Abstract: Temperature difference control (TDC) schemes can clearly suppress the adverse influence of pressure variations on product quality control of various distillation columns (DCs) by employing temperature differences (TDs) between the sensitive stage temperature (T_S) and reference stage temperature (T_R), i.e., T_S-T_R, to infer the controlled product qualities. However, because the TDC scheme has failed to specially take the corresponding relationship between the TD employed in each control loop and the controlled product quality into account, it may suffer from relatively large steady-state errors in the controlled product qualities. To address this problem, an enhanced TDC (ETDC) scheme is proposed in the current article, in which an enhanced TD (ETD), i.e., T_S-α×T_R, is employed to replace the conventional TD for each control loop. While the locations of the sensitive and reference stages of the ETD are respectively determined according to sensitivity analysis and SVD analysis, the adjusted coefficient α is set to be the ratio between the averaged absolute variation magnitudes (AAVMs) of the T_S and T_R so that the relationship between the T_S and T_R can be appropriately coordinated. With reference to the operations of three different distillation systems, i.e., one conventional DC distilling an ethanol (E)/butanol (B) binary mixture, one conventional DC distilling an E/propanol (P)/B ternary mixture, and one dividing-wall distillation column distilling an E/P/B ternary mixture, the performance of the ETDC scheme is assessed by compared with the conventional TDC scheme and the double TD control (DTDC) scheme. The dynamic simulation results show that the ETDC scheme is better than the conventional TDC scheme with reduced steady-state errors in the controlled product qualities and improved dynamic responses, and is comparable with the DTDC scheme despite the less temperature measurements are employed.

Key words: Distillation column, Temperature difference, AAVM, Temperature inferential control, Process control

摘要： Temperature difference control (TDC) schemes can clearly suppress the adverse influence of pressure variations on product quality control of various distillation columns (DCs) by employing temperature differences (TDs) between the sensitive stage temperature (T_S) and reference stage temperature (T_R), i.e., T_S-T_R, to infer the controlled product qualities. However, because the TDC scheme has failed to specially take the corresponding relationship between the TD employed in each control loop and the controlled product quality into account, it may suffer from relatively large steady-state errors in the controlled product qualities. To address this problem, an enhanced TDC (ETDC) scheme is proposed in the current article, in which an enhanced TD (ETD), i.e., T_S-α×T_R, is employed to replace the conventional TD for each control loop. While the locations of the sensitive and reference stages of the ETD are respectively determined according to sensitivity analysis and SVD analysis, the adjusted coefficient α is set to be the ratio between the averaged absolute variation magnitudes (AAVMs) of the T_S and T_R so that the relationship between the T_S and T_R can be appropriately coordinated. With reference to the operations of three different distillation systems, i.e., one conventional DC distilling an ethanol (E)/butanol (B) binary mixture, one conventional DC distilling an E/propanol (P)/B ternary mixture, and one dividing-wall distillation column distilling an E/P/B ternary mixture, the performance of the ETDC scheme is assessed by compared with the conventional TDC scheme and the double TD control (DTDC) scheme. The dynamic simulation results show that the ETDC scheme is better than the conventional TDC scheme with reduced steady-state errors in the controlled product qualities and improved dynamic responses, and is comparable with the DTDC scheme despite the less temperature measurements are employed.

关键词: Distillation column, Temperature difference, AAVM, Temperature inferential control, Process control