The method and device according to the invention provide for recovery of high-pressure oxygen and high-pressure nitrogen by low-temperature separation of air in a distillation-column system. This system comprises a high-pressure column, a low-pressure column, and a main condenser. A first air feed stream is cooled at a first subcritical pressure in a main heat exchanger to approximately dew point and introduced at least partially into the high-pressure column. A second air feed stream is brought to a second, supercritical, pressure, cooled, depressurized, and introduced at least partially into the distillation-column system. A first partial stream of the second air feed stream is cooled in the main heat exchanger, and a second partial stream is cooled in a high-pressure heat-exchanger system. The first and second partial streams are then merged and work-expanded in a liquid turbine.

The object of the present invention is to provide a different solution for revamping existing producing apparatuses so as to increase the production of low pressure pure nitrogen while controlling as far as possible the capital and operation expenditures. The revamping solution comprises increasing the diameter and/or height of a pure nitrogen column to thereby improve the production capacity thereof; choosing to switch the conduits where the waste liquid nitrogen and pure liquid nitrogen are passed through in the subcooler according to the increment of the low pressure pure nitrogen production; adding an additional heat exchanger to conduct a heat exchange between a portion of the medium pressure air and the increased low pressure pure nitrogen; or simultaneously switching the main parts of the conduits which transfer the pure liquid nitrogen and waste liquid nitrogen from a first column of higher pressure to a second column of lower pressure while performing the above revamping. The stepwise revamping solution of the present invention can be used not only to control the cost but also increase the low pressure pure nitrogen production while ensuring a stable operation of the air separation unit.

Process for producing gaseous oxygen by cryogenic distillation of air, wherein a portion of the feed air flow is brought to a pressure P.sub.1, by means of a first compressor, the suction temperature T.sub.0 of which is between 0 and 50 C., the gas at the pressure P.sub.1 is cooled, in order to generate an air stream at the pressure P.sub.1 and the temperature T1 between 5 and 45 C., a portion of the air compressed in the first compressor undergoes an additional compression step starting from the temperature T.sub.1 and pressure P.sub.1 to a pressure P.sub.2 greater than P.sub.1, then is cooled, to the temperature T.sub.2 where T.sub.2 and T.sub.1 differ by less than 10 C.

The present invention relates to a cryogenic air separation process that provides high pressure oxygen for an oxy-fired combustion of a fuel (e.g., a carbonaceous fuel). The air separation process can be directly integrated into a closed cycle power production process utilizing a working fluid, such as CO.sub.2. Beneficially, the air separation process can eliminate the need for inter-cooling between air compression stages and rather provide for recycling the adiabatic heat of compression into a process step in further methods wherein an additional heat supply is beneficial.

A method and system for cryogenic air separation that employs both a primary refrigeration circuit and an auxiliary refrigeration circuit is provided. The auxiliary refrigeration circuit is configured in a manner that it can be easily tied-in or modified to an existing air separation plant.

A system and method for separating air in an air separation plant is provided. The disclosed systems and methods divert a portion of the compressed, purified air stream to a bypass system configured to selectively produce a higher pressure compressed output stream or a lower pressure compressed output stream. The higher pressure and/or lower pressure compressed output streams are cooled in a main heat exchanger by indirect heat transfer with a plurality of product streams from the air separation plant and then rectified in the distillation column system. A second portion of the compressed, purified air stream is partially cooled in the main heat exchanger and expanding in a turbo-expander to produce power and an exhaust stream which is directed to the distillation column system of the air separation plant where it imparts additional refrigeration generated by the expansion of the compressed air stream in the turbo-expander.

A system and method for separating air in an air separation plant is provided. The disclosed systems and methods divert a portion of the compressed, purified air stream to a bypass system configured to selectively produce a higher pressure compressed output stream or a lower pressure compressed output stream. The higher pressure and/or lower pressure compressed output streams are cooled in a main heat exchanger by indirect heat transfer with a plurality of product streams from the air separation plant and then rectified in the distillation column system. A second portion of the compressed, purified air stream is partially cooled in the main heat exchanger and expanding in a turbo-expander to produce power and an exhaust stream which is directed to the distillation column system of the air separation plant where it imparts additional refrigeration generated by the expansion of the compressed air stream in the turbo-expander.

A heat exchanger for indirect heat exchange between a first and a second fluids to be cooled and at least a third fluid to be heated, made up of a plurality of passages, namely a first series of passages for the flow at least of the first and of the second fluids, a second series of passages for the flow of the third fluid to be placed in a heat exchange relationship with the first and second fluids, the exchanger comprising three sections, the second section being between the first and third sections and means for introducing the first fluid into only a portion of the passages of the first series in the second section.