Design And Control Of Reactive Dividing-wall Distillation Columns With Single External Recycle

Reactive distillation represents an effective process intensification technology,in which reaction operation and separation operation are combined into one unit.On the one hand,capital investment costs in the technological process can be reduced greatly.On the other hand,it increases the conversion rate of reactants and restrains the emergence of intermediate largely.Because of the numerous advantages of reactive distillation,reactive distillation becomes an important research direction in process intensification.Dividing-wall distillation column is defined by placing a vertical baffle within the traditional distillation column and thus divided into four parts including rectifying section,stripping section,feed section and middle section.It is actually a special structure of fully coupled thermal distillation column.They are equivalent in thermodynamically if the heat transfer effect of the baffle is ignored.In previous studies,we found that the heat transfer of the reaction tower can be recycled and utilized,which can reduce the energy consumption of the whole system.The combination of reactive distillation column and dividing-wall distillation column has many advantages.If they are combined together,the energy saving effect will be further improved.A reactive dividing-wall distillation column with single external recycle is proposed in the current work.The dividing-wall can restrain the extraction of a large of products from the side stream and the single external recycle leads the unreacted reactants back to the reaction section to react.Based on the esterification of synthesis of methyl acetate,the annual total investment was used as objective function to optimize the number of trays in common rectifying section,the number of trays in common stripping section,the number of trays in reaction section,the number of trays in prefractionator rectifying section,the number of trays in prefractionator stripping section,feeding location of HAc,feeding location of MeOH,feeding location of circulation,extraction location of circulation,circulation flow,vapor phase separation ratio,liquid phase separation ratio and so on.Then,the optimum RDWC-SER is compared to the reactive distillation column with an external recycle from the bottom to certain stage of the reactive section.In addition,the dynamic performance of the double temperature control strategy for the RDWC-SER is studied by feed flow disturbance and feed composition disturbance.The results show that the RDWC-SER design achieves a 7.86%savings in TAC as compared to the reactive distillation column with an external recycle from the bottom to certain stage of the reactive section.It indicates that RDWC-SER has better energy saving effect.In addition,the double temperature control strategy has a better control performance for RDWC-SER structure.Firstly,the control performance for the increase of 10%in the feed flow is better than for the decrease of 10%in the feed flow.Secondly,the control performance for MeOH composition disturbance is better than for HAc composition disturbance.