Method for control of a distillation process

A method for controlling the operation of a petroleum fractional distillation column, wherein a feed stream is provided to said fractional distillation column and a plurality of petroleum fraction product streams are withdrawn from said fractional distillation column, said method comprising the steps of:

• a) providing a composite feed stream to the column;
• b) withdrawing a plurality of product streams from the column by a like number of product stream conduits;
• c) flowing a stream of material through a first recycle conduit from a first location in the column to a second location in the column;
• d) selecting a product stream of interest;
• e) measuring the temperature of said selected product stream of interest and establishing a first signal representative of said first measured temperature;
• f) measuring one of the temperatures selected from the group consisting of the temperature of the product stream being withdrawn from said column immediately above said product stream of interest and the temperature in said column at a point between the point of withdrawal of said product stream of interest and the point of withdrawal of said product stream being withdrawn from said column immediately above said product stream of interest and establishing a second signal representative of said second measured temperature;
• g) measuring one of the temperatures selected from the group consisting of the temperature of the product stream being withdrawn from said column immediately below said product stream of interest and the temperature in said column at a point between the point of withdrawal of said product stream of interest and the point of withdrawal of said stream being withdrawn from said column immediately below said product stream of interest and establishing a third signal representative of said third measured temperature;
• h) measuring the temperature of said feed stream and establishing a fourth signal representative of said fourth measured temperature, wherein the steps of measuring the first, second, third and fourth temperatures may be carried out in any order;
• i) transmitting said first, second, third and fourth signals to a digital computer programmed with a first algorithm and a second algorithm;
• j) utilizing said first, second, third and fourth signals and said first algorithm to estimate in said computer selected points on a true boiling point curve for said product stream of interest;
• k) using said estimated points on said true boiling point curve and said second algorithm to calculate in said computer a substantially complete true boiling point curve for said selected product stream of interest;
• l) using said calculated true boiling point curve to infer selected properties of said selected product stream of interest;
• m) comparing said inferred properties with desired properties of said product stream of interest;
• n) using the differences between said inferred properties and said desired properties to determine an adjustment to be made in at least one selected operating parameter of said fractional distillation column;
• o) establishing a fifth signal representative of said desired adjustment of said selected operating parameter of said distillation column;
• p) transmitting said fifth signal to a control device of said fractional distillation column;
• and
• q) adjusting the operation of said control device responsive to said fifth signal in order to adjust the operation of said fractional distillation column.