subject: summary of nitrogen generator [print this page] summary of nitrogen generator summary of nitrogen generator
The present invention of nitrogen generator provides for a process carried out under cryogenic conditions in an apparatus providing for an efficient recovery of nitrogen from air. In the process of the present invention, a gaseous feed stream is rendered free of impurities, compressed, dried, and cooled, and thereafter, delivered to a feed point in a distillation column. In the distillation column, a nitrogen-enriched vapor is formed at the top, and an oxygen-enriched liquid at the bottom of the column. A portion of the nitrogen-enriched vapor is condensed by indirect heat exchange with a portion of the oxygen-enriched liquid from the bottom of the distillation column in a first reboiler/condenser and thereafter at least partially returned as reflux to the top of the distillation column. The oxygen-enriched liquid stream used to condense the portion of nitrogen-enriched vapor is partially vaporized to result in a liquid fraction relatively rich in oxygen, and a vapor fraction relatively rich in nitrogen. The vapor fraction is withdrawn and compressed for recycle to the distillation column. The liquid fraction rich in oxygen is extracted and expanded into a second reboiler/condenser wherein it forms an oxygen-enriched vapor and a nitrogen-condensate by indirect heat exchange with at least a portion of nitrogen-enriched vapor, at least a part of which vapor is thereafter expanded to provide refrigeration for the overall process. Providing the reboil for the vaporization of the liquid fraction rich in oxygen is a portion of the nitrogen-enriched vapor from the distillation column which, following condensation in the second reboiler/condenser, is preferably returned to the distillation column as reflux.
In the process of the present invention, the distillation is carried out in a single distillation column, and there are no distillation sections in either of the reboiler/condenser sections. The withdrawal of liquid comprising a relatively higher portion of oxygen than the equilibrium vapor from the first reboiler/condenser provides a high nitrogen concentration in the recycle stream, and thereby, higher overall nitrogen recovery.
In the preferred embodiment of the present invention, the expansion turbine which expands a portion of the oxygen-enriched vapor from the second reboiler/condenser is integrally coupled with a cold compressor which serves to compress the recycled nitrogen-enriched vapor from the first reboiler/condenser to the distillation column.
