Dynamic Effect Of Internal Heat Integration On Reactive Distillation Columns

The combination of the reactive operation and the separationoperation in the reactive distillation column reduces the equipmentinvestment and improves the thermodynamic efficiency effectively. Thereactive distillation column is attracting people's increasing attentionbecause of its energy conservation advantage.For the reactive distillation column, distributing reactive sectionstrictly between rectifying section and stripping section is not always agood design option for a reactive distillation column involving reactionswith highly thermal effect, because the potentials of internal heatintegration between the reaction operation and the separation operationinvolved can not be fully exploited. On the basis of the ratio between thethermal heat released by the reactions involved and the latent heat of thereacting mixture separated, we divided the reactive distillation columninto three broad categories: reactive distillation columns involvingreactions with highly thermal effect, moderately thermal effect andnegligibly or no thermal effect for convenience. For the reactivedistillation columns involving reactions with highly thermal effect, three strategies, i.e., the superimposition of reactive section onto strippingsection, relocation of feed stages, and redistribution of catalyst in thereactive section, can achieve internal heat integration between thereaction operation and the separation operation involved. These strategies,if cautiously used in a combinatorial way, are not only effective forenhancing the thermodynamic efficiency of the reactive distillationcolumns involving reactions with highly thermal effect but also likely toexhibit favorable influences towards process dynamics and controllability.With regard to the detailed impact of each individual strategy on processdynamics and controllability, no systematic studies have been conducted,yet. In this work, the dynamic effect of each individual internal heatintegration strategy is explored in terms of a hypothetical ideal reactivedistillation system containing a highly exothermic reaction: A+B C+D and a real example producing methyl acetate from acetic acid andmethanol.Rectifying operation is an exothermic process and strippingoperation is an endothermic process. Therefore, internal integrationbetween reactive section and stripping section reduces system energyconsumption and is called positive integration. While internal integrationbetween reactive section and rectifying section increases energydissipation burden and is called negative integration. For thesuperimposition of reactive section onto stripping section, the ascent of the lower feed stage and the redistribution of catalyst in the reactivesection, positive internal heat integration is achieved and thethermodynamic efficiency can be improved. To guarantee favorableeffect on process dynamics and controllability at the same time, severalseparating stages should be added to the stripping section to makenecessary compensation for mass transfer driving forces. The descent ofthe upper feed stage improves the thermodynamic efficiency of the idealreactive distillation, but the negative internal heat integration is alsointroduced. The introduced negative internal heat integration generatesserious detrimental effect to the dynamic behavior, and should be avoidedin process synthesis and design.