New pyrolysis mechanisms for polymers' dust explosion

Combustible polymer powders pose a significant safety risk because handling and processing operations can generate explosive dust clouds. During a dust explosion, particle heating is followed by pyrolysis and oxidation of the released gases, whose composition influences ignition, flame propagation and pressure development. This thesis investigates the pyrolysis of polyethylene (PE) and polymethyl methacrylate (PMMA) powders and develops simplified reaction mechanisms for future CFD simulations of polymer dust explosions. The study combines particle-size and morphological characterization, particle dispersion analysis, thermogravimetric analysis, minimum ignition temperature measurements, 20-L sphere explosion tests, flash-pyrolysis experiments and mathematical modelling. SEM analysis showed that PE particles were more irregular, whereas PMMA particles were predominantly spherical. TGA revealed mainly single-step decomposition for PE and multi-stage degradation for PMMA, with its principal mass loss associated with depolymerization and methyl methacrylate formation. Both powders were explosible in the 20-L sphere, although explosion severity depended on dust concentration, particle properties, dispersion and turbulence. Flash-pyrolysis experiments were conducted at 600–800 °C under nominal oxygen concentrations of 1%, 5% and 10%. The products were analysed by micro-gas chromatography, focusing on hydrogen, carbon oxides, methane and light hydrocarbons. Gas composition depended on polymer structure, temperature and oxygen availability. Two four-reaction lumped kinetic mechanisms were developed in MATLAB. The models reproduced the main trends and approximate magnitude of several measured gas ratios, while highlighting limitations related to simplified reaction pathways, surrogate species and incomplete gas calibration. The mechanisms provide a useful basis for future CFD simulations, although further validation is required.