Method and apparatus for controlling a distillation system

Claim 1

IN A FRACTIONAL DISTILLATION OPERATION WHEREIN A VAPOROUS OVERHEAD FRACTION AND A LIQUID BOTTOMS FRACTION ARE WITHDRAWN FROM A FRACTIONAL DISTILLATION ZONE, AT LEAST A PORTION OF THE VAPOROUS OVERHEAD FRACTION BEING CONDENSED IN A PAIR OF CONDENSING ZONES OPERATED IN PARALLEL TO PRODUCE A FIRST CONDENSATE AND A SECOND CONDENSATE AND THE REMAINDER BEING INCONDENSED, A METHOD FOR MAINTAINING SAID DISTILLATION ZONE UNDER A PREDETERMINED OPERATING PRESSURE COMPRISING MAINTAINING A REFLUX ACCUMULATION ZONE UNDER A PREDETERMINED PRESSURE LOWER THAN THE FIRST MENTIONED PRESSURE BY PASSING THE UNCONDENSED PORTION OF SAID VAPOROUS OVERHEAD FRACTION INTO SAID ACCUMULATION ZONE IN RESPONSE TO PRESSURE WITHIN SAID ACCUMULATION ZONE, PASSING A PORTION OF THE LIQUID CONDENSATE FROM SAID ACCUMULATION ZONE INTO SAID DISTILLATION ZONE AS REFLUX AT A PREDETERMINED RATE, INTRODUCING FEED STOCK TO BE DISTILLED AND A REBOILING HEAT EXCHANGE MEDIUM INTO SAID DISTILLATION ZONE AT PREDETERMINED OPERABLE RATES, COMBINING THE FIRST AND SECOND CONDENSATES, REGULATING THE TEMPERATURE OF THE COMBINED CONDENSATES AT A PREDETERMINED TEMPERATURE BY REGULATING THE RATE OF WITHDRAWAL OF CONDENSATE FROM ONE OF SAID CONDENSINF ZONES IN RESPONSE TO THE TEMPERATURE OF THE COMBINED CONDENSATE, AND PASSING THE COMBINED CONDENSATE INTO SAID ACCUMULATION ZONE IN RESPONSE TO PRESSURE WITHIN SAID DISTILLATION ZONE.