Seeking help with a question about distillation towers
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2. In a normally operating two-component distillation column, changes in the feed material result in an excessive level of heavy components at the top of the column. The measures that can be considered in such a situation are ( ). A. Increase the reflux ratio B. Lower the feed temperature C. Lower the temperature at the bottom of the column D. Use a reserved pipeline to move the feed inlet up by one tray
ABC can address this by reducing the temperature inside the tower and increasing the reflux ratio
In a normally operating two-component distillation column, changes in the feed material can result in an excessive level of heavy components at the top of the column. The measures that can be considered in such a situation include (a) increasing the reflux ratio
The excessive level of heavy components at the top of the tower is caused, essentially, by an insufficient amount of liquid phase in the distillation section or a relatively large amount of gas phase, which disrupts the existing equilibrium. Option A is feasible – it represents the fastest and most direct solution – but it is also necessary to adjust the utility supplies to the bottom of the tower at appropriate times. Option B is not suitable, as the temperature of the feedstock can sometimes be uncontrollable, and temperature fluctuations do not necessarily affect the quality of the products obtained at the top and bottom of the tower; again, it is necessary to adjust the utility supplies to the bottom of the tower at appropriate times. Option C is not viable: reducing the temperature at the bottom of the tower, with pressure remaining constant, will definitely result in light components ending up in that area； If the pressure changes, it will be necessary to reduce the use of utility services; this seems like a temporary solution that will ultimately affect not only the distillation section but also the stripping section. D is not feasible; moving the feed inlet upward will only make the separation efficiency in the distillation section even lower. Reducing the number of trays in the distillation section as well is not a viable option ； However, if the feed inlet is moved downward, it is necessary to consider whether the light components can be separated easily; if it does not affect the separation results in the stripping section, then moving it downward is acceptable.
Adjusting the reflux ratio is the most appropriate approach. It is easy to adjust, and it will not have a significant impact on the balance of the entire system.
It seems the question isn’t quite complete yet – what about changes in raw materials, and the requirements for the products at the top/bottom of the tower? A is still a relatively conservative option.
Personally, I think all of ABC could be achieved.