle column, respectively. At last, a composition control structure with 5×5composition control loops was established based on the analysis of the energy consumption and side stream compositions. Results showed that the control structure had good control performances under ±20% flow rate and composition disturbances. © 2017, Editorial Office of Acta Petrolei Sinica(Petroleum Processing Section). All right reserved.