The design and control of the pressure swing distillation (PSD) for the separation of methanol and benzene binary minimum azeotropic system were explored based on the pressure sensitivity of the azeotropic composition. Aspen Plus (8.4 V) software was used to simulate and optimize the steady state process by the minimization of total annual cost (TAC). Based on the optimal steady state results, three kinds of the control structure including basic control structure, ratio control structure and double ratio and temperature?component combined control structure for the PSD process were put forward to maintain the purity of the product. According to the temperature slope criterion by Luyben, the stage 13th in the low pressure distillation is selected as the temperature sensitive stage. However, it was somewhat difficulty for selecting the temperature sensitive stage for the high pressure distillation. Because the maximum value of the temperature slope was the stage 21th which was the bottom of this column. If the stage 21th was chosen to the temperature sensitive stage, it was very difficult to maintain the temperature as a constant value. So the stage 20th was selected as the suitable temperature sensitive stage by the liquid composition distribution. The ±20% feed flowrate and composition disturbances were used to test the dynamic performances of these control structures. The results showed that the selection of the temperature sensitive stage was reasonable and the basic control structure can basically achieve robust control, but the problem of product purity deviation due to component disturbances cannot be solved. Ratio control structure can achieve relatively robust control, but the purity of methanol in the bottom stream of the LPC (B1) still cannot return back to the desired value. The double ratio and temperature?component combined control structure can effectively maintain the product purity of 99.90% when the control loop arrives at a new steady state after encountering ±20% changes in feed flowrate and feed methanol.
Liping Lü Hang LI Bing LI Jianhua XU
. Dynamic control of pressure-swing distillation for separating azeotropic system of methanol/benzene[J]. The Chinese Journal of Process Engineering, 2018
, 18(5)
: 1003
-1012
.
DOI: 10.12034/j.issn.1009-606X.217378
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