Patent GB-737347-A (GB)
Title: Process for the separation, by rectification, of a gas mixture containing at least three components
IPC: F25J3/04
Filed: 1953-08-10
Abstract: 737,347. Cold separation of gas mixtures. SOC. L'AIR LIQUIDE, SOC. ANON. POUR L'ETUDE ET L'EXPLOITATION DES PROCEDES G. CLAUDE. Aug. 10, 1953 [Aug. 12, 1952], No. 22017/53. Class 8 (2). In a process for separating a three or more component gas mixture in at least two rectification columns the last one of which receives at the top a washing liquid rich in the most volatile component condensed at the top of at least one previous column working at a lower pressure, improvement in the purity of the most volatile component extracted from the top of the last column is effected by tapping from at least one intermediate point of at least one previous column a liquid rich in at least one intermediate component, expanding it and supplying it to the last column at a point below the inlet for the washing liquid. As applied to the separation from air of argon, argon-free nitrogen and substantially pure gaseous oxygen, compressed air having traversed a heatexchanger 2, Fig. 1, cooled by returning nitrogen and oxygen, a portion of a liquefier 5 and an expander 7 is fed to a high-pressure rectification column 9 from the base of which oxygen-rich liquid passes along a valved duct 16 to a point 18 of the low-pressure column 19 and from a shelf 15 nitrogen-rich liquid condensed by a condenser-vaporizer 14 traverses a valved duct 20 to a point 26a of said column 19. Argon-rich liquid passes from a point 22 of the column 9 through a valved duct 23 to a point 25 of the column 19, and argon-rich gas from a point 27 passes to an auxiliary rectification column 12 supplied with reflux by a condenser-vaporizer 11 traversed by liquid air from the liquefier 5. Product argon gas is discharged at an outlet 28, argon-free nitrogen at an outlet 26 and substantially pure gaseous oxygen at an outlet 31. In a modification wherein argon-free nitrogen is discharged at the point 26, Fig. 2, and argonrich oxygen gas at a point 31, the rectification power of column 9 is increased by extra reflux obtained by passing argon-free nitrogen gas from the vaporizer 14 through a compressor 33, a heat-exchanger 34, a heating coil 35 and an expansion valve 36 to the shelf 15. This process is suitable for the separation of a gaseous mixture of ethane, ethylene and acetylene into ethylene at point 26 and an azeotropic mixture of acetylene and ethane together with ethane at the point 31. In a further modification extra reflux for the low-pressure column is obtained by introducing the argon-rich liquid from the point 22 (Fig. 3, not shown) into an auxiliary concentration column operating at the same pressure as the high-pressure column 9; the argon-rich liquid thus separated being fed to the low-pressure column to serve as reflux and the nitrogen-rich vapour being returned to the column 9. In a process for producing argonfree nitrogen gas, pure oxygen gas and an argonrich mixture of oxygen and nitrogen gas, oxygen-rich liquid from the base of the highpressure column 9, Fig. 4, traverses a valved duct 52 to enter an intermediate pressure column 44 which is heated by vapour from a condenser 45 of the column 9. Argon-rich liquid is tapped from a point 54 through a valved duct 55 to a point 57 of the low-pressure column 19, and argon-free nitrogen liquid passes from a shelf 58 and also from a shelf 15 to the top of column 19 ; product nitrogen, argonrich mixture and oxygen leaving at points 26, 43, 31.