(101b) Assessment of Liquid Distribution in a VGO-Hydroprocessing Trickled Bed Reactor with Computational Fluid Dynamics

Assessment of liquid distribution in a VGO-hydroprocessing trickled bed reactor with computational
fluid dynamics

J. J Arias B., jjariasb@unal.edu.co

A. Molina, amolinao@unal.edu.co

CFD simulations of the liquid distribution in a
Trickled Bed Reactor (TBR) hydro-processing Vacuum Gas Oil (VGO) were carried
out. TBRs are vertical columns with fixed-bed reactors within. Inside the
reactor liquid and gaseous phases pass through the bed on a concurrent,
down-flow mode. This kind of reactor has the capacity to host different kind of
catalytic reactions. Frequently they are used to refine crude oil cuts, as is
the case in hydro-processing, where VGO reacts with hydrogen to eliminate
heteroatoms by hydrogen substitution (hydro-treating) and saturate broken bonds
generated by catalytic cracking with hydrogen atoms (HydroCracking
(HC). Uniform liquid distribution at the top of this kind of reactors, while
fundamental to guarantee proper operation, is very difficult to achieve.

To understand the effect of liquid flow
mal-distribution at the top of TBR, four sections of an industrial-size HC
reactor were modeled. The first section involves the surroundings of the
gas-liquid distributor, itself the second section. A third simulation considered
the distribution tray. The bed was the fourth section modeled considering a
reaction mechanism particularly designed for the analysis of HC processes. To
simulate each of these sections ANSYS Fluent was used. Sections two and three were
modeling using a VOF model while the fourth section used an Eulerian model. The
meshes used were built on ICEM with cell numbers not below 200000 with
non-uniform sizes.

The simulations showed that the velocity
profile at inlet of the gas-liquid distributor unit has velocities values larger
than 15 m/s. In the gas-liquid distributor there is an expansion of the gas
while flows through it, also the gas-liquid distributor disperses the liquid
across the distributor's cross-section. The effect of liquid distribution in
the reactor performance did not show a significant coupling between injection
points. A maldistribution factor was used to evaluate the dispersion of the
liquid at the top of the bed and at the outlet compartment of the gas-liquid
distributor, this factor was used like a measurement of the improvement of the
liquid distribution. Finally the catalytic bed simulation shows that there is an
inefficient use of the catalyst bed and therefore a lower performance of the
reactor when a non-uniform liquid profile is used.

Volume liquid fraction profiles, velocity
profiles at different location and kinetic performance of the TBR were analyzed
on each of the simulations to enhance the liquid distribution over the TBR.