Wet milling is a key production operation used to control particle size distribution (PSD) in high solids content solid/liquid suspensions, or slurries. The optimisation and control of milling is essential as the PSD ultimately impacts the slurry’s rheological properties as well as the performance and the chemical and thermal stability of the final formulated product. A better fundamental understanding of the mills and the milling process is a key step towards more efficient scale up, transfer and plant efficiency. A well-known type of mill design is the so-called “bead mill”, where the beads, or grinding media, are agitated in the slurry to produce shear, thus promoting particle breakage. There are several common configurations including horizontal (rotating) and vertical (stirred) arrangements. These are typically operated in once through (continuous) or on a recirculation loop from a holding stirred tank. These types are relatively well documented in the literature. A further class is the submersible mill, where the media are incorporated in rotor-stator type arrangement that serves not only to mill the process material but also as an impeller for the process vessel. This class of mill is much less well understood, with relatively little scientific literature. Specifically, there are very few reports describing the fundamentals of collisions and the interplay of the different phases of the system. The objective of the EngD is to develop a more fundamental understanding of submersible mills. A dual, synergetic, numerical modelling approach is proposed to extract information on the flow velocity and recirculation, power draw and impact energy. Discrete Element Method (DEM) modelling will be used to simulate the grinding media, flow kinematics and energetics within the mill while Computational Fluid Dynamics (CFD) will be used to investigate fluid flow within vessel. The numerical results will be validated using experimental data obtained with several techniques such as PEPT (Positron Emission Particle Tracking), a method developed at the University of Birmingham for tracking granular flow, will be used to validate the DEM model while flow visualisation techniques will be use likewise for the CFD. The outputs from the above will be used in tandem to enable a reduced model incorporating population balance modelling (PBM) to describe the whole system that will ultimately result in better design, process control and efficiency as well as simplifying development. These methods will be applied to the modelling and improvement of Johnson Matthey’s milling operations.
Funding: £20,609 Tax free bursary, p.a. plus fees paid