Question

What Happens to the bottom and top products if the feed point to a distillation column is switched from the designed optimum to

1. A tray closer to the reboiler?

2. A tray closer to the condenser?

Answer 1

Location of feed plate is calculated by theoretical methods for the required output. If the feed point is shifted then the compostion or rather the quality of products at Top and Bottom changes.

1) When Tray is closer to reboiler, the product at Top that is the distillate will constitute more lighter components than before or we can say lighter compinents at top will more quality. But at the same time reboiler duty increases.

2) When Tray is closer to Condensor, the bottom product will be more 'pure' in terms of heavy component. and Condensor duty increases.

If feed location is changed, then the overall performance of that column is affected because the column was designed to operate at the initial feed location. For example, partial reboiler and partial condensor are considered as stages and it will not function like for what it was designed for. Reflux ratio is changed and liquid level of each tray is affected.

Hope this helps;)

Have a nice day!