M.S. Thesis: Technical and Economic Analysis of Plasma-Assisted Waste-to-Energy Processes
By Caroline Ducharme
Advisor: Prof. Nickolas J. Themelis, Columbia University
Co-advisor: Prof. Marco J. Castaldi, Columbia University
Department of Earth and Environmental Engineering
Fu Foundation School of Engineering & Applied Science
Increasing interest is focusing on plasma-assisted gasification applied to the treatment of municipal solid waste (MSW), especially as it may be a new way to increase Waste-to-Energy (WTE) worldwide. The aim of this thesis was to investigate different such processes under development and their technical and economic viability.
In a simplistic view, a plasma torch is a way to generate heat, via the passage of an electric current through a gas flow. Plasma technology has been used for a long time for surface coating and for destruction of hazardous wastes but its application to MSW has not been explored fully because of the high cost of using electricity as a source of energy. Plasma used entirely for the processing of MSW, i.e. in the absence of partial combustion, was not considered in this study, as it will not be economically feasible for MSW. Hence, we examined what may be called “plasma-assisted gasification” in a WTE process that combines the use of plasma with partial oxidation of the hydrocarbons in MSW. The idea is to produce a syngas (synthetic gas) from the gasification of the waste. The plasma heat is used to either provide the heat for gasification, to “polish” the syngas, and/or to vitrify the ash product of the gasification process. The syngas product is combusted in a gas engine or turbine generator onsite to produce electricity. Although there are some alternatives uses of syngas, e.g. ethanol production, they were not considered in our study. Some of the thermal energy in the gas stream can be also recovered in a steam boiler and the steam used to produce additional electricity.
Air emissions are a main point of our study, as they are one of the reasons why there is opposition to the WTE. Opponents of WTE usually perceive gasification and assisted plasma gasification as only a variation from incineration (“disguised incineration”).