Investigations of Hydrodynamics of Fixed Bed Reactor: Counter-Current Flow

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 various
gas/liquid volumetric ratio on the residence time distribution. The ranges of air -
water ratio is chosen to simulate the hydrogen/oil ratio of typical bench scale hydroprocessing
units, noting the difference that might arise due to the different physical
properties of theliquid. The experiments were conducted in counter-current mode and
the effects of gas/liquid velocities on the hydrodynamics of the reactor were
investigated. This study is done using the tracer method - specifically the pulse input
method. The packed bed reactor used in this study is packed with8x8 mm Raschig
rings. Results show that the increasing gas/liquid ratio increases the mean residence
time. However, operating liquid hold-up and the value of Peclet number, which gives
an indication to the degree of axial dispersion in the system, increase. Second moment
analysis of the reactor, namely the variance of the system, shows a reduction in value
with decreasing gas/liquid ratio suggesting wider liquid distribution through the
system at lowgas flow rates. The discrepancies in experimental results suggested that
there are conditions to be altered in order to eliminate the inconsistency.