Abstract: A fluid mixture is separated by distillation in a two column system in which a portion of the feed is prefractionated in a first column having at least one separation stage above the feed and the prefractionator bottoms provides feed to a second column operating at a lower pressure. Cooling for condensing the overhead vapor of the first column is provided by heat exchange with flashed prefractionator bottoms or with an intermediate fluid in the second column. Another portion of the feed is flashed and introduced into the second column. The two-column system is readily combined with a high pressure column in a three-column distillation system for separating air which is particularly useful for integration with a gasification combined cycle combustion turbine system. Optionally, three nitrogen products can be produced at three different pressures.

Abstract: A self-contained device for the supply of energy to an apparatus (7) driven by gas under pressure, comprises a portable reservoir (1) of cryogenic liquid, and structure associated with the reservoir to withdraw and vaporize liquid from the reservoir and to send it to the apparatus (7). Two circuit portions (2.sub.1, 2.sub.2) incorporate vaporizers (5.sub.1, 5.sub.2) and are delimited between non-return valves (4.sub.1, 4.sub.2) upstream and control valves (6.sub.1, 6.sub.2) downstream. When open, the control valves drive the apparatus (7). The reservoir (1) is of the double wall type (1.sub.1, 1.sub.2), at least one upstream part of the circuit portion (2.sub.1, 2.sub.2) being disposed between these walls (1.sub.1, 1.sub.2). The two circuit portions are in parallel (2.sub.1, 2.sub.2) and the respective valves (6.sub.1, 6.sub.2) are sequentially controlled by a control device (9, 12) which is sensitive to the pressure (P.sub.1, P.sub.2) prevailing in the circuit portions (2.sub.1, 2.sub.2).