A CO2 separation and liquefaction system such as might be used in a carbon capture and sequestration system for a fossil fuel burning power plant is disclosed. The CO2 separation and liquefaction system includes a first cooling stage to cool flue gas with liquid CO2, a compression stage coupled to the first cooling stage to compress the cooled flue gas, a second cooling stage coupled to the compression stage and the first cooling stage to cool the compressed flue gas with a CO2 melt and provide the liquid CO2 to the first cooling stage, and an expansion stage coupled to the second cooling stage to extract solid CO2 from the flue gas that melts in the second cooling stage to provide the liquid CO2.

A method for separating carbon dioxide from flue gas to generate a high purity CO2 stream.

In a method for compressing a gas that is to be separated in a low-temperature CO.sub.2 separation unit using at least one partial condensation step and/or at least one distillation step, the gas that is to be separated has a variable composition and/or variable flow rate, the gas that is to be separated is compressed in a compressor to produce a compressed gas and the inlet pressure of the gas that is to be separated, entering the compressor, is modified according to the CO.sub.2 content and/or the flow rate of the gas that is to be separated so as to reduce the variations in volumetric flow rate of the gas that is to be separated entering the compressor.

A compressing system includes a compression section that compresses a target gas to an intermediate pressure, which is equal to or higher than a critical pressure and lower than a target pressure to generate an intermediate supercritical fluid, a cooling section that cools the intermediate supercritical fluid generated in the compression section to near a critical temperature to generate an intermediate supercritical pressure liquid, and a pumping section that compresses the intermediate supercritical pressure liquid generated in the cooling section to a pressure that is equal to or higher than the target pressure. At least one of the intermediate supercritical pressure liquid compressed in the pumping section, a low-temperature liquid generated by extracting the intermediate supercritical pressure liquid on the upstream side of the pumping section to reduce pressure to near the critical pressure, and an external cooling medium is used as a cooling medium in the cooling section.

A cryogenic technology for the cost-efficient capture of each known component of emissions, such as carbon dioxide, sulfur oxides, nitrogen oxides, carbon monoxide, any other acid vapor, mercury, steam, in a liquefied or frozen/solidified form, and unreacted nitrogen (gas) from industrial plants, such that each of the components is captured separately with minimum use of energy and is industrially useful.

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.

A boosting system which boosts a target gas to a pressure which is equal to or greater than a target pressure higher than a critical pressure includes a compression portion which compresses the target gas to an intermediate pressure which is equal to or greater than the critical pressure and is less than the target pressure to generate an intermediate supercritical fluid, a cooling portion which cools the intermediate supercritical fluid generated by the compression portion to a temperature near to a critical temperature to generate an intermediate supercritical pressure liquid, a pump portion which boosts the intermediate supercritical pressure liquid generated by the cooling portion to a pressure which is equal to or greater than the target pressure, and a cooling temperature adjusting portion which adjusts a temperature of the intermediate supercritical pressure liquid generated by the cooling portion in an upstream side of a pump.

In a method for liquefying a gas rich in carbon dioxide, the gas is compressed to a first pressure greater than its critical pressure in a compressor to form a compressed gas, the compressed gas is cooled through heat exchange with a refrigerant to a variable temperature to form a cooled compressed gas with a density between 370 and 900 kg/m.sup.3, the cooled compressed gas is cooled at supercritical pressure in a first heat exchanger to a temperature below the critical temperature, the gas cooled below the critical temperature is expanded to a second pressure between 45 and 60 bara to form a diphasic fluid which is separated in a phase separator to form a liquid and a gas, and a liquid portion originating from the phase separator provides cold to the first heat exchanger.

In a process for distilling a gas mixture of CO2 and at least one component lighter than CO2, a partially purified liquid CO2 stream is withdrawn at an intermediate level of the distillation column at least one theoretical plate below the top of the distillation column and at least one theoretical plate above the bottom of the distillation column and the stream extracted at the intermediate level of the distillation column is vaporized by heat exchange with the gas mixture, with which it is then compressed.

In this patent we disclose, for the first time, detailed methods of our newly invented state-of-the-art cryogenic technology for the cost effective energy efficient capture of each known component of entire emissions (nearly 100%) such as carbon dioxide (CO.sub.2), sulfur oxides (SO.sub.x), nitrogen oxides (NO.sub.x), carbon monoxide(CO), any other acid vapor, mercury, steam and unreacted nitrogen from industrial plants (coal and natural gas fired power plants, cement plants etc.), in a liquefied or frozen/solidified form, such that each of the components is captured separately and is industrially useful. This new technology includes a novel NH.sub.3 power plant to generate auxiliary electrical power from the heat energy of the flue gas to further improve the energy efficiency and cost effectiveness of the capture processes. It is the most cost effective of all existing emission capture technologies. It does not require use of any chemicals/reagents/external cryogens, unlike the current technologies. It uses only a fixed amount of water needed for the cooling process which can be used repeatedly. We present detailed methods of operations, together with scientific and economic analysis of the energy needed and cost involved for the said capture in two specific examples, and advantages of the new technology over the existing ones.