The method is carried out for continuously producing a liquefied methane gas (LMG) from a pressurized mixed methane gas feed stream. It is particularly well adapted for use in relatively small LMG distributed production plant, for instance those ranging from 400 to 15,000 MT per year, and/or when the mixed methane gas feed stream has a wide range of nitrogen-content proportions, including nitrogen being substantially absent. The proposed concept can also be very useful in the design of medium-scale and/or large-size plants, including ones where the nitrogen content always remains above a certain threshold. The methods and arrangements proposed herein can mitigate losses of methane gas when venting nitrogen, for instance in the atmosphere.

A system for reliquefying boil-off gas includes: a compressor provided to the vessel and compressing boil-off gas generated in a storage tank storing liquefied gas; a reliquefaction line extending from the compressor to the storage tank and reliquefying compressed gas to deliver reliquefied gas to the storage tank; a heat exchanger provided to the reliquefaction line and receiving and cooling the compressed gas; a first refrigerant compression part compressing a refrigerant discharged from the heat exchanger after cooling the compressed gas; a second refrigerant compression part further compressing the refrigerant compressed in the first refrigerant compression part; and a refrigerant expansion part expanding and cooling the refrigerant compressed through the first and second refrigerant compression parts and supplying the refrigerant to the heat exchanger.

The present invention relates to a method and system for producing liquefied natural gas (LNG) from a stream of pressurized natural gas which involves a combination of mechanical refrigeration.

This invention is about an air separation apparatus to produce oxygen and nitrogen through isobaric separation, which is based on the Rankine cycle system of similar thermal energy power circulation apparatus at cryogenic side, a liquid pump is used to input work and the cold is made up to the air separation apparatus with refrigerating media, so as to realize the isobaric separation of air to produce nitrogen and oxygen. The air separation apparatus of this invention can save energy by over 30% as compared with the traditional advanced apparatus with the identical refrigerating capacity, and it can also realize centralize gas supply via the air separation apparatus, therefore it constitutes a breakthrough to the traditional air separation technology and refrigeration theory, with substantial economic, social and environmental protection benefits.

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.

A method and apparatus to obtain a compressed nitrogen product by low-temperature fractionation of air in a distillation column system. The system has a high-pressure column, a low-pressure column, a main condenser, and a low-pressure column top condenser. Bottoms liquid from the low-pressure column is evaporated in the top condenser and the gas formed is decompressed to perform work that drives a cold compressor. A gaseous first compressed nitrogen product stream from the high-pressure column is warmed in the main heat exchanger. A further gaseous nitrogen stream from the low-pressure column is compressed in the cold compressor and warmed as a second compressed nitrogen product stream in the main heat exchanger. The cold compressor overcomes a pressure differential which is at least equal to two thirds of the pressure differential between the top of the high-pressure column and the top of the low-pressure column.

The present invention provides an air separation system and an air separation method. The air separation system comprises an air separation apparatus and a nitrogen liquefier. In the air separation apparatus, multiple output pipelines are led out from a rectification column system via a main heat exchanger. In the nitrogen liquefier, a gas delivery pipeline delivers a gas flow expanded by an expander. The air separation system further comprises an intermediary pipeline. An inlet end of the intermediary pipeline is connected to the gas delivery pipeline of the nitrogen liquefier, and an outlet end of the intermediary pipeline is connected to at least one of the multiple output pipelines of the air separation apparatus at a position between the rectification column system and the main heat exchanger, such that the intermediary pipeline delivers a gas flow to the at least one output pipeline. The air separation system and air separation method can be started up smoothly without the use of liquid nitrogen stored externally in reserve.

The invention relates to an installation for producing liquefied gas comprising a circuit for supplying feed gas, a set of heat exchangers, a refrigerator for cooling some or all of the set of heat exchangers, the supply circuit comprising, between the set of heat exchangers and the downstream end thereof, a final expansion turbine for expanding the feed gas in liquid state, the supply circuit comprising a bypass line of the final expansion turbine fitted with a first expansion valve, a second expansion valve disposed in series upstream or downstream of the first expansion valve and of the final expansion turbine, an additional heat exchange line designed to exchange heat with a heat exchanger of the set of heat exchangers when the feed gas is expanded by the first expansion valve via the bypass line, the additional heat exchange line carrying out this heat exchange with said heat exchanger between the expansion carried out by the first expansion valve and the expansion carried out by the second expansion valve, the additional heat exchange line being located upstream or respectively downstream of the expansion carried out by the first expansion valve.

A system and methods for removing nitrogen from a natural gas or liquid natural gas stream. More particularly, a system and method for removing nitrogen from a natural gas feed stream that uses a two-column system with a first column operating at a pressure that is lower than the operating pressure of the second column. A first nitrogen-enriched vapor stream from the first column is compressed and cooled and the resulting stream is then directed to the second column, which produces a second nitrogen-enriched vapor stream and a second methane-enriched liquid stream. Cooling in the system is provided in heat exchangers that warm a first methane-enriched liquid stream from the first column and the second methane-enriched liquid stream from the second column.

Gas processing plants and methods are contemplated in CO.sub.2 is effectively removed to very low levels from a feed gas to an NRU unit by adding a physical solvent unit that uses waste nitrogen produced by the NRU as stripping gas to produce an ultra-lean solvent, which is then used to treat the feed gas to the NRU unit. Most preferably, the physical solvent unit includes a flash unit and stripper column to produce the ultra-lean solvent.