Apparatus for liquefying air

699,262. Separation of gases. NAAMLOOZE VENNOOTSCHAP PHILIPS' GLOEILAMPENFABRIEKEN. April 23, 1951 [April 26, 1950], No. 9378/51. Class 8 (ii). Compressed gas is cooled and liquefied by first cooling in a heat exchanger 2 Fig. 1 and then cooling by means of a cold-gas cooling machine 4 operating on the reversed hot-gas reciprocating engine principle, the liquid thus formed being subsequently expanded at a nozzle 6; the unliquefied gas serves to cool the exchanger 2. A second heat exchanger 5 is traversed by the gas and liquid mixture leaving the machine 4, and this is also cooled by the expanded gas. As applied to an air separating process, compressed air is cooled by a counter current heat exchanger 32 Fig. 3, a machine 33 corresponding to the machine 4, and a second exchanger 34, and the gas and liquid mixture after traversing an oxygen boiling coil 38 in a reservoir 37 is expanded at a valve 40 before entering the separating column 36 from the head of which nitrogen gas leaves by an outlet 44, and from the base liquid oxygen by an outlet 45. Both constituents serve to cool the exchangers 32, 34. The pressure of the gas is constant during cooling and does not exceed its critical value, and is cooled to a temperature adjacent the point of intersection of the pressure line and the limiting line within the critical range at which the gas liquefies.