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.

In a process for separating at least one heavy impurity such as hydrogen sulfide from crude carbon dioxide comprising significant quantities of at least one light impurity such as non-condensable gases, involving at least one heat pump cycle using carbon dioxide-containing fluid from the process as the working fluid, the light impurity is removed from the crude carbon dioxide and carbon dioxide is subsequently recovered from the removed light impurity, thereby improving overall carbon dioxide recovery and efficiency in terms of energy consumption.

A method for separating nitrogen from an inlet gas having less than 25 mole % nitrogen includes supplying the inlet gas having less than 25 mole % nitrogen to a nitrogen separation system configured with cryogenic refrigeration.

Helium can be recovered from nitrogen-rich natural gas at high pressure with low helium loss by cryogenic distillation of the natural gas after pre-treatment of the gas to remove incompatible impurities and then recovery of natural gas liquid (NGL) from the pre-treated gas by distillation. Overall power consumption may be reduced, particularly if the feed to the helium recovery column system is at least substantially condensed by indirect heat exchange against a first portion of nitrogen-enriched bottoms liquid at first pressure, and a second portion of nitrogen-enriched bottoms liquid at a second pressure that is different from the first pressure.

Overall power consumption in a cryogenic distillation process for recovering helium from nitrogen-rich gases comprising helium may be reduced if the feed to the distillation column system is at least substantially condensed by indirect heat exchange against a first bottoms liquid at first pressure, and a second bottoms liquid at a second pressure that is different from the first pressure.

An air separation unit and associated method for separating air by cryogenic distillation using a distillation column system including a higher pressure column, a lower pressure column, an intermediate pressure kettle column, and an argon column arrangement is provided. The disclosed air separation unit and method is particularly suited for production of an argon product as well as several nitrogen products wherein a portion of the nitrogen overhead intermediate pressure kettle column is taken as an intermediate or elevated pressure nitrogen product. The present air separation unit and associated method employs a once-through kettle column reboiler, a once-through kettle column condenser while the argon condenser condenses an argon-rich vapor stream against a pumped oxygen stream from the bottom of the lower pressure column.

A system and method for removing nitrogen and producing a high pressure methane product stream and an NGL product stream from natural gas feed streams where at least 90%, and preferably at least 95%, of the ethane in the feed stream is recovered in the NGL product stream. The system and method of the invention are particularly suitable for use with feed streams in excess of 5 MMSCFD and up to 300 MMSCFD and containing around 5% to 80% nitrogen. The system and method preferably combine use of strategic heat exchange between various process streams with a high pressure rectifier tower and the ability to divert all or a portion of a nitrogen rejection unit feed stream to optionally bypass a nitrogen fractionation column to reduce capital costs and operating expenses.

An air separation device for distilling air at a low temperature, includes a high-pressure column to separate high-pressure raw material air into high-pressure nitrogen gas and high-pressure oxygen-enriched liquefied air; a low-pressure column to separate the high-pressure oxygen-enriched liquefied air into low-pressure nitrogen gas, low-pressure liquefied oxygen, and argon-enriched liquefied oxygen; an argon column to separate the argon-enriched liquefied oxygen having a pressure higher than the pressure into argon gas and medium-pressure liquefied oxygen; first and second indirect heat-exchangers; first and second gas-liquid separation chambers; a first/second passage which communicates the gas/liquid phase of the low-pressure column and the gas phase of the second gas-liquid separation chamber; and a first/second opening/closing mechanism located on the first/second passage.

The invention relates to a process for the removal of CO.sub.2 from acid gas by cryogenic distillation performed in two steps. The feed mixture is first distilled at high pressure (at least 45 bar) in a first distillation column. The top product or a part thereof is then, after heating, subjected to a second distillation step at a lower pressure (lower than 45 bar). The top product of the second distillation step is methane of high purity (more than 99 mol. %). The bottom product of the second distillation step is recycled back to the first distillation column. The method according to the invention allows complete separation of methane also at higher level of acidic components, is economical and does not result in solid CO.sub.2 build-up, which is a common problem in cryogenic distillation.

The plant is used for producing oxygen by cryogenic air separation. The plant has a high-pressure column, a low-pressure column and a main condenser. An argon-elimination column is in fluid connection with an intermediate point of the low-pressure column and is connected to an argon-elimination column head condenser. An auxiliary column has a sump region, into which gas is introduced from the argon-elimination column head condenser. The head of the auxiliary column is connected to a return flow liquid line, in order to introduce a liquid stream from the high-pressure column or the head condenser. The liquid stream has an oxygen content which is at least equal to that of air. At least one part of the crude liquid oxygen from the sump of the high-pressure column is fed to the auxiliary column at a first intermediate point.