Flow Regime Identification and Optimum Interfacial Area Control of Bubble Columns Using Electrical Impedance Imaging

M. Wang, X. Jia, M. Bennett and R. A. Williams

School of Process, Environmental and Materials Engineering, University of Leeds, LS2 9JT, UK, minmwa@leeds.ac.uk

ABSTRACT

This paper reports a preliminary study where electrical resistance tomography (ERT) is used to measure and control a bubble column. Several methods for identifying flow regimes (e.g. bubbly and churn flows) in the bubble column have been tested, from which two control strategies have been developed and compared. The first strategy relies on the mean pixel values of ‘normal’ ERT images. The second strategy is based on the fluctuations of the mean pixel values of ‘dynamic’ ERT images. The aim of the control is to automatically reach and maintain the flow condition deemed to correspond to the maximum interfacial area, since such a condition is desirable for many chemical reactions and mass transfer operations using bubble columns. In the cases where the background or reference conductivity changes during a single operation (e.g. due to changes in temperature and/or chemical composition), the control strategy based on fluctuations can be shown to be more robust than the other. The Golden search optimisation method has been adopted to determine the set point for PID control. A preliminary study of using electrical resistance tomographic imaging for bubble column measurement and control has been conducted. Serveal methods for identifying flow regimes (e.g. bubbly and churn-turbulent flows) have been developed. The golden section search optimisation method is used to search for the flow rate corresponding to the maximum estimated interfacial area and to determine the set-point for PID control. A simple, flow-parameter control strategy, based on bubble fluctuation as represented by derivatives of dynamic imaging, is reported.

Keywords bubble column, flow regime, electrical resistance tomography, control