Multiscale mathematical models for simulation and scale-up of green processes in the perspective of industrial sustainability
Creators: name: NEVIANI, MATTEO
Publisher: name: Universit� degli studi di Genova
Year: 2019

description: The present work presents research studies aimed at developing tools useful to design
engineering solutions moving in the direction of industrial sustainability. The investigations
hereinafter discussed regard an extraction process of active compounds ? polyphenols ? from
agro-food industry wastes (olive and grape pomaces) and a biorefinery exploiting waste
frying oil, solid organic wastes and algal biomass to produce biofuels. In particular, for the
former topic, a procedure aimed at the evaluation of the technological feasibility at pilot scale
of said process is discussed. The proposed approach takes into consideration the extended
kinetic route coupled with mathematical simulation. Detailed physically-based dynamic
mathematical models, taking into account mass and energy balance equations, are adopted
to describe both the lab-scale and the pilot-scale reactors. Chemical physical parameters
appearing in the models are estimated from the experimental data at lab-scale or are partially
taken from literature. Different heating systems are designed for the pilot scale reactor and
their performance is tested by simulation. Characteristic times are evaluated also during
start-ups and different control loops are analyzed in order to set-up the best process and
operating variables. Average yields in polyphenols are finally evaluated for both the batch
and the continuous operated pilot reactor, by considering feed variability and fluctuations of
process parameters.
For what concerns the biorefinery, special attention was devoted to the modeling of the
airlift reactor, its most delicate and complex component. In fact, to optimize this interesting
microalgae cultivation system, a precise description of the moving interfaces formed by the
liquid and gas phase is critical. In this study, coupled front capturing methods (standard and
conservative level set methods) and finite difference method are used to simulate gas bubbles
dynamics in a pilot-scale external loop air-lift photobioreactor in which microalgae are used
to capture CO2 from flue gas and to treat wastewater. Numerical simulations are carried out
on rectangular domains representing different sections of the vertical axis of the riser. The
data employed was either acquired from previous experimental campaigns carried out in the
airlift reactor or found in the literature. The rise, shape dynamics and coalescence process of
the bubbles of flue gas are studied.
Moreover, for each analyzed applications, a procedure based on Buckingham ?-theorem
to perform a rigorous scale-up is proposed. In this way, scale-invariant dimensionless
groups describing and summarizing the considered processes could be identified. For the
research focused on the scale-up of photobioreactors used to cultivate Chlorella Vulgaris,
an experimental campaign at three levels was designed and carried out to evaluate the
characteristic dimensionless numbers individuated by the theoretical formulation. Since
scale-up regards both geometrical dimensions and type of reactor, passing from lab-scale
stirred tanks to pilot scale tubular and airlift, particular attention was devoted to define
characteristic lengths inside the dimensionless numbers.