What to do if the feed to the distillation tower decreases and the tower pressure drops
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In dynamic simulations using Aspen, it was found that when the feed rate is reduced to 70%, the pressure in the tower drops significantly; this also leads to a decrease in the liquid level at the bottom of the tower as a result of vaporization. So, should the reflux ratio be increased and the reboiler load raised in order to address this issue when the feed rate is reduced?
With reduced feed, the heat source for the reboiler needs to be decreased, and the reflux ratio also needs to be reduced appropriately (in distillation columns)
Well, but if nearly half of the feed is reduced, the output from the tower decreases. If the reflux ratio is also reduced, then the amount of reflux fluid decreases as well, and the heat supplied to the reboiler decreases too. As a result, the amount of steam inside the tower drops significantly. Since the volume of the tower remains unchanged, the tower pressure will decrease greatly!
Once the tower is designed, it has a certain operating range. Within this range, reducing the feed flow rate will result in a lower pressure drop, which is normal. However, if the conditions exceed the tower’s performance limits, problems may arise (such as dry plates or liquid leakage)