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A system and method of purifying gaseous carbon dioxide from a gaseous mixture obtained at low pressure from a flue gas by passing the gaseous mixture through a vacuum swing adsorption unit and then a gas purification unit to produce carbon dioxide having a purity of approximately 97% by volume or m

A system and method of purifying gaseous carbon dioxide from a gaseous mixture obtained at low pressure from a flue gas by passing the gaseous mixture through a vacuum swing adsorption unit and then a gas purification unit to produce carbon dioxide having a purity of approximately 97% by volume or more.

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1. A method of purifying gaseous carbon dioxide from a gaseous mixture comprising 5% to 25% by volume carbon dioxide, said method comprising (a) obtaining a gaseous mixture from a flue gas at a low pressure of 1 to 5 atmospheres absolute;(b) flowing the gaseous mixture into an adsorbent bed of a vac

1. A method of purifying gaseous carbon dioxide from a gaseous mixture comprising 5% to 25% by volume carbon dioxide, said method comprising (a) obtaining a gaseous mixture from a flue gas at a low pressure of 1 to 5 atmospheres absolute;(b) flowing the gaseous mixture into an adsorbent bed of a vacuum swing adsorption unit having one or more adsorbent beds in which carbon dioxide is adsorbed;(c) using a vacuum pump to draw a carbon dioxide-rich stream from the adsorbent beds;(d) directing the carbon dioxide-rich stream through a compressor to produce a compressed carbon dioxide-rich stream;(e) flowing the compressed carbon dioxide-rich stream into a gas purification unit to produce a carbon dioxide product and a carbon dioxide-lean stream, the gas purification unit comprising at least one gas separation membrane; and(f) returning the carbon dioxide-lean stream to the vacuum swing adsorption unit. 2. The method of claim 1, further comprising, prior to step (d), collecting the carbon dioxide-rich stream in a buffer tank. 3. The method of claim 1, wherein the carbon dioxide-lean stream returned to the vacuum swing adsorption unit pressurizes the one or more adsorbent beds in step (b). 4. The method of claim 1, wherein the carbon dioxide-lean stream returned to the vacuum swing adsorption unit combines with the gaseous mixture. 5. The method of claim 1, further comprising: (g) flowing a portion of the carbon dioxide product to the vacuum swing adsorption unit to rinse the one or more adsorbent beds. 6. The method of claim 1, wherein the gaseous mixture comprises a mixture of carbon dioxide and nitrogen. 7. The method of claim 1, wherein the gaseous mixture is at a pressure of approximately 1.5 to approximately 2.5 absolute atmospheres. 8. The method of claim 1, further comprising the step of obtaining the flue gas from a fossil fuel-fired power plant, an industrial furnace, a cement kiln, an oxy or air combustion facility, the exhaust of an engine, or the exhaust of a lime kiln. 9. The method of claim 1, wherein, in step d, the carbon dioxide-rich stream is compressed to a pressure of approximately 5 to approximately 30 bar. 10. The method of claim 1, wherein the carbon dioxide product has a purity of at least about 97% by volume. 11. A carbon dioxide purification system for recovering carbon dioxide from low pressure gaseous mixtures having low concentrations of carbon dioxide comprising: a gaseous mixture obtained from a flue gas, wherein the gaseous mixture contains approximately 5% by volume to approximately 25% by volume carbon dioxide at a pressure of approximately 1 to approximately 5 absolute atmospheres;a vacuum swing adsorption unit adapted to receive the gaseous mixture having one or more adsorbent beds in which carbon dioxide is preferentially adsorbed and a vacuum pump adapted to withdraw a carbon dioxide-rich stream from the adsorbent beds;a gas purification unit adapted to receive the carbon dioxide-rich stream from the vacuum pump and separate the carbon dioxide-rich stream into a carbon dioxide product and a carbon dioxide-lean stream from the carbon dioxide-rich stream, the gas purification unit comprising at least one gas separation membrane; anda conduit fluidly communicating between the gas purification unit and the vacuum swing adsorption unit being adapted to direct a portion of the carbon dioxide-lean stream to the vacuum swing adsorption unit. 12. The system of claim 11, wherein the conduit directs the carbon dioxide-lean stream to an inlet of the vacuum swing adsorption unit to combine with the gaseous mixture. 13. The system of claim 11, wherein the conduit directs the carbon dioxide-lean stream to the one or more adsorbent beds of the vacuum swing adsorption unit to pressurize the one or more adsorbent beds. 14. The system of claim 13, wherein the conduit directs the carbon dioxide-lean stream to the one or more adsorbent beds of the vacuum swing adsorption unit to rinse the one or more adsorbent beds.