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Mitigation of NOx with Pyrolysate fragments of solid fuels and their surrogates

Oluwoye, Ibukun (2017) Mitigation of NOx with Pyrolysate fragments of solid fuels and their surrogates. PhD thesis, Murdoch University.

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This thesis presents a series of scientific studies exploring the thermal mitigation of nitrogen oxides (NOx) with solid fuel (waste polyethylene) and biomass surrogate (morpholine). These studies have revealed new mechanistic insights, have described the associated set of reactions, and have developed a sustainable means of reducing industrially formed NOx, for example, in combustion processes and during blasting of ammonium nitrate explosive.

Comprehensive quantum-mechanical calculations afforded the investigation of low-temperature oxidation of polyethylene (PE) film under representative NOx environments. Investigations of thermal reduction of NOx with recycled PE involved sample characterisation techniques, such as, carbon-hydrogen-nitrogen-sulfur (CHNS) elemental analyses, ion chromatography (IC) and inductively coupled plasma optical emission spectroscopy (ICP-OES), as well as thermogravimetric experiments under practical NOx atmospheres. Innovative application of the on-line Fourier transform infrared (FTIR) spectroscopy and NOx chemiluminescence quantitated the reaction product species and established the removal efficiency of NOx by fragments of pyrolysing PE.

Studies on modelled surrogates, i.e., morpholine, resolved the fundamentals of thermal interaction of biomass with NOx. The experiment applied a flow-through tubular reactor coupled with FTIR spectroscopy and chemiluminescence NOx analysis, at constant pressure, reaction time, and representative fuel-rich condition. Furthermore, density-functional-theory (DFT) calculations uncovered new mechanistic insights into initial nitration reactions, and yielded their energetic characteristics, such as exothermic formation of nitro- and nitroso-adducts.

Results obtained in this study elucidated, for the very first time, initial products of low-temperature reaction of NOx with polymers and biomass, and determined the rate parameters, from the isoconversional degradation analysis, that are of great practical importance. A typical NOx removal efficiency (by fragments of pyrolysing PE) amounts to 80 % at moderate temperatures. Investigations employing a biomass surrogate revealed the sensitising role of NOx in combustion of biomass fuels. NOx reduction by biomass occurs only at temperatures in excess of 800 °C. The thesis also provides kinetic expression for process modelling. The results of the present work prove that, carbon-hydrogen-type waste polymers and biomass provide an effective means of mitigation of NOx emission in combustion processes. Furthermore, the scientific approach can be optimised to deploy solid fuels in bulk ammonium nitrate/fuel oil (ANFO)/emulsions explosive mixtures, so as to reduce the NOx formation during detonation of nitrate-based explosives in mining operations.

Publication Type: Thesis (PhD)
Murdoch Affiliation: School of Engineering and Information Technology
Supervisor: Dlugogorski, Bogdan and Altarawneh, Mohammednoor
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