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 University
Place: Turku/Åbo
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 2020-26-09 at 03:22