System of control for fractionation process

Claim 1

IN A FRACTIONATION PROCESS IN WHICH A FLUID MIXTURE IS SUBJECTED TO FRACTIONATION IN A FRACTIONATING COLUMN AND IN WHICH THE OVERHEAD VAPORS FROM SAID COLUMN ARE COOLED IN AN OVERHEAD COOLING ZONE BY INDIRECT HEAT EXCHANGE WITH FLASH EVAPORATING BOTTOMS LIQUID FROM SAID COLUMN, AND THE REBOILING HEAT FOR SAID COLUMN BEING SUPPLIED BY COMPRESSING THE BOTTOMS VAPORS FROM SAID COOLING ZONE AND RETURNING THE COMPRED AND THUS HEATED VAPORS TO THE BOTTOM OF SAID FRACTIONATING COLUMN, THE IMPROVEMENT WHICH COMPRISES WITHDRAWING UNVAPORIZED BOTTOMS LIQUID FROM SAID OVERHEAD COOLING ZONE AS BOTTOMS PRODUCT, CONTINUOUSLY ANALYZING THE COMPOSITION OF THE BOTTOMS PRODUCT, CONTROLLING THE RATE OF WITHDRAWAL OF BOTTOMS PRODUCT FROM SAID COOLING ZONE IN RESPONSE TO CHANGES IN ITS COMPOSITION, SAID RATE BEING DECREASED WHEN ANALYSIS INDICATES EXCESSIVE CONCENTRATION OF A SPECIFIED MORE VOLATILE CONSTITUENT IN THE BOTTOMS PRODUCT, CONTROLLING THE RATE OF DELIVERY OF BOTTOMS LIQUID FROM SAID FRACTIONATING COLUMN TO SAID COOLING ZONE TO MAINTAIN CONSTANT LIQUID LEVEL IN SAID COOLING ZONE, PASSING SAID COMPRESSED HEATED BOTTOMS VAPORS TO SAID FRACTIONATING COLUMN THROUGH A SECOND COOLING ZONE, AND CONTROLLING THE RATE OF COOLING IN SAID SECOND COOLING ZONE IN RESPONSE TO CHANGES IN THE LIQUID LEVEL IN THE BOTTOM OF SAID FRACTIONATING COLUMN, SAID RATE OF COOLLING BEING INCREASED WITH DECREASING LIQUID LEVEL AND DECREASED WITH INCREASING LIQUID LEVEL IN SAID COLUMN.