3rd meeting of young researchers at UP 1 - IJUP - Universidade do ...

Study of a Gas/Liquid Reactor for the Vanillin production using CFD
tools
E.Costa 1 , J.Mendes 1 , J.Nogueira 1 and M.Pimenta 1
1 Department of Chemical Engineering, Faculty of Engineering, University of Porto, Portugal.
In the framework of “Product Engineering” discipline, whose purpose is to improve or create new
products, by identifying costumers needs, generate and select ideas and manufacturing the product [1],
it was our objective to use Computational Fluid Dynamics (CFD) in order to improve or to create a new
design for the reactor used to produce vanillin at the Laboratory of Separation and Reaction
Engineering. The reactor, an 8 litres bubble column, is constituted by several parts: the liquid
stabilization chamber, gas distributor, reaction body, and the separation head. The main cylindrical
body of the reactor includes a structured packing element, Mellapak 250.Y.[2]
Initially, experiences using CFD program, FLUENT, were conducted in order to identify the reactor
flow problems. For this, 3D and 2D models were created for the G/L reactor using the program
GAMBIT. Then, simulations were conducted for assessing the reactor hydrodynamics by analysing the
velocities profiles in steady state and the residence time distribution obtained in tracer experiments in
transient state.[3,4]
Fig.1. Velocity profiles for original (right) and proposed
(left) liquid stabilization chambers geometries.
The tracer experiments showed that in both geometries the
flow model was plug flow with axial dispersion [5]. The
curves E(t) and F(t) were also obtained and the mean
residence time was calculated for both geometries of the
reactor: 6,03x10 5 and 5,73x10 5 seconds. For the
visualization of the evolution of the tracer molecules
inside the reactor, some pictures were obtained in transient
state, and used to create a video for visualization of the
time evolution of the tracer mass fraction along the
reactor. A 2D model of the packing structure was created
in order to study and to visualize the gas flow in the
The simulations results (see Fig. 1) reveal
flow problems due to the original geometry
of the liquid stabilization chamber,
particularly some recirculation areas and
preferential flow paths, with an estimated
dead volume of 13%. An alternative
geometry was created leading to a 0.1% of
dead volume.
Fig.2. Transient state trace mass fraction
for experiments with (left) and without
(right) structured packing,
packing elements (see Fig. 2). The images obtained in the simulations showed that only a portion of the
packing was used by the gas.
[1] Cussler EL, Moggridge GD, Chemical product design, Cambridge University Press, Cambridge, 2001.
[2] Araújo DPJ, Production of vanillin from lignin present in the Kraft black liquor of the pulp and paper industry, FEUP
edições, 2008.
[3] Madeira MM, Mendes A, Magalhães FD, Teaching Laminar-Flow Reactors: From Experimentation to CFD Simulation.
Int. J. Engng Ed., 2006, 22, 188-196.
[4] Madeira MM, Alves MA, Rodrigues AE, Teaching Nonideal Reactors with CFD Tools. Che Classroom, 2006, 22, 188-
196.
[5] Levenspiel O, Chemical Reaction Engineering, 3rd ed., John Wiley & Sons, New York, 1999.
138 3 rd meeting of young researchers at UP