Evaporator control method and apparatus therefor

Claim 1

IN AN EVAPORATION PROCESS WHICH COMPRISES SEPARATING SOLVENT FROM A SOLUTE-SOLVENT FEED MIXTURE BY HEAT VAPORIZATION OF AT LEAST A PORTION OF SAID SOLVENT IN AN EVAPORATION ZONE, AND WITHDRAWING FROM SAID EVAPORATION ZONE A PRODUCT SOLUTE-SOLVENT MIXTURE; THE METHOD OF CONTROL WHICH COMPRISES MEASURING THE RATE OF FLOW OF SAID FEED MIXTURE TO SAID EVAPORATION ZONE, PASSING A FIRST SIGNAL REPRESENTATIVE OF SAID RATE OF FLOW MEASUREMENT TO A FIRST CONTROL ZONE, MEASURING THE CONCENTRATION OF SAID SOLUTE IN SAID PRODUCT SOLUTE-SOLVENT MIXTURE, PASSING A SECOND SIGNAL REPRESENTATIVE OF SAID CONNECTRATION MEASUREMENT TO A SECOND CONTROL ZONE, COMPARING SAID SECOND SIGNAL WITH A SET POINT IN SAID SECOND CONTROL ZONE REPRESENTATIVE OF A DESIRED CONCENTRATION OF SAID SOLUTE IN SAID SOLUTE-SOLVENT PRODUCT MIXTURE, PASSING A THIRD SIGNAL RESPONSIVE TO THE RESULTANT COMPARISON FROM SAID SECOND CONTROL ZONE TO SAID FIRST CONTROL ZONE, AND PASSING A FOURTH SIGNAL FROM SAID FIRST CONTROL ZONE TO A MEANS FOR MANIPULATING THE RATE OF FLOW OF HEAT TO SAID EVAPORATION ZONE, THEREBY MANIPULATING SAID RATE OF FLOW OF HEAT RESPONSIVE TO SAID FEED RATE OF FLOW MEASUREMENT, SAID SOLUTE CONCENTRATION MEASUREMENT AND SAID SET POINT OF SAID SECOND CONTROL ZONE.