| Along with the global economic recovery after the financial crisis, and the development trend of the world center back on the real economy, the technology innovation and industrial revolution have brought new opportunities to our society. Emerging industry has become a new hotspot, meanwhile, the improvement of the traditional industry has also been a compelling achievement. In the face of energy-intensive distillation industry, energy-saving equipment owns a significant competitive advantage. In traditional separation operation, the foundation of the conventional distillation columns has been challenged by the appearance of the new energy efficient equipments.Dividing-wall distillation column (DWDC) is divided into two parts in vertical space, forming the prefractionator and the main distillation column. The special structure shares the same thermodynamic efficiency with the fully thermally coupling distillation. Compared with the conventional distillation columns, DWDC can not only save capital investment and operation costs, reduce energy consumption, but also achieve the multicomponent mixture separation operation which the products are discharged from the top, side and bottom of the column. However, a DWDC will suffer the so-called black-hole problem when the four-point composition control strategy (i.e., controlling the main compositions of the three products and the ratio between compositions of the two impurities in the intermediate product) is utilized. This potential drawback stems from the material and thermal coupling between the prefractionator and main distillation column.In this work, the steady-state and dynamic mathematic model of the DWDC and the industrial production operation simulation by Aspen are made to establish the comprehensive and systematical research about the inner structure. Then, feed splitting strategy is skillfully used to avoid the black-hole problem in the simple and applicable process synthesis and design. By changing the number, locations, and flow rates of the multiple feeds to the prefractionator, the coupling relationship between the prefractionator and the main distillation column is rebalanced. In addition, two illustrative examples are employed to evaluate the philosophy. Both the steady-state analysis and dynamic studies of two ternary mixtures with hypothetical components, A, B, and C, and ethanol, propanol, and butanol show that feed splitting strategy can be an effective means to circumvent the black-hole problem. Moreover, the strategy is also proved to allow more leverage in energy-saving with respect to the strategy of arrangement of multiple intermediate products to the DWDC. The closed-loop test of the three-point composition control of the design structure after optimization, exhibits that the dynamic characteristic and the controllable performance of the final process design are improved. Furthermore, the promotion degree is speculated to be related to the steady-state energy consumption differences. |
