For most separations fully thermally coupled distillation columns are thermodynamically more efficient than conventional arrangements. In spite of the superiority of double-effect distillation systems to a single column concerning energy savings these systems are not often used in the industrial practice, because of the disadvantages in dynamic operability. Generally the product switchover is a complicated and protracted operation, where many process variables must be changed simultaneously. The economic and ecological interest is to minimize the time of switchover periods, which are generally non-productive and require long times especially for coupled systems. The aim of this study is to reduce the time needed for the product switchover of coupled distillation systems. This paper presents a new product switchover strategy, which will lead to a time saving of 57%. Furthermore, a new startup strategy is developed and verified in experimental studies. The results demonstrate that using the optimized startup strategy a time saving of 57% can be achieved too and thereby these unproductive periods can be reduced significantly. (C) 2001 Elsevier Science B.V. All rights reserved.
