Optimisation of Heat-integrated Distillation Schemes Based on Shortcut Analysis, Pinch Analysis and Rigorous Simulation Mansour Emtir* and Mansour Khalifa Libyan Petroleum Institute, P.O. Box 6431 Tripoli, Libya *e-mail: memtir@yahoo.com Abstract Conventional and non-conventional distillation schemes for the separation of ternary mixture are investigated and optimized based on shortcut calculations, pinch analysis and rigorous simulation in order to achieve the highest saving values in energy and total annual cost (TAC) as the optimization objective function. The studied chemical system is benzene, toluene and m-xylene with feed composition of (25/50/25) and 99.9 mol % product purity. The optimization parameters are feed compositions. The state of feed condition is considered as the optimization parameters; feed at 20 °C, liquid at bubble point and vapor at dew point. The results from shortcut and pinch analysis are found to be very close to rigorous simulation results regarding number of stages, reflux ratios and utilizing trim reboiler or trim condenser in studied distillation schemes. Both shortcut and rigorous optimization results indicate that heat-integrated schemes are consuming less energy compared to non- integrated distillation schemes, consequently TACs of heat-integrated schemes are attractive compared to non-integrated schemes. The state of feed conditions is playing imprtant role on the percentage of saving and direction of integration. Introduction Distillation units are the most widely used technique for the separation of fluid mixtures in chemical and petrochemical industry. It is known that distillation is used for the separation of about 95% of all fluid separations in the chemical industry, and that around 3% of the total energy consumption in the world is used in distillation units (Hewitt et al 1999). The main disadvantage of the distillation is its high-energy requirement. As a result, new distillation sequences are emerging in order to reduce or improve the use of energy so that, there are several techniques which used to overcome this problem like integration of the distillation column with the overall processes which can give significant energy saving, e.g. Smith and Linnhoff (1988), Mizsey and Fonyo (1990), but these kinds of improvements can be limited. There are different configurations or distillation schemes that can be applied to get more energy saving, like integration of distillation columns with forward or backward heat integration, side-stripper, side-rectifier, fully thermally coupled distillation column (Petlyuk column) or dividing-wall column, heat-integrated of sloppy sequence, and double heat integration sequence. Energy-integrated distillation schemes give a great promise of energy savings up to about 70%. In addition to saving energy, which are accompanied by reduced environmental impact and site utility costs; there is also a possibility for reduction in capital costs. Theoretical studies, e.g. Petlyuk et al. (1965), Stupin and Lockhart (1972), Fonyo et al. (1974), Stichlmair and Stemmer (1989), Annakou and Mizsey (1996), Dunnebier and Pantelides (1999), Emtir et al. (2001), Kolbe and Wenzel (2004) have shown that the column coupling configurations are capable of achieving typically 28-33 % of energy