Simulation Of Internally Heat-integrated Distillation Column And Its Energy Efficiency

As a new and energy-efficient distillation technology, internally heat-integrated distillation column (HIDiC) is studied by means of simulation in this paper. The simulation is performed with commercial software ASPEN PLUS and object-oriented programming language VB6.0. The mixture of benzene-toluene and that of propylene-propane systems are taken as the base cases in the simulations of the characteristics and the energy-saving effect of HIDiC,then the results are compared with those of conventional distillation column (CDIC) and heat-pump distillation column (VRC). The results show that the distributions of temperature, flow rate and composition of HIDiC are different from those of CDIC. For benzene-toluene system, the energy-saving performance of VRC, with the value of 40% compared with the CDIC, is the best and in the case of propylene-propane system,the HIDiC provides the best energy-saving performance of 60%~80%.Since the mode of averaged heat duty (AH) distribution is difficult to achieve in reality, a more reasonable heat duty distribution mode called temperature and heat duty matching (THM) is proposed. The influence of compression ratio, feed thermal condition and distribution mode of heat duty on the characteristics and energy-saving performance of HIDiC was analyzed. It is found that the characteristics and energy-saving performance of HIDiC were influenced significantly by compression ratio and feed thermal condition. The energy-saving performance increases with the decrease of the compression ratio, and the compression ratio is however lower bounded by a limit value beyond which the temperature difference between the rectifying section and the striping section will become negative and a reverse heat-transfer will happen. The energy-saving effect of HIDiC increases with the increasing of vapor ratio in the feed (feed thermal condition). In applying THM,the energy-saving effect is nearly the same as AH, but THM can reduce heat transfer area significantly when the compression ratio is small enough.In the case of separation of multi-component mixture in HIDiC, we get the same trends with the binary systems. It is concluded in general that HIDiC favors the separation of mixtures with smaller relative volatility.