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

How to determine if the pressure at the booster end of the air separation equipment expander is normal?

The liquefaction of gases can be divided into forward and reverse cycles. The forward cycle process is the absorption of heat from the higher temperature external heat source and the release of heat to the lower temperature external heat source. The reverse cycle is when the mass draws heat from a lower temperature external heat source and releases it to a higher temperature external heat source. The forward cycle converts heat energy into mechanical energy and the reverse cycle converts mechani...