Simulation Of Fully Thermally Coupled Distillation Column And Its Energy Efficiency

Fully thermally coupled distillation column (Petlyuk) is studied by means of rigorous simulation in this paper. The simulation is performed with commercial software ASPEN PLUS. Primary specifications for the theoretical tray numbers, feed and liquid withdraw locations as well as the reflux ratio are estimated with a shortcut method. By the rigorous simulations, the feed and withdraw tray locations, the overhead fraction of the distributed component in the prefractionator, as well as the split ratios for the gas and liquid phases Rv and Rl respectively are optimized. The ternary mixture of pentane-hexane-heptane is used in the simulation to investigate the characteristics of Petlyuk.The study focused on the influence of vapor split ratio Rv, liquid split ratio Rl on the overall expense and characteristics of Petlyuk and it is found that the influence was significant. The optimal value of Rl was firstly found for a particular Rv and a series of trials were made for different values of Rv to find the optimal solutions for both Rl and Rv in terms of energy cost minimization. The influence of parameters Rv and Rl on the product purities and the operability of the Petlyuk was also investigated.A Petlyuk for the separation of a multi-component mixture of C3~C5 hydrocarbons that may rise in ethylene process industry was simulated for the following thee different kinds of feed conditions: a. equal composition for the three components, b. the composition of component C4 is abundance and c. the composition of component C4 is lack. The simulated results on the consumptions for the thee cases were compared with those for the direct thermally coupled sequence (CTDC)﹑indirect thermally coupled sequence (ITDC)﹑direct conventional sequence (DCS)﹑indirect conventional sequence(ICS). The comparisons demonstrated that the Petlyuk gave the lowest energy consumption for the case of C4 abundance, 15.7% lower than the DCS. And the CTDC and ITDC consumed lower energy than the Petlyuk for the other two cases, 16% lower for the case of lack of C4 and 14.1% lower for the other respectively comparing to the DCS. Then the utility costs and total annual costs of the five different columns are analysed,the results show that the Petlyuk and the indirect thermally coupled sequence(ITCS)cost more than conventional distillation columns as propylene refrigerant is introduced. Direct thermally coupled sequence(DTCS)is the best among all.