Date of Award
Summer 2017
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Mechanical Engineering
First Advisor
Singer, Simcha L.
Second Advisor
Bowman, Anthony J.
Third Advisor
Somesh, Roy
Abstract
Coal is a significant source of energy in today’s world and many studies have been conducted in order to better understand and optimize its use. To address greenhouse effects associated with coal combustion, cleaner methods for harnessing its energy are being explored. One such method is gasification, a process which converts coal into syngas, a mixture consisting primarily of H2 and CO. Syngas can be used to generate electricity or to produce hydrocarbons that can be used as fuels. To better understand and optimize the process, simulations can be used to study the gasification of individual porous char particles that form within the gasifier. Available models range in complexity from zero-dimensional models to CFD simulations. However, most studies simplistically treat the char particle as an effective porous continuum, despite the fact that the presence of large, irregular voids and fractures renders such treatments invalid. This work presents a three-dimensional simulation of a reacting porous char particle that resolves these large voids using micro-CT imaging in order to better understand the interaction between reaction and transport during gasification. In order to correctly gauge the impacts of the resolved structure, a second model was developed which employs the simplistic assumptions in question: a perfectly spherical particle and an effective continuum treatment of the porous structure. To faithfully compare the models, both particles have identical mass, volume, porosity and equivalent diameter. The results of the simulations indicate the necessity of accounting for the presence of large voids in any char consumption model, as they enhance reactant transport into the particle. By introducing additional avenues for transport, the species and temperature profiles within the particle are significantly different in the two models. Furthermore, with enhanced transport, the amount of accessible surface area increases, resulting in faster reaction rates and a reduction in char consumption time.