Representative mathematical modeling is essential for
understanding
the batch cooling crystallization processes. Efficient process design
and operation are relevant to achieving high-quality criteria and
minimizing variation between batches. This work first presents the
modeling of batch cooling crystallization based on online dynamic
image analysis. A flow-through microscope was used to track the temporal
evolution of the crystal population. A population balance modeling
(PBM) approach, parameter estimation, and validation were obtained
for the batch cooling crystallization of potassium sulfate in water.
The performed experiments provided new experimental data, giving dynamic
information about the crystal size throughout each run. The kinetic
model parameters for crystal nucleation and growth were estimated
using a hybrid optimization algorithm, followed by the confidence
region construction using a more exploratory particle swarm algorithm.
In the parameter estimation framework, in addition to solute concentration,
the first fourth-order moments computed throughout all experiments
were included in the objective function. A linear size-dependent growth
rate was found to capture well the dynamics of the potassium sulfate
crystal size distribution. The experimental results evidenced that
the crystal shape of potassium sulfate is predominantly constant,
allowing the adequacy of the developed model. The validated PBM was
also employed as a digital twin of the crystallization process to
develop a machine-learning-based control for the process. Then, a
surrogate model based on a recurrent neural network, called an echo
state network (ESN), was applied in a nonlinear model predictive controller
approach (ESN-NMPC). The ESN model could predict the moments of the
population balance model up to five steps (5 min) forward. The ESN-NMPC
achieved the desired control scenarios for the crystal size and its
coefficient of variation. Its performance was comparable to the controller
that uses the PBM as the internal model (PB-NMPC).