Efeito do teor de solvente sobre o custo anual total, consumo específico de energia e eficiência termodinâmica na obtenção de etanol anidro via destilação extrativa: configurações convencionais e termicamente acoplada.

Abstract

The most popular process for the ethanol/water separation is extractive distillation using ethylene glycol as solvent. Extractive distillation is used widely in a number of processes, but its highenergy consumption is the major disadvantage. Designing economically optimal extractive distillation sequence is still a challenge in the area of process synthesis. This is partially due to the numerical problems arising from the large number of nonlinear equations and strong nonconvexities. Although there are some interesting and successful approaches, the problem still requires suitable solution methodology.An innovative solution to overcome the drawback of energy intensive extractive distillation process is using advanced process intensification, such as thermally coupled distillation columns. Thermally coupled distillation sequences are considered a valid alternative in order to reduce the energy demand and the capital cost of conventional distillation sequences. In both cases, the presence of a large number recycle streams slows down the simulation, making convergence difficult. In this work, we present a very straightforward procedure (based on a new parameter, the solvent content in solvent feed stage of theextractive co!umn)that enables simulation of these systems in such a way that they can be simulated without convergence problems. Besides that, the procedure makes a sensitivity analysis that enable find the optimum global operation point of each sequence considered here. Using the proposed procedure, the thermally coupled sequence is compared with the conventional extractive sequence. The main operation parameters were calculated so that purity of ethanol was specified. Considering the optimum operational point of each sequence, thermally coupled sequence is less energy intensive. But, thermally coupled sequence has a higher remixing effect and hence lower thermodynamic efficiency. The economics of the extractive distillation configurations are evaluated in terms of capital investment and energy costs.The economics of the two alternative processes show that the total annual cost of the thermally coupled extractive distillation sequence is substantially smaller than that of the conventional extractive distillation sequence.