Single packaged air separation apparatus with reverse main heat exchanger

An air separation apparatus comprising:

• (a) a first column, a main condenser evaporator and a second column, wherein the second column surmounts the first column and the first column and the second column are thermally connected by the main condenser evaporator, wherein the first column is operated at a higher pressure than the second column;
• (b) an auxiliary evaporator having a liquefaction space and a vaporization space, the auxiliary evaporator being disposed below the bottom of the second column;
• (c) a main heat exchanger being disposed in between the first column and the auxiliary evaporator for indirect heat exchange between the compressed and purified feed air stream and return gaseous streams from the second column, the main heat exchanger having a warm end and a cold end;
• (d) means for introducing a compressed and purified feed air stream into at least the first column after cooling in the main heat exchanger;
• (e) means for introducing at least a fraction from the first column into the second column;
• (f) means for transporting a liquid oxygen stream from the main condenser evaporator into the vaporization space of the auxiliary evaporator, wherein at least part of the vaporized gaseous oxygen stream is warmed up in the main heat exchanger to form gaseous oxygen product and the remaining liquid oxygen stream is withdrawn as liquid oxygen product;
• and
• (g) means for providing refrigeration to the air separation apparatus;
• wherein the main heat exchanger is configured such that the return gaseous streams enter from the cold end at the top, and exit from the warm end at the bottom of the main heat exchanger.