... part of the expanded air thru expanding in the sub-cooler, is cooled by the oxygen in the LP ... top of the LP column. Liquefied air after being sub-cooled and throttled is being sent to middle level ... level of the LP column, and thru expansion air sub-cooler and main heat exchanger reheating, it is then ... the LP column, and after being reheated in the sub-cooler and main heat exchanger, it is then delivered ...