Effects of fluidized parameters on capture of heavy metal in various bed-material size distributions

Artificial waste was used to simulate agglomeration/defluidization in a fluidized bed and to examine the heavy-metal distribution in bottom ash for various bed-material particle-size distributions (narrow, flat, and Gaussian). Heavy-metal concentration in most particles increased with Na addition, and the largest (> 1.000 mm)- and smallest (< 0.500 mm)-particle-size fractions had the highest metal concentrations. Additionally, Cr had the highest retention rate within the bed particles, followed by Pb and Cd. Comparison of the heavy-metal concentrations and retention rates for different particle-size distributions showed that the total retention rates were higher for narrow and Gaussian distributions than for the flat distribution.

The heavy metal concentration of most particles increased with Na addition and the largest and smallest particles had the highest heavy metal concentrations. When particle size was < 0.500 mm, heavy metal concentration within the particle increased, because there was more surface area for adsorption. When particle size was > 1.000 mm, the heavy metal concentration increased. The low melting point eutectic complex produced by the combination of heavy metals with Na or with liquid eutectic material was likely a more important mechanism of heavy metal capture.Figure optionsDownload as PowerPoint slideHighlights
► Heavy metal concentrations were the highest as bottom ash was outside 0.500–1.000 mm.
► Cr had the highest retention rate within bed particles, followed by Pb and Cd.
► Total retention rates were higher with narrow and Gaussian distributions than flat.