Method of gas treatment, including impurity removing steps

Claim 1

IN A PROCESS FOR FRACTINATING A COMPRESSED GASEOUS MIXTURE IN A LOW-TEMPERATURE EXPANSION AND FRACTIONATING SYSTEM, WHEREIN AN INFLOWING CHARGE STREAM OF SAID COMPRESSED GASEOUS MIXTURE ENTERS SAID SYSTEM AT A PRE-EXPANSION PRESSURE THROUGH A REVERSING HEAT EXCHANGE ZONE IN WHICH SAID INFLOWING STREAM IS COOLED AND IN A COLD PART OF WHICH HIGH-BOILING IMPURITIES ARE PRECIPITATED, AND WHEREIN AN OUTFLOWING PRODUCT STREAM LEAVES SAID SYSTEM AT A POST-EXPANSION PRESSURE THROUGH SAID REVERSING HEAT EXCHANGE ZONE TO ABSORB HEAT AND SCAVENGE SAID PRECIPITATED HIGH-BOILING IMPURITY BY REVAPORIZATION, SAID INFLOWING AND OUTFLOWING STREAMS BEING FLOWED COUNTERCURRENTLY AND ALTERNATELY WITH EACH OTHER THROUGH PERIODICALLY REVERSING PATHS IN A HEAT EXCHANGE RELATION IN SAID REVERSING HEAT EXCHANGE ZONE, A METHOD FOR PREVENTING THE EXCESSIVE ACCUMULATION OF SAID PRECIPITATED IMPURITY IN SAID COLD PART OF THE PATHS OF SAID REVERSING HEAT EXCHANGE ZONE DURING SEVERAL CYCLES OF OPERATION, WHICH METHOD INCLUDES THE STEPS OF: WITHDRAWING A PART OF SAID OUTFLOWING SCAVENGING PRODUCT SUBSEQUENT TO ITS PASSAGE THROUGH AT LEAST PART OF SAID REGION OF PRECIPITATION OF HIGH-BOILING IMPURITY; AND RETURING SAID WITHDRAWN PART TO SAID OUTFLOWING SCAVENGING STREAM AT A POINT UPSTREAM FROM SAID POINT OF WITHDRAWAL.