Air separation schemes for oxygen and nitrogen coproduction as gas and/or liquid products

A cryogenic distillation process for the separation of compressed, dry and contaminant-free air into its constituent components utilizing a distillation column system having at least two distillation columns operating at different pressures, wherein the top of the higher pressure column is in thermal communication with the lower pressure column, wherein a nitrogen product is produced at the top of the higher pressure column and an oxygen product is produced at the bottom of the lower pressure column, characterized in that:

• (a) a portion of the compressed, dry and contaminant-free feed air is condensed thereby producing a liquid air stream;
• (b) feeding at least a portion of the liquid air stream as impure reflux to at least one distillation column of the distillation column system, and (c) removing a waste vapor stream having a nitrogen mole fraction of less than 0.95 from a location in the distillation column system situated not more than four theoretical stages above the location in the column where the liquid air stream of step (b) is fed to the distillation column system.