Numerical and experimental optimization analysis of a jaw crusher and a bubble column reactor

G5 Doctoral dissertation (article)


Internal Authors/Editors


Publication Details

List of Authors: Daniel Legendre
Publisher: Åbo Akademi
Publication year: 2019
ISBN: 978-952-12-3822-2
eISBN: 978-952-12-3823-9


Abstract

More and more awareness is now raising in terms of sustainability of
industrial processes. Thus the necessity to improve energy efficiency of
diverse devices or simplify process schemes arises. Therefore, the
importance of increasing the efficiency of these processes energy and
material usage as means to reduce harmful emissions has increased. The
present research involves the numerical modelling and further
experimental analysis of two different process equipment: crushing and
grinding (comminution) of ore materials and bubble swarm dissolution in a
reactor. Numerical methods are expanded as means to obtain a physical
description relevant for engineering purposes. Moreover, experimental
methods are developed to sustain validity of the simplifications imposed
on the numerical analysis. Concisely in the comminution case, a primary
crusher machinery widely employed in industry known as a jaw crusher is
used as center for optimization and modelling efforts. This is
performed with the goal to explain and describe how energy is used
during the crushing and grinding process and how it can be improved. It
is widely acknowledged that crushing and grinding machinery are highly
inefficient if the study is based only on energy requirements.
Typically, estimated values <10%, with most energy dissipated as
heat, deformation, noise and internal crack propagation in the ore.
First, an energy efficiency is defined in terms of machinery energy use
and after-crushed particle size; with the idea to link new surface area
created by material breakage to the amount of energy required to produce
an effective particle segmentation. Second, a study on design methods
for jaw crusher design through empirical methods, allows to estimate
rough machinery dimensions and operating conditions for different
selection criteria. However, these methods do not provide an insight
into the actual particle breakage phenomena. Further on, the development
of a Discrete Element Method (DEM) model, widely used for the
description of granular materials, allows to generate a dynamic model
capable to mimic jaw crusher operating conditions. Despite of high
computational requirements this gives results comparable to industrial
applications in the field of crushers. The current research is based on
the fundamentals that allow to reproduce breakage patterns on simulated
particle agglomerates. To complement DEM models, an experimental
strategy was designed and tested allowing to compare energy usage of a
laboratory scale jaw crusher with new area created of crushed ~600 gr
pieces of limestone rock. This method in principle can be applied to any
type of comminution machinery regardless its size and could be linked
to simulations efforts.

As a second case, the importance of bubble swarm dissolution arises
with the intention of simplify downstream flow conditions of the
socalled Slag2PCC process for mineral carbonation. This is one example
of many carbon capture and utilization (CCU) processes being developed
worldwide. As a carbonation reactor without any exhaust gasses, i.e.
100% CO2 dissolution would imply simplifications on extra equipment for
gases re-circulation in the reactor. In the first place, the study is
focused on the smallest yet relevant phenomena of the reactor; a single
dissolving bubble on water to further expand the analysis towards
reactor operating conditions. As part of this research a hybrid CFD –
Lagrangian bubble tracking method was developed to obtain preliminary
results on bubble dissolution orders of magnitude and reactor design
dimensions. Consequently, an experimental facility was built. With the
use of a high-speed camera, free rising CO2 bubbles were tracked in a 2 m
height bubble tower. Not only the diameter reduction of the bubbles is
evidenced but also their continuous shape transition from wobbly bubbles
towards a more spherical bubble flow as the initially 5 mm bubbles
dissolve. Results proved to be comparable to previous estimations on
very disperse bubbly flows. Subsequently, a modification to the
experimental facility with the inclusion of pitched blade impellers was
made to measure CO2 bubble flow on actual operating conditions of a
reactor. The evolution of CO2 bubble size distributions in terms of
vertical displacement was measured and a positive influence of the
mixing intensity on the bubbly flow dissolution was shown. Results
presented could aid the development of multiphase flow models at higher
gas volume fractions.


Last updated on 2019-09-12 at 03:05