ABSTRACT
The rectification section of distillation column above the feed point is primarily for removing heavy impurities from the distillate. The frequency of failure rate has increased in the distillate stream because the column temperature is high and more heavy key impurity is in the distillate while the bottoms stream is being overpurified. For the case of an upper specification limit of 1,000 ppm heavy key impurity in the distillate stream and a standard deviation of 100 ppm impurity, the desired impurity concentration may be 700 ppm, that is, 3 standard deviations below the upper specification limit. For the case of a distillate that forms an azeotrope with 30% heavy key impurity, the column may be designed for upper specification limit of 32% heavy key impurity, and the standard deviation of impurity concentration may be 0.2%. The maximum economic return from a distillation column is achieved by reducing variability, striking balance between the distillate and bottoms quality, and reducing energy consumption.
