Sources of unburned carbon in the fly ash produced from low-NO_x pulverized coal combustion

摘要

THe unburned carbon in the fly ash produced from low-NO_x pulverized coal combusiton is shown to consist of a mixture of soot and coal char.The soot was identiifed by the presence of chains or aggregates of 10-50-nm-diameter rimary paticles in electron microscope images of both laboratory smaples and a smaple of fly ash from a power plant oerating low-NO _x burners.Laboratory samples showed increasing earbon content wikth ecreasing nitrogen oxide (NO_x)_ concentration.the expeiments included a high-No_x base case and four low-NO_x cases consisting of (1) staged combustion with short (0.5 s)re sidence time,(2) staged combusiton with long (1.5 s) residence time,(3) a low-No_x burner with lslow mixing and (4) reburning using coal as the reburnig fuel.