Why is the pressure in the lower tower of the air separation equipment higher than that in the upper tower?

Due to improper adjustment of seal gas pressure during operation, liquid oxygen pump can not pump liquid or leak.   From the quality point of view, when the sealing pressure is too high, there will be gas leakage into the pump through the labyrinth seal, resulting in the impeller with gas or even idling, resulting in liquid injection or pressure drop; when the air pressure before sealing is too low, there will be liquid oxygen leakage.   From the quantity point of view, when (p1-p3...

What is the function of the distillation tower in an air separation unit?