On the control of the feed temperature in distillation columns
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I’ve thought about it for a long time and still can’t figure it out. Taking the distillation column in our unit as an example, when the parameters of the product at the top of the column exceed the specified values, adjustments are made to the reflux at the top, as well as to the pressure or temperature there. When the parameters of the product at the bottom of the column change, adjustments are generally made to the temperature of the reboiler. The feed temperature to the distillation column remains essentially unchanged. Therefore, I would like to ask everyone: when exactly should we consider adjusting the feed temperature of the distillation column?
The feed temperature is generally not adjusted; as long as the top and bottom temperatures and pressures are appropriate, the product will not be defective
Then why set up feed control? It must be useful for something, right?
Generally, it is sufficient to maintain stability in the feed flow rate and temperature; there is no need to deliberately adjust the feed temperature. The feed temperature determines the gas and liquid load in the tower, and the tower diameter is determined based on this. If the feed temperature decreases, theoretically this is equivalent to an increase in the reflux rate, which will improve the product specifications; however, the liquid load on the stripping section and the heat load on the reboiler will increase accordingly.
Do you mean that the feed temperature of the tower is determined during the design phase, and as long as this predetermined temperature remains unchanged, there is no need to adjust it? Is that what you mean?
It can be understood in this way; however, there is a certain degree of flexibility in the design of the tower, so the feed temperature can be adjusted appropriately, but it is not considered a priority for adjustment.
Yes, could you tell me when exactly this adjustment was considered?
1. When considering energy savings, preheat the feed to increase its temperature； 2. The flooding rate is high in the stripping section and low in the rectifying section; to improve the gas-liquid load inside the tower, the feed temperature is increased.
I have a gentle question: what is the pan-point rate?
The flooding ratio is the ratio of the operating gas velocity in a distillation column to the flooding gas velocity.
The gas velocity should be related to the gas-phase load, right? Then couldn’t it also be achieved by changing the bottom temperature of the tower?