▁energy ▁for ▁re fr iger ation ▁is ▁provided ▁by ▁the ▁compression ▁of ▁the ▁air ▁at ▁the ▁in let ▁of ▁the ▁unit . ▁ ▁To ▁achieve ▁the ▁low ▁dist ill ation ▁temper atures ▁an ▁air ▁separation ▁unit ▁requires ▁a ▁re fr iger ation ▁cycle ▁that ▁oper ates ▁by ▁means ▁of ▁the ▁J ou le – Th om son ▁effect , ▁and ▁the ▁cold ▁equipment ▁has ▁to ▁be ▁kept ▁within ▁an ▁ins ulated ▁en closure ▁( comm only ▁called ▁a ▁" c old ▁box "). ▁The ▁cool ing ▁of ▁the ▁g ases ▁requires ▁a ▁large ▁amount ▁of ▁energy ▁to ▁make ▁this ▁re fr iger ation ▁cycle ▁work ▁and ▁is ▁delivered ▁by ▁an ▁air ▁compress or . ▁Modern ▁AS Us ▁use ▁expansion ▁tur b ines ▁for ▁cool ing ; ▁the ▁output ▁of ▁the ▁exp ander ▁helps ▁drive ▁the ▁air ▁compress or , ▁for ▁improved ▁efficiency . ▁The ▁process ▁consists ▁of ▁the ▁following ▁main ▁steps : ▁▁ ▁Before ▁compression ▁the ▁air ▁is ▁pre - filter ed ▁of ▁dust . ▁ ▁Air ▁is ▁com pressed ▁where ▁the ▁final ▁delivery ▁pressure ▁is ▁determined ▁by ▁recover ies ▁and ▁the ▁fluid ▁state ▁( gas ▁or ▁liquid ) ▁of ▁the ▁products . ▁Typ ical ▁press ures ▁range ▁between ▁ 5 ▁and ▁ 1 0 ▁bar ▁gauge . ▁The ▁air ▁stream ▁may ▁also ▁be ▁com pressed ▁to ▁different ▁press ures ▁to ▁enh ance ▁the ▁efficiency ▁of ▁the ▁AS U . ▁During ▁compression ▁water ▁is ▁cond ensed ▁out ▁in ▁inter - stage ▁cool ers . ▁ ▁The ▁process ▁air ▁is ▁generally ▁passed ▁through ▁a