Continuously operating superatmos-pheric distillation process control and apparatus therefor

Claim 1

IN A PROCESS FOR THE CONTINUOUS DISTILLATION OF A STREAM OF AN INTAKE MIXTUE WHICH IS CARRIED OUT AT SUPERATMOSPHERIC PRESSURE IN A MULTITRAY DISTILLATION COLUMN HAVING A FEED PREHEAT ZONE AND BOTH A RECTIFYING SECTION AND A STRIPPING SECTION, WHREIN THE OVERHEAD VAPORS ARE CONDENSED IN A CONDENSER AND COLLECTED IN AN ACCUMULATOR AND BOTH REFLUX IN THE UPPER PORTION AND RE-EVAPORATION IN THE BOTTOM PORTION OF THE COLUMN ARE USED, AND WHREIN THE AMOUNT OF REFLUX, THE DEGREE OF REEVAPORATION, THE TOP PRODUCT FLOW AND THE BOTTOM PRODUCT FLOW ARE CONTROLLED SUCH THAT THE TOP PRODUCT ACCUMULATOR LEVEL AND THE BOTTOM PRODUCT LEVEL IN THE COLUM ARE ADJUSTED TO PREDETERMINED RESPECTIVE LEVELS AND THE DESIRED QUALITY OF THE SEPARATION AS MEASURED BY A QUALITY METER IS ATTAINED, THE IMPROVEMENT COMPRISING: ALLOWING THE PRESSURE IN THE COLUMN TO FREELY ADJUST ITSELF BETWEEN THE MAXIMUM AND MINIMUM PERMISSIBLE OPERATING PRESSURES FOR THE COLUMN; SUPPLYING THE MAXIMUM POSSIBLE QUANTITY OF COOLING MEDIUM TO THE CONDENSER BY MAINTAINING THE VALVE GOVERNING THE SUPPLY OF COOLING MEDIUM TO THE CONDENSER OPEN AS WIDE AS POSSIBLE WITHOUT REDUCING THE COLUMN PRESSURE BELOW THE MINIMUM PERMISSIBLE OPERATING RANGE; PREHEATING SAID STREAM OF INTAKE MIXTURE TO THE DISTILLATION COLUMN WITHTHE MINIMUM POSSIBLE QUANTITY OF HEAT BY MAINTAINING THE VALVE GOVERNING THE HEATING MEDIUM TO THE FEED PREHEAT ZONE AS NEARLY CLOSED AS POSSIBLE WITHOUT CAUSING OVERLOADING OF THE TRAYS OF THE STRIPPING SECTION OF THE COLUMN; AND DECREASING THE DEGREE OF RE-EVAPORATION BY REDUCING THE SUPPLY OF HEATING MEDIUM TO THE RE-EVAPORATION SECTION WHENEVER THE MAXIMUM PERMISSIBLE LOAD ON THE COLUMN TRAYS OF THE RECTIFYING SECTION OF THEDISTILLATION COLUMN IS EXCEEDED; WHEREBY THE COSTS OF OPERATING THE DISTILLATION PROCESS ARE MINIMIZED WHEN THE DISTILLATION TAKES PLACE IN A PRESSUE RANGE WHERE HE TRAY LOAD INCREASES WITH INCREASING PRESSURE AND WHERE THE COST OF THE HEATING MEDIUM USED FOR PREHEATING THE FEED IS RELAVTIVELY EXPENSIVE IN COMPARISON WIT THE HEATING MEDIUM USED FOR RE-EVAPORATION.