Implementations described and claimed herein provide systems and methods for processing liquefied natural gas (LNG). In one implementation, a dry feed gas is received. The dry feed gas is chilled with clean vapor from a heavies removal column to form a chilled feed gas. The chilled feed gas is partially condensed into a vapor phase and a liquid phase. The liquid phase retains freezing components. The freezing components are extracted using a reflux stream in the heavies removal column. The freezing components are removed as a condensate. The vapor phase is compressed into a clean feed gas. The clean feed gas is free of the freezing components for downstream liquefaction.

A method includes: recovering and compressing a head stream coming from a separation column, to form a stream of compressed purified natural gas; liquefying the stream of compressed purified natural gas in a liquefaction unit to form a stream of a pressurized liquefied natural gas; flash expanding of the stream of pressurized liquefied natural gas and recovering in a storage; recovering and compressing of a flow of flash gas coming from the expanding; separating the flow of compressed flash gas (132) into a fuel stream and a recycle stream; cooling and expanding the recycle stream, then introducing the cooled and expanded recycle stream at a head stage of the separation column.

A method includes: providing a carbon dioxide recycle stream comprising natural gas liquids; separating, using a first distillation tower, the carbon dioxide recycle stream into a first vapor fraction and a first liquid fraction; cooling and partially condensing the first vapor fraction in a heat exchanger to yield a first carbon dioxide stream and a reflux stream; and separating, using a second distillation tower, the first liquid fraction into a second carbon dioxide stream and a natural gas liquids rich stream.

A method and apparatus for producing liquefied natural gas. A portion of a natural gas stream is cooled in a heat exchanger and combined with the natural gas stream. Heavy hydrocarbons are removed from the combined natural gas stream, and the resulting separated natural gas stream is partially condensed in the first heat exchanger, with a liquid stream separated therefrom. The natural gas stream is warmed in the first heat exchanger and then is compressed and cooled. The resultant cooled compressed natural gas stream is expanded, thereby forming a chilled natural gas stream that is separated into a refrigerant stream and a non-refrigerant stream. The refrigerant stream recycled to the heat exchanger to be warmed through heat exchange with one or more process streams associated with pretreating the natural gas stream, thereby generating a warmed refrigerant stream. The warmed refrigerant stream and the non-refrigerant stream are liquefied.

A method for improving the capacity of an existing air separation unit employing a lost air turbine is provided in which the capacity is increased by operating the existing air separation unit as previously operated, with the exception of collecting the lost air from the lost air turbine, and instead of venting said lost air to the atmosphere, the lost air is compressed in a supplemental air compressor and returned to the air separation unit at a location downstream a front-end purification unit and upstream a booster. This setup advantageously allows for increased production without having to adjust the sizing of the front-end purification unit or main air compressor.

Certain embodiments of the present invention lies in providing a high-purity oxygen production system which is capable of supplying liquid nitrogen in order to supply the cold required by a high-purity oxygen production apparatus, without the use of a costly conventional liquefaction apparatus.

A high-purity oxygen production system in accordance with an embodiment can include: an air separation apparatus including a main heat exchanger, a medium-pressure column and a low-pressure column; and a high-purity oxygen production apparatus including a nitrogen compressor, a nitrogen heat exchanger and at least one (high-purity) oxygen rectification column, an oxygen-containing stream serving as a starting material for high-purity oxygen is supplied from the low-pressure column to the high-purity oxygen production apparatus, and liquid nitrogen obtained from the medium-pressure column is supplied to the high-purity oxygen production apparatus in order to replenish cold heat required for operation of the high-purity oxygen production apparatus.

A method and apparatus for producing liquefied natural gas. A portion of a natural gas stream is cooled in a first heat exchanger and re-combined with the natural gas stream, and heavy hydrocarbons are removed therefrom to generate a separated natural gas stream and a separator bottom stream. Liquids are separated from the separator bottom stream to form an overhead stream, which is cooled and separated to form a recycle gas stream. The recycle gas stream is compressed. A first portion of the compressed recycle gas stream is directed through the first heat exchanger and directed to the separator as a column reflux stream. The separated to natural gas stream is used as a coolant in the first heat exchanger to thereby generate a pretreated natural gas stream, which is compressed and liquefied.

Methods and systems for operating and NGL recovery process are provided. In an exemplary method, an absorber column upstream of a fractionator column is operated at a higher pressure than a pressure in the fractionator column. An NGL (C.sub.3 plus) stream is taken from the bottom of a fractionator column and then ethylene/ethane stream is taken from the top of the fractionator column. A differential pressure between the absorber column and the fraction are column is controlled based, at least in part, on a flow rate of the fractionator feed stream from the absorber column to the fractionator column.

Method for separating air by cryogenic distillation, wherein at least part of the air to be distilled is boosted in an air booster, compressed air is allowed to expand in at least one expansion turbine and, if the pressure drop between two points of the booster passes under a threshold and/or a flow of the booster passes under a minimum flow of the booster, part of the air boosted in the booster is allowed to expand without having been cooled between the booster and the expansion turbine and the boosted expanded air is sent upstream or downstream of the at least one turbine, without having been cooled in the heat exchanger, after having been boosted.

A method for removing heavy hydrocarbons from a feed gas by: feeding, into an absorber, a top reflux stream and a second reflux stream below the top reflux stream, wherein the absorber produces an absorber bottom product stream and an absorber overhead product stream; depressurizing and feeding the absorber bottom product stream to a stripper to produce a stripper bottom product stream and a stripper overhead product stream; cooling and feeding a portion of the absorber overhead product stream back to the absorber as the top reflux stream; and pressurizing and feeding the stripper overhead product stream back to the absorber as the second reflux stream. Systems for carrying out the method are also provided.