Control system for gas separation process

Claim 1

A PROCESS FOR THE SEPARATION OF A MIXTURE OF GASES COMPRISNG PASSING THEMIXTURE THROUGH AN INDIRECT HEAT EXCHANGING ZONE TO LIQUEFY A PORTION OF SAID MIXTURE,INTRODUCING THE THUS COOLED MIXTURE INTO A SEPARATION ZONE, WITHDRAWING UNCONDENSED GASES FROMSAID SEPARATION ZONE, WITHDRAWING LIQUID FROM SAID SEPARATION ZONE, FLASHING THE THUS WITHDRAWN LIQUID, PASSING THE FLASHED FLUID THUS OBTAINED THROUGH SAID HEAT EXCHANGING ZONE IN INDIRECT HEAT EXCHANGEING RELATIONSHIP WITH SAID MIXTURE, AND CONTROLLING AT A POINT DOWNSTREAM OF SAID INDIRECT HEAT EXCHANGING ZONE THE PRESSURE TO WHICH SAID WITHDRAWN LIQUID IS FLASHED AS A FUNCTION OF THE LIQUID LEVEL IN SAID SEPARATION ZONE BY INCREASING THE PRESSURE TO WHICH SAID WITHDRAWN LIQUID IS FLASHED AS A FUNCTION OF AN INCREASE IN SAID LIQUID LEVEL ABOVE A PREDEETERMINED VALUE AND DECREASING THE PRESSURE TO WHICH SAID WITHDRAWN LIQUID IS FLASHED AS A FUNCTION OF A DROP IN SAID LIQUID LEVEL BELOW A PREDETERMINED VALUE TO MAINTAIN SAID LIQUID LEVEL SUBSTANTIALLY CONSTANT.