A method and apparatus for producing compressed nitrogen and liquid nitrogen. A separation system has a high-pressure column, a low-pressure column with a top condenser and a main condenser. Air is compressed in an air compressor, purified, cooled in a heat exchanger and introduced into the high-pressure column. A first part of the gaseous top nitrogen from the low-pressure column becomes compressed nitrogen product. A second part of the gaseous top nitrogen is condensed in the condensing space of the top condenser and vapor is drawn off as a residual gas stream. The vapor is expanded in a first expansion machine. A second compressed nitrogen stream from the top of the high-pressure column is expanded in a second expansion machine and then drawn off as compressed nitrogen product. A part of the nitrogen condensed in the top condenser is drawn off as liquid nitrogen product.

A moderate pressure air separation unit and air separation cycle is disclosed that provides for up to about 96% recovery of argon, an overall nitrogen recovery of 98 percent or greater and limited gaseous oxygen production. The air separation is configured to produce a first high purity oxygen enriched stream and a second lower purity oxygen enriched stream from the lower pressure column, one of which is used as the refrigerant to condense the argon in the argon condenser, with the resulting vaporized oxygen stream used to regenerate the temperature swing adsorption pre-purifier unit. All or a portion of the first high purity oxygen enriched stream is vaporized in the main heat exchanger to produce the gaseous oxygen products.

A moderate pressure air separation unit and air separation cycle is disclosed that provides for up to about 96% recovery of argon, an overall nitrogen recovery of 98 percent or greater and limited gaseous oxygen production. The air separation is configured to produce a first high purity oxygen enriched stream and a second lower purity oxygen enriched stream from the lower pressure column, one of which is used as the refrigerant to condense the argon in the argon condenser, with the resulting vaporized oxygen stream used to regenerate the temperature swing adsorption pre-purifier unit. All or a portion of the first high purity oxygen enriched stream is vaporized in the main heat exchanger to produce the gaseous oxygen products.

A moderate pressure air separation unit and air separation cycle is disclosed that provides for up to about 96% recovery of argon, an overall nitrogen recovery of 98% or greater and limited gaseous oxygen production. The air separation is configured to produce a first high purity oxygen enriched stream and a second lower purity oxygen enriched stream from the lower pressure column, one of which is used as the refrigerant to condense the argon in the argon condenser, with the resulting vaporized oxygen stream used to regenerate the temperature swing adsorption pre-purifier unit. All or a portion of the first high purity oxygen enriched stream is vaporized in the main heat exchanger to produce the gaseous oxygen products.

A moderate pressure air separation unit and air separation cycle is disclosed that provides for up to about 96% recovery of argon and an overall nitrogen recovery of 98% or greater. The air separation is configured to produce a high purity oxygen enriched stream which is used as the refrigerant to condense the argon in the argon condenser, with the resulting vaporized oxygen stream used to regenerate the temperature swing adsorption prepurifier unit. Argon recovery is facilitated with the use of an argon superstaged column.

Process and apparatus for producing pressurized gaseous nitrogen by cryogenic separation of air. The distillation column system includes a high pressure column, a medium pressure column, a main condenser and top condenser both being condenser-evaporators. Compressed and purified feed air is cooled in a heat exchanger and introduced to the distillation system. A gaseous nitrogen stream from the high pressure column is condensed in the main condenser. Bottom liquid of the medium pressure column is evaporated and gaseous nitrogen from the medium pressure column is condensed in the top condenser. Liquid nitrogen from the medium pressure column is pressurized and introduced to the high pressure column. A second gaseous nitrogen stream from the high pressure column is recovered as pressurized gaseous nitrogen product. A portion of the compressed and purified feed air is work-expanded and then warmed in the main heat exchanger.

An apparatus for producing product nitrogen gas and product argon, comprising: a first rectification column into which raw air is introduced; a second rectification column from which product nitrogen gas is drawn; a third rectification column from which product argon gas is drawn; and a first condenser configured to perform heat exchange between a gas accumulated in a column top portion of the first rectification column, and a liquid accumulated in a column bottom portion of the second rectification column, wherein an intermediate portion gas containing nitrogen is drawn from an intermediate portion of the second rectification column and merged with a condenser gas drawn from the first condenser. The merged gases are expanded and cooled by means of an expansion turbine whereby the cold thereof is utilized.

The distillation column system has a high-pressure column, a low-pressure column, a main condenser and a low-pressure-column top condenser. Feed air is cooled in a main heat exchanger and introduced into the high-pressure column. An oxygen-enriched liquid stream is withdrawn from the high-pressure column and introduced into the low-pressure column. A gaseous nitrogen stream is withdrawn from the high-pressure column, warmed in the main heat exchanger and withdrawn as gaseous pressurized nitrogen product. The high-pressure column has a barrier-plate section arranged immediately above the point at which the feed air is introduced. The oxygen-enriched liquid stream is withdrawn from the high-pressure column above the barrier-plate section. A purge stream is withdrawn below the barrier-plate section. The gaseous nitrogen stream, before being warmed in the main heat exchanger, is warmed in a counter-current subcooler in indirect heat exchange with the oxygen-enriched liquid stream from the high-pressure column.

A SPECTRA process for low-temperature fractionation of air is proposed, in which bottoms liquid from an additional second rectification column used to obtain oxygen is evaporated in a second condenser evaporator arrangement. In this second condenser evaporator arrangement, gas that has been evaporated beforehand in a first condenser evaporator arrangement, which is used for condensation of tops gas from a first rectification column, is partially condensed after recompression. The invention also relates to a corresponding plant.

The invention relates to a method for separating air by cryogenic distillation in a set of columns including a first column operating at a first pressure, a second column operating at a second pressure which is lower than the first pressure, and a third column operating at a third pressure, which is lower than the second pressure, wherein the third column includes first and second evaporator-condensers, and nitrogen from a cold compressor is sent to one of the evaporator-condensers.