When the air volume decreases, the rising steam volume and reflux liquid volume in the tower decrease, but the reflux ratio remains unchanged. Under normal conditions, it has little effect on the purity of oxygen and nitrogen products. According to the material balance, when the amount of processing air decreases, the output of oxygen and nitrogen will decrease accordingly.
When the gas volume decreases, the steam flow rate decreases, the liquid volume on the tray also decreases, and the liquid layer thins, so the tray resistance decreases. At the same time, as the main cooling and heating load is reduced, the heat transfer area is rich, and the heat transfer temperature difference can also be reduced. These effects will help to reduce the pressure of the upper and lower towers.
When the gas volume is reduced too much, the liquid on the sieve hole may not be held due to the low gas velocity, and the liquid will leak directly from the sieve hole, resulting in liquid leakage. The leaked liquid does not fully contact with the steam, part of the evaporation is not sufficient, and the nitrogen concentration is high. This will greatly reduce the distillation effect, affect the purity of product oxygen and nitrogen, and even fail to maintain normal production in serious cases. Therefore, the minimum allowable load value is specified for the distillation column, which is related to the structural type of the tray and the selection of parameters during design.
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