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

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 Schaaf^1,*

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