Modeling municipal solid waste gasification: Molecular-level kinetics and software tools

Municipal Solid Waste (MSW) is a valuable energy resource that is underutilized by today's society. Waste-to-Energy (WTE) is a low-hanging fruit in a multifaceted energy landscape that incorporates conventional fuels and a plethora of renewable alternatives. From an environmental standpoint, WTE reduces the storage of MSW in landfills which can contaminate groundwater and release methane, a potent greenhouse gas. The most attractive WTE technology is gasification, a process where nonstoichiometric amounts of oxygen or air are fed to a high temperature reactor. The output from gasification is syngas, a ubiquitous product that can be used for a range of purposes, including liquid fuel synthesis and conversion to electricity via combustion. Plasma-arc gasification is an extension of conventional gasification that utilizes a plasma torch to obtain extreme reactor temperatures. The solid by-product from plasma gasification is an inert vitrified slag, which is usable as a construction material. However plasma-arc gasification is a relatively new WTE technology, and there is a need to better understand the underlying chemistry in order to optimize process parameters.;Molecular-level kinetic modeling has proven valuable in gaining insight on complex process chemistries. To this end, this dissertation focuses on the development and application of a molecular-level kinetic model for MSW gasification. For model development, the MSW stream was divided into plastics and biomass. Kinetic models were constructed separately for the gasification of each of these streams, using literature data. These models were then combined to construct the MSW gasification model.;This model was used to simulate a 1000 metric ton per day plasma-arc gasifier that was divided into three zones for MSW: combustion, gasification, and freeboard. The reactor model was utilized to study the effects of process parameters on syngas quality and tar formation. Increasing the relative oxygen flow to the bed was found to reduce tar formation at the cost of syngas quality. Variations in MSW composition affected the oxygen content in tar molecules but had little impact on syngas quality. Lastly, extreme temperatures in the combustion zone had a potentially negative impact on both syngas quality and tar production due to the oxidation of CO.