Method and appliance for separating a mixture containing carbon dioxide by cryogenic distillation

#This application is a 371 of International PCT Application No. PCT/FR2013/052237 filed Sep. 24, 2013 which claims priority to French Patent Application No. 1258999 filed Sep. 25, 2012, the entire contents of which are incorporated herein by reference.

#The present invention relates to a method and an apparatus for separating a mixture containing carbon dioxide by cryogenic distillation.

#For a variant, it relates to the scrubbing of a liquid mixture of CO2 and impurities dissolved by cryogenic distillation, the tank liquid of the distillation column being reboiled and superheated.

#For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:

#FIG. 1 illustrates one embodiment of the present invention; and

#FIG. 2 illustrates another embodiment of the present invention.

#According to the invention, in FIG. 1, a gaseous mixture 1 containing at least 30%, even at least 40% of carbon dioxide and at least one light impurity, that can be oxygen, carbon monoxide, nitrogen, argon, hydrogen, methane or at least two of these components, is separated to form a fluid richer in carbon dioxide. The gaseous mixture originates from a source 100 that can be an oxycombustion unit followed by scrubbing units for removing the water and other contaminants, such as dust, SOx, NOx. The gaseous mixture is compressed as required, for example to a pressure above 6 bar abs. The pressurized gaseous mixture 1 is cooled in a heat exchanger 43 with brazed aluminum plates or with tubes. The cooled gaseous mixture is, if necessary, treated in a treatment means, for example a separation means 113. This separation means 113 can constitute a phase separator or several phase separators in series to increase the carbon dioxide content of the gaseous mixture upstream of the column 25, for example to reach at least 80% of carbon dioxide for the liquid from a phase separator. The separation means 113 can alternatively or additionally comprise adsorbant beds and/or a distillation column, for example a column to eliminate NOx gases.

#The liquid 11 enriched in carbon dioxide is sent to the head of the separation column at low temperature 10. The head gas is drawn off at the head of the column and is enriched in light components relative to the liquid 11. A part 106 of the gas is discharged to the atmosphere and the rest 6 is reheated in the exchanger 43.

#The tank liquid 101 contains more than 90% of carbon dioxide and is separated into two parts. One part 31 is expanded in a valve 39 and is vaporized in the heat exchanger to form a gaseous product rich in carbon dioxide. The rest 27 is sent to an intermediate level of the heat exchanger 43, is vaporized therein and is heated up to the hot end of the exchanger to a first temperature. The vaporized throughput leaves the exchanger at the hot end at the first temperature and is then divided into two, one part 23 serving as product and the rest 31 being returned to the column 25. The gas 31 is neither compressed nor expanded between the hot end and the column 25. The gas 31 at the first temperature is returned to the bottom part of the column 25, without having been reheated or cooled, in or outside of the exchanger 43, and rises in the column 25 by being enriched in light impurities.