cooling the input air stream 18 while the other is being cooled and purged by nitrogen gas stream 75 and vice versa to balance the cooling nitrogen flows between the main air regenerators 22 and 24 and heat exchanger 42 some of the cooling nitrogen is tapped from the mid point of the air regenerators and delivered via line 77 to the matching temperature location of heat exchanger 42 where the cooling nitrogen mixes with the cooling nitrogen in line 73 of heat exchanger 42 the warm nitrogen stream in line 75 now containing some of the impurities originally present in the input air stream 18 mostly carbon dioxide and water is finally discharged to atmosphere through silencer 103 of course this nitrogen stream can also be collected and after a degree of purification become a separate nitrogen product alternatively in certain applications where the moisture content of the 34 impure 34 nitrogen is low enough this stream could be heated and used as a drying medium typical examples of such applications would be in coal drying in the steel industry and in coal burning power plants of course nitrogen stream 73 could also be similarly used instead of being vented to the atmosphere the medium purity product which accumulates at the bottom of the low pressure upper column 50 at essentially atmospheric pressure is removed as a liquid through line 52 and pumped by the pump 54 to the desired pressure the liquid passes through the subcooler 46 and is then vaporized in the evaporator 44 by the condensing vaporizer stream the product then passes through line 56 and into the heat exchanger 42 where it is heated to ambient temperature then passing through line 58 into the product to boost.