Application of Electrical Resistance Tomography in Evaluating the Influence of Nozzle Design on the Gas Hold­up Distribution in Boiling Bubble Column Reactors

H. Sudhakaran1, E. W. Randall1, U. Ramdhani2, R. Rawatlal1

1 Department of Chemical Engineering, University of Cape Town, Private Bag, Rondebosch, 7701 ,South Africa Email: Randhir.Rawatlal@uct.ac.za

2 Sasol Technology (Pty) Ltd., Research & Development, P.O. Box 1, Sasolburg 1947, South Africa

ABSTRACT

Bubble column reactors are extensively used in the chemicals industry due to the combined advantages of high rates of heat and mass transfer coupled with low operating and maintenance costs. However, the complex hydrodynamics brought about by the multiphase nature of such systems offer significant challenges in modelling, analysis and operation, making experimental measurement of system response of special importance. One such measurement tool is Electrical Resistance Tomography (ERT).

In this paper, the development of an experimental bubble column reactor fitted with 8 rings of 16 electrodes for ERT measurements using an instrument developed at UCT is described. The initial experiments involving air­water and suspended solid objects served as a calibration and showed the system to be recording the response of the fluid phase reliably. A rigorous experimental programme thereafter followed to evaluate the influence of a particular geometric parameter, namely the aperture angle of the nozzle, on the dispersion of the gas. The comparison on the effect of aperture angles is reported.

The bubble column was then adapted for the investigation of the introduction of a sub­cooled butane input rather than air. An experimental program similar to that of the air­water system was then executed and the difference in mixing of both gaseous and sub­cooled systems are compared.

Generally speaking, it was found that since the system response to nozzle geometric parameters cannot easily be predicted by theoretical methods, ERT plays a valuable role in assessing the degree of mixing in the given system.

Keywords: bubble column reactors, gas hold­up, electrical resistance tomography