Hydrodynamic characteristics of gas-liquid co-current up-flow in a packed bed reactor

The residence time distribution (RTD) of a pilot plant
scale packed bed reactor was studied in the present study
using air – water system to investigate the effect of
various gas/liquid ratio on the residence time distribution.
The ranges of air – water velocity ratio is chosen to
simulate the hydrogen / oil ratio of typical bench scale
hydro-processing units, noting the difference that might
arise due to the different physical properties of the liquid.
The experiments were conducted in an up-flow mode and
the effect of gas / liquid velocities on the hydrodynamics
of the reactor were investigated. This study is done using
the tracer method – specifically the pulse input
experiment. The packed bed reactor used in this study is
packed with 8 x 8 mm Raschig rings. Results show that
the increasing gas / liquid ratio increases the mean
residence time and operating liquid hold-up. However,
the value of Peclet number, which gives an indication to
the degree of axial dispersion in the system, decreases,
suggesting an increase in the degree of back-mixing in the
reactor at higher gas flow rates. Second moment analysis
of the reactor, namely the variance of the system, shows a
reduction in value with decreasing gas / liquid ratio
suggesting greater liquid distribution through the system
at low gas flow rate.