(71h) Transport Characteristics of Mellapak 250Y Packing Under Distillation Conditions. Effect of Axial Mixing of the Phases

Authors: 
Rejl, F. J., Institute of Chemical Technology, Prague (ICT)
Valenz, L., Institute of Chemical Technology, Prague (ICT)
Linek, V., Institute of Chemical Technology, Prague (ICT)


Transport characteristics (HETP,
kLa , kGa)
of metal Mellapak 250Y structured packing has been
measured in the distillation column distilling three alcoholic systems (methanol-ethanol,
ethanol-propanol, methanol-propanol) and one standard hydrocarbon system (cyclohexane-heptane)
under total reflux condition at atmospheric pressure. Volumetric mass-transfer
coefficients have been determined using "profile method".

Experimental aparatus
was an atmospheric distillation column of an inner diameter of 0,15m packed
with ten pieces of packing with the total height of the packing 2,1m. The
column is equiped with seven sampling points along
the packing enabling withdrawal of a sample of liquid and vapour directly from
the packing and therefore measurement of concentration profiles in both phases.
Experiments were performed for four powers into a reboiler
up to uG= 1,7m/s.

An axial mixing in terms of Bodenstein numbers BoL,
BoG has been measured independently
in the absorption column with water-air system. There has been found that axial
mixing data transfer from absorption to distillation can be succesfully
achieved using relation suggested by Fair (1999). Volumetric mass-transfer
coefficients evaluated with axial mixing being taken into account differ
substantially from those evaluated with common plug-flow assumption. Results
indicate significant mass-transfer resistance in both phases and significant
influence of axial mixing of the liquid phase on separation process. The effect
of gas phase axial mixing was found negligible. Dependence of volumetric mass-transfer
coefficients on the phase flow rates differs from the ones incorporated in
commonly used models by Olujic', Billet-Schultes and Rocha-Bravo-Fair.