Simulation And Analysis Of Dividing Wall Column Based On The Rigorous Model

Distillation is one of the most important separation methods in chemical industry. It is reported that there is over 40000 distillation columns across the world. Despite its wide application, one important concern on it is its considerable energy consumption, as distillation can account for more than 50% of plant operating cost. Therefore large numbers of researches have been concentrated on energy efficient distillations. The application of dividing wall columns (DWCs) can not only improve the thermodynamic efficiency, reduce energy cost, but also save equipment investment, which attracts much attention both in industry and academia.The structure of DWC is complex with more freedom, which brings difficulty in establishing the exact model. Commercial process simulators still do not include DWC as a distinct model. In general, the two columns, four columns and pump around model are used to approximately simulate the DWC, which are not able to consider the heat transfer across the dividing wall. In this paper, the short-cut method is adopted for the initial design of the DWC. Then a rigorous DWC model considering the heat transfer across the dividing wall is established, which is simulated and solved by the equation-oriented software, i.e. gPROMS.In order to make a comparison with the existing literatures, the separation of Benzene-Toluene-P-xylene (BTX) system was taken as an example to make a simulation of the dividing wall column without considering the heat transfer firstly. The result of simulation was close to what was in the literatures. Based on this, this paper firstly explored the influence of the liquid and vapor split ratio, the middle component recovery at the top of the prefractionator on the heat duty. Moreover, the mixing effects at the both ends of the dividing wall were also studied. An optimization aiming at making the minimum total heat duty was carried out. The results showed that liquid and vapor split ratio had an important influence on the heat duty of DWC. Suitable liquid and vapor split ratios are helpful for reducing the mixing effects at the both ends of the wall, decreasing the thermodynamic inefficiency, thus lowering the energy consumption.Meanwhile, this paper further found that the driving force of heat transfer existed between the dividing wall, thus the heat transfer was subsistent in theory. Then the simulation of dividing wall column considering the heat transfer were carried out, based on which the influence of the liquid, vapor split ratio on the heat duty and an optimized calculation aiming at making the minimum total heat duty were also investigated. By making comparative analysis of the results between with/without the heat transfer, whether the heat transfer across the wall was beneficial were discussed. And then the influence of heat coefficient on the heat duty was qualitatively explored. The results showed that liquid and vapor split ratio had an important influence on the heat duty of dividing wall column considering the heat transfer. Whether the heat transfer across the dividing wall was beneficial or not is strongly dependent on the operation condition. When the operated liquid and vapor split ratio was more closed to the optimal condition without heat transfer, the heat transfer was adverse and would increase the heat duty of DWC. On the contrary, when the operated liquid and vapor split ratio was more closed to the optimal condition with heat transfer, the heat transfer was beneficial and helpful in reducing the heat duty. When the heat transfer was beneficial, the heat transfer under random heat coefficient could reduce the heat duty of DWC. However, when the heat transfer was adverse, with the increase of heat coefficient, the heat duty would increase notably.