(84f) Practical Control of Dividing-Wall Columns

In this paper, we have studied the practical implementation of stabilizing control for dividing-wall distillation columns. The focus is on how to operate the column in practice, where the goal is to achieve acceptable operation using simple control policies. In particular, we investigate the importance of properly adjusting the liquid split ratio, which determines the relative amount of reflux to the two sides of the dividing-wall The examples include the 4-product Kaibel column and the more well-known 3-product Petlyuk column. In the study, we assume that the objective is to maximize the purity of all product streams, and we show that setting the correct liquid split ratio is essential in achieving the potential purities. Control configurations with varying number of temperature loops have been tested and compared. We show that the liquid split can be used to control a temperature in the prefractionator section and thereby reduce the sensitivity to disturbances. Adjusting the liquid split is particularly important in reducing the column's sensitivity to the vapor split ratio. We also show that for high-purity columns the need to adjust the liquid split online is even greater.