Abstract: A desired separation between sidedraw product streams withdrawn from a fractional distillation column is maintained by controlling the flow rate of the external reflux associated with a particular sidedraw product stream in response to the output signal from a temperature controller which is reset by an internal reflux controller. Such cascade control improves the stability of a fractionation process and provides for good control of the separation between sidedraw product streams.

Abstract: In a fractional distillation process in which it is desired to maintain a desired ASTM end point temperature of the overhead liquid product withdrawn from the fractional distillation process, changes in the slope of the equilibrium flash vaporization boiling point line are utilized to determine the actual slope of the ASTM boiling point curve at any particular time. The actual ASTM end point temperature for the overhead liquid product is derived based on the actual slope of the ASTM boiling point curve thus determined. The actual ASTM end point temperature is utilized to control the fractional distillation process so as to maintain a desired ASTM end point temperature for the overhead liquid product withdrawn from the fractional distillation process.

Abstract: In a fractional distillation process in which it is desired to maintain a desired ASTM end point temperature of the overhead liquid product withdrawn from the fractional distillation process, changes in the heat removed by the fractional distillation process per unit of the feed are utilized to determine the equilibrium flash vaporization initial point and the equilibrium flash vaporization end point temperature for the overhead liquid product. The initial point temperature and end point temperature are then utilized to determine the actual slope of the equilibrium flash vaporization boiling point line. Changes in the slope of the equilibrium flash vaporization boiling point line are utilized to determine the actual slope of the ASTM boiling point curve at any particular time. The actual ASTM end point temperature for the overhead liquid product is derived based on the actual slope of the ASTM boiling point curve thus determined.