Don't forget the feed pipe
by Patrick Quotson
It is not uncommon for engineers working on packed distillation towers to thoroughly evaluate the performance of a liquid distributor above a bed of tower packing, only to ignore the consequences of a poor feed pipe design.
The purpose of the feed pipe is to deliver liquid in a manner that will allow the distributor to function properly hydraulically.
- The feed points must be spaced sufficiently so that there is not excessive liquid velocity on the distributor to cause hydraulic gradients.
- It is also necessary to limit the velocity in the outlet pipe so that excessive turbulence is not developed locally in the liquid pool on the distributor. The use of splash baffles may be necessary.
- In applications where the composition of the incoming feed liquid does not match the composition of the overhead liquid, the feed pipe should be designed to distribute the feed uniformly with the overhead liquid.
- In applications where the incoming feed is subcooled more than 30° F, a submerged feed pipe should be considered.
- In some cases, a simplified feed pipe used in conjunction with a parting box may be more suitable.
Due to its impact on the performance of liquid distributors, it is important to consider carefully feed pipe design as part of the entire separation system.
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