(195g) Structural Optimization of the Practical Tube-Typed Heat Integrated Distillation Column (HIDiC)

Heat integrated distillation column (HIDiC), since developed to substantially improve the thermal efficiency of distillation process, has always been a research focus in the field of advanced distillation. Amounts of studies on heat distribution, mathematics model establishment and physical model selection have been carried out for the progressive development of HIDiC. However, the industrialization process of HIDiC is nearly stagnant. There only two or three industrial-grade tube-typed HIDiCs were set up in Japan and Netherlands.

Certainly, considering the operability, economy and pressure capacity, the tube-typed HIDiC is the most practical one among the existing physical models. The production capacity of single tube in tube-typed HIDiC is the major design variable which deserves our devotion. When total production capacity of the HIDiC is decided, the production capacity of single tube have a great influence on both of the operating cost and capital cost. To determine the optimal production capacity of single tube, we initially investigated the relationship between production capacity of single tube and the thermal efficiency of tube-typed HIDiC by plenty of process simulations in Aspen Plus. Aiming to obtain accurate and guidance results, the heat transfer parameters, especially the heat transfer coefficient, were measured via the customized heat transfer testing equipment based on the principle of tube-typed HIDiC. For a specific separation target, we found that there is a maximum production capacity of single tube to guarantee that the tube-typed HIDiC could act as an energy saving distillation process. Also, varied with the production capacity of single tube, the highest thermal efficiencies are not all obtained at the state when either condenser or reboiler are not needed. Adopting the total annual cost (TAC) as the optimizing objective, a systematic optimization procedure, mainly based on the economic evaluation theory of distillation process by Douglas, was built to find out the optimal production capacity of single tube. Tested with different separation system, it was verified that the optimization procedure is qualified.

Further, we also felt anxious with the adaptability of the traditional HIDiC model, which separates the column into high pressure section and low pressure section where the feed stage is. There is no doubt that the initial HIDiC platform would more or less lose its advantage in energy saving when the feed stage is changed as the component of feed and separation requirement vary. To improve the adaptability, a novel HIDiC model was proposed. In this novel HIDiC, the high pressure section and low pressure section will share the same number of stages which is equal to half the number of all column stages, and the feed stage will be placed at either high or low pressure section as needed. The novel HIDiC is so called symmetrical heat transfer HIDiC (sym-HIDiC). Evaluated by process simulation in Aspen Plus, under their optimal structure and operating conditions, sym-HIDiCs had almost the same energy saving performance with comparison to tradition HIDiCs when they shared the same separation targets. However, to adapt the change of separation requirement, the tradition HIDiC will be anatomically rebuilt, but it only need to adjust the position of feed stage in sym-HIDiC as a conventional distillation column. Moreover, the pressure difference between two sections has decreased due to this specific heat transfer form. It enhances the safety of HIDiC, and also reduce the capital cost.