Abstract: In a system for air fractionation by low-temperature rectification, refrigeration is produced in a cooling stage by compression and expansion of the feed air or of nitrogen from rectification. By using the work gained during expansion for compressing only a partial stream of the gas passed through the cooling stage, the system according to this invention operates with increased efficiency and lower operating costs.

Abstract: In the production of gaseous oxygen, a process and apparatus is used which requires low temperature rectification of air. The air is compressed, purified and cooled in a first heat exchanger while a second gas stream is compressed to elevated pressure, and is cooled in a second heat exchanger. Liquid oxygen removed from rectification is pressurized to a desired pressure and is evaporated and heated in heat exchange with the compressed gas stream.

Abstract: In a process for the production of oxygen by two-stage low-temperature rectification of air wherein the air is cooled in a primary heat exchanger, and the product oxygen is withdrawn from the low-pressure stage and warmed by heat exchange in a heat exchanger separate from the primary heat exchanger with a gaseous stream fed to the high-pressure stage, a gaseous stream fed to the high-pressure stage, a gaseous stream being withdrawn as the compensating stream from the high-pressure stage, warmed at least partially in the primary heat exchanger countercurrently to the entering air, and expanded in at least one turbine, the improvement which comprises recooling the compensating stream prior to entering the turbines, by heat exchange with the product oxygen in said heat exchanger separate from the primary heat exchanger.

Abstract: In a process for the fractionation of air wherein the air is subjected to rectification in a high-pressure column and a low pressure column, wherein in a liquefaction cycle, nitrogen is withdrawn in the gaseous phase from the head of the high-pressure column and is liquefied by heating, compression, recooling, and expansion and recycled as liquid to the high-pressure column and wherein a gas, e.g., air is withdrawn from the high pressure column, is preheated, and is then expanded through a low-pressure expansion turbine, the improvement which comprises cooling the gas expanded in the low-pressure expansion turbine in indirect heat exchange with at least a portion of the nitrogen which is heated in the liquefaction cycle.