Date of Award
Spring 2019
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Mechanical Engineering
First Advisor
Singer, Simcha
Second Advisor
Roy, Somesh
Third Advisor
Allen, Casey
Abstract
Char particle combustion typically occurs under internal diffusion control, which results in inter-particle reactant gradients. Reactant concentrations throughout the char’s carbon structure must be known in order to predict overall particle reaction rates. These concentrations can be predicted by analytical models; however, effects of char morphology are typically ignored within these simplified models. In order to incorporate these effects, the morphology of Illinois coal #6 was studied by visualizing their structure in three-dimensions through the use of micro-computed tomography. Morphological characteristics of macro-porosity, macro-porosity location, and wall thickness were then measured for the sampled char particles. The sampled char particles morphology was cenospheric with a wall thickness that could be reasonably predicted using the particle’s macro-porosity and size. A theoretical concentration model, termed hollow sphere model, was developed based on this cenosphere morphology. The effects morphology has on char combustion were then shown by comparing the oxygen concentration and temperature profiles obtained from three dimensional CFD simulations, where three distinct particles were considered. CFD results were compared with two theoretical concentration models for the three particles to determine their accuracy. The hollow sphere model more accurately predicted reactant concentration within the char particles due to its incorporation of morphological effect.