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• We have a problem in one of the main towers (capacity = 150000 bbl/day ) in the company I'm working for. There is an inclination in the tower which may affect the efficiency of separation. So, what's the maximum allowable inclination so that no effect in the separation efficiency may occur?

  Dec-2023

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Answers

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• Marcio Wagner da Silva, Petrobras, marciows@petrobras.com.br

  It's important to consider that distillation columns with industrial applications with high capacity like described in your question normally have an inclination grade.

  The fractionating efficiency will be affected according to the diameter of the distillation column, once higher diameters will lead to a most severe disequilibrium in the liquid holdup in the fractionating stages which will produce an accumulation of liquid in the inclined section of the fractionating stage with higher pressure drop, preferential flowing of the vapor phase and then a reduction in the fractionating efficiency. This phenomenon is called vapor-liquid channelling by specialized literature and a good reference about this topic is the book "Working Guide to Process Equipment" by Norman P. Lieberman and Elizabeth T. Lieberman (Fourth edition, 2014).

  Based on this reference, it's possible to conclude that is not rare to identify a 1 ft out of level in a distillation column with 14 ft diameter ( I believe that 3 % of inclination (based on the column diameter) would be acceptable) and this out of level can be compensated through raising the pressure drop of the liquid flowing through the orifice holes which demand the shutdown of the distillation processing unit. It's important to quote that any inclination will affect the fractionating performance due to the mechanism mentioned above, it's possible to find a tolerated point of performance reduction, but the inclination should be solved as soon as possible to return the processing unit to their optimized point.

  Despite this, I believe that the most important concern should be the stability of the structure considering all efforts and wind load to ensure the process safety requirements.

  Dec-2023