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Usually for protecting trays/column internals from any upsets, an upthrust of 1 or 2 psi is considered. But if the vapor/liquid traffic inside the column is known, how to estimate the upthrust during normal operation?
 
Answers
29/05/2015 A: keith bowers, B and B Consulting, kebowers47@gmail.com
A simple (precise & accurate) pressure measurement of top and bottom of the tower provides excellent reference. Say top pressure in the vapor space was 121.45 psig, and th bottom pressure in the vapor space under the first tray was 126,45 psig, simple arithmetic gives a difference of 5.0 psi. Unless you have a good simulation of the process , a tray to tray simulation, assume equal delta-P per tray.
28/05/2015 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
The vapor above the tray is lower pressure than the vapor below the tray, with the difference being the pressure drop across the tray. The total upward forces on the tray will the the area of the tray times the DP. The tray support rings must hold those forces. In normal operation upthrust is much lower than at upset conditions, so no one normally worries about it as far as I know.