Improvements in the cold separation of air

917,695. Cold separation of air. BRITISH OXYGEN CO. Ltd. Oct. 10, 1961 [Oct. 17, 1960], No. 35556/60. Class 8(2). Compressed air to be rectified in a conventional column (not shown) is pre-cooled in an exchanger 1 traversed by reversely flowing waste nitrogen and is then divided into major and minor streams, the latter is further cooled in an exchanger 2 also traversed by reversely flowing waste nitrogen and is then expanded at a valve 5 to the rectification pressure whilst the major compressed air stream is expanded in an engine 3 with the performance of external work and a portion of the socooled and expanded air is warmed in an intermediate portion EF of exchanger 2 and is then returned to the parent stream prior to its expansion in an engine 4 to the rectification pressure after which the major and minor streams are united and fed to the rectification column.