Controlling the operation of a distillation column

Claim 1

IN A PROCESS WHEREIN A MULTICOMPONENT FEED STREAM IS SEPARATED IN A FRACTIONAL DISTILLATION COLUMN INTO AN OVERHEAD VAPOR STREAM AND A LIQUID BOTTOM PRODUCT STREAM HAVING A SPECIFIED PURITY, SAID OVERHEAD STREAM IS CONDENSED, SOME OF THE CONDENSED OVERHEAD IS RECYCLED TO SAID COLUMN AS AN EXTERNAL REFLUX STREAM, AND SOME OF SoID CONDENSED OVERHEAD IS YIELDED AS A DISTILLATE PRODUCT STREAM HAVING A SPECIFIED PURITY, A CONTROL METHOD COMPRISING THE STEPS OF MEASURING THE AMOUNTS OF LIGHT KEY FEED COMPONENT AND FEED COMPONENTS LIGHTER THAN THE SAID LIGHT KEY FEED; PRODUCING SIGNALS RESPONSIVE TO SAID MEASUREMENTS PROPORTIONAL TO THE AMOUNT OF SAID KEY COMPONENTS; MEASURING A PROCESS VARIABLE INDIICATIVE OF THE FLOW RATE OF FEED TO THE COLUMN; PRODUCING A SIGNAL IN RESPONSE THERETO PROPORTIONAL TO THE FEED FLOW RATE; COMBINING THE FORMER SIGNALS WITH SAID FEED FLOW RATE SIGNAL IN A PREDICATIVE EQUATION DERIVED FROM A MATERIAL BALANCE AROUND SAID COLUMN; COMBINING THE LATTER SIGNALS IN A DISTILLATE FLOW COMPUTER BASED ON THE EXPRESSION: