(45m) Paralleled Double-Effect Distillation: Simulative Case Studies

Multi-effect or heat integrated distillation is one of the effective methods to reduce the consumption of energy. Considering the interaction between investment of plants and energy saving effect, double-effect or heat integrated distillation has been the most widely used in not only research but also field application. It requires less steam and cooling water than the conventional distillation, so as to attain more efficient energy utilization. Sometimes, chemical engineers may have to make a choice between the cascade-effect and the paralleled double-effect when one high pressure column provides heat for two or more columns.

The core of this paper is to rearrange the common distillation schemes by double-effect distillations, and the transformed scheme is evaluated through comparing exergy analyses of the distillation columns in both of the counterparts, which is based on the second law of thermodynamics and a measure of the quality and efficient use of energy. On the basis of the prevalent methanol distillation scheme and organosilicon monomer distillation scheme, novel five-column methanol distillation schemes and paralleled double-effect organosilicon monomer distillation schemes are proposed with the aid of computer simulation. The results of the total exergy loss of these schemes show that the new schemes can cut the corner of energy consumption by 21.5% and 40.41%, respectively, in comparison to their popular cousins.

The two examples clarify that the key of double-effect distillation process lies in the reasonable adjustment of the distribution of energy, the operating conditions and the configuration of some columns. It not only reduces the quantity of energy consumption, but also lowers the quality of energy. For factories with a large numbers of old distillation schemes of high energy requirement, the paralleled schemes head for the way to improve economic benefit.