In a method for regulating a device for separating air by cryogenic distillation, during the change from a low-flow mode to a high-flow mode, two flow rates of reflux sent to the low-pressure column of a double column are increased more rapidly than the flow rate of gaseous air sent to the medium-pressure column of the double column in order to ensure the stability of the oxygen content in the argon bulge of the low-pressure column during the mode change.

A system for removing freezing components from a feed gas includes a heat exchanger, a scrub column and a return vapor expansion device. The heat exchanger includes a reflux cooling passage and a return vapor passage. Vapor from the scrub column is directed through the return vapor expansion device, where the temperature and pressure are lowered. The resulting cooled fluid then travels to the return vapor passage of the heat exchanger and is used to cool a vapor stream in the reflux cooling passage to create a reflux fluid stream that is directed to the scrub column.

Systems and methods that utilize feed gases that are supplied in a wide range of compositions and pressure to provide highly efficient recovery of NGL products, such as propane, utilizing isenthalpic expansion, propane refrigeration, and shell and tube exchangers are described. Plants utilizing such systems and methods can be readily reconfigured between propane recovery and ethane recovery.

A method for operating a natural gas liquids processing (NGL) system, the system being selectively configured in either an ethane rejection configuration or an ethane recovery configuration, the method comprising, when the NGL system is in the ethane rejection configuration, collecting a reboiler bottom stream that, in the ethane rejection configuration, includes ethane in an amount of less than 5% by volume, and when the NGL system is in the ethane recovery configuration, collecting a reboiler bottom stream that, in the ethane recovery configuration, includes ethane in an amount of at least about 30% by volume.

Impurities that are less volatile than carbon dioxide, e.g. hydrogen sulfide, are removed from crude carbon dioxide by processes involving distillation of said crude carbon dioxide in a distillation column system operating at super-atmospheric pressure(s) to produce carbon dioxide-enriched overhead vapor and bottoms liquid enriched with said impurities. Where such processes involve a single heat pump cycle, significant savings in power consumption are realized when the distillation column system is re-boiled by at least partially vaporizing liquid in or taken from an intermediate location in the column system.

The invention relates to a method for the treatment of natural gas containing carbon dioxide, methane and paraffins. The method comprising: a step of extracting the paraffins from the natural gas in a paraffin-removal column, and a step of separating the carbon dioxide and the methane in a distillation column. The operation of the two columns being provided by means of the thermal coupling of said two columns using a thermal coupling heat exchanger.

An overhead recycle process apparatus (100) comprises a heat exchange arrangement (116, 118, 120, 146, 150, 198) and a separator (110) in fluid communication with an absorber (104) and a de-ethaniser (106), the absorber (104) having a reflux inlet port (164). An ethane rectifier (170) in fluid communication with the de-ethaniser (106) is also provided, the de-ethaniser (106) being arranged to provide cooling by heat exchange to an overhead stream path (194) of the ethane rectifier (170). The ethane rectifier (170) comprises a reflux drum (182) having an ethane outlet port (184) and a vapour phase outlet port (185) in fluid communication with the reflux inlet port (164) of the absorber (104).

A system for removing freezing components from a feed gas includes a heavy hydrocarbon removal heat exchanger and a scrub device. The scrub device includes a scrub column that receives a cooled feed gas stream from the heat exchanger and a reflux separation device. Vapor from the scrub column is directed to the heat exchanger and cooled to create a reflux stream that includes a liquid component. This reflux stream is directed to the reflux separation device and a resulting liquid component stream is used to reflux the column. Vapor from the reflux separation device is expanded and directed to the heat exchanger, where it provides refrigeration, and a processed feed gas line.

A nitrogen recovery apparatus for recovering nitrogen from natural gas comprises a separator having a liquid fraction port and a vapour fraction port in fluid communication with a split flow arrangement, the split flow arrangement having a sub-cooled fluid path and an expanded fluid path. A fractionating column has a reflux inlet port in fluid communication with the subcooled fluid path above a middle feed port thereof, the middle feed port being in fluid communication with the expanded fluid path. A bottom feed port of the fractionating column is in fluid communication with the liquid fraction port of the separator. A side reboiler circuit and a reboiler circuit are operably coupled to the fractionating column below the bottom feed port. A bottom hydrocarbon product stream path is in fluid communication with a bottom hydrocarbon port of the fractionating 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.