The azeotropic composition of ethyl-acetate/n-hexane azeotropic system dramatically shifts with pressure. Therefore, this system can be effectively separated by pressure-swing distillation (PSD). In order to save the total annual cost (TAC) and energy, the partially and fully heat-integrated pressure-swing distillation (HIPSD) between condenser and reboiler of two columns were used in this process. The simulation and optimization of different heat-integrated PSD processes were carried out by using Aspen Plus software. The results showed that the energy cost, equipment cost and TAC of the fully HIPSD process had further reductions of 12.24%, 4.38% and 8.60% compared with partially HIPSD process. On the basis of the best optimal process, feed flowrate and composition disturbances with several different degrees were introduced to test the dynamic characteristics of different control structures for partial and fully HIPSD processes by Aspen Dynamics. For partially HIPSD process, three kinds of control structure including basic control structure, proportional control structure and pressure-compensated temperature control structure were developed to test the effectiveness of control structures. The results of the dynamic response showed that the pressure-compensated temperature control structure could handle the feed flowrate and composition disturbances with different degrees and effectively maintain the purity of ethyl acetate and n-hexane products at 99.9wt%. For fully HIPSD process, the composition/temperature cascade control structure could effectively handle the small disturbances (±5% and ±10%) and achieve robust control, but this control structure cannot effectively maintain the product purity of 99.90wt% and realize robust control when subject to ±20% feed and composition disturbances. Compared with the partially HIPSD mode, the fully HIPSD mode could handle much smaller feed flow rate and composition disturbances despite of a little economic benefit. Therefore, the selection of energy-saving modes for the separation process should weigh economy against controllability.
Liping Lü Hang LI Shuhua HE Jianhua XU Bing LI
. Design and control of ethyl acetate/n-hexane azeotropic system separation via different heat-integrated pressure-swing distillation process[J]. The Chinese Journal of Process Engineering, 2019
, 19(6)
: 1167
-1177
.
DOI: 10.12034/j.issn.1009-606X.219115
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