Doctor of Philosophy

dissertationConcern about global warming has called for new combustion systems to be used in order to reduce CO2 emissions from coal-fired power generation. Pressurized oxy-coal combustion coupled with carbon capture and storage as well as cofiring biomass with coal are gaining more interest in building new power plants and retrofitting existing plants. The combustion conditions of these systems could be significantly changed and thus affect the ash formation and deposition. This work aims to reveal the relevant mechanisms under different combustion conditions. Experimental work consists of combustion tests at various scales and conditions, namely, on a 100 kWth rated oxy-fuel combustor (OFC), a 300 kWth rated pressurized reactor (EFPR), a 1.5 MWth rated horizontal multifuel combustor (L1500), and a 500 MWe full-size utility boiler (Hunter). The fuels involved include pulverized coal, torrefied wood, blend fuels of the coal and wood, and coal with K/Cl/S additives. The results of this work provide understanding of how various fundamental variables inherent in solid fuel combustion affect ash formation and fouling deposition in both typical and novel combustion systems. The first topics addressed are the mineral transformation and submicron ash formation during pressurized oxy-combustion. Higher pressure is found to decrease the vaporization of refractory minerals and reduce the PM1 formation, provided that temperature profiles are controlled to be similar. The second topic addressed concerns woody biomass deposition mechanisms, which are shown to be very different from those during coal combustion. However, for both the pilot furnace and full- iv scale boiler, cofiring at a moderate biomass mixing ratio does not cause significant changes in size and composition of the ash aerosols or in the deposits from coal combustion. Lastly, through systematically controlled tests on the OFC, a comprehensive study of the ash aerosols, deposits and gaseous species is presented in order to gain insights into the partitioning of K, Na, Cl and S, a process that particularly affects deposition and corrosion behavior in biomass combustion. Taken as a whole, therefore, this dissertation addresses ash aerosol formation and deposition mechanisms for a range of fossil and biomass solid fuels burned under a wide range of combustion conditions