Energy savings of integrated and coupled distillation systems

Direct separation sequence without, with forward, and with backward energy integration, indirect separation sequence without, with forward, and with b ackward energy integration, sloppy separation sequence without (preflash sy stem), with forward, with backward, and with double energy integration, and thermally coupled sloppy separation sequence (Petlyuk system) are compared with short-cut and rigorous modelling. Based on theoretical considerations and economically evaluated rigorous case studies for ternary mixtures it i s demonstrated that in the most cases the Petlyuk system is not superior to the energy integrated configurations even in energy savings. According to the energy consumption of sharp separation determined by short-cut methodol ogy, all the sloppy sequence structures are equivalent. According to the en ergy losses determined by short-cut methodology, derived here, the energy-i ntegrated structures win almost everywhere in the studied conditions that i nclude a range of relative volatility ratios and the whole feed composition triangle. According to rigorously simulated and optimised results, togethe r with controllability studies, the advantageous application of the thermal ly coupled (Petlyuk) systems is constrained to a very small range of relati ve volatility ratio, feed composition, and price structure. This small rang e is situated somewhere around balanced relative volatility ratio A/B to B/ C, small amount of the middle component B, balanced presence of the two swi ng components A and C in the feed, and high energy costs to investment cost s ratio or slow depreciation rate. (C) 2001 Elsevier Science Ltd. All right s reserved.