Abstract: A process for controlling a distillation column in which a feedstock is distilled for separation into a product from the top of the column having a first predetermined content of an intended component with a high boiling point and a product from the bottom of the column having a second predetermined content of an intended component with a low boiling point. The process includes the steps of computing a desired value of the flow rate of the product from the bottom of the column in accordance with a material balance and controlling the flow rate of the bottom product in accordance with a corrected desired value which is derived from one of deviations between the actual and desired compositions of the top or bottom products or limit values depending upon the magnitude and direction of the deviations. Reflux of part of the top product to the column is also controlled in accordance with the direction of the deviations and their magnitudes or limiting values.

Abstract: A process for controlling a distillation column in which feed liquid supplied thereto is heated by heating steam comprises the steps of: controlling the steam flow rate so that the steam flow rate is increased in response to the difference between the temperature measured at the bottom of a calculated column and the temperature of boiling point of the feed liquid until the former temperature exceeds the latter temperature when the former is not higher than the latter; controlling the steam flow rate so that the temperature around an intermediate tray falls within a first predetermined temperature range when the temperature measured at the bottom of the column exceeds the calculated temperature of the boiling point of the feed liquid; controlling the steam flow rate so that a reflux ratio is adjusted to within a predetermined reflux ratio range when the temperature around the intermediate tray falls in the predetermined temperature range; and controlling the steam flow rate so that the reflux ratio is maintain