This report is a study on the smoldering combustion of natural sawdust from untreated woods. The objective was to develop and test an experimental technique to study the fundamental behavior of sawdust smolder. The experimental setup was an annulus cookstove packed with sawdust between the inner and outer radii creating a central hollow core. The sawdust was ignited by a heating coil wrapped around the inner radius. Thermocouples were embedded in the sawdust bed fanning out in the radial direction, and temperature was recorded throughout the smolder process. Consistent with the literature, the experimental results indicate that wood smolder consists of three pathways, 1) sawdust to char, 2) sawdust to volatiles, and 3) char to ash. Pathways 1 and 3 can be clearly characterized by the temperature profile of the smolder; however, pathway 2 often involves flaming of the sawdust and is beyond the scope of this study. Pathway 1, sawdust to char, is an endothermic reaction that results in a clearly defined char front that propagates across the sawdust bed in the radial direction. As smolder proceeds, the char continues to oxidize and breaks down into non-volatile products such as water vapor and carbon dioxide (CO₂) in further exothermic reactions. Pathway 2, char to ash, is an exothermic reaction that can lead to glowing combustion when exposed to sufficient amounts of oxygen and results in spikes in temperature. In contrast to the clearly defined char front, the ashing zone traces cracks in the sawdust where air can penetrate through, and has no discernible front. Section 1 discusses the motivation behind the study of sawdust cookstoves in third world countries, in particular Ghana, to replace wood with sawdust as a cheap alternative for household fuel. Section 2 details the experimental setup of the cookstove rig and the methodology of the experiments conducted. Section 3 reports the results of the experiments and analyzes the temperature profiles in relation to the three types of chemical reactions as noted above. Section 4 concludes with a summary of the results and discusses efforts in measuring emissions from the smolder and future work to be done. / text

Coal plays a significant role in electricity production worldwide and will into the foreseeable future. Technologies that improve efficiency and lower emissions are becoming more popular. High pressure reactors and oxyfuel combustion can offer these benefits. Designing new reactors effectively requires accurate single particle modeling. This work models a high-pressure, high-temperature, high-heating rate, entrained-flow, char oxidation data set to generate kinetic parameters. Different modeling methods were explored and a sensitivity analysis on char burnout was performed by varying parameters such as total pressure, O2 partial pressure, O2 and CO2 mole fractions, gas temperature, diameter, and pre-exponential factor. Pressure effects on char burnout modeling were found to be dependent on the set of kinetic parameters chosen. Using kinetic parameters from Hurt-Calo (2001) as opposed to values obtained from Niksa-Hurt (2003) yielded a trend seen in real data sets, that reaction order changes with temperature. Varying O2 mole fraction and partial pressure showed the most significant changes in char burnout. Varying diameter, total pressure, the pre-exponential factor, CO2 environment, and gas temperature all changed the char burnout extent as well. The effect of changing those parameters decreases in the order they are listed. Increasing any of these parameters resulted in an increase in char burnout except for particle diameter and CO2 mole fraction which led to a decrease. Char formation pressure affects reactivity, and a peak in reactivity is shown in this work at the 6 atm condition.