Impact Of Simplifications On The Performance Of An Ideal Heat-Integrated Distillation Column (Ideal HIDiC)

As one of most advanced schemes for distillation columns, ideal heat-integrated distillation column (Ideal HIDiC), which is characterized by internal heat integration between rectifying section and stripping section, features highly thermodynamic efficiency and great potentials of energy saving. Although its invention is dated back to 1990s, it still remains at the stage of theoretical studies and is not yet put into applications in the chemical and petrochemical process industries. The reason can be partially attributed to the extreme difficulties and great complexities encountered in the design and implementation of this kind of internal heat integration into a conventional distillation column, due to the quite limited space within the column shell. Therefore, it is necessary to study the philosophy for the synthesis and design of the ideal HIDiC.According to the viewpoint of structural and functional equivalence, it is topologically feasible to approximate internal heat integration between the rectifying section and the stripping section with three heat exchangers. In this thesis, three process simplifications are derived and studied for an ideal heat-integrated distillation column (S-0). These include one with the heat exchangers located in the tops, middles, and bottoms of the heat-integrated sections respectively (S-1), one with the vapor flows from the top of the rectifying section and compressor as hot flows in the top, intermediate, and bottom heat exchangers respectively (S-2), and one with the vapor flow from the top of the rectifying section as hot flows in the top, intermediate, and bottom heat exchangers respectively (S-3).With the established static and dynamic models of the ideal HIDiC and its simplifications, the impacts of process simplifications on the static and dynamic behaviors are examined based on the separation of an ethylene/ethane binary mixture. It is found that the S-1 is inferior to the S-0 in static performance but with comparable dynamic behaviors. The S-2 and S-3 show smaller capital investment and operating cost than the S-1 but with a sharp degradation in process controllability. Although the augment of total heat transfer areas of the three internal heat exchangers could lead to a reduction in operating cost, almost no favorable effect is identified on process operation. In order to derive a feasible simplification of the ideal HIDiC, one has therefore to exercise a careful trade-off between process synthesis and design and process dynamics and controllability.