This thesis presents a systematic approach for the synthesis of reaction-separation-recycle flowsheets including ternary heterogeneous azeotropic mixtures. The methodology incorporates three main components. Firstly, a shortcut distillation model for heterogeneous azeotropic distillation columns is developed. Secondly, a synthesis methodology is proposed for generating, evaluating and screening separation flowsheet alternatives. Finally, the separation flowsheet synthesis methodology is systematically integrated with an existing reactor network design methodology to generate feasible and cost-effective reaction-separation-recycle flowsheets. Heterogeneous azeotropic distillation systems include distillation and decanting operations. Columns with stand-alone decanters and with integrated decanters are considered for separation. A shortcut distillation model is proposed, based on Underwood's method, which is modified to calculate the minimum reflux ratio in ternary heterogeneous distillation columns for direct and indirect splits. The new model requires determination of the controlling fixed point for a given type of split. Case studies demonstrate the applicability of the model for various ternary heterogeneous azeotropic systems. The minimum reflux requirements predicted by the model are in good agreement with those of the more rigorous boundary value method results using commercial software DISTIL and rigorous simulation results using HYSYS. A systematic procedure for synthesising and screening economically promising distillation sequences separating ternary heterogeneous azeotropic mixtures is proposed. The algorithm of Tao et al. (2003) to generate high-purity separation alternatives using distillation and stand-alone decanters is extended to include integrated distillation-decanting configurations. High recoveries of these high-purity products are obtained by recycling non-product streams to suitable destinations within the flowsheet. The recycle destination selection heuristics proposed by Tao et al. (2003) are extended to eliminate uneconomical alternatives. The minimum vapour load of the sequence calculated using the new shortcut model is used as a cost indicator to evaluate and screen separation alternatives. Case studies illustrate the applicability of the synthesis approach and show advantages to integrating distillation and decanting within the separation sequence. A systematic methodology is proposed for synthesising feasible and economically attractive reaction-separation-recycle flowsheets including ternary heterogeneous azeotropic mixtures. Using the separation flowsheet synthesis procedure, flowsheet alternatives are generated and evaluated for separation feed compositions lying in various regions of the ternary composition space. These separation flowsheets are used to construct cost functions in terms of the feed conditions, such as flow rates and compositions. The cost functions are applied within an optimisation framework to explore reaction-separation trade-offs. The reaction-separation-recycle synthesis problem is formulated mathematically with continuous and discrete variables. Economically attractive flowsheets are synthesised by optimisation, using the stochastic optimisation technique of simulated annealing. Two industrially important case studies, vinyl acetate and di-isopropyl ether production, demonstrate the applicability of the proposed approach.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:506227 |
| Date | January 2005 |
| Creators | Vanage, Priti Vasant |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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