(382f) Characterizing Flow and Solid Suspension in Optimax Crystallization Workstation

Characterizing Flow and Solid
Suspension in OPTIMAX Crystallization Workstation

 

M. Sardeshpande¹,
A. Pandit¹, S. Vedantam² and V.V. Ranade^1*
1Industrial Flow modeling Group

Chemical
Engineering and Process Development Division

National
Chemical Laboratory, Pune 411008, INDIA

²Chemical
Engineering Division,

Indian Institute
of Chemical Technology, Hyderabad – 500007, INDIA

*Email:
vv.ranade@ncl.res.in

 

OPTIMAX® (of Mettler-Toledo Ltd.) is one of the widely used
crystallization workstations. OPTIMAX® is an automated reactor, offering
heating and cooling electrically on the basis of Peltier technology. It is
usually equipped with Focused Beam Reflectance Measurement (FBRM) probe for
measuring on-line Chord Length Distributions (CLD). A schematic of the
workstation is shown in Figure 1. In order to appropriately interpret the data
obtained from OPTIMAX® workstation, it is essential to quantitatively
understand flow, heat transfer and solid suspension in it. In this work we have
developed a CFD model to characterize flow and solid suspension in OPTIMAX® workstation.

Figure 1: Schematic of OPTIMAX® crystallization workstation

In order to characterize solid suspension in OPTIMAX® workstation,
we have used the approach proposed by Sardeshpande et al. (2010). Sardeshpande
et al. (2010) reported hysteresis in cloud height observed experimentally in a
stirred tank reactor while increasing and then decreasing the impeller speed. The
hysteresis was then captured using a CFD model which served as a rigorous
validation for the model. In the present work we wish to capture the hysteresis
on increasing and then decreasing the impeller using the FBRM measured particle
counts. A sample of the particle counts measured by the FBRM for increasing
impeller speeds is shown in Figure 2. This relies on measurement of hysteresis
in particle volume fraction (or number of particle counts) with respect to
rotational speed of impeller.  Experiments were carried out with baffled, hemi-spherical
bottom stirred tank reactor. 1000ml of this OPTIMAX reactor contents Focused
Beam Reflectance Measurement (FBRM) probe (used for estimating the Particle Size
Distributions (PSD)). Hysteresis measurements were carried out for three
different particle volume fractions using glass beads.

Figure 2: Particle Counts measured by FBRM as a function of
impeller speed while increasing impeller speed

CFD model of the considered configuration was developed. Multiple
reference frame approach was used to model the rotating impeller and multiple
phases have been simulated using the Eulerian - Eulerian approach. Appropriate
care was taken to ensure that simulated results are independent of numerical
parameters (grid size, discritization scheme, time step and so on). The
simulated results of hysteresis in particle counts are compared with the
experimental data. Critical analysis of obtained results was carried out.

The
presented approach, model and results will be useful to characterize flow and
solid suspension in the OPTIMAX® workstation. The developed CFD model will be useful
for eventual simulations of crystallization process occurring in OPTIMAX® workstation
as also in crystallizer scale up studies.

References

 

Sardeshpande M. V., Juvekar V. A.  and Ranade V.V., 2010 Hysteresis in Cloud Heights During Solid Suspension in
Stirred Tank Reactor: Experiments and CFD Simulations, AIChE Journal, 56(11),
2795-2804