(462a) Steady-State Behavior and Control of Kaibel Distillation Column for Aromatics Separation

Kaibel column permits the separation of a four-component mixture into four pure fractions in a divided-wall column. This work studies the separation of a four-component mixture of benzene, toluene, xylene and tri-methyl-benzene in a Kaibel column. The optimum economic design of the Kaibel column was obtained first, and then seventeen cases of various feed compositions were simulated to investigate the steady state behaviors of the Kaibel column. Results showed that xylene should be controlled at the top of the prefractionator, while toluene should be controlled at the bottom of the prefractionator. The heavy impurities are much larger than the light impurities in the two side streams. These behaviors are very similar to the performances of three -product divided-wall column, but the extra freedom, the xylene side stream, makes it difficult to control. At last, a control structure with five composition control loops was implemented. Simulation showed that it can handle 10% disturbances of flow rate and feed composition, but the xylene side stream sometimes had small purity deviations.