(97i) Pressure Drop and Liquid Hold up in an Open-Structure Random Packed Column with Counter Current Flow

Authors: 
van der Schaaf, J. - Presenter, Eindhoven University of Technology
Schouten, J. C., Eindhoven University of Technology

Pressure drop and liquid hold up in an open-structure
random packed column with counter current flow

L. Pezzi
Martins Loane1, J.C. Schouten1 and J. van der Schaaf1,*

1Eindhoven University of
Technology, P.O. Box 513,

5600 MB Eindhoven, The Netherlands

*Corresponding
author:
J.Vanderschaaf@tue.nl

Structured
foam packing has been proven to enhance mass and heat transfer and decrease
pressure drop due to the intrinsic open pore nature of a foam[1]. The
high accessible surface area that this type of packing offers makes it easy for
fluids to access the catalyst. Furthermore, the heat generated by, or needed
for the reaction is efficiently redistributed into the main stream, avoiding
thus the formation of hot spots. Previous studies focus on a continuous large
piece of foam of the same size as the reactor dimensions. These large blocks of
foam are difficult and labor intensive to incorporate in a column which gives
space to a new type of foam packing, the open-structure random packing, OSRP.
OSRP are essentially small pieces of foam with a specific shape and size. Their
attractiveness lies in the fact that it can be easily dumped into a column,
acting as a packed bed.  The liquid hold
up, the flooding point, and the pressure drop of an OSRP reactor are important
for assessing its performance in comparison with other packings. It is widely
accepted that pressure drop in packed columns with counter current flow can be
estimated using the Ergun equation[2]. In this equation the bed
porosity and the superficial velocity of the gas phase are of great importance
together with the kinetic loss terms, to estimate pressure drop. However for
the OSRP not only the bed porosity will influence the pressure drop but also
the foam porosity.

Experimental
work was performed to determine pressure drop, flooding points and liquid hold
up for gas superficial velocities up to 0.34 m/s and liquid superficial
velocities up to 0.03 m/s for 3 different types of OSRPs.  

The
experiments show that the gas superficial velocity does not influence the
liquid hold up, contrary to what is observed for more conventional packings.
The liquid hold up is determined only by liquid superficial velocity and a
simple correlation is proposed. Another remarkable difference with conventional
packings is that the flooding pressure drop values remain virtually constant
for one type of foam for all investigated liquid flow rates. Additionally, the
dry and wet OSRP packing have different kinetic loss terms. With the
experimental liquid hold up as input, the pressure drop is predicted within 15%
accuracy. A revised pressure drop correlation for OSRPs is proposed.

Figure  SEQ Figuur \* ARABIC 1: Liquid hold up versus Superficial gas velocity,
for foam 'A'.

Figure  SEQ Figuur \* ARABIC 2: Liquid hold up versus superficial liquid
velocity, for foam 'A'.

[1] C.P. Stemmet, J. van der Schaaf, B.F.M. Kuster, J.C.
Schouten, Solid foam packings for multiphase reactors: Modelling of liquid
holdup and mass transfer, Chem. Eng. Research and design 84 (2006) 1134-1141

[2] S. Ergun, A. Orning, Fluid Flow through randomly
packed columns and fluidized beds, Industrial and Engineering Chemistry (1949),
1179-1184