A process for producing liquefied natural gas (14) and liquid carbon dioxide (CO.sub.2) (15) comprising at least the following steps: Step a): separating a natural gas feed gas (1), containing hydrocarbons and carbon dioxide in a treatment unit (2), into a CO.sub.2-enriched gas stream (4) and a CO.sub.2-depleted natural gas stream (3); step b): liquefying the CO.sub.2-depleted natural gas stream (3) resulting from step a) in a natural gas liquefaction unit (5) comprising at least a main heat exchanger (8) and a system (9) for producing frigories; step c): simultaneous liquefying of the CO.sub.2-enriched gas stream (4) resulting from step a) in a CO.sub.2 liquefaction unit (6); characterized in that all of the refrigeration necessary for the liquefaction of the CO.sub.2-enriched gas stream (4) and for the liquefaction of the natural gas is supplied by said frigorie-producing system (9) of the natural gas liquefaction unit (5).

A process for producing liquefied natural gas and liquid carbon dioxide from a natural gas feed gas comprising at least the following steps: Separation of a natural gas feed gas into a CO.sub.2-enriched gas stream and a natural gas stream; Cooling of said natural gas in a heat exchanger; Purification of the in step 1 from compounds containing at least six carbon atoms; At least partial condensation of said gas stream resulting from step 3 to form a two-phase stream; Separation of said two-phase stream resulting from step 4 to form a gas stream and a liquid stream; Condensation of the gas stream resulting from step 5 to form a liquefied gas containing less than 5 ppm by volume of compounds containing at least six carbon atoms; Liquefaction of the CO.sub.2-enriched gas stream resulting from step 1 with a portion of the liquid stream resulting from step 5.

A carbon dioxide capture system includes a first heat exchanger configured to exchange heat between an exhaust stream and a lean carbon dioxide effluent stream. The carbon dioxide capture system also includes a first turboexpander including a first compressor driven by a first turbine. The first compressor is coupled in flow communication with the first heat exchanger. The first turbine is coupled in flow communication with the first heat exchanger and configured to expand the lean carbon dioxide effluent stream. The carbon dioxide capture system further includes a carbon dioxide membrane unit coupled in flow communication with the first compressor. The carbon dioxide membrane unit is configured to separate the exhaust stream into the lean carbon dioxide effluent stream and a rich carbon dioxide effluent stream. The carbon dioxide membrane unit is further configured to channel the lean carbon dioxide effluent stream to the first heat exchanger.

A thermoacoustic refrigerator includes at least one pair of pulse combustion tubes (10), preferably Rijke tubes, each tube (10) having a pair of spaced-apart Stirling engines (12), coupled together but with no separating membrane therebetween.

The invention relates to a method for condensing a carbon dioxide-rich gas stream, wherein a stream of water heated by an exchange of heat with the carbon dioxide-rich stream, which is at least partially condensed, is sent to at least one compressor (3,21) for compressing the carbon dioxide-rich stream or a fluid, the carbon dioxide-rich stream of which is derived, in order to at least partially cool at least one stage of said compressor.

Systems and methods are provided for recovering helium from a feed comprising helium, carbon dioxide, and at least one intermediate component having a volatility between those of helium and carbon dioxide. In particular, processes of the present invention comprise separating the carbon dioxide and the components of intermediate volatility from the helium at a temperature greater than −82.7° C. to form a helium-rich product stream, wherein the concentration of at least one of the intermediate components in the helium-rich product stream is lower than its concentration in the feed stream, and wherein at least part of the separation is effected by contacting a vapor with a liquid.

A method and a plant for producing liquid CO.sub.2 from flue gas as described with reduced energy consumption and a stable behavior.

In a process for the separation of a gas rich in carbon dioxide and containing at least one component lighter than carbon dioxide, the feed gas rich in carbon dioxide is cooled in a first heat exchanger, partially condensed and separated to form a gaseous portion and a liquid, sending the liquid portion to the top of a distillation column, removing a liquid stream richer in carbon dioxide than the feed gas from the bottom of the distillation column, removing a gaseous stream less rich in carbon dioxide than the feed gas from the top of the distillation column and warming the gaseous stream in the first heat exchanger, sending the gaseous portion to a shell and tube heat exchanger having tubes in a bath of triple point carbon dioxide, in which it condenses at least partially to form a liquid fraction, sending the liquid fraction to the top of the distillation column, vaporizing a liquid stream from the bottom of the distillation column outside or within the distillation column to form a gas which is subsequently separated in the distillation column, expanding a liquid stream from the bottom of the distillation column, vaporizing at least part of the expanded liquid stream in the shell and tube heat exchanger to form a vapor and warming the vapor formed in the first heat exchanger.

A method and apparatus for liquefying a natural gas feed stream and removing nitrogen therefrom to produce a nitrogen-depleted LNG product, in which a natural gas feed stream is passed through main heat exchanger to produce a first LNG stream, which is separated to form a nitrogen-depleted LNG product and a recycle stream composed of nitrogen-enriched natural gas vapor, and in which the recycle stream is passed through main heat exchanger to produce a first LNG stream, separately from and in parallel with the natural gas feed stream, to produce a first at least partially liquefied nitrogen-enriched natural gas stream that is separated to provide a nitrogen-rich vapor product.

A process for separating carbon dioxide from a fluid containing carbon dioxide, NO.sub.2, and at least one of oxygen, argon, and nitrogen comprises the steps of separating at least part of the fluid into a carbon dioxide enriched stream, a carbon dioxide depleted stream comprising CO.sub.2 and at least one of oxygen, argon, and nitrogen and a NO.sub.2 enriched stream and recycling said NO.sub.2 enriched stream upstream of the separation step.