| 摘要 |
<p>A first stream of compressed feed air is introduced in vapour state into a higher pressure rectification column 22 and separated therein into nitrogen vapour and oxygen-enriched liquid air, a flow of the nitrogen vapour is condensed in condenser-reboiler 44. A flow of the oxygen-enriched liquid air is separated in a reboiled lower pressure rectification column 40 into nitrogen-rich and oxygen-rich fractions. A first flow of the condensed nitrogen is employed as reflux in the higher pressure rectification column 22 and a second flow of the condensed nitrogen is employed as reflux in the lower pressure rectification column 40. A flow of compressed feed air is expanded in expansion turbine 16 with the performance of external work so as to create refrigeration for the process. Products of the separation include one or both of a gaseous nitrogen product taken from the higher pressure rectification column 22 and a liquid nitrogen product. A second stream of compressed feed air is liquefied. At least a part of the liquefied second air stream is vaporised in vaporiser 28 at a pressure less than that at the top of the higher pressure rectification column 22 by indirect heat exchange with a part of the said flow of nitrogen vapour, and the resulting vaporised air is warmed, is recompressed, and is mixed with feed air upstream of a location from where the first stream is taken. <IMAGE></p> |
