Assessment of the flow modulation technique for measuring axial liquid dispersion coefficients in trickle-bed reactors

This study proposes a novel non-intrusive approach for measuring axial liquid dispersion coefficients in trickle-bed reactors. The approach is based on the flow modulation technique (FMT), which replaces traditional tracer substance injections with a marginal sinusoidal modulation superimposed on the liquid inlet flow. The modulation causes a sinusoidal variation of the liquid holdup in time, i.e. liquid holdup wave. Downstream the inlet, the holdup wave gets damped in amplitude and shifted in phase due to dispersion. Amplitude damping and phase shift are experimentally measured and related to the value of the axial dispersion coefficient using a one-dimensional dispersion model. Recently, the flow modulation has been applied to investigate the axial gas dispersion coefficient in bubble columns. In this study, the approach is adapted to measure liquid dispersion in co-current gas-liquid trickle-bed reactors. In addition, the consequences of the assumptions requested by the axial dispersion model are discussed. Furthermore, the impact of the experimental flow modulation parameters on sensitivity and uncertainty of the dispersion coefficient is analyzed.