Sensing strategies for determining the axial gas dispersion coefficient in bubble columns via gas flow modulation technique

The gas flow modulation technique (GFM) is a recently proposed approach for measuring the axial gas dispersion coefficient in bubble columns. It bases on a time-resolved measurement of the modulated gas holdup at different axial positions in the column and a subsequent calculation of the axial dispersion coefficient from amplitude damping and the phase lag of a gas holdup wave. In recent studies holdup has been measured with gamma-ray densitometry, which is advantageous in terms of measurement accuracy. However, the application of radiative measurement techniques in industrial settings poses several logistical and safety challenges. This study investigates the potential of non-radiative measurement techniques in the context of GFM. In particular, differential pressure sensors, conductivity needle probes and optical probes are considered. The results obtained using these alternative techniques are compared with gamma-ray measurements. The comparison qualifies differential pressure sensors as a particular viable alternative to gamma-ray densitometry.