Separation of oxygen from air

943,669. Cold separation of air. PETROCARBON DEVELOPMENTS Ltd. Nov. 1, 1962 [Nov. 3, 1961], No. 39496/61. Heading F4P. In a single-column air rectification process for the production of liquid oxygen, at least part of the feed air which is at a relatively low pressure e.g. 8 atmos. is further compressed in a brake blower or blowers 15, 15<SP>1</SP> of turbines 16, 16<SP>1</SP> through which is expanded at least part of the feed air to produce cold for the process. As shown the further compressed air is withdrawn from a feed line 10 through a line 11 and is thereafter cooled in a preliminary exchanger 17 followed by exchangers 18, 19 traversed by counterflowing waste effluent leaving the head of column 21 through a line 25 and the so cooled feed air is liquefied in the reboiling coil 20 of the column, sub-cooled in an exchanger 23 traversed by a mixture of air and waste gas having been expanded in turbine 16, and finally expanded at a valve 24 into the column 21. The mixture of air and waste gas leaving the sub-cooler 23 through a line 26 serves to cool exchangers 19, 18. In a modification the whole of the incoming air is further compressed in two blowers in series and after partial cooling by indirect heat exchange with waste gases is expanded in at least one of the turbines and is divided into a first stream which after further cooling by indirect heat exchange with waste gases is expanded into the column, and into a second stream which is expanded in one of the turbines to produce additional cold.