Characterization of Solid Emissions from Atmospheric Fluidized-Bed Combustion of Two Czech Lignites

We investigated composition and morphology of solid residues (fine and coarse fly ashes and bottom ash) from atmospheric fluidized-bed combustion (AFBC) of two Czech lignites that are currently used or that will likely be used for generating energy in Czech thermal power plants. The experiments were carried out on an experimental-scale 100 kW AFBC boiler using ash as a material of the bed. Coarse fly ashes were collected by a process cyclone; fine fly ashes were separated by a low-pressure Berner impactor. The elemental composition of fly ashes was examined by using INAA and PIXE and, for some samples, also by using ion chromatography. Morphology of ashes was investigated by SEM. The fine particles were found to be spherical or smooth aggregates; they were formed by alkaline-earth and alkali metal sulfates, substantially enriched by volatile trace elements. The coarse particles, both spherical and irregular in shape, were formed by partially transformed mineral inclusions remaining after burn out of organic matter. The results indicate that reducing the concentration of sulfur dioxide in the flue gas may reduce the emission of fine particles.