Why is there no side-stream extraction from the pressure tower?

Reconstituted components such as fusel oils accumulate in the atmospheric pressure column; to improve the quality of methanol, a side stream is taken from this column, while the pressurized column ensures the desired quality

Could someone upstairs please answer directly why no side stream is used for extraction in the pressure tower? My understanding is that the pressure column extracts a portion of the methanol, while a large amount of methanol and heavier components remain at the bottom of the column; in other words, these heavier components accumulate in the lower part of the pressure column and are eventually carried to the atmospheric pressure column. Therefore, there is no need to install side streams for extraction in the pressure column. I’m not sure if my understanding is correct

No, this topic of yours is wrong from the start. It’s possible that your facility does not have a side stream for extraction from the pressurized tower, but that doesn’t mean it’s not possible; in fact, many facilities are equipped with side streams for extraction from their pressurized towers. What is extracted here is finished methanol, not fusel oil! Of course, there are also many units that design the product extraction from the pressure tower to take place on the reflux line. In my opinion, this results in more stable product quality. However, if the tower height is properly designed, the reflux ratio is appropriate, and production is stable, then the side stream can also meet the required standards. At the same time, due to the effect of pressure on relative volatility, the reflux ratio in a pressurized column is generally slightly higher than that in an atmospheric-pressure column. Although there is not much difference between the two during design calculations, a difference does exist in actual operation.

Our company uses three-column distillation; the product is taken directly from the reflux line of the pressure column. In fact, the atmospheric column corresponds to the stripping section of the two-column distillation system’s pressure column.

Taking product from the side line of the pressure tower can easily cause fluctuations in tower temperature, resulting in poor system stability and reduced plate efficiency.

In current distillation processes, the product taken from the pressure column generally does not have a side stream; this is because side stream extraction can cause fluctuations in column temperature, resulting in poor system stability and reduced plate efficiency. The side-line extraction is located at the outlet of the return tank, as the pressure there is sufficient for external transfer.