Distillation-based separation systems case studies

A preflash configuration is studied for this case study to reduce vapor load in the main column. The preflash is introduced to separate light products (overhead vapor. Distillate and Heavy Naphtha (HN)) outside the system. In the base case, the feed is heated from 24°C, where the vapor fraction is zero to 335°C to vaporize 76% of the feed. In the preflash configuration, the feed is preheated first from 24°C to 193°C to vaporize 30% of the feed. This preheated feed is flashed in a preflash tank to remove this light material. The vapor product of this preflash tank is processed in a separate column. 

Despite these many studies, reactive distillation is not the best solution to couple reaction and separation, mainly for three reasons (1) in most of the cases, the esterification medium (reagents plus products) is a nonideal system (not really fit for vapor-equilibrium-based technology such as reactive distillation) (2) pure water cannot be selectively removed from the top or the bottom of the column and (3) reactive distillation is a high-energy consumption technology (because separation is based on conventional distillation) (Lim, Park, Hung, Sahimi, Tsotsis, 2002 Drioli Giomo, 2010). 

A comparative study of the energy requirements and control properties of three thermally coupled distillation schemes and two conventional distillation sequences for the separation of ternary mixtures is presented. The responses to set point changes under closed loop operation with proportional-integral (PI) controllers were obtained. Three composition control loops were used, and for each separation scheme, the parameters of the PI controllers were optimized using the integral of the absolute error criterion. The effects of feed composition and of the ease of separability index were considered. The results indicate that there exist cases in which integrated systems may exhibit better control properties than sequences based on conventional distillation columns. 

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