Study of size-fractionated coal-combustion aerosols using instrumental neutron activation analysis

The chemical composition of aerosols emitted during coal combustion was studied as a function of particle size down to 0.01 μm. The aerosol collections were carried out in a 81 MW capacity boiler that burned Venezuelan coal in a circulating fluidized bed combustion chamber. The samples were collected upstream of the electrostatic precipitator using a Berner low-pressure impactor, which was equipped with a cyclone pre-cutter to avoid overloading of the first impaction stages. The samples were analyzed by INAA for up to 40 elements. The elemental concentrations in the particulate matter for each impaction stage were plotted as a function of stage number (particle size). For the elements Na, Al, K, Ca, Sc, Ti, V, Ga, La and Sm, the concentration variation was limited to a factor of 2 to 4, and the concentrations of these elements were lower for the initial and final impactor stages than for the intermediate particle sizes. The variations were also limited to a factor of 2-4 for Mn, Fe, As, Sb and Th, but all these elements showed increasing concentrations with decreasing particle size. Still other elements, such as Ni, Cr, Co, Zn, W, Mo and the halogens, were highly enriched (up to 20-100 fold) in the fine particles when compared with the coarse particles. (author) 21 refs.; 7 figs.; 2 tabs