Understanding attrition of irregular particles using a novel DEM simulation approach

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Irregular particles are ubiquitous, ranging from mineral ores to coffee granules to crystalline active pharmaceutical ingredients. Particle shape has a huge effect on the behaviour of a bulk material. It affects the height and porosity of a static packing of particles, and variability in particle shape can induce segregation in dynamic systems. Particle shapes often change over time due to attrition, i.e., fragmentation or surface abrasion. This has important practical consequences. In the food and pharmaceutical sectors, fine particles generated by undesired attrition impair flow which creates problems during subsequent processing. The particulate catalysts used in oil refining for fluid catalytic cracking (FCC) are susceptible to mechanical degradation which has both environmental and cost implications.The discrete element method (DEM) is a widely used simulation tool used to model complex systems of particles. Currently, there is neither a viable method to simulate particle abrasion in DEM nor an open-source DEM code which can simulate irregular particles of any shape in an efficient manner. This severely limits our particle-scale simulation capabilities, preventing industry from fully understanding their particle processes by simulation.This Fellowship will create an openly-available, efficient and flexible method for simulating irregular, abradable particles. This will have a transformative effect by creating an entirely new field of particle simulations. These numerical advances will be implemented in an open-source code, LAMMPS, with the coding support of Edinburgh Parallel Computing Centre. The code will then be used to simulate two applications of significant economic importance. The first is the attrition of FCC catalyst particles. DEM simulations will be used to predict the catalyst replacement frequency in an industrial FCC unit. The mechanisms of catalyst degradation will be explored, including the effects of particle shape and micro-scale mechanical properties. Having a better scientific understanding of these mechanisms will facilitate more reliable predictions of attrition and hence permit catalysts to be designed with increased attrition resistance. The second application is the breakage of pharmaceutical crystals in agitated filter dryers or granulators. In the pharmaceutical industry, needle- and plate-type crystals are often produced which are highly susceptible to attrition. The modelling approach adopted in this work will enable quantitative prediction of crystal attrition during shear processes including agitated drying and mixing. The extent of this attrition will be linked to changes in bulk density, flowability and other key quality attributes. Better predictive capabilities will enable better control of particle size distributions in manufacturing processes, potentially leading to significant economic savings.This research will be undertaken within the Institute for Infrastructure and Environment, School of Engineering at the University of Edinburgh with the support of three project partners: Sandia National Laboratories, BASF (Refining Catalysts) and AstraZeneca. Sandia are the main developers of the LAMMPS code. They will assist with dissemination by including these code developments in the main, open-source LAMMPS distribution. BASF will provide physical test data on the properties and attrition behaviour of FCC catalysts, and host research visits for collaboration at their premises. Similarly, AstraZeneca will provide experimental data and host research visits, and will also make their laboratory facilities available for testing. The involvement of these partners ensures that the research will be informed by the needs of industry and will have a practical, tangible impact.