▁reverse ▁compress or ). ▁ ▁Alternatively ▁the ▁cond enser ▁may ▁be ▁co o led ▁by ▁inter ch anging ▁heat ▁with ▁a ▁re bo iler ▁in ▁a ▁low ▁pressure ▁( LP ) ▁dist ill ation ▁column ▁( oper ating ▁at ▁ 1 . 2 - 1 . 3 ▁bar ▁abs .) ▁when ▁the ▁AS U ▁is ▁producing ▁pure ▁o xygen . ▁To ▁minim ize ▁the ▁compression ▁cost ▁the ▁combined ▁cond enser / re bo iler ▁of ▁the ▁H P / LP ▁columns ▁must ▁operate ▁with ▁a ▁temperature ▁difference ▁of ▁only ▁ 1 - 2 ▁K , ▁requiring ▁plate ▁fin ▁bra zed ▁al umin ium ▁heat ▁ex ch angers . ▁Typ ical ▁o xygen ▁pur ities ▁range ▁in ▁from ▁ 9 7 . 5 % ▁to ▁ 9 9 . 5 % ▁and ▁influ ences ▁the ▁maximum ▁recovery ▁of ▁o xygen . ▁The ▁re fr iger ation ▁required ▁for ▁producing ▁liquid ▁products ▁is ▁obtained ▁using ▁the ▁J ou le – Th om son ▁effect ▁in ▁an ▁exp ander ▁which ▁fe eds ▁com pressed ▁air ▁directly ▁to ▁the ▁low ▁pressure ▁column . ▁Hence , ▁a ▁certain ▁part ▁of ▁the ▁air ▁is ▁not ▁to ▁be ▁separated ▁and ▁must ▁leave ▁the ▁low ▁pressure ▁column ▁as ▁a ▁waste ▁stream ▁from ▁its ▁upper ▁section . ▁ ▁Because ▁the ▁bo iling ▁point ▁of ▁arg on ▁( 8 7 . 3 ▁K ▁at ▁standard ▁conditions ) ▁lies ▁between ▁that ▁of ▁o xygen ▁( 9 0 . 2 ▁K ) ▁and ▁nit ro gen ▁( 7 7 . 4 ▁K ), ▁arg on