In the process of feeding expanded air into the upper column, what is the effect of increasing the degree of expansion on the argon fraction?

Judging from the popularity, there aren’t many people on this forum who are involved in air separation! Moderators, please help with more development!

　An excessive amount of expanded air entering the upper tower leads to an increase in pressure in that tower. As a result, the liquid-vapor ratio on the trays above the expanded air inlet decreases, weakening the ability to separate the various components. This hinders the effective functioning of the distillation process on those trays, causing the argon fraction to have a lower argon content and a higher nitrogen content. At the same time, the reflux ratio in the stripping section decreases, the pressure in the upper column rises, which increases the liquefaction temperature of liquid oxygen. As a result, the temperature difference in the main cooler decreases, the amount of liquid oxygen evaporating in the main cooler falls, the argon-rich zone moves downward, the oxygen content decreases, and the nitrogen content increases. Hazard: The crude argon column can develop a nitrogen plug. Under normal operating conditions, the nitrogen content should not exceed 0.1% (the typical composition of the argon fraction is: 9%–10% argon, 90%–91% oxygen, with very low levels of nitrogen). In the upper column, the sampling point for the argon fraction remains constant; as the argon-enriched zone in the upper column moves up and down along the tray, the composition of the argon fraction sampled also changes accordingly. When the oxygen purity in the upper column is low, it causes the argon-enriched zone in that column to shift significantly downward, resulting in an excessive nitrogen content in the argon fraction. The heat transfer temperature difference in the condenser of the crude argon column is generally designed based on a nitrogen content of 115% in the crude argon; a significant increase in the nitrogen content leads to a reduction in this temperature difference, preventing the argon fraction from condensing in the condenser and thus causing a nitrogen buildup in the crude argon column.

Thank you for the answer from above; I hope we can communicate more in the future. :handshake

The main function of the upper tower is to separate oxygen from the liquid air; separating oxygen from the expanded air is merely a secondary task. An inappropriate analogy is: Liquefied air is the primary partner of the upper tower, while expanded air is the secondary partner. It’s okay if the secondary character is just an occasional addition, but if her importance is increased, it will be too much to handle when going up the tower. Earlier, the air separation towers did not use expanded air; it was Rahman who later introduced this secondary method.

Hehe. So talented. I’ve learned that the main purpose of introducing Rahman gas is actually to make use of the distillation section at the upper part of the tower. Otherwise, a large portion of the light at the upper part of the tower will be used for the distillation of liquid nitrogen and gaseous nitrogen. It’s a waste for distillation. The amount of expanded air is larger. Too much superheated fluid is entering the tower. This naturally increases the evaporation rate of the tower. The pressure in the tower increases. At the same time, the vapor-liquid ratio above the expanded air inlet increases. As the rising gas increases, the heavy components in the downstream liquid, mainly oxygen and argon, will decrease significantly. Naturally, this leads to an increase in nitrogen content in the argon extraction port at the lower part.