Thermal and catalytic processing of solid fuels to minimise carbon monoxide emissions

This research was conducted to evaluate the amount of carbon monoxide (CO) emissions from the incomplete combustion of solid fuels, the factors responsible for its release and methods to minimize its release and thus the human exposure to CO in different environments. Unintentional CO poisoning has resulted in many deaths, injuries and chronic ailments. Previous efforts to minimise exposure to CO include awareness campaigns, domestic CO alarms, improved designs for cooking stoves, space heating appliances, and postcombustion CO oxidation using catalysts. However, these methods have not fully solved the challenge of CO exposure. In this study, different sold fuels were processed and analysed to investigate their behaviour under different oxidative environments and to establish ways to reduce the amount of CO released during combustion. Areas of solid fuel research of particular interest include physicochemical properties, reactivity and surface chemistry, CO emission properties, and catalyst impregnation on solid fuels to minimise CO emissions. This was achieved by using raw and pyrolysed wood biomass and coal. The results reported in this thesis show that the degradation profile of wood sawdust involved a combination of mechanisms, including diffusion, geometrical contraction, nucleation, and reaction-order models. Pyrolysed charcoal was found be microporous with a low specific surface area. The charcoal contained high quantities of • C-C and • C-O free radicals, and low-temperature oxidation (< 200 °C) produced persistent peroxyl radicals. Mild-temperature (300 – 650 °C) oxidation showed that the charcoal was highly reactive, with low pre-exponential factors and activation energies. At temperatures < 550 °C, charcoal did not appear to glow to the naked eye. However, this temperature range was shown to correspond to the emission of large amounts of CO. In confined environments, the measured CO emissions increased with decrease in ventilation and increase in height above the floor. ii Catalyst impregnation on charcoal reduced CO emissions by up to 97 % and increased the free active sites on the solid fuel surfaces, which decreased at temperatures > 500 oC possibly due to thermal deactivation of the catalyst.