Naked cooling of air separation plant

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

The expansion air volume entering the upper tower increases, and the reflux ratio of the distillation section decreases correspondingly. In order to achieve the required purity of nitrogen products, more tower plates need to be set. When the reflux ratio is reduced to countless Tower plates needed to be set to make the purity of nitrogen reach the required value, then the reflux ratio is called the minimum reflux ratio. The expansion air volume entering the upper tower is first limited by the minimum reflux ratio. The closer the reflux ratio is to the minimum reflux ratio, the faster the number of tower plates needed to ensure the product purity increases, which will lead to the increase of investment, the increase of tower plate resistance, the increase of Operation pressure and the increase of energy consumption. Therefore, the reflux ratio after the inflated air enters the tower should be larger than the minimum reflux ratio. When the purity of nitrogen is required to be low, the...