144
Tecnología y Ciencias del Agua
, vol. VIII, núm. 3, mayo-junio de 2017, pp. 143-150
Campos-Díaz & Alvarez-Cruz,
A proposal of a hydrodynamic model to low Reynolds numbers in a liquid-solid inverse fluidized bed reactor
•
ISSN 2007-2422
Introduction
Fluidization is an operation in which solid
particles enters in contact with a fluid acquir-
ing fluid characteristics (Mukherjee, Mishra, &
Ran, 2009) and is known for its wide use since
the early 50’s. In conventional fluidization,
the solid particles have a higher density than
the fluid therefore the bed solids can be fluid-
ized by an upwards flow, in the case of a bed
of particles having a density smaller than the
fluid (usually liquid), the bed is fluidized by a
downwards flow of the liquid and it is usually
called inverse fluidized bed (Bimal, Uma, & Su-
dip, 2010). Among the advantages presented by
the latest are high mass transfer rates, minimum
carry over of coated microorganisms due to less
solid attrition, efficient control of biofilm thick-
ness and ease of refluIdization in case of power
failure (Garcia, Buffière, & Elmaleh, & Moletta,
1998; Bimal
et al
., 2010). These significant ad-
vantages found many applications of inverse
fluidized beds in biochemical processes like fer-
rous iron oxidation and aerobic and anaerobic
biological wastewater treatment like treatment
of wine distillery wastewater. Previous studies
on liquid-solid inverse fluidized bed reactor
(IFBR) dealt with different hydrodynamic
characteristics such as pressure drop, minimum
fluidization velocity and bed void fraction
e.g
.
(Fan, Muroyama, & Chern, 1982; Karamanev
& Nivkolov, 1992; Renganathan & Krishnaiah,
2007).
The bed void fraction is one of the important
design parameters that determine the height of
fluidized bed during steady state operation. Un-
der normal operating conditions, fluidized bed
reactors operate under steady state. However,
unsteady state operation is encountered during
start-up and shut-down of the reactor and due to
fluctuations in liquid flow rates. Such conditions
may prevail in a wastewater effluent treatment
plant where an IFBR is mostly used. Therefore,
information on the unsteady state bed expan-
sion is required for better understanding of
the fluid dynamics under transient conditions,
which will lead to better control of the reactor
and for the design of IFBR an industrial scale
(Renganathan & Krishnaiah, 2007).
In many processes there are particles with
diameter different in the particles of the bed
greatly modifies its porosity due to the particle’s
size and density variation. This modification in
the bed porosity affects the proper operation
and control of the fluid bed reactor. Therefore,
it is important to have a reliable model in order
to estimate bed porosity for design and scale-up
of fluid bed reactors.
Numerous models have been proposed to
predict the bed porosity in fluidized beds with
spherical and non-spherical particles, but only it
includes a range of Reynolds number from 200
to 6,000. The major and most used until today
by several authors (Yang & Renken, 2003; Akgi-
ray & Soyer, 2006; Renganathan & Krishnaiah,
2007; Fuentes, Scena, Aguirre, & Mussati, 2008;
Soyer & Akgiray, 2009) are: Richardson and
Zaki (1954), Wen and Yu (1966), Ramamurthy
and Subbaraju (1973), Riba and Couderc (1977),
Fan
et al
. (1982), and Setiadi (1995) models.
Mathematical models for prediction of tra-
ditional fluidized bed porosity can be used in
inverse fluidization, nevertheless, some authors
disagrees with this practice (Wen & Yu, 1966;
Ramamurthy & Subbaraju, 1973; Hyun, 2001).
Therefore the general aim of this work is
to study the hydrodynamic of a liquid-solid
inverse fluidized bed reactor with different
polypropylene spherical particles diameters
and different densities to propose a mathematic
model to estimate bed porosity in a range of
Reynolds number from 5.5 to 200, which has
not been studied in this reactor and this hydro-
dynamic characteristics are very important to
low fluidization rates in biotechnology process.
Materials and methods
Liquid and solid phase
Water at 20
o
C was used as fluid work in an
inverse fluidization reactor and polypropylene
spherical particles of average diameter 4.00, 4.16
and 4.18 mm and density of 808, 825 and 867
