Polycyclic aromatic hydrocarbon (PAH) emissions from a coal-fired pilot FBC system

Due to the extensive amount of data suggesting the hazards of these compoun ds, 16 polycyclic aromatic hydrocarbons (PAHs) are on the Environmental Pro tection Agency (EPA) Priority Pollutant List. Emissions of these PAHs in th e flue gas from the combustion of four coals were measured during four 1000 h combustion runs using the 0.1 MW heat-input (MWth) bench-scale fluidized bed combustor (FBC). An on-line sampling system was designed for the 16 PA Hs, which consisted of a glass wool filter, condenser, glass fiber filter, Teflon filter, and a Tenax trap. The filters and Tenax were extracted by me thylene chloride and hexane, respectively, followed by GC/MS analysis using the selective ion monitoring (SIM) mode. In this project, the effects of o perating parameters, limestone addition, chlorine content in the coal, and Ca/S molar ratio on the emissions of PAHs were studied. The results indicat ed that the emissions of PAHs in an FBC system are primarily dependent on t he combustion temperature and excess air ratio. The injection of secondary air with high velocity in the freeboard effectively reduces PAH emissions. The addition of extra limestone can promote the formation of PAHs in the FB C system. Chlorine in the coal can possibly lead to large benzene ring PAH formation during combustion. The total PAH emission increases with an incre ase in the sulfur content of coal. Incomplete combustion results in PAHs wi th four or more benzene rings. High efficiency combustion results in PAHs w ith two or three benzene rings. (C) 2001 Elsevier Science B.V. All rights r eserved.