Design And Control Of Energy-saving Dividing-wall Distillation Column For Separating Azeotropes

As one of the important paths to chemical intensification, dividing-wall columncommonly offers significant energy and capital savings (typically around30%)compared with conventional two-column sequence for separating some ternarymixtures. According to the differences in vertical location of dividing wall pointing tocolumn shell axis, dividing-wall column can be classified to three types: dividing wallin the middle, dividing wall in the top, and dividing wall in the bottom. The pastresearch focused on the dividing wall in the middle type, while the other two typeswere rarely studied. Meanwhile, the previous study concentrated on the design andcontrol of dividing-wall column for separating zeotropic systems, while the study ofdividing-wall column for separating azeotropes was limited.On the basis of reviewing the earlier research fruits, this work aims at studyingthe design and control of energy-saving dividing wall column (dividing wall in thetop/bottom) for the separation of azeotropes. The main original contributions of thiswork were that energy-saving extractive dividing-wall column and aeotropicdividing-wall column were investigated, with special focus on the design procedure,optimization sequence and control strategy. The conclusions reached in this workwere also of generality to some extent.Firstly, the principle methods and typical technologies for distillation processintensification and energy saving were summarized. The state of the art ofdividing-wall column at home and abroad was reviewed, and the problems individing-wall column research were presented. The research methods, objectives andfocuses of this work were also sketched.Secondly, steady-state design and composition control of extractive dividing-wallcolumn (EDWC) were detailed investigated by the case study of methylal/methanolazeotope separation (dimethyl formamide [DMF] as heavy entrainer). The economicoptimal design of EDWC could offer8.3%energy saving compared with conventionaltwo-column sequence. Two effective composition control structures CCS1and CCS2were sequentially explored and tested. The proposed structure CCS2was furtherapplied to isopropanol/water system (dimethylsulfoxide [DMSO] as heavy entrainer), and dynamic simulations gave an effective control, which verified the generality ofthe structure CCS2to some extent.Thirdly, two pure temperature controls and a differential temperature controlwere proposed sequentially for EDWC (again using methyal/methanol/DMF as casestudy) to replace composition control. Several group dynamic comparisons were alsomade to confirm the effectiveness and superiority of the proposed structure TCS2.The proposed structure TCS2was further applied to other two systems(isopropanol/water/DMSO and acetone/methanol/DMSO), and dynamic simulationsrevealed that this structure gave a fairly effective control, which verified thegenerality of the structure TCS2to some extent.Fourthly, design and control of azeotropic dividing-wall column (ADWC) weredetailed explored using simulation method by the employment of ethanol dehydrationsystem with cyclohexane as light entrainer. Economic comparisons among three typesof distillation sequences (azeotropic-recovery distillation column A1,azeotropic-stripping distillation column A2, and ADWC A3) revealed that thesequence A3offered21.4%and10.9%saving in energy consumption compared withthe sequences A1and A2, respectively. Dynamic comparisons were also made toconfirm that the sequence A3gave comparable controllability with the A1andsuperior controllability over the A2.Finally, the main contributions of this work were summarized, and the furtherwork in dividing-wall column design and control area was prospected.