A ONE DIMENSIONAL MODEL FOR TRICKLE BED HYDRODESULFURIZATION

The need for processing of heavy sour crudes is increasing as good quality crude
oil reserves are depleting fast. Presence of sulfur in the crude oil can corrode the
process equipment, poison the catalysts and can lead to environmental pollution.
Trickle bed reactors are widely used for hydrodesulfurization by reacting sulfur in the
crude with hydrogen. Optimal design of these units is possible through development
of easy to use performance models for trickle bed reactors recognizing the multiphase
nature of the reactor and nonlinearities in the parameters.
Liquid holdup in trickle bed reactors is an important hydrodynamic parameter
which controls the liquid residence time in the bed and hence the degree of sulfur
conversion. A new model to estimate liquid holdup in trickle beds is developed
considering gas to flow around particles enveloped by trickling liquid. Ergun’s
equation for gas phase pressure drop is modified incorporating the effect of presence
of liquid phase on gas phase voidage and tortuosity for gas flow. The model is
compared with large experimental database available in the literature to evaluate the
effect of parameters such as gas and liquid velocities, liquid properties, particle shape
and size, operating temperature and pressure. The model equations compare
reasonably well with the experimental observations.
A one-dimensional multiphase cells-in-series model is developed to predict the
steady state behavior of trickle bed reactor applied to the hydrodesulfurization of
vacuum gas oil (VGO). The reactor model is established through mass and enthalpy
balances with reaction using carefully selected correlations and hydrodesulfurization
reaction kinetics based on Langmuir-Hinshelwood mechanism from the literature. The
model is validated with experimental data on hydrodesulfurization of VGO reported
in the literature. The model is simulated to investigate the effect of various parameters
to analyze ways and means to improve the sulfur reduction.