GB1205228A - Method and apparatus for treating gaseous mixtures by heat exchange - Google Patents

Abstract

1,205,228. Cold separation of gas mixtures. TEXACO DEVELOPMENT CORP. 6 Dec., 1967 [20 Dec., 1966], No. 55439/67. Heading F4P. Separation of condensible impurity e.g., carbon dioxide from a warm compressed gas mixture e.g. air at an initial temperature between the triple point and the critical point of the impurity is effected by admission through a line 16, Fig. 1, of the gas mixture and upward passage thereof through at least two seriesarranged cold heat exchangers e.g., accumulators A, B having at least a portion thereof at a temperature below the freezing point of the impurity thus resulting in deposition thereof in the solid phase, maintaining the upward flow until the temperature of at least the lower portion of one of the exchangers A, B rises to above the freezing point of the impurity resulting in melting of the deposits which is withdrawn from the base of the exchanger through lines 19, 21 at a temperature below its boiling point. During the warming-up period of accumulator A, B series arranged accumulators C, D are cooled by downward passage. A cold refrigerant admitted through a line 30 and exhausted through a line 32, the contact being either direct or indirect and a minor portion of the refrigerant may pass downwardly through line 23, 26 and in indirect heat exchange with the on-stream accumulators A, B. As cooling of feed gas mixture proceeds, the zone in which melting of the frozen impurity occurs and known as the transition zone moves upwardly in accumulator A, then upwardly in accumulator B which completes a first cycle. Accumulators A and C are switched and feed mixture is then passed upwardly through B and then through C whilst cold refrigerant is passed downwardly through D and A forming a second cycle. In a third cycle feed mixture is passed through C and D whilst cold refrigerant is passed through A and B whilst in the fourth and last cycle feed mixture is passed through D and A whilst cold refrigerant is passed through C and D. In separating carbon dioxide from admixture with hydrogen, carbon monoxide methane and nitrogen prior to washing with liquid nitrogen in a column 37, Fig. 4, to obtain an effluent of hydrogen and nitrogen feed mixture is divided into a first stream 16A which is cooled and freed of carbon dioxide in direct heat exchange with previously cooled accumulators A, B and into a second stream 10D which is cooled in direct contact with accumulators C, D which are simultaneously cooled by indirect heat exchange with liquid bottoms withdrawn from column 37 through lines 41, 41C, 52D and also by indirect heat exchange with cold effluent withdrawn from column 37 through lines 30, 30C and 26D. The so-cooled feed streams 16A, 16D are combined at 18C and fed through line 18 to column 37 to which liquid wash nitrogen is fed through a line 39. Accumulators A, B are also cooled indirectly by cold effluent passing through lines 30, 30B, 49 and 26 and by liquid bottoms passing through lines 41, 41B, 51, 52A. Liquid carbon dioxide is drained from the accumulator through lines 19, 21, 47. As cooling of feed mixture and warming of accumulators proceeds the accumulators are switched as described above.