Advantages (disadvantages) of controlling the low (high) liquid level in the distillation column bottom tank
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For these two companies, one requires the level in the tower bottom to be controlled at 80%, while another requires it to be kept at 30%. Please explain the advantages of each approach – this is just to stimulate further discussion. With a high liquid level, it’s easier to maintain control, especially when operators in new plants are not yet familiar with the process. A low liquid level reduces steam consumption and prevents unwanted side reactions; it also improves the separation of light components in the tower bottom. The disadvantages are that a high liquid level can lead to flooding of the tower if not managed properly, as well as increased steam usage. A low liquid level can cause flooding issues if not handled correctly, and it may even cause damage to the heat exchangers and the tower itself
There aren’t that many requirements; generally, 50-60 is the ideal range. It shouldn’t be too low or too high, so as to ensure smooth operation! Too high or too low, steam fluctuations can easily cause flooding or drying out of the tower!
Each case must be analyzed on its own; too low a liquid level certainly affects operational stability.
In our original aromatization unit, the liquid level in the tower bottom was generally kept at around 60%; I personally think this level is appropriate as well, as it results in relatively lower energy consumption and helps to avoid the disadvantages associated with either too high or too low liquid levels
Generally, the liquid level should be kept between 30-70%; the main consideration is whether the material inside the reboiler can circulate through convection. If the material has a high viscosity, the level should be kept lower, while if its viscosity is low, it can be kept higher.